Conduction control in nanoparticles

One of the main challenges in ultrafast material science deals with triggering phase transitions that change material properties with short pulses of light, for instance changing their conductivity for electrical current. Such a transition was studied during the first SwissFEL pilot experiment in nanoparticles of Titanium Oxide (Ti3O5). Using femtosecond powder X-ray diffraction,  the particle's structure was studied on ultrafast timescales. Applying conventional algorithms and a dynamic model of changes within the particles, ultrafast changes from microscopic atom motions to sound wave deformations on the crystal lattice length scale could be observed. After light excitation, a pulse of sound waves propagates from the illuminated surface through the particle at the speed of sound and separates the prior semiconducting phase from the newly formed metallic phase. This demonstrates that the conduction state can be transformed at the speed of sound which is several decades faster than a thermal heat diffusion would occur. For the about 100 nm sized particles the transition requires about 15 picoseconds (15 x 10^-12s) which is e.g. comparable to Computer clock speeds. These results obtained at Bernina have been recently published in the Journal "Nature Communications".