Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session LW1: Plasma Applications for Nanotechnology |
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Chair: Uwe Czarnetzki, Ruhr-University Bochum Room: Doubletree Crystal City Crystal Ballroom A |
Wednesday, October 3, 2007 1:30PM - 1:45PM |
LW1.00001: Nanoscale particles in reactive RF plasmas: size-dependent dynamics and influence on plasma I.V. Schweigert, A.L. Alexandrov, D.A. Ariskin, F.M. Peeters, I.I. Stefanovic, E. Kovacevic, J. Bernd, J. Winter A CCRF discharge with growing nanoparticles in Ar and C$_{2}$H$_{2}$ mixture was studied experimentally and with using kinetic PIC-MCC simulations. The dust particle diameter ranged from 0 to 200 nm. It was found that at an initial stage of the growth the nanoparticles are situated near the sheath-plasma boundaries where the ionization rate by the electron impact has peaks. The presence of nanoparticles strongly impacts the plasma, and at some critical nanoparticle size the discharge transits from the active sheath regime to the volume dominated mode. Growing further, the dust particles first gradually spread to discharge center and only weakly disturb plasma parameters and then they form the void. The dust particle distribution was measured using Laser Light Scattering technique. In the experiment the nanoparticles are produced and grown by plasma polymerization and we measure their dynamics from early stage until the formation of the void. Calculated and measured properties of discharge, operation modes and nanoparticle distribution agree quantitatively. [Preview Abstract] |
Wednesday, October 3, 2007 1:45PM - 2:00PM |
LW1.00002: Coagulation in a Nanodusty Plasma Steven Girshick, Lavanya Ravi We recently reported [1] a numerical model and simulations for the spatiotemporal evolution of a parallel-plate RF plasma at 100 mTorr, in which nanoparticles were assumed to nucleate in an initial short burst. These simulations predicted that coagulation did not play a significant role, because neutral particles were rapidly either charged by electron attachment or lost by diffusion to the walls. For the remaining negatively charged particles, coagulation was strongly suppressed by the mutual charge repulsion. In the work reported here, we more realistically allow nucleation to continue wherever the local nanoparticle surface area concentration lies below a critical value. In addition, unlike the previous work [1], we account for the enhancement in coagulation caused by the induced dipole in neutral-charged nanoparticle interactions. The new simulations predict that coagulation does indeed play an important role in particle growth. In particular, most coagulation involves very small (approx. 1 nm in diameter) neutral particles that are scavenged by larger charged nanoparticles near the edges of charged particle trapping regions. [1] S. J. Warthesen and S. L. Girshick, Plasma Chem. Plasma Process. 27, 292 (2007). [Preview Abstract] |
Wednesday, October 3, 2007 2:00PM - 2:30PM |
LW1.00003: Synthesis of Carbon Nanowalls and Challenge for New Functional Devices Invited Speaker: Carbon nanowalls (CNWs), two-dimensional carbon nanostructures consisting of plane graphene layers, have been synthesized on the substrates without catalyst. The large surface area and thin edges of CNWs may provide us with opportunities for the various applications. In particular, vertically standing CNWs with high surface-to-volume ratio serve as an ideal material for the catalyst support for fuel cells and gas storage. Recently it is reported that one graphene sheet potentially has the high electron mobility and huge sustainable current. Therefore, it is expected that CNWs can be applied for the various kinds of electric devices. Moreover, in the case of application to an efficient emitter for electron field emission, thin edges with moderate spacing and the good uniformity in the height distribution of CNWs are very promising. We have proposed the novel plasma enhanced chemical vapor deposition (PECVD), which is a radical-controlled plasma process using radical injection technique, and demonstrated the fabrication of vertically aligned CNWs using PECVD assisted by H radical injection. By using the radical injection PECVD, we were able to control the CF$_{3}$ and H radical density and hereby synthesize the CNWs with a variety of the morphologies and structures. The electric properties of CNWs for advanced nanometer-scaled device were investigated. It was found that the CNWs of n and p-type were successfully formed by radical controlling. In addition, the nano-structure of CNWs indicated the good performance of the electron field emission properties. The surface area with nano-scale high aspect ratio showed the good water repellency, while the surface exposed to O$_{2}$ plasma become hydrophilic. These excellent characteristics can be applied for the bio device. On the basis of these results, the potential of CNWs for new functional devices will be introduced. [Preview Abstract] |
Wednesday, October 3, 2007 2:30PM - 2:45PM |
LW1.00004: Growth Process of Carbon Nanowalls Fabricated Using Radical Injection Plasma Enhanced Chemical Vapor Deposition Shingo Kondo, Olivera Stepanovic, Koji Yamakawa, Mineo Hiramatsu, Masaru Hori Carbon nanowalls (CNWs) consist of two-dimensional graphene sheets standing on the substrate. Due to their unique structures, CNWs have received great attention for various applications. CNWs were fabricated by plasma-enhanced chemical vapor deposition employing C$_{2}$F$_{6}$ gas with H radical injection. In order to clarify the mechanism of CNWs growth, we have investigated the initial growth process. It was found that a thin film of 10 nm in thickness grew at first 1 minute, and then CNWs grew in the vertical direction from the film. In XPS measurements, C and F were detected in the thin film. The thin film contained neither G-band (1590 cm$^{-1})$ nor D-band (1350 cm$^{-1})$ by Raman spectroscopy, on the other hand both bands were clearly detected in CNWs. As a result, the thin film was evaluated to be the amorphous carbon with a little amount of F, and the CNWs were made of graphene sheets. The same results were also obtained by ellipsometry. From these results, it is considered that controlling the structure of thin under layer is very important to synthesize CNWs. [Preview Abstract] |
Wednesday, October 3, 2007 2:45PM - 3:00PM |
LW1.00005: Fabrication of vertically standing carbon nanowalls by electron beam excited plasma-enhanced CVD Mineo Hiramatsu, Takakeru Mori, Masaru Hori Carbon nanowalls (CNWs), two-dimensional carbon nanostructures, have been grown recently. CNWs are the graphite nanostructure with edges, which comprise the stacks of plane graphene sheets standing almost vertically on the substrate. The large surface area and thin edges of vertically standing CNWs are useful as templates for the fabrication of other types of nanostructured materials as well as an electron field emitter, which have potential applications in energy storage, as electrodes for fuel cells, sensors, and field emission display. In this work, an electron beam excited plasma (EBEP)-enhanced CVD was applied to the synthesis of CNWs. The EBEP is a high-density and low-temperature plasma directly produced by a high-current and low-energy electron beam. Growth experiments were carried out at an electron-beam current of 2A and an electron-acceleration voltage of 60-100 V, a total pressure of 2-4 Pa, and the heater temperature of 550-650$^{\circ}$C. Well-defined, vertically standing CNWs were successfully fabricated at growth rate of 32 nm/min by EBEP-CVD employing CH$_{4}$/H$_{2}$ mixtures. CNWs grown here were very thin, and their thickness was less than 3 nm. The density of CNWs (average distance between adjacent nanowalls) was controllable in the range of 50 to 200 nm by changing the total gas pressure. [Preview Abstract] |
Wednesday, October 3, 2007 3:00PM - 3:15PM |
LW1.00006: Damage free PECVD based on atmospheric pressure non-thermal plasma and application to high-purity vertically-aligned single-walled carbon nanotube synthesis Tomohiro Nozaki, Kuma Ohnishi, Ken Okazaki We developed atmospheric pressure plasma enhanced chemical vapor deposition for vertically-aligned single-walled carbon nanotubes synthesis, in which both ion-damage and radical-damage are preferentially avoided in atmospheric pressure [1]. In this study, we performed on-line gas analysis using quadrupole mass spectrometer. A metallic capillary tube (O.D. 450 $\mu$m) was inserted into the cathodic sheath (thickness: 900 $\mu$m) and reacting gas was extracted for real-time gas analysis. The result revealed the main product was C2H6, but CNTs were missing in the C2H6 thermal CVD. Ionic species such as CH4+ would have to be abundant reactive species in the plasma sheath. Those species are believed to once absorb on CNT surface and then migrated towards catalyst particles which are anchored on a substrate. We also studied the effect of total pressure. The D/G Raman peak ratios increased as total pressure decreased from 100 kPa to 20 kPa, although ion damage is neglected in this pressure range. Excessive supply of reactive species simultaneously formed amorphous carbon network that ultimately deteriorate CNT quality. \newline [1] T Nozaki et al. \textit{Carbon}, 45, 364-374 (2007) [Preview Abstract] |
Wednesday, October 3, 2007 3:15PM - 3:30PM |
LW1.00007: Student Excellence Award Finalist: Binary quantum dot arrays: A plasma-based deterministic approach Amanda Rider, Kostya (Ken) Ostrikov Fabrication of size-uniform, compositionally controlled binary quantum dot (QD) [1] arrays is of great interest to the multidisciplinary research community. The increasing number of QD applications in fields ranging from biology to optoelectronics - each with precise structural requirements, necessitates that a more rigorous approach to fabrication be adopted. Conventional fabrication techniques are unable to cope with the myriad requirements for highly tailored QDs. In this paper, emphasis is placed on plasma-related effects such as substrate heating, surface activation energy and the benefits of low-temperature growth offered by thermally non-equilibrium, low-temperature plasma routes. The competitive edge in using plasmas as versatile nanofabrication tools is examined via a comprehensive analysis of available experimental results and numerical simulation of the deterministic plasma-assisted nanofabrication of compositionally controlled, size-uniform QD arrays. The commercial potential of a plasma-based approach compared to common fabrication techniques such as thermal chemical vapor deposition (CVD) and molecular beam epitaxy (MBE) is explored, as is the application of plasma grown QDs in novel biosensors and third generation solar cells. [1] A. E. Rider et al, J. Appl. Phys. 101, 044306 (2007); I. Levchenko, A. E. Rider, K. Ostrikov, Appl. Phys. Lett. 90, 193110 (2007). [Preview Abstract] |
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