The present invention introduces a new technique allowing the fabrication of high-aspect ratio nanoscale semiconductor structures and local device modifications using FIB technology. The unwanted semiconductor sputtering in the beam tail region prevented by a thin slow-sputter-rate layer which responds much slower and mostly to the high-intensity ion beam center, thus acting as a saturated absorber funnel-like mask for the semiconductor. The protective layer can be deposited locally using FIB, thus enabling this technique for local device modifications, which is impossible using existing technology. Furthermore, such protective layers allow much higher resolution and nanoscale milling can be achieved with very high aspect ratios, e.g. Ti layer results in aspect ratio higher than 10 versus bare semiconductor milling ratio of about 3.