A freshly stripped metal substrate was immersed overnight in a 1 mM solution of C6 in ethanol to allow the formation of a SAM on the surface. In the measurement of C3 HAT on Au diluted with hexanethiol, the substrate was immersed in the mixed solution of C3 HAT and hexanethiol (c (C6 HAT) : c (propanethiol) is 1:10) for 2 h. After immersion, the sample was rinsed with ethanol and dried under a N 2 flow. A 1 W UV LED (Xinhuakai Ltd, Shenzhen, China) with a central wavelength of 415 nm and a bandwidth of 25 nm was used as a light source. Another 1W UV LEDs (Xinhuakai Ltd, Shenzhen, China) with central wavelengths of 340 nm and a bandwidth of 50 nm was also used as a light source. The distance between the light source and the sample was kept at 1 mm. The irradiation time was always 1 min.