Figure 1 (a) Peeled-off wall paint (left) and detached films in vacuum chamber (right). (b) Schematic illustration of 2D materials production by ion intercalation-based exfoliation (top) and microstructure production by liquid intercalation (down). (c) SEM image of an array of microtubes on glass substrate. (d) Optical images of different microstructures. (e) Proposed sketch for smart catalytic microtubular engines and SEM image of micromotors with two tubes (inset).

In our daily life, it’s common that wall paint tends to be peeled off from cracks when staying in humid environment for a long time, as a result of the reduced adhesion between paint film and the wall (Figure a-i). A similar phenomenon occurs in the laboratory where bended films are found on the aluminum foil of the vacuum chamber during physical vapor evaporation (Figure a-ii). This relationship between macro and micro world inspires us that nanomembrane delamination can be realized using a completely new method without wet or dry etching of under-layer, which may bring about unexpected destruction and reaction.

Ion intercalation-based exfoliation is utilized as an efficient top-down technique for fabricating 2D materials (the top panel of Figure b). Ions are intercalated between the layers in a liquid environment, which swell the layer spacing and weaken the interlayer adhesion, thus reducing the energy barrier to exfoliation. By replacing ions with liquid, the scope of this exfoliation technique can be extended to the delamination of deposited thin solid films.

 This solid films with internal strain gradient are deposited including a pre-layer to create van der Waals interaction with foreign substrate via vacuum deposition technologies. With a liquid droplet (e.g. water) on the surface, liquid intercalates between pre-layer (i.e. nanomembranes after delamination) and substrate, overcoming the energy barrier of delamination (the down panel of Figure b). Consequently, rolling behavior of patterned nanomembranes is triggered once liquid contacted the periphery of nanomembranes, allowing hundreds of microtubes with the same diameter to be fabricated at one time (Figure c). Furthermore, various substrate and material combination are studied making this rolled-up nanotechnology versatile.

 With this spontaneous delamination, the rolling direction is precisely controlled by choosing the contact point between microdroplet and nanomembrane, which is difficult to be realized using conventional micro and nanofabrication methods as the delamination is established with the etching of underlayer. For instance, a parallelogram-shaped nanomembrane is transformed into microtubes or microhelices with different pitches (Figure d). Moreover, a guidance for structure design is given by quasi-static FEM simulation, which provides a visualized model of resultant microstructures.

Through further combination with pattern design, advanced rolling microstructures with desired materials are proposed and fabricated for a wide range of applications. For example, complicated micromotors containing two microtubes are constructed via improved fabrication method (Figure e). Utilizing this versatile strategy for intelligent construction of rolling microstructures, more progressive micromotors can be achieved in the future. This highly integrative microsystem consists of a catalytic power engine, integrated circuit (IC) controller, a battery of powering the IC, an antenna for communication, a sensor to detect the environment and a component to fulfill a mission. Such an engineered smart microtubular twin jet is expected to meet several parallel requirements for a powerful and intelligent micromotor.

For more information of our research interest, please visit the group website: http://nanomem.fudan.edu.cn/

For more details, please see our article:

Xu, B., Zhang, X., Tian, Z. et al. Microdroplet-guided intercalation and deterministic delamination towards intelligent rolling origami. Nat Commun 10, 5019 (2019)