SEMICONDUCTOR SURFACE PLASMONS: A ROUTE TO TUNABLE THZ DEVICES AND SENSORS
Lead Research Organisation:
UNIVERSITY OF EXETER
Department Name: Physics
Abstract
Numerous important processes in nature occur at THz frequencies: for example, many rotational and vibrational transitions of various liquid and gas molecules lie within the THz frequency band. In particular, the vibrational breathing modes of many large biomolecules occur at these low frequencies, giving a unique fingerprint in the THz region. While it is clear that the THz band is scientifically very rich, research in this frequency region is limited by technology: the so-called THz gap , occupying a large portion of the electromagnetic spectrum between the infrared and microwave bands, remains relatively unexplored due to a lack of efficient laboratory emitters/detectors and optical components compared to neighboring spectral regions.Here, we explore the potential for developing new THz components and sensors based on semiconductor surface plasmon-polaritons (SPPs). SPPs are electromagnetic waves that propagate along the interface between a conductor and insulator, bound to the surface by the free electrons in the conducting medium. To date, most research investigating the properties of SPPs has been limited to frequencies near metallic plasma frequencies (i.e. at visible and infrared frequencies) where SPP modes are strongly confined to metal surfaces. Semiconductors, with plasma frequencies in the THz range, offer the potential for sustaining SPPs at THz frequencies. Furthermore, semiconductors offer a unique and hugely beneficial advantage over metals: since the surface charge density can be modified by, for example chemical doping, plasma frequencies and SPP properties can be tailored within the THz frequency range. An extension of this is the exciting possibility of all-optical plasmon control, i.e. 'photo-doping' a semiconductor with visible frequency light, so that plasma frequencies may be tuned by a visible frequency light source. Using ultrafast laser sources for this purpose, the properties of THz SPP modes can therefore be tailored and switched on very fast (picosecond) timescales, something that is essential for high-bandwidth and/or time resolved applicationsBorrowing from the well established fields of microwave and optical photonics, and by utilizing the intrinsically tunable nature of semiconductors, we aim to manipulate THz light in new ways using semiconductor SPPs. Initially, we wish to explore the underlying physics of SPPs in the THz frequency range, before looking to develop new applications for this concept. Although there are many areas of potential application for semiconductor SPPs, we will concentrate on two specific areas: firstly, the design of optical components (such as tunable filters, modulators and beam steering systems) based on semiconductor SPPs and secondly, spectroscopy/sensing of biomolecules. The development of new optical components is essential for the continued expansion of scientific research in the THz frequency domain, and we will exploit the wealth of experience currently employed in Exeter to investigate similar applications at microwave and optical frequencies. The second of these potential applications involves what is thought to be possibly the future killer application of THz radiation, i.e. using the fingerprint of large molecules in the THz region for biosensing and biomedical applications. In an analogy to recently developed surface plasmon sensors operating at visible frequencies, employing SPPs for THz sensing will significantly improve sensitivity by concentrating THz radiation in a very thin region close to the semiconductor surface, allowing sensing of very low concentration samples.
People |
ORCID iD |
Euan Hendry (Principal Investigator) |
Publications
Abdulrahman NA
(2012)
Induced chirality through electromagnetic coupling between chiral molecular layers and plasmonic nanostructures.
in Nano letters
Barr L
(2021)
Super-resolution imaging for sub-IR frequencies based on total internal reflection
in Optica
Barr L
(2021)
Efficient mm-wave photomodulation via coupled Fabry-Perot cavities
in Journal of Applied Physics
Bonn M
(2017)
Role of Dielectric Drag in Polaron Mobility in Lead Halide Perovskites
in ACS Energy Letters
Brock E
(2011)
Subwavelength lateral confinement of microwave surface waves
in Applied Physics Letters
Davis T
(2013)
Superchiral electromagnetic fields created by surface plasmons in nonchiral metallic nanostructures
in Physical Review B
Edmunds JD
(2011)
Multi-modal transmission of microwaves through hole arrays.
in Optics express
Hendry E
(2011)
Plasmonics for THz frequency applications
Hendry E
(2008)
Optical Control over Surface-Plasmon-Polariton-Assisted THz Transmission through a Slit Aperture
in Physical Review Letters
Hendry E
(2010)
Ultrasensitive detection and characterization of biomolecules using superchiral fields.
in Nature nanotechnology
Description | The project was primarily concerned with the investigation semiconductor plasmon structures, with an aim to develop techniques and components for sensing, spectroscopy and imaging suitable for the THz frequency gap. We investigated the fundamental properties of THz surface plasmons on flat and structured semiconductor surfaces, obtaining parameters essential to the design and implementation of devices and sensors such as propagation and confinement lengths.We also demonstrated the modification and switching of surface plasmon modes utilizing the intrinsically tuneable nature of semiconductors, and carried out proof of principle experiments which showed the potential applications for semiconductor plasmons, particularly in imaging. This is something we have now taken several steps further, as we look towards a Holy Grail: a practical THz microscope |
Exploitation Route | The original proposal was directed towards the development of THz photomodulators and sensors. Indeed, this is still a very active research area for many research groups. However, the most promising and direct application of the findings from this project is in THz imaging, and this is an area that we as a group are very much active, with an ongoing ICASE award. |
Sectors | Aerospace Defence and Marine Pharmaceuticals and Medical Biotechnology |
Description | The most promising and direct application of the findings from this project is in THz imaging, and this is an area that we as a group are very much active, with an ongoing ICASE award. We have shown that by modulating a semiconductor with optical light, one can actually obtain a THz image of samples with optical (micron) resolution. While the techniques is still very much in its infancy, subwavelength THz imaging is something that, in future, could proove invaluable for biomedical imaging. We are currently working towards this goal: a practical THz microscope. In addition, the work carried out and knowledge gained during this project has led to completely new directions in the fields of optical and micrwave frequency plasmonics. |
First Year Of Impact | 2008 |
Sector | Other |
Description | ICASE |
Amount | € 92,000 (EUR) |
Funding ID | Award number 12440575 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2012 |
End | 10/2016 |
Description | Marie Curie Training Network grant |
Amount | € 572,000 (EUR) |
Funding ID | Network grant 607521 |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 09/2013 |
End | 10/2016 |
Description | QinetiQ |
Organisation | Qinetiq |
Department | QinetiQ (Farnborough) |
Country | United Kingdom |
Sector | Private |
PI Contribution | Development of subwavelength THz imaging |
Collaborator Contribution | Materials and optics knowledge. |
Impact | New THz imaging technique developed in Exeter |
Start Year | 2012 |