Anticorrelation between surface and subsurface point defects and the impact on the redox chemistry of TiO2(110).

By using a combination of scanning tunneling microscopy (STM), density functional theory (DFT), and secondary-ion mass spectroscopy (SIMS), we explored the interplay and relative impact of surface versus subsurface defects on the surface chemistry of rutile TiO2 . STM results show that surface O vacancies (VO ) are virtually absent in the vicinity of positively charged subsurface point defects. This observation is consistent with DFT calculations of the impact of subsurface defect proximity on VO formation energy. To monitor the influence of such lateral anticorrelation on surface redox chemistry, a test reaction of the dissociative adsorption of O2 was employed and was observed to be suppressed around them. DFT results attribute this to a perceived absence of intrinsic (Ti), and likely extrinsic interstitials in the nearest subsurface layer beneath inhibited areas. We also postulate that the entire nearest subsurface region could be devoid of any charged point defects, whereas prevalent surface defects (VO ) are largely responsible for mediation of the redox chemistry at the reduced TiO2 (110).

Low-LET microbeam investigation of the track-end dependence of electron-induced damage in normal human diploid fibroblasts.

Using a pulsed electron beam, we investigated the dependence of micronucleus formation on the incident electron energy in AG01522 human diploid fibroblasts after nontargeted irradiations at 25 and 80 keV. Examining the dose response, we found that 25 keV electrons are more effective than 80 keV electrons at producing biological damage for a given dose. Our results demonstrating the induction of micronuclei as a function of incident electron energy offer direct support for the hypothesis that the electron track end is responsible for the biological damage occurring in the cell.

A variable-energy electron microbeam: a unique modality for targeted low-LET radiation.

We have designed and constructed a low-cost, variable-energy low-LET electron microbeam that uses energetic electrons to mimic radiation damage produced by gamma and X rays. The microbeam can access lower regions of the LET spectrum, similar to conventional X-ray or 60Co gamma-ray sources. The device has two operating modes, as a conventional microbeam targeting single cells or subpopulations of cells or as a pseudo broad-beam source allowing for direct comparison with conventional sources. By varying the incident electron energy, the target cells can be selectively exposed to different parts of the energetic electron tracks, including the track ends.

A beaker without walls: formation of deeply supercooled binary liquid solutions of alcohols from nanoscale amorphous solid films.

Layered nanoscale amorphous solid films of methanol and ethanol undergo complete intermixing prior to the onset of measurable desorption at 120 K. This intermixing precedes and inhibits crystallization. Subsequent desorption of the film is described quantitatively by a kinetic model describing evaporation from a continuously mixed ideal binary liquid solution. This occurs at temperatures below the melting point of the binary mixture, indicating ideal behavior for the supercooled liquid solution. This approach provides a new method for preparing and examining deeply supercooled solutions.