Control of the morphology on selective area growth of GaN nanocolumns by rf-plasma-assisted

Selective area growth (SAG) of GaN nanocolumns (NCs), making use of patterned or masked (nanoholes) substrates, yields a periodic, homogeneous distribution of nanostructures, that makes their processing much easier compared with self-assembled ones. In addition, the control on the diameter and density of NCs avoids dispersion in the electrooptical characteristics of the heterostructures based on this type of material (embedded InGaN/GaN quantum disks for example). Selective area growth using a mask with nanohole arrays has been demonstrated by rf-plasma-assisted MBE [1, 2].

Substrate nanopatterning by e-beam lithography to growth ordered arrays of III-nitride nanodetectors, white light emitters, and solar cells

III-nitride nanorods have attracted much scientific interest during the last decade because of their unique optical and electrical properties [1,2]. The high crystal quality and the absence of extended defects make them ideal candidates for the fabrication of high efficiency opto-electronic devices such as nano-photodetectors, light-emitting diodes, and solar cells [1-3]. Nitride nanorods are commonly grown in the self-assembled mode by plasma-assisted molecular beam epitaxy (MBE) [4]. However, self-assembled nanorods are characterized by inhomogeneous heights and diameters, which render the device processing very difficult and negatively affect the electronic transport properties of the final device. For this reason, the selective area growth (SAG) mode has been proposed, where the nanorods preferentially grow with high order on pre-defined sites on a pre-patterned substrate

E-beam nanopatterning for the selective area growth of III-V nitride nanorods

GaN/InGaN nanorods have attracted much scientific interest during the last decade because of their unique optical and electrical properties [1,2]. The high crystal quality and the absence of extended defects make them ideal candidates for the fabrication of high efficiency opto-electronic devices such as nano-photodetectors, light-emitting diodes, and solar cells [1-3]. Nitrides nanorods are commonly grown in the self-assembled mode by plasma-assisted molecular beam epitaxy (MBE) [4]. However, self-assembled nanorods are characterized by inhomogeneous heights and diameters, which render the device processing very difficult and negatively affect the electronic transport properties of the final device. For this reason, the selective area growth (SAG) mode has been proposed, where the nanorods preferentially grow on pre-defined sites on a pre-patterned substrate [5].

E-beam nano-patterning for the ordered growth of GaN/InGaN nanorods

E-beam lithography was used to pattern a titanium mask on a GaN substrate with ordered arrays of nanoholes. This patterned mask served as a template for the subsequent ordered growth of GaN/InGaN nanorods by plasma-assisted molecular beam epitaxy. The mask patterning process was optimized for several holes configurations. The smallest holes were 30 nm in diameter with a pitch (center-to-center distance) of 100 nm only. High quality masks of several geometries were obtained that could be used to grow ordered GaN/InGaN nanorods with full selectivity (growth localized inside the nanoholes only) over areas of hundreds of microns. Although some parasitic InGaN growth occurred between the nanorods during the In incorporation, transmission electron microscopy and photoluminescence measurements demonstrated that these ordered nanorods exhibit high crystal quality and reproducible optical properties.

Advances on MBE selective area growth of III-nitride nanostructures: from nanoLEDs to pseudo substrates

The aim of this work is to provide an overview on the recent advances in the selective area growth (SAG) of (In)GaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs. The first three sections deal with the basic growth mechanisms of GaN SAG and the emission control in the entire ultraviolet to infrared range, including approaches for white light emission, using InGaN disks and thick segments on axial nanocolumns. SAG of axial nanostructures is eveloped on both GaN/sapphire templates and GaN-buffered Si(111). As an alternative to axial nanocolumns, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods. Finally, section 5 reports on the SAG of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the templates is strongly reduced as indicated by a dramatic improvement of the optical properties. In the case of SAG on nonpolar (11-22) templates, the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of these nanostructures.

Scatter factor/hepatocyte growth factor as a regulator of skeletal muscle and neural crest development.

Factors that regulate cellular migration during embryonic development are essential for tissue and organ morphogenesis. Scatter factor/hepatocyte growth factor (SF/HGF) can stimulate motogenic and morphogenetic activities in cultured epithelial cells expressing the Met tyrosine kinase receptor and is essential for development; however, the precise physiological role of SF/HGF is incompletely understood. Here we provide functional evidence that inappropriate expression of SF/HGF in transgenic mice influences the development of two distinct migratory cell lineages, resulting in ectopic skeletal muscle formation and melanosis in the central nervous system, and patterned hyperpigmentation of the skin. Committed TRP-2 positive melanoblasts were found to be situated aberrantly within defined regions of the transgenic embryo, including the neural tube, which overproduced SF/RGF. Our data strongly suggest that SF/HGF possesses physiologically relevant scatter activity, and functions as a true morphogenetic factor by regulating migration and/or differentiation of select populations of premyogenic and neural crest cells during normal mammalian embryogenesis.

Growth of boehmite nanofibers by assembling nanoparticles with surfactant micelles

It is known that boehmite (AlOOH) nanofibers formed in the presence of nonionic poly(ethylene oxide) (PEO) surfactant at 373 K. A novel approach is proposed in this study for the growth of the boehmite nanofibers: when fresh aluminum hydrate precipitate was added at regular interval to initial mixture of boehmite and PEO surfactant at 373 K, the nanofibers grow from 40 to 50 nm long to over 100 nm. It is believed that the surfactant micelles play an important role in the nanofiber growth: directing the assembly of aluminum hydrate particles through hydrogen bonding with the hydroxyls on the surface of aluminum hydrate particles. Meanwhile a gradual improvement in the crystallinity of the fibers during growth is observed and attributed to the Ostwald ripening process. This approach allows us to precisely control the size and morphology of boehmite nanofibers using soft chemical methods and could be useful for low temperature, aqueous syntheses of other oxide nanomaterials with tailorable structural specificity such as size, dimension and morphology.