Measure-by-Wire (MBW): An Automatic Control Framework for High-Throughput Transmission Electron Microscopy

Abstract The impressive advances in the nanosciences (i.e., materials science, nanotechnology, and biotechnology) during the past 20 years have been fueled by newly gained understanding of material properties at the nano- and sub-nanometer scales. Much of this understanding was obtained through different forms of electron microscopy, such as scanning, photoemission, and, in particular, transmission electron microscopy. Transmission electron microscopes (TEMs) are unique in that they provide physical, structural, electronic, magnetic, and chemical information down to the atomic scale. Thus, it is now possible to manufacture and inspect devices such as nanotubes and MEMS, and to determine the properties of the nanoparticles of polymers and catalysts. Moreover, tools such as cryo-TEMs and techniques such as TEM electron tomography now allow the 3-D imaging and study of biological cellular machines and macromolecular complexes that occupy volumes of up to a few cubic micrometers. Clearly, TEMs are the tools of choice for academic and industrial research at the nanoscale, and it is expected that they will be increasingly used to perform large numbers of routine, repetitive measurement tasks. Thus, there is a clear need for a new generation of high-throughput TEMs designed to autonomously extract information from specimens (e.g., particle sizes, chemical composition, structural information etc.). In order to develop high-throughput TEMs that operate with maximum efficiency (in terms of time utilization), a new systematic automation paradigm is needed. We propose here one such paradigm called Measure-by-Wire (MBW), which is based on systems and control principles. With this perspective, TEM operators yield the direct control of the microscope’s internal processes to a hierarchy of feedback controllers and high-level supervisors. These use dynamical models of the main TEM components, along with currently available measurement techniques (and new sensors) to automate and execute in parallel, when possible, processes such as defocus correction, specimen displacement, and specimen drift cancellation. Measure-by-Wire is discussed in depth, and its methodology is illustrated through two detailed examples: the design of a defocus regulator, a type of feedback controller that is akin to existing auto-focus procedures; and an adaptive specimen drift compensator.