Strong quantum size effects in transition metal silicide ultrathin films: Critical role of Fermi surface nesting

Abstract

Using first-principles calculations based on density functional theory, the quantum size effects (QSEs) of CoSi2 ultrathin films with different thickness have been studied. Our results confirm that both the stability and the interlayer relaxation of CoSi2(111) films oscillate in a tri-trilayers by tri-trilayers mode, with a beating period of 16 trilayers. We also predict that the stability of CoSi2(100) films oscillate in a bi-bilayers by bi-bilayers mode, with a beating period of 9 bilayers. Such thickness-depend oscillation of stability and relaxation can be attributed to the QSEs associated with the very flat Fermi surface along the growth direction, resulting in a strong nesting of Fermi sheet. The match of the calculated Fermi wave length and the interlayer space explains the oscillation period well, and the beating period could also be deduced from the electronic structure. Our theoretical research uncovers the underlying mechanisms of the electronic growth of transition metal silicides films reported in the previous experimental work.