Polymeric and Biomolecular Nanostructures: Fabrication by Scanning Probe Lithography
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One central goal of materials engineering is to produce hierarchical materials that are ordered over a range of length scales and in which larger-scale structural and physicochemical properties are controlled by molecular characteristics. Fabricating molecular, polymeric, and biomolecular structures on surfaces and controlling their architecture on the nanometer length scale is important for a wide range of applications. For example, the ability to pattern surfaces with polymers and biomacromolecules has important applications in biosensors, proteomic chips, and nanofluidic devices. To date, fabrication of micropatterns and microstructures for these applications has relied on either photolithography or an ensemble of related techniques termed “soft lithography” that use elastomeric stamps or molds. These techniques have been extremely successful at the micrometer length scale or larger, but have a number of inherent limitations that preclude their extension to the nanometer length scale. X-ray lithography requires expensive mask alignment equipment, and the photoresists and developers commonly used are incompatible with many organic and biomolecules. Furthermore, like electron beam lithography, it requires expensive ultrahigh vacuum equipment.
This review will focus on methods that allow for molecular-level control in the fabrication of polymeric and biomolecular nanostructures using scanning probe lithography (SPL),). Among all the available nanofabrication techniques, SPL has unique advantages because of its simplicity and capability to both manipulate and image nanostructures on surfaces. In contrast to other nanofabrication methods, SPL, which is capable of resolution less than 50 nm is technologically simpler, significantly cheaper, and therefore a much more widely accessible method to most researchers, requiring only a scanning probe microscope (SPM) such as a scanning tunneling microscope (STM. ), an atomic force microscope (AFM ), or a near-field scanning optical microscope (NSOM).
SPL can behave like an interactive plotter, registering with nanostructures on a surface, while offering resolution comparable to electron beam lithography The slow-speed serial nature of the lithography process can be circumvented by employing cantilever arrays.