Quantum Energy Conversion in 2D Materials from Atomic to Wafer Scale

We present three examples of energy conversion processes imaged and manipulated in two-dimensional (2D) materials using ultrahigh-resolution scanning probe microscopy combined with atomic manipulation. These examples span length scales in which material structure is controlled from atomic up to wafer scales.<br/><br/>In recent experiments, we have been able to detect a special class of quantum-mechanical forces arising from non-local interactions mediated by a background particle field due to alterations in the zero-point energy. A famous member of this class is the Casimir effect, where the force is mediated by quantum fluctuations of the bosonic field of photons. In condensed matter, forces of this class can be mediated by a fermionic field. We show the detection and quantification of this force in real space, and demonstrate nanostructures in which 2D electrons can interact and exchange energy with a designer potential energy landscape to amplify this force.<br/><br/>To show that such quantum forces and energy conversion processes can be extended beyond the atomic and nanometer length scale, we present a study in which the underlying 2D electron system can be encapsulated with a monolayer of hexagonal boron nitride (hBN) using a new wafer-scale growth process. We show that the electronic states remain homogeneous in energy and spectral weight, and that the hBN overlayer acts as a protective yet remarkably transparent window on low-energy structure and quantum energy conversion processes below.<br/><br/>Finally, we present an ‘artificial atom’ concept via nanopatterning of monolayer molybdenum disulphide, demonstrating that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funneling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such 2D semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics.