Attofarad capacitance measurement corresponding to single-molecular level structural variations of self-assembled monolayers using scanning microwave microscopy

Scanning microwave microscopy (SMM) proves to be capable of quantitatively measuring the minute capacitance difference between self-assembled monolayers (SAMs) with subnanometer variation in layer thickness. Using decanethiol and octadecanthiol as an example, the coexistence of two different SAMs on the same substrate with a well-known height difference of 0.88 nm is achieved via an atomic force microscopy-based nanolithography method known as nanografting. SMM was first calibrated against a capacitance standard developed by NIST. The measured capacitance difference is about 24 aF under the condition that the effective tip/sample contact area was estimated to be ∼ 60 nm in diameter.