Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system to explore moiré physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moiré superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19°. Our calculations reveal that the Γ-point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moiré physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moiré physics in phosphorene and other van der Waals heterostructures with different lattice configurations.

Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in 1.5–2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.

SnIP could be the first of a new class of inorganic double-helix materials. [7][8][9] With strong intra-helix covalent bonds and weak inter-helix dispersion forces, SnIP belongs to the group of newly emerging 1D van der Waals (vdW) materials with potential applications in nanoelectronics and photonics. [10][11][12][13] In contrast to the DNA structure, which consists of two equal radius helices, SnIP forms with an outer [SnI] + helix wrapping around an inner [P] − helix, as pictured in Figure 1a. SnIP crystallizes monoclinically with a unit cell containing two opposite-handed double helices so that there is no net chirality. It is composed of abundant and non-toxic elements and can grow uninhibited to cm-length needles with a low-temperature synthesis [6,14] (Sections S1 and S2, Supporting Information) or in nanotubes using vapor deposition. [15,16] Its 1.86 eV band gap, as determined by band structure calculations (Figure 1b,c) and verified experimentally (see ref.[ 6 ] and Section S3, Supporting Information), is well situated for solar absorption and photocatalytic water splitting. [8,10,15] SnIP is also an extremely soft and flexible semiconductor and is therefore a promising material for applications in flexible electronics, [6,10] where these properties are highly desirable. [17] It is predicted to have a high carrier mobility; [8] however, as-grown SnIP is highly resistive so that the current lack of doped samples has made it difficult to explore its electronic properties. [6] Moreover, despite the exciting properties and unique structure of SnIP, there have been no investigations probing its ultrafast photophysical properties.Here, we use time-resolved terahertz (THz) spectroscopy (TRTS) to study picosecond charge carrier dynamics in SnIP nanowire films, as shown in Figure 1d. TRTS, a powerful non-contact ultrafast probe, has been used extensively to probe carrier dynamics in low-dimensional materials, accelerating scientific understanding of transport mechanisms and enabling materials optimization for potential applications. [18,19] From analysis of the photoconductivity spectra, along with insight into the highly anisotropic energy landscape from density functional theory (DFT), we make the first measurement of the carrier mobility in SnIP. We find a maximum electron mobility of 280 cm 2 V −1 s −1 along the double-helix axis, an extraordinarily high mobility for a material as soft and flexible as SnIP. On Tin iodide phosphide (SnIP), an inorganic double-helix material, is a quasi-1D van der Waals semiconductor that shows promise in photocatalysis and flexible electronics. However, the understanding of the fundamental photophysics and charge transport dynamics of this new material is limited. Here, time-resolved terahertz (THz) spectroscopy is used to probe the transient photoconductivity of SnIP nanowire films and measure the carrier mobility. With insight into the highly anisotropic electronic structure from quantum chemical calculations, an electron mobility as high as 280 cm 2 V −1 s −1 along the doub...

Polyphosphide–TiO2 hybrid materials, like SnIP@TiO2, are used as photocatalysts for PEC-water-oxidation: SnIP a double helix semiconductor reacted as nanofibers onto and into TiO2 nanotube arrays. Due to synergetic effects an enhanced water splitting performance was found.