Download PDF by Albert G. Ingalls: Amateur Telescope Making

By Albert G. Ingalls

Definitive e-book on beginner telescope making. comprises plans and concept on numerous types. topics coated: Newtonian Telescope replicate Making; Optical checking out; Workshop knowledge; and Observatory constructions.

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The specimen chamber in the SEM is large and sampies up to several inches in diameter can be accommodated. Specimen preparation is generally quite simple, if the materials can withstand drying and high vacuum. Nonconductive materials, such as most polymers, require conductive coatings or the use of low accelerating voltages to prevent them from charging up in the electron beam. SEM images are easy to interpret qualitatively. They appear as though the specimen is viewed from the source of the scanning beam, and illuminated by a light at the detector position.

These two modes are not specific to the STM, but generally applicable to SPM, if they are described as constant height and constant signal modes (Fig. 7). The constant height mode allows higher scanning speeds, but requires that the surface be very smooth in the region scanned. If a protrusion is greater than the set constant height, the probe tip crashes into the sampie. The next SPM to be developed [78] and currently the most important for the study of polymers is the atomic force microscope (AFM) [76,77].

Some polymers, such as PMMA, are quite sensitive to the beam. Extended exposure to the electron beam will cause mass loss and pitting or depression of the surface in the rastered area. Semi-crystalline polymers lose crystallinity on exposure to the electron beam and this can change specimen morphology in thin films. Low accelerating voltages reduce charging effects, beam damage and beam penetration, giving greater sensitivity to surface detail. In the past signal collection was difficult, the electron sources were less bright and stray fields disturbed the image at accelerating voltages less than 5 kV.

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Amateur Telescope Making by Albert G. Ingalls

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