A square pattern is observed in a dielectric barrier discharge system in Ar/air gas mixture. There are two discharge
current pulses in each half cycle of the applied voltage. The spatiotemporal dynamics of the square pattern is investigated
by an intensified charge-coupled device camera within one discharge current pulse. It is found that the square pattern is
an interleaving of two different transient square sublattices, and the evolution of the two sublattices has the time
inversion symmetry. Depending on the discharge sequence, the effect of the wall charges on the evolution of the square
pattern is discussed briefly.
In this paper, we process images of different patterns with a Fast Fourier Transformation (FFT) to investigate
the spatial development of patterns in dielectric barrier discharge system. A bifurcation scenario from hexagonal
pattern to square pattern is observed under circular boundary as the driving voltage increasing. The spatial
characteristics of hexagonal pattern and square pattern are studied by analyzing their related spatial Fourier spectra.
In addition, a transition from hexagons to squares and a further development of square pattern with dislocation
defect are also researched by analyzing their Fourier spectra.
A particle-pair of filaments is obtained by using liquid electrodes in a dielectric barrier discharge system. It travels in the
direction of the larger filaments and rebound at the boundary of discharge area. By using image processing and image
analyzing of the recorded pictures and video, the traveling velocity of particle-pair is calculated to be about 1.2 cm/s.
Moreover, the interparticle distance of particle-pair changes periodically with a period about 0.5 s.
A dielectric barrier discharge system with two liquid electrodes and a photoelectric detection system are specially
designed to study the spatiotemporal dynamics of square superlattice pattern. Two different types of square superlattice
patterns are observed for the first time. They are both composed of the square arranged large and small spots (filaments),
while one is without the glow background (type I), and the other one has (type II). The photoelectric measurements
indicate that they have the same spatial-temporal behaviors, which are an interleaving of two transient square
sublattices - the small-spot square sublattice (S) and the large-spot square sublattice (L). The emerging sequence of the
two sublattices in a one cycle of the applied voltage is S-L-L-S-L-L, which is harmonic with the forcing frequency. The
dynamic of the glow background of the type II square superlattice pattern is also studied. It is found that the glow
background discharge three times in each half cycle of the applied voltage, going with the emergence of each sublattice.
The photoelectric measurement of the hexagon pattern in dielectric barrier discharge is performed. By measuring the
current signals and the light signals of the hexagon pattern, it is found that there are three main pulses in both of the total
current signal and the total light signal. The light signal of a fixed filament in hexagon pattern is also measured. It is
found that the spatial location of the filament is unchanged, while its discharge moment is changed with the time, which
is probably corresponding to the first pulse, the second pulse or the third pulse of the total light signal. However, no
matter when it discharges, the light pulse width for one filament is almost 30 ns, and the ratio of the rising edge to the
falling edge of the pulse is about 1:1.88. In addition, the properties of hexagon patterns with the increased gas pressure
are investigated. The pattern bifurcation sequence is changed accordingly, and pulse widths of the light signals of the
hexagon pattern rises with increasing the gas pressure, which changes from 30ns (at 0.3atm) to 107ns (at 1atm), and the
ratio changes from 1:1.88 to 1:3.
KEYWORDS: Dielectrics, Liquids, Oscilloscopes, Electrodes, Digital cameras, Imaging systems, Glasses, Power supplies, Signal detection, Fluctuations and noise
A dielectric barrier discharge system is specially designed with two liquid electrodes and a corresponding
photoelectricity detection system. The detection system is composed of lens, apertures, multiplier-tube, digital camera,
and an oscilloscope. A rich variety of emission patterns are obtained in the system as the voltage is increased. The
wavelength characteristic of the emission patterns in dielectric barrier discharge is investigated. It is found that the
wavelength of the emission patterns displays a non-monotonic variation as the applied voltage is increased. When the
applied voltage is relatively low, the wavelength of the emission patterns decreases as the applied voltage increases.
When the applied voltage is increased over a critical value, the wavelength of the patterns becomes larger as the voltage
is increased. The wavelength of the emission pattern may maintain approximately invariable when the voltage is
increased within some particular voltage range.
The non-intrusive optical emission spectroscopy of the N2 second positive band system (C3Πu→B3Πg) are used to
measure the vibrational temperature in N2/Ar and air/Ar discharges at atmospheric pressure, respectively. In N2/Ar
discharges, the strip patterns can be obtained at the concentration of N2 from 9.5% to 38% at 10kV and 60kHz, and its
vibrational temperature increases approximately from 1600K to 1750K with increasing the N2 concentration. Increasing
the concentration of N2 from 38% to 96%, the hexagon patterns are formed and its vibrational temperature increases
from 1750K to 1950K. In air/Ar discharges, three patterns (strips, quasisuperlattice and hexagon) are obtained with air
concentration increasing from 9.5% to 96% at 10kV and 60kHz. The vibrational temperature ranges approximately from
1850K to 2750K, which is about 250~600K higher than that in N2/Ar discharges under the same concentration of N2 and
air in two-gas-species. In addition, the quasisuperlattice can be observed at the air concentration from 19% to38%, and
its vibrational temperature is from 2000K to 2300K approximately. It indicates that the gas species and the mixing ratios
affect the patterns and their vibrational temperatures. Furthermore, it is also found that the breakdown voltage and the
moment of discharge initiation are different as a function of the gas species and the mixing ratios.
Spatio-temporal patterns in nonlinear system have been paid much attention in resent years. Among different
nonlinear systems, gas discharge system is more remarkable because proper time scale and abundance in pattern
structures. In this article, pattern formation dynamics is studied in a dielectric barrier discharge system with mixed
working gas of argon and air at pressure of 0.6 atm by optical method. A boundary condition of square structure is used
in the experiments. The experimental results show that the discharge pattern with increasing the applied voltage
undergoes a scenario: uniform discharge, hexagon structure, stochastic micro-discharge filaments, hexagon structure
again, square pattern, regular stripes that bridge the boundary, and uniform discharge again. The emission signals from
the discharge in different pattern are detected by photomultiplier tubes and results show that the waveform of total light
signals under low voltage lower than the voltage of stochastic micro-discharge filaments is only one pulse at each half
cycle of the applied voltage, while it shows two pulses at each half cycle of the applied voltage in the second hexagon
pattern and square pattern, and more pulses appear in the stripe pattern discharge and second uniform discharge. Through
analyzing the temporal sequence of the different filaments in a hexagon, it can be concluded that the hexagon pattern is
an interleaving of two rectangular sub-patterns that the micro-discharge filaments in a sub-pattern volley almost at the
same time. The temporal sequence of the two sub-patterns in consecutive half cycle alternates.
Diverse stable localized states respectively with hexagonal, heptagonal and enneahedral symmetry have been
observed in a dielectric barrier discharge system with two water electrodes. The interacting process of different localized
clusters due to the attractive interaction is shown. The spatiotemporal dynamics of the localized hexagonal states are
measured by photoelectric method. It is found that the seven filaments composing a hexagonal cell discharge nearly at
the same time, with the light intensity of the central filament much stronger than its neighboring six ones. Magnifying the
light signal, however, it is found that the discharge moment of the central filament always precedes that of others
actually.
Dielectric barrier uniform discharges have attracted considerable interest because this type of discharge requires
practically no vacuum devices and plasma with good uniformity can be generated at high pressure. In this paper,
discharges are initiated in air at atmospheric pressure in a dielectric barrier discharge setup composed of two parallel
planar electrodes separated by two layers of dielectric. The characteristics of dielectric barrier discharge are studied
through collecting the emission signals from the discharge with a photomultiplier tube and a spectrometer, respectively.
The results show that the discharge consists of many micro-discharge filaments when the applied voltage is slightly
above the breakdown voltage, and the discharge is uniform when the applied voltage is very high. The waveform of
discharge emission consists of many pulses with duration of several tens nanoseconds in the filamentary discharge mode.
However, it only consists of a single broad electrical pulse (hump) lasting approximately a quarter of a discharge time
period on which significant narrow pulse peaks are superposed. Streamer breakdown mechanism is involved in the
discharge of not only filamentary discharge but also uniform discharge. Spectral emission spectroscopy is used to study
the discharge transition. The intensity ratio of 391.4nm to 337.1nm represents electron energy that is mainly determined
by the electric filed applied to the gas gap. With increasing the applied voltage, the intensity ratio of 391.4nm to 337.1nm
decreases. This experimental result indicates that electron energy decreases with the increasing of the applied voltage.
The electron excited temperature in dielectric barrier discharge under argon at atmospheric pressure is diagnosed by
photoelectric method. The electron excited temperature Texc can be estimated by using spectral lines intensity ratio
method. The spectral lines 763.72nm (2P6→1S5) and 772.63nm (2P2→1S3) in the spectrum range from 690nm to 800nm
are chosen to estimate the electron excite temperature. The power of the discharge gap is calculated by analyzing the
waveform of the apply voltage and the voltage of the test capacitance. The experimental results show that the electron
excited temperature is in the range of 0.19-0.31eV and the discharge power in the gas gap is in the range of 35.7-51.0W
under different discharge gap 0.9-3.0mm. In addition, it is found that the variation tendency of the electron excited
temperature with the discharge gap increasing is similar to that of discharge power, and the electron excited temperature
and discharge power has a minimum value at d=1.1mm. The discharge operates in glow-like mode when the discharge
gap d<1.3mm, and the discharge operates in patterned mode when d>1.3mm. As the discharge gap increase from 1.3mm
to 3.0mm, the streamer channels became brighter, and move faster. The self-organized behavior is also found in the
experiment.
The images of square pattern, square superlattice pattern, and hexagonal pattern observed in dielectric barrier
discharge are processed to get the exactitude binary images for further investigation. By using spatial correlation function,
it is found that both of square and hexagonal patterns show perfect structures, and the square superlattice pattern exhibits
an interleaving of two perfect squares with the same wavelength including large and small spots respectively.
Furthermore, angular spectral distribution is used to study pattern development. It shows that, square and hexagonal
patterns are formed with single modes respectively, while square superlattice pattern is governed by a three wave
resonance.
In this work, a special designed optical system is used to measure the characteristic of square super-lattice pattern in
DBD system. A dielectric barrier discharge system with two liquid electrodes is used, which has a lot of advantages and
convenience to the experiment. A square super-lattice pattern is observed in the system at appropriate experimental
parameters. The patterns follow as random filaments, square pattern, quasi-super-lattice pattern, square super-lattice
pattern, stripe pattern and hexagonal pattern when the applied voltage increases. The influence of the gas pressure p, the
gas gap width d, and the pd value (the product of gas pressure p and the gas gap width d) on the square super-lattice
pattern are investigated. There are some changes of the pattern scenario when the experimental parameters changes. It is
found that the voltage of the square super-lattice pattern increases slightly as d increases. In addition, it is found that the
voltage of the square super-lattice pattern decreases as the gas pressure decreases. The square super-lattice pattern can be
observed stable and regular at atmosphere pressure when 1.36mm < d < 2.2mm, and the gas pressure is reduced less than
atmosphere pressure to obtain the square super-lattice pattern if d >2.2mm.
The transition among three discharge modes, glow-like discharge, filamentary discharge and diffuse discharge, has been obtained in air dielectric barrier discharge at 0.1atm pressure. To get the transition conditions, the electric waveforms and optical emission spectroscopy (OES) of the discharge have been measured. The results show that the wall charges and the ion concentration in the discharge are important to the transition of discharge modes.
Lifetime of micro-discharge filaments in dielectric barrier discharge in air at atmospheric pressure is very short and high temporal resolution device is necessary to study time correlation between micro-discharge filaments. In this paper, a simple optical method is introduced to study time correlation between micro-discharge filaments in dielectric barrier discharge in air at atmospheric pressure by photomultiplier tubes. The waveforms of light emission indicate that the discharge burst within each half cycle of applied voltage consists of a series of discharges pulses. This experimental phenomenon shows that the discharges of two or more filaments would overlap in time. By time correlation study, it is found out that discharge filaments can be categorized to some groups according their spatial position. The filaments can volley almost at the same time within neighboring space whose dimension is less than 3x3mm2. A discharge domain is proposed to denote the group of discharge filaments that volley at the same time and exist in a neighboring space. The temporal behavior of filaments belong to one domain is investigated in many applied voltage cycles. The probability distribution function of the intervals for the discharge filaments in a domain is given at last. The delay time between breakdown moments of two filaments in one domain varies within the range of a few ns order. The physical mechanism involved in photo-ionization is presented to interpret the domain formation.
The influence of the air-concentration on the characteristic of the square super-lattice pattern in dielectric barrier discharge is investigated. The square super-lattice pattern is obtained in the mixture of air and argon at atmosphere pressure, and the air-concentration is changed from 0.1% to 5%. The patterns follow as the square pattern, quasi-crystal state, square super-lattice pattern, stripe pattern and hexagonal pattern when the applied voltage increases. The bifurcation scenario of the patterns dose not changes as the air-concentration changes. But the voltages of the patterns increase as the air-concentration increases. In addition, the influence of the air-concentration on the electron excited of the square super-lattice pattern is studied by using a monochromator with a CCD. The electron excited temperature Te is estimated by using spectral lines intensity ratio method. It is found that the electron excited temperature of both the small spot channels and the large spot channels composing of the square super-lattice pattern increases as the air-concentration increases. In addition, the electron excited temperature of the large spot channels is higher than that of small spot channels. The difference of the electron excited temperature between small spot channels and large spot channels becomes more obvious as the air-concentration increases.
The optical and electrical characteristics from filamentary discharge to pseudo-glow discharge are investigated by a specially designed optical detection systems. The discharges are initiated in mixture of air and argon at atmospheric pressure in a dielectric barrier discharge setup composed of two parallel planar electrodes separated by two layers of dielectric. The optical and electrical characteristics are displayed by the waveforms of the applied voltage, the discharge current and the emission spectral intensity. The waveforms of the applied voltage and the discharge current of two discharge modes have been recorded by oscilloscope. The emission spectra from the discharges are obtained through a spectrometer. When the other conditions are fixed the spectral intensity increases with the increase of voltage and driven frequency. The ratio of spectral intensity to the voltage in the filament discharge is smaller than that in the pseudo-glow discharge.
The influence of different water temperatures on temporal behavior of dielectric barrier discharge in argon at
atmospheric pressure is studied by using an experimental device with water electrodes. It is found that, as the applied
voltage increasing, the evolvement of discharge with different water temperatures shows similar behavior spatially if
argon concentrations are same. The corresponding Fourier transformation is obtained by processing patterns images
with computer program based on the Matlab software. The discharge duration of the first current pulse in half cycle of
different voltage polarity is same in discharge if the two electrodes temperatures are same. But it becomes different if
the two electrodes have different temperatures. The discharge moment is always ahead when the low temperature
electrode is an instantaneous cathode. The analysis shows that the water temperature affects the accumulation of wall
charges, resulting in the differences of temporal behavior of discharge.
The non-intrusive optical emission spectroscopy is used to measure the vibrational temperature and the electron density
in white-eye pattern in dielectric barrier discharge (DBD) in air. The electron density is investigated by stark broadening
of spectral line profile, and the molecule vibrational temperature is calculated by analyzing the intensity ratio of lines in
the second positive system (SPS) of N2 (C3 ∏u
−B3∏g). The results show that the vibrational temperature and electron
density of the spot in white-eye pattern is slightly different from that of the background in white-eye pattern. It indicates
that both the spot discharge and the background discharge are microdischarges.
A dielectric barrier discharge apparatus with two liquid electrodes and a photoelectric detection system are specially
designed to study the photo-electrical characteristic of different patterns. A series of filamentary patterns, in which the
filaments can be fixed for a long time, have been generated from filaments moving stochastically by increasing applied
voltage. It follows the sequence of square pattern, square superlattice pattern and hexagon pattern. The studies of optical
and electrical characteristics, including discharge current, light signals, the voltage drop across discharge gap, transported
charges, and Lissajous figures of these different patterns are realized by the photo-electrical detection method. From the
light signals and waveforms of current, it is found that the square pattern has two discharge pulses, the square
superlattice has three and the hexagon has several pulses in each half cycle of the applied voltage. The voltage drop
across discharge gap and transported charges increase with the increasing of applied voltage. The dissipated power
obtained by the charge-voltage Lissajous figures also increases with the increasing of applied voltage.
The spatio-temporal behavior in pattern formation in dielectric barrier discharge system is hard to be studied in the mixed gas of air and argon at high pd product, for the discharge duration of micro-discharge (filament) in streamer mode is very short. In this paper, pattern formation phenomenon in streamer mode in dielectric barrier discharge is studied by optical method. A rich variety of patterns has been observed in streamer discharge mode in the mixed gas of air and argon. It's found that the appearance of these patterns is very sensitive to air concentration and applied voltage. Regular patterns such as hexagon and square structure can be formed in this system when the parameters space is proper. The applied voltage for obtaining the hexagon (or square) pattern increases with increasing air concentration. These regular patterns sometimes drift in a certain direction and sometimes rotate stochastically. The drifting velocity is estimated through dividing the filament trace length by exposure time of the photo. It is found that the drifting velocity increases generally with increasing air concentration and the drifting velocity of hexagon pattern is larger than that of square pattern. The light waveforms from irregular pattern or random walking filaments are un-orderly and stochastic. On the contrary, the light waveforms of regular patterns are very orderly and periodical, only two pulses in each half cycle of the applied voltage. In our experiments, it is also found that the spatial frequency of pattern increases with increasing air concentration.
The variations of the intensity of argon (2P→1S) spectral lines with various gas mixing ratios in dielectric barrier discharge (DBD) in air/Ar and N2/Ar admixtures are studied. The relative intensity of Ar I I750.39nm/I763.51nm as a function of experiment conditions (pressure, applied voltage and frequency) in Ar discharge is also measured. In air/Ar and N2/Ar admixtures, it is observed that the higher levels of N2 molecules have quenching selectivity for Ar (2P→1S) spectral lines, and the relative intensity of Ar I I750.39nm/I763.51nm increases with increasing air or N2 concentration in two admixtures, respectively. Both Ar (2P→1S)spectral lines and the relative intensity of Ar I I750.39nm/I763.51nm in N2/Ar admixture are higher than that in air/Ar admixture under the same air and N2 concentration in two admixtures. The relative intensity of Ar I I750.39nm/I763.51nm increases from 0.81 to 1.73 when the concentration of air changes from 10% to 73%, but the relative intensity changes from 1.03 to 3.51 when the concentration of N2 increases from 10% to 73% in N2/Ar admixture at a applied voltage of 10kV, a frequency of 26kHz and an atmosphere pressure. Moreover, in Ar discharge, the results demonstrate that the pressure has great effect on the relative intensity of Ar I I750.39nm/I763.51nm, which decreases with increasing the pressure. But it changes slightly with the applied voltage and the frequency.
The spatial-temporal correlation in dielectric barrier discharge is difficult to be studied in the mixed gas of air and argon. In this paper, a simple optical method is introduced to study the temporal correlation intensity between micro-discharge filaments in dielectric barrier discharges at different air concentration in mixed gas of air and argon. The relation of the breakdown voltage and air concentration (Χ) is measured. It's found that the breakdown voltage increases as the air concentration increasing. The experimental results show that the diameter and discharge duration of the filament decrease with the air concentration increasing, at the same time the coherence of the discharge moments of the filaments weakens with the air concentration increasing. The experimental results can be explained with the theory of electron drifting. In addition, the accumulated charges on dielectric surface created by the filament discharge create a field within very time when the duration is small, which against the filament breakdown in its neighboring region. So the coherence of the discharge moments of the filaments can't be realized. While the accumulation of the surface charges will last a long time when the duration of the filament discharge is big, the breakdown can take place in the neighboring region of the filament in the duration, which would be the factor to the coherence of the discharge moments.
In this work, a rich variety of emission spiral patterns have been obtained in dielectric argon/air barrier discharge (DBD) system with a special designed water electrodes setup. We investigate the characteristics of spiral patterns with two kinds of different sidewall materials. By analyzing the image and the light signals of the patterns, it is found that spiral patterns with different sidewall material have different characteristics. The profile of the intensity distribution curve under the glass sidewall appears as a sinusoidal oscillation, while displays in relaxation oscillation mode under plastic sidewall. The space frequency spectrum of spirals under glass sidewall contains only one order spectrum, while the space spectrum of spirals under plastic sidewall contains more than two orders of space frequency spectrum. The experiment results indicate that the sidewall material may affect the excited property of the discharge system.
Edge detection is one of the most demanding tasks in optical image processing for artificial vision and image matching works. In this paper, the self organization theory is used for edge detection. A new algorithm based on a two variable reaction-diffusion equations is proposed. A stable edge pattern can be obtained by choosing suitable control parameters. Compared with the conventional methods, such as Soble, Prewitt and Robert detectors, the new algorithm indicates a higher accuracy and continuity for the image. Moreover, it can also extract exactly the edge of the human face image.
A special dielectric barrier discharge system with two liquid electrodes and a special optical system are designed to study the spatiotemporal dynamics of nonlinear patterns. A rich variety of patterns including square pattern, hexagon pattern, spiral and square superlattice pattern have been obtained. The spatio-temporal dynamics of square superlattice pattern is investigated. Results show that it is an interleaving of two different transient square sublattices with the emerging sequence of S-L-L-S-L-L in one cycle of the applied voltage. The light signals of the two sublattices indicate that the interval of the emergence of each sublattice is at an order of 0.1 μs.
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.
Dielectric barrier discharge is a novel system for studying the pattern formation. In this system, spiral pattern has been observed for the first time. For the element of the pattern emits itself, the image can be obtained to give some information about the behavior of the spiral pattern. The image of spiral pattern is analyzed based on the software Matlab6.1. The spatial distribution of the intensity in the image gives a normal spiral structure. The temporal distribution of the intensity shows that the spiral pattern has a periodical behavior in a second time scale. All of the results are consistent with the theoretical simulations.
KEYWORDS: Image processing, Dielectrics, Spatial frequencies, MATLAB, Physics, Digital imaging, Digital cameras, Electrodes, Analytical research, Control systems
Pattern formation is a process by which a spatially uniform state loses stability to a non-uniform state. A usual effective method for studying the property of patterns is to take pictures or record images of the patterns with digital cameras and get useful information from them. In this work, the structure, the spatial frequency spectrum of the patterns, the precise location of the discharge filaments center and the distribution of the light emission density of filaments are analyzed with Matlab6.1. This work can provide a beneficial reference for researchers who study pattern dynamics in DBD system or other systems.
Dielectric barrier discharge (DBD) has numerous industry applications such as ozone generation, pollution control and sterilization of biological samples. The study of process of excitation and ionization is of great use for industry applications. In this paper, the spectrum of DBD in atmosphere is measured by using the special setup with two water electrodes. Nitrogen molecule spectrum (C3Πu(υ'=0) → B3Πg(υ"=0~4)) is found at range of 300~800nm. Oxygen molecule spectrum (b1∑+g → X3∑-g) is not found at the range. The excitated energy of nitrogen molecule (C3Πu(υ'=0)) is bigger than that of oxygen molecule (b1∑+g). It should be that oxygen molecule spectrum is stronger than nitrogen molecule spectrum. In fact, nitrogen molecule spectrum is very strong, but oxygen molecule spectrum is not found. In order to interpret this contradiction, process of DC discharge in atmosphere has been simulated by the Monte-Carlo computer simulation method. During the period of discharge occurring (the time is very short, about several microseconds), AC DBD can be approximately treated as DC discharge. Elastic collision and inelastic collision considered in air by electron impact, the number of electrons for excitation with E/N is analyzed emphatically. Results show that process of excitated collision of N2 with electron is far stronger than that of O2 when E/N varies from 100Td to 1000Td. The probability of the former is about 30 times bigger than that of the latter. So it is explained the above-mentioned phenomenon. The theoretical simulation is in good agreement with the experiment. The results obtained in this work are of great importance to the research of discharges at atmospheric pressure and its applications. The results provide a reference for the controlling of DBD and are of great importance to the industrial applications.
In this paper, nanocrystalline diamond films had been synthesized by near surface glow discharge chemical vapor deposition on single-crystalline (100) silicon substrates when methane and hydrogen acted as input gases. The characters of the diamond films had been identified by scanning electron microscopy (SEM), Raman Spectrum and X-ray diffraction (XRD). The analytic results show that the high quality nanocrystalline diamond film of (111) orientation had been deposited on single-crystalline (100) silicon substrate at temperature of approximately 850°C. Simultaneously, the studies of the influence of gas pressure and CH4 concentration in feeding gas on the diamond growth were made.
KEYWORDS: Diamond, Nonlinear dynamics, Plasma, Signal processing, Emission spectroscopy, Temperature metrology, Chemical vapor deposition, Diagnostics, Process modeling
In this paper, the experimental synthesis of diamond films and optical emission spectroscopy (OES) of the gaseous phase species are studied in the range of substrate temperature from Ts = 300°C to 850°C. The high quality sub-microcrystalline diamond films are successfully deposited at substrate temperature (330 ≈ 340)°C by adopting glow plasma assisted hot filament chemical vapor deposition (GPCVD). For the first time, in situ OES is applied to diagnose weak signal of GPCVD system when CH4 and H2 are used as the input gas, and the reactive species are identified in diamond growth processes. A primary model of diamond films growing at low temperature is presented by studying dynamic behavior for nonequilibrium plasma reactions.
A special designed setup consisting tow water electrodes is used to investigate the temporal characteristic of micro-discharge in dielectric barrier discharge in Argon by the optical methods on the non-intrusive and in-situ measurement. The nonsymmetrical characteristic of the micro-discharge breakdown moment which the interval between two adjacent discharges varies between long one and short one alternately is discovered by the applied voltage increasing step by step, the influence of wall charges on the temporal behavior characteristic is analyzed at last.
In this paper transition between glow-like discharge and filamentary discharge are found by gas condition being changed in dielectric barrier discharge device, discharge signal is measured by the electric methods and the current waveforms were registered by usign digital oscillography in the course of the transition. The difference between two modes is analyzed and reasons resulting in such difference are discussed.
The pattern formation of hexagonal and square structure is obtained in dielectric barrier discharge in argon at atmospheric pressure. The temporal behavior of total light emission of square pattern is measured with optical method. The experimental results show that there are two current spikes in each half cycle of applied voltage in waveform of total light emission. The possible structure of the pattern is proposed, which has been proved partly by late experiment.
The dynamic process of electron impact oxygen molecule in direct current electric field is simulated by using Monte Carlo method. The distribution of electron excitation and vibrational excitation collision have been obtained for range of 20 ≤ E/N ≤ 2000 Td for oxygen at atmospheric pressure of 300 K (1 Td=10-17 Vcm2). Meanwhile, influence of electric field on excitation lighting in oxygen is also analyzed.
In this work, excimer laser (XeC1 308nm) is adopted to ablate the carbon target in order to deposit high quality nano-crystalline diamond films via electron assisted chemical vapor deposition (EACVD). In experiment, the temperature of substrate is about 300~450 degree Celsius, reacting gas is the mixture of methane and hydrogen in which volume ratio of methane to hydrogen is about 0.7 %, laser power density is 10-710b0 W/cm2. Experimental results show that the sharp peak in Raman spectra of sample films appears at 1332cm-1, which indicates crystalline diamond phase is formed in the samples. And the (lii) characteristic diffraction peak of diamond appears at 20=43.9° in X-ray diffraction spectra. Finally, the growth mechanism of diamond film at low temperature is discussed.
In this paper, diamond film is deposited at low substrate temperature by electron-assisted chemical vapor deposition (EACVD). The quality of diamond film is analyzed by the scanning electron microscope (SEM), Raman spectrum and x-ray diffraction (XRD). The results show that the high quality film of (111) orientation is deposited at low temperature of about 500 degree(s)C by the EACVD technique. Meanwhile, the mechanism of the deposition at low temperature is also discussed.
In this paper, we studied the spatial distribution of atomic hydrogen in diamond deposition. The number of hydrogen dissociation as a function of the ratio of electric field to gas pressure is given. And the number of hydrogen dissociation as a function of distance from the hot filament is also given here. These results are of great importance to the study of diamond deposited by EACVD.
The behaviors of optoelectron have a very important effect on the quality of photosensitive material, especially on the formation of image. In this paper, the dielectric spectrum technology is used to measure the behaviors of optoelectron. The curves of the behaviors of optoelectron are obtained. Many properties of the behaviors of the optoelectron are gotten through the detailed analysis of the results of the measurement. The influences of the behaviors of the optoelectron on the formation of image are analyzed primarily. The results obtained in this paper are valuable to the overall comprehension of the photosensitive mechanism of the silver halide materials and the process of the formation of image.
In this paper, the filamentary pattern of dielectric barrier discharge has been processed by using Photoshop, the coordinates of each filament can also be obtained. By using Photoshop two different ways have been used to analyze the spatial order of the pattern formation in dielectric barrier discharge. The results show that the distance of the neighbor filaments at U equals 14 kV and d equals 0.9 mm is about 1.8 mm. In the scope of the experimental error, the results from the two different methods are similar.
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