Transmission electron radiation damage

Radiation Damage. It has been known for many years that bombardment of a crystal with energetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a soHd with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 due to both electronic and nuclear coUisions. As an ion slows down and comes to rest in a crystal, it makes a number of coUisions with the lattice atoms. In these coUisions, sufficient energy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are caUed primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic coUisions and is coUectively referred to as the coUision, or displacement, cascade. The disorder can be directiy observed by techniques sensitive to lattice stmcture, such as electron-transmission microscopy, MeV-particle channeling, and electron diffraction. 

Transmission electron microscopes (TEM) with their variants (scanning transmission microscopes, analytical microscopes, high-resolution microscopes, high-voltage microscopes) are now crucial tools in the study of materials crystal defects of all kinds, radiation damage, ofif-stoichiometric compounds, features of atomic order, polyphase microstructures, stages in phase transformations, orientation relationships between phases, recrystallisation, local textures, compositions of phases... there is no end to the features that are today studied by TEM. Newbury and Williams (2000) have surveyed the place of the electron microscope as the materials characterisation tool of the millennium . 

Chemical fixation for transmission electron microscopy prepares cells for the preservation of damage due to subsequent washing with aqueous solvents, dehydration with organic solvents such as ethanol or acetone, embedding in plastic resins, polymerization of the resins by heat, exothermic catalysts, or ultraviolet radiation, and imaging with high-energy electron beams in an electron microscope. 

Bursill, L. A., McLaren, A. C. (1966). Transmission electron microscope study of natural radiation damage in zircon (ZrSi04). phys. stat. sol., 13, 331-43. 

Figure 10. Variation of a-decay dose as a function of age for natural pyrochlore (modified after Lumpkin and Ewing 1988). The lower boundary marks the onset of observable radiation damage, as determined by transmission electron microscopy. The upper curve represents complete amorphization. Open circles specimens from a single locality which accurately bracket the a-decay dose for amorphization, closed circles localities for which the amorphization dose was estimated from low-dose specimens, upward triangles locaUties for which complete amorphization was not observed, downward triangles localities which had only amorphous specimens.

Hobbs LW (1979) Application of transmission electron microscopy to radiation damage in ceramics. J Am Ceram Soc 62 267-278... 

The X-ray images of extended lattice imperfections within the crystal arise fi om variations in beam intensity caused by local distortions of the lattice. Dislocation densities of up to 10 mm can be resolved in transmission studies or ten times this by the reflection technique. This resolution is lower than that obtainable by transmission electron microscopy, but the sample used may be thicker and does not have to be examined under high vacuum. X-ray beams also produce less radiation damage in the sample. When decomposition proceeds beyond a > 0.01, distortion of the lattice is such that the X-ray image loses resolution and the exposures required become even longer. Reflection data obtained at several different diffraction angles may be required to characterize the imperfections present. 

The atomic structure of the films was studied by transmission electron microscopy (TEM) using a JEM lOOC electron microscope in the microdiffraction mode. The diffraction patterns were obtained at a low electron beam intensity using the CCD high-sensitive registration system to prevent the films from radiation damage by the electron beam. 

Wald JW, Weber WJ (1984) Effects of self-radiation damage on the leachability of actinide-host phases. In Advances in Ceramics, Vol. 8. Wicks GG, Ross WA (eds) Am Ceram Soc, Columbus, Ohio, p 71-75 Wang LM (1998) Application of advanced transmission electron microscopy techniques in the study of radiation effects in insulators. Nucl Instr Meth Phys Res B 141 312-325 Wang LM and Ewing RC (1992) Ion beam induced amorphization of complex ceramic materials-minerals. Mater Res Soc Bull 17 38-44... 

M.L. Jenkins and M.A. Kirk, Characterisation of Radiation Damage by Transmission Electron Microscopy, lOP Pubhshing Ltd, Bristol, 2001. 

Molecular Crystals Fullerites. Organic crystals are usually prone to ionization damage and decompose very rapidly under electron irradiation they can thus be studied for only a short time (a few. seconds) and only with a very low electron beam intensity. Transmission electron microscopy has, therefore, seldom been applied to organic crystals. However, the all-carbon molecules Qo, C70. etc., (fullerenes) discovered at the end of the 1980s resist electron radiation fairly well. Early structural studies on the crystalline phases of ftil-lerenes (fullerites) were performed mainly by electron microscopy because only small quantities of sufficiently pure material were available. At room... 

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