BiCuTeO is a potential thermoelectric material owing to its low thermal conductivity and high carrier concentration. However, the thermoelectric performance of BiCuTeO is still below average and has much scope for improvement. In this study, we manipulated the nominal oxygen content in BiCuTeO and synthesized BiCuTeOx (x = 0.94–1.06) bulks by a solid-state reaction and pelletized them by a cold-press method. The power factor was enhanced by varying the nominal oxygen deficiency due to the increased Seebeck coefficient. The thermal conductivity was also reduced due to the decrease in lattice thermal conductivity owing to the small grain size generated by the optimal nominal oxygen content. Consequently, the ZT value was enhanced by ∼11% at 523 K for stoichiometric BiCuTeO0.94 compared to BiCuTeO. Thus, optimal oxygen manipulation in BiCuTeO can enhance the thermoelectric performance. This study can be applied to developing oxides with high thermoelectric performances.

The effect of direct current (dc) substrate bias on the promotion of nanocrystallization in Si network has been studied, specifically within He-diluted SiH4 plasma in radio frequency (RF)-plasma-enhanced chemical vapor deposition. In view of organizing nanocrystallinity, controlled transmission of energy to the growing surface is needed and that is obtainable from metastable helium (He*) bombardment and, in particular, ionic helium (He+) bombardment under negative substrate bias. The structural morphology has been adequately regulated to a homogeneous network restraining from an exclusive columnar structure that is coherent to low-temperature growth. Notable improvements in the film quality in terms of enhanced crystallinity with low hydrogen content as well as reduced incubation volume, bulk void, and surface roughness have been demonstrated, even at low substrate temperature and low RF power. Use of appropriate dc substrate-bias has been identified as a supplementary parameter efficiently organizing the growth, making it more device-friendly.

The Cu-based film catalysts with various additive metals have been successfully prepared by the electroless plating on ZnO nanorods/stainless steel substrates. The microstructure features of the Cu-based films are highly porous and composed of plate-type grains. The addition of zirconium, aluminum, and iron into Cu-based film catalyst can improve the activity and the stability of the film catalysts. The catalytic durability of the Cu-based film catalysts has also been improved by addition of Zr, Al, and Fe into Cu-based films. This is attributed to the formation of the stable ZrO2, Al2O3, and Fe2O3 nanoparticles with good dispersion in the films.

The Cu-type and (Cu-Fe)-type film catalysts have been successfully prepared by the electroless plating on ZnO nanorods/stainless steel substrates. The microstructure features of the (Cu-Fe)-type films are high porosity and plate-type grains. The addition of iron into Cu-type film can improve the reducibility and the stability of the film catalysts. The reduction temperature of the (Cu-Fe)-type film catalysts decreases with increasing the addition of Fe. For Cu-5 at% Fe film, the reduction temperature is in the range of 195°C to 216°C as comparison in the range of 208°C to 233°C of the Cu-type film catalysts.

High-quality GaP, GaP@GaN and GaN@GaP nanowires were grown by a convenient vapor deposition technique. The wire-like and two-layers structures of GaP@GaN and GaN@GaP core-shell nanowires were clearly resolved using X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM) and their growth directions were identified. Photoluminescence intensity of GaP@GaN nanowires increased as temperature increased. The result was interpreted by the piezoelectric effect induced from lattice mismatch between two semiconductor layers. An unexpected peak at 386 cm-1 was found in the Raman spectra of GaN@GaP and assigned to a surface phonon mode due to the interface. Detailed synthetic conditions and possible growth mechanisms of those nanowires were proposed.

Raman spectra in CVD diamond films were measured at room temeprature and at high temperatures up to 1200 K. With micron spatial resolution, variations of Raman line from different crystals in the same sample were observed. Both single-peak and multiple-peak analyses were used to assess the stress distribution within the CVD diamond film. In addition, the evolution of Raman line position, line width, and line intensity was monitored as a function of annealing temperature and isothermal holding time. Both (100) and (111) CVD diamond crystals were studied. The detailed evolution of the Raman line width was found to depend on the crystallographic orientation. The temperature dependence of the Raman spectra for CVD and natural diamonds are compared.

The present paper discusses the role of ceria and hafnia dispersions in tungsten alloys on the microstructural evolution and densification kinetics during sintering. Densification kinetics were measured using dilatometry, and microstructural changes were examined using scanning electron microscopy and Auger electron spectroscopy. Activation energies for sintering were obtained by analyzing the shift of the iso-density points as a function of linear heating rate. Sintering of both tungsten and ceria-dispersed tungsten were found to be controlled by grain boundary diffusion, with apparent activation energies of 318±21 and 385±15 kJ/mole, respectively. However, densification of hafnia-dispersed tungsten is not controlled by a single mechanism. Under different conditions hafnia can enhance or retard densification; the mechanisms associated with this behavior are discussed. In particular, the relationships between sintering behavior and the tungsten-ceria and tungsten-hafnia interfaces are examined. Comparison with conventional oxide dispersoids, such as thoria, will also be made.

Particulates produced by 248 nm KrF excimer laser ablation were investigated in two systems: Nb-Al and Cr-Nb. Both systems contain intermetallics which are potentially useful high temperature materials. While the melting temperature of Nb is three times higher than that of Al, the melting temperature difference between Nb and Cr is less substantial. This work focuses on the effects of melting temperature difference between the terminal elements in binary alloy systems on the nature of the particulate matter formed by laser ablation.

Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-rayanalysis (EDX), and optical image analysis were used to characterize the products. The particulate generation rate and the size distribution depend on various growth parameters. In both Nb-Al and Cr-Nb systems, the particulates are all enriched in Nb, with the smallest particulates richest in Nb. Single phase particulates containing barely detectable Al were found in Nb-Al system. In the Cr-Nb system, electron diffraction patterns indicate two types of particulates: one exhibiting a new metastable diamond cubic structure and the other being a two phase mixture of bcc Cr and bcc Nb. A plausible mechanism whereby the lower melting temperature element is depleted as well as the correlation of the particulate size and the overall composition of individual particulate will be discussed. Stoichiometric studies of the particulatesgenerated in the Nb-Al and Cr-Nb systems using the pulsed laser deposition (PLD) technique help illustrate the merits and limitations of the same. One example of the potential applications of the particulate-containing films will be demonstrated.

A novel way of producing particulate intermetallic matrix composites based on Nb-Al in one step using pulsed laser deposition (PLD) has been investigated. One unique characteristic, inherent to laser ablation, is the generation of particulates. These particulates condense on the substrate and become part of the film. In some cases, such as in high Tc superconducting or optical films applications, it is believed that the presence of particulates diminishes the quality of the films. In this work, we demonstrate that it can be advantageous in some applications to incorporate these particulates into the films.

Nb-Al films were prepared by laser ablation from a Nb3Al target using a 248nm KrF excimer laser at various fluences and substrate temperatures. Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Auger electron spectroscopy (AES) were used to characterize the samples. The resultant films consist of a homogeneous matrix with uniformly distributed inclusions. The size of the particles generated by PLD is in the range of a few tens of nanometers to a few microns. EDX shows that the matrix has a composition of Nb7A13 and the particulates contain barely detectable Al. The mechanism of the depletion of Al in the particulates will be discussed. The merit of having a ductile Nb phase embedded in the intermetallic matrix is evident as the cracks generated during TEM sample thinning process propagate in the brittle matrix and finally are arrested at the ductile inclusions.

Systematic experiments have been carried out to characterize the yttria containing zirconia thin films on sapphire substrates by 248nm KrF excimer laser ablation. The deposition rate as a function of laser fluence and O2 pressure at room temperature was measured with a quartz crystal microbalance. The results show different threshold fluences for deposition in vacuum vs. oxygen. While the deposition rate increases with increasing fluence at a given oxygen pressure, the rate eventually saturates at a higher laser fluence. At a given fluence, the oxygen pressure dependence of the deposition rate shows a radical reduction when the O2 pressure increases from 10 mTorr to 1 Torr. Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy were used to obtain stoichiometric information. A very strong pressure dependence of the O/Zr ratio was observed. While the trend of increasing O/Zr and Zr/Y ratio with increasing O2 pressure is apparent, the correlations between O/Zr as well as Zr/Y ratio and other processing conditions are less obvious. RBS results indicate an increasing roughness at the interface between the ZrO2 film and the sapphire substrate as the oxygen pressure exceeds 50 mTorr. The structural information obtained from x-ray diffraction patterns indicates broadening of peak width with increasing laser fluence as well as decreasing substrate temperature. For the film deposited at a lower substrate temperature, a strong (002) texture was observed.

Systematic experiments have been carried out to characterize the yttria containing zirconia thin films on sapphire substrates by 248nm KrF excimer laser ablation. The deposition rate as a function of laser fluence and O2 pressure at room temperature was measured with a quartz crystal microbalance. The results show different threshold fluences for deposition in vacuum vs. oxygen. While the deposition rate increases with increasing fluence at a given oxygen pressure, the rate eventually saturates at a higher laser fluence. At a given fluence, the oxygen pressure dependence of the deposition rate shows a radical reduction when the O2 pressure increases from 10 mTorr to 1 Torr. Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy were used to obtain stoichiometric information. A very strong pressure dependence of the O/Zr ratio was observed. While the trend of increasing O/Zr and Zr/Y ratio with increasing O2 pressure is apparent, the correlations between O/Zr as well as Zr/Y ratio and other processing conditions are less obvious. RBS results indicate an increasing roughness at the interface between the ZrO2 film and the sapphire substrate as the oxygen pressure exceeds 50 mTorr. The structural information obtained from x-ray diffraction patterns indicates broadening of peak width with increasing laser fluence as well as decreasing substrate temperature. For the film deposited at a lower substrate temperature, a strong (002) texture was observed.