探討奈米粒子對PS-b-P4VP雙塊式高分子之影響與PS-b-P4VP雙塊式高分子薄膜應用於記憶體元件

Abstract

此論文主旨為利用小角度散射技術來偵測球狀PS-b-P4VP雙塊式共聚高分子/苯乙基硫醇-Au奈米粒子複合材料於熱處理期間的結構演進。研究結果發現Au奈米粒子起初以具部分團簇隨機地分佈在PS相中，經過170°C真空下熱處理4小時後，由電子顯微鏡與anomalous小角度散射觀察得知，Au遷移至PS與P4VP的界面，進而形成一層包覆在P4VP球外的Au殼排列。此結構更被證實是可以穩定的以PS-Au-P4VP微胞結構保存於甲苯中。 接著，本論文進一步探討分別將親水性的CdSe奈米粒子與疏水性的Au奈米粒子先後操控置入P4VP與PS相中。利用2-D SAXS鑑定發現在含有適當的CdSe與Au體積分率的PS-b-P4VP/CdSe/Au三元複合材料，會使原本為層狀結構之PS-b-P4VP轉變為擬四方體單晶結構。此一相轉變乃由於CdSe與Au奈米粒子分別置入P4VP與PS後造成內聚更強的P4VP/CdSe核與較鬆散的PS/Au殼，導致溶劑移除後PS-b-P4VP/CdSe/Au能以穩定的微包結構取代融合回層狀而存在於固相中，並以溶劑退火(solvent annealing)後堆疊成擬四方體單晶結構。 最後，本論文利用柱狀PS-b-P4VP雙塊式共聚高分子製備可靠的(reliable)有機非揮發性記憶體。Al/PS-b-P4VP/ITO元件乃由溶液製程在ITO基材上旋轉塗佈30奈米厚且具六方堆積(hexagonal)奈米結構之PS-b-P4VP薄膜，並蒸鍍Al為上電極。此一新穎的有機非揮發性記憶體on/off ratio可以達到2×105，寫入和抹除的時間可達到微秒(us)的狀態，且有超過104秒的資料保存時間(retention time)與推估可使用長達10年以上。根據Al/PS-b-P4VP/ITO元件於On-state下的變溫I-V曲線特性分析，元件之電流隨溫度下降而上升，代表導電行為似金屬特性。因此，判定所屬的記憶機制應為金屬導線(metallic filament)。利用此具奈米結構的雙塊式共聚高分子薄膜，經由簡單的溶液製程製備有機記憶體元件，將提供一條新的有機非揮發性記憶體製程途徑。

In this dissertation, we used in situ annealing small-angle X-ray scattering (SAXS) to monitor the structural evolution of a spherical poly(styrene-b-4- vinylpyridine) diblock copolymer (PS-b-P4VP)/2-phenylethanethiol-coated Au nanoparticle (NP) mixture in the solid state during its thermal annealing. We found that the Au NPs that existed initially in a random state with some cluster packing in the PS domain diffused to the interface of the amphiphilic PS-b-P4VP diblock copolymer within 4 h at 170 °C under vacuum to form NP-filled shell-like assemblies, as evidenced from transmission electron microscopy and anomalous SAXS. The Au NP nano-shell assemblies were stable even after redissolving in toluene. Furthermore, we found that two kinds of NPs—hydrophilic pyridine-coated CdSe NPs and hydrophobic dodecanethiol-coated Au NPs—collectively self- assemble in the PS and P4VP blocks, respectively, of a lamellar PS-b-P4VP diblock copolymer to form a pseudo-tetragonal single-crystalline structure as evidenced from SAXS. The formation of a tetragonal-like single crystal results from micelle structures possessing strong hydrophilic P4VP/CdSe cores and hydrophobic PS/Au coronas that prevented the cores from forming the randomly oriented lamellar domains. Instead, the composite microphase separated into a long-range-ordered structure. Finally, we reported the performance of a nonvolatile memory device based on a solution-processed PS-b-P4VP thin film. The Al/PS-b-P4VP/ITO memory device featuring metal-coordinated 30-nm-diameter P4VP cores exhibited an ON/OFF ratio of 2×105, an erase voltage of 0.75 V, a write voltage of –0.5 V, and a retention time of 104 s. The device exhibited metallic behavior in the ON state, suggesting the formation of metallic filaments through the migration of Al atoms into the P4VP domain during writing. Such nanostructured diblock copolymer thin films open up new avenues for fabricating organic memory devices using simple procedures.