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	Diffraction - Wikipedia, the free encyclopedia
		Diffraction also occurs when any group of waves of a finite size is propagating; for example, a narrow beam of light waves from a laser must, because of diffraction of the beam, eventually diverge into a wider beam at a sufficient distance from the laser.
		Diffraction is one particular type of wave interference, caused by the partial obstruction or lateral restriction of a wave.
		The most common demonstration of Bragg diffraction is the spectrum of colors seen reflected from a compact disc: the closely-spaced tracks on the surface of the disc form a diffraction grating, and the individual wavelengths of white light are diffracted at different angles from it, in accordance with Bragg's law.
	en.wikipedia.org /wiki/Diffraction (1581 words)

	Electron Diffraction
		Most electron diffraction is performed with high energy electrons whose wavelengths are orders of magnitude smaller than the interplanar spacings in most crystals.
		Electrons are charged, light particles and their penetration into solids is very limited.
		LEED and RHEED are therefore considered to be surface science techniques, while transmission electron diffraction is limited to specimens less than 1 mm thick.
	www.matter.org.uk /diffraction/electron/electron_diffraction.htm (200 words)

	Diffraction Techniques
		When the scattering of the electrons is from a crystalline surface plane, a diffraction pattern is produced, different from the diffraction from the bulk of the crystal (as occurs with high energy electrons (several keV or higher) or X-rays).
		In the reflection from a surface plane, the momentum of the electron perpendicular to the surface is not conserved.
		The observation of the pattern of the beam spots (intersection of the diffracted beam with the phosphor screen) serves to determineknow the symmetry of the surface structure.
	www.virginia.edu /ep/SurfaceScience/diffract.html (1033 words)

	electron on Encyclopedia.com
		In any particle reaction involving any of the four members of the electron family, the total electron family number (+1 for ordinary particles, -1 for antiparticles) must be conserved (see conservation laws, in physics).
		Electron microscopy for rapid diagnosis of infectious agents in emergent situations (1).
		Electron Beam Imaging The image is printed by (1) charging the drum, (2) adhering the toner to the drum, (3) tra.
	www.encyclopedia.com /html/e1/electron.asp (912 words)

	IBM Research \| Projects \| LEEM: Low Energy Electron Microscopy
		When the electrons pass the objective lens at the entrance of the sample chamber, they are "slowed down" and decelerated to an energy of only a few eV, since the sample, which is located in front of the objective lens, is held at a potential of nearly 15000V.
		When a parallel and coherent beam of low energy electrons hits a single crystal surface composed of atoms arranged on a periodical lattice, the electrons are diffracted at the surface and the result is a diffraction pattern.
		Microdiffraction: By restricting the electron beam only to a very small area on the surface (fraction of a µm), it is possible to determine the LEED pattern of small areas on the surface, like the LEED pattern of single islands or terraces in order to determine their crystal structure and orientation.
	www.research.ibm.com /leem (1504 words)

	Applications of CCD camera in electron crystallography
		The statistical definition of electron diffraction patterns of glucose-embedded crotoxin complex crystals acquired with the slow-scan CCD camera was assessed by examining the intensity distributions in these patterns.
		The highest possible number of electron diffraction patterns, that could be acquired with the slow-scan CCD camera from a single crotoxin complex crystal under the constraints of radiation damage, was assessed by recording successive patterns from the same crystal.
		The overall appearance of an electron diffraction pattern of a protein crystal acquired by the slow-scan CCD camera is rather similar to that recorded on photographic film except for the streak through the pattern's center (Fig.
	ncmi.bcm.tmc.edu /~brink/papers/ccd-edps/ccd.html (7994 words)

	I.F. OTHER MODES OF TRANSMISSION ELECTRON MICROSCOPE OPERATION
		Electrons diffracted in the same directions OA, O'A' come together to form a spot P in the back focal plane of the lens.
		Similarly, the diffraction spot Q is formed by electrons diffracted at an equal angle on the opposite side of the undeviated beam.
		The diffraction spots are discs rather than points because the electron beam is no longer parallel at the specimen, but a cone; each diffracted beam is therefore also a cone, which becomes a disc in the film plane.
	em-outreach.ucsd.edu /web-course/Sec-I.F/Sec-I.F.html (6468 words)

	Description of Low Energy Electron Diffraction (Site not responding. Last check: 2007-10-09)
		Electrons are excellent examples of this and can diffract from a well-ordered arrangement of atoms on the surface of a sample just as a wave diffracts when hitting a solid object.
		For electrons which have been accellerated through a potential of 30 to 500 volts (i.e., their kinetic energy is around 30 to 500 eV), they have a wavelength given by the de Broglie relation which varies from 2.2 Angstroms to 0.5 Angstroms in this case.
		This is a photograph of a LEED image taken with an incident electron beam energy of 65 volts on a platinum surface.
	www.chembio.uoguelph.ca /thomas/oldthom/LEEDEXPL.HTM (319 words)

	Electron Diffraction (Site not responding. Last check: 2007-10-09)
		Diffraction is fundamentally a wave property: even if you could explain diffraction in terms of particles, the explanation in terms of waves is the simplest one — and that’s what it means to say that the electrons behave as waves.
		These electrons leave the cathode and are accelerated by the anode voltage (Va, 2000-5000 V d.c.) to the target.
		In order to detect the electrons, we could use photographs (as Thomson did) or a Faraday box (measure the accumulated charge in a given time), but we will be much more direct and use a fluorescent screen deposited on the inside of the glass bulb.
	www.ph.utexas.edu /~hoffmann/phy453_fall_2003/experiments/Electron_Diffraction/Electron_Diffraction.html (1538 words)

	Journal of Research of the National Institute of Standards and Technology: Electron diffraction using transmission ...
		The use of electron diffraction to solve crystallographic problems was pioneered in the Soviet Union by B. Vainshtein and his colleagues as early as the 1940s (1).
		Diffracted waves scattered by the atomic potential form diffraction spots on the back focal plane after being focused with the objective lens.
		The use of electromagnetic lenses allows diffracted electrons to be focused into a regular arrangement of diffraction spots that are projected and recorded as the electron diffraction pattern.
	www.findarticles.com /p/articles/mi_m0IKZ/is_6_106/ai_86041895 (1299 words)

	Buckyballs Crash Test New Probe
		Electron microscopes use the wavelike nature of electrons to "illuminate" structures too small to be resolved with the longer wavelengths of normal light waves.
		Electron diffraction experiments are the atomic-scale equivalent, which physicists have used for many years to study atoms.
		The most basic electron diffraction effect is identical to that of light traveling through a small hole onto a screen: The light wave interference leads to a bright central spot surrounded by light and dark rings.
	focus.aps.org /story/v2/st15 (568 words)

	Biophysical Journal: Quantitative comparison of zero-loss and conventional electron diffraction from two-dimensional ... (Site not responding. Last check: 2007-10-09)
		Relatively low electron dose required for recording an electron diffraction pattern, which can be less than one-tenth of the dose required for taking an image, gives a further advantage in reducing radiation damage.
		An advantage in using electron diffraction from crystals over imaging for evaluating the effect of energy filtering is that quantitative analyses can be carried out for high-resolution data more easily and reliably.
		Here, we report quantitative analyses of electron diffraction data obtained with and without energy filtering by using a HITACHI EF-2000 electron microscope, which is equipped with a gamma-type energy filter and operated at an accelerating voltage of 200 kV.
	www.findarticles.com /p/articles/mi_qa3938/is_200205/ai_n9026680 (1100 words)

	Incident Beam Diffraction in Electron-Stimulated Desorption (Site not responding. Last check: 2007-10-09)
		Diffraction of the incident electron beam forms (in a time-independent picture) a standing wave with spatially localized maxima and minima in the electron density.
		If we assume that stimulated desorption begins by the excitation or ionization of an electron in the solid, the ESD rate will be a maximum when the charge distribution of the incident electron significantly overlaps that of the target electron.
		Since the interference that determines the incident electron density depends upon the geometric and chemical structure of the surface, measurements of incident beam diffraction in electron stimulated desorption (DESD) yield direct information about the ground-state bonding geometry of the desorbate.
	www.emsl.pnl.gov /docs/csd/annual_report1999/1578b_3i.html (1167 words)

	X-ray, Neutron, and Electron Simulation in MOE (Site not responding. Last check: 2007-10-09)
		X-rays are scattered by the electron density cloud surrounding an atomic nucleus, electrons by the positive potential of the nucleus, and neutrons by the nucleus itself.
		Electrons also interact with matter to a much greater extent, and therefore quantitative measurements from the images obtained may be unreliable.
		Although, in theory, a diffraction pattern is a projection of the weighted crystal reciprocal lattice, in practice, the observed pattern is more complex, being affected by many factors including experimental setup, thermal vibration of the atoms in the crystal, internal reflections which cause interference, and so forth.
	www.chemcomp.com /feature/diffr.htm (1615 words)

	I.F. OTHER MODES OF TRANSMISSION ELECTRON MICROSCOPE OPERATION
		The intermediate lens strength is now adjus-ted so as to form an image of the diffraction pattern from this selected area in the upper conjugate plane of the projector lens, which in turn forms a magnified image of the diffraction pattern on the screen or plate.
		The corresponding 'spotty ring' type of diffraction pattern (upper left) indi-cates that the crystals are oriented in a number of different directions.
		Diffraction patterns are not affected by translational vibrations or unidirectional drift of the specimen since each bundle of parallel diffracted rays is still brought to focus in the same position in the back focal plane of the objective lens regardless of the translational position of the specimen.
	www-ncmir.ucsd.edu /~gina/Sec-I.F/Sec-I.F.html (6461 words)

	6.3 Reflection High Energy Electron Diffraction (RHEED) (Site not responding. Last check: 2007-10-09)
		It is worth noting, however, that the use of glancing incidence ensures that, despite the high energy of the electrons, the component of the electron momentum perpendicular to the surface is small.
		Under these conditions an electron may travel a substantial distance through the solid (in accord with the much longer mean free path of such high energy electrons) without penetrating far into the solid.
		In addition to the change in momentum of the electron perpendicular to the surface, which leads to the apparent reflection, the diffraction process may also lead to a change in momentum parallel to the surface, which leads to the deflection by an angle
	www.chem.qmw.ac.uk /surfaces/scc/scat6_3.htm (563 words)

	Elastic and Inelastic Scattering in Electron Diffraction and Imaging
		Elastic electron diffraction is usually approached based on the convenient theoretical scheme for the specific subject of the book, such as Bloch wave theory for convergent beam electron diffraction and multislice theory for high resolution TEM image simulation.
		The theory of inelastic electron diffraction is complex and difficult because of the incoherent scattering characteristics of the inelastic electrons and, thus, is rarely discussed in the existing books.
		An outline of a first-principles approach to inelastic electron scattering of a crystal in thermal equilibrium with its environment is presented.
	www.nanoscience.gatech.edu /zlwang/book/book1.htm (4725 words)

	ASU Physics & Astronomy \| Research - Electron Diffraction and Imaging (Site not responding. Last check: 2007-10-09)
		The electron diffraction and imaging group at ASU is at the forefront, having been largely responsible for developing the theory necessary for the interpretation of atomic-resolution electron micrographs of crystals, and pursuing novel applications.
		Research efforts have been oriented towards the development of higher resolution instruments and the application of electron diffraction and imaging methods to a wide range of problems in materials science, solid state chemistry, surface science, geology, magnetism and semiconductor physics.
		We are also at the forefront of developing new imaging modes, such as electron holography, energy filtered imaging, Auger electron imaging, etc. We form the core development team of the Center for High Resolution Electron Microscopy (CHREM).
	phy.asu.edu /research/eld/index.asp (832 words)

	(IUCr) Book Review (Site not responding. Last check: 2007-10-09)
		This volume was written to fulfill a need for a comprehensive work on various aspects of electron diffraction, given the significant developments that have taken place with this technique over the past two decades.
		I feel, though, that the real usefulness of electron diffraction data for ab initio structure analyses may be obscured by the copious discussion of cases where it is obvious that multiple-beam interactions are most important.
		Given that the authors of many of these chapters have been at the forefront of theoretical developments in electron diffraction and microscopy, this impressive volume is a very nice collection to have at hand - both as a reference and as a nucleus for research ideas.
	www.se.iucr.org /iucr-top/journals/bookreviews/by0028.html (859 words)

	Laser light diffracts electrons (September 2001) - News - PhysicsWeb
		But light interacts only weakly with electrons, and early attempts to detect coherent electron diffraction failed because the available light sources were too weak.
		A narrow beam of electrons was sent through the grating, and detectors placed 24 centimetres behind the grating map the distribution of the diffracted electrons.
		As Batelaan explains, an electron interferometer could be extremely sensitive because the wavelength associated with electrons is around ten thousand times shorter than that of light.
	physicsweb.org /articles/news/5/9/5 (431 words)

	McGraw-Hill AccessScience: Electron diffraction
		The wave character of electrons is shown most strikingly, and doubtless most conclusively, by the phenomena of interference.
		For this reason, the diffraction of electrons presents the most obvious confirmation of quantum mechanics.
		Because of the dependence of the diffraction pattern on the distances between the atoms, electron diffraction is also an important tool for the study of the structure of crystals and of free molecules, analogous to the use of x-rays for these purposes.
	www.accessscience.com /Encyclopedia/2/22/Est_224000_frameset.html (159 words)

	PHY 598 (Venables) Sect 3.2
		An important aspect of diffraction from 2D structures is that k// (parallel)is conserved to within a surface reciprocal lattice vector G//, whereas k (perpendicular) is not, as shown in diagram 62 (Luth).
		The equipment for both diffraction techniques is simple, involving a fluorescent screen, with energy filtering in addition in the case of LEED, as indicated in diagram 63, to remove inelastically scattered electrons.
		Some of these sensit- ivities are due to the extra diffraction spots associated with particular domains; some of them are due to exploiting the difference between in-phase and out-of-phase scattering (see diagram 62b); some again depend on the small rotations produced by surface steps, and the increase in diffuse scattering.
	venables.asu.edu /grad/sect32.html (1506 words)

	PIRA 7A60.00 X-RAY AND ELECTRON DIFFRACTION (Site not responding. Last check: 2007-10-09)
		A schematic for the electron diffraction apparatus is given.
		Microwave diffraction is observed from a crystal model made of steel bearings mounted in a styrofoam cube.
		X-ray diffraction of a rock salt crystal mounted on a goniometer with GM tube detector.
	www.physics.ncsu.edu /pira/7modern/7A60.html (475 words)

	Electron diffraction. Si (Site not responding. Last check: 2007-10-09)
		Electron diffraction on solid state crystals is determined by the Bragg diffraction law
		where k is the incident electron wave vector, k' is the diffracting one, g is a reciprocal lattice vector.
		Therefore diffraction picture coinsides really with cross-section of the reciprocal lattice by the plane perpendicular to falling electron beam.
	www.ibiblio.org /e-notes/Kat/DifSi.htm (293 words)

	Glossary of Electron Microscopy Terms
		Detection of Backscattered Electrons is achieved by using a "donut" shaped solid state semiconductor device mounted on the bottom of the objective lens.
		An electron probe is tightly focused on a TEM specimen and the resulting pattern of diffracted electrons is observed.
		Electrons and their orbits around the nucleus of an atom account for most of the physical properties of the element.
	www.unl.edu /CMRAcfem/glossary.htm (1402 words)

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