Search

Shape- and phase-controlled ZnSe nanocrystals are synthesized in hot mixtures of long-chain alkylamines and alkylphosphines. The variation in the rate of precursor addition, down to low and controlled levels, allows the nucleation, as well as the growth of the nanocrystals, to switch between the wurtzite and the zinc blend structures. Such a level of control leads to a variety of shapes, from spheres to rods to three-dimensional structures formed by rod sections interconnected through branching points. The temperature- and time-dependence of the chemical potentials for the monomer species in solution are the most relevant parameters involved in the growth mechanism.

A colloidal seeded-growth strategy, relying on time-programmed delivery of selected stabilizing surfactants, has been developed to synthesize bimagnetic hybrid nanocrystals (HNCs) that consist of a single-crystal tetrapod-shaped skeleton of ferrimagnetic (FiM) iron oxide functionalized with multiple polycrystalline spherical domains of ferromagnetic (FM) Co. Due to the direct bonding interfaces formed between the two materials at the relevant junction regions, the HNCs exhibit FiM-FM exchange coupling, which transcribes into a rich scenario of significantly modified properties (not otherwise achievable with any of the single components or with their physical mixtures), including higher saturation magnetization and coercitivity values, exchange biasing, and enhanced thermal stability due to induced extra anisotropy. The availability of these new types of HNCs suggests that development of appropriate synthetic tools for arranging distinct material domains in predetermined spatial arrangements could lead to a more rational design of nanoheterostructures potentially exploitable as active elements in future generations of magnetic recording devices.

Spherical and rod shaped organic-capped TiO2 nanocrystals (NCs), prepared by a hydrolytic route, were deposited as thin films and characterized by means of atomic force microscopy (AFM), X-ray diffraction (XRD) and surface plasmon resonance (SPR). SPR was assessed as transduction technique in order to test the sensing ability of the prepared films for detection of alcohol vapours as a function of NC shape and thermal treatment. The performances of the TiO2 nanocrystals were found to be dependent on the titania nanocrystal morphology and thermal treatment conditions, pointing to the beneficial effect of a rod-like shape as compared to a spherical one, and to a possible role of the titania surface organic coating in enhancing the sensor response. © 2004 Elsevier B.V. All rights reserved.