Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session CM2: Nanoparticles and Nanotubes |
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Chair: Larry Overzet, University of Texas at Dallas Room: Doubletree Hotel Cedar |
Monday, October 17, 2005 10:00AM - 10:30AM |
CM2.00001: Nonthermal Plasmas: Silicon Nanocrystals made easy Invited Speaker: In this presentation, low pressure plasmas are discussed as a superior source for the controlled synthesis of semiconductor nanocrystals. Among the prime advantages of low pressure plasmas are their ability form highly monodisperse, single-crystal nanoparticles which are prevented from agglomeration due to the electrical charge that particles acquire in the plasma. Two examples of this approach are presented: In the first example, a constricted mode capacitive discharge is used to produce single-crystal, virtually defect-free, cube shaped silicon nanoparticles. Particles are between 20-50 nm in diameter with a highly monodisperse particle size distribution. These particles have enabled our recent success in manufacturing single-nanoparticle-based Schottky barrier vertical transistors. Electrical characterization of these devices provides insight into the electronic properties of the silicon nanoparticles. In the second example, a high-yield plasma process is used to form luminescent semiconductor quantum dots in a flow-through reactor. Our work has focused on several Group IV elements due to their compatibility with silicon technology and their low toxicity. Results of the synthesis and application of various materials systems will be presented. [Preview Abstract] |
Monday, October 17, 2005 10:30AM - 10:45AM |
CM2.00002: Synthesis of photoluminescent nanoparticles in a continuous flow non-thermal plasma reactor Lorenzo Mangolini, Elijah Thimsen, Uwe Kortshagen Silicon nanoparticles small enough to show quantum confinement effects exhibit intense room temperature luminescence and might find applications in novel light emitting devices, in microelectronics, and as biological tagging agents. A new approach for the synthesis of luminescent silicon nanocrystals is presented. Silicon nanoparticles with an average size below 5 nm are produced in a continuous flow non-thermal plasma reactor. The reactor consists of a simple 3/8'' quartz tube through which an Argon/Silane mixture is flown. RF power is fed into the system through two ring electrodes. The produced particles are crystalline and show bright red-orange photoluminescence. The influence of the experimental parameters and plasma properties on the produced material is discussed. The system is capable of producing several tens of milligrams per hour of luminescent powder. The process has also been modified to synthesize amorphous hydrogenated carbon nanoparticles, which show efficient luminescence in the blue-green range. These particles are synthesized in an Argon/Methane discharge. The photoluminescence and quantum yield efficiency have been characterized with respect of the experimental conditions. [Preview Abstract] |
Monday, October 17, 2005 10:45AM - 11:00AM |
CM2.00003: Synthesis of nanoparticles in microplasma reactor Tomohiro Nozaki, Daisuke Asahi, Ken Okazaki, Kenji Sasaki Synthesis of silicon-based nanoparticle has been studied in capacitively coupled VHF (144 MHz) microplasma reactor. A mixture of He/H$_{2}$/TEOS(Tetraethoxysilane) was processes in a 470 $\mu $m capillary tube. The process starts with the creation of supersaturated radical condition, followed by homogeneous nucleation, cluster formation and/or particle growth, and annealing including aggregation of particles. The proposed microplasma reactor has several advantages over these processes: (1) Microplasma under high frequency operation easily provides supersaturated environment regardless of thermodynamic equilibrium (Ne$\sim $4$\times $10$^{15}$cc$^{-1}$ at T$_{rot}\sim $1800K), (2) Micrometer scale reactor equalizes radical density and temperature, realizing uniform nucleation, (3) Charged particles prevent aggregation, (4) Particle synthesis due to consecutive reaction is easily optimized with short-residence time reactor ($\sim \mu $s). Optimum gas mixture such as He/1000sccm, H$_{2}$/1sccm, and TEOS/(less than 100 ppm) deposited 50 nm particles on a substrate. Detailed analysis of those particles is now being conducted. * This work has been supported by the Grants-in-Aid for Scientific Research on the Priority Area of Microplasmas from the Japanese Ministry of Education, Culture, Sports, Science and Technology. [Preview Abstract] |
Monday, October 17, 2005 11:00AM - 11:15AM |
CM2.00004: Spatial-grid-independent 1D hybrid kinetic-hydrodynamic plasma simulations for nanoparticle deposition Pavlo Rutkevych The present code is created in order to describe nanoparticle movement in a combined bulk-presheath-sheath region and confirm our earlier proposed simple models of nanoparticle deposition. The required quantities are densities and average velocities of each species at each spatial cell; the plasma particles are described according to their velocity distribution function, and they are moving with respect to their velocities. The time evolution is performed until the stabilization process is finished. The model is found to be sensitive to the time step (the optimum time step has been investigated for each species separately), however it is much less sensitive to the spatial grid, allowing strongly irregular coordinate cells. The model includes external electric field, collision with neutrals, ionization and various boundary conditions at the wall. Currently the model describes electrons, one kind of positive ions and nanoparticles, though it can be easily extended to a larger number of species, common for chemically-active discharges. [Preview Abstract] |
Monday, October 17, 2005 11:15AM - 11:30AM |
CM2.00005: Deposition of Aligned Carbon Nanofibers in Highly Collisional Sheath Tomohiro Nozaki, Kuma Ohnishi, Ken Okazaki, Joachim Heberlein, Uwe Kortshagen Deposition of vertically oriented carbon nanofibers (CNFs) has been studied in atmospheric pressure radio frequency discharge (APRFD) where dielectric barrier is not inserted between metallic electrodes. If frequency is sufficiently high so that ions are trapped in the gap, the operating voltage is remarkably decreased. Then transition of glow discharge into arc discharge is suppressed without dielectric barrier. More importantly, trapped ions produce cathodic sheath in the boundary of bulk plasma and electrode where large potential drop exists. The primary interest of present work is to study how such highly collisional cathodic sheath works on the alignment of CNFs. The absence of dielectric barrier enables us to superpose external DC potential to the substrate, which might provide sufficient field strength in the boundary for the orientation of CNFs, while the damage of CNFs due to ion bombardment should be negligible in atmospheric pressure. Emission distribution of He (706 nm), H$\alpha $ (656 nm), and CH (432 nm) clearly showed that negative DC bias enhances the formation of cathodic sheath near the substrate. Both deposition rate and alignment of CNFs are remarkably improved by the application of negative DC bias. [Preview Abstract] |
Monday, October 17, 2005 11:30AM - 11:45AM |
CM2.00006: Atmospheric Pressure Plasma Jet Process for Carbon Nanotube growth Anand Chandrashekar, Jeong Soo Lee, Gil Sik Lee, Lawrence Overzet In this study, an atmospheric jet RF helium plasma (13.56 MHz) is used to synthesize Carbon nanotubes on large area silicon substrates, using acetylene precursor gas. Downstream, a copper hot plate is heated to temperatures of 600C and above, after the substrate is set on it. Iron (catalyst) is either evaporated on the substrate and annealed, or added to the process by evaporating ferrocene in a Vapor Delivery System (VDS). The plasma and thermal energy dissociate the precursor molecules, and carbon nanotubes deposit on the substrate. SEM micrographs of film cross-section predict that taller nanotubes can be obtained at higher plate temperatures and plasma powers. Film growth saturates with time if only pre-evaporated iron catalyst is used, but this phenomenon is overcome by introducing ferrocene. It was determined using Raman spectroscopy that higher plasma power and temperature lend purer nanotube films, due to efficient graphitization. [Preview Abstract] |
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