Scientists have invented a new kind of microscope capable of magnifying an object 300 million times -- so powerful it can take pictures of individual atoms that make up the surface of ordinary objects.
Atoms, the device reveals, really do look like the little, fuzzy balls of popular imagination.
The images are giving scientists their first view of the tiny particles that make up all forms of ordinary matter, either in the fixed combinations that constitute molecules or in the indefinitely repeating latticework-patterns of crystals.
The breakthrough microscope is so much more powerful than existing kinds because it uses a newly discovered phenomenon -- electron tunneling -- that can be used to make a picture of a surface's topography in such detail that every atom shows up as a fuzzy ball or, at least, a bump.
"What we're seeing is absolutely remarkable," said Gerd Binnig, one of the developers of the method at the IBM Zurich Research Laboratory in Switzerland. Although the first devices were built at Zurich, several other researchers around the world are experimenting with other versions. "I think it will be used in many different ways. We're just beginning to think of what you can do with this."
The microscope shows something scientists have known but never seen -- that no matter how smooth the surface, a high enough magnification will reveal it to be as bumpy as a cobblestone street, each bump being a single atom.
To reveal this, the new device magnifies images as much as 300 million times. More important, its ability to distinguish features that are close together, called the resolving power, can show bumps that rise above the surface by as little as one-tenth the diameter of an atom, or 0.1 angstrom. (All atoms are about the same size: 4 billion in a row would measure an inch.)
Electron microscopes, which work on a different principle and until now were the most powerful, can magnify up to 1 million times and resolve distances of 5 angstroms. Light microscopes magnify up to about 2,000 power and resolve distances of 2,000 angstroms.
The new microscope is expected to prove important in studying a long-neglected middle range of phenomena between the bulk properties of matter familiar to any cook or chemist and the behavior of the atom's internal components -- its nucleus of protons and neutrons and its cloud of orbiting electrons.
Between these two extremes is the little-known realm of the behavior and organization of whole atoms. Microelectronics engineers, for example, are finding that lack of this knowledge is hampering miniaturization. This is because they are reaching the point where the thousands of components in computer "chips" must each consist of layers only a few atoms thick.
The microscope will show whether manufacturing processes can achieve this limit and whether impurities -- atoms of an unwanted element -- have drifted in to alter the layer's properties.
There also are applications in the life sciences. At the Universidad Autonoma in Madrid, for example, Nicolas Garcia is using the powerful device to gain information about the atomic topography of viruses and protein molecules. Garcia also is studying the inner surfaces of artificial blood vessels to learn more about the subtle features thought to trigger blood clots, a problem that has limited use of such prosthetics.
The new microscope is not the first to reveal atoms. Electron microscopes of a special type have been used on specially prepared samples of certain types of materials, but the latest microscope works on ordinary materials that need no special preparation and reveals atoms in much sharper detail.
Called a scanning tunneling microscope, the device works because of a curious phenomenon that happens when two electrodes are brought close together but do not quite touch.
If the electrodes touch, an electric current -- a barrage of electrons -- will flow from one to the other. Or, if the current is high enough, the electrons will have the energy to jump the gap as a spark.
But, if the current is too low to spark, electrons still can cross the gap if it is small enough -- only a few atomic diameters wide. Since the electrons lack the energy (from the voltage) to "jump over" the insulating barrier, physicists say the electrons are "tunneling through" it.
The exact physics of tunneling is not well understood, but it is thought to be possible because of the way electrons normally are distributed around every atom.
Rather than moving in fixed orbits like planets, electrons whiz about the atom's nucleus in all directions. Most of the time they are in regions relatively near the nucleus, but every once in a while one will fly out to a much greater distance. In other words, electrons exist, like the Earth's atmosphere, in a cloud that thins with altitude. If electrodes come close enough that the outer reaches of their electron clouds mingle, electrons can tunnel from one electrode to the other.
With a tunneling microscope, the surface to be studied acts as one electrode and the other electrode is a needle-sharp metal point, or tip. The tip is brought close enough to the surface being studied so that electrons begin tunneling at a certain rate.
Then the tip is moved, or scanned, sideways. If the surface were perfectly smooth, the tip-to-surface distance would stay constant, and so would the tunneling rate and the current. In reality, however, all surfaces are bumpy, and the size of the bump -- even if it is only an atom -- is enough to narrow the gap and increase the tunneling rate.
Electronic devices record the changes in tunneling rate and present the data on paper, most commonly as a series of nearly parallel lines tracing the surface scanned or as something resembling a photograph in which different tunneling rates are assigned gray tones corresponding to the tunneling rate.
Devices that move the tip up and down as it scans a surface can produce the same kinds of images. In this system, the tunneling rate is kept constant by moving the tip so that it is always the same distance from the surface it is scanning.
The tip, scientists have been surprised to find, does not need to be very special. It must only be a durable metal, such as tungsten, sharpened on a lathe. Its point may be thousands of atoms wide, but the electrons that tunnel from the tip follow the path of least resistance, jumping off only from the one atom that is closest to the surface under study.