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Transcript of Chem 125 Lecture 7 9/20/06 Projected material This material is for the exclusive use of Chem 125...
Chem 125 Lecture 79/20/06
Projected material
This material is for the exclusive use of Chem 125 students at Yale and may not
be copied or distributed further.
It is not readily understood without reference to notes from the lecture.
Exam 1 - Friday, Sept. 29 !
Covers Lectures through next Wednesday
Including:
Functional GroupsX-Ray Diffraction
1-Dimensional Quantum Mechanics(Sections I-IV of webpage
& Erwin Meets Goldilocks)
Get-aquainted session Friday afternoon 4-5:30 in 160 SCL
In 1895 RöntgenDiscovers X-Rays
Shadow ofFrau Röntgen'sHand (1895)
In 1912 LaueInventsX-Ray
DiffractionCuSO4 Diffraction
(1912)
Wm. Lawrence Bragg(1890-1971)
Determined structure of ZnS from Laue'sX-ray diffraction
pattern (1912)
Youngest Nobel Laureate(1915)
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Tungsten Interconnect in Computer Chip
Nanotomography Comes of Age, Nature, August 10, 2006
“They then use tomographic methods to combine images taken at different incident X-ray angles, allowing internal structures and - given sufficent spectral resolution - chemical bondings to be discerned with a spatial resolution of around 60 nanometers.”
Blurring Problem
Blurring Problem from Motion and Defects
Time Averaging
Space Averaging in Diffraction(Cooperative Scattering)
Advantage for SPM(Operates in Real Space)
What can X-ray diffraction show?
How does diffraction work?
Like all light, X-rays are waves.
Atoms?Molecules? Bonds?
Real Space "Reciprocal" Space
Material Diffraction Photo
Molecular Structure Fuzzy Pattern
Crystal Lattice Viewing Holes
Decreasing Spacing Increasing Spacing
Direct
Two Scattering Directions are Always Exactly in Phase
“scattering vector”
Specular perpendicular to scattering vector
All electrons on a planeperpendicular to
the scattering vectorscatter in-phase at
the specular angle !
Specular
scattering vector
10
Simplification from Electrons-on-a-Plane Trick
3
+2
+4
+1
12
3
Net in-phasescattering
TotalElectrons
3 24 1
Water
Oil“Thickness” ~ 200 nm
Path Difference = 400 nm
= 0.5
Strong400 nm
Scattering
No800 nm
Scattering
= 1
scattering vector
scattering vector
Simplification from Electrons-on-a-Plane Trick
10
3
+2
+4
+1
Net in-phasescattering
TotalElectrons
12
3
Suppose first path difference is half a wavelength.(increase or decrease angle)
3
+2
-4
-1
0
0.51
1.5
3 24 1
Filament
Light BulbFilament(helix)
X angle tellshelix pitch
Spot spacingtells scale
Spot spacingtells scale
Spots weakensuccessively
(from wirethickness)
(given &
screen dist)