Nanotechnology can be defined as the study of material properties and interactions on a nanometer length scale. Our experimental group focuses on investigating size-tunable material properties, and the rational self-assembly and fabrication of nanostructures with atomic detail. This research finds applications in microelectronics and photonics, spintronics, coatings, sensors and biotechnology.

Synthesis:

Nanowires have great potential in the study of unidirectional current flow and as local interconnects of nanometer-scale electronic devices. The synthesis and characterization of nanowires is critical in accessing their use. Germanium nanowires several micrometers in length can be grown at supercritical temperature and pressures in cyclohexane using gold nanocrystals to seed the wire growth. The temperature, concentration of the solution and nature of the precursor have and effect on the nanowires morphology. Characterization of the nanowires includes XPS, XRD, high-resoln. TEM and SEM, nanometer-scale EDS mapping, and DTA.

We have developed the synthesis of silicon and germanium nanocrystals in high temperature supercritical fluids. Thermal decomposition or reduction of silicon precursors at high temperatures and pressures results in sterically stabilized, highly crystalline particles with size-tunable optical properties. Characterization of the nanocrystals includes TEM, XPS, XRD, SAXS, photoluminescence, NMR, IR, mass spectroscopy, AFM and UV-Vis spectroscopy.

Devices:

Some examples of device fabrication include 3D close packed silver nanoparticles in interdigitated arrays. These nanoparticle superlattices show linear current-voltage behavior while ordered fcc. At a particular temperature the fcc superlattice goes through a order-disorder transisition. Below this temperature, the superlattice behaves like a metal and above it behaves like an insulator. Disordered close packed nanocrystals exhibited insulating behavior at all temperatures. Other devices presently being explored include electron transport through nanowires and individual particles.

Biotechnology:

Interfacing nerve cells with nanostructures opens the doors for biomanipulation of the structures. This can be accomplished by either antibody-antigen recognition, or peptide recognition groups. Our group has explored the use of both of these techniques to attach fluoroescent semiconductor nanoparticle to living neurons. In addition, attempts are currently being made to establish electrical interactions between the nanocrystals and the biological systems, particularly through interactions directed at the nanometer scale.

Supercritical Fluids:

Silver and gold nanoparticles sterically stabilized by ligands can be dispersed in supercritical ethane and carbon dioxide. The dispersibility is a strong function of the size of the particle, the density of the solvent and the chemistry. For example, “CO2-philic” ligands are required to stabilize particles in supercritical CO2, whereas, hydrophobic alkane ligands stabilize the particles in supercritical ethane. Increased solvent density is needed to disperse larger particles with higher Van der Waals attractive forces, which can be utilized for size-selective particle separations.

Material & Magnetic Properties:

Manganese doped indium arsenide, grown in epitaxial layers, has been shown to exhibit a ferromagnetic Curie temperature that is dependent on the electric field strength and direction that the sample is subjected to. We are synthesizing new dilute magnetic semiconductor nanocrystals and nanowires, such as manganese-doped indium arsenide, and studying their unique size and composition tunable optical, electronic and magnetic properties. Much of the physical properties of these materials are largely unexplored and their study depends on the ability to overcome the synthetic challenges of controlling nanostructure size and composition. For example, this line of research involves incorporating dopants uniformly through the nanocrystals, controlling the dopant amount, measuring the concentration of components in the sample, and characterizing the properties of these new materials.