Lecture 13

chichi's version from 2018-04-29 00:05

Section 1

Question Answer
x-raysform of electromagnetic radiation with a wavelength in the range of 10 to 0.1 nm, corresponding to frequencies in the range of 30 to 3000 PHz
x-ray diffractioncrystallographic patter produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. Understanding of the material and molecular structure of a substance
Bragg's Lawn(lambda) =2dsin(theta)
nan integer, or order of diffraction
lambdathe wavelength of x-rays
dthe spacing between the planes in the atomic lattice
thetaangle between the incident ray and the scattering planes

Section 2

Question Answer
Debye-Scherrer formula:D(hkl)=k(lambda)/(Beta)cos(theta)(angstrom)
k0.8-0.9 (usually 0.9)
(lambda)wavelength of the radiation (lambda) copper = 1.54056 angstrom
(beta)FWHM (full width at half maximum, or half-width) in radiance (degree)
(theta)the position of the maximum of diffraction peak
How does a SEM work?consists of a column cabinet (including electron column and main console), an operation console, and an evacuation system. To observe the specimen, the electron column contains the electron-optics system and the specimen chamber. A circuit also has been built for controlling the lens system and the image processing system. The operation console includes mouse, keyboard, operation panel for SEM operation, and display for observation
Field emission gunthe emitter consists of a single-crystalline tungsten wire, about 1 mm long and 125 mm in diameter. One end of the wire is etched down to a tip with a diameter of about 1 mm. Halfway along the wire a reservoir of ZrOx is attached, and at the other end the wire is spot-welded to a polycrystalline tungsten loop. This loop is fixed to two poles, which are embedded in a cylindrical ceramic base 1 cm in diameter. By running 2.0-2.5 A of current through the loop the emitter is heated through resistive heating and thermal conduction

Section 3

Question Answer
SEM Setup Electron/Specimen InteractionsWhen the electron beam strikes a sample, both photon and electron signals are emitted
X-raysthrough thickness composition info
Secondary electronstopographical
Primary backscattered electronsatomic number and topographical
Auger electrons surfacesensitive compositional
specimen currentelectrical

Section 4

Question Answer
TEMan imaging technique whereby a beam of electrons are focused onto a specimen causing a enlarged version to appear on a fluorescent screen
More about TEMinvolves a high voltage electron beam
How does a TEM work? #1the electron beam that has been partially transmitted through the very thin (and so semitransparent for electrons) specimen carries information about the inner structure of the speicmen
How does a TEM work? #2the spatial variation in this information (the "image") is then magnified by a series of magnetic lenses until it is
How does a TEM work? #3the image detected by the CCD may be displayed in real time on a monitor or computer

Section 5

Question Answer
HRTEMnew generation of aberration correctors has been able to overcome spherical aberration
TEM is limitedby spherical and chromatic aberration (Lens imperfections lead to different focal lengths in centre and at edges of lens)
What does the software correction do?Software correction of spherical aberration has allowed the production of images with sufficient resolution to show carbon atoms in diamond separated by only 0.89 Angstrom (89 picometers) and atoms in silicon at 0.78 angstroms (78 picometers) at magnifications of 50 million times

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