(Invited) Fabrication of Porous Hollow Spheres of Metal Oxide by Anodization of Small Metal Particles

A description of the microstructure of heterogeneous catalysts is important in understanding the mechanisms for catalysis and may result in improvements in catalyst performance. Many commercial catalysts consist of small metal particles and/or metal oxide particles dispersed on a porous support. For bimetallic catalysts, the metals may be in the form of alloys, metal mixtures or completely phase separated. HREM has been demonstrated to be a powerful technique for determining the lattice spacing from small particles[l]. In many studies of catalysts it is necessary to prepare TEM samples by microtomy so that the particle location relative to the porous support is preserved. However, such samples show a reduction in particle visibility and signal-to-noise ratio of lattice fringes. In spite of these difficulties, we have been able to routinely use HREM to rapidly determine the relative distributions of metal and metal oxides in many systems because of the large difference in spacing between strong reflections from the metal and metal oxide (typically 20 %).

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Electron Microscopy of the Shape of Small Metal Particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079024 ◽

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.

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Investigation of cluster layers of small netal particles by TEM, SEM, EELS and by photoacoustic spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174382 ◽

1990 ◽

Vol 48 (4) ◽

pp. 250-251

Author(s):

H. Seiler ◽

U. Haas ◽

K.H. Körtje

Keyword(s):

Bulk Material ◽

High Vacuum ◽

Optical Methods ◽

Metal Particles ◽

Silver Particles ◽

Low Loss ◽

Plasmon Excitation ◽

First Results ◽

Diffraction Patterns ◽

Small Metal Particles

The physical properties of small metal particles reveal an intermediate position between atomic and bulk material. Especially Ag has shown pronounced size effects. We compared silver layers evaporated in high vacuum with cluster layers of small silver particles, evaporated in N2 at a pressure of about 102 Pa. The investigations were performed by electron optical methods (TEM, SEM, EELS) and by Photoacoustic (PA) Spectroscopy (gas-microphone detection).The observation of cluster layers with TEM and high resolution SEM show small silver particles with diameters of about 50 nm (Fig. 1 and Figure 2, respectively). The electron diffraction patterns of homogeneous Ag layers and of cluster layers are similar, whereas the low loss EELS spectra due to plasmon excitation are quite different. Fig. 3 and Figure 4 show first results of EELS spectra of a cluster layer of small silver particles on carbon foil and of a homogeneous Ag layer, respectively.

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Coherent electron nanodiffraction from clean silver nano particles in a UHV STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015112x ◽

1993 ◽

Vol 51 ◽

pp. 1058-1059

Author(s):

J. Liu ◽

M. Pan ◽

G. E. Spinnler

Keyword(s):

Supported Catalysts ◽

Imaging Techniques ◽

Nano Particles ◽

Metal Particles ◽

Shape Structure ◽

Dynamical Simulations ◽

Small Metal Particles ◽

Extract Information

Small metal particles have peculiar chemical and physical properties as compared to bulk materials. They are especially important in catalysis since metal particles are common constituents of supported catalysts. The structural characterization of small particles is of primary importance for the understanding of structure-catalytic activity relationships. The shape and size of metal particles larger than approximately 5 nm in diameter can be determined by several imaging techniques. It is difficult, however, to deduce the shape of smaller metal particles. Coherent electron nanodiffraction (CEND) patterns from nano particles contain information about the particle size, shape, structure and defects etc. As part of an on-going program of STEM characterization of supported catalysts we report some preliminary results of CEND study of Ag nano particles, deposited in situ in a UHV STEM instrument, and compare the experimental results with full dynamical simulations in order to extract information about the shape of Ag nano particles.

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