Picosecond-Resolved Raman Response of a Si Nanotip for Probing Temperature and Thermal Stress in the Confined Regime under Laser Heating

Tip-assisted lithography is a technique full of potential for nanofabrication and data storage, allowing for nanofabrication within several nanometers using the heated nanotip. Thus, the knowledge of the instantaneous thermal response of the nanotip under the laser heating is important for temperature control. In this work, a prototype of an ultrafast thermal probing method for the apex of a silicon nanotip has been achieved. Instead of obtaining an average thermal response over the entire nanotip, the temperature and thermal stress in the confined apex region of the nanotip were successfully measured in picosecond duration. Furthermore, to understand the heat transfer process in the nanotip, comparative studies were conducted on a silicon micro-cantilever and a silicon wafer, respectively. Experiment-based simulation further revealed that the equivalent thermal conductivity of the nanotip is ∼35 W/(m·K), substantiating the reduction in the thermal conductivity of nanomaterials due to the size effect. Both nonuniform laser absorption and heat transfer deterioration in the nanotip contribute to the nonuniform temperature distribution, thermal stress, and thermal deformation. This work is expected to provide important insights into the thermal response of the nanotip and an effective way for fast thermal characterization of nanomaterials.