Boron doped nanocrystalline diamond films (BDND) were grown on reticulated vitreous carbon (RVC) heat treated at 1000 and 1700 °C. Silver (Ag) nanoparticles were electrodeposited on RVC and RVC/BDND composites by potentiostatic reduction of AgNO3 solution. The samples were characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and cyclic voltammetry. The samples conductivities influenced the Ag deposition amount as well as the Ag particle sizes where the smaller Ag particles were observed for RVC/BDND composites. The stability of Ag nanoparticles was also confirmed by cyclic voltammetry.

We have studied the diffusion mechanism of lithium ions in glassy oxide-based solid state electrolytes using elastic and quasielastic neutron scattering. Samples of xLi2SO4-(1-x)(Li2O-P2O5) were prepared using conventional melt techniques. Elastic and inelastic scattering measurements were performed using the triple-axis spectrometer (TRIAX) at Missouri University Research Reactor at University of Missouri and High Flux Backscattering Spectrometer (HFBS) at NIST Center for Neutron Research, respectively. These compounds have a base glass compound of P2O5 which is modified with Li2O. Addition of Li2SO4 leads to the modification of the structure and to an increase lithium ion (Li+) conduction. We find that an increase of Li2SO4 in the compounds leads to an increase in the Lorentzian width of the fit for the quasielastic data, which corresponds to an increase in Li+ diffusion until an over-saturation point is reached (< 60% Li2SO4). We find that the hopping mechanism is best described by the vacancy mediated Chudley-Elliot model. A fundamental understanding of the diffusion process for these glassy compounds can help lead to the development of a highly efficient solid electrolyte and improve the viability of clean energy technologies.

To reduce the amount of chalcogen needed in the post-annealing process, we demonstrate significantly increased sulfur incorporation into pure sulfide CZTS films achieved by increasing the thiourea content of DMSO-based precursor solution. The increase of sulfur content was confirmed by thermogravimetric analyses (TGA). To understand how the elemental distribution across the CZTS layer is affected by extra thiourea, a systematic compositional study was carried out using X-ray photoelectron spectroscopy (XPS). XPS depth profiling reveals increased sulfur incorporation in the final CZTS films when more thiourea is added to the solution. The grain size was reduced slightly with increased sulfur content and the surface morphology was changed significantly. The effect on the surface of the CZTS film has been investigated using scanning electron microscopy (SEM), Raman spectroscopy, and XPS. External-quantum-efficiency (EQE) measurements with an electrolyte contact were used to investigate the optoelectronic properties of the deposited CZTS films.

Nanostructures offer the opportunity to control the vibrational properties of via the scattering of phonons due to boundaries and mass disorder as well as through changes in the phonon dispersion due to spatial confinement. Advances in understanding these effects have the potential to lead to thermoelectrics with an improved figure of merit by lowering the thermal conductivity and to provide insight into electron-phonon scattering rates in nanoelectronics. Characterizing the phonon population in nanomaterials has been challenging because of their small volume and because optical techniques probe only a small fraction of reciprocal space. Recent developments in x-ray scattering now allow the phonon population to be evaluated across all of reciprocal space in samples with volumes as small as several cubic micrometers. We apply this approach, synchrotron x-ray thermal diffuse scattering (TDS), to probe the population of phonons within a Si/SiGe/Si trilayer nanomembrane. The distributions of scattered intensity from Si/SiGe/Si trilayer nanomembranes and Si nanomembranes with uniform composition are qualitatively similar, with features arising from the elastic anisotropy of the diamond structure. The TDS signal for the Si/SiGe/Si nanomembrane, however, has higher intensity than the Si membrane of the same total thickness by approximately 3.75%. Possible origins of the enhancement in scattering from SiGe in comparison with Si include the larger atomic scattering factor of Ge atoms within the SiGe layer or reduced phonon frequencies due to alloying.

Large scale molecular dynamics (MD) simulations are carried out to investigate the failure response of nanocrystalline Mg using the EAM potential under conditions of uniaxial tensile stress and uniaxial tensile strain loading. The MD simulations are carried out at a strain rate of 109s-1 for grain sizes in the range of 10 nm to 30 nm. The effect of grain size on the strength of the metal is investigated and the critical grain size for transition to inverse Hall-Petch regime is identified.

Two-Dimensional materials open up great prospects in photodetector applications owing to their sharp optical properties and the ability to combine them in layered heterostructures. Among this new class of materials, colloidal nanoplatelets (NPL) made of cadmium chalcogenides readily combine the thickness control at the atomic level together with the large scale production and ease of processing of colloidal materials. As a strategy to overcome the limited mobility inherent to nanocrystal based devices, the photocarrier lifetime is increased by building an electrolyte-gated phototransistor to passivate the electron traps. NPL can also be coupled with a graphene transport layer collecting the photogenerated charges, thus bypassing the transport bottleneck. We show that the charge transfer is driven by the large exciton binding energy of the NPL, which can be engineered by heterostructured NPL. This allows us to control the magnitude and the direction of the charge transfer to graphene. Eventually, we use nanotrench electrodes to decrease the transit time of the carriers, suppress the influence of film defects and provide an electric field large enough to overcome the large exciton binding energy of NPL.

Thorium has long been considered a possible source of fuel for use in power generating nuclear reactors. While much attention and interest have focused on thorium oxide, metallic thorium alloys were investigated in the past as fuel candidates for fast and thermal breeder reactors. In this work, thorium’s two solid allotropes (face centered cubic α and body centered cubic β) are modelled using Density Functional Theory (DFT). The Vienna Ab Initio Simulation Package (VASP) is used to determine structural and elastic properties, as well as the density of states. The Voigt-Reuss-Hill approximations are used to predict the phases’ bulk moduli, shear moduli, Young’s moduli, and Poisson’s ratios. Four exchange-correlation potentials are used and compared. These are the LDA, the PBE-GGA, the RPBE, and the PBEsol. All potentials showed relatively good accuracy when predicting the lattice constant. The RPBE was the most accurate, slightly over predicting by < 0.2%. The RPBE and the PBE-GGA were the most accurate in predicting elastic properties, performing almost equally, while slightly over predicting most values.

Novel 2D materials with interesting properties have been synthetized and characterized recently. In particular, unlike graphene, silicene or germanene, phosphorene has attracted a lot of attention because of its intrinsic band gap. This property allows for a wide range of applications where semiconductor thin films are traditionally used (e.g. electronics, optoelectronics, thermoelectrics). For each application, the device efficiency depends on how well an electrical current is extracted from the active materials, and depends on a variety of electron scattering processes. Some of these scattering processes can considerably improve or degrade device efficiencies. In this contribution we focus on non-radiative electron-hole pair generation and recombination processes, i.e. impact ionization (charge carrier multiplication) and Auger processes (charge carrier recombination). The rate of these processes is calculated from first principles and their effects on device operation are estimated.

The intracortical neural interface (INI) is a key component of brain machine interfaces (BMI) which offer the possibility to restore functions lost by patients due to severe trauma to the central or peripheral nervous system. Unfortunately today’s neural electrodes suffer from a variety of design flaws, mainly the use of non-biocompatible materials based on Si or W with polymer coatings to mask the underlying material. Silicon carbide (SiC) is a semiconductor that has been proven to be highly biocompatible, and this chemically inert, physically robust material system may provide the longevity and reliability needed for the INI community. The design, fabrication, and preliminary testing of a prototype all-SiC planar microelectrode array based on 4H-SiC with an amorphous silicon carbide (a-SiC) insulator is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary data is presented which shows a proof of concept for an all-SiC microelectrode device.

Phase pure Pb[(Fe0.5-xScx)Nb0.5]O3 [x= 0 to 0.5] multiferroic relaxors have been synthesized to study theeffect of Sc on dielectric phase tansition. Rietveld refinement of x-raydiffraction patterns confirm that the structure transforms from monoclinic (Cm)to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectricresponse in compositions with low Sc content attributed to interfacialpolarizabilty arising due to differences in conductivities of grain and grainboundary. Moreover, value of diffusivity parameter (γ) of high of Sccontent compositions is near to 2, confirms relaxor charactertistic of thesecompositions. However, an essential feature of relaxors i.e., frequencydependent dielectric permittivity as a function of temperature is observed onlyin x = 0.5 composition[Pb(Sc0.5Nb0.5)O3 (PSN)]. In addition,ferroelectric phase transition temperature (Tmax) increases initiallyat lower Sc content (upto x ≤ 0.25), and further drops beyond x≥ 0.3. Such behavior of Tmax in these compositions is due to theonset of B'-B" local cation ordering at x = 0.3. Hightemperature Raman spectra of Pb(Sc0.5Nb0.5)O3(x = 0.5) confirm the stability of cation ordering in compositions withhigh Sc content well above the phase transition temperature.

Working gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.7x10-2 mbar (high pressure sputtering, HIPS) and 7.3x10-3 mbar (low pressure sputtering, LPS). The morphological characterization was carried out by means of SEM. The photocurrent measurement was conducted under 1.5 AM Sun under no bias. Nanostructured photodetectors of HIPS-CIS/GLAD-In2S3 (i.e. HIPS-GLAD) were shown to demonstrate enhanced photoresponse with a photocurrent value of 98 μA, which is about ∼230% higher than that of LPS-GLAD devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices incorporating an In2S3 film coated either with HIPS or LPS CIS layer. Nanorod devices with high and low pressure CIS films showed photocurrent values ∼20 times and ∼ 19 times higher compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photo-generated carriers. Therefore, the results of this work can pave way to the development of high photoresponse core-shell semiconductor devices fabricated by physical vapor deposition techniques.

This work studied the effect of plasma treatment on the wettability of composite materials constituted of polyethylene glycol (PEG) and polyhydroxybutyrate (PHB) processed through the spin-coating and electrospinning techniques. For this purpose different polymeric solutions of PEG:PHB with proportions of 100:0, 80:20, 50:50, 20:80, and 0:100 were prepared. It found that the hydrophobicity of the as-prepared composite films processed by electrospinning was higher than those processed by spin-coating, using the same proportions of PEG:PHB. The electrospun samples with higher content of PHB (20:80 and 0:100) showed a surface morphology constituted by fibers of 1.7-1.9 μm in size. On the other hand, the electrospun samples processed with a lower content of PHB (100:0, 80:20, 50:50) did not form fibers and exhibited a rough surface. The subsequent plasma treatment with argon plasma of the electrospun samples produced a decrease in the contact angle, even in the samples with surface roughness. These contact angle values were similar to those obtained by spin-coating, or even lower, as in the case of the sample with PEG:PHB content of 20:80 in which the dip-coated film, the as-prepared membrane, and the plasma-treated membrane showed contact angles of 49°, 77.4°, and 0° (superhydrophilic) respectively.

Dislocations are line like crystal defects mediating plasticity in single crystals. In the current contribution we review classical continuum concepts of dislocation theory from a topological view point. Subsequently, we introduce a new measure for the density of jogs mutually impaired on each other by dislocations on different slip systems. This jog density is closely related to a topological measure of the interlinkage of the dislocations on the involved slip systems, known as relative helicity in other branches of physics.

This paper introduces the theoretical and experimental investigation of flexoelectric behavior in a graphene composite structure consisting of multilayer CVD-graphene deposited on an ALD-platinum catalyst layer deposited on top of n-silicon substrate. The polarization induced by varying the radius of curvature from 200–1500 mm by applying bending stresses was investigated experimentally. Meanwhile, due to the cluster-growth nature of the ALD-platinum catalyst layer, a strong correlation was observed between the resulting number of graphene layers and the Pt catalyst layer thickness, which subsequently had a strong impact on the induced polarization. A polarization current of up to 7.4 mA was detected when the composite structure was bent through a 600-mm radius of curvature. Residual stresses at the interface of the different layers were estimated experimentally in the order of 85–217 MPa. The effect of thermally-induced stresses, residual stresses at the interface layers, thickness of graphene layers, and radius of curvature were investigated theoretically using the finite element method (FEM) and first-principle analyses. Theoretically, it was confirmed that non-uniform strain results in an appreciable non-uniform graphene band gap opening, in addition to non-uniform change of the band structure across the surface and thickness which results in increasing the potential energy difference between the graphene layers. FEM confirmed that thermally induced strains could further enhance the power output of the device by inducing a flexoelectric current combined with the thermionic response. This is verified by estimating a lattice displacement up to 0.31 Å in response to 2-mW heat flux, which corresponds to an appreciable graphene band opening and a potential energy difference across the graphene layers in the order of 1.23 eV, as estimated by the tight binding model.

Ferroelectric materials such as BaTiO3 have been studied for emergingnon-volatile memory applications. However, most of the previous work has beenfocused on this material when it was deposited on insulting oxide substratessuch as SrTiO3. Unfortunately, this substrate is not suitable forCMOS-based microelectronics applications. This motivated us to carry out thepresent work. We have studied the resistive switching behavior inBaTiO3/La0.7Sr0.3MnO3 (BTO/LSMO)heterostructures integrated with semiconducting substrates Si (100) usingMgO/TiN buffer layers by pulsed laser deposition. Current-Voltage (I-V)measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K. We haveobserved a broad hysteresis in forward and reverse voltage sweeps which is animportant property for memory applications. Secondly, theRON/ROFF ratio is estimated at ∼ 150,consistent with the reported numbers (30-100) in the literature. Thirdly, thedevice is stable at least up to 50 cycles. However, we found that hystereticbehavior was suppressed upon oxygen annealing of the device at 1 atmosphericpressure, 200° C for 1hr, inferring the important role ofoxygen vacancies in the resistive switching behavior of BTO/LSMO device. Futurework will focus on investigating the correlation between ferroelectricity andresistive switching in these devices using local probe technique piezo forcemicroscopy (PFM) technique.

The boron-content dependence of magnetic domain structures and magnetic properties of nanocrystalline Zr16Co82.5−x Mo1.5Bx (x = 0, 1, 2, 3, 4) melt-spun ribbons have been investigated. Compared to x = 0, the smaller average domain size with a relatively short magnetic correlation length of 120 nm and largest root-mean-square phase shift value of 0.94° are observed for x = 1. The best magnetic properties of coercivity H c = 5.4 kOe, maximum energy product (BH) max = 4.1 MGOe, and saturation polarization J s = 7.8 kG, were obtained for the ribbon with x = 1. The optimal B addition enhances the content of hard magnetic phase, promotes magnetic domain structure refinement, and increases the surface roughness, results in the enhancement of magnetic anisotropy, and thus leads to a significant increase in coercivity and energy product in this sample.

Three different methods are evaluated for the introduction of graphene nanoplatelets (GNP) in hierarchical carbon- or glass fiber reinforced plastics. They involve; (1) direct infusion of GNP filled epoxy resin, (2) spray coating of GNP on fiber preforms and (3) the use of dissolvable thermoplastic interleaf carrier films. Direct infusion of GNP filled resin is the easiest method to deliver GNP into composite laminates but may lead to viscosity and filtration issues. Automated spray coating was set up to manufacture GNP modified carbon- or glass fiber fabrics, while graphene filled phenoxy interleaf films were manufactured by bar coating, both followed by resin infusion using neat epoxy resin to produce GNP modified epoxy laminates, without the disadvantages of GNP filled resins. No substantial difference in interlaminar shear strength (ILSS) for composites manufactured using the different delivery methods is found. However, the electrical conductivity of the GNP modified glass-fiber composites manufactured by spray coating of glass fabrics is two orders of magnitude higher than for laminates made by direct infusion of GNP modified resin.

Two approaches have been employed in the preparation of hierarchical composite laminates with a carbon nanotube (CNT) phase. Glass fibers were coated with CNTs using electrophoretic deposition (EPD) prior to infusion with epoxy resin. The CNTs were functionalized using an ultrasonicated-ozone process followed by reaction with polyethyleneimine (PEI) to enhance CNT to fiber and matrix adhesion. Chemical vapor deposition (CVD) was also used to grow CNTs onto quartz fibers, prior to infusion with an epoxy resin modified with a thermoplastic nanophase. The mechanical performance of the two CNT laminates types were similar, however, the fracture surfaces indicated distinct differences. The EPD laminates showed fracture in the CNT-rich interphase region, whereas, the CVD laminates showed that strength was limited by adhesion failure at the CNT-fiber interface. The electrical conductivity of CVD laminates was 100 times higher than EPD laminates. For the EPD laminates the PEI functionalization increases the CNT-CNT distance resulting in reduced conductivity, while the high CNT packing density and residual iron catalyst on the fiber surface in the CVD laminates creates conducting pathways resulting in higher conductivities.

Design and fabrication of hollow silicate micro-/ nanoparticles (HSMNP) with varied sizes and morphologies are of great interest especially in developing new generation of thermal insulation materials for building applications. Efficient energy use, simply called energy-saving, involves efforts to reduce the amount of energy required and recover wasted energy. This is important since building constitutes a substantial part in the total global energy consumption. Therefore, the current study is aimed at developing new HSMNP for thermal insulation application.

Carbon monofluoride (CFx) has been extensively used as a reliablecathode material in lithium primary batteries because of its high energy densityand long shelf life. However, the implementation of Li/ CFx batteriesin high-power applications is limited by the low power capability resulting fromthe insulative nature of CFx material. In this work, we incorporatedmulti-walled carbon nanotubes into CFx electrodes and studied theimpact on the electrochemical performances when CNTs were used as a conductiveadditive material and current collector substrate. Our work demonstrated thepromising utilization of CNTs in CFx electrodes in improving thepractical capacity and power capability of Li/ CFx batteries.