Ichikawa Group

Observation and Formation of Atomic Scale Structure Using Beam Technology

Masakazu Ichikawa

■Object

Research objective of our group is to establish fundamental technology for formation of atomic/nano-scale structures using beam-induced surface reactions

In order to accomplish the objective, we propose the following method. In situ characterizations of structure and composition of surfaces and interfaces are performed at atomic/nano-scale by combining scanning interference electron microscopy (SIEM, a kind of electron holography) and scanning tunneling microscopy (STM). The focused beams for the characterization are also used for formation of atomic/nano-scale structures. Local area surface reactions are induced by irradiation of focused electron beams, interference fringes of the electron wave created by SIEM and by voltage application using STM. Some heterogeneous areas are produced by the surface reactions. Supply of some materials with controlled internal energy to the surface, induces growth, etching and doping on the heterogeneous area to form atomic/nano-scale structures in self-organization mechanism.

■Results in Fiscal Year

1. For the development of the formation technology of nanoscale structures, studies for nanoscale control of Ge growth and oxidation on Si(111) surfaces have been made using the combined microscope with scanning reflection electron microscope and STM (atomic manipulation microscope). Some phenomena for developing the technology have been found, such as nanoscale Ge clusters are formed only on stripes of clean Si surface in Ga adsorbed Si surface, and Si oxide films are selectively desorbed during annealing from areas on which focussed electron beams are irradiated. (Fig. 1)

2. For the development of the atomic level doping technology, in situ observation of adsorbed Ga atoms on Si(111) surface at the atomic level has been made with the high temperature STM. Some phenomena associated with local atomic level doping have been found, such as a nanoscale stripe of clean Si is created on a Ga adsorbed Si surface by a nanoscale self-organization. The self-organization is induced by only removing Ga atoms from a certain area on the whole Ga adsorbed Si surface with a STM tip. (Fig. 2)

3. For the development of the nanoscale etching technology, in situ observation of Si(111) surface during Ar ion etching has been made with scanning reflection electron microscope. Some phenomena for developing the technology have been found, such as the etching mode is changed depending on the sample temperature, and atomic step movement on the Si surface during the etching process can be controlled by making carbon lines on the atomic steps using electron beam-stimulated deposition method.(Fig. 3)

4. For the development of extremely high vacuum technology, gas flow rates have been able to be measured in 10-12 Pa range using conductance modulation method.

Fig. 1 Selective thermal desorption of SiO2 on Si(111) induced by focused electron beam.

Fig. 2 Nanoscale self-organization on Si(111) surface induced by STM tip.

Fig. 3 Etching process of Si(111) surface by Ar ion sputtering.