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Hierarchical Materials Synthesis

Personnel: Nari Jeon, In Soo Kim, Spencer Park
Collaborators: P. Voorhees, B. Wessels
Applications: photovoltaics, energy storage, sensors, novel logic devices

New bottom-up approaches to crystal growth enable the realization of complex heterostructured materials with useful functions built-in during synthesis. Current research efforts focus on the development of new catalysts for semiconductor nanowire growth that provide better control over doping and composition modulation.

Branched Nanowire Growth

Metal nanoparticles can be used to seed the growth of nanowires of controlled diameter, length, and composition. We showed that dendritic (highly branched) nanowires could be grown by introducing a metal precursor during nanowire growth. Mn atoms deposited from the vapor phase self-assembled into catalysts for InAs nanowires, leading to generations of branches. This work demonstrated a new route to hierarchical nanowire structures.

S. J. May, J. G. Zheng, B. W. Wessels, & L. J. Lauhon, “Manganese mediated dendritic growth of InAs nanowires,” Advanced Materials17, 598-602 (2005). (Cover Article)

Self-assembled Quantum Dots

Ferromagnetic MnAs quantum dots were grown epitaxially on InAs nanowires through on-nanowire self-assembly. Magnetic force microscopy was used to study the switching behavior of individual quantum dots and correlate with electron microscopy and diffraction studies of their crystal structure. The hybrid ferromagnetic/semiconductor QD/NW properties provide a promising basis for the development of nanowire spin-valves and magnetic memory devices.

D. G. Ramlan, S. J. May, J.-G. Zheng, J. E. Allen, B. W. Wessels, & L. J. Lauhon, “Ferromagnetic Self-Assembled Quantum Dots on Semiconductor Nanowires,” Nano Letters 6, 50 (2006).

Syntaxial Nanowire Growth

We discovered a novel syntaxial growth mechanism whereby two different nanowires- one metallic and one semiconducting- grow simultaneously from a common interface. The mechanism provides a useful approach to ideal nanoscale metal-semiconductor heterojunctions and represent the growth of electrical contacts ‘in situ’. The metallic phase is also magnetic, creating the opportunity to study spin-injection into a well-defined one-dimensional system.

J. L. Lensch-Falk, E. R. Hemesath, and L. J. Lauhon, "Syntaxial Growth of Ge/Mn-Germanide Nanowire Heterostructures," Nano Letters 8, 2669-2673 (2008).

Additional References