Maximizing the dielectric response of molecular thin films via quantum chemical design

Henry M. Heitzer, Tobin J Marks, Mark A Ratner

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Developing high-capacitance organic gate dielectrics is critical for advances in electronic circuitry based on unconventional semiconductors. While high-dielectric constant molecular substances are known, the mechanism of dielectric response and the fundamental chemical design principles are not well understood. Using a plane-wave density functional theory formalism, we show that it is possible to map the atomic-scale dielectric profiles of molecule-based materials while capturing important bulk characteristics. For molecular films, this approach reveals how basic materials properties such as surface coverage density, molecular tilt angle, and π-system planarity can dramatically influence dielectric response. Additionally, relatively modest molecular backbone and substituent variations can be employed to substantially enhance film dielectric response. For dense surface coverages and proper molecular alignment, conjugated hydrocarbon chains can achieve dielectric constants of >8.0, more than 3 times that of analogous saturated chains, ∼2.5. However, this conjugation-related dielectric enhancement depends on proper molecular orientation and planarization, with enhancements up to 60% for proper molecular alignment with the applied field and an additional 30% for conformations such as coplanarity in extended π-systems. Conjugation length is not the only determinant of dielectric response, and appended polarizable high-Z substituents can increase molecular film response more than 2-fold, affording estimated capacitances of >9.0 μF/cm2. However, in large π-systems, polar substituent effects are substantially attenuated.

Original languageEnglish
Pages (from-to)12587-12600
Number of pages14
JournalACS Nano
Volume8
Issue number12
DOIs
Publication statusPublished - Dec 23 2014

Fingerprint

Molecular orientation
Thin films
thin films
Permittivity
Capacitance
conjugation
Dielectric films
Gate dielectrics
capacitance
alignment
Hydrocarbons
permittivity
coplanarity
Density functional theory
Conformations
Materials properties
augmentation
Semiconductor materials
determinants
Molecules

Keywords

  • density functional theory
  • dielectric computation
  • field-effect transistor
  • organic dielectric film
  • self-Assembled monolayer

ASJC Scopus subject areas

  • Engineering(all)
  • Materials Science(all)
  • Physics and Astronomy(all)

Cite this

Maximizing the dielectric response of molecular thin films via quantum chemical design. / Heitzer, Henry M.; Marks, Tobin J; Ratner, Mark A.

In: ACS Nano, Vol. 8, No. 12, 23.12.2014, p. 12587-12600.

Research output: Contribution to journalArticle

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