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Abstract: The effect of O2 adsorption on the electron transport behavior of Fe-porphyrin molecule is investigated by the first-principles computational approach. The current–voltage characteristics of Fe-porphyrin and O2 adsorbed Fe-porphyrin between gold electrodes are calculated. We find that the conductance of the Fe-porphyrin decreases dramatically upon the adsorption of O2, which suggests that this system has potential application as a molecular sensor or a switch. This switching-behavior is analyzed from the evolutions of the transmission spectra and the molecular projected self-consistent Hamiltonian states of the molecular systems. [Copyright &y& Elsevier]

Abstract: Dielectric properties and leakage current behavior in CaCu3Ti4O12 (CCTO) films with different thickness are studied. It is found that the permittivity is affected simultaneously by the electrode interface and the microstructure of the film. The influence of the interfacial layer reduces and the ac electric process transfers from grain boundary to bulk conductivity relaxation with the film thickness increasing. The Poole–Frenkel emission is dominated in thicker CCTO film. Interface-related conductive process coexists with the bulk-limited process in thinner film. [Copyright &y& Elsevier]

Abstract: Ferroelectric BaTiO3 nanocrystalline films (BTNFs) with the crystalline sizes of about 30 nm were grown on Pt/Ti/SiO2/Si substrates by a modified sol–gel method. Spectroscopic ellipsometry (SE) was used to characterize the films in the photon energy range of 1.5–5.0 eV with a five-phase layered model (air/surface rough layer/BaTiO3/interface layer/Pt). The optical properties in the transparent and absorption regions have been investigated with the Forouhi–Bloomer dispersion relation. With the aid of the structural and dielectric function models, the microstructure and electronic structure of the BTNFs can be readily obtained. It was found that the refractive index reaches the value of 2.20 in the transparent region. Based on the Sellmeier dispersion analysis, the single-oscillator energy is about 4.7 eV for the BTNFs. The long wavelength refractive index can be estimated to about 2.00 at zero point. The direct optical band gap energy approaches approximately 4.2 eV and Urbach band tail energy is and respectively with increasing crystalline size. A higher band gap observed can be owing to the known quantum confinement effect in the nanocrystalline formation and different fraction of amorphous and crystalline components. The theoretical analysis based on the effective mass approximation theory is well used to explain these experimental data. [Copyright &y& Elsevier]