Photolithography method creates complex patterns using inorganic nanocrystals as colorful inks

Controlling the surface chemistry of inorganic nanocrystals, also known as quantum dots, has enabled researchers to devise a photolithography process for making all-inorganic patterned thin films. Unlike conventional lithography, the new technique requires no polymeric photoresists. The method, which requires fewer steps and could reduce fabrication costs for electronics, has been applied to metal, semiconductor, magnetic, and oxide nanocrystals (Science 2017, DOI: 10.1126/science.aan2958). Conventional lithography provides electronics manufacturers with a procedure for patterning semiconductors such as silicon wafers, forming millions of circuit elements simultaneously. The patterning relies on a stencil-like photoresist that masks the semiconductor and responds to light, becoming either soluble or insoluble in a given solvent, depending on the specifics of the process. A team led by the University of Chicago’s Dmitri V. Talapin has built that photosensitivity directly into quantum dots by functionalizing them with light-sensitive capping ligands. The researchers apply colloidal quantum dot solutions as colorful inks to various substrates, then expose select regions of the films to UV light, making those regions insoluble in a chosen solvent. Then they wash away the unexposed, soluble regions. For example, the team has drawn complex patterns from solutions of red CdSe/ZnS, green InP/ZnS, and blue ZnSe/ZnS quantum dots all capped with NH₄CS₂N₃ ligands, which decompose under UV light.