Fabrication Of Metallic Nanostructure By Nanoimprint Lithography

As an important part of nanoscience and nanotechnology, nanomanufacturingtechnology has attracted great attention of scientist and industry because of itsimportant scientific value and broad application in energy, information, electronics etc.As the continued development of the technology, the device integration isbecoming higher, and the size of the nanostructure is getting smaller and smaller,which make the traditional photolithography are no longer meet the industrial demand.On this basis, the next-generation lithography technology was quickly developed,such as electron beam (EBL) lithography, focused ion beam lithography, x-raylithography and extreme ultraviolet lithography. At the same time, the nanoimprintlithography (NIL) was first proposed by Stephen Chou in1995. The resolution of thefabricated nanostructure by using this method did not suffer from the opticaldiffraction limit, thus this method can be used for fabricate ultra-high resolutionnanostructures, in addition, this method still has the unique advantages of high yield,low cost which is suitable for industrial applications, and shows the extremelycompetitive and broad application prospects. But the nanoimprint molds, especiallynanoscale molds are mainly fabricated by EBL and other direct-write methods whichmake the cost very high, and become a major obstacle to restrict the development ofnanoimprint lithography. It is very important to develop new method for fabricatingnanostructures or molds by using the micro-scale mold. At the same time, metallic nanostructures have attracted great attention becauseof its potential applications in environment detection, surface plasmon resonance(SPR), solar cell, nanomedcine et al. But how to fabricate the function metallicnanostructures with low cost and large areas is still a big challenge.Based on above considerations, we have demonstrated some new methods tofabricate nanostructures by using the micro-scale molds. And by using these methods,the one dimensional metallic nanowire grating, two dimensional nanoantenna arraysand three dimensional metallic nanohole arrays are successfully fabricated. This thesisincludes the following three parts.Firstly, we demonstrated a feasible method which called twice-NIL (T-NIL) forthe fabrication of periodic Ag nanowires with the scale of sub-100nm by using themicro-scale mold. Furthermore, the metal nanowires with different widths andheights can be generated by adjusting the imprinting parameters with the same stamp.This method can be applied for other materials and structures. In addition to fabricatethe metal nanowires, the PMMA nanostructure can be transferred to a siliconsubstrate or h-PDMS and used as the nanoimprint mold.Secondly, through the T-NIL, we fabricate PMMA bowtie nanoantennas (BNAs)by using grating mold. The PMMA BNAs are transferred to silicon substrate and h-PDMS and used as the NIL molds. Each fabricated BNA is consisting of two oppositesemicircle, which is different from the type of the previously reported BNAsconsisting of two opposing tip-to-tip triangles. To the best of our knowledge, suchkind of BNAs is the first time to be fabricated. The metallic bowtie nanoantennaarrays were successfully fabricated by using this mold. The distance between thepaired metallic nanoantennas can be reduced to10nm. The finite-difference time-domain calculation and surface-enhanced Raman scattering experiment demonstratethat this kind of bowtie nanoantenna array has the similar property as other bowtie nanoantennas.Thirdly, by the combination of tilted evaporate and nanotransfer lithography, thethree-dimensional metallic hollow taper nanohole arrays are fabricated. By select thedeposition angle and deposition times, we have fabricated three kinds of this structurewith different gap. Using this method, three-dimensional metallic nanostructures withlarge areas can be easily fabricated without obvious defects. Due to the damagednanostructure symmetry, these metal structures showing the unique reflection andtransmission spectra property, which is expected to be applied to the localized surfaceplasmon resonance sensing.