Ailing Ji

Atmospheric pressure plasma jet: Effect of electrode configuration, discharge behavior, and its formation mechanism

Atmospheric pressure plasma jet (APPJ) can protrude several centers into the ambient air; therefore it holds remarkable promise for many innovative applications. The mechanism underlying this nonthermal discharge, however, remains unsettled that it has been often taken as resulting from dielectric barrier discharge or vaguely referred as streamerlike. We generated APPJ by using a quartz capillary tube with three distinct electrode configurations: conventional double dielectric electrodes for making dielectric barrier discharges, single dielectric electrode, and single bare metal electrode attached to the tube orifice. The jets generated by using the double dielectric electrodes were found consisting of three distinct parts and of different origins. The plasma jet starting from the active electrodes is essentially the propagation of streamers induced by corona discharge. With one single electrode, plasma jets can be generated in both downstream and upstream directions simultaneously; and more importantly a...

Atmospheric pressure plasma jets beyond ground electrode as charge overflow in a dielectric barrier discharge setup

With a proper combination of applied voltage and the width of ground electrode, atmospheric pressure plasma jets extending beyond the ground electrode, whether it sits on the downstream or the upstream side, can be equally obtained with a dielectric barrier discharge setup, which can be ascribed to the overflow of deposited charges [J. Appl. Phys. 106, 013308 (2009)]. Here, we show that, by using narrower ground electrodes, such an overflow jet can be successfully launched at a much reduced voltage (down to below 10 kV). Moreover, by using transparent and triadic ground electrodes, development of charge overflow beneath the ground electrode was temporally and spatially resolved. Temporal evolution of discharge currents measured on the severed ground electrode helps establish the propagation dynamics of discharges along the dielectric surface beneath ground electrode, and also reinforces the conception that the streamer’s head is in connection to the active electrode via a conducting channel. A small propa...

Ternary Cu3NPdx exhibiting invariant electrical resistivity over 200K

Electrical resistivity is a physical property of enormous importance, but it is usually a complicated function of temperature. Here the authors report a vanishing temperature coefficient of electrical resistance (<3.0×10−6∕K) in the temperature range from 240to5K measured in Cu3NPd0.238, following the semiconducting-to-semimetallic transition in Cu3NPdx with x increasing from zero. It results from a delicate balance between the opposite changes of the number of carriers and the carrier mobility with temperature, which is possible only in a semimetal. This finding will inspire the search for similar materials and promote an in-depth investigation of the detailed operating mechanism.

Stressed Fibonacci spiral patterns of definite chirality

Fibonacci spirals are ubiquitous in nature, but the spontaneous assembly of such patterns has rarely been realized in laboratory. By manipulating the stress on Ag core/SiO2 shell microstructures, the authors obtained a series of Fibonacci spirals (3×5to13×21) of definite chirality as a least elastic energy configuration. The Fibonacci spirals occur uniquely on conical supports-spherical receptacles result in triangular tessellations, and slanted receptacles introduce irregularities. These results demonstrate an effective path for the mass fabrication of patterned structures on curved surfaces; they may also provide a complementary mechanism for the formation of phyllotactic patterns.

Exploring extreme particle density and size for blue photoluminescence from as-deposited amorphous Si-in-SiNx films

The number density of silicon particles in a silicon compound matrix that are smaller than 3.0 nm is subject to a few restrictive factors. We report the growth of amorphous Si-in-SiNx thin films containing small particles (down to 2.2 nm) of a density over 1.4×1013∕cm2, as determined from transmission electron microscopic graphs. Intense blue photoluminescence centered at 440 nm could be measured in such as-deposited films, and the external quantum efficiency was estimated to be at the 0.1–1.0 % level by comparing against that from a high-quality GaN sample. Rapid annealing for two minutes at 500 °C induced only slight enhancement of photoluminescence intensity. Further effort to increase the particle density led to particle conglomeration, and continued reduction of particle size endangers the survival of nanoparticles in matrix material. Clues for a more realistic mechanism are discussed based on the correlation of photoluminescence features to the microstructure of the films.

Nearly constant electrical resistance over large temperature range in Cu3NMx (M = Cu, Ag, Au) compounds.

Electrical resistance is a material property that usually varies enormously with temperature. Constant electrical resistivity over large temperature range has been rarely measured in a single solid. Here we report the growth of Cu3NMx (M = Cu, Ag, Au) compound films by magnetron sputtering, aiming at obtaining single solids of nearly constant electrical resistance in some temperature ranges. The increasing interstitial doping of cubic Cu3N lattice by extra metal atoms induces the semiconductor-to-metal transition in all the three systems. Nearly constant electrical resistance over 200 K, from room temperature downward, was measured in some semimetallic Cu3NMx samples, resulting from opposite temperature dependence of carrier density and carrier mobility, as revealed by Hall measurement. Cu3NAgx samples have the best performance with regard to the range of both temperature and doping level wherein a nearly constant electrical resistance can be realized. This work can inspire the search of other materials of such a quality.

Nanoparticle enhanced evaporation of liquids: A case study of silicone oil and water

Evaporation is a fundamental physical phenomenon, of which many challenging questions remain unanswered. Enhanced evaporation of liquids in some occasions is of enormous practical significance. Here we report the enhanced evaporation of the nearly permanently stable silicone oil by dispersing with nanopariticles including CaTiO3, anatase and rutile TiO2. An evaporation rate as high as 1.33 mg/h·cm2 was measured in silicone oil when dispersed with 100 nm-sized CaTiO3 particles. Dependence of evaporation rate on the chemistry, size and structure of the particles suggests that some weak absorption sites on the particles half floating on the liquid surface are responsible for the facilitated evaporation of liquid molecules. Enhanced evaporation is also observed for water when dispersed with anatase TiO2 particles. The results can inspire the research of atomistic mechanism for nanoparticle enhanced evaporation and exploration of evaporation control techniques for treatment of oil pollution and restoration of ...

Formation of a rosette pattern in copper nitride thin films via nanocrystals gliding.

By sputtering synthesis of cubic Cu(3)N, which decomposes at moderate temperatures, film growth proceeds with simultaneous nitrogen reemission from inside, leading to the formation of some unusual structures or morphology. We report a relief morphology comprising densely packed rosette-like features. The rosettes, typically 20 microm in size, show a radial furcation followed by successive bifurcation at approximately 74 degrees , resulting in a fivefold symmetric structure sometimes. The area expansion of the features can be as large as ten per cent with regard to the underlying bottom. Scanning electron micrographs reveal that it is the gliding of Cu(3)N nanocrystals along the Cu-rich {111}-planes that is responsible for the unusually large area expansion. The gliding and packing along the {111}-planes also explain the bifurcation angle of the ramified rosettes. Such a relief morphology can serve as a template for large-area fabrication of concave structures by inverse duplication, adding to the already abundant innovative applications of this material.

Helium corona-assisted air discharge

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb—for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Fast vapor phase growth of SiO2 nanowires via surface-flow on Ag core/SiO2 shell structure

Uniform, millimeter-long SiO2 nanowires were grown from co-evaporation of Ag2O and SiO powders. The ‘frozen’ growth scenario by cooling enables revelation of the vapor-liquid-solid mechanism here in action, which is generally inaccessible due to the high temperature and high pressure condition. Ag core/SiO2 shell preformed in the vapor and wetting the substrate will expose its liquid Ag-core to catalyze nanowire growth, at a rate over 10 nm/s, via viscous flow of the encasing SiO2 layer which precipitates through a liquid neck zone. This method is characteristic of high-yield of catalytic seeds free from overgrowth or consuming, easy control of wire thickness by vapor pressure adjustment, enhanced rooting ability since catalyst deposition on substrate becomes dispensable, etc. Also spinning growth of nanowires observed in many other circumstances can be explained by the viscous flow mechanism.