Structure of Ultrathin Native Oxides on III-Nitride Surfaces.

When pristine material surfaces are exposed to air, highly reactive broken bonds can promote the formation of surface oxides with structures and properties differing greatly from bulk. Determination of the oxide structure is often elusive through the use of indirect diffraction methods or techniques that probe only the outermost layer. As a result, surface oxides forming on widely used materials, such as group III-nitrides, have not been unambiguously resolved, even though critical properties can depend sensitively on their presence.

Numerical modeling of specimen geometry for quantitative energy dispersive X-ray spectroscopy.

Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios.

A reliable approach to prepare brittle semiconducting materials for cross-sectional transmission electron microscopy.

Here, we present a sample preparation approach that simplifies the thinning of very brittle wide bandgap semiconducting materials in cross-section geometry for (scanning) transmission electron microscopy. Using AlN thin films grown on sapphire and AlN substrates as case studies, we demonstrate that high-quality samples can be routinely prepared while greatly reducing the preparation time and consumables cost. The approach removes the sample preparation barrier to studying a wide variety of materials by electron microscopy.

Influence of experimental conditions on atom column visibility in energy dispersive X-ray spectroscopy.

Here we report the influence of key experimental parameters on atomically resolved energy dispersive X-ray spectroscopy (EDX). In particular, we examine the role of the probe forming convergence semi-angle, sample thickness, lattice spacing, and dwell/collection time. We show that an optimum specimen-dependent probe forming convergence angle exists to maximize the signal-to-noise ratio of the atomically resolved signal in EDX mapping.

Quantitative atomic resolution elemental mapping via absolute-scale energy dispersive X-ray spectroscopy.

Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain.