INSITU STUDIES OF AMORPHIZATION OF THE GE-AL AND SI-AL SYSTEMS INDUCED BY 1 MEV ELECTRON-IRRADIATION

Ge-Al and Si-Al bilayer specimens, and also Al-2.3at.%Ge two-phase all oy specimens, were irradiated in situ with 1 MeV electrons at temperat ures in the range 10-190 K in a high voltage electron microscope. The Ge precipitates in the Al-2.3at.%Ge alloy disappeared completely at a critical fluence (PHI(c)) of approximately 2.4 x 10(23) cm-2 (24 displ acements per atom (dpa) in Ge and 14 dpa in Al) for specimens irradiat ed at 10 or 50 K; this is the same value of PHI(c) at which Ge-Al bila yers are found to contain an amorphous phase. At 10 K an irradiated Ge -Al bilayer specimen is found to have an amorphous phase at the interf ace only when a Ge layer faces the incident electron beam, while for a Si-Al bilayer specimen amorphization occurs at the interface independ ent of the direction of the incident beam with respect to a bilayer. F or Ge-Al bilayer specimens PHI(c) is approximately 2.5 x 10(23) cm-2 ( 25 dpa in Ge and 15 dpa in Al). For Si-Al bilayers PHI(c) is approxima tely 3 x 10(23) cm-2 (19 dpa in Si and 18 dpa in Al). The temperature dependence of PHI(c) is also studied for a Ge-Al bilayer specimen. The value of PHI(c) is a constant for T < almost-equal-to 160 K, and then it increases rapidly with increasing T; PHI(c) becomes immeasurably l arge (more than 70 dpa in Ge and more than 43 dpa in Al) at a critical temperature of about 190 K. The temperature dependence of the crystal line to amorphous transition is explained in terms of a recoil-implant ation mechanism, coupled with a radiation-enhanced monovacancy diffusi on mechanism for Ge atoms in Al, and an athermal contribution to Ge di ffusion in Al via an electron-beam stimulated monovacancy migration me chanism.