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Binary compound bismuth selenide (Bi 2 Se 3) in the orthorhombic phase is an n-type semiconductor with optoelectronic properties desirable for applications in photosensitive devices. Obtaining this phase at room temperature is challenging, resulting in limited literature on the subject, thereby restricting the available information about this phase. In this study, we present our findings on the aqueous medium synthesis and stability of nanocrystalline Bi 2 Se 3 thin films over a Si substrate, predominantly exhibiting an orthorhombic phase (>92%), utilizing the electrodeposition technique. By changing the concentration of the electrolyte and deposition potential, it was possible to modify the morphology, absorbance, optical gap, and the magnitude of photocurrent signal in the photoelectrochemical cell (PEC), with no dramatical change in the chemical composition and crystalline phase of the films. The samples presented an inverse correlation between crystallite size and band gap, associated with the deposition conditions. Stability in the transient photocurrent signal with amplitudes around 9 µA/cm2 at 0.30 V SCE was observed for the sample growth at more negative potential. [ABSTRACT FROM AUTHOR]

As topological insulators (TIs) are becoming increasingly intriguing, the community is exploring transformative applications that require interfacing TIs with other materials such as ferromagnets or superconductors. Herein, we report on the manifestations of superconducting electrons carried by topological surface states (TSS) in Bi 2 Se 3 films. As key signatures of TSS-carried Cooper pairs, we uncover the hysteresis of magnetoresistance (MR) and the switching behavior of anisotropic magnetoresistance (AMR). For in-plane fields perpendicular to the injected current, AMR shows negative switching (resistance drop) when the contacts become superconducting, which is consistent with a cooperative Zeeman effect enabled by the spin-momentum locking of TSS. The MR and AMR behaviors are robust, occurring reliably in multiple samples, from different sources, and with different defect concentrations. Our findings can guide novel developments in superconductor/TI quantum devices relying on supercurrent detection as well as lead to more refined transport signatures of Majorana zero-modes in the future.

This paper reports a facile solvothermal method for the synthesis of Bi 2 S 3 flower-like nanostructures grown in situ on a nitrogen-doped reduced graphene oxide (Bi 2 S 3 @N-G) surface. Thiourea was used as the nitrogen source and reducing agent for graphene oxide. The surface morphology of the as-prepared Bi 2 S 3 @N-G composites was analyzed by field emission scanning electron microscopy and transmission electron microscopy. The crystalline structure and surface chemical states were examined by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The as-prepared Bi 2 S 3 @N-G composite was deposited on a glassy carbon (GC) electrode, and the modified electrode was employed for the electrocatalytic detection of H 2 O 2 . The calculated diffusion coefficient and catalytic rate constant of the Bi 2 S 3 @N-G modified electrode were 4.9 × 10 −6  cm 2  s −1 and 5671 M −1  s −1 , respectively. The Bi 2 S 3 @N-G/GC electrode demonstrated a wide concentration range for H 2 O 2 , from 10 to 42,960 μM, with a sensitivity of 0.1535 μA μM −1 and an obtained limit of detection of 1.9 μM. [ABSTRACT FROM AUTHOR]

Bi 2 Se 3 -doped FeSe crystals were synthesized from self-flux method. The crystalline, morphological, transport and magnetization properties have been investigated. The obtained samples have mix structures of hexagonal and tetragonal phases. The ratio of the tetragonal phase and the superconducting transition temperature increased with increasing doping content when the dopant concentration was low, and then decreased at higher dopant concentration. Superconducting phase coexisting with ferromagnetic phase were found in all samples. [ABSTRACT FROM AUTHOR]

The production of topological insulator and thermoelectric nanostructures is mostly done with physical vapor deposition techniques. Because Bi 2 Se 3 nanostructures are used in a variety of different disciplines in science, such as medicine, material science or condensed matter research, a simple synthesis with the possibility of a scale up is required. Here we report on a simple and cheap, chemical synthesis of 2D Bi 2 Se 3 nanostructures with an ultra high aspect ratio of 10 3 and correspondingly high surface area to volume ratio of 0.4 nm −1 . The size and stoichiometry of these nanostructures are adjustable. With one temperature, one precursor per element and a surfactant, we synthesize the nanostructures with an open or closed synthesis and analyze them with size histograms, TEM, EDX, SEM, Raman spectroscopy, and AFM. For the closed synthesis, our results show all four Raman peaks, the correct stoichiometry, and single crystallinity. The synthesis can be extended to make markers for cancer treatment, samples for the condensed matter research on the transport behavior of protected surface states or for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Here, Bi 1- x Ba x CuSe 1- x Te x O ( x  = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Ba/Te doping on the thermoelectric properties have been investigated systematically. For Ba doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration; for the Te doping based on Ba doping, it can profoundly reduce the difference of electronegativity in (Cu 2 Se 2 ) 2- layer, increase bond covalency, and then increase the electrical conductivity. The results indicate that the substitution of Ba/Te resulted in significant increases of electrical conductivity and power factor. Based on this, modulation doping leads to the simultaneous increase of the electrical conductivity and Seebeck coefficient. Finally, the maximum power factor of 0.98 mW m −1 K −2 and ZT value of 1.17 were obtained for the modulation doped Bi 0.90 Ba 0.10 CuSe 0.90 Te 0.10 O bulk, which were ~ 3.5 and ~ 2.2 times respectively as those of the pristine BiCuSeO ceramic. [ABSTRACT FROM AUTHOR]

Bi 2 Se 3 has extensive application as thermoelectric materials. Here, large-scale Bi 2 Se 3 single-crystal hexagonal nanoplates with size 7.50–10.0 μ m were synthesized successfully by hydrothermal method. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) were used to characterize the Bi 2 Se 3 nanoplates, which confirm the single-crystal quality and smooth surface morphology with large size. Micro-Raman spectra over a temperature range of 83–603 K were furthermore used to investigate the lattice dynamics of Bi 2 Se 3 nanoplates. Both 2A g 1 and 1E g 2 modes shift evidently with reduced temperature. The line shape demonstrates a significant broadening of full width at half maximum (FWHM) and red-shift of frequency with increased temperature. The temperature coefficient of A 1 g 1 , E g 2 , A 1 g 2 modes were determined to be −1.258 × 10 − 2 cm − 1 /K, −1.385 × 10 − 2 cm − 1 /K, −2.363 × 10 − 2 cm − 1 /K, respectively. Such low temperature coefficient may favor the obtaining of a high figure of merit (ZT) and indicate that Bi 2 Se 3 nanoplates were used as excellent candidates of thermoelectric materials. [ABSTRACT FROM AUTHOR]

Bi(0001) films with thicknesses up to several bilayers (BLs) are grown on Se-terminated Bi 2 Se 3 (0001) surfaces, and low energy electron diffraction (LEED), low energy ion scattering (LEIS) and atomic force microscopy (AFM) are used to investigate the surface composition, topography and atomic structure. For a single deposited Bi BL, the lattice constant matches that of the substrate and the Bi atoms adjacent to the uppermost Se atoms are located at fcc-like sites. When a 2nd Bi bilayer is deposited, it is incommensurate with the substrate. As the thickness of the deposited Bi film increases further, the lattice parameter evolves to that of bulk Bi(0001). After annealing a multiple BL film at 120 °C, the first commensurate Bi BL remains intact, but the additional BLs aggregate to form thicker islands of Bi. These results show that a single Bi BL on Bi 2 Se 3 is a particularly stable structure. After annealing to 490 °C, all of the excess Bi desorbs and the Se-terminated Bi 2 Se 3 surface is restored. [ABSTRACT FROM AUTHOR]

Abstract: Despite their huge application capabilities, millimeter‐ and terahertz‐wave photodetectors still face challenges in the detection scheme. Topological insulators (TIs) are predicted to be promising candidates for long‐wavelength photodetection, due to the presence of Dirac fermions in their topologically protected surface states. However, photodetection based on TIs is usually hindered by the large dark current, originating from the mixing of bulk states with topological surface states (TSSs) in most realistic samples of TIs. Here millimeter and terahertz detectors based on a subwavelength metal–TI–metal (MTM) heterostructure are demonstrated. The achieved photoresponse stems from the asymmetric scattering of TSS, driven by the localized surface plasmon‐induced terahertz field, which ultimately produces direct photocarriers beyond the interband limit. The device enables high responsivity in both the self‐powered and bias modes even at room temperature. The achieved responsivity is over 75 A/W, with response time shorter than 60 ms in the self‐powered mode. Remarkably, the responsivity increases by several orders of magnitude in the biased configuration, with the noise‐equivalent power (NEP) of 3.6 × 10−13 W Hz−1/2 and a detectivity of 2.17 × 1011 cm Hz−1/2 W−1 at room temperature. The detection performances open a way toward realistic exploitation of TIs for large‐area, real‐time imaging within long‐wavelength optoelectronics. [ABSTRACT FROM AUTHOR]

We adopted and extended an efficient Grüneisen formalism to study the phonon anharmonicity and linear thermal expansion coefficients (TECs) of trigonal bismuth selenide (Bi 2 Se 3 ) and antimony telluride (Sb 2 Te 3 ). Anharmonicity of the systems is studied via extensive calculation of Grüneisen parameters that exploit symmetry-preserving deformations. Consistent with experimental findings, a large anisotropy between the TECs in the a and c directions is found. The larger anharmonicity inherent in Sb 2 Te 3 , as compared to Bi 2 Se 3 is offset by the volumetric effect, resulting in comparable temperature dependence of their linear TECs. The Debye temperatures deduced from our first-principles data also agree very well with the existing tabulated values. The highly efficient methodology developed in this work, applied for the first time to study the linear TECs of two trigonal thermoelectric systems, opens up exciting opportunities to address the anharmonic effects in other thermoelectrics and other low-symmetry materials. [ABSTRACT FROM AUTHOR]

Using surface X‐ray diffraction we have studied the atomic structure of ultra‐thin sliver films deposited in the one monolayer thickness‐regime on the (0001) surface of the Topological Insulator Bi2Se3. Depending on the preparation of the substrate surface, different interface structures are formed. For sputter‐annealed single crystalline Bi2Se3 (0001) silver atoms substitute bismuth atoms within the first quintuple layer and simultaneously reside in surface hollow sites. When silver is deposited on a substrate grown by molecular beam epitaxy and which was only annealed prior to silver deposition, only adsorption in surface hollow sites is observed. Neither intercalation into the van der Waals gap nor its vertical expansion is observed in any case. An expansion induced appearance of surface states can be excluded. [ABSTRACT FROM AUTHOR]

Using surface X‐ray diffraction we have studied the atomic structure of ultra‐thin sliver films deposited in the one monolayer thickness‐regime on the (0001) surface of the Topological Insulator Bi2Se3. Depending on the preparation of the substrate surface, different interface structures are formed. For sputter‐annealed single crystalline Bi2Se3 (0001) silver atoms substitute bismuth atoms within the first quintuple layer and simultaneously reside in surface hollow sites. When silver is deposited on a substrate grown by molecular beam epitaxy and which was only annealed prior to silver deposition, only adsorption in surface hollow sites is observed. Neither intercalation into the van der Waals gap nor its vertical expansion is observed in any case. An expansion induced appearance of surface states can be excluded. [ABSTRACT FROM AUTHOR]

Epitaxial growth of thin films is an effective approach to minimize the contribution of bulk carriers for topological insulator (TI) Bi2Se3. Parameters used in preparation process are key factors for growing high quality thin films, especially for TI films. In this paper, magnetron sputtering was used for growing Bi2Se3 thin films on Si (100) substrates. Different working pressure and sputtering power were investigated. High-quality films could be obtained under relatively low pressure and low power. Linear and nonsaturated high-field linear magnetoresistance (LMR) was observed in high-quality films. [ABSTRACT FROM AUTHOR]

Exploring and developing novel semiconductor photo-catalysts for visible-light-driven water splitting are of great scientific significance to solve energy and environmental problems. Herein, Bismuth Selenide (Bi 2 Se 3 ) nanosheets decorated with a thin layer of Bi 2 SeO 2 to form Bi 2 Se 3 /Bi 2 SeO 2 nanocomposites were successfully prepared using a conventional reflux and heating method. Fabricated Bi 2 Se 3 /Bi 2 SeO 2 heterojunctions were characterized via X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. It has revealed that, the thickness of outer Bi 2 SeO 2 layer can be tuned upon the annealing temperatures, which strongly influenced the performance of catalyst towards water splitting performances. Annealed at 200 °C, the Bi 2 Se 3 /Bi 2 SeO 2 heterojunction with ∼5 nm of Bi 2 SeO 2 layer yielded the highest hydrogen production rate of 136 μmol g −1 h −1 . This enhanced photo-catalytic activity was ascribed to the synergy effect between the Bi 2 Se 3 /Bi 2 SeO 2 layer, increased the visible light absorbance capacity, adjustment of the band gap and accelerate the electron-hole separation efficiency. The results represent a simply solution-based method towards a material with high photo-catalytic performance through the appropriate regulation of the oxidation degree of Bi 2 Se 3 nanosheets, promising their industrial applications. [ABSTRACT FROM AUTHOR]

We report on the synthesis, and structural – magnetic characterizations of Mn doped Bi 2 Se 3 towards achieving a magnetically doped topological insulator. High quality single crystals of Mn x Bi 2−x Se 3 (x = 0, 0.03, 0.05, 0.1) are grown and analysed by X-ray diffraction (XRD), Low Energy Electron Diffraction (LEED), Scanning electron microscopy (SEM), and X-ray absorption near-edge structure spectroscopy (XANES). Magnetic properties of these samples under ZFC-FC protocol and isothermal magnetization confirm ferromagnetic correlation above x = 0.03 value. XANES measurements confirm that the dopant Mn is in Mn 2+ state. This is further reconfirmed to be in high spin state by fitting magnetic data with Brillouin function for J = 5/2. Both Hall and Seebeck measurements indicate a sign change of charge carriers above x = 0.03 value of Mn doping. We propose Mn doped Bi 2 Se 3 to be a potential candidate for electromagnetic and thermoelectric device applications involving topological surface states. [ABSTRACT FROM AUTHOR]

In the present study we report the one step facile synthesis of pristine lead bismuth selenide (PbBi2Se4) and reduced graphene oxide (rGO) and its composites with PbBi2Se4. Formation of pristine PbBi2Se4 and rGO-PbBi2Se4 composite were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The surface morphology and topography investigated by using scanning electron microscopy and transmission electron microscopy revealed the formation of nano-flowers pristine PbBi2Se4. After coupling pristine PbBi2Se4 with rGO the surface morphology shows the formation of sharp vertically protruded nano-sheets/nano-flaks originated from the nano-flowers. Finally, the field emission properties of pristine PbBi2Se4 and rGO-PbBi2Se4 composite have been investigated. It has been observed that the rGO-PbBi2Se4 composite emitter exhibited excellent field emission properties with low turn-on field (~ 2.8 V/µm for 10 µA/cm2), high emission current density (~ 1288 µA/cm2 at 3.9 V/µm) and superior current stability (~ 4.5 h for ~ 1 µA) compare to pristine PbBi2Se4 emitter. Thus, the facile one step synthesis approach and robust nature of rGO-PbBi2Se4 composite emitter can provide prospects for the future development of large-area emitter applications such as flat-panel-display and vacuum micro/nanoelectronics devices. [ABSTRACT FROM AUTHOR]

Topological insulators are a quantum state of matter that has recently created a great interest among the scientific community, with Bi 2 Se 3 being one of the most extensively studied materials. Here, we demonstrate that polycrystalline nanostructured samples of Bi 2 Se 3 preserve the existence of topological surface states, where electrons cannot be localised. The nanosheet crystals were synthesised by a microwave-assisted method and their structure, composition and morphology thoroughly characterised. The transport properties of a textured polycrystalline sample with strong preferred orientation along the c -axis were measured, showing the presence of the weak anti-localisation effect and Shubnikov-de Haas oscillations. These features are robust against the presence of non-magnetic impurities and structural defects. [ABSTRACT FROM AUTHOR]

We compare the magnetic and electronic configuration of single Mn atoms in molecular beam epitaxy (MBE) grown Bi 2 Se 3 thin films, focusing on electron paramagnetic (ferromagnetic) resonance (EPR and FMR, respectively) and superconducting quantum interference device (SQUID) techniques. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) reveal the expected increase of disorder with increasing concentration of magnetic guest atoms, however, Kikuchi patterns show that disorder consists majorly of μm-scale 60° twin domains in the hexagonal Bi 2 Se 3 structure, which are promoted by the presence of single unclustered Mn impurities. Ferromagnetism below T C ~ (5.4±0.3) K can be well described by critical scaling laws M ( T ) ~ ( 1 − T / T C ) β with a critical exponent β = ( 0.34 ± 0.2 ) , suggesting 3D Heisenberg class magnetism instead of e.g. 2D-type coupling between Mn-spins in van der Waals gap sites. From EPR hyperfine structure data we determine a Mn 2+ (d 5 , S = 5/2) electronic configuration with a g-factor of 2.002 for −1/2 → +1/2 transitions. In addition, from the strong dependence of the low temperature FMR fields and linewidth on the field strength and orientation with respect to the Bi 2 Se 3 (0001) plane, we derive magnetic anisotropy energies of up to K 1 = −3720 erg/cm 3 in MBE-grown Mn-doped Bi 2 Se 3 , reflecting the first order magneto-crystalline anisotropy of an in-plane magnetic easy plane in a hexagonal (0001) crystal symmetry. We observe an increase of K 1 with increasing Mn concentration, which we interpret to be correlated to a Mn-induced in-plane lattice contraction. Across the ferromagnetic-paramagnetic transition the FMR intensity is suppressed and resonance fields converge the paramagnetic limit of Mn 2+ (d 5 , S = 5/2). [ABSTRACT FROM AUTHOR]

We report Shubnikov-de Haas (SdH) and Hall oscillations in Cu-doped high quality bismuth selenide single crystals. To increase the accuracy of Berry phase determination by means of the of the SdH oscillations phase analysis we present a study of n-type samples with bulk carrier density n ∼ 10 19 − 10 20 cm − 3 at high magnetic field up to 60 Tesla. In particular, Landau level fan diagram starting from the value of the Landau index N = 4 was plotted. Thus, from our data we found π -Berry phase that directly indicates the Dirac nature of the carriers in three-dimensional topological insulator (3D TI) based on Cu-doped bismuth selenide. We argued that in our samples the magnetotransport is determined by a general group of carriers that exhibit quasi-two-dimensional (2D) behaviour and are characterized by topological π -Berry phase. Along with the main contribution to the conductivity the presence of a small group of bulk carriers was registered. For 3D-pocket Berry phase was identified as zero, which is a characteristic of trivial metallic states. [ABSTRACT FROM AUTHOR]

As new family of superconductors with a layered structure, BiS 2 -based materials have attracted much interest. Eu 3 Bi 2 S 4 F 4 is a newly discovered member which shows superconductivity at 1.5 K without extrinsic doping, however, superconductivity is strongly suppressed by Sr-doping. In this contribution, we present, in terms of local atomic displacement, an insight into the relationship between Sr-doping and the suppression of superconductivity in Eu 3- x Sr x Bi 2 S 4 F 4 by Bi and Eu L 3 -edge X-ray absorption spectroscopy. Upon Sr-doping, the distance between Eu 3 F 4 blocking layers and BiS 2 layers is significantly elongated, accompanied by the breaking of Eu-S-Bi channel, which makes it more difficult to transfer electrons into BiS 2 layers. Moreover, distortions in the Bi-S1 plane increase with Sr content, reducing the overlap among Bi(6 p x /6 p y )-S(3 p ) orbitals within the superconducting plane. The decoupling between blocking and BiS 2 layers, as well as the distortions in the superconducting Bi-S1 plane, may contribute to the suppression of superconductivity in Sr-doped Eu 3 Bi 2 S 4 F 4 compounds. [ABSTRACT FROM AUTHOR]

The article focuses on a study regarding superconducting pairing of topological surface states in bismuth selenide films on niobium. Topics discussed include topological insulator film coupled to a simple isotropic s-wave superconductor substrate can foster helical pairing of the Dirac fermions, photoemission spectroscopy (ARPES) measurements of the film surface and mechanism of coupling between the topological surface states.

Abstract: As an emerging 2D layered material, Bi2O2Se has shown great potential for applications in thermoelectric and electronics, due to its high carrier mobility, near‐ideal subthreshold swing, and high air‐stability. Although Bi2O2Se has a suitable band gap for infrared (IR) applications, its photoresponse properties have not been investigated. Here, high‐quality ultrathin Bi2O2Se sheets are synthesized via a low‐pressure chemical vapor deposition method. The thickness of 90% Bi2O2Se sheets is below 10 nm and lateral sizes mainly distribute in the range of 7–11 µm. In addition, it is found that triangular sheets largely lack “O” content, even only 0.2 for Bi2O0.2Se. The near‐IR photodetection performance of Bi2O2Se nanosheets is systematically studied by variable temperature measurements. The response time, responsivity, and detectivity can approach up to 2.8 ms, 6.5 A W−1, and 8.3 × 1011 Jones, respectively. Additionally, the critical performance parameters, including responsivity, rising time, and decay time, remain at almost the same level when the temperature is changed from 80 to 300 K. These phenomena are likely due to the fact that as‐grown ultrathin Bi2O2Se sheets have no surface trap states and shallow defect energy levels. The findings indicate ultrathin Bi2O2Se sheets have great potentials for future applications in ultrafast, flexible near‐IR optoelectronic devices. [ABSTRACT FROM AUTHOR]

In the present report, nanostructured bismuth selenide (Bi 2 Se 3 ) thin films have been successfully deposited by using arrested precipitation technique (APT) at room temperature. The effect of three different surfactants on the optostructural, morphological, compositional and photoelectrochemical properties of Bi 2 Se 3 thin films were investigated. Optical absorption data indicates direct and allowed transition with a band gap energy varied from 1.4 eV to 1.8 eV. The X-ray diffraction pattern (XRD) revealed that Bi 2 Se 3 thin films are crystalline in nature and confirmed rhombohedral crystal structure. SEM micrographs shows morphological transition from interconnected mesh to nanospheres like and finally granular morphology. Surface topography of Bi 2 Se 3 thin films was determined by AFM. Compositional analysis of all samples was carried out by energy dispersive X-ray spectroscopy (EDS). Finally, all Bi 2 Se 3 thin films shows good PEC performance with highest photoconversion efficiency 1.47%. In order to study the stability of Bi 2 Se 3 thin films four cycles are repeated after gap of one week each. Further PEC performance of all Bi 2 Se 3 thin films are also supported by electrochemical impedance (EIS) measurement study. [ABSTRACT FROM AUTHOR]

We propose to further enhance the thermoelectric performance of BiCuSeO using the biaxial strain. The effect of biaxial strain on the thermoelectric property of BiCuSeO is investigated by using the first-principles calculations combined with the Semiclaasical Boltzmann theory. When the biaxial strain is applied, the Seebeck coefficient is largely enhanced by tensile strain, while the electrical conductivity can be greatly enhanced by compressive strain. The largest zT value of 1.7 at 900 K is then conservatively estimated by using the experimental thermal conductivity, which is 4 times larger than that without biaxial strain. Our results indicate that the biaxial strain could be an effect method to enhance the thermoelectric performance of BiCuSeO. [ABSTRACT FROM AUTHOR]

Abstract: Thermo‐chemotherapy combining photothermal therapy (PTT) with chemotherapy has become a potent approach for antitumor treatment. In this study, a multifunctional drug‐delivery nanoplatform based on polyethylene glycol (PEG)‐modified mesoporous silica‐coated bismuth selenide nanoparticles (referred to as Bi2Se3@mSiO2‐PEG NPs) is developed for synergistic PTT and chemotherapy with infrared thermal (IRT) imaging of cancer cells. The product shows no/low cytotoxicity, strong near‐infrared (NIR) optical absorption, high photothermal conversion capacity, and stability. Utilizing the prominent photothermal effect, high‐contrast IRT imaging and efficient photothermal killing effect on cancer cells are achieved upon NIR laser irradiation. Moreover, the successful mesoporous silica coating of the Bi2Se3@mSiO2‐PEG NPs cannot only largely improve the stability but also endow the NPs high drug loading capacity. As a proof‐of‐concept model, doxorubicin (DOX) is successfully loaded into the NPs with rather high loading capacity (≈50.0%) via the nanoprecipitation method. It is found that the DOX‐loaded NPs exhibit a bimodal on‐demand pH‐ and NIR‐responsive drug release property, and can realize effective intracellular drug delivery for chemotherapy. The synergistic thermo‐chemotherapy results in a significantly higher antitumor efficacy than either PTT or chemotherapy alone. The work reveals the great potential of such core–shell NPs as a multifunctional drug‐delivery nanosystem for thermo‐chemotherapy. [ABSTRACT FROM AUTHOR]

Bi2Se3, one of the most widely studied topological insulators (TIs), is naturally electron-doped due to n-type native defects. However, many years of efforts to achieve p-type Bi2Se3 thin films have failed so far. Here, we provide a solution to this long-standing problem, showing that the main culprit has been the high density of interfacial defects. By suppressing these defects through an interfacial engineering scheme, we have successfully implemented p-type Bi2Se3 thin films down to the thinnest topological regime. On this platform, we present the first tunable quantum Hall effect (QHE) study in Bi2Se3 thin films and reveal not only significantly asymmetric QHE signatures across the Dirac point but also the presence of competing anomalous states near the zeroth Landau level. The availability of doping tunable Bi2Se3 thin films will now make it possible to implement various topological quantum devices, previously inaccessible. [ABSTRACT FROM AUTHOR]

Understanding the mutual interaction between electronic excitations and lattice vibrations is key for understanding electronic transport and optoelectronic phenomena. Dynamic manipulation of such interaction is elusive because it requires varying the material composition on the atomic level. In turn, recent studies on topological insulators (TIs) have revealed the coexistence of a strong phonon resonance and topologically protected Dirac plasmon, both in the terahertz (THz) frequency range. Here, using these intrinsic characteristics of TIs, we demonstrate a new methodology for controlling electron-phonon interaction by lithographically engineered Dirac surface plasmons in the Bi2Se3 TI. Through a series of time-domain and time-resolved ultrafast THz measurements, we show that, when the Dirac plasmon energy is less than the TI phonon energy, the electron-phonon coupling is trivial, exhibiting phonon broadening associated with Landau damping. In contrast, when the Dirac plasmon energy exceeds that of the phonon resonance, we observe suppressed electron-phonon interaction leading to unexpected phonon stiffening. Time-dependent analysis of the Dirac plasmon behavior, phonon broadening, and phonon stiffening reveals a transition between the distinct dynamics corresponding to the two regimes as the Dirac plasmon resonance moves across the TI phonon resonance, which demonstrates the capability of Dirac plasmon control. Our results suggest that the engineering of Dirac plasmons provides a new alternative for controlling the dynamic interaction between Dirac carriers and phonons. [ABSTRACT FROM AUTHOR]

Nanoparticles made of 'pure' and Ni-'doped' BiSe prototype topological insulators were successfully prepared using the chemical hot-injection method. In both cases, the reaction is kept for a relatively long period, where samples are taken from the reaction flask at successive time steps. High resolution transmission electron microscopy revealed significant morphology differences for the pure and Ni-doped samples at all reaction times. The pure BiSe samples exhibit spiral-like shapes turning into large sheets with wires-like features at very long reaction times, whereas the Ni-doped samples evolve, with the reaction time, from highly spherical, partially elongated, and finally well-defined nanorods. In addition, Co-doped BiSe samples, prepared under the same conditions, exhibit large non-uniform flakes at long reaction time. The crystallinity of all pure and magnetic-doped samples was ensured from electron diffraction, and quantitatively obtained from X-ray diffraction measurements. The latter justified the same rhombohedral crystal structure for both the pure and magnetically doped samples, and the absence of other phases. The energy dispersive X-ray spectroscopy was used to quantify the present elements, where the Bi, Se, Ni, and Co peaks were identified. The present study provides a way for tuning the nanoparticles size/morphology of BiSe and related-compounds by the slight addition of magnetic dopants, which subsequently allows the engineering of various BiSe-based nanoarchitectures. [ABSTRACT FROM AUTHOR]

The increasing demand for new materials with narrow bandgap energy, capable of harvesting the photons in the visible range, is central in the remediation of environmental pollutants by photocatalytic reactions. For the first time, we report a novel visible light driven photocatalyst of Bi 2 Se 3 /Bi 1.007 Se 0.993 by the formation of solid solution composite. Both the individual Bi 2 Se 3 and Bi 1.007 Se 0.993 have very low photocatalytic efficiency under visible light irradiation; however, Bi 2 Se 3 /Bi 1.007 Se 0.993 provides much higher efficiency in decomposing methylene blue (MB). Especially in the presence of H 2 O 2 , the reaction rate was enhanced by 15 times and 100% of MB degradation was obtained in 90 min. Characterization results confirmed that the bandgap of Bi 2 Se 3 /Bi 1.007 Se 0.993 was greatly broadened to 1.38 eV compared with Bi 2 Se 3 of 0.3 eV, which matched well with visible range. Moreover, the relative conduction band position vs. NHE of Bi 2 Se 3 /Bi 1.007 Se 0.993 was −0.3 V, which was more negative than that of Bi 1.007 Se 0.993 of +0.2 V. It was responsible to the excellent photocatalytic activity due to harvesting the photons in the visible range. Finally, N-type semiconductor based reduction O 2 to O 2 •- and photoreduction of H 2 O 2 into • OH involved reaction mechanism under the visible light irradiation was proposed based on all the experimental results. [ABSTRACT FROM AUTHOR]

Granular nanocrystalline Bi2(Se1-xTex)3films were prepared from highly crystalline bulk alloys used as source materials by means of thermal evaporation under vacuum (2 × 10−6mbar). The nanofilms were deposited onto highly cleaned glass substrates of BK7 type. The structural characteristics, including surface morphology, roughness, and crystallite size, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis. Perfect crystallinity and nanoscalability of the prepared samples were asserted. Transmittance and reflectance spectra of the prepared nanofilms were investigated over the wavelength range of 400–2,700 nm. In the visible light region, all of the films showed an opaque behavior; however, as the wavelength increased into the infrared region, a growing transparency was observed. Based on the measured transmission and reflection spectra, the coefficients of absorbance and extinction as well as the optical band gap were determined. The refractive index was deduced from the reflectance measurements using the determined extinction coefficient. Direct allowed band transitions were confirmed in all films with a band gap energy of 0.85–1.05 eV, depending on the Te content. The possibility of an indirect band gap in the lower photon energy region was discussed. The Seebeck coefficient and electrical conductivity were measured in the temperature range of 300–500 K. Very large values of the power factor of 80 and 131were obtained for Be2Se3films at room temperature and 473 K, respectively; the latter is three times larger than best previously reported values for similar film systems. [ABSTRACT FROM AUTHOR]

The influence of individual impurities of Fe on the electronic properties of topological insulator Bi2Se3 is studied by Scanning Tunneling Microscopy. The microscope tip is used in order to remotely charge/discharge Fe impurities. The charging process is shown to depend on the impurity location in the crystallographic unit cell, on the presence of other Fe impurities in the close vicinity, and on the overall doping level of the crystal. We present a qualitative explanation of the observed phenomena in terms of tip-induced local band bending. Our observations evidence that the specific impurity neighborhood and the position of the Fermi energy with respect to both the Dirac point and bulk bands have to be taken into account when considering the electron scattering on the disorder in topological insulators. [ABSTRACT FROM AUTHOR]

The influence of individual impurities of Fe on the electronic properties of topological insulator Bi2Se3 is studied by Scanning Tunneling Microscopy. The microscope tip is used in order to remotely charge/discharge Fe impurities. The charging process is shown to depend on the impurity location in the crystallographic unit cell, on the presence of other Fe impurities in the close vicinity, and on the overall doping level of the crystal. We present a qualitative explanation of the observed phenomena in terms of tip-induced local band bending. Our observations evidence that the specific impurity neighborhood and the position of the Fermi energy with respect to both the Dirac point and bulk bands have to be taken into account when considering the electron scattering on the disorder in topological insulators. [ABSTRACT FROM AUTHOR]

We report a positive hydrostatic pressure derivative of the superconducting transition temperature in the doped topological insulator Nb 0.25 Bi 2 Se 3 via dc SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary to reports on the homologues Cu x Bi 2 Se 3 and Sr x Bi 2 Se 3 where smooth suppression of T c is observed. This difference may be attributable to an electronic structure composed of multiple bands whereas the other materials in the superconducting doped Bi 2 Se 3 family are believed to be single-band. [ABSTRACT FROM AUTHOR]

Bi 2 Se 3 with layered structure has been considered as a promising host for Li ion batteries due to its high electrical conductivity. However, the disadvantages such as dissolution loss of selenium species and the large volume expansion extremely hinder its practical application. Here, the electrochemical performance is improved by synthesizing CNTs@C@Bi 2 Se 3 nanocomposites. The electrochemical measurements results indicate that the CNTs@C@Bi 2 Se 3 delivers high rate capacity (222 mA h g −1 at 2000 mA g −1 ) and long-term cycle stability (243 mA h g −1 after 300th cycles at 1000 mA g −1 ). Moreover, the electrochemical reaction mechanism is proposed based on the ex situ HRTEM technique. [ABSTRACT FROM AUTHOR]

The linear magnetoresistance (MR) effect is an interesting topic due to its potential applications. In topological insulator Bi2Se3, this effect has been reported to be dominated by the carrier mobility (l) and hence has a classical origin. Here, we study the magnetotransport properties of Bi2Se3 thin films and observe the linear MR effect, which cannot be attributed to the quantum model. Unexpectedly, the linear MR does not show the linear dependence on l, in conflict with the reported results. However, we find that the observed linear MR is dominated by the inverse disorder parameter 1/kFl, where kF and l are the Fermi wave vector and the mean free path, respectively. This suggests that its origin is also classical and that no μ-dominated linear MR effect is observed which may be due to the very small l values in our samples. [ABSTRACT FROM AUTHOR]

Bismuth selenide (Bi 2 Se 3 ) and transition metal (nickel) doped (5 and 7.5 mol %) Bi 2 Se 3 have been prepared by solvothermal approach for investigation of thermoelectric properties of the materials. The morphological characterization reveals plate and flake like structures for undoped and doped samples respectively. There is a decrease in lattice constant, computed from Rietveld refinement data and crystallite size, found using Debye-Scherrer equation for doped samples. Doping by nickel increases the electrical conductivity and reduces both thermo power and thermal conductivity of the materials than pure Bi 2 Se 3 . Reduction in thermal conductivity of the doped samples by 42%, results in an increase in figure of merit (ZT) of nickel doped (5%) materials by one order of magnitude (0.02–0.22) compared to pure Bi 2 Se 3 . [ABSTRACT FROM AUTHOR]

• Bi 2 Se 3 single-crystal was grown by Bridgeman-Stockbarger method. • Single-crystal Bi 2 Se 3 is capable of retaining most of its initial volume (≈94%) once subjected to wear. • COF value of the material is compatible to that of GaN, a common semiconductor. • Strain hardening properties measured using novel method based on pile-up height. Single crystal Bi 2 Se 3 was grown using the novel Bridgeman-Stockbarger method. Surface characteristics in terms of wear rate (W), wear coefficient (K), coefficient of friction (COF), and strain hardening exponent (n) were investigated using nanoindentation and nano scratch techniques. Our results revealed that the remarkable wear properties of single-crystal Bi 2 Se 3 are promising for nanoscale design of topological insulators. [ABSTRACT FROM AUTHOR]

• Bi 2 Se 3 layers were prepared on the ITO substrate through the electrodeposition method. • Structural, compositional, and morphological characterization of Bi 2 Se 3 was studied. • The electrochemical performance shows that the Bi 2 Se 3 films can be used for energy storage. • Maximum specific capacitance of 66.3 mF g −1 obtained at a current density of 2 mA g −1. Bismuth selenide (Bi 2 Se 3) layers have proved useful as electrode materials for capacitors. This material was prepared via electrodeposition method with the different deposition time and characterized by X-ray diffraction, Scanning electron microscopy, and Energy dispersive X-ray spectroscopy techniques. It is found that the films of Bi 2 Se 3 provoke the formation of a biphasic, orthorhombic and rhombohedral crystal structure, with uniform spherical particles. Furthermore, the electrochemical properties of Bi 2 Se 3 were investigated using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in 1 M HNO 3 aqueous electrolyte. Galvanostatic charge-discharge measurements deliver a specific capacitance of 49.7 mF g −1 which leads to a specific energy density of 0.0034 Wh kg−1 and specific power of up to 5 kW kg−1 at a current of 0.01 A g −1. The electrochemical impedance data were fitted with an equivalent circuit containing a constant phase element and fitted parameters were calculated. [ABSTRACT FROM AUTHOR]

The chemical reaction of gas adsorption/desorption is strongly correlated with the surface state of sensitive films. Thus, understanding the surface state and kinetic process of gas-sensing reactions is crucial to design highly active sensing films. In this study, bismuth selenide (Bi 2 Se 3) was selected as the platform to clarify those matters. The noble metal nanocrystals (Au, Ag and Pt) were decorated on the (001) surface of layered Bi 2 Se 3 to tune the surface state and improve the dynamical gas sensing parameter. The response and response rate toward 10 ppm of NO 2 were respectively improved by 2.5 and 3.8 times by the Au decoration, and 2.3 and 3.2 times by the Ag decoration, and 1.3 and 2.7 times by the Pt decoration. The gas adsorption/desorption isotherm was established to analyze the reaction kinetic parameters of the response (S), kinetic reaction rate (kr and k-r) and beta value (β). These results demonstrate that noble metals can greatly promote the reaction kinetic parameters by modulation the surface state. Especially, the Au10 sample acquired maximum kr values of 633.963, which is 9.3 times higher than pure Bi 2 Se 3. This work provides an important strategy for designing gas sensing performance between topological insulators and noble metal particles. • The topological insulator was served as a platform for novel surface chemistry and catalysis. • Au, Ag and Pt were decorated to design high gas sensing performance by tuning the surface states. • The adsorption/desorption isotherm were established to clarify the mechanism. • This work paves a way to design high activity gas sensor [ABSTRACT FROM AUTHOR]