**Preface to "Crystal Plasticity at Micro- and Nano-scale Dimensions"**

The advent of "nanotechnology" in the 1980s is often credited to the foresight expressed in one of Nobel Prize winner Richard Feynman's lectures given in late 1959, "There's Plenty of Room at the Bottom". The lecture featured the potential advantages in chemistry to be gained by the manipulation of atoms on an atomic scale, and that nano-scale mechanical devices would be designed and developed in future engineering applications. The lecture pre-staged the Nobel Prize-winning developments of atomic force microscopy and scanning tunneling microscopy. An important industrial impetus was provided by the development of microelectromechanical system (MEMS) devices and also later by the development of both nano-scale testing systems, such as nano-indentation hardness testing, and micro-scale specimen fabrication methods, such as the focused ion beam (FIB) manufacturing of micro-pillars and the production of nanoparticles and nano-wires.

Less attention has been given to the order-of-magnitude mechanical strength level advantage enabled at micro- to nanoscale crystal dimensions and within nano-polycrystalline microstructures, both of which are topics included in the present Crystals journal's Special Issue, now issued as an e-book. Such an achievement in the strength level has coincided with other recent advancements in the crystal dislocation mechanics theories that have recently been developed to explain these exceptional crystal strength properties. The advanced testing methods and accompanying model simulations of crystal properties provide an opportunity for quantitatively accounting for the character of individual dislocations as well as their interactions within small groups. The aim of the present Special Issue was to provide a welcome venue for contributed works on this rapidly developing subject.

We Guest Editors express our appreciation to the authors of the articles contained in the present e-book and to the approximately two times greater number of peer reviewers who have helped to present these final collected works in the best possible light. Such recognition is especially deserved because of all persons coping with the worldwide pandemic generated by the coronavirus. Dr. Stephen Walley at the Cavendish Laboratory, University of Cambridge, is thanked for providing helpful contacts with a number of prospective authors. A special note of gratitude is expressed to Ms. Dancy Yu for the very considerable assistance provided in every aspect of achieving both the initial Special Issue and the present e-book summary of results.

> **Ronald W. Armstrong, Wayne L. Elban** *Editors*
