High-resolution imaging of graphene by tip-enhanced coherent anti-Stokes Raman scattering

Coherent anti-Stokes Raman scattering (CARS) is able to enhance molecular signals by vibrational coherence compared to weak Raman signal. The surface or tip enhancement are successful technologies, which make it possible for Raman to detect single molecule with nanometer resolution. However, due to technical difficulties, tip-enhanced CARS (TECARS) is not as successful as expected. For single molecular detection, high sensitivity and resolution are two main challenges. Here, we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm, which has ever been reported. The highest EFTECARS/CARS is about 10(4), the similar order of magnitude with SECARS (EF of tip is usually smaller than that of substrates). Such resolution and sensitivity is promising for medical, biology and chemical applications in the future.