Tungsten Oxide / Vanadium Oxide Heterojunction Nanosensitivity Materials

Tunsten trioxide is a metal oxide semiconductor. It is a surface conductance (resistance) controlled gas sensitive material. The atomic properties of WO₃ crystal surface are active and it is easy to adsorb gas molecules. When gas molecules adsorb on the crystal surface, the carrier concentration inside the WO₃ crystal will change correspondingly, which shows the change of sensor resistance. Because the active atoms of tungsten oxide are located on the surface of the crystal, the contact area between the crystal surface and gas is greatly enlarged, which can effectively improve the gas sensing performance. It can be used in indoor environment detector, air purifier assembly, dangerous gas alarm device and so on.

In recent years, scientists have found that tungsten oxide with one-dimensional nanowire structure can greatly improve the sensitivity of gas detection, but it still can not meet the requirements of market-oriented and integrated applications. In order to obtain high selectivity, high sensitivity, low operating temperature and high stability gas sensor, gas sensing performance is mainly improved by modifying gas sensing materials.

A kind of tungsten oxide/vanadium oxide heterojunction nanowire arrays and their preparation methods have been provided. The tungsten oxide/vanadium oxide heterojunction nanowire arrays with good morphology have been fabricated by vapor-phase method, which are realized by the following technical schemes:

Step 1, deposit tungsten film material layer on the polished silicon wafer by target magnetron sputtering. The metal tungsten is used as the target material, argon is used as the sputtering gas, the sputtering pressure is 2.0 Pa, the sputtering power is 80W, and the sputtering time is 20 minutes.

STep 2, tungsten oxide nanowires were grown by crystallization of tungsten films prepared in step 1 in a vacuum high temperature tubular furnace. The ambient atmosphere was a mixture of oxygen and argon. During the growth of tungsten oxide nanowires, the oxygen and argon flow rates were controlled at 0.1 SCCM and 35 sccm, respectively. The growth pressure in the furnace was 140 Pa. The growth pressure in the tubular furnace was controlled from 0.1 SCCM to 35 sccm. The room temperature rises to 700 degrees Celsius at 25 degrees Celsius, the heating rate is 5 degrees Celsius / min, the temperature is kept at 700 degrees Celsius for 1 hour, then the temperature is lowered for 1 hour to 400 degrees Celsius, and finally the temperature is naturally cooled to 25 degrees Celsius.

Step 3, the tungsten oxide nanowires were annealed at 500 ℃ for 1 hour in an air atmosphere to further stabilize the orientation of the nanowires.

Step 4, vanadium film was deposited on the tungsten oxide nanowire layer on the substrate prepared by step 3 magnetron sputtering. Vanadium was used as the target material, argon was used as sputtering gas, inert gas flow was 50 sccm, sputtering pressure was 2.0 Pa, sputtering power was 110 W, and sputtering time was 5 min.

Step 5, annealing heat treatment of vanadium is carried out, and the substrate of the deposited vanadium film is annealed at 500 ℃ and in air atmosphere for 1 hour.

The tungsten oxide/vanadium oxide heterojunction nanowire arrays were tested. The length of tungsten oxide/vanadium oxide heterojunction nanowires was 300-800 nm, the diameter of tungsten oxide nanowires was 10-20 nm, and the tungsten oxide nanowires were coated with vanadium oxide uniformly to form coaxial core-shell heterostructure. This structure is the best heterostructure. The coaxial core-shell heterojunction has the largest effective heterojunction area compared with the hybrid-dispersed and stacked structure, which plays an important role in the heterojunction excellence.

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