Papers by Keyword: Nitridation

Abstract: We explain the role of nitrogen in simultaneously increasing the inversion channel mobility and reducing the threshold voltage of SiC MOSFET. A variety of computational techniques have been used to compute the atomic scale configuration of a nitridated SiC/SiO2 interface, and the corresponding change in Fermi level, inversion channel mobility, and threshold voltage. X-ray photoelectron spectroscopy (XPS) has been used to investigate the SiC/SiO2 interface to determine the nitrogen concentrations and chemical bonding. We elucidate the physics behind improved channel mobility due to NO anneal and demonstrate that the trade-off between threshold voltage and inversion channel mobility can be correlated to the extent of nitridation.

Abstract: AlN powders by the chemical vapor synthesis (CVS) process in the AlCl3-NH3-N2-H2 system were successfully synthesized. Gasified AlCl3 as a starting material was generated by pre-heating system and transported to the tube furnace in NH3-N2-H2 atmosphere. High crystalline AlN was synthesized at over 900°C. The average particle size of spherical AlN powders decreased from 250 to 40nm with increasing the reaction temperature of the tube furnace. Porous nano-size particles synthesized at high reaction temperature have low oxygen contents.

Abstract: The colored TaON and Ta3N5 were synthesized by ammonolysis of amorphous Ta(OH)5 in the temperature range of 800-1000°C. Ta(OH)5 were prepared by titration process from TaCl5. TaON were synthesized at 900°C for 2 hr, and Ta3N5 were synthesized at 1000°C for 5 hr. In general, Ta3N5 powders were easily oxidized at 500°C with changing colority from red to white. To minimize the oxidation problem of Ta3N5 powders, we proposed silica coated system using TEOS and APTES as a surfactant. Tonality of silica coated Ta3N5 has very little changing which means silica coating actually minimizes the oxidation of the Ta3N5 particles.

Abstract: New porous materials with hybrid pore structure “Fibers-In-Pores” structure were produced by developing Si3N4 whiskers in pores of partially-sintered silicon by nitriding. Because silicon and Si3N4 have excellent heat resistance, the proposed porous materials are expected to utilize high-temperature applications such as gas filters. Porous silicon was produced by sintering Si powder at 1300°C for 1 h in a stream of Ar gas. Porous Si bodies were nitrided at 1300°C for 1 h with N2 gas to develop long Si3N4 whiskers in pores of partially-sintered silicon. Specific surface area was increased and gas permeability was decreased by applying the nitridation process at 1300°C.

Abstract: Removal of fine particles from some gas-product effluents from motors and industries, using filters, is an important subject in the field of public health and environment. In the present work, a porous silicon filter was produced, which is able to capture most of the particles undesirable for the environment (transported by gases), larger than the pore diameter (micrometer) of the filter and even smaller size particles. The development of whiskers inside of the pores of the silicon filter, improve its ability to catch smaller particles than the filter’s size pores. Those whiskers are made of Silicon Nitride, produced by a Nitridation process. A different time-temperature schedule for the formation of -silicon nitride (-Si3N4) whiskers by direct Nitridation of the porous silicon filter was studied, in order to optimize the amount of whiskers and improve the filter quality. Four different temperatures (1000, 1100, 1200 and 1300 °C) were selected, each with two different holding times (15 min and 1 hour) for complete Nitridation with N2 and N2+H2 gases. The as-formed whiskers were characterized by SEM, XRD techniques and the process conditions were studied. The filter with the Si3N4 whiskers was characterized evaluating mechanical properties of the porous silicon filter (Micro Hardness and Young Modulus). The permeability measurements were made before and after the Nitridation process. Analysis indicates that the higher Si3N4 whiskers formation temperature was 1300 °C for the gas (N2+H2) phase reaction results from the lower PSiO2/Psio ratio in the Si-N system. Titanium (99% pure) was used with the purpose of reduction of the oxygen partial pressure and the increase of the amount of -silicon nitride whiskers. The porous silicon filter improved its conditions with the silicon nitride whiskers, even though decreases also the fluid permeability measurement. However, it has a smaller flow decrement than filters with smaller porosity. The mechanical properties did not have variation at all, the porosity size increased because of the diffusion of Si to form whiskers in the Nitridation process.

Abstract: Rare-earth activated oxynitride or nitride luminescent materials have attracted considerable attention due to their potential applications as phosphors and pigments. Eu2+-doped -sialon has been reported to represent a new class of green phosphors with high efficiency. In this study, -sialon phosphor was synthesized by reduction nitridation of a zeolite. Eu ion-exchanged zeolite was fired at 1400 °C for 1 hour under NH3 gas containing 0.5 vol%C3H8. As a result, formation of -sialon with green emission under UV irradiation was confirmed.

Abstract: We have analyzed the effect of post-oxidation nitride anneals (usually with either NO or N2O gases) on SiC MOSFETs. Two 4H:SiC wafers were identically prepared except that one wafer had a nitridation anneal after the gate oxide was formed, while the other was tested as-oxidized. We compared the two processes by making measurements on lateral MOSFETs and MOS capacitors using ID-VGS, C-V, and charge pumping. There was no change in either flatband voltage or interface trap density near the valence band, suggesting that the net fixed charge remained constant (within a few 1011cm-2). However, there was a large shift in the threshold voltage which, when combined with the C-V results, indicates a strong reduction of interface traps near the conduction band of roughly 6.0x1012cm-2 by using the nitridation process. The charge pumping measurements also showed a strong reduction of interface traps. Charge pumping measured a trapping density of 2.5x1012cm-2 for the as-oxidized samples and 5.3x1011cm-2 for the nitrided samples. The frequency-dependence of the charge pumping signal also indicates a spatial distribution of traps, with volumetric trap densities of roughly 1.3x1019cm-3 over 25Å on as-oxidized and 3.8x1018cm-3 over 19Å for nitrided.

Abstract: The oxidation and nitridation of pure chromium and of chromium alloys containing 0.5 to 5at% silicon was investigated at 1300°C in several atmospheres. Global methods like thermogravimetry were associated to thickness measurements and microstructural characterisation to evaluate oxidation mechanisms. The contribution of nitridation to weight gain during high temperature exposure is discussed, examining nitride volume fraction. Experiments demonstrate that the presence of nitrogen in the substrate is always consecutive to a breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer. Silicon, when present in chromium solid solution, slows down the oxidation kinetics and limits the progression of nitrogen in the chromium lattice and at grain boundaries. The absence of the Cr2N layer beneath the metal/oxide interface does not benefit to the adherence of the oxide scale. Oxidation of silicon in chromium leads to the formation of discontinuous particles of SiO2 at the metal/oxide interface, at the grain boundaries and dispersed in the bulk in the alloy sub-surface.

Abstract: The present study focuses on the high temperature oxidation of a AISI 304 chromiaforming nitrided alloy. Isothermal oxidations were performed in air, at 800°C. The effect of nitridation on the steel surface depends on the temperature of the treatment. It leads whether to a γN solid solution formation or to CrN formation. In situ X-ray diffraction has been used to follow the oxides formation. Results show the concomitant growth of CrN and Fe2O3 at the beginning of the test. Then, Cr2O3 quickly appears which leads to the formation of a protective oxide scale (a parabolic rate law is observed). Our conclusions suggest that nitridation increases the high temperature oxidation resistance of 304 steels at 800°C.

Abstract: In this study, chromium based alloys containing a hardening NiAl phase are investigated from 1100°C to 1300°C in air. The influence of the NiAl content and of the Al/Ni ratio on microstructure modification and on oxidation behaviour are characterized by metallography and thermogravimetry. Increasing the Al/Ni ratio leads to a higher Al content in the chromium solid solution but does not modify the amount of primary NiAl. At high temperature, and for NiAl content exceeding 16 at%, a duplex oxide layer forms at the surface of the alloys exposed in air, alumina in the inner part, and chromia in the outer part. The oxidation behavior is discussed according to oxidation profile and to the thermodynamic predominance diagram of the involved species.