Title:	Electronic and atomic structure of surfaces, surface alloys and 2D materials
DNr:	LiU-2016-00020-13
Project Type:	LiU Compute
Principal Investigator:	Roger Uhrberg <roger.uhrberg@liu.se>
Affiliation:	Linköpings universitet
Duration:	2016-05-21 – 2022-06-01
Classification:	10304
Keywords:

Abstract

The project involves studies of the electronic and atomic structures of surfaces using normal angle resolved photoelectron spectroscopy (ARPES), spin-resolved ARPES, and scanning tunneling microscopy (STM). The experimental results together with theoretical methods, makes a powerful combination to derive the atomic structure from which the electronic band structure as well as STM images can be calculated. A general aim is to obtain a better understanding of basic phenomena such as surface reconstruction, phase transitions, atomic bonding, electronic structure at surfaces and interfaces, spin polarization of electron bands, surface alloying, etc. This project contains mainly three sub projects which can be viewed individually, but which are also naturally connected. We will explore the following three sub-projects, which are all of current interest in the research community. i) Binary surface alloys on semiconductor surfaces: Presently, very little is known about ordered 2D multi component alloys, which represent a novel class of 2D materials. Taking into consideration the large number of combinations of atomic species, the number of potentially interesting ordered alloys could be quite large. An example of a particularly well-defined alloy is the one atomic layer thick Sn/Ag binary alloy formed on Si(111) which exhibits a metallic surface band structure similar to that of graphene. (J.R. Osiecki, H.M. Sohail, P.E.J. Eriksson, and R.I.G. Uhrberg, PRL 109, 057601 (2012)). The aim is to identify and to thoroughly characterize ordered surface alloys with physically interesting electronic and atomic structures which could be further exploited in various applications. ii) Group IV and V surface alloys on Ag(111): Surface alloys present unique chemical and physical properties that are not observed in the bulk. For instance, Rashba type of spin splits have been observed on several 2D ordered surface alloys. In particular, Ag(111) has turned out to be an important substrate on which well-ordered surface alloys can be formed with a variety of elements. Our recent study of the Ge induced alloy reveals an unexpected striped phase which has a profound influence on the electronic structure (W. Wang, H.M. Sohail, J.R. Osiecki, and R.I.G. Uhrberg, Phys. Rev. B 89, 125410 (2014)). A thorough understanding of the striped phase requires theoretical atomic and electronic structure calculations. iii) Two-dimensional materials: Silicene and germanene are the silicon and germanium counterparts to graphene. A significant interest is now focused on silicene with the hope to find similar unique electronic properties as those of graphene. Since essentially all integrated circuits are silicon based it is urgent to explore the properties of silicene for future applications. Experimental ARPES and STM data in combination with theoretical band structures and simulated STM data make a strong combination for the determination of the atomic and electronic properties of graphene like materials. (Refs on silicene: W. Wang, W. Olovsson, and R. I. G. Uhrberg, Phys. Rev. B 92, 205427 (2015) and W. Wang, W. Olovsson, and R. I. G. Uhrberg, Phys. Rev. B 93, 081406(R) (2016))