Room-temperature assembly of germanium photonic crystals through colloidal crystal templating

Robert G. Shimmin, Robert Vajtai, Richard W. Siegel, Paul V. Braun

Research output: Contribution to journalArticlepeer-review


Using an evaporation-driven, room-temperature infiltration technique, we filled the interstitial space within an opal formed from 1 μm polystyrene spheres with preformed germanium nanoparticles. Subsequently, the Ge nanoparticles were bound together by backfilling with a photocuring adhesive, and the original polystyrene template was etched away to yield an inverse opal of air spheres in a matrix of Ge nanoparticles and photoadhesive. The reflectance spectra of these photonic materials were compared to computed band structures to deduce the refractive index of the air-germanium and air-photoadhesive composites; in conjunction with the Maxwell-Garnett model of dielectric mixing, this comparison also allowed the estimation of the Ge volume fraction within each composite material. On the basis of these methods, the interstitial space of the initial polystyrene opal template was filled to 49 vol % with Ge nanoparticles, acquiring an effective refractive index of 1.74. Backfilling with photoadhesive, followed by removal of the polystyrene opal, produced a Ge-in-polymer composite with a refractive index contrast of 2.05.

Original languageEnglish (US)
Pages (from-to)2102-2107
Number of pages6
JournalChemistry of Materials
Issue number8
StatePublished - Apr 17 2007

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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