Investigation of GaN nanowires containing AlN/GaN multiple quantum discs by EBIC and CL techniques.

In this work, nanoscale electrical and optical properties of n-GaN nanowires (NWs) containing GaN/AlN multiple quantum discs (MQDs) grown by molecular beam epitaxy are investigated by means of single wire I(V) measurements, electron beam induced current microscopy (EBIC) and cathodoluminescence (CL) analysis. A strong impact of non-intentional AlN and GaN shells on the electrical resistance of individual NWs is put in evidence. The EBIC mappings reveal the presence of two regions with internal electric fields oriented in opposite directions: one in the MQDs region and the other in the adjacent bottom GaN segment. These fields are found to co-exist under zero bias, while under an external bias either one or the other dominates the current collection. In this way EBIC maps allow us to locate the current generation within the wire under different bias conditions and to give the first direct evidence of carrier collection from AlN/GaN MQDs. The NWs have been further investigated by photoluminescence and CL analyses at low temperature. CL mappings show that the near band edge emission of GaN from the bottom part of the NW is blue-shifted due to the presence of the radial shell. In addition, it is observed that CL intensity drops in the central part of the NWs. Comparing the CL and EBIC maps, this decrease of the luminescence intensity is attributed to an efficient charge splitting effect due to the electric fields in the MQDs region and in the GaN base.

Carrier Localization in GaN/AlN Quantum Dots As Revealed by Three-Dimensional Multimicroscopy.

The localization of carrier states in GaN/AlN self-assembled quantum dots (QDs) is studied by correlative multimicroscopy relying on microphotoluminescence, electron tomography, and atom probe tomography (APT). Optically active field emission tip specimens were prepared by focused ion beam from an epitaxial film containing a stack of quantum dot layers and analyzed with different techniques applied subsequently on the same tip. The transition energies of single QDs were calculated in the framework of a 6-bands k.p model on the basis of APT and scanning transmission electron microscopy characterization showing that a good agreement between experimental and calculated energies can be obtained, overcoming the limitations of both techniques. The results indicate that holes effectively localize at interface fluctuations at the bottom of the QD, decreasing the extent of the wave function and the band-to-band transition energy. They also represent an important step toward the correlation of the three-dimensional atomic scale structural information with the optical properties of single light emitters based on quantum confinement.

N-acetylcysteine Treatment in Chronic Obstructive Pulmonary Disease (COPD) and Chronic Bronchitis/Pre-COPD: Distinct Meta-analyses.

INTRODUCTION: N-acetylcysteine (NAC) is a mucolytic agent with antioxidant properties. Oxidative stress is a key pathogenic mechanism in chronic respiratory conditions such as COPD and chronic bronchitis (CB). In these meta-analyses we investigated the efficacy of NAC in subjects with COPD or CB, the latter being a potential pre-COPD condition (CB/pre-COPD). METHODS: The meta-analyses were conducted according to PRISMA guidelines. Exacerbations were assessed using total number of exacerbations. Improvement in patients' respiratory symptoms and/or patients quality of life (QoL) were measured by validated tools or assessed at the end of the study. RESULTS: Twenty studies were included, of which seven evaluated NAC in patients with symptoms of CB/pre-COPD as entry criterion. NAC treated patients showed a significant reduction of the incidence of exacerbations as compared to placebo both in COPD (IRR=0.76; 95% confidence interval (CI) 0.59-0.99) and CB/pre-COPD (IRR=0.81; 95% CI 0.69-0.95). Sensitivity analyses in studies with duration higher than 5 months, confirmed the overall results. CB/pre-COPD patients treated with NAC were significantly more likely to experience an improvement in symptoms and/or QoL compared to placebo (odds ratio (OR)=3.47; 95% CI 1.92-6.26). A similar trend was observed in the few COPD studies evaluable. Sensitivity analyses showed a significant association of NAC with improvement in symptoms and/or QoL both in CB/pre-COPD and COPD patients. CONCLUSIONS: These findings provide novel data of NAC on the improvement in symptoms and QoL in addition to prevention of exacerbations in COPD and CB/pre-COPD. PROSPERO registry no. CRD42023468154.

Development of spray-dried N-acetylcysteine dry powder for inhalation.

N-acetylcysteine (NAC) has both antioxidant and immunomodulatory activities and has been used as adjuvant therapy in several viral infections. Recently, NAC attracted attention for its possible role in reducing the affinity of the spike protein receptor binding domain to angiotensin-converting enzyme (ACE2) receptors. Since only NAC solutions are available for inhalation, the purpose of the work was to develop a NAC dry powder for inhalation using mannitol or leucine as excipient. The powder was successfully produced using co-spray-drying with leucine. ATR-FTIR analyses evidenced spectral variations ascribed to the formation of specific interactions between NAC and leucine. This effect on the NAC environment was not evident for NAC-mannitol powders, but mannitol was in a different polymorphic form compared to the supplied material. Both the feedstock concentration and the leucine content have an impact on the powder aerodynamic features. In particular, to maximize the respirable fraction, it is preferable to produce the powder starting from a 0.5 % w/v feedstock solution using 33 to 50 % w/w leucine content. The NAC-leucine powder was stable for ten months maintaining NAC content of 50 % (w/w) and about 200 µg of NAC was able to deposit on a transwell insert, useful for future in vitro studies.