Increasing Ar Pressure Research Articles

Nanoporosity in plasma deposited amorphous carbon films investigated by small-angle X-ray scattering

Amorphous carbon films were deposited by plasma enhanced chemical vapor deposition (PECVD) and d.c.-magnetron sputtering and their porosity was investigated by small-angle X-ray scattering (SAXS). In the case of sputtered films, the X-ray scattering intensity increased with the argon pressure used for the film deposition, while the atomic density decreased. The analysis of the SAXS results was performed using the GNOM code assuming a distribution of spherical pores. This analysis suggested that the maximum of these distributions occur for a radius value below 1 nm. The films deposited at 0.17 Pa were essentially pore-free. As the Ar pressure increases, the pore size distribution widens and the volume occupied by the pores increases. A direct relation between the atomic density of carbon films deposited by sputtering and the pore volume fraction was also obtained. The low scattering intensity observed for the films deposited by PECVD showed that they were compact and homogeneous regardless of the self-bias voltage employed in the range between −100 V and −500 V.

Phase composition of sputtered films from a hydroxyapatite target

Hydroxyapatite (HA) was coated onto a cellulose filter acting as a substrate from a crystalline HA powder target using radio-frequency magnetron sputtering at Ar pressure of 0.5–5.0 Pa and discharge power of 50–150 W. After coating, the films were heated to 700 °C to remove the substrate and the crystalline phases were identified using XRD. The Ca/P ratio of the films was analyzed using EDS. The films were composed of HA, β-tricalcium phosphate (TCP), β-calcium pyrophosphate (PYR) and CaO. The weight ratio of HA and the Ca/P ratio of the films decreased with increasing Ar pressure and were largest at 100 W of discharge power. After coating, the surface of the HA target was decomposed into α-TCP, β-TCP and CaO.

Preparation of nanocrystalline titania films by pulsed laser deposition at room temperature

Titanium oxide (titania) nanoparticles/thin films were deposited on a non-heated substrate by the ablation of a rutile TiO 2 target in Ar atmosphere using an ArF excimer laser under off-axis configuration. The ambient pressure was changed to evaluate its influence on the morphology and crystal structure of the deposited titanium oxide. The ablated species tend to form thin film or nanoparticles embedded in the thin film at low growth pressure while moderate pressure favors the formation of monodispersed nanoparticles. Transmission electron microscopic (TEM) results showed that an increase of Ar pressure from 13.3 to 133 Pa leads to an increase in mean diameter of the primary nanoparticle from 5.9 to 32 nm and reached a maximum. The further increase of the growth pressure leads to a decrease in mean diameter of the primary nanoparticles. The selected area electron diffraction (SAED) rings and X-ray diffraction (XRD) peaks were observed for the titania prepared in the Ar pressure range of 133 Pa and 1.06 kPa at room temperature. Under the pressure range higher than 1.06 kPa or lower than 133 Pa the products were less-oxidized amorphous phase, TiO 2− x .

Stress Changes and Stability of Sputter-Deposited Mo/B4C Multilayer Films for Extreme Ultraviolet Mirrors

Periodic Mo/B4C multilayer films (MLs) for extreme ultraviolet mirrors were deposited by an rf-enhanced plasma magnetron sputtering system with changing the sputtering Ar pressure and layer thickness ratio. Internal stresses in the entire film were measured by Newton's rings method. Microscopic internal stresses in Mo crystallites in Mo/B4C MLs and in Mo single layer film were also determined by wide-angle X-ray diffraction from which lattice spacing in Mo (110) planes was measured. The internal stresses changed from a compressive value of about 1.1 GPa to a tensile value of about 0.6 GPa with increasing Ar pressure from 1.3 to 6.0 mTorr. The transition point of changing the stress from compressive to tensile shifted to lower Ar pressure with increasing the Mo layer thickness ratio. From atomic force microscope observation, the surface roughness of Mo/B4C multilayer films was found to increase monotonically from 0.11 to 0.23 nm (rms) with increasing Ar pressure. We examined the effect of the storage conditions of the films under vacuum, in low-humidity air and in air saturated with water vapor. Deterioration of film quality in Mo/B4C MLs was observed within a few weeks in the samples stored in open air with high humidity.

Structural and electrical properties of Cu films deposited on glass by DC magnetron sputtering

Abstract Cu films with thicknesses of 290–350 nm were deposited on glass substrates without heating by DC magnetron sputtering in pure Ar gas. Ar pressure was maintained in 0.5, 1.0 and 1.5 Pa, respectively. The target voltage was fixed at 400 V, but the target current increased from 69 to 200 mA with increasing Ar pressure. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used to observe the structural characterization of the films. The resistivity of the films was measured using four-point probe technique. At all Ar pressures, the Cu films have mixture crystalline orientations of [1 1 1], [2 0 0] and [2 2 0] in the direction of the film growth. The film deposited at a lower pressure shows a slightly more [1 1 1] orientation while that deposited at a higher pressure has a slightly more [2 2 0] orientation. The amount of larger grains decreases with an increase in Ar pressure. Roughness of the film surface is about 5 nm independent of Ar pressure. The resistivity of the films increases with increasing Ar pressure. The increasing of Ar pressure causes the decrease in both the average energy of reflected Ar atoms and the ratio of energetic Ar atoms to Cu atoms as well as the increase in the deposition rate, resulting in the decrease in grain size and the increase in resistivity of the Cu film.

Dependences of the activation volumes on Ar sputtering pressure in Co/Pt multilayers prepared by dc magnetron sputtering

We investigated the wall-motion and nucleation activation volumes of Co/Pt multilayer films prepared by dc magnetron sputtering under various Ar sputtering pressures. Delicate analysis of time-resolved domain evolution patterns reveals that the nucleation activation volume is generally smaller than the wall-motion activation volume in all the samples, which is consistent with the nucleation-dominant magnetization reversal behavior observed in this system. Interestingly, the activation volume is found to decrease with increasing Ar pressure, despite a decreasing trend in saturation magnetization. Decreasing grain size with increasing Ar pressure, smaller than the typical size of a Co single domain, is believed to be the origin of the unexpected observation.

Hardness, intrinsic stress, and structure of the a-C and a-C:H films prepared by magnetron sputtering

The 1.5-μm thick carbon films prepared by magnetron sputtering of a carbon target in Ar, Ar +CH 4 and Ar+O 2 gas mixtures show that the higher their intrinsic stress, the higher their microhardness and the lower their resistivity. The a-C films obtained without ion bombardment (unbiased; the mean free path of sputtered C atoms larger or equal to the cathode–anode distance) show microhardness up to 25 GPa. The biased a-C films (i.e. with ion bombardment) achieve the highest microhardness (up to 50 GPa) and the lowest resistivity (0.01 Ω cm). An increase in Ar pressure, or the optional addition of O 2, results in a decrease in the microhardness and intrinsic stress and an increase in the film resistivity. In comparison to a-C films, by adding CH 4 to Ar up to certain limit, the microhardness and intrinsic stress of these a-C:H films increase and subsequently decrease steeply. It was specified by analysis of the electron diffraction patterns of thin films (30–60 nm) deposited under the same conditions that the radius of the first co-ordination sphere of C atoms for all the films is in a good agreement with the value for graphite. The prime interplanar distance for biased a-C films is considerably lower than that for unbiased ones and for graphite. Our data indicate the sp 2-bonded carbon structure of the deposited hard carbon films, in which the prime interplanar distance is reduced due to intrinsic stress. Thus, it is more suitable to explain the hardness origin as a consequence of the film nanostructure rather than the presence of sp 3 bonds .

Structural, magnetic, Mössbauer and magnetostrictive studies of amorphousTb(Fe0.55Co0.45)1.5films

Films with a nominal composition of Tb(Fe0.55Co0.45)1.5 werefabricated by rf-magnetron sputtering from a fixed target configuration atvarious Ar gas pressures. Samples were investigated by means of x-raydiffraction (XRD), scanning electron microscopy (SEM), vibrating samplemagnetometer (VSM), conversion electron Mössbauer spectra (CEMS) andmagnetostriction measurements. As the Ar pressure increases, the Tb and Fecontent increases slightly, whereas the Co content decreases. In addition, asmall amount of Ar is introduced into the films. The as-deposited films areamorphous alloys, but their magnetic behaviour depends strongly on thedeposition conditions: a perpendicular magnetic anisotropy is obtained only infilm deposited at lowest Ar pressure and a parallel magnetic anisotropyexhibits in remaining films. These samples show an intrinsic magnetostriction(λ≈10-3) in an applied field of 0.7 T. In this state, it wasdetermined that the hyperfine field reaches the value Bhf = 24.5 T. Effectsof the heat treatment on the magnetostrictive softness are also reported. Theparallel magnetostriction with a huge magnetostrictive susceptibility(χλ = 1.8×10-2 T-1) obtained at (µ0H = 10 mT)makes these materials useful for applications.

Pulsed laser deposition of metals in low pressure inert gas

The influence of an ambient Ar gas on the pulsed laser deposition (PLD) of metallic systems (Ag, Fe, Fe/Ag) is examined. Time-of-flight (TOF) measurements and measurements of the deposition rate are presented showing a reduction of particle energy with increasing Ar pressure and a reduction of resputtering and interface mixing. The determined Ar pressure for significant changes of the effective sputter yield is about 0.04 mbar. The experimental results are explained by scattering of a dense cloud of ablated material in a diluted gas.

Effects of Ar pressure on ion flux energy distribution and ion fraction in r.f.-plasma-assisted magnetron sputtering

In r.f.-plasma-assisted sputtering, the ion fraction of the sputtered metal is thought to be enhanced by increasing Ar pressure. In this study, effects of Ar pressure on ion energy distribution and ion fraction of the metal flux have been investigated. The experiments have been performed by using a 55 mm diameter Ti magnetron cathode and a 60 mm diameter copper r.f. coil. The ion energy distribution of the depositing flux was measured by an energy-resolved mass spectrometer . The experimental results show that the number of Ti + ions increases with Ar pressure, whereas that of Ar + ions decreases. The ion fraction of the Ti flux reached 80% at an Ar pressure of 4.0 Pa. The electron temperature decreased with increasing Ar pressure as a result of plasma quenching induced by the ionization of the Ti metal atoms that have a lower ionization potential . The results emphasize the strong effects of Ar pressure on the ion fraction and plasma conditions. The Penning ionization is thought to be the dominant ionization process for Ti atoms in the r.f.-plasma-assisted sputtering.

Pressure dependence of the morphology and size of cobalt (II,III) oxide nanoparticles prepared by pulsed-laser ablation

The effect of ambient Ar pressure on the mean diameters and aggregate state of cobalt (II,III) oxide nanoparticles prepared by pulsed-laser ablation is investigated. TEM images show that the mean diameters of the primary nanoparticles are in the range 1.2–3.2 nm when the ambient pressure is varied from 13.3 Pa to 13.3 kPa. With the increase of Ar pressure, the mean diameters of the primary nanoparticles increase and show a maximum at a pressure of 100 Pa. A further increase of ambient pressure results in a decrease in mean diameter of the primary nanoparticles. In the pressure range from 267 Pa to 2.67 kPa, the mean diameters of the prepared nanoparticles are almost constant, and aggregated nanoparticles are observed. Above 2.67 kPa, aggregated Co3O4 particles dominate the ablated product and the mean diameter of the primary nanoparticles decreases with increasing ambient pressure. A dynamic process is suggested to explain the experimental results.

高周波支援マグネトロンスパッタリング法におけるＡｒ｀＋´及びＴｉ｀＋´のエネルギー分布のＡｒ圧力依存性

Effects of Ar pressure on the number of the 48Ti+ ions incident to the substrate have been investigated in inductively coupled rf plasma enhanced magnetron sputtering. The energy distributions of the 40Ar+ and 48Ti+ ions incident to the substrate were measured by an energy-resolved mass spectrometer. In addition to the energy distribution measurements, plasma conditions have been measured by a Langmuir probe technique to investigate the effects of Ar pressure on plasma. The experimental results of the ion energy distribution measurements show that the number of 48Ti+ ions arriving at the substrate increased as Ar partial pressure increased and that the number of 40Ar+ ions arriving at the substrate increased to an Ar pressure of 1.0 Pa and decreased for further increase in Ar pressure. From electron temperature measurement results, it was found that electron temperature decreased with increasing Ar pressure. The main process of Ti ionization is ascribed to the Penning effect, the ionization of Ti by the excited neutral Ar, resulting in a decrease of plasma temperature. It is concluded that an increase in Ar pressure enhances the ionization probability of Ti sputtered atoms.

Superfluorescence from optically trapped calcium atoms

We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 \ensuremath{\mu}m were generated on the Ca $4s4p{}^{1}{P}_{1}--3d4s{}^{1}{D}_{2}$ transition from a column of calcium vapor buffered with Ar by optically pumping the ${4s}^{2}{}^{1}{S}_{0}--4s4p{}^{1}{P}_{1}$ transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our situation in which the conditions resemble swept excitation. The delay times were found to be in agreement with a fully quantum mechanical calculation which describes the initiation of SF. Measurements of the densities of the three levels, the absolute SF photon yield, and the spatial distribution of the excited states indicate that the system has a quantum yield of unity. The SF intensity increases with an increase in Ar pressure due to collisional redistribution until the collisional dephasing rate inhibits SF. The conditions describing the transition of SF to amplified spontaneous emission allow us to measure the collisional broadening rate for the SF transition.

Effects of Ar pressure during CoCrPt sputter-deposition on read/write and related properties of CoCrPt/Cr magnetic recording media formed at low temperatures

Structures, magnetic properties and read/write properties were studied for low-temperature-growth CoCrPt/Cr magnetic recording media, of which CoCrPt films were sputter-deposited under various Ar pressures. Increase of Ar pressure causes both isolation enhancement and size decrease of CoCrPt grains, which are epitaxially grown on Cr grains. Coercivity increases as Ar pressure increases upto 20–30 mTorr. With an increase of Ar pressure, fluctuation field increases more rapidly than the case when the magnetic film thickness is decreased. Consequently, an increase of Ar pressure for sputter deposition significantly decreases medium noise with a slight decrease of output signal. The highest signal-to-noise ratio of 26.4 dB for 75 kFCI recording was obtained with the Ar pressure of 30 mTorr. This fabrication technique, which requires neither a thick Cr underlayer nor a Cr underlayer deposited under high Ar pressure, is especially suitable for the media with plastic substrates.

Structural and surface properties of sputtered Nb films for multilayer devices

Nb/Al-AlO x/Nb Josephson junctions are widely used as single or stacked devices for high-frequency applications. The quality of these junctions depends on the morphological and structural properties of the Nb base film, which must be optimized. To this purpose, niobium films (200 nm thick) have been deposited by RF magnetron sputtering at argon pressures between 0.75 and 3 Pa on different substrates. Measurements of the substrate curvature indicate that the stress changes from strongly compressive to zero as the Ar pressure increases. The film surfaces, as reconstructed by scanning tunneling microscopy (STM), show grains with a size varying between 30 and 100 nm. The measured roughness is larger for films deposited at higher Ar pressures because of the presence of larger voids between grains. At low deposition pressures, films show a smooth surface with a roughness close to 1 nm.

X-Ray Nonspecular Scattering from Amorphous Mo Films

X-ray nonspecular scattering method is used to study the structures of Mo thin films fabricated with magnetron sputtering under different Ar pressures. The results show that with the increase of Ar pressure, the density of amorphous Mo film decreased; the surface roughness of the films increased, while the surface coherent length decreased. The abnormal glow discharging in the sputtering processes interprets the observed results well.

Dependence of the thickness profile of pulsed laser deposited bismuth films on process parameters

High resolution, two-dimensional thickness profiles of ArF excimer laser deposited Bi films are recorded by a microdensitometer. The azimuthal dependent cross-sectional profiles are consistently fitted by linear combinations of a cos4Θ evaporation-like component and a much more sharply peaked one with exponents ranging from 8 to 61. When keeping the laser spot dimensions fixed, no dependence on laser fluence is obtained. An increase in Ar pressure from 10−6 to 10−1 Torr leads to the sharpening of the angular distribution along both axes: the forward directed component narrows from cos23Θ to cos61Θ along the short, and from cos9Θ to cos17Θ along the long axis, respectively. Further increase in pressure results in a sudden broadening leading to circular symmetry at around 0.5 Torr. Above 10−4 Torr the deposition rate continuously decreases with increasing Ar pressure. In He atmosphere only narrowing is obtained above 10−1 Torr.

Effect of Ar gas pressure on growth, structure, and mechanical properties of sputtered Ti, Al, TiAl, and Ti 3Al films

Single layers of Ti, Al, TiAl and Ti 3Al were sputter deposited on to 2″ oxidized Si 〈111〉 wafers and 7059 Corning Glass to study the effect of film thickness, temperature, and sputtering gas pressure on the mechanical and physical properties. In the present investigation, sputtering gas pressure was varied from 2 mT to 10 mT. The film thickness was varied from 1000 Å to 2 μm. The as-deposited Ti, Al and Ti 3Al films are well crystallized over the entire thickness range. Ti and Ti 3Al films show preferred orientation in the 〈0002〉 direction. On the other hand, Al films are random polycrystalline. TiAl films are nearly amorphous for all the thicknesses under consideration. TiAl films show formation of Ti (Al) solid solution phase with increasing Ar pressure. All the materials under consideration, show average film stress to be independent of thickness for thicker films. The nature of the stress (compressive or tensile) depends upon working gas pressure, sputtering power and the target material used. A definite trend is observed in the film stress as a function of Ar gas pressure. Both power and gas pressure influence the energetic bombardment of ions/atoms which in turn influence the average film stress. The nature of the intrinsic stress is explained by the atomic peening model. The Young's modulus of thin films is calculated by using the slope of the stress-temperature plots. The E values seem to change with deposition conditions, however, there is no obvious trend between the sputtering gas pressure and the Young's modulus of these thin films.

Control of Oxygen Content in Heavily Sb-Doped CZ Si Crystal by Adjusting Ambient Pressure

AbstractIn Czochralski-grown (CZ) silicon single crystals, antimony (Sb) doping decreases the oxygen concentration by enhancing oxygen evaporation from the melt surface. In this study, Ar ambient pressures of around 100 Torr over the silicon melt were found to suppress evaporation of oxide species. To clarify the effect of the growth chamber ambient pressure on oxygen concentration, heavily Sb-doped CZ silicon crystals were grown under Ar pressures of 30, 60, and 100 Torr. Increasing Ar pressure increases the oxygen and Sb concentrations at the melt surface. The oxygen concentration under an Ar pressure of 100 Torr was 1.2 times higher that under 30 Torr when the solidified fractions are 0.5 or larger. The oxygen evaporation rate is controllable by gas phase transport of Sb2O at high Ar pressures.

Sputtering pressure effects and temperature-dependent magnetism of Co/Pd multilayers

The temperature dependence of the sputtering Ar pressure effects on magnetic properties and the coercivity mechanism of Co(2 Å)/Pd(13 Å) multilayers were studied as the sputtering Ar pressure varied from 3–15 mTorr and the temperature from 300 to 35 K. It is found that the roughness of the interfaces or film surface increases with increasing sputtering pressure, the anisotropy increases with decreasing temperature and increasing Ar pressure and shows a maximum at PAr≊12 mTorr, and the coercivity increases with Ar pressure and shows stronger temperature dependence at higher Ar pressure. The coercivity mechanism was analyzed in terms of the coercivity predicted by Kronmüller’s theory [Phys. Status Solidi B 144, 385 (1987)]. Wall pinning is found to be the main mechanism and the size of the pinning site increases slightly as the Ar pressure increases.