Structure, magnetic and electrical transport properties of cosputtered Fe0.5Ge0.5 nanocomposite films

Fe_0.5Ge_0.5 nanocomposite films with different film thicknesses were fabricated using cosputtering. The films are composed of Ge, Fe and Fe₃Ge₂, and are ferromagnetic at room temperature. The saturation magnetization and magnetic interaction including dipolar interaction and exchange coupling increase with the increasing film thickness. The electrical conductance mechanism turns from metallic to semiconducting and the saturation Hall resistivity ρ_xys increases with the decreasing film thickness. At 28 nm, ρ_xys is ∼137 μΩ cm at 2 K, about 150 times larger than that of pure Fe film (0.9 μΩ cm) and four orders larger than that of bulk Fe. The ρ_xy-H curves of all the films show the same linearity character in low-field range even though the temperature-independent slope is different at different film thicknesses. At high temperatures, the skew scattering mechanism is dominant. At low temperatures, side-jump effect should be dominant at large resistivity ρ_xx regime for the thin films, and the skew scattering is dominant at small ρ_xx regime for the thick films.     

Effect of annealing temperature on the optical and electrical properties of amorphous As45.2Te46.6In8.2 thin films

The optical absorption of the As-prepared and annealed As_45.2Te_46.6In_8.2 thin films are studied. Films annealed at temperatures higher than 453 K show a decrease in the optical energy gap (E_o). The value of E_o increases from 1.9 to 2.43 eV with increasing thickness of the As-prepared films from 60 to 140 nm. The effect of thickness on high frequency dielectric constant (?_∞) and carrier concentration (N) is also studied. The crystalline structures of the As_45.2Te_46.6In_8.2 thin films resulting from heat treatment of the As-prepared film at different elevated temperatures is studied by X-ray diffraction. An amorphous-crystalline transformation is observed after annealing at temperatures higher than 453 K. The electrical conductivity at low temperatures is found due to the electrons transport by hopping among the localized states near the Fermi level. With annealing the films at temperatures higher than 473 K (the crystallization onset temperature) for 1 h, the electrical conductivity increases and the activation energy decreases, which can be attributed to the amorphous-crystalline transformations.     

Exchange coupling and remanence enhancement in nanocomposite Nd–Fe–B/FeCo multilayer films

Nd–Fe–B-type hard phase single layer films and nanocomposite Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀ multilayer films with Mo underlayers and overlayers have been fabricated on Si substrates by rf sputtering. The hysteresis loops of all films indicated simple single loops for fixed Nd–Fe–B layer thickness (10 nm) and different FeCo layer thickness (d_FeCo=1–50 nm). The remanence of these films is found to increase with increasing d_FeCo and the coercivity decrease with increasing d_FeCo. It is shown that high remanence is achieved in the nanocomposite multilayer films consisting of the hard magnetic Nd–Fe–B-type phase and soft magnetic phase FeCo with 20 nm?d_FeCo?3 nm. The sample of maximum energy product is 27 MG Oe for d_FeCo=5 nm at room temperature. The enhancement of the remanence and energy products in nanocomposite multilayer films is attributed to the exchange coupling between the magnetically soft and hard phases.     

Solid phase epitaxy of Ge films on CaF2/Si(1 1 1)

At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF₂/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 °C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 °C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.     

The size effect of Ba0.6Sr0.4TiO3 thin films on the ferroelectric properties

Barium strontium titanate (BST) thin films were prepared by RF magnetron sputtering. The dielectric constant-voltage curves and the hysteresis loops of BST thin films with different grain sizes and film thicknesses were investigated. When the grain size increases from 12 nm to 35 nm, remarkable increases in dielectric constant and tunability were observed. Above 12 nm, the BST films exhibited size effects, i.e. a decrease in maximal polarization (P_m) and an increase in coercive electric field (E_c) with reduction in grain size. In our investigation, the dielectric constant, tunability and maximal polarization increased as the film thickness increased. Furthermore, the size dependence of the dielectric constant and tunability of Ba_0.6Sr_0.4TiO₃ thin films is determined by that of the maximal polarization and the coercive electric field.     

Crystallization and electrical properties of V2O5 thin films prepared by RF sputtering

V₂O₅ thin films were prepared under various conditions by using reactive RF sputtering technique. The microstructure and electrical properties of the films are have been investigated. X-ray diffraction data revealed the films deposited at low O₂/Ar ratio are amorphous. The orthorhombic structure of film improved after post annealing at 873 K. The microstructure parameters (crystallite/domain size and macrostrain) have been evaluated by using a single order Voigt profile method. Using the two-point probe technique, the dark conductivity as a function of the condition parameters such as film thickness, oxygen content and temperature are discussed. It was also found that, the behaviour of ρd versus d was found to fit properly with the Fuchs-Sondheimer relation with the parameters: ρ_o = 2.14 × 10⁷ Ω cm and ?_o = 112 ± 2 nm. At high temperature, the electrical conductivity is dominated by grain boundaries, the values of activation energy and potential barrier height were 0.90 ± 0.02 eV and 0.92 ± 0.02 V, respectively.     

Structural characterization of thermally evaporated Bi2Te3 thin films

Thermally evaporated Bi₂Te₃ thin films were deposited on glass substrates. X-ray diffraction study confirmed that the growned films are polycrystalline in nature having hexagonal structure. The film exhibits preferential orientation along the [0 1 5] direction for the films of all thickness together with other abundant planes [0 1 1 1] and [1 1 0]. Various structural parameters such as lattice constants, crystallite size, strain, and dislocation density have been calculated and they are found to be thickness dependent. The lattice parameters are found to be a=4.38 Å and c=30.40 Å. The grain size of the films increases with thickness as the dislocation density and the microstrain decreases with thickness. The mean bond energy and the average coordination number of Bi₂Te₃ thin film are found to be 1.72 eV and 2.4, respectively.     

Thickness-dependent magnetization reversal in CoZrNb amorphous films

Structure and magnetization of CoZrNb amorphous films prepared by DC magnetron sputtering have been studied as a function of film thickness (t), from 35 to 840 nm. Using comprehensive characterization, we show that the CoZrNb amorphous films possess a single phase and no nanocrystalline can be detected. The magnetic measurements indicate that the magnetization reversal of CoZrNb films is strongly dependent on t. That is, the coercivity is abruptly reduced to be lower than 4 Oe with t increasing from 35 to 105 nm, and then gradually decreases to ∼0.2 Oe as t increases. This coercivity transition versus t is accompanied by the strong magnetization reversal when t is larger than 105 nm. The results reveal that CoZrNb amorphous films with comparatively large film thickness (>100 nm) are suitable for sensors and anti-faked materials.     

Early-stage ordering in in-situ annealed Fe51Pt49 films

We evidenced an early-stage ordering (ESO) in Fe₅₁Pt₄₉ film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L1₀ phase for samples deposited at substrate temperatures (T_s) 400 °C and higher was verified by X-ray diffraction. Surface roughness of Fe₅₁Pt₄₉ films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11 Å as T_s is increased from 25 to 275 °C. As further increase of T_s to 375 °C, the roughness drops to 3.2 Å and then increases again to 38 Å with T_s up to 700 °C. Measurement on residual strain demonstrates that it is initially compressive at T_s<400 °C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing T_s up to 700 °C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at T_s>250 °C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460 Oe as T_s increase from 25 to 375 °C (ESO) and then from 460 to 10,700 Oe with T_s 375-700 °C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before T_s 400 °C.     

Characterization of TiO2/Au/TiO2 films deposited by magnetron sputtering on polycarbonate substrates

Transparent and conducting TiO₂/Au/TiO₂ (TAuT) films were deposited by reactive magnetron sputtering on polycarbonate substrates to investigate the effect of the Au interlayer on the optical, electrical, and structural properties of the films. In TAuT films, the Au interlayer thickness was kept at 5 nm. Although total thickness was maintained at 100 nm, the stack structure was varied as 50/5/45, 70/5/25, and 90/5/5 nm.In XRD pattern, the intermediate Au films were crystallized, while all TAuT films did not show any diffraction peaks for TiO₂ films with regardless of stack structure. The optical and electrical properties were dependent on the stack structure of the films. The lowest sheet resistance of 23 Ω/□ and highest optical transmittance of 76% at 550 nm were obtained from TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films. The work function was dependent on the film stack. The highest work function (4.8 eV) was observed with the TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm film stack. The TAuT film stack of TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films is an optimized stack that may be an alternative candidate for transparent electrodes in flat panel displays.     

Texture development and magnetic properties of [ZrO2/CoPt]n/Ag nanocomposite films

The L1₀ CoPt films with (0 0 1) preferred orientation are achieved by fabricating on the glass substrates and post annealing at 600° C for 30 min. The preferred orientation of [ZrO₂/CoPt]_n/Ag films dependence of the Ag underlayer thickness, ZrO₂ and CoPt interlayer thickness is investigated. A large perpendicular magnetic anisotropy and a nearly perfect L1₀ CoPt (0 0 1) texture are obtained in the [ZrO₂ (3 nm)/CoPt (5 nm)]₃/Ag (10 nm) film. The existence of ZrO₂ plays an important role in reducing the intergranular interactions and in determining the size of CoPt grains. Magnetic reversal in textured CoPt films are close to a Stoner-Wolfarth rotation.     

Structural characterization of La0.9Ba0.1MnO3/Y-ZrO2 film by X-ray diffraction

Perovskite manganite La_0.9Ba_0.1MnO₃(LBMO) films were deposited on (0 0 1)-oriented single crystal yttria-stabilized zirconia (YSZ) substrate by 90° off-axis radio frequency magnetron sputtering. The film thickness ranged from 10 nm to 100 nm. Grazing incidence X-ray diffraction technique and high resolution X-ray diffraction were applied to characterize the structure of LBMO films. The LBMO film mainly consisted of (0 0 1)-orientated grain as well as weakly textured (1 1 0)-orientated grain. The results indicated that an amorphous layer with thickness of about 4 nm was formed at the LBMO/YSZ interface. The strain in LBMO film was small and averaged to be about -0.14%. The strain in the film was not lattice mismatch-induced strain but residual strain due to the difference in thermal expansion coefficient between film and substrate.     

Influence of heat treatment on the structure and magnetic properties of the Co/Zr and Co/Hf multilayer amorphous films

The influence of annealing on the structure and magnetic properties of amorphous Co/Zr and Co/Hf multilayer films was studied with particular attention to the dependence of the magnetic properties, thermal stability and crystallization process on layer composition and thickness. The temperature at which crystallization commences increases from 400 to 460 °C as the layer thickness d_Zr or d_Hf increases from 6 to 18 Å, and decreases from 450 to 400 °C as d_Co increases from 12 to 18 Å. Multilayers containing 19–60 at% Zr were studied. The specific magnetization was found to increase even below the temperature at which crystallization commences. Our data are compared with non-multilayer Co–Zr amorphous films and rapidly quenched metallic glasses.     

Enhancement of L10 ordered FePt by Pt buffer layer

L₁₀-ordered FePt thin films prepared by molecular-beam epitaxy on MgO (0 0 1) substrate at 320 °C with different thickness of Pt buffer layer have been investigated. The out-of-plane coercivity increases with increasing thickness of Pt buffer. The maximum values of the long-range order parameter and uniaxial magnetic anisotropy energy are 0.72 and 1.78×10⁷ erg/cm³, respectively, for films with 12 nm thick Pt buffer layer, where the c/a ratio (0.976) shows the minimum value. The reason for the enhancement in ordering is due to the proper lattice strains Pt buffer bestows on FePt layer, these strains are equal to the contraction in lattice parameter c and the expansion in a. Studies of angular-dependent coercivity revealed that the magnetization reversal behaviour shifts from a domain-wall motion dominated case towards a near rotational mode with increasing thickness of Pt buffer layer.     

Microstructure and dielectric properties of La2O3 doped amorphous SiO2 films as gate dielectric material

As a potential gate dielectric material, the La₂O₃ doped SiO₂ (LSO, the mole ratio is about 1:5) films were fabricated on n-Si (0 0 1) substrates by using pulsed laser deposition technique. By virtue of several measurements, the microstructure and electrical properties of the LSO films were characterized. The LSO films keep the amorphous state up to a high annealing temperature of 800 °C. From HRTEM and XPS results, these La atoms of the LSO films do not react with silicon substrate to form any La-compound at interfacial layer. However, these O atoms of the LSO films diffuse from the film toward the silicon substrate so as to form a SiO₂ interfacial layer. The thickness of SiO₂ layer is only about two atomic layers. A possible explanation for interfacial reaction has been proposed. The scanning electron microscope image shows the surface of the amorphous LSO film very flat. The LSO film shows a dielectric constant of 12.8 at 1 MHz. For the LSO film with thickness of 3 nm, a small equivalent oxide thickness of 1.2 nm is obtained. The leakage current density of the LSO film is 1.54 × 10⁻⁴ A/cm² at a gate bias voltage of 1 V.     

Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films

We have grown lead iron niobate thin films with composition Pb(Fe_1/2Nb_1/2)O₃ (PFN) on (0 0 1) SrTiO₃ substrates by pulsed laser deposition. The influence of the deposition conditions on the phase purity was studied. Due to similar thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN perovskite phase. By optimizing the kinetic parameters, we succeeded in identifying a deposition window which resulted in epitaxial perovskite-phase PFN thin films with no identifiable trace of impurity phases appearing in the X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were smooth and epitaxially oriented with the substrate and as demonstrated by RHEED streaks which were aligned with the substrate axes. X-ray diffraction showed that the films were completely c-axis oriented and of excellent crystalline quality with low mosaicity (X-ray rocking curve FWHM?0.09°). The surface roughness of thin films was also investigated by atomic force microscopy. The root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm for 100-nm-thick films. We also observe a correlation between grain size, surface roughness and film thickness.     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

Laser-induced voltage characteristics of Bi2Sr2Co2Oy thin films on LaAlO3 substrates

We report the laser-induced voltage (LIV) effects in c-axis oriented Bi₂Sr₂Co₂O_y thin films grown on (0 0 1) LaAlO₃ substrates with the title angle α of 0°, 3°, 5° and 10° by a simple chemical solution deposition method. A large open-circuit voltage with the sensitivity of 300 mV/mJ is observed for the film on 10° tilting LaAlO₃ under a 308 nm irradiation with the pulse duration of 25 ns. When the film surface is irradiated by a 355 nm pulsed laser of 25 ps duration, a fast response with the rise time of 700 ps and the full width at half maximum of 1.5 ns is achieved. In addition, the experimental results reveal that the amplitude of the voltage signal is approximately proportional to sin 2α and the signal polarity is reversed when the film is irradiated from the substrate side rather than the film side, which suggests the LIV effects in Bi₂Sr₂Co₂O_y thin films originate from the anisotropic Seebeck coefficient of this material.     

Out-of-plane low field anisotropic magnetoresistance in Nd0.51Sr0.49MnO3 thin films

A comparative study of the out-of-plane anisotropic magnetoresistance (AMR) in single crystalline and polycrystalline thin films of phase separated manganite Nd_0.51Sr_0.49MnO₃ has been carried out. On-axis DC magnetron sputtering was used to deposit the single crystalline films (30 and 100 nm in thickness) on single crystal (0 0 1) LaAlO₃ (LAO) and polycrystalline films (100 nm) on (1 0 0) Yttrium-stabilized ZrO₂ (YSZ) substrates. The in-plane and out-of-plane magnetotransport properties of these films differ significantly. A large low field AMR is observed in all the films. AMR shows a peak below the insulator-metal transition temperature in the single crystalline films, while the same increases monotonically in the polycrystalline film. Relatively larger low field AMR (∼20% at T=78 K and H=1.7 kOe) in the polycrystalline films suggests the dominance of the shape anisotropy.