Cantilever Beam Stress Measurements During Ion Irradiation
- PDF / 360,259 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 29 Downloads / 250 Views
ABSTRACT In-situ stress measurements on single crystal MgO and A120 3 have been performed during ion irradiation. A cantilevered beam sample arrangement was used, with the stress in the implanted layer determined from the deflection of the sample as measured by the change in capacitance between the free end of the sample and a reference electrode. Point defect concentrations are obtained by dividing the volume strain by the defect relaxation volume, with saturation values of 0.8 to 1.2% obtained for 1.0 MeV Ne, Ar and Kr irradiations. Defect production is sublinear with dose, with an efficiency of less than 25% compared to KinchinPease predictions. Ionization induced annealing is evaluated with 1.0 MeV He and 1.0 MeV H irradiations following heavy ion irradiation. INTRODUCTION Energetic particle irradiation of materials typically results in the production of point defects which produce a volume expansion or contraction if the irradiated material is free to expand. During ion irradiation, however, a thin (< 2 [im) irradiated surface layer develops on a much thicker underlying unirradiated layer (effectively a substrate). If the irradiated layer remains coherent with the substrate, it will be constrained from expanding in the plane of the layer but free to expand out of plane (I_to surface). The degree of constraint in-plane will be determined by the thickness and modulus of the substrate, which must bend in order for the irradiated layer to expand. Essentially this situation is similar to deposited metal films on a thin substrate for which the biaxial in-plane stress in the film was first evaluated by Stoney1' 2 as, crl =
6( 1-_v)t
1
R
where Es and vs are the Young's modulus and Poisson's ratio of the substrate, ts and tf are thicknesses of the substrate and film and R is the radius of curvature of the substrate (for tr 7
OH •,>--"---_2
'j''irradiation
and Ne in MgO and 1.0 MeV Kr in
0Ar "/
1.0/
Y
Figure 4. Light ion annealing with 1.0 MeV He and H with Kr,
/"PA1203.
1.0 1cr/1.01-t/ NWO
10-3
i012 .
013
16 1014
O .
'O16015'
l'' 17
Do~se (ions/cný)
Using the theoretical estimates for the anion and cation Frenkel defect volumes in MgO
of 1.84 and 1.87 molar volume15 , which have been reasonably confirmed by experiment' 6, the total defect concentrations shown in Figure 2 are obtained from the volume strain. The concentration of each type of defect (anion vacancy, anion interstitial, cation vacancy, cation interstitial) is then 1/4 the total defect concentration, which ranged from 0.8% to 1.2% at saturation for MgO irradiated with 1.0 MeV Ne, Ar and Kr. Optical absorption measurements by Evans' 7 , following 1.0 MeV Ne irradiation, indicated a saturation concentration of F and F+ centers (neutral or +1 charged, isolated anion vacancies) of 0.04% as shown in Figure 5. If 1/4 of the defect concentration found in the present study represents the number of anion vacancies present as either isolated vacancies or contained within clusters or dislocation loops, this would indicate that -5x as many vacanc
Data Loading...
