Z. Hubička

Notes on the photo-induced characteristics of transition metal-doped and undoped titanium dioxide thin films.

This study reports the preparation of thin nanoparticulate films of titanium dioxide and its modified version doped with a transition metal. The behavior of prepared films was described by means of their photocatalytic and photo-induced electrochemical properties. The TiO(2) and M/TiO(2) (M=Ag, Zr, Fe) thin films were produced via a standard sol-gel method using titanium n-butoxide, acetylacetone, and transition metal acetylacetonates as precursors. Prepared films were analyzed by a series of techniques involving XRD, Raman spectroscopy, SEM, AFM, and XPS. Their photocatalytic activity was monitored with the aid of decomposition of the model compound Rhodamine B in water. All films were then tested for their photo-induced electrochemical properties based on evaluation of polarization curves (photocurrents). The highest reaction rate constant (0.0101min(-1)), which was even higher than that for pure TiO(2), was obtained for the Ag/TiO(2) sample. The highest quantum yield of the charge collection was determined for the undoped TiO(2) film.

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.

Barrier-torch discharge plasma source for surface treatment technology at atmospheric pressure

The description and investigation of a new atmospheric plasma source for the treatment and coatings of surfaces are presented in this paper. This new system is a modification of a well-known atmospheric torch discharge stabilized by a flowing channel of the working gas through an RF powered nozzle. The new version of this source prevents the transition to the regime with hot electrodes. This modification is suitable for surface and coatings applications of such substrates sensitive to overheating causing undesirable phase transition or melting. The new source called in our paper as an RF barrier-torch atmospheric discharge employs dielectrically coated nozzles instead of bare metallic ones. In that case, the plasma jet has quite different properties, as it is clear from presented experiments. The new version allowed excitation of the atmospheric plasma channel interacting with the substrate independently on the conductivity of the substrate. Simultaneously it is possible to hold the substrate temperature under atmospheric jet interaction below the limit point of aluminium melting or below an even lower limit of 80°C in a pulse-modulated mode. Extension to the multi-nozzle barrier-torch system was attained with the application of nine quartz nozzles. This multi-plasma jet excitation and its interaction was demonstrated with the substrate made of either quartz or aluminium plate, both possibly with non-flat shape. Emission spectroscopy and RF voltage and current amplitude measurements were employed in order to characterize the RF barrier-torch discharge.

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.

Investigation of RF and DC plasma jet system during deposition of highly oriented ZnO thin films

Abstract RF and DC plasma jet sputtering systems were investigated as sources for deposition of ZnO thin films. Deposited zone films have a strong orientation of hexagonal crystallites with the ‘ c ’ axis perpendicular to the substrate surface. Temperature of the substrate did not exceed 150 °C during the deposition. Langmuir probe measurement performed at the substrate revealed two groups of electrons with different temperatures in the DC plasma jet. A single group of electrons was found in the RF plasma jet system. Electron concentration in the RF jet was found to be about n eRF ≈5×10 9 –10 10 cm −3 with temperature T eRF ≈2.5–3.5 eV. In the DC plasma jet, concentration of cold electrons was usually n ec ≈10 9 cm −3 with temperature T ec ≈0.5 eV and concentration of hot electrons was n eh ≈10 8 cm −3 with temperature T eh ≈2–3.5 eV. Photographs also confirmed that the plasma density is higher in the position of the substrate in the RF jet than in the DC jet. Other obtained macroscopic parameters as plasma potential and floating potential relative to the grounded reactor are presented.

Deposition of InxOy and SnOx thin films on polymer substrate by means of atmospheric barrier-torch discharge

Abstract Barrier torch discharge was used for low temperature deposition of In x O y and SnO x thin films at atmospheric pressure on polymer substrates. Vapors of Sn- and In-acetylacetonat were used as growth precursors for the deposition process of SnO x and In x O y thin films. Transparent films of conductivity σ SnO ≈10 S/cm for SnO x and σ InO ≈10 2 S/cm for In x O y were deposited on polymer substrates under conditions when the atmospheric plasma jet directly interacted with the polymer substrate. Plasma jet excitation had to be pulse modulated in order to avoid thermal damages of the polymer substrate. SnO x and In x O y were also deposited in a different discharge mode, in which interaction of the light emitting plasma jet with the substrate did not directly occur. In this case, the films had pure adhesion and had electrical conductivity lower than σ −3 S/cm. The analysis by an electron microprobe system has shown that the films had chemical composition close to SnO 2 and In 2 O 3 , respectively. XRD diffraction did not confirm any crystalline phase in all the deposited samples.

Investigation of the RF plasma jet system for deposition of LiCOOx thin films

Abstract The RF plasma jet system was investigated as a source for the sputtered deposition of LiCoO x thin films. As preliminary results of experiments, LiCoO x films with hexagonal high temperature structure were deposited. The RF hollow cathode in the shape of the cylindrical nozzle was sintered from powder of LiCoO 2 . This hollow cathode was reactively sputtered in Ar+O 2 . Plasma jet parameters were investigated during the sputtering process by a Langmuir probe system in the position of the substrate. The electron energy distribution function (EEDF) deviated from the Maxwellian distribution mainly in the energetic range below 5 eV. For higher energies above this value, the EEDF could be approximated with a Maxwellian fit in the limited interval of energies. Obtained electron concentrations were in the range n e =10 9 –6×10 10 cm −3 and were strongly dependent on the magnitude of the applied RF power P RF . Electron temperature T eh describing only the limited energy part of EEDF was calculated from this Maxwellian fit and the dependence of T eh on P RF is discussed. Besides XRD, deposited films were investigated by electron microprobe system, scanning electron microscopy and cyclic voltammetry.

Low-pressure RF multi-plasma-jet system for deposition of alloy and composite thin films

A plasma-chemical reactor with a multi-plasma-jet RF hollow-cathode system has been developed for the deposition of alloy and composite thin films. Two primary plasma-jet channels and one secondary plasma channel were created in the volume of the reactor. High-density plasma flowing in these plasma-jet channels is generated inside the nozzles. These work simultaneously as RF hollow cathodes. An RF hollow cathode discharge is generated in these nozzles and is subsequently blown out of the reactor, creating flowing plasma jets. These jets were used for the deposition of SiGe and ZrCN thin films as an example of the deposition of alloy and composite thin films with this system. Co-sputtering or reactive co-sputtering of the nozzle material using high-density RF hollow-cathode plasma was applied for the deposition process. Control of the composition of the thin films was accomplished by setting the relative distance between the nozzle outlets without changing the plasma density inside the RF hollow cathodes. The composition of films was investigated with an electron microprobe system equipped with an X-ray microanalyser. This apparatus allowed quantitative analysis of the films. The stoichiometric homogeneity of the films was studied with this technique. Optical emission spectroscopy was used to investigate the secondary plasma-jet channel.

CNx coatings deposited by pulsed RF supersonic plasma jet: hardness, nitrogenation and optical properties

Abstract A low pressure pulsed RF supersonic plasma jet system (RPJ) has been used for deposition of CN x thin films. The aim of the CN x thin films deposition was an application for tribological coatings. Chemical composition, mechanical and optical properties of deposited CN x films have been measured. The obtained parameters were found to be similar to those of CN x films prepared by DC magnetron sputtering. The deposition rate for the CN x films prepared in RPJ reactor was of approximately 2 μm/h. During the deposition process, the substrate temperature did not exceed 250°C, as required for certain kinds of machine tribological coatings. A strong correlation between DC bias magnitude, nitrogen concentration and mechanical properties was found. The value of the substrate bias V DC =−100 V was found to be optimal for deposition of hard CN x films with maximum microhardness H =22 GPa. The films with the highest microhardness had the lowest atomic concentration of nitrogen. Analogous correlation has been found in ‘Diamond Relat. Mater. 7 (1998) 417’, although the deposition method and conditions were quite different. The chemically active plasma has been investigated in the RF supersonic plasma jet channel during the deposition process by means of ‘in situ’ emission spectroscopy. The mechanism of CN x formation has been studied as well.

Investigation of the atmospheric RF torch-barrier plasma jet for deposition of CeOx thin films

Abstract An atmospheric pressure RF torch-barrier discharge system with flowing plasma jet channel was studied as a tool for coatings of aluminum substrates by CeO x thin films. Cerium precursors were supplied to the plasma jet in the form of aerosol of the water solution of cerium salts. CeO x thin films were obtained on the Al substrate at certain deposition conditions. Properties of deposited CeO x films were studied by electron microprobe system. Surface of the films was analyzed by XPS method. ‘In situ’ emission spectroscopy of active plasma jet channel was performed in order to obtain more parameters about atmospheric plasma jet channel.