SCANNING-TUNNELING-MICROSCOPY OF HYDROGEN-TERMINATED SI(111) SURFACE

Hydrogen (H-) terminated Si surfaces were studied by scanning tunnelin g microscopy. On H-terminated Si(111) surfaces prepared by dipping int o hydrofluoric acid (HF) solutions, the surface micro-roughness was co ntrolled mainly by the pH values of the HF solutions: Rough and many a dsorbates for low pH values; smooth and few adsorbates for high pH val ues. Treatment by HF solutions with pH = 8 with initial flattening pro vided the perfect surface with no defects. Atomistic images confirmed the existence of two types of H-related structures, SiH and SiH3. On s amples prepared by exposing atomic H atoms on a clean surface in ultra high vacuum, there existed hydrogenated Si clusters (amorphous Si) on a Si(111)-1 x 1:H surface. During thermal desorption of the H atoms, t he Si clusters decomposed and there appeared a disordered phase origin ated by the migration of SiH species onto an unreconstructed Si(111)-1 x 1 surface around 490 degrees C. When the sample temperature was mai ntained at a certain level above 490 degrees C, the area of the disord ered phase decreased with time and changed into a Si(111)-root 3 x roo t 3R30 degrees structure as a result of the desorption of the H atoms. Based on these findings, we proposed a new desorption kinetics for th e H atoms.