Hexagonal Bi Research Articles

Low energy electron diffraction of epitaxial growth of bismuth on Si(1 1 1)

The epitaxial growth of Bi on Si(1 1 1) studied by spot profile analyzing low energy electron diffraction shows for low coverage rotationally disordered Bi cluster with preferred orientations following the threefold symmetry of the Si substrate. With further deposition the Bi cluster coalesces and the surface orientation changes from the pseudo cubic Bi(1 1 0) surface orientation of the Bi cluster into the hexagonal Bi(1 1 1) surface of the resulting Bi film.

STM/STS Studies of the Structural Phase Transition in the Growth of Ultra-Thin Bi Films on Si(111)

Growth of thin metal films on semiconductors has been always an important subject for extensive experimental and theoretical studies. As the applicability of well-ordered nanostructures in electronic applications depends strongly on their size and distribution, it is necessary to understand the processes that govern the growth of such structures. In this paper we present the results of investigation of the room temperature growth of thin Bi film on Si(111). In our study we clarified that rotationally disordered, pseudo-cubic Bi{012} islands with uniform height of 13 A are formed in the initial stage of Bi film growth. With increase in the amount of bismuth on the surface, islands interconnect maintaining however their uniform height. This process is further accompanied by the unique and unexpected structural phase transition of the {012} film into a hexagonal Bi(001) film.

Preparation and characterization of wire-like Sb 2Se 3 and flake-like Bi 2Se 3 nanocrystals

Crystalline Sb 2Se 3 and Bi 2Se 3 have been prepared through the reaction between SbCl 3 (or BiCl 3) and elemental selenium using sodium sulfite as a reducing reagent. TEM images show that the as-prepared Sb 2Se 3 comprise uniform nanowires, while Bi 2Se 3 crystals exhibit a hexagonal flake-like morphology. The optical absorption of the products has been investigated, and the optical band gap energy for direct transition in Sb 2Se 3 nanowires is found to be 1.46 eV. The composition of the as-prepared products has been identified by XPS. The reaction mechanism is discussed in detail, and it is proposed that the oriented growth behavior of Sb 2Se 3 and Bi 2Se 3 crystals is determined by their cleavage nature. The chain-like arrangement of Sb and Se atoms parallel to the c-axis in the orthorhombic lattice and the two-dimensional assembly of Bi and Se atoms perpendicular to the c-axis in the hexagonal cell contribute to the formation of wire-like Sb 2Se 3 and flake-like hexagonal Bi 2Se 3 crystals, respectively. These arguments can also be applied to explain the growth behavior of other V 2VI 3-type crystals.

Ion-Beam-Assisted Nanocrystal Formation in Silicon Implanted with High Doses of Pb+ and Bi+ Ions

In this paper we discuss ion-beam-assisted nanocrystal nucleation in amorphized silicon (a-Si) layers produced by high-dose implantation of Pb+ and Bi+. (100)-oriented Si wafers were implanted at room temperature (RT) with 50 keV Pb+ and Bi+ ions at doses ranging from 5×1013 to 1×1018 cm-2 and a constant ion current density of 10 µA cm-2. The resulting structures were studied by conventional transmission electron microscopy (CTEM), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectroscopy (RBS) in combination with computer simulations. The dynamics of the ion-beam-induced crystallization of new phases and precipitates evolution in the implanted layer were studied as a function of implant dose. It is established that the front of the new phase crystallization (cubic Pb and hexagonal Bi nanocrystals) starts approximately at the peaks of the implanted species profiles; the crystallography of the nucleated nanocrystal is examined as a function of the dose.

Lead-antimony sulfosalts from Tuscany (Italy). IV. Crystal structure of pillaite, Pb9Sb10S23ClO0.5, an expanded monoclinic derivative of hexagonal Bi(Bi2S3)9I3, from the zinkenite group

The crystal structure of pillaite, a recently described Pb-Sb oxy-chloro-sulfosalt from the Buca della Vena mine, Tuscany (Italy), was solved and refined to a residual R of 0.045 in the monoclinic system, with space group C2/m, and a = 49.49(1), b = 4.1259(8), c = 21.828(4) A, β = 99.62(3) 0 , V = 4394(2) A3. The structural formula is Pb 9.16 Sb 9.84 S 23 ClO 0.5 , corresponding to the electron-microprobe one Cu 0.10 Pb 9.16 Sb 9.84 S 22.94 Cl 1.06 O 0.5 (ideally Pb 9 Sb 10 S 23 ClO 0.5 ), with Z = 4 and D cale. = 5.87. The crystal structure is organized around pseudo-threefold axes where chlorine atoms are in a trigonal prismatic coordination with Pb atoms. An oxygen position, half-filled, is bonded to two Sb atoms, like in scainiite. Pairs of pseudo-trigonal rods parallel to the elongation b-direction are connected along [102] to form rod-layers. The pillaite structure is an expanded homologue of hexagonal Bi(Bi 2 S 3 ) 9 I 3 . Among lead sulfosalts, it belongs to the zinkenite group of cyclically twinned structures. Pillaite is the first example of a Pb-Sb sulfosalt where small amounts of two anion species simultaneously play a specific crystal chemical role, which is essential for the stabilization of the crystal structure: chlorine, like in dadsonite, and oxygen, like in scainiite.

Synthesis and Formation Mechanism of Bi(Se,S) Nanowires via a Solvothermal Template Process

Abstract Hexagonal Bi(Se,S) nanowires (20 nm × 1.5 µm) were prepared for the first time via a mild solvothermal template reaction of BiCl3 with triphenylphosphine sulfide (TPPS) and elemental Se in ethylenediamine (en) at 120 °C for 20 h. In this process, the sulfur source TPPS as a template, the solvent ethylenediamine, and reaction temperature were critical factors of forming hexagonal Bi(Se,S) nanowires.

ChemInform Abstract: Ionic Conductivity and Structural Phase Transformations for Hexagonal and Cubic Bi1.33U0.33La0.33O3.5 Polymorphs.

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Ionic Conductivity and Structural Phase Transformations for Hexagonal and Cubic Bi1.33U0.33La0.33O3.5 Polymorphs

The hexagonal and cubic Bi1.33U0.33La0.33O3.5 polymorphs have been synthesized by heating at 950 °C a mixture of Bi2O3 and LaUO4+x. When the reaction mixture is slowly cooled to room temperature, the hexagonal phase with cell parameters aH = 4.0285(3) Å, cH = 9.5494(8) Å is formed. Quenching of the mixture from 950 °C leads to the formation of the cubic phase with a fluorite-type structure, aC = 5.641(1) Å. The hexagonal and cubic materials are good oxide ion conductors, the conductivity being higher for the cubic polymorph. The conductivity vs temperature for both polymorphs shows several linear dependencies, which are ascribed to different crystalline phases identified by X-ray powder diffraction. An intermediate hexagonal phase different from the starting hexagonal one is found. The schemes of the structural transformations with temperature are established, and the relationships between conductivity properties and phase transformations are pointed out.

Low temperature crystal growth of MnBi films

The relation between deposition conditions of Bi and Mn layers and crystal growth of MnBi were investigated to reduce the MnBi annealing temperature for its application to a magneto-optical disk. We found that higher c-axis orientation of the hexagonal Bi layer and lower Mn oxide concentration in the Mn layer reduces the annealing temperature. Growth of MnBi below 150/spl deg/C, which is much lower than the decomposition temperature of photo-polymer (about 200/spl deg/C), was achieved by optimizing deposition conditions of Bi and Mn layers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multilayered structure and anisotropic electrical properties of (SiO2)100−x(Pb0.6Bi0.4)x alloys prepared by a combined technique of mechanical alloying and hot pressing

Compacted (SiO2)100−x(Pb0.6Bi0.4)x (x=20–80 at. %) materials, prepared by mechanical alloying (MA) of amorphous SiO2, fcc Pb, and rhombohedral hexagonal Bi followed by hot pressing of the MA powder at 473 K for 1.8 ks under an applied stress of 250 MPa, were found to have a unique layered structure consisting of amorphous SiO2 and hexagonal close-packed (hcp) ε(Pb-Bi) phases which developed along the direction perpendicular to the uniaxial applied load. The thickness and interlayer distance of the layered ε (Pb-Bi) phase are about 1.5 and 7 μm, respectively, for (SiO2)50Pb30Bi20. Furthermore, the multilayered compacts exhibited a strong anisotropy of electrical resistivity and superconducting properties when their properties are measured along the directions parallel or perpendicular to the layer. Electrical resistivity at 300 K, superconducting critical temperature (Tc), and upper critical magnetic field (Hc2) at 4.2 K are 10.5 μΩ m, 8.5 K, and 2.29 T, respectively, for the parallel direction and 950 μΩ m, 6.9 K, and 0.24 T, respectively, for the perpendicular direction. The strong anisotropy of electrical resistivity and superconducting properties is presumably due to a significant difference in the linkage of electrical path between the parallel and perpendicular directions.

Adsorption and growth modes of Bi on Pt(111)

The vapor deposition of Bi on Pt(111) at 110 and ∼600 K have been characterized by Auger electron spectroscopy (AES), thermal desorption mass spectroscopy (TDMS), low-energy electron diffraction (LEED), and changes in the work function (Δφ). At 110 K Bi growth follows a layer-by-layer mechanism. At ∼600 K Bi fills the first monolayer (θBi≂0.56) relatively uniformly, followed by 3D island growth. Bi desorption is characterized by a large, coverage-dependent desorption energy, Edes =(81−34.2 θBi ) kcal mol−1, in the first monolayer, and zero-order kinetics with constant activation energy (Edes =53–56 kcal mol−1) for the multilayer. Many LEED patterns are observed within the first monolayer for both cold and hot substrates. Structural models for these are proposed which are consistent with coverages obtained by AES. Annealed structures show continuous compression of hexagonal Bi overlayers with increasing coverage, subject to mild substrate constraints. At 110 K and θBi &amp;gt;0.33, uniaxial compression is instead seen, due to an unsurmounted energy barrier. Weakly repulsive lateral Bi–Bi interactions (due to dipole repulsions) dominate submonolayer growth. These results for the semimetal Bi are intermediate in behavior between alkali and transition metal overlayers on Pt(111). This is consistent with the relative strengths of the surface dipole of these adsorbed metals.

Photoelectric emission and work functions of InSb, GaAs, Bi 2Te 3 and germanium

Measurements have been made of the energy distributions of photoelectrons emitted by various semiconductor surfaces freshly exposed by breaking in high vacuum ( $ ̃ 10 −8 mm). The data have been used to obtain the variation with energy of the density of states in the valence band, multiplied by a photoelectric excitation probability. Spectral distributions of the photoelectric yield and accelerating field characteristics were also measured. Marked differences were found between the energy-dependence of the photoemission of the hexagonal structure Bi 2Te 3 on the one hand, and the three diamond-structure semiconductors on the other. Work functions found were: 4.57 eV for InSb, 4.69 eV for GaAs, and 4.75 eV for germanium, the clean faces being composed of (110) facets for the intermetallic semiconductors and of (111) facets for the germanium. For Bi 2Te 3, mirror-like (0001) cleavage planes had a work function of 5.30 eV.