Microscopy and Surface Analysis 1

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. 1 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 2 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 3 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 4 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 5 ... - tailieumienphi.vn