Optical band-gap and cathode luminescence (CL) properties of anatase TiO2 nanopowders mixed with γ- Al2O3 powders by planetary ball mill were evaluated as a function of a powder mass ratio (x=Al2O3/TiO2) of 0 to 0.5 and their correlation with XRD spectra was also investigated. The optical band-gap of TiO2 increased from 3.36 eV to 3.41eV with increasing milling time (t m) up to 600 min, which was in good agreement with the blue shifts observed in the CL spectra with increasing t m and it was interpreted as a quantum size effect. In addition, the optical band-gap of TiO2 powders mixed with Al2O3 with t m=60min greatly increased from 3.36 eV to 3.48 eV with increasing x up to x=0.5. On the other hand, the optical band-gap of all the powders was decreased by annealing at temperatures above 600°C, which was evidenced by the XRD spectra to be due to the growth of grain size.

Nitridation of GeO2 interfacial layer (IL) was done using continuous wave (CW) and pulsed wave (PW) decoupled plasma nitridation (DPN) processes. Langmuir probe analysis of the N2 plasma demonstrates that at the same effective power and pressure, PW plasma has similar electron density (Ne) with lower electron temperature (kTe) and plasma potential (Vp) as compared to CW plasma. This results in softer plasma conditions using a PW process leading to lower plasma-related damage in the IL, but without reducing the overall nitrogen concentration. The plasma parameters were further correlated to mobility (μ) and interface trap density (Dit) extracted from fabricated Ge n-MOSFETs. As expected from the plasma analysis, at the same effective power and pressure, the PW DPN process shows 1.2X higher electron mobility as compared to a CW process. This improvement can enable GeON as an IL for future Ge CMOS gate stack technology.

Hot Isostatic Pressing of Cs-exchanged IONSIV IE-911 samples is shown to produce a mixture of ceramic phases, the nature and mass fractions of these have been determined by Rietveld analysis of powder X-ray diffraction data. The main Cs phase that forms is Cs2TiNb6O18, after this reaches approximately 30% of the total crystalline content the remaining Cs is partitioned into Cs2ZrSi6O15. Durability tests using the PCT-B method for 7 days at 90 °C with deionised water lead to Cs leach rates of 0.032 and 0.038 g∙m−2∙day−1 for samples exchanged to 6 and 12 wt% Cs, respectively, indicating a durable wasteform is produced.

To enhance cycleability of LiMn2O4 at elevated-temperature we use atomic layer deposition (ALD) method to deposit a variety of ultrathin and highly conformal amphoteric oxide (ZnO, ZrO2, Al2O3) coatings for surface modification of LiMn2O4 electrodes. High-resolution transmission electron microscopic (HRTEM) images of ZnO, ZrO2 and Al2O3 ALD coated LiMn2O4 particles demonstrate the high qualities of ALD coatings with respect to remarkable conformity, homogeneity and uniformity. Two types of ALD-modified LiMn2O4 electrodes are fabricated: one is ALD-coated LiMn2O4 composite electrode, the other is electrode composed of ALD-coated LiMn2O4 particles and uncoated carbon/poly-vinylidenefluoride (PVDF) network. All LiMn2O4 electrodes modified with 6 oxide ALD layers (as thin as ∼1 nm) reveal significantly enhanced electrochemical performances than bare electrodes at both 25°C and 55°C. After 100 electrochemical cycles at 1 C at 55°C, the electrode consisting of LiMn2O4 particles coated with 6 ZnO ALD layers remains the highest capacity of 56.1 mAh/g, higher than 51.1 mAh/g of ZrO2 coated LiMn2O4 particles, 45.8 mAh/g of Al2O3 coated LiMn2O4 particles and 27.0 mAh/g of the bare composite electrode as well as 44.5 mAh/g of the composite electrode coated with 6 ZnO ALD layers. These results indicate that ZnO ALD coating is the most effective protective film for improved cycling stability, followed by ZrO2 and Al2O3. It is also found that amphoteric oxide coating on LiMn2O4 particles is more effective to enhance the cycleability of LiMn2O4 than coating on composite electrode. Furthermore, for coating either on composite electrode or on LiMn2O4 particles, the effect of ALD coating on improving capacity retention and increasing specific capacity of LiMn2O4 is more phenomenal at elevated temperature than at room temperature.

Microstructral and charge-trap properties of single Hf-silicate dielectric films are presented versus annealing treatment. The as-grown films were found to be homogeneous and amorphous. It is shown that annealing treatment results in the formation of alternated Hf-rich and Si-rich layers. The mechanism responsible for this phenomenon is found to be surface directed spinodal decomposition. The increase of annealing temperature up to 1000-1100°C resulted in the crystallization of Hf-rich phase. The stability of its tetragonal phase caused an enhancement of film permittivity was observed. The evolution of charge trapping properties of the films results in the memory effect which nature was discussed.

We report a transformative, all inorganic method-based synthesis of supported bimetallic alloy nanoparticles. We use Pd3Ag as a proof of concept. The method involves breaking down bulk Pd3Ag alloy into the nanoparticles in liquid lithium, converting metallic Li to LiOH, transferring Pd3Ag nanoparticles/LiOH mixture onto non-water soluble supports, followed by leaching off the LiOH with water under ambient conditions. The size of the resulting Pd3Ag nanoparticles was found narrowly distributed around 2.3 nm characterized by transmission electron microscope (TEM). In addition, studies by X-ray diffraction (XRD) showed that the resulting Pd3Ag nanoparticles inherited similar structure as the starting bulk Pd3Ag.

InGaN epilayers have been investigated for use in photovoltaic solar cells for the past years. At present, almost all photovoltaic device structures reported have exhibited very low short circuit currents and thus very low solar conversion efficiency. This phenomenon has been attributed to point and extended defect chemistry in InGaN epilayers (e.g. vacancies, misfit dislocations, and V-defects), as well as to spinodal decomposition of the strained InGaN wurtzite lattice system. These defects become more dominant for higher indium concentration InGaN epilayers needed for multijunction photovoltaic device structures. In this work, we will report on the growth and characterization of indium-rich InGaN epilayers that have been grown by novel MOCVD growth technology, including the growth at superatmospheric reactor pressures.

We studied physical properties of titanium hafnium oxide (Tix Hf1-x O2) alloy thin films deposited by pulsed DC reactive magnetron sputtering with AC substrate bias. Thin films of two end oxides, hafnium oxides (HfO2) and titanium oxides (TiO2), and their alloys Tix Hf1-x O2 with a range of compositions deposited with and without the substrate bias were compared to study the dependence of physical properties of the thin films on the substrate bias. Structural, chemical and optical properties of the thin films were analyzed to assess inter-relationship among these properties. Thin films deposited with the AC substrate bias consistently show much higher refractive index and significantly lower optical extinction coefficient than those of thin films deposited without the substrate bias suggesting that characteristic microstructures developed in these thin films are responsible for the differences in the optical properties.

Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising absorber material for photovoltaic applications. Nanoscale electrical conductivity and overall electronic quality of this material are significantly affected by film microstructure, specifically the density and dimension of grains and grain-boundaries (GB). Local charge distribution at grains and grain/GB interfaces of nc-Si:H was studied by Electrostatic Force Microscopy (EFM) in constant force mode under illumination of white LED. Bias voltage from -3V to +3V was applied on the tip. Scanning Kelvin Force (KFM) images were taken before and after illumination to study the change in surface photovoltage (SP). EFM and KFM analysis were combined with film topography to draw a correlation between surface morphology and nanoscale charge distribution in this material. After illumination, small blister like structures were observed whose size and density increase with time. Raman spectroscopy confirmed these new structures as nanocrystalline silicon. This change was assumed due to relaxation of strained Si-Si bonds as an effect of photo response. Nanocrystalline grain interiors were at lower potential and amorphous grain boundaries were at higher potential for negative bias; it was opposite for positive bias. Change in polarity in bias voltage reversed the polarity of the potential in grains and GBs indicating the dominance of negative type of defects. Further study with current sensing AFM in dark and illumination with variable bias voltages will be able to identify the type and density of defects in grains and grain/GB interfaces.

The oxygen conductor yttria-stabilized-zirconia (YSZ) is widely used in miniaturized solid oxide fuel cells (µSOFC) and may be suitable for solid state ion emitter applications e.g. as miniaturized ion engines for electric propulsion. Since the YSZ films are not completely free of stress during the growth, cracks in fabricated free-standing membranes are often observed.

YSZ thin films were deposited on silicon substrates by radio frequency sputtering. Free-standing YSZ membranes were fabricated by partially removing the Si substrate by anisotropic wet-chemical etching using different masking patterns defined by electron beam lithography. We show how different sizes and etching conditions influence the strain in the fabricated membranes. To characterize these membranes we used optical microscopy and scanning electron microscopy.

The thermoelectric properties of Mg2Si coatings prepared by Atmospheric Plasma Spray (APS), and Vacuum Plasma Spray (VPS) are presented. Seebeck coefficient results of both APS and VPS have been reported. XRD and SEM analysis of the samples are also presented to understand how microstructure influences the coating thermoelectric properties. The results suggest significant improvements can be made on the reduction of impurity including oxidation and pure silicon by using proper spray method and parameters. Thermal spray has been demonstrated before to be effective way to reduce thermal conductivity which may due to the coating microstructure. VPS result shows higher Seebeck coefficient than APS which may due to lower level of oxidization.

The aim of this study was to investigate the application of modified clay as a support in the synthesis of silver nanoparticles. Silver nitrate (AgNO3) was used as the silver precursor in several concentrations (0.005 M, 0.01 M, 0.02 M, 0.05 M, and 0.1 M) to obtain Ag-MMT purified and modified clay nanocomposites. The properties of nanocomposites were also studied as a function of the concentration of the reducing agent, sodium borohydride (NaBH4). It was observed through X-ray Diffraction that the MMT purified structure was gradually exfoliated with increased concentrations of AgNO3, while the modified clay structure remained intact. As observed through UV-vis spectra, samples of Ag+-MMT were reduced with NaBH4 to produce Ago and its particle diameter is dependent on the concentration of NaBH4.

Transport properties (thermal conductivity, electrical resistivity and thermopower) of decagonal quasicrystal d-AlCoNi, and approximant phases Y-AlCoNi, o-Al13Co4, m-Al13Fe4, m-Al13(Fe,Ni)4 and T-AlMnFe have been reviewed. Among all presented alloys the stacking direction (periodic for decagonal quasicrystals) is the most conductive one for the charge and heat transport, and the in/out-of-plane anisotropy is much larger than the in-plane anisotropy. There is a strong relationship between periodicity length along stacking direction and anisotropy of transport properties in both quasicrystals and their approximants suggesting a decrease of the anisotropy with increasing number of stacking layers.

In this paper we present systematic investigations on the growth of SnS van der Waals epitaxies (vdWEs) on different substrates, including crystalline and layered substrates, by molecular beam epitaxy (MBE). Experimental growth of SnS on conventional 3D substrates, such as GaAs, indicates strong interaction between the SnS layer and the substrate resulting in poor crystallinity in general. Substantial improvement in the film crystallinity can be obtained when the deposition is made on layered substrates, with saturated surface bonds, as observed in SnS films deposited on mica and crystalline substrates with a graphene buffer layer. Crystal size as large as one micron and rocking curve FWHM of 0.118° was observed despite the large lattice mismatches. This represents significant improvement over the reported value of ∼3°. Several symmetric growth orientations are observed for films grown on mica substrates. The results indicate that weak vdW interactions between the saturated bonds of the substrate surface and the SnS unit layer which is an important factor for achieving high quality epitaxy layered materials.

Ultrathin layers of positively charged poly(diallyl dimethylammonium) choloride (PDDA) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) were deposited on SiO2/ polyethylene glycol hybrid membranes via layer-by-layer assembly technique, and carbon dioxide absorption/separation properties were investigated. Quartz crystal microbalance (QCM) measurements revealed that both PDDA and PSS nanocoatings have a good affinity for CO2 absorption. PDDA-deposited film shows about two times higher CO2 ideal gas selectivity compared with unmodified silica film.

A simple method is proposed for the chemical modification of carbon nanotubes (CNT) thin film counter electrodes (CE) for the replacement of fluorine-doped tin oxide (FTO) and platinum catalyst (Pt) while retaining light transparency. In order to decrease the sheet resistance, CNT thin films underwent various concentrations (≤10 M) and durations of HNO3 treatment prior to cell fabrication, and the effect on thin film properties was analyzed. P-doping was observed, and the maximum change in work function was found to be +0.35 eV with 4 M HNO3. Optimum sheet resistance reduction (50%) and work function increment were achieved after 1 h treatment with 4 M HNO3. Changes in optical transmittances for all samples were negligible (± 5%). Pristine and HNO3 treated films on plastic substrates were tested as CE in flexible bifacial dye sensitized solar cells (DSSC). Most significant improvements in conversion efficiencies were obtained when CNT on plastic substrates were pretreated with 8 M HNO3 (from 1.18% to 1.40% under roomlight, from 0.19% to 0.26% under 1 Sun).

This research shows the influence of the synthesis route in the structural and morphological characteristics as well as in the luminescent properties of doped with europium and pure SrTiO3 (STO) powders prepared by microwave assisted hydrothermal synthesis, MWH, and by the polymeric precursor method, PPM. The XRD at room temperature of the STO powders nominally pure obtained by PPM at 700°C for 3 hours, as well as by the MWH at 190°C by 30 minutes present all the reflection peaks for the cubic perovskite structure (JCPDS-ICDD 35-734). The morphology varies according to the synthesis route. The particles of pure STO obtained by PPM presents morphology in the form of plates and the morphology of the particles synthesized by MWH is spherical with approximately 150 nm. The photoluminescent analysis shows for pure STO wide bands associated with the transition of charge transfer from the titanates group (TiO3)2- that are centered on 450 nm. In both preparation methods the emission bands obtained in the composites spectra were found to be asymmetric and low intense. However, in the case of the STO prepared by the PPM a bigger FWHM of the band can be observed. The excitation of the samples was done using a laser (Coherent Innova) with wavelength of 350 nm.

Flexible devices utilizing crystalline semiconductor nano or microstructures materials are attractive for many applications. However, these materials are fabricated or grown in unusable forms for flexible systems due to their rigid crystalline mother substrates. We demonstrate a transfer printing technique for transferring vertical arrays of one-dimensional (1D) materials from mother substrates to flexible substrates with subsequent device fabrication steps to create flexible devices from these arrays. The transfer printing technique is based on vertical embossing of arrays of 1D materials into thermoplastic (Poly (methyl methacrylate) (PMMA)) transfer layers, while the device fabrication steps rely on encapsulation with insulating polymers and contact deposition. We investigated the use of flexible insulating layers like polydimethylsiloxane (PDMS) and polyurethane (PU) which are shown to be effective for encapsulation and contact isolation. Representative flexible resistive devices were created from these transferred arrays and insulating layers which showed a reversible tactile characteristic. Electronic characterization and flexibility testing was carried out to show the potential of these methods for enabling large-scale integrations of nano and microstructures into vertical and flexible packages.

Papers in the Appendix were published in electronic format as Volume 1534

Grain boundary chemistry in an X750 Ni alloy was analyzed by atom probe tomography in an effort to clarify the possible roles of elemental segregation and carbide presence on the stress corrosion cracking behavior of Ni alloys. Two types of cracks are observed: straight cracks along twin boundaries and wavy cracks at general boundaries. It was found that carbides (M23C6 and TiC) are present at both twin and general boundaries, with comparable B and P segregation for all types of grain boundaries. Twin boundaries intercept γ’ precipitates while the general boundaries wave around the γ’ and carbide precipitates. Near a crack tip, oxidation takes place on the periphery of carbide precipitate.