Ion bombardment of crystals and its applications

Ming-Show Wong, Marquette University


The damage characteristics of crystal structures have been studied by ion irradiation using 3 MeV and 150 keV inert gas ions. The diamond structure of C, Si and Ge, zinc-blende structure of GaAs and InSb, and wurtzite structure of InN, GaN and AlN have been examined. For diamond the (111) x-ray diffraction peak is observed to broaden and shift toward lower angles; the lattice expansion, da/a$\sb o$ approaches limiting values with increasing ion fluence (10-30 ion/nm$\sp2),$ consistent with a model based on displacement involving a dynamic equilibrium between the production and the radiation-annealing of the defects. The average volume increment per defect is determined to be 13 $\pm$ 2 $\times$ 10$\sp{-4}$ nm$\sp3$. The x-ray diffraction peaks of Si, Ge, GaAs and InSb do not shift or broaden significantly with ion irradiation but decrease in intensity with increasing ion fluence, consistent with a two-phase model, one crystalline and the other non-crystalline. The curve of I$\sb{\rm F}$/I$\sb o$ versus fluence can be expressed by I$\sb{\rm F}$/I$\sb o$ = $e\sp{-D\sb{M}F},$ where I$\sb o$ and I$\sb{\rm F}$ are x-ray diffraction intensities before and after irradiation at fluence F; D$\sb{\rm M}$ is defined as the metamict damage cross-section. The damage cross-section of Ge to argon (3 MeV) ions is 0.35 $\pm$ 0.05 nm$\sp2$ and 1.0 $\pm$ 0.2 nm$\sp2$ for Kr (3 MeV) ions. Silicon has a damage cross-section of 0.15 $\pm$ 0.10 nm$\sp2$ for Kr (3 MeV) ions. The damage cross-sections for GaAs and InSb to Kr (3 MeV) ions are 0.2 $\pm$ 0.10 and 0.40 $\pm$ 0.15 nm$\sp2$, respectively. The response of GaN, AlN and InN to ion irradiation were dramatically different. GaN and AlN do not appear to become damaged, while InN decomposed under ion bombardment. When InN is irradiated by (3 MeV) Kr ions on a W substrate, indium tungstate is formed. By contract, bombardment at 150 keV results in decomposition but no further reaction. The formation of indium tungstate is due to an ion beam mixing reaction induced by the ions of energy 3 MeV. Powder mixtures are difficult to analyze since they give complex x-ray diffraction patterns. The differential changes in the x-ray diffraction patterns of a powder mixture after ion bombardment can be used to distinguish the separate components unambiguously.

Recommended Citation

Wong, Ming-Show, "Ion bombardment of crystals and its applications" (1987). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI8811067.