E. Andrade

Growth, structure and optical characterization of high quality ZnO thin films obtained by spray pyrolysis

Abstract Zinc oxide thin films were prepared by spray pyrolytic decomposition of zinc acetate onto a glass substrate. Auger spectroscopy showed that the film stoichiometry is close to the ZnO phase with a little excess of oxygen. X-ray diffraction spectra show that the structure belongs to the hexagonal wurtzite crystal type, with a mean crystallite size in the range 20–33xa0nm. Under optimized deposition conditions films are c -axis oriented, having a full width at half-maximum (FWHM) value of the (002) X-ray diffraction line of 0.23°. Microstructure was analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution electron microscopy (HREM). In regard to the crystal growth, a critical temperature was found to be around 600xa0K. Above this critical temperature the film is c -axis oriented and almost all grains became round shaped. Optical constants, n and k , were determined using only transmittance data and a direct band gap of 3.28xa0eV was deduced.

Influence of Al, In, Cu, Fe and Sn dopants in the microstructure of zinc oxide thin films obtained by spray pyrolysis

Abstract A spray pyrolytic system was used to obtain ZnO: X films doped with different elements, X =Al, In, Cu, Fe and Sn. A 0.1 M solution of zinc acetate in a mixture of ethanol and deionised water, in a volume proportion of 3:1, was employed. Dopant sources were aluminium chloride, indium acetate, copper acetate, iron chloride and tin tetrachloride. The atomic percentage of dopant in solution were X /Zn=1, 3, 5, 7, 10 and 15 at.%. The proportion between dopant atoms and Zn atoms are not the same in the film as in solution, only indium-doped films maintain almost the same proportion. In the other cases, the dopant proportion in the film is less than that in the solution. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to study the microstructure and surface morphology of the films. We can conclude that the amount as well as the type of dopant modifies the film growth process and by consequence the microstructure and surface morphology. Since it goes from non-oriented growth, for undoped films, to strongly (002) oriented, at intermediate (~1 at.%) doping level; and finally again to non-oriented and poor crystallinity, at high (>3 at.%) doping level. This behaviour is the same for all the dopants treated in this work and the highest (002) orientation seems to be happening at about the same concentration (~1 at.%). Cross section micrographs show that the microstructure of the films consists of densely packed grains, which can be interpreted as a transition structure between a porous arrangement of tapered crystallites and dense columnar grains.

Structure and morphology of high quality indium-doped ZnO films obtained by spray pyrolysis

Abstract Indium-doped zinc oxide thin films were prepared by spray pyrolytic decomposition of zinc acetate with indium acetate in an alcoholic solution. The films were deposited onto soda lime glass substrate, alumina, and sodium chloride crystal. X-Ray energy dispersive spectroscopy (EDS) and rutherford backscattering spectroscopy (RBS) were used to determine film composition. More detailed information about the crystallographic structure of the films was obtained with the application of Rietveld refinement method to analyse X-ray diffraction spectra. From the position and shape of the X-ray line profiles lattice parameters, domain size and micro strains were determined. Small In amounts (

Structural and Optical Characteristics of Gallium Oxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

Amorphous gallium oxide thin films were prepared by the ultrasonic spray pyrolysis method using gallium acetylacetonate as source material and water as oxidizer. Samples annealed at 850°C during 1 h show the crystalline β-phase of Ga 2 O 3 . Rutherford backscattering results indicate that both as-deposited and annealed films have the stoichiometric chemical composition without incorporation of carbon impurities. Infrared (IR) spectroscopic measurements show that there is no incorporation of O-H and Ga-OH radicals in any of the studied films. The IR spectra for amorphous films show a broad absorption band from 400 to 900 cm -1 , typical for some amorphous metallic oxides. Meanwhile, for the annealed films the IR spectra show well-defined peaks located at 450 and 670 cm -1 related to the β-phase of Ga 2 O 3 . The refractive index of the films shows a strong change from 1.846 for the amorphous films to 1.935 for the annealed ones. The optical bandgap energy values are 4.94 eV for the as-deposited films and 4.99 eV for the annealed films. All these changes are associated with a different microstructure of the annealed films.

Growth and structure of tin dioxide thin films obtained by an improved spray pyrohydrolysis technique

Abstract Undoped and doped tin dioxide thin films have been prepared by an improved method of spray pyrohydrolytic decomposition of SnCl4·5H2O onto a glass substrate. We show that, with this overhead hot-plate and counter flux spray, the gravitational force plays an important role in distinguishing droplets with a radius greater than 26 μm. X-ray diffraction spectra show that the structure is polycrystalline, with a grain size in the range 24–100 nm and a preferred orientation that is thickness dependent. It is shown by observations of the film microstructure by transmission electron microscopy that there is first an amorphous layer with embedded crystallites over which many crystals grow. This microstructure suggests that the films start to grow in an amorphous manner, then film growth continues with the nucleation of many small crystallites and finally some of them grow until a closely packed microstructure of crystallites is formed. Scanning electron microscopy of film surfaces indicates that surface roughness could be responsible for the large decrease in optical transmission of some films. Rutherford backscattering spectroscopy shows that film stoichiometry is close to the SnO2 phase and no significant chlorine contamination is present in the films.

Characterization of amorphous aluminum oxide films prepared by the pyrosol process

Abstract Amorphous aluminum oxide films were deposited by the pyrosol process using aluminum acetylacetonate as source material dissolved in a mixture of three parts of deionized water and one part of methanol. An accelerator ion beam analysis technique was used to obtain the areal density and the chemical composition of the aluminum oxide films, which result in being oxygen-rich when films are deposited at a substrate temperature of 480°C. The infrared spectra show a broad-absorption band from 400 to 1000 cm −1 typical of the vibrations of the Al 2 O 3 . IR analysis also shown that there are no O–H or alanol (Al–OH) groups incorporated in the films and that films kept at air atmosphere at room temperature have a high stability against water adsorption. The refractive index of the films measured by ellipsometry was 1.647. The optical transmission has a value of the order of 88% in the range from 400 to 900 nm for films deposited onto pyrex glass and fused quartz slices. There is no optical absorption edge for wavelengths around 190 nm, which indicates that the deposited films have an energy band gap of at least 6.2 eV. The current density-electric field characteristics of MIM structures, incorporating insulating aluminum oxide films, show current injection across the film for electric fields higher than 2 MV/cm. Electric breakdown was not observed for applied electric fields of the order of 4.5 MV/cm.

Photoluminescence from thin porous films of silicon carbide

Abstract Luminescent porous films were obtained from amorphous epitaxial SiC thin films (200–600xa0nm) deposited on Si substrates using an electrochemical anodization in HF/ethylene glycol solution at high anodic voltages. Porous SiC films possess nearly the same chemical composition as a-SiC ones with slight depletion in carbon. Their photoluminescence peaks at 810xa0nm and achieves maximum intensity at 150–200K. The luminescence mechanism is thought to be due to Si nanoparticles crystallized in the SiC matrix during the anodization process.

Dependency of reactive magnetron-sputtered SiC film quality on the deposition parameters

Abstract SiC thin films have been prepared by using RF reactive magnetron sputtering (RF-RMS). The deposition parameters have been varied over a wide range to optimize the quality of the films; substrate temperature from 700 to 1000°C, Ar/CH 4 composition from 80:20 to 50:50 and RF power from 100 to 200 W. The samples have been characterized by X-ray diffraction, Rutherford backscattering, profilometry, FTIR spectroscopy and ellipsometry. The results show that good quality silicon carbide films can be prepared by using the RF-RMS technique.

Preparation and properties of precursor Ba–Ca–Cu–(O, F) thin films deposited from fluorides for superconducting Tl- and Hg-based films

Abstract Precursor Ba–Ca–Cu–(O, F) thin films prepared by thermal evaporation of BaF2, CaF2 and Cu show good chemical resistance against the atmosphere even after a partial defluorination by means of vacuum annealing with subsequent oxidation. The prepared precursor films were characterized by X-ray diffraction (XRD) analyses and Raman scattering measurements. A possible explanation for the observed properties is presented. According to the XRD measurements performed in the grazing incidence set-up, a polycrystalline cubic BaCuO2 is the main phase after defluorination followed by oxidation. No peaks attributable to carbides (as a consequence of atmospheric exposure of the samples) were identified. Raman analysis confirmed the presence of another phase, namely CuO.