THEORY OF SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY ON SI(100) RECONSTRUCTED SURFACES

A method for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) is proposed, which is effective at realistic tip-to-surface distances of 5-10 angstrom, and its application is reported for Si(100) reconstructed surfaces. The vacuum tails of wave functions cannot be accurately described either by linear combination of atomic orbitals or by pure plane-wave expansion. An attempt is made to effectively describe the tail parts by combining this method with realistic calculations of the sample surface electronic states. The method is applied to Si(100) reconstructed surfaces and the features of the STM images and STS spectra of 2 X 1 dimer structures are clarified. This method confirms that the experimental c(4 X 2) image of STM is actually obtained from the c (4 X 2) structure and reveals how the buckling of dimers is reflected on the STM image.