Modern semiconductor technology rests upon the ability to draw features, or patterns, of microscopic size. From 2019 to 2023, the NSF supported through grant CHE-1905290 the advancement of a process for patterning called DOLFIN (Direct Optical Lithography of Functional Inorganic Materials) into a well-understood, fully general technique for the deposition of inorganic materials in arbitrary patterns with sub-micron resolution. A complete step of the DOLFIN process consists of (1) the coating of a surface with a layer of nanometer-size particles using a colloidal solution or ink, (2) exposure of the layer to a stimulus that rendered the exposed regions insoluble in their original solvent and (3) removal of the unexposed regions of the layer using a developer solvent. At the outset of CHE-1905290, DOLFIN had only been demonstrated with a very limited scope (in 2017) using deep ultraviolet light with a wavelength of 254 nanometers. This project set out to thoroughly investigate the mechanisms underlying pattern formation: surface chemical changes, surfactant degradation pathways, efficiency of response to stimuli, and material and reagent requirements.

Work from CHE-1905290 first dramatically expanded the number of tools through which DOLFIN could be achieved designing a series of spectrally selective photoactive ligands that responded to various photon energies, spanning from the deep ultraviolet to well into the visible range (450 nm). Optimized ligands achieved good patternability at doses of light below that of most commercial resists. Use of milder (longer-wavelength) light sources allowed DOLFIN to pattern materials which would normally decompose under ionizing radiation, such as the vigorously researched lead halide perovskites, and to form much thicker layers of material. Additionally, DOLFIN was found to be transferable to electron-beam lithography (DELFIN), which is the highest-resolution patterning technology.

Additional strategies were found that resolved major problems for future applications. High-resolution patterning of light-emitting quantum dots (QDs) was finally achieved without destroying their luminescence properties by formulating QD inks with adjuvants that decomposed along with the ligands to provide species that repaired or prevented damage caused by the patterning stimulus. Nanoparticle-surfactant combinations that did not absorb light could be patterned by incorporation of sensitizing nanoparticles, rather than new surfactant molecules, simplifying the process for many materials. Finally, a new strategy for controlling the solubility of nanomaterials with high resolution was introduced called heat-induced patterning of inorganic nanomaterials (HIPIN). Here, the decomposition of surfactant is induced by heat, which can be supplied by infrared light, pulsed high-power lasers, or heated stencils. HIPIN may even be able to push the resolution of DOLFIN below the diffraction limit, owing to the strongly nonlinear kinetics of surfactant decomposition with temperature.

In sum, CHE-1905290 realized DOLFIN as a powerful, reliable, and general process that could be a major player in making the transition from individual proof-of-concept devices using colloidal nanomaterials to real-world applications and new, currently unanticipated technologies. Work during the grant period initiated the launch of NanoPattern Technologies, a high-tech startup in Chicago, which aims to bring DOLFIN into the commercial and industrial space.

Under this project, an ongoing, extensive outreach program to the greater community on Chicago’s South Side was also considerably strengthened. The core of this effort was a series of after-school science clubs and science nights at various institutions, many especially dedicated to serving underrepresented minorities and low-income populations, spanning grades K-12. Attendees got hands-on experience with scientific experimentation and developed investigative and problem-solving skills. UChicago also introduced with this grant’s assistance the South Side Science Festival, a major campus-wide event that attracted thousands of attendees from around UChicago to a day of outdoor science exploration and free-form interaction with faculty and students.

Last Modified: 02/08/2024
Modified by: Dmitri V Talapin