Toshihiko Kataoka

Observation of nanostructure by scanning near-field optical microscope with small sphere probe

Abstract Step and terrace structure has been observed in an area of 1 μm × 1 μm on the cleaved surface of KCl–KBr solid-solution single crystal by scanning near-field optical microscope (SNOM) with a small sphere probe of 500 nm diameter. Lateral spatial resolution of the SNOM system was estimated to be 20 nm from the observation of step width and the scanning-step interval. Vertical spatial resolution was estimated to be 5–2 nm from the observation of step height and noise level of photomultiplier tube (PMT). With applying a dielectric dipole radiation model to the probe surface, the reason why such a high spatial resolution was obtained in spite of the 500 nm sphere probe, was understood as the effect of the near-field term appeared in the radiation field equations.

Yield Strength and Dislocation Mobility of KCl-KBr Solid Solution Single Crystals

The concentration and strain rate dependence of the critical shear stress in KCl–KBr solid solutions was measured by compression tests. These data were compared with the stress dependence of the dislocation velocity measured by an etch pit technique. Edge dislocation moved slower than screw dislocation at the same stress level. The critical stress was determined by the edge dislocation mobility, and the mobile dislocation density at yielding was about 1.2×1011 m-2 for the three kinds of composition tested. An analytical model of the hardening mechanism is proposed on the basis of the elastic interaction (size misfit) between an edge dislocation and solute atoms. When compared with experimental results, this model gives satisfactory results not only for KCl–KBr but also for NaCl–NaBr, and NaBr–KBr solid solutions.

Atomically resolved scanning tunneling microscopy of hydrogen-terminated Si(001) surfaces after HF cleaning

Atomic structures of hydrogen-terminated Si(001) surfaces after HF cleaning are investigated by scanning tunneling microscopy. It is revealed that the surface is macroscopically rough but is composed of terraces and steps. Inside a terrace, 1×1 structures are formed. This corresponds to the ideal 1×1 dihydride structure. The step edges run along the 〈110〉 direction. On the other hand, the 1×1 dihydride structure disappears when the surface is subsequently rinsed with ultrapure water, because every other dihydride row of the ideal 1×1 structure is preferentially etched in ultrapure water.

Atomic structures of hydrogen-terminated Si(001) surfaces after wet cleaning by scanning tunneling microscopy

Scanning tunneling microscopy observations are performed on a H-terminated Si(001) surface treated with HF solutions and ultrapure water with very low dissolved oxygen and total organic carbon contents. Over a large area, row structures are observed in [110] and [110] directions. Pyramidal-shaped etch pits are also observed, which are caused by anisotropic etching by OH ions. Detailed images clearly show 2×1 periodic structures. It is suggested that every other row of the ideally dihydride 1×1 surface is etched preferentially by OH ions. This explains the mechanism by which the smallest etch pits are formed.

Plasma CVM (Chemical Vaporization Machining) : An Ultra Precision Machining Technique Using High-pressure Reactive Plasma

Conventional machining processes, such as turning, grinding, or lapping, are still applied for many materials including functional ones. But these processes give rise to deformed layers which means that the machined surfaces cannot perform original functions. In order to avoid this, plasma CVM has been developed. Plasma CVM is a chemical machining method utilizing radical reaction. In plasma CVM, high density radicals are generated in plasma under atmospheric pressure, so that the removal rate is very high (>or=200 mu m min-1 for Si) and is equivalent to mechanical machining methods. In this paper, basic concepts and some applications of plasma CVM will be introduced.

Atomic image of hydrogen-terminated Si(001) surfaces after wet cleaning and its first-principles study

Atomic arrangements of the hydrogen-terminated Si(001) surface after wet cleaning are investigated by scanning tunneling microscopy and by first-principles calculations. The hydrogen-terminated Si(001) surface after dilute HF cleaning is atomically rough with a structure of terraces and steps. In addition, it is confirmed that 1×1 dihydride structures are formed inside the terraces. First-principles calculations reveal that the maxima of the local density of states string parallel to the Si–H direction on the 1×1 dihydride structure, which makes it possible to determine the atomic arrangement of the observed atomic images. When the surface after HF cleaning is subsequently rinsed with ultrapure water, rows emerge along the 〈110〉 direction. Atomic images show that the rows are mainly formed by a 2×1 unit cell. To elucidate the atomic structure of the 2×1 unit cell, it is proposed that every other row of the ideal 1×1 dihydride surface is preferentially etched with ultrapure water. Total energy calculations...

Solution Hardening and Softening in KCl–KBr Single Crystals at Low Temperatures

The temperature and concentration dependence of the critical resolved shear stress (CRSS) for KCl and KCl–KBr solid solutions was measured from 4.2 K to 293 K. At lower temperatures the solid solutions with the concentration below 10 mol% KBr and above 90 mol% KBr showed solution softening. The other concentrations of solid solutions were hardened at all temperatures tested. The concentration dependence of the CRSS was given by a c(1-c) relation except for the case of lower concentrations at lower temperatures. The activation free energy of deformation varied linearly with temperature and independently of the concentration. It was concluded from the analysis of the activation volume that the dislocation motion in the higher concentration region was impeded only by the solute ions, and that in the lower concentration region by the Peierls barriers in addition to the solute ions.

Development of a scanning near-field optical microscope with a probe consisting of a small spherical protrusion

Abstract The probe of the scanning near-field optical microscope (SNOM) is a dielectric sphere 500 nm in diameter on a transparent substrate. The probe sphere is illuminated by evanescent waves which are formed by the incidence of a HeNe laser with the wavelength of 632.8 nm under the condition of total internal reflection. The light from the probe is collected by a conventional microscope through the substrate. The detected light intensity varies markedly when a sample is brought into the near-field around the probe. The variation of the detected light intensity in the near-field depends on the complex index of refraction of samples; the smaller the real part of the refractive index, the more marked the increase of the detected light intensity. This result is explained through the use of an electric dipole model for the electromagnetic interaction between the probe and sample. The vertical and lateral resolutions of about 1 nm and 10 nm, respectively, are obtained for a standard sample which is prepared by vacuum evaporation of metal.

Scanning tunneling microscopy study of hydrogen-terminated Si(001) surfaces after wet cleaning

Abstract A scanning tunneling microscopy (STM) study of the atomic structure of hydrogen-terminated Si(001) surfaces after wet cleaning is presented. Surface morphologies strongly depend on wet cleaning procedures. After being dipped into dilute HF solution, the surface is constructed by piling round, small terraces along the 〈110〉 direction. On the other hand, atomic rows along the 〈110〉 direction are clearly observed when the surface is subsequently rinsed by ultrapure water, and the corrugation pattern is identified as a 2×1 structure. With STM and Fourier-transform infrared attenuated total reflection (FTIR–ATR) observations, it is proposed that etching with ultrapure water proceeds in two steps. First, atomic steps perpendicular to dihydride rows of the upper layer are etched quickly to form step edges parallel to the dihydride rows and to produce large terraces with fewer steps. Second, etching occurs inside a terrace. Every other row of an ideally 1×1 dihydride terrace is removed preferentially in ultrapure water.

Direct observation of glide dislocations in a KCl crystal by the light scattering method

The edge‐like dislocations in a KCl single crystal produced by plastic deformation have been observed successfully by a 90° angle light scattering method using a scanning type microscope constructed with a high‐power Ar‐ion laser (2 W for a wavelength of 514 nm) and a conventional optical microscope. The image of glide dislocations was very sharp and uniform compared with that of grown‐in dislocations. The orientation dependence of light scattering agreed with Moriya–Ogawa’s theory [Philos. Mag. A 41, 191 (1980)].