A linear magnetoresistance (LMR) with strong temperature dependence and peculiar non-symmetry with respect to the applied magnetic field is observed in high-index (221) Bi 2 Se 3 films. Different from the LMR observed in the previous studies which emphasize the role of gapless linear energy dispersion, this LMR is of disorder origin and possibly arises from the electron surface accumulation layer of the film. Besides, an abnormal negative magneto-resistance that shows a non-monotonic temperature dependence and persists even at high temperatures and in strong magnetic fields is also observed. V

A high-index topological insulator thin film, Bi2 Se3 (221), is grown on a faceted InP(001) substrate by molecular-beam epitaxy (see model in figure (a)). Angle-resolved photoemission spectroscopy measurement reveals the Dirac cone structure of the surface states on such a surface (figure (b)). The Fermi surface is elliptical (figure (c)), suggesting an anisotropy along different crystallographic directions. Transport studies also reveal a strong anisotropy in Hall conductance.

Abstract:Superlattices ( Author to whom correspondence should be addressed. Email: mhxie@hku.hk Along with the extensive researches of materials and properties of three-dimensional (3D) topological insulators (TIs), 1 Therefore, the two are chemically and structurally compatible, suitable for growth of the SL or MQW structures.The growth experiments and surface characterizations of the heterostructures are made in a customized MBE system, where indium (In), bismuth (Bi) and selenium (Se) fluxes are generated from Knudsen cells. 6 In situ reflection high energy electron diffraction (RHEED) is employed to monitor the growing surfaces in real-time to assess the film growth mode, lattice misfit strain and surface reconstructions. The RHEED specular-beam intensity is recorded, and from its oscillations we obtain the deposition rates of the films. 6 Room temperature (RT) scanning tunneling microscopy (STM) is used to examine the morphologies of the grown samples, where the tunneling current is 0.2 nA and the sample bias is -0.45 V. The substrates are nominally flat Si(111), which are deoxidized at ≥1000 ºC in vacuum for clear (7 × 7) surfaces as evidenced by the RHEED. Afterwards, we prepare a thin InSe buffer on Si(111)-(7 × 7) by firstly depositing about 3 monolayers In at ~ 220 K, followed by annealing in a flux of Se at 490K until a set of (√3 × √3)R30° pattern appears in the RHEED. The distance between the main diffraction streaks is found to change by about 5% from that of Si, suggesting a lattice constant of ~ 4 Å. This is consistent with the lattices of the layered α-phase In 2 Se 3 . On the other hand, some previous studies showed the (√3 × √3)R30° surfaces only for γ-phase In 2 Se 3 . 5,7 However, γ-phase In 2 Se 3 has a lattice parameter (~ 4.26Å) that is far larger than that measured by the RHEED. Therefore, we tend to believe the buffer is of α-phase In 2 Se 3 . As for the origin of the (√3 × √3)R30° superstructure on such a surface, it remains unclear.Bi 2 Se 3 deposition on In 2 Se 3 buffer is conducted at 180 ºC using a Bi to Se flux ratio of 1:10.From the persistence of the streaky RHEED patterns, we infer that two-dimensional layer-bylayer growth of Bi 2 Se 3 is achieved. Indeed, the RHEED intensity starts to oscillate upon the epifilm, but also Kiessig fringes with the period corresponding well with film thickness, implying good film uniformity and sharp interfaces. No In 2 Se 3 -related peak is seen in the XRD data, however, probably because the buffer is too thin, or they overlap those of Bi 2 Se 3 film. The inset (ii) in Fig. 1 Strain states of the heterostructures during the SL sample growth are monitored by the RHEED as well. The evolution of the measured reciprocal lattice parameter D (defined in the inset (i) of Fig. 2(a) is shown in Fig. 2(b). Firstly, one observes that the lattices of heteroepitaxial Lastly in Fig. 2, we observe the surfaces and strain states to evolve highly repeatedly during different periods of …In 2 Se 3 /Bi 2 Se 3 … SL growth. It implies high uniformity of the struc...

Blue phosphorene (blue-P), an allotrope of black phosphorene, is prone to oxidize under ambient conditions, which significantly hinders its incorporation in anode for Li/Na ion batteries (LIBs/NIBs). Combining blue-P and hexagonal boron nitride (h-BN) together to construct h-BN/blue-P heterostructure (BN/P) can break the limitation of the restricted properties of blue-P. By means of first-principles computations, we explored the potential of using BN/P as anode material for LIBs/NIBs. Our computations show that the adsorption energies of Li/Na in BN/P are stronger than those in blue-P. Interestingly, although Li has similar chemical properties to Na, their the most energetically favorable sites on BN/P are different. Li prefers to insert into the interlayer of BN/P while Na prefers to absorb on the blue-P surface of BN/P. Furthermore, BN/P can achieve high theoretical specific capacities 801 and 541 mAh/g and low diffusion barriers 0.08 and 0.07 eV for LIBs and NIBs, respectively. All these characteristics suggest that the BN/P could be an ideal candidate used as promising anode material for high-performance LIBs/NIBs.

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