Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

A WF₆–H₂–N₂ precursor system was used for plasma-enhanced chemical vapor deposition (PECVD) of WN_x films. We examined the microstructural changes of the WN_x films depending on N₂/H₂ flow-rate ratio and post-annealing (600–800 °C for 1 h). As the N₂/H₂ flow rate was increased from 0 to 1.5, as-deposited WN_x films exhibited various different crystalline states, such as nanocrystalline and/or amorphous structure comprising W, WN, and W₂N phases, a fine W₂N granular structure embedded in an amorphous matrix, and a crystalline structure of β-W₂N phase. After post-annealing above 600 °C, crystalline recovery with phase separation to β-W₂N and α-W was observed from the WN_x films deposited at an optimized deposition condition (flow-rate ratio = 0.25). From this PECVD method, an excellent step coverage of ∼90% was obtained from the WN_x films at a contact diameter of 0.4 μm and an aspect ratio of 3.5.     

Nb doping effect on TiO2−x films for bolometer applications

Nb-doped TiO_2−x thin films were deposited using a 1 at% niobium doped titanium target by RF reactive magnetron sputtering at various oxygen partial pressures (pO₂). The films appeared amorphous in the pO₂ range of 4.4–4.7% with resistivity ranging from 0.39 Ω cm to 2.48 Ω cm. Compared to pure TiO_2−x films, the resistivity of the Nb-doped TiO_2−x films did not change sensitively with the oxygen partial pressure, indicating that the resistivity of the films can be accurately controlled. 1/f noise parameter of Nb-doped TiO_2−x films were found to decrease largely while the measured temperature coefficient of resistance (TCR) of the films was still high. The obtained results indicate that Nb-doped TiO_2−x films have great potential as an alternative bolometric material.     

Substrate bias effects during diamond like carbon film deposition by microwave ECR plasma CVD

Diamond like carbon (DLC) coatings were deposited on silicon(1 1 1) substrates by microwave electron cyclotron resonance (ECR) plasma CVD process using a plasma of Ar and CH₄ gases under the influence of DC self bias generated on the substrates by application of RF (13.56 MHz) power. DLC coatings were deposited under the varying influence of DC bias (−60 V to −150 V) on the Si substrates. Deposited films were analyzed by different techniques like: X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), Hardness and elastic modulus determination technique, Raman spectroscopy, scanning electron microscopy (SEM) and contact angle measurement. The results indicate that the film grown at −100 V bias has optimised properties like high sp³/sp² ratio of carbon bonding, high refractive index (2.26–2.17) over wide spectral range 400–1200 nm, low roughness of 0.8 nm, high contact angle (80°) compared to the films deposited at other bias voltages (−60 V and −150 V). The results are consistent with each other and find august explanation under the subplantation model for DLC growth.     

Influence of Sr substitution on thermoelectric properties of La1−xSrxFeO3 ceramics

Perovskite La_1−xSr_xFeO₃ (0.10 ⩽ x ⩽ 0.20) ceramics have been synthesized by the conventional solid-state reaction technique. Their electrical resistivity, Seebeck coefficient and thermal conductivity have been measured. It has been found that the increase of Sr content reduces significantly both the electrical resistivity and the Seebeck coefficient, but slightly increases the high-temperature thermal conductivity. An adiabatic hopping conduction mechanism of small polaron is suggested from the analysis of the temperature dependence of the electrical resistivity. Seebeck coefficients decrease with increasing temperature, and saturate at temperature above 573 K. The saturated value of Seebeck coefficient decreases with increasing of Sr contents, from 200 μV/K for x = 0.10 to 100 μV/K for x = 0.20. All samples exhibit lower thermal conductivity with values around 2.6 W/m K. The highest dimensionless figure of merit is 0.031 at temperature 973 K in La_0.88Sr_0.12FeO₃.     

Temperature coefficient of resistance and thermal conductivity of Vanadium oxide ‘Big Mac’ sandwich structure

In this paper, we synthesize and characterize a thin film thermometer structure for infrared microbolometers. The structure is composed of alternating multilayers of Vanadium pentoxide (V₂O₅), 25 nm, and Vanadium (V), 5 nm, thin films deposited by rf magnetron and dc magnetron sputtering respectively and annealed for 20, 30 and 40 min at 300 °C in Nitrogen (N₂) atmosphere. The best achieved temperature coefficient of resistance (TCR) was found to be −2.57%/K for 40 min annealed samples. Moreover, we apply, for the first time, the photo-thermal deflection (PTD) technique for measuring the thermal conductivity of the synthesized thin films. The thermal conductivity of the developed thin films reveals an increase in thermal conductivity from 2 W/m K to 5.8 W/m K for as grown and 40 min annealed samples respectively.     

Deposition of superconducting CeCoIn5 thin films by co-sputtering and evaporation

Thin superconducting films of CeCoIn₅ were prepared in situ by simultaneous thermal evaporation of indium and dc magnetic field assisted sputtering of planar metallic Ce and Co targets. To achieve an effective sputtering of the magnetic Co target a special geometry with two facing planar targets (Ce and Co) and magnetic field perpendicular to the targets was used. The stoichiometric (0 0 1)-oriented CeCoIn₅ films were grown on r-cut sapphire substrates with a high-rate of 100 nm/min. The temperature dependence of the electrical resistivity revealed the characteristic heavy-fermion behavior and a superconducting transition at about 2 K in agreement with the literature data for CeCoIn₅ bulk material and thin films.     

Microstructure and characterization of Al-doped ZnO films prepared by RF power sputtering on Al and ZnO targets

Al-doped zinc oxide (AZO) transparent conductive films were prepared on a glass substrate using a magnetron sputtering system with a pure zinc oxide (ZnO) target and a pure Al target sputtered using radio frequency (RF) power. The RF power was set at 100 W for the ZnO target and varied from 20 to 150 W for the Al target. The morphology of the thin films was examined by field-emission scanning electron microscope (FE-SEM), and their composition was analyzed by the equipped energy-dispersive X-ray spectroscopy (EDS). The cross section of the films determined through FE-SEM indicated that their thickness was around 650 nm. EDS analysis revealed that the Al-dopant concentration of the AZO films increased in the following order: 0.85 at.% (20 W) < 1.60 at.% (40 W) < 3.52 at.% (100 W) < 4.34 at.% (150 W). Analysis of the films using X-ray diffractometer (XRD) indicated that all films had a wurtzite structure with a texture of (0 0 2). High-resolution transmission electron microscopy (HRTEM) revealed a number of defects in the films, such as stacking faults and dislocations. Ultraviolet photoelectron spectroscopy (UPS) was used to estimate the optical energy gap (E_g) for the AZO thin films. The energy gap increases from 3.39 to 3.58 eV as the RF power applied to the Al target increase. The electrical resistivity of the films decreased from 3.43 × 10^?2 Ω cm to 3.29 × 10^?3 Ω cm as the RF power increased from 20 to 150 W when a four-point probe was used to investigate. Atomic force microscope (AFM) revealed that the surface roughness of the films increased with increasing RF power. The average optical transmittance of the films was determined by UV–visible spectrometer. The films are suitable for use as transparent conductive oxide films in the optoelectronic industry. A decrease in the electrical resistivity of the film with increasing Al-dopant concentration was ascribed to an increase in the carrier concentration and density of stacking faults in the films.     

Electrical and mechanical properties of diluted magnetic semiconductor Zn1−xMnxS nanocrystalline films

Nanostructured Zn_1−xMn_xS films (0 ⩽ x ⩽ 0.25) were deposited on glass substrates by simple resistive thermal evaporation technique. All the films were deposited at 300 K in a vacuum of 2 × 10⁻⁶ m bar. All the films temperature dependence of resistivity revealed semiconducting behaviour of the samples. Hot probe test revealed that all the samples exhibited n-type conductivity. The nanohardness of the films ranges from 4.7 to 9.9 GPa, Young’s modulus value ranging 69.7–94.2 GPa.     

Composition-dependent metal-insulator transition in perovskite CaXPb(1−X) TiO3 (CPT) ceramic

Ceramic compositions of a complex perovskite Ca_XPb(_1?X)TiO₃ (CPT) systems with x=0.6, 0.7 and 0.8 were prepared by mechanical mixing of their oxides (CaTiO₃ and PbTiO₃). The structure of the (CPT) ceramics was characterized by X-ray diffraction (XRD) The ceramics transform gradually from orthorhombic phase (pseudo cubic phase) to cubic phase by increasing pb content percent. The dc resistivity ρ(t) versus temperature (range 300–525 K) for x=0.6, 0.7 and 0.8. The ρ.T/curves reveal that samples exhibit a metallic behaviour at low temperature and undergo a metal-semiconductor transition with increasing temperature at T_p=373 K, 343 K and 333 K, for x=0.6, 0.7 and 0.8, respectively. The nature of conduction mechanism is studied in semiconductor region by studying the current–voltage temperature characteristics. The current–voltage characteristics were interpreted in terms of Poole–Frenkel type of conduction mechanism.     

Growth mode of Pt1−xNix films biased dc-sputter-deposited on MgO(0 0 1)

A study is made by TEM, XRD and by measuring electrical/magnetic properties, of growth mode and properties of Pt_1−xNi_x alloy films deposited on MgO(0 0 1) at 250°C by dc-sputtering at 2.5–2.7 kV in Ar. A bias voltage V_s≤−160 V was applied to the substrate during deposition. It was confirmed that the Pt film was polycrystalline with the texture of Pt(1 1 1)/MgO(0 0 1) while the films of Pt_0.14Ni_0.86 and Pt_0.19Ni_0.81 were epitaxially grown with Pt–Ni(0 0 1)[1 0 0]/MgO(0 0 1)[1 0 0] similarly to the case of Ni/MgO(0 0 1). Thus the growth mode transformation between Pt–Ni(1 1 1)/MgO(0 0 1) and Pt–Ni(0 0 1)/MgO(0 0 1) may be induced at x less than 0.81 for Pt_1−xNi_x alloy films. The temperature coefficient of resistance TCR from 100 to 300 K of Pt_0.14Ni_0.86 films was estimated to be 0.0044–0.0053 K⁻¹ and saturation magnetization at 300 K to be 1.7–3.2 kG, respectively, while TCR of Pt films was estimated to be 0.0035–0.0048 K⁻¹.     

Characteristics of pulse plated CdxZn1−xSe films

Cd_xZn_1−xSe films (0 ⩽ x ⩽ 1) were deposited for the first time by the pulse plating technique at different duty cycles in the range 6–50% at room temperature from an aqueous bath containing zinc sulphate, cadmium sulphate and selenium oxide. To the author’s knowledge this is the first report on pulse plated Cd_xZn_1−xSe films. The deposition potential was −0.9 V (SCE). The as deposited films exhibited cubic structure. Composition of the films was estimated by Energy Dispersive Analysis of X-ray studies. X-ray photoelectron spectroscopy studies indicated the binding energies corresponding to Zn(2p_3/2), Cd(3d_5/2 and 3d_3/2) and Se(3d_5/2 and 3d_3/2). Optical band gap of the films varied from 1.72 to 2.70 eV as the composition varied from CdSe to ZnSe side. Atomic force microscopy studies indicated grain size in the range of 20–150 nm.     

Enhanced mangnetoelectric voltage in multiferroic particulate Ni0.83Co0.15Cu0.02Fe1.9O4−δ/PbZr0.52Ti0.48O3 composites – dielectric,piezoelectric and magnetic properties

Multiferroic particulate composites of Ni_0.83Co_0.15Cu_0.02Fe_1.9O_4−δ– NCCF and lead zirconate titanate (PZT) were prepared conventional ceramic method. The generic formulae x NCCF + (1−x) PZT where x = 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mole fractions. The presence of two phases in multiferroic was confirmed with XRD technique. The dielectric constant and loss tangent were studied as a function of frequency (100 Hz to 1 M Hz) and temperature (30–500 °C). The piezoelectric coefficient d₃₃ were also studied on these particulate composites. The hysteresis behaviour was studied to understand the magnetic properties such as saturation magnetization (Ms) and magnetic moment (μ_B). The static magnetoelectric (ME) voltage coefficient was measured as a function of dc magnetic bias field. A high value of ME output (3151 mV/Oe.cm) was obtained in the composite containing 50% highly magnetostrictive ferrite component NCCF – 50% highly piezoelectric ferroelectric component PZT. These multiferroic particulate composites are used as phase shifters, magnetic sensors, cables etc.     

Terahertz pulse driven Josephson junctions

The voltage response of a Josephson junction to a pulsed terahertz current is evaluated in the limit of a negligible junction capacitance (overdamped limit). The time-dependent superconductor phase difference across the junction is calculated in the framework of the standard resistive shunted junction model by using a perturbative method. The pulsed current bias affects the time average value of the voltage across the junction and current steps are induced in the current–voltage characteristics for voltage values depending on the pulse repetition rate. The current step height is proportional to the square of the pulse time width (τ) to the period (T) ratio. A fast response detector for pulsed Terahertz radiation is proposed, with an expected responsivity of the order of 0.1 V/W and an equivalent noise power of about 3 × 10^?10 W/Hz^1/2.     

Modified Lanthanum Zirconium Oxide buffer layers for low-cost,high performance YBCO coated conductors

The pyrochlore Lanthanum Zirconium Oxide, La₂Zr₂O₇ (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO₂ cap/YSZ barrier/Y₂O₃ seed on Ni–5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La₂O₃–ZrO₂ system. Using a metal–organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of La_xZr_1?xO_y (x = 0.2–0.6) on standard Y₂O₃ buffered Ni–5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2–0.6 in La_xZr_1?xO_y. Both CeO₂ cap layers and MOD–YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, I_c of 274–292 A/cm at 77 K and self-field were achieved for MOD–YBCO films grown on La_xZr_1?xO_y (x = 0.4–0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD La_xZr_1?xO_y (x = 0.25) films were grown directly on biaxially textured Ni–3W substrates. About 3 μm thick YBCO films grown on a single MOD–LZO buffered Ni–3W substrates using pulsed laser deposition show a critical current density, J_c, of 0.55 MA/cm² (I_c of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.     

Surface topographic study of chalcogenide thin films of GexSb(As)40−xS50Te10 glasses

The surface topography and fractal properties of Ge_xSb(As)_40−xS₅₀Te₁₀ (x = 10, 20, 27 at.%) films, evaporated onto glass substrates, have been studied by atomic force microscopic imaging at different scales. The surface of the chalcogenide films is smooth (<5 nm roughness), isotropic and having some particular differences in texture. All films are self-similar with Mean Fractal Dimension in the range of 2.25–2.63. The films with Ge_xSb_40−xS₅₀Te₁₀ composition are more uniform in terms of surface morphology (grains structure) than those with Ge_xAs_40−xS₅₀Te₁₀ composition for which the film surface exhibits a superimposed structure of large particles at x = 10 and 20 at.%.     

Influence of substrate temperature on physical properties of sprayed Zn0.85Mn0.15O films

Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 °C for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (0 0 2) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 °C and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ∼3.35 eV and the electrical resistivity was found to be high, ∼10⁴ Ω cm. The films deposited at higher temperatures (>350 °C) showed ferromagnetic behaviour at 10 K.     

Giant magnetoresistance in the Ge-rich magnetocaloric compound,Gd5(Si0.1Ge0.9)4

We have measured the zero-field electrical resistivity in the temperature range 5–295 K and magnetoresistance in magnetic fields of up to 12 T of Gd₅(Si_0.1Ge_0.9)₄. The resistivity changes drastically at the magnetostructural first-order transition (T_C≅80 K on heating). This transition can be induced reversibly by the application of an external magnetic field above T_C, producing a concomitant giant magnetoresistance (GMR) effect, Δρ/ρ≅−50%. This study demonstrates that (in addition to giant magnetocaloric and magnetoelastic effects) GMR can be tuned between ∼20 and ∼290 K in Gd₅(Si_xGe_1−x)₄ with x⩽0.5 by simply adjusting the Si : Ge ratio.     

Extraordinary fast oxide ion conductivity in La1.61GeO5−δ thin film consisting of nano-size grain

Thin films of La_1.61GeO_5−δ, a new oxide ionic conductor, were fabricated on dense polycrystalline Al₂O₃ substrates by a pulsed laser deposition (PLD) method and the effect of the film thickness on the oxide ionic conductivity was investigated on the nanoscale. The deposition parameters were optimized to obtain La_1.61GeO_5−δ thin films with stoichiometric composition. Annealing was found necessary to get crystalline La_1.61GeO_5−δ thin films. It was also found that the annealed La_1.61GeO_5−δ film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La_1.61GeO_5−δ thin films increased with the decreasing thickness as compared to that in bulk La_1.61GeO_5−δ. In particular, the improvement in conductivity of the film at low temperature was significant .The electrical conductivity of the La_1.61GeO_5−δ film with a thickness of 373 nm is as high as 0.05 S cm^− 1 (log(σ/S cm^− 1) = − 1.3) at 573 K.     

Synthesis of superhydrophobic PTFE-like thin films by self-nanostructuration in a hybrid plasma process

Superhydrophobic poly(tetrafluoro-ethylene) (PTFE) like thin films were grown on silicon wafers using a plasma-based hybrid process consisting on sputtering a carbon target in an Ar/CF₄ atmosphere. The influence of the bias voltage applied to the substrate (V_Bias) as well as of the gas mixture composition (%CF₄) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated.The chemical composition measured by X-ray Photoelectron Spectroscopy (XPS) has revealed that the F/C atomic ratio is always lower than for conventional PTFE (F/C = 2) and that it decreases when V_Bias increases (from F/C = 1 for V_Bias = ? 100 V to F/C = 0.75 for V_Bias = ? 200 V). This behavior is associated with the preferential sputtering of the fluorine atoms during the plasma-assisted growth of the films. Consecutively, a self-nanostructuration enhanced when increasing V_Bias is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine concentration and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCAs, a small hysteresis between the advancing and receding WCAs is observed (< 10°) allowing these films to fulfill completely the requirements of superhydrophobicity. The nanostructuration is probably due to the chemical etching by fluorine atoms of the fluorinated group.In order to get more understanding on the wettability mechanisms of these surfaces, the topography of the films has been evaluated by atomic force microscopy (AFM). The data have revealed, for all films, a dense and regular structure composed by conic objects (A_vH is their average height and A_vD is the average distance between them) for which the dimensions increase with V_Bias. A correlation between A_vH/A_vD, defined as the “morphological ratio”, with the WCA was established. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin film surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations.     

Ferroelectric polarization and resistive switching characteristics of ion beam assisted sputter deposited BaTiO3 thin films

In this work, 150 nm thick polycrystalline BaTiO₃ (BTO) films were deposited on Pt/TiO₂/SiO₂/Si substrate by ion beam assisted sputter deposition technique. The bias voltage dependent resistive switching (RS) and ferroelectric polarization characteristics of Au/BTO/Pt devices are investigated. The devices display the stable bipolar RS characteristics without an initial electroforming process. Fittings to current–voltage (I–V) curves suggest that low and high resistance states are governed, respectively, by filamentary model and trap controlled space charge limited conduction mechanism, where the oxygen vacancies act as traps. Presence of oxygen vacancies is evidenced from the photoluminescence spectrum. The devices also display P–V loops with remnant polarization (P_r) of 5.7 μC/cm² and a coercive electric field (E_c) of 173.0 kV/cm. The coupling between the ferroelectric polarization and RS effect in BTO films is demonstrated.