Atomic-Scale Chemical Conversion of Single-Layer Transition Metal Dichalcogenides.

Chemical conversion by atomic substitution offers a powerful route toward the creation of unusual structures and functionalities. Here, we demonstrate the progressive transformation of single-layer TiTe2 into TiSe2 by reaction with a Se flux in vacuum. Angle-resolved photoemission spectroscopy and scanning tunneling microscopy reveal intriguing reaction patterns involving TiSe2 island ingrowth starting from the TiTe2 island edges, while the band structure and core level signatures of TiSe2 grow in intensity at the expense of those corresponding to TiTe2. Lattice mismatch between TiTe2 and TiSe2 results in misfit holes and lattice distortions over a distance behind a seamless fingerlike reaction front. The regions of TiSe2 and TiTe2 are distinguished by a height difference and a charge density wave (CDW) at different transition temperatures. The method of in situ chemical conversion offers opportunities for atomic-scale engineering of layered transition metal dichalcogenides that host useful properties arising from CDW, Dirac, Weyl, superconducting, spin-valley, and magnetic structures.

Controlling the Polarity of the Molecular Beam Epitaxy Grown In-Bi Atomic Film on the Si(111) Surface.

Synchrotron radiation core-level photoemission spectroscopy, scanning tunneling microscopy (STM), and first-principles calculations have been utilized to explore the growth processes and the atomic structure of the resulting films during the two-step molecular beam epitaxy (MBE) of In and Bi on the Si(111) surface. Deposition of 1.0-ML Bi on the In/Si(111)-(4 × 1) surface at room temperature results in Bi-terminated BiIn-(4 × 3) structures, which are stable up to ~300 °C annealing. By contrast, deposition of In on the ß-Bi/Si(111)-(√3 × âˆš3) surface at room temperature results in three dimensional (3D) In islands. In both cases, annealing at 460 °C results in the same In-terminated In0.75Bi/Si(111)-(2 × 2) surface. Our DFT calculations confirm that the surface energy of In-terminated In0.75Bi/Si(111)-(2 × 2) system is lower than that of Bi-terminated Bi0.75In/Si(111)-(2 × 2). These findings provide means for the control of the polarity of the MBE In-Bi atomically thick films.

A microtubule inhibitor, ABT-751, induces autophagy and delays apoptosis in Huh-7 cells.

The objective was to investigate the upstream mechanisms of apoptosis which were triggered by a novel anti-microtubule drug, ABT-751, in hepatocellular carcinoma-derived Huh-7 cells. Effects of ABT-751 were evaluated by immunocytochemistry, flow cytometric, alkaline comet, soft agar, immunoblotting, CytoID, green fluorescent protein-microtubule associated protein 1 light chain 3 beta detection, plasmid transfection, nuclear/cytosol fractionation, coimmunoprecipitation, quantitative reverse transcription-polymerase chain reaction, small-hairpin RNA interference and mitochondria/cytosol fractionation assays. Results showed that ABT-751 caused dysregulation of microtubule, collapse of mitochondrial membrane potential, generation of reactive oxygen species (ROS), DNA damage, G2/M cell cycle arrest, inhibition of anchorage-independent cell growth and apoptosis in Huh-7 cells. ABT-751 also induced early autophagy via upregulation of nuclear TP53 and downregulation of the AKT serine/threonine kinase (AKT)/mechanistic target of rapamycin (MTOR) pathway. Through modulation of the expression levels of DNA damage checkpoint proteins and G2/M cell cycle regulators, ABT-751 induced G2/M cell cycle arrest. Subsequently, ABT-751 triggered apoptosis with marked downregulation of B-cell CLL/lymphoma 2, upregulation of mitochondrial BCL2 antagonist/killer 1 and BCL2 like 11 protein levels, and cleavages of caspase 8 (CASP8), CASP9, CASP3 and DNA fragmentation factor subunit alpha proteins. Suppression of ROS significantly decreased ABT-751-induced autophagic and apoptotic cells. Pharmacological inhibition of autophagy significantly increased the percentages of ABT-751-induced apoptotic cells. The autophagy induced by ABT-751 plays a protective role to postpone apoptosis by exerting adaptive responses following microtubule damage, ROS and/or impaired mitochondria.

Ordered 2D Structure Formed upon the Molecular Beam Epitaxy Growth of Ge on the Silicene/Ag(111) Surface.

Growth of Ge by molecular beam epitaxy (MBE) on top of the silicene monolayer on the Ag(111) surface results in either a dispersed adlayer or a two-dimensional (2D) ordered structure depending on the silicene phase. Scanning tunneling microscopy (STM) images show that the ordered adsorbed Ge atoms on (3 × 3)Si domains occupy a position directly on top of down atoms in the buckled silicene layer, similar to the adatom positions on the Ge(111)-c(2 × 8) surface. By contrast, no long-range ordering of Ge adatoms is observed on the domain, possibly partly because of the interference effects of the Ag substrate. Results herein suggest that the deposited Ge atoms tend to build an additional three-dimensional bulk layer on the silicene monolayer and that the growth of the 2D germanene/silicene heterostructure may not be achieved in a straightforward manner.