posted on 2024-01-03, 21:30authored byChristopher M. Smyth, John M. Cain, Alex Boehm, James A. Ohlhausen, Mila Nhu Lam, Xiaodong Yan, Stephanie E. Liu, Thomas T. Zeng, Vinod K. Sangwan, Mark C. Hersam, Stanley S. Chou, Taisuke Ohta, Tzu-Ming Lu
Inconsistent
interface control in devices based on two-dimensional
materials (2DMs) has limited technological maturation. Astounding
variability of 2D/three-dimensional (2D/3D) interface properties has
been reported, which has been exacerbated by the lack of direct investigations
of buried interfaces commonly found in devices. Herein, we demonstrate
a new process that enables the assembly and isolation of device-relevant
heterostructures for buried interface characterization. This is achieved
by implementing a water-soluble substrate (GeO2), which
enables deposition of many materials onto the 2DM and subsequent heterostructure
release by dissolving the GeO2 substrate. Here, we utilize
this novel approach to compare how the chemistry, doping, and strain
in monolayer MoS2 heterostructures fabricated by direct
deposition vary from those fabricated by transfer techniques to show
how interface properties differ with the heterostructure fabrication
method. Direct deposition of thick Ni and Ti films is found to react
with the monolayer MoS2. These interface reactions convert
50% of MoS2 into intermetallic species, which greatly exceeds
the 10% conversion reported previously and 0% observed in transfer-fabricated
heterostructures. We also measure notable differences in MoS2 carrier concentration depending on the heterostructure fabrication
method. Direct deposition of thick Au, Ni, and Al2O3 films onto MoS2 increases the hole concentration
by >1012 cm–2 compared to heterostructures
fabricated by transferring MoS2 onto these materials. Thus,
we demonstrate a universal method to fabricate 2D/3D heterostructures
and expose buried interfaces for direct characterization.