Theoretical and experimental studies have recently attempted to investigate the role of molecular complexes in the Earth's atmosphere. The extent to which these weakly bound molecular species affect atmospheric chemistry and the climate is ultimately determined by their abundance. In this paper, we discuss the standard statistical procedures that are used in calculating equilibrium constants and dimer abundances. We also highlight the competition that arises between energy and entropy when complexation is considered at atmospherically relevant temperatures. For illustration, the abundance of select hydrated complexes, namely, O2−H2O, O3−H2O, H2O−H2O, and HNO3−H2O, are estimated. Using the results of our calculations, we evaluate and compare the physicochemical properties of these hydrated complexes and discuss how monomer concentrations, temperature, and dimer binding energies influence their calculated atmospheric abundances. We further examine the shortcomings of our estimates and include a short analysis outlining the inherent sensitivity of our computational method to discrepancies that exist in the available database for hydrated complexes.

Complexes of atmospheric molecules and atoms with water, H 2 O‚X, where X is H 2 O, N 2 , O 2 , Ar, and CO 2 , are investigated to evaluate their possible role in the absorption of solar energy and consequently in influencing the Earth's climate. The atmospheric abundance and absorption spectra of these complexes are calculated and used in a line-by-line radiative transfer model to assess their contribution. We have used statistical mechanics to calculate equilibrium constants and the harmonically coupled anharmonic oscillator local mode model to calculate fundamental and overtone OH-stretching vibrational band frequencies and intensities. Parameters for these calculations were obtained with the use of ab initio methods. Apart from the water dimer, no OH-stretching bands are significantly frequency shifted compared to those in the water monomer, implying that observation of the vibrational spectra of these hydrates in the atmosphere will be difficult. Of the studied complexes, we find that the O 2 and N 2 monohydrates are likely to contribute the most to absorption of solar radiation; however, the absolute absorption is highly dependent on the band shape of the vibrational transitions.

Self-assembled monolayers (SAMs) of 1-alkenes on hydrogen-passivated silicon substrates were successfully patterned on the nanometer scale using an atomic force microscope (AFM) probe tip. Nanoshaving experiments on alkyl monolayers formed on H-Si(111) not only demonstrate the flexibility of this technique but also show that patterning with an AFM probe is a viable method for creating well-defined, nanoscale features in a monolayer matrix in a reproducible and controlled manner. Features of varying depths (2-15 nm) were created in the alkyl monolayers by controlling the applied load and the number of etching scans made at high applied loads. The patterning on these SAM films is compared with the patterning of alkyl siloxane monolayers on silicon and mica.

An alternative method for fabricating functionalized, atomic force microscopy (AFM) tips is presented. This technique is simple and requires only minimal preparation and tip modification to generate chemically sensitive probes that have a robust organic monolayer of flexible terminal chemistry attached to the surface. Specifically, commercially microfabricated Si3N4 AFM tips were modified with self-assembled monolayers (SAMs) of octadecyltrichlorosilane and (11-bromoundecyl)trichlorosilane after removing the native silicon oxide surface layer with concentrated hydrofluoric acid. The structure of these SAM films on solid silicon nitride surfaces was studied using contact angle goniometry and Fourier transform infrared spectroscopy. Pull-off force measurements on various bare (mica, graphite, and silicon) and SAM-functionalized substrates confirm that mechanically robust, long-chain organic silane SAMs can be formed on HF-treated Si3N4 tips without the presence of an intervening oxide layer. Adhesion experiments show that the integrity of the organic film on the chemically modified tips is maintained over repeated measurements and that the functionalized tips can be used for chemical sensing experiments since strong discrimination between different surface chemistries is possible.

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