Integration of Top-Down and Bottom-Up Nanofabrication Schemes
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Integration of Top-Down and Bottom-Up Nanofabrication Schemes Pascale Maury,a Olga Crespo-Biel,a Mária Péter,a David N. Reinhoudt,a Jurriaan Huskensa,b Laboratory of Supramolecular Chemistry & Technology and bMESA+ Strategic Research Orientation Nanofabrication University of Twente, MESA+ Institute for Nanotechnology PO Box 217, 7500 AE, The Netherlands [email protected] a
ABSTRACT The fabrication of 3D nanostructures, which have tunable, sub-100 nm dimensions in all three directions, is a key issue of nanotechnology. Here we describe the integration of top-down nanoimprint lithography (NIL) and bottom-up layer-by-layer (LBL) assembly for the preparation of 3D hybrid nanostructures. NIL provided down to sub-100 nm poly(methylmethacrylate) (PMMA) structures. These were employed to fabricate patterned selfassembled monolayers of cyclodextrin (CD) host molecules on silicon oxide . The consecutive LBL assembly with adamantyl guest-functionalized dendrimers and CD-modified gold nanoparticles resulted in patterned multilayer structures with thicknesses of 3-30 nm. The x,y control by NIL and the z control by LBL assembly ultimately allowed the fabrication of circular structures with a radius of 25 nm and a thickness of 20 nm. The integration of the two methods has thus yielded a versatile 3D nanofabrication methodology comprising of 10-40 process steps.
INTRODUCTION Nanotechnology deals with enabling technologies for the fabrication and study of materials (atoms, molecules, particles, etc.) on the nanoscale. In order to study nanoobjects, the preparation of nanoobjects is not enough: careful study of its individual properties usually require anchoring to a substrate, and preferably to targeted or prepatterned areas of a substrate. Nanofabrication is the subdiscipline that deals with the development of general fabrication methodologies for the preparation of nanoobjects as well as of patterned substrates and of assembly methods for the anchoring of the objects to the patterned areas. In general, nanofabrication methods fall into two classes, which are called top-down and bottom-up. Examples of the former are: lithography, soft lithography, and evaporation techniques (e.g. shadow mask evaporation), while the latter consist of e.g. supramolecular assembly, nanoparticle formation, monolayer self-assembly, directed self-assembly, and probe lithography. However, the dividing line between the two classes is sometimes vague and a matter of opinion. Nevertheless, the integration of top-down and bottom-up nanofabrication schemes is considered a key issue for the advance of nanotechnology. In the following, we will show an elaborate example of such an integration attempt. We chose to use nanoimprint lithography (NIL) as the top-down technique, because it is a technique that allows sub-10 nm resolution in pattern replication and has recently been put forward by the semiconductor industry as the most promising technique to be implemented in future chip fabrication processes. As the bottom-up technique, we chose lay
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