Kazutaka Mitsuishi

Electron-beam-induced deposition using a subnanometer-sized probe of high-energy electrons

Electron-beam-induced deposition was performed to fabricate nanostructures using a subnanometer-sized probe of high-energy electrons emitted by a 200 kV transmission electron microscope equipped with a field emission gun. We fabricated nanometer-sized dots with a diameter of less than 5 nm, controlling their position and size by the introduction of a organometallic precursor gas near the substrate surface. The relation between the size of the deposit and the deposition time was studied, and, in addition, the effect of the substrate thickness was examined.

Thickness measurements with electron energy loss spectroscopy

Measurements of thickness using electron energy loss spectroscopy (EELS) are revised. Absolute thickness values can be quickly and accurately determined with the Kramers‐Kronig sum method. The EELS data analysis is even much easier with the log‐ratio method, however, absolute calibration of this method requires knowledge of the mean free path of inelastic electron scattering λ. The latter has been measured here in a wide range of solids and a scaling law λ ∼ ρ−0.3 versus mass density ρ has been revealed. EELS measurements critically depend on the excitation and collection angles. This dependence has been studied experimentally and theoretically and an efficient model has been formulated. Microsc. Res. Tech., 2008.

High-resolution electron microscopy of detonation nanodiamond

The structure of individual nanodiamond grains produced by the detonation of carbon-based explosives has been studied with a high-vacuum aberration-corrected electron microscope. Many grains show a well-resolved cubic diamond lattice with negligible contamination, thereby demonstrating that the non-diamond shell, universally observed on nanodiamond particles, could be intrinsic to the preparation process rather than to the nanosized diamond itself. The strength of the adhesion between the nanodiamond grains, and the possibility of their patterning with sub-nanometer precision, are also demonstrated.

Micrometer-Scale Photonic Circuit Components Based on Propagation of Exciton Polaritons in Organic Dye Nanofibers

Since photonic circuits possess advantages over electronic circuits in bandwidth and resistance to electromagnetic wave interference, miniaturized photonic circuits offer promising applications in various fi elds. [ 1 ] However, the diffraction limit of light restricts the degree to which conventional optical waveguide circuits can be miniaturized. Hence, plasmon waveguides, [ 2 , 3 ] photonic crystal waveguides, [ 4 , 5 ] and semiconductor nanofi bers [ 6 , 7 ] have been extensively developed to guide optical signals and to manipulate them below the diffraction limit. In this communication, we report a novel approach to create micrometer-scale photonic circuits by using the propagation of exciton polaritons (EPs) in organic dye nanofi bers. EPs are quasi-particles formed by strong coupling between photons and excitons. This coupling leads to a signifi cantly large refractive index of the crystal, which may allow quasi-one-dimensional structures (nanofi bers) to guide EPs and to manipulate them below the diffraction limit of light. This in turn enables one to create EP-based photonic circuits that can be highly miniaturized as compared to conventional optical waveguide circuits. Organic dye thiacyanine (TC, Figure 1 a) self-assembles into nanofi bers with lengths of up to ∼ 250 μ m in solution. [ 8–10 ]

Impact bonding and rebounding between kinetically sprayed titanium particle and steel substrate revealed by high-resolution electron microscopy

Micrometres-sized titanium particles were deposited on a steel substrate by kinetic spraying at an impact velocity of about 760 m s−1, and the bonding between titanium and steel was characterized by high-resolution electron microscopy. A thin interfacial layer composed of titanium, oxygen and iron was identified between the particle and the substrate. Moreover, although titanium particles appeared well bonded to the substrate, their central parts did partially detach. Remarkably, the detachment occurred not at the titanium/steel interface but inside the steel substrate.

Self-Assembly of Symmetric GaAs Quantum Dots on (111)A Substrates: Suppression of Fine-Structure Splitting

Great suppression of fine-structure splitting (FSS) is demonstrated in self-assembled GaAs quantum dots (QDs) grown on AlGaAs(111)A surface. Due to the three-fold rotational symmetry of the growth plane, highly symmetric excitons with significantly reduced FSS are achieved. Scanning tunneling microscopy and cross-sectional transmission microscopy demonstrate a laterally symmetric dot shape with abrupt interface. Polarized photoluminescence spectra confirm excitonic transition with FSS smaller than ~20 µeV, a substantial reduction from that of QDs grown on (100).

The growth behavior of self-standing tungsten tips fabricated by electron-beam-induced deposition using 200keV electrons

Self-standing tungsten tips were fabricated by electron-beam-induced deposition in a 200kV scanning transmission electron microscope to study their growth behavior. By increasing deposition time from 0.2to2400s, the tip growth rate decreases from 5–7nm∕s to zero and the root diameter increases from 2to60–65nm. Tips preferably grow downward at the beginning stage with a saturation length of 80–120nm. Dynamic Monte Carlo simulation was carried out, and 200keV electrons were proved to be more capable to fabricate tip with smaller lateral size and higher ratio than the 20keV electrons.

GaAs∕AlGaAs quantum dot laser fabricated on GaAs (311)A substrate by droplet epitaxy

We have demonstrated photopumped laser action of self-assembled GaAs∕AlGaAs quantum dots (QDs) grown on GaAs (311)A substrate by droplet epitaxy. Due to the short migration distance of Ga adatoms across the (311)A surface, high-density QDs were created with high uniformity. The QDs exhibited a narrow spectral band of intense photoluminescence from the QD ensemble, reflecting their small size distribution and high quality. Using the QDs on the (311)A surface as an active laser medium, we observed multimodal stimulated emissions at temperatures of up to 300K.

Mechanisms of nano-hole drilling due to nano-probe intense electron beam irradiation on a stainless steel

Holes with diameters of a few nanometers were drilled in a stainless steel foil using intense electron beams of 2.4nm nominal probe size from a field-emission electron gun in a high-resolution transmission electron microscope. Drilling experiments were carried out at regions of different foil thicknesses for different durations using three different condenser lens apertures. A better understanding of the mechanisms of nano-hole drilling by nano-probe electron beams has been achieved in this article. It was observed that the drilling process initiates from the bottom surface of a thin region while it initiates from the top surface for a thick region. It is concluded that material removal during nano-hole drilling is mainly by localized vaporization within the foil and drilling progresses through the formation of a row of interconnected nano-voids along the irradiated volume across the foil thickness.

Nanostructure characterization of tungsten-containing nanorods deposited by electron-beam-induced chemical vapour decomposition

Electron-beam-induced chemical vapour decomposition was performed in a scanning transmission electron microscope using a precursor of tungsten carbonyl (W(CO)6). The self-supporting nanorods were grown from the edges of a C film with widths that depend on the electron-beam scanning speed used in the fabrication process. The nanostructure of as-deposited nanorods has been characterized in detail using energy-dispersive X-ray spectroscopy, selected-area electron diffraction, microdiffraction and high-resolution transmission electron microscopy. A mixture of nanocrystallites and amorphous phases was observed for all beam scanning speeds used for deposition. High-resolution transmission electron microscopy demonstrated that the size of nanocrystallites in as-deposited nanorods ranges between 1.5 and 2.0 nm. The direct evidence of the presence of pure W nanocrystallites in as-deposited nanorods was revealed by microdiffraction.