AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA1
A Novel Real-time Technique for Monitoring Adatom Surface Diffusion and Island Nucleation

Thursday, November 5, 1998, 2:00 pm, Room 308

Session: Surface Diffusion
Presenter: P.M. DeLuca, Northwestern University
Authors: P.M. DeLuca, Northwestern University
S.A. Barnett, Northwestern University
Correspondent: Click to Email
The surface diffusion coefficient of Ga adatoms, along with two-dimensional (2D) island nucleation and coarsening were measured in real-time on vicinal GaAs(001) 2x4 surfaces using specular ion current measurements (SICM). In this new technique, 3 keV Ar ions were incident upon the surface at a glancing angle (typically 1° to 3°), and the specularly scattered ion current measured. Since specular scattering requires a locally-flat surface, surface defects cause a decrease in the scattered ion current, providing a measure of average adatom and/or step-edge density. The time dependence of the Ga adatom population was measured during and after the deposition of 0.1 monolayers of Ga on vicinal GaAs(001)2x4. The scattered ion current dropped with an exponential dependence upon opening the Ga shutter and increased exponentially upon closing the shutter, in good agreement with a simple model for adatom diffusion across terraces to step edges. Diffusion coefficients, D, were obtained using the measured adatom lifetimes,@tau@, and the 70Å terrace width, x, (the miscut was 2.3 ° towards (1 1 0)) in the expression D=x2/@pi@ 2 @tau@, yielding D=(8.89x10-10 cm@super 2@/sec) exp (0.74/kT) for an As@sub 4@ ambient over the temperature range 450 to 570°C. For larger Ga coverages and/or lower substrate temperatures, deviations from simple exponentials and much longer time constants were observed, suggesting that 2D islands had nucleated. The island nucleation and coarsening behaviors will be described.