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The contrast due to a strain field at an amorphous silicon/crystalline silicon (a-Si/c-Si) interface relative to the bulk crystal is studied with a scanning transmission electron microscope equipped with a low angle annular dark field (LAADF) detector and a high angle ADF (HAADF) detector. Experimental observations suggest that strain contrast depends closely on sample thickness and collection angle. For a thin sample (<100 Å) strain contrast is negative in both the LAADF and HAADF images. For a thick sample (>150 Å) strain contrast is positive in the LAADF image and negative in the HAADF image. Theoretical calculations of the effect of a random strain field are carried out. First, a simple model based on atomic scattering with an extra Debye–Waller factor is employed. It predicts a positive strain contrast in the LAADF image and no contrast in the HAADF image. The simple model fails for the HAADF contrast because it does not consider the propagation process of the electron beam inside the sample. Therefore multislice simulations including propagation details are carried out. The multislice simulation results agree well with the experimental observations. A measure of the strain amplitude is attained by comparing the experimental data with multislice simulation results. Quantitative measurements of strain contrast are only possible if the sample thickness is known. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recently, transmission electron microscopy (TEM) and related techniques have brought unique insights to graphene research, demonstrating remarkable flexibility in characterizations ranging from atomic ordering to charge distribution. Such TEM studies have helped advance areas including the understanding of graphene growth and the effects of defects and dopants on the mechanical and electrical properties of graphene. Electron microscopy has proved particularly useful in determining the structure of crystals and grain boundaries across six orders of magnitude—from the shapes, arrangements, and stacking sequences of grains to the atomic arrangements at grain boundaries. Meanwhile, graphene is becoming a promising two-dimensional laboratory bench for electron microscopy, for example, turning graphene into a medium for nanosculpting by transforming buckyballs into graphene and vice versa. Finally, graphene has been used as an ultrathin support membrane for TEM, enabling studies of the motion of single atoms, direct imaging of two-dimensional amorphous materials, and even formation of nano-aquaria for imaging bacteria or nanoparticles in liquid media. Rapid developments in the fields of both electron microscopy and graphene will continue to provide a rich ground for future insights. [ABSTRACT FROM PUBLISHER]