Multiscale dislocation dynamics plasticity (MDDP) model is used to investigate the evolution of dislocation microstructure in copper single crystals subjected to low cycle fatigue loading. Half cycle total plastic strain simulations are carried out at strain amplitudes ranging from 1×10-3 to 8×10-3. The initial hardening is investigated and the micro-structural cause behind it is presented. In addition, the loading history is presented and the effect of the initial micro-structure and dislocation distribution on the hardening behavior is studied. In addition, the evolution of the microstructures is examined. In depth analyses of the dislocation microstructures show that: 1) dislocation planes that are parallel and very close to each other are formed, 2) these walls contain dipoles that keep on zipping and unzipping during the first few cycles until they reach some stable zipping configuration. We can see that the hardening rate decreases with the increase of the number of cycles where we have large hardening rate in the first cycles then we reach to somehow constant stress. Our results are qualitatively in good agreement with recent experimental results of low cycle fatigue deformation.

Single crystals of E21 (L12) Ni3AlC1-x were prepared by the unidirectional solidification using the optical floating zone melting method to determine their mechanical properties. Particularly the effects of interstitial carbon atoms on mechanical properties were evaluated by compression tests at room temperature. Operative slip system of E21 Ni3AlC is {111}<011> type which is the same as that of L12 Ni3Al. Strength of Ni3AlC single crystals increases with carbon concentration due to the solid solution effect, though the stress relief of yielding behavior is enhanced at the intermediate carbon content at around 3at%. A large gap appears in the carbon concentration dependence of critical resolved shear stress (as well as yield stress) at almost the same carbon content. This discontinuity in strengthening is attributed to the interaction between multiple solute carbon atoms and mobile dislocations.

We fabricated Cu2ZnSn(SxSe1-x)4 (CZTSSe) solar cells by a printing and high-pressure sintering (PHS) process. First, the CZTSSe solid solution powders were synthesized by heating the elemental mixtures at 550oC for 5 h in an N2 gas atmosphere. We fabricated CZTSSe films by a printing and high-pressure sintering (PHS) process. The obtained dense CZTSSe film was post-annealed at 550oC for 10 min under an N2 +5% H2S gas atmosphere. We fabricated CZTSSe solar cells with the device structure of Ag/ITO/i-ZnO/CdS/CZTSSe/Mo/soda-lime glass. The CZTSSe solar cell showed an efficiency of 2.1%, with V oc of 272 mV, J sc of 18.0 mA/cm2 and FF of 0.44.

Making field effect transistors (FETs) on thin flake of single crystal isolated from layered materials was pioneered by the success of graphene. To overcome the difficulties of the zero band gap in graphene electronics, we report the fabrication of an electric double layer (EDL) transistor, a variant of FET, based on another layered material, MoS2. Using strong carrier tunability found in EDL coupled by ion movement, MoS2 transistor displayed an unambiguously ambipolar operation in addition to its commonly observed n-type transport. A high on/off ratio >104, large “ON” state conductivity of ∼mS, and a high reachable n 2D ∼ 1×1014 cm-2 confirmed the high performance transistor operation being important for application. The high-density carriers of both holes and electrons can drive the MoS2 channel to metallic states indicating that new electronic phases could be accessed using the protocol established in making EDL gated transistors on layered materials.

Titanium (IV) oxide, TiO2, has been the object of intense scrutiny for energy applications. TiO2 is inexpensive, non-toxic, and has excellent corrosion resistance when exposed to electrolytes. A major drawback preventing the widespread use TiO2 for photolysis is its relatively large band gap of ∼3eV. Only light with wavelengths shorter than 400 nm, which is in the ultraviolet portion of the spectrum, has sufficient energy to be absorbed. Less than 14 percent of the solar irradiation reaching the earth’s surface has energy exceeding this band gap. Adding dopants such as transition metals has long been used to reduce the gap and increase photocatalytic activity by accessing the visible part of the solar spectrum. The degree to which the band gap is reduced using transition metals depends in part on the overlap of the d-orbitals of the transition metals with the oxygen p-orbitals. Therefore, doping with anions such as nitrogen to modify the cation-anion orbital overlap is another approach to reduce the gap. Recent studies suggest that using a combination of transition metals and nitrogen as dopants is more effective at introducing intermediate states within the band gap, effectively narrowing it. Here we report the synthesis of mesoporous TiO2 spheres, co-doped with transition metals and nitrogen that exhibit a nearly flat absorbance response across the visible spectrum extending into the near infrared.

Forming voltage (V Form) and initial resistance of NiO-based resistive switching (RS) cells with various NiO films were investigated. Deposited NiO films were 〈111〉-oriented and the lattice constant was larger than that of bulk. It was revealed from XRD analyses that there were residual compressive stresses in NiO films. The magnitude of the residual stress was different among NiO films depending on their deposition conditions, and V Form monotonically increases with the increase in the magnitude of the residual stress. The relationship between V Form and the residual stress may be ascribed to the changes in the density of oxygen vacancies in NiO films. NiO films were also post annealed in Ar at 450°C. RS cells with annealed NiO films having small oxygen composition exhibited forming-free behavior, indicating the generation of conductive filaments by the annealing. The region whose lattice constant is smaller than that of bulk appeared after annealing only in such NiO films, suggesting that the small lattice-constant region may be linked to the generation of the filaments.

The work takes advantage of a newly developed measurement system which enables to investigate the thermodynamic properties of thin films including battery layer sequences. This technique, Thin-Film Calorimetry (TFC), is based on the detection of resonance frequency shifts of bulk acoustic wave resonators. Thin films with a thickness of several micrometers of the material of interest are deposited on the resonators. By measuring the temperature dependent shift of the resonance frequency, the device is working as a precise temperature sensor. The production or consumption of latent heat by the active layer(s) results in temperature fluctuations with respect to the furnace where the sensor is placed. Those information enable to extract the temperature and time dependence of phase transformations as well as the associated enthalpies. To cover a temperature range from -20 to 900 °C high-temperature stable piezoelectric resonators made of langasite crystals (La3Ga5SiO14) are applied.

Initially, metallic layers of tin and aluminum are used to test and verify this approach. The temperatures and enthalpies of solid-liquid as well as of solid-solid phase transformation are observed in the correct manner. Further, the thermodynamic data of the battery materials Li(Ni0.8Co0.15Al0.05)O2-δ (NCA) and LiMn2O4-δ (LMO) obtained by TFC are determined and discussed. Both cathode materials are amorphous after deposition and show crystallization during heating at 460 °C (NCA) and 600 °C (LMO). The associated enthalpies are 5.3 kJ/mol (55 J/g) and 17.3 kJ/mol (96 J/g), respectively.

A large area nanogap electrode fabrication method combinig conventional lithography patterning with the of focused ion beam (FIB) is presented. Lithography and a lift-off process were used to pattern 50 nm thick platinum pads having an area of 300 μm × 300 μm. A range of 30-300 nm wide nanogaps (length from 300 μm to 10 mm ) were then etched using an FIB of Ga+ at an acceleration voltage of 30 kV at various beam currents. An investigation of Ga+ beam current ranging between 1-50 pA was undertaken to optimise the process for the current fabrication method. In this study, we used Monte Carlo simulation to calculate the damage depth in various materials by the Ga+. Calculation of the recoil cascades of the substrate atoms are also presented. The nanogap electrodes fabricated in this study were found to have empty gap resistances exceeding several hundred MΩ. A comparison of the gap length versus electrical resistance on glass substrates is presented. The results thus outline some important issues in low-conductance measurements. The proposed nanogap fabrication method can be extended to various sensor applications, such as chemical sensing, that employ the nanogap platform. This method may be used as a prototype technique for large-scale fabrication due to its simple, fast and reliable features.

We have fabricated novel shellac-cells composite microcapsules capable of pH-stimulus induced release of cells in a narrow pH range. The microcapsules were produced with yeast cells as a model for probiotics which were co-precipitated from an aqueous solution of ammonium shellac doped with pH-sensitive polyelectrolytes. The yeast cells in the composite shellac-cell microcapsules retained their viability even when treated with aqueous solutions of very low pH and subjected to shear stress. We studied the pH triggered release of cells from these microcapsules and measured their disintegration times. These microcapsules showed versatile responses ranging from slow release to explosive swelling at higher pH depending on the type and concentration of the polyelectrolyte integrated in the shellac microcapsules. We also observed growth-triggered release of cells from these microcapsules upon exposure to culture media. In both cases the cells retained their viability following their release from the microcapsules into the aqueous solution.

A new multiphysics, multiscale framework is presented which is capable of capturing and predicting both wafer-scale and feature-scale defects. Through physics-based modeling, the empirical wear/Preston coefficient often found in popular feature scale models has been eliminated. Simulation results show the topography evolution of an actual metal 1 layout between two dies located in different positions on a wafer during the CMP process.

Vanadium dioxide (VO2) is a promising material for an optical switch due to the ultrafast and reversible transition between its two phases with contrasting optical, as well as electronic, properties. Meanwhile, erbium (Er3+) has been a standard optical amplifier for the current fiber-optic communication system. Hence, a combination of the two could be expected to make an optical switch capable of simultaneous optical amplification. In the present work, the optical switching and photoluminescence of Er-implanted VO2 were successfully demonstrated. Post-implantation annealing at 800°C or above was seen crucial for the activation of the Er centers in the VO2 crystals.

We have investigated the migration energy of Cd atom in CuInSe2 (CIS) with a Cu vacancy by first-principles calculations. The activation energy of Cd migration in CIS and migration pathways are obtained by means of the combination of linear and quadratic synchronous transit (LST/QST) methods and nudged elastic band (NEB) method. The theoretical migration energy of Cd atom in CIS is 0.99 eV. The migration energy of Cd atom (Cd→VCu) in CIS is comparable to that of Cu migration (Cu→VCu) in CIS (1.06 eV). This result indicates that Cd diffusion in CIS easily occurs like Cu diffusion.

Uric acid biosensor has been developed using tin oxide (SnO2) thin film. The electrochemistry of the developed thin film based electrode is investigated by using cyclic voltammetry. The obtained results demonstrate that the semiconducting SnO2 matrix offers a striking electrocatalytic activity to the immobilized uricase towards the oxidation of uric acid and promotes the transfer of electrons from the active sites of enzyme onto the electrode. SnO2 thin film matrix gives a high sensitivity of 0.2 mA/mM and a shelf life of 20 weeks. Moreover, SnO2 electrode exhibits excellent selectivity and outstanding analytical stability and reproducibility, which enables a reliable and selective determination of uric acid. The SnO2 based uric acid biosensor shows a linear variation in a wide range from 0 to 1.0 mM of uric acid concentration and the Michaelis Menten Constant (Km) is estimated to be 0.28 mM which indicated the high affinity of uricase towards its analyte (uric acid). The results indicate that the SnO2 thin film matrix offers a new and promising platform for the development of novel biosensors.

Dye-sensitized solar cells (DSSCs) are attractive alternatives to conventional solid-state photovoltaic devices because of performance, stability, environmental compatibility and cost. In contrast to the conventional systems where the semiconductor assumes both the task of light absorption and charge carrier transport, these two functions are separate in DSSC and, therefore, efficiency is very sensitive to the cell structure/composition. High-efficiency DSCs based on mesoporous nanocrystalline titanium dioxide (TiO2) electrodes have received considerable research attention in the past decade. Grain size and thickness of the mesoporous TiO2 film have shown a dominant effect on the efficiency of the photovoltaic devices.

We have investigated screen printed TiO2 films deposited on a textured fluorinated SnO2 (FTO) glass substrate, using Raman spectroscopy and spectroscopic ellipsometry. Materials were prepared by repeating a same screen-printing procedure once, twice and three times, using TiO2 paste with 10nm, 20 nm and 200nm particles sequentially. Raman spectra of PV devices cells taken at different excitation (266 nm, 325 nm, 364 nm, 532 nm, 633 nm, and 1064 nm) as well as pure TiO2 oxides are presented. Different excitation wavelengths allow to probe different depth of the sample. It was found that there is strong correlation of the position and the width of E2g mode of anatase at 144 cm-1 and size of TiO2 particles. The samples show that this peak shifts to the high frequency region and becomes broader for small size particles. The position and broadening of the peak can be described by optical confinement model that depends on the size of nano-crystals. Results showed varying grain sizes as correlated with different TiO2 paste applied. Thickness, optical constants and porosity of TiO2 films were determined by spectroscopic ellipsometry. In this work, we have demonstrated the use of Raman Spectroscopy and Spectroscopic Ellipsometry for non-destructive characterization of nanocrystalline TiO2 films for dye-sensitized solar cells.

We conducted phase-field simulations of microstructural evolution in C11b-MoSi2 / C40-NbSi2 dual phase alloy with and without Cr-addition to examine the factors responsible for the formation and stability of the lamellar structure on the basis of thermodynamics, micromechanics and first-principles calculations. The first principles calculation was used for evaluating the interfacial energy, segregation energy of solute Cr-atoms and lattice parameters of imaginary disilicides for estimating the effects of solute distribution on the lattice misfit. When both of lattice misfit and the anisotropy of interfacial energy is taken into account, a lamellar structure similar to that observed experimentally is formed. In the absence of Cr-addition, the straightness of lamellar structure decreased slightly. When an isotropic interfacial energy is assumed, lamellar structure is not formed. Instead, a microstructure with habit planes parallel to {1 0 $\bar 1$ 1} plane of C40-phase is formed. Thus, the anisotropy of interfacial energy is crucial for the lamellar structure formation rather than the elastic energy due to lattice misfit.

In this paper, we focused on sintering of inkjet-printed copper nanoparticle ink structures using a continuous wave 808nm diode laser. Laser sintering in printed electronics is a rapid sintering method which enables localized sintering. Sintering of Cu inks is usually done in nitrogen atmosphere but the novelty of this study is that successful sintering of Cu ink was done under ambient conditions. The used ink consists of copper nanoparticles covered with a dispersion agent. Photonic sintering is needed to speed up the sintering process to prevent oxidation during sintering. Electrical and mechanical performance of the printed structures was analyzed. Resistivity of 10-12 μΩcm with good repeatability as well as excellent adhesion, were achieved.

The addition of high refractive index (RI) inorganic nanoparticles (NPs) to LED encapsulation materials can lead to higher light extraction efficiency. In addition, the NPs can be carriers for additional functionality such as color conversion. Using a simple “grafting-to” approach, bimodal polydimethylsiloxane (PDMS) brushes were grafted onto high-RI ZrO2 NPs. Subsequently, an organic phosphor, 6-[fluorescein-5(6)-carboxamido]hexanoic acid (FCHA), was attached onto the PDMS-grafted ZrO2 NPs via a facile ligand exchange process. The bimodal polymer brush design enables homogenous dispersion of the surface functionalized NPs within the silicone matrix. The functionalized NPs with ∼53 wt% ZrO2 core have a ∼0.08 higher RI than neat silicone, and the NP-filled silicone nanocomposites exhibit a transparency of ∼ 90% in the 550-800 nm wavelength range. In addition, the nanocomposites could be excited at a wavelength around 455 nm by a blue LED and undergo secondary yellow emission at around 571 nm. It is expected that the prepared nanocomposites can be used as high-efficiency, non-scattering, color-tuned materials for advanced LED encapsulation.

Pt catalysts are the leading catalysts for use in ORR. However, Pt is an expensive catalyst and with limited supply can not be considered a sustainable material for feasible application that is scalable in the economy. This calls for new solutions for catalyst materials that either mitigate the amount of Pt used in catalysts by developing hybrid catalysts, or to replace Pt altogether with a material with similar or better catalytic activity. Perovskite LSCF and Fluorite GDC materials with proven catalytic activity in solid oxide fuel cells are herein explored for their catalytic reduction of oxygen for use at low temperatures. Since the materials lack electronic conductivity at low temperatures, we have improved their conductivity with graphene. The resulting materials are compared to Pt in their ORR catalytic capabilities and electronic conductivity.