Progress on the growth of two-dimensional single crystals on insulating substrates
Two-dimensional(2D)materials,characterized by their atomic thickness and exceptional electrical,optical,magnetic,and thermal properties,hold great promise for applications in electronics,optoelectronics,and energy.As silicon-based transistors approach their theoretical physical limits,the continuation of Moore's law faces significant challenges.It is expected that 2D materials will surpass silicon-based materials to enable the development of a new generation of electronic devices.The key to achieving their high performance and large-scale applications lies in the controllable preparation of large-sized single-crystal 2D films.Over the past decade,substantial progress has been made in growing single crystal 2D materials such as graphene(a typical 2D conductor),semiconductor transition metal chalcogenides(TMD),and insulators like hexagonal boron nitride(hBN).These materials have expanded from micron-level sizes to wafer scales.However,for optimal performance,it is generally necessary to layer 2D material films on insulating substrates.Therefore,the ultimate goal is direct growth of single-crystal 2D materials on insulating substrates.Due to the inherent properties of insulating substrates,such as their catalytic inertness towards precursor decomposition and the high energy barrier for reactive substances like carbon and boron nitride,growing 2D materials,especially graphene and hBN,on insulating substrates presents unique challenges.In contrast to metal substrates,the coupling interaction between 2D materials and insulating substrates is notably weak.As a result,obtained graphene and hBN films often exhibit significant defects and limited crystal quality,which negatively impact the physical integrity and electrical performance of devices based on these 2D materials.Consequently,achieving orientation control of 2D domains on insulating substrates proves exceptionally challenging.In this review,we first discussed the growth behavior of 2D materials on different substrates,including both catalytic and non-catalytic substrates.Subsequently,we reviewed the progress on the direct growth of 2D materials on insulating substrates,and we focused on the advancements made in producing representative 2D single crystals,including TMD,graphene and hBN.In detail,we reviewed the progress in the preparation of TMD single crystals on insulating substrates,including the synthesis discussion of atomic step control and seed crystal-assisted growth.We also discussed the advancements in the preparation of graphene single crystals on insulating substrates,such as the high-temperature growth of graphene using electromagnetic induction heating and the growth of graphene through multi-cycle plasma etching-assisted-chemical vapor deposition.Besides,we primarily discussed the scalability of atomic stamping techniques in the preparation of large-area hBN single crystals.These techniques have proven to be effective in producing high-quality 2D single crystals on specific insulating substrates.Finally,we discussed existing challenges and future perspectives regarding the direct growth of high-quality 2D materials on insulating substrates and looked forward to future research on the direct growth on semiconductor devices at low-temperatures,the growth of layer-,stacking-,and twist-controlled 2D single crystals and their heterostructures.In conclusion,the direct growth of 2D single crystals on insulating substrates is a rapidly evolving field with significant potential for future technological advancements.We hope this review can propel in-depth comprehension of the direct growth of 2D single crystals on insulators.
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