Tungsten Trioxide Nanosheets Preparation by Thermal Oxidation

Tungsten trioxide is an important semiconductor material, which has important applications in gas sensing, catalysis, photoelectric conversion, field emission and other fields. Tungsten trioxide nanosheets with two-dimensional structure have attracted more and more attention in recent years because of their unique photoelectric properties.

With the progress of nanotechnology, some scholars have proposed a method to prepare tungsten oxide nanosheets directly by thermal oxidation of tungsten metal without any catalyst. This method can achieve localized preparation. The prepared tungsten oxide nanosheets have large area and good application performance. The process of preparing tungsten oxide nanosheets by thermal oxidation includes the following steps:

1)Clean the glass substrates by ultrasonic cleaning with acetone, ethanol and deionized water for 15 minutes each.

2)Tungsten thin film is deposited on the substrate; the thickness of the film is 200 nm; the photoresist is coated on ITO thin film by rotary glue coating machine. The thickness of the photoresist is about 1 micron, and the baking temperature is 120 ℃. The photoresist was exposed by a UV exposure machine through a mask. The exposed samples were developed with developer, cleaned with deionized water and dried with nitrogen. The photolithographic samples were deposited into tungsten films deposited by magnetron sputtering, and the thickness of the films was about 600 nm. After degumming with acetone solution, it is cleaned with acetone, alcohol and deionized water in turn.

3)The sample obtained in step 2 is put into a heated chamber, and N₂, or inert gas, or mixture of oxygen and N₂, or oxygen and inert gas are injected into the chamber to reduce the oxygen concentration in the chamber to less than 10%. The inert gas is preferred to Ar.

4)The temperature in the chamber rises to 400 ℃~800 ℃ and keeps warm. In this process, N₂ or Ar gas is needed, and the flow rate is generally smaller than step 3.

5)Cool down naturally without ventilation or with inert gas until room temperature, and finally take out the sample.

Raman spectroscopy was used to measure the composition of the oxidized samples. The results show that after the above process, the oxidized products are WO₃ without any other impurities. The surface morphology and structure of WO₃ nanosheets prepared by thermal oxidation were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It can be seen that the average height and thickness of tungsten trioxide nanosheets grown on locally prepared W films are 3 microns and 10 nanometers. The prepared tungsten trioxide nanosheets have single crystal structure.

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