The Department of Materials Science and Engineering invites you to join us for a seminar this afternoon:

N. Ravishankar

 The Center for Future Energy Systems and Dept. Materials Science and Engineering,

Rensselaer Polytechnic Institute, Troy NY 12180

On Sabbatical Leave from

Materials Research Center, Indian Institute of Science, Bangalore 560012, India

Host:  Nathan Swami, ECE

Talk Title: " Multi-scale Interfacial Engineering of Nanostructures”

Date: Monday, April 27th

Time: 4:00 to 5:00 PM

Refreshments: 3:30 to 4:00

Room: Wilsdorf 101

Abstract:

Interfaces play a key role in controlling every conceivable property in advanced functional materials. I will present some of our recent work on engineering and probing the structure, microstructure and chemistry of interfaces over multiple length scales in a variety of material systems for different applications.  Recent results on understanding morphology control during wet-chemical synthesis of nanostructures, structure-property correlations in calcium phosphate based bioceramics, interface and bandgap engineering in all-inorganic photovoltaics and a new patterning technique exploiting surface reconstruction in ceramics will be presented.

One of the intriguing issues in nanostructure synthesis is the formation of anisotropic structures (for instance, nanowires or plates) of high-symmetry crystals. I shall present examples of formation of nanowires and plate-shaped structures of cubic metals and describe the symmetry-breaking necessary for the formation of such structures. This fundamental understanding answers several long-standing questions on the morphology of synthetic crystals as well as some naturally grown ones like the apatite phase in the bone. Our approach to extend this understanding for producing nanoporous/hybrid structures for energy application will be presented. In the second part, I will discuss issues relating to tailoring interfaces in bioceramics including a novel method to porous biphasic scaffolds and direct methods to probe the anisotropy in mechanical behavior of calcium phosphate-based bioceramics. I will also discuss novel methods to create paintable solar cells based on quantum dot-sensitized TiO₂. In the third part, I will discuss a new non-lithographic method that we have developed for site-specific deposition of metal nanostructures on the hills of a reconstructed ceramic surface. Understanding the electrostatic origin of the process has enabled the development of a new electron-beam-induced deposition (EBID) method in the TEM. While the resolution (size of nanostructures) in conventional EBID is limited by the size of the electron probe, our method can produce nanostructures using a parallel beam of electrons over a large area.  Mechanistic details of the method will be discussed.

¹       Viswanath, B., Kundu, P., Mukherjee, B. and Ravishankar, N. Predicting the growth of two-dimensional nanostructures. Nanotechnology 19, 195603 (2008).

²       Halder, A. and Ravishankar, N. Ultrafine single-crystalline gold nanowire arrays by oriented attachment. Adv. Mater. 19, 1854 (2007).

³       Viswanath, B. and Ravishankar, N. Controlled synthesis of plate-shaped hydroxyapatite and implications for the morphology of the apatite phase in bone. Biomaterials 29, 4855 (2008).

⁴       Viswanath, B. and Ravishankar, N. Porous biphasic scaffolds and coatings for biomedical applications via morphology transition of nanorods. Nanotechnology 18, 475604 (2007).

⁵       Viswanath, B., Raghavan, R., Ramamurty, U. and Ravishankar, N. Mechanical properties and anisotropy in hydroxyapatite single crystals. Scripta Mater. 57, 361 (2007).

⁶       Basu, J., Carter, C. B., Divakar, R., Shenoy, V. B. and Ravishankar, N. Modified electron-beam-induced deposition of metal nanostructure arrays using a parallel electron beam. Appl. Phys. Lett. 93, 133104 (2008).

⁷       Ravishankar, N., Shenoy, V. B. and Carter, C. B. Electric field singularity assisted

nanopatterning. Adv. Mater. 16, 76 (2004).