, where 𝜌 is the polypeptoid density (taken as 1.2 g cm -3 based on reported values in literature), ~1 nm and a contour length ~7 nm based on previous SANS measurements of similar polypeptoids in close to 𝜃-conditions. With the brush thickness comparable to Rg, it suggests that the polypeptoid brush grafting density is relatively low, possibly in a "mushroom" regime close to an overlap density as the brush top surface still appears smooth. Using the "mushroom" to "brush" transition (Σ = 𝜎𝜋𝑅 ' ( ~1), it suggests the polypeptoid grafting density is near or below this transition 𝜎 ~0.26 chain nm -2 , which is consistent with the earlier estimation. A relatively low grafting density is common in brushes prepared via the "grafting to" method. To further probe and confirm the chemical characteristics of polypeptoid brush monolayers post lithographic patterning, the nanopatterned brush monolayers are mapped with IR PiFM at two wavenumbers, 1658 cm -1 and 1113 cm -1 , with the former corresponding to the amide C=O stretching of polypeptoids, and the latter corresponding to the Si-O-Si stretching of the native oxide layer at the Si substrate surface. The combined PiFM image shows the line-space patterns are well-defined chemically, with the Si (SiO2) trenches with unobservable polypeptoid residues, as indicated by the near-zero PiF-IR signal intensity ratio of 1658 cm -1 /1113 cm -1 at location 2, 4, 6, 8 (Figure ). More importantly, comparing the averaged full PiF-IR spectrum of sampled locations on the nanopatterned polypeptoid brush monolayer (location 1, 3, 5, 7) and the spectrum of a pristine polypeptoid monolayer before lithographic patterning, no distinct difference is observed between the two PiF-IR spectra, with the characteristic peak of polypeptoid amide C=O stretching ~1660 cm -1 clearly observed post electron-beam lithographic patterning (Figure ).