電漿子材料磊晶成長及光學應用

金屬薄膜或超表面在光子或電子的激發下表現出突破衍射極限的獨特性質，該性質在適當的條件下可導致深亞波長區域的強場約束和場增強效應。這些迷人的光學現象源於壹種被稱為“表面電漿子共振”的表面電子集體振蕩，並且這種振蕩對材料介電函數和納米結構的幾何形狀非常敏感。目前，貴金屬如金(Au)、銀(Ag) 和鋁(Al) 常被用於不同的電漿子頻率域，這些頻率域受到材料損耗和帶間躍遷(ITs) 的限制。在上述材料中，鑒於鋁很窄的帶間躍遷範圍(∼800 nm)，與銀相比鋁具有從全可見（Vis）到紫外(UV) 的極寬電漿子頻率範圍，由此鋁可以充當銀的替代角色。此外，成本低廉的鋁不僅具有更穩定的自然氧化層，而且可以與互補金屬氧化物半導體(CMOS) 技術相兼容。同樣，可見光和近紅外電漿子材料金（ITs∼500 nm ）也可以用難熔金屬化合物氮化鈦(TiN) 來代替，這種金屬化合物在極端環境(高溫、化學腐蝕等) 下表現出優異的穩定性，並具有半導體技術和生物相容性。認識到濕化學合成膠體晶體尺寸和傳統沈積方法(如反應濺射) 生長的多晶材料的局限性，人們對超高真空分子束磊晶生長技術進行了廣泛的研究。外延磊晶法可用於在適當晶格匹配的襯底上生長高質量的原子平整度薄膜或納米結構。本論文中，我們研究了如何生長完整晶圓的單晶氮化鈦（TiN）薄膜，以及在鋁薄膜上發展自旋-軌道耦合效應, 並且這些技術都可以和目前的量產技術進行整合。本論文主要分為兩個部分:(1) 外延生長單晶難熔電漿子材料氮化鈦（TiN）及其超表面光學性質研究。采用氮電漿輔助分子束磊晶技術(MBE) 在c 面藍寶石襯底上生長單晶且符合化學計量的氮化鈦薄膜。我們的實驗結果證明，由於金的帶間躍遷影響，導致其損耗在短波長範圍內(<500 nm) 較大，由此外延單晶氮化鈦作為替代電漿材料要優於金。另壹方面，表面電漿子幹涉的光學響應和化學計量氮化鈦的納米孔超表面都已經證明了它在可見區域的應用。(2) 非線性區域能夠打破二維(2D) 納米結構的圓二向色性(CD) 遠場簡並態。制備在外延鋁膜上的二維手性螺旋槽在自旋軌道耦合(SOC) 效應下產生了線性和非線性光學渦旋場，並已經通過線性近場激光光電子顯微鏡(PEEM) 和非線性遠場光學測量驗證了其手性。除此之外, 我們發現表面電漿渦旋做為壹個平臺，從線性到非線性轉換過程中可以提高表面電漿渦旋場的拓撲數(TC)。再者, 我們還利用二硫化鎢與電漿渦旋場耦合來實現二硫化鎢非能谷（non-valleytronics）位置的二次諧波圓二色性，並且嘗試探索光學渦旋(TC=l) 對二硫化鎢能谷（valleytronics）位置自旋電子器件的影響。由此可知，控制良好的亞波長鋁渦旋可以大幅縮小光學渦旋尺寸、構造從整數到分數的任意拓撲數渦旋場，為渦旋場的研究和應用提供了便利。

關鍵字

分子束磊晶；氮化鈦；介電函數；表面電漿子幹涉；自旋軌道耦合；表面電漿子渦旋場；光電子顯微鏡；二次諧波；拓撲數；二硫化鎢；自旋電子器件

並列摘要

Metallic films and metasurfaces excited by photons or electrons exhibit unique possibilities breaking the diffraction limit, leading to strong field confinement and enhancement in deep subwavelength regions under suitable conditions. These fascinating optical phenomena have been explained to originate from collective oscillations of surface electrons, which are described as the surface plasmon resonance and very sensitive with material dielectric function and geometry of nanostructure. At present, the common noble metal such as gold (Au), silver (Ag) and aluminum (Al) are used for different plasmonic frequency regimes which are limited by their losses of material and the presence of interband transitions (ITs). In above materials, aluminum could be acted as alternative role of silver because aluminum has a narrow-band behavior in ITs (∼800 nm) which can exhibit broader plasmonic frequency range from full visible to ultraviolet (UV) regime comparison to silver; else, the low-cost aluminum not only has more stable self-protected layer, but also could be compatible with complementary metal oxide semiconductor (CMOS) technology. Gold (ITs∼500 nm) visible and near-infrared plasmonic material also can be replaced by a refractory metallic compound titanium nitride (TiN), which show excellent stability at the extreme environment (high temperature, chemical corrosion, etc.) and compatible applications with semiconductor and biology. Recognizing the limitations of colloidal crystals size of wet-chemical synthesizing method and polycrystalline materials grown by conventional deposition methods (e.g. reactive sputtering), extensive research efforts have been devoted to ultrahigh vacuum molecular-beam epitaxy (MBE) growth techniques. Epitaxial method either use to grow high quality atomic flatness film or nanostructures on appropriate lattice match substrate. In this thesis, we have studied how to fabricate whole wafer single-crystalline titanium nitride film and develop optical spin-orbital coupling effect on as-grown aluminum film which are all available for state-of-the-art integrated technology. There are two main parts of this thesis: (1) Epitaxial growth single crystalline refractory plasmonic material titanium nitride and dissecting its metasurface optical properties. Nitrogen-plasma-assisted molecular-beam epitaxy (MBE) was adopt to grow single-crystalline and stoichiometric TiN films on c-plane sapphire substrates. Our experiment results have proved that epitaxy single crystalline TiN as alternative role is better than gold in the short-wavelength range (<500 nm), where gold suffers from strong loss due to ITs. On the other hand, optical response of surface plasmon interferometry and nano-holes metasurfaces of stoichiometric TiN have demonstrated its visible-spectrum applications.(2) Usually, chirality of two-dimensional matesurface can only by investigated by using near field measurement techniques, such as scanning near-field optical microscopy (SNOM) and photoemission electron microscopy (PEEM), while nonlinear optical response breaks the degeneration of far-field circular dichroism (CD). 2D Archimedes spiral slits fabricated on an atomically flat aluminum epitaxial film, have emerged as a versatile approach to generate far-field plasmonic vortex fields with tunable topological charges under optical spin-orbit coupling (SOC). This thesis demonstrates very strong far-field chiral second-harmonic generation (SHG) in the visible region (400–600 nm). Beyond that, we have found SPP vortex as a platform could improve topological charge (TC)l, transferring from linear to nonlinear range. Moreover, we also have utilized WS2 coupling with plasmon vortex for arriving at circular dichroism of second harmonic generation at intrinsic non-valleytronics point and exploring optical vortex (TC=l) effect of spintronic device at its valleytronics point. Well-controlled subwavelength aluminum vortex opens a door for significantly shrinking the optical vortex dimension and constructing vortex with arbitrary topological charges from integer to fraction value.

並列關鍵字

Molecular-Beam Epitaxy ； Titanium Nitride ； Dielectric Function ； Surface Plasmon Interferometry ； Spin Orbital Coupling ； Plasmon Vortex ； Photoemission Electron Microscopy ； Second Harmonic Generation ； Topological Charge ； Tungsten Disulfide ； Spintronic Device