We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455-basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self-assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates.

Intermetallic phases formed along a Sn-Ag eutectic solder/Cu interface during solid-state aging have been characterized and the activation energies of Cu3Sn and Cu6Sn 5 growth have been calculated. Diffusion couples consisting of Cu/ 96.5Sn-3.5Ag/Cu were aged at 110 to 208~ for 0 to 32 days. After aging, the Cu/ solder interfaces were examined using scanning electron microscopy and energy dispersive x-ray spectroscopy. The growth rate constants for each intermetallic layer were calculated assuming a simple parabolic diffusion-controlled growth model. The activation energy for Cu3Sn growth is 0.73 eV/atom and the activation energy for Cu6Sn 5 growth is 1.11 eV/atom.

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The biopolymer calf thymus deoxyribonucleic acid (DNA) is employed to stabilize cadmium sulfide ctystallites in the quantum confinement size regime (Q-CdS). In this work, the synthesis and characterization of these semiconductor 'quantum dots' is described. These O-CdS clusters are easily prepared in aqueous solution at room temperature and are extremely stable (for more than 17 months when stored at 5'C). High-resolution transmission electron microscopy shows that the crystallites have an average diameter of 5.6nm. with lattice images and diffraction patterns consistent with the zinc-blende structure of CdS. For approximately 15% of the particles, unique hollow-sphere-or hollow-hemisphereshaped CdS structures are observed. and their presence attributed to the influence of the DNA host. Spectroscopically. these clusters show an absorption edge blueshifted from that of the bulk, consistent with quantum confinement, and broad trap emission characteristic of an appreciable number of defect sites at t h e semiconductor ciuster interface. apparentiy induced in pari by the hosi polynucleotide. The effects of the Q-CdS clusters on the macroscopic propelties of the DNA are illustrated by the change in intrinsic viscosity upon addition of cadmium ions and subsequent CdS formation.

We report here a comparison of the ability of the monodentate Lewis base n-propylamine and the bidentate molecule ethylenediamine to quench the photoluminescence of light-emitting silicon in three different structural environments. These include porous silicon fabricated from p-type substrates; porous silicon from n-type substrates, and Si nanocrystallites derived from porous silicon. Both types of porous Si substrates were characterized by conventional transmission electron microscopy, while the Si nanocrystallites were characterized by high-resolution transmission electron microscopy. The fractional changes in photoluminescence as a consequence of amine addition were measured and fitted to a static equilibrium model from which adduct formation constants were calculated. It is found that the Si lumophores embedded in the porous oxides on n-and p-type substrates interact similarly with n-propylamine and ethylenediamine; however, ultrasonic extraction of the nanocrystalline Si fragments from the porous oxide layers and subsequent exposure to these amines reveals a near order of magnitude difference between the equilibrium constants for n-propylamine (log K ∼ 4.9) and ethylenediamine (log K ∼ 5.8) addition.