Recent scientific progress has isolated nanomaterials that are only 1 to 3 atomic layers thick, with semi- metallic (e.g. graphene), semiconducting (e.g. molybdenum disulphide) and insulating properties (e.g. boron nitride). Unlike well-known bulk materials such as silicon, these atomically thin materials have no dangling bonds, while possessing high electrical and thermal conductivity in the plane of the atomic layers, yet very low conductivity in the direction perpendicular to the atomic layers. In this project, the Stanford team (Pop, Goodson, Saraswat, Wong) will explore fundamental measurements guided by computer simulations, leveraging the unique anisotropic properties of atomically thin materials. The team will also focus on thermoelectric measurements, an area that has received less attention. Applications of this research could include energy-efficient electronics generating little heat, and flexible energy harvesters for wearable sensors and medical devices. Many of the benefits and insights generated from this work could also be applicable to conventional electronics, thus further improving the return on investment for the National Science Foundation, for society, and for education. The project will educate students from high school interns through undergraduate and graduate researchers, who will be exposed to a unique training program at the Stanford Design School. This program seeks to create ?T-shaped? engineers (with technical depth in nanotechnology and lateral ability to collaborate across disciplines). The societal impact of such a new workforce could be just as important as that of the novel nanoscience and nanotechnology enabled by the proposed research.
The technical goals of the research are organized into five tasks: (1) Modeling and simulation of atomically thin materials and devices, guiding their design and assembly. Computational exploration will support the electrical, thermal and thermoelectric experiments. (2) Large scale synthesis and integration of atomic layers into electronic and thermoelectric devices. Atomic layers will be assembled into heterogeneous stacks with controlled angular orientation. (3) Examine and improve electrical inter- faces to atomically thin materials, learning how to connect them to the outside world. The team will leverage doping, and both ?surface? and ?edge? contacts to minimize electrical contact resistance. (4) Thermal and thermoelectric characterization. The researchers will examine thermal interfaces and probe dynamic changes to thermal conductivity, particularly in the cross-plane direction of the atomic layers. These could enable applications like thermal diodes and thermoelectrics. (5) Enable energy- efficient devices and electronics through an approach that ties together the fundamental theory and experiments from Tasks #1-4. The team will examine the possibility of transistors and memory that leverage built-in thermoelectric effects to shift or manipulate hot spots, and that of layered thermoelectric modules for flexible substrates and mobile environments where natural heat sinking is restricted. A key part of the intellectual significance of this project is that it combines expertise from three disciplines: Electrical, Thermal/Mechanical and Materials Engineering. The team leaders have experience collaborating and co-advising students in a multi-disciplinary environment; they will also build on a strong track record of mentoring women and underrepresented minorities (who have gone on to positions in academia and industry) and a strong record of online teaching and learning, including lectures and simulation codes posted on the NSF-sponsored nanoHUB.org. The Stanford environment is uniquely suited for translating fundamental scientific advances to long-term industrial partnerships, and the team will also partner with the Air Force Research Labs for thermoelectric measurements, with Sandia National Labs for atomically thin contacts, and internationally with IMEC (Belgium) and University of Tokyo for material synthesis and experimental approaches for materials integration.
