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L14-Other_Techniques

L14-Other_Techniques - Other Spectroscopic Techniques Using...

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Other Spectroscopic Techniques Using electrons, x-rays and ions
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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.
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Inputs - Outputs Sources Optical (UV, VIS, IR) X-rays Electrons Ions Emissions Optical X-rays Electrons Backscattered Secondary Auger Ions Backscattered Sputtered
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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.
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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
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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
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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
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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
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X-Ray Analyzers Wavelength Dispersive Use a crystal and x-ray diffraction just ;like an optical spectrometer.
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