Biomedical subjects

Shaul Aloni

Publications and source records attributed to Shaul Aloni.

6 recordsLinked to original sources

PubMed2006

Symmetry breaking in boron nitride nanotubes.

We have imaged boron nitride nanotubes with atomic scale resolution using scanning tunneling microscopy. While some nanotubes show the expected triangular lattice pattern, the majority of the nanotubes show unusual stripe patterns which break the underlying symmetry of the boron nitride lattice. We identify the origin of the symmetry breaking and demonstrate that conventional STM imaging analysis is inadequate for boron nitride nanotubes.

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PubMed2006

Faceting of nanocrystals during chemical transformation: from solid silver spheres to hollow gold octahedra.

We demonstrate that performing a replacement reaction on single crystalline Ag nanospheres of approximately 10 nm in diameter in an organic solvent produces hollow Au nanocrystals with an octahedral shape. Different from those Au shells made by starting with Ag particles about 1 order of magnitude larger, which largely reproduce that of the sacrificial Ag counterparts, the hollow nanocrystals obtained in this work show significant changes in the external morphology from the spherical Ag precursors. This evolution of a faceted external morphology during chemical transformation is made possible by the enhanced role of surface effects in our smaller nanocrystals. The competition between the Au atom deposition and Ag atom dissolution on various nanocrystal surfaces is believed to determine the final octahedral shape of the hollow Au nanocrystals. Simultaneous achievement of surface-mediated shape control and a hollow morphology in a one-pot, single-step synthetic procedure in this study promises an avenue to finer tuning of particle morphology, and thus physical properties such as surface plasmon resonance.

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PubMed2005

The effect of adsorbed oxygen on the surface potential of n-GaAs(110).

Potential variations on semiconductor surfaces are often mapped using a combination of constant current topographic and local surface photo-voltage (SPV) imaging. SPV imaging provides a direct measurement of surface-potential variations at large lateral distances from a charged defect or adsorbate. However, directly above the defect, variations in the SPV signal need to be interpreted in terms of surface screening, traps, and band bending. We have examined these effects using isolated oxygen atoms on a GaAS(110) surface, which is free of surface states. We interpret variations in the SPV signal in terms of a simple electrostatic model which considers the oxygen-induced Coulomb potential and corresponding image potential, both of which affect the surface density of states.

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PubMed2005

Understanding the role of oxidative etching in the polyol synthesis of Pd nanoparticles with uniform shape and size.

Uniform cubooctahedral nanoparticles of Pd were synthesized using a modified polyol process. Like the silver system, the Pd nanoparticles underwent dissolution due to oxidative etching by Cl-/O2. In the early stage of etching, the twinned particles in a sample were selectively removed to leave behind uniform, single-crystal cubooctahedra. If the etching was allowed to continue, the single-crystal cubooctahedra were also attacked and partially dissolved. Understanding the role of oxidative etching is critical to the achievement of both uniform shape and size.

Ethylene Glycol↗

PubMed2005

Observation of the giant stark effect in boron-nitride nanotubes.

Bias dependent scanning tunneling microscopy and scanning tunneling spectroscopy have been used to characterize the influence of transverse electric fields on the electronic properties of boron-nitride nanotubes (BNNTs). We find experimental evidence for the theoretically predicted giant Stark effect. The observed giant Stark effect significantly reduces the band gap of BNNTs and thus greatly enhances the utility of BNNTs for nanoscale electronic, electromechanical, and optoelectronic applications.

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PubMed2004

Identifying defects in nanoscale materials.

We have developed a novel iterative experimental-theoretical technique which can identify the atomic structure of defects in many-atom nanoscale materials from scanning tunneling microscopy and spectroscopy data. A given model for a defect structure is iteratively improved until calculated microscopy and spectroscopy data based on the model converge on the experimental results. We use the technique to identify a defect responsible for the electronic properties of a carbon nanotube intramolecular junction. Our technique can be extended for analysis of defect structures in nanoscale materials in general.

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