Resolution in scanning near-field cathodoluminescence microscopy

The lateral resolution in scanning near-field cathodoluminescence microscop y, in the case of bulk materials, is theoretically and experimentally studi ed. Although the theoretical resolution of near-field optical collection sy stems is determined by the probe size and thus should not be dependent on t he energy dissipation volume in the material, it is theoretically shown tha t the contribution of the far-field signal caused by the radiative centers situated far from the probe can alter the resolution by adding a background noise to the near-field signal. In order to see the role of the energy dis sipation volume, the electron beam accelerating voltage is varied and its i nfluence on lateral resolution is studied in the case of a material that do es not present a large energy transfer range, a fluorite doped with 0.3% eu ropium. Cathodoluminescence images of this one confirm that the resolution is improved by working at low accelerating voltage to limit the energy diss ipation volume, hence the contribution of the far-field radiative centers. On the other hand, for materials having a large energy transfer range (seve ral micrometers) and therefore for which the far-field contribution can be strongly disturbing, the question concerning the efficiency of the near-fie ld collection systems arises. Our experimental results on indented MgO crys tal, which presents a large energy transfer range, demonstrates that near-f ield collection, despite the large contribution of the radiative centers si tuated far from the tip, gives still a better resolution than far-field col lection. (C) 2000 American Vacuum Society. [S0734-211X(00)12903-8].