Figure 1a provides a schematic illustration of the design and assembly process for a 3D photodetector system. Briefly, the complete device results from sequential patterning of an epoxy-based negative photoresist (PR, SU-8), graphene, and MoS2 on an SiO2/Si wafer. Patterned encapsulation using SU-8 yields thick and thin regions designed specifically to aid in guiding the assembly process. Finally, a layer of photoresist (PR) serves to pattern the exposure of selected regions to ultraviolet (UV) ozone. After removing the SiO2 by immersion in an etchant, transfer printing with a flat slab of polydimethylsiloxane (PDMS) delivers the planar device assembly onto a film of polyvinyl alcohol (PVA) such that the topside can be exposed to UV ozone. Subsequent lamination onto a pre-stretched elastomeric substrate, pre-exposed to UV ozone, leads to strong bonding at the regions of SU-8 previously treated with UV ozone. Removing the PR layer leaves a slight physical separation between the device platform and the elastomeric substrate at corresponding regions. Releasing the substrate (Fig. 1a, right) initiates spontaneous assembly of the full 3D structure. The final architecture depends on the relevant design parameters, such as the degree of pre-stretch, the 2D geometry, and the thicknesses of the active and passive layers.Fig. 1Assembly and mechanical analysis of 3D photodetector structures from 2D materials. a Schematic illustration of processes for fabricating the 3D systems. b FEA results describing the formation of arrays of photodetectors based on graphene and MoS2 in the form of an octagonal prism, and corresponding colorized SEM images of the final configuration including MoS2 (green), graphene (light gray), and SU-8 (gray). c, d Similar FEA results for the cases of an octagonal prismoid and a hemisphere. Colors represent the magnitude of the maximum principal strain. e Central angle and radius of a cross-section of the hemisphere in d vs. the released pre-strain. Here, the insets denote an intermediate state (εreleased = 21.4%) and the final state (εreleased = 46%) of pre-strain release, with the dashed and solid lines representing the profiles from FEA and fitting arcs, respectively. f FEA results and analytic predictions of the height of three photodetector structures in b–d. g Computational study of tensile strain applied to the SU-8, graphene, and MoS2 layers vs. pre-strain during the 3D assembly (squares, circles, and triangles denote the octagonal frustum, hemisphere, and octagonal prism, respectively). h Experimentally measured variation in the resistance in graphene during repeated buckling processes