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Open AccessArticle

Growth of Ca_xCoO₂ Thin Films by A Two-Stage Phase Transformation from CaO–CoO Thin Films Deposited by Rf-Magnetron Reactive Cosputtering

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Biplab Paul

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Jun Lu

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Per Eklund

Nanomaterials 2019, 9(3), 443; https://doi.org/10.3390/nano9030443 - 15 Mar 2019

Cited by 4 | Viewed by 2470

Abstract

The layered cobaltates A_xCoO₂ (A: alkali metals and alkaline earth metals) are of interest in the area of energy harvesting and electronic applications, due to their good electronic and thermoelectric properties. However, their future widespread applicability depends on the simplicity [...] Read more.

The layered cobaltates A_xCoO₂ (A: alkali metals and alkaline earth metals) are of interest in the area of energy harvesting and electronic applications, due to their good electronic and thermoelectric properties. However, their future widespread applicability depends on the simplicity and cost of the growth technique. Here, we have investigated the sputtering/annealing technique for the growth of Ca_xCoO₂ (x = 0.33) thin films. In this approach, CaO–CoO film is first deposited by rf-magnetron reactive cosputtering from metallic targets of Ca and Co. Second, the as-deposited film is reactively annealed under O₂ gas flow to form the final phase of Ca_xCoO₂. The advantage of the present technique is that, unlike conventional sputtering from oxide targets, the sputtering is done from the metallic targets of Ca and Co; thus, the deposition rate is high. Furthermore, the composition of the film is controllable by controlling the power at the targets. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Electrospinning of Polystyrene/Polyhydroxybutyrate Nanofibers Doped with Porphyrin and Graphene for Chemiresistor Gas Sensors

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Giuseppe Scarascia-Mugnozza

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Antonella Macagnano

Nanomaterials 2019, 9(2), 280; https://doi.org/10.3390/nano9020280 - 17 Feb 2019

Cited by 35 | Viewed by 4356

Abstract

Structural and functional properties of polymer composites based on carbon nanomaterials are so attractive that they have become a big challenge in chemical sensors investigation. In the present study, a thin nanofibrous layer, comprising two insulating polymers (polystyrene (PS) and polyhydroxibutyrate (PHB)), a [...] Read more.

Structural and functional properties of polymer composites based on carbon nanomaterials are so attractive that they have become a big challenge in chemical sensors investigation. In the present study, a thin nanofibrous layer, comprising two insulating polymers (polystyrene (PS) and polyhydroxibutyrate (PHB)), a known percentage of nanofillers of mesoporous graphitized carbon (MGC) and a free-base tetraphenylporphyrin, was deposited onto an Interdigitated Electrode (IDE) by electrospinning technology. The potentials of the working temperature to drive both the sensitivity and the selectivity of the chemical sensor were studied and described. The effects of the porphyrin combination with the composite graphene–polymer system appeared evident when nanofibrous layers, with and without porphyrin, were compared for their morphology and electrical and sensing parameters. Porphyrin fibers appeared smoother and thinner and were more resistive at lower temperature, but became much more conductive when temperature increased to 60–70 °C. Both adsorption and diffusion of chemicals seemed ruled by porphyrin according its combination inside the composite fiber, since the response rates dramatically increased (toluene and acetic acid). Finally, the opposite effect of the working temperature on the sensitivity of the porphyrin-doped fibers (i.e., increasing) and the porphyrin-free fibers (i.e., decreasing) seemed further confirmation of the key role of such a macromolecule in the VOC (volatile organic compound) adsorption. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Notable Enhancement of Phase Transition Performance and Luminous Transmittance in VO₂ Films via Simple Method of Ar/O Plasma Post-Treatment

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Nanomaterials 2019, 9(1), 102; https://doi.org/10.3390/nano9010102 - 16 Jan 2019

Cited by 7 | Viewed by 3056

Abstract

Ar/O plasma irradiation is proposed for post-treatment of vanadium dioxide (VO₂) films. Oxidation and surface migration were observed in the VO₂ films following irradiation. This combined effect leads to an effective stoichiometry refinement and microstructure reconstruction in the interfacial area. [...] Read more.

Ar/O plasma irradiation is proposed for post-treatment of vanadium dioxide (VO₂) films. Oxidation and surface migration were observed in the VO₂ films following irradiation. This combined effect leads to an effective stoichiometry refinement and microstructure reconstruction in the interfacial area. A notable improvement in luminous transmittance and an enhancement in phase transition performance of the treated VO₂ films were achieved. Compared with that of as-deposited VO₂ films, the electrical phase transition amplitude of treated films increased more than two-fold. The relative improvement in luminous transmittance (380–780 nm) is 47.4% (from 25.1% to 37%) and the increase in solar transmittance is 66.9% (from 29.9% to 49.9%), which is comparable to or better than the previous work using anti-reflection (AR) coatings or doping methods. The interfacial boundary state proved to be crucial and Ar/O plasma irradiation offers an effective approach for further refinement of thermochromic VO₂ films. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Linear Birefringent Films of Cellulose Nanocrystals Produced by Dip-Coating

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Arturo Mendoza-Galván

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Tania Tejeda-Galán

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Amos B. Domínguez-Gómez

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Reina Araceli Mauricio-Sánchez

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Kenneth Järrendahl

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Hans Arwin

Nanomaterials 2019, 9(1), 45; https://doi.org/10.3390/nano9010045 - 31 Dec 2018

Cited by 19 | Viewed by 4270

Abstract

Transparent films of cellulose nanocrystals (CNC) are prepared by dip-coating on glass substrates from aqueous suspensions of hydrolyzed filter paper. Dragging forces acting during films’ deposition promote a preferential alignment of the rod-shaped CNC. Films that are 2.8 and 6.0 µm in thickness [...] Read more.

Transparent films of cellulose nanocrystals (CNC) are prepared by dip-coating on glass substrates from aqueous suspensions of hydrolyzed filter paper. Dragging forces acting during films’ deposition promote a preferential alignment of the rod-shaped CNC. Films that are 2.8 and 6.0 µm in thickness show retardance effects, as evidenced by placing them between a linearly polarized light source and a linear polarizer sheet in the extinction configuration. Transmission Mueller matrix spectroscopic ellipsometry measurements at normal incidence as a function of sample rotation were used to characterize polarization properties. A differential decomposition of the Mueller matrix reveals linear birefringence as the unique polarization parameter. These results show a promising way for obtaining CNC birefringent films by a simple and controllable method. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Ultra-Thin Platinum Deposits by Surface-Limited Redox Replacement of Tellurium

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Marie-Christine Record

Nanomaterials 2018, 8(10), 836; https://doi.org/10.3390/nano8100836 - 15 Oct 2018

Cited by 3 | Viewed by 4198

Abstract

Platinum is the most employed electrocatalyst for the reactions taking place in energy converters, such as the oxygen reduction reaction in proton exchange membrane fuel cells, despite being a very low abundant element in the earth’s crust and thus extremely expensive. The search [...] Read more.

Platinum is the most employed electrocatalyst for the reactions taking place in energy converters, such as the oxygen reduction reaction in proton exchange membrane fuel cells, despite being a very low abundant element in the earth’s crust and thus extremely expensive. The search for more active electrocatalysts with ultra-low Pt loading is thus a very active field of investigation. Here, surface-limited redox replacement (SLRR) that utilizes the monolayer-limited nature of underpotential deposition (UPD) was used to prepare ultrathin deposits of Pt, using Te as sacrificial metal. Cyclic voltammetry and anodic potentiodynamic scanning experiments have been performed to determine the optimal deposition conditions. Physicochemical and electrochemical characterization of the deposited Pt was carried out. The deposit comprises a series of contiguous Pt islands that form along the grain interfaces of the Au substrate. The electrochemical surface area (ECSA) of the Pt deposit obtained after 5 replacements, estimated to be 18 m²/g, is in agreement with the ECSA of extended surface catalysts on flat surfaces. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

On the Structure of Ultrathin FeO Films on Ag(111)

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Nanomaterials 2018, 8(10), 828; https://doi.org/10.3390/nano8100828 - 13 Oct 2018

Cited by 8 | Viewed by 3832

Abstract

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk [...] Read more.

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moiré superstructure with 45 Å periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films’ preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Passive Sampling of Gaseous Elemental Mercury Based on a Composite TiO₂NP/AuNP Layer

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Nanomaterials 2018, 8(10), 798; https://doi.org/10.3390/nano8100798 - 07 Oct 2018

Cited by 8 | Viewed by 2676

Abstract

Passive sampling systems (PASs) are a low cost strategy to quantify Hg levels in air over both different environmental locations and time periods of few hours to weeks/months. For this reason, novel nanostructured materials have been designed and developed. They consist of an [...] Read more.

Passive sampling systems (PASs) are a low cost strategy to quantify Hg levels in air over both different environmental locations and time periods of few hours to weeks/months. For this reason, novel nanostructured materials have been designed and developed. They consist of an adsorbent layer made of titania nanoparticles (TiO₂NPs, ≤25 nm diameter) finely decorated with gold nanoparticles. The TiO₂NPs functionalization occurred for the photocatalytic properties of titania-anatase when UV-irradiated in an aqueous solution containing HAuCl₄. The resulting nanostructured suspension was deposited by drop-casting on a thin quartz slices, dried and then incorporated into a common axial sampler to be investigated as a potential PAS device. The morphological characteristics of the sample were studied by High-Resolution Transmission Electron Microscopy, Atomic Force Microscopy, and Optical Microscopy. UV-Vis spectra showed a blue shift of the membrane when exposed to Hg⁰ vapors. The adsorbed mercury was thermally desorbed for a few minutes, and then quantified by a mercury vapor analyzer. Such a sampling system reported an efficiency of adsorption that was equal to ≈95%. Temperature and relative humidity only mildly affected the membrane performances. These structures seem to be promising candidates for mercury samplers, due to both the strong affinity of gold with Hg, and the wide adsorbing surface. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessFeature PaperArticle

Surface-Limited Electrodeposition of Continuous Platinum Networks on Highly Ordered Pyrolytic Graphite

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Nanomaterials 2018, 8(9), 721; https://doi.org/10.3390/nano8090721 - 13 Sep 2018

Cited by 4 | Viewed by 2971

Abstract

Continuous thin platinum nanoplatelet networks and thin films were obtained on the flat surface of highly ordered pyrolytic graphite (HOPG) by high overpotential electrodeposition. By increasing the deposition time, the morphology of the Pt deposits can be progressively tuned from isolated nanoplatelets, interconnected [...] Read more.

Continuous thin platinum nanoplatelet networks and thin films were obtained on the flat surface of highly ordered pyrolytic graphite (HOPG) by high overpotential electrodeposition. By increasing the deposition time, the morphology of the Pt deposits can be progressively tuned from isolated nanoplatelets, interconnected nanostructures, and thin large flat islands. The deposition is surface-limited and the thickness of the deposits, equivalent to 5 to 12 Pt monolayers, is not time dependent. The presence of Pt (111) facets is confirmed by High Resolution Transmission Electron Microscopy (HRTEM) and evidence for the early formation of a platinum monolayer is provided by Scanning Transmission Electron Microscopy and Energy Dispersive X-rays Spectroscopy (STEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) analysis. The electroactivity towards the oxygen reduction reaction of the 2D deposits is also assessed, demonstrating their great potential in energy conversion devices where ultra-low loading of Pt via extended surfaces is a reliable strategy. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Symmetry-Induced Structuring of Ultrathin FeO and Fe₃O₄ Films on Pt(111) and Ru(0001)

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Nanomaterials 2018, 8(9), 719; https://doi.org/10.3390/nano8090719 - 12 Sep 2018

Cited by 3 | Viewed by 4036

Abstract

Iron oxide films epitaxially grown on close-packed metal single crystal substrates exhibit nearly-perfect structural order, high catalytic activity (FeO) and room-temperature magnetism (Fe₃O₄). However, the morphology of the films, especially in the ultrathin regime, can be significantly influenced by [...] Read more.

Iron oxide films epitaxially grown on close-packed metal single crystal substrates exhibit nearly-perfect structural order, high catalytic activity (FeO) and room-temperature magnetism (Fe₃O₄). However, the morphology of the films, especially in the ultrathin regime, can be significantly influenced by the crystalline structure of the used support. This work reports an ultra-high vacuum (UHV) low energy electron/synchrotron light-based X-ray photoemission electron microscopy (LEEM/XPEEM) and electron diffraction (µLEED) study of the growth of FeO and Fe₃O₄ on two closed-packed metal single crystal surfaces: Pt(111) and Ru(0001). The results reveal the influence of the mutual orientation of adjacent substrate terraces on the morphology of iron oxide films epitaxially grown on top of them. On fcc Pt(111), which has the same mutual orientation of adjacent monoatomic terraces, FeO(111) grows with the same in-plane orientation on all substrate terraces. For Fe₃O₄(111), one or two orientations are observed depending on the growth conditions. On hcp Ru(0001), the adjacent terraces of which are ‘rotated’ by 180° with respect to each other, the in-plane orientation of initial FeO(111) and Fe₃O₄(111) crystallites is determined by the orientation of the substrate terrace on which they nucleated. The adaptation of three-fold symmetric iron oxides to three-fold symmetric substrate terraces leads to natural structuring of iron oxide films, i.e., the formation of patch-like magnetite layers on Pt(111) and stripe-like FeO and Fe₃O₄ structures on Ru(0001). Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Protective Properties of a Microstructure Composed of Barrier Nanostructured Organics and SiO_x Layers Deposited on a Polymer Matrix

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Nanomaterials 2018, 8(9), 679; https://doi.org/10.3390/nano8090679 - 31 Aug 2018

Cited by 27 | Viewed by 3054

Abstract

The SiO_x barrier nanocoatings have been prepared on selected polymer matrices to increase their resistance against permeation of toxic substances. The aim has been to find out whether the method of vacuum plasma deposition of SiO_x barrier nanocoatings on a polyethylene [...] Read more.

The SiO_x barrier nanocoatings have been prepared on selected polymer matrices to increase their resistance against permeation of toxic substances. The aim has been to find out whether the method of vacuum plasma deposition of SiO_x barrier nanocoatings on a polyethylene terephthalate (PET) foil used by Aluminium Company of Canada (ALCAN) company (ALCAN Packaging Kreuzlingen AG (SA/Ltd., Kreuzlingen, Switzerland) within the production of CERAMIS^® packaging materials with barrier properties can also be used to increase the resistance of foils from other polymers against the permeation of organic solvents and other toxic liquids. The scanning electron microscopy (SEM) microstructure of SiO_x nanocoatings prepared by thermal deposition from SiO in vacuum by the Plasma Assisted Physical Vapour Deposition (PA-PVD) method or vacuum deposition of hexamethyldisiloxane (HMDSO) by the Plasma-enhanced chemical vapour deposition (PECVD) method have been studied. The microstructure and behavior of samples when exposed to a liquid test substance in relation to the barrier properties is described. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Electrodeposition of Two-Dimensional Pt Nanostructures on Highly Oriented Pyrolytic Graphite (HOPG): The Effect of Evolved Hydrogen and Chloride Ions

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Mario A. Alpuche-Aviles

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Nanomaterials 2018, 8(9), 668; https://doi.org/10.3390/nano8090668 - 28 Aug 2018

Cited by 10 | Viewed by 3958

Abstract

We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode (E_appl = ca. −2.2 V vs. NHE, normal hydrogen electrode). The deposition conditions are discussed in terms of [...] Read more.

We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode (E_appl = ca. −2.2 V vs. NHE, normal hydrogen electrode). The deposition conditions are discussed in terms of the electrochemical behavior of the electrodeposition precursor (H₂PtCl₆). We performed cyclic voltammetry (CV) of the electrochemical Pt deposit on HOPG and on Pt substrates to study the relevant phenomena that affect the morphology of Pt deposition. Under conditions where the Pt deposition occurs and H₂ evolution is occurring at the diffusion-limited rate (−0.3 V vs. NHE), Pt forms larger structures on the surface of HOPG, and the electrodeposition of Pt is not limited by diffusion. This indicates the need for large overpotentials to direct the 2D growth of Pt. Investigation of the possible effect of Cl⁻ showed that Cl⁻ deposits on the surface of Pt at low overpotentials, but strips from the surface at potentials more positive than the electrodeposition potential. The CV of Pt on HOPG is a strong function of the nature of the surface. We propose that during immersion of HOPG in the electrodeposition solution (3 mM H₂PtCl₆, 0.5 M NaCl, pH 2.3) Pt islands are formed spontaneously, and these islands drive the growth of the 2D nanostructures. The reducing agents for the spontaneous deposition of Pt from solution are proposed as step edges that get oxidized in the solution. We discuss the possible oxidation reactions for the edge sites. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Comparison of Surface-Bound and Free-Standing Variations of HKUST-1 MOFs: Effect of Activation and Ammonia Exposure on Morphology, Crystallinity, and Composition

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Christopher K. Beaudoin

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Mary E. Anderson

Nanomaterials 2018, 8(9), 650; https://doi.org/10.3390/nano8090650 - 23 Aug 2018

Cited by 9 | Viewed by 3931

Abstract

Metal-organic frameworks (MOFs) are extremely porous, crystalline materials with high surface area for potential use in gas storage, sequestration, and separations. Toward incorporation into structures for these applications, this study compares three variations of surface-bound and free-standing HKUST-1 MOF structures: surface-anchored MOF (surMOF) [...] Read more.

Metal-organic frameworks (MOFs) are extremely porous, crystalline materials with high surface area for potential use in gas storage, sequestration, and separations. Toward incorporation into structures for these applications, this study compares three variations of surface-bound and free-standing HKUST-1 MOF structures: surface-anchored MOF (surMOF) thin film, drop-cast film, and bulk powder. Herein, effects of HKUST-1 ammonia interaction and framework activation, which is removal of guest molecules via heat, are investigated. Impact on morphology and crystal structure as a function of surface confinement and size variance are examined. Scanning probe microscopy, scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and energy dispersive X-ray spectroscopy monitor changes in morphology and crystal structure, track ammonia uptake, and examine elemental composition. After fabrication, ammonia uptake is observed for all MOF variations, but reveals dramatic morphological and crystal structure changes. However, activation of the framework was found to stabilize morphology. For activated surMOF films, findings demonstrate consistent morphology throughout uptake, removal, and recycling of ammonia over multiple exposures. To understand morphological effects, additional ammonia exposure experiments with controlled post-synthetic solvent adsorbates were conducted utilizing a HKUST-1 standard powder. These findings are foundational for determining the capabilities and limitation of MOF films and powders. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

New Insights into the Role of Weak Electron–Phonon Coupling in Nanostructured ZnO Thin Films

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Nanomaterials 2018, 8(8), 632; https://doi.org/10.3390/nano8080632 - 20 Aug 2018

Cited by 8 | Viewed by 3489

Abstract

High-quality crystalline nanostructured ZnO thin films were grown on sapphire substrates by reactive sputtering. As-grown and post-annealed films (in air) with various grain sizes (2 to 29 nm) were investigated by scanning electron microscopy, X-ray diffraction, and Raman scattering. The electron–phonon coupling (EPC) [...] Read more.

High-quality crystalline nanostructured ZnO thin films were grown on sapphire substrates by reactive sputtering. As-grown and post-annealed films (in air) with various grain sizes (2 to 29 nm) were investigated by scanning electron microscopy, X-ray diffraction, and Raman scattering. The electron–phonon coupling (EPC) strength, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminished by reducing the ZnO grain size, which mainly relates to the Fröhlich interactions. Our finding suggests that in the spatially quantum-confined system the low polar nature leads to weak EPC. The outcome of this study is important for the development of nanoscale high-performance optoelectronic devices. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Optical Study and Experimental Realization of Nanostructured Back Reflectors with Reduced Parasitic Losses for Silicon Thin Film Solar Cells

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Pere I Roca Cabarrocas

Nanomaterials 2018, 8(8), 626; https://doi.org/10.3390/nano8080626 - 18 Aug 2018

Cited by 3 | Viewed by 3438

Abstract

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O₂ plasma etching of the polystyrene [...] Read more.

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O₂ plasma etching of the polystyrene spheres, we managed to fabricate hexagonal nanostructured back reflectors. With the help of rigorous modeling, we study the parasitic losses in different back reflectors, non-active layers, and last but not least the light enhancement effect in the silicon absorber layer. Moreover, simulation results have been checked against experimental data. We have demonstrated hexagonal nanostructured amorphous silicon thin film solar cells with a power conversion efficiency of 7.7% and around 34.7% enhancement of the short-circuit current density, compared with planar amorphous silicon thin film solar cells. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Nanostructured Hydrogels by Blend Electrospinning of Polycaprolactone/Gelatin Nanofibers

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Lode Daelemans

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Iline Steyaert

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Ella Schoolaert

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Camille Goudenhooft

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Hubert Rahier

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Karen De Clerck

Nanomaterials 2018, 8(7), 551; https://doi.org/10.3390/nano8070551 - 20 Jul 2018

Cited by 27 | Viewed by 4002

Abstract

Nanofibrous membranes based on polycaprolactone (PCL) have a large potential for use in biomedical applications but are limited by the hydrophobicity of PCL. Blend electrospinning of PCL with other biomedical suited materials, such as gelatin (Gt) allows for the design of better and [...] Read more.

Nanofibrous membranes based on polycaprolactone (PCL) have a large potential for use in biomedical applications but are limited by the hydrophobicity of PCL. Blend electrospinning of PCL with other biomedical suited materials, such as gelatin (Gt) allows for the design of better and new materials. This study investigates the possibility of blend electrospinning PCL/Gt nanofibrous membranes which can be used to design a range of novel materials better suited for biomedical applications. The electrospinnability and stability of PCL/Gt blend nanofibers from a non-toxic acid solvent system are investigated. The solvent system developed in this work allows good electrospinnable emulsions for the whole PCL/Gt composition range. Uniform bead-free nanofibers can easily be produced, and the resulting fiber diameter can be tuned by altering the total polymer concentration. Addition of small amounts of water stabilizes the electrospinning emulsions, allowing the electrospinning of large and homogeneous nanofibrous structures over a prolonged period. The resulting blend nanofibrous membranes are analyzed for their composition, morphology, and homogeneity. Cold-gelling experiments on these novel membranes show the possibility of obtaining water-stable PCL/Gt nanofibrous membranes, as well as nanostructured hydrogels reinforced with nanofibers. Both material classes provide a high potential for designing new material applications. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

Interfacial Model and Characterization for Nanoscale ReB₂/TaN Multilayers at Desired Modulation Period and Ratios: First-Principles Calculations and Experimental Investigations

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Shangxiao Jin

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Dejun Li

Nanomaterials 2018, 8(6), 421; https://doi.org/10.3390/nano8060421 - 10 Jun 2018

Cited by 3 | Viewed by 2976

Abstract

The interfacial structure of ReB₂/TaN multilayers at varied modulation periods (Λ) and modulation ratios (t_ReB2:t_TaN) was investigated using key experiments combined with first-principles calculations. A maximum hardness of 38.7 GPa occurred at Λ [...] Read more.

The interfacial structure of ReB₂/TaN multilayers at varied modulation periods (Λ) and modulation ratios (t_ReB2:t_TaN) was investigated using key experiments combined with first-principles calculations. A maximum hardness of 38.7 GPa occurred at Λ = 10 nm and t_ReB2:t_TaN = 1:1. The fine nanocrystalline structure with small grain sizes remained stable for individual layers at Λ= 10 nm and t_ReB2:t_TaN = 1:1. The calculation of the interfacial structure model and interfacial energy was performed using the first principles to advance the in-depth understanding of the relationship between the mechanical properties, residual stresses, and the interfacial structure. The B-Ta interfacial configuration was calculated to have the highest adsorption energy and the lowest interfacial energy. The interfacial energy and adsorption energy at different t_ReB2:t_TaN followed the same trend as that of the residual stress. The 9ReB₂/21TaN interfacial structure in the B-Ta interfacial configuration was found to be the most stable interface in which the highest adsorption energy and the lowest interfacial energy were obtained. The chemical bonding between the neighboring B atom and the Ta atom in the interfaces showed both covalency and iconicity, which provided a theoretical interpretation of the relationship between the residual stress and the stable interfacial structure of the ReB₂/TaN multilayer. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Open AccessArticle

In-Situ Growth of NiAl-Layered Double Hydroxide on AZ31 Mg Alloy towards Enhanced Corrosion Protection

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Nanomaterials 2018, 8(6), 411; https://doi.org/10.3390/nano8060411 - 07 Jun 2018

Cited by 44 | Viewed by 3706

Abstract

NiAl-layered double hydroxide (NiAl-LDH) coatings grown in-situ on AZ31 Mg alloy were prepared for the first time utilizing a facile hydrothermal method. The surface morphologies, structures, and compositions of the NiAl-LDH coatings were characterized by scanning electron microscopy (SEM), three dimensional (3D) optical [...] Read more.

NiAl-layered double hydroxide (NiAl-LDH) coatings grown in-situ on AZ31 Mg alloy were prepared for the first time utilizing a facile hydrothermal method. The surface morphologies, structures, and compositions of the NiAl-LDH coatings were characterized by scanning electron microscopy (SEM), three dimensional (3D) optical profilometer, X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results show that NiAl-LDH coating could be successfully deposited on Mg alloy substrate using different nickel salts, i.e., carbonate, nitrate, and sulfate salts. Different coatings exhibit different surface morphologies, but all of which exhibit remarkable enhancement in corrosion protection in 3.5 wt % NaCl corrosive electrolyte. When nickel nitrate was employed especially, an extremely large impedance modulus at a low frequency of 0.1 Hz (|Z|_f _{= 0.1 Hz}), 11.6 MΩ cm², and a significant low corrosion current density (j_corr) down to 1.06 nA cm⁻² are achieved, demonstrating NiAl-LDH coating’s great potential application in harsh reaction conditions, particularly in a marine environment. The best corrosion inhibition of NiAl-LDH/CT coating deposited by carbonate may partially ascribed to the uniform and vertical orientation of the nanosheets in the coating. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Self-Catalyzed CdTe Wires

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Nanomaterials 2018, 8(5), 274; https://doi.org/10.3390/nano8050274 - 25 Apr 2018

Cited by 4 | Viewed by 2961

Abstract

CdTe wires have been fabricated via a catalyst free method using the industrially scalable physical vapor deposition technique close space sublimation. Wire growth was shown to be highly dependent on surface roughness and deposition pressure, with only low roughness surfaces being capable of [...] Read more.

CdTe wires have been fabricated via a catalyst free method using the industrially scalable physical vapor deposition technique close space sublimation. Wire growth was shown to be highly dependent on surface roughness and deposition pressure, with only low roughness surfaces being capable of producing wires. Growth of wires is highly (111) oriented and is inferred to occur via a vapor-solid-solid growth mechanism, wherein a CdTe seed particle acts to template the growth. Such seed particles are visible as wire caps and have been characterized via energy dispersive X-ray analysis to establish they are single phase CdTe, hence validating the self-catalysation route. Cathodoluminescence analysis demonstrates that CdTe wires exhibited a much lower level of recombination when compared to a planar CdTe film, which is highly beneficial for semiconductor applications. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Effect of Laminating Pressure on Polymeric Multilayer Nanofibrous Membranes for Liquid Filtration

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Fatma Yalcinkaya

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Jakub Hruza

Nanomaterials 2018, 8(5), 272; https://doi.org/10.3390/nano8050272 - 24 Apr 2018

Cited by 23 | Viewed by 4390

Abstract

In the new century, electrospun nanofibrous webs are widely employed in various applications due to their specific surface area and porous structure with narrow pore size. The mechanical properties have a major influence on the applications of nanofiber webs. Lamination technology is an [...] Read more.

In the new century, electrospun nanofibrous webs are widely employed in various applications due to their specific surface area and porous structure with narrow pore size. The mechanical properties have a major influence on the applications of nanofiber webs. Lamination technology is an important method for improving the mechanical strength of nanofiber webs. In this study, the influence of laminating pressure on the properties of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) nanofibers/laminate was investigated. Heat-press lamination was carried out at three different pressures, and the surface morphologies of the multilayer nanofibrous membranes were observed under an optical microscope. In addition, air permeability, water filtration, and contact angle experiments were performed to examine the effect of laminating pressure on the breathability, water permeability and surface wettability of multilayer nanofibrous membranes. A bursting strength test was developed and applied to measure the maximum bursting pressure of the nanofibers from the laminated surface. A water filtration test was performed using a cross-flow unit. Based on the results of the tests, the optimum laminating pressure was determined for both PAN and PVDF multilayer nanofibrous membranes to prepare suitable microfilters for liquid filtration. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Fabrication of Sericin/Agrose Gel Loaded Lysozyme and Its Potential in Wound Dressing Application

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Nanomaterials 2018, 8(4), 235; https://doi.org/10.3390/nano8040235 - 13 Apr 2018

Cited by 30 | Viewed by 5647

Abstract

Sericin is a biomaterial resource for its significant biodegradability, biocompatibility, hydrophilicity, and reactivity. Designing a material with superabsorbent, antiseptic, and non-cytotoxic wound dressing properties is advantageous to reduce wound infection and promote wound healing. Herein, we propose an environment-friendly strategy to obtain an [...] Read more.

Sericin is a biomaterial resource for its significant biodegradability, biocompatibility, hydrophilicity, and reactivity. Designing a material with superabsorbent, antiseptic, and non-cytotoxic wound dressing properties is advantageous to reduce wound infection and promote wound healing. Herein, we propose an environment-friendly strategy to obtain an interpenetrating polymer network gel through blending sericin and agarose and freeze-drying. The physicochemical characterizations of the sericin/agarose gel including morphology, porosity, swelling behavior, crystallinity, secondary structure, and thermal property were well characterized. Subsequently, the lysozyme loaded sericin/agarose composite gel was successfully prepared by the solution impregnation method. To evaluate the potential of the lysozyme loaded sericin/agarose gel in wound dressing application, we analyzed the lysozyme loading and release, antimicrobial activity, and cytocompatibility of the resulting gel. The results showed the lysozyme loaded composite gel had high porosity, excellent water absorption property, and good antimicrobial activities against Escherichia coli and Staphylococcus aureus. Also, the lysozyme loaded gel showed excellent cytocompatibility on NIH3T3 and HEK293 cells. So, the lysozyme loaded sericin/agarose gel is a potential alternative biomaterial for wound dressing. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Scalable Fabrication of High-Performance Transparent Conductors Using Graphene Oxide-Stabilized Single-Walled Carbon Nanotube Inks

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Linxiang He

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Chengzhu Liao

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Sie Chin Tjong

Nanomaterials 2018, 8(4), 224; https://doi.org/10.3390/nano8040224 - 07 Apr 2018

Cited by 11 | Viewed by 4289

Abstract

Recent development in liquid-phase processing of single-walled carbon nanotubes (SWNTs) has revealed rod-coating as a promising approach for large-scale production of SWNT-based transparent conductors. Of great importance in the ink formulation is the stabilizer having excellent dispersion stability, environmental friendly and tunable rheology [...] Read more.

Recent development in liquid-phase processing of single-walled carbon nanotubes (SWNTs) has revealed rod-coating as a promising approach for large-scale production of SWNT-based transparent conductors. Of great importance in the ink formulation is the stabilizer having excellent dispersion stability, environmental friendly and tunable rheology in the liquid state, and also can be readily removed to enhance electrical conductivity and mechanical stability. Herein we demonstrate the promise of graphene oxide (GO) as a synergistic stabilizer for SWNTs in water. SWNTs dispersed in GO is formulated into inks with homogeneous nanotube distribution, good wetting and rheological properties, and compatible with industrial rod coating practice. Microwave treatment of rod-coated films can reduce GOs and enhance electro-optical performance. The resultant films offer a sheet resistance of ~80 Ω/sq at 86% transparency, along with good mechanical flexibility. Doping the films with nitric acid can further decrease the sheet resistance to ~25 Ω/sq. Comparing with the films fabricated from typical surfactant-based SWNT inks, our films offer superior adhesion as assessed by the Scotch tape test. This study provides new insight into the selection of suitable stabilizers for functional SWNT inks with strong potential for printed electronics. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Metal (Ag/Ti)-Containing Hydrogenated Amorphous Carbon Nanocomposite Films with Enhanced Nanoscratch Resistance: Hybrid PECVD/PVD System and Microstructural Characteristics

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Marios Constantinou

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Petros Nikolaou

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Loukas Koutsokeras

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Apostolos Avgeropoulos

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Dimitrios Moschovas

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Constantinos Varotsis

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Panos Patsalas

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Pantelis Kelires

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Georgios Constantinides

Nanomaterials 2018, 8(4), 209; https://doi.org/10.3390/nano8040209 - 30 Mar 2018

Cited by 9 | Viewed by 4210

Abstract

This study aimed to develop hydrogenated amorphous carbon thin films with embedded metallic nanoparticles (a–C:H:Me) of controlled size and concentration. Towards this end, a novel hybrid deposition system is presented that uses a combination of Plasma Enhanced Chemical Vapor Deposition (PECVD) and Physical [...] Read more.

This study aimed to develop hydrogenated amorphous carbon thin films with embedded metallic nanoparticles (a–C:H:Me) of controlled size and concentration. Towards this end, a novel hybrid deposition system is presented that uses a combination of Plasma Enhanced Chemical Vapor Deposition (PECVD) and Physical Vapor Deposition (PVD) technologies. The a–C:H matrix was deposited through the acceleration of carbon ions generated through a radio-frequency (RF) plasma source by cracking methane, whereas metallic nanoparticles were generated and deposited using terminated gas condensation (TGC) technology. The resulting material was a hydrogenated amorphous carbon film with controlled physical properties and evenly dispersed metallic nanoparticles (here Ag or Ti). The physical, chemical, morphological and mechanical characteristics of the films were investigated through X-ray reflectivity (XRR), Raman spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and nanoscratch testing. The resulting amorphous carbon metal nanocomposite films (a–C:H:Ag and a–C:H:Ti) exhibited enhanced nanoscratch resistance (up to +50%) and low values of friction coefficient (<0.05), properties desirable for protective coatings and/or solid lubricant applications. The ability to form nanocomposite structures with tunable coating performance by potentially controlling the carbon bonding, hydrogen content, and the type/size/percent of metallic nanoparticles opens new avenues for a broad range of applications in which mechanical, physical, biological and/or combinatorial properties are required. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Porous Aluminum Oxide and Magnesium Oxide Films Using Organic Hydrogels as Structure Matrices

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Zimei Chen

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Dirk Kuckling

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Michael Tiemann

Nanomaterials 2018, 8(4), 186; https://doi.org/10.3390/nano8040186 - 22 Mar 2018

Cited by 6 | Viewed by 5110

Abstract

We describe the synthesis of mesoporous Al₂O₃ and MgO layers on silicon wafer substrates by using poly(dimethylacrylamide) hydrogels as porogenic matrices. Hydrogel films are prepared by spreading the polymer through spin-coating, followed by photo-cross-linking and anchoring to the substrate surface. [...] Read more.

We describe the synthesis of mesoporous Al₂O₃ and MgO layers on silicon wafer substrates by using poly(dimethylacrylamide) hydrogels as porogenic matrices. Hydrogel films are prepared by spreading the polymer through spin-coating, followed by photo-cross-linking and anchoring to the substrate surface. The metal oxides are obtained by swelling the hydrogels in the respective metal nitrate solutions and subsequent thermal conversion. Combustion of the hydrogel results in mesoporous metal oxide layers with thicknesses in the μm range and high specific surface areas up to 558 m²∙g⁻¹. Materials are characterized by SEM, FIB ablation, EDX, and Kr physisorption porosimetry. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Strongly Iridescent Hybrid Photonic Sensors Based on Self-Assembled Nanoparticles for Hazardous Solvent Detection

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Nanomaterials 2018, 8(3), 169; https://doi.org/10.3390/nano8030169 - 16 Mar 2018

Cited by 8 | Viewed by 3883

Abstract

Facile detection and the identification of hazardous organic solvents are essential for ensuring global safety and avoiding harm to the environment caused by industrial wastes. Here, we present a simple method for the fabrication of silver-coated monodisperse polystyrene nanoparticle photonic structures that are [...] Read more.

Facile detection and the identification of hazardous organic solvents are essential for ensuring global safety and avoiding harm to the environment caused by industrial wastes. Here, we present a simple method for the fabrication of silver-coated monodisperse polystyrene nanoparticle photonic structures that are embedded into a polydimethylsiloxane (PDMS) matrix. These hybrid materials exhibit a strong green iridescence with a reflectance peak at 550 nm that originates from the close-packed arrangement of the nanoparticles. This reflectance peak measured under Wulff-Bragg conditions displays a 20 to 50 nm red shift when the photonic sensors are exposed to five commonly employed and highly hazardous organic solvents. These red-shifts correlate well with PDMS swelling ratios using the various solvents, which suggests that the observable color variations result from an increase in the photonic crystal lattice parameter with a similar mechanism to the color modulation of the chameleon skin. Dynamic reflectance measurements enable the possibility of clearly identifying each of the tested solvents. Furthermore, as small amounts of hazardous solvents such as tetrahydrofuran can be detected even when mixed with water, the nanostructured solvent sensors we introduce here could have a major impact on global safety measures as innovative photonic technology for easily visualizing and identifying the presence of contaminants in water. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Enhancing the Microparticle Deposition Stability and Homogeneity on Planer for Synthesis of Self-Assembly Monolayer

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Nanomaterials 2018, 8(3), 164; https://doi.org/10.3390/nano8030164 - 14 Mar 2018

Cited by 2 | Viewed by 3095

Abstract

The deposition stability and homogeneity of microparticles improved with mask, lengthened nozzle and flow rate adjustment. The microparticles can be used to encapsulate monomers, before the monomers in the microparticles can be deposited onto a substrate for nanoscale self-assembly. For the uniformity of [...] Read more.

The deposition stability and homogeneity of microparticles improved with mask, lengthened nozzle and flow rate adjustment. The microparticles can be used to encapsulate monomers, before the monomers in the microparticles can be deposited onto a substrate for nanoscale self-assembly. For the uniformity of the synthesized nanofilm, the homogeneity of the deposited microparticles becomes an important issue. Based on the ANSYS simulation results, the effects of secondary flow were minimized with a lengthened nozzle. The ANSYS simulation was also used to investigate the ring-vortex generation and why the ring vortex can be eliminated by adding a mask with an aperture between the nozzle and deposition substrate. The experimental results also showed that particle deposition with a lengthened nozzle was more stable, while adding the mask stabilized deposition and diminished the ring-vortex contamination. The effects of flow rate and pressure were also investigated. Hence, the deposition stability and homogeneity of microparticles was improved. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Influence of InAlN Nanospiral Structures on the Behavior of Reflected Light Polarization

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Yu-Hung Kuo

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Roger Magnusson

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Elena Alexandra Serban

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Nanomaterials 2018, 8(3), 157; https://doi.org/10.3390/nano8030157 - 12 Mar 2018

Cited by 2 | Viewed by 3381

Abstract

The influence of structural configurations of indium aluminum nitride (InAlN) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and [...] Read more.

The influence of structural configurations of indium aluminum nitride (InAlN) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet–visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (P_c) value of 0.75 is obtained from a sample consisting of 1.2 μm InAlN nanospirals grown at 650 °C. A film-like structure is formed at temperatures lower than 450 °C. At growth temperatures higher than 750 °C, less than 0.1 In-content is incorporated into the InAlN nanospirals. Both cases reveal very low P_c. A red shift of wavelength at P_c peak is found with increasing nanospiral pitch in the range of 200–300 nm. The P_c decreases to 0.37 for two-turn nanospirals with total length of 0.7 μm, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 μm, which yields a low P_c around 0.5, caused by the excessive scattering of incident light. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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Electrical Properties and Interfacial Issues of HfO₂/Ge MIS Capacitors Characterized by the Thickness of La₂O₃ Interlayer

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Nanomaterials 2019, 9(5), 697; https://doi.org/10.3390/nano9050697 - 04 May 2019

Cited by 10 | Viewed by 2760

Abstract

Effects of the La₂O₃ passivation layer thickness on the interfacial properties of high-k/Ge interface are investigated systematically. In a very thin range (0~15 cycles), the increase of La₂O₃ passivation layer deposition cycles improves the surface smoothness of [...] Read more.

Effects of the La₂O₃ passivation layer thickness on the interfacial properties of high-k/Ge interface are investigated systematically. In a very thin range (0~15 cycles), the increase of La₂O₃ passivation layer deposition cycles improves the surface smoothness of HfO₂/Ge structures. The capacitance-voltage (C-V) characteristics show that the thickness of La₂O₃ passivation layer can affect the shift of flat band voltage (V_FB), hysteretic behaviors, and the shapes of the dual-swept C-V curves. Moreover, significant improvements in the gate leakage current and breakdown characteristics are also achieved with the increase of La₂O₃ interlayer thickness. Full article

(This article belongs to the Special Issue Design and Development of Nanostructured Thin Films)

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