Dependence of band structure and carrier concentration of metallic (13, 13) and semiconducting (13, 0) single wall carbon nanotube on temperature

The electronic band structure, density of states (DOS) and carrier concentration of a (13,13) metallic and a (13,0) semiconducting Single Wall Carbon Nanotube (SWCNT) have been estimated and simulated by using the Fermi-Dirac distribution function. The energy dispersion E(k) relation for metallic SWCNT near the minimum energy is linear and the Fermi level was independent of temperature (T). On the other hand for semiconducting SWCNT the E(k) relation is parabolic. The normalized Fermi-Energy (EF – EC) in the nondegenerate regime is a weak (logarithmic) function of carrier concentration and varies linearly with T. In the degenerate condition, the Fermi level was independent of T and was a strong function of carrier concentration

Effects of annealing conditions on the surface morphology and crystallinity of sputtered ZnO nano films

The effects of annealing parameters on crystallinity and surface morphology of RF sputtered zinc oxide nano films were investigated. The structure and morphology of the nano films were dependent on temperature, gas flow rate and time of annealing. The results from atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) showed smooth and uniform growth of c-axis orientation films with an average grain sizes from 10 to 30 nm. Increments of the annealing temperature from 400 to 800°C led to bigger grain size, better crystallinity and also increase of the surface roughness. Moreover, the results showed that the crystallinity was independent of the annealing time up to 40 min after starting the annealing process. Increase in the percentage of oxygen in the O/Ar (mixture of annealing gases) from 50% to 100% results in no changes in AFM results, but XRD revealed that the (100) peak intensity was decreased, the position of (002) peak was slightly shifted towards higher angle and FWHM of (002) peak was improved

Carbon ion-beam-induced modification in structural and electrical properties of ZnO nanowires

Zinc oxide nanowires (ZnO NWs) have an efficacious place in nanoworld due to their tremendous properties and applications. In the present work, structural and electrical properties of ZnO NWs have been modified by carbon (C) ions- beam irradiation. With ion-beam energy of 0.8MeV, the physical behaviors of NWs have been studied under different doses from 1×1012 to 1×1014 ions/cm2. The microstructural and Raman spectroscopy studies showed that the wurtzite crystal structure of the ZnO NWs has been changed into disordered amorphous one under high C ion doses. Whereas, the XRD results showed that Zn nanoparticles are fabricated at high C ion-beam irradiation on ZnO NWs. Scanning electron microscopy (SEM) depicts the formation of cross junctions and parallel junctions between ZnO NWs after C ion irradiation. DC conductivity measurements have confirmed that the conductivity of NWs decreases with increase in C ion doses. It is concluded that the lattice defects significantly contribute to decrease in the conductivity of ZnO NWs

Control growth of silicon nanocolumns' epitaxy on silicon nanowires

The epitaxial growth of Si nanocolumns on Si nanowires was studied using hot-wire chemical vapor deposition. A single-crystalline and surface oxide-free Si nanowire core (core radius ~21 ± 5 nm) induced by indium crystal seed was used as a substance for the vapor phase epitaxial growth. The growth process is initiated by sidewall facets, which then nucleate upon certain thickness to form Si islands and further grow to form nanocolumns. The Si nanocolumns with diameter of 10-20 nm and aspect ratio up to 10 can be epitaxially grown on the surface of nanowires. The results showed that the radial growth rate of the Si nanocolumns remains constant with the increase of deposition time. Meanwhile, the radial growth rates are controllable by manipulating the hydrogen to silane gas flow rate ratio. The optical antireflection properties of the Si nanocolumns' decorated SiNW arrays are discussed in the text. © 2013 Springer Science+Business Media Dordrecht

Composition and optical property controlled in In 2 O 3 /W 2 N nanostructure composites by nitrogen plasma assisted in-situ thermal annealing

In2O3/W2N nanostructure composites were grown by nitrogen plasma assisted in-situ thermal annealing at different hot-filament temperatures, Tf. The in-situ thermal annealing changes the as-grown In2O3 nanostructure to In2O3/W2N nanostructure composite with decreasing the grain size from 200 to 300 nm to ~ 100 nm. The optical spectroscopy results indicate that the optical energy gap of the nanostructure composites (3.7–2.7 eV) can be effectively tailored by monotonically increasing the W2N incorporation. The formation of W2N is attributed to the high energetic ion bombardment of N adatoms and incorporation of W adatoms. Furthermore, the effects of the filament temperature, Tf on the compositions in relation with the optical properties of the nanostructure composite are discussed

Effect of substrate temperature on gold-catalyzed silicon nanostructures growth by hot-wire chemical vapor deposition (HWCVD)

The effect of substrate temperature on the structural property of the silicon nanostructures deposited on gold-coated crystal silicon substrate by hot-wire chemical vapor deposition (HWCVD) was studied. The uniformity and size of the as-grown silicon nanostructures is highly influenced by the substrate temperature. XRD, Raman and HRTEM measurements show the silicon nanostructures consist of small crystallites embedded within amorphous matrix. The crystallite size of the as-grown silicon nanostructures decreases with increases in substrate temperature. FTIR shows that these silicon nanostructures are highly disordered for sample prepared at substrate temperature above 250 degrees C. The correlation of crystallinity and structure disorder of the silicon nanostructures growth at different substrate temperature was discussed. (C) 2010 Elsevier B.V. All rights reserved

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/mu m 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. (C) 2011 Elsevier B.V. All rights reserved

Annealing effect on the structural and optical properties of embedded au nanoparticles in silicon suboxide films

Au/SiOx nanocomposite films have been fabricated by co-sputtering Au wires and SiO2 target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiOx films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiOx films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiOx films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiOx NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 degrees C. (C) 2012 Elsevier Ltd. All rights reserved

Radial growth of slanting-columnar nanocrystalline Si on Si nanowires

The synthesis of Si nanowires was achieved via hot-wire chemical vapor deposition using an indium catalyst. In addition to the axial catalytic growth of Si nanowires, the radial growth of columnar structures occurred on the walls of the nanowires. The HRTEM results revealed that a mixture of amorphous Si and nanocrystalline Si grains was present within the columnar structure. The nanocrystalline Si nanocolumns were slanted at an angle of similar to 66 degrees towards the wall of the NWs. The amorphous Si background in the XRD pattern and asymmetric broadening in the Si peak of the Raman spectra provided evidence for the formation of nanocrystalline Si. (C) 2011 Elsevier B.V. All rights reserved