M. Čada

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.

Photoanodes with Fully Controllable Texture: The Enhanced Water Splitting Efficiency of Thin Hematite Films Exhibiting Solely (110) Crystal Orientation.

Hematite, α-Fe2O3, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity of hematite is a substantial limitation reducing its efficiency in real experimental conditions. Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to 4 orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. Here, we present a strategy for controlling the crystal orientation of very thin hematite films by adjusting energy of ion flux during advanced pulsed reactive magnetron sputtering technique. The texture and effect of the deposition mode on the film properties were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott-Schottky analysis. The precise control of the synthetic conditions allowed to fabricate hematite photoanodes exhibiting fully textured structures along (110) and (104) crystal planes with huge differences in photocurrents of 0.65 and 0.02 mA cm(-2) (both at 1.55 V versus RHE), respectively. The photocurrent registered for fully textured (110) film is among record values reported for thin planar films. Moreover, the developed fine-tuning of crystal orientation having a huge impact on the photoefficiency would induce further improvement of thin hematite films mainly if cation doping will be combined with the controllable texture.

Time-resolved investigation of dual high power impulse magnetron sputtering with closed magnetic field during deposition of Ti–Cu thin films

Time-resolved comparative study of dual magnetron sputtering (dual-MS) and dual high power impulse magnetron sputtering (dual-HiPIMS) systems arranged with closed magnetic field is presented. The dual-MS system was operated with a repetition frequency 4.65 kHz (duty cycle ≈50%). The frequency during dual-HiPIMS is lower as well as its duty cycle (f=100 Hz, duty 1%). Different metallic targets (Ti, Cu) and different cathode voltages were applied to get required stoichiometry of Ti–Cu thin films. The plasma parameters of the interspace between magnetrons in the substrate position were investigated by time-resolved optical emission spectroscopy, Langmuir probe technique, and measurement of ion fluxes to the substrate. It is shown that plasma density as well as ion flux is higher about two orders of magnitude in dual-HiPIMS system. This fact is partially caused by low diffusion of ionized sputtered particles (Ti+,Cu+) which creates a preionized medium.

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.

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.

Plasma diagnostics of low pressure high power impulse magnetron sputtering assisted by electron cyclotron wave resonance plasma

This paper reports on an investigation of the hybrid pulsed sputtering source based on the combination of electron cyclotron wave resonance (ECWR) inductively coupled plasma and high power impulse magnetron sputtering (HiPIMS) of a Ti target. The plasma source, operated in an Ar atmosphere at a very low pressure of 0.03 Pa, provides plasma where the major fraction of sputtered particles is ionized. It was found that ECWR assistance increases the electron temperature during the HiPIMS pulse. The discharge current and electron density can achieve their stable maximum 10 μs after the onset of the HiPIMS pulse. Further, a high concentration of double charged Ti++ with energies of up to 160 eV was detected. All of these facts were verified experimentally by time-resolved emission spectroscopy, retarding field analyzer measurement, Langmuir probe, and energy-resolved mass spectrometry.

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.

Investigation of ionized metal flux in enhanced high power impulse magnetron sputtering discharges

The metal ionized flux fraction and production of double charged metal ions Me2+ of different materials (Al, Cu, Fe, Ti) by High Power Impulse Magnetron Sputtering (HiPIMS) operated with and without a pre-ionization assistance is compared in the paper. The Electron Cyclotron Wave Resonance (ECWR) discharge was employed as the pre-ionization agent providing a seed of charge in the idle time of HiPIMS pulses. A modified grid-free biased quartz crystal microbalance was used to estimate the metal ionized flux fraction ξ. The energy-resolved mass spectrometry served as a complementary method to distinguish particular ion contributions to the total ionized flux onto the substrate. The ratio between densities of doubly Me2+ and singly Me+ charged metal ions was determined. It is shown that ECWR assistance enhances Me2+ production with respect of absorbed rf-power. The ECWR discharge also increases the metal ionized flux fraction of about 30% especially in the region of lower pressures. Further, the suppression o...

Ionization of sputtered Ti, Al, and C coupled with plasma characterization in HiPIMS

The ionization of sputtered Ti, Al, and C has been investigated in non-reactive high-power impulse magnetron sputtering discharges using Ar as a process gas. Two complementary techniques, time-reso ...