Presence Of Argon Research Articles

Microcrystalline diamond growth in presence of argon in millimeter-wave plasma-assisted CVD reactor

The additions of argon and oxygen to H 2–CH 4 feed gas and high-electron-density plasma generated by the millimeter-wave power were used to deposit microcrystalline diamond films having high quality and high growth rate simultaneously. Microcrystalline diamond films were grown on silicon substrates with 60–90 mm diameter in the millimeter-wave plasma-assisted CVD reactor based on 10 kW gyrotron operating at a frequency of 30 GHz. The growth process and morphology of diamond films at wide variation of parameters (gas pressure, substrate temperature, microwave power, argon and oxygen concentrations in gas mixtures Ar–H 2–CH 4 and Ar–H 2–CH 4–O 2) are investigated. For understanding of growth conditions the investigations of the plasma parameters (electron density and gas temperature) in novel CVD reactor are presented.

Ion Mobility of Ground and Excited States of Laser-Generated Transition Metal Cations

The application of ion mobility to separate the electronic states of first-, second-, and third-row transition metal cations generated by the laser vaporization/ionization (LVI) technique is presented. The mobility measurements for most of the laser-generated transition metal cations reveal the presence of two or three mobility peaks that correspond to ground and excited states of different electronic configurations. The similarity of the measured reduced mobilities for the metal cations generated by LVI, electron impact, and glow discharge ion sources indicates that the same electronic configurations are produced regardless of the ion source. However, in comparison with electron impact of volatile organometallic compounds, the LVI populates fewer excited states due to the thermal nature of the process. Significant contributions to the production and populations of excited states of Ni+, Nb+, and Pt+ cations have been observed in the presence of argon during the LVI process and attributed to the Penning ionization mechanism. The origin of the mobility difference between the ground and the excited states is mainly due to the different interaction with helium. The ratio of the reduced mobilities of the excited and ground states decreases as one goes from the first- to the second- to the third-row transition metal cations. This trend is attributed to the ion size, which increases in the order 6sd(n-1) > 5sd(n-1) > 4sd(n-1). This work helps to understand the mechanisms by which transition metal cations react in the gas phase by identifying the ground and excited states that can be responsible for their reactivity.

Plasma Polymerization of Amines and Acetone: Functionalized Surfaces for Microarray Applications

AbstractPlasma polymerization (PP) afforded amine as well as carbonyl containing films which are suitable for use in microarray analysis. The polymerization process with acetone (AC), ethylenediamine (EDA) and diethylamine (DEA) has to be performed in the presence of argon as a carrier gas to be successful. Different activation steps of the polymer based support yield surfaces which differ significantly in their elemental composition after the PP step. Angle dependent XPS proves a take off angle dependence of the carbonyl PP film in contrast to a homogeneous PP film for amine functionalized PP layers while microarray experiments have been successful for both functional films.

Measurement of the pressure dependence of emission induced by electrons

The fluorescence detection of ultra high energy ({approx}> 10{sup 18} eV) cosmic rays requires a detailed knowledge of the fluorescence light emission from nitrogen molecules, which are excited by the cosmic ray shower particles along their path in the atmosphere. We have made a precise measurement of the fluorescence light spectrum excited by MeV electrons in dry air. We measured the relative intensities of 34 fluorescence bands in the wavelength range from 284 to 429 nm with a high resolution spectrograph. The pressure dependence of the fluorescence spectrum was also measured from a few hPa up to atmospheric pressure. Relative intensities and collisional quenching reference pressures for bands due to transitions from a common upper level were found in agreement with theoretical expectations. The presence of argon in air was found to have a negligible effect on the fluorescence yield. We estimated that the systematic uncertainty on the cosmic ray shower energy due to the pressure dependence of the fluorescence spectrum is reduced to a level of 1% by the AIRFLY results presented in this paper.

Studies on electrochromic smart windows based on titanium doped WO 3 thin films

Titanium doped tungsten oxide thin films have been deposited by co-sputtering metallic titanium and tungsten in the presence of argon and oxygen. The oxygen chamber pressure was varied in the range 1 × 10 − 3 –4 × 10 − 3 mbar keeping the sputtering power of titanium and tungsten constant at 2 W/cm 2 and 3 W/cm 2 respectively. The effect of oxygen chamber pressure on the electrochromic (EC) properties of titanium doped WO 3 has been investigated in three steps. First, the material properties of EC film were investigated by XRD, SEM, and UV–Vis spectrophotometer; the thickness and the optical constants were estimated from the reflectance measurements. Second, the electrochromic behavior of the EC films was characterized by cyclic voltammetry (CV) using 1.0 M HCl as electrolyte. The optical modulation (Δ T) and coloration efficiency (CE) of the titanium doped tungsten oxide thin film deposited at an O 2 pressure of 4 × 10 − 3 mbar was found to be better with typical values of Δ T = 70% and CE = 66 cm 2/C (at λ = 550 nm). Finally, EC devices consisting of five layers (Glass/ITO/Ti:WO 3/Ta 2O 5/NiO/ITO) have been fabricated and tested.

Polyynes Formation from Electric Arc in Liquid Argon in Presence of Methane

The carbon arc in liquid argon in presence of methane produces the complete series of polyynes from C4H2 to C12H2 which have been collected in a cold trap and analyzed by electronic absorption spectroscopy and by liquid chromatography (HPLC‐diode array). The relative abundance of the polyynes series has been determined. In addition to polyynes the decomposition of methane in the argon arc produces also vinylacetylene and naphthalene. Thermodynamic calculations explain why the polyynes are formed so easily in the carbon arc.

Measurement of the pressure dependence of air fluorescence emission induced by electrons

The fluorescence detection of ultra high energy (≳10 18 eV) cosmic rays requires a detailed knowledge of the fluorescence light emission from nitrogen molecules, which are excited by the cosmic ray shower particles along their path in the atmosphere. We have made a precise measurement of the fluorescence light spectrum excited by MeV electrons in dry air. We measured the relative intensities of 34 fluorescence bands in the wavelength range from 284 to 429 nm with a high resolution spectrograph. The pressure dependence of the fluorescence spectrum was also measured from a few hPa up to atmospheric pressure. Relative intensities and collisional quenching reference pressures for bands due to transitions from a common upper level were found in agreement with theoretical expectations. The presence of argon in air was found to have a negligible effect on the fluorescence yield. We estimated that the systematic uncertainty on the cosmic ray shower energy due to the pressure dependence of the fluorescence spectrum is reduced to a level of 1% by the AIRFLY results presented in this paper.

Growth of zinc platelets on zinc single crystals under diffusion conditions

The surface morphology of zinc platelets on zinc single crystals in the presence of hydrogen or argon is investigated. Platelets appear only on the pyramidal and prismatic faces and not upon the basal face of the zinc single crystals. It is shown that the smooth basal faces of the platelets change their shape in skeletal. The results are discussed and are in conformance with Chernov's theory for the disturbance of the morphological stability of crystal forms. The kinetics of growth of platelets on the pyramidal {1 0 1¯ 1} and prismatic {1 0 1¯ 0} faces of zinc single crystals and the alteration with time t the edge length a of the {0 0 0 1} basal face of the same crystals in the presence of argon were studied. The results of measurement of the edge a with time show that at the moment when the critical size a k is reached, the transition from kinetic to diffusion regimes starts. The comparison between the time when the visible platelets appear on the zinc crystals and the a 2 vs. t curves revealed that the first platelets grow exactly at the transition between the two regimes. It has been established that during the initial stage, when the size L is small, the platelets grow at a constant rate. During further growth, as the size L increases and reaches the critical dimension L k , a change in the L 2 vs. t curves appear: the linear curve is transformed into parabolic one. In conformance with the morphological theory of Chernov in the isotropic case, it is concluded that the platelets grow in a kinetic and a diffusion regime. During the growth of the platelets, part of them after reaching a certain thickness terminate their growth. The termination of the frontal growth is probably related to the transformation of their atomically rough surfaces into flat faces. The kinetic investigations led to the conclusion that part of the platelets do not grow following a screw dislocation mechanism. The observed transformation of triangular platelets into trapezoidal suggests that their frontal faces are atomically rough. The growth of the trapezoidal platelets is discussed and explained by a normal mechanism, while the growth of triangular platelets is attributed to a screw dislocation growth pattern.

Anoxia-Induced Changes in Pyridine Nucleotide Redox State in Cortical Neurons and Astrocytes

NAD(P)H autofluorescence was used to verify establishment of metabolic anoxia using primary cultures of cortical neurons and astrocytes. Cells on cover slips were placed in a chamber and O(2) was displaced by continuous infusion of argon. Perfusion with medium at PO(2) < 0.4 mm Hg caused an increase in NAD(P)H fluorescence, albeit to levels lower than that obtained with cyanide. Addition of the nitric oxide-generating agent DETA-NO to the hypoxic medium further increased fluorescence to the level with cyanide. Fluorescence under anoxia remained high in the presence of glucose, but declined in neurons and not in astrocytes when glucose was substituted with 2-deoxyglucose. Reoxygenation of neurons resulted in a decline in fluorescence and a loss in fluorescent gradient between fully reduced and fully oxidized (plus respiratory uncoupler). We conclude that (1) DETA-NO is useful for generating metabolic anoxia in the presence of argon (2) Exogenous glucose is necessary to maintain NAD(P)H in a reduced state during metabolic anoxia in neurons but not astrocytes (3) Neurons undergo a partially irreversible decline in NAD(P)H fluorescence during metabolic anoxia and reoxygenation that could contribute to prolonged metabolic failure.

Study of properties of O2-Ar mixture in DC glow discharge at medium pressures

The positive column of DC glow discharge sustained in pure O2, Ar and O2-Ar mixtures with several concentration ratios has been studied in two U-shaped discharge tubes made from different materials for discharge currents up to 30 mA. Total mixture pressures were 3 and 7 Torr. Parameters of discharge — electrical field strength and emission spectra — were studied by means of double-probe method and optical emission spectroscopy. We have focused on the investigation of affecting the intensities of the oxygen spectral lines and bands by the presence of argon for different ratios of the components in mixtures.

Spectroscopic study of plasmons in ion-irradiated single-walled carbon nanotubes

The electronic structure of single-walled carbon nanotubes was experimentally investigated using x-ray photoelectron spectroscopy, reflection electron energy-loss spectroscopy, and Auger electron spectroscopy. A shake-up satellite structure observed near the C 1s core-level lines in the x-ray photoelectron spectra at high binding energies in the range 284–330 eV due to excitation of π and π + σ plasmons was studied. The effect of irradiation by 1-keV argon ions on the shape of the spectra was analyzed. The shape of the C 1s satellite spectra was found to be sensitive to Ar+ irradiation in the electron energy loss range 10–40 eV corresponding to excitation of π + σ plasmons. Auger spectroscopy revealed the presence of argon on the surface of ion-irradiated samples. The argon content increased to ∼4 at. % with increasing irradiation dose. An analysis of the results obtained and their comparison with the data available in the literature led to a qualitative conclusion that the bond angles of the carbon atoms making up the walls of single-walled carbon nanotubes are distorted at sites exposed to Ar+ irradiation.

Structural and catalytic properties of ultra-dispersed silver powders prepared by metal evaporation with high-power electron beam. 2. Catalytic properties in ethylene epoxidation with molecular oxygen

Catalytic properties of ultra-dispersed silver powders synthesized via electron-beam evaporation of silver in Ar, N 2 or He were studied in the ethylene epoxidation. The highest selectivity was observed for a Ag(Ar) sample. It was associated with the formation on the silver surface of specific oxide-like species formed in the presence of argon. The nature of these species was also studied with UV-vis and XPS spectroscopy as well as with TPD.

Thermodynamic study of decomposition of dichlorodifluoromethane in thermal plasma

Decomposition of dichlorodifluoromethane in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving carbon, chlorine and fluorine in presence of argon (which is assumed to be the main plasma gas) and/or in addition of hydrogen and calcium together with hydrogen. The calculations were carried out for the temperature range between 500 and 6000 K and for the total pressure of the system of 1 bar. Use is made of the fact that a thermal plasma is a plasma in (local) thermal equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system and assuming that the equilibrium of the system corresponds to its minimum energy state. The results of calculations show that toxic molecules and radicals can be, under convenient conditions (appropriate temperature and amount of added substances), converted into stable non-toxic species like CaF2 and CaCl2.

Synthesis and luminescence properties of novel ZnO nanostructures: micro and nanospheres, polyhedral cages, tetra-pods, needles, tipped nanorods, nanowires and other “microphone–shaped” structures

ABSTRACTNovel ZnO nanostructures such as hollow nanospheres, nano-cages, nanoneedles, tetra-pods, nanowires, aligned nanorods and nanotubes are synthesized via thermal evaporation of ZnO and graphite powder mixtures in reduced oxygen atmosphere in the presence of argon and nitrogen flows. The ZnO nanostructures, especially nanospheres, have a unique shape and are hollow inside with walls densely decorated with aligned nanowires. Photoluminescence of synthesized ZnO structures measured at 300 K exhibits a strong near band edge peak at ∼380 nm and deep level green band centered at ∼550 nm. Fabricated ZnO structures can be studied for various applications in optoelectronics and sensors.

Sonolysis of actinide(IV) β-diketonates in alkanes

Ultrasonic irradiation with the frequency of 20–22 kHz and absorbed acoustic power about 0.4 W ml –1 causes degradation of An(IV) tetrakis-β-diketonates, AnL 4, where An(IV) is Th(IV), Np(IV), and Pu(IV), and HL is hexafluoroacetylacetone (HFAA) and dibenzoylmethane (HDBM), in hexadecane solutions in the presence of argon. The rate of the sonochemical process corresponds to a first-order kinetic law with respect to metal β-diketonate concentrations. The first-order rate constant of sonolysis increases with the increase in the volatility of the metal complexes. Solid sonication products consisted of a mixture of actinide carbides and partial degradation products, PDP, of initial metal β-diketonates. It is assumed that metal carbides are formed within the cavitating bubbles as a result of high-temperature process with participation of actinide(IV) β-diketonates and solvent vapours. PDP formation is attributed to the thermolysis of the complexes in a liquid reaction zone surrounding the cavitating bubble. To cite this article: S.I. Nikitenko et al., C. R. Chimie 7 (2004) .

Effect of argon additive on H− density and temperature in volume negative ion source

Various plasma parameters were measured for several hydrogen–argon mixtures in the multicusp H− ion source Camembert III, equipped with tantalum filaments. The density and the temperature of electrons were measured with the Langmuir probe situated in the center of the source and associated with the photodetachment diagnostics. The two-laser photodetachment diagnostics was used to obtain the temperatures of the two negative ion populations. At low hydrogen pressure (0.8 mTorr) a small concentration of argon additive enhances the hydrogen negative ion density (by approximately 60%), it also increases the electron density. The negative ion population fractions having the high- and low-temperature values behave differently when varying the total pressure in pure hydrogen and in hydrogen with argon additive. Several possible explanations of the drastic change of the relative ratio of negative ion populations when the argon fraction is increased, are proposed. Another interesting phenomenon observed during the experiments is the decrease with time of the H− density in the presence of argon. After adding the argon during the time interval of ∼1 h the H− density goes down and finally establishes at a minimum value. The final H− density is lower than the H− density in pure hydrogen plasma before adding argon. This “poisoning” is discussed in terms of wall production of vibrationally excited H2 molecules.

Self-sustained magnetron co-sputtering of Cu and Ni

The study of Cu/Ni thin films obtained by simultaneous standard magnetron sputtering (in argon atmosphere) and self-sustained magnetron sputtering (without any working gas) has been presented. Sputtering processes were performed using two separate magnetrons (50 mm in target diameter). To deposit Cu and Ni films in self-sustained sputtering mode a very high target power density was necessary (a few hundreds of W/cm 2). During one sputtering process, the Cu/Ni films of different composition were deposited on a couple of glass substrates. The Cu/Ni films constitution was determined from the thickness distribution characteristics of Cu and Ni films deposited separately in relation to the total Cu/Ni films thickness. The films, containing Cu44%Ni56%, have properties like bulk constantan. As for these films, the resistivity and temperature coefficient of resistance were respectively: ρ≅65 μΩ cm, TCR≅20 ppm/K (Cu/Ni films obtained in argon atmosphere—standard sputtering) and ρ≅45 μΩ cm, TWR≅400 ppm/K (Cu/Ni films obtained without the argon presence—sustained self-sputtering). The presence of argon ‘impurity’ caused the decrease of TCR of Cu/Ni films.

Laser photolysis of carboxymethylated chitin derivatives in aqueous solution. Part 1. Formation of hydrated electron and a long-lived radical.

Laser photolysis experiments on carboxymethylated chitin derivatives, such as carboxymethyl chitin (CM-chitin) and carboxymethyl chitosan (CM-chitosan), in aqueous solution by a 248 nm excimer laser were carried out for the first time. The transient absorption spectra of photolyzed CM-chitin or CM-chitosan solutions revealed a strong band with the maximum at 720 nm, which was assigned to the hydrated electron (eaq-). In the presence of argon, the eaq- decays by reacting with CM-chitin or CM-chitosan, and the rate constants are (6.1 +/- 0.1) x 10(7) M(-1) s(-1) and (3.7 +/- 0.1) x 10(7) M(-1) s(-1), respectively. Long-lived radicals with relatively weak absorption intensity were detected in the near-UV region. The absorption band was not notably characteristic and showed only an increasing absorption toward shorter wavelengths. It is similar to the signal of *CM-chitin or *CM-chitosan macroradicals formed by the reaction of CM-chitin or CM-chitosan with an OH* radical. It was assigned to *CM-chitin- or *CM-chitosan- macroradicals formed by eaq- + CM-chitin or CM-chitosan reaction. CM-chitin aqueous solutions were further examined by pulse radiolysis in order to confirm the site of the long-lived radical.

Plasma modified polymers as a support for enzyme immobilization II. Amines plasma

Polysulfone films were modified by ammonia, n-butylamine and allylamine remote plasma using various sample-to-plasma distances. Contact angle measurements, FTIR-ATR and XPS spectroscopy proved the presence of polar, including amine, groups on the modified surface. Presence of argon in the plasma environment made the plasma more stable and in most cases left the surface more hydrophilic but with a lower amount of nitrogen moieties on it. Glucose isomerase was successfully immobilized on the plasma-treated samples. Its activity correlates well with the concentration of C–N bonds on the surface. The highest enzyme activity was achieved for samples treated with allylamine/Ar plasma close to the plasma edge.

Radiative transport and collisional transfer of excitation energy in Cs vapors mixed with Ar or He

This paper is a review (with a few original additions) on the radiative transport and collisional transfer of energy in laser-excited cesium vapors in the presence of argon or helium. Narrow-band excitation of lines with Lorentz, Doppler and Voigt profiles is studied in order to calculate effective rates for pumping of spectral lines with profiles comprising inhomogeneous broadening components. The radiative transport of excitation energy is considered, and a new, simple and robust, but accurate theoretical method for quantitative treatment of radiation trapping in relatively optically thin media is presented. Furthermore, comprehensive lists of experimental values for the excitation energy transfer cross-sections related to thermal collisions in Cs–Ar and Cs–He mixtures are given. Within the collected cross-section data sets, specific regularities with respect to the energy defect, as well as the temperature, are discerned. A particular emphasis is put on the radiative and collisional processes important for the optimization of resonance–fluorescence imaging atomic filters based on Cs–noble gas systems.