The thickness-dependent optical constants and annealed phase transitions of atomic-layer-deposited ZnO ultrathin films with a thickness of less than 50 nm have been demonstrated by spectroscopic ellipsometry. The thickness dependence of refractive index and extinction coefficient was discussed, and the mechanisms were given in the molecule level based on previous reports. Furthermore, the optical properties of ZnO ultrathin films varied with annealing temperatures, and the phase transition was found at high annealing temperature. The thickness of the ultrathin films decreased obviously, and the refractive index of the ultrathin films changed a lot after annealing at high temperature while Zn2SiO4 formed at a temperature above 800 °C. The low phase transition temperature of Zn2SiO4 may be due to the ultrathin scale effect. What’s more, photoluminescence spectra showed the annealing effect on ultrathin films and the enhanced defects luminescence were observed. We believe that these investigations will help improved understanding of essential physical chemistry and optoelectronic devices based on ultrathin oxide films for optical and photoelectric applications.

We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe2/MoS2 vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics.Keywords: interlayer transition; MoS2; MoTe2; type-II band alignment; van der Waals heterostructure

Strain engineering is an effective method to tune the properties of electrons and phonons in semiconductor materials, including two-dimensional (2D) layered materials (e.g., MoS2 or graphene). External artificial stress (ExAS) or heterostructure stacking is generally required to induce strains for modulating semiconductor bandgaps and optoelectronic functions. For layered materials, the van der Waals-stacked interlayer interaction (vdW-SI) has been considered to dominate the interlayer stacking and intralayer bonding. Here, we demonstrate self-induced uniaxial strain in the MoS2 monolayer without the assistance of ExAS or heterostructure stacking processes. The uniaxial strain occurring in local monolayer regions is manifested by the Raman split of the in-plane vibration modes E2g1 and is essentially caused by local vdW-SI within the single layer MoS2 due to a unique symmetric bilayer stacking. The local stacked configuration and the self-induced uniaxial strain may provide improved understanding of the fundamental interlayer interactions and alternative routes for strain engineering of layered structures.Keywords: first-principles plane-wave calculations; MoS2; Raman; self-induced; uniaxial strain; van der Waals stacking;

Hybrid structures composed of layered materials have received much attention due to their exceptional tunable optical, electronic and catalytic properties. Here, we describe a hydrothermal strategy for coupling vertical ZnO nanorods on MoS2 monolayers without a catalyst. These vapor-solid-grown MoS2 monolayers aid in growing vertical ZnO nanorods via epitaxy. Enhanced Raman and photoluminescence emissions were observed from the MoS2 monolayers under the ZnO nanorods in these coupled structures, which was attributed to the light antenna effect of the ZnO nanorods. These hybrid and incorporation protocols for layered materials will provide new perspectives and opportunities for promoting the construction of heterojunctions with adjustable layered structures leading to fascinating fundamental phenomena and advanced devices.

A metallosupramolecular polymer (MP-Zn) bearing dibenzo-24-crown-8 (DB24C8) arms is constructed by coordinating Zn2+ with a conjugated bis-terpyridine ligand, which indicates concentration-dependent emissions from cyan to white to yellow. Successively, reversible emissions are realized by acid–base controllable recognition of DB24C8 moieties in MP-Zn with dialkylammonium ion centers.

We demonstrated revertible shifts of surface-dependent localized surface plasmon resonances (LSPRs) in CuS nanodisks. Oleylamine (OYA) served as a solvent and surface ligand covering on CuS nanodisks during the thermolysis of single-source precursor copper ethylxanthate (Cu(ex)2). When OYA ligand was unloaded and reloaded on the surface of CuS nanodisks, the wavelength of LSPRs blue-shifted due to more oxygen exposure and then reverted through surface repassivation. The surface-dependent shift of LSPRs was dominated by the concentration of free holes in CuS nanodisks, which was modulated by the coverage and exchange of surface ligands, and the oxygen exposure dose and time. The semiconductor nanocrystals with tunable LSPRs have great potential in advanced plasmonics.Keywords: absorption spectra; copper sulfide; free carrier; localized surface plasmon resonance; nanocrystals; surface ligand;

We describe the fabrication of radial ZnO/Au/ZnO hybrid nanorods by analogously inserting a Au nanoparticle interlayer in single-crystalline ZnO nanorods through a feasible secondary growth process. The construction features of the ZnO/Au/ZnO hybrid nanorods can be tuned by the extent of the nanoparticle coverage and the growth processes. Investigations on the photoluminescence of the hybrid nanorods have preliminarily indicated that the metal nanoparticles lead to enhanced near-band-edge (NBE) emission and suppressed deep level emission (DLE). Such alternative processes and hybrid nanostructures are potential candidates for application in plasmonics and advanced optical devices.

TiO2 nanocrystal/nanotube hybrids were presented and prepared by incubating non-prefabricated TiO2 nanocrystals in anodized TiO2 nanotubes. TiO2 nanocrystals were incubated inside the nanotubes with tuning size and aggregation morphology by means of a block copolymer-assisted evaporation induced self-assembly (EISA) process. Compared with that of the bare TiO2 nanotubes, a ∼44% increase of the concentration of dye absorbed in the TiO2 nano-hybrids was estimated from the absorption spectra. The nanostructure hybrids increased internal surface area, and were used to optimize TiO2-based photo-electrochemical conversion. The contrast of light conversion efficiency revealed an improvement from 0.75% to 1.87% when the TiO2 nano-hybrids were used as photoanodes instead of the bare nanotube arrays.Graphical abstractTiO2 nanocrystal/nanotube hybrids fabricated by incubating non-prefabricated TiO2 nanocrystals in TiO2 nanotubes for optimizing light-harvesting.Highlights► To combine nanocrystals and nanotubes aims to optimize light harvesting and electron transport in photo-electrochemical conversion. ► An alternative method was established to achieve nano-hybrids including nanocrystals and nanotubes. ► TiO2 nanocrystals were incubated inside TiO2 nanotubes by means of a wet-chemical and block copolymer-assisted assembly process. ► Such nano-hybrids have been preliminarily used and confirmed in harvesting more light and then improving light conversion efficiency. ► These will open up alternative pathways for the structure manipulations and optimizations for nanostructure-based photovoltaics and photocatalysis.

We describe a flexible and competent solution for fabrication of non-prefabricated nanocrystal mesoporous TiO2-based photoanodes whose thicknesses are tunable from several hundreds of nanometers up to 12.4 μm. The combination of rapid thermal process and layer-by-layer spin-coating is successfully used to manipulate the structure and morphology of non-prefabricated nanocrystal mesoporous TiO2 films. The photovoltaic performances of mesoporous TiO2-based dye-sensitized solar cells depended on the thickness and the annealing temperature of mesoporous photoanodes. We systematically investigated and noted that the non-prefabricated nanocrystal mesoporous TiO2 films ∼6.3 μm thick annealed at 500 °C displayed better features in the short-circuit current density and overall conversion efficiency of mesoporous TiO2-based dye-sensitized solar cells.Keywords: dye-sensitized solar cells; layer-by-layer coating; mesoporous structure; non-prefabricated nanocrystal photoanode; rapid thermal process; TiO2

A metallosupramolecular polymer (MP-Zn) bearing dibenzo-24-crown-8 (DB24C8) arms is constructed by coordinating Zn2+ with a conjugated bis-terpyridine ligand, which indicates concentration-dependent emissions from cyan to white to yellow. Successively, reversible emissions are realized by acid–base controllable recognition of DB24C8 moieties in MP-Zn with dialkylammonium ion centers.