scholarly journals Totally Ecofriendly Synthesis of Silver Nanoparticles from Aqueous Dissolutions of Polysaccharides

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
M. A. Garza-Navarro ◽  
J. A. Aguirre-Rosales ◽  
E. E. Llanas-Vázquez ◽  
I. E. Moreno-Cortez ◽  
A. Torres-Castro ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Experimental Evidence ◽  
Weight Ratio ◽  
Spectroscopic Techniques ◽  
Contrast Imaging ◽  
Synthesis Mechanism ◽  
Synthesis Of Nanoparticles ◽  
Means Of Transmission ◽  
Experimental Findings ◽  
Z Contrast

In this contribution, a totally ecofriendly synthesis of silver nanoparticles from aqueous dissolution of polysaccharides is reported. The synthesis of nanoparticles was performed using aqueous dissolutions of silver nitrate (AgNO3) and carboxymethyl-cellulose (CMC) as both reducing and stabilization agent and using different AgNO3 : CMC weight ratios. Resultant yellowish to reddish dispersions were characterized by means of transmission electron microscopy and their related techniques, such as bright field and Z-contrast imaging and electron diffraction, as well as ultraviolet-visible and infrared spectroscopic techniques. The experimental evidence suggests that the morphology and particle size distribution of the silver nanoparticles depend on the AgNO3 : CMC weight ratio. This feature seems to be related to the stabilization given by the CMC matrix, which, according to our experimental findings, is steric in nature. Regarding such experimental evidence, a synthesis mechanism in which CMC acts as stabilizer and reducing agent is proposed.

Complementary Z-Contrast Imaging and Digital Image Processing

1985 ◽  
Vol 43 ◽  
pp. 304-305
Author(s):  
K. N. Colonna ◽  
G. Oliphant
Keyword(s):  
Image Processing ◽  
Heavy Metal ◽  
Digital Image Processing ◽  
Digital Image ◽  
Biological Tissue ◽  
Biological Imaging ◽  
Tissue Preparation ◽  
Contrast Imaging ◽  
Imaging Tool ◽  
Z Contrast

Harmonious use of Z-contrast imaging and digital image processing as an analytical imaging tool was developed and demonstrated in studying the elemental constitution of human and maturing rabbit spermatozoa. Due to its analog origin (Fig. 1), the Z-contrast image offers information unique to the science of biological imaging. Despite the information and distinct advantages it offers, the potential of Z-contrast imaging is extremely limited without the application of techniques of digital image processing. For the first time in biological imaging, this study demonstrates the tremendous potential involved in the complementary use of Z-contrast imaging and digital image processing.Imaging in the Z-contrast mode is powerful for three distinct reasons, the first of which involves tissue preparation. It affords biologists the opportunity to visualize biological tissue without the use of heavy metal fixatives and stains. For years biologists have used heavy metal components to compensate for the limited electron scattering properties of biological tissue.

Atomic resolution Z-contrast imaging of bulk crystal surfaces in Scanning Reflection Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 414-415
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Elastic Scattering ◽  
Dark Field ◽  
Contrast Imaging ◽  
Crystal Lattices ◽  
Small Probe ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Image Position ◽  
Z Contrast

The success of obtaining atomic-number-sensitive (Z-contrast) images in scanning transmission electron microscopy (STEM) has shown the feasibility of imaging composition changes at the atomic level. This type of image is formed by collecting the electrons scattered through large angles when a small probe scans across the specimen. The image contrast is determined by two scattering processes. One is the high angle elastic scattering from the nuclear sites,where ϕNe is the electron probe function centered at bp = (Xp, yp) after penetrating through the crystal; F denotes a Fourier transform operation; D is the detection function of the annular-dark-field (ADF) detector in reciprocal space u. The other process is thermal diffuse scattering (TDS), which is more important than the elastic contribution for specimens thicker than about 10 nm, and thus dominates the Z-contrast image. The TDS is an average “elastic” scattering of the electrons from crystal lattices of different thermal vibrational configurations,

High-resolution z-contrast imaging of semiconductor interfaces

1989 ◽  
Vol 47 ◽  
pp. 468-469
Author(s):  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Phase Contrast ◽  
Contrast Imaging ◽  
Compositional Modulation ◽  
Semiconductor Interfaces ◽  
Complex Figure ◽  
Thin Region ◽  
Stem Image ◽  
Annular Detector ◽  
Z Contrast

Using a high-angle annular detector on a high-resolution STEM it is possible to form incoherent images of a crystal lattice characterized by strong atomic number or Z contrast. Figure 1 shows an epitaxial Ge film on Si(100) grown by oxidation of Ge-implanted Si. The image was obtained using a VG Microscopes' HB501 STEM equipped with an ultrahigh resolution polepiece (Cs ∽1.2 mm, demonstrated probe FWHM intensity ∽0.22 nm). In both crystals the lattice is resolved but that of Ge shows much brighter allowing the interface to be located exactly and interface steps to be resolved (arrowed). The interface was indistinguishable in the phase-contrast STEM image from the same region, and even at higher resolution the location of the interface is complex. Figure 2 shows a thin region of an MBE-grown ultrathin super-lattice (Si8Ge2)100. The expected compositional modulation would show as one bright row of dots from the 2 Ge monolayers separated by 4 rows of lighter Si columns. The image shows clearly that strain-induced interdiffusion has occurred on the monolayer scale.

Quantitative structure determination of interfaces through Z-contrast imaging and electron energy loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 104-105
Author(s):  
S. J. Pennycook ◽  
P. D. Nellist ◽  
N. D. Browning ◽  
P. A. Langjahr ◽  
M. Rühle
Keyword(s):  
Grain Boundaries ◽  
Cuprate Superconductors ◽  
Structure Refinement ◽  
3D Structure ◽  
Real Space ◽  
Contrast Imaging ◽  
Coordination Polyhedra ◽  
Burgers Vector ◽  
Z Contrast ◽  
Contrast Image

The simultaneous use of Z-contrast imaging with parallel detection EELS in the STEM provides a powerful means for determining the atomic structure of grain boundaries. The incoherent Z-contrast image of the high atomic number columns can be directly inverted to their real space arrangement, without the use of preconceived structure models. Positions and intensities may be accurately quantified through a maximum entropy analysis. Light elements that are not visible in the Z-contrast image can be studied through EELS; their coordination polyhedra determined from the spectral fine structure. It even appears feasible to contemplate 3D structure refinement through multiple scattering calculations.The power of this approach is illustrated by the recent study of a series of SrTiC>3 bicrystals, which has provided significant insight into some of the basic issues of grain boundaries in ceramics. Figure 1 shows the structural units deduced from a set of 24°, 36° and 65° symmetric boundaries, and 24° and 45° asymmetric boundaries. It can be seen that apart from unit cells and fragments from the perfect crystal, only three units are needed to construct any arbitrary tilt boundary. For symmetric boundaries, only two units are required, each having the same Burgers, vector of a<100>. Both units are pentagons, on either the Sr or Ti sublattice, and both contain two columns of the other sublattice, imaging in positions too close for the atoms in each column to be coplanar. Each column was therefore assumed to be half full, with the pair forming a single zig-zag column. For asymmetric boundaries, crystal geometry requires two types of dislocations; the additional unit was found to have a Burgers’ vector of a<110>. Such a unit is a larger source of strain, and is especially important to the transport characteristics of cuprate superconductors. These zig-zag columns avoid the problem of like-ion repulsion; they have also been seen in TiO2 and YBa2Cu3O7-x and may be a general feature of ionic materials.

Green Synthesis of Silver Nanoparticles by Allamanda cathartica L. Leaf Extract and Evaluation for Antimicrobial Activity

2013 ◽  
Vol 6 (4) ◽  
pp. 2260-2268
Author(s):  
M. Linga Rao ◽  
Bhumi G ◽  
Savithramma N
Keyword(s):  
Antimicrobial Activity ◽  
Silver Nanoparticles ◽  
Leaf Extract ◽  
Fusarium Species ◽  
Inhibition Zone ◽  
Fungal Species ◽  
Green Technology ◽  
Metallic Silver ◽  
Synthesis Of Nanoparticles ◽  
Aqueous Leaf Extract

Silver nanoparticles (SNPs) exhibit tremendous applications in medicine as antimicrobial agent.  The use of different parts of plants for the synthesis of nanoparticles is considered as a green technology as it does not involve any harmful chemicals.  In the present study, we report a rapid biosynthesis of silver nanoparticles from aqueous leaf extract of medicinal plant Allamanda cathartica.  The active phytochemicals present in the plant were responsible for the quick reduction of silver ion to metallic silver nanoparticles. The reduced silver nanoparticles were characterized by using UV-Vis spectrophotometry, Scanning Electron Microscope (SEM), Energy Dispersive Analysis of X-ray (EDAX) and Atomic Force Microscopy (AFM).  The spherical shaped silver nanoparticles were observed and it was found to 19-40 nm range of size.  These phytosynthesized SNPs were tested for their antimicrobial activity and it analyzed by measuring the inhibitory zone. A. cathartica aqueous leaf extract of SNPs showed highest toxicity to Pseudomonas followed by Klebsiella, Bacillus and E. coli and lowest toxicity towards Proteus. In fungal species, highest inhibition zone was noted against Rhizopus followed by Curvularia, Aspergillus flavus and Aspergillus niger and minimum inhibition zone was observed against Fusarium species.  These results suggest a promising potential of Indian plant-based green chemistry for production of SNPs for biomedical and nanotechnology applications.

scholarly journals Nanoscale bubble domains with polar topologies in bulk ferroelectrics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jie Yin ◽  
Hongxiang Zong ◽  
Hong Tao ◽  
Xuefei Tao ◽  
Haijun Wu ◽  
...  
Keyword(s):  
Physical Properties ◽  
Bulk Material ◽  
Condensed Matter ◽  
Time Dependent ◽  
Morphology Evolution ◽  
Contrast Imaging ◽  
Ferroelectric Films ◽  
Modulated Phases ◽  
Ferroelectric Memories ◽  
Z Contrast

AbstractMultitudinous topological configurations spawn oases of many physical properties and phenomena in condensed-matter physics. Nano-sized ferroelectric bubble domains with various polar topologies (e.g., vortices, skyrmions) achieved in ferroelectric films present great potential for valuable physical properties. However, experimentally manipulating bubble domains has remained elusive especially in the bulk form. Here, in any bulk material, we achieve self-confined bubble domains with multiple polar topologies in bulk Bi0.5Na0.5TiO3 ferroelectrics, especially skyrmions, as validated by direct Z-contrast imaging. This phenomenon is driven by the interplay of bulk, elastic and electrostatic energies of coexisting modulated phases with strong and weak spontaneous polarizations. We demonstrate reversable and tip-voltage magnitude/time-dependent donut-like domain morphology evolution towards continuously and reversibly modulated high-density nonvolatile ferroelectric memories.

scholarly journals Biodirected Synthesis of Silver Nanoparticles Using Aqueous Honey Solutions and Evaluation of Their Antifungal Activity against Pathogenic Candida Spp.

2021 ◽  
Vol 22 (14) ◽  
pp. 7715
Author(s):  
Grzegorz Czernel ◽  
Dominika Bloch ◽  
Arkadiusz Matwijczuk ◽  
Jolanta Cieśla ◽  
Monika Kędzierska-Matysek ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Antifungal Activity ◽  
Fungal Pathogens ◽  
Fungal Growth ◽  
Disc Diffusion ◽  
Candida Spp ◽  
Antifungal Effect ◽  
Synthesis Of Nanoparticles ◽  
Honey Solution ◽  
Diffusion Assay

Silver nanoparticles (AgNPs) were synthesized using aqueous honey solutions with a concentration of 2%, 10%, and 20%—AgNPs-H2, AgNPs-H10, and AgNPs-H20. The reaction was conducted at 35 °C and 70 °C. Additionally, nanoparticles obtained with the citrate method (AgNPs-C), while amphotericin B (AmB) and fluconazole were used as controls. The presence and physicochemical properties of AgNPs was affirmed by analyzing the sample with ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, scanning electron microscopy (SEM), and dynamic light scattering (DLS). The 20% honey solution caused an inhibition of the synthesis of nanoparticles at 35 °C. The antifungal activity of the AgNPs was evaluated using opportunistic human fungal pathogens Candida albicans and Candida parapsilosis. The antifungal effect was determined by the minimum inhibitory concentration (MIC) and disc diffusion assay. The highest activity in the MIC tests was observed in the AgNPs-H2 variant. AgNPs-H10 and AgNPs-H20 showed no activity or even stimulated fungal growth. The results of the Kirby–Bauer disc diffusion susceptibility test for C. parapsilosis strains indicated stronger antifungal activity of AgNPs-H than fluconazole. The study demonstrated that the antifungal activity of AgNPs is closely related to the concentration of honey used for the synthesis thereof.

Altruistic Punishment: The Golden Keystone of Human Cooperation and Social Stability?

2020 ◽  
Vol 42 (2) ◽  
pp. 255-284
Author(s):  
Peter Lewisch
Keyword(s):  
Social Norms ◽  
Experimental Evidence ◽  
Social Order ◽  
Social Stability ◽  
Altruistic Punishment ◽  
Costly Punishment ◽  
Open Questions ◽  
Experimental Findings ◽  
Emotional Basis ◽  
Instrumental Goal

Abstract ‘Altruistic punishment’ (i.e., costly punishment that serves no instrumental goal for the punisher) could serve, as suggested by the pertinent experimental literature, as a powerful enforcer of social norms. This paper discusses foundations, extensions, and, in particular, limits and open questions of this concept-and it does so mostly based on experimental evidence provided by the author. Inter alia, the paper relates the (standard) literature on negative emotions as a trigger of second party punishment to more recent experimental findings on the phenomenon of ‘spontaneous cooperation’ and ‘spontaneous punishment’ and demonstrates its (tight) emotional basis. Furthermore, the paper discusses the potential for free riding on altruistic punishment. While providing valuable insights into the understanding of social order, ‘altruistic punishment’ is thus not the golden keystone of social stability.

Investigating Ca Segregated to a Grain Boundaries in MgO Using Multiple Scattering Analysis of Electron Energy Loss Spectra

1998 ◽  
Vol 4 (S2) ◽  
pp. 776-777
Author(s):  
J. P. Buban ◽  
J. Zaborac ◽  
H. Moltaji ◽  
G. Duscher ◽  
N. D. Browning
Keyword(s):  
Energy Loss ◽  
Grain Boundaries ◽  
Electron Energy ◽  
Structural Model ◽  
Boundary Structure ◽  
Structure Property ◽  
Contrast Imaging ◽  
Scale Properties ◽  
Z Contrast ◽  
Electron Energy Loss

Although grain boundaries typically account for only a small fraction of a material, they can have far reaching effects on the overall bulk scale properties. These effects are usually simply linked to the boundary having a different atomic arrangement to the bulk. A necessary first step in understanding the structure-property relationships is therefore a detailed determination of the boundary structure.One means of obtaining detailed information on the structure of grain boundaries is through correlated Z-contrast imaging and electron energy loss spectroscopy (EELS). The Z-contrast image generates a map of the grain boundary which can be used to position the probe in defined locations for spectroscopy. In the case of oxides, a structural model of the metal atom positions can be determined directly from the image. Furthermore, using a simple bond-valence sum minimization routine, the oxygen atoms can be placed so that the structure contains atoms that have valences consistent with their expected formal valence state.

Towards 3D image-based nanocrystallography by means of transmission electron goniometry

2004 ◽  
Vol 839 ◽  
Author(s):  
Peter Moeck ◽  
Wentao Qin ◽  
Philip B. Fraundorf
Keyword(s):  
Lattice Structure ◽  
Three Dimensions ◽  
Structural Defects ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Z Contrast ◽  
Individual Nanoparticles ◽  
Nanocrystal Model ◽  
The Ideal

ABSTRACTIt is well known that the crystallographic phase and morphology of many materials changes with the crystal size in the tens of nanometer range and that many nanocrystals possess structural defects in excess of their equilibrium levels. A need to determine the ideal and real structure of individual nanoparticles, therefore, arises. High-resolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM (STEM) when combined with transmission electron goniometry offer the opportunity of develop dedicated methods for the crystallographic characterization of nanoparticles in three dimensions. This paper describes tilt strategies for taking data from individual nanocrystals “as found”, so as to provide information on their lattice structure and orientation, as well as on the structure and orientation of their surfaces and structural defects. Internet based java applets that facilitate the application of this technique for cubic crystals with calibrated tilt-rotation and double-tilt holders are mentioned briefly. The enhanced viability of image-based nanocrystallography in future aberration-corrected TEMs and STEMs is illustrated on a nanocrystal model system.

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