Focused chromium ion beam

Abstract

With the goal of expanding the capabilities of focused ion beam microscopy and milling systems, the authors have demonstrated nanoscale focusing of chromium ions produced in a magneto-optical trap ion source. Neutral chromium atoms are captured into a magneto-optical trap and cooled to 100 μK with laser light at 425 nm. The atoms are subsequently photoionized and accelerated to energies between 0.5 and 3 keV. The accelerated ion beam is scanned with a dipolar deflector and focused onto a sample by an einzel lens. Secondary electron images are collected and analyzed, and from these, a beam diameter is inferred. The result is a focused probe with a 1 standard-deviation radius as small as 205±10 nm. While this probe size is in the useful range for nanoscale applications, it is almost three times larger than is predicted by ray-tracing simulations. Possible explanations for this discrepancy are discussed.