T. Ichinokawa

Electronic states of monolayer graphite formed on TiC(111) surface

Abstract Electronic states of a monolayer graphite formed on TiC(111) surface have been investigated by means of XPS, UPS, and work-function measurement. The chemical shift of C1s peaks in XPS spectra has inhibited a large electron transfer from the substrate to the monolayer graphite. On the other hand, the band structure of the graphite overlayer has altered from that of bulk graphite. The work-function measurement has suggested an electron redistribution in the graphite layer. These results indicate that the electronic states of the graphite monolayer are modified not by the charge transfer, but mainly by the orbital hybridization between the graphite monolayer and the substrate, which differs from graphite intercalation compounds.

UHV-SEM observations of cleaning process and step formation on silicon (111) surfaces by annealing

Abstract The cleaning process and step formation by high temperature annealing up to 1250°C on the Si(111) surface are observed by an ultra-high-vacuum scanning electron microscope (UHV-SEM). The clean surface is composed of alternate planes of terraces and step bands with widths of several μm and 1 μm, respectively, in the 〈112〉 direction. Both planes are inclined by about 10° to each other. The surface steps are not only monolayer steps, but also higher steps comprising several monolayers. Monolayer steps join to form a high step, and 70–80 steps of several monolayers high form a step band by bunching in an average distance of several hundred A toward the 〈110〉 direction. The step structure depends on the annealing temperature and on the angle at which the cutting plane is off from the exact 〈111〉 orientation. In several studies of high energy reflection electron microscopy under small grazing angle incidence monolayer steps were observed on the terrace, but no rough structures like the step bands and high steps could be discerned. The step structure observed by the present experiment is compared with those observed by previous workers.

Si(100)2 × n structures induced by Ni contamination

It has been reported that phases of 2 × n structures (6<n<10) are formed on a clean surface of Si(100) by quenching at temperatures higher than 800°C. These phases have been explained by ordered structures of an excess of missing-dimer defects. In the present experiment, it is found that the Si(100)2 × n structures are induced by Ni contamination in the range between 0.35 and 0.95% of the Auger electron peak ratio, Ni LMM/Si LVV. Appearance of the 2 × n structures and the variation of n are closely correlated with the surface Ni concentration which depends on quenching temperature and cooling rate. By intensity analysis of LEED patterns, it is concluded that the 2 × n structures are ordered phases of missing-dimer defects induced by Ni contamination which is supposed to influence the ordering of missing-dimer defects.

Surface structures of Si(100)-Al phases

Abstract The surface structures of Si(100)-Al phases of coverages less than one monolayer were studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). 2 × 2, 2 × 3, 4 × 5, 1 × 7 and c (4 × 12) structures appeared depending on the coverage and substrate temperature during deposition. On the basis of the similarity of their LEED patterns in Si(100)-column-III systems (Al, Ga and In) and the fine structures of the surface states measured by AES in the present experiment, the structure models of Si (100)2 × 2-Al and 2 × 3-Al are presented.

Formation and atomic configuration of Si(100)c(4 × 4) structure

Abstract It was reported that the Si(100)c(4 × 4) structure appears rarely during heat treatments of surface cleaning in ultra-high vacuum. In the present experiment, the c(4 × 4) structure is formed reproducibly by special surface processing at a hydrogen exposure higher than 10 −2 L (10 −6 Torr·.s) and afterwards annealing at 570–690 °C. The high hydrogen exposure produces missing-dimer defects by vaporization of volatile silane and subsequent annealing causes order of missing-dimer defects. By intensity analysis of low energy electron diffraction patterns of c(4 × 4) and the hydrogenated surface c(4 × 4)-H. it is concluded that c(4 × 4) is one of the ordered structures with missing-dimer defects formed on the basic 2 × 1 structure.

Scanning tunneling microscope combined with scanning electron microscope

Abstract A scanning tunneling microscope (STM) has been installed in a usual scanning electron microscope (SEM) with a vacuum of 10−6 Torr. The STM image is displayed on the cathode ray tube of the SEM, 512 × 512 pixels, with a scanning rate of 80 s/picture. The spatial resolution of the STM is about 1 A, while that of the SEM is several tens of angstroms. The combined scanning microscope covers a wide magnification range from 10 to 107, where STM covers the high magnification region from 105 to 107.

Reconstructions and growth of Ag on Si(001)(2 × 1)

Abstract Complex growth and reconstructions of Ag on Si(001)(2 × 1) were studied by STM, LEED, AES and SEM. We find that Ag is first adsorbed at the silicon SB step edge and preferentially forms dimers on the Si terraces. At room temperature Ag grows in a pseudo Stranski-Krastanov (SK) mode. The first layer is not homogeneous and does not cover the substrate completely. In this layer several different structures coexist (e.g. (2 × 2), c(4 × 2), depending on the Ag induced buckling of the Si dimer rows). During the formation of the inhomogeneous layer, three-dimensional islands grow with the orientation Ag(111)//Si(001). At a substrate temperature of 770 K real SK growth is observed and the first layer is homogeneous. This layer has a (2 × 3) structure. On the top of this (2 × 3) layer, Ag islands grow with Ag(001)//Si(001).

Electronic structure of monolayer graphite on some transition metal carbide surfaces

Abstract It has been revealed that monolayer graphite on the (111) surfaces of transition-metal carbides differs substantially from bulk graphite in the lattice constant and the phonon dispersion, while those of monolayer graphite on the (100) surfaces are hardly modified. In this work, the electronic structure of monolayer graphite formed on TiC(111), (100), and TaC(100) surfaces has been investigated by XPS, UPS, and EELS. From the results of XPS and UPS, we have concluded that these large changes are caused not by charge transfer but mainly by orbital hybridization between the graphite overlayer and the (111) surface. This is in contrast to the case of graphite intercalation compounds. By angle-resolved EELS, in addition, we have clearly detected a two-dimensional character of the plasmons in monolayer graphite.

Contrast mechanisms in scanning ion microscope imaging for metals

The contrast of the secondary electron images in scanning ion microscopy (SIM) is compared with that in scanning electron microscopy (SEM) with ultrahigh vacuum for Al, Cu, Ag, and Au metals deposited on the Si(100) clean surface. The order of the secondary electron yields as a function of the atomic number (Z2) for ion bombardment is opposite to that for electron bombardment. The brightness of the secondary electron images observed by a focused Ga+ ion beam at 30 keV decreases with increasing Z2, while that by the electron beam increases with Z2. On the other hand, the order of the total secondary ion yields in SIM increases with Z2. The secondary electron image observed by a focused Ar+-ion beam at 3 keV shows the similar contrast to that of the Ga+-ion beam. The different Z2 dependence of the secondary electron yields between SEM and SIM was quantitatively confirmed by the total secondary electron spectra and is discussed based on the range profile below the surface, and it is concluded that the decrea...

Low energy scanning electron microscopy combined with low energy electron diffraction

Abstract An ultra-high-vacuum (UHV) scanning-electron microscope (SEM) with a field-emission gun (FEG) is operated in a low energy region from 100 eV to 3 keV. The functions of scanning low energy electron diffraction microscopy and scanning Auger microscopy have been implemented and their performance is demonstrated. Observations in the SEM mode, the low energy electron diffraction (LEED) mode and the Auger mode have been made on the following examples: the step structure of the clean Si(111) surface, the structure of islands and their movement on the Au evaporated surface of Si(111), different orientations of grains on the polycrystalline Si surface and the coexistence of different super-structures on the Au-evaporated surface of Si(111).