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標題: | 雙光子聚合製程之模擬與改善 Simulation and Improvements of Two-Photon Polymerization Fabricating Process |
作者: | Chin-Te LIN 林錦德 |
指導教授: | 鍾添東 |
關鍵字: | 雙光子聚合,製作模擬,微晶片雷射,光束品質,雷射功率校正,轉角缺陷, two-photon polymerization,fabricating simulation,micro-chip laser,beam quality,laser correction method,angular defect, |
出版年 : | 2012 |
學位: | 博士 |
摘要: | 雙光子聚合是一種基於雙光子吸收的非線性光學技術,可用於產生次微米解析度的任意造型三維微物件。因微晶片雷射的發展以及多樣化感光聚合物的發現,雙光子聚合系統不但物廉價美,而且應用面日趨廣泛。在應用面的急切需求下,更好的解析度與良善的製造品質成為近年來重要的雙光子聚合研究方向。
為了預測聚合後的造型,本研究發展一套雙光子聚合的虛擬製作程式。當利用雙光子聚合製作時,雷射的適當曝光會在感光聚合物內形成一個雙光子聚合之基本構造元素:體素。在雷射掃瞄所有設計的體素且清洗聚合程度不足的部分後,可獲得由體素組合的微物件。虛擬製作程式是利用聚合程度是否高於不被洗去的門檻來計算微物件的外型。光致聚合程度與起始基群濃度成正比,而起始基群濃度又正比於雷射強度的二次方。在無擴散效應的自由基模型中,局部起始基群濃度分佈可以疊加成整體濃度分佈,所以累加所有局部體素的結果即可獲得整體的濃度聚合程度。利用這個方法,可以找出聚合實體邊界並且決定微物件製作後的造型。 因雙光子聚合的區域與雷射強度相關高,本研究進行聚焦後雷射的光強度研究。由於雙光子聚合系統的架設,準直後的雷射光必須先經由數值孔徑大的物鏡、浸鏡油與蓋玻片才能聚焦於感光聚合物內部。本研究利用點分散函數的數學式計算聚焦後雷射的真實強度分佈,其結果顯示真實雷射光束不是完美的高斯光束。為了瞭解真實強度分佈的影響,本研究製作一系列雙光子聚合的奈米直線。藉由高解析度電子顯微鏡的量測與虛擬製作程式的模擬,確認這些樣本的外型可利用真實光束的模型量化。因此真實雷射光束的模型可以解釋雙光子聚合所產生之外型與解析度。 為了提升雙光子立體顯影的產品品質,本研究提出轉角缺陷的雷射功率校正方法。在雙光子立體顯影的製作過程中,雷射沿著計畫好的軌跡循序曝光所有的體素以構成複雜的微結構。當軌跡中有銳角時,雷射將會在給予銳角處過多的曝光並產生較大的聚合結構,即轉角缺陷。轉角缺陷可利用虛擬製作程式診斷,並且利用原子力顯微鏡量測樣品的轉角缺陷以驗證診斷的正確性。為了校正轉角缺陷,本研究提出校正雷射功率的方法與校正功率的數學式。該數學式推導是來自於修正缺陷區域的曝光條件使其等同於直線區域之值。藉著量測使用雷射功率校正方法的樣品,其結果驗證該方法在消除轉角缺陷是有效的。此雷射功率校正方法將有助於改善外型輪廓掃瞄法的製作品質。 Two-photon polymerization (TPP) is a non-linear optics technology based on two-photon absorption (TPA) and able to produce three-dimensional micro-objects with arbitrary shapes and sub-micron resolutions. Owing to the development of micro-chip lasers and the discovery of various photopolymers, the TPP systems are not only sold with affordable prices, but also have wider and wider fields of the applications. For the urgent requirements of the applications, TPP fabrication studies for better quality controls and higher resolutions have become interesting topics during the last decade. A virtual fabrication program for TPP is developed to predict the TPP polymerized shapes. During the TPP fabrications, a laser gives an exposure to form a voxel, which is the TPP basic element. After all designed voxels are scanned with the laser and the insufficiently compact polymer is removed in a rinsing process, a micro-object composed of the voxels can be obtained. The virtual fabrication program computes the shapes of micro-objects by determine whether the polymerizing level is over a threshold value. The photo-polymerizing level is linear to the initiating radical species concentration, which is proportional to the square the laser intensity. In the TPP free-radical mathematic model without the consideration of diffusion effects, the local initiating radical species concentrations can be summed up to the global concentration. Thus, the global polymerizing level can be defined by accumulating all results of the local voxels. Through this manner, the boundary of the polymerized solid will be found out, and the produced shapes of micro-object can be determined. The effect of the intensity of the focused laser is studied because the polymerized region of the TPP strongly depends on the laser intensity. The setup of the TPP system makes a collimating laser beam go through an objective lens with a high numerical aperture, immersion oil, and a coverslip before the beam focuses inside the photopolymer. The real intensity distribution of the focused beam can be calculated with the analytical expressions of the point spread function (PSF), and the result indicates that the passage causes the beam imperfect. In order to study the effect of the real beam, a series of the nano-lines are fabricated. With the measurement of the high resolution scanning electrical microscopy (SEM) and the simulation of the virtual fabrication program, it can be observed that the produced shapes of these samples can be quantified by the real beam model. Therefore, it can be concluded that the polymerized behaviors of the TPP would be defined by the characteristics of the real beam. Laser power correction approach of angular defects is carried out to improve the product quality fabricated by TPP. During TPP fabrication, the laser follows calculated trajectories and exposures all voxels to give rise to complex microstructures. When the trajectories have sharp angles, the laser will give the angles more exposure and produce large structures, called angular defects. The angular defects are diagnosed by the help of the virtual fabrication program, and the diagnosis is verified by the atomic force microscopy (AFM) measurements of the samples with angular defects. To correct angular defects, a method of the laser power correction and formulas for the correcting power are proposed. The formulas are derived from the comparison of both exposure conditions of the line region and the defect region. Samples are fabricated with the laser correction approach and then measured, and the results show that the proposed method is effective to remove the angular defects. This manner will benefit the TPP fabrications using the contour scanning methods. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/64787 |
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顯示於系所單位: | 機械工程學系 |
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