报告时间：2016年5月30日周一上午9:30
报告地点：科技创新大楼C501室
报告题目：First-principles predictions of substrate effects on silicene

Biography
Udo Schwingenschlögl is a Professor of Materials Science & Engineering at King Abdullah University of Science and Technology (KAUST), Saudi Arabia. Hepreviously worked at the International Center of Condensed Matter Physics in Brasilia, Brazil, and the University of Augsburg in Germany.

Abstract
Silicene is the Si analogue of graphene with the same honeycomb structure and linear dispersions of the π and π* bands at the K point of the Brillouin zone. It is predicted to realize a buckled structure, due to sp2-sp3 hybridization, and is compatible with the current Si-based nano-electronics. Silicene yet has not been achieved by mechanical exfoliation, because of the sp3 bonding, but can be deposited on metallic substrates such as Ag(111), Ir(111), and ZrB2(0001). Regrettably, strong interaction to these substrates destroys the Dirac physics. For this reason, semiconducting substrates including Si(111) and SiC(0001) have been explored theoretically whether they lead to a Dirac cone with reasonable band gap (which is essential for applications). However, surface passivation is inevitable for these and similar substrates, due to their dangling bonds. Layered materials such as MgBr2(0001), MoX2, and GaX2 (X = S, Se, and Te), on the other hand, preserve the characteristic electronic states of silicene and additionally simplify the preparation procedure as passivation is not required. The predicted effects of different substrates on silicene will be compared and evaluated with respect to technological requirements.
From a methodological point of view, the interlayer distance between silicene and the chosen substrate is crucial for the calculated electronic properties. However, this key quantity appears to be incorrectly described by most van der Waals density functionals. The interlayer distance in high-buckled silicene is predicted to be 3.5 Å by the vdW-DF1 functional, while the experiment finds 3.0 Å. Although a closer value of 3.1 Å is obtained by the DFT-D2 functional, the description of the charge density in this case suffers from the semi-empirical approach. Strongly deviating values of 2.93 Å and >3.1 Å are obtained for low-buckled silicene on monolayer GaS, for example, giving rise to a semiconducting and metallic nature, respectively. Though experimental results are not available, the contradictory theoretical values already reflect a limited accuracy of such calculations. For this reason, various density functionals will be compared regarding the prediction of the structural and electronic properties of silicene, using MoS2 as a template.