2D monolayers represent some of the most deformable inorganic materials, with bending stiffnesses approaching those of lipid bilayers. Achieving 2D heterostructures with similar properties would enable a new class of deformable devices orders of magnitude softer than conventional thin‐film electronics. Here, by systematically introducing low‐friction twisted or heterointerfaces, interfacial engineering is leveraged to tailor the bending stiffness of 2D heterostructures over several hundred percent. A bending model is developed and experimentally validated to predict and design the deformability of 2D heterostructures and how it evolves with the composition of the stack, the atomic arrangements at the interfaces, and the geometry of the structure. Notably, when each atomic layer is separated by heterointerfaces, the total bending stiffness reaches a theoretical minimum, equal to the sum of the constituent layers regardless of scale of deformation—lending the extreme deformability of 2D monolayers to device‐compatible multilayers.

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Due to their high in-plane stiffness and low flexural rigidity, twodimensional (2D) materials are excellent candidates for engineering threedimensional (3D) nanostructures using crumpling. An important new direction is to integrate 2D materials into crumpled heterostructures, which can have much more complex device geometries. Here, we demonstrate phototransistors from crumpled 2D heterostructures formed from graphene contacts to a monolayer transition-metal dichalcogenide (MoS 2 , WSe 2 ) channel and quantify the membrane morphology and optoelectronic performance. First, we examined the morphology of folds in the heterostructure and constituent monolayers under uniaxial compression. The 2D membranes relieve the stress by delaminating from the substrate and creating nearly periodic folds whose spacing depends on the membrane type. The matched mechanical stiffness of the constituting layers allows the 2D heterostructure to maintain a conformal interface through large deformations. Next, we examined the optoelectronic performance of a biaxially crumpled graphene−WSe 2 phototransistor. Photoluminescence (PL) spectroscopy shows that the optical band gap of WSe 2 shifts by less than 2 meV between flat and 15% biaxial crumpling, corresponding to a change in strain of less than 0.05%. The photoresponsivity scaled as P −0.38 and reached 20 A/W under an illumination power density of 4 μW/cm 2 at 20 V bias, a performance comparable to flat photosensors. Using photocurrent microscopy, we observe that the photoresponsivity increases by only 20% after crumpling. Both the PL and photoresponse confirm that crumpling and delamination prevent the buildup of compressive strain leading to highly deformed materials and devices with similar performance to their flat analogs. These results set a foundation for crumpled all-2D heterostructure devices and circuitry for flexible and stretchable electronic applications.

The low bending stiffness of atomic membranes from van der Waals ferroelectrics such as α-In2Se3 allow access to a regime of strong coupling between electrical polarization and mechanical deformation at extremely high strain gradients and nanoscale curvatures. Here, we investigate the atomic structure and polarization at bends in multilayer α-In2Se3 at high curvatures down to 0.3 nm utilizing atomic-resolution scanning transmission electron microscopy, density functional theory, and piezoelectric force microscopy. We find that bent α-In2Se3 produces two classes of structures: arcs, which form at bending angles below ∼33°, and kinks, which form above ∼33°. While arcs preserve the original polarization of the material, kinks contain ferroelectric domain walls that reverse the out-of-plane polarization. We show that these kinks stabilize ferroelectric domains that can be extremely small, down to 2 atoms or ∼4 Å wide at their narrowest point. Using DFT modeling and the theory of geometrically necessary disclinations, we derive conditions for the formation of kink-induced ferroelectric domain boundaries. Finally, we demonstrate direct control over the ferroelectric polarization using templated substrates to induce patterned micro- and nanoscale ferroelectric domains with alternating polarization. Our results describe the electromechanical coupling of α-In2Se3 at the highest limits of curvature and demonstrate a strategy for nanoscale ferroelectric domain patterning.

Resolving hierarchical structures in carbon nanotube (CNT) composites is crucial for their processing and performance optimization. We report here that self-consistent analyses of small- and ultrasmall-angle neutron scattering (SANS and USANS, respectively) patterns can be used to extract both the size and morphology of the hierarchical structures in carbon nanotube networks. In particular, this study investigates the correlation of structure and electrical conductivity of CNT-PEDOT:PSS (poly­(3,4-ethylene­dioxythiophene):poly­(styrene­sulfonate)) composite films where distinguishable dispersion states of nanotubes in the PEDOT:PSS matrix were achieved by varying the CNT concentration, duration of sonication, and addition of ethylene glycol (EG) to the predeposition solutions. It was concluded that five hierarchical levels of structure, spanning a few nanometers to tens of micrometers, exist in all samples. The results suggest a strong variation in the structure of the nanocomposites at larger length scales and, to a lesser extent, at smaller length scales with the variation in processing. Electrical conductivity of samples was largely affected by the morphological changes at larger scales. The EG addition affected the electrical conductivity by both increasing the matrix conductivity and improving CNT dispersion. The presented analysis is also useful for the characterization of structures in pure CNT and low CNT composite samples.