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Secondary ion mass spectrometry(SIMS)
By:Mohsen Mahmoudi
Dr. Kolahdoz
School of Electrical and Computer EngineeringCollege of Engineering
University of TehranFall 91
Supervisor:
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Outline
o Introduction to MassSpectrometero Introduction & Application of SIMSo How does SIMS work?o Limitations of SIMS
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Mass Spectrometer (MS)
o Is a kind of machine which uses an analytical technique to measure the mass-to-charge ratio of charged particles(ions)
o This analytical technique is also known as Mass Spectrometry.
o MS works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios
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MS Application
Determining masses of particles
Determining the elemental composition of a sample or molecule
Elucidating the chemical structures of molecules, such
as peptides and other chemical compounds
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General Structure of Mass Spectrometer
o Generally, a typical Mass Spectrometer consists of three parts: an ion source, a mass analyzer and a detector
o The function of the ion source is to produce ions from the sample.
o The function of the Mass Analyzer is to separate ions with different mass-to-charge ratios
o Then the numbers of different ions are detected by the detector
o Finally, the mass spectrum is generated after all the data have been collected
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o The output, i.e. mass spectrum, is an intensity vs. m/z (mass-to-charge ratio) graph
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Types of Mass Spectrometers
o Due to the differences in ionization techniques, various analyzers and detectors, the mass spectrometers can be divided into several types.
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o For example: o ICP-MS (Inductively coupled plasma-mass spectrometry)o AMS (Accelerator mass spectrometry)o TIMS (Thermal ionization-mass spectrometry)o SSMS (Spark source mass spectrometry)o IRMS (Isotope ratio mass spectrometry)o SIMS( Secondary ion mass spectrometry)
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Introduction to SIMS
o SIMS is based on the observation that charged particles (Secondary Ions) are ejected from a sample surface when bombarded by a primary beam of heavy particles.
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Structure of SIMS
Typically, a secondary ion mass spectrometer consists of:
o Primary ion gun generating the primary ion beam primary ion column, accelerating and focusing the beam onto the sample
o High vacuum sample chamber holding the sample and the secondary ion extraction lens
o Mass analyzer separating the ions according to their mass- to- charge ratio
o Ion detection unit.
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How Does SIMS Work?
o Typical schematic of a SIMS instrument.
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Step 1, 2
High energy ions are supplied by an ion guno SIMS Primary Ion Sources:
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Step 3, 4
Accelerating and focusing the beam onto the target sample
Which ionizes and sputters some atoms off the surfaceo This leads to the ejection (or sputtering) of both
neutral and charged (+/-) species from the surface.
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Static and dynamic modes
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Sputtering Effects
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Step 5, 6
These secondary ions are then collected by ion lenseso Ions generated by this process form the secondary
beam and are subsequently transmitted within a continuous high vacuum environment to a mass spectrometer
Filtered according to atomic mass
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Mass analyzers
Depending on the SIMS type, there are three basic analyzers available:
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Quadrupole
time-of-flightsector
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Step 7
Then projected onto an electron multiplier (top), Faraday cup ( bottom)
o Ion detectors
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Faraday cup
Electron multiplier
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Step 8
CCD screen
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Mass spectrum diagramDepth of profiling3D Image
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Limitations
o Generally does not produce quantitative analyses o Optical capabilities are typically limitedo Charging may be a problem in some sampleso There is commonly an image shift when changing from positive to
negative ion data collection mode; o Too much data
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A Typical SIMS
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References
[1] J. D. Plummer, M. D. Deal, and P. B. Griffin.“Silicon VLSI Technology: Fundamentals, Practice, and Modeling,” Prentice Hall, 2000
[2] L, Cheng. “Introduction to Mass Spectrometer,” Helsinki, 2007. http://www.bioacademy.gr
[3] P. K. Chu. “Secondary Ion Mass Spectrometry,” University of Hong Kong[4] http://www.chm.bris.ac.uk[5] http://serc.carleton.edu[6] http://en.wikipedia.org[7] http://www.eaglabs.com[8] http://researcher.watson.ibm.com
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Thanks for Your Attention.
University of TehranSchool of Electrical and Computer
EngineeringFall 91