When thiol self-assembled monolayers (SAMs) form on gold surfaces, it is widely believed that, upon adsorption, the thiol molecules dissociate via S-H bond scission. This mechanism is hard to verify since hydrogen is difficult to detect during this process. Hence, other reaction schemes such as nondissociative thiol adsorption have also been proposed. Here we present experimental evidence that clearly shows that hydrogen is released during dissociative thiol adsorption and interacts with the monolayer terminus. Vacuum vapor deposition was used to form SAMs of 4-nitrophenylthiol, 4'-nitro-1,1'-biphenyl-4-thiol, and bis-(4,4'-nitrophenyl)-disulfide on gold surfaces. X-ray photoelectron spectroscopy shows that the nitro groups of the thiol SAMs are partly reduced to amino groups, while those of the disulfide SAMs are not. The reduction is attributed to hydrogen released in the dissociation of S-H bonds during thiol adsorption. Possible pathways for the interaction of hydrogen with the nitro groups are discussed.

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All relevant steps of discontinuous thin film growth of para-hexaphenylene on muscovite mica (0 0 1) from wetting layer over small and large clusters to nanofibers are observed and investigated in detail by a combined polarized fluorescence and atomic force microscopy study. From a variation of film thickness and surface temperature, we determine effective activation energies for cluster growth of 0.17 eV, for nanofiber length growth of 0.46 eV, for width growth of 0.19 eV, and for height growth of 0.07 eV. The corresponding exponential prefactors for the nanofiber growth are 1 x 10(9), 6 x 10(4), and 3 x 10(2) nm. Polarized fluorescence studies reveal that nanofibers grow along the grooves of the mica surface and that they do not change direction if they cross an even number of mica surface steps, while they change direction by 120 degrees for an odd number of steps. These results are taken as an input for a model of the unidirectional growth process on mica. Absolute parameters allowing one to grow nanofibers of predetermined morphology via organic molecular beam epitaxy are also given.

Self-assembled monolayers (SAMs) of 10-undecene-1-thiol on Au were functionalized with nitrogen-containing groups using an approach in which multilayer ammonia (NH(3)) films were deposited at low temperature onto the SAMs and subsequently exposed to 15 eV electrons. The result of this process was investigated after removal of the remaining NH(3) by annealing to room temperature using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). HREELS shows that the CC double bonds disappear during electron exposure, while XPS gives evidence that about 25% of the terminal double bonds of the SAM were functionalized. Also, XPS shows that a sufficiently thick NH(3) layer protects the underlying SAM from electron-induced damage. The process suggested here thus represents a particularly gentle approach to the functionalization of ultrathin molecular layers. Thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments on condensed layers of NH(3) reveal production of N(2) but show that significant amounts of the initial NH(3) as well as N(2) produced during electron exposure desorb. Hydrogen released upon formation of N(2) is held responsible for the reduction of double bonds and protection of the SAMs from damage.