Self-Assembly of Low-Dimensional Molecular Nanoclusters on Au(ll)) Surfaces

Joachim Hossick Schott, Christopher M. Yip, Michael D. Ward

Research output: Contribution to journalArticle

Abstract

Two-dimensional nanoclusters of (TTFXTCNQ) (TTF = tetrathiafulvalene, TCNQ = tetracyanoquin-odimethane) and Li+TCNQ“, formed on Au(ll)) surfaces by vapor phase sublimation under ambient conditions prior to growth of bulk crystals of these low-dimensional organic conductors, have been observed with scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The molecular planes of the constituents in individual nanoclusters are oriented perpendicular to the Au(ll)) substrate, while the clusters exhibit azimuthal orientations conforming to the 3-fold Au (110) directions. The nanocluster morphology and structure suggest that self-assembly of the nanoclusters is governed by specific interactions between the molecular species and the substrate and molecular diffusion along (110) troughs on the Audi 1) substrate surface. In the case of the (TTF)(TCNQ) nanoclusters, TTF and TCNQ molecules assemble into molecular rows normal to the stacking direction, with intermolecular distances along the stacking direction which are nearly identical to those observed in bulk (TTF)(TCNQ). In contrast, the intermolecular spacings between TCNQ molecules along the molecular stacking axis in Li+TCNQ- nanoclusters are substantially larger than that observed in bulk M+TCNQ- salts. The large intermolecular spacing in Li+TCNQ“ nanoclusters is consistent with Coulomb repulsion between fully reduced q = 1 TCNQ- anion sites (q = formal charge). The smaller spacings observed for (TTFXTCNQ) nanoclusters are consistent with reduced Coulomb repulsion, in agreement with the fractional charge known to exist in the bulk material (o = 0.59+ and 0.59- for TTF and TCNQ sites, respectively). The preferred direction of growth of the nanoclusters is transverse to the molecular stacking axes in both compounds, whereas the macroscopic morphologies reflect preferred growth parallel to the stacking direction. These observations indicate that morphology and molecular packing of crystal nuclei at the nanoscale are not necessarily identical to the corresponding characteristics observed at the macroscopic scale.

Original languageEnglish (US)
Pages (from-to)177-185
Number of pages9
JournalLangmuir
Volume11
Issue number1
DOIs
StatePublished - Jan 1 1995

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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