Given the large thermal activation energy of acceptors in high %Al AlGaN, a new approach is needed to control p-type
conductivity in this material. One promising alternative to using impurity doping with thermal activation is using the
intrinsic characteristics of the III-nitrides to activate dopants with polarization-induced charge in graded heterostructures.
In this work polarization-induced activation of dopants is used in graded AlGaN nanowires grown by plasma-assisted
molecular beam epitaxy to form ultraviolet light-emitting diodes. Electrical and optical characterization is provided,
showing clear diode behavior and electroluminescent emission at 336nm. Variable temperature electrical measurements
show little change in device performance at cryogenic temperatures, proving that dopant ionization is polarizationinduced
rather than thermally activated.
In this paper, we will describe the experimental processes involved in analytical atomic-resolution scanning transmission electron microscopy (STEM) of supported nano-scale systems. We show that the combination of high-resolution Z-contrast imaging and electron energy loss spectroscopy (EELS) provides an analytical tool with unprecedented chemical and spatial sensitivity that is vital for studying interfaces in heterogeneous catalyst systems. We apply the described methods to study two example heterogeneous catalyst systems: Pt/SiO<sub>2</sub>, and Cu/Al<sub>2</sub>O<sub>3</sub>. In particular, the presence of a few monolayers of platinum oxide in Pt/SiO<sub>2</sub> can be clearly seen, and changes in the chemistry of the SiO<sub>2</sub> support within ~1 nm of the metal-oxide interface can be characterized as a function of the catalyst preparation conditions. The Cu/Al<sub>2</sub>O<sub>3</sub>, reduced at various temperatures, exhibits an increasing oxidation of the Cu-particles upon higher temperature reduction.