Harm Wulff

Structural studies of ITO thin films with the Rietveld method

Abstract Tin doped indium oxide (ITO) films of different tin concentrations were deposited by e-beam evaporation onto glass substrates. These ITO films were investigated using grazing incidence X-ray diffractometry (GIXRD). The application of the Rietveld refinement to GIXRD patterns provides information about the crystallographic structure of the films. Lattice constants, atomic positions and bond lengths were calculated for different doping concentrations. From the shifting and broadening of X-ray line profiles domain sizes and microstrains were calculated. Small tin amounts cause decreasing lattice constants and also a decrease in In/Sn1 In/Sn2 bond lengths. The In/Sn1 O bond length increases and the distortion of the asymmetric In/Sn2 O octahedron becomes stronger. At larger doping concentrations both lattice constants and In/Sn1 In/Sn2 lengths increase. The In/Sn1 O bond length and the distortion of the In/Sn2 octahedron first decrease, but with further tin insertion an increase of these parameters is observed. The microstrains calculated from X-ray line profile analysis correlate with the distortion behaviour of the In/Sn2 O octahedrons. With increasing domain sizes the resistivity of the films decreases. Therefore it can be concluded that the conductivity of tin doped In 2 O 3 films is not dominated by grain boundaries. Some mechanisms of the tin insertion into the In 2 O 3 lattice are discussed.

Formation of TiOx films produced by high-power pulsed magnetron sputtering

Formation of thin TiOx films produced by pulsed planar magnetron sputtering deposition is reported in this paper. The formation process and layer growth were controlled by (i) the ratio of reactive O2 in Ar/O2 working gas mixture and (ii) the pressure in the vacuum chamber. The magnetron, operated in a high-power pulse mode with a low repetition frequency of 250 Hz, reached maxima peak current Ip ~ 50 A and magnetron current density peaks at ip ~ 1 A cm−2. Particular spectral lines (Ar = 420.07 nm, Ar+ = 487.98 nm, Ti = 518.96 nm) emitted by the discharge were investigated using time-resolved photon counting measurements. The phases of deposited TiOx films were determined by grazing incidence x-ray diffractometry and thickness and density were calculated from x-ray reflectometry measurements; in addition composition and chemical bounds were revealed by x-ray photoelectron spectroscopy. The film diagnostics survey the existence of different crystalline phases in the Ti–O system and their formation. Discharge properties for example, deposition rate and time evolution of discharge current are also discussed.

Effect of nitrogen doping on TiOxNy thin film formation at reactive high-power pulsed magnetron sputtering

The paper is focused on a study of formation of TiOxNy thin films prepared by pulsed magnetron sputtering of metallic Ti target. Oxygen and nitrogen were delivered into the discharge in the form of reactive gases O2 and N2. The films were deposited by high-power impulse magnetron sputtering working with discharge repetition frequency f = 250 Hz at low (p = 0.75 Pa) and high (p = 10 Pa) pressure. The substrates were on floating potential and thermally stabilized at room temperature during the deposition process. Post-deposition thermal annealing was not employed. The chemical composition from x-ray photoelectron spectroscopy diagnostic reveals formation of TiOxNy structure at low flow rate of oxygen in the discharge gas mixture. This result is confirmed by XRD investigation of N elements incorporation into the Ti–O lattice. Decrease in band-gap to values Eg ~ 1.6 eV in TiOxNy thin film is attributed to formed Ti–N bonds. The discharge properties were investigated by time-resolved optical emission spectroscopy. Time evolution of particular spectral lines (Ar+, Ti+, Ti) is presented together with peak discharge current.

Physical properties of homogeneous TiO2 films prepared by high power impulse magnetron sputtering as a function of crystallographic phase and nanostructure

Optical, photo-electrochemical, crystallographic and morphological properties of TiO2 thin films prepared by high power impulse magnetron sputtering at low substrate temperatures (<65 °C) without post-deposition thermal annealing are studied. The film composition—anatase, rutile or amorphous TiO2—is adjusted by the pressure (p ~ 0.75–15 Pa) in the deposition chamber. The different crystallographic phases were determined with grazing incidence x-ray diffractometry. The surface morphology and size of TiO2 grains/clusters were imaged with atomic force microscopy. Basic plasma parameters were determined by means of the time-resolved Langmuir probe technique. The power density influx on the substrate was estimated from calorimetric probe measurement. The data from calorimetric probe measurements and time-resolved Langmuir probe served as input parameters for the calculation of influx contributions of particular species. The band-gap energy Eg depends on the film composition and crystallographic phase. Optical parameters (refractive index n + ik, transmittance T, reflectance R and absorbance A) are measured as functions of photon energy in the UV–Vis range by spectroscopic ellipsometry. For the rutile and anatase films agreement with the respective bulk phase is found. Incident photon-current conversion efficiency determined by photo-electrochemical measurements reached the highest values (0.312) for the anatase film.

Electrochemical behaviour of solid lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) in an aqueous electrolyte system

Abstract Lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) were synthesized by self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. These transition metal oxides were mechanically immobilized on the surface of paraffin-impregnated graphite electrodes and their cyclic voltammetric behaviour in aqueous alkali electrolytes was examined. It was shown that both the oxides undergo proton insertion upon the reduction of Co3+ to Co2+ in LiCoO2 and Mn4+ to Mn3+ in LiMn2O4, while they deintercalate protons on the reverse oxidation. Scanning electron microscopy reveals spherical LiCoO2 particles with a very narrow size distribution. Energy dispersive X-ray detection proved the absence of metal cation intercalation.

Examples for application and diagnostics in plasma?powder interaction

Low-pressure plasmas offer a unique possibility of confinement, control and fine tailoring of particle properties. Hence, dusty plasmas have grown into a vast field and new applications of plasma-processed dust particles are emerging. There is demand for particles with special properties and for particle-seeded composite materials. For example, the stability of luminophore particles could be improved by coating with protective Al2O3 films which are deposited by a PECVD process using a metal-organic precursor gas. Alternatively, the interaction between plasma and injected micro-disperse powder particles can also be used as a diagnostic tool for the study of plasma surface processes. Two examples will be provided: the interaction of micro-sized (SiO2) grains confined in a radiofrequency plasma with an external ion beam as well as the effect of a dc-magnetron discharge on confined particles during deposition have been investigated.

Investigation of diffusion and crystallization processes in thin ITO films by temperature and time resolved grazing incidence X-ray diffractometry

Oxygen diffusion into metallic In/Sn films and crystallite growth of thin indium tin oxide (ITO) films were investigated by in situ high temperature grazing incidence X-ray diffractometry (HT-GIXRD) at temperatures ranging from 100 to 300 °C. The investigated films were deposited by dc magnetron sputtering from a metallic target at different oxygen flows and bias voltages. The deposition process influences not only the film properties but also the film reactions during the post-deposition annealing process. The ITO formation is determined by two processes: the diffusion of oxygen into the metallic grains and a fast crystallization process. Kinetic parameters for both processes were derived. A model was developed which allows the determination of the diffusion coefficient D from the time dependence of the integral intensity of the ITO X-ray reflection. Diffusion coefficients as well as the activation energies are influenced by the bias voltage but not by the oxygen flow. According to the Johnson–Mehl–Avrami theory, the crystallization can be described as a two-dimensional process.

Characterization of the energy flux toward the substrate during magnetron sputter deposition of ZnO thin films

The characterization of energy influxes from plasma to substrate during sputter deposition of ZnO films is presented and discussed. Measurements were carried out in a triple rf magnetron sputter deposition system using calorimetric probes in various Ar/N2 and Ar/H2 mixtures at typical substrate positions. By variation of the probe bias the different contributions originating from the kinetic energy of charge carriers, the recombination of charge carriers (electrons and ions) at the surface as well as the contributions from the impact of neutral sputtered particles and subsequent film growth were determined. Radial scans in the substrate plane were recorded to obtain information about inhomogeneities in the total energy influx.The results show that the crystallinity reaches its optimum at that Ar/N2 ratio where the influence of the bombarding ions reaches its lowest value, indicating the destructive character of ion impact. Radial measurements indicate the influence of the magnetic field on the homogeneity of the energy influx caused by the superposition of the three (balanced) magnetic configurations. The superposition leads to an ?unbalanced character? resulting in a lowering of the electron trapping. The admixture of H2 leads to a drastic increase in the energy influx due to molecule formation at the (substrate/probe) surface.

Nonaqueous Atomic Layer Deposition of Aluminum Phosphate

Aluminum phosphate was deposited onto bundles of carbon fibers and flat glassy carbon substrates using atomic layer deposition by exposing them to alternating pulses of trimethylaluminum and triethylphosphate vapors. Energy dispersive X-ray spectroscopy (EDXS) and solid state nuclear magnetic resonance (SS-NMR) spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic (SEM) images revealed that the coatings are uniform and conformal. After coating, the fibers are still separated from each other like the uncoated fibers. Thermogravimetric analysis (TGA) indicates an improvement of oxidation resistance of the coated fibers compared to uncoated fibers.

Complex (dusty) plasmas: Examples for applications and observation of magnetron- induced phenomena*

Low-pressure plasmas offer a unique possibility of confinement, control, and fine tailoring of particle properties. Hence, dusty plasmas have grown into a vast field, and new applications of plasma-processed dust particles are emerging. During the deposition of thin amorphous films onto melamine formaldehyde (MF) microparticles in a C2H2 plasma, the generation of nanosized carbon particles was also studied. The size distribution of those particles is quite uniform. In another experiment, the stability of luminophore grains could be improved by coating with protective Al2O3 films that are deposited by a plasma-enhanced chemical vapor deposition (PECVD) process using a metal-organic precursor gas. Coating of SiO2 microparticles with thin metal layers by magnetron sputtering is also described. Especially the interaction of the microsized grains confined in a radio frequency (rf) plasma with the dc magnetron discharge during deposition was investigated. The observations emphasize that the interaction between magnetron plasma and injected microdisperse powder particles can also be used as a diagnostic tool for the characterization of magnetron sputter sources.