A smart hybrid nanowire array consisting of Co3O4 porous nanowire core and a MnO2 ultrathin nanosheet shell is fabricated using a general 3D interfacial carbon‐assisted hydrothermal method. The array exhibits a high capacitance with good cycle performance and remarkable rate capability that is ranging among the best reported to date for hybrid metal oxide systems in the absence of a conducting matrix.

A hexagonal deformation of the Fermi surface of Bi 2 Se 3 has been for the first time observed by angleresolved photoemission spectroscopy. This is in contrast to the general belief that Bi 2 Se 3 possesses an ideal Dirac cone. The hexagonal shape is found to disappear near the Dirac node, which would protect the surface state electrons from backscattering. It is also demonstrated that the Fermi energy of naturally electron-doped Bi 2 Se 3 can be tuned by 1% Mg doping in order to realize the quantum topological transport. DOI: 10.1103/PhysRevLett.105.076802 PACS numbers: 73.20.Àr, 79.60.Ài After the theoretical prediction and experimental realization of two-dimensional topological insulators in the HgTe=CdTe quantum well [1-4], a spectroscopic discovery of a three-dimensional topological insulator by probing the odd number of massless Dirac cones has generated a great interest in this new state of quantum matter [5][6][7][8][9]. Unlike the conventional Dirac fermions as found in graphene, this novel electronic state possesses helical spin textures protected by time-reversal symmetry, which could realize the quantum spin transport without heat dissipation. This new state of matter has been predicted to exist in a number of materials, for example, in Bi 1Àx Sb x , Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 [10]. Among them, stoichiometric Bi 2 Se 3 is theoretically predicted to be a 3D topological insulator with a single Dirac cone within a substantial bulk energy gap (0.3 eV), which makes it the most suitable candidate for the high-temperature spintronics application [10]. However, in the actual situation, the bulk conduction band is energetically lowered and crosses the Fermi energy through natural electron doping from vacancies or antisite defects, which allows bulk electron conduction. In order to avoid the bulk electron conduction and realize the quantum spin Hall phase, the Fermi energy must be tuned by additional doping [11,12].In ideal topological insulators with perfect linear dispersion, the surface state electrons should be protected from backscattering by nonmagnetic impurities between timereversal partners with opposite momenta because of their opposite spin configurations. However, recent scanning tunneling microscopy experiments for the Bi 2 Te 3 surface show a clear quasiparticle interference pattern as a result of backscattering nearby the step edge or at the point defect on the surface [13,14]. Theoretically, it is pointed out that the hexagonal Fermi surface warping would also induce the quasiparticle interference pattern [15]. It is generally believed that, owing to a large band gap (0.35 eV), which exceeds the thermal excitation energy at room temperature, Bi 2 Se 3 features a nearly ideal Dirac cone, in contrast to Bi 2 Te 3 [16,17]. In the present Letter, we show by a precise angle-resolved photoemission spectroscopy (ARPES) measurement that the Fermi surface of naturally electrondoped Bi 2 Se 3 is hexagonally deformed, while the constant energy contour is circular-shaped near the Dirac point...

We report a novel “sacrificial template-accelerated hydrolysis” (STAH) approach to the synthesis of iron oxide-based nanotube arrays including hematite α-Fe2O3 and magnetite Fe3O4 on centimeter-scale conducting alloy substrates. ZnO nanowire arrays are chosen as the inexpensive and sacrificial templates that do not contribute to the component of final iron oxide nanotubes but can be in situ dissolved by the acid produced from the Fe3+ precursor hydrolysis. Interestingly, the ZnO template dissolution in turn accelerates the Fe3+ hydrolysis, which is essential to initiating the nanotube formation. Such a STAH approach provides a morphology-reservation transformation, when various shaped ZnO templates are adopted. Moreover, by introducing glucose into the precursor solution, we also successfully obtain carbon/hematite(C/α-Fe2O3) composite nanotube arrays on large-area flexible alloy substrate, with a large number of pores and uniform carbon distribution at a nanoscale in the nanotube walls. These arrays have been demonstrated as excellent additive-free anode materials for lithium ion batteries in terms of good cycling performance up to 150 times (659 mA h g−1) and outstanding rate capability. Our result presents not only a new route for inorganic nanotube formation but also an insight for rational design of advanced electrode materials for electrochemical batteries and sensors.

Carbon/ZnO nanorod arrays on nickel substrate have been fabricated over a large area by the simple carbonization of preadsorbed glucose on ZnO arrays at 500 °C in argon gas. The uniform coating of average 6 nm carbon shell on ZnO nanorod surface is confirmed. The novel array architecture possesses both the electroactivity of carbon and the electrochemical advantages of array structure on conductive substrate. When used as anode for Li ion batteries, it displays significantly improved performance in terms of cycling stability and rate capability. The observed lithium storage ability ranges among the best reported to date for ZnObased anode. We believe that the novel carbon-coating route is general and can be extendable to other metal oxide nanoarray electrodes.

We have developed a general two-step synthesis of large-scale arrays of one-dimensional (1D) nanostructured Co3O4 directly on various substrates. Throughout a controllable hydrothermal process using urea as mineralizer and hereafter with a postcalcination process under air atmosphere, Co3O4 1D nanostructure arrays have been grown firmly on insulating substrates, such as glass slides and ceramics, which is quite convenient for the construction of gas sensor devices without any extra electrode preparation process. Furthermore, this direct-growth approach can be readily extended to conductive substrates (ITO, Ti, Fe−Co−Ni alloy), and meanwhile due to the robust mechanical adhesion and one-dimensional carrier transportation architecture firmly contacted to the metal, the metal substrate-supported Co3O4 arrays could act as a promising electrode material and be straightforwardly integrated into electronic and electrochemical nanodevices.