Fabrication of High Aspect Ratio Nanoscale Pit Using Carbon Nanotube Probe
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Fabrication of High Aspect Ratio Nanoscale Pit Using Carbon Nanotube Probe Norikazu Arima and Akihito Matsumuro Department of Micro/nano System Engineering, Nagoya University, Furo-cho Chikusa-ku Nagoya 464-0863, Japan ABSTRACT We developed a method to fabricate nanoscale pits having high aspect ratio, using a scanning tunneling microscope with an attached carbon nanotube (CNT) probe. CNT probes used in this study were synthesized by the pulling method. The nanostructures were produced in Au thin film in an ambient pressure and room temperature. The results of our experiment show that a threshold value exists for the fabrication of the pits between 1 V and 2 V. The depth and diameter of the pit increased with the increase in the bias voltage and tunnel current, respectively. Consequently, a bias voltage of 3 V and tunnel current of 4 nA were found to be the optimum conditions for a high aspect ratio nanoscale pit fabrication. In changing the fabrication time at the optimum conditions, the depth of the pit increased with the increase in the fabrication time, with little change in the diameter of the pit. This demonstrates that CNT probes can be useful for fabricating nanoscale structures.
INTRODUCTION Fabrication of high aspect ratio nanoelectromechanical systems (NEMs) and nanodevices (below 50 nm) is an inevitable challenge as microelectromechanical systems shrink towards the nanoscale. However, at present, the technology to build NEMS is very limited and a great deal of improvement is required in key areas such as lithography. Here, we focus our attention on a fabrication technique that makes use of the scanning tunneling microscope (STM) [1]. Nanofabrication by STM has been demonstrated by several researchers for a wide range of sizes, from atom manipulation [2] to several tens of nanometers [3-5]. The fabrication of high aspect ratio nanostructures however, is not yet realized. We have tried to establish a fabrication method for high aspect ratio nanostructures using carbon nanotube (CNT) [6] as the probe. In this study, we have clarified the relationship between fabrication conditions (bias voltage, tunnel current, fabrication time) and pit configurations (depth and diameter of pit). The results were then used to determine the optimum conditions for the fabrication of high aspect ratio nanostructures.
EXPERIMENTAL DETAILS A commercial STM system was used for the fabrication of Au thin films. CNT probes used in this study were synthesized by the pulling method. Figure 1 (a) shows schematic diagram of the pulling method. This method that we devised utilizes viscosity and surface tension of a solvent and electrophoresis between an etched tungsten
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(a)
Tungsten probe
(b) CNT
CNT dispersion liquid
Conductive substrate
Tungsten probe 1 µm
Figure 1. (a) Schematic diagram of CNT probe processing, and (b) SEM image of CNT probe after deposition of the amorphous carbon layer. probe and CNT dispersion liquid (kind of solvent: isopropyl alcohol, CNT concentration: 0.05 mg/mL). The CNT can be atta
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