Shadowing surface features

Because of the low penetrating power of electrons, specimens for examination in transmission have to be very thin, depending on the circumstances tens or hundreds of nanometres in thickness. Surface features on thick specimens can be examined by making a thin replica. A standard technique is to evaporate a thin film of carbon on to the surface of interest, to shadow it by depositing an even thinner layer of platinum at a different angle, and then to remove the deposited replica, for example, by dissolution of the original specimen. 

Figure 4. A schematic illustrates the effect of shadowing during oblique-angle deposition. Islands of different height are initially nucleated at the surface. Subsequently, the incident flux of material that strikes the surface with an oblique angle a is preferentially deposited onto the top of surface features that have larger height values.

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... 

A shadow-mask technique has been applied for the local metal deposition to exclude metal residues on other designs processed on the same wafer (Fig. 4.2b). Such metal residues may be caused by imperfections in the patterned resist due to topographical features on the processed CMOS wafers or dust particles. The metal film is only deposited in those areas on the wafer, where it is needed for electrode coverage on the microhotplates. This also renders the lift-off process easier since no closed metal film is formed on the wafer, so that the acetone has a large surface to attack the photoresist. Another advantage of the local metal lift-off process is its full compatibility with the fabrication sequence of chemical sensors based on other transducer principles [20]. 

By means of the one step replica with tungsten as pre-shadow-ing metal, the electron micrograph of the surface of an unannealed membrane is shown in Figure 5. In the micrograph we can find the pores whose sizes range between 10 and 27 A. The greater part of them is between 15 - 25 A. The surface appears just like crater and there are also observed some wave-like features, the sizes of... 

When such features exist, they are penetrated by the electron beam so the material is represented by a three-dimensional point lattice and diffraction only occurs when the Ewald sphere intersects a point. This produces a transmission-type spot pattern. For smooth surfaces, the diffraction pattern appears as a set of streaks normal to the shadow edge on the fluorescent screen, due to the interaction of the Ewald sphere with the rods projecting orthogonally to the plane of the two-dimensional reciprocal lattice of the surface. The reciprocal lattice points are drawn out into rods because of the very small beam penetration into the crystal (2—5 atomic layers). We would emphasize, however, that despite contrary statements in the literature, the appearance of a streaked pattern is a necessary but not sufficient condition by which to define an atomically flat surface. Several other factors, such as the size of the crystal surface region over which the primary wave field is coherent and thermal diffuse scattering effects (electron—phonon interactions) can influence the intensity modulation along the streaks. 

Fig. 12. Diagrammatic sketch of B6nard s direct-shadow system for locating the cell centers and cell partitions on the surface of the liquid. With the viewing screen at Pi, the cell centers appeared to be bright spots, A, B, and C on a dark background, whereas, when the screen was moved closer to the liquid, as at P2, the image became one of dark lines on a bright background. B nard s apparatus was actually somewhat different than shown, but the diagram illustrates its important features.

Fig. 7a. A glass cover plate protects the cell. Sunlight passes through the cover plate and the electrolyte to illuminate the semiconductor surface. Electrical current passes between the semiconductor and the counterelectrode through slots cut in the semiconductor. Characteristic features of this configuration are that no shadows are cast upon the semiconductor and that reaction products could be separated if a membrane were placed between the semiconductor and the counterelectrode.

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