Characterization of the photon-stimulated desorption of halogenated ailicon surfaces with standing X-ray wave fields / Charakterisierung der Photonen-stimulierten Desorption von halogenierten Siliziumoberflaechen mit stehenden Roentgenwellenfeldern
- Authors
- Publication Date
- Jan 01, 2004
- Source
- OpenGrey Repository
- Keywords
- Language
- German
- License
- Unknown
Abstract
The structure of the adsorbate systems Cl/Si(001), Cl/Si(113) and Cl/Si(111) have been studied using X-ray standing waves (XSW), scanning tunneling microscopy (STM) and X-ray photoemission (XPS). In addition the X-ray induced photodesorption of Cl"+ and Cl"2"+ ions from Si surfaces has been investigated in detail. Ab initio total energy calculations using density functional theory were also performed. The STM measurements revealed the surface morphology of the samples and provided information about surface roughening and etching. The symmetrical dimer model for the Cl/Si(001)-(2 x 1) system was confirmed for majority adsorption sites. In addition various defect sites including dichloride species were calculated using DFT and were found to be consistent with the XSW and XPS results. The combination of XSW with photodesorption detection revealed that direct and indirect desorption processes for Cl"+ ions occur in a 2: 1 ratio. For the Cl/Si(113) adsorbate system the experimental and theoretical results revealed a model comprised of dimers, adatoms and on-top sites (DAO-Model). The model explains the (2 x n)-reconstruction found by STM and is consistent with the XSW results. The XPS data showed that only monochloride species were present. The PSD measurements revealed predominantly direct desorption of Cl"+ and Cl"2"+ ions from majority sites. For an adsorption temperature of 600 C anisotropic surface reorganization with step edges aligned along the [1 anti 10]-direction was observed in STM. For the Cl/Si(111)-(1 x 1) surface preferential stimulated desorption of Cl"+ and Cl"2"+ species from SiCl_3 minority sites was identified from the XSW/PSD experimental data combined with an XSW simulation based on structural models from the DFT studies. The minority sites contributed about 3% to the total Cl-coverage. The site specific desorption cross sections for excitation at the Cl K-edge were 430 barn for Cl"+ ions and 73 barn for Cl"2"+ ions which are 60-80 times higher than the corresponding values for photodesorption from the on-top site. For chlorine adsorption at RT followed by annealing the STM images revealed the formation of etch pits with a depth of two atomic layers and three-fold symmetry with step edges perpendicular to < anti 1 anti 12>-directions. In contrast for chlorine adsorption at 600 C atomically smooth step edges extending over several hundred nm perpendicular to < anti 1 anti 12>-directions were observed. (orig.) / Available from TIB Hannover: RA 8919(2004-003) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / SIGLE / DE / Germany
