The Raman spectra of a wide range of disordered and amorphous carbons have been measured under excitation from 785 to 229 nm. The dispersion of peak positions and intensities with excitation wavelength is used to understand the nature of resonant Raman scattering in carbon and how to derive the local bonding and disorder from the Raman spectra. The spectra show three basic features, the D and G around 1600 and 1350 cm Ϫ1 for visible excitation and an extra T peak, for UV excitation, at ϳ1060 cm Ϫ1. The G peak, due to the stretching motion of sp 2 pairs, is a good indicator of disorder. It shows dispersion only in amorphous networks, with a dispersion rate proportional to the degree of disorder. Its shift well above 1600 cm Ϫ1 under UV excitation indicates the presence of sp 2 chains. The dispersion of the D peak is strongest in ordered carbons. It shows little dispersion in amorphous carbon, so that in UV excitation it becomes like a density-of-states feature of vibrations of sp 2 ringlike structures. The intensity ratio I(D)/I(G) falls with increasing UV excitation in all forms of carbon, with a faster decrease in more ordered carbons, so that it is generally small for UV excitation. The T peak, due to sp 3 vibrations, only appears in UV Raman, lying around 1060 cm Ϫ1 for H-free carbons and around 980 cm Ϫ1 in hydrogenated carbons. In hydrogenated carbons, the sp 3 C-H x stretching modes around 2920 cm Ϫ1 can be clearly detected for UV excitation. This assignment is confirmed by deuterium substitution.

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The identification of materials suitable for non-volatile phase-change memory applications is driven by the need to find materials with tailored properties for different technological applications and the desire to understand the scientific basis for their unique properties. Here, we report the observation of a distinctive and characteristic feature of phase-change materials. Measurements of the dielectric function in the energy range from 0.025 to 3 eV reveal that the optical dielectric constant is 70-200% larger for the crystalline than the amorphous phases. This difference is attributed to a significant change in bonding between the two phases. The optical dielectric constant of the amorphous phases is that expected of a covalent semiconductor, whereas that of the crystalline phases is strongly enhanced by resonant bonding effects. The quantification of these is enabled by measurements of the electronic polarizability. As this bonding in the crystalline state is a unique fingerprint for phase-change materials, a simple scheme to identify and characterize potential phase-change materials emerges.

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Herein, we demonstrate that the surface charge of gold nanoparticles (AuNPs) plays a critical role in modulating membrane potential of different malignant and nonmalignant cell types and subsequent downstream intracellular events. The findings presented here describe a novel mechanism for cell-nanoparticle interactions and AuNP uptake: modulation of membrane potential and its effect on intracellular events. These studies will help understand the biology of cell-nanoparticle interactions and facilitate the engineering of nanoparticles for specific intracellular targets.