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Modification of octadecanethiolate self-assembled monolayers on Au by nitrogen−oxygen or argon−oxygen downstream microwave plasma with a low oxygen content (estimated below several percent) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and water contact angle measurements. For both types of plasma, the primary processes were found to be the loss of conformational and orientational order and the oxidation of the alkyl matrix and headgroup−substrate interface. At the same time, the film modification occurred much faster and with different intermediates for the nitrogen plasma than for the argon plasma. The reasons for these differences are considered in terms of the different reactivities and different efficiencies of the energy transfer between the plasma constituents in these two types of plasma.

Methyl radicals are generated by pyrolysis of azomethane, and the condition for achieving neat adsorption on Cu(110) is described for studying their chemisorption and reaction characteristics. The radical−surface system is examined by X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, temperature-programmed desorption, low-energy electron diffraction (LEED), and high-resolution electron energy loss spectroscopy under ultrahigh vacuum conditions. It is observed that a small fraction of impinging CH3 radicals decompose into methylene possibly on surface defect sites. This type of CH2 radical has no apparent effect on CH3(ads) surface chemistry initiated by dehydrogenation to form active CH2(ads) followed by chain reactions to yield high-mass alkyl products. All thermal desorption products, such as H2, CH4, C2H4, C2H6, and C3H6, are detected with a single desorption peak near 475 K. The product yields increase with surface coverage until saturation corresponding to 0.50 monolayer of CH3(ads). The mass distribution is, however, invariant with initial CH3(ads) coverage, and all desorbed species exhibit first-order reaction kinetics. LEED measurement reveals a c(2 × 2) adsorbate structure independent of the amount of gaseous exposure. This strongly suggests that the radicals aggregate into close-packed two-dimensional islands at any exposure. The islanding behavior can be correlated with the reaction kinetics and is deemed to be essential for the chain propagation reactions. Some relevant aspects of the CH3/Cu(111) system are also presented. The new results are compared with those of prior studies employing methyl halides as radical sources. Major differences are found in the product distribution and desorption kinetics, and these are attributed to the influence of surface halogen atoms present in those earlier investigations.

A zone-plate-focused soft X-ray microbeam was utilized for direct patterning of a monomolecular resist:  aliphatic and aromatic self-assembled monolayers. The fabricated patterns were subsequently imaged and characterized by a scanning photoelectron microscope (SPEM) using the same microbeam as the excitation source. The observed contrasts could be explained in terms of specific beam-resist interactions. The spatial resolution of the X-ray patterning was about 0.5 μm, which was mostly determined by the current SPEM settings and can be noticeably improved.

A sequence of long-chain alkene products is found to evolve from chemisorbed methyl groups on Cu(111) in temperature-programmed reaction. The results of low-energy electron diffraction measurements suggest the formation of 2D islands for the chemisorbed radicals. The close-packed adsorption geometry and the reaction kinetics to generate high mass species are closely correlated. From this and other studies, we infer that the tendency of the methyl radicals to aggregate even at submonolayer coverages is crucial in promoting the chain growth, and the observed islanding effect may be significant in other hydrocarbon catalytical systems.