Charge Transfer In Heterostructures Research Articles

Interfacial tuning in FeP/ZnIn2S4 Ohm heterojunction: Enhanced photocatalytic hydrogen production via Zn-P charge bridging

Interfacial regulation is key to photocatalytic performance, yet modulating interfacial charge transfer in heterostructures remains challenging. Herein, a novel nanoflower-like FeP/ZnIn2S4 Ohm heterostructure is first designed, with Zn atoms in ZnIn2S4 (ZIS) acting as potential anchoring sites around P atoms, forming liganded Zn-P bonds. Combining 1D FeP nanowires and 2D ZIS nanosheets enhances the mobility of photogenerated electrons. The synergistic chain-type “electron pickup” mechanism of the Ohm heterojunction coupled with the Zn-P bond speeds up electron transport at the interface. The Ohm heterojunction initiates an internal electric field, creating a driving force to further transfer photogenerated electrons through the Zn-P rapid electron transport channel to FeP, which acts as a reservoir for active sites to release H2. The optimized FeP/ZIS demonstrates a remarkable H2 evolution rate at 4.36 mmol h−1 g−1, 3.6 times that of pristine ZIS. This work provides novel insights into optimizing photocarrier dynamics via interfacial microenvironment modulation.

Ferroelectric polarization enhancing photocatalytic performance of 2D carbon and oxygen co-doping g-C3N4/α-In2Se3 heterostructure: A conversion of traditional type-II to S-scheme

Ferroelectric materials with internal spontaneous polarization are conducive to enhancing photocatalytic performance by promoting photogenerated carriers separation. However, the traditional perovskite-type ferroelectric photocatalysts possess a typical 3D structure that is constrained by few exposed catalytic active sites and low specific surface area when compared to a 2D structure. In our study, the electronic properties of the 2D ferroelectric heterostructure for carbon and oxygen co-doping g-C3N4 (COCN)/In2Se3 with different out-of-plane ferroelectric polarization directions are investigated by first-principle calculations, namely, COCN/DOWN and COCN/UP heterostructures. The results show that when the ferroelectric polarization of the 2D In2Se3 layer in heterostructures is reversed, the heterostructure switches from traditional type-II (COCN/DOWN heterostructure) with an indirect bandgap of 1.58 eV to S-scheme (COCN/UP heterostructure) with a direct bandgap of 1.43 eV, in which the band edge positions of the S-scheme COCN/UP heterostructure satisfy the redox potential of the efficient photocatalytic selective oxidation of toluene to benzaldehyde. Further investigations revealed that the application of an electric field 0 ∼ +0.3 V/Å can reduce the bandgap and enhance the out-of-plane polarization of the COCN/UP heterostructure, which improve the photocatalytic activity of the S-scheme COCN/UP heterostructure. This work highlights the significance of ferroelectric polarization for charge transfer in heterostructures and provides theoretical guidance for the design of high-performance S-scheme photocatalysts.

Interfacial Ti-S Bond Modulated S-Scheme MOF/Covalent Triazine Framework Nanosheet Heterojunctions for Photocatalytic C-H Functionalization.

Constructing photocatalyst systems to functionalize the inert C-H bonds has attracted extensive research interest. However, purposeful modulation of interfacial charge transfer in heterostructures remains a challenge, as it usually suffers from sluggish kinetics. Reported herein is an easy strategy to construct the heteroatom-induced interface for developing the titanium-organic frameworks (MOF-902) @ thiophene-based covalent triazine frameworks (CTF-Th) nanosheets S-scheme heterojunctions with controllable oxygen vacancies (OVs). Specifically, Ti atoms were first anchored onto the heteroatom site of CTF-Th nanosheets, and then grown into MOF-902 via an interfacial Ti-S linkage, generating OVs. Using in situ X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations, the enhanced interfacial charge separation and transfer induced by moderate OVs in the pre-designed S-scheme nanosheets was validated. The heterostructures exhibited an improved efficiency in photocatalytic C3-acylation of indoles under mild conditions with a yield 8.2 times larger than pristine CTF-Th or MOF-902 and enabled an extended scope of substrates (15 examples). This performance is superior to state-of-the-art photocatalyst and can be retained, without significant loss, after 12 consecutive cycles.

Interfacial Ti−S Bond Modulated S‐Scheme MOF/Covalent Triazine Framework Nanosheet Heterojunctions for Photocatalytic C−H Functionalization

AbstractConstructing photocatalyst systems to functionalize the inert C−H bonds has attracted extensive research interest. However, purposeful modulation of interfacial charge transfer in heterostructures remains a challenge, as it usually suffers from sluggish kinetics. Reported herein is an easy strategy to construct the heteroatom‐induced interface for developing the titanium‐organic frameworks (MOF‐902) @ thiophene‐based covalent triazine frameworks (CTF‐Th) nanosheets S‐scheme heterojunctions with controllable oxygen vacancies (OVs). Specifically, Ti atoms were first anchored onto the heteroatom site of CTF‐Th nanosheets, and then grown into MOF‐902 via an interfacial Ti−S linkage, generating OVs. Using in situ X‐ray photoelectron spectroscopy (XPS), extended X‐ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations, the enhanced interfacial charge separation and transfer induced by moderate OVs in the pre‐designed S‐scheme nanosheets was validated. The heterostructures exhibited an improved efficiency in photocatalytic C3‐acylation of indoles under mild conditions with a yield 8.2 times larger than pristine CTF‐Th or MOF‐902 and enabled an extended scope of substrates (15 examples). This performance is superior to state‐of‐the‐art photocatalyst and can be retained, without significant loss, after 12 consecutive cycles.

Second Harmonic Generation in van der Waals Heterostructure of Centrosymmetric ReS2 and Graphene

AbstractVan der Waals (vdW) heterostructures of two‐dimensional (2D) materials promise exotic properties beyond the reach of existing material systems and open unprecedented opportunities for device applications. Here, it is demonstrated that vdW stacking of centrosymmetric ReS2 and graphene into heterostructure could induce strong second harmonic generation (SHG), though there is not any SHG from the individual ReS2 or graphene. It could be attributed to the interfacial charge transfer in the heterostructure. With the distorted 1T crystal structure of ReS2 and electrostatic screening effect, the charge transfer gives rise to non‐uniform charge distribution across the ReS2's atomic layers, resulting in the broken centrosymmetry for the second‐order hyperpolarizability. At the specific pump wavelength of 1550 nm, the strength of the induced SHG in a trilayer ReS2/graphene vdW heterostructure is approximately twice of that from a monolayer MoS2. This work reveals vdW stacking is a simple and efficient method for inducing SHG in 2D materials with centrosymmetry, which could be considered as another unique attribute of 2D materials. It also indicates that SHG spectroscopy is a valid technique for probing charge transfer and distribution in heterostructures of 2D materials.

Efficient Charge Transfer in Heterostructures of CdS/NaTaO3 with Improved Visible-Light-Driven Photocatalytic Activity.

Photocatalyst NaTaO3 with a cube-shaped morphology and an average particle size of 100 nm was synthesized using an effortless hydrothermal method. The composite heterostructures of CdS/NaTaO3 with variable concentrations of CdS were fabricated after the surface functionalization of bare NaTaO3 using 3-mercaptopropionic acid. As-synthesized photocatalysts were characterized using powder X-ray diffraction analysis, Raman spectroscopy, field-emission scanning and transmission electron microscopies with energy-dispersive X-ray spectroscopy furnished with elemental mapping, multipoint Brunauer–Emmett–Teller (BET), and UV–vis diffuse reflectance spectroscopy. Average lifetime (τavg) of photoexcitons in heterostructures was studied using photoluminescence (PL) empowered with the time-correlated single-photon counting technique. The diminishing PL peak intensity and reduced average lifetime (τavg) of photoexcitons in heterostructures indicate the inhibition of photoexciton recombination along with efficient photoexciton exchange between heterostructures. As-synthesized heterostructures demonstrate enhanced visible-light harvesting and appreciably increased the photocatalytic performance toward the degradation of dye rhodamine B. This work highlights the importance of heterostructures with new archetypes which may provide a lead to develop highly capable and reusable photocatalysts to organic dye degradation.

Ultrafast Interlayer Electron Transfer in Incommensurate Transition Metal Dichalcogenide Homobilayers.

Two-dimensional materials, such as graphene, transition metal dichalcogenides, and phosphorene, can be used to construct van der Waals multilayer structures. This approach has shown potentials to produce new materials that combine novel properties of the participating individual layers. One key requirement for effectively harnessing emergent properties of these materials is electronic connection of the involved atomic layers through efficient interlayer charge or energy transfer. Recently, ultrafast charge transfer on a time scale shorter than 100 fs has been observed in several van der Waals bilayer heterostructures formed by two different materials. However, information on the transfer between two atomic layers of the same type is rare. Because these homobilayers are essential elements in constructing multilayer structures with desired optoelectronic properties, efficient interlayer transfer is highly desired. Here we show that electron transfer between two monolayers of MoSe2 occurs on a picosecond time scale. Even faster transfer was observed in homobilayers of WS2 and WSe2. The samples were fabricated by manually stacking two exfoliated monolayer flakes. By adding a graphene layer as a fast carrier recombination channel for one of the two monolayers, the transfer of the photoexcited carriers from the populated to the drained monolayers was time-resolved by femtosecond transient absorption measurements. The observed efficient interlayer carrier transfer indicates that such homobilayers can be used in van der Waals multilayers to enhance their optical absorption without significantly compromising the interlayer transport performance. Our results also provide valuable information for understanding interlayer charge transfer in heterostructures.

Observation of Charge Transfer in Heterostructures Composed of MoSe2 Quantum Dots and a Monolayer of MoS2 or WSe2

Monolayer transition metal dichalcogenides (TMDs) are atomically thin semiconductor films that are ideal platforms for the study and engineering of quantum heterostructures for optoelectronic applications. We present a simple method for the fabrication of TMD heterostructures containing MoSe2 quantum dots (QDs) and a MoS2 or WSe2 monolayer. The strong modification of photoluminescence and Raman spectra that includes the quenching of MoSe2 QDs and the varied spectral weights of trions for the MoS2 and WSe2 monolayers were observed, suggesting the charge transfer occurring in these TMD heterostructures. Such optically active heterostructures, which can be conveniently fabricated by dispersing TMD QDs onto TMD monolayers, are likely to have various nanophotonic applications because of their versatile and controllable properties.

Charge transfer in heterostructures of strongly correlated materials

In this work, recent theoretical investigations by the authors in the area of oxidemultilayers are briefly reviewed. The calculations were carried out using modelHamiltonians and a variety of non-perturbative techniques. Moreover, new results are alsoincluded here. They correspond to the generation of a metallic state by mixinginsulators in a multilayer geometry, using the Hubbard and double-exchangemodels. For the latter, the resulting metallic state is also ferromagnetic. Thisillustrates how electron or hole doping via transfer of charge in multilayers canlead to the study of phase diagrams of transition metal oxides in the clean limit.Currently, these phase diagrams are much affected by the disordering standardchemical doping procedure, which introduces quenched disorder in the material.