1. Novel Characterization Technique for 2D materials: LEEM/μLEED-IV Zhongwei Dai,1 Maxwell Grady,1 Wencan Jin,2 Jerry I. Dadap,2 Richard M. Osgood, Jr.,2 Jerzy T. Sadowski,3 Karsten Pohl1 (advisor) 1University of New Hampshire, Department of Physics and Materials Science Program; 2Columbia University; 3Brookhaven National Lab, Upton, NY
Motivations
Why 2D Materials?
Simulation and Results
Investigating atomic structure of emerging 2D materials:
Study of surface relaxation of bulk MoS2 and atomic structure of suspended single layer MoS2
Determination of surface termination element of MBE grown toplogical insulator SnSe thin film and its surface structure
Determination of surface buckling of black phosphorus, a newly discoverd 2D material
Mechanically strong.
High carrier mobility.
Applications in photovoltaic, modern electronics and photocatalysts.
IV spectra calculation and optimization
Bulk MoS2 and Monolayer MoS2
Low energy e- (5-200eV)
A proposed bilayer BP and MoS2 thin film heterostructure flexble solar-cell is predicted to have a power conversion efficiency as high as 18%.
Scattering of the electrons by a single atom is calculated first
Then the atoms are arranged to form an atomic layer for which layer
diffraction matrices are computed
Methods
LEEM (Low Energy Electron Microscopy) imaging
An image at E = 17 eV. FOV = 30 m.
Sample: Multi-layers MoS2 flakes
Aberraion -corrected LEEM system
The electron multiple scattering IV calculations are based on the muffin-tin model of the crystal potential [5]
Black Phosphorus Surface buckling
The detailed surface atomic structure was determined for the first time experimentally. Surface buckling on BP was found to be around 0.2 Å.
Layers are stacked to a crystal to yield
the total reflection matrix of the surface
SnSe: a novel toplogical insulator
Single-layer MoS2 transistor
μLEED pattern at selected area E=95 eV
log (R)
db (Å)
Surface structure of newly MBE grown SnSe thin film was characterzied to be Sn-terminated with oscillatory surface relaxation
Electronic structure was measrured using ARPES. The observed Dirac surface state is shown to yield a high Fermi velocity which potentially may lead to high-speed electronic devices and spintronic applications.
d12 (Å)
Local μLEED-IV Extraction
LEEM
μLEED
LEEM: real-space, in situ, direct imaging
Spatial resolution: ~ 2 nm
Field of view: 1 ~ 30 m
Low beam energy: 5 ~ 150 eV
Conclusions
Investigated the surface of bulk MoS2 and suspended monolayer MoS2 .
Determined the surface termincation of newly grown TCI SnSe to be Sn-terminated and has an oscillatory surface relaxation.
Surface buckling of BP was determined to be 0.2 Å, which is much bigger than previsously reported value.
Acknowledgement
References
Young Duck Kim, James Hone (Columbia University, USA)
Suresh Vishwanath, Huili Grace Xing (Cornell University, USA)
This work is supported by grants from the National Science Foundation, # EPS , to the NH EPSCoR program, and # DMR
[1] Jun Dai and Xiao Cheng Zeng, J. Phys. Chem. Lett. 5, 1289 (2014)
[2] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti and A. Kis, Nature Nanotechnol. 6, 147 (2011);
[3] R.M. Tromp and J.B.Hannon et. al., Ultramicroscopy 110, 852 (2010)
26th October, 2016