Observation of Perpendicular Orientation in Symmetric Diblock Copolymer Thin Films on Rough Substrates
Observation of Perpendicular Orientation in Symmetric Diblock Copolymer Thin Films on Rough Substrates
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DOI：
10.1021/ma021625f
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发表时间：
2003-07
期刊：
影响因子：
5.5
通讯作者：
E. Sivaniah;Y. Hayashi;M. Iino;T. Hashimoto;K. Fukunaga
中科院分区：
文献类型：
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作者：
E. Sivaniah;Y. Hayashi;M. Iino;T. Hashimoto;K. Fukunaga
在过去的十年里，关于固体衬底上层状嵌段共聚聚合物薄膜的取向问题已经有了大量的研究。继首次报道支撑薄膜中平行的片层取向之后，1进一步的研究揭示了层状区的阶梯状形成，以及薄膜厚度和由此产生的所谓的“岛或孔”聚合物表面形态之间的内在联系。2虽然其他地方给出了很好的评价，3最相关的发现是基材和空气表面的嵌段共聚物相互作用是至关重要的。当嵌段共聚物的某一组分在这些表面上存在优先的热引力时，观察到嵌段共聚物片层的表面定向平行取向。平衡嵌段共聚物组分和结合表面之间的焓相互作用会改变这一取向。由两个中性面对称结合的嵌段共聚聚合物薄膜在聚苯乙烯-嵌段-聚甲基丙烯酸甲酯(PS-PMMA)薄膜中观察到垂直取向。4在非对称边界条件下，当PS-b-PMMA薄膜的上表面暴露在非中性气氛(如空气)中时，出现了混合取向(平行和垂直)。5最近，一些研究着眼于衬底地形或粗糙度对决定片状嵌段共聚聚合物薄膜行为的影响。根据特纳和乔安妮的预测，6李等人。7在含有周期性栅状衬底形貌的衬底上寻找平行片层取向的反保角振荡的出现。Fasolka等人。8在开槽硅衬底上观察到超薄(小于片状微区尺寸)嵌段共聚物薄膜中的“横向微区”。据我们所知，没有文献报道表明衬底的粗糙度可以用来抑制衬底导向的平行片层的生长。在这一简短的交流中，我们介绍了这种现象被推断已经发生并导致(与中性空气/聚合物界面一起)形成垂直取向片层的情况。参考文献7和8中使用的栅状衬底被认为是理想的，因为它们具有良好控制和各向异性的垂直幅度(R)和横向特征波长(λ)。QR(式中Q≡2π/λ)是表征基片粗糙度的一个方便的参数。我们发现，玻璃基板上的某些氧化铟锡(ITO)涂层(古口化学株式会社，日本东京)也可以具有类似的良好控制的基板粗糙度，尽管不表现出各向异性的表面特征。虽然这种交流并没有试图理解ITO中结构形成的本质，但这一特征与凝聚的ITO合金在沉积过程中的晶化有关。
In the past decade, there has been a significant amount of research related to the orientation of lamellar block copolymer thin films supported on a solid substrate. Following the first reports of parallel lamellar orientation in supported thin films, 1 further studies revealed terrace-like formation of lamellar domains and the intrinsic relationship between thin film thickness and the resulting so-called “island or hole” polymer surface morphology. 2 While excellent reviews are given elsewhere, 3 the most relevant discovery was that the block copolymer interactions at the substrate and air surfaces were crucial. When there was a preferential enthalpic attraction for one of the block copolymer components at these surfaces, a surface-directed parallel orientation of block copolymer lamellae was observed. Equalizing the enthalpic interactions between the block copolymer components and the bounding surfaces alters this orientation. A block copolymer thin film symmetrically bounded by two neutral surfaces led to the observation of perpendicular orientation in poly (styrene)-block-poly (methyl methacrylate)(PS-PMMA) thin films. 4 A mixed orientation (parallel and perpendicular) is seen under asymmetric boundary conditions, eg, when the upper surface of the PS-b-PMMA thin film is exposed to a nonneutral atmosphere (eg, air). 5 More recently, some research has looked at the effects of substrate topography or roughness in determining the behavior of lamellar block copolymer thin films. Following predictions by Turner and Joanny, 6 Li et al. 7 looked for the appearance of anticonformal oscillations of a parallel lamellar orientation on a substrate containing a periodic grating-like substrate topography. Fasolka et al. 8 observed “lateral domains” in ultrathin (less than the lamellar domain size) block copolymer films on grooved silicon substrates. To our knowledge, there are no reports in the literature to suggest that the roughness of a substrate can be used to inhibit the growth of substrate-directed parallel lamellae formation. In this brief communication we present situations where this phenomenon was inferred to have occurred and resulted (in conjunction with a neutral air/polymer interface) in the formation of perpendicularly oriented lamellae. The grating-like substrates used in refs 7 and 8 are considered ideal in the sense that they have a vertical amplitude (R) and lateral characteristic wavelength (λ) that are well-controlled and anisotropic. qR (where q≡2π/λ) is a convenient parameter to characterize the roughness of the substrate. We have found that certain indium tin oxide (ITO) coatings on glass substrates (Furuuchi Chemical Co., Tokyo, Japan) can have similarly well-controlled substrate roughness, though not exhibiting the anisotropic topographical characteristics. Though this communication does not try to understand the nature of structure formation in ITO, this feature is related to crystallization of the condensed ITO alloy during deposition.