Michal Novotný

Study of plasma processes during pulsed laser ablation of graphite target in nitrogen

Abstract Plasma processes during CN x films deposition were studied in a pulsed laser deposition system equipped with a KrF excimer laser (500 mJ, 20 ns). The laser plasma was characterized in a pressure range from 2 to 100 Pa of nitrogen gas. We report on an optical emission spectroscopy, which was used for a spatial and time resolved investigation of the plasma species. Analysis includes estimation of vibrational and rotational temperatures of the CN molecule.

Pulsed laser deposition of CNx films: role of r.f. nitrogen plasma activation for the film structure formation

Abstract Thin CN x films were deposited by pulsed laser deposition (PLD) equipped with KrF excimer laser. An additional radio-frequency discharge of the nitrogen gas was applied. The role of atomic nitrogen in CN radical formation was studied using optical emission spectroscopy (OES). The composition of the films was measured by WDX. The N/C ratio of all films was approximately 1 and did not vary greatly with nitrogen pressure.

Positron annihilation study of cavities in black Au films

Defects in a black Au film were studied using variable energy positron annihilation spectroscopy. Black Au films exhibit porous morphology similar to cauliflower. This type of structure enhances the optical absorption due to a multiple reflections in the micro-cavities. A nanostructured black Au film was compared with conventional smooth Au films with high reflectivity. The black Au film exhibited a remarkably enhanced S-parameter in sub-surface region. This is caused by a narrow para-Positronium contribution to the annihilation peak.

Defect studies of ZnO films prepared by pulsed laser deposition on various substrates

ZnO thin films deposited on various substrates were characterized by slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD). All films studied exhibit wurtzite structure and crystallite size 20–100 nm. The mosaic spread of crystallites is relatively small for the films grown on single crystalline substrates while it is substantial for the film grown on amorphous substrate. SPIS investigations revealed that ZnO films deposited on single crystalline substrates exhibit significantly higher density of defects than the film deposited on amorphous substrate. This is most probably due to a higher density of misfit dislocations, which compensate for the lattice mismatch between the film and the substrate.

Preparation of nanostructured ultrathin silver layer

Silver is widely used for a fabrication of plasmonic devices due to its unique optical constants. Nanostructured Ag layer can exhibit strong localized surface plasmon resonance, which mainly affects its optical behavior in visible and near infrared spectra. The nanostructure of the Ag layer is mainly influenced during the initial stage of the silver nucleation. Therefore we focused our attention on the study of this stage of the silver growth. The nanostructured ultra-thin silver layers were prepared by means of the magnetron sputtering. The nucleation mode and the resulting nanostructure was controlled by the deposition conditions. The initial stage of the nucleation and the layer growth was studied by means of an optical monitoring, which is based on a principle of spectrophotometric measurement of sample reflectivity. The measured data were fitted to a model of layered structure. The non-continual (Volmer-Weber) mode of the layer nucleation was clearly distinguished in the monitored data. Thus we were able to estimate the point of the non-continual layer coalescence as well as the subsequent evolution of the surface roughness. The prepared nanostructured Ag layers were analyzed by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Optical properties were studied by spectroscopic ellipsometry and spectrophotometry.

Characterisation of Defects in ZnO Implanted by Hydrogen

In the present work, defects created by implantation of hydrothermally grown ZnO single crystals of high quality with H+ ions were investigated by positron annihilation lifetime (LT) spectroscopy combined with measurements of optical transmittance (OT) and photoluminescence (PL). First, zinc vacancies attached with one hydrogen impurity (VZn – 1H) atom were identified in the virgin ZnO single crystal. The ZnO single crystals were then bombarded by H+ ions with the energy of 2.5 MeV to the fluence of 1016 cm-2. It was found that VZn – VO divacancies were introduced into ZnO by H+-implantation. Effects of H+-implantation on the optical activity of defects in ZnO lattice are characterised in the light of the present OT and PL data.

Rare Earth Doped Gallium Gadolinium Orthogallate Films Prepared by Pulsed Laser Deposition

The decomposition of Gd3Ga5O12 single crystal target induced by a KrF excimer laser pulse during the deposition process was observed. This phenomenon was studied ex situ by EDX analyse of ablated target and in situ by Optical Emission Spectroscopy of the laser plasma. The decomposition process depends mainly on the absorption coefficient of the target on the corresponding laser wavelength and oxygen partial pressure in the deposition chamber during laser ablation. Taking into account the differences between absorption coefficients of Pr:Gd3Ga5O12 and Yb:Gd3Ga5O12 targets the Pr:GdGaO3 and Yb:GdGaO3 thin films were successfully fabricated at different oxygen pressures of 1 Pa and 2.5 Pa, respectively. The structural properties of the fabricated films were studied by RBS and XRD.