Innovative Tunable Optical Properties in Nanocrystal-based Films by Employing Mechanical Instabilities

Michigan State University, East Lansing MI

Investigators

Abstract

The future of technology for health monitoring, energy storage and use, and communications is moving towards flexible, bendable, and stretchable devices, including wearable devices and "electronic skins". To reach the maximum potential of these applications, there is a need to discover materials that exhibit exciting optical and electronic properties while remaining part of a mechanically flexible system. Nanocrystals present an ideal system to investigate for this purpose, as they have tunable electromagnetic absorption and emission properties, are easy and inexpensive to make, and can be integrated into thin films on stretchable substrates. Despite this, there have been few studies on the deformation behavior of these systems. This award supports research to create thin films of luminescent nanocrystals on deformable and flexible substrates, to measure their optical and mechanical properties, and to describe and predict the behavior of these films during flexion/stretching. The projected applications of these systems include forming optical metamaterials such as tunable gratings and filters, wearable sensors for body metrics, and flexible energy devices (e.g., light-emitting devices and solar photovoltaics). The research approach is to combine ideas across mechanical engineering, materials science, and nanotechnology to create a robust understanding of how layers of nanocrystals can be controllably deformed. This research will be used in year-round outreach events to inspire and educate future engineers including interactions with the general public and targeted events for underrepresented groups. Nanocrystals, used often in traditional rigid electronic devices, have the potential to withstand the strain of deformable device operation. Moreover, they can be made using environmentally friendly techniques and materials and exhibit exciting size-dependent properties such as luminescence. In addition, tunable wrinkling, due to instability formation, in thin films of nanocrystals on pre-stretched elastomeric substrates can be used to generate new electromagnetic and acoustic meta-materials. The problem is that the mechanical responses of nanocrystal films to stretching/flexion of the film substrate are almost completely unknown. This research will be devoted to experimentally and theoretically filling this knowledge gap. The research will include experimental studies on the mechanical behavior and instability formation in nanocrystal/substrate systems, depending on nanocrystal size and film porosity/thickness. These studies will be complemented by theoretical modeling of the mechanical properties of the systems to describe the instability formation. The research will then be integrated and used for predicting and designing the instabilities in nanocrystal films with ultimate application areas in stretchable electronics, sensors, and optical/acoustic metamaterials.