Electrochemical control and layered semimetals
The unique layer-stacking in two-dimensional (2D) van der Waals materials facilitates the formation of nearly degenerate phases of matter, and opens novel routes for the design of low-power, reconfigurable functional materials.
Electrochemical ion intercalation between stacked layers offers a promising approach to stabilise bulk metastable phases and to explore the effects of extreme carrier doping and strain - however, in situ characterisation methods to study the structural evolution and dynamical functional properties of these intercalated materials remains limited.
In the paper 'Electrochemical control of the ultrafast lattice response of a layered semimetal' published in Advanced Science, the authors (who include Dr Andrey D Poletayev of this department) present a novel experimental platform capable of simultaneously performing electrochemical lithium-ion intercalation and multimodal ultrafast characterisation of the lattice using both electron diffraction and nonlinear optical techniques.
Using the layered semimetal WTe2 as a model system, the interlayer shear phonon mode that modulates stacking between 2Dlayers is probed, showing that small amounts of lithiation enhance the amplitude and lifetime of the phonon, contrary to expectations. This resulted from the dynamically fluctuating and anharmonic structure between nearly degenerate phases at room temperature which could be stabilised by electronic carriers accompanying the inserted lithium ions. At high lithiation, the Td' structure emerged and quenched the phonon response.
The authors conclude that this work defines new approaches for using electrochemistry to engineer the dynamic structure of 2D materials.
