K–edge X–ray absorption spectra of argon in sputtered aluminum films

We have measured K–edge X–ray absorption spectra of argon in sputtered aluminum films at a synchrotron radiation facility (the Photon Factory). We found that the energy and shape of white line change when the film is annealed at 500 °C and the spectrum becomes resembling that of argon implanted in silicon. From the analyses of the X–ray absorption spectra and TEM observation we concluded that argon exists as very small atom clusters with a diameter less than 1 nm or exist as isolated atoms in the as–sputtered aluminum film, and that the size of the clusters become as big as 10 nm diameter when the film is heated.     

Electron–ion recombination in radiation tracks in liquid argon: a computer simulation study

A simulation method is proposed to model electron–ion recombination in radiation tracks in liquid argon at 87 K. The method is applied to calculate the electron escape probability in clusters of up to 20 pairs of electrons and cations that represent a fragment of the track. The results reproduce the basic features of the track recombination in liquid argon observed in experiment.     

Comparison between a radio-frequency and direct current glow discharge in argon by a hybrid Monte Carlo–fluid model for electrons,argon ions and fast argon atoms

A hybrid Monte Carlo–fluid model has been developed for the electrons, argon ions and fast argon atoms in an argon glow discharge, either operated in the dc mode or the capacitively coupled rf mode. Typical working conditions for rf GD-OES are considered, i.e. approximately 6 torr argon gas pressure and approximately 10 W power. Typical results of the model, like the potential distributions, densities, fluxes and ionization rates, will be presented and compared between the two operation modes. It will be demonstrated that the rf discharge yields more efficient ionization than the dc discharge, and hence the rf discharge requires lower voltages to obtain the same amount of power, which is in good correspondence to experimental observations.     

Collisional–radiative model for the sputtered copper atoms and ions in a direct current argon glow discharge

A collisional–radiative model is developed for various levels of the sputtered copper (Cu) atoms and their ions in an argon (Ar) direct current glow discharge, used as an analytical source for optical emission spectrometry. In this application, attention is paid to the photons emitted by sputtered atoms and ions, and hence to the behavior of excited levels of these species. 8 Cu atomic and 7 Cu⁺ ionic levels are considered in the model, as well as the Cu²⁺ ions. Typical results of the model are the level populations (in two dimensions) of the various levels, and the relative contributions of the different populating and depopulating processes. This model is not only of interest for analytical glow discharge optical emission spectrometry, but also for plasma diagnostic tools and for copper–vapor lasers.     

Excitation of singly-ionized argon species in helium-matrix Grimm glow discharge plasmas II – Comparison between argon and neon

A considerable intensity enhancement of several Ar II lines assigned to the 3p(4)4p-3p(4)4s transition in a helium-argon Grimm glow discharge plasma has been previously reported and attributed to argon ions excited by metastable helium atoms. In this paper the behavior of Ne II lines assigned to the 2p(4)3p-2p(4)3s transition in a helium-neon plasma was investigated to obtain detailed information on the excitation of plasma gases in the helium-matrix plasmas. No Ne II lines with enhanced emission intensities have been found; on the contrary, the intensities of the doublet Ne II lines decreased in the helium-matrix plasma.     

Styrylbenzimidazolium dye–borate complex as an effective,singlet state photoinitiator in an argon laser-induced TMPTA photopolymerization

Dye photoinitiators consisting of styrylbenzimidazolium cations, acting both as light absorbers and as electron acceptors and n-butyltriphenylborate anions being electron donors were tested in order to reveal the effect of a dye structure on the efficiency of multiacrylate photoinitiated polymerization. The efficiency of tested systems depends on the ΔG_el of electron transfer between borate anion and hemicyanine cation. The latter value was experimentally determined for 9 photoredox pairs. The relationship between the rate of polymerization and the free energy of activation of electron-transfer reaction shows the dependence predicted by the classical theory of electron-transfer phenomena. The kinetic studies clearly demonstrated that the styrylbenzimidazolium borate photoredox pairs are very promising photoinitiators for multiacrylates free radical polymerization. They initiate the polymerization reaction with the efficiency comparable to RBAX, Rose Bengal derivative, common triplet state initiator.     

Physical and analytical characteristics of an atmospheric pressure argon–helium radiofrequency capacitively coupled plasma

A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5–70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar–He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500–2100 K), He (3000–3500 K) and H (2500–3200 K), the rotational temperature of the OH band (1300–2900 K), the electron temperature (5500–6500 K) and the electron number density (8 · 10¹³–2 · 10¹⁴ cm^− 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.     

Dissociation of internally excited UF6− ions in collision with argon atoms

Uranium hexafluoride negative ions (UF₆⁻) of controlled average internal and kinetic energy were collided with argon. A qualitative change was observed in the dependence of ionic fragmentation on internal excitation prior to collision, as the laboratory collision energy was increased above 150 eV.     

Chiral effect in the sechenov parameters of argon solubility in aqueous α-valine and α-phenylalanine solutions

Data on the solubility of argon in water and aqueous solutions of L and D enantiomers of α-valine and α-phenylalanine at T = 283–328 K and partial pressure of argon p ₂ = 0.1 MPa are used to calculate the standard parameters of the Sechenov salt effect. Parameters of the solute-solute pair interaction are estimated within the formalism of the McMillan-Mayer theory. Evidence is provided for the presence of the chiral effect in the Sechenov parameters.     

Isotopic ratio νHX/νDX of hydrogen halide complexes in solid argon

The wavenumbers of the ν_HCl band in B… HCl complexes and of the central HF bond in B… (HF)₂ complexes in solid argon have a minimum value     

Molecular dynamics simulation on explosive boiling of thin liquid argon films on cone-shaped Al–Cu-based nanostructures

Journal of Thermal Analysis and Calorimetry - The aim of this study is to investigate the effects of Al and Cu nanostructures on the explosive boiling of a thin layer of liquid argon atoms on the...     

The oxidation behaviour of niobium containing γ-TiAl based intermetallics in air and argon/oxygen

The oxidation behaviour of -TiAl based alloys with different Nb contents (2–10 At.%) was investigated in air and in argon-20% oxygen at 900 °C using thermogravimetric analysis. The oxide scales were characterized by a combination of optical microscopy, SEM/EDX and X-ray diffraction analyses. Although in all studied cases the presence of niobium improves the oxidation resistance of -TiAl, the oxidation kinetics, scale morphology and composition in air differed strongly from that in argon-oxygen. In air the oxidation resistance increases with increasing niobium-content. In Ar/O₂ the niobium dependence is far more complex because internal oxidation occurs which is favoured by the presence of niobium. SNMS analysis revealed that the differences in behaviour in the two atmospheres are related to the formation of Ti-rich nitride at the scale/alloy interface during air oxidation. The positive effect of niobium on the oxidation resistance of -TiAl is mainly caused by a decrease of the transport processes in the heterogeneous TiO₂/Al₂O₃-surface scale. Nitride formation and/or niobium enrichment at the scale/alloy interface also affect the oxidation behaviour, however these factors are believed to be the result of the decreased transport processes rather than the main reason for the niobium effect.     

The argon 3s photoelectron satellite spectrum at high resolution (hv = 60–170 eV)

The argon 3s binding energy spectrum has been measured at high energy resolution using magic angle photoelectron spectroscopy and monochrornatized synchrotron radiation in the photon energy range 60–170 eV. The well-resolved fine structure in the Ar 3s satellite spectrum includes several newly observed ion states. This new and much more detailed spectroscopie information clarifies and corrects earlier conclusions based on the interpretation of lower resolution PES, XPS and EMS binding energy spectra and their comparison with theory.     

New Phase in the Bi–Sr–Ca–Cu–O System

Cooling a melt of a Bi–Sr–Ca–Cu–O system (Bi:Sr:Ca:Cu = 4:3:3:4 or 2:2:2:4) from 1000°C-1050°C yielded crystals of a new red-colored nonsuperconducting phase, accompanying the superconducting 2212 and 2201 phases. Based on the EPR spectra, it was concluded that copper is univalent in this compound. The new phase has a composition Bi_2.2Sr_1.6Ca_1.3Cu₂Ox. The X-ray diffraction pattern has been indexed, and the unit cell parameters of the phase have been determined: space group P2/m, a = 12.93, b = 4.55, c = 10.94 ; = 102.72°.     

Reactions of photogenerated fluorine atoms with molecules trapped in solid argon. 4. Spectroscopic characteristics of β-C2H2F· radicals generated in reactions of mobile F atoms with C2H2 molecules trapped in solid argon

Reactions of mobile fluorine atoms with C₂H₂, C₂D₂, and C₂HD molecules in solid argon were studied by ESR and IR spectroscopic techniques. Highly resolved ESR spectra of the stabilized radicals CHF=^·CH, CDF=^·CD, CHF=^·CD, and CDF=^·CH were obtained for the first time. Isotropic hyperfine constants on fluorine and proton nuclei were measured. It was found that the radicals formed in the reaction F + C₂H₂ correspond to the cis--C₂H₂F^· isomer. A comparison of the measured HFC constants with the values calculated by modern quantum-chemical methods allows the identification of the isomeric form of the radical, whereas vibrational analysis of the IR absorption spectra gives unreliable results. The calculation of the energy of the radical isomers predicts that cis--C₂H₂F^· is more stable than trans--C₂H₂F^· by 1.0 kJ mol^–1.