Interlayer Charge Research Articles

Building block effect induces horizontally oriented bottom Zn(002) deposition for a highly stable zinc anode

The practical application of zinc anodes for rechargeable aqueous zinc-ion batteries is hindered to uncontrollable dendritic zinc deposition and side reactions. And the deposition of zinc is like building blocks layer by layer, typically considered as nucleation, growth and evolution driven by electric field. Yet the important role of the bottommost deposits is generally ignored. Here, we developed a highly self-adaptable polydimethylsiloxane (PDMS)/montmorillonite (MMT) film to regulate the process of zinc deposition sustainably. In the nucleation and growth stages of zinc, the two-step regulation of the building block effect benefits from the adsorption of oxygen-containing sites on PDMS and fast zinc ion nanochannels in the negatively charged interlayer of MMT to achieve targeted-capture of zinc ions and ordered-deposition, thus inducing horizontally oriented Zn(002) deposition in the initial nucleation layer and providing a flat deposition site for the subsequently deposited metal. In the evolutionary stage of Zn, the PDMS/MMT (PMZn) interfacial layer can achieve a conformal contact with the anode due to the high dynamic adaptability and self-healing of the micro-crosslinking of Si-O-Si and B-O bonds. Consequently, PMZn@Cu||Zn offers higher coulombic efficiency(CE) (99.77%) and the PMZn@Zn anodes exhibit an ultra-long cycle life of 2000 h, more than 10 times that of bare zinc anodes. The stability of the high capacity of PMZn@Zn||MnO2 full cells far exceeds that of Zn||MnO2. This strategy provides an effective approach to develop a stable Zn metal anode for aqueous rechargeable Zn batteries.

Effects of iron corrosion products on the degradation of bentonite structure and properties

Bentonite is a key material for engineering barriers to prevent groundwater and nuclide migration in the multi-barrier system of high-level radioactive waste (HLW) geological disposal. However, its barrier property will be degraded under the action of iron corrosion products of steel disposal containers. In this paper, the effects of iron corrosion products on the degradation of bentonite structure and properties were investigated in the simulated environments for HLW geological disposal. The results showed that Fe2+/Fe3+ dissolved from iron powder could enter montmorillonite (Mt) interlayer and substituted part of Na+, which caused the decrease of the volume and interlayer spacing of Mt, and the structural integrity of Mt was destroyed. Macroscopically, the water absorption and swelling property of bentonite were significantly decreased. The degradation mechanism of Mt structure was mainly that Fe2+/Fe3+ generated by iron corrosion entered the interlayer domain of Mt to compensate for the interlayer charge deficit.

Controllable Resistive Switching in ReS2 /WS2 Heterostructure for Nonvolatile Memory and Synaptic Simulation.

Memristors with nonvolatile storage performance and simulated synaptic functions are regarded as one of the critical devices to overcome the bottleneck in traditional von Neumann computer architecture. 2D van der Waals heterostructures have paved a new way for the development of advanced memristors by integrating the intriguing features of different materials and offering additional controllability over their optoelectronic properties. Herein, planar memristors with both electrical and optical tunability based on ReS2 /WS2 van der Waals heterostructure are demonstrated. The devices show unique unipolar nonvolatile behavior with high Roff /Ron ratio of up to 106 , desirable endurance, and retention, which are superior to pure ReS2 andWS2 devices. When decreasing the channel length, the set voltage can be notably reduced while the high Roff /Ron ratios are retained. By introducing electrostatic doping through the gate control, the set voltage can be tailored in a wide range from 4.50 to 0.40V. Furthermore, biological synaptic functions and plasticity, including spike rate-dependent plasticity and paired-pulse facilitation, are successfully realized. By employing optical illumination, resistive switching can also be modulated, which is dependent on the illumination energy and power. A mechanism related to the interlayer charge transfer controlled by optical excitation is revealed.

TiO2–x@C/MoO2 Schottky junction: Rational design and efficient charge separation for promoted photocatalytic performance

Limited solar light harvesting, sluggish charge transfer kinetics, and inferior affinity for adsorbed hydrogen species (H*) severely restrict the photocatalytic hydrogen generation activity of TiO2 photocatalysts. Herein, we present a novel TiO2–x@C/MoO2 Schottky junction prepared via a simple one-step in situ phase-transition-regulation strategy. Crucially, the abundant oxygen vacancies in TiO2–x@C/MoO2 narrow the bandgap and introduce defects to improve the photoresponse. The strongly bonded carbon layer not only serves as a fast charge-transport channel to improve the interlayer charge transfer efficiency but also protects oxygen vacancies from oxidation. Moreover, the Schottky barrier effectively impairs the recombination of electrons and holes and promotes the utilization of photogenerated electrons. Furthermore, the MoO2 cocatalyst optimizes the Gibbs free energy for H2 evolution. As a result of the favorable synergy, the resulting TiO2–x@C/MoO2 presents a significantly enhanced photocatalytic H2 production rate of 506 μmol g−1 h−1 compared to those of TiO2–x and TiO2–x@C (125.5- and 15.8-times larger, respectively). Moreover, outstanding stability over 27 h was achieved because of the protection provided by the surface carbon layer. This ingenious design and facile synthetic strategy offer exciting avenues for the design of strongly coupled Schottky junction photocatalysts for efficient solar-to-chemical conversions.

Polaritonic Probe of an Emergent 2D Dipole Interface.

The use of work-function-mediated charge transfer has recently emerged as a reliable route toward nanoscale electrostatic control of individual atomic layers. Using α-RuCl3 as a 2D electron acceptor, we are able to induce emergent nano-optical behavior in hexagonal boron nitride (hBN) that arises due to interlayer charge polarization. Using scattering-type scanning near-field optical microscopy (s-SNOM), we find that a thin layer of α-RuCl3 adjacent to an hBN slab reduces the propagation length of hBN phonon polaritons (PhPs) in significant excess of what can be attributed to intrinsic optical losses. Concomitant nano-optical spectroscopy experiments reveal a novel resonance that aligns energetically with the region of excess PhP losses. These experimental observations are elucidated by first-principles density-functional theory and near-field model calculations, which show that the formation of a large interfacial dipole suppresses out-of-plane PhP propagation. Our results demonstrate the potential utility of charge-transfer heterostructures for tailoring optoelectronic properties of 2D insulators.

Interlayer charge transfer in supported and suspended MoS2/Graphene/MoS2 vertical heterostructures.

In this letter, we report on the optical and structural properties of supported and suspended MoS2/Graphene/MoS2 vertical heterostructures using Raman and photoluminescence (PL) spectroscopies. Vertical heterostructures (VH) are formed by multiple wet transfers on micro-sized holes in SiO2/Si substrates, resulting in VH with different configurations. The strong interlayer coupling is confirmed by Raman spectroscopy. Additionally, we observe an enhancement of the PL emission in the three-layer VH (either support or suspended) compared with bare MoS2 or MoS2/Graphene. This suggests the formation of a spatial type-II band alignment assisted by the graphene layer and thus, the operation of the VH as a n++/metal/n junction.

Incommensurate charge-stripe correlations in the kagome superconductor CsV3Sb5−xSnx

The class of AV3Sb5 (A=K, Rb, Cs) kagome metals hosts unconventional charge density wave states seemingly intertwined with their low temperature superconducting phases. The nature of the coupling between these two states and the potential presence of nearby, competing charge instabilities however remain open questions. This phenomenology is strikingly highlighted by the formation of two ‘domes’ in the superconducting transition temperature upon hole-doping CsV3Sb5. Here we track the evolution of charge correlations upon the suppression of long-range charge density wave order in the first dome and into the second of the hole-doped kagome superconductor CsV3Sb5−xSnx. Initially, hole-doping drives interlayer charge correlations to become short-ranged with their periodicity diminished along the interlayer direction. Beyond the peak of the first superconducting dome, the parent charge density wave state vanishes and incommensurate, quasi-1D charge correlations are stabilized in its place. These competing, unidirectional charge correlations demonstrate an inherent electronic rotational symmetry breaking in CsV3Sb5, and reveal a complex landscape of charge correlations within its electronic phase diagram. Our data suggest an inherent 2kf charge instability and competing charge orders in the AV3Sb5 class of kagome superconductors.

Halogen atom-doped graphene/MoSe2 heterojunction Schottky barrier height modulation

Achieving lower Schottky barrier heights in logic devices remains a formidable challenge. In this paper, the effect of halogen atoms doping on the type and height of graphene/MoSe2 Schottky is investigated using density functional theory. For monolayer MoSe2, the doping of halogen atoms introduces impurity energy levels in the energy band and leads to a change in the position of the Fermi energy level. Graphene and MoSe2 bonding retains their respective intrinsic electrochemical properties and bond with weak van der Waals forces to form n-type Schottky contacts. The doping of halogen atoms effectively changes the Schottky type and height of graphene/MoSe2. The Schottky type of heterojunctions doped with F, Cl, and Br atoms changes from n-type contacts to ohmic contacts. I and At atoms effectively reduce the Schottky barrier height of graphene/MoSe2. The disparity charge density indicates that the electrons in graphene are transferred to MoSe2, forming a built-in electric field pointing from graphene to MoSe2. After the doping of halogen atoms, the interlayer charge transfer between graphene and MoSe2 is significantly reduced, and the Fermi energy level appears to be shifted downward, which eventually leads to the reduction of the Schottky barrier height.

Adjusting the Stacking Model of Two-Dimensional Covalent Organic Frameworks for Volatile Acid Sensing via Spatial Effects.

Covalent organic frameworks (COFs) are polymer networks with a precise structure and permanent porosity, making them an attractive platform for the detection of volatile analytes due to their chemical stability and accessible active sites. In this study, based on electron-rich N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine moiety, two 2D COFs with different topological structures and stacking models were designed by the strategy of spatial effect. The conductivity of the AB-stacked COF-NUST-20 was an order of magnitude higher than that of the AA-stacked COF-NUST-30. With the protonation of the imine bond, both COFs exhibited a strong, rapid, and reversible visible color change in response to corrosive HCl vapor. In addition, the AB-stacked COF-NUST-20, which facilitates both interlayer and intralayer charge transfer, shows better sensing performance. These findings demonstrate the usefulness of all-aromatic 2D COFs as real-time responsive chemosensors and provide insight into the design of sensing materials with high sensitivity.

Infiltration of C-ring into crystalline carbon nitride S-scheme homojunction for photocatalytic hydrogen evolution

Enhancing the carrier separation in graphitized carbon nitride (g-C3N4) is advantageous for improving its photocatalytic activity. Herein, we propose a feasible method for preparing CN-C by thermal polymerization to gradually infiltrate carbon rings (C-rings) into the surface of crystalline carbon nitride (CN), enabling photogenerated electrons to be transferred rapidly between the CN inner layers and the CN/C outer layer. Successful penetration and distribution of carbon rings into carbon nitride were confirmed by secondary ion mass spectroscopy using ratio analysis of C and N elements at various depths of the prepared photocatalyst. Theoretical calculations indicated that CN and CN/C in the molecule generated different Fermi levels to form an S-scheme homojunction, establishing appropriate built-in electric fields and thus enabling interlayer charge migration. Moreover, the overlap of the conjugate plane of C-rings with carbon nitride led to the formation of photogenerated in-plane charge transfer tunnels. The two-electron transfer tunnels greatly improved the dissociation efficiency of photogenerated electrons. The prepared sample loaded with 3 wt% Pt as a co-catalyst for hydrogen production under visible light irradiation, and the prepared optimal sample CN-C showed a maximum quantum efficiency of 15.56% for photocatalytic H2 evolution at 385 nm. This research introduces a new idea for constructing a directional transfer path for charge carriers in-plane and intralayer.

An interlayer-based positive charge compensation strategy for the preparation of highly selective Mg2+/Li+ separation nanofiltration membranes

The Mg2+/Li+ screening selectivity determines the practical application of nanofiltration technology in lithium extraction from salt-lake brines and industrial lithium production. In this work, a membrane structure design strategy based on the interlayers was developed to prepare nanofiltration (NF) membranes with high Mg2+/Li+ separation selectivity and high permeability. Through investigating the influence of the interlayer charge on the structure and performance of the NF membrane, the interlayer for the preparation of the NF membrane with high Mg2+/Li + separation selectivity was screened. Relevant characterizations indicate that the positively charged interlayer can endow the NF membrane with appropriate pore size and surface charge density to achieve high Mg2+/Li+ separation selectivity through the synergistic effect of size sieving and Donnan exclusion. Moreover, the pore size of the NF membrane is controlled by the release rate of the piperazine (PIP) from the interlayer, while the surface charge density of the NF membrane is jointly determined by the charge of the interlayer and PA layer. The performance evaluation suggests that the NF membrane prepared with the best screened interlayer has a Mg2+/Li+ separation factor up to 88.6 while maintaining a high permeability (22.5 L m−2 h−1·bar−1), which is better than that of the most membranes reported in the literature. Overall, this work is expected to promote the practical application of NF membranes in lithium extraction from salt-lake brines and industrial lithium production.

Two-dimensional MoS2/Ti2CX2 (X = S, Se, Te) heterostructures with tunable electrical contact type

The tunable electrical contact type in van der Waals (vdW) heterostructures plays an important role in promoting the efficiency of ultrathin electronic devices. From the first-principles calculations, the electronic properties and electrical contact type of the MoS2/Ti2C heterostructure and its ramifications MoS2/Ti2CX2 (X = S, Se, Te) heterostructures are verified. The strong interfacial interaction is found in pristine MoS2/Ti2C heterostructure, resulting in the metallization of MoS2 layer. The functionalization of S, Se, and Te atoms can weaken the interfacial interaction, forming metal-semiconductor contact. The p-type Schottky contact is formed in MoS2/Ti2CS2 and MoS2/Ti2CSe2 heterostructures, while Ohmic contact is formed in MoS2/Ti2CTe2 heterostructure. The application of external electric field can efficiently modulate the contact type of MoS2/Ti2CX2 (X = Se and Te) heterostructures. The discrepancy of electron affinity of S, Se, and Te atoms leads to the different interlayer charge transfer, and thus the different electrical contact type can be realized in MoS2/Ti2CX2 (X = S, Se, Te) heterostructures. The tunable contact type makes these heterostructures become potential candidate materials for enhancing the nanoelectronic devices’ efficiency.

Ultrafast Laser Control of Antiferromagnetic-Ferrimagnetic Switching in Two-Dimensional Ferromagnetic Semiconductor Heterostructures.

Realizing ultrafast control of magnetization switching is of crucial importance for information processing and recording technology. Here, we explore the laser-induced spin electron excitation and relaxation dynamics processes of CrCl3/CrBr3 heterostructures with antiparallel (AP) and parallel (P) systems. Although an ultrafast demagnetization of CrCl3 and CrBr3 layers occurs in both AP and P systems, the overall magnetic order of the heterostructure remains unchanged due to the laser-induced equivalent interlayer spin electron excitation. More crucially, the interlayer magnetic order switches from antiferromagnetic (AFM) to ferrimagnetic (FiM) in the AP system once the laser pulse disappears. The microscopic mechanism underpinning this magnetization switching is dominated by the asymmetrical interlayer charge transfer combined with a spin-flip, which breaks the interlayer AFM symmetry and ultimately results in an inequivalent shift in the moment between two FM layers. Our study opens up a new idea for ultrafast laser control of magnetization switching in two-dimensional opto-spintronic devices.

Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material.

High light absorption (∼15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs) make them ideal candidates for optoelectronic device applications. Competing interlayer charge transfer (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hexagonal boron nitride (hBN), due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.

Changes in the photoluminescence of ultra-weak interlayer coupled MoSe2/PbI2 van der Waals heterostructures

Photo-generated dynamics have been extensively studied in two-dimensional (2D) heterostructures, such as MoSe2/WSe2 and MoSe2/MoS2. Here, we fabricate few-layer PbI2 and monolayer MoSe2 van der Waals (vdW) heterostructures. The excited-wavelength dependent measurements of photoluminescence (PL) and transient dynamic absorption spectra show that there is almost no photo-generated charge transfer between PbI2 and MoSe2. PL changes of MoSe2 are rather dominated by the Fermi level (EF) modulation through the interlayer charge transfer. Density functional theory calculation shows that binding energies in the heterostructures of MoSe2/WSe2 or MoSe2/MoS2 are 2–3 times higher than that of the MoSe2/PbI2 heterostructure, suggesting the weaker interlayer coupling between MoSe2 and PbI2. We propose that the weak interlayer vdW coupling cannot drive the photo-generated interlayer charge transfer while the EF modulation can be achieved through the interlayer charge transfer. The findings will be helpful to fundamental research and applications for novel optoelectronic devices based on 2D material vdW heterostructures.

Graphene/Janus ZnO heterostructure to build highly efficient photovoltaic properties

We investigated the effect of F and Cl functionalization of Janus ZnO on the optoelectronic propertiesof Graphene/ZnO (Gra/ZnO) heterojunctions by using Density Functional Theory (DFT). The calculated results show that the Janus ZnO/Gra heterojunction is a van der Waals heterojunction with layer spacing >3 Å for both stacking styles. In addition, the functionalized heterojunction retains the original structure of Gra and has an interface formation energy of <0, making it easy to prepare chemically. Furthermore, different stacking styles can convert heterojunctions from n-type Schottky to ohmic contacts, which has promising applications in field-effect transistors. Moreover, functionalized Janus ZnO/Gra can effectively enhance interlayer charge transfer and improve the transmittance of the heterojunction, which is beneficial for applications in nanoelectronic devices.

Highly Efficient Synthesis of High‐Value Olefins from Syngas over Layered Fe‐Mn/Magadiite Catalyst

AbstractThe simultaneous realization of high olefin/paraffin (O/P) ratio and low CH4 selectivity has always been a bottleneck for the conversion of syngas to high‐value olefins (HVOs). Magadiite (MAG) is a layered silicate material with active SiOH, which increases the interlayer charge density and ion‐exchange ability. Herein, a MAG‐supported, Mn‐modified Fe3O4 microsphere catalyst exhibits excellent CO conversion of 76.5 % and HVO selectivity, with a high O/P ratio of 5.02 and low CH4 selectivity of 16.1 % for conversion of syngas to HVOs. The layered structure of the MAG support promotes dispersion of the active centers and the Mn promoter improves the basic properties of the catalyst. Moreover, the Mn promoter and MAG support have a synergistic effect, which promotes CO dissociation and suppresses H2 adsorption, thereby resulting in high HVO selectivity and low CH4 selectivity.

Enhanced Interlayer Charge Injection Efficiency in 2D Multilayer ReS2 via Vertical Double-Side Contacts.

Two-dimensional (2D) van der Waals (vdW) layered materials have provided novel opportunities to explore interesting physical properties such as thickness-dependent bandgap, moiré excitons, superconductivity, and superfluidity. However, the presence of interlayer resistance along the thickness and Schottky barrier in metal-to-2D vdW semiconducting materials causes a limited interlayer charge injection efficiency, perturbing various intrinsic properties of 2D vdW multilayers. Herein, we report a simple but powerful contact electrode design to enhance interlayer carrier injection efficiency along the thickness by constructing vertical double-side contact (VDC) electrodes. A 2-fold extended contact area of VDC not only strongly limits an interlayer resistance contribution to the field-effect mobility and current density at the metal-to-2D semiconductor interface but also significantly suppresses both current transfer length (≤1 μm) and specific contact resistivity (≤1 mΩ·cm2), manifesting clear benefits of VDC in comparison with those in conventional top-contact and bottom-contact configurations. Our layout for contact electrode configuration may suggest an advanced electronic device platform for high-performing 2D optoelectronic devices.

Suppression of substrate-induced charge doping in hBN-encapsulated monolayer WS2

Strong coupling between a two-dimensional material and substrate is problematic in that interlayer charge transfer at the interface often complicates optoelectronic device applications. Such substrate-induced charge doping effects are particularly large for two-dimensional materials on SiO2/Si substrate. Here, we report a Raman study of monolayer WS2 encapsulated with hexagonal boron nitride (hBN) to unveil substrate-related charge doping phenomena under the influence of laser irradiation. Raman correlation analysis between the E′ and A1′ phonon frequencies of WS2 reveals that the encapsulation of WS2 with hBN leads to a screening of electron transfer from SiO2 to WS2. Further, photo-induced charge doping in WS2 is completely suppressed by hBN encapsulation. Our results demonstrate that understanding the photo-induced charge doping effects in two-dimensional heterostructures is useful in characterizing the role of hBN encapsulation and, thus, shed light on design strategies for efficient two-dimensional optoelectronic applications where a precise control of charge doping is required.

External screening and lifetime of exciton population in single-layer ReSe2 probed by time- and angle-resolved photoemission spectroscopy

The semiconductor ${\mathrm{ReSe}}_{2}$ is characterized by a strongly anisotropic optical absorption and is therefore promising as an optically active component in two-dimensional heterostructures. However, the underlying femtosecond dynamics of photoinduced excitations in such materials has not been sufficiently explored. Here, we apply an infrared optical excitation to single-layer ${\mathrm{ReSe}}_{2}$ grown on a bilayer graphene substrate and monitor the temporal evolution of the excited state signal using time- and angle-resolved photoemission spectroscopy. We measure an optical gap of $(1.53\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, consistent with resonant excitation of the lowest exciton state. The exciton distribution is tunable via the linear polarization of the pump pulse and exhibits a biexponential decay with time constants given by ${\ensuremath{\tau}}_{1}=(110\ifmmode\pm\else\textpm\fi{}10)$ fs and ${\ensuremath{\tau}}_{2}=(650\ifmmode\pm\else\textpm\fi{}70)$ fs, facilitated by interlayer charge transfer to the underlying bilayer graphene and recombination via an in-gap state that is pinned at the Fermi level. By extracting the momentum-resolved exciton distribution we estimate its real-space radial extent to be greater than $(17\ifmmode\pm\else\textpm\fi{}1)$ \AA{}, implying significant spatial broadening of the distribution due to screening from the bilayer graphene substrate.