Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence with unusual properties and, thus, have been the focus of intense research. Nonetheless, the origin of their photoluminescence is still unclear and the subject of scientific debates. Here, we present a single particle comprehensive study of carbon nanodot photoluminescence, which combines emission and lifetime spectroscopy, defocused emission dipole imaging, azimuthally polarized excitation dipole scanning, nanocavity-based quantum yield measurements, high resolution transmission electron microscopy, and atomic force microscopy. We find that photoluminescent carbon nanodots behave as electric dipoles, both in absorption and emission, and that their emission originates from the recombination of photogenerated charges on defect centers involving a strong coupling between the electronic transition and collective vibrations of the lattice structure.

The three-dimensional growth of GaN structures as a basis for the fabrication of 3D GaN core-shell LEDs has attracted substantial attention in the past few years. GaN nanorods or microrods with high aspect ratios can be grown by selective area epitaxy on a GaN buffer through a SiO x mask. It has been found earlier that silane substantially initiates vertical growth, with the exact underlying mechanisms being still unclear. Here, the influence of silane on the 3D GaN column growth was investigated by performing detailed growth experiments in combination with a thorough surface analysis in order to get insight into these mechanisms. The vertical growth rate is significantly enhanced by high silane fluxes, whereas the saturation of growth rate with the time is reduced. Thus, homogenous GaN columns with an aspect ratio of more than 35 could be achieved. A thin Si-rich layer on the non-polar m-plane facets of the columns has been detected using a combination of transmission electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. This layer is suggested to be the reason for the increase in growth rate, modifying the effective collection range of the species along the sidewalls, and preventing the lateral growth.

Thermal spin-transfer torque describes the manipulation of the magnetization by the application of a heat flow. The effect has been calculated theoretically by Jia et al. in 2011. It is found to require large temperature gradients in the order of Kelvins across an ultra thin MgO barrier. In this paper, we present results on the fabrication and the characterization of magnetic tunnel junctions with 3 monolayer thin MgO barriers.The quality of the interfaces at different growth conditions is studied quantitatively via high-resolution transmission electron microscopy imaging. We demonstrate tunneling magneto resistance ratios of up to 55% to 64% for 3 to 4 monolayer barrier thickness. Magnetic tunnel junctions with perpendicular magnetization anisotropy show spin-transfer torque switching with a critical current of 0.2 MA/cm 2 . The thermally generated torque is calculated ab initio using the Korringa-Kohn-Rostoker and non-equilibrium Green's function method. Temperature gradients generated from femtosecond laser pulses were simulated using COMSOL, revealing gradients of 20 K enabling thermal spin-transfer-torque switching.

InN‐nanocolumns are an attractive system for light harvesting applications. To understand the mechanism of self organized growth of nanocolumns in plasma assisted MBE, InN samples were produced under various conditions on p‐Si(111). Depending on the growth parameters different growth regimes for nanocolumns were identified according to their final shape. High‐resolution TEM pictures show a very good crystal quality. This is also confirmed by Raman and PL measurements. Nanocolumns with diameters of 20‐200 nm and lengths of up to 2 mm were produced. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, we present the structural, optical, and electrical characterization of InGaN/GaN core-shell micro-LED structures selectively grown by metal organic vapor phase epitaxy (MOVPE) in arranged arrays. In particular we analyze the core-shell geometry of the pillars, consisting of a fivefold InGaN/GaN multiple quantum well and a p-type layer on all sidewall and top facets. Additionally we analyze the optical properties of the structure and the active region with high spatial resolution by cathodoluminescence. Electron beam induced current measurements (EBIC) are performed using an SEM based manipulator setup, giving proof of the presence of a depletion region as well as the intended doping polarity of the n-type core and a p-type shell wrapped around the whole structure. Using a p-n-p configuration also current crowding is discussed by EBIC and electroluminescence is demonstrated by measuring emission patterns from single core-shell structures.Color overlay of SE image (grey, FOV ¼ 12.7 mm) and EBIC image (red) of a cleaved core-shell LED pillar contacted by two probe tips at a substrate tilt of 308.