Onset of hard magnetic L10 FePt phase with (001) texture

The perpendicular anisotropic magnetic properties of in-situ deposited FePt/Pt/Cr trilayer films were elucidated as functions of the deposition temperature and the sputtering rate of the FePt magnetic layer. Ordered L1₀ FePt thin films with perpendicular anisotropy and a (001) texture can be developed at a temperature as low as 300 °C with the sputtering of a FePt layer at a low rate. The larger Pt(001)[100] lattice induced an expansion of the FePt a- and b-axis, leading to the contraction of the FePt c-axis, enabling the epitaxial growth of the L1₀ FePt(001) texture to occur. A low rate of sputtering of the FePt thin film promotes the formation of the magnetically hard FePt(001) texture on the surface of the Pt(001) buffer layer at low temperature, while the high sputtering rate of FePt layer suppresses the phase transformation.     

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.     

Epitaxial growth of Ni films sputter-deposited on a GaAs(001) surface covered with a MgO film

We studied the epitaxial growth of a Ni film prepared on a GaAs(001) substrate covered with a thin epitaxial MgO buffer film, assuming that this buffer film plays a key role in the epitaxial growth of the Ni film. The MgO and Ni films were deposited by radio-frequency magnetron sputtering of the MgO and Ni targets in pure Ar gas. First, a MgO film of thickness ranging from 78 to 4.4 nm was deposited on the GaAs(001) substrate at a temperature ranging from ambient temperature to 700 °C, and then, a 136-nm-thick Ni film was deposited on the MgO/GaAs substrate at a temperature range 300-500 °C. Using transmission electron microscopy and X-ray diffractometry, we showed that the MgO film grows with the epitaxial relationship MgO(001)[001]//GaAs(001)[001] on GaAs(001) at 500 °C, and that the structure of the Ni film depends on three factors: the MgO/GaAs substrate temperature, the MgO thickness, and the annealing condition of the MgO/GaAs substrate before the Ni deposition. In conclusion, we proved that the Ni film grows with the epitaxial relationship Ni(001)[001]//MgO(001)[001]//GaAs(001)[001] on MgO/GaAs with the 4.4-nm-thick MgO film when the MgO/GaAs substrate is annealed in situ at room temperature before the Ni deposition and maintained at 300 °C during the Ni deposition.     

Substrate temperature dependence of the properties of Ga-doped ZnO films deposited by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. The influence of substrate temperature on the structural, electrical, and optical properties of ZnO:Ga films was investigated. The X-ray diffraction (XRD) studies show that higher temperature helps to promote Ga substitution more easily. The film deposited at 350 °C has the optimal crystal quality. The morphology of the films is strongly related to the substrate temperature. The film deposited is dense and flat with a columnar structure in the cross-section morphology. The transmittance of the ZnO:Ga thin films is over 90%. The lowest resistivity of the ZnO:Ga film is 4.48×10⁻⁴ Ω cm, for a film which was deposited at the substrate temperature of 300 °C.     

Pb(Zr0.52Ti0.48)O3/TiNi multilayered heterostructures on Si substrates for smart systems

Ferroelectric/shape memory alloy thin film multilayered heterostructures possess both sensing and actuating functions and are considered to be smart. In this article, Pb(Zr_0.52Ti_0.48)O₃ (PZT) ferroelectric thin films and Ti-riched TiNi shape memory alloy thin films have been deposited on Si and SiO₂/Si substrates in the 400-600 °C temperature range by pulsed laser deposition technique. Deposition processing, microstructure and surface morphology of these films are described. The TiNi films deposited at 500 °C had an austenitic B2 structure with preferred (110) orientation. The surfaces of the films were very smooth with the root-mean-square roughness on a unit cell level. The structure of the TiNi films had a significant influence on that of the subsequently deposited PZT films. The single B2 austenite phase of the TiNi favored the growth of perovskite PZT films. The PZT/TiNi heterostructures with the PZT and TiNi films respectively deposited at 600 and 500 °C exhibited a polarization-electric field hysteresis behavior with a leakage current of about 2 × 10^− 6 A/cm².     

Thickness dependence of structural, electrical and optical properties of sprayed ZnO:Cu films

ZnO:Cu thin films have been deposited by spray pyrolysis techniques within two different (450 °C and 500 °C) substrate temperatures. The structural properties of ZnO:Cu thin films have been investigated by X-ray diffraction techniques. The X-ray diffraction spectra showed that ZnO:Cu thin films are polycrystalline with the hexagonal structure and show a good c-axis orientation perpendicular to the substrate. The most preferential orientation is along the (002) direction for all spray deposited ZnO:Cu films together with orientations in the (100) and (101) planes also being abundant. Some parameters of the films were calculated and correlated with the film thickness for two different substrate temperatures. The optical properties of ZnO:Cu thin films have been investigated by UV/VIS spectrometer and the band gap values were found to be ranging from 3.29 eV to 3.46 eV.     

Effect of growth temperature on the structural and transport properties of magnetite thin films prepared by pulse laser deposition on single crystal Si substrate

Magnetite (Fe₃O₄) thin films are prepared by pulsed laser deposition using an α-Fe₂O₃ target on silicon (111) substrate in the substrate temperature range of 350 °C to 550 °C. X-ray diffraction (XRD) measurement shows that the film deposited at 450 °C is a single phase Fe₃O₄ film oriented along [111] direction. However, the film grown at 350 °C reveals mixed oxide phases (FeO and Fe₃O₄), while the film deposited at 550 °C is a polycrystalline Fe₃O₄. X-ray photoelectron spectroscopy study confirms the XRD findings. Raman measurements reveal identical spectra for all the films deposited at different substrate temperatures. We observe abrupt increase in the resistivity behavior of all the films around Verwey transition temperature (T_V) (125 K-120 K) though the transition is broader in the film deposited at 350 °C. We observe that the optimized temperature for the growth of Fe₃O₄ film on Si is 450 °C. The electrical transport behavior follows Shklovskii and Efros variable range hopping type conduction mechanism below T_V for the film deposited at 450 °C possibly due to the granular growth of the film.     

Structural and optical properties of heteroepitaxial beta Ga2O3 films grown on MgO (100) substrates

Gallium oxide (Ga₂O₃) films were deposited on MgO (100) substrates by metalorganic vapor phase epitaxy. Structure analyses showed that the films deposited at 550-700 °C were epitaxial β-Ga₂O₃ films with an out of plane relationship of β-Ga₂O₃(100)||MgO(100). The film deposited at 650 °C showed the best crystallinity and the microstructure of the film was investigated by high resolution transmission electron microscopy. A theoretical model of the growth mechanism was proposed and the in-plane epitaxial relationship was given to be β-Ga₂O₃[001]||MgO<011>. A four-domain structure inside the epitaxial film was clarified. The β-Ga₂O₃ film deposited at 650 °C showed an absolute average transmittance of 95.9% in the ultraviolet and visible range, which had an optical band gap of 4.87 eV.     

Nanogranular L1(0) FePt-C-Ta2O5 composite media for perpendicular recording applications

In this report, the effect of simultaneously adding two dopants (C and Ta2O5) in FePt was investigated. (Fe55Pt45)79C21-(x vol%) Ta2O5 films (where x = 0% to 20%) were prepared using both low and high power magnetron sputtering on MgO (2 nm)/CrRu (30 nm) underlayers with in-situ heating at 350 degrees C. Films deposited at low power showed a decrease in exchange coupling with increasing Ta2O5 content. Out-of-plane coercivity of 7.2 kOe was observed even with up to 20 vol% Ta2O5. X-Ray diffraction spectra showed presence of FePt(001) texture for all compositions of Ta2O5 ranging from 0 to 20 vol% suggesting that the perpendicular anisotropy was maintained even with up to 20 vol% of dopant content. Films deposited at high power showed a different behavior with an initial increase in out-of-plane coercivity to 8.2 kOe and a reduction in exchange coupling with loop slope parameter (alpha) approaching a fully decoupled value of 1. Further increase in doping content led to deterioration in the out-of-plane coercivity, as well as an increase in the exchange coupling.     

Sputter deposited nanocrystalline Ni-25Al alloy thin films and Ni/Ni3Al multilayers

Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni₃Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a strongly textured columnar growth morphology and consisted of a mixture of metastable phases. Nanoindentation studies carried out on this film exhibited a strong strain hardening tendency. In contrast, the film deposited at 200 °C exhibited a recrystallized non-textured microstructure consisting of grains of a partially ordered Ni₃Al phase. At higher deposition temperatures (∼400 °C), larger grains of the bulk equilibrium, long-range ordered, Ll₂ Ni₃Al phase were observed in the film. Unlike the film deposited on an unheated substrate, the films deposited at elevated temperatures did not exhibit any dependence of the hardness on the indentation depth and, consequently no strain hardening. The average hardness of the film deposited at 200 °C was higher than the one deposited at 400 °C. In addition to monolithic Ni-25Al thin films, multilayered Ni/Ni3Al thin films were also deposited. Multilayers deposited non-epitaxially on unheated substrates exhibited a strong {111} fiber texture while those deposited epitaxially on (001) NaCl exhibited a {001} texture. Free-standing multilayers of both types of preferred orientations as well as of different layer thicknesses were deformed in tension untill fracture. Interestingly, the {111} oriented multilayers failed primarily by a brittle fracture while the {001} multilayers exhibited features of ductile fracture.     

Fabrication of ferromagnetic Ni epitaxial thin film by way of hydrogen reduction of NiO

The ferromagnetic epitaxial Ni (111) thin film on the oxide substrate could be obtained by an epitaxy method, employing pulsed laser deposition (PLD) of epitaxial NiO (111) film on the sapphire (α-Al₂O₃) substrate and successive hydrogen reduction. The epitaxial NiO (111) film was deposited on the sapphire (0001) substrate at room temperature by PLD, and was reduced into the Ni epitaxial film by annealing (300 °C to 700 °C) in the hydrogen atmosphere, suggesting the possible formation of epitaxial [Ni metal/α-Al₂O₃] multilayer. The epitaxy of Ni film was proved by ex situ X-ray diffraction. The ferromagnetic anisotropy of the epitaxial Ni film was examined by superconducting quantum interference magnetometry.     

Epitaxial growth of Cu(100) and Pt(100) thin films on perovskite substrates

Pulsed laser deposition has been used to grow epitaxially oriented thin films of Cu and Pt on (100)-oriented SrTiO₃ and LaAlO₃ substrates. X-ray diffraction results illustrated that purely epitaxial Cu(100) films could be obtained at temperatures as low as 100 °C on SrTiO₃ and 300 °C on LaAlO₃. In contrast, epitaxial (100)-oriented Pt films were attained on LaAlO₃(100) only when deposited at 600 °C. Atomic force microscopy images showed that films deposited at higher temperatures consisted of 3D islands and that flat, layered films were obtained at the lowest deposition temperatures. Importantly, Cu films deposited at 100 °C on SrTiO₃(100) were both purely (100)-oriented and morphologically flat. Pt and Cu films displaying both epitaxial growth and smooth surfaces could be obtained on LaAlO₃(100) only by using a three-step deposition process. High-resolution transmission electron microscopy demonstrated an atomically sharp Cu/SrTiO₃ interface. The crystalline and morphological features of Cu and Pt films are interpreted in terms of the thermodynamic and kinetic properties of these metals.     

Epitaxial growth of SrRuO3 thin films by RF sputtering and study of surface morphology

We report on the epitaxial growth of SrRuO₃ (SRO) thin films on Pt (111)/γ-Al₂O₃ (111) nSi (111) substrates. The grown thin films are crystalline and epitaxial as suggested by RHEED and XRD experiments. With the use of γ-Al₂O₃ (001)/nSi (001) and γ-Al₂O₃ (111)/nSi (111) substrates, crystalline but not epitaxial films have grown successfully. This result implies that lattice mismatch between nSi and SRO prevents the epitaxial growth of SRO film directly on nSi. However, the buffer Pt (111) layer mitigates lattice mismatch that provides to grow epitaxial film on nSi of quality. Morphological study shows a good surface with moderate roughness. Film grown at 700°C is smoother than the film grown at 750°C, but the variation of temperature does not affect significantly on the epitaxial nature of the films.     

ZnO thin films deposited by a CVT technique in closed ampoules

ZnO thin films were prepared on quartz glass, Si (100), and sapphire (001) substrates by a chemical vapour transport (CVT) technique. During the growing processes, the source and substrate temperatures were maintained at 1000 °C and 600 °C, respectively. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements showed that the crystalline qualities of ZnO thin films were sensitively dependent on substrates. ZnO thin film deposited on sapphire substrate exhibited the best morphology with the largest crystallite size of more than 20 μm. Meanwhile, the XRD patterns showed that ZnO thin film deposited on sapphire substrate was strongly c-axis preferred-oriented with high crystalline quality. The optical properties of ZnO thin films were investigated by photoluminescence (PL) spectroscopy at room temperature (RT). The results suggested that the optical properties of ZnO thin films were highly influenced by their crystalline qualities and surface morphologies.     

CdTe thin film solar cells: Interrelation of nucleation, structure, and performance

The performance of CdTe solar cells as prototype of thin film solar cells strongly depends on film morphology. The needs for high solar cell performance using thin film materials will be addressed covering nucleation and growth control of thin film materials. In order to understand the basic growth mechanisms and their impact on cell performance, we have systematically investigated the growth of CdTe thin films by Close Spaced Sublimation (CSS) using the integrated ultra-high vacuum system DAISY-SOL. CdTe thin films were deposited on TCO/CdS substrates (transparent conductive oxide) held at 270 °C to 560 °C. The properties of the films were determined before and after CdCl₂ treatment using X-ray diffraction and electron microscopy. In addition, solar cells were prepared to find correlations between material properties and cell efficiency. At low sample temperature the films tend to form compact layers with preferred (111) orientation which is lost at elevated temperatures above 450 °C. For CdS layers without (0001) texture there is in addition a low temperature regime (350 °C) with (111) texture loss. After activation treatment the (111) texture is lost for all deposited layers leading to strong recrystallisation of the grains. But the texture still depends on the previous growth history. The loss of (111) texture is evidently needed for higher performance. A clear correlation between cell efficiency and the texture of the CdTe film is observed.     

Precursor chemistry for the solution deposition of epitaxial La0.66Sr0.33MnO3 (LSMO) thin films

A new chemical solution deposition method for the epitaxial growth of La_0.66Sr_0.33MnO₃ (LSMO) thin films from metal acetates, acetylacetonates and propionic acid is presented. Using this method, epitaxial LSMO thin films were grown on (001) SrTiO3 (STO) single crystalline substrates in the temperature range from 800 °C to 1100 °C, both in air and in oxygen atmosphere. The LSMO thin films exhibit good structural and electrical properties. The FWHM of the ω-scan for the (002) peak has a mean value of 0.06°. The Curie temperature of the LSMO thin films is about 320 K and 350 K for the annealed in oxygen and air, respectively.     

Crystallographic structure and magnetic properties in L1(0) FePt thin films deposited at different temperature

The crystallographic structure and magnetic properties of L1(0) FePt thin films deposited at different substrate temperature were investigated systematically in present paper. The ordered L1(0) FePt thin film was developed when substrate temperature is higher than 300 degrees C. The ordering parameter S, the degree of tetragonality c/a, and the epitaxial quality of the films, increase with increasing substrate temperature. The squareness and coercivity in the direction perpendicular to the film increase as the substrate temperature is increased and the perpendicular anisotropy is developed when the substrate temperature is higher than 300 degrees C. The magnetic anisotropy Ku increases with increasing substrate temperature and it might be concluded that the magnetic anisotropy of ordered L1(0) FePt thin films mainly stems from the magnetocrystalline origin and also possibly due to pair ordering mechanism.     

The growth of BaTiO3 films on (001) MgAl2O4 substrates by pulsed laser deposition technique

The microstructural evolution of the BaTiO₃ films grown on (001) MgAl₂O₄ spinel substrates at different temperatures by means of pulsed laser deposition technique is studied via transmission electron microscopy (TEM). The BaTiO₃ film grown at 850 °C consists of columnar grains of random orientations. Once the substrate temperature is over 900 °C, the BaTiO₃ films grow on (001) MgAl₂O₄ substrates epitaxially. The cross-sectional TEM study reveals that the boundaries and interfaces act as the sources to emit stacking faults and twins which are detrimental to the film quality. The quality of epitaxial films increases with the growth temperature, and is optimized at the growth temperature of 1050 °C. The evolution of film microstructures with the growth temperature is discussed in view of the growth temperature, the surface structure of MgAl₂O₄ substrates, and the phase transition of BaTiO₃.     

Deposition of hydroxyapatite thin films by Nd:YAG laser ablation: a microstructural study

Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation at λ = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 °C and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at λ = 335 nm laser wavelength and 300 °C substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP).     

Effect of Pt content on structure and magnetic properties of Fe100−xPtx films deposited on thermally oxidized Si substrates by rapid thermal annealing

Fe_100-xPt_x films with Pt contents (x) = 29–65 at.% were deposited directly onto thermally oxidized Si(100) substrate by dc magnetron sputtering. The films were then post-annealed at 700 °C for 3 min by rapid thermal annealing (RTA) at a high heating ramp rate of 100 °C/s. Experimental results show that Fe₃Pt film displayed (111) preferred orientation and tended towards in-plane magnetic anisotropy when the Pt content was 29 at.%. When the Pt content was increased to 49 at.%, the FePt film inclined towards (001)-texture and perpendicular magnetic anisotropy. Its out-of-plane coercivity (Hc_⊥), saturation magnetization (M_s) and out-of-plane squareness (S_⊥) reached 1010 kA/m, 0.47 T and 0.8, respectively. These results reveal its significant potential as perpendicular magnetic recording media for high-density recording. Upon further increasing the Pt content to 65 at.%, the coercivity of the films decreased drastically to below 65 kA/m and tended towards in-plane magnetic anisotropy.