Resolving the Electron\nPlume within a Scanning Electron\nMicroscope

Scanning electron microscopy (SEM), a century-old technique,\nis\ntoday a ubiquitous method of imaging the surface of nanostructures.\nHowever, most SEM detectors simply count the number of secondary electrons\nfrom a material of interest, and thereby overlook the rich material\ninformation contained within them. Here, by simple modifications to\na standard SEM tool, we resolve the momentum and energy information\non secondary electrons by directly imaging the electron plume generated\nby the electron beam of the SEM. Leveraging these spectroscopic imaging\ncapabilities, our technique is able to image lateral electric fields\nacross a prototypical silicon p–n junctions and to distinguish\ndifferently doped regions, even when buried beyond depths typically\naccessible by SEM. Intriguingly, the subsurface sensitivity of this\ntechnique reveals unexpectedly strong surface band bending within\nnominally passivated semiconductor structures, providing useful insights\nfor complex layered component designs, in which interfacial dynamics\ndictate device operation. These capabilities for noninvasive, multimodal\nprobing of complicated electronic components are crucial in today’s\nelectronic manufacturing but is largely inaccessible even with sophisticated\ntechniques. These results show that seemingly simple SEM can be extended\nto probe complex and useful material properties.