Radio Frequency Diode Sputtering Research Articles

Enhanced photopromoted electron transfer over a bilayer WO3 n–n heterojunction prepared by RF diode sputtering

A bilayer WO3 photoelectrode was obtained by radio frequency (RF) plasma sputtering in a reactive 40%O2/Ar atmosphere by depositing two successive WO3 coatings on a tungsten foil at two different total gas pressures (3 Pa and 1.7 Pa, respectively), followed by calcination at 600 °C. Two monolayer samples deposited at each of the two pressures and a bilayer sample deposited at inverted pressures were also prepared. Their photoelectrocatalytic (PEC) activity was evaluated by both Incident Photon-to-Current Efficiency (IPCE) measurements and separate evolution of H2 and O2 by water splitting in a two-compartment PEC cell. SEM analysis revealed that the photoanodes have a nanostructured porous double layer surmounting a columnar basement (Staffa-like morphology, after the name of the Scottish island). Mott–Schottky analysis showed that the single layer deposited at 3 Pa has a conduction flat band potential 0.1 V more positive than that deposited at 1.7 Pa. The equivalent n–n heterojunction at the interface of the double-layer creates a built-in electric field that facilitates the photopromoted electron transfer toward the lower lying conduction band material, while the columnar innermost layer introduces percolation paths for efficient electron transport toward the conductive tungsten foil. Both phenomena contribute to decrease the interfacial charge transfer resistance (Rct) and lead up to a ca. 30% increase in the PEC performance compared to the monolayer and the inverted bilayer coatings and to a 93% faradaic efficiency, which is among the highest reported so far for WO3 photoanodes. Upon methanol addition an outstanding 4-fold photocurrent density increase up to 6.3 mA cm−2 was attained over the bilayer WO3 photoanode, much larger than the usually observed current doubling effect.

Acceptor Doping in Sputtered ZnO Thin Films

Acceptor doping of zinc oxide thin films prepared by radio-frequency diode sputtering, using nitrogen as a doping source, was realized during sputtering in Ar/N2 gas mixture or via ion implantation of 180 keV N ions. Effects of N doping and (Al,Ga):N co-doping on the films' properties have been studied. Highly resistive ZnO:N films with p-type carrier concentrations ranging 1014÷1015 cm−3 and more random orientation of the crystallites were obtained. The co-doped ZnO:Al:N and ZnO:Ga:N films maintained a c-axis texture in the direction of the surface normal. The carrier concentration of the p-type films was on the order of 1017÷1018 cm−3. 180 keV N ions were implanted in sputtered ZnO:Ga thin films. The implant doses varied 1015÷2×1016 cm−2. Annealing studies were performed under O2 and N2 ambient at different temperatures and times. N-implanted films were polycrystalline with a preferred c-axis orientation of the crystallites. Post-implantation annealing caused the increase of the (002) diffraction line integrated area and reduction in resistivity and the biaxial stress. After annealing in N2, a p-type conduction was observed with a carrier concentration and average transmittance on the order of 2.8×1019 cm−3 and 81 % respectively.

Piezoresistive and electrical properties of Cr containing diamond-like carbon films

In the present study Cr containing diamond-like carbon (DLC) films were deposited by radio frequency diode sputtering on polycrystalline alumina and monocrystalline silicon substrates. Piezoresistive properties and the thermal coefficient of resistance (TCR) were investigated. Structure and chemical composition of the synthesized films were studied by Raman scattering spectrometry and X-ray photoelectron spectroscopy (XPS). It was found, that the sp3/sp2 ratio in the synthesized Cr, containing DLC films, increased with C2H2/Ar gas flux ratio, while Cr atomic concentration in the deposited DLC films decreased with the increase of C2H2/Ar gas flux ratio. For the Raman scattering spectra of the samples deposited by using 1 and 1.5% C2H2/Ar gas flux ratio, photoluminescence background was observed. It was revealed, that gauge factor of Cr containing DLC films increased with increase of the C2H2/Ar gas flux ratio. The gauge factor of Cr containing DLC films deposited by using >1.5% C2H2/Ar gas flux was directly proportional to the sp3/sp2 ratio and increased with decrease of the sp2 cluster size. TCR of those films decreased with the decrease of sp3/sp2 ratio and increase of the sp2 cluster size. TCR increased at higher C2H2/Ar flux ratios, while negative TCR was observed for Cr containing DLC film deposited by using C2H2/Ar gas flux ratio 1.5%. The gauge factor and TCR of Cr containing DLC films linearly decreased with increase of the Cr/C atomic concentration ratio. The gauge factor of Cr containing DLC films increased with resistance by law k~log(R). The observed results are in good accordance with the percolation model of conductor–insulator compounds.

Extraordinary Hall effect in nanoscale nickel films

The extraordinary Hall effect was studied in 1 to 10nm thick nickel films prepared by radio-frequency diode sputtering (plasma) and electron-beam evaporation of Ni. The Hall resistance, R H, does not reach saturation in fields up to 0.5 T in films that are not uniform while for uniform films, R H saturates at 0.3 T. The films prepared by plasma sputtering showed a jump-like behavior of the extraordinary Hall coefficient, R S, that is due to the presence of two phases—tetragonal (nonmagnetic) and face-centered cubic(fcc) (magnetic)—in the initial growth stage and subsequent phase transition of the tetragonal lattice to fcc at a film thickness of about 4 nm around which the extraordinary Hall coefficient R S increases abruptly reaching its maximum. The films prepared by electron-beam evaporation consist only of the fcc phase and have a dome-like R S dependence on film thickness.

ZnO Doping and Co-doping Paradigm and Properties

Here, we report on experimental studies of the role of doping and co-doping on the properties of ZnO thin films deposited by radio-frequency diode sputtering at varying nitrogen content in the sputtering gas. Co-doping improved the crystalline structure, and ZnO:Al:N films maintain a c-axis texture in the direction of the surface normal. Depending on the content, the estimated crystallite size varies from 8 to 37 nm for ZnO:N and 21–33 nm for ZnO:Al:N. Nitrogen doping results in an increased absorption around the bandedge and the bandgap narrowing .

Silicon Nitride Films Deposited by RF Sputtering for Microstructure Fabrication in MEMS

In the present work, we report silicon nitride films deposited by a radio-frequency (RF) sputtering process at relatively low temperatures (<260°C) for microelectromechanical system (MEMS) applications. The films were prepared by RF diode sputtering using a 3-inch-diameter Si 3 N 4 target in an argon ambient at 5 mTorr to 20 mTorr pressure and an RF power of 100 W to 300 W. The influence of the film deposition parameters, such as RF power and sputtering pressure, on deposition rate, Si-N bonding, surface roughness, etch rate, and stress in the films was investigated. The films were deposited on single/double-side polished silicon wafers and transparent fused-quartz substrates. To explore the RF-sputtered silicon nitride film as a structural material in MEMS, microcantilever beams of silicon nitride were fabricated by bulk, surface, and surface-bulk micromachining technology. An RF-sputtered phosphosilicate glass film was used as a sacrificial layer with RF-sputtered silicon nitride. Other applications of sputtered silicon nitride films, such as in the local oxidation of silicon (LOCOS) process, were also investigated.

Transparent and conductive ZnO:Al prepared by RF diode sputtering

High transparent and conductive, aluminium - doped zinc oxide thin films (ZnO:Al), were prepared by radio - frequency (RF) diode sputtering from ZnO+2 wt. % Al2O3 target on Corning glass 7059 substrates. The RF power and the substrate temperature modified their structure and surface morphology, electrical and optical parameters. The XRD patterns reveal only one sharp (002) diffraction line, providing a clear evidence for highly textured ZnO films, with a preferential c-axis orientation. Maximum intensity and the lowest full-width at half-maximum (FWHM) (3.26°) of the ΩM-scan were obtained for ZnO:Al deposited at 800 W RF power and 200°C substrate temperature. The developed ZnO:Al have a low electrical resistivity (2 × 10−3 Ωcm) and high optical transmittance (> 82 %, including Corning glass substrate) in the visible region. The direct optical band gap (~ 3.3 eV) increases with the increasing carrier concentration.

Growth of amorphous TeOx (2≤x≤3) thin film by radio frequency sputtering

Thin films of Tellurium oxide TeOx over a wide range of x (2 to 3) were prepared by radio frequency diode sputtering at room temperature on corning glass and quartz substrate. The deposited films are amorphous in nature and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy shows the variation in the stoichiometry of TeOx film from x=2 to 3 with an increase in oxygen percentage (25 to 100%) in processing sputtering gas composition. Raman spectroscopy depicts the formation of TeO3 trigonal pyramid besides TeO4 disphenoid in the amorphous TeOx film with increase in the value of x. The varying stoichiometry of TeOx thin film (x=2 to 3) was found to influence the optical, electrical, and elastic properties. The optical band gap of film increases from 3.8 to 4.2 eV with increasing x and is attributed to the decrease in density. The elastic constants (C11 and C44) of the deposited films are lower than the corresponding value reported for TeO2 single crystal.

Surface modification of maize starch films by low-pressure glow 1-butene plasma

Plasma polymerisation was used to modify the surface of maize starch films in order to reduce their water affinity. Films were prepared by casting starch suspensions heated for different periods of time. Glycerol was added as a plasticiser. To produce a hydrogenated-carbon coating, films were exposed to low-pressure glow plasma generated in 1-butene gas from a radio frequency diode sputtering system. Atomic force microscopy (AFM) was used to investigate possible changes in surface morphology and roughness of plasma-coated films in relation to the corresponding substrates. AFM phase contrast images at high magnification revealed characteristic features at the surfaces of plasma-coated starch films. Water absorption experiments and contact angle measurements were carried out to verify the effect of deposited layers on the water sensitivity of those surface-modified films. The results indicated that the coating process reduced significantly the hydrophilic character of starch films.

Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering

ABSTRACTUsing radio frequency (RF) diode sputtering of sintered stoichiometric (Eu,Y)2O3:7Ta2O5 ceramic targets, thin films (0.2–0.6 m) of Eu- and Y-polytantalates, and their solid solution EuxY1-xTa7O19 were deposited on fused silica, Si (100) and sapphire (001) substrates under various sputtering conditions. As-grown films were amorphous, and were crystallized by post-annealing in oxygen at 900 to 1000 °C. The influences of deposition gases (Ar and O2-partial pressure) substrate material, deposition time, substrate temperature, and post-annealing time and temperature on the structural, morphological and photo-luminescence (PL) properties of Eu 3+-ions in the films have been studied and compared to properties of sintered (Eu,Y)Ta7O19 ceramic and EuTa7O19 single crystals.

Structural and electrochemical characterization of ‘open-structured’ ITO films

Tin-doped indium oxide (ITO) thin films were deposited by radio-frequency diode sputtering at ambient temperature under a low sputtering voltage (1600 V) and a high chamber pressure (Ar and O 2, 0.2 torr). Investigations by X-ray diffraction, transmission electron microscopy, atomic force microscopy, and infrared reflectance spectroscopy showed that the ITO films were poorly crystallized, abounded with grain boundaries, and had more ‘epitaxy’ on oxide substrates than on silicon wafers. Cyclic voltammetry measurements indicated that the ITO films deposited on commercial ITO glass substrates showed considerable reversible charging capacity in 1 M LiClO 4/propylene carbonate solution. X-ray photoelectron spectroscopy study indicated that lithium insertion took place irreversibly at the initial cycling stages. Besides, the charging/discharging process was hardly accompanied by electrochromic effect from the ITO films. Therefore, the reversible charging of the ‘open-structured’ ITO films is attributed mainly to the double layer effect.

Oxygen incorporation in thin films of In2O3:Sn prepared by radio frequency sputtering

Polycrystalline In2O3:Sn (ITO) films have been prepared by reactive radio frequency diode sputtering of an oxidic target using various oxygen/argon mixtures. They mostly contain more oxygen than the ideal crystal. When deposited at low pressure, the crystals have an expanded lattice (up to 3.5%) and, for small oxygen addition to the sputter gas, are also denser than the ideal crystal. This is explained by an incorporation of additional oxygen in the bixbyite structure, possibly into constitutional vacancies. Upon annealing, the lattice relaxes, however, the additional oxygen remains in the films. A model of oxygen segregation into grain boundaries is developed, that could also explain the grain–subgrain structure sometimes reported for ITO films.

Effect of nitrogen on the properties of sputter deposited NiFeRe films

Bias layers for soft adjacent biased magnetoresistance (MR) heads require low coercivity, high permeability magnetic materials that can be magnetized easily by a current in the adjacent MRE layer. While the advantage of (SAL) MR heads include the ability to adjust the bias field by optimizing the bias current, a major disadvantage of this biasing technique is arises from electrical shunting due to the finite electrical resistivity of the SAL material. The introduction of N2 in the deposition ambient was found to increase the electrical resistivity, and decrease both anisotropy and saturation magnetization of the films. The increase in resistivity was attributed primarily to a decrease in the grain size of the films. As a result a series of NiFeRe films for SAL biased MR heads were deposited by radio frequency diode sputtering in a series of N2 containing ambient atmospheres.

Masks for x-ray lithography with a point source stepper

We describe some key aspects of proximity x-ray technology currently being developed at AT&amp;T, from mask fabrication to wafer patterning. The masks are primarily based on polycrystalline Si membranes, 1 μm thick, which are formed directly on optically flat glass disks. A tungsten absorber layer is deposited on the membranes by radio-frequency diode sputtering, with in situ stress control in the deposition chamber so that stresses ≤10 MPa are routinely achieved. Patterns are defined in an organosilicon negative resist, P(SI-CMS), using an electron beam writing tool and a neural network based proximity correction algorithm. The patterns are transferred into metallic absorber layers by reactive ion etching in a parallel plate plasma system. Using the above procedure, we have fabricated masks with 0.25 μm features and also some test patterns with lines and spaces as small as 0.1 μm. X-ray exposures were done with a Hampshire 5000P point source stepper, using AZ PF-114 resist from Hoechst–Celanese.

Process effects on radio frequency diode reactively sputtered ZrO2 films

The ZrO2 thin film is deposited by means of a reactive radio frequency diode sputtering from an elemental zirconium target in an argon–oxygen mixture gas. The influence of the deposition process parameters on the microinstructure, composition, film stress, and refractive index is investigated. It is noted that the process parameters, in particular substrate bias, have a profound effect on the structure and properties. The possible mechanism, in terms of bombardment of energetic particles and adatom mobility on the film surface, is discussed.

Irradiation effects of argon ion on a plate-type raney nickel catalyst.

The present paper deals with restoration of the catalytic activity of Raney nickel deactivated by heat treatment (1), electrochemical oxidation (2) slow oxidation in water by dissolved oxygen (3) and quick oxidation in air (4). The plate-type Raney nickel catalyst used in this experiment is convenient for this particular ion-bombarding technique. The fine powder catalyst usually used could not be applied to this technique.The catalysts deactivated by the methods (2, 3) were activated by means of radio frequency diode sputtering system. An ordinary nickel plate and Raney nickel catalyst heated at high temperature (method 1) or burned in air (method 4) could not be activated by argon ion bombardment, because of the strong Ni-Ni and Ni-O bonds. The appearance of activity in Raney nickel catalyst generally results from amorphous nickel structure, when aluminum is leached from Ni-Al alloy. Activity restoration of catalyst by argon ion bombardment is satisfactly explained on the basis of the same reason.