Search

Annular dark-field (ADF) imaging in a scanning transmission electron microscope (STEM) has been used to measure concentration profiles across thin Ga(As,Bi) layers grown by molecular beam epitaxy, from which the segregation lengths for bismuth surface segregation have been calculated. Performing this for layers grown at two different temperatures, the activation energies for Bi surface segregation have been determined for the lower (GaAsBi-on-GaAs) and for the upper (GaAs-on-GaAsBi) interface. The inequivalence observed is attributed to strain driving the larger Bi atoms preferably towards the free surface during growth. [ABSTRACT FROM AUTHOR]

Abstract: For thin Bi films with thicknesses d=10–60nm the dependences of the Hall coefficient, Seebeck coefficient, electrical conductivity, and Hall carrier mobility on d have been obtained at room temperature. Distinct oscillations of the transport properties with period Δd=(5±1)nm have been observed in the thickness range d=25–60nm and attributed to quantization of the energy spectrum of holes. It has been suggested that a deep minimum observed in the thickness dependences of the kinetic coefficients at d∼25nm is connected with the manifestation of the electronic spectrum quantization and/or manifestation of a semimetal–semiconductor transition. The experimental data are in good agreement with the results of theoretical calculations. [Copyright &y& Elsevier]

Thin bismuth films of various thicknesses between 5 and 32 nm grown by molecular beam epitaxy on Si (111) substrates were investigated. The samples were characterized by the x-ray diffraction method, which allowed us to identify two types of Bi crystallographic structures— α and β bismuth. Terahertz radiation pulses emitted from the samples after their illumination by femtosecond optical pulses with different wavelengths were characterized. The main THz emission features were similar for both types of Bi layers. Due to 2D confinement, the electron energy band structure depends on the thickness. With the terahertz excitation spectroscopy method, direct bandgaps were determined to be in the range from 0.25 to 0.5 eV—much greater than the indirect bandgaps of the layers. A simple model was used to describe the nature of THz emission from these films, which is the cause of uncompensated lateral photocurrents occurring because of the diffusive electron scattering at the Bi/Si interface. [ABSTRACT FROM AUTHOR]

Bismuth films with thicknesses between 6 and ∼30 nm were grown on Si (111) substrate by molecular beam epitaxy (MBE). Two main phases of bismuth — α -Bi and β -Bi — were identified from high-resolution X-ray diffraction (XRD) measurements. The crystal structure dependencies on the layer thicknesses of these films were analyzed. β -Bi layers were epitaxial and homogenous in lateral regions that are greater than 200 nm despite the layer thickness. Further, an increase in in-plane 2 θ values showed the biaxial compressive strain. For comparison, α -Bi layers are misoriented in six in-plane directions and have β -Bi inserts in thicker layers. That leads to smaller (about 60 nm) lateral crystallites which are compressively strained in all three directions. Raman measurement confirmed the XRD results. The blue-sift of Raman signals compared with bulk Bi crystals occurs due to the phonon confinement effect, which is larger in the thinnest α -Bi layers due to higher compression. [ABSTRACT FROM AUTHOR]

Abstract We have investigated how the presence of an adsorbed hydrogen layer affects the nucleation and properties of Bi layers grown by dc electrodeposition at different overpotentials on n-GaAs(111)B substrates with a carrier concentration of 1.3 ·1017 cm−3 in darkness and at 300 K. The kinetics of Bi(III) ions reduction is controlled by the overpotential but also negatively affected by the adsorbed hydrogen layer, as deduced from the deconvolution of the current density transients recorded during the nucleation of the films. The surface morphology and the structural properties of the Bi films are correlated with the nucleation process and therefore, influenced by both the overpotential and the adsorbed hydrogen layer. At low overpotentials, porous and rough Bi films with a low crystal quality are obtained due to the low rate of proton and Bi(III) ion reduction. As the overpotentials raises, the rate of these reactions increase leading to flatter and more compact Bi films with a higher crystal quality. The electrical properties of the Bi/n-GaAs interface depend on the interfacial states whose origin is again the combined effect of the adsorbed hydrogen layer and growth overpotential. Graphical abstract Image 1 Highlights • The reduction of Bi(III) ions on lower-doped n-GaAs substrates is inhibited. • The n-GaAs surface is blocked by adsorbed hydrogen (H ads) in acidic solutions. • Bi(III) ions cannot get reduced until the reduction of the H ads starts. • The nucleation is affected by the overpotential and the adsorbed hydrogen layer. • The properties of the Bi layers are correlated to the nucleation process. [ABSTRACT FROM AUTHOR]

We investigated spin-to-charge current conversion in sputtered Y3Fe5O12 (YIG)/granular bismuth selenide (GBS) bi-layers at room temperature. The spin current is pumped to the GBS layer by the precession of magnetization at ferromagnetic resonance in the YIG layer. The spin-mixing conductance is determined to be as large as (13.64 ± 1.32) × 1018 m−2, which is larger than that of YIG/Pt and comparable or better than that of YIG/crystalline bismuth selenide indicating that GBS is a good spin-sink. The figure of merit of spin-to-charge conversion, the inverse Edelstein effect length ( λ IEE ), is estimated to be as large as (0.11 ± 0.03) nm. λ IEE shows GBS film thickness dependence, and its value is three times as large as in crystalline bismuth selenide. The λ IEE value larger than that of crystalline bismuth selenide and other topological insulators indicates that the spin-to-charge conversion is due to the spin-momentum locking. As the thickness of GBS increases, λ IEE decreases, which means the figure-of-merit of spin-to-charge conversion is influenced by grain size. [ABSTRACT FROM AUTHOR]

Abstract: Thin Bi layers were deposited by simple immersion of silicon chip into diluted HF aqueous solution, containing bismuth(III) ions. Bi nanoparticles or continuous up to 300nm thick Bi film can be grown on silicon by the variation of the temperature and deposition time. Prepared surfaces have been characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, photoluminescence and resistivity measurement methods. It was found that thinner Bi layers have a yellowish colour. [Copyright &y& Elsevier]

Well-dispersed Au/Bi nanoparticles with average size below 10 nm were prepared by using NaBH to reduce HAuCl with glucose as dispersant. The obtained Au/Bi NPs were well characterized by UV-Vis spectra, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements. The electrochemical study found that Bi adlayers on the surface of Au nanoparticles owns two kinds of surface structures, including a low coverage (2 × 2)-Bi adlayer and a close-packed (p × √3)-2 Bi adlayer due to the strong interaction between the two Bi layers and the below Au atoms, which is same with that bulk on Au surface. [ABSTRACT FROM AUTHOR]

Bismuth (Bi), as an impurity element in copper and copper-based alloys, usually leads to the catastrophic intergranular fracture even with a ppm concentration. However, the intrinsic mechanisms of the embrittlement remain largely unclear and the control of such a brittleness has been rarely reported. Here, we investigate the influence of trace amounts of Bi on the ductility of ultrahigh-purity copper (99.99999%) at temperatures between room temperature (RT) and 900 °C. On this basis, the ductility improvement of Cu Bi alloy by adding different concentration of Ce is also systematically studied. Compared to the ultrahigh-purity copper, the Bi-containing alloy exhibits a remarkable decrease in ductility, with the severe reduction occurs at 450–900 °C. This is caused by the grain boundary (GB) segregation of Bi layers, which reduces the GB cohesion because of the weak Bi Bi bonds. However, after trace Ce are added, the ductility of Cu Bi alloy in the temperature range of 450–900 °C is significantly increased. The obvious enhancement is due to the reaction behavior of Ce and Bi to form the precipitated phases, as well as the preferential segregation of Ce to GBs and phase boundaries, which change the existing form of Bi in copper. Our findings provide a comprehensive understanding on the microstructural origin of Bi-induced GB embrittlement and an effective way for inhibiting such an embrittlement. • The ductility of ultrahigh-purity copper, Cu Bi and Cu-Bi-Ce alloys in the temperature range of RT–900 °C are systematically investigated. • The configuration of Bi atoms at GBs and the embrittlement of Cu Bi alloy between 450 and 900 °C are investigated. • The mechanism of ductility improvement due to the inhibition of trace Ce on Bi segregation is revealed. [ABSTRACT FROM AUTHOR]

Examines the molecular beam epitaxial growth of cadmium telluride (CdTe) and bismuth (Bi) layers on CdTe substrates. Exhibition of streaked diffraction patterns in Bi layers; Effect of CdTe layers on Bi; Observation of polarity inversion of the CdTe terminating surface.

Bismuth (Bi)-doped Cu(In,Ga)Se2 (CIGS) films were prepared by the so-called 'multi-layer precursor method', obtained by depositing them onto Bi layers with various thicknesses on Mo-coated soda-lime glass (SLG) substrates. Material composition (Cu, In, Ga, and Se) profiles of the CIGS films are almost identical, whereas sodium (Na) is reduced, when Bi thickness is increased. Moreover, the incorporation of Bi into the CIGS film is enhanced with thicker Bi layer. With Bi thickness from 0 to 70 nm, the 2.4-μm-thick CIGS absorbers demonstrate the increase in CIGS grain size, carrier lifetime, and carrier concentration, thus improving their cell performances, especially open-circuit voltage ( VOC). With further increase in Bi thickness of above 70 nm, the CIGS films show the deterioration of CIGS film quality owing to the formation of Bi compounds such as Bi, BiSe, and Bi4Se3. Consequently, Bi-doped CIGS absorber with thickness of 2.4 μm, prepared with the 70-nm-thick Bi layer on Mo-coated SLG substrate, gives rise to the improvement of photovoltaic performances, especially VOC. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A Pt 0 (Bi)/CNW catalyst is synthesized by the galvanic displacement of Bi layers sputtered on carbon nanowalls in a PtCl 4 2 - solution (with 0.5 M H 2 SO 4 as the supporting electrolyte). The Pt 0 (Bi)/CNW catalysts are characterized by various methods (SEM, XPS, ICP-AES, OCPT, and CVA). It is shown that nearly 90 at.% Bi is displaced. However, no core–shell structure with a sufficiently dense Pt shell is formed. This is explained by the great difference in the type and parameters of Pt and Bi lattices. The Pt 0 (Bi)/CNW catalyst exhibits the high stationary specific activity in the formic acid oxidation reaction (FAOR), ∼30 times exceeding (at 200 mV vs. RHE) the activity of Pt electrodeposits on CNW. The catalytic effect is explained by the inhibition of accumulation of strongly chemisorbed species on the bismuth-modified Pt surface and the formation of new active sites for the one-site adsorption of weakly-bound species through which the direct path of the FAOR passes. Thus, the prospects of the practical application of Pt–Bi catalysts highly active in FAOR are demonstrated. [ABSTRACT FROM AUTHOR]

We report the formation and phase transformation of Bi-containing clusters in Bi epilayers upon annealing. The Bi layers were grown by molecular beam epitaxy under low (220 ) and high (315 ) temperatures and subsequently annealed using different temperatures and annealing times. Bi-containing clusters were identified only in the annealed samples that were grown at low temperature, revealing a relatively homogeneous size distribution. Depending on the annealing temperature and duration, the clusters show different sizes ranging from 5 to 20 nm, as well as different crystallographic phase, being coherently strained zincblende Bi (zb Bi-rich Ga(As, Bi)) clusters or rhombohedral pure Bi (rh-Bi) clusters. We found that: (1) the formation of the zb Bi-rich Ga(As, Bi) clusters is driven by the intrinsic tendency of the alloy to phase separately and is mediated by the native point defects present in the low temperature grown epilayers; (2) the phase transformation from zb Bi-rich Ga(As, Bi) to rh-Bi nucleates in zincblende {111} planes and grows until total consumption of Bi in the GaAs matrix. We propose a model accounting for the formation and phase transformation of Bi-containing clusters in this system. Furthermore, our study reveals the possibility to realize self-organized zb Bi-rich Ga(As, Bi) clusters that can exhibit QD-like features. [ABSTRACT FROM AUTHOR]

Abstract: Electrodeposition of Bi in magnetic gradient fields was performed from two different electrolytes. The first electrolyte contained only diamagnetic Bi3+-ions; the second one additionally contained electrochemically inert paramagnetic Mn2+-ions. While homogeneous Bi deposits were obtained from the former, structured Bi layers were derived from the latter. The structured deposits show an inverse correlation between deposit thickness and superimposed magnetic field gradient. Minima of film thickness are observed in regions of maximum magnetic gradients. This demonstration of magneto-electrochemical structuring by deposition of diamagnetic ions is discussed considering the acting magnetic forces. Several possibilities explaining the structuring mechanism are presented. [Copyright &y& Elsevier]

Abstract: We have studied the formation of a Bi-induced (2×2) reconstruction on the InAs(111)B surface. In connection to the development of the (2×2) reconstruction, a two dimensional charge accumulation layer located at the bottom of the InAs conduction band appears as seen through a photoemission structure at the Fermi level. Not well ordered Bi layers do not induce a charge accumulation. The Bi-induced reconstruction reduces the polarization of the pristine surface and changes the initial charge distribution. InAsBi alloying occurs below the surface where Bi acts as charge donor leading to the charge accumulation layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchically porous Mo 2 C (PMC) was used as a support for Bi nanodot deposition. • Ultrasmall Bi (6.4 nm) nanodots offered short transport length for the Li+-ions diffusion. • Highly-conductive PMC support could hinder the volume expansion of Bi upon cycling. • High capacity (422 mAh g−1) and stability (0.002 mAh g−1 decay/cycle) resulted. • High energy density (352 Wh kg−1, 563 Wh L–1) could be expected in full-cell design. The use of carbon-based supports, such as graphene and porous carbon, is a well-established approach to overcome the rapid capacity fading issues associated with alloy-based anode materials in lithium-ion batteries (LIBs). However, adopting carbonaceous materials that typically exhibit a low density eventually diminishes the primary purpose of alloys as high-energy–density anode materials. In this study, we introduce three-dimensional hierarchically porous molybdenum carbide (PMC) with high energy density, robust mechanical strength, and high electronic conductivity, which make it a promising alternative support for suppressing the huge volume expansion of alloying-based materials. Carbon-coated, ultrasmall Bi nanodots with an average size of 6.4 nm are uniformly embedded on the PMC surface (denoted as C-Bi/PMC) by facilitating heterogeneous nucleation. When tested as an anode in an LIB, the C-Bi/PMC electrode exhibits a high reversible capacity of 422 mAh g−1 at 50 mA g−1, high-rate capacity of 268 mAh g−1 at 1000 mA g−1, and long-term stability of 400 mAh g−1 at 250 mA g−1 over 500 cycles followed by 0.002 mAh g−1 decay per cycle at 5000 mA g−1 over subsequent 1000 cycles. When paired with LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode as full-cell LIBs, the C-Bi/PMC anode deliver high gravimetric and volumetric energy densities of 352 Wh kg−1 and 563 Wh L–1, respectively. In-situ X-ray diffraction patterns captured during cycling reveal that the Li+-ion insertion mechanism in the voltage plateau region at 0.7–1.0 V consists of the intercalation between Bi layers followed by the formation of triclinic LiBi phase and the subsequent transition of triclinic LiBi to cubic Li 3 Bi phase. [ABSTRACT FROM AUTHOR]

Abstract: The impingement and interdiffusion of adsorbed Pb and Bi layers spreading from separated 3D pure bulk sources on Cu(100) has been studied, at T =513K, by in situ scanning Auger microscopy. When the leading edges of the pure Pb and Bi diffusion profiles impinge, they both consist of low-coverage lattice gas surface alloyed phases. In these low-coverage phases, Pb displaces surface alloyed Bi and the point of intersection of the profiles drifts towards the Bi source. These features lead to the conclusion that Pb atoms are more strongly bound at surface alloyed sites in Cu(100) than Bi atoms. Once the total coverage (Pb+Bi) on the substrate reaches about one monolayer, Pb and Bi are dealloyed from the substrate, and the interdiffusion profiles become essentially symmetric. Pb and Bi mix in all proportions, with an interdiffusion coefficient of ∼10−13 m2/s. This is considerably smaller than the self-diffusion coefficients previously observed for pure Pb and Bi in their respective high-coverage phases, indicating that the mechanism of interdiffusion is different from that of self-diffusion. As interdiffusion proceeds, the point of intersection of the Pb and Bi profiles reverses its drift direction, leading to the conclusion that binding of Bi atoms to the Cu(100) substrate is stronger than that of Pb atoms in the highest-coverage surface dealloyed layers. [Copyright &y& Elsevier]

Abstract: The spreading of Pb and Bi adsorbed layers from pure bulk sources, and their intermixing, on a Cu substrate, has been studied by scanning Auger microscopy at 473K. The pure Pb layer spreads faster than the Bi layer. When the pure layers meet, two phenomena are observed. The junction line of the two adsorbed layers drifts due to a replacement of adsorbed Pb by Bi. Superimposed on this drift, the Pb and Bi layers undergo interdiffusion. The interdiffusion coefficient has been analyzed by the Boltzmann–Matano method. [Copyright &y& Elsevier]

[Display omitted] • Nanoporous silicon (PS) was elaborated by electrochemical anodization of p-type Si. • Deposition of variable thickness of Bismuth (III) solution on porous silicon (PS) by dip-coating chemical process. • Effect of Bi (III) solution treatment on the structural and optical properties of p-type porous silicon is investigated. • A specific emphasis is put on the photoluminescence in terms of Bismuth oxide thickness. This work focuses on the impact of Bismuth (Bi) solution treatment on the optical properties of p-type porous silicon prepared by electrochemical anodization. Bi-layers of variable thickness are incorporated in porous silicon via a dip coating technique. The changes in the structural and optical properties of Bi (III)/PS nanostructures are monitored by Atomic Force Microscopy, Fourier transform infrared measurements and photoluminescence spectroscopy. These analyses highlight a relevant impact of the deposition process, which modifies the intrinsic properties of the porous silicon by the incorporation of Bi (III) in its pores. It is found that ultra-thin films of bismuth oxide formed after a heat treatment in air at 400 °C and deposited on PS samples leads to its stability as well as to passivating its dangling bands. For thicknesses ranging from 6 to 20 nm, the photoluminescence property in the visible region of Bi/PS nanostructures has been improved. This may be of interest for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

We show that III-V bismuth-based two-dimensional (2D) materials grown on an anion-terminated SrTe (111) substrate are 2D topological insulators. The III-Bi layers exhibit large nontrivial band gaps, ranging from 0.15 to 0.72 eV, depending on the passivation on the top surface, i.e., using hydrogen or halogens. We find that Γ-centered Dirac helical states, protected by time-reversal symmetry, appear at the edges of nanoribbon structures made of III-Bi layers on the SrTe substrate. The nontrivial character of the band gap is also determined by calculations of the Z2 invariant. We also find that the topological phase is maintained in the ultrathin quantum well heterostructures SrTe/III-Bi/SrTe, i.e., when the 2D materials are sandwiched between SrTe along the [111] direction, opening a new route for the fabrication of nanostructured devices based on 2D quantum spin Hall insulators. [ABSTRACT FROM AUTHOR]

We present the structural evolution of Bi on Au(111) from monolayer to multilayer regimes explored mainly by scanning tunneling microscopy. At the monolayer regime, Bi clusters distribute homogeneously to make an array with 5×5 periodicity. Further increase of the coverage converts these clusters to the two-dimensional periodic (√37×√37)R25.3° and (p×√3) structures. We propose a model of the (√37×√37)R25.3° structure based on the STM measurements and density-functional theory calculations. In the multilayer regime, superstructures at first appear with long-range periodicities arising from the moiré structures due mainly to the stacking of Bi layers. Then, the thicker films grow whose lattice constants are close to those of the (110) surface of rhombohedral Bi crystal. The Bi(110) films of more than 60 layers grow stably. Thus, this system provides a good stage for further investigation of the peculiar electronic properties of Bi(110). [ABSTRACT FROM AUTHOR]