Contrast of Highly Dispersed Metal Nanoparticles in High-resolution Secondary Electron and Backscattered Electron Images of Supported Metal Catalysts

2000 ◽  
Vol 6 (4) ◽  
pp. 388-399
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Secondary Electron ◽  
Light Element ◽  
Pt Nanoparticles ◽  
Carbon Support ◽  
Supported Metal Catalysts ◽  
Backscattered Electrons ◽  
Supported Pt Catalysts ◽  
Backscattered Electron ◽  
Small Metal Particles

Abstract Platinum nanoparticles finely dispersed in activated carbon powders have been observed with high contrast in secondary electron (SE) and backscattered electron (BE) images. The factors that contribute to the visibility of small metal particles in high-resolution BE and SE images are discussed. Monte Carlo simulations provided insight into the scattering of electrons by small, heavy-element particles located on, or embedded in, light-element supports. The visibility of Pt nanoparticles in BE images depends on many factors including the size and the location of the Pt particles, the energy of the incident electrons, and the size of the electron probe. The SE signals generated by backscattered electrons may not significantly contribute to the visibility of small Pt particles in high-resolution SE images of carbon supported Pt catalysts. Only those small Pt particles that are located on or very close to the surface of the carbon support can be revealed in high-resolution SE images.

Contrast of Highly Dispersed Metal Nanoparticles in High-resolution Secondary Electron and Backscattered Electron Images of Supported Metal Catalysts

2000 ◽  
Vol 6 (4) ◽  
pp. 388-399 ◽  
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Secondary Electron ◽  
Light Element ◽  
Pt Nanoparticles ◽  
Carbon Support ◽  
Supported Metal Catalysts ◽  
Backscattered Electrons ◽  
Supported Pt Catalysts ◽  
Backscattered Electron ◽  
Small Metal Particles

AbstractPlatinum nanoparticles finely dispersed in activated carbon powders have been observed with high contrast in secondary electron (SE) and backscattered electron (BE) images. The factors that contribute to the visibility of small metal particles in high-resolution BE and SE images are discussed. Monte Carlo simulations provided insight into the scattering of electrons by small, heavy-element particles located on, or embedded in, light-element supports. The visibility of Pt nanoparticles in BE images depends on many factors including the size and the location of the Pt particles, the energy of the incident electrons, and the size of the electron probe. The SE signals generated by backscattered electrons may not significantly contribute to the visibility of small Pt particles in high-resolution SE images of carbon supported Pt catalysts. Only those small Pt particles that are located on or very close to the surface of the carbon support can be revealed in high-resolution SE images.

High Resolution Imaging by Means of Backscattered Electrons in the Scanning Electron Microscope

2007 ◽  
Vol 567-568 ◽  
pp. 313-316
Author(s):  
Petr Wandrol ◽  
Jiřina Matějková ◽  
Antonín Rek
Keyword(s):  
High Resolution ◽  
Secondary Electron ◽  
Backscattered Electrons ◽  
Detection Systems ◽  
Advantages And Disadvantages ◽  
Electron Detection ◽  
Crystal Scintillation ◽  
Backscattered Electron ◽  
Resolution Imaging ◽  
Scanning Electron

This paper deals with imaging by means of backscattered electrons in the high resolution scanning electron microscopy. Possible backscattered electrons detection systems are outlined and one of the most efficient, the high take of angle single crystal scintillation detector, is described in detail. Its advantages and disadvantages are discussed and the comparison with the secondary electron detection modes is shown. The high resolution micrographs taken by the backscattered electron detector as well as by the secondary electron detectors are displayed.

The use of high-resolution FESEM to study solid-state phase transformations and reactions

1994 ◽  
Vol 52 ◽  
pp. 1028-1029
Author(s):  
P. G. Kotula ◽  
D. D. Erickson ◽  
C. B. Carter
Keyword(s):  
Solid State ◽  
High Resolution ◽  
Phase Transformations ◽  
High Efficiency ◽  
Sol Gel ◽  
Quantitative Information ◽  
Solid State Reactions ◽  
Critical Dimensions ◽  
Backscattered Electrons ◽  
Backscattered Electron

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3 enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3 system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.

High-Resolution Scanning Electron Microscopy and Microanalysis of Supported Metal Catalysts

1999 ◽  
Vol 589 ◽  
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Supported Catalysts ◽  
Metal Catalysts ◽  
Supported Metal Catalysts ◽  
Surface Sensitivity ◽  
Brightness Field ◽  
Backscattered Electron ◽  
Enhanced Surface ◽  
Supported Metal

AbstractThe use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.

Visibility of Small Metalllic Catalyst Particles in High-Resolution Secondary and Backscattered Electron Images

1999 ◽  
Vol 5 (S2) ◽  
pp. 720-721
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Metallic Nanoparticles ◽  
Low Voltage ◽  
High Surface ◽  
High Surface Area ◽  
Metal Catalyst ◽  
Catalyst Supports ◽  
Metallic Particles ◽  
Backscattered Electrons ◽  
Backscattered Electron

Metallic nanoparticles finely dispersed onto high surface-area supports play an important role in heterogeneous catalysis. The performance of a supported metal catalyst can be directly related to the size and spatial distribution of the metallic nanoparticles. With the recent development of highresolution SEM instruments, it is now possible to observe nanoparticles in a field emission SEM. At low voltages, surface details of catalyst supports as well as metallic nanoparticles can be observed. The particle contrast in low voltage SEM images, however, is still not well understood. We have previously shown that the contrast of metallic particles can be enhanced if a small positive potential is applied to the sample. It is suggested that backscattered electrons (BE) significantly contribute to the visibility of metallic nanoparticles in high-resolution SE images. In this paper, we report further study on the origin of particle contrast in high-resolution SE images.Figure 1 shows a set of SE images of the same area of a carbon supported Pt catalyst.

Image Formation With Upper and Lower Secondary Electron Detectors in the Low Voltage Field-Emission SEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 260-261
Author(s):  
J. Liu
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Secondary Electron ◽  
Low Voltage ◽  
Incident Beam ◽  
Sample Surface ◽  
Backscattered Electrons ◽  
Sample Chamber ◽  
Scale Surface ◽  
Short Working

High-resolution secondary electron (SE) imaging was first demonstrated at 100 kV in the STEM a decade ago. High-resolution SE imaging is now routinely obtainable in field-emission SEMs. Although nanometer-scale surface features can be examined at low incident beam voltages we still do not fully understand the factors that affect the contrast of low voltage SE images. At high incident beam voltages, SE1 (SEs generated by the incident probe) and SE2 (SEs generated by backscattered electrons at the sample surface) can be spatially separated. SE1 carries high-resolution detail while SE2 contributes to background. At low incident beam voltages, however, the interaction volume of the incident electrons shrinks rapidly with decreasing incident beam voltage. Thus, both the SE1 and SE2 signals carry high-resolution information. At low incident beam voltages, SE3 (SEs generated by backscattered electrons impinging on the sample chamber, pole pieces and etc.) also carries high-resolution detail and contributes significantly to the collected signal, especially for high atomic number materials and at short working distances.

Contrast and Resolution in Scanning Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 256-257
Author(s):  
Shizuo Kimoto ◽  
Hiroshi Hashimoto ◽  
Kiyoshi Mase
Keyword(s):  
Secondary Electron ◽  
Primary Electron ◽  
Secondary Electron Image ◽  
Scattered Electron ◽  
Secondary Electrons ◽  
Backscattered Electrons ◽  
Electron Image ◽  
Backscattered Electron ◽  
Electron Microscopes ◽  
Scanning Electron

In scanning electron microscopy, secondary and backscattered electrons play a most important role. When considering these two forms of signal source, it is necessary to treat them separately on the basis of contrast and resolution, since their production processes and energies are different. In practice, the electrons detected by the secondary electron detector consist of secondary electrons excited by a primary electron probe, those excited by backscattered electrons in the specimen and secondary electrons liberated from the specimen's environmental parts during backscattered electron bombardment. Consequently, it is difficult to completely eradicate the effect of backscattered electrons upon the secondary electron image. This paper presents information in regards to the differences in contrast and resolution between the secondary and back- scattered electron image under the condition of optimum secondary/backscattered electron separation. First, it was shown how secondary electron image contrast is affected by secondary electrons liberated by backscattered electrons.

Ultra-high resolution backscattered imaging

1992 ◽  
Vol 50 (2) ◽  
pp. 1284-1285
Author(s):  
David C Joy
Keyword(s):  
High Resolution ◽  
Layered Structure ◽  
Beam Energy ◽  
High Angle ◽  
Backscattered Electrons ◽  
Energy Filtering ◽  
Backscattered Electron

A recent paper by Ogura displays backscattered electron (BSE) images from a bulk, layered structure of AlAs/GaAs with repeat spacings of the order of 10nm. Typically BSE images are thought of as being inherently limited in resolution to a level which is of the order of a fraction of the Bethe range of the incident electrons, which for the beam energy and specimen used in these experiments would be of the order of 5 μm. The purpose of this paper is, therefore, to examine the conditions required for the nanometer level resolution achieved in this case.Backscattered electrons can be grouped into two classes, the BSI which are backscattered by a single high angle event soon after their entry into the specimen, and the BSII which are produced as the cumulative result of plural scattering. There is no sharp division between these groups but the two classes can be separated experimentally by energy filtering, since the BSI will have lost little energy in their short transit through the sample.

Problem of Subsurfae Observation in Backscattered Electron Mode

1980 ◽  
Vol 38 ◽  
pp. 660-661
Author(s):  
K. Ogura ◽  
A. Laudate
Keyword(s):  
Electron Beam ◽  
Epoxy Resin ◽  
Secondary Electron ◽  
Biological Tissues ◽  
Surface Structures ◽  
Backscattered Electrons ◽  
Electron Mode ◽  
Backscattered Electron ◽  
The Mean ◽  
Constituent Elements

Recently, the study of biological tissues by means of the SEM has not been limited to the observation of specimens' surface structures, but extended to the observation of their inner structures using various techniques. The most widely used methods of observing inner structures by secondary electron (SE) image include the frozen solvent fracturing method and the frozen resin fracturing method using epoxy resin and others.1) The information obtained from a specimen when irradiated with an electron beam includes SEs and backscattered electrons (BEs) . It is well known that the yield of BEs is mainly dependent on the meen atomic numbers of the constituent elements of the specimen, and the mean energy of BEs is almost the same as that of incident electrons.2) Accordingly, the BEs which are scattered back from the inside of the specimen can be easily released from the specimen surface, so that BEs are useful signals for obtaining the inner information on the specimen.3)

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