ABSTRACT
Alternatives to numerical approaches, physical experiments, if repeatable, offer reliable and, in many cases, insightful investigations of nanoscale fluid flows through direct or indirect measurements of specific properties. For system setup and parameter measurements, there is no significant difference in experiments at the macro- and nanoscales. In terms of fabrication techniques and flow investigation methods, however, nanoscale flow experiments do have special characteristics as compared with macroscale experiments. Experiments for macroscale flows can be conducted on a prototype, i.e., a physical system, or a model, which is similar to the prototype but may have different dimensions. For nanoscale flows, unfortunately, investigations usually cannot be conducted in a large-scale model because the surface effects in large-scale systems become insignificant and the key flow physics for nanoscale flows may be lost. Therefore, nanoscale flow experiments can be mainly performed in nanofluidic systems. This requires the fabrication of nanoscale flow channels and fluidic devices, which is more challenging than that of macroscale systems. Most of the fabrication techniques for microelectromechanical systems (MEMS) can be employed for nanostructure fabrication. Nanochannels can be etched in a substrate or constructed on a surface. These can also be formed by using advanced nanomaterials, such as CNTs. Due to the way that nanochannels are fabricated, nanochannel fabrication techniques are categorized into bulk nanomachining, surface nanomachining, nanoimprint lithography (NIL), nanolithography, and nanomaterial-based fabrication. Except for the last method, nanomaterial-based fabrication, nanochannels are fabricated on a substrate, which needs to be well-cleaned before the fabrication. In the following sections, wafer cleaning and substrate preparation are discussed first, which are followed by the introduction of different fabrication techniques.
