Fto coated glass slides

The FTO coated glass slides, an electrically conductive substrate, were purchased from Sigma-Aldrich (No. 735159, Saint Louis, MO, USA). The FTO substrates were sonicated in acetone, ethanol, and water for 30 min, washed with acetone, and dried by N₂. To synthesize Au NPs on a clean FTO substrate, 1.5 mg of fresh AuCl powder (99.9%, Aldrich) was placed in the center of the heating zone in a furnace with a 1 inch diameter inner quartz tube, and an FTO substrate was placed 15–20 mm from the AuCl powder toward the downstream side. Next, the furnace was heated to the desired temperature and maintained for 30 min under a flow of Ar (150 sccm). The pressure of the chamber was 0.7 Torr.

All vials and tweezers used for cleaning of silicon were previously decontaminated in 3/1 v/v concentrated H₂SO₄/30% H₂O₂ at 105 °C for 30 min, followed by copious rinsing with ultrapure water. Caution: the concentrated aqueous H₂SO₄/H₂O₂ (piranha) solution is very dangerous, particularly in contact with organic materials, and should be handled extremely carefully. The n-type silicon (0.3–0.7 Ω cm resistivity, phosphorus-doped, double side polished, 275–325 μm) (100) and p⁺-type silicon wafers (0.001 Ω cm resistivity, boron-doped, single side polished 275–325 μm) (100) were purchased from Siltronix. All the Si surfaces were degreased by sonication in acetone, ethanol, and ultrapure water for 10 min respectively. The surfaces were then decontaminated and oxidized in piranha solution at 105 °C for 30 min, followed by rinsing with copious amounts of ultrapure water. FTO-coated glass slides were purchased from Sigma Aldrich. The FTO slides were cleaned by sonication in LGC-300 (Transene), acetone, ethanol, and ultrapure water for 10 min respectively and dried under Ar flow.