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Quantitative structural parameters of pyrochlore Nd2Ru2O7, with temperature dependence, have been derived upon fitting XRD and EXAFS data. An anomalous expansion of the lattice parameter and the Ru-O bond length indicates a structural instability at low temperatures; in particular, an increase in the non-thermal term of the mean square fluctuation in the bond length is the evidence for a static disorder of Ru atoms. This static disorder is closely correlated with a decrease in the average Ru-O-Ru bond angle with decreasing temperature, favoring the short-range ferromagnetic coupling in the material. This ferromagnetic coupling formed thus triggered the spin frustration at low temperature when the contradictory constraints of antiferromagnetic interaction act upon the same Ru site in the corner-sharing tetrahedrons of pyrochlore Nd2Ru2O7. This study demonstrates that the spin frustration arising from the competition of ferromagnetic/antiferromagnetic interactions in pyrochlore Nd2Ru2O7 will cause structural instability especially on the atomic scale, which provides a new point of view to help understand its particular magnetic state.

A facile, green, HF-free process for fabricating silicon solar cells safely at home or in school is presented.

This paper introduces a photo-assisted atomic force microscope (AFM) local oxidation technique which is capable of producing highly smooth oxide patterns with heights reaching several tens of nanometres on both n-and p-types of GaN (and in principle on most semiconductors) without the use of chemicals. The novel methodology relies on UV illumination of the surface of the substrate during conventional AFM local oxidation. A low 1.2 V threshold voltage for n-type GaN was obtained, which can be explained by UV photo-generation of excess electron-hole pairs in the substrate near the junction, thereby reducing the electric field required to drive carrier flow through the tip-sample Schottky barrier. It was demonstrated that the presence or absence of light alone was sufficient to switch the growth of the oxide on or off. The photo-assisted AFM oxidation technique is of immediate interest to the semiconductor industry for the fabrication of GaN-based complementary metal-oxide-semiconductor devices and nanodevices, improves chances for AFM-type data storage, and presents new degrees of freedom for process control technique.