A low energy electron microscopy study of the growth and surface dynamics of silver/germanium(111) and gold/germanium(111).

摘要

In this dissertation, low energy electron microscopy (LEEM) has been used to study the surface phenomena of the Ag/Ge(111) and Au/Ge(111) systems that are relevant to semiconductor devices. LEEM is a unique tool for this study which is especially suited to exploring dynamic processes on surfaces.;In the second part of the dissertation, the Au/Ge(111) system is studied. Growth occurs first by an initial layer with a (√3x√3)R30° structure up to 1.0 ML, followed by the growth of 3-D islands following the Stranski-Krastanov growth mode. Heating the sample to ∼600°C, a phase transition is observed from the (√3x√3)R30° phase to a (1x1) phase. The phase transition takes place over a 2°C range and within the coexistence region small domains fluctuate between the two phases. These fluctuations are studied, and it is determined that thermal changes in adatom density could not produce the effects observed by LEEM. For coverages greater than 1.0 ML, the 3-D islands that are formed are found to be mobile at 300°C. Islands can move across the surface at up to three times their diameter in a second. Islands moving across steps cause kinks to form that point in the direction of island motion.;The first part of this dissertation discusses the growth, phase transitions, and thermal desorption of the Ag/Ge(111) system. Two main surface structures are formed for the first monolayer of adsorbed Ag: the low density (4x4) and high density (√3x√3)R30° phases. At high temperatures the growth of the (4x4) phase begins at steps due to the increased mobility of Ag adatoms and, more importantly, of Ge atoms because of faceting at the steps. The growth processes at low and high temperatures have been studied and compared, and it was found that adatom mobility plays a crucial role in the growth of Ag on Ge(111). At 575°C, the Ag begins to desorb from the surface. LEEM shows that desorption first occurs by phase transitions from the (√3x√3)R30° phase to the (4x4) phase, and then to a disordered (1x1) phase. Desorption of Ag is shown to occur from the (1x1) phase.