Solitary filamentary structures and nanosecond dynamics in atmospheric-pressure plasmas driven by tailored dc pulses

Nanosecond dynamics of two separated discharge cycles in an asymmetric dielectric barrier discharge is studied using time-resolved current and voltage measurements synchronized with high-speed (∼5 ns) optical imaging. Nanosecond dc pulses with tailored raise and fall times are used to generate solitary filamentary structures (SFSs) during the first cycle and a uniform glow during the second. The SFSs feature ∼1.5 mm thickness, ∼1.9 A peak current, and a lifetime of several hundred nanoseconds, at least an order of magnitude larger than in common microdischarges. This can be used in alternating localized and uniform high-current plasma treatments in various applications.

Room-temperature, atmospheric plasma needle reduces adenovirus gene expression in HEK 293A host cells

Room-temperature, atmospheric-pressure plasma needle treatment is used to effectively minimize the adenovirus (AdV) infectivity as quantified by the dramatic reduction of its gene expression in HEK 293A primary human embryonic kidney cells studied by green fluorescent protein imaging. The AdV titer is reduced by two orders of magnitude within only 8 min of the plasma exposure. This effect is due to longer lifetimes and higher interaction efficacy of the plasma-generated reactive species in confined space exposed to the plasma rather than thermal effects commonly utilized in pathogen inactivation. This generic approach is promising for the next-generation anti-viral treatments and imunotherapies.

Gold nanoresistors with near-constant resistivity in the cryogenic-to-room temperature range

Using a multiple plasma deposition-annealing (MDA) technique, we have fabricated an Au nanoisland-based thin film nanoresistor with a very low temperature coefficient of electrical resistivity in a cryogenic-to-room temperature range of 10 to 300 K. The nanoislanded gold film was deposited on a SiO2/Si wafer (500 nm SiO2 thickness) between two 300 nm thick Au electrodes which were separated by 100 m. A sophisticated selection of the thickness of the nanoislanded gold film, the annealing temperature, as well as the number of deposition/annealing cycles resulted in the fabrication of a nanoresistor with a temperature coefficient of electrical resistivity of 2.1 × 10-3 K-1 and the resistivity deviation not exceeding 2% in a cryogenic-to-room temperature range. We have found that the constant resistivity regime of the nanoisland-based thin film nanoresistor corresponds to a minimized nanoisland activation energy (approximately 0.3 meV). This energy can be minimized by reducing the nearest neighbor distance and increasing the size of the Au nanoislands in the optimized nanoresistor structure. It is shown that the constant resistivity nanoresistor operates in the regime where the thermally activated electron tunneling is compensated by the negative temperature dependence of the metallic-type conductivity of nanoislands. Our results are relevant to the development of commercially viable methods of nanoresistor production for various nanoelectronics-based devices. The proposed MDA technique also provides the opportunity to fabricate large arrays of metallic nanoparticles with controllable size, shapes and inter-nanoparticle gaps.

Control of density of self-organized carbon nanotube arrays by catalyst pretreatment through plasma immersion ion implantation

A simple and effective method of controlling the growth of vertically aligned carbon nanotube arrays in a lowerature plasma is presented. Ni catalyst was pretreated by plasma immersion ion implantation prior to the nanotube growth by plasma-enhanced chemical vapor deposition. Both the size distribution and the areal density of the catalyst nanoparticles decrease due to the ion-surface interactions. Consequently, the resulting size distribution of the vertically aligned carbon nanotubes is reduced to 50 ∼ 100 nm and the areal density is lowered (by a factor of ten) to 10 8 cm -2, which is significantly different from the very-high-density carbon nanotube forests commonly produced by thermal chemical vapor deposition. The efficiency of this pretreatment is compared with the existing techniques such as neutral gas annealing and plasma etching. These results are highly relevant to the development of the next-generation nanoelectronic and optoelectronic devices that require effective control of the density of nanotube arrays.

Energy and matter-efficient size-selective growth of thin quantum wires in a plasma

It is shown that plasmas can minimize the adverse Gibbs-Thompson effect in thin quantum wire growth. The model of Si nanowirenucleation includes the unprecedented combination of the plasma sheath, ion- and radical-induced species creation and heating effects on the surface and within an Au catalyst nanoparticle. Compared to neutral gas thermal processes, much thinner, size-selective wires can nucleate at the same temperature and pressure while much lower energy and matter budget is needed to grow same-size wires. This explains the experimental observations and may lead to energy- and matter-efficient synthesis of a broader range of one-dimensional quantum structures.

Nanoscale control of energy and matter in plasma–surface interactions : toward energy- and matter-efficient nanotech

The approach to control the elementary processes of plasma–surface interactions to direct the fluxes of energy and matter at nano- and subnanometer scales is introduced. This ability is related to the solution of the grand challenge of directing energy and matter at nanoscales and is critical for the renewable energy and energy-efficient technologies for a sustainable future development. The examples of deterministic synthesis of self-organized arrays of metastable nanostructures in the size range beyond the reach of the present-day nanofabrication are considered to illustrate this possibility. By using precisely controlled and kinetically fast nanoscale transfer of energy and matter under nonequilibrium conditions and harnessing numerous plasma-specific controls of species creation, delivery to the surface,nucleation, and large-scale self-organization of nuclei and nanostructures, the arrays of metastable nanostructures can be created, arranged, stabilized, and further processed to meet the specific requirements of the envisaged applications.

Dielectric barrier discharge plasma in Ar/O2 promoting apoptosis behavior in A549 cancer cells

The Ar/O2plasma needle in the induction of A549 cancer cells apoptosis process is studied by means of real-time observation. The entire process of programmed cell death is observed. The typical morphological changes of A549 apoptosis are detected by 4′, 6-diamidino-2-phenylindole staining, for example, chromatin condensation and nuclear fragmentation. Cell viability is determined and quantified by neutral red uptake assay, and the survival rate of A549 from Ar/O2plasmas is presented. Further spectral analysis indicates the reactive species, including O and OH play crucial roles in the cell inactivation.

Real-time monitoring of nucleation-growth cycle of carbon nanoparticles in acetylene plasmas

Quantum cascade laserabsorption spectroscopy was used to measure the absolute concentration of acetylene in situ during the nanoparticle growth in Ar + C2H2 RF plasmas. It is demonstrated that the nanoparticle growth exhibits a periodical behavior, with the growth cycle period strongly dependent on the initial acetylene concentration in the chamber. Being 300 s at 7.5% of acetylene in the gas mixture, the growth cycle period decreases with the acetylene concentration increasing; the growth eventually disappears when the acetylene concentration exceeds 32%. During the nanoparticle growth, the acetylene concentration is small and does not exceed 4.2% at radio frequency (RF) power of 4 W, and 0.5% at RF power of 20 W. An injection of a single acetylene pulse into the discharge also results in the nanoparticlenucleation and growth. The absorption spectroscopy technique was found to be very effective for the time-resolved measurement of the hydrocarbon content in nanoparticle-generatingplasmas.

Control of dense carbon nanotube arrays via hierarchical multilayer catalyst

Effective control of dense, high-quality carbon nanotube arrays using hierarchical multilayer catalyst patterns is demonstrated. Scanning/transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and numerical simulations show that by changing the secondary and tertiary layers one can control the properties of the nanotube arrays. The arrays with the highest surface density of vertically aligned nanotubes are produced using a hierarchical stack of iron nanoparticles and alumina and silica layers differing in thickness by one order of magnitude from one another. The results are explained in terms of the catalyst structure effect on carbon diffusivity.

Magnetic control of breakdown : toward energy-efficient hollow-cathode magnetron discharges

Characteristics of electrical breakdown of a planar magnetron enhanced with an electromagnet and a hollow-cathode structure, are studied experimentally and numerically. At lower pressures the breakdown voltage shows a dependence on the applied magnetic field, and the voltage necessary to achieve the self-sustained discharge regime can be significantly reduced. At higher pressures, the dependence is less sensitive to the magnetic field magnitude and shows a tendency of increased breakdown voltage at the stronger magnetic fields. A model of the magnetron discharge breakdown is developed with the background gas pressure and the magnetic field used as parameters. The model describes the motion of electrons, which gain energy by passing the electric field across the magnetic field and undergo collisions with neutrals, thus generating new bulk electrons. The electrons are in turn accelerated in the electric field and effectively ionize a sufficient amount of neutrals to enable the discharge self-sustainment regime. The model is based on the assumption about the combined classical and near-wall mechanisms of electron conductivity across the magnetic field, and is consistent with the experimental results. The obtained results represent a significant advance toward energy-efficient multipurpose magnetron discharges.

Deterministic plasma-aided synthesis of high-quality nanoislanded nc-SiC films

Despite major advances in the fabrication and characterization of SiC and related materials, there has been no convincing evidence of the synthesis of nanodevice-quality nanoislanded SiC films at low, ultralarge scale integration technology-compatible process temperatures. The authors report on a low-temperature (400 °C) plasma-assisted rf magnetron sputtering deposition of high-quality nanocrystalline SiC films made of uniform-size nanoislands that almost completely cover the Si(100) surface. These nanoislands are chemically pure, highly stoichiometric, have a typical size of 20-35 nm, and contain small (∼5 nm) nanocrystalline inclusions. The properties of nanocrystalline SiC films can be effectively controlled by the plasma parameters.

Nanowire sensor response to reactive gas environment

The response of an originally developed catalytic sensor with a Nb2 O5 nanowire array at its outer surface to the varying density of O atoms is experimentally and numerically studied. This technique can be used to measure one order of magnitude lower densities of O atoms and achieve a stable linear response in a significantly broader pressure range compared to conventional catalytic probes with a flat surface. The nanostructured outer surface also acts as a thermal barrier against sensor overheating. This approach is generic and can be used for reactive species detection in other reactive gas environments.

Control of morphology and nucleation density of iron oxide nanostructures by electric conditions on iron surfaces exposed to reactive oxygen plasmas

The possibility to control the morphology and nucleation density of quasi-one-dimensional, single-crystalline α -Fe2 O3 nanostructures by varying the electric potential of iron surfaces exposed to reactive oxygen plasmas is demonstrated experimentally. A systematic increase in the oxygen ion flux through rf biasing of otherwise floating substrates and then an additional increase of the ion/neutral density resulted in remarkable structural transformations of straight nanoneedles into nanowires with controlled tapering/aspect ratio and also in larger nucleation densities. Multiscale numerical simulations relate the microscopic ion flux topographies to the nanostructure nucleation and morphological evolution. This approach is applicable to other metal-oxide nanostructures.

Ion-assisted precursor dissociation and surface diffusion : enabling rapid, low-temperature growth of carbon nanofibers

Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase and surface processes common to chemical vapor deposition, the model includes (unique to plasma-exposed catalyst surfaces) ion-induced dissociation of hydrocarbons, interaction of adsorbed species with incoming hydrogen atoms, and dissociation of hydrocarbon ions. It is shown that at low, nanodevice-friendly process temperatures the nanofibers grow via surface diffusion of carbon adatoms produced on the catalyst particle via ion-induced dissociation of a hydrocarbon precursor. These results explain a lower activation energy of nanofiber growth in a plasma and can be used for the synthesis of other nanoassemblies. © 2007 American Institute of Physics.

Controlled electronic transport in single-walled carbon nanotube networks : selecting electron hopping and chemical doping mechanisms

The electronic transport in both intrinsic and acid-treated single-walled carbon nanotube networks containing more than 90% semiconducting nanotubes is investigated using temperature-dependent resistance measurements. The semiconducting behavior observed in the intrinsic network is attributed to the three-dimensional electron hopping mechanism. In contrast, the chemical doping mechanism in the acid-treated network is found to be responsible for the revealed metal-like linear resistivity dependence in a broad temperature range. This effective method to control the electrical conductivity of single-walled carbon nanotube networks is promising for future nanoscale electronics, thermometry, and bolometry. © 2010 American Institute of Physics.