Determination of the electronic transport in type separated carbon nanotubes thin films doped with gold nanocrystals.

We report a systematic theoretical and experimental investigation on the electronic transport evolution in metallic and semiconducting carbon nanotubes thin films enriched by gold nanocrystals. We used an ultra-clean production method of both types of single-walled carbon nanotube thin films with/without gold nanocrystals, which were uniformly dispersed in the whole volume of the thin films, causing a modification of the doping level of the films (verified by Raman spectroscopy). We propose a modification of the electronic transport model with the additional high-temperature features that allow us to interpret the transport within a broader temperature range and that are related to the conductivity type of carbon nanotubes. Moreover, we demonstrate, that the proposed model is also working for thin films with the addition of gold nanocrystals, and only a change of the conductivity level of our samples is observed caused by modification of potential barriers between carbon nanotubes. We also find unusual behavior of doped metallic carbon nanotube thin film, which lowers its conductivity due to doping.

Study of the absorption coefficient of graphene-polymer composites.

In this work, we have prepared a series of polydimethylsiloxane (PDMS) composites containing various graphene flakes loadings (0.02-2 wt%), and their broadband optical properties are being investigated. We demonstrate the tunability and evolution of transmittance and reflection spectra of the composites in a wide spectral range (0.4-200 µm) as a function of graphene content. Using these data we derive the broadband wavelength-dependent absorption coefficient (α) values. Our results show that α is roughly constant in the visible and IR ranges, and, surprisingly, is approximately one order of magnitude lower in the terahertz regime, suggesting different terahertz radiation scattering mechanism in our composite. Our material could be useful for applications in optical communication, sensing or ultrafast photonics.

Statistical analysis of the reduction process of graphene oxide probed by Raman spectroscopy mapping.

We propose a method for monitoring the large-scale homogeneity of the reduction process of graphene oxide. For this purpose, a Raman mapping technique is employed to probe the evolution of the phonon properties of two different graphene oxide (GO) thin films upon controllable thermal reduction. The reduction of GO is reflected by the upshift of the statistical distribution of the relative intensity ratio of the G and D peaks (I D/I G) of the Raman spectra and is consistent with the ratio obtained for chemically reduced GO. In addition, the shifts of the position distributions of the main Raman modes ([Formula: see text], [Formula: see text]) and their cross-correlation with the I D/I G ratio provides evidence of a change of the doping level, demonstrating the influence of reduction processes on GO films.

Spectroscopy of f-f radiative transitions of Y b(³+) ions in ytterbium doped orthophosphates at ambient and high hydrostatic pressures.

Studies of absorption and luminescence spectra, and luminescence decay times of the intrashell f-f transitions of Y b(³+) ions in bulk orthophosphates at different temperatures and at high hydrostatic pressures are presented. The spectroscopic properties of Y0.99Y b0.01PO4 crystal with a tetragonal zircon structure and Gd0.99Y b0.01PO4 and La0.95Y b0.05PO4 crystals with a monoclinic monazite structure are compared. Experiments at ambient pressure were performed at temperatures from 10 to 295 K whereas measurements at high pressure were performed in a diamond-anvil cell at 10 K with a pressure up to 160 kbar. The results reveal a high thermal and pressure stability of the optical properties of the examined crystals as well as the dependence of Y b(³+) emission properties on the local symmetry of the site occupied by the ytterbium dopant.