Top-down and Bottom-up approaches to nanotechnology An overview in the context of developing Proton-fountain Electric-field-assisted Nanolithography (PEN):

I. ABSTRACT Nanomaterials fabrication methods can be classified according to whether their assembly followed either i) the so called bottom-up approach, where smaller components of atomic or molecular dimensions self-assemble together, according to a natural physical principle or an externally applied driving force, to give rise to larger and more organized systems; or ii) the top-down approach, a process that starts from a large piece and subsequently uses finer and finer tools for creating correspondingly smaller structures. These two approaches to nanotechnology are briefly reviewed in this lecture. The objective is not to offer a comprehensive review but, instead, to illustrate the main principles characterizing the two approaches to nanotechnology. On the top-down side, we include the description of radiation and non-radiation based lithography methods used for fabricating electronic nano-devices; on the bottom-up side we include self-assembly methodology to fabricate polymer nanostructures. To provide coherence to this narrative, this review is written from a perspective gained while developing Proton-fountain Electric-field-assisted Nanolithography (PEN), a new technique being developed by our group. PEN aims at building nanostructures with stimuli responsive polymer materials. We are motivated by the fact that the development of chemically functionalized materials, such that their physical properties can vary in response to external mechanical, chemical, or optical stimuli, offers potential applications in a wide range of fields, namely microfluidics, electronic memory devices, sensors and actuators.