Bi2Se3 Nanostructures Research Articles

The effect of temperature on Bi2Se3 nanostructures synthesized via chemical vapor deposition

Bismuth selenide (Bi2Se3) nanostructures have been synthesized via chemical vapor deposition at different temperatures. In order to reduce the Se vacancy in Bi2Se3, the ultrapure Bi2Se3 mixed with the Se powder source is used to supply a sufficient selenium atmosphere. The crystallization, composition, morphology of the products effected by temperature were characterized by XRD, SEM, EDX, HRTEM, SAED and Raman. The results show that the nanostructures of Bi2Se3 deposited at 500 °C is optimized in our experimental conditions. Meanwhile, it provided an evidence to synthesize Bi2Se3 nanostructures, which is more advantageous to investigate the exotic surface states and potential applications in spintronics.

Two-step vapor transport deposition of large-size bridge-like Bi2Se3 nanostructures

A “two-step growth” method for obtaining large dimensional bridge-like Bi2Se3 nanostructures was proposed for the first time.

Multi-layered nanostructure Bi2Se3 grown by chemical vapor deposition in selenium-rich atmosphere

High quality multi-layered nanostructured bismuth selenide (Bi2Se3) with an asymmetric, elongated hexagonal morphology were obtained in a selenium-rich atmosphere by chemical vapor deposition (CVD) using high purity Se and Bi2Se3 powder as source materials. The measurement results reveal that Au particles only serve as the initial stage nucleation of the Bi2Se3 nanostructures at a low temperature. The Se powder in the source materials is helpful to ensure the stoichiometry and decrease the selenium vacancies, and causes the wide Bi2Se3 nanoribbons to grow along the lateral direction.

Screw-dislocation-driven bidirectional spiral growth of Bi₂Se₃ nanoplates.

Bi2Se3 attracts intensive attention as a typical thermoelectric material and a promising topological insulator material. However, previously reported Bi2Se3 nanostructures are limited to nanoribbons and smooth nanoplates. Herein, we report the synthesis of spiral Bi2Se3 nanoplates and their screw-dislocation-driven (SDD) bidirectional growth process. Typical products showed a bipyramid-like shape with two sets of centrosymmetric helical fringes on the top and bottom faces. Other evidence for the unique structure and growth mode include herringbone contours, spiral arms, and hollow cores. Through the manipulation of kinetic factors, including the precursor concentration, the pH value, and the amount of reductant, we were able to tune the supersaturation in the regime of SDD to layer-by-layer growth. Nanoplates with preliminary dislocations were discovered in samples with an appropriate supersaturation value and employed for investigation of the SDD growth process.

Screw‐Dislocation‐Driven Bidirectional Spiral Growth of Bi2Se3 Nanoplates

AbstractBi2Se3 attracts intensive attention as a typical thermoelectric material and a promising topological insulator material. However, previously reported Bi2Se3 nanostructures are limited to nanoribbons and smooth nanoplates. Herein, we report the synthesis of spiral Bi2Se3 nanoplates and their screw‐dislocation‐driven (SDD) bidirectional growth process. Typical products showed a bipyramid‐like shape with two sets of centrosymmetric helical fringes on the top and bottom faces. Other evidence for the unique structure and growth mode include herringbone contours, spiral arms, and hollow cores. Through the manipulation of kinetic factors, including the precursor concentration, the pH value, and the amount of reductant, we were able to tune the supersaturation in the regime of SDD to layer‐by‐layer growth. Nanoplates with preliminary dislocations were discovered in samples with an appropriate supersaturation value and employed for investigation of the SDD growth process.

The electrochemical self-assembly of hierarchical dendritic Bi2Se3 nanostructures

Bismuth selenide (Bi2Se3) has proven to be an important material in thermoelectric and topological insulator applications. We report here a simple electrochemical self-assembly route for the preparation of well-defined hierarchical dendritic Bi2Se3 nanostructures. Cyclic voltammetry was used to study the electrochemical reactions relevant to the growth of the prepared bismuth selenide. The compositional, morphological and structural properties of the deposited nanostructures were characterized using energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-Ray Photoelectron Spectroscopy (XPS). The band gap of the prepared Bi2Se3 dendritic nanostructures was estimated to be 0.50 ± 0.01 eV by a UV-VIS-NIR spectrophotometer and the dendritic Bi2Se3 nanostructures showed an excellent photoelectrochemical activity. Additionally, based on the investigation on the evolution of the morphology and composition during electrochemical growth, a possible formation mechanism of the dendritic structures was concluded. Furthermore, the effects of some synthesis conditions on the morphologies of the deposited bismuth selenide nanostructures were studied.

A solution synthetic route toward Bi2Se3layered nanostructures with tunable thickness via weakening precursor reactivity

We developed a solution synthetic route to Bi2Se3 layered nanostructures through weakening the reactivity of precursors in a hot-injection process. Oleylamine (OYA) and its content in precursor solutions determined reliable synthesis and tunable thickness of Bi2Se3 layered nanostructures. The Raman shift of the out-of-plane vibration mode () suggested that the minimum thickness of Bi2Se3 layered nanostructures could be down to ∼3 nm [about three quintuple layers (QLs)] by varying the content of OYA. Both energy dispersive spectroscopy and X-ray photoelectronic spectroscopy proved that there were no inorganic impurities imported into Bi2Se3 nanostructures. This synthetic approach would bring about more opportunities for flexible preparation of promising layered nanomaterials with tunable thickness for thermoelectric conversion, electrochemical hydrogen storage, and even topological insulators.

Substrate-independent catalyst-free synthesis of high-purity Bi2Se3 nanostructures

We describe a catalyst-free vapor-solid synthesis of bismuth selenide (Bi2Se3) nanostructures at ambient pressure with H2 as carrier gas. The nanostructures were synthesized on glass, silicon, and mica substrates and the method yields a variety of nanostructures: nanowires, nanoribbons, nanoplatelets, and nanoflakes. The materials' analysis shows high chemical purity in all cases, without sacrificing the crystalline structure of Bi2Se3. Low-temperature measurements of the nanostructures indicate contributions from the surface states with a tunable carrier density. Samples synthesized on flexible mica substrates show no significant change in resistance upon bending, indicating robustness of as-grown Bi2Se3 nanostructures and their suitability for device applications.

Synthesis and Quantum Transport Properties of Bi2Se3 Topological Insulator Nanostructures

Bi2Se3 nanocrystals with various morphologies, including nanotower, nanoplate, nanoflake, nanobeam and nanowire, have been synthesized. Well-distinguished Shubnikov-de Haas (SdH) oscillations were observed in Bi2Se3 nanoplates and nanobeams. Careful analysis of the SdH oscillations suggests the existence of Berry's phase π, which confirms the quantum transport of the surface Dirac fermions in both Bi2Se3 nanoplates and nanobeams without intended doping. The observation of the singular quantum transport of the topological surface states implies that the high-quality Bi2Se3 nanostructures have superiorities for investigating the novel physical properties and developing the potential applications.

Raman spectroscopy determination of the Debye temperature and atomic cohesive energy of CdS, CdSe, Bi2Se3, and Sb2Te3 nanostructures

We have formulated the size and temperature dependence of the phonon relaxation dynamics for CdS, CdSe, Bi2Se3, and Sb2Te3 nanostructures based on the framework of bond order–length–strength correlation, core-shell configuration, and local bond averaging approach. The Raman shifts are correlated directly to the identities (nature, order, length, and energy) of the representative bond of the specimen without needing involvement of the Grüneisen mode parameters or considering the processes of phonon decay or multi-phonon resonant scattering. Quantitative information of the Debye temperature, the atomic cohesive energy, the reference frequencies from which the Raman shifts proceed, and the effective coordination numbers of the randomly sized particles, as well as the length and energy of the representative bond, has been obtained. It is clarified that the size-induced phonon softening arises intrinsically from the cohesive weakening of the undercoordinated atoms in the skin up to three atomic layers and the thermally derived phonon softening results from the thermally lengthening and weakening of bonds. Developed approach empowers the Raman technique in deriving quantitative and direct information regarding bond stiffness relaxation with applied stimuli such as coordination, mechanical, thermal, and chemical environment, which are crucial to practical applications.

Controlled MOCVD growth of Bi2Se3 topological insulator nanoribbons

Topological insulators are a new class of materials that support topologically protected electronic surface states. Potential applications of the surface states in low dissipation electronic devices have motivated efforts to create nanoscale samples with large surface-to-volume ratios and highly controlled stoichiometry. Se vacancies in Bi2Se3 give rise to bulk conduction, which masks the transport properties of the surface states. We have therefore developed a new route for the synthesis of topological insulator nanostructures using metalorganic chemical vapour deposition (MOCVD). MOCVD allows control of the Se/Bi flux ratio during growth. With the aim of rational growth, we vary the Se/Bi flux ratio, growth time, and substrate temperature, and observe morphological changes which indicate a growth regime in which nanoribbon formation is limited by the Bi precursor mass flow. MOCVD growth of Bi2Se3 nanostructures occurs via a distinct growth mechanism that is nucleated by gold nanoparticles at the base of the nanoribbon. By tuning the reaction conditions, we obtain either single-crystalline ribbons up to 10 μm long or thin micron-sized platelets.

Chemical Synthesis and Properties of Novel Bi2Se3 Nanostructures and Microplatelets

Bi2Se3 nanostructures, microsised fibre bundles, and platelets have been synthesised through a simple chemical spray pyrolysis route on glass substrates. Low substrate temperatures (Tsub) favoured growth of nanostructures while elevated Tsub was accompanied by increased grain growth and formation of microsised platelets. The nanostructures were identified as nanorods, nanofibers, nanotubes, nanoflowers, and nanoneedles of various aspect ratios. There was an observed red shift of the optical band gap (Egopt) with increased Tsub from 2.40 eV at 95°C to 1.25 eV at 360°C. Thermo probe measurements confirmed n-type conductivity with dark resistivities which followed a near exponential decline with elevated Tsub. The observed changes in optoelectronic properties existing in the different Tsub regimes were explained on the basis of microstructural and textural changes in the pristine clusters.

Resist–substrate interface tailoring for generating high-density arrays of Ge and Bi2Se3 nanowires by electron beam lithography

The authors report a chemical process to remove the native oxide on Ge and Bi2Se3 crystals, thus facilitating high-resolution electron beam lithography (EBL) on their surfaces using a hydrogen silsesquioxane (HSQ) resist. HSQ offers the highest resolution of all the commercially available EBL resists. However, aqueous HSQ developers such as NaOH and tetramethylammonium hydroxide have thus far prevented the fabrication of high-resolution structures via the direct application of HSQ to Ge and Bi2Se3, due to the solubility of components of their respective native oxides in these strong aqueous bases. Here we provide a route to the generation of ordered, high-resolution, high-density Ge and Bi2Se3 nanostructures with potential applications in microelectronics, thermoelectric, and photonics devices.

Flower-like Bi2Se3 nanostructures: Synthesis and their application for the direct electrochemistry of hemoglobin and H2O2 detection

In this paper, flower-like Bi2Se3 nanostructures consisting of intercrossed nanosheets networks have been synthesized via a facile hydrothermal technique and applied to the protein electrochemistry for the first time. The prepared Bi2Se3 nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The direct electrochemistry of hemoglobin (Hb) has been achieved by immobilizing Hb on the prepared Bi2Se3 nanostructures and Nafion (Nf) modified glassy carbon electrode. Bi2Se3 nanostructures show significant promotion to the direct electron-transfer of Hb. The immobilized Hb retained its biological activity well and shows high catalytic activity to the reduction of hydrogen peroxide (H2O2). Under the optimal experimental conditions, the catalytic currents are linear to the concentrations of H2O2 in the range of 2.0×10−6 to 1.0×10−4M. The corresponding detection limits are 6.3×10−7M. The prepared flower-like Bi2Se3 nanostructures provide an alternative matrix for protein immobilization and biosensor preparation.

Ultra-low carrier concentration and surface-dominant transport in antimony-doped Bi2Se3 topological insulator nanoribbons

A topological insulator is the state of quantum matter possessing gapless spin-locking surface states across the bulk band gap, which has created new opportunities from novel electronics to energy conversion. However, the large concentration of bulk residual carriers has been a major challenge for revealing the property of the topological surface state by electron transport measurements. Here we report the surface-state-dominant transport in antimony-doped, zinc oxide-encapsulated Bi(2)Se(3) nanoribbons with suppressed bulk electron concentration. In the nanoribbon with sub-10-nm thickness protected by a zinc oxide layer, we position the Fermi levels of the top and bottom surfaces near the Dirac point by electrostatic gating, achieving extremely low two-dimensional carrier concentration of 2×10(11) cm(-2). The zinc oxide-capped, antimony-doped Bi(2)Se(3) nanostructures provide an attractive materials platform to study fundamental physics in topological insulators, as well as future applications.

Synthesis and Thermoelectric Properties of Bi2Se3 Nanostructures.

Bismuth selenide (Bi2Se3) nanostructures were synthesized via solvothermal method. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of rhombohedral Bi2Se3. Electron microscopy examination indicates that the Bi2Se3 nanoparticles have hexagonal flake-like shape. The effect of the synthesis temperature on the morphology of the Bi2Se3 nanostructures has also been investigated. It is found that the particle size increases with the synthesis temperature. Thermoelectric properties of the Bi2Se3 nanostructures were also measured, and the maximum value of dimensionless figure of merit (ZT) of 0.096 was obtained at 523 K.

Controllable synthesis and electrochemical hydrogen storage properties of Bi2Se3 architectural structures

Two kinds of Bi2Se3 nanostructures, 3D rose-like hierarchitectures and monodisperse nanospheres, have been synthesized through adjusting the supersaturation of the precursor solution. Noticeable hydrogen storage capacity, amounting to 185 mA h g-1, has been found for the 3D rose-like hierarchitectures, which arises from the special micro/nano-hierarchitectures with highly crystallized flake-substructures.