Secondary ion mass spectrometry (SIMS) By: Mohsen Mahmoudi Dr. Kolahdoz School of Electrical and...

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

1/18 Secondary ion mass spectrometry (SIMS)


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


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


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


o The output, i.e. mass spectrum, is an intensity vs. m/z (mass-to-charge ratio) graph


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.


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)


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.



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.



How Does SIMS Work?

o Typical schematic of a SIMS instrument.



Step 1, 2

High energy ions are supplied by an ion guno SIMS Primary Ion Sources:



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.



Static and dynamic modes



Sputtering Effects



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



Mass analyzers

Depending on the SIMS type, there are three basic analyzers available:


Quadrupole

time-of-flightsector


Step 7

Then projected onto an electron multiplier (top), Faraday cup ( bottom)

o Ion detectors


Faraday cup

Electron multiplier


Step 8

CCD screen


Mass spectrum diagramDepth of profiling3D Image


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




A Typical SIMS


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


Thanks for Your Attention.

University of TehranSchool of Electrical and Computer

EngineeringFall 91

Secondary ion mass spectrometry (SIMS) By: Mohsen Mahmoudi Dr. Kolahdoz School of Electrical and...

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