Oxygen Gas Pressure Research Articles

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si <100> substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03Pa and sputtering power of 70W. X-ray diffraction results revealed that the films were amorphous until 550°C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2nm to 4.53nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.

Effect of oxygen gas pressure on the kinetics of alumina film growth during the oxidation of Al(111) at room temperature

We have studied the effect of oxygen pressure on the self-limiting oxidation of an Al(111) surface at room temperature for oxygen pressures from 1x10{sup -8} to 5 Torr. Using x-ray photoelectron spectroscopy measurements, we monitor the oxidation kinetics and the oxide film thickness for different oxidation times and pressures. After a rapid initial growth stage, the oxide film reaches a saturated thickness, which depends on the oxygen pressure. The kinetic potential, oxide growth rate, oxide film limiting thickness, and the density of oxygen anions on the oxide surface are determined by the measured oxidation kinetics. These quantities show a Langmuir isotherm dependence on the oxygen gas pressure.

Effect of Oxygen Gas Pressure on Electrical, Optical, and Structural Properties of Al-Doped ZnO Thin Films Fabricated by Pulsed Laser Deposition for Use as Transparent Electrodes in All-Solid-State Electrochromic Devices

Low-resistivity and high-transmittance Al-doped ZnO (AZO) thin films were obtained by pulsed laser deposition with the substrate at room temperature. The electrical, optical, and structural properties of the AZO thin films deposited at various oxygen gas pressures (PO2) were investigated. X-ray diffraction shows that the AZO thin films have (002) preferred orientation and the diffraction angle of the (002) plane shifts to a higher value with increasing oxygen gas pressure. All AZO thin films deposited under ambient oxygen gas pressure conditions have an optical transmittance of over 80% in the visible region. AZO thin films deposited at lower PO2 of ≤1 Pa have resistivities of <10-3 Ω cm that increase with increasing PO2 > 1 Pa. The AZO film deposited at PO2 = 1 Pa had the lowest resistivity (5.8 ×10-4 Ω cm) with a high carrier concentration of 1.1 ×1021 cm-3.

Effect of Oxygen Gas Pressure on Electrical, Optical, and Structural Properties of Al-Doped ZnO Thin Films Fabricated by Pulsed Laser Deposition for Use as Transparent Electrodes in All-Solid-State Electrochromic Devices

Effect of Oxygen Gas Pressure on Electrical, Optical, and Structural Properties of Al-Doped ZnO Thin Films Fabricated by Pulsed Laser Deposition for Use as Transparent Electrodes in All-Solid-State Electrochromic Devices

Tuning the Limiting Thickness of a Thin Oxide Layer on Al(111) with Oxygen Gas Pressure

We report an x-ray photoelectron spectroscopy study of the oxidation of Al(111) surfaces at room temperature, which reveals that the limiting thickness of an aluminum oxide film can be tuned by using oxygen pressure. This behavior is attributed to a strong dependence of the kinetic potential on the oxygen gas pressure. The coverage of oxygen anions on the surface of the oxide film depends on the gas pressure leading to a pressure dependence of the kinetic potential. Our results indicate that a significantly large oxygen pressure (>1 Torr) is required to develop the saturated surface coverage of oxygen ions, which results in the maximum kinetic potential and therefore the saturated limiting thickness of the oxide film.

Pulsed laser deposition of manganese oxide thin films for supercapacitor applications

Thin films of manganese oxides have been grown by the pulsed laser deposition (PLD) process on silicon wafer and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of processing parameters such as temperature and oxygen pressure during the PLD process, pure crystalline phases of Mn2O3, Mn3O4 as well as amorphous phase of MnOx were successfully fabricated as identified by X-ray diffraction. The pseudo-capacitance behaviours of these different phases of manganese oxides have also been evaluated by the electrochemical cyclic voltammetry measured in 0.1M Na2SO4 aqueous electrolyte at different scan rates. Their specific current and capacitance determined by electrochemical measurements were compared and the results show that crystalline Mn2O3 phase has the highest specific current and capacitance, while the values for crystalline Mn3O4 films are the lowest. The specific current and capacitance values of the amorphous MnOx films are lower than Mn2O3 but higher than Mn3O4. The specific capacitance of Mn2O3 films of 120nm thick reaches 210Fg−1 at 1mVs−1 scan rate with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for screening high performance active materials for supercapacitor applications due to its excellent flexibility and capability of easily controlling chemical composition, microstructures and phases of materials.

Relation between crystallinity and chemical nature of surface on wettability: A study on pulsed laser deposited TiO2 thin films

Pure titania (TiO2) polycrystalline thin films in rutile, anatase and mixed phase have been grown on amorphous glass substrates by pulsed laser deposition method at various oxygen gas pressure. Wettability investigations have been carried out on these films. Consistent with our previous report [J. Phys. D: Appl. Phys. 41, 155308 (2008)] it has been observed that for nearly same surface roughness large contact angle or superhydrophobicity is present when sample has a pure single phase and lower contact angle or hydrophobicity when mixed phases were present. Structural characterizations suggest that in addition to roughness, pure phase film surface associated with hydrophobic sites and mixed phase film surface show association of both hydrophobic and hydrophilic sites, which might be inducing specific wetting character. UV treatment induces superhydrophilicity in the films. It was observed that UV irradiation causes nonequilibrium state on the TiO2 surface, leading to changes in the electron density, which in turn produces decrement in the crystallinity and lattice expansion. Reversible changes in the wetting state on the pure phase surfaces were observed to be faster than those on the mixed phase surfaces. We tried to establish the possible relation between crystalline phases, chemical nature of surface on reversible wettability besides the main governing parameter viz. surface roughness.

Visible and near infrared light absorbance of Ag thin films deposited on ZnO under layers by magnetron sputtering

The correlation among the electrical, optical and structural properties of Ag thin films was investigated. Low-emissivity (low-e) coatings consisting of glass/ZnO/Ag were deposited by magnetron sputtering. The ZnO thin films were deposited under various oxygen gas pressures to vary the property of Ag thin films deposited on them. When the ZnO thin films were deposited in low oxygen gas pressure, the Ag thin films deposited on the ZnO thin films exhibited low resistivity and smooth surface. Besides, it was found that the low-emissivity coatings with low visible and near infrared light absorbance were obtained using the low-resistive and smooth Ag thin films. It was concluded from the results that the light absorbance became low with decreasing the resistivity of Ag thin films in accordance with Drude's theory in the case where the Ag thin films exhibited sufficiently smooth surface. Furthermore, it can be considered that the surface plasmon polariton of Ag thin films had an influence on the optical property when their surface became rough. The optical absorbance of the low-e coatings should be determined as the result of the competition between two factors: resistivity and surface roughness of Ag thin films.

Controllable low energy ion assistance as a tool for tailoring properties of gold oxide and gold–silver oxide thin films

In the present study, gold oxide (AuOx) and gold–silver oxide (AuAgOx) thin films are deposited by reactive sputtering in a magnetron with unbalanced ratio continuously controlled by the current Is trough an external solenoid. Two film characteristics: the specific electric resistivity ρo of as deposited films and their life-times τ are systematically investigated in dependence of the oxygen gas pressure pO2, magnetron discharge power Pm and solenoid current Is.It is demonstrated that employing optimal regime of ion assistance and gradient sublayers, AuOx and AuAgOx films with a high electric resistivity and long life-times (up to 3years) can be deposited.Incorporation of the more reactive silver atoms into the film structure significantly changes the behavior of AuAgOx films as compared to that of AuOx films. While the initial electric resistivity and the life-time of AuAgOx films monotonously increase with the combined parameter IspO2/Pm, tending to saturation at higher values of this parameter, films of thermodynamically unstable gold oxide with long life-times can be produced within a narrow range of deposition parameters, only.

Structural properties of pulsed laser deposited SnOx thin films

AbstractNanocrystalline SnOx thin films were grown by means of pulsed laser deposition onto substrates held at relatively low temperature (470K) and by varying the background oxygen gas pressure up to 66.7Pa. The formation of the nanocrystalline structures in the films has been investigated in detail by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results showed that, upon increasing oxygen gas pressure up to 13.3Pa, the laser induced plasma expands forming a shock wave and it is possible to obtain almost stoichiometric films composed of nanoparticles exceeding 10nm in size and essentially with a tetragonal rutile crystalline structure. Further increase of the oxygen pressure up to 66.7Pa induces a worsening of the material’s structural properties with a drastic reduction of the nanoparticles size down to 1nm and the development of a large amount of an amorphous phase. The analysis of the SAED patterns shows that the unit cell shrinks along the principal crystallographic axes, due to oxygen atoms vacant sites, in agreement with the stoichiometry parameter values determined from X-ray core level photoemission spectroscopy measurements.

Nitrogen doping in pulsed laser deposited ZnO thin films using dense plasma focus

Pulsed laser deposition synthesized ZnO thin films, grown at 400 °C substrate temperature in different oxygen gas pressures, were irradiated with 6 shots of pulsed nitrogen ions obtained from 2.94 kJ dense plasma focus to achieve the nitrogen doping in ZnO. Structural, compositional and optical properties of as-deposited and nitrogen ion irradiated ZnO thin films were investigated to confirm the successful doping of nitrogen in irradiated samples. Spectral changes have been seen in the nitrogen irradiated ZnO thin film samples from the low temperature PL measurements. Free electron to acceptor emissions can be observed from the irradiated samples, which hints towards the successful nitrogen doping in films. Compositional analysis by X-ray photoelectron spectroscopy and corresponding shifts in binding energy core peaks of oxygen and nitrogen confirmed the successful use of plasma focus device as a novel source for nitrogen ion doping in ZnO thin films.

On physical properties of undoped and Al and In doped zinc oxide films deposited on PET substrates by reactive pulsed laser deposition

Undoped and Al and In doped ZnO films were deposited on flexible PET substrates by Reactive Pulsed Laser Deposition (R-PLD). The morphological and structural characteristics of the obtained structures were investigated by AFM, SEM and XRD respectively. The transmittance spectra were recorded in the 300–1200 nm wavelength range and the electrical conductivity was measured. The samples appeared as granular and polycrystalline with high transparency and had a good electrical conductivity. The crystallinity of the undoped ZnO films improved with increasing pressure of the reactive oxygen gas. Doping of ZnO with Al or In modified the energy band gap and the resistivity of the material. The possibility for the application of such structures for the development of hybrid photovoltaic cells on flexible substrates will be demonstrated.

Basic Characteristics of a Simultaneous Double-Side CMP Machine, Housed in a Sealed, Pressure-Resistant Container

We designed and manufactured a prototype of a unique CMP machine, which can perform double-side CMP simultaneously in a sealed and pressure container as regarding effective action of the processing atmosphere around workpieces as important. Polishing experiments with single crystal silicon (Si) wafers (100) are performed by charging the container with various gases. As a result, the removal rates increased by up to 25% under high pressure oxygen gas atmosphere.

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm2/V s. By using the ZnO thin film grown by two-step PLD and a HfO2 high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×106 and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.

Electrical and Structural Properties of ZnO/Ag Multilayers Deposited by Magnetron Sputtering for Energy-Efficient Windows

The low-emissivity (low-e) coatings consisting of glass/ZnO/Ag were prepared and the microstructures of Ag thin films were investigated as a function of oxygen gas pressure during the ZnO underlayer deposition. It was found from X-ray diffraction measurement that the Ag thin films exhibited well-crystallization and (111)-preferred orientation when the ZnO underlayers were deposited in low oxygen gas pressure. Furthermore, glancing X-ray reflectivity measurement revealed that the surface roughness of Ag thin films decreased with decreasing oxygen gas pressure during the ZnO deposition. It can be said from these results that the highly crystallized and smooth Ag thin films grew on the ZnO thin films deposited in low oxygen gas pressure. Besides, it can be considered that the Ag thin films were heteroepitaxially grown using the smooth and highly crystallized ZnO underlayers which can be obtained under low oxygen gas pressure; as a result, the microstructures of Ag thin films should be improved.

Phase controlled structure formation of the nanocrystalline zirconia using thermal plasma technique

Nanocrystalline ZrO2 powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO2 is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO2 shows high ionic conductivity. ZrO2 is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO2 powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.

Fabrication of Gd 0.5Sr 0.5CoO 3 film for SOFC cathode by pulsed laser deposition

Gd 0.5Sr 0.5CoO 3 (GSCO) film has been fabricated by pulsed laser deposition (PLD) to be used as the cathode of the solid oxide fuel cell (SOFC). The GSCO thin film obtained has a columnar crystalline structure so that it will have a high permeation property. The PLD technique has been found suitable for growing a film of complex composition because of its good control of stoichiometry and thus for fabricating a GSCO film used as the cathode of the SOFC. The GSCO film has been studied for porosity electrical conductivity and power density. The GSCO film grown at a substrate temperature of 1100 K and oxygen gas pressure of 100 Pa has high electrical conductivity which is 820 S cm − 1 at 973 K with post annealing at a rather low temperature (1000 K). This value is higher than that of the GSCO film prepared by RF-sputtering with post annealing at a higher temperature (1273 K).

Pulsed laser deposition of indium tin oxide films on flexible polyethylene naphthalate display substrates at room temperature

Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films on polyethylene napthalate (PEN) flexible display substrates. The electrical, optical, microstructural, mechanical and adhesive properties of the functional thin layer were investigated as a function of a narrow range of background oxygen gas pressure at room temperature, which is the most desirable thermal condition for growing transparent conducting oxides on flexible display polymer substrates. ITO films (240 ± 35 nm thick) deposited on PEN at room temperature in the range of 0.33 to 2.66 Pa background oxygen pressure are observed to exhibit low electrical resistivity (~ 10 − 4 Ω cm) and high optical transmission (~ 90%). Electromechanical uniaxial tensile testing, of the hybrid thin structures, results in crack onset nominal strains of around 2%. The ITO surface adhesion reaches a maximum at 1.33 Pa deposition pressure.

Preparation of WO 3 nanoparticles and application to NO 2 sensor

WO 3 nanoparticles were prepared by evaporating tungsten filament under a low pressure of oxygen gas, namely, by a gas evaporation method. The crystal structure, morphology, and NO 2 gas sensing properties of WO 3 nanoparticles deposited under various oxygen pressures and annealed at different temperatures were investigated. The particles obtained were identified as monoclinic WO 3. The particle size increased with increasing oxygen pressure and with increasing annealing temperature. The sensitivity increased with decreasing particle size, irrespective of the oxygen pressure during deposition and annealing temperature. The highest sensitivity of 4700 to NO 2 at 1 ppm observed in this study was measured at a relatively low operating temperature of 50 °C; this sensitivity was observed for a sensor made of particles as small as 36 nm.

ZnO Nanowire-Based Oxygen Gas Sensor

We report the growth of vertically well-aligned ZnO nanowires on ZnO:Ga/glass templates and the fabrication of resistive ZnO nanowire-based oxygen gas sensor. It was found that the ZnO nanowires are grown preferred oriented in the (002) direction with a small X-ray diffraction full-width-half-maximum. From high resolution transmission electron microscopy, scanning electron microscopy and micro-Raman measurements, it was found that the ZnO nanowires prepared in this study are single crystalline with good crystal quality. It was also found that measured sample resistance increased logarithmically as the oxygen gas pressure in the chamber was increased. Such a relationship suggests that the device is potentially useful for resistive oxygen gas sensing at room temperature.