Ligand-Mediated Revival of Degraded α-CsPbI3 to Stable Highly Luminescent Perovskite.

Although α-CsPbI3 is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ-phase under ambient conditions. Here, we present a simple approach to revive degraded ("optically sick") α-CsPbI3 through "medication" with thiol-containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α-CsPbI3 nanocrystals to cubic crystals in the presence of thiol-containing ligands is visualized through high-resolution transmission electron microscopy and supported by X-ray diffraction analysis. We found that 1-dodecanethiol (DSH) effectively revives degraded CsPbI3 and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs4 PbI6 phase, thus reverting them back to the cubic CsPbI3 phase, leading to enhanced PL and environmental stability.

Role of vacancy sites and UV-ozone treatment on few layered MoS2 nanoflakes for toxic gas detection.

Various issues like global warming and environmental pollutions have led to the research of toxic gas detection worldwide. In this work, we have tried to develop a molybdenum disulfide (MoS2) based gas sensor to detect toxic gases like ammonia and NO. MoS2, an inorganic analog of graphene, has attracted lots of attention for many different applications recently. This paper reports the use of liquid exfoliated MoS2 nanoflakes as the sensing layer in a handheld, resistive toxic gas sensor. The nanoflakes were exfoliated from MoS2 bulk powder using a sonication based exfoliation technique at room temperature. The successful exfoliation of the nanoflakes was characterized using different techniques e.g., optical microscopy, atomic force microscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy and ultraviolet-visible spectrophotometry. The characterization results showed that few-layered nanoflakes have successfully been exfoliated. The MoS2 nanoflakes showed reasonable sensing towards ammonia and NO. In order to explore the effect of particle size on ammonia sensing, the MoS2 flakes were also exfoliated using different sonication times. We also observed that various factors like presence of vacancy sites, ambient oxygen, humidity, different contact electrodes have significant effect on the sensing characteristics. In fact, the response of the sensing layer against 400 ppm of ammonia increased from 54.1% to ∼80% when it was UV-ozone treated. This work holds promises to developing cost-effective, reliable and highly sensitive MoS2 based ammonia sensors.

Gold nanoparticles decorated 2D-WSe2 as a SERS substrate.

Developing well-defined surface enhanced Raman scattering (SERS)-active substrates with superior performance is potentially attractive for many areas of research such as new generation sensing and analysis. Here, a nanohybrid SERS platform has been developed by decorating two-dimensional (2D) tungsten diselenide (WSe2) flakes with zero-dimensional (0D) plasmonic gold nanoparticles (Au NPs). The morphology studies showed that under optimal conditions densely populated Au NPs were formed on the WSe2 surface. Here, we report the utility of the Au NPs/WSe2 nanohybrid structure as an efficient SERS substrate by performing concentration-dependent SERS measurements of a highly fluorescent molecule (Rhodamine 6G, R6G). The hybrid substrate displays promising SERS activity with the detection limit as low as 1 × 10-9 M, which is several orders of magnitude higher than the bare WSe2 on its own (10-3 M). The substrate also exhibits reliable signal stability and reproducibility. These results indicate that the nanohybrid structure has great potential in SERS applications.