Millisecond Flash Photonic Regeneration of Conductive Copper From CuO Thin Films

The oxidation state of copper governs the functional properties of its oxides but is difficult to set and stabilize. Here, flash photonic heating (FPH) with millisecond pulses partially reduces dense, pulsed‐laser‐deposited CuO films (≈50 nm) in dilute H ₂ , creating a laterally heterogeneous Cu/Cu ₂ O/CuO composite through the film. Cross‐sectional elemental mapping resolves Cu‐rich domains spanning the film, while X‐ray diffraction, Raman, and photoelectron spectroscopy show that oxides are never eliminated. The number of pulse‐train repetitions is a single control knob: the lateral conductance recovers by more than six orders of magnitude, and Kelvin probe force microscopy resolves reduced and oxidized domains. In air, reoxidation is self‐limiting, following a single logarithmic oxide‐growth law: the work function relaxes toward CuO within ≈33 h, while the conductance falls by only ≈5% over 200 h. FPH thus offers a rapid, scalable route to oxidation‐state engineering in oxide films.