University of Pennsylvania Researchers Demonstrate a Flexible, One-Step Assembly of Nanoscale Structures

July 28, 2008

PHILADELPHIA -- Scientists at the University of Pennsylvania have created a one-step, repeatable method for the production of functional nanoscale patterns or motifs with adjustable features, size and shape using a single master "plate."

Researchers took advantage of the elastic instability of a widely used, flexible polymer membrane, polydimethylsiloxane, or PDMS. When exposed to a solvent, circular pores in the membrane elliptically deform, and elastic interactions between them generate long-range orientational order of their axes into a "diamond plate" pattern. By lacing the solvent with iron nanoparticles, the team found that evaporation of the solvent drives the assembly of the nanoparticles onto the membrane surface along these distorted pores.

This results in two-dimensional patterns with sub-100 nanometer features. The traditional fabrication process can take as long as a month and cost $50,000 per print. In this new process, a master can be made for a fraction of the cost and can be reused many times. The Penn team's technique does not require delicate surface preparation or the complex chemistry of standard lithographic processes. Instead, the new process relies on patterns that form spontaneously in equilibrium. The resulting, "diamond-plate" pattern persists over the entire sample, as large as a square centimeter, with no imperfections.

The features of the resultant nanoparticle patterns are up to 10 times sharper than the original membrane. The resulting symmetry of the film can be transferred onto a substrate, both flat or curved, where it can be used to generate similar anisotropic magnetic, photonic, phononic and plasmonic properties.

"These functional nano-motifs could in turn benefit novel technologies that are sensitive to local environment change such as smart clothing, biomarkers and eco-friendly buildings," Shu Yang, assistant professor in the Department of Materials Science and Engineering of the School of Engineering and Applied Science at Penn, said. "Using similar pattern transformation principles, our technique could be extended to pattern a variety of material systems such as polymers and composites, creating a new design mechanism for nanoscale manufacturing."

The team modeled the elastic instability of the membrane in terms of elastically interacting "dislocation dipoles" and found complete agreement between the theoretical ground state and the observed pattern. This model allows for the manipulation of the structural details of the membrane to tailor the elastic distortions and generate a variety of nanostructures.

"It is both surprising and serendipitous that the simple theory is corroborated by experiment and by complex numerical simulations by other groups," Randall Kamien, professor in the Department of Physics and Astronomy in the School of Arts and Sciences at Penn, said.

The natural world provides many examples of the type of intrinsic, bottom-up effects that engineers see here, from the arrangement of growing leaves on a plant to the pattern of animal stripes to fingerprints. In these systems, instabilities, packing constraints and simple geometries drive the formation of delicate, detailed and beautiful patterns. Mechanical instabilities in soft polymers, precipitated by dewetting, swelling and buckling during the production stage, are often viewed as failure mechanisms that can interfere with the performance of devices. However, these instabilities are now being exploited to assemble complex patterns, to fabricate novel devices such as stretchable electronics and flexible microlenses and to provide a metrology for measuring elastic moduli and the thickness of ultrathin films.

PDMS membranes have been widely used in soft lithography for low-cost fabrication of microdevices. The Penn team replica-molded a PDMS membrane with circular pores from an array of 1 μm diameter silicon pillars spaced 2 μm apart on a square lattice. When exposed to the organic solvent toluene, PDMS gels swell by as much as 130 percent. As the osmotic pressure builds, the circular pores in the PDMS deform and eventually snap shut to relieve the stress, much as the joints in railways and bridges expand and contract to maintain structural integrity in response to changes in moisture and temperature.

Because the elastic deformation of the PDMS membrane is induced by solvent swelling, the diamond plate pattern in PDMS is stable in the wet state and snaps back to the original square lattice once the solvent evaporates. To capture the diamond plate before evaporation and, more important, to utilize this deformation for assembly of complex functional structures, the team suspended superparamagnetic Fe3O4 nanoparticles in toluene and applied the solution to the PDMS membrane. As the PDMS swells, the convective assembly of the nanoparticles follows, faithfully replicating the deformed PDMS membrane. Once dry, the elastic membrane returns to its original state and can be reused.

The study was published in the journal Nano Letters and was conducted by members of the Laboratory for Research on the Structure of Matter at Penn: Ying Zhang, Anna Peter, Pei-Chun Lin and Yang of the Department of Materials Science and Engineering and Elisabetta A. Matsumoto and Kamien of the Department of Physics and Astronomy.

Funding was provided by the National Science Foundation MRSEC Program and an NSF Career Award bestowed upon Yang.

University of Pennsylvania

---

---

	Nanoscale Structure and Assembly at Solid-Fluid Interfaces: Volume I: Interfacial Structures versus Dynamics, Volume II: Assembly in Hybrid and ... (Nanostructure Science and Technology) (v. 1) by Xiang Yang Liu (Editor), James J. De Yoreo (Editor) All of us have read about the vast potential inherent in nanotechnology and the exciting impact it has had in changing our lifestyle in the 21st century. One of the basic issues confronting us is how to fabricate devices or materials on the nano scale. What is the basic physics governing the formation of nano phases? How can biological systems inspire us to formulate nano scale architectures, in the way nature has always done and continues to do? These are two main areas of focus in this book. The aim of this reference is to take us to the root of these issues: the solid-fluid interfacial structures and the basic interactions between structural units that determine the kinetics of nano particles and assembly formation, and subsequently the resulting structures and functionalities of...
	Nanoscale Structure and Properties of Microbial Cell Surfaces by Elena P. Ivanova (Editor) This book presents an accessible and comprehensive survey of recent advances in the understanding of the structure and properties of microbial cell surfaces. Gathering leading experts in the field, it is the first book to cover the fundamental knowledge of microbial cell surfaces at the nanometre-scale resolution that is now provided by various scanning probe microscopy techniques (SPM). The advent of SPM has recently opened up a wide range of novel and fascinating applications for biological research. The book presents the most recent advances in the application of SPM techniques to study cell surfaces. It is a useful guide for researchers that are seeking to tap the power and scope of this technology to further their own work on cell surface structure and properties. The book also...
	Physical Properties of Ceramic and Carbon Nanoscale Structures: The INFN Lectures, Vol. II (Lecture Notes in Nanoscale Science and Technology) by Stefano Bellucci (Editor) This is the second volume in a series of books on selected topics in Nanoscale Science and Technology based on lectures given at the well-known INFN schools of the same name. The aim of this collection is to provide a reference corpus of suitable, introductory material to relevant subfields, as they mature over time, by gathering the significantly expanded and edited versions of tutorial lectures, given over the years by internationally known experts. The present set of notes stems in particular from the participation and dedication of prestigious lecturers, such as Andrzej Huczko, Nicola Pugno, Alexander Malesevic, Pasquale Onorato and Stefano Bellucci. All lectures were subsequently carefully edited and reworked, taking into account the extensive follow-up discussions. A tutorial...
	Heat and Fluid Flow in Microscale and Nanoscale Structures (Developments in Heat Transfer) by Mohammad Faghri (Author), Mohammad Faghri (Editor), B. Sunden (Editor) Over the last 20 years, micro/nanoscale flow and heat transfer have been a most active area of interdisciplinary research, involving scientists from various specialities including engineering, physics, chemistry and materials science. Presenting state-of-the-art knowledge in heat transfer and fluid flow in micro- and nanoscale structures, this book provides invaluable information for both graduate researchers and R&D engineers in industry and consultancy. All of the chapters are invited contributions from some of the most prominent scientists in the field and follow a unified outline and presentation to aid accessibility.
	Nanoscale Multifunctional Materials: Science & Applications by S. Mukhopadhyay (Author) A multidisciplinary approach that explores the diverse properties, functions, and applications of nanomaterialsDrawing together the many scientific and engineering disciplines underlying the development of nanomaterials, Nanoscale Multifunctional Materials provides a multidisciplinary review of the diverse properties, functions, and applications of nanomaterials. The book examines both nanoparticles, which have larger-scale equivalents, and uniquely assembled nanomaterials, which do not have larger-scale equivalents. Readers will gain a tremendous appreciation of the versatility of nanomaterials as well as an understanding of how the same nanomaterial can have several distinct applications across a broad range of fields and industries.Nanoscale Multifunctional Materials is divided into...
	Photonic Structures Inspired by Nature (Springer Theses) by Mathias Kolle (Author) Unlike most natural colours that are based on pigment absorption, the striking iridescent and intense colouration of many butterflies, birds or beetles stems from the interaction of light with periodic sub-micrometer surface or volume patterns, so called “photonic structures”. These “structural colours” are increasingly well understood, but they are difficult to create artificially and exploit technologically. In this thesis the field of natural structural colours and biomimetic photonic structures is covered in a wide scope, ranging from plant photonics to theoretical optics. It demonstrates diffractive elements on the petal surfaces of many flowering plant species; these form the basis for the study of the role of structural colours in pollinator attraction. Self-assembly...
	Embedded Memories for Nano-Scale VLSIs (Integrated Circuits and Systems) by Kevin Zhang (Editor) The book provides a comprehensive and in-depth view on the state-of-the-art embedded memory technologies. The book helps practicing engineers grasp key technology attributes and advanced design techniques in nano-scale VLSI design. It also helps them make decisions concerning the right design tradeoffs in real product development. This book first provides an overview on the landscape and trend of embedded memory in various VLSI system designs, including high-performance microprocessor, low-power mobile handheld devices, micro-controllers, and various consumer electronics. It then shows an in-depth view on each different type of embedded memory technology, including high-speed SRAM, ultra-low-voltage and alternative SRAM, embedded DRAM, embedded nonvolatile memory, and emerging or...
	Complex Phenomena in Nanoscale Systems (NATO Science for Peace and Security Series B: Physics and Biophysics) by Giulio Casati (Editor), Davron Matrasulov (Editor) Nanoscale physics has become one of the rapidly developing areas of contemporary physics because of its direct relevance to newly emerging area, nanotechnologies. Nanoscale devices and quantum functional materials are usually constructed based on the results of fundamental studies on nanoscale physics. Therefore studying physical phenomena in nanosized systems is of importance for progressive development of nanotechnologies. In this context study of complex phenomena in such systems and using them for controlling purposes is of great practical importance. Namely, such studies are brought together in this book, which contains 27 papers on various aspects of nanoscale physics and nonlinear dynamics.
	Isotope Low-Dimensional Structures: Elementary Excitations and Applications (SpringerBriefs in Physics) by Vladimir G. Plekhanov (Author) This Briefs volume describes the properties and structure of  elementary excitations in isotope low-dimensional structures. Without assuming prior knowledge of quantum physics, the present book provides the basic knowledge needed to understand the recent developments in the sub-disciplines of nanoscience isotopetronics, novel device concepts and materials for nanotechnology. It is the first and comprehensive interdisciplinary account of the newly developed scientific discipline isotopetronics.
	Zein self-assembled nanoscale structures for microencapsulation.: An article from: Emerging Food R&D Report by Gale Reference Team (Author) This digital document is an article from Emerging Food R&D Report, published by Thomson Gale on July 1, 2007. The length of the article is 427 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Zein self-assembled nanoscale structures for microencapsulation. Author: Gale Reference Team Publication: Emerging Food R&D Report (Newsletter) Date: July 1, 2007 Publisher: Thomson Gale Volume: 18 Issue: 4 Page: NA Distributed by Thomson...