Bi Films Research Articles

Generation of terahertz radiation from the island films of topological insulator Bi2-xSbxTe3-ySey

The aim of the research was the studying of the topological insulators Bi2-xSbxTe3-ySey thin films with the different thickness and chemical composition. The obtained time dependences of terahertz radiation have indicated that the generation of THz waves was more efficient in the island film having a total thickness of about tens nanometers with the composition close to the Ren’s curve, where the volume contribution to the conductivity was suppressed. We have demonstrated an amplification of the THz radiation power by applying an external electric field to a topological insulator. This effect can be useful for fabricating photoconductive THz antennas based on topological insulators.

Bismuth/hydroxyapatite-modified carbon screen-printed electrode for heavy-metal ion detection in aqueous media

Square-wave voltammetric stripping analysis is attractive for environmental monitoring and trace metal ion determination. The sensitivity is a result of analytes preconcentration steps on the electrode and advanced measurement procedures, where metal analytes are stripped away from the electrode at appropriate potential scan. Screen-printed electrode (SPE) has great advantages for in situ assays of heavy metal ions. Modification of SPE with bismuth (Bi) film improves the amalgamation of metal ions and the addition of hydroxyapatite (HA) increases the ion sorption, and enhances the current response due to the large porous structure and surface active sites for the metal ion binding. The ionization of the functional groups on the electrode surface upon contact with the aqueous system further assists the cation binding. The analytical performance of Bi and HA-modified SPE for simultaneous detection of Cd(II) and Pb(II) ions by square wave anodic stripping voltammetry (SWASV) was evaluated. Under the optimized electrochemical working conditions, calibration graph is linear for 240 s deposition time, in 0.1 M acetate buffer at pH 7.6 with the detection limit of 16.8 ppb for Pb(II). Two peaks corresponding to Cd(II) at -0.8 V and Pb(II) at -0.6 V can be discerned suggesting that Bi-HA modification had increased the current responses.

Galvanic Displacement Deposition of Bismuth on Copper in the Ambient Ethaline Deep Eutectic Solvent in the Absence and Presence of Water and Additives

A facile approach of forming bismuth (Bi) films on copper (Cu) substrates via galvanic displacement using the deep eutectic solvent (DES) Ethaline (choline chloride-ethylene glycol; ChCl-EG) as the reaction medium was studied. Electronic absorption spectra and cyclic voltammetric behavior implied that Cu atoms were displaced by Bi atoms via the consumption of Bi(III) complex ions and the formation of Cu(I) species; the latter was oxidized to Cu(II) under ambient air. It is evident that the concentration of Bi(III) in Ethaline as well as the reaction temperature affect the surface morphologies and crystallization of the formed Bi layers, which follows the conventional behavior of nucleation and growth similar to the electrodeposition. Water content in the Ethaline DES seemed to promote the galvanic displacement by decreasing the solution viscosity, and enhancing the mass transport rate of the reacting species. Additives such as cetyltrimethylammonium bromide (CTAB), and molecular thiourea (TU) showed significant effects on the surface morphologies of the Bi layers.

Compositional analysis by RBS, XPS and EDX of ZnO:Al,Bi and ZnO:Ga,Bi thin films deposited by d.c. magnetron sputtering

Rutherford backscattering spectrometry, X-ray photoelectron and X-ray energy dispersive spectroscopies were employed to analyse Bi incorporation into ZnO:Al and ZnO:Ga transparent and electrically conductive thin films deposited by d.c. magnetron sputtering, with thickness in the range of 300–400 nm. Sputtering was performed in an argon atmosphere from two targets in confocal geometry being one composed of either ZnO:Al2O3 or ZnO:Ga2O3 composites and the other a Bi metal target. The content of bismuth dopant in the ZnO matrix was controlled by the respective target current density (JBi) in order to attain a high optical transparency (>80%) in the visible region. For ZnO:Al,Bi films Bi content varied from 0.1 to a maximum of 1.5 at.% when varying JBi from 0.06 to 0.26 mA cm−2. However, for ZnO:Ga,Bi films, deposited in similar conditions, Bi reached a maximum overall layer content of 2.4 at.%, with a surface enrichment content that varied from 1.3 to 8.8 at.%. It was also observed that the Bi content in the topmost layers of the films is slightly depleted due to thermal evaporation upon thermal annealing in vacuum at 350 °C. It is envisaged applications for these films as transparent photoelectrodes and thermoelectric materials.

Tuning spin-charge interconversion with quantum confinement in ultrathin bismuth films

Spin-charge interconversion (SCI) phenomena have attracted a growing interest in the field of spintronics as means to detect spin currents or manipulate the magnetization of ferromagnets. The key ingredients to exploit these assets are a large conversion efficiency, the scalability down to the nanometer scale and the integrability with opto-electronic and spintronic devices. Here we show that, when an ultrathin Bi film is epitaxially grown on top of a Ge(111) substrate, quantum size effects arising in nanometric Bi islands drastically boost the SCI efficiency, even at room temperature. Using x-ray diffraction (XRD), scanning tunneling microscopy (STM) and spin- and angle-resolved photoemission (S-ARPES) we obtain a clear picture of the film morphology, crystallography and electronic structure. We then exploit the Rashba-Edelstein effect (REE) and inverse Rashba-Edelstein effect (IREE) to directly quantify the SCI efficiency using optical and electrical spin injection.

Infrared Spectroscopy of the Topological Surface States of Bi_{2}Se_{3} by Use of the Berreman Effect.

The Berreman effect (BE) allows one to study the electrodynamics of ultrathin conducting films at the surface of dielectrics by use of grazing-angle infrared spectroscopy and polarized radiation. Here, we first apply the BE to the two-dimensional electron system (2DES) at the interface between a high-purity film of the topological insulator Bi_{2}Se_{3} and its sapphire substrate. We determine for the 2DES a charge density n_{s}=(8±1)×10^{12} cm^{-2}, a thickness d=0.6±0.2 nm, and a mobility μ^{IR}=290±30 cm^{2}/V s. Within errors, all of these parameters result in being independent of temperature between 300 and 10K. These findings consistently indicate that the 2DES is formed by topological surface states, whose infrared response is then directly observed here.

Microstructure and electrical transport in electrodeposited Bi films

The semimetal character of bismuth and its large photon absorbing power make of this element the most suitable absorber material for X-ray low temperature detectors. This application requires coatings of Bi with thicknesses and properties that only electrodeposition methods may achieve. Although there are studies on electrodeposition of bismuth for these detectors and other devices, the process is not straightforward and has not been sufficiently studied in terms of the desired final properties, neither the effect of different parameters is well known or easily reproduced. This work reports the influence of two different electrolytes, of the deposition method, and of heating and stirring on the structure, microstructure and transport properties of bismuth films. Typically, rhombohedral Bi is obtained upon electrodeposition with very good crystallinity, and some crystal preferential orientation, while significant empirical correlations are found among electrochemical parameters, microstructure, and resistivity. Such correlation allows the identification of the deposition parameters for coatings that yield the optimal functional properties.

Structural and electronic properties of atomically thin Bismuth on Au(111)

Atomically thin Bismuth (Bi) films are predicated to be candidates for high temperature quantum spin hall materials. Here, we reported the structural evolutions and the corresponding electronic properties of Bi ultrathin films on Au(111) at initial stage as a function of coverage using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and photoemission spectroscopy (PES). The small window for a stable two dimensional (2D) Bi in Kagome and honeycomb lattice on Au(111) has been optimized. LEED and STM results show that Bi atoms self-assemble into dimered (5 × 5) superdots, (37×37)R25.3∘ in a Kagome lattice and (p × √3) stripes sequentially in the first monolayer regime and into bi-layered Bi (110) islands afterwards. UPS results show the disappearance of Au(111) surface states at coverage of 0.18 ML, revealing the Van der Waals interactions between Au(111) and Bi adatoms. The repulsive interactions between Bi atoms prevent the 2D Bi structure from islands forming at initial stage and benefit large domains in (37×37)R25.3∘ Kagome lattice. Such 2D Bi may be interesting because of its relevance in terms of novel physical properties.

Effects of oblique angle deposition on structural, electrical and wettability properties of Bi thin films grown by thermal evaporation

Oblique angle deposition is a promising technique for tuning the physical properties of thin films. Structural, surface morphology, electrical and wettability properties are strongly influenced by the angle of deposition. A comparison of these physical properties of normally and obliquely deposited Bi films is carried out in this study. X-ray diffraction studies show that films have highly oriented hexagonal crystal structure and crystallite size is smaller for obliquely deposited (70 nm) film as compared to that of normally deposited film (111 nm). Raman spectra of the films consist of peaks corresponding to Eg and A1g first-order Raman modes of bismuth. The atomic force and scanning electron microscopy studies show that the surface roughness of obliquely deposited film is higher as compared to that of normally deposited film. Contact angle measurements reveal that both films are strongly hydrophobic in nature with the contact angles of 105 ± 1° and 119 ± 1° for normally and obliquely deposited films respectively. Oblique angle deposition enhances the hydrophobicity of the film. The electrical conductivity of the film is significantly reduced by oblique angle deposition. The activation energies for electrical conduction were determined by four-probe measurements and are 0.0166 ± 0.0003 eV and 0.0178 ± 0.0003 eV for normally and obliquely deposited films respectively.

Bismuth nanodendrites deposited on glassy carbon electrode as a sensitive electrochemical sensor for simultaneous detection of Cd2+ and Pd2+ ions

AbstractIn this study, bismuth nanodendrites (BiNDs) were fabricated on glassy carbon electrode by chronopotentiometric method. The hierarchical structure and high population matrix of BiNDs provides high surface active area to enhance the electrochemical signals of measured Cd2+ and Pb2+ ions. The developed bismuth nanodendritic structure was well‐observed and characterzied by scanning electron microscopy (SEM). Electrochemical behaviours of developed BiNDs electrodes were studied by the cyclic voltammetric (CV) method. The fabrication conditions for BiNDs such as the applied current and deposition time were optimized as ‐10 mA and 90 s, respectively. Under this optimized condition, the highest peaks of Cd2+ and Pb2+ ions at concentration of 20 ppb were obtained. The Cd2+ and Pb2+ signals acquired by BiNDs are almost three times greater than that measured by the Bi film electrode.

Atomic Scale Growth Processes of Thin Films As Revealed By Fast Surface X-Ray Diffraction

X-ray crystal truncation rod (CTR) scattering and reciprocal space mapping (RSM) are widely used to characterize the structure of thin films. The methods can provide the structural information, such as the atomic structure, shape and size of crystalline domain, and strain distribution, in any ambient conditions without destructing the specimen. The use of the methods is often limited in the static structure analysis, because the acquisitions of CTR scattering profile and RSM dataset are often time consuming (mins to hrs). Our group has developed a method that can measure a wide range of CTR profile and RSM in a single acquisition by using an energy-dispersive converging X-rays [1]. The technique allows the in-operando observation of atomic scale processes of photo-induced surface phenomenon [2] and electrochemical processes at the solid-liquid interface [2] with a time resolution of 1 s. The time frame is also reasonable to study the thin film growth processes. In this contribution talk, we show the atomic scale growth processes of ultra thin films, Bi and Bi2Se3, as reveled by the energy-dispersive surface X-ray diffraction. In the growth of Bi film, we observed: the formation of wetting atomic layer at the interface, the growth of black phosphorous phase, which does not exists in bulk, below the thickness of ~2 nm, and the growth of bulk Bi structure in the upper layer. In the growth of Bi2Se3 film, we observed a strained Bi2Se3 structure in the first a few Bi2Se3 layers. The relationships between the growth behaviors and the electronic properties, namely, the quantum confinement effect in Bi and the topological phase transition of Bi2Se3, are discussed. [1] T. Matsushita, T. Takahashi, T. Shirasawa, E. Arakawa, H. Toyokawa, and H. Tajiri, J. Appl. Phys. 110, 102209 (2011). [2] T. Shirasawa, W. Voegeli, E. Arakawa, T. Takahashi, and T. Matsushita, J. Phys. Chem. C 120, 29107 (2016). [3] T. Shirasawa, T. Masuda, W. Voegeli, E. Arakawa, C. Kamezawa, T. Takahashi, K. Uosaki, and T. Matsushita, J. Phys. Chem. C 121, 24726 (2017).

Ultrafast Surface State Spin-Carrier Dynamics in the Topological Insulator Bi_{2}Te_{2}Se.

Topological insulators are promising candidates for optically driven spintronic devices, because photoexcitation of spin polarized surface states is governed by angular momentum selection rules. We carry out femtosecond midinfrared spectroscopy on thin films of the topological insulator Bi_{2}Te_{2}Se, which has a higher surface state conductivity compared to conventionally studied Bi_{2}Se_{3} and Bi_{2}Te_{3}. Both charge and spin dynamics are probed utilizing circularly polarized light. With a sub-band-gap excitation, clear helicity-dependent dynamics is observed only in thin (<20 nm) flakes. On the other hand, such dependence is observed for both thin and thick flakes with above-band-gap excitation. The helicity dependence is attributed to asymmetric excitation of the Dirac-like surface states. The observed long-lasting asymmetry over 10ps even at room temperature indicates low backscattering of surface state carriers which can be exploited for spintronic devices.

Tuning vortex fluctuations and the resistive transition in superconducting films with a thin overlayer

It is shown that the temperature of the resistive transition $T_r$ of a superconducting film can be increased by a thin superconducting or normal overlayer. For instance, deposition of a highly conductive thin overlayer onto a dirty superconducting film can give rise to an "anti-proximity effect" which manifests itself in an initial increase of $T_r(d_2)$ with the overlayer thickness $d_2$ followed by a decrease of $T_r(d_2)$ at larger $d_2$. Such a nonmonotonic thickness dependence of $T_r(d_2)$ results from the interplay of the increase of a net superfluid density mitigating phase fluctuations and the suppression of the critical temperature $T_c$ due to the conventional proximity effect. This behavior of $T_r(d_2)$ is obtained by solving the Usadel equations to calculate the temperature of the Berezinskii-Kosterletz-Thouless transition, and the temperature of the resistive transition due to thermally-activated hopping of single vortices in dirty bilayers. The theory incorporates relevant materials parameters such as thicknesses and conductivities of the layers, interface contact resistance between them and the subgap quasiparticle states which affect both phase fluctuations and the proximity effect suppression of $T_c$. The transition temperature $T_r$ can be optimized by tuning the overlayer parameters, which can significantly weaken vortex fluctuations and nearly restore the mean-field critical temperature. The calculated behavior of $T_r(d_2)$ may explain the nonmonotonic dependence of $T_r(d_2)$ observed on (Ag, Au, Mg, Zn)-coated Bi films, Ag-coated Ga and Pb films or NbN and NbTiN films on AlN buffer layers. These results suggest that bilayers can be used as model systems for systematic investigations of optimization of fluctuations in superconductors.

Band Structures of Ultrathin Bi(110) Films on Black Phosphorus Substrates Using Angle-Resolved Photoemission Spectroscopy**Supported by National Key R&D Program of China under Grant Nos 2017YFA0402901, 2016YFA0401004 and 2016YFB0901600, the National Natural Science Foundation of China under Grant Nos 11534010, 11404172, U1532136, U1632102, U1632272, 11574201, 11674296 and 11190022, the National Basic Research Program of China under Grant No 2014CB921102, the Key

The band structures of two-monolayer Bi(110) films on black phosphorus substrates are studied using angle-resolved photoemission spectroscopy. Within the band gap of bulk black phosphorus, the electronic states near the Fermi level are dominated by the Bi(110) film. The band dispersions revealed by our data suggest that the orientation of the Bi(110) film is aligned with the black phosphorus substrate. The electronic structures of the Bi(110) film strongly deviate from the band calculations of the free-standing Bi(110) film, suggesting that the substrate can significantly affect the electronic states in the Bi(110) film. Our data show that there are no non-trivial electronic states in Bi(110) films grown on black phosphorus substrates.

Herramienta de software para determinar constantes ópticas en celdas solares tipo película delgada

En este trabajo se desarrolló una herramienta de software que permite determinar las propiedades ópticas de materiales semiconductores, esta herramienta es de utilidad para investigadores que trabajan en la caracterización de películas delgadas semiconductoras. El software calcula las constantes ópticas: índice de refracción (n), coeficiente de absorción (α) y brecha de energía prohibida (Gap), además del espesor aproximado de la película; con el programa desarrollado se calcularon las constantes ópticas de películas delgadas de ZnS, SnS:Bi y SnS2:Bi, que son usadas como capas buffer y absorbentes en celdas solares, en este trabajo se presentan los resultados obtenidos con una película de SnS2:Bi. El software fue creado en el lenguaje de programación Python dentro de una interfaz sencilla inglés-español y para desarrollarlo se tuvo en cuenta el método propuesto por Swanepoel, el cual toma como base el espectro de transmitancia experimental del material semiconductor.

Halogen Adsorption and Reaction with Bi2(Se,Te)3 and Bi/Bi2(Se,Te)3

Bi$_2$Se$_3$ and Bi$_2$Te$_3$, and these same surfaces covered with Bi films, are exposed to Br$_2$ and Cl$_2$ in ultra-high vacuum. Low energy electron diffraction (LEED) and low energy ion scattering (LEIS) are used to investigate the surface composition before and after halogen exposure. It is found that Br$_2$ weakly chemisorbs to the Se- or Te-terminated clean surfaces and light annealing removes the adsorbates restoring the intact surfaces. In contrast, halogens dissociatively adsorb onto surfaces covered with an additional bilayer of Bi, having a p-doping effect. Annealing these halogen-covered surfaces at 130{\deg}C causes Bi atoms to be chemically etched away and the surface reverts to a Se- or Te-termination. This work shows how halogen adsorption and reaction can be used to modify the surface termination of such materials.

The growth of bismuth on Bi2Se3 and the stability of the first bilayer

Bi(0001) films with thicknesses up to several bilayers (BLs) are grown on Se-terminated Bi2Se3(0001) surfaces, and low energy electron diffraction (LEED), low energy ion scattering (LEIS) and atomic force microscopy (AFM) are used to investigate the surface composition, topography and atomic structure. For a single deposited Bi BL, the lattice constant matches that of the substrate and the Bi atoms adjacent to the uppermost Se atoms are located at fcc-like sites. When a 2nd Bi bilayer is deposited, it is incommensurate with the substrate. As the thickness of the deposited Bi film increases further, the lattice parameter evolves to that of bulk Bi(0001). After annealing a multiple BL film at 120 °C, the first commensurate Bi BL remains intact, but the additional BLs aggregate to form thicker islands of Bi. These results show that a single Bi BL on Bi2Se3 is a particularly stable structure. After annealing to 490 °C, all of the excess Bi desorbs and the Se-terminated Bi2Se3 surface is restored.

Experiments on hydrolysis of Bi(2201) thin film via atomic force microscope

In this paper, large-scale Bi(2201) nanofilm was mechanically exfoliated. The thin film Bi(2201) was characterized by means of optical image and XRD spectrum analysis. AFM is used to study the stability of Bi(2201) thin film. We found that the Bi(2201) nanofilm was less sensitive to CO2 while it extremely got affected by humidity. With the rise in the humidity, the hydrolytic speed of Bi(2201) film was greatly increased. When the relative humidity of the air is lower than 20%, the Bi(2201) thin film can be stable in two days. However, when the relative humidity is about 90% RH, Bi(2201) film will be hydrolyzed in few minutes.

High efficiency preparation of Bi2Sr2CaCu2O8+δ superconducting thin films by an acetate based Sol-Gel process

Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting thin films with c-axis epitaxial orientation were prepared on LaAlO3 (LAO) single crystal substrates via a Sol-Gel technique using metallic acetates as starting materials. The influence of the growth temperature and oxygen partial pressure (pO2) on the phase purity and superconducting properties of Bi-2212 was discussed. The results show that Bi-2212 films prepared at 820 °C with the pO2 of 1.4 KPa exhibit good in-plane and out-of-plane growth textures and excellent superconducting properties with high critical transition temperature (Tc) of 88 K and narrow transition width (ΔTc) of 4.8 K.

Effect of RF Isolation of Intrinsic Josephson Junctions Made of Solid Bi-2212 Film for Terahertz Radiation

This is the first report of terahertz (THz) radiation from intrinsic Josephson junction devices made of solid Bi 2 Sr 2 CaCu 2 O 8+δ thin films. It is shown that in situ laser trimming of the current lead structure could activate initially THz inactive devices. The trimming increased inductive reactance and improved RF isolation of intrinsic Josephson junctions. It is considered that the RF isolation is a key component to maintain a cavity resonance within intrinsic Josephson junctions essential to create THz waves from solid Bi-2212 film IJJ devices.