Effect of Ag underlayer on microstructures and perpendicular magnetic properties of CoPt nanocomposite thin films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.     

Magnetic properties and microstructures of sputtered epitaxial Co-rich Co-Pt films

Co₃Pt films of various thicknesses were deposited on Pt underlayers by conventional sputtering in order to investigate the effects of Pt underlayers and annealing temperatures on their microstructure and the magnetic properties. XRD and HRTEM analyses reveal perpendicular magnetic anisotropy in films of good epitaxial growth of Co₃Pt (002) on the Pt (111) underlayer when annealed at 300 °C. However, Pt atoms in the Pt underlayer will diffuse seriously into the Co₃Pt layer when the annealing temperature is increased to 375 °C. This changes the compositions to approach equiatomic CoPt, and shows in-plane magnetic anisotropy with soft magnetic properties.     

Film thickness dependence of microstructures and magnetic properties in single-layered FePt films by in-situ annealing

The FePt films with various thicknesses (t) of 5 to 50 nm are deposited on Si(100) substrate without any underlayer by in-situ annealing at substrate temperature (Ts) of 620 °C. A strong (001) texture of L1₀ FePt film is obtained and presents high perpendicular magnetic anisotropy as the film thickness increases to 30 nm. By further increasing the thickness to exceed 30 nm, the (111) orientation of L1₀ FePt is enhanced greatly, indicating that the quality of perpendicular magnetic anisotropy degrades when the thickness of the FePt film is greater than 30 nm. The single-layered FePt film with thickness of 30 nm by in-situ depositing at 620 °C shows good perpendicular magnetic properties (perpendicular coercivity of 1033 kA/m (13 kOe), saturation magnetization of 1.08 webers/m² and perpendicular squareness of 0.91, respectively), which reveal its significant potential for perpendicular magnetic recording media.     

Nearly perfect (001)-oriented Ag/[CoPt/C]5/Ag composite films deposited on glass substrates

Sandwich Ag/[CoPt(3 nm)/C(3 nm)]₅/Ag films were deposited on glass substrates by magnetron sputtering. After annealing at 600 °C for 30 min, a nearly-perfect (001)-oriented L1₀ CoPt film with extremely high perpendicular anisotropy was obtained when the thickness of Ag top- and underlayer were both equal to 5 nm. The strain energy caused by the Ag layer together with the diffusion of Ag and C atoms, resulted in the enhancement of the ordering degree of the L1₀ CoPt phase and the development of the (001) texture of the films.     

Self-assembled nano-size FePt islands for ultra-high density magnetic recording media

To find a method to form nano-size FePt alloy for ultra-high density magnetic recording media, this work concentrated on the formation mechanisms of nano-island FePt films on amorphous glass substrates. FePt films of different thicknesses (1-10 nm) were deposited on amorphous glass substrates and post-annealed at 700 °C for 10 and 30 min. The configuration of the film changed during the annealing process due to the surface energy difference between the glass substrate and FePt alloy. Investigation of the microstructures and magnetic properties of the ordered L1₀ FePt films revealed that the 1 nm FePt film annealed at 700 °C for 10 min had perpendicular magnetic anisotropy and good reproducibility of forming well-separated FePt nano-size islands for ultra-high density magnetic recording media.     

High roughness Ag back reflector on a metal underlayer for thin film solar cell applications

The roughness development of Ag film was investigated for potential as a back reflector material in thin film solar cells on flexible stainless steel (STS) substrates. The influence of metal underlayers was evaluated in order to obtain a rough Ag film at a low deposition temperature (≤400 °C). By depositing Ag on a 100 nm Al underlayer to induce Ag–Al alloying, the film roughness was increased three times more than that of Ag films on bare STS at 400 °C. The Ag film deposited on an Al underlayer at 350 °C exhibited 75 nm roughness and uniformly distributed crystallites, which was effective for visible light scattering. The Ag–Al alloy phase was also controlled using the thickness ratio of Ag and Al. The present work clearly demonstrated that an Ag back reflector film with a higher roughness could be fabricated through inserting a metal underlayer at a deposition temperature much lower than the 500 °C that has been reported in earlier works.     

Effects of AlN layer thickness on magnetic anisotropy and transport phenomena of CoPt/AlN layered structure

The magnetic anisotropy was studied as a function of the AlN layer thickness in [AlN(x nm)/CoPt(2 nm)]5/AlN(x nm) layered structure (x is AlN layer thickness, and 5 is the number of multilayer series). The multilayered film was deposited by a sputtering apparatus equipped with two pairs of facing targets. It was found that, in the range of AlN layer thickness below 30 nm, CoPt/AlN multilayers transform from an enhanced in-plane magnetic anisotropy to perpendicular magnetic anisotropy (PMA) through thermal annealing in vacuum, with an optimized AlN thickness of 10 nm for strong PMA. However, beyond this thickness range, the PMA did not occur, and thermal annealing only results in magnetic isotropy in both parallel and perpendicular directions. The related structure analysis revealed that smooth interface and good texture of CoPt (111) make positive contributions to interface anisotropy energy and magnetocrystalline anisotropy energy for producing PMA in CoPt/AlN layered structure. In addition, the transport phenomena were also studied by using a four-probe method.     

Coercivity variation in exchange-coupled Fe/FePt bilayer with perpendicular magnetization

The soft/hard Fe/FePt film with perpendicular magnetization has been deposited on a glass substrate. The (001) oriented L1₀ FePt film was obtained when annealed by rapid thermal process at 800 °C and a Fe layer was deposited at room temperature with thicknesses of 2 nm to 20 nm. Controlling the Fe layer thickness allowed modification of the hysteresis loops from out-of-plane rigid magnet to in-plane exchange-spring like magnet due to the nanometer scale interface coupling. When the Fe layer thickness increased to 2 nm, the out-of-plane coercivity is reduced to 5.9 kOe but the remanence ratio (0.98) is still high. The Fe (2 nm)/FePt film shows perpendicular magnetization with linear in-plane hysteresis loop. The remanence ratio is reduced to 0.85 when the Fe layer thickness increased to 5 nm. When the Fe layer thickness was varied up to 10-20 nm, the in-plane hysteresis loop shows exchange-spring like behavior with two-step magnetization reversal processes. The films with perpendicular coercivity were moderated by the thickness of soft magnetic layer.     

The effect of annealing on structural, electrical and optical properties of nanostructured ZnS/Ag/ZnS films

In this paper a ZnS/Ag/ZnS (ZAZ) nano-multilayer structure is designed theoretically and optimum thicknesses of ZnS and Ag layers are calculated at 35 and 17 nm, respectively. Several conductive transparent ZAZ nano-multilayer films are deposited on a glass substrate at room temperature by thermal evaporation method. Changes in the electrical, structural, and optical properties of samples are investigated with respect to annealing in air at different temperatures. High-quality nano-multilayer films with the sheet resistance of 8 Ω/sq and the optical transmittance of 83% at 200 °C annealing temperature are obtained. The figure of merit is applied on the ZAZ films and their performance as transparent conductive electrodes are determined.     

Diffusion induced columnar structure, high perpendicular anisotropy and low transformation temperature in thick FePt films

Thick FePt films (800 nm) were deposited by electroplating using Ag electrode. 2 at.% Ag doping into the electrolyte can lead to a columnar structure after annealing. The annealed film shows a high coercivity and perpendicular anisotropy. The additive of Ag can also significantly reduce fct-phase ordering temperature to 400 °C, comparing with an ordering temperature of 700 °C without Ag doping. The diffusion from Ag electrode and dopant is attributed to the formation of columnar structure, perpendicular anisotropy and reduced ordering temperature.     

Aluminum-induced crystallization of amorphous silicon films deposited by hot wire chemical vapor deposition on glass substrates

Aluminum-induced crystallization of amorphous silicon films is discussed. Amorphous Si films were deposited by hot wire chemical vapor deposition onto Al coated glass substrates at 430 °C. Complete crystallization of a-Si films was achieved during a-Si deposition by controlling Al and Si layer thicknesses. The grain structure of the poly-Si films formed on glass substrate was evaluated by optical and electron microscopy. Continuous poly-Si films were obtained using Al layers with a thickness of 500 nm or less. The average grain size was found to be 10-15 μm, corresponding to a grain size/thickness ratio greater than 20.     

Comparative study of resistivity characteristics between transparent conducting AZO and GZO thin films for use at high temperatures

This paper compares in detail the resistivity behavior of transparent conducting Al-doped and Ga-doped ZnO (AZO and GZO) thin films for use in an air environment at high temperatures. AZO and GZO thin films with thicknesses in the range from approximately 30 to 100 nm were prepared on glass substrates at a temperature of 200 °C by rf superimposed dc or conventional dc magnetron sputtering deposition, pulsed laser deposition or vacuum arc plasma evaporation techniques. In heat-resistance tests, the resistivity was measured both before and after heat tests for 30 min in air at a temperature up to 400 °C. The resistivity stability of AZO thin films was found to be always lower than that of GZO thin films prepared with the same thickness under the same deposition conditions, regardless of the deposition technique. However, the resistivity of all AZO and GZO thin films prepared with a thickness above approximately 100 nm was stable when heat tested at a temperature up to approximately 250 °C. It was found that the resistivity stability in both GZO and AZO thin films is dominated by different mechanisms determined by whether the thickness is below or above approximately 50 nm. With thicknesses above approximately 100 nm, the increase in resistivity found in GZO and AZO films after heat testing at a temperature up to 400 °C exhibited different characteristics that resulted from a variation in the behavior of Hall mobility.     

Influence of underlayers on the c-axis distribution in Co80Pt20 thin films

A series of approximately 40 nm thick Co₈₀Pt₂₀ thin films have been sputter-deposited onto a combination of Ta, Pt and Ru underlayers grown at different layer thicknesses. The addition of a Ta seed layer to the Pt and Ru underlayers caused the {0002} hexagonal close packed (hcp) Co₈₀Pt₂₀'s c-axis dispersion's full width at half maximum to narrow from approximately 12° to approximately 2°. In-situ stress measurements taken during deposition showed that the Ta seed layer reduced the growth stresses for the Pt and an initial 1 nm of growth for the Ru underlayers. The Ru layer thickness controlled the c/a ratio of the hcp Co₈₀Pt₂₀ film which regulated the degree of magnetic easy-axis alignment in the Co₈₀Pt₂₀ film. The optimal underlayer material stack for Co₈₀Pt₂₀ with a narrow c-axis dispersion and a high degree of magnetic easy-axis alignment was 5 nm Ta/10 nm Pt/5 nm Ru.     

Low temperature ordering of FePt films by in-situ heating deposition plus post deposition annealing

FePt thin films with 40 nm thickness were prepared on thermally oxidized Si (001) substrates by dc magnetron sputtering at the nominal growth temperature 375 °C. The effects of annealing on microstructure and magnetic properties of FePt thin films were investigated. The as-deposited FePt thin films show soft magnetic properties. After the as-deposited FePt thin films were annealed at various temperatures and furnace cooled, it is found that the ordering temperature of L1₀ FePt phase could be reduced to 350 °C. For FePt thin films annealed at 350 °C, the in-plane and out-of-plane coercivities of the films increased to 510 and 543 kA/m, respectively, and the films had hard magnetic properties. A highly (001) orientation was obtained, when FePt thin films were annealed at 600 °C. And the hysteresis loops of FePt thin films annealed at 600 °C show out-of-plane magnetic anisotropy.     

Optical properties of thermochromic VO2 thin films on stainless steel: Experimental and theoretical studies

Thermochromic films of VO₂ were deposited by DC reactive magnetron sputtering on stainless steel substrate. Complex refractive indexes of VO₂ were determined by ellipsometric spectroscopy (0.35-16.5 μm) for different film thicknesses. Optical simulations were performed to model the spectral reflectance of the film/substrate system for a film thickness of 100 nm and 200 nm and to monitor the optical contrast of the thermochromic layers by comparing the spectral reflectance at 25 °C and 100 °C. The good agreement observed between experimental and theoretical spectra demonstrates the adequacy of the model for predicting the optical properties of the samples.     

Thickness dependence of the amorphous-cubic and cubic-hexagonal phase transition temperatures of GeSbTe thin films on silicon nitride

The crystallization temperature of GeSbTe thin films with thicknesses between 11 and 87 nm on silicon nitride was studied through resistance versus temperature measurements. The amorphous-cubic phase transition occurs at ~ 150 °C for all films thicknesses, whereas the cubic-hexagonal phase transition temperature increases with film thickness, from ~ 200 °C for the 20 nm film to ~ 250 °C for the 87 nm film. The cubic-hexagonal transition occurs gradually for the 11 nm film. Implications for phase-change memory devices are discussed.     

Microstructure and magnetic properties of (0 0 1)-oriented L10 FePt films: Role of Ag underlayer and Fe/Pt ratio

FePt multilayer films were deposited on Si(1 0 0) substrate with thermally grown SiO₂ film and sputtered Ag underlayer at room temperature by dc magnetron sputtering and subsequently annealing in vacuum. Experimental results suggest that proper thickness of Ag underlayer and slightly rich of Fe content can effectively induce the (0 0 1) texture of FePt films. A Fe_57.4Pt_42.6 thin film on the 8 nm Ag underlayer exhibits a large perpendicular coercivity of 7.6 kOe with magnetic remanence close to 1.     

Magnetic properties and microstructures of single-layered Fe100 − xPtx films deposited onto heated substrates

The single-layered Fe_100 − xPt_x films of 30 nm thick with Pt contents (x) of 35-57 at.% are deposited on heated Si (100) substrate at a temperature (Ts) of 620 °C by magnetron co-sputtering. When the Pt content in the Fe-Pt alloy film is 35 at.%, the value of in-plane coercivity (Hc_//) is close to perpendicular coercivity (Hc_⊥) and both values are about 800 kA/m. The FePt films exhibit perpendicular magnetic anisotropy when the Pt content increases to the values of between 45 and 51 at.%. The perpendicular coercivity, saturation magnetization (Ms) and perpendicular squareness (S_⊥) for Fe₅₄Pt₄₆ film are as high as 1113 kA/m, 0.594 Wb/m² and 0.96, respectively. These magnetic properties reveal its significant potential as perpendicular magnetic recording media. Upon further increasing the Pt content to 57 at.%, the coercivity of the Fe-Pt film decreases drastically to below 230 kA/m and tends to be closer to in-plane magnetic anisotropy.     

Optimization of L10-FePt/MgO/CrRu thin films for next-generation magnetic recording media

L1₀-FePt thin films were deposited on silicon substrates with the structure of Si/CrRu/MgO/FePt. The magnetic and microstructural properties were optimized by varying the FePt sputter pressure and temperature, as well as the thicknesses of all three layers. High coercivity films greater than 1.8 T were grown when the FePt sputter pressure was at 1.33 Pa with a thickness of only 4 nm, on CrRu and MgO underlayers as thin as 10 nm and 2 nm, respectively.     

Optical response and surface morphology of In/Ag bilayer thin films

In/Ag bilayer thin films were fabricated by maintaining the Ag layer thickness constant at 5 nm while varying the In layer thickness between 3 and 30 nm. It was observed that the grain size in the films increased with increase in thickness. In the case of the single layer In films the grain size increased from 60 to 350 nm as the thickness increased from 3 to 30 nm while the grain size increased from 80 to 280 nm in as the bilayer thickness increased from 8 to 35 nm. There is a red shift in the plasmon resonance from 372 to 522 nm in the case of the pure In layers whereas it was from 492 to 618 nm for the bilayer system. The Ag single layers exhibit a plasmon resonance at 540 nm. On coupling the In and Ag layers in the bilayers, additional resonances appear in the spectrum. The origin of the additional plasmon resonance peaks can be traced to the excitation of localized surface plasmons.