Abstract
We identify the SiCl3 bonding geometry as the most desorption-active site in x-ray photon-stimulated desorption (XPSD) of positive chlorine ions from chlorinated Si(1 1 1) surfaces due to their much higher desorption cross-section in comparison to the on-top majority site. The novel combination of x-ray standing waves (XSW), XPSD and density functional theory (DFT) allows to quantitatively determine this trichloride adsorption geometry with high spatial resolution and to deduce the site-specific desorption cross-sections for Cl+ and Cl2+ ions, respectively. Additionally, these SiCl3 groups are shown to exhibit a preferential crystallographic orientation which is confirmed by both XSW and DFT. Moreover, the analoguous identification of desorption-active SiBr3 species for Br/Si(1 1 1) suggests a common physical origin of the site-specific desorption cross-sections.
Highlights
MC1 θ sample incident beam intensity monitor measurements at the undulator beamline BW1 at HASYLAB/DESY
The in situ preparation of the samples, which was routinely monitored by low-energy electron diffraction (LEED) and photoelectron spectroscopy, proceeded in the following way: Cl/Si(111)-(1 × 1) surfaces were obtained by Cl deposition onto Si(111)-(7 × 7) substrates either at room temperature followed by subsequent annealing at 580◦C for 30 s or longer [6] or by Cl2 saturation exposure at 600◦C and 2 min annealing, respectively
Before we turn to the analysis of the surface structure and to the topic of PSD, we introduce the Cl/Si(1 1 1) system by means of scanning tunnelling microscopy (STM)
Summary
The XSW–PSD experiments were performed under ultra-high-vacuum conditions (p ≈ 1 × 10−10 mbar) at the undulator beamline BW1 at the Hamburg Synchrotron Radiation Laboratory. The in situ preparation of the samples, which was routinely monitored by low-energy electron diffraction (LEED) and photoelectron spectroscopy, proceeded in the following way: Cl/Si(111)-(1 × 1) surfaces were obtained by Cl deposition onto Si(111)-(7 × 7) substrates either at room temperature followed by subsequent annealing at 580◦C for 30 s or longer [6] or by Cl2 saturation exposure at 600◦C and 2 min annealing, respectively Both procedures lead to a change from a sharp (7 × 7) to another sharp (1 × 1) LEED pattern, and no difference between the XSW results for either type of preparation was found
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