Line-of-sight process

As seen in Fig. 3, the LPCAT flame is relatively narrow implying that a uniform luminous gas phase is not created in the expansion chamber. Consequently, the treatment that can be achieved by an LPCAT is governed by the line of sight process, regardless of whether the substrate touches the luminous gas flame or not, and limited to a relatively small area that is exposed to the flame or near the tip of flame. When a substrate is placed along the line of the jet stream, the well-identifiable flame is destroyed, and gaseous species scatter in the downstream of the substrate. The scattered species could cause surface treatment effects however, their extents are much smaller than that by the jet. 

Since utilization of IR depends upon absorption, it becomes essentially a line of sight process. Of course, a highly conductive substrate (e.g., metal) will distribute the thermal energy out of the line of sight. Conversely, an insulating substrate (e.g., wood) will do little to distribute the heat, and hot spots can develop if exposure is nonuniform. 

Evaporation is carried out under reduced pressure. The chamber is evacuated and back filled with the required gas at a suitable low pressure. Since evaporation is a line of sight process, the component must be rotated and turned to provide a uniform coating on complex shapes. The adhesion of the coating can be improved by heating the substrate, using quartz lamps or a diffuse electron beam. 

A vacuum technique closely related to CVD is PVD (physical vapor deposition), in which a solid (metal or compound) is evaporated in a vacuum by heating or by a plasma (called sputtering) and condensed on a substrate to form a coating. Often there is no chemical reaction during deposition—hence the name. PVD is a line-of-sight process, and unlike CVD it suffers from shadowing on profiled surfaces if the substrates are stationary with respect to the source. 

Line-Of-Sight Process Coating that is applied only on the surfeces that face the emission source of the coating material. 

Chemical vapor deposition CVD has the ability to coat complex shapes internally and externally because it is a non-line-of-sight process with strong throwing power... 

Based on the analysis earned out in the present section, it can be concluded that only simple stoichiometric compounds can be deposited using standard CVD and PVD methods, as each component has to be evaporated at a different tanperature due to their different vapor pressures. Moreover, the CVD process also apphes very toxic precursors (Choy 2000,2003). The constituents have to be deposited from independently controlled sources, adding complexity to the system. At the same time, PVD is a line-of-sight process, meaning that it has difficulty in coating complex-shaped components. 

The combination of plasma and ion beams in the process of plasma immersion ion implantation (PHI) has been developed during the last few years [63-66], and it seems that this new technique shows promise in bringing down the costs of ion implantation [67]. For homogeneous implantation of workpieces with complicated geometries the process has the particular advantage that it is not a line of sight process as in conventional ion implan-... 

Vacuum Deposition. Vacuum deposition, sometimes called vacuum evaporation, is a PVD process in which the material is thermally vaporized from a source and reaches the substrate without coUision with gas molecules in the space between the source and substrate (1 3). The trajectory of the vaporized material is therefore line-of-sight. Typically, vacuum deposition takes place in the pressure range of 10 10 Pa (10 10 torr), depending on the level of contamination that can be tolerated in the resulting deposited film. Figure 3 depicts a simple vacuum deposition chamber using a resistively heated filament vaporization source. 

The potential for interference with the normal operation and maintenance of a process vessel is high. A major design effort is required to overcome this disadvantage. All aspects of the process vessel operation must be considered. Lines of sight for process vessel and crane operators, access for crane-held ladles and buckets, process vessel movements, and maintenance access must be accommodated by the enclosure design. This is more easily achieved in a new installation. 

It i s not restricted to a line-of-sight deposition which is a general characteristic of sputtering, evaporation and other PVD processes. As such, CVD has highthrowingpower. 

Multiply charged ions of minor abundance are frequently observed in FI and FD mass spectra. Their increased abundance as compared to El spectra can be rationalized by either of the following two-step processes i) Post-ionization of gaseous M ions can occur due to the probability for an M ion to suffer a second or even third ionization while drifting away from the emitter surface. [69,70] Especially ions generated in locations not in line-of-sight to the counter electrode pass numerous whiskers on their first 10-100 pm of flight ... 

Tunable diode-laser sensors offer considerable promise for combustion research and development and also for process sensing and control applications. These devices are rugged and relatively easy to operate and they have been demonstrated to yield simple and quantitative measurements of species, temperature, and velocity, where line-of-sight measurements are useful or preferred. These techniques will grow in use as costs of laser sources and fiber-optic components decrease and access to more wavelength regions improves. 

The parylcne process has certain similarities with vacuum metallizing. The principal distinction is that truly conformal parylene coatings are deposited even on complex, three-dimensional substrates, such as on sharp points and in hidden or recessed areas. Vacuum metallizing, on the other hand, is a line-of-sight coating technology. 

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