The adsorption and decomposition of acetylene on Si(100)-(2xl) have been studied in ultrahigh vacuum by Auger electron spectroscopy, temperature-programmed desorption, and changes in the partial pressure of acetylene as measured by a quadrupole mass spectrometer during the formation of a monolayer. Acetylene was found to chemisorb onto Si( 100)-(2X1) via a mobile precursor. The difference between the activation energy for desorption from the precursor and that for reaction from the precursor into the chemisorbed state was found to be (£d -£r) = 1.9 ± 0.6 kcal mol"1. At a low surface temperature, reaction from the precursor state dominates, giving a chemisorption probability of unity at submonolayer coverages. The saturated acetylene coverage is measured to be one C2H2 per Si2 dimer. Thermochemical arguments are presented, which indicate that acetylene bonds as a dispecies to dimer sites in which the Si-Si dimer bond has been cleaved. Chemisorbed acetylene was found to undergo two thermal reactions. A minor pathway (<5%) involves acetylene desorption, and a major pathway (>95%) involves the dissociation of acetylene to produce chemisorbed carbon and H2 (g). At temperatures above 800 K, the surface carbon begins to diffuse into the bulk of the silicon crystal.

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The heteronucleobase (adenine and uracil)-functionalized poly(ε-caprolactone) (A-PCL-U) possessing supramolecular structure has been successfully synthesized through the combination of ring-opening polymerization and Michael addition reaction. Attachment of multiple hydrogen-bonding units to chain ends of PCL results in phase separation and substantial increase in the viscosity. The association constant (K a) between adenine and uracil groups of A-PCL-U calculated from NMR measurement is 18.9 M−1. XRD and DSC analyses indicate that the crystalline structure of the A-PCL-U is changed to some extent due to phase segregation as compared to the PCL homopolymer. The AFM micrograph demonstrates that phase segregation is formed from the hard nucleobase chain ends and the soft poly(ε-caprolactone) chains of the supramolecular complex.

A convenient kinetic uptake method has been employed to determine the absolute saturation monolayer coverage of C2H2 and C2H4 on a Si(100)(2×1) surface. Such measurements are important for postulating the structure of the chemisorbed hydrocarbon species on this surface. The saturation surface coverage for both chemisorbed molecules at 105 K is 2.5(±0.2)×1014 molecules/cm2 . This number is consistent with 1 hydrocarbon molecule per Si dimer site at monolayer coverage when the role of surface defects on Si(100) is considered. A di-σ bonding model for both molecules is proposed at saturation coverage.

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