Freeform Electronic and Photonic Landscapes in Hexagonal Boron Nitride

Abstract

Atomically smooth hexagonal boron nitride (hBN) flakes have revolutionized two-dimensional (2D) optoelectronics. They provide the key substrate, encapsulant, and gate dielectric for 2D electronics while offering hyperbolic dispersion and quantum emission for photonics. The shape, thickness, and profile of these hBN flakes affect device functionality. However, researchers are restricted to simple, flat flakes, limiting next-generation devices. If arbitrary structures were possible, enhanced control over the flow of photons, electrons, and excitons could be exploited. Here, we demonstrate freeform hBN landscapes by combining thermal scanning-probe lithography and reactive-ion etching to produce previously unattainable flake structures with surprising fidelity. We fabricate photonic microelements (phase plates, grating couplers, and lenses) and show their straightforward integration, constructing a high-quality optical microcavity. We then decrease the length scale to introduce Fourier surfaces for electrons, creating sophisticated Moirépatterns for strain and bandstructure engineering. These capabilities generate opportunities for 2D polaritonics, twistronics, quantum materials, and deepultraviolet devices.

Generating smooth potential landscapes with thermal scanning-probe lithography

“…For some applications periodic structures are required [16][17][18], where the minimum periodicity can be described as two indents separated by their width, Λ min (d) = 2w (d), which is governed by the tip shape and pattern depth, plotted in figure 2(b). The plot is calculated for realistic experimental values of w 0 = 10 nm, θ = 22 • , w tm = 1 nm, and w c ranges from 0 to 20 nm during the patterning process.…”

“…Recent investigations have shown that these smooth topographical surfaces (patterned in a polymer layer) can be transferred to a variety of materials to produce potential landscapes to manipulate photons [16][17][18][19], surface-plasmon polaritons [16], electrons [17], excitons [20], and nanoparticles [21]. In this paper, 'potential landscape' is used as a general term to describe the influence of the surface topography on the band-structure, confinement, or trajectories of waves/particles such as photons, electrons, excitons, or nanoparticles.…”

WSe2 Light-Emitting Device Coupled to an h-BN Waveguide

“…For optically excited systems, this has been achieved by sandwiching monolayer transition metal dichalcogenides (TMDs) as active materials inside a free-standing microdisk made of Si 3 N 4 /hydrogen silsesquioxane (HSQ) . A similar approach was adopted for photonic devices entirely made of 2D materials, namely, by sandwiching TMDs between thick slabs of hexagonal boron nitride (h-BN). ,, The h-BN platform has evolved as an attractive candidate for on-chip photonics − for which, moreover, the monolithic integration of quantum emitters has been demonstrated . However, all of these structures rely on optical excitation with external lasers, which prevents full-scale integration.…”

An Inverse-Designed Nanophotonic Interface for Excitons in Atomically Thin Materials

“…Encapsulation protects the optically active medium from environmental effects that are most prominent at the exposed surface. Therefore, recent efforts have focused on creating nanophotonic devices by directly etching the encapsulating hBN, which serves a dual purpose: maintaining the excellent optical quality of the atomically thin semiconductor, and providing a resonant photonic structure. − …”