L14-Other_Techniques

L14-Other_Techniques - Other Spectroscopic Techniques Using electrons x-rays and ions Basic Idea The concept is similar to optical spectroscopy

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Unformatted text preview: Other Spectroscopic Techniques Using electrons, x-rays and ions Basic Idea ¡ The concept is similar to optical spectroscopy. ¡ Send in an excitation (sources). ¡ Collect and resolve the emission (analyze). ¡ Detect the emission (detectors). ¡ The particular excitation-collection pair determines what aspect of the thin film you are measuring. Inputs - Outputs ¡ Sources ¢ Optical (UV, VIS, IR) ¢ X-rays ¢ Electrons ¢ Ions ¡ Emissions ¢ Optical ¢ X-rays ¢ Electrons ¡ Backscattered ¡ Secondary ¡ Auger ¢ Ions ¡ Backscattered ¡ Sputtered Electron Sources ¡ Electrons can be emitted from a metal by thermionic emission . ¡ A high enough electric field applied to the metal pulls electrons off the metal surface. ¡ The number of electrons emitted is proportional to the temperature of the metal and inversely proportional to its work function. Issues ¡ Thermionic emission sources are not narrow- band. ¡ The thermal heating results in a Boltzmann distribution of emitted electron energies. ¡ Some filament designs require less heating and therefore result in a narrower electron energy distribution. ¡ There is an upper limit to the electron density due to electron repulsion. Hairpin filament Field emitter tip Electron Analyzers ¡ They use electrostatic or electromagnetic fields to deflect electrons and sort them according their initial kinetic energy. ¡ Some types are: ¢ Cylindrical Mirror Analyzer (CMA) ¢ Hemispherical Sector Analyzer (HSA) ¢ Retarding Field Analyzer (RFA) ¢ Cylindrical Sector Analyzer (CSA) CMA Electron Detectors ¡ The detector receives electrons. ¡ Each electron contributes to a current that is measured. ¡ An amplification scheme is usually incorporated. ¡ Some types are: ¢ Electron multiplier ¢ Channeltron ¢ Channel plate Basic design of an electron detector X-Ray Sources Bremmstrahlung Synchrotron ¡ Created by sudden stopping of electrons ¡ Suitable for small labs ¡ Low maintenance ¡ Complex emission spectrum ¡ Subject to contamination ¡ Created by accelerated electrons ¡ National lab type facility ¡ High brilliance source ¡ Narrow, tunable lineshape X-Ray Analyzers ¡ Wavelength Dispersive ¢ Use a crystal and x-ray diffraction just ;like an optical spectrometer....
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This document was uploaded on 02/29/2012.

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L14-Other_Techniques - Other Spectroscopic Techniques Using electrons x-rays and ions Basic Idea The concept is similar to optical spectroscopy

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