Tomihiro Hashizume

Scanning tunneling microscopy of III-V compound semiconductor (001) surfaces

While the (001) oriented substrate of compound semiconductors are most commonly used in fabrication of wireless and opto-electronic devices by molecular beam epitaxy, metallorganic chemical vapor deposition and related techniques, their surface structures have been puzzling from the beginning of the development of the techniques with which these materials are artificially prepared. This paper reviews the advances in comprehensive understanding of the geometric and electronic structures and chemical properties of the principal reconstructions found on the (001) surface of III-V compound semiconductors including arsenides, such as GaAs, InAs and AlAs, phosphides, such as GaP and InP, antimonides, such as GaSb, AlSb and InSb, and also nitrides (GaN), with the emphasis on the GaAs(001), during the first decade following the invention of scanning tunneling microscopy.

Scanning tunneling microscopy study of fullerenes

Scanning tunneling microscopy investigations of adsorption and film growth of various fullerenes on semiconductor and metal surfaces are reviewed. The fullerenes being studied are C60, C70, C84, Sc@C82 and Y@C82 and the substrates being used for adsorption are Si (111), Si (100), Ge (111), GaAs (110), GaAs (001), Au (111), Au (110), Au (100), Cu (111) and Ag (111) surfaces.

Field ion-scanning tunneling microscopy

Abstract A scanning tunneling microscope combined with a field ion microscope, which we call “FI-STM” has been constructed and tested successfully. The details of the principles and performance of the FI-STM are described. Several examples of its applications for Si (111) and Si (100) surfaces are presented as illustrations of the power of the instrument.

Field ion-scanning tunneling microscopy study of C60 on the Si(100) surface

Field ion-scanning tunneling microscopy was employed to study the monolayer and multilayer adsorption behaviors of the C60 fullerene on the Si(100)2×1 surface. The C60 molecules reside stably in the trough at room temperature without rotation, encompassing the 8 neighbouring dimer-forming surface Si atoms with the nearest neighbour distance of 12 A. For the first and second layers, only local ordering of square and quasi-hexagonal patterns was observed. The orderly Stranski-Krastanov mode island formation with the hexagonal packing was observed above the third layer with its lattice constant of 10.4 A.

Interaction of Ga Adsorbates with Dangling Bonds on the Hydrogen Terminated Si(100) Surface

Adsorption of Ga on the hydrogen terminated Si(100)–2×1–H surface has been investigated by scanning tunneling microscopy (STM). We have found that the thermally deposited Ga atoms preferentially adsorb on the hydrogen-missing dangling bonds and on the surface impurities. We desorb hydrogen atoms by the STM current and fabricate atomic-scale dangling-bond wires, in the similar way as was reported by Lyding et al. [Appl. Phys. Lett. 64 (1994) 2010]. In order to fabricate more detailed dangling bond structures, several methods of manipulating (detaching, attaching and moving) the individual hydrogen atoms are tested. We are able to thermally deposit Ga atoms on a dangling-bond wire and fabricate an atomic-scale Ga wire on the Si surface.

Scanning Tunneling Microscopy of C60 on the Si(111)7?7 Surface

Adsorption of C60 molecules on the Si(111)7×7 surface was investigated using a field ion-scanning tunneling microscope. C60 adsorbs preferentially on the faulted half of the 7×7 unit and stays still without rotation at room temperature, implying the reasonably strong interaction with the Si substrate. The internal structure of individual C60 molecules can be understood if we assume that the C=C double bonds are imaged brightly. Unlike the case of its adsorption on the Si(100)2×1 surface, C60 do not form ordered mono/multi layers on the 7×7 surface.

Ordering of Ag-O chains on the Ag(110) surface

Abstract When the Ag(110) surface is exposed to O 2 at room temperature, rapid growth of a linear Ag-O compound was observed on the Ag(110) surface; the growth being parallel with the 〈001〉 direction. With increasing O 2 exposure, the Ag-O chains form various ordered arrangements on the Ag(110) surface. The surface exposed to 760 L of O 2 is covered with Ag-O chains by making (3 × 1) and (5 × 1) ordered domains, where the (5 × 1) domain is composed of an alternate arrangement of (3 × 1) and (2 × 1) structures. When the Ag(110) surface covered with Ag-O rows in the p(2 × 1) structure was heated to about 500 K in vacuum, the p(2 × 1) overlayer was rearranged to p(4 × 1) structures, where the p(4 × 1) phase is composed of four out-of-phase p(4 × 1) domains. The domain boundaries as well as the boundary of the out-of-phase p(4 × 1 ) structures took necessarily one-dimensional fluctuating structures. The models indicate the existence of energetically degenerate sites for the Ag-O rows at the boundaries, which are responsible for the fluctuation of the boundaries.

Scanning tunneling microscopy study of GaAs(001) surfaces

Abstract While GaAs(001) is the most commonly used substrate in fabrication of wireless and opto-electronic devices based on III–V compound semiconductors by molecular beam epitaxy (MBE), metallorganic chemical vapor deposition (MOCVD) and related techniques, its surface structure have been disputed since the beginning of development of the techniques. Invention of scanning tunneling microscopy (STM) has revolutionized the approach of surface/interface investigation, contributing greatly in the atomistic understanding of the GaAs surface phases. This paper reviews the STM studies of principal reconstructions, from As-rich c(4×4), 2×4, 2×6 to Ga-rich 4×2 and 4×6, found on the GaAs (001) surface. These studies, together with advanced theoretical efforts, have helped us to establish a unified structural model for various reconstructions, with which we can now explain most of the observations and long-standing controversies in atomic structures and surface stoichiometries.

Field ion‐scanning tunneling microscopy of alkali metal adsorption on the Si(100) surface

We have constructed a scanning tunneling microscope (STM) equipped with a field ion microscope (FIM), by which one can monitor and shape the STM probe tip on an atomic scale in situ in the STM chamber. Taking advantage of a well‐defined tip prepared by a FIM, we have greatly improved the stability and reproducibility of the performance of the STM. Li and K adsorption on the Si(001) 2×1 surface has been investigated by field ion‐scanning tunneling microscopy (FI‐STM). The STM images have shown that at the initial stage of adsorption, Li (K) atoms (1) adsorb on top of one of the dimer‐forming Si surface atoms and (2) stabilize the asymmetric (buckled) dimerization, and (3) form linear chains, perpendicular to the substrate 2×1 dimer rows. Our observations suggest that alkali metal adsorption on the Si(001) 2×1 surface may be significantly different from the conclusions of earlier reports.

Scanning tunneling microscopy observation of copper-phthalocyanine molecules on Si(100) and Si(111) surfaces

Abstract Molecules of Cu-phthalocyanine (CuPc) deposited on Si(100) and Si(111) surfaces have been observed by an ultra high vacuum field ion scanning tunneling microscope (FI-STM). On a Si(100) surface, STM images with four-fold symmetry are observed, which reflect the shape of the CuPc molecule. The STM pictures show that CuPc molecules are deposited with the molecular plane parallel to the substrate surface and have three kinds of adsorption configurations on the dimer-row of Si(100). The images of the CuPc are modified by the electronic state of the Si(100) surface. This behavior suggests strong interaction between the molecule and the substrate. The molecular images on the Si(111) surface have a unique bias-voltage dependence. At a sample bias of 1.6 V, the molecule looks transparent by STM, and becomes dark like a vacancy at 1.2 V. From the bias dependence, the electronic interaction between the CuPc molecule and the Si surface is discussed.