Abstract
Precise measurement and characterization of electrostatic potential structures and the concomitant electric fields at nanodimensions are essential to understand and control the properties of modern materials and devices. However, directly observing and measuring such local electric field information is still a major challenge in microscopy. Here, differential phase contrast imaging in scanning transmission electron microscopy with segmented type detector is used to image a p-n junction in a GaAs compound semiconductor. Differential phase contrast imaging is able to both clearly visualize and quantify the projected, built-in electric field in the p-n junction. The technique is further shown capable of sensitively detecting the electric field variations due to dopant concentration steps within both p-type and n-type regions. Through live differential phase contrast imaging, this technique can potentially be used to image the electromagnetic field structure of new materials and devices even under working conditions.
Highlights
Unlike transmission electron microscopy (TEM) or Fresnel mode in Lorentz TEM, where imposing large defocus or other lens aberrations is essential to make the phase shifts imparted by the sample visible in the recorded intensity[13], optimal Differential phase contrast (DPC) imaging occurs at the in-focus condition[14]
This makes DPC imaging compatible with standard scanning transmission electron microscopy (STEM) imaging modes like annular dark-field (ADF), which can be used simultaneously to provide further information for structural characterization
These data are noisier, because holography reconstructs the potential which must be differentiated to give the electric field profile. They have been scaled, suggesting that the active thickness differed between the holography and DPC experiments which were not carried out on precisely the same region of the specimen
Summary
Unlike TEM or Fresnel mode in Lorentz TEM, where imposing large defocus or other lens aberrations is essential to make the phase shifts imparted by the sample visible in the recorded intensity[13], optimal DPC imaging occurs at the in-focus condition[14]. This makes DPC imaging compatible with standard STEM imaging modes like ADF, which can be used simultaneously to provide further information for structural characterization. DPC STEM can be applied to the electromagnetic field structure of new materials and devices as a tool for analysis but as a tool for discovery
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