Xe Mixtures Research Articles

Infrared emission spectrum and potentials of 0+u and 0+g states of Xe2 excimers produced by electron impact

We present an investigation of the Xe2 excimer emission spectrum observed in the near-infrared range about 7800 cm−1 in pure Xe gas and in an Ar (90%)–Xe (10%) mixture for P = 0.1 MPa at T = 300 K obtained by exciting the gas with energetic electrons. The Franck–Condon simulation of the spectrum shape suggests that the emission stems from a bound–free molecular transition never studied before. The states involved are assigned as the bound (3)0+u state related to the 6p[1/2]0 atomic limit and the dissociative (1)0+g state with the 6s[3/2]1 limit. A comparison with the spectrum simulated by using theoretical potentials for internuclear distances over which the vibrational eigenfunctions of the bound state have non-negligible amplitude shows that the dissociative potential does not reproduce correctly the spectrum features. A best fit, purely repulsive potential is thus proposed to accurately reproduce the observed spectrum.

Spatiotemporal behavior of excited Xe*(1s4,1s5) and Kr*(1s5) atoms measured by laser-absorption spectroscopy in unit cell of a plasma display panel with Xe–Kr–Ne ternary gas mixture

We have studied the effects of ternary gas mixtures of Xe(10%)–Kr(20% and 40%)–Ne on the luminous efficiency in ac plasma display panels. Spatiotemporal behaviors of near infrared (IR) emission was measured by an intensified charge-coupled device camera equipped with a narrow bandpass filter and absolute densities of excited Xe* and Kr* atoms in the lowest resonance (1s4) and metastable (1s5) levels were measured by a technique of microscopic laser absorption spectroscopy. We have found interesting features from both emission and absorption experiments, such as longer near-IR emission (0.3–0.4μs) and different temporal behaviors between the excited Kr*(1s5) atoms and Xe*(1s4,1s5) atoms. We have also found that the order of magnitude of the peak density of excited Kr*(1s5) atoms (∼1012cm−3) was ten times smaller than that of Xe*(1s4,1s5) atoms, and that their decay time was remarkably short (∼0.3μs). These results have then been compared with those for a binary gas mixture of Xe(10%)–Ne. At a certain range of the sustain voltage, the production rate of Xe*(1s4,1s5) atoms and the luminous efficiency have turned out to be slightly improved for the ternary gas mixtures, compared to the binary gas mixture.

Lighting from thin (

Flat lamps, having radiating areas as large as 15 × 15 cm2 and comprising arrays of Al/Al2O3 microcavity plasma devices, have been fabricated and characterized in the rare gases. Sealed arrays of devices with microcavities having diamond-shaped cross-sections yield lamps with an overall thickness of ∼800 µm (of which ∼500 µm is the quartz output window) and luminance and luminous efficacy values greater than 1600 cd m−2 and 10 lm W−1, respectively, are observed in preliminary experiments in which microplasmas in a Ne/20%Xe mixture illuminate a commercial green phosphor in a transmission arrangement with the ∼10 µm thick phosphor film situated immediately above the array. Efficacy values well in excess of 20 lm W−1 are expected when the array design and microcavity-phosphor geometry are optimized. Fully flexible arrays sealed in polymeric packaging have also been demonstrated, thereby providing access to new opportunities for lighting in which lightweight arrays are mounted onto curved surfaces.

Reduction of Ion Energies From a Multicomponent $Z$ -Pinch Plasma

This paper studies the expanding plasma dynamics of ions produced from a 5J Z-pinch xenon light source used for extreme ultraviolet (EUV) lithography. Fast ion debris produced in such plasmas cause damage to the collector mirror surface. Because of the great degree of erosion and the change in surface roughness properties, the reflectivity of EUV light at 13.5 nm drops drastically. Reducing ion energies and stopping the ion flux are a potential solution toward the success of EUV lithography. Ion energies are measured in kiloelectronvolt range using a spherical sector electrostatic energy analyzer. Preliminary computational work indicates that the observed high energies of ions are probably resulting from Coulomb explosion initiated by pinch instability. Mixed fuel experiments are performed using a mixture of Xe, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The average energy of the expelled Xe ions is significantly decreased if the mobile lighter gas species are present in the main fuel. The magnitude of the Xe ion signal is reduced as well. This reduction in the quantity of heavy ions and their energy could greatly extend the lifetime of the collector optics used in EUV lithography.

Extending the shelf-life of asparagus spears with a compressed mix of argon and xenon gases

Noble gases that form clathrate hydrates when dissolved into water and restrict water molecule activity can prolong the shelf life of fruits and vegetables. Physiological and physical aspects of asparagus spears treated with mixtures of compressed (1.1 MPa absolute) argon (Ar) and xenon (Xe) (2:9 in partial pressure) were compared with controls under normal preservation in modified atmosphere packaging (5% O 2 and 5% CO 2) and cold storage (4 °C). The bract opening and respiration rates of asparagus spears were reduced slightly after the Ar–Xe treatment. A clear reduction between the compressed air and compressed mixture of Ar and Xe was only observed on the 6th and 15th days of storage for the bract opening rate and the 15th day of storage for the respiration rate. The climacteric peak was comparatively inconspicuous. The increase of crude fiber was reduced and both vitamin C and chlorophyll preserved. Based on comprehensive evaluation, asparagus spears treated for 24 h with mixtures of Ar and Xe could be kept in good quality for 12 days at 4 °C.

Operation of a single-GEM in noble gases at high pressures

We report the performance of a single-Gas Electron Multiplier (GEM) operating in pure Ar, Xe, and in Ar-50lmbar Xe mixtures, in the range of 1–7lbar. The maximum gain and voltage that can be applied to the GEM are investigated as a function of filling pressure and compared to the results obtained with triple-GEM and MHSP (Micro Hole and Strip Plate) multipliers. The maximum gain achieved at 1lbar Xe is about 103, presenting a fast decrease with pressure to values around 300, 50 and 10 at 2, 3 and 5lbar, respectively. Gains around 100 were achieved in Ar up to 4lbar, decreasing to values of few tens at 6lbar. On the other hand, gains around 500 can be achieved in Ar-50lmbar Xe mixtures up to 5lbar, presenting a fast reduction at higher pressures due to the limitations on the maximum gain imposed by the GEM discharge limit. Nevertheless, gains above 100 can be obtained for pressures between 6 and 7lbar, indicating a good potential for neutron detection.

Laboratory Observation of Secondary Shock Formation Ahead of a Strongly Radiative Blast Wave

We have previously reported the experimental discovery of a second shock forming ahead of a radiative shock propagating in Xe. The initial shock is spherical, radiative, with a high Mach number, and it sends a supersonic radiative heat wave far ahead of itself. The heat wave rapidly slows to a transonic regime and when its Mach number drops to two with respect to the downstream plasma, the heat wave drives a second shock ahead of itself to satisfy mass and momentum conservation in the heat wave reference frame. We now show experimental data from a range of mixtures of Xe and N2, gradually changing the properties of the initial shock and the environment into which the shock moves and radiates (the radiative conductivity and the heat capacity). We have successfully observed second shock formation over the entire range from 100% Xe mass fraction to 100% N2. The formation radius of the second shock as a function of Xe mass fraction is consistent with an analytical estimate.

The influence of H2addition on the discharge characteristics of Ne-Xe in color alternate current plasma display panel

The influence of H 2 addition on the discharge characteristics of Ne-Xe in a AC-PDP macro-cell was studied in this paper. The experimental results show that there are remarkable decreases of the firing voltage and the minimum sustaining voltage, and a remarkable increase of the discharge current, and an increase of the sustaining voltage memory margin by an amount of H 2 addition in Ne + 4%Xe mixture when the sustaining voltage frequency is in the range of 12.5–93.5 kHz. As for H 2 % = 0.12 and f = 15.5 kHz, the discharge current is 6 times of the discharge current without H 2 addition in Ne + 4%Xe mixture. The maximum value of the increase of discharge current can be obtained at f = 32.5 kHz as well as the firing voltage and the minimum sustaining voltage have the decreases of 12 V and 11 V. The maximum value of the sustaining voltage can be obtained at H 2 % = 0.12 and f = 93.5 kHz. The firing voltage and sustaining voltage can be depressed remarkably without deterioration of the voltage memory margin by an amount of H 2 addition in Ne + 4%Xe.

Collisional energy transfer in the intermediate states used for optical–optical double resonance excitation of ion-pair states in I2

The optical-optical double resonance spectra of I(2) and I(2)-Xe mixtures at room temperature reported in the literature using a fixed-wavelength, broad band pump laser have now been recorded using a tuneable, narrow band source. We show that during the time of the overlapped laser pulses ( approximately 10 ns) and with 10-20 Torr of Xe there is widespread collisional energy transfer in the intermediate state and that this phenomenon offers an alternative explanation for the broad bands in the excitation spectrum, assigned to XeI(2) complexes by the authors of the earlier study (M. E. Akopyan, I. Y. Novikova, S. A. Poretsky and A. M. Pravilov, Chem. Phys., 2005, 310, 287). Dispersed emission bands, previously attributed to direct fluorescence from the ion-pair state(s) of the complexes, are re-assigned to emission from ion-pair states of the parent I(2) that are populated by collisional energy transfer out of the initially excited state.

Refined interpretation of broadband radiation from a gas-discharge plasma of a krypton-xenon mixture

The earlier interpretation of the broadband continuum observed in the VUV emission spectra of a gas-discharge plasma in a Kr + Xe mixture is refined. On the assumption that this continuum is caused by the bound-free transitions v,0+(3 P 1) → e, 0+(1 S 0) in KrXe* and Xe2 molecules, the distribution of the population over the vibrational levels v of the states 0+(3 P 1) of both molecules is obtained and the vibrational temperature for different methods of excitation of the spectrum is determined. Internuclear potentials 0+(3 P 1) and 0+(1 S 0) available from the literature are used. To improve the agreement between the calculated and experimental spectra, it is proposed to modify the positive branch of the potential curve 0+(1 S 0) of the KrXe* molecule.

One quarter million (500×500)pixel arrays of silicon microcavity plasma devices: Luminous efficacy above 6lumens∕watt with Ne/50% Xe mixtures and a green phosphor

Arrays comprising 250 000 Si microcavity plasma devices, each with an emitting aperture of 50×50μm2 and tapered sidewalls (inverted pyramid cavity), have been fabricated in 100-mm (4″) diam. wafers and operated in the rare gases and Ar∕N2 mixtures with sinusoidal ac or bipolar dc excitation. Having an overall active area of 25cm2 and a 25% filling factor, these 500×500 arrays exhibit the pixel-to-pixel emission uniformity characteristics of arrays at least a factor of 6 smaller, and yet are efficient in generating vacuum ultraviolet (VUV) radiation. Luminous efficacies above 6lm∕W and luminance values approaching 2000cd∕m2 are measured when a 500×500 array, operating with a Ne/50% Xe gas mixture, illuminates a 20-μm-thick film of a commercial green phosphor (Mn:Zn2SiO4). Despite the nonoptimal transmission geometry of the array-phosphor structure, the efficacy and luminance produced by the VUV-driven phosphor for a Ne/50% Xe mixture and a total pressure of 800Torr are measured to be 7.2±0.6lm∕Watt and 525±75cd∕m2, respectively, for a 20-kHz sinusoidal ac voltage of ∼284V rms. Maximizing the luminous efficacy–luminance product lowers the optimal pressure of Ne/50% Xe mixtures to roughly 1atm. The magnitude of the radiant output generated by these arrays, in addition to the rapid rise in emitting efficiency with increased Xe content in Ne/10%–50% Xe mixtures, suggest that this microplasma array structure will be of value for both microdisplay and biomedical applications.

18.3: Microcavity Plasma Devices for Display Applications: Independently Addressable Arrays with Improved Luminous Efficacy

Independently addressable arrays of microcavity plasma devices have been fabricated and tested. This presentation reports data demonstrating that these devices provide a basis for alternative PDP cell structures of improved luminosity. The radiant output of Si arrays yields values for the luminous efficacy exceeding 7 lumens/W at 800 Torr of a Ne/50% Xe mixture. Measurements of the unoptimized radiant output of 500 × 500 (250,000) arrays of Si microplasma devices, operating in Ne/(5–50)% Xe mixtures and photoexciting (in transmission mode) a 20 μm thick film of green phosphor, yield values of the luminous efficacy up to 7.2 ± 0.6 lumens/W for a Ne/50% Xe mixture (total pressure of 800 Torr) excited by a 20 kHz sinusoidal voltage waveform. Sustaining voltages ranging from ∼250 to 340 V (RMS) yield luminance values up to ∼2000 cd-m−2 for Ne/50% Xe mixtures without incorporation of MgO. Recent laser spectroscopic measurements of Xe2 (a3∑u+ absorption in the visible and near-infrared suggest steps to be taken in PDP cell design, particularly as the Xe content in Ne/Xe mixtures is increased.

Pulsed excitation of low-pressure He–Xe glow discharges

Theoretical and experimental investigations of the temporal behaviour of the column plasma of square-wave-pulsed low-pressure glow discharges in mixtures of helium and xenon are presented. In the framework of the time-dependent, radially averaged model the equations for the external electrical circuit accounting for an approximate treatment of the electrode regions, rate equations for 13 xenon and 3 helium states and the time-dependent Boltzmann equations of the electrons are self-consistently solved. The experimental studies comprise time-resolved measurements of the electrical characteristics and of the axis densities of the lowest excited states of xenon. The main aspects of the self-consistent model and of the electrical and spectroscopic measurements are given and the results for the He–Xe mixtures containing 2% of xenon in a discharge tube with a diameter of 17.5 mm and an electrode distance of 20 cm at applied voltages between 140 and 250 V and gas pressures between 1 and 4 Torr are presented. The agreement between experimental and theoretical data is generally good during the entire pulse period. The analysis shows that the velocity distribution function of the electrons is subject to large structural alterations as a result of the periodic change between the on-phase of the discharge, driven by the electric field, and the off-phase when chemo-ionization process gets large importance. However, the chemo-ionization processes are not efficient enough to act as a reservoir of charged particles under the conditions considered. Concerning the excited xenon atoms it is found, in particular, that their temporal behaviour is significantly influenced by their mixing due to electron collision processes for optically forbidden transitions in the afterglow period.

Modelling the broad-band continuum of the gas-discharge plasma of a krypton+xenon mixture

A semiempirical calculational procedure is used to study the broad-band continuum observed in the VUV emission spectra of the gas-discharge plasma in a Kr+Xe mixture. On the assumption that the indicated continuum is caused by bound-free v, 0+(3P1)→epsilon var,0+(1S0) transitions in KrXe* and Xe2 molecules, the population distribution over the vibrational levels of the 0+(3P1) states of both molecules is obtained, and their vibrational temperature is determined using various methods of exciting the spectrum. In order to obtain better agreement of the calculated and experimental spectra, it is proposed to modify the repulsive branch of the 0+(1S0) potential curve of the KrXe* molecule.

Calculation of Ion Mobilities and their Effects on Gas Discharge of AC Plasma Display Cells

We have found that ion mobilities in a gas mixture greatly affect discharge characteristics of a plasma display cell. Therefore, correct ion mobilities are required to obtain meaningful simulation results on plasma display cells. Since plasma display panels use microdischarges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of the discharge gas mixtures is one of the main factors that determine luminous efficacy. Thus, intensive studies on the discharge gas mixture are essential to optimize it and the accurate determination of ion mobilities in it is necessary. We have discussed how to determine necessary values of ion mobilities in various discharge gas mixtures including the three-species He–Ne–Xe mixture. Calculated ion mobilities and their effect on the discharge of an AC plasma display cell have also been presented and discussed. We have revealed that the enhanced ion mobilities in the gas mixture resulting from adding He gas to the conventional Ne–Xe mixture play an important role in increasing the luminous efficacy of a plasma display cell sustained in the He–Ne–Xe mixture by decreasing the cathode fall potential.

Adsorption Purification of Xenon to Remove Hexafluoroethane Impurities

We present the individual isotherms for Xe and C2F6 adsorption on activated carbon (T = 213 K), curves of C2F6 adsorption on activated carbon from a mixture of Xe and N2 (T = 160 K), and calculated output curves for Xe and C2F6 on activated carbon (T = 160 K).

Control of dissociation by varying oxygen pressure in noble gas admixtures for plasma processing

The electron density, electron temperature, and atomic oxygen density are measured in mixtures of oxygen and noble gas discharges as a function of the input power and the oxygen partial pressure. The atomic oxygen density is measured by both actinometry and appearance mass spectrometry and plasma density and electron temperature are monitored with Langmuir probes. The background noble gas determines the electron density and temperature as long as the partial pressure of oxygen remains small. The dissociated atomic neutral oxygen density is highest in O2∕Xe mixtures and lowest in O2∕He mixtures, increases with electron density, and decreases with electron temperature. Estimates of the dominant source and sink rates of atomic oxygen are used to explain these results using a simple zero-dimensional dissociation kinetics and transport model. The use of noble gas/oxygen mixtures allows for a larger range of atomic oxygen density and ion density than in pure oxygen plasmas, and also allows for independent control of the ion density and the atomic oxygen density.

Environmental influence on the IR fluorescence of Xe2* molecules in electron beam excited Ar–Xe mixture at high density

We report new measurements of the near infrared (NIR) Xe$_2^*$ excimer fluorescence in an electron--beam--excited Ar (90%)--Xe (10 %) mixture at room temperature. Previous measurements up to a density $N\approx 2\times 10^{26}$ m$^{-3}$ discovered a broad excimer fluorescence band at $\approx 7800$ cm$^{-1},$ whose center is red--shifted by increasing $N$ (A. F. Borghesani, G. Bressi, G. Carugno, E. Conti, and D. Iannuzzi, {\em J. Chem. Phys.}, {\bf 115}, 6042 (2001)). The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density--dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to $N\approx 6\times 10^{26}$ m$^{-3}, $ confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credence to the validity of the proposed explanation of the experimental findings.

Implications of microcavity plasma devices for new plasma-display-panel cell structures with improved luminosity

— The unique properties of microcavity plasma devices, and their potential to provide the basis for alternative PDP cell structures of improved luminosity, are described. Arrays as large as 500 × 500 (250,000) inverted pyramid microcavity devices, each with an emitting aperture of 50 × 50 μm2 and designed for AC or bipolar excitation, have been fabricated in Si and operated in the rare gases and Ar/N2 mixtures at pressures up to and beyond 1 atm. For a device pitch of 100 μm, the array filling factor is 25% and the device packing density is 104 cm−2. Measurements of the unoptimized radiant output of 500 × 500 arrays of Si microplasma devices, operating in Ne/(5–50)% Xe mixtures and photoexciting (in transmission mode) a 20-μm-thick film of green phosphor, yield values of the luminous efficacy up to 7.2 ± 0.6 lm/W for a Ne/50% Xe mixture (total pressure of 800 Torr) excited by a 20-kHz sinusoidal voltage waveform. Sustaining voltages ranging from ∼250 to 340 V (RMS) yield luminance values up to ∼2000 cd/m2 for Ne/50% Xe mixtures but the incorporation of field emitters or MgO into the microcavity is expected to significantly reduce the required operating voltage. Also, the fabrication of microplasma devices in ceramic multilayer structures or glass for scaling the display area is discussed briefly. Recent laser spectroscopic measurements of Xe(a 3Σu+) absorption in the visible and near-infrared suggest steps to be taken in PDP cell design, particularly as the Xe content in Ne/Xe mixtures is increased.

Emission Characteristics of a Glow Discharge in a Mixture of Heavy Inert Gases with Iodine Vapor

The results of a systematic investigation of the emission characteristics of a low-pressure UV excimer-halogen lamp pumped by a longitudinal dc glow discharge are presented. The discharge was initiated in mixtures of heavy inert gases with iodine vapor at a total pressure of 100–2000 Pa and a power deposited into the plasma of 10–100 W. Current-voltage characteristics of the glow discharge and emission spectra of the plasma in the region of 190–360 nm are studied. The radiation intensity at the resonance line of the iodine atom (206.2 nm) and the intensity at the peaks of the XeI(B-X) (253 nm) and I2(B-X) (342 nm) emission bands are analyzed as functions of the pressure and partial composition of the mixtures of Ar, Kr, and Xe with iodine vapor, as well as the electric power of the glow discharge. The most efficient gas mixtures are determined for an electric-discharge UV iodine vapor lamp with continuous-wave emission and a long service life before a change of the mixture is required.