Interfacial Plating Driving Convection-Like Motion of a Sandwiched Nanocrystal

In crystalline solids, thermally driven atomic fluxes are generally linked to surface reshaping or coarsening, not sustained translation of an intact crystal. We show that when nanoscale Cu, Ag, and Al crystals are confined between two plates and subjected to axial temperature gradients approaching 10⁸ K m^-1, they sustain a persistent, convection-like bidirectional mass flow. Thermo-mechanical-induced surface migration transports atoms from the hot end to the cold end, where interfacial insertion generates a self-regulated compressive back stress of up to 10² MPa-sufficient to push the crystalline core in the reverse direction. This closed-loop transport, coupling directional surface diffusion with rigid-body motion, is supported by molecular dynamics simulations and theoretical analysis. The findings reveal a previously unrecognized regime of mass-stress coupling in solids, opening new routes for solid-based thermal actuation and informing the thermal-mechanical reliability of nanoscale devices.