Direct measurement of the built-in potential in a nanoscale heterostructure

We combine transmission electron microscopy with electrostatic force microscopy to determine the built-in potential across individual isolated ${\text{Cu}}_{2}\text{S-CdS}$ heterostructured nanorods. We observe a variation of potentials for different bicomponent nanorods, ranging from 100 to 920 mV with an average of 250 mV. Nanorods of a uniform composition with no heterojunction do not show a built-in potential, as expected. The results are particularly relevant for applications of colloidal nanocrystals in optoelectronic devices such as photovoltaics.