This Account focuses on our recent and systematic effort in the development of generic scanning probe lithography (SPL)-based methodologies to produce nanopatterns of self-assembled monolayers (SAMs). The key to achieving high spatial precision is to keep the tip-surface interactions strong and local. The approaches used include two AFM-based methods, nanoshaving and nanografting, which rely on the local force, and two STM-based techniques, electron-induced diffusion and desorption, which use tunneling electrons for fabrication. In this Account we discuss the principle of these procedures and the critical steps in controlling local tip-surface interactions. The advantages of SPL will be illustrated through various examples of production and modification of SAM nanopatterns and their potential applications.

In the past decade, scanning tunneling microscopy (STM) has revealed new information regarding self-assembled monolayers (SAMs) of organothiols on Au(111) at the molecular level. The periodicity, defects, morphology, and various phases during the self-assembly process have been visualized with unprecedented detail. Using STM under ultrahigh vacuum, new insights regarding SAMs have been revealed from the perspective of potential applications in molecular devices. This article focuses on a molecular-level understanding of the formation of adatom and vacancy islands and reveals how the structure is impacted by introducing aromatic termini. The thermal stability and thermally induced structural evolution of SAMs are monitored in situ. The behavior of alkanethiol molecules under local electric field and tunneling current are studied with molecular resolution. Molecular-level insight regarding negative differential resistance of SAMs is also discussed.

Nanostructures down to a few nanometers in size and composed of close-packed and well-ordered molecules have been fabricated by simultaneous nanoshaving using an atomic force microscopy (AFM) tip and alkanethiols' self-assembly on gold. Compared with other microfabrication methods, this procedure allows more precise control in terms of the size and geometry of the fabricated features. An edge resolution better than 2 nm can be routinely obtained. In addition, the fabricated nanostructures can be quickly changed, modified, and characterized in situ. These advantages should make this method very useful in the development of prototypical nanoelectronic devices and, perhaps more importantly, in the study of spatially confined chemical reactions.

The structural basis of the outer membrane permeability for the bacterium Escherichia coli is studied by atomic force microscopy (AFM) in conjunction with biochemical treatment and analysis. The surface of the bacterium is visualized with unprecedented detail at 50 and 5 Å lateral and vertical resolutions, respectively. The AFM images reveal that the outer membrane of native E. coli exhibits protrusions that correspond to patches of lipopolysaccharide (LPS) containing hundreds to thousands of LPS molecules. The packing of the nearest neighbor patches is tight, and as such the LPS layer provides an effective permeability barrier for the Gram-negative bacteria. Treatment with 50 mM EDTA results in the release of LPS molecules from the boundaries of some patches. Further metal depletion produces many irregularly shaped pits at the outer membrane, which is the consequence of progressive release of LPS molecules and membrane proteins. The EDTA-treated cells were analyzed for metal content and for their reactivities toward lysozyme and antibodies specific for LPS. The experiments collectively indicate that the metal depletion procedure did not remove all the LPS molecules despite a dramatic decrease in the metal content. The remaining LPS molecules are present outside the pits, whereas the bottom of the pits is devoid of these molecules. This new structure for the outer membrane exhibits higher permeability than that for the native cells.

In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two‐dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3 cm2 V−1 s−1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport.