ABSTRACT
Memory to Light Emitters .........................................................................444 16.6 Liquid-Phase Exfoliation: A Cost-Eective Synthesis of 2D
Heterostructures .........................................................................................448 16.7 Concluding Remarks .................................................................................. 451 Acknowledgements ............................................................................................... 452 References ............................................................................................................... 452
Heterostructures have already played a crucial role in technology, giving us semiconductor lasers, light-emitting diodes and fast electronic switches [1]. However, thus far the choice of materials has been extended to those that can be grown (typically by molecular beam epitaxy) one on top of another, thus limiting the types of heterostructures that can be prepared. Instead, two-dimensional (2D) crystals, characterised by out-of-plane Van der Waals (VdW) interactions, can be easily combined in one stack with atomic precision, similar to ‘LEGO bricks’, oering unprecedented control on the properties and functionalities of the resulting heterostructures [2,3], Figure 16.1. Such heterostructures do not suer from lattice mismatch requirements because of the lack of out-of-plane covalent bonds. Interactions and transport between the layers allow one to go beyond simple incremental improvements in performance: the resulting three-dimensional (3D) structures can combine the conductivity of one 2D crystal, strength of another, chemical reactivity of the third, while the optical properties will be determined by the whole heterostructure. By carefully choosing and arranging the individual components, one can produce materials with tailored properties, determined by the design of the material itself. In addition to 2D crystals, alternative classes of nanostructures can also be incorporated into the heterostructure: from plasmonic nanostructures for improving optical absorption [4] to high quality organic crystalline lms, useful for a variety of electronic and opto-electronic applications [5]. One of the major advantages of this technology is given by its compatibility with so polymeric or plastic substrates: the 2D thickness allows for the maximum amount of mechanical exibility [6]. erefore, 2D crystalbased heterostructures are expected to produce a strong impact on future exible and transparent electronics.
