Nanocrystals: Dynamics of Shape-Controlled Nanocrystals and Self-Assembling Nanocrystals

Topics Covered

Background

Discovery of a New Technique for Controlling the Shapes and Sizes of Platinum Particles

Using Nanoparticles to Form Superlattice Structures

Particle Shape in the 3-D Assembling of Nanocrystals, and the Self-Assembly of Magnetic Nanocrystals

Incorporating FePt and Fe₃O₄ Particles into Binary Assemblies

Background

Nanosize colloidal platinum (Pt) particles are potentially important in industrial catalysis. The selectivity and activities of Pt particles strongly depend on their sizes and shapes. Much effort has been devoted to synthesize smaller size Pt particles for increasing the surface to volume atom ratio.

Discovery of a New Technique for Controlling the Shapes and Sizes of Platinum Particles

Searching for techniques which can produce monoshape Pt particles has attracted a lot of interest because the chemical activities of Pt between {100} and {111} facets have distinct differences. Dr. Zhong L. Wang's (of the Georgia Institute of Technology) collaboration with Prof. M.A. El-Sayed had led to a new technique based on colloidal chemistry for controlling the shapes and sizes of Pt particles at room temperature [Science 272 (June 1996) 1924]. Following this development, the growth mechanism of shape controlled Pt nanocrystals was studied using in-situ transmission electron microscopy. The shape transformation and melting behavior of the Pt nanocrystals were revealed for the first time.

Using Nanoparticles to Form Superlattice Structures

The physical and chemical functional specificity of nanoparticles suggest that they are ideal building blocks for two- and three-dimensional cluster self-assembled superlattice structures in which the particles behave as well-defined molecular matter, and they are arranged with long-range translational and orientational order. In 1996, Dr. Wang, collaborating with the research group of Prof. R.L. Whetten, obtained concrete experimental results demonstrating success of forming such superlattice structures using Au nanocrystals.

Particle Shape in the 3-D Assembling of Nanocrystals, and the Self-Assembly of Magnetic Nanocrystals

Following this, Dr. Wang has concentrated on the preparation of size and shape controlled Ag and CoO nanocrystals. His group was the first to study the role of particle shape in determining the crystallography of 3-D assembling of nanocrystals, and the structural stability and molecular bonding between nanocrystals. Dr. Wang's recent research has been focused on self-assembly of magnetic nanocrystals for ultrahigh density data storage media. His paper (Phys. Rev. Lett., 79 (No. 13) (1997) 2570-2573) won the 1998 Georgia Tech Sigma Xi Best Paper Award in a campus wide competition.

Incorporating FePt and Fe₃O₄ Particles into Binary Assemblies

Dr. Wang and his collaborators at IBM (H. Zeng and S. Sun) and University of Texas Arlington (J.P. Liu) have developed a process that incorporates FePt and Fe₃O₄ particles with different mass and radii ratio into binary assemblies (Nature, 420 (2002) 395-398). Controlled annealing results in metallic composites with magnetically hard and soft phase exchange coupled. The approach offers precise engineering control on the dimension of the components and their nanoscale interactions in the composite, rendering isotropic FePt-based nanocomposites with energy product value of 20 MGOe that exceeds the theoretical limit of 13 MGOe for single phase FePt. This paper is being published by Nature.

Source: The Nanotechnology and Nanoscience Research Group at the School of Materials Science and Engineering, the Georgia Institute of Technology.

For more information on this source please visit the Nanotechnology and Nanoscience Research Group.