Z. Charles Ying

Metal coverage dependence of local optical properties of semicontinuous metallic films

Semicontinuous silver films on insulator substrates, which exhibit unique electrical and optical properties, were studied experimentally and theoretically. The percolation threshold of the films, which were synthesized by laser ablation, was determined from a combination of studies of the surface morphology by electron microscopy and the dc electrical resistance as a function of metal concentration. Local optical properties measured by near-field optical microscopy were compared with theoretical results obtained using the Block elimination method, with good agreement. Local field distributions were found to depend on the metal concentration and wavelength of illumination. The degree of localization was found to increase at metal concentrations above and below the percolation threshold.

Study of local photomodification of nanomaterials using near-field optics

Thin films of randomly distributed silver nanoparticles are studied experimentally using photon scanning tunneling microscopy and theoretically using real-space renormalization group method. The studies reveal large variations of local optical intensity at sub-wavelength scales. In addition, irradiation of the film by nanosecond laser pulses is observed to yield substantial changes in the local optical response. The threshold for the photomodification is less than 10 mJ/cm2. It is believed that particles within some areas of nanometer scales are restructured during nanosecond laser irradiation. The geometric changes in turn result in modification of the local optical intensity.

Extraordinary localization of collective electronic states in random media

The surface plasmons (SPs) eigenproblem which arises in inhomogeneous metal-dielectric films is studied at resonance conditions. We show that short-range correlations present in the governing Kirchhoff Hamiltonian (KH) result in delocalization of the eigenstates at the center of the spectrum. The delocalization is manifested as a power law/logarithmic singularity for the density of states and SPs localization lengths. Based on the SPs eigenproblem, analytical relationships are derived for the electromagnetic response of the semicontinuous film in resonance and off-resonance regimes. Experimental studies indirectly confirm the existence of delocalized SP states in the random system.