Figure 1

Fabrication of the monotonically varying ion fluence with defined ion beam profile. (a) Sketch of the ion bombardment procedure for constant fluence gradient along the x-direction. The cumulative fluence F versus x position after six tracks of an ion beam with the idealized rectangular intensity cross-section (dashed line) and the experimental intensity cross-section (solid line) of the beam profile shown in (b). The ‘wavy’ edges of the beam intensity at x ≈ 0.5 and 2.5 are artifacts caused by measurement procedure (in which a Faraday cup with an opening of 0.1-mm diameter scans the beam along the x-direction).