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Laterally large (~3 micrometers), atomically-thin two-dimensional (2D) Bi2O2CO3 nanosheets (2D bismuth oxycarbonate, 2D bismutite) are fabricated via sonochemically-assisted template-free synthesis. Key to the synthesis of the freestanding, laterally large 2D Bi2O2CO3 nanosheets from bulk Bi powder is choice of suspension medium, controlled reaction temperatures and several hours processing time. Lateral sizes of 2D Bi2O2CO3 can be controlled between micrometer-sized nanosheets and tens of nm sized nanoflakes solely based on the choice of suspension medium. The here introduced 2D Bi2O2CO3 nanosheets/-flakes are then hybridized by a simple mix-and-match approach with TiO2 nanoparticles for testing in suspension-type photocatalytic hydrogen production via water splitting. This introduces the 2D Bi2O2CO3 with TiO2 as a promising noble-metal-free co-catalyst for photocatalytic hydrogen evolution. Our results enrich the fabrication toolbox of emerging 2D pnictogen oxycarbonates towards large 2D nanosheets and demonstrate the promising potential of 2D Bi2O2CO3 as an advantageous (co-)catalyst for hydrogen evolution in photocatalytic water splitting.

Two-dimensional (2D) antimony (Sb, antimonene) recently attracted interest due to its peculiar electronic properties and its suitability as anode material in next generation batteries. Sb however exhibits a large polymorphic/allotropic structural diversity, which is also influenced by the Sb's support. Thus understanding Sb heterostructure formation is key in 2D Sb integration. Particularly 2D Sb/graphene interfaces are of prime importance as contacts in electronics and electrodes in batteries. We thus study here few-layered 2D Sb/graphene heterostructures by atomic-resolution (scanning) transmission electron microscopy. We find the co-existence of two Sb morphologies: First is a 2D growth morphology of layered beta-Sb with beta-Sb(001)||graphene(001) texture. Second are one-dimensional (1D) Sb nanowires which can be matched to beta-Sb with beta-Sb[2-21] perpendicular to graphene(001) texture and are structurally also closely related to thermodynamically non-preferred cubic Sb(001)||graphene(001). Importantly, both Sb morphologies show rotational van-der-Waals epitaxy with the graphene support. Both Sb morphologies are well resilient against environmental bulk oxidation, although superficial Sb-oxide layer formation merits consideration, including formation of novel epitaxial Sb2O3(111)/beta-Sb(001) heterostructures. Exact Sb growth behavior is sensitive on employed processing and substrate properties including, notably, the nature of the support underneath the direct graphene support. This introduces the substrate underneath a direct 2D support as a key parameter in 2D Sb heterostructure formation. Our work provides insights into the rich phase and epitaxy landscape in 2D Sb and 2D Sb/graphene heterostructures.

Bulk chalcogenide perovskite BaZrS3 (BZS), with a direct band gap in visible region, is an important photovoltaic material, albeit with limited applicability owing to its antiferroelectric (AF) nature. Presently, ferroelectric (FE) perovskite-based photovoltaics are attracting enormous attention for environmental stability and better energy conversion efficiency through enhanced charge separation, owing to loss of center of inversion symmetry. We report on antiferroelectric-ferroelectric (AF-FE) phases of BZS thin film, grown with chemical vapor deposition (CVD), using temperature-dependent Raman investigations and first-principles calculations. The origin of FE phases is established from anomalous behavior of A7g ~ 300 cm-1 and B1g5 ~ 420 cm-1 modes, which involves the vibration of atoms at apical site of ZrS6 octahedra. Additionally, below 60 K, B1g1 and B2g2 ( ~ 85 cm-1) modes appear whereas B12g (~ 60 cm-1) disappears to stabilize the Pnma structure against ferroelectricity by local distortion. Here, B2g2 and B1g2 involve vibrations of Ba atoms in AF manner while B1g1 involves, in addition, the rotation of octahedra as well. Our first-principles calculations confirm that FE appears as a result of loss of center of inversion symmetry in ZrS6 octahedra due to existence of oxygen (O) impurities placed locally at apical sites of sulfur (S) atom., Comment: 7 figurs

Organic-inorganic halide perovskites are intrinsically unstable when exposed to moisture and/or light. Additionally, the presence of lead in many perovskites raises toxicity concerns. Herein is reported a thin film of BaZrS3, a lead-free chalcogenide perovskite. Photoluminescence and X-ray diffraction measurements show that BaZrS3 is far more stable than methylammonium lead iodide (MAPbI3) in moist environments. Moisture- and light-induced degradations in BaZrS3 and MAPbI3 are compared by using simulations and calculations based on density functional theory. The simulations reveal drastically slower degradation in BaZrS3 due to two factors - weak interaction with water, and very low rates of ion migration. BaZrS3 photo-detecting devices with photo-responsivity of ~46.5 mA W-1 are also reported. The devices retain ~60% of their initial photo-response after 4 weeks in ambient conditions. Similar MAPbI3 devices degrade rapidly and show ~95% decrease in photo-responsivity in just 4 days. The findings establish the superior stability of BaZrS3 and strengthen the case for its use in optoelectronics. New possibilities for thermoelectric energy conversion using these materials are also demonstrated.

The segregation of brain fiber tractography data into distinct and anatomically meaningful clusters can help to comprehend the complex brain structure and early investigation and management of various neural disorders. We propose a novel stacked bidirectional long short-term memory(LSTM) based segmentation network, (BrainSegNet) for human brain fiber tractography data classification. We perform a two-level hierarchical classification a) White vs Grey matter (Macro) and b) White matter clusters (Micro). BrainSegNet is trained over three brain tractography data having over 250,000 fibers each. Our experimental evaluation shows that our model achieves state-of-the-art results. We have performed inter as well as intra class testing over three patient's brain tractography data and achieved a high classification accuracy for both macro and micro levels both under intra as well as inter brain testing scenario., Comment: Deep Learning in Irregular Domains - British Machine Vision Conference (DLID-BMVC)