Studying the world of micro scale scientists developed more and more precise optical microscopes at the beginning of the 20th century. Unfortunately it became evident that constructing even still more precise microscopes wouldn't let objects smaller than few tenths of a micrometer (1 micrometer equals 0,000001 metre) be observed. The fact is caused by one of the phenomena connected with wave properties of light. The phenomenon is diffraction. When distances between observed objects are as close as the wavelength of light, then the images of the objects begin to blend. Of course, one can see more details if decreasing the wavelength of light shining on and reflected from the observed objects. But the problem is that when you use an optical microscope there is some limit in decreasing the wavelength (The shortest wave of the visible range is the violet one). The fact was limiting observations for a long time. The very tiny objects can be observed since the thirties of the 20th century when the electron microscope was invented.
As you know, all particles have dual nature. It is, of course, true also for the electron. There is some wave bound up with that particle. Its wavelength depends on the electron's velocity - the lower velocity, the shorter wave. We can obtainlectrons, whose wave is of a couple of orders of magnitude shorter than the shortest light wave. A beam of electrons can be used similarly as a beam of light. How? First, one has to accelerate electrons to very high speed. And then they have to be directed to a very thin specimen of a studied material. They go through it, and than they fall in a magnetic field (Their trajectories are deflected in such field.). The field takes is an equivalent of a lens of an optical microscope. Once the electrons leave the magnetic field they fall on a fluoroscopic screen. A magnified image of the specimen is created on that screen. Of course, this view inside an electron microscope is very simplified. But it shows the idea of such instrument. Yet we canobtain images of samples magnified even 1 000 000 times.
In 1938 Manfred von Ardenne developed another instrument for researches of microstructure. It is called the scanning electron microscope. It doesn't require the specimens being very thin as it works a bit differently from a simple electron microscope. Also in the scanning microscope there is a beam of electrons directed on the specimen. But the beam is not static. Special deflector coils make the beam flowing regularly around the specimen. When the beam falls on the specimen some of the electrons are dissipated, and some get inside the specimen causing secondary emissions of electrons, X-rays, and visible light. Near the sample there are special detectors placed, which detect the dissipated electrons, the secondary electrons, or radiation. The detectors transform the signals they register into digital signals. The digital signals are then transformed into an image on a visual display unit.
Except for the electron microscope scientists have developed many more, complicated instruments for "watching" the world of micro scale. So there are ionic microscopes (they gave first images of single atoms), scanning electron microscopes (SEM), tunnelling microscope (constructed in the early eighties; has the resolving power of order of magnitude of one nanometer = 0,0000000001 meter). These pieces of equipment enable more and more discerning and precise observation of atoms and particles.
But what is the use of those more and more precise microscopes? Well they have many applications in science. In biology they enable getting to know new organisms, making researches of a single cell, of the smallest organisms - bacteria, and of viruses. Electron microscopes have also technical use, which is for example searching for defects in the crystalline structure of some studied material. Thanks to electron microscopes structures of different materials are known, so their properties can be yet changed. Modern electronics is in a considerable range based on researches made by using electron microscopes. They are used in many branches of modern industry and of course, in forensic tests. But they are also used in archaeology and historical researches. You can also find them in physical and chemical laboratories.
Lately scanning tunnelling microscopes are used for creating some structures from single atoms. For example a sign IBM, whose height was only five atoms was "writen". Now it still may look like a childish game but manipulating single atoms can be considered birth of nanoengineering . This new field of science that in future will let us create new kinds of materials and medicines, new, miniature electronic components, new chemical compounds, and maybe even tiny robots consisting of only a few atoms. As you see electron microscopes are very useful and also form our future expectations and ideas.
