The structure of the Si(111}&3&&3-Gasurface has been studied by dynamic analysis of lowenergy 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}&3 & &3-Al surface.Among the reconstructed surface structures which are formed on the (111) surface of crystals with fcc or diamond structures, the~3 X &3 structure is the most frequently observed, and many experimental and theoretical studies related to it have already been published. ' However, in only a few cases has the geometry of the surface been successfully determined. In most cases, this is mainly due to inadequate use of the methods of measurement. In the case of low-energy electron-difFraction (LEED) studies, sufficient data to determine the surface geometry can be obtained by measuring the intensityenergy (I-V) curves of diffracted beams. Shortcomings of LEED analyses include the necessity of complicated calculations and the considerable computing time required to perform this kind of calculation. ' However, recent advances in computer technology enable us to study reconstructed surface structures whose surface unit cells contain fairly large numbers of atoms.In this study we report the results of dynamic analysis of the I-V curves of LEED from the Si(111)&3Xv 3-Ga surface.We used n-type silicon wafers of high resistivity ( & 10 kQcm), cut to within 1' parallel to the (111) plane, as substrates. A molecular beam of Ga from a Knudsen cell was impinged on the silicon surface. The saturation coverage of Ga atoms for the +3X +3 structure has been determined as -, ' of a monolayer by quadrupole mass spectroscope observation of the increase in intensity of the desorption Aux of Ga atoms from the Si surface after the completion of the &3 X &3 phase at high substrate temperatures, and by observing the break points in curves of Auger-electron-spectroscopy signal versus deposition time. ' %'hen -, ' of a monolayer of Ga atoms was deposited at 740 K, an unambiguous Si(111)/3 X &3 structure was observed. I-V curves from the Si(ill)v 3Xv 3 surface have been obtained by measuring the brightness of the bright spots on the Auorescent screen by means of a spot photometer. The calculations of I-V curves were performed using a renormalized forward-scattering algorithm. The scattering matrices for nonequivalent composite layers were calculated by a matrix inversion formalism, and the intensity of the beams rejected from a stack of these composite layers 0 0 0 0 0 o Ga FIG. 1. Top and side views of the surface structural model. was obtained by the renormalized forward scattering perturbation method. The computer programs developed by Pendry and by Tong and van Hove were modi6ed to apply to cases in which the substrate layers c...

Scanning tunneling microscopy (STM) has been used to determine the surface structure of the &3 X &3 reconstruction induced by Bi on the Si(111)surface. The STM images show that there are two distinct ordered surfaces with &3 X &3 periodicity. At -,-monolayer Bi coverage, the &3 X &3 phase consists of one Bi adatom per unit cell adsorbed at T4 sites on a Si(111) bilayer. At nearly one monolayer of Bi coverage, STM images show protrusions with a complex shape dependent on bias voltage.These STM images are discussed and compared with structural models derived from previous experimental studies.The characterization of metal-induced reconstructions of semiconductor surfaces is a significant subject that pertains to the understanding of both metal-semiconductor interface formation and general growth processes on semiconductor surfaces. Ordered surface structures with +3 X +3 periodicity are commonly seen for metaldeposited Si(111) surfaces, including group-III metals, ' noble metals, and some group-V elements (Sb, Bi).Column III metals [Al, " Ga, In (Ref. 6)] in the &3 X v'3 structure have been well studied and consist of -, ' of a monolayer (ML) of metal adatoms bonded at T~s ites directly above second-layer Si atoms. However, the column V metals [Sb, Bi (Ref. 8)] are known to make another V3X&3 structure with 1 ML of metal atoms forming trimers on the surface. The currently accepted model, called the milkstool model, is derived from analysis of photoelectron and x-ray-diffraction data, ' as well as electronic structure calculations. ' A recent dynamical low-energy electron-diffraction (LEED) study has shown that there are two different &3XV 3 structures induced by Bi. " At less than -, '-ML coverage, Bi atoms adsorb as adatom monomers at the T4 site. This is basically the same structure as for the column III metals. At nearly 1 ML, Bi atoms form trimer clusters centered over the T4 site. The Bi atoms in the trimer are each bonded to the two other metal atoms in the trimer, and have one remaining bond to an underlying Si atom, forming milkstool structures. Scanning tunneling microscopy (STM) is a direct tool for studying both surface geometric and electronic structure. We have taken STM images of Bi deposited on the Si(111) surface at metal coverages up to 1 ML. We have imaged both the low coverage and high coverage &3X&3 reconstructions. The appearance of the STM images is discussed in terms of previously proposed structural models for these surfaces, '" and the bias dependence of the images is explained in terms of what is known about the surface electronic structure. 'All sample preparation and measurements were performed in an ultrahigh-vacuum (UHV) system having base pressure better than 5X10 "Torr. The Si(111)surfaces were cleaned by chemical cleaning, UV pretreatment, and annealing at 1150'C in vacuum better than 2 X 10 ' Torr. Bi was deposited from a heated tungsten filament and metal coverages were determined by timed exposure to an evaporant Aux previously calibrated by a quartz crystal microbalance. All s...

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Similar step bunchings which consist of 7–9 single steps were observed by scanning tunneling microscopy on both vicinal GaAs(100) surfaces grown by metalorganic chemical-vapor deposition (MOCVD) and annealed in AsH3 atmosphere. Growth parameters, including deposition rate, layer thickness, V/III ratio, and growth temperature, did not affect the morphology of the step bunching. These results indicate that step bunching is induced during the annealing process and its surface morphology is preserved during MOCVD growth for a wide range of growth parameters.

The evaporation rate and saturated vapor pressure (p) for functional organic materials have been evaluated by thermogravimetry in vacuum. A series of metal phthalocyanines (M-Pc) such as Cu-Pc, Ni-Pc, Pb-Pc and TiO-Pc, Tris(8-hydroxy-quinoline) aluminum complex ( Alq3), fullerene (C60) and tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ are examined, together with the relationship between p and the enthalpy of evaporation.