Vít Kudrle

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.

Characterization of a periodic instability in filamentary surface wave discharge at atmospheric pressure in argon

This study reports on a periodic instability in a microwave atmospheric pressure surface wave plasma. Time-resolved observation by means of a high-speed camera reveals that the discharge can operate in two different regimes. The discharge operates either in a static mode of a controlled number of filaments propagating alongside the wall of the fused silica tube or in a dynamic mode of one or more straight filaments together with one revolving filament. Microwave power and argon flow rate are interpreted as the scaling parameters that govern the self-organization in the discharge. The operating diagram is formed by alternating stripes of static and dynamic mode with well-defined borders.

PECVD of nanostructured SiO2 in a modulated microwave plasma jet at atmospheric pressure

Atmospheric pressure plasma enhanced chemical vapour deposition (AP-PECVD) of thin films by means of a microwave plasma jet operating with mixtures of argon and tetrakis(trimethylsilyloxy)silane (TTMS) is reported for the first time. In contrast to other siloxy-alkanes that are commonly used for PECVD, the molecule of TTMS (C12H36O4Si5) exhibits a complex and symmetric molecular structure which is presumably essential for a large scale nanostructuring of the films. Deposited films have been characterized by means of electron microscopy (SEM), x-ray spectroscopy (EDX), and infra-red spectroscopy (FTIR). The applied methods demonstrate the prevalent inorganic SiO2-like character of the films and their highly fractalized nanostructure over a wide range of dimension 100?104?nm. Contact angle measurements show the superhydrophobicity of the films, while the dispersive component of the surface energy can be varied in a controlled way by low-frequency amplitude modulation of the excitation power of the MW discharge. The modulation regimes of the jet have been investigated by means of time-resolved optical emission spectroscopy in order to describe the oscillations of plasma parameters e.g. rotational temperature from OH and relative emission of silicon atoms to substantiate the reproducibility of the deposition conditions and to correlate the plasma properties with the resulting film properties.

On the oxygen addition into nitrogen post-discharges

It is well known that the dissociation degree of nitrogen can be substantially increased if a small amount of oxygen is added into an active discharge. In this work it is experimentally shown that a very similar phenomenon occurs also when oxygen is added into the nitrogen late post-discharge. A detailed kinetic model, valid for the oxygen addition into the active discharge, fails to interpret these new experimental observations, and, consequently, its completeness has to be questioned.

Mechanical and microwave absorbing properties of carbon-filled polyurethane.

Polyurethane (PU) matrix composites were prepared with various carbon fillers at different filler contents in order to investigate their structure, mechanical and microwave absorbing properties. As fillers, flat carbon microparticles, carbon microfibers and multiwalled carbon nanotubes (MWNT) were used. The microstructure of the composite was examined by scanning electron microscopy and transmission electron microscopy. Mechanical properties, namely universal hardness, plastic hardness, elastic modulus and creep were assessed by means of depth sensing indentation test. Mechanical properties of PU composite filled with different fillers were investigated and the composite always exhibited higher hardness, elastic modulus and creep resistance than un-filled PU. Influence of filler shape, content and dispersion was also investigated.

Surface Treatment by Atmospheric-Pressure Surfatron Jet

Using an atmospheric-pressure surface-wave-driven jet, the surfatron, we carried out the surface treatment of the silicon, polyamide, and wood. The changes in surface energy of the samples were determined by the contact angle measurements. Some of the results show rather quick treatment time, probably due to a high power density in the surfatron device.

Simultaneous measurement of N and O densities in plasma afterglow by means of NO titration

In this work we describe a method based on NO titration that permits us to measure at the same time the absolute concentrations of N and O atoms in the gas phase. This method is suitable for low concentrations of oxygen atoms. We also discuss the validity of the titration method, especially the influence of the reaction time. It was used to study the influence of O2 admixture on the degree of dissociation of nitrogen in the afterglow. The results of the NO titration technique were compared with those obtained by means of electron paramagnetic resonance and with the relative values determined from emission of .

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.

SYNTHESIS OF CARBON NANOSTRUCTURES BY PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION AT ATMOSPHERIC PRESSURE

Synthesis of Carbon Nanostructures by Plasma Enhanced Chemical Vapour Deposition at Atmospheric Pressure Carbon nanostructures present the leading field in nanotechnology research. A wide range of chemical and physical methods was used for carbon nanostructures synthesis including arc discharges, laser ablation and chemical vapour deposition. Plasma enhanced chemical vapour deposition (PECVD) with its application in modern microelectronics industry became soon target of research in carbon nanostructures synthesis. Selection of the ideal growth process depends on the application. Most of PECVD techniques work at low pressure requiring vacuum systems. However for industrial applications it would be desirable to work at atmospheric pressure. In this article carbon nanostructures synthesis by plasma discharges working at atmospheric pressure will be reviewed.

α-Fe nanopowder synthesised in low-pressure microwave plasma and studied by Mössbauer spectroscopy

An iron-based nanocomposite has been prepared by the microwave plasma method: Fe(CO)5 vapour was introduced into an argon discharge at ~1 kPa. The synthesised nanopowder was passivated in situ with a mixture of Ar and air. The as-prepared nanopowder was characterised by XRD, TEM, Raman and M?ssbauer spectroscopies. In the XRD pattern of the nanopowder the ?-Fe (dXRD = 14 nm, 76 wt.%) and Fe3O4 (dXRD = 3 nm, 24 wt.%) phases were identified only. ?-Fe cores covered with oxide shells were observed under TEM. A huge increase of M?ssbauer absorption was observed after the sample was cooled down to 5 K. The results of magnetic and thermal properties studies at low and high temperature are presented. The heat capacity of the sample exhibited an unexpectedly high value of 599 J/kg/K.