X-ray photoelectron spectroscopy and conducting atomic force microscopy investigations on dual ion beam sputtered MgO ultrathin films

Ultrathin films of MgO (~ 6 nm) were deposited on Si(100) using dual ion beam sputtering in different partial pressures of oxygen. These thin films were characterized by X-ray photoelectron spectroscopy (XPS) for chemical state analysis and conducting atomic force microscopy for topography and local conductivity map. No trace of metal Mg was evidenced in these MgO films. The XPS analysis clearly brought out the formation of oxygen interstitials and Mg(OH)₂ primarily due to the presence of residual water vapors in the chamber. An optimum value of oxygen partial pressure of ~ 4.4 × 10^− 2 Pa is identified with regard to homogeneity of film and stoichiometry across the film thickness (O:Mg::0.93-0.97). The local conductivity mapping investigations also established the film homogeneity in respect of electrical resistivity. Non-linear local current-voltage curves revealed typical tunneling characteristics with barrier width of ~ 5.6 nm and barrier height of ~ 0.92 eV.     

Control of oxidation state of copper in flame deposited films

The deposition of thin copper based films onto carbon steel surface is described, using premixed flames with different oxygen/methane ratios doped with aqueous copper nitrate as precursor. We investigated the chemical properties of the copper as a function of oxygen/methane ratio. Using fuel rich flames (equivalence ratio 0.665), the deposited copper film was entirely metallic. When the equivalence ratio was increased to 0.850 or greater the copper film contained predominantly Cu^2 +. Furthermore, the flame can be used for post deposition modification, as demonstrated by reduction of Cu^2 + containing films to Cu metal. All the films were characterised by X-ray diffraction, Raman and scanning electron microscopy (SEM). A rotating sample holder was employed to avoid over heating of the sample and the critical variables such as sample height in the flame and deposition time were optimised. Deposition for 20 min, which translated to a total residence time in the flame of approx. 76 s, produces metallic copper films of thickness 169 ± 18 nm as determined by anodic stripping and SEM. The microstructure of the metallic films was clearly composed of fused copper spheres of 100-150 nm, which are probably formed in the flame and subsequently deposited on the surface with good adhesion.     

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al₂O₃) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 °C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al₂O₃-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.     

Near infrared transparent conducting cadmium oxide deposited by MOCVD

Polycrystalline cadmium oxide has been deposited on to glass substrates for use as transparent conducting oxides for thin film photovoltaics. The films were deposited by metal organic chemical vapour deposition (MOCVD). The oxygen precursor was tertiary butanol, which was chosen to avoid the pre-reaction often seen for more reactive oxygen sources when combined with the cadmium source, dimethylcadmium. This combination of precursors promoted a surface reaction to yield high quality CdO films with large grain size. The cadmium oxide, deposited at 280 °C, yielded a minimum resistivity of 3.9 × 10^− 4 Ω cm whilst maintaining an average transmittance between 450 and 2500 nm of 80%. This exceptional near-IR transmittance coupled with good electrical conduction is well suited to match the infrared requirements of multi-junction photovoltaics designed to capture greater proportions of the solar spectrum.     

An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV-Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm-19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.     

Fabrication of Y2O3-doped BaZrO3 thin films by electrostatic spray deposition

Electrostatic spray deposition (ESD) technique was used to fabricate dense Y₂O₃-doped BaZrO₃ (BYZ) thin films, which have been extensively studied for the protonic ceramic fuel cell electrolyte. Effects of the ESD process parameters (i.e. substrate temperature, type of precursor, flow rate and applied voltage) on the microstructure of as-deposited films were studied. The uniform as-deposited films were obtained using a mixture of zirconium acetylacetonate, barium chloride dihydrate and yttrium chloride hexahydrate precursors in a solvent mixture of butyl carbitol and deionized water at a volume ratio of 50:50. The optimum deposition parameters were obtained at the substrate temperature of 250 °C with the applied voltage and flow rate in a range of 10-12 kV and 1.4-2.8 ml/h, respectively. The as-deposited films were subsequently annealed at 1350 °C for 10 h to ensure the complete chemical reactions of the precursors. X-ray diffraction patterns reveal the perovskite structures of the annealed BYZ films (deposited on yttria stabilized zirconia substrates) with only traces of Y₂O₃ phase, which could arise from the loss of BaO at high annealing temperatures.     

Texture optimization process of ZnO:Al thin films using NH4Cl aqueous solution for applications as antireflective coating in thin film solar cells

ZnO:Al thin films varying the thickness from 80 to 110 nm were deposited on polished float zone < 100 > Si wafers by radio frequency magnetron sputtering at 100 °C. To texturize these surfaces with the aim of being used as antireflective coating, a wet etching process based on NH₄Cl was applied. Taking into account that the layer thickness was small, the control of the etch parameters such as etchant concentration and etching time was evaluated as a function of the textured film properties. An appropriate control of the etching rate to adjust the final thickness to the 80 nm required for the application was realized. Using NH₄Cl concentrations of 10 wt.% and short times of up to 25 s, an increase of the film roughness up to a factor of 5.6 of the as-deposited films was achieved. These optimized textured films showed weighted reflectance values below 15% and considerable better electrical properties than the as-deposited 80 nm-thick ZnO:Al films.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Room temperature deposition of ZnSe thin films by successive ionic layer adsorption and reaction (SILAR) method

The zinc selenide (ZnSe) thin films are deposited onto glass substrate using relatively simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The films are deposited using zinc acetate sodium selenosulphate precursors. The concentration, pH, immersion and rinsing times and number of immersion cycles have been optimized to obtain good quality ZnSe thin films. The X-ray diffraction (XRD) study and scanning electron microscopy (SEM) studies reveals nanocrystalline nature alongwith some amorphous phase present in ZnSe thin films. Energy dispersive X-ray (EDAX) analysis shows that the films are Se deficient. From optical absorption data, the optical band gap ‘E_g’ for as-deposited thin film was found to be 2.8 eV and electrical resistivity in the order of 10⁷ Ω cm.     

Influence of oxygen pressure on the structural, electrical and optical properties of VO2 thin films deposited on ZnO/glass substrates by pulsed laser deposition

The influence of oxygen pressure on the structural and electrical properties of vanadium oxide thin films deposited on glass substrates by pulsed laser deposition, via a 5-nm thick ZnO buffer, was investigated. For the purposes of comparison, VO₂ thin films were also deposited on c-cut sapphire and glass substrates. During laser ablation of the V metal target, the oxygen pressure was varied between 1.33 and 6.67 Pa at 500 °C, and the interaction and reaction of the VO₂ and the ZnO buffer were studied. X-ray diffraction studies showed that the VO₂ thin film deposited on a c-axis oriented ZnO buffer layer under 1.33 Pa oxygen had (020) preferential orientation. However, VO₂ thin films deposited under 5.33 and 6.67 Pa were randomly oriented and showed (011) peaks. Crystalline orientation controlled VO₂ thin films were prepared without such expensive single crystal substrates as c-cut sapphire. The metal-insulator transition properties of the VO₂/ZnO/glass samples were investigated in terms of electrical conductivity and infrared reflectance with varying temperatures, and the surface composition was investigated by X-ray photoelectron spectroscopy.     

Growth and characterization of tin oxide thin films and fabrication of transparent p-SnO/n-ZnO p–n hetero junction

p-Type and n-type tin oxide thin films were deposited by rf-magnetron sputtering of metal tin target by varying the oxygen pressure. Chemical composition of SnO thin film according to the intensity of the XPS peak is about 48.85% and 51.15% for tin and oxygen respectively. Nearest neighbor distance of the atoms calculated from SAED patterns is 2.9 Åand 2.7 Åfor SnO and SnO₂ respectively. The Raman scattering spectrum obtained from SnO thin films showed two peaks, one at 113 cm⁻¹ and the other at 211 cm⁻¹. Band gap of as-deposited SnO_x thin films vary from 1.6 eV to 3.2 eV on varying the oxygen partial pressure from 3% to 30% which indicates the oxidization of metallic phase Sn to SnO and SnO₂. p-Type conductivity of SnO thin films and n-type conductivity of SnO₂ thin films were confirmed through Hall coefficient measurement. Transparent p–n hetero junction fabricated in the structure glass/ITO/n-ZnO/p-SnO shows rectification with forward to reverse current ratio as 12 at 4.5 V.     

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

Effects of precursor evaporation temperature on the properties of the yttrium oxide thin films deposited by microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition

Yttrium oxide thin films are deposited using indigenously developed metal organic precursor (2,2,6,6-tetra methyl-3,5-hepitane dionate) yttrium, commonly known as Y(thd)₃ (synthesized by ultrasound method). Microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition process was used for these depositions. Depositions were carried out at a substrate temperature of 350 °C with argon to oxygen gas flow rates fixed to 1 sccm and 10 sccm respectively throughout the experiments. The precursor evaporation temperature (precursor temperature) was varied over a range of 170-275 °C keeping all other parameters constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and refractive index of the coatings are measured by the spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique.C-Y₂O₃ phase is deposited at lower precursor temperature (170 °C). At higher temperature (220 °C) cubic yttrium oxide is deposited with yttrium hydroxide carbonate as a minor phase. When the temperature of the precursor increased (275 °C) further, hexagonal Y₂O₃ with some multiphase structure including body centered cubic yttria and yttrium silicate is observed in the deposited film. The properties of the films drastically change with these structural transitions. These changes in the film properties are correlated here with the precursor evaporation characteristics obtained at low pressures.     

An effective fabrication method for ultra thin aluminum structures

In this paper we discuss the various effects on resistivity of thin metal films, concluding that grain boundary scattering and the material's electron-mean-free-path are the dominant factors. We also present an effective procedure for the fabrication of patterned ultra thin aluminum (sub 100 nm thick) structures on thermally grown SiO₂ substrates, the results of which are compared to other commonly used electrode fabrication methods. A general 4-point probe measurement of an as-deposited 60 nm aluminum film's resistivity was performed. We also found our unique wet-etching method to deliver reproducible results with varying film thickness and yielding a favorable environment for the integration of nanomaterials.     

Morphology and growth of e-beam deposited YSZ thin films

Yttria-stabilized zirconium (YSZ) thin films were grown from the tetragonal phase of ZrO₂ stabilized by 8 wt% of Y₂O₃ (8% of YSZ) ceramic powders using e-beam deposition technique (EB-PVD). The influence of the type of substrate on the microstructure of deposited YSZ thin films was analysed. YSZ thin films (2-3 μm of thickness) were deposited on three different types of substrates: optical quartz (SiO₂), porous Ni-YSZ substrates and Alloy 600 (Fe-Ni-Cr). The dependence of the substrate temperature (from 20 to 600 °C) on the thin film structure and the surface morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that (i) the substrate temperature has an influence on the crystallite size, which varied between 12 and 50 nm, (ii) the substrate type has an influence on the growth mechanism of YSZ thin films, and (iii) a bias voltage applied to the substrate during the deposition of thin films has an influence on the densification of YSZ layers.     

Effect of the nanostructure on room temperature ferromagnetism and resistivity of undoped ZnO thin films grown by chemical vapor deposition

Undoped zinc oxide thin films having various types of morphology and nanostructure were deposited by metal organic chemical vapor deposition (MOCVD) on single-crystalline substrates. Water-assisted MOCVD process at low temperatures (300-500 °C) was applied along with conventional MOCVD in oxygen-containing atmosphere at 500 and 600 °C. The strong correlation between room-temperature ferromagnetism of the films, their electrical properties and morphology at nano-scale was demonstrated.     

Effect of deposition temperature and thermal annealing on the dry etch rate of a-C: H films for the dry etch hard process of semiconductor devices

The effect of deposition and thermal annealing temperatures on the dry etch rate of a-C:H films was investigated to increase our fundamental understanding of the relationship between thermal annealing and dry etch rate and to obtain a low dry etch rate hard mask. The hydrocarbon contents and hydrogen concentration were decreased with increasing deposition and annealing temperatures. The I(D)/I(G) intensity ratio and extinction coefficient of the a-C:H films were increased with increasing deposition and annealing temperatures because of the increase of sp² bonds in the a-C:H films. There was no relationship between the density of the unpaired electrons and the deposition temperature, or between the density of the unpaired electrons and the annealing temperature. However, the thermally annealed a-C:H films had fewer unpaired electrons compared with the as-deposited ones. Transmission electron microscopy analysis showed the absence of any crystallographic change after thermal annealing. The density of the as-deposited films was increased with increasing deposition temperature. The density of the 600 °C annealed a-C:H films deposited under 450 °C was decreased but at 550 °C was increased, and the density of all 800 °C annealed films was increased. The dry etch rate of the as-deposited a-C:H films was negatively correlated with the deposition temperature. The dry etch rate of the 600 °C annealed a-C:H films deposited at 350 °C and 450 °C was faster than that of the as-deposited film and that of the 800 °C annealed a-C:H films deposited at 350 °C and 450 °C was 17% faster than that of the as-deposited film. However, the dry etch rate of the 550 °C deposited a-C:H film was decreased after annealing at 600 °C and 800 °C. The dry etch rate of the as-deposited films was decreased with increasing density but that of the annealed a-C:H films was not. These results indicated that the dry etch rate of a-C:H films for dry etch hard masks can be further decreased by thermal annealing of the high density, as-deposited a-C:H films. Furthermore, not only the density itself but also the variation of density with thermal annealing need to be elucidated in order to understand the dry etch properties of annealed a-C:H films.     

Synthesis and characterization of electrolyte-grade 10%Gd-doped ceria thin film/ceramic substrate structures for solid oxide fuel cells

In the present research, spray pyrolysis technique is employed to synthesize 10%Gd-doped ceria (GDC) thin films on ceramic substrates with an intention to use the "film/substrate" structure in solid oxide fuel cells. GDC films deposited on GDC substrate showed enhanced crystallite formation. In case of NiO-GDC composite substrate, the thickness of film was higher (~ 13 μm) as compared to the film thickness on GDC substrate (~ 2 μm). The relative density of the films deposited on both the substrates was of the order of 95%. The impedance measurements revealed that ionic conductivity of GDC/NiO-GDC structure was of the order of 0.10 S/cm at 500 °C, which is a desirable property for its prospective application.     

Correlation study between structural, magnetic and transport properties of annealed Co thin films

This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 °C in steps of 100 °C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 °C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H_c) of 26 Oe, and it is increased to 94 Oe for 500 °C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 °C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.     

Influence of deposition temperature on structure and morphology of nanostructured SnO2 films synthesized by pulsed laser deposition

Nanostructured tin oxide thin films were deposited on the Si (100) substrate using the pulsed laser deposition technique at different substrate temperatures (300, 450 and 600 °C) in an oxygen atmosphere. The structure and morphology of the as-deposited films indicate that the film crystallinity and surface topography are influenced by the deposition temperature by changing from an almost amorphous to crystalline microstructure and smoother topography at a higher substrate temperature. The photoluminescence measurement of the SnO₂ films shows three stable emission peaks centered at respective wavelengths of 591, 554 and 560 nm with increasing deposition temperature, contributed by the oxygen vacancies.