Why electron microscopes have higher resolution than optical microscopes
The magnification of an optical microscope is smaller than that of an electron microscope. Optical microscopes can only observe microscopic structures, such as cells and chloroplasts, whereas electron microscopes are able to observe sub-microscopic structures, i.e., the structure of organelles, as well as viruses and bacteria, can be seen.
Electron microscopy is the accelerated and aggregated electron beam projected onto a very thin sample, the electrons collide with the atoms in the sample and change direction, resulting in stereo angular scattering. The size of the scattering angle is related to the density and thickness of the sample, so that different light and dark images can be formed, which will be displayed on imaging devices (such as fluorescent screens, films, and photocouplers) after magnification and focusing.
Due to the very short De Broglie wavelength of electrons, the resolution of a transmission electron microscope is much higher than that of an optical microscope, reaching 0.1 to 0.2 nm, with a magnification of tens of thousands to millions of times. Therefore, the use of transmission electron microscopy can be used to observe the fine structure of a sample, or even the structure of a single row of atoms, which is tens of thousands of times smaller than the smallest structure that can be observed by an optical microscope.TEM is an important analytical method in many fields of science related to physics and biology, such as cancer research, virology, materials science, as well as nanotechnology, semiconductor research and so on.
Principle of Optical Microscope
Light incident on an object is magnified by at least two optical systems (objective and eyepiece). First, the objective lens produces a magnified image, and the human eye observes this magnified image through the eyepiece, which acts as a magnifying glass. A typical light microscope has several interchangeable objectives so that the observer can change the magnification as needed.
These objectives are generally placed on a rotatable objective disk, rotating the objective disk can make different eyepieces convenient access to the optical path, the objective disk in English is Nosepiece, also translated as nose wheel.
Nowadays, the construction of optical microscopes is very complex and precise. In order to image accurately, the optical path of the microscope must be rigorously designed and controlled. Nevertheless, the principle of operation of an optical microscope is very simple.
The simple objective lens is made of high-resolution glass and has a very short focal length of about 160 mm, which produces a magnified inverted image, so that it appears to be very close to the specimen to be viewed, and by focusing it produces a solid image that can be seen with the naked eye without the need for an eyepiece or imaged on a piece of paper. In most microscopes, the eyepiece is a pair of mirrors, one at the eye, which produces an imaginary image that is magnified to the naked eye, and one near the objective lens, which produces a real image.
