Preparation of Gold Films on MoS₂ with Subatomic Surface Roughness by Sputtering

We have determined that gold films with subatomic surface roughness can be prepared onto MoS₂ surfaces using a simple sputtering process at room temperature. To explore integration with semiconductor devices and/or substrates for further growth, the used substrates were either standard silicon wafers with a native oxide (SiO₂/Si), or MoS₂ bilayers sputtered onto such silicon wafers (MoS₂/SiO₂/Si). It was immediately apparent that the gold deposited onto the MoS₂/SiO₂/Si substrates were far superior. Gold films deposited onto bare silicon wafer substrates had nanometer scale (or larger) RMS surface roughness. Gold films deposited on the sputtered MoS₂ bilayers had RMS surface roughness of less than 300 pm. For gold films with thicknesses between 10 to 15 nm, the surface roughness was consistently less than 100 pm, which is approximately the resolution of the atomic force microscope (AFM) used in these experiments. It was especially interesting to see that the gold films were flatter than both the native oxide of the silicon wafer and the sputtered MoS₂ bilayers. We found no evidence for granular structure even for AFM scans exceeding 100 square microns. Our ultraflat gold films should be highly useful for any research requiring extremely smooth surfaces, such as the exploration of self-assembled monolayers. We also found that the surface roughness is easily tunable by annealing above 200° C, making them potentially useful for substrates utilizing surface enhanced techniques such as Raman spectroscopy.