Nanoporous artificial materials: confining the THz excited surface plasmon polariton

Terahertz light can be found between visible light and microwaves in the electromagnetic spectrum. It is relatively unexploited because compact, powerful sources have been particularly difficult to make in this region. Furthermore, it suffers from a shortage of materials which produce efficient (i.e. low loss) devices to guide and manipulate the terahertz light. It is, however, an interesting region because it is energetically similar to many biological processes, so we can study protein behaviour and DNA. It is able to excite intramolecular vibrations which means that drugs and explosives can be readily identified. This proposal builds on our expertise in the design and development of so-called artificial materials. An artificial material has electromagnetic properties which have been engineered. This means that we can control what happens when the terahertz light interacts with the material. A typical approach to tailor the electromagnetic properties involves incorporating small (sub-wavelength) features into and on readily available materials (e.g. metals such as gold and copper). Here we will produce artificial materials which are capable of producing a special type of wave when the terahertz light illuminates the material's surface. This special type of wave, or oscillation of charge, is known as a surface plasmon polariton (SPP), and its properties are highly dependent on the type of material that is in contact with the surface. This makes it suitable for sensing a wide variety of materials with excellent selectivity. The approach will enable us to monitor activity and changes on a very short (picosecond) timescale. Unfortunately, when excited by terahertz light, this wave extends some distance from the surface. This makes it less sensitive to events at the surface (e.g. biomolecules attaching). The aim of this research is improve the confinement of the SPP by introducing a nanoporous layer to our existing artificial material designs (based on copper foils with arrays of microscale apertures). The team includes microfabrication engineers and physicists who will work together to design, fabricate and test the materials.

The results from this research will have impact in the academic community because they will enable us to gain a greater understanding of how terahertz light interacts with nanoporous metal surfaces. They will also provide an insight into the design rules that are required to engineer the interaction such that it produces a highly confined surface charge oscillation known as a surface plasmon polariton (SPP). This will lead to new types of artificial material which may have useful properties for sensing biological and chemical samples due to improved confinement of the SPP to the surface. The long wavelength (compared to visible light) wavelength with terahertz radiation means that it is difficult to sense biological or chemical changes which occur at a surface. The ability to sense and study such events is important because it will help us to understand the mechanisms of biology, and hence life, through, for example, by revealing the behaviour of proteins, DNA and stem cells. Such understanding is crucial to the future development of new medicines and the treatment of chronic medical conditions.

We will aim to report the results from this research to the public through an open lecture, as well as to School children participating in Durham's outreach programmes. This will help to convey the importance of science research as well as providing encouragement for children to pursue science and engineering based study and careers. As a team, we have links to industry and the medical sector, along with experience in the development of readily manufacturable devices. This will provide a route to the commercial exploitation of the technology, if appropriate.