Electron Microscopy of the Shape of Small Metal Particles

1977 ◽  
Vol 35 ◽  
pp. 300-301
Author(s):  
M. Jose Yacaman
Keyword(s):  
Electron Microscopy ◽  
Metal Particle ◽  
Field Experiments ◽  
Size Range ◽  
Dark Field ◽  
Metal Particles ◽  
Bragg Condition ◽  
Crystal Particle ◽  
Small Metal Particle ◽  
Small Metal Particles

In the Study of small metal particles the shape is a very Important parameter. Using electron microscopy Ino and Owaga(l) have studied the shape of twinned particles of gold. In that work electron diffraction and contrast (dark field) experiments were used to produce models of a crystal particle. In this work we report a method which can give direct information about the shape of an small metal particle in the amstrong- size range with high resolution. The diffraction pattern of a sample containing small metal particles contains in general several systematic and non- systematic reflections and a two-beam condition can not be used in practice. However a N-beam condition produces a reduced extinction distance. On the other hand if a beam is out of the bragg condition the effective extinction distance is even more reduced.

Alignment of small Ru and Au Particles on MgO

1986 ◽  
Vol 44 ◽  
pp. 786-787
Author(s):  
A. G. Shastri
Keyword(s):  
Epitaxial Growth ◽  
Size Range ◽  
Electronic Materials ◽  
Metal Salt ◽  
Metal Particles ◽  
Bimetallic Clusters ◽  
Random Orientation ◽  
Indirect Exposure ◽  
Materials Research ◽  
Small Metal Particles

The alignment of small metal particles on semiconducting or insulating substrates is of considerable importance in the areas of heterogeneous catalysis and electronic materials research. Previous work has shown an epitaxial growth of 2nm Au particles on MgO smoke prepared by an indirect exposure of the oxide to evaporated Au atoms. Others reported an epitaxial growth or random orientation of An on MgO depending on whether the oxide was vacuum cleaved or air cleaved. EDS showed the presence of bimetallic clusters in supported Ru-Au/MgO catalysts prepared by coimpregnation of the oxide with aqueous precursor metal salt solutions. A μED study of two bimetallic samples having a total metal loading of 3.75 wt % (with 93 atom % Ru) and 3.37 wt % (with 14 atom % Ru) was carried out to understand the structure of small bimetallic clusters and the relative alignment of metal particles on MgO. In spite of the bulk immiscibil ity of Ru and Au, bimetallic clusters were identified by EDS in the size range of < 5 nm.

STEM studies of small metal particles

1983 ◽  
Vol 41 ◽  
pp. 332-333
Author(s):  
J.M. Cowley ◽  
W.B. Monosmith
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Image Resolution ◽  
Metal Particles ◽  
Resolution Limit ◽  
Catalytic Systems ◽  
Additional Advantage ◽  
Platinum Particles ◽  
Small Metal Particles

Small metal particles having diameters in the range of 5 to 100Å are currently being studied intensively because of their importance in catalytic systems. High resolution electron microscopy is a particularly valuable tool for such studies. Scanning transmission electron microscopy offers the additional advantage that high resolution images may be correlated with microdiffraction and microanalysis from selected regions of diameter close to the image resolution. In practise it is usual to obtain either microdiffraction patterns or microanalysis from regions larger than the resolution limit because of the requirements for ready interpretability of the diffraction patterns and for convenient count rates in the case of microanalysis using either ELS or EDS. In the case of small platinum particles, evidence from various techniques suggests that some oxygen may be present in a surface layer and X-ray diffraction and EXAFS studies suggest that particles in the 15-20Å size range after exposure to air, may consist almost entirely of Pt3O4 and PtO.

scholarly journals The Outer Fringe of a Stacking Fault

1969 ◽  
Vol 22 (5) ◽  
pp. 569 ◽  
Author(s):  
AK Head
Keyword(s):  
Electron Microscopy ◽  
Stacking Faults ◽  
Dark Field ◽  
Stacking Fault ◽  
Specimen Thickness ◽  
Bragg Condition ◽  
Bright Field

The rule of Hashimoto, Howie, and Whelan, much used in electron microscopy for determining the nature of stacking faults, is known to be true when the specimen thickness t is sufficiently great. It is shown that sufficiently great means that the product (t;gg)(gglg~) must be greater than 0�2 for bright field or greater than O� 25 for dark field, these values being for reasonable deviations from the Bragg condition.

Examination by Electron Microscopy of Osmium Catalysts Supported on Thin Aluminium-Oxide Films

1982 ◽  
Vol 40 ◽  
pp. 658-659
Author(s):  
B. Tesche ◽  
E. Zeitler ◽  
E. A. Delgado ◽  
H. Knözinger
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Metal Atom ◽  
Supported Catalysts ◽  
Metal Particles ◽  
Transmission Electron ◽  
High Area ◽  
Instrumental Resolution ◽  
Electron Microscopes ◽  
Small Metal Particles

It is easy to obtain resolutions of atomic dimensions with current conventional transmission electron microscopes. Hence, in principle, the examination of small metal particles or metal atom ensembles (≤1 nra) in supported catalysts is not limited by the instrumental resolution. However, usually the metal is located on dispersed high-area supports such as silica or alumina and the characterization by electron microscopy of these systems down to the atomic dimension is not directly possible, since the contrast in the micrographs is an unknown combination of phase and amplitude contrast. This uncertainty can result in incorrect determinations of particle size, shape and distribution.

A microdiffraction study of Os10C(Co)24-2 in the Scanning Transmission Electron Microscope

1986 ◽  
Vol 44 ◽  
pp. 696-697 ◽  
Author(s):  
M. E. Mochel ◽  
R. I. Masel ◽  
J. M. Mochel
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Structural Information ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Metal Particles ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Small Metal Particles

Recent papers have discussed some of the difficulties in determining the structure of very small (<10Å) metal particles using electron microscopy. One of the ideas in the literature is that electron diffraction could provide structural information even under conditions where imaging is difficult. The purpose of the work reported here is to demonstrate that one can use electron diffraction techniques to obtain structural information about small metal particles, in this case 5Å osmium particles on a carbon film.

Imaging small particles with secondary electrons

1992 ◽  
Vol 50 (2) ◽  
pp. 1288-1289 ◽  
Author(s):  
J. Liu ◽  
G. E. Spinnler ◽  
A. E. Ron
Keyword(s):  
Electron Microscopy ◽  
Supported Catalysts ◽  
Collection Efficiency ◽  
Particle Surface ◽  
Mean Free Path ◽  
Metal Particles ◽  
Small Particles ◽  
Secondary Electrons ◽  
Mean Escape Depth ◽  
Small Metal Particles

High resolution secondary electron microscopy (HRSEM) in dedicated scanning transmission electron microscopy (STEM) instruments has proved very useful for characterizing supported catalysts. In order to understand the contrast mechanisms of HRSEM images of small particles, clean samples and UHV environments are needed since the emission of secondary electrons (SEs) can be significantly influenced by contamination on the particle surface. In this paper we report results on imaging small metal particles by HRSEM in a UHV STEM instrument. In addition, we show that with computer assistance digitized HRSEM images of small metal particles can be used to estimate the average inelastic mean free path and the mean escape depth of the collected SEs.The Vacuum Generators UHV STEM HB-501S, codenamed MIDAS (a Microscope for Imaging, Diffraction and Analysis of Surfaces), was used for these experiments. Detailed descriptions of the MIDAS system have been published previously. The collection efficiency of SEs approaches 100% through the use of magnetic ‘parallelizers’ situated inside the objective pole pieces.

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