We are preparing nanomaterials of different shapes (spheres, rods, tetrapods, dumbbells) and composition using high-temperature organo-metallic syntheses.
We are studying the spectroscopic and electrical properties of these materials.
Another important aspect of our research concerns the controlled assembly of these nanoparticles into small clusters, in the form of homogeneous monolayers, pinned along edges or aligned within nanoscale devices.
Nanorod accumulation and alignment in nanoscale devices
Local electric fields generated by nanopatterned electrodes were used to control the position and orientation of well-isolated as well as closely packed colloidal semiconducting CdTe and CdSe nanorods (NRs) drop-cast from solution. Postdeposition imaging using transmission-electron microscopy and atomic-force microscopy revealed strong NR alignment to the direction of the applied field and dense accumulation around and onto voltage-biased electrodes when deposited from dilute and concentrated solutions, respectively.
The degree of alignment under the applied electric field is characterized by a nematic order parameter S~0.8 in contrast to the zero-field case when S~0.1.
We have also achieved solid-state CdSe nanorod smectic superstructures on a millimeter scale by exploiting capillary flow kinetics of a drying droplet. Nanorods assemble side-to-side into micrometer-long tracks, acting as individual building blocks that assemble by capillary forces into smectic superstructures. The size of the superstructures and the short drying time makes the capillary-flow mechanism of ordered self-assembly attractive for general NR-superstructure studies and applications.
For more details on the nanorod accumulation and alignment:
Zonghai Hu, Michael D. Fischbein, Claudia Querner and Marija Drndic
“Electric-field-driven accumulation and alignment of CdSe and CdTe nanorods in nanoscale devices”
Nano Letters 6 (11), 2585-2591, 2006.
Claudia Querner, Michael D. Fischbein, Paul A. Heiney and Marija Drndic
“Millimeter-scale assembly of CdSe nanorods into smectic superstructures by solvent drying kinetics”
Advanced Materials 20 (12), 2308-2314, 2008.