For my Physics PhD, I investigated the properties of nano-materials for futuristic solar cells. Besides a bunch of computer simulations, nanowire growth chemistry and a whole slew of electrical and optical measurements, the highlight of my dissertation involved scanning photocurrent microscopy (SPCM). This custom type of microscopy scans a really small laser point over a single nanowire device while simultaneously measuring the current produced by the laser.
In the image below, I've depicted the SPCM setup (top right) along with a typical SPCM result (bottom right). For a simplified interpretation, one can deduce the nanowire's absorption characteristics by measuring the length and magnitude of the red/blue photocurrent spots. I also included a scanning electron microscope image (left) of a representative nanowire growth before being incorporated into a circuit.