Tokumoto Group

Measurement and Control of Atomic Level Structures by Mechanical Probe

Hiroshi Tokumoto

We develop the scanning probe techniques for observation and manipulation of atoms and molecules on solid surfaces and then explore new nanoscale structures showing new physical phenomena. For this purpose, we utilize several physical and chemical interactions such as tunneling current, atomic force, magnetic force, chemical force, electric field and tunneling photon, which are combined with, for example, laser light, microwave and electron beams. After collecting various information simultaneously on an atomic or molecular resolution by these techniques in air, liquid and UHV and at various temperatures, we analyze these data to understand the atomic scale surface physics and chemistry as well as to identify chemical species of atoms and molecules. Finally we try to modify the surfaces on a atomic precision to realize the desired surface properties.

■Results in Fiscal Year

1. To establish technologies for identification of atoms and molecules, we developed novel tools such as STM/AFM, X-STM (impurity), force controlled AFM (elastic), microwave STM (non-linear), SNOM combined with PL /Raman (optical), and STM combined with AP/FIM (chemical analysis). By using these techniques, numerous results have been obtained: distribution and self-organization of doped impurity in compound semiconductors, control of the local elasticity of polymers, second/third order harmonics signals from modified graphite surfaces, identification of sub-surface structure by SNOM/PL, etc.

2. To determine and control atomic/nanoscale structures of solid surfaces, semiconductor, metal, ferroelectrics, superconductor and organic films were examined and modified at atomic and molecular levels by STM/AFM. The following results were obtained: perfect Si(001) surface by HF treatment, layer-by-layer manipulation and quantum conductance of Si atomic wires, self-organized GaAs/AlAs quantum wire, step formation by nanoinden-tation on Au, self-assembled nanometer-scale wires, molecular arrangement of CuPc on H terminated Si surface, control of ferroelectric domain, microscopic analyses of polymer systems, modification of Hi-Tc superconductor surface, etc.

3. As innovative scanning probe microscope, we tried to develop magnetic force controlled AFM suitable for UHV and microwave STM. Preliminary results have been obtained. For spin-related phenomena and measurements of physical properties of nanoscale structures, we have decided to develop a low temperature UHV-STM equipped with high magnetic field (12 Tesla).

Quantum conductance of Si atomic wires formed by atomic manipulation on Si (111)

Self-assembeld nanometer-scale wires (b, c) of ODT on AlGaAs/GaAs heterostructure (a)