Sakama Hiroshi

The structure of a Si(100)2 X 2-Al surface at 0.5 monolayers is determined by tensor low-energy electron diffraction. The parallel dimer model is more favorable than the orthogonal dimer model. The R factor for the optimized parallel dimer structure is 0.15. The bond length of the Al dimer is almost equal to the value expected from the Pauling covalent radii. All bond lengths in five surface layers including Si-Al and Si dimer bonds are within the range of 5% from the bulk value. The distortion extends at least through the first five layers into the bulk.

Bi-adsorbed Si(110) surfaces are investigated by scanning tunneling microscopy (STM). The 2 x 3 structures where two protrusions are observed in a unit cell at the positive and negative sample bias voltages are formed at 700 K. The up and down terraces of the clean 16 x 2 structure still remain when Bi atoms are deposited at room temperature, while a rather flat surface with boundaries parallel to [-1, 1, 2] (or [1, -1, 2]) is formed by the adsorption of Bi at 570 K. The 2 x 3 structures of short-range order are also formed on the flat surface at 570 K.

ZnS:Mn electroluminescent (EL) devices were fabricated by the technique of hydrogen plasma sputtering (HPS). ZnS films were grown by HPS followed by annealing at 500-degrees-C for 1 h in a vacuum. Greater brightness was obtained when the growth of ZnS:Mn film was performed at 30-degrees-C than at 200-degrees-C. From the results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), it was found that the quality of ZnS:Mn film deposited at 200-degrees-C is poor due to the lack of sulfur atoms. The films grown at 30-degrees-C are sulfur-rich and have better crystallinity. Manganese concentration of the HPS film increases with decreasing sputtering pressure. The growth rate shows the similar tendency with decreasing the pressure, which is explained by the glow discharge theory.

The structures of Ga-adsorbed Si(110) surfaces were studied by means of QMS, AES and LEED. There exist three adsorption phases (alpha, beta, gamma), two of which are two-dimensional phases (alpha, beta). The saturation coverage of the alpha, beta phase is 0.11 and 0.17, respectively. The unit cell of surface structure "A" which corresponds to the alpha phase is 9 times larger than that of the bulk structure and the unit cell of structure "B" for the beta phase is 12 times larger. The "A" structure is observed at a substrate temperature of 800 < T(s) < 870 K, while "B" is observed at 755 < T(s) < 800 K.

The structure of the Si(111)Š3 × Š3 -Ga surface has been studied by dynamic analysis of low-energy electron-diffraction curves of intensity versus energy (I-V). It has been found that a structure in which Ga atoms are located on the second layer of Si atoms well explains the experimentally obtained I-V curves. In this geometry, a large deformation of the surface layer results from the stable adsorption of Ga atoms. The optimum configuration is close to that proposed by Northrup in his study of the Si(111)Š3 × Š3 -Al surface. © 1988 The American Physical Society.