Tunneling electron induced bromine hopping on Si(100)-(2 x 1)

Tunneling electrons from the tip of a scanning tunneling microscope can be used to induce adatom hopping on Br-terminated Si(100)-(2x1) at low current and without voltage pulses. Hopping does not occur when electrons tunnel from a sample to a tip. The threshold energy is +0.8 V, and tunneling spectroscopy shows antibonding Si-Br states 0.8 eV above the Fermi level. Electron capture in these states is a necessary condition for hopping, but repulsive adsorbate interactions that lower the activation barrier are also required. Such interactions are strong near saturation for Br but are insufficient when the coverage is low or when Br is replaced by Cl.     

Measurement of the energetics of metal film growth on a semiconductor: Ag/Si(100)-(2 x 1)

The first direct calorimetric measurements of the energetics of metal film growth on a semiconductor surface are presented. The heat of adsorption of Ag on Si(100)-(2 x 1) at 300 K decreases from approximately 347 to 246 kJ/mol with coverage in the first monolayer (ML) due to overlap of substrate strain from nearby Ag islands. It then rises quickly toward the bulk sublimation enthalpy (285 kJ/mol) as 3D particles grow. A wetting layer grows to 1.0 ML, but is metastable above approximately 0.55 ML and dewets when kinetics permit. This may be common when adsorbate islands induce a large strain in the substrate surface nearby.     

Vacancy dynamics and reorganization on bromine-etched Si(100)-(2 x 1) surfaces

Halogen etching of Si(100) surfaces has long been considered to involve the selective removal of atoms from an essentially static surface. Here we show that vacancy sites produced by etching are mobile at elevated temperature and rearrange to form features that were considered to be the direct products of etching. We demonstrate that the etch features observed at different temperatures are not due to different mechanisms. Rather, kinetic etch products formed at low temperatures are transformed into thermodynamically more stable features at higher temperatures.     

Dimer-anticorrelation-induced stabilization of adsorbate clustering on the Si100-(2 x 1) surface

It is well established that absorbate-absorbate interactions play a key role in determining the distribution of adsorbates on surfaces. In cases where these interactions are repulsive adsorbates frequently arrange so as to minimize these unfavorable interactions. This simple picture, however, neglects the influence of adsorption on the properties on the underlying substrate. Here, using STM, we show that on Si(100) many intrinsically repulsive adsorbates cluster to form surface patches even at low surface coverages. With the aid of density functional theory calculations and Monte Carlo simulations, we show that patch formation is an intrinsic property of the Si(100) surface that is driven by the energy lowering associated with the formation of extended regions of bare dimers. The enhanced attraction between anticorrelated tilted bare dimers is sufficient to offset the repulsions between adsorbates.