Transmission Electron Microscopy Investigation of Local Atomic Environment of Nitrogen inside Voids Formed at GaN/Sapphire Interface

Abstract

The interrupter technique, the simplest method for measuring airflow resistance (R int ) is particularly valuable under field conditions. We investigate whether during tidal breathing, variations in the flow at which interruption occurs contribute to variability of results. Using a portable device with mouthpiece, sets of 10 measurements of R int (R int,mo ) were made in inspiration and expiration at 0.05 l s −1 intervals from 0.1 up to 0.9 l s −1 flow in 22 normal adults, 11 children (5-9 years) and 12 COPD patients. R int was also measured via nasal-mask in normal adults (R int,na ). Intra-subject coefficient of variation was obtained at each flow and flow-dependence of R int was assessed. In normal subjects, R int -flow relationships were consistent, with a narrow range of absolute values. R int,na , but not R int,mo , rose with increasing flow, especially >0.4 l s −1 . Repeatability was poor at flows <0.3 l s −1 but improved with increasing flow and was better in inspiration than expiration. In children, repeatability was better than in adults and R int,mo was not flow dependent at 0.4 l s −1 . By contrast, in COPD patients repeatability was less good and R int,mo increased with increasing flows. R int,mo and R int,na should be measured at fixed inspiratory flows. The best signal-to-noise ratios were obtained at 0.4 l s −1 for R int in normal adults and COPD patients and at 0.3 l s −1 in children.

Double-crystal X-ray topography of freestanding HVPE grown n-type GaN

“…These defects are observed for the first time by HRXT, and their origin is believed to be due to the lift-off process of the GaN films from the sapphire substrates or some other growth-related interface defects. The TEM studies by Matsubara and Shoda [18] and some others have attributed similar voids to the escape of nitrogen creating voids in the freestanding GaN. During the HVPE growth of GaN on sapphire, it is possible that there is some nitrogen trapped by dangling bonds between the GaN epilayers and the substrate, which are broken in the lift-off process and nitrogen escapes from the films.…”

Characterization of Fe-N nanocrystals and nitrogen–containing inclusions in (Ga,Fe)N thin films using transmission electron microscopy

“…The background-subtracted N-K edge peaks were integrated in the energy range between 398 and 448 eV. On the assumption of single scattering and that the bubble is spherical with a diameter d B ~ 20 nm, the density of the nitrogen was estimated to be 1.4 ± 0.3 g/cm 3 , which corresponds to a gas pressure of ~ 3 GPa at 300 K according to a N 2 pressure -density isotherm calculated by Strak et al, 34 or to ~ 2.8 GPa according to a volumepressure diagram for N 2 determined by Mills et al 35 Bubbles with higher densities of (probably solid) nitrogen have been found in sapphire close to a GaN/sapphire interface by Matsubara et al, 36 due to nitridation of the surface. Our pressure estimate is simplified, as it does not consider differences in scattering cross-section between the bubble and the GaN or the unknown temperature of the bubble resulting from the large thermal conductivity difference between nitrogen gas and the GaN host.…”

Nitrogen Nanobubbles in a-SiOxNy Coatings: Evaluation of Its Physical Properties and Chemical Bonding State by Spatially Resolved Electron Energy-Loss Spectroscopy

“…[30][31][32] Most of them were done in a semi-quantitative way based on the variation of the N-K edge intensity over the nitride matrix and over the pore. [30][31] Indeed, the quantification of the nitrogen density inside small pores is a more challenging problem than for helium.…”

“…[30][31][32] Most of them were done in a semi-quantitative way based on the variation of the N-K edge intensity over the nitride matrix and over the pore. [30][31] Indeed, the quantification of the nitrogen density inside small pores is a more challenging problem than for helium. The main reason is that the N-K edge position is quite far from the elastic peak and due to the limited dynamical range of the CCD detectors, the low-loss (LL) and core-loss (CL) energy range have to be recorded separately, with different dwell times.…”