Showing papers by "Margrit Hanbücken published in 2002"

Preferential carbon etching by hydrogen inside hexagonal voids of 6H-SiC(0001)

Abstract: 6H-SiC(0001) samples have been etched in a hot-wall chemical vapor deposition reactor at a hydrogen pressure of 13 mbar at 1800 ° C . The surface morphology and elemental composition have been studied by scanning electron microscopy and micro-Auger analysis. Stoichiometric etching of SiC with equal atomic concentrations of Si and C is found on the flat sections of the surface, but in hexagonal voids of the SiC samples, a selective removal of C, leading to a pure Si surface at the bottom of the voids, is observed. Fast gas diffusion is the main transport mechanism for etching of the flat surface, while Knudsen diffusion becomes important inside the voids. It is proposed that the lower diffusion constant of reaction products containing Si compared to those containing C, leads to a preferential removal of C and a Si enrichment inside the voids.

Controlled tuning of periodic morphologies on vicinal Si(111) surfaces

Abstract: Regular hole patterns have been produced on vicinal Si(111) surfaces by optical lithography. Under heat treatment in ultrahigh vacuum, morphological rearrangements of the patterned surfaces occur. In situ light diffraction experiments were carried out during heat treatment to monitor the formation of the desired morphologies by an observation of the diffraction pattern. The surface morphology was characterized by different microscopy techniques after the heat treatment. Structured surfaces with periodic two-dimensional step arrangements and one-dimensional structures of atomically flat terraces uniformly separated by straight steps were obtained. The periodic structures extend over several μm.

Study by scanning tunneling microscopy of hydrogen adsorption and desorption on Si(111)7x7 at room temperature and at high temperature

Abstract: An overview is given on the use of scanning tunneling microscopy (STM) for investigation of the adsorption of hydrogen on Si(111)7×7 both at room temperature and at elevated temperature to finally obtain a hydrogen-saturated surface of Si(111). The initial stages are characterized by high reactivity of Si adatoms of the 7×7 structure. After adsorption of hydrogen on the more reactive sites in the beginning of the adsorption experiments a regular pattern, which is different for room and elevated temperature, is observed for the less reactive sites. In agreement with previous work, local 1×1 periodicity of the rest atom layer and the presence of di- and trihydride clusters is observed for hydrogen-saturated surface. STM has also been used to characterize surfaces from which the hydrogen atoms have been removed by thermal desorption. Finally, tip-induced desorption by large positive sample-bias voltages and by increasing the tunneling current will be described.