Restructuring Due to Quantum Size Effects During Annealing in Ultrathin Films of Ag/Si(111)*

Ultrathin films of silver have been epitaxially grown \textit{in situ }at low temperature and studied with scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED). Restructuring occurs during annealing to 300 K producing flat-topped islands two atomic layers in height in accordance with previous work.\footnote{Gavioli, et. al., \textit{Phys. Rev. Lett., }\textbf{82}(1) 1999, p. 129-132.} Further annealing produces a diverse distribution of heights and sizes of flat topped, vertical-sided islands. At higher coverage, a smooth films anneal to dentritic structures of a single height. A RHEED transmission pattern is formed after annealing the films and crystal orientation is determined. Finally, annealing above 550K produces typical 3D island ``wedding cake'' structures atop the $\sqrt{3} \times \sqrt{3}$ wetting layer on Si(111). These results will be discussed in an ``electronic growth'' model where Quantum Size Effects are thought to stabilize particular island heights, producing this unusual flat island growth.