To see or not to see: Imaging surfactant coated nano--particles using HIM and SEM

Nano--particles are of great interest in fundamental and applied research. However, their accurate visualization is often difficult and the interpretation of the obtained images can be complicated. We present a comparative scanning electron microscopy and helium ion microscopy study of cetyltrimethylammonium--bromide (CTAB) coated gold nano--rods. Using both methods we show how the gold core as well as the surrounding thin CTAB shell can selectively be visualized. This allows for a quantitative determination of the dimensions of the gold core or the CTAB shell. The obtained CTAB shell thickness of 1.0 nm--1.5 nm is in excellent agreement with earlier results using more demanding and reciprocal space techniques.