Petr Synek

Sensing properties of multiwalled carbon nanotubes grown in MW plasma torch: electronic and electrochemical behavior, gas sensing, field emission, IR absorption.

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures.

Synthesis of carbon nanotubes by plasma-enhanced chemical vapor deposition in an atmospheric-pressure microwave torch

There are many different techniques for the synthesis of carbon nanotubes (CNTs), and plasma technologies experience a significant competitor in thermal chemical vapor deposition (CVD) processes. A particular process is, therefore, selected according to the specific requirements of an application, which clearly differ for the development of composites as compared to nanoelectronics, field emission, displays, sensors, and the like. This paper discusses the method for the synthesis of CNTs using an atmospheric-pressure microwave (MW) torch. It was successfully applied in the fast deposition of multiwalled nanotubes (MWNTs) on a substrate without the necessity of any vacuum or heating equipment. Dense straight-standing nanotubes were prepared on Si substrates with and also without barrier SiOx layer. Therefore, it was possible to produce CNTs directly on conductive Si and to use them as an electron-emitting electrode of the gas pressure sensor. The CNTs grown in MW torch were also used to create a gas sensor based on the changes of electrical resistance measured between two planar electrodes connected by the CNTs.

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.

Study of Microwave Torch Plasmachemical Synthesis of Iron Oxide Nanoparticles Focused on the Analysis of Phase Composition

This work presents the results obtained on the single-step route towards the synthesis of iron oxide nanoparticles in a microwave plasma torch. The torch is supplied by 660xa0sccm of Ar mixed with 1xa0sccm of Fe(CO)5 and a variable amount of O2. The influence of oxygen addition on the phase composition of the synthesized powder was studied. Magnetite and maghemite phases could not be distinguished using the standard X-ray diffraction (XRD) analysis. Therefore, a combined XRD and Raman spectra analysis had to be applied, which is based on fitting of selected diffraction peaks and spectral features. According to XRD and Raman spectroscopy, the powder synthesized from Ar/Fe(CO)5 consisted about 50xa0% of magnetite, Fe3O4, the rest being α-Fe and FeO. An increase in oxygen flow rate led to an increase in γ-Fe2O3 percentage, at the expense of α-Fe, FeO and Fe3O4. Almost pure γ-Fe2O3 was synthesized at oxygen flow rates 25–75×xa0higher than the flow rate of Fe(CO)5. A further increase in the oxygen flow rate led to α-Fe2O3 and ε-Fe2O3 production. The distributions of nanoparticles’ (NPs) diameters were obtained using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The mean diameter of the NPs measured by TEM was 13xa0nm while the DLS measurements led to the mean diameter of 12xa0nm. About 90xa0% of all particles had the diameter in the range of 5–21xa0nm but a few larger particles were observed in TEM micrographs.

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.

State-by-state emission spectra fitting for non-equilibrium plasmas: OH spectra of surface barrier discharge at argon/water interface

Optical emission spectroscopy applied to non-equilibriumnplasmas in molecular gases can give important information onnbasic plasma parameters, including the rotational andnvibrational temperatures and densities of the investigatednradiative states. In order to precisely understand thennon-equilibrium of rotational-vibrational state distributionnfrom the investigated spectra without limiting presumptions, anstate-by-state temperature-independent fitting procedure is thenideal approach. In this paper, we present a novel software toolndeveloped for this purpose, freely available for the scientificncommunity. The introduced tool offers a convenient way tonconstruct Boltzmann plots even from partially overlappingnspectra, in a user-friendly environment. We apply the novelnsoftware to the challenging case of OH spectra in surfacenstreamer discharges generated from the triple-line of thenargon/water/dielectrics interface. After the barrier dischargenis characterised by ICCD and electrical measurements, thenspatially and phase resolved rotational temperatures fromnN2(C-B) and OH(A-X) spectra are determined and compared. Thenprecise analysis shows that OH(A) states with quantum numbersn(v=0, 9 <= N <= 13) are overpopulated with respect to thenfound two-Boltzmann distribution. We hypothesise that fastnvibrational-energy transfer is responsible for this phenomenon,nobserved here for the first time. Finally, the vibrationalntemperature of the plasma and the relative populations of hotnand cold OH(A) states are quantified spatially and phasenresolved.

Iron-Based Nanopowders Containing α-Fe, Fe3C, and γ-Fe Particles Synthesised in Microwave Torch Plasma and Investigated with Mössbauer Spectroscopy

Two Fe-based nanopowders were synthesised using microwave torchndischarge at 1 bar. The main channel of the discharge wasnoperating in Ar, which flowed through the central nozzle of annelectrode, whereas the reactive mixture H(2)/Fe(CO)(5) wasnadded through a concentric outer nozzle. Besides rarelynobserved gamma-Fe particles (for the first sample: d(XRD) = 30nnm, 35 wt %; for the second sample: d(XRD) = 9 nm, 33wt %)nsamples also included alpha-Fe, Fe(3)C, andnFe(3)O(4)/gamma-Fe(2)O(3) particles. The presence of gamma-Fenphase was proved by the interpretation of the XRD patterns andnthe Mossbauer spectra taken at 293 and 5 K.

An Array of Micro-hollow Surface Dielectric Barrier Discharges for Large-Area Atmospheric-Pressure Surface Treatments

A robust, commercial micro-hollow plasma source was used to generate atmospheric-pressure plasma, of surface area 18xa0×xa018xa0mm, in ambient air, nitrogen and argon. An electrode system consisting of 105 micro-hollow surface dielectric barrier discharges was powered by sinusoidal high-voltage at a frequency of 26.7xa0kHz. The influence of the plasmas on the polycarbonate surface was investigated by means of surface energy measurements and X-ray photoelectron spectroscopy. It emerged that short plasma exposures led to significant increases in surface energy. It is suggested that this may arise out of incorporation of polar groups on the polycarbonate surface. A thermal camera was used to monitor the plasma source surface temperatures for the gases at flow rates ranging from 0 to 5xa0L/min. It was found that the temperature of the micro-hollow ceramic when operated upon in ambient air decreased significantly from 147xa0°C at 0xa0L/min to 49xa0°C at 5xa0L/min. In order to investigate further the thermal properties of the plasma, optical emission spectroscopy was employed to monitor the vibrational and rotational temperatures of the plasma generated in ambient air. CCD camera spectroscopic measurements estimated plasma thickness and temperature distribution at high spatial resolution.

On the interplay of gas dynamics and the electromagnetic field in an atmospheric Ar/H2 microwave plasma torch

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.