Function Of Argon Pressure Research Articles

EFFECT OF ARGON WORKING GAS PRESSURE ON MECHANICAL STRESSES IN Mo/Si MULTILAYER X-RAY MIRRORS

By the method of X-ray tensometry (=0.154 nm), the dependences of residual stresses in Mo/Si multilayer Xray mirrors (MXMs) obtained by direct-current magnetron sputtering were studied as a function of the sputtering Ar pressure in the range of 1…4 mTorr. It is shown that an increase in pressure is accompanied by an increase in stresses from ~ 0.4 to ~ 0.8 GPa for a group of mirrors with periods near 7 nm and from ~ 0.9 to ~ 1.6 GPa for a group of mirrors with periods near 14 nm. The angles of texture misorientation for Mo crystallites were measured as a function of argon pressure. Mechanisms have been proposed to explain the reasons for the increase in stresses.

Time-resolved double-resonance spectroscopy: Lifetime measurement of the electronic state of molecular sodium.

We report on the lifetime measurement of the state of Na2 molecules, produced in a heat-pipe oven, using a time-resolved spectroscopic technique. The level was populated by two-step two-color double resonance excitation via the intermediate state. The excitation scheme was done using two synchronized pulsed dye lasers pumped by a Nd:YAG laser operating at the second harmonics. The fluorescence emitted upon decay to the final state was measured using a time-correlated photon counting technique, as a function of argon pressure. From this, the radiative lifetime was extracted by extrapolating the plot to collision-free zero pressure. We also report the calculated radiative lifetimes of the ro-vibrational levels in the range of = 0-200 with J = 1 and J = 31 using the LEVEL program for bound-bound and the BCONT program for bound-free transitions. Our calculations reveal the importance of the bound-free transitions on the lifetime calculations and a large difference of about a factor of three between the J = 1 and J = 31 for the = 40 and = 100, respectively, due to the wavefunction alternating between having predominantly inner and outer well amplitude.

Shifts in average energy of deposited atoms by magnetron sputtering through modifications in anode geometry: a simulation study

The deposition of titanium and gadolinium films by magnetron sputtering was simulated by using software SiMTra. The main goal is to analyze the average energy of deposited atoms as a function of argon pressure at different anode geometries. Two different anode configurations were used: a grid inserted between the target and the substrate, in the so-called grid-assisted magnetron sputtering, and a disk with different apertures. In the case of grid anode, simulations were also performed with a shutter in front of the substrate. The presence of the grid increases the average energy of atoms arriving at the substrate for pressures in the range between 1.0 and 8.0 Pa. The disk anode also changes the average energy, but such effect depends on the size of aperture.

Argon-Induced Pressure Broadening, Shifting, and Narrowing in the CN A2Π–X2Σ+ (1–0) Band

Selected isolated rotational transitions in the 1-0 band of the red A(2)Π-X (2)Σ(+) system in CN have been recorded with transient frequency modulation spectroscopy as a function of argon pressure up to 0.2 atm at room temperature. Line shapes were fit using Fourier transforms of a parametrized time correlation function, including Doppler and velocity-dependent collisional broadening, and collisional shifts. Deviations from Voigt line shapes can be equally well fit by modeling the narrowing with a speed-dependent collision model or with a velocity-changing collisional narrowing model. Pressure broadening coefficients were observed with little rotational state dependence, in the range of 0.070-0.075 cm(-1) atm(-1). In contrast, stronger and qualitatively different rotational state dependences are observed for both pressure-dependent blue shift coefficients and the narrowing parameters. No asymmetry in the pressure broadened lines was observed.

Collisional transfer of population and orientation in NaK

Collisional satellite lines with |ΔJ| ≤ 58 have been identified in recent polarization spectroscopy V-type optical-optical double resonance (OODR) excitation spectra of the Rb(2) molecule [H. Salami et al., Phys. Rev. A 80, 022515 (2009)]. Observation of these satellite lines clearly requires a transfer of population from the rotational level directly excited by the pump laser to a neighboring level in a collision of the molecule with an atomic perturber. However to be observed in polarization spectroscopy, the collision must also partially preserve the angular momentum orientation, which is at least somewhat surprising given the extremely large values of ΔJ that were observed. In the present work, we used the two-step OODR fluorescence and polarization spectroscopy techniques to obtain quantitative information on the transfer of population and orientation in rotationally inelastic collisions of the NaK molecules prepared in the 2(A)(1)Σ(+)(v' = 16, J' = 30) rovibrational level with argon and potassium perturbers. A rate equation model was used to study the intensities of these satellite lines as a function of argon pressure and heat pipe oven temperature, in order to separate the collisional effects of argon and potassium atoms. Using a fit of this rate equation model to the data, we found that collisions of NaK molecules with potassium atoms are more likely to transfer population and destroy orientation than collisions with argon atoms. Collisions with argon atoms show a strong propensity for population transfer with ΔJ = even. Conversely, collisions with potassium atoms do not show this ΔJ = even propensity, but do show a propensity for ΔJ = positive compared to ΔJ = negative, for this particular initial state. The density matrix equations of motion have also been solved numerically in order to test the approximations used in the rate equation model and to calculate fluorescence and polarization spectroscopy line shapes. In addition, we have measured rate coefficients for broadening of NaK 3(1)Π ← 2(A)(1)Σ(+)spectral lines due to collisions with argon and potassium atoms. Additional broadening, due to velocity changes occurring in rotationally inelastic collisions, has also been observed.

Preparation and characterization of the defect–conductivity relationship of Ga-doped ZnO thin films deposited by nonreactive radio-frequency–magnetron sputtering

Ga-doped ZnO (ZnO:Ga) thin films were prepared by radio-frequency–magnetron sputtering on conventional glass substrates at room temperature. The structural, electrical, and optical properties of these films as a function of argon pressure and film thicknesses were studied. All the films crystallized with the hexagonal wurtzite structure. The x-ray diffraction studies show that the ZnO:Ga films are highly oriented with their crystallographic c-axis perpendicular to the substrate. We discuss a methodology of using a “standardized platform” for comparison of samples deposited at different pressures, which provides an insight into the defect–resistivity relationship of each sample with respect to their microstructure. After the first annealing, the electrical properties of the films are dependent on the atmosphere used during postdeposition annealing treatment. A resistivity of 2.5 × 10−3 Ω · cm was obtained after vacuum annealing, and the films became an insulator after air annealing. The reproducibility of this treatment was verified. The average transmittance of all ZnO:Ga thin films is more than 85% in the visible range.

Sub-milli-torr magnetron sputter deposition of magnetic thin films

Thin films of magnetic and nonmagnetic constituents of spin-valve and magnetic tunnel junction multilayers were deposited using magnetron sputtering techniques as a function of argon pressure. Depositions in the sub-milli-Torr pressure regime have greatly improved film surface smoothness but also induced significant changes in film stress and, therefore, magnetostriction. The comparable values of magnetic thickness loss generated at various magnetic/nonmagnetic interfaces by the sub-milli-Torr deposition suggests comparable energetic deposition to ion beam deposition. A proper selection of deposition conditions for the component layers is critical to ensure optimal performance of spin-valve and magnetic tunnel junction multilayers.

An rf sustained argon and copper plasma for ionized physical vapor deposition of copper

Langmuir probe, optical emission spectroscopy, and biased quartz crystal microbalance measurements were used to investigate an argon and copper plasma used for ionized physical vapor deposition of copper. Copper vapor generated by a magnetron sputter discharge is ionized upon passing through an argon discharge excited by an internal rf induction antenna. Argon plasma characteristics such as electron temperatures Te, plasma densities ne, and plasma and floating potentials Vp and Vf, were studied as a function of argon pressure and rf power. An increase of plasma density versus rf discharge power and argon pressure was observed. The radial profile of plasma density measured by a Langmuir probe reveals a peak ion density at the center of the rf antenna and an increase in the radial ion concentration gradient with argon pressure. The ratios of optical emission intensities from Cu+ ion and Cu neutral lines increase with rf discharge power and argon pressure. The biased quartz crystal microbalance measurements show an increase of both Cu+ ion flux and the ratio of Cu+ ion to Cu neutral fluxes with rf power and argon pressure; however, they also show a decrease of total Cu flux with increasing argon pressure.

Capture and ionization of argon within liquid helium droplets

Liquid helium droplets of initial mean cluster size, 〈N〉, ranging from 600 to 8000 atoms are doped with argon using the pick-up technique. The doped clusters are ionized by electron impact, and the resulting fragment ions are monitored as a function of argon pressure in the pick-up volume. Analysis of the pressure dependent ion signals is used to determine (1) the probability for charge transfer from He+ to the Ar atoms within the droplet, and (2) the probability for fragmentation of the Ark subclusters upon ionization. The measured charge transfer probability from He+ to Ar ranges from 0.05±0.02 for clusters of mean original size 〈N〉=8000 to 0.26±0.05 for 〈N〉=600. Charge transfer to the Ark constituent results in the following qualitative trends; a single Ar atom yields HenAr+ ions; Ar2 mainly yields Ar2+, and Ar3 mainly fragments to yield Ar2+. Simulations of the results are performed to extract information on how the charge transfer and fragmentation processes within the ionized droplet dependent on the size of the helium droplet and the number of argon atoms captured. We use the positive-hole resonant-hopping mechanism to determine that the He+ hops 3–4 times prior to localization with either the Ar dopant or another He atom to form He2+. This corresponds to a time scale for He2+ formation of 60–80 fs.

Experimental study of an RF magnetron discharge for thin-film deposition

An investigation by optical emission spectroscopy and Langmuir probe was performed on an RF magnetron discharge used to sputter deposit tungsten and titanium in an argon plasma. The dependence on gas pressure and RF power of some Ti, W and Ar emission line intensities, electron density and temperature are studied in the center of the discharge. A simple model for the excitation process of the Ar, W and Ti atoms allows us to calculate the density of sputtered atoms in the plasma. The variations of electron density as a function of argon pressure and discharge power obtained by probe measurements are well correlated with the Ar (750.4 nm) line intensity. Owing to the transport regime of W and Ti sputtered species across the discharge, the existence of a correlation between the target composition, tungsten and titanium densities in the plasma and film composition on the substrate must be studied carefully.

Characterization of magnetron-sputtered diamond-like thin films for optical coatings in IR

The microstructural, optical, mechanical and electrical properties of diamond-like carbon films prepared by d.c. magnetron sputtering have been investigated as a function of argon pressure and substrate bias. The films were characterized by spectroscopic ellipsometry, scanning and transmission electron microscopy, electron diffraction, resistivity and hardness measurements. The pseudoband gap was found to rise and the hardness decrease with increasing pressure. Ellipsometric modelling indicated a change in the bonding configuration under the above conditions. This effect does not appear to be the result of a change in the energetics of the bombarding ions. Increasing substrate bias resulted in a densification of the films.

In-plane anisotropy studies in amorphous CoFeNb films

Uniaxial anisotropy field, H/sub k/, and local anisotropy fluctuation were studied as a function of argon pressure during deposition for RF sputtered amorphous CoFeNb films. Influence of P/sub Ar/ on anistropy field H/sub k/, local anisotropy constant K/sub loc/, and S (structure constant) is discussed. The magnitude of S and K/sub loc/V/sup 1/2/ were found to be strongly dependent on P/sub Ar/. >

Transmission electron microscopic analysis of microstructural features in magnetic recording media

A study of the relationships between the microstructure and magnetic properties of cobalt alloy magnetic thin films and chromium underlayers deposited onto circumferentially textured NiP/Al substrates is presented. The variation of the chromium microstructure as a function of argon pressure and substrate temperature during sputtering is analyzed using high-resolution scanning electron microscopy and transmission electron microscopy (TEM). This combination shows that the layers grow in columns which have increasing physical separation with increasing pressure and decreasing temperature. Crystallographic grain separation, however, follows a different trend because intercolumnar crystallographic alignment decreases with increasing temperature. TEM is also used to show how the growth of the chromium underlayer affects the cobalt alloy layer and to analyze the resulting microstructures in different magnetic alloy layers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In-plane anisotropy studies in amorphous FeBSi films

Uniaxial anisotropy field, H/sub k/, and local anisotropy fluctuation were studied as a function of argon pressure during deposition for RF sputtered amorphous CoFeNb films. Influence of P/sub Ar/ on anistropy field H/sub k/, local anisotropy constant K/sub loc/, and S (structure constant) is discussed. The magnitude of S and K/sub loc/V/sup 1/2/ were found to be strongly dependent on P/sub Ar/. >

Production and decay of ground-state gaseous lead from the 308-nm photodissociation of gaseous lead diiodide

An extensive investigation of the production and decay of ground-state lead atoms from the 308-nm XeCl excimer laser photodissociation of PbI[sub 2](g) is reported. The laser fluence dependences of the Pb(g) and PbI(g) yields along with energetic considerations suggest that Pb(g) is produced by a two-photon process and PbI(g) is produced by a one-photon process. Pb decay profiles as a function of argon pressure, PbI[sub 2](g) number density, laser fluence, and cell temperature were determined. The rates of Pb decay were found to be approximately second order in Pb. The second-order rate constants were found to increase with PbI[sub 2](g) number density, to not change with argon pressure, and to decrease with increasing laser fluence and cell temperature. These results are consistent with a complex mechanism that can be described as the PbI[sub 2](g)-catalyzed recombinations of Pb and PbI with I involving an exothermic preequilibrium, I + PbI[sub 2] = PbI[sub 3], with [Delta]H [approx] [minus]22 [plus minus] 6 kcal/mol. The proposed mechanism is capable of reproducing the observed Pb(g) decay profiles under all conditions studied when reasonably large values of rate coefficients for the various elementary steps are used.

Emission spectra of KrF in the chemical reaction of KrF_2 with SiH_4

Strong emission has been observed in the reaction of KrF2 with SiH4. The emission spectra have been identified to be the B2∑ → X2∑ transition of KrF. The dependence of the spectral shape of the emission has been examined as a function of argon pressure. The pressure dependence of the spectral shape appears to be due to vibrational relaxation in the B2∑ state. The emission intensity as a function of SiH4 and KrF2 concentration has been measured. Since the KrF(X2∑) ground-state binding energy is less than 100 cm−1, which is substantially smaller than the room-temperature thermal energy, the ground-state bottlenecking of KrF is negligible. Therefore, for any branching ratio of B to X formation, there should be a population inversion on the KrF B2∑ → X2∑ transition.

Analysis of anomalous vibrational and rotational distributions in the CN(B 2Σ +) state produced in the reaction of Ar( 3P 0,2) metastables with BrCN

The CN(B 2Σ + - X 2Σ +) tail band emission system for μ′ = 11–20 resulting from the energy transfer reaction Ar( 3P 0,2) + BrCN in a flowing afterglow apparatus was measured. The vibrational and rotational distributions were determined as a function of argon pressure. Numerous perturbed rotational lines were observed; analysis of the dependences of these lines on argon pressure, with the aid of experimental information already published, led to the following assignments as to the origins of the perturbations: For μ′ = 11, N′ = 20 and μ′ = 13, N′ = 9, the perturbing state is a 4Σ +; for μ′ = 12, N′ = 10 and 14, μ′ = 14, N′ = 7 and 10, and μ′ = 17, N′ ≈ 17–19 the perturbing state is A 2Π i. The perturbed rotational line, μ′ = 11, N′ = 20, is found to be the primary source of intensity in the μ′ =11 vibrational band, but in all other cases the perturbed rotational lines do not significantly aid in the populating of the vibrational state. The anomalously high vibrational populations found in the tail band emission system (μ′ = 12, 14, 17 and 18), as well as the significantly high rotational excitations observed in the μ′ = 12–20 vibrational bands, apparently arise directly from the reaction intermediate.

Experiment and theory for CO2 laser-induced CF2HCl decomposition rate dependence on pressure and intensity

A laser-excited fluorescence method has been used to determine the rates at which CF2HCl molecules dissociate into CF2+HCl fragments during CO2 laser pulses of uniform fluence and known intensity. A study has been made of the dependence of the rate on CO2 laser intensity and pressure of Ar buffer gas from the collision-free regime to atmospheric pressure. The effect of increasing Ar pressure is initially to increase the CF2HCl dissociation rate; above a moderate pressure (∼50 Torr), the rate is independent of Ar pressure up to atmospheric pressure. The data has been compared to a model, which adequately reproduces all the experimental data. The model treats the effect of collision between CF2HCl and the argon buffer gas in terms of rotational equilibration or ’’hole filling’’ in the discrete energy level region of CF2HCl. The discrete energy levels are interfaced to a quasicontinuum of vibrational–rotational states in a self-consistent manner which incorporates a background of nonpumpable CF2HCl states as a finite heat bath interacting with the pump mode. The model is used to calculate the rate of formation of product CF2 molecules as a function of argon pressure and CO2 laser intensity. The quasicontinuum for CF2HCl is predicted to begin about four quanta above the ground state. The absorption cross section in the quasicontinuum is shown to decrease from 10−18 to 10−20 cm2 at V=15. The energy distribution in CF2HCl is predicted to be decidedly nonthermal both below and beyond threshold.

The rate of vaporization of tungsten in argon

The vaporization kinetics of thin tungsten wires has been measured under natural convection conditions in high-purity argon. The rate was determined as a function of argon pressure and filament temperature in the range between 80 and 300 mm and 2850 and 3150 K. The vaporization rate is exponentially related to temperature with an activation energy of approximately 190 kcal/mole and inversely proportional to total pressure to the 0.87 power. The activation energy predicted by stagnant-film mass transfer theory is 202.5 kcal/mole, while the theoretically predicted inverse pressure dependence is 0.90. The rate was also sensitive to reactive impurities in the argon; thus,in situ, purification of the atmosphere was required.

Argon Concentration in Tungsten Films Deposited by dc Sputtering

The relative argon concentrations of dc-sputtered tungsten films were determined as a function of argon pressure, target-to-substrate voltage, substrate bias, and target-to-substrate distance, for both the diode and triode configurations. The results for films sputtered in the diode mode support Winters and Kay’s conclusions that the adsorption mechanism is due to entrapment of energetic neutral argon atoms. This model, however, does not. apply for all the argon content in films sputtered in the triode mode. An additional mechanism resulting in a greater entrapment of argon is proposed, namely, the entrapment of low energy argon ions originating from the supporting glow discharge. Measurements of the argon content of the tungsten films were determined using the rf spark-source mass spectrograph.