Surface atomic structure determination of three-dimensional yttrium silicide epitaxially grown on Si(111)

Abstract

The surface atomic structure of thin layers of three-dimensional yttrium silicide epitaxially grown on Si͑111͒ 7 ϫ 7 has been investigated by means of dynamical low-energy electron diffraction analysis. We determine the interlayer distances as well as the lateral and/or vertical relaxations of the atoms in the superficial planes. The epitaxial silicide consists of stacked hexagonal rare-earth planes and graphitelike Si planes with an ordered arrangement of Si vacancies. The ordered net of Si vacancies in the inner planes is responsible for the lateral relaxations of the surrounding Si atoms. The topmost layer does not present a graphitelike structure, forming a buckled Si layer with no vacancies. One of the three Si atoms in the lower plane of this bilayer is closer to the yttrium layer due to the presence of the vacancy in the last Si plane just below. This produces vertical relaxation in the termination layer.

First principles total energy calculations of the surface atomic structure of yttrium disilicide on Si(111)

“…[24]. Our result is in good agreement with the LEED result of Rogero et al [25] of the YSi 1.7 /Si(1 1 1) system. We find a difference in the vertical positions of 0.14 Å between the Si down atom on top of a vacancy with respect to the other down atoms (a similar result was found in Ref.…”

“…Our total energy calculations favored the model of Martin-Gago et al [16,17] as the most stable atomic geometry. We shall mention that this model has been corroborated by LEED experiments on YSi 1.7 / Si(1 1 1)-( ffiffi ffi 3 p  ffiffi ffi 3 p ) [25]. First principles total energy also found a similar structure for the clean YSi 2 surface [24].…”

“…At higher YSi coverage the reconstruction is of ð ffiffi ffi 3 p  ffiffi ffi 3 p ÞR30 0 periodicity and a three-dimensional metallic silicide is obtained. Very recently a detailed surface structural study of the three-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was done [25] using dynamical low energy electron diffraction (LEED). Accurate values were found of the atomic positions in the last surface planes.…”

Subsurface structure of epitaxial rare-earth silicides imaged by STM

“…10,11 As a result of the periodic arrangement of the vacancies, a ͑ ͱ 3 ϫ ͱ 3͒R30 ‫ؠ‬ pattern appears in low-and high-energy electron diffraction ͑LEED and HEED͒. 7,12,13 However, and in spite of their technological relevance, the surface structure of the RE silicides is still an open issue. Although it is well accepted that these surfaces are terminated in a bulklike Si bilayer without vacancies, 14 two different structural models have been proposed based on two independent STM studies on the ErSi 1.7 surface epitaxially grown on Si͑111͒.…”

“…11 In a LEED study Rogero et al attained a good agreement with experiment for the p3m case. 12 On the other hand, Duverger et al 17 were able to reproduce theoretically the p6-type images, although hardly any reference was made to the p3m phase.…”