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.
A detailed study of temperature‐dependent phonon properties of exfoliated titanium disulphide (TiS2) nanosheets probed by Raman spectroscopy in the 80‐ to 450‐K temperature range is reported here. The TiS2 Raman mode (Eg, A1g, and Sh) positions exhibit linear shift dependences; however, in contradiction to typical behavior, the Sh mode surprisingly exhibits positive first‐order temperature coefficient (χ=0.0592 cm‐1/K) with increase of the temperature. In addition, the widths of studied peaks typically increase with temperature and peak intensity ratio shows no changes proving that relative phonon population is not affected by temperature. Our findings can be useful for further analysis of phonon properties and determination of thermal conductivity of supported TiS2 thin films for advanced electronics devices.
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 /I) 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 /I ratio provides evidence of a change of the doping level, demonstrating the influence of reduction processes on GO films.
In this work, we study optical spectroscopy of graphene flakes and its derivatives such as graphene oxide and reduced graphene oxide in the same surfactant-free aqueous solution. We show that transmittance (T) and absorbance (A) spectra of different graphene suspension is nearly feature-less as a function of wavelength (λ) in the VIS-NIR range (350-1000 nm) except graphene oxide solution and the smallest graphene flakes, and they change linearly with concentration. The optical absorption coefficient (at 660 nm) of pure graphene solution seems to be flake-size dependent, changing from ∼730 mL·mg−1m−1 (for ∼25 µm flake size) to ∼4400 mL·mg−1m−1 (for ∼2 µm flake size), and it is several times higher than in the case of graphene oxide, which also varies with type and level of doping/defects (checked by FTIR and statistical Raman spectroscopy). Finally, we show wavelength-dependent evolution of optical absorption coefficient in the VIS-NIR range, which is roughly mimicking the A(λ) function but is strongly material-dependent. Our study could be useful for application of graphene solution in optofluidic devices, functional inks or printed flexible optoelectronics.
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