scholarly journals The optical response of artificially twisted MoS$$_2$$ bilayers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Grzeszczyk ◽  
J. Szpakowski ◽  
A. O. Slobodeniuk ◽  
T. Kazimierczuk ◽  
M. Bhatnagar ◽  
...  
Keyword(s):  
Twist Angle ◽  
Interlayer Coupling ◽  
Layered Materials ◽  
Emission Lines ◽  
Effect Of Temperature ◽  
Energy Separation ◽  
Optical Study ◽  
Coupling Energy ◽  
Additional Degree ◽  
Indirect Emission

AbstractTwo-dimensional layered materials offer the possibility to create artificial vertically stacked structures possessing an additional degree of freedom—theinterlayertwist. We present a comprehensive optical study of artificially stacked bilayers (BLs) MoS$$_2$$ 2 encapsulated in hexagonal BN with interlayer twist angle ranging from 0$$^{\circ }$$ ∘ to 60$$^{\circ }$$ ∘ using Raman scattering and photoluminescence spectroscopies. It is found that the strength of the interlayer coupling in the studied BLs can be estimated using the energy dependence of indirect emission versus the A$$_\text {1g}$$ 1g –E$$_\text {2g}^1$$ 2g 1 energy separation. Due to the hybridization of electronic states in the valence band, the emission line related to the interlayer exciton is apparent in both the natural (2H) and artificial (62$$^\circ $$ ∘ ) MoS$$_2$$ 2 BLs, while it is absent in the structures with other twist angles. The interlayer coupling energy is estimated to be of about 50 meV. The effect of temperature on energies and intensities of the direct and indirect emission lines in MoS$$_2$$ 2 BLs is also quantified.

scholarly journals Numerical modeling of the effect of energy-separation in the ranque-hilsch tube

2020 ◽  
Vol 27 ◽  
pp. 00109
Author(s):  
Boris L. Ivanov ◽  
Bulat G. Ziganshin ◽  
Andrey V. Dmitriev ◽  
Maxim A. Lushnov ◽  
Manuel O. Binelo
Keyword(s):  
Gas Flow ◽  
Vortex Tube ◽  
Turbulence Models ◽  
Effect Of Temperature ◽  
Energy Separation ◽  
Hydrodynamic Characteristics ◽  
Two Phase ◽  
Cross Sectional ◽  
Model Calculations ◽  
Temperature Separation

Currently, there are a lot of applications of vortex technologies. The vortex effect is used in gasdynamic cold generators and vortex cooling chambers. Vortex devices are also used as dehumidifiers, separators, for cooling and heating hydraulic fluids, separating two-phase media, gas mixtures, evacuating, etc. Scientists study the applicability of vortex equipment for traditional and freeze-drying of agricultural products. However, the influence of geometric parameters of vortex devices on the productivity and energy efficiency of temperature separation of gas flows is poorly studied. Research aimed at finding opportunities and expanding the field of application of vortex tubes is an urgent task. The paper describes twodimensional and three-dimensional mathematical models of the swirling gas flow arising in a vortex tube. It presents results of its implementation in the Anсs-Fluent software package. Thermodynamic and hydrodynamic characteristics confirm the effect of temperature separation in a vortex tube. The dependences of temperature separation on the swirl angle and inlet pressure were obtained. For a two-dimensional vortex tube model, calculations were carried out using various turbulence models. The influence of the cross-sectional area at the hot gas flow outlet on temperature separation was studied.

scholarly journals Evolution of high-frequency Raman modes and their doping dependence in twisted bilayer MoS2

Nanoscale ◽  
2020 ◽  
Vol 12 (33) ◽  
pp. 17272-17280 ◽  
Author(s):  
Rahul Debnath ◽  
Indrajit Maity ◽  
Rabindra Biswas ◽  
Varun Raghunathan ◽  
Manish Jain ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Coupling Strength ◽  
First Principles ◽  
High Frequency ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Raman Modes ◽  
Systematic Evolution

Here, we demonstrate the systematic evolution of the interlayer coupling and electron-phonon coupling strength with twist angle in bilayer MoS2 using a combination of Raman spectroscopy and a combination of classical and first-principles based simulations.

DISORDER INDUCED COHERENCE-INCOHERENCE CROSSOVER IN RANDOM GaAs/AlGaAs SUPERLATTICES

2004 ◽  
Vol 18 (27n29) ◽  
pp. 3629-3632
Author(s):  
Y. A. PUSEP ◽  
M. B. RIBEIRO ◽  
H. ARAKAKI ◽  
C. A. DE SOUZA ◽  
S. MALZER ◽  
...  
Keyword(s):  
Fermi Energy ◽  
Interlayer Coupling ◽  
Diffusive Transport ◽  
Electron Systems ◽  
Disorder Strength ◽  
Coupling Energy ◽  
Vertical Coupling ◽  
Weakly Coupled ◽  
Breaking Time

The coherence of electrons was studied in intentionally disordered GaAs / AlGaAs superlattices as a function of the vertical interlayer coupling. Depending on the relation of the disorder energy and the Fermi energy the coherent and incoherent diffusive transport regimes were distinguished. New features of weakly coupled layered electron systems such as the vertical coupling energy and the in-plane phase-breaking time were observed by magnetoresistance measurements in the coherent and incoherent regimes respectively. Both of them were found to decrease with increasing disorder strength. This demonstrates the disorder induced break-down of the interlayer coherence of quasi-particles which drastically affected their intralayer coherence.

scholarly journals Multi-shaped strain soliton networks and moiré-potential-modulated band edge states in twisted bilayer SiC

RSC Advances ◽  
2021 ◽  
Vol 11 (39) ◽  
pp. 24366-24373
Author(s):  
Dawei Kang ◽  
Zheng-Wei Zuo ◽  
Zhaowu Wang ◽  
Weiwei Ju
Keyword(s):  
Twist Angle ◽  
Layered Materials ◽  
Degree Of Freedom ◽  
Band Edge ◽  
Two Dimensional ◽  
Edge States

Tuning the interlayer twist angle provides a new degree of freedom to exploit the potentially excellent properties of two dimensional layered materials.

scholarly journals Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene

Nano Research ◽  
2021 ◽  
Author(s):  
Eva A. A. Pogna ◽  
Xianchong Miao ◽  
Driele von Dreifus ◽  
Thonimar V. Alencar ◽  
Marcus V. O. Moutinho ◽  
...  
Keyword(s):  
Electronic Band Structure ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Relaxation Dynamics ◽  
Carrier Distribution ◽  
Absorption Bands ◽  
Electronic Band ◽  
Angle Dependence ◽  
Twisted Bilayer Graphene

AbstractVan der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle has opened new possibilities for tailoring the optoelectronic properties of these heterostructures. Twisted bilayer graphene with a strong interlayer coupling is a prototype of twisted heterostructure inheriting the intriguing electronic properties of graphene. Understanding the effects of the twist angle on its out-of-equilibrium optical properties is crucial for devising optoelectronic applications. With this aim, we here combine excitation-resolved hot photoluminescence with femtosecond transient absorption microscopy. The hot charge carrier distribution induced by photo-excitation results in peaked absorption bleaching and photo-induced absorption bands, both with pronounced twist angle dependence. Theoretical simulations of the electronic band structure and of the joint density of states enable to assign these bands to the blocking of interband transitions at the van Hove singularities and to photo-activated intersubband transitions. The tens of picoseconds relaxation dynamics of the observed bands is attributed to the angle-dependence of electron and phonon heat capacities of twisted bilayer graphene.

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.

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