WANG ET AL. VOL. 8 ’ NO. 7 ’ 7497–7505 ’ 2014 www.acsnano.org 7497 July 02, 2014 C 2014 American Chemical Society Van der Waals Epitaxy and Photoresponse of Hexagonal Tellurium Nanoplates on Flexible Mica Sheets Qisheng Wang, † Muhammad Safdar, † Kai Xu, Misbah Mirza, Zhenxing Wang, and Jun He * National Center for Nanoscience and Technology, Beijing 100190, China. † Q. Wang and M. Safdar contributed equally. V an der Waals epitaxy (vdWE) has recently been identified as a facile synthesis technique in the growth of ultrathin two-dimensional (2D) layered materials 1À3 and their vertical heterostruc- tures. 4,5 Unlike conventional heteroepitaxy, vdWE utilizes substrates whose surface is chemically inert because of the absence of surface dangling bonds such as fluoro- phlogopite mica. 6,7 In the vdWE growth, the overlayer and substrate are mainly con- nected by weak van der Waals interaction instead of strong chemical bonding. 8 There- fore, vdWE can circumvent strict require- ment of lattice matching, enabling the growth of defect-free overlayer with differ- ent crystalline symmetry to that of substrate. In addition, vdWE allows overlayer to be perfectly relaxed without excessive strain in the heterointerface. These superior prop- erties of vdWE make it a powerful technique to grow various 2D layered materials with highly single crystalline. As mentioned initi- ally, vdWE has been successfully applied to prepare layered topological insulator Bi 2 X 3 (X = Se or Te) nanoplates on mica, 7 graphene flakes on h-BN 9 or mica, 10 atomically thin IIIÀVI semiconductor flakes on mica 3,11 and transition-metal dichalcogenide nanoplates on graphene 12 or mica. 1,13 Meanwhile, some researchers have dedicated their efforts to the vdWE growth of nonlayered materials such as ZnSe quantum dots on GaSe, 14 ZnO nanowire arrays on graphene, 15 InAs nano- wires array on graphene 16 and GaAs nano- wires array on graphene. 17 Very recently, Q. Xiong et al. further conducted the incom- mensurate vdWE growth of vertically aligned ZnO nanowires array 18 and IIÀVI tripod nanocrystals 19 on mica. These works are a big breakthrough in the development of vdWE since they extend the utilization of vdWE to the growth of nonplanar/nonlamellar nanoarchitectures. However, the utilization and characteristics of vdWE on 2D nanoarch- itectures for many important nonlayered materials are still not very well documented. Furthermore, 2D nanoarchitectures are of great importance in fabricating electronic and optoelectronic device due to their com- patibility with traditional microfabrication techniques. A fundamental research of vdWE effects on the growth of planar/lamellar nanoarchitectures of nonlayered materials * Address correspondence to hej@nanoctr.cn. Received for review May 23, 2014 and accepted July 2, 2014. Published online 10.1021/nn5028104 ABSTRACT Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates- based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials. KEYWORDS: van der Waals epitaxy . 2D tellurium nanoplate . mica substrate . flexible device . photodetector ARTICLE