Semiconductor-to-metal surface reconstruction in copper selenide/copper heterostructures steered by photoinduced interlayer atom migration

The photoinduced semiconductor-to-metal transition (PSMT) unveils crucial photodynamic mechanisms and holds great promise for information storage, sensing, optoelectronics, optical switches, etc. All previously reported PSMTs have occurred between two structural phases of the same material, lacking real-space evidence at the atomic or molecular level. Herein, we report atomic-scale observations of a photoinduced 'face changing': light irradiation transforms a semiconductor copper selenide (Cu2Se) surface layer on Cu(111) into a well-defined metallic Cu layer. Se atoms sink to form a new Cu2Se sublayer, while the original subsurface Cu atoms are lifted to the top layer. The Cu2Se-to-Cu transition barrier is significantly lower in the excited state compared to the ground state. Thermoactivation enables the reverse transition. The photoinduced Cu2Se-to-Cu and thermoactivated Cu-to-Cu2Se transitions are highly reversible. This work, which demonstrates PSMT between two distinct materials and photo-driven interlayer atom migration, unlocks an unconventional and intriguing route for PSMT and surface modification technologies. Photoinduced semiconductor-to-metal transitions are usually between different phases of the same material. Here the authors show the transformation of a single layer Cu2Se on Cu(111) into a metallic Cu surface layer and uncover its mechanism.