Lithographically Patterned Functional Polymer–Graphene Hybrids for Nanoscale Electronics

Abstract

Two-dimensional (2D) materials are believed to hold significant promise in nanoscale optoelectronics. While significant progress has been made in this field over the past decade, the ability to control charge carrier density with high spatial precision remains an outstanding challenge in 2D devices. We present an approach that simultaneously addresses the dual issues of charge-carrier doping and spatial precision based on a functional lithographic resist that employs methacrylate polymers containing zwitterionic sulfobetaine pendent groups for noncovalent surface doping of 2D materials. We demonstrate scalable approaches for patterning these polymer films via electron-beam lithography, achieving precise spatial control over carrier doping for fabrication of high-quality, all-2D, lateral p-n junctions in graphene. Our approach preserves all of the desirable structural and electronic properties of graphene while exclusively modifying its surface potential. The functional polymer resist platform and concept offers a facile route toward lithographic doping of graphene- and other 2D material-based optoelectronic devices.

Electronic Tuning of Monolayer Graphene with Polymeric “Zwitterists”

“…First-principles DFT calculations were performed to gain microscopic insights into graphene/zwitterion interactions. As in our prior work, 30 the DFT calculations employed the key components of the system, namely, the zwitterionic moiety and a graphene sheet supported on a Cu(111) slab (Gr/Cu slab). The two limiting cases of zwitterion adsorption configurations, flat and standing, are illustrated in Figure 3b,c.…”

“…, is statistically less likely to be observed (Figure )). For the flat configuration, only a small component of the zwitterion dipole moment is normal to the Gr/Cu slab, resulting in a smaller Δϕ DFT (lower bound). The standing configuration, in contrast, displays the largest possible μ ⊥ and thus the largest Δϕ DFT (upper bound).…”

“…Our recent work on hard–soft interfaces involving copolymers of SBMA and methyl methacrylate (MMA) produced positive-tone electron beam resists on graphene/SiO 2 /Si with an observed shift in the charge neutrality point attributed to a localized, noncovalent surface doping . In explaining these findings, density functional theory (DFT) calculations pointed to a zwitterion orientation that produced a net dipole moment of 4.7 D normal to graphene.…”

“…27−29 Our recent work on hard−soft interfaces involving copolymers of SBMA and methyl methacrylate (MMA) produced positive-tone electron beam resists on graphene/ SiO 2 /Si with an observed shift in the charge neutrality point attributed to a localized, noncovalent surface doping. 30 In explaining these findings, density functional theory (DFT) calculations pointed to a zwitterion orientation that produced a net dipole moment of 4.7 D normal to graphene. These results prompted us to examine how zwitterion chemical structure impacts the electronic properties of the contacting graphene, as described here via a combination of synthesis, computation, and electronic characterization.…”

Scalable first-principles-informed quantum transport theory in two-dimensional materials

“…Electron scattering due to imperfections, dopants/impurities, and phonons determine the carrier dynamics in 2D materials. Carrier transport properties can also be engineered by creating potential patterns and quantum confinements, such as through the application of local potentials via STM/AFM tips [10,11], surface functionalization by organic molecules [12][13][14], or through spatial confinement in lateral heterostructures [15]. Density-functional theory (DFT) [16] provides a parameter-free method for electronic structure calculations and the accurate determination of atomistic potentials associated with heterointerfaces, defects, and impurities.…”