Sample preparations & requirements

Thickness of the probed surface is in the range of few atomic layers (Fig. 2).

This is important to realize when analyzing thicker samples such as tissues: features seen in a microscope, obtained for example in a transmission or fluorescence mode, may not be “visible” to NanoSIMS if they are buried deeper within the sample.

Since most samples will not be sufficiently conductive, they can be coated with a thin conductive layer (ideally Au, but also C or Pt-Pd) to achieve the desired effect.

For samples on support substrates (e.g. cells or tissues deposited on a filter or a glass slide), the conductive layer can be added before or after the sample deposition.

The GeoLab offers coating instruments (Au, C or Pt-Pd) to support sample preparation.

This is required to minimize artifacts caused by surface topography of samples (e.g., micron-scale surface roughness may cause small variations in isotope ratios or secondary ion yields).

Preferably, samples should be prepared as thin sections.

For geological samples (e.g., rocks), we advise a final polishing step using a 30-50 nm powder.

The GeoLab offers polishing instruments to support sample preparation.

Samples must withstand a vacuum of <10^-7 Pa (<10^-9 mbar).

Samples should not contain any volatile substances (e.g., water or other solvents).

Available NanoSIMS sample holders only have circular holes for samples (Fig. 5). Therefore, samples should be flat and ideally round. The nominal diameter of the holes are 5 mm, 10 mm, ½ inch, or 1 inch. For these nominal hole diameters, the exact range of diameters of samples that will fit into the hole but will not fall through the opening are summarized in Table 1:

Samples that are not round can sometimes be attached to a round stub that fits the holder (e.g., using a copper tape; Fig. 5). In this case, extra spacers will have to be added.

Sample thickness should not exceed 6 mm. This is because brass clips push the sample against the holder from the back to keep it in a fixed position (Fig. 5).

Areas that are very close to the edge of the sample will not be measurable because the surface to be measured is pushed against a narrow rim at the front of the holder.