Vacuum Ultraviolet Light Emission Research Articles

Efficient photo-dissociation-induced production of hydrogen radicals using vacuum ultraviolet light from a laser-produced plasma

One of the critical issues in lithography using extreme ultraviolet (EUV) light is tin contamination of the EUV collector mirrors in the tin-based LPP-EUV light source. The contamination can be removed by the reaction of tin atoms with hydrogen radicals producing stannane (SnH4), which is gaseous at the normal temperature. Hydrogen radicals can be produced from hydrogen molecules through photo-dissociation and photo-ionization induced by broadband radiation emitted from the EUV light source. In this work, an efficient production of hydrogen radical using vacuum ultraviolet (VUV) light emitted from laser-produced high-Z plasma is experimentally demonstrated. A two-dimensional radiation hydrodynamic simulation, coupled with photoionization and photo-dissociation cross sections, also shows the efficient hydrogen radical production by increased VUV light emission, as observed in the experiment.

Role of excimer formation and induced photoemission on the Ar metastable kinetics in atmospheric pressure Ar–NH3 dielectric barrier discharges

Tunable diode laser absorption spectroscopy was used to record the space-and time-resolved number density of argon metastable atoms, Ar(1s3) (Paschen notation), in plane-to-plane dielectric barrier discharges (DBDs) operated in a Penning Ar–NH3 mixture at atmospheric pressure. In both low-frequency (LF 650 V, 50 kHz) discharges and dual LF–radiofrequency (RF 190 V, 5 MHz) discharges operated in α–γ mode, the density of Ar(1s3) revealed a single peak per half-period of the LF voltage, with rise and decay times in the sub-microsecond time scale. These results were compared to the predictions of a 1D fluid model based on continuity and momentum equations for electrons, argon ions (Ar+ and Ar2 +) and excited argon 1s atoms as well electron energy balance equation. Using the scheme commonly reported for Ar-based DBDs in the homogeneous regime, the Ar metastable kinetics exhibited much slower rise and decay times than the ones seen in the experiments. The model was improved by considering the fast creation of Ar2 * excimers through three-body reactions involving Ar(1s) atoms and the rapid loss of Ar2 * by vacuum ultraviolet light emission. In optically thin media for such photons, they can readily reach the dielectric barriers of the DBD electrodes and induce secondary electron emission. It is shown that Ar2 * and photoemission play a significant role not only on the Ar metastable kinetics, but also on the dominant ionization pathways and possible α–γ transition in dual frequency RF–LF discharges.

Numerical investigation of the electronic and optical properties of LiLuF4 vacuum ultraviolet material

The electronic band structure and optical properties of a perfect LiLuF4 crystal were calculated using density functional theory within the projector-augmented wave method and a hybrid exchange-correlation functional. LiLuF4 is found to have a direct band gap of 10.55 eV, which is attributed to the transition between the F 2p and Li 3s bands. The dominant absorption peak originates from transitions between the F 2p to Lu 6d states and therefore, efficient emission in the vacuum ultraviolet (VUV) region is expected from LiLuF4 by exciting into the Lu 6d states using 15.21 eV (82 nm) of pump energy. The LiLuF4 crystal is highly transparent with a transmission edge of 10.37 eV (119 nm). Moreover, it is optically isotropic down to the transmission edge. Optical isotropy and transparency are desirable in the development of optical components for VUV applications, whereas the direct band gap transition is essential for efficient VUV light emission.

Intense vacuum ultraviolet and infrared scintillation of liquid Ar-Xe mixtures

Vacuum ultraviolet light emission from xenon-doped liquid argon is described in the context of liquid noble gas particle detectors. Xenon concentrations in liquid argon from 0.1 ppm to 1000 ppm were studied. The energy transfer from the second excimer continuum of argon to the second excimer continuum of xenon is observed by recording optical emission spectra. The transfer almost saturates at a xenon concentration of for which, in addition, an intense emission in the infrared at a peak wavelength of with photons per MeV deposited by electrons had been found. The corresponding value for the VUV emission at a peak wavelength of 174 nm (second excimer continuum of xenon) is determined to be photons per MeV electron energy deposited. Under these excitation conditions pure liquid argon emits photons per MeV electron energy deposited at a peak wavelength of 127 nm. An electron-beam–induced emission spectrum for the 10 ppm Ar-Xe liquid mixture ranging from 115 nm to is presented. VUV emission spectra from xenon-doped liquid argon with exponentially varied xenon concentrations from 0.1 ppm to 1000 ppm are also shown. Time structure measurements of the light emissions at well-defined wavelength positions in the vacuum ultraviolet as well as in the near-infrared are presented.

Vacuum ultra-violet emission of plasma discharges with high Xe partial pressure using a cathode protective layer with high secondary electron emission

In this work, the mechanism of the vacuum ultra-violet (VUV) emission of plasma discharges, with high Xe partial pressure and high ion-induced secondary electrons emission protective layer, is studied by measuring the VUV light emission directly and comparing it with two-dimensional simulations. From the panel measurement, we find that the high intensity of excimer VUV mainly contributes to the high luminous efficacy of SrCaO-plasma display panels (PDP) at a low sustain voltage. The unchanged Xe excitation efficiency indicates that the electron temperature is not decreased by the high secondary electrons emission protective layer, even though the sustain voltage is much lower. From the two-dimensional simulations, we can find that the ratio of excimer VUV to resonant VUV, which is determined by the collision rate in the discharge, is only significantly affected by the Xe partial pressure, while it is independent of the sustain voltage and the secondary-electrons-emission capability of protective layer. The unchanged average electron energy at the moment when the electric field becomes maximum confirms that the improvement of the VUV production efficiency mainly is attributed to the increase in electron heating efficiency of a PDP with high ion-induced secondary electrons emission protective layer. Combining the experimental and the simulation results, we conclude about the mechanism by which the VUV production is improved for the plasma display panel with a high Xe partial pressure and a cold cathode with high ion-induced secondary electrons emission.

Ballistic electron emission from quantum-sized nanosilicon diode and its applications

A quantum confinement effect renders silicon a functional wide-gap material with useful functions. For instance, a diode based on nanocrystalline silicon (nc-Si) exhibits characteristic quasi-ballistic emission effects in various media. As means for physical excitation and probing, the applicability to parallel electron beam lithography and high-sensitivity image-pickup has been demonstrated in vacuum. The energetic electron incidence into air and Xe ambient induces negative ion generation by electron attachment into oxygen molecules and vacuum ultraviolet light emission by internal excitation of Xe molecules, respectively. Another effect is that the nc-Si ballistic emitter can supply highly reducing electrons into aqueous and metal-salt solutions without the use of counter electrodes. This is an attractive process that will be applicable to hydrogen generation and thin metal film deposition.

Direct excitation of xenon by ballistic electrons emitted from nanocrystalline‐silicon planar cathode and vacuum‐ultraviolet light emission

Abstract— To verify the possible use of energetic electrons for direct excitation of inert gas molecules, a nanocrystalline‐silicon (nc‐Si) planar ballistic emitter is operated in a high‐pressure xenon gas ambience. Under the pulse drive, vacuum‐ultraviolet (VUV) light emission is detected without any signs of discharge. The transient behavior of the VUV light emission properly corresponds to that of the nc‐Si emitter. In accordance with quantitative analyses of electron‐emission characteristics and the VUV output, the electron‐to‐photon conversion efficiency reaches 81% in the relatively efficient emitter case. The VUV output power is mainly determined from the number of electrons with energies compatible the with internal excitation of xenon. The emission spectrum observed at a pressure of 10 kPa shows peaks at 152 and 172 nm, which are thought to be originated from metastable Xe2* states. In contrast to the case of conventional impact ionization, no near‐infrared (NIR) peaks are seen in the spectrum. These results strongly suggest that the incidence of energetic electrons causes direct excitation of xenon molecules followed by radiative relaxation through intermediate states. The generated VUV light can be easily converted to visible light using a phosphor screen. As a discharge‐free VUV light emission, this phenomenon is potentially applicable to mercury‐free, high‐efficacy, and high‐stability flat‐panel light‐emitting device.

Vacuum-ultraviolet light emission from xenon directly excited by ballistic output electrons of nanocrystalline silicon planar cathode

The effect of electron incidence into xenon gas molecules has been investigated by using a nanocrystalline silicon (nc-Si) planar ballistic emitter. Vacuum-ultraviolet light emission is observed without discharging when the nc-Si device is driven in xenon gas. The emission spectrum of xenon at 10kPa shows peaks at 152 and 172nm which originate from Xe2* radiation. These results strongly suggest that energetic electrons directly excite xenon molecules followed by radiative relaxations. The observed effect is potentially applicable to mercury-free, efficient, and stable flat panel light sources.

Vacuum Ultra-Violet Light Emission and its Photoelectric Effect Using a Flash Photolysis Techniques.

A flash photolysis technique is useful to study chemical reactions of explosively burning hydrocarbon/oxidizer mixtures associated with emission and absorption spectra observations. When a single ion probe is inserted into the reacting gases to measure the ion current. it is positively or negatively electrified for a moment according to the conditions at the beginning of chemical reactions. A vacuum ultra-violet light (VUV) appears together with the CH, OH and C2 spectra and causes a photoelectric effect not only on the probe surface but also on the inner surface of the quartz combustion tube. The positive or negative electrification can be derived theoretically from the photoelectric effect on the quartz tube. It is concluded that the emitter is highly excited carbon monoxide, because the VUV photon should have an energy higher than 10 eV to cause electron emission from the quartz tube inner surface.

VUV emission and breakdown in parallel-plate chambers

The emission of vacuum ultraviolet (VUV) light by the electron avalanches is responsible for the photon feedback in gaseous detectors, worsening their performance at high gains. It is also generally assumed that there is a connection between breakdown and photon feedback in these detectors. We measured the VUV light emission from the avalanches in a parallel-plate avalanche chamber (PPAC) in the spectral region 120–170 nm. The radiation was detected by a photosensitive wire chamber coupled to the PPAC through an UV-transparent window. By choosing the gas filling of the wire chamber several spectral bands could be selected, suggesting an identification of the emission origin. The breakdown limit of the PPAC was simultaneously-measured and found to be fairly independent of the measured VUV emission. The results obtained provide a guide to the selection of gaseous mixtures for practical use in photon-counting detectors, minimizing the photon feedback.

Multiple-harmonic generation in rare gases at high laser intensity.

We present experimental measurements of vacuum ultraviolet light emission processes in a 15-Torr rare-gas medium exposed to a strong 1064-nm laser field. Apart from a small number of lines which correspond to discrete transitions, and a broad continuum emission, we essentially observe the odd harmonics of the laser field, up to very high order. At a 3\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ laser intensity, the highest-order harmonics observed are the 33rd in Ar, the 29th in Kr, and the 21st in Xe. The harmonic distribution presents three regions: a steep decrease for the first harmonics, a plateau, and a sudden cutoff at high order. We study the variation of the conversion efficiency for some of the harmonics as a function of the incident laser intensity and the atomic density. Finally, we analyze the harmonic-generation results as thoroughly as possible, in particular, by characterizing the phase-matching conditions in our experiment.

Vacuum ultraviolet light emission from low-pressure hydrocarbon-oxygen flames

The complete vacuum ultraviolet emission spectrum of hydrocarbon-oxygen flames has been measured by working at low pressure to reduce self-absorption and collisional de-excitation. The spectrum is emitted by flames of C 2 H 2 , C 2 H 4 , C 3 H 8 , and CH 4 with approximately the same intensity distribution, but with intensity diminishing in the order given. All the bands correlate with known bands of the CO fourth positive system, and transitions arising from the first seven vibrational levels of the upper state with excitation energies of 185 to 213 kcal/mole have been observed. Two series of quantitative measurements of the emission spectrum have been made for comparison with measurements of chemi-ionization by a Langmuir probe and total collection, respectively. The chemiluminescence arising from CH, OH, C 2 , and possibly CHO as well as the (CO) (O) continuum have also been measured. No evidence of a chemical mechanism linking any of the measured quantities could be found.