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Unconstrained optimisation in surface crystallography by LEED: Preliminary results of its application to CdTe(110)
A321 Surface Science 187 (1987) 175-193 North-Holland, Amsterdam
175
UNCONSTRAINED OPTIMISATION IN SURFACE CRYSTALLOGRAPHY BY LEED: PRELIMINARY RESULTS OF ITS APPLICATION
TO CdTe(ll0)
P.G. COWELL
Department of Physics, University of York, Heslington, York Y01 5DD, UK and V.E. DE CARVALHO
Departarnento de Fisica - ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil Received 21 November 1986; accepted for publication 15 April 1987 This paper describes the application to LEED of a form of the well-known method of unconstrained optimisation, originally developed by Hooke and Jeeves. It has been found to be of great use in the iterative searching that must be performed as a part of the process of discovering the atomic geometry of a surface using LEED. By using such an optimisation scheme, the speed with which a crystal surface structure may be found is greatly increased. The codification of the search strategy used in LEED in this way should also result in greater confidence being placed in LEED as a surface structure analysis technique. The CdTe(110) surface is used as the first application of this new scheme using newly collated, high quality experimental data. Nine structural and non-structural parameters were investigated to give a preliminary result for this surface.
194 RHEED INTENSITIES Ayahiko ICHIMIYA
FROM
STEPPED
Surface Science 187 (1987) 194-200 North-Holland, Amsterdam SURFACES
Department of Applied Physics, Faculty of Engineer~ng~ Nagoya University, Chikasa-ku, Nagoya 464, Japan Received 5 December 1986; accepted for publication 25 March 1987 Analytical formulae of intensifies of electron diffraction spots from stepped surfaces are obtained using Kirchhoff's diffraction theory. From the calculations it is shown that integrated intensities of RHEED scarcely depend on step distributions, but the intensities of reciprocal rods depend sensitively on the step densities and terrace areas. RHEED intensity oscillations and the damping during molecular beam epitaxial growth are also discussed with model calculations for a GaAs(O01) surface.
175
UNCONSTRAINED OPTIMISATION IN SURFACE CRYSTALLOGRAPHY BY LEED: PRELIMINARY RESULTS OF ITS APPLICATION
TO CdTe(ll0)
P.G. COWELL
Department of Physics, University of York, Heslington, York Y01 5DD, UK and V.E. DE CARVALHO
Departarnento de Fisica - ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil Received 21 November 1986; accepted for publication 15 April 1987 This paper describes the application to LEED of a form of the well-known method of unconstrained optimisation, originally developed by Hooke and Jeeves. It has been found to be of great use in the iterative searching that must be performed as a part of the process of discovering the atomic geometry of a surface using LEED. By using such an optimisation scheme, the speed with which a crystal surface structure may be found is greatly increased. The codification of the search strategy used in LEED in this way should also result in greater confidence being placed in LEED as a surface structure analysis technique. The CdTe(110) surface is used as the first application of this new scheme using newly collated, high quality experimental data. Nine structural and non-structural parameters were investigated to give a preliminary result for this surface.
194 RHEED INTENSITIES Ayahiko ICHIMIYA
FROM
STEPPED
Surface Science 187 (1987) 194-200 North-Holland, Amsterdam SURFACES
Department of Applied Physics, Faculty of Engineer~ng~ Nagoya University, Chikasa-ku, Nagoya 464, Japan Received 5 December 1986; accepted for publication 25 March 1987 Analytical formulae of intensifies of electron diffraction spots from stepped surfaces are obtained using Kirchhoff's diffraction theory. From the calculations it is shown that integrated intensities of RHEED scarcely depend on step distributions, but the intensities of reciprocal rods depend sensitively on the step densities and terrace areas. RHEED intensity oscillations and the damping during molecular beam epitaxial growth are also discussed with model calculations for a GaAs(O01) surface.