We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots) by combining-the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases With the Not volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on E in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mu s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems

We study ion-damaged crystalline silicon by combining nanocalorimetric experiments with an off-lattice kinetic Monte Carlo simulation to identify the atomistic mechanisms responsible for the structural relaxation over long time scales. We relate the logarithmic relaxation, observed in a number of disordered systems, with heat-release measurements. The microscopic mechanism associated with this logarithmic relaxation can be described as a two-step replenish and relax process. As the system relaxes, it reaches deeper energy states with logarithmically growing barriers that need to be unlocked to replenish the heat-releasing events leading to lower-energy configurations.

Transparent and smooth silica thin films with a very high porosity were prepared by linking zeolitic nanoslabs into open mesoporous networks. Calcined films characterized by ellipsometric porosimetry presented pore sizes in the range of 6-18 nm and porosities of 70-90% depending on the temperature of assembly of the nanoslabs in the presence of Pluronic P123 triblock copolymer. The films were disordered according to grazing incidence small angle X-ray scattering and transmission electron microscopy. The most spacious film had a very low refractive index of 1.08 (at 632.8 nm) and exhibited reversible shrinkage of up to 30% of its original thickness upon capillary condensation of adsorbate vapor. The mechanical flexibility of the film was confirmed by the low Young modulus of 0.9 GPa determined by nano-indentation. The full accessibility of the porosity and the convenience for chemical functionalization were demonstrated using Atomic Layer Deposition (ALD) of TiO 2 monitored with Rutherford Backscattering Spectroscopy. Using ALD the porosity and mechanical flexibility of the film could be fine tuned.

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