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Seminar

Linnaeus Physics Colloquium: Scanning tunneling microscopy and photoemission studies of Ag films on metal/semiconductor surfaces

Welcome to Linnaeus Physics Colloquium, a series of seminars delivered by renowned researchers in physics.

Title: Scanning tunneling microscopy and photoemission studies of Ag films on metal/semiconductor surfaces
Lecturer: Samuel Starfelt, Institutionen för ingenjörsvetenskap och fysik, Karlstad University
Place: Kalmar: room Ma348, building Magna. Live: https://lnu-se.zoom.us/j/416290322. Coffee and buns will be served.

The seminar is part of the activities of the Linnaeus Knowledge Environment Advanced materials.

Abstract

Metal-induced Si (and Ge)-√3×√3 surfaces offer two main benefits for growth of Ag films, compared to depositing directly on a semiconductor substrate. One advantage is the ability to grow films at room temperature, instead of using a two-step process including deposition at low temperature, which has been the standard for a long time. The other advantage is that for Si, the silver films grow as atomically uniform layers for thicknesses lower than 5 monolayers (the previous limit). For such thin films, the film/substrate interface will have a larger effect on the properties of the discrete quantum well states, which are formed by spatial confinement of electrons in the direction perpendicular to the surface. The presentation will cover both STM/STS and photoemission studies on Ag thin films on Ga, In and Sn-induced Si(111) (and Ge(111)) -√3×√3 surfaces. On the √3×√3 surfaces, the first layer of Ag forms a special interface, which facilitates layer-by-layer growth of Ag, even for thicknesses as low as 2 ML. The valence band electronic structures of the films show quantum well states, whose characteristics have been analyzed within the existing theoretical framework.

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Figure 1: STM image (empty state) of 0.5 ML of Ag on the Sn/Ge(111)-√3×√3
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Figure 2: ARPES spectra of Ag films on the Ga/Si(111) -√3×√3 surface with film thicknesses of 3,6,9,12 ML (taken with photon energy 40 eV)