The electronic conductivity of Langmuir-Blodgett monolayers of silane-passivated silicon nanoparticles (core diameter 3.86 ± 0.85 nm) was examined by electrochemical measurements within the context of photoirradiation and at controlled temperatures. Temperature dependence of the dark conductivity indicated that the interparticle charge transfer followed a thermal activation mechanism within the temperature range of 200-320 K; whereas at lower temperature, the ensemble conductance was determined by tunneling between (clusters of) nanoparticles that were of equivalent energy states. When exposed to photoexcitation with photon energy greater than the effective particle bandgap, the particle ensemble conductivity exhibited a drastic enhancement as compared to that in the dark; and, at a specific excitation wavelength, the conductivity became virtually independent of temperature. This suggested efficient ionization of the photoexcited quantum-confined electron-hole pairs by the applied electric field, most probably because of the relatively slow (radiative and nonradiative) recombination dynamics. Furthermore, whereas the photoconductivity increased with increasing photon energy in photoirradiation, the enhancement diminished gradually with increasing temperature, as a consequence of the combined effects of enhanced radiative and nonradiative recombination rate and increasing contribution from thermally activated interparticle charge transfer.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films