which is located in the near-infrared and visible region. [9] Bandgaps in TMDCs are tunable by applying external electric field or mechanical strain. Combined with broad-band optical absorption and mechanical flexibility, TMDCs are one of appealing materials for the application in optoelectronic devices such as field effect transistors, photodetectors, and light-emitting diodes. Photodetectors based on molybdenum disulfide (MoS 2 ), [1,3] tungsten disulfide (WS 2 ), [10,11] molybdenum diselenide (MoSe 2 ), [7,8] and their heterojunctions [12] were constructed and exhibited photoresponsivity ranging from a few mA W −1 to several hundred A W −1 , which is related to the materials selected, layer numbers, and device contacts. Intrinsically, the photoresponsivity is restricted by their absorption cross section and present lower values because of small thickness of TMDCs. [9] Integration of TMDC materials into photonic structures such as photonic crystals and microcavities offers a solution to enhance the photoresponsivity. [13][14][15] For example, Fano-resonant photonic crystals could significantly boost light absorption in monolayer MoS 2 and the absorption can reach up to 90% at the resonant wavelength. [13] Another typical approach to enhancing photoresponsivity is to hybridize TMDCs with plasmonic structures. A MoS 2 photodetector hybridized with Ag nanowire network was demonstrated and presented greatly enhanced photocurrent over the pristine MoS 2 photodetectors because of surface plasmon coupling. [5] However, the photoresponsivity can be only enhanced at designed and selected wavelength in these hybrid photodetectors mentioned above. It is promising that 3D mesostructures could enhance light absorption over wide range due to its circular geometry and thus improve photoelectric performance. [16][17][18][19] Rolled-up inorganic nanomembrane-based 3D architectures, [20][21][22] such as nanoscrolls and nanosprings, have great potential in applications of supercapacitors, [23] optical microcavity, [24][25][26] actuators, [27,28] resistive random access memory, [29] motors, [30] etc., because of their distinct properties arising from 3D geometry. In this work, a 3D tubular photodetector is proposed to increase the photoresponsivity of 2D materials benefiting from the significantly enhanced light absorption. We introduce this tubular microstructure into the MoSe 2based photodetector for improved detection performance. 3D photodetector based on rolled-up MoSe 2 nanomembrane was Transition metal dichalcogenides, as a kind of 2D material, are suitable for near-infrared to visible photodetection owing to the bandgaps ranging from 1.0 to 2.0 eV. However, limited light absorption restricts photoresponsivity due to the ultrathin thickness of 2D materials. 3D tubular structures offer a solution to solve the problem because of the light trapping effect which can enhance optical absorption. In this work, thanks to mechanical flexibility of 2D materials, self-rolled-up technology is applied to build up a 3D tubular structure ...

Two additional structural forms, free-standing nanomembranes and microtubes, are reported and added to the vanadium dioxide (VO) material family. Free-standing VO nanomembranes were fabricated by precisely thinning as-grown VO thin films and etching away the sacrificial layer underneath. VO microtubes with a range of controllable diameters were rolled-up from the VO nanomembranes. When a VO nanomembrane is rolled-up into a microtubular structure, a significant compressive strain is generated and accommodated therein, which decreases the phase transition temperature of the VO material. The magnitude of the compressive strain is determined by the curvature of the VO microtube, which can be rationally and accurately designed by controlling the tube diameter during the rolling-up fabrication process. The VO microtube rolling-up process presents a novel way to controllably tune the phase transition temperature of VO materials over a wide range toward practical applications. Furthermore, the rolling-up process is reversible. A VO microtube can be transformed back into a nanomembrane by introducing an external strain. Because of its tunable phase transition temperature and reversible shape transformation, the VO nanomembrane-microtube structure is promising for device applications. As an example application, a tubular microactuator device with low driving energy but large displacement is demonstrated at various triggering temperatures.

Nanocrystalline diamond nanomembranes with thinning-reduced flexural rigidities can be shaped into various 3D mesostructures, such as tubes, jagged ribbons, nested tubes, helices, and nested rings. Microscale helical diamond architectures are formed by controlled debonding in agreement with finite-element simulation results. Rolled-up diamond tubular microcavities exhibit pronounced defect-related photoluminescence with whispering-gallery-mode resonance.

Palladium nanomembranes roll into microscale actuators and their active array responses upon hydrogen stimuli within seconds.

Robots with submillimeter dimensions are of interest for applications that range from tools for minimally invasive surgical procedures in clinical medicine to vehicles for manipulating cells/tissues in biology research. The limited classes of structures and materials that can be used in such robots, however, create challenges in achieving desired performance parameters and modes of operation. Here, we introduce approaches in manufacturing and actuation that address these constraints to enable untethered, terrestrial robots with complex, three-dimensional (3D) geometries and heterogeneous material construction. The manufacturing procedure exploits controlled mechanical buckling to create 3D multimaterial structures in layouts that range from arrays of filaments and origami constructs to biomimetic configurations and others. A balance of forces associated with a one-way shape memory alloy and the elastic resilience of an encapsulating shell provides the basis for reversible deformations of these structures. Modes of locomotion and manipulation span from bending, twisting, and expansion upon global heating to linear/curvilinear crawling, walking, turning, and jumping upon laser-induced local thermal actuation. Photonic structures such as retroreflectors and colorimetric sensing materials support simple forms of wireless monitoring and localization. These collective advances in materials, manufacturing, actuation, and sensing add to a growing body of capabilities in this emerging field of technology.

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Future advances in materials will be aided by improved dimensional control in fabrication of 3D hierarchical structures. Self-rolling technology provides additional degrees of freedom in 3D design by enabling an arbitrary rolling direction with controllable curvature. Here, we demonstrate that deterministic helical structures with variable rolling directions can be formed through releasing a strained nanomembrane patterned in a "utility knife" shape. The asymmetry of the membrane shape provides anisotropic driving force generated by the disparity between the etching rates along different sides in this asymmetric shape. A transient finite element method (FEM) model of diagonal rolling is established to analyze the relationships among geometries, elastic properties, and boundary conditions. On the basis of this model, a diamond-based helical framework consisting of two or three helical segments has been fabricated to mimic the shapes of natural plants. Further experiment has been done to extend this approach to other materials and material combinations, such as MoSe/Cr, Cr/Pt, and VO. To demonstrate the possible application accessible by our technology to new fields, VO-based helical microscale actuation has been demonstrated with photocontrollable bending in a selected region, as well as morphable and recognizable helix. This study offers a new way to construct helical mesostructures that combine special properties of the advanced materials, thus possess novel features and potential applications.

Motile plant structures such as Mimosa pudica leaves, Impatiens glandulifera seedpods, and Dionaea muscipula leaves exhibit fast nastic movements in a few seconds or less. This motion is stimuli-independent mechanical movement following theorema egregium rules. Artificial analogs of tropistic motion in plants are exemplified by shape-morphing systems, which are characterized by high functional robustness and resilience for creating 3D structures. However, all shape-morphing systems developed so far rely exclusively on continuous external stimuli and result in slow response. Here, we report a Gaussian-preserved shape-morphing system to realize ultrafast shape morphing and non-volatile reconfiguration. Relying on the Gaussian-preserved rules, the transformation can be triggered by mechanical or thermal stimuli within a microsecond. Moreover, as localized energy minima are encountered during shape morphing, non-volatile configuration is preserved by geometrically enhanced rigidity. Using this system, we demonstrate a suite of electronic devices that are reconfigurable, and therefore, expand functional diversification.