Fabrication and Physical Characteristic Research on Biomimetic Micro/Nano Interfacial Structure

本論文發展以仿生出發的微奈米介面結構之製程與相關物理現象研究，隨著科技的發展，仿生科技逐漸被大家所重視，自然界微奈米結構的發現被廣泛的模仿與應用在科學與工程領域上，例如：模仿蜘蛛絲的人造纖維、蝴蝶翅膀光子晶體結構、水母的微透鏡陣列、壁虎的乾黏著層、蓮花葉子的自我潔淨效應等。因為微奈米介面結構廣泛的應用，所以是仿生科技重要的發展趨勢之一。仿生科技的躍進除了仰賴觀察儀器與製程儀器的發展之外，適當與精密的量測儀器也是非常的重要。本論文在第二章先對奈微米表面結構的水滴濕潤性作理論上的討論，從Wenzel和Cassie-Boxter所提出的理論出發並配合微奈米結構表面實際的情況，了解微奈米介面結構對於水滴接觸角改變的關係，理論部分的了解有利於發展與設計所需的微奈米介面結構。在第三章介紹兩種奈米纖毛介面結構的製成，分別為纖毛網狀結構與纖毛組成的山狀結構，這兩種結構的製程都是利用聚對二甲苯(parylene)沉積在多孔隙的氧化鋁薄模後脫模所製作而成，除此之外，並對結構表面作化學性的修飾以達到花辦效應，每個試片都進行接觸角與水滴遲滯效應的量測，人造微奈米纖毛結構的量測結果與玫瑰花瓣進行比較與討論，顯示其有類似花辦效應般的超斥水性與高遲滯效應。在第四章介紹利用彎曲與拉伸方式對微奈米介面結構濕潤特性的調整，所使用的微奈米結構為第三章所製作出的兩種奈米纖毛介面結構，利用水滴的接觸角量測評估彎曲與拉伸對於試片的濕潤特性研究，由於介面結構是由微奈米纖毛所組成，因此彎曲所造成的改變並不大；而微奈米介面結構的濕潤特性可以有效的利用拉伸方式改變。壁虎的乾黏著層與自我潔淨效果最近受到科學界與工程界的關注，在第五章提出利用電子束微影系統製作仿生自我潔淨的微奈米纖毛介面結構，並且利用原子力顯微鏡的力模式去量測黏著力，而水滴接觸角的量測用來評估自我潔淨的能力，實驗結果顯示接觸角與黏著力強度呈現相反的趨勢，因此乾黏著層纖毛介面結構必須達到奈米等級才會有高黏著力與自我潔淨的效果。花瓣效應是指花瓣表面的多層次結構造成的高接觸角與強的水滴吸附力。在第六章介紹利用自我對準的製成方式製作高真球度的探針，這種探針可以用在量測奈微米結構的表面輪廓或是相關物理特性上，而這製程包含兩個部分：高真球度的微米球製程與自我對準的探針柱製程。高真球度的微米球是利用負光阻(SU-8)高分子在液體中利用表面張力形成高球度的形狀並進行固化，而在探針柱的製作方式則是利用SU-8負光阻的光波導管特性在探針球的底部形成探針柱，用此方法所製做出的探針柱軸心一定與球心同軸，若需要更高的探針柱，則可以利用乾蝕刻對矽基板進行蝕刻即可完成。In this dissertation, the fabrication and the physical characteristic research on biomimetic interfacial structures has been conducted. Accompanying recently quick technology development, biomimetics has attracted many attentions of scientists and engineers. The nature’s micor-/nano- structures have been imitated and applied widely in many fields such as artificial fiber which mimicked spider silk, photonic crystal on the butterfly wings, microlen array on brittle star body surface, dry adhesive on the gecko foot, and the self-cleaning effect on the lotus leaf surface. The study of micro/nano interfacial structure is one of the important development trends for biomimetics because of its versatile applications. With the advancement of the observation and fabrication apparatus, various biomimetic mico/nano structures have been realized in this dissertation. In addition, the development of the suitable measurement has been conducted. In chapter 2, the theoretical models which provided relationships between the roughness, contact angle and contact angle hysteresis were presented and discussed. A droplet on the textured surface in practice can be categorized into air-trapped state, Wenzel state, and penetrating film state. The boundary between these three states is related to the roughness and the relative fractions of the solid phase under the droplet. Besides, the contact angle hysteresis was quantified as a function of the geometric roughness and the relative fraction area of the solid contact phase. In chapter 3, the large contact angle with high contact angle hysteresis on the hierarchical structure of the rose petal surface was introduced. Inspired from the petal effect, two types of artificial structure, fibril mesh and fibril microhills, were fabricated and compared with the rose petal surface. The fibril mesh composed of parylene nanofibrils and underneath capillary structures was fabricated using template-assisted deposition. The fibril microhills were formed by peeling the fibril mesh off. The contact angle and contact angle hysteresis on these two surfaces treated by various surface modifications for enhancing the hydrophobicity were measured. The fabricated surface showed similar wetting behavior to the rose petal which is hydrophobic and sticky to water droplet. The relation between the contact angle and the contact angle hysteresis on the various artificial surfaces and the rose petal were discussed. The qualitative estimations of the contact angle hysteresis for the various artificial surfaces were presented. In chapter 4, the effects of the curvature and stretch on the both artificial fibril surfaces fabricated in chapter 3 were discussed based on the wetting characteristics. The tunable wetting behavior on the both flexible nanofibril surface was discussed. The effect of the curvature change on tuning the wetting behavior on both two types of nanofibril surface was limited because the nanofibril surface had no obvious change after the membrane was bent to possess millimeter radius of curvature. The wetting behavior in both nanofibril surfaces can be tuned effectively by stretching. Besides the contact angle measurement in the static state on the stretch test, the contact angle measurement in the dynamic state was carried out during the stretching. Comparing with the invariable contact angle on the flat parylene film, both fibril structural surfaces had larger adhesion to the droplet. Inspired from gecko foot-hairs, the chapter 5 presented the fabrication and characterization of e-beam photoresist nano-pillar array as biomimetic self-cleaning dry adhesives. Resist pillars of different widths and pitches were designed and fabricated using e-beam lithography. An AFM plateau tip was used to measure and to characterize the adhesion force of the resist pillar array. The adhesion strengths significantly increased with the decreasing pillar width at the same pillar pitch and height. The contact angle measurement was used to evaluate the self-cleaning effect. Since the contact angle and the adhesion strength had opposite trends with the contact area ratio, the result indicated that the dry adhesive needed to decrease to nanometer scale for obtaining the self-cleaning effect. The chapter 6 presented a self-alignment fabrication of the stylus with high sphericity for micro coordinate measurement machine (μCMM), a mechanical system using micro-scale contact probes to measure the profile of high-aspect-ratio micro-structures or physical characteristics. This new process combined micro-pellets and stylus into one mechanical device. The micro-pellets were configured inside liquid environment in which the surface tension driveed the pellets into prefect spheres. Stylus arrays were patterned by the microlens-assisted self-writing of SU-8 resist waveguides. The high-aspect-ratio stylus pin consisted of a SU-8 portion and a silicon portion which was fabricated by deep reactive ion etching