261 research outputs found
Evolution of Glassy Carbon Microstructure: In Situ Transmission Electron Microscopy of the Pyrolysis Process
Glassy carbon is a graphene-rich form of elemental carbon obtained from
pyrolysis of polymers, which is composed of three-dimensionally arranged,
curved graphene fragments alongside fractions of disordered carbon and voids.
Pyrolysis encompasses gradual heating of polymers above 900 degree C under
inert atmosphere, followed by cooling to room temperature. Here we report on an
experimental method to perform in situ high-resolution transmission electron
microscopy (HR-TEM) for the direct visualization of microstructural evolution
in a pyrolyzing polymer in the 500-1200 degree C temperature range. The results
are compared with the existing microstructural models of glassy carbon.
Reported experiments are performed at 80 kV acceleration voltage using
MEMS-based heating chips as sample substrates to minimize any undesired
beam-damage or sample preparation induced transformations. The outcome suggests
that the geometry, expansion and atomic arrangement within the resulting
graphene fragments constantly change, and that the intermediate structures
provide important cues on the evolution of glassy carbon. A complete
understanding of the pyrolysis process will allow for a general process tuning
specific to the precursor polymer for obtaining glassy carbon with pre-defined
properties.Comment: Revised version due to minor corrections in the text and addition of
an autho
Elucidating the structural composition of a Fe-N-C catalyst by nuclear and electron resonance techniques
FeāNāC catalysts are very promising materials for fuel cells and metalāair batteries. This work gives fundamental insights into the structural composition of an FeāNāC catalyst and highlights the importance of an inādepth characterization. By nuclearā and electronāresonance techniques, we are able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of Ī±āiron and, surprisingly, iron oxide. Our work makes it questionable to what extent FeN4 sites can be present in FeāNāC catalysts prepared by pyrolysis at 900āĀ°C and above. The simulation of the iron partial density of phonon states enables the identification of three FeN4 species in our catalyst, one of them comprising a sixfold coordination with endāon bonded oxygen as one of the axial ligands
Graphitizability of Polymer Thin Films: An In Situ TEM Study of Thickness Effects on Nanocrystalline Graphene/Glassy Carbon Formation
Polymer pyrolysis has emerged as a versatile method to synthesize graphenoid (graphene like) materials with varying thickness and properties. The morphology of the thin film, especially the thickness, greatly affects the graphitizability and the properties of the graphenoid material. Using in situ current annealing inside a transmission electron microscope (TEM), the thickness-dependent structural evolution of the polymer film with a special focus on thickness effects is followed. At high temperatures, thin samples form large graphene layers oriented parallel to the substrate, whereas in thick samples multi-walled cage-like structures are formed. Moleclar Dynamics (MD) simulations reveal a film thickness of 40 Ć
below which, the carbonized layers align parallel to the surface. For thicker samples, the orientation of the layers becomes increasingly misoriented starting from the surface to the center. This structural change can be attributed to the formation of bonded multi-layers from the initially unsaturated activated edges. The resulting cage-like structures are stable even during simulated annealing at temperatures as high as 3500 K. An atomistic understanding of the formation of these structures is presented. The results clearly indicate the critical effect of thickness on the graphitizability of polymers and provide a new understanding of the structural evolution during pyrolysis
MOSAIC: Multi-Object Segmented Arbitrary Stylization Using CLIP
Style transfer driven by text prompts paved a new path for creatively
stylizing the images without collecting an actual style image. Despite having
promising results, with text-driven stylization, the user has no control over
the stylization. If a user wants to create an artistic image, the user requires
fine control over the stylization of various entities individually in the
content image, which is not addressed by the current state-of-the-art
approaches. On the other hand, diffusion style transfer methods also suffer
from the same issue because the regional stylization control over the stylized
output is ineffective. To address this problem, We propose a new method
Multi-Object Segmented Arbitrary Stylization Using CLIP (MOSAIC), that can
apply styles to different objects in the image based on the context extracted
from the input prompt. Text-based segmentation and stylization modules which
are based on vision transformer architecture, were used to segment and stylize
the objects. Our method can extend to any arbitrary objects, styles and produce
high-quality images compared to the current state of art methods. To our
knowledge, this is the first attempt to perform text-guided arbitrary
object-wise stylization. We demonstrate the effectiveness of our approach
through qualitative and quantitative analysis, showing that it can generate
visually appealing stylized images with enhanced control over stylization and
the ability to generalize to unseen object classes.Comment: Camera ready, New Ideas in Vision Transformers workshop, ICCV 202
Understanding the graphitization and growth of free-standing nanocrystalline graphene using: In situ transmission electron microscopy
Dry adhesives from carbon nanofibers grown in an open ethanol flame
Based on magnetic-field-assisted growth of carbon nanofibers in an open ethanol flame we fabricated arrays of carbon nanofibers with different degrees of orientation. Inspired by the dry adhesive system of geckos we investigated the adhesive properties of such carbon nanofiber arrays with ordered and random orientation. AFM-based force spectroscopy revealed that adhesion force and energy rise linear with preload force. Carbon nanofibers oriented by a magnetic field show a 68% higher adhesion (0.66 N/cm2) than the randomly oriented fibers. Endurance tests revealed that the carbon nanofiber arrays withstand 50.000 attachment/detachment cycles without observable wear
Metadata schema to support FAIR data in scanning electron microscopy
The development and the adoption of metadata schemas and standards are a key aspect in data management. In this paper, we introduce our approach to a metadata model in the field of Materials Science. We present the specific use case of a metadata schema for Scanning Electron Microscopy, a characterization technique which is routinely used in Materials Science. This metadata schema is aiming to be a de-facto standard which will be openly available for reuse and further extension to other electron microscopy techniques
Polyaramid-Based Flexible Antibacterial Coatings Fabricated Using Laser-Induced Carbonization and Copper Electroplating
Interferon-Gamma Release Assay (Modified QuantiFERON) as a Potential Marker of Infection for Leishmania donovani, a Proof of Concept Study
Visceral leishmaniasis is caused by a parasite of the Leishmania species, but infection does not always lead to overt clinical disease. To detect infection, the Montenegro test or Leishmanin Skin Test (LST) is used along with serological markers. The LST is a test of the delayed-type hypersensitivity response read 48ā72 hours after intradermal injection of leishmanin antigen. LST has many drawbacks, as complex administration and reading, boosting of anamnestic immune responses and difficult sourcing of GMP-compliant product and alternative tools for epidemiological research are badly needed. We evaluated whether a Interferon-Ī³ Release Assay based on the QuantiFERON-TB test format, which was approved by the Food and Drug Administration (FDA) as a test for detecting latent Mycobacterium tuberculosis infection, could become an in vitro diagnostic aid for the measurement of cell-mediated immune reactivity against L.donovani. We obtained good results with one of five of the antigens we evaluated and confirm the potential of this assay
Development and Diffusion of Sorghum Improved Cultivars In India: Impact on Growth and Stability in Yield
Sorghum [Sorghum bicolor (L.) Moench] is one of the major staple foods for the poorest and most food-insecure people across the semi-arid tropics of the world. Sorghum bicolor ssp. Verticilliflorum is believed to be the progenitor of cultivated sorghum (Harlan, 1972). It is cultivated in wide geographic areas in Africa, Asia, Americas and the Pacific regions. While it is the fifth most important cereal crop in the world after wheat, maize, rice and barley, in India, sorghum is the fourth largest cereal crop after rice, wheat and pearl millet and the second major food crop in Africa after maize. Sorghum is often a recommended option for farmers operating in harsh environments where other crops do poorly, as it can be grown with limited rainfall (400-500 mm) and often without or with limited application of fertilizers and other inputs. In India, sorghum is grown in both rainy (2.6 million ha) and postrainy (3.5 million ha) seasons. An estimated 2 million ha is under forage sorghum, grown in the summer season. Nearly 30-40% of the rainy season sorghum is grown as the sole crop while the rest is cultivated as an intercrop with pulses and oilseeds in India. On the other hand, 90% of postrainy season sorghum is grown as a sole crop, which is most preferred for food purposes
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