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have been measured following excitation by 59.54 keV ␥ rays from a 200 mCi 241 Am point source. Comparison of the intensity ratios for Ni with the multiconfiguration Dirac-Fock calculations indicates decreasing 3d electron population with the increase of silicon concentration, a trend similar to the one predicted by the previous theoretical calculations ͓O. Bisi and C. Calandra, J. Phys. C 14, 5479 ͑1982͔͒. However, quantitatively our results for the Ni 3d electron population are different from the results reported there. The intensity ratios for Ni and Cu in disilicide compounds indicate enhancement of the K␤-to-K␣ ratio over the pure metal values, but for the other silicide compounds the Ni intensity ratios show opposite behavior than Cu, suggesting a difference in the nature of electron delocalization.

Information on the polarization properties of scattered light from plasmonic systems are of paramount importance due to fundamental interest and potential applications. However, such studies are severely compromised due to the experimental difficulties in recording full polarization response of plasmonic nanostructures. Here, we report on a novel Mueller matrix spectroscopic system capable of acquiring complete polarization information from single isolated plasmonic nanoparticle/nanostructure. The outstanding issues pertaining to reliable measurements of full 4 × 4 spectroscopic scattering Mueller matrices from single nanoparticle/nanostructures are overcome by integrating an efficient Mueller matrix measurement scheme and a robust eigenvalue calibration method with a dark-field microscopic spectroscopy arrangement. Feasibility of quantitative Mueller matrix polarimetry and its potential utility is illustrated on a simple plasmonic system, that of gold nanorods. The demonstrated ability to record full polarization information over a broad wavelength range and to quantify the intrinsic plasmon polarimetry characteristics via Mueller matrix inverse analysis should lead to a novel route towards quantitative understanding, analysis/interpretation of a number of intricate plasmonic effects and may also prove useful towards development of polarization-controlled novel sensing schemes.

The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.

The electronic structure of hexagonal potassium tungsten bronze K 0.25 WO 3 has been investigated by highresolution angle-resolved photoemission spectroscopy ͑ARPES͒. The experimentally determined band structure resolves the long-standing puzzles concerning the anomalous transport properties in this hexagonal bronze. We find that the ARPES-derived Fermi surface is the consequence of hidden one-dimensional ͑1D͒ bands, in good agreement with the calculated Fermi surface. These results indicate that the high-temperature anomaly in the electrical resistivity originates in the possible charge-density-wave formation associated with the hidden 1D Fermi surfaces.