Computer simulation of Frank loop contrast in field ion images
Thesis. A computer model for simulation of the image contrast caused by Frank dislocation loops in field ion tips of fcc materials is presented. The model is based on the shell model for ion image simulation, whereas the displacenient field of Frank loops is computed from the exact displacement equation for a closed dislocation loop in an isotropically elastic continuum. A method for taking surface effects into account by superposition of the displacement field of an image loop is introduced. The results -indicate that Frank loops will cause image contrast while wholly beneath the surface of the tip, and that vacancy and interstitial loops will cause qualitatively different contrast. The effect of surface relaxation, while quantitatively substantial, does not qualitatively alter these results. Special emphasis is placed on small loops, with respect to which existing contrast theory is inadequate. Some micrographs of ion bombarded iridium tips are presented. These micrographs display contrast effects in excellent agreement with computer plots of interstitial loop contrast. (51 figures, 42 references) (auth)
- Research Organization:
- California Univ., Berkeley (USA). Lawrence Berkeley Lab.
- DOE Contract Number:
- W-7405-ENG-48
- NSA Number:
- NSA-29-005467
- OSTI ID:
- 4403175
- Report Number(s):
- LBL--2200
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
*DISLOCATIONS-- FRANK DISLOCATIONS
*FCC LATTICES-- DISLOCATIONS
*ION MICROSCOPY-- IMAGES
*TRITIUM-- PHYSICAL RADIATION EFFECTS
EVAPORATION
FIELD EMISSION
INTERSTITIALS
N50230* --Metals
Ceramics
& Other Materials--Metals & Alloys--Properties
Structure & Phase Studies
SIMULATION
STACKING FAULTS
SURFACES
VACANCIES FRANK DISLOCATIONS