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In this paper CH 4 / H 2 gas flow rate effect on polycrystalline diamond deposition was studied using a time-series exposure technique of modulated induction thermal plasma (M-ITP) and non-modulated induction thermal plasma (NM-ITP). The M-ITP was used to make nucleation of diamond particles in the first stage, and then non-modulated ITP was used to grow diamond particles in the next stage. The diamond films fabricated after exposure by M-ITP and then by NM-ITP were studied in terms of morphology and constituents. Experimental results showed that higher CH 4 / H 2 gas flow rate condition to 0.1/10 slpm provided a higher deposition rate of polycrystalline diamond film. This result implied that higher CH 4 / H 2 gas flow rate would give a higher neutral hydrocarbon fluxes onto the substrate, which was also supported from the numerical simulation model. [ABSTRACT FROM AUTHOR]

In this paper, numerical calculations were made for Ar loop-type inductively coupled thermal plasma (loop-ICTP). The loop-ICTP was developed originally by the authors' group for rapid surface modification of large areas. Loop-ICTP is sustained with a unique three-dimensional (3D) configuration inside a circular loop quartz tube and on the substrate. A 3D and two-temperature thermofluid thermal plasma model was adopted for this calculation. Mass, momentum, and energy conservation equations were solved using a Maxwell equation for vector potential, an electron energy transport equation, and Saha's equation in the 3D space. Results indicate that Ar loop-ICTP can be sustained and formed in the loop tube and also on the substrate. Moreover, the heavy particle temperatures reaches 1800–2000 K, whereas the electron temperature is about 10,000 K. Loop size effects on the gas temperature and gas flow field were also investigated using the developed model. Results show that adoption of a larger loop tube can be expected to improve the plasma uniformity on the substrate when applied to rapid surface modification. [ABSTRACT FROM AUTHOR]

A numerical model was developed on the evaporation process of intermittently fed feedstock into pulse-modulated induction thermal plasma (PMITP). This experimental method combining the PMITP with intermittent feedstock feeding has been developed for the synthesis of large amounts of nanoparticles. To treat this method, a full transient numerical model for the PMITP was combined with transient equations of particle behaviour with different time steps. Transient two-way interactions from particle evaporation to the PMITP were also taken into account at each time step as source terms in mass, momentum and energy conservations. The temperature, gas flow field and mass fraction of feedstock vapor were obtained in the transient state in the PMITP with the motion of feedstock particles. The calculation results were compared with the experimental results for the Ar I line and feedstock atomic line. They were found to be in fair agreement even in the transient state. [ABSTRACT FROM AUTHOR]

This paper describes the use of loop-type inductively coupled thermal plasmas (loop-ICTP) for two-dimensional (2D) rapid oxidation processing. The unique and original loop-ICTP torch has been developed for large-area rapid materials processing. We applied the loop-ICTP to surface oxidation of a Si substrate as an example of materials processing. A part of the Ar/O2 loop-ICTP is formed, lying linearly on the surface of the substrate. In addition, scanning the Si substrate enabled 2D oxidation for the whole Si substrate surface. The uniformity of the oxide layer thickness and the oxidation rate were estimated by measuring the thickness of the oxide layer fabricated on the Si substrate. As a result, controlling the pressure offered more uniform oxide layer thickness, and gas injection onto the linear plasma on the substrate improved the uniformity of the oxide thickness. It should be noted that only three minutes of exposure of Ar/O2 loop-ICTP is sufficient to create an oxide layer with approximately 100 nm thickness for a 2-inch Si substrate surface. [ABSTRACT FROM AUTHOR]

A unique method of large-scale synthesis of Al-doped TiO2 nanopowder was developed, using 20�kW Ar–O2 pulse-modulated induction thermal plasmas (PMITP) with time-controlled feedstock feeding (TCFF). This PMITP–TCFF method is characterized by intermittent feedstock powder feeding synchronized with modulation of the power of the PMITP. The method enables heavy-load feeding of raw material powder to the thermal plasmas for complete evaporation. The nanopowder synthesized was analysed using different methods including field emission scanning electron microscopy, x-ray diffraction (XRD) spectroscopy, bright-field transmission electron microscopy (TEM), TEM/energy dispersive x-ray (EDX) mapping, x-ray photoelectron spectroscopy, and spectrophotometry. The results showed that Al-doped TiO2 nanopowder can be synthesized with mean diameters of 50–60�nm. The Al doping in TiO2 was confirmed from the constituent structure in the XRD spectra, the uniform presence of Al in the nanopowder in the TEM/EDX mapping, the chemical shift in the x-ray photoelectron spectra, and the absorption edge shift in the optical properties. The rate of production of the Al-doped TiO2 nanopowder was estimated as 400�g�h−1. [ABSTRACT FROM AUTHOR]

A new modulated induction thermal plasma system, called a feedback control type of modulated induction thermal plasma system, was developed for quasi-direct control of thermal plasma temperature for advanced materials processing. The system is based on the arbitrary-waveform modulation induction thermal plasma system developed previously in our work, and a real-time spectroscopic observation system. The Ar excitation temperature was measured in real time using a spectroscopic observation technique. Its time evolution was controlled to trace externally given waveform periodical signals between 6000 and 8000 K such as rectangular, triangular and sawtooth waveforms. In addition, the developed system was confirmed to adopt an automatic power injection control, synchronized with gas injection as a disturbance. [ABSTRACT FROM AUTHOR]