10.1021/nn2025868.s001 Huigao Duan Huigao Duan Hailong Hu Hailong Hu Karthik Kumar Karthik Kumar Zexiang Shen Zexiang Shen Joel K. W. Yang Joel K. W. Yang Direct and Reliable Patterning of Plasmonic Nanostructures with Sub-10-nm Gaps American Chemical Society 2011 application ultrasmall gaps plasmonic structures lithography tunable plasmonic nanostructures nm pattern SERS HSQ method fabrication 2011-09-27 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Direct_and_Reliable_Patterning_of_Plasmonic_Nanostructures_with_Sub_10_nm_Gaps/2611288 Nanoscale gaps in metal films enable strong field enhancements in plasmonic structures. However, the reliable fabrication of ultrasmall gaps (<10 nm) for real applications is still challenging. In this work, we report a method to directly and reliably fabricate sub-10-nm gaps in plasmonic structures without restrictions on pattern design. This method is based on a lift-off process using high-resolution electron-beam lithography with a negative-tone hydrogen silsesquioxane (HSQ) resist, where the resulting nanogap size is determined by the width of the patterned HSQ structure, which could be written at less than 10 nm. With this method, we fabricated densely packed gold nanostructures of varying geometries separated by ultrasmall gaps. By controlling structure sizes during lithography with nanometer precision, the plasmon resonances of the resulting patterns could be accurately tuned. Optical and surface-enhanced Raman scattering (SERS) measurements on the patterned structures show that this technique has promising applications in the fabrication of passively tunable plasmonic nanostructures with ultrasmall gaps.