The Fröhlich coupling strength of individual GaAs nanowires is investigated by resonant micro-Raman spectroscopy measurements near the direct bandgap E g . Large 2LO/1LO intensities up to 5.7 are observed in an individual GaAs nanowire. A 2LO resonance profile of the GaAs nanowire agrees well with a two-phononscattering model, suggesting excitonic scattering. These results advance the understanding of electron-phonon coupling and exciton scattering in quasi-one-dimensional systems and in GaAs at E g , allowing for the development and optimization of nanowire optoelectronic devices. DOI: 10.1103/PhysRevB.80.201314 PACS number͑s͒: 63.22.Gh, 63.20.kd, 71.35.Ϫy, 78.30.Fs Nanowires are quasi-one-dimensional crystals that can exhibit radial quantum confinement, resulting in nanoscale properties different from those of the bulk. Individual semiconductor nanowires have been employed in nanoscale optoelectronic devices, such as electrically driven lasers, 1 lightemitting diodes, 2 and photodetectors, 3 among other applications. 4 A fundamental understanding of electronphonon interaction within nanowires is required to tailor their optical and electrical properties 5 and could further the development of nanowire electronic devices. For example, photoluminescence peak broadening is largely attributed to the coupling of electronic charge to phonons, 6 which can inhibit the ability to spectrally distinguish individual photons; further, phonon coupling to the electron of a bound exciton could drastically affect optoelectronic properties in nanowire devices, especially in regimes of strong quantum confinement. 7,8Fröhlich-induced electron-phonon coupling in assemblies of nanowires has been previously investigated under nonresonance conditions. 9,10 However, a disparity in growth directions, size, and structure of nanowires within an assembly can result in averaged spectral data hindering information on a single-nanowire level. Resonant Raman spectroscopy is sensitive to structural variations of individual nano-objects within a population, 11 but no resonant Raman studies on individual nanowires have been reported to date. Here, we study individual nanowires by resonant micro-Raman spectroscopy near the energy bandgap E g to understand electronphonon coupling and exciton scattering in quasi-onedimensional systems. Notably, previous attempts have been hampered by excessive photoluminescence ͑PL͒.12 A model is presented for two-phonon excitonic scattering, which fits well with the observed 2LO resonance intensities from a single GaAs nanowire and allows us to assess the Fröhlich coupling strength and the exciton damping constant.GaAs nanowires were grown using metalorganic chemical vapor deposition catalyzed by 90 nm Au nanoparticles, as reported previously.13 Nanowire structural properties were investigated using a JEOL 6320FV high-resolution scanning electron microscope ͑SEM͒ and by JEOL 2010F fieldemission transmission electron microscope ͑TEM͒. For Raman experiments, nanowires were removed from the growth substrates by so...

The understanding of the near field is essential for scanning near-field optical microscopy. We present here a simple model experiment to examine the polarization of the near field in the proximity of a subwavelength aperture. We make use of microwaves, a fast diode, and different apertures. This allows us to model a polarization-sensitive scanning near-field optical microscope by mapping the field intensity around the aperture in the near-field region.