scholarly journals Optical versus electron diffraction imaging of Twist-angle in 2D transition metal dichalcogenide bilayers

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
S. Psilodimitrakopoulos ◽  
A. Orekhov ◽  
L. Mouchliadis ◽  
D. Jannis ◽  
G. M. Maragkakis ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Transition Metal ◽  
Second Harmonic ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Transition Metal Dichalcogenide ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Diffraction Imaging ◽  
Pixel Mapping

AbstractAtomically thin two-dimensional (2D) materials can be vertically stacked with van der Waals bonds, which enable interlayer coupling. In the particular case of transition metal dichalcogenide (TMD) bilayers, the relative direction between the two monolayers, coined as twist-angle, modifies the crystal symmetry and creates a superlattice with exciting properties. Here, we demonstrate an all-optical method for pixel-by-pixel mapping of the twist-angle with a resolution of 0.55(°), via polarization-resolved second harmonic generation (P-SHG) microscopy and we compare it with four-dimensional scanning transmission electron microscopy (4D STEM). It is found that the twist-angle imaging of WS2 bilayers, using the P-SHG technique is in excellent agreement with that obtained using electron diffraction. The main advantages of the optical approach are that the characterization is performed on the same substrate that the device is created on and that it is three orders of magnitude faster than the 4D STEM. We envisage that the optical P-SHG imaging could become the gold standard for the quality examination of TMD superlattice-based devices.

D-STEM: A Parallel Electron Diffraction Technique Applied to Nanomaterials

2010 ◽  
Vol 16 (5) ◽  
pp. 614-621 ◽  
Author(s):  
K.J. Ganesh ◽  
M. Kawasaki ◽  
J.P. Zhou ◽  
P.J. Ferreira
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
Dark Field ◽  
Transmission Electron ◽  
Electron Diffraction Technique ◽  
Scanning Transmission ◽  
Stem Image ◽  
Diffraction Imaging ◽  
Diffraction Patterns

AbstractAn electron diffraction technique called D-STEM has been developed in a transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM) instrument to obtain spot electron diffraction patterns from nanostructures, as small as ∼3 nm. The electron ray path achieved by configuring the pre- and postspecimen illumination lenses enables the formation of a 1–2 nm near-parallel probe, which is used to obtain bright-field/dark-field STEM images. Under these conditions, the beam can be controlled and accurately positioned on the STEM image, at the nanostructure of interest, while sharp spot diffraction patterns can be simultaneously recorded on the charge-coupled device camera. When integrated with softwares such as GatanTMSTEM diffraction imaging and Automated Crystallography for TEM or DigistarTM, NanoMEGAS, the D-STEM technique is very powerful for obtaining automated orientation and phase maps based on diffraction information acquired on a pixel by pixel basis. The versatility of the D-STEM technique is demonstrated by applying this technique to nanoparticles, nanowires, and nano interconnect structures.

Rocking Beam Microarea Diffraction Applied to Metallic thin Films

1976 ◽  
Vol 34 ◽  
pp. 396-397
Author(s):  
R. H. Geiss
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Small Area ◽  
Objective Lens ◽  
Electron Optics ◽  
Metallic Thin Films ◽  
Transmission Electron Diffraction ◽  
Transmission Electron ◽  
Sample Height ◽  
Scanning Transmission

The theory and practical limitations of micro area scanning transmission electron diffraction (MASTED) will be presented. It has been demonstrated that MASTED patterns of metallic thin films from areas as small as 30 Åin diameter may be obtained with the standard STEM unit available for the Philips 301 TEM. The key to the successful application of MASTED to very small area diffraction is the proper use of the electron optics of the STEM unit. First the objective lens current must be adjusted such that the image of the C2 aperture is quasi-stationary under the action of the rocking beam (obtained with 40-80-160 SEM settings of the P301). Second, the sample must be elevated to coincide with the C2 aperture image and its image also be quasi-stationary. This sample height adjustment must be entirely mechanical after the objective lens current has been fixed in the first step.

scholarly journals Second-harmonic generation enhancement in monolayer transition-metal dichalcogenides by using an epsilon-near-zero substrate

2021 ◽  
Vol 3 (1) ◽  
pp. 272-278
Author(s):  
Pilar G. Vianna ◽  
Aline dos S. Almeida ◽  
Rodrigo M. Gerosa ◽  
Dario A. Bahamon ◽  
Christiano J. S. de Matos
Keyword(s):  
Dielectric Constant ◽  
Transition Metal ◽  
Harmonic Generation ◽  
Nonlinear Effect ◽  
Second Harmonic ◽  
2D Materials ◽  
Transition Metal Dichalcogenides ◽  
Transition Metal Dichalcogenide ◽  
Metal Dichalcogenides ◽  
Epsilon Near Zero

The scheme illustrates a monolayer transition-metal dichalcogenide on an epsilon-near-zero substrate. The substrate near-zero dielectric constant is used as the enhancement mechanism to maximize the SHG nonlinear effect on monolayer 2D materials.

Twist-Angle-Dependent Optoelectronics in a Few-Layer Transition-Metal Dichalcogenide Heterostructure

2018 ◽  
Vol 11 (2) ◽  
pp. 2470-2478 ◽  
Author(s):  
Woosuk Choi ◽  
Imtisal Akhtar ◽  
Malik Abdul Rehman ◽  
Minwook Kim ◽  
Dongwoon Kang ◽  
...  
Keyword(s):  
Transition Metal ◽  
Twist Angle ◽  
Transition Metal Dichalcogenide ◽  
Layer Transition

scholarly journals Serial protein crystallography in an electron microscope

2019 ◽  
Author(s):  
Robert Bücker ◽  
Pascal Hogan-Lamarre ◽  
Pedram Mehrabi ◽  
Eike C. Schulz ◽  
Lindsey A. Bultema ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Scanning Transmission Electron Microscope ◽  
Dose Fractionation ◽  
X Ray Crystallography ◽  
Minimal Sample ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Alternative Means ◽  
Occlusion Bodies

AbstractSerial X-ray crystallography at free-electron lasers allows to solve biomolecular structures from sub-micron-sized crystals. However, beam time at these facilities is scarce, and involved sample delivery techniques are required. On the other hand, rotation electron diffraction (MicroED) has shown great potential as an alternative means for protein nano-crystallography. Here, we present a method for serial electron diffraction of protein nanocrystals combining the benefits of both approaches. In a scanning transmission electron microscope, crystals randomly dispersed on a sample grid are automatically mapped, and a diffraction pattern at fixed orientation is recorded from each at a high acquisition rate. Dose fractionation ensures minimal radiation damage effects. We demonstrate the method by solving the structure of granulovirus occlusion bodies and lysozyme to resolutions of 1.55 Å and 1.80 Å, respectively. Our method promises to provide rapid structure determination for many classes of materials with minimal sample consumption, using readily available instrumentation.

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