Hexagonal Bi Research Articles

Fabrication and characterization of Sn-57 wt% Bi film by pulse DC current co-electrodeposition and reflow

The electrodeposited Sn-Bi eutectic alloys can satisfy the need for micro-bumps with low melting point in 3D packaging. We deposited Sn-Bi film by pulse DC current in electroplating solutions based on methane sulfonic acid (MSA). The effects of MSA concentrations and pulse frequencies on morphology and composition of deposits were investigated. As the MSA concentration increased from 120 ml/L to 160 ml/L, the hydrogen evolution reaction weakened resulting in smoother deposited surfaces, and the Bi content decreased. In the use of pulses allowing deposits to become more uniform and denser, the Sn-56.73 wt% Bi film with smooth surfaces were fabricated at a pulse frequency of 4 Hz and an MSA concentration of 120 ml/L, of which melting point was 134.35 °C. By using transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD), the structures were characterized more microscopically, which are essential for diffusion and electromigration of micro-bumps. The near-eutectic deposits, both before and after reflowing, consisted of uniformly distributed tetragonal β-Sn phases and hexagonal Bi phases, and the most preferred orientations after reflowing were the same as before reflowing, that were (220)//ND for β-Sn and (1̅012)//ND for Bi. The average grain sizes of Sn and Bi in the deposits after reflowing were 1.44 µm and 0.64 µm, respectively, which were much smaller than those of Sn58Bi alloy obtained by rapid solidification. Dislocations were observed in Sn grains and misorientation values in β-Sn phases were larger, which illustrated that the β-Sn phase carried larger strains. As evaluated by constant loading rate (CLR) nanoindentation tests, the hardness and modulus were significantly improved after reflowing, and creep stress indices of the deposits before and after reflowing were 51.74 and 7.07, respectively.

Reversible Lithium-Ion Storage in h-Bi2Ge3O9-Based Anode: Experimental and Theoretical Studies

The new Li-ion host anode, h -Bi 2 Ge 3 O 9 , exhibits a remarkably high capacity after 200 cycles, which is promoted by its moderate volume expansion and its low activation energy of diffusion for Li-ions. • The hexagonal Bi 2 Ge 3 O 9 structure can deliver a stable performance as Li-host anode. • The h -Bi 2 Ge 3 O 9 structure can store 40Li/mol and suffer a moderate expansion of 112%. • Li-ion diffusion into the h -Bi 2 Ge 3 O 9 structure occurs via a zigzag movement. A promising high-capacity anode material, h -Bi 2 Ge 3 O 9 with benitoite phase, was successfully prepared by a versatile two-step method that involves: (i) an initial sol–gel process, followed by (ii) air thermal treatment at high temperature. Due to its unique physico-chemical and electrochemical features, the h -Bi 2 Ge 3 O 9 -based electrode can reversibly store 18.1 mols of lithium (Li) per mol of h -Bi 2 Ge 3 O 9 , delivering a high capacity of 621.9 mAh/g at 200 mA g −1 with good coulombic efficiency of >99.5 %, reasonable capacity retention of 77 % and low electrode polarization (41 mV) after 200 cycles. According to density functional theory (DFT) calculations, the h -Bi 2 Ge 3 O 9 structure could store 40Li atoms, Li 40 Bi 2 Ge 3 O 9 , with a stable formation energy ( E f ) of −1.20 eV, suffering a volume expansion of 112 %. Also, the simulation revealed the rupture of Bi-O and Ge-O bonds, which promote the formation of new interactions as Li-Bi, Bi-Bi, Li 3 Bi, Li-Ge, Ge-Ge and Li 4 Ge in the h -Bi 2 Ge 3 O 9 crystal as the concentration of lithium rises upon lithiation. Initially, Li-ions are preferentially stored at tetrahedral sites, coordinated with 4 oxygen atoms ( E f = − 0.49 eV), and its diffusion into h -Bi 2 Ge 3 O 9 crystal occurs via a zig-zag movement through its monolayer with a favorable activation energy barrier of ∼0.70 eV.

The impact of intermetallic compound on microstructure, mechanical characteristics, and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder

PurposeThis study aims to study the impact of intermetallic compound on microstructure, mechanical characteristics and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder.Design/methodology/approachIn this paper, a new group of lead-free high-temperature Pb-free solder bearing alloys with five weight percentages of different silver additions, Bi-Agx (x = 3.0, 3.5, 4.0, 4.5 and 5.0 Wt.%) have been developed by rapidly solidification processing (RSP) using melt-spun technique as a promising candidate for the replacement of conventional Sn-37Pb common solder. The effect of the addition of a small amount of Ag on the structure, microstructure, thermal and properties of Bi-Ag solder was analyzed by means of X-ray diffractometer, scanning electron microscopy, differential scanning calorimetry and Vickers hardness technique. Applying the RSP commonly results in departures from conventional microstructures, giving an improvement of grain refinement. Furthermore, the grain size of rhombohedral hexagonal phase Bi solid solution and cubic IMC Bi0.97Ag0.03 phase is refined by Ag addition. Microstructure analysis of the as soldered revealed that relatively uniform distribution, equiaxed refined grains of secondary IMC Bi0.97Ag0.03 particles about 10 µm for Bi-Ag4.5 dispersed in a Bi matrix. The addition of trace Ag led to a decrease in the solidus and liquidus temperatures of solder, meanwhile, the mushy zone is about 11.4°C and the melting of Sn-Ag4.5 solder was found to be 261.42°C which is lower compared with the Sn-Ag3 solder 263.60°C. This means that the silver additions into Bi enhance the melting point. The results indicate that an obvious change in electrical resistivity (?) at room temperature was noticed by the Ag addition. It was also observed that the Vickers microhardness (Hv) was increased with Ag increasing from 118 to 152 MPa. This study recommended the use of the Bi-Ag lead-free solder alloys for higher temperature applications.FindingsSilver content is very important for the soldering process and solder joint reliability. Based on the present investigations described in this study, several conclusions were found regarding an evaluation of microstructural and mechanical deformation behavior of various Bi-Ag solders. The effect of Ag and rapid solidification on the melting characteristics, and microstructure of Bi-Ag alloys were studied. In addition, the mechanical properties of Bi with different low silver were investigated. From the present experimental study, the following conclusions can be drawn. The addition of Ag had a marked effect on the melting temperature of the lead-free solder alloys, it decreases the melting temperature of the alloy from 263.6 to 261.42°C. Bi-Ag solders are comprised of rhombohedral Hex. Bi solid solution and cubic Ag0.97Bi0.03 IMC is formed in the Bi matrix. The alloying of Ag could refine the primary Bi phase and the Bi0.97Ag0.03 IMC. With increasing Ag content, the microstructure of the Bi-Ag gradually changes from large dimples into tiny dimple-like structures. The refinement of IMC grains was restrained after silver particles were added into the matrix. The inhibition effect on the growth of IMC grains was most conspicuous when solder was doped with Ag particles. As a result, the Vickers microhardness of the Bi-Ag lead-free solder alloys was enhanced by more than 100% ranging from 118.34 to 252.95 MPa. Bi-Ag high-temperature lead-free solders are a potential candidate for replacing the tin-lead solder (Sn-37Pb) materials which are toxic to human and the environment and has already been banned.Originality/valueThis study recommended the use of the Bi-Ag lead-free solder alloys for high-temperature applications.

Ultrathin epitaxial Bi film growth on 2D HfTe2 template

Among ultrathin monoelemental two-dimensional (2D) materials, bismuthene, the single layer of heavier group-VΑ element bismuth (Bi), has been predicted to have large non trivial gap. Here, we demonstrate the growth of Bi films by molecular beam epitaxy on 2D-HfTe2 template. At the initial stage of Bi deposition (1–2 bilayers, BL), both the pseudocubic Bi(110) and the hexagonal Bi(111) phases are formed. When reaching 3 BL Bi, a transformation to pure hexagonal Bi(111) occurs. The electronic band structure of 3 BL Bi(111) films was measured by angle-resolved photoemission spectroscopy showing very good matching with the density functional theory band structure calculations of 3 BL free standing Bi(111). The grown Bi(111) thin film was capped with a protective Al2O3 layer and its stability under ambient conditions, necessary for practical applications and device fabrication, was confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy.

On the importance of hexagonal phases in TM (TM = Ti, Zr, and Hf) mono-nitrides

Phase transitions are an important topic in the understanding of the properties of IVb group mono-nitrides (IVbTMNs) and their applications. Until now, only structural phase transitions concerning cubic phases that are far away from the ground state have been reported. However, previous reports have suggested a possible transformation to the Bk(BN-type) hexagonal phase as well. With this in mind, this work aims to study the stability of phase transitions involving hexagonal phases. Here, we perform a complete theoretical study based on the density functional theory approach of the crystal and vibrational and electronic structures of several phases for IVbTMN (TM = Ti, Zr, and Hf) compounds. Among these, the hexagonal phases are known to be stable in the V−VITMN homologous systems. Our study reveals the existence of a new pressure-induced phase transformation at the compression regime from B1 (Nacl-type) to Bi (AsTi-type) for ZrN and from B1 to Bk at the expansion regime for all IVbTMN. In addition, we have found that hexagonal Bi, Bk, and trigonal LiSnS2-type phases are close to the ground state and are dynamically stable. However, the metal weight plays a crucial role in the stability of hexagonal phases. The stability of the Bi and Bk hexagonal phases is important since they might represent intermediate states in the cubic B1 to B4 phase transition of the alloyed IVbTMN.

Nanobismuth enhanced plasmonic, emission and Faraday rotation properties of diamagnetic tellurite glasses

Bismuth has played important roles in metal and condensed matter physics. This paper reports the influence of Bi nanoparticle to diamagnetic tellurite glass-forming, structure, spectra andproperties. 30 nm hexagonal pure Bi nanoparticles (NPs) presented an obvious SPR effect around 275 nm, broad emission FWHM (200 nm) and superparamagnetic behavior. Successfully incorporated of nanobismuth (<5%) into glass and the BiNPs modifications on TeO4, TeO3 and NBOs structure has been confirmed through FT-IR, Raman spectra, DSC and Urbach energy measurement. UV–visible spectra showed SPR peak of BiNPs at 508 (glass) and 700 nm (metal-glass) with gradually increased intensities and gradually broadened cross-sections with doping amount. The visible and infrared luminescence show characteristic emission of BiNPs at 460 nm, 730 nm, 910 nm and 1150 nm respectively. All samples exhibited diamagnetic property and the magnetization increased with the doping amount due to the diamagnetic nature of host and dopant. The increased polarizability and intense SPR effect enhanced Faraday rotation and a large Verdet constant (0.1828 min/G.cm) at 633 nm was obtained for 5%BiNPs doped glass which also exhibited large thermal stability and good luminescence performance.

Low-Energy Phases of Bi Monolayer Predicted by Structure Search in Two Dimensions.

We employ an ab-initio structure search algorithm to explore the configurational space of bismuth in quasi-two dimensions. A confinement potential is introduced to restrict the movement of atoms within a predefined thickness to find the stable and metastable forms of monolayer Bi. In addition to the two known low-energy structures (puckered monoclinic and buckled hexagonal), our calculations predict three new phases: α, β, and γ. Each phase exhibits peculiar electronic properties, ranging from metallic (α and γ) to semiconducting (puckered monoclinic, buckled hexagonal, and β)monolayers. Topologically nontrivial features are predicted for buckled hexagonal and γ phases. We also remark on the role of 5d electrons on the electronic properties of Bi monolayer. We conclude that Bi provides a rich playground to study distortion-mediated metal-insulator phase transitions in quasi-2D.

The study of the structure stability of hexagonal Bi(PO4)(H2O)0.67 under high pressure

In this work, the structure stability of hexagonal Bi(PO[Formula: see text](H2O)[Formula: see text] has been investigated by high-pressure synchrotron X-ray diffraction measurements. The results show that the structure is stable within the pressure up to 18.3 GPa. The diffraction data are refined and the lattice constants [Formula: see text] and [Formula: see text] are determined, which is compressed by 6.3(7)% and 3.5(0)% within the experimental pressure, respectively. By fitting the pressure dependence of [Formula: see text] (unit cell volume divided by that at ambient pressure) with the second-order Birch equation of state, the bulk modulus [Formula: see text] is given to be about 87.1(0) GPa.

Shape and stoichiometry control of bismuth selenide nanocrystals in colloidal synthesis

Temperature-dependent synthesis of hexagonal, disk-like and octahedron-like Bi–Se nanocrystals.

Synthesis and characterization of high-purity, single phase hexagonal Bi2Te3 nanostructures

Schematic solvothermal synthesis of Bi2Te3 (a) producing Bi2Te3 hexagonal nanoplates (TEM) (b) which was converted into pellet (c). The electrical characterization (d) of the Bi2Te3 pellet surface showed significantly high current (more than 100 times) than through the pellet.

Large Hexagonal Bi‐ and Trilayer Graphene Single Crystals with Varied Interlayer Rotations

AbstractBi‐ and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high‐quality large‐size bi‐ and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid‐like hexagonal bi‐ and trilayer graphene single‐crystal domains on Cu foils using chemical vapor deposition is reported. The as‐produced graphene domains show almost exclusively either 0° or 30° interlayer rotations. Raman spectroscopy, transmission electron microscopy, and Fourier‐transformed infrared spectroscopy were used to demonstrate that bilayer graphene domains with 0° interlayer stacking angles were Bernal stacked. Based on first‐principle calculations, it is proposed that rotations originate from the graphene nucleation at the Cu step, which explains the origin of the interlayer rotations and agrees well with the experimental observations.

Large Hexagonal Bi‐ and Trilayer Graphene Single Crystals with Varied Interlayer Rotations

Bi- and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high-quality large-size bi- and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid-like hexagonal bi- and trilayer graphene single-crystal domains on Cu foils using chemical vapor deposition is reported. The as-produced graphene domains show almost exclusively either 0° or 30° interlayer rotations. Raman spectroscopy, transmission electron microscopy, and Fourier-transformed infrared spectroscopy were used to demonstrate that bilayer graphene domains with 0° interlayer stacking angles were Bernal stacked. Based on first-principle calculations, it is proposed that rotations originate from the graphene nucleation at the Cu step, which explains the origin of the interlayer rotations and agrees well with the experimental observations.

Nontrivial topological electronic structures in a single Bi(111) bilayer on different substrates: A first-principles study

Electronic structures, minimum energy configurations, and band topology of strained Bi(111) single bilayers placed on a variety of semiconducting and insulating substrates are investigated using first-principles calculations. A topological phase diagram of a free-standing Bi bilayer is presented to help guide the selection of suitable substrates. The insulating hexagonal-BN is identified as the best candidate substrate material for supporting nontrivial topological insulating phase of Bi bilayer thin films. A planar hexagonal Bi layer is predicted under tensile strain, which we show could be realized on a SiC substrate. The Bi bilayer becomes metallic under the compressive strain induced by Si and Ge substrates.

Microstructure and magnetic properties of a novel 10-H hexagonal perovskite nanosheet in a Bi–Fe–Cr–O system

A novel 10-H hexagonal Bi(FeCr)O3 (BFCO) perovskite nanosheet is synthesized by pulsed-laser ablation. Transmission electron microscopy (TEM) studies prove that the crystal structure of this phase is hexagonal-type with a P63/mmc space group. The atomic stacking sequence, revealed by high-resolution TEM, can be described as hhhcchhhcc in h–c notation. The magnetic properties of 10-H hexagonal BFCO perovskites are studied by both magnetic hysteresis loop measurements and first-principles calculations. The net magnetization of 10-H hexagonal BFCO comes from the anti-parallel spin moment of the Fe3+ and Cr3+ cations. The stability of the novel 10-H BFCO is also discussed by calculating its Goldschmidt factor and formation enthalpy. This work demonstrates the structural diversity in the Bi–Fe–Cr–O system, which may open the feasibility to explore the multi-functionality of this system.

Growth of Bi2Te3 quantum dots/rods in glass: a unique highly stable nanosystem with novel functionality for high performance magneto optical devices

Magneto optical materials are currently of great interest, primarily for modern applications in optical isolation, modulation and switching in telecommunication. However, single crystals are the benchmark materials still used in these devices which are rather expensive and very difficult to fabricate. In this context, we are reporting herewith a stable and novel Bi(2)Te(3) quantum dot-glass nanosystem obtained using a controlled thermo-chemical method. The Q-dots of hexagonal Bi(2)Te(3) of size 4 to 14 nm were grown along the <1 1 3> direction. Surprisingly, we obtained quantum rods of Bi(2)Te(3) of size 6 × 10 nm for the first time. The strong quantum confinement in the nanosystem is clearly shown by the optical study. The band gap of the host glass was drastically reduced (from 4.00 to 1.88 eV) due to the growth of Bi(2)Te(3) quantum dots whereas photoluminescence showed a Stokes shift ~175 meV. Faraday Rotation (FR) investigations of the Bi(2)Te(3) quantum dot-glass nanosystem show a nonlinear response in Verdet constant with a decrease in the Bi(2)Te(3) dot sizes. The Bi(2)Te(3) Q-dot-glass nanosystem with ~4 nm dots shows significant enhancement (70 times) in Verdet constant compared to the host glass and more radically better than conventional single crystal (TGG). This is the first time that such a type of unique nanosystem has been architectured and has given extremely good magneto-optical performance. We strongly feel that this novel nanosystem has tremendous applications in magneto-optical devices. It is noteworthy that expensive single crystals can be replaced with this cost effective novel glass nanosystem. Interestingly, the present quantum dot-glass nanosystem can be transformed into optical fibers very easily, which will have an exceptionally high impact on the fabrication of high performance magneto optical devices.

Influence of NaOH on the formation and morphology of Bi 2Te 3 nanostructures in a solvothermal process: From hexagonal nanoplates to nanorings

Abstarct Hexagonal bismuth telluride (Bi 2 Te 3 ) nanoplates and nanorings were synthesized by a simple solvothermal process. The composition, morphology and size of the as-prepared products were investigated by X-ray diffraction and transmission electron microscopy in detail. The systemically experiments have been performed to investigate the effect of alkaline additive NaOH on composition and morphology of Bi 2 Te 3 nanostructures. The results indicate that alkaline additive NaOH is not necessary for the formation of Bi 2 Te 3 nanostructures in a solvothermal process. However, NaOH plays an important role in determining the morphology and size of Bi 2 Te 3 nanostructures. When the experiment was carried out with NaOH concentration ranging from 5 to 7 M, hexagonal Bi 2 Te 3 nanoplates with edge length of 140–280 nm were synthesized. When the experiment was carried out at higher NaOH concentration of 9–11 M, hexagonal Bi 2 Te 3 nanorings were fabricated by dissolving the inner part of the hexagonal nanoplates with NaOH for the first time. A possible formation mechanism has been proposed based on the experimental results and analysis. This work may open a new rational route for the synthesis of hexagonal Bi 2 Te 3 nanorings which may have some scientific and technological applications in various functional devices.

Raman scattering investigation of Bi 2Te 3 hexagonal nanoplates prepared by a solvothermal process in the absence of NaOH

Hexagonal Bi 2Te 3 nanoplates were synthesized by a simple solvothermal process in the absence of NaOH. The composition, morphology and size of the as-prepared products were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Raman scattering optical properties of the as-prepared Bi 2Te 3 nanoplates were investigated by micro-Raman spectroscopy. The Raman spectrum shows that infrared (IR) active mode (A 1u), which must be odd parity and is Raman forbidden for bulk crystal due to its inversion symmetry, is greatly activated and shown up clearly in Raman scattering spectrum. We attribute the appearance of infrared active (A 1u) in Raman spectrum to crystal symmetry breaking of Bi 2Te 3 hexagonal nanoplates. The as-grown Bi 2Te 3 hexagonal nanoplates, exhibiting novel Raman optical properties compared with bulk crystals, may find potential applications in thermoelectric devices.

Structure and reactivity of Bi allotropes on the fivefold icosahedral Al–Pd–Mn quasicrystalsurface

The growth of Bi on a pseudomorphic Bi monolayer on the fivefold surface ofthe icosahedral Al–Pd–Mn quasicrystal has been investigated using low energyelectron diffraction and scanning tunnelling microscopy. Initially randomly orientedpseudocubic islands are formed with a preference for an even number of layers.Subsequently a morphological transformation takes place to hexagonal Bi islands,which align along high symmetry directions of the substrate. The Bi fluxis found to have a strong effect on which island structure is preferred. WhenC60 is adsorbed on the three different allotropes of Bi present in this system, hexagonalC60 islands are formed in each case. On the pseudocubic and hexagonal islands, theC60 islands are aligned with the substrate. We discuss the energetic, kinetic and geometricalfactors which influence the morphological transformation referred to above.

Synthesis and characterization of carbon nanotube supported Bi 2Te 3 nanocrystals

Multiwalled carbon nanotube (MWNT) supported Bi 2Te 3 nanoparticle heterostructures were firstly synthesized using a microwave-polyol method assistant with titration. The microwave heating process was adopted to yield nanoscale Bi 2Te 3 by accelerating chemical reaction rate. And the titration of Bi 2Te 3 precursors was conducted to make the nanoparticles grow onto surfaces of MWNTs easily. The general morphology of resulting composites is hexagonal Bi 2Te 3 nanoplates and their aggregates attached on surfaces of MWNTs randomly. When the diameter of MWNT is rather shorter, Bi 2Te 3 crystallites are encapsulated into inner cores of nanotubes.

STM/STS STUDIES OF THE INITIAL STAGE OF GROWTH OF ULTRA-THIN Bi FILMS ON 7 × 7-Si(111) SURFACE

The results of investigation of the room temperature growth of thin Bi films on Si (111)-7 × 7 are present. In the initial stage of Bi film growth the rotationally disordered, pseudo-cubic, Bi {012} islands with a uniform height of 13 Å are formed. With increasing bismuth on the surface, islands interconnect, maintaining however their uniform height, and structural phase transition of the {012} film into a hexagonal Bi (001) film takes place.