Zdeněk Frgala

Atmospheric pressure microwave torch for synthesis of carbon nanotubes

The microwave (mw) plasma torch at atmospheric pressure has been studied for carbon nanotube (CNT) synthesis. The depositions were carried out on silicon substrates with 515 nm thin iron catalytic overlayers from the mixture of argon, hydrogen and methane. The optical emission spectroscopy of the torch showed the presence of C2 and CH radicals as well as carbon and hydrogen excited atoms. The vicinity of the substrate influenced the relative intensities and increased the emission of C2. For fixed mw power, the temperature of the substrate strongly depended on its position with respect to the nozzle electrode and on the gas mixture, particularly the amount of H2. The speed of the substrate heating during an early deposition phase had a significant effect on the CNT synthesis. An abrupt increase of the temperature at the beginning increased the efficiency of theCNTsynthesis. Areas of dense straight standing CNTs, 30 nm in average diameter, with approximately the same sized iron nanoparticles on their tops were found in accordance with the model of growth by plasma enhanced chemical vapour deposition. However, the deposit was not uniform and a place with only several nanometres thick CNTs grown on much larger iron particles was also found. Here, taking into account the gas temperature in the torch, 31003900 K, we can see similarities with the dissolutionprecipitation model of the CNT growth by high temperature methods, arc or laser ablation.

Electron density measurements in afterglow of high power pulsed microwave discharge

In the paper we study, be means of microwave interferometry, the evolution of electron density in afterglow of pulsed driven nitrogen discharge. Recombination coeffients are derived, too.

An experimental study of high power microwave pulsed discharge in nitrogen

We investigated a plasma excited by high power pulsed microwaves (MWs) (pulse duration 2.5 µs, repetition rate 400 Hz, peak power 105 W, frequency 9.4 GHz) in nitrogen at reduced pressure (pressure range 10–2000 Pa) with the aim of a better understanding of such types of discharge. The construction of the experimental device suppresses the plasma–wall interactions and therefore the volume processes are predominant. To obtain the temporal evolution of the electron density we used two MW interferometers at frequencies of 15 and 35 GHz with dielectric rod waveguides which gives them the capability of localized measurements. We estimated the effective collision frequency from the absorption of a measurement beam. Time resolved optical emission spectroscopy of the 1st negative system and the 2nd positive system was carried out, too. Due to a high power input the discharge dynamics was fast and the steady state was typically reached in 1 µs. We found that the effective collision frequency has the same temporal behaviour as the 2nd positive system of N2, including a characteristic maximum at the beginning of the pulse.

Raman bands in microwave plasma assisted chemical vapour deposited films

Raman spectroscopy is employed to characterize thin diamond films deposited by microwave plasma assisted chemical vapour deposition technique using a gas mixture of methane and hydrogen. The surface morfology of the films was analyzed by scanning electron microscopy. We have identified submicron crystals on (100) facets of diamond crystals which gave rise to bands in the Raman spectrum centred at 1170 and 1456 cm-1.

Study of Carbon Films on Silicon Substrates

Carbon based films on silicon substrates have been studied by high resolution FE SEM equipped by an EDS analyzer. The first type are carbon nanotube (CNT) [1] films prepared on Si/SiO2 substrates with Ni or Fe layers by radiofrequency plasma chemical vapor deposition. Dependence of nanotube films properties on Ni and Fe thickness and deposition conditions have been studied. The second type of films discussed are microcrystalline and nanocrystalline diamond films grown on pre-treated Si substrates by microwave plasma chemical vapor deposition (MPCVD). The pre-treatment was varied and its effect on diamond films was studied.