Synthesis and Structural Characterization of Ferromagnetic Au/Co Nanoparticles

2014 ◽  
Vol 1708 ◽  
Author(s):  
Nabraj Bhattarai ◽  
Subarna Khanal ◽  
Daniel Bahena ◽  
Robert L. Whetten ◽  
Miguel Jose-Yacaman
Keyword(s):  
Quantum Interference ◽  
Magnetic Measurements ◽  
Ferromagnetic Behavior ◽  
Contrast Imaging ◽  
Uniform Size ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Co Nanoparticles ◽  
Z Contrast

ABSTRACTThe synthesis of bimetallic magnetic nanoparticles is very challenging because of the agglomeration and non-uniform size. In this paper, we present the synthesis of monodispersed 3-5 nm sized thiolated bimetallic alloyed Au/Co nanoparticles with decahedral and icosahedral shape, their characterization using Cs-corrected scanning transmission electron microscopy (STEM) and magnetic measurements using superconducting quantum interference device (SQUID) magnetometer. The Z-contrast imaging and energy dispersive X-ray spectroscopy (EDS) mapping showed an inhomogeneous alloying with minor segregation between Au and Co at nanoscale and the SQUID measurement exhibited the ferromagnetic behavior.

Synthesis and Characterization of Bimetallic Pd-Co Nano Magnetic Materials in Mesoporous Silica

2008 ◽  
Vol 1118 ◽  
Author(s):  
Balaji Tatineni ◽  
Dhananjay Kumar ◽  
Joslyn Perkins ◽  
Sergey Yarmolenko ◽  
Debasish Kuila
Keyword(s):  
Mesoporous Silica ◽  
Magnetic Measurements ◽  
Ammonium Bromide ◽  
Ferromagnetic Behavior ◽  
X Ray Diffraction ◽  
One Pot ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Cetyl Trimethyl Ammonium ◽  
Co Nanoparticles

ABSTRACTAn one-pot procedure was developed for the synthesis of mesoporous silica containing bimetallic PdCo using Pd(NO3)2 and CoCl2, and cetyl trimethyl ammonium bromide (CTAB) as the templating agent, and tetramethoxy silane (TMOS) as the precursor. The materials were characterized using high resolution scanning transmission electron microscopy (HRSTEM), elemental analysis, X-ray diffraction (XRD), and magnetic measurements. The data indicate that the bimetallic Pd-Co nanoparticles are uniformly distributed on the inner pore walls of silica. The magnetic measurements of reduced Pd-Co nanoparticles (4-5 nm) in mesoporous silica reveal a typical ferromagnetic behavior up to 20 K and exhibit superparamagnetic properties above 30 K.

Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y Kotaka ◽  
T. Yamazaki ◽  
Y Kikuchi ◽  
K. Watanabe
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Contrast Imaging ◽  
High Spatial Resolution Image ◽  
Transmission Electron ◽  
Eigen Value ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam ◽  
Z Contrast

AbstractThe high-angle annular dark-field (HAADF) technique in a dedicated scanning transmission electron microscope (STEM) provides strong compositional sensitivity dependent on atomic number (Z-contrast image). Furthermore, a high spatial resolution image is comparable to that of conventional coherent imaging (HRTEM). However, it is difficult to obtain a clear atomic structure HAADF image using a hybrid TEM/STEM. In this work, HAADF images were obtained with a JEOL JEM-2010F (with a thermal-Schottky field-emission) gun in probe-forming mode at 200 kV. We performed experiments using Si and GaAs in the [110] orientation. The electron-optical conditions were optimized. As a result, the dumbbell structure was observed in an image of [110] Si. Intensity profiles for GaAs along [001] showed differences for the two atomic sites. The experimental images were analyzed and compared with the calculated atomic positions and intensities obtained from Bethe's eigen-value method, which was modified to simulate HAADF-STEM based on Allen and Rossouw's method for convergent-beam electron diffraction (CBED). The experimental results showed a good agreement with the simulation results.

Dopant Distribution Analysis in Carbon Nanotubes By Z-Contrast Imaging

2001 ◽  
Vol 7 (S2) ◽  
pp. 208-209
Author(s):  
E.C. Dickey
Keyword(s):  
Carbon Nanotubes ◽  
Ex Situ ◽  
Distribution Analysis ◽  
Contrast Imaging ◽  
New Class ◽  
Transmission Electron ◽  
Structural Applications ◽  
Donor Type ◽  
Scanning Transmission ◽  
Z Contrast

Similar to graphite and carbon fullerenes, the physical properties of carbon nanotubes (NTs) can be altered by ex-situ doping or by functionalizing the nanotube walls. Such mechanisms for tailoring the properties of carbon NTs expand their potential utility in electronic, optical and structural applications. Both acceptor (e.g. I2, Br) and donor-type (e.g. K, Rb) dopants have been successfully intercalated into single-wall NT (SWNT) bundles, and the transport properties of these doped species are greatly altered. For example, iodine-doped SWNTs exhibit a 40% decrease in DC conductivity. Doped SWNTs are a completely new class of nanostructured materials, and there is a large demand for understanding the structure of the various doped-compounds as well as the ramifications for the electronic properties of the material.In this paper we demonstrate the utility of Z-contrast scanning transmission electron microscopy (STEM) for elucidating the structure of doped nanotubes.

Analysis of Nanometer Sized Pyrogenic Particles by Scanning Transmission Electron Microscopy

1995 ◽  
Vol 53 ◽  
pp. 218-219
Author(s):  
DJ Wallis ◽  
ND Browning ◽  
CM Megaridis
Keyword(s):  
Operating Conditions ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Chemical Mechanisms ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Physical And Chemical ◽  
Electron Energy Loss

Iron is a ubiquitous element on the earth's surface, and is thus involved in most naturally occurring fires. Iron organometalic compounds have also been known to suppress carbonaceous soot emissions under certain operating conditions of practical combustors. In order to unravel the physical and chemical mechanisms of influence, of iron on the emission of carbonaceous pyrogenic particles, finescale characterization techniques need to be implemented.The combined techniques of Z-contrast imaging and electron energy loss spectroscopy (EELS) in a VG HB-501 dedicated STEM are ideally suited to study such a system. The sensitivity of the Z-contrast imaging technique to high-Z materials makes it ideal for location of the iron particles within the much lower atomic number matrix. As only the high-angle scattering is used in the image formation, EELS can be performed simultaneously from a position defined in the image. This accurate positioning of the probe by the Z-contrast image permits both compositional and bonding information to be obtained with a spatial resolution approaching the atomic scale.

Direct Observation of Intercalant and Catalyst Particle in Single Wall Carbon Nanotubes

1999 ◽  
Vol 593 ◽  
Author(s):  
X. Fan ◽  
E. C. Dickey ◽  
P. Eklund ◽  
K. Williams ◽  
L. Grigorian ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Catalyst Particle ◽  
Single Wall Carbon Nanotubes ◽  
Contrast Imaging ◽  
Single Wall Carbon ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Dopant Atoms ◽  
Z Contrast ◽  
Electron Energy Loss

ABSTRACTThe Z-contrast scanning transmission electron microscopy (STEM) imaging technique has been used to study dopant atoms and catalyst particles in single wall carbon nanotubes (SWNT). Iodine and bromine have been doped respectively in arc-grown SWNTs. We have directly observed the dopant sites and distributions. Both dopants appear to be incorporated linearly within the SWNT bundles. SWNT were also grown by pulsed laser ablation with mixed Ni and Co catalyst, and the size and distribution of catalytic particles was studied. By using Z-contrast imaging, we found that the size distribution of the catalyst particles varied over a large range, but even the smallest were larger than the diameter of an individual SWNT. Furthermore, electron energy loss spectroscopy (EELS) is used to determine the composition of individual nanocatalyst particles, and were found to consist of a uniform alloy of Co and Ni.

Atomic resolution determination of the structure and chemistry of ceramic grain boundaries

1995 ◽  
Vol 53 ◽  
pp. 320-321
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Grain Boundaries ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Secondary Phases ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Contrast Technique ◽  
Z Contrast

Characterization of grain boundaries in ceramics is complicated by the multicomponent nature of the materials, the presence of secondary phases, and the tendency for the grain boundary plane to “wander” on the length scale of a few nanometers. However, recent developments in the scanning transmission electron microscope (STEM) have now made it possible to correlate directly the structure, composition and bonding at grain boundaries on the atomic scale. This direct experimental characterization of grain boundaries is achieved through the combination of Z-contrast imaging (structure) and electron energy loss spectroscopy (EELS) (composition and bonding). For crystalline materials in zone-axis orientations, where the atomic spacing is larger than the probe size, the Z-contrast technique provides a direct image of the metal (high Z) columns. This image, being formed from only the high-angle scattering, can be used to position the electron probe with atomic precision for simultaneous EELS. Under certain collection conditions, the spectrum can have the same atomic spatial resolution as the image, thus permitting the spectra to be correlated with a known atomic location.

TEM Z-contrast imaging with wide-angle hollow-cone illumination

1990 ◽  
Vol 48 (4) ◽  
pp. 400-401
Author(s):  
J. Bentley ◽  
K. B. Alexander ◽  
Z. L. Wang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Wide Angle ◽  
Hollow Cone ◽  
Contrast Imaging ◽  
Field Mode ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast

High resolution scanning transmission electron microscopy (STEM) images with contrast sensitive to atomic number (Z-contrast) have been obtained with the use of a high-angle annular detector. The equivalent conventional transmission electron microscopy (TEM) dark-field mode reciprocally related to Z-contrast STEM is wide-angle hollow-cone illumination with an on-axis objective aperture. There are two ways to obtain hollow cone illumination; with an annular condenser aperture or by conically scanning the beam tilt coils. As in the case of STEM Z-contrast imaging, resolution with hollow-cone illumination should theoretically be higher than for phase contrast imaging in the same instrument.Philips CM30/STEM, CM12/STEM, and EM400T/FEG/STEM instruments have been used to investigate this imaging technique. The conical illumination dark-field mode is standard on the CM series and was implemented with a hybrid diffraction unit on the EM400. Commercial (SPI Supplies #1780) copper annular apertures with inner and outer diameters of 600 and 900 μm, respectively, spot welded to suitable supports for use as condenser apertures, resulted in cone angles too small to give good Z-contrast in the microprobe mode, because there is still a large diffraction contrast contribution.

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