Measuring individual carbon nanotubes and single graphene sheets using atomic force microscope infrared spectroscopy

Atomic force microscope infrared spectroscopy (AFM-IR) combines the spatial resolution of AFM with the chemical specificity of IR spectroscopy. In AFM-IR, sample absorption of pulsed IR light causes rapid thermomechanical expansion, which excites resonance in an AFM cantilever in contact with the sample. The cantilever resonant amplitude is proportional to the local sample IR absorption coefficient. It is difficult to detect thermomechanical expansion in the smallest samples such as 1D and 2D nanomaterials. In this work, we overcome this limitation and use AFM-IR to measure nanometer-scale IR absorption in individual single walled carbon nanotubes and monolayer graphene. By placing a thin layer of polymer beneath the sample, the AFM-IR signal may be increased by up to two orders of magnitude. The polymer beneath the sample thermally insulates the sample and amplifies thermomechanical expansion. Finite element simulations agree with the measurements and provide a general framework for applying this approach to arbitrary samples, including other 1D and 2D materials and thin biological samples.