Behind the hull, which consists of tiny hollow spheres, in our image is a diatom just a few micrometers in size. It becomes visible with the help of a very special microscope.
Most diatoms are microscopic, around 50 μm in size. Typical of them is a hard shell made of silica, which can be box-shaped, round, filamentous or elliptical. This shell gets its stability from crystals of silicon dioxide which, with the help of the peptide, form small spherical clusters. These nanostructures give the diatom shells their “granular” appearance under an optical microscope.
However, optical microscopes are not sufficient to illuminate the fine structure of the diatom shells and their nanostructures. The exact structure of these shells is not visible in detail even in a scanning electron microscope, because samples must be coated with gold or other precious metals. This sticks to some of the subtle structural details.
On the other hand, helium ion microscopy provides a more suitable alternative. This shell from the globular diatom was also taken with it. For this microscopic technique
Helium atoms ionize at the tip of a super-fine tungsten needle and accelerate away from the needle. Then a helium ions package is assembled and directed to the material to be examined.
In order to create an image, the intensity of the beam passing through the sample and the reflected beam is measured as well as the number of secondary electrons generated. This allows scientists to visualize surfaces of samples only a few nanometers across – like the diatom in our image – in detail and in sharp focus.
“Because of these properties, concentrated ion beams have great potential for many other applications in the field of nanotechnology,” explains Gregor Hlwachsch of the Helmholtz Center Dresden Rusendorf. “For example, surfaces can be flexibly structured in the nanoscale or the properties of local materials can be specifically changed.”