2018-06-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/701119摘要：二維（2D）材料的出現開啟了奇特的物理學和應用的巨大潛力。多種有趣的物理特性已經在二維材料中展示，如亞納米厚度的過渡金屬二硫化物（TMDCs）。[1-3]同時，二維范德瓦爾材料開闢了直接設計和異構結構的不同用途。[4]然而，為了在這些系統中使用旋轉，大多數自旋源仍依賴於傳統的鐵磁（FM）金屬和絕緣體，這會引起復雜的界面並抑制製造困難。 磁性2D范德瓦爾層可以優雅地取代傳統材料。雖然聲稱在2D結構中禁止遠程磁性[5]，但在理論和實驗上都報導了幾個FM 2D層[6,7]，包括TMDC族的成員，如MoS2和VSe2。[8,9]在少層2H MoS2中的結構缺陷具有淨自旋矩並形成遠程鐵磁性。據報導，單層VSe2即使在室溫下也是鐵磁性的;此外，通過插入其他2D TMDC層可以調節剩磁和矯頑力。結合FM TMDC層將擴展自旋電子學中的2D異質結構的可用性以及依賴於自旋的谷電子學和光學。 憑藉我們在磁性薄膜和緊急2D材料方面的專業知識[10-12]，在這個項目中，我們建議通過具有同步輻射的不同工具來研究2D TMDC層的磁性和電子結構。在FM TMDC單層（例如改性的MoS 2和VSe 2）的顯影系統化學氣相沉積（CVD）生長的幫助下製備樣品，並通過分子束外延（MBE）產生。還可以使用散裝材料的剝離來製造高質量的2D單層，並且將執行CVD和剝離方法以獲得用於運輸和光學測量的磁性TMDC單層。除了原始材料外，我們還將對TMDC單層膜上的磁性簇和薄膜的沉積進行修改，以便在引入傳統FM材料後解決界面磁性和電子行為。 使用基於同步輻射的工具（例如XMCD，XPS，ARPES，PEEM等）將實現磁性TMDC系統的特徵化。元素化測量通過顯示個體的自旋貢獻來幫助解決樣品中磁性的起源。元素以及化學鍵合。結果將闡明TMDC堆疊，結構缺陷和鄰近效應對2D層中鐵磁性的影響，並將極大地有益於2D層旋轉器件的設計。另一方面，台灣Photon Source，Hsinchu正在建設的自旋分辨ARPES將提供FM 2D層中Fermi水平附近的自旋紋理信息，並闡明有趣的帶結構，如FM 2H中的山谷的自旋特性TMDCs。已在我們的小組中成功演示的自旋極化STM也可用於在磁性2D層中映射納米級磁性域。<br> Abstract: The emergence of two dimensional (2D) materials opens up exotic physics and great potential to applications. Versatile intriguing physical properties have been unveiled in 2D materials like transition metal dichalcogenides (TMDCs) within sub-nm thickness.[1-3] Meanwhile, the 2D van der Waal materials open straightforward designs and fabrications of heterostructures for different uses.[4] However, to make spin in use in these systems, most of spin sources still rely on conventional ferromagnetic (FM) metals and insulators, which induces complicated interfaces and suppresses fabcrications into difficulties. Magnetic 2D van der Waal layers may elegantly replace the conventional materials. While long-range magnetism was claimed to be prohibited in 2D structures[5], several FM 2D layers were reported both theoretically and experimentally[6, 7], including members of the TMDC family, such as MoS2 and VSe2.[8, 9] Structural defects in few-layer 2H MoS2 possess net spin moment and form long-range ferromagnetism. It has also been reported that monolayer VSe2 are ferromagnetic even at room temperature; furthermore, the remanence and coercivity are adjustable via insertion of other 2D TMDC layers. Incorporation of the FM TMDC layers will expand availabilities of the 2D heterostructues in spintronics as well as spin-dependent valleytronics and optics. With our expertise in magnetic thin films and emergent 2D materials[10-12], in this project, we propose to investigate magnetism and electronic structure of 2D TMDC layers via different tools with synchrotron radiation. The samples will be prepared with help of a developing systematic chemical vapor deposition (CVD) growths of FM TMDC monolayers, such as modified MoS2 and VSe2, and produced via molecular beam epitaxy (MBE). High quality 2D monolayer can also be fabricated using exfoliation from bulk materials, and both CVD and exfoliation methods will be performed to acquire magnetic TMDC monolayers for transport and optical measurements. In addition to pristine materials, we will carry out modifications such as deposition of magnetic clusters and thin films on the TMDC monolayers, in order to resolve interfacial magnetic and electronic behaviors after introducing conventional FM materials. Charaterization of the magnetic TMDC systems will be achieved using synchrotron-radiation-based tools such as XMCD, XPS, ARPES, PEEM, etc.. Element-spcified measurements help to resolve the origin of magnetism in the samples by showing the spin contribution of individual elements as well as chemical bondings. The results will elucidate influences of TMDC stacking, structural defects, and proximity effects on ferromagnetism in the 2D layers, and will benefit designs of 2D-layer-based spin devices greatly. On the other hand, the spin-resolved ARPES under construction in Taiwan Photon Source, Hsinchu, will give information of spin textures near the Fermi level in the FM 2D layers, and clarify intriguing band structures such as spin properties of the valleys in FM 2H TMDCs. Spin-polarized STM, which has been successfully demonstred in our group, may also be utilized to map nanoscale mangetic domains in the magnetic 2D layers.二維材料磁性電子結構同步輻射MagnetismElcetronic Strutcure2D MaterialsSynchrotron Radiation