Young’s modulus of crystalline C60 nanotubes studied by in situ transmission electron microscopy

Bending tests of crystalline nanotubes composed of fullerene C₆₀ molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C₆₀ nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C₆₀ nanowhiskers. The result concerning the increase in the Young’s modulus of the C₆₀ nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C₆₀ nanowhiskers.     

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.     

Structure and mechanical properties of nanocrystalline Ag/MgO composites

Nanocrystalline Ag/MgO composites were prepared by the ultrafine-powder-compaction method. The structure was investigated for the first time by high-resolution electron microscopy. Nanometre-sized Ag grains and MgO grains in the composites bonded directly without any intermediate phase layer. Certain preferred orientation relationships were observed between the Ag and MgO grains. The nanocrystalline Ag/MgO composites retained their grain size during annealing up to 873 K. Vickers microhardness measurements were performed on the as-compacted and annealed specimens. Generation and propagation of cracks were less active in the nanocrystalline Ag/MgO composites than in a single-phase nanocrystalline MgO. The Vickers microhardness of the nanocrystalline Ag/MgO composites remained up to 1073 K. Hot-pressing deformation tests showed that the nanocrystalline Ag/MgO composites deformed plastically at 1073 K.     

Electron spin resonance of thin films of organic light-emitting material tris(8-hydroxyquinoline) aluminum doped by magnesium

We have successfully observed electron spin resonance (ESR) signals of radical anions in thin films of tris(8-hydroxyquinoline) aluminum (Alq₃), a compound widely used as electron transporting and luminescent layers in organic light-emitting diodes. To obtain definitely defined radical-anion states in Alq₃, we doped Alq₃ with Mg by co-evaporating these materials. The obtained g value and peak-to-peak ESR linewidth ΔH_pp of Alq₃ radical anions are 2.0030 and 2.19 mT, respectively. Theoretical g value and hyperfine interactions were calculated by density functional theory method, which are in good agreement with the experimental results. A quantitative evaluation of doping concentration was performed. We confirmed that doped charges are localized at deep trapping sites by the lineshape analysis and temperature dependence of the ESR signals. Morphological investigation using transmission electron microscopy clarified that the co-evaporated Mg atoms form clusters.     

Synthesis of oriented bundle fibers of fullerene C70 crystal nanotubes

We synthesized oriented bundle fibers of C70 crystal nanotubes (NTs) by a liquid-liquid interfacial precipitation method. The bundle fibers were characterized by transmission electron microscopy and scanning electron microscopy. We deduced that in the formation process, bundle fibers of C70 nanowhiskers (NWs) precipitate initially, and then elution occurs in the interior region of each NW to form C70 NT bundle fibers.     

Breakdown of ballistic conduction in Single-atom-width gold wires

Single-atom-width gold wires were produced by stretching gold nanocontacts using piezomanipulation inside a high-resolution transmission electron microscope. The structure of the wires was observed in situ with simultaneous conductance measurements. The conductance of the wires depended on the length; the conductance decreased from 1G0 to 0.1G0 (G0 = 2e2/h, where e is the charge of an electron and h is Planck's constant) as the length increased from 1 atom to 7 atoms. The results show that ballistic conduction breaks down in the wires.     

Individual cathodoluminescence and photoluminescence spectroscopy of zinc oxide nanoparticles in combination with in situ transmission electron microscopy

The functions of scanning near-field optical microscopy (SNOM) were installed in high-resolution transmission electron microscopy (TEM) for cathodoluminescence spectroscopy and photoluminescence spectroscopy of individual nanostructures. Optical fiber probes used in SNOM were allowed to approach nanoparticles by piezomanipulation with simultaneous observation by TEM. As an application of this method, cathodoluminescence and photoluminescence from zinc oxide nanoparticles were measured at room temperature and 130 K. It was demonstrated that the present method directly provides the relationships between structural features of individual nanoparticles and spectra.     

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.     

Fabrication of silicon oxide nanotips by mechanical contact and elongation methods

We investigated the thinning process of silicon oxide tips by mechanical contact and elongation by in situ high-resolution transmission electron microscopy with functions of atomic force microscopy and scanning tunneling microscopy. The processing precision of thinning reached the atomic scale. However, the stability of the thinned tips determined their minimum size; the size of the produced tips was at least approximately 1 nm. We produced thin, long nanotips for optical fiber probes by this method. We also performed the aperture opening of optical fiber probes for scanning near-field optical microscopy. Scraping produced an aperture of approximately 15 nm.