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Nano-Curved Smart Curled Origami

Edit: Ccdanni 2020-03-17 Mobile

  The three-dimensional micro-nano structures of various functional materials have important applications in the fields of micro-nano electromechanical systems, micro robots, metamaterials and other fields. In various methods for preparing three-dimensional micro / nano structures, the origami technique using the curling behavior can easily convert the designed planar film into three-dimensional micro / nano structures. The resulting micro-nanotubes or spring structures have shown their unique application potential in the fields of optics, electricity and biomedicine. Therefore, how to prepare a curly three-dimensional micro-nano structure with controllable structure according to our needs has become the most important point for further application and exploration. At present, researchers have developed various ways to achieve the directional peeling and curling of films, including designing asymmetric material systems, stress structures, and planar patterns. However, these methods have more or less restrictions on materials and shapes, and it is difficult to achieve precise control of the curling behavior.

  Recently, Professor Mei Yongfeng from the Department of Materials Science of Fudan University and others published an article entitled "Microdroplet-guided intercalation and deterministic delamination towards intelligent rolling origami" in Nature Communications. A simple method for preparing the three-dimensional micro-nano structure of the coil, and confirmed the extensive material compatibility, large-scale preparation ability and precise control of the coiling behavior of this method.

  Figure 1 (a) Peeled off wallpaper (left) and the desorbed film in the vacuum cavity (right); (b) Preparation of micro-nano structures based on ion intercalation to strip two-dimensional materials (top) and liquid intercalation (bottom) Schematic diagram of the process; (c) SEM image of a coiled tubular micro / nano structure array on a glass substrate; (d) Optical micrograph of a three-dimensional micro / nano structure with different coils; (e) A smart dual-tube catalytic micro / nano motor, schematic illustration SEM image of a dual tube micro / nano motor.

  In daily life, we often find that those wallpapers that have been in a humid environment for a long time are prone to crack and peel off from the wall, which is caused by the weakened adhesion between the wallpaper and the wall (Figure 1a-i) . A similar phenomenon exists in the laboratory. We often find that curved films appear on the aluminum foil of the vacuum cavity during the physical vapor deposition process (Figure 1a-ii). From this connection between the macro world and the micro world, we think of a new way to achieve the peeling of nano-films and avoid unpredictable physical damage and chemical reactions during the dry or wet etching of the underlying sacrificial layer. .

  In recent years, people have used ion-exfoliation-based stripping as a top-down technique to prepare two-dimensional materials (Figure 1b, top). In a liquid environment, ions are inserted from layer to layer, which increases the distance between layers and weakens the adhesion between layers, thereby reducing the energy barrier required for peeling. If droplets are used instead of ions, this stripping technique can be further applied to the deposited solid film.

  First, we used a vacuum deposition technique to deposit a solid film system with an internal strain gradient on the substrate. In order to reduce the adhesion between the nano-film and the substrate, we designed a pre-deposited layer as the first layer to form a film with the substrate. Vals combined. After the deposition is completed, a drop of liquid (such as water) is directly added to the surface to complete the preparation process. The liquid is interposed between the pre-deposited layer and the substrate during the diffusion process, thereby overcoming the energy barrier of film peeling to achieve spontaneous peeling and curling of the film (Figure 1b below). Therefore, once the droplet contacts the boundary of the patterned nanofilm, the self-curling behavior of the film can be triggered, and a large-scale array of three-dimensional tubular micro-nano structures with the same size can be prepared at the same time (Figure 1c). In addition, we have proven the universality of this self-coiling technology by studying various combinations of substrates and pre-deposited layer materials.

  Secondly, with the above-mentioned spontaneous peeling method, we can further control the self-curling direction of the film by further selecting the contact points of the micro-droplets and the nano-film. For example, a three-dimensional micro-nano structure of springs with different tube and pitches can be prepared from nano-films of parallelograms (Figure 1d). In contrast, in the traditional micro / nano processing method, thin film peeling is based on the etching of the sacrificial underlying layer, and it is difficult to achieve such precise control. Similarly, we also provide a reliable visual expectation model for structural design through a quasi-static finite element analysis model.

  By further combining with graphic design, we propose and prepare finer self-curling micro / nano structures with a wider range of applications. For example, we used a modified fabrication method to build a micro-nano motor with a complex double-tube structure (Figure 1e). Using this technology to intelligently build a self-curling micro / nano structure, a micro / nano motor with a more complex structure and more advanced functions can be obtained in the future. Such a highly integrated microsystem consists of a catalytic drive motor, an integrated circuit controller, a battery for powering the integrated circuit, a communication antenna, sensors for environmental detection, and functional components. This engineered dual-tube microstructure is expected to meet the requirements of an efficient and intelligent micro / nano motor.

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