Shinji Matsui

Inducing graphite tube transformation with liquid gallium and flash discharge

We found that a flash motion of Ga droplets with Joule heating transformed an amorphous carbon pillar into multiwalled carbon nanotube. Flush discharge into the pillar quickly heated up Ga droplets, which originally incorporated in the pillar due to the fabrication technique with focused-ion-beam-induced chemical vapor deposition, inducing a flash motion of Ga toward negative electrode. Thus, the Ga droplets dug out a tunnel inside the pillar, simultaneously inducing a catalytic transformation into a multiwalled graphitic tube.

Comparison of Young's Modulus Dependency on Beam Accelerating Voltage between Electron-Beam- and Focused Ion-Beam-Induced Chemical Vapor Deposition Pillars

We investigated Youngs modulus of amorphous carbon (a-C) pillars that exhibited different properties depending on which of two fabrication methods were used, electron-beam-induced chemical vapor deposition (EB-CVD) or focused ion-beam-induced CVD (FIB-CVD). The Youngs modulus of the FIB-CVD pillars was almost linearly proportional to the accelerating voltage, while that of the EB-CVD pillars showed a completely opposite results. Secondary electrons seemed to play an important role in the increase of Youngs modulus of the pillars grown using EB-CVD.

In-situ Visualization of Local Field Enhancement in an Ultra Sharp Tungsten Emitter under a Low Voltage Scanning Transmission Electron Microscope

We found that field emissions from a multi-walled carbon nanotube soften the bottom of the tungsten by Joule heating, and the coulomb attraction to the nanotube finery pulled off from the tungsten tip resulted in an ultra sharp apex of the tungsten probe having 5 nm in radius of curvature. We also found that a locally enhanced field at the probe apex can be visualized using scanning transmission electron microscopy (STEM) under low accelerating voltage operation. The primary electrons were deflected by the local field out of the detector and created a dark shadow surrounding the probe apex in the STEM image. Simple Rutherford scattering model could be adopted to analyze the local electric field at the tip apex.

Growth Manner and Mechanical Characteristics of Amorphous Carbon Nanopillars Grown by Electron-Beam-Induced Chemical Vapor Deposition

We investigated the growth manner and mechanical characteristics of amorphous carbon (a-C) nanopillars formed by electron-beam-induced chemical vapor deposition (EB-CVD). The pillars inclinations were well explained if we assumed the vertical growth rate to be almost constant within a specified distance from the substrate. The pillars Youngs modulus evaluated by deflection measurement was approximately 29 GPa, which was almost equivalent to that of bismuth, but much smaller than that observed in focused ion-beam-induced chemical vapor deposition (FIB-CVD) pillars.

Elastic Double Structure of Amorphous Carbon Pillar Grown by Focused-Ion-Beam Chemical Vapor Deposition

Amorphous carbon pillars grown by focused ion beam induced chemical vapor deposition (FIB-CVD) had been considered to form in a cylindrical double structure. In this structure, the core containing Ga originating from the primary ion is surrounded by an amorphous carbon shell grown by the secondary electrons that were emitted during the inelastic scattering process of the primary ions penetration. We measured the Youngs modulus in a series of inclined pillars; the thickness of the pillars was reduced with the inclination. However, the Youngs modulus of the inclined pillars of thinner diameter increased. Here, we found that such FIB-CVD pillars had an elastic double structure that is comprised of a very stiffened core with 300 GPa of Youngs modulus, and an extremely soft shell having 30 GPa of Youngs modulus. We also confirmed that the oxygen plasma thinning of the perpendicular pillars considerably increased the Youngs modulus of the FIB-CVD pillars.

Driving force of an iron particle's movement in solid-phase graphitization

Solid-phase graphitization, and thus solid-phase nanotube growth, was induced by the movement of iron particles into an amorphous carbon matrix at a certain temperature around 600 °C. We analyzed this iron particle movement in an amorphous carbon wall by in situ monitoring by scanning transmitted electron microscopy (STEM). Isotropic diffusion of iron particles with a diffusion constant of approximately 0.06 nm2/min at 680 °C during furnace heating was observed. In contrast, during anisotropic heating, which was realized by heating a wall-shaped specimen on a fine tungsten filament, the Gaussian distribution of the iron particles shifted toward lower temperature. Iron particles in solid-phase graphitization preferred to move to a lower temperature region, where an exothermic reaction can catalyze amorphous carbon into graphite.

In situ visualization of local electric field in an ultrasharp tungsten emitter under a low voltage scanning transmission electron microscope

Field emissions from a multiwalled carbon nanotube embedded in a conventional electropolished tungsten probe soften the tip of the tungsten by Joule heating, and the Coulomb attraction to the nanotube finery pulled from the tungsten tip resulted in an ultrasharp apex of the tungsten probe having a curvature of 5nm radius. We also found that scanning transmission electron microscopy (STEM), when operated at low accelerating voltage, can visualize a local electric field at the probe apex. This local electric field, induced around the probe apex, deflected the primary electron beam of the STEM, producing a dark circular shadow surrounding the probe apex in the STEM image. The authors analyzed the distribution of this local field using a simple Rutherford scattering model.

Position-Controlled Carbon Fiber Growth Catalyzed Using Electron Beam-Induced Chemical Vapor Deposition Ferrocene Nanopillars

We demonstrated nanotube growth on a position-controlled catalyst using electron beam-induced chemical vapor deposition (EB-CVD) ferrocene nanopillars. While solid phase graphitization was induced at 650°C, iron nanoparticles only appeared on the surface by eroding the surrounding graphite triggered by the gas phase carbon fiber growth, at a temperature higher than 800°C using ethanol vapor. The precise position control achieved by EB-CVD directly reflected that of carbon fiber growth, which is a promising position-controlled carbon nanotube growth method for future device applications.

Effect of Annealing and Electron Irradiation on Young's Modulus of Amorphous Carbon Pillars Grown by FIB-CVD

The paper reports on the effect of vacuum annealing and and electron shower irradiation on the Youngs modulus of amorphous carbon pillars grown by focused-ion-beam-induced chemical vapor deposition, particularly at low acceleration voltages. TEM image revealed that many fine pores, were formed in the pillars after annealing at 600degC. It was shown that low-energy electron irradiation, is effective in increasing the Youngs modulus of the pillar.

In-situ visualization of local fields at a sharp tungsten emitter using low-voltage scanning transmission electron microscope

In this paper, we demonstrate that the local electric field distribution at a sharp tip can be drawn as a contour map and it agrees well with numerical calculations based on finite element method (FEM). In the Rutherford scattering scheme, when the primary electron beam passes close to the tip apex, it is strongly deflected toward the anode by the local field and is interrupted at the orifice edge. Thus, the interruption generates a circular dark shadow in the STEM image (see Fig. 1(b)). In contrast, an electron beam scanned far from the tip apex is slightly deflected, and also reaches the orifice edge, producing the actual orifice shape, as shown in Fig. 2(a). Here, we define the impact factor b as the distance between the shadow boundary and the tip apex, and the deflection angle as the angle between those two electron-beam trajectories.