We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.

International audienceWe observe experimentally by photoluminescence the band structure and specific emission properties of an in-plane, light-diffracting photonic crystal formed onto a multimode gallium nitride waveguide. Clear-cut two-dimensional photonic crystal effects are reported. Comparison with modeling results in identification of the band structure, provides insight into the light diffraction mechanism and points out design issues for enhancement of the extraction efficiency

Magnetic colloidal nanocrystals tend to aggregate in solution because of magnetic dipolar interactions. A diblock copolymer was used as a stabilizer to limit these effects, especially those leading to aggregation in solution. Cobalt nanoparticles have been synthesized within inverse micelles of polystyrene-block-poly(2-vinylpyridine) copolymer in toluene by the pyrolysis of dicobalt octacarbonyl at 115°C. The nanoparticle structure at different reaction times was investigated using transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). At early reaction stages, the nanoparticles were found to be noncrystalline from TEM, and FT-IR showed that the precursor was only partially decomposed. After 15 min of reaction, the nanoparticles became crystalline, forming chains due to magnetic interactions. The noncrystalline nanoparticles could be crystallized upon heating to 420°C on grids in the transmission electron microscope. This produced nearly monodisperse single nanocrystals inside each micelle, with limited aggregation, but such annealing led to the degradation of the polymer.Magnetic colloidal or micellar chemically synthesized monodisperse nanoparticles (NPs) or nanocrystals (NCs) have recently been the subject of numerous studies because of their possible implementation into future ultrahigh density (>100 Gbit/in 2 ) patterned magnetic media (PMM) 1-5 or magnetoresistive devices, 6-8 among other applications. It is now well established that such NCs can act as single bits for information storage. 3,9 However, there are two major difficulties that should be overcome if PMM with such NCs is ever to be achieved. First, monodispersity (reduced standard deviation of the NCs population size distribution σ below 10%) has to be reached. This can be achieved by temporally separating the nucleation and growth stages involved in the synthesis of the NCs 10 or by focusing the size distribution by adjusting the precursor concentration during the synthesis. 11 Because monodisperse particles are difficult to synthesize in practical situations, postsynthesis operations such as filtering and/or size-selective precipitation 12 are used, limiting the yield of the synthesis. Furthermore, chemically synthesized magnetic colloidal NCs, each consisting of a crystalline core surrounded by small organic molecule surfactants, have, in addition to van der Waals interactions, an attractive magnetic dipole 13 that tends to cause these to aggregate in solution. Such a lack of stability in solution causes poor postsynthesis processing ability. It is possible to obtain soft magnetic or paramagnetic NCs and recrystallize them to harder magnetic phases. This method was introduced by Sun et al. with the transition from disordered fcc-FePt to fct-FePt at 560°C. 3 A similar idea was employed with cobalt (lower anisotropy than FePt but a higher magnetic moment per NC): -Co f hcp-Co at 300°C 5 or fcc-Co at 500°C. 14 Yet, there is still no real control over the interparticle distance, and this can give rise to magnet...

We present a study of the light extraction from CdSe/ZnS core/shell colloidal quantum dot thin films deposited on quantum well InGaN/GaN photonic crystal structures. The two-dimensional photonic crystal defined by nanoimprint lithography is used to efficiently extract the guided light modes originating from both the quantum dot thin films and the InGaN quantum wells. Far-field photoluminescence spectra are used to measure the extraction enhancement factor of the quantum dot emission (x1.4). Microphotoluminescence measurements show that the guided mode effective extraction lengths range between 70 and 180 microm, depending on the wavelength of light.

Fabrication of three-dimensional photonic crystal structures by interferometric lithography and nanoparticle selfassembly Appl. Phys. Lett. 93, 071105 (2008); 10.1063/1.2971202Simulation studies of self-assembly of end-tethered nanorods in solution and role of rod aspect ratio and tether length

The encapsulation of the nanocrystalline manganese‐doped zinc sulfide (ZnS:Mn) in poly(styrene‐b‐2vinylpyridine) (PS‐PVP) diblock copolymers is reported. Below the critical micelle concentration in the absence of nanocrystals (NCs), inverse micelles of PS‐PVP were induced by adding ZnS:Mn NCs, the presence of which was confirmed by scanning force microscope and dynamic light scattering. In toluene, a PS‐selective solvent, the less‐soluble PVP blocks preferentially surround the ligand‐coated ZnS:Mn NCs. For PS‐PVP encapsulated ZnS:Mn NCs, the ratio of blue emission to orange emission of ZnS:Mn NCs is dependent on both the concentration of PS‐PVP and the solvent quality. The pyridine of PVP blocks form complexes with the Zn atoms via the nitrogen lone pair and thus the sulfur vacancies are passivated. As a result, the defect‐related blue emission is selectively quenched even when the micelles are not formed. As the concentration of PS‐PVP encapsulating the ZnS:Mn NCs increases, the intensity of blue emission decreases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3227–3233, 2006

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