Charged species, transport, plasma

Like the performance of chemical reactors, in which the transport and reactions of chemical species govern the outcome, the performance of electronic devices is determined by the transport, generation, and recombination of carriers. The main difference is that electronic devices involve charged species and electric fields, which are present only in specialized chemical reactors such as plasma reactors and electrochemical systems. Furthermore, electronic devices involve only two species, electrons and holes, whereas 10-100 species are encountered commonly in chemical reactors. In the same manner that species continuity balances are used to predict the performance of chemical reactors, continuity balances for electrons and holes may be used to simulate electronic devices. The basic continuity equation for electrons has the form... 

The above combinations of electricity with chemistry deal with the generation of charged species in either a gas of a liquid medium. This requires ionization, which occurs by electron transfer and transport of charged species in a closed electrical circuit. The charged species themselves, or the radicals generated by them (e.g., radicals generated by electron impact in the gas phase, in a plasma) can be used as activated species taking part in chemical reactions. 

The experimental aspects of neutral plasma gas-phase chemistry are very similar to those discussed above in conjunction with MOVPE. The development of in situ diagnostics and kinetic studies are needed to unravel the complex free radical-dominated gas-phase chemistry. The unique aspects of plasma processing stem from the transport and reactions of charged species. Besides providing insight into the underlying fundamentals, tech-... 

Up until the early 1990s, simulations that solved for the radio frequency (RF) plasma dynamics (so-called glow discharge models) were confined to one spatial dimension (1-D) [36, 113-126]. In addition, most of these simulations did not solve for the transport and reaction of neutrals, i.e., the effect of gas excitation and/or dissociation on the plasma characteristics was not accounted for. This can sometimes be a severe limitation since even minute quantities of excited species can alter the discharge properties [36]. Self-consistent RF plasma simulations which solve for the coupled effects of charged and neutral species transport and chemistry have only been reported within the past several years in 1-D [36, 121, 123], 2-D [97, 100, 127-132] and 3-D [109, 110]. Multidimensional simulations are particularly useful since they can address the important issue of plasma uniformity and the spatiotemporal plasma... 

Neutral species within a plasma undergo diffusive and convective transport identical to that in a gas, however, charged species have an additional restriction as a result of the conservation of charge neutrality over distances which are greater than the Debye length of the plasma (of the order of 100 pm). Therefore, in a plasma which contains an equal number of positive ions and electrons, their transport is coupled through the coulombic interactions forcing them to have an equal diffusivity called the ambipolar diffusivity, DA3). 

The plasma transport properties of various charged species are usually described by drift velodty and drift mobility in tlw electric fiekl. Correspondingly the electrical conductivity and diffusion coefficients are introdiK d. 

Mass, momentum, and energy transport of charged and neutral species coupled with plasma chemistry. 

Contribution of Reactive Neutral Species to Sterilization Effect of Non-Thermal Plasma. Compare contribution to sterilization of OH-radicals generated in plasma and then transported to the surface of biomaterials (see section 12.5) with that of OH-radicals produced inside of the biomaterials from plasma-generated charged particles (see section 12.1.4). Analyze rates of OH-production by surface bombardment with electrons and with positive and negative ions. What is the effect of electric field in the non-thermal atmospheric-pressure air discharges on the balance between the channels of OH production ... 

Plasma sheaths are thin regions present in every gaseous discharge perpendicular to the surface of a solid in contact with a plasma and have a net electrical charge, usually positive, surrounding the body. Plasma sheaths are important from the viewpoint of materials treatment since they control the transport process of the chemically activated species generated in the plasma towards the surface of the substrate, as well as the bombardment with positive ions of that surface and the chemical reactivity of surface induced by it. 

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