The new generation of aberration corrected scanning transmission electron microscope (STEM) instruments optimized for high spatial resolution energy dispersive x-ray (EDX) spectroscopy provide exciting opportunities for elemental analysis of nanoscale objects. Here I will discuss recent example applications where these new analytical capabilities have provided new insights to explain the properties and hence speed up nanomaterial development.
For example, I will present recent work where the light emitting diode devices have been produced by mechanical exfoliation and subsequent layering of 13 different 2D crystals, including 4 MoS2 monolayer quantum wells [Withers et al, Nature Materials, 2015]. Using cross sectional STEM spectrum imaging we reveal that the atomic structure of such devices is atomically flat and provide detailed structural information to help to explain the electroluminescence results obtained. Other 2D crystal heterostructures will also be discussed including those incorporating air sensitive 2D crystals that require fabrication under an Argon atmosphere to preserve the device performance [Cao et al, Nano Letters 2015].
A complementary area of active research in my group is the investigation of bimetallic nanoparticle catalysts. Elementally sensitive STEM EDX electron tomography provides a route to understanding the full 3D morphology of such systems. I will demonstrate results showing the effect of different elemental segregation on catalytic performance as well as discussing the current limitations of this technique [Slater et al, Nano Letters 2014; Slater et al, Ultramicroscopy 2015].
Finally recent work demonstrating the application of high spatial resolution EDX spectrum imaging during in-situ gas and liquid phase experiments will also be discussed [Lewis et al, Chemical Communications 2014, Lewis et al Nanoscale, 2014].