Penetration experiments, scanning

Penetration—Indentation. Penetration and indentation tests have long been used to characterize viscoelastic materials such as asphalt, mbber, plastics, and coatings. The basic test consists of pressing an indentor of prescribed geometry against the test surface. Most instmments have an indenting tip, eg, cone, needle, or hemisphere, attached to a short rod that is held vertically. The load is controlled at some constant value, and the time of indentation is specified the size or depth of the indentation is measured. Instmments have been built which allow loads as low as 10 N with penetration depths less than mm. The entire experiment is carried out in the vacuum chamber of a scanning electron microscope with which the penetration is monitored (248). 

Cano Barrita [27] cast concrete specimens with w/c of 0.6, dried the specimens at 38 °C and 20% relative humidity, then measured the penetration of water in a capillary uptake type of experiment. A 3D centric scan SPRITE measurement was selected, as an image could be acquired in 150 s and the image would therefore be weighted only by the T2 decay. 3D images were acquired at various exposure times and the central 2D image slice was extracted from the data to measure the penetration depth with time. 

Surface diffraction experiments have to be done in UHV. Otherwise the surfaces are covered with a monolayer of adsorbed molecules. At this point the reader might ask why do we not have to use UHV in scanning tunneling or the atomic force microscope In both techniques the tip penetrates through the surface contamination layer. In the scanning tunneling microscope it is often just invisible because contamination layers are usually not good conductors. In... 

It can be seen that most of the electrons are localized in the 3.5 pm thick layer and only a few of them penetrate to a depth of 3.8 pm. In our experiments a 0.5 mm thick LiNbC>3 crystal was spin-coated with 3.5 pm thick photoresist layer (Shipley 1818). The prepared sandwiched structure was exposed using a commercial eb lithography system (elphy Plus) adapted to a jeol jsm 6400 scanning electron microscope on the C -face of the LiNb03 sample under various accelerating voltages and surface charge densities, as shown in Table 10.1. 

Generally mesophases form rapidly which leads to a diffusion-limited growth. Times of order seconds or less have been reported in T-jump experiments where a homogeneous sample is subjected to a temperature change and the time for the mesophase to form is measured 13), However, in some penetration scan experiments times much longer than a second have been observed. 

In most penetration scans performed in surfactant dissolution experiments the phases are homogeneous and the interface between them is sharp. However, in some cases the interface becomes unstable and dramatic instobilities can be observed. There are many examples of instabilities that are well understood that maybe rationalized in terms of kinetic maps or dissolution paths, or dynamic instabilities involving fluid flow (e.g. Marangoni effects) or other Laplacian growth instabilities , such as Mullins-Sekerka instabilities (3J). However, myelins (Figure 1) are an example of an instability that remains poorly understood. 

TMA consists of a quartz probe which rests on top of a flat sample (a few mm square) in a temperature controlled chamber. When set up in neutral buoyancy then as the temperature is increased the probe rises in direct response to the expansion of the sample yielding thermal expansion coefficient versus temperature scans. Alternatively, with a penetration probe under dead loading a thermal softening profile is obtained (penetration distance versus temperature). Although this is a simple and versatile experiment, it gives only a semi-quantitative indication of mechanical modulus versus temperature. 

The ATR method is more efficient for in situ studies in the presence of solvent, which fulfills the function of the immersion medium (Section 2.7.3). For low solution concentrations (<10 " M), a typical experiment will involve (1) spreading a reference paste over the IRE surface (this paste contains pure powder wetted with pure solvent and is spread to a thickness comparable to the depth of penetration of IR radiation beyond the IRE-film interface), (2) scanning the background spectrum, (3) treating the paste directly in the accessory or changing... 

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