Micrometer point contact

Fig. 6.4. One of the first typical point-contact configurations. The apparatus is mounted in a vacuum can suspended in a superinsulated Dewar filled with liquid He. Shown (insert) are the (1) vacuum can flange, (2) stainless steel (ss) support structure, (3) differential micrometer, (4) ss gear, (5) pinion rod, (6) spindle, (7) piezoelectric transducers, (8) electrode holder, (9) tip, (10) sample cell, (11) sample platform, (12) coarse sample positioning screw, and (13) coarse sample positioning screw to set sample-tip gap [modified from ref. 6.12]...

Although most of the water in the meniscus evaporates once the tip has been retracted, residual structures can be observed in a radius of several tens of micrometers (depending on humidity and contact time) around the original contact point. For the tip radius and loads used in these experiments, the contact radius is approximately 10 A. The residual structures are in the form of flat islands and sometimes droplets. In our first experiments the perturbation created by a brief tip contact was not fuUy appreciated. Accidental tip contacts during approach of the tip to the surface do often occur. In such cases the tip is subsequently moved to an adjacent area, several micrometers away, to study the unperturbed surface. However, as stated already, the perturbed areas can extend over tens of micrometers away from the contact point. Droplets can be observed when the relative humidity is... 

A dilatometer constructed by Sauer is shown in Fig. 45. The sensing element is a linear variable differential transformer, whose rectified output is recorded directly. A pivot arm connects the transformer (A) to the bearing arm (B) and a micrometer screw allows for calibration and adjustment of the transformer. By adjustment of the compensating screw, the pivot arm can be moved so that the contact point (B) is exactly one sample length from the fulcrum. Temperatures above and below ambient can be obtained by circulating gas round the specimen. 

The growth front of a PS layer (not individual pores) is always perpendicular to the surface of the substrate with back electrical contact. The growth front is planar, independent of the orientation of the silicon samples, because the growth of pores depends on the supply of carriers which are transported from the back of the sample. The interface between the PS layer and silicon substrate is essentially flat with a difference between high and low points within a few micrometers. 

First electrical contact with the colony was not reproducible, and an uncertainty of about 5 micrometers exists. Furthermore, the signal from the microelectrode tended to be wildly erratic near the point of first contact. First contact with the agar remote from the colony was also somewhat erratic. While no proof is offered, it is thought that outer cells or a thin film of moisture can draw away from the electrode as a result of electrical stimulation. When advanced a few microns past the point of first electrical contact, the microelectrode delivered a stable signal. 

In the contacting measurement techniques, the micrometer caliper is a common instrument. The micrometer, however, can only be used for pot measurements and this is done manually. A spring-loaded dial gauge can be moved over the extrudate if the thickness variations are small. Thus, the dial gauge can be used to monitor the variation of thickness with time, i. e., in the extrusion direction. If an accurate traversing mechanism is constructed, the dial gauge can also measure the thickness variation perpendicular to the extrusion direction. At the point of measurement, the opposite side of the extrudate has to be firmly supported to avoid measurement errors. 

This catalyst may also be referred to as the molten salt catalyst, as referred to by Idles et al, according to the catalyst materials of this type reported to date. It is well known that some of the transition metal oxides, alkaline, and alkaline-earth metal oxides promote carbon oxidation. These oxides are solid and immobile at room temperature but become mobile on the surfaces of soot and support materials on a micrometer scale above certain temperatures, the melting point, or so-called Tamman temperature. In such a mobile state, the catalyst can maintain contact with the soot while the soot surfaces are continually excavated by oxidation. 

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