Molecular Thin Films Enable the Synthesis and Screening of Nanoparticle Megalibraries Containing Millions of Catalysts

Megalibraries are centimeter-scale chips containing millionsofmaterials synthesized in parallel using scanning probe lithography.As such, they stand to accelerate how materials are discovered forapplications spanning catalysis, optics, and more. However, a long-standingchallenge is the availability of substrates compatible with megalibrarysynthesis, which limits the structural and functional design spacethat can be explored. To address this challenge, thermally removablepolystyrene films were developed as universal substrate coatings thatdecouple lithography-enabled nanoparticle synthesis from the underlyingsubstrate chemistry, thus providing consistent lithography parameterson diverse substrates. Multi-spray inking of the scanning probe arrayswith polymer solutions containing metal salts allows patterning of>56 million nanoreactors designed to vary in composition and size.These are subsequently converted to inorganic nanoparticles via reductivethermal annealing, which also removes the polystyrene to deposit themegalibrary. Megalibraries with mono-, bi-, and trimetallic materialswere synthesized, and nanoparticle size was controlled between 5 and35 nm by modulating the lithography speed. Importantly, the polystyrenecoating can be used on conventional substrates like Si/SiOx, as well as substrates typically more difficult to pattern on, suchas glassy carbon, diamond, TiO2, BN, W, or SiC. Finally,high-throughput materials discovery is performed in the context ofphotocatalytic degradation of organic pollutants using Au-Pd-Cunanoparticle megalibraries on TiO2 substrates with 2,250,000unique composition/size combinations. The megalibrary was screenedwithin 1 h by developing fluorescent thin-film coatings on top ofthe megalibrary as proxies for catalytic turnover, revealing Au0.53Pd0.38Cu0.09-TiO2 as themost active photocatalyst composition.

Automated summary

Megalibraries are centimeter-scale chips containing millions of materials synthesized in parallel using scanning probe lithography. They can accelerate the discovery of materials for various applications. A challenge is the availability of compatible substrates for megalibrary synthesis. Polystyrene films were developed as universal substrate coatings to overcome this challenge. Different materials were synthesized in megalibraries and their photocatalytic activity was evaluated.