Photothermally induced microchemical functionalization of organic monolayers.
Photothermally induced microchemical functionalization of organic monolayers.
复制标题
光热诱导有机单层的微化学功能化。
作者：
Benjamin Klingebiel;A. Schröter;S. Franzka;N. Hartmann
有机涂层的光图案化代表了从微芯片制造到生物阵列和微流体器件设计等许多技术应用中的关键步骤。从根本上讲，这些应用依赖于光化学过程，其中化学反应是通过直接或底物介导的电子激发引发的。在最简单的情况下，涂层会发生分解。然而，广泛的光化学程序也允许有机涂层的局部功能化。反过来，横向分辨率通常受到光学衍射的限制，也就是说，即使使用高聚焦光学器件，所制造的结构也不会比波长小很多。当然，扫描近场光刻可以实现亚波长图案化。然而，处理速度非常慢并且仅限于小区域。增强远场光学技术横向分辨率的方法是利用非线性效应。例如，在光热激光加工中，聚焦激光束用于局部加热基材表面并热引发化学反应。因此，光热加工在激光功率密度方面具有高度非线性，并且有利于亚波长图案化。近年来，有机单层作为光热图案化平台特别引人注目。一般来说，横向分辨率取决于涂层的热稳定性和化学稳定性。强结合涂层，例如基于硅烷的单层，可以从微米范围到亚 100 nm 范围进行图案化。这些图案已被用作化学模板，以从纳米级组件构建功能性表面结构。这些结果强调了光热程序在有机界面微米和纳米制造中的能力。但通常，有机单层的光热处理会导致涂层的局部分解。当然，与光化学程序类似，探索允许局部功能化有机单层的光热程序是很诱人的。这些过程为更复杂的化学表面结构（例如多功能模板和化学梯度）开辟了一条简便的途径。作为原型示例，我们在此提出了在气态溴环境中对表面氧化的硅基材上的烷基硅氧烷单层进行局部功能化的光热程序。如下所述，该过程利用了常见光溴化反应的一些特征。碳氢化合物的光溴化代表了有机合成中的经典反应。之前的贡献还研究了聚合物界面和有机单层的大面积光溴化。与其他化学转化相结合，这提供了获得多种官能团的有效途径。反应（1）-（5）概括了潜在的自由基反应机制。
Photopatterning of organic coatings represents a key step in many technological applications ranging from microchip fabrication to the design of bioarrays and microfluidic devices. Fundamentally, these applications rely on photochemical proACHTUNGTRENNUNGcesses, in which chemical reactions are initiated via direct or substrate-mediated electronic excitations. In the simplest case decomposition of the coating takes place. A broad range of photochemical routines, though, also allows for local functionalization of organic coatings. The lateral resolution, in turn, usually is limited by optical diffraction, that is, the fabricated structures are not much smaller than the wavelength even when highly focusing optics is used. Scanning near-field photolithography, of course, allows for sub-wavelength patterning. Processing, though, is very slow and restricted to small areas. A means to enhance the lateral resolution of far-field optical techniques takes advantage of nonlinear effects. In photothermal laser processing, for example, a focused laser beam is used to locally heat the substrate surface and to thermally initiate chemical reactions. For this reason, photothermal processing is highly nonlinear in laser power density and facilitates sub-wavelength patterning. In recent years, organic monolayers have gained particular attraction as photothermally patternable platforms. Generally, the lateral resolution depends on the thermal and chemical stability of the coating. Strongly bound coatings, for example silane-based monolayers, can be patterned from the micrometer range down to the sub 100 nm range. Such patterns have been used as chemical templates to build up functional surface architectures from nanoscopic components. These results emphasize the capabilities of photothermal routines in microand nanofabrication of organic interfaces. Commonly, though, photothermal processing of organic monolayers results in local decomposition of the coating. In analogy to photochemical routines, of course, it is tempting to explore photothermal procedures which allow to locally functionalize organic monolayers. Such procedures open up a facile avenue towards more complex chemical surface structures such as multifunctional templates and chemical gradients. As a prototype example, we here address a photothermal procedure for local functionalization of alkylsiloxane monolayers on surface-oxidized silicon substrates in a gaseous bromine ambient. As outlined below, this procedure takes advantage of some characteristic features of common photobromination reactions. Photobromination of hydrocarbons represents a classical reaction in organic synthesis. Previous contributions also investigated large-area photobromination of polymer interfaces and organic monolayers. In conjunction with other chemical transformations this provides an efficient route to a broad variety of functional groups. Reactions (1)–(5) recapitulates the underlying radical reaction mechanism.