Micro-Raman Spectroscopy for Stress Evaluation of 3C-SiC Epitaxially Grown on Si Substrate by Hot Wall CVD

GROWTH of large area3C-SiC films on Si hasattracted great interest since the early report onhetero-epitaxial growth by means of chemical vapordeposition(CVD)[1],due to its outstanding thermal,chemical and electrical properties for deviceapplications,such as,wide-band gap(2.3eV),highthermal conductivity(4.9W/cmK),high electronmobility(lOOOcmVVs)and high electron saturationdrift velocity(2.7xl07cm/s)[l,2].To our knowledge,the reports on the growth of SiC involved largely on the(100)Si,wi…     

电子回旋共振等离子体技术新进展

叙述了电子回旋共振（ＥＣＲ）微波等离子体技术的基本工作原理，主要特点以及发展概况，着重从ＥＣＲ等离子体实验系统、工艺应用、诊断技术和机理研究等方面对ＥＣＲ技术进行了讨论。由于ＥＣＲ微波等离子体技术具有密度高、电离度大、工作气压低、表面损伤小等特点，在反应离子刻蚀（ＲＩＥ）、等离子体化学气相淀积（ＣＶＤ）和溅射方面具有广阔的应用前景。     

Carbon-modified TiO2 for photocatalysis

ABSTRACT: Here we present a method to produce TiO2 nanocrystals coated by thin layer of graphitic carbon. The coating process was prepared via chemical vapor deposition (CVD) with acetylene used as a carbon feedstock with TiO2 used as a substrate. Different temperatures (400°C and 500°C) and times (10, 20, and 60 s) of reaction were explored. The prepared nanocomposites were investigated by means of transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy/diffuse reflectance spectroscopy and ultraviolet-vis (UV-vis)/diffuse reflectance spectroscopy. Furthermore, photocatalytic activity of the materials was investigated under visible and UV-vis light irradiation in the process of phenol decomposition. It was found that TiO2 modification with carbon resulted in a significant increase of photoactivity under visible irradiation and decrease under UV-vis light irradiation. Interestingly, a shorter CVD time and higher process temperature resulted in the preparation of the samples exhibiting higher activity in the photocatalytic process under visible light irradiation.     

Development of an All-ceramic Module with Silica Membrane Tubes for High Temperature Hydrogen Separation

Abstract

Heat resistant hydrogen selective membranes are desired for use as membrane reactors in low-temperature hydrogen production via the steam reforming of hydrocarbons, which are usually operated over 1000 K. In addition, developing a multi-tubular type of membrane unit that can process more reactants is becoming more and more important in order to realize the practical use of membrane reactors.

In this study, an all-ceramic module consisting of 6 silica membrane tubes with a comparatively large membrane area of around 0.04 m² was fabricated by a counter-diffusion chemical vapor deposition technique. As a result, the H₂/N₂ ideal separation factor and the H₂ permeance of the module were 1300 and 1.9 × 10^?7 mol·m^?2s^?1Pa^?1 at 873 K, respectively. In a 1000-hour thermal stability test for the silica membrane module, it was found that the H₂ permeance initially decreased by about 30% and then became steady under ΔP = 0.95 MPa at 773 K.     

Electrical characterization of C-coated nickel silicide nanowires grown on Ni-loaded Si substrate

Carbon-coated nickel silicide nanowires (C-coated NiSi NWs) were grown in a home-made chemical vapor deposition (CVD) reactor. The coating of semiconductor or metal nanowires with nano-sized carbon layer is effective to prevent the oxidation of the nanowires, resulting in the stabilization of electrical properties of nanodevices. The growth of the NiSi nanowires and the coating of the NWs with carbon layers simultaneously took place in the reaction. The current-voltage curve of individual NiSi nanowire showed highly linear behavior, indicating the good ohmic contact without the insulating layer. The resistivity of the NiSi nanowire was about 370 ΜΩ-cm at room temperature, decreased monotonically as the temperature was lowered, and became saturated at low temperatures, indicating the growth of metallic NiSi nanowires. Field emission measurements showed that the C-coated NiSi nanowires were an excellent field emitter with large emission current densities at very low electric field.     

Synthesis and microwave absorption properties of bamboo-like β-SiC nanowires

Lightweight and strong microwave adsorption property have become the foremost crucial factors in the practical application of modern microwave absorbers. This study mainly dealt with synthesize of bamboo-like β-SiC nanowires with high-performance microwave absorption property via a polymer pyrolysis CVD (PPCVD) approach. The PPCVD process was conducted by cleverly placing the polymer powders into two temperature zones to produce reactant gases with alternating concentrations. The morphological study revealed that the nodes exhibited abundant stacking faults as compared to the stem segments, which was beneficial for the microwave losses. The optimal reflection loss value of −35.47 dB was gained at 18 GHz corresponding to 2.0-mm absorber thickness, and the corresponding −10 dB bandwidth (>90% absorption) was 3.22 GHz. It has turned out that the as-prepared nanowires could be applied at different frequencies by adjusting the thickness. Especially, it exhibits a good prospect in the fields of ultrathin absorbers. Furthermore, the microwave absorption mechanisms of the nanowires were explored. This present investigation has opened a high-efficient facile approach to develop ultrathin, lightweight, and high-performance microwave absorbers.     

Preparation of Nano-titanium Dioxide in Propane/Air Diffusion Flame

Titanium dioxide (TiO2) nanoparticles were synthesized by the oxidation of titanium tetrachloride (TiCl4), in propane/air diffusion flame. The propane/air diffusion flame is generated using a multi-port diffusion type burner composed of 4 concentric tubes. Flow rates of TiCl4 and combustion gases such as air, industrial propane and carrier gas were chosen as key experimental variables for the control of the particle size and morphology. Effects of propane/air mole ratio and precursor flow rate on particle size, morphology, structure and carbon dots of titanium dioxide particles were studied.     

Mechanical properties of nanocrystalline diamond/amorphous carbon composite films prepared by microwave plasma chemical vapour deposition

Nanocrystalline diamond films (NCD) have been deposited by microwave plasma chemical vapour deposition from CH₄/N₂ mixtures with varying methane content. They consist of diamond nanocrystallites with sizes of 3–5 nm embedded in an amorphous matrix with grain boundary widths of 1–1.5 nm. The CH₄ content in the gas phase has almost no influence on the microscopic structure but a strong effect on the macroscopic structure and morphology. The mechanical and tribological properties of these films have been investigated by nanoindentation, nano tribo tests, and nano scratch tests. The hardness of a 4-μm-thick film deposited with 17% methane was about 40 GPa, the indentation modulus 387 GPa, and the elastic recovery 75%. Ball-on-disk tests against an Al₂O₃ ball revealed, after initially higher values, a friction coefficient of ≤0.1. Tribo tests and scratch tests proved a strong adhesion and a protective effect on silicon substrates. Finally, the correlations between the macroscopic structure of the films and their mechanical and tribological properties are discussed.     

Morphology of the growth tip of carbon microcoils/nanocoils

Single-helix twisted carbon nanocoils and single-helix spring-like carbon micro/nanocoils were prepared by the CVD process of the catalytic pyrolysis of acetylene at 700–800 °C over Fe-containing alloys in large scale, with a high purity and good reproducibility and with the coil yield of about 60%. The morphology and microstructure were examined. The catalyst grains on the growth tip of the nanocoils were observed closely. The results indicated that most of the twisted nanocoils grown by a two directional growth mode; that is, two twisting nanocoils grew out of a catalyst grain in opposite chirality and the fibers are grown in the herring-bone structure. Spring-like carbon coils were prepared with over sputtered Fe alloys on ceramics supporters, with a high purity and good reproducibility and with the coil yield of about 20%. All of the spring-like carbon coils are of one directional growth mode, and their coiling diameter and coil pitch are about the same size of several hundred nanometers. It is very common to observe spring-like nanocoils with laces, TEM investigation results showed that the spring-like nanocoils are of tubular coils.     

Thermodynamic analysis of liquid source chemical vapor deposition process for the preparation of a Ba-Sr-Ti oxide film

The equilibrium concentrations of the chemical species in a Ba-Sr-Ti-C-H-O system, corresponding to a liquid source chemical vapor deposition (LSCVD) process used in the preparation of barium strontium titanium oxide (BST) films, were determined by thermodynamic calculations. Ba(dipivaloylmethanato)2, Sr(dipivaloylmethanato)2, and Ti(tetra-isopropoxide) were assumed as the metal sources, and tetrahydrofuran (THF) and O₂ as the solvent and oxidant, respectively. An increase in the amounts of THF, a major source of graphite production, significantly increases the equilibrium concentrations of metal oxides and carbonates in the system. On the other hand, an increase in the O₂ content decreases the graphite content and increases the amount of carbonates. Based on these results, the conditions for an LSCVD process that produces minimum amounts of carbon impurities in a BST film were identified as a function of the process temperature and the O₂/THF ratio. The results of the equilibrium calculations are in reasonable agreement with experimental data, which indicates that the results can be used as a basis for identifying LSCVD conditions needed to prepare BST films with defined compositions. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.