Polarized Raman Confocal Microscopy Maps Nanowires

Daniel S. Burgess

Scientists at the University of California, Berkeley, Lawrence Berkeley National Laboratory, also in California, and Université Bordeaux 1 in Talence, France, have reported that polarized Raman confocal microscopy may be used to collect information regarding physical characteristics of individual GaN nanowires that determine their electrical and optical properties. They propose that the approach will have utility in the characterization of semiconductor nanostructures for the development of nanoscale optoelectronic devices and sensors.

Polarized Raman confocal microscopy reveals information regarding the crystalline phase, growth direction and radial crystallographic orientation of individual GaN nanowires. Each polarized Raman map takes approximately 1 hour to create. In these examples, both the excitation and response were horizontally polarized (“HH”) or vertically polarized (“VV”). Courtesy of Peter Pauzauskie, University of California, Berkeley.

Using a LabRam HR Raman microscope from Horiba Jobin Yvon of Edison, N.J., the investigators mapped the Raman spectra of individual 170-nm-diameter GaN nanowires under 514.5-nm excitation by an argon-ion laser. They selected the polarization of the excitation using a half-wave plate and that of the response using a polarizer.

A high-resolution piezoelectric stage manufactured by PI (Physik Instrumente) LP of Auburn, Mass., enabled them to collect spectra in 200-nm steps, which they compiled to produce 2-D maps at various polarization configurations.

The polarized Raman maps, each of which took approximately an hour to create, reveal information about a nanowire’s crystalline phase, growth direction and radial crystallographic orientation.

The researchers suggest that employing a high-resolution spectrometer with the technique should offer further details on stress-induced shifts and crystallinity modifications of the nanostructures at various growth temperatures.

JACS, Dec. 14, 2005, pp. 17146-17147.