Pressure Cascade Arc Torch

The spatially decoupled activation and deactivation can be also seen in a mode of PP known as low-pressure cascade arc torch (LPCAT) polymerization), which is described in Chapter 16. The activation of a carrier gas (e.g., argon) occurs in a cascade arc generator, and the chemical activation of a monomer or a treatment gas takes place near the injection point of the argon torch in the deposition chamber. The material deposition (deactivation) occurs in the deposition chamber. This is the same situation as the HWCVD, except that the mode of activation is different. 

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. 

The existence of the dissociation glow in DC discharge strongly suggests that the creation of chemically reactive species in LCVD involves different mechanism than those in the electron impact ionization. However, in DC discharge, electron impact and ion impact reactions cannot be eliminated. Low-pressure cascade arc torch (LPCAT) provides a unique opportunity to investigate the formation of chemically reactive species with minimal influence of ions and electrons. That is, the creation of chemically reactive species from an organic molecule by the luminous... 

Figure 4.13 Electron density (cm ) as a function of axial position and methane flow rate in low pressure cascade arc torch (LPCAT) 8.00 A, 2000 seem argon, and 560mtorr (75 Pa).

In low-pressure cascade arc torch (LPCAT), the electrical power is applied in the cascade arc generator, in which only carrier gas, generally Ar, is activated to create luminous gas. The luminous gas created in the cascade arc generator is blown into the second expansion chamber, in which the monomer is introduced. Thus, the luminous gas of Ar neutrals primarily creates polymerizable species, and following these two steps should treat the deposition kinetics. Principles described in this chapter apply to each of the two steps. Details of deposition kinetics in LPCAT are described in Chapter 16. 

CASCADE ARC GENERATOR AND LOW-PRESSURE CASCADE ARC TORCH REACTOR... 

A single monoatomic gas, e.g., argon or helium, is used as the carrier gas of the cascade arc discharge. When the luminous gas is injected into an expansion chamber under low pressure, e.g., 1 torr or less, the flame extends a significant length (e.g., 1 m), which depends on the fiow rate, input power, diameter of the nozzle, and pressure of the expansion chamber. This mode of cascade arc torch is termed low-pressure cascade arc torch (LPCAT), which is useful in the surface modification by means of low-pressure cascade arc torch treatment and low-pressure cascade arc torch polymerization. 

Low-pressure cascade arc torch can be utilized in the following three modes in the surface modification of materials ... 

Low-Pressure Cascade Arc Torch (Without Addition of the Second Gas)... 

Low-pressure cascade arc torch polymerization or coating could be considered more or less the same as the plasma polymerization or coating by other conventional plasma processes. The ultrathin layers prepared by LPCAT polymerization have the general characteristics of plasma polymers, i.e., amorphous (noncrystalline), high concentration of the dangling bonds (free radicals trapped in immobile solid phase), and the high degree of the internal stress in the layer. 

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