Phases matter

Synopsis

Abstract:  The progress achieved in the development of aberration correctors, allowing a resolution of 0.1 nm, has made transmission electron microscopy (TEM) a unrivaled and indispensable tool for nanoscience.  However, the intensity distribution that one gets in a common TEM image has lost the phase information of the electron passing through the specimen, making most TEM techniques "blind" to electric and magnetic fields within the specimen.  Electron holography (EH) is a TEM technique able to circumvent this issues by division of the wavefront method, in the same fashion as the Fresnel biprism. The recovery of the phase information provides invaluable in formation about the mean inner potential and junction potentials in bulk and interfaces across a variety of specimens, from semiconductor devices to low atomic number specimens like polymers. A main drawback though, is that one needs to have a- priori information about the local specimen thickness. Usually, thickness measurements are easily extrapolated for highly symmetric objects, but for non-symmetric objects this can become a daunting  task. We will talk about how combining EH with tomography one can get phase and voltage maps from non- symmetric objects as well [1]. Finally, we will discuss how charging induced by the electron beam affects EH measurements in semiconductor p-n junctions.

References:

[1] C. Cordoba, X.  Zeng,  D. Wolf,  M. T.  Borgström, E. Barrigon, A. Lubk, and K. L. Kavanagh, Nano Lett .19, 6, (2019).