Christophe Cachoncinlle

Fluorescence of high-pressure argon excited by an energetic flash X-ray source

The fluorescence from high-pressure argon plasmas (1-30 bar) has been excited with an intense flash X-ray device. For the first time a spectrum from 110 to 700 nm has been recorded under such conditions. The spectra obtained in the UV-VUV were very similar to those recorded with alpha -particle excitation at equivalent pressures. The dominant features were the so-called second and third continua of argon. The visible fluorescence was found to be negligible in comparison with the VUV continua.

Time-resolved spectroscopy of high pressure rare gases excited by an energetic flash X-ray source

Abstract Fluorescence from high pressure (0.1–30 bar) rare gas plasmas has been excited using an intense flash X-ray source specially developed and optimized for this experiment. Spectral analysis of the so-called “third continuum” of rare gases is presented. Time-resolved spectroscopy, absorption measurements and pressure dependence studies have provided an extended database on this longer wavelength continuum of rare gases. These data allow us to understand some of the previously contradictory results reported in the literature. They strongly support a multi-component spectral aspect of the previously called “third continuum”. In fact, the observed fluorescence result from the superposition of several continua whose relative intensities are strongly dependent upon pressure. This suggests that different species are at its origin. The name of “third continuum” does not seem anymore appropriate when speaking of the whole fluorescence emitted in the longer wavelength continuum by high pressure rare gas plasmas. Generally speaking, the flash X-ray device was proven to be a very convenient and powerful tool for the study of high pressure plasmas resulting in UV-VUV fluorescence.

Third continuum of argon in high pressure plasmas excited by dielectric controlled discharge

Abstract In this work we report what we believe to be the first observation of the third continuum of argon in plasmas, at pressures between 100 and 4000 Torr, created by discharge excitation. This continuum, centered at 188 nm, has been clearly seen not only in pure argon, but also in presence of various reactants and especially in argon-helium mixtures which has not been reported before.

Transparent conductive Nd-doped ZnO thin films

Transparent Nd-doped ZnO films with thickness in the range of 70 to 250 nm were grown by pulsed-laser deposition (PLD) on c-cut sapphire substrates at various oxygen pressures and substrate temperatures. A wide range of optical and electrical properties of the films were obtained and correlated to the composition and crystalline structure. The Nd-doped ZnO films are smooth, dense, and display the wurtzite phase. Different epitaxial relationships between films and substrate as a function of growth pressure and substrate temperature were evidenced by asymmetric x-ray diffraction measurements. By varying PLD growth conditions, the films can be tuned to have either metallic or semiconductor characteristics, with good optical transmittance in the visible range. Moreover, a low-temperature metal-insulator transition may be observed in Nd-doped ZnO films grown under low oxygen pressure. Resistivities as low as 6 × 10−4 Ω cm and 90% optical transmittance in the visible range and different near-infrared transmittance are obtained with approximately 1.0–1.5 at.% Nd doping and growth temperature of approximately 500 °C.

Discharge-based sources of XUV-X radiations: development and applications

There is an increasing use of high energy photons in many fields of research and in industry. Where large installations such as synchrotrons or dedicated laser based source facilities can provide solutions for specific needs, they are presently unable to bring convenient solutions for on-site experiments or industrial processes. Compact discharge based devices appear to be a very interesting response to the demand in many cases. They can provide high photon fluxes in a wide spectral range, from VUV to hard x-rays, covering most of the actual needs. Certainly, they still need a lot of improvement and optimization to meet the most stringent requirements. In this paper, we will present some of the recent results we obtained in that field along with new applications. Among them, we will present our report on the performance of a novel and truly compact xenon-filled fast capillary discharge system which generates radiation mostly in the EUV region (10–16 nm) developed in the framework of an EUV lithography program. We will also present results obtained in the field of hard x-ray generation with a new source capable of producing high dose pulses in quasi-continuous or burst mode at a very high frequency developed for high speed cineradiography.

Time-resolved spatial distribution of an ablative capillary discharge obtained with a pinhole camera

Time- and space-resolved measurements of an ablative polyethylene capillary discharge using a pinhole camera are presented in this paper. Measurements with and without a 0.1 µm thick polyimide filter allowed us to identify the soft x-ray production zones. The images show that the plasma, mainly composed of highly ionized carbon, was not detached from the capillary wall during the heating phase. This plasma behaviour does not favour the development of a recombination-pumped x-ray laser. For two capillary lengths, the plasma dynamics were observed at constant power density in a first run and at identical current waveform in a second run. In both cases, they were different and could induce errors on gain measurement when varying capillary lengths. To our knowledge, this is the first report of time-resolved pinhole images of ablative carbon capillary discharges used as soft x-ray sources.

Compact flash X-ray sources and their applications

Abstract Compact flash X-ray machines are opening up extended fields of applications. X-ray diodes driven by repetitive small size pulsers have been shown able to deliver high dose rates of X-rays in pulses of nanosecond to microsecond duration. Improvements have been carried out on the lifetime of the diodes and reliability of the systems to allow operation at constant emitted dose over long periods of time. After a brief review of recent developments, described here, in more details, is the progress obtained at the GREMI laboratory in the development of true table-top flash X-ray sources producing strong X-ray doses in nanosecond pulses at a high repetition rate (50 Hz). Doses up to 2 R (5.2 × 10−4 C/kg), measured at the output window, of X-rays between 5 and 200 keV can be generated from either a linear source (up to 10 cm long) or from a focal spot of less than 300 μm in diameter depending on the electrode configuration. Of the numerous applications of compact flash X-ray sources, an example is given of the use of these devices for the excitation of high pressure gas samples, realized at GREMI. Such an energetic excitation leads to important populations of highly excited ionic species.

Tailored electric and optical properties of Nd-doped ZnO: from transparent conducting oxide to photon down-shifting thin films

Nd-doped ZnO films with highly tunable properties were grown by pulsed electron beam deposition at 500 °C on Si and c-cut single crystal substrates under oxygen gas. The effects of a slight change in the oxygen pressure (10−2 to 2 × 10−2 mbar) on the composition, structure and physical properties of the films were studied. Films grown at 10−2 mbar present a low resistivity (5 × 10−3 Ω cm) and high transparency in visible range and do not show any near-infrared emission due to Nd3+ ions. On the contrary, films grown at 2 × 10−2 mbar have high resistivity (>16 Ω cm), high optical transparency and near infrared emission of the Nd3+ ions is observed under indirect excitation at 335 nm (i.e. absorption by the ZnO matrix and transfer to Nd3+ ions). These significant changes in physical properties, leading from transparent conducting oxide to photon down-shifting thin films, are related to growth mode in pulsed-electron beam deposition.

Spectroscopic and energetic investigation of capillary discharges devoted to EUV production for new lithography generation

In this work, ablative and gas capillary discharges have been investigated as potential sources for the EUV lithography technology. Carbon and lithium ablative discharge spectroscopy and EUV energy measurements have been performed. Gas (O2, Ne, Ar, Kr and Xe) capillary discharge were powered by fast, nanosecond, high voltage Blumlein-like pulser. Detailed investigation of capillary length and diameter, gas pressure, capacitance and inductance of the electrical driver are documented. The energy density, expressed in J cm-3, appears as a monitoring factor for an efficient production of 13.5 nm radiation band. The measurement and the evaluation of measurement uncertainties lead to the conclusion that the in band, 13.5 nm +/- 0.9 nm, energy radiated by the Xe lamp developed in this work ranges from 0.5 mJ/sr/shot to 20 mJ/sr/shot for a 7 J energy input. Repetition rate investigation of the first prototype have shown operation at 50 Hz in continuous mode and up to 350 Hz in burst mode.

Compact flash x-ray source producing high average powers in nanosecond pulses

X‐ray diodes driven by repetitively pulsed Blumleins have been shown to be able to deliver high dose rates of x rays in pulses of nanosecond duration. Reported here is a study of the scaling of such devices conducted to isolate the primary factors limiting performance. Low residual gas pressure in the output diode together with the critical alignment of the electrodes were found essential for enhanced output. Optimizations served to increase the x‐ray yield by an order of magnitude and the resulting performance is reported. At the output window, dose rates exceeding 1.4 kR min−1 were obtained in nanosecond pulses from the finished device of table top size at a charging voltage of 30 kV and a pulse repetition rate of 50 Hz.