A. Saedi

Playing Pinball with Atoms

We demonstrate the feasibility of controlling an atomic scale mechanical device by an external electrical signal. On a germanium substrate, a switching motion of pairs of atoms is induced by electrons that are directly injected into the atoms with a scanning tunneling microscope tip. By precisely controlling the tip current and distance we make two atom pairs behave like the flippers of an atomic-sized pinball machine. This atomic scale mechanical device exhibits six different configurations.

Spatial mapping of the inverse decay length using scanning tunneling microscopy

We present a scanning tunneling spectroscopy technique that allows one to make spatial maps of the characteristic length, i.e., the inverse decay length (), in electron tunneling. The method requires that the tunneling current i and its first and second derivative with distance di/dz and d2i/dz2, respectively, are simultaneously recorded. The derivatives di/dz and d2i/dz2 are recorded using a lock-in technique. A spatial map of provides valuable information on the electronic structure of surfaces, especially in case of semiconductors, nanostructured surfaces and molecules at surfaces. We have coined this spectroscopic technique microscopy.

Hydrogen adsorption configurations on Ge(001)probed with STM

The adsorption of hydrogen on Ge(001) has been studied with scanning tunneling microscopy at 77 K. For low doses (100 L) a variety of adsorption structures has been found. We have found two different atomic configurations for the Ge-Ge-H hemihydride and a third configuration that is most likely induced by the dissociative adsorption of molecular hydrogen. The Ge-Ge-H hemihydride is either buckled antiparallel or parallel to the neighboring Ge-Ge dimers. The latter configuration has recently been predicted by M. W. Radny et al. [J. Chem. Phys. 128, 244707 (2008)], but not observed experimentally yet. Due to the presence of phasons some dimer rows appear highly dynamic.

Study of dynamic processes on semiconductor surfaces using time-resolved scanning tunneling microscopy

The time resolution of a conventional scanning tunneling microscope can be improved by many orders of magnitude by recording open feedback loop current-time traces. The enhanced time resolution comes, however, at the expense of the ability to obtain spatial information. In this paper, we first consider the Ge(111)-c(2 × 8) surface as an example of how surface dynamics can show up in conventional STM images. After a brief introduction to the time-resolved scanning tunneling microscopy technique, its capabilities will be demonstrated by addressing the dynamics of a dimer pair of a Pt modified Ge(001).