Graphene transistor based on tunable Dirac fermion optics

We present a quantum switch based on analogous Dirac fermion optics (DFO), in which the angle dependence of Klein tunneling is explicitly utilized to build tunable collimators and reflectors for the quantum wave function of Dirac fermions. We employ a dual-source design with a single flat reflector, which minimizes diffusive edge scattering and suppresses the background incoherent transmission. Our gate-tunable collimator–reflector device design enables the quantitative measurement of the net DFO contribution in the switching device operation. We obtain a full set of transmission coefficients between multiple leads of the device, separating the classical contribution from the coherent transport contribution. The DFO behavior demonstrated in this work requires no explicit energy gap. We demonstrate its robustness against thermal fluctuations up to 230 K and large bias current density up to 102A/m, over a wide range of carrier densities. The characterizable and tunable optical components (collimator–reflector) coupled with the conjugated source electrodes developed in this work provide essential building blocks toward more advanced DFO circuits such as quantum interferometers. The capability of building optical circuit analogies at a microscopic scale with highly tunable electron wavelength paves a path toward highly integrated and electrically tunable electron-optical components and circuits.

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TUNNELING FOR DIRAC FERMIONS IN CONSTANT MAGNETIC FIELD

International Journal of Geometric Methods in Modern Physics ◽

10.1142/s0219887810004622 ◽

2010 ◽

Vol 07 (06) ◽

pp. 909-931 ◽

Cited By ~ 6

Author(s):

EL BOUÂZZAOUI CHOUBABI ◽

MOHAMED EL BOUZIANI ◽

AHMED JELLAL

Keyword(s):

Magnetic Field ◽

Constant Magnetic Field ◽

Resonant Tunneling ◽

Continuity Equation ◽

Energy Gap ◽

Tunneling Effect ◽

Dirac Fermions ◽

Two Dimensional ◽

Transmission Coefficients ◽

Total Transmission

The tunneling effect of two-dimensional Dirac fermions in a constant magnetic field is studied. This can be done by using the continuity equation at some points to determine the corresponding reflexion and transmission coefficients. For this, we consider a system made of graphene as superposition of two different regions where the second is characterized by an energy gap t'. In fact, we treat concrete systems to practically give two illustrations: barrier and diode. For each case, we discuss the transmission in terms of the ratio of the energy conservation and t'. Moreover, we analyze the resonant tunneling by introducing a scalar Lorentz potential where it is shown that a total transmission is possible.

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Factors Affecting Molecular Self-Assembly and Its Mechanism

Scientific Research Journal ◽

10.24191/srj.v9i1.5385 ◽

2012 ◽

Vol 9 (1) ◽

pp. 43 ◽

Cited By ~ 1

Author(s):

Hueyling Tan

Keyword(s):

Self Assembly ◽

Building Blocks ◽

Molecular Engineering ◽

Molecular Structures ◽

Polymer Science ◽

New Approach ◽

Factors Affecting ◽

Dna Structures ◽

Self Assembling ◽

Wide Range

Molecular self-assembly is ubiquitous in nature and has emerged as a new approach to produce new materials in chemistry, engineering, nanotechnology, polymer science and materials. Molecular self-assembly has been attracting increasing interest from the scientific community in recent years due to its importance in understanding biology and a variety of diseases at the molecular level. In the last few years, considerable advances have been made in the use ofpeptides as building blocks to produce biological materials for wide range of applications, including fabricating novel supra-molecular structures and scaffolding for tissue repair. The study ofbiological self-assembly systems represents a significant advancement in molecular engineering and is a rapidly growing scientific and engineering field that crosses the boundaries ofexisting disciplines. Many self-assembling systems are rangefrom bi- andtri-block copolymers to DNA structures as well as simple and complex proteins andpeptides. The ultimate goal is to harness molecular self-assembly such that design andcontrol ofbottom-up processes is achieved thereby enabling exploitation of structures developed at the meso- and macro-scopic scale for the purposes oflife and non-life science applications. Such aspirations can be achievedthrough understanding thefundamental principles behind the selforganisation and self-synthesis processes exhibited by biological systems.

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Stereospecific, Palladium-catalyzed C(sp3)–H Alkenylation and Alkynylation of a Proline Derivative Enabled by 8-Aminoquinoline as a Directing Group

10.26434/chemrxiv.12034743 ◽

2020 ◽

Author(s):

Aleksandra Balliu ◽

Aaltje Roelofje Femmigje Strijker ◽

Michael Oschmann ◽

Monireh Pourghasemi Lati ◽

Oscar Verho

Keyword(s):

Carboxylic Acid ◽

Building Blocks ◽

Wide Range ◽

Palladium Catalyzed ◽

Directing Group ◽

High Yields ◽

Vinyl Iodides ◽

Initial Results

In this preprint, we present our initial results concerning a stereospecific Pd-catalyzed protocol for the C3 alkenylation and alkynylation of a proline derivative carrying the well utilized 8‑aminoquinoline directing group. Efficient C–H alkenylation was achieved with a wide range of vinyl iodides bearing different aliphatic, aromatic and heteroaromatic substituents, to furnish the corresponding C3 alkenylated products in good to high yields. In addition, we were able show that this protocol can also be used to install an alkynyl group into the pyrrolidine scaffold, when a TIPS-protected alkynyl bromide was used as the reaction partner. Furthermore, two different methods for the removal of the 8-aminoquinoline auxiliary are reported, which can enable access to both cis- and trans-configured carboxylic acid building blocks from the C–H alkenylation products.

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Efficient Prediction of Structural and Electronic Properties of Hybrid 2D Materials Using DFT and Machine Learning

10.26434/chemrxiv.6254756.v1 ◽

2018 ◽

Author(s):

Sherif Tawfik ◽

Olexandr Isayev ◽

Catherine Stampfl ◽

Joseph Shapter ◽

David Winkler ◽

...

Keyword(s):

Machine Learning ◽

Band Gap ◽

Density Functional ◽

2D Materials ◽

Van Der Waals ◽

Building Blocks ◽

Machine Learning Techniques ◽

Interlayer Distance ◽

Computational Screening ◽

Wide Range

Materials constructed from different van der Waals two-dimensional (2D) heterostructures offer a wide range of benefits, but these systems have been little studied because of their experimental and computational complextiy, and because of the very large number of possible combinations of 2D building blocks. The simulation of the interface between two different 2D materials is computationally challenging due to the lattice mismatch problem, which sometimes necessitates the creation of very large simulation cells for performing density-functional theory (DFT) calculations. Here we use a combination of DFT, linear regression and machine learning techniques in order to rapidly determine the interlayer distance between two different 2D heterostructures that are stacked in a bilayer heterostructure, as well as the band gap of the bilayer. Our work provides an excellent proof of concept by quickly and accurately predicting a structural property (the interlayer distance) and an electronic property (the band gap) for a large number of hybrid 2D materials. This work paves the way for rapid computational screening of the vast parameter space of van der Waals heterostructures to identify new hybrid materials with useful and interesting properties.

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Application of Nitrogen Heterocyclic Carbenes in Organocatalysis

Current Catalysis ◽

10.2174/2211544709999201201120617 ◽

2020 ◽

Vol 09 ◽

Author(s):

Minita Ojha ◽

R. K. Bansal

Keyword(s):

Asymmetric Catalysis ◽

Building Blocks ◽

Structural Features ◽

Heterocyclic Carbenes ◽

Stetter Reaction ◽

Metal Pollutants ◽

Synthetic Strategy ◽

Wide Range ◽

Benzoin Condensation ◽

Nitrogen Heterocyclic

Background: During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes (NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods: By manipulating structural features and selecting appropriate substituent groups, it has been possible to control the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of Nalkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction. Results: The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions, isomerization, etc. The present review includes all these examples published during the last 10 years, i.e. from 2010 till date. Conclusion: The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They provide the synthetic strategy which does not burden the environment with metal pollutants and thus fit in the Green Chemistry.

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MXenes for future nanophotonic device applications

Nanophotonics ◽

10.1515/nanoph-2020-0060 ◽

2020 ◽

Vol 9 (7) ◽

pp. 1831-1853

Author(s):

Jaeho Jeon ◽

Yajie Yang ◽

Haeju Choi ◽

Jin-Hong Park ◽

Byoung Hun Lee ◽

...

Keyword(s):

Solar Cells ◽

Transition Metal ◽

Wide Spectrum ◽

Building Blocks ◽

Optoelectronic Device ◽

High Yield ◽

Saturable Absorption ◽

Nanophotonic Device ◽

Wide Range ◽

Device Applications

AbstractTwo-dimensional (2D) layers of transition metal carbides, nitrides, or carbonitrides, collectively referred to as MXenes, are considered as the new family of 2D materials for the development of functional building blocks for optoelectronic and photonic device applications. Their advantages are based on their unique and tunable electronic and optical properties, which depend on the modulation of transition metal elements or surface functional groups. In this paper, we have presented a comprehensive review of MXenes to suggest an insightful perspective on future nanophotonic and optoelectronic device applications based on advanced synthesis processes and theoretically predicted or experimentally verified material properties. Recently developed optoelectronic and photonic devices, such as photodetectors, solar cells, fiber lasers, and light-emitting diodes are summarized in this review. Wide-spectrum photodetection with high photoresponsivity, high-yield solar cells, and effective saturable absorption were achieved by exploiting different MXenes. Further, the great potential of MXenes as an electrode material is predicted with a controllable work function in a wide range (1.6–8 eV) and high conductivity (~104 S/cm), and their potential as active channel material by generating a tunable energy bandgap is likewise shown. MXene can provide new functional building blocks for future generation nanophotonic device applications.

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Synthesis of sp3-Enriched β-Fluoro Sulfonyl Chlorides

Synthesis ◽

10.1055/s-0040-1706101 ◽

2020 ◽

Author(s):

Oleksandr O. Grygorenko ◽

Rustam Gurbanov ◽

Andriy Sokolov ◽

Sergey Golovach ◽

Kostiantyn Melnykov ◽

...

Keyword(s):

Drug Discovery ◽

Double Bond ◽

Building Blocks ◽

Protecting Groups ◽

Sulfonyl Chlorides ◽

Wide Range ◽

Cyclic Compounds

AbstractA three-step approach to the synthesis of sp3-enriched β-fluoro sulfonyl chlorides starting from alkenes is reported. The method was successfully applied to a wide range of acyclic and cyclic substrates, bearing either an exocyclic or an endocyclic double bond. The procedure worked with a wide range of substrates and tolerated a number of functional and protecting groups. Moreover, the target cyclic compounds were obtained as single cis diastereomers on a multigram scale. The title compounds are promising building blocks for drug discovery that can be used to obtain sp3-enriched β-fluoro and α,β-unsaturated sulfonamides.

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The Band-Gap Studies of Short-Period CdO/MgO Superlattices

Nanoscale Research Letters ◽

10.1186/s11671-021-03517-y ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Ewa Przeździecka ◽

P. Strąk ◽

A. Wierzbicka ◽

A. Adhikari ◽

A. Lysak ◽

...

Keyword(s):

Band Gap ◽

Layer Thickness ◽

Energy Gap ◽

Band Gaps ◽

Short Period ◽

Wide Range ◽

Salt Structure ◽

Short Period Superlattices ◽

Direct Band ◽

Sublayer Thickness

AbstractTrends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

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Novel Bloch wave excitation platform based on few-layer photonic crystal deposited on D-shaped optical fiber

Scientific Reports ◽

10.1038/s41598-021-90504-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Esteban Gonzalez-Valencia ◽

Ignacio Del Villar ◽

Pedro Torres

Keyword(s):

Optical Fibers ◽

High Performance ◽

Light Propagation ◽

Fiber Optic ◽

Layer Structure ◽

Optical Network ◽

Building Blocks ◽

Bloch Wave ◽

Nanophotonic Devices ◽

Wide Range

AbstractWith the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.

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Future trends in diagnosis using laboratory-on-a-chip technologies

Parasitology ◽

10.1017/s0031182099004126 ◽

1999 ◽

Vol 117 (7) ◽

pp. 191-203 ◽

Cited By ~ 16

Author(s):

M. S. TALARY ◽

J. P. H. BURT ◽

R. PETHIG

Keyword(s):

Gene Expression ◽

Lower Cost ◽

Building Blocks ◽

Cancer Diagnostics ◽

Future Trends ◽

Biotechnological Applications ◽

Environmental Testing ◽

Current State ◽

Microelectronic Fabrication ◽

Wide Range

There has been an enormous growth in the development of biotechnological applications, where advances in the techniques of microelectronic fabrication and the technologies of miniaturization and integration in semiconductor industries are being applied to the production of Laboratory-on-a-Chip devices. The aim of this development is to create devices that will perform the same processes that are currently carried out in the laboratory in reduced timescales, at a lower cost, requiring less reagents, and with a greater resolution of detection and specificity. The expectations of this Laboratory-on-a-Chip revolution is that this technology will facilitate rapid advances in gene discovery, genetic mapping and gene expression with broader applications ranging from infectious diseases and cancer diagnostics to food quality and environmental testing. A review of the current state of development in this field reveals the scale of the ongoing revolution and serves to highlight the advances that can be perceived in the development of Laboratory-on-a-Chip technologies. Since miniaturization can be applied to such a wide range of laboratory processes, some of the sub-units that can be used as building blocks in these devices are described, with a brief description of some of the fabrication processes that can be used to create them.

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