Paper AS-TuA11
Nanospectroscopy of Single Silicon Nanowire Surface using Energy Filtered X-ray PhotoElectron Emission Microscopy (XPEEM)

Tuesday, October 16, 2007, 5:00 pm, Room 610

Interest in silicon nanowires (Si NWs) continues to grow, fuelled by novel applications in nanotechnology. This requires precise wire engineering in order to tailor specific surface properties of Si NWs like electron emission properties and surface chemistry, which can be altered by the growth process.¹ Within this perspective, the implementation of novel, non destructive experimental techniques offering both spectroscopic and microscopic capabilities is needed. In this contribution, we present recent results of a surface study using synchrotron radiation induced X-ray PhotoElectron Emission Microscopy (XPEEM) of 250 nm-diameter single NWs dispersed on gold after growth by the Vapour-Liquid-Solid process from gold-silicon catalysts. Here, XPEEM is implemented with the first commercially available NanoESCA spectromicroscope featuring a fully electrostatic PEEM column together with an aberration-corrected energy filter (double hemispherical energy analyser) allowing both a high lateral and energy resolutions.^2-4 The instrument allows laboratory XPEEM experiments with a bright AlKα source, and can also be periodically moved to the European Synchrotron Radiation Facility (ESRF) to benefit from the high brightness and energy tunability of ID08, a soft X-ray beamline.⁴ We focus on results related to the energy-filtered, secondary electron images at the photoemission threshold that reveal differences in the local work function and enable investigation, along the nanowire, of the sidewall wetting by the catalyst and the catalyst properties. The double-photoemission threshold shape of the generated nanospectra along the NW surface is a superposition of that characteristic of the Si NW surface and of the gold substrate indicating that gold diffusion and dewetting along the NW sidewall occurs, giving rise to the formation of a non-continuous gold layer. This is confirmed by the Au4f core-level images and SEM observations on the same nanowire. This experiment demonstrates the powerful capabilities of XPEEM nanospectroscopy with the NanoESCA for the surface chemical characterization of single nanostructures.

¹ J.B. Hannon et al., Nature 440 (2006) 69.
² M. Escher et al., J. Phys.: Condens. Matter 17 (2005) S1329.
³ O. Renault et al., Surf. Interface Anal. 2006 ; 38 : 375-377.
⁴O. Renault et al., Surf. Sci. 2007 (in press).