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 | Figure 1: The image of
an ant magnified 9 times.
Compare it to the actual
size given in the inset
at the top left corner.
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The invention of the first microscope took place long after people discovered lenses, the essential component of microscopes. Many things can act as a magnifying lens. A glass of water, a bead of glass or a gemstone can all bend light and make an object appear larger. People have known this phenomena for thousands of years, but it was not until glass spectacles reached 13th century Europe that the invention of the microscope was made possible. The very first microscope is thought to have been constructed around 1595 by Hans and Sacharias Janssen a father and son who operated a Dutch lens grinding business. The first microscopes were more of a novelty than a scientific tool since maximum magnification was only around 9X and the images were somewhat blurry. It was about 60-80 years later that major discoveries were made with microscopes.
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 | Figure 2: Ma-
rcello Malpigi
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Marcello Malpighi, Robert Hooke and Antonio van Leeuwenhoek were all contemporary microscopists that made historic discoveries with the microscope. Malpighi, who is considered the father of embryology and early histology, was the first to prove a controversial theory of the time that stated that the blood circulates in a circular motion from the heart around the body and back to the heart. Although we take this idea for granted, it was not until 1660 when Malpigi actually saw capillaries, the microscopic connection between arteries and veins, that this theory was accepted. Unfortunately for the originator of the circulation theory, William Harvey, this discovery was made three years after his death.
 | Figure 3: Drawing of one of
Hooke's microscopes, and a
drawing of cork made by Hooke
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Robert Hooke is credited with the microscopic milestone of discovering the basic unit of all life, the cell. Hooke made his discovery while studying a sample of cork. The structural mesh he saw reminded him of the small monastic rooms called cells. Hooke is also credited with being the first to use the basic three-lens configuration that is still used in microscopes today.
 | Figure 4: Van
Leeuwenhooke
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 | Figure 5: Leeuwen-
hooke's microscope
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Van Leeuwenhooke was an amateur scientist who outdid his contemporaries by discovering ways to make superior lenses. Although his microscopes only used a single lens they were capable of magnifications of up to 200X. Other microscopes of the time were lucky to achieve 50X magnification. Because of his superior magnification Leeuwenhoek was the first to see bacteria, protozoa and spermatoza.
Before discoveries like Malpighi's, Hooke's and Leeuwenhoek's the microscope was doubted as a tool of scientific discovery. People did not realize that magnification might reveal structures that had never been seen before. The idea that all life might be made up of tiny components unseen by the unaided eye was simply not even considered.
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Solving Chromatic Abberation-Chester Hall:In order for light microscopes to achieve better resolution 3 basic problems had to be overcome. The first problem, called chromatic aberration, is the unequal bending of different colors of light that occurs in a lens. Although others patented and benefited from the solution to this problem, the problem was first solved by Chester Hall in the 1730's. He discovered that if he used a second lens of different shape and light bending properties he could realign the colors without losing all of the magnification of the first lens.
 |  | | Figure 6: The problem of chromatic aberration and its solution - the achromatic lens.
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 | Figure 7: Microscope built by
Lister with correction for
spherical aberration
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Solving Spherical Abberation- Joseph Jackson Lister: The second problem, spherical aberration, is the unequal bending of light that hits different parts of a lens. Joseph Jackson Lister, the father of Lord Joseph Lister, the surgeon who founded aseptic technique, solved this problem in 1830. He discovered that by putting lenses at precise distances from each other the aberration from all but the first lens could be eliminated. Low power low curvature lenses could be made with minimal aberration and by using a lens of this type as the first in a series, the problem could be virtually eliminated.
Reaching the Theoretical Limit of Resolution for Optical Microscopy-Ernst Abbe: The third problem is that for a microscope to be as good as physically possible it must collect a cone of light that is as wide as possible. Ernst Abbe worked out the solution to this problem in the 1870's. He determined the physical laws that govern the collection of light by an objective and maximized this collection by using water and oil immersion lenses. The maximum resolution that Abbe was able to achieve is about 10 times better than the resolution Leeuwenhoek had achieved about 100 years earlier. This resolution of 0.2 microns or 200 nanometers is a physical limit imposed by the wavelength of light. With the exception of some ultraviolet techniques or some very unusual immersion fluids this limit cannot be overcome with standard optical microscopy.
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 | Figure 8: Ard-
enne, Malvon
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As was the case with the first optical microscope, the first electron microscope was very crude compared to its modern progeny. It did however, put important ideas about how to image with electrons into practice. Instead of using glass to bend and focus light, electron microscopes use magnetic coils to do the same thing with electrons. H. Busch was the first to use a magnetic coil like a lens in 1926. E. Ruska made the first image producing electron microscope in 1933 and used it to take pictures of gold and copper surfaces.
 | Figure 9: Ruska,
Ernst
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Interestingly enough this instrument produced images at about 10X, about the same magnification as the 1595 Janssen microscope. The development of the electron microscope was much quicker than that of the optical microscope however, so it was not long until electron microscopes far surpassed the resolution of their optical cousins. That same year (1933) Ruska constructed a microscope that surpassed the 200 nanometer optical limit.
The Quick Development of Electron Microscopy:
 | Figure 10: A simplified TEM
schematic
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There are two major types of electron microscope: the transmission electron microscope (TEM) and the scanning electron microscope (SEM). These two types evolved at different rates but in general the development of electron microscopy was about 10 times more rapid than that of optical microscopy. The primary innovations in electron microscopy took only about 30 years whereas nearly 300 years passed from the invention of the first compound microscope to the achievement of maximum resolution. Some of the landmarks in the development of electron microscopy are shown below:
Discoveries of the Electron Microscope:
 | Figure 11: A simplified SEM
schematic
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Following the development of the first commercial available electron microscope by Ruska and the company Siemens in 1939, the electron microscope rapidly became an invaluable tool to science and engineering. Structures never before seen in biological and material samples became the subjects of countless scientific papers. Much of what we know about the nano universe we owe to the electron microscope. Although the technique of X-ray diffraction preceded the invention of the electron microscope and provided compelling evidence for atomic crystal structure, atoms themselves had never been seen until high resolution.
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 | Figure 12: Binnig,
Gerd
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The newest type of microscope to be developed is the scanning probe microscope. Instead of using focussed light or electron beams to image a sample it uses a tiny needle like probe that is scanned back and forth across a sample's surface. The interactions of the probe with the sample's surface are recorded and put together to form an image.
 | Figure 13: Rohrer,
Heinrich
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The first member of the scanning probe microscope family was the scanning tunneling microscope (STM). Gerd Binnig and Heinrich Rohrer developed it over 1979-1981 at the IBM Research Laboratory in Switzerland. They were awarded the Nobel prize in physics in 1986 for their work.
Visualizing Properties- Expanding the Meaning of Resolution: Like electron microscopes, scanning probe microscopes have achieved atomic resolution but unlike electron microscopes they have been able to do this without vacuum and even in liquid. In the less than 20 years since Binning and Rohrer developed the STM, scanning probe microscopes have developed into a diverse family of microscopes that can not only make three dimensional nanoscale images of a surface's topographical features but also of that surface's properties. These microscopes can image friction, hardness, thermal properties, magnetic properties, electrical properties, chemical binding and optical properties on the nanoscale. Resolving properties on this scale had not been possible before the SPM. This family of microscopes quickly became invaluable to exploration of the nano universe. Manipulation of the nano universe also became possible as researchers began to use the needle like probes to actually move and cut the molecules they were imaging.
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Arizona State University
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