(a) Normalized photocurrent map of the bare Pt90Ir10 tip (0.5 mm in diameter). The photocurrent is normalized with respect to the maximum current detected in the same plot; (b) normalized photocurrent map of a CNT-based smart tip (0.25 mm Pt90Ir10 wire coated with 350 nm SiO2, attached to a CNT, as shown in the insert). A thick boron nitrite film is applied to the tip holder to additionally reduce the photocurrent. The black dash line is used as a guide to show where the tip apex is. The result shows that photocurrent is generated by the whole bare tip apex while the photocurrent of the smart tip is drastically reduced after coating the tip with SiO2.