Thickness dependence of the elastic modulus of tris(8-hydroxyquinolinato) aluminium

Jessica M. Torres, Nathan Bakken, Christopher M. Stafford, Jian Li, Bryan D. Vogt

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The intrinsic flexibility of organic molecular films has been suggested to enable bendable electronics in comparison to their stiffer, inorganic counterparts. However, very little is known regarding the mechanical properties of these molecular glasses that are commonly utilized in organic electronics. To begin to address these issues, the elastic modulus of vapor deposited tris(8-hydroxyquinolinato)aluminium (Alq3) films, commonly used in organic light emitting devices (OLEDs), is determined as a function of thickness from 10 nm to 100 nm using a wrinkling-based metrology. These thicknesses correspond well with the range actually utilized in OLEDs. The direct deposition of Alq3 onto a polydimethylsiloxane (PDMS) elastomer results in anomalous results due to diffusion of Alq3 into the PDMS substrate. Conversely, a thin polystyrene (PS) film can be used as a diffusion barrier, enabling the elastic moduli to be accurately measured. Similar to most organic glasses, the Young's modulus of Alq3 is on the order of 1 GPa and is statistically invariant for thicknesses >20 nm. Interestingly, there is a significant increase in the Young's modulus for thinner films. The modulus of a 10 nm Alq3 film is found to be nearly twice that of a thicker film. Corresponding to this change in modulus is a loss of the optical adsorption peak associated with aggregation of Alq3, which suggests that the modulus change is related to the local packing of the molecule. This result illustrates that the thickness of active layers in OLEDs impacts not only the device performance but also their elastic properties, both of which are important for use in flexible devices.

Original languageEnglish (US)
Pages (from-to)5783-5788
Number of pages6
JournalSoft Matter
Volume6
Issue number22
DOIs
StatePublished - Nov 21 2010

Fingerprint

Aluminum
modulus of elasticity
Elastic moduli
aluminum
Electronic equipment
Elastomers
Glass
Diffusion barriers
Polystyrenes
wrinkling
Thick films
glass
elastomers
electronics
Agglomeration
Vapors
metrology
thick films
polystyrene
flexibility

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics

Cite this

Thickness dependence of the elastic modulus of tris(8-hydroxyquinolinato) aluminium. / Torres, Jessica M.; Bakken, Nathan; Stafford, Christopher M.; Li, Jian; Vogt, Bryan D.

In: Soft Matter, Vol. 6, No. 22, 21.11.2010, p. 5783-5788.

Research output: Contribution to journalArticle

Torres, JM, Bakken, N, Stafford, CM, Li, J & Vogt, BD 2010, 'Thickness dependence of the elastic modulus of tris(8-hydroxyquinolinato) aluminium', Soft Matter, vol. 6, no. 22, pp. 5783-5788. https://doi.org/10.1039/c0sm00364f
Torres, Jessica M. ; Bakken, Nathan ; Stafford, Christopher M. ; Li, Jian ; Vogt, Bryan D. / Thickness dependence of the elastic modulus of tris(8-hydroxyquinolinato) aluminium. In: Soft Matter. 2010 ; Vol. 6, No. 22. pp. 5783-5788.
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