Geometrical shadowing

Therefore, Cext is a well-defined observable quantity we measure U with and without the particle interposed between source and detector. Because Cext is inherently positive, the effect of the particle is to reduce the detector area by Cext this, then, is the interpretation of Cext as an area. In the language of geometrical optics we would say that the particle casts a shadow of area Cext However, as stated previously, this shadow can be considerably greater—or much less—than the particle s geometrical shadow. We note from (3.33) that Cext is the maximum observable extinction. The scattering term fi(D) X =0/k2 cannot be greater than Csca and is positive therefore, the observed extinction Cext lies within the limits... 

FIGURE 3.2 A Fraunhofer diffraction pattern under two different contrast levels. The circle drawn around the right hand pattern has a radius 1.5 times that of the geometrical shadow of the object. The area between the shadow and the circle represents the area from which the light to form the pattern is obtained. (The patterns were calculated using the Fresnel Diffraction Explorer, which may be obtained from Danger Research http //daugerresearch.com/)... 

Figure 6.11. The HIAC photozone stream counter characterizes fineparticles by the power drop they cause as they pass through a beam of white l t. a) Arrangement of the inspection zone of the HIAC counter, b) Calibration curve for the HIAC counter showing that the curve deviates from the predicted relationship for power blocked by a geometric shadow.

Diffraction spreading of light around the contour of a fineparticle beyond the limits of its geometrical shadow with small deviation from redtilinear propagation. 

Smooth surfaces will typically yield denser PVD coatings than rough surfaces due to the lack of macro-columnar morphology (Sec. 10.4.2) resulting from geometrical shadowing of... 

Figure 6.10 Geometrical Shadowing of the Deposition Flux by a Particle on the Surface...

Geometrical shadowing effects (angle-of-incidence effects)... 

Angle-of-incidence of the adatom flux effects - i.e. geometrical shadowing... 

In zone 1 of the MD model and in the Thornton model, the adatom surface diffusion is insufficient to overcome the geometrical shadowing by the surface features. This means that open boundaries between the colunms are formed. This morphology produces a film with a high surface area and a film surface that has a mossy surface appearance. Higher gas... 

Pinholes are uncovered areas of the surface. They can be formed by geometrical shadowing during deposihon or after deposihon by the local loss of adhesion of a small area of material (pinhole baking). Parhculates on the surface present very local changes in surface... 

Mouse hole (film growth) The void left at the comer of the bottom of a trench during film deposition due to the top closing before the bottom is filled. Caused by geometrical shadowing. See also Keyholing. 

Particulate contamination (cleaning) Contamination by particulates. A major source of pinholes in thin films either by geometrical shadowing or by holes generated when the particle is dislodged from the surface. 

If particles have significant anisotropic shapes, such as rods or platelets, then LD significantly overestimates the breadth and can even give bimodal distributions for monodispersed cylinders (Gabas et al. 1994). This is because the diffraction pattern depends on the geometric shadow of the particle with respect to its orientation with the laser beam. If the anisotropic particles are randomly oriented as they go through the analysis zone, then data from all orientations are produced and only if there is a constant form factor (constant thickness for plates or constant diameter for rods) can some information be carefully extracted from LD measurements (Bowen 2002). 

Optics. Diffraction leads to light deviating from rectilinear distribution, bending around opaque obstacles and penetrating into an area of geometrical shadow. 

Figure 6.12 Diagram of penetration of the diffraction radiation into the area of geometrical shadow.

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