Photoelectron holography studies of Bi on Si(111)
Photoelectron holography is applied to Bi atoms adsorbed on Si(111) for a determination of the three-dimensional atomic structure. Instead of measuring the absolute intensity as a function of photon energy as is traditionally done, a differential measurement is carried out to yield the logarithmic derivative of the intensity. This leads to intensity self-normalization, and significantly improves the accuracy. The resulting images show a well-resolved trimer structure for the adsorption geometry.
New experimental technique for determining real-space atomic images applied to aluminum adsorbed on silicon (111).
The holographic principle is used to invert experimental photoelectron diffraction spectra to reveal the surface structure of Si(111)(√3×√3)-Al. A new transformation method is applied to measured scanned-photon-energy photoemission spectra. The results of each inversion are summed over the set of angles giving images which clearly show the local geometry near the emitting atom, Al. Images are also obtained by theoretical simulation and agree well with experiment. The results demonstrate the technique as a direct, model-independent structural method, yielding bond distances and directions
Cohesive energy of the two-dimensional Si(111)3 × 1 Ag and Si(111)√3-R(30°)Ag phases of the Silver (deposit)-silicon(111) (substrate) system
The growth of silver on Si(111) is reexamined and new experiments are carried out using the method of isothermal desorption spectroscopy with AES. A correlation between LEED patterns and AES data upon adsorption and desorption permits one to precise the domain of existence of both 3 × 1 and √3 phases (respectively completed at 13 and 23 of a monolayer) and therefore to draw a 2D phase diagram and propose new structural models. We extend a kinetic model proposed earlier for the case of desorption of 2D phases, to the desorption of 3D crystallites. We thus show that using a simple kinetic method, thermodynamic parameters may be directly derived, namely the cohesive energy and the vibrational frequency of each phase. The values obtained, close to the ones of bulk silver, are respectively: E = 68 kcalmole−1, ν = 2.3 × 1012s−1 for the 3 × 1 phase; E = 65 kcalmole−1, ν = 1.8 × 1012s−1 for the √3 phase; E = 67 kcalmole−1, ν = 4 × 1012s−1 for the 3D crystallites.