Sub-10 nm Graphene Nanomeshes Fabricated via … NNT 2016.docx · Web viewshows the AFM-acquired...
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NNT 2016 Nanoimprint-Assisted Shear Exfoliation + Transfer Printing (NASE+TP) for Producing Emerging Transition Metal Dichalcogenide Heterostructures Xiaogan Liang *, Da Li, and Sungjin Wi Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109, USA Emerging layered transition metal dichalcogenides (TMDCs, e.g., WSe 2 and MoS 2 ) are attractive materials for making new optoelectronic and nanoelectronic devices due to their superior electronic, photonic, and mechanical properties. [1-2] In addition, TMDCs have high-quality 2D surfaces with extremely low densities of defects and dangling bonds. Therefore, heterostructures with high-quality interfaces free of charge traps can be made through the direct stacking of different TMDC layers. This simple stacking process does not need exquisite epitaxial growth tools (e.g., molecular beam epitaxy (MBE)) and is potentially compatible with cost-effective roll-to-roll manufacturing processes. The produced vertically stacked TMDC heterostructures can be exploited for modulating the electronic band structures of various nanoelectronic and optoelectronic devices. One of the important applications is the generation of built-in potentials in TMDC-based photoresponse devices for facilitating the separation of photo-generated excitons and resulting in high photo-responsivity. [3] However, we still lack a top-down nanofabrication approach capable of producing arrays of such attractive TMDC heterostructures. We present an upscalable nanoimprint/nanoprint-based technique capable of producing uniform multilayer TMDC heterostructure arrays into device sites. Specifically, using this technique, we have demonstrated the fabrication of uniform multilayer WSe 2 /MoS 2 heterostructure arrays. These heterostructures can be used for making photo-response devices. Fig. 1 illustrates the presented nanofabrication technique, which involves two critical sub-processes. Firstly, our previously developed nanoimprint-assisted shear exfoliation (NASE) technique is used to exfoliate prepatterned TMDC features with uniform thicknesses from a bulk TMDC stamp onto a PDMS 1 * Email: [email protected]
Transcript of Sub-10 nm Graphene Nanomeshes Fabricated via … NNT 2016.docx · Web viewshows the AFM-acquired...
NNT 2016
Nanoimprint-Assisted Shear Exfoliation + Transfer Printing (NASE+TP) for Producing Emerging Transition Metal Dichalcogenide Heterostructures
Xiaogan Liang*, Da Li, and Sungjin WiMechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109, USA
Emerging layered transition metal dichalcogenides (TMDCs, e.g., WSe2 and MoS2) are attractive materials for making new optoelectronic and nanoelectronic devices due to their superior electronic, photonic, and mechanical properties.[1-2] In addition, TMDCs have high-quality 2D surfaces with extremely low densities of defects and dangling bonds. Therefore, heterostructures with high-quality interfaces free of charge traps can be made through the direct stacking of different TMDC layers. This simple stacking process does not need exquisite epitaxial growth tools (e.g., molecular beam epitaxy (MBE)) and is potentially compatible with cost-effective roll-to-roll manufacturing processes. The produced vertically stacked TMDC heterostructures can be exploited for modulating the electronic band structures of various nanoelectronic and optoelectronic devices. One of the important applications is the generation of built-in potentials in TMDC-based photoresponse devices for facilitating the separation of photo-generated excitons and resulting in high photo-responsivity.[3] However, we still lack a top-down nanofabrication approach capable of producing arrays of such attractive TMDC heterostructures.
We present an upscalable nanoimprint/nanoprint-based technique capable of producing uniform multilayer TMDC heterostructure arrays into device sites. Specifically, using this technique, we have demonstrated the fabrication of uniform multilayer WSe2/MoS2
heterostructure arrays. These heterostructures can be used for making photo-response devices. Fig. 1 illustrates the presented nanofabrication technique, which involves two critical sub-
processes. Firstly, our previously developed nanoimprint-assisted shear exfoliation (NASE) technique is used to exfoliate prepatterned TMDC features with uniform thicknesses from a bulk TMDC stamp onto a PDMS transfer stamp (Steps 1-4).[4] These TMDC features on the PDMS stamp are subsequently transferred into the ordered device sites on the target substrate (Steps 5, 6) through a transfer-printing (TP) process. During the TP process, prepatterned metal contacts or already-printed TMDC layers can serve as effective adhesion layers for immobilizing as-printed TMDC flakes. The repetitive operation of this NASE+TP process for printing different TMDC materials can generate vertically stacked TMDC heterostructure arrays. Fig. 2 displays the optical micrographs (OMs) of (a) uniform WSe2 mesa arrays exfoliated from a bulk WSe2
stamp onto a PDMS transfer stamp, (b) the same WSe2 mesa arrays transfer-printed onto prepatterned Au contacts on a SiO2 substrate, and (c) MoS2 mesa arrays subsequently transfer-printed on top of WSe2 structures, forming uniform vertically-stacked multilayer WSe2/MoS2
heterostructure arrays. Fig. 3 shows the AFM-acquired thickness data measured from (a) WSe2
mesa arrays (the 1st layer) and (b) WSe2/MoS2 heterostructure arrays (total thicknesses for two layers). The relative standard deviation of the total thickness data measured from WSe2/MoS2
heterostructure flakes is estimated to be ~7%, which is much smaller than those of multilayer structures produced by previously reported exfoliation methods.[5] The final presentation will also include the characterization of WSe2/MoS2 photoresponse devices.
This work advanced the critical nanofabrication technology to leverage the superior electronic and structural properties of TMDCs for practical device applications.[1] G. Eda and S. A. Maier, ACS Nano, 7, 5660-5665 (2013)[2] L. Britnell, R. M. Ribeiro, A Eckmann and A. H. C. Neto, Science, 340, 1311-1314 (2013) [3] M. Furchi, A. Pospischil, F. Libisch, J. Burgdörfer, and T. Mueller, Nano Lett. 14, 4785-4791 (2014)
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* Email: [email protected]
NNT 2016
[4] M. Chen, H. Nam, H. Rokni, K. Kurabayashi, W. Lu and X. liang, ACS Nano, 9, 8773 (2015)[5] X. Liang, Z. Fu, and S. Chou, Nano Lett. 7, 3774-3780 (2007)
Fig. 1 Schematic steps for printing uniform multilayer TMDC arrays into device sites on the substrate: The whole process consists of two critical sub-processes – Steps (1)-(4): nanoimprint-assisted shear exfoliation (NASE) of pre-patterned TMDC mesas from a bulk TMDC stamp onto a PDMS transfer stamp; Steps (5) to (6): transfer-printing of TMDC mesas from the PDMS stamp onto the device sites on the final substrate. The repetitive application of this process for printing different TMDC flakes can generate vertically stacked TMDC heterostructures.
Fig. 2 Optical micrographs of (a) NASE-produced WSe2 mesa arrays on a PDMS transfer stamp, (b) WSe2 mesa arrays transfer-printed onto the prepatterned Au contacts on the final device substrate, and (c) MoS2 mesas subsequently printed on top of WSe2 mesas, resulting in vertically stacked WSe2/MoS2 heterostructure arrays.
Fig. 3 AFM-acquired thickness data measured from (a) WSe2 mesa arrays and (b) WSe2/MoS2
heterostructure arrays (total thicknesses for two layers). The relative standard deviation of the total thickness data measured from WSe2/MoS2 heterostructure flakes is estimated to be ~7%.
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* Email: [email protected]
(a) (b) (c)
