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Register a new userInterfacial charge transfer and interaction in the MXene/TiO2 heterostructures
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Hybrid materials of MXenes (2D carbides and nitrides) and transition-metal oxides (TMOs) have shown great promise in electrical energy storage and 2D heterostructures have been proposed as the next-generation electrode materials to expand the limits of current technology. Here we use first principles density functional theory to investigate the interfacial structure, energetics, and electronic properties of the heterostructures of MXenes (Tin+1CnT2; T=terminal groups) and anatase TiO2. We find that the greatest work-function differences are between OH-terminated-MXene (1.6 eV) and anatase TiO2(101) (6.4 eV), resulting in the largest interfacial electron transfer (~0.9 e/nm2 across the interface) from MXene to the TiO2 layer. This interface also has the strongest adhesion and further strengthened by hydrogen bond formation. For O-, F-, or mixed O-/F- terminated Tin+1Cn MXenes, electron transfer is minimal and interfacial adhesion is weak for their heterostructures with TiO2. The strong dependence of the interfacial properties of the MXene/TiO2 heterostructures on the surface chemistry of the MXenes will be useful to tune the heterostructures for electric-energy-storage applications.
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Heterostructures of 2D van der Waals semiconductor materials offer a diverse playground for exploring fundamental physics and potential device applications. In InSe/GaSe heterostructures formed by sequential mechanical exfoliation and stacking of 2D monochalcogenides InSe and GaSe, we observe charge transfer between InSe and GaSe due to the 2D van der Waals interface formation and a strong hysteresis effect in the electron transport through the InSe layer when a gate voltage is applied through the GaSe layer. A gate voltage dependant conductance decay rate is also observed. We relate these observations to the gate voltage dependant dynamical charge transfer between InSe and GaSe layers.
Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistance and the zero-gate-voltage conductance are consistent with such charge transfer. Short channel conduction in devices with Pt contacts is greatly enhanced compared to analogous devices with Au contacts, consistent with charge transfer expectations. Alternating current scanning tunneling microscopy (ACSTM) provides further evidence that holes are transferred from Pt into P3HT, while much less charge transfer takes place at the Au/P3HT interface.
MXene-based heterostructures have received considerable interest owing to their unique properties. Herein, we examine various heterostructures of a prototypical MXene and graphene using density functional theory. We find that the adhesion energy, charge transfer, and band structure of these heterostructures are sensitive not only to the surface functional group, but also to the stacking order. Difference in work function dictates the direction and amount of electron transfer across the interface, which causes a shift in the Dirac point of the graphene bands in the heterostructures of monolayer graphene and monolayer MXene. In the heterostructures of bilayer graphene and monolayer MXene, the interface breaks the symmetry of the bilayer graphene; in the case of the AB-stacking bilayer, the electron transfer leads to an interfacial electric field that opens up a gap in the graphene bands at the K point. This internal polarization strengthens both the interfacial adhesions and the cohesion between the two graphene layers. The MXene-graphene-MXene and graphene-MXene-graphene sandwich structures behave as two mirror-symmetric MXene-graphene interfaces. Our first principles studies provide a comprehensive understanding for the interaction between a typical MXene and graphene.
(LaNiO3)n/(LaMnO3)2 superlattices were grown using ozone-assisted molecular beam epitaxy, where LaNiO3 is a paramagnetic metal and LaMnO3 is an antiferromagnetic insulator. The superlattices exhibit excellent crystallinity and interfacial roughness of less than 1 unit cell. X-ray spectroscopy and dichroism measurements indicate that electrons are transferred from the LaMnO3 to the LaNiO3, inducing magnetism in LaNiO3. Magnetotransport measurements reveal a transition from metallic to insulating behavior as the LaNiO3 layer thickness is reduced from 5 unit cells to 2 unit cells and suggest a modulated magnetic structure within LaNiO3.
An interesting interplay between two different modifiers and the surface of titanium dioxide leads to a significant change in photoelectrochemical properties of the designed hybrid materials. The semiconductor is photosensitized by one of the counterparts and exhibits the photoelectrochemical photocurrent switching effect thanks to interactions with graphene oxide - the second modifier mediates charge transfer processes in the system, allowing us to design the materials response at the molecular level. Based on the selection of molecular counterpart we may affect the behaviour of hybrids upon light irradiation in a different manner, which may be useful for the applications in photovoltaics, optoelectronics and photocatalysis. Here we focus particularly on the nanocomposites made of titanium dioxide with graphene oxide combined with either 2,3,5,6-tetrachlorobenzoquinone or 2,3-dichloro-5,6-dihydroxybenzoquinone - for these two materials we observed a major change in the charge transfer processes occurring in the system.
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