Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
X-Ray Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Nano Lett. 2017 Dec 13;17(12):7814-7823. doi: 10.1021/acs.nanolett.7b04028. Epub 2017 Nov 21.
Template-free directed self-assembly of ultrathin (approximately tens of nanometers) lamellar block copolymer (l-BCP) films into vertically oriented nanodomains holds much technological relevance for the fabrication of next-generation devices from nanoelectronics to nanomembranes due to domain interconnectivity and high interfacial area. We report for the first time the formation of full through-thickness vertically oriented lamellar domains in 100 nm thin polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films on quartz substrate, achieved without any PMMA-block wetting layer formation, quartz surface modification (templating chemical, topographical) or system modifications (added surfactant, top-layer coat). Vertical ordering of l-BCPs results from the coupling between a molecular and a macroscopic phenomenon. A molecular relaxation induced vertical l-BCP ordering occurs under a transient macroscopic vertical strain field, imposed by a high film thermal expansion rate under sharp thermal gradient cold zone annealing (CZA-S). The parametric window for vertical ordering is quantified via a coupling constant, C (= v∇T), whose range is established in terms of a thermal gradient (∇T) above a threshold value, and an optimal dynamic sample sweep rate (v ∼ d/τ), where τ is the l-BCP's longest molecular relaxation time and d is the T - T distance. Real-time CZA-S morphology evolution of vertically oriented l-BCP tracked along ∇T using in situ grazing incidence small angle X-ray scattering (GISAXS) exhibited an initial formation phase of vertical lamellae, a polygrain structure formation stage, and a grain coarsening phase to fully vertically ordered l-BCP morphology development. CZA-S is a roll-to-roll manufacturing method, rendering this template-free through-thickness vertical ordering of l-BCP films highly attractive and industrially relevant.
无模板导向自组装超薄（约数十纳米）层状嵌段共聚物（l-BCP）薄膜形成垂直取向纳米区，由于具有良好的域间连通性和高界面面积，在从纳米电子学到纳米膜的下一代器件制造方面具有重要的技术相关性。我们首次报道了在石英衬底上的 100nm 厚聚苯乙烯-嵌段-聚甲基丙烯酸甲酯（PS-b-PMMA）薄膜中形成完全贯穿厚度的垂直取向层状畴，无需形成任何 PMMA 嵌段润湿层、石英表面改性（模板化学、形貌）或体系改性（添加表面活性剂、顶层涂层）。l-BCP 的垂直有序是由分子和宏观现象之间的耦合作用产生的。在急剧温度梯度冷区退火（CZA-S）下，由于薄膜热膨胀率高导致瞬时宏观垂直应变场的作用下，分子弛豫诱导垂直 l-BCP 有序化。通过耦合常数 C（=v∇T）定量了垂直有序的参数窗口，其范围是根据高于阈值的温度梯度∇T 和最佳动态样品扫描速率 v（∼d/τ）建立的，其中τ是 l-BCP 的最长分子弛豫时间，d 是 T-T 距离。使用原位掠入射小角 X 射线散射（GISAXS）跟踪垂直取向 l-BCP 的实时 CZA-S 形态演变，沿∇T 显示了垂直片层的初始形成相、多晶结构形成阶段和晶粒粗化相，最终形成完全垂直有序的 l-BCP 形态。CZA-S 是一种卷对卷制造方法，使得这种无模板贯穿厚度的 l-BCP 薄膜垂直有序化具有很高的吸引力和工业相关性。
