Electrostatic Self-Assembly of Nanoparticles
Summary:
NanoSonic, Inc., is refining a molecular self-assembly process, called electrostatic self-assembly (ESA), that produces thin films with material properties that can be precisely controlled. The synthesis can be performed at room temperature, is environmentally benign, and can be done on a variety of substrate materials. ESA could be used to produce materials with superior electrical, mechanical, and optical constitutive properties. NanoSonic is currently developing novel materials and associated devices.
Technology Description:
NanoSonic, Inc., (Blacksburg, VA) is refining a molecular self-assembly process, called electrostatic self-assembly (ESA), that can produce thin film materials with nanoscale-level molecular uniformity: as such, it is an enabling technology for producing thin films with precise control of their physical properties. In comparison to conventional manufacturing methods, ESA processing offers a number of advantages. ESA is a simple, low-cost fabrication method that is performed at room temperature and is environmentally benign. It requires little capital investment, since little specialized equipment is required, and offers many technical advantages such as 1) the capability to deposit on almost any substrate, including plastics and irregularly-shaped or very large substrates, which pose a problem for alternate techniques, 2) the capability to precisely grade optical, electrical, mechanical, thermal, and other properties on the nanometer scale, and 3) the potential to easily pattern the resulting films.
In ESA synthesis, a substrate is simply dipped into alternate aqueous solutions containing anionic and cationic materials such as polymer complexes; metal and oxide nanoclusters; cage-structured molecules such as fullerenes; and proteins and other biomolecules. Nearly perfect molecular order is achieved by individual molecules seeking least energy configurations (the tendency of any substance to change to the state of least energy). Adsorbed from water solutions, these molecules bond with others already attached at the substrate surface. Material properties can then be precisely controlled through the successive stacking of ultra-uniform, nanometer-thick layers of the film.
Other advantages of the ESA process include:
•Fast thin-film formation: The ESA molecular adsorption process should only require seconds for molecules to form least energy configurational bonds at the substrate surface, making practical the rapid formation of robust multilayer systems.
•Large surface-area application: Using simple dipping or spraying, alternating ionic bonding allows the fabrication of multilayer thin films over very large surfaces of structural materials.
•Thin-film synthesis at room temperature and pressure: Avoidance of high-temperature burnout processing means that multilayer coatings can be created on any solid substrate or active device material, including polymer composite structural members and separation membrane materials without material degradation. Flexible electronic material design allows a wide variety of organic and inorganic materials to be used; this additionally allows tailoring of the electronic work function, thus improving the external quantum efficiency of electronic and electro-optic devices.
•Compatibility with conventional low-cost photolithographic processes: Multiple ESA material layers self-assembled by ionic bonding may be patterned using charge stamping, photolithography, nanoimprint lithography, UV laser irradiation, and other methods to create large-scale integrated devices. ESA is an environmentally friendly process, involving no volatile organic compounds and consuming negligible electricity.
MDA Origins:
Through BMDO STTR and SBIR contracts, NanoSonic demonstrated the feasibility of using ESA to develop a variety of materials. One class of material demonstrated was nonlinear optical (NLO) thin films. NLO thin films can replace telecommunications mechanical components, improving speed and reliability. Additional BMDO SBIR work was undertaken to demonstrate the feasibility of using ESA processes to integrate such multiple functions as electromechanical actuation, semiconductor junction-based signal processing, thermal transport, optical switching and modulation into nanostructured organic/inorganic thin-film actuator materials. These materials could be useful in spacecraft control. ESA has also received SBIR development funding from DARPA, the Air Force, NASA, the National Science Foundation, and NIST.
Spinoff Applications:
The potential commercial product applications of self-assembled nanomaterials, and devices that may be formed using such materials, is widespread for several reasons. Fundamentally, the nanometer-scale dimension of the molecules used to form such materials leads to important variations in energy band properties. These variations result in the modification and improvement of macroscopic engineering properties in these nanomaterials as opposed to those found in conventional bulk materials. The improvements are in such characteristics as electrical conductivity, magnetic permeability, and mechanical hardness.
Self-assembled nanomaterials have numerous product applications. For instance, ESA could be used to produce materials with superior electrical properties, such as conformal electrodes on ultrasmall electronic devices and electrically conducting surface coatings on ceramic, polymer, and other substrates. NanoSonic has demonstrated the ability to form metal nanocluster/polymer composite films as thin as several tens of nanometers. The electrical conductivity of these films is in excess of that of conducting polymers and conventional opto-electronic electrode materials such as indium tin oxide (ITO). Another possible application would be for specially tailored polymer/polymer and nanocluster/polymer nanocomposites that can display piezoelectric behavior. These would include such products as ultrasmall actuation or sensing elements for microelectromechanical devices, biological probes and manipulators, and conformal large-area actuators.
A third possible market may be for nonlinear optical (NLO) films. NanoSonic found that the ESA processing method yields noncentrosymmetric molecular structures that possess a remarkably large second-order NLO response, without the need for electric field poling that other methods require. This second-order response allows nonlinear optics to alter the frequency, signal strength, or other characteristics of light through an electrical control signal, which means they can replace bulkier mechanical components such as beam splitters and switches.
Commercialization:
NanoSonic is developing novel materials and associated devices based on ESA. Current products include a range of precursor materials and aqueous solutions suitable for ESA-based material synthesis, a custom robotic system for ESA manufacturing, and prototype functional materials for laboratory analysis. Within 2-5 years, the company will start selling selected thin films and eventually sell a full line of films and machines, while also licensing out its processes to other companies.
Company Profile:
NanoSonic Inc. is a Blacksburg, Virginia based company, created in 1998 in cooperation with Virginia Polytechnic Institute and State University, and with the State of Virginia. The company employs 11 people.
NanoSonic exclusively licensed nine ESA-related patents from Virginia Tech (from Virginia Tech Intellectual Properties, Inc.), where it was first developed. It has also separately developed its own intellectual property to enable process, material, and device commercialization. The company has created a ''library'' of self-assembled materials and has demonstrated the synthesis of more than 2,000 individual material layers.
NanoSonic maintains 7,000 square feet of newly renovated laboratory and office space. Facilities include equipment for the design and synthesis of material precursors, the formation of synthesized precursors into thin- and thick-film materials, the engineering of materials into devices, and the manufacture of multiple elements.
Contact Information:
Richard O. Claus, Ph.D. (president)
NanoSonic, Inc.
1425 South Main Street SE
Blacksburg, VA 24060
Tel:540-953-1785
Fax:540-953-5022
email: info@nanosonic.com
web: www.nanosonic.com
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