A highly selective formaldehyde (HCHO) gas sensor using a tin oxide nanoparticles−reduced graphene oxide (rGO−SnO 2 ) composite has been fabricated and investigated for room-temperature sensing. The rGO−SnO 2 composite is synthesized by cost-effective wet chemical method. The fabricated sensor exhibits remarkable sensing performance, including a higher response, a low detection limit of ≈33 ppb (theoretical), good selectivity, and long-term stability. Furthermore, the effects of humidity level and calcination temperature have also been investigated. The response and recovery times for 10 ppm HCHO vapor are found to be 35 and 10 s, respectively. The promising results in the lab-scale HCHO detection with pre-treated fish opens up avenues for the non-invasive detection of HCHO in food adulteration. The density functional theory study is in good agreement with the experimental results. The electronic charge density differences of the rGO−SnO 2 composite in the proximity of HCHO show significant variation. In addition, the sensing mechanism of the rGO−SnO 2 composite toward HCHO has also been discussed.

2D van der Waals heterostructure paves a path towards next generation semiconductor junctions for nanoelectronics devices in the post silicon era. Probing the band alignment at a real condition of such 2D contacts and experimental determination of its junction parameters is necessary to comprehend the charge diffusion and transport through such 2D nano-junctions. Here, we demonstrate the formation of the p-n junction at the MoS2/Black phosphorene (BP) interface and conduct a nanoscale investigation to experimentally measure the band alignment at real conditions by means of measuring the spatial distribution of built-in potential, built-in electric field, and depletion width using the Kelvin probe force microscopy (KPFM) technique. We show that optimization of lift scan height is critical for defining the depletion region of MoS2/BP with nanoscale precision using the KPFM technique. The variations in the built-in potential and built-in electric field with varying thicknesses of MoS2 are revealed and calibrated.

Solar spectrum and sensitivity of human eyes peak at green wavelength range of visible light, and the materials that can respond to a larger part of the visible spectrum are highly sought after. Two-dimensional graphene-like zinc oxide (gZnO) is a wide band gap semiconductor, but photogeneration of electron–hole pairs in it at visible wavelengths has not been achieved so far. Here, the sub-band gap excitation in 2D zinc oxide layers covered with gold nanoparticles is reported. The sub-band gap excitation and corresponding emission are correlated with oxygen interstitials introduced by AuNP deposition in the gZnO lattice. Attachment of AuNPs on gZnO also leads to increased electron availability at oxygen sites of the gZnO lattice, which translates into greater electron availability for sub-band gap excitation. The plasmonically enhanced trap level to conduction band transition constitutes sub-band gap excitation and manifests itself in local surface potential measurements carried out using a Kelvin probe force microscope.