Fabrication of mechanically stable Au-coatings on probes of atomic force microscopes for nano-mechanical and -optical measurements

We propose a method to fabricate mechanically stable coatings of Au on AFM probes for nano-mechanical and -optical measurements. The procedure involves 1) pre-heating at 1000 °C; 2) the first deposition of Au; 3) annealing at high temperature (900 °C); 4) the second deposition of Au; and 5) post-heating at low temperature (300 °C). Repeating force curve measurements revealed that the proposed method provided extremely higher stability compared to probes fabricated by conventional processes of metal deposition. The shape of the tip apex of the newly fabricated probes did not change significantly after more than 20,000 cycles of force curve measurements, while still maintaining Au grains at the tip apices. The application of the probes in tip-enhanced Raman scattering spectroscopy confirmed that the Au-coated tips induced enhancement of the signal comparable to the conventional one. This method enables AFM-based nano-mechanical and -optical experiments with a large number of measuring points under stronger loading force to probes without the need to change the probes.