ABSTRACT
Significant progress has been made in two-dimensional material-based sensing devices over the past decade. Organic vapor sensors, particularly those using graphene and transition metal dichalcogenides as key components, have demonstrated excellent sensitivity. These sensors are highly active because all the atoms in the ultra-thin layers are exposed to volatile compounds. However, their selectivity needs improvement. We propose a novel gas-sensing device that addresses this challenge. It consists of two side-by-side sensors fabricated from the same active material, few-layer molybdenum disulfide (MoS2), for detecting volatile organic compounds like alcohol, acetone, and toluene. To create a dual-channel sensor, we introduce a simple step into the conventional 2D material sensor fabrication process. This step involves treating one-half of the few-layer MoS2 using ultraviolet-ozone (UV-O3) treatment. The responses of pristine few-layer MoS2 sensors to 3000 ppm of ethanol, acetone, and toluene gases are 18%, 3.5%, and 49%, respectively. The UV-O3-treated few-layer MoS2-based sensors show responses of 13.4%, 3.1%, and 6.7%, respectively. This dual-channel sensing device demonstrates a 7-fold improvement in selectivity for toluene gas against ethanol and acetone. Our work sheds light on understanding surface processes and interaction mechanisms at the interface between transition metal dichalcogenides and volatile organic compounds, leading to enhanced sensitivity and selectivity.
ABSTRACT
Ultraviolet-ozone (UV-O3) treatment is a simple but effective technique for surface cleaning, surface sterilization, doping, and oxidation, and is applicable to a wide range of materials. In this study, we investigated how UV-O3 treatment affects the optical and electrical properties of molybdenum disulfide (MoS2), with and without the presence of a dielectric substrate. We performed detailed photoluminescence (PL) measurements on 1-7 layers of MoS2 with up to 8 min of UV-O3 exposure. Density functional theory (DFT) calculations were carried out to provide insight into oxygen-MoS2 interaction mechanisms. Our results showed that the influence of UV-O3 treatment on PL depends on whether the substrate is present, as well as the number of layers. Additionally, 4 min of UV-O3 treatment was found to be optimal to produce p-type MoS2, while maintaining above 80% of the PL intensity and the emission wavelength, compared to pristine flakes (intrinsically n-type). UV-O3 treatment for more than 6 min not only caused a reduction in the electron density but also deteriorated the hole-dominated transport. It is revealed that the substrate plays a critical role in the manipulation of the electrical and optical properties of MoS2, which should be considered in future device fabrication and applications.
ABSTRACT
The synthetic dyes over fifty are used in many areas including the food industry around the world. Sunset Yellow FCF and Brilliant Blue FCF are used as colorant food additives in many food products. The present study investigated the genotoxic and cytotoxic effects of Sunset Yellow and Brilliant Blue. Genotoxic and cytotoxic activities of the food additives were evaluated in lymphocyte cell cultures using mitotic index, replication index and micronucleus assay. Mitotic index frequencies and replication index values were decreased and micronucleus frequency was increased with increasing concentrations of Sunset Yellow and Brilliant Blue. The changes in mitotic index and micronucleus are statistically significant (p<0.05). The results show that the Sunset Yellow and Brilliant Blue can have cytotoxic and genotoxic potential. It care must be taken when using these materials as a food additive.
