New LEAP microscopy plays important role in developing semiconductor nanostructures

Researchers at Northwestern University are using atom-probe tomography to map the composition of semiconductor nanowires in three dimensions with single-atom sensitivity and sub-nm resolution. Their results establish atom probe tomography as a uniquely powerful tool for analyzing the chemical composition of semiconductor nanostructures.
The research, conducted by Lincoln Lauhon of the Department of Materials Science and Engineering at Northwestern, demonstrates the three-dimensional composition mapping of a semiconductor nanowire with single-atom sensitivity and subnanometer spatial resolution using atomprobe tomography. A new class of atom probe, the electrode atom probe (LEAP) microscope at Northwestern, was used to map the position of single Au atoms in an InAs nanowire and to image the interface between a Au catalyst and InAs nanowire in three dimensions with 0.3-nm resolution. These results establish atom probe tomography as a uniquely powerful tool for analyzing the chemical composition of semiconductor nanostructures.
In an article in the Feb. 8, 2006 issue of Nano Letters, "Three-Dimensional Nanoscale Composition Mapping of Semiconductor Nanowires" the researchers demonstrate the three-dimensional composition mapping of a semiconductor nanowire with single-atom sensitivity and subnanometer spatial resolution using atom probe tomography. A new class of atom probe, the local electrode atom probe microscope, was used to map the position of single Au atoms in an InAs nanowire and to image the interface between a Au catalyst and InAs in three dimensions with 0.3-nm resolution.
Semiconducting nanowires of controlled composition and doping show great promise as multifunctional components in a number of emerging device technologies. The continued advancement of these nanometer-scale devices will depend critically on knowledge of their atomic-scale structure because compositional fluctuations as small as a single dopant atom can affect device performance. It is therefore highly desirable to determine the composition of individual nanowires with the utmost precision. The spatial resolution of secondary ion mass spectroscopy (SIMS) has been pushed below 100 nm, but the nanowire length-scales of interest are much smaller. Transmission electron microscopy (TEM) is capable of imaging single dopant atoms under specific conditions10 but TEM cannot yet be considered a general tool for the volumetric mapping of low-concentration elements in nanostructures. The important challenge of doping atoms into the "bulk" of nanowires and nanocrystals while avoiding surface segregation further emphasizes the need for three-dimensional composition characterization in these nanostructures.