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Showing papers in "MRS Advances in 2021"


Journal ArticleDOI
TL;DR: In this paper, a series of EPDM elastomer/carbon-black composites were studied to quantify the effect of additional ceramic fillers, especially of the interfacial contributions, on the dielectric properties of the composites.
Abstract: A systematic series of ethylene-propylene-diene (EPDM) elastomer/carbon-black composites were studied to quantify the effect of additional ceramic fillers, especially of the interfacial contributions, on the dielectric properties of the composites. Substantial interfacial contributions to the composites’ dielectric properties were present in all systems. For all composites studied—using ceramic fillers with varied dielectric nature and spanning orders of magnitude in dielectric constants—the interfacial contributions overwhelmed the ceramic filler k-values and dominated the dielectric performance of the composites. Non-trivial interplays between the carbon black and the ceramic fillers were also manifested, casting doubts on the validity of standard models used for the prediction of dielectric permittivities of such composites.

17 citations


Journal ArticleDOI
TL;DR: It is suggested that Ch-Mn3O4 nanohybrid has the potential to function as a target-specific redox buffering agent in both in-vitro and in-cellulo systems.
Abstract: A crucial balance between oxidative eustress and distress is important for maintaining redox homeostasis in the cellular milieu. Therefore, sustaining the intracellular redox buffer condition with exogenous agents could be a therapeutic strategy against diseases caused by redox imbalance. Here, we synthesized chitosan-functionalized Mn3O4 nanoparticles (Ch-Mn3O4 NPs) and tested their redox buffering capability in in-vitro and in-cellulo. Chitosan is easily absorbed by the intestine and can be used as a target-specific delivery agent to the intestine, while Mn3O4 NPs have redox modulatory properties. Therefore, combination of chitosan and Mn3O4 NPs provide the opportunity for targeted redox buffering. Targeted delivery of a drug and remediation of the corresponding indication qualify the drug to be a theranostic agent. Our spectroscopic studies suggest ROS generation as well as antioxidant ability of Ch-Mn3O4 NPs. In-cellulo studies using A549 cell lines confirmed the efficacy of the nanohybrid in redox homeostasis. The outcomes suggest that Ch-Mn3O4 nanohybrid has the potential to function as a target-specific redox buffering agent in both in-vitro and in-cellulo systems.

10 citations


Journal ArticleDOI
TL;DR: The first batch of pure U-oxide microparticles produced in Juelich was successfully certified regarding the isotopic composition and the U amount per particle and applied in an international laboratory exercise NUSIMEP-9.
Abstract: The analysis of individual micrometre- and submicrometre-sized particles collected by IAEA’s safeguards inspectors on swipe samples during in-field verification activities requires the implementation of a sustainable quality control system such as suitable microparticulate reference materials. To this end, pure and neodymium-doped uranium oxide-based microparticles utilising an aerosol-based particle production process were prepared. SEM/EDX measurements confirmed the monodispersity of the produced microspheres as well as the incorporation of 15 mol% Nd into the compound particles. The timeline of structural investigations mirror the ongoing alteration of particles being stored under laboratory atmosphere. While results from in-SEM Raman (CEA, DAM) on microparticles after two years storage time point to the formation of U3O8 and a minor fraction of schoepite phase (hydrated UO3), in U L3-edge XAFS after four months storage time and U M4-edge HR-XANES after ten months storage time spectra (INE-Beamline and ACT station @ KIT synchrotron radiation source) mainly U(IV) and U(V), respectively, was observed. These results provide new insight into ageing mechanism of the microparticles after preparation. From these results important conclusions with respect to storage conditions and shelf life of the reference particles can be drawn. The first batch of pure U-oxide microparticles produced in Juelich was successfully certified regarding the isotopic composition and the U amount per particle and applied in an international laboratory exercise NUSIMEP-9.

9 citations


Journal ArticleDOI
TL;DR: In this article, the capacitance-voltage characteristics of metal-ferroelectric-metal (MFM) thin-film capacitors with various Zr doping for varactor applications were investigated.
Abstract: In this article, we investigate the capacitance–voltage (C–V) characteristics of $$\text {Hf}_{x}\text {Zr}_{1-x}\text {O}_{2}$$ metal-ferroelectric-metal (MFM) thin-film capacitors with various Zr doping for varactor applications. The impact of field cycling during the wake-up process on the capacitance was analyzed. In addition, the effect of antiferroelectric-like (AFE) behavior on tuning was investigated. The transition between ferroelectric (FE) and AFE regime is particularly interesting for varactor application, as a reduced bias is required for tuning. The cycle dependence of the FE and AFE properties at elevated temperatures was also investigated, where it was shown that with an increase of temperature, the tunability is reduced. Temperature measurements also comply with recent studies of ferroelastic nature of AFE behavior.

8 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of the stable Laves phase is preceded by the creation of the metastable Heusler phase in Fe-Al-Nb alloys with different Al and Nb contents and with or without boron doping.
Abstract: It is known for Fe–Al–Ta alloys, that a homogeneous distribution of strengthening Laves phase precipitates in the matrix and aligned at the grain boundaries can be obtained when the formation of the stable Laves phase is preceded by the formation of the metastable Heusler phase. Several Fe–Al–Nb alloys with different Al and Nb contents and with or without boron doping are studied to elucidate whether comparable microstructures can be obtained in this system. It was found that the Heusler phase only occurs within a limited composition range. The time-dependent evolution of the microstructure shows that the transformation proceeds faster in Fe–Al–Nb alloys. Microhardness was measured in dependence on the microstructural evolution with increasing annealing time, and compressive yield stress was determined for alloys annealed 700 °C/1000 h to evaluate the influence of microstructure and composition.

7 citations


Journal ArticleDOI
TL;DR: The demonstration of acoustic focusing in concert with diffusive self-assembly to rapidly assembly and print multiscale, mm-length colloidal solids on a timescale of seconds to minutes supports the promising capabilities of acoustic field-assisted deposition-based printing to achieve spatial control of printed microstructures with deterministic, long-range ordering across multiple length scales.
Abstract: Acoustic forces are an attractive pathway to achieve directed assembly for multi-phase materials via additive processes. Programmatic integration of microstructure and structural features during deposition offers opportunities for optimizing printed component performance. We detail recent efforts to integrate acoustic focusing with a direct-ink-write mode of printing to modulate material transport properties (e.g., conductivity). Acoustic field-assisted printing, operating under a multi-node focusing condition, supports deposition of materials with multiple focused lines in a single-pass printed line. Here, we report the demonstration of acoustic focusing in concert with diffusive self-assembly to rapidly assembly and print multiscale, mm-length colloidal solids on a timescale of seconds to minutes. These efforts support the promising capabilities of acoustic field-assisted deposition-based printing to achieve spatial control of printed microstructures with deterministic, long-range ordering across multiple length scales.

7 citations


Journal ArticleDOI
TL;DR: In this paper, solid microneedle arrays were created out of the polymer RESOMER LG 855 S using injection molding, which can be used for "poke and flow" transdermal delivery of a drug.
Abstract: A solid microneedle array can be used for “poke and flow” transdermal delivery of a drug, which involves the infusion or diffusion of a drug through pores in the skin that were created by the microneedle array. In this paper, solid microneedle arrays were created out of the polymer RESOMER LG 855 S—poly(l-lactide-co-glycolide) using injection molding. Scanning electron microscopy revealed that the microneedle in the injection-molded four-by-one microneedle array closely matched the dimensions that were used for injection molding. X-ray photoelectron spectroscopy revealed that the carbon bonding in the microneedle material matched that expected for poly(l-lactide-co-glycolide). The reduced elastic modulus of the microneedle material, 6.04 ± 0.17 GPa, was noted to be appropriate for skin penetration applications. The microneedle array was used for the delivery of the model drug methyl blue to surgically discarded human underarm skin. These results suggest that injection molding of RESOMER LG 855 S—poly(l-lactide-co-glycolide) may be an appropriate approach for large-scale manufacturing of solid microneedles.

7 citations


Journal ArticleDOI
TL;DR: Several important aspects in force field development are discussed and features in BLAST (Bridging Length/time scales via Atomistic Simulation Toolkit) that enable its functionalities and ease of use are highlighted.
Abstract: The ever-increasing power of supercomputers coupled with highly scalable simulation codes has made molecular dynamics an indispensable tool in applications ranging from predictive modeling of materials to computational design and discovery of new materials for a broad range of applications. Multi-fidelity scale bridging between the various flavors of molecular dynamics, i.e., ab-initio, classical, and coarse-grained models has remained a long-standing challenge. Here, we introduce our framework BLAST (Bridging Length/Timescales via Atomistic Simulation Toolkit) that leverages machine learning principles to address this challenge. BLAST is a multi-fidelity scale bridging framework that provides users with the capabilities to train and develop their own classical atomistic and coarse-grained interatomic potentials (force fields) for molecular simulations. BLAST is designed to address several long-standing problems in the molecular simulation community, such as unintended misuse of existing force fields due to knowledge gap between developers and users, bottlenecks in traditional force field development approaches, and other issues relating to the accuracy, efficiency, and transferability of force fields. Here, we discuss several important aspects in force field development and highlight features in BLAST that enable its functionalities and ease of use.

7 citations


Journal ArticleDOI
TL;DR: In this article, the first part of a sequential ion exchange process in transforming calcite into a Pb-free perovskite material for solar cell applications is described. But no oxides of Sn were formed.
Abstract: Tin (Sn2+) and strontium (Sr2+), two potential alternatives to lead (Pb2+) in perovskite formation, were explored in transforming calcium carbonate (CaCO3) into a leaving group in a cation exchange reaction. This is the first part of a sequential ion exchange process in transforming calcite into a Pb-free perovskite material for perovskite solar cell applications. Calcite, a polymorph of CaCO3, was successfully transformed into strontianite (SrCO3) through a cation exchange reaction. In the Sn substitution reaction on the other hand, no SnCO3 formation was noted. Instead, oxides of Sn were formed. The wider spaces in between Ca2+ cations in (100) orientation account for the higher atomic Sn2+ and Sr2+ concentrations as compared to (001) orientation, where the cation movement is restricted. X-ray absorption and photoelectron spectroscopies were used to investigate the ion-exchange transformation of calcite towards the formation of an intermediate carbonate material.

6 citations


Journal ArticleDOI
TL;DR: Polydopamine-coated substrate induces increased fibronectin deposition of mesenchymal stem cells, and promotes cell migration via integrin-initiated FAK signaling, compared to non- coated polystyrene-based standard tissue culture surface.
Abstract: Rapid migration of mesenchymal stem cells (MSCs) on device surfaces could support in vivo tissue integration and might facilitate in vitro organoid formation. Here, polydopamine (PDA) is explored as a biofunctional coating to effectively promote MSC motility. It is hypothesized that PDA stimulates fibronectin deposition and in this way enhances integrin-mediated migration capability. The random and directional cell migration was investigated by time-lapse microscopy and gap closure assay respectively, and analysed with softwares as computational tools. A higher amount of deposited fibronectin was observed on PDA substrate, compared to the non-coated substrate. The integrin β1 activation and focal adhesion kinase (FAK) phosphorylation at Y397 were enhanced on PDA substrate, but the F-actin cytoskeleton was not altered, suggesting MSC migration on PDA was regulated by integrin initiated FAK signalling. This study strengthens the biofunctionality of PDA coating for regulating stem cells and offering a way of facilitating tissue integration of devices. Polydopamine-coated substrate induces increased fibronectin deposition of mesenchymal stem cells, and promotes cell migration via integrin-initiated FAK signaling, compared to non-coated polystyrene-based standard tissue culture surface. In this way, multifunctional PDA coating could support in vivo tissue integration on implant surface and promote in vitro organoid formation.

6 citations


Journal ArticleDOI
TL;DR: In this article, the authors have shown that the presence of impurities (i.e., copper, manganese, nickel) in the crystalline structures of ZnS nanoparticles can enhance their optical properties and consequently their catalytic capacity.
Abstract: Semiconductor quantum dots such as zinc sulfide have interesting potential applications, due to their size-dependent optical properties. These nanostructures can be used for applications in agriculture, environmental chemistry, and fluorescence microscopy. The great rise in nanotechnology has sparked the scientific community’s interest in nanomaterials for the use of photodegradation in aquatic bodies. Quantum Dots (QDs) such as ZnS nanoparticles (NPs) can absorb electromagnetic radiation and generate subsequently reactive oxygen species (ROS) directly in aqueous phase. The presence of ROS in aquatic environments can be used to destroy organic contaminants by photocatalysis. Previous studies had evidenced that the presence of impurities (i.e. copper, manganese, nickel) in the crystalline structures of QDs can enhance their optical properties and consequently their catalytic capacity. Because of this, the present investigation was focused on generating water stable ZnS nanoparticles with catalytic properties. In this work, we have synthesized pure and doped ZnS nanoparticles using a reflux method. The morphology of these QDs was characterized by transmission electron microscopy (TEM). We also studied the photocatalytic properties of these nanostructures. A red shift was observed in the photoluminescence peak of pure ZnS nanoparticles when they were doped with heavy metals. Pure ZnS NPs and Mn-doped ZnS NPs showed luminescent peaks at 444 nm and 596 nm, respectively. Photodegradation studies were evaluated in the presence of organic dyes like Tropaeolin O (TO) and different concentrations of quantum dots (250 ppm and 500 ppm). The photodegradation of TO was dependent on the QDs concentration and exposure time. The destruction of organic dyes in the presence of photo-excited ZnS nanoparticles is envisioned as a fast and clean technology. The destruction of organic dyes in the presence of photo-excited ZnS nanoparticles is envisioned as a fast and clean technology.

Journal ArticleDOI
TL;DR: In this paper, a combination of in-situ optical microscopy and Digital Imaging Correlation (strain mapping) techniques was used to study compressive deformation and cracking phenomena in a novel solid-state Li-ion electrolyte.
Abstract: Solid-state batteries are generally considered to be safer than their liquid-state counterparts due to their decreased potential for fire or short circuiting. The fabrication of solid-state batteries relies on the application of stack crimping pressure that increases the interfacial surface contacts between electrolytes and the electrodes. However, excessive compressive crimping stresses (that occur in cell assembly) can give rise to cracking phenomena that can degrade battery performance and lead to thermal runaway or failure. It is, therefore, important to develop an understanding of failure mechanisms in solid-state Li-ion electrolytes. In this paper, we use a combination of in-situ optical microscopy and Digital Imaging Correlation (strain mapping) techniques to study compressive deformation and cracking phenomena in a novel solid-state Li-ion electrolyte. The stress states associated with the different stages of compressive deformation are also presented along with those due to charge–discharge cycles. The implications of the results are discussed for the material design of robust solid-state Li ion batteries.

Journal ArticleDOI
TL;DR: In this article, the degradation property of magnesium alloy WE43 was investigated experimentally using parametric studies using the finite element method to optimize the stent geometry and strut thickness to improve conformability in stent applications.
Abstract: Biodegradable stents, especially those composed of magnesium alloy-based materials, can provide a temporary scaffold that support vessels while naturally resorbing in the body after the targeted vessel heals, thereby preventing the restenosis and late thrombosis issues caused by their metallic predecessors However, due to limitations in the intrinsic mechanical properties of magnesium, further investigation is required to optimize its degradation property, as well as the design, geometry and strut thickness to improve conformability in stent applications This study aimed to investigate experimentally the degradation property of magnesium alloy WE43 and to optimize the stent geometry through parametric studies using the finite element method Results of the degradation testing showed that the WE43 with a secondary polycaprolactone dip-coating offered a greater resistance to biodegradation and increased the lifespan of the stent On average, the resistance to biodegradation increased by 5% in the WE43 magnesium alloy compared with its counterpart lacking any surface coating The parametric studies have indicated that the stent with honeycomb geometry and a radial thickness of 015 mm had demonstrated promising mechanical performance with minimal dog-boning, foreshortening and recoil

Journal ArticleDOI
TL;DR: In this article, a multi-disciplinary approach is proposed to take advantage of 3D-printing techniques and shape-memory hydrogels synergistically to mimic the functional traits of the climbing cactus Selenicereus setaceus.
Abstract: Inspired by the interesting functional traits of a climbing cactus, Selenicereus setaceus, found in the forest formations of Southeastern Brazil, we formulated a hypothesis that we can directly learn from the plants to develop multi-functional artificial systems by means of a multi-disciplinary approach. In this context, our approach is to take advantage of 3D-printing techniques and shape-memory hydrogels synergistically to mimic the functional traits of the cactus. This work reports on the preliminary investigation of cactus-inspired artificial systems. First, we 3D-printed soft polymeric materials and characterized them, which defines the structure and is a passive component of a multi-material system. Second, different hydrogels were synthesized and characterized, which is an active component of a multi-material system. Finally, we investigated how the hydrogel can be integrated into the 3D-printed constructs to develop artificial functional systems.

Journal ArticleDOI
TL;DR: In this article, the phase-change properties of nanopillars of varied radii along the spectrum and elaborate on the scattering features of the metasurfaces to create a library of phase change characteristics.
Abstract: Mie resonances facilitate an efficient manipulation of light on the subwavelength scale in high-refractive-index metasurfaces These ultra-thin high-refractive-index nanostructures have been utilized in wave-front engineering devices for amplitude and phase modulation on the subwavelength scale in dielectric metasurfaces with high transmission efficiencies We seek to establish a guideline for the desired phase modulation of each element in the metasurfaces integrated with light-emitting devices Numerical simulations of gallium arsenide (GaAs) nanopillar metasurfaces are carried out over the visible and near-infrared spectral ranges We analyze the scattering properties of the nanopillars of various sizes along with reflection, transmission, absorption, and phase-change spectra of the nanopillar arrays We study phase-change properties of nanopillars of varied radii along the spectrum and elaborate on the scattering features of the metasurfaces to create a library of phase-change characteristics The results indicate that the nanostructures respond with strong resonances and the corresponding phase-change features in the visible and near-infrared frequencies By the variation of the nanopillar dimensions, one can control the light phase change and shift the features along the spectrum

Journal ArticleDOI
TL;DR: In this paper, the effect of current density and temperature on electrodeposited cobalt (Co) nanowires synthesized via a template-assisted process was studied and the length and growth characteristics of the formed cobalt wires were analyzed and discussed.
Abstract: Processing conditions during the deposition process affect the nanowire properties significantly in template-assisted electrodeposition, an effective method for growing freestanding and well-dispersed nanowires. In this work, we study the effect of current density and temperature on electrodeposited cobalt (Co) nanowire synthesized via a template-assisted process. Scanning electron microscopy was used to study the morphology of formed cobalt nanowires with EDS analysis, confirming Co as the main element. In addition, the length and growth characteristics of the formed nanowires are analyzed and discussed. SEM morphology and deposition length characteristics of electrodeposited cobalt nanowires at different current densities and temperatures.

Journal ArticleDOI
TL;DR: In this paper, a 3D convolutional neural network was used to predict the S-strain curves of thermoplastic elastomers by combining hierarchical simulation and deep learning.
Abstract: We achieved high-throughput prediction of the stress–strain (S–S) curves of thermoplastic elastomers by combining hierarchical simulation and deep learning ABA triblock copolymer with a phase-separated structure was used as a thermoplastic elastomer model The S–S curves of the ABA triblock copolymers were calculated from the hierarchical simulation of self-consistent field theory calculations and coarse-grained molecular dynamics simulations Because such hierarchical simulations require considerable computational resources, we applied a deep learning technique to accelerate the prediction Sets of phase-separated structures and the S–S curves obtained from the hierarchical simulation were used to train a 3D convolutional neural network Using the trained network, we confirmed that the predicted S–S curves of the untrained structures accurately reproduced the simulation results These results will enable us to design novel polymers and phase-separated structures with desired S–S curves by high-throughput screening of a wide variety of structures

Journal ArticleDOI
TL;DR: In this article, the electrochemical response of phenyl hydrazine and 2,4-dinitrophenyl hyrazine-based polymeric materials for the quantification of the neurotransmitter thrombotonin was highlighted.
Abstract: This article highlighting the electrochemical response of phenyl hydrazine and 2,4-dinitrophenyl hydrazine-based polymeric materials for the quantification of the neurotransmitter thrombotonin. The electrochemical analysis was performed on phenyl hydrazine and 2,4-dinitrophenyl hydrazine electropolymers on pencil graphite electrode using cyclic and differential pulse voltammetry. The electrochemical behavior of thrombotonin on the modified electrode was investigated in pH 7 buffer solution of 0.1 M and the oxidation of thrombotonin seemed to be an irreversible adsorption-diffusion-controlled process The modification of the pencil graphite electrode was confirmed by field-emission scanning electron microscopy, X-ray diffraction analysis, electrochemical impedance spectroscopy and Fourier transmittance infrared spectrometry. The fabricated electrochemical sensor can be applied for the quantification of thrombotonin from human blood sample in the linear range from 0.1 to 250 μM with a lower detection limit of 0.01 μM and the sensitivity of the electrode obtained was 2.47 μA/μM/cm2. The fabricated electrode shows enhanced sensitivity, selectivity with good reproducibility, and prolonged stability compared to previously reported differential pulse voltammetric sensors. The research paper is entitled as “Phenyl hydrazine and 2,4-dinitrophenyl hydrazine-based polymeric materials for the electrochemical quantification of thrombotonin”. The developed sensor is highly selective and sensitive and can be used for the determination of thrombotonin in real samples.

Journal ArticleDOI
TL;DR: In this article, a reactive forcefield for Zr/O/S was developed to study the oxidation dynamics of transition metal dichalcogenides and showed anisotropic oxidation rates between (210) and (001) surfaces.
Abstract: Transition metal dichalcogenides have shown great potential for next-generation electronic and optoelectronic devices. However, native oxidation remains a major issue in achieving their long-term stability, especially for Zr-containing materials such as ZrS2. Here, we develop a first principles-informed reactive forcefield for Zr/O/S to study oxidation dynamics of ZrS2. Simulation results reveal anisotropic oxidation rates between (210) and (001) surfaces. The oxidation rate is highly dependent on the initial adsorption of oxygen molecules on the surface. Simulation results also provide reaction mechanism for native oxide formation with atomistic details.

Journal ArticleDOI
TL;DR: In this article, the effect of distilled water (S1) and NaOH solution (S2) on the starch isolation of Ramon seed flour was evaluated, and the results indicated that both types of starch presented spherical morphology, similar functional groups and crystallinity values.
Abstract: Brosimum alicastrum is a native tree widely distributed in the Yucatan peninsula where is called Ramon. Some studies have reported that Ramon seeds contain high starch content, recently used in developing novel and sustainable biomaterials. This work aimed to evaluate the effect of the extractive solution on the starch isolation Ramon seed flour; for that, distilled water (S1) and NaOH solution (S2) were used. The Ramon starch yield was 28.0 ± 1.4% and 31.9 ± 1.7% for S1 and S2. The morphology of starches was observed with scanning electronic microscopy, the functional groups were determined through Fourier-transform Infrared Spectroscopy and crystallinity was calculated by X-ray diffraction analysis. The results indicate that both types of starch presented spherical morphology, similar functional groups and crystallinity values, suggesting that both extraction methods are suitable. The starches isolated exhibited similar thermal behavior assessed by differential scanning calorimetry and thermogravimetric analysis.

Journal ArticleDOI
TL;DR: Tay et al. as mentioned in this paper developed inkjet-printed surface-enhanced Raman spectroscopy (SERS) sensors that are specifically designed to work with field portable Raman analyzers for the detection of chemical and biological agents.
Abstract: We have developed inkjet-printed surface-enhanced Raman spectroscopy (SERS) sensors that are specifically designed to work with field portable Raman analyzers for the detection of chemical and biological agents (Tay et al. in J Raman Spectrosc, 2020). These SERS sensors are inkjet-printed on filter paper or fabric substrates. They are flexible and lightweight and provide point-of-sampling capabilities that other rigid planar SERS substrates lack. Conventionally, performance of a SERS substrate is characterized by its enhancement factor which is defined as the ratio of the normalized SERS to normal Raman intensity. This is an inadequate measure for a chemical/biological sensor. The performance of a chemical/biological sensor is best characterized by its sensitivity, probability of true positive detection, false positive rate, and its response time. The sensor using receiver operating characteristic (ROC) captures the performance trade-off between all these factors. Here, we outline the application of ROC analysis to the SERS sensors. This can be applied for all SERS sensors but we will focus its use with the printed SERS sensor. Specifically, the use of printed SERS sensor for the detection of fentanyl, a common opioid found in illicit drug, analyzed with ROC concept is demonstrated.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the growth of crack-free 4-μm thick aluminum Nitride (AlN) layers in a custom build vertical cold wall metal-organic chemical vapor deposition (MOCVD) reactor using N2 carrier gas on a sapphire substrate without any additional substrate preprocessing steps.
Abstract: We report the growth of crack-free 4 μm thick Aluminum Nitride (AlN) layers in a custom build vertical cold wall metal–organic chemical vapor deposition (MOCVD) reactor using N2 carrier gas on 02° offcut sapphire substrate without any additional substrate preprocessing steps The growth process includes a low-temperature pulsed rough buffer layer followed by a high-temperature layer with continuous growth without any interlayer The structural properties of the AlN were analyzed using atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy The AFM image of the 4 µm AlN layer shows an atomically smooth 2-dimensional surface with terrace-like steps The dislocation density of 1 × 109 cm−2 was calculated using Williamson and Hall process for a 4 µm AlN sample Additionally, strain calculation from XRD and stress calculation from Raman spectroscopy of AlN grown with N2 carrier gas are discussed


Journal ArticleDOI
TL;DR: In this paper, a machine learning solution was proposed to predict long-term properties of SARS-CoV-2 spike glycoproteins (S-protein) through the analysis of its nanosecond backbone RMSD (root-mean-square deviation) simulation data at varying temperatures.
Abstract: Molecular dynamics (MD) simulations are a widely used technique in modeling complex nanoscale interactions of atoms and molecules. These simulations can provide detailed insight into how molecules behave under certain environmental conditions. This work explores a machine learning (ML) solution to predicting long-term properties of SARS-CoV-2 spike glycoproteins (S-protein) through the analysis of its nanosecond backbone RMSD (root-mean-square deviation) MD simulation data at varying temperatures. The simulation data were denoised with fast Fourier transforms. The performance of the models was measured by evaluating their mean squared error (MSE) accuracy scores in recurrent forecasts for long-term predictions. The models evaluated include k-nearest neighbors (kNN) regression models, as well as GRU (gated recurrent unit) neural networks and LSTM (long short-term memory) autoencoder models. Results demonstrated that the kNN model achieved the greatest accuracy in forecasts with MSE scores over around 0.01 nm less than those of the GRU model and the LSTM autoencoder. Furthermore, it demonstrated that the kNN model accuracy increases with data size but can still forecast relatively well when trained on small amounts of data, having achieved MSE scores of around 0.02 nm when trained on 10,000 ns of simulation data. This study provides valuable information on the feasibility of accelerating the MD simulation process through training and predicting supervised ML models, which is particularly applicable in time-sensitive studies. SARS-CoV-2 spike glycoprotein molecular dynamics simulation. Extraction and denoising of backbone RMSD data. Evaluation of k-nearest neighbors regression, GRU neural network, and LSTM autoencoder models in recurrent forecasting for long-term property predictions.

Journal ArticleDOI
TL;DR: In this paper, the effects of model nuclear waste glass composition on the corrosion of Monofrax® K-3 refractory, using machine learning (ML) methods for data investigation and modeling of published borosilicate glass composition data and refining performance.
Abstract: The goal of this study was to determine the effects of model nuclear waste glass composition on the corrosion of Monofrax® K-3 refractory, using machine learning (ML) methods for data investigation and modeling of published borosilicate glass composition data and refractory corrosion performance. First, statistical methods were used for exploration of the data, and the list of features (model terms) was determined. Several model types were explored, and the Bayesian Ridge type was the most promising due to low mean average error and mean standard error as well as high R2 value. Parameters and model results using previously identified model features and those from this study are compared. ML methods appear to give results at least as good as previously available models for describing the effects of glass composition on refractory corrosion.

Journal ArticleDOI
TL;DR: In this paper, the photocatalytic performance of two sizes of CeO2 NPs at two sizes, and medium acid and basic pH, was studied, and the results showed shoulder peaks at 285 and 300 nm for small size and big size NPs, respectively.
Abstract: Cerium oxide nanoparticles (CeO2 NPs) have shown a potential capacity to destroy organic dyes because of their ability to generate reactive oxygen species (ROS) in aqueous phase. The photodegradation process can be influenced by the superficial area of the nanoparticle and the pH of the solution. This work studied the photocatalytic performance of CeO2 NPs at two sizes, and medium acid and basic. UV–Vis results showed shoulder peaks at 285 nm and 300 nm for small size (< 5.0 nm) and big size Nps (< 25.0 nm), respectively. Preliminary studies have reported that CeO2 NPs (size < 5 nm) generate ROS, which was evidenced for their toxicity in 100% to marine crustaceans after 24 and 48 h of exposure. We optimized the photocatalytic capacity of CeO2 Nps (< 25.0 nm) by modifying it to a basic pH, which resulted in a more significant degradation percent (40%) of Tropaeolin O.

Journal ArticleDOI
TL;DR: In this paper, the influence of shape and size on the elastic properties of gold nanowires was demonstrated using in-situ mechanical testing in scanning and transmission electron microscopy by means of resonance excitation and uniaxial tension.
Abstract: Size effects decisively influence the properties of materials at small length scales. In the context of mechanical properties, the trend of ‘smaller is stronger’ has been well established. This statement refers to an almost universal trend of increased strength with decreasing size. A strong influence of size on the elastic properties has also been widely reported, albeit without a clear trend. However, the influence of nanostructure shape on the mechanical properties has been critically neglected. Here, we demonstrate a profound influence of shape and size on the elastic properties of materials on the example of gold nanowires. The elastic properties are determined using in-situ mechanical testing in scanning and transmission electron microscopy by means of resonance excitation and uniaxial tension. The combination of bending and tensile load types allows for an independent and correlative calculation of the Young's modulus. We find both cases of softening as well as stiffening, depending critically on the interplay between size and shape of the wires.

Journal ArticleDOI
TL;DR: In this paper, the authors conduct uniaxial compressions in situ inside of a scanning electron microscope to characterize the mechanical response of individual micron-sized particles of a molecular crystal, hexanitrohexaazaisowurtzitane (CL-20).
Abstract: Microstructures and corresponding properties of compacted powders ultimately depend on the mechanical response of individual particles. In principle, computational simulations can predict the results of powder compaction processes, but the selection of appropriate models for both particle–particle interactions and particle deformations across all relevant length scales remain nontrivial tasks, especially in material systems lacking detailed mechanical property information. The work presented here addresses these issues by conducting uniaxial compressions in situ inside of a scanning electron microscope to characterize the mechanical response of individual micron-sized particles of a molecular crystal, hexanitrohexaazaisowurtzitane (CL-20). This experimental approach enabled the collection of quantitative force and displacement data alongside simultaneous imaging to capture morphology changes. The results reveal information about elastic deformation, yield, plastic deformation, creep, and fracture phenomena. Accordingly, this work demonstrates a generalizable approach for assessing the mechanical response of individual micron-sized molecular crystal particles and utilizing those responses in particle-level models.

Journal ArticleDOI
TL;DR: In this article, a nonlinear nanomechanical model is developed to evaluate the mechanical behavior of silicon nanowires and the intrinsic stress and surface parameters are examined based on Raman spectroscopy measurements and molecular dynamics simulations, respectively.
Abstract: This work proposes a new approach to characterize the mechanical properties of nanowires based on a combination of nanomechanical measurements and models. Silicon nanowires with a critical dimension of 90 nm and a length of 8 μm obtained through a monolithic process are characterized through in-situ three-point bending tests. A nonlinear nanomechanical model is developed to evaluate the mechanical behavior of nanowires. In this model, the intrinsic stress and surface parameters are examined based on Raman spectroscopy measurements and molecular dynamics simulations, respectively. This work demonstrates a new approach to measure the mechanical properties of Si nanowires by considering the surface effect and intrinsic stresses. The presented technique can be used to address the existing discrepancies between numerical estimations and experimental measurements on the modulus of elasticity of silicon nanowires.

Journal ArticleDOI
TL;DR: In this article, the basics of positron annihilation spectroscopy are reviewed, and preliminary work on undoped and doped CeO2 is shown and compared to the literature results from UO2.
Abstract: Disposal of spent nuclear fuel poses significant challenges, as the UO2 and fission products are under constant irradiation and must be safely stored for millennia. CeO2 is a non-radioactive analog for UO2 for studying microstructure and its evolution. Many techniques have been applied to uranium and cerium oxides to investigate point defects. Positron annihilation spectroscopies (PAS) are sensitive to neutral and negatively charged vacancy-like point defects and impurity vacancy complexes. PAS has been applied previously to UO2+x to investigate nuclear fuels, but virtually no PAS work exists on CeO2. Here, the basics of positron annihilation spectroscopy is reviewed, and preliminary work on undoped and doped CeO2 is shown and compared to the literature results from UO2. To simulate fission product incorporation in spent nuclear fuels, CeO2 samples were doped at different concentration with yttrium. Select samples were irradiated with heavy ions at different doses. Doping and irradiation are shown to give rise to different defect characteristics.