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Du K, Wathuthanthri I, Liu Y, Xu W, Choi CH.
ACS Appl Mater Interface2012 Oct 24;4(10):5505-14
Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
Abstract
In this paper, we report on a cost-effective and simple, nondestructive pattern transfer method that allows the fabrication of metallic nanostructures on a polydimethylsiloxane (PDMS) substrate on a wafer scale. The key idea is to use holographic nanopatterns of a photoresist (PR) layer as template structures, where a metal film is directly deposited in order to replicate the nanopatterns of the PR template layer. Then, the PDMS elastomer is molded onto the metal film and the metal/PDMS composite layer is directly peeled off from the PR surface. Many metallic materials including Ti, Al, and Ag were successfully nanopatterned on PDMS substrates by the pattern transfer process with no use of any adhesion promoter layer or coating. In case of Au that has poor adhesion to PDMS material, a salinization of the metal surface with 3-(aminopropyl)-triethoxysilane (APTES) monolayer promoted the adhesion and led to successful pattern transfer. A series of adhesion tests confirmed the good adhesion of the transferred metal films onto the molded PDMS substrates, including scotch-tape and wet immersion tests. The inexpensive and robust pattern transfer approach of metallic nanostructures onto transparent and flexible PDMS substrates will open the new door for many scientific and engineering applications such as micro-/nanofluidics, optofluidics, nanophotonics, and nanoelectronics.
Additional Information
Wafer-scale lightweight, stretchable and bendable plasmonic nanostructures that can be used for highly sensitive structural detection of low concentration analytes are boosting prospects of in-situ biomedical detection. Recently, such materials have been developed by the research group of Prof. Choi at the Stevens Institute of Technology and published in the journal of ACS Applied Materials & Interfaces [1]. Many groups have been working on the development of efficient ways to fabricate uniform arrays of nanoscale features based on noble metals such as gold and silver in a large area (up to several inches) for the applications to plasmonic sensing. However, most of these efforts were limited by the high cost and low throughput of the fabrication process such as electron-beam lithography or focused ion beam lithography. So far, none of these is recognized as efficient for wafer-scale nanopatterning techniques. By contrast, researchers at Prof. Choi’s group, including Mr. Ke Du, Mr. Ishan Wathuthanthri, Dr. Yuyang Liu, and Dr. Wei Xu, have made groundbreaking advances by using laser interference lithography to create uniform polymer nanoarrays on a polished silicon substrate [2-4]. The nanopatterns defined by the laser inteference lithography are then used as template for the direct deposition and transfer of a nanopatterned metal film onto various substrate materials [1, 5]. Metal layer was uniformly deposited on the polymer template so that the reversed nanopatterns were transferred to the deposited metal surface. Polydimethylsiloxane (PDMS), one type of flexible, transparent and bio-compatible polymer was then directly molded and cured on the metal film to transfer the metallic nanopatterns onto the PDMS by mechanically peeling the nanopatterned metal film off from the initial silicon substrate. By using this technique, nanowell and nanograting patterns can be easily created on PDMS substrate. One of the key advantages of the technique is that the pattern periodicity and shapes of the nanostructures can be easily tuned by simply modulating the incident angle of the laser interference lithography system. The development of these highly flexible metal nanostructures on PDMS substrate, which cover a large area, is of great significance in flexible plasmonic sensors for probing chemical species in a wide range of fields down to single molecule level.
References
K. Du, I. Wathuthanthri, Y. Liu, W. Xu, C.-H. Choi, “Wafer-Scale Pattern Transfer of Metal Nanostructures on Polydimethylsiloxane (PDMS) Substrates via Holographic Nanopatterns”, ACS Applied Materials & Interfaces 4, 5505-5514 (2012).
I. Wathuthanthri, W. Mao, C.-H. Choi, “Two Degrees-of-Freedom Lloyd-Mirror Interferometer for Superior Pattern Coverage Area”, Optics Letters 36, 1593-1595 (2011).
W. Mao, I. Wathuthanthri, C.-H. Choi, “Tunable Two-Mirror Interference Lithography System for Wafer-Scale Nanopatterning”, Optics Letters 36, 3176-3178 (2011).
I. Wathuthanthri, Y. Liu, K. Du, W. Xu, C.-H. Choi, “Simple Holographic Patterning for High-Aspect-Ratio Three-Dimensional Nanostructures with Large Coverage Area”, Advanced Functional Materials 23, 608-618 (2013).
K. Du, I. Wathuthanthri, W. Mao, W. Xu, C.-H. Choi, “Large-Area Pattern Transfer of Metallic Nanostructures on Glass Substrates via Interference Lithography”, Nanotechnology 22, 285306 (2011).
