Scanning Tunneling Microscopy and Spectroscopy of Novel Silver–Containing DNA Molecules

The quest for a suitable molecule to pave the way to molecular nanoelectronics has been met with obstacles for over a decade. Candidate molecules such as carbon nanotubes lack the appealing trait of self‐assembly, while DNA seems to lack the desirable feature of conductivity. Silver‐containing poly(dG)–poly(dC) DNA (E‐DNA) molecules have recently been reported as promising candidates for molecular electronics, owing to the selectivity of their metallization, their thin and uniform structure, their resistance to deformation, and their maximum possible high conductivity. Ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) of E‐DNA presents an elaborate high‐resolution morphology characterization of these unique molecules, along with a detailed depiction of their electronic level structure. The energy levels found for E‐DNA indicate a novel truly hybrid metal–molecule structure, potentially more conductive than other DNA‐based alternatives.     

Temperature Dependence of the STM Morphology and Electronic Level Structure of Silver‐Containing DNA

Understanding the effect of external conditions, temperature in particular, on novel nanomaterials is of great significance. The powerful ability of scanning tunneling microscopy (STM) to characterize topography and electronic levels on a single molecule scale is utilized herein to characterize individual silver‐containing poly(dG)–poly(dC) DNA molecules, at different temperatures. These measurements indicate that the molecule is a truly hybrid metal–organic nanomaterial with electronic states originating from both the DNA and the embedded silver. The temperature dependence of this density of states (DOS) leads to the temperature dependent STM apparent height of the molecule—a phenomenon that has not been observed before for other complex nanostructures.     

Cover Picture: Lithography‐Free,Self‐Aligned Inkjet Printing with Sub‐Hundred‐Nanometer Resolution (Adv. Mater. 8/2005)

The inherently low resolution of inkjet printing on unpatterned surfaces can be overcome by selective surface modification of a first printed pattern, resulting in hydrophobic repulsion of subsequently deposited aqueous polymer dispersions. This technique, reported by Sirringhaus and co‐workers on p. 997, is capable of achieving sub‐100 nm resolution without any lithographic step. The cover shows an array of polymer transistors patterned with this method on three different length scales, as well as a schematic of the process.     

Cover Picture: DNA‐Templated Silver Nanorings (Adv. Mater. 23/2005)

The cover shows that toroidal condensates of duplex DNA can be used as templates for facile preparation of monodisperse nanorings of noble metals. In the work by Zinchenko and co‐workers, reported on p. 2820, conformational transition of long DNA chains from elongated coils into compact toroidal condensates changes the manner of reduced silver deposition, from DNA chain metallization with nanoparticles to the formation of silver rings. A one‐pot, three‐step, simple preparation method leads to formation of well‐defined monodisperse silver nanorings (100 nm in diameter) dispersed in water.