Preferential orientation growth of AIN thin films on Si (111) substrates by LP-MOCVD

Aluminum nitride (AIN) thin films were deposited on Si (111) substrates by low pressure metalorganic chemical vapor deposition system. The effects of the V/III ratios on the film structure and surface morphology were systematically studied. The chemical states and vibration modes of AIN films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The optical absorption property of the AIN films, characterized by ultraviolet-visible-near infrared spectrophotometer, exhibited a sharp absorption near the wavelength of 206 mm. The AIN (002) preferential orientation growth was obtained at the V/III ratio of 10,000 and the preferential growth mechanism is presented in this paper according to the thermodynamics and kinetics process of the AIN growth.

Effect of partial preferential orientation and distortions in octahedral clusters on the photoluminescence properties of FeWO4 nanocrystals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of partial preferential orientation and distortions in octahedral clusters on the photoluminescence properties of FeWO4 nanocrystals

This communication is a report of our initial research to obtain iron tungstate (FeWO4) nanocrystals by the microwave-hydrothermal method at 170 degrees C for 45 min. X-ray diffraction patterns showed that the FeWO4 nanocrystals prepared with polyethylene glycol-200 have a partial preferential orientation in the (011) plane in relation to other nanocrystals prepared with sodium bis(2-ethylhexyl) sulfosuccinate and water. Rietveld refinement data indicates that all nanocrystals are monophasic with wolframite-type monoclinic structures and exhibit different distortions on octahedral [FeO6]/[WO6] clusters. High resolution transmission electron microcopy revealed an oriented attachment mechanism for the growth of aggregated FeWO4 nanocrystals. Finally, we observed that the photoluminescence properties of these nanocrystals are affected by partial preferential orientation in the (011) plane and distortions on [FeO6]/[WO6] clusters.

Growth mechanism of ZnO nanostructures for ultra-high piezoelectric d(33) coefficient

A comparative morphological study of different ZnO nanostructures was carried out with different varying process parameters for energy harvesting. Molarity, temperature, growth duration and seed layer were such fundamental controlling parameters. The study brings out an outstanding piezoelectric coefficient (d(33)) of 44.33 pm/V for vertically aligned ZnO nanorod structures, considered as the highest reported d(33) value for any kind of ZnO nanostructures. XRD analysis confirms wurtzite nature of this nanorod structure with 0001] as preferential growth direction. Semiconducting characteristic of nanorods was determined with temperature induced I/V characterization.

Growth Mechanism And Joint Structure Of Zno Tetrapods

Regular zinc oxide (ZnO) tetrapods with a flat plane have been obtained on Si(1 0 0) substrate via the chemical vapour deposition approach. The x-ray diffraction result suggests that these tetrapods are all single crystals with a wurtzite structure that grow along the (0 0 0 1) direction and corresponding electron backscatter diffraction analysis reveals the crystal orientation of growth and exposed surface. Furthermore, we find some ZnO tetrapods with some legs off and the angles between every two legs are measured with the aid of scanning electron microscopy and image analysis, which benefit to reveal the structure of ZnO tetrapods joint. The structure model and growth mechanism of ZnO tetrapods are proposed. Besides, the stable model of the interface was obtained through the density-functional theory calculation and the energy needed to break the twin plane junction was calculated as 5.651 J m(-2).

On the Growth Mechanism of Nickel and Cobalt Nanowires and Comparison of Their Magnetic Properties

Magnetic nanowires (NWs) are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic fi eld. Highly crystalline and textured nanowires of nickel (Ni NWs) and cobalt (Co NWs) with high aspect ratio (~330) and high coercivity have been synthesized by electrodeposition using nickel sulphate hexahydrate (NiSO4·6H2O) and cobalt sulphate heptahydrate (CoSO4·7H2O) respectively on nanoporous alumina membranes. They exhibit a preferential growth along〈110〉. A general mobility assisted growth mechanism for the formation of Ni and Co NWs is proposed. The role of the hydration layer on the resulting one-dimensional geometry in the case of potentiostatic electrodeposition is verified. A very high interwire interaction resulting from magnetostatic dipolar interactions between the nanowires is observed. An unusual low-temperature magnetisation switching for fi eld parallel to the wire axis is evident from the peculiar high fi eld M(T) curve

Nanoporous InP: anodic formation and growth mechanism in aqueous electrolytes

Porous layers can be formed electrochemically on (100) oriented n-InP substrates in aqueous KOH. A nanoporous layer is obtained underneath a dense near-surface layer and the pores appear to propagate from holes through the near-surface layer. In the early stages of the anodization transmission electron microscopy (TEM) clearly shows individual porous domains that appear to have a square-based pyramidal shape. Each domain appears to develop from an individual surface pit which forms a channel through this near-surface layer. We suggest that the pyramidal structure arises as a result of preferential pore propagation along the <100> directions. AFM measurements show that the density of surface pits increases with time. Each of these pits acts as a source for a pyramidal porous domain. When the domains grow, the current density increases correspondingly. Eventually the domains meet, forming a continuous porous layer, the interface between the porous and bulk InP becomes relatively flat and its total effective surface area decreases resulting in a decrease in the current density. Current-time curves at constant potential exhibit a peak and porous layers are observed to form beneath the electrode surface. The density of pits formed on the surface increases with time and approaches a plateau value. Porous layers are also observed in highly doped InP but are not observed in wafers with doping densities below ~5 × 1017 cm-3. Numerical models of this process have been developed invoking a mechanism of directional selectivity of pore growth preferentially along the <100> lattice directions. Manipulation of the parameters controlling these curves shows that the fall-off in current is controlled by the rate of diffusion of electrolyte through the pore structure with the final decline in current being caused by the termination of growth at the pore tips through the formation of passivating films or some other irreversible modification of the pore tips.

Single-step, catalyst-free plasma-assisted synthesis and growth mechanism of single-crystalline aluminum nitride nanorods

Synthesis of one-dimensional AlN nanostructures commonly requires high process temperatures (>900 °C), metal catalyst, and hazardous gas/powder precursors. We report on a simple, single-step, catalyst-free, plasma-assisted growth of dense patterns of size-uniform single-crystalline AlN nanorods at a low substrate temperature (∼650 °C) without any catalyst or hazardous precursors. This unusual growth mechanism is based on highly effective plasma dissociation of N2 molecules, localized species precipitation on AlN islands, and reduced diffusion on the nitrogen-rich surface. This approach can also be used to produce other high-aspect-ratio oxide and nitride nanostructures for applications in energy conversion, sensing, and optoelectronics. © 2010 American Institute of Physics.

Sol-Gel Template Synthesis, Structural Characterization and Growth Mechanism of Barium Zirconate Nanotubes

In this paper, we report the synthesis of barium zirconate, BaZrO3, (BZ) nanotubes fabricated by the modified sol-gel method within the nanochannels of anodic aluminum oxide (AAO) templates. The morphology, structure, and composition of as prepared nanotubes were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), selected-area electron diffraction ( SAED), high resolution TEM (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). The results of XRD and SAED indicated that postannealed (at 650 degrees C for 1 h) BZ nanotubes (BZNTs) exhibited a polycrystalline cubic perovskite crystal structure. SEM and TEM analysis revealed that BZNTs possessed a uniform length and diameter (similar to 200 nm) and the thickness of the wall of the BZNTs was about 20 nm. Y-junctions, multiple branching and typical T-junctions were also observed in some BZNTs. EDX analysis demonstrated that stoichiometric BaZrO3 was formed. HRTEM image confirmed that the obtained BZNTs were composed of nanoparticles in the range of 5-10 nm. The possible formation mechanism of BZNTs was discussed.

Growth Mechanism of Cadmium Sulfide Nanocrystals

We investigate the growth kinetics of CdS nanocrystals in the quantum confinement regime using time-resolved small-angle X-ray scattering. In contrast to earlier reports for similar systems, we establish that the growth kinetics in this case follows the Lifshitz-Slyozov-Wagner theory, for not only growth of the average diameter of the nanocrystals but also the time dependence of the size distribution and the temperature dependence of the rate constant. This is the first rigorous example of the coarsening process in the quantum confinement (< 5 nm)regime. Ab initio studies for the reaction pathways provide a microscopic understanding of this finding.

Facile hydrothermal synthesis and observation of bubbled growth mechanism in nano-ribbons aggregated microspherical Covellite blue-phosphor

Well uniform microspheres of phase pure Covellite were synthesized through a simple hydrothermal approach using poly vinyl pyrrolidone (PVP) as surfactant. The micro-spheres were constituted of numerous self-organized knitted nano-ribbons of similar to 30 nm thickness. The effect of conc. PVP in the hydrothermal precursor solution on the product morphology was investigated. Based on the out-coming product micro-architecture a growth mechanism was proposed which emphasized bubbled nucleation inside the hydrothermal reactor. In a comparative study on linear optical properties, enhancement of luminescent intensity was observed for nano-ribbon clung microspheres rather than that of agglomerates of distorted particles, which may be attributed to better crystallinity as well as reduced surface defects and ionic vacancies for ribbon-like nano-structures.

Growth mechanism of phases by interdiffusion and diffusion of species in the niobium-silicon system

The integrated diffusion coefficient of the phases and the tracer diffusion coefficients of the species are determined in the Nb-Si system by the diffusion couple technique. The diffusion rate of Si is found to be faster than that of Nb in both the NbSi2 and Nb5Si3 phases. The possible atomic mechanism of diffusion is discussed based on the crystal structure and on available details of the defect concentration data. The faster diffusion rate of Si in the Nb5Si3 phase is found to be unusual. The growth mechanism of the phases is also discussed on the basis of the data calculated in this study. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Diffusion Parameters and Growth Mechanism of Phases in the Cu-Sn System

The tracer diffusion coefficients of the elements as well as the integrated interdiffusion coefficients are determined for the Cu3Sn and Cu6Sn5 intermetallic compounds using incremental diffusion couples and Kirkendall marker shift measurements. The activation energies are determined for the former between 498 K and 623 K (225 A degrees C and 350 A degrees C) and for the latter between 423 K and 473 K (150 A degrees C and 200 A degrees C). Sn is found to be a slightly faster diffuser in Cu6Sn5, and Cu is found to be the faster diffuser in Cu3Sn. The results from the incremental couples are used to predict the behavior of a Cu/Sn couple where simultaneous growth of both intermetallics occurs. The waviness at the Cu3Sn/Cu6Sn5 interface and possible reasons for not finding Kirkendall markers in both intermetallics in the Cu/Sn couple are discussed.

Growth mechanism of phases, Kirkendall voids, marker plane position, and indication of the relative mobilities of the species in the interdiffusion zone

Often, wrong conclusions about the mobilities of species are drawn from the position of the Kirkendall marker plane or voids in the interdiffusion zone. To clarify, I have discussed the growth mechanism of the phases and the position of the marker plane depending on the relative mobilities of the species. The formation of different kinds of voids in the interdiffusion zone is discussed. Further, the microstructure that could be found because of the Kirkendall effect is also explained.