Y. Xia

Bio: Y. Xia is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 621 citations.

Patterning: Principles and Some New Developments

Abstract: This article provides an overview of various patterning methodologies, and it is organized into three major sections: generation of patterns, replication of patterns, and three-dimensional patterning. Generation of patterns from scratch is usually accomplished by serial techniques that are able to provide arbitrary features. The writing process can be carried out in many different ways. It can be achieved using a rigid stylus; or a focused beam of photons, electrons, and other energetic particles. It can also be accomplished using an electrical or magnetic field; or through localized add-on of materials such as a liquid-like ink from an external source. In addition, some ordered but relatively simple patterns can be formed by means of self-assembly. In replication of patterns, structural information from a mask, master, or stamp is transferred to multiple copies with the use of an appropriate material. The patterned features on a mask are mainly used to direct a flux of radiation or physical matter from a source onto a substrate, whereas a master/stamp serves as the original for replication based on embossing, molding, or printing. The last section of this article deals with three-dimensional patterning, where both vertical and lateral dimensions of a structure need to be precisely controlled to generate well-defined shapes and profiles. The article is illustrated with various examples derived from recent developments in this field.

Soft lithography for micro- and nanoscale patterning

Abstract: This protocol provides an introduction to soft lithography--a collection of techniques based on printing, molding and embossing with an elastomeric stamp. Soft lithography provides access to three-dimensional and curved structures, tolerates a wide variety of materials, generates well-defined and controllable surface chemistries, and is generally compatible with biological applications. It is also low in cost, experimentally convenient and has emerged as a technology useful for a number of applications that include cell biology, microfluidics, lab-on-a-chip, microelectromechanical systems and flexible electronics/photonics. As examples, here we focus on three of the commonly used soft lithographic techniques: (i) microcontact printing of alkanethiols and proteins on gold-coated and glass substrates; (ii) replica molding for fabrication of microfluidic devices in poly(dimethyl siloxane), and of nanostructures in polyurethane or epoxy; and (iii) solvent-assisted micromolding of nanostructures in poly(methyl methacrylate).

Soft robotics for chemists

Abstract: In areas from assembly of machines to surgery, and from deactivation of improvised explosive devices (IEDs) to unmanned flight, robotics is an important and rapidly growing field of science and technology. It is currently dominated by robots having hard body plans—constructions largely of metal structural elements and conventional joints—and actuated by electrical motors, or pneumatic or hydraulic systems. Handling fragile objects—from the ordinary (fruit) to the important (internal organs)—is a frequent task whose importance is often overlooked and is difficult for conventional hard robots; moving across unknown, irregular, and shifting terrain is also. Soft robots may provide solutions to both of these classes of problems, and to others. Methods of designing and fabricating soft robots are, however, much less developed than those for hard robots. We wish to expand the methods and materials of chemistry and soft-materials science into applications in fully soft robots. A robot is an automatically controlled, programmable machine. The limbs of animals or insects—structures typically based on rigid segments connected by joints with constrained ranges of motion—often serve as models for mobile elements of robots. Although mobile hard robots sometimes have limb-like structures similar to those of animals (an example is “Big Dog” by Boston Robotics), more often, robots use structures not found in organisms—for example, wheels and treads. The robotics community defines “soft robots” as: 1) machines made of soft—often elastomeric—materials, or 2) machines composed of multiple hard-robotic actuators that operate in concert, and demonstrate soft-robot-like properties; here, we consider only the former. Soft animals offer new models for manipulation and mobility not found, or generated only with difficulty and expense, using hard robots. Because materials from which this class of devices will be fabricated will usually be polymers (especially elastomers), they fall into the realm of organic materials science. The use of soft materials allows for continuous deformation. This type of deformation, in turn, enables structures with ranges of motion limited only by the properties of the materials. Soft robots have the potential to exploit types of structures found, for example, in marine organisms, and in non-skeletal parts of land animals. The tentacles of squid, trunks of elephants, and tongues of lizards and mammals are such examples; their structures are muscular hydrostats. Squid and starfish 14] are highly adept locomotors; their modes of movement have not been productively used, and permit solutions of problems in manipulation, locomotion, and navigation, that are different from those used in conventional hard robotics. The prototypical soft actuator—muscle—developed through the course of evolution. There is currently no technology that can replicate the balanced performance of muscle: it is simultaneously strong and fast, and enables a remarkable range of movements (such as those of a tongue). Muscle-like contraction and dilation occur in ionic polymeric gels on changes in the acidity or salinity of a surrounding ionic solution, but actuation in macroscopic structures is masstransport limited, and typically slow. Other electroactive polymers (EAPs) include dielectric elastomers, electrolytically active polymers, polyelectrolyte gels, and gel-metal composites. Pneumatically-driven McKibben-type actuators are among the most highly developed soft actuators, and have existed for more than fifty years; they consist of a bladder covered in a shell of braided, strong, inextensible fibers. These actuators can be fast, and have a length-load dependence similar to that of muscle but possess only one actuation mode—contraction and extension when pressurization changes. They are, in a sense, an analogue to a single muscle fibril ; using them for complex movements requires multiple actuators acting in series or parallel. Pneumaticallydriven flexible microactuators (FMAs) have been shown to be capable of bending, gripping, and manipulating objects. Roboticists have explored scalable methods for gripping and manipulating objects at the micro and nano scales. The use of compliant materials allows grippers to manipulate objects such as fruit with varied geometry. The field of robotics has not yet caught the attention of soft-materials scientists and chemists. Developing new materials, techniques for fabrication, and principles of design will create new types of soft robots. The objective of this work is to demonstrate a type of design that provides a range of behaviors, and that offers chemists a test bed for new materials and methods of fabrication for soft robots. Our designs use embedded pneumatic networks (PneuNets) of channels in elastomers [*] Prof. G. M. Whitesides Wyss Institute for Biologically Inspired Engineering Harvard University, 3 Blackfan Circle, Boston, MA 02115 (USA) Fax: (+ 1)617-495-9857 and Kavli Institute for Bionano Science & Technology 29 Oxford Street, Cambridge MA (USA) E-mail: gwhitesides@gmwgroup.harvard.edu Homepage: http://gmwgroup.harvard.edu/

Shape-Controlled Synthesis and Surface Plasmonic Properties of Metallic Nanostructures

Abstract: The interaction of light with free electrons in a gold or silver nanostructure can give rise to collective excitations commonly known as surface plasmons. Plasmons provide a powerful means of confining light to metal/dielectric interfaces, which in turn can generate intense local electromagnetic fields and significantly amplify the signal derived from analytical techniques that rely on light, such as Raman scattering. With plasmons, photonic signals can be manipulated on the nanoscale, enabling integration with electronics (which is now moving into the nano regime). However, to benefit from their interesting plasmonic properties, metal structures of controlled shape (and size) must be fabricated on the nanoscale. This issue of MRS Bulletin examines how gold and silver nanostructures can be prepared with controllable shapes to tailor their surface plasmon resonances and highlights some of the unique applications that result, including enhancement of electromagnetic fields, optical imaging, light transmission, colorimetric sensing, and nanoscale waveguiding.