We suggest that such model could be applicable here considering a thin native oxide layer on the silicon surface. It is likely that physisorption, chemisorption, or desorption of gas species govern the observed charge dynamics. In a gaseous environment, both the internal and external charge transfer mechanisms occur in PS simultaneously but on different time scales resulting in non-trivial transients. The initial fast process during the light-on transient could be related to the drift of the illumination-induced electrons in Si TH-302 towards the bulk and holes towards
the Si/oxide interface due to the electric field in the space charge region (cf. ). On the other hand, the electrons in the trap states at the interface may recombine with the flux of holes from the Si side leading to the initial decrease of the CPD in the light-on transient. The decrease in the band bending reduces the depletion width and the barrier height. More electrons can now cross the barrier, tunnel through the oxide layer and become captured by the physisorbed gas species at the free surface and convert them into chemisorbed ones. This increases the negative charge at the free surface and consequently the band bending yielding a slow increase in the CPD of the light-on
transient. However, when similar measurements were performed in vacuum, slow components were absent in transients (Figure 3). We propose that in vacuum, the physisorbed species Selleck Ilomastat could be removed from the surface during evacuation. Thus, only the PS internal mechanism would contribute to the SPV transients in vacuum during the light-on process, explaining the observed behavior. In addition, our experiments show that there is no
difference between the 17-DMAG (Alvespimycin) HCl SPV transients for the bare and PFT�� datasheet Ni-filled PS. This fact indicates that the metal deposits inside the pores do not influence the optoelectronic transport properties of PS, an important observation considering potential multifunctional (magnetic/chemical/pressure) sensor applications of Ni-filled PS. Conclusions In this work, employing transient SPV, we studied charge dynamics of mesoporous silicon and Ni-filled mesoporous silicon in different gas ambients and vacuum. We found that SPV transients for both types of samples in gaseous environments showed a non-trivial behavior during the light-on and light-off events. Vacuum transients showed a different behavior without the slow component. The time scale of the light-on and light-off events in vacuum and in gaseous ambients differs by three orders of magnitude. We suggest that the observed behavior is related to the charge exchange between the silicon/oxide interface and free-surface adsorbates. Acknowledgements The authors thank the Institute for Electron microscopy at the University of Technology Graz, Austria, for SEM investigations of the samples.