Gas-sensing behaviors of TiO2-layer-modified SnO2 quantum dots in self-heating mode and effects of the TiO2 layer

SnO2 quantum dots (QDs) were synthesized, after which, TiO2 was deposited to produce TiO2-layer-modified SnO2 QDs. The TiO2 layer was deposited by atomic layer deposition (ALD); by controlling the number of ALD cycles, the thickness of the TiO2 layer was adjusted to 10, 30, or 60 nm. The synthesized products were characterized to demonstrate the formation of TiO2-layer-modified SnO2 QDs with the desired morphology and composition. Both pristine and modified QD gas sensors were tested under external heating conditions, as well as self-heating conditions, by applying different voltages (1-20 V). Gas-sensing results for NO2 under an applied voltage of 20 V (optimal applied voltage) indicate that pristine SnO2 QD gas sensors delivered the best performance. In contrast, for CO sensing, a TiO2 thickness of 30 nm yielded the best performance. The relevant gas-sensing mechanism is discussed. Our results confirm the possibility for realization of high-performance gas sensors using morphology engineering for TiO2 layer-modified QD structures.