The presentation shows the efficacy of power-dependent and high-spatial resolution Cathodoluminescence (CL) in investigating the optical properties of In x Ga 1-x N/GaN MQWs and Ga x As 1-x N x :H and of single ZnO TPs and core shell SiO2/SiC NWs. Power dependent CL spectroscopy Internal field screening in InGaN QWs to restore flat band conditions Efficient field screening of the polarization fields in low In content (x<0.07) InxGa1-xN/GaN multiple QWs is demonstrated in CL steady-state

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... ection conditions and compared with time integrated PL approach (see FIG. 1 ). The blue-shift of the QW emission decreases from about 70 to 17 meV by decreasing the well width from 3.5 to 2 nm. A bowing parameter of 5.7 eV is obtained contrary to literature values of 2.5 eV that cannot explain the QW peak energy at high injection limit (near flat band conditions) for these InGaN alloys (x < 7 %) [1] . Controlled in-plane band gap modulation in hydrogenated dilute Nitrides By focusing an energetic electron beam (Ib = 400 nA, Eb = 5 keV) on the surface of an hydrogenated GaAs1-xNx layer ("writing process"), a controlled decrease of the crystal band gap in the irradiated region is achieved. This is due to the electron beam-induced braking of the bonds of the N-H2 complexes formed during the hydrogenation. Collecting CL spectra after 40 sec of irradiation ("probing process"), a complete restoring of the band gap values before hydrogenation is achieved (FIG. 2 ). By using shorter electron-irradiation times or doses any intermediate band gap value can be obtained. The "write and probe" approach allows a simultaneous band gap modulation and reading and to design paths with different Eg values in a single run [2] . CL spectroscopy and imaging of single NWs Shell-induced cathodoluminescence enhancement in SiO2/SiC core shell NWs The experiment presented reports on an accurate study of the emissions from 3C-SiC/SiO2 core/shell NWs. Controlled HF etching procedures demonstrate that the presence of the silicon dioxide shell enhances the silicon carbide NBE luminescence at 2.36 eV. That is due to the formation of a type I quantum well and the consequent diffusion of carriers from the larger band-gap shell to the narrower band-gap core (FIG. 3 ). This effect can open different possibilities to develop suitable inorganic/organic sensors based on highly biocompatible silicon carbide. CL spectroscopy and imaging of unpredicted cubic phase in hexagonal ZnO TPs The conventional picture is that ZnO arms are thermodynamically stable only in the wurtzite phase. This study reports on the first experimental evidence of unpredicted extended zinc blend phases (50-60 nm long) embedded in the arms of ZnO wurtzite tetrapods. Decisive evidence is obtained from the one-to-one correlation between high lateral resolution CL spectroscopy (λ ZB = 377 nm (3.29 eV)), monochromatic contrast maps and atomic resolution TEM images of ZnO single TPs [3] . The growth of WZ ZnO branched nanostructures containing the ZB phase, allows in principle to interface different crystallographic structures exhibiting different band gaps, electronic and elastic properties. That offers novel routes in the design of nanodevices made by a single nanostructure.