Secondary Ion Mass Spectrometry (SIMS) for Surface Analysis

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1 Secondary Ion Mass Spectrometry (SIMS) for Surface Analysis

2 General overview of SIMS - principles, ionization, advantages & limitations SIMS as a surface analysis technique - operation modes, information obtained Examples of the use of SIMS for Ca analysis among other elements

3 SIMS a desorption/ionization technique Primary ion source 1960s - A. Benninghoven, University of Münster, Germany (Benninghoven A., Rudenauer F.G., Werner H.W., Secondary Ion Mass Spectrometry: Basic Concepts, Instrumental Aspects, Applications and Trends, John Wiley & Sons, 86 (1986). Mass analyzer (sector, TOF, etc)

5 Principles sample: analyte deposited on a solid support material (matrix) bombardment with primary ions (Cs +, O 2+, Ar +, Ga +, C 60+, etc.) secondary ions (+/-) are sputtered from the surfaces (MS) Castner, D. G., Nature 2003, 422 (6928),

6 Unique features high incident ion energies (>1 kev) easy to focus primary electrons sensitive elemental analysis requires small sample size but fragmentation of molecules Static SIMS: primary ion beam is up to 0.3 mm wide Microprobe imaging: 2 μm

7 Primary ion gun Secondary ion source Mass analyzer (TOF or magnet) Detector Microscope

8 Mass analysis positive or negative ions may be detected secondary ions are small (<1000 Da) due to the high energies of primary ions

9 NanoSIMS 50, based on a double focusing magnetic sector, allowing the parallel detection of five elemental or isotopic masses.

12 SIMS variants : Statics SIMS Dynamic SIMS Imaging SIMS used for monolayer elemental analysis used for obtaining compositional information as a function of depth below the surface used for spatially resolved elemental analysis

13 Example: Static SIMS spectra from the surface of PTFE (polytetrafluoroethylene) Aim: obtain sufficient signal to provide compositional analysis of the surface layer without removing a significant fraction of a monolayer - i.e. limit analysis to less than 10 % of a monolayer for a 1 cm 2 sample).

14 Si + 2 Si + 2 Fe + Fe +

15 O + 2 O + 2 S + S +

16 Cu + Cu + S 2 + S 2 +

17 Dynamic SIMS mode The primary ion dose is not limited. The instrument must be equipped with at least two primary ion beams: e.g. O - and Cs +. kev ion bombardment of a solid surface: Secondary particules are ejected from the top atomic monolayers. Some primary ions are implanted in the sample. The primary ion concentration (O - or Cs + ) will reach an equilibrium, leading to a sputtering steady state. Low bombarding energy (down to 150eV) is used to reduce atomic mixing on surface layers and improve depth resolution down to the sub-nm level. High energy (up to 20 kev) is used to investigate deeper (10-20 microns).

Experimental: SIMS SIMS data were acquired using a Model 7200 Physical Electronic instrument (PHI, Eden Prairie, MN) with an 8 kev Cs + primary ion source.

19 Experimental: SIMS SIMS data were acquired using a Model 7200 Physical Electronic instrument (PHI, Eden Prairie, MN) with an 8 kev Cs + primary ion source. Data were taken over a mass range from m/z = for both positive and negative secondary ions. The differences between the expected and observed masses were less than 20 ppm.

20 CaCO 3 positive ions CaCO 3 negative ions

21 Application: NanoSIMS - An Analytical Tool for Trace Metal Detection in Bone and Liver from Haemodialysis Patients John Denton, Francois Hillion, Francois Horreard, Alan G. Cox, University of Manchester, UK, CAMECA, Paris, FR, Centre for Analytical Sciences, University of Sheffield, UK.

22 Purpose of study: Use the CAMECA NanoSIMS 50 as an ion microprobe for the analysis (mapping) of specific elements in bone and liver. Sample: tissues derived from an end stage renal haemodialysis patient receiving both aluminium and iron.

23 Renal dialysis patients develop elevated levels of phosphorous hyperphosphatemia, a severe metabolic disorder. Oral phosphate binders (e.g. Al(OH) 3 ) are used to block absorption of dietary phosphate to counteract hyperphosphatemia. Al(OH) 3 results in serious toxic effects, e.g. development of anemia. Iron supplementation in the form of whole blood transfusion therapy can be used to counteract anemia. Tissue samples: i) liver biopsy, ii) trans-iliac bone biopsy from an end stage renal disease, from a hemodialysis treated patient.

28 Conclusions of the study Trace levels of both aluminium and iron in liver and bone tissue were detected with high spatial resolution: a correlation was found. The ion mapping of cellular components containing carbon, nitrogen, sulphur and phosphorous gives a clear visualization of the different tissue composition. The use of stable isotopes as tracers offers a powerful and quantitative technique in cellular biology.

Secondary Ion Mass Spectrometry (SIMS) for Surface Analysis

Secondary Ion Mass Spectrometry (SIMS) for Surface Analysis General overview of SIMS - principles, ionization, advantages & limitations SIMS as a surface analysis technique - operation modes, information