Pillared-graphene is one of nanocarbon hybrids. It consists of graphene sheets and carbon nanotubes (CNTs); the latter are bonded vertically to the former. In order to investigate the hardness of pillared-graphene, indentation simulations are performed using a molecular dynamics method. It is revealed that the hardness of pillared-graphene increases with increasing the diameter of the CNTs, whereas it decreases with increasing the distance between CNTs or temperature. Such tendencies can be understood by considering the deformations of graphene and CNTs individually.

SnO2 doped with Sb and Nb has been investigated for its use as catalyst support materials replacing carbon to enhance PEM fuel cells stability. Nanostructured powders of various doping levels were prepared by flame spray pyrolysis (FSP). The specific requirements of surface area >50 m2g-1 and electronic conductivity >0.01 Scm-1 were obtained, and pore sizes ranging mainly from 10 to 100 nm. Pt particles (9-20 wt.% in loading targeted) of ∼1 nm well dispersed in Sb-doped SnO2 was prepared by a one-step FSP procedure providing microstructures of high interest for further investigations as cathode in PEM fuel cells.

Thermal characterization of nano-featured devices is a critical challenge for the development of high performance devices. Although far-field thermoreflectance imaging is limited in spatial resolution by the optical diffraction limit, it is more amenable to absolute temperature calibration of plasmonic devices than existing near-field scanning probe tip methods. We have built an advanced thermoreflectance microscope capable of 50 ns time-resolved, diffraction-limited temperature imaging that can account and correct for thermal expansion, sample drift, numerical aperture, and polarization induced variations in the apparent thermoreflectance coefficient of nanoscale structures. We developed a per-pixel transient calibration technique using this microscope to measure the absolute temperature of an operating heat-assisted magnetic recording (HAMR) head, including features as narrow as 200 nm. The resulting temperature information can be used to experimentally validate numerical models in the design process of such plasmonic devices.

The deformation behavior and shape recovery of an Fe-added AuCuAl shape memory alloy micropillar were investigated. XRD analysis revealed that Au-28Cu-22Al-2Fe (at.%) alloy contained a second phase which was evaluated to be α-Fe (bcc). SEM observation also confirmed the second phase at the surface of the micropillar specimen. A polycrystalline micropillar with 20 x 20 x 40μm rectangular was fabricated by a focused ion beam (FIB) system, and micro compress test was performed at room temperature. It was found that the yield stress of micropillar showed 50MPa, which must correspond to stress for inducing martensite. After the heating of the compressed micropillar, 1.75% shape recovery was recognized which is comparable to the transformation strain. Then, the Fe-added AuCuAl micropillar was concluded to possess good shape memory property, and thus this alloy may be suitable for small endovascular treatment which requires good X-ray radiography.

Two-dimensional (2D) materials are very promising with respect to their integration into optoelectronic devices. Monolayer tungsten diselenide (WSe2) is a direct-gap semiconductor with a bandgap of ∼1.6eV, and is therefore a complement to other two-dimensional materials such as graphene, a gapless semimetal, and boron nitride, an insulator. The direct bandgap distinguishes monolayer WSe2 from its bulk and bilayer counterparts, which are both indirect gap materials with smaller bandgaps. This sizable direct bandgap in a two-dimensional layered material enables a host of new optical and electronic devices. In this work, a comprehensive analysis of the effect of optical excitation on the transport properties in few-layer WSe2 is studied. Monolayer WSe2 flakes from natural WSe2 crystals were transferred onto Si/SiO2 (270nm) substrates by mechanical exfoliation. The flakes were observed under an optical microscope. A FET based on mechanically exfoliated WSe2 was fabricated using photolithography with Molybdenum as metal contact and Silicon as back gate and the electronic properties were measured in a wide range of temperatures. The mobility of our device was found to be 0.2 cm /V-S at room temperature. The schottky barrier height was found to decrease from 80 meV to 25 meV as the gate voltage increases.

Multiferroic materials are of great interest from the scientific and technological viewpoints based on their multifunctional behavior involving ferroelectricity, ferromagnetism, ferroelasticity and strong electromagnetic coupling properties. Among these materials, BiFeO3 (BFO), is a well-known multiferroic with simultaneous ferroelectricity (TC=1103K) and G-type antiferromagnetism (TN=643K). In this work, we doped BiFeO3 with Mn species and studied the doping effect on the corresponding magnetic properties, expected from the substitution of Bi3+ by Mn2+. Additionally, the optimum processing conditions to minimize the formation of any impurity phase were also identified. X-Ray Diffraction (XRD) characterization confirmed the formation of powdered impurity-free BFO in pure and 7 at.% Mn-BFO only after annealing of the precursor compounds at suitable temperatures and time (700°C, 15 minutes). Scanning Electron Microscopy (SEM) analyses were used to determine the size and morphology of synthetized powders. Vibrating sample magnetometry (VSM) measurements showed that maximum magnetization values increased with doping and reached a maximum value in the 7 at.% Mn-doped BFO annealed at 700°C for 15min; the corresponding magnetization in the non-saturated MH loops reached 0.68 emu/g. This behavior can be attributed to the actual incorporation of Mn species into the BFO lattice and the substitution of non-magnetic Bi species.

Charge carrier trapping in diamond surface conduction field effect transistors (FETs) has been analyzed. For these devices two methods were used to obtain a negative electron affinity diamond surface; either plasma hydrogenation or annealing in an H2 environment. In both cases the Al2O3 gate dielectric can trap both electrons and holes in deep energy levels with emission timescales of seconds, while the diamond – Al2O3 interface traps exhibit much shorter time scales in the microsecond range. Capacitance-Voltage (CV) analysis indicates that these interface traps exhibit acceptor-like characteristics. Correlation with CV based free hole density measurements indicates that the conductance based interface trap analysis provides a method to quantify surface characteristics that lead to surface conduction in hydrogenated diamond where atmospheric adsorbates provide the acceptor states for transfer doping of the surface.

The objective of this research is to evaluate the microstructure of a coating layer composed of Zn / Zn-5 % Al. It was performed by the double-dip method of a steel AISI 1020. The temperature of the immersion bath was 550°C and the coatings were performed using different immersion times. Microstructural characterization was done using optical microscopy, SEM, EDX and XRD. All coatings showed three defined zones. The first zone, corresponding to the steel/coating interface, it presents typical properties of a traditional galvanization process at high temperatures. In zone II, a very heterogeneous microstructure was observed; zone III showed a Zn-Fe matrix with compounds particles of Fe2Al5Znx. The XRD characterization detected the presence of Zn and Fe2Al5Zn0,4. It was concluded than microstructural properties of the coatings were similar for the three immersion times. It is important to remark that the presence of Fe and Al throughout the coating, due to the diffusion of iron from the base metal and aluminum, presents in the second immersion bath.

We examine how stress has the potential to shape the character of the electron transport that occurs within ZnO. In order to narrow the scope of this analysis, we focus on a determination of the velocity-field characteristics associated with bulk wurtzite ZnO. Monte Carlo simulations of the electron transport are pursued for the purposes of this analysis. Rather than focusing on the impact of stress in of itself, instead we focus on the changes that occur to the energy gap through the application of stress, i.e., energy gap variations provide a proxy for the amount of stress. Our results demonstrate that stress plays a significant role in shaping the form of the velocity-field characteristics associated with ZnO. This dependence could potentially be exploited for device application purposes.

At high activation energy, kinetic processes require the accumulation of several excitations in order to take place. This accumulation implies an entropy, which we call multi-excitation entropy. This explains the isokinetic rule, which itself explains the existence of isoequilibrium relations. Understanding the implications of these effects helps clarify the microscopic mechanisms in kinetic processes, including hydrogen storage, and transport of protons, and potentially, of other ions, in condensed matter.

Ni-based bulk metallic glasses and composites with high absolute densities exceeding 11 g/cm3 were synthesized via spark plasma sintering of Ni45Co10Ta25Nb20 powders produced from pulverized, melt-spun amorphous ribbons. Optimizing the synthesis via selection of sintering temperature, uniaxial load pressure, and powder mechanical screening yielded samples with relative densities of nearly 100% and hardness values in excess of 12.5 GPa without cracking. Mechanical testing included Weibull modulus determination for hardness and compression testing at 10-3 s-1 and 103 s-1 strain rates. The capability of using spark plasma sintering to fabricate high hardness, high density, large scale metallic glasses is demonstrated. The mechanical properties of these compacted comminuted melt-spun glass ribbons are presented.

We present a study of the energy levels in a FTO/TiO2/CH3NH3PbI3/Spiro solar cell device. The measurements are performed using a novel ambient pressure photoemission (APS) technique alongside Contact Potential Difference data from a Kelvin Probe. The Perovskite Solar Cell energy band diagram is demonstrated for the device in dark conditions and under illumination from a 150W Quartz Tungsten Halogen lamp. This approach provides useful information on the interaction between the different materials in this solar cell device. Additionally, non-destructive macroscopic DC and AC Surface Photovoltage Spectroscopy (SPS) studies are demonstrated of different MAPBI3 device structures to give an indication of overall device performance. AC-SPS measurements, previously used on traditional semiconductors to study the mobility, are used in this case to characterise the ability of a perovskite solar cell device to respond rapidly to chopped light. Two different device structures studied showed very different characteristics: Sample A (without TiO2): (ITO/PEDOT:PSS/polyTPD/CH3NH3PbI3/PCBM) had ∼4 times the magnitude of AC-SPS response compared to Sample B (including TiO2): (ITO/TiO2/ CH3NH3PbI3/Spiro). This demonstrates that the carrier speed characteristics of device architecture A is superior to device architecture B. The TiO2 layer has been associated with carrier trapping which is illustrated in this example. However, the DC-SPV performance of sample B is ∼5 times greater than that of sample A. The band gap of the MAPBI3 layer was determined through DC-SPS (1.57 ± 0.07 eV), Voc of the devices measured and qualitative observations made of interface trapping by DC light pulsing. The combination of these (APS, KP, AC/DC-SPV/SPS) techniques offers a more general method for measuring the energy level alignments and performance of Organic and Hybrid Solar Cell Devices.

Aerogels are a promising material for aerospace applications and have recently been explored for biomedical applications also. In both environments, exposure to radiation is inevitable, such as from radiation in space or, radiation-based sterilization and tracking of implants. X-ray radiation, in particular, is of a concern. Here, polyurea-crosslinked silica aerogel (PCSA) samples were exposed to approximately 170- and 500-Gy X-irradiation at room temperature under varying environmental conditions and characterized using electron spin resonance (ESR) technique. Results obtained for PCSA were compared with those from polyether-ether ketone (PEEK) and ultra-high molecular weight polyethylene (UHMWPE) which served as benchmarks for this study. PEEK is known to be very radiation resistant, while UHMWPE is known to be less radiation resistant. All materials (PCSA, PEEK, and UHMWPE) were exposed to the same treatments and exposure conditions. Two exposure times were tested: 10 min and 30 min which corresponded to “low” and “high” conditions, as well as comparisons of nitrogen vs. air environments during exposure and post-exposure storage. Results showed significant quantities of free radicals produced in PCSA after exposure to X-irradiation which scaled with radiation dosage; quantities were in-between those produced in PEEK and UHMWPE. The storage conditions (air vs. nitrogen) also played an important role in the free radical levels detected and are reported in this study.

Point defects in diamond such as vacancies act as a strong donor compensation center; therefore, remarkably reduce electron conductivity of diamond-based devices. Artificial synthesis methods of n-type diamond utilize the hydrogen-containing precursors enabling its diffusion into diamond crystal and subsequent formation of hydrogen-vacancy complexes. Here we employ spin-polarized, hybrid density functional theory calculations, in order to characterize the electronic properties and stability of hydrogen-passivated vacancies in diamond. We found strong thermodynamic preference for hydrogen passivation of four vacancy-related dangling bonds. An analysis of formation energy vs Fermi level diagrams indicate, that strong donor compensation effect associated with vacancies can be entirely neutralized by hydrogen incorporation. Thus, a careful control of hydrogen partial pressure in the growth process might be crucial to improve the electron conductivity of n-type diamond.

A disposal measure for fuel debris generated at the accident in the Fukushima Daiichi Nuclear Power Station has been studied so far. However, physical and chemical properties of the fuel debris located in reactor containment vessels have not yet been obtained. In order to investigate the safety function of barriers required for disposal of fuel debris, sensitivity analysis for radionuclide migration was carried out, considering with uncertainty of the properties. As a result, it is indicated that it was important for evaluation of fuel debris disposal to obtain the physical and chemical properties of 14C and 129I during release to groundwater, in addition to 238U.

Supercapacitor is a newly-developed device for electrochemical energy storage with high power density, long life span, as well as rapid capture and storage of energy. Carbon-based materials, from carbon nanospheres, nanotubes and nanofibers to graphene, are the most commonly used electrode materials for supercapacitors. Our group has engaged in the research of carbon nanomaterials over the past decade. Herein we summarize some typical carbon nanomaterials and their synthetic routes based on our published works, which is expected to provide the theoretical and experimental basis for further applications on carbon-based energy storage devices.