Argon Target Research Articles

Compact inline optical electron polarimeter

A compact optical electron polarimeter using a helium target is described. It offers a maximum fluorescence detection efficiency of ~20 Hz/nA, which is an order of magnitude higher than that of earlier designs. With an argon target, this device is expected to have a polarimetric figure-of-merit of 270 Hz/nA. By relying on a magnetic field to guide a longitudinally spin-polarized electron beam, the present instrument employs fewer electrodes. It also uses a commercially available integrated photon counting module. These features allow it to occupy a smaller volume and make it easier to operate.

Sputtered Nickel Oxide Films for NO<sub>2 </sub>Gas Sensors

In recent years, lot of efforts was made to develop many types of nitrogen oxide gas sensors. Among them, most interesting are WO3, V2O5, TiO2, SnO2 and NiO thin films as gas sensing layers. Relatively small effort has been done to examine nickel oxide. But reasonably good electrical properties and stability in air make it feasible for the fabrication of nickel oxide thin film based gas sensors. Hence, in the present study NiO thin films were deposited by dc reactive magnetron sputtering technique from a nickel metal target in argon and oxygen mixed atmosphere and studied its gas sensing properties towards NO2 gas. The effect of process parameters on the morphological and electrical properties of NiO was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Hall effect studies respectively. The films prepared at optimum conditions showed superior electrical properties and exhibited fine and uniform grains with RMS roughness 9.4 nm. These films were tested for gas sensing characteristics of NO2 gas. The sensitivity of NiO thin film was investigated in the temperature range 373 to 573 K. The dynamic response for the NiO films was observed at an operating temperature of 473 K and gas concentration of 50 ppm for NO2 gas.

Operating the GridPix detector in dark matter search experiments

The DARWIN (dark matter WIMP search with noble liquids) design study aims to use liquid argon and liquid xenon targets to look for nuclear recoils due to weakly interacting massive particles (WIMPs). To measure the recoil energy in dual-phase noble gas time projection chambers the combination of scintillation and ionisation detection is used to discriminate nuclear from electron recoils. Current experiments use an array of photomultiplier tubes to detect the primary scintillation and the ionisation electrons via secondary scintillation in the gas phase. Within the research framework for DARWIN, one candidate for an alternative direct charge readout is GridPix, a micro-pattern gaseous detector composed of a Micromegas-like amplification grid over the Timepix 65k pixel readout chip. It can achieve a single-electron detection efficiency of up to 98% and has thus great potential to identify the ionisation electrons in dark matter search experiments. The main challenges for this application are low outgassing, thermal robustness, and operation in pure (thus quencher-free) noble gas. To investigate its applicability we operated a GridPix detector in an argon cryostat. We proved GridPix's performance in pure argon. The gas amplification was confirmed in pure argon in the broad temperature range from 300K down to 87K. Additionally, we discuss results of thermal tests of GridPix devices at liquid xenon temperature in a dry nitrogen atmosphere.

Electrical properties of BaCe0.8Zr0.1Y0.1O3 − α ceramics and thin films designed by reactive magnetron sputtering: Effect of the electrochemical cell configuration

BaCe0.8Zr0.1Y0.1O3−α (BCZY10) protonic conductor coatings were co-sputter deposited from Ba, Zr and Ce0.9Y0.1 metallic targets in argon–oxygen reactive gas mixtures. The targeted composition of the coatings was obtained using suitable discharge currents applied on Zr and Ce0.9Y0.1 targets and discharge current applied on Ba target. The as-deposited coatings were amorphous and presented a good chemical stability against carbonation in air up to 573K. The films crystallised in BaCO3 and CeO2 mixture after annealing treatment around 873K for 2h in air. Nevertheless, the crystallization in the expected perovskite structure was obtained after annealing treatment under vacuum (5×10−3Pa) at 873K during 2h to prevent the carbonation of the coating. The crystallized films kept their initial morphological properties. The strong influence of the electrochemical cell configuration (substrate, electrodes nature…) on the electrical conductivity of the samples was demonstrated and discussed. The best electrical properties were obtained for a cermet-supported film, and were found close to that of a reference bulk sample of the same composition in the same conditions, whereas platinum based collectors gave very poor conductivity due to interfacial blocking effect.

Mechanical Behavior of Bioactive TiC Nanocomposite Thin Films

Carbon-based nanocomposite thin films have large application potential because they possess unique mechanical properties, especially high hardness, high elasticity, and a low widely adjustable friction coefficient. In this work, relatively easy preparation of the nanocomposite Ti and C system with good mechanical properties and bioactivity was showed. Formation of physical and mechanical processes, relationship between the evolving structure and other properties of TiC films were studied. The films were deposited on oxidized silicon substrates by dc magnetron sputtering of Ti and C targets in argon and nitrogen at different temperatures between 25°C and 800°C. The composite films consisted of metallic nanocrystalls embedded in a carbon matrix. Highest hardness ~ 18 GPa and reduced modulus of elasticity ~ 205 GPa were obtained when the crystalline nanoparticles were separated by 2-3 nm thin carbon matrix consisting of amorphous and graphite-like carbon phases. In these films the H/E ratio in the both cases is ~ 0,1. Bioactivity studies were carried out on human osteoblast-like cell line MG-63. The number of initially adhering cells on day 7 after seeding was significantly higher on the TiC surface than on the control culture dishes. Good biocompatibility and bioadhesion of these surfaces are attained by a favourable combination of surface roughness and chemistry.

Microstructural evolution of thin film vanadium oxide prepared by pulsed-direct current magnetron sputtering

Vanadium oxide (VOx) thin films have been deposited by pulsed-DC magnetron sputtering using a metallic vanadium target in a reactive argon and oxygen environment. While the process parameters (power, total pressure, oxygen-to-argon ratio) remained constant, the deposition time was varied to produce films between 75 ± 6 and 2901 ± 30 Å thick, which were then optically and electrically characterized. The complex dielectric function spectra (ε = ε1 + iε2) of the films from 0.75 to 5.15 eV were extracted by ex situ, multiple-angle spectroscopic ellipsometry (SE) measurements for the series of varied thickness VOx samples. Significant changes in ε and resistivity occur as a function of thickness, indicating the correlations exist between the electrical and the optical properties over this spectral range. In addition, in situ measurements via real time SE (RTSE) were made on the film grown to the largest thickness to track optical property and structural variations during growth. RTSE was also used to characterize changes in the film occurring after growth was completed, namely during post sputtering in the presence of argon and oxygen while the sample is shielded, and atmospheric exposure. RTSE indicates that the exposure of the film to the argon and oxygen environment, regardless of the shutter isolating the target, causes up to 200 Å of the top surface of the deposited film to become more electrically resistive as evidenced by variations in ε. Exposure of the VOx thin film to atmospheric conditions introduces a similar change in ε, but this change occurs throughout the bulk of the film. A combination of these observations with RTSE results indicates that thinner, less ordered VOx films are more susceptible to drastic changes due to atmospheric exposure and that microstructural variations in this material ultimately control its environmental stability.

Study of nuclear recoils in liquid argon with monoenergetic neutrons

In the framework of developments for liquid argon dark matter detectors we assembled a laboratory setup to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (Ekin = 2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3" liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from alpha particles at working points relevant for dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the population strength of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.

High performance self-aligned top-gate ZnO thin film transistors using sputtered Al2O3 gate dielectric

High performance self-aligned top-gate zinc oxide (ZnO) thin film transistors (TFTs) utilizing high-k Al2O3 thin film as gate dielectric are developed in this paper. Good quality Al2O3 thin film was deposited by reactive DC magnetron sputtering technique using aluminum target in a mixed argon and oxygen ambient at room temperature. The resulting transistor exhibits a field effect mobility of 27cm2/Vs, a threshold voltage of −0.5V, a subthreshold swing of 0.12V/decade and an on/off current ratio of 9×106. The proposed top-gate ZnO TFTs in this paper can act as driving devices in the next generation flat panel displays.

Quasi-elastic neutrino charged-current scattering off medium-heavy nuclei:40Ca and40Ar

The charged-current quasi-elastic scattering of muon neutrinos on calcium and argon targets is calculated for neutrino energy up to 2.8 GeV. The calculations are done within the framework of the relativistic distorted-wave impulse approximation, which was earlier successfully applied to describe electron-nucleus data. The model is first tested against experimental data for electron scattering off calcium and then it is applied to calculate (anti)neutrino cross sections on 40Ca and 40Ar. We show that reduced exclusive cross sections for neutrino and electron scattering are similar. A significant nuclear model dependence of both inclusive and total cross sections for energy about 1 GeV was found. From the comparison of the (anti)neutrino differential and total cross sections per (proton)neutron, calculated for the carbon, oxygen, and argon targets it is evident that the cross sections decrease slowly with the mass-number of the target due to nuclear effects.

XUV radiation from gaseous nitrogen and argon target laser plasmas

Laser plasma created in gaseous target is studied as a source of radiation in the "water window" wavelength range. Plasma is created by focusing an 800 mJ/7 ns Nd:YAG laser pulse into the gas-puff target. Using nitrogen gas results in emission of an intense quasi-monochromatic radiation with the wavelength 2.88 nm, corresponding to the quantum transition 1s2p → 1s2 of helium –like nitrogen ion. The emission spectrum with argon target covers all the water window range. Laboratory and computer experiments have been performed for both target gases. The spatial distributions of emitted energy in the water window spectral range were compared. The total emitted energy with argon was one order higher than with nitrogen.

Dark matter inverse problem: Extracting particle physics from scattering events

The primary observable in dark matter direct detection is the spectrum of scattering events. We simulate multiple positive direct detection signals (on germanium, xenon, and argon targets) to explore the extent to which the underlying particle physics, manifested in the momentum dependence of the operator mediating the scattering, can be extracted. Taking into account realization (Poisson) noise, a single target nucleus with 300 events has limited power to discriminate operators with momentum dependence differing by ${q}^{\ifmmode\pm\else\textpm\fi{}2}$ for a wide range of dark matter masses from 10 GeV to 1 TeV. With the inclusion of multiple targets (or a factor of several more events on a single target), the discrimination of operators with different momentum dependence becomes very strong at the 95% confidence level for dark matter candidates of mass 50 GeV and above. On the other hand, operator discrimination remains poor for 10 GeV candidates until multiple experiments each collect 1000 or more events.

X-ray measurements of nanometer-thick tantalum oxide and hafnium oxide films on silicon substrates for thickness and composition determination

The thicknesses and oxygen concentration of tantalum oxide (TaO) and hafnium oxide (HfO) films, prepared by magnetron sputtering Ta and Hf in oxygen onto heated silicon (100) substrates, were measured by three different techniques. The first method uses X-ray reflectivity, which yields a thickness value independent of the film composition. The second method uses the simultaneous measurement of Ta and Hf fluorescence counts. For these <200-nm-thick films there is very little matrix effect so that the Ta and Hf fluorescence counts are expected to, and are observed to, increase linearly with the film thickness. The third method uses the attenuation of the Si Kα X-ray line from the underlying Si excited by a glancing incident X-ray beam for measurement. The TaO and HfO films were observed to grow for the sputtering conditions employed, in an initial mode characterized by a high mass absorption times density product and then grow as characterized by a lower mass absorption times density product. This change over occurred for the HfO films, at a film thickness of 13 nm. The change over occurred for the TaO films at a film thickness of 23 nm. Pure Ta and Hf films were also made by magnetron sputtering from Ta and Hf targets in argon. All X-ray measurements, including the reflectivity measurements, were made, with the addition of an X-ray fluorescence detector, using a Panalytical MRD system.

Characterization of multi-jet gas puff targets for high-order harmonic generation using EUV shadowgraphy

Characterization measurements of multi-jet gas puff targets, developed for investigations on high-order harmonic generation (HHG) by a focused laser beam in a gas medium of modulated density, are presented. The targets produced by pulsed injection of gas through a nozzle in a form of a chain of small orifices have been characterized by EUV backlighting at 13.5nm wavelength. Measurements were performed for nozzles with 5, 7 and 9 orifices of 0.5mm in diameter each. Density profiles for argon targets have been obtained for the first time.

Plasma potential mapping of high power impulse magnetron sputtering discharges

Pulsed emissive probe techniques have been used to determine the plasma potential distribution of high power impulse magnetron sputtering (HiPIMS) discharges. An unbalanced magnetron with a niobium target in argon was investigated for a pulse length of 100 μs at a pulse repetition rate of 100 Hz, giving a peak current of 170 A. The probe data were recorded with a time resolution of 20 ns and a spatial resolution of 1 mm. It is shown that the local plasma potential varies greatly in space and time. The lowest potential was found over the target’s racetrack, gradually reaching anode potential (ground) several centimeters away from the target. The magnetic presheath exhibits a funnel-shaped plasma potential resulting in an electric field which accelerates ions toward the racetrack. In certain regions and times, the potential exhibits weak local maxima which allow for ion acceleration to the substrate. Knowledge of the local E and static B fields lets us derive the electrons’ E×B drift velocity, which is about 105 m/s and shows structures in space and time.

On the elastic modulus and hardness of co-sputtered Zr–Cu–(N) thin metal glass films

This work focuses on the properties of Zr–Cu–(N) deposits obtained by magnetron co-sputtering of Zr and Cu targets in pure argon or in argon nitrogen gas mixtures. Microstructure and mechanical properties (hardness and Young's modulus) were investigated versus deposition parameters. The composition of the Zr–Cu alloy films on the full binary range was accurately controlled by means of the discharge current intensity on both Zr and Cu targets. Deposits were observed to be amorphous single phased in a large range of copper content, the hardness and Young's modulus of the amorphous phase increasing with the latter. A small amount of nitrogen in the gas mixture leads to higher hardness and Young's modulus values.

Ab initiostudy of charge exchange in collisions of B2+ions with Ne and Ar targets

The electron-capture processes in collisions of B${}^{2+}$ ions with neon and argon targets have been studied theoretically using ab initio multireference configuration interaction potential-energy curves and nonadiabatic couplings. The cross sections for the simple capture process have been calculated using the semiclassical collision methods in the 10${}^{\ensuremath{-}2}$--2-a.u. velocity range (${E}_{\mathrm{lab}}$ \ensuremath{\approx} [0.02--1080 keV]) and have been compared with the available experimental data. The charge-transfer mechanism is analyzed with regard to the radial and rotational interactions and appears to be quite different for both systems. Good agreement is found with the measured cross sections.

Soft X-ray characterization of an elongated gas-puff target dedicated for laser–matter interaction experiments and high harmonic generation

A slit-shaped elongated nozzle, capable of forming an extended gas density profile, is presented and studied in detail. Argon and xenon target density backlighting measurements revealed the elongated density profiles with gas density that can be tuned by changing valve backing pressure and valve timing. Two dimensional density maps for Ar and Xe targets, obtained at soft X-ray wavelengths around 7Å, are shown and spatially characterized. Moreover the influence of valve backing pressure and valve timing on gas puff target density is studied. This geometry of the nozzle has potential applications in high harmonic generation for an efficient conversion of femto-second duration, intense infrared pulses to extreme ultraviolet (EUV) region.

Photocatalytic Properties of Columnar NanostructuredTiO2Films Fabricated by Sputtering Ti and Subsequent Annealing

Columnar nanostructured TiO2films were prepared by sputtering Ti target in pure argon with glancing angle deposition (GLAD) and subsequent annealing at 400°C for different hours in air. Compared with sputtering TiO2target directly, sputtering Ti target can be carried out under much lower base pressure, which contributes to obtaining discrete columnar nanostructures. In the present study, TiO2films obtained by annealing Ti films for different hours all kept discrete columnar structures as the Ti films deposited in GLAD regime. The longer the annealing time was, the better the phase transition accomplished from Ti to TiO2(a mixture of rutile and anatase), and the better it crystallized. In addition, those TiO2films performed photocatalytic decolorization effectively and showed a law changing over annealing time under UV light irradiation towards methyl orange, which demonstrated the potential applications for treatment of effluent.

Condition of MeV Electron Bunch Generated from Argon Gas-Jet Target in the Self-Modulated Laser Wakefield Regime

Condition of MeV Electron Bunch Generated from Argon Gas-Jet Target in the Self-Modulated Laser Wakefield Regime

Behaviour of Charge Carriers in As-Deposited and Annealed Undoped TCO Films

We examine the structures, cut-off points of transmittance spectra and electric properties of undoped ZnO, SnO2 and CdO films by scanning electron microscopy, x-ray diffraction, spectrophotometer and Hall-effect measurements, respectively. The films are deposited by using an rf magnetron sputtering system from powder targets in argon and then annealed in vacuum. The structures and properties of the as-deposited films are compared with those of the annealed one. We try to explain the behaviour of charge carriers based on the semiconductor physics theory.