J. Nogami

Observation of tilt boundaries in graphite by scanning tunneling microscopy and associated multiple tip effects

Tilt boundaries have been observed on the (0001) surface of graphite by scanning tunneling microscopy (STM). Rotation angles about the c axis of 6.5°, 8°, and 19° were found, indicating no preferential orientation of grains in the basal plane of graphite. The grain boundary region between crystallites appears disordered with a width varying between 10 and 100 A. Moire patterns are observed near grain boundaries when multiple tips scanning over different grains contribute to the image simultaneously. Such images support the theory that multiple isolated tips, occasionally hundreds of angstroms apart, can contribute to STM images.

Structure of the Sb‐terminated Si(100) surface

The structure of the Sb‐terminated Si(100) surface has been studied by scanning tunneling microscopy. The images show that the surface is terminated in a symmetric Sb dimer structure. The long‐range order of the Sb‐terminated surface is broken up by a high density of antiphase domain boundaries which accounts for the low intensity of the half‐order spots in the 2×1 low‐energy electron diffraction pattern. Images on single‐domain Si(100) substrates demonstrate that the Sb grows as an additional layer of dimers, rather than substituting for the topmost layer of Si dimers.

Behavior of Ga on Si(100) as studied by scanning tunneling microscopy

The behavior of gallium on the Si(100) surface has been studied with scanning tunneling microscopy at low metal coverages. The Ga atoms are more mobile on Si(100) than on Si(111) under the same conditions. At less than 0.1 monolayer, the Ga atoms line up in rows parallel to the Si dimerization direction with a two unit cell periodicity. At higher metal densities, these rows are organized into areas of 3×2 two‐dimensional order. The relevance of these results to studies of the initial stages of growth of GaAs on Si is discussed.

Behavior of indium on the Si(111)7×7 surface at low‐metal coverage

We have used scanning tunneling microscopy to study the behavior of indium on the Si(111)7×7 surface at low‐metal coverages. At sufficiently low densities, In atoms replace Si in the 7×7 adatom positions, preserving the 7×7 structure. In this case the In atoms have a tendency to occupy positions along the edges of the unit cell rather than adjacent to the corner holes. Agglomeration of higher In densities around atomic steps can lead to local areas of √3×√3 reconstruction. Examination of a phase boundary between 7×7 and √3×√3 allows the identification of the bonding site of the In adatoms in the √3×√3 structure as the threefold symmetric site above a second layer Si atom in the surface Si double layer.

An STM study of the gallium induced 3 × 3 reconstruction of Si(111)

Abstract We present scanning tunneling microscope images that confirm a 1 3 ML adatom model for the Ga induced 3 × 3 reconstruction of Si(111). We have also identified the bonding site of the Ga adatoms in this structure as the threefold site above second layer Si atoms. The images also show the presence of defects that arise from Si adatom replacement.

Au(111) autoepitaxy studied by scanning tunneling microscopy

Abstract Using a scanning tunneling microscope in ultra-high vacuum, we have studied several stages of autoepitaxy on Au(111) from submonolayer up to twenty monolayer coverage at room temperature. The substrate, Au(111) epitaxially grown on mica, exhibits several hundred →ngstrom wide atomatically flat terraces separated by monoatomic steps. At submonolayer coverages, the gold nucleates into single layer clusters arranged preferentially in rows along 〈11 2 〉 directions. As the metal coverage increases, cluster coalescence by growth is observed. Cluster size distributions and spatial correlation functions have been extracted from the STM data. Higher layers start forming before the lower ones are completely filled. The number of incomplete layers increases with deposition rate and total thickness of the film. Room temperature diffusion smooths the terrace structure over a period of several hours. This process is observed to accelerate with a moderate anneal.

Structure of submonolayers of tin on Si(111) studied by scanning tunneling microscopy

The structure of different reconstructions of Sn on Si(111) has been studied by scanning tunneling microscopy. For less than a monolayer (ML) of Sn, three reconstructions are seen with 7×7, 7/8 × 7/8 , and 2 7/8 ×2 7/8 periodicities. The 7×7 structure is similar to that of the clean surface. The 7/8 × 7/8 phase is a (1)/(3) ML array of adatoms similar to that of Al, Ga, or In on Si(111). The 2 7/8 ×2 7/8 structure is twofold symmetric with three possible orientations on the surface giving the threefold symmetry apparent in the low‐energy electron diffraction pattern. All three surface phases coexist above 0.3 ML.

Charge density waves of 1T‐TaS2 imaged by atomic force microscopy

The layer‐structure transition‐metal dichalcogenide 1T‐TaS2 has been imaged in air at room temperature by atomic force microscopy (AFM). The images reveal both the atomic lattice and the periodic lattice distortion (PLD) associated with the charge density wave. The PLD period, orientation relative to the atomic lattice, and amplitude all agree with diffraction measurements. Under different imaging conditions the PLD can appear with a large amount of disorder or as a near‐perfect superlattice. This difference is attributed to the tip‐sample interaction. Simultaneous force and current images are shown that demonstrate the different imaging mechanisms of scanning tunneling microscopy and AFM.

Scanning Tunneling Microscopy: Instrument Design And Application In Air And Vacuum

The scanning tunneling microscope(STM) has the capability of mapping the topography of a surface with unprecedented resolution in both vertical and lateral directions. STM has been used to obtain real space images of individual atoms on a surface. In this paper we review the principles and technical aspects of STM, and give some examples of its applications both in air and vacuum. These include images of graphite, silicon, and indium on silicon. Several techniques of digital image processing developed to facilitate the analysis of STM data are also described.

Surface Order and Disorder Studied by Scanning Tunneling Microscopy

Epitaxial growth of sub-monolayer coverages of an adsorbate on a substrate produces a surface that simultaneously exhibits order and disorder on various length scales below 1000 A. We present examples of different ordering phenomena from scanning tunneling microscope (STM) studies of the growth of metals on semiconductor and metal surfaces. These results illustrate the local ordering of surface reconstructions and the effect of substrate surface reconstruction on nucleation and growth. The STM provides information about these surfaces that is largely inaccessible to other analytical techniques.