We report a significant reduction in the lattice thermal conductivity of the CoSb3 skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb3 skutterudite samples (Te0.1Co4Sb12, Se0.1Co4Sb12, Te0.05Se0.05Co4Sb12) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb3 skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773 K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb3 skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb3 skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb3 skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ∼ 0.9 W/mK at 773 K is achieved in Te0.1Co4Sb12 skutterudites, which is the lowest value reported so far in CoSb3 skutterudites, doped with single Te chalcogen atom.

The confinement of water in quasi two-dimensional layers is intriguing because its physical properties can be significantly different when compared to those of the bulk fluid. This work describes spectroscopic ellipsometry study of confined water layers trapped between sheets of graphene oxide at varied thermal annealing temperatures. The wavelength-dependent refractive index of graphene oxide changes abruptly with annealing temperatures for Tann ≈ 125–160 °C, and we demonstrate that these changes are primarily governed by the expulsion of trapped water. This expulsion is associated with the decrease of interlayer separation of graphene oxide sheets from 7.8 Å to 3.4 Å. Graphene oxide annealed at high temperatures lacks trapped water layers and robust estimates of refractive index can be obtained within a Lorentz oscillator model. The trends in oscillator parameters are extended to lower annealing temperatures, where trapped water is present, in order to estimate the refractive index of confined water, whose value is found to be enhanced as compared to that of bulk. Temperature-dependent ellipsometry data show anomalous changes in ellipsometric parameters over a wide temperature interval (−10 to 10 °C) about the ice-point and these may be attributed to possible phase transition(s) of confined water.

Using X-ray reflectivity, spectroscopic ellipsometry and Raman spectroscopy, we have studied the stratified structure and the two glass-like thermal transitions in sufficiently aged glassy polystyrene films. We find that favorable interaction between the solid substrate and the polymer film induces stratification within the film resulting in different densities across the film thickness. Existence of two glass-like thermal transitions (one at 70 °C and the other at 95 °C) is independently confirmed by temperature dependent spectroscopic ellipsometry and Raman spectroscopy measurements. Interestingly, the thermal coefficient of expansion of the polymer film displays anomalous behavior with temperature and is found to have the lowest value over the temperature range 70-95 °C, i.e. between the two observed glass-like thermal transition temperatures.

We study desorption of water from a confined biopolymer (chitosan thin films) by employing temperature dependent specular X-ray reflectivity and spectroscopic ellipsometry. The water desorption is found to occur via three distinct stages with significantly different desorption rates. The distinct rates of water desorption are attributed to the presence of different kinds of water with disparate mobilities inside the biopolymer film. We identify two characteristic temperatures (T and T) at which the water desorption rate changes abruptly. Interestingly, the characteristic temperatures decrease with decreasing the film thickness. The thickness dependence of the characteristic temperature is interpreted in the context of a higher mobility of polymer chains at the free surface for polymers under one-dimensional confinement.

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A strongly adsorbed, tightly bound polymer layer can exist at the polymer/substrate interface in polymer thin films and polymer nanocomposites. The characteristics of the tightly bound layer have long been...

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