Nevena Puač

Time resolved optical emission images of an atmospheric pressure plasma jet with transparent electrodes

We study development of plasma packages in atmospheric pressure plasma jet from their formation as a discharge close to the instantaneous cathode, following their motion between and inside the electrodes up to their emergence at the edge of the glass tube and formation of a plasma bullet. Inside both electrodes, plasma is concentrated close to the walls and is bright, while outside it is located at the axis. This paper opens issues of the geometry of electrodes, fields, and atomic processes, allowing some predictions to be made about pertinent mechanisms.

Improved properties of oxygen and argon RF plasma-activated polyester fabrics loaded with TiO2 nanoparticles.

The potentials of low-pressure capacitively coupled RF oxygen and argon plasmas for the activation of polyester fibers surface that can enhance the deposition of colloidal TiO(2) nanoparticles were discussed. SEM and XPS analysis confirmed the plasma-induced morphological and chemical changes on the surface of polyester fibers. Oxygen and argon plasma pretreated polyester fabrics loaded with TiO(2) nanoparticles provided maximum reduction of Gram-negative bacteria E. coli and UV blocking. The self-cleaning effects tested on blueberry juice stains and photodegradation of methylene blue in aqueous solution proved excellent photocatalytic activity of TiO(2) nanoparticles deposited onto fiber surface. Although both plasmas significantly contributed to overall improvement of properties of such nanocomposite textile material, oxygen plasma treatment, in particular, enhanced the deposition of colloidal TiO(2) nanoparticles and thus ensured superior effects.

The effect of a plasma needle on bacteria in planktonic samples and on peripheral blood mesenchymal stem cells

In this paper, we study the application of a plasma needle to induce necrosis in planktonic samples containing a single breed of bacteria. Two different types of bacteria, Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922), were covered in this study. In all experiments with bacteria, the samples were liquid suspensions of several different concentrations of bacteria prepared according to the McFarland standard. The second system studied in this paper was human peripheral blood mesenchymal stem cells (hPB-MSC). In the case of hPB-MSC, two sets of experiments were performed: when cells were covered with a certain amount of liquid (indirect) and when the cell sample was in direct contact with the plasma.Most importantly, the study is made with the aim to see the effects when the living cells are in a liquid medium, which normally acts as protection against the many agents that may be released by plasmas. It was found that a good effect may be expected for a wide range of initial cell densities and operating conditions causing destruction of several orders of magnitude even under the protection of a liquid. It was established independently that a temperature increase could not affect the cells under the conditions of our experiment, so the effect could originate only from the active species produced by the plasma. In the case of those hPB-MSC that were not protected by a liquid, gas flow proved to produce a considerable effect, presumably due to poor adhesion of the cells, but in a liquid the effect was only due to the plasma. Further optimization of the operation may be attempted, opening up the possibility of localized in vivo sterilization.

Measurements of voltage–current characteristics of a plasma needle and its effect on plant cells

In this paper we present voltage–current–power characteristics of a plasma needle operating in the flow of helium at atmospheric pressure. In addition, we show some examples of how such a plasma affects plant tissues. In the characterization of the plasma needle, current and voltage waveforms were recorded by two derivative probes. These two probes are similar to the probes previously used by Puac et al for measuring transmitted power in low pressure CCP rf discharge. The instantaneous power was calculated from current and voltage waveforms and U–I characteristics of the discharge were determined. Regimes of operation with and without the grounding ring at the tip of the needle were considered. We have chosen two model systems to study the effect of the plasma needle on plant cells and tissues: sweet fern gametophyte (prothallus) and calli produced in vitro. Since the prothallus consists of a single layer of cells, the cytological effects could be easily examined. In addition, calli and prothallus are easy to manipulate and in vitro culture provides a possibility to work under constant and controlled conditions.

Environmental impact of plasma application to textiles

Plasma technology is currently implemented in a wide range of industrial processes due to high efficiency, low environmental impact and simplicity. Low-temperature plasma treatment can be an alternative to traditional wet processes in textile preparation and finishing, causing modification of the fibre surface, which is mainly responsible for the material end-use properties i.e. wettability, dyeability, printability, shrinking, pilling etc. Appropriate choice of gas and control of plasma operation conditions provide a variety of effects on textiles (improvement of dyeability, printability and colour fastness, improvement of adhesion properties of coated fabrics, increase in hydrophobicity and water resistance, etc.). However, in spite of extraordinary efficiency, multifunctionality and simplicity, low-temperature plasma treatments still cannot replace all wet finishing processes, though they can be viable pretreatments that offer plenty of environmental and economical benefits.

Functionalization of Polyester Fabric by Ar/N2 Plasma and Silver

The objective of this research was to use Ar/N2 (50%:50%) plasma to increase the adhesion of nano silver particles to raw polyester fabric. RUCO-BAC AGP was applied using the exhaust method. X-ray photoelectron spectroscopy revealed differences in surface composition between the Ar/N2 plasma-treated and untreated raw fabrics. The Ar/N2 plasma treatment was found to increase the surface carbon concentration and decrease the concentration of C-O and O-C=O groups on the surface. After plasma etching, the specific surface of the polyester fabric and properties related to it were found to change significantly. This change was confirmed by a decrease in the whiteness index and an increase in the dyeability of the polyester fabric with disperse dye. Morphological changes in the surface of plasma-treated polyester fabric enabled greater adhesion of nano silver particles and increased the antimicrobial effect with respect to Pseudomonas aeruginosa, Escherichia coli and Streptococcus faecalis.

Mass analysis of an atmospheric pressure plasma needle discharge

Mass spectrometric measurements of a plasma needle (an example of atmospheric pressure non-equilibrium plasma source) were made for neutrals and ions. The measurements were performed for the same geometry as the standard plasma needles albeit for a somewhat increased gas flow. We discuss some of the problems of performing mass analysis at atmospheric pressures.The yields of N, O and NO radicals from the plasma needle were determined for different powers of the RF source and different flow rates of working gas. Positive ions generated by the plasma needle itself were measured for the first time. Significant conversion of feed gases (nitrogen and oxygen) into radicals and ions of N and O, and NO was observed as well as depletion of atomic radicals N and O which in chemical reactions form more complex molecules. Biomedical and nanotechnology applications of atmospheric pressure plasmas require a detailed understanding of the source, and mass analysis is perhaps the best technique to focus on chemical kinetics and in many ways interaction with surfaces.

Low Pressure RF Capacitively Coupled Plasma Reactor for Modification of Seeds, Polymers and Textile Fabrics

Plasma reactor operating at low pressures (0.2-1 Torr) at 13.56 MHz has been developed with an idea to optimize the treatment of polymers, biological and textile materials. The reactor proved very effective in treatment of polymer surfaces and wool fabrics in order to improve wettability, efficiency of dyeing and printing as well as to reduce the felting shrinkage. It also gave good results in improving germination of seeds. The basic conditions that the reactor has to satisfy are: the energy of ions that hit the surface has to be low and the reactor should be efficient in production of active radicals. Two systems with different geometries were studied, both capacitively coupled plasma reactors operating at 13.56 MHz. Cylindrical geometry was selected in order to minimize the energy of ions reaching the surface. Modeling of the discharge was performed with an aim to verify the energy distribution function of ions. As a critical diagnostic test of the system, voltage and current probes were developed to check the operation mode of the discharge. Oxygen, air and argon were used with different results.

Spectroscopic ellipsometry of few-layer graphene

The optical properties of few-layer graphene (FLG) films were measured in the ultraviolet and visible spectrum using a spectroscopic ellipsometer equipped with a 50-mu m nominal microspot size. The FLG thickness was found by atomic force microscopy. Measurements revealed that the microspot is larger than the FLG flake. The ellipsometric data was interpreted using the island-film model. Comparison with graphite and recently published graphene data showed reasonable agreement, but with some features that could not be explained. The error margin for the optical constants was estimated to be +/- 10%.

Characterization and global modelling of low-pressure hydrogen-based RF plasmas suitable for surface cleaning processes

In this paper we present results of measurements and global modelling of low-pressure inductively coupled H2 plasma which is suitable for surface cleaning applications. The plasma is ignited at 1 Pa in a helicon-type reactor and is characterized using optical emission measurements (optical actinometry) and electrical measurements, namely Langmuir and catalytic probe. By comparing catalytic probe data obtained at the centre of the chamber with optical actinometry results, an approximate calibration of the actinometry method as a semi-quantititative measure of H density was achieved. Coefficients for conversion of actinometric ratios to H densities are tabulated and provided. The approximate validity region of the simple actinometry formula for low-pressure H2 plasma is discussed in the online supplementary data (stacks.iop.org/JPhysD/46/475206/mmedia). Best agreement with catalytic probe results was obtained for (Hβ, Ar750) and (Hβ, Ar811) actinometric line pairs. Additionally, concentrations of electrons and ions as well as plasma potential, electron temperature and ion fluxes were measured in the chamber centre at different plasma powers using a Langmuir probe. Moreover, a global model of an inductively coupled plasma was formulated using a compiled reaction set for H2/Ar gas mixture. The model results compared reasonably well with the results on H atom and charge particle densities and a sensitivity analysis of important input parameters was conducted. The influence of the surface recombination, ionization, and dissociation coefficients, and the ion–neutral collision cross-section on model results was demonstrated.