Marie Netrvalová

Thickness dependent wetting properties and surface free energy of HfO2 thin films

We show here that intrinsic hydrophobicity of HfO2 thin films can be easily tuned by the variation of film thickness. We used the reactive high-power impulse magnetron sputtering for preparation of high-quality HfO2 films with smooth topography and well-controlled thickness. Results show a strong dependence of wetting properties on the thickness of the film in the range of 50–250 nm due to the dominance of the electrostatic Lifshitz-van der Waals component of the surface free energy. We have found the water droplet contact angle ranging from ≈120° for the thickness of 50 nm to ≈100° for the thickness of 2300 nm. At the same time the surface free energy grows from ≈25 mJ/m2 for the thickness of 50 nm to ≈33 mJ/m2 for the thickness of 2300 nm. We propose two explanations for the observed thickness dependence of the wetting properties: influence of the non-dominant texture and/or non-monotonic size dependence of the particle surface energy.

Preparation of transparent conductive AZO thin films for solar cells

A study of the effect of technology parameters (sputtering power, substrate temperature and post-deposition annealing) on structural, electrical and optical properties of aluminium-doped zinc oxide (AZO) thin films was carried out. The optimal technology parameters of preparation were found to get necessary properties of AZO thin films for application in solar cells - the high figure of merit (F ges 4 %/Omega), low electrical sheet resistance (Rs les 10 Omega/square) and high optical transmittance (T ges 82%, including the glass substrate).

Preparation of shell nanocrystalline Ga-doped ZnO ultra-thin films by sputtering

In this paper the possibility to form ultra-thin homogenous films doped by Ga (ZnO:Ga) by continual or sequential sputtering is presented. An influence of post-deposition annealing on crystalline structure of films was studied. The ability to create a highly consistent coverage (shell) of three dimensional nanostructures (GaP nanowires) by the sequential mode of sputtering was proven.

Influence of deposition temperature on amorphous structure of PECVD deposited a-Si:H thin films

The effect of deposition temperature on the structural and optical properties of amorphous hydrogenated silicon (a-Si:H) thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane diluted with hydrogen was under study. The series of thin films deposited at the deposition temperatures of 50–200°C were inspected by XRD, Raman spectroscopy and UV Vis spectrophotometry. All samples were found to be amorphous with no presence of the crystalline phase. Ordered silicon hydride regions were proved by XRD. Raman measurement analysis substantiated the results received from XRD showing that with increasing deposition temperature silicon-silicon bond-angle fluctuation decreases. The optical characterization based on transmittance spectra in the visible region presented that the refractive index exhibits upward trend with increasing deposition temperature, which can be caused by the densification of the amorphous network. We found out that the scale factor of the Tauc plot increases with the deposition temperature. This behaviour can be attributed to the increasing ordering of silicon hydride regions. The Tauc band gap energy, the iso-absorption value their difference were not particularly influenced by the deposition temperature. Improvements of the microstructure of the Si amorphous network have been deduced from the analysis.

Optical properties of zinc titanate perovskite prepared by reactive RF sputtering

Abstract In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of ZnTiO3 perovskite thin films deposited on glass by reactive magnetron co-sputtering. The members of the series differ by the titanium content that was revealed as an origin of the changes not only in structure but also in dispersive optical properties. Low porosity has been discovered and calculated using the Bruggeman effective medium approximation. An apparent blue-shift of the optical band gap energies with increasing titanium content was observed. The observed band gap engineering is a good prospective for eg optoelectronic and photocatalytic applications of ZnTiO3.

Sputtering of ZnO:Ga thin films with the inclined crystalic texture

In this paper the possibility to form thin films with the inclined crystalic texture by the RF diode sputtering is presented. Two oblique deposition arrangements were used for the preparation of ZnO:Ga thin films with the deviation of their columnar structures in the range of 12 ÷ 15 deg to the substrate normal, i.e. an inclination of their ordinary optical axis. The inclined texture of films has changed their optical transmittance spectra as well as it caused the blue-shift and the change of the optical band-gap.

Structure and optical properties of the hydrogen diluted a-Si:H thin films prepared by PECVD with different deposition temperatures

The paper deals with the hydrogenated amorphous silicon (a-Si:H) films about 300 nm in thickness prepared by using rf-PECVD with hydrogen dilution R = 10 of the silane source gas in the amorphous growth regime onto clean Corning Eagle 2000 glass substrates at different deposition temperatures ranging from 50 to 200 °C. Structural and optical properties of the films were obtained from X-ray diffraction and UV-Vis spectrophotometry. The full width at half maximum of the first scattering peak decreases with increasing of the deposition temperature up to 150 °C and then remains constant. Optical band-gaps are from 1.65 to 1.76 eV, which slightly decrease with increasing deposition temperature, whereas the refractive index increases with increasing deposition temperature. This indicates that the density of the films at higher temperature has increased.

Effect of Doping on the Optical and Structural Properties of ZnO Thin Films Prepared by RF Diode Sputtering

Transparent conductive zinc oxide (ZnO) is a wide direct band gap (3.37 eV at room temperature) semiconductor. Conductive (ρ = 2 x 10 Ωcm) and high transparent (T > 82 %, including Corning glass substrate) n-type ZnO:Al thin films were prepared by RF diode sputtering [1]. Research efforts have been put on the development of p-type ZnO materials for photovoltaics, transparent electronics and organic optoelectronics applications. We obtained p-type ZnO films (minimum ρ = 790 Ωcm, maximum hole concentration p ∼ 2.6 x 10 cm and μ = 22 cmVs) by nitrogen (N2) doping (ZnO:N), and nitrogen-aluminum co-doping (ZnO:Al:N) (ρ = 21 Ωcm, p ∼ 7.8 x 10 cm, μ = 0.4 cmVs) [2,3].

Transparent and conductive ZnO:Al prepared by RF diode sputtering

High transparent and conductive, aluminium - doped zinc oxide thin films (ZnO:Al), were prepared by radio - frequency (RF) diode sputtering from ZnO+2 wt. % Al2O3 target on Corning glass 7059 substrates. The RF power and the substrate temperature modified their structure and surface morphology, electrical and optical parameters. The XRD patterns reveal only one sharp (002) diffraction line, providing a clear evidence for highly textured ZnO films, with a preferential c-axis orientation. Maximum intensity and the lowest full-width at half-maximum (FWHM) (3.26°) of the ΩM-scan were obtained for ZnO:Al deposited at 800 W RF power and 200°C substrate temperature. The developed ZnO:Al have a low electrical resistivity (2 × 10−3 Ωcm) and high optical transmittance (> 82 %, including Corning glass substrate) in the visible region. The direct optical band gap (~ 3.3 eV) increases with the increasing carrier concentration.

Transition from A-Si:H to Si 3 N 4 in thin films deposited by PECVD technology from silane diluted with nitrogen

Series of a-SiN:H thin films similar in thickness (380 ± 10 nm) and a-Si:H/a-Si3N4 multi-layered films (515 ± 20 nm) were prepared by PECVD technology from silane mixed with argon (90 % Ar/10 % SiH4) on Corning Eagle 2000 glass, SiO2 and silicon substrates. Deposition of thin films was carried out on a Samco PD 220 NA PECVD system. Multi-layered films were consequently annealed at high temperatures (700-1100°C) in order to obtain silicon nanocrystals embedded in a dielectric matrix suitable for photovoltaic and photonic applications. X-ray diffraction, Raman and FTIR spectroscopies, TEM, SEM, UV Vis spectrophotometry and spectroscopic ellipsometry were used for the evaluation of material properties of the films.