DC Arc plasma-jet

Emission spectrometer incorporating a sample nebulizer, grating monochromator, photomultiplier detection system and microprocessor controller. Excitation by dc-arc plasma jet, or inductively coupled plasma. Laser excitation sometimes used. 

A hybrid plasma reactor was developed for the synthesis of fine ceramic powders (59). The reactant SiCl4 was injected into a DC-arc plasma jet and decomposed completely in a hybrid plasma an RF-plasma superimposed on the DC-arc plasma. The reaction with the second reactant NH3 and/or CH4 gas, which was injected into the tail flame of the plasma, formed Si3N4 UFPs and/or Si3N4 + SiC mixed UFPs, with structures that were amorphous. 

DC Arc Plasma Jet Gas Stabilized Arc DC arc discharge formed between nonsample electrodes in flowing gas streams of argon or helium. Sample introduced separately. liquids, powders 1500-3500... 

An argon-hydrogen plasma is created in a dc thermal arc (cascaded arc) operated at high pressure 0.5 bar) [556, 559. 560] (the cascaded arc is also employed in IR ellipsometry, providing a well-defined source of intense IR radiation see Section 1.5.4 [343]). As the deposition chamber is at much lower pressure (0.1-0.3 mbar), a plasma jet is created, expanding into the deposition chamber. Near the plasma source silane is injected, and the active plasma species dissociate the silane into radicals and ions. These species can deposit on the substrate, which is positioned further downstream. 

Arcs can be considered as gaseous resistance heaters and offer temperatures up to 50,000°K. The sustained temperatures realizable from electric arcs can be divided into three general regions according to the current density of the conducting path. The lower temperatures (up to 4000°K. and a current density of 60 amp./cm.2) make the anode material incandescent, but as the current density is increased beyond a critical level the voltage drop shifts suddenly from a uniform drop between cathode and anode to a drop concentrated at the anode surface (for a dc arc—at both electrodes for an ac arc). The transition from the conventional to a high intensity arc is marked by pronounced increases in brilliance and temperature the arc path becomes distorted, and a jet of plasma, called the tail flame, issues from the rapidly... 

Dc plasma jets were first described as useful devices for solution analysis by Korolev and Vainshtein [366] and by Margoshes and Scribner [367]. The sample liquids were brought into an aerosol form by pneumatic nebulization and arc plasmas operated in argon and with a temperature of about 5000 K were used. 

The dc plasma jet described for example by Margoshes and Scribner [367] is a current-carrying plasma. This also applies to the disk stabilized arc according to Riemann [352], where the form of the plasma is stabilized by using several disks with radial gas introduction keeping the plasma form stable under different sample loads and the influence of the plasma composition on the plasma properties low. However, the plasma described by Kranz [368] is a transferred plasma. 

A modification of the arc discharge method is reahzed in the so-called DC-arc jet (plasma jet). In this case, the electrodes are arranged in a way to form a sort of nozzle for the reactant gases. The cathode encloses the anode in a certain distance, and the gas mixture is led through the resultant gap. It partly decomposes between the electrodes before it hits the cooled substrate where the diamond film is deposited then (Figure 6.16). In this manner, an accurate control of the deposition zone is achieved, yet the results are highly dependent on the nozzle geometry and on a very constant reactant flow. 

A common DC glow discharge PACVD system may be varied by operating the plasma at higher pressures and powers at which a DC arc discharge between the electrodes can be produced. In 1988, Kurihara et al.t l first reported the use of the DC plasma arc-jet CVD method, in which... 

Fig. 4i8. Experimental set up for ceramics synthesis in a crucible heated by a DC plasma jet with the arc transferred on the crucible. Reprinted from...

Deposition from the Vapor Phase Submicron (3-SiC can be continuously produced by decomposing gaseous or volatile compounds of silicon and carbon in inert or reducing atmospheres, at temperatures above 1400 °C [83]. The particle size and morphology will depend considerably on the reaction temperature and on the composition of the gas phase. A wide variety of reactants, and several methods of heating (e.g., dc arc jet plasma [84], high-frequency plasma [85], laser [86, 87] and thermal radiation [88]) are possible. 

The luminous gas phase created by a special mode of DC discharge recognized as the low-pressure cascade arc torch (LPCAT) provides an especially important case for understanding the fundamental aspects of the luminous gas phase. The luminous gas phase in form of luminous gas jet stream or torch are created by blowing out DC discharge into an expansion chamber in vacuum. The luminous gas jet of Ar mainly consists of photon-emitting excited neutral species of Ar, which is certainly not the plasma of classical definition. The core of LPCAT is the tip of injection nozzle however, it is not the core of electrical discharge. 

Gas-phase activation above the deposition surface is essential for achieving appreciable diamond growth rates. The various CVD methods differ primarily in the way they produce gas-phase activation. The most abundant carbon-containing gaseous species present in most activated systems are methyl radicals and acetylene molecules which are also considered to be predominant growth precursors for diamond, almost independent of the deposition methods used. However, in systems that dissociate a significant fraction of H2, such as DC plasma arc-jet CVD, carbon atoms, aside from acetylene, are also abundant in the gas phase. 

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