Fabrication of Metallic Tungsten Diselenide Nanosheet via Ammonium Paratungstate

Transition metal photodetectors operating from visible to ultraviolet (UV) have gained a lot scientific interest owing to its great potential to apply in industry. Tungsten is a transition metals, some tungsten oxides such as tungsten diselenide (WSe2) have excellent photo response properties to be used in photo detection.

A hydrothermal process to synthesis metallic WSe2 with photoresponse performances have been reported. The synthesis procedures are as below:

The raw analytical reagents directly purchased without further purification. The samples in this work were prepared by the following routes. First, 10 ml W4+ precursor solution with a concentration of 0.20 mol/l was prepared with ammonium paratungstate (APT) and 10 ml deionized water. 2.5 ml HCl aqueous solution (37%) was added into the two W4+ solutions to reduce the W6+ to W4+. Citrate acid (C6H8O7) with a molar ratio of citric acid/W4+ = 1.5 as a chelating agent was also added. 5 ml Se2− aqueous solutions with a concentration of 0.8 mol/l were prepared with selenium powder and reducing agent potassium borohydride (KH4B). Afterword, the W4+ solutions and Se2− aqueous solutions were mixed in 25 ml hydrothermal kettle. Meanwhile, polyethylene naphtholate (PEN) substrates were ultrasonically cleaned and then vertically placed into the kettles. After stirring for 5 min, the kettle was sealed and undergone a hydrothermal treatment at 160 °C for 24 h. When naturally cooled for 12 h, the films on the PEN substrate were rinsed with deionized water and the powders were collected by washing with deionized water for five times. Final products were dried at 50 °C for 10 h. The films on the PEN substrate were further constructed to be a photodetection device by depositing Au electrodes. The powder samples were used for some characterizations.

The samples were characterized with X-Ray diffractometer (XRD), G2 F20 S-TWING2 transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Renishaw-invia Raman spectrophotometer.

Conclusion

The metallic structure WSe2 nanostructures led to a remarkably enhanced photocurrent because of high carrier mobility. The WSe2 nano photodetectors showed extremely intense light responses. The photoresponsivity of the WSe2 reached ~89 A/W. The times of rising and decay of the light response were as short as 0.001 and 0.002 s, respectively. Moreover, the photodetectors showed selectively intenser spectra responses in the UV–visible range of 300–700 nm than in longer wavelength, the band edge appeared at ~770 nm.

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