Recipe for valuable chemical improved
Study details why 2D molybdenum disulfide formation gets a speed boost
from salt

Date:
April 18, 2022
Source:
Rice University
Summary:
Theorists show why salt gives a significant speed boost to valuable
2D molybdenum disulfide, an effect they say may work for other 2D
materials as well.



FULL STORY ========================================================================== Skipping ahead in a line is rude, but sometimes it's
acceptable. Especially for salt. The Rice University lab of materials
theorist Boris Yakobson shows why in its follow-up to a 2018 study that demonstrated how salt simplifies the formation of valuable 2D molybdenum disulfide (MoS2) with a first-principles analysis of the process that
could refine it even further.


==========================================================================
The theoretical study by Yakobson and colleagues Jincheng Lei, Yu Xie
and Alex Kutana, all alumni of his lab, and researcher Ksenia Bets shows through the simulation of atom-level energies why salt -- particularly
iodized salt - - lowers the reaction temperature in a chemical vapor
deposition (CVD) furnace necessary to form MoS2.

It does so by helping to skip some steps and leap high energy barriers
in conventional CVD growth to yield far more MoS6, an essential precursor
to 2D MoS2.

Their study in the Journal of the American Chemical Societyfocused on
how salt lowers activation barriers to enhance the sulfurization of
molybdenum oxyhalides, the gas feedstock in MoS2 crystallization.

MoS2 is a natural compound known in bulk form as molybdenite, and in
2D form is highly coveted for its semiconducting properties, which
promise advances in electronic, optoelectronic, spintronic, catalytic
and medical applications. But 2D MoS2 remains hard to manufacture in
commercial quantities.

The Rice team first entered the fray when labs in Singapore, China, Japan
and Taiwan used salt to make a "library" of 2D materials that combined transition metals and chalcogens. Why it worked so well was a mystery, prompting them to call upon the Yakobson lab's expertise in modeling
materials -- even only theoretical ones -- from the ground up.



========================================================================== Their comprehensive models show that while the international labs used
chloride salts to make their library of materials, the iodide salts
commonly found on kitchen tables are better at speeding up the synthesis
of MoS2.

"Fast and large-scale synthesis is imperative for the widespread
application of MoS2," Lei said. "We carefully studied the entire growth process, hoping to optimize it as much as possible. It turned out that
by simply changing chloride to iodide, one could synthesize MoS2 much
faster while at even lower growth temperatures." This happens when salt
and the precursor form a eutectic, a mixture of substances that melt and solidify at a single temperature that's lower than the melting points
of the constituents.

"After salt-assisted synthesis was shown to enable the growth of many
more TMD (transition metal dichalcogenide) compounds than was possible beforehand and significantly improved growth conditions for previously synthesized ones, it became clear that there is something special about
this process," Bets said.

"Some experimental groups attempted to investigate further, but monitoring
the molecular composition of the gas phase under growth conditions is not
a simple task," she said. "Even then, you cannot see the whole picture.



==========================================================================
"We were very thorough, following up on Jincheng's work on the mechanism
of conventional MoS2 growth. We simulated all parts of the process,
from sulfurization to the 2D crystal growth. This comprehensive approach
paid off." In simulations, the Rice team directly observed the entire sulfurization process as oxygen and chlorine atoms were gradually replaced
by sulfur in MoO2Cl2, a common precursor, under CVD conditions.

The lab said the eutectic effect may be a common phenomenon in the CVD synthesis of 2D dichalcogenide monolayers, and thus worth continued study.

Lei is now a postdoctoral researcher at Yale University. Xie is now a
professor at Xi'an University, China. Kutana is an assistant professor at Nagoya University, Japan. Yakobson is the Karl F. Hasselmann Professor
of Engineering and a professor of materials science and nanoengineering
and of chemistry.

The Department of Energy, Basic Energy Sciences (DE-SC0012547) and the
Welch Foundation (C-1590) supported the research.


========================================================================== Story Source: Materials provided by Rice_University. Original written
by Mike Williams. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jincheng Lei, Yu Xie, Alex Kutana, Ksenia V. Bets, Boris
I. Yakobson.

Salt-Assisted MoS2 Growth: Molecular Mechanisms from the First
Principles. Journal of the American Chemical Society, 2022; DOI:
10.1021/ jacs.2c02497 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220418120409.htm

--- up 7 weeks, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)