Crystalline Bi Research Articles

(Invited) Thermal Atomic Layer Deposition of Elemental Antimony and Bismuth Films

The elements antimony (Sb) and bismuth (Bi) are important components of many thin film materials. In many applications, films need to be grown in high aspect ratio features with perfect conformality and Angstrom-level control of film thicknesses. Atomic layer deposition (ALD) is a method that can afford uniform thickness and conformal films, even in narrow and deep nanoscale features. To date, there have been several ALD processes reported for elemental Sb films using SbCl3 and Sb(SiR3)3 (R = Me, Et), but no reports of Bi films grown by ALD have been published.1,2 Herein, several families of thermal ALD processes will be described for the growth of elemental Sb and Bi films. Precursors that were explored for Sb and Bi include SbCl3, BiCl3, BiPh3, and Bi(NMe2)3. Reducing precursors encompassed 2-methyl-1,4-bis(trimethylsilyl)-2,5-cyclohexadiene,3 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine,3 and nitrogen sources such as ammonia, hydrazine, alkyl hydrazines, and alkyl amines. The processes employing the nitrogen co-reactants are proposed to occur through unstable SbN and BiN, which then decompose with loss of N2 to afford elemental Sb and Bi films. Self-limited Sb and Bi film growth was established between 25 and 175 °C. High purity Sb (>98%) and Bi (>94%) films were demonstrated by X-ray photoelectron spectroscopy analysis. X-ray diffraction analyses revealed the growth of crystalline Sb and Bi films. The results of additional film characterization will be presented. Al Hareri, M.; Emslie, D. J. H. Chem. Mater. 2022, 34, 2400-2409.Pore, V.; Knapas, K.; Hatanpää, T.; Sarnet, T.; Kemell, M.; Ritala, M.; Leskelä, M.; Mizohata, K. Chem. Mater. 2011, 23, 247– 254.Klesko, J. P.; Thrush, C. M.; Winter, C. H. Chem. Mater. 2015, 27, 4918-4921.

Phase Interface Regulating on Amorphous/Crystalline Bismuth Catalyst for Boosted Electrocatalytic CO2 Reduction to Formate.

Electroreduction of carbon dioxide into readily collectable and high-value carbon-based fuels is greatly significant to overcome the energy and environmental crises yet challenging in the development of robust and highly efficient electrocatalysts. Herein, a bismuth (Bi) heterophase electrode with enriched amorphous/crystalline interfaces was fabricated via cathodically in situ transformation of Bi-based metal-phenolic complexes (Bi-tannic acid, Bi-TA). Compared with amorphous or crystalline Bi catalyst, the amorphous/crystalline structure Bi leads to significantly enhanced performance for CO2 electroreduction. In a liquid-phase H-type cell, the Faraday efficiency (FE) of formate formation is over 90% in a wide potential range from -0.8 to -1.3 V, demonstrating a high selectivity toward formate. Moreover, in a flow cell, a large current density reaching 600 mA cm-2 can further be rendered for formate production. Theoretical calculations indicate that the amorphous/crystalline Bi heterophase interface exhibits a favorable adsorption of CO2 and lower energy barriers for the rate-determining step compared with the crystalline Bi counterparts, thus accelerating the reaction process. This work paves the way for the rational design of advanced heterointerface catalysts for CO2 reduction.

Novel methodology to determine thermal properties of nanoparticles exclusively based on SAXS measurements applied to Bi nanocrystals and nanodroplets in a glass matrix

A novel methodology is presented to determine thermal properties of polydisperse nanocrystals and/or nanodroplets embedded in a homogeneous matrix using small-angle X-ray scattering (SAXS). It is based solely on SAXS measurements at multiple temperatures and multiple moduli of the scattering vector. The proposed methodology can quantify the linear coefficients of thermal expansion of confined spherical nanocrystals and/or nanodroplets and the radius dependence of the melting temperature of confined spherical nanocrystals, even in samples with a broad size distribution. It is described through its application on a nanocomposite consisting of Bi nanocrystals/nanodroplets embedded in a sodium borate glass matrix. The linear coefficient of thermal expansion of Bi nanocrystals in the glass was ca 50% higher than that of bulk crystalline Bi, and the coefficient of liquid Bi nanodroplets was 25% smaller than that of bulk liquid Bi. The melting temperature of the spherical Bi nanocrystals decreased by ca 130 K when particle radii decreased from 82 to 23 Å. Even though SAXS measurements are generally expected to provide low-resolution structural parameters, this demonstrates that this technique allows for the characterization of rather weak temperature-dependent variations of size parameters during in situ heating processes and across melting transitions.

Observation of spin-momentum locked surface states in amorphous Bi2Se3.

Crystalline symmetries have played a central role in the identification and understanding of quantum materials. Here we investigate whether an amorphous analogue of a well known three-dimensional strong topological insulator has topological properties in the solid state. We show that amorphous Bi2Se3 thin films host a number of two-dimensional surface conduction channels. Our angle-resolved photoemission spectroscopy data are consistent with a dispersive two-dimensional surface state that crosses the bulk gap. Spin-resolved photoemission spectroscopy shows this state has an anti-symmetric spin texture, confirming the existence of spin-momentum locked surface states. We discuss these experimental results in light of theoretical photoemission spectra obtained with an amorphous topological insulator tight-binding model, contrasting it with alternative explanations. The discovery of spin-momentum locked surface states in amorphous materials opens a new avenue to characterize amorphous matter, and triggers the search for an overlooked subset of quantum materials outside of current classification schemes.

Heterogeneous crystalline–amorphous interface for boosted electrocatalytic nitrogen reduction to ammonia

Crystalline Bi–amorphous MoOxinterfaces anchored on RGO exhibit superior electrocatalytic NRR performance by enhancing the N2adsorption/activation while suppressing the competitive HER process.

The effect of negative pressures on the superconductivity of amorphous and crystalline bismuth

Materials may behave in non-expected ways when subject to unexpected conditions. For example, when Bi was turned into an amorphous phase (a-Bi) unexpectedly it became a superconductor at temperatures below 10 K. Using the superconductivity of the amorphous phase we provided an explanation as to why crystalline bismuth (c-Bi) had not been found to superconduct, and even predicted an upper limit for its superconducting transition temperature Tc. This was experimentally corroborated within the following year. We now decided to investigate what happens to the crystalline, Wyckoff structure, and amorphous Bi when pressures below the atmospheric are applied. Here it is shown that, within the BCS approach, under expansion the Wyckoff c-Bi increases its superconducting transition temperature minimally, whereas the amorphous phase decreases its Tc. The electron densities of states (eDoS), the vibrational densities of states (vDoS) and the Debye temperatures (θD) are calculated to perform this qualitative evaluation. Expansion can be obtained in the laboratory by chemically etching Bi-based alloys, for example, a process also known as dealloying.

Growth parameters of Bi0.1Y2.9Fe5O12 thin films for high frequency applications

• Growth parameters are reported for Bi 0.1 Y 2.9 Fe 5 O 12 thin films on Gd 3 Ga 5 O 12 . • Effect of Bi ions (at dodecahedral site) in Bi 0.1 Y 2.9 Fe 5 O 12 (111)–orientation shown. • Increase in ferromagnetic resonance linewidth in (111)–orientation is observed. • Thickness dependent magnetization dynamics is studied. • Four–fold anisotropy is seen in in–plane angular dependent study. The growth and characterization of Bismuth (Bi) substituted YIG (Bi–YIG, Bi 0.1 Y 2.9 Fe 5 O 12 ) thin films are reported. Pulsed laser deposited (PLD) films with thicknesses ranging from 20 to 150 nm were grown on Gadolinium Gallium Garnet substrates. Two substrate orientations of (100) and (111) were considered. The enhanced distribution of Bi 3+ ions at dodecahedral site along (111) is observed to lead to an increment in lattice constant from 12.379 Å in (100) to 12.415 Å in (111) oriented films. Atomic force microscopy images showed decreasing roughness with increasing film thickness. Compared to (100) grown films, (111) oriented films showed an increase in ferromagnetic resonance linewidth and consequent increase in Gilbert damping. The lowest Gilbert damping values are found to be (1.06±0.12) × 10 −4 for (100) and (2.30±0.36) × 10 −4 for (111) oriented films with thickness of ≈150 nm. The observed values of extrinsic linewidth, effective magnetization, and anisotropic field are related to thickness of the films and substrate orientation. In addition, the in–plane angular variation established four–fold symmetry for the (100) deposited films unlike the case of (111) deposited films. This study prescribes growth conditions for PLD grown single–crystalline Bi–YIG films towards desired high frequency and magneto–optical device applications.

Effect of polar solvents on the growth, morphology and thermoelectric properties of Bi2Te3 nano particles

Morphological tuning of nanostructures aims to enhance thermoelectric figure of merit (ZT) through a rise in the density of states near the fermi level and spatial confinement of acoustic phonons leading to reduction in thermal conductivity. In this work, we prepared Bi 2 Te 3 nanostructures with diverse morphology, by a facile and scalable single-pot hydro/solvothermal synthesis, and investigated the effect of different polar solvents on the morphology of the synthesized nanostructures. Single-phase and highly crystalline Bi 2 Te 3 with diverse morphologies including nanoparticles, nanosheets, nano and micro flakes, nanotubes and nanoflowers were grown in different polar solvent media. The Materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and selected area diffraction pattern (SAED). A possible growth mechanism for Bi 2 Te 3 nanostructures is proposed by considering the physical and chemical properties of the polar solvents, with special focus on their dielectric properties. The thermoelectric properties of the hot pressed samples were investigated in the temperature range of 300–480 K. The fermi level is found to be shifted by morphological tuning of nanostructures. The carrier concentration and transport parameters are found to be greatly influenced by the morphology of consolidated particles. A peak figure of merit of 0.46 was obtained for the in-situ fullerite coated sample synthesized with ethylene glycol as medium (BTEGEDTA) at a temperature of 474 K. • Bi 2 Te 3 nanoparticles with diverse morphology were grown in different solvents as media and the thermoelectric properties are found to be varied. • In-situ fullerite coated B i2 T e3 was obtained by using ethylene glycol as medium • A possible growth mechanism is suggested by considering the chemical and physical properties of the medium. • The fermi level is found to be shifted with morphological tuning.

Structural and superconducting properties of low-temperature ultrathin PbBi<sub>3</sub> films

Bismuth (Bi), as a stable heaviest element in the periodic table of elements, has strong spin-orbit coupling, which has attracted a lot of attention as the parent material of various known topological insulators. Previous calculations predicted that Bi(111) with a thickness less than eight bilayers and the ultrathin black-phosphorus-like Bi(110) films are single-element two-dimensional (2D) topological insulators. However, it is generally believed that these crystalline bismuth phases are not superconducting or their transition temperature should be lower than 0.5 mK. Lead (Pb) is a good superconducting elementary material, and there is a relatively small difference in radius between the Bi atom and Pb atom. According to the Hume-Rothery rule, it is expected that Pb/Bi alloys in an arbitrary ratio should be superconducting. One may thus expect to form crystalline Bi based superconductors by Pb substitution, which might host intriguing topological superconductivity. While our previous work has demonstrated a low-temperature stable Pb<sub>1–<i>x</i></sub>Bi<sub><i>x</i></sub> (<i>x</i>~0.1) alloy phase in which Pb in the Pb(111) structure is partially replaced by Bi, the Bi crystalline structure-based phases of the superconducting alloys still lack in-depth research. Here, we report a new low-temperature phase of Pb-Bi alloy thin film, namely PbBi<sub>3</sub>, on the Si(111)-(7 × 7) substrate, by co-depositing Pb and Bi at a low temperature of about 100 K followed by an annealing treatment of 200 K for 2 h. Using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS), we characterize <i>in situ</i> the surface structure and superconducting properties of the Pb-Bi alloy film with a nominal thickness of about 4.8 nm. Two spatially separated phases with quasi-tetragonal structure are observed in the surface of the Pb-Bi alloy film, which can be identified as the pure Bi(110) phase and the PbBi<sub>3</sub> phase, respectively, based on their distinct atomic structures, step heights and STS spectra. The PbBi<sub>3</sub> film has a base structure similar to Bi(110), where about 25% of the Bi atoms are replaced by Pb, and the surface shows a <inline-formula><tex-math id="M2">\begin{document}$\sqrt 2 \times \sqrt 2 R{45^ \circ }$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M2.png"/></alternatives></inline-formula> reconstructed structure. The superconducting behavior of the PbBi<sub>3</sub> phase is characterized using variable-temperature STS spectra. We obtain that the superconducting transition temperature of PbBi<sub>3</sub> is about 6.13 K, and the <inline-formula><tex-math id="M3">\begin{document}$2\varDelta (0)/{k_{\text{B}}}{T_{\text{c}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M3.png"/></alternatives></inline-formula> ratio is about 4.62 using the fitting parameter of <inline-formula><tex-math id="M4">\begin{document}$\varDelta (0) = 1.22{\text{ meV}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220050_M4.png"/></alternatives></inline-formula> at 0 K. By measuring the magnetic field dependent superconducting coherence length, the critical field is estimated at larger than 0.92 T. We further investigate the superconducting proximity effect in the normal metal-superconductor (N-S) heterojunction consisting of the non-superconducting Bi(110) domain and the superconducting PbBi<sub>3</sub> domain. The N-S heterojunctions with both in-plane configuration and step-like configuration are measured, which suggest that the atomic connection and the area of the quasi-2D Josephson junctions and the external magnetic field can affect the lateral superconducting penetration length. We also observe the zero-bias conductance peaks (ZBCPs) in the superconducting gap of the PbBi<sub>3</sub> surface in some cases at zero magnetic field. By measuring d<i>I</i>/d<i>V</i> spectra at various temperatures and by adopting a superconducting Nb tip, we identify that the ZBCP originates from the superconductor-insulator-superconductor (S-I-S) junction formed between a superconducting tip and the sample. Nevertheless, the Bi(110)-based PbBi<sub>3</sub> phase may provide a possible platform to explore the intriguing topological superconducting behaviors at the vortexes under magnetic fields, or in the vicinity of the potentially topological superconducting Bi(110) islands by considering the proximity effect.

Hot carrier transport limits the displacive excitation of coherent phonons in bismuth

We performed femtosecond transient reflectivity measurements on epitaxially grown bismuth (Bi) films in the weak photoexcitation regime. Single crystalline ultrathin Bi films down to a thickness of 7 nm enabled us to determine a clear correspondence between the amplitude of the coherent A1g phonon and the photoexcitation level. We were able to empirically measure the effective hot carrier penetration length that determines the excited carrier density governing the magnitude of the coherent A1g phonon in Bi. Our findings suggest that the transport behavior of hot carriers is to be taken into consideration in order to provide insights into the mechanism for the displacive excitation of coherent phonons.

A novel Bi-based crystalline molecular material: fluorescence response of the high efficient detection and recognition of the organic amines and white luminescence tuning

A novel Bi-based crystalline molecular materials Bi(C2O4)3(NMP)2 (Bi-NMP) have successfully synthesized by the reaction of Bi(NO3)3.5H2O, N-Methylpyrrolidone (NMP) in the solution of methyl alcohol. Structural analysis indicates that the Bi-NMP shows a novel 2D planar structure. The luminescent behavior for the Bi-NMP has been investigated at room temperature. The results have shown that Bi-NMP can be used as a chemical sensor for multifunctional testing such as aliphatic amines and aromatic amines detection, because of its strong fluorescence properties. When detecting cyclohexylamine (CHA), the K was 2.5 × 105 M−1, and the detection limit was 0.99 μM. When detecting m-phenylenediamine(MPD), the Ksv was 5.5 × 103 M−1, and the detection limit was 45.7 μM. When detecting o-phenylenediamine (OPD), the K was 5.4 × 103 M−1, and the detection limit of Bi-NMP was calculated to be 49.9 μM. In particular, for o-phenylenediamine (OPD), Bi-NMP has a unique switching effect. Therefore, Bi-NMP has not only a detection function but also a recognition function for o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD). In addition, white-light emission is achieved through a reasonable tuning proportion by mixing Sm3+ in Bi-NMP.

Crystalline Sb or Bi in amorphous Ti-based oxides as anode materials for sodium storage

A simple synthesis has been developed for watermelon-like nanocomposites with Ti-based oxides as the matrix. Using the case of Sb nanocrystals in amorphous TiPOx as an example, in-situ/ex-situ techniques, first-principle calculations and control experiments confirm that the formation of Ti-based oxides promotes the reduction of Sb3+ to Sb by NH3 at an elevated temperature. A similar synthesis process also succeeds for Sb nanocrystals in amorphous TiO2 and for Bi nanocrystals in amorphous TiPOx, confirming the promising potential of this synthesis. More importantly, the nanocomposite composed by crystalline Sb in an amorphous TiPOx matrix, as the anode material for sodium storage, concurrently exhibits a long cycle life (~1000 cycles) and a high capacity retention (~82%), suggesting the advantages of watermelon-like structures.

Ultrastable High‐Energy On‐Chip Nickel–Bismuth Microbattery Powered by Crystalline Bi Anode and Ni–Co Hydroxide Cathode

On‐chip microbatteries (MBs) with excellent electrochemical performance have attracted great attention for applications in miniaturized electronics. However, the lack of strategy for well‐suited integration of microelectrodes with decent mechanical properties and high electrochemical performance in microdevices restricts the development of on‐chip MBs. This work proposes a promising planar nickel–bismuth (Ni//Bi) MB, constructed through the microelectromechanical system‐based fabrication process and facile electrodeposition of Bi anode and Ni1−xCox(OH)2 cathode. Benefiting from the large surface area and effective integration of electrodes, the fabricated Ni//Bi MB achieves a relatively high energy density of 12.3 μWh cm−2 and high stability with 84.44% capacity retention after 1000 cycles. With an attractive fabrication technique and outstanding electrochemical performance, the Ni//Bi MB shows great potential for prospective applications in portable devices/systems.

Chemical, physical and mineralogical attributes of the soils of the Sertanejo pediplain in the sisal-growing areas of the semiarid Bahia

Information and available knowledge of the soils of the Sertanejo pediplain are relatively scarce and restricted to survey data. Researches about soil characterization and classification contributes to the knowledge of different soil orders within a region and allows information to be obtained systemically based on the physical, chemical, and mineralogical properties of the soil. This study aimed to evaluate the genesis of the Sertanejo pediplain soils, through the characterization of the chemical and mineralogical properties and classification of the soils of the sisal-growing region. Five soil profiles located in Araci, Retirolândia, St. Dominic, and Valente, cities located in the sisal-growing areas of the Bahia semiarid region, were studied, described morphologically, and analyzed for chemical (pH H2O and KCl, Ca2+, Mg2+, K+, Na+, Al3+, H+ + Al3+, P, and TOC) and mineralogical attributes. Most evaluated soil classes were formed by lithological discontinuity of material. The main processes involved in the formation of such soil classes were: cumulization, accretion, and lessivage. The mineralogy of the clay fraction observed was complex and included a variety of minerals, with a predominance of kaolinite and bayerite. In addition, we also found goethite and illite in most of the studied profiles, both in the sediment, horizons P1 C2, and in the crystalline horizon P1 Cr, P2 Bi, P3 2Cr, and P5 Bi. The soils were classified up to the fourth category level, as Entisol Eutrophic Inceptisol (RRE), Alfisols Haplic typical Eutrophic (SXE), and Inceptisols Ta Eutrophic vertissólico (CXve).

Weathering of Bi-bearing tennantite

The tennantite-tetrahedrite solid-solution series [called fahlore; (Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] is widespread in many geological environments. Since it incorporates heavy metals and toxic elements, a better understanding of its weathering behaviour and details of its weathering process is important to evaluate environmental risks (emerging mainly from the mobilization of As-Sb-Bi) and local and global metal fluxes in stream waters and oceans. In this study, weathering of Bi-rich members of this mineral group was investigated using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, μXRD, and MLA.Observations reveal a succession of four distinct stages of weathering: During stage 1, irregular tubes within fahlore show an assemblage of nm- to μm-sized roméite group minerals, tripuhyite, crystalline Cu-oxides and Cu-sulfides. Stage 1 textures and secondary sulfides indicate a low redox-potential and a low fluid/rock ratio, typical of cementation zones. Mass balance calculations show that during this stage all Zn and the majority of As and S are released to the weathering fluids. Bismuth is immobile in this stage and Sb and Fe are immobile, if Bi is sufficiently available from fahlore, but both are partly released, if the fahlore did not contain sufficient Bi. During stage 2, amorphous and nano-crystalline arsenates replace fahlore as weathering fronts. Such assemblages indicate a higher redox-potential than in stage 1, typical for oxidation zones. Mass balance calculations reveal that Zn, Sb, S and partially Cu are lost. Arsenic and Bi are immobile. Stage 3 occurs only locally, dissolving former weathering stages and/or precipitating amorphous Cu-arsenates/silicates reflecting processes in micro-compartments, not characteristic for the general weathering process. Stage 4 is characterized by the formation of crystalline Bi-, Cu-, Ba-, Ca- or Al-bearing arsenates and Cu-carbonates, spatially independent of the precursor fahlore. Copper and As originate from older weathering assemblages, whereas many other elements are derived externally (Ca, Ba, Al). This stage reflects the increasing importance of the local host rock and gangue mineralogy, as it is typical in near-surface environments of oxidation zones or on mine dumps, where elements are highly mobile and a high fluid/rock ratio prevails (gossan mineralization).The temporal evolution of fahlore weathering textures reflects the transition from fresh ore to cementation zone, oxidation zone and gossan assemblages in one hand specimen. Thus, one fahlore grain can record the uplift and erosion and the increasing fluid/rock interaction of a weathered ore deposit with time. Tube-like textures similar to the ones observed in stage 1 have been reported from other weathering environments and from a variety of element, oxide, arsenide, and sulfide phases. They also were produced during experimental work in ilmenite. This is clear evidence, that the diffusive process during the first contact with alteration fluids is a basic physical process and that it is not only valid for fahlore.The importance of Bi to stabilize Sb-bearing supergene phases (and thereby for the immobilization of toxic Sb) shown in the present work, may stimulate further investigations on the environmental immobilization of toxic elements by “companion metals” during weathering processes.

Growth of a bismuth thin film on the five-fold surface of the icosahedral Ag-In-Yb quasicrystal

We present a study of growth of quasicrystalline bismuth (Bi) thin films on the five-fold surface of the icosahedral Ag-In-Yb quasicrystal using scanning tunnelling microscopy (STM). The main building block of the Ag-In-Yb quasicrystal is a rhombic triacontahedral (RTH) cluster, which is formed by successive shells of atoms. The surface is formed at bulk planes which intersect the centres of the RTH clusters. We show that the deposited Bi atoms occupy vacant sites above the surface where the atoms of the RTH clusters would be and thus Bi grows with three-dimensional quasicrystalline order. Further deposition of Bi yields crystalline Bi islands aligned along high symmetry directions of the substrate.

Sulfur-vacancy-dependent geometric and electronic structure of bismuth adsorbed on MoS2

Through Bi deposition on the single-crystalline $\mathrm{Mo}{\mathrm{S}}_{2}$ surface, we find that the density of the sulfur vacancy is a critical parameter for the growth of the crystalline Bi overlayer or cluster at room temperature. Also, the $\mathrm{Mo}{\mathrm{S}}_{2}$ band structure is significantly modified near \ensuremath{\Gamma} due to the orbital hybridization with an adsorbed Bi monolayer. Our experimental observations and analysis in combination with density functional theory calculation suggest the importance of controlling the sulfur vacancy concentration in realizing an exotic quantum phase based on the van der Waals interface of Bi and $\mathrm{Mo}{\mathrm{S}}_{2}$.

Controlling conductivity by quantum well states in ultrathin Bi(111) films

Epitaxial Bi(111) films were subject to many and partly even controversial studies on the semimetal-semiconductor transition triggered by a robust quantum confinement. The residual conductance was ascribed to conducting surface channels. We investigated ultrathin crystalline Bi films on Si(111) as a function of film thickness $d$ between 20 and 100 bilayers by means of electric transport measurements. Varying temperature and magnetic field, we disentangled two transport channels. One remains indeed metallic at all thicknesses investigated and exhibits a slightly increasing conductance as a function of $d$, whereas the second is activated with a ${d}^{\ensuremath{-}1}$ dependence of the activation energy, indicating a quasiharmonic confining potential. Both channels reflect the electronic properties of the entire film and do not allow us to strictly separate surface and bulk states. While there is clearly no bulk conductivity, the activated channel is consistently described as electronic excitation into the partly occupied quantum well states, which are also responsible for the metallic conductance and preferentially located close to both interfaces of the film.

A highly crystalline bismuth superstructure for ultrastable and high-performance flexible aqueous nickel–bismuth batteries

This work constitutes a facile and realizable electrochemical approach to prepare a three-dimensional (3D) highly crystalline Bi superstructure as a high-performance anode for aqueous nickel–bismuth batteries.

TEMPERATURE DEPENDENCE ON THE MORPHOLOGICAL EVOLUTION OF DILUTE InAsBi/GaAs NANOSTRUCTURES GROWN BY METALORGANIC VAPOR PHASE EPITAXY

In this work, we discuss the growth of dilute InAsBi nanostructures grown by metalorganic vapor phase epitaxy on GaAs substrates. The surface morphology of InAsBi nanostructures is carefully investigated, as a function of the growth temperature, by scanning electronic microscopy and atomic force microscopy. (004) High-resolution X-ray diffraction configuration has been used to characterize the crystalline quality and Bi incorporation in the InAsBi films. Low temperature and low Bi flow favor the formation of elongated nanostructures during growth. We give a quantitative description of the elemental processes for the formation of these nanostructures. Our description is based on the Tersoff and Tromp theoretical model.