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A novel photochemical mechanism is reported for the site-selective deposition of quantum dots onto nanocrystalline TiO₂ films. The patterning mechanism involves the combination of surfactant-mediated self-assembly and monolayer photolithography. In the self-assembly process, CdS and CdSe quantum dots were attached to TiO₂ surfaces through bifunctional mercaptoalkanoic acid (MAA) linkers. MAAs were adsorbed to the TiO₂ surface as the deprotonated carboxylates, primarily through monodentate coordination to Ti⁴⁺ sites. CdSe quantum dots were bound to the terminal thiol groups of surface-adsorbed MAAs, with a surface adduct formation constant, K_ad, of (2.1 ± 0.7) × 10⁴ M^-1. The color and optical density of the quantum dot-functionalized TiO₂ films were tunable. Monolayer photopatterning involved the TiO₂-catalyzed oxidative degradation of surface-adsorbed mercaptohexadecanoic acid (MHDA). A …