Table 1.

WS₂ gas sensor characteristics (resistance and chemical composition) for different ambient exposure and the concentrations of each element in the WS₂ active surface, which are calculated from the NAP-XPS survey spectra in each step.

Steps	NAP-XPS Chamber Environment	R (kΩ)	W (%)	S (%)	O (%)	S/W
0	UHV at RT	110	34.8	52.1	13.1	1.5
1	1000 ppm H2 at RT	120	33.6	48.8	17.6	1.5
2	5000 ppm H2 at RT	145	32.6	49.6	17.8	1.5
3	UHV at RT	135	32.0	50.0	18.0	1.6
4	UHV with the device heating at 150 °C	80	33.5	48.8	17.7	1.5
5	1000 ppm H2 with the device heating at 150 °C	110	31.3	49.8	18.9	1.6
6	UHV with the device heating at 150 °C	75	27.1	42.7	30.2	1.6