Spectroscopic characterizations of individual single-crystalline GaN nanowires in visible/ultra-violet regime

Spectroscopic investigations of individual single-crystalline GaN nanowires with a lateral dimensions of ～30–90 nm were performed using the spatially resolved technique of electron energy-loss spectroscopy in conjunction with scanning transmission electron microscope showing a 2-Å electron probe. Positioning the electron probe upon transmission impact and at aloof setup with respect to the nanomaterials, we explored two types of surface modes intrinsic to GaN, surface exciton polaritons at ～8.3 eV (～150 nm) and surface guided modes at 3.88 eV (～320 nm), which are in visible/ultra-violet spectral regime above GaN bandgap of ～3.3 eV (～375 nm) and difficult to access by conventional optical spectroscopies. The explorations of these electromagnetic resonances might expand the current technical interests in GaN nanomaterials from the visible/UV range below ～3.5 eV to the spectral regime further beyond.