X. Wang, K. Kang, S. Fu, K. Godin, S. Chen, E-H Yang
Stevens Institute of technology,
Keywords: tungsten disulfide, transfer, photoluminescence intensity
Summary:Chemical vapor deposition (CVD)-grown transition metal dichalcogenides (TMDs) have been widely studied for electronic and optoelectronics. These TMDs are often required to be transferred onto another substrate for device applications. The PMMA-based wet etching transfer is the most popular method to transfer TMDs. However, after transfer, PL intensity is heavily quenched due to water molecules trapped between the TMD and the substrate , substrate doping  or solvent/polymer used for transfer. Here, we evaluated the effects of solvents and polymers involved in the wet etching transfer on the PL property of WS2. We used CVD-grown WS2 sample and simulate the transfer process by applying each solvent and polymer to WS2 respectively. The PL mapping results showed there is no significant reduction of PL intensity of WS2 before and after acetone, IPA, DI water and PMMA treatment. We then studied the effect of KOH on the PL intensities by transferring WS2 onto PDMS substrate using the Cu-based transfer method . After 30% KOH solution treatment, the sample showed significant reduction of PL intensity compared to it before KOH treatment. We attribute that KOH molecules are adsorbed onto WS2, which can be removed through acid neutralization or high vacuum annealing.  J. O. Varghese, et. al., Advanced Materials, 27 (17), 2734 (2015).  Y. Yu, et. al.,Advanced Functional Materials, 26 (26), 473 (2016).  Z. Lin, et. al., Scientific reports, 5, 18596 (2015).