Characterization of facial and meridional Alq3 thin films fabricated from physical vapor transport at high substrate temperatures

Shang Yu Hung, Ruei Lin Kao, Ku Yen Lin, Chun Chuen Yang, Kuen Song Lin, Yu Chiang Chao, Jyh Shyang Wang, Ji Lin Shen, Kuan Cheng Chiu

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

During a thermal annealing process, the isomeric transformation from meridional (mer) into facial (fac) tris(8-hydroxyquinoline)-aluminum (Alq3) based on the infrared absorption was observed to be nearly complete around 375 °C. Then, in a physical vapor transport process with post-annealed fac-Alq3 as source powder (at source temperature of 375 °C), the effects from various substrate temperatures (Tsub from 285 to 346 °C) on the transformation from fac-Alq3 into mer-Alq3 isomers re-condensed on the substrate were studied again, and an isomeric transformation occurs at Tsub = 316 ± 2 °C. For Tsub below 316 ± 2 °C, the re-condensed mer-Alq3 isomers tend to aggregate to form close-packed micron-rods, which are composed of α-phase crystallites with an average coherent length L ∼ 46 nm. The photoluminescence (PL) spectra for these as-fabricated mer-Alq3 films show typical green emission. However, for Tsub above 316 ± 2 °C, the adsorbed fac-Alq3 molecules on the substrate preserve their corresponding isomeric structure from the post-annealed fac-Alq3 source and self-organize into flexible submicron-fibers. These samples are dominated by δ-phase crystallites with L ∼ 57 nm. The PL spectra for these as-fabricated fac-Alq3 films do emit blue luminescence. Besides, Raman scattering for these mer-Alq3 and fac-Alq3 molecules are also compared.

Original languageEnglish
Pages (from-to)100-106
Number of pages7
JournalMaterials Chemistry and Physics
Volume154
DOIs
Publication statusPublished - 2015 Mar 15
Externally publishedYes

Keywords

  • Crystal structure
  • Evaporation
  • Optical properties
  • Organometallic compounds
  • Phase transitions
  • Thin films

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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