We have developed a multistep route to the formation of covalently linked adducts of single-wall carbon nanotubes (SWNT) and deoxyribonucleic acid (DNA) oligonucleotides. X-ray photoelectron spectroscopy was used to characterize the initial chemical modification to form amine-terminated SWNTs, which were then covalently linked to DNA. The resulting DNA−SWNT adducts hybridize selectively with complementary sequences, with only minimal interaction with noncomplementary sequences.

We demonstrate that modifying pentacene to incorporate an acid-labile moiety into its molecular structure leads to a new precursor that can be easily deposited, photopatterned, and processed via wet-chemical methods to produce organic semiconducting devices exhibiting good electrical characteristics. Acidic conditions produced by ultraviolet illumination of a co-deposited photoacid generator greatly accelerate the local conversion of this N-sulfinyl-tert-butylcarbamate pentacene adduct back to pentacene. Photopatterned thin-film transistors exhibit carrier mobilities in excess of 0.1 cm2 V-1 s-1, making this an attractive precursor for fabrication of large-area organic electronics via solution-phase methods.

The interactions between pentacene and the Si(001)-(2 × 1) surface have been investigated using Fourier transform infrared spectroscopy (FTIR), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). The pentacene molecules in the first layer react with the Si surface atoms through the CdC double bonds and via cleavage of C-H bonds. This chemisorption is accompanied by disruption of the conjugated π electron system. The disrupted interfacial layer is stable throughout deposition and evaporation of thicker pentacene films. Pentacene molecules in layers beyond the first layer adsorb molecularly and yield well-defined valence band features that are characteristic of a conjugated π electron system. Functionalization of the Si surface with a monolayer of cyclopentene inhibits dissociation of subsequently deposited pentacene molecules.

The nucleation and growth of pentacene thin films are controlled largely by the energies associated with the interfaces. We have used low-energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) to investigate the nucleation and growth of pentacene thin films on Si(001) surfaces modified with two different molecular monolayers. Clean Si(001)-(2 × 1) surfaces were modified with either 1,5-cyclooctadiene or 1-dodecene prior to pentacene growth to study the effects of exposed π bonds at the interface, orientation of those π bonds relative to each other, and rigidity of the molecular layer on pentacene nucleation, growth, and crystalline orientation. Both molecular monolayers weaken the substrate-pentacene interaction sufficiently to allow for low pentacene nucleation density and good pentacene diffusion, leading to the growth of pentacene grains as large as 100 µm. Pentacene grows epitaxially on both functionalized surfaces, adopting an orthorhombic unit cell that follows the orientation of the underlying Si surface reconstruction. Our results show that in addition to improving the ultimate size of pentacene crystals, molecular monolayers are able to impose the substrate orientation on pentacene nuclei and thereby control the crystalline orientation of the thin film.

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to compare the reaction of 1,2-cyclohexanedione (1,2-CHD) with Si(001) and diamond(001) surface dimers under ultra-high-vacuum conditions. 1,2-CHD is known to undergo a keto-enol tautomerization, with the monoenol being the primary equilibrium species in the solid and gas phases. XPS and FTIR data demonstrate that 1,2-CHD reacts with diamond(001) through the OH group of the monoenol, resulting in only one O atom being bonded to the surface. In contrast, XPS and FTIR data suggest that both oxygen atoms in the 1,2-CHD molecule bond via Si-O-C linkages to the Si(001) surface dimer, and that the molecule undergoes an intramolecular 1,3-H shift. While the Si(001) and diamond(001) surfaces are both comprised of surface dimers, the diamond(001) dimer is symmetric, with little charge separation, whereas the Si(001) dimer is tilted and exhibits zwitterionic character. The different reaction products that are observed when clean Si(001) and diamond(001) surfaces are exposed to 1,2-CHD demonstrate the importance of charge separation in promoting a 1,3-H shift and provide new mechanistic insights that may be applicable to a variety of organic reactions.