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Abstract
A critical assumption underlying in situ transmission electron microscopy studies is that the electron beam (e-beam) exposure does not fundamentally alter the intrinsic deformation behavior of the materials being probed. Here, we show that e-beam exposure causes increased dislocation activation and marked stress relaxation in aluminum and gold films spanning a range of thicknesses (80–400 nanometers) and grain sizes (50–220 nanometers). Furthermore, the e-beam induces anomalous sample necking, which unusually depends more on the e-beam diameter than intensity. Notably, the stress relaxation in both aluminum and gold occurs at beam energies well below their damage thresholds. More remarkably, the stress relaxation and/or sample necking is significantly more pronounced at lower accelerating voltages (120 kV versus 200 kV) in both the metals. These observations in aluminum and gold, two metals with highly dissimilar atomic weights and properties, indicate that e-beam exposure can cause anomalous behavior in a broad spectrum of nanostructured materials, and simultaneously suggest a strategy to minimize such artifacts.
Highlights
A critical assumption underlying in situ transmission electron microscopy studies is that the electron beam (e-beam) exposure does not fundamentally alter the intrinsic deformation behavior of the materials being probed
By systematically controlling the beam conditions during cyclic deformation and stress relaxation experiments we show that, contrary to School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287, USA. 2Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090
The microstructure of the films was characterized by Transmission electron microscopy (TEM) and x-ray diffraction (XRD)
Summary
During in situ TEM Deformation of Nanostructured Metals received: 17 August 2015 accepted: 12 October 2015. Using quantitative in situ TEM tensile straining of aluminum and gold films with a range of thicknesses (80–400 nm) and mean grain sizes (d ~ 50–220 nm) we provide direct evidence that e-beam exposure causes increased dislocation activation, significant stress relaxation and anomalous changes in sample geometry. The experiments reveal that e-beam exposure causes an unexpected necking of the samples along their width, which depends more on the beam diameter than intensity These observations in two metals with highly dissimilar atomic weights and properties strongly suggest that the e-beam can significantly alter the deformation response of a broad spectrum of nanostructured materials.
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