Ultramicroscope

An ultra-microscope is a special form of a dark-field microscope for observation of very small objects that would be with an imaging light microscope can not be seen alone. These include, for example, colloidal particles, fog droplets, or smoke particles. The term " Ultramicroscopy " came on around 1900. He described the microscopic examination of so-called " ultramicrons " in which they are particles that are smaller than the resolution limit of light microscopy, ie less than 0.2 microns.

A variant is the gap ultra-microscope, which was developed in the early 20th century by Henry Siedentopf and Richard Adolf ZSIGMONDY. In places lit by bright sunlight, the two scientists were able to prove in 1902 Rubin glasses particles of less than 4 nanometers. As a result, the ultra-microscope of ZSIGMONDY was further developed in 1912 for immersion ultra-microscope and allowed the observation of nanoparticles in ( aqueous ) solution.

ZSIGMONDY received in 1925 for his research on colloids and the ultra-microscope the Nobel Prize in Chemistry.

Structure of the gap ultramicroscope

The observation objects are suspended in a gas or a liquid. They are observed in a possible dark, absorbent, environment with an imaging light microscope and examined from the perspective perpendicular to the observation axis with a bright convergent light beam. This light beam is focused in the field of view of the microscope, and generates in the observation volume of each particle observed a luminous cone of the Tyndall cone.

Since the observation objects are smaller than the resolution limit of the imaging microscope, they could not alone be observed. But in the lighting design of the ultra microscope they produce diffraction rings that appear in the imaging microscope as bright spots against the dark background.

Use

Ultra microscopes were used to study the Brownian motion, in Millikan's experiment to determine the elementary charge and the observation of particle tracks in cloud chambers.

The illumination geometry of the gap ultramicroscope was picked up during the 1990s and 2000s in fluorescence microscopy and is used today in the light disc microscopy.