Plasma-generated Species Research Articles

Copper-Capped Carbon Nanocones on Silicon: Plasma-Enabled Growth Control

Controlled self-organized growth of vertically aligned carbon nanocone arrays in a radio frequency inductively coupled plasma-based process is studied. The experiments have demonstrated that the gaps between the nanocones, density of the nanocone array, and the shape of the nanocones can be effectively controlled by the process parameters such as gas composition (hydrogen content) and electrical bias applied to the substrate. Optical measurements have demonstrated lower reflectance of the nanocone array as compared with a bare Si wafer, thus evidencing their potential for the use in optical devices. The nanocone formation mechanism is explained in terms of redistribution of surface and volumetric fluxes of plasma-generated species in a developing nanocone array and passivation of carbon in narrow gaps where the access of plasma ions is hindered. Extensive numerical simulations were used to support the proposed growth mechanism.

Assessing embryonic stem cell response to surface chemistry using plasma polymer gradients

The control of cell–material interactions is the key to a broad range of biomedical interactions. Gradient surfaces have recently been established as tools allowing the high-throughput screening and optimization of these interactions. In this paper, we show that plasma polymer gradients can reveal the subtle influence of surface chemistry on embryonic stem cell behavior and probe the mechanisms by which this occurs. Lateral gradients of surface chemistry were generated by plasma polymerization of diethylene glycol dimethyl ether on top of a substrate coated with an acrylic acid plasma polymer using a tilted slide as a mask. Gradient surfaces were characterized by X-ray photoelectron spectroscopy, infrared microscopy mapping and profilometry. By changing the plasma polymerization time, the gradient profile could be easily manipulated. To demonstrate the utility of these surfaces for the screening of cell–material interactions, we studied the response of mouse embryonic stem (ES) cells to these gradients and compared the performance of different plasma polymerization times during gradient fabrication. We observed a strong correlation between surface chemistry and cell attachment, colony size and retention of stem cell markers. Cell adhesion and colony formation showed striking differences on gradients with different plasma polymer deposition times. Deposition time influenced the depth of the plasma film deposited and the relative position of surface functional group density on the substrate, but not the range of plasma-generated species.

S055034 高温・高圧下でのDBD空気プラズマ流の反応性流動特性

Plasma is a multi-functional flow with high energy density. In the nonequilibrium plasma flow, active species such as radicals, excited species and charged particles are effectively generated by high energy electron impact reactions. Oxygen radical and ozone in plasma-generated active species have strong oxidation potential and play an important role in chemical reactions. Recently researches on the application of nonequiriblium plasma flow to combustion enhancement in an internal combustion engine has been extensively conducted. However, most of the researches of nonequilibrium plasma flow were conducted under atmospheric pressure condition and fundamental characteristics of nonequilibrium plasma under high pressure condition as in the internal engines have not been clarified in detail. It is important to clarify the fundamental characteristics of nonequilibrium plasma flow under high temperature and high pressure conditions. Therefore, the purpose of this research is to provide the fundamental data such as radicals and ozone generation in nonequilibrium plasma flow under high temperature and high pressure conditions for the application to combustion enhancement in an internal combustion engine. Experimental analysis of air plasma flow by dielectric barrier discharge was conducted. Fundamental characteristics of discharge such as the oxygen radical and ozone productions by dielectric barrier discharge for various operating conditions were discussed in detail.

The roles of various plasma species in the plasma and plasma-catalytic removal of low-concentration formaldehyde in air

The contributions of various plasma species to the removal of low-concentration formaldehyde (HCHO) in air by DC corona discharge plasma in the presence and absence of downstream MnO x /Al 2O 3 catalyst were systematically investigated in this study. Experimental results show that HCHO can be removed not only by short-living active species in the discharge zone, but also by long-living species except O 3 downstream the plasma reactor. O 3 on its own is incapable of removing HCHO in the gas phase but when combined with the MnO x /Al 2O 3 catalyst, considerable HCHO conversion is seen, well explaining the greatly enhanced HCHO removal by combining plasma with catalysis. The plasma-catalysis hybrid process where HCHO is introduced through the discharge zone and then the catalyst bed exhibits the highest energy efficiency concerning HCHO conversion, due to the best use of plasma-generated active species in a two-stage HCHO destruction process. Moreover, the presence of downstream MnO x /Al 2O 3 catalyst significantly reduced the emission of discharge byproducts (O 3) and organic intermediates (HCOOH).

DNA strand scission induced by a non-thermal atmospheric pressure plasma jet

The DNA molecule is observed to be very susceptible to short-term exposures to an atmospheric pressure plasma jet. The DNA damage induced by plasma-generated species, i.e. excited atoms, charged particles, electrons and UV light is determined.

Plasma heating effects in catalyzed growth of carbon nanofibres

A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) that accounts for the nanostructure heating by ion and etching gas fluxes from the plasma is developed. Using the model, it is shown that fluxes from the plasma environment can substantially increase the temperature of the catalyst nanoparticle located on the top of the CNF with respect to the substrate temperature. The difference between the catalyst and the substrate temperatures depends on the substrate width, the length of the CNF, the neutral gas density and temperature as well as the densities of the ions and atoms of the etching gas. In addition to the heating of the nanostructure, the ions and etching gas atoms from the ionized gas environment also strongly affect the CNF growth rates. Due to ion bombardment, the CNF growth rates in plasma enhanced chemical vapour deposition may be much higher than the rates in similar neutral gas-based thermal processes. The CNF growth model, which accounts for the nanostructure heating by the plasma-generated species, provides the growth rates that are in better agreement with the available experimental data on CNF growth than the models in which the heating effects are ignored.

Deterministic Surface Growth of Single-Crystalline Iron Oxide Nanostructures in Nonequilibrium Plasma

An innovative approach to precise tailoring of surface density, shapes, and sizes of single-crystalline α-Fe 2O 3 nanowires and nanobelts by controlling interactions of reactive oxygen plasma-generated species with the Fe surface is proposed. This strongly nonequilibrium, rapid, almost incubation-free, high-rate growth directly from the solid-solid interface can also be applied to other oxide materials and is based on deterministic control of the density of oxygen species and the surface conditions, which determine the nanostructure nucleation and growth.

Characterization of gaseous species in scanning atmospheric rf plasma with transmission infrared spectroscopy

A scanning atmospheric radio-frequency (rf) plasma was analyzed with transmission infrared (IR) spectroscopy. The IR analyses were made for the plasmas used for hydrophobic coating deposition and superhydrophobic coating deposition processes. Since the rf plasma was generated in a small open space with a high gas flow rate in ambient air, the density of gas-phase molecules was very high and the plasma-generated reactive species seemed to undergo various reactions in the gas phase. So, the transmission IR spectra of the scanning atmospheric rf plasma were dominated by gas-phase reaction products, rather than plasma-generated intermediate species. In the CH4∕He plasma used for hydrophobic coating deposition, C2H6, C2H2, and a small amount of C2H4 as well as CO were detected in transmission IR. The intensities of these peaks increased as the rf power increased. The CO formation is due to the activation of oxygen and water in the air. In the CF4∕H2∕He plasma used for deposition of superhydrophobic coatings, C2F6, CF3H, COF2, and HF were mainly detected. When the H2∕CF4 ratio was ∼0.5, the consumption of CF4 was the highest. As the H2∕CF4 ratio increased higher, the C2F6 production was suppressed while the CF3H peak grew and the formation of CH4 were detected. In both CH4∕He and CF4∕H2∕He plasma systems, the undissociated feed gas molecules seem to be highly excited vibrationally and rotationally. The information on plasma-generated reactive species and their reactions was deduced from the distribution of these gas-phase reaction products.

Plasma-assisted self-organized growth of uniform carbon nanocone arrays

The self-organized growth of uniform carbon nanocone arrays using low-temperature non-equilibrium Ar + H 2 + CH 4 plasma-enhanced chemical vapor deposition (PECVD) is studied. The experiment shows that size-, shape-, and position-uniform carbon nanocone arrays can develop even from non-uniformly fragmented discontinuous nickel catalyst films. A three-stage scenario is proposed where the primary nanocones grow on large catalyst particles during the first stage, and the secondary nanocones are formed between the primary ones at the second stage. Finally, plasma-related effects lead to preferential growth of the secondary nanocones and eventually a uniform nanopattern is formed. This does not happen in a CVD process with the same gas feedstock and surface temperature. The proposed three-stage growth scenario is supported by the numerical experiment which generates nanocone arrays very similar to the experimentally synthesized nanopatterns. The self-organization process is explained in terms of re-distribution of surface and volumetric fluxes of plasma-generated species in a developing nanocone array. Our results suggest that plasma-related self-organization effects can significantly reduce the non-uniformity of carbon nanostructure arrays which commonly arises from imperfections in fragmented Ni-based catalyst films.

Plasma-assisted co-evaporation of β-indium sulfide thin films

Abstract This paper describes the development of plasma-assisted co-evaporation (PACE) for the formation of β -In 2 S 3 thin films. Indium was supplied by conventional thermal evaporation, while the chalcogen gas precursor (H 2 S) was activated using an inductively coupled plasma (ICP) source. Using a combination of optical emission spectroscopy and mass spectrometry it was shown that the ICP effectively dissociated H 2 S, producing atomic sulfur. Transport modeling was used to quantify the flux distributions of the co-evaporated metal and the plasma-generated species impinging the substrate. Model predictions were validated by measurements of deposition rate and film properties. Substantial improvements in both materials utilization and substrate temperature reduction were realized with respect to conventional co-evaporation. β -In 2 S 3 was formed as low as 100 °C and it was observed that quality was a strong function of S/In ratio. The grain size decreased and the optical band gap increased as the substrate temperature was reduced.

Efficient polyatomic interference reduction in plasma-source mass spectrometry via collision induced dissociation

Evidence is provided that illustrates quadrupole ion traps can be used to selectively attenuate strongly bound diatomic ions occurring at the same nominal mass as an analyte ion of interest. Dissociation rates for TaO+ (D0 ∼ 750 kJ mol−1) are found to be at least an order of magnitude larger than the loss rate of Au+ due to scattering under “slow heating” resonance excitation conditions at qz = 0.67 and using neon as the bath gas. This rate difference is sufficient for the selective removal of this strongly-bound diatomic ion over the loss of the Au+ at the same mass-to-charge ratio. Other examples of quadrupole ion trap CID for the selective reduction of common plasma-generated species are also evaluated by examining the dissociation of GdO+ in the presence of Yb+, and Cu2+ in the presence of Te+. In each case, a different method of applying the excitation signals is presented, and the attenuation rates for the diatomic species due to CID are substantially larger than scattering losses for the bare metal ions. Evidence is also presented that demonstrates CID can be accomplished in concert with a slow mass analysis scan, thereby providing a means of (1) eliminating polyatomic ions (formed in the plasma or reaction cell) over an extended mass range, (2) recovering metal ion signal from the metal-containing polyatomic ions, and (3) minimizing deleterious secondary reactions of product ions.

An examination of the role of plasma treatment for lean NO x reduction over sodium zeolite Y and gamma alumina Part 2 : Formation of nitrogen

NO x reduction with NO 2 as the NO x gas in the absence of plasma was compared to plasma treated lean NO x exhaust where NO is converted to NO 2 in the plasma. Product nitrogen was measured to prove true chemical reduction of NO x to N 2. With plasma treatment, NO as the NO x gas, and a NaY catalyst, the maximum conversion to nitrogen was 50% between 180 and 230 °C. The activity decreased at higher and lower temperatures. At 130 °C a complete nitrogen balance could be obtained, however between 164 and 227 °C less than 20% of the NO x is converted to a nitrogen-containing compound or compounds not readily detected by gas chromatograph (GC) or Fourier transform infrared spectrometer (FT-IR) analysis. With plasma treatment, NO 2 as the NO x gas, and a NaY catalyst, a complete nitrogen balance is obtained with a maximum conversion to nitrogen of 55% at 225 °C. For γ-alumina, with plasma treatment and NO 2 as the NO x gas, 59% of the NO x is converted to nitrogen at 340 °C. A complete nitrogen balance was obtained at these conditions. As high as 80% NO x removal over γ-alumina was measured by a chemiluminescent NO x meter with plasma treatment and NO as the NO x gas. When NO is replaced with NO 2 and the simulated exhaust gases are not plasma treated, the maximum NO x reduction activity of NaY and γ-alumina decreases to 26 and 10%, respectively. This is a large reduction in activity compared to similar conditions where the simulated exhaust was plasma treated. Therefore, in addition to NO 2, other plasma-generated species are required to maximize NO x reduction.

ADVERSE CONSEQUENCES OF ERYTHROCYTE EXPOSURE TO MENADIONE: INVOLVEMENT OF REACTIVE OXYGEN SPECIES GENERATION IN PLASMA

Previous studies demonstrated that menadione, a representative quinone compound, reacts nonenzymatically with thiols in plasma, resulting in the generation of reactive oxygen species and potentiation of menadione-induced platelet damage. Because of the reported association of menadione with hemolytic anemia in vivo, investigations were undertaken to identify the free radicals generated from the interaction of menadione with plasma, and to assess the potential role of plasma-generated free-radical species in menadione-dependent erythrocyte toxicity. In rat plasma, menadione increased the rate of oxygen consumption and both luminol- and lucigenin-amplified chemiluminescence in a concentration-dependent manner. Superoxide dismutase (SOD) inhibited lucigenin-amplified chemiluminescence, suggesting formation of superoxide anion. Menadione also induced significant increases in chemiluminescence when erythrocytes were suspended in plasma, but not when cells were suspended in buffer. Consistent with these findings, menadionedependent hemolysis of erythrocytes occurred only when the cells were suspended in plasma. Various free-radical inhibitors were tested for their ability to inhibit menadioneinduced hemolysis. Catalase and mannitol each produced significant inhibition, including an additive effect when both compounds were present, while SOD had no marked effect. In addition, pretreatment with 3-amino-1,2,4-triazole, an intracellular catalase inhibitor, potentiated menadione-induced cytotoxicity in the presence of plasma. These results suggest that both hydrogen peroxide and hydroxyl radicals are involved in menadionemediated plasma erythrocyte cytotoxicity; however, superoxide anion does not appear to play a direct role.

Surface functionalization of polymeric substrates from radio frequency-plasma-generated silylium ions

The mechanism of rf-discharge-induced fragmentation of SiCl4 was studied by separating the components of the molecular mixture (GC-MS, HR-MS) resulting from the ex situ recombination of plasma-generated active species and by simulating the plasma-induced chemistry under low-energy electron mass spectroscopy conditions. It was found that SiCl+3 (silylium) ions and corresponding radicals were the predominant molecular fragments in the discharge; accompanied by small quantities of SiCl2- and SiCl-based species. Plasma origin SiClx active species were effectively implanted onto polypropylene, polyester, cellulose, and polytetrafluoroethylene surfaces and the modified relative surface atomic compositions were evaluated by photoelectron spectroscopy. Analytical data indicate that SiClx fragments can effectively replace H, OH, and even fluorine atoms on the polymeric structures. Surface characteristics like wettability and morphology of the plasma modified polymeric substrates were estimated by dynamic contact angle evaluation and atomic force microscopy. It was demonstrated that the surface modifications are reproducible and stable with time. Potential applications of SiCl4 plasma modified polymeric surfaces are suggested.