Congrats to Chris Regan and William Hubbard for Receiving the 2019 Microscopy Today Innovation Award
The editors of Microscopy Today congratulate the winners of the tenth Microscopy Today Innovation Award competition. The ten innovations advance microscopy in several areas: light microscopy, electron microscopy, and scanning probe microscopy. These innovations will make microscopy and microanalysis more powerful, more productive, and easier to accomplish.Secondary Electron Electron-BeamInduced-Current (SEEBIC) Imaging University of California at Los Angeles Developers: Chris Regan and William Hubbard. While intimately related to prior electron-beaminduced-current (EBIC) methods in the SEM, secondary electron electron-beaminduced-current (SEEBIC) imaging is qualitatively and quantitatively different. What makes the SEEBIC system new is that both the secondary electron (SE) and hole signals are detected in a scanning transmission electron microscope (STEM). SEEBIC differs from traditional EBIC in several ways. The measuring circuits are wired differently. In the former case the end of the device remote from the transimpedance amplifier is extremely high impedance, while in the latter it is tied to a low impedance (usually ground) to allow charge neutralization. While traditional EBIC imaging is sensitive to holes, it only generates contrast in regions where the sample supports an electric field that will separate electron-hole pairs. In most samples such regions are special and localized, for example, in a p-n junction. Thus, most of the sample generates no contrast when imaged with traditional EBIC. SEEBIC, on the other hand, is an inevitable consequence of imaging a thin specimen with an energetic electron beam, and SEEBIC imaging generates contrast everywhere in a sample. SEEBIC imaging has not been demonstrated previously for a couple reasons. First, the typical SEM sample is electron-opaque, and primary beam absorption produces a large background; thus, the SEEBIC signal is buried in the noise of the traditional SEM EBIC apparatus. This background is largely absent in the electron-transparent samples used in STEM. Secondly, the secondary electron (SE) yield drops with increasing beam energy; therefore, the SE signal is even smaller in a 200 kV STEM than in a 30 kV SEM. Detection of the signal requires a current measuring system that is low-noise and protected from electromagnetic interference (1 pA EBIC corresponds to ∼6,000 electrons in a 1 ms dwell time). SEEBIC is sensitive to electric potential, electric field, work function, conductivity, and temperature, and it can probe these quantities with atomic resolution in a modern STEM. STEM SEEBIC can image a functioning resistive random access memory (RRAM). For example, in a HfO2-based RRAM, the conducting filament is thought to consist of oxygen vacancies. Oxygen vacancies are basically invisible in a standard STEM image, but they give excellent contrast when viewed with STEM EBIC imaging.
