“…Since its first discovery in the late 1970s, 6 SERS has thus been an object of great interest in many areas of science and technology, including chemical analysis, corrosion, lubrication, heterogeneous catalysis, biological sensors, and molecular electronics. [7][8][9][10][11] It has long been believed that two enhancement mechanisms, one called a long-range electromagnetic (EM) effect, and the other called a short-range chemical (CHEM) effect, are simultaneously operative for SERS. 1,3,12 Theoretically, at least 8 -10 orders of magnitude can arise from electromagnetic surface plasmon excitation, while the enhancement factor due to the chemical effect is 10 1 -10 2 times.…”