scholarly journals Dynamics of optical vortices in 2D materials

2022 ◽  
Author(s):  
Yaniv Kurman ◽  
Raphael Dahan ◽  
Hanan Herzig Sheinfux ◽  
Gilles Rosolen ◽  
Eli Janzen ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
Hexagonal Boron Nitride ◽  
2D Materials ◽  
Condensed Matter ◽  
Pair Creation ◽  
Optical Vortices ◽  
Free Electrons ◽  
2D Material ◽  
Transmission Electron ◽  
Planar Geometries

Abstract Optical vortices in planar geometries are a universal wave phenomenon, where electromagnetic waves possess topologically protected integer values of orbital angular momentum (OAM). The conservation of OAM governs their dynamics, including their rules of creation and annihilation. However, such dynamics remained so far beyond experimental reach. Here, we present a first observation of creation and annihilation of optical vortex pairs. The vortices conserve their combined OAM during pair creation/annihilation events and determine the field profile throughout their motion between these events. We utilize free electrons in an ultrafast transmission electron microscope to probe the vortices, which appear in the form of phonon polaritons in the 2D material hexagonal boron nitride. These results provide the first observation of optical vortices in any 2D material, which were predicted but never observed. Our findings promote future investigation of vortices in 2D materials and their use for chiral plasmonics, toward the control of selection rules in light-matter interactions and the creation of optical simulators of phase transitions in condensed matter physics.

scholarly journals Cherenkov radiation generated in hexagonal boron nitride using extremely low-energy electrons

Nanophotonics ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1491-1499
Author(s):  
Tuo Qu ◽  
Fang Liu ◽  
Yuechai Lin ◽  
Kaiyu Cui ◽  
Xue Feng ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Electromagnetic Waves ◽  
Cherenkov Radiation ◽  
Hexagonal Boron Nitride ◽  
Uniform Motion ◽  
Lattice Vibrations ◽  
Free Electrons ◽  
Low Energy Electrons ◽  
Anisotropic Lattice ◽  
New Research

AbstractCherenkov radiation (CR) is the electromagnetic shockwaves generated by the uniform motion of charged particles at a velocity exceeding the phase velocity of light in a given medium. In the Reststrahlen bands of hexagonal boron nitride (hBN), hyperbolic phonon polaritons (HPPs) are generated owing to the coupling between mid-infrared electromagnetic waves and strong anisotropic lattice vibrations. This study theoretically and numerically investigates the generation of volume CR based on HPPs in hBN with super-large wavevectors. Results reveal that CR can be generated using free electrons with an extremely low kinetic energy of 1 eV—two orders of magnitude lower than that reported in extant studies. The findings of this investigation provide new insights into significantly reducing the electron energy required for CR generation and potentially open new research avenues in the fields of CR and HPP.

scholarly journals Graphene and Other 2D Material Components Dynamic Characterization and Nanofabrication at Atomic Scale

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Wei Wang ◽  
Xing Wu ◽  
Jian Zhang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Recent Progress ◽  
2D Materials ◽  
Atomic Scale ◽  
Dynamic Characterization ◽  
Tem Analysis ◽  
2D Material ◽  
Analysis Techniques ◽  
Transmission Electron

We demonstrate how abreaction corrected transmission electron microscopy (TEM) analysis techniques that are commonly used in nanostructure characterization can be used to study the morphology of graphene and other 2D materials at atomic scale, even subangstrom scale, and evolution of nanostructure and from which we determine the graphene components nanofabrication process. The key contributions of this work are perhaps focused on two areas: (1) recent progress on graphene characterization from the TEM aspect and (2) how the electron beam can be used to fabricate nanoribbon from graphene or similar 2D material.

scholarly journals Spatiotemporal imaging of 2D polariton wave packet dynamics using free electrons

Science ◽  
2021 ◽  
Vol 372 (6547) ◽  
pp. 1181-1186
Author(s):  
Yaniv Kurman ◽  
Raphael Dahan ◽  
Hanan Herzig Sheinfux ◽  
Kangpeng Wang ◽  
Michael Yannai ◽  
...  
Keyword(s):  
Wave Packet ◽  
2D Materials ◽  
Wave Packets ◽  
Two Dimensional ◽  
Free Electrons ◽  
Polariton Wave ◽  
Wave Packet Dynamics ◽  
Transmission Electron ◽  
Optical Phenomena ◽  
Nonlinear Optical Phenomena

Coherent optical excitations in two-dimensional (2D) materials, 2D polaritons, can generate a plethora of optical phenomena that arise from the extraordinary dispersion relations that do not exist in regular materials. Probing of the dynamical phenomena of 2D polaritons requires simultaneous spatial and temporal imaging capabilities and could reveal unknown coherent optical phenomena in 2D materials. Here, we present a spatiotemporal measurement of 2D wave packet dynamics, from its formation to its decay, using an ultrafast transmission electron microscope driven by femtosecond midinfrared pulses. The ability to coherently excite phonon-polariton wave packets and probe their evolution in a nondestructive manner reveals intriguing dispersion-dependent dynamics that includes splitting of multibranch wave packets and, unexpectedly, wave packet deceleration and acceleration. Having access to the full spatiotemporal dynamics of 2D wave packets can be used to illuminate puzzles in topological polaritons and discover exotic nonlinear optical phenomena in 2D materials.

Dynamic studies of silicide-mediated crystallization of amorphous silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1352-1353
Author(s):  
C. Hayzelden ◽  
J. L. Batstone
Keyword(s):  
Ion Implantation ◽  
Solid Phase ◽  
Metallic Phase ◽  
Single Crystal Substrate ◽  
Free Electrons ◽  
Melt Temperature ◽  
Transmission Electron ◽  
Crystal Substrate ◽  
High Resolution Tem

Epitaxial reordering of amorphous Si(a-Si) on an underlying single-crystal substrate occurs well below the melt temperature by the process of solid phase epitaxial growth (SPEG). Growth of crystalline Si(c-Si) is known to be enhanced by the presence of small amounts of a metallic phase, presumably due to an interaction of the free electrons of the metal with the covalent Si bonds near the growing interface. Ion implantation of Ni was shown to lower the crystallization temperature of an a-Si thin film by approximately 200°C. Using in situ transmission electron microscopy (TEM), precipitates of NiSi2 formed within the a-Si film during annealing, were observed to migrate, leaving a trail of epitaxial c-Si. High resolution TEM revealed an epitaxial NiSi2/Si(l11) interface which was Type A. We discuss here the enhanced nucleation of c-Si and subsequent silicide-mediated SPEG of Ni-implanted a-Si.Thin films of a-Si, 950 Å thick, were deposited onto Si(100) wafers capped with 1000Å of a-SiO2. Ion implantation produced sharply peaked Ni concentrations of 4×l020 and 2×l021 ions cm−3, in the center of the films.

scholarly journals Photoinduced multistage phase transitions in Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Q. M. Liu ◽  
D. Wu ◽  
Z. A. Li ◽  
L. Y. Shi ◽  
Z. X. Wang ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Lattice Structure ◽  
Condensed Matter ◽  
Electronic States ◽  
Excitation Intensity ◽  
Coherent Phonon ◽  
Optical Penetration Depth ◽  
Transmission Electron ◽  
Metal Phase Transition ◽  
Atom Displacement

AbstractUltrafast control of material physical properties represents a rapidly developing field in condensed matter physics. Yet, accessing the long-lived photoinduced electronic states is still in its early stages, especially with respect to an insulator to metal phase transition. Here, by combining transport measurement with ultrashort photoexcitation and coherent phonon spectroscopy, we report on photoinduced multistage phase transitions in Ta2NiSe5. Upon excitation by weak pulse intensity, the system is triggered to a short-lived state accompanied by a structural change. Further increasing the excitation intensity beyond a threshold, a photoinduced steady new state is achieved where the resistivity drops by more than four orders at temperature 50 K. This new state is thermally stable up to at least 350 K and exhibits a lattice structure different from any of the thermally accessible equilibrium states. Transmission electron microscopy reveals an in-chain Ta atom displacement in the photoinduced new structure phase. We also found that nano-sheet samples with the thickness less than the optical penetration depth are required for attaining a complete transition.

scholarly journals Chlorosulfuric acid-assisted production of functional 2D materials

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Mohsen Moazzami Gudarzi ◽  
Maryana Asaad ◽  
Boyang Mao ◽  
Gergo Pinter ◽  
Jianqiang Guo ◽  
...  
Keyword(s):  
Hexagonal Boron Nitride ◽  
2D Materials ◽  
Real Life ◽  
Large Area ◽  
Polar Solvents ◽  
Aspect Ratios ◽  
Two Dimensional Materials ◽  
Liquid Phase Exfoliation

AbstractThe use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

scholarly journals Topological vectors as a fingerprinting system for 2D-material flake distributions

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Joyce C. C. Santos ◽  
Mariana C. Prado ◽  
Helane L. O. Morais ◽  
Samuel M. Sousa ◽  
Elisangela Silva-Pinto ◽  
...  
Keyword(s):  
Distribution Function ◽  
2D Materials ◽  
Shape Parameters ◽  
Representation System ◽  
Statistical Characterization ◽  
2D Material ◽  
Fast Pace ◽  
Parameter Distributions

AbstractThe production of 2D material flakes in large quantities is a rapidly evolving field and a cornerstone for their industrial applicability. Although flake production has advanced in a fast pace, its statistical characterization is somewhat slower, with few examples in the literature which may lack either modelling uniformity and/or physical equivalence to actual flake dimensions. The present work brings a methodology for 2D material flake characterization with a threefold target: (i) propose a set of morphological shape parameters that correctly map to actual and relevant flake dimensions; (ii) find a single distribution function that efficiently describes all these parameter distributions; and (iii) suggest a representation system—topological vectors—that uniquely characterizes the statistical flake morphology within a given distribution. The applicability of such methodology is illustrated via the analysis of tens of thousands flakes of graphene/graphite and talc, which were submitted to different production protocols. The richness of information unveiled by this universal methodology may help the development of necessary standardization procedures for the imminent 2D-materials industry.

scholarly journals MoS2/h-BN/Graphene Heterostructure and Plasmonic Effect for Self-Powering Photodetector: A Review

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1672
Author(s):  
Umahwathy Sundararaju ◽  
Muhammad Aniq Shazni Mohammad Haniff ◽  
Pin Jern Ker ◽  
P. Susthitha Menon
Keyword(s):  
Flexible Electronics ◽  
Hexagonal Boron Nitride ◽  
2D Materials ◽  
Optical Power ◽  
Active Regions ◽  
Green Technology ◽  
Plasmonic Effect ◽  
Zero Bias ◽  
Electrical Signals ◽  
Self Powered

A photodetector converts optical signals to detectable electrical signals. Lately, self-powered photodetectors have been widely studied because of their advantages in device miniaturization and low power consumption, which make them preferable in various applications, especially those related to green technology and flexible electronics. Since self-powered photodetectors do not have an external power supply at zero bias, it is important to ensure that the built-in potential in the device produces a sufficiently thick depletion region that efficiently sweeps the carriers across the junction, resulting in detectable electrical signals even at very low-optical power signals. Therefore, two-dimensional (2D) materials are explored as an alternative to silicon-based active regions in the photodetector. In addition, plasmonic effects coupled with self-powered photodetectors will further enhance light absorption and scattering, which contribute to the improvement of the device’s photocurrent generation. Hence, this review focuses on the employment of 2D materials such as graphene and molybdenum disulfide (MoS2) with the insertion of hexagonal boron nitride (h-BN) and plasmonic nanoparticles. All these approaches have shown performance improvement of photodetectors for self-powering applications. A comprehensive analysis encompassing 2D material characterization, theoretical and numerical modelling, device physics, fabrication and characterization of photodetectors with graphene/MoS2 and graphene/h-BN/MoS2 heterostructures with plasmonic effect is presented with potential leads to new research opportunities.

scholarly journals Simulation of bonding effects in HRTEM images of light element materials

2011 ◽  
Vol 2 ◽  
pp. 394-404 ◽  
Author(s):  
Simon Kurasch ◽  
Jannik C Meyer ◽  
Daniela Künzel ◽  
Axel Groß ◽  
Ute Kaiser
Keyword(s):  
Density Functional ◽  
Structural Information ◽  
Hexagonal Boron Nitride ◽  
Light Element ◽  
Model Systems ◽  
Single Atom ◽  
Transmission Electron ◽  
Relative Contrast ◽  
Oxygen Substitution ◽  
Simulation Scheme

The accuracy of multislice high-resolution transmission electron microscopy (HRTEM) simulation can be improved by calculating the scattering potential using density functional theory (DFT) Gemming, T.; Möbus, G.; Exner, M.; Ernst, F.; Rühle, M. J. Microsc. 1998, 190, 89–98. doi:10.1046/j.1365-2818.1998.3110863.xDeng, B.; Marks, L. D. Acta Crystallogr., Sect. A 2006, 62, 208–216. doi:10.1107/S010876730601004X. This approach accounts for the fact that electrons in the specimen are redistributed according to their local chemical environment. This influences the scattering process and alters the absolute and relative contrast in the final image. For light element materials with well defined geometry, such as graphene and hexagonal boron nitride monolayers, the DFT based simulation scheme turned out to be necessary to prevent misinterpretation of weak signals, such as the identification of nitrogen substitutions in a graphene network. Furthermore, this implies that the HRTEM image does not only contain structural information (atom positions and atomic numbers). Instead, information on the electron charge distribution can be gained in addition. In order to produce meaningful results, the new input parameters need to be chosen carefully. Here we present details of the simulation process and discuss the influence of the main parameters on the final result. Furthermore we apply the simulation scheme to three model systems: A single atom boron and a single atom oxygen substitution in graphene and an oxygen adatom on graphene.

Laser assisted synthesis of WS2 nanorods by pulsed laser ablation in liquid environment

2021 ◽  
pp. 2140007
Author(s):  
Pankaj Koinkar ◽  
Kohei Sasaki ◽  
Tetsuro Katayama ◽  
Akihiro Furube ◽  
Satoshi Sugano
Keyword(s):  
Electron Microscopy ◽  
Laser Ablation ◽  
2D Materials ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Laser Ablation In Liquid ◽  
Simple Method ◽  
Liquid Environment ◽  
Transmission Electron ◽  
Specific Morphology

Two dimensional (2D) materials are widely attracting the interest of researchers due to their unique crystal structure and diverse properties. In the present work, tungsten disulfide (WS[Formula: see text] nanorods were synthesized by a simple method of pulsed laser ablation in liquid (PLAL) environment. The prepared WS2 are analyzed by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and Raman spectroscopy to confirm the surface morphology, phase and structure. A possible growth mechanism of WS2 is proposed. This study indicates new door for the preparation of 2D materials with specific morphology.

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