An experimental study on the capillary filling of nanoporous silicon with different fluids is presented. Thin nanoporous membranes were obtained by electrochemical anodization, and the filling dynamics was measured by laser interferometry, taking advantage of the optical properties of the system, related with the small pore radius in comparison to light wavelength. This optical technique is relatively simple to implement and yields highly reproducible data. A fluid dynamic model for the filling process is also proposed including the main characteristics of the porous matrix (tortuosity, average hydraulic radius). The model was tested for different ambient pressures, porous layer morphology, and fluid properties. It was found that the model reproduces well the experimental data according to the different conditions. The predicted pore radii quantitatively agree with the image information from scanning electron microscopy. This technique can be readily used as nanofluidic sensor to determine fluid properties such as viscosity and surface tension of a small sample of liquid. Besides, the whole method can be suitable to characterize a porous matrix.

An optofluidic method that accurately identifies the internal geometry of nanochannel arrays is presented. It is based on the dynamics of capillary-driven fluid imbibition, which is followed by laser interferometry. Conical nanochannel arrays in anodized alumina are investigated, which present an asymmetry of the filling times measured from different sides of the membrane. It is demonstrated by theory and experiments that the capillary filling asymmetry only depends on the ratio H of the inlet to outlet pore radii and that the ratio of filling times vary closely as H(7/3). Besides, the capillary filling of conical channels exhibits striking results in comparison to the corresponding cylindrical channels. Apart from these novel results in nanoscale fluid dynamics, the whole method discussed here serves as a characterization technique for nanoporous membranes.

Inverted organic cells are promising devices for sustainable and low-cost future electric generation. In this work, we present the degradation mechanisms studied in ITO/TiO 2 /PTB7:PC 70 BM/V 2 O 5 /Ag inverted organic solar cells (iOSCs) by impedance spectroscopy (IS). Measurements were performed on encapsulated (controlled environment) and nonencapsulated (ambient condition) cells following their temporal evolution under AM1.5 illumination for several voltage biases. From the impedance spectra, analyzed in terms of resistive/capacitive equivalent circuits, we were able to identify that the most sensitive layers inside of the device are contact layers. According with presented, IS technique is useful for determining the materials that have more influence on the degradation of organic solar cells. We demonstrate that IS is a powerful technique to identify the limiting mechanisms and to establish the limiting materials inside of the iOSCs.

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The evolution of FTIR spectra of PS during oxidation is studied in the range 450‐1300 cm–1. We show that the small scale of the PS structure leads to a significant scattering cross section for Fröhlich surface modes associated to stretching modes in siloxane bridges. The kinetics of the evolution of both bulk‐ and surface‐related modes are studied using Principal Component Analysis. As a result, two independent components are found, one of them related to TO modes associated to silicon oxide covering large structures and the other one associated to the oxidation of a distribution of prolate ellipsoids with nanoscopic size. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Porous silicon (pSi) is a nanomaterial with salient properties for optical biosensor applications.

Review of a matrix method used in optics of thin films for the calculation of reflectance, transmittance, absorptance, the electric field distribution inside the stack and the photonic dispersion considering the stack as perfect unidimensional crystals -Distributed Bragg mirrors-. We emphasizes the discussion on transfer matrices and give an alternative approach with scattering matrices for the propagation of light as plane waves through a homogeneous layered system.