J. Budai

Reactive pulsed laser deposition of hydrogenated carbon thin films: The effect of hydrogen pressure

Diamondlike properties of amorphous carbon films can be enhanced by applying reactive hydrogen atmosphere during pulsed laser deposition (PLD) as shown by recent studies. The complex phenomena occurring during carbon plume expansion has not been examined yet thoroughly. Therefore we deposited amorphous hydrogenated carbon thin films in hydrogen ambient atmosphere (4×10−4–25Pa) by PLD at room temperature. The deposited films were characterized by Rutherford backscattering spectrometry, elastic recoil detection analysis, Raman spectroscopy, infrared spectroscopy, variable angle spectroscopic ellipsometry, and nanoindentation measurements. At low hydrogen pressures (below ∼0.1Pa), when the mean free path of plasma constituents in the background gas is larger than the target substrate distance, the deposited films show diamondlike properties. At higher pressures (above ∼0.1Pa) the deposited films change their diamondlike carbon character towards to a structure which contains increasing amount of sp2 bonded ca...

Laser-induced backside dry etching : wavelength dependence

The laser-induced backside dry etching (LIBDE) method has been developed by analogy with the well-known LIBWE technique for micromachining of transparent materials. In our experiments tin thin films were applied as absorbing layers and the dependence of the etch depth on the applied laser wavelength was investigated. Multipulse irradiation experiments at different wavelengths have also been carried out. A fused silica plate coated by a tin layer was used as a target. The metal film–transparent material interface was irradiated through the fused silica plate by the most frequently used nanosecond excimer laser beams: ArF (193 nm), KrF (248 nm) and XeCl (308 nm). It was found that the etch depth increased linearly with decreasing wavelength in investigated range. Multipulse investigations proved that the energy of the absorbed photons has a strong influence on the mechanism of LIBDE. The etch depth–pulse number curves showed saturation at 1500 mJ cm−2 applied laser fluence at around 2, 3 and 30 pulses for 308 nm, 248 nm and 193 nm wavelengths, respectively. This indicates that the effectiveness of multipulse LIBDE increases when the wavelength of the applied laser source is decreased in the UV range. XPS and spectroscopic ellipsometric analyses showed that formation and embedding of tin-oxides into the upper surface layer can be responsible for the shift of the saturation in the case of ArF as compared with the other studied wavelengths.

Interactions at the Peptide/Silicon Surfaces: Evidence of Peptide Multilayer Assembly

Selective deposition of peptides from liquid solutions to n- and p-doped silicon has been demonstrated. The selectivity is governed by peptide/silicon adhesion differences. A noninvasive, fast characterization of the obtained peptide layers is required to promote their application for interfacing silicon-based devices with biological material. In this study we show that spectroscopic ellipsometry-a method increasingly used for the investigation of biointerfaces-can provide essential information about the amount of adsorbed peptide material and the degree of coverage on silicon surfaces. We observed the formation of peptide multilayers for a strongly binding adhesion peptide on p-doped silicon. Application of the patterned layer ellipsometric evaluation method combined with Sellmeier dispersion led to physically consistent results, which describe well the optical properties of peptide layers in the visible spectral range. This evaluation allowed the estimation of surface coverage, which is an important indicator of adsorption quality. The ellipsometric findings were well supported by atomic force microscopy results.

Measurement of nanoplasmonic field enhancement with ultrafast photoemission

Plasmonic enhancement of optical near-fields at nanostructures provides for localization of the energy of light on the nanoscale. This phenomenon allowed pioneering applications in spectroscopy, photovoltaics and sensorics. It remains a challenge to measure the extent of the maximum achievable nanoplasmonic field enhancement for a particular sample. Even though near-field probing methods such as scanning near-field optical microscopy (SNOM) can reach a resolution down to 8–10 nm, probing near-fields on ∼1 nm scale needs a different approach. Here, we demonstrate a method for nanoplasmonic near-field measurement with the help of photoemitted electrons induced by femtosecond laser pulses.

Ellipsometric Analysis of Aligned Carbon Nanotubes for Designing Catalytic Support Systems

Vertically aligned CNT carpets combined with inorganic semiconductors are expected good prospect in practical applications, especially in photocatalysis. If these devices are in production, a fast and non-invasive characterization method will be required. Ellipsometry is widely used in industry as an in-line monitoring tool, so in this study the applicability of ellipsometry for characterizing CNT carpets is investigated. It is shown that ellipsometric evaluation can provide information about the density and the optical properties of the nanotubes; however, the properties of the individual nanotubes (diameter, wall number) can not be taken into account during ellipsometric modeling. To overcome these limitations, numerical simulations are also presented.