Hidden Functional Nanoparticles in Semiconductor Crystals.

Controlling the internal placement of functional metals within single-crystalline semiconductors remains a formidable challenge, because lattice mismatch and thermodynamic limitations generally preclude additive incorporation. Here, we show a general strategy to embed polymer-stabilized Au nanoparticles within single-crystalline anatase titanium dioxide (TiO2) while preserving its long-range lattice order. Interfacial polymer engineering overcomes intrinsic metal-oxide incompatibility, directing Au nanoparticles into the crystal interior with spatial precision. The resulting Au-TiO2 nanocomposite crystals feature dense, atomically intimate junctions and Au nanoparticles act as internal electron sinks, dramatically enhancing charge separation and transport. Remarkably, these internally confined Au nanoparticles actively drive photocatalytic hydrogen evolution, yielding rates 188 times higher than pristine TiO2 and highlighting the critical role of interior Au nanoparticles. This work establishes a conceptual paradigm for engineering crystalline composites with programmable, spatially resolved functional additives, opening new avenues to tailor the intrinsic properties of semiconductors.