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Nanostructure Visualization

Personnel: James Riley, Nari Jeon, Xiaochen Ren, Zhiyuan Sun
Collaborators: D. Seidman, G.T. Wang (Sandia National Lab)
Applications: conventional and novel semiconductor device technologies

The nanotechnology revolution is driven by advances in both materials and characterization. We have developed approaches to map the positions of individual atoms in three dimensions with atomic resolution, enabling structure-property relationships to be defined down to the ultimate length-scale of materials.

3D Atomic Composition Mapping

Intentional impurity atoms, or dopants, are used to control the electronic properties of semiconductors, but it is very challenging to determine the concentration and distribution of dopant atoms in extremely small structures such as nanowires. We pioneered the use of atom probe tomography to map the positions of dopant atoms in semiconductor nanowires (see also references below). This ability enables the quantitative correlation of electrical properties and the development of much needed models of nanowire doping (with Voorhees).

D. E. Perea, E. R. Hemesath, E. J. Schwalbach, J. L. Lensch-Falk, P. W. Voorhees, and L. J. Lauhon, "Direct Measurement of Dopant Distribution in an Individual Vapor-Liquid-Solid Nanowire" Nature Nanotechnology 4, 315-319 (2009).

Single Atom Imaging

The vapor-liquid-solid method of nanowire growth is one of the most widely used, yet there is significant concern that metal nanoparticles used to grow the nanowires may lead to impurity incorporation. We have established both upper and lower bounds on the degree of gold catalyst contamination in silicon nanowires.

J. E. Allen, E. R. Hemesath, D. E. Perea, J. L. Lensch-Falk, Z.Y. Li, F. Yin, M. H. Gass, P. Weng, A. L. Bleloch, R. E. Palmer, and L. J. Lauhon, "High-resolution detection of Au catalyst atoms in Si nanowires," Nature Nanotechnology 3, 168-173 (2008).

Polytypes in Nanowire Structures

Ordered arrays of stacking faults in semiconductors can lead to the formation of distinct polytypes- materials with the same chemical formula but distinct electronic structure. We have observed the formation of hexagonal inclusions within cubic silicon nanowires using correlated Raman spectroscopy and electron diffraction. Further investigations of the nanowire growth process may lead to the controlled growth of homojunction structures with novel electrical and optical properties.

F. J. Lopez, E. R. Hemesath, and L. J. Lauhon, “Ordered Stacking Fault Arrays in Silicon Nanowires” Nano Letters 9 (7) 2774-2779 (2009).

Additional References