Optical studies of cobalt disilicide, aluminum, copper, gold, iron, and silicon nanoparticles

The optical properties of three different systems of nanoparticles are studied by ellipsometry and spectrophotometry. In the study of CoSi{dollar}sb2{dollar} metal particles embedded in a Si crystalline matrix, we first determined the complex dielectric function {dollar}varepsilon{dollar}(E) of epitaxial CoSi{dollar}sb2{dollar} films on Si from 0.062 to 22.3 eV by ellipsometry and reflectance measurements. The energy dependencies of the dielectric functions show Drude behavior at energies lower than {dollar}sim{dollar}0.2 eV with Drude parameters {dollar}hbaromegasb{lcub}rm p{rcub} = (5.8 pm 0.2){dollar} eV and {dollar}hbar/tau = (0.09 pm 0.02){dollar} eV. The energy-loss function, calculated from the optical constants, shows two peaks which correspond to the screened plasma oscillation of the free electrons and the volume plasma oscillation of all valence electrons. Using the measured optical function, a composite thin film of epitaxial CoSi{dollar}sb2{dollar} nanoparticles embedded in Si is shown to have the absorptance peak due to a surface plasmon resonance in the CoSi{dollar}sb2{dollar} particles. The peak shifts to higher energy as the ellipsoidal particles become more elongated, in good agreement with recent observations by Fathauer et al. (Phys. Rev. B 44, 1345 (1991)).; In the study of Si semiconductor nanocrystallites embedded in a CaF{dollar}sb2{dollar} insulator crystalline matrix, the optical functions n({dollar}lambda{dollar}) of Si and CaF{dollar}sb2{dollar} composite film on the Si substrate at wavelengths from 0.4 to 2.0 {dollar}mu{dollar}m have been measured by ellipsometry and spectrophotometry for different effective concentrations of Si in composite films. It has been found that the optical function n({dollar}lambda{dollar}) increases as the effective concentration of Si increases. The Maxwell-Garnett effective medium theory was used to fit the optical function n({dollar}lambda{dollar}), and the parameters from the best fit imply that the Si particles have oblate spheroidal shapes.; In the study of the system of Al, Au, Cu and Fe nanoparticles on glass substrates, we have observed the excitation of a new type of long-range surface mode from Au, Al, Cu and Fe metal-particle films. These metal-particle films have the imaginary part of the effective dielectric constant larger than the real part at the wavelength 632.8 nm, which is distinctively different from those of the bulk metals. This indicates that the long-range surface mode supported by these metal-particle films is not the free-electron surface plasmon mode but a new type of long-range surface mode. Our study shows that this type of surface mode can exist in any metal-particle film, even for the metals which are not suitable for supporting the free-electron surface plasmon mode, as long as the film has the proper thickness and appropriate boundary layers.