Ulvac phi 5000 versaprobe

A single step growth method was used for doping. Manganese chloride (MnCl₂, Alfa Aesar, Haverhill, MA, USA, purity 97%) was placed in the first heating zone and tungsten trioxide powder was placed in the second heating zone. The first and second heating zones were set at 1140 °C, while the third zone was set at 1060 °C. Then, 10 sccm of oxygen and 90 sccm of argon were introduced as the reaction gas and carrier gas, respectively. The temperature was held for six hours and then cooled down to room temperature naturally. As for synthesis of potassium-doped tungsten oxide nanowires, potassium iodide (KI, Sigma-Aldrich, St. Louis, MO, USA, purity 99.5%) was placed in the first heating zone of the tube furnace tube, while tungsten trioxide powder was placed in the third heating zone with 100 sccm of argon as the carrier gas. The rest of the procedures were the same as the manganese doping experiment. Investigation and characterization of the synthesized WO₃, Mn-doped, and K-doped WO₃ nanowires were conducted with AFE-SEM (Zeiss Auriga, CarlZeiss, Jena, Germany) HR-TEM (JOEL JEM-2100F CS STEM, Tokyo, Japan), (EDS (Bruker, Billerica, MA, USA), and XPS (ULVAC-PHI 5000 Versaprobe, Chigasaki, Kanagawa, Japan).