Haruo Uyama

Synthesis of ammonia in high-frequency discharges

The synthesis of ammonia from nitrogen-hydrogen plasma prepared using radiofrequency discharge and microwave discharge was studied under the same experimental conditions except the driving frequency. Twice larger amounts of ammonia were adsorbed on zeolite used as adsorbent in the microwave discharge than in the radiofrequency discharge. Relative intensities of NH band head (A3Π−X3Σ−,0−0) as well as hydrogen atomic line (H\) observed in the plasma prepared using microwave discharge were one order of magnitude larger than those in the plasma prepared using radiofrequency discharge. Since NHx radicals and H atoms are considered ammonia precursors, the advantage of microwave discharge over radiofrequency discharge on ammonia synthesis is discussed from the results obtained above and from the plasma parameters,kTe andne, obtained by the electric double probe technique.

Synergistic effects of catalysts and plasmas on the synthesis of ammonia and hydrazine

The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NHx formed in the plasma on the catalyst surface followed by the formation of NH3 and N2H4 are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.

Synthesis of ammonia in high-frequency discharges. II. Synthesis of ammonia in a microwave discharge under various conditions

The synthesis of ammonia from nitrogen-hydrogen plasma prepared using microwave discharge was studied by changing some experimental conditions, such as pressure (260–2600 Pa), power input (30–280 W), and nitrogen-hydrogen mixing ratio [H2/(N2+H2)=0−1.0]. The ammonia yield increased with decreasing pressure and saturated at lower pressures. When the power input and the nitrogen-hydrogen mixing ratio were changed, the maximum yield of ammonia was obtained at the optimum experimental conditions (power input ≈150W; H2/(N2+H2)≈0.75). Amounts of NH, H, and H2 in the plasma also changed by changing the experimental conditions. From the changes in ammonia yield and amounts of NH, H, and H2 by changing the experimental conditions, it is suggested that ammonia molecules are formed by the reaction of NH radicals not only with hydrogen atoms but also with hydrogen molecules. Otherwise, the formation and the decomposition of ammonia would occur simultaneously.

Catalytic Effect of Iron Wires on the Syntheses of Ammonia and Hydrazine in a Radio-Frequency Discharge'

The catalytic effect of iron wires on plasma syntheses of ammonia and hydrazine has been studied in the nitrogen-hydrogen plasma prepared using rf discharge at a pressure of 650 Pa (5 Torr). The product was mainly ammonia including a small amount of hydrazine. When iron wires were placed in the plasma downstream of the gas flow, the yields of both products increased, about two times in ammonia and two orders of magnitude in hydrazine. The yields increased with increasing number of wires (the surface area of the catalyst). The dissociative adsorption of nitrogen molecules and/or molecular ions on the iron surface and the formation of NHx by the reaction with hydrogen in the plasma followed by the formation of NH3 or N2H4 are considered as a reaction scheme. This is supported by the identification of NH3 with XPS of the surface of iron wires.

Diamond deposition with plasma jet at reduced pressure

Carburizing and diamond deposition experiments were done on titanium, niobium, and molybdenum substrates with argon-methane-hydrogen gas mixture plasma jets at a pressure of 200 torr for various hydrogen concentrations. Diamond deposition was obtained at a volume of 7% hydrogen added to the plasma jet. The deposits were markedly different on the different metal substrates. Diamond deposits with habit planes were clearly observed on niobium and molybdenum, while the deposit on titanium consisted of ball-like particles. The emission spectra from the plasma jet were the same, for all the substrates, proving that the difference in the diamond deposit depends on the substrate characteristics. CH, C/sub 2/, hydrogen, and carbon atoms were identified in the plasma jet. The difference in the deposits is attributed to the reactivity of carbon species in the plasma with the metal surface as well as to the solubility of hydrogen in metals. >

Low temperature deposition of titanium–oxide films with high refractive indices by oxygen-radical beam assisted evaporation combined with ion beams

The effect of simultaneous irradiation of an oxygen-ion beam (O-IB) or an argon-ion beam (Ar-IB) on an oxygen-radical beam assisted evaporation (O-RBAE) was studied to deposit titanium–oxide films with high refractive indices at low substrate temperature. In O-RBAE, the oxygen-radical beam (O-RB) was irradiated to completely oxidize titanium Ti, which was simultaneously evaporated onto a glass substrate from an electron beam source. In addition to O-RB, O-IB or Ar-IB was simultaneously irradiated to make the deposited films dense onto the substrate. The substrate temperature rose to less than 100 °C during the film deposition. The refractive indices n, the film densities, and the morphology of the films deposited by O-RBAE combined with O-IB (O-RBAE/O-IB) and Ar-IB (O-RBAE/Ar-IB) were compared with those of the films deposited only by O-RBAE. In O-RBAE/O-IB, compared with O-RBAE, the n value increased from 2.37 to 2.51, the film density increased from 3.87 to 4.02 g cm−3, and the morphology changed from a...

Vaporization of Graphite in Plasma Arc and Identification of C 60 in the Deposit

Vaporization of graphite in the argon-helium plasma arc at atmospheric pressure has been carried out. Carbon soot sample was deposited on the wall of the arc chamber in a higher deposition rate. Small amounts of C 60 was identified in the product by means of visible-UV spectroscopy and x-ray diffraction methods. The existence of C 60 in the benzene soluble fraction of the deposit was made sure by means of Raman spectroscopy as well as by mass spectroscopy.

Low-temperature deposition of optical films by oxygen radical beam-assisted evaporation

Abstract Titanium and silicon oxides were deposited as optical films on glass substrates at low temperature (below 100°C) by oxygen radical beam-assisted evaporation (RBAE). Ti and Si were used as the starting material. Conventional reactive evaporation using neutral oxygen gas was compared with RBAE. The optical properties (refractive index n , and extinction coefficient k ) and chemical structures of the deposited films were investigated. The radical beam source used in this study generated oxygen radicals with negligible ionic species. The films deposited by RBAE reached high oxidation states, compared with those deposited by conventional reactive evaporation. The n and k values of the films deposited by RBAE were almost constant over a wide range of Ti and Si evaporation rates. On the other hand, n and k values of the films deposited by conventional evaporation increased immediately with an increase in Ti and Si evaporation rates. An anti-reflective coating based on a multi-layer of TiO 2 and SiO 2 deposited by RBAE, which showed good performance in low reflectance and high transmittance, was demonstrated. It indicates that RBAE is an effective process for film deposition at low temperature.

Diamond deposition from an ArCCl4H2 plasma jet at 13.3 kPa

Abstract We deposited diamond from an ArCCl4(0.03 vol.%)H2 plasma jet, because the dissociation energy of CCl4 is smaller than that of CH4 which is usually used as the carbon source. First, the deposition of diamond from CCl4H2 plasma prepared using microwave discharge at 1.3 kPa as a reference was confirmed on silicon and α-alumina substrates, although the surface of the deposit was covered with amorphous components. Second, diamond was deposited from the plasma jet including CCl4. A molybdenum substrate was placed on the water-cooled holder in the reactor chamber and the ArCCl4H2 plasma jet, generated by the introduction of CCl4 vapour into the ArH2 jet at a pressure of 13.3 kPa and 2.0 kW power input, impinged on the substrate. Diamond deposition was identified on the substrate. Diamond exhibiting crystalline habit planes was observed by scanning electron microscopy in the deposit after 60 min exposure. The deposits were identified as diamond including small amounts of amorphous carbon by X-ray diffraction and Raman spectroscopy without covering by amorphous components. In diamond deposition from the plasma jet containing CCl4, CCl radicals prepared in the plasmas contribute to deposit diamond.

Temperature measurement of polymer substrates during plasma irradiation

In the web coating process of some materials using sputtering, plasma-assisted evaporation, and plasma-enhanced C VD, heat damage of polymer substrates by plasma irradiation is problem for the quality of products. During deposition, the substrate is heated by condensation of deposits, heat from the source or plasmas, and so on. However, it is difficult to distinguish these processes and the change of the temperature plasma irradiation must be minimized. In this paper, we have researched the effect of discharge conditions on the plasma heating of the polymer substrate independently of the other heat sources. The Ar, O2 and N2 plasmas were created by AC discharge with magnetic field using web coating. PET(Polyethylene terephthalate) substrate was passed through the plasma region at different conditions, such as gaseous species, pressure, discharge power, and web speed. The temperature of the substrate was measured using thermometer before and after passing through the plasma region. In ordinary case, the temperature of the substrate increased immediately when the substrate entered the plasma region and had the maximum at the center of the plasma region. When the power input increased, the temperature slightly increased in both plasmas. Pressure also affected the increment of the substrate temperature. The change of the web speed influenced upon the residence time of the substrate in the plasma region. In this experimental conditions, although the temperature change of the substrate were 0.4–3°C, this would not ignore for the polymer substrate. The change of the substrate temperature passing through plasma region will be discussed together with the results of plasma diagnostics and some the surface analysis of the substrate.