Skip to Main content Skip to Navigation
Journal articles

Dielectric relaxation properties of carboxylic acid-terminated n-alkyl monolayers tethered to Si(1 1 1): dynamics of dipoles and gauche defects

Abstract : Molecular-level insights into the organization and dynamics of n-alkyl monolayers covalently bonded to Si(1 1 1) were gained from admittance measurements of dipolar relaxation in rectifying Hg|| HOOC-C10H(25-n) Si junctions performed as a function of applied voltage and temperature. A collective behavior of dipole dynamics is inferred from the non-Debye asymmetric relaxation peak shape and strong coupling of the dipole relaxation path with some bending vibrations of the n-alkyl OML (multi-excitation entropy model). A variety of relaxation mechanisms is observed in the frequency range (0.1 Hz-10 MHz) with different dependence of relaxation frequency and dipolar strength on measurement temperature and applied voltage. Their microscopic origin is discussed by comparing the activation energy of relaxation frequency with previous molecular mechanics calculations of saddle point energy barriers for structural defects such as gauche conformations or chain kinks in n-alkanes assemblies. Gauche conformations organized in pairs (kinks) have vanishing relaxation strength below an order-disorder transition temperature T(D) =  175 K and their probability strongly increases with applied reverse voltage, above T(D). The presence of hydrogen bonds between terminal carboxylic acid functionalities is inferred from a comparison with a similar junction bearing a low density of carboxylic acid end groups. This temperature-dependent hydrogen-bond network provides some additional stiffness against external electrostatic stress, as deduced from the rather weak sensitivity of relaxation frequencies to applied bias voltage.
Complete list of metadatas

Cited literature [41 references]  Display  Hide  Download

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01301355
Contributor : Laurent Jonchère <>
Submitted on : Friday, April 22, 2016 - 3:27:46 PM
Last modification on : Tuesday, March 3, 2020 - 10:35:49 AM
Long-term archiving on: : Saturday, July 23, 2016 - 1:28:26 PM

Identifiers

Citation

Christian Godet. Dielectric relaxation properties of carboxylic acid-terminated n-alkyl monolayers tethered to Si(1 1 1): dynamics of dipoles and gauche defects. Journal of Physics: Condensed Matter, IOP Publishing, 2016, 28 (9), pp.094012. ⟨10.1088/0953-8984/28/9/094012⟩. ⟨hal-01301355⟩

Share

Metrics