A452

334

EAM study of surface self-diffusion of single Ni, Cu, A1, Ag, Au, Pd, and Pt C.L. Liu a, J.M. Cohen b, J.B. Adams a and A.F. Voter b a Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA h Theoretical Division, T-12, MS-B268, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Received 27 December 1990; accepted for publication 7 February 1991

Surface Science 253 (t991) 334-344 North-Holland

adatoms of fcc metals

Self-diffusion of single adatoms on the (100), (110), (111), (311), and (331) surfaces of fcc metals is investigated with the embedded atom method (EAM). The general trend of activation energies for these surfaces is consistent with experimental observations. The calculated activation energies for Ni are in excellent agreement with experimental data, but those for AI and Pt differ from experimental values by up to a factor of 3. The estimated pre-exponential factors are in the range of 10-4-10-2 cm2/s, in good agreement with experiment.

Surface Science 253 (1991) 345-352 345 North-Holland

Rate constants for cesium ion and atom desorption on iridium with graphite islands: parallel processes studied by field reversal Tony Hansson, Jan B.C. Pettersson and Leif Holmlid Department of Physical Chemistry GU, University of Gb'teborg and Chalmers University of Technology, S-412 96 GOteborg, Sweden

Received 9 November 1990; accepted for publication 20 February 1991

The desorption of Cs as ions and neutrals from Ir polycrystalline surfaces is studied by the field reversal kinetics method, which involves molecular beam techniques in an UHV environment. The electric field outside the surface under study is switched rapidly between accelerating and retarding field. The surface temperatures studied lie between 1100 and 1900 K. The shortest ionic desorption time constant measured in this study is 300 ns, and the longest neutral time constant is 0.5 s. Two neutral desorption channels and two ionic channels are observed in the temperature dependence of the desorption rate constants. The results agree with a model where graphite islands with a total coverage of less than 10 -2 exist on the surface. The desorption energy of Cs + on Ir is 2.10 5:0.05 eV, in excellent agreement with previous low-temperature results by Zandberg et aL On graphite, the desorption energy for Cs + is 2.67 + 0.11 eV, which agrees very well with the previous results from our group. The two neutral desorption energies, which both correspond to desorption via the graphite islands, are found to be 3.10 + 0.35 and 2.38 + 0.10 eV. A barrier of approximately 0.7 eV for transport from the iridium surface to the graphite islands is also found.

Surface Science 253 (1991) 353-364 353 North-Holland

Reconstruction of STM and AFM images distorted by finite-size tips David Keller Department of Chemistry, University of New Mexico, Albuquerque, NM 87131, USA

Received 11 October 1990; accepted for publication 5 February 1991

A local, nonlinear transform is derived that allows an STM or A F M image which has been distorted by a nonideal tip to be reconstructed. The image reconstruction transform is related to the Legendre transforms of the distorted image surface and the tip surface. Two sunple examples are solved analytically. It is shown that the local curvature of the true, undistorted sampl e surface is the sum of the curvatures of the tip and the distorted inmge surface. Some distorted images are, strictly ~ n g , not invertible, that is, cannot be completed reconstructed. The reason for this is discussed, and it is shown that in these cases the transform correctly reconstructs the parts of the ~ that are invmrfible, and leaves "holes" whenever a noninvertible section of an image is encountered. Numerical calculations are premmted in which s e r i a l a r t i ~ y generated images and One e x p e r i m e n ~ o b ~ n e d STM image of a photoresist grating are reconstructed.