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. 

Plasma polymerization is a vapor phase-activated (by plasma) A/D-coupled CVD. Parylene polymerization is a vapor phase-activated (by thermal process) A/D-decoupled CVD. Cascade arc torch (CAT) polymerization is a vapor phase-activated (by plasma) A/D-decoupled CVD. General CVD is a surface-activated (by thermal process) A/D-coupled CVD. HWCVD is a hot wire activated A/D-decoupled CVD. Coupled and decoupled refer only to the spatial separation. 

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. 

Figure 11.8 FTIR spectra of plasma polymers prepared by cascade arc torch from (a) tetramethydisiloxane (TMDSO), (b) hexamethydisiloxane (HMDSO), and (c) vinylpenta-methyldisiloxane (VpMDSO) 750 seem argon, 4.0 A arc current, 5.0 seem monomers.

In general plasma polymerization processes it has been established that the deposition rate and properties of a plasma polymer primarily depend on the value of the normalized energy input parameter WjFM, as described in Chapter 8. In LPCAT polymerization processes, as described in Chapter 16, the deposition rate of a plasma polymer primarily depends on the value of the normalized energy input parameter, which is given by W FM)J FM). In this composite parameter, W is the power input applied to arc column, FM) is the mass flow rate of carrier gas (argon), and FM) is the mass flow rate of monomer that is injected into the cascade arc torch. The quantity of W FM)J FM) can be considered as the energy, which is transported by carrier gas plasma, applied to per mass unit of monomers. 

Figure 11.11 Dependence of internal stress on the energy input parameter, W (FM)c/ (FM)m, for cascade arc torch polymerization.

Figure 11.14 Qualitative correlation of internal stress with refractive index of cascade arc torch plasma polymer films.

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. 

Figure 16.3 Pictorial view of cascade arc torch reactor.

The electron impact ionization does not occur in the cascade arc torch, and the energy transfer between excited neutrals of the carrier gas and the added gases becomes the dominant mechanism, i.e., the Penning-type reaction or resonance... 

DEPOSITION IN CASCADE ARC TORCH 4.1. Activation of Monomer by Luminous Gas... 

Figure 16.17 Dependence of the normalized deposition rate of silicones and hydrocarbon monomers on the parameter W (FM)J(FM) in cascade arc torch polymerization. The deposition rates were obtained at an axial position of 27.5 cm from the luminous gas jet inlet.

Figure 18.9 Surface contact angle changes of LTCAT Ar treated PTFE with varying (a) argon flow rate at 6.0 A arc current and (b) arc current at 1500 seem argon for 10 s exposure to a low-temperature cascade arc torch.

Figure 18.10 Surface contact angle changes of PTFE with exposure time in a low-temperature cascade arc torch at sample positions of 9 in. (in glow) and 14 in. (out of glow) from the torch inlet 1500 seem argon, 6.0 A arc current.

Figure 18.15 SEM pictures of PTFE surfaces treated by a low-temperature cascade arc torch, (a) Untreated PTFE (b) 10 s treatment (c) 1 min treatment. Treatment conditions are 1500 seem argon, 9 in. sample position, 6.0 A arc current.

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