How Mass Spectrometry Works 2009 How stuf MWorks Stream of lon Positively Charged Stream C lon Stream A lons 00666 Stream B MA- Electromagnet ESA ESA Electrostatic MA analyzer(ESA) Select theKE B、 Select the m/e of ions Detector Energy focal plane Slit Direction Detector cal plane exIt Mass Spectrometer Layout
ESA MA MA
Ion detectors http://www.eaglabs.com/mc/sims-secondary-ion-detectors.html#next Ion Collector A Faraday cup measures the suppressor electrode Ion beam ion current hitting a metal T To amplifier cup, and is sometimes used Load for high current secondary ion Detector Faraday resistor signals. With an electron S cage multiplier an impact of a Faraday cup single ion starts off an Ion Detector electron cascade, resulting in beam slit Sucessivly higher voltage a pulse of10° electrons which is recorded directly Electrons To amplifier Usually it is combined with a Discrete dynode Dynode electron multiplier Be/Cu surface fluorescent screen, and Secondary electron Multiplier signals are recorded either 20 dynodes Current gain 107 with a CCD-camera or with a fluorescence detector https://www.youtube.com/watch?v=nuih9-6fm6uatm5:18-6:50andtow9:25
Ion Detectors Faraday Cup Secondary electron Multiplier 20 dynodes Current gain 107 A Faraday cup measures the ion current hitting a metal cup, and is sometimes used for high current secondary ion signals. With an electron multiplier an impact of a single ion starts off an electron cascade, resulting in a pulse of 108 electrons which is recorded directly. Usually it is combined with a fluorescent screen, and signals are recorded either with a CCD-camera or with a fluorescence detector. http://www.eaglabs.com/mc/sims-secondary-ion-detectors.html#next https://www.youtube.com/watch?v=NuIH9-6Fm6U at~5:18-6:50 and to~9:25
Mass resolution Several definitions of mass resolution(R) R- capability of a mass spectrometer to differentiate between masses If M=1000 and M=l, then R =1000 △M AM- mass difference between two adjacent peaks that are just resolved M-nominal mass of the first peak or mean mass of two peak Resolution is also defined as the full width at half maximum(FWHm) of a peak 28.0313 HN+ 280187 △M=0.0126 28.0061 M+△M CO+ 27.9949 28.0313+28.0187 R 2220 0.0126 Time M/ amu
M/z
High Mass resolution Pyrite〔FeS2) Grain 12 10 x0EoE Lineal 31.96 3197 31.98 31.99 32.00 Mass Mass spectrometers enables to resolve atomic ions from interfering molecular ions if the resolution is high enough Spectrum in both linear and semi-log scales
Time of Flight (TOF) SIMs-Reflectron http://www.youtube.com/watch?v=zoauxsebunkTof-sims http://www.youtube.com/watch?v=kawu6smvhjc 1. Ion source with a TOF SIMS is based on the fact that ions with the same energy but different masses travel pulsed a g0 deflector with different velocities. Basically, ions formed 2. Liquid metal by a short ionization event are accelerated by source an electrostatic field to a common energy and 3. target travel over a drift path to the detector. The 4. Single stage reflector lighter ones arrive before the heavier ones and 5. Detector a mass spectrum is recorded. Measuring the flight time for each ion allows the determination of its mass 日::日 5 (TOF) SIMS enables the analysis of an unlimited mass range with high sensitiv ity and quasi-simultaneous detection of all secondary Schematic of time of flight ( TOF) ions collected by the mass spectrometer
Time of Flight (TOF) SIMS - Reflectron (TOF) SIMS enables the analysis of an unlimited mass range with high sensitivity and quasi-simultaneous detection of all secondary ions collected by the mass spectrometer. TOF SIMS is based on the fact that ions with the same energy but different masses travel with different velocities. Basically, ions formed by a short ionization event are accelerated by an electrostatic field to a common energy and travel over a drift path to the detector. The lighter ones arrive before the heavier ones and a mass spectrum is recorded. Measuring the flight time for each ion allows the determination of its mass. Schematic of time of flight (TOF) spectrometer - reflectron http://www.youtube.com/watch?v=ZoAUxsEBUnk TOF-SIMS http://www.youtube.com/watch?v=KAWu6SmvHjc