Fig. 7: Contact resonance-enhanced dynamic contrasts of infrared (IR) amplitude and phase contrast.

Contact resonance-enhanced amplitude contrast (left—CR-Amp) and contact resonance-enhanced phase contrast (right – CR-Phase) variations with setpoint @ 1416 cm⁻¹ on a DxO@mGO and b @ 1455 cm⁻¹ on MxD@mGO. The x-axis and y-axis scales of a DxO@mGO is 0.49 µm × 0.39 µm and that of b MxD@mGO is 3.66 µm × 3.6 µm. The long-timescale conduction dissipation path is measured from the cantilever deflection as IR amplitude contrast while the transitional dissipation path is measured from resonance fluctuations from the phase signal locked in at the contact resonance IR pulsing frequency. As clear from the results DxO has IR absorbance peak at 1416 cm⁻¹, while MxD has an absorption peak at 1455 cm⁻¹. The IR peak observed at 1416 cm⁻¹ for DxO@mGO is a representative signature of the vibration modes of skeletal rings of a DxO molecule (four rings per molecule)^64,65. The 1455 cm⁻¹ peak of for MxD@mGO is attributed to the vibration mode corresponding to aromatic C=C stretch (three bonds per molecule)^66,67. In contrast, the generated IR-contrast and phase lag contrast in the case of mGO shows no variations as a function of contact setpoint or its equivalent A_cr/A₀, where A₀, in this case, is the contact mode mean deflection and A_cr is the contact resonance amplitude at 100% IR power. Contact resonance characteristics relevant to the experiments are discussed in the Supplementary section H. DxO and MxD clusters on the other hand have appreciable IR absorbance and are reflected in the IR and phase-contrast images. Essentially IR-contrast (CR-Amplitude) and phase-contrast (CR-Phase) are complementary – locations having higher long-timescale dissipation reflect lesser dissipation by the transitional path and vice versa. These are more evident in the phase-contrast probability distributions showing an increase in phase contrast as a function of the contact mode setpoint in the case of DxO@mGO and MxD@mGO, respectively. mGO on the other hand does not show any variation since the contact resonance is not initiated.