Uniform Coating of Separated Nanodiamonds via Thin Polymer-assisted Electrostatic Self-Assembly for Thermal Sensing

Abstract

Nanodiamonds (NDs) with nitrogen-vacancy (NV) centers have shown significant potential for nano- and micro-scale local temperature sensing and imaging. However, the challenge lies in achieving non-invasive measurement, due to a high thermal conductivity of diamond that can cause strong thermal spreading and heat dissipation. A solution is to prepare separated NDs for thermal sensing. Here we introduce a method for uniform coating of separated NDs by a rapid thin polymer-assisted electrostatic self-assembly process. This method can be applied to a large scale with a low cost under ambient conditions. Testing with negatively charged carboxylated 100 nm NDs, we demonstrate ND coatings with a controlled area density (up to 1.74 × 10⁹ cm^-2) and a low optical transmission loss of 1.21 %. Despite size variation of the NDs, the separated ND coating exhibits a low measurement error of 1.32 °C in thermal mapping between 27 and 80 °C. Furthermore, by steady-state thermal simulations, we show a >7× lower thermal spreading of the separated ND coating compared to a 100 nm thick ND film. This work offers a simple method for large-scale coating of separated NDs, paving a path for achieving non-invasive and accurate ND-based thermal sensing.