Laser‐Based In Situ Diagnostics of Temperature and Material‐Growth Dynamics in Photothermal Laser Nanoprinting of ZnO

ABSTRACT Photothermal laser printing using liquid inks has emerged as a facile alternative to multi‐photon laser nanoprinting of semiconductor and metal structures. Applications lie, for example, in printed microelectronics. In previous experiments on ZnO, steady‐state local temperatures in the laser spot, temperature dynamics, temperature profiles, and the dynamics of material growth have essentially been unknown. Herein, to determine these unknowns, we present in situ experiments using two co‐focused lasers. A first continuous‐wave laser at 405 nm wavelength heats a thin silicon film that serves as an absorber and thereby induces material deposition from a liquid ink. A second continuous‐wave laser at 730 nm wavelength probes the local temperature via the calibrated temperature‐dependent silicon‐film optical transmission. The second laser also allows for monitoring the time‐dependent laser‐induced ZnO deposition via scattering of light. We find temperature increases of about 113 degrees Celsius at 1 mW laser power at 405 nm wavelength, with a fast component of the temperature change that rises and decays in the range of 1 µs. Furthermore, we find smooth material deposition beyond some ms timescales at low laser powers, whereas the transmission signal exhibits pronounced rapid temporal fluctuations at elevated laser powers.