Deposition of a-C:H films on UHMWPE substrate and its wear-resistance

In prosthetic hip replacements, ultrahigh molecular weight polyethylene (UHMWPE) wear debris is identified as the main factor limiting the lifetime of the artificial joints. Especially UHMWPE debris from the joint can induce tissue reactions and bone resorption that may lead to the joint loosening. The diamond like carbon (DLC) film has attracted a great deal of interest in recent years mainly because of its excellent tribological property, biocompatibility and chemically inert property. In order to improve the wear-resistance of UHMWPE, a-C:H films were deposited on UHMWPE substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-PECVD) technology. During deposition, the working gases were argon and acetylene, the microwave power was set to 800 W, the biased pulsed voltage was set to −200 V (frequency 15 kHz, duty ratio 20%), the pressure in vacuum chamber was set to 0.5 Pa, and the process time was 60 min. The films were analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, anti-scratch and wear test. The results showed that a typical amorphous hydrogenated carbon (a-C:H) film was successfully deposited on UHMWPE with thickness up to 2 μm. The nano-hardness of the UHMWPE coated with a-C:H films, measured at an applied load of 200 μN, was increased from 10 MPa (untreated UHMWPE) to 139 MPa. The wear test was carried out using a ball (Ø 6 mm, SiC) on disk tribometer with an applied load of 1 N for 10000 cycles, and the results showed a reduction of worn cross-sectional area from 193 μm² of untreated UHMWPE to 26 μm² of DLC coated sample. In addition the influence of argon/acetylene gas flow ratio on the growth of a-C:H films was studied.     

Effect of N content on phase configuration, nanostructure and mechanical behaviors in Ti-Cx-Ny thin films

Ti-C_x-N_y thin films with different nitrogen contents were deposited by way of incorporation of different amounts of nitrogen into TiC_1.02 using unbalanced reactive unbalanced dc magnetron sputtering method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and microindentation methods were used to investigate their phase configurations, nanostructures and mechanical behaviors in order to investigate their dependences on nitrogen content. The result indicated that the nitrogen content had a significant effect on phase configuration, nanostructure and mechanical behaviors of Ti-C_x-N_y thin films. The nitrogen-free TiC_1.02 films exhibited a polycrystallite with nano-grains. On one hand, incorporated nitrogen substituted C in TiC_1.02, producing Ti(C,N), and subsequently linked to the substituted C, forming C-N. On the other hand, the substituted C lined to each other, forming C-C. As a result, nanocomposite thin films consisting of nanocrystalline Ti(C,N) and amorphous (C, C-N) were produced. With further incorporation of nitrogen more C was substituted, accompanying with formation of more amorphous matrices and decrease of size of nanocrystalline Ti(C,N). The trend was enhanced with further increase of nitrogen content. A microhardness maximum of ∼58 GPa was obtained in nitrogen-free TiC_1.02 thin films. This value was linearly decreased with incorporation of N or increase of N content, and finally a hardness value of about 28 GPa was followed at a N content of ∼25 at.%. Both elastic modulus and residual compressive stress values exhibited similar trends.     

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 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.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Raman spectroscopy of a-C:H:N films deposited using ECR-CVD with mixed gas

Ultraviolet (UV) and visible Raman spectroscopy were used to study a-C:H:N films deposited using ECR-CVD with a mixed gas of CH₄ and N₂. Small percentage of nitrogen from 0 to 15% is selected. Raman spectra show that CN bonds can be directly observed at 2220 cm⁻¹ from the spectra of visible and UV Raman. UV Raman enhances the sp¹ CN peak than visible Raman. In addition, the UV Raman spectra can reveal the presence of the sp³ sites. For a direct correlation of the Raman parameter with the N content, we introduced the G peak dispersion by combining the visible and UV Raman. The G peak dispersion is directly relative to the disorder of the sp² sites. It shows the a-C:H:N films with higher N content will induce more ordered sp² sites. In addition, upper shift of T position at 244 nm excitation with the high N content shows the increment of sp² fraction of films. That means the films with high N content will become soft and contain less internal stress. Hardness test of films also confirmed that more N content is with less hardness.     

Spectroscopy of X2Y4 (D2h) molecules: tensorial formalism adapted to the O(3)⊃D2h chain, Hamiltonian and transition moment operators

A tensorial formalism adapted to the case of the X₂Y₄ molecules with D_2h symmetry has been developed in the same way as in the previous works on XY₄ (T_d) and XY₆ (O_h) spherical tops and XY₅Z (C_4v) symmetric tops. Here, we use the O(3)⊃D_2h group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain and used in the case of the Hamiltonian and transition moment operators.     

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.     

Coalescence of BnNn fullerenes: A new pathway to produce boron nitride nanotubes with small diameter

Using density functional theory calculations, we predict that single-walled hemispherical-caped boron nitride (BN) nanotubes with small diameters can be produced via the coalescence of stable nanoclusters. Specifically, the assembly of B_nN_n (n=12,24$n=12,24$) clusters exhibiting particularly high stability and leading to armchair (3,3)$(3,3)$ and (4,4)$(4,4)$ BN nanotubes, respectively, are considered. The formed finite-length BN nanotubes have semiconducting properties with wide band gaps attractive to nano-device applications.     

Fabrication of FeSe1−x superconducting films with bulk properties

We have fabricated high-quality FeSe_1−x superconducting films with a bulk T_c of 11–12 K on different substrates, Al₂O₃(0 0 0 1), SrTiO₃(1 0 0), MgO(1 0 0), and LaAlO₃(1 0 0), by using a pulsed laser deposition technique. All the films were grown at a high substrate temperature of 610 °C, and were preferentially oriented along the (1 0 1) direction, the latter being to be a key to fabricating of FeSe_1−x superconducting thin films with high T_c. According to the energy dispersive spectroscopy data, the Fe:Se composition ratio was 1:0.90 ± 0.02. The FeSe_1−x film grown on a SrTiO₃ substrate showed the best quality with a high upper critical magnetic field [H_c2(0)] of 56 T.     

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.     

Low-voltage cathodoluminescence property of Li-doped Gd2−xYxO3:Eu

Cathodoluminescent (CL) spectra of Li-doped Gd_2−xY_xO₃:Eu³⁺ solid-solution (0.0?x?0.8) were investigated at low voltages (300 V-1 kV). The CL intensity is maximum for the composition of x=0.2 and gradually reduces with increasing the amount of substituted Y content. In particular, small (∼100 nm) particles of Li-doped Gd_1.8Y_0.2O₃:Eu³⁺ are obtained by firing the citrate precursors at only 650°C for 18 h. Relative red-emission intensity at 300 V of this phosphor is close to 180% in comparison with that of commercial red phosphor Y₂O₃:Eu³⁺. An increase of firing temperature to 900°C results in 400-600 nm sized spherical particles. At low voltages (300-800 V), the CL emission of 100 nm sized particles is much stronger than that of 400-600 nm sized ones. In contrast, the larger particles exhibit the higher CL emission intensity at high voltages (1-10 kV). Taking into consideration small spherical morphology and effective CL emission, Li-doped Gd_1.8Y_0.2O₃:Eu³⁺ appears to be an efficient phosphor material for low voltage field emission display.