旋光結構調控單層二硫化鉬圓偏振螢光

Abstract

本論文中，我們展示了調控由單層二硫化鉬覆蓋之掌性結構產生之圓偏振光的可能性。標準電子束微影技術以及乾蝕刻技術被用於在氮化鎵上定義出左手及右手性螺旋狀掌性結構。高達1.2的不對稱因子可以藉由線性偏振激發光測得，這個結果在過去的研究中是很難實現的。為了取得高度的圓偏振發光，帶有二硫化鉬的樣品必須被圓偏振光激發。與由鎘化硒量子點和氮化鎵測得之微小不對稱因子比較，由單層二硫化鉬測得之高度不對稱因子可以歸因於其獨特的能帶結構，而這樣的能帶結構源自於存在單層過渡金屬二硫族化合物(transition metal dichalcogenide)中的反轉對稱破缺(inversion symmetry breaking)及自旋軌道耦合(spin-orbit coupling)引起的谷旋閉鎖效應(spin-valley locking)。 可以肯定是，我們在此所呈現的結果可以為製作小尺度與超薄圓偏振光源奠定重要的基礎。

In this thesis, we demonstrate the possibility to control circularly polarized emission arising from monolayer MoS2 covering on chirality structures. Standard E-beam lithography and dry etching techniques were used to define the patterns of left-chiral and right-chiral spiral structures on GaN substrate. A dissymmetry factor as high as 1.2 can be obtained with a linear polarized pumping source, which is quite difficult from all the results ever reported. In order to obtain high degree of circularly polarization of emission, the MoS2 samples have to be pumped by circularly polarized light beam. Compared with the very small dissymmetry factor from CdSe quantum dots and GaN, the large dissymmetry factor of monolayer MoS2 can be attributed to the unique band structure which is due to the spin-valley locking caused by inversion symmetry breaking and spin-orbit coupling in transition metal dichalcogenide monolayers. It is believed that our work shown here can pave a key step to build a compact and ultra-thin circularly polarized light source.