Morphogenesis of anisotropic nanoparticles: self-templating via non-classical, fibrillar Cd2Se intermediates

Semiconductor nanorods nucleate via a fibrillar intermediate that is able to template its own preferential growth direction.

Influence of Time and Temperature on Directional Growth of MoO3

Two-dimensional microstructures of molybdenum trioxide (MoO3) were synthesized by heptamolybdate tetrahydrate ammonium acidification, followed by calcination. A solution of the precursor compound heptamolybdate tetrahydrate ammonium acidified to pH 3,5 using glacial acetic acid followed by hydrothermal treatment for 150, 180 and 200 °C for 1, 6 and 12 hours. Then, the intermediate was calcined at 300 °C for varying time 6 and 12h to obtain MoO3. X-ray diffraction revealed that the crystals grew with crystalline structure corresponding to the orthorhombic phase of MoO3 (a-MoO3) as major phase, with a preferential growth direction along the planes (0K0). Raman spectroscopy and IR confirmed the formation of the characteristic modes of molybdenum trioxide for stage found. With Scanning Electron Microscopy (SEM) was possible to observe the formation of nanoplates.

Novel Zn-Doped SnO2 Hierarchical Architectures: Facile Synthesis, Structural Characterization and Enhanced Photocatalytic Property

Zn-doped SnO2 seaflower like hierarchical architectures have been synthesized via a solvothermal synthesis route in the mixed solvents of ethanol and deionized water. The observations of field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) showed that Zn-doped SnO2 seaflower like hierarchical architectures were assembled by the nanowires. The preferential growth direction of nanowires was determined based on the analysis of high resolution transmission electron microscopy (HRTEM). The products were also characterized by X-ray diffraction (XRD) and X-photoelectron spectrum (XPS), and the results indicated that Sn4+ ions were successfully substituted by Zn2+. The photocatalytic activity of Zn-doped SnO2 seaflower like hierarchical architectures was evaluated by the degradation of RhB aqueous solution and the results showed that the product had high photocatalytic activity efficiency.

Experimental Analysis of Seed Effect on the Directional Solidification of Sn-Pb Alloy

In this paper, an experiment model for the directional solidification of Lead/Tin alloy is built and the effects of different-shape seeds on the microstructures on the solidification microstructure are investigated. In a casting process, the temperature and concentration fields will affect the microstructures of materials and this influence is the key point of improving their mechanical and physical properties. It is not easy to control the morphology of solidifying microstructures. The scheme of directional solidification can make the microstructures grow along a fixed direction and it is also the base of single-crystal growth. In the experiment, a poly-grain seed with the same initial concentration of the solidifying casting is used to induce the columnar growth at the bottom portion of the casting, which could avoid the equiaxed growth due to the high undercooling or cooling rate there. In the experimental analysis, we studied the influences of different geometry seeds on the constrained growth, the preferential growth direction of dendrite, the grain size, the temperature gradient, the growth rate, the primary arm spacing and the secondary arm spacing. From the microstructure observation, the adding seed casting reduced the chill-affected and extended the directional solidification zone. This is expected to have the better or more complete structure of directional solidification. Keywords: Directional Solidification, Seed, Heat Transfer and Microstructure

SYNTHESIS AND LUMINESCENCE PROPERTIES OF ZnO:Eu3+ NANOWIRE ARRAYS VIA ELECTRODEPOSITED METHOD

ZnO:Eu3+ nanowire arrays (NWAs) were prepared using anodic alumina membranes (AAMs) via an electrodeposited method. The XRD patterns, high resolution transmission electron microscopy (HRTEM) and infrared absorption spectra indicate that Eu3+ has entered ZnO crystal lattice. SEM images show that the as-prepared NWAs were embedded in Al2O3 nanotube arrays (NTAs) and the uniform diameters of those nanowires are about 80 nm. The Fourier Transform pattern of the HRTEM shows that the NWAs are single crystals with preferential growth direction along the [0001]. The PL spectra show that the ratio of relative emission intensity of 612 and 597 nm increases with the increase of dopant concentration of Eu3+ . There is no emission peak at 597 nm with the dopant concentration of 10% Eu3+ . The PL results also show that a new UV emission band centered at 306 nm appears.

ANISOTROPIC GOLD NANOCRYSTALS: SYNTHESIS AND CHARACTERIZATION

In this letter we report on successful preparation and characterization of anisotropic gold nanocrystals bio-synthesized by reduction of aqueous chloroaurate ions in pelargonium plant extract. The nanocrystals have been characterized by means of Transmission Electron Microscopy (TEM), UV-VIS absorption spectroscopy and tapping mode atomic force microscopy (TM-AFM). Using these investigation techniques, the successful formation of anisotropic single nanocrystals with the preferential growth direction along the gold (111) plane has been confirmed. The high detail phase images could give us an explanation concerning the growth mechanism of the nanocrystals.

OPTICAL PROPERTIES OF Ge NANOWIRES GROWN ON SILICON (100) AND (111) SUBSTRATES

ABSTRACTIn this paper, we report Raman Scattering (RS) and photoluminescence (PL) measurements of Ge nanowires (NWs) grown via vapor-liquid-solid (VLS) using chemical vapor deposition silicon substrates consisting of (100) and (111) crystallographic orientations. Ge NWs grown are ∼40 nm in diameter, approximately a micrometer in length, and a sharp narrow Raman peak at ∼300 cm−1 indicates single crystal quality. An absence of SiGe peak in the Raman spectra indicates that SiGe interdiffusion is insignificant for the NW volume. Low temperature PL-intensity-dependence spectra indicate that the observed emission originates at the Ge NW – Si substrate interface, where SiGe intermixing has been detected. This interface is formed differently for (111) and (100) oriented Si substrates due to the <111> preferential growth direction of Ge NWs.