Ehsan Izadi

In Situ TEM Straining of Ultrafine-grained Aluminum Films of Different Textures Using Automated Crystal Orientation Mapping.

Several studies have shown that metal films with similar thickness and grain size but dissimilar texture show significant differences in their mechanical behavior. For instance, ultrafine-grained (UFG) Al films with no preferred texture show lower flow stress and more pronounced nonlinear behavior during unloading compared to films with a bicrystalline microstructure. [1] [2] However, no systematic study has been focused on understanding the deformation mechanisms responsible for such differences in mechancial behavior.

In situ tensile testing of tin (Sn) whiskers in a focused ion beam (FIB)/scanning electron microscope (SEM)

Abstract Tin and tin-alloyed electroplated films are known to be susceptible to whisker growth under a range of conditions, many of which result in the generation of compressive stresses in the film. Compressive stress is considered to be one of the primary causes for whisker nucleation and growth. While extensive investigations have been performed on whisker growth, there have been few studies on the mechanical properties of tin whiskers themselves. We report on the tensile behavior of tin whiskers that were obtained by indentation and furnace aging of electroplated tin films on copper disks. Tensile tests of the whiskers were conducted in situ in a dual beam focused ion beam (FIB)-scanning electron microscope (SEM) system using a micro electro-mechanical systems (MEMS) based tensile testing stage. The strength of the whiskers was found to decrease with an increase in gage length and aged whiskers were found to be weaker than their indented counterparts. The observed gage length effect can be attributed to the probability of finding more defects as the whisker length increases. The effect of processing on the observed strength variation was investigated by analyzing the oxygen content in the whiskers via energy dispersive spectroscopy and the microstructure through transmission electron microscopy (TEM). The deformation mechanisms of whiskers were also inferred using post-mortem TEM. It was observed that the whiskers grown by indentation were dislocation free both before and after deformation. In contrast, whiskers grown by aging showed notable dislocation content (arranged in low energy configurations) even before deformation.

Revealing anelasticity and structural rearrangements in nanoscale metallic glass films using in situ TEM diffraction

ABSTRACT We used a novel diffraction-based method to extract the local, atomic-level elastic strain in nanoscale amorphous TiAl films during in situ transmission electron microscopy deformation, while simultaneously measuring the macroscopic strain. The complementary strain measurements revealed significant anelastic deformation, which was independently confirmed by strain rate experiments. Furthermore, the distribution of first nearest-neighbor distances became narrower during loading and permanent changes were observed in the atomic structure upon unloading, even in the absence of macroscopic plasticity. The results demonstrate the capability of in situ electron diffraction to probe structural rearrangements and decouple elastic and anelastic deformation in metallic glasses. GRAPHICAL ABSTRACT IMPACT STATEMENT This paper employs a novel in situ electron diffraction technique to reveal deformation-induced structural rearrangements, and decouple atomic-level elastic strain from larger scale anelastic strain in metallic glasses.

Interfacial Strain Mapping and Chemical Analysis of Strained-Interface Heterostructures by Nanodiffraction and Electron Energy-Loss Spectroscopy

Strain engineering is a relevant optimization route to introduce and/or optimize defects for mixed ionicelectronic conducting oxides. Interfacial strain control of electrical conductivity [1] and resistive switching [2] was reported for sideways-contacted Gd0.1Ce0.9O2-δ|Er2O3 (GCO|ERO) ‘microdot’ heterostructures with alternating monolayers of insulating ERO and mixed-conducting GCO, whose lattice mismatch yielded compressive strain in the GCO layers. Here we explore these and other GCO heterostructures with alternative straining oxides that impart varying degrees of tensile strain on GCO, such as Bi4NbO8.5|GCO (BNO|GCO). We apply local strain and chemical mapping, along with high resolution imaging in the TEM and scanning TEM (STEM) to provide nanoscale insights regarding strained heterostructure design.

In Situ TEM Investigation of the Deformation Mechanisms and Microstructural Changes in Ultrafine-grained Non-textured Aluminum Film Using Automated Crystal Orientation Mapping

Automated crystal orientation mapping in TEM (ACOM-TEM), with a precessing nanoprobe electron beam scanning over the specimen to collect spot diffraction patterns, is highly suitable to study the deformation mechanisms and monitor the microstructural evolution of UFG/NC metals during deformation. This technique enables direct acquisition of orientation/phase map over micron-sized areas while enhancing the ability to identify grains, microtexture and twin boundaries using the orientation maps of the sample that are extracted from the indexed diffraction patterns.