Phonons in bcc transition-metal interfaces

A49 K.-M. HO Ames Laboratory, US Department of Energy and Department of Physics, lowa State University, Ames, 1,4 50011, USA Received 5 September 1988; accepted for publication 25 October 1988 Using first-principles total-energy calculations the geometry of the N a ( l l 0 ) surface has been determined. We found a small contraction of the first interlayer spacing by 1.6%_+0.5%. The electronic band structure of N a ( l l 0 ) shows no significant difference to the projected bulk band structure, especially there are no occupied electronic surface states. Use of the H e l l m a n n - F e y n m a n theorem allowed the calculation of forces and thus the determination of force constants. We found an increase of up to 60% for the surface force constants perpendicular to the surface in comparison to the corresponding bulk values. This has considerable influence on the surface p h o n o n frequencies.

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Surface Science 209 (1989) 492-500 North-Holland, A m s t e r d a m

P H O N O N S IN bee TRANSITION-METAL INTERFACES R.A. BRITO-ORTA*, V.R. VELASCO and F. G A R C i A - M O L I N E R Instituto de Cieneia de Materiales, CSIC, Serrano 123, 28006 Madrid, Spain Received 28 June 1988; accepted for publication 24 November 1988 The surface Green function matching method is applied to calculate p h o n o n bands and local densities of states for the W(001)/Mo(001) interfaces. A phenomenological lattice dynamical model including two-body forces up to third-nearest neighbours and three-body forces up to second-nearest neighbours is used. N o Stoneley modes are found but localized modes lying between the gaps of the bulk bands are obtained.

Surface Science 209 (1989) 501-511 North-Holland, A m s t e r d a m

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SELECTION RULES FOR THE INELASTIC S C A I T E R I N G OF ELECTRONS FROM SURFACES WITH GLIDE PLANES Talat S. R A H M A N and Larry WEAVER Department of Physics, Cardwell Hall, Kansas State University, Manhattan, KS 66506, USA Received 16 December 1987; accepted for publication 4 August 1988 If a surface has glide reflection as a symmetry then the phonon modes in the surface can be characterized by their behavior under this operation. We exploit this observation to study phonon modes excited by electron scattering off the reconstructed Ni(100) surface with a c(2 x 2) carbon overlayer. The space group of this structure contains glides, while the space group of the unreconstructed surface contains simple reflections instead. We show the connection between p h o n o n modes in the two structures and find the selection rules that relate the m o m e n t u m lost by a scattered electron to the q-vector and symmetry of the phonon mode excited by the scattering. Our results agree with the data of Rocca et al. on this system and are more widely applicable.