Radiation damage of self-assembled monolayers, which are prototypes of thin organic layers and highly organized biological systems, shows a strong dependence on temperature. Two limiting cases could be identified. Reactions involving transport of single atoms and small fragments proceed nearly independent of temperature. Reactions requiring transport of heavy fragments are, however, efficiently quenched by cooling. We foresee the combined use of temperature and irradiation by electrons or photons for advanced tailoring of self-assembled monolayers on surfaces. In addition, our results have direct implications for cryogenic approaches in advanced electron and x-ray microscopy and spectroscopy of biological macromolecules and cells.
Freestanding silicon nanocrystals (Si‐ncs) offer unique optical and electronic properties for new photovoltaic, thermoelectric, and other electronic devices. A method to fabricate Si‐ncs which is scalable to industrial usage has been developed in recent years. However, barriers to the widespread utilization of these nanocrystals are the presence of charge‐trapping defects and an oxide shell formed upon ambient atmosphere exposure hindering the charge transport. Here, we exploit low‐cost post‐growth treatment routes based on wet‐etching in hydrofluoric acid plus surface hydrosilylation or annealing enabling a complete native oxide removal and a reduction of the defect density by up to two orders of magnitude. Moreover, when compared with only H‐terminated Si‐ncs we report an enhancement of the conductivity by up to a factor of 400 for films of HF etched and annealed Si‐ncs, which retain a defect density below that of untreated Si‐ncs even after several months of air exposure. Further, we demonstrate that HF etched and hydrosilylated Si‐ncs are extremely stable against oxidation and maintain a very low defect density after a long‐term storage in air, opening the possibility of device processing in ambient atmosphere.
The paramagnetic defects in and on Si nanowires (SiNWs) obtained by oxide-assisted growth were studied by conventional electron spin resonance spectroscopy. For the as-grown nanowires, three different defects were found: Dangling bonds or Pb-centers with g=2.0065, located at the interface of the crystalline core to the surrounding oxide, E′-centers with g=2.0005 and EX-centers with g=2.00252, located in the oxide. For the EX-centers, the characteristic hyperfine lines separated by 16.4G were detected. The as-grown SiNWs showed a spin density of about 1018cm−3. H termination of the nanowires via hydrofluoric acid decreases the spin density drastically to 3×1016cm−3. The optical absorption spectra of SiNWs determined by photothermal deflection spectroscopy are comparable to those of microcrystalline silicon and show a similar decrease of defect density upon H termination.
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