Search

Nanogranular CoAlO thin films were fabricated by rf magnetron sputtering using Co target partially covered by Al2O3 chips in argon atmosphere. The films consist of Co nanograins with a mean diameter of 5–30 nm surrounded by an amorphous Al–O phase. It was found that Co grains of face-centered-cubic and hexagonal-close-packed structures coexist in the films with relatively low (Al,O) content, whereas Co grains of face-centered-cubic structure are preferentially formed in the films with higher (Al,O) content. Due to the microstructure changes with increasing (Al,O) content in the films, coercivity and magnetization decrease but the anisotropy field increases. The high frequency properties of the CoAlO films were experimentally characterized, and the effects of magnetization, anisotropy field, and damping factor on the permeability spectrum are also analyzed using the Landau-Lifshitz-Gilbert equation. The ferromagnetic resonance frequency was found to increase from 2.1 to 2.8 GHz with the microstructure change in the films. [ABSTRACT FROM AUTHOR]

Rare-earth iron-boron (RE-Fe–B) thin films with a c-axis texture were prepared on a Ta (110) buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The microstructure, magnetic structure, and magnetic properties of these films were studied as a function of the deposition temperature. The results show that c-axis texture can be obtained over a wide range of deposition temperatures and that the degree of c-axis orientation improves with deposition temperature. It was established that deposition of a RE-Fe–B thin film to obtain grains with a strong c-axis RE2Fe14B texture, coexisting with an amorphous phase, followed by annealing at higher temperature, is an effective route for obtaining excellent hard magnetic properties. Initial results show that a film, which was deposited at 470 °C and annealed at 590 °C, had a high perpendicular coercivity of 1.8 T, in combination with a large maximum energy product of 238 kJ/m3. [ABSTRACT FROM AUTHOR]

Hollow glass microspheres coated with thin Ni films of various thicknesses (about 50–250 nm) were obtained by electroless plating technique. The resultant magnetic microspheres had very low densities (∼0.39–1.28 g cm-3) and low coercivities (<40 Oe). As-plated films comprised of nanocrystallites embedded in amorphous matrix and postannealing treatment led to a submicrocrystalline structure and an increased saturation magnetization. The high frequency properties of the composites consisting of Ni-plated microspheres and polymer were investigated. The permittivity and permeability increased with increasing microsphere content in the composite and increasing Ni film thickness. These composites had ferromagnetic resonance peak in the range of 5–12 GHz. Postannealing also had an effect on the microwave properties. The reflection loss of the composite was found dependent on the absorber material thickness, polymer:microsphere ratios, the Ni film thickness, as well as the heat treatment of the microspheres. [ABSTRACT FROM AUTHOR]

FeCoN soft magnetic thin films with various nitrogen contents were fabricated by varying the gas flow rates of the argon and nitrogen gas mixture used during reactive rf magnetron sputtering. It was found that the resistivity of FeCoN film increased up to 211 μΩ cm with increasing nitrogen content. The film produced at the gas flow rate of 7 sccm exhibited the best soft magnetic properties with small coercivity and relatively large saturation magnetization. The microstructure of the films was examined by high-resolution transmission electron microscopy and α″-FeCo phase with very high saturation magnetization was observed in the films. The high-frequency properties of the FeCoN thin films were experimentally characterized and theoretically examined. The Hoffmann’s ripple theory was used to explain the permeability spectra for the films with strong magnetization dispersion. We found that the ripple effect is responsible for the large damping in the films, and those films with larger coercivities have stronger magnetization dispersion. With the gas flow rate of the argon and nitrogen gas mixture increasing from 0 to 15 sccm, the low-frequency permeability decreased from 680 to 245 and the ferromagnetic resonance frequency increased from 2.09 to 2.99 GHz. [ABSTRACT FROM AUTHOR]

A cool-down step deposition process (multistep deposition with cool-down interval) was used to grow nanocomposite FeAlO thin films of various thicknesses up to 440 nm by magnetron sputtering at a substrate temperature of 15 °C. The effect of the number of cool-down steps on the soft magnetic properties and high frequency characteristics of the nanocomposite FeAlO films were investigated. The deposition process was proved very effective in improving the soft magnetic properties and high frequency characteristics of the films. The eight-layered samples, fabricated by eight cool-down step deposition process, of thicknesses of 220 and 440 nm had obvious in-plane uniaxial anisotropies while the single-layered films were nearly isotropic. The resulting real permeability value of the eight-layered films was larger than 300 for the 220 nm film and between 200 and 300 for the 440 nm film. [ABSTRACT FROM AUTHOR]

The FeTaN thin films were deposited on the flexible plastic substrates by rf magnetron sputtering. Good soft magnetic properties with coercivity <10 Oe have been obtained in the films with thickness <250 nm. Relatively high values of the complex permeability and ferromagnetic resonance frequency were obtained and they can be adjusted by changing the film thickness. However, compared to the films on the rigid substrate, a decrease of the permeability level and a shift of the resonance peak in the permeability spectra have been noticed for the films on the flexible substrate. The electric properties, including sheet resistance, resistivity, and magnetoresistance for the films with various thicknesses, have also been investigated. [ABSTRACT FROM AUTHOR]

FeZrN thin films with in-plane anisotropy were deposited on both rigid substrate (Si) and flexible substrate (Kapton) by magnetron sputtering. The as-prepared films had the microstructure of nanocrystallites with a small amount of intergranular amorphous phase. The thickness dependent coercivity showed different behaviors for flexible and rigid films. The dynamic magnetic properties of the films have been characterized. Although the high frequency characteristics are closely related to the thickness, composition, and anisotropy, the flexible films have relatively smaller values of real permeability μ' but larger values of ferromagnetic resonance frequency fr than the rigid films. Due to the flexibility, the properties of the flexible films varied with each other. Nevertheless, both rigid and flexible films can find important applications in microwave absorber due to their excellent high frequency properties up to 5 GHz. [ABSTRACT FROM AUTHOR]

The effect of a variation in Si and N concentration on the microstructure, crystal structure and high-frequency magnetic properties of Fe–Co–Si–N nanogranular thin films was investigated. The films, prepared by rf magnetron sputtering, consisted of nanosized grains of FeCo as well as a Si and N rich intergranular amorphous phase. The Si concentration had a significant effect on the crystal structure of the FeCo phase. The resistivities of the Fe–Co–Si–N films were significantly enhanced by an increase in Si concentration. The resonant frequency of the Fe–Co–Si–N films could be tuned from 0.45 GHz to 2.1 GHz by controlling Si concentration. The N concentration greatly influenced magnetic properties and the variation in resonant frequency is in agreement with Kittel’s equation. [ABSTRACT FROM AUTHOR]

ZnO nanowires were synthesized by a relatively simple process—oxidizing granular Zn films at a relatively low temperature (450–600 °C) without catalyst. The zinc film was initially fabricated by sputter deposition in an argon atmosphere at ambient temperature using Zn metal as the sputter target. After subsequent annealing in an air or oxygen atmosphere, ZnO nanowires were found to grow from individual Zn nanograins. The investigation has also showed that the nanowires preferably grow from relatively porous Zn film and a small amount of oxygen flow is beneficial to the growth of nanowires. The resultant single crystal ZnO nanowires obtained from annealing at 600 °C in an oxygen atmosphere had a mean diameter less than 50 nm and had a very good structural quality. This process provides an alternative method to produce ultra-fine ZnO nanowires standing on the substrate. [ABSTRACT FROM AUTHOR]

Zn1-xCdxO films (0≤=x≤=0.179) were grown on Si (001) substrates at 750 °C with a radio-frequency reactive magnetron sputtering method. Difference between the photoluminescence (PL) spectra taken at room temperature (RT) and at 12 K is reported and is deduced to be the result of PL emission from the ZnCdO phases with wurtzite and zinc blende structures. It is also found that the RT PL intensity is in inverse proportion to the carrier concentration in the films. Cd incorporation results in the transform of conductivity from p type to n type and a decrease of carrier mobility [ABSTRACT FROM AUTHOR]

Using reactive radio-frequency magnetron sputtering, epitaxial growth of ZnO film was observed on Si (001) substrate at different temperatures ranging from room temperature to 750 °C. The epitaxial relationship was determined to be ZnO(001)∥Si(001) in the direction normal to the surface of the films with a deviated angle less than 3° and ZnO[100]∥Si[110] or ZnO[310]∥Si[110] in the plan view. Based on (2×1) reconstruction of Si (001), a heteroepitaxial model was suggested to discuss the influence of Si (001) substrate on the growth and morphology of ZnO films at different temperatures. [ABSTRACT FROM AUTHOR]

N-doped and (Al,N)-codoped ZnO films were synthesized by oxidative annealing of (Zn + Zn3N2) films, which were fabricated by reactive magnetron sputtering. Both n- and p-type conductions were obtained in these ZnO:N and ZnO:AlN films. Optimal oxidation treatments for achieving p-type ZnO are annealing at 400-600 °C for 10-60 min, depending on the film thickness and morphology. The electric properties were found to be very sensitive to the annealing conditions and film structure. As-deposited (Zn + Zn3N2) films with and without Al addition had carrier concentrations of 1021-1022 cm-3. After conversion to ZnO, the n-type films had a carrier concentrations up to 1019 cm-3, whereas the p-type ZnO:N films had hole concentrations of 1014-1016 cm-3. (Al,N)-codoping increased the hole concentration of p-type film to 1018 cm-3 despite a decrease in Hall mobility. The photoluminescence properties of the p-type ZnO films were also investigated. The synthesis of p-type ZnO:AlN by oxidative annealing is believed to provide an alternative approach to realize p-type conduction in codoped ZnO film by using N2 as the N source. [ABSTRACT FROM AUTHOR]