Bi Se Research Articles

Magnetic Exchange Mechanism and Quantized Anomalous Hall Effect in Bi2Se3 Film with a CrWI6 Monolayer.

Magnetizing the surface states of topological insulators without damaging their topological features is a crucial step for realizing the quantum anomalous Hall (QAH) effect and remains a challenging task. The TI-ferromagnetic material interface system was constructed and studied by the density functional theory (DFT). A two-dimensional magnetic semiconductor CrWI6 has been proven to effectively magnetize topological surface states (TSSs) via the magnetic proximity effect. The non-trivial phase was identified in the Bi2Se3 (BS) films with six quantum layers (QL) within the CrWI6/BS/CrWI6 heterostructure. BS thin films exhibit the generation of spin splitting near the TSSs, and a band gap of approximately 2.9 meV is observed at the Γ in the Brillouin zone; by adjusting the interface distance of the heterostructure, we increased the non-trivial band gap to 7.9 meV, indicating that applying external pressure is conducive to realizing the QAH effect. Furthermore, the topological non-triviality of CrWI6/6QL-BS/CrWI6 is confirmed by the nonzero Chern number. This study furnishes a valuable guideline for the implementation of the QAH effect at elevated temperatures within heterostructures comprising two-dimensional (2D) magnetic monolayers (MLs) and topological insulators.

Elemental Composition of the Leaves of the Hanging Birch (<i>Betula pendula</i> Roth) in the Area of the Transbaikalia Gold Deposit

The influence of gold mining on the concentration of chemical elements in Betula pendula Roth leaves was studied. The intensity of absorption by the plant of a number of chemical elements, the possibility of using birch as a medicinal and forage plant, as well as for monitoring habitat changes were investigated. The study was conducted in plant communities located at production facilities and natural habitats in the area of the Baley gold deposit: tailings dumps of gold recovery factories (ZIF-1 and ZIF-2), a drainage landfill, a dump of the SredneGolgotai gold deposit, a tailings dump after processing monocytes, as well as in natural plant communities located in the vicinity of Baley at 13 trial sites in 2008, 2008 and 2021. The concentrations of elements in the leaves were arranged in descending order in the following sequence: Ca Mg P Mn Fe Zn Na Ba B Cr Ni As Cu Mo Sb Pb Co Li V Cd Bi Se Be. With respect to the clark of terrestrial plants, the concentrations of the elements were in the following order: Cr As Sb Li Ni Ba Fe Mo Bi Co Zn Mg Clark Mn P Ca Cu B Pb Se Cd V Be Na. The absorption of As at production facilities exceeded the norm established for medicinal plant raw materials. The use of branch feed in a number of areas is not allowed due to the high level of Zn, Fe, Sb, Ni, Cr, Co, As, Cd. A relatively high coefficient of biological absorption by birch leaves Zn, Mn, P, Ca, Mg was obtained.

In vivo toxicity evaluation and antibacterial assessment of vanadium doped Bi2Se3 synthesized by cost effective method

Bismuth selenide-based nanomaterials are introduced as theranostic agents, primarily enhancing their antimicrobial, anti-cancerous, antitumor, and antioxidant properties. Pure Bi2Se3 and V doped Bi2Se3 with V = 0.07 g, 0.12 g, and 0.15 g were synthesized by using Sol-gel Technique. X-ray Diffraction (XRD) patterns demonstrated that the manufactured samples were crystalline in nature having rhombohedral structure. The average crystallite sizes of VxBi2-xS3 were calculated by Scherrer formula in the range (24.9–11.0 nm). The average crystallite size reduced as doping concentrations increased (0–0.15 g). The FTIR (Fourier transform infrared) spectra confirms that the peaks corresponds to 900–600 cm−1 indicates Bi–Se bond stretching, whereas vibrations exhibit peaks between 704 cm−1 - 830 cm−1 in doped samples correspond to V–O bond. UV–Visible analysis shows that the band gap of doped Bi2Se3 increased from (2.57 eV–2.90 eV) having standard error 0.02, 0.01, 0.02, and 0.02 respectively as the concentrations of doping increased (0.0–0.15 g), respectively. SEM (Scanning electron microscopy) study of pure Bi2Se3 showed nanosized particles, and for doped, a clear change in morphology occurred with the particles tending to agglomerate. EDAX also confirms the purity of synthesized samples. XPS analysis confirms the presence of Bi, Se and Vanadium along with chemisorbed oxygen. Antibacterial potential of synthesized samples was analyzed against Pseudomonas, Escherichia coli and cocci bacteria, which showed that the vanadium doped bismuth selenide has greater zone of inhibition than undoped bismuth selenide. Pseudomonas shows more ZOI (Zone of Inhibition) than E.coli and cocci. The maximum inhibition zone was 25 mm against Pseudomonas for V0.15Bi1.85Se3. The In-Vivo toxicity experiment was also applied on mice's (Swiss Albino) with a higher dosage of 20 mg per kg of the prepared doped sample. The blood samples were collected and examined after 3rd, 7th, 14th and 21st day of treatment. The entire treatment does not cause any severe damage to mice. An evaluation of a p-value based on hematological and biochemical data was non-significant this ensures that vanadium doped Bi2Se3 nanoparticles are non-toxic and biocompatible. This work proves that V-doped Bi2Se3 is good for further study in many other Applications in the biomedical field, such as photo thermal therapy, imaging etc.

5GSOLAR: On track for effective project commercialisation

5GSOLAR: On track for effective project commercialisation Maciej Sibiński, Research Professor from Tallinn University of Technology, highlights the 5GSOLAR project, which is on track to commercialise solar cells. The development of the new Sb2(S,Se)3, (Sb,Bi)2Se3 solar cells is currently underway, but effective commercialisation is crucial for successful growth, and proper perspective and potential technology applications are vital for future advancement. Intense effort was recently put into the development of Sb2S3 and Sb2Se3 structures in the Tallinn University of Technology’s Laboratory for Thin Film Energy Materials group, bringing about significant progress in both technology and efficiency levels. By using low-temperature and low-energy-consumption closed-spaced sublimation and chemical spray pyrolysis methods, the manufacturing technology was elaborated to achieve an industrial level.

Efficient photocatalytic reduction of Cr(VI) and degradation of tetracycline by Bi2Se3@ZnIn2S4 binary heterostructures enriched with sulfur vacancies: Mechanism and mineralization analysis

Constructing a sulfur-vacancy-enriched heterostructure offers advantages in enhancing photocatalytic performance due to the synergy between the vacancy’s electron-trapping and the internal electric field (IEF) features. In this study, a series of IEF-modulated type-I heterostructures containing sulfur vacancies-rich ZnIn2S4 (SV-ZIS) and Bi2Se3 (BSe) was rationally developed by hydrothermal and reduction methods. The optimized BSe@SV-ZIS catalyst shows an outstanding photocatalytic Cr(VI) reduction and tetracycline degradation rates, which are ∼ 2.1 and ∼ 1.5 times higher than that of pure SV-ZIS and BSe, respectively. Notably, the enhanced catalytic performance of binary samples could be linked to efficient absorption of the full spectrum of light, heterojunction formation and larger contact area to enhance the charge carriers movement at their interface and exceptional photo-stability. By assisting DRS, VB-XPS, and UPS analyses, details of the energy band position, charge carriers transport route, and preliminary photocatalytic mechanism were systematically explored. Furthermore, radical scavenging and electron paramagnetic resonance experiments were conducted to provide evidence of the participation of the reactive species during photocatalysis over BSe@SV-ZIS. Kinetic analysis revealed that the rate of photocatalytic process adheres to the Langmuir–Hinshelwood kinetic model. These results demonstrated that the heterostructuring approach holds significant potential as an effective avenue for developing photocatalysts that can harness both visible and NIR light, offering promising solutions to contemporary challenges in the realms of environmental decontamination and energy.

Enhanced Photocharacteristics by Fermi Level Modulating in Sb2 Te3 /Bi2 Se3 Topological Insulator p-n Junction.

Topological insulators have recently received attention in optoelectronic devices because of their high mobility and broadband absorption resulting from their topological surface states. In particular, theoretical and experimental studies have emerged that can improve the spin generation efficiency in a topological insulator-based p-n junction structure called a TPNJ, drawing attention in optospintronics. Recently, research on implementing the TPNJ structure is conducted; however, studies on the device characteristics of the TPNJ structure are still insufficient. In this study, the TPNJ structure is effectively implemented without intermixing by controlling the annealing temperature, and the photocharacteristics appearing in the TPNJ structure are investigated using a cross-pattern that can compare the characteristics in a single device. Enhanced photo characteristics are observed for the TPNJ structure. An optical pump Terahertz probe and a physical property measurement system are used to confirm the cause of improved photoresponsivity. Consequently, the photocharacteristics are improved owing to the change in the absorption mechanism and surface transport channel caused by the Fermi level shift in the TPNJ structure.

Holographic Nano-Imaging of Terahertz Dirac Plasmon Polaritons in Topological Insulator Antenna Resonators.

Excitation of Dirac plasmon polaritons (DPPs) in bi-dimensional materials have attracted considerable interest in recent years, both from perspectives of understanding their physics and exploring their transformative potential for nanophotonic devices, including ultra-sensitive plasmonic sensors, ultrafast saturable absorbers, modulators, and switches. Topological insulators (TIs) represent an ideal technological platform in this respect because they can support plasmon polaritons formed by Dirac carriers in the topological surface states. Tracing propagation of DPPs is a very challenging task, particularly at terahertz (THz) frequencies, where the DPP wavelength becomes over one order of magnitude shorter than the free space photon wavelength. Furthermore, severe attenuation hinders the comprehensive analysis of their characteristics. Here, the properties of DPPs in real TI-based devices are revealed. Bi2Se3 rectangular antennas can efficiently confine the propagation of DPPs to a single dimension and, as a result, enhance the DPPs visibility despite the strong intrinsic attenuation. The plasmon dispersion and loss properties from plasmon profiles are experimentally determined, along the antennas, obtained using holographic near-field nano-imaging in a wide range of THz frequencies, from 2.05 to 4.3THz. The detailed investigation of the unveiled DPP properties can guide the design of novel topological quantum devices exploiting their directional propagation.

Magnetic coupling mechanism of the interface in Bi2Se3/La0.7Sr0.3MnO3

The magnetic proximity effect in Bi2Se3 (BS)/La0.7Sr0.3MnO3 (LSMO) heterostructures is studied by first-principles calculations based on the density functional theory (DFT). Two heterogeneous structures LSMO (La, Sr, O termination layer, labeled as LaSrO)/BS and LSMO (Mn, O termination layer, labeled as MnO2)/BS are configured. In the LaSrO/BS system, the larger interfacial distance (2.88 Å) and higher interfacial binding energy (−6.36 eV) indicate a greater degree of stability for this structure. The spin polarization density distribution and spin magnetic moment results show BS can be effectively magnetized in both heterostructures. The magnetic coupling effect and observed charge transfer in MnO2/BS are more pronounced, suggesting potential differences in the magnetic exchange mechanisms between LaSrO/BS and MnO2/BS. The projected density of states (PDOS) and spin polarizability suggest that electron exchange and orbital hybridization between Mn-3d orbitals and BS play a crucial role in inducing magnetic order in BS. In MnO2/BS, the magnetic proximity effect is stronger, and more spin electron transfer between Mn-d and Se-p orbital of BS. These results may promote the application of TIs in the spintronic devices field.

Metavalent or Hypervalent Bonding: Is There a Chance for Reconciliation?

A family of solids including crystalline phase change materials such as GeTe and Sb2 Te3 , topological insulators like Bi2 Se3, and halide perovskites such as CsPbI3 possesses an unconventional property portfolio that seems incompatible with ionic, metallic, or covalent bonding. Instead, evidence is found for a bonding mechanism characterized by half-filled p-bands and a competition between electron localization and delocalization. Different bonding concepts have recently been suggested based on quantum chemical bonding descriptors which either define the bonds in these solids as electron-deficient (metavalent) or electron-rich (hypervalent). This disagreement raises concerns about the accuracy of quantum-chemical bonding descriptors is showed. Here independent of the approach chosen, electron-deficient bonds govern the materials mentioned above is showed. A detailed analysis of bonding in electron-rich XeF2 and electron-deficient GeTe shows that in both cases p-electrons govern bonding, while s-electrons only play a minor role. Yet, the properties of the electron-deficient crystals are very different from molecular crystals of electron-rich XeF2 or electron-deficient B2 H6 . The unique properties of phase change materials and related solids can be attributed to an extended system of half-filled bonds, providing further arguments as to why a distinct nomenclature such as metavalent bonding is adequate and appropriate for these solids.

Cation Defect-Engineered Boost Fast Kinetics of Two-Dimensional Topological Bi2 Se3 Cathode for High-Performance Aqueous Zn-Ion Batteries.

The challenge with aqueous zinc-ion batteries (ZIBs) lies in finding suitable cathode materials that can provide high capacity and fast kinetics. Herein, two-dimensional topological Bi2 Se3 with acceptable Bi-vacancies for ZIBs cathode (Cu-Bi2-x Se3 ) is constructed through one-step hydrothermal process accompanied by Cu heteroatom introduction. The cation-deficient Cu-Bi2-x Se3 nanosheets (≈4nm) bring improved conductivity from large surface topological metal states contribution and enhanced bulk conductivity. Besides, the increased adsorption energy and reduced Zn2+ migration barrier demonstrated by density-functional theory (DFT) calculations illustrate the decreased Coulombic ion-lattice repulsion of Cu-Bi2-x Se3 . Therefore, Cu-Bi2-x Se3 exhibits both enhanced ion and electron transport capability, leading to more carrier reversible insertion proved by in situ synchrotron X-ray diffraction (SXRD). These features endow Cu-Bi2-x Se3 with sufficient specific capacity (320mAhg-1 at 0.1Ag-1 ), high-rate performance (97mAhg-1 at 10Ag-1 ), and reliable cycling stability (70mAhg-1 at 10Ag-1 after 4000 cycles). Furthermore, quasi-solid-state fiber-shaped ZIBs employing the Cu-Bi2-x Se3 cathode demonstrate respectable performance and superior flexibility even under high mass loading. This work implements a conceptually innovative strategy represented by cation defect design in topological insulator cathode for achieving high-performance battery electrochemistry.

High-pressure synthesis of metastable Bi–S crystalline compounds: Crystal structure and electron transport

A new metastable Bi3S4 single crystal has been obtained on the initial Bi: S = 2 : 3 mixture at a pressure of 8.0–8.5 GPa with slow cooling from 1300 to 800 °C at a rate of ∼3 °C/min followed by quenching. The crystal has a triclinic structure formed by Bi-centered S-polyhedrons and chain-like clusters of Bi atoms. The relationship between the triclinic model based on single-crystal X-ray diffraction data and the orthorhombic model previously proposed for high-pressure Bi–S and Bi–Se phases with a similar structural motif based on X-ray powder diffraction data is discussed. The new Bi3S4 phase is a narrow-gap (band gap of 0.234 eV) intrinsic n-type semiconductor with a shallow impurity level. Metastable Bi3S4 recovers the structure of bismuthinite Bi2S3 after annealing at 200 °C.

Mineralogy and mineral chemistry of the ABM replacement-style volcanogenic massive sulfide deposit, Finlayson Lake district, Yukon, Canada

The ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide deposit (VMS) that is hosted by back-arc affinity rocks of the Yukon–Tanana terrane in the Finlayson Lake VMS district, Yukon, Canada. Massive sulfide zones occur as stacked and stratabound lenses subparallel to the volcanic stratigraphy, surrounded by pervasive white mica and/or chlorite alteration. Remnant clasts of volcanic rocks and preserved bedding occur locally within the massive sulfide lenses and indicate that mineralization formed through subseafloor replacement of pre-existing strata. Three mineral assemblages occur at the ABM deposit: (1) a pyrite–chalcopyrite–magnetite–pyrrhotite assemblage that is associated with Cu–Bi–Se–Co-enrichment and occurs at the center of the massive sulfide lenses; (2) a pyrite–sphalerite assemblage, which occurs more commonly towards lens margins and is enriched in Zn–Pb–Ag–Au–Hg–As–Sb–Ba; and (3) a minor assemblage comprising chalcopyrite–pyrrhotite–pyrite stringers associated with pervasive chlorite alteration, which occurs mostly at the sulfide lens margins. Petrographic observations of preserved primary, zone refining, and metamorphic textures in combination with in situ geochemistry show that the pyrite–sphalerite assemblage formed at lower temperatures (< 270 °C) than the other two mineral assemblages (~ 270–350 °C), and that mineral chemistry in all mineral assemblages was affected by greenschist facies metamorphism, although the effects are limited to recrystallization, small-scale remobilization (< 1 m) and trace element redistribution.

Phase diagrams of Bi–Sb–Se–Te system

Bi–Sb–Se–Te is one of the most important material systems for thermoelectric applications. Phase diagrams of its constituent binary and ternary systems are reviewed and assessed. The Bi–Sb–Se–Te isothermal section tetrahedron at 400 °C and liquidus projection tetrahedron were proposed. Ternary compounds are only found in the Bi–Sb–Se system. There are eight three-phase regions at 400 °C and seven primary solidification phases in the Bi–Sb–Se system, including (Bi,Sb), (Bi2)m(Bi2Se3)n, Bi2Se3, Se, Sb2Se3, Bi3Sb5Se2, Bi3Sb12Se15. In the Bi–Sb–Te system, there are four three-phase regions at 400 °C. The (Bi,Sb)2Te3 and (Bi,Sb) are continuous solid solutions. There are six primary solidification phases, including (Bi,Sb)2Te3, (Te), γ, δ, (Bi,Sb), and (Bi2)m(Bi2Te3)n. In the Bi–Se–Te system, there is one three-phase region. (Bi2)m(Bi2Se3)n and (Bi2)m(Bi2Te3)n form a continuous solid solution phase at 400 °C. There are four primary solidification phases, including Bi, (Bi2)m(Bi2(Se,Te)3)n, Bi2(Se,Te)3 and (Se,Te). In the Sb–Se–Te system, there are five three-phase regions and six primary solidification phases, including (Sb), δ-(Sb2Te), γ-(SbTe), Sb2Te3, and (Se,Te). A wide range of (Bi,Sb)2(Se,Te)3 single-phase region was observed in the Bi–Sb–Se–Te quaternary system.

Calculation of Component Activities for Se-Based Binary Systems by NRTL Equation

The interaction energy parameters of the Nonrandom two-liquid (NRTL) equation for the Bi–Se, Pb–Se, Sb–Se, and Tl–Se binary systems were determined. The difference in the goodness of fit between the systems was discussed for each system. The activities of components at corresponding temperatures for the four binary systems were calculated and discussed using the NRTL equation. The mixing enthalpies and Gibbs free energies of these systems were obtained. The calculations for the four binary systems are in agreement with the experimental data from the literature. It shows that the NRTL equation is reasonable and accurate based on the concept of local composition and two-fluid theory, especially for binary systems containing liquid–liquid equilibria. The results we obtained using the NRTL equation can be very useful in performing vacuum experiments for crude selenium.

Topological Insulator Bi2 Se3 -Assisted Heterostructure for Ultrafast Charging Sodium-Ion Batteries.

The development of fast charging materials offers a viable solution for large-scale and sustainable energy storage needs. However, it remains a critical challenge to improve the electrical and ionic conductivity for better performance. Topological insulator (TI), a topological quantum material that has attracted worldwide attention, hosts unusual metallic surface states and consequent high carrier mobility. Nevertheless, its potential in promising high-rate charging capability has not been fully realized and explored. Herein, a novel Bi2 Se3 -ZnSe heterostructure as excellent fast charging material for Na+ storage is reported. Ultrathin Bi2 Se3 nanoplates with rich TI metallic surfaces are introduced as an electronic platform inside the material, which greatly reduces the charge transfer resistance and improves the overall electrical conductivity. Meanwhile, the abundant crystalline interfaces between these two selenides promote Na+ migration and provide additional active sites as well. As expected, the composite delivers the excellent high-rate performance of 360.5 mAh g-1 at 20 A g-1 and maintains its electrochemical stability of 318.4 mAh g-1 after 3000 long cycles, which is the record high for all reported selenide-based anodes. This work is anticipated to provide alternative strategies for further exploration of topological insulators and advanced heterostructures.

Integration of Self-Passivated Topological Electrodes for Advanced 2D Optoelectronic Devices.

With the rapid development of two-dimensional semiconductor technology, the inevitable chemical disorder at a typical metal-semiconductor interface has become an increasingly serious problem that degrades the performance of 2D semiconductor optoelectronic devices. Herein, defect-free van der Waals contacts have been achieved by utilizing topological Bi2 Se3 as the electrodes. Such clean and atomically sharp contacts avoid the consumption of photogenerated carriers at the interface, enabling a markedly boosted sensitivity as compared to counterpart devices with directly deposited metal electrodes. Typically, the device with 2D WSe2 channel realizes a high responsivity of 20.5AW-1 , an excellent detectivity of 2.18×1012 Jones, and a fast rise/decay time of 41.66/38.81ms. Furthermore, high-resolution visible-light imaging capability of the WSe2 device is demonstrated, indicating its promising application prospect in future optoelectronic systems. More inspiringly, the topological electrodes are universally applicable to other 2D semiconductor channels, including WS2 and InSe, suggesting its broad applicability. These results open fascinating opportunities for the development of high-performance electronics and optoelectronics.

Role of Magnetic Defects in Tuning Ground States of Magnetic Topological Insulators.

Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi2 Se3 -based dilute ferromagnetic (FM) TIs and MnBi2 Te4 (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb2 Te3 form strong AFM dimer singlets within a quintuple block. The AFM superexchange coupling occurs via Mn-Te-Mn linear bonds and is identical to the AFM coupling between antisite defects and the FM Mn layer in MBT, establishing common interactions in the two materials classes. It is also found that the FM correlations in (Sb1-x Mnx )2 Te3 are likely driven by magnetic defects in adjacent quintuple blocks across the van der Waals gap. In addition to providing answers to long-standing questions about the evolution of FM order in dilute TI, these results also show that the evolution of global magnetic order from AFM to FM in Sb-substituted MBT is controlled by defect engineering of the intrablock and interblockcoupling.

Dual Topology of Dirac Electron Transport and Photo-galvanic Effect in Low-dimensional Topological Insulator Superlattices.

Dual topological insulators, simultaneously protected by time-reversal symmetry and crystalline symmetry, open great opportunities to explore different symmetry-protected metallic surface states. However, the conventional dual topological states located on different facets hinders integration into planar opto-electronic/spintronic devices. Here, we construct dual topological superlattices (TSLs) Bi2 Se3 -(Bi2 /Bi2 Se3 )N with limited stacking layer number N. Angle-resolved photoelectron emission spectra of the TSLs identify the coexistence and adjustion of dual topological surface states on Bi2 Se3 facet. The existence and tunability of spin-polarized dual-topological bands with N on Bi2 Se3 facet result in an unconventionally weak antilocalization effect (WAL) with variable WAL coefficient α (maximum close to 3/2) from quantum transport experiments. Most importantly, we identify the spin-polarized surface electrons from dual topological bands exhibit circularly and linearly polarized photo-galvanic effect (CPGE and LPGE). We anticipate that the stacked dual-topology and stacking layer number controlled bands evolution provide a platform for realizing intrinsic CPGE and LPGE. Our results show that the surface electronic structure of the dual TSLs is highly tunable and well-regulated for quantum transport and photoexcitation, which shed light on engineering for opto-electronic/spintronic applications. This article is protected by copyright. All rights reserved.

Bi2 Te3 /Bi2 Se3 /Bi2 S3 Cascade Heterostructure for Fast-Response and High-Photoresponsivity Photodetector and High-Efficiency Water Splitting with a Small Bias Voltage.

Large-scale multi-heterostructure and optimal band alignment are significantly challenging but vital for photoelectrochemical (PEC)-type photodetector and water splitting. Herein, the centimeter-scale bismuth chalcogenides-based cascade heterostructure is successfully synthesized by a sequential vapor phase deposition method. The multi-staggered band alignment of Bi2 Te3 /Bi2 Se3 /Bi2 S3 is optimized and verified by X-ray photoelectron spectroscopy. The PEC photodetectors based on these cascade heterostructures demonstrate the highest photoresponsivity (103mAW-1 at -0.1V and 3.5mAW-1 at 0V under 475nm light excitation) among the previous reports based on two-dimensional materials and related heterostructures. Furthermore, the photodetectors display a fast response (≈8ms), a high detectivity (8.96×109 Jones), a high external quantum efficiency (26.17%), and a high incident photon-to-current efficiency (27.04%) at 475nm. Due to the rapid charge transport and efficient light absorption, the Bi2 Te3 /Bi2 Se3 /Bi2 S3 cascade heterostructure demonstrates a highly efficient hydrogen production rate (≈0.416mmolcm-2 h-1 and ≈14.320µmolcm-2 h-1 with or without sacrificial agent, respectively), which is far superior to those of pure bismuth chalcogenides and its type-II heterostructures. The large-scale cascade heterostructure offers an innovative method to improve the performance of optoelectronic devices in the future.

Fabrication, characterization and optical properties of Au-decorated Bi2Se3 nanoplatelets

Au-decorated Bi2Se3 nanoplatelet heterostructures are fabricated by a two-step process of thermal CVD at 600 °C and magnetron sputtering at room-temperature. The crystal structures and binding energies of rhombohedral Bi2Se3 and FCC Au are determined by XRD, HRTEM, XPS, and Raman spectroscopy. XPS and Raman spectroscopy reveal the interaction between Au and Bi2Se3 by shifting in the binding energies of Au–Au, Au–Se and Bi–Se bonds and the wavenumber of A1g2 and Eg2 modes. Au-decorated Bi2Se3 nanoplatelet heterostructures are observed using FESEM, and confirmed by XPS, Raman spectroscopy, and HRTEM imaging. Their optical band gap of the Au-decorated Bi2Se3 nanoplatelet heterostructures increases with Au thickness about 1.92-fold as much as that of pristine Bi2Se3 (0.39 eV), owing to the Burstein-Moss effect. The optical absorptance of the Au-decorated Bi2Se3 nanoplatelet heterostructures revealed increment with wavelength from 200 to 500 nm and decrement with increasing wavelength from 500 to 800 nm.