Polarity Effect Of Silent Discharge

Hydrogenated diamond-like carbon (DLC) films have been deposited on silicon substrates from dielectric barrier discharge (DBD) plasmas of CH4 at room temperature under a pressure of 0.4-4.0 Torr. The effects of discharge gas pressure (P), the applied peak voltage and the distance of the discharge gas spacing (d) on the film quality have been systematically investigated. The film hardness is mainly dependent on the Pd value and applied peak voltage. The best films of ϕ40-70 mm with Knoop hardness up to 20 GPa can be deposited at 30 kV peak voltage with a Pd value of about 2 Torr mm. The deposited films were characterized by scanning electron microscopy, Raman and FTIR spectroscopy. These analyses show that the deposited films are homogeneous hydrogenated amorphous carbon films with very smooth surfaces containing significant amounts of sp3 C-C bonding. The high-voltage and current waveform measurements of the discharge indicate that the low-pressure DBD consists of uniform (along the whole electrode) glow-like single breakdowns with half-widths of several microseconds. The DBD-induced deposition technique used in this work has many advantages, including the simplicity of the experimental set-up, large area deposition of DLC films and a lower consumption of feed gas and electric power.

Section: Low-pressure Dielectric Barrier Discharge Physicssupporting

confidence: 72%

Plasma-assisted CVD of hydrogenated diamond-like carbon films by low-pressure dielectric barrier discharges

Liu

Shan-xin

et al. 2001

“…Eliasson et al have reported a linear variation of the charge per FD with the gap length [177], and Pietsch and co-workers have linked the relative charge per unit gap length to the specific capacitance (ratio between dielectric permittivity and thickness [170]). Besides, the simultaneous development of multi-FD in small volume arises from uv photo-emission induced by the first FD creating new electrons [181,182]. Despite local heterogeneities around each FD, homogeneous distribution of similar FD are repeated at ac frequency 1-100 time per centimetre square and half-cycle.…”

Section: Ac Dbd In Airmentioning

confidence: 99%

Nucleation and aerosol processing in atmospheric pressure electrical discharges: powders production, coatings and filtration

Borra¹

2006

161

146

This review addresses the production of nano-particles and the processing of particles injected in atmospheric pressure electrical discharges (APED). The mechanisms of formation and the evolution of particles suspended in gases are first presented, with numerical and experimental facilities. Different APED and related properties are then introduced for dc corona, streamer and spark filamentary discharges (FD), as well as for ac filamentary and homogeneous dielectric barrier discharges (DBD). Two mechanisms of particle production are depicted in APED: when FD interact with the surface of electrodes or dielectrics and when filamentary and homogeneous DBD induce reactions with gaseous precursors in volume. In both cases, condensable gaseous species are produced, leading to nano-sized particles by physical and chemical routes of nucleation. The evolution of the so-formed nano-particles, i.e. the growth by coagulation/condensation, the charging and the collection are detailed for each APED, with respect to fine powders production and thin films deposition. Finally, when particles are injected in APED, they undergo interfacial processes. Non-thermal plasmas charge particles for electro-collection and trigger heterogeneous chemical reactions for organic and inorganic films deposition. Heat exchanges in thermal plasmas enable powder purification, shaping, melting for hard coatings and fine powders production by reactive evaporation.

“…They proposed an explanation for the occurrence of a group of microdischarges. The UV emission from a preceding microdischarge can preionize the air and triggers the temporal superposition of microdischarges [22]. The grounded electrode was thus divided into two parts to limit the number of series per period and the number of pulse per series.…”

Section:  Calculation Of the Instantaneous Discharge Currentmentioning

confidence: 99%

“…It is rather difficult to distinguish the contribution of each single microdischarge among the others on the resulting current. Series of microdischarges [21] and chains of microdischarges [22] are the terms used to describe the fact that several microdischarges are triggered, at different positions in the gap, in a time lapse smaller than the duration of a microdischarge or even at the same time. Murata et al proved that the series occur in limited space of about one square centimetre.…”

Section: Electrical Measurements the Ac High Voltagementioning

confidence: 99%

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Electrical characterization of microdischarges produced by dielectric barrier discharge in dry air at atmospheric pressure

Jidenko

Petit

Borra

2006

This work addresses the case of millimetre sized plane-to-plane dielectric barrier discharge with sinusoidal voltage between 1 and 60 kHz for different configurations in air at atmospheric pressure. The first aim of this work is to achieve a representative statistical analysis of the electrical characteristics of the microdischarges. The numerical data treatment presented here, enables to determine the maximum current, the duration, the amount of charge, and the triggering voltage for each current pulse. Both the average values as well as the deviations are checked. The relative influence of the operating parameters (voltage, gas flow rate, gap width, frequency) on the local surface polarization, electron attachment and temperature affecting microdischarge characteristics has been depicted in different arrangements. A special attention is paid to the influence of dielectric walls inside the discharge gap, perpendicular to the electrodes. Besides, this study allows the identification of the operating conditions for which all the microdischarges can be considered identical to study the local physical and chemical processes around each microdischarge.