Effect of oxidation temperature on microstructure, mechanical behaviors and surface morphology of nanocomposite Ti-Cx-Ny thin films

Two nanocomposite Ti-C_x-N_y thin films, TiC_0.95N_0.60 and TiC_2.35N_0.68, as well as one pure TiN, were deposited at 500 °C on Si(1 0 0) substrate by reactive unbalanced dc-magnetron sputtering. Oxidation experiments of these films were carried out in air at fixed temperatures in a regime of 250-600 °C with an interval of 50 °C. As-deposited and oxidized films were characterized and analyzed using X-ray diffraction (XRD), microindentation, Newton's ring methods and atomic force microscopy (AFM). It was found that the starting oxidation temperature of nanocomposite Ti-C_x-N_y thin films was 300 °C irrespective of the carbon content; however their oxidation rate strongly depended on their carbon content. Higher carbon content caused more serious oxidation. After oxidation, the film hardness value remained up to the starting oxidation temperature, followed by fast decrease with increasing heating temperature. The residual compressive stress did not show a similar trend with the hardness. Its value was first increased with increase of heating temperature, and got its maximum at the starting oxidation temperature. A decrease in residual stress was followed when heating temperature was further increased. The film surface roughness value was slightly increased with heating temperature till the starting oxidation temperature, a great decrease in surface roughness was followed with further increase of heating temperature.     

Effect of nitrogen content on phase configuration, nanostructure and mechanical behaviors in magnetron sputtered SiCxNy thin films

SiC_xN_y thin films with different nitrogen contents were deposited by way of incorporation of different amounts of nitrogen into SiC_0.70 using unbalanced reactive dc magnetron sputtering method. Their phase configurations, nanostructures and mechanical behaviors were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM) and microindentation methods. The result indicated SiC_0.70 and all SiC_xN_y thin films exhibited amorphous irrespective of the nitrogen content. The phase configuration and mechanical behaviors of SiC_xN_y thin films strongly depended on nitrogen content. SiC_0.70 exhibited a mixture consisting of SiC, Si and a small amount of C. Incorporated nitrogen, on one hand linked to Si, forming SiN_x, on the other hand produced CN_x and C at the expense of SiC. As a result, an amorphous mixture consisting of SiC, SiN_x, C and CN_x were produced. Such effects were enhanced with increase of nitrogen content. A low hardness of about 16.5 GPa was obtained at nitrogen-free SiC_0.70. Incorporation of nitrogen or increase of nitrogen content increased the film hardness. A microhardness maximum of ∼29 GPa was obtained at a nitrogen content of 15.7 at.%. This value was decreased with further increase of N content, and finally a hardness value of ∼22 GPa was obtained at a N content of ∼25 at.%. The residual compressive stress was consistent with the hardness in the nitrogen content range of 8.6-25.3 at.%.     

Effect of annealing temperature on microstructure, hardness and adhesion properties of TiSixNy superhard coatings

A series of TiSi_xN_y superhard coatings with different Si contents were prepared on M42 steel substrates using two Ti and two Si targets by reactive magnetron sputtering at 500 °C. These samples were subsequently vacuum-annealed at 500, 600, 700, 800 and 900 °C, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microindenter, Rockwell hardness tester and scratch tester were applied to investigate the microstructure, phase configuration, hardness and adhesion properties of as-deposited and annealed samples. The results indicated that there were two bonds, TiN and Si₃N₄, in all presently deposited TiSi_xN_y thin films, that structure was nanocomposite of nanocrystalline (nc-) TiN embedded into amorphous Si₃N₄ matrices. Annealing treatment below 900 °C played a little role in microstructure and hardness of the coatings although it greatly affected those of steel substrates. The film-substrate adhesion strength was slightly increased, followed by an abrupt decrease with increasing annealing temperature. Its value got to the maximum at 600 °C. Annealing had little effect on the friction coefficient with its value varying in the range of 0.39-0.40.     

Role of carbon in the formation of hard Ge1−xCx thin films by reactive magnetron sputtering

We have deposited germanium carbide (Ge_1−xC_x) films on Si(1 0 0) substrate via radio-frequency (RF) reactive magnetron sputtering in a CH₄/Ar mixture discharge, and explored the effects of carbon content (x) on the chemical bonding and hardness for the obtained films. We find that x significantly influences the chemical bonding, which leads to a pronounced change in the hardness of the film. To reveal the relationship between the chemical bonding and hardness, first-principles calculations have been carried out. It is shown that as x increases from 0 to 0.33, the fraction of sp³ C-Ge bonds in the film increases at the expense of Ge-Ge bonds, which promotes formation of a strong covalently bonded network, and thus enhances the hardness of the film. However, as x further increases from 0.33 to 0.59, the fraction of sp³ C-Ge bonds in the film gradually reduces, while that of sp³ C-H and graphite-like sp² C-C bonds increases, which damages the compact network structure, resulting in a sharp decrease in the hardness. This investigation suggests that the medium x (0.17<x<0.40) is most favorable to the preparation of hard Ge_1−xC_x films due to the formation of dominant sp³ C-Ge bonds.     

BiFeO3/Zn1−xMnxO bilayered thin films

BiFeO₃/Zn_1−xMn_xO (x = 0-0.08) bilayered thin films were deposited on the SrRuO₃/Pt/TiO₂/SiO₂/Si(1 0 0) substrates by radio frequency sputtering. A highly (1 1 0) orientation was induced for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO thin films demonstrate diode-like and resistive hysteresis behavior. A remanent polarization in the range of 2P_r ∼ 121.0-130.6 μC/cm² was measured for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO (x = 0.04) bilayer exhibits a highest M_s value of ∼15.2 emu/cm³, owing to the presence of the magnetic Zn_0.96Mn_0.04O layer with an enhanced M_s value.     

Structural and electrical characterization of SxSe100−x thin films

Thin films of samples of the glassy S_xSe_100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S_xSe_100−x were discussed. The characteristic temperatures (T_g, T_c and T_m) were evaluated. Dark electrical resistivities, ρ, of S_xSe_100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.     

Electrodeposition of BixSb2−xTey thermoelectric thin films from nitric acid and hydrochloric acid systems

The electrochemical behaviors of Bi^III, Te^IV and Sb^III single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, Bi_xSb_2−xTe_y thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of Bi^III, Te^IV and Sb^III in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although Bi_xSb_2−xTe_y thermoelectric thin film which structure is consistent with the standard pattern of Bi_0.5Sb_1.5Te₃ can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions.     

Nanostructured two-phase nc-TiN/a-(TiB2, BN) nanocomposite thin films

Thin films of Ti-B-N with different N contents were deposited on Si(1 0 0) at room temperature by reactive unbalanced close-field dc-magnetron sputtering using three Ti targets and one TiB₂ target in an Ar-N₂ gas mixture. The effect of N content on bonding structure, microstructure, phase configuration, surface roughness and mechanical properties have been investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and microindentation measurements. It was found that the N content significantly affected phase segregation and microstructure. The nitrogen-free TiB_0.65 films showed an amorphous compound consisting of Ti and TiB₂ (Ti-TiB₂). After adding about 28 at.% N, Ti was preferentially bonded to N to form TiN, accompanying with formation of small amounts of TiB and BN bonds. At this stage they combined TiB₂ to form a two-phase nanocomposite with microstructures comprising of nanocrystalline (nc-) TiN phase in nitrogen-containing amorphous (a-) TiB₂ matrix. Addition of more N promoted formation of BN bonding at cost of TiB₂, which resulted in formation of nanocomposite nc-TiN/a-(TiB₂, BN) thin films. A small grain less than 8 nm in size was found at low N content, and the grain size increased with increasing N content. A low microhardness value of about 20 GPa was obtained in the amorphous Ti-TiB₂ compound, and a maximum microhardness value of about 50 GPa was achieved in nc-TiN/a-TiB₂. A decrease of microhardness took place after formation of BN (i.e. amorphous matrix composed by both TiB₂ and BN) with further increasing N content, and a hardness value of about 35 GPa was followed at high N contents. The surface roughness strongly depended on the phase configuration. The higher the mole fraction of nanocrystalline TiN phase, the rougher the surface became.     

Effect of substrate temperature on the morphology, structural and optical properties of Zn1−xCoxO thin films

Zn_1−xCo_xO thin films with c-axis preferred orientation were deposited on sapphire (0 0 0 1) by pulsed laser deposition (PLD) technique at different substrate temperatures in an oxygen-deficient ambient. The effect of substrate temperature on the microstructure, morphology and the optical properties of the Zn_1−xCo_xO thin films was studied by means of X-ray diffraction (XRD), atomic force microscopy (AFM), UV-visible-NIR spectrophotometer, fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted as substrate temperature rose. The structure of the samples was not distorted by the Co incorporating into ZnO lattice. The surface roughness of all samples decreased as substrate temperature increased. The Co concentration in the film was higher than in the target. Emission peak near band edge emission of ZnO from the PL spectra of the all samples was quenched because the dopant complexes acted as non-radiative centers. While three emission bands located at 409 nm (3.03 eV), 496 nm (2.5 eV) and 513 nm (2.4 eV) were, respectively, observed from the PL spectra of the four samples. The three emission bands were in relation to Zn interstitials, Zn vacancies and the complex of V_O and Zn_i (V_OZn_i). The quantity of the Zn interstitials maintained invariable basically, while the quantity of the V_OZn_i slightly decreased as substrate temperature increased.     

Structure and electrical properties of Bi5GexSe95−x thin films

Bi₅Ge_xSe_95−x (30, 35, 40 and 45 at.%) thin films of thickness 200 nm were prepared on glass substrates by the thermal evaporation technique. The influence of composition and annealing temperature, on the structural and electrical properties of Bi₅Ge_xSe_95−x films was investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX). The XRD patterns showed that the as-prepared films were amorphous in nature with few tiny crystalline peaks of relatively low intensity for 30 and 45 at.% and the Bi₅Ge₄₀Se₅₅ annealed film was polycrystalline. The chemical composition of the Bi₅Ge₃₀Se₆₅ film has been checked using energy dispersive X-ray spectroscopy (EDX). The electrical conductivity was measured in the temperature range 300-430 K for the studied compositions. The effect of composition on the activation energy (ΔE) and the density of localized states at the Fermi level N(E_F) were studied, moreover the electrical conductivity was found to increase with increasing the annealing temperature and the activation energy was found to decrease with increasing the annealing temperature. The results were discussed on the basis of amorphous-crystalline transformations.     

Composition, microstructure, and properties of CrNx films deposited using medium frequency magnetron sputtering

CrN_x films were deposited on stainless steel and Si (1 1 1) substrates via medium frequency magnetron sputtering in a N₂ + Ar mixed atmosphere. The influence of N₂ content on the deposition rate, composition, microstructure, mechanical and tribological properties of the as-deposited films was investigated by means of the X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), nanoindentation and tribometer testing. It was found that the N atomic concentration increased and the phase transformed from a mixture of Cr₂N + Cr(N) to single-phase Cr₂N, and then Cr₂N + CrN to pure CrN phase with the increase of N₂ content. The Cr 2p_3/2 and N 1s of XPS spectra also confirmed the evolution of phase. Accordingly, all films exhibited a typical columnar structure which lies in the zone T of Thornton Model. The mixed Cr₂N and Cr(N) phases showed low hardness and high friction coefficient. Cr₂N possessed higher hardness than CrN while CrN exhibited lower friction coefficient.     

Effect of nitrogen content on the properties of CrNxOyCz coating prepared by DC reactive magnetron sputtering

The CrN_xO_yC_z coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N₂ content on composition and structure of the CrN_xO_yC_z coatings was investigated. The structure of the CrN_xO_yC_z coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrN_xO_yC_z coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrN_xO_yC_z coatings depended on N₂ content. The evolution of the structure of CrN_xO_yC_z coatings was consistent with CrN_x-based coatings, and the CrN_xO_yC_z coatings contained Cr₂O₃, CrO₂, CrO, Cr₃C₂, CrN_x (Cr, CrN, Cr₂N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing.     

Structural, optical and electrical properties of Zn1−xCdxO thin films prepared by PLD

Ternary polycrystalline Zn_1−xCd_xO semiconductor films with cadmium content x ranging from 0 to 0.23 were obtained on quartz substrate by pulse laser deposited (PLD) technique. X-ray diffraction measurement revealed that all the films were single phase of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing. Atomic force microscopy observation revealed that the grain size of Zn_1−xCd_xO films decreases continuously as the Cd content x increases. Both photoluminescence and optical measurements showed that the band gap decreases from 3.27 to 2.78 eV with increasing the Cd content x. The increase in Cd content x also leads to the broadening of the emission peak. The resistivity of Zn_1−xCd_xO films decreases evidently for higher values of Cd content x. The shift of PL emission to visible light as well as the decrease of resistivity makes the Zn_1−xCd_xO films potential candidate for optoelectronic device.     

Optical properties of MgxZn1−xO thin films deposited on silicon and sapphire substrate by rf magnetron sputtering

The index dispersion at UV–VIS range for polycrystalline Mg_xZn_1−xO films on silicon with different Mg concentration was obtained by spectroscopic ellipsometry (SE) method. It decreases with the increase of the Mg content. Above the relative peak wavelength, they are well fitted by the first-order Sellmeier relation. The band gap of films on sapphire of different Mg content was determined from transmission measurements. Photoluminescence (PL) illustrated that for Mg_xZn_1−xO films every PL peak corresponded to a special excitation wavelength. The wavelength of the PL peak was proportional to the special excitation wavelength. A strong peak was obtained in the blue band for the films due to the large amount of oxygen vacancies caused by excess Zn and Mg atoms, while weak peak at ultraviolet band.     

High-throughput characterization of BixY3−xFe5O12 combinatorial thin films by magneto-optical imaging technique

Bi_xY_3−xFe₅O₁₂ thin films have been grown on GGG (Gd₃Ga₅O₁₂) (1 1 1) substrates by the combinatorial composition-spread techniques under substrate temperature (T_sub) ranging from 410 to 700 °C and O₂ pressure of 200 mTorr. In order to study the effect of substrates on the deposition of Bi_xY_3−xFe₅O₁₂ thin films, garnet substrates annealed at 1300 °C for 3 h were also used. Magneto-optical properties were characterized by our home-designed magneto-optical imaging system. From the maps of Faraday rotation angle θ_F, it was evident that the Faraday effect appears only when T_sub = 430-630 °C. θ_F reaches to the maximum value (∼6°/μm, λ = 632 nm) at 500 °C, and is proportional to the Bi contents. XRD and EPMA analyses showed that Bi ions are easier to substitute for Y sites and better crystallinity is obtained for annealed substrates than for commercial ones.     

Luminescent properties of HTP AgGd1−xW2O8:Eux and AgGd1−x(W1−yMoy)2O8:Eux phosphor for white LED

Intense red phosphors, AgGd_1−xEu_x(W_1−yMo_y)₂O₈ (x=0.0-1.0, y=0.0-1.0), have been synthesized through traditional solid-state reaction and characterized by X-ray diffraction (XRD) and photoluminescence (PL). XRD results reveal that AgGd_1−xEu_xW₂O₈ synthesized at 1000 °C has a tetragonal crystal structure, which is named as high temperature phase (HTP) AgGdW₂O₈. All phosphors compositions with Eu³⁺ show red and green emission on excitation either in the charge-transfer or Eu³⁺ levels. Analysis of the emission spectra with different Eu³⁺ concentrations reveal that the optimum dopant concentration for Eu³⁺ is x=0.6 in the HTP AgGd_1−xEu_xW₂O₈ (x=0.0-1.0). Studies on the AgGd_0.4Eu_0.6(W_1−yMo_y)₂O₈ (y=0.0-1.0) and AgGd_1−xEu_x(W_0.7Mo_0.3)₂O₈ (x=0.0-1.0) show that the emission intensity is maximum for compositions with y=0.3 and x=0.5, respectively, and a decrease in emission intensity is observed for higher y or x values. The Mo⁶⁺ and Eu³⁺ co-doped AgGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped AgGd(WO₄)₂ in UV region. The intense emission of the tungstate/molybdate phosphors under 394 and 465 nm excitations, respectively, suggests that these materials are promising candidates as red-emitting phosphors for near-UV/blue GaN-based white LED for white light generation.     

Properties of MgxZn1−xO thin films sputtered in different gases

Mg_xZn_1−xO alloy films were prepared on sapphire substrates using Ar and N₂ as the sputtering gases. The effect of the sputtering gas on the structural, optical and electrical properties of the Mg_xZn_1−xO films was studied. By using N₂ as the sputtering gas, the Mg_xZn_1−xO film shows p-type conductivity and the band gap is larger than that employing Ar as the sputtering gas. The reason for this phenomenon is thought to be related to the reaction between N-O or N-Zn, and the N-doping.     

Spray pyrolytic synthesis of large area NiOx thin films from aqueous nickel acetate solutions

Non-stoichiometric nickel oxide thin films were prepared by pyrolytic decomposition of aerosol droplets of aqueous nickel acetate solution. Conventional un-nebulized spray pyrolysis system was used for the synthesis of thin films. The fine droplets were atomized by employing compressed air as carrier gas and allowed to decompose onto pre-heated Sn doped In₂O₃ (ITO) coated glass. The preparative parameters such as substrate temperature, solution concentration, distance from spray-nozzle to substrate, pressure of carrier air, etc., were optimized to obtain large area, uniform, thin films. The appropriate substrate temperature was selected after thermo-gravimetric analysis of nickel acetate. The temperature range of 330-420 °C was investigated for pyrolysis. Structural studies using X-ray diffraction (XRD) show the formation of cubic NiO. Morphological aspects of the films as-prepared and air annealed films have been studied by employing scanning electron microscopy. The optical absorption studies give direct band gap equal to 3.61 eV. The compositional analysis was carried out from the elemental depth profiles employing Auger electron spectroscopy. These indicate the formation of non-stoichiometric nickel oxide thin films. By studying I-V characteristics in alkaline electrolyte, electrocatalytic activity is tested.     

Characterization and properties of ZnO1−xSx alloy films fabricated by radio-frequency magnetron sputtering

A series of ZnO_1−xS_x alloy films (0 ≤ x ≤ 1) were grown on quartz substrates by radio-frequency (rf) magnetron sputtering of ZnS ceramic target, using oxygen and argon as working gas. X-ray diffraction measurement shows that the ZnO_1−xS_x films have wurtzite structure with (0 0 2) preferential orientation in O-rich side (0 ≤ x ≤ 0.23) and zinc blende structure with (1 1 1) preferential orientation in S-rich side (0.77 ≤ x ≤ 1). However, when the S content is in the range of 0.23 < x < 0.77, the ZnO_1−xS_x film consists of two phases of wurtzite and zinc blende or amorphous ZnO_1−xS_x phase. The band gap energy of the films shows non-linear dependence on the S content, with an optical bowing parameter of about 2.9 eV. The photoluminescence (PL) measurement reveals that the PL spectrum of the wurtzite ZnO_1−xS_x is dominated by visible band and its PL intensity and intensity ratio of UV to visible band decrease greatly compared with undoped ZnO. All as-grown ZnO_1−xS_x films behave insulating, but show n-type conductivity for w-ZnO_1−xS_x and maintain insulating properties for β-ZnO_1−xS_x after annealed. Mechanisms of effects of S on optical and electrical properties of the ZnO_1−xS_x alloy are discussed in the present work.     

Population analysis solution to hardness enhancement in TiCxN1−x

We investigated the hardness enhancement in titanium carbonitrides (TiC_xN_1−x) by the population analysis method based on first-principles calculations. Populations for bonds TiC and TiN in TiC_xN_1−x (0.25<x<0.75) are all positive. The enhanced hardness for titanium carbonitrides is well explained by overlap population analysis. Intrinsic hardness of TiC_xN_1−x has been calculated based on the obtained overlap populations. The calculated results are in good agreement with the available experimental data.