Fabrication and characteristics of La,Cd and Sn doped BST thin films by sol–gel method

Ba_1−x Sr _x TiO₃ (BST) thin films doped with La, Cd and Sn were prepared by sol–gel method on the Pt/Ti/SiO₂/Si substrate. X-ray diffraction analysis and atomic force microscopy showed that dopant La and Cd causes decreased grain size of BST thin films obviously, and Sn-doped BST thin films was similar to BST films in grain size. La and Cd doped decreased the tunability of BST thin films and Sn doped increased it, which may be explained by stress, electronegativity and oxygen vacancies factors. All the doped BST thin films improved the leakage current characteristic.     

Structural characterization and thermally stimulated discharge conductivity (TSDC) study in polymer thin films

The electrical conductivity of naphthalene doped polystyrene (PS) films (≈61·58 μm thick) was studied as a function of dopant concentration and temperature. The formation of charge transfer (CT) complexes and strong concentration dependence of carrier mobility point out that the current carriers are transported through doped polymer system via hopping among sites associated with the dopant molecules. The activation energy, E _a, was calculated from the graph of log σ vs 10³/T plot within low and high temperature regions.     

Optical, structural and electrical properties of Mn doped tin oxide thin films

Mn doped SnO_x thin films have been fabricated by extended annealing of Mn/SnO₂ bilayers at 200°C in air for 110 h. The dopant concentration was varied by controlling the thickness of the metal layer. The overall thickness of the film was 115 nm with dopant concentration between 0 and 30 wt% of Mn. The films exhibit nanocrystalline size (10-20 nm) and presence of both SnO and SnO₂. The highest transmission observed in the films was 75% and the band gap varied between 2.7 and 3.4 eV. Significantly, it was observed that at a dopant concentration of ∼4 wt% the transmission in the films reached a minimum accompanied by a decrease in the optical band gap. At the same value of dopant concentration the resistivity also reached a peak. This behaviour appears to be a consequence of valence fluctuation in Sn between the 2+ and 4+ states. The transparent conductivity behaviour fits into a model that attributes it to the presence of Sn interstitials rather than oxygen vacancies alone in the presence of Sn^{2 +}.     

Electron diffraction study of TlGa<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>X<Subscript>2</Subscript> (X = S,Se, Te) nanofilms

The formation of thin TlGa_{1 − x} Ge _x X₂ (X = S, Se, Te) films has been studied by high-energy electron diffraction. The results demonstrate that the dopant (Ge) concentration influences the structure of the films (30 nm in thickness). The epilayer-substrate orientation relationships are identified.     

Structural and Optical Properties of Co-Doped ZnO Thin Films

Co-doped zinc oxide thin films (Zn_1–xCo_xO) have been deposited on c-plane sapphire substrates by dual-beam pulsed laser deposition. The films have lattice parameters similar to that of ZnO, and the lattice parameters are closely distributed. The films grew along a preferred direction, following the epitaxial relationship Zn_1–xCo_xO (0001)substrate (0001). Excitonic emission was suppressed at higher Co-dopant concentration in ZnO because of increase in the distortion of host lattice and defects. When more Zn is replaced by Co, more impurity levels are developed within the bandgap, and more defect are generated. Under our experimental conditions, the bandgap of the films tends to increase with increasing dopant concentration.     

Dielectric properties of doped polystyrene and polymethylmethacrylate

About 1 μm thick films of polystyrene (PS) and polymethylmethacrylate (PMMA) doped with diphenylsulfoxide (DS) up to 40 wt.% were prepared from solutions using spin-coating method. Glass transition temperature (T _g) of doped polymer films was determined by DSC technique. The depth profile and surface concentration of DS dopant were measured by RBS and XPS methods, respectively. The temperature dependence of relative permittivity of the films was determined from capacitance measurement. The dependence of polarization (P) on electric field (E) was measured using a standard Sawyer–Tower circuit. The glass transition temperature T _g of both composites was found to be decreasing function of the DS concentration. The DS doping leads to an increase of relative permittivity of the PS and PMMA films. RBS and XPS measurements reveal an outward diffusion of DS dopant in PS/DS films at elevated temperature. No such effect was observed in PMMA/DS films. PMMA/DS layers were found to be more thermally stable comparing to PS/DS.     

Preparation and properties of reactively co-sputtered transparent conducting films

The method of reactive co-sputtering was used to determine the optimum dopant concentration for low resistivity In₂O₃/SnO₂ and SnO₂/Sb₂O₅ films. The optimum concentration of SnO₂ in In₂O₃ was approximately 10 mol. % and of Sb₂O₅ in SnO₂ about 7 mol. %. The resistivity increased sharply at lower dopant concentrations but changed only slightly at higher dopant concentrations. The lowest resistivity for reactively sputtered highly transparent In₂O₃/SnO₂ films was 1.5 × 10^-3 Ω cm and for SnO₂/Sb₂O₅ films 3 × 10^-3 Ω cm. Reactively sputtered In₂O₃/SnO₂ films show a strong (111) texture and have an extremely smooth surface.     

A novel method of introducing PbO dopant and (the study of) its influence on the electrical properties of semiconducting Cd2−x Pb x SnO4 thick films

The sheet resistance of Cd₂SnO₄ thick films was reduced from 15580 to 0.09 k with respect to dopant concentration and peak firing temperature (600 to 900° C). Distinct colour changes were observed in these films. The inorganic binder introduced an impurity which greatly induce changes in its electrical properties. The Arrhenius relation (logR–10³/T) generally indicated slopes of 2 to 3 for all the compositions of Cd_2–x Pb _x SnO₄ (x=0.002, 0.01, 0.02, 0.04 and 0.1). The donor ionization energies (E _d) varied from 0.01 to 0.76 eV. Resistance measurements during heating-cooling cycles indicated the possible presence of structural defects such as oxygen vacancies and cadmium interstitials. The oxidation of dopant (Pb²⁺Pb⁴⁺+2e) contributed in a major way to the overall conductivity. Scanning electron micrographs showed a progressive network formation due to sintering, thus contributing to the carrier mobility.     

Oxygen diffusion and defect mechanism in c-axis textured thin films of YBa2Cu3O7−x by resistivity measurements

Isothermal resistivity measurements have been carried out to study the dynamics of oxygen out- and in-diffusion in thin films of YBa₂Cu₃O_7−x in the temperature range 648–773 K. The activation energies for the out- and in-diffusion were determined to be 1·36 and 0·7 eV respectively. We have modelled the resistance-time plots for the oxygen in-diffusion using an equation for one dimensional diffusion into a plane. The microstructural defects such as low angle grain boundaries associated with the c-axis oriented grains are believed to provide the required diffusion paths in thin films of YBCO.     

Microwave surface impedance of YBa2Cu3O7?x:S-wave versusD-wave pairing

The low temperature behavior of the microwave surface resistanceR _s and the penetration provides information on the pairing state. Fully oxygenated films with low de-resistivity in the normal state exhibit an exponential temperature dependence corresponding to values of the energy gap up to 10 meV. For oxygen deficient films a linearR _s(T) was observed, similar to single crystals. This can be explained qualitatively by induced superconductivity in the copper-oxygen chains.     

Effect of Zr (IV) doping on the optical properties of sol–gel based nanostructured indium oxide films on glass

Zr (IV) doped indium oxide thin films (55 nm) were deposited onto pure silica glass by the sol–gel dip coating technique utilizing the precursors of 6 wt% equivalent oxide content. Three different Zr (IV) oxide (ZrO₂) dopant concentrations (5.0, 10.0 and 15.0 wt% w.r.t. total oxides) were chosen. XRD patterns suggested the films were of distinct cubic symmetry of In₂O₃. Nanostructured surface feature was revealed by FESEM images. Average cluster size decreased with increasing dopant concentration as evidenced from TEM study. Blue shift of band gap and UV cut off wavelength (lambda-50) occurred with increase in dopant concentration. The refractive index gradually increased with doping. Baking atmosphere plays an important role in tailoring the refractive index (RI) of the films and relatively high RI was obtained in the case of baking in pure oxygen. Presence of both free and bound excitons was detected by the photoluminescence (PL) study. The 5 wt% doped film exhibited relatively high PL intensity at 380 nm responsible for free exciton. The PL emissions gradually quenched with increase in dopant concentration. Similar behaviour was also observed when the film was baked in pure oxygen atmosphere.     

Microstructural properties of ZnO:Sn thin films deposited by intermittent spray pyrolysis process

Zinc oxide films have been prepared via spray pyrolysis using a perfume atomizer. ZnCl₂ has been used as precursor. The influence of the precursor solution and dopant concentration has been investigated. Homogeneous films are obtained with a precursor concentration ranging between 0.3 and 0.4 M and a SnCl₂ dopant concentration of 1–2%. The films exhibit broad band gaps and small conductivity. The microstructural properties of these films have been compared with that of films deposited using a classical nozzle. Films deposited by perfume atomizer are rougher, with smaller grain size, compared to films deposited with a classical nozzle.     

Effect of oxygen intercalation on properties of sputtered CuYO<Subscript>2</Subscript> for potential use as <Emphasis Type="Italic">p</Emphasis>-type transparent conducting films

Transparent films of copper yttrium oxide doped with 2% calcium have been prepared by rf magnetron sputtering. The films show a conductivity of 8 Scm⁻¹ on intercalation of oxygen at high pressure, which reduced the transparency in the visible region. The Ca-doped CuYO₂ films before oxygen intercalation show an average transmission of about 60% which reduces to about 45% upon oxygen intercalation. The temperature dependence of the conductivity indicates semiconductor behaviour with low activation energy of 0·59 eV at room temperature. The positive sign of Seebeck coefficient (+274 μVK⁻¹) confirms the p-type conductivity of the films. The optical bandgap of CuYO₂ was found to be 3·15 eV.     

High transmittance–low resistivity cadmium oxide films grown by reactive pulsed laser deposition

High transmittance, low resistivity, and highly oriented cadmium oxide thin films were prepared by pulsed Nd:YAG laser ablation of Cd target in the presence of oxygen as reactive atmosphere. The structural, optical, and electrical properties of CdO films were dependent on the background oxygen pressure PO₂. The XRD data show that the grown CdO film at 350 Torr oxygen pressure exhibited preferential orientation along (111) crystal plane. The average transmittance of the CdO films in the visible region was found to be in the range of 65–85% and the corresponding optical energy gap found to be in the range of 2.5–2.8 eV depending on oxygen pressure. The lowest electrical resistivity was found to be 7.56 × 10⁻³ Ωcm for CdO film prepared at 350 Torr of oxygen ambient without using post-deposition heat treatment.     

Spectroscopic study of Co-doped BaTiO3 thin films

Co-doped BaTiO₃ thin films with the perovskite structure were prepared by pyrolysis of metalorganic compounds. According to optical-absorption and luminescence data, the introduction of Co had an insignificant effect on the Curie temperatureT _C of the films (about 120δC), presumably because of the competitive effects of the Co dopant, reducingT _C , and the large compressive strain due to the thermal expansion mismatch, raisingT _C . An absorption band tentatively attributed to a small-radius polaron was observed in the near-infrared spectral region.     

Oxygen incorporation duringin situ growth of YBCO films on both sides of substrates

Oxygen out-diffusion during cooling and heating ofin situ grown {ie685-1} (YBCO) films in low oxygen pressure used during growth by pulsed laser deposition was studied in the temperature range 700−450°C usingin situ resistance measurements. Results indicate that irrespective of the number of cooling and heating cycles seen by the films, full oxygenation of the films can be realized by the final cooling from the growth temperature in 500 torr oxygen pressure. This result has been successfully used to sequentially grow high quality YBCO films on both sides of LaAlO₃ substrates. These films have been used for the fabrication of X-band microstrip resonators with superconducting ground plane.     

Characterization of boron nitride films deposited from BCl3-NH3-H2 mixtures in chemical vapour infiltration conditions

Boron nitride (BN) thin films deposited by isopressure and isothermal chemical vapour infiltration (ICVI) from BCl₃-NH₃-N₂ mixtures have been characterized from a physicochemical point of view as functions of both the deposition conditions and the destabilizing action of moisture. As-deposited (deposited at 773 K and post-treated at 1273 K), the BN films are turbostractic (d _{0 0 2}=0.36 nm, L _c=1.5 nm), have a low density (1.4 g cm^–3) and contain oxygen (about 20 at%). A first oxygen content (191.5 eV by XPS) is inserted in the films during the CVI step in relation to the hygroscopy of intermediate solid products and the quasi-equilibrium between the formation of BN and B₂O₃. A second oxygen content (192.5 eV) is due to the hydrolysis of BN by moisture which induces a very drastic transformation of BN. This destabilization affects both boron and nitrogen atoms and leads to the formation of ammonium borate hydrates. Different post-treatments have been investigated to stabilize the BN films and it appears that nitriding under ammonia is the most efficient.     

Combinatorial synthesis and sputter parameter optimization of chromium-doped yttrium aluminum garnet photoluminescent thin films

Chromium-doped Y₃Al₅O₁₂ or YAG thin films emitting at 688 nm due to the ⁴A₂-⁴E₂ transition were synthesized in a combinatorial fashion using reactive sputtering approach. Multilayer YAG and Cr thin films were sputter deposited with a gradient in the Cr thickness and subsequently annealed to diffuse the Cr dopant into the YAG matrix. The combinatorial thin film sputtering technique was used to rapidly determine that ∼ 0.69 at.% is the optimum chromium concentration for maximum photoluminescence (PL) intensity in YAG. This result was consistent with previous work in YAG:Cr powders. Design of experiments was conducted to determine the effects of various sputter parameters, namely, substrate bias, substrate temperature and oxygen flow rate on PL intensity and crystallinity of co-sputter deposited Cr-doped YAG thin films. The optimum sputtering condition consisted of high substrate bias and low oxygen flow rate and was independent of substrate temperature. The PL temperature dependent behavior of YAG:Cr film was also investigated. Thermal quenching was observed at ∼ 110 K where the total integrated PL emission intensity was found to rapidly decrease. A non-radiative activation energy of 25.2 meV was determined and is attributed to electron-phonon coupling.     

Characterization of bi-phased Zr2ON2–ZrO2 coatings deposited by RF magnetron sputtering

The aim of this work is to develop zirconium oxynitride coatings by RF magnetron sputtering on silicon substrates. The film properties were analyzed as a function of oxygen flux percentage in two different inert gas atmospheres namely argon and helium. At low oxygen flux percentage, Zr₂ON₂ and ZrO₂ phases are observed from the structural characterization by X-ray diffraction. The atomic ratio of nonmetallic to metallic atoms (N + O)/Zr content varies from 1.22 to 2.03 for zirconium oxynitride films deposited in argon atmosphere and from 1.43 to 2.33 for films deposited in helium atmosphere. The thickness of the film was measured by surface profiler and the growth rate decreases from 11.33 to 5.1 nm/min for films deposited in argon atmosphere and from 7.01 to 3.75 nm/min for films deposited in helium atmosphere with increase in oxygen flux percentage. The films deposited are hydrophobic and the contact angle was measured by contact angle measuring system. Higher surface roughness and maximum contact angle values of 100° and 103° are observed for films deposited in argon and helium atmosphere respectively at low oxygen flux percentage (2.5%). The surface energy of films was calculated by two methods: Owens-Wendt's geometric mean and Wu's harmonic mean approach. The elevated surface energy values were observed with increase in oxygen flux percentage. The stress measurements of the deposited films were done by sin²ψ X-ray diffraction method which depends on the variation of Zr₂ON₂ and m-ZrO₂ phases.     

Structural and optical properties of indium tin oxide (ITO) thin films with different compositions prepared by electron beam evaporation

Tin-doped Indium oxide thin films in different compositions (Sn = 0,5,10,15,20 at.wt%) were prepared on glass substrates at the substrate temperature of 250 °C in an oxygen atmosphere by electron beam evaporation. The structural and morphological studies were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grain size of the ITO films decreased when increasing the dopant concentration of Sn in the In₂O₃ lattice. Optical properties of the films were studied in the UV-Visible-NIR region (300-1000 nm). The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths was found to increase from 3.61 to 3.89 eV revealing the ascending loading profile of dopant concentration. Optical Parameters, such as absorption depth, refractive index (n), extinction coefficient (k), packing density, porosity, dispersion energy and single effective oscillator energy were also studied to show the composition dependence of tin-doped indium oxide films.