Three-Dimensional Metal Microprinting Based on Controlled Removal of Self-Assembled Monolayers

随着微机电系统（MEMS）、光学精密系统、微全分析系统等的发展，对微/纳米金属构件的高效制造提出了更高的要求。目前，3D金属打印主要通过基于热的工艺实现，例如选择性激光烧结（SLS），电子束熔化（EBM）和基于液态金属液滴的制造。这些基于热的技术涉及金属材料的熔化和凝固过程，这总是导致部件中的许多缺陷（粗晶、残余应力集中、微孔和裂纹的存在）。这些缺陷导致该构件的力学性能非常差，阻碍了其工业应用。此外，这些技术不能用于微金属部件的制造。该提案提出了基于自组装单分子层（SAMs）和电沉积的可控去除的三维（3D）金属微印刷的独特方法。迄今为止，阻碍电沉积在3D金属打印中应用的事实是无法对电沉积进行时间和位置选择性控制，这是该项目有望克服的问题。可以阻碍电沉积的绝缘自组装膜将被用作掩模。微弯月面或光束将被用于位置选择性地去除绝缘SAM并触发原位电沉积。在停止照射时，SAM将重新形成并终止金属沉积。主要目标是：（i）发展结合电化学系统和微弯月面操控系统的实验装置（2）揭示了利用弯月面和光在液体环境中选择性去除自组装膜的机理并建立了相应的技术;（3）揭示了利用弯月面去除自组装膜时金属离子在界面处的迁移机理;（iv）最终开发一种新型弯月面或光学控制的3D金属微印刷技术，该技术能够以前所未有的效率制造微型金属部件。与基于热的技术相比，所提出的技术是基于热少电沉积工艺，因此，预计将打印无缺陷的组件。通过本研究，将为最终发明一种具有巨大科学和工业应用价值的新型3D金属微打印技术奠定理论和技术基础。

The development of micro electromechanical systems (MEMS), optical precision systems, micro total analysis system and other similar systems increased the demand for the efficient manufacture of micro/nano metallic components. Currently, 3D metal printing is mainly achieved by thermal based processes, such as selective laser sintering (SLS), electron beam melting (EBM) and liquid metal droplet-based manufacturing. These thermal based techniques involve melt and solidification processes of metal material which always lead to lots of defects in the components (coarse grain, concentration of residual stress, existence of micro holes and cracks). Those defects result in very poor mechanical property of the component and hindered their industrial application. Furthermore, these techniques are incapable for fabrication of micro metal component. This proposal presents unique approaches for three-dimensional (3D) metal microprinting based on controlled removal of self-assembled monolayers (SAMs) and electrodeposition. The fact that has hindered the application of electrodepostion for 3D metal printing to date, is the incapacity of temporal and site-selectively control of the electrodeposition, a problem that is expected to be conquered by this project. Insulating SAMs, which can hinder the electrodepostion, will be used as the mask. Micro meniscus or light beam will be used to site-selectively remove the insulating SAM and trigger the in situ electrodepostion. Upon stop of illumination, the SAM will re-form and terminate the metal deposition. The key aims are to: (i) develop the experimental set up which combines the electrochemical system and micro meniscus manipulation system (or optical system); (ii) reveal the site-selective removal mechanism of SAMs in liquid environments by meniscus and light and establish the corresponding techniques; (iii) reveal the metal ions transfer mechanism at interface when meniscus is used for removing the SAMs; (iv) ultimately develop a novel meniscus or optical controlled 3D metal microprinting technique which is capable for fabrication of micro metal component at unprecedented efficiency. Compared to the thermal based techniques, the proposed technique is based on thermal less electrodeposition process, therefore, defect-free components are expected to be printed. By this research, theoretical and technical foundation will be laid for the ultimate invention of a new 3D metal microprinting technology with both huge scientific and industry applications.