Measurement Challenges in Dynamic and Nonequilibrium Nanoscale Systems.

Abstract

Biological systems exhibit strikingly sophisticated properties, including adaptability, directed motion, regulation, and self-organization. Such systems are often described as being "nonequilibrium" or "out-of-equilibrium", and it can be instructive to think of them as adopting thermodynamic states that require a constant supply of energy to maintain. Despite their ubiquity, systems that demonstrate these abilities require a remarkably stringent set of chemical requirements to exist. Broadly speaking, they must be (a) capable of consuming some external source of energy that (b) acts as a fuel to do some form of work, (c) all while maintaining highly organized structural features at the nanometer length scale that persist in space and over time. It remains a grand challenge in the field of chemistry to synthesize artificial systems capable of similarly complex nonequilibrium behavior both as a means for greater fundamental understanding and as a way to imbue non-natural structures with dynamic behavior for various applications. Yet an oft-overlooked challenge in this field involves not just the synthesis of nonequilibrium materials but also their characterization. The requirements for measuring nanometer-scale systems of nonequilibrium building blocks with the appropriate temporal and spatial resolution are demanding and have heretofore been largely unavailable to researchers. In this Perspective, we highlight challenges and recent advances in the measurement of dynamic nanoscale systems. We argue that progress in this area is crucial and must occur in parallel to synthetic goals if any meaningful understanding is to occur.