Reported conversion efficiencies of lead based perovskite solar cells keep increasing steadily. But next to the demand for high efficiency, the need for analogue non-toxic material systems remains. One promising lead free absorber material is the double perovskite Cs2AgBiBr6. Interest in this and other double perovskites has been increasing in the last three years and several solar cells using different device structures have been reported. However, the efficiency of these solar cells is merely in the range of 2%. To further improve solar cell performance we prepared mixed bismuth-antimony double perovskite Cs2AgBi1-xSbxBr6 where different fractions of antimony (x=0.125, 0.25, 0.375, 0.50) are used. This was motivated by reports of lower bandgap values in these mixed system. After the optimization of preparation of these thin films, we have carefully analysed the effects on the structure, composition, electronic structure, as well as optical properties. Finally, we have fabricated Bi-Sb mixed double perovskite solar cells in a mesoscopic device architecture.

Impacts of a forming process on bipolar resistive switching (RS) characteristics in Pt/TaOx/Ta2O5/Pt cells were investigated. We found that the forming resulted in a transition from an initial state to a particular high resistance state (HRS) in most of the Pt/TaOx/Ta2O5/Pt cells. Evaluation of electrical characteristics after the transition to the particular HRS revealed that two modes of bipolar RS with the conventional polarity based on valence change mechanism and with the opposite polarity could be selectively obtained by adjusting the magnitude of the applied voltage. Moreover, the cell resistance decreased gradually during set processes in the bipolar RS with the opposite polarity.

Power source plays an important role in keeping normal functions of biodegradable electronic devices. In this paper, we proposed a fabrication method of biodegradable supercapacitor (BSC), which can provide energy for portable and implantable medical electronics. The BSC has a sandwich-like symmetric structure, which was assembled layer by layer. The electrochemical performances of BSC were measured, including the cyclic voltammetry test, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Titanium foil was used as a template to generate microstructure for polylactic acid (PLA) supporting substrate. The microstructure provided strong adhesion force for iron film in sputtering process. The nanoporous zinc oxide layer was prepared by evaporation-driven self-assembly technology on iron film. The nanoporous structure was in favour of ionic storage in charging-discharging process. About 60% of capacitance retention was achieved after 3000 times of cycling test. After connecting three BSC in series, a green LED pattern was lighted up immediately, indicating that the energy was stored in BSC device successfully. After immersing the BSC in DMEM, the BSC can be totally degraded gradually. This work provided a feasible scheme for developing biodegradable energy storage device, it also gave a possible avenue for powering biodegradable electronic devices.

Roll-to-roll slot-die coating with a meniscus guide is used to deposit several layers in a P-I-N perovskite solar cell stack, including the perovskite layer. The use of various length meniscus guides as part of the slot-die head allows controlled coating of these layers at a common coating speed. The length of meniscus guide used is optimised and related to the rheology of the coated ink and appropriate choice of meniscus guide length provides a way to avoid flooding of the coated area and improve coating definition. Initial coating trial results suggest the low-flow limit of slot-die coating is still applicable when using a meniscus guide, which is an important and previously unreported observation, application of this theory to meniscus guide coating provides a useful tool for rapidly determining the appropriate coating conditions that can be used as part of a manufacturing process. This is further explored through the deposition of perovskite solar cells by roll-to-roll slot-die coating. The perovskite layer is deposited using a sequential slot-die deposition process using a low toxicity dimethyl sulfoxide ink for the lead iodide layer, it is found that increasing the drying oven temperature and air flow rate can be used to improve the uniformity of the layer but this can also result in deformation of the plastic substrate. Functioning perovskite solar cells are demonstrated using this technique, but a large variation is found between device performances which is attributed to the poor uniformity of the perovskite layer and damage caused to the substrate by excessive heating.

Several technologically important alloys like Al-Li-Zr, Al-Li-Sc, Al-Sc-Zr, Al-Li-Sc-Zr, modified Inconel etc., exhibit compact precipitates in their microstructure. We present a phase-field model in two dimensions to study the morphological evolution of composite precipitates in ternary alloys. The model employs a modified regular solution description of the bulk free energy of the disordered matrix phase and ordered precipitates. Elastic strain energy of the three-phase system is described using Khachaturyan’s microelasticity theory. The temporal evolution of the spatially dependent field variables is determined by numerically solving coupled Cahn-Hilliard and Allen-Cahn equations for composition and order parameter fields, respectively. We systematically vary the misfit strains, alloy chemistry and mobilities of the diffusing species to study their effect on the development of compact precipitates. Compact core-shell morphology destabilizes when the precipitate phases have misfit strains of opposite signs with the matrix phase although the relative interfacial energies between the phases satisfy Cahn’s spontaneous wetting condition. Thus, the stability of “monodisperse” core-shell microstructures is determined by the interplay between the relative interfacial energies and elastic interactions between the phases. Further, our simulations show that low solute mobility within the core leads to sluggish coarsening of the compact particles.

Polymer-mineral composite solid electrolytes have been prepared by hot pressing using lithium ion-exchanged bentonite (LIEB) and mineral derived LATSP (Li1.2Al0.1Ti1.9Si0.1P2.9O12) NASICON materials as solid electrolyte fillers in the polyethylene oxide (PEO) polymer containing LiTFSI salt. The mineral based solid electrolyte fillers not only increase ionic conductivity but also improve thermal stability. The highest ionic conductivities in the PEO-LIEB and PEO-LATSP composites were found to be 9.4×10-5 and 3.1×10-4 S·cm-1 at 40°C, respectively. The flexible, thermal stable and mechanical sturdy polymer-mineral composite solid electrolyte films can be used in the all-solid-state batteries.

Climate change and an increase in endangered species, are examples of technological advances negatively impacting the environment. As technology demands increase, an earnest effort to reduce the environmental impact of processing and manufacturing related activities is critical. From a business perspective, minimizing or removing toxic process chemicals is a high impact area that can increase work environment safety and decrease waste management costs. This work presents processing considerations when transitioning to greener alternative polymer resist solvents, for applications in nanomanufacturing with sustainability considerations. Within government contracting, process modifications that change product form, fit, or function require qualification and at minimum justification. This work presents the conversion from a chlorobenzene to anisole based solvent using a 495 kMW polymetheyl methacrylate polymer resin, without impacting form fit or function of the intended device. Resist conversion is of interest as the difference in the substituents of the two solvents, impact the effective toxicity of the polymer resists. Specifically, the oral median lethal dose (LD50) in rats for chlorobenzene is 1110 mg/kg, while anisole is 3700 mg/kg. Therefore, developing a process utilizing anisole and replacing chlorobenzene addresses safety concerns and contributes to green initiatives worldwide. Within this work electron beam lithography fabricated transistor components consisting of a double layered source, and gate were converted from a chlorobenzene to anisole based process; while maintaining process of record specifications. The purpose of this work is to provide a starting platform for individuals seeking to convert from a chlorobenzene solvent to an anisole based resist for sub-micron lithography steps.

Pure metallic nanofoams in the form of interconnected networks have shown strong potentials over the past few years in areas such as catalysts, batteries and plasmonics. However, they are often fragile and difficult to integrate in engineering applications. In order to better understand their deformation mechanisms, a multiscale approach is required to simulate the mechanical behavior of the nanofoams, although these materials will operate at the macroscale, they will still be maintaining an atomistic ordering. Hence, in this work we combine molecular dynamics (MD) and finite element analysis (FEA) to study the mechanical behavior of copper (Cu) nanofoams. Molecular dynamics simulations were performed to study the yield surface of a representative cell structure. The nanofoam structure has been generated by spinodal decomposition of binary alloy using an atomistic approach. Then, the information obtained from the molecular dynamics simulations in the form of yield function is transferred to the finite element model to study the macroscopic behavior of the Cu nanofoams. The simulated mechanical behavior of Cu nanofoams is in good agreement of the real experiment results.

Thermoelectric materials can play an important role to develop a sustainable energy source for internet of things devices near room temperature. In this direction, it is important to have a thermoelectric material with high thermoelectric performance. Cesium tin triiodide (CsSnI3) single crystal perovskite has shown high value of Seebeck coefficient and ultra low thermal conductivity which are necessary conditions for high thermoelectric performance. Here, we report the thermoelectric response of CsSnI3 thin films. These films are prepared by cost effective wet spin coating process at different baking temperature. Films were characterized using X-ray diffraction and scanning electron microscopy. In our case, films baked at 130°C for 5 min have shown the best thermoelectric performance at room temperature with: Seebeck coefficient 115 μV/K and electrical conductivity 124 S/cm, thermal conductivity 0.36 W/m·K and figure of merit ZT of 0.137.

Organic-inorganic hybrid materials have shown a remarkable and rapid development during the past decade because they can be tailored to obtain new device concepts with controlled physical properties. Here, we report on the electronic and magnetic properties of multilayer organic-inorganic hybrid films. Electrical transport properties arising from the π electrons in the organic layer are characteristic of a metallic state at high temperature and evolve into a state described by two-dimensional variable range hopping when temperature decreases below 150 K. The intrinsic electronic behavior of the hybrid films was further studied via the optical properties in the IR range. The optical response confirms the metallic character of the hybrid films. In the second part, the magnetic properties are discussed. A long-range ferromagnetic order with an ordering temperature of ∼ 1 K is revealed in the Gd-based hybrid film. The Cu-based hybrid film, however, shows more extended ferromagnetic exchange interactions than the Gd-based hybrid LB film.

The amorphous structures of poly-CO, P-N and N-CO extended solids at high pressures were predicted using density functional theory (DFT) and evolutionary algorithms employing variable and fixed concentrations of components methods. Compression of random network of poly-CO up to 45 GPa results in elimination of small rings of the amorphous network. The amorphous structure with stoichiometry N9P was found to be dynamically stable (no imaginary frequencies in phonon-dispersion curve), stable relative transformation to solid nitrogen and phosphorus, but metastable according to convex hull calculations. The amorphous structure of the N-CO extended solid was obtained with various concentrations of N atoms under isotropic compression up to 50 GPa and release of pressure down to 5 GPa calculated using DFT. The higher concentration of CO is found to be favourable for stabilization of an amorphous covalent N-C-O network consisting of chains and a cage of the network. Upon lowering the pressure and decomposition of the compressed extended solid, atoms are disconnected first from the ends of polymeric chains, while rings of random network are sustained almost intact. Results of a calculated Raman spectra are compared with available experimental results.

There is widespread research and popular interest in developing micro-invasive neural interfacing modalities. An increasing variety of probes have been developed and reported in the literature. Newer, smaller probes show significant benefit over larger ones in reducing tissue damage and scarring. A different set of obstacles arise, however, as probes become smaller. These include reliable insertion and robustness. This review articulates the impact of various design parameters (material, geometry, size) on probe insertion mechanisms, chronic viability, and glial scarring. We highlight various emerging technologies utilizing novel form factors including micron-scale interfaces and bio-inspired designs for probe insertion and steering.

The “safety case” approach has been developed to address the issue of evaluating the performance of a geologic repository in the face of the large uncertainty that results for evaluations that extend over hundreds of thousands of years. This paper reviews the concept of the safety case as it has been defined by the international community. We contrast the safety case approach with that presently used in the U.S. repository program. Especially, we focus on the role of uncertainty quantification. There are inconsistencies between the initial proposal to dealing with uncertainties in a safety case and current U.S. practice. The paper seeks to better define the safety case concept so that it can be usefully applied to the regulatory framework of the U.S. repository program.

To shorten the time for designing and developing new materials, fast evaluation of microstructure-property relation is required. In this research, we applied machine learning to perform crystal phase segmentation and extracted microstructure features of Cr-based duplex alloys from the scanning electron microscope (SEM) images. The results show that the accuracy of crystal phase segmentation was improved when the backscattered electron (BSE) images with controlled channeling contrast was used. This indicates that measurement conditions of the BSE images are important for obtaining high segmentation accuracy. The segmented images were used for the extraction of microstructure features. With the extracted features, the reliable prediction of mechanical properties of Cr-based duplex alloys was verified with a prediction error less than 10%. We demonstrated a method of using microstructure features extracted from SEM images for fast evaluation of microstructure-property relation.

The present work is aimed to study a comparison among synthesized graphene films, deposited on copper substrates and commercial graphene films; both decorated with Eu2O3 particles, with the purpose of promoting photoluminescence. The decoration procedure was achieved using the radio frequency sputtering (R.F. Sputtering) technique for the deposition of Eu2O3 on synthesized or commercial graphene films. The SEM obtained images, show differences in morphology when commercial and synthesized graphene films are compared. Our results indicate that the type of surface is the main factor that accounts for the europium oxide spatial distribution that ultimately leads to luminescence enhancing. The x-ray photoelectron spectroscopy (XPS) analyses, showed the trivalent oxidation state of europium and the atomic content of Europium for both; the commercial graphene film and synthesized one, where the first one presented the higher europium concentration. Analysis by Raman spectroscopy reveals that graphene films become disordered after the decoration is achieved. The main Raman bands of the commercial graphene films undergo a remarkable red shift, as a consequence of the presence of europium oxide It was observed that the interaction of Eu2O3 with the sp2 levels of graphene, improves the red photoluminescence of the samples grown on both, commercial and prepared graphene films.

Soil samples were obtained from three different locations; Ijapo, Ibule and FUTA North Gate in Akure, Ondo State, Nigeria. The materials were dried, crushed and calcined by heating the samples in a muffle furnace to 850 °C, holding for three hours and and then brought out of the furnace to cool in the laboratory so that the organic and volatile matter escaped, and the oxide content increased. The calcined materials were milled with a ball mill and then sieved with 75 µm mesh size British standard sieves. The samples that passed through the sieves were collected for analysis to determine their extender characteristics through x-ray flouresence (XRF) spectroscopy, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), specific gravity, oil absorption, pH and refractive index measurements as well as the determination of their resistance to chemicals. XRF results showed that materials are kaolinite in nature. XRD results showed the phase compositions of each sample as materials suitable for applications as extenders in the paints industry. SEM micrographs showed the homogeneity of the samples from Ijapo and FUTA North Gate while the sample from Ibule showed segregation of the phase compositions. The specific gravity, pH, oil absorption and refractive index of each material were within the range of those of commercial extenders used in the paints industry. The calcined materials were found to be resistant to various chemical media. The characterized materials will be suitable as extenders and pigments in the paints industry.

Sulfur loss from the surface of MoS2(0001) is observed following the adsorption of methanol on MoS2 at 86 K and subsequent annealing of MoS2 near 300 K. This sulfur loss, at the MoS2 surface, leads to suppression of inverse photoemission features characteristic of the unoccupied states associated with MoS2. This sulfur loss is counteracted by further annealing to 350 K, as is evident in the temperature dependent sulfur to molybdenum integrated X-ray photoemission intensity ratios near 300 to 350 K. Upon further annealing to 350 K, inverse photoemission additionally indicates a reestablishment of characteristic features associated with the unoccupied states of MoS2. These results are indicative of sulfur segregation to the surface and compensation of surface vacancy sites.

We have investigated the chemical and electrical properties of a thin SiO2/TiO2 stacking layer deposited on n-Si and heavily phosphorus-doped n++ Si substrates to elucidate effects of phosphorus doping of Si absorbers on the band alignment and electrical performance of a SiO2/TiO2 stack-based electron-selective contact deposited on the differently doped Si substrates. From our XPS study, we show a shift of the TiO2 energy levels up to ∼0.13 eV with respect to those of Si as the doping level of Si substrates changes. We also show that the conduction band offset of the SiO2/TiO2 stacking layer at the interface with the n++ Si substrate seems to smaller than that of the SiO2/TiO2 stacking layer at the interface with n-Si substrate. Finally, from our electrical transport measurements, we could conclude that the thinner tunneling barrier, the increased electron density in front of the SiO2 layer in the n++ Si surface, and/or the reduced barrier height by heavy doping, seem to enhance the majority electron transport property of the SiO2/TiO2/n++ Si samples compared to that of the SiO2/TiO2/n-Si samples.

Rigorous coupled wave analysis (RCWA) simulation was used to model the absorption in periodic arrays of GaAs0.73P0.27 nanowires (NWs) on Si substrates dependent upon the diameter (D), length (L), and spacing (center-to-center distance, or pitch, P) of the NWs. Based on this study, two resonant arrangements for a top NW array sub-cell having the highest limiting short-circuit current densities (Jsc) were found to be close to D = 150 nm, P = 250 nm and D = 300 nm, P = 500 nm, both featuring the same packing density of 0.28. Even though a configuration with thinner NWs exhibited the highest Jsc = 19.46 mA/cm2, the array with D = 350 nm and P = 500 nm provided current matching with the underlying Si sub-cell with Jsc = 18.59 mA/cm2. Addition of a rear-side In0.81Ga0.19As nanowire array with D = 800 nm and P = 1000 nm was found to be suitable for current matching with the front NW sub-cell and middle Si. However, with thinner and sparser In0.81Ga0.19As NWs with D = 700 nm and P = 1000 nm, the Jsc of the bottom sub-cell was increased from 17.35 mA/cm2 to 18.76 mA/cm2 using a planar metallic back surface reflector, thus achieving a current matching with the top and middle cells.

In this paper, the effect of TiN metal gate deposition conditions on the crystal orientation and size of TiN grains has been investigated. We have focused on process conditions that reduce the grain size or provide a unique orientation, which might impact CMOS threshold voltage variability. We have shown that the grain size can be significantly modulated by the RF power and pressure, with grain size as low as 5.2 nm. Further it has been shown that for a few optimized conditions, a unique grain orientation can be obtained. Then, the impact of these process conditions on TiN gate mechanical stress and electrical properties has been investigated. Mechanical stress and sheet resistance are modulated by pressure and RF power and have been correlated to the deposition rate and TiN grain size respectively. The effect of TiN process conditions on MOS capacitor effective workfunction (WFeff) has been investigated, and the trend is opposite to the expected modulation of the intrinsic TiN metal gate workfunction with grain orientation. On the contrary, WFeff variation is well correlated to the Ti/N ratio, suggesting an effect related to dipole at the SiO2/high-k interface.