Transparent Metal Films for Detection of Single-Molecule Optical Absorption by Scanning Tunneling Microscopy

Atomically flat, conductive, and transparent noble metal films are produced to extend the wavelength range of room-temperature single-molecule optical absorption detected by scanning tunneling microscopy (SMA-STM). Gold films grown on a platinum underlayer to 15 nm total thickness, deposited by electron beam evaporation onto c-plane sapphire substrates, show sufficient light transmission for backside illumination for laser-assisted STM experiments. Low resistance, transparency, and the atomically flat island surfaces make these good substrates for SMA-STM studies. Monte Carlo lattice kinetics were simulated to allow for a better understanding of the growth modes of the Pt–Au films and of the achieved morphologies. SMA-STM is detected for a quantum dot deposited by aerosol spraying onto Pt–Au films, demonstrating the suitability of such films for single-molecule absorption spectroscopy studies