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Microscopy and Surface Analysis 1
Lecture Date: March 11th, 2008
Reading Assignments for Microscopy and Surface Analysis
Skoog, Holler and Nieman, Chapter 21, “Surface Characterizationby Spectroscopy and Microscopy”
Hand-out ReviewArticle: R. J. Hamers, “Scanned Probe Microscopies in Chemistry,” J. Phys. Chem., 1996, 100, 13103-13120.
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Microscopy and Surface Analysis
Microscopic and imaging techniques: – Opticalmicroscopy
– Confocal microscopy
– Electronmicroscopy (SEM and TEM, related methods)
– Scanning probe microscopy (STM andAFM, related methods)
Surface spectrometric techniques:
– X-ray fluorescence (fromelectron microscopy) – Auger electron spectrometry
– X-ray photoelectron spectrometry (XPS/UPS/ESCA) – Other techniques:
Secondary-ionmass spectrometry (SIMS) Ion-scatteringspectrometry (ISS)
IR/Ramanmethods
Why Study Surfaces?
Surface – the interface between two of matter’s common phases:
– Solid-gas(we will primarily focus on this) – Solid-liquid
– Solid-solid – Liquid-gas – Liquid-liquid
The majority of present studies are applied to this type of system, and the techniques availableare extremely powerful
The properties of surfaces often control chemical reactions
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Microscopy
Why is microscopy useful? Whatcan it tell the analytical chemist?
– Sampletopography
– Structural stress/strain
– Electromagnetic properties – Chemicalcomposition
Plus - a range of spectroscopic techniques,from IR to X-ray wavelengths/energies,have been combined with microscopy to create some of the most powerful analytical tools available…
Imaging Resolution and Magnification
Some typical values for microscopic methods:
Method
HumanEye
Optical Microscopy
Electron Microscopy
Probe Microscopy
Resolution
0.1-0.2mm
0.1-0.2um
30-50Å
<1 Å
Magnification (x) -
~1200
10-75,000
> 500,000
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Optical Microscopy - History
An ancient technique – the lens has been around for thousands of years. Chinese tapestries dating from 1000 B.C. depict eyeglasses.
In 1000 A.D., anArabian mathematician (Al Hasan) made the first theoreticalstudy of the lens.
Copernicus (1542A.D.) made the first definitiveuse of a telescope.
As glass polishing skills developed, microscopes became possible. John and Zaccharias Jannsen (Holland) made the first commercial and first compound microscopes.
Then came lens grinding,Galileo,the biologists,and many great discoveries….
Modern Optical Microscopy in Chemistry
As optical microscopy developed,the compound microscope was applied to the study of chemical crystals.
The polarizingmicroscope (1880):can see boundaries between materials with differentrefractive indices, while also detecting isotropic and anisotropic materials.
http://www.microscopyu.com/articles/polarized/polarizedintro.html
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Optical Microscope Design
Microscope design has not changed much in 300 years
– But the lenses are more perfect – free of abberations
Objective lenses are characterizedNA (numerical aperature)
– The numerical aperture of a microscopeobjectiveis a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance
– Large NA= finer detail = better light gathering
Diagram from Wikipedia (public domain)
http://www.microscopyu.com/articles/polarized/polarizedintro.html
The Diffraction Limit
The image of an infinitely small point of light is not a point – it is an “Airy” disk with concentric bright/dark rings 0.61
airy NA min NA = nsin
The minimum distance between resolved point objects of equal
intensity is the “Airy” disk radius (rairy), since resolution of a conventionaloptical microscope is limited by Fraunhoferdiffraction at the entrance aperture of the objective lens
Resolved Not resolved
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm,http://www.olympusmicro.com/primer/java/mtf/airydisksize/ See YGarini, CurrentOpinion in Biotechnology2005,16:3–12
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