奈米級紅熒烯/鈷薄膜的物理特性研究
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2019
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近期可撓式電子產品日益增加，且有機半導體材料具有由於低成本，且易於低溫製程，所以引起了很多關注，其中紅熒烯是具有高載子移動率的有機半導體。本研究中第一部分為紅熒烯奈米級雙層結構研究。X光反射率實驗與擬合，其中紅熒烯薄膜出現雙層模型特性，同時可定出紅熒烯表層的厚度為2.7±0.2奈米，且表層的散射密度長度數值低於下層塊材。紅熒烯厚度增加時，可以觀察到紅熒烯的表面形貌變化，從小顆粒轉變成大顆粒的奈米域(nano domain)。透過X光繞射實驗中，得知紅熒烯薄膜中具有相位分離的分層現象，代表紅熒烯薄膜中具有非單一晶相的奈米域，其中表層具有兩種次要結構，且下層塊材會有另一主要結構。不同厚度下紅熒烯薄膜彈性模量實驗，也可觀察到紅熒烯薄膜具有雙層模型特性趨勢，而後結合雙層模型彈性模量理論進行擬合時，可得知紅熒烯薄膜中表層與下層塊材間彈性模量等。四點探針電性測量時，紅熒烯薄中的雙層性質可用於表現在它的電阻行為，其中觀察到界面粗糙度對傳導電子的傳輸路徑敏感，該訊息對於有機半導體在可撓式面板中的未來應用是具有相當價值。
第二部分的研究為鈷與紅熒烯在矽(100)上形成複合性薄膜的表面與磁性的研究，實驗中嘗試鈷與紅熒烯的比例為1:0.33、1:0.5、1:1。而複合薄膜成長時會傾向層狀方式成長，上層主要為紅熒烯，下層主要為鈷-紅熒烯。當複合薄膜厚度較厚時，其中足夠量的紅熒烯會形成界面活性劑，降低薄膜與矽(100)基板間界面的交互作用，使薄膜表面會非常平坦，且此時樣品的矯頑力較低，當複合薄膜厚度較薄時，表面會有殘留一些鈷的顆粒，薄膜表面較粗糙，其中粗糙的表面代表薄膜中有許多的缺陷，才會使磁化翻轉時矯頑力較大。在鈷與紅熒烯複合薄膜中，當提升紅熒烯薄膜的量時，讓複合薄膜中的鈷與紅熒烯的界面增加，且增加紅熒烯的界面活性劑作用機會，進而提升複合薄膜的品質。
第三部分的研究為紅熒烯插層在鈷/矽(100)的表面與結構對磁性影響的研究。在鈷/矽(100)中會形成奈米鈷晶粒，在插層紅熒烯薄膜之後，紅熒烯會向上層的鈷擴散，讓鈷偏向形成非特殊晶相的膜，並且矯頑力的降低歸因於磁性材料中的缺陷密度下降。而在矯頑力數值附近的鈷/矽(100)柯爾顯微鏡圖像，觀察到在暗圖像中具有一些隨機分佈的缺陷，通過增加外加磁場，缺陷並不會在不同的磁場下移動，並且作為磁域壁運動的釘扎點，通過對鈷/紅熒烯/矽(100)的缺陷密度和矯頑力分析，進而得知樣品中鈷薄膜的磁域會以一維彎曲模型進行磁化翻轉，且缺陷與磁域壁為較強的交互作用。此研究主要透過磁光柯爾顯微鏡直接觀察到薄膜中的缺陷並定量出薄膜中的缺陷密度，如果此技術更加成熟，可以提供給磁性材料一個快速篩檢缺陷的方式。透過紅熒烯界面活性劑效應，改變薄膜中的缺陷，最後影響到薄膜中的磁特性，如果未來能結合薄膜彈性模量的研究，可以提供在可撓式有機磁性面板的開發。
Because of the increasing interests in low-cost-, low-temperature-, and flexible-substrate-based electronics, semiconducting organic materials have attracted much attention. Rubrene (5,6,11,12-tetraphenylnaphthacene) is an organic semiconductor with the highest carrier mobility. The physical properties of rubrene thin films in nanometer scale are explored in this dissertation. Our findings indicate that a rubrene/Si(100) that is thinner than 10 nm typically has a cluster-type morphology. By further increasing the film thickness, the coexistence of structural phases in rubrene films causes the formation of a nano domain structure. Our research propose that structural phase-related bilayer model can be used to explain the layered nature of the rubrene films with layers comprised of different structures. The increase of elastic moduli shows a layered structure of the films where a softer surface layer is lying on a harder underlayer. In additional, the electric conductivities of the surface layer and the underlayer are resolved using four-probe method ad shows the possible applications in organic electronics. In the second part of the dissertation, structures and magnetic properties of Co-rubrene composite films on Si(100) have been studied. For composite films prepared by co-depositions of Co and rubrene on Si(100), the surface is smooth while a layered distribution of Co atoms is detected. The structural change of buried Co is explored using AFM after washing out the rubrene molecules in the composite films. For thin composite films, the formation of separated Co clusters in the films results in a larger coercive force due to the imperfection introduced by rough interface to impede the magnetization reversal. By changing the rubrene concentration, rubrene served as a surfactant and the optimal condition for a better quality of the films could be obtained. These information are valuable for future applications of organic molecules in spintronics. In the final part, experimental evidences shows the formation of nanocrystalline cobalt for Co/Si(100). After insertion of rubrene layer, the segregation of rubrene modifies the growth behavior of the deposited Co to form an amorphous film and the reduction of the coercive force is attributed to the less imperfections in magnetic materials. By further exploration of the defects in the films by magneto-optical Kerr microscopy, the point defects of Co/rubrene/Si(100) follow the one-dimensional bowing model with strong defect-domain wall interactions. The information concerning the surfactant effects of rubrene for growing Co/Si(100) is valuable for future applications of organic semiconductors for spintronics devices.
Because of the increasing interests in low-cost-, low-temperature-, and flexible-substrate-based electronics, semiconducting organic materials have attracted much attention. Rubrene (5,6,11,12-tetraphenylnaphthacene) is an organic semiconductor with the highest carrier mobility. The physical properties of rubrene thin films in nanometer scale are explored in this dissertation. Our findings indicate that a rubrene/Si(100) that is thinner than 10 nm typically has a cluster-type morphology. By further increasing the film thickness, the coexistence of structural phases in rubrene films causes the formation of a nano domain structure. Our research propose that structural phase-related bilayer model can be used to explain the layered nature of the rubrene films with layers comprised of different structures. The increase of elastic moduli shows a layered structure of the films where a softer surface layer is lying on a harder underlayer. In additional, the electric conductivities of the surface layer and the underlayer are resolved using four-probe method ad shows the possible applications in organic electronics. In the second part of the dissertation, structures and magnetic properties of Co-rubrene composite films on Si(100) have been studied. For composite films prepared by co-depositions of Co and rubrene on Si(100), the surface is smooth while a layered distribution of Co atoms is detected. The structural change of buried Co is explored using AFM after washing out the rubrene molecules in the composite films. For thin composite films, the formation of separated Co clusters in the films results in a larger coercive force due to the imperfection introduced by rough interface to impede the magnetization reversal. By changing the rubrene concentration, rubrene served as a surfactant and the optimal condition for a better quality of the films could be obtained. These information are valuable for future applications of organic molecules in spintronics. In the final part, experimental evidences shows the formation of nanocrystalline cobalt for Co/Si(100). After insertion of rubrene layer, the segregation of rubrene modifies the growth behavior of the deposited Co to form an amorphous film and the reduction of the coercive force is attributed to the less imperfections in magnetic materials. By further exploration of the defects in the films by magneto-optical Kerr microscopy, the point defects of Co/rubrene/Si(100) follow the one-dimensional bowing model with strong defect-domain wall interactions. The information concerning the surfactant effects of rubrene for growing Co/Si(100) is valuable for future applications of organic semiconductors for spintronics devices.
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紅熒烯, 鈷, 彈性模量, 磁光柯爾效應, rubrene, cobalt, modulus, magneto-optical Kerr effect