We demonstrate, both theoretically and experimentally, that an anomalous field enhancement occurs in the vicinity of contact points between two plasmon-resonant surfaces. The theoretical model involves two spheres in contact, and the enhancement is shown to result from the localization of surface plasmon polaritons in the vicinity of the contact point brought on by a decrease of the wavelength and an enhancement of the field of plasmons propagating toward the tip. This model is applied to experiments involving silver films having mesoscopic surface protrusions which are irradiated by intense laser pulses: films in close contact (where the protrusions touch) suffer laser-induced damage which is absent in separately irradiated films. This is interpreted as arising from the additional field enhancement, relative to the well-known enhancement occurring at isolated silver surface protrusions, brought on by the contacts.

No abstract

No abstract

The colloidal QDs of GaAs and CdS semiconductors with the radiuses about 20Å and 30Å correspondingly have been formed by laser ablation method in the liquid media. The optical absorption and the photoluminescence spectra of the GaAs and CdS colloidal QDs have been investigated experimentally and theoretically. The considerable blue shift of the photoluminescence connected with the size effects has been registered. The theoretical analysis of the optical properties has been performed on the basis of the quantum-mechanical consideration of the electron-hole system in the spherical QD in the effective mass approximation. The influence of the surface charge of the QD and of impurity centers on the absorption edge and on the luminescence properties is discussed. The dependence of the interband absorption edge wavelength λ0 (in nm) of the QD on the radius d (in nm)

No abstract