Growth and properties of vertically well-aligned GaN nanowires by thermal chemical vapor deposition process

The vertically well-aligned GaN nanowires on c-Al₂O₃ substrates were grown via a vapor-liquid-solid mechanism. X-ray diffraction indicated the GaN nanowires to have epitaxial and homogeneous in-plan alignment with the c-Al₂O₃ substrates and a strong preferred orientation along the c-axis. The GaN nanowires had a single-crystalline hexagonal structure and c-axis orientation, as confirmed by high resolution transmission electron microscopy.     

Synthesis of single crystal Bi2Te3 nanoplates via an inorganic-surfactant-assisted solvothermal route

Single crystal Bi₂Te₃ nanoplates have been successfully obtained by a solvothermal method adopting a lamellar structure as the precursor. Various techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) have been used to characterize the obtained products. The results show that the as-synthesized samples are rhombohedral-structured Bi₂Te₃ single-crystal nanoplates, whose growth direction is perpendicular to c-axis. In addition, some important experiment parameters such as the water/ethanol volume ratio and pH value have been discussed.     

Uniform Bi2S3 nanowires: Structure, growth, and field-effect transistors

Large-scale single-crystalline Bi₂S₃ nanowires were prepared by a simple one-step hydrothermal reaction between Bi(NO₃)₃ and Na₂S₂O₃, without using any organics in the experiment. These Bi₂S₃ nanowires have uniform size diameters which are about 60 nm. The structure of the nanowires is determined to be of the orthorhombic phase, and the growth direction is along the [001] direction. The growth mechanism of the nanowires was investigated based on high-resolution transmission electron microscopy observations. The field-effect transistors (FETs) have been fabricated using a single Bi₂S₃ nanowire, n-type semiconductor behavior has been observed, and high on/off ratio of about 3 orders of magnitude has been achieved.     

Building crystalline Sb2S3 nanowire dandelions with multiple crystal splitting motif

Crystalline dandelion-like antimony (III) sulfide (Sb₂S₃) nanowires were synthesized by a PEG-assisted solvothermal process. The orthorhombic crystal structure and dandelion-like multi-branched nanowire morphology were revealed by X-ray diffractometry (XRD) and scanning electron microscopy (SEM) respectively. High-resolution transmission electron microscopy (TEM) identified that the highly crystalline Sb₂S₃ nanowires grew along the [001] direction with individual wire diameter of 195 ± 52 nm. The band gap of the Sb₂S₃ nanowires was measured to be ca. 1.67 eV. A combination of PEG-templated assembly and crystal splitting mechanism was likely responsible for the growth of the observed nanowire dandelion structures.     

Preparation and Characterization of Nanometer Grained High Temperature Superconducting High-Quality Epitaxial Bi-2223 Thin Films Grown by DC Sputtering

Bi₂Sr₂Ca₂Cu₃O_10+?? HTSC epitaxial thin films with thickness in the order of 6.0?nm were prepared onto (100) aligned SrTiO₃ single-crystal substrates by DC sputtering from stoichiometric targets. As-grown samples were characterized by X-ray diffraction, AC-susceptibility and scanning electron microscopy. X-ray diffraction patterns show that all obtained superconducting thin films were c-axis oriented with a Bi-2223 phase. All reflections (except the substrate ones) can be assigned to the (00l) reflections of the film material (h=k=0, l??0), indicating that the films were grown preferentially with the c-axis normal to the film plane. In order to investigate the crystal quality of these Bi-2223 films, the rocking curves of the (0012) peaks were explored by ??-scans. The rocking curve of the (0012) reflection had a full width at half maximum (FWHM) of 0.30??. This demonstrates that our prepared Bi-2223 thin films have good crystalline quality and high degree of c-axis orientation. The grain size has well known important effects in the magnetic, optical, and electrical properties of metals and alloys. High temperature superconducting thin films, obtained in this work, have nanometer grain size. The mean size of the grains of the samples were determined by X-ray diffraction (XRD) and found to be in the order of 34.8?nm. The superconducting transitions temperature of several Bi-2223 samples is about 103?K. Surface morphology of the films and chemical composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX).     

Preparation of Bi2S3 nanorods via a hydrothermal approach

Large-scale bismuth sulfide (Bi₂S₃) nanorods with uniform size have been prepared by hydrothermal method using bismuth chloride (BiCl₃) and sodium sulfide (Na₂S·9H₂O) as raw materials at 180 °C and pH = 1-2 for 12 h. The powder X-ray diffraction (XRD) pattern shows the Bi₂S₃ crystal belongs to the orthorhombic phase with calculated lattice constants a = 1.1187 nm, b = 1.1075 nm and c = 0.3976 nm. Furthermore, the quantification of X-ray photoelectron spectra (XPS) analysis peaks gives an atomic ratio of 1.9:3.0 for Bi:S. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopic (TEM) studies reveal that the appearance of the as-prepared Bi₂S₃ is rod-like with typical lengths in the range of 2-5 μm and diameters in the range of 10-30 nm. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of Bi₂S₃ nanorods is proposed.     

Enhancement of photosensitivity by annealing in Bi2S3 thin films grown using SILAR method

Bi₂S₃ thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi₂S₃ thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi₂S₃ thin film gives good photoresponse as compared to as deposited thin film and Bi₂S₃ thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi₂S₃ thin films revealed n-type electrical conductivity.     

D-penicillamine assisted hydrothermal synthesis of Bi2S3 nanoflowers and their electrochemical application

Single crystalline flower-like Bi₂S₃ nanostructures were successfully synthesized via a simple, facile and green hydrothermal method, with the assistance of D-penicillamine. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and found their morphologies mainly depend on the ratios of Bi^3 + to D-penicillamine, as well as the reaction temperature and time. And the possible growth mechanism has been discussed in some detail. In addition, the as-prepared Bi₂S₃ nanoflowers show good hydrogen storage ability. This strategy can be potentially expanded to prepare other metal chalcogenides materials.     

Synthesis of ZnO nanowires by the hydrothermal method,using sol–gel prepared ZnO seed films

Zinc oxide (ZnO) nanowires with various morphologies are synthesized by the hydrothermal method on silicon substrates coated with ZnO thin films. The ZnO films are used as the seed layer and are prepared using the sol–gel technique. Experimental results demonstrate that the synthesis of ZnO nanowires is dependent on the crystalline properties of the ZnO seed-layer films. Sol concentration is the controlled parameter for the preparation of ZnO seed-layer films in this study. The ZnO films are found to have the hexagonal wurtzite structure with highly preferred growth along the c-axis at suitable sol concentrations. The vertically aligned ZnO nanowire arrays on the substrates are believed to be the result of the epitaxial growth of the ZnO seed layer. Scanning electron microscopy shows that nanowires with uniform distribution in length, diameter, and density are obtained. X-ray diffraction patterns clearly reveal that the ZnO nanowires are primarily grown along the c-axis direction. Transmission electron microscopy and selected-area electron diffraction measurements show that the nanowires have good crystalline properties. The well-aligned and high surface areas of the ZnO nanowires make them a potential candidate for applications in solar cells, field emission devices, and ultra-sensitive gas sensors.     

A simple route to the synthesis of single crystalline copper metagermanate nanowires

Single crystalline copper metagermanate (CuGeO₃) nanowires with the diameter of 30–300 nm and length of longer than 100 µm have been prepared by a simple hydrothermal deposition route. X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman analyses confirm that the nanowires are orthorhombic single crystals with a main growth direction along <101>. Room temperature photoluminescence (PL) measurement shows a strong blue emission peak at 442 nm with a broad emission band. The blue emission may be ascribed to radiative recombination of oxygen vacancies and oxygen–germanium vacancies. The formation process of CuGeO₃ nanowires is also discussed.     

Microwave-assisted synthesis and characterization of 3D flower-like Bi2S3 superstructures

Bismuth sulfide (Bi₂S₃) microcrystallines with three-dimensional (3D) flower-like superstructures were prepared by the microwave irradiation method with bismuth nitrate (Bi(NO₃)₃·5H₂O) and thiourea ((NH₂)₂CS) as raw materials and ethylene glycol as solvent. The powder X-ray diffraction (XRD) pattern shows the product belongs to the orthorhombic Bi₂S₃ phase. The quantification of X-ray photoelectron spectra (XPS) analysis peaks gives an atomic ratio of 1.9:3.0 for Bi:S. Transmission electron microscopic (TEM) and scanning electron microscopy (SEM) studies reveal that the superstructure of the as-prepared Bi₂S₃ consists of sticks extending radially from a nucleation site. The reaction progress and a possible mechanism were proposed.     

Rapid synthesis of Bi2S3 nanocrystals with different morphologies by microwave heating

Single-crystalline Bi₂S₃ nanocrystals with urchinlike and rod-like morphologies have been successfully synthesized using Bi₂O₃, HCl, Na₂S₂O₃ and ethylene glycol (EG) by a simple and fast microwave heating method. Both urchinlike and rod-like Bi₂S₃ nanostructures could be formed under microwave heating at 190 °C for 30 s. Urchin-like Bi₂S₃ nanostructures were prepared using sodium dodecyl sulfate (SDS) or in the absence of any surfactant. However, Bi₂S₃ nanorods were obtained in the presence of cetyltrimethylammonium bromide (CTAB). The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED) and ultraviolet-visible (UV-Vis) absorption spectra.     

Synthesis, characterization, and hydrophobic properties of Bi2S3 hierarchical nanostructures

Novel Bi₂S₃ hierarchical nanostructures self-assembled by nanorods are successfully synthesized in mild benzyl alcohol system under hydrothermal conditions. The hierarchical nanostructures exhibit a flower-like shape. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to characterize the as-synthesized samples. Meanwhile, the effect of various experimental parameters including the concentration of reagents and reaction time on final product has been investigated. In our experiment, PVP plays an important role for the formation of the hierarchical nanostructures and the possible mechanism was proposed. In addition, Bi₂S₃ film prepared from the flower-like hierarchical nanostructures exhibits good hydrophobic properties, which may bring nontrivial functionalities and may have some promising applications in the future.     

The LP-MOCVD of CdS/Bi2S3 bilayers using single-molecule precursors

The single-molecule precursors [Cd(S₂CNMe n-Hex)₂] and [Bi(S₂CNMe n-Hex)₃] (Me=methyl; n-Hex=n-hexyl) were used to prepare CdS/Bi₂S₃ layers by low-pressure metal organic chemical vapour deposition (LP-MOCVD). The bilayers were deposited onto glass substrates at 400–450 °C for varying growth conditions. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical measurements. The results were compared with those obtained for the single phases.     

Bi2S3-modified TiO2 nanotube arrays: easy fabrication of heterostructure and effective enhancement of photoelectrochemical property

A novel heterostructure of Bi₂S₃ nanoparticles (NPs) and TiO₂ nanotube arrays (NAs) was fabricated by a conventional hydrothermal method. The morphological features and the X-ray diffractogram of the obtained Bi₂S₃/TiO₂ NAs were characterized by field-emission scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. The photoelectrochemical property of Bi₂S₃/TiO₂ NAs was also evaluated. The results demonstrated that photoelectrochemical solar cells based on Bi₂S₃/TiO₂ NAs had a short-circuit current of 4.54 mA/cm² and photoelectric conversion efficiency of 1.86 %. Surface photovoltage spectroscopy and field-induced surface photovoltage spectroscopy data indicated the existence of a strong interfacial electronic field between the two components Bi₂S₃ NPs and TiO₂ NAs, which can enhance the separation of photogenerated charge carriers.     

A simple chemical route to Bi2S3 hierarchical columniform structures assembled by nanorod-based lamellae

Bi₂S₃ hierarchical columniform structures assembled by nanorod-built lamellae have been first synthesized by a simple wet chemical method through the reaction between Bi(NO₃)₃?5H₂O and CS₂ at 80 °C for 14 h using DMSO as solvent without any surfactants. These new Bi₂S₃ structures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared to ethylene glycol and DMF, DMSO supplied an excellent chemical environment favorable to the generation of Bi₂S₃ quickly in heterogeneous condition. The influences of the synthetic parameters were discussed and a possible growth mechanism for the formation of these complex structures was proposed.     

Fabrication of three-dimensional snowflake-like bismuth sulfide nanostructures by simple refluxing

Three-dimensional snowflake-like bismuth sulfide nanostructures were successfully synthesized by simple refluxing at 160 °C in ethylene glycol, using bismuth citrate and thiourea as reactants. The crystal structures and morphologies of the products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). The Bi₂S₃ nanostructure was built up by highly ordered one-dimensional Bi₂S₃ nanorods, which was aligned in an orderly fashion. Ethylene glycol plays a critical role in the creation of bismuth sulfide three-dimensional nanostructures, which serves as an excellent solvent and structure director. Bismuth citrate, a linear polymer, also makes for the formation of the three-dimensional nanostructures.     

Characterization of Bi2S3 nanorods and nano-structured flowers prepared by a hydrothermal method

Bismuth sulfide nanorods and nano-structured flowers were synthesized by hydrothermal reaction of bismuth nitrate pentahydrate and thiourea solutions, containing 1 and 2 ml of 65% HNO₃, respectively. By using X-ray diffraction (XRD), selected area electron diffraction (SAED), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), the products were specified as orthorhombic Bi₂S₃ in the shapes of nanorods and flower-like clusters of nanorods, with the growth of nanorods in the [001] direction. A diffraction pattern was also simulated, and was in good accordance with the SAED pattern obtained from the experiment.     

Crystalline thin films of β-phase poly(9,9-dioctylfluorene)

The detailed structure of crystalline β-phase poly(9,9-dioctylfluorene) (PFO) films was studied by polarized optical measurements, transmission electron microscopy, and grazing-incidence X-ray diffraction. Crystalline β-phase PFO thin films were fabricated by a friction transfer technique and subsequent vapor treatment. Compared to the α-phase, the lattice parameters of the β-phase crystals shrank along the a-axis (film thickness direction) and elongated along the b-axis (side-chain direction), but the period along the c-axis (main-chain direction) remained nearly equal. These changes in molecular packing were consistent with a planar conformational change from the α-phase to the β-phase of PFO.     

High-resolution electron microscopy and low-temperature electron diffraction studies of a Bi2212 single crystal grown by the floating zone method

High-resolution electron microscopy of a Bi₂Sr₂CaCu₂O₈ (Bi2212) single crystal prepared by the floating zone method shows that the single crystal is of high quality; there is no intergrowth faulting in the layered structure along thec-axis. Low-temperature selected area diffraction and convergent beam electron diffraction (CBED) studies of this high-quality single crystal show that there is no detectable change for both the point group symmetry of the basic structure and the modulated structure from room temperature to about 15 K. However, a lattice anomaly around 215 K was suggested by measuring the temperature dependence of the ratio between the cross-point distances of the HOLZ lines in high-index CBED patterns. The presence of the lattice anomaly was further confirmed by low-temperature X-ray diffraction.