Ultrathin Atomically Flat Gold Film for Scanning Tunneling Microscopy and Single-Particle Fluorescence Spectroscopy

To enable rear illumination (e.g., TIRF), single-particle fluorescence microscopy, and scanning tunneling microscopy (STM) on the same nanoparticle sample, we investigate the smoothness limit and the thickness limit of template-stripped gold films made with a simple room-temperature deposition protocol ranging from 1 to 200 pm/s on four common substrates: mica, fused silica, silicon, and quartz. The resulting transparent conductive gold film achieves a thickness as low as 9 nm, absorbance as low as 0.2, and a root-mean-square roughness of 80 pm over a 100 × 100 nm² area. We further assess whether such gold films enable single-particle characterization by fluorescence imaging and STM imaging on the same sample. Carbon dots, made by a top-down method, with a height as low as 1.0 nm (∼3 layers), can be resolved clearly on the gold film island surfaces by using both atomic force microscopy and STM, and the carbon dot single-particle fluorescence blinking can be measured by confocal microscopy. In this way, both optical and electronic characterization can be enabled on the same sample using a substrate that is relatively easy to make in batches.