In Situ Probing Molecular Intercalation in Two-DimensionalLayered Semiconductors
2019
The
electrochemical molecular intercalation of two-dimensional
layered materials (2DLMs) produces stable and highly tunable superlattices
between monolayer 2DLMs and self-assembled molecular layers. This
process allows unprecedented flexibility in integrating highly distinct
materials with atomic/molecular precision to produce a new generation
of organic/inorganic superlattices with tunable chemical, electronic,
and optical properties. To better understand the intercalation process,
we developed an on-chip platform based on MoS2 model devices
and used optical, electrochemical, and in situ electronic characterizations
to resolve the intermediate stages during the intercalation process
and monitor the evolution of the molecular superlattices. With sufficient
charge injection, the organic cetyltrimethylammonium bromide (CTAB)
intercalation induces the phase transition of MoS2 from
semiconducting 2H phase to semimetallic 1T phase, resulting in a dramatic
increase of electrical conductivity. Therefore, in situ monitoring
the evolution of the device conductance reveals the electrochemical
intercalation dynamics with an abrupt conductivity change, signifying
the onset of the molecule intercalation. In contrast, the intercalation
of tetraheptylammonium bromide (THAB), a branched molecule in a larger
size, resulting in a much smaller number of charges injected to avoid
the 2H to 1T phase transition. Our study demonstrates a powerful platform
for in situ monitoring the molecular intercalation of many 2DLMs (MoS2, WSe2, ReS2, PdSe2, TiS2, and graphene) and systematically probing electronic, optical,
and optoelectronic properties at the single-nanosheet level.
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