Studies of structure and morphology of sputter-deposited stainless steel–nitrogen films

Stainless steel films doped with nitrogen were deposited on heated and unheated (100) silicon substrates by radio-frequency magnetron sputtering of an austenitic stainless steel target in argon and nitrogen gas mixtures, containing a range of nitrogen compositions. The evolution of phases, morphologies and grain structures in the resultant films was studied by X-ray diffraction and field emission scanning electron microscopy. It was found that, with increasing nitrogen composition in the gas mixture, the crystalline structure of the films deposited on the heated substrates changed from bcc ferrite (α), to nitrogen-stabilized fcc austenite (γ), then to distorted expanded austenite phase (γ_N) with nitrogen supersaturation, and finally to the newly discovered fcc ‘MN’ phase with ideal cubic symmetry and further enlarged lattice. On the unheated substrates, the phase-evolution trend was found to be different for % N₂ above 10. For the 25% N₂ film, amorphous phase formed along with the crystalline austenite and ferrite phases, while the percentage of amorphous content decreased when % N₂ was increased to 50. This different trend was understood to be due to the role of increase in % N₂ in decreasing the energy loss of sputtered species through collisions. The dependence of crystalline phase formation on the energy of sputtered species is less severe on the heated substrates. Although all the films deposited experienced three-dimensional fibrous growths, they exhibited different surface morphology and grain structure. There exists a correlation between film morphology and phase constituents, while grain size was influenced by the nucleation density and the energy and mobility of adatoms that are reduced due to nitrogen incorporation. PACS 68.55.-a; 81.15.Cd     

CEMS study of oxide layers formed on stainless steel (SUS304 and SUS316)

Stainless steel (SUS304 and SUS316) was chemically treated and heated at various temperatures, and the oxide films formed on the surface were analyzed by conversion electron Mössbauer spectrometry (CEMS). Three magnetic components of iron species were detected in the top oxide layers of stainless steels heated below 600°C and the fine particles of iron oxides were initially produced in the inner oxide layers of the samples heated at temperatures higher than 700°C. Only paramagnetic iron species were detected in the oxide layers of the stainless steels prepared by chemical treatment.     

Characterization of oxide layers and interface layers of ferrite stainless steel (SUS430) by57Fe CEMS

The oxide layers on stainless steel formed by heating at various high temperatures and by dipping in LiF + BeF₂ molten (Flibe) bath at 600 °C were characterized by CEMS. Hematite was a major iron product at 600 °C and fine oxides with paramagnetic Fe(III) species were produced at the higher temperatures than 700 °C. The interface of stainless steel beneath oxide films was characterized as the hyperfine field distributions. Paramagnetic Fe(III) species were produced on Cr depleted layers in the Flibe bath. CEMS is effective for simultaneous characterization of both oxide surface and interface layers of the ferritic stainless steel.     

Hematite thin films: growth and characterization

We have grown hematite (α–Fe ₂ O ₃) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mössbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α–Fe ₂ O ₃. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.     

Epitactic growth of a decagonal phase in an Al–Ni–Co alloy film deposited on a (0001) sapphire substrate

Thin films of Al–Ni–Co alloy with an average thickness of 15?nm were produced by means of conventional vacuum deposition technique on (0001) sapphire substrates heated at various test temperatures. The microstructures and textures of the films obtained were thoroughly investigated by atomic force microscopy, X-ray diffraction and transmission electron diffraction and imaging techniques. The diffraction measurements have evidenced that the vacuum deposition of Al₇₂Ni₁₅Co₁₃ alloy on the substrates heated above 400°C allows a homogeneous poly-quasicrystalline film, consisting of the Ni-rich basic decagonal phase to grow. It has been further indicated by in-plane XRD analysis that the film deposited at 550°C contains a considerable amount of the decagonal grains epitaxially grown on the sapphire substrate. Possible epitaxial relations occurring between the deposit and the substrate will be detailed on the basis of results obtained from electron diffraction measurements.     

Magnetic and structural properties of nanocomposite Co-Ni-Cr-Al-Y-N thin films

The relation between structural and magnetic properties of Co-Ni-Cr-Al-Y-N thin films deposited by reactive r.f. magnetron sputtering was investigated. A marked change in the magnetic behaviour of the films with the different nitrogen partial pressure in the Ar/N₂ deposition atmosphere was observed and qualitatively explained in correlation with the phase composition. The nanocrystalline metal solid-solution obtained at low N₂ content and the nanocrystalline nitride/amorphous composite obtained at high N₂ content are not magnetic, whereas the amorphous phase produced for intermediate N₂ pressures behaves like a ferromagnetic semi-permanent material. The results demonstrate the possibility of modulating the magnetic properties of r.f. magnetron sputtered Co-Ni-Cr-Al-Y-N thin films, thus opening a new route for magnetic multilayer deposition. PACS 68.55.-a; 75.70.Ak; 75.75.+a; 85.70.-w     

The effect of different ambient gases, pressures, and substrate temperatures on TiO2 thin films grown on Si(100) by laser ablation technique

Pure titanium dioxide (TiO₂) thin films were deposited on single-crystal Si(100) substrates by laser ablation. We investigated the effects of ambient gas (O₂ or Ar), pressures, and substrate temperatures on film quality. From the annealing experiment of the deposited TiO₂ thin film under Ar or O₂ ambient gas, we see the chemical effect of ambient gas on film quality. The crystallinity of the deposited TiO₂ thin film is best at 700 °C in the substrate temperature range attempted, 400-700 °C, and at pressures of 0.1 Torr and below. The rutile phase is dominant under most experimental conditions. Only under very extreme conditions did we obtain a thin film of the anatase phase.     

Lanthanide-doped titanium dioxide layers as photocatalysts

Films (∼0.5 mg/cm²) from TiO₂ doped with 1-10 mol% Ln³⁺ (Ln = La or Gd) are deposited on different types of substrates by spray-pyrolysis using ethylene glycol solutions of Ti⁴⁺-Ln³⁺ citric complexes as starting material and O₂ as a carrier gas. The films are post-deposition heated at 500 °C. Their phase composition, crystal structure, morphology, sorption ability and photocatalytic activity are studied. Aqueous solution of methylene blue is applied as a model pollutant. A film with 5 mol% La on Ti-coated stainless steel substrate shows significantly higher photocatalytic activity than the best performing samples produced from commercially available titania.     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

Physical investigations on pulsed laser deposited nanocrystalline ZnO thin films

The nanocrystalline ZnO thin films were deposited by pulsed laser deposition on quartz and i-Si (100) substrates at different substrate temperatures (473 K–873 K) and at different mixed partial pressures (0.05, 0.01, and 0.5 mbar) of Ar+O₂. The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and at lower substrate temperatures were c-axis oriented with predominant (002) crystallographic orientation. At 873 K along with (002) orientation, additional crystallographic orientations were also observed in case of films deposited at 0.01 and 0.5 mbar pressures. The composition of Zinc and Oxygen in ZnO films from EDAX reveals that the films deposited at lower partial pressures were have high at.% of O₂ whereas higher partial pressures and substrate temperatures had high at.% Zn. The surface microstructure of the films show that the films deposited at lower partial pressures (0.05 mbar ) and at lower substrate temperatures (473 K) were found to have nanoparticles of size 15 nm where as films deposited at 873 K have nanorods. The length of these nanorods increases with increasing Ar+O₂ partial pressure to 0.5 mbar. The optical energy gap of the film deposited at lower partial pressure and substrate temperature was 3.3 eV and decrease with the increase of substrate temperatures. The films deposited at 0.5 mbar and at 873 K emitted an intense luminescence at a wavelength of 390 nm. The measured thickness of deposited films by spectroscopic ellipsometry is around 456 nm.     

Application of conversion electron Mössbauer spectrometry to the study of reactive sputtered iron oxide films

The reactive sputtered iron oxide films were investigated by conversion electron Mössbauer spectrometry. The film deposited under controlled oxygen concentration and deposition rate was composed of a non-stoichiometric Fe_3?xO₄, deposited on Al₂O₃ heated at 150°C. This value of x was estimated to be 0.12 and the easy axes of magnetic spin tended to be oriented perpendicular to the surface. The Fe_3?xO₄ film was transformed into γ?Fe₂O₃ by oxidation in air at the temperature range between 205 and 355°C.     

Surface analysis of Fe-Si-Al sputtered alloy films by conversion electron Mössbauer spectrometry

Fe-Si-Al alloy films were deposited on silicon wafers heated to various temperatures by DC Ar sputtering and the microstructure of the films was analyzed by CEMS. As-prepared films on cooled substrate contained superparamagnetic components in addition to magnetic components. The fine grains included yielded a random orientation of magnetic spins in the films. The spin orientation became perpendicular to the surface by annealing the sputtered films at more than 773 K. The magnetic fields in sputtered films on a heated substrate were parallel to the surface.     

Photoluminescence characteristics of ZnGa2O4 thin films prepared by chemical solution method

Zinc gallate (ZnGa₂O₄) thin film phosphors have been formed on ITO glass substrates by a chemical solution method with starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxiethanol as a solution. The thin films were firstly dried at 100 °C and fired at 500 °C for 30 min and then, annealed at 500 °C and 600 °C for 30 min under an annealing atmosphere of 3% H₂/Ar. XRD patterns of the thin film phosphors showed (311) and (220) peak indicating ZnGa₂O₄ crystalline phase in which all the (311) peaks of the film phosphors synthesized on ITO glass and soda-lime glass revealed high intensity with increasing annealing temperature from 500 °C to 600 °C. The ZnGa₂O₄ thin film phosphors represented marked change in AFM surface morphologies according to an annealing temperature under an annealing atmosphere (3% H2/Ar). The film phosphor, annealed at 600 °C, showed the embossed pattern with relatively regular spacing in AFM surface morphology. The ZnGa₂O₄ thin film phosphors formed on ITO glass, which were annealed at different temperatures and showed distinctive spectra with peak wavelengths of 434 nm and 436 nm in the blue emission region.     

Internal stresses and stability of the tetragonal phase in zirconia thin layers deposited by OMCVD

Zirconia thin films were deposited by OMCVD (organo-metallic chemical vapour deposition) at various temperatures and oxygen partial pressures on a AISI 301 stainless steel substrate with Zr(thd)₄ as precursor. The as deposited 250 nm thin zirconia films presented a structure consisting of two phases: the expected monoclinic one and also an unexpected tetragonal phase. According to the literature, the stabilization of the tetragonal phase (metastable in massive zirconia) can be related to the crystallite size and/or to the generated internal compressive stresses.To analyze the effect of internal and external stresses on the thin film behaviour, in-situ tensile experiments were performed at room temperature and at high temperature (500 °C).Depending on the process parameters, phase transformations and damage evolution of the films were observed. Our results, associated to XRD (X-ray diffraction) analyses, used to determine phase ratios and residual stresses within the films, before and after the mechanical experiments, are discussed with respect to their microstructural changes.     

Pressure-controlled preparation of nanocrystalline complex oxides using pulsed-laser ablation at room temperature

Nanocrystalline thin films of complex oxides such as BaTiO₃ and LaFeO₃ were prepared by pulsed laser ablation without substrate heating. Targets under various Ar pressures were irradiated using an ArF excimer laser. The off-axis configuration of targets and substrates was used to synthesize the films. The crystallinity and chemical composition of the deposited films were strongly dependent on the processing Ar gas pressure. In case of BaTiO₃, the film deposited at 10 Pa was a single phase of BaTiO₃ with a crystallite size around 7.2 nm. With increasing Ar pressure to 200 Pa, XRD peaks of BaTiO₃ as well as BaCO₃ were observed. The by-products could be due to reaction with carbon dioxide in air after taking the sample out of the chamber. For LaFeO₃, the films deposited under 50 to 200 Pa had a single phase with a crystallite size below 10 nm. When the Ar pressure exceeded 100 Pa, the crystallite size tended to decrease for both BaTiO₃ and LaFeO₃, which could be due to formation of aggregated nanoparticles. Below 10 Pa, oxygen deficiency was observed. Over 50 Pa, the atomic concentration of all the constituent elements was almost constant, especially the [Ba]/[Ti] and [La]/[Fe] ratios, which were nearly unity. Received: 19 June 2002 / Accepted: 24 June 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +81-298/61-6355, E-mail: yoon-jw@aist.go.jp     

Influence of the reaction conditions on the formation of Tl(Re)-Ba-Ca-Cu-O superconducting thin films by thallination in open system

Rhenium avoids air degradation of the target as well as of precursor thin films during the preparation of high temperature Tl-based superconductors. Addition of Re has been used during synthesis of oriented Tl(Re)-Ba-Ca-Cu-O films. High temperature superconducting Tl-based thin films were prepared by a two step method combining RF magnetron sputtering and ex-situ thallination. Precursors with a composition of Re_0.1Ba₂Ca₂Cu₃O_x were deposited on a CeO₂ buffered R-plane sapphire substrate. The sputtered films were prepared at room temperature in an Ar atmosphere. The thallination of the precursor films was performed in a one zone configuration, where both the pellet and precursor film were kept at the same temperature. The thallination temperature varied in the range of 850–880°C and samples were held for 30, 45 and 60 min at this temperature in a flowing oxygen atmosphere. Besides Tl-2212, X-ray diffraction reveals the possibility of also preparing the Tl-2223 phase, which was until now not reported in a Re doped form. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Optical and electrical properties of p-type transparent conducting CuAlO2 thin film synthesized by reactive radio frequency magnetron sputtering technique

Thin films of p-type transparent conducting CuAlO₂ have been synthesized through reactive radio frequency magnetron sputtering on silicon and glass substrates at substrate temperature 300°C. Reactive sputtering of a target fabricated from Cu and Al powder (1:1.5) was performed in Ar+O₂ atmosphere. The deposition parameters were optimized to obtain phase pure, good quality CuAlO₂ thin films. The films were characterized by studying their structural, morphological, optical and electrical properties.     

Perpendicular magnetic anisotropy of CoPt–AlN composite film with nano-fiber structure

Co–Pt–AlN films were prepared by sputtering a Co–Pt–Al composite target in Ar+N₂ atmosphere. Upon thermal annealing at elevated temperatures, fcc CoPt and a-AlN are formed in the films as phases separated from one other. Both phases develop as fiber-like columnar grains vertical to the substrate and with their lateral size less than 10 nm. Because of the shape anisotropy of the magnetic fiber grains the CoPt–AlN film shows a perpendicular magnetic anisotropy at a thickness equal to or larger than about 25 nm while the Co–TiN [6] and CoPt–TiO₂ [11] films do not unless their thicknesses reach 50 and 100 nm, respectively. This suggests that both the shape anisotropy of the CoPt magnetic fiber grains and their mutual separation in an a-AlN medium work more effectively in the formation with the perpendicular magnetic anisotropy. Such a perpendicular magnetic anisotropy of the CoPt–AlN film associated with the nano-scale feature makes it a very promising candidate for future recording media with ultra-high area density . PACS 75.30.Gw; 75.50.Kj; 81.15.Cd     

LiFePO4 thin films grown by pulsed laser deposition: Effect of the substrate on the film structure and morphology

Well crystallized and homogeneous LiFePO₄/C (LFPO) thin films have been grown by pulsed laser deposition (PLD). The targets were prepared by the sol-gel process at 600 °C. The structure of the polycrystalline powders was analyzed with X-ray powder diffraction (XRD) data. The XRD patterns were indexed having a single phase olivine structure (Pnma). LFPO thin films have been deposited on three different substrates: aluminum (Al), stainless steel (SS) and silicon (Si) by pulsed laser deposition (PLD). The structure of the films was analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It is found that the crystallinity of the thin films depends on the substrate temperature which was set at 500 °C. When annealed treatments were used, secondary phases were found, so, one step depositions at 500 °C were made.Stainless steel is demonstrated to be the best choice to act as substrate for phosphate deposition. LiFePO₄ thin films grown on stainless steel plates exhibited the presence of carbon, inducing a slight conductivity enhancement that makes these films promising candidates as one step produced cathodes in Li-ion microbatteries.     

Improvement of corrosion resistance of carbon steel using chemical vapor deposition from Cr(CO)6 with an ArF excimer laser

Corrosion resistance of carbon steel coated with thin film deposited from Cr(CO)₆ using an ArF excimer laser (193 nm) has been evaluated by an electrochemical method as a function of laser beam intensity. The carbon steel coated with the film formed at higher beam intensity shows higher corrosion resistance. Microstructure, composition, and thickness of the films have also been investigated. SEM micrographs show that the films consist of small grains which decrease in size with increasing beam intensity. Auger electron spectroscopy (AES) combined with Ar⁺ beam sputtering reveals that the films deposited at higher beam intensity give higher chromium content, and that the thickness at a fixed total irradiation energy increases up to the intensity of 10 MW cm^–2, falling above this intensity. In addition, the change of film thickness by addition of buffer gases (Ar, CO, and H₂O) has been investigated. The thickness is 10 times smaller under the addition of H₂O, and twice smaller under the addition of Ar or CO than without the addition of gases. A deposition mechanism based on photolysis of Cr(CO)₆ in the gas phase is proposed related to the experimental data after the discussion of several possible mechanisms.