Figure 2: Point projection microscopy of axially doped NWs.

InP NWs (radius 15 nm, length 3.5 μm) with p-i-n axial doping profile and 60 nm i-segment in the centre are spanned across 2 μm holes in a gold substrate (a). Instead of being a real shadow image of the objects shape, projection images are strongly influenced by local fields surrounding the NW, which becomes apparent by the bright NW projection recorded in constant current (field emission) mode at a tip voltage of −90 V (b; scale bar: 500 nm). In addition, a spatial inhomogeneity of the projected diameter along the NW with a step of δ_NW≈60 nm from the left to the right side of the NW centre (marked by the white arrows in b) is observed (c). The projected diameter is plotted in d as a function of distance from the NW centre for both left side (blue) and right side (green) of the NW, illustrating the lensing effects occurring when approaching the edges of the hole. The diameter difference δ_NW between the left and right side of the NW, as plotted in e, remains constant at a value of δ_NW≈60 nm. This corresponds to a potential difference in the 100 meV range and a difference in the radial field around the NW on the order of a few MV m⁻¹, as found by simulations (see Methods).