The IHO films were deposited on silica glass substrates by a radio frequency (RF) magnetron sputtering system (Beijing Technol Science Co., Ltd) at room temperature. A high-purity ceramic In 2 O 3 target (Zhongnuo Advanced Material Technology Co., Ltd; 99.99%) was used as a sputtering target. At a base pressure of <10 -4 Pa, an Argon-Hydrogen-Gas mixture with a ratio of 99:1 and flow rates of 30 standard cubic centimetres per minute was introduced. After the gas pressure was stabilized at 0.22 Pa, a sputtering power of 150 W was applied for 20 to 35 min, resulting in a film thickness of 250 to 400 nm. The as-deposited IHO films were annealed at 280 °C for 90 seconds under N 2 . From the central part of each IHO coated glass slide, pieces of 2.5 x 6 cm are cut and cleaned in an ultrasonic bath by submersion in acetone and hexane for 15 min each and rinsed with isopropanol.