Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TF2: Emerging Plasma Technology |
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Chair: Irina Schweigert, The George Washington University Room: Oregon Convention Center A105 |
Friday, November 9, 2018 9:30AM - 9:45AM |
TF2.00001: Variable-Frequency Capacitively Coupled Discharge as Tunable Impedance Element for RF Systems Andrey Khomenko, Sergey Macheret Plasmas are attractive for next-generation reconfigurable RF electronics because plasmas can be turned on/off, have their properties varied in a wide range, and handle much higher power than semiconductors can. Tunable capacitors and inductors are key elements of any reconfigurable system. Previously, a DC discharge in abnormal glow regime was shown to provide tunable capacitance for an LC resonator due to the sheath thickness variation with current. In this work, capacitively-coupled RF discharge in the alpha regime was operated in air at 1 Torr at a constant voltage in a wide range of frequencies, 10-300 MHz. The impedance characteristics and the sheath and plasma parameters were inferred from current and voltage measurements. At frequencies below about 100 MHz, the sheath thickness turned out to be inversely proportional to the driving RF frequency, so that the capacitance was proportional to the frequency, in good agreement with theory. At very high driving RF frequencies, the sheath impedance becomes negligible, and due to negative permittivity of the plasma, the overall impedance becomes inductive. Thus, the variable-frequency alpha-mode discharge can be used as a widely tunable capacitor or even be switched from capacitor to an inductor. Such a tunable element can be operated at frequencies different from the driving (i.e. plasma-generating) frequencies. [Preview Abstract] |
Friday, November 9, 2018 9:45AM - 10:00AM |
TF2.00002: Effects of in-situ irradiation of nitrogen-hydrogen plasma on flatness and composition of GaN surfaces before epitaxial growth by a radical-enhanced metalorganic chemical vapor deposition Hiroki Kondo, Amalraj Frank Wilson, Dhasiyan Arun Kumar, Yi Lu, Naohiro Shimizu, Osamu Oda, Kenji Ishikawa, Masaru Hori Nitride semiconductors, such as GaN, AlN, InN and their composites, have attracted much attention for optical and electronic devices, due to their excellent properties such as wide bandgap energies. Recently, we have developed a radical-enhanced metalorganic chemical vapor deposition (REMOCVD) using a 100 MHz-excited plasma, and realized reduction of growth temperature of GaN without ammonia. Since native oxides are troublesome regardless of deposition methods, an in-situ cleaning to realize atomically-flat surface without any contaminant is strongly required. In this study, effects of in-situ plasma irradiation on GaN surfaces were investigated. N2/H2 plasma was irradiated to chemically-cleaned GaN surfaces. Flow rates of N2 and H2 were 750 and 250 sccm, respectively. The surfaces cleaned by the plasma with 400 W looked flat, and fine steak lines were found in their reflective high-energy electron diffraction (RHEED) patterns. They were kept even after ramp-up to 600C with plasma, although they became spotty without plasma which means nitrogen out-diffusion and formation of Ga droplets. Increase in plasma power also induced surface degradation. These indicated that the in-situ plasma irradiation is effective to obtain fine surface preferred epitaxial growth. [Preview Abstract] |
Friday, November 9, 2018 10:00AM - 10:30AM |
TF2.00003: Atomic Layer Defect-free Etching and Deposition Processes for future sub-10-nm devices. Invited Speaker: Seiji Samukawa In the fabrication of semiconductor devices, reactive plasmas are widely used in key processes such as etching and film deposition. There is now demand for atomic level processing precision and for deposition accuracy that allows the control of structures at the molecular level. However, in ultra-miniature nanoscale devices that will become the mainstream in the future, the use of plasma processes can cause serious problems such as abnormal etching, sub-surface material damage, and breakdown of insulation films by the accumulation of ions or electrons emitted from the plasma. Also, surface defects (dangling bonds) of over a few tens nm in depth can form by exposure to ultraviolet (UV)emissions from the plasma. Process induced defects during plasma processing can have a large influence on the electrical and optical properties of devices as nano-scale devices have a larger surface area compared with the bulk material. Furthermore, since future nano-devices will require size control of three-dimensional structures with atomic precision, it will be absolutely essential to control surface chemical reactions with high accuracy and selectivity at the atomic layer level. Neutral beam process technology has attracted attention as a way of realizing these requirments. The neutral beam suppresses the incidence of charged particles and UV photon radiation onto the substrate, and is able to expose the substrate only to energy controlled neutral beam enabled by precisely controlling ion acceleration energy with the applied electric field before neutralization. This is certainly true atomic layer etching (ALE) and deposition (ALD). [Preview Abstract] |
Friday, November 9, 2018 10:30AM - 11:00AM |
TF2.00004: Towards understanding of plasma-based synthesis of carbon nanomaterials. Invited Speaker: Yevgeny Raitses This work reports on a comprehensive parametric characterization of an atmospheric pressure DC arc discharge for synthesis of carbon nanoparticles and nanostructures such as nanotubes. Applying a set of the in-situ diagnostics of plasma and nanoparticles, our synthesis experiments revealed that the carbon arc between two graphite electrodes forms a highly inhomogeneous plasma consisting of distinguishable regions with different dominant species, including ions, atoms, molecules and clusters, and nanoparticles [1,2]. Experimental and modeling results demonstrate that different steps of the synthesis process, including generation of a feedstock of carbon species, formation of larger molecules and clusters, agglomeration of nanoparticles in large particles, and growth of nanotubes occur in different regions of the arc discharge. In particular, it was shown that the ablation of the graphite anode is governed by the anode sheath which may change from electron repelling to electron attractive with the current density in the hot core region of the arc [3]. \textit{In-situ} measurements revealed clouds of nanoparticles in the arc periphery bordering the region with a high density of diatomic carbon molecules [2]. Two-dimensional CFD simulations of the arc combined with thermodynamic modeling show that this is due to the interplay of the condensation of carbon molecular species and the convection flow pattern [1]. These results show that the nanoparticles can form in the colder, peripheral regions of the arc. The formation of nanoparticles is strongly affected by unstable arc behavior [4]. The behavior manifests itself in a sporadic motion of the arc attachment to the anode, and the arc core giving rise to arc oscillations [2,5]. Mechanisms of these oscillations and their effect on synthesis of nanomaterials will be discussed in this talk. [1] S. Yatom et al., MRS. Comm. 1 (2018) [2] V. Vekselman et al., Plasma Sources Sci. Technol. \textbf{27}, 025008 (2018) [3] V. Nemchinskiy, and Y. Raitses, Plasma Sources Sci. Technol. \textbf{25}, 035003 (2016) [4] S. Yatom et al., Carbon \textbf{125}, 336 (2017) [5] S. Gershman, and Y. Raitses, J. Phys. D. Appl. Phys. \textbf{49}, 345201 (2016).\\ \\In collaboration with V. Vekselman A. Khrabry, S. Yatom, I. D. Kaganovich, V. Nemchinsky, S. Gershman, Y-W. Yeh, M. Keidar, M. Shneider, B. Stratton, P. Krstic, L. Han, B. E. Koel, R. S. Selinsky, B. Santra, A. Gerakis, and R. Car [Preview Abstract] |
Friday, November 9, 2018 11:00AM - 11:15AM |
TF2.00005: Plasma-Enhanced Pulsed Laser Deposition of metal-oxide thin films Erik Wagenaars, David Meehan, Sudha Rajendiran, Andrew Rossall Plasma-Enhanced Pulsed Laser Deposition (PE-PLD) is a novel technique for depositing metal-oxide thin films. It combines traditional PLD of metals with a low-temperature oxygen background plasma to create metal-oxide thin films. The chosen material for our proof-of-concept is copper oxide thin films. Copper oxide is a p-type semiconductor with a direct band gap of between 1.2eV and 2.13 eV and it is investigated for many (potential) applications, e.g. solar cell fabrication, supercapacitors and bio sensors. There are two (stable) forms of copper oxide, CuO and Cu$_{\mathrm{2}}$O, both of which are of interest for applications as long as a single-phase material can be obtained. In our proof-of-concept study we show that using PE-PLD, we can deposit stoichiometric, high-quality, poly-crystalline films of both Cu$_{\mathrm{2}}$O and CuO, depending only on oxygen pressure. Deposition rates are 1-3 nm/min, comparable to traditional PLD. Importantly, PE-PLD does not need substrate heating or post-annealing to achieve high-quality films, allowing deposition on sensitive substrates. We demonstrate that PE-PLD can produce copper-oxide films on flexible polypropylene (PP) film substrates. Finally, we show that PE-PLD can also produce other poly-crystalline, stoichiometric metal-oxide thins films; Aluminium oxide and Zinc oxide. [Preview Abstract] |
Friday, November 9, 2018 11:15AM - 11:30AM |
TF2.00006: Particle in Cell Simulation of Plasma Assisted Carbon Nanotubes Formation Sergey Averkin Nano materials have a wide range of applications, ranging from drug delivery in medical applications to new composite materials in aerospace applications. Experimental data on nanoparticle growth exists, but numerical simulations are needed to understand the underlying physical mechanisms and to enable better prediction of nanomaterial production. The numerical models of plasma assisted production span from detailed atomistic models including interaction of individual atoms to fluid models coupled with Maxwell equations that determine plasma composition and kinetic models describing the nanoparticle growth. However, existing models are either computationally extremely expensive as in the case of atomistic models or don't include kinetic effects that are important for the nanoparticles production. We present Particle-In-Cell (PIC) simulations of growth rates of carbon nanotubes using commercial software VSim. Because PIC is less computationally expensive than atomistic simulations and can still capture kinetic effects that fluid simulations cannot, it is able to address this important issue in a unique way. In addition, PIC predictions can be fed to existing plasma fluid codes for more accurate production modeling. [Preview Abstract] |
Friday, November 9, 2018 11:30AM - 11:45AM |
TF2.00007: Effect of strong electric field on plasma-enhanced catalytic growth of carbon nanofibers Xuewei Zhang, Mikhail Shneider There has been much previous work on the kinetics of carbon nanofiber (CNF) growth via plasma enhanced chemical vapor deposition (PECVD). In contrast, very few modeling and computational studies have been devoted to the dynamics of CNF growth starting from catalyst nanoparticles on a substrate. Our paper contributes to the development of such a modeling framework which can be used to reveal various dynamic aspects of the process. To be more specific, in this work, we consider the effect of strong electric field in the vicinity of the catalyst nanoparticle. Based on two recent papers, the inclusion of electric field causes an increase in the flux of neutral molecules to the nanoparticle which in turn speeds up the growth process. When the CNF grows to such a length that field emission becomes strong, the resultant heating effect will significantly raise the nanoparticle temperature, which may slow down and eventually turn off the CNF synthesis. This could be a termination mechanism of CNF growth via PECVD, as an alternative to the traditional catalyst poisoning mechanism. [Preview Abstract] |
Friday, November 9, 2018 11:45AM - 12:00PM |
TF2.00008: Determination of BNNT growth precursors using thermodynamic analysis Alexander Khrabry, Shurik Yatom, Igor Kaganovich, Vladislav Vekselman, Yevgeny Raitses Recent works [1], [2] demonstrated high-yield production of high-quality boron-nitride nanotubes (BNNTs) in ICP plasma and laser ablation reactors. Common vision on the BNNTs growth is a root-grow mechanism. When B-N gas mixture cools down, boron droplets form first. Then, boron within the droplets reacts with nitrogen-containing radicals from the ambient gas, and BNNTs grow at the droplets surfaces. Ab-initio molecular dynamic simulations [3] have witnessed in favor of this mechanism. However, what are the gas species that provide nitrogen for the BNNTs growth, is still and open question. To determine these precursors, we performed thermodynamic calculations of the gas composition. Broad set [4] of molecular species was considered, condensation of boron was taken into account. We show that B$_{\mathrm{2}}$N molecules are the major nitrogen source. The presence of B$_{\mathrm{2}}$N molecules in the gas was confirmed in our experiments using optical emission spectroscopy (OES) of a gas over laser-ablated boron-rich targets. With addition of hydrogen, NH and BH molecules serve as nitrogen sources, which accords with OES measurements [1]. [1] K.S. Kim et al., ACS Nano \textbf{12} (2018) 884. [2] R. Arenal et al., J. Am. Chem. Soc. \textbf{129} (2007) 16. [3] B. Santra et al., arxiv.org/pdf/1803.11374.pdf (2018). [4] J. Radic-Peric, Mater. Sci. Forum \textbf{518} (2006) 349. [Preview Abstract] |
Friday, November 9, 2018 12:00PM - 12:15PM |
TF2.00009: Plasma Processing for Graphene-Based Materials Mineo Hiramatsu, Keigo Takeda, Hiroki Kondo, Masaru Hori Graphene-based materials such as carbon nanotube and graphene itself have attracted much attention due to their emerging applications. Graphene-based materials can be synthesized by several plasma enhanced chemical vapor deposition (PECVD) techniques on heated substrates employing CH4 and H2 mixtures. For example, plane graphene can be formed by PECVD on Ni in the remote plasma configuration at relatively low temperatures. Excess flux of carbon precursors causes supersaturation and ion bombardment induces the nucleation of nanographene, resulting in the formation of vertical nanographene (carbon nanowall, CNW). CNWs are few-layer graphenes standing on a substrate to form a self-supported network of wall structures. The maze-like architecture of CNWs with large-surface-area would be useful as electrodes for energy devices, electrochemical and biosensors. Morphology and electrical property of carbon nanostructures should be controlled according to their applications. Plasma processing has a significant role in fabricating carbon-based materials and achieving their practical use in many areas. We report the current status of the synthesis of graphene-based materials using several PECVD techniques, and focus on the structure control during growth processes as well as post treatment such as etching and surface termination. [Preview Abstract] |
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