Role of silicon vacancies in yttrium-disilicide compounds from ab initio calculations

Abstract

The structural properties of the compound YSi 2 are investigated by means of ab initio simulations based on density-functional theory. More particularly we emphasize the role played by Si vacancies, show that the Th 3 Pd 5 structure can be deduced from the AlB 2 structure by a relaxation process around the Si vacancies within the ͑0001͒ plane. A specific ordered arrangement of the Si vacancies along the ͓0001͔ direction is found to be energetically the most favorable. Geometries obtained from our theoretical calculations are in good agreement with experimental results. ͓S0163-1829͑97͒06920-8͔

Lattice stability of Ca, Sr and Yb disilicides

“…8(b)) in which the relaxation displacement of the Si atoms surrounding a vacancy is shown. As observed also for ErSi 1.7 and YSi 1.7 [24,9] the relaxation of the internal atomic positions of the vacant hR3 supercells leads Si atoms surrounding the vacant sites to move towards them. The resulting Si planar sheet is significantly distorted compared to an ideal fully occupied honeycomb layer: the average displacement of the Si atoms is 0.19 Å .…”

“…However, the experimentally observed Si vacancies in some hR3 RESi 2 phases appear not to be randomly distributed, leading to the formation of superstructures [20,22]. The Y and Er compounds have been studied theoretically by Magaud et al [23,24], Allan et al [25] and Stauffer et al [9] and in particular, a Th 3 Pd 5 -like structure (hP8) has been found for both YSi 1.7 and ErSi 1.7 phases. The hP8 lattice is derived from the hR3 structure by losing one Si atom in each honeycomb ring such that the concentration of Si vacancies is h Si ¼ 0.1667.…”

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

“…The interfaces of RE silicides with Si(1 1 1) have very small lattice mismatches [2], sharp interfaces, and low Schottky barrier heights [3], making them ideal in devices, such as infrared detectors and rectifying contacts. Similar properties can be seen in the adsorption of silicides of transition metals such as YSi [4] and ScSi.…”

Electronic structure and Fermi surface of two-dimensional rare-earth silicides epitaxially grown on Si(111)

“…The pseudopotentials were expressly generated after relativistic atomic calculations, taking into account previous works. 5,15 For Si, we employed the usual 3s 2 3p 2 configuration with a cutoff radius of r cl ϭ1.89 a.u. for all l values ͑beyond r cl the pseudowave-functions match all the electron wave functions͒.…”

“…In the Si planes one atom out of six is missing, forming a p(ͱ3 ϫͱ3)R30°superstructure, and leading to a RESi 1.7 stoichiometry. 5,6 Most of the RE silicides present a p(1 ϫ1) 2D phase at coverages of about 1 ML. [7][8][9] In contrast to the bulk, this phase does not include Si vacancies and therefore the film presents a RESi 2 stoichiometry.…”