Enhancing humidity sensing performance of polyaniline/water soluble graphene oxide composite.

The humidity sensing performance of Polyaniline/Water soluble graphene oxide [PWGO] composites have been presented in this work. Various mass ratios of Water soluble graphene oxide [WGO] were mechanically mixed with Polyaniline [PANI] prepared by in-situ polymerization process to form PANI / WGO composites. For the purpose of humidity sensing studies, the samples were structurally characterized by FTIR, Raman, XRD, SEM and TEM techniques and comparatively analyzed. The film of the samples prepared by deposition on ordinary glass substrate using cost effective spin coating technique were tested for their humidity sensing performance in the relative humidity (RH) range of 11-97%. Of the four composites studied, the PWGO-4 composite recorded a good response time of 8 s and a recovery time of 9 s and a very low humidity hysteresis. The mechanism for sensing has been explained on the basis of three sequential steps: chemisorption, physisorption and condensation process. The humidity sensing stability of the composites were tested over a period of 2 months.

Negative Differential Resistance Device from Organic/Inorganic Hybrid Nanostructures.

Negative differential resistance device (NDR) fabricated by spin coating of organic/inorganic hybrid nanostructures at room temperature, is reported in the present paper. The coated organic layer is MEH-PPV (poly-[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] and inorganic layer is ZnO nanoparticles. The device shows negative differential resistance at low voltage and I­V characteristics of the device show multiple peaks at low voltage values. A value of 13 and 4 for the peak- to-valley ratio of current are reported in bi-layer and single layer structures respectively. Depending on the observed NDR signature, operating mechanisms are explored based on carrier (resonant) tunneling process and donor like trap mechanisms. This results show that the MEH-PPV/ZnO thin films gives good performance and is relevant for applications in optoelectronic devices such as a negative differential resistance.

Observation of room temperature negative differential resistance in multi-layer heterostructures of quantum dots and conducting polymers.

Multi-layer heterostructure negative differential resistance devices based on poly-[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conducting polymer and CdSe quantum dots is reported. The conducting polymer MEH-PPV acts as a barrier while CdSe quantum dots form the well layer. The devices exhibit negative differential resistance (NDR) at low voltages. For these devices, strong negative differential resistance is observed at room temperature. A maximum value of 51 for the peak-to-valley ratio of current is reported. Tunneling of electrons through the discrete quantum confined states in the CdSe quantum dots is believed to be responsible for the multiple peaks observed in the I-V measurement. Depending on the observed NDR signature, operating mechanisms are explored based on resonant tunneling and Coulomb blockade effects.