Search

We manipulated the stacking configuration of a few-layer MoS2 to investigate the impact of interlayer coupling on electrical band engineering. By simultaneously synthesizing two distinct stacking types of MoS2 islands, wedding cake (W) and spiral (S), on the same substrate, we explored layer-dependent electrical properties under identical experimental conditions. We used multiple scanning probe microscopy techniques to map local electronic properties with respect to the number of layers, stacking configurations, and local heterogeneities. First-principles calculations verified the role of distinct interlayer coupling in terms of the interlayer distance. Our findings highlight the critical role of interlayer coupling in applications of transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Structural stability, local density of states, bonding information, and charge distribution differences of C‐substituted ZnO (C/VZnxOy) monolayer structures, as well as their interactions with lithium atoms, are investigated using the density functional theory (DFT) method. The energy required to generate vacancies in pristine ZnO monolayers is considerably high, but since the C atoms are strongly adsorbed in the vacant sites, the energy required to form C/VZnxOy structures is reduced. These lattice substitutions cause an alteration of the Zn d‐states. The bonding analysis shows that the C−O interaction is stronger than the C−Zn interaction. So, it generates high stability for these structures. Furthermore, because the development of C/VZnxOy is aimed at lithium battery electrode applications, the most fundamental thing that needs to be examined initially is the interaction between the C/VZnxOy surfaces and the lithium atoms. Li3 strongly binds on all C/VZnxOy surfaces, and it turns to Li3+ based on a simple analysis of charge distribution differences. These findings will have a substantial impact on the future development of ZnO monolayers, and their potential as lithium battery electrodes can be studied further. [ABSTRACT FROM AUTHOR]

We investigate how the electronic and transport properties of six arm-chair graphene nanoribbon-based structures are modified with the introduction of symmetrical and asymmetrical geometrical V-cuts on their edges. A tight-binding model based on numerical non-equilibrium Green's function method is used to compute the transport properties such as local density of states, transmission and current–voltage characteristics. We report the existence of nearly flat mid-bands for certain topologies after edge patterning. These bands give rise to non-zero transmission at low bias voltages. We uncover how this transmission varies with width, length, and biasing of the channel and also the temperature of the contacts. For structures in which flat mid-bands are absent, we show how their band gaps could be tuned by varying the width and length of the modified unit cells. [ABSTRACT FROM AUTHOR]

Flat band has attracted more and more interest in recent years, motivated by its discovery in twisted bilayer graphene (TBG). In this work, we report our study of the impurity effect on this flat band system, which is an important issue for real materials. Employing the Lanczos recursive method, we solve the local density of states (LDOS) around a potential impurity. We find for large impurity size, a series of bound states are formed inside the impurity, and the flat band peak in LDOS is suppressed near the impurity boundary and shifted by the impurity potential deep inside the impurity. As the impurity size becomes smaller, the effect on the flat band becomes weaker, as anticipated from the large scale of the underlying Wannier function. This property distinguishes with the usual flat band systems with small localized Wannier orbitals, and indicates the flat band in TBG is more stable against small-size impurities. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots display remarkable optical and electrical characteristics with the potential for extensive applications in contemporary nanotechnology. As an ideal instrument for examining surface topography and local density of states (LDOS) at an atomic scale, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has become indispensable approaches to gain better understanding of their physical properties. This article presents a comprehensive review of the research advancements in measuring the electronic orbits and corresponding energy levels of colloidal quantum dots in various systems using STM and STS. The first three sections introduce the basic principles of colloidal quantum dots synthesis and the fundamental methodology of STM research on quantum dots. The fourth section explores the latest progress in the application of STM for colloidal quantum dot studies. Finally, a summary and prospective is presented. [ABSTRACT FROM AUTHOR]

Recent advances in inverse-design approaches for discovering optical structures based on desired functional characteristics have reshaped the landscape of nanophotonic structures, where most studies have focused on how light interacts with nanophotonic structures only. When quantum emitters (QEs), such as atoms, molecules, and quantum dots, are introduced to couple to the nanophotonic structures, the light–matter interactions become much more complicated, forming a rapidly developing field – quantum nanophotonics. Typical quantum functional characteristics depend on the intrinsic properties of the QE and its electromagnetic environment created by the nanophotonic structures, commonly represented by a scalar quantity, local-density-of-states (LDOS). In this work, we introduce a generalized inverse-design framework in quantum nanophotonics by taking LDOS as the bridge to connect the nanophotonic structures and the quantum functional characteristics. We take a simple system consisting of QEs sitting on a single multilayer shell–metal–nanoparticle (SMNP) as an example, apply fully-connected neural networks to model the LDOS of SMNP, inversely design and optimize the geometry of the SMNP based on LDOS, and realize desirable quantum characteristics in two quantum nanophotonic problems: spontaneous emission and entanglement. Our work introduces deep learning to the quantum optics domain for advancing quantum device designs; and provides a new platform for practicing deep learning to design nanophotonic structures for complex problems without a direct link between structures and functional characteristics.

The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications.

We exploit InSb’s magnetic-induced optical properties to design THz sub-wavelength antennas that actively tune the radiative decay rates of dipole emitters at their proximity. The proposed designs include a spherical InSb antenna and a cylindrical Si-InSb hybrid antenna demonstrating distinct behaviors. The former dramatically enhances both radiative and non-radiative decay rates in the epsilon-near-zero region due to the dominant contribution of the Zeeman-splitting electric octupole mode. The latter realizes significant radiative decay rate enhancement via magnetic octupole mode, mitigating the quenching process and accelerating the photon production rate. A deep-learning-based optimization of emitter positioning further enhances the quantum efficiency of the proposed hybrid system. These novel mechanisms are promising for tunable THz single-photon sources in integrated quantum networks.

Anisotropic gold nanoparticles (AuNPs) were synthesized using microwave (MW)-assisted route. Lemon extract was used as both reducing and stabilizing agent. Subsequent UV treatment was carried out to modify the particle size and shape. Distribution of triangular and pentagonal-shaped particles were found to increase in number. Moreover, up to 60% increase in particle size was also observed. Change in optical property and appearance of plasmon modes were clear indication of the modification caused. Local density of photonic states (LDOS) and electric field distribution were obtained through computational simulation using MATLAB toolbox. Experimental results were used as the input values for the simulation. Dipolar distribution was observed along the boundaries of the spherical NPs, while for triangular and pentagonal-shaped NPs, they were found to be concentrated along their edges and corners. The results presented here encourage us to choose an alternative eco-friendly, quick and simple route to synthesize gold NPs of various shapes for various application such as in viral detection, nanobiomaterials, biomedical images, detection-therapy, etc. New, rapid, and eco-friendly route to synthesize anisotropic gold nanoparticles (AuNPs) using microwave-assisted method is proposed. Subsequent UV treatment of the synthesized AuNPs did modify their size and shape. An increase in their size of up to 60% was recorded along with the change in their shape from spheroidal to triangular, pyramidal, and pentagonal. Plasmonic peaks obtained experimentally were used in theoretical study to understand the distribution of electrical fields. Using simulated results, the dominant geometric contributions of the plasmon resonances were mapped. [ABSTRACT FROM AUTHOR]

The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications. [ABSTRACT FROM AUTHOR]

Dissipation, often associated with plasmons, leads to decoherence and is generally considered fatal for quantum nonlinearities and entanglement. Counterintuitively, by introducing a dissipative plasmonic nanoantenna into a typical cavity quantum electrodynamics (QED) system, we unveil the wide existence of the atom-photon quasi-bound state (qBS), a kind of exotic eigenstate with anomalously small decay, in the hybrid plasmonic-photonic cavity. To derive the analytical condition of atom-photon qBS, we formulate a quantized two-mode model of the local density of states by connecting the interacting uncoupled cavity modes to the macroscopic QED. With resonant plasmon-photon coupling, we showcase the single-atom qBS that improves the efficiency of single-photon generation over one order of magnitude; and the two-atom qBS that significantly enhances spontaneous entanglement generation compared with a bare photonic cavity. Notably, such single-atom and multi-atom qBS can be simultaneously accessed in realistic plasmonic-photonic cavities, providing a versatile platform for advanced quantum technologies, such as quantum light sources, quantum computation, and quantum information.

The lattice-matched system (GaAs)n/(AlAs)n superlattice is calculated for two different values of n=3 and 6 within ab initio pseudopotential density-functional theory using Quantum Espresso package of program exploiting the ultra-soft atomic pseudopotentials. Their band offsets, which is a well-known and inextricable problem at semiconductor interfaces, have been determined in this paper and were compared with experimental results. Discontinuities of valance and conduction bands were obtained as 0.46 and 0.25 eV, respectively. The averaged self-consistent potential across the [001] interface in GaAs is about 0.061 eV higher than its value in AlAs. The local density of states for both superlattices was also studied. The effect of different factors e.g. orientation, transitivity, and composition dependence is reported in this study. We found that, in the [110] direction of GaAs/AlAs superlattice, the dependence of the band offset on the orientation is negligible. The calculated band gap of is linearly dependent on aluminum content.

The optical Raman cooling implies enhanced anti-Stokes scattering compared to Stokes scattering. Plasmon-enhanced Raman scattering in a layered insulator-metal-insulator (IMI) system occurs due to the modification of the local density of electromagnetic states (LDOS) near a metallic layer. Because both eigenmodes with frequencies below the plasma frequency are surface modes and the high-frequency mode is delocalized, energy is capable of dissipating into free space through anti-Stokes scattering. In this work, we carry out the numerical simulation of LDOS for IMI structures with a varied thickness of the metallic layer. Our work is a step towards the development of structured photonic materials for optical cooling of solids. [ABSTRACT FROM AUTHOR]

Probing light–matter interaction at the nanometer scale is one of the most fascinating topics of modern optics. Its importance is underlined by the large span of fields in which such accurate knowledge of light–matter interaction is needed, namely nanophotonics, quantum electrodynamics, atomic physics, biosensing, quantum computing and many more. Increasing innovations in the field of microscopy in the last decade have pushed the ability of observing such phenomena across multiple length scales, from micrometers to nanometers. In bioimaging, the advent of super-resolution single-molecule localization microscopy (SMLM) has opened a completely new perspective for the study and understanding of molecular mechanisms, with unprecedented resolution, which take place inside the cell. Since then, the field of SMLM has been continuously improving, shifting from an initial drive for pushing technological limitations to the acquisition of new knowledge. Interestingly, such developments have become also of great interest for the study of light–matter interaction in nanostructured materials, either dielectric, metallic, or hybrid metallic-dielectric. The purpose of this review is to summarize the recent advances in the field of nanophotonics that have leveraged SMLM, and conversely to show how some concepts commonly used in nanophotonics can benefit the development of new microscopy techniques for biophysics. To this aim, we will first introduce the basic concepts of SMLM and the observables that can be measured. Then, we will link them with their corresponding physical quantities of interest in biophysics and nanophotonics and we will describe state-of-the-art experiments that apply SMLM to nanophotonics. The problem of localization artifacts due to the interaction of the fluorescent emitter with a resonant medium and possible solutions will be also discussed. Then, we will show how the interaction of fluorescent emitters with plasmonic structures can be successfully employed in biology for cell profiling and membrane organization studies. We present an outlook on emerging research directions enabled by the synergy of localization microscopy and nanophotonics.

In this paper, we numerically study the transport properties of a resonant tunneling diode (RTD) based on graphene nanoribbon (GNR) with an H-type antidote between the contacts. The structure may also be thought of as having two parallel (W-shape) parts connecting the contacts, each having a wider channel region sandwiched between two narrower barrier regions. The energy at which quasi-bound states occur in each part depends on the dimensional parameters of the respective portion in the structure. We study how the transmission through quasi-bound states is influenced by the edge states on the contacts and dimensional parameters such as barrier length and also by the ambient temperature. The results are compared with those of an RTD with a single part connecting the contacts. Transmission peaks at different energies are observed for an RTD with asymmetrical lower and upper parts between the contacts. This is then utilized for the creation of two negative differential resistance (NDR) peaks. For numerical computation, the non-equilibrium Green's function formalism (NEGF) based on the nearest neighbor tight-binding model is employed. • Numerical study of RTD based on GNR with an H-type antidote between contacts. • Investigation of transmission through quasi-bound states influenced by edge states, barrier length, and ambient temperature. • Comparison with RTD having a single part connecting contacts. • Observation of two NDR peaks for RTD with asymmetrical lower and upper parts. • Utilization of NEGF formalism for numerical computation [ABSTRACT FROM AUTHOR]

In this paper, we first characterize a superlattice structure created by repeating a heterostructure formed from two armchair graphene nanoribbon (AGNR) segments with different widths. We investigate the electronic and transport properties of this structure by varying its widths and lengths to demonstrate the tunability of its overall band gap. The plot of the local density of states shows the formation of localized states at the low band gap segments of the superlattice. The superlattice is then used as a barrier to create a double barrier quantum well (DBQW) to design a proposed resonant tunneling diode (RTD) structure. We observe this device's negative differential resistance (NDR) operation for a range of bias voltages between the contacts. We study the effect of dimensional parameters on the RTD performance. The non-equilibrium Green's function method, based on a tight-binding model, is employed for numerical computation. • Tight binding approach considering overlapping matrix and hopping parameter up to 3rd nearest neighbor. • Band gap modulation of U-cut edge patterned AGNR. • Transport properties of DBQWs for graphene nanoribbon using Non equilibrium green's function. • LDOS at the quasi bound state due to quantum well. • Performance of graphene based Resonant Tunneling Diode. [ABSTRACT FROM AUTHOR]

This paper aims to elucidate the effect of an air‐formed native oxide covering mild steel surface on the contrast in the scanning electron microscopy (SEM) images obtained with the landing energy from 5 keV down to 0 eV. Part of the mild steel surface was in‐situ cleaned by Ar+ ion sputtering process in order to remove native oxide from the surface. It enabled us to observe the oxide‐free and the naturally oxidized area on the mild steel surface simultaneously in the SEM micrographs. Presence of the native oxide starts to play a role in the SEM images acquired at landing energy below roughly 3 keV. Contrast between differently oriented grains situated inside the area covered by the native oxide starts to be negligible with landing energy decreasing below 3 keV, up to some ultra‐low values where the contrast increases again. Total reflectivity contrast between the clean and the oxidized area increases exponentially with landing energy decreasing below 3 keV. The reflectivity‐versus‐energy curves of the cleaned and the naturally oxidized mild steel surface are markedly different. The reflectivity of the electrons is correlated with the density of states (DOS), as is demonstrated at very low landing energies. Sensitivity of the very low‐energy electrons to the electronic structure was verified by comparison of the experimental data with the simulations of reflectivities, band structure, and DOS. The theoretical predictions are based on the density‐functional theory calculations and they have been performed in energy range corresponding to specular reflectivities of the Fe‐BCC (001) orientation. We have also observed that close to the mirror condition, that is, near‐zero landing energies, the primary electrons become sensitive to the surface potential differences caused by the work function differences of clean and native oxide‐covered steel surfaces. [ABSTRACT FROM AUTHOR]

The properties of thin films are often influenced by the crystal's preferred orientation. In the present study, we report the strong dependence of surface conductivity on the preferred orientation of TiN film that acts as the coating material for Ti bipolar plate. The preferred orientation of TiN film is successfully controlled along the (111) or (200) planes by adjusting the N2 flow rate or Ti substrate temperature during the deposition process via DC (direct current) reactive magnetron sputtering. Small N2 flow rate of 3 to 6 sccm or low substrate temperature (e.g., 25 °C) facilitates the growth of TiN films along the (111). The (111) preferred orientated TiN films show much lower interfacial contact resistance (ICR) than the (200) preferred orientated films. A considerably low ICR value of 1.9 mΩ·cm2 at 140 N/cm2 is achieved at the N2 flow of 4 sccm and the substrate temperature of 25 °C. [ABSTRACT FROM AUTHOR]

Probing light–matter interaction at the nanometer scale is one of the most fascinating topics of modern optics. Its importance is underlined by the large span of fields in which such accurate knowledge of light–matter interaction is needed, namely nanophotonics, quantum electrodynamics, atomic physics, biosensing, quantum computing and many more. Increasing innovations in the field of microscopy in the last decade have pushed the ability of observing such phenomena across multiple length scales, from micrometers to nanometers. In bioimaging, the advent of super-resolution single-molecule localization microscopy (SMLM) has opened a completely new perspective for the study and understanding of molecular mechanisms, with unprecedented resolution, which take place inside the cell. Since then, the field of SMLM has been continuously improving, shifting from an initial drive for pushing technological limitations to the acquisition of new knowledge. Interestingly, such developments have become also of great interest for the study of light–matter interaction in nanostructured materials, either dielectric, metallic, or hybrid metallic-dielectric. The purpose of this review is to summarize the recent advances in the field of nanophotonics that have leveraged SMLM, and conversely to show how some concepts commonly used in nanophotonics can benefit the development of new microscopy techniques for biophysics. To this aim, we will first introduce the basic concepts of SMLM and the observables that can be measured. Then, we will link them with their corresponding physical quantities of interest in biophysics and nanophotonics and we will describe state-of-the-art experiments that apply SMLM to nanophotonics. The problem of localization artifacts due to the interaction of the fluorescent emitter with a resonant medium and possible solutions will be also discussed. Then, we will show how the interaction of fluorescent emitters with plasmonic structures can be successfully employed in biology for cell profiling and membrane organization studies. We present an outlook on emerging research directions enabled by the synergy of localization microscopy and nanophotonics. [ABSTRACT FROM AUTHOR]

In this article we consider asymptotics for the spectral function of Schrödinger operators on the real line. Let PWL2(R) ! L².R/have the form P:= - d²/dx² C W; where W is a self-adjoint first order differential operator with certain modified almost periodic structure. We show that the kernel of the spectral projector,- Shterenberg and Sobolev with Melrose's scattering calculus. [ABSTRACT FROM AUTHOR]

In this paper, we calculate the local density of states using dyadic Green’s functions for a defective one-dimensional photonic crystal of finite size composed of alternating air and semiconductor layers. Herein, spatial periodicity is broken as one of the semiconductor layers increases its layers. In this study, we consider that the refractive index of semiconductor materials, such as GaAs, Si, and SiO2, changes with the amount of the applied pressure. We determined the existence of a confined mode within the cavity with a maximum value of the local density of states. The results show that, as pressure increases, the local density of states decreases within the confined mode. However, for the GaAs cavity, the results reveal that increased pressure favors the appearance of a larger number of confined modes at frequencies within the second photonic band gaps.

SnSe, an environmental-friendly group-IV monochalcogenide semiconductor, demonstrates outstanding performance in various applications ranging from thermoelectric devices to solar energy harvesting. Its ultrathin films show promise in the fabrication of ferroelectric nonvolatile devices. However, the microscopic identification and manipulation of point defects in ultrathin SnSe single crystalline films, which significantly impact their electronic structure, have been inadequately studied. This study presents a comprehensive investigation of point defects in monolayer SnSe films grown via molecular beam epitaxy. By combining scanning tunneling microscopy (STM) characterization with first-principles calculations, we identified four types of atomic/molecular vacancies, four types of atomic substitutions, and three types of extrinsic defects. Notably, we have demonstrated the ability to convert a substitutional defect into a vacancy and to reposition an adsorbate by manipulating a single atom or molecule using an STM tip. We have also analyzed the local atomic displacement induced by the vacancies. This work provides a solid foundation for engineering the electronic structure of future SnSe-based nanodevices.

In this work, we have investigated the structural and electronic properties of Mg-doped GaAs(111) nanowires synthesized through a vapor–liquid–solid growth mechanism. The crystalline structure of these nanowires was measured using synchrotron X-ray diffraction, while their electronic structure was addressed by scanning tunneling spectroscopy. Scanning tunneling microscopy measurements revealed that conducting Ga2Mg/Mg clusters are observed at {110} nanowire lateral surfaces, allowing electrical contacts with reduced Schottky barriers. This suggests that similar alloyed surfaces can be produced with other dopants, enabling the development of distinct Ohmic contacts in these systems. Density functional theory was used to investigate the electronic response of Ga2Mg. While at room temperature, electronic variable-range hopping drives the nanowires into a metallic behavior, quantum confinement is observed at low temperatures. [ABSTRACT FROM AUTHOR]

We present an approach based on local representation of frequency spectrum to calculate the surface contribution to thermodynamic properties of solids. The Green function theory of isolated point defects is discussed in detail which is also applicable to vibrations of surface atoms. The expression for local spectra of atoms is obtained in terms of the same site Green functions. The surface contribution to thermodynamic properties of solids is expressed in terms of the local frequency spectra of atoms in a few surface layers and the frequency spectrum of the infinite crystal satisfying the cyclic boundary condition. The usefulness of the formulation along with the ability of the recursion method to calculate local spectra without a recourse to detailed frequency calculations of slabs is emphasized. As an illustrative example, we present the surface contribution to low temperature lattice specific heat of tungsten due to (100) surface. [ABSTRACT FROM AUTHOR]

Density functional theory method was used to study the interaction of 3d-transition metal ions with divacancy in graphene. Calculations demonstrate that in all cases, except for that of the structure with the Sc ion, the metal is located in the divacancy center, compensating for the four dangling chemical bonds of carbon atoms. Interaction energies are close to 1000 kJ/mol. The strongest interaction was found for the Ni ion. Analysis of the local density of states of nanoparticles shows that additional energy levels appear in the energy gap between the highest occupied and lowest unoccupied levels of the graphene cluster due to the presence of a transition metal ion. In the case of clusters with Co, Ti, and V ions, the highest occupied level of the cluster lies in the region of electronic states with non-zero local density on the ion. [ABSTRACT FROM AUTHOR]

We propose theoretically a tunable circular Bragg microcavity to enhance the intensity of the emission band of interest in rare-earth-doped materials and to suppress the unwanted emission bands which produce noise and diminish the efficiency of the emission of interest. The surrounding of the microcavity comprises of alternating layers of high-index and low-index materials. The luminescent ions such as neodymium Nd3+ having different emission bands in different host materials are placed in the microcavity, and single emission band with stronger intensity can be observed, and other emission bands are suppressed. The wavelength of the single emission peak can be changed from one wavelength to other wavelengths by varying the refractive index, radius of the microcavity and thus modifying the local density of states of the microcavity. The fluorescence branching ratio of emission band of interest can be enhanced from 10% to 100% due to suppression of the unwanted emission bands.

A novel family of disordered systems is proposed. This family belongs to the class of systems containing random substitutional non-Hermitian impurities. We limit our consideration to a rather simple case when the presence of substitutional point defects results in the model Hamiltonian featuring a diagonal disorder. In contrast to known models of non-Hermitian impurities, the nonzero density of states for each isolated from the host impurity is restricted to a continuous band of finite width. A method to construct corresponding impurity Hamiltonians is provided. [ABSTRACT FROM AUTHOR]

The electronic spectrum of graphene with a single point impurity is considered. Local densities of states at the impurity site and its nearest neighbors are calculated analytically. Their evolution with increasing the impurity potential is examined. It is shown that in the domain of the well-defined impurity resonance the local density of states at the first-nearest neighbor of the impurity site is approximately a scaled-up copy of the local density of states at the impurity site. The corresponding factor is found to be proportional to the squared impurity potential. [ABSTRACT FROM AUTHOR]

The total electron densities of states for graphene nanoribbons with edges of different chirality, as well as the electron local densities of states for individual atoms in these nanoribbons, are calculated and analyzed. There are sharp resonance peaks near the Fermi level in the total electron densities of states of graphene nanoribbons with zigzag edges, which emerge only in the local densities of atoms from the sublattice that goes directly to the nearest edge (i.e., whose atoms have dangling bonds). Semiconducting gaps appear in the spectra of graphene nanobands with armchair chirality edges having a number of constituent atomic lines that is either a multiple of three, or gives a remainder of one when divided by three. The width of this gap only depends on the width of the nanoribbon, and is the same for all its atoms. The electron spectra of graphene nanoribbons with armchair-chirality edges have a metallic behavior if the number of atomic lines gives a remainder of two when divided by three. However, semiconducting gaps still manifest on the local densities of the atoms belonging to some lines of such nanoribbons. [ABSTRACT FROM AUTHOR]

We compute the resonance energy transfer (RET) in a system composed of two quantum emitters near a host dielectric matrix in which metallic inclusions are inserted until the medium undergoes a dielectric-metal transition at percolation. We show that there is no peak in the RET rate at percolation, in contrast to what happens with the spontaneous emission rate of an emitter near the same critical medium. This result suggests that RET does not strongly correlate with the local density of states. [ABSTRACT FROM AUTHOR]

In this paper, we used green's function approach in microscopic theory to investigate a resonant tunneling diode (RTD). We introduced the detailed Hamiltonian for each part of the photovoltaic p-i-n system, then by calculating the green's function components in tight-binding approximation, we calculate local density of states and current-voltage characteristic of the p-i-n structure. Our results show a non-Ohmic behavior and negative differential resistance in RTD. As a result of a longitudinal electric field, the local density of states varies by changing the applied potential. Moreover, we study the effect of changing the physical parameters on the current of the device. Entering quantum dots in the middle of device causes a negative differential resistance, which is a consequence of resonant tunneling phenomenon.

• Isotope engineering of near-field thermal diodes is explored for the first time. • Over 20% rectification enhancement is predicted for a wide parameter space. • At experimentally friendly gaps around 400 nm, 6-fold enhancement is possible. • Isotope-induced SPhP line shift and broadening are the key physical mechanisms. • Two guidelines for isotope engineering are proposed and supported with examples. Guided by a rational design approach centering on the electromagnetic local density of states (LDOS), we explore the potential of isotopically engineering radiative thermal diodes for enhanced rectification with a focus on the near field. Based on fluctuational electrodynamics, we theoretically demonstrate that for thermal diodes pairing thin films of intrinsic silicon (i -Si) and lithium hydride (LiX), the rectification ratio can increase by over six times with varying isotopic compositions. This is because by leveraging the isotope-induced shift and broadening of the surface phonon polaritons in LiX, more LDOS contrast provided by i -Si can be effectively converted into thermal rectification. Moreover, we show that such improvement is fairly robust, as evidenced by the prediction of over 20% rectification enhancement across a wide physical and geometric parameter space. Finally, inspired by insights from the i -Si-based thermal diodes, we propose general guidelines for implementing isotope engineering in the design of practical devices, which are further illustrated via representative diodes employing vanadium dioxide and silicon carbide as the active materials. Our work highlights the efficacy of isotopes in boosting the performance of radiative thermal diodes, which also holds promise for broader applications such as thermal transistors, thermal switches, and thermophotovoltaics. [ABSTRACT FROM AUTHOR]

Graphene nanoribbon (GNR) heterojunctions have been synthesized by a bottom-up approach on an Au (111) substrate from a mixture of two structurally similar but visually distinct chevron-type molecular precursors. The resulting heterojunctions were composed of the units of chevron GNRs (cGNRs) and new laterally extended chevron GNRs (eGNRs), which contained an additional benzene ring. Because of their intentional visual difference, cGNR and eGNR units could be conveniently distinguished in scanning tunneling microscopy images. Differential conductance (d I /d V ) mapping of GNR heterojunctions revealed differences in electronic structures of cGNRs and eGNRs. Interestingly, the characteristic conduction band states of cGNRs in the d I /d V maps were shown to be sensitive to the effects of both lateral extension of ribbons and the edge defects, emphasizing the importance of synthesizing GNRs and GNR heterojunctions with atomic precision. The d I /d V maps further showed that both effects could be localized within the corresponding GNR units even if they are bonded to structurally and electronically different neighbors, which suggests a possibility of engineering complex GNR-based electronic nanostructures with nanoscale modulation of properties. The new eGNR units could be potentially combined with other chevron-type GNRs, such as nitrogen-doped cGNRs, into a variety of new GNR heterojunctions. [ABSTRACT FROM AUTHOR]

• A gradient-free topological optimization framework to customize desired Dirac-like cones and extended problems. • Some novel photonic crystals with unprecedented performance are designed. • Pseudo-spin topological insulators with ultra-wide overlapping bandgap (26.95%) are designed. • Various wave manipulation capabilities of optimized photonic crystals are demonstrated. As the cornerstone of various exotic optical properties, the Dirac-like cones (DCs) in photonic crystals (PhCs) have attracted ever-increasing attention. Based on the concept of local density of states (LDOS) and the method of material-field series expansion (MFSE), this study proposes a general topology optimization framework to systematically realize the inverse design of customizing DCs considering different frequencies, structural symmetries, degeneracies, and even degenerate modes. According to the proposed framework, we further develop some novel PhCs with unprecedented performance, such as the PhCs with dual-polarization DCs that combine good manufacturability and high accuracy of degeneracy, frequency-separated dual-DCs for single/dual polarization in nonlinear optical, semi-Dirac cones with strict and special dispersion relationship for asymmetric transmission, and a pair of pseudo-spin topological insulators with ultra-wide overlapping band gap (26.95%). Full-wave numerical simulations validate various wave manipulation capabilities of optimized PhCs, such as cloaking effect, electromagnetic tunneling, asymmetric transport, unidirectional and topologically protected transport. This work contributes towards the development of complex multi-functional PhCs with desired DCs, and provides an effective and robust inverse design toolbox for topological optics. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We propose a method to probe the local density of states (LDOS) of atomic systems that provides both spatial and energy resolution. The method combines atomic and tunneling techniques to supply a simple, yet quantitative and operational, definition of the LDOS for both interacting and non-interacting systems: it is the rate at which particles can be siphoned from the system of interest by a narrow energy band of non-interacting states contacted locally to the many-body system of interest. Ultracold atoms in optical lattices are a natural platform for implementing this broad concept to visualize the energy and spatial dependence of the atom density in interacting, inhomogeneous lattices. This includes models of strongly correlated condensed matter systems, as well as ones with non-trivial topologies.

Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and −2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms. [ABSTRACT FROM AUTHOR]

Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling modulation-doped field-effect transistors (MODFETs) using $$\hbox {next}{} \mathbf{nano}^{3}$$ software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green's function formalism, which has been integrated into the $$\hbox {next}\mathbf{nano}^{3}$$ software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}$$ on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of $$x = 20\,\%$$ of barrier layers, cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ superlattice nanostructures with very high density of states of 407 $$\hbox {eV}^{-1}$$ at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications. [ABSTRACT FROM AUTHOR]

Using the first principles ground state method, the electronic properties of single Fe dopant in bulk and GaAs(1 1 0) surface are studied. Our calculations show that on-site correlations have significant effects on local geometrical and electronic structures for both bulk GaAs and GaAs(1 1 0) surface. Both t 2 g and e g orbitals of Fe impurity are split by on-site correlations and surface effects. Moreover, our calculated local density of states (LDOS), topography of in-gap states and valence band states based on DFT + U method agree well with experiments. Our calculated LDOS for Fe impurity on the GaAs(1 1 0) surface presents several electronic states above and below the Fermi level, and these states can be well interpreted with the hybridization between Fe 3d orbitals and p-like orbitals of host atoms. [ABSTRACT FROM AUTHOR]

We explore a model of armchair graphene nanoribbons tuned by functionalizing the edge states. Edge modifications are modeled by changing the electronic energy of the edge states in specific periodic patterns. The model can be considered to mimic a controlled doping process with different elements. The band structure, density of states, conductance, and local density of states are calculated, using the tight binding approach, Green's function methodology, and the Landauer formula. The results show interesting behaviors, which are considerably different from the properties of the perfect nanoribbons. The hybridization of conducting bands with non-conducting bands, which appear perfectly flat in the perfect ribbon, opens up and modifies gaps in conductance near the Fermi level. One particular pattern of edge functionalization causes a strong, symmetric, and systematic band gap change about the Fermi level, modifying the electronic characteristics in the energy dispersion, density of states, local density of states, and conductance. [ABSTRACT FROM AUTHOR]

We study the effect of mechanical deformations on the electronic properties of hexagonal flakes of bilayer graphENe. The behavior of electrons induced by triaxial strain can be described by an effective pseudo ‐ magnetic field which is homogENeous in the cENter of the flake. We find that in ‐ plane strain, applied to both layers equally, can break the layer symmetry leading to differENt behavior in the top and bottom layers of graphENe. At low ENergy, just one of the layers feels the pseudo ‐ magnetic field: the zero ‐ ENergy pseudo ‐ Landau level is missing in the second layer, thus creating a gap betweEN the lowest non ‐ zero levels. While the layer asymmetry is most significant at zero ENergy, interaction with the edges of the flake extENds the effect to higher pseudo ‐ Landau levels. The behavior of the top and bottom layers may be reversed by rotating the triaxial strain by 60°. (© 2015 WILEY ‐ VCH Verlag GmbH &Co. KGaA, Weinheim) Part of Focus Issue on ”Carbononics” (Eds.: Pawel Hawrylak, Francois Peeters, Klaus Ensslin) The influENce of mechanical deformations on the electronic properties of bilayer graphENe can be described by an effective pseudo ‐ magnetic field. The authors show that in ‐ plane triaxial strain, applied to both layers equally, can break the layer symmetry leading to differENt pseudo ‐ Landau level spectra in the top and bottom layers of graphENe. [ABSTRACT FROM AUTHOR]