G. Carlson

Optical and microstructural characterization of chemically synthesized gallium nitride nanopowders

Thermal decomposition of an amido precursor; [Ga2(NMe2)6, Me=CH3] in an ammonia atmosphere yielded nanostructured gallium nitride powder. The x-ray diffraction spectrum of the nanosized gallium nitride exhibited reflections corresponding to the lattice planes of fcc (zinc blende) GaN. High resolution transmission electron microscopy confirmed the cubic structure of the material and evidence of stacking faults within the fcc structure. Infrared spectra showed the characteristic Ga–N stretch at 550 cm−1. Transmission electron microscope measurements indicated that the GaN consisted of ≈50 nm sized particles which in turn are agglomerates of smaller particles with ≈5 nm domain sizes. The photoluminescence (PL) emission spectrum of the GaN was found to be sensitive to the excitation wavelength exhibiting peaks at 378 and 317 nm. The PL excitation spectrum showed resonances in the 200–300 nm region. These PL results suggest the effect of quantum confinement in these GaN particles.

Synthesis and characterization of a nanostructured gallium nitride–PMMA composite

Nanostructured gallium nitride (GaN) has been prepared by the decomposition of a dimeric precursor, Ga2[N(CH3)2]6. The resulting greyish solid exhibited X-ray diffraction peaks at 2θ= 35.5, 58 and 69°, corresponding, respectively, to the (111), (220), and (311) lattice planes of face-centred cubic (zinc blende) GaN. HRTEM showed that the material was fee, with numerous stacking faults. The GaN consisted of primary domains of diameter 5 nm agglomerated into large secondary particles, which were de-agglomerated using sonication. This process yielded single-crystal particles, which were dispersed in poly(methyl methacryate)(PMMA). The particle size was 5.5 ± 2.6 nm and the loading was approximately 9 mg ml–1. The composites have a strong optical resonance in the blue region, at ca. 320 nm.

Microscopic structure of gold particles in a metal polymer composite film

Gold particles embedded in a polymer are studied using high resolution electron microscopy, nanodiffraction, and image processing. These particles have interesting properties such as nonlinear optical susceptibility. It is found that most of the nanoparticles are single crystals, and twins and planar defects are scarcely observed. On the other hand, it is found that nanoparticles do not show smooth facets but they are instead very rough. The effects of this extended roughness in the optical properties are discussed.

Synthesis and nonlinear optical characterization of nanostructured gold/polymer composites and suspensions

Abstract Nanometric gold particles were synthesized by a liquid/liquid phase-transfer reaction. Composites of these particles were prepared by free-radical polymerization of suspensions of the particles in styr ene and methyl methacrylate monomer. Concentrations of 1.0, 1.3, and 4.4 mg/ml were prepared,with no noticeable agglomeration of particles during processing. These composites and toluene suspensions (0.18 mg/ml) showed a linear absorption peak at 530 nm, which is characteristic of nanosized gold. High-resolution electron microscopy measurement showed that the particle diameters varied from 5 to 10 nm. Degenerate four-wave mixing experiments at 532 nm yielded, on 10-micron films, a maximum value of 1.0 × 10 −10 e.s.u. for the third-order nonlinear optical susceptibility. The toluene suspension had a susceptibility of 7.7 × 10 −12 e.s.u.

DRIFTS characterization of a nanostructured gallium nitride powder and its interactions with organic molecules

Nanoparticles of gallium nitride, which are of great interest in optical technology, were synthesized and characterized. The surface chemical composition of these nanoparticles, which can affect the overall properties of the material, was analyzed by diffuse reflectance Fourier transform infrared spectrometry. The interaction of the GaN first atomic layer with acetic acid was investigated as a preliminary step for the deagglomeration study of the nanoparticles in polymer matrixes.

Synthesis and characterization of nanostructured gallium nitride/PMMA composite

Abstract Nanostructured gallium nitride (GaN) was prepared by the decomposition of a dimeric precursor, Ga 2 [N(CH 3 ) 2 ] 6 . The resulting grayish solid exhibited X-ray diffraction peaks at 2θ = 35.5°, 58°, and 69°, corresponding, respectively, to the (111), (220), and (311) lattice planes of face-centered cubic (zincblende) GaN. High-resolution transmission electron microscopy (HRTEM) showed that the material was fcc, with numerous stacking faults. The GaN consisted of primary domains of five nanometers diameter which agglomerated into large secondary particles, which were de-agglomerated using sonication. This process yielded single-crystal particles, which were dispersed in poly(methyl methacryate) (PMMA). The particle size was 5.5 ± 2.6 nm and the loading was approximately 9 mg/ml. The composites have a strong optical resonance in the blue region, at ∼320 nm.

The Formation of Polymer Monolayers: From Adsorption to Surface Initiated Polymerizations

Gold particles with diameters in the nanometer range, stabilized by the presence of alkanethiols bound to the particle surface have been synthesized. A portion of these alkanethiols contained a terminal hydroxyl group, which was shown to be capable of coordinating titanium(1V). The resultant titanium(IV) alkoxide species was able to catalyze the polymerization of hexyl isocyanate under very mild conditions. The final product of the synthesis was a gold nanoparticle with poly(hexyl isocyanate) covalently bound to the surface. Proton NMR was used to confirm the formation of poly(hexyl isocyanate). Dynamic light scattering experiments showed that the hydrodynamic radii of the particles increased markedly after the polymerization reaction, verifying that the polymer formed was bound to the particles.