Direct Observation of the Wind Force in Aluminum Nanowires*

Using recently developed techniques based on in situ mapping of valence electron energy loss spectra (EELS) in a transmission electron microscope (TEM), it is now possible to efficiently determine electron density changes in nanowires with parts-per-thousand precision. By mapping the bulk plasmon energy we quantify density changes throughout an aluminum wire with sub-10 nm spatial resolution, both while it carries electric current and after the current has been switched off. We observe changes in the wire density that are both even and odd in the sign of the applied current, which we attribute to thermal expansion and an electron wind force respectively. Our measurements are the first direct observation of the Blech effect, whereby strain in a current-carrying wire is induced to balance an applied force.