I was doing crystal synthesis of MoSe2 via chemical vapour transport. And after a 12 hr period, I got thin flakes of MoSe2. But on closer examination, I found clump like deposits, which were found to be of selenium, from EDS measurements.
Excess Selenium, from what I read was the usual thing to get which can be removed by drying under vacuum.
The interesting part was that they were arranged in patterns of ripples, leaf-like ripples and floral patterns. as depicted in the attached images.
Can someone explain what causes these patterns?
Dear Gokul, thank you for your very interesting tecchnical question and for sharing these pretty unusual findings. Apparently such ripple-like patterns on crystal surfaces have already been reported for closely related transition metal dichalcogenode materials like MoS2, MoSe2 and WSe2. For relevant references about this rather strange phenomenon please have a look at the following potentially useful articles:
Ripples and Layers in Ultrathin MoS2 Membranes
Article Ripples and Layers in Ultrathin MoS2 Membranes
Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain
Article Coherent, atomically thin transition-metal dichalcogenide su...
and
Emergence of highly linearly polarized interlayer exciton emission in MoSe2/WSe2 heterobilayers with transfer-induced layer corrugation
https://arxiv.org/pdf/2004.05624.pdf
The second article is freely available as public full text on RG. Please find attached the pdf file of the third paper. I hope this helps.
Good luck with your research and best wishes, Frank Edelmann
Dear Gokul Krishna ,
in addition to the papers mentioned by Frank T. Edelmann please see
Article Ripple pattern formation on silicon surfaces by low-energy i...
in the case of Si during ion-beam erosion.
Thank you for the rocommeneded papers Frank T. Edelmann & Gerhard Martens .
But in these papers, the ripples were of the material itself, were pretty ordered, small and there were no flower-like patterns.
In my case, the material is of MOSe2 and the ripples are of Se. The distribution is random and there are flower-like, leaf-like and small expanding wavelike patterns.
And many crystals flakes are totally devoid of them too.
and these are a few microns wide.
Dear Vadim S. Gorshkov
, my purpose was simply to synthesise Single crystals and exfoliate them to work on the thin films.The transport agent has selenium in it, and you are right the composition was Mo : Se : : 35 : 65, it is a bit to the Mo side. But the precursor microcrystals also showed the same compositions.
It is the physical problem then which is disturbing me, why are the patterns forming when they could just all deposit as a layer(there were layer depositions too since when I did the EDS measurement with low potential, Se concentration on the surface was higher implying the presence of a layer.)
And specifically why the floral and the leaf-like patterns? What conditions cause them to deposit like this? Are the questions whose answers I am seeking.
Dear Gokul Krishna please allow me one personal remark. The ripple-like patterns on your MoSe2 crystals are a really interesting finding. I'm wondering if it's a good idea to present the pictures in public prior to publication. At some stage you want to publish your results, so you should perhaps better discuss this matter with your supervisor and do a careful literature search yourself.
With very best wishes, Frank Edelmann
In addition to the responses already given, also take a look at https://pubs.acs.org/doi/10.1021/nn503287m
Hello Krishna,
Kindly look at this paper.
https://core.ac.uk/download/pdf/38913809.pdf
The pattern may be caused by nodes in oscillations of the fluid in the vessel. In that case, the pattern shape (streaks or flowers) must depend on the shape of the vessel (rectangular or round).
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