Approach to surface structure determination with the scanning tunneling microscope: Multiple-gap imaging and electron-scattering quantum-chemistry theory

We have successfully developed and tested a method of quantitative surface structure determination using scanning tunneling microscopy (STM). Image simulations of the c(2x2) S on Mo(100) chemisorption system were calculated as a function of surface and tip structure using electron-scattering quantum-chemistry STM theory. STM images with a wide range of tunneling gap resistance values were acquired in a ''multiple-gap'' mode which preserves information on the z separation and lateral registry between the images under different tunneling conditions. The best fit of a numerical comparison of the image simulations with experimental data simultaneously determined two structural parameters of the surface. The STM results differ from those of dynamical LEED by approximately 0.1 A, which we estimate to be the level of accuracy obtainable with the present implementation of the method