Disinfection mechanism of the photocatalytic activity of SnO2 thin films against Candida albicans, proposed from experimental and simulated perspectives.

Nosocomial infections are an important health problem and cause of complications and death in hospitalized patients. This problem should be solved from the preventive angle, avoiding the spread of infections by designing disinfection methods based on the photocatalytic activity of semiconductor materials such as tin oxide (SnO2). The antimicrobial activity of UV light was tested by using inoculation with Candida albicans ATCC10231 on SnO2 thin films and counting colony forming units (CFU). The interaction of UV light with SnO2 was analyzed by density functional theory (DFT) and the extension to the Hubbard model (DFT+U) schemes to predict the electron behavior at the subatomic level. After exposure to UV light, C. albicans showed a reduction of 36.5% in viable cells, and when SnO2 was included, cell viability was reduced by 60.2%. Measurements of the electronic structure obtained by the first-principle calculations under the DFT and DFT+U schemes showed that the O-p orbitals mediate the oxidation process in the bulk semiconductor. By including the surface effects when cleaving the (1 0 0) plane, the three orbitals O-p, Sn-p, and Sn-s are the mediators. SnO2 films are promising antimicrobial coatings because UV light has a synergic activity with thin films, resulting in faster disinfection.

Effect of Native Defects on Transport Properties in Non-Stoichiometric CoSb3.

The effect of native defects originated by a non-stoichiometric variation of composition in CoSb3 on I-V curves and Hall effect was investigated. Hysteretic and a non-linear behavior of the  I-V curves at cryogenic temperatures were observed; the non-linear behavior originated from the Poole-Frenkel effect, a field-dependent ionization mechanism that lowers Coulomb barriers and increases emission of charge carriers, and the hysteresis was attributed to the drastic decrease of specific heat which produces Joule heating at cryogenic temperatures. CoSb3 is a narrow gap semiconductor and slight variation in the synthesis process can lead to either n- or p-type conduction. The Sb-deficient CoSb3 presented an n-type conduction. Using a single parabolic model and assuming only acoustic-phonon scattering the charge transport properties were calculated at 300 K. From this model, a carrier concentration of 1.18 × 1018 cm-3 and a Hall factor of 1.18 were calculated. The low mobility of charge carriers, 19.11 cm²/V·s, and the high effective mass of the electrons, 0.66 m0, caused a high resistivity value of 2.75 × 10-3 Ω·m. The calculated Lorenz factor was 1.50 × 10-8 V²/K², which represents a decrease of 38% over the degenerate limit value (2.44 × 10-8 V²/K²).