The plasma-assisted carbon-film coating of the inner walls of nuclear fusion devices, which is a new technical trend, is reviewed in view of plasma-surface interactions. A great advantage of the easiness for both wide-area and repeated coatings is due to the so-called in situ coating of the walls compared with the precoating. The amorphous carbon films produced by this in situ plasma coating contain ordinarily a large number of H atoms (H/C=0.4∼0.6), which lead to recycling of a large amount of hydrogen (release and implantation of H atoms) in nuclear fusion discharges. This demerit of the plasma method can be covered by reducing the H content in the films under suitable coating conditions, and also by conditioning the film surface with a helium glow discharge. A simple model for the interaction between a-C: H film and hydrogen plasma is proposed. Further, another low-Z material coating, that is in situ boron coating, is briefly discussed.
Physical properties of carbon films, prepared by using a plasma CVD apparatus, have been studied in terms of crystal structure, chemical bond, hardness, depth composition profile, and hydrogen concentration. The relation between the film properties and the plasma parameters was also studied. The structure of carbon films became amorphous carbon at a total pressure of 1.3 Pa, while the graphite like structure was grown at a lower total pressure and higher plasma space potential. When the structure became graphite type, the hydrogen concentration decreased from 40 to 5%, leading to an increase in the Knoop hardness from 80 to 500 kg/mm2. These results are discussed in comparison to the properties of the carbon films prepared by using different deposition techniques.
Structural characterization technique of hetero-interfaces using surface-sensitive EXAFS is reviewed. Principles and experimental techniques are briefly described. Results of application to structural studies of Si/Ge/Si (100) hetero-interfaces perepared by molecular beam epitaxy (MBE) are reported. The formation of ordered Si/Ge/Si interface is evidenced by Fourier transform analysis of Ge K-EXAFS oscillations. Future prospects for in-situ stuctural analysis of epitaxially-grown semiconductor interfaces using a high brilliance synchrotron radiation are discussed.
Problems in the derivation process of Griffith's equation on the critical condition of crack propagation are discussed, and new equations are derived according to his energy balance criterion. One of the typical equation which has similar expression to that of Griffith's is under plane stress condition.σ0=2(Eγs/l)1/2, where, σ0 is critical tensile stress for crack propagation, i.e. static fatigue limit and E is Young's modulus, γs surface free energy and l specimen length. Assumptions used in the derivation of the above equation are, (1) crack extends in a plane normal to the stress axis, (2) specimen has a uniform cross-sectional area “aΤ”; along the stress axis, and (3) the area of inherent crack “;a”; satisfies a condition a<<aΤ. Under these assumptions, existence of the small crack (a<<aΤ) causes little change in the critical stress σ0.
Plasma-polymerized hexamethyldisiloxane (PPHMDS) was deposited on polytetrafluoroethylene (PTFE) films by changing the conditions for the plasma pre-treatment of PTFE surface prior to PPHMDS coating. The adhesion strength measured by the direct pull method increased from about 30 kg/cm2 for the untreated films to about 80 kg/cm2 for the treated ones in Ar and N2 plasmas for 10 minutes. In the case of O2 plasma treatment, the adhesion strength increased to about 70 kg/cm2 by 1 minute treatment, but then decreased rapidly to the value lower than that of the untreated surface. The fracture of PPHMDS/PTFE system took place cohesively in the PTFE films except for the substrate films treated in O2 plasma for about more than 5 minutes. The increase in adhesion strength is due to the sputtering of the surface layers of PTFE films which otherwise might produce weak boundary layers at the interface, while the rapid decrease, in the case of O2 plasma treated PTFE films, is due to the lowering of cohesive force of the surface layers caused by the scission of the polymer chain by atomic oxygen in plasma.
Our previous work on Ti containing alloys shows that TiC precipitated at the alloy surfaces acts as an adhesive between the ceramics and the alloy. It is important, therefore, to elucidate the mechanism of the TiC surface precipitation on the alloys. It is noted that precipitation of small TiC particles in alloy matrices produces the interfacial and strain energy at the interface, and the extra energy from these sources appears to be responsible for the precipitation of these TiC particles to the surface. This work shows that small TiC particles are present in the matrix of these Ti contain ing alloys throughout the temperature region in which the extensive surface precipitation of TiC is observed, although according to an available phase diagram the TiC precipitate is absent in the matrix of these alloys. If the surface TiC originates from TiC in the matrix, the TiC surface precipitation rate must increase with increasing diffusivity of Ti and C in the matrix. This diffusivity effect was experimentally confirmed. These results are in accord with the presumption that the driving force for the surface precipitation is the interfacial and strain energy.
A quantitative analysis method with a low-energy photo-electron counter in the atmosphere was developed for pigment on surface of polymer particles, and the detectable depth of this method for organic compounds was experimentally estimated using LB-film. First, we investigated the changes of photo-electron emission property (i. e. ionization energy and line inclination of emission yield vs. irradiation energy) of aluminum substrate, when the thickness of LB-film on it increased according to the number of arachidic acid monolayers. Thereby the detectable depth was estimated to be less than 90 Åf. Next, samples covered with varying amounts of carbon black were prepared for determining the correlation between surface carbon black coverage and photo-electron property. Based on this correlation, surface carbon black concentration on dispersive complex-particles was estimated, and the result was found to be consistent with the observation of the particle surface with SEM.
The application of niobium films on copper for superconducting rf cavities is expected. We have developed a method for depositing adhesive niobium films on copper which were stable below 4.2 K. Niobium films were deposited on the polished copper substrates with rf magnetron sputtering. The niobium films deposited directly on the mechanically, chemically or electrolytically polished copper substrates exfoliated or blistered. We installed, therefore, a titanium layer as an intermediate layer to deposit adhesive niobium films on copper. Thus deposited niobium were very adhesive under the thermal cyclic test from 2.5 K to 300 K, and showed as good superconducting rf properties as those for a niobium sheet.
A method to prepare a sharp tip for scanning tunneling microscope was described. A sharp W tip was obtained by electropolisching usingathin electrolyte layer formed on CCl4 solution. Thus obtained tip was applied for the measurement of an optical disc stamper surafce with dense pits.
Adsorption processes seem to be effective for the recovery of rare metals in the effluent from mines, the removal of water pollutants, the collection of useful resources in sea water, the separation and purification of bioproducts etc., especially at low concentrations. In the practical processes, however, excellent adsorbents from both functional and economical standspoints are essential. The liquid-phase adsorption with silica-containing mixed-oxides in amorphous state is reviewed.