Composition and Strain Imaging of Epitaxial In-Plane SiGe Alloy Nanowires by Micro-Raman Spectroscopy

We report micro-Raman imaging of in-plane SiGe alloy nanowires grown by molecular beam epitaxy on Si(001) substrates. The spatial resolution of the Raman images allows us to study individual nanowires. We observe differences in Raman scattering intensity when the light polarization is parallel or perpendicular to the nanowire axis. These variations are shown to be originated from anisotropic absorption in thin nanowires whereas the intrinsic Raman efficiency is less affected by the nanostructuration. Quantitative analysis of the Raman spectra yields the composition and strain variations in the sample, in particular within each nanowire in which we resolve vertical gradients from the base to the top surfaces. These Raman results provide unique insights into the growth processes

Magneto-Optical Enhancement by Plasmon Excitations in Nanoparticle/Metal Structures

Coupling magnetic materials to plasmonic structures provides a pathway to dramatically increase the magneto-optical response of the resulting composite architecture. Although such optical enhancement has been demonstrated in a variety of systems, some basic aspects are scarcely known. In particular, reflectance/transmission modulations and electromagnetic field intensification, both triggered by plasmon excitations, can contribute to the magneto-optical enhancement. However, a quantitative evaluation of the impact of both factors on the magneto-optical response is lacking. To address this issue, we have measured magneto-optical Kerr spectra on corrugated gold/dielectric interfaces with magnetic (nickel and iron oxide) nanoparticles. We find that the magneto-optical activity is enhanced by up to an order of magnitude for wavelengths that are correlated to the excitation of propagating or localized surface plasmons. Our work sheds light on the fundamental principles for the observed optical response and demonstrates that the outstanding magneto-optical performance is originated by the increase of the polarization conversion efficiency, whereas the contribution of reflectance modulations is negligible