Welcome
Welcome to the home page of the Paul Braun Research Group at the University of Illinois at Urbana-Champaign. Our group members perform research in the fields of materials chemistry, polymers, biomaterials, organic and inorganic self-assembly, electronic materials and photonics.
3D Multifunctional Ceramic Composites MURI
Department of Materials Science and Engineering at UIUC
Frederick Seitz Materials Research Laboratory
University of Illinois at Urbana-Champaign
Beckman Institute for Advanced Science and Technology
News
January 2008, Cover of Nature Photonics
Vol.2 No.1 January 2008
Photonic crystals, artificially engineered nanoscale structures that can manipulate
the flow of light, show great promise for building sophisticated optical circuitry that
can route, filter, store or suppress optical signals. However, fabricating such circuitry
presents a great challenge as defects need to be carefully incorporated into the
photonic-crystal structure with great precision. Although this has been accomplished
for two-dimensional designs that confine light in a plane, it is still an ongoing challenge
for so-called complete-bandgap materials, where the defects need to be embedded
into a three-dimensional structure. In this issue, Paul Braun and colleagues report
the introduction of defects into a silicon three-dimensional photonic crystal by using
a technique called two-photon polymerization. The result is waveguides that guide
near-infrared light around sharp corners.
Article p52,News & Views p9, UIUC Press Release
Beckman Institute researchers, led by Paul Braun and Ben Grosser, receive $1.99 million National Science Foundation MRI award to acquire nano-CT instrument (see press release)
June 2007, Cover of Advanced Materials, Vol. 19, Issue 12
Germanium inverse woodpile 3D photonic crystals with a large (25%) photonic band gap in the infrared (background image) were fabricated through a multistep replication procedure. A polymer scaffold was first created by direct-write assembly, followed by the conformal growth of oxide and semiconductor layers, and removal of the polymer and oxide (foreground), ...as reported on p. 1567 by F.
García-Santamaría, M. Xu, V. Lousse, S. Fan, P. V. Braun,
and J. A. Lewis.
May 2007: INVERSE WOODPILE STRUCTURE HAS EXTREMELY LARGE PHOTONIC BAND GAP
Researchers at the U. of I. have built an inverse woodpile structure
of germanium, a material with a higher refractive index than silicon.
http://www.news.uiuc.edu/news/07/0521woodpile.html
November 2006, Cover of Advanced Functional Materials, Vol. 16, Issue 17
The direct ink writing of three-dimensional functional materials is detailed in the Feature Article by Lewis on p. 2193. The left side of the cover image displays schematic images that show the conversion of a direct-write polymer woodpile to a silicon hollow-woodpile structure. The 3 × 3 image matrix showcases the resulting silicon photonic crystal (center) surrounded by a higher-magnification view of a representative hollow silicon feature (ca. 1 m in diameter). The figure was prepared by F. Garcia-Santamaria, G. M. Gratson, and P. V. Braun.
The ability to pattern materials in three dimensions is critical for several technological applications, including composites, microfluidics, photonics, and tissue engineering. Direct-write assembly allows one to design and rapidly fabricate materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in direct ink writing are reviewed with an emphasis on the push towards finer feature sizes. Opportunities and challenges associated with direct ink writing are also highlighted.
June 22, 2004 Cover of Langmuir, Vol. 20, Issue 13
Cover illustration by Wonmok Lee and Paul V. Braun showing to the left a scanning electron microscope image of a substrate patterned with a periodic array of dimples formed through focused ion beam lithography and to the right a laser scanning confocal microscope cross section of a 3-D colloidal crystal formed by gravity-driven sedimentation from a binary mixture of 1.18 m diameter colloidal microspheres and 6 nm diameter highly charged nanoparticles onto this patterned substrate. After microsphere settling, the nanoparticle solution surrounding the colloidal crystal was gelled in situ by introducing ammonia vapor, which increased the pH and enabled drying with minimal microsphere rearrangement. The confocal image shown here was generated by infilling the dried colloidal crystal with an index-matched fluorescent dye solution prior to imaging. These colloidal crystals have very low defect densities and may be suitable for use as photonic crystals and as templates for photonic band gap materials. The dimple pitch and the volume fraction of microspheres in solution were found to strongly impact the quality of the resulting colloidal crystal. For more information see "Nanoparticle-Mediated Epitaxial Assembly of Colloidal Crystals on Patterned Substrates" by Wonmok Lee, Angel Chan, Michael A. Bevan, Jennifer A. Lewis, and Paul V. Braun on pages 5262-5270 of this issue. Copyright 2004 American Chemical Society
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@uiuc.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign