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Gold-Based Nanoparticle Liquids for Electronic Applications

These liquids may be useful as self-healing, electrically conductive lubricants.

Electrically conductive, solventless nanoparticle liquids, consisting of gold nanoparticles chemically functionalized with large organic molecular groups, have been investigated for potential utility in electronic and electrical applications. These and other solventless nanoparticle liquids, including electrically nonconductive ones, have been topics of recent research directed toward understanding and exploiting their unusual properties. The most obvious unusual property is that a collection of nanoparticles of this type can flow in a liquid-like fashion, notwithstanding the absence of free solvent molecules. By modifying the attractive and repulsive forces between the nanoparticles through modifications of the surface chemistry of the organic ligands, the properties of the resulting nanoparticle liquids can be tailored for specific applications.

A Nanoparticle-Liquid Specimen was made by exchanging 30-nm citrate-capped gold nanoparticles MPS, then treating the MPS-functionalized nanoparticles with methyltrialkyl(C8-C10)ammonium chloride. In this transmission electron micrograph, the gold nanoparticles appear dark and a corona of methyltrialkyl(C8-C10)ammonium chloride linking the nanoparticles is shown at low contrast against the background. The scale bars represent a length of 50 nm.
In the investigation, citrate-capped and dodecanethiol-capped gold nanoparticles were synthesized, then solutions containing the capped nanoparticles were exposed to a variety of alkythiol solutions and the resulting chemical reactions allowed to proceed to effect tailored functionalization of the nanoparticles with 3-mercapto-1-propanesulfonic acid (MPS). Next, nanoparticle liquids were prepared by treating the variously-MPS-functionalized gold nanoparticles with a series of cationic surfactants. In each case, the cationic species formed an ionic liquid corona around the anionic MPS-functionalized nanoparticles (see figure).

The nanoparticle liquids were chemically characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, zeta-potential measurements, inductively-coupled-plasma atomic-emission spectroscopy, and nuclear magnetic resonance. These characterizations were performed to contribute to understanding of the effects of the chemical synthesis and treatment processes and thereby to enable improvement of these processes.

Mechanical tests were performed to study the potential utility of nanoparticle liquids as electrically conductive lubricants in relay switches in micro-electromechanical systems. For these tests, the nanoparticle liquids were spin-coated to an average thickness of 2 to 3 nm (amounting to sub-monolayer coverage) on gold substrates. In the test of each such coated substrate, a ball was pressed onto the substrate with a controllable, reproducible force, and the resulting contact resistance was measured as the ball was slid across the surface in a cyclic motion at a frequency of 5 Hz. For comparison, the same tests were performed on uncoated gold substrates. The results of these tests were interpreted as demonstrating that the gold-nanoparticle coatings increased the durabilities (quantified in terms of numbers of cycles until failure) by factors ranging from about 10 to about 103.

It is speculated that a nanoparticle-liquid coat of the type tested can reconfigure itself through fluid-like motion and thereby can heal itself when it is damaged by rubbing in use as an electrically conductive lubricant. More specifically, it is speculated that as such a lubricant in a relay-switch contact becomes worn out through mechanical deformation of the nanoparticles and ashing of the carbonaceous coats on the nanoparticles, the undamaged portions of the lubricant can flow into the damaged areas and thereby heal the coat.

This work was done by Robert I. MacCuspie, Andrea M. Elsen, Steve Patton, J. David Jacobs, Steve Diamanti, Michael Arlen, Andrey A. Voevodin, and Richard A. Vaia of the Air Force Research Laboratory.

AFRL-0054

Topics:
Chemicals Coatings, colorants and finishes Coatings, colorants, and finishes Conductivity Imaging and visualization Lubricants Magnetic materials Materials Materials properties Microscopy Nanomaterials Nanotechnology Optics Sensors and actuators Spectroscopy
This Brief includes a Technical Support Package (TSP).
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Gold-Based Nanoparticle Liquids for Electronic Applications

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    Defense Tech Briefs Magazine

    This article first appeared in the April, 2008 issue of Defense Tech Briefs Magazine (Vol. 2 No. 2).

    Read more articles from the archives here.

    Overview

    The document titled "Nanoparticle Liquids for Reconfigurable Electronic Materials" discusses the innovative use of high inorganic volume fraction, solventless nanoparticle liquids in various applications, particularly in the field of reconfigurable electronic materials. Authored by a team from the Air Force Research Laboratory, the paper emphasizes the potential of these materials to enhance the performance and longevity of electronic devices.

    Nanoparticle liquids are characterized by their ability to flow like liquids while containing solid nanoparticles. This unique property arises from the presence of large organic ligands that are chemically and electrostatically bound to the nanoparticles, allowing for tailored interactions between them. The optimization of these interactions can lead to the development of materials with specific desired properties, making them suitable for various applications.

    One significant application highlighted in the document is the use of conductive lubricants in Micro-Electro-Mechanical Systems (MEMS). These lubricants can improve relay switch performance, which is crucial for the reliability of MEMS devices. The ability of the conductive nanoparticles to reconfigure themselves and fill voids in damaged areas is particularly noteworthy, as it can significantly extend the lifespan of devices that may otherwise fail due to local defects.

    The research also points to the growing interest in solventless solid nanoparticles that exhibit liquid-like behavior, which represents a shift in material science. The document references work by Giannelis and colleagues, who have explored metal oxide and metal nanoparticle liquids that do not contain free solvent, yet maintain the ability to flow. This advancement opens new avenues for the design and application of electronic materials.

    Overall, the paper presents a compelling case for the potential of nanoparticle liquids in creating reconfigurable electronic materials. By leveraging the unique properties of these materials, researchers and engineers can develop more resilient and efficient electronic devices, ultimately contributing to advancements in technology and materials science. The findings underscore the importance of continued research in this area, as it holds promise for future innovations in various fields, including electronics, MEMS, and beyond.

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