Silver nanostructure arrays abundant in sub-5Â nm gaps as highly Raman-enhancing substrates

► A simple method to fabricate Ag nanostructures with narrow gaps was proposed. ► Controlling template temperature and deposited thickness lead to gap's formation. ► The SERS enhancement factors reach 107 due to existence of numerous sub-5 nm gaps. ► High gaps density and narrow gaps size could improve substrates' SERS activity.