Bi Thin Films Research Articles

Study of the integrated fluence threshold condition for the formation of β-Bi2O3 on Bi thin films by using ns laser pulses

The formation of β-Bi2O3 through laser irradiation of a bismuth (Bi) thin film is reported. The bismuth thin films were irradiated in atmospheric air using Nd:YAG laser pulses of 7 ns duration and 1064nm wavelength. A set of irradiations was done on the samples varying the total irradiation time (i. e. the number of pulses) for a fix per pulse laser fluence of 25mJ/cm2. The laser processed regions were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and microRaman spectroscopy (mRS). OM results show that the laser modified cross section on the film is smaller than the laser beam cross section, which means a thermally confined interaction; SEM micrographs reveled the formation of submicron sized particles as a result of the multi-pulse laser irradiation; using microRaman spectroscopy characterization we were able to determine the formation of the β-Bi2O3 crystalline phase within the laser irradiated spot on the sample.

Studying The Optical Properties of CdO and CdO: Bi Thin Films

Cadmium Oxide and Bi doped Cadmium Oxide thin films are prepared by using the chemical spray pyrolysis technique a glass substrate at a temperature of (400?C) with volumetric concentration (2,4)%. The thickness of all prepared films is about (400±20) nm. Transmittance and Absorbance spectra are recorded in the wave length ranged (400-800) nm. The nature of electronic transitions is determined, it is found out that these films have directly allowed transition with an optical energy gap of (2.37( eV for CdO and ) 2.59, 2.62) eV for (2% ,4%) Bi doped CdO respectively. The optical constants have been evaluated before and after doping.

Room-temperature electrochemical reduction of epitaxial Bi2O3 films to epitaxial Bi films

A new facile approach to fabricate high-quality epitaxial Bi thin films at room-temperature with enhanced magnetotransport properties has been reported.

Nonlinear optical properties of zinc oxide doped bismuth thin films using Z-scan technique

ZnO doped Bi thin films were grown on glass substrates by spray ultrasonic technique. This paper presents the effect of Bi doping concentration on structural and nonlinear optical properties of zinc oxide thin films. These thin films were characterized by X-ray diffractometer technique. XRD analysis revealed that the ZnO:Bi thin films indicated good preferential orientation along c-axis perpendicular to the substrate. The nonlinear optical properties such as nonlinear absorption coefficient (β) and third order nonlinear susceptibility (Imχ(3)) are investigated. The calculations have been performed with a Z scan technique using Nd:YAG laser emitting 532nm. The reverse saturable absorption (RSA) mechanism was responsible for the optical limiting effect. The results suggest that this material considered as a promising candidate for future optical device applications.

Two-dimensional topological phases and electronic spectrum ofBi2Se3thin films fromGWcalculations

High-quality $G\phantom{\rule{0}{0ex}}W$ calculations of the quasiparticle band structure in thin films of topological insulator Bi${}_{2}$Se${}_{3}$ show that the topological nature of the surface states is $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t$ the spin-polarized quantum spin Hall state, but the less interesting trivial topology. This is in strong contrast to the expected topology of the surface states of $b\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}k$ Bi${}_{2}$Se${}_{3}$ and the predictions of density functional theory and parametrized calculations for Bi${}_{2}$Se${}_{3}$ thin films, which produce fundamentally less accurate predictions of the band gap than the $G\phantom{\rule{0}{0ex}}W$ approach.

Strain Localization in Thin Films of Bi(Fe,Mn)O3 Due to the Formation of Stepped Mn(4+)-Rich Antiphase Boundaries.

The atomic structure and chemistry of thin films of Bi(Fe,Mn)O3 (BFMO) films with a target composition of Bi2FeMnO6 on SrTiO3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn4+-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 Å. Outside the area enclosed by the antiphase boundaries, the out-of-plane lattice parameter is much closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO3 on the SrTiO3 substrate to minimise any Mn-Ti interactions.

Crystallization engineering as a route to epitaxial strain control

The controlled synthesis of epitaxial thin films offers opportunities for tuning their functional properties via enabling or suppressing strain relaxation. Examining differences in the epitaxial crystallization of amorphous oxide films, we report on an alternate, low-temperature route for strain engineering. Thin films of amorphous Bi–Fe–O were grown on (001)SrTiO3 and (001)LaAlO3 substrates via atomic layer deposition. In situ X-ray diffraction and X-ray photoelectron spectroscopy studies of the crystallization of the amorphous films into the epitaxial (001)BiFeO3 phase reveal distinct evolution profiles of crystallinity with temperature. While growth on (001)SrTiO3 results in a coherently strained film, the same films obtained on (001)LaAlO3 showed an unstrained, dislocation-rich interface, with an even lower temperature onset of the perovskite phase crystallization than in the case of (001)SrTiO3. Our results demonstrate how the strain control in an epitaxial film can be accomplished via its crystallization from the amorphous state.

Strongly compressed Bi (111) bilayer films on Bi2Se3 studied by scanning tunneling microscopy

Ultra-thin Bi films show exotic electronic structure and novel quantum effects, especially the widely studied Bi (111) film. Using reflection high-energy electron diffraction and scanning tunneling microscopy, we studied the structure and morphology evolution of Bi (111) thin films grown on Bi2Se3. A strongly compressed, but quickly released in-plane lattice of Bi (111) is found in the first three bilayers. The first bilayer of Bi shows a fractal growth mode with flat surface, while the second and third bilayer show a periodic buckling due to the strong compression of the in-plane lattice. The lattice slowly changes to its bulk value with further deposition of Bi.

Crystalline characteristics and superconducting properties of Bi2212 thin films by Pechini sol–gel method: effect of heating rate on the film growth

High-quality c-axis epitaxial Bi2Sr2CaCu2O8+δ (Bi2212) superconducting thin films prepared by the Pechini sol–gel method using nitrates as reactants have been grown on SrTiO3(100) single-crystal substrates. The precursor sol was deposited on the substrates via spin-coating method. Through the optimization of experimental parameters, 2.0 K min−1 was found to be the optimal heating rate of pre-sintering stage. Below this heating rate of pre-sintering stage, partial composition segregation occurred in the precursor films that resulted in dispersion of impurity phases in sintered thin films and caused the degradation of superconducting properties. Above this heating rate of pre-sintering stage, the surface morphology of thin films was destroyed, as the macroscopic defects, such as cracks and holes caused by excessive gas emissions during organic matter decomposition process and a sharp increase in roughness of precursor film was observed. Furthermore, through the optimization of heating rate at sintering stage, 3.5–3.0 K min−1 was found to be an optimal heating rate range at which Bi2212 thin films exhibited excellent phase purity and crystalline properties. In optimized growth condition, T c,onset rose to above 95 K. Through the optimization of heating rates of pre-sintering and sintering stages, the excellent Bi2212 superconducting thin films without macroscopic defects were prepared by Pechini sol–gel method using nitrate as reactant.

One-dimensional edge state of Bi thin film grown on Si(111)

The geometric and electronic structures of the Bi thin film grown on Si(111) were investigated by using scanning tunneling microscopy and spectroscopy. We have found two types of edges, one of which hosts an electronic state localized one-dimensionally. We also revealed the energy dispersion of the localized edge state from the evolution of quasiparticle interference patterns as a function of energy. These spectroscopic findings well reproduce those acquired for the cleaved surface of the bulk Bi crystal [I. K. Drozdov et al., Nat. Phys. 10, 664 (2014)]. The present results indicate that the deposited Bi film provides a tractable stage for further scrutiny of the one-dimensional edge state.

Influence of Bi doping on the electrical and optical properties of ZnO thin films

Transparent conducting ZnO doped Bi thin films were prepared on glass substrates by ultrasonic spray method. The influence of Bi doping concentration on the structural, optical and nonlinear optical properties of ZnO thin films was studied. The X-ray diffraction (XRD) analysis show that all studied films have a hexagonal wurtzite structure and are preferentially oriented along the c-axis from substrate surface. Optical transmittance measurements show that all samples have average 80% transparency in the visible light. Optical band gap values range between 3.14 and 3.28eV. ZnO film with 3wt% of Bi showed the highest electrical conductivity. In addition, the second and third order nonlinear susceptibilities were determined and their values have been calculated.

Impact of bismuth incorporation into (Ga,Mn)As thin films on their structural and magnetic properties

AbstractStructural and magnetic properties of thin films of the (Ga,Mn)(Bi,As) quaternary diluted magnetic semiconductor grown by the low‐temperature molecular‐beam epitaxy technique on GaAs substrates have been investigated. High‐resolution X‐ray diffraction has been applied to characterize the structural quality and misfit strain in the films. Ferromagnetic Curie temperature and magneto‐crystalline anisotropy of the films have been examined by using SQUID magnetometry and low‐temperature magneto‐transport measurements. Post‐growth annealing treatment of the films has been shown to reduce the strain in the films and to enhance their Curie temperature. Significant increase in the magnitude of magneto‐transport effects caused by incorporation of a small amount of Bi into the films is interpreted as a result of enhanced spin‐orbit coupling in the (Ga,Mn)(Bi,As) films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancing Phase Purity of CSD Bi-2223 Thin Films Through Protected Sintering Method

Pure Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) phase is hard to be achieved in Bi-2223 thin films fabricated by using chemical solution deposition (CSD) due to the volatilization of specific elements. Two protected sintering methods were proposed in this work to enhance the phase purity of CSD Bi-2223 thin films. One method is two deposited thin films stacked “face-to-face” (FTF) and then sintered. A “substrate/precursor film/precursor film/substrate” architecture was used during sintering instead of common “precursor film/substrate” architecture. The other method was named “sealed face-to-face” (SFTF). The FTF structure was buried in Bi-2223 powders and then sealed in a silver envelope before sintering. Different sintering temperature and sintering time were investigated in an 8% O 2 (N 2 balance) atmosphere. The volume fraction of Bi-2223 phase could be enhanced to 17% by using the FTF method, and 68% by using the SFTF method.

Catalyst free growth of single-crystalline bismuth nanorods by closed space sublimation technique

Abstract In the present study, bismuth (Bi) thin films having thickness of 335 nm have been deposited onto a glass substrate by closed space sublimation (CSS) technique. Besides this, spontaneous growth of Bi nanorods has also been investigated for the first time, without template and catalyst assistance in a substrate temperature range of 380 to 430 °C using CSS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate microstructure, morphology and roughness of the Bi nanorods. The diameter and length ranges of Bi nanorods were 80 to 400 nm and 3 to 5 μm, respectively. Moreover, they exhibited a rhombohedral structure with a dominant peak indexed at (012), (104), and (110). The mass percentage of Bi, determined by energy dispersive X-ray (EDX), was 99.93 %. The studies of electrical resistivity, Hall coefficient, magnetoresistivity, hole mobility and carrier concentration of Bi thin films were performed at 300 to 350 K and the electrical properties were found to be a function of temperature. The basic aim was to investigate the spectacular evolution of Bi nanostructures on as-deposited thin films and effects of thickness on their structural, electrical and dielectric properties. Detailed examination of SEM micrographs eliminated all other growth modes except self-catalytic tip growth by Vapor-Solid (VS) growth process which is believed to provide the driving force for spontaneous nanorod growth at high substrate temperature. Deposition of thinner Bi films provided a new possibility for fabrication of Bi nanorods of high quality.

Nanostructural Defects and Critical Current Densities in High-Quality <inline-formula> <tex-math notation="TeX">$\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{CaCu}_{2}\hbox{O}_{8+{\rm X}} $</tex-math></inline-formula> Epitaxial Thin Films Prepared by MOCVD

Nanostructural defects were investigated by transmission electron microscopy in c-axis-oriented epitaxial Bi 2 Sr 2 CaCu 2 O 8+X (Bi2212) thin films with high T c (R = 0) ≥ 83 K and high transport critical current density ofJ c >10 10 A/m 2 at 10 K. We observed misfit dislocations at twin boundaries, dislocations associated with stacking faults parallel to the a-b plane, and antiphase boundaries. We compared the magnetic-field dependent J c values at various temperatures in two Bi2212 films. About 110-nm-thick film A showed lower J c than ~280-nm-thick film B at low temperatures (≤ 20 K) or in low magnetic fields (≤ 0.1 T). However, the J c of film B decreased more rapidly in high magnetic fields, leading to a crossover of the two J c -B curves at temperatures of 30 K and above. This is probably because film B contained a higher density of antiphase boundaries, which caused stronger pinning and higher J c values at low temperatures but may have caused enhanced thermally activated motion of pancake vortices that eventually resulted in lower Jc values in high magnetic fields at moderate temperatures.

Low-temperature growth of bismuth thin films with (111) facet on highly oriented pyrolytic graphite.

The epitaxial growth of artificial two-dimensional metals at interfaces plays a key role in fabricating heterostructures for nanoelectronics. Here, we present the growth of bismuth nanostructures on highly oriented pyrolytic graphite (HOPG) under ultrahigh vacuum (UHV) conditions, which was investigated thoroughly by a combination of scanning tunneling microscopy (STM), ultraviolet photoemission spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). It was found that (111)-oriented bilayers are formed on as-cleaved high-quality HOPG at 140 K, which opens the possibility of making Bi(111) thin films on a semimetal, and this is a notable step forward from the earlier studies, which show that only Bi(110) facets could be formed at ultrathin thickness at room temperature. XPS investigation of both C 1s and Bi 4f reflects the rather weak bonding between the Bi film and the HOPG substrate and suggests a quasi layer-by-layer growth mode of Bi nanostructures on HOPG at low temperature. Moreover, the evolution of the valence band of the interface is recorded by UPS, and a transition from quantum well states to bulk-like features is observed at varying film thickness. Unlike semimetallic bulk bismuth, ultrathin Bi(111) films are expected to be topological insulators. Our study may therefore pave the way for the generation of high quality Bi nanostructures to be used in spin electronics.

Temperature-dependent thermal conductivity of nanoporous Bi thin films by controlling pore size and porosity

We have recently reported that 2D nanoporous Bi thin films have a thermal conductivity that is ∼6 times smaller than that of the bulk materials at room temperature. Extending from this, we further realized the significance of temperature dependence of thermal conductivity in nanoporous Bi thin films. Therefore, in this study we investigate the thermal conductivities of 50-nm-thick thin films with film porosities in the 20–300K temperature range. The behavior on the temperature-dependent thermal transport can be quantitatively explained by enhanced phonon scattering. Furthermore, our experimental and calculated results confirmed that the porosity rather than the pore size of nanoporous Bi thin films does indeed play a strong effect in the reduction of their thermal conductivities.

BixTi1–xOz Functionalized Heterojunction Anode with an Enhanced Reactive Chlorine Generation Efficiency in Dilute Aqueous Solutions

Ir_(0.7)Ta_(0.3)O_y/Bi_xTi_(1–x)O_z heterojunction anodes have been developed and characterized for reactive chlorine species (RCS) generation in dilute aqueous solution (50 mM NaCl). The primary objective of the research was to control the electro-stationary speciation of hydrous metal oxides between hydroxyl radical (>MO_x(·OH)) and higher valence-state oxides (>MO_(x+1)). An underlying layer of the mixed-metal oxide, Ir_(0.7)Ta_(0.3)O_y, was synthesized to serve as a primary Ohmic contact and electron shuttle. Binary thin films of Bi_xTi_(1–x)O_z were prepared from the thermal decomposition of an aqueous solution mixture of Ti/Bi complexes. With these core components, the measured current efficiency for RCS generation (η_(RCS)) was enhanced where the values observed for x = 0.1 or 0.3 were twice of the η_(RCS) of the Ir_(0.7)Ta_(0.3)O_y anode. At the same time, the rates of RCS generation were enhanced by factors of 20–30%. Partial substitution of Ti with Bi results in a positive shift in surface charge allowing for stronger interaction with anions, as confirmed by FTIR-ATR analysis. A kinetic model to describe the formate ion degradation showed that an increasing fraction of Bi in the composite promotes a redox transition of >MO_x(·OH) to >MO_(x+1). In accelerated life tests under conditions corresponding to a service life of 2 years under an operational current density of 300 A m^(–2), dissociation of the Ti component from Ir_(0.7)Ta_(0.3)O_y/TiO_2 was found to be minimal, while Bi_xTi_(1–x)O_z in the surface layers undergoes oxidation and a subsequent dissolution.

Thin films of a three-dimensional topological insulator in a strong magnetic field: Microscopic study

The response of thin films of Bi$_2$Se$_3$ to a strong perpendicular magnetic field is investigated by performing magnetic bandstructure calculations for a realistic multi-band tight-binding model. Several crucial features of Landau quantization in a realistic three-dimensional topological insulator are revealed. The $n=0$ Landau level is absent in ultra-thin films, in agreement with experiment. In films with a crossover thickness of five quintuple layers, there is a signature of the $n=0$ level, whose overall trend as a function of magnetic field matches the established low-energy effective-model result. Importantly, we find a field-dependent splitting and a strong spin-polarization of the $n=0$ level which can be measured experimentally at reasonable field strengths. Our calculations show mixing between the surface and bulk Landau levels which causes the character of levels to evolve with magnetic field.

Crystalline characteristics and superconducting properties of Bi2212 thin films prepared by the Pechini sol–gel method: the effect of different substrates on the film growth

Bi2Sr2CaCu2O8+δ(Bi2212) superconducting thin films were prepared by the Pechini sol–gel method using nitrates as reactants. The precursor sol was deposited on LaAlO3(100) and MgO(100) single-crystal substratesviathe spin-coating method. The results revealed that the phase formation temperature region of the pure Bi2212 phase and perfectly epitaxial Bi2212 films deposited on LaAlO3substrates was significantly expanded to 8 K, indicating an improvement in crystallization of Bi2212 films. In addition, the phase formation temperature region of the pure phase andc-axis-grown Bi2212 films deposited on MgO substrates was reduced to 5 K because of the deterioration of epitaxy of Bi2212 films sintered at higher temperature. According to the investigation, theTc,onsetvalues of Bi2212 films grown on MgO substrates were about 92 K. Meanwhile, the optimalTc,onsetvalue of Bi2212 superconducting films grown on LaAlO3substrates rose to 96 K.