Ku-Ding Tsuei

Chemical composition on the top of a surface determined with the evolution of surface states

The epitaxial growth of Cu on Ag(111) was explored on monitoring the evolution of its surface states with angle-resolved photoemission spectroscopy; the chemical element on the top of Cu islands on Ag(111) with a (9×9) reconstruction was determined to be not Cu but Ag. Our result demonstrates a technique with which the chemical property associated with a surface state is explorable and an identification of the chemical element in the topmost layer of the surface becomes feasible.

An energy-dependent photoemission study on line-shape analysis in determining the absolute coverage of metallic thin films

Energy-dependent photoemission was measured to investigate the validity of the analysis of line shape in determining the absolute coverage of atomically flat, metallic thin films. The surface states of two Ag/Au(1u20091u20091) thin films with carefully controlled coverage of Ag were measured and analysed. Our results confirm that line-shape analysis is a valid procedure; the absolute error associated with this technique is within 0.1u2009ML, which makes the technique advantageous over other techniques to determine the film coverage. The experimental procedure in our work provides a routine to determine an appropriate photon energy for use in line-shape analysis. Our results indicate that the widely accessible He Iα line is a suitable excitation source to utilize line-shape analysis for confined states in a Ag film.

Precise determination of absolute coverage of thin films by layer-resolved surface states

We report a technique to determine the coverage of metallic thin films by analyzing layer-resolved surface states with photoemission by using atomically flat Ag∕Au(111) thin films as a test system. We analyzed the surface state on Au(111) covered with Ag up to 4 ML with atomic resolution, and precisely determined the total Ag coverage of Ag∕Au(111) through a line-shape analysis. With precise measurements of the absolute coverage of thin films becoming possible, one can calibrate the tooling factor of evaporators with unprecedented accuracy.