A series of nanoscale chemical patterning methods based on soft and hybrid nanolithographies have been characterized using scanning electron microscopy with corroborating evidence from scanning tunneling microscopy and lateral force microscopy. We demonstrate and discuss the unique advantages of the scanning electron microscope as an analytical tool to image chemical patterns of molecules highly diluted within a host self-assembled monolayer and to distinguish regions of differential mass coverage in patterned self-assembled monolayers. We show that the relative contrast of self-assembled monolayer patterns in scanning electron micrographs depends on the operating primary electron beam voltage, monolayer composition, and monolayer order, suggesting that secondary electron emission and scattering can be used to elucidate chemical patterns.

The authors describe a chemical patterning technique, “microcontact insertion printing,” that utilizes conventional microcontact printing to pattern isolated molecules diluted within a preexisting self-assembled monolayer. By modifying the preexisting monolayer quality, the stamping duration, and/or the concentration of the patterned molecule, they can influence the extent of molecular exchange and precisely control the molecular composition of patterned self-assembled monolayers. This simple methodology can be used to fabricate complex patterns via multiple stamping steps and has applications ranging from bioselective surfaces to molecular-scale electronic components.

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Layer-by-layer (LBL) growth of terpyridinyl ligands with a range of metal ions is reported. Monolayers of mercaptophenyl terpyridine on gold were used to initiate LBL assembly by complexing the first layer of metal ions. Tetra-2-pyridinylpyrazine was used as a linking ligand between subsequent metal ion layers. The assembly of the terpyridines with 21 different metals was evaluated using UV absorbance spectroscopy, variable-angle spectroscopic ellipsometry, and atomic force microscopy. Successful LBL growth appears to depend on the ionic radius of the metal ion. Metals that formed multilayered LBL structures were primarily limited to a small range of effective ionic radii between 66 and 73 pm. Metal ions with smaller ionic radii usually formed initial layers but seldom exhibited consistent LBL growth, while ions with radii larger than 73 nm generally did not demonstrate any evidence of LBL growth.

In this perspective, we explore hybrid approaches to nanometer-scale patterning, where the precision of molecular self-assembly is combined with the sophistication and fidelity of lithography. Two areas--improving existing lithographic techniques through self-assembly and fabricating chemically patterned surfaces--will be discussed in terms of their advantages, limitations, applications, and future outlook. The creation of such chemical patterns enables new capabilities, including the assembly of biospecific surfaces to be recognized by, and to capture analytes from, complex mixtures. Finally, we speculate on the potential impact and upcoming challenges of these hybrid strategies.