Ethanedithiol

Materials. All chemicals were reagent grade and were used as received. All solutions were prepared in mesitylene (99%, Aladdin). Ethanedithiol (C2), butanedithiol (C4), hexanedithiol (C6), octanedithiol (C8), decanedithiol (C10) were purchased from Alfa Aesar. 0.25 mm platinum wire (99.99%) was purchased from Tianjing Lucheng Metal. A ready-to-use fewlayer graphene (10 mm ×10 mm) on top of a nickel layer was purchased from the Graphene Supermarket, US. Tip preparation. Pt tips were prepared using electrochemistry etching previously reported. 28 Briefly, the procedure was divided into two steps. In the first step, the Pt wire was ultrasonically cleaned in acetone for 10 mins. Then a piece of ~15 mm long Pt wire was cut and immersed into a calcium chloride electrolyte with a concentration of 30 wt. %. The amount of wire immersed into the solution was approximately 2-3 mm. An AC voltage of 35 V was applied between the platinum and graphite counter electrode. After 90 s, for the second stage the voltage was then reduced to 18 V for fine etching in order to sharpen the tips. The etching reaction stopped automatically when the platinum wire section immersed the electrolyte broke off.