Mitsuru Egashira

Microcreep deformation measurements by a moire method using electron beam lithography and electron beam scan

Microcreep deformations in pure copper specimens are studied by a new moire method. In this method, a fine micrograting prepared by electron beam lithography is used as a model grating, and a scanning exposure ofthe primary electron beam in a scanning electron microscope (SEM) as a master grating. The scanning exposure of the electron beam on the specimen with the model grating produces moire fringes of bright and dark lines formed in response to the different amounts of the emitted secondary electrons for each primary electron. This new method makes it possible to obtain a clear and fine moire fringe without an image-processing system and to observe the moire fringe pattern and the SEM image at the same time. By this method, the inhomogeneous microcreep deformations such as grain boundary sliding, coarse slip, and localized strain are measured with high accuracy. It is confirmed that the creep strain is nonuniform even in the same grain and the strain distribution is caused mainly by the grain boundary sliding.

Isotropic photonic band gap and anisotropic structures in transmission spectra of two-dimensional fivefold and eightfold symmetric quasiperiodic photonic crystals

We measured and calculated the transmission spectra of two-dimensional quasiperiodic photonic crystals (PCs) based on a fivefold (Penrose) or eightfold (octagonal) symmetric quasiperiodic pattern. The photonic crystal consisted of dielectric cylindrical rods in air placed normal to the basal plane on vertices of tiles composing the quasiperiodic pattern. An isotropic photonic band gap (PBG) appeared in the TM mode, where electric fields were parallel to the rods, even when the real part of a dielectric constant of the rod was as small as 2.4. An isotropic PBG-like dip was seen in tiny Penrose and octagonal PCs with only six and nine rods, respectively. These results indicate that local multiple light scattering within the tiny PC plays an important role in the PBG formation. Besides the isotropic PBG, we found dips depending on the incident angle of the light. In this study, anisotropic structures were clearly observed in transmission spectra of quasiperiodic PCs. Based on rod-number and rod-arrangement dependence, it is thought that the shapes and positions of the anisotropic dips are determined by global multiple light scattering covering the whole system. In contrast to the isotropic PBG due to local light scattering, we could not find any PBGs due to global light scattering even though we studied transmission spectra of a huge Penrose PC with 466 rods.

Powder Particle Manipulation and Assemblage Using Microprobe

Powder particle manipulation and welding techniques using a microprobe have been developed for use of microassembling. These techniques were applied to fabrication of microstructures by assembling powder particles. For the microprobe, a needle with a tip of 2 Am in diameter was prepared. Au and Ni alloy powder particles of about 60-100 Jim diameter were used for the manipulation and welding experiments. The experiments showed that Au powder particles can be easily picked up, moved to a predetermined point and deposited at the point by controlling the voltage between the W microprobe and the substrate. Furthermore, the powder particle can be welded into the substrate or other powder particles on the substrate by glow discharge between the tip of the probe and the substrate. By utilization of the powder particle manipulation and welding, microstructures composed of Au and Ni alloy powder particles were fabricated. It was demonstrated that the microprobe technique is very useful for the fabrication of micromachines and microdevices. Also, the technique is thought to be useful for the creation of intelligent materials.

Local Strain Sensing Using Piezoelectric Polymer

Local strain sensing methods are developed for damage detection in structural materials, and their validities are demonstrated. As strain sensors, piezoelectric polymers were coated on the surfaces of aluminum sheets. Local strains in the ten sile tested aluminum sheets were measured by an operational amplifier circuit with a scanning probe, and then observed using the voltage contrast technique in a scanning electron microscope. The preliminary results indicate that these methods using piezoelectric polymers are sensitive and useful for detection and measurement of local static strains in structural materials.

An arrangement of micrometer-sized powder particles by electron beam drawing

The creation of new advanced functional materials is anticipated by assembling micrometer-sized particles which have various functions. In this work, a new concept for assembling powder particles is proposed and preliminary research results of the assembling process are reported. The process for assembling is as follows: (1) electrified patterns are formed on an insulating substrate using an electron beam drawing and are observed with an SEM by the voltage contrast method, (2) the substrates are dipped into a solvent in which particles are dispersed, and (3) the particles are adhered to the electrified patterns under suitable conditions. The number of adhered particles depends on the concentration of particles in a solvent, the electron dose of electrification and the dipping time of the substrate into the solvent. Using adequate values of these parameters, spherical silica particles of 5 μm diameter were arranged on calcium titanate substrates.

Optical transmission spectra of two-dimensional quasiperiodic photonic crystals based on Penrose-tiling and octagonal-tiling systems

We measured and calculated optical transmission spectra of two-dimensional quasiperiodic photonic crystals based on 5- and 8-fold symmetric patterns (Penrose and octagonal patterns). In our photonic crystals, dielectric cylindrical rods stood perpendicular to a basal plane on vertices of tiles in the patterns in air. In the TM mode, where electric fields of incident light are parallel to the rods, we found an isotropic photonic band gap even when the dielectric constant is as small as 2.4. Besides, we observed several dips depending on the incident direction of the light, which may be due to long-range multiple scattering.

Development of novel method to create two-dimensional photonic crystals

We have developed a novel method for simple and quick fabrication of various 2D photonic crystals consisting o polymer rods arranged regularly in air using molds made by laser light. Square- and honeycomb-lattice photonic crystals, in which the radius of a rod, the spacing between nearest-neighbor rods, and the real part of a dielectric constant of the polymer were 22 micrometers , 90-100 micrometers and 3.7, respectively, were created, and far-IR transmission spectra were measured. The experimental and calculated result agreed with each other, indicating that our samples were genuine photonic crystals. In addition to well-known opaque regions in transmission spectra due to photonic band gaps and optical branches of uncoupled mode, we have discovered that the transmission is suppressed drastically at branches with flat dispersion due to the influence of absorption of light.

Evaluation of the Wear Energy Consumption of Nitrogenated Diamond-Like Carbon Against Alumina

The wear energy consumption of nitrogenated diamond-like carbon (NDLC) in the tribo-test against alumina was evaluated. The energy input induced by the power source of the tribometer is applied to the contact area of two sliding bodies. The energy is dissipated into the two bodies with various transforming energies, such as (1) wear energy, (2) friction heat, (3) strain energy, (4) plastic deformation energy, and (5) chemical reaction energy used to form the tribo-layer. Determining the breakdown of the energy consumption into each mode is notably important for the investigation of the tribological mechanism. The surface fracture energy of NDLCs was evaluated by the micro-indentation method. The newly created surface area was estimated using the wear particles size distribution measured by image processing. The consumed wear energy was obtained by the surface fracture energy multiplied by the new created surface area corresponding to the generation of the wear particles in the tribo-test. The index numbers of the wear consumption energy/energy input ratio of the NDLCs were almost the same as those of their wear coefficients.

Manipulation and welding of metal spheres above 10 μm using needle-like probe

Abstract A needle-like probe is the simplest tool to manipulate fine spheres. It catches fine spheres by adhesion forces without any holding device. Metallic spheres of 10–100 mm are difficult to manipulate with the needle-like probe, because the gravity rivals the adhesion forces in the dynamics of the spheres. Large and heavy spheres arranged on a substrate areeasily disturbed because of the same reason. Here, a manipulator equipped with a direct power source, which applies voltage to the probe, is fabricated. Large and heavy spheres are adhered by the controllable electrostatic force. Besides the manipulation, the apparatus is designed to weld the spheres by using the probe as electrode for spot/arc welding. Experiments on the manipulation showed that the probe caught gold spheres of 40–80 µm by applying 20–50 V and released by putting them down after cutting the power off. Following to manipulation, welding experiments were carried outat various conditions. Two power sources, a high-voltage and low-current power source and a low-voltage and high-current power source, and two welding methods, arc welding and spot welding, are examined. The experiments showed that the gold spheres of 40–80 mm can be welded by the spot welding using the high-voltage and low-current power source, of which maximum power rating is 10 kV×1 mA. The probe is kept to touch the sphere and 4 kV or more is applied. Electric sparks are generated at the interface of the probe and the substrate, and the sphere is welded to the substrate. In both the manipulation and welding, the contact pressure must be very low. A tower of gold spheres is fabricated as an example of three-dimensional microstructures composed of fine spheres.

Manipulation by dipole probe

Abstract A dipole probe is fabricated to manipulate millimeter- to submillimeter-sized objects. A tungsten needle, an alumina tube and a stainless tube are arranged concentrically in order inside the probe. The tip of the stainless tube is ground to form a needle. They are embedded in an epoxy resin and the tip of the probe is shaped hemispherically. The probe has two electrodes, a tungsten needle and a stainless steel needle, inside it. The probe can attract objects by gradient force likea bipolar electrostatic chuck. The attraction force is measured as a function of the applied voltage, and they are compared with those calculated by a 3D FEM. Both the experimental values and the calculated values are proportional to the squareof the applied voltage. The determined values are, however, three times greater than those by the calculated values. The difference is ascribed to the incomplete shape of the probe model and the difference of dielectric constants of materials. The probe can attract both conductive gold particles and dielectric foam styrene particles. The probe is placed above the particle and a voltage supplier is turned on. The particle jumps up and adheres at the tip of the probe. The adhesive position is not on the center axis of the probe but the opposite side to the stainless needle against the center of the probe.The distances from the center of the probe are at a range of 0.4–1.05 mm for 20 experiments. The FEM calculation shows that maximum attraction force is for the particle placed at the opposite side to the stainless needle. Release is possible only by turning the voltage supplier off. The particle moves to the bottom of the probe, and falls after 1–2 s. The delay is due to the attenuation period of electrons accumulated at the surface of the probe.