Flexible and Wearable Metamaterials: new frontiers in biomedical and safety & security applications

https://www.isc.cnr.it/news/flexible-and-wearable-metamaterials-new-frontiers-in-biomedical-and-safetysecurity-applications/

Metamaterials are engineered material having periodic structures that exhibit unique properties when they interact with electromagnetic waves in comparison with natural materials. They offer interesting applications throughout the electromagnetic spectrum and are crucial in the Terahertz (THz) frequency band which lies between microwave and infrared and thus invisible to the human eye. This band is a new frontier both for research and technological applications in sectors ranging from astronomy to cultural heritage.

An interesting area of research is the development of metamaterial absorbers at the THz frequencies due to the difficulty of finding natural materials with high absorption in narrow spectral bands which can be suitably integrated into planar device technology.

An ultra-light, ultra-thin, biocompatible THz device, exhibiting high-absorption which is easy to manufacture, capable of being rolled up and suitable in wearable applications has been developed by two Cnr teams. The Institute for Microelectronics and Microsystems (IMM) together with the Institute of Complex Systems (ISC), led by Luca Maiolo and Mauro Missori, respectively, and the research group coordinated by Fabrizio Frezza of the Department of Information Engineering,Electronics and Telecommunications of Sapienza University.

Three-dimensional graphene: Experiment at BESSY II shows that optical properties are tuneable

SEM-images of 3-D graphene with different pore size (a,b,c, scale = 1μm). Optical properties (d,e,f) change with pore size. Credit: Nature Communications: 10.1038/ncomms14885

 https://phys.org/news/2017-05-three-dimensional-graphene-bessy-ii-optical.html#jCp

An international research team has for the first time investigated the optical properties of three-dimensional nanoporous graphene at the IRIS infrared beamline of the BESSY II electron storage ring. The experiments show that the plasmonic excitations (oscillations of the charge density) in this new material can be precisely controlled by the pore size and by introducing atomic impurities. This could facilitate the manufacture of highly sensitive chemical sensors.

Carbon is a very versatile element. It not only forms diamonds, graphite, and coal, but can also take a planar form as a hexagonal matrix - graphene. This material, consisting of only a single atomic layer, possesses many extreme properties. It is highly conductive, optically transparent, and is mechanically flexible as well as able to withstand loads. André Geim and Konstantin Novoselov received the 2010 Nobel Prize in Physics for the discovery of this exotic form of carbon. And just recently, a Japanese team has been successful in stacking two-dimensional graphene layers in a three-dimensional architecture with nanometre-sized pores.

Tuneable plasmons

A research team operated by a group at Sapienza University in Rome has now for the first time made a detailed investigation of the optical properties of 3D graphene at BESSY II. The team was able to ascertain from the data how charge density oscillations, known as plasmons, propagate in three-dimensional graphene. In doing so, they determined that these plasmons follow the same physical laws as 2D graphene. However, the frequency of the plasmons in 3D graphene can be very precisely controlled, either by introducing atomic impurities (doping), by the size of the nanopores, or by attaching specific molecules in certain ways to the graphene. In this way, the novel material might also lend itself to manufacturing specific chemical sensors, as the authors write in Nature Communications. In addition, the new material is interesting as an electrode material for employment in solar cells.

Advantages provided by the IRIS beamline

The researchers used the IRIS beamline at the BESSY II synchrotron source in Berlin to their advantage for their investigations. Broad-band infrared is available there, which especially facilitates spectroscopic analysis of novel materials using terahertz radiation. "A special operating mode of the BESSY II storage ring called low-alpha allowed us to measure the optical conductivity of three-dimensional graphene with a particularly high signal-to-noise ratio. This is hardly possible with standard methods, especially in the terahertz region. However, it is exactly this region that is important for observing critical physical properties", says Dr. Ulrich Schade, head of the group at the infrared beamline.

 Explore further: Non-flammable graphene membrane developed for safe mass production

More information: Fausto D'Apuzzo et al, Terahertz and mid-infrared plasmons in three-dimensional nanoporous graphene, Nature Communications (2017). DOI: 10.1038/ncomms14885