Phase mapping of aging process in InN nanostructures: oxygen incorporation and the role of the zincblende phase

Uncapped InN nanostructures undergo a deleterious natural aging process at ambient conditions by oxygen incorporation. The phases involved in this process and their localization is mapped by Transmission Electron Microscopy (TEM) related techniques. The parent wurtzite InN (InN-w) phase disappears from the surface and gradually forms a highly textured cubic layer that completely wraps up a InN-w nucleus which still remains from original single-crystalline quantum dots. The good reticular relationships between the different crystals generate low misfit strains and explain the apparent easiness for phase transformations at room temperature and pressure conditions, but also disable the classical methods to identify phases and grains from TEM images. The application of the geometrical phase algorithm in order to form numerical moire mappings, and RGB multilayered image reconstructions allows to discern among the different phases and grains formed inside these nanostructures. Samples aged for shorter times reveal the presence of metastable InN:O zincblende (zb) volumes, which acts as the intermediate phase between the initial InN-w and the most stable cubic In2O3 end phase. These cubic phases are highly twinned with a proportion of 50:50 between both orientations. We suggest that the existence of the intermediate InN:O-zb phase should be seriously considered to understand the reason of the widely scattered reported fundamental properties of thought to be InN-w, as its bandgap or superconductivity.Comment: 18 pages 7 figure

Mie-resonances, infrared emission and band gap of InN

Mie resonances due to scattering/absorption of light in InN containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than currently accepted 0.7 eV. Micro-cathodoluminescence studies complemented by imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises from In aggregates, and is likely associated with surface states at the metal/InN interfaces.Comment: 4 pages, 5 figures, submitted to PR

Magnetic imaging of ferromagnetic domains by room temperature scanning hall probe microscopy using GaAs/AlGaAs and bismuth micro-hall probes

Heterostructure GaAs/AlGaAs and bismuth (Bi) micro-Hall probes were integrated into a room temperature scanning Hall probe microscope system (RT-SHPM) for imaging localized magnetic fluctuations at the surfaces of floppy disks, crystalline garnet thin films, and strontium ferrite permanent magnets. At a drive current of 800 μA the sensitivity of the Bi micro-probes was 0.38 G/√ Hz and comparable with the GaAs/AlGaAs probes. Bi nano-Hall probes with an active region of 200 nm × 200 nm were fabricated by focused ion beam milling and successfully used for magnetic imaging of ferromagnetic domains structures. Bismuth was found to be a practical alternative to semiconductors for fabricating ultra-high resolution nanometer scale Hall probes