Sodium Passivation of the Grain Boundaries in CuInSe2 and Cu2ZnSnS4 for High‐Efficiency Solar Cells

It is well known that sodium at grain boundaries (GBs) increases the photovoltaic efficiencies of CuInSe₂ and Cu₂ZnSnS₄ significantly. However, the mechanism of how sodium influences the GBs is still unknown. Based on the recently proposed self‐passivation rule, it is found that the dangling bonds in the GBs can completely be saturated through doping the Na, thus GB states are successfully passivated. It is shown that the Na can easily incorporate into the GB with very low formation energy. Although Cu can also passivate the GB states, it requires a copper rich condition which, however, suppresses the formation of copper vacancies in the bulk and thus decreases the concentration of hole carriers, so copper passivation is practically not as beneficial as sodium. The present work reveals the mechanism about how the Na enhances the photovoltaic performance through passivating the dangling bonds in the GBs of chalcogenide semiconductors, and sheds light on how to passivate dangling bonds in GBs with alterative processes.     

Nano-scale simulation based study of creep behavior of bimodal nanocrystalline face centered cubic metal

In this paper, the creep behavior of nanocrystalline Ni having bimodal grain structure is investigated using molecular dynamics simulation. Analysis of structural evolution during the creep process has also been performed. It is observed that an increase in size of coarse grain causes improvement in creep properties of bimodal nanocrystalline Ni. Influence of bimodality (i.e., size difference between coarse and fine grains) on creep properties are found to be reduced with increasing creep temperature. The dislocation density is observed to decrease exponentially with progress of creep deformation. Grain boundary diffusion controlled creep mechanism is found to be dominant at the primary creep region and the initial part of the secondary creep region. After that shear diffusion transformation mechanism is found to be significantly responsible for deformation as bimodal nanocrystalline Ni transforms to amorphous structure with further progress of the creep process. The presence of <0, 2, 8, 5>, <0, 2, 8, 2 >, and <0, 1, 10, 2 > distorted icosahedra has a significant influence on creep rate in the tertiary creep regime according to Voronoi cluster analysis.     

Structural evolution and dislocation behaviour study during nanoindentation of Mo20W20Co20Ta20Zr20 high entropy alloy coated Ni single crystal using molecular dynamic simulation

In this present study, deformation behaviour of Mo₂₀W₂₀Co₂₀Ta₂₀Zr₂₀ high entropy alloy (HEA) coated single crystal (SC) nickel (Ni) subjected to nanoindentation test have been investigated to study the mechanical properties and underlying mechanism during nanoindentation test using molecular dynamics (MD) simulation with embedded atom method (EAM) potential. Centro-Symmetry Parameter (CSP) Analysis and Radial Distribution Function (RDF) plots are obtained to get insight of structural evolution during nanoindentation and thereby determine the underlying physics of deformation. During nanoindention test Stacking faults (SFs) formation, dislocation generation, dislocation loops, Lomer–Cottrell (LC) lock and Hirth lock formation due to dislocation-dislocation interaction are observed. At higher indentation depth, formation of dislocation loops is augmented, which indicates nanoindentation deformation is found to be Stacking Fault dominated deformation. The accumulation and relaxation of shear stress near indenter tip at the time of deformation process under nanoindentation test causes the variation of dislocation density, strain hardening, and plastic deformation, which is influenced by the formation of dislocation barriers (LC and Hirth locks) and dislocation loops (shear and prismatic loops).     

Prognostic value of stem cell markers in glioblastoma

Abstract

Background/Context: Glioblastoma (GB) is the most common primary brain tumour in adults and it is associated with a high mortality rate. According to the stem cell theory, the growth, relapse and treatment response of GB is determined by the stem cell subpopulation present in the tumour.

Objective: Our aim is to study the prognostic value of stem cell markers (CD44, Nestin, Olig2 and SOX2) in a series of homogeneously treated GBs.

Material and methods: We study 280 GBs treated with STUPP acheme with a histologican review of the cases and TMA with a máximum of 4 spots for each case. Each slide was immunohistochemically stained and Reading. We compared the immunohistochemical results with survival tme.

Results: Only SOX2 immunoexpression (IE) excedding 10% of the tumour cells was found to be related to good survival (p= 0.037) in univariate analysis. However, amultivariate analysis indicate the age, surgery and MGMT promotes methylation but no SOX2 IE are prognostic factors.

Conclusions: We conclude the immunohistochemical studies of stem cell markers in GB are not useful for predicting prognosis in daily practice.     

Single-crystal Al–Cu50Zr50 metallic glass cold welds: tensile and creep behaviour

ABSTRACT

Tensile and creep properties of dissimilar cold weld joints (Al (metal)–Cu₅₀Zr₅₀ (metallic glass)) are investigated using molecular dynamics simulations. Embedded atom method potential is used to model the interactions between Al–Cu–Zr atoms. Cold welding is carried out at three different velocities (20, 30 and 40?m/s) and for three interferences (0.4, 1.3 and 2.3?nm). The strength of the welded joints is measured using the tensile test carried out at a strain rate of 1.5 × 10⁹/s. Structure studies by radial distribution function analysis indicate amorphisation of Al in the weld regions. Tensile studies show that the maximum strength is obtained in the sample that is welded for 1.3?nm interference. Creep studies carried out over range of stresses (200–350?MPa) and temperatures (200–500?K) show very short primary creep and significant steady-state creep. The stress exponent n has two values; at lower stress, n?=?1.2, and at higher stress, n?=?4.06, respectively. The deformation mechanisms are observed to be slip by Shockley partial dislocation and by twinning in Al region. The icosahedral cluster population in metallic glass decreases as the temperature increases and contributes to large plastic strain.     

Engineering Mixed Ionic Electronic Conduction in La0.8Sr0.2MnO3+δ Nanostructures through Fast Grain Boundary Oxygen Diffusivity

Nanoionics has become an increasingly promising field for the future development of advanced energy conversion and storage devices, such as batteries, fuel cells, and supercapacitors. Particularly, nanostructured materials offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. However, the enhancement of the mass transport properties at the nanoscale has often been found to be difficult to implement in nanostructures. Here, an artificial mixed ionic electronic conducting oxide is fabricated by grain boundary (GB) engineering thin films of La_0.8Sr_0.2MnO_3+δ. This electronic conductor is converted into a good mixed ionic electronic conductor by synthesizing a nanostructure with high density of vertically aligned GBs with high concentration of strain‐induced defects. Since this type of GBs present a remarkable enhancement of their oxide‐ion mass transport properties (of up to six orders of magnitude at 773 K), it is possible to tailor the electrical nature of the whole material by nanoengineering, especially at low temperatures. The presented results lead to fundamental insights into oxygen diffusion along GBs and to the application of these engineered nanomaterials in new advanced solid state ionics devices such are micro‐solid oxide fuel cells or resistive switching memories.     

Solvation-Driven Grain Boundary Passivation Improving the Performance of Perovskite Solar Cells

The efficiency of perovskite solar cells (PSCs) is hindered by substantial defects within the grain boundaries (GBs) of polycrystalline perovskite films. Conventional post-treatment strategies struggle to precisely repair these defects at GBs. Here, a targeted grain boundary passivation strategy through solvent effects by incorporating symmetrical biphenyl molecules is proposed, 4,4′-diaminodiphenyl sulfone (DDS) and 4,4′-sulfodiphenol (SDP), aiming to mitigate defects at GBs and optimize energy level arrangements through their electric dipole effects. Compared to the pristine device, the SDP-modified device exhibits significant improvements, including a champion efficiency of 24.39% and an impressive fill factor, along with excellent operation stability. This work provides an effective and straightforward solution for improving the performance of PSCs.     

Properties of Polycrystalline Diamond: Multiscale Modeling Approach

Abstract

Two modeling techniques to characterize fracture behavior of polycrystalline diamond films are discussed. The first technique is a multiscale modeling method in which first-principles local density approximation calculations on selected structures are combined with an analytic mesoscale model to obtain energies and cleavage fracture energies for symmetric ?001? tilt grain boundaries (GBs) over the entire misorientation range. The second technique is large-scale atomistic simulation of the dynamics of failure in notched polycrystalline diamond samples under an applied strain. Electronic characteristics of selected ?001? symmetrical tilt GBs calculated with a semiempirical tight-binding Hamiltonian are also presented, and the possible role of graphitic defects on field emission from polycrystalline diamond is briefly discussed.     

Delimiting the geographical background in species distribution modelling

Aim The extent of the study area (geographical background, GB) can strongly affect the results of species distribution models (SDMs), but as yet we lack objective and practicable criteria for delimiting the appropriate GB. We propose an approach to this problem using trend surface analysis (TSA) and provide an assessment of the effects of varying GB extent on the performance of SDMs for four species. Location Mainland Spain. Methods Using data for four well known wild ungulate species and different GBs delimited with a TSA, we assessed the effects of GB extent on the predictive performance of SDMs: specifically on model calibration (Miller’s statistic) and discrimination (area under the curve of the receiver operating characteristic plot, AUC; sensitivity and specificity), and on the tendency of the models to predict environmental potential when they are projected beyond their training area. Results In the training area, discrimination significantly increased and calibration decreased as the GB was enlarged. In contrast, as GB was enlarged, both discriminatory power and calibration decreased when assessed in the core area of the species distributions. When models trained using small GBs were projected beyond their training area, they showed a tendency to predict higher environmental potential for the species than those models trained using large GBs. Main conclusions By restricting GB extent using a geographical criterion, model performance in the core area of the species distribution can be significantly improved. Large GBs make models demonstrate high discriminatory power but are barely informative. By delimiting GB using a geographical criterion, the effect of historical events on model parameterization may be reduced. Thus purely environmental models are obtained that, when projected onto a new scenario, depict the potential distribution of the species. We therefore recommend the use of TSA in geographically delimiting the GB for use in SDMs.     

Embryonic expression of a decapentaplegic gene in the oligochaete annelid Tubifex tubifex

We have cloned and characterized the expression of a decapentaplegic homologue (designated Ttu-dpp) from the oligochaete annelid Tubifex tubifex. RT-PCR analysis and in situ hybridization revealed that Ttu-dpp begins to be expressed around the time of the onset of ectodermal germ band (GB) elongation (i.e., the onset of gastrulation). At this time, Ttu-dpp expression is detected in the anteriormost part of the GBs. As development proceeds and the GBs elongate, the domain of Ttu-dpp-expressing cells extends posteriorly. Then Ttu-dpp-expressing cells within the GB are divided into two groups: one group occurs along the ventral midline and coincides with the domain of ventral ganglia; the other is located more dorsally. The latter group of Ttu-dpp-expressing cells subsequently undergoes dorsalward expansion, which results in the formation of a lateral stripe of cells in every segment except the first (i.e., segment I). In embryos that undergo body elongation (that is one of the last morphogenetic movements occurring prior to hatchout), Ttu-dpp expression in the lateral region is confined to setal sacs, which are arranged in the same transverse plane around the periphery of each segment (except segment I).     

Grain size effect on the plastic deformation of nanocrystalline silver

The plastic deformation of nanocrystalline Ag, with columnar grains, has been studied by molecular dynamics simulations. The nanocrystalline systems show two types of deformation mechanisms. One is the split of grain boundary that occurs before the activation of the dislocation in nanocrystalline Ag, and almost no dislocation debris and twins are left in the grains. Moreover, split of grain boundary is shown between the grains of nanocrystalline Ag. Another mechanism consists in partial dislocations dominating the process of plastic deformation. Plenty of stacking faults and twins remain in the grains of nanocrystalline Ag. It is revealed that different grain aspect ratios have induced the difference in deformation mechanisms of nanocrystalline Ag. When the grain aspect ratio is less than or equal to 1, the process of plastic deformation is dominated by partial dislocations. Otherwise, the process is dominated by split of grain boundary. The grain aspect ratio is the height in z direction to length in x direction ratio, which was found to noticeably impact yield strength, grain coarsening, indicating that the observed behaviour should have contributed to the plastic deformation significantly.     

Engineering Grain Boundaries in Cu2ZnSnSe4 for Better Cell Performance: A First‐Principle Study

Through first‐principle density functional theory (DFT) calculations, the atomic structure and electronic properties of intrinsic and passivated Σ3 (114) grain boundaries (GBs) in Cu₂ZnSnSe₄ (CZTSe) are studied. Intrinsic GBs in CZTSe create localized deep states within the band gap and thus act as Shockley‐Read‐Hall recombination centers, which are detrimental to cell performance. Defects, such as Zn_Sn (Zn atoms on Sn sites), Na⁺_i (interstitial Na ions), and O_Se (O atoms on Se sites), prefer to segregate into GBs in CZTSe. The segregation of these defects at GBs exhibit two beneficial effects: 1) eliminating the deep gap states via wrong bonds breaking or weakening at GBs, making GBs electrically benign; and 2) creating hole barriers and electron sinkers, promoting effective charge separation at GBs. The results suggest a unique chemical approach for engineering GBs in CZTSe to achieve improved cell performance.     

Impaired cytoprotective function of muscle in human gallbladders with cholesterol stones

Acute cholecystitis develops in gallbladders (GB) with excessive bile cholesterol (Ch). Increased membrane Ch content affects membrane function and may affect PGE(2) receptors involved in the cytoprotection against acute inflammation. This study was aimed at determining whether the cytoprotective response to PGE(2) is affected by lithogenic bile with Ch. Muscle cells from human GB with cholesterol stones (ChS) or pigment stones (PS) were obtained by enzymatic digestion. PGE(2) levels were measured by radioimmunoassay, and activities of superoxide dismutase (SOD) and catalase were assayed by spectrophotometry. The contraction in response to H(2)O(2) in muscle cells from PS was 14 +/- 0.3%, not different from normal controls, and decreased after the cells were incubated with Ch-rich liposomes (P < 0.05), which increase the Ch content in the plasma membranes. In muscle cells from GB with ChS, H(2)O(2)-induced contraction was only 9.2 +/- 1.3% and increased to 14 +/- 0.2% after Ch-free liposome treatment to remove Ch from the plasma membranes (P < 0.01). H(2)O(2) caused a similar increase in the levels of lipid peroxidation and PGE(2) content in muscle cells from GBs with ChS and PS. However, the activities of SOD and catalase were significantly lower in muscle cells from GBs with ChS compared with those with PS. The binding capacity of PGE(2) receptors was also significantly lower in muscle cells from GBs with ChS compared with those with PS. In conclusion, the cytoprotective response to reactive oxygen species is reduced in muscle cells from GBs with ChS despite a normal increase in the cellular levels of PGE(2). This impaired cytoprotective response may be due to a dysfunction of PGE(2) receptors with decreased binding capacity resulting from excessive Ch levels in the plasma membrane.     

Contribution of vertebral [corrected] bodies, endplates, and intervertebral discs to the compression creep of spinal motion segments

Spinal segments show non-linear behavior under axial compression. It is unclear to what extent this behavior is attributable to the different components of the segment. In this study, we quantified the separate contributions of vertebral bodies and intervertebral discs to creep of a segment. Secondly, we investigated the contribution of bone and osteochondral endplate (endplates including cartilage) to the deformation of the vertebral body. From eight porcine spines a motion segment, a disc and a vertebral body were dissected and subjected to mechanical testing. In an additional test, cylindrical samples, machined from the lowest thoracic vertebrae of 11 porcine spines, were used to compare the deformation of vertebral bone and endplate. All specimens were subjected to three loading cycles, each comprising a loading phase (2.0 MPa, 15 min) and a recovery phase (0.001 MPa, 30 min). All specimens displayed substantial time-dependent height changes. Average creep was the largest in motion segments and smallest in vertebral bodies. Bone samples with endplates displayed substantially more creep than samples without. In the early phase, behavior of the vertebra was similar to that of the disc. Visco-elastic deformation of the endplate therefore appeared dominant. In the late creep phase, behavior of the segment was similar to that of isolated discs, suggesting that in this phase the disc dominated creep behavior, possibly by fluid flow from the nucleus. We conclude that creep deformation of vertebral bodies contributes substantially to creep of motion segments and that within a vertebral body endplates play a major role.     

The effect of temperature shock and grain morphology on alpha-amylase in developing wheat grain

Background and Aims

The premature production of alpha-amylase without visible germination has been observed in developing grain of many cereals. The phenomenon is associated with cool temperatures in the late stages of grain growth but the mechanisms behind it are largely unknown. The aim of this study was to replicate the phenomenon under controlled conditions and investigate the possibility of a mechanistic link with grain size or endosperm cavity size.

Methods

Five wheat (Triticum aestivum) genotypes differing in their susceptibility to premature alpha-amylase were subjected to a range of temperature shocks in controlled environments. A comparison was then made with plants grown under ambient conditions but with grain size altered by using degraining to increase the assimilate supply. At maturity, alpha-amylase, grain area and endosperm cavity area were measured in individual grains.

Key Results

Both cold and heat shocks were successful in inducing premature alpha-amylase in susceptible genotypes, with cold shocks the most effective. Cold shocks also increased grain area. Degraining resulted in increased grain area overall, but the larger grain did not have higher alpha-amylase. Analysis of individual grain found that instances of high alpha-amylase were not associated with differences in grain area or endosperm cavity area.

Conclusions

Pre-maturity alpha-amylase is associated with temperature shocks during grain filling. In some cases this coincides with an increase in grain area, but there is no evidence of a mechanistic link between high alpha-amylase and grain or endosperm cavity area.Key words: Alpha-amylase, pre-maturity alpha-amylase, late maturity alpha amylase, temperature, grain size, endosperm cavity, wheat, Triticum aestivum     

Tailoring Impurity Distribution in Polycrystalline CdTe Solar Cells for Enhanced Minority Carrier Lifetime

Passivation of grain boundaries (GBs) and interfaces to suppress recombination and to improve minority carrier lifetime (MCLT) is essential for the functionality of devices based on polycrystalline materials. Improvement of MCLT is believed to be a very promising way to bring CdTe solar cells to the next efficiency level. However, which parameters significantly affect MCLT is not well understood. Here, high‐efficiency CdTe solar cells in an unconventional inverted structure are used to approach this issue. Advanced characterization tools such as secondary ion mass spectroscopy 3D chemical imaging, atom probe tomography, and X‐ray photoelectron spectroscopy are used to detect small amounts of impurities at GBs and are synergetically used together with time resolved photoluminescence measurements to correlate impurity distribution with electronic properties in CdTe solar cells. MCLT increases by an order of magnitude upon sulfur diffusion along GBs of the CdTe layer, which can occur by an elemental exchange with oxygen. Chlorine segregates at GBs and at the CdS/CdTe interface and bonding to cadmium and tellurium is indicated. CdTe solar cells in the inverted structure are presented with a certified efficiency of 13.5%. The results give guidance to further improve the performance of CdTe solar cells.     

Multidentate Coordination Induced Crystal Growth Regulation and Trap Passivation Enables over 24% Efficiency in Perovskite Solar Cells

Crystal growth regulation has become an effective solution to reduce the defects at grain boundaries (GBs) and surfaces of perovskite films for better photovoltaic performances. Oxime acid materials are maturely used as selective collectors in the flotation separation of oxide minerals. Such materials, showing a strong coordination effect and high selectivity with lead, may have great potential in controlling the crystal growth and passivating the defect of perovskite film, which are rarely applied in perovskite solar cells (PerSCs). Herein, an oxime acid-based material with multi-coordination sites, ethyl 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetate (EHA), is incorporated into the PbI₂ precursor solution to fabricate high-performance PerSCs using a two-step method. The multidentate coordination effect of EHA can link and integrate the PbI₂ colloidal clusters to achieve pre-aggregation in the PbI₂ precursor solution, facilitating the sequent crystal growth progress of perovskite film. Meanwhile, EHA can connect grains and fill GBs, which is favorable for charge transfer and passivating both Pb-I anti-site and iodine vacancy defects. As a result, the optimal devices show an enhanced efficiency of 24.1% and excellent humidity and thermal stability. This work affords a promising strategy to fabricate efficient and stable PerSCs via multidentate coordination-induced crystallization control and GB passivation.     

Deformation mechanisms in nanotwinned γ-TiAl by molecular dynamics simulation

ABSTRACT

In this work, the plastic deformation mechanisms and fracture toughness of nanotwinned γ-TiAl with different twin boundary (TB) spacing are investigated by using molecular dynamics simulation. The simulation results reveal that there are pronounced shifts in the mechanical behaviour of nanotwinned γ-TiAl when the TB spacing is 3.50, 4.20 and 4.90?nm. In addition, the variation of the dislocation density with strain at these three TB spacing illustrates that a smaller TB spacing induces a higher dislocation density. Different TB spacing has an influence on the dislocation behaviour. The dislocation pile-up, dislocation–dislocation, dislocation–twin and twin–twin reactions, hierarchical twins including their generation and density, step formation, dislocation emission from steps and TB migration are the main plastic deformation mechanisms. The results also show that TB migration, twinning formation and interaction of crack and TB dominate the deformation mechanism of nanotwinned γ-TiAl with crack. The generation of hierarchical twins, lower distance between crack surface plane and twin plane, dislocation–twin, twin–twin interaction and crack deflection increase the fracture toughness of nanotwinned γ-TiAl.     

The diversity of woodland vegetation in Central Albania along an altitudinal gradient of 1300 m

Abstract

The woodland vegetation of Central Albania is studied and discussed along an altitudinal gradient in the Dajti National Park (DNP). The plant species combinations recorded in 168 plots were classified and subjected to indirect gradient analysis using environmental variables of geology, soil, topography, disturbance and grazing impact. The transect over more than 1300 m reflects the biogeographically intermediate paramediterranean vegetation zonation and the relatively humid Mediterranean “hygric series” at its eastern margins. It reveals the total range of woodland types known to occur in Central Albania, thus stressing the representativity of the area regarding biodiversity and biogeography, and its importance for nature conservation. Along the elevation gradient, we found three plant communities of the mesomediterranean Quercetalia ilicis, five of the supramediterranean Quercetalia pubescentis and five of the montane or oromediterranean Fagetalia sylvaticae.     

Chemical composition, particle form and annealing temperature of amalgam alloy versus creep of the resulting amalgam

The influence of the chemical composition, particle form and annealing temperature of the amalgam alloy upon the creep of the resulting amalgam was investigated by means of a multiple regression model. Because no, or only little, information was available about the heat treatments of the different commercial alloys, the alloys were subjected to additional heat treatments at four different temperatures. The influence upon the creep of the amalgam of the Zn content, particle form and annealing temperature was found to be very significant. A higher Zn content as well as a spherical alloy resulted in less creep of the corresponding amalgam. The dependence of the creep upon the annealing temperature showed a minimum: more creep was obtained for amalgams prepared from the alloys heat treated at 150 degrees C and 435 degrees C than those from the alloys annealed at 315 degrees C and 319 degrees C, respectively.