Thermophysical properties viz. surface tension, viscosity, density, and ultrasonic velocity of three ionic liquids 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO 4 ], 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM]-[PF 6 ], and 1-ethyl-3-methyl imadazolium methanesulfonate [EMIM][MeSO 3 ] have been measured in a wide temperature range. Experimental data so obtained have been used to calculate isentropic compressibility, isothermal expansion coefficient, surface entropy, surface enthalpy, and critical temperature (temperature where the distinction between liquid and gas phase vanishes and the surface tension tends to zero). Structure−property correlation for different ILs is also discussed.

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The high leakage current in divalent ion doped BiFeO 3 systems is limiting their large scale application. It is clearly shown that the methodology of oxygen annealing will prove to be an effective procedure for suppressing the detrimental consequences that originate from the oxygen vacancies. The samples annealed under oxygen also show different particle morphologies and packing density that can help in tuning the relevant physical properties, viz., magnetic, ferroelectric, and magnetoelectric. The difference in magnetic behaviour in samples annealed in air and oxygen can be explained in terms of the modification in the Fe-O-Fe bonds, domain wall pinning centres, and crystal anisotropy. Another important observation is the stabilization of a dielectric anomaly near the magnetic transition temperature. This observation can make this multiferroic system very interesting for application in sensors where the change in the magnetic parameters can be observed by monitoring the electrical parameters. Detailed analysis of the dielectric and impedance curves indicate towards the presence of non-Debye type processes in samples obtained by annealing in air or oxygen. From the calculated activation energy values, the vacancy related relaxation mechanism is predominant in air annealed samples, while the oxygen annealed samples show the presence of two type of relaxation processes, viz., electron hopping mechanism stabilizes at low temperature while, at higher temperatures, the process associated with the diffusion of doubly ionized oxygen ions predominates. The ac-conductivity data suggests that the correlated barrier tunnelling mechanism, where single electron or two electrons hopping through neighbouring lattice sites leads to ac-conduction. V C 2014 AIP Publishing LLC.

High-quality, continuous transition-metal dichalcogenide (TMD) thin films with large-area coverage are the prerequisites for practical device applications. To address the growing demand, here we report high photoresponse and high detectivity of WS2 nanosheet/Si p–n heterojunction diodes for potential application in UV–visible broadband photodetection based on the wafer-scale deposition of WS2 nanosheets. Monolayer equivalent efficiency, i.e., high responsivity and high detectivity, has been achieved in these devices utilizing its nanotextured morphology. Nanotexturization in the surface morphology increased the effective area for absorption as well as contributed to quantization, leading to superior device performance. RF sputtering followed by high-temperature annealing in the sulfur-rich environment has been adopted to achieve stoichiometric WS2 films with high crystalline quality. The valence band offset for the WS2/Si heterointerface has been determined to be 0.48 ± 0.2 eV, for the band alignment of heterojunction devices. The fabricated n-WS2/p-Si junction diode displayed excellent rectifying characteristics (rectification ratio of ∼630) with a low leakage current (∼1 × 10–7 A). The photodiode exhibits a superior photo-to-dark current ratio (∼1200) and very high photoresponsivity (>4 A/W) under the reverse bias condition. Moreover, a high detectivity of ∼4.8 × 1012 Jones with a linear dynamic range (LDR) of 62 dB at −3 V has also been achieved. A reasonably fast response time, of approximately a few milliseconds of the fabricated photodiode, has made them excellent candidates for large-area photodetectors, operational for the broadband spectral range (300–800 nm).

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