藉由操控奈米物質的陣列排列與異質結構之新穎特性

Novel Physical Properties based on Manipulation of Patterned Nanomaterials and Heterostructures

鄭景丞(Ching-Cheng Cheng)

指導教授 ： 陳永芳

國立臺灣大學/理學院/物理學研究所/博士(2018年)

https://doi.org/10.6342/NTU201800428

摘要

在本論文中，首先我們報導了一種簡單的方法，利用有方向性的空間侷限，去控制奈米金屬柱自組裝整齊排列於基板上。其次，我們設計製作了石墨烯、氧化鋅、矽基板組成的三位能階接面結構元件，展示了一個自我驅動的光偵測器，此光偵測器具有高敏感度、極快的反應與光波長400奈米至1000奈米的寬頻寬偵測範圍。最後，我們整合了石墨烯、半導體與額外的特殊費米能階篩子結構，製作了一個奈米組合氣體偵測器，此偵測器具有極高的敏感度跟極快的反應時間。
1.在沒有結構的基板上，控制金屬自主裝方向
利用具有柵狀週期結構的彈性印模，我們展示了一種簡單的方法去控制達成某種預定的奈米金屬柱自主裝方向在沒有結構的基板上。非常有趣的是，經由選擇不同親水性的基板，自主裝排列一制性可以被控制操作垂直或是平行於柵狀週期結構。
2.由石磨烯、氧化鋅與矽基板組成的三接面自驅動、廣頻寬光偵測器
我們設計製作了石墨烯、氧化鋅、矽基板組成的三金屬接面結構元件，展示了一個自我驅動的光偵測器，此光偵測器具有高敏感度、極快的反應與光波長400奈米至1000奈米的寬偵測範圍。石墨烯在此扮演一種透明、有效率的導電光點子蒐集層，基於其良好的費米能階調整性。氧化鋅在此做為抗反射層，用來捕捉光子增加光的吸收效率。此外，加入一層氧化鋅在石墨烯與矽基板中間，會使石墨烯/氧化鋅、氧化鋅/矽基板的接面產生內建的接面電場，此接面電場極大量的增加了由光電效應產生電子電洞對的分離機率。進而，此元件的靈敏度與反應速度都明顯的增加。相信我們以這種挑選適合的原件設計、適合的材料物理能階結構、適合的光學參數方法去整合達成高效率的自驅動光偵測器手段，可以整合到其他種材料元件上，以製作更特殊的實質光電元件應用。
3.利用巨大的蕭基接面費米能階偏移與設計的費米能篩模組製作超快、超敏感氣體偵測器
氣體偵測器在很多領域都有重要的應用，像是智能偵測有毒氣體系統等。即使這些應用的重要性已經引起人們的注意，然後在氣體偵測，得反應速度仍然非常慢。為了解決這個問題，我們在這邊嘗試整合了石墨烯、半導體與一個特殊設計的費米能篩模組製作了一個超快、超敏感氣體偵測器。這個設計的費米能篩模組有適合得位能結構可以阻擋經由氣體分子沾附元件表面產生的分離載子復合回原本底層的半導體材料。我們發現氣體偵測的敏感度可以低至百萬分一之得程度，而且反應響應時間，也低至60微秒，在過去的石墨烯為基礎的氣體偵測元件文獻中，這兩個極佳的特性是前所未見的。因此，我們的成果非常有用，而且對於目前高效能、高應用性的氣體偵測器發展幫助很大。

關鍵字

金奈米柱 ； 光偵測器 ； 氣體偵測器 ； 石墨烯

並列摘要

In this thesis, we have reported a simple methodology to control the orientation of AuNRs assembly into directional aligned film structure under confinement in the beginning. Then a self-powered photodetector with ultrahigh sensitivity, fast photoresponse, and wide spectral detectivity covering from 1000 nm to 400 nm based on graphene/ZnO/Si triple junctions has been designed, fabricated, and demonstrated. In the end, we provide a seminal attempt with the integration of graphene, semiconductor, and an additional sieve layer forming a nanocomposite gas sensor with ultrahigh sensitivity and ultrafast time response.
1.Controllable orientation of assembled gold nanorods on unstructured substrates
A facile methodology to control the orientation of assembled Au nanorods with a preferential direction on unstructured substrates has been demonstrated by the assistance of an elastomer grating stamp. Quite surprisingly, by choosing the hydrophobicity of the substrate, the aligned orientation can be manipulated to be perpendicular or parallel to the grating direction.
2.Self-powered and broadband photodetectors based on graphene/ZnO/silicon triple junctions
A self-powered photodetector with ultrahigh sensitivity, fast photoresponse, and wide spectral detectivity covering from 1000 nm to 400 nm based on graphene/ZnO/Si triple junctions has been designed, fabricated, and demonstrated. In this device, graphene serves as a transparent electrode as well as an efficient collection layer for photogenerated carriers due to its excellent tunability of Fermi energy. The ZnO layer acts as an antireflection layer to trap the incident light and enhance the light absorption. Furthermore, the insertion of the ZnO layer in between graphene and Si layers can create build-in electric field at both graphene/ZnO and ZnO/Si interfaces, which can greatly enhance the charge separation of photogenerated electron and hole pairs. As a result, the sensitivity and response time can be significantly improved. It is believed that our methodology for achieving a high-performance self-powered photodetector based on an appropriate design of band alignment and optical parameters can be implemented to many other material systems, which can be used to generate unique optoelectronic devices for practical applications.
3.Ultrafast and Ultrasensitive Gas Sensors Derived from a Large Fermi-Level Shift in the Schottky Junction with Sieve-Layer Modulation
Gas sensors play an important role in numerous fields, covering a wide range of applications, including intelligent systems and detection of harmful and toxic gases. Even though they have attracted much attention, the response time on the order of seconds to minutes is still very slow. To circumvent the existing problems, here, we provide a seminal attempt with the integration of graphene, semiconductor, and an addition sieve layer forming a nanocomposite gas sensor with ultrahigh sensitivity and ultrafast response. The designed sieve layer has a suitable band structure that can serve as a blocking layer to prevent transfer of the charges induced by adsorbed gas molecules into the underlying semiconductor layer. We found that the sensitivity can be reduced to the parts per million level, and the ultrafast response of around 60 ms is unprecedented compared with published graphene-based gas sensors. The achieved high performance can be interpreted well by the large change of the Fermi level of graphene due to its inherent nature of the low density of states and blocking of the sieve layer to prevent charge transfer from graphene to the underlying semiconductor layer. Accordingly, our work is very useful and timely for the development of gas sensors with high performance for practical applications.

並列關鍵字

gold nanorod ； photo sensor ； gas sensor

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