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Chemical self-assembly Silica nano-wires - New generation of integrated optical devices

DCN Corp®/Credit - Image courtesy of an international Australia-France research team

Silica micro-wires are tiny and relatively underused cousin of optical fibers.  It is claimed if the wires can be precisely manufactured, then they could enable applications and technology not presently feasible via a relatively bulkier optical fiber.  Excitingly by carefully controlling the shape of water droplets within an ultraviolet laser - a team of researchers from Australia - The University of Sydney (UoS) - and France have discovered a means to 'coax' silica nanoparticles to chemically self-assemble into a greater degree of uniformity.  The international team provide a description of their novel manufacturing technique and its potential applications in a paper published in Optical Society's (OSA) open-access journal Optics Materials Express (29/01/2013).  It is claimed the technique is significant, because it will enable for the first time silica to be combined with any other material through a process of micro-wire chemical self-assembly.

The UoS School of Chemistry, Professor John Canning, claimed "we're currently living in the 'Glass Age' - silica's high thermal processing, ruggedness, and unbeatable optical transparency over long distances equate to unprecedented capacity to transmit data and information all over the world."  However, a long-term commercialisation challenge has been its incompatibility with majority of other materials, and so preventing silica functionalisation, which would allow silica to do more than just carry light.  An additional commercialisation 'gap' has been the need for light-speed transmission of data (through silica) as well as the creation of next generation electronic and photonic components, whereby the feasibility has been hindered due to lack of providing sufficient form of interconnection.  Unfortunately, such a transition is highly inefficient when employing traditional optical fibers compounded by the fact that interconnection losses remain one of the major unresolved commercialisation issues in the optical communications industry.

Alternatively if silica micro-wires can be manufactured or chemically self-assembled in certain places, then the potential is there to operate as optical interconnects.  Such micro-wires could also achieve new functionality by the addition of different chemicals through the sole introduction by chemical self-assembly.  Positively silica wires unlike their optical fiber counter-parts have no issue with cladding - meaning greater scope of light confinement into a small structure, which is well suited for interconnection, greater minimising losses and expansion of physical space.  As explained by Canning "so we were motivated to solve the great silica incompatibility problem."

It is claimed the key to carrying the innovation forward, is ensuring that the manufacturing process is perfect and that reflected in the fabrication of highly uniform wires via nanoparticles suspended in a solution (as described by research published in Optical Materials Express).  The manufacturing challenge has been that as naturally formed droplets evaporate they can easily produce uneven silica mirco-wires.  The unevenness is primarily due to the micro-fluidic currents inside the droplet, which can inadvertently aggregate the nanoparticles into specific uneven patterns.  Such patterns are typically held together by intermolecular attractive forces, and when the solvent - usually water and/or other impurities - fully evaporates the nanoparticles crystalline and form as a thin film.

However, Canning and his team have realised that by altering the shape of the droplet and elongating it slightly, then it can result in the flow patterns inside the droplet concurrently changing, thus, allowing control onto how the nanoparticles assemble.  The researchers managed to induce a controlling factor by changing the "wettability" properties of the glass base substrate.   The alteration/patterning was undertaken under an ultraviolet laser with a glass base substrate consisting of the mineral borosilicate.  The subsequent patterning ensured to make the surface topology more wettable via finite controlling - enabling any droplet to assemble into a more oblong shape.  Such subtle shape changes would be enough to alter the microscope flows as any solvent evaporated, whereby the silica micro-wires would form more straighter and uniform-like.

In summary, the researchers predict their processing technology will allow the complete control of nanoparticle self-assembly for a variety of emerging nanotechnologies - including the following:-

  • Microwave devices and sensors
  • Photon sources
  • Possibly silica-based integrated circuits
  • Production of selective devices, such as chemical and biological sensors
  • Photovoltaic structures
  • Novel switches in both optical fiber form and on wave-guides

Original article available here

Clearly Canning's research is positive and quite substantive in its future nano-commercialisation claims, but, again, the company strongly believes it can provide a competitor dip coating concept.  Interestingly DCN Corp's concept of homogeneous nano-fabrication, also, works on the same principle of chemical self-assembly within an encapsulation chamber set-up.  Therefore, if you or your colleagues are interested in making the above a reality - please ensure to contact the company as soon as practicably possible.