Hybridization Of Electronic States Research Articles

Twist-Angle-Dependent Electronic Properties of Exfoliated Single Layer MoS2 on Au(111).

Synthetic materials and heterostructures obtained by the controlled stacking of exfoliated monolayers are emerging as attractive functional materials owing to their highly tunable properties. We present a detailed scanning tunneling microscopy and spectroscopy study of single layer MoS2-on-gold heterostructures as a function of the twist angle. We find that their electronic properties are determined by the hybridization of the constituent layers and are modulated at the moiré period. The hybridization depends on the layer alignment, and the modulation amplitude vanishes with increasing twist angle. We explain our observations in terms of a hybridization between the nearest sulfur and gold atoms, which becomes spatially more homogeneous and weaker as the moiré periodicity decreases with increasing twist angle, unveiling the possibility of tunable hybridization of electronic states via twist angle engineering.

Hybrid Metal-Ligand Interfacial Dipole Engineering of Functional Plasmonic Nanostructures for Extraordinary Responses of Optoelectronic Properties.

Programmable manipulation of inorganic-organic interfacial electronic properties of ligand-functionalized plasmonic nanoparticles (NPs) is the key parameter dictating their applications such as catalysis, photovoltaics, and biosensing. Here we report the localized surface plasmon resonance (LSPR) properties of gold triangular nanoprisms (Au TNPs) in solid state that are functionalized with dipolar, conjugated ligands. A library of thiocinnamate ligands with varying surface dipole moments were used to functionalize TNPs, which results in ∼150 nm reversible tunability of LSPR peak wavelength with significant peak broadening (∼230 meV). The highly adjustable chemical system of thiocinnamate ligands is capable of shifting the Au work function down to 2.4 eV versus vacuum, i.e., ∼2.9 eV lower than a clean Au (111) surface, and this work function can be modulated up to 3.3 eV, the largest value reported to date through the formation of organothiolate SAMs on Au. Interestingly, the magnitude of plasmonic responses and work function modulation is NP shape dependent. By combining first-principles calculations and experiments, we have established the mechanism of direct wave function delocalization of electrons residing near the Fermi level into hybrid electronic states that are mostly dictated by the inorganic-organic interfacial dipole moments. We determine that both interfacial dipole and hybrid electronic states, and vinyl conjugation together are the key to achieving such extraordinary changes in the optoelectronic properties of ligand-functionalized, plasmonic NPs. The present study provides a quantitative relationship describing how specifically constructed organic ligands can be used to control the interfacial properties of NPs and thus the plasmonic and electronic responses of these functional plasmonics for a wide range of plasmon-driven applications.

Local hybridized states of adsorbed atomic Sn on WS2 substrate

We study the growth of Sn and the local electronic properties of Sn grown WS2 surfaces by in-situ scanning tunneling microscopy (STM), scanning tunneling spectroscopy, and first principles density functional theory calculations. Our investigations suggest substitutional doping of Sn at the S sites, with Sn atoms occupying a slightly elevated position of 80 pm on the WS2 surface. These results agree well with our STM observations on room temperature growth of atomic Sn, indicating commensurate or nearly commensurate adsorption at the top S sites with a buckling height of 40 ± 10 pm. Pristine WS2 without any S vacancies on the surface exhibits a bandgap of 1.39 eV, while ingap local density of states comprised of W d and S p orbitals are detected when S vacancies are considered. Upon adsorption of Sn atoms, we find the signature of modulated hybridized ingap electronic states of Sn p and W d orbitals with a spin orbit coupling interaction up to 38 meV at the K point of the Brillouin zone. These results throw important light on the future fabrication of Janus like SnWS vertical heterojunctions with atomic level doping accuracy, which will have enormous device applications.

33‐4: Supramolecules in Thin Films and OLED Efficiencies

This work demonstrates a multi‐tiered computational workflow to accurately and efficiently investigate the electronic properties of OLED materials in realistic thin‐film morphologies. We apply a range of robust atomistic‐scale modeling and simulation methods to reveal hybrid electronic states in OLED films. This work paves the way for efficient materials screening before laborious synthesis and device fabrication.

Chiral Perovskite Nanoplatelets with Tunable Circularly Polarized Luminescence in the Strong Confinement Regime

AbstractChiral perovskite nanocrystals have emerged as an interesting chiral excitonic platform that combines both structural flexibility and superior optoelectronic properties. Despite several recent demonstrations of optical activity in various chiral perovskite nanocrystals, efficient circularly polarized luminescence (CPL) with tunable energies remains a challenge. The chirality imprinting mechanism as a function of perovskite nanocrystal dimensionality remains elusive. Here, atomically thin inorganic perovskite nanoplatelets (NPLs) are synthesized with precise control of layer thickness and are functionalized by chiral surface ligands, serving as a unique platform to probe the chirality transfer mechanism at the organic/perovskite interface. It is found that chirality is successfully imprinted into mono‐, bi‐, and tri‐layer inorganic perovskite NPLs, exhibiting tunable circular dichroism (CD) and CPL responses. However, chirality transfer decreases in thicker NPLs, resulting in decreased CD and CPL dissymmetry factors for thicker NPLs. Aided by large‐scale first‐principles calculations, it is proposed that chirality transfer is mainly mediated through a surface distortion rather than a hybridization of electronic states, giving rise to symmetry breaking in the perovskite lattice and spin‐split conduction bands. The findings described here provide an in‐depth understanding of chirality transfer and design principles for distorted‐surface perovskites for chiral photonic applications.

Catalytic aqueous CO2 reduction to formaldehyde at Ru surface on hydroxyl-groups-rich LDH under mild conditions

Various value-added chemicals such as formic acid, carbon monoxide, methane, methanol, have been obtained using CO2 as a feedstock. However, formaldehyde generation from CO2 is less reported. Here, we performed CO2 hydrogenation with H2 in additive-free water and used layered double hydroxide supported Ru as the heterogeneous catalyst. It was found that gaseous CO2 and H2 could be efficiently and selectively converted to formaldehyde dissolved in water even at room temperature with ambient pressure. The highest gaseous CO2 conversion of 89.7% and a formaldehyde yield of 58.7% were achieved using a Ru/LDH-red catalyst in water at 30 °C with 10 bar CO2 and 10 bar H2. Combined with experimental and theoretical studies, HCOOH was found as the important reaction intermediate. The rich surface –OH of LDH and hybrid electronic state of Ru over Ru/LDH-red catalyst resulted in highly efficient HCHO formation. Our findings offer opportunities to one energy-efficient formaldehyde synthesis method.

Efficient Hot Electron Capture in CuPc/MoSe2 Heterostructure Assisted by Intersystem Crossing.

Efficient hot electron extraction is a promising approach to develop photovoltaic devices that exceed the Shockley-Queisser limit. However, experimental evidence of hot electron harvesting employing an organic-inorganic interface is still elusive. Here, we reveal the hot electron dynamics at a CuPc/MoSe2 interface using steady-state spectroscopy and transient absorption spectroscopy. A hot electron transfer efficiency of greater than 78% from MoSe2 to CuPc is observed, comparable to that achieved in quantum dot hybrid systems. The mechanism is proposed as follows: the photogenerated hot electrons in MoSe2 transfer to CuPc and form singlet charge transfer states, which subsequently transform into triplet charge transfer states assisted by the rapid intersystem crossing, inhibiting back-donation of electrons and facilitating exciton dissociation into CuPc polarons with a nanosecond lifetime. Our results demonstrate that the intersystem crossing of the hybrid electronic state at organic-inorganic interfaces may serve as a scheme to enable efficient hot electron extraction in photovoltaic devices.

Transition metal Dual–Atom Ni2/TiO2 catalysts for photoelectrocatalytic hydrogen Evolution: A density functional theory study

Dual-atom catalysts (DACs), compared with single-atom catalysts (SACs) that have been widely studied, are now in their infancy, although they are expected to have unique catalytic properties. Here, we propose and investigate the Ni2 dimer on TiO2 system, Ni2/TiO2, that is taken as a representative of metal oxide-supported transition metal DACs, for electrocatalytic and photocatalytic hydrogen evolution using density functional theory calculations. A bottom-up self-assembly approach is developed, which can be generalized to transition metal DACs. The localization and hybridization of electronic states of the Ni2 dimer are illustrated from the coordination environments. As compared with Ni1/TiO2 SACs, the delocalized states of the Ni2 dimer of Ni2/TiO2 not only increase the reaction sites and the reduction capacities, but also positively change the H adsorption kinetics and thermodynamics, facilitating hydrogen production. The band gap of Ni2/TiO2 is narrowed into the visible region, and deep trap levels in the gap are smeared, improving the photoactivity efficiency. Our study presents a facile adsorption-deposition method to design and fabricate oxide-supported transition metal DACs for photo(electro)catalytic H2 production.

Multiband superconductivity in strongly hybridized 1T′−WTe2/NbSe2 heterostructures

The interplay of topology and superconductivity has become a subject of intense research in condensed matter physics for the pursuit of topologically non-trivial forms of superconducting pairing. An intrinsically normal-conducting material can inherit superconductivity via electrical contact to a parent superconductor via the proximity effect, usually understood as Andreev reflection at the interface between the distinct electronic structures of two separate conductors. However, at high interface transparency, strong coupling inevitably leads to changes in the band structure, locally, owing to hybridization of electronic states. Here, we investigate such strongly proximity-coupled heterostructures of monolayer 1T'-WTe$_2$, grown on NbSe$_2$ by van-der-Waals epitaxy. The superconducting local density of states (LDOS), resolved in scanning tunneling spectroscopy down to 500~mK, reflects a hybrid electronic structure, well-described by a multi-band framework based on the McMillan equations which captures the multi-band superconductivity inherent to the NbSe$_2$ substrate and that induced by proximity in WTe$_2$, self-consistently. Our material-specific tight-binding model captures the hybridized heterostructure quantitatively, and confirms that strong inter-layer hopping gives rise to a semi-metallic density of states in the 2D WTe$_2$ bulk, even for nominally band-insulating crystals. The model further accurately predicts the measured order parameter $\Delta \simeq 0.6$~meV induced in the WTe$_2$ monolayer bulk, stable beyond a 2~T magnetic field. We believe that our detailed multi-band analysis of the hybrid electronic structure provides a useful tool for sensitive spatial mapping of induced order parameters in proximitized atomically thin topological materials.

Realization of Oriented and Nanoporous Bismuth Chalcogenide Layers via Topochemical Heteroepitaxy for Flexible Gas Sensors.

Most van der Waals two-dimensional (2D) materials without surface dangling bonds show limited surface activities except for their edge sites. Ultrathin Bi2Se3, a topological insulator that behaves metal-like under ambient conditions, has been overlooked on its surface activities. Herein, through a topochemical conversion process, ultrathin nanoporous Bi2Se3 layers were epitaxially deposited on BiOCl nanosheets with strong electronic coupling, leading to hybrid electronic states with further bandgap narrowing. Such oriented nanoporous Bi2Se3 layers possessed largely exposed active edge sites, along with improved surface roughness and film forming ability even on inkjet-printed flexible electrodes. Superior room-temperature NO2 sensing performance was achieved compared to other 2D materials under bent conditions. Our work demonstrates that creating nanoscale features in 2D materials through topochemical heteroepitaxy is promising to achieve both favorable electronic properties and surface activity toward practical applications.

Visualizing band structure hybridization and superlattice effects in twisted MoS2/WS2 heterobilayers

A mismatch of atomic registries between single-layer transition metal dichalcogenides (TMDs) in a two-dimensional (2D) van der Waals heterostructure produces a moiré superlattice with a periodic potential, which can be fine-tuned by introducing a twist angle between the materials. This approach is promising both for controlling the interactions between the TMDs and for engineering their electronic band structures, yet direct observation of the changes to the electronic structure introduced with varying twist angle has so far been missing. Here, we probe heterobilayers comprised of single-layer MoS2 and WS2 with twist angles ranging from 2∘ to 20∘ and determine the twist angle-dependent evolution of the electronic band structure using micro-focused angle-resolved photoemission spectroscopy. We find strong interlayer hybridization between MoS2 and WS2 electronic states at the -point of the Brillouin zone, leading to a shift of the valence band maximum in the heterostructure. Replicas of the hybridized states are observed at the center of twist angle-dependent moiré mini Brillouin zones. We confirm that these replica features arise from the inherent moiré potential by comparing our experimental observations with density functional theory calculations of the superlattice dispersion. Our direct visualization of these features underscores the potential of using twisted heterobilayer semiconductors to engineer hybrid electronic states and superlattices that alter the electronic and optical properties of 2D heterostructures for a wide range of twist angles.

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Identification of hidden orbital contributions in the La0.65Sr0.35MnO3 valence band

Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of ${\mathrm{La}}_{0.65}{\mathrm{Sr}}_{0.35}{\mathrm{MnO}}_{3}$ (LSMO), a landmark system for spintronics applications, a description based solely on Mn $3d$ and O $2p$ electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La $5p$, Mn $4s$, and O $2s$ orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.

The optical response of artificially twisted MoS_2 bilayers

Two-dimensional layered materials offer the possibility to create artificial vertically stacked structures possessing an additional degree of freedom—theinterlayertwist. We present a comprehensive optical study of artificially stacked bilayers (BLs) MoS_2 encapsulated in hexagonal BN with interlayer twist angle ranging from 0^{circ } to 60^{circ } using Raman scattering and photoluminescence spectroscopies. It is found that the strength of the interlayer coupling in the studied BLs can be estimated using the energy dependence of indirect emission versus the A_text {1g}–E_text {2g}^1 energy separation. Due to the hybridization of electronic states in the valence band, the emission line related to the interlayer exciton is apparent in both the natural (2H) and artificial (62^circ ) MoS_2 BLs, while it is absent in the structures with other twist angles. The interlayer coupling energy is estimated to be of about 50 meV. The effect of temperature on energies and intensities of the direct and indirect emission lines in MoS_2 BLs is also quantified.

CdSe/Ag Hybrid Aerogels: Integration of Plasmonic and Excitonic Properties of Metal–Semiconductor Nanostructures via Sol–Gel Assembly

Metal–semiconductor hybrid nanomaterials (HNMs) exhibit unique properties that are distinct from individual nanostructures, leading to promising applications in optical technologies. The interfacial linkage of semiconductor and metal nanoparticles (NPs) via cogelation is an effective strategy to produce HNMs that show strong plasmon‐exciton coupling and improved physical properties. However, optical properties of these hybrids show little to no tunability. Herein, CdSe/Ag hybrid aerogels that show tunable absorption and photoluminescence (PL) are produced by cogelation of CdSe nanorods (NRs) or NPs with Ag hollow NPs. Hybrid electronic states are created by overlapping the excitonic absorption of CdSe NRs or NPs with the plasmonic absorption of Ag NPs. Physical characterization of the hybrids reveals an interconnected network of hexagonal CdSe and cubic Ag NPs, linked by Ag+ and Se2− surface species, without intervening ligands. PL spectra exhibit maxima at 640 and 720 nm for the CdSe NPs/Ag and CdSe NRs/Ag hybrids, respectively, corresponding to new radiative decay mechanisms. Time‐resolved PL data support the emergence of new radiative pathways, kinetically and energetically distinct from the excitonic and plasmonic properties of primary NPs. This new approach of metal–semiconductor hybrid formation through cogelation is intriguing for the design of high‐efficiency HNMs without detrimental PL quenching.

Tackling voltage losses

Voltage losses limit the performance of organic solar cells, yet their origins are not fully understood. Now, a theoretical model encompassing electronic state hybridization and thermal population of vibrational states explains the reduced non-radiative voltage losses in efficient non-fullerene acceptor systems.

Magnetic proximity effect induced spin splitting in two-dimensional antimonene/Fe3GeTe2 van der Waals heterostructures

Recently, two-dimensional van der Waals (vdW) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe3GeTe2 vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum (CBM) and the valence-band maximum (VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from –5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile, as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb–Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.

Substrate orientation dependent structural, electronic and magnetic properties of V and Cr linear chains

In order to gauge the effect of substrate orientation on the structural, electronic and magnetic properties of linear chains (LCs) of transition metals we have investigated the chain + substrate systems comprising LCs of V and Cr on different orientations of Cu substrate (Cu(110), Cu(001) and Cu(111)). We find that Cu(110) mimics the Cu bulk in a better manner than Cu(001) and Cu(111) substrates for the same number of atomic layers used to build these substrates. Structural relaxation unfurls the surface reconstruction of Cu(001) and Cu(111) chain + substrate systems. The strength of chain + substrate interaction depends on the substrate orientation as well as on the type of chain atom. The magnetic moment of chain atoms quenches to some extent when deposited over the substrates. Furthermore, Cu(110) is found to be energetically favoured for deposition of these chains, though it affects the magnetic moment on chain atoms more adversely than Cu(001) and Cu(111). Hybridization of electronic states of chain and substrate atoms is illustrated by broadening of the density of states (DOS) for chain + substrate systems.

Giant magnetoresistance due to orbital-symmetry mismatch in transition metal benzene sandwich molecules

Achieving large magnetoresistance (MR) effects in atomic-scale junctions is of great importance in the field of molecular spintronics. In this work, using ab initio quantum transport calculations, we report on the spin transport properties of molecular junctions made of single transition metal benzene sandwich molecules $(\mathrm{TM}{\mathrm{Bz}}_{2})$ bridged by ferromagnetic electrodes. We find that relative magnetic orientations of two electrodes and the molecule can dramatically affect low-bias transport properties of the junction. While the $\mathrm{TM}{\mathrm{Bz}}_{2}$ are insulating in the gas phase, their corresponding molecular junctions bridged between the two electrodes are half-metallic minority-spin conductors (i.e., almost 100% spin polarization) and display very large MR. More interestingly, even larger molecular MR, corresponding to a reversal of molecular spin moment, are found due to the spin-valve behavior of the molecule controlled by the magnetic impurity. Such a particular performance is attributed to strong spin-selective hybridization of electronic states at the molecule/metal interface due to orbital-symmetry mismatch between the electrode's and molecular states. We also discuss the importance of the shape of electrodes on spin transport efficiency.

Organic Neutral Radical Emitters: Impact of Chemical Substitution and Electronic-State Hybridization on the Luminescence Properties.

Neutral donor-acceptor (D-A•) organic radicals have recently attracted a great deal of attention as promising luminescent materials due to their strong doublet emission. Here, we consider a series of emitters based on substituted triarylamine (TAA) donors and a radical-carrying perchlorotriphenylmethyl (PTM) acceptor. We evaluate, by means of quantum-chemical calculations and theoretical modeling, how chemical substitution affects the electronic structures and radiative and nonradiative decay rates. Our calculations show that the radiative decay rates are dominated in all instances by the electronic coupling between the lowest excited state, which has charge-transfer (CT) character, and the ground state. On the other hand, the nonradiative decay rates in the case of TAA-PTM radicals that have high CT energies are defined by the electronic hybridization of the CT state with local excitations (LE) on the PTM moiety; also, these nonradiative rates deviate significantly from the gap law dependence that is observed in the TAA-PTM radicals that have low CT energies. These findings underscore that hybridization of the emissive state with high-energy states can, in analogy with the intensity borrowing effect commonly invoked for radiative transitions, enhance as well the nonradiative decay rates. Our results highlight that in order to understand the emissive properties of D-A• radicals, it is required that the electronic hybridization of the CT states with both the ground and the LE states be properly considered.