Abstract
Two-dimensional (2D) van der Waals ferroelectrics provide an unprecedented architectural freedom for the creation of artificial multiferroics and nonvolatile electronic devices based on vertical and coplanar heterojunctions of 2D ferroic materials. Nevertheless, controlled microscopic manipulation of ferroelectric domains is still rare in monolayer-thick 2D ferroelectrics with in-plane polarization. Here we report the discovery of robust ferroelectricity with a critical temperature close to 400 K in SnSe monolayer plates grown on graphene and the demonstration of controlled room-temperature ferroelectric domain manipulation by applying appropriate bias voltage pulses to the tip of a scanning tunneling microscope (STM). This study shows that STM is a powerful tool for detecting and manipulating the microscopic domain structures in 2D ferroelectric monolayers, which are difficult for conventional approaches such as piezoresponse force microscopy, thus facilitating the hunt for other 2D ferroelectric monolayers with in-plane polarization with important technological applications.
Highlights
Two-dimensional (2D) van der Waals ferroelectrics provide an unprecedented architectural freedom for the creation of artificial multiferroics and nonvolatile electronic devices based on vertical and coplanar heterojunctions of 2D ferroic materials
Microscopic imaging and controlled manipulation of the outof-plane polarization in 2D ferroelectric materials via piezoresponse force microscopy (PFM) have been demonstrated in MoTe2 MLs,[2] freestanding perovskite thin films,[22] as well as several-layer thick van der Waals ferroelectrics.[5,11,13,15−17] PFM studies of in-plane ferroelectricity have been reported in several nanometer thick layered materials,[13−15,18−20] to the best of our knowledge none of the current PFM studies of inplane polarized ferroelectrics has reached the thickness limit of a single van der Waals ML
Since scanning tunneling microscope (STM) is extremely sensitive to the surface electronic structures of atomically flat samples, in-plane polarization can be detected through measuring the electronic band bending induced by the bound charges at the edges and ferroelectric domain walls of the films
Summary
K.C. and J.-R.J. prepared the samples and performed the VT-STM experiments. F.K. and P.S. conducted the LT-STM experiments. B.J.M. and S.B.-L. carried out the ab initio calculations. J.-L.Z. performed the numerical simulations of electric fields. K.C., P.S., S.B.-L., and S.S.P.P. wrote the manuscript. All coauthors read and commented on the manuscript. Notes The authors declare no competing financial interest
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