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Polaron formation is considered to play a crucial role to enhance photoelectric performance of hybrid halide perovskites. Here, the authors report the real-time observation of polaron formation process by terahertz emission spectroscopy and reveal two different polaron modes in FAPbI3 films.

Monolayer (ML) transition-metal dichalcogenides (TMDs) have attracted a lot of research interest in recent years due to their many interesting properties as well as their application promises. Depending on the specific combinations of metals (e.g., Mo and W) with chalcogen elements (e.g., S, Se, and Te), binary TMDs exhibit a wide spectrum of physical characteristics, e.g., from metal to semiconductor and/or superconductor. Extension from binary to ternary compounds and alloys may offer even wider variations of properties and are thus of interest from both fundamental and practical points of view. In this work, we substitute Mo for niobium (Nb) and rhenium (Re) in ML MoSe2 during molecular-beam epitaxy and probe their effects on structural and electrical properties. We find that low-concentration Nb and Re in ML-MoSe2 are both shallow dopants, with Re being an electron donor and Nb acceptor, respectively. By changing Nb(Re)/Mo flux ratios, we can effectively tune the Fermi level by varying electron or hole concentrations in MoSe2. On the other hand, both Nb and Re are found to cause mirror-twin domain boundary defects to proliferate in MoSe2.

Abstract Band bending near mirror twin domain boundaries (MTBs) in a MoSe2 monolayer grown on different substrates, i.e., highly oriented pyrolytic graphite (HOPG), graphene‐on‐SiC, and crystalline Au(110), is investigated by low temperature scanning tunneling microscopy/spectroscopy. Upshift bending of the valence band edge near MTB is observed on both graphene and HOPG substrates, whereas a downshift bending is found on Au(110). For the former, the magnitudes of bending are different. This is explained based on the static charge model, where an accumulative charge exists at MTBs due to both the electrical dipole discontinuity across the MTB as well as charge transfer between the substrate and MoSe2 epilayer. The relevance of the static electric model is further affirmed by noting a geometric effect on the band bending, where it is asymmetric across the vertex of an MTB loop.

Abstract Ultrathin two‐dimensional transition‐metal dichalcogenides (TMDs) have been pursued extensively in recent years for interesting physics and application potentials. For the latter, it is essential to synthesize crystalline TMD monolayers at wafer‐scale. Here, we report growth of single‐crystalline MSe2 (M = Mo, W) monolayers at wafer‐scale by molecular‐beam epitaxy at low temperatures (200–400°C) on nominally flat Au(1 1 1) substrates. The epifilms have low intrinsic defect densities of low 1012 cm−2. The grown films have then been exfoliated and transferred onto SiO2/Si by a wet chemical process, on which some optical measurements are performed, revealing high spatial uniformity of the samples. We also establish that MSe2 grows on Au via the van der Waals epitaxy mechanism, where a continuous film extends across the whole surface, overhangs atomic‐layer steps on substrate. We identify that the growth of highly crystalline MSe2 is promoted by an enhanced interaction between Au substrate and MSe2 islands rather than by the guidance of surface steps on substrate. The latter only arrests MSe2 lateral growth if they are multilayer high. Key points MBE growth of wafer‐scale highly crystalline TMD monolayers at low‐temperature is achieved. Island‐substrate interaction is found to play a critical role in vdW epitaxy of single‐crystalline TMDs on on‐axis substates. The TMD monolayers are of high uniformity and low intrinsic defect density.

Trigeminal neuralgia caused by paroxysmal and severe pain in the distribution of the trigeminal nerve is a rare chronic pain disorder. It is generally accepted that compression of the trigeminal root entry zone by vascular structures is the major cause of primary trigeminal neuralgia, and vascular decompression is the prior choice in neurosurgical treatment. Therefore, accurate preoperative modeling/segmentation/visualization of trigeminal nerve and its surrounding cerebrovascular is important to surgical planning. In this paper, we propose an automated method to segment trigeminal nerve and its surrounding cerebrovascular in the root entry zone, and to further reconstruct and visual these anatomical structures in three-dimensional (3D) Magnetic Resonance Angiography (MRA). The proposed method contains a two-stage neural network. Firstly, a preliminary confidence map of different anatomical structures is produced by a coarse segmentation stage. Secondly, a refinement segmentation stage is proposed to refine and optimize the coarse segmentation map. To model the spatial and morphological relationship between trigeminal nerve and cerebrovascular structures, the proposed network detects the trigeminal nerve, cerebrovasculature, and brainstem simultaneously. The method has been evaluated on a dataset including 50 MRA volumes, and the experimental results show the state-of-the-art performance of the proposed method with an average Dice similarity coefficient, Hausdorff distance, and average surface distance error of 0.8645, 0.2414, and 0.4296 on multi-tissue segmentation, respectively.