Increasing Ar Pressure Research Articles

Comprehensive investigation of sputtering deposition pressure effects on a-InGaZnO Schottky diodes

The effects of Ar sputtering deposition pressure on the optical, structural, morphological, and electrical properties of amorphous InGaZnO thin films were investigated. The InGaZnO thin films, which have amorphous structures determined by grazing incidence x-ray diffraction, contained In, Ga, Zn, and O confirmed by secondary ion mass spectrometry method. Additionally, when the thicknesses of the deposited thin films are examined, it was seen that the profilometer measurement results of the crater formed by secondary ion mass spectrometer and scanning electron microscope measurement results are nearly similar, and it is approximately 100 nm. The surface roughness, obtained from Atomic Force Microscopy results, show that decreased up to a particular value with the increase of the working pressure, and then the surface roughness increased. The optical band gaps of the films were obtained in the range of 3.50 eV−3.58 eV via Tauc relation by using the Ultraviolet-Visible measurements carried out in the wavelength range of 200 nm−1100 nm. It was seen that the optical band gap was decreased with the increase in Ar pressure. The electrical properties of InGaZnO thin film-based Schottky diodes, such as the barrier height, ideality factor, saturation current, series resistance, and shunt resistance, have also been studied comprehensively. The electrical results showed that diode properties change with increasing deposition pressure.

Radio-frequency magnetron sputter deposition of ultrathick boron carbide films

The deposition of thick B4C films with low residual stress by conventional direct-current magnetron sputtering is accompanied by the formation of dust particulates contaminating the target, chamber, and substrates and leading to the formation of nodular defects in films. Here, we demonstrate that the formation of particulates is greatly reduced during radio-frequency magnetron sputtering (RFMS). We systematically study properties of B4C films deposited by RFMS with a substrate temperature of 330 °C, a target-to-substrate distance of 10 cm, Ar working gas pressure in the range of 4.5–12.0 mTorr (0.6–1.6 Pa), and substrate tilt angles of 0°–80°. All films are x-ray amorphous. A columnar structure develops with increasing either Ar pressure or substrate tilt. For columnar films, the column tilt angle decreases with increasing Ar pressure, which we attribute to a corresponding increase in the width of the distribution of impact angles of deposition flux. In contrast to the Keller–Simmons rule, the deposition rate increases with increasing Ar pressure, which suggests a better coupling of the RF energy to the plasma processes that lead to target sputtering at higher pressures. There is a critical substrate tilt angle above which the total residual stress is close to zero. This critical substrate tilt angle is ∼0° for an Ar pressure of 12 mTorr (1.6 Pa). The lower residual stress state, necessary for depositing ultrathick films, is characterized by a larger concentration of nanoscale inhomogeneities and decreased mechanical properties. Based on these results, RFMS deposition of 60-μm-thick B4C films is demonstrated.

In situ optical and electrical analysis of transient plasmas generated by ns-laser ablation for Ag nanostructured film production

The continuous effort for transitioning pulsed laser deposition (PLD) technique from an experimental tool into an industrial one can be sustained by the use of complex tools for in situ real-time monitoring of the deposition process. Langmuir Probe (LP) and optical emission spectroscopy (OES) measurements were used for plasma monitoring during PLD of silver films under various Ar pressure conditions. The LP measurements revealed a multi-structured distribution of the ions, which was strongly influenced by the increase of Ar pressure. The generation of highly energetic ions with the addition of Ar and the degree of Ar gas ionization was confirmed by OES measurements. A perturbative effect was seen under pressures higher than 10 Pa, where the presence of high electronic charges leads to an unstable behavior of plasma in the vicinity of the LP. The effect of these complex dynamics on the structure and quality of the deposited thin film was investigated revealing a strong correlation between the electronic distribution in plasma and thin film thickness profile.

Influence of the Ar pressure on the structure of the NiTi foams produced by self-propagating high-temperature synthesis

The influence of the Ar pressure in the reactor on the structure and martensitic transformation of the NiTi foams produced by self-propagating high-temperature synthesis (SHS) was studied. It was shown that an increase in Ar pressure significantly affected the porous structure due to the process of combustion wave propagation changed from the stationary to the pulse regime. Regardless of the Ar pressure, the porous partitions included the NiTi phase as well as Ti2Ni, Ni3Ti2, Ni4Ti3 precipitates. An increase in Ar pressure decreased the transformation temperatures, which might be caused by an increase in the Ni concentration in the NiTi phase due to a decrease in the volume fraction of the Ni-rich precipitates.

Magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction in exchange biased Pt/Co/NixOy films

We show that a trilayer magnetic structure, consisting of a heavy metal (Platinum) as a buffer, an ultrathin ferromagnet (Cobalt) as a functional layer, and an antiferromagnetic insulator (Nickel oxide, NixOy) as a capping, is a host of intriguing physical phenomena desirable for spintronics. X-ray photoelectron spectroscopy revealed changes in the ratio of NixOy phases with different stoichiometry. Due to strong spin–orbit coupling, the Pt layer induces perpendicular magnetic anisotropy in Co, breaks its structural inversion symmetry, and causes an additive effect of Pt/Co and Co/NixOy interfaces to the effective interfacial Dzyaloshinskii-Moriya interaction (Deff). Manipulation the magnetic anisotropy can be realized by the ferromagnetic layer thickness variation and modification of the Co/NixOy interface. The NixOy capping layer induces the exchange bias in Co, which effective field |Beb| can be controlled in the range from 0 to 24 mT. The magnitude and direction of Beb does not affect Deff. The increase of Ar pressure leads to structural transformation of the Co/NixOy interface and, consequently, to decrease of the surface Dzyaloshinskii-Moriya interaction (Ds), the source of which is the NiO phase. We demonstrate that the studied Pt/Co/NixOy system has a number of functional properties useful for future logic and memory applications.

Influence of argon pressure on the structural properties of polycrystalline sputtered Fe0.89Ga0.11 thin films

In this work, we present a systematic study on the relation between the elastic behavior and the structural properties of polycrystalline Fe0.89Ga0.11 thin films deposited on Si(100) substrates. By carrying out pole figure (PF) measurements, we determined the evolution of the texture components, residual stress and Young's modulus (Ys) as a function of the Ar pressure. The samples display several fiber-like texture components (where the fiber axes is always along the growth direction) beside to a random component; the texture component weights depend on the Ar pressure. The study of the residual stress reveals that the samples present a tensile stress, that relaxes when the Ar pressure increases. In the case of Ys, the estimated values vary slightly within the Ar pressure range studied. Finally, the residual stress and Ys behavior is correlated with the microstructure evolution by using the orientation distribution function (ODF) simulated from the PFs.

Strategies for Scalable Gas-Phase Preparation of Free-Standing Graphene

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

Vital role of Ar ambient pressure in controlled properties of nanocrystalline CdS thin films

A report on the manipulation of structural, optical, and electrical properties of nanocrystalline CdS (ncCdS) thin films in the framework of varying Ar ambient pressure in pulsed laser deposition (PLD) is presented here. Increase in Ar ambient pressure results in reduction of crystallite size which in turns increases the structural imperfections and structural phase transformation of ncCdS thin films. The most significant observation here is the bleaching of multiphonon Raman modes (MRMs) particularly LO + 2E2, 2LO + 2E2, etc. in ncCdS thin films. An acute investigation on the reason of bleaching of LO + 2E2, 2LO + 2E2, etc. modes is carried out here and concluded that it is due to the fading of E2 mode with increasing Ar pressure as confirmed by low-frequency micro-Raman measurements. UV–visible absorption and photoluminescence spectroscopies are used to examine the optical properties like bandgap and possible electronic transitions in ncCdS thin films. Further, transport properties of ncCdS thin films are investigated using Hall measurement and I–V characteristics.

Direct Regulation of O/W Stoichiometric Ratio and Microstructure in Tungsten Oxide Electrochromic Films by Ar Pressure Using Oxide Target Sputtering

Herein, amorphous tungsten oxide electrochromic (EC) films are successfully prepared by radiofrequency (RF) magnetron sputtering in pure Ar atmosphere using an oxide target. The effect of Ar pressure on the apparent color, deposition rate, crystal structure, O/W ratio, surface morphology, and EC properties of the as‐deposited tungsten oxide films is systematically investigated using spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, X‐ray diffraction, scanning electron microscopy, and cyclic voltammetry. Interestingly, the Ar gas pressure plays a key role in regulating the O/W ratio, microstructure, and EC properties of the obtained tungsten oxide films. The films are all substoichiometric, and the O/W ratio changes from 2.79 to 2.89 with the increase in Ar pressure. In addition, the loose surface microstructure is shown as Ar pressure increases. The tungsten oxide films deposited at the Ar gas pressure of 1.2 Pa reaches the deposition rate of 13.0 nm min−1, the largest optical modulation of 71.2% at 550 nm, and the EC efficiency of 51.3 cm2 C−1. This film also reveals excellent electrochemical stability and sustains more than 200 cycles. These results provide a simple solution for preparing high‐quality tungsten oxide EC films using oxide ceramic targets in pure Ar atmosphere.

Magnetic behavior of amorphous Fe–Zr thin films sputtered at different Ar pressures

Abstract Amorphous Fe–Zr thin films with similar compositions exhibit a considerable change in their magnetic behaviors when they are sputtered at different Ar pressures. The change is well explained by a parameter – the SPM ratio – devised in this study, which is defined as the ratio of the magnetization due to the superparamagnetic behavior to the saturation magnetization. The change in the magnetic behavior of thin films with 40–70 at.% Fe depends on an increase in the SPM ratio, and it is more prominent at higher Fe contents; for example, the SPM ratio of a thin film with ∼60 at.% Fe increases from ∼0 to 0.69 with increasing Ar pressure from 2 to 10 mTorr. Subsequent annealing of the thin film fabricated at the Ar pressure of 10 mTorr at 150 °C leads to a 10-fold decrease in its SPM ratio from that in the as-deposited state. This decreased SPM ratio is, nevertheless, still higher than that of the thin film fabricated at the Ar pressure of 2 mTorr. These results indicate that the magnetic behaviors of amorphous Fe–Zr thin films are highly sensitive to the Ar pressure. Thus, it is crucial to take this parameter into account in the analysis of the magnetic behaviors of amorphous Fe–Zr thin films.

Influence of deposition conditions on mechanical properties of a-C:H:SiOx films prepared by plasma-assisted chemical vapor deposition method

A series of a-C:H:SiOx films was deposited on polished silicon and glass substrates by plasma-assisted chemical vapor deposition combined with pulsed bipolar substrate bias from mixtures of argon and polyphenylmethylsiloxane vapors. Different Ar pressures and substrate bias voltages were applied for the synthesis of a-C:H:SiOx films having different mechanical properties. Detailed characterization of the mechanical properties of a-C:H:SiOx films was made using the nanoindentation. Hardness and elastic modulus were used for the evaluation of the endurance capability (H/E) and resistance to plastic deformation (H3/E2). The structural properties of the deposited films were analyzed by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It was shown that the Ar pressure and substrate bias variation can change the film properties and the growth rate and these changes are not linear. So, depending upon application, deposition conditions are to be optimized. In all of the examined coatings, increase of Ar pressure and amplitude of negative pulse of substrate bias lead to improvement in mechanical properties. According to the results of FTIR and Raman spectroscopy; this improvement is due to an increase in the sp3 bonded carbon content and decrease of hydrogen content in the films.

Normal and grazing incidence pulsed laser deposition of nanostructured MoSx hydrogen evolution catalysts from a MoS2 target

Pulsed laser ablation of a MoS2 target causes enhanced splashing of the material. So, for MoSx films obtained by pulsed laser deposition (PLD) in the conventional normal incidence (NI) configuration, their typical morphology is characterized by an underlying granular structure with an overlayer of widely dispersed spherical Mo and MoSx particles possessing micro-, sub-micro- and nanometer sizes. We investigated the possibility of using high surface roughness, which occurs due to particle deposition, as a support with a large exposed surface area for thin MoSx catalytic layers for the hydrogen evolution reaction (HER). For comparison, the HER performance of MoSx layers formed by grazing incidence (GI) PLD was studied. During GI-PLD, a substrate was placed along the direction of laser plume transport and few large particles loaded the substrate. The local structure and composition of thin MoSx layers formed by the deposition of the vapor component of the laser plume were varied by changing the pressure of the buffer gas (argon, Ar). In the case of NI-PLD, an increase in Ar pressure caused the formation of quasi-amorphous MoSx (x ≥ 2) films that possessed highly active catalytic sites on the edges of the layered MoS2 nanophase. At the same time, a decrease in the deposition rate of the MoSx film appeared due to the scattering of the vapor flux by Ar molecules during flux transport from the target to the substrate. This effect prevented uniform deposition of the MoSx catalytic film on the surface of most particles, whose deposition rate was independent of Ar pressure. The scattered vapor flux containing Mo and S atoms was a dominant source for MoSx film growth during GI-PLD. The thickness and composition distribution of the MoSx film on the substrate depended on both the pressure of the buffer gas and the distance from the target. For 1.0–2.5 cm from the target, the deposition rate was quite sufficient to form S-enriched quasi-amorphous MoSx (2.5 < x < 6) catalytic films that consisted of densely packed 30–50 nm nanoparticles. The GI-PLD films possessed a greater density of catalytically active sites with a distinct local atomic configuration including edge sites of the layered MoS2 nanophase and diverse S ligands in the amorphous phase, which contained Mo3-S clusters. At a modest loading of ∼300 μg/cm2 on glassy carbon substrates and an overpotential of -140 mV, these films activated H2 production with geometric current densities up to −10 mA/cm2.

Formation of Germanium-Carbon Core-Shell Nanowires by Laser Vaporization in High-Pressure Ar Gas without the Addition of Other Metal Catalysts

Germanium (Ge)-carbon (C) core-shell nanowires (NWs), 15 - 80 nm thick and <1 μm long, were grown using continuous-wave laser vaporization of Ge-graphite composite targets in high pressure (0.1 - 0.9 MPa) Ar gas. The NW core was crystalline Ge and the shell was amorphous C. The fraction of the NWs in deposits was changed significantly by the Ge content in the targets and had a maximum at the Ge content of 40 atomic %. With increasing Ar pressure, thicker NWs were grown. A strong correlation was evident between the two diameters of the NW and nanoparticle (NP) attached with the tip of the NW. The growth of the NWs can be explained by the formation of Ge-C liquid-like molten NPs having a specific range of size and composition and precipitation of Ge and C followed by phase separation.

The Effect of Ar Ambient Pressure and Annealing Duration on the Microstructure, Superconducting Properties and Activation Energies of MgB2 Superconductors

MgB2 samples are produced by ex situ reaction method under vacuum, and various (0, 10, 20 Bar) Ar pressure for 0.5 and 1 h. The effect of ambient pressure and annealing duration on the microstructure and electrical properties of bulk samples are investigated. XRD, SEM, and magnetoresistance measurements are made. The a and c lattice parameters and the grain size values are the highest for the samples produced under vacuum and their values decrease with increasing Ar pressure. Moreover, these values increase when the annealing duration increases from 0.5 to 1 h. The increasing pressure reduces the bond lengths between the atoms thus the grain sizes decrease. Smaller grain size promotes the connection between grains which results in an increase of the critical current density (Jc). SEM micrographs reveal that the produced samples have granular structure which is a characteristic feature of MgB2. The decrease of grain sizes and thus enhancement in grain connectivity with increasing pressure is also confirmed by SEM images. Magneto resistivity measurements show that Tc values of the samples produced under vacuum are the highest. Tc values decrease with increasing ambient pressure and applied magnetic field. The activation energies (U0) of the samples are calculated using Arrhenius plots due to thermally activated flux flow theory. Existence and increase of Ar pressure causes increase of activation energies. The samples produced with 0.5-h annealing have higher activation energies than the ones produced with 1-h annealing.

Pulsed laser deposited alumina thin films

Thin films of amorphous alumina were fabricated using pulsed laser deposition. Topography, structural, and optical properties of alumina films were investigated depending on process parameters, specifically deposition time under vacuum and partial pressure of argon. Deposited films present good uniformity with RMS roughness ranging from 0.35 to 2.50nm. Alumina films with thickness lower than 40nm deposited under vacuum present a non-negligible void content that induces a decrease of the effective refractive index of the layers. Furthermore, introduction of argon gas (at 5×10−4 and 5×10−2mbar) during the deposition process induces grainy structure of the thin films documented by an increase of RMS roughness from 0.35 to 1.5nm. A decrease of the alumina layers' refractive index is observed in the 300–7500nm spectral range when increasing Ar pressure.

合金ターゲットを用いて作製したスパッタZrCuNiAl金属ガラス薄膜

Metallic glass alloy can be a promising structural material for MEMS application because of its superior properties. However, there was limited information on fabrication and properties of thin metallic glass films. This paper reports the metallic glass film deposited by rf magnetron sputtering using a Zr65Cu17.5Ni10Al7.5 alloy target. Although the composition of as-deposited films changes along with the substrate position, it was found that films grew with relatively uniform composition at the substrate holder center facing within the target erosion circle. Ar pressure also affected the film composition. Residual stress of deposited films changes from compressive to tensile with increasing Ar pressure as crystalline metallic films did. Tensile fracture stress of deposited films rapidly decreased when the Ar pressure was higher than 0.7Pa, while the microhardness of deposited films were ∼6GPa regardless of Ar pressure. The deposited films showed glass transition behavior and the ability of micro-molding.

High-resolution x-ray analysis of graphene grown on 4H–SiC (000) at low pressures

Abstract

Phase Composition of Sputtered Film from a Mixture Target of Hydroxyapatite and Strontium-apatite

To obtain an Sr-substituted hydroxyapatite thin film, sputter-coating was performed on a cellulose filter acting as a substrate from the mixture target of hydroxyapatite (HA) and strontium-apatite (SrAp) at an Ar pressure of 0.5–5.0 Pa. The ratio of the SrAp in the mixture target was varied from 25% to 100%. After coating, the films were heated at 700 °C to remove the cellulose filter substrate, and the crystalline phases were identified by X-ray diffraction (XRD). The sputter-coated film was identified as the Sr-substituted β-tri-calcium phosphate (TCP) and the Sr-substituted β-calcium pyrophosphate (CPP) as well as the Sr-substituted HA. The weight ratio of the Sr-substituted HA decreased with increasing Ar pressure or with an increasing ratio of SrAp to HA in the target. The average Sr/(Ca + Sr) molar ratio in the film was 1.9%–3.5% slightly lower than the initial SrAp ratio of the target, and the ratio was not influenced by the Ar pressure. In the (Sr + Ca)/P ratio, the ratio decreased while increasing the SrAp ratio in the target.

Influence of working gas pressure on the performance of W/Si multilayers

The effect of Ar pressure on the performance of W/Si multilayers is investigated. W/Si multilayers were deposited by a high vacuum DC magnetron sputtering system. The Ar pressure was changed from 1.0 to 5.0 mTorr with an interval of 1.0 mTorr during the deposition process. Electron probe microanalysis and Rutherford backscattering are performed to determine the Ar content incorporated within these multilayers. The results demonstrate that less Ar is incorporated within the sample when more Ar is used in the plasma, which could be explained by the increase of the collision probability and the decrease in the kinetic energy of Ar ions arriving at the substrate when more Ar exists. The grazing incident X-ray reflectivity (GIXR) at 0.154 nm is used to determine the structural parameters of the layers. The results show that the structures of these multilayers prepared at different Ar pressure are very similar and that the interface roughness increases quickly when the Ar pressure is higher than 3.0 mTorr. The measurements of the extreme ultraviolet (EUV) reflectivity indicate that the reflectivity decreases when Ar pressure increases. The fitting results of GIXR and EUV reflectivity curves indicate that with an increase of Ar pressure, the density and decrement of the refractive index are increased for W and decreased for Si, which is mainly due to (1) the decrease in Ar content incorporated within these multilayers which affects their performance and (2) the increase of collision probability for sputtered W and Si, the decrease of their average kinetic energy arriving at the substrate, and thus the loosing of their layers.

Damage Analysis of Plasma-Etched n-GaN Crystal Surface by Nitrogen K Near-Edge X-ray Absorption Fine Structure Spectroscopy

The surface of an n-GaN crystal etched with an Ar, Kr, or Xe plasma was analyzed by nitrogen K near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS spectroscopy was carried out with the total electron yield (TEY) method in a sample current mode and the total fluorescence yield (TFY) method by measuring the amount of fluorescence using a photodiode. The shapes of the spectra of Ar plasma-etched samples obtained by the TEY method became smooth (blunt) with increasing Ar pressure from 10 to 200 mTorr. However, those obtained by the TFY method did not change with pressure. These results indicate that the etching damage was restricted in the shallow region of less than a few nm from the surface. A change in the NEXAFS spectral shape of Kr or Xe plasma-etched samples was not observed even when measured by the TEY method. This result indicates that the surface damage in Kr or Xe plasma-etched samples was less pronounced than that in Ar plasma-etched samples.