Observing and measuring strain in nanostructures and devices with transmission electron microscopy

The evolution of elastic strain engineering in nanostructures and devices requires characterization tools that can be used to not only observe but also quantify the actual strain in a sample, whether this strain is intrinsic or applied. Strain contrast in crystalline samples has always been one of the primary contrast mechanisms used for imaging the microstructure of a material in a transmission electron microscope (TEM). In this regard, TEM is a particularly powerful tool due to its ability to spatially resolve strain information with high precision and spatial resolution. This article reviews the techniques currently available for directly measuring strain in the TEM. Examples are given for measuring strain in semiconductor devices using imaging, diffraction, and holographic techniques. For strain measurement during in situ mechanical testing, two general methods are presented: the conversion of displacement from an actuation device or the direct measurement of strain using image features during deformation.