Rabih Zaouk

A Case for Fractal Electrodes in Electrochemical Applications

Fractal electrode designs are proposed for electrochemical devices. A zeroth-order approximation fractal model is analyzed and basic insights into the scaling laws of the electrical properties and the surface-to-area ratio are derived. Fractal electrodes can minimize internal resistance while maximizing surface-to-volume ratios. Recent carbon microelectromechanical systems CMEMS techniques show great promise for use in the fabrication of fractal electrodes for electrochemical applications. Preliminary results showing carbon fractal electrodes fabricated using C-MEMS techniques are presented.

Introduction to microfabrication techniques.

The advent of photolithography literally brought about the integrated circuit (IC) revolution of the latter part of the twentieth century. Almost all electronic devices that we use today have one or more ICs inside. Improving lithography techniques led to smaller and smaller transistors, which translated into faster and more efficient computing machines. Photolithography also powered the advent of MicroElectroMechanical Systems (MEMS), which are now starting to become more and more diverse in commercial products from mechanical to biomedical devices, helping to change the way people perceive the applicability of IC technology. In this chapter, we examine basic photolithography techniques and their uses in soft lithography and MEMS.

Design and fabrication of an ac-electro-osmosis micropump with 3D high-aspect-ratio electrodes using only SU-8

Lab-on-a-chip devices require integrated pumping and fluid control in microchannels. A recently developed mechanism that can produce fluid flow is an integrated ac-electro-osmosis micropump. However, like most electrokinetic pumps, ac-electro-osmotic pumps are incapable of handling backpressure as the pumping force mechanism acts on the surface of the fluid rather than the bulk. This paper presents a novel 3D electrode structure designed to overcome this limitation. The electrodes are fabricated using carbon-MEMS technology based on the pyrolysis of the photo-patternable polymer SU-8. The novel ac-electro-osmosis micropump shows an increase in the flow velocity compared to planar electrodes.

Carbon as a MEMS material: micro and nanofabrication of pyrolysed photoresist carbon

Carbon, like Si, is an attractive and very versatile engineering material and is available in more structural varieties than Si. Carbon materials are already in use in a wide variety of applications because of their widely differing crystalline structures and properties, which enable very different physical, chemical, mechanical, thermal and electrical uses. Carbon-based Microelectromechanical Systems (MEMS) and Nanoelectromechanical Systems (NEMS), with sizes ranging from millimetre to nanometre, can provide solutions, alone or in combination with Si and other materials for microelectronics, nanoelectronics, sensors, miniaturised power systems, etc. In this review, Carbon-MEMS (C-MEMS) and Carbon-NEMS (C-NEMS) technology based on pyrolysis of patterned photoresist is reviewed. The fabrication process and the most promising applications are introduced.

Fabrication of polydimethylsiloxane microfluidics using SU-8 molds.

We detail the widely prevalent technique of polydimethylsiloxane (PDMS) molding using SU-8 for creating microfluidic chambers and channels. Although other techniques such as injection molding are more apt for mass manufacturing and cost-effective, PDMS molding is used almost exclusively for rapid prototyping in corporate and research environments because of its simplicity and fast turnaround time.

Fabrication of microelectrodes using the lift-off technique.

The lift-off technique is one of the most prevalent methods for fabricating microelectrodes on a flat surface (e.g., a silicon [Si] wafer). It represents an alternative for metal-etching techniques that often utilize hazardous chemicals in order to define a pattern. This chapter presents an example of patterning gold electrodes on an Si wafer.

Validation of lithography based on the controlled movement of light-emitting particles

A novel particle-based lithography is proposed. In this approach a particle moving in a liquid in contact with a light-sensitive substrate creates traces on that substrate (for example on a photoresist or on a photographic film). The light-emitting particle causes photochemical/photoelectric changes in the light-sensitive substrate, creating a latent image. A group of these particles can be used to write many features on the same substrate in a parallel manner. We investigate the use of electrokinetic forces to move the particles over the light-sensitive substrate. We also report on the use of high-aspect-ratio carbon MEMS (C-MEMS) electrodes as 3D dielectrophoretic traps for the light-emitting particles and investigate the feasibility of using these carbon electrodes to manipulate the light-emitting particles to trace sub-micron patterns on a light-sensitive surface. We propose two types of particle-based lithography schemes and discuss applicable scaling laws. Feasibility experiments were carried out using microscale devices.

Fractal Carbon-MEMS Electrodes: Theory and Preliminary Fabrication

Fractal electrode designs are proposed for electrochemical devices. A zeroth-order approximation fractal model is analyzed and basic insights into the scaling laws of the electrical properties and the surface-to-area ratio are derived. Fractal electrodes can minimize internal resistance while maximizing surface to volume ratios. Recent C-MEMS techniques show great promise for use in the fabrication of fractal electrodes for electrochemical applications. Preliminary results showing carbon fractal electrodes fabricated using C-MEMS techniques are presented.

C-MEMS/NEMS: A Novel Technology for Nanoscale Material Formation From Graphite Fiber to Ni and Si Nanowires

Carbon microelectromechanical systems (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have received much attention because of the many potential applications. Some important applications include: DNA arrays, glucose sensors, microbatteries and biofuel cells. Microfabrication of carbon structures using current processing technology, including focused ion beam (FIB)1 and reactive ion etching (RIE)2 , is time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as widely varying properties of the resulting devices limits the use of screen printing of commercial carbon inks for C-MEMS. Our newly developed C-MEMS microfabrication technique is based on the pyrolysis of photo patterned resists34 . Figure 1(a) shows a typical SEM image of C-MEMS/NEMS features with carbon posts connected by carbon fibers. Figure 1(b) shows a typical carbon post with carbon nanofibers on its side surfaces.Copyright