Molecular Beam Epitaxy of ß-(InxGa1-x)2O3 on ß-Ga2O3 (010): Compositional Control, Layer Quality, Anisotropic Strain Relaxation, and Prospects for Two-Dimensional Electron Gas Confinement.

In this work, we investigate the growth of monoclinic ß-(InxGa1-x)2O3 alloys on top of (010) ß-Ga2O3 substrates via plasma-assisted molecular beam epitaxy. In particular, using different in situ (reflection high-energy electron diffraction) and ex situ (atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, and transmission electron microscopy) characterization techniques, we discuss (i) the growth parameters that allow for In incorporation and (ii) the obtainable structural quality of the deposited layers as a function of the alloy composition. In particular, we give experimental evidence of the possibility of coherently growing (010) ß-(InxGa1-x)2O3 layers on ß-Ga2O3 with good structural quality for x up to ≈ 0.1. Moreover, we show that the monoclinic structure of the underlying (010) ß-Ga2O3 substrate can be preserved in the ß-(InxGa1-x)2O3 layers for wider concentrations of In (x ≤ 0.19). Nonetheless, the formation of a large amount of structural defects, like unexpected (102̅) oriented twin domains and partial segregation of In is suggested for x > 0.1. Strain relaxes anisotropically, maintaining an elastically strained unit cell along the a* direction vs plastic relaxation along the c* direction. This study provides important guidelines for the low-end side tunability of the energy bandgap of ß-Ga2O3-based alloys and provides an estimate of its potential in increasing the confined carrier concentration of two-dimensional electron gases in ß-(InxGa1-x)2O3/(AlyGa1-y)2O3 heterostructures.

Realistic microplastics harness bacterial presence and promote impairments in early zebrafish embryos: Behavioral, developmental, and transcriptomic approaches.

The plastisphere is a newly recognized ecosystem. However, its interaction with early life stages of aquatic vertebrates is a multifaceted issue that requires further research. This study investigated the involvement of bacteria in shaping realistic microplastics hazards in zebrafish Danio rerio embryos. Fish were exposed to bottle micro-fragments (FR) and textile micro-fibers (FI) of polyethylene terephthalate (5-15 µm), concomitant with Aeromonas salmonicida achromogenes challenge from 2h post-fertilization for 3 days. Egg chorion showed affinity for FR and FI, inducing earlier embryo hatching. However, this effect was masked by biofilm invasion. Fragments were more detrimental than fibers on developmental parameters, while bacterial presence compromised body length, eye, and yolk sac surface area. In a further finding, MPs alone increased locomotor activity in zebrafish larvae, without synergistic effect when combined with bacteria. Data showed that realistic MPs had no significant effects except for downregulated sod and cyp1a gene expression, whereas bacterial challenge inhibited larval potency for most of the evaluated mRNA levels (mpx (immune system), apoeb (lipid metabolism), nfkb and tfa (inflammation), cyp and sod (oxidative stress)). This study provides new insights into realistic microplastic effects under relevant conditions when combined with environmental pathogen within the first life stages of aquatic vertebrates.

Application of silver-based biocides in face masks intended for general use requires regulatory control.

Silver-based biocides are applied in face masks because of their antimicrobial properties. The added value of biocidal silver treatment of face masks to control SARS-CoV-2 infection needs to be balanced against possible toxicity due to inhalation exposure. Direct measurement of silver (particle) release to estimate exposure is problematic. Therefore, this study optimized methodologies to characterize silver-based biocides directly in the face masks, by measuring their total silver content using ICP-MS and ICP-OES based methods, and by visualizing the type(s) and localization of silver-based biocides using electron microscopy based methods. Thirteen of 20 selected masks intended for general use contained detectable amounts of silver ranging from 3 µg to 235 mg. Four of these masks contained silver nanoparticles, of which one mask was silver coated. Comparison of the silver content with limit values derived from existing inhalation exposure limits for both silver ions and silver nanoparticles allowed to differentiate safe face masks from face masks that require a more extensive safety assessment. These findings urge for in depth characterization of the applications of silver-based biocides and for the implementation of regulatory standards, quality control and product development based on the safe-by-design principle for nanotechnology applications in face masks in general.

Tackling Disorder in γ-Ga2 O3.

Ga2 O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2 O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2 O3 presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure-electronic-structure relationship. Here, density functional theory is used in combination with a machine-learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ-Ga2 O3 . The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by photoluminescence excitation spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step toward exploring how their electronic structure can be understood in terms of local coordination and overall structure.