Showing papers in "MRS Advances in 2020"

Fabrication of CsPbBr3 Thick Films by Using a Mist Deposition Method for Highly Sensitive X-ray Detection

Abstract: X-ray imaging is a valuable technique used for medical imaging and non-destructive inspection of industrial products. However, the radiation may put humans at risk of developing cancer. Consequently, highly sensitive X-ray detectors, which enable X-ray imaging at a low dose rate, are required. Metal halide perovskite materials have demonstrated excellent X-ray detection performance including a high sensitivity owing to their high absorption coefficient, high carrier mobility, and long carrier lifetime. However, perovskite thick films with a large area, which is essential to realize the application of such materials to X-ray imaging devices have not been extensively investigated. To this end, in this study, a polymer is employed as a buffer layer to avoid film exfoliation, which makes it difficult to fabricate perovskite thick films, and a 110-μm-thick CsPbBr3 film is successfully obtained using a scalable solution method. In addition, an X-ray detector based on the CsPbBr3 thick film is fabricated, which demonstrates a sensitivity of 11,840 μC Gyair-1 cm-2. This sensitivity is approximately 600 times higher than that of the existing commercial a-Se X-ray detectors.

Antimicrobial Copper Cold Spray Coatings and SARS-CoV-2 Surface Inactivation

Abstract: This article contextualizes how the antimicrobial properties and antipathogenic contact killing/inactivating performance of copper cold spray surfaces and coatings and can be extended to the COVID-19 pandemic as a preventative measure. Specifically, literature is reviewed in terms of how copper cold spray coatings can be applied to high-touch surfaces in biomedical as well as healthcare settings to prevent fomite transmission of SARS-CoV-2 through rapidly inactivating SARS-CoV-2 virions after contaminating a surface. The relevant literature on copper-based antipathogenic coatings and surfaces are then detailed. Particular attention is then given to the unique microstructurally-mediated pathway of copper ion diffusion associated with copper cold spray coatings that enable fomite inactivation.

Oxides and the high entropy regime: A new mix for engineering physical properties

Abstract: Historically, the enthalpy is the criterion for oxide materials discovery and design. In this regime, highly controlled thin film epitaxy can be leveraged to manifest bulk and interfacial phases that are non-existent in bulk equilibrium phase diagrams. With the recent discovery of entropy-stabilized oxides, entropy and disorder engineering has been realized as an orthogonal approach. This has led to the nucleation and rapid growth of research on high-entropy oxides – multicomponent oxides where the configurational entropy is large but its contribution to its stabilization need not be significant or is currently unknown. From current research, it is clear that entropy enhances the chemical solubility of species and can realize new stereochemical configurations which has led to the rapid discovery of new phases and compositions. The research has expanded beyond studies to understand the role of entropy in stabilization and realization of new crystal structures to now include physical properties and the roles of local and global disorder. Here, key observations made regarding the dielectric and magnetic properties are reviewed. These materials have recently been observed to display concerted symmetry breaking, metal-insulator transitions, and magnetism, paving the way for engineering of these and potentially other functional phenomena. Excitingly, the disorder in these oxides allows for new interplay between spin, orbital, charge, and lattice degrees of freedom to design the physical behavior. We also provide a perspective on the state of the field and prospects for entropic oxide materials in applications considering their unique characteristics.

A facile synthesis method and fracture toughness evaluation of catfish bones-derived hydroxyapatite

Abstract: In this study, biological hydroxyapatite (HAp) was synthesized from catfish (Pangasius hypophthalmus) bones. First, the as-received catfish bones were de-proteinized in open air, and then converted to HAp by a solid state heat treatment method at a temperature of 900 °C for a holding time of 2 h in a muffle furnace. X-ray diffraction (XRD) analysis confirmed that HAp with high crystallinity of 99.9% was formed matching the structural properties of flouro-apatite with crystallite sizes of approximately 37.1 nm. The morphology of the HAp prepared showed irregularly shaped particles and revealed the appearance of open pores with a less agglomerated structure and a Ca/P ratio of about 1.58. The specific mechanical properties: hardness, compressive strength and fracture toughness of the catfish derived scaffolds were recorded as 480 MPa, 1.92 MPa, and 5.72 Mpa.m1/2, respectively. The fracture toughness of the HAp derived scaffolds suggests that the produced biomaterial is promising for biomedical applications. These findings are useful for the production and application of the HAp powders prepared from catfish bones, and further suggests a possible low-cost route for producing inexpensive ceramics using natural catfish bones.

Materials Data Science for Microstructural Characterization of Archaeological Concrete

Abstract: Ancient Roman concrete presents exceptional durability, low-carbon footprint, and interlocking minerals that add cohesion to the final composition. Understanding of the structural characteristics of these materials using X-ray tomography (XRT) is of paramount importance in the process of designing future materials with similar complex heterogeneous structures. We introduce Materials Data Science algorithms centered on image analysis of XRT that support inspection and quantification of microstructure from ancient Roman concrete samples. By using XRT imaging, we access properties of two concrete samples in terms of three different material phases as well as estimation of materials fraction, visualization of the porous network and density gradients. These samples present remarkable durability in comparison with the concrete using Portland cement and nonreactive aggregates. Internal structures and respective organization might be the key to construction durability as these samples come from ocean-submersed archeological findings dated from about two thousand years ago. These are preliminary results that highlight the advantages of using non-destructive 3D XRT combined with computer vision and machine learning methods for systematic characterization of complex and irreproducible materials such as archeological samples. One significant impact of this work is the ability to reduce the amount of data for several computations to be held at minimalistic computational infrastructure, near real-time, and potentially during beamtime while materials scientists are still at the imaging facilities.

Confinement Effect in Thermoelectric Properties of Two-Dimensional Materials

Abstract: Thermoelectric (TE) materials, or materials that can generate an electrical energy from temperature gradient, are promising for renewable energy technology. One fundamental aspect in the TE research is the demand to maximize the TE power-factor, PF = S2 σ, by having as large Seebeck coefficient (S) and electrical conductivity (σ) as possible. In the early 90s, Hicks and Dresselhaus proposed the PF enhancement by using low-dimensional materials, in which electrons are confined in certain directions and they move freely in the other directions. This quantum effect is known as the confinement length (L) effect, in which L is the thickness or diameter of the two-dimensional (2D) or one-dimensional materials, respectively. However, a key challenge is to understand the critical value of L, at which the PF can be significantly enhanced. Recently, we reevaluated the confinement theory of the low-dimensional materials to solve this issue. We showed that electrons are fully confined only when L is smaller than an intrinsic length Λ, the so-called thermal de Broglie wavelength, which depends on the materials and can be experimentally measured. Monolayer 2D materials naturally satisfy the condition of L < Λ since their confinement length is ∼ 1 nm, while their thermal de Broglie wavelength is ∼ 5-10 nm. Therefore, they could be a good candidate for TE materials. In this review article, we first review the TE materials with low dimensions. Then, we show the basic concept of the confinement effect and the consequence of such an effect. Finally, based on this effect, we turn our attention to the progress achieved recently in the TE properties of the 2D materials such as monolayer InSe, GaN electron gas, and SrTiO3 superlattices.

Small Angle Scattering Data Analysis Assisted by Machine Learning Methods

Abstract: Small angle scattering (SAS) is a widely used technique for characterizing structures of wide ranges of materials. For such wide ranges of applications of SAS, there exist a large number of ways to model the scattering data. While such analysis models are often available from various suites of SAS data analysis software packages, selecting the right model to start with poses a big challenge for beginners to SAS data analysis. Here, we present machine learning (ML) methods that can assist users by suggesting scattering models for data analysis. A series of one-dimensional scattering curves have been generated by using different models to train the algorithms. The performance of the ML method is studied for various types of ML algorithms, resolution of the dataset, and the number of the dataset. The degree of similarities among selected scattering models is presented in terms of the confusion matrix. The scattering model suggestions with prediction scores provide a list of scattering models that are likely to succeed. Therefore, if implemented with extensive libraries of scattering models, this method can speed up the data analysis workflow by reducing search spaces for appropriate scattering models.

Synthesis and Characterization of Zinc Oxide Nanoparticles (ZnO NPs) in Powder and in Thin Film using Corn Husk Extract via Green Chemistry

Abstract: In this study, zinc oxide nanoparticles (ZnO NPs) in powder and in thin film were successfully synthesized first time using an eco-friendly, simple and cost effective green synthesis method mediated by corn husk (Zea mays) extract as an effective chelating agent, and zinc nitrate hexahydrate as precursor. Diverse characterizations techniques such as High Resolution - Scanning Electron Microscopy (HR-SEM), Energy Dispersive X- rays Spectroscopy (EDS), X-Rays Diffraction (XRD), and UV - Vis - NIR spectroscopy as well as Photoluminescence (PL) were investigated to confirm ZnO NPs nature. For the ZnO NPs powder, highly crystalline ZnO nanoparticles (ZnO NPs) annealed at 500°C which are 48.635 nm in particles size were characterised by HR-SEM and XRD analysis. The structure morphology and the constituents of the resultant ZnO powder were investigated respectively by HR-SEM and EDS. UV - Visible spectroscopy analysis was investigated on the optical band gap of ZnO NPs, which was calculated to be 3.31 eV. This result indicates that ZnO NPs can be used in metal oxide semiconductor-based devices. For the ZnO NPs thin film, XRD patterns of hexagonal wurtzite structure with c/a ratio about of 1.60 and μ - parameter of 0.38 were obtained. PL measurements showed a broad emission band in the 380 - 800 nm range, centred at 481 nm. ZnO NPs thin film yielded relatively more intense photoluminescence spectra than the ZnO NPs powder. The intrinsic point defects and defect level transitions responsible for the broad emission are discussed.

Effect of dopant on the morphology and electrochemical performance of Ni1-xCaxCo2O4 (0 ≤ x ≤ 0.8) oxide hierarchical structures

Abstract: The binary metal oxides are increasingly used as supercapacitor electrode materials in energy storing devices. Particularly NiCo2O4 has shown promising electrocapacitive performance with high specific capacitance and energy density. The electrocapacitive performance of these oxides largely depends on their morphology and electrical properties governed by their energy band-gaps and defects. The morphological structure of NiCo2O4 can be altered via the synthesis route, while the energy band-gap could be altered by doping. Also, doping can enhance crystal stability and bring in grain refinement, which can further improve the much-needed surface area for high specific capacitance. Given the above, this study evaluates the electrochemical performance of Ca-doped Ni1-xCaxCo2O4 (0 = x = 0.8) compounds. This stipulates promising applications for electrodes in future supercapacitors.

Influence of Rice Husk Ash on Characteristics of Earth Cement Blocks

Abstract: This paper presents an experimental study on the characteristics of earth cement blocks with Rice Husk Ash (RHA) as a partial replacement to cement. The replacement of RHA content is limited to 0%, 5%, 10%, 15% and 20% by mass of the total binder in the earth cement block. The experiments on earth cement blocks investigate the compressive strength and flexural tensile strength for mechanical properties and water absorption, sorption rate and erosion against water spray for its durability. Due to the high content of SiO2 in RHA with great reactivity, a significant increase in the compressive and flexural tensile strength of earth cement blocks was observed up to 10% RHA content. However, the durability of earth cement blocks becomes adverse with the increasing percentage of RHA replacement, but within the allowable limit. The experimental results indicate that to some extent, RHA based earth cement blocks have a significant potential for reduction in cement used in the construction industry.

Effect of production and curing conditions on the performance of stabilized compressed earth blocks: Kaolinite vs quartz-rich earthen material

Abstract: This study investigated the effect of production and curing parameters on the mechanical performance of compressed earth blocks (CEBs) stabilized with 0-20 wt % CCR (calcium carbide residue). Kaolinite (K) and quartz (Q)-rich earthen materials were mixed with the CCR and used to mould CEBs at optimum moisture content (OMC) and OMC+2 % of the dry mixtures, cured at 20 °C, ambient temperature in the lab (30±5 °C) and 40 °C for 0-90 days. After curing, the reactivity of the materials and compressive strength of dry CEBs were tested. Increasing the moulding moisture from OMC to OMC+2 decreased the compressive strength 0.3 times (4.4 to 3.3 MPa) for the CEBs stabilized with 20 % CCR cured at 30±5 °C for 45 days. Similarly, the compressive strength (4.4 MPa) was reached by CEBs stabilized with 10 and 20 % CCR after 28 and 45 days of curing, respectively. At 40 °C, the compressive strength increased 3.3 times (1.1 to 4.7 MPa with 0 to 20 % CCR) for K-rich and 2.5 times (2 to 7.1 MPa) for Q˗rich materials. At 20 °C, the compressive strength increased only 1.3 times (1.1 to 2.5 MPa) for K˗rich and barely 0.7 times (2 to 3.4 MPa) for Q-rich materials. These suggest that CCR is useful for stabilization and improving the performances of CEBs in hot regions.

Cobalt Metal ion Doped Cerium Oxide (Co-CeO2) Nanoparticles Effect Enhanced Photocatalytic Activity

Abstract: The REE (rare-earth-elements) cerium (Ce) is the most abundant earth-crust element and their oxides have great attention in the form of nanocrystalline nature with superior physical and chemical properties. Pure and Co (1%, 3% and 5%) doped CeO2 nanoparticles (NPs) synthesized by co-precipitation technique were characterized through X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-visible spectroscopy. XRD shows face-centred-cubic (FCC) crystal symmetry with average crystallite size 6–12nm. HRTEM exhibits almost identical cubical shaped particles with average size 4–10nm. Tuned band-gap may be observed from UV-visible spectrum of CeO2-NPs upon Co (1%, 3% & 5%) incorporation. Enhancement of the photocatalytic activity observed for Co-doped (1%, 3% & 5%) to the degradation of methylene-blue (MB) dye under visible-light absorption.

On the Use of Moringa Oleifera Leaves Extract for the Biosynthesis of NiO and ZnO Nanoparticles

Abstract: This contribution reports on the biosynthesis of nickel oxide and zinc oxide nanoparticles (NiO-NPs & ZnO-NPs) via a natural extract from Moringa Oleifera leaves as an effective chelating and/or oxidizing/reduction agent of nickel nitrate hexahydrate and zinc nitrate hexahydrate. The structural and optical properties of these two types of semiconductors obtained in a similar procedure are investigated using X-rays Diffraction (XRD), Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR), diffuse reflectance UV-Visible-NIR and Photoluminescence (PL) techniques. The structural analysis shows the formation of pure cubic NiO-NPs and pure wurtzite ZnO-NPs with an average crystallite size of 17.80 nm and 10.81 nm respectively. Their band gaps, calculated from the diffuse reflectance analysis were found to be 4.28 eV and 3.35 eV respectively.

On Alteration Rate Renewal Stage of Nuclear Waste Glass Corrosion

Abstract: The three generically accepted stages of glass corrosion are reviewed with focus on final stage termed alteration rate renewal (or resumption) stage when the glass may re-start corroding with the rate similar to that at the initial stage. It is emphasized that physical state and physical changes that occur in the near-surface layers can readily lead to an effective increase of leaching rate which is similar to alteration rate renewals. Experimental data on long-term (during few decades) corrosion of radioactive borosilicate glass K26 designed to immobilize high-sodium operational NPP radioactive waste evidence on resumption-like effects of radionuclides (137,134Cs) leaching. The cause of that was however related not to chemical changes in the leaching environment but rather to physical state of glass surface due to formation of small cracks and new pristine glass areas in contact with water.

Mechanical Properties of Diamond Schwarzites: From Atomistic Models to 3D-Printed Structures

Abstract: Triply Periodic Minimal Surfaces (TPMS) possess locally minimized surface area under the constraint of periodic boundary conditions. Different families of surfaces were obtained with different topologies satisfying such conditions. Examples of such families include Primitive (P), Gyroid (G) and Diamond (D) surfaces. From a purely mathematical subject, TPMS have been recently found in materials science as optimal geometries for structural applications. Proposed by Mackay and Terrones in 1991, schwarzites are 3D crystalline porous carbon nanocrystals exhibiting a TPMS-like surface topology. Although their complex topology poses serious limitations on their synthesis with conventional nanoscale fabrication methods, such as Chemical Vapour Deposition (CVD), schwarzites can be fabricated by Additive Manufacturing (AM) techniques, such as 3D Printing. In this work, we used an optimized atomic model of a schwarzite structure from the D family (D8bal) to generate a surface mesh that was subsequently used for 3D-printing through Fused Deposition Modelling (FDM). This D schwarzite was 3D-printed with thermoplastic PolyLactic Acid (PLA) polymer filaments. Mechanical properties under uniaxial compression were investigated for both the atomic model and the 3D-printed one. Fully atomistic Molecular Dynamics (MD) simulations were also carried out to investigate the uniaxial compression behavior of the D8bal atomic model. Mechanical testings were performed on the 3D-printed schwarzite where the deformation mechanisms were found to be similar to those observed in MD simulations. These results are suggestive of a scale-independent mechanical behavior that is dominated by structural topology.

Electrochemical study of Nickel Oxide (NiO) nanoparticles from cactus plant extract

Abstract: P-type NiO powders with an average crystallite size of 16 nm as shown by x-ray diffraction analysis were produced via biosynthesis using cactus plant extract. SEM showed that the NiO powders consisted of particles with sizes in the 20-35 nm range. A cyclic voltammetric study of the NiO nanopowders showed a quasi-reversible redox processes with the NiO powder showing potential for pseudo capacitance. Through these findings the use of natural Cactus extracts is hereby shown to be a cost-effective and environmentally friendly alternative for preparing Nickel oxide nanosized powders that can be of use in a variety of energy storage applications.

Highly Sensitive and Fast Detection of C-Reactive Protein and Troponin Biomarkers Using Liquidgated Single Silicon Nanowire Biosensors

Abstract: C-reactive protein (CRP) and cardiac troponin I (cTnI) biomolecules represent the earliest enzymes that appear in the blood when a cardiac injury occurs. Real-time and selective detection of these biomarkers is essential for the prediction and detection of cardiovascular diseases at an early stage. Here we report on the label-free specific detection of both proteins at picomolar concentrations using fabricated nanowire-based biosensors. We demonstrate a novel functionalization technique based on the attachment of dibenzocyclooctyne (DBCO)- linked troponin-specific aptamers to azide-functionalized silicon (Si) nanowire (NW) surface. Due to the fast and reliable immobilization of cTnI-specific aptamers and CRP-specific antibodies on the Si NWs, the fabricated devices can rapidly detect target biomolecules demonstrating high sensitivity. We confirm the attachment of proteins to the surface of Si NWs by atomic force microscopy (AFM). Moreover, we demonstrate that nanowire structures of different sizes enable the detection of biomarkers in a wide concentration range (from 1 pg/ml to 1 μg/ml), corresponding to CRP and cTnI elevation levels during the early stage of disease formation.

A feasibility investigation of laboratory based X-ray absorption spectroscopy in support of nuclear waste management

Abstract: X-ray Absorption Spectroscopy is a technique of fundamental importance in nuclear waste management, as an element specific probe of speciation, which governs radionuclide solubility, immobilisation and migration. Here, we exploit recent developments in laboratory instrumentation for X-ray Absorption Spectroscopy, based on a Rowland circle geometry with a spherically bent crystal analyser, to demonstrate speciation in prototype ceramic and glass-ceramic waste forms. Laboratory and synchrotron XANES data acquired from the same materials, at the Ce and U L3 edges, were found to be in excellent quantitative agreement. We establish that analysable laboratory XANES data may be acquired, and interpreted for speciation, even from quite dilute absorber concentrations of a few mol%, albeit with data acquisition times of several hours. For materials with suitable absorber concentrations, this approach will enable routine element specific speciation studies to support rapid optimisation of radioactive waste forms and analysis of radiological materials in a purpose designed laboratory, without the risk associated with transport and manipulation at a synchrotron radiation facility.

RNA Delivery via DNA-Inspired Janus Base Nanotubes for Extracellular Matrix Penetration.

Abstract: RNA delivery into deep tissues with dense extracellular matrix (ECM) has been challenging. For example, cartilage is a major barrier for RNA and drug delivery due to its avascular structure, low cell density and strong negative surface charge. Cartilage ECM is comprised of collagens, proteoglycans, and various other noncollagneous proteins with a spacing of 20nm. Conventional nanoparticles are usually spherical with a diameter larger than 50-60nm (after cargo loading). Therefore, they presented limited success for RNA delivery into cartilage. Here, we developed Janus base nanotubes (JBNTs, self-assembled nanotubes inspired from DNA base pairs) to assemble with small RNAs to form nano-rod delivery vehicles (termed as “Nanopieces”). Nanopieces have a diameter of ~20nm (smallest delivery vehicles after cargo loading) and a length of ~100nm. They present a novel breakthrough in ECM penetration due to the reduced size and adjustable characteristics to encourage ECM and intracellular penetration.

Photocatalytic Degradation of 2-chlorophenol under γ-Bi2MoO6/Graphene Oxide

Abstract: The present research was aimed to study the degradation of 2-Chlorophenol through the use of bismuth molybdate (γ-Bi2MoO6) structures supported on graphene oxide (GO) which is intended to control the recombination of charge carriers. γ-Bi2MoO6/GO systems were doped with nitrogen via chemical reaction, to reduce their energy gap, improving their photocatalytic activity. Structural and physicochemical characterization of the resulting catalysts were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis. The obtained compounds show good photo catalytic performance when using visible energy to degrade 2-Chlorophenol, obtaining 80% of degradation in 65 min.

Development of Dissipative Particle Dynamics framework for modeling hydrogels with degradable bonds

Abstract: Controlled degradation of hydrogels enables several applications of these materials, including controlled drug and cell release applications and directed growth of neural networks. These applications motivate the need of a simulation framework for modeling controlled degradation in hydrogels. We develop a Dissipative Particle Dynamics (DPD) framework for hydrogel degradation. As a model hydrogel, we prepare a network formed by end-linking tetra-arm polyethylene glycol precursors. We model bond breaking during degradation of this hydrogel as a stochastic process. The fraction of degradable bonds follows first order degradation kinetics. We characterize the rate of mass loss during degradation process.

Merging Materials and Data Science: Opportunities, Challenges, and Education in Materials Informatics

Abstract: Since the launch of the Materials Genome Initiative (MGI) the field of materials informatics (MI) emerged to remove the bottlenecks limiting the pathway towards rapid materials discovery. Although the machine learning (ML) and optimization techniques underlying MI were developed well over a decade ago, programs such as the MGI encouraged researchers to make the technical advancements that make these tools suitable for the unique challenges in materials science and engineering. Overall, MI has seen a remarkable rate in adoption over the past decade. However, for the continued growth of MI, the educational challenges associated with applying data science techniques to analyse materials science and engineering problems must be addressed. In this paper, we will discuss the growing use of materials informatics in academia and industry, highlight the need for educational advances in materials informatics, and discuss the implementation of a materials informatics course into the curriculum to jump-start interested students with the skills required to succeed in materials informatics projects.

Influence of Soil Grading on the Mechanical Behavior of Earth Cement Blocks

Abstract: The characteristics of earth cement blocks depend on soil composition, grading of the soil, cement-soil ratio and water content, etc… In the present study, an experimental program is conducted to evaluate the influence of soil grading in the mechanical properties of earth cement blocks. Five gradings of soil used for the preparation of earth cement blocks. Soil grading effect on following properties of earth-cement blocks such as block density, compressive strength in wet and dry condition, flexural tensile strength in wet and dry condition, and water absorption was compared. Results show that the properties of the earth cement blocks are dependent upon the fine content and uniformity coefficient of the soil. The increase in the finer content in mortar improves water absorption, compressive strength and flexural tensile strength.

Anisotropic Optical Properties of 2D Silicon Telluride

Abstract: Silicon telluride (Si2Te3) is a silicon-based 2D chalcogenide with potential applications in optoelectronics. It has a unique crystal structure where Si atoms form Si-Si dimers to occupy the “metal” sites. In this paper, we report an ab initio computational study of its optical dielectric properties using the GW approximation and the Bethe-Salpeter equation (BSE). Strong in-plane optical anisotropy is discovered. The imaginary part of the dielectric constant in the direction parallel to the Si-Si dimers is found to be much lower than that perpendicular to the dimers. The optical measurement of the absorption spectra of 2D Si2Te3 nanoplates shows modulation of the absorption coefficient under 90-degree rotation, confirming the computational results. We show the optical anisotropy originates from the particular compositions of the wavefunctions in the valence and conduction bands. Because it is associated with the Si dimer orientation, the in-plane optical anisotropy can potentially be dynamically controlled by electrical field and strain, which may be useful for new device design. In addition, BSE calculations reduce GW quasiparticle band gap by 0.3 eV in bulk and 0.6 eV in monolayer, indicating a large excitonic effect in Si2Te3. Furthermore, including electron-hole interaction in bulk calculations significantly reduces the imaginary part of the dielectric constant in the out-of-plane direction, suggesting strong interlayer exciton effect in Si2Te3 multilayers.

Bottom-Up Approaches for Precisely Nanostructuring Hybrid Organic/Inorganic Multi-Component Composites for Organic Photovoltaics

Abstract: Achieving control over the morphology of conjugated polymer (CP) blends at nanoscale is crucial for enhancing their performances in diverse organic optoelectronic devices, including thin film transistors, photovoltaics, and light emitting diodes. However, the complex CP chemical structures and intramolecular interactions often make such control difficult to implement. We demonstrate here that cooperative combination of non-covalent interactions, including hydrogen bonding, coordination interactions, and π-π interactions, etc., can be used to effectively define the morphology of CP blend films, in particular being able to achieve accurate spatial arrangement of nanoparticles within CP nanostructures. Through UV-vis absorption spectroscopy and transmission electron microscopy, we show strong attachment of fullerene molecules, CdSe quantum dots, and iron oxide nanoparticles, onto well-defined CP nanofibers. The resulting core/shell hybrid nanofibers exhibit well-defined donor/acceptor interface when employed in photovoltaic devices, which also contributes to enhanced charge separation and transport. These findings provide a facile new methodology of improving CP/nanoparticle interfacial properties and controlling blend morphology. The generality of this methodology demonstrated in current studies points to a new way of designing hybrid materials based on organic polymers and inorganic nanoparticles towards applications in modern electronic devices.

Epitaxial Growth of Bendable Cubic NiO and In2O3 Thin Films on Synthetic Mica for p- and n-type Wide-Bandgap Semiconductor Oxides

Abstract: Bendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] ∥ (001) synthetic mica [100]. In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sn-doped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with non-doped In2O3, Sn doping decreased the sheet resistance by two digits.

Performance of Stabilized Earth with Wheat Straw and Slag

Abstract: Stabilized earth is a very ancient material that has been used in many countries as a low cost, environment friendly construction material. However, its durability under humid environments is low. Stabilization using cement, lime and natural fibres could enhance its durability and lowers the risk of cracking. This paper presents an experimental investigation into the performance of stabilised local soil by either, cement mixed with a proportion of granulated blast furnace slag (GBFS) /or straw naturel fibres. Unconfined compressive strength (UCS), shrinkage, wetting and drying, capillary absorption and thermal conductivity tests were performed on both untreated soil samples and stabilised soil samples. The results show that stabilising the soil with cement and GBFS increased both compressive strength, durability, thermal conductivity and decreased the capillary absorption and the shrinkage. The addition of natural wheat fibres increased the capillary absorption but leads to a decrease in the thermal conductivity and to a further reduction in the shrinkage and hence a better insulating less prone to cracking material.

MOVPE of Large-Scale MoS2/WS2, WS2/MoS2, WS2/Graphene and MoS2/Graphene 2D-2D Heterostructures for Optoelectronic Applications

Abstract: Most publications on (opto)electronic devices based on 2D materials rely on single monolayers embedded in classical 3D semiconductors, dielectrics and metals. However, heterostructures of different 2D materials can be employed to tailor the performance of the 2D components by reduced defect densities, carrier or exciton transfer processes and improved stability. This translates to additional and unique degrees of freedom for novel device design. The nearly infinite number of potential combinations of 2D layers allows for many fascinating applications. Unlike mechanical stacking, metal-organic vapour phase epitaxy (MOVPE) can potentially provide large-scale highly homogeneous 2D layer stacks with clean and sharp interfaces. Here, we demonstrate the direct successive MOVPE of MoS2/WS2 and WS2/MoS2 heterostructures on 2” sapphire (0001) substrates. Furthermore, the first deposition of large-scale MoS2/graphene and WS2/graphene heterostructures using only MOVPE is presented and the influence of growth time on nucleation of WS2 on graphene is analysed.

Overview of Si Tandem Solar Cells and Approaches to PV-Powered Vehicle Applications

Abstract: Development of high-efficiency solar cell modules and new application fields are significant for the further development of photovoltaics (PV) and creation of new clean energy infrastructure based on PV. Especially, development of PV-powered EV applications is desirable and very important for this end. This paper shows analytical results for efficiency potential of various solar cells for choosing candidates of high-efficiency solar cell modules for automobile applications. As a result of analysis, Si tandem solar cells are thought to be some of their candidates. This paper also overviews efficiency potential and recent activities of various Si tandem solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, perovskite/Si and nanowire/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of high efficiency with efficiencies of more than 36% for 2-junction and 42 % for 3-junction tandem solar cells under 1-sun AM1.5 G, lightweight and low-cost potential. Recent results for our 28.2 % efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si 3-junction solar cell are also presented. Approaches to automobile application by using III-V/Si tandem solar cells and static low concentration are presented.

Solar-Blind Ultraviolet Photodetectors Based on Vertical Graphene-Hexagonal Boron Nitride Heterostructures

Abstract: Photodetectors operating in the ultraviolet (UV) play a pivotal role in applications such as ozone monitoring and biosensing. One key factor to successfully implementing such photodetectors is that they must be solar-blind to avoid detecting ambient visible and infrared light. Unfortunately, UV photodetectors based on silicon and other typical semiconductors are not natively solar-blind, since their band gap energies are in the visible range. Hexagonal boron nitride (h-BN) is an example of a wide band gap semiconductor which shows promise for use as the absorbing medium in a UV photodetector device, since its band gap is wide enough to make it inherently insensitive to light in the visible range and above. Here we report on the fabrication and characterization of a graphene-h-BN-heterostructure photodetector which utilizes a vertical geometry, in principle allowing for highly scalable production. We find that our device shows a finite photoresponse to illumination by a 254nm light source, but not to a 365nm source, thus suggesting that our device is solar-blind.