Tip and Surface Determination from Experiments and Simulations of Scanning Tunneling Micros.pdf

Tip and Surface Determination from Experiments and Simulations of Scanning Tunneling Microscopy and Spectroscopy Óscar Paz,∗ Iván Brihuega, José M. Gómez-Rodríguez, and José M. Soler† Departamento de Física de la Materia Condensada, C-III, Universidad Autónoma de Madrid, E-28049 Madrid, Spain (Dated: November 10, 2004) We present a very efficient and accurate method to simulate scanning tunneling microscopy images and spec- tra from first-principles density functional calculations. The wave-functions of the tip and sample are calculated separately on the same footing, and propagated far from the surface using the vacuum Green’s function. This allows to express the Bardeen matrix elements in terms of convolutions, and to obtain the tunneling current at all tip positions and bias voltages in a single calculation. The efficiency of the method opens the door to real time determination of both tip and surface composition and structure, by comparing experiments to simulated images for a variety of precomputed tips. Comparison with the experimental topography and spectra of the Si(111)-(7×7) surface show a much better agreement with Si than with W tips, implying that the metallic tip is terminated by silicon. PACS numbers: 68.37.Ef, 71.15.-m, 07.79.Cz, 68.35.Bs The development of scanning tunneling microscopy [1] of most experiments. (STM) and spectroscopy (STS) has provided an unprece- In this Letter we present an efficient perturbative method dented knowledge about a rich variety of surf