Ultrasmooth gold surfaces prepared by chemical mechanical polishing for applications in nanoscience.

Abstract

For over 20 years, template stripping has been the best method for preparing ultrasmooth metal surfaces for studies of nanostructures. However, the organic adhesives used in the template stripping method are incompatible with many solvents, limiting the conditions that may subsequently be used to prepare samples; in addition, the film areas that can be reliably prepared are typically limited to ∼1 cm(2). In this article, we present chemical-mechanical polishing (CMP) as an adhesive-free, scalable method of preparing ultrasmooth gold surfaces. In this process, a gold film is first deposited by e-beam evaporation onto a 76-mm-diameter silicon wafer. The CMP process removes ∼4 nm of gold from the tops of the grains comprising the gold film to produce an ultrasmooth gold surface supported on the silicon wafer. We measured root-mean-square (RMS) roughness values using atomic force microscopy of 12 randomly sampled 1 μm × 1 μm areas on the surface of the wafer and repeated the process on 5 different CMP wafers. The average RMS roughness was 3.8 ± 0.5 Å, which is comparable to measured values for template-stripped gold (3.7 ± 0.5 Å). We also compared the use of CMP and template-stripped gold as bottom electrical contacts in molecular electronic junctions formed from n-alkanethiolate self-assembled monolayers as a sensitive test bed to detect differences in the topography of the gold surfaces. We demonstrate that these substrates produce statistically indistinguishable values for the tunneling decay coefficient β, which is highly sensitive to the gold surface topography.