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Surface Science 216 (1989) 153-159 North-Holland, Amsterdam

153

-- THE PHONON SPECTRUM OF Ag(100) IN THE r-X DIRECTION MEASURED BY EELS

M. ROCCA, L. RISSO, B. VICENZI and U. VALBUSA

Dipartimento di Fisica, Universitri di Genova and GNSM- CISM Unitd di Genova, Genova, Italy

Received 22 December 1988; accepted for publication 23 January 1989

EELS measurements of the dispersion curve of the Rayleigh wave on Ag(100) are reported -- along the T-X direction up to the Brillouin zone border. The comparison of the measured spectra with the theoretical predictions by Castiel et al. and Black et al. shows that the surface is not contracted in contrast with the behavior of the same face of Cu and Ni. The sign and magnitude of the change of the surface force constants are therefore shown to be related not only to the surface structure but also to the (sp)-d hybridization of the electronic states at the surface.

160 Surface Science 216 (1989) 160-172 North-Holland, Amsterdam

ELASTIC ELECTRON FINE STRUCTURE: FIRST PRINCIPLE CALCULATION

B.Y. LIN and A. KAHN

Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA

Received 12 December 1988; accepted for publication 20 January 1989

A first principle electron multiple scattering calculation is carried out for a two atom system to obtain total elastic scattering intensity as a function of energy. The total elastic electron scattering intensity from an amorphous material (Si) is calculated by averaging that from two atom systems. An excellent match is obtained between the calculated and experimental result. The calculation supports our interpretation of the fine structure found in the elastically reflected electron intensity and provides the theoretical foundation for the practical application of the technique in surface and interface studies.

Surface Science 216 (1989) 173-188 North-Holland, Amsterdam

173

DECOMPOSITION OF TRIMETHYLGALLIUM ON Si(100): SPECTROSCOPIC IDENTIFICATION OF THE INTERMEDIATES

F. LEE, A.L. BACKMAN, R. LIN, T.R. GOW and R-1. MASEL *

University of Illinois, 1209 W. California Street, Urbana, IL 61801, USA

Received 18 November 1988; accepted for publication 24 January 1989

The decomposition of trimethylgallium (TMG) on a heated Si(100) substrate is studied using TPD, XPS and EELS. It is found that the decomposition of TMG is largely an intramolecular process. The TMG adsorbs molecularly at low temperatures. Upon heating, one of the methyl groups in the TMG reacts with a hydrogen on another methyl group liberating methane. This

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leaves a CH, group bound to the gallium which is seen clearly with EELS. Upon further heating, another hydrogen reacts with the remaining methyl group producing additional methane. Simulta- neously, the remaining fragments decompose into gallium atoms and CH groups. The CH groups dissociate above 750 K yielding adsorbed hydrogen and adsorbed carbon. The hydrogen desorbs between 750 and 850 K while the carbon gets incorporated into the growing film. These results show that carbon incorporation is an intrinsic part of the TMG decomposition process. Thus, TMG would not be an appropriate source gas when one needs to produce films with very low carbon levels.

Surface Science 216 (1989) 189-197 North-Holland, Amsterdam

189

AUGER FINE STRUCTURES OF SURFACE STATES FOR Si(111)7 X 7 AND Si(lll)& X O-AI

T. IDE, T. NISHIMORI, T. TAN1 and T. ICHINOKAWA

Department of Applied Physics, Waseda University, 3-4-1, Ohkubo, Shinjuku-ku, Tokyo 160, Japan

Received 28 October 1988; accepted for publication 19 January 1989

Auger fine structures of SiLW and AlLW spectra are observed for Si(111)7X 7 and Si(lll)fi x &-Al in the second derivative mode and regarded as transitions from surface states to 2p levels. For Si(111)7 X 7, three satellite peaks are observed close to the bulk peak of SiLW, whereas for Si(lll)fiXfi-Al, two and one satellite peaks are observed in the AlLW and SiLW spectra, respectively. The origin of these satellite peaks is analyzed referring to the surface states which were observed in photoemission spectroscopy. The Auger energies of these satellite peaks consist with the surface state energies measured in photoemission and scanning tunneling spectroscopy (STS). As a result, it is found that possible Auger transitions from surface states to 2p levels are localized in the individual surface atoms to which the initial and final states belong and explained reasonably by assuming DAS and modified T4 structure models for Si(111)7X7 and Si(lll)fi x G-Al, respectively.

198 Surface Science 216 (1989) 198-208 North-Holland, Amsterdam

A NEW METHOD FOR ELLIPSOMETRIC INVERSION WITH MICROCOMPUTERS: CHARACTERIZATION OF OPTICALLY ABSORBING FILMS USING MULTIPLEANGLEOF-INCIDENCE

T. EASWARAKHANTHAN, P. MAS, M. RENARD and S. RAVELET

Laboratoire d’Electronique et de Physique des Interfaces, Ecole SupPrieure des Sciences et Technologies de I’Inghziew, UniversitJ de Nancy I, Pare Robert Bentz, 545W Vandoeuvre 16s Nancy, France Received 30 September 1988; accepted for publication 9 January 1989

An inversion method has been developed to extract the optical constants and thickness of an absorbing film overlaid on an absorbing substrate from multiple-angle elhpsometry measure- ments. The method proved to be efficient in producing rapid and enhanced convergence owing to the reduction of the three-parameter problem to a two-dimensional search and to the introduction of numerical techniques. A quantitative error analysis equally carried out allows one to define the angles of incidence from which the propagation of experimental errors of the measured quantities to the physical parameters evaluated, is minimum. The entire procedure is illustrated with an example.