Colloidal inorganic nanocrystal based nanocomposites: Functional materials for micro and nanofabrication

The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices. © 2010 by the authors

Development of Graphene and Graphene-Nanoparticle Composites for Sensor Applications

The goal of this research was the synthesis of graphene and graphene nanocomposite for use as sensor materials. This dissertation describes the optimization of a novel approach to the synthesis of few layer graphene films on SiC, the modification of the graphene surface by wet chemical methods, the nucleation of nanoparticles to form graphene-nanoparticle composites, the fabrication of chemoresistive sensor structures from these materials, and the characterization of these surfaces and films.;In this work, the basic graphene synthesis method which uses halogen based plasma etching and ultra-high vacuum annealing (UHVA), has been optimized to reliably produce one, two, and three layer graphene on SiC films. The process has also been extended by replacing the UHVA step with rapid thermal annealing (RTA) in atmospheric pressure argon. Graphene films produced by both methods have been characterized using x-ray photoelectron spectroscopy (XPS), Raman microscopy, and atomic force microscopy (AFM). The UHVA process produces films with halogen-based and possibly some oxygen-based defects, whereas the RTA processes produces exclusively oxygen-based defects which include epoxide, hydroxyl, and carbonyl groups similar to, but at much lower levels, than that observed for graphene oxide (GO). As in the case for GO, the defect density was further reduced by wet chemical surface modification.;Nanoparticles (Ag, Au, Pt, Ir) were attached to these surfaces using solution based methods. The particle diameter and height distributions along with surface coverage were characterized using AFM methods. Key parameters in these studies included solution composition and incubation time. For electrical characterization and sensor testing, two structures were then fabricated using lithography free methods and electron beam evaporation. The first of these structures, referred to as the transmission line method (TLM) structure, was used in the present work for electrical characterization. Using the TLM structure, the electrical properties were characterized using two and four point probe methods. The films exhibited semiconducting behavior which is believed to be due to the opening of a band gap by the halogen- and oxygen-based defects. Using the two and four pint methods, the Schottky barrier height, the carrier density, electrical resistivity, and the carrier mobility were determined. The electrical resistivity was found to have an inverse relationship with number of graphene layers for one, two, and three layer films. The second device structure was a simple interdigitated sensor structure which was passed on to other researchers for sensor studies. Overall, reliable and reproducible synthesis and fabrication methods for graphene and graphene-nanoparticle composites have been developed for the next stage of testing and sensor development

A Novel Nanocomposite with Photo-Polymerization for Wafer Level Application

©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.A novel nanocomposite photo-curable material which can act both as a photoresist and a stress redistribution layer applied on the wafer level was synthesized and studied. In the experiments, 20-nm silica fillers were modified by a silane coupling agent through a hydrolysis and condensation reaction and then incorporated into the epoxy matrix. A photo-sensitive initiator was added into the formulation which can release cations after ultraviolet exposure and initiate the epoxy crosslinking reaction. The photo-crosslinking reaction of the epoxy made it a negative tone photoresist. The curing reaction of the nanocomposites was monitored by a differential scanning calorimeter with the photo-calorimetric accessory. The thermal mechanical properties of photo-cured nanocomposites thin film were also measured. It was found that the moduli change of the nanocomposites as the filler loading increasing did not follow the Mori–Tanaka model, which indicated that the nanocomposite was not a simple two-phase structure as the composite with micron size filler. The addition of nano-sized silica fillers reduced the thermal expansion and improved the stiffness of the epoxy, with only a minimal effect on the optical transparency of the epoxy, which facilitated the complete photo reaction in the epoxy

Advanced micro and nano fabrications for engineering applications

This document is a compilation of my selected research publications in micro and nano fabrications. The papers are largely arranged in chronological order to show the development of research interests. The research works are grouped into three sections. Section one consists of 34 research papers on micro fabrication in various materials. The research was motivated by the development of a finger nail sized micro engine as explained in Papers 1 and 2. Section two of the document includes some research activities and achievements on nanocomposite materials embedded in metallic and ceramic matrices. Section 3 includes the papers to reflect the research in developing nanostructure fabrication processes. The research contained in this DSc submission shows a continuous exploration and development of novel micro/nano fabrication processes. Although the submission covers research activities spanning 15 years, from 2000 to 2015, many of the research results represent the top technology of the time. They have contributed to the ever progressing manufacturing capability of the world. The research has encompassed both theoretical and experimental studies, contributing to the understanding of the processes and materials involved

From Cleanroom to Desktop: Emerging Micro-Nanofabrication Technology for Biomedical Applications

This review is motivated by the growing demand for low-cost, easy-to-use, compact-size yet powerful micro-nanofabrication technology to address emerging challenges of fundamental biology and translational medicine in regular laboratory settings. Recent advancements in the field benefit considerably from rapidly expanding material selections, ranging from inorganics to organics and from nanoparticles to self-assembled molecules. Meanwhile a great number of novel methodologies, employing off-the-shelf consumer electronics, intriguing interfacial phenomena, bottom-up self-assembly principles, etc., have been implemented to transit micro-nanofabrication from a cleanroom environment to a desktop setup. Furthermore, the latest application of micro-nanofabrication to emerging biomedical research will be presented in detail, which includes point-of-care diagnostics, on-chip cell culture as well as bio-manipulation. While significant progresses have been made in the rapidly growing field, both apparent and unrevealed roadblocks will need to be addressed in the future. We conclude this review by offering our perspectives on the current technical challenges and future research opportunities

FABRICATION OF MAGNETIC TWO-DIMENSIONAL AND THREE-DIMENSIONAL MICROSTRUCTURES FOR MICROFLUIDICS AND MICROROBOTICS APPLICATIONS

Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production. This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications

Incorporating nanomaterials with MEMS devices.

This dissertation demonstrates an elegant method, known as \u27micro-origami\u27 or strain architecture to design and fabricate three-dimensional MEMS structures which are assembled using actuation of a metal-oxide bilayer with conventional planar lithography. Folding allows creating complex, robust, three-dimensional shapes from two-dimensional material simply by choosing folds in the right order and orientation, small disturbances of the initial shape may also be used to produce different final shapes. These are referred to as pop-up structures in this work. The scope of this work presented the deposition of colloidal gold nanoparticles (GNPs) into conformal thin films using a microstenciling technique. Results illustrated that the gold nanoparticle deposition process can easily be integrated into current MEMS microfabrication processes. Thin films of GNPs deposited onto the surfaces of siliconbased bistable MEMS and test devices were shown to have a significant effect on the heating up of microstructures that cause them to fold. The dissertation consists of four chapters, covering details of fabrication methods, theoretical simulations, experimental work, and existing and potential applications. Chapter II illustrates how control of the folding order can generate complex three-dimensional objects from metal-oxide bilayers using this approach. By relying on the fact that narrower structures are released from the substrate first, it is possible to create multiaxis loops and interlinked objects with several sequential release steps, using a single photomask. The structures remain planar until released by dry silicon etching, making it possible to integrate them with other MEMS and microelectronic devices early in the process. Chapter III depicts the fabrication process of different types of bistable structures. It describes the principle of functioning of such structures, and simulations using CoventorWare are used to support the concept. We talk over about advantages and disadvantages of bistable structures, and discuss possible applications. Chapter IV describes fabrication procedure of nanoparticle-MEMS hybrid device. We introduce a convenient synthesis of GNPs with precisely controlled optical absorption in the NIR region by a single step reaction ofHAuCl4 and Na2S203. We take a look at different techniques to pattern gold nanoparticles on the surface of MEMS structures, and also provide a study of their thermal properties under near IR stimulation. We demonstrate the first approach of laser-driven bistable MEMS actuators for bioapplications. Finally, in Conclusion discuss the contributions of this dissertation, existent limitations and plans of the future work