Difference In Density Of States Research Articles

Physical insights of interface traps and self-heating effect on electrical response of DMG FinFETs in overlap and underlap configurations: analog/RF perspective

This paper presents a thorough analysis on analog/RF parameters including interface trap charges (ITCs) of two different densities of states (DOS) along with self-heating on the performance of DMG FinFETs in Overlap and Underlap configurations. Initially, the independent simulations for acceptor ITCs and Self-heating in conventional device reveals that performance degradation caused by Self-heating is more prominent (25.03%) than uniform acceptor ITCs (9.46%). In consecutive step, the cumulative impact of both acceptor ITCs and Self-heating on DC and RF/analog parameters are carried out. Investigation reveals that as the impact of self-heating is larger in overlap configuration, the degradation in drain current is higher in overlap configuration (45.2%, 54.5%) as compared to conventional (30.4%, 40.96%) and underlap (37.2%, 52.8%) configurations for both Uniform and Gaussian trap distributions, respectively.

Information hidden behind a single peak in the C 1s spectrum of graphene on Ir(111)

The energy resolution that can be achieved in x-ray photoelectron spectroscopy experiments allows to disentangle the contribution arising from the presence of a large variety of surface atoms in non-equivalent configurations which manifests itself not only with the appearance of different spectral components, but also as unusual lineshape.In the present work, we show that the fit of the C 1s core level spectrum of graphene grown on Ir(111) realized using 200 peaks based on ab initio calculations, accounting for the non-equivalent C atoms in the 10×10 moiré cell, does not improve the fit quality with respect to the use of a single component. On the contrary, the quantitative fit quality can be drastically increased by introducing a dependency of the Lorentzian width on the distance between C and Ir first-layer atoms. This result is associated to the different electronic properties, and in particular to the different density of states of the σ and π bands, of C atoms sitting on TOP (hills) or FCC (valleys) regions of graphene which affect the lifetimes of the core-holes generated during the photoemission process.

Near-Isotropic Local Attosecond Charge Transfer within the Anisotropic Puckered Layers of Black Phosphorus.

Black phosphorus possesses useful two-dimensional (2D) characteristics of van der Waals coupled materials but additionally features an in-plane anisotropic puckered layer structure that deviates from common 2D materials. Three distinct directions exist within the lattice of black phosphorus: the in-plane armchair and zigzag directions and the out-of-plane direction, with each distinct phosphorus 3p partial density of states. This structural anisotropy is imprinted onto various collective long-range properties, while the extent to which local electronic processes are governed by this directionality is unclear. At the P L1 edge, the directional selectivity of the core-hole clock method was used to probe the local charge transfer dynamics of electrons excited into the 3p-derived conduction band on an attosecond time scale. Here we show that the surprisingly small anisotropy of 3p electron transfer times reflects the similarly small differences in the 3p-derived unoccupied density of states caused by the underlying phosphorus bonding angles within the puckered layers.

Thermodynamic properties on the homologous temperature scale from direct upsampling: Understanding electron-vibration coupling and thermal vacancies in bcc refractory metals

We have calculated thermodynamic properties of four bcc refractory elements---V, Ta, Mo, and W---up to the melting point with full density-functional-theory accuracy, using the recently developed direct-upsampling method [J. H. Jung et al., npj Comput. Mater. 9, 3 (2023)]. The direct-upsampling methodology takes full account of explicit anharmonic vibrations and electron-vibration coupling very efficiently using machine-learning potentials. We have thus been able to compute highly converged free-energy surfaces for the PBE exchange-correlation functional, from which accurate temperature dependencies of various thermodynamic properties such as the heat capacity, thermal expansion coefficient, and bulk modulus are accessible. For all four elements, the electronic contribution is large, including a strong coupling with the thermal vibrations. The atomic forces in W are even affected by the temperature-consistent Fermi broadening, which alters the free energy by around 3 meV/atom at the melting point. Trends within group V and group VI refractory elements are observed and explained by qualitative differences in the electronic density of states. We also provide an estimate of the Gibbs energies of vacancy formation and the vacancy contribution to the thermodynamics. Lastly and most importantly, our results are analyzed in terms of the homologous temperature scale relative to theoretically predicted melting points (for the PBE functional). The homologous temperature dependencies show a remarkable agreement with experiments and reveal the predictive power of self-consistently determined ab initio thermodynamic properties.

Anomalous Interfacial Electron-Transfer Kinetics in Twisted Trilayer Graphene Caused by Layer-Specific Localization.

Interfacial electron-transfer (ET) reactions underpin the interconversion of electrical and chemical energy. It is known that the electronic state of electrodes strongly influences ET rates because of differences in the electronic density of states (DOS) across metals, semimetals, and semiconductors. Here, by controlling interlayer twists in well-defined trilayer graphene moirés, we show that ET rates are strikingly dependent on electronic localization in each atomic layer and not the overall DOS. The large degree of tunability inherent to moiré electrodes leads to local ET kinetics that range over 3 orders of magnitude across different constructions of only three atomic layers, even exceeding rates at bulk metals. Our results demonstrate that beyond the ensemble DOS, electronic localization is critical in facilitating interfacial ET, with implications for understanding the origin of high interfacial reactivity typically exhibited by defects at electrode-electrolyte interfaces.

Platinum Nanotubes Calculated Using Relativistic Cylindrical Wave Technique: Chiral Induced Spin Selectivity

Electronic and spin properties of chiral platinum nanotubes are calculated using the relativistic linear augmented cylindrical waves method. The spin-orbit coupling induces the strong splitting of nonrelativistic dispersion curves for the Fermi energy region. The large differences in spin densities of states for spins up and down can be used to create pure spin currents through the tubules. In the two series Pt (5, n2) and Pt (10, n2), the (5, 3) and (10, 7) nanotubes show the strongest chirality-induced spin selectivity effects.

Characteristics and exchange interactions observed in L-emission spectra of Fe, Mn and their oxides by using a high-energy-resolution soft X-ray emission spectroscopy instrument.

For examining the characteristics of L-emission spectra of Fe, Mn and their oxides, a larger energy-dispersion spectrometer for an electron probe microanalyser was constructed. The energy resolution was evaluated to be 0.3 eV at the Fermi edge observed for the B K-emission of LaB6. The Lα,β-emission profiles and peak positions of those oxides were different from those of pure metals, reflecting the different density of states of valence bands and different charge states of metal elements. The Lℓ-emission profiles of the oxides showed shoulder structures, even though the emission is caused by transitions between two inner shell levels. The presence of the shoulder structures was assigned to the result of the 3s3d exchange interaction in the final state of the Lℓ emission, in which the 3s state has a spin. The Lℓ profiles were decomposed into two peaks by Lorentz fit, and the energy separation was evaluated to be ∼3 eV.

Structural and electronic properties of double perovskite ruthenates; A2GdRuO6 (where A = Ba, Sr)

We report the findings of an experimental and theoretical analysis of the structural, electronic, and vibrational characteristics of Ba 2 GdRuO 6 and Sr 2 GdRuO 6 double perovskite ruthenates. The samples of Ba 2 GdRuO 6 and Sr 2 GdRuO 6 were synthesized using solid state reaction method. The samples have been characterized by X-ray diffraction (XRD) technique where phase purity and space group information have been obtained using FullProf Rietveld refinement method. The Rietveld-fitted XRD patterns show that Ba 2 GdRuO 6 has a single-phase cubic structure with space group F m 3 ¯ m and that Sr 2 GdRuO 6 has a monoclinic structure with space group P 2 1 ∕ n . The vibrational properties were measured, via. , Raman spectroscopy performed at room temperature. The structures predicted from XRD were studied theoretical using accurate plane wave pseudo-potential method based on density functional theory (DFT) with Hubbard parameter, U (DFT+U). The Ba 2 GdRuO 6 is found to be metallic with difference in density of states for spin up and spin down electrons; whereas Sr 2 GdRuO 6 is insulating with a band gap of 4.0 eV. The vibrational analysis of pervoskites shows A 1 g , E g and 2 F 2 g , Raman active modes for Ba 2 GdRuO 6 ; while for Sr 2 GdRuO 6 the observed active modes were A g and B g , respectively . It’s worth noting that the experimentally measured values match those predicted by our DFT calculations. • An integrated experimental and theoretical approach for Ru based double perovskites has been discussed. • Future perspective to explore the role of rare-earth metal ions to further tune the electronic properties of such perovskites has been discussed. • The interesting interplay between Ru and transition metal ions can be understood as a transition from metallic for Ba 2 GdRuO 6 to insulating behavior for Sr 2 GdRuO 6 .

Organic self-assembled monolayers on superconducting NbSe2: interfacial electronic structure and energetics* *This article is dedicated to the memory of Professor Enrico Clementi, our mentor, friend, and a scientific giant on whose shoulders we stand.

While organic self-assembled monolayers (SAMs) have been widely used to modify the work function of metal and metal-oxide surfaces, their application to tune the critical temperature of a superconductor has only been considered recently when SAMs were deposited on NbSe2 monolayers (Calavalle et al 2021 Nano Lett. 21 136–143). Here, we describe the results of density functional theory calculations performed on the experimentally reported organic/NbSe2 systems. Our objectives are: (i) to determine how the organic layers impact the NbSe2 work function and electronic density of states; (ii) to understand the possible correlation with the experimental variations in superconducting behavior upon SAM deposition. We find that, upon adsorption of the organic monolayers, the work-function modulation induced by the SAM and interface dipoles is consistent with the experimental results. However, there occurs no significant difference in the electronic density of states near the Fermi level, a consequence of the absence of any charge transfer across the organic/NbSe2 interfaces. Therefore, our results indicate that it is not a SAM-induced tuning of the NbSe2 density of states near the Fermi level that leads to the tuning of the superconducting critical temperature. This calls for further explorations, both experimentally and theoretically, of the mechanism underlying the superconducting critical temperature variation upon formation of SAM/NbSe2 interfaces.

Quadrupolar Ultrafast Charge Transfer in Diaminoazobenzene-Bridged Perylenediimide Triads.

Strong push-pull interactions between electron donor, diaminoazobenzene (azo), and an electron acceptor, perylenediimide (PDI), entities in the newly synthesized A-D-A type triads (A=electron acceptor and D=electron donor) and the corresponding A-D dyads are shown to reveal wide-band absorption covering the entire visible spectrum. Electrochemical studies revealed the facile reduction of PDI and relatively easier oxidation of diaminoazobenzene in the dyads and triads. Charge transfer reversal using fluorescence-spectroelectrochemistry wherein the PDI fluorescence recovery upon one-electron oxidation, deterring the charge-transfer interactions, was possible to accomplish. The charge transfer state density difference and the frontier orbitals from the DFT calculations established the electron-deficient PDI to be an electron acceptor and diaminoazobenzene to be an electron donor resulting in energetically closely positioned PDIδ- -Azoδ+ -PDIδ- quadrupolar charge-transfer states in the case of triads and Azoδ+ -PDIδ- dipolar charge-transfer states in the case of dyads. Subsequent femtosecond transient absorption spectral studies unequivocally proved the occurrence of excited-state charge transfer in these dyads and triads in benzonitrile wherein the calculated forward charge transfer rate constants, kf , were limited to instrument response factor, meaning >1012 s-1 revealing the occurrence of ultrafast photo-events. The charge recombination rate constant, kr , was found to depend on the type of donor-acceptor conjugates, that is, it was possible to establish faster kr in the case of triads (∼1011 s-1 ) compared to dyads (∼1010 s-1 ). Modulating both ground and excited-state properties of PDI with the help of strong quadrupolar and dipolar charge transfer and witnessing ultrafast charge transfer events in the studied triads and dyads is borne out from the present study.

Density of quasi-localized modes in athermal glasses

A careful examination of the Quasi-Localized Modes (QLMs) that exist in a generic atomistic model of a glass former reveals at least two types of them, each exhibiting a different density of states, one depending on the frequency as and the other as . The properties of the glassy energy landscape that is responsible for the two types of modes is examined here, explaining the analytic feature responsible for the creations of (at least) two families of QLMs. It is argued that the QLMs that are revealed by diagonalizing the Hessian matrix are not related to possibly existing Two-Level Systems (TLS).

Relation between the Density of States in Different Cases and the Corresponding Examples

The study of particle system is inevitable to study its statistical law, and understanding the distribution of particles is fundamental and important. In this paper, the author points out the relation between the number of states of free particles in the relativistic and non-relativistic cases, and gives formulae for each case. Furthermore, the author enumerates some popular and basic particle systems, as well as classifies them in terms of relativistic and non-relativistic cases, also their basic formulae are deduced and enumerated in this paper. These particle systems are applicable to different formulae for the density of states for relativistic or non-relativistic cases. It is concluded that the different densities of states in different cases are related to each other through the de Broglie relation and the energy formula.

Structure and dynamics of aromatic and alkyl substituted Imidazolium-based ionic liquids

The structure and dynamics of two ionic liquids based on imidazolium cations with the common anion dicyanamide, [N(CN)2]-, were studied and compared: one with an aromatic side chain, 1-benzyl-3-methylimidazolium dicyanamide [BzC1Im][N(CN)2], and another with a normal alkyl chain, 1-n-heptyl-3-methylimidazolium dicyanamide [C7C1Im][N(CN)2]. We use classical molecular dynamics (MD) simulations in order to unveil subtle structural differences between these two systems. The collective dynamics were analyzed by considering the spectra of the mass current correlation functions, which were analyzed within the framework of the Zwanzig-Mori formalism. This allowed to compare the effect of aromatic or non-aromatic substituents on the high-frequency collective dynamics and its relationship to a low-frequency transport property such as viscosity. It is found that even though the aromatic-substituted system is a denser and more viscous liquid, the high-frequency dynamics at finite momentum transfers and frequencies, i.e. within the length and timescales of the intermediate-range order (IRO), is only slightly altered. In the low-wavevector limit, however, there are significant differences in the vibrational density of states and viscosity. The scenario put forward by the MD simulations is that even though the role of ionic packing dominates over specific interactions, the different structural motifs within the IRO range imply signatures on the macroscopic dynamics of aromatic and aliphatic substituted imidazolium ionic liquids.

Electronic and Magnetic Properties of Building Blocks of Mn and Fe Atomic Chains on Nb(110).

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction. To gain physical insight, the dependence on the crystallographic direction as well as on the atomic coordination number is analyzed via an orbital decomposition of this isotropic interaction based on the spin-cluster expansion and the difference in the local density of states between ferromagnetic and antiferromagnetic configurations. A spin-spiral ground state is obtained for Fe chains along the [] direction as a consequence of the frustration of the isotropic interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. This may lead to the observation of spin spirals of different wave vectors and chiralities in longer chains instead of a unique ground state.

Synthesis, spectroscopic, quantum computation, electronic, AIM, Wavefunction (ELF, LOL) and Molecular Docking investigation on (E)-1-(2,5-dichlorothiophen-3-yl)-3-(thiophen-2-yl)-2-propen-1-one

The compound (E)-1-(2,5-dichlorothiophen-3-yl)-3-(thiophen-2-yl)-2-propen-1-one (DClTP) was synthesized and analyzed using FT-IR, FT-Raman and 1H and13C NMR spectroscopic tools. The Gaussian computations were carried out by DFT method using B3LYP functional and 6–311G(d,p) as basis sets. The 13CNMR and 1H NMR were calculated by using the Gauge Independent Atomic Orbital (GIAO) method. AIM topology analysis was done on the molecule. NBO analysis was used to study the donor – acceptor interaction in the molecule. Chemical reactive site of the molecule was analyzed in MEP profile. The significance of Mulliken charge in the molecule and corresponding charge in Fukui function were also discussed. The different density of states was also computed by the same method. Various thermodynamic parameters were also discussed at various temperatures. Molecular docking was carried out using Autodock programming package for DClTP compound which exhibits the inhibitor human chorionic gonadotropin protein.

A computational study to explore the effects of copper doping concentration on phase stability, electronic band structure and optical properties of CsSrF3 fluro-perovskite

ABSTRACT In this work we have computed the electronic, structural, and optical properties of pure and Cu-doped cubic CsSrF3 in the context of density functional theory (DFT). The optimised lattice parameter for pure material was obtained 4.99 Å which has great correspondence to its reported value that is 4.83 Å. The concentration of copper was varied (from x = 0, 0.03, 0.11, 0.22 0.33) that led to an increase in the lattice constant of doped CsSrF3 from 4.99 to 5.150 Å. The electronic bandgap is analysed by investigating the combination of different densities of states. The bandgap of pure CsSrF3 was obtained at 5.66 eV which was direct in nature. Due to variation in copper concentration, the band gap was reduced from 5.66 to 0.727 eV which was also direct in nature. Cu as a dopant at Cs sites in CsSrF3 not only alters electronic but also affects the optical properties of the pure material. The value of pure dielectric function increased from 2.1 to 2.6 in visible region; simultaneously the value of refractive index was changed from 1.4 to 1.6. Due to low refractive index this fluoride-type material can be used for protective coating and for anti-reflection and optical properties are enhanced in lower energy regime.

Landau theory for non-equilibrium steady states

We examine how non-equilibrium steady states close to a continuous phase transition can still be described by a Landau potential if one forgoes the assumption of analyticity. In a system simultaneously coupled to several baths at different temperatures, the non-analytic potential arises from the different density of states of the baths. In periodically driven-dissipative systems, the role of multiple baths is played by a single bath transferring energy at different harmonics of the driving frequency. The mean-field critical exponents become dependent on the low-energy features of the two most singular baths. We propose an extension beyond mean field.

Visualization of the Borazine Core of B3N3-Doped Nanographene by STM.

Electronic interface properties and the initial growth of hexa-peri-hexabenzocoronene with a borazine core (BN-HBC) on Au(111) have been studied by using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A weak, but non-negligible, interaction between BN-HBC and Au(111) was found at the interface. Both hexa-peri-hexabenzocoronene (HBC) and BN-HBC molecules form well-defined monolayers. The different contrast in STM images of HBC and BN-HBC at different tunneling voltages with submolecular resolution can be ascribed to differences in the local density of states (LDOS). At positive and negative tunneling voltages, STM images reproduce the distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as determined by density functional theory (DFT) calculations very well.

Spectroscopic Comparison of Thermal Transport at Organic-Inorganic and Organic-Hybrid Interfaces Using CsPbBr3 and FAPbBr3 (FA = Formamidinium) Perovskite Nanocrystals.

Thermal transport across interfaces depends on the matching of vibrational structure at the interface. This work examines the transfer of thermal excitation from an organic ligand coating to either all-inorganic cesium lead tribromide (CsPbBr3) nanocrystals or hybrid organic-inorganic formamidinium lead tribromide (FAPbBr3) nanocrystals using selective infrared optical excitation. These two semiconductors are directly compared because they (or similar semiconductors) are currently envisioned as strong candidates in many optoelectronic technologies and they differ due to the presence of an organic or inorganic cation, which introduces substantial differences in the phonon density of states in otherwise quite similar semiconductors. Infrared excitation of C-H vibrations of surface-bound ligands generates a temperature gradient between the organic ligand shell and nanocrystal core, which results in heat flow, measured by probing changes of the semiconductor band gap. Heat transfer to both perovskite compositions of comparable sizes is similar (25-30 ps), due to fast intramolecular vibrational relaxation and similar matching of low-energy phonons with the organic ligand, but FAPbBr3 samples show a slow bleaching kinetic on the order of 1 ns. This slow, heat-induced change in the semiconductor band gap is attributed not to interfacial heat transfer but instead to thermal equilibration between the organic and inorganic sublattices of FAPbBr3. Ab initio molecular dynamics simulations support the hypothesis that low-energy inorganic sublattice phonon modes are populated initially in the heat transfer process, with a slow thermal population of the higher-energy phonon modes associated primarily with the organic cation. Slow thermal equilibration of FAPbBr3 is likely to substantially impact the time-dependent response of optoelectronic devices that heat the semiconductor active layer and provide further evidence that the poor bulk thermal transport of hybrid perovskite materials extends to microscopic thermal processes.

Study of elastic, structural, electronic, magnetic, and topological properties of η-Fe2C carbide under pressure

This paper studies the elastic, structural, electronic, magnetic, and topological properties of the η-Fe2C carbide under pressure by resorting to DFT-GGA's first principle via FPLAPW-WIEN2K and ElaStic1.0 software. Properties were calculated for strain vectors and pressures shown to maintain the orthorhombic structure of the carbide. Electronic bands, Fermi surfaces, and electron states are slightly distorted in the direction of the strain vector considered. The density of states, dominated by the 3d electrons of Fe, and to a lesser extent, by the 2p electrons of C, is lower in the pressure-borne compressed state than in the expanded one, a degree of hybridization existing between these states in certain energy regions, in tandem with a more extended first Brillouin zone and a higher Fermi level, which translates into greater structural stability in the latter state. The resulting magnetic anisotropy is a consequence of the difference in density of states between the spin-up and spin-down configurations, mainly in the orbitals of the aforesaid electrons. The pressure was also found to affect the number of bond, ring, and cage critical points (CP) found, as well as their distance from the atom.