Size changes of polystyrene latex particles in the electron microscope under controlled physical conditions
✍ Scribed by Cermola, Michele ;Schreil, Werner-Hans
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1987
- Tongue
- English
- Weight
- 900 KB
- Volume
- 5
- Category
- Article
- ISSN
- 0741-0581
No coin nor oath required. For personal study only.
✦ Synopsis
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 pm (+0,0060 pm) 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 &p2. 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 I1 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 once the spheres initiate shrinking.