Indium selenide/silver phosphate hollow microsphere S-scheme heterojunctions for photocatalytic hydrogen production with simultaneous degradation of tetracycline

Designing heterojunction photocatalysts with strong interfacial interactions is an effective way to reduce the recombination of photogenerated charge carriers. Here, silver phosphate (Ag₃PO₄) nanoparticles are coupled with hollow flower-like indium selenide (In₂Se₃) microspheres by a facile Ostwald ripening and in-situ growth method, resulting in the construction of In₂Se₃/Ag₃PO₄ hollow microsphere step-scheme (S-scheme) heterojunction with a large contact interface. The flower-like In₂Se₃ with hollow and porous structure provides a large specific surface area and numerous active sites for photocatalytic reactions to take place. The photocatalytic activity was tested by measuring the hydrogen evolution from antibiotic wastewater, and the H₂ evolution rate of In₂Se₃/Ag₃PO₄ reached 4206.4 µmol g^-1h^-1 under visible light, which is approximately 2.8 times greater than that of In₂Se₃. In addition, the amount of tetracycline (TC) degradation when it was used as a sacrificial agent is about 54.4% after 1 h. On the one hand, Se-P chemical bonds act as electron transfer channels in the S-scheme heterojunctions, which can facilitate the migration and separation of photogenerated charge carriers. On the other hand, the S-scheme heterojunctions can retain the useful holes and electrons with higher redox capacities, which is very favorable for the generation of more •OH radicals and the photocatalytic activity is greatly enhanced. This work provides an alternative design approach for photocatalysts toward hydrogen evolution in antibiotic wastewater.

Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial β-In2Se3 Thin Films

Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In₂Se₃ has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of β-In₂Se₃ films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer β-In₂Se₃ is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer β-In₂Se₃/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In₂Se₃ film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality β-In₂Se₃ thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial β-In₂Se₃ films.

Molecular-Beam Epitaxy of Two-Dimensional In2Se3 and Its Giant Electroresistance Switching in Ferroresistive Memory Junction

Ferroelectric thin film has attracted great interest for nonvolatile memory applications and can be used in either ferroelectric Schottky diodes or ferroelectric tunneling junctions due to its promise of fast switching speed, high on-to-off ratio, and nondestructive readout. Two-dimensional α-phase indium selenide (In₂Se₃), which has a modest band gap and robust ferroelectric properties stabilized by dipole locking, is an excellent candidate for multidirectional piezoelectric and switchable photodiode applications. However, the large-scale synthesis of this material is still elusive, and its performance as a ferroresistive memory junction is rarely reported. Here, we report the low-temperature molecular-beam epitaxy (MBE) of large-area monolayer α-In₂Se₃ on graphene and demonstrate the use of α-In₂Se₃ on graphene in ferroelectric Schottky diode junctions by employing high-work-function gold as the top electrode. The polarization-modulated Schottky barrier formed at the interface exhibits a giant electroresistance ratio of 3.9 × 10⁶ with a readout current density of >12 A/cm², which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of In₂Se₃ to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.

Thermal replacement reaction: a novel route for synthesizing eco-friendly ZnO@γ-In2Se3 hetero-nanostructures by replacing cadmium with indium and their photoelectrochemical and photocatalytic performances

A novel route called thermal replacement reaction was demonstrated for synthesizing eco-friendly ZnO@γ-In2Se3 hetero-structural nanowires on FTO glass by replacing the element cadmium with indium for the first time. The indium layer was coated on the surface of the ZnO nanowires beforehand, then CdSe quantum dots were deposited onto the coated indium layer, and finally the CdSe quantum dots were converted to γ-In2Se3 quantum dots by annealing under vacuum at 350 °C for one hour. The prepared ZnO@γ-In2Se3 hetero-nanostructures exhibit stable photoelectrochemical properties that can be ascribed to the protection of the In2O3 layer between the ZnO nanowire and γ-In2Se3 quantum dots and better photocatalytic performance in the wide wavelength region from 400 nm to nearly 750 nm. This strategy for preparing the ZnO@γ-In2Se3 hetero-nanostructures not only enriches our understanding of the single replacement reaction where the active element cadmium can be replaced with indium, but also opens a new way for the in situ conversion of cadmium-based to eco-friendly indium-based nano-devices.

Control of III/VI Ratios in the Preparation of ln2Se3 thin Films

CuInSe2 (CIS) thin films on glass substrates were successfully grown by the metal organic chemical vapour deposition method by using three precursors [Cu-precursor, trimethyl-indium (TMI) and hydrogen selenide (H2Se)]. The flow rates of TMI and H2Se can be adjusted independently to gain different lll/VI ratios, which is different from the single-precursor technique. Good chalcopyrite phase from CIS films was demonstrated by X-ray diffraction. The optical band gap of CIS thin films can be adjusted by controlling the growth conditions.