G. D. Hale

Light scattering from dipole and quadrupole nanoshell antennas

Metal nanoshells are nanoscale optical components that allow for the controllable redirection of electromagnetic radiation via careful engineering of their multilayer structures. By varying the core size and shell thickness of these nanoparticles, nanoscale “antennas” are constructed that can be selectively driven into a dipolar or quadrupolar oscillation pattern. With scattering cross sections many times larger than their physical cross section, these antennas efficiently couple to the incident electromagnetic wave. These structures can focus, redirect, or split the incident light with subwavelength precision, and may find useful applications in the remote coupling of electromagnetic signals into nanoscale machines or devices.

Threefold Electron Scattering on Graphite Observed with C60-Adsorbed STM Tips

The scanning tunneling microscope (STM) has been used to observe threefold symmetric electron scattering from point defects on a graphite surface. These theoretically predicted electronic perturbations could not be observed with a bare metal tip but could only be imaged when a fullerene (C60) molecule was adsorbed onto the tunneling region (apex) of an STM tip. Functionalizing an STM tip with an appropriate molecular adsorbate alters the density of states near the Fermi level of the tip and changes its imaging characteristics.

Enhancing the active lifetime of luminescent semiconducting polymers via doping with metal nanoshells

We report a dramatic, concentration-dependent decrease in the rate of photo-oxidation of semiconducting polymers due to the addition of small amounts of metal nanoshells to the polymer. In each case, the nanoshell resonances are tuned to the triplet exciton-ground state energy of the polymer. The nanoshell dopants slow the oxidation rate yet do not affect the photoluminescent properties of the polymers to which they have been added.

EFFECTS OF PHOTO-OXIDATION ON CONJUGATED POLYMER FILMS

We have used two-photon photoemission as a sensitive monitor of the effects of photo-oxidation on poly[2-methoxy,5-(2′-ethylhexoxy)-1,4-phenylenevinylene] films. We observe a downward shift in the triplet exciton energy as well as a dramatic narrowing of the triplet exciton photoemission linewidth as photo-oxidation progresses. Both of these effects are attributed to changes in the physical and electronic structure of the film due to carbonyl defect formation on the polymer chains. This technique provides a highly sensitive probe of photo-oxidation which may be useful in the optimization of conjugated-polymer-based devices and displays.

Direct observation of fullerene‐adsorbed tips by scanning tunneling microscopy

We have succeeded in imaging individual C60 molecules that have been adsorbed onto the tunneling region of a scanning tunneling microscopy tip. The individual tip‐adsorbed molecules are imaged by scanning the fullerene‐adsorbed tip over a defect covered graphite surface. The defects are generated by low energy argon ion bombardment and protrude from the graphite surface. These nanometer‐size defects serve as a surface tip array which inverse images the molecules adsorbed to the tip when the surface is scanned.

Fullerene functionalized scanning tunneling microscope tips- preparation, characterization and applications

Abstract We have succeeded in adsorbing individual C60 molecules onto the tunneling region of an STM tip. The individual tip-adsorbed molecules are imaged by scanning the fullerene-adsorbed tip over a defect covered graphite surface. These tips were subsequently used to observe three fold symmetric electron scattering from point defects on a graphite surface, an effect that could not be observed using bare metal tips. Functionalizing an STM tip with an appropriate molecular adsorbate alters the density of states near the Fermi level of the tip and modifies its imaging characteristics.