Effects of Mo vapor concentration on the morphology of vertically standing $MoS_{2}$ nanoflakes

Content Provider	Scilit
Author	Johari, Muhammad Hilmi Sirat, Mohamad Shukri Mohamed, Mohd Ambri Nasir, Siti Nur Farhana Mohd Teridi, Mohd Asri Mat Mohmad, Abdul Rahman
Copyright Year	2020
Description	Journal: Nanotechnology Vertically standing $MoS_{2}$ nanoflakes are favourable in applications such as energy storage devices, hydrogen evolution reactions, and gas sensors due to having large surface area and a high density of exposed edges. In this work, we report the effect of Mo vapor concentration on the morphology of vertical $MoS_{2}$ nanoflakes prepared by chemical vapor deposition at atmospheric pressure. A series of $MoS_{2}$ samples were grown under different Mo vapor concentrations by varying the separation distance (x) between the $MoO_{3}$ source and the substrate. Field emission scanning electron microscopy showed the sample grown at x =1 cm to have a high density of vertical flakes (7 vertical $flakes/µm^{2}$) with an average flake length of ~770 nm and thickness of ~10 nm. As x increased to 4 cm, average flake length reduced to ~150 nm while flake orientation changed from vertical to lateral. That is, high Mo vapor concentration favours the formation of large and vertical $MoS_{2}$ nanoflakes. However, oversupply of Mo vapor results in significantly thicker flakes. Raman spectra of all samples showed two main peaks at 380 and 407 $cm^{-1}$ that correspond to the $E^{1} _{2g}$ and $A_{1g}$ vibrational peaks of $MoS_{2}$. As x decreased from 4 to 1, the peak intensity ratio $(E^{1} _{2g}/A_{1g}$) reduced from 0.58 to 0.42, suggesting greater dominance of vertical flakes at low x. X-ray diffraction data showed a prominent peak at $14.4^{o}$, which corresponded to the (002) diffraction peak of 2H $MoS_{2}$. Transmission electron microscopy verified the flakes to consist of eight layers with an interlayer spacing of 0.62 nm. Based on hydrogen evolution reaction measurements, samples with thin flakes have high catalytic activity. This work highlights the importance of optimizing Mo vapor concentration to obtain a high density of thin, large, and vertically standing $MoS_{2}$ nanoflakes.
Related Links	https://iopscience.iop.org/article/10.1088/1361-6528/ab8666/pdf
ISSN	09574484
e-ISSN	13616528
DOI	10.1088/1361-6528/ab8666
Journal	Nanotechnology
Issue Number	30
Volume Number	31
Language	English
Publisher	IOP Publishing
Publisher Date	2020-04-03
Access Restriction	Open
Subject Keyword	Journal: Nanotechnology Chemical Vapor Deposition Transition Metal Dichalcogenides Vertical Nanoflakes
Content Type	Text
Resource Type	Article
Subject	Chemistry Nanoscience and Nanotechnology Mechanics of Materials Mechanical Engineering Bioengineering Electrical and Electronic Engineering