Plastic Deformation and Annealing of Zr- and Cu- Based Bulk Metallic Glasses

Plastic deformation in crystalline metals occurs by the motion and multiplication of lattice defects called dislocations, resulting in strain hardening. Metallic glasses, in contrast, lack long-range order; therefore, dislocation-mediated plasticity is not possible in these materials. Metallic glasses undergo plastic deformation through the nucleation and propagation of defects called shear bands, which cause strain softening. This strain softening can be recovered after annealing, i.e., annealing makes the plastically strained metallic glasses harder, in sharp contrast to the annealing-induced softening typically observed in crystalline metals. During annealing, hardness initially recovers more rapidly in heavily deformed specimens than in lightly deformed ones, at a rate that varies inversely as the shear band spacing. With increasing annealing time and temperature, hardness further increases, at the same rate whether pre-strained or not. If the deformed and annealed metallic glass is plastically deformed again, reversible softening is observed. To our knowledge, this is the first time that such reversible softening in metallic glasses has been reported. These hardness changes were correlated with shear band patterns around/underneath a Vickers indent. Shear bands produced during indentation of as-cast glass were semi-circular and radial, consistent with the maximum stress distribution beneath the indenter. In contrast, shear bands in the pre-strained glass were irregular and convoluted, and appeared to be a mixture of shear bands produced during the preceding compression and those in as-cast glass. This indicates that shear band regions are softer than the surrounding undeformed matrix and act as preferred sites for subsequent deformation during indentation, consistent with the macroscopic strain softening vi observed after plastic deformation. After annealing, shear bands tend to recover the originally semi-circular and radial shapes associated with the hardness increase

Biofouling characteristics in Xinghua Bay of Fujian, China

Biofouling is one of the main factors affecting the efficiency and safety of cooling water systems in coastal nuclear power plants. Understanding the population dynamics, succession rules and cumulative effects of major fouling organisms is the basis for targeted prevention and control. A 1-year simulated concrete panel test was conducted from December 2020 to November 2021 in Xinghua Bay, China. A total of 78 species of fouling organisms were recorded by combining the monthly, seasonal, semiannual, annual and monthly cumulative panels, and the community composition was dominated by nearshore warm-water species, making for a typical subtropical inner bay-type community. The fouling organisms had a peak attachment period from June to October. Significantly more attachment was observed during summer (from June to August) than during the other three seasons. The attachment amount in the second half-year (from June to November) was much higher than that in the first half-year (from December to May). The attachment thickness, density, and biomass of the bottom summer panels reached 20 cm, 105,150 ind./m2, and 19,274.50 g/m2, respectively, while those of the bottom annual panels were 40 cm, 27,300 ind./m2, and 17,762.50 g/m2, respectively. The dominant fouling organisms with calcified shells mainly included Amphibalanus reticulatus and Pernaviridis. These species had high attachment amounts,could accumulate attachments for a long time, and even might cause secondary blockage, making them the most detrimental to the safety of a cooling system. Moreover,the seasonal upward growth of hydroids and bryozoans can also significantly reduce the efficiency of cooling water intake. We suggest that targeted prevention and control should be carried out according to the larval attachment period of different dominant groups of fouling organisms during June-October, which can greatly improve the prevention and control efficiency. Strengthening the research on the biological cycle phenomenon of the main species and their main environmental impact factors, and establishing a scientific and effective early-warning model are the governance direction of formulating and implementing scientific pollution prevention and control in the future

Discovery of a nanodiamond-rich layer in the Greenland ice sheet

We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5!106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 0.1 ka. However, more investigation is needed to confirm this association

The effects of cadmium on germination and seedling growth of Suaeda salsa

Cadmium ion (Cd2+) is a ubiquitous toxic heavy metal in the environment and presents a potential threat to human health via the food chain through plant root uptake systems. The halophyte, Suaeda salsa is the pioneer plant in the Yellow River Delta and has been widely applied as a model plant in environmental pollution assessment. In this work, the study was conducted using a liquid culture with a series of Cd2+ concentrations. Germination rates and activities of three enzymes (catalase (CAT), glutathione peroxidase (GPX), glutathione S-transferase (GST)) in the seedling were investigated. Results showed that the germination indices and growth inhibition indices of S. salsa decreased significantly (p<0.05) at the concentration of 0.1mg/L CdCl2, and the inhibition effect was increased with the increasing concentration of Cd2+. GPX and GST changed similarly, which reached the maximum when Cd2+ was 0.1mg/L, then it declined sharply with the increasing concentration of Cd2+. However, for CAT, the reverse trend was observed. Overall, these results indicated that all the bio-indicators mentioned above for S. salsa were quite sensitive to Cd2+. It could be applied to monitor Cd2+ pollution in Yellow River Delta. (C) 2012 Selection and/or peer-review under responsibility of Basel Convention Coordinating Centre for Asia and the Pacific and National Center of Solid Waste Management, Ministry of Environmental Protection of China

Interdiffusion at the BaCuSeF/ZnTe interface

BaCuSeF/ZnTe is a model system to investigate physical and chemical properties of the interfaces of non-oxide wide-bandgap p-type semiconductors with materials used in chalcogenide solar cells. The BaCuSeF/ZnTe interface was studied using electron microscopy and photoelectron spectroscopy. Both techniques indicate that Se and Cu from BaCuSeF diffuse into ZnTe creating an interdiffused layer between these two materials. The interdiffusion may be attributed to the differences in materials formation enthalpies and to Fermi level pinning in BaCuSeF

Electron Tomography of Au-Catalyzed Semiconductor Nanowires

Electron tomography based on Z-contrast scanning transmission electron microscopy (STEM) can be applied to study 3D morphology of nanomaterials at high resolution, that is, 1 nm in all three spatial dimensions, to provide comprehensive insights into the structure of nanomaterials and their interfaces. Here, we report the 3D characterization of Au-catalyzed Ge and Si nanowires using a full-space tilting holder to address the “missing wedge” problem in STEM electron tomography. Electron tomography specimens were prepared by a novel two-step sample preparation process to minimize surface damage induced by focused ion beam (FIB) milling. The quality of specimen preparation protocol is demonstrated by the clear visibility of {112} facets in the reconstructed volume, and 3D morphology of Au nanoparticles on the nanowire surface. The 3D distribution of the Au nanoparticles on the coated Ge nanowires is also established. The integrated combination of innovative specimen preparation and full-tilt tomography represents a useful advance in the 3D analysis of nanostructures

Electron Tomography of Au-Catalyzed Semiconductor Nanowires

Electron tomography based on Z-contrast scanning transmission electron microscopy (STEM) can be applied to study 3D morphology of nanomaterials at high resolution, that is, 1 nm in all three spatial dimensions, to provide comprehensive insights into the structure of nanomaterials and their interfaces. Here, we report the 3D characterization of Au-catalyzed Ge and Si nanowires using a full-space tilting holder to address the “missing wedge” problem in STEM electron tomography. Electron tomography specimens were prepared by a novel two-step sample preparation process to minimize surface damage induced by focused ion beam (FIB) milling. The quality of specimen preparation protocol is demonstrated by the clear visibility of {112} facets in the reconstructed volume, and 3D morphology of Au nanoparticles on the nanowire surface. The 3D distribution of the Au nanoparticles on the coated Ge nanowires is also established. The integrated combination of innovative specimen preparation and full-tilt tomography represents a useful advance in the 3D analysis of nanostructures

Brunfelsia americana

Electron tomography based on Z-contrast scanning transmission electron microscopy (STEM) can be applied to study 3D morphology of nanomaterials at high resolution, that is, 1 nm in all three spatial dimensions, to provide comprehensive insights into the structure of nanomaterials and their interfaces. Here, we report the 3D characterization of Au-catalyzed Ge and Si nanowires using a full-space tilting holder to address the “missing wedge” problem in STEM electron tomography. Electron tomography specimens were prepared by a novel two-step sample preparation process to minimize surface damage induced by focused ion beam (FIB) milling. The quality of specimen preparation protocol is demonstrated by the clear visibility of {112} facets in the reconstructed volume, and 3D morphology of Au nanoparticles on the nanowire surface. The 3D distribution of the Au nanoparticles on the coated Ge nanowires is also established. The integrated combination of innovative specimen preparation and full-tilt tomography represents a useful advance in the 3D analysis of nanostructures