Grazing-angle x-ray reflectivity (XRR) is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy (EELS). We formally define an interband effective electron mass $m^{*},$ which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average $m^{*}=0.87m$ for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, $m^{*}=\left[1-{n\left(0\right)\mathrm{}}^{-2}\right]m,$ where $n\left(0\right)\mathrm{}$ is the refractive index at zero optical frequency. The fraction of ${\mathrm{sp}}^2$ bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of “magic” incidence and collection angles in the scanning transmission electron microscope can give ${\mathrm{sp}}^2$ fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and ${\mathrm{sp}}^3$ content for carbon films.

We report the characterization by Raman spectroscopy of rutile nanocrystals embedded in cluster-assembled $\mathrm{Ti}{\mathrm{O}}_2$ films produced by supersonic cluster beam deposition. Thermal annealing of the as-deposited films promotes the growth of rutile and anatase nanoparticles with a dimension distribution peaked around $10\mathrm{nm}$. We show that a phonon confinement model is not adequate to explain the features of the lattice dynamics of rutile nanocrystals. The coexistence of the two crystalline phases allows us to identify the role of chemical and structural inhomogeneities in the film potentially affecting the Raman spectra. Our results suggest that the lattice dynamics of rutile nanocrystals is influenced by the dielectric constant of the cluster-assembled films.

A systematic study of the shift and linewidth of the $E_g$ Raman peak at $144{\mathrm{cm}}^{-1}$ of anatase $\mathrm{Ti}{\mathrm{O}}_2$ nanopowders, produced by a flame aerosol technique, is here presented. The analysis was performed as a function of the crystal domain size and of the degree of oxidation. In the nanopowders, a clear contribution of the stoichiometry defects to the peak shift was evidenced, while the peak width seems to be less affected by the oxygen content. The Raman peak behavior due to size reduction has been interpreted in the framework of a phonon quantum confinement model. A critical review of the different approaches to this model, adopted in the literature to explain the behavior of the anatase Raman spectra as a function of the domain size, is presented. In particular, the hypothesis of a three-dimensional isotropic model for the dispersion relations is discussed. This analysis evidences general limits in the application of the phonon confinement model to the study and characterization of nanoparticles and nanostructured materials, showing how an uncritical use of the confinement theory can yield distorted results.

In this work we present a detailed Raman scattering investigation of zinc oxide and aluminum-doped zinc oxide (AZO) films characterized by a variety of nanoscale structures and morphologies and synthesized by pulsed laser deposition under different oxygen pressure conditions. The comparison of Raman spectra for pure ZnO and AZO films with similar morphology at the nano/mesoscale allows to investigate the relation between Raman features (peak or band positions, width, relative intensity) and material properties such as local structural order, stoichiometry, and doping. Moreover Raman measurements with three different excitation lines (532, 457, and 325 nm) point out a strong correlation between vibrational and electronic properties. This observation confirms the relevance of a multi-wavelength Raman investigation to obtain a complete structural characterization of advanced doped oxide materials.

Nanostructured carbon films produced by supersonic cluster beam deposition have been studied by in situ Raman spectroscopy. Raman spectra show the formation of a $s{p}^2$ solid with a very large fraction of $sp$-coordinated carbyne species with a long-term stability under ultrahigh vacuum. Distinct Raman contributions from polyyne and cumulene species have been observed, as well as different stabilities under gas exposure. Our experiments confirm theoretical predictions and demonstrate the possibility of producing a carbyne-rich pure carbon solid. The stability of the $s{p}^2\mathrm{\text{−}}sp$ network has important implications for astrophysics and for the production of novel carbon-based systems.