Professor C. C. (Chih-Chung) Yang's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 楊志忠教授

Preparation of a high-concentration Au nanoring (NRI) water solution and its applications to the enhancement of image contrast in optical coherence tomography (OCT) and the generation of photothermal effect in a bio-sample through localized surface plasmon (LSP) resonance are demonstrated. Au NRIs are first fabricated on a sapphire substrate with colloidal lithography and secondary sputtering of Au, and then transferred into water solution through a liftoff process. By controlling the NRI geometry, the LSP dipole resonance wavelength in tissue can cover the spectral range of 1300 nm for OCT scanning of deep tissue penetration. The extinction cross sections of the fabricated Au NRIs in water are estimated to give the levels of 10^-10-10^-9 cm² near their LSP resonance wavelengths. The fabricated Au NRIs are then delivered into pig adipose samples for OCT scanning. It is observed that when resonant Au NRIs are delivered into such a sample, LSP resonance-induced Au NRI absorption results in a photothermal effect, making the opaque pig adipose cells transparent. Also, the delivered Au NRIs in the intercellular substance enhance the image contrast of OCT scanning through LSP resonance-enhanced scattering. By continuously OCT scanning a sample, both photothermal and image contrast enhancement effects are observed. However, by continually scanning a sample with a low scan frequency, only the image contrast enhancement effect is observed. Figure 1 shows the SEM image of an Au NRI. Figure 2 shows the extinction spectra of two NRI samples (A and B) obtained through transmission measurement. The major peak of each curve corresponds to the LSP dipole resonance. Figure 3 shows the OCT scanning image of a pig adipose sample with delivered Au NRIs. The adipose cells have become transparent. Figure 4 shows the lateral line-scan profiles of the OCT images of the heated pig adipose samples with and without Au NRIs. Enhanced scattering through LSP resonance of Au NRIs can be seen.

Fig. 1 SEM image of an Au NRI.	Fig. 2 Extinction spectra of Au NRIs (samples A and B).

Fig. 3 OCT image of a pig adipose sample with Au NRIs.	Fig. 4 Lateral line-scan profiles of the OCT images of the heated pig adipose samples with and without Au NRIs.

Numerical Synthesis of Metallic Nanostructures for Enhancing the Emission of a Dipole through Surface Plasmon Coupling

Professor Yean-Woei Kiang's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 江衍偉教授

In this study, we numerically synthesize a two-dimensional metallic nanostructure consisting of a Au half-space and two separate Ag elliptical cylinders by the simulated annealing (SA) method. The simulated nanostructure is so designed that the surface plasmon polariton (SPP) and the localized surface plasmon (LSP) are simultaneously excited at their common resonant wavelength (535 nm), leading to the enhancement of emission of a nearby dipole source. This enhancement effect is more significant than that of the case where only one of SPP and LSP is excited. In numerically synthesizing a metallic nanostructure, we try to maximize both the downward emission (in the direction away from the metallic structure) and the emission efficiency. A cost function is defined as some combination of the downward emission and the emission efficiency. We adjust the simulated structure by SA to minimize the cost function at a designated resonant wavelength, and calculate and analyze the spectra of downward emission and emission efficiency for the optimal structure. Other structures are also investigated for comparison. From numerical simulations, it is demonstrated that the enhancement of dipole emission is better for optimization at wavelength 535 nm than at other wavelengths. Note that the downward emission and the emission efficiency can reach maxima almost simultaneously when the SPP and the LSP couple effectively at a common resonant wavelength. This implies that the lighting efficiency of green light-emitting diodes (LEDs) can be increased by the coupling effect at a common resonant wavelength of SPP and LSP.

Fig. 1 Variation of cost function in the iteration process. The solid curve represents the cost function and the dashed curve represents the chosen temperature distribution used in the SA process. The synthetic metallic nanostructure is shown schematically in the insert. An x-oriented dipole, denoted by an arrow and labeled by Jx, is located at (x, y) = (0, -h). The metal-dielectric flat interface is at y = 0.

Fig. 2 Spectra of (a) total emission (dashed curve) and downward emission (solid curve), and (b) enhancement factor of total emission (dashed curve) and downward emission (solid curve) for structure A (structure parameters: a = 12 nm, d = 60 nm, t = 10 nm, h = 21 nm).

姓名：田堃正   指導教授：吳忠幟教授

論文題目：微製程技術與光學系統之整合設計與應用—有機可形變面鏡與微透鏡陣列

姓名：謝欣達   指導教授：蘇國棟教授

— 資料提供：影像顯示科技知識平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃巖教授、陳韋仲 —

MIT同時實現熱電轉換、太陽能發電和熱水供應 

由美國麻省理工學院（MIT）、美國熱電轉換技術開發公司（GMZ Energy）、美國波士頓學院及阿拉伯聯合大公國（UAE）馬斯達爾理工學院（Masdar Institute of Science and Technology）所組成研究小組，開發出採用熱電轉換元件的平板型太陽能發電兼熱水供應系統。該系統能夠「熱電聯產」，不僅能發電還能同時供應熱水。發電的轉換效率為5%左右，同時還能提供50℃左右的熱水。

有關技術詳情論文已發表在學術雜誌《Nature Materials》。該研究提到其發電轉換效率比同類型系統提高了7～8倍，今後轉換效率還可能達到10%以上。另外，由於製造成本有希望比使用光電轉換方式的太陽能電池（PV）低，而且能夠供應熱水，折舊年限又比太陽能電池長，將來可能會成為太陽能電池的強勁對手。波士頓學院教授任志鋒在接受《日經電子》採訪時表示：「相對於發電功率的製造成本大約在0.5美元/W。由於還能供應熱水，因此完全可以與太陽能電池展開競爭。」

以前也有過利用熱電轉換元件進行太陽能發電的嘗試。但是，很難產生對熱電轉換至關重要的大溫差，而且轉換效率非常低，只有0.63%。

此次研究小組透過三大改善措施實現了高轉換效率，分別為：（1）開發出利用高效吸收陽光的平板匯聚200～300倍太陽熱量的系統，從而確保了溫差；（2）用玻璃真空容器包圍發電面板，大幅降低熱損耗；（3）採用MIT等最近開發的的BiTe類熱電轉換元件，其ZT指數高達1.03。

實際的面板是利用面積約714 mm²或約1090 mm²的兩塊銅（Cu）板夾住尺寸為1.35mm×1.35mm×1.65mm的n型和p型兩種熱電轉換材料，然後用玻璃真空容器密封而成。兩塊銅板中，接受陽光照射的表面銅板上貼有高效吸收陽光的材料，背面銅板上貼有起散熱作用的陶瓷板。另外，背面銅板透過水冷式冷卻使溫度保持在20～60℃。面板的面積是熱電轉換元件本身面積的196倍或299倍。這種系統與集光式太陽能電池的主要差異在於：不需要大型聚光鏡等，能夠製成超薄的平板狀，不需要追隨太陽轉動。

當照射一般陽光（其光譜為Air Mass（AM）1.5左右、能量密度為1kW/m²或1.5kW/m²）時，表面Cu板的溫度達到160～250℃，最大可發電約60mW。轉換效率對冷卻端面板的溫度依賴性較小，冷卻端面板的溫度維持在20℃時，轉換效率為4.6～5.2%;即使冷卻端面板的溫度達到50℃，轉換效率也保持在3.5～4%。「因此，冷卻系統直接就是『熱電聯產』的太陽能熱水器」。

該技術的特點是理論值與實測值差距很小。在論文中，理論轉換效率與實際測量值基本上是一致的。理論轉換效率大部分取決於熱電轉換材料的性能。「如果能夠實現ZT＝2的熱電轉換元件，那麼發電面板的轉換效率就能夠達到14%」。

另一方面，製造成本比現有太陽能電池低。因為採用集熱式，所以可以採用小型熱電轉換元件，且無需追隨太陽轉動，論文部分也提到「（此次採用的）BiTe類材料的採購成本只有0.17美元/W」。另外關於採用真空容器這一點，論文介紹說「在中國，採用真空管的太陽能熱水器已經導入73GW以上。這些產品的耐用年限為15年。」此外，此次系統的真空度比原有太陽能熱水器差兩個等級也沒關係。