Back-electron-transfer (ET) dynamics in Fe II (CN) 6 4--sensitized colloidal TiO 2 nanoparticles are studied using ultrafast pump probe spectroscopy. Excitation of the adsorbate-to-nanoparticle charge-transfer band at 400 nm leads to direct injection of electrons from Fe II (CN) 6 4-to TiO 2 . The kinetics of back electron transfer from TiO 2 to the Fe III (CN) 6 3-are measured by monitoring the bleach recovery of the charge-transfer band in the 430-600 nm region. The measured back-ET kinetics are non-single-exponential, and a multiexponential fit requires at least four components on the <1 ns time scale. The kinetics are independent of pump power, indicating a geminate recombination process. Recombination kinetics are very similar in two samples of 5 and 11 nm (A-type) particles prepared from dried nanoparticle powder, but they are noticeably different from those in samples of 3 and 9 nm (B-type) nanoparticles prepared directly from colloids without drying. This result indicates that the back-ET kinetics in this system are more influenced by the surface properties of the nanoparticles than their sizes. Two models with different distributions of trapped electrons are used to describe the back-ET kinetics. Model I assumes a homogeneous distribution of electrons on the surface of the entire particle. This model predicts a large particle size dependence and cannot fit the observed kinetics. Model II assumes a more localized distribution of injected electrons and takes account of relaxation from shallow to deep trap states during the recombination process. This model can fit the back-ET kinetics with three fitting parameters. According to this model, the injected electrons are trapped near the adsorbate, which accounts for the size independent back-ET kinetics. This model also predicts that trapped electrons at longer distance and/or larger trap energy recombine slower. A distribution of distance and trap energy as well as relaxation between trap states give rise to multiexponential back-ET kinetics.

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Recent studies have shown that posterior communicating artery (PComA) aneurysms are more likely to rupture. However, surgical intervention for PComA aneurysms may be associated with increased treatment-related morbidity rate. Therefore, it is meaningful to investigate the factors related to PComA aneurysm rupture. The purpose of this study was to identify morphological parameters that significantly correlate with PComA aneurysm rupture. We divided 14 pairs of mirror posterior communicating artery aneurysms (PComA-MANs) into ruptured and unruptured groups. Computed tomography angiography (CTA) imaging was evaluated with three-dimensional (3D) Slicer to generate models of the aneurysms and surrounding vasculature. Nine morphological parameters [size, height, width, neck width, aspect ratio (AR), bottleneck factor (BNF), height/width ratio (H/W), size ratio (SR), and bleb formation] were examined in the two groups for significance with respect to rupture. By contrast, statistically significant differences were found in ruptured and unruptured group for size, AR, BNF, SR, and bleb formation (P < 0.05). Parameters that had no significant differences between the two groups were height (P = 0.103), width (P = 0.078), neck width (P = 0.808), and H/W (P = 0.417). We conclude that MANs may be a useful model for the morphological analysis of intracranial aneurysm rupture. Larger size, higher AR, BNF, SR, and bleb formation may be related to rupture of PComA aneurysms. Larger sample studies minimizing the interference from patient-related factors and aneurysm type were expected for acquiring more accurate assessment of the relationship between these parameters and PComA aneurysm rupture.

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Carrier dynamics of titanic acid nanotubes (phase of H2Ti2O5.H2O) deposited on a quartz plate was examined by visible/near-IR transient absorption spectroscopy with an ultraviolet excitation. The carrier dynamics of titanic acid nanotubes follows the fast trapping process which attributed to the intrinsic tubular structure, the relaxation of shallow trapped carriers and the recombination as a second-order kinetic process. Transient absorption of titanic acid nanotubes was dominated by the absorption of surface-trapped holes in visible region around 500 nm, which was proved by the faster decay dynamics in the presence of polyvinyl alcohol as a hole-scavenger. However, the slow relaxation of free carriers was much more pronounced in the TiO2 single crystals, as compared with the transient absorption spectra of titanic acid nanotubes under the similar excitation.