Dong Lf

Direct measurement of electron density in microdischarge at atmospheric pressure by Stark broadening

We present a method and results for measurement of electron density in atmospheric-pressure dielectric barrier discharge. The electron density of microdischarge in atmospheric pressure argon is measured by using the spectral line profile method. The asymmetrical deconvolution is used to obtain Stark broadening. The results show that the electron density in single filamentary microdischarge at atmospheric pressure argon is 3.05×1015cm−3 if the electron temperature is 10 000 K. The result is in good agreement with the simulation. The electron density in dielectric barrier discharge increases with the increase of applied voltage.

Generation of high-power-density atmospheric pressure plasma with liquid electrodes

We present a method for generating atmospheric pressure plasma using a dielectric barrier discharge reactor with two liquid electrodes. Four distinct kinds of discharge, including stochastic filaments, regular square pattern, glow-like discharge, and Turing stripe pattern, are observed in argon with a flow rate of 9slm. The electrical and optical characteristics of the device are investigated. Results show that high-power-density atmospheric pressure plasma with high duty ratio in space and time can be obtained. The influence of wall charges on discharge power and duty ratio has been discussed.

Concentric-roll pattern in a dielectric barrier discharge in air

Concentric-roll pattern in a dielectric barrier discharge in air at pd value 29.3 hPa cm is observed in the presence of circular boundary and studied by an optical method for the first time. The weak correlation between microdischarges in concentric-roll patterns indicates that the concentric roll is a spatiotemporal chaos although the space integral of microdischarges is quasiperiodic in time. Spatiotemporal measurements of microdischarges suggest that the effective electric field near the boundary is weaker than that in the interior region. The bifurcation of concentric-roll patterns with the increase of voltage and selection of characteristic wavelength are also studied.

Textured diamond films growth on (100) silicon via electron-assisted hot filament chemical vapor deposition

Textured (100) diamond films are successfully grown on single-crystalline (100) silicon substrate by electron assisted hot filament chemical vapor deposition from a gas mixture of methane and hydrogen. The effects of various parameters have been studied. The optimal growth conditions are obtained and the oriental growth character is discussed.

Pattern formation in dielectric barrier discharges with different dielectric materials

The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.

Temporal symmetry of individual filaments in different spatial symmetry filaments pattern in a dielectric barrier discharge

The temporal behavior of individual filament in different spatial symmetry filaments patterns in dielectric barrier discharge is investigated by using an optical method. A series of return maps of the discharge moments of individual filaments is given. It is found that the temporal symmetry of individual filament changes with the change of the spatial symmetry of filaments pattern as the applied voltage increases. The role of wall charges for this phenomenon is analyzed.

Square grid state in dielectric barrier discharge system

A square grid state and a hexagonal grid state are observed in a dielectric barrier discharge system. They are selected by different resonance mechanisms, namely, a four-wave interaction for the square grid state and a three-wave interaction for the hexagonal grid state. The spatiotemporal dynamics of the square grid state is studied by an optical method. It is found that the square grid state is an interleaving of three different sublattices, which correspond to a harmonic mode and two subharmonic modes.

Diagnosis of the electron temperature in dielectric barrier discharge by optical emission spectroscopy

Glow dielectric barrier discharge appears as an attractive solution to realize near atmospheric pressure cold plasma process suitable for all the surface treatments including thin film coating and material making. Such development requires a large understanding of the dielectric barrier discharge (DBD) physical and chemical process. The objective of this work is to contribute to that understanding. In this paper, we report the results of the measurement of the spectrum from 690nm to 800nm in DBD in argon. The electron temperature Te has been estimated using intensity ratio method by optical emission spectroscopy under difference experimental conditions. According to Local Thermodynamic Equilibrium (LTE) theory, the electron temperature Te can be assumed equal (equals) to the excitation temperature Texc, namely Te=Texc=T. Therefore, the plasma temperature T can be determined by comparing the relative intensities of spectral lines from the same element and ionization stage. The spectral lines 763.72nm (2P6→1S5) and 772.63nm (2P2→1S3) of Ar atom are chosen to estimate the electron excitated temperature. The experimental results show that the electron excitated temperature is in the range of 0.3-8eV in Ar under different pressures. The results also show that the electron excitated temperature increases with the decreasing of the applied voltage. The results provide a reference for the controlling of DBD and are of great importance to the industrial applications.

Temporal characteristic of discharge pulse vs gas flow rate in dielectric barrier discharge

Summary form only given. We present a method to generate atmospheric pressure plasma. The device is a dielectric barrier discharge reactor with two water electrodes. Regular square pattern and glow-like discharge are observed in both flowing Ar gas and stationary Ar gas. The electrical and optical characteristics of the device are investigated. Results show that pulse width and pulse spacing of two consecutive pulses of flowing Ar gas are larger than those of stationary Ar gas. The influence of wall charges on spatio-temporal characteristic of discharge and discharge power has been discussed.

The diagnosis of electron temperature in dielectric barrier discharge at atmospheric pressure

Summary form only given. Glow dielectric barrier discharge and dynamics of pattern appears as an attractive solution to realize an atmospheric pressure cold plasma process suitable for all the surface treatments including thin film coating and material making. Such development requires a large understanding of the DBD physics and chemistry. The objective of this work is to contribute to that understanding. We report results of the measurement of the spectrum from 690 nm to 800 nm of Ar DBD under atmosphere pressure. It is shown that the spectra are diverse depending on experimental conditions. The electron temperature T/sub e/ has been measured using intensity ratio (763.72 nm, 2P/sub 6//spl rarr/1S/sub 5/; 772.63 nm, 2P/sub 2//spl rarr/1S/sub 3/) by optical emission spectroscopy under different experimental conditions. It is shown that the temperature in flow-gas is lower than in stationary gas under the same conditions. Which is about 0.1 eV/spl sim/0.3 eV in flow-gas while 0.3 eV/spl sim/0.5 eV in stationary gas. But the spectrum line intensity ratio of 763.72 nm (2P/sub 6//spl rarr/1S/sub 5/, 13.172 eV) and 696.73 nm (2P/sub 2//spl rarr/1S/sub 5/, 13.328 eV) is less than 1 in flow gas while which is bigger than 1 in stationary gas at the same energy input. The results are likely to be explained by Penning ionization.