NGI uses twist to engineer 2D semiconductors with built-in memory
functions

Date:
March 3, 2022
Source:
University of Manchester
Summary:
A team of researchers has demonstrated that slightly twisted 2D
transition metal dichalcogenides (TMDs) display room-temperature
ferroelectricity.



FULL STORY ==========================================================================
A team of researchers at The University of Manchester's National
Graphene Institute (NGI) and the National Physical Laboratory (NPL) has demonstrated that slightly twisted 2D transition metal dichalcogenides
(TMDs) display room- temperature ferroelectricity.


==========================================================================
This characteristic, combined with TMDs' outstanding optical properties,
can be used to build multi-functional optoelectronic devices such
as transistors and LEDs with built-in memory functions on nanometre
length scale.

Ferroelectrics are materials with two or more electrically polarisable
states that can be reversibly switched with the application of an external electric field. This material property is ideal for applications such as non-volatile memory, microwave devices, sensors and transistors. Until recently, out-of- plane switchable ferroelectricity at room temperature
had been achieved only in films thicker than 3 nanometres.

2D heterostructures Since the isolation of graphene in 2004, researchers
across academia have studied a variety of new 2D materials with a wide
range of exciting properties.

These atomically thin 2D crystals can be stacked on top of one another to create so-called heterostructures -- artificial materials with tailored functions.

More recently, a team of researchers from NGI, in collaboration with NPL, demonstrated that below a twist angle of 2o, atomic lattices physically reconstruct to form regions (or domains) of perfectly stacked bilayers separated by boundaries of locally accumulated strain. For two monolayers stacked parallel to each other, a tessellated pattern of mirror-reflected triangular domains is created. Most importantly, the two neighbouring
domains have an asymmetric crystal symmetry, causing an asymmetry in
their electronic properties.



========================================================================== Ferroelectric switching at room temperature In the work, published in
Nature Nanotechnology,the team demonstrated that the domain structure
created with low-angle twisting hosts interfacial ferroelectricity in
bilayer TMDs. Kelvin probe force microscopy revealed that neighbouring
domains are oppositely polarised and electrical transport measurements demonstrated reliable ferroelectric switching at room temperature.

The team went on to develop a scanning electron microscope (SEM) technique
with enhanced contrast, using signal from back-scattered electrons. This
made it possible to apply an electric field in-situwhile imaging changes
to the domain structure in a non-invasive manner, providing essential information on how the domain switching mechanism works. The boundaries separating the oppositely polarised domains were found to expand and
contract depending on the sign of the applied electric field and led to
a significant redistribution of the polarised states.

This work clearly demonstrates that the twist degree of freedom can
allow the creation of atomically thin optoelectronics with tailored and multi-functional properties.

Wide scope for tailored 2D materials Lead author Astrid Weston (pictured
right) said: "It's very exciting that we can demonstrate that this simple
tool of twisting can engineer new properties in 2D crystals. With the
wide variety of 2D crystals to choose from, it provides us with almost unlimited scope to create perfectly tailored artificial materials."
Co-author Dr Eli G Castanon added: "Being able to observe the pattern and behaviour of ferroelectric domains in structures that have nanometre
thickness with KPFM and SEM was very exciting. The advancement of characterisation techniques together with the extensive possibilities
for the formation of novel heterostructures of 2D materials paves the
way to achieve new capabilities at the nanoscale for many industries." ========================================================================== Story Source: Materials provided by University_of_Manchester. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* 2D_semiconductors ========================================================================== Journal Reference:
1. Astrid Weston, Eli G. Castanon, Vladimir Enaldiev, Fa'bio Ferreira,
Shubhadeep Bhattacharjee, Shuigang Xu, He'ctor Corte-Leo'n, Zefei
Wu, Nicholas Clark, Alex Summerfield, Teruo Hashimoto, Yunze
Gao, Wendong Wang, Matthew Hamer, Harriet Read, Laura Fumagalli,
Andrey V. Kretinin, Sarah J. Haigh, Olga Kazakova, A. K. Geim,
Vladimir I. Fal'ko, Roman Gorbachev. Interfacial ferroelectricity
in marginally twisted 2D semiconductors. Nature Nanotechnology,
2022; DOI: 10.1038/s41565-022- 01072-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220303102757.htm

--- up 3 days, 10 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)