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Researchers from the University of Illinois at Urbana-Champaign have developed arrays of tiny nano-antennas that can enable sensing of molecules that resonate in the infrared (IR) spectrum.

Nanoantennas made of semiconductor can help scientists detect molecules with infrared light.

“The identification of molecules by sensing their unique absorption resonances is very important for environmental monitoring, industrial process control, and military applications,” said team leader Daniel Wasserman, a professor of electrical and computer engineering and a researcher at the Micro and Nano Technology Laboratory at Illinois.

The food and pharmaceutical industries use light to detect contaminants and to ensure quality. The light interacts with the bonds in the molecules, which resonate at particular frequencies, giving each molecule a “spectral fingerprint.” Many molecules and materials more strongly resonate in the IR end of the spectrum, which has very long wavelengths of light – often larger than the molecules themselves.

“The absorption signatures of some of the molecules of interest for these applications can be quite weak, and as we move to nano-scale materials, it can be very difficult to see absorption from volumes smaller than the wavelength of light,” Wasserman said. “It is here that our antenna array surfaces could have a significant impact.”

Other nano-scale antenna systems cannot be tuned to a longer light wavelength because of the limitations of traditional nanoantenna materials. The Illinois team used highly doped semiconductors, grown by a technique called molecular beam epitaxy that is used to make IR lasers and detectors.

Nanoantennas made of semiconductor can help scientists detect molecules with infrared light.

“We have shown that nanostructures fabricated from highly doped semiconductors act as antennas in the infrared,” said Stephanie Law, a postdoctoral researcher at Illinois and the lead author of the work. “The antennas concentrate this very long wavelength light into ultra-subwavelength volumes, and can be used to sense molecules with very weak absorption resonances.”

The semiconductor antenna arrays allow long-wavelength light to strongly interact with nano-scale samples, so the arrays could enhance the detection of small volumes of materials with a standard IR spectrometer – already a commonplace piece of equipment in many industrial and research labs.

The researchers further demonstrated their ability to control the position and strength of the antenna resonance by adjusting the nanoantenna dimensions and the semiconductor material properties.

The group will continue to explore new shapes and structures to further enhance light-matter interaction at very small scales and to potentially integrate these materials with other sensing systems.

“We are looking to integrate these antenna structures with optoelectronic devices to make more efficient, smaller, optoelectronic components for sensing and security applications,” Wasserman said.

1 Nanometer – 1 x 10-9m.

Applications of nano technology in civil engineering are numerous. Some of the applications are elaborated below.

Application in concrete

Addition of nanoscale materials into cement could improve its performance. Use of nano-SiO2 could significantly increase the compressive strength for concrete, containing large volume fly ash, at early age and improve pore size distribution by filling the pores between large fly ash and cement particles at nanoscale. The dispersion/slurry of amorphous nanosilica is used to improve segregation resistance for self-compacting concrete. It has also been reported that adding small amount of carbonnanotube (1%) by weight could increase both compressive and flexural strength.

Cracking is a major concern for many structures. University of Illinois Urbana-Champaign is working on healing polymers, which include a microencapsulated healing agent and a catalytic chemical trigger. When the microcapsules are broken by a crack, the healing agent is released into the crack and contact with the catalyst. The polymerization happens and bond the crack faces. The selfhealing polymer could be especially applicable to fix the microcracking in bridge piers and columns. But it requires costly epoxy injection.

Application in Steel

Steel is a major construction material. Its properties, such as strength, corrosion resistance, and weld ability, are very important for the design and construction. It is possible to develop new, low carbon, highperformance steel (HPS). The new steel was developed with higher corrosion-resistance and weld ability by incorporating copper nanoparticles from at the steel grain boundaries.

Coating

The coatings incorporating certain nanoparticles or nanolayers have been developed for certain purpose. It is one of the major applications of nanotechnology in construction. For example, TiO2 is used to coat glazing because of its sterilizing and anti fouling properties. The TiO2 will break down and disintegrate organic dirt through powerful catalytic reaction. Furthermore, it is hydrophilic, which allow the water to spread evenly over the surface and wash away dirt previously broken down. Other special coatings also have been developed, such as anti-fraffiti, thermal control, energy sawing, antireflection coating.

Nanosensors

Nanosensor

Sensors have been developed and used in construction to monitor and/or control the environment condition and the materials/structure performance. One advantage of these sensors is their dimension (10 -9m to 10-5m). These sensors could be embedded into the structure during the construction process. Smart aggregate, a low cost piezoceramic-based multi-functional device, has been applied to monitor early age concrete properties such as moisture, temperature, relative humidity and early age strength development. The sensors can also be used to monitor concrete corrosion and cracking. The smart aggregate can also be used for structure health monitoring. The disclosed system can monitor internal stresses, cracks and other physical forces in the structures during the structures’ life. It is capable of providing an early indication of the health of the structure before a failure of the structure can occur.