Transfer Of Two Dimensional Micro/nano-Structure And Its Preliminary Application

As the interface form of nanomaterials, the two-dimensional (2D) micro/nano-structure (including continuous thin films, isolated nano-arrays, etc) is one of the most important branches of nanomaterials, which has been paid extensive attention due to its scientific value and promising applications. In the fabrication of the 2D structure the substrate has played a crucial role. The fabrication substrate directly participates the formation of the structure, and determines its morphology and property sometimes. However, because of the requirement of the preparation on the physical and chemical properties of the substrate, the substrate has restricted the application range of the structure to some extent. It would be of great significance to develop a method to transfer the 2D structure from its as-grown substrate to an arbitrary surface, which could help the 2D structure break loose from the restrain of the substrate and expand its application range. It would become an effective extension of the current fabrication technology.Based on the above consideration, the dissertation has developed two kinds of 2D structure transfer methods. One is utilizing the soluble material as the carrier to transfer 2D inorganic micr/nano-structure, the other is transferring and superimposing organic thin film through the free-standing form.In the second chapter, the transfer method that utilizes poly(lactic acid) (PLA) as the carrier to transfer the inorganic structure from the as-grown substrate to an arbitrary surface has been developed. Briefly, the parent thin film was first covered by a drop-casted PLA layer and then the resulting hybrid film was peeled off from the as-grown substrate with tweezers. Afterwards, the resulting freestanding film is adhered onto the target surface with the aid of water. Finally, the polymer layer was removed by washing with solvent. Utilization of this method to transfer electrochemically deposited Au and Cu micr/nano-structures and chemically deposited silver mirror film has been investigated. The SEM results showed the morphologies of the micro/nano-structures kept intact after transfer and the contact angle tests showed their wetting properties kept constant after transfer, indicating the surface properties of the structures maintained. These data indicated that the transfer is feasible and successful. Based on the transfer method, a multilayer film using the silver mirror film as the modular block has been fabricated. Thanks to the special double-layer structure of the silver mirror film, the resulting multilayer film had a well-defined stratified architecture with alternate porous/compact layers. As a consequence of the distinct structure, the interaction between the adjacent layers was so weak that the multilayer film could be layer-by-layer stripped. The top layer in the film could provide an effective protection on the morphology and surface property of the underlying layers. These suggest that if the surface of the film was deteriorated, the top layer could be peeled off and the freshly exposed surface would still maintain the original function. The successful preparation of the layer-by-layer strippable silver multilayer demonstrates that the transfer method is an effective method to create novel and attractive micro/nano-structures, having great potential in the fabrication of nanodevices and coatings.In the third chapter, a 2D micro/nano-structures/macromolecular layer/substrate sandwiched architecture has been built up by using the transfer method. Briefly, after the structure/PLA hybrid layer was peeled off the as-grown substrate, the macromolecular layer was fabricated on the bottom of the 2D structure. Transfer of the resulting multilayer film onto the target surface could obtain the desired architecture. By this method, an adhesive poly(acrylic acid)/poly(ethylenimine) layer-by-layer film was inserted into an Au nanoarray and the substrate. After the insertion, the UV-Vis spectrum and the RIU of the LSPR signal of the Au nanoarray kept constant and the SEM observation confirmed the morphology of the array didn’t shown any change. All of these results suggested the insertion of the layer-by-layer film was successful. Meanwhile, the inserted adhesive layer could greatly improve the stability of the Au array on the surface. After ultrasonication for about 90 min, the UV-Vis absorbance of the pristine array remained only 32.6%, and the transferred one remained about 86.2%, about 2.6 time. In addition, the similar architecture and result has been obtained for the Ag nanohole array as well. These indicate that the insertion of the adhesive layer is a feasible and effective method to improve the stability of the 2D structure on the substrate.In the fourth chapter, the transfer method that uses the agarose gel as the transfer carrier has been studied. This method could avoid the organic solvent in the transfer process and transfer the micro/nano-structure into the narrow container. With this method the electrochemically deposited Au micr/nano-structure and silver mirror film has been transferred to the bottom of ELISA plates. The SEM observation showed that the transfer didn’t cause any remarkable damage on the structure morphology. In addition, the transferred Au film was employed in ELISA test. The results showed the signal of the plates with the Au film is about 90% higher than that of the plates without film, which indicates the potential of the transfer method in the biological detection.In the fifth chapter, a method to fabricate multilayer film by superimposing free-standing films has been developed. Briefly, the PLA free-standing film was prepared by using poly(vinyl alcohol) (PVA) as a sacrificial layer and the PLA film was layer-by-layer overlaid by transfer. The SEM observation showed that the multilayer film could fully cover the target surface and the morphology was basically smooth. The thickness of the multilayer film was in agreement with the expected value. All of these indicated that the multilayer fabrication was successful. Furthermore, the multilayer PLA film was employed to control the drug release. The experiments showed the transferred film was more efficient than the in-situ spin film. This may be attributed to the gap between the transferred free-standing films, which holds the released drug, retarding the release rate. The work to fabricate the multilayer by superimposing free-standing film provides a new approach to control drug release and has promising potential in the biological materials.The research of the dissertation indicates that the transfer method could help the 2D micro/nano-structure expand the application scope, improve the overall performance and create novel architectures having great potential as an effective operation strategy.