Effect of copper-oxide segregation on the dielectric properties of CaCu3Ti4O12 thin films fabricated by pulsed-laser deposition

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO₂/SiO₂/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 °C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (∼ 20 °C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, ε_r, of CCTO thin films deposited at 750 °C with severe surface segregation (ε_r ∼ 750 at 10 kHz) was found to be much lower than that (ε_r ∼ 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries.     

Pulsed laser ablated off-stoichiometric thin films of the Heusler alloy Co2TiSn on Si (100) substrate

We report the growth of thin films of ferromagnetic Heusler alloy Co₂TiSn on Si (100) substrate using KrF excimer pulsed laser ablation. Films of thicknesses ranging from 8 to 220 nm were deposited on Si (100) substrate heated up to 200 ± 10 °C, with an aim to study the structural, morphological and magnetic properties. The grown films are off-stoichiometric, polycrystalline, having single-phase with high degree of (220) texturing. Angle dependent fluorescence measurements suggest no segregation of alloying elements as a function of depth. X-ray reflectivity measurements indicate that all the films are having low density layer at the top as well as at the film-substrate interface. Magneto optical Kerr effect measurements at room temperature reveal clear hysteresis loops suggesting ferromagnetic behavior of the films. Thermal annealing at temperature ≥ 220 °C suggest transformation of Co₂TiSn phase into cobalt silicide phase, which confirms the necessity of low substrate temperature (< 220 °C) to produce such single-phase Co₂TiSn films.     

Phase separation in Ga and N co-incorporated ZnO films and its effects on photo-response in photoelectrochemical water splitting

Ga and N co-incorporated ZnO thin films [ZnO:(Ga:N)] with reduced bandgaps were deposited by co-sputtering at different N₂ gas flow rate in mixed N₂ and O₂ ambient at room temperature followed by postannealing at 500 °C in air for 2 h. We found that all of the ZnO:(Ga:N) films exhibited enhanced crystallinity which can suppress the recombination rate between the photogenerated electrons and holes. However, phase segregation of Zn₃N₂ occurred in ZnO:(Ga:N) thin films in nitrogen-rich sputtering ambient. We found that ZnO:(Ga:N) thin films without phase separation of Zn₃N₂ exhibited much better photoelectrochemical (PEC) response, due to the reduced bandgap and better crystallinity. Our results suggest that growth conditions must be controlled carefully to avoid phase separation in Ga and N co-incorporated ZnO thin films to improve PEC response.     

Electrical characteristics of mixed Zr-Si oxide thin films prepared by ion beam induced chemical vapor deposition at room temperature

Mixed Zr-Si oxide thin films have been prepared at room temperature by ion beam decomposition of organometallic volatile precursors. The films were flat and amorphous. They did not present phase segregation of the pure single oxides. A significant amount of impurities (-C-, -CH_x, -OH, and other radicals coming from partially decomposed precursors) remained incorporated in the films after the deposition process. This effect is minimized if the Ar content in the O₂/Ar bombarding gas is maximized. Static permittivity and breakdown electrical field of the films were determined by capacitance-voltage and current-voltage electrical measurements. It is found that the static permittivity increases non-linearly from ~ 4 for pure SiO₂ to ~ 15 for pure ZrO₂. Most of the dielectric failures in the films were due to extrinsic breakdown failures. The maximum breakdown electrical field decreases from ~ 10.5 MV/cm for pure SiO₂ to ~ 45 MV/cm for pure ZrO₂. These characteristics are justified by high impurity content of the thin films. In addition, the analysis of the conduction mechanisms in the formed dielectrics is consistent to Schottky and Poole-Frenkel emission for low and high electric fields applied, respectively.     

Structural characterization of the (AgCu)(InGa)Se2 thin film alloy system for solar cells

A detailed structural analysis of the (AgCu)(InGa)Se₂ thin film alloy system was undertaken via X-ray diffraction in order to determine its phase behavior and the chalcopyrite phase lattice constants of the alloy system. Thin films were grown by elemental co-evaporation with time-invariant flux, for the compositions 0 ≤ [Ag]/([Cu] + [Ag]) ≤ 1 for fixed [Ga]/([In] + [Ga]) = 0.5. Lattice constants were determined from the diffraction patterns by the Cohen method and were found to deviate from Vegard's rule. While films were predominantly single-phase, minor secondary phase reflections were observed for films with [Ag]/([Cu] + [Ag]) ≥ 0.5. However, this secondary phase behavior is not consistent with chalcopyrite-chalcopyrite phase segregation in earlier reports.     

Nanograins dependent dielectric constant, tunability, phase transition, impedance spectroscopy and leakage current of (Pb1 − xSrx)TiO3 thin films

Nanostructured (Pb_1 − xSr_x)TiO₃ (PST) (x = 0.1, 0.2 and 0.3) thin films have been prepared by chemical solution deposition process using spin coating technique. The solution as such was deposited on Pt/Ti/SiO₂/Si substrates and annealed at 650 °C/3h. Nanograins dependent dielectric properties of PST films show dielectric constant up to the higher frequency region, low losses, large tunability and phase transition at small temperature. The impedance data has been fitted by Cole-Cole model to study the effect of grain boundaries on the dielectric properties. The current-voltage characteristics have been measured to study leakage current in PST films and described by Poole-Frenkel emission model. It is suggested that the key carrier transport process in PST films is emission of electrons from a trap state near the metal-film interface into a continuum of states associated with each conductive dislocation. The activation energy value for carrier transport in PST films is obtained from temperature-dependent current-voltage characteristics.     

Electrical and optical properties of nanocrystalline yttrium-doped hafnium oxide thin films

Yttrium-doped hafnium oxide (YDH) films have been produced by sputter-deposition by varying the growth temperature (T_s) from room-temperature (RT) to 400 °C. The electrical and optical properties of YDH films have been investigated. Structural studies indicate that YDH films grown at T_s = RT − 200 °C were amorphous and those grown at 300-400 °C are nanocrystalline. The crystalline YDH films exhibit the high temperature cubic phase of HfO₂. Spectrophotometry analysis indicates that all the YDH films are transparent. The band gap of YDH films was found to be in the range of 6.20-6.28 eV. Frequency variation of frequency dependent resistivity indicates the hopping conduction mechanism operative in YDH films. While the electrical resistivity (ρ_ac) is ~ 1 Ω-m at low frequencies (100 Hz), ρ_ac decreases to ~ 10^− 4 Ω-cm at higher frequencies (1 MHz).     

Photoelectrochemical properties of nitrogen-doped indium tin oxide thin films prepared by reactive DC magnetron sputtering

Nitrogen-doped indium tin oxide (N-ITO) thin films are deposited on unheated ITO glass substrates in this study. The structural properties of the N-ITO thin films, determined by X-ray diffraction (XRD) and Raman scattering, show that the indium nitride (InN) phase is liable to form in N-ITO films prepared in 20% N₂. A broad XRD peak around 2θ = 33° and Raman peak around 490 cm^− 1 are assigned to the InN phase, but no such peak is observed from the ITO film. Hence, the bandgap is narrowed by N-doping for absorbing light of longer wavelengths of ~ 500 nm. However, under illumination by ultraviolet, the N-ITO film prepared in 20% N₂ exhibits the least photocurrent response, which is less than one third that of the N-ITO catalyst that was doped in 16.4% N₂. This result is attributed mostly to the fact that the valence and conduction band potentials are not positioned properly between the newly formed InN and host ITO phases, rendering inefficient inter-semiconductor electron transfer. Therefore, higher N-doped samples exhibit a lower photocurrent response. Interestingly, the N-ITO film prepared in 16.4% N₂ exhibits the highest photocurrent density of about 165.5 μA/cm² at an applied bias of 1.2 V. This implies that the N-ITO films should be prepared at a low N₂ ratio to ensure a favorable photoelectrochemical activity.     

Growth of Cu2ZnSnS4 thin films using sulfurization of stacked metallic films

We fabricated Cu₂ZnSnS₄ (CZTS) thin films through sulfurization of stacked metallic films. Three types of Cu-Zn-Sn metallic films, i.e., Cu-rich, Cu-correct and Cu-poor precursor films were sputtered onto Mo-coated glass. The sulfurization of stacked Cu-Zn-Sn alloy films was performed at a relatively high temperature, 570 °C, with S-powder evaporation. CZTS films from Cu-rich and Cu-correct precursors showed a Cu_2 − xS phase on the film surface, while CZTS films from Cu-poor precursors didn't show the Cu_2 − xS phase. However, all films didn't exhibit any extra secondary phase and exhibited good crystalline textures even with Cu-ratio differences in metallic precursor films. Fabricated CZTS films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman scattering measurements. SEM cross-section images of CZTS films showed that Cu-poor CZTS films were grown with more smooth film surface compared with other types of CZTS films.     

Superhydrophilicity of TiO2 thin films using TiCl4 as a precursor

TiO₂ thin films on soda lime glass were prepared by the sol-gel method and spin coating process using TiCl₄ as a precursor. The AFM images indicate that the surface morphology of the films is granular with 72 nm particle size. The roughness and thickness of the films are about 3 nm and 140 nm, respectively. The XRD spectrum shows polycrystalline anatase phase without any considerable impurity phase. The UV-vis spectroscopy of the films show 80-90% transmission in the visible region. The absorption edge is at 370 nm, which corresponds to 3.3 eV energy band gap. The films have a high superhydrophilicity character after being exposed to UV illumination for about 10 min. The surfaces, which were synthesized by this method, can retain their superhydrophilicity property for at least 24 h. Our results are consistent with the idea that UV-induced wetting of TiO₂ surface is caused by the removal of hydrophobic layers of hydrocarbons by TiO₂-mediated photooxidation, which leads to the attractive interaction of water with clean TiO₂ surface. TiO₂ thin films on Si(1 1 1), Si(1 0 0), and quartz substrates need less time than glass and polycrystalline Si substrates to be converted to superhydrophilic surface.     

Thermal stability of amorphous molybdenum trioxide films prepared at different oxygen partial pressures by reactive DC magnetron sputtering

Thin films of MoO₃ were prepared on quartz and Si (1 0 0) substrates by reactive dc magnetron sputtering of a Mo target in an oxygen and argon atmosphere. The structural and optical changes induced in the films due to post-growth annealing have been systematically studied by Rutherford backscattering (RBS), X-ray diffraction (XRD), X-ray reflectivity (XRR) and by optical methods. RBS studies reveal no change in composition of the films upon annealing at high temperatures. Grazing angle XRD studies show that the as-deposited films are amorphous and crystallize to β-MoO₃ phase with small contribution of α-MoO₃ upon annealing at 300 °C. The film prepared at 0.40 Pa transforms to α-MoO₃ upon annealing at 650 °C, while the film deposited at 0.19 Pa still has some β-MoO₃ phase contribution. XRR measurements reveal that the film thickness decreases upon annealing with simultaneous increase of film density. The surface roughness of the films strongly increases after crystallization. The contraction of the film deposited at 0.40 Pa is much greater than the contraction of the film prepared at 0.19 Pa. The mass variation of the film deposited at 0.19 Pa and that deposited at 0.40 Pa are completely different. The optical properties of MoO₃ films deposited at 0.19 and 0.40 Pa are changed strongly by annealing.     

Low temperature amorphous growth of semiconducting Y-Ba-Cu-O oxide thin films in view of infrared bolometric detection

YBa₂Cu₃O_6 + x (YBCO) compounds are well known to exhibit superconducting properties for x > 0.5 and semiconducting properties for lower oxygen content. In this work, YBCO oxide thin films of the semiconducting phase were deposited by direct-current (DC) hollow cathode sputtering at low temperature in the 100 to 400 °C range. Structural, electrical and optical properties are investigated and discussed in relation with the envisaged bolometric detection application. Structural characterizations show that films are amorphous, with a granular structure of low roughness (3 nm rms). DC electrical measurements both reveal that films grown at 100 °C exhibit a high temperature coefficient of resistance (TCR ~ − 3% K^− 1 to − 4% K^− 1 at 300 K) and an optimized low resistivity value of 345 Ω·cm at 300 K. Consequently, this material is suitable for uncooled infrared bolometer application and can be deposited at 100 °C in a complementary metal-oxide-semiconductor compatible technological process for co-integration with readout circuitry. In addition, optical measurements performed in the 0.5 to 2.2 μm wavelength range on films grown at 100 °C highlight optical conductivity values in line with those expected for YBCO material, as well as the presence of two optical band gaps that are discussed with respect to the film nanostructure.     

Synthesis of luminescent SrMoO4 thin films by a non-reversible galvanic cell method

Well-crystallized SrMoO₄ thin films were synthesized directly on a molybdenum substrate by a non-reversible galvanic cell method through 150 h electrochemical reaction at room temperature. The as-synthesized thin films are a single phase SrMoO₄ with a scheelite-type structure and show uniform and homogeneous surfaces. When excited by 290 nm ultraviolet ray at room temperature, the thin films emit the maximum peaks at 485 nm. The densification, chemical-physical and photoluminescence properties of the SrMoO₄ thin films synthesized by the non-reversible galvanic cell method are significantly improved.     

Tl2Ba2CaCu2O8 thin films on 2 in. LaAlO3(0 0 1) substrates

High quality Tl₂Ba₂CaCu₂O₈ (Tl-2212) superconducting thin films are prepared on both sides of 2 in. LaAlO₃(0 0 1) substrates by off-axis magnetron sputtering and post-annealing process. XRD measurements show that these films possess pure Tl-2212 phase with C-axis perpendicular to the substrate surface. The thickness unhomogeneity of the whole film on the 2 in. wafer is less than 5%. The superconducting transition temperatures T_cs of the films are around 105 K. At zero applied magnetic field, the critical current densities J_cs of the films on both sides of the wafer were measured to be above 2 × 10⁶ A/cm² at 77 K. The microwave surface resistance R_s of film was as low as 350 μΩ at 10 GHz and 77 K. In order to test the suitability of Tl-2212 thin films for passive microwave devices, 3-pole bandpass filters have been fabricated from double-sided Tl-2212 films on LaAlO₃ substrates.     

Epitaxial film growth of chromium dioxide by low pressure chemical vapor deposition using chromium carbonyl

Epitaxial chromium dioxide (CrO₂) thin films have been deposited by low pressure chemical vapor deposition (LPCVD) on (100) TiO₂ substrates using the precursor chromium hexacarbonyl (Cr(CO)₆) within a narrow temperature window of 380-400 °C. Normal θ-2θ Bragg x-ray diffraction results show that the predominant phase is CrO₂ with only a small amount of Cr₂O₃ present, mostly at the film surface. The LPCVD films have a reasonably smooth surface morphology with a root mean square roughness of 4 nm on a scale of 5 μm. Raman spectroscopy confirms the existence of rutile CrO₂ in the deposited films, while transmission electron microscopy confirms the single-crystalline nature of the films. The LPCVD films showing a dominant CrO₂ phase exhibit clear uniaxial magnetic anisotropy with the easy axis oriented along the c direction.     

Microstructure and electrical properties of Ba0.7Sr0.3(Ti1 − xZrx)O3 thin films prepared on copper foils with sol-gel method

Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0, 0.1, 0.2) (BSZT) thin films have been prepared on copper foils using sol-gel method. The films were annealed in an atmosphere with low oxygen pressure so that the substrate oxidation was avoided and the formation of the perovskite phase was allowed. The X-ray diffraction results show a stable polycrystalline perovskite phase, with the diffraction peaks of the BSZT films shifting toward the smaller 2θ with increasing Zr content. Scanning electron microscopy images show that the grain size of the BSZT thin films decreases with increasing Zr content. High resolution transmission electron microscopy shows the clear lattice and domain structure in the film. The dielectric peaks of the BSZT thin films broaden with increasing Zr content. Leakage current density of Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0.1) thin film is the lowest over the whole applied voltage.     

Preparation of LaNiO3 thin films with very low room-temperature electrical resistivity by room temperature sputtering and high oxygen-pressure processing

LaNiO₃ (LNO) thin films were deposited by radio frequency magnetron sputtering on n-type Si (100) wafers at room temperature (RT). The as-sputtered LNO thin films were amorphous and had very high RT electrical resistivity even after post-annealing at 800 °C. The amorphous as-sputtered LNO films could be transformed to polycrystalline LNO films in rhombohedral phase by heating at 400 °C in an O₂ atmosphere at pressure ranging from 1.5 to 8.0 MPa. Very low RT resistivity of LNO films were obtained by this high oxygen-pressure processing. The lowest value was as low as 1.09 × 10^− 4 Ω cm by processing at oxygen pressure of 8 MPa. Such preparation of LNO thin films is compatible with the Si-based readout integrated circuits. Highly (100)-oriented perovskite structure of Pb(Zr_0.52Ti_0.48)O₃ thin films was formed on this rhombohedral phase LNO, and good ferroelectricity could also be obtained on these HOPP-processed rhombohedral phase LNO films.     

Structure and dielectric properties of sputtered bismuth magnesium niobate thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O₂/(O₂ + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O₂/(O₂ + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi_1.5MgNb_1.5O₇ cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.     

Effect of Cu dopant on microstructure and phase transformation of ZnTiO3 thin films prepared by radio frequency magnetron sputtering

Cu doped zinc titanate (ZnTiO₃) films were prepared using radio frequency magnetron sputtering. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that the as-deposited films were amorphous and contained 0.84 at.% Cu. This was further confirmed by the onset of crystallization that took place at annealing temperatures 600 °C. The phase transformation for the as-deposited films and annealed films was investigated in this study. The results showed that Zn₂Ti₃O₈, ZnTiO₃, and TiO₂ can coexist at 600 °C. When annealed at 700 °C, the results revealed that mainly the hexagonal ZnTiO₃ phase formed, accompanied by minority amounts of TiO₂ and Zn₂Ti₃O₈. Unlike pure zinc titanate films, this result showed that the Zn₂Ti₃O₈ phase can be stable at temperatures above 700 °C. Moreover, Cu addition in zinc titanate thin film could result in the decomposition of hexagonal (Zn,Cu) TiO₃ phase at 800 °C. When the Cu content was increased in zinc titanate thin films from 0.84 at.% to 2.12 at.%, there were only two phases; Zn₂Ti₃O₈ and ZnTiO₃, coexisting at temperatures between 700 and 800 °C. This result indicated that a greater presence of Cu dopants in zinc titanate thin films leads to the existence of the Zn₂Ti₃O₈ phase at higher temperatures.     

Sputtering deposition of amorphous cadmium stannate as transparent conducting oxide

In this work we studied deposition conditions by RF sputtering of ternary oxides of Cd and Sn, starting from Cd₂SnO₄ target and varying substrate temperature, sputtering power and deposition gas (from inert Ar to oxidizing 50% Ar-50% O₂ atmosphere). The aim of this study was to obtain thin films for use as Transparent Conducting Oxide (TCO). TCOs are oxides that couples low sheet resistance and high transparency that find application in many fields like solar cells, light emitting diodes and transparent thin film transistors.Thin films functional properties were characterised by means of sheet resistance and transmittance measurements in the visible region, and film composition and structure were investigated by total reflection X ray fluorescence and glancing incidence X ray diffraction. Morphology was studied by Atomic Force Microscopy and Scanning Electron Microscope and showed very smooth surface suitable for solar cells application. Composition and phase analysis allowed us to discuss possible correlation of film structure with functional properties. Deposition in inert atmosphere at 400 °C substrate temperature was selected for its low sheet resistance and high transparency that are comparable to the ones of commercial TCOs like indium tin oxide or SnO₂: F. The thin film obtained in these conditions was amorphous, and it crystallized into CdSnO₃ ilmenite phase when annealed at 700 °C; segregation of Sn₃O₄ was also observed. Since sheet resistance of thin films increases after annealing treatments, amorphous thin film was selected for future applications.