Magnetic-field-assisted solvothermal growth of single-crystalline bismuth nanowires

The magnetic-field-assisted approach has been used in the shape-controlled synthesis of single Bi nanocrystals. By tuning the magnetic field strength in the solvothermal process, Bi nanowires with dimension of 40-200?nm and lengths up to tens of micrometers were synthesized. Various techniques such as x-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectrometry have been used to characterize the products obtained. The results show that the magnetic field plays a key role in the crystal growth of the Bi nanowires. All nanowires were highly oriented single crystals with the growth direction along the c-axis.     

Synthesis and characterization of bismuth sulfide nanowires through microwave solvothermal technique

One-dimensional (1D) bismuth sulfide (Bi₂S₃) semiconducting nanowires have been successfully synthesized through mircrowave assisted solvothermal technique. The obtained product was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometry. The result shows that the Bi₂S₃ nanowires are single crystals grown along the [001] (c-axis) direction. The growth of Bi₂S₃ nanofibers with a preferential direction of c-axis can be ascribed to its particular structure. The optical measurement shows a blue shift relative to the bulk orthorhombic Bi₂S₃, which might be ascribed to the high aspect ratio of the nanowires.     

Formation and stabilization of single-crystalline metastable AuGe phases in Ge nanowires

We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable γ-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.     

Synthesis of single-crystalline silver sulfide nanowires by diffusion in porous anodic aluminium oxide template

Highly ordered single-crystalline silver sulfide (Ag₂S) nanowires have been successfully achieved directly using silver nitrate and thioacetamide (TAA) as the reactants, by diffusion in the channels of anodic aluminium oxide (AAO) membrane. The products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The results of the research show that the as-prepared Ag₂S nanowires are monodisperse with sizes of about 50 nm in diameter, closely corresponding to the pore size of the AAO membrane. Furthermore, its photoluminescence properties and the growth mechanism are also discussed.     

Ultrafast growth of single-crystalline Si nanowires

Silicon nanowires (SiNWs) have been catalytically synthesized by heat treatment of Si nanopowder at 980 °C. The SiNWs comprise crystalline Si nanoparticles interconnected with metal catalyst. The formation mechanism of nanowires generally depends on the presence of Fe catalysts in the synthesis process of solid–liquid–solid (SLS). Although gas phase of vapor–liquid–solid (VLS) method can be used to produce various of different nanowire materials, growth model based on the SLS mechanism by heat treatment is more ascendant for providing ultrafast growth of single-crystalline Si nanowires and controlling the diameter of them easily. The growth of single-crystalline SiNWs and morphology were discussed.     

Magnetic properties of single-crystalline CoSi nanowires

We have observed unusual ferromagnetic properties in single-crystalline CoSi nanowire ensemble, in marked contrast to the diamagnetic CoSi in bulk. High-density freestanding CoSi nanowires with B20 crystal structure are synthesized by a vapor-transport-based method. The reaction of cobalt chloride precursor with a Si substrate produces high-aspect-ratio CoSi nanowires. The high-resolution transmission electron microscopy and electron diffraction studies reveal superlattice structure in CoSi nanowires with twice the lattice parameter of simple cubic CoSi lattice. The zero-field-cooled and field-cooled (ZFC-FC) measurements from the nanowire ensemble show freezing of the disordered surface spins at low temperatures. The magnetoresistance (MR) measurements of single nanowire devices show a negative MR whose magnitude gets larger at lower temperatures.     

Synthesis of single-crystalline bismuth nanobelts and nanosheets

Single-crystalline bismuth nanobelts have been synthesized successfully by solution-phase route, using ethylene glycol as reductant and solvent. It was speculated that the final morphology resulted from the layered structure of rhombohedral bismuth.     

Surfactant-assisted preparation of single-crystalline Fe3O4 nanowires under low magnetic field

Fe₃O₄ nanowires were successfully synthesized from ferrous chloride (FeCl₂·4H₂O) and diamine hydrate (H₄N₂·H₂O) via the surfactant-assisted redox hydrothermal process induced by low magnetic field. The products as-prepared were characterized by X-ray diffraction, TEM and HRTEM. The mechanism for the formation of single-crystalline Fe₃O₄ nanowires was discussed based on the oriented growth of magnetic materials.     

Properties of uniform diameter InN nanowires obtained under Si doping

High quality, well-separated, homogeneous sizes and high aspect ratio Si-doped InN nanowires (NWs) were grown by catalyst-free molecular beam epitaxy (MBE) after optimization of the growth conditions. To this end, statistical analysis of NW density and size distribution was performed. The high crystal quality and smooth NW surfaces were observed by high resolution transmission electron microscopy. Spectral photoluminescence has shown the increase of the band filling effect with Si flux, indicating successful n-type doping. A Raman LO scattering mode appears with a pronounced low energy tail, also reported for highly doped InN films.     

Synthesis and optical properties of ZnTe single-crystalline nanowires

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.     

Deposition of bismuth sulfide and aluminum doped bismuth sulfide thin films for photovoltaic applications

Journal of Materials Science: Materials in Electronics - Binary bismuth sulfide (Bi2S3) and ternary aluminum-doped bismuth sulfide (Al@Bi2S3) thin films were prepared by the chemical bath...     

Solvothermal fabrication of uniform silver nanowires

Conventional polyol synthesis has been widely used for the preparation of silver nanostructures with different morphologies. However, there is a drawback that it is difficult to control the reaction parameters for shape-controlled synthesis of silver nanostructures, such as the rate of the addition of silver ions to the solution. In this paper, we combine polyol process and solvothermal method for easily synthesizing silver nanostructures. Importantly, the introduction of cuprous chloride (CuCl) to the reaction leads to increasing the population of twinned Ag seeds (required for wire growth) at the expense of that of single Ag seeds. Silver nanowires (Ag NWs) with uniform width (~80?nm in width) can be obtained in the presence of poly(vinyl pyrrolidone) (PVP). Some other parameters, such as the reaction temperature and molar ratios of the repeating unit of PVP to AgNO₃ (R), also have been discussed. A possible mechanism is put forward to understand the evolution of silver nanostructures.     

Promoted growth of Bi single-crystalline nanowires by sidewall-induced compressive stress in on-film formation of nanowires

To increase the density of Bi nanowires grown by our unique on-film formation of nanowires (OFF-ON) method, we introduced a technique for enhancing compressive stress, which is the driving force for the nanowire growth. The compressive stress could be controlled by modifying the substrate structure. A combination of photolithography and a reactive ion etching technique was used to fabricate patterns on a thermally oxidized Si(100) substrate. It was found that the density of Bi nanowires grown from Bi films in 100 x 100 microm2-sized SiO2 patterns increases by a factor of seven over that from non-patterned substrates. Our results indicate that the density of Bi nanowires can be increased by enhanced compressive stress arising from a sidewall effect in the optimized pattern size and array.     

Fabrication of vertically stacked single-crystalline Si nanowires using self-limiting oxidation

A simple method for fabricating vertically stacked single-crystal silicon nanowires on standard bulk silicon wafers is presented. The process uses inductively coupled plasma (ICP) etching to create silicon fins with uneven yet controllable vertical profiles. The fins are then thermally oxidized in a self-limiting process, and the narrow regions are completely consumed to create multiple nanowires vertically stacked on each other. It was found that the number of nanowires in the vertical stack depends on the number of ICP cycles. A mechanism for the formation of the nanowires is proposed and confirmed with numerical simulations.     

Structural and optical properties of single-crystalline ultraviolet-emitting needle-shaped ZnO nanowires

Well-crystallized with excellent optical properties, needle-shaped ZnO nanowires have been synthesized on silicon substrate in a high density via the thermal evaporation of metallic zinc powder without the use of catalysts or additives. Extensive structural analysis showed that the grown nanowires are highly crystalline with the wurtzite hexagonal phase, grown along the [0001] in the c-axis direction. The presence of an optical-phonon E₂ mode in Raman spectrum at 437 cm^{− 1} and sharp and strong UV emission at 379 nm with no green emission in the room-temperature photoluminescence (PL) spectrum confirms good crystallinity with the excellent optical properties for the deposited nanowires.     

Electronic transport mechanism and photocurrent generations of single-crystalline InN nanowires

Nanodevices using individual indium nitride nanowires are fabricated by e-beam lithography. The nanowires have diameters of 40-80?nm, lengths up to several tens of micrometres and single-crystalline nature. We observed ohmic I-V behaviour of InN nanowires above nearly 100?K, which is consistent with the pinning Fermi level of the metal electrode near the conduction band edge of InN nanowire. At low temperatures, the device shows typical semiconductor behaviour along with a quantum tunnelling effect through the Schottky barrier rather than thermally activated transport. The activation energy calculated above and below 80?K is 28.2 and 5.08?meV, respectively. We have also fabricated a photocurrent generation device using InN nanowires. The photocurrent of an acceptor-sensitizer dyad with di-(3-aminopropyl)-viologen (DAPV) and a Ru complex on an InN nanowires/ITO plate was 8.3?nA?cm(-2), which increased by 62.7% compared to that without InN nanowire layers.     

Graphene enhances Li storage capacity of porous single-crystalline silicon nanowires

We demonstrated that graphene significantly enhances the reversible capacity of porous silicon nanowires used as the anode in Li-ion batteries. We prepared our experimental nanomaterials, viz., graphene and porous single-crystalline silicon nanowires, respectively, using a liquid-phase graphite exfoliation method and an electroless HF/AgNO3 etching process. The Si porous nanowire/graphene electrode realized a charge capacity of 2470 mAh g(-1) that is much higher than the 1256 mAh g(-1) of porous Si nanowire/C-black electrode and 6.6 times the theoretical capacity of commercial graphite. This relatively high capacity could originate from the favorable charge-transportation characteristics of the combination of graphene with the porous Si 1D nanostructure.     

Al-doped single-crystalline SiC nanowires synthesized by pyrolysis of polymer precursors

Al-doped 6H-SiC nanowires are synthesized by catalyst-assisted pyrolysis of polymer precursors. The obtained nanowires were characterized using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and selective area electron diffraction. We demonstrate that doping concentrations can be controlled by tailoring the Al concentrations in the precursors. We also find that Al-doping has a profound effect on the morphology and emission behavior of the SiC nanowires. The current results suggest a simple technique for synthesizing Al-doped SiC nanomaterials in a controlled manner, which are promising for applications in optical and electronic nanodevices.     

Correction to: Deposition of bismuth sulfide and aluminum doped bismuth sulfide thin films for photovoltaic applications

Journal of Materials Science: Materials in Electronics -