ICSC: a program for calculating inelastic scattering cross sections for fast electrons incident on crystals

A computer program which calculates inner-shell ionization and backscattering cross sections for fast electrons incident on a crystal is presented. The program calculates the inelastic scattering coefficients for inner-shell ionization, pertinent to electron energy loss spectroscopy and energy dispersive X-ray analysis, using recently presented parameterizations of the atomic scattering factors. Orientation-dependent cross sections, suitable for atom location by channelling enhanced microanalysis, may be calculated. Inelastic scattering coefficients that allow the calculation of orientation-dependent annular dark-field and Rutherford backscattering maps are calculated using an Einstein model. In all cases, absorption due to thermal diffuse scattering, also calculated using an Einstein model, can be included.

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An Automated and Rapid Process for Determining Number of Atoms in Supported Ultra-Small Metal Clusters

Microscopy and Microanalysis ◽

10.1017/s1431927600016809 ◽

1999 ◽

Vol 5 (S2) ◽

pp. 696-697

Author(s):

J.C. Yang ◽

S. Bradley ◽

J.M. Gibson

Keyword(s):

Amorphous Carbon ◽

Cross Sections ◽

Scanning Transmission Electron Microscope ◽

Dark Field ◽

Spectroscopic Technique ◽

Measured Intensity ◽

Transmission Electron ◽

Scanning Transmission ◽

Annular Dark Field ◽

Scattering Cross Sections

Since heterogeneous catalysis depends on surface chemistry, insights into the structure of supported catalytic materials is vital for understanding catalysis. We have developed a mass spectroscopic technique using very high angle annular dark field images in a scanning transmission electron microscope (STEM), that gives the number of atoms per cluster. We have also developed a robust interactive computer program to analyze these images rapidly. In this proceeding, we will present our method and results on analyzing ultra-small and dispersed Pt clusters on amorphous carbon, as well as our preliminary results of Pt on γ-A12 O3.The ultra-small Pt clusters on the amorphous carbon Cu grid were made by a proprietary technique. Imaging for the STEM-based mass-spectroscopic technique was performed on a Field Emission Gun (FEG) VG HB601 STEM operated at l00kV. The absolute measured intensity from the clusters were converted to scattering cross-sections, which can then be converted to number of atoms: More details of this method can be found in Singhal, Yang and Gibson.

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A Novel Stem-Based Mass Spectroscopic Technique: Applications to Catalytic Materials

MRS Proceedings ◽

10.1557/proc-466-227 ◽

1996 ◽

Vol 466 ◽

Author(s):

J. C. Yang ◽

A. Singhal ◽

S. Bradley ◽

J. M. Gibson

Keyword(s):

Elastic Scattering ◽

Cross Sections ◽

Absolute Intensity ◽

Scanning Transmission Electron Microscope ◽

Dark Field ◽

Spectroscopic Technique ◽

Scattering Cross ◽

Scanning Transmission ◽

Annular Dark Field ◽

Scattering Cross Sections

ABSTRACTVery high angle (∼ 100mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the mass of a cluster on a support material. With knowledge of the annular dark field (ADF) detector efficiency, the absolute intensity of very HAADF images can be converted to elastic scattering cross-sections. By comparing the theoretical and experimental elastic scattering cross-sections, the number of atoms can be determined. Statistical measurement of absolute cross-sections from Re-6 clusters show good agreement with theoretical cross-sections. The experimental error corresponded to ±2 Re atoms. Our experiments demonstrate the exceptional stability of the Re-6 organometallic compound relative to Re-8 clusters. This technique is presently being applied to Pt clusters.

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The measurement of inner-shell ionization cross aections by electron impact in a TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130961 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1266-1267

Author(s):

Raynald Gauvin ◽

Gilles L'Espérance

Keyword(s):

Electron Impact ◽

Cross Sections ◽

Weight Fraction ◽

Thin Foil ◽

Specimen Thickness ◽

Ionization Cross ◽

Electron Dose ◽

Total Electron ◽

Inner Shell Ionization ◽

Shell Ionization

Values of cross sections for ionization of inner-shell electrons by electron impact are required for electron probe microanalysis, Auger-electron spectroscopy and electron energy-loss spectroscopy. In this work, the results of the measurement of inner-shell ionization cross-sections by electron impact, Q, in a TEM are presented for the K shell.The measurement of QNi has been performed at 120 KeV in a TEM by measuring the net X-ray intensity of the Kα line of Ni, INi, which is related to QNi by the relation :(1)where i is the total electron dose, (Ω/4π)is the fractional solid angle, ω is the fluorescence yield, α is the relative intensity factor, ε is the Si (Li) detector efficiency, A is the atomic weight, ρ is the sample density, No is Avogadro's number, t' is the distance traveled by the electrons in the specimen which is equal to τ sec θ neglecting beam broadening where τ is the specimen thickness and θ is the angle between the electron beam and the normal of the thin foil and CNi is the weight fraction of Ni.

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Neutron diffraction, inelastic scattering and the structure of amphiphiles and macromolecules in solution

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1975.0129 ◽

1975 ◽

Vol 345 (1640) ◽

pp. 119-144 ◽

Cited By ~ 5

Keyword(s):

Neutron Diffraction ◽

Inelastic Scattering ◽

Cross Sections ◽

Biological Molecules ◽

Variation Method ◽

Contrast Variation ◽

Structure And Dynamics ◽

Spin Resonance ◽

Scattering Lengths ◽

Scattering Cross Sections

The methods by which neutron diffraction and inelastic scattering may be used to study the structure and dynamics of solutions are reviewed, with particular reference to solutions of amphiphile and biological molecules in water. Neutron methods have particular power because the scattering lengths for protons and deuterons are of opposite sign, and hence there exists the possibility of obtaining variable contrast between the scattering of the aqueous medium and the molecules in it. In addition, the contrast variation method is also applicable to inelastic scattering studies whereby the dynamics of one component of the solution can be preferentially studied due to large and variable differences in the scattering cross sections. Both applications of contrast variation are illustrated with examples of amphiphile-water lamellar mesophases, diffraction from collagen, viruses, and polymer solutions. Inelastic scattering observations and the dynamics of water between the lamellar sheets allow microscopic measurements of the water diffusion along and perpendicular to the layers. The information obtained is complementary to that from nuclear magnetic resonance and electron spin resonance studies of diffusion.

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