(284b) Quantifying the Impact of Solvent on Optical Printing for Quantum Technologies

Emerging quantum technologies such as quantum computing require precise fabrication control to create a quantum chip of interacting qubits. Colloidal nanocrystals, especially metal halide perovskite nanocrystals, promise an exciting platform for quantum technology that use the spin of carriers. These materials also have immense chemical tunability. Similarly, quantum sensing technologies based on deep defects are enhanced when placed in colloidal nanocrystals. However, effectively using these colloids requires an assembly technique that offers a high level of positional and angular precision at the single particle level, which present extremely challenging manufacturing requirements. Optical printing is a technique that utilizes a highly focused laser beam to manipulate a micro or nanomaterial in two-dimensions, while also offering angular control over these nanomaterials. By putting the focal plane of the laser on a surface, nanomaterials are driven to the focal point of the laser, where the Van der Waals forces of the surface lock the nanomaterial in place, effectively printing it. Previous work on optical printing has shown positional accuracy better than 100 nm, which is approaching the desirable positioning accuracy for quantum devices (<30 nm). However, optical printing experiments have exclusively studied colloids dispersed in pure water. For metal halide perovskite nanocrystals, water is not a suitable solvent, and organic solvents must be used instead. Changing the solvent changes the interactions between the substrate and colloid and therefore should play a major role in optical printing processes. Understanding how the solvent impacts this process represents a critical step in developing optical printing.

Here, we studied the impact of the solvent as a mediator of the interaction between substrate and colloid to understand how the solvent can impact printing measurables like accuracy for quantum technologies. To investigate the role of the solvent, we used DLVO theory as a basis for understanding the interactions between the colloid and the substrate. As a model system, we first used a colloidal 300 nm TiO₂ dispersion in water and varied the DLVO interactions in the solvent by adding NaCl as an electrolyte. By carefully tuning the concentration of NaCl, we were able to investigate the impact of the DLVO interactions on printing accuracy. We combined this with DLVO simulations to create a complete framework for understanding the role that the solvent has in optical printing experiments. We identify three regimes in printing experiments, according to the relative energy barrier that the substrate repels the particle with. Different accuracy vs. laser power relationships can be extracted for each region, providing key insights into the optical printing process. By tuning the solvent, each regime can be accessed, providing different advantages and disadvantages for colloidal printing processes. In addition, we found that there is a minimum printing accuracy achievable, which results from additional external forces in the experiment. We then took the information gained from TiO₂ particle experiments and used it to perform printing experiments with perovskite nanocrystals. This work describes how the solvent plays a pivotal role in optical printing processes, leading to a development in the precise assembly of individual colloidal materials. Based on these results, we are better equipped to use optical printing as a tool for fabrication of quantum devices which rely on the precise placement of individual colloidal materials. At the end of this talk, I will present new results using what we learned to print halide perovskite nanocrystals in optical cavities. More broadly, this technique can be used in any field that requires the precise placement of individual colloidal materials such as catalysis, photonic materials, and more.