title: Chemical, electrochemical, and structural stability of low-density self-assembled monolayers.
abstract: The stability of low-density self-assembled monolayers of mercaptohexadecanoic acid on gold is studied under a variety of storage conditions--air at room temperature, argon at room temperature and 4 degrees C, and ethanol at room temperature. The structural monotony of the low-density monolayers was assessed by monitoring the alkyl chains of LDSAMs by grazing-angle Fourier transform infrared spectroscopy as a function of time. Independently of the storage conditions, both symmetric and asymmetric methylene stretches at 2923 and 2852 cm-1 decreased after 4 weeks to 2919 and 2849 cm-1, respectively. These data suggest an increased ordering of the alkyl chains that is distinctly different from that of conventional high-density monolayers of mercaptohexadecanoic acid included as a reference in this study. As a further extension of this observation, the electrochemical barrier properties of the low-density monolayers were assessed by electrochemical impedance spectroscopy and did not change significantly for any of the storage conditions over a period of 4 weeks. Moreover, X-ray photoelectron spectroscopy was used to assess the chemical changes in the low-density monolayers over time. The chemical composition was essentially unaltered for all storage conditions. Specifically, oxidation of the sulfur headgroup, a common cause of monolayer degradation, was excluded for all test conditions on the basis of XPS analysis. This study confirms excellent storage stability for low-density monolayers under commonly used storage conditions and bridges an important technological gap between these systems and conventional high-density systems.
authors.affiliation: Department of Chemical Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, Michigan 48105, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Peng
authors.forename: Joerg
authors.initials: J
authors.lastname: Lahann
mesh_terms: D004563:Electrochemistry / Q000379:methods*; D004573:Electrolytes / Q000737:chemistry; D005453:Fluorescence; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D045663:Quantum Dots; D012996:Solutions
chemical_list: D004573:Electrolytes; D012996:Solutions