Journal ArticleDOI
Hopping transport on a fractal: ac conductivity of porous silicon.
TLDR
The frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz-100 kHz at different temperatures is measured, in terms of activated hopping in a fractal network.Abstract:
We have measured the frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz-100 kHz at different temperatures. The conductivity data exhibit a strong frequency dependence. When normalized to the dc conductivity, our data obey a universal scaling law, with a well-defined crossover, in which the real part of the conductivity sigma' changes from an sqrt(omega) dependence to being proportional to omega. We explain this in terms of activated hopping in a fractal network. The low-frequency regime is governed by the fractal properties of porous Si, whereas the high-frequency dispersion comes from a broad distribution of activation energies. Calculations using the effective-medium approximation for activated hopping on a percolating lattice give fair agreement with the data.read more
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Journal ArticleDOI
Porous silicon: a quantum sponge structure for silicon based optoelectronics
TL;DR: The photoluminescence properties of porous silicon have attracted considerable research interest since their discovery in 1990 as discussed by the authors, which is due to excitonic recombination quantum confined in Si nanocrystals which remain after the partial electrochemical dissolution of silicon.
Journal ArticleDOI
Theory of the electrochemical impedance of anomalous diffusion
Juan Bisquert,Albert Compte +1 more
TL;DR: In this article, a physically grounded framework is provided for the behavior Z(iω)∝( iω)−β/2 (0<β<2), thus generalising the Warburg impedance (β=1).
Journal ArticleDOI
Doubling Exponent Models for the Analysis of Porous Film Electrodes by Impedance. Relaxation of TiO2 Nanoporous in Aqueous Solution
Juan Bisquert,Germà Garcia-Belmonte,Francisco Fabregat-Santiago,Noemı́ S. Ferriols,and Peter Bogdanoff,Ernesto C. Pereira +5 more
TL;DR: In this article, the authors considered the small signal ac impedance of porous film electrodes in contact with solution, and the resulting relaxation functions were classified in terms of two characteristic frequencies: one for coupled transport and interfacial polarization and another one for the interfacial reaction.
Journal ArticleDOI
Anomalous transport effects in the impedance of porous film electrodes
TL;DR: In this paper, the authors proposed a model for the analysis of disordered materials by impedance, based on a macroscopic phenomenological theory that accounts for the retarded nature of the response to a locally acting force due to the localization of the carriers.
Journal ArticleDOI
A novel surface-micromachined capacitive porous silicon humidity sensor
TL;DR: In this article, the design, fabrication and characterisation of a novel humidity sensor is presented, which consists of a capacitor with a porous silicon dielectric, two thermoresistors and a refresh resistor.