Nanomaterials

11 pages, 9894 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of Air-Stable Cu Nanoparticles Using Laser Reduction in Liquid

by Ashish Nag, Laysa Mariela Frias Batista and Katharine Moore Tibbetts

Nanomaterials 2021, 11(3), 814; https://doi.org/10.3390/nano11030814 - 23 Mar 2021

Cited by 21 | Viewed by 4896

We report the synthesis of air-stable Cu nanoparticles (NPs) using the bottom-up laser reduction in liquid method. Precursor solutions of copper acetlyacetonate in a mixture of methanol and isopropyl alcohol were irradiated with femtosecond laser pulses to produce Cu NPs. The Cu NPs [...] Read more.

We report the synthesis of air-stable Cu nanoparticles (NPs) using the bottom-up laser reduction in liquid method. Precursor solutions of copper acetlyacetonate in a mixture of methanol and isopropyl alcohol were irradiated with femtosecond laser pulses to produce Cu NPs. The Cu NPs were left at ambient conditions and analyzed at different ages up to seven days. TEM analysis indicates a broad size distribution of spherical NPs surrounded by a carbon matrix, with the majority of the NPs less than 10 nm and small numbers of large particles up to ∼100 nm in diameter. XRD collected over seven days confirmed the presence of fcc-Cu NPs, with some amorphous Cu₂O, indicating the stability of the zero-valent Cu phase. Raman, FTIR, and XPS data for oxygen and carbon regions put together indicated the presence of a graphite oxide-like carbon matrix with oxygen functional groups that developed within the first 24 h after synthesis. The Cu NPs were highly active towards the model catalytic reaction of para-nitrophenol reduction in the presence of NaBH₄. Full article

(This article belongs to the Special Issue Laser Synthesis of Nanomaterials)

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22 pages, 4842 KiB

Open AccessEditor’s ChoiceArticle

Progress in Traceable Nanoscale Capacitance Measurements Using Scanning Microwave Microscopy

by François Piquemal, José Morán-Meza, Alexandra Delvallée, Damien Richert and Khaled Kaja

Nanomaterials 2021, 11(3), 820; https://doi.org/10.3390/nano11030820 - 23 Mar 2021

Cited by 8 | Viewed by 3941

Abstract

Reference samples are commonly used for the calibration and quantification of nanoscale electrical measurements of capacitances and dielectric constants in scanning microwave microscopy (SMM) and similar techniques. However, the traceability of these calibration samples is not established. In this work, we present a [...] Read more.

Reference samples are commonly used for the calibration and quantification of nanoscale electrical measurements of capacitances and dielectric constants in scanning microwave microscopy (SMM) and similar techniques. However, the traceability of these calibration samples is not established. In this work, we present a detailed investigation of most possible error sources that affect the uncertainty of capacitance measurements on the reference calibration samples. We establish a comprehensive uncertainty budget leading to a combined uncertainty of 3% in relative value (uncertainty given at one standard deviation) for capacitances ranging from 0.2 fF to 10 fF. This uncertainty level can be achieved even with the use of unshielded probes. We show that the weights of uncertainty sources vary with the values and dimensions of measured capacitances. Our work offers improvements on the classical calibration methods known in SMM and suggests possible new designs of reference standards for capacitance and dielectric traceable measurements. Experimental measurements are supported by numerical calculations of capacitances to reveal further paths for even higher improvements. Full article

(This article belongs to the Special Issue Nanometrology)

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9 pages, 2451 KiB

Open AccessEditor’s ChoiceArticle

Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas

by Joscha Detzmeier, Kevin Königer, Tomasz Blachowicz and Andrea Ehrmann

Nanomaterials 2021, 11(3), 800; https://doi.org/10.3390/nano11030800 - 21 Mar 2021

Cited by 11 | Viewed by 4377

Abstract

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero [...] Read more.

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Nanomaterials)

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22 pages, 1969 KiB

Open AccessEditor’s ChoiceArticle

Experimental Evolution of Magnetite Nanoparticle Resistance in Escherichia coli

by Akamu J. Ewunkem, LaShunta Rodgers, Daisha Campbell, Constance Staley, Kiran Subedi, Sada Boyd and Joseph L. Graves, Jr.

Nanomaterials 2021, 11(3), 790; https://doi.org/10.3390/nano11030790 - 19 Mar 2021

Cited by 25 | Viewed by 3099

Abstract

Both ionic and nanoparticle iron have been proposed as materials to control multidrug-resistant (MDR) bacteria. However, the potential bacteria to evolve resistance to nanoparticle bacteria remains unexplored. To this end, experimental evolution was utilized to produce five magnetite nanoparticle-resistant (FeNP_1–5) populations [...] Read more.

Both ionic and nanoparticle iron have been proposed as materials to control multidrug-resistant (MDR) bacteria. However, the potential bacteria to evolve resistance to nanoparticle bacteria remains unexplored. To this end, experimental evolution was utilized to produce five magnetite nanoparticle-resistant (FeNP_1–5) populations of Escherichia coli. The control populations were not exposed to magnetite nanoparticles. The 24-h growth of these replicates was evaluated in the presence of increasing concentrations magnetite NPs as well as other ionic metals (gallium III, iron II, iron III, and silver I) and antibiotics (ampicillin, chloramphenicol, rifampicin, sulfanilamide, and tetracycline). Scanning electron microscopy was utilized to determine cell size and shape in response to magnetite nanoparticle selection. Whole genome sequencing was carried out to determine if any genomic changes resulted from magnetite nanoparticle resistance. After 25 days of selection, magnetite resistance was evident in the FeNP treatment. The FeNP populations also showed a highly significantly (p < 0.0001) greater 24-h growth as measured by optical density in metals (Fe (II), Fe (III), Ga (III), Ag, and Cu II) as well as antibiotics (ampicillin, chloramphenicol, rifampicin, sulfanilamide, and tetracycline). The FeNP-resistant populations also showed a significantly greater cell length compared to controls (p < 0.001). Genomic analysis of FeNP identified both polymorphisms and hard selective sweeps in the RNA polymerase genes rpoA, rpoB, and rpoC. Collectively, our results show that E. coli can rapidly evolve resistance to magnetite nanoparticles and that this result is correlated resistances to other metals and antibiotics. There were also changes in cell morphology resulting from adaptation to magnetite NPs. Thus, the various applications of magnetite nanoparticles could result in unanticipated changes in resistance to both metal and antibiotics. Full article

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9 pages, 4521 KiB

Open AccessEditor’s ChoiceArticle

A Facile Chemical Method Enabling Uniform Zn Deposition for Improved Aqueous Zn-Ion Batteries

by Congcong Liu, Qiongqiong Lu, Ahmad Omar and Daria Mikhailova

Nanomaterials 2021, 11(3), 764; https://doi.org/10.3390/nano11030764 - 18 Mar 2021

Cited by 31 | Viewed by 5358

Abstract

Rechargeable aqueous Zn-ion batteries (ZIBs) have gained great attention due to their high safety and the natural abundance of Zn. Unfortunately, the Zn metal anode suffers from dendrite growth due to nonuniform deposition during the plating/stripping process, leading to a sudden failure of [...] Read more.

Rechargeable aqueous Zn-ion batteries (ZIBs) have gained great attention due to their high safety and the natural abundance of Zn. Unfortunately, the Zn metal anode suffers from dendrite growth due to nonuniform deposition during the plating/stripping process, leading to a sudden failure of the batteries. Herein, Cu coated Zn (Cu–Zn) was prepared by a facile pretreatment method using CuSO₄ aqueous solution. The Cu coating transformed into an alloy interfacial layer with a high affinity for Zn, which acted as a nucleation site to guide the uniform Zn nucleation and plating. As a result, Cu–Zn demonstrated a cycling life of up to 1600 h in the symmetric cells and endowed a stable cycling performance with a capacity of 207 mAh g⁻¹ even after 1000 cycles in the full cells coupled with a V₂O₅-based cathode. This work provides a simple and effective strategy to enable uniform Zn deposition for improved ZIBs. Full article

(This article belongs to the Special Issue Nanomaterials for Ion Battery Applications)

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8 pages, 3328 KiB

Open AccessEditor’s ChoiceArticle

High Gain and Broadband Absorption Graphene Photodetector Decorated with Bi₂Te₃ Nanowires

by Tae Jin Yoo, Wan Sik Kim, Kyoung Eun Chang, Cihyun Kim, Min Gyu Kwon, Ji Young Jo and Byoung Hun Lee

Nanomaterials 2021, 11(3), 755; https://doi.org/10.3390/nano11030755 - 17 Mar 2021

Cited by 19 | Viewed by 3864

Abstract

A graphene photodetector decorated with Bi₂Te₃ nanowires (NWs) with a high gain of up to 3 × 10⁴ and wide bandwidth window (400–2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to [...] Read more.

A graphene photodetector decorated with Bi₂Te₃ nanowires (NWs) with a high gain of up to 3 × 10⁴ and wide bandwidth window (400–2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to the gain of a photodetector using a graphene/Bi₂Te₃ nanoplate junction. Additionally, the position of photocurrent generation was investigated at the graphene/Bi₂Te₃ NWs junction. Eventually, with low bandgap Bi₂Te₃ NWs and a graphene junction, the photoresponsivity improved by 200% at 2200 nm (~0.09 mA/W). Full article

(This article belongs to the Special Issue Graphene-Based Nanomaterials)

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14 pages, 3343 KiB

Open AccessEditor’s ChoiceArticle

Optical Polymer Waveguides Fabricated by Roll-to-Plate Nanoimprinting Technique

by Vaclav Prajzler, Vaclav Chlupaty, Pavel Kulha, Milos Neruda, Sonja Kopp and Michael Mühlberger

Nanomaterials 2021, 11(3), 724; https://doi.org/10.3390/nano11030724 - 13 Mar 2021

Cited by 21 | Viewed by 4980

Abstract

The paper reports on the properties of UV-curable inorganic-organic hybrid polymer multimode optical channel waveguides fabricated by roll-to-plate (R2P) nanoimprinting. We measured transmission spectra, refractive indices of the applied polymer materials, and optimized the R2P fabrication process. Optical losses of the waveguides were [...] Read more.

The paper reports on the properties of UV-curable inorganic-organic hybrid polymer multimode optical channel waveguides fabricated by roll-to-plate (R2P) nanoimprinting. We measured transmission spectra, refractive indices of the applied polymer materials, and optimized the R2P fabrication process. Optical losses of the waveguides were measured by the cut-back method at wavelengths of 532, 650, 850, 1310, and 1550 nm. The lowest optical losses were measured at 850 nm and the lowest average value was 0.19 dB/cm, and optical losses at 1310 nm were 0.42 dB/cm and 0.25 dB/cm at 650 nm respectively. The study has demonstrated that nanoimprinting has great potential for the implementation of optical polymer waveguides not only for optical interconnection applications. Full article

(This article belongs to the Special Issue Nanoimprint Lithography Technology and Applications)

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30 pages, 5564 KiB

Open AccessEditor’s ChoiceArticle

Guiding Chart for Initial Layer Choice with Nanoimprint Lithography

by Andre Mayer and Hella-Christin Scheer

Nanomaterials 2021, 11(3), 710; https://doi.org/10.3390/nano11030710 - 11 Mar 2021

Cited by 4 | Viewed by 3314

Abstract

When nanoimprint serves as a lithography process, it is most attractive for the ability to overcome the typical residual layer remaining without the need for etching. Then, ‘partial cavity filling’ is an efficient strategy to provide a negligible residual layer. However, this strategy [...] Read more.

When nanoimprint serves as a lithography process, it is most attractive for the ability to overcome the typical residual layer remaining without the need for etching. Then, ‘partial cavity filling’ is an efficient strategy to provide a negligible residual layer. However, this strategy requires an adequate choice of the initial layer thickness to work without defects. To promote the application of this strategy we provide a ‘guiding chart’ for initial layer choice. Due to volume conservation of the imprint polymer this guiding chart has to consider the geometric parameters of the stamp, where the polymer fills the cavities only up to a certain height, building a meniscus at its top. Furthermore, defects that may develop during the imprint due to some instability of the polymer within the cavity have to be avoided; with nanoimprint, the main instabilities are caused by van der Waals forces, temperature gradients, and electrostatic fields. Moreover, practical aspects such as a minimum polymer height required for a subsequent etching of the substrate come into play. With periodic stamp structures the guiding chart provided will indicate a window for defect-free processing considering all these limitations. As some of the relevant factors are system-specific, the user has to construct his own guiding chart in praxis, tailor-made to his particular imprint situation. To facilitate this task, all theoretical results required are presented in a graphical form, so that the quantities required can simply be read from these graphs. By means of examples, the implications of the guiding chart with respect to the choice of the initial layer are discussed with typical imprint scenarios, nanoimprint at room temperature, at elevated temperature, and under electrostatic forces. With periodic structures, the guiding chart represents a powerful and straightforward tool to avoid defects in praxis, without in-depth knowledge of the underlying physics. Full article

(This article belongs to the Special Issue Nanoimprint Lithography Technology and Applications)

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11 pages, 3941 KiB

Open AccessEditor’s ChoiceArticle

Hydrophobic/Oleophilic Structures Based on MacroPorous Silicon: Effect of Topography and Fluoroalkyl Silane Functionalization on Wettability

by Pilar Formentín and Lluís F. Marsal

Nanomaterials 2021, 11(3), 670; https://doi.org/10.3390/nano11030670 - 9 Mar 2021

Cited by 9 | Viewed by 3522

Abstract

The effect of the morphology and chemical composition of a surface on the wettability of porous silicon structures is analyzed in the present work. Hydrophobic and superhydrophobic macroporous substrates are attractive for different potential applications. Herein, different hydrophobic macroporous silicon structures were fabricated [...] Read more.

The effect of the morphology and chemical composition of a surface on the wettability of porous silicon structures is analyzed in the present work. Hydrophobic and superhydrophobic macroporous substrates are attractive for different potential applications. Herein, different hydrophobic macroporous silicon structures were fabricated by the chemical etching of p-type silicon wafers in a solution based on hydrofluoric acid and coated with a fluoro silane self-assembled monolayer. The surface morphology of the final substrate was characterized using a scanning electron microscope. The wettability was assessed from contact angle measurements using water and organic solvents that present low surface energy. The experimental data were compared with the classical wetting states theoretical models described in the literature. Perfluoro-silane functionalized macroporous silicon surfaces presented systematically higher contact angles than untreated silicon substrates. The influence of porosity on the surface wettability of macoporous silicon structures has been established. These results suggest that the combination of etching conditions with a surface chemistry modification could lead to hydrophobic/oleophilic or superhydrophobic/oleophobic structures. Full article

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9 pages, 2078 KiB

Open AccessEditor’s ChoiceArticle

Anisotropy of the In-Plane and Out-of-Plane Resistivity and the Hall Effect in the Normal State of Vicinal-Grown YBa₂Cu₃O_7−δ Thin Films

by Gernot Heine, Wolfgang Lang, Roman Rössler and Johannes D. Pedarnig

Nanomaterials 2021, 11(3), 675; https://doi.org/10.3390/nano11030675 - 9 Mar 2021

Cited by 7 | Viewed by 3177

Abstract

The resistivity and the Hall effect in the copper-oxide high-temperature superconductor YBa

_{2}

Cu

_{3}

O

_{7 - δ}

(YBCO) are remarkably anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO

_{3}

substrate allows one to investigate these anisotropic [...] Read more.

The resistivity and the Hall effect in the copper-oxide high-temperature superconductor YBa

_{2}

Cu

_{3}

O

_{7 - δ}

(YBCO) are remarkably anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO

_{3}

substrate allows one to investigate these anisotropic transport properties in a planar and well-defined sample geometry employing a homogeneous current density. In the normal state, the Hall voltage probed parallel to the copper-oxide layers is positive and strongly temperature dependent, whereas the out-of-plane Hall voltage is negative and almost temperature independent. The results confirm previous measurements on single crystals by an entirely different measurement method and demonstrate that vicinal thin films might be also useful for investigations of other layered nanomaterials. Full article

(This article belongs to the Special Issue Applications of Nanoparticles in Superconducting Materials)

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16 pages, 7007 KiB

Open AccessEditor’s ChoiceArticle

Tuning Green to Red Color in Erbium Niobate Micro- and Nanoparticles

by Susana Devesa, Joana Rodrigues, Sílvia Soreto Teixeira, Aidan P. Rooney, Manuel P. F. Graça, David Cooper, Teresa Monteiro and Luís C. Costa

Nanomaterials 2021, 11(3), 660; https://doi.org/10.3390/nano11030660 - 8 Mar 2021

Cited by 4 | Viewed by 2478

Abstract

Tetragonal Er_0.5Nb_0.5O₂ and monoclinic ErNbO₄ micro- and nanoparticles were prepared by the citrate sol–gel method and heat-treated at temperatures between 700 and 1600 °C. ErNbO₄ revealed a spherical-shaped crystallite, whose size increased with heat treatment temperatures. [...] Read more.

Tetragonal Er_0.5Nb_0.5O₂ and monoclinic ErNbO₄ micro- and nanoparticles were prepared by the citrate sol–gel method and heat-treated at temperatures between 700 and 1600 °C. ErNbO₄ revealed a spherical-shaped crystallite, whose size increased with heat treatment temperatures. To assess their optical properties at room temperature (RT), a thorough spectroscopic study was conducted. RT photoluminescence (PL) spectroscopy revealed that Er³⁺ optical activation was achieved in all samples. The photoluminescence spectra show the green/yellow ²H_11/2, ⁴S_3/2→⁴I_15/2 and red ⁴F_9/2→⁴I_15/2 intraionic transitions as the main visible recombination, with the number of the crystal field splitting Er³⁺ multiplets reflecting the ion site symmetry in the crystalline phases. PL excitation allows the identification of Er³⁺ high-energy excited multiplets as the preferential population paths of the emitting levels. Independently of the crystalline structure, the intensity ratio between the green/yellow and red intraionic transitions was found to be strongly sensitive to the excitation energy. After pumping the samples with a resonant excitation into the ⁴G_11/2 excited multiplet, a green/yellow transition stronger than the red one was observed, whereas the reverse occurred for higher excitation photon energies. Thus, a controllable selective excited tunable green to red color was achieved, which endows new opportunities for photonic and optoelectronic applications. Full article

(This article belongs to the Special Issue Photonic Nanomaterials)

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11 pages, 6264 KiB

Open AccessEditor’s ChoiceArticle

Biomimetic Transparent Eye Protection Inspired by the Carapace of an Ostracod (Crustacea)

by Andrew R. Parker, Barbara P. Palka, Julie Albon, Keith M. Meek, Simon Holden and F. Tegwen Malik

Nanomaterials 2021, 11(3), 663; https://doi.org/10.3390/nano11030663 - 8 Mar 2021

Cited by 2 | Viewed by 2643

Abstract

In this study we mimic the unique, transparent protective carapace (shell) of myodocopid ostracods, through which their compound eyes see, to demonstrate that the carapace ultrastructure also provides functions of strength and protection for a relatively thin structure. The bulk ultrastructure of the [...] Read more.

In this study we mimic the unique, transparent protective carapace (shell) of myodocopid ostracods, through which their compound eyes see, to demonstrate that the carapace ultrastructure also provides functions of strength and protection for a relatively thin structure. The bulk ultrastructure of the transparent window in the carapace of the relatively large, pelagic cypridinid (Myodocopida) Macrocypridina castanea was mimicked using the thin film deposition of dielectric materials to create a transparent, 15 bi-layer material. This biomimetic material was subjected to the natural forces withstood by the ostracod carapace in situ, including scratching by captured prey and strikes by water-borne particles. The biomimetic material was then tested in terms of its extrinsic (hardness value) and intrinsic (elastic modulus) response to indentation along with its scratch resistance. The performance of the biomimetic material was compared with that of a commonly used, anti-scratch resistant lens and polycarbonate that is typically used in the field of transparent armoury. The biomimetic material showed the best scratch resistant performance, and significantly greater hardness and elastic modulus values. The ability of biomimetic material to revert back to its original form (post loading), along with its scratch resistant qualities, offers potential for biomimetic eye protection coating that could enhance material currently in use. Full article

(This article belongs to the Special Issue Photonic Properties of Nanostructured Biomaterials)

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17 pages, 3745 KiB

Open AccessEditor’s ChoiceArticle

Investigation on the Mass Distribution and Chemical Compositions of Various Ionic Liquids-Extracted Coal Fragments and Their Effects on the Electrochemical Performance of Coal-Derived Carbon Nanofibers (CCNFs)

by Shuai Tan, Theodore John Kraus, Mitchell Ross Helling, Rudolph Kurtzer Mignon, Franco Basile and Katie Dongmei Li-Oakey

Nanomaterials 2021, 11(3), 664; https://doi.org/10.3390/nano11030664 - 8 Mar 2021

Cited by 2 | Viewed by 2479

Abstract

Coal-derived carbon nanofibers (CCNFs) have been recently found to be a promising and low-cost electrode material for high-performance supercapacitors. However, the knowledge gap still exists between holistic understanding of coal precursors derived from different solvents and resulting CCNFs’ properties, prohibiting further optimization of [...] Read more.

Coal-derived carbon nanofibers (CCNFs) have been recently found to be a promising and low-cost electrode material for high-performance supercapacitors. However, the knowledge gap still exists between holistic understanding of coal precursors derived from different solvents and resulting CCNFs’ properties, prohibiting further optimization of their electrochemical performance. In this paper, assisted by laser desorption/ionization (LDI) and gas chromatography–mass spectrometry (GC–MS) technologies, a systematic study was performed to holistically characterize mass distribution and chemical composition of coal precursors derived from various ionic liquids (ILs) as extractants. Sequentially, X-ray photoelectron spectroscopy (XPS) revealed that the differences in chemical properties of various coal products significantly affected the surface oxygen concentrations and certain species distributions on the CCNFs, which, in turn, determined the electrochemical performances of CCNFs as electrode materials. We report that the CCNF that was produced by an oxygen-rich coal fragment from C₆mimCl ionic liquid extraction showed the highest concentrations of quinone and ester groups on the surface. Consequentially, C₆mimCl-CCNF achieved the highest specific capacitance and lowest ion diffusion resistance. Finally, a symmetric carbon/carbon supercapacitor fabricated with such CCNF as electrode delivered an energy density of 21.1 Wh/kg at the power density of 0.6 kW/kg, which is comparable to commercial active carbon supercapacitors. Full article

(This article belongs to the Special Issue Nanomaterials and Textiles)

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15 pages, 3365 KiB

Open AccessEditor’s ChoiceArticle

Structural Evolution of Nanophase Separated Block Copolymer Patterns in Supercritical CO₂

by Tandra Ghoshal, Timothy W. Collins, Subhajit Biswas, Michael A. Morris and Justin D. Holmes

Nanomaterials 2021, 11(3), 669; https://doi.org/10.3390/nano11030669 - 8 Mar 2021

Cited by 2 | Viewed by 2823

Abstract

Nanopatterns can readily be formed by annealing block copolymers (BCPs) in organic solvents at moderate or high temperatures. However, this approach can be challenging from an environmental and industrial point of view. Herein, we describe a simple and environmentally friendly alternative to achieve [...] Read more.

Nanopatterns can readily be formed by annealing block copolymers (BCPs) in organic solvents at moderate or high temperatures. However, this approach can be challenging from an environmental and industrial point of view. Herein, we describe a simple and environmentally friendly alternative to achieve periodically ordered nanoscale phase separated BCP structures. Asymmetric polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin film patterns of different molecular weight were achieved by annealing in supercritical carbon dioxide (sc-CO₂). Microphase separation of PS-b-PEO (16,000–5000) film patterns were achieved by annealing in scCO₂ at a relatively low temperature was previously reported by our group. The effects of annealing temperature, time and depressurisation rates for the polymer system were also discussed. In this article, we have expanded this study to create new knowledge on the structural and dimensional evolution of nanohole and line/space surface periodicity of four other different molecular weights PS-b-PEO systems. Periodic, well defined, hexagonally ordered films of line and hole patterns were obtained at low CO₂ temperatures (35–40 °C) and pressures (1200–1300 psi). Further, the changes in morphology, ordering and feature sizes for a new PS-b-PEO system (42,000–11,500) are discussed in detail upon changing the scCO₂ annealing parameters (temperature, film thickness, depressurization rates, etc.). In relation to our previous reports, the broad annealing temperature and depressurisation rate were explored together for different film thicknesses. In addition, the effects of SCF annealing for three other BCP systems (PEO-b-PS, PS-b-PDMS, PS-b-PLA) is also investigated with similar processing conditions. The patterns were also generated on a graphoepitaxial substrate for device application. Full article

(This article belongs to the Special Issue Block Copolymer Nano-Objects)

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17 pages, 2486 KiB

Open AccessEditor’s ChoiceArticle

A Comparative Assessment of the Chronic Effects of Micro- and Nano-Plastics on the Physiology of the Mediterranean Mussel Mytilus galloprovincialis

by Marco Capolupo, Paola Valbonesi and Elena Fabbri

Nanomaterials 2021, 11(3), 649; https://doi.org/10.3390/nano11030649 - 7 Mar 2021

Cited by 63 | Viewed by 4943

Abstract

The ocean contamination caused by micro- and nano-sized plastics is a matter of increasing concern regarding their potential effects on marine organisms. This study compared the effects of a 21-day exposure to 1.5, 15, and 150 ng/L of polystyrene microplastics (PS-MP, 3-µm) and [...] Read more.

The ocean contamination caused by micro- and nano-sized plastics is a matter of increasing concern regarding their potential effects on marine organisms. This study compared the effects of a 21-day exposure to 1.5, 15, and 150 ng/L of polystyrene microplastics (PS-MP, 3-µm) and nanoplastics (PS-NP, 50-nm) on a suite of biomarkers measured in the Mediterranean mussel Mytilus galloprovincialis. Endpoints encompassed immunological/lysosomal responses, oxidative stress/detoxification parameters, and neurotoxicological markers. Compared to PS-MP, PS-NP induced higher effects on lysosomal parameters of general stress. Exposures to both particle sizes increased lipid peroxidation and catalase activity in gills; PS-NP elicited greater effects on the phase-II metabolism enzyme glutathione S-transferase and on lysozyme activity, while only PS-MP inhibited the hemocyte phagocytosis, suggesting a major role of PS particle size in modulating immunological/detoxification pathways. A decreased acetylcholinesterase activity was induced by PS-NP, indicating their potential to impair neurological functions in mussels. Biomarker data integration in the Mussel Expert System identified an overall greater health status alteration in mussels exposed to PS-NP compared to PS-MP. This study shows that increasing concentrations of nanoplastics may induce higher effects than microplastics on the mussel’s lysosomal, metabolic, and neurological functions, eventually resulting in a greater impact on their overall fitness. Full article

(This article belongs to the Special Issue Do Nanoplastics Represent a Risk for Aquatic Organisms? From Bio-Nano-Interactions to Possible Impacts at Population and Community Level)

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14 pages, 27701 KiB

Open AccessEditor’s ChoiceArticle

Artificial Neural Network-Based Prediction of the Optical Properties of Spherical Core–Shell Plasmonic Metastructures

by Ehsan Vahidzadeh and Karthik Shankar

Nanomaterials 2021, 11(3), 633; https://doi.org/10.3390/nano11030633 - 4 Mar 2021

Cited by 20 | Viewed by 4546

Abstract

The substitution of time- and labor-intensive empirical research as well as slow finite difference time domain (FDTD) simulations with revolutionary techniques such as artificial neural network (ANN)-based predictive modeling is the next trend in the field of nanophotonics. In this work, we demonstrated [...] Read more.

The substitution of time- and labor-intensive empirical research as well as slow finite difference time domain (FDTD) simulations with revolutionary techniques such as artificial neural network (ANN)-based predictive modeling is the next trend in the field of nanophotonics. In this work, we demonstrated that neural networks with proper architectures can rapidly predict the far-field optical response of core–shell plasmonic metastructures. The results obtained with artificial neural networks are comparable with FDTD simulations in accuracy but the speed of obtaining them is between 100–1000 times faster than FDTD simulations. Further, we have proven that ANNs does not have problems associated with FDTD simulations such as dependency of the speed of convergence on the size of the structure. The other trend in photonics is the inverse design problem, where the far-field optical response of a spherical core–shell metastructure can be linked to the design parameters such as type of the material(s), core radius, and shell thickness using a neural network. The findings of this paper provide evidence that machine learning (ML) techniques such as artificial neural networks can potentially replace time-consuming finite domain methods in the future. Full article

(This article belongs to the Special Issue Computational Study of Nanomaterials)

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9 pages, 3189 KiB

Open AccessEditor’s ChoiceArticle

Kinetics of Guided Growth of Horizontal GaN Nanowires on Flat and Faceted Sapphire Surfaces

by Amnon Rothman, Jaroslav Maniš, Vladimir G. Dubrovskii, Tomáš Šikola, Jindřich Mach and Ernesto Joselevich

Nanomaterials 2021, 11(3), 624; https://doi.org/10.3390/nano11030624 - 3 Mar 2021

Cited by 5 | Viewed by 2831

Abstract

The bottom-up assembly of nanowires facilitates the control of their dimensions, structure, orientation and physical properties. Surface-guided growth of planar nanowires has been shown to enable their assembly and alignment on substrates during growth, thus eliminating the need for additional post-growth processes. However, [...] Read more.

The bottom-up assembly of nanowires facilitates the control of their dimensions, structure, orientation and physical properties. Surface-guided growth of planar nanowires has been shown to enable their assembly and alignment on substrates during growth, thus eliminating the need for additional post-growth processes. However, accurate control and understanding of the growth of the planar nanowires were achieved only recently, and only for ZnSe and ZnS nanowires. Here, we study the growth kinetics of surface-guided planar GaN nanowires on flat and faceted sapphire surfaces, based on the previous growth model. The data are fully consistent with the same model, presenting two limiting regimes—either the Gibbs–Thomson effect controlling the growth of the thinner nanowires or surface diffusion controlling the growth of thicker ones. The results are qualitatively compared with other semiconductors surface-guided planar nanowires materials, demonstrating the generality of the growth mechanism. The rational approach enabled by this general model provides better control of the nanowire (NW) dimensions and expands the range of materials systems and possible application of NW-based devices in nanotechnology. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires)

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13 pages, 2875 KiB

Open AccessEditor’s ChoiceArticle

A Molecularly Imprinted Sol-Gel Electrochemical Sensor for Naloxone Determination

by Narges Shaabani, Nora W. C. Chan and Abebaw B. Jemere

Nanomaterials 2021, 11(3), 631; https://doi.org/10.3390/nano11030631 - 3 Mar 2021

Cited by 18 | Viewed by 3485

Abstract

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide [...] Read more.

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide (ITO) electrode. The sol-gel layer was obtained from acid catalyzed hydrolysis and condensation of a solution composed of triethoxyphenylsilane (TEPS) and tetraethoxysilane (TES). The fabrication, structure and properties of the sensing material were characterized via scanning electron microscopy, spectroscopy and electrochemical techniques. Parameters affecting the sensor’s performance were evaluated and optimized. A sensor fabricated under the optimized conditions responded linearly between 0.0 µM and 12 µM NLX, with a detection limit of 0.02 µM. The sensor also showed good run-to-run repeatability and batch-to-batch performance reproducibility with relative standard deviations (RSD) of 2.5–7.8% (n = 3) and 9.2% (n = 4), respectively. The developed sensor displayed excellent selectivity towards NLX compared to structurally similar compounds (codeine, fentanyl, naltrexone and noroxymorphone), and was successfully used to measure NLX in synthetic urine samples yielding recoveries greater than 88%. Full article

(This article belongs to the Special Issue Electrochemical Sensing Applications of Nanomaterials)

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24 pages, 6764 KiB

Open AccessEditor’s ChoiceArticle

Ball Milled Graphene Nano Additives for Enhancing Sliding Contact in Vegetable Oil

by Emad Omrani, Arpith Siddaiah, Afsaneh Dorri Moghadam, Uma Garg, Pradeep Rohatgi and Pradeep L. Menezes

Nanomaterials 2021, 11(3), 610; https://doi.org/10.3390/nano11030610 - 1 Mar 2021

Cited by 21 | Viewed by 3444

Abstract

Graphite nanoplatelets (GNPs) as an oil nano additive has gained importance to enhance the lubrication properties of renewable lubricants, such as vegetable oils. Using appropriately processed GNPs is necessary to gain the required tribological advantage. The present study investigated ball-milled GNPs, to understand [...] Read more.

Graphite nanoplatelets (GNPs) as an oil nano additive has gained importance to enhance the lubrication properties of renewable lubricants, such as vegetable oils. Using appropriately processed GNPs is necessary to gain the required tribological advantage. The present study investigated ball-milled GNPs, to understand the effect of GNPs concentration, and applied load on tribological behavior. Pin-on-disk tests were employed, to investigate the tribological performance of the nano-additive oil-based lubricant in the boundary lubrication regime. In order gain an understanding of the lubrication mechanism, Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Raman Spectroscopy were performed for characterization. The study found that there is a critical concentration of GNPs, below and above which a reduced wear rate is not sustained. It is found that the tribological enhancements at the optimum concentration of GNP in boundary lubrication condition are a result of reduced direct metal–metal contact area at the interface. This phenomenon, along with the reduced shear strength of the ball-milled GNPs, is indicated to reduce the formation of asperity junctions at the interface and enhance tribological properties of the nano-additive oil-based lubricant. Full article

(This article belongs to the Special Issue The Potential of Nano Additives in Lubricants and Heat Transfer Fluids)

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8 pages, 1829 KiB

Open AccessEditor’s ChoiceArticle

Correlation between Optical Localization-State and Electrical Deep-Level State in In_0.52Al_0.48As/In_0.53Ga_0.47As Quantum Well Structure

by Il-Ho Ahn, Deuk Young Kim and Sejoon Lee

Nanomaterials 2021, 11(3), 585; https://doi.org/10.3390/nano11030585 - 26 Feb 2021

Cited by 4 | Viewed by 2457

Abstract

The peculiar correlationship between the optical localization-state and the electrical deep-level defect-state was observed in the In_0.52Al_0.48As/In_0.53Ga_0.47As quantum well structure that comprises two quantum-confined electron-states and two hole-subbands. The sample clearly exhibited the Fermi edge [...] Read more.

The peculiar correlationship between the optical localization-state and the electrical deep-level defect-state was observed in the In_0.52Al_0.48As/In_0.53Ga_0.47As quantum well structure that comprises two quantum-confined electron-states and two hole-subbands. The sample clearly exhibited the Fermi edge singularity (FES) peak in its photoluminescence spectrum at 10–300 K; and the FES peak was analyzed in terms of the phenomenological line shape model with key physical parameters such as the Fermi energy, the hole localization energy, and the band-to-band transition amplitude. Through the comprehensive studies on both the theoretical calculation and the experimental evaluation of the energy band profile, we found out that the localized state, which is separated above by ~0.07 eV from the first excited hole-subband, corresponds to the deep-level state, residing at the position of ~0.75 eV far below the conduction band (i.e., near the valence band edge). Full article

(This article belongs to the Special Issue Semiconductor Heterostructures (with Quantum Wells, Quantum Dots and Superlattices))

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27 pages, 1896 KiB

Open AccessEditor’s ChoiceArticle

Elastostatics of Bernoulli–Euler Beams Resting on Displacement-Driven Nonlocal Foundation

by Marzia Sara Vaccaro, Francesco Paolo Pinnola, Francesco Marotti de Sciarra and Raffaele Barretta

Nanomaterials 2021, 11(3), 573; https://doi.org/10.3390/nano11030573 - 25 Feb 2021

Cited by 19 | Viewed by 2304

Abstract

The simplest elasticity model of the foundation underlying a slender beam under flexure was conceived by Winkler, requiring local proportionality between soil reactions and beam deflection. Such an approach leads to well-posed elastostatic and elastodynamic problems, but as highlighted by Wieghardt, it provides [...] Read more.

The simplest elasticity model of the foundation underlying a slender beam under flexure was conceived by Winkler, requiring local proportionality between soil reactions and beam deflection. Such an approach leads to well-posed elastostatic and elastodynamic problems, but as highlighted by Wieghardt, it provides elastic responses that are not technically significant for a wide variety of engineering applications. Thus, Winkler’s model was replaced by Wieghardt himself by assuming that the beam deflection is the convolution integral between soil reaction field and an averaging kernel. Due to conflict between constitutive and kinematic compatibility requirements, the corresponding elastic problem of an inflected beam resting on a Wieghardt foundation is ill-posed. Modifications of the original Wieghardt model were proposed by introducing fictitious boundary concentrated forces of constitutive type, which are physically questionable, being significantly influenced on prescribed kinematic boundary conditions. Inherent difficulties and issues are overcome in the present research using a displacement-driven nonlocal integral strategy obtained by swapping the input and output fields involved in Wieghardt’s original formulation. That is, nonlocal soil reaction fields are the output of integral convolutions of beam deflection fields with an averaging kernel. Equipping the displacement-driven nonlocal integral law with the bi-exponential averaging kernel, an equivalent nonlocal differential problem, supplemented with non-standard constitutive boundary conditions involving nonlocal soil reactions, is established. As a key implication, the integrodifferential equations governing the elastostatic problem of an inflected elastic slender beam resting on a displacement-driven nonlocal integral foundation are replaced with much simpler differential equations supplemented with kinematic, static, and new constitutive boundary conditions. The proposed nonlocal approach is illustrated by examining and analytically solving exemplar problems of structural engineering. Benchmark solutions for numerical analyses are also detected. Full article

(This article belongs to the Special Issue Multiscale Innovative Materials and Structures)

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12 pages, 2369 KiB

Open AccessEditor’s ChoiceArticle

Protein Adsorption on SiO₂-CaO Bioactive Glass Nanoparticles with Controllable Ca Content

by Martin Kapp, Chunde Li, Zeqian Xu, Aldo R. Boccaccini and Kai Zheng

Nanomaterials 2021, 11(3), 561; https://doi.org/10.3390/nano11030561 - 24 Feb 2021

Cited by 13 | Viewed by 3446

Abstract

Bioactive glass nanoparticles (BGNs) are emerging multifunctional building blocks for various biomedical applications. In this study, the primary aim was to develop monodispersed binary SiO₂-CaO BGNs with controllable Ca content. We successfully synthesized such spherical BGNs (size ~110 nm) using a [...] Read more.

Bioactive glass nanoparticles (BGNs) are emerging multifunctional building blocks for various biomedical applications. In this study, the primary aim was to develop monodispersed binary SiO₂-CaO BGNs with controllable Ca content. We successfully synthesized such spherical BGNs (size ~110 nm) using a modified Stöber method. Our results showed that the incorporated Ca did not significantly affect particle size, specific surface area, and structure of BGNs. Concentrations of CaO in BGN compositions ranging from 0 to 10 mol% could be obtained without the gap between actual and nominal compositions. For this type of BGNs (specific surface area 30 m²/g), the maximum concentration of incorporated CaO appeared to be ~12 mol%. The influence of Ca content on protein adsorption was investigated using bovine serum albumin (BSA) and lysozyme as model proteins. The amount of adsorbed proteins increased over time at the early stage of adsorption (<2 h), regardless of glass composition and protein type. Further incubation of BGNs with protein-containing solutions seemed to induce a reduced amount of adsorbed proteins, which was more significant in BGNs with higher Ca content. The results indicate that the Ca content in BGNs is related to their protein adsorption behavior. Full article

(This article belongs to the Special Issue Biodegradable Inorganic Nano-Architectures)

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9 pages, 1968 KiB

Open AccessEditor’s ChoiceArticle

Electric Transport in Gold-Covered Sodium–Alginate Free-Standing Foils

by Carlo Barone, Monica Bertoldo, Raffaella Capelli, Franco Dinelli, Piera Maccagnani, Nadia Martucciello, Costantino Mauro and Sergio Pagano

Nanomaterials 2021, 11(3), 565; https://doi.org/10.3390/nano11030565 - 24 Feb 2021

Cited by 6 | Viewed by 2712

Abstract

The electric transport properties of flexible and transparent conducting bilayers, realized by sputtering ultrathin gold nanometric layers on sodium–alginate free-standing films, were studied. The reported results cover a range of temperatures from 3 to 300 K. In the case of gold layer thicknesses [...] Read more.

The electric transport properties of flexible and transparent conducting bilayers, realized by sputtering ultrathin gold nanometric layers on sodium–alginate free-standing films, were studied. The reported results cover a range of temperatures from 3 to 300 K. In the case of gold layer thicknesses larger than 5 nm, a typical metallic behavior was observed. Conversely, for a gold thickness of 4.5 nm, an unusual resistance temperature dependence was found. The dominant transport mechanism below 70 K was identified as a fluctuation-induced tunneling process. This indicates that the conductive region is not continuous but is formed by gold clusters embedded in the polymeric matrix. Above 70 K, instead, the data can be interpreted using a phenomenological model, which assumes an anomalous expansion of the conductive region upon decreasing the temperature, in the range from 300 to 200 K. The approach herein adopted, complemented with other characterizations, can provide useful information for the development of innovative and green optoelectronics. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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23 pages, 4624 KiB

Open AccessEditor’s ChoiceArticle

Scavenger Receptor A1 Mediates the Uptake of Carboxylated and Pristine Multi-Walled Carbon Nanotubes Coated with Bovine Serum Albumin

by Mai T. Huynh, Carole Mikoryak, Paul Pantano and Rockford Draper

Nanomaterials 2021, 11(2), 539; https://doi.org/10.3390/nano11020539 - 20 Feb 2021

Cited by 9 | Viewed by 3595

Abstract

Previously, we noted that carboxylated multi-walled carbon nanotubes (cMWNTs) coated with Pluronic^® F-108 (PF108) bound to and were accumulated by macrophages, but that pristine multi-walled carbon nanotubes (pMWNTs) coated with PF108 were not (Wang et al., Nanotoxicology2018, 12, 677). [...] Read more.

Previously, we noted that carboxylated multi-walled carbon nanotubes (cMWNTs) coated with Pluronic^® F-108 (PF108) bound to and were accumulated by macrophages, but that pristine multi-walled carbon nanotubes (pMWNTs) coated with PF108 were not (Wang et al., Nanotoxicology2018, 12, 677). Subsequent studies with Chinese hamster ovary (CHO) cells that overexpressed scavenger receptor A1 (SR-A1) and with macrophages derived from mice knocked out for SR-A1 provided evidence that SR-A1 was a receptor of PF108-cMWNTs (Wang et al., Nanomaterials (Basel) 2020, 10, 2417). Herein, we replaced the PF108 coat with bovine serum albumin (BSA) to investigate how a BSA corona affected the interaction of multi-walled carbon nanotubes (MWNTs) with cells. Both BSA-coated cMWNTs and pMWNTs bound to and were accumulated by RAW 264.7 macrophages, although the cells bound two times more BSA-coated cMWNT than pMWNTs. RAW 264.7 cells that were deleted for SR-A1 using CRISPR-Cas9 technology had markedly reduced binding and accumulation of both BSA-coated cMWNTs and pMWNTs, suggesting that SR-A1 was responsible for the uptake of both MWNT types. Moreover, CHO cells that ectopically expressed SR-A1 accumulated both MWNT types, whereas wild-type CHO cells did not. One model to explain these results is that SR-A1 can interact with two structural features of BSA-coated cMWNTs, one inherent to the oxidized nanotubes (such as COOH and other oxidized groups) and the other provided by the BSA corona; whereas SR-A1 only interacts with the BSA corona of BSA-pMWNTs. Full article

(This article belongs to the Special Issue Nanoparticle-Macrophage Interactions: Implications for Nanosafety and Nanomedicine)

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8 pages, 996 KiB

Open AccessEditor’s ChoiceArticle

A Proposition for the Estimation of the Maximum Tensile Strength of Variously Charged Nanocellulosic Film Materials Provided by Vacuum Filtration

by Tom Lindström

Nanomaterials 2021, 11(2), 543; https://doi.org/10.3390/nano11020543 - 20 Feb 2021

Cited by 4 | Viewed by 2673

Abstract

This short investigation deals with a review of the tensile strength properties of six different types of nanocellulose films (carboxymethylated, carboxymethylcellulose-grafted, enzymatically pretreated, phosphorylated, sulfoethylated, and alkoxylated nanocellulose films) manufactured using identical protocols and the determination of the apparent nanocellulose yield of the [...] Read more.

This short investigation deals with a review of the tensile strength properties of six different types of nanocellulose films (carboxymethylated, carboxymethylcellulose-grafted, enzymatically pretreated, phosphorylated, sulfoethylated, and alkoxylated nanocellulose films) manufactured using identical protocols and the determination of the apparent nanocellulose yield of the same nanocelluloses and their tensile strength properties at different extents of delamination (microfluidization). The purpose was to test a previously suggested procedure to estimate the maximum tensile strength on these different procedures. A second goal was to investigate the impact of the nanocellulose yield on the tensile strength properties. The investigations were limited to the nanocellulose research activities at RISE in Stockholm, because these investigations were made with identical experimental laboratory protocols. The importance of such protocols is also stressed. This review shows that the suggested procedure to estimate the maximum tensile strength is a viable proposition, albeit not scientifically proven. Secondly, there is a relationship between the nanocellulose yield and tensile strength properties, although there may not be a linear relationship between the two measures. Full article

(This article belongs to the Special Issue Cellulose Based Nanomaterials and Their Applications)

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17 pages, 6086 KiB

Open AccessEditor’s ChoiceArticle

Smart Electrospun Hybrid Nanofibers Functionalized with Ligand-Free Titanium Nitride (TiN) Nanoparticles for Tissue Engineering

by Viraj P. Nirwan, Eva Filova, Ahmed Al-Kattan, Andrei V. Kabashin and Amir Fahmi

Nanomaterials 2021, 11(2), 519; https://doi.org/10.3390/nano11020519 - 18 Feb 2021

Cited by 19 | Viewed by 3719

Abstract

Herein, we report the fabrication and characterization of novel polycaprolactone (PCL)-based nanofibers functionalized with bare (ligand-free) titanium nitride (TiN) nanoparticles (NPs) for tissue engineering applications. Nanofibers were prepared by a newly developed protocol based on the electrospinning of PCL solutions together with TiN [...] Read more.

Herein, we report the fabrication and characterization of novel polycaprolactone (PCL)-based nanofibers functionalized with bare (ligand-free) titanium nitride (TiN) nanoparticles (NPs) for tissue engineering applications. Nanofibers were prepared by a newly developed protocol based on the electrospinning of PCL solutions together with TiN NPs synthesized by femtosecond laser ablation in acetone. The generated hybrid nanofibers were characterised using spectroscopy, microscopy, and thermal analysis techniques. As shown by scanning electron microscopy measurements, the fabricated electrospun nanofibers had uniform morphology, while their diameter varied between 0.403 ± 0.230 µm and 1.1 ± 0.15 µm by optimising electrospinning solutions and parameters. Thermal analysis measurements demonstrated that the inclusion of TiN NPs in nanofibers led to slight variation in mass degradation initiation and phase change behaviour (T_m). In vitro viability tests using the incubation of 3T3 fibroblast cells in a nanofiber-based matrix did not reveal any adverse effects, confirming the biocompatibility of hybrid nanofiber structures. The generated hybrid nanofibers functionalized with plasmonic TiN NPs are promising for the development of smart scaffold for tissue engineering platforms and open up new avenues for theranostic applications. Full article

(This article belongs to the Section Synthesis, Interfaces and Nanostructures)

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11 pages, 2708 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Performance and Diffusion Robustness of Phase-Change Metasurfaces via a Hybrid Dielectric/Plasmonic Approach

by Joe Shields, Carlota Ruiz de Galarreta, Jacopo Bertolotti and C. David Wright

Nanomaterials 2021, 11(2), 525; https://doi.org/10.3390/nano11020525 - 18 Feb 2021

Cited by 11 | Viewed by 5152

Abstract

Materials of which the refractive indices can be thermally tuned or switched, such as in chalcogenide phase-change alloys, offer a promising path towards the development of active optical metasurfaces for the control of the amplitude, phase, and polarization of light. However, for phase-change [...] Read more.

Materials of which the refractive indices can be thermally tuned or switched, such as in chalcogenide phase-change alloys, offer a promising path towards the development of active optical metasurfaces for the control of the amplitude, phase, and polarization of light. However, for phase-change metasurfaces to be able to provide viable technology for active light control, in situ electrical switching via resistive heaters integral to or embedded in the metasurface itself is highly desirable. In this context, good electrical conductors (metals) with high melting points (i.e., significantly above the melting point of commonly used phase-change alloys) are required. In addition, such metals should ideally have low plasmonic losses, so as to not degrade metasurface optical performance. This essentially limits the choice to a few noble metals, namely, gold and silver, but these tend to diffuse quite readily into phase-change materials (particularly the archetypal Ge₂Sb₂Te₅ alloy used here), and into dielectric resonators such as Si or Ge. In this work, we introduce a novel hybrid dielectric/plasmonic metasurface architecture, where we incorporated a thin Ge₂Sb₂Te₅ layer into the body of a cubic silicon nanoresonator lying on metallic planes that simultaneously acted as high-efficiency reflectors and resistive heaters. Through systematic studies based on changing the configuration of the bottom metal plane between high-melting-point diffusive and low-melting-point nondiffusive metals (Au and Al, respectively), we explicitly show how thermally activated diffusion can catastrophically and irreversibly degrade the optical performance of chalcogenide phase-change metasurface devices, and how such degradation can be successfully overcome at the design stage via the incorporation of ultrathin Si₃N₄ barrier layers between the gold plane and the hybrid Si/Ge₂Sb₂Te₅ resonators. Our work clarifies the importance of diffusion of noble metals in thermally tunable metasurfaces and how to overcome it, thus helping phase-change-based metasurface technology move a step closer towards the realization of real-world applications. Full article

(This article belongs to the Section Nanophotonics Materials and Devices)

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13 pages, 10157 KiB

Open AccessEditor’s ChoiceArticle

Germanium Nanowires as Sensing Devices: Modelization of Electrical Properties

by Luca Seravalli, Claudio Ferrari and Matteo Bosi

Nanomaterials 2021, 11(2), 507; https://doi.org/10.3390/nano11020507 - 17 Feb 2021

Cited by 6 | Viewed by 2650

Abstract

In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering [...] Read more.

In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering a p-doped nanowire with surface traps. We simulate three different types of interactions: (1) Passivation of surface traps; (2) Additional surface charges; (3) Charge transfer from molecules to nanowires. By analyzing simulated I–V characteristics, we observe that: (i) the largest change in current occurs with negative charges on the surfaces; (ii) charge transfer provides relevant current changes only for very high values of additional doping; (iii) for certain values of additional n-doping ambipolar currents could be obtained. The results of these simulations highlight the complexity of the molecular sensing mechanism in nanowires, that depends not only on the NW parameters but also on the properties of the molecules. We expect that these findings will be valuable to extend the knowledge of molecular sensing by germanium nanowires, a fundamental step to develop novel sensors based on these nanostructures. Full article

(This article belongs to the Special Issue Growth, Characterization, and Modelling of Nanostructures for Applications in Sensing)

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15 pages, 2640 KiB

Open AccessEditor’s ChoiceArticle

Chemically-Gated and Sustained Molecular Transport through Nanoporous Gold Thin Films in Biofouling Conditions

by Barath Palanisamy, Noah Goshi and Erkin Seker

Nanomaterials 2021, 11(2), 498; https://doi.org/10.3390/nano11020498 - 16 Feb 2021

Cited by 6 | Viewed by 2931

Abstract

Sustained release and replenishment of the drug depot are essential for the long-term functionality of implantable drug-delivery devices. This study demonstrates the use nanoporous gold (np-Au) thin films for in-plane transport of fluorescein (a small-molecule drug surrogate) over large (mm-scale) distances from a [...] Read more.

Sustained release and replenishment of the drug depot are essential for the long-term functionality of implantable drug-delivery devices. This study demonstrates the use nanoporous gold (np-Au) thin films for in-plane transport of fluorescein (a small-molecule drug surrogate) over large (mm-scale) distances from a distal reservoir to the site of delivery, thereby establishing a constant flux of molecular release. In the absence of halides, the fluorescein transport is negligible due to a strong non-specific interaction of fluorescein with the pore walls. However, in the presence of physiologically relevant concentration of ions, halides preferentially adsorb onto the gold surface, minimizing the fluorescein–gold interactions and thus enabling in-plane fluorescein transport. In addition, the nanoporous film serves as an intrinsic size-exclusion matrix and allows for sustained release in biofouling conditions (dilute serum). The molecular release is reproducibly controlled by gating it in response to the presence of halides at the reservoir (source) and the release site (sink) without external triggers (e.g., electrical and mechanical). Full article

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14 pages, 3828 KiB

Open AccessEditor’s ChoiceArticle

Ice-Templated Cellulose Nanofiber Filaments as a Reinforcement Material in Epoxy Composites

by Tuukka Nissilä, Jiayuan Wei, Shiyu Geng, Anita Teleman and Kristiina Oksman

Nanomaterials 2021, 11(2), 490; https://doi.org/10.3390/nano11020490 - 15 Feb 2021

Cited by 27 | Viewed by 4667

Abstract

Finding renewable alternatives to the commonly used reinforcement materials in composites is attracting a significant amount of research interest. Nanocellulose is a promising candidate owing to its wide availability and favorable properties such as high Young’s modulus. This study addressed the major problems [...] Read more.

Finding renewable alternatives to the commonly used reinforcement materials in composites is attracting a significant amount of research interest. Nanocellulose is a promising candidate owing to its wide availability and favorable properties such as high Young’s modulus. This study addressed the major problems inherent to cellulose nanocomposites, namely, controlling the fiber structure and obtaining a sufficient interfacial adhesion between nanocellulose and a non-hydrophilic matrix. Unidirectionally aligned cellulose nanofiber filament mats were obtained via ice-templating, and chemical vapor deposition was used to cover the filament surfaces with an aminosilane before impregnating the mats with a bio-epoxy resin. The process resulted in cellulose nanocomposites with an oriented structure and a strong fiber–matrix interface. Diffuse reflectance infrared Fourier transform and X-ray photoelectron spectroscopy studies revealed the presence of silane on the filaments. The improved interface, resulting from the surface treatment, was observable in electron microscopy images and was further confirmed by the significant increase in the tan delta peak temperature. The storage modulus of the matrix could be improved up to 2.5-fold with 18 wt% filament content and was significantly higher in the filament direction. Wide-angle X-ray scattering was used to study the orientation of cellulose nanofibers in the filament mats and the composites, and the corresponding orientation indices were 0.6 and 0.53, respectively, indicating a significant level of alignment. Full article

(This article belongs to the Special Issue Advanced Nanocellulose-Based Materials: Production, Properties and Applications)

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26 pages, 8784 KiB

Open AccessEditor’s ChoiceArticle

Hypericum perforatum L.-Mediated Green Synthesis of Silver Nanoparticles Exhibiting Antioxidant and Anticancer Activities

by Abdalrahim Alahmad, Armin Feldhoff, Nadja C. Bigall, Pascal Rusch, Thomas Scheper and Johanna-Gabriela Walter

Nanomaterials 2021, 11(2), 487; https://doi.org/10.3390/nano11020487 - 14 Feb 2021

Cited by 99 | Viewed by 7539

Abstract

This contribution focuses on the green synthesis of silver nanoparticles (AgNPs) with a size < 100 nm for potential medical applications by using silver nitrate solution and Hypericum Perforatum L. (St John’s wort) aqueous extracts. Various synthesis methods were used and compared with [...] Read more.

This contribution focuses on the green synthesis of silver nanoparticles (AgNPs) with a size < 100 nm for potential medical applications by using silver nitrate solution and Hypericum Perforatum L. (St John’s wort) aqueous extracts. Various synthesis methods were used and compared with regard to their yield and quality of obtained AgNPs. Monodisperse spherical nanoparticles were generated with a size of approximately 20 to 50 nm as elucidated by different techniques (SEM, TEM). XRD measurements showed that metallic silver was formed and the particles possess a face-centered cubic structure (fcc). SEM images and FTIR spectra revealed that the AgNPs are covered by a protective surface layer composed of organic components originating from the plant extract. Ultraviolet-visible spectroscopy, dynamic light scattering, and zeta potential were also measured for biologically synthesized AgNPs. A potential mechanism of reducing silver ions to silver metal and protecting it in the nanoscale form has been proposed based on the obtained results. Moreover, the AgNPs prepared in the present study have been shown to exhibit a high antioxidant activity for 2, 2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation, and super oxide anion radical and 2,2-diphenyl-1-picrylhydrazyl. Synthesized AgNPs showed high cytotoxicity by inhibiting cell viability for Hela, Hep G2, and A549 cells. Full article

(This article belongs to the Section Nanofabrication and Nanomanufacturing)

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16 pages, 7362 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Benefits of Polyamide Nanofibrous Materials: Antibacterial Activity and Retention Ability for Staphylococcus Aureus

by Simona Lencova, Kamila Zdenkova, Vera Jencova, Katerina Demnerova, Klara Zemanova, Radka Kolackova, Kristyna Hozdova and Hana Stiborova

Nanomaterials 2021, 11(2), 480; https://doi.org/10.3390/nano11020480 - 13 Feb 2021

Cited by 10 | Viewed by 4710

Abstract

Although nanomaterials are used in many fields, little is known about the fundamental interactions between nanomaterials and microorganisms. To test antimicrobial properties and retention ability, 13 electrospun polyamide (PA) nanomaterials with different morphology and functionalization with various concentrations of AgNO₃ and chlorhexidine [...] Read more.

Although nanomaterials are used in many fields, little is known about the fundamental interactions between nanomaterials and microorganisms. To test antimicrobial properties and retention ability, 13 electrospun polyamide (PA) nanomaterials with different morphology and functionalization with various concentrations of AgNO₃ and chlorhexidine (CHX) were analyzed. Staphylococcus aureus CCM 4516 was used to verify the designed nanomaterials’ inhibition and permeability assays. All functionalized PAs suppressed bacterial growth, and the most effective antimicrobial nanomaterial was evaluated to be PA 12% with 4.0 wt% CHX (inhibition zones: 2.9 ± 0.2 mm; log₁₀ suppression: 8.9 ± 0.0; inhibitory rate: 100.0%). Furthermore, the long-term stability of all functionalized PAs was tested. These nanomaterials can be stored at least nine months after their preparation without losing their antibacterial effect. A filtration apparatus was constructed for testing the retention of PAs. All of the PAs effectively retained the filtered bacteria with log₁₀ removal of 3.3–6.8 and a retention rate of 96.7–100.0%. Surface density significantly influenced the retention efficiency of PAs (p ≤ 0.01), while the effect of fiber diameter was not confirmed (p ≥ 0.05). Due to their stability, retention, and antimicrobial properties, they can serve as a model for medical or filtration applications. Full article

(This article belongs to the Special Issue Synthesis, Structures, and Applications of Electrospun Nanofibers)

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16 pages, 8167 KiB

Open AccessEditor’s ChoiceArticle

Functional and Morphological Changes Induced in Mytilus Hemocytes by Selected Nanoparticles

by Manon Auguste, Craig Mayall, Francesco Barbero, Matej Hočevar, Stefano Alberti, Giacomo Grassi, Victor F. Puntes, Damjana Drobne and Laura Canesi

Nanomaterials 2021, 11(2), 470; https://doi.org/10.3390/nano11020470 - 12 Feb 2021

Cited by 19 | Viewed by 3532

Abstract

Nanoparticles (NPs) show various properties depending on their composition, size, and surface coating, which shape their interactions with biological systems. In particular, NPs have been shown to interact with immune cells, that represent a sensitive surveillance system of external and internal stimuli. In [...] Read more.

Nanoparticles (NPs) show various properties depending on their composition, size, and surface coating, which shape their interactions with biological systems. In particular, NPs have been shown to interact with immune cells, that represent a sensitive surveillance system of external and internal stimuli. In this light, in vitro models represent useful tools for investigating nano-bio-interactions in immune cells of different organisms, including invertebrates. In this work, the effects of selected types of NPs with different core composition, size and functionalization (custom-made PVP-AuNP and commercial nanopolystyrenes PS-NH₂ and PS-COOH) were investigated in the hemocytes of the marine bivalve Mytilus galloprovincialis. The role of exposure medium was evaluated using either artificial seawater (ASW) or hemolymph serum (HS). Hemocyte morphology was investigated by scanning electron microscopy (SEM) and different functional parameters (lysosomal membrane stability, phagocytosis, and lysozyme release) were evaluated. The results show distinct morphological and functional changes induced in mussel hemocytes depending on the NP type and exposure medium. Mussel hemocytes may represent a powerful alternative in vitro model for a rapid pre-screening strategy for NPs, whose utilization will contribute to the understanding of the possible impact of environmental exposure to NPs in marine invertebrates. Full article

(This article belongs to the Special Issue An Evolutionary and Environmental Perspective of the Interaction of Nanomaterials with the Immune System-The Outcomes of the EU Project PANDORA)

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16 pages, 1146 KiB

Open AccessEditor’s ChoiceArticle

Polarization Anisotropies in Strain-Free, Asymmetric, and Symmetric Quantum Dots Grown by Droplet Epitaxy

by Marco Abbarchi, Takaaki Mano, Takashi Kuroda, Akihiro Ohtake and Kazuaki Sakoda

Nanomaterials 2021, 11(2), 443; https://doi.org/10.3390/nano11020443 - 10 Feb 2021

Cited by 4 | Viewed by 2987

Abstract

We provide an extensive and systematic investigation of exciton dynamics in droplet epitaxial quantum dots comparing the cases of (311)A, (001), and (111)A surfaces. Despite a similar s-shell exciton structure common to the three cases, the absence of a wetting layer for (311)A [...] Read more.

We provide an extensive and systematic investigation of exciton dynamics in droplet epitaxial quantum dots comparing the cases of (311)A, (001), and (111)A surfaces. Despite a similar s-shell exciton structure common to the three cases, the absence of a wetting layer for (311)A and (111)A samples leads to a larger carrier confinement compared to (001), where a wetting layer is present. This leads to a more pronounced dependence of the binding energies of s-shell excitons on the quantum dot size and to the strong anti-binding character of the positive-charged exciton for smaller quantum dots. In-plane geometrical anisotropies of (311)A and (001) quantum dots lead to a large electron-hole fine interaction (fine structure splitting (FSS) ∼100 μeV), whereas for the three-fold symmetric (111)A counterpart, this figure of merit is reduced by about one order of magnitude. In all these cases, we do not observe any size dependence of the fine structure splitting. Heavy-hole/light-hole mixing is present in all the studied cases, leading to a broad spread of linear polarization anisotropy (from 0 up to about 50%) irrespective of surface orientation (symmetry of the confinement), fine structure splitting, and nanostructure size. These results are important for the further development of ideal single and entangled photon sources based on semiconductor quantum dots. Full article

(This article belongs to the Special Issue Quantum Nanostructures by Droplet Epitaxy for Optoelectronics and Quantum Information Technologies)

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13 pages, 3078 KiB

Open AccessEditor’s ChoiceArticle

Towards Control of the Size, Composition and Surface Area of NiO Nanostructures by Sn Doping

by María Taeño, David Maestre, Julio Ramírez-Castellanos, Shaohui Li, Pooi See Lee and Ana Cremades

Nanomaterials 2021, 11(2), 444; https://doi.org/10.3390/nano11020444 - 10 Feb 2021

Cited by 17 | Viewed by 3647

Abstract

Achieving nanostructures with high surface area is one of the most challenging tasks as this metric usually plays a key role in technological applications, such as energy storage, gas sensing or photocatalysis, fields in which NiO is gaining increasing attention recently. Furthermore, the [...] Read more.

Achieving nanostructures with high surface area is one of the most challenging tasks as this metric usually plays a key role in technological applications, such as energy storage, gas sensing or photocatalysis, fields in which NiO is gaining increasing attention recently. Furthermore, the advent of modern NiO-based devices can take advantage of a deeper knowledge of the doping process in NiO, and the fabrication of p-n heterojunctions. By controlling experimental conditions such as dopant concentration, reaction time, temperature or pH, NiO morphology and doping mechanisms can be modulated. In this work, undoped and Sn doped nanoparticles and NiO/SnO₂ nanostructures with high surface areas were obtained as a result of Sn incorporation. We demonstrate that Sn incorporation leads to the formation of nanosticks morphology, not previously observed for undoped NiO, promoting p-n heterostructures. Consequently, a surface area value around 340 m²/g was obtained for NiO nanoparticles with 4.7 at.% of Sn, which is nearly nine times higher than that of undoped NiO. The presence of Sn with different oxidation states and variable Ni³⁺/Ni²⁺ ratio as a function of the Sn content were also verified by XPS, suggesting a combination of two charge compensation mechanisms (electronic and ionic) for the substitution of Ni²⁺ by Sn⁴⁺. These results make Sn doped NiO nanostructures a potential candidate for a high number of technological applications, in which implementations can be achieved in the form of NiO–SnO₂ p-n heterostructures. Full article

(This article belongs to the Special Issue Functional Inorganic Nanomaterials)

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11 pages, 347 KiB

Open AccessEditor’s ChoiceArticle

Adsorption of an Ideal Gas on a Small Spherical Adsorbent

by Bjørn A. Strøm, Dick Bedeaux and Sondre K. Schnell

Nanomaterials 2021, 11(2), 431; https://doi.org/10.3390/nano11020431 - 9 Feb 2021

Cited by 6 | Viewed by 2868

Abstract

The ideal gas model is an important and useful model in classical thermodynamics. This remains so for small systems. Molecules in a gas can be adsorbed on the surface of a sphere. Both the free gas molecules and the adsorbed molecules may be [...] Read more.

The ideal gas model is an important and useful model in classical thermodynamics. This remains so for small systems. Molecules in a gas can be adsorbed on the surface of a sphere. Both the free gas molecules and the adsorbed molecules may be modeled as ideal for low densities. The adsorption energy,

U^{s}

, plays an important role in the analysis. For small adsorbents this energy depends on the curvature of the adsorbent. We model the adsorbent as a sphere with surface area

Ω = 4 π R^{2}

, where R is the radius of the sphere. We calculate the partition function for a grand canonical ensemble of two-dimensional adsorbed phases. When connected with the nanothermodynamic framework this gives us the relevant thermodynamic variables for the adsorbed phase controlled by the temperature T, surface area

Ω

, and chemical potential

μ

. The dependence of intensive variables on size may then be systematically investigated starting from the simplest model, namely the ideal adsorbed phase. This dependence is a characteristic feature of small systems which is naturally expressed by the subdivision potential of nanothermodynamics. For surface problems, the nanothermodynamic approach is different, but equivalent to Gibbs’ surface thermodynamics. It is however a general approach to the thermodynamics of small systems, and may therefore be applied to systems that do not have well defined surfaces. It is therefore desirable and useful to improve our basic understanding of nanothermodynamics. Full article

(This article belongs to the Special Issue Nanoscale Thermodynamics)

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14 pages, 5831 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Silver Content on Mechanical Properties of Ti-Cu-Ag Thin Films

by Saqib Rashid, Marco Sebastiani, Muhammad Zeeshan Mughal, Rostislav Daniel and Edoardo Bemporad

Nanomaterials 2021, 11(2), 435; https://doi.org/10.3390/nano11020435 - 9 Feb 2021

Cited by 13 | Viewed by 3958

Abstract

In this work, the ternary titanium, copper, and silver (Ti-Cu-Ag) system is investigated as a potential candidate for the production of mechanically robust biomedical thin films. The coatings are produced by physical vapor deposition—magnetron sputtering (MS-PVD). The composite thin films are deposited on [...] Read more.

In this work, the ternary titanium, copper, and silver (Ti-Cu-Ag) system is investigated as a potential candidate for the production of mechanically robust biomedical thin films. The coatings are produced by physical vapor deposition—magnetron sputtering (MS-PVD). The composite thin films are deposited on a silicon (100) substrate. The ratio between Ti and Cu was approximately kept one, with the variation of the Ag content between 10 and 35 at.%, while the power on the targets is changed during each deposition to get the desired Ag content. Thin film characterization is performed by X-ray diffraction (XRD), nanoindentation (modulus and hardness), to quantitatively evaluate the scratch adhesion, and atomic force microscopy to determine the surface topography. The residual stresses are measured by focused ion beam and digital image correlation method (FIB-DIC). The produced Ti-Cu-Ag thin films appear to be smooth, uniformly thick, and exhibit amorphous structure for the Ag contents lower than 25 at.%, with a transition to partially crystalline structure for higher Ag concentrations. The Ti-Cu control film shows higher values of 124.5 GPa and 7.85 GPa for modulus and hardness, respectively. There is a clear trend of continuous decrease in the modulus and hardness with the increase of Ag content, as lowest value of 105.5 GPa and 6 GPa for 35 at.% Ag containing thin films. In particular, a transition from the compressive (−36.5 MPa) to tensile residual stresses between 229 MPa and 288 MPa are observed with an increasing Ag content. The obtained results suggest that the Ag concentration should not exceed 25 at.%, in order to avoid an excessive reduction of the modulus and hardness with maintaining (at the same time) the potential for an increase of the antibacterial properties. In summary, Ti-Cu-Ag thin films shows characteristic mechanical properties that can be used to improve the properties of biomedical implants such as Ti-alloys and stainless steel. Full article

(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)

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12 pages, 2763 KiB

Open AccessEditor’s ChoiceArticle

Analog Memristive Characteristics of Square Shaped Lanthanum Oxide Nanoplates Layered Device

by Wonkyu Kang, Kyoungmin Woo, Hyon Bin Na, Chi Jung Kang, Tae-Sik Yoon, Kyung Min Kim and Hyun Ho Lee

Nanomaterials 2021, 11(2), 441; https://doi.org/10.3390/nano11020441 - 9 Feb 2021

Cited by 5 | Viewed by 3142

Abstract

Square-shaped or rectangular nanoparticles (NPs) of lanthanum oxide (LaO_x) were synthesized and layered by convective self-assembly to demonstrate an analog memristive device in this study. Along with non-volatile analog memory effect, selection diode property could be co-existent without any implementation of [...] Read more.

Square-shaped or rectangular nanoparticles (NPs) of lanthanum oxide (LaO_x) were synthesized and layered by convective self-assembly to demonstrate an analog memristive device in this study. Along with non-volatile analog memory effect, selection diode property could be co-existent without any implementation of heterogeneous multiple stacks with ~1 μm thick LaO_x NPs layer. Current–voltage (I–V) behavior of the LaO_x NPs resistive switching (RS) device has shown an evolved current level with memristive behavior and additional rectification functionality with threshold voltage. The concurrent memristor and diode type selector characteristics were examined with electrical stimuli or spikes for the duration of 10–50 ms pulse biases. The pulsed spike increased current levels at a read voltage of +0.2 V sequentially along with ±7 V biases, which have emulated neuromorphic operation of long-term potentiation (LTP). This study can open a new application of rare-earth LaO_x NPs as a component of neuromorphic synaptic device. Full article

(This article belongs to the Special Issue Smart Nano-Devices)

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12 pages, 2649 KiB

Open AccessEditor’s ChoiceArticle

Incorporation of CNF with Different Charge Property into PVP Hydrogel and Its Characteristics

by Wanhee Im, Shin Young Park, Sooim Goo, Simyub Yook, Hak Lae Lee, Guihua Yang and Hye Jung Youn

Nanomaterials 2021, 11(2), 426; https://doi.org/10.3390/nano11020426 - 8 Feb 2021

Cited by 10 | Viewed by 3449

Abstract

Cellulose nanofibril (CNF)-added polyvinylpyrrolidone (PVP) hydrogels were prepared using different types of CNFs and their properties were investigated. CNFs with different morphology and surface charge properties were prepared through quaternization and carboxymethylation pretreatments. The quaternized CNF exhibited the narrow and uniform width, and [...] Read more.

Cellulose nanofibril (CNF)-added polyvinylpyrrolidone (PVP) hydrogels were prepared using different types of CNFs and their properties were investigated. CNFs with different morphology and surface charge properties were prepared through quaternization and carboxymethylation pretreatments. The quaternized CNF exhibited the narrow and uniform width, and higher viscoelastic property compared to untreated and carboxymethylated CNF. When CNF was incorporated to PVP hydrogel, gel contents of all hydrogels were similar, irrespective of CNF addition quantity or CNF type. However, the absorptivity of the hydrogels in a swelling medium increased by adding CNF. In particular, the quaternized CNF-added PVP hydrogel exhibited the highest swelling ability. Unlike that of hydrogels with untreated and carboxymethylated CNFs, the storage modulus of PVP hydrogels after swelling significantly increased with an increase in the content of the quaternized CNF. These indicate that a PVP hydrogel with a high absorptivity and storage modulus can be prepared by incorporating the proper type of CNF. Full article

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17 pages, 5811 KiB

Open AccessEditor’s ChoiceArticle

Air-Filled Bubbles Stabilized by Gold Nanoparticle/Photodynamic Dye Hybrid Structures for Theranostics

by Roman A. Barmin, Polina G. Rudakovskaya, Olga I. Gusliakova, Olga A. Sindeeva, Ekaterina S. Prikhozhdenko, Elizaveta A. Maksimova, Ekaterina N. Obukhova, Vasiliy S. Chernyshev, Boris N. Khlebtsov, Alexander A. Solovev, Gleb B. Sukhorukov and Dmitry A. Gorin

Nanomaterials 2021, 11(2), 415; https://doi.org/10.3390/nano11020415 - 6 Feb 2021

Cited by 23 | Viewed by 4255

Abstract

Microbubbles have already reached clinical practice as ultrasound contrast agents for angiography. However, modification of the bubbles’ shell is needed to produce probes for ultrasound and multimodal (fluorescence/photoacoustic) imaging methods in combination with theranostics (diagnostics and therapeutics). In the present work, hybrid structures [...] Read more.

Microbubbles have already reached clinical practice as ultrasound contrast agents for angiography. However, modification of the bubbles’ shell is needed to produce probes for ultrasound and multimodal (fluorescence/photoacoustic) imaging methods in combination with theranostics (diagnostics and therapeutics). In the present work, hybrid structures based on microbubbles with an air core and a shell composed of bovine serum albumin, albumin-coated gold nanoparticles, and clinically available photodynamic dyes (zinc phthalocyanine, indocyanine green) were shown to achieve multimodal imaging for potential applications in photodynamic therapy. Microbubbles with an average size of 1.5 ± 0.3 μm and concentration up to 1.2 × 10⁹ microbubbles/mL were obtained and characterized. The introduction of the dye into the system reduced the solution’s surface tension, leading to an increase in the concentration and stability of bubbles. The combination of gold nanoparticles and photodynamic dyes’ influence on the fluorescent signal and probes’ stability is described. The potential use of the obtained probes in biomedical applications was evaluated using fluorescence tomography, raster-scanning optoacoustic microscopy and ultrasound response measurements using a medical ultrasound device at the frequency of 33 MHz. The results demonstrate the impact of microbubbles’ stabilization using gold nanoparticle/photodynamic dye hybrid structures to achieve probe applications in theranostics. Full article

(This article belongs to the Special Issue Hybrid Plasmonic Nanostructures and Their Applications)

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13 pages, 12522 KiB

Open AccessEditor’s ChoiceArticle

High-Quality Few-Layer Graphene on Single-Crystalline SiC thin Film Grown on Affordable Wafer for Device Applications

by Norifumi Endoh, Shoji Akiyama, Keiichiro Tashima, Kento Suwa, Takamasa Kamogawa, Roki Kohama, Kazutoshi Funakubo, Shigeru Konishi, Hiroshi Mogi, Minoru Kawahara, Makoto Kawai, Yoshihiro Kubota, Takuo Ohkochi, Masato Kotsugi, Koji Horiba, Hiroshi Kumigashira, Maki Suemitsu, Issei Watanabe and Hirokazu Fukidome

Nanomaterials 2021, 11(2), 392; https://doi.org/10.3390/nano11020392 - 4 Feb 2021

Cited by 12 | Viewed by 4310

Abstract

Graphene is promising for next-generation devices. However, one of the primary challenges in realizing these devices is the scalable growth of high-quality few-layer graphene (FLG) on device-type wafers; it is difficult to do so while balancing both quality and affordability. High-quality graphene is [...] Read more.

Graphene is promising for next-generation devices. However, one of the primary challenges in realizing these devices is the scalable growth of high-quality few-layer graphene (FLG) on device-type wafers; it is difficult to do so while balancing both quality and affordability. High-quality graphene is grown on expensive SiC bulk crystals, while graphene on SiC thin films grown on Si substrates (GOS) exhibits low quality but affordable cost. We propose a new method for the growth of high-quality FLG on a new template named “hybrid SiC”. The hybrid SiC is produced by bonding a SiC bulk crystal with an affordable device-type wafer and subsequently peeling off the SiC bulk crystal to obtain a single-crystalline SiC thin film on the wafer. The quality of FLG on this hybrid SiC is comparable to that of FLG on SiC bulk crystals and much higher than of GOS. FLG on the hybrid SiC exhibited high carrier mobilities, comparable to those on SiC bulk crystals, as anticipated from the linear band dispersions. Transistors using FLG on the hybrid SiC showed the potential to operate in terahertz frequencies. The proposed method is suited for growing high-quality FLG on desired substrates with the aim of realizing graphene-based high-speed devices. Full article

(This article belongs to the Special Issue Nanoporous Carbon: Synthesis, Characterization, and Applications)

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10 pages, 4409 KiB

Open AccessEditor’s ChoiceArticle

Cellulose Nanofiber Composite with Bimetallic Zeolite Imidazole Framework for Electrochemical Supercapacitors

by Hemraj M. Yadav, Jong Deok Park, Hyeong Cheol Kang, Jeonghun Kim and Jae-Joon Lee

Nanomaterials 2021, 11(2), 395; https://doi.org/10.3390/nano11020395 - 4 Feb 2021

Cited by 23 | Viewed by 4899

Abstract

Cellulose nanofiber (CNF) and hybrid zeolite imidazole framework (HZ) are an emerging biomaterial and a porous carbonous material, respectively. The composite of these two materials could have versatile physiochemical characteristics. A cellulose nanofiber and cobalt-containing zeolite framework-based composite was prepared using an in-situ [...] Read more.

Cellulose nanofiber (CNF) and hybrid zeolite imidazole framework (HZ) are an emerging biomaterial and a porous carbonous material, respectively. The composite of these two materials could have versatile physiochemical characteristics. A cellulose nanofiber and cobalt-containing zeolite framework-based composite was prepared using an in-situ and eco-friendly chemical method followed by pyrolysis. The composite was comprised of cobalt nanoparticles decorated on highly graphitized N-doped nanoporous carbons (NPC) wrapped with carbon nanotubes (CNTs) produced from the direct carbonization of HZ. By varying the ratio of CNF in the composite, we determined the optimal concentration and characterized the derived samples using sophisticated techniques. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of CNF in the metallic cobalt-covered N-doped NPC wrapped with CNTs. The CNF–HZNPC composite electrodes show superior electrochemical performance, which is suitable for supercapacitor applications; its specific capacitance is 146 F/g at 1 A/g. Furthermore, the composite electrodes retain a cycling stability of about 90% over 2000 charge–discharge cycles at 10 A/g. The superior electrochemical properties of the cellulose make it a promising candidate for developing electrodes for energy storage applications. Full article

(This article belongs to the Special Issue Metal Organic Frameworks in Energy Storage)

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19 pages, 26313 KiB

Open AccessEditor’s ChoiceArticle

Inorganic Nanocarriers for Encapsulation of Natural Antimicrobial Compounds for Potential Food Packaging Application: A Comparative Study

by Tina Gulin-Sarfraz, Georgios N. Kalantzopoulos, Marit Kvalvåg Pettersen, Anette Wold Åsli, Ingunn Tho, Lars Axelsson and Jawad Sarfraz

Nanomaterials 2021, 11(2), 379; https://doi.org/10.3390/nano11020379 - 2 Feb 2021

Cited by 16 | Viewed by 3850

Abstract

Design and development of novel inorganic nanocarriers for encapsulation of natural antimicrobial substances for food packaging applications have received great interest during the last years. Natural nanoclays are the most investigated nanocarriers and recently interest has also grown in the synthetically produced porous [...] Read more.

Design and development of novel inorganic nanocarriers for encapsulation of natural antimicrobial substances for food packaging applications have received great interest during the last years. Natural nanoclays are the most investigated nanocarriers and recently interest has also grown in the synthetically produced porous silica particles. However, these different carrier matrices have not been compared in terms of their loading capability and subsequent release. In this study, the feasibility of porous silica particles (with different pore structures and/or surface functionalities) and commercially available nanoclays were evaluated as encapsulation matrices. Two well-studied antimicrobial substances, thymol and curcumin, were chosen as volatile and non-volatile model compounds, respectively. The encapsulation efficiency, and the subsequent dispersibility and release, of these substances differed significantly among the nanocarriers. Encapsulation of the volatile compound highly depends on the inner surface area, i.e., the protective pore environment, and an optimal nanocarrier can protect the encapsulated thymol from volatilization. For the non-volatile compound, only the release rate and dispersibility are affected by the pore structure. Further, water-activated release of the volatile compound was demonstrated and exhibited good antimicrobial efficacy in the vapor phase against Staphylococcus aureus. This comparative study can provide a base for selecting the right nanocarrier aimed at a specific food packaging application. No nanocarrier can be considered as a universally applicable one. Full article

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8 pages, 1685 KiB

Open AccessEditor’s ChoiceArticle

Control of Light Transmission in a Plasmonic Liquid Metacrystal

by Alexander Zharov, Zacharias Viskadourakis, George Kenanakis, Vanessa Fierro and Alain Celzard

Nanomaterials 2021, 11(2), 346; https://doi.org/10.3390/nano11020346 - 1 Feb 2021

Cited by 5 | Viewed by 2650

Abstract

In this study, we experimentally demonstrated the control of light transmission through a slab of plasmonic liquid metacrystal by an external electric field. By applying the external static field, we were able to induce macroscopic anisotropy, which caused the polarization-dependent suppression of transmission [...] Read more.

In this study, we experimentally demonstrated the control of light transmission through a slab of plasmonic liquid metacrystal by an external electric field. By applying the external static field, we were able to induce macroscopic anisotropy, which caused the polarization-dependent suppression of transmission at resonant frequencies. Such behavior indicates the selective plasmon excitation governed by the orientation of the meta-atoms with respect to the polarization of the electromagnetic wave. The problem of light transmission through a plasmonic liquid metacrystal was analyzed theoretically from first principles, and the obtained results were compared with the experimental data. Full article

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12 pages, 2806 KiB

Open AccessEditor’s ChoiceArticle

Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering

by Serguei Savilov, Evgeniya Suslova, Vsevolod Epishev, Evgeniya Tveritinova, Yuriy Zhitnev, Alexander Ulyanov, Konstantin Maslakov and Oksana Isaikina

Nanomaterials 2021, 11(2), 352; https://doi.org/10.3390/nano11020352 - 1 Feb 2021

Cited by 18 | Viewed by 2907

Abstract

We analyze how the changes in the dimension of carbon nanomaterial (CNM) affect their catalytic conversion of secondary aliphatic alcohols. Carbon nanotubes (CNTs) consolidated by spark plasma sintering (SPS) were inactive in the conversion of secondary C₃-C₄ aliphatic alcohols because [...] Read more.

We analyze how the changes in the dimension of carbon nanomaterial (CNM) affect their catalytic conversion of secondary aliphatic alcohols. Carbon nanotubes (CNTs) consolidated by spark plasma sintering (SPS) were inactive in the conversion of secondary C₃-C₄ aliphatic alcohols because of the «healing» of defects in carbon structure during SPS. Gas-phase treatment of consolidated CNTs with HNO₃ vapors led to their surface oxidation without destruction of the bulk structure of pellets. The oxygen content in consolidated CNTs determined by X-ray photoelectron spectroscopy increased from 11.3 to 14.9 at. % with increasing the oxidation time from 3 to 6 h. Despite the decrease in the specific surface area, the oxidized samples showed enhanced catalytic activity in alcohol conversion because of the increased number of oxygen radicals with unpaired electrons, which was established by electron paramagnetic resonance spectroscopy. We conclude that the structure of CNM determines the content and/or ratio of sp² and sp³-hybridized carbon atoms in the material. The experimental and literature data demonstrated that sp³-hybridized carbon atoms on the surface are probably the preferable site for catalytic conversion of alcohols. Full article

(This article belongs to the Special Issue Surface Modifications of Carbon Nanomaterials)

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12 pages, 7162 KiB

Open AccessEditor’s ChoiceArticle

Ruling Factors in Cinnamaldehyde Hydrogenation: Activity and Selectivity of Pt-Mo Catalysts

by Marta Stucchi, Maela Manzoli, Filippo Bossola, Alberto Villa and Laura Prati

Nanomaterials 2021, 11(2), 362; https://doi.org/10.3390/nano11020362 - 1 Feb 2021

Cited by 9 | Viewed by 3454

Abstract

To obtain selective hydrogenation catalysts with low noble metal content, two carbon-supported Mo-Pt bimetallic catalysts have been synthesized from two different molybdenum precursors, i.e., Na₂MoO₄ and (NH₄)₆Mo₇O₂₄. The results obtained by X-ray [...] Read more.

To obtain selective hydrogenation catalysts with low noble metal content, two carbon-supported Mo-Pt bimetallic catalysts have been synthesized from two different molybdenum precursors, i.e., Na₂MoO₄ and (NH₄)₆Mo₇O₂₄. The results obtained by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) combined with the presence and strength of acid sites clarified the different catalytic behavior toward cinnamaldehyde hydrogenation. After impregnating the carbon support with Mo precursors, each sample was used either as is or treated at 400 °C in N₂ flow, as support for Pt nanoparticles (NPs). The heating treatment before Pt deposition had a positive effect on the catalytic performance. Indeed, TEM analyses showed very homogeneously dispersed Pt NPs only when they were deposited on the heat-treated Mo/C supports, and XPS analyses revealed an increase in both the exposure and reduction of Pt, which was probably tuned by different MoO₃/MoO₂ ratios. Moreover, the different acid properties of the catalysts resulted in different selectivity. Full article

(This article belongs to the Special Issue Design and Synthesis of Nanostructured Materials for Catalytic Applications)

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13 pages, 20670 KiB

Open AccessEditor’s ChoiceArticle

Real-Time Tracking of Highly Luminescent Mesoporous Silica Particles Modified with Europium β-Diketone Chelates in Living Cells

by Jong-Seok Kim, Sung Ki Lee, Hansol Doh, Myeong Yun Kim and Do Kyung Kim

Nanomaterials 2021, 11(2), 343; https://doi.org/10.3390/nano11020343 - 29 Jan 2021

Cited by 9 | Viewed by 3841

Abstract

Highly luminescent europium complexes modified mesoporous silica particles (MSP) were synthesized as an imaging probes for both in-vitro diagnostic and in-vivo cellular tracking agents. Europium β-diketone chelates (4,4,4-trifluoro-l-(2-thienyl)-l,3-butanedione) trioctylphosphine europium (III) (Eu(TTA)₃(P(Oct)₃)₃) were incorporated inside the nanocavities [...] Read more.

Highly luminescent europium complexes modified mesoporous silica particles (MSP) were synthesized as an imaging probes for both in-vitro diagnostic and in-vivo cellular tracking agents. Europium β-diketone chelates (4,4,4-trifluoro-l-(2-thienyl)-l,3-butanedione) trioctylphosphine europium (III) (Eu(TTA)₃(P(Oct)₃)₃) were incorporated inside the nanocavities that existed in hierarchical MSP (Eu@MSP). The MSP and Eu@MSP on mouse bone marrow-derived macrophages (BMDMs) did not show any toxic effect. The MSP and Eu@MSP in the BMDMs were found at cytoplasm without any degradation and immunogenicity. However, both pro- and anti-inflammatory cytokines of macrophages were significantly increased when lipopolysaccharide and a high concentration (100 μg/mL) of MSP and Eu@MSP were treated simultaneously. Full article

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13 pages, 1589 KiB

Open AccessEditor’s ChoiceArticle

Novel Nano-Filled Coatings for the Protection of Built Heritage Stone Surfaces

by Mariateresa Lettieri, Maurizio Masieri and Mariaenrica Frigione

Nanomaterials 2021, 11(2), 301; https://doi.org/10.3390/nano11020301 - 25 Jan 2021

Cited by 13 | Viewed by 3532

Abstract

An experimental nano-filled coating, based on a fluorine resin containing SiO₂ nano-particles, was applied on calcareous stones, representative of materials used in buildings and monuments of the Mediterranean basin; for comparison purposes, two commercial products were applied on the same substrates. The [...] Read more.

An experimental nano-filled coating, based on a fluorine resin containing SiO₂ nano-particles, was applied on calcareous stones, representative of materials used in buildings and monuments of the Mediterranean basin; for comparison purposes, two commercial products were applied on the same substrates. The efficacy of the protective treatments was assessed by analyzing different characteristics of the three experimental/commercial products, i.e., color changes and permeability to water vapor to evaluate the treatments’ harmlessness; capillary water absorption and water stone contact angle to evaluate the protection against water ingress; oleophobicity of the treated surfaces and the behavior under staining by acrylic blue-colored spray paint and felt-tip marker to verify the anti-graffiti action. Finally, the properties of the treated stone surfaces were analyzed also after the application of pancreatin, used to simulate bird excreta (guano). The protective coatings were found to promote graffiti removal, reducing also the detrimental effects due to simulated guano. The experimental nano-filled product, in addition, was able to provide outstanding performance but using smaller amounts of product in comparison to commercial systems. Full article

(This article belongs to the Special Issue Nanotechnologies for Diagnostic, Conservation and Restoration of Cultural Heritage)

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15 pages, 4351 KiB

Open AccessEditor’s ChoiceArticle

Effect of Size and Shape on Electrochemical Performance of Nano-Silicon-Based Lithium Battery

by Caroline Keller, Antoine Desrues, Saravanan Karuppiah, Eléa Martin, John P. Alper, Florent Boismain, Claire Villevieille, Nathalie Herlin-Boime, Cédric Haon and Pascale Chenevier

Nanomaterials 2021, 11(2), 307; https://doi.org/10.3390/nano11020307 - 25 Jan 2021

Cited by 50 | Viewed by 6999

Abstract

Silicon is a promising material for high-energy anode materials for the next generation of lithium-ion batteries. The gain in specific capacity depends highly on the quality of the Si dispersion and on the size and shape of the nano-silicon. The aim of this [...] Read more.

Silicon is a promising material for high-energy anode materials for the next generation of lithium-ion batteries. The gain in specific capacity depends highly on the quality of the Si dispersion and on the size and shape of the nano-silicon. The aim of this study is to investigate the impact of the size/shape of Si on the electrochemical performance of conventional Li-ion batteries. The scalable synthesis processes of both nanoparticles and nanowires in the 10–100 nm size range are discussed. In cycling lithium batteries, the initial specific capacity is significantly higher for nanoparticles than for nanowires. We demonstrate a linear correlation of the first Coulombic efficiency with the specific area of the Si materials. In long-term cycling tests, the electrochemical performance of the nanoparticles fades faster due to an increased internal resistance, whereas the smallest nanowires show an impressive cycling stability. Finally, the reversibility of the electrochemical processes is found to be highly dependent on the size/shape of the Si particles and its impact on lithiation depth, formation of crystalline Li₁₅Si₄ in cycling, and Li transport pathways. Full article

(This article belongs to the Special Issue Silica and Silicon Based Nanostructures)

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10 pages, 1301 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Homodyne Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses with Static Electric Fields

by Alessandro Tomasino, Riccardo Piccoli, Yoann Jestin, Boris Le Drogoff, Mohamed Chaker, Aycan Yurtsever, Alessandro Busacca, Luca Razzari and Roberto Morandotti

Nanomaterials 2021, 11(2), 283; https://doi.org/10.3390/nano11020283 - 22 Jan 2021

Cited by 9 | Viewed by 2583

Abstract

We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, [...] Read more.

We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, which involves demanding square-wave voltage amplifiers, phase-locked to the THz pulse train, as well as an electronic circuit for the demodulation of the readout signal. Here, we demonstrate that the SSBCD technique can be operated via a very simple homodyne scheme, exploiting plain static bias voltages. We show that the homodyne SSBCD signal turns into a bipolar transient when the static field overcomes the THz field strength, without the requirement of an additional demodulating circuit. Moreover, we introduce a differential configuration, which extends the applicability of the homodyne scheme to higher THz field strengths, also leading a two-fold improvement of the dynamic range compared to the heterodyne counterpart. Finally, we demonstrate that, by reversing the sign of the static voltage, it is possible to directly retrieve the absolute THz pulse polarity. The homodyne configuration makes the SSBCD technique of much easier access, leading to a vast range of field-resolved applications. Full article

(This article belongs to the Special Issue Materials for Sources and Detectors in the GIGA-TERA-MIR and NIR-IR Ranges)

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