| AVS 55th International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuP |
| Session: | Aspects of Surface Analysis Poster Session |
| Presenter: | D.-A. Luh, National Central University, Taiwan |
| Authors: | D.-A. Luh, National Central University, Taiwan C.-M. Cheng, National Synchrotron Radiation Research Center, Taiwan K.-D. Tsuei, National Synchrotron Radiation Research Center, Taiwan |
| Correspondent: | Click to Email |
An important application of nanotechnology is the construction of nanodevices for specific problems. Size is typically the parameter that engineers vary while adjusting the physical properties of nanodevices. Because of electronic confinement from the boundary, the properties of a nanostructure depend strongly on its size; this effect is called the quantum size effect (QSE), which has been reported on various physical properties. To study the QSE properly, one must determine and control the size of nanostructures with an atomic resolution. Failure to do so not only makes the analysis of the QSE less confident, but also makes the process of manufacturing nanostructures unreliable. To address this issue, we report a technique to determine film coverage precisely by analyzing layer-resolved signals in one photoemission spectrum. We demonstrate that the coverage of a metallic thin film on the (111) surface of noble metals is determined precisely on analyzing its layer-resolved confined states measured with angle-resolved photoelectron spectra. In our work, the surface state on a Ag film of 1~4 ML and the quantum well states on a Ag film of 7~13 ML on Au(111) were analyzed with atomic resolution. Through analysis of the line shape with tabulated binding energies, we determined precisely the absolute Ag coverage of a Ag/Au(111) film on analyzing a single spectrum. For this technique to work, photoemission cross sections for signals corresponding to adjacent thicknesses are assumed to be similar, and the intensities of the signals are directly proportional to the domain area of their corresponding film thicknesses. This assumption disagrees with previous authors who reported the variation of photoemission cross sections with photon energy in many systems. To investigate the prospective inconsistency, we performed energy-dependent photoemission measurements on atomically flat thin films with well-controlled coverage. Our results show that the line-shape analysis is valid with an absolute error in the measured absolute coverage within 0.1 ML for a Ag film on Au(111) when the photon energy is appropriately chosen. The experimental procedure employed in our work not only validates the line-shape analysis but also serves as a routine to determine an appropriate photon energy for the line-shape analysis. The line-shape analysis with absolute error possesses great advantages over other techniques with relative error, especially for a higher film coverage.