Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session TF1: Diagnostics II |
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Chair: Azer Yalin, Colorado State University Room: Ballroom I |
Friday, October 4, 2013 10:30AM - 10:45AM |
TF1.00001: Time-resolved in-situ quantum cascade laser absorption spectroscopy in dielectric barrier discharges S. Welzel, F. Brehmer, M.C.M. van de Sanden, R. Engeln Modern mid-infrared laser sources, known as quantum cascade lasers (QCLs), provide a means for highly time-resolved absorption spectroscopy in the molecular ``fingerprint'' region. Pulsed distributed feedback QCLs are especially suited for diagnostic studies on transient plasmas as the time-resolution can be as good as a few tens of nanoseconds. Dielectric barrier discharges in CO$_{2}$ operated in the mid-frequency (kHz) range were studied by means of in-situ QCL absorption spectroscopy in single and multiple-pass configuration. Different synchronisation schemes were applied to achieve phase-resolved measurements during individual AC cycles as well as to monitor molecular absorption signals during pulsed operation. Mixing ratios of CO in its electronic and vibrational ground state were of the order of a few percent and thus confirmed ex-situ studies of the effluent. Interestingly, the concentrations levels were changing only slowly in time, i.e. of the order of the residence time. A direct CO$_{2}$-to-CO dissociation through electron impact appears very unlikely under these conditions. The kinetics of low-lying ro-vibrational states of CO$_{2}$ along with the evolution of the CO concentration were measured on a sub-millisecond time-scale to establish the (rotational) gas temperatures. [Preview Abstract] |
Friday, October 4, 2013 10:45AM - 11:00AM |
TF1.00002: Analytical Study of the Curling Probe: Resonance Frequencies Ali Arshadi, Ralf Peter Brinkmann The term ``active resonance spectroscopy'' refers to a class of plasma diagnostic techniques which utilizes the ability of plasmas to resonate on or near to the electron plasma frequency. The curling probe is a newly developed variant which may be called an optimized (in particular: miniaturized)hair pin probe [1, 2]. The device can be mounted coplanar in the discharge chamber wall where it practically causes no perturbation of the plasma. Like the hair pin probe, it is resonant with a frequency $f_0$ under vacuum conditions, but experiences a frequency shift in the presence of plasma. However, no reliable analysis exists which relates the magnitude of this shift to the absolute value of the plasma density. In this contribution, we will fill this gap. We first derive a formula for the phase velocity of an electromagnetic wave which propagates along a slit in a thin, perfectly conducting screen located between to dielectrics, and then show how this result can be used to describe the resonance frequencies of the curling probe.\\[4pt] [1] R. B. Piejak \textit{et. al.}: J. Appl. Phys. 95 (2004) 3785.\\[0pt] [2] I. Liang \textit{et. al.}: Appl. Phys. Express 4 (2011) 066101. [Preview Abstract] |
Friday, October 4, 2013 11:00AM - 11:30AM |
TF1.00003: Quantitative diagnostics of reactive, multicomponent low-temperature plasmas Invited Speaker: Thomas Schwarz-Selinger The special emphasis in this work is put on the quantitative determination of the plasma composition of an inductively coupled low temperature plasma (ICP). Several standard plasma diagnostic techniques were applied. As a test case for a multi-component low-temperature plasma argon-hydrogen as well as argon-hydrogen-nitrogen mixed plasmas were investigated. For steady-state plasma operation the ion density and electron temperature were determined with a single tip Langmuir probe. A multi-grid miniature retarding-field analyzer was used to measure the mass integrated ion flux. An energy-dispersive mass spectrometer - a so-called plasma monitor (PM) - was applied to sample ions from the plasma to derive the ion composition. The degree of dissociation of hydrogen and the gas temperature were derived from optical emission spectroscopy. The gas temperature was estimated by the rotational distribution of the Q-branch lines of the hydrogen Fulcher-$\alpha $ diagonal band for the argon-hydrogen mixed plasmas and from the second positive system of N$_{2}$ in argon-hydrogen-nitrogen mixed plasmas. The degree of dissociation of hydrogen was measured by actinometry. The influence of the substrate material of the counter electrode (stainless steel, copper, tungsten, Macor, and aluminium) on the atomic hydrogen concentration was investigated by OES. In addition, ionization-threshold mass spectrometry (ITMS) was used to determine the densities of atomic nitrogen (N) and atomic hydrogen (H and D). Pulsed plasma operation was applied to directly measure the loss rate of H, D and N in the afterglow from the temporal decay of the ITMS signal. From these data the wall loss probability of atomic hydrogen was determined. Furthermore, a zero-dimensional rate equation model was devised to explain the ion composition in these mixed plasmas with different admixture ratios. In addition to the experimental data on electron density, gas temperature, total pressure, atomic hydrogen density, and Ar, H$_{2}$, and N$_{2}$ fraction, the chamber geometry and the required collisional rate coefficients are input parameters for the model. The model was applied to calculate the ion densities and the electron temperature and describes the main features reasonably well supporting the validity of the plasma diagnostics applied. [Preview Abstract] |
Friday, October 4, 2013 11:30AM - 11:45AM |
TF1.00004: Absolute atomic oxygen and nitrogen densities in radio-frequency driven atmospheric pressure cold plasmas: synchrotron vacuum ultra-violet high-resolution Fourier-transform absorption measurements K. Niemi, D. O'Connell, N. de Oliveira, D. Joyeux, L. Nahon, J.P. Booth, T. Gans Reactive atomic species play a key role in emerging cold atmospheric pressure plasma applications, in particular in plasma medicine. Absolute densities of atomic oxygen and atomic nitrogen were measured in a radio-frequency driven non-equilibrium plasma operated at atmospheric pressure using vacuum ultra-violet (VUV) absorption spectroscopy. The experiment was conducted on the DESIRS synchrotron beamline using a unique VUV Fourier-transform spectrometer. Measurements were carried out in plasmas operated in helium with air-like $N_2$-$O_2$ (4:1) admixtures. A maximum in the O-atom concentration of 9.1 10$^{20}$ m$^{-3}$ was found at admixtures of 0.35 vol\%, while the N-atom concentration exhibits a maximum of 5.7 10$^{19}$ m$^{-3}$ at 0.1 vol\%. [Preview Abstract] |
Friday, October 4, 2013 11:45AM - 12:00PM |
TF1.00005: Spatially resolved measurement of Ar excited species in magnetized inductively coupled plasma using multi-port optical emission spectroscopy Yun-Gi Kim, Chang-Seung Ha, Moon-Ki Han, Kwon-Sang Seo, Dong-Hyun Kim, Hae June Lee, Ho-Jun Lee, Il Gyo Koo, Soojin Lee, Hyo-Seong Seong Optical emission spectrometry (OES), which is the spectral analysis of the light emanating from plasma, is probably the most widely used method for monitoring and diagnosis of plasma processes. This technique has the advantage of being external to the reactor and vacuum system. However, the OES method is limited to measure spatial distribution of species accurately. In this work, multi-port optical emission spectroscopy system was developed to improve the space-resolved ability. This multi-port OES system consists of Si wafers, optical fibers, prisms and windows. The Si wafers are used for making the same condition while this device is put in the etching or deposition reactor. The emission light from plasma is collected and transferred through the optical fibers. The spatial distribution of Ar excited species is measured using this device in inductively coupled plasma with and without external axial magnetic field. The off-axis density profile of electron, Ar ion and excited species are appeared in weakly magnetized inductively coupled plasma. Also the emission intensity was changed in this experimental condition. Two-dimensional simulation was studied to verify this experimental result. [Preview Abstract] |
Friday, October 4, 2013 12:00PM - 12:15PM |
TF1.00006: Polymerizable Supramolecular Sensor for Plasma Diagnostics on Wafer Level Hyo-Chang Lee, Seong-Ho Jeon, Jong-Man Kim, Chin-Wook Chung Low temperature reactive plasma allows fabrication of high quality nano-device owing to the synergy effect of the plasma, especially ions impinging on the wafer. We have developed a large area wafer-type plasma diagnostic system based on the polymerizable supramolecular sensor (PSS) that affords colorimetric and fluorometric monitoring of spatial ion density distribution. The PSS system does not require electric circuits or batteries and is found to be very sensitive to the plasma and allows efficient mapping of the ion density distribution. The readily available and conceptually new method should find great utility in the field of plasma diagnostics. [Preview Abstract] |
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