Recent investigations have shown that cycloaddition reactions, widely used in organic chemistry to form ring compounds, can also be applied to link organic molecules to the (001) surfaces of crystalline silicon, germanium, and diamond. While these surfaces are comprised of Si=Si, Ge=Ge, and C=C structural units that resemble the C=C bonds of organic alkenes, the rates and mechanisms of the surface reactions show some distinct differences from those of their organic counterparts This article reviews recent studies of [2 + 2], [4 + 2] Diels-Alder, and other cycloaddition reactions of organic molecules with semiconductor surfaces and summarizes the current understanding of the reaction pathways.

Nanopores that approach molecular dimensions demonstrate exotic transport behaviour and are theoretically predicted to display discontinuities in the diameter dependence of interior ion transport because of structuring of the internal fluid. No experimental study has been able to probe this diameter dependence in the 0.5-2 nm diameter regime. Here we observe a surprising fivefold enhancement of stochastic ion transport rates for single-walled carbon nanotube centered at a diameter of approximately 1.6 nm. An electrochemical transport model informed from literature simulations is used to understand the phenomenon. We also observe rates that scale with cation type as Li þ 4K þ 4Cs þ 4Na þ and pore blocking extent as K þ 4Cs þ 4Na þ 4Li þ potentially reflecting changes in hydration shell size. Across several ion types, the pore-blocking current and inverse dwell time are shown to scale linearly at low electric field. This work opens up new avenues in the study of transport effects at the nanoscale.

The (001) surface of silicon contains pairs of atoms that are held together with a strong σ bond and a weak π bond. The interaction of styrene with the Si(001) surface has been investigated as a model system for understanding the interaction of conjugated π-electron systems to π-bonded semiconductor surfaces. Scanning tunneling microscopy images show one primary bonding configuration, slightly off-center from the middle of a dimer row. Infrared spectra using isotopically labeled styrene establish that attachment occurs in a highly selective way, bonding through the external vinyl group and leaving the aromatic ring almost completely unperturbed. Ab initio calculations reveal that the interaction between the π electrons of the vinyl group of styrene and the electron-deficient end of a SiSi dimer is strongly attractive. It is proposed that this attraction facilitates a low-symmetry interaction between the surface dimers and the vinyl group, leading to a highly selective reaction pathway for which Woodward−Hoffmann rules do not apply. The implications for selective attachment of other conjugated π-electron systems to other π-bonded semiconductor surfaces are discussed.

The adsorption of pyrrole, aniline, 3-pyrroline, and pyrrolidine on the Si(001)-(2 × 1) surface has been studied using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Both pyrrole and aniline retain their aromatic character after bonding to the surface. Spectroscopic evidence indicates that each of these aromatic molecules can attach to the Si(001) surface via cleavage of one N-H bond, linking the molecule to the surface through a Si-N tether. Isotopic studies of pyrrole show evidence for additional cleavage of C-H bonds. While strong selectivity favoring bonding through the nitrogen atom is observed for the aromatic molecules, the unsaturated molecule 3-pyrroline shows evidence for at least two bonding configurations. XPS and FTIR data show that 3-pyrroline can bond either through the nitrogen atom with cleavage of an N-H bond, or through the CdC bond via the surface equivalent of a [2 + 2] cycloaddition reaction. Pyrrolidine appears to bond only through the nitrogen atom. Potential factors controlling the selectivity in bonding and the role of aromaticity in controlling reaction pathways on silicon surfaces are discussed. † Part of the special issue "John T. Yates, Jr. Festschrift".

The interaction of NH3 and NO2 with heterogeneous bundles of carbon single-walled nanotubes (SWNTs) has been studied using FTIR spectroscopy and temperature-programmed desorption (TPD). Both NH3 and NO2 adsorb at room temperature, and the interaction results in strong shifts of the vibrational modes of the molecules relative to the gas phase. The data suggest that NH3 adsorbs via both its lone pair and its H atoms. NO2 adsorbs in an asymmetric configuration via at least one of the oxygen atoms. Analysis of the IR data suggests that these molecules adsorb by interacting with multiple nanotubes within a bundle of SWNTs. Additionally, trimethylamine, a compound similar to NH3, does not adsorb at room temperature. It is postulated that the size of trimethylamine prevents it from entering the grooves between nanotubes in the sample, whereas NH3 and NO2 are small enough to enter the grooves and interact with multiple nanotubes.