Journal of the Korean Physical Society, Vol. 77, No. 10, November 2020, pp. 884∼887 Van Der Waals Force Mediated, Rotationally Aligned Dry-Transfer-Stacking of Two-Dimensional Tungsten Diselenide Debottam Daw and Riya Sebait Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Department of Energy Science, Sungkyunkwan University, Suwon 16419, Korea Chandan Biswas ∗ Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Suwon 16419, Korea. (Received 6 December 2019; revised 5 February 2020; accepted 19 February 2020) Rotationally aligned, two-dimensional (2D), transition-metal dichalcogenides (TMDs) exhibit unique electronic, optical, and optoelectronic properties compared to random stacking. Rotation- ally aligned graphene stacking was demonstrated previously for numerous exotic phenomena, such as superconductivity, resonant tunneling, and moir´ e pattern. However, rotationally aligned dry- transfer techniques of TMDs, have yet to be demonstrated. Here, we show a simple method of selective cutting of a few-layer tungsten diselenide (WSe2) flake and rotationally aligning it by us- ing dry-transfer stacking. The dry transfer techniques used for this study were adapted to maintain low sample contamination, a high-quality interface, a low number of defects. A combination of viscoelastic and thermoelastic materials was used for the TMD pickup and release to facilitate the rotationally aligned stacking. Aligned WSe2 stacks were characterized by Raman and photolumi- nescence spectroscopy to evaluate the integrity of the fabricated stack. This study highlights the possibility of using a rotationally aligned, artificial stacking method for exfoliated TMD materials for future electronic and optoelectronic applications. Keywords: Rotationally aligned stacking, 2D nanomaterial, Transition-metal dichalcogenides, Dry transfer, Photoluminescence, Raman spectroscopy DOI: 10.3938/jkps.77.884 I. INTRODUCTION Recent developments of transition-metal dichalco- genides (TMDs) highlight numerous unique electronic, optical, and optoelectronic properties due to strong car- rier interactions in two-dimensional (2D) space [1–7]. Two-dimensional (2D) graphene exhibits several attrac- tive properties such as superconductivity, resonant tun- neling, moir´ e excitons, and exciton condensation, de- pending on the twisted stacking angle between individual graphene layers [8–11]. Such exotic phenomena can be realized in angle-dependent TMD stacking while main- taining high interface quality, a low number of crys- tal defects, and a minimum amount of transfer-induced contaminations. Recent optoelectronic studies highlight strong interlayer coupling between rotationally aligned TMD monolayers grown by chemical vapor deposition (CVD) [12]. On the other hand, CVD-grown TMDs have a high number of crystal defects and a large amount of precursor contamination, which can result in severe * E-mail: chandan@skku.edu complications for sensitive device fabrication and ob- servations of the above-mention phenomena. Mechani- cally exfoliated flakes from high-quality chemical-vapor- transport (CVT) grown single crystals show a much lower defect density and improved electronic and opto- electronic performances compared to CVD-grown sam- ples. However, unlike CVD-grown flakes, the crystal axis of exfoliated CVT flakes can not be visualized geomet- rically to be used for rotational alignments. The only possible solution is the selective cutting and pickup of an exfoliated flake and its release on top of the unpicked flake area while maintaining the desired stacking angle. Here, we show a simple method of selective cutting of a few-layer tungsten diselenide (WSe 2 ) flake and rota- tionally aligned, dry-transfer stacking. Selective WSe 2 flake area cutting is based on the strong van der Waals interaction between hexagonal boron nitride (h-BN) and the WSe 2 layers. A polymethyl methacrylate (PMMA)- free, all dry transfer technique was adapted for this study so that low sample contamination, a high-quality interface and low number of defects could be main- tained. A combination of viscoelastic polydimethylsilox- pISSN:0374-4884/eISSN:1976-8524 -884- c 2020 The Korean Physical Society