Ravindra Kumar Jha; Raghubeer Singh; Debasree Burman; Sumita Santra; Prasanta Kumar Guha
Volume 1, Issue 2 , 2016, , Pages 125-130
Abstract
We report herein exfoliation of WS2, which is one of the most promising but less investigated among 2D TMDs in binary mixture of diethyl ether (with boiling point=34.6°C) and water. The bulk WS2 powder was first ball milled in toluene for few minutes and at low rpm. Subsequently the powder was kept ...
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We report herein exfoliation of WS2, which is one of the most promising but less investigated among 2D TMDs in binary mixture of diethyl ether (with boiling point=34.6°C) and water. The bulk WS2 powder was first ball milled in toluene for few minutes and at low rpm. Subsequently the powder was kept at 4°C for 20 hours in binary mixture of diethyl ether and water with their volume fraction varying from 10% to 90%, before taking for the ultrasonication. It should be noted that neither diethyl ether nor water is capable of disperse WS2 alone. Ultrasonic waves generate cavitation bubbles that collapse into high-energy jets, breaking up the layered crystallites and producing exfoliated nanoflakes. Hansen Solubility Parameters (HSP) for the binary mixture has been calculated and the mixture which minimizes the Hansen distance has been selected for further characterization of few layered nature of thin sheets. Field emission scanning electron microscopy (FESEM) has been utilized to monitor the progress in exfoliation at different stages. Atomic force microscopy (AFM) confirms the formation of <8nm thin sheets with lateral dimension of few hundred nm. Raman spectroscopy has been utilized for further confirmation. Transmission electron microscopy (TEM) has been utilized to show the crystallinity of nanosheets which agrees with the X-ray diffraction results. Ultra-violet-visible (UV-Vis) and Fourier transform infrared (FTIR) have been used as spectroscopy tools throughout the work. This exfoliation technique is unique in the sense of producing pristine nanosheets due to the involvement of very low boiling point solvents.
Debasree Burman; Ravindra Kumar Jha; Sumita Santra; Prasanta Kumar Guha
Abstract
In our paper, few layered MoS2 nanoflakes were exfoliated from the bulk powder in mixed solvent using a simple sonication assisted liquid exfoliation technique at room temperature. The successful exfoliation of the nanoflakes was characterized using various characterization tools like Scanning Electron ...
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In our paper, few layered MoS2 nanoflakes were exfoliated from the bulk powder in mixed solvent using a simple sonication assisted liquid exfoliation technique at room temperature. The successful exfoliation of the nanoflakes was characterized using various characterization tools like Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), and Atomic Force Microscopy (AFM). The humidity sensor was fabricated by drop-casting MoS2 nanoflakes on Pt-based Interdigitated Electrodes (IDEs). The sensing was carried out in an in-house gas test setup interfaced with a Semiconductor Parameter Analyzer (SPA) to record the measurements. The response of the sensor was studied by passing different levels of humidity through the gas chamber. The response was found to increase with increase in humidity level and was better than few recently reported results. The maximum response was found to be ~16 times at 75% RH. Since water is an electron donor and MoS2 is inherently n-type semiconductor, the conductivity of the MoS2 sensing layer increased in presence of humidity. The large surface to volume ratio and presence of inherent defects facilitated the adsorption and desorption of a large number of H2O molecules. The response time and recovery time of the sensor was 65 seconds and 72 seconds respectively. Thus we conclude that our MoS2 based humidity sensor with a maximum response of 16 times (75% RH) can act as a low power, highly sensitive and fast humidity sensor in various applications like indoor air quality monitoring, agriculture, semiconductor industry etc.
