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A comparative study of Sr-doped LaMnO <sub/>3</sub> synthesised via solid-state reaction and sol–gel methods
摘要： This work deals with the synthesis of hole-doped La1-xSrxMnO3 (x = 0.25 and 0.33) perovskite via two different ways, namely a solid-state reaction method and a sol–gel process. Various properties of the samples have been investigated and compared by means of different techniques, namely X-ray diffraction (XRD), temperature-dependent resistivity measurements in the temperature range 25–300 K using a closed cycle refrigerator and vibrating sample magnetometry (VSM). All samples have orthorhombic crystal symmetry and an irregular variation in unit-cell volume with increase in Sr content. The average crystallite size was determined from the XRD data and found to lie in the range 19–22 nm. Metal–insulator transitions (MIT) were observed in all the samples via low-temperature electrical characterisations. The magnetic measurements confirm that the magnetisation does not saturate for the 25% Sr doped samples up to the available field of 10 kOe. The magnetic response also supports the interpretation of XRD and resistivity data. The obtained results are explained on the basis of double-exchange and super-exchange mechanisms.
关键词： CMR,manganites,metal to insulator transition (MIT),sol–gel method,Solid-state reaction
更新于2025-09-23 15:22:29
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Transition from Hopping to Band-like Transport in Weakly-coupled Multilayer MoS2 Field Effect Transistors
摘要： In this article, multilayer MoS2 manufactured from multiple-transfer process of chemical vapor deposition (CVD) grown monolayer MoS2 is studied. Due to the lattice mismatch and larger distance between adjacent MoS2 layers, the interlayer-interaction is weakened and the band structure transition from direct to indirect as well as band-gap shrinkage effect in multilayer is suppressed, as indicated by Raman and photoluminescence (PL) spectra. These structural differences from that of the exfoliated MoS2 make stacked MoS2 layers a better configuration for fabricating high-performance MoS2 FET. Here, back-gate MoS2 field effect transistors (FETs) with different number of layers were fabricated. As the number of layers increases from 1 to 3, the devices’ mobility and on/off ratio show an enhancement from 2 to 62cm2/s·V and 106 to 108, respectively. Metal to insulator transition (MIT) phenomena is also observed in bilayer MoS2 FET. A distributed resistance based model is proposed to study the conductivity of weak-coupled MoS2 layers. Combining the resistance model with temperature dependence characteristics, it is demonstrated that the electron mobility in monolayer MoS2 is limited by hopping transport mechanism, whereas the electron in bilayer can be excited to band-like transport mode due to the immunity of the influence from the charge traps at substrate, which explain the enhancement of mobility and MIT phenomena. This study is universally valid for other two dimensional (2D) materials, paving a way to fabricate high performance nano-electronics for integrated circuits.
关键词： CVD,MoS2,multilayer,metal-to-insulator transition,FET
更新于2025-09-19 17:13:59
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Application of mosaicity induced disorder controlled rare earth nickelate thin films as THz transmission modulator
摘要： Here, we have studied mosaicity induced disorder (a unique type of disorder which is transferred from substrate template to film) controlled properties of rare earth nickelate thin films. While highly oriented film exhibits sharp metal to insulator transition (MIT) and Drude type of terahertz (THz) conductivity behavior, mosaic film exhibit much more subtle and broad transition and Drude-Smith type THz conductivity behavior. On the basis of such contrasting behavior, we propose application of these films as thermally controlled THz transmission modulator: oriented film as digital modulator while mosaic film as analog modulator.
关键词： metal to insulator transition,Drude-Smith model,rare earth nickelate,THz transmission modulator,mosaicity induced disorder
更新于2025-09-16 10:30:52