Pure Krypton Research Articles

Sputtering of amorphous Si by low-energy Ar+, Kr+, and Xe+ ions

Atomic layer plasma technologies require localizing ions' impact within nanometers up to an atomic layer. The possible way to achieve this is the decrease in the ion energy up to surface binding energy. At such low ion kinetic energies, the impact of different plasma effects, causing the surface modification, can be of the same order as kinetic ones. In this work, we studied the sputtering of amorphous silicon films by Ar+, Kr+, and Xe+ ions at energies of 20–200 eV under the low-pressure inductively coupled plasma discharge in pure argon, krypton, and xenon, respectively, at a plasma density of 1–1.5 × 1010 cm−3. Under the plasma conditions, a high asymmetry of discharge allowed to form ion flux energy distribution functions with narrow energy peak (5 ± 2 eV full width at half maximum). Real time in situ control over the ion composition and flux as well as the sputtering rate (the ratio of the film thickness change to the sputtering time) provided accurate determination of the sputtering yields Y(Ei). It is shown that at ion energy above ∼70 eV, the “classical” kinetic sputtering mechanism prevails. In this case, Y(Ei) grows rather rapidly with ion energy, increasing with the decrease in the ion mass: the closer the ion mass to the target atom mass, the higher the Y(Ei). Below 70 eV, the growth of Y(Ei) strongly slows down, with Y(20eV) being still high (>10−3), indicating the impact of plasma. The obtained trends of Y(Ei) are discussed in light of surface modification studied by atomic force microscopy and angular x-ray photoelectronic spectroscopy.

Improvement of gas proportional counter performance by registration krypton and argon escape peaks in Mössbauer spectroscopy

Proportional gas counters are commonly used in the 57Fe Mössbauer spectroscopy for their good energy resolution and insensitivity to magnetic field. However, their counting rate is usually limited by relatively long dead time. This paper demonstrates a detection performance improving technique by registration Kα escape peaks coupled together with main full energy peaks. The validity of using both peaks was verified by transmission and conversion X-rays Mössbauer spectra recording, while using proportional gas counters filled with pure krypton and a mixture of argon and methane. The influence of this method on the resulted α-Fe Mössbauer spectra was studied in a view of resonance effect, energy resolution, spectra baseline, and statistical quality. The presented technique showed that the counting rate of Mössbauer spectra accumulation was increased by 95% while using pure krypton, whereas by using a mixture of argon and methane, the counting rate reached an increase of 27%.

Secondary scintillation yield in pure krypton

The absolute secondary scintillation yield is of paramount importance for modelling dual-phase or high-pressure gas detectors, to be used in contemporary and in future rare event detection experiments. In addition, the search for neutrinoless double electron capture complements the search for neutrinoless double beta decay and has been measured for 124Xe in several Dark Matter and Double Beta decay detectors, operating at present. Krypton presents itself as an interesting candidate for double electron capture detection experiments. We have studied the krypton secondary scintillation yield, at room temperature, as a function of electric field in the gas scintillation gap. A large area avalanche photodiode has been used to allow the simultaneous detection of the scintillation pulses as well as the direct interaction of x-rays, the latter being used as a reference for the calculation of the number of charge carriers produced by the scintillation pulses and, thus, the determination of the number of photons impinging the photodiode. An amplification parameter of 113 photons per kV per drifting electron and a scintillation threshold of 2.7 Td (0.7 kVcm−1bar−1 at 293 K) was obtained, in good agreement with the simulation data reported in the literature. On the other hand, the ionisation threshold in krypton was found to be around 13.5 Td (3.4 kVcm−1bar−1), less than what had been obtained by the most recent simulation work-package. The krypton amplification parameter is about 80% and 140% of those measured for xenon and argon, respectively.

Phase states and the mechanism of crystallization of condensed Ar−Kr mixtures

The structure characteristics of Ar−Kr mixtures deposited under special conditions have been investigated in the whole interval of concentrations applying the transmission electron diffraction technique (THEED). The samples were prepared in situ by condensing a gas mixture preliminary cooled down to the sub-liquid-nitrogen level onto substrates at T = 6 K and 20 K. The experimental results show that the structure and morphology of the Ar−Kr condensates are dependent on the nucleation dynamics prevailing in the course of the sample formation. It is shown that cooling a gas mixture is favorable to the clusterization of solute atoms in the gas flow. The krypton small clusters can serve as condensation clusters. The phase boundaries of the condensates have been determined. Regular Ar−Kr solutions are formed when the contents of one of the components are low (0−10 mol % Ar), (0−5 mol % Kr). The diffraction patterns of the condensates with prevailing Kr contents corresponded to a mixture of Kr-enriched fcc solutions and a dispersed phase of argon. The excess Kr contents are due to the specific morphology of the solutions dictated by condensation conditions. The Ar-based samples contained a mixture of two crystalline phases (an fcc solution and the hcp phase of nearly pure argon) and a glass phase of nearly pure krypton. In the concentration range 58−78 mol % Ar the new morphological form of the Ar−Kr condensates resembles the gel. The phase state diagram of the Ar−Kr condensates has been obtained.

Probing pure and mixed neon ECR plasma—An effort for understanding the mechanism of isotope anomaly and gas mixing effect

We report the charge state distributions of the pure and mixed (25%, 50%, and 75% with oxygen and helium gases) neon electron cyclotron resonance (ECR) plasma to probe the hitherto unrevealed mechanism of the gas mixing effect and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63, 2875 (1992) and A. G. Drentje, Rev. Sci. Instrum. 74, 2631 (2003)]. The multiply charged (up to +7) neon plasma was produced using a 10 GHz all-permanent-magnet NANOGAN ECR ion source. The intensities of highly abundant two isotopes, viz., 20Ne (∼90.48%) and 22Ne (∼9.25%), have been measured by extracting the ions from the plasma, accelerating with different potentials and, finally, analyzing them in mass and energy using a high resolution, large acceptance analyzer-cum-switching dipole magnet. The gas mixing studies show that the addition of oxygen with neon is more effective than that of the helium, particularly on the ion intensities of 20Ne. The higher the fractions of mixing gases, the better are the intensities of highly charged neon ions in the plasma. With and without gas mixing, the intensity ratio of 22Ne to 20Ne shows clear evidence of the isotope anomaly. However, the anomalous effect tends to disappear with increasing oxygen and helium gas mixing. Contrary to the behavior of recently studied pure and oxygen mixed krypton plasma [Kumar et al., J. Mass. Spectrom. 51, 1090 (2016)], the present results are in good agreement with the prediction of linear Landau wave damping theory for selective ion heating in a two-component plasma.

Theoretical Kinetics Investigation of Krypton Dielectric Barrier Discharge for UV Lamp

This work presents an electric and kinetic study of homogeneous dielectric barrier discharge (DBD) in pure krypton (Kr). The electrical characterization and kinetic analyses of the DBD in Kr are performed. The plasma formation in DBD, excited by sinusoidal voltage at high pressure, was studied. The discharge development, with homogeneous model approach and using extended kinetic scheme, is simulated. The study is based on a spatial homogeneity model including the plasma chemistry, the electrical circuit and the Boltzmann equations’. The temporal variations of discharge voltage, dielectrics voltage, discharge current, electric field and species concentrations are calculated. The plasma kinetics is discussed with the aim to finding the optimal efficiency. The photon generation, under typical operating conditions, was investigated and discussed. The effect of some parameters on the excilamp like pressure, applied voltage, and frequency are investigated in order to identify the optimal parameters for maximum luminous efficiency in the UV range.

Radiative Emissions in Visible–IR of Krypton Excilamp: Experimental and Theoretical Interpretations

The paper presents an experimental and theoretical study of the radiative emission in the pure krypton lamp excited by dielectric barrier discharge. Parametric studies were made in the aim to observe the influence of the applied voltage, the gas pressure and the frequency on the radiation intensity emission from visible to infrared range. Stable dielectric barrier discharges were achieved between two identical insulated electrodes separated by 2 mm gap containing pure krypton at pressure from 129 to 460 mbar. The discharge was powered with a sinusoidal supply at frequencies from 10 to 50 kHz. Electrical characteristics of the DBD were studied. A spectroscopic and kinetic analysis of a pure krypton dielectric barrier discharge is reported here. The discharge emits radiations in UV, visible and IR range. In order to understand the emission process a theoretical interpretation of the results is given in the IR range by describing the chemical properties of the lamp. IR emission and a detailed study of kinetics allow to follow the population of metastable excited states of Krypton in (Kr*(3P0,2)). This population is indirectly responsible for UV emission.

Viscosity Measurements of Krypton at Temperatures from (253.15 to 473.15) K with Pressures up to 2 MPa

Viscosity measurements of pure krypton were carried out in the temperature range from (253.15 to 473.15) K at pressures up to 2 MPa utilizing a rotating-body viscometer. Herewith, the viscosity is ...

Gas mixing effect on Kr ion currents from an ECR ion source

Pure and different support gas-mixed krypton plasmas are produced using the 14.5 GHz all permanent-magnet based electron cyclotron resonance (ECR) ion source. The ions are extracted and the charge state distributions (CSDs) are studied. The H2, He, N2, O2, Ne, Ar, CH4 and CO2 gases are used as support gases. One of the support gases are mixed with Kr at several mixing ratios and its effect on the outputs currents of the Kr ions are studied. The total effective charge, as well as effective charges of Kr and mixing gas ions are calculated from the measured ion currents. The total ion loss rates are also calculated. The gases N2, O2, Ar and CO2 are found to exhibit better mixing effect in the enhancement of output of highly charged ions. The best enhancement in the output currents of Kr ions is observed in case of O2 as the mixing gas under certain conditions. To the best of our knowledge such a detail comparative study on the influence of mixing gas has not been reported so far for ECR ion-beam application.

Forbidden component of the Be II 436.1 nm line recorded from pulsed gas discharge plasma

We report results of the experimental study of the singly charged beryllium spectral line 436.1 nm, transition , and forbidden component, transition , which is for the first time identified in this work. Beryllium lines are recorded from gas discharge, after ablation of a beryllium oxide discharge tube, running in pulsed regime with the following gases: helium with traces of hydrogen, argon with traces of hydrogen and pure krypton. The ratio of line intensities and wavelength separation of the Be II 436.1 nm line and neighbouring line located at the blue wing are followed in the electron density range (1.16–6.4) × 1022 m−3 determined from the hydrogen Balmer beta line () in the electron temperature interval between 10500 K and 15500 K. The functional dependence of the wavelength separation range and peak intensity ratio of these lines upon electron number density suggests the complex profile of the forbidden and allowed line, which can be used for diagnostics of low-temperature beryllium containing plasmas.

Gain characteristics of a 100 μm thick GEM in Krypton-CO2 mixtures

The operation of a Micropattern Gaseous Detector (MPGD) comprising a cascade of two non-standard Gas Electron Multipliers (GEM) made from a 100 μm kapton foil was evaluated in pure krypton and in krypton-CO2 mixtures. The final avalanche charge was collected in a 2D strip readout, providing an active area of 10×10 cm2 for the entire detection system. For each mixture, the effective gain and energy resolution were measured as a function of the electric field in the drift, transfer and induction regions. Using X-rays from a 55Fe radioactive source (5.9 keV), gains close to 104 and energy resolution of 22% (FWHM) were achieved in pure krypton under stable conditions, showing the potential of the experimental setup for the following imaging studies.

Femtosecond laser excitation of mixed Ar/Kr clusters: peculiarities of K-line x-ray production from nanoplasma under varied fraction of initial gas components

For the first time, we defined the range of krypton fraction (CKr) in an initial binary Ar–Kr gas mixture that provides the production of large (N ~ 106 atoms/cluster) mixed Ar/Kr clusters under co-expansion of the mixture at room temperature and the stagnant pressure of 25 bar. Mixed Ar/Kr clusters exist at the krypton fraction of 3–15%. The presence of mixed clusters is detected by the simultaneous generation of both x-ray Kα lines of argon (E = 3.1 keV) and krypton (E = 12.7 keV) from nanoplasma originating as a result of femtosecond nonlinear laser excitation with intensity about 5 · 1017 W cm−2. It was shown that the amplitude of lines in dual-energy x-ray spectrum can be controlled by proper selection of the fraction of initial gas mixture components. Maximal laser energy conversion efficiency to krypton x-ray line is achieved for pure krypton clusters (i.e. CKr = 100%) and reaches 2 · 10−7 at laser intensity of 5 · 1017 W cm−2. The laser energy conversion efficiency to argon x-ray line reaches the maximal value of 3 · 10−6 at Ckr = 0%.

A Gas Proportional Scintillation Counter with krypton filling

A Gas Proportional Scintillation Counter filled with pure krypton was studied. Energy resolution below 10% for 5.9-keV X-rays was obtained with this prototype. This value is much better than the energy resolution obtained with proportional counters or other MPGDs with krypton filling. The krypton electroluminescence scintillation and ionisation thresholds were found to be about 0.5 and 3.5 kV cm−1bar−1, respectively.

Charge state distribution studies of pure and oxygen mixed krypton ECR plasma – signature of isotope anomaly and gas mixing effect

We report the charge state distributions of the pure, 25% and 50% oxygen mixed krypton plasma to shed more light on the understanding of the gas mixing and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63 (1992) 2875 and Y Kawai, D Meyer, A Nadzeyka, U Wolters and K Wiesemann, Plasma Sources Sci. Technol. 10 (2001) 451] in the electron cyclotron resonance (ECR) plasmas. The krypton plasma was produced using a 10 GHz all-permanent-magnet ECR ion source. The intensities of the highly abundant four isotopes, viz. 82 Kr (~11.58%), 83 Kr (~11.49%), 84 Kr (~57%) and 86 Kr (17.3%) up to ~ +14 charge state have been measured by extracting the ions from the plasma and analysing them in the mass and the energy using a large acceptance analyzer-cum-switching dipole magnet. The influence of the oxygen gas mixing on the isotopic krypton ion intensities is clearly evidenced beyond +9 charge state. With and without oxygen mixing, the charge state distribution of the krypton ECR plasma shows the isotope anomaly with unusual trends. The anomaly in the intensities of the isotopes having quite closer natural abundance, viz. 82 Kr, 86 Kr and 83 Kr, 86 Kr is prominent, whereas the intensity ratio of 86 Kr to 84 Kr shows a weak signature of it. The isotope anomaly tends to disappear with increasing oxygen mixing in the plasma. The observed trends in the intensities of the krypton isotopes do not follow the prediction of linear Landau wave damping in the plasma. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of copper nanoparticle inclusions on pressure-induced fluid-polynanocrystalline structural transitions in krypton

The dependence of nanoscale crystal formation from a noble element fluid on the rate of hydrodynamic compression was explored using molecular dynamics. Results were obtained for pure krypton samples as well as ones containing a cubic- or spherical-shaped fcc copper nanocrystal inclusion for compression rates of 1, 10, and 20 MPa/ps. In the absence of Cu, Kr crystals nucleate with apparently random locations and orientations in the sample; slower compression leads to larger nanocrystal size. The effect of the Cu inclusion is to partially mediate the location, orientation, and size of the formed crystals. The effect is larger for the slower compression rate and when the inclusion is cubic rather than spherical in shape. For sufficiently slow compression, the stress state in the cubic Cu inclusion changes from hydrostatic to non-hydrostatic as a consequence of the formation of extended orthotropic hcp/fcc nanostructures in the Kr. The mechanism of the dynamic stress-induced nanostructural transition is explained qualitatively in terms of known geometric effects on the quasi-static indentation response of crystalline materials.

The mechanism of domain-wall structure formation in Ar-Kr submonolayer films on graphite

Using Monte Carlo simulation method in the canonical ensemble, we have studied the commensurate-incommensurate transition in two-dimensional finite mixed clusters of Ar and Kr adsorbed on graphite basal plane at low temperatures. It has been demonstrated that the transition occurs when the argon concentration exceeds the value needed to cover the peripheries of the cluster. The incommensurate phase exhibits a similar domain-wall structure as observed in pure krypton films at the densities exceeding the density of a perfect $(\sqrt{3}\times\sqrt{3})R30^\circ$ commensurate phase, but the size of commensurate domains does not change much with the cluster size. When the argon concentration increases, the composition of domain walls changes while the commensurate domains are made of pure krypton. We have constructed a simple one-dimensional Frenkel-Kontorova-like model that yields the results being in a good qualitative agreement with the Monte Carlo results obtained for two-dimensional systems.

Exciton luminescence in krypton cryocrystals with an admixture of molecular deuterium

Data on the VUV and UV cathodoluminescence spectra of the Kr-based solid solutions, Kr-D2, Kr-D2-O2, and Kr-Xe-O2, as functions of dopant concentration are presented. Introducing deuterium impurity into krypton crystals produces no new spectral features, which indicates that electron bombardment of these crystals does not cause excitation or dissociation of D2. The intensity of the intrinsic emission from the matrix increases substantially, the more so for higher concentrations of D2. The observed intensity increase is found to be caused by localization of matrix excitons within a limited volume of the crystal as they undergo quasielastic scattering by impurity deuterium molecules, which leads to a substantial reduction in the mean free path and diffusion length for the excitons, as well as to their faster self-localization. Possible mechanisms for luminescence quenching in pure krypton cryocrystals are discussed. It is shown that quenching is caused by annihilation of excitons as they interact among themselves or with other electronic excitations of the crystal.

Pathway to Cryogen Free Production of Hyperpolarized Krypton-83 and Xenon-129

Hyperpolarized (hp) 129Xe and hp 83Kr for magnetic resonance imaging (MRI) are typically obtained through spin-exchange optical pumping (SEOP) in gas mixtures with dilute concentrations of the respective noble gas. The usage of dilute noble gases mixtures requires cryogenic gas separation after SEOP, a step that makes clinical and preclinical applications of hp 129Xe MRI cumbersome. For hp 83Kr MRI, cryogenic concentration is not practical due to depolarization that is caused by quadrupolar relaxation in the condensed phase. In this work, the concept of stopped flow SEOP with concentrated noble gas mixtures at low pressures was explored using a laser with 23.3 W of output power and 0.25 nm linewidth. For 129Xe SEOP without cryogenic separation, the highest obtained MR signal intensity from the hp xenon-nitrogen gas mixture was equivalent to that arising from 15.5±1.9% spin polarized 129Xe in pure xenon gas. The production rate of the hp gas mixture, measured at 298 K, was 1.8 cm3/min. For hp 83Kr, the equivalent of 4.4±0.5% spin polarization in pure krypton at a production rate of 2 cm3/min was produced. The general dependency of spin polarization upon gas pressure obtained in stopped flow SEOP is reported for various noble gas concentrations. Aspects of SEOP specific to the two noble gas isotopes are discussed and compared with current theoretical opinions. A non-linear pressure broadening of the Rb D1 transition was observed and taken into account for the qualitative description of the SEOP process.

High-brightness optical-field-ionization collisional-excitation extreme-ultraviolet lasing pumped by a 100-TW laser system in an optically preformed plasma waveguide

Recent study on optical-field-ionization collisional-excitation extreme-ultraviolet lasing of Ni-like krypton at 32.8 nm pumped by a 100-TW laser system with an optically preformed plasma waveguide is reported. By using a 9-mm-long pure krypton plasma waveguide fabricated with the axicon-ignitor-heater scheme, the 32.8-nm extreme-ultraviolet laser provided an average output of 1012 photons/pulse at pump energy of 1 J, more than one order of magnitude enhancement relative to the previous results with the same scheme at pump energy of 235 mJ. It is also found the far-field pattern of laser beams varies from a single peak profile at low pump energy to an annular profile at high pump energy due to over-ionization of krypton ions at the center of the plasma channel.

Investigating 2K-capture in 78Kr with a large-volume copper proportional counter

A component analysis of the background of a copper proportional counter with allowance for its input to the parametric region of events due to the expected 2K-capture in 78Kr is presented. The technique of discriminating the simulated events on the edges of the working length of the anode wire is described by comparing the pulse amplitudes of the sought pulse and the first afterpulse in a detector filled with pure krypton without quenchers. The limit on 2K(2ν)-capture for the ground state 78Se (0+ → 0+, g.s.) was found to be T1/2 ≥ 2.4 × 1021 yr (90% confidence level).