Title: Colloidal semiconductor nanocrystals: novel strategies for optoelectronic devices 

Speaker: Prof. Roman Krahne (Department of Nanochemistry, Italian Institute of Technology (IIT), Italy)   

Time: OCT. 29, 2015 10:30AM 

Venue: Academic Conference Center, IOS, CAS

Abstract: CdSeCdS core-shell nanocrystals with a dot-in-a-rod architecture show extremely bright luminescence, demonstrate low-threshold optical gain and even lasing from self-assembled coffee rings. This makes them an emerging material for light-emitting applications like LEDs and lasers. Such nanocrystals can be chemically transformed via cation exchange, which involves replacement of the sublattice of cations in a crystal with a new sublattice of different cations, while the sublattice of anions remains in place.

I will discuss the optical properties of CdSe/CdS dot-in-rods and different approaches for their self-assembly in 2D and 3D, with emphasis on applications as laser devices. Then I will introduce a novel approach that enables pattering of colloidal nanocrystal structures by combining direct e-beam writing with cation exchange from Cd to Cu. The selective protection induced by the electron beam enabled to design patterns that are formed by chemically different nanomaterials (for example CdS and Cu2S), yet in a homogeneous nanocrystal film or structure. The potential of this masked-cation lithography will be explored towards optoelectronic devices

Biography：Roman Krahne is leader of the Optoelectronics group at the Italian Institute of Technology (IIT) in Genoa. He received his M.S. and PhD in Applied Physics from the University of Hamburg (Germany) in 1996 and 2000, respectively. In 2001 he joined the Weizmann Institute of Science (Israel) as a postdoc. Roman Krahne became researcher at the National Nanotechnology Laboratory of the National Research Council (CNR) in Italy in 2003, and 2009 he joined IIT as Senior Researcher. In 2013 he was appointed Guest Professor by the Institute of Semiconductors at the CAS. His research interests are centered on optoelectronic properties of nanocrystal thin films and assemblies, lasing of self-assembled microcavities, exciton-plasmon interaction in hybrid metal-semiconductor nanostructures, and Raman scattering on confined phonon modes in nanosize crystals.