Measuring the Optical Absorption of Single Nanowires

In this work we present a method to quantitatively measure the optical absorption of single nanowires that can be applied over a wide range of temperatures and with a high enough sensitivity to enable the measurement of below-band-gap absorption (as well as the absorption of single molecules). The method is based on accurately measuring the heat flow coming from a nanowire when it is illuminated by a laser beam. We experimentally verify this method by measuring the absorption of both a zincblende and a wurtzite GaAs, a wurtzite GaP, and a superlattice Zn₃P₂ nanowire. Furthermore, we find that the Zn₃P₂ nanowires have the largest absorption of all these materials. We analyze the advantages and disadvantages of the method and study its range of applicability.