California NanoSystems Institute, University of California, Los Angeles , Los Angeles, California 90095, United States.
Department of Chemistry and Biochemistry, University of California, Los Angeles , Los Angeles, California 90095, United States.
Acc Chem Res. 2016 Aug 16;49(8):1449-57. doi: 10.1021/acs.accounts.6b00034. Epub 2016 Apr 11.
We discuss the origins, motivation, invention, development, applications, and future of chemical lift-off lithography, in which a specified pattern of a self-assembled monolayer is removed, i.e., lifted off, using a reactive, patterned stamp that is brought into contact with the monolayer. For Au substrates, this process produces a supported, patterned monolayer of Au on the stamp in addition to the negative pattern in the original molecular monolayer. Both the patterned molecular monolayer on the original substrate and the patterned supported metal monolayer on the stamp are useful as materials and for further applications in sensing and other areas. Chemical lift-off lithography effectively lowers the barriers to and costs of high-resolution, large-area nanopatterning. On the patterned monolayer side, features in the single-nanometer range can be produced across large (square millimeter or larger) areas. Patterns smaller than the original stamp feature sizes can be produced by controlling the degree of contact between the stamp and the lifted-off monolayer. We note that this process is different than conventional lift-off processes in lithography in that chemical lift-off lithography removes material, whereas conventional lift-off is a positive-tone patterning method. Chemical lift-off lithography is in some ways similar to microtransfer printing. Chemical lift-off lithography has critical advantages in the preparation of biocapture surfaces because the molecules left behind are exploited to space and to orient functional(ized) molecules. On the supported metal monolayer side, a new two-dimensional material has been produced. The useful important chemical properties of Au (vis-à-vis functionalization with thiols) are retained, but the electronic and optical properties of bulk Au or even Au nanoparticles are not. These metal monolayers do not quench excitation and may be useful in optical measurements, particularly in combination with selective binding due to attached molecular recognition elements. In contrast to materials such as graphene that have bonding confined to two dimensions, these metal monolayers can be straightforwardly patterned-by patterning the stamp, the initial monolayer, or the initial substrate. Well-developed thiol-Au and related chemistries can be used on the supported monolayers. As there is little quenching and photoabsorption, spectroscopic imaging methods can be used on these functionalized materials. We anticipate that the properties of the metal monolayers can be tuned by varying the chemical, physical, and electronic connections made by and to the supporting molecular layers. That is, the amount of charge in the layer can be determined by controlling the density of S-Au (or other) connections and the molecular backbone and functionality, which determine the strength with which the chemical contact withdraws charge from the metal. This process should work for other coinage-metal substrates and additional systems where the binding of the outermost layers to the substrate is weaker than the molecule-substrate attachment.
我们讨论了化学掀离光刻的起源、动机、发明、发展、应用和未来，在这种光刻中，使用与自组装单层接触的反应性、图案化的压印模具来去除指定的自组装单层图案，即掀离。对于 Au 基底，该过程除了在原始分子单层中的负图案之外，还在压印模具上产生 Au 的支撑图案化单层。原始基底上的图案化分子单层和压印模具上的图案化支撑金属单层都可用作材料，并可进一步用于传感和其他领域。化学掀离光刻有效地降低了高分辨率、大面积纳米图案化的障碍和成本。在图案化单层方面，可以在大（平方毫米或更大）面积上产生单纳米级的特征。通过控制压印模具和掀离的单层之间的接触程度，可以产生小于原始压印模具特征尺寸的图案。我们注意到，与光刻中的常规掀离过程不同，化学掀离光刻去除材料，而常规掀离是一种正性图案化方法。化学掀离光刻在制备生物捕获表面方面具有关键优势，因为留下的分子被用来空间和定向功能（化）分子。在支撑金属单层方面，已经产生了一种新的二维材料。Au 的有用的重要化学性质（相对于与硫醇的功能化）得以保留，但块状 Au 甚至 Au 纳米粒子的电子和光学性质则没有。这些金属单层不会猝灭激发，并且可能在光学测量中有用，特别是与由于附着的分子识别元件而产生的选择性结合结合使用时。与具有限于两个维度的键合的材料（如石墨烯）不同，这些金属单层可以通过图案化压印模具、初始单层或初始基底来简单地进行图案化。可以在支撑的单层上使用成熟的硫醇-Au 和相关化学物质。由于猝灭和光吸收很少，因此可以在这些功能化材料上使用光谱成像方法。我们预计，通过改变支撑分子层的化学、物理和电子连接，可以调整金属单层的性质。也就是说，可以通过控制 S-Au（或其他）连接的密度以及分子骨架和功能来确定层中的电荷量，这决定了化学接触从金属中提取电荷的强度。该过程应该适用于其他 coinage-metal 基底和其他外层与基底的结合弱于分子-基底附着的附加系统。
