SYNTHESIS OF ULTRASMALL CD0.3ZN0.7SENANOCRYSTALS VIA MECHANOCHEMICAL ROUTE

Mechanical alloying through severe plastic deformation (SPD) was used to synthesize ultrasmall nanocrystals of (Cd0.3Zn0.7Se)with a diameter (d = 1.3 nm) after 20 hours milling time. A high-resolution electron microscope was (HRTEM) used to examine the mechanical deformation on the nanocrystals. The images reveal a bulk-like cluster structure without a distinctive regular shape. The atoms appear to be located entirely at the surface. The energy band-gap of the ultrasmall was determined to be 4.56 eV from UV-Vis absorption spectra.

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An Analysis of Dissociation of Molecules in a High Resolution Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100072873 ◽

1973 ◽

Vol 31 ◽

pp. 486-487

Author(s):

Mihir Parikh

Keyword(s):

Electron Microscope ◽

High Resolution ◽

Cross Sections ◽

Resolving Power ◽

Peak Intensity ◽

Molecular Film ◽

Resolution Electron ◽

Dissociation Cross Section ◽

High Resolution Electron Microscope ◽

The Stability

It is well known that the resolution of bio-molecules in a high resolution electron microscope depends not just on the physical resolving power of the instrument, but also on the stability of these molecules under the electron beam. Experimentally, the damage to the bio-molecules is commo ly monitored by the decrease in the intensity of the diffraction pattern, or more quantitatively by the decrease in the peaks of an energy loss spectrum. In the latter case the exposure, EC, to decrease the peak intensity from IO to I’O can be related to the molecular dissociation cross-section, σD, by EC = ℓn(IO /I’O) /ℓD. Qu ntitative data on damage cross-sections are just being reported, However, the microscopist needs to know the explicit dependence of damage on: (1) the molecular properties, (2) the density and characteristics of the molecular film and that of the support film, if any, (3) the temperature of the molecular film and (4) certain characteristics of the electron microscope used

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Computer-Controlled Hrem Alignment Using Automated Diffractogram Analysis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181415 ◽

1990 ◽

Vol 48 (1) ◽

pp. 532-533

Author(s):

G.Y. Fan ◽

O.L. Krivanek

Keyword(s):

Electron Microscope ◽

High Resolution ◽

The Other ◽

Full Information ◽

Resolution Electron ◽

Skilled Operator ◽

Automatic Alignment ◽

High Resolution Electron Microscope ◽

Computer Controlled ◽

Recorded Image

Full alignment of a high resolution electron microscope (HREM) requires five parameters to be optimized: the illumination angle (beam tilt) x and y, defocus, and astigmatism magnitude and orientation. Because neither voltage nor current centering lead to the correct illumination angle, all the adjustments must be done on the basis of observing contrast changes in a recorded image. The full alignment can be carried out by a computer which is connected to a suitable image pick-up device and is able to control the microscope, sometimes with greater precision and speed than even a skilled operator can achieve. Two approaches to computer-controlled (automatic) alignment have been investigated. The first is based on measuring the dependence of the overall contrast in the image of a thin amorphous specimen on the relevant parameters, the other on measuring the image shift. Here we report on our progress in developing a new method, which makes use of the full information contained in a computed diffractogram.

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