High-pressure Argon Research Articles

The role of oxygen in the intrinsic tensile residual stress evolution in sputter-deposited thin metal films

The intrinsic tensile stress and oxygen content in thin Cr films sputter deposited at high argon pressure are investigated as a function of negative substrate bias. With increasing bias from 0 to −100 V, the tensile stress increases to a maximum while the oxygen content decreases. At bias higher than −100 V, the tensile stress decreases but no significant change is observed in the oxygen content. A similar trend in stress evolution with bias is also observed in Cr films capped with Al to protect from postdeposition oxidation. It is concluded that, for a given deposition condition, the incorporation of oxygen may lower the magnitude of tensile stress without affecting the trends in stress evolution with increasing substrate bias. These effects are discussed using a model that correlates the film microstructure with long range attractive forces predicted from interatomic potentials.

Direct comparison of experimental and theoretical results on the antenna loading and density jumps in a high pressure helicon source

Operation modes of helicon discharge excited by double m = 0 antenna at high argon pressures of 51 and 6 mTorr are examined experimentally and theoretically. The behaviour of the discharge, including abrupt density jumps, is found to depend strongly on the relative directions of the currents in the antenna loops (on the antenna spectrum). Experimental results are interpreted in terms of theory which considers the radio frequency power absorption with due regard to the conversion of helicon waves into electrostatic waves. Computed dependences of the plasma load resistance on plasma density and input power, and magnetic field profiles satisfactorily agree with experimental data over a wide range of operation parameters. Thresholds for density jumps estimated from the power balance consideration are also in agreement with experimental values.

Measurement of ionic energy from femtosecond laser-heated argon clusters

The high backing pressure argon gases adiabatically expand into vacuum through a pulsed gas jet to nucleate into large clusters. The clusters were heated by a 45fs, 2.3×1016 Wcm-2 Ti: sapphire laser. The high energy of the ions produced in the cluster explosion was measured using time-of-flight spectrometry. The maximum and average kinetic energy of the ions were 0.2MeV and ~12.5keV, respectively, indicating that the femtosecond laser interactions with argon clusters are more energetic than interactions with atoms and molecules.

Effect of process parameters on the optical constants of thin metal films

In this study, we show that the optical constants of sputter-deposited chromium depend on the argon pressure used for the deposition. Higher argon pressure gives lower extinction coefficients. Sheet resistance measurements show that those materials with lower extinction coefficients also have lower conductivity. Whereas the argon pressure strongly affects the resulting optical constants of the film material, the choice of substrate material does not affect the resulting optical constants of the film.

Mechanism of forward development of a plasma produced by an excimer laser in high-pressure argon gases

In high-pressure argon gases up to 150 atm, the plasma produced by a XeCl excimer laser developed not only backward but also forward. The model for the forward development, called a forward breakdown wave, could not predict the developmental behavior in the latter stage. The development model was modified, newly taking into account the laser absorption by the plasma when the laser light was transmitted through the backward plasma. The time variation of the absorption coefficient at each distance was calculated using the inverse bremsstrahlung by the electron–ion impact. This modified model could better predict the forward development behavior than the previous model.

Influence of atomising gas on particle characteristics of Al, Al–1 wt-%Li, Mg, and Sn powders

The influence of physical and flow properties of atomising gas on the particle characteristics of gas atomised Al, Al–1 wt-%Li, Mg, and Sn powders was investigated in a pilot plant gas atomiser with IN4/ON18/3·5–4·0 type ‘confined design’ nozzle. In the tests, Al powders were produced under high and low pressures of argon, under air, (N2 + O2 ) mixture, nitrogen, and helium; Al–1 wt-%Li binary alloy powders were produced under argon and helium; Mg powders were produced under high and low pressures of argon and helium; and finally Sn powders were produced under argon, nitrogen, and helium. The morphology, size, size distribution, and surface features of the powders used in the present study were examined under SEM together with dry and wet sieving, used for sizing the powders. It was observed that high gas velocities and/or low atomising gas densities not only affect powder particle size, but also shape and surface texture. The oxygen content of the atomising gases also has an influence on the powder particle shape. In this context, powders produced under helium are finer in size owing to efficient secondary breakup; more spherically shaped in their fine size fraction in non-oxidising or difficult to oxidise atomising liquids (such as Sn and Al), because the time to breakup is shorter than that for solidification; and more irregularly shaped in their coarse size fraction in oxidising atomising liquids (such as Mg and Al–Li) owing to oxygen (the time to breakup is longer than that for solidification) compared with other atomising gases such as argon, air, (N2 +O2 ) mixtures, and pure nitrogen.

Kinetics of Ar*2 in high-pressure pure argon

The kinetics of argon dimer (Ar2*) are studied in detail by model calculations. The model is applicable to discharge as well as e-beam excitation of high-pressure argon gas. The time-transient behaviour of the temperature and the vibration-translational relaxation of the excited state dimer have been considered in the model calculations. The model validity is verified by comparing the model predictions with discharge and e-beam experiments. Excellent agreement has been reached for the e-beam experiments. The predicted discharge voltage and current waveforms are in good agreement with the experiments of Ninomiya and Nakamura. The predicted net gain of 0.002 cm-1 at 3.5 atm is about three times smaller.

Influence of high gas pressure on combustion synthesis of the solid–solid reaction of NiAl compound

We show the advantage of using high gas pressure in the improvement of combustion synthesis conditions for NiAl compound synthesis. Experiments on high pressure of argon between 10 and 500 MPa showed that the exothermicity of Ni–Al reactions was considerably reduced, with a complete reaction giving NiAl compound. Thermodynamic and kinetic studies were carried out. The results indicate that pressure has relatively little influence on heat capacity or on the enthalpy of the reaction. We show that high pressure lowers the exothermicity of the reaction primarily by increasing the thermal conductivity of the sample. We propose an evolution of thermal conductivity as a function of pressure in the range 10–500 MPa. The main interest of this study is a pressure–heating rate diagram developed for self-propagating high-temperature synthesis (SHS) of NiAl.

Giant magnetoresistive spin valves with a strong exchange bias field and a weak interlayer coupling field

Spin valve multilayers exhibiting enhanced giant magnetoresistive (GMR) effect and weak interlayer coupling as well as strong exchange biasing were fabricated by a two-step deposition procedure. The down sublayers (i.e., buffer layer Ta/free layer NiFe/interlayer Cu) were deposited at a lower argon pressure, then the upper sublayers (i.e., pinned layer NiFe/pinning layer FeMn/cover layer Ta) were deposited at a higher argon pressure. The former promoted formation of the strong (111) textures, smooth interfaces, and dense Cu film, resulting in a weak interlayer coupling. The latter promoted small domains and less diffusive interfaces, resulting in a strong exchange biasing and an enhanced GMR ratio. This shows that independent control of magnetoresistance, interlayer coupling, and exchange biasing is possible.

Growth and Structure of Metallic Barrie Laye and Interconnect Films I: Exeriments

AbstractWe present experimental results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.

Growth and Structure of Metallic Barrier Layer and Interconnect Films I: Exeriments

ABSTRACTWe present experimental results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.

Modeling of a nonequilibrium cylindrical column of a low-current arc discharge

Numerical modeling of a wall-stabilized low-current arc discharge in the high pressure argon plasma is performed with account both of a deviation of the electron temperature from the heavy-particle temperature and of a deviation from the ionization equilibrium. Results are presented for a current range from currents of the order of 100 A down to several A, in which a regime of the discharge varies from the one typical for an arc discharge (local thermodynamic equilibrium (LTE) in the hot core, energy supplied to electrons by the electric field is mainly removed by the electron heat conduction) to the one typical for a glow discharge. (The electron temperature is substantially higher than the heavy-particle temperature and does not change much across the column, the ionization exceeds or substantially exceeds the recombination in every point of the column, energy supplied to electrons by the electric field is mainly locally transferred to heavy particles). On the axis of the discharge, the deviations from LTE become appreciable when the current decreases to several tens A. The deviation from the ionization equilibrium comes into play at higher currents than the deviation from the thermal equilibrium. Comparison with available experimental data is given.

レーザ反応性溶射によるチタンとニッケル複合ワイヤからのＴｉＮｉ皮膜の創製とその耐摩耗性

In this study we have tried to produce TiNi intermetallic compound spray coating on aluminium substrate using a composite wire of titanium wire (φ300μm) and nickel wire (φ300μm). The composite wire was melted by using CO2 laser in an atmosphere of argon gas and atomized and coated on the aluminium substrate by a high pressure argon gas. Effects of spray conditions on porosity of coating layer were investigated. Wear resistance of the coating was also evaluated by using an Ohgoshi wear tester.It was possible to produce TiNi intermetallic compound layer using a composite wire by a laser reactive spraying method. 100% TiNi intermetallic compound was found from the X-ray diffraction analysis of coating layer. As the spray distance increased from 50 mm to 200 mm and the atomize gas pressure decreased from 392 kPa to 196 kPa, the porosity of coating layer decreaced. A porosity of 5% was obtained at the spray distance of 200 mm and the atomize gas pressure of 196 kPa. The wear resistance of the coating increased by about ten times than that of aluminiun substrate.

Investigation of a -discharge plasma under an increased pressure of Ar and in narrow tubes

The electrokinetic characteristics (the electron energy distribution function, the strength of the longitudinal electric field and the concentration and average energy of electrons) are measured and calculated in a -discharge plasma under a high pressure of argon (up to 30 Torr) and in narrow tubes (the tube radius is less than 1.0 cm). A simple method of treating the second derivative of the probe current with respect to the probe potential is proposed for a straightforward way to obtain the electron energy distribution function under a high pressure of a gas. It is shown that the main assumptions on which modelling of the plasma of mercury luminescent lamps is based are also valid for the plasma in question. This leads to the existence of special similarity laws and gives a new possibility for diagnostics based on the similarity properties of the plasma. The approach proposed in the work can be easily extended to the mixtures of mercury vapour and other rare gases.

Power supply design considerations for maintaining a minimum sustaining current in a vortex water wall high-pressure argon arc lamp

Vortex water wall high-pressure argon arc lamps are used to generate intense light and are capable of operating at radiative efficiencies greater than 50%. These lamps are being considered for use in a pulsed DC mode of operation in the next generation of rapid thermal processing applications. The results of a series of experiments have shown that the breakdown to arc transition consists of a prethermionic electrode emission phase and a prethermal ionization phase. The large dynamic voltage and current range between the breakdown phase and the arc phase necessitates the use of three different power circuit topologies. A high-voltage ignition circuit is connected in series with an arc-sustaining power source. The series connection ensures that the arc-sustaining power supply is isolated from the high-voltage ignition circuit. The arc-sustaining current source power source consists of a step-down hysteresis-current-controlled DC/DC converter cascaded with a constant off-time output-voltage-controlled step-up DC/DC converter. The current-controlled converter supplies the minimum arc-sustaining current, whereas the step-up converter provides the minimum post-ignition prethermal ionization voltage. The inclusion of a shorting switch allows one to reduce the current ratings of the high-voltage circuit components. Finally, experimental verification of a simplified circuit model of the ignition to arc transition, the circuit operation, a power supply design procedure, and a design example are provided.

Superplastic Foaming of Titanium and Ti-6Al-4V

ABSTRACTSolid-state foaming of metals can be achieved by hot-isostatic pressing of powders in presence of argon followed by expansion of the resulting high-pressure argon bubbles at ambient pressure and elevated temperature. This foaming technique was first demonstrated by Kearns et al. [1] for Ti-6Al-4V, but is limited by its low creep rate and ductility, which lead to early cell wall fracture. We address these issues by performing the foaming step under superplastic conditions. Rather than using microstructural superplasticity (requiring fine grains which are difficult to achieve in porous powder-metallurgy materials), we used transformation superplasticity, which occurs at all grain sizes by biasing with a deviatoric stress (from the pore pressure) of internal stresses (from the allotropic mismatch during thermal cycling about the allotropic temperature range). As compared to control experiments performed under isothermal creep conditions, superplastic foaming under temperature cycling of unalloyed titanium and alloyed Ti-6Al-4V led to a significantly higher pore volume fraction and higher foaming rate.

Surface self-diffusivity ofTiO2under high-pressure gas

The surface diffusion coefficient of ${\mathrm{TiO}}_{2}$ under a high-pressure gas of 100 MPa was estimated by using simulation of a sintering model consisting of surface and volume diffusion. The value of the volume diffusion coefficient of ${\mathrm{TiO}}_{2}$ estimated using the present simulation is similar to the value of the diffusion coefficient of oxygen in ${\mathrm{TiO}}_{2}.$ The surface diffusivity was considered independently of the inert gas atmosphere. The present work, however, shows that the value of the surface diffusion coefficient of ${\mathrm{TiO}}_{2}$ under a high-pressure argon gas of 100 MPa is about 30 times higher than that under 1 atm.

Protective carbon films deposited by dc-bias facing targets sputtering with microscopic ultraflatness and strong sp3 coordination

Carbon thin films were deposited on hard disks as protective layers by facing targets sputtering (FTS), and their characteristics were evaluated to determine whether they would be suitable protective layers for thin-film magnetic recording media. The performance and lifetime of a hard disk drive (HDD) are intimately related to the head-disk interface. Increase in performance due to reduction of the flying height and magnetic spacing, and longer product lifetime are related to the properties of protective layers covering the surfaces of hard disks. Currently, such layers are generally sputtered amorphous carbon films, whose characteristics are strongly dependent on various sputtering conditions such as the argon gas pressure, substrate temperature, and dc and rf bias voltages. In this study, the dependence of the characteristics of carbon films on the dc bias voltage of the FTS was investigated, and the characteristics were also compared with those obtained without a dc bias voltage supply. The carbon films were deposited at an argon gas pressure of 0.2 mTorr and a substrate temperature of 25 °C as room temperature, with several dc bias voltages and also without any bias voltage. There have been no reports to date of the successful use of such low gas pressures to realize excellent protective layers. The properties of the films were characterized by Raman spectroscopy, and the results were compared with previously reported ones obtained in different sputtering conditions at high argon pressures. Carbon films deposited, without plasma damage, by FTS, with dc bias voltage at argon gas pressures as low as 0.2 mTorr, showed a large population of sp3 coordination, columnless morphology, and a microscopically flat surface. These are better properties than those obtained with no dc bias voltage, and may lead to an intrinsically excellent protective layer for hard disks.

Observation of forward breakdown mechanism in high-pressure argon plasma produced by irradiation by an excimer laser

When a XeCl excimer laser beam was focused in a high-pressure argon gas up to 150 atm, a hot and dense plasma was produced at the focal spot. The plasma developed not only backward but also forward, which differed from one produced by a visible laser. The radius of the forward plasma became smaller beyond the focal spot. There had been no explanation for the development mechanism of the forward plasma. A new model for the forward development mechanism called a forward breakdown wave was proposed. The forward plasma was calculated assuming that the laser beam transmitted through the plasma was further focused by the plasma. This model could predict the forward development behavior considerably well.

Modeling of high-pressure rare gas plasmas excited by an energetic flash X-ray source

In this paper, a comprehensive description of the kinetics of argon plasmas has been formulated for atmospheric pressures. It has been used to attribute to molecular species the ultraviolet-vacuum ultraviolet (UV-VUV) continua, observed between 150 and 300 nm in pure argon. The participation of both ionic dimers and trimers has been found to be necessary to explain the whole fluorescence emitted by the rare gases (Rg). A simple kinetic model of high-pressure (1-30 bar) argon plasmas created by flash X-ray excitation is reported. The photoexcitation of Rg at high pressure by X-ray photons with energy of about 10 keV is shown to produce plasmas with significant density gradients of ionic and excited species. Spatial analysis of the energy position along the X-ray penetration path is performed in order to account for these concentration gradients. The calculation of electron density in different Rg (Ar, Kr, Xe) excited by X-ray photons of various energies (0.2-10 keV) is also reported. From these results, it appears that hash X-ray excitation of Rg can be a very interesting means to produce high-electron-density plasmas designed to selectively emit intense fluorescence in the UV-VUV spectral domain.