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Preferential Growth Direction (preferential + growth_direction)
Selected AbstractsSynthesis and Lasing Properties of Highly Ordered CdS Nanowire Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2007L. Cao Abstract Highly ordered large-area arrays of wurtzite CdS nanowires are synthesized on Cd-foil substrates via a simple liquid reaction route using thiosemicarbazide and Cd foil as the starting materials. The CdS nanowires are single crystals growing along the [001],direction and are perpendicular to the surface of the substrate. The characteristic Raman peaks of CdS are red-shifted and show asymmetric broadening, which is ascribed to phonon confinement effects arising from the nanoscale dimensions of the nanowires. Significantly, the uniform CdS nanowire arrays can act as laser cavities in the visible-light range, leading to bandgap lasing at ca.,515,nm with obvious modes. The high density of nuclei and the preferential growth direction induce the formation of aligned CdS nanowires on the metal substrate. [source] Oxide-Assisted Growth of Semiconducting Nanowires,ADVANCED MATERIALS, Issue 7-8 2003R.-Q. Zhang Abstract In this contribution, we outline oxide-assisted growth (OAG) (distinct from the conventional metal-catalytic vapor,liquid,solid (VLS) process) for the growth of nanostructured materials. This synthesis technique, in which oxides instead of metals play an important role in inducing the nucleation and growth of nanowires, is capable of producing large quantities of high-purity silicon nanowires with a preferential growth direction, uniform size, and long length, without the need for a metal catalyst. The OAG 1D nanomaterials synthesis is complementary to, and coexistent with, the conventional metal-catalyst VLS approach, and can be utilized to produce nanowires from a host of materials other than Si including Ge nanowires, carbon nanowires, silicon and SnO2 nanoribbons, and Group III,V and II,VI compound semiconductor nanowires. [source] Collagen orientation in periosteum and perichondrium is aligned with preferential directions of tissue growthJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2008Jasper Foolen Abstract A feedback mechanism between different tissues in a growing bone is thought to determine the bone's morphogenesis. Cartilage growth strains the surrounding tissues, eliciting alterations of its matrix, which in turn, creates anisotropic stresses, guiding directionality of cartilage growth. The purpose of this study was to evaluate this hypothesis by determining whether collagen fiber directions in the perichondrium and periosteum align with the preferential directions of long bone growth. Tibiotarsi from chicken embryos across developmental stages were scanned using optical projection tomography (OPT) to assess preferential directions of growth at characteristic sites in perichondrium and periosteum. Quantified morphometric data were compared with two-photon laser-scanning microscopy images of the three-dimensional collagen network in these fibrous tissues. The diaphyseal periosteum contained longitudinally oriented collagen fibers that aligned with the preferential growth direction. Longitudinal growth at both metaphyses was twice the circumferential growth. This concurred with well-developed circumferential fibers, which covered and were partly interwoven with a dominant network of longitudinally oriented fibers in the outer layer of the perichondrium/periosteum at the metaphysis. Toward both articulations, the collagen network of the epiphyseal surface was randomly oriented, and growth was approximately biaxial. These findings support the hypothesis that the anisotropic architecture of the collagen network, detected in periosteum and perichondrium, concurs with the assessed growth directions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1263,1268, 2008 [source] Synthesis and photoluminescence properties of silicon nanowires treated by high-pressure water vapor annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007B. Salhi Abstract This paper reports on silicon nanowires (SiNWs) growth on porous silicon (PS) template using vapor-liquid-solid (VLS) technique and the effect of high-pressure water vapor annealing (HWA) on their optical properties. Gold nanoparticles (Au NPs) with average mean diameter of 50 and 20 nm were used as catalysts. The SiNWs were obtained by thermal decomposition of silane gas (SiH4) at high temperature (540 °C) catalyzed by the Au NPs. The resulting nanostructures display comparable diameter to the initial gold catalysts and are few microns long without a preferential growth direction. We have next examined the optical properties of the 20 nm diameter SiNWs. As-prepared SiNWs display a weak photoluminescence (PL), which is related to the recombination emissions from defect centers. High-pressure water vapor annealing (HWA) at 260 °C and 2.6 MPa of the SiNWs led to an increase of the PL by a factor 10 without significant changes in the emission band. TEM analysis of the HWA-treated SiNWs showed a crystalline silicon core surrounded by an amorphous oxide layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by CrystallizationADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Yeo-Wan Chiang Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source] | ||||||||||