Silicon Suboxides as Driving Force for Efficient Light Enhanced Hydrogen Generation on Silicon Nanowires

Efficient light stimulated hydrogen generation from top down produced highly doped n type silicon nanowires SiNWs with silver nanoparticles AgNPs in water containing medium under white light irradiation is reported. It is observed that SiNWs with AgNPs generate at least 2.5 times more hydrogen than SiNWs without AgNPs. The authors results, based on vibrational, UV vis, and X ray spectroscopy studies, strongly suggest that the sidewalls of the SiNWs are covered by silicon suboxides, by up to a thickness of 120 nm, with wide bandgap semiconductor properties that are similar to those of titanium dioxide and remain stable during hydrogen evolution in a water containing medium for at least 3 h of irradiation. Based on synchrotron studies, it is found that the increase in the silicon bandgap is related to the energetically beneficial position of the valence band in nanostructured silicon, which renders these promising structures for efficient hydrogen generatio

Volcanic Eruption in the Nanoworld Efficient Oxygen Exchange at the Si SnO2 Interface

Here, a phenomenon of efficient oxygen exchange between a silicon surface and a thin layer of tin dioxide during chemical vapor deposition is presented, which leads to a unique Sn SiO2 layer. Under thermodynamic conditions in the temperature range of 725 735 C, the formation of nanostructures with volcano like shapes in active and dormant states are observed. Extensive characterization techniques, such as electron microscopy, X ray diffraction, synchrotron radiation based X ray photoelectron, and X ray absorption near edge structure spectroscopy, are applied to study the formation. The mechanism is related to the oxygen retraction between tin IV oxide and silicon surface, leading to the thermodynamically unstable tin II oxide, which is immediately disproportionate to metallic Sn and SnO2 localized in the SiO2 matrix. The diffusion of metallic tin in the amorphous silicon oxide matrix leads to larger agglomerates of nanoparticles, which is similar to the formation of a magma chamber during the natural volcanic processes followed by magma eruption, which here is associated with the formation of depressions on the surface filled with metallic tin particles. This new effect contributes a new approach to the formation of functional composites but also inspires the development of unique Sn SiO2 nanostructures for diverse application scenarios, such as thermal energy storag