Special Issue "Characterization of Nanocrystalline Materials"

A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (31 July 2020).

Special Issue Editors

Prof. Dr. Paolo Scardi
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Guest Editor
Department of Civil, Environmental & Mechanical Engineering, University of Trento, 38123 via Mesiano 77, Trento, Italy
Interests: nanostructured materials; nanocrystalline chalcogenides; multinary systems; disordered systems; metal sulfides; selenides; tellurides; thermoelectric materials; thin-film thermoelectric materials; thermoelectric generators
Special Issues and Collections in MDPI journals
Prof. Dr. Edoardo Bemporad
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Guest Editor
Università degli Studi Roma Tre, Rome, Italy
Interests: surface engineering; mechanical characterization by nanoindentation; residual stress at the micro and sub-micro scale; focussed ion beam microscopy; transmission microscopy
Dr. Marco Sebastiani
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Guest Editor
Università degli Studi Roma Tre, Engineering Department, Rome, Italy
Interests: materials characterization; nanoindentation; residual stress; thin films; surface engineering

Special Issue Information

Dear Colleagues,

The tumultuous development of nanocrystalline materials in the last twenty years has been accompanied by a flourishing of characterization techniques, often developed for nanoscale investigations. With the advent of quantum dots, nanowires, nanotubes, graphene, and the like, metastable nano-sized multiphase materials and high-entropy alloys, nanostructured or amorphous films and coatings with graded or controlled properties down to the sub-micron scale, the concept of dimensionality has been radically changed, paving the way for new materials with properties that are surprisingly different from those of the corresponding bulk form. In this respect, traditional techniques for studying materials require substantial modifications to adapt to the specificities of nanocrystalline materials. This is based on a rather simple but not always understood concept, that nanocrystals cannot simply be considered as a small portion of a macroscopic crystal and the clear knowledge of interaction volume between the probe and the material is paramount in the understanding of what is being measured and the inferred properties from the nanoscale, eventually up to the whole device. Even the usual concepts of symmetry, for example, translational, and the concept itself of crystalline structures, are unsuitable and require a paradigm shift in the use of traditional techniques. Mechanical properties at this scale also have to be carefully described and understood so to obtain useful data on the effective mechanical performances, in terms of load-bearing and load transmission, elastic, plastic and viscous behavior, fatigue, and, finally, wear resistance. This Special Issue is dedicated to the characterization of nanocrystalline materials and their aggregates, including new and advanced techniques as well as the more traditional ones, as they evolved and were modified to study materials at the nanoscale. Specific case studies are welcome as well as short reviews.

Prof. Dr. Paolo Scardi
Prof. Dr. Edoardo Bemporad
Dr. Marco Sebastiani
Guest Editors

Manuscript Submission Information

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Keywords

  • Nanocrystalline materials
  • Characterization techniques
  • Nanoscale

Published Papers (10 papers)

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Research

Open AccessEditor’s ChoiceArticle
Influence of the Silver Content on Mechanical Properties of Ti-Cu-Ag Thin Films
Nanomaterials 2021, 11(2), 435; https://doi.org/10.3390/nano11020435 - 09 Feb 2021
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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Open AccessArticle
Large-Area Nanocrystalline Caesium Lead Chloride Thin Films: A Focus on the Exciton Recombination Dynamics
Nanomaterials 2021, 11(2), 434; https://doi.org/10.3390/nano11020434 - 09 Feb 2021
Abstract
Caesium lead halide perovskites were recently demonstrated to be a relevant class of semiconductors for photonics and optoelectronics. Unlike CsPbBr3 and CsPbI3, the realization of high-quality thin films of CsPbCl3, particularly interesting for highly efficient white LEDs when [...] Read more.
Caesium lead halide perovskites were recently demonstrated to be a relevant class of semiconductors for photonics and optoelectronics. Unlike CsPbBr3 and CsPbI3, the realization of high-quality thin films of CsPbCl3, particularly interesting for highly efficient white LEDs when coupled to converting phosphors, is still a very demanding task. In this work we report the first successful deposition of nanocrystalline CsPbCl3 thin films (70–150 nm) by radio frequency magnetron sputtering on large-area substrates. We present a detailed investigation of the optical properties by high resolution photoluminescence (PL) spectroscopy, resolved in time and space in the range 10–300 K, providing quantitative information concerning carriers and excitons recombination dynamics. The PL is characterized by a limited inhomogeneous broadening (~15 meV at 10 K) and its origin is discussed from detailed analysis with investigations at the micro-scale. The samples, obtained without any post-growth treatment, show a homogeneous PL emission in spectrum and intensity on large sample areas (several cm2). Temperature dependent and time-resolved PL spectra elucidate the role of carrier trapping in determining the PL quenching up to room temperature. Our results open the route for the realization of large-area inorganic halide perovskite films for photonic and optoelectronic devices. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Optimization of Photogenerated Charge Carrier Lifetimes in ALD Grown TiO2 for Photonic Applications
Nanomaterials 2020, 10(8), 1567; https://doi.org/10.3390/nano10081567 - 10 Aug 2020
Abstract
Titanium dioxide (TiO2) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts [...] Read more.
Titanium dioxide (TiO2) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO2 in devices incorporating organic or polymer components. In this study, we exploited low temperature (100–150 °C) atomic layer deposition (ALD) of 30 nm TiO2 thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO2 thin films grown at 150 °C and heat-treated at as low as 300 °C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300–500 °C. The average carrier lifetime for amorphous TiO2 is few picoseconds but increases to >400 ps upon crystallization at 500 °C. The samples deposited at 100 °C were also crystallized as anatase but the carrier lifetime was <100 ps. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Multi-Channel Exploration of O Adatom on TiO2(110) Surface by Scanning Probe Microscopy
Nanomaterials 2020, 10(8), 1506; https://doi.org/10.3390/nano10081506 - 31 Jul 2020
Abstract
We studied the O2 dissociated state under the different O2 exposed temperatures with atomic resolution by scanning probe microscopy (SPM) and imaged the O adatom by simultaneous atomic force microscopy (AFM)/scanning tunneling microscopy (STM). The effect of AFM operation mode on [...] Read more.
We studied the O2 dissociated state under the different O2 exposed temperatures with atomic resolution by scanning probe microscopy (SPM) and imaged the O adatom by simultaneous atomic force microscopy (AFM)/scanning tunneling microscopy (STM). The effect of AFM operation mode on O adatom contrast was investigated, and the interaction of O adatom and the subsurface defect was observed by AFM/STM. Multi-channel exploration was performed to investigate the charge transfer between the adsorbed O and the TiO2(110) by obtaining the frequency shift, tunneling current and local contact potential difference at an atomic scale. The tunneling current image showed the difference of the tunneling possibility on the single O adatom and paired O adatoms, and the local contact potential difference distribution of the O-TiO2(110) surface institutively revealed the charge transfer from TiO2(110) surface to O adatom. The experimental results are expected to be helpful in investigating surface/interface properties by SPM. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional [email protected] Heterostructures
Nanomaterials 2020, 10(8), 1434; https://doi.org/10.3390/nano10081434 - 23 Jul 2020
Cited by 1
Abstract
A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating [...] Read more.
A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs ([email protected]), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and [email protected], respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from [email protected] heterostructures. The reasons behind the superior improvement of the [email protected] performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where [email protected] heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Correlation between Crystal Structure, Surface/Interface Microstructure, and Electrical Properties of Nanocrystalline Niobium Thin Films
Nanomaterials 2020, 10(7), 1287; https://doi.org/10.3390/nano10071287 - 30 Jun 2020
Cited by 1
Abstract
Niobium (Nb) thin films, which are potentially useful for integration into electronics and optoelectronics, were made by radio-frequency magnetron sputtering by varying the substrate temperature. The deposition temperature (Ts) effect was systematically studied using a wide range, 25–700 °C, using Si(100) [...] Read more.
Niobium (Nb) thin films, which are potentially useful for integration into electronics and optoelectronics, were made by radio-frequency magnetron sputtering by varying the substrate temperature. The deposition temperature (Ts) effect was systematically studied using a wide range, 25–700 °C, using Si(100) substrates for Nb deposition. The direct correlation between deposition temperature (Ts) and electrical properties, surface/interface microstructure, crystal structure, and morphology of Nb films is reported. The Nb films deposited at higher temperature exhibit a higher degree of crystallinity and electrical conductivity. The Nb films’ crystallite size varied from 5 to 9 (±1) nm and tensile strain occurs in Nb films as Ts increases. The surface/interface morphology of the deposited Nb films indicate the grain growth and dense, vertical columnar structure at elevated Ts. The surface roughness derived from measurements taken using atomic force microscopy reveal that all the Nb films are characteristically smooth with an average roughness <2 nm. The lowest electrical resistivity obtained was 48 µΩ cm. The correlations found here between growth conditions electrical properties as well as crystal structure, surface/interface morphology, and microstructure, could provide useful information for optimum conditions to produce Nb thin films for utilization in electronics and optoelectronics. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Molecular Dynamics Simulation of Polyacrylamide Adsorption on Cellulose Nanocrystals
Nanomaterials 2020, 10(7), 1256; https://doi.org/10.3390/nano10071256 - 28 Jun 2020
Cited by 1
Abstract
Classical molecular dynamics simulations of polyacrylamide (PAM) adsorption on cellulose nanocrystals (CNC) in a vacuum and a water environment are carried out to interpret the mechanism of the polymer interactions with CNC. The structural behavior of PAM is studied in terms of the [...] Read more.
Classical molecular dynamics simulations of polyacrylamide (PAM) adsorption on cellulose nanocrystals (CNC) in a vacuum and a water environment are carried out to interpret the mechanism of the polymer interactions with CNC. The structural behavior of PAM is studied in terms of the radius of gyration, atom–atom radial distribution functions, and number of hydrogen bonds. The structural and dynamical characteristics of the polymer adsorption are investigated. It is established that in water the polymer macromolecules are mainly adsorbed in the form of a coil onto the CNC facets. It is found out that water and PAM sorption on CNC is a competitive process, and water weakens the interaction between the polymer and CNC. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
In Situ Formation of Nanoporous Silicon on a Silicon Wafer via the Magnesiothermic Reduction Reaction (MRR) of Diatomaceous Earth
Nanomaterials 2020, 10(4), 601; https://doi.org/10.3390/nano10040601 - 25 Mar 2020
Cited by 3
Abstract
Successful direct route production of silicon nanostructures from diatomaceous earth (DE) on a single crystalline silicon wafer via the magnesiothermic reduction reaction is reported. The formed porous coating of 6 µm overall thickness contains silicon as the majority phase along with minor traces [...] Read more.
Successful direct route production of silicon nanostructures from diatomaceous earth (DE) on a single crystalline silicon wafer via the magnesiothermic reduction reaction is reported. The formed porous coating of 6 µm overall thickness contains silicon as the majority phase along with minor traces of Mg, as evident from SEM-EDS and the Focused Ion Beam (FIB) analysis. Raman peaks of silicon at 519 cm−1 and 925 cm−1 were found in both the film and wafer substrate, and significant intensity variation was observed, consistent with the SEM observation of the directly formed silicon nanoflake layer. Microstructural analysis of the flakes reveals the presence of pores and cavities partially retained from the precursor diatomite powder. A considerable reduction in surface reflectivity was observed for the silicon nanoflakes, from 45% for silicon wafer to below 15%. The results open possibilities for producing nanostructured silicon with a vast range of functionalities. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Angular Dependence of the Ferromagnetic Resonance Parameters of [Ti/FeNi]6/Ti/Cu/Ti/[FeNi/Ti]6 Nanostructured Multilayered Elements in the Wide Frequency Range
Nanomaterials 2020, 10(3), 433; https://doi.org/10.3390/nano10030433 - 29 Feb 2020
Abstract
Magnetically soft [Ti(6)/FeNi(50)]6/Ti(6)/Cu(500)/Ti(6)/[FeNi(50)/Ti(6)]6 nanostructured multilayered elements were deposited by rf-sputtering technique in the shape of elongated stripes. The easy magnetization axis was oriented along the short size of the stripe using deposition in the external magnetic field. Such configuration is [...] Read more.
Magnetically soft [Ti(6)/FeNi(50)]6/Ti(6)/Cu(500)/Ti(6)/[FeNi(50)/Ti(6)]6 nanostructured multilayered elements were deposited by rf-sputtering technique in the shape of elongated stripes. The easy magnetization axis was oriented along the short size of the stripe using deposition in the external magnetic field. Such configuration is important for the development of small magnetic field sensors employing giant magnetoimpedance effect (GMI) for different applications. Microwave absorption of electromagnetic radiation was experimentally and theoretically studied in order to provide an as complete as possible high frequency characterization. The conductor-backed coplanar line was used for microwave properties investigation. The medialization for the precession of the magnetization vector in the uniformly magnetized GMI element was done on the basis of the Landau–Lifshitz equation with a dissipative Bloch–Bloembergen term. We applied the method of the complex amplitude for the analysis of the rotation of the ferromagnetic GMI element in the external magnetic field. The calculated and experimental dependences for the amplitudes of the imaginary part of the magnetic susceptibility tensor x-component and magnetoabsorption related to different angles show a good agreement. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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Open AccessArticle
Cation Disorder and Local Structural Distortions in AgxBi1–xS2 Nanoparticles
Nanomaterials 2020, 10(2), 316; https://doi.org/10.3390/nano10020316 - 12 Feb 2020
Abstract
By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of AgxBi1−xS2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent [...] Read more.
By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of AgxBi1−xS2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent contradiction between the evidence provided by X-ray absorption and diffraction measurements is solved by means of the simulations. We find that disorder in the cation sublattice induces strong local distortions, leading to the appearance of short Ag–S bonds, the overall lattice symmetry remaining close to hexagonal. Full article
(This article belongs to the Special Issue Characterization of Nanocrystalline Materials)
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