Thickness-dependent structural evolutions and growth models in relation to carrier transport properties in polycrystalline pentacene thin films

Horng-Long Cheng, Yu Shen Mai, Wei-Yang Chou, Li Ren Chang, Xin Wei Liang

Research output: Contribution to journalArticle

140 Citations (Scopus)

Abstract

Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (θtilt) of the pentacene molecule from the c-axis toward the a-axis. We propose a growth model that rationalizes the θtilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C-C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries.

Original languageEnglish
Pages (from-to)3639-3649
Number of pages11
JournalAdvanced Functional Materials
Volume17
Issue number17
DOIs
Publication statusPublished - 2007 Nov 23

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Carrier transport
Transport properties
Film thickness
Atomic force microscopy
film thickness
transport properties
atomic force microscopy
Polymorphism
Interfacial energy
X ray diffraction
Thin films
Molecules
surface energy
Contact angle
Raman spectroscopy
Monolayers
thin films
diffraction
molecules
microstructure

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

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abstract = "Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (θtilt) of the pentacene molecule from the c-axis toward the a-axis. We propose a growth model that rationalizes the θtilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C-C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries.",
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Thickness-dependent structural evolutions and growth models in relation to carrier transport properties in polycrystalline pentacene thin films. / Cheng, Horng-Long; Mai, Yu Shen; Chou, Wei-Yang; Chang, Li Ren; Liang, Xin Wei.

In: Advanced Functional Materials, Vol. 17, No. 17, 23.11.2007, p. 3639-3649.

Research output: Contribution to journalArticle

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