Jiří Bulíř

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. The aim of this work was to study the formation of nanostructured Ag layer and its correlation to the optical behavior.

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.

Nitrogen rich carbon nitride thin films deposited by hybrid PLD technique

Highly nitrogenated CN x films were created by pulsed laser deposition (PLD), combined with radiofrequency (RF) and hollow cathode (HC) discharges. The N/C ratio higher than 1 was measured. Deposition set- up and results of optical measurement are discussed.

Defect studies of Mg films deposited on various substrates

In the present work the structure of Mg films deposited by RF magnetron sputtering was characterized using variable energy positron annihilation spectroscopy combined with scanning electron microscopy and X-ray diffraction. The effect of deposition parameters, namely temperature, type of substrate and deposition rate, on the microstructure was examined. All Mg films studied grow with the basal (0001) plane parallel with the substrate and exhibit only negligible in-plane stress. Films deposited at room temperature are characterized by nanocrystalline structure with high volume fraction of grain boundaries. and positrons are preferentially trapped in open volume defects present at grain boundaries. In these films positrons are trapped predominantly in open-volume defects present at grain boundaries. With increasing deposition temperature the mean grain size increases and the volume fraction of grain boundaries decreases. Hence, in Mg films prepared at elevated temperatures positrons are trapped mainly at misfit dislocations compensating different atomic spacing in the films and the substrate. Moreover, it was found that slow deposition rate leads to higher density of defects compared to fast deposition rate. By annealing of Mg film with thin 20 nm Pd overlayer at 300°C for 1 hour Pd layer is mixed with Mg film forming a Mg-Pd compound. The Mg-Pd phase likely contains structural open-volume defects which trap positrons.

Structural studies of thin Mg films

In the present work variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of defects in Mg films. VEPAS characterization was combined with scanning electron microscopy and X-ray diffraction in order to determine grain size and texture respectively. The aim of this study was to examine the effect of deposition temperature and various substrates on structure and defects in Mg films prepared by RF magnetron sputtering. SEM observations revealed that films deposited on sapphire (0001) substrate exhibit always smaller grains than films deposited on amorphous fused silica and silicon (100) substrates, which have comparable grain size. Defect studies by VEPAS showed that positrons in Mg films studied are trapped at misfit dislocations and at vacancy-like defects in grain boundaries. Moreover, the films deposited on a substrate heated at 300 °C exhibited lower concentration of defects and larger grain size compared to the films deposited at room temperature. Subsequent annealing at 300 °C for 1 h of the films deposited at room temperature causes a slight decrease of defect density due to coarsening of grains.