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Since the invention of electron microscopes there have been huge advancements throughout scientific fields with the ability to view microscopic organisms and objects.
An electron microscope is a very powerful microscope which uses beams of electrons instead of beams of light. Electron microscopes are capable of magnifying objects up to 10,000,000 times, which is much higher than any light-based microscopes are capable of achieving considering conventional optical microscopes are only capable of magnifying objects between 40 and 2000 times. The wavelength of an electron is up to 100,000 times smaller than a light wave, which makes photons effectively clumsy in comparison to electrons when one wants to observe a microscopic sample. These electron microscopes are very helpful in scientific research as they are capable of magnifying objects to the point you can see objects as small as viruses, bacteria, and even atoms and molecules.
An electron microscope uses high-speed electrons in order to view nano images and objects. Alongside a rather large electron gun, EMs make use of several thousand-volt electric fields which aid in the shooting of the electrons at the samples. Using a high voltage, the electrons are accelerated.
In the most common type of EM, a Scanning Electron Microscope, the electrons are accelerated while in the electron gun at which point they then go through a scanning coil. The scanning coil applies an electric field which scans the electron beams over the prepared sample; within a vacuum as the electrons wouldn’t make it very far travelling in air.
These electrons essentially excite the electrons in the sample and an image is then created based on the change in electron energy and the tracked electrons which are reflected or emitted.
There isn’t just one type of electron microscope in existence. In fact, there are many, but the two main types of electron microscopes are Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM). The different types all have their uses for different aspects of science. The main difference between a TEM and SEM is that the TEM creates images based on the electrons which pass through a sample, while SEM uses the scattered electrons to create an image. This allows for TEM to be better for learning about the inner structure of the sample, such as crystal structure, morphology and stress state information, while SEM is intended more for learning about the surface and structure. TEMs also allow for higher magnifications; TEMs are able to magnify their samples by more than 50 million times, but the SEM can only magnify up to 1-2 million times.
The very first microscope made for electron microscopy was the Transmission EM. A TEM uses high voltage electron beams which it shoots at a thin sliver of a sample. These high-speed electrons either pass through the sample, or they are scattered. The ones which pass through the sample are the ones which the objective lens picks up, allowing the machine to create images based on the spatial information received from the electrons which passed though. This image is shown on a monitor for the operators viewing after being captured by a photographic mechanism. The images which pass through a sample in a TEM interact with the sample and then are emitted, allowing for a much higher resolution image than if the machine were to pick up on the electrons which are scattered. TEM samples require a large amount of preparation and operators must be trained thoroughly in how to properly prepare them.
The other most common type of electron microscope is the Scanning EM. Scanning electron microscopes are used typically on things such as cells and through a combination of scanning and reflected electrons provide a rather accurate image of the outer surface and structure of a given object or organism. A SEM works by emitting a thin beam of electrons at an objects surface which probe and “examine” the surface in a designated area. SEMs track the change in electron energy and track the scattering and emitted electrons in order to create their image. Due to the way these machines work, they provide a realistic 3D view of the object.
Some other types of electron microscopes are REM (Reflection Electron Microscopes), STEM (Scanning Transmission Electron Microscopes), and LVEM (Low Voltage Electron Microscope).
The very first prototype of an electron microscope was created in 1931 and was a collaborative effort between Ernst Ruska and Max Knoll. This first electron microscope was able to magnify up to 400x; light beam microscopes are normally only capable of magnifying 500x to 1000x.
The purpose in exploring alternative methods for creating microscopes was to increase this magnification abilities so they didn’t stop there. In 1933, only 2 years later, Ruska succeeded in designing a new electron microscope model which succeeded the best light-based, or optical, microscope of that time.
In 1931, Ruska and Knoll had sold the patent to the Siemens Company and by 1937, the company had begun funding the research for further development, with a focus on electron microscopes for use in biology. By 1939, the Siemens Company had released the first ever commercial electron microscope.
Since the 30s, when the electron microscopes were first created and released for purchase, the field of electron microscopy has undergone huge advancements and played a large role in further scientific advances.
One of the main reasons electron microscopes have played such a large role in science since their development is the incredibly powerful magnification.
Optic microscopes are limited by the size of wavelengths of visible light, which is a problem which electron microscopes do not experience. Therefor, the absolute smallest object which can be viewed through an optic microscope is 0.4 micrometers as anything smaller cannot reflect the light. Electron microscopes bypass this limitation by not making use of light and light rays, but by using electrons and tracking their activity (i.e. reflection, deflection) in order to produce an accurate image. This is proven when you consider that electron microscopes can magnify up to 10,000,000x, whereas optical microscopes typically can only magnify between 50x and 2000x. This has allowed for scientists to gain a much better understanding of structures which are smaller than light itself.
The depth of field in an electron microscope is much better than that of a light-based microscope.
Optic microscopes struggle to produce accurate three-dimensional images of small objects because, unlike electron microscopes, they are only able to focus on one layer of space at a time. In attempting to use an optic microscope to view small objects, it can be seen that one layer will be in focus and the rest will be blurry. Especially in weaker microscopes or smaller objects, this can also result in some blurring in the main image itself. This isn’t an issue in electron microscopes as they can have multiple two-dimensional layers in focus at a time which results in a much more accurate three-dimensional image.
Electron microscopes also allow for a wider variety of magnifications. Typical optical microscopes found within schools tend to have magnification settings of 10x, 100x, and 400x and nothing between them. Due to the way electron microscopes work, there aren’t the set magnifications, but rather a range, which can be used.
Beyond that, electron microscopes have opened up doors for huge advancements in various scientific fields, while also proving useful in some industrial settings.
Due to the magnification abilities, EMs have proven to be very useful in discovering previously unknown things about organisms and objects to small for an optic microscope, in many scientific fields. Biology, medical and forensic sciences, gemology, nanotechnology, and metallurgy are all fields of science which electron microscopes have given the ability for further advancements.
In work-related settings, electron microscopes have also begun to be used. A notable example of this is in quality control as now the objects can be viewed in extreme precision and detail to examine any possible flaws. Some other places which these microscopes have begun to be seen are computer chip manufacturing, semiconductor inspection, and even in production lines in factories.
Despite the many benefits and gains created by electron microscopes, there are also issues with them.
A major problem is the cost.
The cost for both the initial purchase and installation of the equipment ranges from costs around $1,000 for a lesser quality machine or a machine with less abilities, all the way up to costs nearing $1,000,000 for the higher quality electron microscopes. The average costs tend to be over $50,000. These costs can vary drastically between machines, however. There are many different types of electron microscopes, and depending on what one is looking for the prices can be in the lower range or they can be hundreds of thousands to purchase. The price of a used electron microscope, depending on type, quality, and condition, can easily vary from the cost of the same machine new up to 50%. The cost doesn’t just end here; there is also the cost of operating the microscope, necessary supplies and keeping it in optimal condition for continued usage. If one chooses to purchase one of these machines, there is then the cost of shipping added on top. Although these microscopes can provide a huge benefit to laboratories and scientific personal who have access to them, the costs are very high and many cannot afford them.
The size of the equipment can also prove to be an issue, especially combined with its sensitivity.
Electron microscopes, whether they are SEMs, TEMs, or another type, are large, bulky pieces of equipment worth huge amounts of money. These pieces of equipment are also highly sensitive to magnetic fields, temperature, humidity and vibrations, making the area in which they are kept a large factor in how well they preform. This sensitivity to magnetic fields and vibrations can result in the machine being prone to damage. It is highly recommended for facilities with electron microscopes to have properly trained technicians hired in order to properly maintain them. Tying into the cost once again, facilities with smaller budgets or economic issues may not be able to afford the costs involved in the proper upkeep of the equipment. Proper upkeep includes stable voltage supplies, circulation of cool water, and currents to the electromagnetic lens/coils. This will enable samples to avoid damage or to avoid being destroyed from the heat, a by-product of the process of keeping electrons energized.
Vibrations from the air and from the floor can highly affect an EMs performance and it is recommended to do ones best to isolate the equipment from them for its continued maintenance and accuracy. One of the most highly recommended methods to protect the machine from vibrations is to have it sit upon a concrete pad rather than directly on the floor. It is also recommended to store equipment such as pumps and compressors, gas cylinders and water chillers which maintain a constant temperature for the electromagnetic lenses in a separate room. Any electrical or water lines immediately near the machine can easily disrupt the results, and as such, a suitable room has them throughout but not right near the equipment. The temperature remaining consistent is another factor.
Overall, these machines require a massive amount of work to maintain and use.
Preparing the samples is also a costly and time-consuming endeavor. These microscopes require the samples to be viewed while contained within a vacuum in order to prevent the molecules found within the air from scattering or disrupting the electrons.
Since the invention of microscopes there have been drastic advances in various scientific fields as they allow humans to view things at a microscopic level that would otherwise be invisible to the naked eye. Before the electron microscope was created, the cell theory sprouted from work with optic microscopes and later on, the beginning of the study of bacteria and, eventually, the invention of the electron microscope. Since the invention of the microscope, our knowledge of the microscopic world has grown drastically. Since this new knowledge, there have been advancements in in the fields of medicine, surgery, pharmaceutical industry, biology, taxonomy, genetics, engineering, material and environmental sciences, and even in hospital laboratories.
Overall, the invention of electron microscopes has been hugely beneficial in many ways for humankind.
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