Stacking-dependent exciton multiplicity in WSe2 bilayers

Abstract Twisted layers of atomically thin two-dimensional materials realize a broad range of novel quantum materials with engineered optical and transport phenomena arising from spin and valley degrees of freedom and strong electron correlations in hybridized interlayer bands. Here, we report experimental and theoretical studies of WSe2 homobilayers obtained in two stable configurations of 2H (60° twist) and 3R (0° twist) stackings by controlled chemical vapor synthesis of high-quality large-area crystals. Using optical absorption and photoluminescence spectroscopy at cryogenic temperatures, we uncover marked differences in the optical characteristics of 2H and 3R bilayer WSe2 which we explain on the basis of beyond-DFT theoretical calculations. Our results highlight the role of layer stacking for the spectral multiplicity of momentum-direct intralayer exciton transitions in absorption, and relate the multiplicity of phonon sidebands in the photoluminescence to momentum-indirect excitons with different spin valley and layer character. Our comprehensive study generalizes to other layered homobilayer and heterobilayer semiconductor systems and highlights the role of crystal symmetry and stacking for interlayer hybrid states.

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Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe2

Nature Communications ◽

10.1038/ncomms10847 ◽

2016 ◽

Vol 7 (1) ◽

Cited By ~ 68

Author(s):

Pranab Kumar Das ◽

D. Di Sante ◽

I. Vobornik ◽

J. Fujii ◽

T. Okuda ◽

...

Keyword(s):

Degrees Of Freedom ◽

Transition Metal Dichalcogenides ◽

Photoemission Spectroscopy ◽

Two Dimensional ◽

Quantum Phenomenon ◽

Two Dimensional Materials ◽

Metal Dichalcogenides ◽

Electron And Hole States ◽

Dependent Behaviour

Abstract The behaviour of electrons and holes in a crystal lattice is a fundamental quantum phenomenon, accounting for a rich variety of material properties. Boosted by the remarkable electronic and physical properties of two-dimensional materials such as graphene and topological insulators, transition metal dichalcogenides have recently received renewed attention. In this context, the anomalous bulk properties of semimetallic WTe2 have attracted considerable interest. Here we report angle- and spin-resolved photoemission spectroscopy of WTe2 single crystals, through which we disentangle the role of W and Te atoms in the formation of the band structure and identify the interplay of charge, spin and orbital degrees of freedom. Supported by first-principles calculations and high-resolution surface topography, we reveal the existence of a layer-dependent behaviour. The balance of electron and hole states is found only when considering at least three Te–W–Te layers, showing that the behaviour of WTe2 is not strictly two dimensional.

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Large Area Position Sensitive Detector Based on Amorphous Silicon Technology

MRS Proceedings ◽

10.1557/proc-297-981 ◽

1993 ◽

Vol 297 ◽

Cited By ~ 20

Author(s):

E. Fortunato ◽

M. Vieira ◽

L. Ferreira ◽

C.N. Carvalho ◽

G. Lavareda ◽

...

Keyword(s):

Amorphous Silicon ◽

Chemical Vapor ◽

Position Sensitive Detector ◽

Back Side ◽

Sensitive Detector ◽

Metal Contacts ◽

Key Factors ◽

Large Area ◽

Position Sensitive

We have developed a rectangular dual-axis large area Position Sensitive Detector (PSD), with 5 cm × 5 cm detection area, based on PIN hydrogenated amorphous silicon (a-Si:H) technology, produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). The metal contacts are located in the four edges of the detected area, two of them located on the back side of the ITO/PIN/A1 structure and the others two located in the front side. The key factors of the detectors resolution and linearity are the thickness uniformity of the different layers, the geometry and the contacts location. Besides that, edge effects on the sensor's corner disturb the linearity of the detector. In this paper we present results concerning the linearity of the detector as well as its optoelectronic characteristics and the role of the i-layer thickness on the final sensor performances.

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Controlled Island Formation of Large-Area Graphene Sheets by Atmospheric Chemical Vapor Deposition: Role of Natural Camphor

ACS Omega ◽

10.1021/acsomega.9b00051 ◽

2019 ◽

Vol 4 (5) ◽

pp. 8758-8766 ◽

Cited By ~ 1

Author(s):

Harsh A. Chaliyawala ◽

Narasimman Rajaram ◽

Roma Patel ◽

Abhijit Ray ◽

Indrajit Mukhopadhyay

Keyword(s):

Chemical Vapor Deposition ◽

Vapor Deposition ◽

Chemical Vapor ◽

Graphene Sheets ◽

Large Area ◽

Island Formation

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On the Role of Local Many-Body Interactions on the Thermoelectric Properties of Fullerene Junctions

Entropy ◽

10.3390/e21080754 ◽

2019 ◽

Vol 21 (8) ◽

pp. 754

Author(s):

Carmine Antonio Perroni ◽

Vittorio Cataudella

Keyword(s):

Thermoelectric Properties ◽

Coulomb Blockade ◽

Degrees Of Freedom ◽

Chemical Potential ◽

Local Electron ◽

Strong Electron ◽

Adiabatic Approach ◽

Many Body Interactions ◽

Electron Interactions

The role of local electron–vibration and electron–electron interactions on the thermoelectric properties of molecular junctions is theoretically analyzed focusing on devices based on fullerene molecules. A self-consistent adiabatic approach is used in order to obtain a non-perturbative treatment of the electron coupling to low frequency vibrational modes, such as those of the molecule center of mass between metallic leads. The approach also incorporates the effects of strong electron–electron interactions between molecular degrees of freedom within the Coulomb blockade regime. The analysis is based on a one-level model which takes into account the relevant transport level of fullerene and its alignment to the chemical potential of the leads. We demonstrate that only the combined effect of local electron–vibration and electron–electron interactions is able to predict the correct behavior of both the charge conductance and the Seebeck coefficient in very good agreement with available experimental data.

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Moiré excitons in MoSe2-WSe2 heterobilayers and heterotrilayers

Nature Communications ◽

10.1038/s41467-021-21822-z ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Michael Förg ◽

Anvar S. Baimuratov ◽

Stanislav Yu. Kruchinin ◽

Ilia A. Vovk ◽

Johannes Scherzer ◽

...

Keyword(s):

Transition Metal ◽

Van Der Waals ◽

Transition Metal Dichalcogenides ◽

Transition Metal Dichalcogenide ◽

Hybrid Layer ◽

Layered Semiconductor ◽

Two Dimensional Materials ◽

Metal Dichalcogenides ◽

Experimental And Theoretical Studies

AbstractLayered two-dimensional materials exhibit rich transport and optical phenomena in twisted or lattice-incommensurate heterostructures with spatial variations of interlayer hybridization arising from moiré interference effects. Here, we report experimental and theoretical studies of excitons in twisted heterobilayers and heterotrilayers of transition metal dichalcogenides. Using MoSe2-WSe2 stacks as representative realizations of twisted van der Waals bilayer and trilayer heterostructures, we observe contrasting optical signatures and interpret them in the theoretical framework of interlayer moiré excitons in different spin and valley configurations. We conclude that the photoluminescence of MoSe2-WSe2 heterobilayer is consistent with joint contributions from radiatively decaying valley-direct interlayer excitons and phonon-assisted emission from momentum-indirect reservoirs that reside in spatially distinct regions of moiré supercells, whereas the heterotrilayer emission is entirely due to momentum-dark interlayer excitons of hybrid-layer valleys. Our results highlight the profound role of interlayer hybridization for transition metal dichalcogenide heterostacks and other realizations of multi-layered semiconductor van der Waals heterostructures.

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Strong exciton-photon coupling in large area MoSe2 and WSe2 heterostructures fabricated from two-dimensional materials grown by chemical vapor deposition

2D Materials ◽

10.1088/2053-1583/abc5a1 ◽

2020 ◽

Vol 8 (1) ◽

pp. 011002

Author(s):

Daniel J Gillard ◽

Armando Genco ◽

Seongjoon Ahn ◽

Thomas P Lyons ◽

Kyung Yeol Ma ◽

...

Keyword(s):

Chemical Vapor Deposition ◽

Vapor Deposition ◽

Chemical Vapor ◽

Two Dimensional ◽

Large Area ◽

Two Dimensional Materials ◽

Photon Coupling

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Synthesis of layered vs planar Mo2C: role of Mo diffusion

2D Materials ◽

10.1088/2053-1583/ac43fa ◽

2021 ◽

Author(s):

Muhammad Arslan Shehzad ◽

Paul C. Masih Das ◽

Alexander C. Tyner ◽

Matthew Cheng ◽

Yea-Shine Lee ◽

...

Keyword(s):

Density Functional ◽

Chemical Vapor ◽

Vital Role ◽

Large Area ◽

Functional Theory ◽

Precise Control ◽

Metal Diffusion ◽

Diffusion Limited ◽

Cvd Growth

Abstract Chemical Vapor Deposition (CVD) growth of Metal Carbides is of great interest as this method provides large area growth of MXenes. This growth is mainly done using a melted diffusion-based process; however, different morphologies in growth process is not well understood. In this work, we report deterministic synthesis of layered (non-uniform c-axis growth) and planar (uniform c-axis growth) of Molybdenum Carbide (Mo2C) using a diffusion-mediated growth. Mo-diffusion limited growth mechanism is proposed where the competition between Mo and C adatoms determines the morphology of grown crystals. Difference in thickness of catalyst at the edge and center lead to enhanced Mo diffusion which plays a vital role in determining the structure of Mo2C. The layered structures exhibit an expansion in the lattice confirmed by the presence of strain. Density Functional Theory (DFT) shows consistent presence of strain which is dependent upon Mo diffusion during growth. This work demonstrates the importance of precise control of diffusion through the catalyst in determining the structure of Mo2C and contributes to broader understanding of metal diffusion in growth of MXenes.

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Large-area niobium disulfide thin films as transparent electrodes for devices based on two-dimensional materials

Nanoscale ◽

10.1039/c7nr07593f ◽

2018 ◽

Vol 10 (3) ◽

pp. 1056-1062 ◽

Cited By ~ 22

Author(s):

Hunyoung Bark ◽

Yongsuk Choi ◽

Jaehyuck Jung ◽

Jung Hwa Kim ◽

Hyukjoon Kwon ◽

...

Keyword(s):

Thin Films ◽

Vapor Deposition ◽

Chemical Vapor ◽

Chemical Vapor Deposition Method ◽

Two Dimensional ◽

Deposition Method ◽

Transparent Electrodes ◽

Large Area ◽

Two Dimensional Materials ◽

Niobium Disulfide

Large-area NbS2 films have been synthesized by using the chemical vapor deposition method and exhibited their potential as transparent electrodes for 2D semiconductor devices.

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