Crystallization kinetics of V2AlC

X-ray amorphous V₂AlC and hexagonal (V,Al)₂C_x thin films were synthesized by magnetron sputtering from a compound target with the composition of V₂AlC. The crystallization kinetics was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). During continuous heating up to 1200 °C, one exothermal peak is observed between 565 and 675 °C. XRD data suggest that the DSC peak is associated with the formation of V₂AlC. The activation energy of crystallization of V₂AlC is ~ 308 kJ/mol based on the Kissinger approach. This value is close to the 287 kJ/mol activation energy obtained here for the transformation of magnetron sputtered (V,Al)₂C_x thin films to V₂AlC. The here reported phase formation temperature of V₂AlC is about 800 °C lower than during hot pressing of elemental powders.     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

Growth and Raman scattering characterization of Cu2ZnSnS4 thin films

In the present work we report the results of the growth, morphological and structural characterization of Cu₂ZnSnS₄ (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence of the sulfurization temperature on the morphology, composition and structure of the films has been studied. With the presented method we have been able to prepare CZTS thin films with the kesterite structure.     

Current noise in MgB2 superconducting thin films

In this paper we present some experimental results concerning the current noise produced during the resistive transition in MgB₂ thin films. Preliminary investigations evidenced the presence of electrical noise whose power spectrum has a region of the 1/fⁿ type with n 3. We suggest that the noise may originate from abrupt rearrangement of the current distribution inside the specimen during the percolative process of a diphasic system. Experimental measurements of the spectral components of the current noise taken during the resistive transition will be given and discussed.     

Synthesis and characterization of p-type transparent conducting CuAlO2 thin film by DC sputtering

P-type transparent conducting thin films of copper aluminium oxide were prepared by DC sputtering of polycrystalline CuAlO₂ target, which was fabricated by heating a stoichiometric mixture of Cu₂O and Al₂O₃ at 1375 K for 24 h. Thin films of CuAlO₂ were deposited on Si (4 0 0) and glass substrates. The sputtering was performed in Ar+O₂ (40 vol.%) atmosphere and the substrate temperature was 453 K. X-ray diffraction spectra of the films showed the peaks that could be assigned with those of the crystalline CuAlO₂. Fourier transform infrared spectra showed Cu---O, Al---O, O---Cu---O bonding. UV–Vis–NIR spectrophotometric measurement showed high transparency of the films in the visible region. Both direct and indirect band gaps were found to exist and their corresponding estimated values were 3.66 and 2.1 eV, respectively. The room temperature conductivity of the film was fairly high and was of the order of 0.08 S cm⁻¹, while the activation energy was 0.26 eV. Thermoelectric power measurement indicated positive value of Seebeck coefficient and its room temperature value was +128 μV K⁻¹. Positive value of Hall coefficient (R_H=+16.7 cm³ C⁻¹) also confirmed p-type conductivity of the films.     

Fabrication and characterization of Fe3O4 thin films deposited by reactive magnetron sputtering

Fe-O thin films with different atomic ratio of iron to oxygen were deposited on glass and thermally oxidized silicon substrates at temperatures of 300, 473 and 593 K, by reactive magnetron sputtering in Ar+O₂ atmosphere. The composition and structure of the thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrical resistivity. It was found from XRD that with increasing the oxygen partial pressure in the working gas, the crystalline structure of the Fe-O films deposited at the substrate temperature of 473 K gradually changed from α-Fe, amorphous Fe-O, Fe₃O₄, γ-Fe₂O₃ to Fe_21.34O₃₂. The structure and chemical valence of the Fe₃O₄ films were analyzed by electron microscopy and XPS, respectively.     

Synthesis and characterization of boron-oxygen-hydrogen thin films at low temperatures

We have studied the influence of synthesis temperature on chemical composition and mechanical properties of X-ray amorphous boron-oxygen-hydrogen (B-O-H) films. These B-O-H films have been synthesized by RF sputtering of a B-target in an Ar atmosphere. Upon increasing the synthesis temperature from room temperature to 550 °C, the O/B and H/B ratios decrease from 0.73 to 0.15 and 0.28 to 0.07, respectively, as determined by elastic recoil detection analysis. It is reasonable to assume that potential sources of O and H are residual gas and laboratory atmosphere. The elastic modulus, as measured by nanoindentation, increases from 93 to 214 GPa, as the O/B and H/B ratios decreases within the range probed. Hence, we have shown that the effect of impurity incorporation on the elastic properties is extensive and that the magnitude of the incorporation is a strong function of the substrate temperature.     

Normal metal, ohmic contacts to high-temperature superconducting YBa2Cu3O7-δ thin films suitable for multichip modules

Normal metal, ohmic contacts to high-temperature superconductor (HTSC) materials will be used to form via structures between HTSC interconnect levels, and also, substrate bonding pads in a superconducting multichip module (SMCM). Specific contact resistivities below 10⁻⁸ Ω cm² will be required for such contacts to control signal attenuation and local contact heating of the LN₂cooled SMCM. Previous work on normal metal/superconducting contacts has not focused on metallization schemes which will be stable during subsequent high-temperature processing. Metal contacts of gold, silver, and palladium were formed on superconducting thin films of YBa₂Cu₃O_7-δ via evaporation and sputtering through a shadow mask followed by annealing in various ambients and at several temperatures. Palladium contacts oxidized readily during anneal, and sputtered gold contacts required additional processing and exhibited higher specific contact resistivities. The best contacts were obtained by a controlled-cooling oxygen anneal of evaporated gold or silver, as indicated by normal-state specific contact resistivities of 3 × 10⁻⁵ Ω cm² and 4 × 10⁻⁵ Ω cm², respectively. This work differs from previously published results by describing contacts which required no extensive preparation of the HTSC surface and were stable to 700 °C, indicating these contacts would be compatible with subsequent high-temperature processing of the additional HTSC layers required in a multi-level SMCM.     

Strain analysis of photocatalytic TiO2 thin films on polymer substrates

Titania (TiO₂) thin films have been deposited on polymer sheets by magnetron sputtering at room temperature. Previous X-ray diffraction experiments revealed, for a wide range of deposition parameters, that the as-deposited titania thin films are predominantly amorphous; however, Raman scattering experiments revealed small traces of crystalline phases. The photocatalytic behaviour of the titania coatings was determined by combined ultra-violet (UV) irradiation and absorption measurements of a chosen dye (pollutants) in the presence of this catalyst. In order to assess the mechanical behaviour of the as-sputtered films, the film/substrate composite system was loaded unidirectionally using a tensile testing machine. As the system was stretched, cracks transverse to the loading direction developed in the film. The number of cracks increased as the applied strain increased, thus the relation between the measured crack density and the applied strain has been used to characterize the film strength and has also been correlated with the film photocatalytic efficiency. As a result of moderate fissuring on the titania film, it was found that for strain deformations up to 5% the photocatalytic activity is enhanced due to the exposure of more catalyst surface area for the pollutant to be adsorbed and subsequently dissociated upon UV illumination.     

Point contact investigation on Bi2Sr2CaCu2O8+y thin films

We have measured point contacts with a gold tip on Bi₂Sr₂CaCu₂O_8+y thin films and Bi₂Sr₂CaCu₂O_8+y/SrTiO₃ double layers. The results show tunneling or direct conductivity behaviour depending on the junction parameters and can be fitted by corresponding theoretical models. From fitting procedure of differential characteristics by modified Blonder-Tinkham-Klapwijk (BTK) theory the Fermi velocity v_F=5×10⁵ m/s, ratio 2(4.2K)/kT_c=7.9 and coherence length _ab=3.5 nm were obtained. The changing of the interface transmission by additional layers of different thickness corresponding to metallic or insulating behaviour is shown. In the frame of the inelastic scattering of quasiparticles the linear background of differential conductance is discussed.This work was supported by German BMFT under Contract No.l3N5924A and Slovak Grant Agency for Sciences (Grants Nos. 2/990125/93 and 2/999185/92).     

Composition, structure and optical properties of sputtered thin films of CuInSe2

Thin films of copper indium selenide (CuInSe₂) were produced by radio frequency (RF) sputtering due to the ability of this technique to achieve stoichiometric layers and its scalability to large-area devices. Results of energy dispersive analysis of X-rays (EDAX) revealed that the sputtered films were near to stoichiometry for substrate temperatures T_Sub not exceeding 200 °C. X-ray diffraction (XRD) patterns indicate that the films exhibited some pattern similar to that of bulk crystals of tetragonal chalcopyrite, predominantly [112] oriented. Based on the XRD patterns, the lattice parameters and grain sizes were examined. The band gap E_g, estimated from optical absorption data, was between 0.6-1.08 eV, depending on sputtering conditions such as substrate temperature and bias voltage. High optical absorption coefficients (> 10⁴ cm^− 1) were found.     

Hydrophilicity of anatase TiO2/Cr-doped TiO2 thin films with different band gaps

Based on the concept that the electron-hole separation effect caused by a different band-gap structure would improve its hydrophilicity, anatase-TiO₂/Cr-doped TiO₂ thin films were synthesized by DC magnetron sputtering. The optical band gaps of TiO₂ thin films decreased from 3.23 to 2.95 eV with increasing Cr-doping content. Multilayer TiO₂ thin films with different band gaps exhibited a superhydrophilicity under UV illumination. In particular, in anatase TiO₂ (3.23 eV)/4.8% Cr-doped TiO₂ (2.95 eV), the hydrophilicity, which indicated a contact angle of less than 20°, lasted for 48 h in the dark after UV illumination was discontinued. This outstanding result has rarely been reported for TiO₂ thin films, which confirmed that the prominent superhydrophilicity of anatase TiO₂/Cr-doped TiO₂/glass could be attributed to the retardation of electron-hole recombination caused by the band-gap difference.     

Hydrophilicity on carbon-doped TiO2 thin films under visible light

Carbon-doped TiO₂ thin films in the anatase phase with dopant concentrations of 1.1, 0.9, and 0.7 mol% were fabricated by a radio-frequency magnetron sputtering method. Dopant carbons were located at the oxygen sites. Carbon substitution caused the absorbance edge and/or the shoulder of TiO₂ to shift to a higher wavelength region. Carbon-doped TiO₂ thin films underwent a hydrophilic conversion when irradiating with visible light (400–530 nm). The hydrophilic property under visible light was inferior to that under ultraviolet light, which is explained by considering that the visible light sensitivity originates from the localized C 2p formed in the band-gap.     

Nanocrystalline SnO2 and Au:SnO2 thin films prepared by direct current magnetron reactive sputtering

Nanocrystalline pure and gold doped SnO₂(Au:SnO₂) films were prepared on unheated glass substrates by dc magnetron reactive sputtering and, subsequently, the as deposited films were annealed in air. The films structure, surface morphology, photoluminescence, electrical and optical properties were investigated. After annealing the as deposited SnO₂ films, crystallinity increased and the surface roughness decreased. The intensity of PL peaks increases sharply with the annealing temperature. The optical transmittance of the films was around 89% after annealing the as deposited SnO₂ films at 450 °C. The as deposited Au:SnO₂ films show better crystallinity than the as deposited SnO₂ films, the average grain size was around 4.4 nm. The emission peaks of Au:SnO₂ films are slightly blue shifted as compare to undoped SnO₂ films. The Au:SnO₂ films show the lowest electrical resistivity of 0.001 Ωcm with optical transmittance of 76%, after annealing at 450 °C.     

Substrate and Fe-doping effects on the hydrophilic properties of TiO2 thin films

Titanium dioxide films are known for their hydrophilic and photocatalytic characteristics. Increasing specific surface area and doping can enhance their photocatalytic activity and hydrophilicity. We report here results regarding the enhancement of the photocatalytic properties of titania by both controlling surface morphology and the anatase/rutile ratio. The samples were deposited on glass, indium tin oxide covered glass, and SrTiO₃ by sputtering and laser ablation techniques. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. Film hydrophilicity was assessed from contact angle measurements during- and post-irradiation with UV light. The contact angle data are discussed in terms of the synergic effects of surface morphology, structure and composition of the films.     

Microanalysis of Pd and V-doped TiO2 thin films prepared by sputtering

Thin films of TiO₂ doped with vanadium and palladium, prepared by the magnetron sputtering method, were studied by means of X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Disperse Spectrometer (SEM-EDS) and Atomic Force Microscopy (AFM). Investigations have brought important information about microstructure due to dopant incorporation in the TiO₂ host lattice. Directly after deposition thin films were XRD-amorphous and SEM investigations did not reveal details on the microstructure. Analysis of the topography of prepared thin films required application of Atomic Force Microscope. The AFM images show that as-deposited sample was dense with grain sizes varied in the range of 5.5 nm-10 nm, that indicated high quality nanocrystalline behavior. Additional annealing results in the formation of three phases in the thin film, e.g. (Ti,V)O₂ — solid solution, PdO and metallic inclusions of Pd. SEM-EDS system allowed analysis of the elemental composition, especially the V one, which lines have not been evidenced in the XRD diffraction pattern. EDS maps show homogenous distribution of elements Ti, O, V, Pd in prepared thin films.     

Preparation and characterization of Al2O3-Ti3SiC2 composites and its functionally graded materials

Alumina/titanium silicon carbide (Al₂O₃-Ti₃SiC₂) composites and its functionally graded materials (FGMs) were fabricated by a powder metallurgy processes and their microstructure and properties were investigated, respectively. The experimental results showed that the Vickers hardness of composites decreased with increasing Ti₃SiC₂ content while the fracture toughness and strength exhibited the opposite trend. Minimum Vickers hardness (4 GPa), maximum strength (598 MPa) and maximum toughness (11.24 MPa m^1/2) were reached in the pure Ti₃SiC₂ material. Strength and hardness of FGMs were evaluated. Observation using an scanning electron microscope (SEM) indicated that the presence of Ti₃SiC₂ of FGMs inhibited the growth of alumina grains through a pinning mechanism. The study shows that the combination of the layered Ti₃SiC₂ structure and the fine alumina grains can result in a Al₂O₃-Ti₃SiC₂ composites possessing a high toughness and low Vickers hardness without a sacrifice in the strength.     

Crystallographic properties of four-fold grain K3Li2Nb5O15 thin films

The structural properties of a potassium lithium niobate (KLN; K₃Li₂Nb₅O₁₅) thin film deposited by rf-magnetron sputtering on a Pt/Ti/SiO₂/Si(100) substrate were investigated. The crystalline structures of the Pt under layer and KLN thin films were examined using θ-2θ, θ-rocking, and mesh scan X-ray diffraction (XRD). The XRD results revealed that the Pt under layer was a strong (111) direction orientated poly crystal. Unlike the Pt under layer film, the KLN(001) peak was found to consist of two separate peaks, one with a broad full width half maximum (FWHM) and the other with a narrow FWHM, indicating that the KLN film had a single crystalline structure. The surface and cross-section morphology were investigated using a scanning electron microscope (SEM). Accordingly, from the results of the SEM and XRD experiments, it was concluded that the KLN film was composed of small single crystals, which had a four-fold symmetry morphology with a c-axis normal to the substrate.     

Synthesis and characterization of Cr2AlC ceramics prepared by spark plasma sintering

The investigation of bulk Cr₂AlC ceramic fabricated by Spark Plasma Sintering (SPS) from coarse powders (CAC10) and fine powders (NCAC10) in the temperature range of 1100-1400 °C was carried out. The XRD results indicate that Cr₂AlC, as major phase, always appears with minor and trace amount of Cr₇C₃ and Cr₂Al respectively in both NCAC10 and CAC10 samples and the amounts of later two phases decrease with increase in temperature. However, the Cr₂AlC phase content in NCAC10 is higher than that of CAC10 sintered at the same temperature. The micrographs of back-scattered SEM show that grains with smaller size and pores with fewer amounts appear in SPSed NCAC10 in comparison to that of CAC10. As consequence, the higher hardness (5.6 GPa) of NCAC10 than that (3.9 GPa) of CAC10 was obtained. The patterns of XRD, microstructure and hardness of samples HPed at 1400 °C for the same composition were also presented for comparison.     

On the existence of a nanometric multilayered structure in Al2O3/Al thin films

Al₂O₃/Al films (period thickness Λ=20, 40 nm) were deposited onto (1 0 0) silicon substrate by reactive r.f. sputtering for substrate temperatures (T_s) ranging from −90 to 600 °C. Secondary ion mass spectrometry demonstrated the deposition of Al₂O₃/Al stratified thin films with the generation of periodic signals. X-ray reflectometry confirmed the periodicity with the presence of Bragg peaks in the experimental patterns. Nevertheless, the multilayered character of Al₂O₃/Al films is less and less pronounced as T_s increases. At low T_s, the relevant parameter to account for the absence of abrupt interfaces is the roughness of layers due to the aluminium layers, while at high T_s, the chemical interdiffusion clearly dominates.