Strong Interplay between Sodium and Oxygen in Kesterite Absorbers: Complex Formation,Incorporation, and Tailoring Depth Distributions

Sodium and oxygen are prevalent impurities in kesterite solar cells. Both elements are known to strongly impact performance of the kesterite devices and can be connected to efficiency improvements seen after heat treatments. The sodium distribution in the kesterite absorber is commonly reported, whereas the oxygen distribution has received less attention. Here, a direct relationship between sodium and oxygen in kesterite absorbers is established using secondary ion mass spectrometry and explained by defect analyses within the density functional theory. The calculations reveal a binding energy of 0.76 eV between the substitutional defects Na_Cu and O_S in the nearest neighbor configuration, indicating an abundance of Na? O complexes in kesterite absorbers at relevant temperatures. Oxygen incorporation is studied by introducing isotopic ¹⁸O at different stages of the Cu₂ZnSnS₄/Mo/soda‐lime glass baseline processing. It is observed that oxygen from the Mo back contact and contaminations during the sulfurization are primary contributors to the oxygen distribution. Indeed, unintentional oxygen incorporation leads to immobilization of sodium. This results in a strong correlation between sodium and oxygen, in excellent agreement with the theoretical calculations. Consequently, oxygen availability should be monitored to optimize postdeposition heat treatments to control impurities in kesterite absorbers and ultimately, the solar cell efficiency.     

Structural analysis of ligand‐bound states of the Salmonella type III secretion system ATPase InvC

Translocation of virulence effector proteins through the type III secretion system (T3SS) is essential for the virulence of many medically relevant Gram‐negative bacteria. The T3SS ATPases are conserved components that specifically recognize chaperone–effector complexes and energize effector secretion through the system. It is thought that functional T3SS ATPases assemble into a cylindrical structure maintained by their N‐terminal domains. Using size‐exclusion chromatography coupled to multi‐angle light scattering and native mass spectrometry, we show that in the absence of the N‐terminal oligomerization domain the Salmonella T3SS ATPase InvC can form monomers and dimers in solution. We also present for the first time a 2.05 å resolution crystal structure of InvC lacking the oligomerization domain (InvCΔ79) and map the amino acids suggested for ATPase intersubunit interaction, binding to other T3SS proteins and chaperone–effector recognition. Furthermore, we validate the InvC ATP‐binding site by co‐crystallization of InvCΔ79 with ATPγS (2.65 å) and ADP (2.80 å). Upon ATP‐analogue recognition, these structures reveal remodeling of the ATP‐binding site and conformational changes of two loops located outside of the catalytic site. Both loops face the central pore of the predicted InvC cylinder and are essential for the function of the T3SS ATPase. Our results present a fine functional and structural correlation of InvC and provide further details of the homo‐oligomerization process and ATP‐dependent conformational changes underlying the T3SS ATPase activity.     

Selection for genetics‐based architecture traits in a native cottonwood negatively affects invasive tamarisk in a restoration field trial

Climate change and competition from invasive species remain two important challenges in restoration. We examined the hypothesis that non‐native tamarisk (Tamarix spp.) reestablishment after aboveground removal is affected by genetics‐based architecture of native Fremont cottonwood (Populus fremontii) used in restoration. As cottonwood architecture (height, canopy width, number of stems, and trunk diameter) is, in part, determined by genetics, we predicted that trees from different provenances would exhibit different architecture, and mean annual maximum temperature transfer distance from the provenances would interact with the architecture to affect tamarisk. In a common garden in Chevelon, AZ, U.S.A. (elevation 1,496 m), with cottonwoods from provenances spanning its elevation distribution, we measured the performance of both cottonwoods and tamarisk. Several key findings emerged. On average, cottonwoods from higher elevations were (1) two times taller and wider, covered approximately 3.5 times more basal area, and were less shrubby in appearance, by exhibiting four times fewer number of stems than cottonwoods from lower elevations; (2) had 50% fewer tamarisk growing underneath, which were two times shorter and covered 6.5 times less basal area than tamarisk growing underneath cottonwoods of smaller stature; and (3) the number of cottonwood stems did not affect tamarisk growth, possibly because the negative relationship between cottonwood stems and basal area. In combination, these findings argue that cottonwood architecture is affected by local conditions that interact with genetics‐based architecture. These interactions can negatively affect the growth of reinvading tamarisk and enhance restoration success. Our study emphasizes the importance of incorporating genetic and environmental interactions of plants used in restoration.     

Sperm number assessed by flow cytometry in species of Daphnia (Crustacea,Cladocera)

Daphnia magna and Daphnia pulex are two important model species in ecotoxicology. In daphniids, studies of the effects of contaminants have mostly focused on female life history traits, yet it would also be important to examine male reproductive traits, particularly in relation to endocrine disruptors. In this study, we developed a protocol that uses flow cytometry to measure sperm number in individual males of different species of Daphnia. We tested our protocol on 114 males from several clones of three common species of Daphnia. Sperm count varied widely among individuals and reached high numbers (up to 1.45 × 10⁵). Positive relationships between male length and sperm number were observed in D. pulex and Daphnia pulicaria, but not in D. magna. Important inter‐clonal differences in sperm production were observed in all species, with some clones producing very little sperm. Duplicated sperm samples showed on average only 6% difference in sperm counts. Sperm counts were stable at least over a 2‐hr period and up to 5 hr for most samples. This sperm isolation protocol and flow cytometric enumeration approach will be of major interest to ecotoxicologists.     

Self‐assembling amyloid‐like peptides as exogenous second harmonic probes for bioimaging applications

Amyloid‐like peptides are an ideal model for the mechanistic study of amyloidosis, which may lead to many human diseases, such as Alzheimer disease. This study reports a strong second harmonic generation (SHG) effect of amyloid‐like peptides, having a signal equivalent to or even higher than those of endogenous collagen fibers. Several amyloid‐like peptides (both synthetic and natural) were examined under SHG microscopy and shown they are SHG‐active. These peptides can also be observed inside cells (in vitro). This interesting property can make these amyloid‐like peptides second harmonic probes for bioimaging applications. Furthermore, SHG microscopy can provide a simple and label‐free approach to detect amyloidosis. Lattice corneal dystrophy was chosen as a model disease of amyloidosis. Morphological difference between normal and diseased human corneal biopsy samples can be easily recognized, proving that SHG can be a useful tool for disease diagnosis.