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Rechargeable aqueous zinc-ion batteries present low-cost, safe, and environmentally-friendly battery technology but suffer from the limited choice of cathode materials because of the sluggish kinetics of divalent zinc-ion associated with the high adsorption and migration energy barrier. Herein, a reversible zinc/bismuth selenide mild aqueous system was demonstrated for the first time, where bismuth selenide nanoplate cathode delivers a high specific capacity of 263.2 mA h g−1 at 0.1 A g−1 and robust rate capability of 100.6 mA h g−1 even at 10 A g−1 with long-term lifespan (82.3% retention after 1000 cycles). Benefiting from the layered structure and nanoplate morphology of the bismuth selenide cathode, surface-dominated ion storage is verified by a quantitative kinetics analysis, particularly at high current rates. Notably, unlike conventional batteries with only the reversible intercalation of alkali ions into metal chalcogenides, zinc/bismuth selenide aqueous batteries possess a sequential proton and zinc-ion insertion/extraction process, identified by in situ synchrotron radiation-based X-ray diffraction. Density functional theory analysis approves the low adsorption energy and preferential embedding process of protons, and that can further optimize Zn2+ adsorption and migration abilities in bismuth selenide nanoplate, which is mainly responsible for the excellent performance.

The effect of nanoscale inhomogeneities (protrusions) of a metal contact on bipolar resistive switching in a planar heterostructure based on bismuth selenide is investigated in the previously proposed model of the critical field. The numerical calculations show that such inhomogeneities, depending on their shape, size, and location relative to the edge of the contact, can significantly change the high and low resistive states of the given heterostructure, and also noticeably affect the voltage required for switching between these states.

Titanium dioxide (TiO2) has been widely studied in the field of photocatalysis. However, the development of TiO2 was limited by the photoresponse only in the ultraviolet region and the rapid recombination of photogenerated electron–hole pairs. In this work, we prepare a novel TiO2 and two-dimensional (2D) bismuth selenide (Bi2Se3) hybrid nanosheets (TiO2/Bi2Se3 HNs) via a simple water bath ultrasonic route. X-ray diffraction pattern and Raman spectra were carried out to confirm that as-prepared samples were pure and well crystalized. Besides, TEM characterization proves that 2D Bi2Se3 nanosheets have high specific surface area and it can be clearly observed that the TiO2 with 60 nm particles are uniformly supported on the surface. Furthermore, photoelectrochemical (PEC) measurements demonstrate that the TiO2/Bi2Se3 HNs exhibit excellent photocatalytic performance of 4.3 µA/cm2 under 100 W of visible light, which were almost 2.5 times that of pure TiO2. More importantly, our results show that the photocurrent density was quite stable and only dropped by 10% after 125 cycles. In summary, the improved photocatalytic activity is due to the unique characteristic of 2D Bi2Se3 nanosheets, such as maximized reaction sites and good electrical conductivity, and the positive coupling effect of the TiO2/Bi2Se3 heterojunction. These extraordinary properties make the TiO2/Bi2Se3 HNs photocatalysts have excellent potential for photocatalytic application.

Background: Thermoelectric material with high performance and low cost is the basic need of today. Bismuth selenide is a thermoelectric material. A set of bismuth selenide thin films having different stoichiometry ratios varying Bi/Se ratio from 0.123 to 0.309 have been prepared. Objective: The present work deals with the synthesis and characterization of various thin films of bismuth selenide. The thermoelectric properties of thin films were also investigated. The aim of this work is to investigate the effect of composition ratio on the structural and thermoelectric properties and to find out the best stoichiometry ratio of bismuth selenide thin films that can be used in the application of thermoelectric devices. Methods:: A set of bismuth selenide thin films having different elemental compositions were prepared by employing the thermal evaporation technique. The crystal structure and elemental composition of thin films were investigated by XRD and EDAX, respectively. The roughness of films was analyzed by AFM. The thermoelectric properties of various thin films were also measured. Results: XRD spectrum confirms the formation of phases formed in thin films which slightly matched with standard data. AFM results indicated that the surface of films was smooth and nanoparticles were generated on the surface. AFM results indicated that the surfaces of annealed thin films were smoother than as-deposited thin films. Seebeck coefficient was found negative throughout the temperature range. The power factor was also calculated by the Seebeck coefficient and results revealed the effect of composition ratio on Seebeck coefficient, electrical conductivity, and power factor. Thin films having a composition ratio of 0.182 exhibited the highest power factor. Conclusion: This study provides relevant basic information on the thermoelectric property of thin films, as well as presents the effect of compositional variation on thermoelectric measurements. From the application point of view in the thermoelectric devices, the best stoichiometric thin films out of four prepared thin films have been presented.

Spin-momentum locking in the surface mode of topological insulators leads to the surface accumulations of spin-polarized electrons caused by bias currents through topological insulator samples. It is demonstrated in this letter that surface spin-polarized electron accumulations caused by the above bias currents can be sensed by using scanning tunneling microscopy. The experimental results of this sensing are presented for tin-doped bismuth selenide samples by employing iron-coated tungsten tips as well as nonmagnetic tungsten tips. A linear increase in the spin accumulation as a function of bias current through topological insulator samples is observed.

Intercalation of lithium and ammonia into the layered semiconductor Bi2Se3 proceeds via a hyperextended (by >60%) ammonia-rich intercalate, to eventually produce a layered compound with lithium amide intercalated between the bismuth selenide layers which offers scope for further chemical manipulation., New lithium amide/ammonia intercalates of Bi2Se3 are revealed using in situ X-ray powder diffraction.

Metal selenides as promising anode materials for potassium ion batteries (PIBs) have attracted great research attention. However, it is still a challenge to promote its practical application due to the unsatisfactory cyclability resulting from large volume variation and sluggish kinetics. Herein, we tackle this issue by focusing on a promising but undemonstrated anode, bismuth selenide for PIBs which possesses a high theoretical capacity and good electronic conductivity. Benefitting from the carbon layer coating, Bi2Se3@C has the capability to inhibit self-aggregation and buffer the volume expansion, leading to outstanding potassium-ion storage capability. It exhibits a very high reversible capacity of 526 mA h g−1 at 50 mA g−1, as well as superior cyclability and rate capability while maintaining a high capacity of 214 mA h g−1 at 1.0 A g−1 after 1000 cycles. Furthermore, its fast and reversible ion storage mechanism was verified, which first involves conversion and subsequent alloying redox reactions. This work enriches the understanding and development of stable conversion/alloying-based anodes for high-performance potassium-ion batteries.

The photovoltaic characteristics of high-quality Bi2Se3 grown on black phosphorus (BP) heterostructure via modulated elemental reactants (MER, annealed in situ at 220 °C for 20 min in a vacuum of 10−9 torr) growth of a Bi2Se3 topological insulator (TI) film on an exfoliated BP two-dimensional (2D) nanosheet was investigated. The Bi2Se3/BP heterostructure showed high-efficiency photocharacteristics (responsivity: 12.1 mA W−1, rise time: 1.3 ms, and broadband detection range: λ = 350–950 nm), which are attributed to the narrow band gap of the bulk state and mobility of the Dirac surface state. Moreover, the Bi2Se3/BP heterostructure can produce heterojunctions in the sharp interface region, thereby resulting in the contribution of a strong built-in electric field and photoexcited carrier tunnel through the interactive interfacial region at the TI/2D heterostructure based on the photovoltaic device. This work demonstrates practical photovoltaic applications, as well as the integration of such TIs on 2D materials, which can offer great opportunities for the realization of next-generation optoelectronic devices.

Models that describe bipolar resistive switching (BRS) in planar microstructures based on oxide compounds (Bi2Sr2CaCu2O8 + x and Nd2 – xCexCuO4 – y) and bismuth selenide are considered. Metal/insulator/metal planar-type memristor heterostructures in which the microsize is formed by an electrode with a diameter much smaller than the total size of the structure (which can be both Sharvin-type microcontacts and film electric electrodes) are investigated. Another important feature of these heterostructures is the presence of a surface layer several tens of nanometers thick with the specific conductivity significantly reduced relative to the bulk conductivity. The change in the resistive properties of such heterostructures is caused by the formation or destruction of a conducting channel through the mentioned layer. Numerical simulation has shown that the BRS is significantly affected by the topology of the electric field’s distribution. To describe the experimentally observed memristor effects in the investigated heterostructures, a model of a critical field is proposed. In this model it is assumed that the change in the specific conductivity occurs in those parts of the surface layer where the electric field strength exceeds some critical value. The critical field model is based on the numerical calculation of the electrical potential distribution from the distribution of the specific conductivity in the structure. In addition, a model that enables analysis of the influence of the electrodiffusion of oxygen ions on resistive switching in the heterostructures based on Bi2Sr2CaCu2O8 + x is considered. In the numerical realization of the models, a combination of the integrodifferential approximation of differential equations, the multigrid approach for localization of heterogeneities in physical characteristics, the iterative decomposition method, and the composite adaptive meshes are used. This allows tracking the investigated processes with the necessary accuracy. The simulation results are compared with the experimental data.

Topological superconductivity is of great contemporary interest and has been proposed in doped Bi2Se3, in which electron-donating atoms such as Cu, Sr or Nb have been intercalated into the Bi2Se3 structure. For NbxBi2Se3, with Tc ~ 3 K, it is assumed in the literature that Nb is inserted in the van der Waals gap. However, in this work an alternative origin for the superconductivity in Nb-doped Bi2Se3 is established. In contrast to previous reports, it is deduced that Nb intercalation in Bi2Se3 does not take place. Instead, the superconducting behaviour in samples of nominal composition NbxBi2Se3 results from the (BiSe)1.10NbSe2 misfit phase that is present in the sample as an impurity phase for small x (0.01 ≤ x ≤ 0.10) and as a main phase for large x (x = 0.50). The structure of this misfit phase is studied in detail using a combination of X-ray diffraction and transmission electron microscopy techniques.

Polycrystalline samples of (Bi1-xInx)2Se2.7Te0.3 (x = 0.00, 0.02, and 0.04) were prepared by the solid-state reaction technique. X-ray diffraction pattern confirms that the polycrystalline samples have a hexagonal structure with spacegroup R$$\stackrel{-}{3}$$ 3 - m. The surface morphologic study reveals the existence of porous behavior in the studied samples due to the volatilization of Selenium. Energy dispersive X-ray analysis validates the expected and observed elemental composition of the samples. Electrical resistivity has shown metallic behavior. Hall effect and Seebeck coefficient measurements indicate the p-type and n-type conduction for the pristine sample Bi2Se3 and the (Bi1-xInx)2Se2.7Te0.3 samples, respectively. The thermal conductivity and electrical resistivity were found to reduce by 7.5 and 9 times, respectively, for (Bi0.96In0.04)2Se2.7Te0.3 compared to the pristine sample Bi2Se3.

In the present investigation, a series of molybdenum-doped bismuth selenide (MoxBi(2−x)Se3) (x = 0.01 to 0.05) thin films have been deposited by simple and low-cost arrested precipitation technique (APT) onto substrate for the first time. The deposition has been carried out from aqueous alkaline bath using nonhazardous triethanolamine as a complexing agent at low temperature. The deposited thin films have been characterized to study optical, structural, morphological, compositional, electrical, and photoelectrochemical properties by using UV–Vis, XRD, SEM, AFM, TEM, SAED, EDS, XPS, EC, TEP, and PEC techniques. In the series of MoxBi(2−x)Se3 thin films, properties were altered with increase in molybdenum content. Optical absorption study shows red shift of absorbance in visible region and reflected in bandgap energy, which decreases from 1.48 to 1.30 eV. The SEM images show granular surface morphology without any cracks and increases in particle size with Mo content in film. The AFM analysis shown average roughness of the film which is 4.79 nm/µm2. TEM analysis gives agglomerated and granular morphology of the material. The SAED pattern gives excellent agreement with XRD results. EDS and XPS analysis confirms the presence of Mo, Bi, and Se elements with + 4, + 3, and − 2 oxidation states, respectively. From electrical conductivity measurements, activation energy was calculated and it decreases from 0.9565 to 0.1162 eV with increase in Mo content. Electrical conductivity increases with temperature indicates semiconducting nature of the films. TEP measurement shows negative Seebeck coefficient which confirms n-type semiconductor property. The PEC power conversion efficiency increases from 0.042 to 0.456% with increase in Mo content.

This paper explore the ability of bismuth selenide (Bi2Se3) as an alternative light sensitizer for photoelectrochemical (PEC) solar cell. Herein, we applied novel chemical route, namely, chemical bath deposition (CBD) for growth of Bi2Se3 nanoparticles over spin-coated TiO2 at room temperature. The structural, surface morphological, and optical properties of TiO2/Bi2Se3 films are systematically studied. The deposition time for the growth of Bi2Se3 using CBD can enable to tune the size of Bi2Se3 nanoparticles over porous TiO2 which significantly influences the physical properties of resultant heterostructure. The potential of Bi2Se3 nanoparticles in PEC solar cell is demonstrated by preparing FTO|TiO2|Bi2Se3|polysulphide electrolyte|carbon-coated FTO device structure and tested with current density–voltage (J-V) and electrochemical impedance spectroscopy (EIS) measurements. The result presented in this study established that the photoconversion efficiency and electron life time of device are affected by deposition time for Bi2Se3 using CBD. The J-V measurement done with above-proposed devices shows maximum photoconversion efficiency around 0.152% for 20 min deposited Bi2Se3.

A synthesis of bismuth selenide with a thickness of 3-4 nm on the surface of mica taken as a matrix was investigated using the gas-solid mechanism. Since discovery of two-dimensional atomic crystals of graphene in 2004, scientists have grown interested in exploring methods for synthesis of two-dimensional atomic crystal nanofilms. Among them, of particular interest are sulfides and transition metal selenides, such as molybdenum sulfide, tungsten selenide, bismuth selenide. Bismuth selenide possesses special thermoelectric, photoelectric properties, therefore there are wide possibilities for its use in such areas as thermoelectric devices, photosensitive elements, optical information keepers, etc. In this connection, there are many studies on the search for optimal methods for the synthesis of bismuth selenide. Each of the proposed methods has its own advantages and disadvantages. In the article, a variety of the recently used gas-liquid-solid mechanism (V-L-S) is used as a method for the synthesis of bismuth selenide. When using amorphous silicon dioxide as a matrix, the synthesized bismuth selenide is not uniform, and the synthesis process is uncontrollable. Therefore, in the work fluorinated gold mica was used as a matrix. The effect of temperature, gas feed rate on the size, shape and thickness of the film was investigated.

Molybdenum bismuth selenide (MoBi2Se5) has been proved to be a promising material for photoelectrochemical solar cell application. As MoBi2Se5 thin films are more corrosion resistant than bismuth (III) selenide (Bi2Se3) thin films, MoBi2Se5 can also be used as a buffer layer due to its distinctive optostructural properties. In this study, the authors synthesized surfactant-assisted nanostructured MoBi2Se5 thin films by using a cost-effective chemical route – namely, the arrested precipitation technique. The synthesized thin films were analyzed for optostructural, surface morphological, compositional and photovoltaic applications using the X-ray diffraction (XRD) technique, ultraviolet–visible spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy, and their photoelectrochemical solar cell performance was checked. The nanocrystalline nature of MoBi2Se5 thin films was confirmed from the XRD patterns. An increment in the optical bandgap energy was observed with surfactant mediation. The surface morphology of MoBi2Se5 changed from spherical to spongy-ball-like nanofibrous surface morphology after surfactant assistance. Furthermore, both the as-synthesized and surfactant-assisted MoBi2Se5 thin films showed photoelectrochemical solar cell applicability.

The direct control of topological surface states in topological insulators is an important prerequisite for the application of these materials. Conventional attempts to utilize magnetic doping, mechanical tuning, structural engineering, external bias, and external magnetic fields suffer from a lack of reversible switching and have limited tunability. We demonstrate the direct control of topological phases in a bismuth selenide (Bi2Se3) topological insulator in 3 nm molecular beam epitaxy-grown films through the hybridization of the topological surface states with the hafnium (Hf) d-orbitals in the topmost layer of an underlying oxygen-deficient hafnium oxide (HfO2) substrate. The higher angular momentum of the d-orbitals of Hf is hybridized strongly by topological insulators, thereby enhancing the spin-orbit coupling and perturbing the topological surface states asymmetry in Bi2Se3. As the oxygen defect is cured or generated reversibly by external electric fields, our research facilitates the complete electrical control of the topological phases of topological insulators by controlling the defect density in the adjacent transition metal oxide. In addition, this mechanism can be applied in other related topological materials such as Weyl and Dirac semimetals in future endeavors to facilitate practical applications in unit-element devices for quantum computing and quantum communication.

We have employed atomic layer deposition to produce uniform films of $$\hbox {Bi}_{2}\hbox {Se}_{3}$$, which is a 3D topological insulator (TI), over 5 cm $$\times $$ 5 cm $$\hbox {SiO}_{2}$$-coated Si substrates. The crystalline properties of the films were characterized via Raman spectroscopy, x-ray diffraction, cross-sectional transmission microscopy, and atomic force microscopy, which confirmed the high quality of the films. The TI properties were examined using Hall bridge structures and recording magnetoresistance at 1.9 K. A weak anti-localization effect was observed at low field, from which a phase coherent length of 242 nm and prefactor $$\alpha $$ value of 1 were determined, indicating desirable topological properties. This approach for film growth provides a path for integrating a 3D topological insulator with silicon integrated circuit technology.

Bismuth (Bi) nanoparticles (NPs) are emerging as promising photothermal agents for computed tomography imaging-guided photothermal therapy. However, it is challenging to improve their photothermal conversion efficacy and prevent their oxidation. Herein, Bi@bismuth selenide (Bi2Se3) core@shell NPs were designed and fabricated for improving the photothermal performance due to the staggered energy levels between Bi and Bi2Se3. With near-infrared light irradiation, both the materials could be excited to generate hot carriers due to their extremely narrow bandgaps. The hot electrons would transfer to the conduction band of Bi2Se3 and the hot holes to the valence band of Bi, leading to the effective separation of hot carriers. Then, these hot electrons and holes would recombine nonradiatively at the interface of Bi and Bi2Se3 and produce more phonons, resulting in an enhanced photothermal conversion efficacy. Moreover, the presence of Bi2Se3 on the surface of Bi NPs could prevent Bi from surface oxidation due to the higher stability of Bi2Se3. In fact, Bi@Bi2Se3 NPs showed excellent biocompatibility and photothermal therapeutic efficacy against cancer cells.

Thermoelectric materials have been around since more than a hundred years with applications related to cooling and power generation. The most commonly used thermoelectric materials were typically semiconductors like tellurides and selenides of bismuth, lead, antimony and their alloys. A recent revival of interest in the study of these materials has been propelled by the global needs for alternative sources of energy and by the advances in field of novel material synthesis and characterization. In particular, bismuth selenide (Bi2Se3) has been characterized as efficient n-type thermoelectric materials. Another intriguing property of Bi2Se3 is that it behaves like a topological insulator with a conducting surface and an insulating bulk. This has also led to extensive studies on electronic properties of Bi2Se3.The thermoelectric effect or Seebeck effect is the direct con-version of heat into electric energy when two junctions made up of two dissimilar conductors are held at two different temperatures, T1and T2, with T1 > T2 lead to a voltage being developed between the two junctions. In the present investigation Bismuth selenide nanoparticles are synthesized by two different physical methods namely co-precipitation and hydrothermal method. The resultant nanostructures are characterized by X ray diffraction , SEM , FTIR , UV spectroscopy etc.

A method is presented that enables the template assisted electrochemical deposition of tens of micrometer thick, compact and stoichiometric Bi2Se3 micropillars. This is achieved by modifying the acidic electrolyte that contains 1 M HNO3 with potassium chloride salt and introducing resting pulses during the plating process. We demonstrate the successful deposition into photoresist templates with mold diameters down to 30 µm and thicknesses up to 45 µm. Cross-sectional EDX line measurements confirm an optimal stoichiometry of Bi:Se 40:60 along the growth direction, independent of the micropillar diameter. XRD and Raman measurements after electrochemical deposition point to a primarily orthorhombic structure. To illustrate the potential of this electrochemical method for thermoelectric applications, Seebeck coefficient and electrical conductivity of 45 µm thick orthorhombic Bi2Se3 pillars with 30 and 50 µm diameter are measured for five different electrodeposition runs. An average electrical conductivity of 8.6 S/m (SD = 4.5 S/m) and a high average negative Seebeck coefficient of -162 µV/K (SD = 32 µV/K) was determined. The process presented here is highly promising for the reliable synthesis of Bi2Se3 micropillars, which can be integrated in thermoelectric micro generators or sensors., Electrochimica Acta, 403, ISSN:0013-4686, ISSN:1873-3859

This paper reports on the antibacterial properties of bismuth selenide prepared by cost effective methods; sol–gel and hydrothermal method for which 2:3 of bismuth nitrate pentahydrate and elemental selenide are used. X-ray diffraction (XRD), ultraviolet–visible absorption (UV–Vis.) and Fourier-transform infrared spectroscopy (FTIR) were carried out to characterize the synthesized samples. Structural analysis of synthesized samples using XRD revealed that the grain size of samples is nanosized and possess crystalline nature showing orthorhombic structure (sol–gel) with average grain size of particles to be 24.05 nm (standard deviation 4.55 nm), and rhombohedral (hydrothermal) with average grain size of particles to be 12.20 nm (standard deviation 3.3 nm). UV–Vis analysis revealed the absorption region for Bi2Se3 nanoparticles and their corresponding energy bandgap between 1.47eV and 1.74 eV range. FTIR spectrum shows the region of vibrational stretching between 600cm-1 and 1000 cm−1 that corresponds to Bi and Se bonding. Disk diffusion method was used to check the antibacterial activity successfully against gram-positive bacteria S. aureus and gram-negative bacteria E. coli.

We demonstrate memristive functions of the room temperature thermoelectric material Bi-Se fabricated by electrochemical deposition in combination with active electrode Ag-based contacts. We present microfabrication steps for creating polymer molds for the growth of compact memristive films. The electrical measurements show clear forming-free resistive switching behaviour for the electrochemically deposited material while temperature dependent measurements point to Schottky and space-charge-limited-current conduction mechanisms. For the envisioned combination of the memristors with a thermoelectric device we can conclude that electrodeposition is a viable method to produce silver-chalcogenide based non-volatile memristors for co-integration in zero power sensors.

Two-dimensional inorganic semiconductor materials have aroused tremendous research interest and found their potential in resolving the present urgent global issues, such as cancer therapy and fresh water shortage. Particularly, the near-infrared (NIR) photothermal conversion efficiency is a significant parameter in photothermal therapy. However, lack of an effective improvement strategy and their relatively low NIR phothermal conversion efficiency would restrict their wide and further application. Here, this work reports that enhanced NIR photothermal conversion is achieved in topological Bi2Se3 nanosheets by introducing a lanthanide dopant. Specifically, lanthanide Pr-doped Bi2Se3 nanosheets possess a photothermal conversion efficiency of 49.5%, which is higher than those of undoped Bi2Se3 nanosheets (31.0%) and numerous reported photothermal materials. The electronic structure of Pr-doped Bi2Se3 nanosheets was also analyzed by first-principles simulation. Furthermore, an interfacial evaporation system based on the developed nanosheets has been established, demonstrating a superior solar-thermal conversion efficiency of 91.5% and a water evaporation rate of 1.669 kg m-2 h-1 under 1 sun irradiation. The present work would provide new insights for the increase in the efficiency of photothermal materials.

In this report, two-dimensional (2D) bismuth selenide (Bi2Se3) nanosheets (NSs) and reduced graphene oxide (rGO) (Bi2Se3/rGO) composites have been prepared via a hydrothermal method. The microstructures and morphology properties of Bi2Se3/rGO composites were analyzed by scanning electron microscopy (SEM) and Raman spectra, indicating a well prepared and high crystalline material. Photoelectrochemical (PEC) tests demonstrate that Bi2Se3/rGO heterojunction exhibits enhanced photocatalytic performance of the pure Bi2Se3, which is about five times higher than Bi2Se3 NSs, which is because rGO acts as a conduction pathway, resulting in efficient separation of photogeneration of electron–hole pairs on the Bi2Se3/rGO composites. The as-prepared composite provides a novel insight in the field of photocatalysis.

It is challenging to achieve highly efficient thermoelectric materials due to the conflicts between thermopower (Seebeck coefficient) and electrical conductivity. These parameters are the core factors defining the thermoelectric property of any material. Here, we report the use of isovalent substitution as a tool to decouple the interdependency of the Seebeck coefficient and the electrical properties of cerium-doped bismuth selenide thermoelectric material. With this strategy, we can achieve a simultaneous increase in both the electrical conductivity and the Seebeck coefficient of the material by tuning the concentration of cerium doping, due to formation of neutral impurities and consequently the improvement of carrier mobility. Our theoretical calculation reveals a downward shift of the valence band with cerium concentration, which influences the thermoelectric enhancement of the synthesized materials. Finally, an order of magnitude enhancement of the figure of merit is obtained due to isovalent substitution, thus providing a new avenue for enhancing the thermoelectric performance of materials.

Bismuth selenide layers and nanowires have been grown by molecular beam epitaxy on self-assembled Stranski–Krastanov InAs quantum dots of different sizes and densities on GaAs substrates. The size ...

Herein, a one-step thermal evaporation was used for fabrication of silver bismuth selenide (AgBiSe2) thin films of various thickness. The influence of thickness on the structural, optical and electrical properties of AgBiSe2 thin films has been studied. The X-ray diffraction confirmed single hexagonal structure of deposited AgBiSe2 thin films. The average grain sizes D and microstrain e of deposited AgBiSe2 films were estimated by Williamson-Hall (W-H) relation. The grain size increases from 11.52 to 29.12 nm as the thickness was increased from 150 to 550 nm, whereas strain dislocation density ( ξ ) and the number of crystallites N tends to decrease with thickness. The selected area electron diffraction pattern (SAED) obtained by high resolution transmission electron microscopy (HRTEM) verified the polycrystalline nature of samples and it is found to nearly agree with X-ray diffraction data. The elemental composition measurement of the as-deposited AgBiSe2 thin film showed that the as-deposited film is near stoichiometric in compound. The influence of film thickness on the optical parameters of the AgBiSe2 thin films, such as refractive index n, extinction coefficient k, real dielectric e1, imaginary dielectric constant e2, skin depth and the optical band gap, Eg has been studied. It is found that the values of energy gap decrease from 1.88 to 1.68 eV with increasing thickness, while the values of Urbach energy follow an opposite trend. The electrical conductivity was measured by four-probe experiment in the range from 300 to 500 K. The analysis of dc conductivity data revealed the presence of two distinct regions with two various slopes confirming the transformation from hexagonal phase to rhombohedral phase at about 460 K.

The unique properties of topological insulators such as Bi2Se3 are intriguing for their potential implementation in novel device architectures for low power and defect-tolerant logic and memory devices. Recent improvements in the synthesis of Bi2Se3 have positioned researchers to fabricate new devices to probe the limits of these materials. The fabrication of such devices, of course, requires etching of the topological insulator, in addition to other materials including gate oxides and contacts which may impact the topologically protected surface states. In this paper, we study the impact of He+ sputtering and inductively coupled plasma Cl2 and SF6 reactive etch chemistries on the physical, chemical, and electronic properties of Bi2Se3. Chemical analysis by X-ray photoelectron spectroscopy tracks changes in the surface chemistry and Fermi level, showing preferential removal of Se that results in vacancy-induced n-type doping. Chlorine-based chemistry successfully etches Bi2Se3 but with residual Se–Se bonding and interstitial Cl species remaining after the etch. The Se vacancies and residuals can be removed with postetch anneals in a Se environment, repairing Bi2Se3 nearly to the as-grown condition. Critically, in each of these cases, angle-resolved photoemission spectroscopy (ARPES) reveals that the topologically protected surface states remain even after inducing significant surface disorder and chemical changes, demonstrating that topological insulators are quite promising for defect-tolerant electronics. Changes to the ARPES intensity and momentum broadening of the surface states are discussed. Fluorine-based etching aggressively reacts with the film resulting in a relatively thick insulating film of thermodynamically favored BiF3 on the surface, prohibiting the use of SF6-based etching in Bi2Se3 processing.

We investigated spin-to-charge conversion in sputtered Bi43Se57/Co20Fe60B20 heterostructures with in-plane magnetization at room temperature. High spin-to-charge conversion voltage signals have been observed at room temperature. The transmission electron microscope images show that the sputtered bismuth selenide thin films are nanogranular in structure. The spin-pumping voltage decreases with an increase in the size of the grains. The inverse Edelstein effect length (λIEE) is estimated to be as large as 0.32 nm. The large λIEE is due to the spin-momentum locking and is further enhanced by quantum confinement in the nanosized grains of the sputtered bismuth selenide films. We also investigated the effect on spin-pumping voltage due to the insertion of layers of MgO and Ag. The MgO insertion layer has almost completely suppressed the spin-pumping voltage, whereas the Ag insertion layer has enhanced the λIEE by 43%.

Using electrodeposition to prepare thermoelectric thin films enables the fabrication of energy-harvesting devices with low manufacturing cost. However, it is difficult to compute the thermal conductivity of these electrodeposited thin films owing to their large surface roughness. In this work, we prepared electrodeposited bismuth selenide (Bi2Se3) thin films using hydrochloric acid (HCl) and nitric acid (HNO3) solutions and measured the thermal conductivity using the 3ω method. The Bi2Se3 thin films prepared using the HCl solution consisted of round grains with relatively large pores that reached the substrate appearing between the grains. In contrast, the Bi2Se3 thin films prepared using the HNO3 solution were composed of flake-like grains with the appearance of relatively small and shallow pores. As a result, the thermal conductivity could only be measured for the Bi2Se3 thin films synthesized utilizing HNO3 solution; however, the measured thermal conductivity was about 0.14 W/(m⋅K). The low value of thermal conductivity was attributed to their amorphous structure. To improve the electrical properties of Bi2Se3 thin films, the electrodeposited samples were subjected to a thermal annealing treatment. An improvement in the electrical properties of the thin films was noticed with an annealing temperature of 300 °C; however, the thermal conductivity also increased to 0.76 W/(m⋅K). Therefore, the dimensionless quantity which represents the performance of the Bi2Se3 thin film, ZT, was determined to be 0.08–0.09. Therefore, the effectiveness of the proposed method for preparing electrodeposited thin films while estimating the thermal conductivity and ZT was successfully demonstrated.

Nanohybrids have significant potential in improving the performance of Li–ion batteries (LIBs). Herein, bismuth selenide nanosheets/nitrogen–doped carbon hybrids (Bi2Se3@NC) are prepared by selenylation of bismuth (III) metal–organic frameworks (Bi–MOFs), which are obtained by solvothermal reaction in a mixed solvent of N, N–dimethylformamide and methanol. When served as anodes for Li–ion batteries, it was found that the post–treatment temperature of Bi–MOFs has a powerful impact on Li storage performance. Compared to Bi2Se3@NC–500 and Bi2Se3@NC–600 hybrids, Bi2Se3@NC–400 hybrids deliver large specific capacity, outstanding rate performance, and good cyclic stability. 410.6 mAh g−1 of capacity is gained after 50 cycles at 100 mA g−1. Even at 500 mA g−1, 335.8 mAh g−1 is achieved after 400 cycles. The superior Li storage feature of Bi2Se3@NC–400 hybrids is ascribed to the synergetic effect between Bi2Se3 nanosheets and N–doped nanocarbon. Bi2Se3@NC–400 hybrids is a promising anode material for LIBs.

Transitions in the resistive switching of diode heterostructures based on bismuth selenide, in which bipolar resistive switching is implemented, are investigated. It is found that the time of transitions from one metastable state to another has a fast component on the order of microseconds and a slow component (a shuttle tail). Results are described using the model of a critical electric field, and the parameters of the investigated structures are calculated numerically.

Surface electronic properties of Bi2Se3 and Bi2Te3 topological insulators are known to evolve with varying surface termination. In this work, the (1 1 1) surface of Bi2Se3 has been studied with a comprehensive combination of experimental and computational (density functional theory) methods. It has been demonstrated that with proper preparation conditions the system can be forced into a new stable surface termination – a sub-monolayer of bismuth acquired through selective Se desorption – which has not been explored yet.

2D heterostructures are more than a sum of the parent 2D materials, but are also a product of the interlayer coupling, which can induce new properties. In this paper we present a method to tune the interlayer coupling in Bi2Se3/MoS2 2D heterostructures by regulating the oxygen presence in the atmosphere, while applying laser or thermal energy. Our data suggests the interlayer coupling is tuned through the diffusive intercalation and de-intercalation of oxygen molecules. When one layer of Bi2Se3 is grown on monolayer MoS2, an influential interlayer coupling is formed that quenches the signature photoluminescence (PL) peaks. However, thermally annealing in the presence of oxygen disrupts the interlayer coupling, facilitating the emergence of the MoS2 PL peak. DFT calculations predict intercalated oxygen increases the interlayer separation ~17%, disrupting the interlayer coupling and inducing the layers to behave more electronically independent. The interlayer coupling can then be restored by thermally annealing in N2 or Ar, where the peaks will re-quench. Hence, this is an interesting oxygen-induced switching between "non-radiative" and "radiative" exciton recombination. This switching can also be accomplished locally, controllably, and reversibly using a low-power focused laser, while changing the environment from pure N2 to air. This allows for the interlayer coupling to be precisely manipulated with submicron spatial resolution, facilitating site-programmable 2D light-emitting pixels whose emission intensity could be precisely varied by a factor exceeding 200x. Our results show that these atomically-thin 2D heterostructures may be excellent candidates for oxygen sensing.

Topological insulator (TI), a band insulator with topologically protected edge states, is one of the most interesting materials in the field of condensed matter. Bismuth selenide (Bi2Se3) is the mo...

Using ab initio calculations, an investigation of the electronic structure of the magnetic insulator/topological insulator heterostructures is performed. Bismuth selenide is used as a topological insulator and monolayers of vanadium-based van der Waals materials VSe2 and VBi2Se4 – as magnetic materials. The formation of the latter one is possible via diffusion of the deposited vanadium and selenium atoms into the surface block of the layered Bi2Se3. A comparison of the electronic structure of the two heterostructures is performed and peculiar features of interaction of the Dirac state of the topological insulator with the magnetic states of vanadium are revealed.

Bismuth Selenide (Bi2Se3) is a thermoelectrical material showing high Seebeck coefficient and figure of merit. It can be obtained by electrodeposition which makes it highly suitable for application in sensor and thermoelectric generators. Here, electrodeposition of Bi2Se3 on silicon(100) substrate was studied using different deposition baths by changing the salts and acid concentrations. The thin films were characterized to obtain the morphology, structural and thermoelectric properties. An optimal bath was found that leads to crystalline thin films with compact and uniform morphology, showing high values of Seebeck coefficient. The total salt concentration directly changes the structural properties of the samples, while the relative salt concentration essentially modifies the stoichiometry of deposits. The acid concentration, otherwise, promotes changes in the grain size and morphology.

Multi-channel Bi2Se3 thin films were grown by combining molecular beam epitaxy and atomic layer deposition. High-resolution transmission electron microscope images showed that c-axis oriented Bi2Se3 grew on amorphous Al2O3 even after multiple stacking. While the surface morphology degraded for the upper layers, each layer was electrically similar. The electrical transport measurements showed that the weak anti-localization effect was quantitatively enhanced upon increasing the number of Bi2Se3 channels. Our results provide a promising approach to exploit diverse combinations of layered topological insulator films vertically stacked with amorphous insulator films.

We experimentally demonstrate Q-switched and mode-locked Erbium-doped fiber laser (EDFL) by using topological insulator (TI) Bismuth Selenide (Bi2Se3) as saturable absorber (SA). The fabricated Bi2Se3 SA exhibits modulation depth and saturation intensity at 39.8% and 90.2 MW/cm2, respectively. By incorporating the fabricated Bi2Se3 SA into the laser cavity, Q-switching operation is generated with repetition rate ranging from 23.5 kHz to 68.2 kHz, pulse width ranging from 2.4 μs to 8.6 μs and maximum peak power is calculated at 19.9 mW. Our cavity can also generate soliton mode-locked pulse with repetition rate of 23.3 MHz and pulse width of 0.63 ps by inserting an additional 5 m long single mode fiber (SMF) into the existing laser cavity. Spectral peaks due to Kelly side-bands and four wave mixing (FWM) were observed on the soliton spectrum. Both Q-switching and mode-locking pulses are stable in the laboratory environment, allowing the realization of compact and low cost pulsed fiber laser with Bi2Se3 SA for various photonics applications.

Polyaniline (PANI) when composited with bismuth selenide nanoflakes (Bi2Se3 NFs), a low bandgap semiconductor, reveals enhanced photocatalytic activity for degradation of organic dyes under irradiation of visible light. The composites synthesized using Bi2Se3NFs templates with different weight percentages of PANI by in-situ chemical oxidative polymerization have been used as efficient photocatalysts for degradation of anionic dye, Methyl Orange (MO), and cationic dyes, Rhodamine B (RhB) and Malachite Green (MG). Based on radical trapping experiments, the mechanism for the photocatalytic degradation of the dyes were proposed taking into account the synergistic effect of PANI with Bi2Se3NFs. The efficient visible-light active photocatalytic property of the polymer-inorganic composites is attributed to composites’ enhanced separation of photogenerated carriers compared to its individual constituents.

Nanoparticle-based cell differentiation therapy has attracted increasing research interest as it is a promising substitute for conventional cancer treatment methods. Here, the topological insulator bismuth selenide nanoparticle (Bi2Se3 NP) was core-shelled with silver (Ag@Bi2Se3) to represent remarkable biocompatibility and plasmonic features (ca. 2.3 times higher than those of Ag nanoparticle). Moreover, a newly developed RNA three-way junction (3WJ) structure was designed for the quad-functionalization of any type of nanoparticle and surface. One leg of the 3WJ was attached to the Ag@Bi2Se3, and the other leg harbored a cell-penetrating RNA and a florescence tag. The third leg was designed to inhibit micro-RNA-17 (miR-17) and to further release retinoic acid (RA). A new drug delivery mechanism was developed for the slow release of RA inside the cytosol based on the prerequisite inhibition of miR-17 using a strand displacement strategy. In this paper, we report a simple methodology for resolving the hydr...

Crystalline thin films of Bi Te Se were deposited onto well cleaned glass substrates (BK7 type) by the vacuum thermal evaporation technique at a pressure of 10−3 Pa. Bulk samples were used as targets to evaporate the corresponding films. The internal microstructure of bulk samples and films were characterized by x-ray diffraction (XRD). Identifications of the microstructure and the surface morphology of the bulk and thin film samples were determined using scanning electron microscopy (SEM). Powder of the bulk alloys and the thin films of our products were observed to be polycrystalline in the form of hexagonal Bi2Se3 and Bi2Te3 structure. The material characteristic power factor of 74 μ W/mK2 was observed as the maximum value of power factor obtained in our study, and that was for Bi2Te3 near room temperature. The dimensionless figure of merit (ZT) was estimated based on Seebeck coefficient and electrical conductivity measurements alongside with thermal conductivity estimations. ZT values of Bi2Se3 and Bi2Se1.5Te1.5 were significantly enhanced as temperature increased, whilst, ZT of Bi2Te3 exhibited an opposite behavior. A mechanical stress test was performed in order to investigate the suitability of our films for thermoelectric modulus.

The successful commercial applications as thermoelectric devices and, due to their exotic electronic properties, as topological insulators of bismuth telluride (Bi2Te3) and bismuth selenide (Bi2Se3) have stimulated research interest on Bi2Se3/Bi2Te3-based chemical compounds. Based on the first-principles calculations, we investigate the electronic, optical, vibrational and transport properties of new monolayer Bi2TeSe2 obtained by transmuting one Se atom into its neighboring Te atom in the same group from Bi2Se3. We find that the monolayer Bi2TeSe2 maintains a stable hexagonal structure up to 700 K. Monolayer Bi2TeSe2 possesses a direct bandgap of 0.29 eV due to the strong spin–orbit coupling effects, and it remains a direct semiconductor for strains in a moderate range. The optical absorption covers a wide range from the green region to the ultraviolet region, which may lead to applications in optoelectronic devices like saturable absorbers. An extremely high electron mobility of 20 678 cm2 V−1 s−1 along the zigzag direction can be achieved by strain engineering with −6% compressive strain, which is nearly ten times larger than the intrinsic mobility. These indicate that monolayer Bi2TeSe2 is a promising candidate for future high-speed (opto)electronic devices.

This work experimentally investigated quantum transport characteristics of heavily doped bismuth selenide topological insulator nanoribbons to understand their physical origins. Transport properties of nanoribbons were measured via a suspended micro-device for eliminating the substrate effect. A series of quantum transport behaviors such as weak antilocalization, Shubnikov-de Haas oscillations, universal conductance fluctuation, and linear perpendicular-field magnetoresistance have been systematically studied to achieve a coherent understanding on their origins in topologically protected surface states, band bending, or bulk states. The parallel-field magnetoresistance, however, is found to be diverse, which can exhibit negative or positive values for the whole measurement range of the magnetic field strength or change from positive to negative values with the increase of the magnetic field strength. The tunable behavior of the parallel-field magnetoresistance is suggested to be the collective effects of the positive magnetoresistance from surface transport and the negative magnetoresistance possibly owing to the axial anomaly, resulting from long-range ionic impurity-scattering processes in bulk carriers. The transport properties of nanoribbons of heavily doped bismuth selenide, a topological insulator, have been systematically studied in suspended devices. Hao Tang, Juekuan Yang, Minghui Lu, Dongyan Xu and colleagues from several Chinese institutions characterized nanoribbons with different carrier densities and surface-area-to-volume ratios; they observed quantum signatures such as weak antilocalization, Shubnikov-de Haas oscillations, universal conductance fluctuations, and linear magnetoresistance, discussing whether they originate from the surface states, band bending, or bulk states. In particular, the magnetoresistance is anisotropic, and whereas the perpendicular-field magnetoresistance displays the same behavior for all samples, the parallel-field magnetoresistance varies from sample to sample and can be tuned from positive to negative values. The authors thus identify it as a collective effect, with contributions from both the topologically protected surface states and scattering processes in the bulk.

Optical properties evolution of Bi1-xSex films with different compositions were investigated by spectroscopic ellipsometry (SE). A significant dispersion of penetration depth of Bi0.38Se0.62 films was observed, which would lead to a varying carrier concentration with the different wavelength because of the topologically protected surface state. To describe the special properties of topological insulators, dispersive plasma energy was introduced into traditional dielectric function model. Optical properties of Bi0.38Se0.62 film were acquired by this modified model and the topologically protected surface state could be represented from the dispersion properties of free carrier concentration with the smaller plasma energy versus the deeper penetration depth. We demonstrated that SE is a useful tool for characterizing the properties of the topological insulators.

Topological insulator bismuth selenide (Bi2Se3) thin films with a thickness of 6.0 quintuple layers (QL) to 23 QL are deposited using pulsed laser deposition (PLD). The arithmetical mean deviation of the roughness (Ra) of these films is less than 0.5 nm, and the root square mean deviation of the roughness (Rq) of these films is less than 0.6 nm. Two-dimensional localization and weak antilocalization are observed in the Bi2Se3 thin films approaching 6.0 nm, and the origin of weak localization should be a 2D electron gas resulting from the split bulk state. Localization introduced by electron–electron interaction (EEI) is revealed by the temperature dependence of the conductivity. The enhanced contribution of three-dimensional EEI and electron–phonon interaction in the electron dephasing process is found by increasing the thickness. Considering the advantage of stoichiometric transfer in PLD, it is believed that the high quality Bi2Se3 thin films might provide more paths for doping and multilayered devices.

Superconductivity in a doped topological insulator (TI) is a very interesting phenomenon and constitute a new finding of the modern day condensed matter physics. Here we have investigated the physical and transport properties of such an intercalated TI, namely, Bi$_2$Se$_3$ via a strong coupling route. The unique bandstructure of Bismuth Selenide with a dirac cone is strongly influenced with the intercalation by Silver (Ag) (Gold (Au) is included to compare and contrast) at high densities, along with novel structural effects, leading to the emergence of orbital selective metal insulator transition with possible superconductivity at low temperature. Here we have explored the part of multi orbital electron electron correlations in Ag and Au intercalated Bi$_2$Se$_3$ via dynamical-mean-field theory with local density approximation, and the impact of this intercalation in establishing new physical properties and possible energy applications.

Bismuth selenide exhibits high thermoelectric performance, which is a promising candidate for thermal-electrical energy conversion. Here, Bi2Se3 core thermoelectric fibers with K9 glass cladding were fabricated by a molten core drawing method. The 50-μm-diameter Bi2Se3 core fibers exhibit an ultrahigh Seebeck coefficient of −150.85 μV/K. In addition, it has a high dimensionless figure of merit of 0.18 (at 300 K) and a long-term stability in air. The results indicate that the drawing approach is an effective way to fabricate high-performance and high-stability thermoelectric fibers, which will have potential application in fiber-integrated thermoelectric devices.