Shingo Kondo

Initial growth process of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition

We synthesized carbon nanowalls (CNWs) using radical injection plasma-enhanced chemical vapor deposition. The initial growth process of CNWs was investigated with and without O2 gas addition to a C2F6 capacitively coupled plasma with H radical injection. In the case of the CNW synthesis without the addition of O2 gas, scanning electron microscopy (SEM), transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that a 10-nm-thick interface layer composed of nanoislands was formed on a Si substrate approximately 1 min prior to CNW formation. In contrast, with O2 gas addition, SEM and XPS revealed that an interface layer was not formed and that CNWs were grown directly from nanoislands. Moreover, Raman spectroscopy suggested that the interface layer was composed of amorphous carbon and that O2 gas addition during CNW growth is effective for achieving a high graphitization of CNWs. Therefore, O2 gas addition has the effect of reducing the amorphicity and disorde...

Highly reliable growth process of carbon nanowalls using radical injection plasma-enhanced chemical vapor deposition

Two-dimensional carbon nanostructures, carbon nanowalls (CNWs), were fabricated on a Si substrate using radical injection plasma-enhanced chemical vapor deposition, employing fluorocarbon (C2F6) and hydrogen (H2) mixtures. The influence of the surface conditions of the chamber wall on CNW growth was investigated in order to determine the optimum conditions for CNW growth with high stability and reproducibility. In order to monitor the surface conditions of the chamber wall, optical emission spectroscopy in the plasma was measured, and the correlation between CNW growth and the surface conditions in the chamber wall was investigated. The growth rate and morphology of grown CNWs were determined to be influenced by the surface conditions of the chamber wall. Furthermore, O2 plasma chamber cleaning followed by predeposition for passivation was found to be effective for maintaining steady conditions to attain CNWs with high reproducibility.

Critical Factors for Nucleation and Vertical Growth of Two Dimensional Nano-Graphene Sheets Employing a Novel Ar+ Beam with Hydrogen and Fluorocarbon Radical Injection

Two-dimensional nano-graphene sheets, standing vertically on carbon nanowalls (CNWs) substrates, were synthesized by multi-beam chemical vapor deposition employing three types of irradiation, Ar+ beam with tunable fluxes and energies, hydrogen (H) and fluorocarbon radicals, which could be independently controlled. The CNWs growth processes were investigated by changing the Ar+ irradiation conditions. Irradiation of Ar+ ions with appropriate fluxes and energies on fluorocarbon layers evolved nanoislands for growth of the CNWs. By tuning the fluxes and energies of the incident Ar+ on amorphous carbon nanoislands, critical factors for controlling nucleation and growth of CNWs were determined.

Optical Properties of Evolutionary Grown Layers of Carbon Nanowalls Analyzed by Spectroscopic Ellipsometry

Carbon nanowalls (CNWs), vertically standing graphene sheets, grown by the radical injection plasma-enhanced chemical vapor deposition system were analyzed by spectroscopic ellipsometry. The refractive indexes (n), extinction coefficients (k), and optical band gaps (Eg) of evolutionary growth layers were evaluated using the Tauc–Lorentz model with the effective medium approximation. It was observed that an amorphous carbon interfacial layer with n of 1.9–2.0 was formed prior to the growth of CNWs with n of 1.2–1.5. Moreover, the imaginary parts of complex dielectric functions analyzed using the Tauc–Lorentz model indicate the possibility that the CNWs have semiconducting features.

Reactive Ion Etching of Carbon Nanowalls

Two-dimensionally standing graphene sheets, i.e., carbon nanowalls (CNWs), were synthesized on a Si substrate employing a capacitively coupled fluorocarbon plasma-enhanced chemical vapor deposition system together with H radical injection. To apply CNWs in electronic devices and/or membrane filters, we have demonstrated the reactive ion etching (RIE) of CNWs. RIE employing H2/N2 gases showed that the CNW films were anisotropically etched at a relatively high rate of more than 250 nm/min. However, the 10-nm-thick interface layer between a CNW film and the Si substrate remained and the interface layer was not completely etched. In contrast, RIE employing Ar/H2 gases enabled us to completely remove the interface layer. Ar/H2 RIE was also carried out from the bottom surface of CNW films after exfoliating them from the Si substrate. As a result, a free-standing CNW film of 550 nm thickness without an interface layer as a membrane filter was successfully formed.

Etching Processes of Carbon Nanowalls Using Dual-frequency Parallel-plate Capacitively Coupled Plasma

Carbon nanowalls (CNWs) is synthesized using the radical injection plasma enhanced chemical vapor deposition (CVD) system. In the initial growth process of CNWs on a Si substrate fabricated by the system, the carbon thin film of approximately 10 nm in thickness is deposited for 1 minute before CNWs grow in the vertical direction. The thin film is etched by using dual-frequency parallel-plate capacitively coupled plasma. SEM images characterise the CNWs. The etching rates of the CNWs and the carbon thin film are 150 nm/min and 15 nm/min, respectively. In order to extend applications of CNWs, the carbon thin film is removed from CNWs.

Non-Linearity in Position Sensing with Cathode Strips of a Single Wire Proportional Counter

The nonlinearity in the position readout from cathode strips has been investigated by a single-wire proportional counter using the charge-division method. The measured nonlinearities depended on the width of the cathode strip. This dependence agrees very well with theoretical predictions based on the formulate of Gatti et al. and Gordon and Mathieson. Obtainable position resolutions are independent of the strip width.