Spontaneous Formation of Ag and Au Particles in Alcohols

1994 ◽  
Vol 351 ◽  
Author(s):  
Z.-Y. Huang ◽  
M. Quinn ◽  
G. Mills ◽  
W. Galef
Keyword(s):  
Light Scattering ◽  
Metal Particles ◽  
Small Particles ◽  
Plasmon Band ◽  
Spontaneous Reduction ◽  
Silica Surfaces ◽  
Spontaneous Formation ◽  
Ag Particles ◽  
Solvent Molecules ◽  
Small Metal Particles

ABSTRACTMetal particles are generated via the spontaneous reduction of Ag+ and AuCl4− ions by solvent molecules that takes place in air-saturated alcoholic solutions containing hydroxide ions. Changes in the plasmon band of the Ag particles are observed when the metal particles are in contact with Ag20 particles. The optical changes are explained in terms of surface effects of the metal particles. Larger shifts of the Au plasmon band and light scattering were observed at the initial stages of the particle formation process. These effects are explained in terms of formation of networks consisting of small metal particles. It is proposed that generation of small Au particles occurs mainly on silica surfaces, and that particle-networks are formed when small particles desorb from the surfaces.

THE KUBO EFFECTS IN SMALL PARTICLES OF METALS

1996 ◽  
Vol 03 (01) ◽  
pp. 3-7 ◽  
Author(s):  
SHUN-ICHI KOBAYASHI
Keyword(s):  
Electronic Properties ◽  
Metal Particles ◽  
Small Particles ◽  
Mesoscopic Systems ◽  
Level Statistics ◽  
Theoretical Paper ◽  
Charging Energy ◽  
Level Quantization ◽  
Nmr Properties ◽  
Small Metal Particles

This talk is to commemorate Kubo’s pioneering theoretical paper in 1962 on the electronic properties of very small metal particles. We discuss mainly the NMR properties of the particles. Emphasis is placed on factors such as the level quantization, the level statistics, the finiteness of systems, and the single electron charging energy, which are current topics in the field of mesoscopic systems.

The Characterization of Thin Platinum Films on Alumina

1986 ◽  
Vol 83 ◽  
Author(s):  
E. I. Altman ◽  
R. J. Gorte
Keyword(s):  
Particle Size ◽  
Catalytic Properties ◽  
Metal Particles ◽  
Small Particles ◽  
Oxide Substrate ◽  
Porous Oxide ◽  
Temperature Programmed ◽  
Thin Platinum ◽  
Small Metal Particles

ABSTRACTIndustrial metal catalysts are usually in the form of small metal particles supported on a porous oxide. The typical size of these metal particles ranges between 1.0 and 10.0 nm and it is well known that the particle size and the oxide substrate can affect the catalytic properties of the metal for some important reactions[1]. Previous work with adsorption on small particles has indicated that desorption temperatures[2–4] and the ability to dissociate CO[5,6] can also be affected by the particle size. To further investigate these size and substrate effects, we have examined the adsorption properties of several simple gases on small Pt particles supported on alumina using temperature programmed desorption (TPD). We will show that the desorption curves for CO, H2, and NO on these particles are very similar to curves measured on single crystals.

Structure Studies of Supported Metal Catalyst Particles by Microdiffraction Technique

1987 ◽  
Vol 45 ◽  
pp. 202-203
Author(s):  
M. Pan ◽  
J.M. Cowley ◽  
I.Y. Chan ◽  
R. Garcia
Keyword(s):  
Metal Particles ◽  
Metal Catalyst ◽  
Supported Metal Catalysts ◽  
Small Particles ◽  
Structure Information ◽  
The Past ◽  
Transmission Electron ◽  
And Performance ◽  
Small Metal Particles ◽  
Supported Metal

Understanding the structures of the small metal particles (<5nm) in supported metal catalysts can provide some basis for understanding the properties and performance of these catalysts. High resolution transmission electron microscopy (HRTEM) has been extensively used to characterize the structures of small particles in the past few years. As a complement to HRTEM, microdiffraction technique has its unique advantage of being able to provide local structure information within regions of diameter 1-2nm.In our VG HB-5 STEM an electron beam with diameter of 1-1.5nm can be easily generated at the specimen level and microdiffraction patterns from such small regions are routinely observed with the help of the attached optical system. Two series of catalyst samples, Pt/γ-Al2 O3 and Rh/CeO2 with various metal loadings and reduction temperatures, have been studied. The series of Pt/γ-Al2 O3 catalyst included both calcined and reduced samples. Both series of catalysts contain high dispersions of metal particles (<5nm). In the case of Rh/CeO2 Rh particles usually have sizes of 2-3nm.

Electron Beam Driven Disordering in Small Particles

1996 ◽  
Vol 439 ◽  
Author(s):  
Richard R. Vanfleet ◽  
Jack Mochel
Keyword(s):  
Electron Beam ◽  
Critical Size ◽  
Scanning Transmission Electron Microscope ◽  
Metal Particles ◽  
Small Particles ◽  
Transmission Electron ◽  
Platinum Clusters ◽  
Scanning Transmission ◽  
The Individual ◽  
Small Metal Particles

AbstractSmall metal particles in the range of a few nanometers in diameter are seen to progressively disorder when the 100 keV electron beam of a Scanning Transmission Electron Microscope (STEM) is held stationary on the particle. The diffraction pattern of the individual particle is seen to progress from an initial array of indexable diffraction spots to a mixture of diffraction spots and amorphous-like rings and finally to rings with no persistent diffraction spots. After the electron beam is removed, the particles will recrystallize after minutes or hours. Only particles below a critical size are seen to fully disorder. We have observed this in Platinum, Palladium, Rhodium, and Iridium and based on our model of disordering process believe it is a universal effect. It has also been observed with a Platinum Ruthenium alloy. We discuss the mechanism of this disordering and the structure of the resulting disordering particle for the case of Platinum clusters.

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.

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.

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

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.

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

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.

Interfacial Interactions in Silica Reinforced Silicones

1989 ◽  
Vol 170 ◽  
Author(s):  
Mirta I. Aranguren ◽  
Christopher W. Macosko ◽  
Bima Thakkar ◽  
Matthew Tirrell
Keyword(s):  
Low Molecular Weight ◽  
Complex Structures ◽  
Small Particles ◽  
Carbon Blacks ◽  
Silica Surfaces ◽  
Reinforcing Fillers ◽  
Fractal Characteristics ◽  
Physical Forces ◽  
A New Technique ◽  
Silicone Rubbers

AbstractThe study of the type and strength of the filler-polymer linkages is of great importance in understanding the reinforcement of elastomers. Silicone rubbers are weak elastomers and the addition of reinforcing fillers is essential in order to obtain useful, strong materials. The best reinforcing filler for these elastomers are fumed silicas. These fillers, like reinforcing carbon blacks, have very complex structures. Both have fractal characteristics, small particles fused together forming open aggregates that can cluster by physical forces. Silicas have sometimes more complex structures than carbon blacks, but have a better understood surface chemistry. Interactions between polydimethylsiloxanes and silica surfaces have been studied using heat of adsorption measurements of mostly low molecular weight analogs or inferring the strength of the adsorption by the shift of particular peaks in the infrared spectrum [1]. Here we will present a new technique that measures directly the strength of the adsorption of the polymer segments onto glass and between themselves. It also allows for comparison of the strength of such bonds with the strength of a polymer entanglement “link”.

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