Physics
Electron Microscopes
Electron microscopes are powerful tools used to observe objects at the nanoscale level. They use a beam of electrons to create high-resolution images, allowing scientists to study the fine details of materials and biological specimens. Unlike optical microscopes, electron microscopes have much higher magnification and resolution, making them essential for research in various scientific fields.
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11 Key excerpts on "Electron Microscopes"
- Lakshmanan, A(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Chapter 6 Electron and Probe Microscopy for Nanometrology K. Raja 1 , N. Natarajan 2 , C. Sharmila Rahale 1 , S. Shanmugapriya 1 and J.Mohanraj 1 1 Department of Nano Science and Technology, 2-Retd. Professor, Department of Seed Science and Technology, Tamil Nadu Agricultural University, Coimbatore – 641 003, Tamil Nadu Microscopes are optical instruments used to examine micro-scale structures of plants, animals and material samples that are too small to be seen by the naked eye. Owing to the advent of advancement in sciences, scientists have started to examine the specimens at nano or atomic scales for which conventional optical microscopes may be of least importance. Due to limitations of the light microscope on the magnification of 1000X or the maximum of 2000X and resolution of 200 nm, advanced microscopic techniques i.e. Electron Microscopes were developed. The limitation in the use of optical light microspore had been reached during the early 20 th century, and there was a scientific desire to see the fine details of the ultrastructures of cells such as nucleus, mitochondria. Golgi bodies, endoplasmic reticulum, etc. ). This required 10,000X plus magnification which was just not possible using light microscopes. Electron Microscopes are scientific instruments that use a beam of highly energetic electrons to examine objects on a very fine scale. This examination can yield information about the topography (surface features of an object), morphology (shape and size of the particles making up the object), composition (the elements and compounds that the object is composed of and the relative amounts of them) and crystallographic information (how the atoms are arranged in the object). Unit 3: Principles and Application of Major Nanotechnological Instruments and Software This ebook is exclusively for this university only. Cannot be resold/distributed.
eBook - PDF- Peter J. Goodhew, John Humphreys, John Humphreys(Authors)
- 2000(Publication Date)
- CRC Press(Publisher)
Chapter I Microscopy with light and electrons 1.1 Introduction A microscope is an optical system which transforms an ‘object’ into an ‘image’. We are usually interested in making the image much larger than the object, that is magnifying it, and there are many ways in which this can be done. This book deals with several sophisticated techniques for magnifying images of very small objects by large amounts, but many of the principles involved are just the same as those which have been developed for light microscopes over the past 400 years. The concepts of resolution, magnification, depth of field and lens aberra-tion are very important in electron microscopy and so we deal with them in this first chapter in the more familiar context of the light microscope. When we consider Electron Microscopes in later chapters it will be found that instead of becoming more complicated, many areas of the subject become simpler because we are dealing with electrons rather than light. Thus although apparently more complex, and certainly much more expensive, Electron Microscopes are almost as easy to understand (in principle) as their humble stable-mate, the magnifying glass. The techniques which are given the most detailed coverage in this book are scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the analytical techniques which are made available by using them. At the simplest level an SEM can be thought of as providing images of external morphology, rather similar in appearance to those formed by the eye, while a TEM probes the internal structure of solids and gives us access to micro- structural or ultrastructural detail not familiar to the human eye. In both cases several different types of image can be formed. Consequently it is necessary to understand not only how such microscopes work, but also how to interpret the images which they produce. This is particularly true for the TEM, and accounts for the length of Chapter 4.
eBook - PDF- Sam Zhang, Lin Li, Ashok Kumar(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
153 6 Transmission Electron Microscopy 6.1 Basics of Transmission Electron Microscopes Small objects about 100 nm in size can be closely observed with an elec-tron microscope, but are impossible to observe with a light microscope because of the long wavelength of the detecting light. The transmission electron microscope (TEM) has been widely used in such fields as mate-rial and biological sciences, as electrons going through specimens contain significant information pertaining to crystal structure and bonding state. Figure 6.1 shows the schematics of (a) a light microscope and (b) a TEM. The light microscope is mainly made up of a visible light source and a system of optical glasses such as condenser, objective, and eyepiece lenses. The specimen is mounted between the condenser and objective lenses, and the light transmitted through the specimen produces its magnified view. The resulting image is directly detected by eye, whereas the resolving power of an ordinary light microscope is about 0.2 µm because of the diffrac-tion limit of visible light having a wavelength range of about 400–700 nm. Specimens with smaller sizes than the resolution of the light microscope can not be observed, for example, viruses, voids and inclusions in crystal, and crystalline lattices. The TEM operates under a similar basic principle as the light microscope, but uses electrons instead of visible light. Max Knoll, a German electrical engineer, and Ernst Ruska, a German physicist, developed an electron microscope in 1931, which had about 13 magni-fications. The first practical TEM was built by Albert Prebus and James Hillier at the University of Toronto in 1938. As can be seen in Figure 6.1b, the electrons generated by an electron gun are applied to the specimen. A high resolution of about 0.3 nm is theoretically obtained in the TEM, because the electron beam accelerated at several hundred kilovolts indi-cates an extremely shorter wavelength compared with visible light.
eBook - PDF- Denis Rousseau(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The devel-opment of scanning Electron Microscopes (SEMs) has resulted in a greatly improved depth of field over that of light microscopes, and a more recogniz-able three-dimensional view can be obtained. Moreover, the signal from SEMs is much more amenable to image processing because the data are already obtained in a time-sequence mode. Such advantages of electron imaging over light imaging have made electron microscopy indispensable to biological research. But electron microscopy can only be properly utilized with a proper understanding of the limitations of the instrument and speci-men preparation processes. III. The Instrument Electron Microscopes may be classified, according to the mode of operation, into two major types of instruments. The fixed-beam microscope operates with the electron beam illuminating the entire field of view of the specimen. This mode of operation is analogous to the conventional light microscope. This type of microscope is also referred to as the conventional transmission electron microscope (CTEM). The scanning type of microscope operates 6. ELECTRON MICROSCOPY 351 with a small electron-beam pencil moving over the specimen. At any given time only a small point of the specimen is illuminated. When the transmit-ted electrons are utilized to form images, the instrument is called a scanning transmission electron microscope (STEM). On the other hand, a scanning microscope that is designed to obtain surface information of very thick specimens, as is often the case, is generally referred to simply as the scanning electron microscope (SEM). Both fixed-beam and scanning-beam Electron Microscopes may be modified for special purposes. For instance, an elec-tron microscope may be used to collect compositional rather than morpho-logical information about the specimen. This type of microscope is called an analytic electron microscope.
- Jay A. Glasel, Murray P. Deutscher(Authors)
- 1995(Publication Date)
- Academic Press(Publisher)
Electron microscopic examination of biological samples can provide unique information. Additionally, certain types of information can be obtained more rapidly and easier than with other methods. The 1000-fold greater resolution of the electron microscope compared to the light microscope can provide details of structure in the 1-nm range. Identification of subcellular structures in sec- tions and in isolated preparations is greatly facilitated. Electron microscopy, in combination with the use of specific antibodies or nucleotide probes, can yield data on the distribution and localization of biologically relevant antigens and Chapter 5 ElectronMicroscopy 209 nucleic acid sequences. Finally, detection and analysis of the interactions of electrons with atoms of the specimen can provide information on its composi- tion. II. Principles of Electron Optics A. Properties of Electrons and Electron Beams 1. Electrons Electrons are subatomic particles of small mass, 9.1 • 10 -31 kg, which carry a negative charge of 1.6 • 10-19 C. As with light and other forms of electromag- netic radiation, electron behavior exhibits properties of both waves and parti- cles, and can be predicted using the same principles that are applied to light optics, de Broglie showed that the wavelength of electrons is inversely related to their energy, A = h/mv, (1) where A is the wavelength, h is Planck's constant (6.626 • 10-23 ergs/sec), m is the mass of the electron, and v is the velocity of the electron. In an electron microscope, the energy of the electrons is determined by the accelerating volt- age or potential difference between the cathode (negative electrode) and anode (positive electrode). For a potential difference of 60,000 V (60 kV), a common accelerating voltage used in transmission Electron Microscopes (TEMs), the wavelength can be calculated to be approximately 0.005 nm. For comparison, the wavelength of visible light ranges from 400 to 800 nm.
eBook - PDF- C. F. A. Culling, R. T. Allison, W. T. Barr(Authors)
- 2014(Publication Date)
- Butterworth-Heinemann(Publisher)
PartX Electron microscopy This page intentionally left blank 34 The electron microscope Brian Amer, FIMLS Department of Pathology, Southmead Hospital, Bristol, UK Transmission electron microscopy (TEM) The transmission electron microscope has been widely used in routine histopathology in recent years, particularly in the fields of renal disease, tumour pathology and virus infections. Scanning electron microscopy is also used in some instances and when employed in conjunction with analysis systems can identify substances by their chemical composition. The light microscope lens systems have been perfected to such a degree that resolution is limited by the physical properties of image formation rather than the properties of the lenses themselves. From the discussion of optical theory it was seen that the resolution of any optical system is limited by the wavelength of light employed, and that an object that is smaller than this wavelength will cause so little perturbation of the light beam that it will not be resolved in the image. The best light microscopes are, therefore, limited to a resolution of about 200 nm. The ultraviolet microscope, by using wavelengths about one half that of white light, achieves a resolution of 100 nm. By using an electron beam instead of light rays, the electron microscope gives much better resolution (Figure 34,1). The wavelength of moving electrons depends on their velocity. At an acceleration of 50 000 V they have a wavelength of about 0.001 nm, and one may expect to resolve images of about this order. Due to lens defects which can be corrected in the light microscope but have not so far been corrected in the electron microscope, the resolution is limited to about 0.4 nm, which is still several orders of magnitude better than the best optical microscopes. Tissue to be examined in the transmission electron microscope must be processed so that sections of approximately 50 nm thickness can be cut.
eBook - PDFModern Metallography
The Commonwealth and International Library: Metallurgy Division
- R. E. Smallman, K. H. G. Ashbee, W. S. Owen, D. W. Hopkins, H. M. Finniston(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER VII ELECTRON MICROSCOPY-I ELECTRON MICROSCOPE ELECTRON WAVELENGTH It was discussed in Chapter I that in order to increase the resolving power of an optical microscope it is necessary to employ light of shorter wavelengths. Thus, ultra-violet light may be used, but even then the resolution can hardly exceed 1000À. As a consequence, the electron microscope has been developed to allow the resolution of structure having dimen-sions down to 10À. Moving electrons may be considered as particle waves with a wavelength given by the De Broglie equation = hjmv where h is Planck's constant and mv is the momentum of the electron. If the electrons are accelerated by voltage V, the kinetic energy they acquire is mv 2 /2 = Ve where e is the charge on an electron and therefore = hIVlmVe = V150/KÂ When the velocity of the electrons is comparable to the speed 107 108 MODERN METALLOGRAPHY of light, c, a relativistic correction to this equation is required and the expression becomes = Vl50/(1 + 97-88 X 10 8 K) - Vl50/(1 + 10 6 ). The relativistic correction to the classical expression for only amounts to about 5% at 100 kV; at 10 6 kV there would be an error of / /2, i.e., 30%. The values of at the accelerat-ing voltages commonly used in electron microscopy are shown in Table 3, from which it is seen that the variation of with accelerating voltage is small. TABLE 3. VARIATION OF ELECTRON WAVELENGTH WITH APPLIED VOLTAGE Accelerating voltage (kV) 70 80 90 100 Electron wavelength (A) 0-0449 0-0418 0-0392 0-0370 THE ELECTRON MICROSCOPE General Description An electron microscope consists of an electron gun and an assembly of lenses all enclosed in a column evacuated to about 10~ 5 mm Hg. Figure 61(a) shows a schematic arrangement of such an instrument and Fig. 61(b) a vertical cross-section through an A.E.I. E.M.6 model. The optical arrangement is similar to that of a light microscope but additional stages of magnification are used.
- Leland J. Cseke, Ara Kirakosyan, Peter B. Kaufman, Margaret V. Westfall(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
667 38 Microscopy: Scanning Electron, Environmental Scanning Electron, and Transmission Electron Casey R. Lu, Peter B. Kaufman, Ara Kirakosyan, and Leland J. Cseke Electron. microscopes. (scanning. electron. microscope/environmental. scanning. electron. micro. -scope.(SEM/ESEM).and.transmission.electron.microscope.(TEM)).are.technologically.advanced. instruments.that.have.allowed.scientists.to.make.major.conceptual.breakthroughs.in.cellular.and. molecular.biology.Scanning.electron.microscopy.allows.one.to.visualize.3D.images.of.the.surfaces. of.whole.organisms,.organs,.tissues,.and.cells.or.parts.of.cells,.made.possible.by.the.large.depth-of-field.capabilities.of.the.SEM.X-ray.analysis.of.the.distribution.of.elements.present.in.the.cells.or.tissues. can.be.performed.with.the.SEM.as.well.The.ESEM.allows.one.to.observe.uncoated,.hydrated,. living.organisms.and.tissues.in.the.SEM.Subcellular.ultrastructural.studies.and.immunolocal-ization.of.specific.gene.products.using.antibody.labels.requires.knowledge.of.TEM.and.specialized. techniques.of.tissue.fixation,.embedding,.and.ultrathin.sectioning.Recent.advances.in.lens.aber-ration.correction.have.pushed.the.resolving.limit.of.TEMs.below.the.10.Angstrom.dimension.in. commercially.available.TEMs,.making.possible.investigations.on.the.subatomic.level! In.this.chapter,.we.explore.the.principles.underlying.how.the.SEM,.ESEM,.and.TEM.work,.how. to.operate.them,.and.a.number.of.applications.in.biology.and.medicine.where.these.techniques.have. been.used.successfully 1–12 CONTENTS 381. Scanning.Electron.Microscope.668 3811. Principles.of.Operation.668 3812. Preparation.of.Biological.Tissues.for.SEM. 672 38121. Fresh.Biological.Material 672 38122. Fixed.Biological.Materials. 673 382. Environmental.Scanning.Electron.Microscope. 673 3821. Principles.of.Operation. 673 3822. ESEM.Applications. 674 383. Transmission.Electron.Microscopy. 676 3831. Conventional.Transmission.Electron.Microscope. 676 3832.
eBook - PDF- Gerald Oster, Arthur W. Pollister, Gerald Oster, Arthur W. Pollister(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
II. Basic Principles of Electron Microscopy 1. T H E LENS SYSTEM In its general lines of construction and operation the electron microscope closely resembles the optical microscope. Each requires a source of illumi-nation, a condenser lens for controlling it, an objective lens and one or more further lenses for providing high magnification. The main differences be-tween the two instruments are those of detailed design, arising from the special properties of electron beams as compared with light. Some minor differences of principle arise from the same cause, e.g., the electron image is viewed on a fluorescent screen, not directly, and interchangeable lenses are not required owing to the continuously variable power of magnetic fields. Since practically all commercially available Electron Microscopes employ magnetic lenses, the discussion will be carried on in terms of these rather than of electrostatic lenses. The differences between the two types are in any case matters of practical details of design and operation rather than of principle or ultimate performance. A schematic diagram of the imaging process in the electron microscope (Fig. 3), compared with an optical microscope (inverted from its normal ELECTRON MICROSCOPY 467 position) makes clear the essential similarity of the two. The electron illu-mination is drawn from a white hot tungsten filament C by the strong electric field maintained by a negative high potential applied between C and an anode A, which is grounded. A shield electrode, at a slightly higher neg-ative voltage than C, surrounds it and serves to increase the brilliance of the beam that emerges from the aperture in A. The whole assembly is known as the electron gun and serves to deliver an intense narrow beam into the condenser lens L c , which transmits part of it.
eBook - PDFThe Microscope Past and Present
Pergamon International Popular Science Series
- S. Bradbury(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
This micro- scope, although appearing crude by present-day standards, worked and produced pictures by transmitted electrons of objects at a resolution about five times better than it was possible to obtain with the light microscope. At the end of 1934, however, the future of the instrument was still not certain, and research was dropped for lack of immediate support. At this stage it is convenient to leave the story of the development of this embryonic electron microscope in order to describe briefly the similarities and differences between the electron microscope and the optical instrument and to indicate the special requirements of the electron microscope. Basically the two systems are composed of ana- logous components; from Fig. 7.3 it can be seen that the light source of the optical microscope corresponds to the source of electrons (the electron "gun") in the electron microscope. Both instruments have a 232 The Microscope condenser to concentrate the radiation on the specimen, and the primary magnification in both types of microscope is produced by an objective lens. In Fig. 7.3, the optical microscope is shown arranged to project an image by means of the eyepiece which consists of two separate lenses. In the electron microscope these lenses are represented by the separate intermediate and projector lenses respectively. In the optical microscope it is customary to arrange the system with the eyepiece FIG. 7.3. A block diagram comparing the lens arrangements of the optical microscope (a) and the electron microscope (b). projecting an image upwards onto, say, a photographic plate which is held at the top of the bellows extension of a vertical camera. For reasons of convenience in construction and stability imposed upon it by the long tube, the electron microscope usually has the electron gun at the top of the column and the final viewing screen and the photographic plates are located at the lower end of the column.
eBook - PDFHandbook of Microscopy
Applications in Materials Science, Solid-State Physics, and Chemistry, Methods II
- S. Amelinckx, Dirk van Dyck, J. van Landuyt, Gustaaf van Tendeloo(Authors)
- 2008(Publication Date)
- Wiley-VCH(Publisher)
The electronics provide control of the amplification, DC offset, and bandwidth of the signal. Increasingly the detector output is passed 542 Scanning Electron Microscopy through an analog to digital converter (ADC) and then handled digitally rather than as an analog video signal. This permits images to be stored, enhanced, combined, and analyzed using either an internal or an external computer. Although the majority of images are still recorded on to photo- graphic film, digital images can be stored directly to magnetic or magneto-optic discs and hardcopy output of the images can then be obtained using laser or dye-subli- mation printers. The scan drive currents to the scan coils may also be digitized to provide precision control of the beam posi- tion although analog scans are still most commonly encountered. Typically scan repetition rates ranging from 15 or 20 frames per second (TV rate) to one frame in 30 to 60s (photographic rate) are provided. In addition individual pixels, or arrays of pixels, within an image field may be accessed if required. 2.1.3 Performance It is usual to define the performance of a microscope in terms of the spatial resolu- tion that it can produce. In the case of the SEM the attainable resolution is deter- mined by a number of factors including the diameter d of the electron-beam probe that can be generated, the current Z, con- tained in that probe, the magnification of the image, and the type of imaging mode that is being used. Over most of the oper- ating energy range (5-30 keV) of the SEM the probe size and beam current are related by an expression of the form [8] where X is the wavelength of the electrons (A M 1 .226Ei”2 nm where Eo is the incident electron energy in eV), p is the brightness of the electron gun in A cmP2 steradian-’, and C, is the spherical aberration coefficient of the objective lens.
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