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• The Au-thiolate bond is strong - homolytic bond strength 44 kcal/mol - and contributes to the stability of the SAMs together with the van der Waals forces between adjacent methylene groups, which amount to 1.4-1.8 kcal/mol. The latter forces add up to significant strength for alkyl chains of 10-20 methylenes and play an important role in aligning the alkyl chains parallel to each other in a nearly alltrans configuration. At low temperatures, typically 100 K, the order is nearly perfect, but even at room temperature there are only few gauche defects, concentrated to the outermost alkyl units. One convenient method of checking a SAM for well-ordered and dense structure is infrared reflection-absorption spectroscopy (IRAS). The CH stretching vibrations of the alkyl chain are very sensitive to packing density and to the presence of gauche defects, which makes them ideally suited as probes to determine SAM quality. In particular, the antisymmetric CH2 stretching vibration (d-) at ~2918 cm-1 is a useful indicator; its position varies from 2916 or 2917 cm-1 for SAMs of exceptional quality or cooled below room temperature, via 2918 cm-1 which is the normal value for a highquality SAM, to ~2926 cm-1 which is indicative of a heavily disordered, "spaghetti-like" SAM. A typical IRAS spectrum of the CH stretching region of a hexadecanethiolate (HS(CH2)15CH3 ) SAM is shown in the following Figure...
IRAS spectrum of a hexadecanethiolate SAM in the CH stretching region. The most prominent vibrations are indicated. d+ and d- are the symmetric and antisymmetric CH2 stretches; r+ and r- are the symmetric and antisymmetric CH3 stretches, respectively. At the measurement temperature (82 K), the ra- and rb-components of the r- peak are resolved.
Page 1 and 2: CHE499 : A Nanotechnology Course in
Page 3 and 4: History • Nuzzo, R. G.; Allara, D
Page 5 and 6: Applications: • Applications are
Page 7 and 8: Tail Groups: Functionalization •
Page 9: Characterization: • Among the mos
Page 13: Lithography
Page 16 and 17: In Si(100), the anisotropic etch ch
Page 18 and 19: DNA SAMs
Page 21 and 22: Mercury Removal: SAMs in Mesopores
Page 23 and 24: Mercury Removal: SAM in Mesopores (
Page 25 and 26: • Molecular self-assembly is a un

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