Effect of composition and structure modification of SnOx films on the electron secondary emission

By the use of different r.f. sputtering parameters, SnO_x films with different values of x (0.9 ? x < 1.8) were deposited and a variety of maximum secondary electron emission yields δ_m was obtained. Values of δ_m higher than that for bulk SnO₂ were observed in the films (e.g. δ_m = 5.4 at E_m = 500 eV compared with δ_m = 3.2 at 650 eV for bulk SnO₂). A direct correlation between x (determined by Auger electron spectroscopy) and the probability that an electron escapes from the surface of the SnO_x film was found. δ_m increase with increasing O₂ partial pressure p_O2 for any r.f. sputtering power.     

Preparation of homogeneous VOX thin films by ion beam sputtering and annealing process

Polycrystalline VO_x thin films that were prepared for thermal-sensitive material of far infrared sensor had been deposited on Si substrates by ion beam sputtering deposition. Scanning electron microscopy images indicated that VO_x thin films (oxygen pressure of 1.5×10⁻³ Pa) were grown into compact and ultra-fine grains (?50 nm), the film surfaces seemed smooth and uniform. Four-point probe measurements showed that the homogeneity of the films was better than 98% in a size of 30×30 mm². The four-point probe measurement on hot plate presented the sheet resistance and the temperature coefficient of resistance of the VO_x thin film that were 50 kΩ/square and −0.021 K⁻¹ at 28°C, respectively. In addition, some samples annealed in Ar atmosphere had their resistance decreased. Thus, vanadium oxide films containing more amount VO₂ were obtained.     

退火处理对TiO2薄膜结构和透射的影响

在常温下,采用射频反应磁控溅射方法在不同溅射功率下于K9双面抛光玻璃基底上制备二氧化钛薄膜.将制备的样品进行450℃退火6h热处理.利用X射线衍射仪(XRD)对比分析了退火前后薄膜的微观结构,采用光栅光谱仪测试了退火前后薄膜样品的透射谱.实验结果表明,退火前薄膜样品是非晶态,退火后薄膜晶化为晶态,但不同溅射功率下制备的薄膜结晶取向有差异;退火热处理对薄膜的折射率有一定影响,表现为退火前后透射谱偏移.     

Deposition and characterization of thin SiOx films

Thin (less than 500 Å) homogeneous SiO_x (1.5 < x < 2.0) films prepared from the glow discharge reaction of silane or a silane derivative with an oxidant such as nitrous oxide or oxygen have shown considerable promise as dielectric layers. The chemical composition and properties of these films are relatively insensitive to the glow discharge geometry, the gas composition and the power. Oxidant-rich plasma mixtures provide denser films and thus greater protection against atmospheric attack on the underlying material. The films were characterized using infrared spectroscopy, Auger depth profile analysis, transmission electron microscopy, scanning electron microscopy, multiple-drop liquid contact angle measurements and ellipsometry.     

SnOx obtaining by thermal oxidation of nanoscale tin films in the air and its characterization

Nanocrystalline films of metal tin with a thickness of 30, 100 nm were annealed in the air for 1 h at constant temperatures varying from 170 to 750 °C.Transmission electron microscopy and X-ray absorption near edge structure experimental data show the dependence of phase composition not only on the temperature of treatment but also on the thickness of initial metal layer.Optical investigations of absorption show a considerable dependence of position of the fundamental edges on the thickness of the films. The observed maxima of absorption at ∼ 3.6 eV are related with the defect states, mainly, with oxygen vacancies of non-stoichiometric oxide.     

Experimental and theoretical study of the role of the gas composition and plasma-surface interactions on the SnOx films stoichiometry prepared by DC magnetron reactive sputtering

In this paper, we have studied the tin oxide films deposition by DC magnetron reactive sputtering. We have investigated the discharge parameters such as discharge voltage and deposition rate and the discharge composition as a function of the input oxygen partial pressure. We have compared these results with the deposited films stoichiometry. In the constant current discharge mode, we observe, with increasing oxygen partial pressure, a decrease of the discharge voltage followed by a slight increase, and a drop of the deposition rate. For each experimental conditions, we measure the gas composition by mass spectrometry (glow discharge mass spectrometry mode and residual gas analysis mode (RGA)) and the deposited films stoichiometry by X-ray photoemission spectroscopy. The results are fitted by means of a model, taking into account the plasma-surface interactions. All the data are fitted by the same equation, with only four fitting parameters, namely the sticking-reaction coefficients of O and O₂ on Sn and SnO surfaces. Our results show that the main reaction is the reaction between the atomic oxygen and the metallic part (Sn) of the substrate. This reaction is characterized by a sticking coefficient value (α₁⁰) of 0.96.     

Raman spectra and structural analysis in ZrOxNy thin films

Raman spectroscopy has been used as a local probe to characterize the structural evolution of magnetron-sputtered decorative zirconium oxynitride ZrO_xN_y films which result from an increase of reactive gas flow in the deposition. The lines shapes, the frequency position and widths of the Raman bands show a systematic change as a function of the reactive gas flow (a mixture of both oxygen and nitrogen). The as-deposited zirconium nitride film presents a Raman spectrum with the typical broadened bands, due to the disorder induced by N vacancies. The recorded Raman spectrum of the zirconium oxide film is typical of the monoclinic phase of ZrO₂, which is revealed also by X-ray diffraction. Raman spectra of zirconium oxynitride thin films present changes, which are found to be closely related with the oxygen content in films and the subsequent structural changes.     

Reactively sputtered GaAsxN1−x thin films

Thin films of GaAs_xN_1−x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from ∼ 7 μm/h to ∼ 2 μm/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5-10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride.     

The effect of the annealing of electrode films on the electrical resistivity of thin aluminium films

The resistance of aluminium films, coated on glass substrates with annealed and unannealed thick films of gold, silver, copper and aluminium as electrodes, was measured. The percentage variation in resistance of the aluminium films differs with the use of annealed and unannealed electrodes. This variation was found to be greater for gold, silver and copper electrodes and not very marked for aluminium electrodes. The respective roles of factors such as oxide formation and alloying at the film-electrode junction are discussed by considering the observed variation in the resistance of the films. An attempt is also made to correlate this variation with the microscopic features seen at particular electrode-film junctions.     

Electrical resistivity of polycrystalline AgInSe2 thin films

Thin films of AgInSe₂ are grown onto glass substrates by flash evaporation technique at temperatures ranging from 30 to 300°C and their electrical resistivity is studied. It is observed that the films deposited at 200°C have minimum resistivity. The variation of resistivity is explained in terms of the compositional variation in the films, which was carried out by EDAX (energy dispersive analysis of X-rays). The activation energies of the compound films grown at different substrate temperatures are determined. The implications are discussed.     

Structural properties of thin Bi1−xSbx alloy films

Measurements of the structural properties of thin films of Bi_1?xSb_x alloy using an electron microscope and X-ray diffractometer were performed. The change in the lattice parameter of the alloy depending on the Sb concentration was established to be in agreement with Vegard's law. The existence of texture in thin films of Bi_1?xSb_x alloy was also confirmed. The dependence of the linear dimension of the average size of the crystallites on the antimony concentration was investigated.     

Hard BCxNy thin films grown by dual ion beam sputtering

Boron carbonitride thin films were deposited by sputtering of a B₄C target with Ar-N₂ ion assistance. BC_xN_y films were grown onto Si (001) at room temperature. The chemical composition and the type of bonding were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The hardness of the films was measured with a nanoindenter. The chemical analysis of the samples indicates the formation of two different compounds, a ternary BC_xN_y and a binary carbonitride CN_x. All the films showed high hardness, in the range 16-33 GPa, which clearly increases as the BC_xN_y content in the sample increases. In this study the highest hardness (i.e. 33 GPa) was obtained when the BC_xN_y content in the sample was 50%. The average composition of this BC_xN_y was estimated by XPS as 20 at.% carbon and 12 at.% nitrogen.     

Compositional effects on the optical properties of Gex Sb40−x Se60 thin films

Ge_x Sb_40−x Se₆₀ (x = 0, 2.42 and 23.41 at.%) thin chalcogenide films were deposited on glass and quartz substrates by the conventional thermal evaporation technique at 300 K. The chemical composition of the bulk material and as-deposited films were determined by energy dispersive analysis X-ray spectrometry (EDAX). X-ray diffraction pattern (XRD) of Ge_x Sb_40−x Se₆₀ (x = 0, 2.42 and 23.41 at.%) thin films indicates that they have amorphous structure. The optical transmission and reflection spectra were measured in the range of 500 to 2500 nm. The optical absorption coefficient spectra were studied for deposited samples. It is observed that the optical absorption edge shift to higher energy range, as the germanium content, x, increases in the film. The type of electronic transition, responsible for the optical properties, is indirect allowed transition. It is found that the optical band gap increases as the Ge content increases.The average coordination number (N_c) in Ge_x Sb_40−x Se₆₀ films increases, but the number of chalcogenide atoms remains constant. The number of Ge - Se bonds and the average bond energy of the system increase with the increase of the average coordination number. The optical band gap, E_g, increases with the increase of the average coordination number, (N_c). Also the energy gap, E₀₄, is discussed in terms of its relation to the chemical composition. The dispersion of the refractive index (n) is discussed in terms of the Single Oscillator Model (SOM) (Wimple - Didomenico model). The single oscillator energy (E₀), the dispersion energy (E_d) and the optical dielectric constant (?_∞) are also estimated.     

The effect of the annealing of indium electrode films on the electrical resistivity of thin metal films

The resistances of thin films of gold, silver, copper and aluminium deposited onto glass substrates were measured using annealed and unannealed films of indium as electrodes. The percentage variation in resistance for the different metal films differs with annealed and unannealed electrodes. The effect of factors such as oxide formation, bubble formation and alloying at the electrode-film junction are discussed in the light of the observed variations in resistance of the films. An attempt is also made to correlate this variation with the microscopic features observed at particular electrode-film junctions.     

The influence of structure changes in the properties of TiCxOy decorative thin films

The main purpose of this work consists in the preparation of titanium oxycarbide, TiC_xO_y, thin films, in which the presence of oxygen changed the film properties between those of titanium carbide and those of titanium oxide. Varying the oxide/carbide ratio allowed to tune the structure of the films between titanium oxide and carbide and consequently electronic, mechanical and optical properties of the films. The depositions were carried out from a TiC target by direct current, dc, reactive magnetron sputtering, varying the oxygen flow rate. The obtained results showed that the film's properties can be divided into 3 different regimes — i) carbide, ii) a transition zone and iii) an oxide one. X-ray diffraction results revealed the occurrence of a face-centered cubic phase (TiC-type) for low oxygen content, also obtained in the TiC_1.6(O) film, with a clear tendency towards amorphization with the increase of the oxygen flow rate. For the highest oxygen contents, the results revealed the development of a mixture of poorly crystallized TiO₂ phases. The colour results indicated a strong dependence on the O/Ti ratio. A progressive reduction of hardness and residual stresses with the increase of the O/Ti ratio was also observed. The residual stresses, as well as the film structure, seem to play an important role on the adhesion of the coatings. The static friction coefficient revealed also some correlation with the mechanical properties, but mainly with the surface roughness.     

Structural and photocarrier radiometric characterization of Cux(CdTe)yOz thin films growth by reactive sputtering

This research presents a structural and photocarrier radiometric (PCR) characterization of Cu_x(CdTe)_yO_z thin films grown using reactive radiofrequency co-sputtering. Electronic distribution induced by variations in dopant concentration as a function of the position was studied using photocarrier radiometric images. Optical and structural characterization of these thin films was carried out by using micro Raman spectroscopy and X-ray diffraction. Due to its nondestructive and noncontact characteristics, the PCR is an excellent technique that permits one to obtain details of lateral electronic distribution across the sample. It was found that Cu target power influences the electronic distribution and produces different phases such as Cu₂Te and CdO.     

Preparation and characterization of increased-efficiency photocatalytic TiO2-2xNx thin films

We report here on the characteristics of RF-sputtered 300 nm thick films of TiO_2-2xN_x prepared on glass substrates at 350 °C, by adjusting the N₂:Ar partial pressure ratio in the deposition chamber between 0.00 and 0.33. XRD, XPS, AFM and contact angle data were used to derive film structure, elemental composition and oxidation state of Ti, surface morphology and hydrophilicity, respectively. The band gap was derived from spectral data in the 350-450 nm range. Film structure and composition were changed by adjusting the partial pressure of the reactive gases during sputtering and by post-deposition annealing at 400 °C in air, for 90 min. The values of the contact angle of films' surface with de-ionized water and of surface free energy per unit area show that films are super-hydrophilic for high-nitrogen content. Correlations are made between film structure, elemental composition, electronic and wettability properties.     

The effect of substrate temperature,deposition rate and annealing on the electrical resistivity of thin yttrium films

The effect of substrate temperature, deposition rate and annealing on the electrical resistivity of thin yttrium films in the thickness range 10 to 80 nm is reported. The resistivity of films decreases at higher deposition rates and substrate temperatures. These experimental results are analysed using the Fuchs—Sondheimer and Mayadas—Shatzkes theories. The annealing behaviour of yttrium films is in agreement with the Vand theory.     

Perovskite oxynitride LaTiOxNy thin films: Dielectric characterization in low and high frequencies

Lanthanum titanium oxynitride (LaTiO_xN_y) thin films are studied with respect to their dielectric properties in low and high frequencies. Thin films are deposited by radio frequency magnetron sputtering on different substrates. Effects of nitrogen content and crystalline quality on dielectric properties are investigated. In low-frequency range, textured LaTiO_xN_y thin films deposited on conductive single crystal Nb-STO show a dielectric constant ε′ ≈ 140 with low losses tanδ = 0.012 at 100 kHz. For the LaTiO_xN_y polycrystalline films deposited on conductive silicon substrates with platinum (Pt/Ti/SiO₂/Si), the tunability reached up to 57% for a weak electric field of 50 kV/cm. In high-frequency range, epitaxial LaTiO_xN_y films deposited on MgO substrate present a high dielectric constant with low losses (ε′ ≈ 170, tanδ = 0.011, 12 GHz).