Nanoscale fabrication by nonconventional approaches.

An overview of three major nonconventional approaches in nanofabrication, scanning probe microscopy lithography, self-assembly, and imprint lithography, is presented. Typically, these nonconventional approaches are emerging technologies based on simple principles with potential cost-effective manufacturability, as compared to those conventional processes that are widely used and highly developed for making microelectronic circuits. Following the introduction of nonconventional technologies and their significances in nanofabrication, the details of each approach are presented. The lithographic applications of scanning probe microscopy, which involves three major variations: scanning tunneling microscopy, atomic force microscopy, and scanning near-field optical microscopy, are first evaluated with emphasis on their abilities in making structures with subnanoscale resolutions. The principles and processes for each technique are presented while their differences are also discussed. For the second approach, self-assembly, which uses a bottom-up fabrication strategy, is reported starting with an introduction of its basic principle. Self-assembly, with and without externally controlled forces for patterning nanoscale structures, is then examined. The associated principles and procedures of key assembling processes are presented. The third one, imprint lithography, is addressed with an emphasis on its recent progress and challenges. The nanolithographic abilities of different techniques developed using the general imprinting principle are examined. Finally, concluding remarks are provided to summarize the major technologies studied and to recommend the scopes for technology improvement and future research.