A strength of the modern electron microprobe is its ability to provide 2D compositional information about materials. These images give the ability to observe features that might otherwise pass unseen. Elements at the trace element level are generally ignored due to the high detection limits imposed by mapping under “standard” EMP conditions.

Trace element mapping requires beam regulation at high (e.g. 300 nA) to very high (e.g. 3 μA) faraday cup currents, reliable beam and stage control, and suitable samples and mounting media. The ability to operate at high accelerating voltage to maximize Pk2/Bkg is desirable (Robinson and Graham, 1992), although we have encountered column difficulties above 25-30 kV.

We are mapping trace and minor elements including Y, Sc, P, Cr, Mn, Ca, in garnets. Fig. 1 shows Y, Sc and Cr maps (Spear and Kohn, 1996; Kohn, Spear and Valley, 1997), and Fig. 2 Y and Sc maps (Cameron, unpub. data), produced with a Cameca SX51.