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.

While the structures of self-assembled monolayers (SAMs) of alkanethiols on Au(111) are extensively studied and well-known, new structures and complex phase behavior have been progressively discovered when coverage of these layers falls below saturation. Structures and phase transitions of annealed decanethiol monolayers on Au(111) surfaces were systematically investigated using scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Rich structures were revealed as a result of annealing in UHV. At temperatures below 345 K, no significant changes in coverage were observed, although the size of two-dimensional crystalline c(4√3 × 2√3)R30° domains increases as annealing progresses. A two-dimensional melting occurs at 345 ± 5 K and was captured in situ from time-dependent STM studies. Above 400 K, significant desorption takes place. In the temperature range of 345−400 K, within which desorption progresses to gradually decrease the surface coverage, a variety of striped phases have been observed, each having distinct molecular-level packing and unit cells. Well-known striped phases have been confirmed:  (p × √3), with p values (integer or half-integer multiples of the Au(111) periodicity) of 7.5, 9, and 11. In addition, new structures such as mixed striped phases and mesh-like structures are revealed, which are often found to coexist with the regions of pure striped phases. The systematic investigations of the structural and phase evolution shed light on the SAM desorption process at the molecular level.

Self-assembled monolayers (SAMs) of 4-[4′-(phenylethynyl)-phenylethynyl]-benzenethiols on Au(111) surfaces are investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum. STM images reveal longrange order in these SAMs with a rectangular unit cell containing two molecules. In high-resolution images, two new structural features are resolved, which cannot be explained by the previously proposed ( 3 × 2 3)-R30°commensurate structure which consists of three equivalent domains. First, six equivalent domains are present, and the orientations of these domains with respect to the three 〈121〉 directions of Au( 111) are (5°. Second, superstructures are observed. Periodical ridges are observed as a modulation of the STM imaging contrast within the ordered domains. A new model is proposed, which is very similar to the crystalline structure of p-terphenyl. The closest-packed row is aligned along the next-nearest neighbor or 〈121〉 direction of Au-( 111) with phenyl planes arranged in a herringbone fashion. The lack of simple commensurate structure of arenethiol SAMs is mainly attributed to intermolecular interactions.