Helicon Plasma Sputtering Research Articles

Structural and magnetic properties of transition metals doped ZnO(TM)/ZnO multilayers

ZnO(Fe)/ZnO multilayers (MLs) with Fe 6.5% (Fe-doped sample) and ZnO(FeNi)/ZnO MLs with Fe22Ni78 6.5% (Ni-doped sample) prepared by helicon plasma sputtering were investigated. Structures of as-prepared Fe- and Ni-doped samples show the layer structures and the ZnO crystalline structures. However, the samples annealed at 773 K induced the formation of ZnFe2O4 for Fe doped sample, and the growth of metallic Ni for Ni-doped sample. Furthermore, Fe atoms in the annealed Fe-doped sample are dispersed mainly in the surface region, and Ni atoms in as-prepared and annealed Ni-doped samples are located uniformly in the film. The ionic states of Fe in Fe-doped sample and Ni in Ni-doped sample before and after annealing are the mixed Fe2+/3+ and metallic Ni, respectively. Therefore, it is considered that the as-prepared and the annealed Ni-doped samples form Ni particles. As-prepared samples showed the paramagnetic properties. However, the magnetic state of the as-prepared Ni-doped sample is partly superparamagnetic due to the existence of small Ni particles. On the other hand, annealed samples show the ferromagnetic characteristics due to formation of ZnFe2O4 for Fe-doped ones and growing metallic Ni particles for Ni-doped ones.

Structural Evolution of Fe Particles in Fe–Al2O3 Granular Films by Ar Ion Irradiations

Fe–Al2O3 granular films were prepared by helicon plasma sputtering. Fe64(Al2O3)36 in volume percent of as-prepared films was irradiated with 400 keV Ar ions in the fluence range of 1×1015–5×1016 ions/cm2. The growth of Fe particles with increasing ion fluence was observed from X-ray diffraction (XRD) patterns, magnetization curves, and conversion electron Mössbauer (CEM) spectra. The magnetization curves and CEM spectra of as-prepared Fe–Al2O3 films indicated the superparamagnetic nature and the ferromagnetic nature with increasing ion fluence. In addition, the reduction of Fe3+ component to the Fe2+ and metallic Fe components by ion irradiation was observed from CEM spectra.

Tunneling Magnetoresistance (TMR) on Fe-Al<sub>2</sub>O<sub>3</sub> Nano Granular Film Growth by Helicon Plasma Sputtering

Fe-Al 2 O 3 nanogranular thin film by helicon plasma sputtering with the variation of Fe content from 0.1 to 0.7 volume fraction have been prepared. The magnetic and magnetoresistance properties were investigated by a Vibrating Sample Magnetometer (VSM) and a Four Point Probe (FPP). The Rutherford BackScattering (RBS) was performed with the SIMNRA software. Conversion Electron Mossbauer Spectroscopy (CEMS) study was also performed to estimate the fraction of Fe and α-Fe 2 O 3 in the granular film. The results suggested that the percolation concentration occured at 0.55 Fe volume fractions, with the maximum Magnetoresistance (MR) ratio of 3%. The present MR ratio that was lower than the previous results may be related to the existence of α-Fe 2 O 3 phase.

Characterization of nanocrystalline nitrogen-containing titanium oxide obtained by N2/O2/Ar low-field helicon plasma sputtering

TiO2 and nitrogen-containing TiO2 thin films were deposited on glass and silicon wafer substrates using a helicon-assisted reactive plasma sputtering process in a gas mixture of Ar/O2/N2. The growth mechanism, chemical composition and crystalline structure were probed by x-ray photoelectron spectroscopy, x-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy. The presence of nitrogen in the film induces the formation of some Ti3+ defects states, which introduces oxygen vacancies in the TiOxNy structure. It is also observed that nitrogen substitution selectively hinders the formation of the crystalline rutile phase and promotes the growth of a polycrystalline anatase phase film. Moreover, the film exhibits a red-shift in light absorption from UV to visible spectrum as a function of the nitrogen doping. This work shows that crystalline TiO2 thin films can be obtained with a low temperature process and also shows that using nitrogen can control the desired crystalline structure.

Low temperature growth of nanocrystalline TiO 2 films with Ar/O 2 low-field helicon plasma

TiO 2 thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO 2 was obtained for ion density on the substrate below 7 × 10 16 m − 3 . Increasing the ion density over 7 × 10 16 m − 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO 2. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO 2 thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.

Irradiation Effect of Argon Ion on Interfacial Structure Fe(2nm)/Si(t&lt;sub&gt;si&lt;/sub&gt;=0.5-2 nm) Multilayer thin Film

Investigation includes formation of interfacial structure of Fe(2nm)/Si(t Si = 0.5-2 nm) multilayer thin film and the behavior of antiferromagnetic coupling between Fe layers due to Argon ion irradiation was investigated. [Fe(2nm)/Si]30 multilayers (MLs) with a thickness of Si spacer 0.5 - 2 nanometer were prepared on n-type (100) Si substrate by the helicon plasma sputtering method. Irradiation were performed using 400keV Ar ion to investigate the behavior of magnetic properties of the Fe/Si MLs. The magnetization measurements of Fe/Si MLs after 400keV Ar ion irradiation show the degradation of antiferromagnetic behavior of Fe layers depend on the ion doses. The Magnetoresistance (MR) measurements using by Four Point Probe (FPP) method also confirm that MR ratio decrease after ion irradiation. X-ray diffraction (XRD) patterns indicate that the intensity of a satellite peak induced by a superlattice structure does not change within the range of ion dose. These results imply that the surface of interface structures after ion irradiation become rough although the layer structures are maintained. Therefore, it is considered that the MR properties of Fe/Si MLs also are due to the metallic superlattice structures such as Fe/Cr and Co/Cu MLs. Received: 2 April 2009; Revised: 2 September 2009; Accepted: 5 January 2010

Structural and magnetic properties of Fe-Al2O3 films prepared by helicon plasma sputtering

Fe-Al2O3 films have been prepared by on-off deposition of Fe with continuous Al2O3 deposition, and also subsequently irradiated by 400 keV Ar ions for controlling of the structural and magnetic properties of the films. CEM spectra of the as-deposited films show the decrease in the average hyperfine fields (Hhfs) with decreasing Fe/ Fe-Al2O3 volume ratio with keeping the Hhfs orientation parallel to the film plane. The decrease in Hhfs indicates the decrease of the Fe particle size and the in-plane orientation of Hhfs implies the non spherical shape of Fe particles in the film. On the other hand, 400 keV Ar ion irradiation induces the change from the superparamagnetic characteristics to the ferromagnetic one; the ferromagnetic peaks showing the random orientation of Hhfs appear and indicate the spherical growth of Fe particles in Al2O3 matrix.

Low Temperature Operation of Single Chamber Fuel Cell Using BaCeO3 Electrolyte Film as Proton Conductor Grown by Helicon Plasma Sputtering

Thin film single chamber solid oxide fuel cell (SC-SOFC) with Barium Cerium Oxide (BaCeO3) electrolyte film as proton conductor, grown by the helicon plasma sputtering, was studied to determine the power generation property at lower operating temperatures between 200 and 400°C in the gas mixtures of hydrogen and oxygen. An SC-SOFC with a BaCeO3 electrolyte film thickness of 5 μm could be operated at 400°C in the gas mixtures of hydrogen and oxygen and had a maximum open circuit voltage of 455 mV. However, a V-I property at 400°C of SC-SOFC was considerably poor as a development index of SOFC, because the cell resistance with a several kΩ was due mainly to the interface reaction resistance of between the Pt catalytic electrodes and an amorphous electrolyte film.

Effect of Nafion and platinum content in a catalyst layer processed in a radio frequency helicon plasma system

A helicon plasma sputtering system is used to deposit small amounts of platinum on microporous carbon support composed of Vulcan XC 72 carbon particles (known as gas diffusion layer) to form Pt catalyzed electrodes for proton exchange membrane fuel cells. Electrodes with low Pt loading are prepared, assembled in custom-made membrane electrode assemblies (MEAs) and tested for the hydrogen oxydation and the oxygen reduction. Initially, the Nafion® loading spread on these plasma prepared electrodes is optimized by measuring the MEA performance. It is found that the optimum Nafion® loading is 1 mg cm−2 for an electrode previously covered with 0.1 mgPt cm−2 using the helicon plasma system. For a commercial electrode prepared by ink processes with 0.5 mgPt cm−2, the optimized Nafion® loading is 2 mg cm−2. Using the respective optimized Nafion® loading, the electrical performance of the custom-made MEA with one plasma prepared electrode (either anode or cathode) is compared with that of a reference MEA from Electrochem Inc. (Pt loading per electrode of 0.5 mg cm−2 and maximum power density of 425 mW cm−2) without gas humidification. The custom-made MEA fitted with an anode covered with 0.005 mgPt cm−2 leads to the same performance as that of the reference MEA at low current density (<500 mA cm−2) and high gas backpressure (3 bar). This result indicates that the catalyst utilization efficiency in the plasma prepared anode is 100 times higher than that in the commercial anode ( versus ). For plasma prepared cathodes with 0.1 mgPt cm−2, the cathodic Pt utilization efficiency is , which is 3 times higher than that obtained in the commercial cathode.

High frequency characteristics of soft magnetic Fe–O alloy thin films fabricated by helicon plasma sputtering

The effect of oxygen-doping has been studied on the magnetic properties of Fe thin films produced at room temperature by a helicon-plasma-enhanced RF magnetron sputter-deposition. A reduction in magnetic coercivity due to grain refinement was achieved using very low dose of oxygen, which did not lead to the formation of crystalline Fe oxides with the low saturation magnetization. Moreover, it was demonstrated that oxygen-doping also enhances the in-plane uniaxial magnetic anisotropy of Fe films and thus can be applied beneficially to increase high-frequency permeability which is needed in microwave applications.

Preparation and characterization of ilmenite-hematite thin films

Ilmenite-hematite solid solution (Fe 2− x Ti x O 3) is one of the candidates for practical magnetic semiconductors with the high Curie temperature ( T C). We have successfully prepared well-crystallized and epitaxial Fe 1.4Ti 0.6O 3 films by using a reactive helicon plasma sputtering technique. The structural characterizations indicated that the films had the order structure ( R 3 ¯ symmetry), where Ti- and Fe-rich layers were stacked alternately along the c-axis, without any secondary phase. The subsequent annealing of the films in vacuum at 700 °C promoted the R 3 ¯ symmetry. Only the films having the good R 3 ¯ symmetry had large ferrimagnetic moments at room temperature. The resistivities of the films clearly showed semiconducting behavior, i.e., logarithmic resistivity showed a monotonous increase with increasing the inverse temperature. The minimum room temperature resistivity of the films was about 10 −1 Ω cm. From the Hall effect measurement all films had n-type conduction. The carrier concentration was estimated to be about 10 19–10 21 cm −3, depending on the annealing conditions.

Structure and Polarization Properties of Zn–Nb Films Formed on Steel Sheet by Sputtering

Zn–Nb films were formed on a steel sheet by helicon plasma sputtering in an argon gas atmosphere at 1.0 Pa, at RF power of 50 W and DC power of 50 mA. The structure and polarization properties of these films were studied using EPMA, X-ray diffraction and polarization curve measurements. Zn plate-like crystals in Zn–Nb films decreased with increasing Nb content, resulting in a smooth surface over the entire film at Nb content of 30 mass% and above. The preferred orientation plane of Zn plate-like crystals was (0002) at 0 mass% Nb, while the orientation indices of (1011) and (1010)Zn increased with rising Nb content. At 30–60 mass% Nb, the X-ray diffraction spectra showed a halo pattern characteristic of an amorphous structure. The corrosion current of Zn–Nb films, which was determined by polarization curves in 3% NaCl solution, decreased with increasing Nb content to reach a minimum value at 30–60 mass% Nb, corresponding to an amorphous structure.

Magnetic properties of Fe/sub 1.2/Ti/sub 0.8/O/sub 3//Fe/sub 2/O/sub 3/ bilayered films

Hematite-ilmenite (/spl alpha/-Fe/sub 2/O/sub 3/-FeTiO/sub 3/) solid solution system is one of the candidates for high-temperature magnetic semiconductors. The intermediate composition, Fe/sub 1.2/T/sub 0.8/O/sub 3/, is known to have the maximum saturation magnetization at low temperature. We have successfully prepared well-crystallized Fe/sub 1.2/Ti/sub 0.8/O/sub 3/ and Fe/sub 1.2/Ti/sub 0.8/O/sub 3//Fe/sub 2/O/sub 3/ bilayered films by using reactive helicon plasma sputtering. The Fe/sub 1.2/Ti/sub 0.8/O/sub 3/ films without Fe/sub 2/O/sub 3/ layers showed lower T/sub C/ of about 200 K, while the T/sub C/ of Fe/sub 1.2/Ti/sub 0.8/O/sub 3/ layers in the bilayered films increased to about 220 K. The bilayered films had a sharp interface between Fe/sub 1.2/Ti/sub 0.8/O/sub 3/ and /spl alpha/-Fe/sub 2/O/sub 3/. The strong magnetic coupling between two layers seemed to increase the T/sub C/ of the attached Fe/sub 1.2/Ti/sub 0.8/O/sub 3/ layers.

Preparation and characterization of epitaxial FeTiO3+δ films

Abstract Epitaxial FeTiO3+δ(0 0 1) films were prepared on α-Al2O3(0 0 1) substrates by helicon plasma sputtering technique. Structure and magnetic properties of FeTiO3+δ film were largely dependent on the residual oxygen pressure (PO2) during the sputtering deposition. The films prepared at lower PO2 had an ilmenite ( R 3 ) structure, while a corundum ( R 3 c ) structure was observed in the case of higher PO2. The oxidation state of Fe in FeTiO3+δ films changed monotonically from Fe2+ to Fe3+ with increasing the PO2. The films with the R 3 symmetry were ferrimagnitic at low temperature, while the nonstoichiometric FeTiO3+δ with the R 3 c symmetry were antiferromagnetic at room temperature.

Effects of ion irradiation on structural and magnetic properties of Fe/Si multilayers prepared by helicon plasma sputtering

Helicon plasma sputtering has been used to prepare Fe/Si MLs with an Fe layer thickness around t Fe=2–5 nm for a Si spacer fixed at the thickness of t Si=1 and 1.5 nm. Present study found that the Fe/Si MLs of the Si spacer thickness at t Si=1 nm exhibit antiferromagnetic nature, but the other Fe/Si MLs are ferromagnetic. The maximum value of magnetoresistance (MR) ratio in Fe/Si MLs appears at t Fe=3 nm, t Si=1 nm and is about 0.22%. We performed 400 keV Ar ion irradiation to investigate the behavior of magnetic properties in Fe/Si MLs. The magnetization measurements of Fe/Si MLs after 400 keV Ar ion irradiation show the degradation of antiferromagnetic behavior and the values of MR ratio after ion irradiation decrease. X-ray diffraction (XRD) patterns indicate that the peak intensity of a satellite peak originated in superlattice structure does not change within the range of ion dose used. These results imply that the interface structures after ion irradiation become rough although the superlattice structures remain. Therefore, we consider that the change of MR properties in Fe/Si MLs by 400 keV Ar ion irradiation is due to the thickness dependence of Si layers like metallic superlattice structures.

Preparation and photoelectrochemical properties of TiO2 films by reactive helicon plasma sputtering method

Preparation and photoelectrochemical properties of TiO2 films by reactive helicon plasma sputtering method

Structural and Magnetic Properties of Helicon-Sputtered Fe/Si Multilayers

In Fe/Si multilayers (MLs) prepared by helicon plasma sputtering, we have investigated the structural and magnetic properties as a function of Fe and Si layer thickness systematically. In [Fe 2 nm/ Si 1 nm] 30 and [Fe 3 nm/Si 1 nm] 20 MLs, large lateral Fe grains grow suggesting small atomic intermixing of Fe and Si, and antiferromagnetic coupling between Fe layers occurs, causing a magnetoresistance of about 0.1%. With decreasing the Fe layer thickness and increasing the Si layer thickness, X-ray diffraction patterns indicate peak broadening due to atomic intermixing between Fe and Si layers, and the magnetization curves indicate the change from antiferromagnetic to ferromagnetic coupling between Fe. Furthermore, in this case, the conversion electron Mossbauer spectra show that the hyperfine field decreases due to the solution of Si atoms in the bulk Fe phase. Doublet peaks appear because of the formation of iron silicides which cause the degradation of antiferromagnetic coupling.

Preparation of Au/SiO&lt;SUB&gt;2&lt;/SUB&gt; Nano-Composite Multilayers by Helicon Plasma Sputtering and Their Optical Properties

Au/SiO 2 nano-composite multilayers were prepared by helicon plasma sputtering. The Au particles dispersed in the SiO 2 matrix grew with increasing deposition time in the initial time less than 10 s, then changed from network-like to film-like microstructure with increasing deposition time. The optimum deposition time for preparing the Au particles was 8 s, and the size of Au particles was about 6 to 8 nm. The absorption peak due to the surface plasmon resonance of Au particles was observed at the wavelength of 560 nm in the optical absorption spectra for the as-deposited Au/SiO 2 thin films containing 3.3 to 10.3 vol%Au. The intensity of the absorption peak increased with increasing Au content, and the optimum Au content was about 10.3 vol%.

Preparation of Au/SiO2 Nano-composite multilayers by Helicon Plasma Sputtering and Their Optical Properties

Preparation of Au/SiO2 Nano-composite multilayers by Helicon Plasma Sputtering and Their Optical Properties

Nonstoichiometry of Epitaxial FeTiO3+δFilms

ABSTRACTEpitaxial thin films of (001)-oriented FeTiO3+δwere prepared on α-Al2O3(001) single crystalline substrates by helicon plasma sputtering technique. The FeTiO3+δfilms had large oxygen nonstoichiometry, which seriously depended on both substrate temperature and oxygen pressure during the sputtering deposition. The valence states of Fe ions in FeTiO3+δchanged monotonically from Fe2+to Fe3+with decreasing the substrate temperature from 900 to 400°C or with increasing the oxygen pressure from 0.9 to 1.8×10-6Pa. The change of Fe valence states from Fe2+to Fe3+induced the magnetic phase transition only for the films prepared at 900°C. The films containing Fe2+were paramagnetic while those with Fe3+were antiferromagnetic at room temperature. The oxygen nonstoichiometry of the FeTiO3+δfilms was probably produced by cation vacancies and disarrangement of Fe3+and Ti4+ions, which randomly occupied both interstitial and substitutional sites of the FeTiO3related structure.