Conventional instrument: Spatial resolution about 20-50 µm

NanoSIMS Spatial resolution about 50-200 nm

An ion microprobe is a SIMS technique Secondary Ion Mass-Spectroscopy Objective: generate secondary ions Sputtering a sample with beam of primary ions

1 mm

Lophelia deep-sea coral

NanoSIMS Normal SIMS

5-20 nm

NanoSIMS primary ions: Cs+ or O-

Mass spectrometry: Lorentz Force: F = q·v×B

Force = q·v×B = m·a Circular motion: a = v2/r r = (m/q) · (v/B)

I(iM) = db * S * Sy * XM * iAM * YM * T

C/S

primary ions s * area

area

Sputter yield: atoms removed from surface per incoming ion

Atomic fraction

Ionization yield: Mi / M sputtered

Transmission

Isotopic abundance

How many counts per seconds of the isotope iM of the element M?

I(iM) = db * S * Sy * XM * iAM * YM * T The useful yield τ :

τ = YM * T

τ is the fraction of sputtered atoms M that are ionized and detected.

1/τ is the number of atoms M that must be removed from the sample in order to detect one iM.

Typically 1/τ is on order of 103-105.

What can τ teach us? How big a volume we have to sputter to get one detection of a trace element: Example (Fontcuberta): 100 nm thick GaAs nanowire with trace-amounts of Si ρ  = 4.4*1022 atoms/cm3

XSi = 4.5*10-4

1/τ = 1000

To detect one Si ion, we need to sputter a volume of:

(1/τ) * (1/XSi) * (1/ρ) ≈ 5*10-5 µm3

(Assume that Si has only one isotope. 28Si is 92 % : iAM ≈ 1)

To detect one Si ion, we need to sputter a volume of:

(1/τ) * (1/XSi) * (1/ρ) ≈ 5*10-5 µm3

With a beam spot of 50*50 nm2 = 2.5*10-3 µm2 the required sputter depth is: 5*10-5 µm3 / 2.5*10-3 µm2 = 0.02 µm = 20 nm But the GaAs nanowire is only 100 nm thick. Thus, only about 5 counts of Si can be expected before the wire has been sputtered away! To get 100 counts (10% precision): 20 * 20 nm = 400 nm

Distribution Si dopant in two different YAG (Ytrium, Aluminum Garnet) samples showing two different segregation patterns (grain boundary and triple points) after thermal treatment. Field: 10µm x 10µm. Maximum Silicon concentration at grain boundary: 0.1 at. % => 50 counts

0.1µm lateral resolution

Distribution Si dopant in two different YAG (Ytrium, Aluminum Garnet) samples showing two different segregation patterns (grain boundary and triple points) after thermal treatment. Field: 10µm x 10µm. Maximum Silicon concentration at grain boundary: 0.1 at. % => 50 counts

0.1µm lateral resolution

Typical beam size in conventional ion miroprobe

Symbiosis between corals an dinoflagellate algae (zooxanthellae) Essential for coral reef ecosystems

Dinoflagellate cell of the genus Symbiodinium

P. damicornis coral nubbin (5 cm height) Localization of dinoflagellates in coral tissue

Coral-dinoflagellate metabolic interactions are poorly understood, especially at (sub)-cellular levels Isotopic labeling experiments: 15NH4

+,15NO3-, 15N-aspartic acid and 13C-bicarbonate

Transmission Electron Microscopy (TEM) NanoSIMS isotopic imaging

TEM 12C14N- 12C15N- 12C15N-/12C14N-

15N-hotspots (white arrows) are crystalline inclusions of uric acid (EELS and GC-IRMS)

15NH4+ incubation

90 minutes

15N incorporation at the scale of individual zooxanthellae

N storage in uric acid crystals C5H4N4O3

TEM ultrastructural characterization of uric acid crystals (white arrows) within dinoflagellates

NanoSIMS map allows δ15N values to be assigned to each subcellular compartment separately

uric acid deposits 15N “hotspots’

Combining TEM and NanoSIMS images

Nitrogen translocation from the dinoflagellates to the coral host - a nitrate experiment

Direct imaging of N translocation from the symbiotic dinoflagellates to their coral host. This translocation begins ca. 6 hours after nitrogen incorporation by the algal cells (delayed transfer).

Biomineralization - pearl (nacre) forming oyster:

Time-of-Flight SIMS (TOF-SIMS)

Bombardment with primary ions (Ga+, In+, Aun+, Bin+, Cs+, Ar+, Xe+, C60+, …) Energy 5-25 keV Secondary Ions(+/-): Depth of origin 1-3 monolayers

Kinetic energy = qV = ½*v2/m

=> v = (2qV/m)1/2 = L / t Flight-time t = L * (m/2qV)1/2 L = effective length of flight path V = accelerating voltage q = charge of ion m = ion mass v = velocity 2 = two

TOF-SIMS spectra are generated with very short pulses of primary ions (<1 ns). The ability to distinguish different masses of secondary ions is directly related to the width (in time) of the primary beam pulse. If the pulse is not short, the ejection time is not well-defined and ions not well separated in time at the detector.

With each pulse of primary ions: a complete mass spectrum is obtained from H to molecules of thousands of daltons

TOF-SIMS gives a chemical/isotopic finger print of what is at the surface, but its hard to quantify

Ekin = EK - EL1 – EL2,3 orbital energies are unique to an atom of a specific element,

Cylindrical Mirror Analyzer: Electron energies.