Abstract
Specimen damage and heating by high-energy electron irradiation can be exploited to affect local specimen composition/temperature to drive phase transformations. Field-emission (FEG) sources are especially prone to inducing damage/heating, because their high brightness provides focused ~1nm FWHM/1.0nA probes. The physics of beam heating and damage are reviewed by Reimer (1,2). Heating is related to energy-loss mechanisms broadly summarized by the Bethe formula for stopping power. Radiation damage can cause atomic displacement, ionization, and bond scission. Displacement increases the point-defect concentration. Composition changes occur when displacements eject atoms from the specimen. This paper outlines first results using focused-probe irradiation in a Philips CM20 FEG TEM/STEM to locally crystallize an amorphous 80nm Ge48Te52 film. Ex-situ annealing leads to spherulitic crystallites. The crystallization kinetics have been studied by time-resolved reflectivity (3) and in-situ hot-stage optical microscopy (4). In-situ TEM annealing was done with a single-tilt hot stage. Films were floated from carbon-coated mica onto Cu grids. In-situ annealing under a parallel (low dose) beam leads to crystallization much like the ex-situ studies except that the crystallite morphology is highly anisotropic due to non-uniform film heating (5).
Publisher
Cambridge University Press (CUP)