Makiko Kohno

Dynamic observation of silicon homoepitaxial growth by high‐temperature scanning tunneling microscopy

The dynamic process of Si crystal growth on a Si(111)7×7 surface was studied in situ using high‐temperature scanning tunneling microscopy. Si was evaporated onto a Si(111)7×7 surface, kept at 350 °C, and the crystal growth was observed. Both step‐flow growth and island growth were observed. In the step‐flow growth, the [112] steps became jagged with [2] steps. At the [112] steps, new adatoms appeared in rows along the step edges. In the island growth, the multilayer growth was observed. A rearrangement of adatoms in the first layer was observed when the second layer was formed on the first layer.

Initial stage of oxygen adsorption onto a Si(111=-7×7 surface studied by scanning tunneling microscopy

The initial stage of oxygen adsorption onto a Si(111)-7×7 surface has been studied at room temperature by scanning tunneling microscopy. The surface was exposed to oxygen under a partial pressure of 1×10-9 Torr. Initial exposure led to bright and dark features at adatom sites. This dark feature, which was previously reported as a main channel for oxidation, only appeared in the faulted half of the dimer adatom stacking-fault (DAS) structure. The images suggest that the adsorption onto the un-faulted half starts after the faulted half are occupied with oxygen atoms. This clearly indicates that oxygen adsorption occurs at adatom sites with higher energy states.

Initial stages of oxygen adsorption onto a Si(111)-7×7 surface studied by STM

Abstract The initial stage of oxygen adsorption onto a Si(111)-7×7 surface has been studied by scanning tunneling microscopy. The substrate was exposed to oxygen under a partial pressure of 1× 10−9 Torr at room temperature during the observation. Dark features, which have been reported as a main channel for oxidation, appeared exclusively in the faulted halves of the DAS structure though bright features appeared in both halves. This difference can be explained by the adsorption site of oxygen. That is, the greater energy difference of the dangling-bonds of adatoms between both halves than that of the back-bonds causes the exclusive appearance of the dark feature, which has an oxygen atom on on-top site in addition to the other in the back-bond.

Cu film growth on a Si(111) surface studied by scanning tunneling microscopy

We observed a change in growth mode of Cu, while dynamically observing Cu film growth on a Si(111)-7 x 7 surface during Cu deposition at room temperature by scanning tunneling microscopy (STM). Initially, Cu atoms were adsorbed mostly on the faulted halves of the 7 x 7 structure. Then, up to about 2 ML coverage, small Cu islands appeared. As the coverage increased from 2 to 3 ML, the growth mode changed into quasi-layer-by-layer growth. With further deposition, 3-D islands having hexagonal terraces grew.

STM modification of MoS2 in the nanometer-scale using a gas—solid reaction

Abstract We report on the nanometer-scale modification of a MoS 2 surface by scanning tunneling microscopy (STM) with an electric field lower than that required for field evaporation by STM. It is known that a Pt−Ir STM tip dissolves H 2 gas into atomic hydrogen which is chemically active. We applied this phenomenon to STM modification to lower the electric field necessary for atom detachment. A Pt−Ir lip was used to dissolve the H 2 gas on the MoS 2 surface. The gas-solid reaction enhanced the evaporation of the top-layer sulfur atoms, which were removed at a low electric field of about 2.4 V nm −1 . The present study shows that we can control STM modification well with the same feedback loop as that used for STM observation.