Examples of LT-SEM magnification capability.
Most samples of snow crystals are observed by researchers at relatively moderate magnifications (30X-500X),
however the capabilities of the electron microscope allow observation of fine structures at over 100,000X.
The following set of photographs demonstrates a magnification series using a low temperature scanning electron
microscope (LT-SEM) covering this range. By contrast, the light microscope is only capable of viewing meaningful
details at magnifications of about 1,000X and is very limited in depth of field. Snow samples are very fragile
and exposure to the light necessary to photograph them, using light microscopes, can change structures and even
melt them. Using LT-SEM, samples are frozen to temperatures below -170 degrees Centigrade where they can be placed
in a vacuum and observed for many hours with no structural changes. These photographs show the extraordinary
symmetry of snow crystals even at high magnification. Magnification bars are accurate but X factors (lower left) are for 8"x10" prints.
Upper: Single stellar snow crystal with sectorlike extensions where one arm has been broken off during descent through the atmosphere. Magnified 100X (Each subsequent photograph in this series has been doubled in magnification from that of the previous photo).
Lower: Higher magnification view of two lower arms on the same snow crystal on which a high degree of symmetry is noticeable Magnified 300X.
Upper: Further magnified view of the left arm of the previous photo in which parallel groove and pit structure shows a high degree of hexagonal structure and symmetry. Magnified 900X.
Lower: Smooth structure of groove and pit interiors as contrasted by asperities covered surfaces of etched crystal faces are visible at 1,800X.
At 3,000X (Upper) and 7,000X (Lower) Symmetry is still very noticable however many differences are beginning to become apparent in the etched surface structure.
At 18,000X (Upper) and 36,000X (Lower) less additional information on the surface structure of these crystals is obtainable, however fractured interiors of many ice samples can reveal additional ultrastructure.
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