Gas monitoring is a relevant activity for industrial and domestic applications due to usage of dangerous gases as methane, which has been increasingly used as domestic and industrial fuel. In this field of research, metallic oxides such as SnO2, ZnO and Fe2O3 have been widely studied, but we are far from reaching the total understanding of all the parameters that can be varied; in order to improve the gas sensing properties of the metallic oxides. In this work, we present the change of properties derived from using different solvents during the preparation of SnO2 nanoparticles via the sol-gel process. The nanoparticles suspended in two different solvents were deposited on glass substrates by the dip-coating method. The addition of Sb as a dopant was studied at two different Sb:Sn ratios of 1:99 and 1:2. SEM showed differences in the nanostructured topology of the samples and EDS analysis was performed to determine the elemental composition of the samples and the ratios of doping. XRD spectroscopy was used to determine the phase of the materials and the crystallite size. Measurements of the electric response of the coatings to methane, under controlled conditions at different temperatures, were carried out and curves of sensitivity versus temperature were obtained.

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.

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.

Surfactant-free oil-in-water-in-oil (O/W/O) emulsions were successfully prepared through a facile approach using natural ingredients (biopolymers and crystalline fat particles) as stabilizers. Microstructure (PLM, cryo-SEM and confocal microscopy) and diffusive NMR studies revealed that emulsions with ultra-high loading of internal oil droplet phase with high storage stability could be easily prepared in absence of low-molecular weight synthetic surfactants. The internal oil droplets were stabilized by the presence of interfacial layers of gelled biopolymers while the encased water droplets were stabilized by a combination of interfacial crystal accumulation (Pickering stabilization) and network stabilization created by bulk crystallization of fat particles. Small (oscillatory shear rheology) and large (force-displacement measurements) deformation studies were used to gain important insights into the ‘structure-properties’ links. Furthermore, on monitoring the stability of these emulsions in terms of droplet size changes and diffusion of the internal oil phase (over a period of 3 months), they showed exceptional stability with absence of any droplet coalescence and minimal oil diffusion to the external phase. Such complex colloids stabilized by natural ingredients could find important industrial applications in development of novel products in bio-related fields of pharmaceuticals, cosmetics and foods.

This work describes the electrical behavior of dye sensitized solar cells manufactured with TiO2-nanocrystalline semiconductor sensitized with diverse natural tints. A number of natural sensitizers have been tested, including red fruits as blackberries, hibiscus and beet in order to comprehend the relationship between anthocyanin and electron transfer and green vegetables as spinach and grass, as well as for known the relationship between chlorophyll and electron transfer. The nanocrystalline semiconductor was characterized by XRD, FTIR and SEM. The bands observed at 931, 667 and 514 cmˉ1 in the FTIR spectrum confirmed the presence of Ti-O-Ti bonds. From DRX analysis it is confirmed the presence of TiO2 in its anatase form. This study confirms the great potential of the use of organic dyes for sensitized the TiO2-semiconductor. Principally, in blackberries it has reached values around 300 mV owing to high concentrations of purple pigment due to the molecule called anthocyanin and the anchoring properties of the anthocyanin with the TiO2-nanocrystalline semiconductor.

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.

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.

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.

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.

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.

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.

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.

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.

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.