Ultrafast pump-probe spectroscopy studies of CeO2 thin film deposited on Ni-W substrate by RF magnetron sputtering

This study presents the first investigation of rapid dynamical processes that occur in pure CeO₂ thin film, using ultra fast pump-probe spectroscopy at room temperature. For this purpose we have used a single (200) oriented CeO₂ film deposited on biaxially textured Ni-W substrate by RF magnetron sputtering technique. The ultrafast transient spectra show initial sharp rise transition followed by an exponential photon decay. This rise time is about 10 ps irrespective of the probe wavelengths range 500–800 nm. The initial decay constant (τ) at 500 nm probe wavelength is found to be 171 ps, while at 800 nm probe wavelength it is 107.5 ps. The ultrafast absorption spectra show two absorption peaks at 745 and 800 nm, and are attributed to the electronic transitions from ²F_7/2–²F_5/2 and ¹S₀–¹F₃ respectively. The relatively high intensity absorption peak at 745 nm indicates dominant f–f electronic transition. Further, the absorption peak at 745 nm splits into two distinct peaks with respect to delay time, and is attributed to the charge transfer in between Ce⁴⁺ and Ce³⁺ ions. These results indicate that CeO₂ itself is a potential candidate and can be used for optical applications.     

Infrared transmission properties of germanium carbon thin films deposited by reactive RF magnetron sputtering

Germanium carbon (GeC) thin films were prepared on ZnS substrates by reactive RF magnetron sputtering in Ar and CH₄ mixtures with a Ge disc as the target. H content in the films was studied as a function of the deposition parameters and low H content GeC film was obtained. RF power had a little effect on IR absorptions, hence had a little effect on H content. IR absorption of the GeC film increased a little with the increase in partial pressure of CH₄ as well as total pressure of gas mixture. Increase in substrate temperature decomposed CH₄ and CH_x in the GeC film into C and H and H was desorbed from the film, lowering the IR absorption. However, high substrate temperature prevented CH₄ or CH_x from adsorbing onto the substrate, which decreased C content in the GeC film and increased the film's refractive index. Higher annealing temperature of the GeC film reduced H content, but high annealing temperature (500 °C) caused the graphitization of the GeC film and destroyed its continuity.     

Investigation of BST thin films deposited by RF magnetron sputtering in pure Argon

Ba_0.5Sr_0.5TiO₃ (BST) thin films were deposited by rf magnetron sputtering using a Ba_0.5Sr_0.5TiO₃ target in pure Argon on two electrodes (Pt and RuO₂) at room temperature. The interface formation between BST and bottom electrode (Pt or RuO₂) was investigated by XPS for thicknesses in the 1 to 50 nm range. The chemical composition of the BST layers can be modified by the electrode nature over the first five nanometers. A 1 h ex-situ annealing, under flowing oxygen at 600 °C, was necessary to obtain crystallized 150 nm thick BST films, as evidenced by XRD and TEM analysis.     

Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.     

Photoemission study of the tin doped cerium oxide thin films prepared by RF magnetron sputtering

Ce-Sn-O mixed oxide films prepared by simultaneous Sn metal and cerium oxide magnetron sputtering were studied by high resolution photoemission. The analysis showed that the degree of reduction of the cerium oxide depends on the tin concentration in the film. Ce⁴⁺ → Ce³⁺ conversion is explained by a charge transfer from Sn atoms to unoccupied orbital Ce 4f⁰ of cerium oxide by forming Ce 4f¹ state. The X-ray Photoelectron Spectroscopy data were compared with study of the single-crystalline CeO₂ thin films and Sn/CeO₂(111) model system prepared and studied in situ excluding air exposure effects.     

Indium zinc oxide semiconductor thin films deposited by dc magnetron sputtering at room temperature

Amorphous indium zinc oxide (IZO) thin films were prepared on glass substrates by dc magnetron sputtering at room temperature. The resistivity of IZO films could be controlled between 3.8 × 10⁻³ and 2.5 × 10⁶ Ω cm by varying the oxygen partial pressure during deposition, while keep the average transmittance over 83%. With IZO films as channel layers, whose surface root-mean-square roughness was less than 1 nm, thin film transistors were fabricated at room temperature, showing enhanced mode operation with good saturation characteristics, mobility of 5.2 cm² V⁻¹ s⁻¹, threshold voltage of 0.94 V and on/off ratio of ∼10⁴.     

Low resistivity transparent conducting CdO thin films deposited by DC reactive magnetron sputtering at room temperature

Transparent conducting cadmium oxide (CdO) films were deposited on PET (polyethylene terephthalate) substrate by DC reactive magnetron sputtering at room temperature. All the films deposited at room temperature were polycrystalline in rock-salt structure. Dependences of the physical properties of the CdO films on the oxygen partial pressure were systematically studied. The films deposited at low oxygen flow rate were (200) oriented, while the films deposited at an oxygen flow rate greater than 20 sccm were (111) oriented. The average grain size of the CdO films decreased as the oxygen flow rate increases as determined by XRD and SEM. The Hall effect measurement showed that CdO films have high concentration, low resistivity, and high mobility. Both the mobility and the concentration of the carrier decreased with the increase of the oxygen flow rate. A minimum sheet resistance of 36.1 Ω/□, or a lowest resistivity of 5.44 × 10^− 4 Ω cm (6.21 × 10²⁰/cm³, μ = 19.2 cm²/Vs) was obtained for films deposited at an oxygen flow rate of 10 sccm.     

Al-Mg-B thin films prepared by magnetron sputtering

Hard, nanocomposite aluminum magnesium boride thin films were prepared on Si (100) substrates with a three target magnetron sputtering system. The films were characterized by X-ray diffraction, atomic force microscope, electron micro-probe, Fourier transform infrared spectroscopy and nanoindentation. The results show that the maximum hardness of the as-deposited films is about 30.7 GPa and these films are all X-ray amorphous with smooth surfaces. The influences of substrate temperature and boron sputtering power on the quality of the films are discussed. From the results of this work, magnetron sputtering is a promising method to deposit Al-Mg-B thin films.     

Influence of process parameters on structure and optical properties of GeC thin films deposited by RF magnetron sputtering

Germanium carbide (Ge_1 − xC_x) films on silicon and quartz substrates have been prepared by the radio frequency (RF) reactive sputtering of a pure Ge target in a CH₄/Ar discharge. Their structural and optical properties have been investigated as functions of the substrate temperature (T_S) and the CH₄ percentage to the gas mixture. The optical band gap of the films lies within the range 0.96-1.65 eV, varying proportionally with the carbon content and in inverse proportionality with T_S.     

Low-temperature deposited Titanium-doped zinc oxide thin films on the flexible PET substrate by DC magnetron sputtering

Transparent conducting Titanium-doped zinc oxide thin films (TZO) with high transparency and relatively low resistivity were firstly deposited on water-cooled polyethylene terephthalate (PET) substrates at room temperature by DC magnetron sputtering. The microstructure, optical and electrical properties of the deposited films were investigated and discussed. The XRD patterns show that all the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity decreases when the sputtering power increases from 45 W to 60 W. However, as the puttering power continue increases from 60 W to 90 W, the electrical resistivity increases rapidly. When the puttering power is 60 W, the films deposited on PET substrate have the lowest resistivity of 4.72 × 10⁻⁴ Ω cm and a relatively high transmittance of above 92% in the visible range.     

Characterization of electrolyte films deposited by using RF magnetron sputtering a 20 mol% gadolinia-doped ceria target

20 mol% Gd-doped ceria (20GDC) electrolyte films on poly-crystalline Al₂O₃ substrates were prepared by radio frequency (RF) magnetron sputtering from a 20GDC oxide target, which was made by the processes of colloidal dispersion-pressure casting-sintering. Material characteristics of the 20GDC oxide target and the deposited films before and after annealed at 900 °C for 2 h were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and conductivity measurements. Crack-free and dense 20GDC electrolyte films were observed by the deposition conditions of 200 W (RF power). Homogeneity tests revealed the chemical compositions (Ce and Gd) were uniformly distributed through the bulk of the target and the deposited films. 20GDC film with a comparable conductivity of 1.00 × 10^− 3 S/cm at 650 °C is higher than that of bulk yttria-stabilized zirconia (YSZ), but smaller than that of bulk GDCs (10GDC and 20 GDC). Sputtered-GDC films in this study can be also suggested to be used as the electrolyte films for solid oxide fuel cells (SOFCs) systems as compared to the well-known YSZ.     

Preferentially oriented vanadium nitride films deposited by magnetron sputtering

Because of solid state lubricious properties of vanadium oxides, wear resistant coatings based on nitrides and carbides of that metal are still of interest for research teams. The aim of this report is to show phase composition evolution from metallic vanadium through intermediate phases up to δ-VN phase supersaturated with nitrogen in thin films deposited by reactive, pulsed magnetron sputtering from vanadium target. This analysis is completed by remarks on preferential orientation, lattice constant and crystallite size. Presented work is a part of research on composite hard coatings for woodworking tools where vanadium nitrides and carbides are considered as a component reducing friction.     

Deposition by magnetron sputtering and characterization of indium tin oxide thin films

In this work the properties of indium tin oxide (ITO) films deposed on glass substrates by magnetron sputtering technique in the temperature range below 200 °C are studied by various methods. The physical properties of ITO thin films have been investigated using optical transmittance, photoluminescence, atomic force microscopy, ellipsometry, Hall-effect and four point probe methods. It is established that properties of ITO layers depend drastically on the temperature and oxygen partial pressure during the deposition process and exhibit some peculiarities of the surface morphology. It is found that the band gap energy of this material varies in the energy range from 4.1 to 4.4 eV and depends on the growth conditions. It is suggested that local deviations from the stoichiometry and defects are the main physical reasons of Burstein-Moss shift of the optical band gap.     

溅射功率对磁控溅射ZnO∶Al(ZAO)薄膜性能的影响

采用射频磁控溅射工艺,以高密度氧化锌铝陶瓷靶为靶材,衬底温度控制在室温,在玻璃基底上制备了透明导电Zn O∶Al(ZAO)薄膜。利用X射线衍射仪(XRD)、原子力显微镜(AFM)、紫外-可见光谱仪和范德堡法,系统研究了不同溅射功率对薄膜的结构、形貌及光电特性的影响。结果表明,不同溅射功率对薄膜的光透射率影响不大,而对薄膜结晶和电学性能影响较大。XRD表明薄膜为良好的c轴择优取向;可见光区(400~600 nm)平均透过率达到85%以上;在120W下沉积的薄膜电学性能达到了最佳。     

Properties of Ce-doped ITO films deposited on polymer substrate by DC magnetron sputtering

Ce-doped indium tin oxide (ITO:Ce) films were deposited on flexible polyimide substrates by DC magnetron sputtering using ITO targets containing various CeO₂ contents (CeO₂ : 0, 0.5, 3.0, 4.0, 6.0 wt.%) at room temperature and post-annealed at 200 °C. The crystallinity of the ITO films decreased with increasing Ce content, and it led to a decrease in surface roughness. In addition, a relatively small change in resistance in dynamic stress mode was obtained for ITO:Ce films even after the annealing at high temperature (200 °C). The minimum resistivity of the amorphous ITO:Ce films was 3.96 × 10^− 4 Ωcm, which was deposited using a 3.0 wt.% CeO₂ doped ITO target. The amorphous ITO:Ce films not only have comparable electrical properties to the polycrystalline films but also have a crystallization temperature > 200 °C. In addition, the amorphous ITO:Ce film showed stable mechanical properties in the bended state.     

The selective growth of rutile thin films using radio-frequency magnetron sputtering

Using unbalanced radio-frequency (RF) magnetron sputtering crystalline rutile films were synthesised on glass substrates at (combined Ar and O₂) pressures of 0.4 Pa or less, at RF powers of 500 and 600 W with substrate to magnetron distances of 40 mm or longer. Anatase films were deposited at the greater pressure of 1.2 Pa (substrate to magnetron distance of 40 mm) or shorter substrate to magnetron distance of 20 mm (at 0.4 Pa). A mixture of anatase and rutile was formed at 0.5 Pa with all other conditions being as for those required for rutile or the power was reduced along with the substrate to magnetron distance (500 W and 20 mm). The crystallite sizes of rutile obtained were 1 - 3 nm. It is proposed that the greater the energy imparted to the substrate surface by the impinging positive species the greater the activation energy to crystalline phase formation that can be overcome. Hence the formation of rutile over anatase is favoured at greater power, longer magnetron to substrate distances and decreased pressure. Moreover, not only is it possible to control the phase of TiO₂ formed it appears to be possible to control the degree of oxygen non-stoichiometry in the rutile films formed. Smaller O₂ partial pressures, shorter substrate to magnetron distances and greater RF power are believed to produce an environment of reduced reaction of sputtered Ti species with O₂ and to result in the formation of non-stoichiometric rutile structures resulting in increased band gap energies and decreased refractive indices.     

Structural characterization of ZnO thin films deposited by dc magnetron sputtering

In this work we present recent results on ZnO thin films grown by dc magnetron sputtering technique at room temperature (RT), focusing on structural and surface characterization using conventional cross-section transmission electron microscopy (XTEM) and high resolution cross section transmission electron microscopy (HRXTEM) in an attempt to understand the thickness influence on film, mechanical and optical properties as well as photoreduction/oxidation conductivity changes. Films were found to be polycrystalline with a columnar mode of growth. For films with thickness over 100 nm, XTEM and HRTEM analysis evidenced the presence of a small grains transition layer near interface with the substrate, feature which plays an important role in ZnO thin films for gas sensing application. The control of such structural parameters is proved to be critical for the improvement of their gas sensing performance.     

Structures and properties of the Al-doped ZnO thin films prepared by radio frequency magnetron sputtering

Al-doped ZnO thin films were deposited by radio frequency magnetron sputtering using a ZnO target with 2 wt.% Al₂O₃. The structures and properties of the films were characterized by the thin film X-ray diffraction, high resolution transmission electron microscopy, Hall system and ultraviolet/visible/near-infrared spectrophotometer. The Al-doped ZnO film with high crystalline quality and good properties was obtained at the sputtering power of 100 W, working pressure of 0.3 Pa and substrate temperature of 250 °C. The results of further structure analysis show that the interplanar spacings d are enlarged in other directions besides the direction perpendicular to the substrate. Apart from the film stress, the doping concentration and the doping site of Al play an important role in the variation of lattice parameters. When the doping concentration of Al is more than 1.5 wt.%, part of Al atoms are incorporated in the interstitial site, which leads to the increase of lattice parameters. This viewpoint is also proved by the first principle calculations.     

Effect of target properties on transparent conducting impurity-doped ZnO thin films deposited by DC magnetron sputtering

For the purpose of using transparent conducting impurity-doped ZnO thin films in liquid crystal display (LCD) applications, the relationship between the properties of dc magnetron sputtering (dc-MS) deposited thin films and the properties of the oxide targets used to produce them is investigated. Both Al-doped and Ga-doped ZnO (AZO and GZO) thin films were deposited on glass substrates using a dc-MS apparatus with various high-density sintered AZO or GZO disk targets (diameter of about 150 mm); the target and substrate were both fixed during the depositions. Using targets with a lower resistivity results in attaining more highly stable dc-MS depositions with higher deposition rates and lower arcing. In addition, dc-MS depositions using targets with a lower resistivity produced improvements in resistivity distribution on the substrate surface. It was found that the oxygen content in deposited thin films decreased as the oxygen content of the target used in the deposition was decreased. As a result, the dc-MS deposition of transparent conducting impurity-doped ZnO thin films suitable for LCD applications requires the preparation of significantly reduced AZO and GZO targets with low oxygen content.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.