A metal-coated carbon nanotube (CNT) tip for scanning tunneling microscope (STM) has been developed. By pulsed laser deposition (PLD), a CNT attached to a tungsten tip was uniformly coated with 3–6 nm of tungsten thin layer. The observation of a Si(111)-7×7 surface using the tungsten-coated CNT tip demonstrated stable atomic imaging and potentiality of scanning tunneling spectroscopy (STS) measurement, which can be achieved from the pristine stage. It was demonstrated that the mechanical robustness and flexibility of the tip were maintained by virtue of the thin coated layer.
We have investigated the effect of oxygen addition to methane on the growth of vertically oriented carbon nanotubes (VCNTs) by radio-frequency plasma-enhanced chemical-vapor deposition (RFCVD). By adding moderate concentrations of oxygen to methane during RFCVD, highly crystalline VCNTs were densely grown at 430°C. With increasing oxygen concentration, the length of the VCNTs was increased and the linearity was degraded, whereas when excess oxygen was added to methane, no VCNTs were grown. Plasma states were investigated by optical emission spectroscopy during RFCVD. In the case of RFCVD with oxygen added to methane, peaks due to CO and OH radicals were dominant. The CO species appear to be one of the key factors in the growth of well-crystallized VCNTs. Moreover, VCNTs were grown at temperatures as low as 350°C with the addition of moderate amounts of oxygen to methane in RFCVD.
Vertically aligned carbon nanotube (VACNT) films have been grown by RF plasma chemical vapor deposition (RF-PECVD) with a controlling plasma condition. From the in situ optical emission spectroscopy (OES) and self-bias measurements, we have investigated the relationship between the morphology of VACNTs and the plasma condition in PECVD. CH radical and atomic hydrogen peaks were prominent in the OES spectra of CH 4 plasma. The plasma condition was changed by varying the interelectrode distance in PECVD. With increasing interelectrode distance, the diameter and density of VACNTs increased as a result of the increase in plasma density, the fraction of CH radicals, and self-bias. It is likely that the fraction of CH radicals in plasma influences promotion of the growth of CNTs, while the self-bias induces their vertical alignment.
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