Topological Insulator Bi2Se3 Research Articles

A silver nanoparticle (AgNP)-loaded Bi2Se3 topological insulator p-n heterojunction photodiode for a near-infrared (NIR) photodetector

Near-infrared (NIR) photons are expanding advanced applications in optoelectronics. However, while 2D materials like graphene offer an attractive route for NIR photodetection, the alternative for high-performance NIR detection is still evolving. Hence, solution-processed n-Bi2Se3 /p-Si-based 2D heterojunction photodiodes have been fabricated here and used for high-performance NIR detection. Further, we report high photoresponsivity of 248 mA W−1 at 1100 nm, high external quantum efficiency of 22, 23 and 28% for Ag-loaded (at 5, 7.5 and 10%) Bi2Se3 and good stability. The chemical states of Bi2Se3 and Ag are detected using the core-level spectra of x-ray photoelectron spectroscopy. Photoresponse I–V characteristics are investigated under both dark and illumination; the high photocurrent achieved for Ag-loaded Bi2Se3 and the increase in the forward photocurrent under both dark and bright conditions are reported. The temporal photoresponse curve confirms the good stability (photoswitching behavior) and reproducibility with a response time of 0.74 s and a decay time of 0.18 s. Therefore, these unique performance and device parameters of a manufactured photodiode strongly recommend as a potential heterojunction photodiode for an NIR photodetector.

First-principles study on electronic and optical properties of sn-doped topological insulator Bi2Se3

Electronic structures and optical properties of pure and sn-doped Bi2Se3 were investigated by first-principles calculations based on density functional theory (DFT). For Bi2-xSnxSe3 (x = 0, 0.083, 0.167, 0.25), the introduction of Sn induced impurity bands near the Fermi level. Sn@(0,3) configuration with longer sn-Sn distance was more stable for the smallest formation energy. From the charge density result, sn-doped Bi2Se3 was the material with covalent and ionic characteristic. There was obvious blue shifting in the dielectric function and ultraviolet absorption edges for sn-doped Bi2Se3. The results had implications for the fabrication of sn-doped Bi2Se3 optical devices that can be blue-shifted in ultraviolet (UV) region.

Relativistic ratcheting on the surface of topological insulator Bi2Se3 attached to spiral multiferroic oxide

Relativistic ratcheting of Dirac fermions on the surface of topological insulator Bi2Se3 attached to a spiral multiferroic oxide is investigated. We find that the Dirac fermions on the surface of topological insulator Bi2Se3 exhibit pronounced Brownian motion, tuned by the strength of exchange field established by the interaction of spin degrees of Dirac fermions and multiferroic oxide. The surface Dirac fermions show ratchet effect as a net current under the influence of orthogonal, commensurate ac drives in the presence of a symmetric periodic potential set by the exchange field.

Moiré modulation of lattice strains in PdTe2 quantum Films

We report the epitaxial growth of PdTe2 ultrathin films on a topological insulator Bi2Se3. A prominent moiré pattern was observed in scanning tunneling microscope measurements. The moiré periodicity increases as film thickness decreases, indicating a lattice expansion of epitaxial PdTe2 thin films at lower thicknesses. In addition, our simulations based on a multilayer relaxation technique reveal uniaxial lattice strains at the edge of PdTe2 domains, and anisotropic strain distributions throughout the moiré supercell with a net change in lattice strain up to ∼2.9%. Our density functional theory calculations show that this strain effect leads to a narrowing of the band gap at Γ point near the Fermi level. Under a strain of ∼2.8%, the band gap at Γ closes completely. Further increasing the lattice strain makes the band gap reopen and the order of conduction band and valence bands inverted in energy. The experimental and theoretical results shed light on a method for constructing quantum grids of topological band structure under the modulation of moiré potentials.

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

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

Ordered Assembly of DNA on Topological Insulator Bi2Se3 and Octadecylamine for a Sensitive Biosensor.

Controlling the assembly of DNA in order on a suitable electrode surface is of great significance for biosensors and disease diagnosis, but it is full of challenges. In this work, we creatively assembled DNA on the surface of octadecylamine (ODA)-modified topological insulator (Tls) Bi2Se3 and developed an electrochemical biosensor to detect biomarker DNA of coronavirus disease 2019 (COVID-19). A high-quality Bi2Se3 sheet was obtained from a single crystal synthesized in our lab. A uniform ODA layer was coated in argon by chemical vapor deposition (CVD). We observed and analyzed the assembly and mechanism of single-strand DNA (ssDNA) and double-strand DNA (dsDNA) on the Bi2Se3 surface through atomic force microscopy (AFM) and molecular dynamics (MD) simulations. The electrochemical signal revealed that the biosensor based on the DNA/ODA/Bi2Se3 electrode has a wide linear detection range from 1.0 × 10-12 to 1.0 × 10-8 M, with the limit of detection as low as 5 × 10-13 M. Bi2Se3 has robust surface states and improves the electrochemical signal-to-noise ratio, while the uniform ODA layer guides high-density ordered DNA, enhancing the sensitivity of the biosensor. Our work demonstrates that the ordered DNA/ODA/Bi2Se3 electrode surface has great application potential in the field of biosensing and disease diagnosis.

Surface states modulation of topological insulator Bi2Se3 by noble metal decoration for gas sensing kinetic engineering

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 (Bi2Se3) 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 Bi2Se3 to tune the surface state and improve the dynamical gas sensing parameter. The response and response rate toward 10 ppm of NO2 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 Bi2Se3. This work provides an important strategy for designing gas sensing performance between topological insulators and noble metal particles.

The effect of Fe-doping on structural, elemental, magnetic, and weak anti-localization properties of Bi2Se3 topological insulator

The effect of Fe-doping on structural, elemental, magnetic, and weak anti-localization properties of Bi2Se3 topological insulator

Topological insulator Bi2Se3 for highly sensitive, selective and anti-humidity gas sensors

Chemiresistive gas sensors generally surfer from low selectivity, inferior anti-humidity, low response signal or signal-to-noise ratio, severely limiting the precise detection of chemical agents. Herein, we exploit high-performance gas sensors based on topological insulator Bi2Se3 that is distinguished from conventional materials by robust metallic surface states protected by time-reversal symmetry. In the presence of Se vacancies, Bi2Se3 nanosheets exhibit excellent gas sensing capability toward NO2, with a high response of 93% for 50ppm and an ultralow theoretical limit of detection concentration about 0.06ppb at room temperature. Remarkably, Bi2Se3 demonstrates ultrahigh anti-humidity interference characteristics, as the response with standard deviation of only 3.63% can be achieved in relative humidity range of 0-80%. These findings are supported by first-principles calculations, with analyses on adsorption energy and charge transfer directly revealing the anti-humidity and selectivity. This work may pave the way for implementation of exotic quantum states for intelligent applications.

Ion-Induced Lateral Damage in the Focused Ion Beam Patterning of Topological Insulator Bi2Se3 Thin Films

Focused Ion Beam patterning has become a widely applied technique in the last few decades in the micro- and nanofabrication of quantum materials, representing an important advantage in terms of resolution and versatility. However, ion irradiation can trigger undesired effects on the target material, most of them related to the damage created by the impinging ions that can severely affect the crystallinity of the sample, compromising the application of Focused Ion Beam to the fabrication of micro- and nanosized systems. We focus here on the case of Bi2Se3, a topological material whose unique properties rely on its crystallinity. In order to study the effects of ion irradiation on the structure of Bi2Se3, we irradiated with Ga+ ions the full width of Hall-bar devices made from thin films of this material, with the purpose of inducing changes in the electrical resistance and characterizing the damage created during the process. The results indicate that a relatively high ion dose is necessary to introduce significant changes in the conduction. This ion dose creates medium-range lateral damage in the structure, manifested through the formation of an amorphous region that can extend laterally up to few hundreds of nanometers beyond the irradiated area. This amorphous material is no longer expected to behave as intrinsic Bi2Se3, indicating a spatial limitation for the devices fabricated through this technique.

SPADExp: A photoemission angular distribution simulator directly linked to first-principles calculations

We develop a software package SPADExp (simulator of photoemission angular distribution for experiments) to calculate the photoemission angular distribution (PAD), which is the momentum dependence of spectrum intensity in angle-resolved photoemission spectroscopy (ARPES). The software can directly load the output of the first-principles software package OpenMX, so users do not need to construct tight-binding models as previous studies did for PAD calculations. As a result, we can calculate the PADs of large systems such as quasicrystals and slab systems. We calculate the PADs of sublattice systems (graphene and graphite) to reproduce characteristic intensity distributions, which ARPES has experimentally observed. After that, we investigate twisted bilayer graphene, a quasicrystal showing 12-fold rotational symmetric spectra in ARPES, and the surface states of the topological insulator Bi2Se3. Our calculations show good agreement with previous ARPES measurements, showing the correctness of our calculation software and further potential to investigate the photoemission spectra of novel quantum materials.

Development of a laser-based angle-resolved-photoemission spectrometer with sub-micrometer spatial resolution and high-efficiency spin detection.

Angle-resolved photoemission spectroscopy with sub-micrometer spatial resolution (μ-ARPES), has become a powerful tool for studying quantum materials. To achieve sub-micrometer or even nanometer-scale spatial resolution, it is important to focus the incident light beam (usually from synchrotron radiation) using x-ray optics, such as the zone plate or ellipsoidal capillary mirrors. Recently, we developed a laser-based μ-ARPES with spin-resolution (LMS-ARPES). The 177nm laser beam is achieved by frequency-doubling a 355nm beam using a KBBF crystal and subsequently focused using an optical lens with a focal length of about 16mm. By characterizing the focused spot size using different methods and performing spatial-scanning photoemission measurement, we confirm the sub-micron spatial resolution of the system. Compared with the μ-ARPES facilities based on the synchrotron radiation, our LMS-ARPES system is not only more economical and convenient, but also with higher photon flux (>5 × 1013 photons/s), thus enabling the high-resolution and high-statistics measurements. Moreover, the system is equipped with a two-dimensional spin detector based on exchange scattering at a surface-passivated iron film grown on a W(100) substrate. We investigate the spin structure of the prototype topological insulator Bi2Se3 and reveal a high spin-polarization rate, confirming its spin-momentum locking property. This lab-based LMS-ARPES will be a powerful research tool for studying the local fine electronic structures of different condensed matter systems, including topological quantum materials, mesoscopic materials and structures, and phase-separated materials.

Dirac Bands in the Topological Insulator Bi2Se3 Mapped by Time‐Resolved Momentum Microscopy

AbstractThe energy dispersion of the unoccupied Dirac bands of the topological insulator Bi2Se3 has been studied up to large parallel momenta and intermediate state energies using a setup for laser‐based time‐resolved momentum microscopy with 6 eV probe‐photons. A strongly momentum‐dependent evolution of the topologically protected Dirac states into a conduction band resonance is observed, highlighting the anisotropy dictated by the symmetry of the surface. The results are in remarkable agreement with the theoretical surface spectrum obtained from a GW‐corrected tight‐binding model, suggesting the validity of the approach in the prediction of the quasiparticle excitation spectrum of large systems with non‐trivial topology. After photoexcitation with 0.97 eV photons, assigned to a bulk valence band‐conduction band transition, the out‐of‐equilibrium population of the surface state evolves on a multi‐picosecond time scale, in agreement with a simple thermodynamical model with a fixed number of particles, suggesting a significant decoupling between bulk and surface states.

Enhanced Magnetic Anisotropy and Curie Temperature by the Absence of Se Atoms at the Interface of EuS/Bi2Se3

The heterojunction composed of ferromagnetic insulator (EuS) and topological insulator (Bi2Se3) is interesting due to several unusual behaviors produced by the interfacial effects. Previous experiments suggest a largely enhanced Curie temperature up to room temperature and perpendicular magnetic anisotropy at the interface [F. Katmis et al., Nature 533, 513 (2016).]. However, a recent experiment indicates that room‐temperature ferromagnetic behavior is absent, and only in‐plane anisotropy is observed [A.I. Figueroa et al., PRL 125, 226 801 (2020).]. To understand the puzzling observations in EuS/Bi2Se3, Se‐missing interfacial system is constructed and the magnetic anisotropy energy and the Curie temperature based on density functional calculations are studied. The results suggest that the absence of Se atoms greatly enhance the perpendicular magnetic anisotropy and the estimated Curie temperature based on Ising model can be up to room temperature. Therefore, the puzzling observations may be concerned with the details of the interfacial system.

Investigation of Raman depolarization ratio in topological insulator Bi2Se3 epitaxial films

Bismuth selenide (Bi2Se3) epitaxial films were grown at different substrate temperatures (T s) by molecular beam epitaxy. In the optimization of T s, a Bi2Se3 film with the smallest root mean square roughness (Rq) and the lowest electron density was grown at T s = 120 °C. In the optimized growth condition, Bi2Se3 epitaxial films with 3−85 quintuple layers (QL: 1 QL ≈ 1 nm) were grown. In unpolarized Raman spectra, the positions of A 1 1g and E 2 g-modes shifted to the low wavenumbers at film thickness below 10 QL. The polarized Raman spectra showed that the depolarization ratio ρ also changed with film thickness. The change in ρ was more significant than the change in the position shift. This indicates that the measurement of ρ is an effective method to evaluate the thickness of Bi2Se3 ultrathin films.

Distinguishing high-harmonic generation from surface and bulk states in topological insulator Bi2Se3

We demonstrated a scheme to differentiate the high-harmonic generation (HHG) originating from the surface states and bulk states of the topological insulator Bi2Se3. By adopting two-color mid-infrared laser fields on Bi2Se3, we found that the nonlinear response sensitively depends on the relative phase of the driving fields. The even harmonics arise from the surface states with a clear signature, whose modulation period equals the cycle of the second-harmonic generation (SHG) field. We reveal that the weak SHG perturbs the nontrivial dipole phase of the electron-hole pair in surface states, and thus leads to the modulation of HHG. It provides a means to manipulate the ultrafast dynamics in surface states through adopting a weak perturbing laser field.

Topological insulator bismuth selenide with a unique cloud-like hollow structure as a bidirectional electrocatalyst for robust lithium–sulfur batteries

Topological insulator Bi2Se3 with a unique cloud-like hollow structure was synthesized and employed as a separator modifier for lithium–sulfur batteries, which can significantly accelerate sulfur conversion kinetics and mitigate the shuttle effect.

Electronic structure and x-ray magnetic circular dichroism in cr-doped topological insulator bi2se3

We have studied the structural, electronic, and magnetic properties of the Cr-doped topological insulator Bi2Se3 within the density functional theory using the generalized gradient approximation in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The X-ray absorption spectra and X-ray magnetic circular dichroism at the Cr K and L2,3 edges have been investigated theoretically from the first principles. The calculated results are in good agreement with the experimental data. The complex fine structure of the Cr L2,3 X-ray absorption spectra in Cr-doped Bi2Se3 has been found to be not compatible with a Cr2+ valency state. Its interpretation demands a mixed valent state.

First-Principles Study on Electronic and Optical Properties of Sn-Doped Topological Insulator Bi2se3

First-Principles Study on Electronic and Optical Properties of Sn-Doped Topological Insulator Bi2se3

Topological insulator Bi2Se3 based electrochemical aptasensors for the application of sensitive detection of interferon-γ.

Interferon-γ (IFN-γ) is one of the crucial inflammatory cytokines as an early indicator of multiple diseases. A fast, simple, sensitive and reliable IFN-γ detection method is valuable for early diagnosis and monitoring of treatment. In this work, we creatively developed an electrochemical aptasensor based on the topological material Bi2Se3 for sensitive IFN-γ quantification. The high-quality Bi2Se3 sheet was directly exfoliated from a single crystal, which immobilized the synthesized IFN-γ aptamer. Under optimal conditions, the electrochemical signal revealed a wide linear relation along with the logarithmic concentration of IFN-γ from 1.0 pg mL-1 to 100.0 ng mL-1, with the limit of detection as low as 0.5 pg mL-1. The topological material Bi2Se3 with Dirac surface states improved the electrochemical signal/noise ratio and thus the sensitivity of the sensors. Furthermore, this electrochemical aptasensor exhibited excellent specificity and stability, which could be attributed to the large-scale smooth surface of the Bi2Se3 sheet with few defects decreasing the non-specific absorption. The developed biosensor has the same good performance as the ELISA method for detecting the real serum samples. Our work demonstrates that the developed electrochemical aptasensors based on topological materials have great potential in the field of clinical determination.