MoS2 is an intrinsic piezoelectric material which offers applications such as energy harvesting, sensors, actuators, flexible electronics, energy storage and more. Surprisingly, there are not any suitable, yet economical methods that can produce quality nanosheets of MoS2 in large quantities, hence limiting the possibility of commercialisation of its applications. Here, we demonstrate controlled synthesis of highly crystalline MoS2 nanosheets via liquid phase exfoliation of bulk MoS2, following which we report piezoelectric response from the exfoliated nanosheets. The method of piezo force microscopy was employed to explore the piezo response in mono, bi, tri and multilayers of MoS2 nanosheets. The effective piezoelectric coefficient of MoS2 varies from 9.6 to 25.14 pm V−1. We attribute piezoelectric response in MoS2 nanosheets to the defects formed in it during the synthesis procedure. The presence of defects is confirmed by x-ray photoelectron spectroscopy.

Polyethylene terephthalate-based nanocomposites with hexagonal boron nitride nanosheets (BNNs) were prepared by a solution casting method with varying concentrations of BNNs from 0.5 wt% to 4 wt%. Melting and crystallization behaviour of the composites were investigated by differential scanning calorimetry, which suggests that with increasing presence of nanosheets, the crystallinity increases and hence the polyethylene terephthalate chain mobility gets restricted, which leads to suppression of crystal growth. The nanoindentation measurements on the composite films exhibit improved mechanical properties. Enhancement of 33.3% of elastic modulus and 32.4% of hardness was observed with 2 wt% infusion of boron nitride nanosheets in polyethylene terephthalate.

No abstract

We report our studies on the nanoscale electrical conductivity in monolayers of n-alkyl cyanobiphenyl materials deposited on solid surface. Initially, the 8CB, 9CB, and 10CB monolayer films were prepared by the Langmuir technique at air-water interface and characterized by surface manometry and Brewster angle microscopy. The monolayer films were transferred on to solid substrates by the Langmuir-Blodgett (L-B) technique. The 8CB, 9CB, and 10CB monolayer L-B films were deposited on freshly cleaved mica and studied by atomic force microscope (AFM), thereby measuring the film thickness as ∼1.5 nm. The electrical conductivity measurements were carried out on 9CB and 10CB monolayer L-B films deposited onto highly ordered pyrolytic graphite using current sensing AFM. The nanoscale current-voltage (I-V) measurements show a non-linear variation. The nature of the curve indicates electron tunneling to be the mechanism for electrical conduction. Furthermore, analysis of the I-V curve reveals a transition in the electron conduction mechanism from direct tunneling to injection tunneling. From the transition voltage, we have estimated the values of barrier height for 9CB and 10CB to be 0.71 eV and 0.37 eV, respectively. For both 9CB and 10CB, the effective mass of electron was calculated to be 0.021 me and 0.065 me, respectively. These parameters are important in the design of molecular electronic devices.

No abstract