The energy dissipation Ed and the increase of the viscous damping factor of tip vibration ∆γ were calculated from the excitation voltage applied for the constant amplitude of sensor deflection . ∆ƒ-z (frequency shift versus distance) curves were obtained by scanning the probe along a path perpendicular to the solid surface in approaching and retracting direction, and the corresponding ∆γ-z (damping factor versus distance) curves were obtained simultaneously by tracing ∆γ during the ∆ƒ-z curves measurement. Also, the cross-sectional two-dimensional (2D) ∆ƒ maps in the vertical plane to the substrate were obtained by doing these measurements sequentially on each horizontal point across the lateral path. Approximately 0.5 µL of PDMS was dropped onto 1 × 1 cm 2 mica substrates in a dry chamber (dew point < -50 ℃) and then spin-coated in an ambient condition to spread over the surface of the substrates, which is to reduce the probe's immersion length in the liquid since the resonant quality factor of sensors decreased by increasing the immersion length . The speed and duration for spin-coating were 2000 r min -1 and 90 min, as determined for the minimum duration required to spread PDMS over the entire substrate. The thickness of the liquid film measured by AFM was about 5 µm, which agreed well with the theoretically calculated value . The spin-coated substrates were settled at room temperature or annealed at 80 ℃ (heated by a hot plate) for a specific time in a dry chamber, then investigated by qPlus AFM in an ambient condition at room temperature.