Crater shape

Figure 1.13. Dark-field TEM images of single-crystal calcite shocked to 85 GPa, displaying (a) the crossing of multiple twins, a large number of perfect dislocations and (b) numerous partial dislocations decorating the twin planes, (c) Secondary electron image of compacted calcite powder shocked to 85 GPa. The recovered specimen is composed of numerous foamy aggregates containing bubbles, voids, and crater-shaped objects.

Refining the LIBS approach entails improving the focusing optics and using lasers with a more uniform energy distribution across the beam. The influence of laser focus on crater shape is shown in Fig. 9.11. The parameter working distance (WD) is defined as the difference between the lens-to-sample distance (g) and the focal distance (/) WD S f Advances in these areas will provide surface craters of controlled shape, which will in turn result in improved spatial resolution in LIBS. 

Fig. 9.10. Effect of beam power on crater shape and size. For details, see text.

Fig. 9.11. Influence of the focusing conditions on crater shape and size. WD working distance, g lens-to-sample distance,/ focal distance, SEM scanning electron microscopy.

The heat conductance through the sample and in the plasma is responsible for the fact that with the Nd YAG lasers available today, the crater diameters are still much wider than the values determined by the diffraction limitations. When using conventional lasers with pulses in the ns and ps range the plasma shields the radiation, whereas with the femtosecond lasers that are now available a free expanding plasma is obtained, where the heating of the plasma appears to be less supplemented by the laser radiation. This leads to less fractionated volatilization of the solid sample and differences in crater shape, which need to be investigated further [229]. 

Figure 6. Damage distribution and mean stress contour plot at 2.0 ms in computer simulation of Experiment 79—10. The contour level and plot dimensions are the same as in Figure 1. Note that the bottom of the charge is at the same depth as in Experiment 79-8 (Figures 1-4), but the charge is larger and extends closer to the free surface. The shallower effective depth of burial has resulted in the formation of a crater-shaped damage region, much as was observed in the corresponding field experiment.

Edges of macro-colony are raised higher than center (crater-shape). 

In case of microanalysis, a small beam diameter of a few micrometers is required. A flat-top beam prohle is required with depth profiling because of the evolving crater shape. Gaussian beam prohles have to be shaped for this purpose with different beam processing devices (focusing, spatial filtering, and homogenizing) [76]. 

High-depth resolution in the analysis of coatings and thin films using GD-MS requires crater shapes (Figure 41.2) with a flat bottom and perpendicular walls [35]. Nevertheless, optimum operating conditions to obtain adequate crater shapes do not usually match the optimum conditions to obtain the maximum sensitivity, thus, a compromise must be used. 

The parameters that affect the characteristics of the crater shape are closely related to the ion source design (e.g., electrical potential distribution in front of the cathode). Furthermore, gas flows are of special... 

Depth resolution in MS sputtering techniques is limited by crater shape and layer mixing and also by the ion transfer processes between the ablated layer and the detection system. Relevant parameters here include ... 

There would appear to be several types of paint film defect associated with foams and antifoams. Most are described as cratering, where crater-shaped depressions are present in films, which are attributed to a variety of causes by Kornum and Nielsen [29]. One cause concerns bubbles that burst only after the drying latex film has at least partially fused so that the shape of the bubble is largely preserved in the paint film as depicted in the sketch in Figure 9.5. Antifoams are of course included in paint formulations in order to rupture such foam films before fusion of the latex film. They may, however, themselves cause defects. Thus, Kornum and Nielsen [29] attribute some defects caused by antifoams to Marangoni flows induced by, for example, spreading from silicone oil drops. Such flows produce only transient depressions in... 

Soil liquefaction is a phenomenon in which cyclic shear deformation of soil causes high pore water pressure and reduces dramatically the shear rigidity of soil. Liquefied subsoil deforms profoundly and the function of the affected structure is lost. Liquefaction is likely to occur in loose, young, cohesionless, and water-saturated soil that is subjected to strong earthquake shaking. The high pore water pressure induces water flow toward the ground surface and this water flow transports soils. As a consequence, sandy deposits of crater shape remain (Fig. 30). 

Macroscopic models have been applied to the MALDI plume, including a hydrodynamic approach and that of a pre-accelerated adiabatic expansion. These cannot directly account for mixed gas/clusters in the ablation regime, but are still useful as a first approximation. They also cannot account for changes in plume development as the desorption/ablation crater shape changes.In contrast, the mixed-phase aspect of ablation is a natural part of molecular dynamics, even though it is not computationally possible to include the full temporal and spatial extent of a real experiment. Nevertheless, molecular dynamics has illuminated numerous aspects of the phase transition aspect of MALDI. " - ... 

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