Bismuth Selenide Research Articles

Tuning thermal conductivity of bismuth selenide nanoribbons by reversible copper intercalation

Actively tuning thermal transport properties of materials at nanoscale is of great interest in many applications. In this work, we demonstrated reversible copper (Cu) intercalation on individual bismuth selenide (Bi2Se3) nanoribbons and investigated the effects of intercalation/de-intercalation of Cu atoms on their thermal transport properties. Distinct from prior studies that have shown reduced thermal conductivity (κtot) after intercalation, a crossover in κtot was observed over the measured temperature range in this work, i.e., κtot is significantly suppressed at low temperatures but enhanced above 250 K by Cu intercalation. This intriguing crossover phenomenon is attributed to the interplay between the enhanced electronic thermal conductivity (κe) and the reduced lattice thermal conductivity (κph), both of which result from the intercalated Cu atoms. Moreover, we showed that thermal conductivity could be further tuned by the de-intercalation of Cu atoms. Compared to the pristine nanoribbon, a dramatically lower in-plane κph was observed for intercalated and de-intercalated nanoribbons due to the formation of the Cu/Bi2Se3 superlattice structure. Theoretical modeling revealed that the reduced κph was primarily owing to the enhancement of phonon boundary scattering and point defect scattering. This work provides a facile approach to tune thermal transport properties at nanoscale, which can be potentially used in thermal switch and thermoelectric applications.

New Metastable Phase of Bismuth (III) Selenide: Crystal Structure and Electrical Properties

Using high‐pressure–high‐temperature treatment at P = 4–7.7 GPa; T = 1373–1473 K with subsequent quenching, a new metastable phase of bismuth selenide (m‐Bi2Se3) is synthesized and its crystal structure, electrical resistivity, and annealing at heating are investigated. Using X‐ray powder diffraction, and analogy with high‐pressure structures of the rare‐earth element sesquichalcogenides, the crystal structure of the new metastable phase of m‐Bi2Se3 is determined as an orthorhombic distorted cation‐deficient structure of the Th3P4 type with the Fdd2 space group and Z = 10.66. The unit‐cell dimensions are: a = 13.4660(7) Å, b = 12.7772(7) Å, c = 9.0896(5) Å. The density of m‐Bi2Se3 (7.47 g cm−3) is slightly less than the initial rhombohedral phase of Bi2Se3, but the coordination number (CN) = 8 is higher than CN = 6 of the initial phase. The period of stability under ambient conditions of the new m‐Bi2Se3 phase is only about 2 months. After 300 °C annealing, m‐Bi2Se3 completely returns to the initial layered structure, and differential scanning calorimetry confirms that the reverse transformation as well as the direct transition occur through an amorphous state. The new phase is a narrow bandgap semiconductor with the energy gap of about 80 meV.

Studies of surface states in Bi2Se3 induced by the BiSe substitution in the crystal subsurface structure

We present a systematic theoretical study of bismuth selenide electronic structure in the presence of spin-orbit interaction. It is confirmed that the inversion of Bi pz and Se pz states in the bulk band structure is induced by spin-orbit coupling. The energy gap in the bulk electronic structure is closed by pz states associated mainly with Bi atoms from the first quintuple layer. We elucidate the influence of Bi substitution in the fifth atomic layer on the local density of electronic states in the top quintuple layer. Finally, we describe how it develops into the additional p states in the surface electronic structure, which produce the triangular protrusion observed in Scanning Tunnelling Microscopy measurements and characteristic narrow features in Scanning Tunnelling Spectroscopy results.

AC magnetoresistance and its frequency-dependence of Fe-doped Bi2Se3 topological insulator

Bismuth selenide (Bi2Se3) is one of the most important base materials in the study of topological insulators. Doping with iron is a direct method to manipulate the magnetic order in Bi2Se3. In this paper, we first report the measurements of magnetoresistance of Fe-doped Bi2Se3 with alternating current. Unlike the DC magnetoresistance, skin effect plays an important role in AC magnetoresistance. Another interesting finding is that resonance occurs at a certain frequency, which implies an internal relaxation mechanism. The relations between resistance, magnetic field and current frequency are discussed.

Получение нанопленок двухмерного атомного кристалла селенида висмута увеличенной площади

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.

Электрохимическая полимеризация поли(анилин-о-анизидина) и его антикоррозионные свойства

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.

Accurate measurement of in-plane thermal conductivity of layered materials without metal film transducer using frequency domain thermoreflectance.

Measuring anisotropic thermal conductivity has always been a challenging task in thermal metrology. Although recent developments of pump-probe thermoreflectance techniques such as variable spot sizes, offset pump-probe beams, and elliptical beams have enabled the measurement of anisotropic thermal conductivity, a metal film transducer enabled for the absorption of the modulated pump laser beam and the detection of the thermoreflectance signal. However, the existence of the transducer would cause in-plane heat spreading, suppressing the measurement sensitivity to the in-plane thermal conductivity. In addition, the transducer film also adds complexity to data processing, since it requires careful calibration or fitting to determine extra parameters such as the film thickness and conductivity, and interface conductance between the transducer and the sample. In this work, we discussed the methodology for measuring in-plane thermal conductivity of layered semiconductors and semimetals without any transducer layer. We show that the removal of transducer results in the dominantly large sensitivity to in-plane thermal conductivity compared with other parameters, such as cross-plane thermal conductivity and the absorption depth of the laser beams. Transducerless frequency-domain thermoreflectance (FDTR) measurements are performed on three reference layered-materials, highly ordered pyrolytic graphite, molybdenum disulfide (MoS2), and bismuth selenide (Bi2Se3) and demonstrated using the analytical thermal model that the measured in-plane thermal conductivity showed much-improved accuracy compared with conventional FDTR measurement with a transducer.

Investigating the photovoltaic performance of surfactant-assisted MoBi2Se5 thin films

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.

Correlated plasmons in the topological insulator Bi2Se3 induced by long-range electron correlations

Recently, electron correlation has been shown to play an important role in unconventional plasmon generation in highly correlated electron systems. Electrons in topological insulators, on the other hand, are massless and insensitive to nonmagnetic scattering due to their protection by time-reversal symmetry, which makes these materials appealing platforms for hosting exotic plasmonic excitations. Here, using a combination of angle-dependent spectroscopic ellipsometry and angle-resolved photoemission spectroscopy as a function of temperature supported by first-principles calculations, we reveal a new pair of correlated plasmonic excitations at 1.04 and 1.52 eV and a significant Fermi level shift of 0.12 eV accompanied by spectral weight transfer in the topological insulator bismuth selenide (Bi2Se3). Interestingly, such a spectral weight transfer over a broad energy range causes a drastic change in the charge carrier density whereby the contribution of charge carriers in the bulk starts to rival those in the surface states and Bi2Se3 becomes more uniformly conducting. Our results show the importance of electronic correlations in determining the electronic structure and appearance of correlated plasmons in topological insulators and their potential applications in plasmonics.

Preparation and characterization of layer-diffusion processed InBi2Se4 thin films for photovoltaics application

In this research work, optoelectronic properties of Indium bismuth selenide (InBi2Se4) thin films are studied for their potentials for photovoltaic applications. The InBi2Se4 films are prepared via a thermal co-evaporation technique on glass substrate using Bi2S3 powders and indium granules. The as-deposited films are then annealed at different temperatures to convert into InBi2Se4 thin films. Results show that the obtained InBi2Se4 films possess excellent optoelectronic properties as an optimum bandgap of 1.2 eV was obtained for the film annealed at 350 °C. Based on characterization results of current and voltage realiationships, both as-deposited and annealed InBi2Se4 thin films show a linear relationship between current and annealing temperature. It was also noted that with increasing grain-size of the film, the current is also increased at a fixed applied voltage.

Chemical migration and dipole formation at van der Waals interfaces between magnetic transition metal chalcogenides and topological insulators

Metal and magnetic overlayers alter the surface of the topological insulator (TI) bismuth selenide (Bi$_2$Se$_3$) through proximity effects but also by changing the composition and chemical structure of the Bi$_2$Se$_3$ sub-surface. The interface between Bi$_2$Se$_3$ and Mn metal or manganese selenide was explored using x-ray photoelectron spectroscopy (XPS) revealing chemical and electronic changes at the interface. Depositing Mn metal on Bi$_2$Se$_3$ without an external source of Se shows unexpected bonding within the Mn layer due to Mn-Se bonding as Se diffuses out of the Bi$_2$Se$_3$ layer into the growing Mn film. The Se out-diffusion is further evidenced by changes in Bi core levels within the Bi$_2$Se$_3$ layers indicating primarily Bi-Bi bonding over Bi-Se bonding. No out-diffusion of Se occurred when excess Se is supplied with Mn, indicating the importance of supplying enough chalcogen atoms with deposited metals. However, Bi$_2$Se$_3$ core level photoelectrons exhibited a rigid chemical shift toward higher binding energy after depositing a monolayer of MnSe$_{2-x}$, indicating a dipole within the overlayer. Stoichiometry calculations indicated that the monolayer forms MnSe preferentially over the transition metal dichalcogenide (TMD) phase MnSe$_2$, providing a consistent picture of the dipole formation in which a plane of Se anions sits above Mn cations. This study shows that chemical diffusion and dipole formation are important for Mn-Bi$_2$Se$_3$ and MnSe$_{2-x}$-Bi$_2$Se$_3$ and should be considered carefully for TMD/TI interfaces more generally.

Controlled synthesis of two-dimensional (2-D) ultra-thin bismuth selenide (Bi2Se3) nanosheets by bottom-up solution-phase chemistry and its electrical transport properties for thermoelectric application

Bismuth Selenide and associated compounds inheriting stacked layered structure represent a unique class of materials where bulks are insulating with conducting surfaces, best known as thermoelectric materials. The bottom-up solution-based approach is a convenient alternative producing ultrathin high quality two-dimensional Bi2Se3 nanosheets. The present investigation deals with glycol mediated synthesis of highly crystalline ultrathin Bi2Se3 nanosheets. The as-synthesized Bi2Se3 nanosheets exhibit a rhombohedral crystal structure with a substantial surface-to-volume ratio that can possess several potential applications. Besides, the ultrathin Bi2Se3 nanosheets produced herein, found to be n-type with robust spatial confinement of charge carriers advantageous for thermoelectric applications, delivering a high-power factor of 1.55 μW/cmK2 at 150 °C. The method demonstrates the generic feature of the solution phase technique for the synthesis of highly crystalline nanosheets allowing mass production of identical ultra-thin nanosheets that can be easily integrated into devices for several promising applications, including spintronics, energy storage, and topological quantum computation.

EXPERIMENTAL INVESTIGATION OF ELECTRICAL PROPERTIES OF BISMUTH SELENIDE THIN FILMS

Developing high efficient energy materials with low toxicity is present need of research. Today bismuth selenide, a topological insulator has attracted great attention due to its electrical properties. Solid samples of bismuth selenide of different elemental ratio of Bi/Se have been prepared by solid state reaction and thin films of these solid sample have been deposited on glass substrate using thermal evaporation technique. Transport properties of bismuth selenide thin films were investigated. Electric properties of these films were studied by Hall measurements. A comparative study among different thin films along with annealing effect has been reported.

Photoelectrodes of Cu2O with interfacial structure of topological insulator Bi2Se3 contributes to selective photoelectrocatalytic reduction of CO2 towards methanol

Artificial photosynthesis emerges as feasible solution to diminish CO2 content in the atmosphere. Photoelectrocatalysis can diminish CO2 concentration while generating useful resources such as methanol. Here an alternative multilayer photoelectrode of FTO/Cu/Bi2Se3-Se/Cu2O is developed to enhance selective reduction of CO2 towards methanol. A novel electrosynthetic approach is described as strategy to modulate the atomic composition of p-type bismuth selenide chalcogenide intralayer. This method enhanced performance and selectivity of n-type Cu2O photoelectrocatalysts. Alkaline pH conditions favored yield and selectivity towards methanol production from CO2. The formation of an n-p heterojunction affects the Cu2O performance on CO2 reduction. The novel engineered FTO/Cu/Bi2Se3-Se/Cu2O multilayer photoelectrodes allowed obtaining up to 4.5 mM of methanol, which correspond to 3-fold higher concentration than conventional FTO/Cu2O electrodes reported in literature. Photoelectrodes of FTO/ Cu/Bi2Se3-Se/Cu2O overperform conventional Cu2O in terms of kinetics and selectivity towards methanol production.

Synthesis and characterization of bismuth selenide thin films by thermal evaporation technique

Synthesis and characterization of bismuth selenide thin films by thermal evaporation technique

Topological Phase Control of Surface States in Bi2Se3 via Spin-Orbit Coupling Modulation through Interface Engineering between HfO2-X.

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.

Application of numerical simulation in investigation of memristor structures based on oxides and chalcogenides

Models that describe bipolar resistive switching in planar microstructures based on oxide compounds (Bi2Sr2CaCu2O8+x, Nd2-xCexCuO4-y) and bismuth selenide are considered. Metal-isolator-metal planar-type meristor heterostructures were investigated, in which the micro-size is formed by an electrode whose diameter is much smaller than the total size of the structure (it can be both Chervinsky-type microjunctions and film electric electrodes). Another important feature of these heterostructures is the presence of a surface layer several tens of nanometers thick with specific conductivity significantly reduced relative to volume. The change in the resistive properties of such heterostructures is caused by the formation or destruction of the conductive channel through the above-mentioned layer. Numerical simulation has shown that the bipolar resistive switching is significantly influenced by the electrical field distribution topology. A “critical field” model is proposed to describe experimentally observed memristor effects in investigated heterostructures. In this model it is assumed that the change in specific conductivity occurs in those parts of the surface layer where the electric field strength exceeds some critical value. The model of the “critical field” is based on the numerical calculation of the distribution of electrical potential on the distribution of specific conductivity in the structure. In addition, the model allowing to analyze the influence of electrodiffusion of oxygen ions on resistive switching in heterostructures based on Bi2Sr2CaCu2O8+x is considered. At numerical realization of the models a combination of the integro-differential approximation of the differential equations, the multi-grid approach for localization of heterogeneities of physical characteristics, the iterative decomposition method and composite adaptive meshes was used. It allowed tracking the processes under investigation with necessary accuracy. The comparison of simulation results with experimental data is presented.

Synthesis, characterization and applications of Aniline passivated bismuth selenide thermoelectric nanoparticles

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.

Coherent narrowband light source for ultrafast photoelectron spectroscopy in the 17-31 eV photon energy range.

Here, we report on a novel narrowband High Harmonic Generation (HHG) light source designed for ultrafast photoelectron spectroscopy (PES) on solids. Notably, at 16.9 eV photon energy, the harmonics bandwidth equals 19 meV. This result has been obtained by seeding the HHG process with 230 fs pulses at 515 nm. The ultimate energy resolution achieved on a polycrystalline Au sample at 40 K is ∼22 meV at 16.9 eV. These parameters set a new benchmark for narrowband HHG sources and have been obtained by varying the repetition rate up to 200 kHz and, consequently, mitigating the space charge, operating with electrons/s and photons/s. By comparing the harmonics bandwidth and the ultimate energy resolution with a pulse duration of ∼105 fs (as retrieved from time-resolved experiments on bismuth selenide), we demonstrate a new route for ultrafast space-charge-free PES experiments on solids close to transform-limit conditions.

Study of Surface Spin-Polarized Electron Accumulation in Topological Insulators Using Scanning Tunneling Microscopy

The results of scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying bismuth selenide ($Bi_2Se_3$) samples are reported. Asymmetry in tunneling currents with respect to the change in the direction of bias currents through $Bi_2Se_3$ samples has been observed. It is argued that this asymmetry is the manifestation of surface spin-polarized electron accumulation caused by the ninety-degree electron spin-momentum locking in the topologically protected surface current mode. It is demonstrated that the manifestation of surface spin-polarized electron accumulation is enhanced by tin doping of $Bi_2Se_3$ samples. Furthermore, the appearance of spin-dependent density of states in current carrying $Bi_2Se_3$ samples has also been observed.