When I was seven years old, I received a microscope for Christmas.
It was my favorite gift ever, a window to a whole new world, especially when I turned it on pond water teeming with protozoa.
Last week, scientists got their own belated Christmas gift with the announcement that the world’s most powerful transmission electron microscope, TEAM 0.5, has been installed at the National Center for Electron Microscopy in Berkeley, California.
It’s so powerful, it can produce images with a resolution of a half-angstrom. That’s half a ten-billionth of a meter, or, to put it another way, less than the diameter of a single hydrogen atom.
We’ve certainly come a long way from the original microscopes, which were simply magnifying lenses (and have been around since at least 700 B.C.: the earliest were made from rock crystal).
Magnifying lenses, or “simple” microscopes, are limited in their resolution. To increase magnification, you need more lenses. Zacharias Jannsen of Middelburg, Holland, conceived the “compound” microscope about 1600, but glass was of such poor quality that simple microscopes were still preferable for several years: adding extra lenses simply increased distortion.
The father of modern micrography was Dutch biologist Anton van Leeuwenhoek. His simple microscope, built in 1673, consisted of a single almost-spherical lens set between two glass plates, with a pointer on which a specimen was placed, but it could magnify objects more than 300 times, allowing him to become the first person to see bacteria, protozoa, and many other things.
As glass improved, so did compound microscopes: but even the best optical microscope is limited to a magnification of about 2,000. Visible light has a wavelength too long for it to illuminate anything smaller.
Fortunately, in 1927 Hans Busch discovered that a magnetic coil can focus electrons just like a lens focuses light, and in 1930 Max Knoll and Ernst Ruska used this new knowledge to build the very first electron microscope.
Their microscrope bombarded its specimen (which had to be sliced very thin and kept in a vacuum) with electrons, and used magnetic coils to focus and magnify the beam onto a fluorescent screen.
With electron microscopes’ ability to magnify objects up to one million times, scientists were able to see viruses and the internal structure of cells in fine detail.
Many years later, the scanning electron microscope did away with the need for observing a thin slice of specimen, instead sending a tightly focused beam of electrons back and forth over a specimen to create a three-dimensional view.
Then came the scanning tunneling microscope, which scans the surface of a specimen with a probe only a single atom wide, creating a kind of contour map that allowed scientists to detect the pattern of individual atoms in specimens.
An out-of-focus or distorted glass lens can suffer from spherical distortion, which makes points of light look like disks. The same thing plagues electron microscopes. The new TEAM 0.5 use a series of magnetic lenses to eliminate spherical aberration: something which has long been known to be theoretically possible, but has only become practical because of better electronics and faster computers.
This even makes it possible to adjust the focus of the microscope atom by atom. By imaging a sample at different angles and adjusting the focus, a computer can determine the position of individual atoms in a structure.
The advanced specimen stage that will make this possible will be installed next year in the TEAM 1, a more advanced version of the miscroscope that will also be able to correct chromatic aberration.
In a glass lens, this produces a rainbow halo around bright lights as the glass refracts different wavelengths at different angles. Electrons of different wavelengths can also be refracted differently by the magnetic lenses of an electron microscope, again making the image less clear.
All of these advances combined, says the project director, Uli Dahmen, “brings us within reach of meeting the great challenge posed by the famous physicist Richard Feynman in 1959: the ability to analyze any chemical substance simply by looking to see where the atoms are.”
You don’t have to be seven years old to think that’s one of the coolest things ever.