Heating of TEM specimens during ion milling

Sample heating during preparation of electron-thin specimens for observatio n in transmission electron microscopy (TEM) can produce artefacts which inv alidate observations. This is particularly true of two-phase materials such as metal matrix composites, for which sample cooling with liquid nitrogen cannot be used to preserve the substructure during milling. A series of exp eriments is conducted using an age-hardenable aluminium alloy which produce s a trace of peak temperature attained by TEM specimens during ion milling. It is shown that peak temperatures of the order of 650 K can be attained u sing conventional milling parameters; the technique must therefore be used with caution with materials such as metal matrix composites. A simplified o ne-dimensional heat transfer analysis of the problem is conducted to show t hat the most critical parameter is heat transfer along the sample holder le gs and across interfaces along the heat path. Temperature differentials wit hin the TEM specimen are shown to be less significant, yet these alone are capable of reaching 60 K within a dimpled specimen under usual milling cond itions. (C) 2001 Elsevier Science B.V. All rights reserved.