Tokushi Kizuka

Phonon confinement effect of silicon nanowires synthesized by laser ablation

A gradual downshift and asymmetric broadening of the Si optical phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires (SiNWs) synthesized by laser ablation. This downshift and broadening can be interpreted by the phonon confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

Simultaneous Observation of Millisecond Dynamics in Atomistic Structure, Force and Conductance on the Basis of Transmission Electron Microscopy

High-resolution transmission electron microscopy (HRTEM) has been developed to possess functions of atomic force microscopy and scanning tunneling microscopy. Dynamics of subnano Newton-scale force and conductance were simultaneously observed at intervals of 1/30–1/3840 s during HRTEM imaging of contact, deformation and fracture processes between nanometer-sized tips. The experimental basis of the atomic-scale mechanics of materials was developed on the basis of the present microscopy.

Phonon confinement and self-limiting oxidation effect of silicon nanowires synthesized by laser ablation

The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.

Metal-Insulator Transition in Stable One-Dimensional Arrangements of Single Gold Atoms

The atomic arrangement and conductance during the separation process of gold point contacts were simultaneously observed in situ by high-resolution transmission electron microscopy. One-dimensional arrangements of gold single atoms, i.e., atomic wires, appeared between two tips at the point contacts. They were stable when their length was increased up to 2.6 nm. The interatomic distance of the wires was 0.25–0.31 nm. It was found that metal-insulator transition occurs in the wires.

Buckling of C60 whiskers

The authors demonstrated the mechanics of materials for crystalline whiskers composed of C60 molecules; compressive deformation of the whiskers was observed by in situ transmission electron microscopy with simultaneous force measurement by means of an optical cantilever method, as used in atomic force microscopy. In response to compression along the long axis, the whiskers bent first elastically, then buckled. A whisker with 160nm diameter fractured brittlely at a strain of 0.08. According to Euler’s formula, Young’s modulus of the whisker was estimated to be 32–54GPa, which is 160%–650% of that of C60 bulk crystals.

Selective processing of individual carbon nanotubes using dual-nanomanipulator installed in transmission electron microscope

Nanoscale processings such as deformation, cutting off, and bonding of individual carbon nanotubes (NTs) have been selectively performed using a dual-nanomanipulation system installed in a high-resolution transmission electron microscope. These processes are directly observed in situ at a lattice resolution of 0.1 nm. At high applied electric field between the NT tip and Au tip, we have found a carbon monolayer extending out from the carbon cluster which was deposited on the NT tip. The cutting off and bonding of individual NT tips can be performed by contacting the NT tips and the opposite nanometer-sized tips at an applied bias voltage. The threshold voltage of the processing is approximately 2 V.

Dynamic high-resolution electron microscopy of diffusion bonding between zinc oxide nanocrystallites at ambient temperature

Abstract The process of diffusion bonding between nanometre-sized zinc oxide crystallites in vacuum-deposited films is observed dynamically at atomic resolution by transmission electron microscopy for the first time. It is found that the nanocrystallites, having clean surfaces, bond without any solders at ambient temperature, and that neck growth proceeds instantly after contact under electron irradiation.

High-resolution electron microscopy of nanocrystalline Ni-Al alloys: instability of ordered structure and dynamic behaviour of grain boundaries

High-resolution transmission electron microscopy was performed on vacuum-deposited nanocrystalline nickel aluminide films. Several nickel aluminide ordered structures, i.e. L12(Ni3Al)-, B2(NiAl)-, D513(Ni2Al3)- and D020(NiAl3)-type structures, were observed in the deposited films. The L12 and B2 ordered structures became unstable with decreasing grain sizes. The critical grain size on transformation from the L12- and B2-type ordered structures into disordered structures was ca. 5 nm at ambient temperatures. High atomic diffusion, sufficient for grain growth, and an increase in the ordering occurred just above 400°C in the nanocrystalline Ni-Al films with L12- and B2-type structures. The diffusion bonding process, at ambient temperatures, between Ni-Al nanocrystallites with an L12-type structure was observed dynamically at atomic resolution under strong electron irradiation. It was found that the nanocrystallites rotated and slid without crack generation, and neck-growth proceeded even at ambient temperatures.

Light-emitting filaments composed of nanometer-sized carbon hollow capsules

Filaments composed of multilayered carbon hollow capsules less than 10nm in diameter have been synthesized from crystalline whiskers of fullerene C60 of submicrometer in diameter by preliminary heating at 1373K and successive impression of current. The structural, electrical and optical properties of the filaments were studied by in situ transmission electron microscopy combined with the functions of scanning probe microscopy. We found that the filaments easily emit visible light at a maximum wavelength of 700-730 nm by the application of a few volts.

Lateral Displacement of an AFM Tip Observed by In-Situ TEM/AFM Combined Microscopy: The Effect of the Friction in AFM

When the lateral displacement of an AFM tip due to friction is comparable to or larger than the scan size, for example during atomic-scale friction measurement, the interpretation of the friction image is different from the situation where the scan size is much larger than the lateral displacement of the tip and the image is a simple direct mapping of the friction value. This is because, due to the lateral displacement of the tip, the tip is not at the position where the scan indicates, as can be clearly observed by an in-situ TEM/AFM combined microscopy and atomic-scale friction analysis. This lateral displacement of the tip at the nanometer scale affects the shape of the force-distance curve. We discuss the effect of the tip lateral displacement in AFM data and its normal load dependence.