Characteristic adsorption ofXeon aSi(111)−(7×7)surface at low temperature

Abstract

Site-dependent adsorption structures of Xe atoms on a Si(111)-7ϫ7 surface were studied by scanning tunneling microscopy at 8 K. Xe atoms initially adsorb as dimers on the site between a rest atom and its two neighboring center adatoms, and then near the corner adatom site. Similar structures were formed at both the faulted half ͑FH͒ and the unfaulted half ͑UH͒ of the 7ϫ7 unit. The observed structure is in excellent agreement with that estimated by the rigid ball model, however, site-dependent bias dependence and different stabilities were observed for them, indicating the existence of different interactions between Xe and Si atoms in the 7 ϫ7 unit despite the stable electronic structure of Xe. Based on the results with thermal desorption spectroscopy, the adsorption energies are estimated to be 200 and 220 meV for FH and UH units, respectively.

Characteristic intra- and interunit interactions of Kr atoms adsorbed on theSi(111)−7×7surface

“…6 When Kr atoms that form dimers were located at the same positions as Xe atoms, i.e., in contact with a rest atom, its neighboring center adatom, and one of the Si atoms to which the center adatom is bonded, the calculated distance between the two Kr atoms is approximately 0.44 nm, which is significantly larger than the diameter of the Kr atom, 0.41 nm. This disagreement might have caused the instability of the isolated dimer adsorbate, contrary to the Xe case, which results in the growth mode based on trimer units in UH units and a completely different structure in FH units.…”

“…[1][2][3][4][5][6] For example, Xe atoms on Pt͑111͒ and Cu͑111͒ surfaces show completely different adsorption behaviors despite the similarity of the substrate geometries. The complicated interactions between rare gases can be interpreted as follows.…”

“…The I/V characteristic of STM images and the stability of Xe atoms under STM scanning also showed a considerable site dependence, which is a direct indication of the occurrence of interactions between Xe and Si substrate atoms. 6 The observed characteristic properties are difficult to explain, in consideration of the stable electronic structures of the rare gases and of the fact that they have been adopted as a model for analyzing the interaction of ideal gases even on metal surfaces.…”

“…1, these structures consist of the one dimerϩone corner Kr atom (1Dϩ1C) structural unit which is the same structure as that observed in the case of Xe. 6 However, despite the same final structure, 3Dϩ3C, the adsorption processes were different for Kr. Xe atoms first adsorb in a dimer form, resulting in the hexagonal shape formed by three dimers ͑six green circles in Fig.…”

“…1 of Ref. 6. Since the energy is not a simple additional form, a many body effect may need to be taken into account even in such a case.…”