ISSN:
0741-0581
Keywords:
Dow latex
;
Internal standards
;
Electron microscope magnification
;
calibration
;
Latex sphere instability
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Natural Sciences in General
Notes:
In the early days of electron microscopy polystyrene latex particles were used as magnification standards. But in contrast to optical diffraction grating replicas made with carbon or SiO with precise line spacings resistant to electron irradiation, the latex spheres undergo changes, and conflicting reports have created some confusion. We used a highly stabilized electron microscope with controlled unchanging objective current in contamination-free conditions to expose standard Dow latex spheres of 0.399 μm (±0,0060 μm) under defined electron beam conditions. We measured the direct intensity of the electron current impinging on the screen. Removing the object from the beam, it is possible to measure the quantity of electrons absorbed by the latex spheres, expressed in nA/μ2. We used two standard intensities: a low intensity with widespread beam, equivalent to a 2-sec exposure time on Kodak electron image plates, and a higher intensity, obtained by increasing Condenser II current (two coarse plots towards crossover) that gives rise to a brightly illuminated observation screen. This is equivalent to a 1-sec exposure time on the same type of plates. It could be shown that all polystyrene particles uniformly decrease in size. This loss of material manifests itself immediately after the start of irradiation. The decrease follows a hyperbolic curve and reaches values of 14.35% size decrease for low radiation intensity after 15 min. An even greater decrease (namely 16.08% size decrease) was found for medium intensity electron bombardment. Sandwiching the particles with thin carbon film has no protective effect. Particle size has been determined on the photographic plates by measuring the shadow cast by 30° angle platinum shadowing and the shrinking particle itself. Particles “shadowed” with an angle 90° permit us to measure the annular concentric “shadow” once the spheres initiate shrinking.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jemt.1060050207
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