In this paper, nitrogen dielectric barrier discharge (DBD) plasma was generated in a quartz tube with coaxial wire-cylinder electrodes at atmospheric pressure. By varying the nitrogen gas flow (FN) in the range of 0-1 m 3 /h, the plasma optical emission spectra (OES) were measured and studied. The vibration (T vib) and rotation temperature (Trot) of nitrogen were obtained, by fitting the rovibronic bands of N2(C 3 Πu − B 3 Πg, 0-1), and by the Boltzmann plot method for purposes of comparison. T vib increased up to 2481 K with increasing nitrogen flow till 0.2 m 3 /h, and then decreased with further increasing FN , while Trot decreased monotonously and approached to ∼350 K for FN ≥ 0.6 m 3 /h. The intensity of N2(C 3 Πu − B 3 Πg, 0-0, 1-0, 0-3) and N + 2 (B 2 Σ + u − X 2 Σ + g , 0-0) exhibited similar evolution with increasing FN to those of the T vib and Trot, respectively. The discharge photos revealed that the discharge filaments gradually decreased with increasing FN , and eventually disappeared, which implied that a discharge mode transition emerged with increasing FN. The possible mechanism for the discharge mode transition is studied in detail according to the vibration (T vib) and rotation temperature (Trot) of nitrogen.
High-power pulsed magnetron sputtering (HPPMS or HiPIMS) is an emerging coating technology that produces very dense plasmas and highly ionized sputtering atoms. This paper is focused on discharge properties, unbalanced features and temporal evolution of pulse current of the HPPMS discharge. A hollow cathode was used to suppress the scattering of charges. A coaxial coil surrounding the target was used to control the breakdown voltage and pulse repetition frequency by varying the coil current. A Langmuir probe and an oscilloscope were used to simultaneously measure the floating potential, pulse voltage and pulse current signals. The pulse power density in the discharge reached 10 kW/cm 2 with frequencies as high as ∼40 Hz and a pulse width about 1∼5 ms. The characteristics of the discharge evolution were analyzed using magnetron discharge dynamics.
In this paper a numerical simulation of a planar DC magnetron discharge is performed with the Particle-in-Cell/Monte Carlo Collision (PIC/MCC) method. The magnetic field used in the simulation is calculated with finite element method according to experimental configuration. The simulation is carried out under the condition of gas pressure of 0.665 Pa and voltage magnitude of 400V. Typical results such as the potential distribution, charged particle densities, the discharge current density and ion flux onto the target are calculated. The erosion profile from the simulation is compared with the experimental data. The maximum erosion position corresponds to the place where the magnetic field lines are parallel to the target surface.
High Power impulse Unbalanced Magnetron Sputtering has been coupled to a direct current source (dc-HPPUMS or dc-HiPUMS). A coaxial coil and an attached hollow cathode were applied to control discharge properties and improve pulsed power density. A large extent breakdown was induced for avalanche discharge mechanism. The magnetic trap on sputtering target traps the secondary electrons excited by the avalanche and forms a drift current in magnetic trap. The peak pulse current density is higher than 100 A/cm2 with a pulse frequency less than 40 Hz. The space charge limited condition controls the discharge for plasma far away from equilibrium. The discharge theory was taken to describe the high ionization mechanism in dc-HPPUMS discharge. The parameters deduced from Child law agree with the experimental results.
Dielectric barrier discharge (DBD) can produce non-equilibrium plasma at atmospheric pressure, and it has become a hot point in recent years. For the DBD excited by pulsed or alternated currents, the effects of the loading performance of power supply, the matching between supply and discharge reactor and the discharge phenomena on its discharge are interesting issues. The studies of these issues are of great importance for understanding the DBD processes and improving the power supply efficiency. In this paper, the Lissajous figures of a DBD reactor with coaxial electrode configuration are measured. The loading performance of the DBD reactor and the dependences of excitation voltage and air flow rate on the dielectric layer equivalent capacitance are studied in atmospheric air. According to the experimental data and circuit modeling analysis, it is proved that the dielectric layer capacitance decreases with the increase of air flow rate, but increases with the increase of excitation voltage. The amplitude-frequency performance of the reactor reveals significant RLC circuit resonance. The resonance frequency of the reactor has the same behavior as its dielectric layer capacitance. Therefore it shows that the dielectric layer capacitance is the main factor for the resonance frequency evolution. A possible mechanism responsible for the dielectric layer capacitance is also presented.
An experimental study of the effect of applied magnetic field on the properties of the plasma and electrostatic oscillations in an unbalanced magnetron sputtering discharge was carried out. The apparatus consists of a magnetron sputtering target, using the conventional magnetic field configuration, and a coaxial coil around the target for an applied axial magnetic field. The dependencies of plasma parameters on the coil current were studied by two Langmuir probes. The resonance properties of electrostatic oscillations were observed. The results indicate that the applied magnetic field affects the plasma properties for the coil current in a range of 0 A to 8 A. The frequency bandwidth of the electrostatic oscillations in the unbalanced magnetron sputtering plasma is in a range of 0 kHz to 300 kHz. From the spectrum analysis, the eigenfrequency near the target is in a range of 20 kHz to 50 kHz under typical experimental conditions where all the magnetic field, pressure, and power etc are able to have full impact on the spectrum characteristics. The calculated value of the electron temperature as per an ion acoustic standing wave pattern inside the magnetic trap is in good agreement with the experimental result.
The coupling resonance is induced by the plasma electrostatic oscillation in the magnetic trap consisting of the cross-field at the surface of the unbalanced magnetron sputtering target and the potential well composed of the magnetron sputtering target and the opposite bias substrate in parallel. Langmuir probe was used to study the plasma properties and power spectra density (PSD) of the floating potential signals. Under typical discharge conditions, the eigenfrequencies in both traps were respectively in the range of 30—50 kHz or 10—20 kHz, and the electron temperatures in both traps calculated with the acoustic standing wave mode conformed with the experimental results.
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