Synthesis and optical properties of ordered 30 nm PbS nanowire arrays fabricated into sulfuric anodic alumina membrane

Crystalline PbS nanowire arrays have been successfully fabricated by AC applied DC electrochemical deposition from aqueous solutions of dimethylsulfoxide DMSO solution containing lead chloride and elemental sulfur into sulfuric anodic alumina membranes (AAM). These nanowires have uniform diameters of approximately 30 nm, and their lengths are up to tens of micrometers. Scanning electron microscopy indicates that the ordered PbS nanowire arrays are completely embedded. The results of X-ray diffraction show that the as-synthesized nanowires are crystalline with highly preferential orientation. Energy dispersive spectrometer analysis shows that the composition ratio is very close to 1:1. Finally PL and UV–VIS illustrate the quantum confinement effects of PbS nanowire arrays.     

Growth of mane-like ZnS nanostructures by using a two-heating zone-tube furnace: structural characterization and photoluminescence

We have synthesized ZnS nanowires with mane-like branches by thermal evaporation of ZnS powder on the Au-coated Si(100) substrate using a two-heating zone tube furnace. The ZnS powder and the Si substrate were kept at 1,000 and 850 °C, respectively, in a nitrogen atmosphere during synthesis of the ZnS nanostructures. Field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and photoluminescence (PL) spectroscopy analyses were performed to investigate the structure, morphology and photoluminescence properties of the products. The axial nanowires grow along the [002] direction and have diameters of 100–200 nm, while on the other hand the branch nanowires grow along the [101] direction and their diameters and lengths are 30–50 and 800–100 nm, respectively. The room temperature PL spectrum with a Gaussian fitting exhibits two visible light emission bands centered at around 397 and 458 nm.     

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.     

Carbonization-assisted integration of silica nanowires to photoresist-derived three-dimensional carbon microelectrode arrays

We propose a novel technique of integrating silica nanowires to carbon microelectrode arrays on silicon substrates. The silica nanowires were grown on photoresist-derived three-dimensional carbon microelectrode arrays during carbonization of patterned photoresist in a tube furnace at 1000?°C under a gaseous environment of N(2) and H(2) in the presence of Cu catalyst, sputtered initially as a thin layer on the structure surface. Carbonization-assisted nucleation and growth are proposed to extend the Cu-catalyzed vapor-liquid-solid mechanism for the nanowire integration behaviour. The growth of silica nanowires exploits Si from the etched silicon substrate under the Cu particles. It is found that the thickness of the initial Cu coating layer plays an important role as catalyst on the morphology and on the amount of grown silica nanowires. These nanowires have lengths of up to 100 μm and diameters ranging from 50 to 200 nm, with 30 nm Cu film sputtered initially. The study also reveals that the nanowire-integrated microelectrodes significantly enhance the electrochemical performance compared to blank ones. A specific capacitance increase of over 13 times is demonstrated in the electrochemical experiment. The platform can be used to develop large-scale miniaturized devices and systems with increased efficiency for applications in electrochemical, biological and energy-related fields.     

Synthetic control of large-area, ordered silver nanowires with different diameters

Silver (Ag) nanowires with different diameters (28, 38, 55, 80, 200 nm) have been successfully fabricated into the anodic alumina membranes (AAMs) by direct-current electrochemical deposition technique. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation independent of the nanowire diameters. Transmission electron microscopy and field-emission scanning electron microscopy investigation reveal that the large-area and highly ordered Ag nanowire arrays with smooth surface and uniform diameter are synthesized, and they have the high aspect ratio. The formation mechanism of the silver nanowires is also discussed. The nanowire arrays with different diameters may have potential applications in the future nanodevices.     

Large scale synthesis of highly pure single crystalline tellurium nanowires by thermal evaporation method

Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300 degrees C at 1 torr and condensed on the Si substrate at 100-150 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications.     

Synthesis of single-crystal GaN nanowires on Si(111) substrate by ammonification technology

GaN nanowires have been synthesized on Si(111) substrate through ammoniating Ga₂O₃/BN films under flowing ammonia atmosphere at the temperature of 900 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that the nanowires are hexagonal wurtzite GaN and possess a smooth surface with diameters ranging from 40 to 100 nm and lengths up to several tens of micrometers. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Gallium nitride nanowires doped with magnesium

GaN nanowires doped with Mg have been synthesized on Si (111) substrate through ammoniating Ga₂O₃ films doped with Mg under flowing ammonia atmosphere. The Mg-doped GaN nanowires were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The results demonstrate that the nanowires were single crystalline with hexagonal wurzite structure. The diameters of the nanowires ranged 20-30 nm and the lengths were about hundreds of micrometers. The intense PL peak at 359 nm showed a blueshift from the bulk band gap emission, attributed to Burstein-Moss effect. The growth mechanism of the crystalline GaN nanowires is discussed briefly.     

Fabrication and structure properties of GaN nanowires by ammoniating Ga2O3 films

The GaN nanowires were successfully synthesized on Si(111) substrates by ammoniating the Ga₂O₃/ZnO films at 900 °C. The structure and morphology of the as-prepared GaN nanowires were studied by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM) and field-emission transmission electron microscopy (FETEM). The results show that the single-crystal GaN nanowires have a hexagonal wurtzite structure with lengths of about several micrometers and diameters ranging from 30 nm to 120 nm, which are conducive to the application of nanodevices. Finally, the growth mechanism is also briefly discussed.     

Investigation of indium oxide as a self-catalyst in ZnO/ZnInO heterostructure nanowires growth

We investigated the self-catalytic role of indium oxide in the growth process of ZnO/ZnInO heterostructure nanowires on Si(111). The prepared nanowires had hexagonal cross sections and were tapered with tip diameters of 90 ± 5 nm and base diameters of 230 ± 5 nm. Energy dispersive X-ray and field emission Auger spectroscopies indicated that the grown nanowires were heterostructures of ZnO and ZnInO. Analysis of the early growth process revealed that indium may play a self-catalytic role. Therefore, the vapor-liquid-solid mechanism is likely to be responsible for growth of ZnO/ZnInO nanowires. X-ray diffraction and room temperature photoluminescence (PL) data demonstrated that the presence of indium results in a decrease in nanowires' crystallinity. These wires produced a large PL emission peak in the ultraviolet (UV) region and a smaller peak in the green region of the electromagnetic spectrum. The UV peak of the ZnO/ZnInO nanowires is blue-shifted with respect to that of pure ZnO nanowires.     

Silicon nanowire growth on glass substrates using hot wire chemical vapor deposition

We report here, the first observation of silicon nanowire growth via the VLS route at 400 °C using the HWCVD technique with gold (Au) as catalyst. The supersaturation of the alloy droplet, due to a large flux of atomic silicon generated due to efficient dissociation of the silane over the hot wire, leads to the precipitation of Si nanowires. The hot wire process plays a dual role in the entire nanowire growth. Firstly, the atomic hydrogen generated from the hot wire leads to the formation of the metal nanoclusters. Secondly, it offers a continuous supply of silicon atoms enabling efficient diffusion of Si into the Si-Au eutectic alloy leading to the growth of dense silicon nanowires as observed in the SEM. The Raman and TEM data show that the Si nanowires are amorphous in nature. Precise tuning of the hot wire CVD process parameters gives rise to a high density of silicon nanowires having diameters as small as 50 nm and lengths of about a few microns.     

The oxides growth during high-temperature oxidation of Si1-xGe(x) nanowires

Concerning the oxidation behavior of Si1-xGe(x) (x = 0.15, 0.3) nanowires at high temperature, Si1-xGe(x) nanowires were thermally oxidized for various lengths of time compared with Si nanowires, Si and Si1-xGe(x) thin films. The structural and compositional properties of the oxidized nanowires were characterized using several transmission electron microscopy (TEM) techniques including energy dispersive X-ray spectroscopy (EDS), which confirm that the oxidation rates of Si1-xGe(x) and Si (silicon) nanowires were saturated with increasing oxidation time due to retarding behavior, while the oxidation rate of Si1-xGe(x) nanowires were faster than that of Si nanowires. In addition, the differences in Ge (germanium) content and stress distribution contribute to the observed differences in oxidation behavior.     

Forest of ultra thin silicon nanowires: realization of temperature and catalyst size

One of the most important progresses in the field of nano science and technology was partially due to the high surface to volume ratio of quasi one-dimensional silicon nanowires (SiNWs) with various applications in biological and chemical sensors, optoelectronic devices, catalysis, Li ion batteries and solar cells. In this study we have prepared a uniform forest of ultrathin SiNWs using plasma enhanced chemical vapor deposition method. Uniformly distributed SiNWs were obtained based on an Au layer containing gold nano-seeds with the average diameters ranging from 10 to 40 nm at various temperatures. The physicochemical properties of SiNWs were characterized using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), photoluminescence (PL) and high-resolution transmission electron microscopy. Microscopic assessments revealed that crystalline-amorphous core–shell SiNWs with different diameters and lengths ranging from 35 to 130 nm and ~?0.7 to 1.9 µm are formed during the vapor–liquid–solid mechanism, respectively. The XRD spectra show that the main lattice directions are Si(111), Si(220) and Si(311) which confirm crystalline structure of synthesized NWs. The PL spectrum reveal two distinct emission peaks at wavelengths of about 480 nm (blue range) and 690 nm (red range) as sharp and a broad peak, respectively.     

Synthesis and properties of semiconducting iron pyrite (FeS2) nanowires

We report the growth and structural, electrical, and optical characterization of vertically oriented single-crystalline iron pyrite (FeS(2)) nanowires synthesized via thermal sulfidation of steel foil for the first time. The pyrite nanowires have diameters of 4-10 nm and lengths greater than 2 μm. Their crystal phase was identified as cubic iron pyrite using high-resolution transmission electron microscopy, Raman spectroscopy, and powder X-ray diffraction. Electrical transport measurements showed the pyrite nanowires to be highly p-doped, with an average resistivity of 0.18 ± 0.09 Ω cm and carrier concentrations on the order of 10(21) cm(-3). These pyrite nanowires could provide a platform to further study and improve the physical properties of pyrite nanostructures toward solar energy conversion.     

Synthesis of GaN nanowires through Ga2O3 films' reaction with ammonia

GaN nanowires were synthesized by ammoniating Ga₂O₃ films on Ti layers deposited on Si (111) substrates at 950 °C. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD, FTIR and HRTEM studies showed that these nanowires were hexagonal GaN single crystals. SEM observation demonstrated that these GaN nanorods with diameters ranging from 50 nm to 100 nm and lengths up to several micrometers intervene with each other on the substrate.     

Growth and characterization of tetragonal Mn3O4 nanowires

Mn3O4 nanowires were synthesized by calcination of a precursor obtained in a novel microemulsion. Transmission electron microscopy, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and selected area electron diffraction were used to characterize the structural features and chemical compositions of the as-synthesized nanowires. The results showed that the as prepared nanowires are composed of tetragonal Mn3O4, the diameters range from 50 to 800 nm, and lengths reach tens of micrometers. The nanowires are highly promising for applications in magnetic materials and sensors.     

Highly efficient charge separation and collection across in situ doped axial VLS-grown Si nanowire p-n junctions

VLS-grown semiconductor nanowires have emerged as a viable prospect for future solar-based energy applications. In this paper, we report highly efficient charge separation and collection across in situ doped Si p-n junction nanowires with a diameter <100 nm grown in a cold wall CVD reactor. Our photoexcitation measurements indicate an internal quantum efficiency of ~50%, whereas scanning photocurrent microscopy measurements reveal effective minority carrier diffusion lengths of ~1.0 μm for electrons and 0.66 μm for holes for as-grown Si nanowires (d(NW) ≈ 65-80 nm), which are an order of magnitude larger than those previously reported for nanowires of similar diameter. Further analysis reveals that the strong suppression of surface recombination is mainly responsible for these relatively long diffusion lengths, with surface recombination velocities (S) calculated to be 2 orders of magnitude lower than found previously for as-grown nanowires, all of which used hot wall reactors. The degree of surface passivation achieved in our as-grown nanowires is comparable to or better than that achieved for nanowires in prior studies at significantly larger diameters. We suggest that the dramatically improved surface recombination velocities may result from the reduced sidewall reactions and deposition in our cold wall CVD reactor.     

Nitrogen-doped tungsten oxide nanowires: low-temperature synthesis on Si, and electrical, optical, and field-emission properties

Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.     

Synthesis and characterization of amorphous silicon oxide nanowires embedded with Ni nanoparticles

The growth of silicon oxide nanowires (SiOxNWs) was obtained by thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafer in mixed gases of nitrogen (N₂) and hydrogen (H₂). TEM analysis showed that SiOxNWs had diameters ranging from 100 to 200 nm with lengths extending up to a few μm and their structure was amorphous. SiOxNWs were grown by the reaction between Ni NPs and Si wafer and Ni NPs acted as catalysts. Ni silicides (NixSi) were also formed inside the wafer by Ni diffusion into Si wafer.     

Synthesis of silver sulfide nanowires in ethylene glycol through a sacrificial templating route

In this study, Ag₂S nanowires were prepared in ethylene glycol using single-crystal silver nanowires as a sacrificial templating and choosing suitable sulfur sources for the sulfuration reaction. X-ray powder diffraction and a transmission electron microscope equipped with an energy dispersive X-ray analysis were used to characterize the products. The results indicated Ag₂S nanowires with diameters of about one hundred nanometers and lengths up to several micrometers could be obtained through this method. The selected area electron diffraction pattern and high-resolution transmission electron microscope imaging indicated that the Ag₂S nanowires thus formed were crystalline.