Papers

ICMCTF2007 Session G3: Atmospheric Plasma, Hollow Cathode, and Hybrid Plasma Processing

Tuesday, April 24, 2007 2:50 PM in Room Royal Palm 4-6

Tuesday Afternoon

Start	Invited?	Item
2:50 PM		G3-5 Synthesis of Vertically-Oriented Single-Walled Carbon Nanotubes in Highly Collisional Plasma Sheath T. Nozaki, K. Okazaki (Tokyo Institute of Technology, Japan) Plasma enhanced chemical vapor deposition (PE-CVD) is recognized as one of the viable fabrication techniques of carbon nanotubes (CNTs). The special advantage of PE-CVD is that vertically-oriented CNTs are synthesized due to the electric field normal to the substrate. However, energetic ions accelerated in the cathodic sheath severely deteriorate patterned catalyst nanoparticles as well as growing CNTs: CNTs fabricated by PE-CVD are overwhelmingly carbon nanofibers and multi-walled carbon nanotubes. Tremendous interest in the preparation and characterization of single-walled carbon nanotubes (SWCNTs) and related applications has not been realized in the scope of PE-CVD until recently. We have developed atmospheric pressure radio frequency discharge (APRFD) and successfully synthesized defect-free vertically-oriented SWCNTs. The APRFD is virtually free from ion damage while large potential drop still exists in the cathodic sheathe which is indispensable for vertically-oriented growth of SWCNTs. A highly-collisional cathodic sheath, which is recognized as a thin dark space on momentary cathode, was clearly identified in low-current α-mode regime. Optical emission spectroscopy and related electrical measurements in this operation regime were well correlated with SWCNTs morphology. Although growth rate dramatically increased with discharge power (4 µm/min), excessive input power induced high-current γ-mode discharge and deteriorated SWCNTs. The advantage of ion-damage free PE-CVD realized by atmospheric pressure reactive plasma will be discussed.
3:50 PM		G3-8 Scaling up Quantities in Hollow Cathode Discharges with the Invariant Parameter V.H. Baggio-Scheid, J.W. Neri (General-Command of Aerospace Technology, Brazil) In this work we introduce the invariant parameter of a hollow cathode discharge, associated with the current density. Using the similarity relations and taking into account the variations of pressure and cathode dimensions we have obtained the generic parameter lj/p, where l is the length of the cathode, j is the current density at the cathode surface and p is the pressure. By plotting the discharge voltage as a function of the invariant parameter the experimental points follow a single curve denominated discharge characteristic. Furthermore, if two discharges are similar the experimental points of both follow the same characteristic curve. We have observed that, beside voltage, may other discharge quantities, e.g., electron density, sputtering rate and light intensities emitted by sputtered cathode atoms, when plotted as a function of the invariant parameter also follow a characteristic curve. Whenever a characteristic curve can be fitted through the experimental points, this quantity might be scaled up for other discharges with different dimensions and operated under different conditions. In this work we present results of quantities, which were scaled up for several hollow cathode discharges.
4:10 PM		G3-9 Comparison of Pulsed DC and RF Hollow Cathode Depositions of CrN Films L. Bardos, H. Baránková (Uppsala University, Sweden) A cylindrical chromium hollow cathode powered by pulsed DC generator was used for PVD of Cr and CrN films to compare the DC pulsed power deposition with the radio frequency (RF) deposition at comparable power. The CrN films were deposited in pure nitrogen and Cr films in pure argon, both at gas pressures of 0.5 Torr in the chamber. The target-to-substrate distance was 10 mm. The 500 nm pulses with 250 kHz repetition frequency were applied in the power range between 100 W and 400 W to study the effect on the film deposition rate and the film properties. The maximum deposition rate of CrN films exceeded 1 µm/min in the arc regimes where temperature of the hollow cathode outlet exceeded 1300°C. The films were deposited on unheated silicon substrates. It was found that at the same power the RF deposition rates of CrN films were higher than those in the pulsed DC regime. The microcrystalline structure and morphology of Cr and CrN films deposited at different powers were studied in more details.