Department of Materials Science and Engineering and ‡Department of Fiber and Polymer Science, North Carolina State University , Raleigh, North Carolina 27695, United States.
ACS Nano. 2014 Nov 25;8(11):11522-8. doi: 10.1021/nn5057673. Epub 2014 Nov 6.
The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2.
合成二维 MoS2 薄膜的转移对于基础研究和应用研究都非常重要。然而，由于生长机制和表面性质的不同，将适用于石墨烯的成熟转移工艺应用于 MoS2 会存在问题。在这里，我们展示了一种表面能辅助的工艺，可以完美地将厘米级的单层和少层 MoS2 薄膜从原始生长衬底转移到任意衬底上，没有观察到褶皱、裂纹和聚合物残留物。该工艺中使用的独特策略包括利用水在疏水性 MoS2 薄膜和亲水性生长衬底之间的渗透来将薄膜抬起，并在抬起后将薄膜干燥转移。这与之前合成 MoS2 薄膜的转移工艺形成鲜明对比，后者通过热碱溶液对生长衬底的刻蚀来抬起薄膜。我们的转移工艺可以有效地消除由气泡产生、化学蚀刻剂攻击以及之前转移工艺中在溶液外转移薄膜时的毛细力引起的机械力，这些是之前转移效果不理想的主要原因。我们的转移工艺还受益于使用聚苯乙烯 (PS) 作为载体聚合物，而不是之前广泛使用的聚甲基丙烯酸甲酯 (PMMA)。PS 可以与 MoS2 薄膜形成比 PMMA 更紧密的相互作用，对于在转移过程中保持薄膜的完整性非常重要。这种表面能辅助的方法可以广泛应用于其他二维材料的转移，例如 WS2。
