Metastability in Nanomaterials
The MNM theme aims to understand nanoscale material dynamics in response to supplied energy and dissipation, enabling driven, adaptive, and active functionalities that drastically deviate from the equilibrium state.
Key inspiration comes from fascinating dynamic phenomena in non-equilibrium systems including spontaneous symmetry breaking, self-organization, self-regulation. Rich non-equilibrium dynamics enable high-level functionalities, ranging from self-healing and adaptation to complex and highly efficient information processing. Nanoscale is the new frontier for such phenomena, providing opportunities to address such questions as: Can active functions be intrinsically controlled at the nanoscale, e.g., via boundary conditions, in confined, templated, or other nanostructured environments? Do thermodynamic principles established for active colloid and related mesoscale systems also apply to nanoscale entities within materials, from dislocations to domain walls to isolated vacancies? Can we predict dynamic and metastable behaviors from atoms up? Understanding driven phenomena will enable new kinds of nanoscale materials and functionalities and provide pathways to control active functions from the nanoscale. At the same time, this effort will expand the capacity for computation and experimental techniques to capture time, energy and length-scales required to understand and control non-equilibrium systems. Three interconnected aims will guide MNM theme research:
- Emergence and control of cooperative phenomena in driven nanomaterials: Active phenomena, such as spontaneous self-organization and evolution in response to applied stimulus, may emerge in an ensemble of interacting entities upon continuous supply of and dissipation of energy. Here we focus on dynamics of metastable states comprising interacting entities of the order of few nm - from ensembles of atomic vacancies and molecules to domain walls, vortices and dislocations. Nanoscience has made great successes in understanding some of these entities in their frozen forms. We will seek new approaches to drive materials with electric, thermal and strain fields on the nanoscale, combined with visualization techniques that measure the coordinated motion, emergent structures and non-equilibrium phases. Ultimately we want to reveal unique properties of driven nanomaterials, such as increased non-linearities. Beyond fundamental significance, it is possible that already existing practical devices, such as single photon detectors and neuromorphic materials achieve their remarkable sensitivities and extreme non-linearities because of unique properties of the non-equilibrium state.
- Scalable modeling of metastability: Metastability plays a central role in non-equilibrium systems, both by providing states that a system can be driven to by external stimuli and in noisy environments, and crucially by allowing the system to escape from deep metastable minima that would otherwise constrain dynamic phenomena. Since the characteristic dimensions of such agents approach the atomic-scale, analysis of such entities and their dynamics generally requires consideration of length and timescales that are beyond the reach of atomistic modeling. We will seek scalable theoretical and computational methodologies that balance accuracy and scalability to predict material responses under a supply of energy. We plan to (1) develop multiscale modeling methodologies by combining neural network assisted molecular dynamics based on reactive force fields to identify key variables that dictate the dynamical-evolution of the system under non-equilibrium conditions and (2) build a generic phase field framework involving those variables, to capture long-time/length-scale specific dynamics. These modeling methodologies will be used to study field-driven dynamics of domain walls in classical ferroic and relaxor materials, binary and ternary ferro-ionic materials that show correlated vacancy/ion motion, and neuromorphic materials. In these cases, we are looking to establish the laws of motion governing individual building blocks as well as a range of emergent and non-linear behaviors that may arise from their collective interactions.
- Advancing new material functionalities through ‘learning’ and adaptive behavior: Most notably non-equilibrium responses enable functions to be encoded into adaptive materials in a self-consistent cycle of stimulus-response-refinement. Here, we will pursue the fundamental understanding of the material mechanisms that perform the adaptation using already known functional forms, such as resistive switching in binary and ternary oxides. At the same time, informed by aims 1 and 2, we will pursue expansion of the range of adaptive material systems. The unique setting of the nanoscale is not only the ability to peer into the functioning of the non-equilibrium systems, but to also provide energy density, energy gradients, and quench rates inaccessible at the macroscale. Therefore, nanoscience can reveal new kinds of states, dynamic material properties and derivative functionalities that may be unachievable on the macroscale.