Direct synthesis of SiC nanowires by multiple reaction VS growth

β-SiC nanowires were directly synthesized by heating single-crystal silicon wafer and graphite without metal catalysts. The diameter of SiC nanowires is in the range of 10–30 nm, and the length is up to a few millimeters. Two kinds of SiC nanowires, namely pure SiC nanowires and SiC/SiO₂ composite nanowires, formed at higher temperature (the holding stage) and lower temperature (the cooling stage), respectively. A multiple-reaction model was proposed to explain the formation of SiC nanowires.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

Synthesis of indium-catalyzed Si nanowires by hot-wire chemical vapor deposition

Indium (In) catalyzed silicon nanowires (SiNWs) were synthesized by using hot-wire chemical vapor deposition (HWCVD) technique. Indium droplets were deposited on Si substrates by hot-wire evaporation of In wire, which was immediately followed by the growth of SiNWs from the droplets. Three sets of samples were prepared by varying the length of In wires, l, as 3, 1 and 0.5 mm. The sizes of In catalyst droplets decreased from 271.4 ± 66.8 to 67.4 ± 16.6 nm when the l was reduced from 3 to 0.5 mm. Larger size of In droplets (271.4 ± 66.8 nm) was found to induce the growth of worm-like NWs. The decrease in size of In catalyst droplets induced the formation of aligned and tapered NWs with smaller tips. The smallest value of tapering parameter, T_p of 40.5 nm/μm is correlated to the SiNWs induced by the smallest size of In droplets (67.4 ± 16.6 nm). The as-grown SiNWs showed high purity and good crystalline structure.     

Fabrication of large-scale ultra-fine Cd-doped ZnO nanowires

We demonstrate bulk synthesis of highly crystal Cd-doped ZnO nanowires by using (Cd + Zn) powders at 600 °C. These mass ultra-fine ZnO nanowires with about 0%, 1%, 4% and 8% Cd so obtained have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM). They have the uniform diameter of about 20 nm and several hundred microns in length. The growth of the as-synthesized nanowires is suggested for self-catalyzed vapor–liquid–solid.     

Size effects of nano-pattern in Si(1 1 1) substrate on the selective growth behavior of GaN nanowires by MOCVD

We report on the size effects of nano-patterned Si(1 1 1) substrates on the selective growth of GaN nanowires (NWs) using metal organic chemical vapor deposition. The nano-patterns on Si(1 1 1) substrates were fabricated by etching process of Au nano-droplets. The size of nano-patterns fabricated on Si(1 1 1) substrates were corresponding to size of Au nano-droplets, and the diameter of GaN NWs grown on nano-patterns was similar to the size of nano-pattern. Dense and well-oriented GaN NWs were grown on Si(1 1 1) substrates corresponding to the nano-patterns with an average diameter of about 50 nm. However, only a few GaN bulk grains, and mixed phase of a few NWs and bulk crystal of GaN were grown on the nano-patterned Si(1 1 1) having too small and large diameter, respectively, compare to the nano-patterns with diameter of 50 nm. Our results suggested that the selective growth of GaN NWs is strongly affected by the size of nano-patterns and its related mechanism.     

Structural characterization of β-SiC nanowires synthesized by direct heating method

Crystal structure of β-SiC nanowires was investigated using Raman spectroscopy, FT-IR, XRD, transmission electron microscopy and selected area electron diffraction. Cubic β-SiC nanowires were synthesized by heating NiO catalyzed Si substrates with WO₃ and graphite mixed powders in the growth temperature of 1000–1100 °C. HRTEM image showed atomic arrangements of the grown SiC nanowires with a main growth direction of [111]. Raman spectra showed two characteristic peaks at 796 cm^− 1 and 968 cm^− 1, which are corresponding to transversal optic mode and longitudinal optic mode of β-SiC, respectively. Also, FT-IR absorption spectroscopy showed a SiC characteristic absorption band at ∼792 cm^− 1.     

A green and facile route to synthesize calcium silicate nanowires

Large-scale single crystalline calcium silicate nanowires have been synthesized via a simple and facile hydrothermal route using nanoscale SiO₂ and CaO powders as the starting materials. Xonotlite [Ca₆(Si₆O₁₇)(OH)₂] nanowires were first achieved after hydrothermal treatment at 220 °C for 12 h. After being calcinated at 800 °C for 1 h, the Ca₆(Si₆O₁₇)(OH)₂ nanowires are completely transformed into β-CaSiO₃ nanowires. The β-CaSiO₃ nanowires have a diameter of 30–150 nm and a length of tens of micrometers. The hydrothermal conditions and the size of the raw materials play important roles on the size of the nanowires. A possible growth mechanism of the nanowires is also proposed.     

Novel method to synthesize SiC nanowires and effect of SiC nanowires on flexural strength of Cf/SiC composite

The graphite fiber toughened silicon carbide (C_f/SiC) composite was annealed at 1500, 1600, 1700, 1750, 1800 and 1850 °C for 30 min and the flexural strength increased first and then decreased as annealing temperature increased. The maximum flexural strength was obtained for the sample annealed at 1750 °C. The microstructure observation indicated that the amount and length of in situ formed SiC nanowires increased as the annealing treatment time increased, which was very favorable to the improvement of flexural strength. The formation of SiC nanowires was attributed to the presence of the metal La and Al. The vapor–liquid–solid growth mechanism of the SiC nanowires along 〈1 1 1〉 direction is proposed. Furthermore, the purpose of this paper is to report novel method to synthesize SiC nanowires.     

Synthesis of SiO2 covered SiC nanowires with milled Si,C nanopowders

SiO₂ covered β-SiC nanowires were directly synthesized with a novel method, annealing the milled Si,C nanopowders at 900–1100 °C on Si wafer or Al₂O₃ substrate, and there is no any metal catalysts used. The diameters of the nanowires are range of 20 to 50 nm, and the lengths of the nanowires are up to several hundreds of microns. There is a uniform SiO₂ amorphous layer on the surface of SiC nanowires. The axial direction of SiC nanowires is < 111>, and there are stacking faults and twin lamellae in the SiC nanowires. The synthetic mechanism of SiC nanowires includes two solid–solid reactions and one gas–solid reaction between SiO, Si, C and CO.     

Synthesis and characterization of silicon nanowires using tin catalyst for solar cells application

Tin-catalyzed silicon nanowires were synthesized for solar cells application. Voluminous silicon nanowires were fabricated on single crystalline silicon wafer. Optical reflectance and solar cell efficiency of the synthesized silicon nanowires were explored. The reflectance of as-synthesized silicon nanowires was obtained approximately 5% in the short wavelength region (λ < 500 nm). A short circuit current of 2.3 mA/cm² and open circuit voltage of 520 mV for 1 cm² SiNWs solar cell was obtained.     

Formation and photoluminescence properties of amorphous silicon oxide nanowires

The silicon oxide nanowires (SiOxNWs) were grown by the thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafers in mixed gasses of nitrogen (N₂) and hydrogen (H₂) at temperatures of 900, 1000, and 1100 °C. Each NW was about 20–100 nm in diameter embedding with Ni NPs inside, and its structure was amorphous. The ratio of Si and oxygen (O) was 1:2.18. Blue emission spectrum was observed at the wavelength of 450 nm and the peak intensity increased with the increasing process temperature.     

Structure and field emission properties of SnO2 nanowires

SnO₂ nanowires were fabricated using a simple and economical method of rapid heating SnO₂ and graphite powders at 850 °C in a flow of high-purity N₂ as carrier gas. Research by using X-ray diffraction (XRD) indicates that SnO₂ nanowires are primitive tetragonal in structure with the lattice constant a = b = 0.443 nm and c = 0.372 nm. Observations by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that SnO₂ is of nanowire structure. The selected area electron diffraction (SAED) shows that the nanowires are perfect single crystal structure. The Fourier transform infrared (FT-IR) exhibits the difference of nanostructure materials and general materials. The field emission (FE) properties had also been studied.     

Evaluation of processing parameters effects on the formation of Si3N4 wires synthesized by means of ball milling and nitridation route

Crystalline silicon nitride (Si₃N₄) wires have been synthesized by means of ball milling and nitridation route. The influence of temperature of reaction and starting condition of the powder (milled or unmilled) on the synthesis of Si₃N₄ wires were studied. The reduced size of silicon particle during the milling process led to an increased degree of nitridation.Silicon powders with higher surface energy can react incessantly with nitrogen to form silicon nitride wires. The results show that the Si₃N₄ was fully formed with two kinds morphologies including globular and wire with a width of 100–300 nm and a length of several microns at temperature of 1300 °C for 1 h by employing the milled silicon powder. The infrared adsorption of wires exhibit absorption bands related to the absorption peaks of Si–N band of Si₃N₄.     

Synthesis of magnesium borate (Mg2B2O5) nanowires,growth mechanism and their lubricating properties

Large quantities of single crystalline magnesium borate nanowires of the form Mg₂B₂O₅ with typical diameter about 120–180 nm and length about 0.2 mm have been successfully synthesized by a new and simple method of heating the mixed tablet of Mg(BO₂)₂ and graphite directly in vacuum at 1200 °C for 1 h. The products have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and selected area electron diffraction. The process of the nucleation and the growth of nanowires have been analyzed by VS mechanism. The results of the lubricating properties show that the friction coefficient of the oil is significantly decreased by the addition of Mg₂B₂O₅ nanowires. Our results indicate that the new method we use is effective in synthesis of Mg₂B₂O₅ nanowires and the nanowires can be used as additive to antiwear nanodevices.     

SiC nanowires grown on activated carbon in a polymer pyrolysis route

β-SiC nanowires are a novel type of photocatalysts. However, they tend to be entangled together especially at high concentrations when dispersed in water, which may reduce the photocatalytic activity. It is reasonable to expect that β-SiC nanowires would provide better photocatalytic activity if they are grown on activated carbon. In the letter we report the successful synthesis of quantities of β-SiC nanowires grown on the surfaces of the activated carbon by pyrolysis of polycarbosilane at 1300 °C. The nanowires, with the diameters of 50–100 nm and the length of tens of micrometers, are composed of single crystal β-SiC along the 〈1 1 1〉 direction. Both the VLS and the VS mechanisms were employed to interpret the nanowires growth.     

Synthesis and photoluminescence of zinc sulfide nanowires by simple thermal chemical vapor deposition

We present a synthetic method of zinc sulfide nanowires by a simple and safe reaction of zinc oxide and iron sulfide powders on a gold-coated silicon substrate through chemical vapor transport and condensation. High quality ZnS nanowires with single crystalline wurtzite structures are grown along [0 0 1] direction with diameters in the range of 10–30 nm and lengths up to tens of micrometers. Photoluminescence spectrum shows strong emission near 339 nm. These nanowires with cleaved ends could be a prominent candidate material for a nanoscale cavity as a ultra-violet nanolaser.     

Hydrothermal synthesis and magnetic properties of α-MnO2 nanowires

In the present study, one-dimensional (1D) α-MnO₂ nanowires with width of 50–60 nm, length about several micrometers have been successfully prepared under hydrothermal conditions in the presence of sodium carboxymethyl cellulose. The samples were characterized by X-ray diffraction, scanning electron microscope, superconducting quantum interference device and N₂ adsorption–desorption experiment. The magnetic measurement reveals that the α-MnO₂ nanowires exhibit a ferromagnetic behavior at 5 K and a paramagnetic behavior at 300 K. The N₂ adsorption–desorption experiment shows that surface area is 160.4 m² g^?1, which is even larger than those of mesoporous nanostructures. At the same time, the possible formation mechanism for the formation of α-MnO₂ nanowires has been proposed according to the experimental results.     

Sol–gel-hydrothermal synthesis and sintering of K0.5Bi0.5TiO3 nanowires

The sol–gel-hydrothermal processing of K_0.5Bi_0.5TiO₃ (KBT) nanowires as well as their sintering behavior at 1000–1100 °C were investigated. The morphological analyses indicated that sol–gel-hydrothermal route led to the formation of KBT nanowires with diameters of 4 nm and lengths of 100 nm at low processing temperature of 200 °C with KOH concentration of 6 M. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowires. The KBT ceramics with a relative density of more than 95% can be successfully fabricated from the high quality KBT nanowires even by a conventional sintering process. The KBT ceramics sintered at 1050 °C showed typical characteristics of relaxor ferroelectrics, and the dielectric properties were better than that prepared by all other methods reported previously.     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Growth of SiO2 hierarchical nanostructure on SiC nanowires using thermal decomposition of ethanol and titanium tetrachloride and its FTIR and PL property

Novel SiO₂ hierarchical nanostructure has been grown on SiC nanowires using thermal decomposition of a mixture of ethanol and titanium tetrachloride. Novel nanostructure was realized in one synthesis route. Based on SEM and TEM observations, the hierarchical nanostructure consists of core-shell SiC–SiO₂ main stem nanowire and a lot of SiO₂ nanorod branches grown on the main stem. A mean diameter of SiC central cores was about 40 nm and their lengths reach about 100 μm. The lengths and diameters of SiO₂ nanorod-like branches were ranged in 400–800 nm and 30–120 nm, respectively. The growth of core-shell SiC–SiO₂ nanowires obeyed vapor–liquid–solid mechanism and the SiO₂ nanorod-like branches grew via vapor–solid mechanism. The infrared absorption and photoluminescence properties of the grown nanostructure were investigated.