Properties of MoNxOy thin films as a function of the N/O ratio

The main purpose of this work is the preparation of single layer films of molybdenum oxynitride, MoN_xO_y. The films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure Mo target and varying the flow rate of reactive gases. This allowed tuning of the crystallographic structure between insulating oxides and metallic nitrides and consequently changes in the electronic, mechanical and optical properties of the material. X-ray diffraction (XRD) results revealed the presence of molybdenum nitride for the films with low oxygen fraction: face-centered cubic phases (γ-Mo₂N) for low nitrogen flow rate or cubic MoN_x and hexagonal phase (δ-MoN) for high nitrogen flow rate. The increase of oxygen content induces an amorphization of the nitride phases and the appearance of MoO₃ phases. The increase of the oxygen fraction in the films induces also a high decrease in the film's hardness. Residual stresses were compressive, in the range of very few tenths of GPa to − 2 GPa. These results will be presented as a function of the deposition parameters, the chemical composition and the structure of the films.     

Annealing effect on crystallization behavior of cubic MgxZn1−xO films on A-plane and M-plane sapphire

Cubic Mg_xZn_1−xO thin films with Mg composition around 70% were deposited on A-plane and M-plane sapphire substrates by rf-reactive magnetron sputtering. Measured structural and optical properties of these thin films indicated an optimal annealing temperature of 700 °C which produced high quality cubic MgZnO thin films on both substrates. Moreover, when the annealing temperature exceeded 750 °C, a much rougher surface resulted, and several large mosaic particles on the surface of the annealed films appeared. From EDX results, the Mg composition was lower than that found in other sections of the annealed films. We attributed this to thermally induced reconstruction of the crystallites. This phenomenon was more obvious for annealed MgZnO films on A-plane sapphire than that on M-plane sapphire. Thermal expansion mismatch with the substrate is the principal reason.     

MgxZn1−xO (x = 0-1) films fabricated by sol-gel spin coating

Mg_xZn_1−xO films were deposited onto the glass substrate by a sol-gel spin coating method. The drying and annealing temperatures were 300 and 500 °C in air. As x varies from 0 to 1, it was observed that the crystal structure is changed from wurtzite ZnO to cubic MgO. The morphology characterizations of these films were observed by scanning electron microscope. The randomly oriented hexagonal nanorods were gown on the glass surface when x = 0 and 0.25, which became disappeared with increasing Mg contents. The optical properties of these films were investigated by room-temperature photoluminescence (PL) and UV-vis absorption spectra, which show that the optical band gap and photoluminescence in the visible and UV regions can be ideally tuned by varying the Mg contents in the Mg_xZn_1−xO alloy films.     

Preparation of (ZnO)1−x(GaN)x:Mn powder and its photoluminescence properties

(ZnO)_1−x(GaN)_x:Mn²⁺ powder was prepared by a conventional solid-state reaction under an NH₃ gas flow. The sample preparation conditions including the mixing ratio of the raw materials, the annealing temperature, and the annealing time were varied. The crystallinity and the photoluminescence (PL) intensity of this fluorescent material were improved by increasing the amount of ZnO and by increasing the annealing time, and no changes was observed in the PL wavelength. The crystallinity of the samples was enhanced and the PL intensity increased markedly at annealing temperatures of 700 °C and 800 °C, respectively. Moreover, it was clarified that the sample could be synthesized at annealing temperatures of above about 650 °C.     

Regulate the content of magnesium in MgxZn1−xO films by vacuum anneal

Mg_xZn_1−xO thin films were grown on c-sapphire substrates by metal-organic chemical vapor deposition (MOCVD), followed by annealing in vacuum at different temperatures for 1 h. The UV emission peak was blue shifted in the photoluminescence (PL) spectra and a dramatic shift of (0 0 2) diffraction peak to higher angle was observed in X-ray diffraction (XRD) pattern with increasing anneal temperature. This suggested the band gap and the lattice parameter of Mg_xZn_1−xO had been affected by annealing in vacuum. Furthermore, the structure of the film became sparser due to annealing in vacuum. From the X-ray photoelectron spectroscopy (XPS) and ICP of the Mg_xZn_1−xO film, we can find that the anneal temperature have an effect on the content of each element in Mg_xZn_1−xO quantitatively. In addition, the value of x in Mg_xZn_1−xO varied slightly as the annealing temperature increased. The above phenomena indicated that annealing in vacuum could slightly adjust the percentage of Mg indirectly in Mg_xZn_1−xO film and offer a good idea in Mg_xZn_1−xO devices facture.     

Chemical bonding of a-Ge1−xCx:H films grown by RF reactive sputtering

Amorphous hydrogenated germanium-carbon (a-Ge_1−xC_x:H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH₄/(CH₄+Ar) in a discharge Ar/CH₄, and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH₄/(Ar+CH₄), and the Ge-C, Ge-H, C-H bonds were formed in the films. The fraction of Ge-C, Ge-H, and C-H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge-Ge and C-C bonding. Based on the change of the chemical bonding of a-Ge_1−xC_x:H films with the flow rate ratio CH₄/(CH₄+Ar), an optimal experimental condition for the application of infrared windows was obtained.     

Magnetron sputtering of TiOxNy films

This article reports on the characterization and preparation of N-doped titanium dioxide (TiO₂) films by reactive magnetron sputtering from Ti(99.5) targets in a mixture of Ar/O₂/N₂ atmosphere on unheated glass substrates. A dual magnetron system supplied by a dc bipolar pulsed power source was used to sputter the TiO_xN_y films. The amount of N in the TiO_xN_y film ranges from 5 to 40 at%. Its structure was measured using X-ray diffraction (XRD), the optical band gap was calculated from Tauc plots and the decrease of the water contact angle α_ir after the film activation by UV irradiation was investigated as a function of at% of N in the TiO_xN_y film. The yellow-coloured TiO_xN_y films with high (≈8 at%) amount of N exhibited a strong decrease of the band gap E_g down to 2.7 eV. A significant decrease of the water contact angle α_ir after UV irradiation has been observed for 2 μm thick transparent nanocrystalline (anatase+rutile) N-doped TiO₂ films containing less than 6 at% of N.     

Optical and electrical properties of TiOx thin films deposited by electron beam evaporation

The TiO_x thin films were prepared by electron beam evaporation using TiO as the starting material. The effect of the annealing temperature on the optical and electrical properties was investigated. The spectra of X-ray photoelectron spectroscopy reveal that Ti in the films mainly exist in the forms of Ti²⁺ and Ti³⁺ below 400 °C 24 h annealing. The charge transfer between different titanium ion contribute greatly to the color, absorption, and electrical resistance of the films.     

Mechanical and environmental properties of Ge1−xCx thin film

Ge_1−xC_x thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ as precursors and its mechanical and environmental properties were investigated. The samples were measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum, FT-IR spectrometer, WS-92 testing apparatus of adhesion and FY-03E testing apparatus of salt and fog. The results show that the infrared refractive index of Ge_1−xC_x thin film varies from 2 to 4 with different x values. The adhesion increases with increasing gas flow ratio of GeH₄/CH₄ and decreases with increasing film thickness. The nanoindentation hardness number decreases with increasing germanium content. Three series films exhibit the best anti-corrosion property when the RF power is about 80 W, or substrate temperature is about 150 °C, or DC bias is about −100 V. Furthermore, increasing the gas flow ratio of GeH₄/CH₄ improves the anti-corrosion property of these films.     

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn_1 − xMg_xO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn_1 − xMg_xO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70 mol%. AFM images of the Zn_1 − xMg_xO films (x = 0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn_1 − xMg_xO. The variation of the cation-anion bond length to Mg content shows that the lattice constant of the hexagonal Zn_1 − xMg_xO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16 eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.     

Influence of electron irradiation on characteristics of Si1−xGex p-n-structures

Electrically active defects induced by irradiation with 4 MeV electrons and their influence on dynamic and static parameters of p-n-structures with bases on boron doped Si_1−xGe_x alloys (0<x?0.06) have been investigated. It has been found that after irradiation with the electron fluence Φ=2×10¹⁴ cm⁻² lifetime of minority charge carriers decreases more than 12 times and forward voltage increases twice. Deep level transient spectroscopy (DLTS) studies have shown that interstitial carbon atoms are dominant electrically active defects induced by the irradiation. These defects are transformed into the complexes “interstitial carbon—interstitial oxygen” upon annealing of irradiated samples in the temperature range 50-100 °C.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Influence of Se on the electron mobility in thermal evaporated Bi2(Te1−xSex)3 thin films

Thermoelectric solid solutions of Bi₂ (Te_1−xSe_x)₃ with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were grown using the Bridgman technique. Thin films of these materials of different compositions were prepared by conventional thermal evaporation of the prepared bulk materials. The temperature dependence of the electrical conductivity σ, free carriers concentration n, mobility μ_H, and seebeck coefficient S, of the as-deposited and films annealed at different temperatures, have been studied at temperature ranging from 300 to 500 K. The temperature dependence of σ revealed an intrinsic conduction mechanism above 400 K, while for temperatures less than 400 K an extrinsic conduction is dominant.The activation energy, ΔE, and the energy gap, E_g, were found to increase with increasing Se content. The variation of S with temperature revealed that the samples with different compositions x are degenerate semiconductors with n-type conduction. Both, the annealing and composition effects on Hall constant, R_H, density of electron carriers, n, Hall mobility, μ_H, and the effective mass, m^∗/m₀ are studied in the above temperature range.     

Tuning the optical properties of alloyed CdSexS1 − x nanoparticles by changing the constituent stoichiometry

The spherical particles CdSe_xS_1 − x with 30-80 nm in radius have been successfully prepared by the hydrothermal reaction at 200 °C. The structure characterization which has been carried out using X-ray diffraction (XRD) shows hexagonal crystal structure. Novel properties have been observed via UV-visual absorption spectra and photoluminescence (PL) spectra. The absorption shoulder and the luminescence emission peaks have been tuned by changing the mole ratio of Se in the CdSe_xS_1 − x samples.     

Characterization of N-doped TiO2 films prepared by reactive sputtering using air/Ar mixtures

Nitrogen-doped titanium dioxide (TiO_2 − xN_x) thin films desirable for visible light photocatalysts were prepared by reactive sputtering using air/Ar mixtures. Using air as the reactive gas allows the process to conduct at high base pressures (low vacuum), which reduces substantially the processing time. The obtained films transformed from mixed phases to anatase phase as the air/Ar flow ratio increased. Substitutional doping of nitrogen verified by X-ray photoelectron spectroscopy accounts for the red-shift of absorption edge in the absorption spectra. Anatase TiO_2 − xN_x films could incorporate up to about 7.5 at.% substitutional nitrogen and a maximum of 23 at.% nitrogen was determined in the films with mixed phases. The optical band gaps of the TiO_2 − xN_x films calculated from Tauc plots varied from 3.05 to 3.11 eV and those of the mixed phase ranged from 2.77 to 3.00 eV, which are all lower than that for pure anatase TiO₂ and fall into the visible light regime.     

TixSiyN nanocomposites by cathodic arc plasma deposition

We have deposited Ti_xSi_yN nanocomposites by means of a custom-made cathodic arc evaporation system, using a TiSi 80/20 at% compound target in a reactive Ar-N₂ atmosphere. We have studied the influence of different process parameters, like the amount of nitrogen in the gas, the total pressure, the arc current or the deposition temperature, on the properties of the material. We have analysed the films by X-ray diffraction (XRD), which has allowed us to determine the optimum conditions to obtain TiN nanocrystals with a good degree of texture. We have found that a moderate increase in the deposition temperature leads to an improvement in the crystalline quality of the films; however, the results as to their hardness are not as good as we expected. We have not been able to confirm the existence of Si₃N₄ by Fourier-transform infrared (FT-IR) spectrometry measurements. Additionally, glow-discharge optical emission spectroscopy (GD-OES) analyses show a high amount of oxygen incorporated to the films (around 5.5 at%).     

Effect of post-annealing treatment in oxygen on dielectric properties of K0.5Na0.5NbO3 thin films prepared by chemical solution deposition

K_0.5Na_0.5NbO₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method with different annealing temperatures of 550 °C, 600 °C, 700 °C. The post-annealing treatment was introduced at 550 °C for 3 min in oxygen ambient. It is found that the films were composed of pure provskite phase, and the post-annealing treatment promoted the crystallization and improved the quality of the films, which resulted in the enhancement of the dielectric property of the films. The effect of the post-annealing on the dielectric properties of the films was also discussed.     

Formation and transformation of ZnTiO3 prepared by sputtering process

Zinc titanate (ZnTiO₃) films were prepared using RF magnetron sputtering at substrate temperatures ranging from 30 to 400 °C. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that all as-deposited films were amorphous, as confirmed by XRD. 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 were investigated in this study. The results revealed that pure ZnTiO₃ (hexagonal phase) can exist, and was obtained at temperatures between 700 and 800 °C. However, it was found that decomposition from hexagonal ZnTiO₃ to cubic Zn₂TiO₄ and rutile TiO₂ took place with a further increase in temperature to 900 °C.     

Multi-stage evaporation of Cu2ZnSnS4 thin films

Multi-stage evaporation is a well-established method for the controlled growth of chalcopyrite thin films. To apply this technique to the deposition of Cu₂ZnSnS₄ thin films we investigated two different stage sequences: (A) using Cu₂SnS₃ as precursor to react with Zn-S and (B) using ZnS as precursor to react with Cu-Sn-S. Both Cu₂SnS₃ and ZnS are structurally related to Cu₂ZnSnS₄. In case (A) the formation of copper tin sulphide in the first stage was realized by depositing Mo/SnS_x/CuS (1 < x < 2) and subsequent annealing. In the second stage ZnS was evaporated in excess at different substrate temperatures. We assign a significant drop of ZnS incorporation at elevated temperatures to a decrease of ZnS surface adhesion, which indicates a self-limited process with solely reactive adsorption of ZnS at high temperatures. In case (B) firstly ZnS was deposited at a substrate temperature of 150 °C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 °C we find a strong decrease of Sn-incorporation and also a Zn-loss in the layers. The re-evaporation of elemental Zn has to be assumed. XRD measurements after KCN-etch on the layers prepared at 380 °C show for both sample types clearly kesterite, though an additional share of ZnS and Cu₂SnS₃ can not be excluded. SEM micrographs reveal that films of sample type B are denser and have larger crystallites than for sample type A, where the porous morphology of the tin sulphide precursor is still observable. Solar cells of these absorbers reached conversion efficiencies of 1.1% and open circuit voltages of up to 500 mV.