Radiation-enhanced diffusion

The defects generated in ion—soHd interactions influence the kinetic processes that occur both inside and outside the cascade volume. At times long after the cascade lifetime (t > 10 s), the remaining vacancy—interstitial pairs can contribute to atomic diffusion processes. This process, commonly called radiation enhanced diffusion (RED), can be described by rate equations and an analytical approach (27). Within the cascade itself, under conditions of high defect densities, local energy depositions exceed 1 eV/atom and local kinetic processes can be described on the basis of ahquid-like diffusion formalism (28,29). 

The depth resolution (i.e. the ability to discriminate between atoms in adjacent thin layers) is limited by the primary beam causing redistribution of target atoms prior to their emission as ions, and to segregation and radiation-enhanced diffusion processes. The local topography can also lead to a loss of depth resolution with sputter depth. 

Keywords Compact fuel cell Proton conductive oxide Radiation induced conductivity Radiation enhanced diffusion... 

An increase in dose slowly destroys the ordered crystal structure, leading to a distribution similar to the amorphous case. The channeling effect in polycrystalline material is much smaller compared with single crystals, b) At elevated temperature the diffusion of the implanted atoms very often leads to a broadening of the profile. In addition diffusion processes play a role at low temperatures during the irradiation, leading to radiation enhanced diffusion (Sect. 2.6). Fig. 7 illustrates the effect. 

During ion implantation in Si, the vacancy concentration can be very high. Using SRIM, calculate the vacancy concentration at the damage peak for 40 keV B implanted to a dose of 1 x 1014 B cm-2. The sample will be heated to 1,000°C for 10 s to activate the B. What enhancement is expected in the diffusivity due to radiation-enhanced diffusion ... 

Ionizing radiation can also cause radiation-enhanced diffusion that leads to defect annealing. Ouchani et al. (1997) demonstrated in a dual-beam irradiation (220 keV Pb and 0.3 to 3.2 MeV He) that the critical amorphization dose increases due to defect annealing caused by electron energy loss processes. Soulet et al. (2001) recently studied... 

In-pile self-diffusion of uranium in stoichiometric UO2 and UC has been measured by Hoh and Matzke 3J6). The diffusion coefficients obtained at a nominal irradiation temperature of 900°C and a fission rate of 1 x 10 //cm indicated that radiation-enhanced diffusion was higher by a factor of 10 to lO than determined by extrapolation of thermal diffusion coefficients. They suggested that the data are of immediate relevance to the understanding and the prediction of such quantities as in-pile sintering and densification, diffusion-controlled creep, and fission gas behavior in the outer zones of the fuel. 

Different secondary ions can also display different depth resolution values for the same substrate. As an example. Copper typically yields poor depth resolution because of its high diffusion coefficient, particularly when sputtered. This sputter-induced enhancement is otherwise referred to as radiation-enhanced diffusion. Radiation-induced segregation may also be initiated, with different primary ion/secondary ion combinations resulting in different trends. As a result, any emissions collected as a result of this form of sputtering will always emanate from what is termed an altered layer, as opposed to the initial intrinsic substrate layer. Exceptions are sometimes noted for large cluster ion impact, because, as mentioned in Section 4.1.1.3, these can remove sputter-induced damage. 

T.R. AUen, G.S. Was, Radiation-Enhanced Diffusion and Radiation-Induced Segregation. Radiation Effects in Solids, Springer, 2007, p. 123. 

Blondiaux et al. (50)(53) showed that copper, nickel and cobalt diffuse into silicon samples. At 240° only a very small penetration of nickel is noticed after a 3 h irradiation. At 560 and 800°C an important diffusion of cobalt, nickel and copper was observed, namely several hundred m. Diffusion in a furnace at identical temperatures and during identical periods of time led to the same results. It was thus shown that in the cases studied, radiation enhanced diffusion is negligible compared to the thermal one. Deep thermal diffusion can lead to analytical errors in spite of etching after irradiation. It thus seems necessary to take the thermal diffusion coefficients in account in order to evaluate possible errors and to limit the temperature of the sample by adequate cooling. 

Ion bombardment before and during deposition can introduce defects into the surface region and diffusion can he enhanced by mechanisms similar to those found in radiation enhanced diffusion For example, in the aluminum metallization of silicon, it has been shown that there is little diffusion of aluminum into siUcon during high temperature processing if the silicon surface is undamaged. However, extensive diffusion occurs if the surface is damaged by ion bombardment prior to the deposition. 

Radiation-enhanced diffusion The enhancement of the diffusion rate by radiation damage from heavy-particle irradiation, which generates lattice defects in the near-surface region. 

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