A349 Surface Science 172 (1986) 509-523 North-Holland, Amsterdam 509 A SIMPLIFIED METHOD TO DETERMINE THE COVERAGE DEPENDENCE OF SURFACE DIFFUSION COEFFICIENT!3 C.H. MAK and S.M. GEORGE Department of Chemistry Stanford University, Stanford Calqomia 94305, USA Received 5 September 1985; accepted for publication 10 January 1986 A new method to determine the coverage dependence of surface diffusion coefficients from coverage-gradient experiments is presented. The initial coverage-gradient employed is an evacuated circular region surrounded by a constant coverage. In order to demonstrate this method, Fick’s second law equation was numerically solved using coverage-dependent surface diffusion coefficients. An analysis of the results demonstrates that the coverage dependence of the surface diffusion coefficient can be determined using a simple extrapolation procedure. The coverage dependence can be obtained for a wide range of functional forms for the surface diffusion coefficient. The extrapolation procedure requires only that the number of adsorbates that have diffused back into the initially evacuated region be measured as a function of time. This method should be useful in the interpretation of coverage-gradient surface diffusion experiments, especially those performed using laser-induced thermal desorption techniques. Surface Science 172 (1986) 525-532 North-Holland, Amsterdam 525 ON THE DENSITY OF SURFACE ACOUSTIC WAVES AND SURFACE TI-bZRMODYNAMICS IN A PIEZOELEtXRIC * L. FERNANDEZ ? V.R. VELASCO and F. GARCIA-MOLINER Institute de Fisica a’elEstado Sdlido, Serrano 123, E-28006 MaaX4 Spain Received 20 December 1985; accepted for publication 25 February 1986 Piexoelectricity introduces new modes and modifies part of the elastic vibrational spectrum for both bulk and surface waves. This has a direct bearance on surface thermodynamics. A simple phenomenological model is studied analytically and exactly. This bears out the basic physics involved and allows for a quick and easy estimate of the changes to be expected, which turn out to be substantial. Surface Science 172 (1986) 533-543 North-Holland, Amsterdam 533 SHLF-CONSISTENT THEORY OF WATER ADSORPTION ON METAL SURFACES E.E. MOLA *. and J.L. VICENTE Institute de Investigaciones Fisicoquimikas Tebricas y Aplicadas-INIFTA, Divisibn Quimica TebricG CaMa de Correo 16, Sucursal4, 1900 La Plato, Argentina Received 10 October 1985; accepted for publication 4 February 1986

On the density of surface acoustic waves and surface thermodynamics in a piezoelectric

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Page 1: On the density of surface acoustic waves and surface thermodynamics in a piezoelectric

A349

Surface Science 172 (1986) 509-523 North-Holland, Amsterdam

509

A SIMPLIFIED METHOD TO DETERMINE THE COVERAGE DEPENDENCE OF SURFACE DIFFUSION COEFFICIENT!3 C.H. MAK and S.M. GEORGE

Department of Chemistry Stanford University, Stanford Calqomia 94305, USA Received 5 September 1985; accepted for publication 10 January 1986

A new method to determine the coverage dependence of surface diffusion coefficients from coverage-gradient experiments is presented. The initial coverage-gradient employed is an evacuated circular region surrounded by a constant coverage. In order to demonstrate this method, Fick’s second law equation was numerically solved using coverage-dependent surface diffusion coefficients. An analysis of the results demonstrates that the coverage dependence of the surface diffusion coefficient can be determined using a simple extrapolation procedure. The coverage dependence can be obtained for a wide range of functional forms for the surface diffusion coefficient. The extrapolation procedure requires only that the number of adsorbates that have diffused back into the initially evacuated region be measured as a function of time. This method should be useful in the interpretation of coverage-gradient surface diffusion experiments, especially those performed using laser-induced thermal desorption techniques.

Surface Science 172 (1986) 525-532 North-Holland, Amsterdam

525

ON THE DENSITY OF SURFACE ACOUSTIC WAVES AND SURFACE TI-bZRMODYNAMICS IN A PIEZOELEtXRIC * L. FERNANDEZ ? V.R. VELASCO and F. GARCIA-MOLINER Institute de Fisica a’el Estado Sdlido, Serrano 123, E-28006 MaaX4 Spain

Received 20 December 1985; accepted for publication 25 February 1986

Piexoelectricity introduces new modes and modifies part of the elastic vibrational spectrum for both bulk and surface waves. This has a direct bearance on surface thermodynamics. A simple phenomenological model is studied analytically and exactly. This bears out the basic physics involved and allows for a quick and easy estimate of the changes to be expected, which turn out to be substantial.

Surface Science 172 (1986) 533-543 North-Holland, Amsterdam

533

SHLF-CONSISTENT THEORY OF WATER ADSORPTION ON METAL SURFACES E.E. MOLA *. and J.L. VICENTE Institute de Investigaciones Fisicoquimikas Tebricas y Aplicadas-INIFTA, Divisibn Quimica TebricG CaMa de Correo 16, Sucursal4, 1900 La Plato, Argentina

Received 10 October 1985; accepted for publication 4 February 1986