ACS Applied Materials & Interfaces · 2020 · 69 citations · 55 references
By means of experiments and theory, the gas-sensing properties of tin diselenide (SnSe<sub>2</sub>) were elucidated. We discover that, while the stoichiometric single crystal is chemically inert even in air, the nonstoichiometric sample assumes a subnanometric SnO<sub>2</sub> surface oxide layer once exposed to ambient atmosphere. The presence of Se vacancies induces the formation of a metastable SeO<sub>2</sub>-like layer, which is finally transformed into a SnO<sub>2</sub> skin. Remarkably, the self-assembled SnO<sub>2</sub>/SnSe<sub>2-x</sub> heterostructure is particularly efficient in gas sensing, whereas the stoichiometric SnSe<sub>2</sub> sample does not show sensing properties. Congruently with the theoretical model, direct sensing tests carried out on SnO<sub>2</sub>/SnSe<sub>2-<i>x</i></sub> at an operational temperature of 150 °C provided sensitivities of (1.06 ± 0.03) and (0.43 ± 0.02) [ppm]<sup>-1</sup> for NO<sub>2</sub> and H<sub>2</sub>, respectively, in dry air. The corresponding calculated limits of detection are (0.36 ± 0.01) and (3.6 ± 0.1) ppm for NO<sub>2</sub> and H<sub>2</sub>, respectively. No detectable changes in gas-sensing performances are observed in a time period extended above six months. Our results pave the way for a novel generation of ambient-stable gas sensor based on self-assembled heterostructures formed taking advantage on the natural interaction of substoichiometric van der Waals semiconductors with air.
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Generalized Gradient Approximation Made Simple
John P. Perdew, Kieron Burke, Matthias Ernzerhof · Physical Review Letters · 1996 · 203.9K citations · Full text
Special points for Brillouin-zone integrations
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