| 摘要: | 本研究主要探討弱分離嵌段共聚物—聚苯乙烯-b-聚（甲基丙烯酸甲酯）（PS-b-PMMA））與低分子量均聚物—聚苯乙烯（hPS）以及氘代聚苯乙烯（dPS）的混摻薄膜於熱退火之形態探討。通過簡單的熱退火過程，根據調整混合物中均聚物的含量、薄膜厚度以及退火溫度的不同，以獲得幾種不同之奈米形態。由於低分子量的hPS以及dPS相較於嵌段共聚物PS及PMMA鏈段皆具較低表面能，因此經由退火過程後的薄膜傾向以平行基材（SiOx/Si）的排列方向形自組裝奈米形態，且薄膜樣品表面皆會有一層潤濕層（wetting layer）。
為了觀察材料的內部結構，本實驗主要以氧氣離子電漿蝕刻的方式移除潤濕層以及增強PS與PMMA鏈段間的對比度，利用光學顯微鏡（OM）、掃描式電子顯微鏡（SEM）、低掠角小角度X光散射技術（GISAXS）、X光反射率掃描量測（XRR）與中子反射儀（ToF-NR）鑑定其混摻薄膜結構，探討低混摻量薄膜所形成的平行穿孔層結構（perforated layer, PL//）。
透過臨場實驗（in-situ）以及量測不同入射角之方式（angle-dependent），以獲得五個顯著的繞射及散射特徵，分別為（I）truncation rods,（II）Yoneda streaks,（III）shoulder arcs,（IV）meridian streaks（V）a circle of diffraction spots。在薄膜中心區域主要可觀察到特徵（I）至（IV），而特徵（V）則主要來自於厚膜較厚邊緣之處所形成的雙螺旋結構（double-gyroid, DG）。由於雙螺旋結構為一亞穩態，故透過延長退火時間得以消除此結構的產生。
然而，由於折射效應（refraction distortion effect）的影響，沿qz方向的定量分析具有一定的挑戰性。本研究透過定量分析特徵（I）與特徵（III）可判別水平穿孔層之堆疊方式，結果如下：230 oC下退火，主要為ABC堆疊；270 oC下退火，主要為AB堆疊。此外，亦透過中子反射儀（ToF-NR）的量測，擬合薄膜平行穿孔層結構之單層厚度以及薄膜整體厚度，發現相比於270°C下進行退火，在230°C條件下之dPS鏈段更容易優先聚集於薄膜自由表面而產生表面偏析現象（surface segregation）。
;We have demonstrated the phase behavior of substrate-supported films of a symmetric weakly segregated polystyrene-block-poly (methyl methacrylate), P(S-b-MMA), block copolymer, and its blends with low-molecular-weight homopolystyrene (hPS) & deuterated-polystyrene (dPS) at different compositions. Upon finely tuning the blending ratio, film thickness, and temperature, we can obtain several nanostructures. All the nanodomains were obtained simply by thermal annealing. For the annealed films, self-assembled nanodomains tend to adopt parallel orientation on SiOx/Si. Because of low molecular weights, both dPS and hPS homopolymers have lower surface energies than the PS and PMMA blocks. As a result, there should be a PS overlayer on the surface.
Surface morphologies and structures in blend films were characterized by an optical microscope (OM), a scanning electron microscope (SEM), grazing-incidence small-angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) or time of flight neutron reflectivity (ToF-NR). To remove the surface wetting layer and to increase the contrast between the PS and PMMA nanodomains for morphological observations through SEM characterization, the blend films on SiOx/Si were etched by oxygen plasma. The morphological observations and structural characterization demonstrate that the blend films formed perforated layers (PL//) with parallel orientation.
In-situ and angle-dependent GISAXS results demonstrate five features: (i) truncation rods, (ii) the Yoneda streaks, (iii) shoulder arcs on the equatorial axis, (iv) meridian streaks and (v) a circle of diffraction spots. Features (i)-(iv) are shown in the GISAXS region and feature (v) is shown in the GTSAXS region. Features (i)-(iv) were produced from the middle region of the blend films. For thick films, feature (v) was present and produced from the film edge. The quantitative analysis of features (i) and (iii) demonstrate that PS-b-PMMA/PS blend films formed perforations with either AB stacks or ABC stacks. Feature (v) indicate that the edge of the thick films preferentially formed double gyroid. The double-gyroid phase is a metastable phase because it cannot preserve after prolonged annealing. Due to the refraction distortion effect, the quantitative analysis along the qz direction remains a challenging task. For thick blend films, ABC stacks of perforations are favored at 230 oC and AB stacks of perforations are favored at 270 oC. ABC and AB stacks of perforations were deeply studied by in-situ and angle-dependent GISAXS. Furthermore, a time-of-flight neutron reflectometer (ToF-NR) demonstrates that the surface of a PS-b-PMMA/dPS film was enriched with dPS chains when the film was annealed at 230 oC. The surface preference of dPS chains could be prohibited at 270 oC. |
