Preparation, phase transformation and microstructure of ZrxTi1−xO2 (x = 0.1-0.9) fine fibers

Zr_xTi_1−xO₂ (x = 0.1-0.9) fibers were prepared by the sol-gel dry-spinning method. Polyacetylacetonatozirconium (PAZ) and tetrabutyl titanate (C₁₆H₃₆O₄Ti) were used as raw materials. The green fibers were obtained from the amorphous spinnable solution and then heat-treated to convert into polycrystalline fibers. The main phase changes from TiO₂ to zirconium titanate (ZT) and then tetragonal ZrO₂ with increasing ZrO₂ content. The crystallization temperature varied with the molar ratio of Zr:Ti. The heat-treated fibers at 1050 °C have few pores and no cracks with diameters of 10-20μm and lengths of 1-5 cm.     

Transition between amorphous and crystalline phases of SiC deposited on Si substrate using H3SiCH3

This paper presents a study of the transition between amorphous and crystalline phases of SiC films deposited on Si(1 0 0) substrate using H₃SiCH₃ as a single precursor by a conventional low-pressure chemical vapor deposition method in a hot-wall reactor. The microstructure of SiC, characterized by X-ray diffraction and high-resolution transmission electron microscopy, is found to vary with substrate temperature and H₃SiCH₃ pressure. The grain size decreases with increasing MS pressure at a given temperature and also decreases with reducing temperature at a given MS pressure. The deposition rates are exponentially dependent on the substrate temperature with the activation energy of around 2.6 eV. The hydrogen compositional concentration in the deposited SiC films, determined by secondary ion mass spectrometry depth profiling, is only 2.9% in the nanocrystalline SiC but more than 10% in the amorphous SiC, decreasing greatly with increasing deposition temperature. No hydride bonds are detected by Fourier transform infrared spectroscopy measurements. The chemical order of the deposited SiC films improves with increasing deposition temperature.     

Preparation of Sb2S3 nanomaterials with different morphologies via a refluxing approach

Single-crystalline antimony trisulfide (Sb₂S₃) nanomaterials with flower-like and rod-like morphologies were successfully synthesized under refluxing conditions by the reaction of antimony trichloride (SbCl₃) and thiourea with PEG400 and OP-10 as the surfactants. X-ray diffraction (XRD) indicates that the obtained sample is orthorhombic-phase Sb₂S₃ with calculated lattice parameters a=1.124 nm, b=1.134 nm and c=0.382 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the flower-like Sb₂S₃ is 9–10 μm in size, which is composed of thin leaves with thickness of 0.05–0.2 μm, width of 0.8–2.2 μm and length of 2.5–3 μm, and the rod-like Sb₂S₃ is 45–360 nm in diameter and 0.7–4 μm in length, respectively. UV–Vis analysis indicates that the band gap of Sb₂S₃ nanorods is 1.52 eV, suitable for photovoltaic conversion. A possible mechanism of formation was proposed. The effects of reaction time and surfactants on the growth of nanomaterials with different morphologies were also investigated.     

Thermal and some physical properties of glasses in the La2O3−CaO−B2O3 ternary system

Glasses in the La₂O₃−CaO−B₂O₃ ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La₂O₃ with constant B₂O₃ content of 71.4 mol%, and in glasses of constant La₂O₃:CaO ratio of 1:4 with B₂O₃ content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La₂Ca₂B₁₀O₁₉ was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO₃ crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (T_g), dilatometric softening point (T_d), linear coefficient of expansion (α), onset crystallization temperature (T_x), exothermal peak temperature (T_P), density (ρ) and index of refraction (n_D) in the clear glasses.     

The effect of thermal annealing on the structural and mechanical properties of a-C:H thin films prepared by the CFUBM magnetron sputtering method

a-C:H films were prepared by closed-field unbalanced magnetron (CFUBM) sputtering on silicon substrates using argon (Ar) and acetylene (C₂H₂) gases, and the effects of post-annealing temperature on structural and mechanical properties were investigated. Films were annealed at temperatures ranging from 300 °C to 700 °C in increments of 200 °C using rapid thermal annealing equipment in vacuum ambient. Variations in microstructure were examined using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface and mechanical properties were investigated by atomic force microscopy (AFM), nano-indentation, residual stress tester, and nano-scratch tester. We found that the mechanical properties of a-C:H films deteriorated with increased annealing temperature.     

Influence of growth temperature on the selective area MOVPE of InAs nanowires on GaAs (1 1 1) B using N2 carrier gas

The influence of temperature on selective area (SA) InAs nanowire growth was investigated for metal-organic vapor phase epitaxy (MOVPE) using N₂ as the carrier gas and (1 1 1) B GaAs substrates. In contrast to the growth temperature range – below 600 °C – reported for hydrogen ambient, the optimal growth temperature between 650 and 700 °C was 100 K higher than the optimal ones for H₂ carrier gas. At these temperatures, nanowires with aspect ratios of about 80 and a symmetric hexagonal shape were obtained. The results found are attributed to the physical and chemical properties of the carrier gas.     

Selective area growth of GaN nanorods on patterned W/SiO2/Si substrates by RF-MBE

We report on the selective area growth (SAG) of GaN nanorods on Si substrates masked with W or SiO₂ and also on bare Si substrates by RF plasma-assisted molecular beam epitaxy (RF-MBE). The growth of GaN (i.e. irradiation of Ga and RF plasma-activated N₂) on the W mask layer results in the appearance of a ring reflection high-energy electron diffraction (RHEED) pattern coming from α-W. In contrast, broken ring RHEED patterns from GaN nanorods are clearly observed on SiO₂ and Si surfaces. Ex-situ scanning Auger microscopy analysis confirms that no growth of GaN takes place on W. Utilizing this phenomenon, we have demonstrated the SAG of GaN nanorods on Si substrates partly masked with W. We will discuss this phenomenon in terms of the difference in the desorption energy of Ga on W, SiO₂, and Si.     

Influence of pulsed laser deposition rate on the microstructure and thermoelectric properties of Ca3Co4O9 thin films

The effects of deposition rate on the microstructure and thermoelectric (TE) properties of Ca₃Co₄O₉ thin films fabricated by pulsed laser deposition (PLD) technique were investigated. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca_xCoO₂ secondary phase. Formation of Ca_xCoO₂ was inevitable during the thin film growth, and this was discussed from both structural and compositional point of view. With longer deposition interval or with sufficient oxygen at a lower deposition rate, the Ca_xCoO₂ phase was able to transit into the desired Ca₃Co₄O₉ phase during the coalescence process. The quality of the thin films was further analyzed by electrical properties measurements. The Ca₃Co₄O₉ thin film fabricated at a slower deposition rate was found to exhibit a low electrical resistivity of 9.4 mΩ cm and high Seebeck coefficient of 240 μV/K at about 700 °C, indicating a good quality film.     

Effect of the annealing process on the microstructure of La2Zr2O7 thin layers epitaxially grown on LaAlO3 by metalorganic decomposition

La₂Zr₂O₇ (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.     

The effect of temperature and ammonia flux on the surface morphology and composition of InxAl1−xN epitaxial layers

An interesting recent development in the Group III nitrides is the growth of InAlN lattice matched to GaN, with applications in distributed Bragg reflectors (DBRs), high electron mobility transistors (HEMTs) and as etch-layers. This work presents a systematic study of the effects of changing the key growth conditions of ammonia flux and growth temperature in InAlN growth by metal-organic vapour phase epitaxy (MOPVE) and describes our current optimised parameter set. We also particularly concentrate on the details of surface morphology assessed by atomic force microscopy (AFM). The nanoscale surfaces are characterised by low hillocks and dislocation pits, while at a larger scale microscopic indium droplets are also present. However, these droplets are eliminated when the layers are capped with GaN. Other trends observed are that increasing the growth temperature will lower the indium incorporation approximately linearly at a rate of approximately 0.25% per °C, and that increasing the ammonia flux from 44.6 to 178.6 mmol min⁻¹ increased the indium incorporation, but further increases to 446 mmol min⁻¹ did not result in any further increase.     

Effect of NH3 flow rate on m-plane GaN growth on m-plane SiC by metalorganic chemical vapor deposition

This paper reports a study of the effect of NH₃ flow rate on m-plane GaN growth on m-plane SiC with an AlN buffer layer. It is found that a reduced NH₃ flow rate during m-plane GaN growth can greatly improve the recovery of in situ optical reflectance and the surface morphology, and narrow down the on-axis (1 0 1¯ 0) X-ray rocking curve (XRC) measured along the in-plane a-axis. The surface striation along the in-plane a-axis, a result of GaN island coalescence along the in-plane c-axis, strongly depends on the NH₃ flow rate, an observation consistent with our recent study of kinetic Wulff plots. The pronounced broadening of the (1 0 1¯ 0) XRC measured along the c-axis is attributed to the limited lateral coherence length of GaN domains along the c-axis, due to the presence of a high density of basal-plane stacking faults, most of which are formed at the GaN/AlN interface, according to transmission electron microscopy.