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A topological insulator (TI) is an exotic material that has a bulk insulating gap and metallic surface states with unique spin-momentum locking characteristics. Despite its various important applications, large scale integration of TI into MOSFET technologies and its coherent transport study are still rarely explored. Here, we report the growth of high quality Bi2Se3 thin film on amorphous SiO2/Si substrate using MBE. By controlling the thickness of the film at ∼7 nm and capping the as grown film in situ with a 2 nm-thick Se layer, largest electrostatic field effect is obtained and the resistance is changed by almost 300%. More importantly, pronounced gate-tunable weak antilocalization (WAL) is observed, which refers to modulation of α from ∼−0.55 to ∼−0.2 by applying a back gate voltage. The analysis herein suggests that the significant gate-tunable WAL is attributable to the transition from weak disorder into intermediate disorder regime when the Fermi level is shifted downward by increasing the negative back gate voltage. Our findings may pave the ways towards the development of TI-based MOSFET and are promising for the applications of electric-field controlled spintronic and magnetic device.

Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE).

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We report a systematic study on the structural and electronic properties of Bi2Te3−xSex topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3−xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3−xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi2Te3−xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

In this study we visualized thermodynamically stable chalcogen compounds in the vicinity of a Py/Bi2Se3 interface with dual magnetic order due to a phase separation effect.

A 3D trenched-structure metal-insulator-metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ~300 μF cm(-2) is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al2O3) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (!5 × 10(10) cm(-2)) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal-insulator-metal or metal-insulator-semiconductor nanocapacitors using similar porosity dimensions of the support materials.

An intriguing system featuring a wide band gap silica nanowire (SiO x NW) that absorbs visible light (532 nm) via the surface plasmons (SPs) of embedded gold nanoparticles (Au NPs) is reported for sensing applications. We report SP resonanceenhanced molecular oxygen sensing by single Au-NPs@SiO x NWs under 532-nm illumination (visible light) at room temperature. Excellent selectivity of the Au-NPs@SiO x NWs to molecular oxygen in air has been demonstrated. Illumination improved the sensing properties in terms of response and fast recovery time, which can be attributed to the photogenerated hole-mediated oxygen desorption. A general strategy of light-modulated sensing, vis-à -vis dark, is demonstrated in a wide band gap single NW system that could potentially open up routes for biosensing, because silica and Au both lack biotoxicity. NPG Asia Materials (2013) 5, e49; doi:10.1038/am.2013.17; published online 24 May 2013 Keywords: gas sensor; nanowire; silica; surface plasmon INTRODUCTION Oxide-based semiconductor nanostructured materials have been widely investigated for chemical and biosensing applications because of their biocompatibility, relatively easy large-scale synthesis, superior thermal and chemical stabilities and high surface-to-volume ratios. 1,2 However, improving the sensing performance requires improved sensitivity, good selectivity or specificity, short rise and fall times of signals (high-speed response and recovery) and an easily attainable working temperature, ideally in the room-temperature range. Because of their large surface areas, nanostructures such as nanowires (NWs), 3 nanotubes, 4,5 nanorods 6 and nanoparticles (NPs) 7 offer large reaction cross sections for signal generation. To further enhance the sensing performance of these nanostructures, surface modification, [8][9][10] applications of high electrical bias 11 and high operational temperatures (T4100 1C) 12 have been used.Improving the sensing performance with light has also been demonstrated using ZnO-based nanostructures under UV illumination. 13 However, most of these approaches have required high operational temperatures, high biases and light outside the visible range (400-800 nm), which has somewhat limited their general applicability. We demonstrated how Au NPs embedded in single amorphous silica NW (Au-NPs@SiO x silica NW) can be used as an oxygen gas sensor by amperometric routes in this work. According to that study, the silica shell is amorphous, containing various defects within the NW, such as nonbridging oxygen atoms, dangling bonds,