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Integrated THz Plasmonic Chemical and Biological Sensors


OBJECTIVE: To design, fabricate, and demonstrate a new class of plasmonic sensors for chemical and biological sensing based on terahertz (THz) frequency quasi-optical spectroscopy. DESCRIPTION: The Army has an urgent need for new sensor-based plasmonic architectures for biological and chemical sensing, with superior sensitivity and high-volume processing capability. Examples include a novel nano-biosensor system comprising plasmonic emitters, waveguides, and detectors which can be integrated with other nanoelectronic circuit elements and components, such as switches and modulators, thereby resulting in enormous signal functionality, integration and processing speed. Recent development on metallic nanoparticles (MNPs), metallic nanoshells (MNSs) and metallic nanowires (MNWs) seemed promising, because the plasmonic nano-architectures provide a promising way to integrate with optical-electronic (including long wavelength THz regime) devices by localizing the light at a subwavelength scale [1-5]. Toward that end, THz signal transducers using the metallic metamaterial---because surface plasmon polariton (SPP) modes generate the weakly localized mode confinement in the THz domain---will need to be developed to fully realize the potential of the new class of THz plasmonic sensors. Specifically, it may be necessary to build holes, grooves, dimples, and other surface textures at the subwavelength scale, thus creating the spoof surface plasmon polariton (SSPP) modes similar to surface plasmon polariton (SPP) existing at the IR-Optical spectrum [6,7]. For example, various THz transducers such as waveguides, multiplexers and Mach-Zender interferometers using the sub-wavelength periodic gap structures need to be developed. Additionally, to improve the signal to noise figure of merit, it may be necessary to employ metallic photonic crystal materials consisting of cavities. It is also possible that the signal detection emitted by nanometer-scale atoms and molecules would be enhanced by strong near field confinement and extraordinary transmission of the plasmonic architectures. The artificially designed metallic photonic crystal slabs comprising of cavities with high Q-factor and small effective volume will make it possible to obtain ultrahigh sensitivity for chem.-/biosensor devices. Plasmonic waveguide structures such as slot waveguides, when combined with plasmonic switches, can deliver optical (THz) excitations to spectroscopy-based sensor arrays, and collect optical (THz) spectral information from these array elements, and subsequently direct them to desired output terminals. With such a design paradigm, the optical/THz plasmonic sensors"high sensitivity is accentuated, and at the same time, large throughput of sensory processing information is made possible. The ultimate goal of this project is to define a new class of THz plasmonic nanostructures which are highly effective for spectroscopy-based sensing and that are scalable and reproducible. Namely, when produced by available standard nanomanufacturing techniques required for realizing large sensor arrays, excited and interrogated by large number of plasmonic waveguide channels connected to the optical/THz input/output, uniform response properties will be exhibited by these sensors systems. PHASE I: In the Phase I effort, a complete design of a chem./biosensor based on the THz plasmonic nanostructures should be formulated, and the fabrication procedures should be developed for a representative device implementation. It is expected that physical attributes such as the plasmon resonance frequencies and local field enhancements will be predicted as a function of the geometric and material parameters of the plasmonic nanostructures. The Phase I effort should include fabrication experiments and benchmarking that demonstrate an adequate capability for the meeting the expected challenges in fabricating the proposed sensors. PHASE II: In the Phase II effort, a prototypical sensor array based on THz plasmonic nanostructured architecture, with plasmonic waveguides connected to the input/output optical/THz excitation and spectral collection/determination, will be fabricated and their ultrahigh detection sensitivity should be demonstrated. The performances of the THz plasmonic sensor array should be fully evaluated in terms of processing speed and amount of information processed. Although the THz plasmonic sensor array will be designed to be functional at one specific laser wavelength, the project needs to deliver theoretical/experimental results that provide guidance regarding how the sensor array can be designed and fabricated for other excitation wavelengths and possibly broad-band/sweep-frequency operations. PHASE III DUAL USE APPLICATIONS: The Phase III work will demonstrate scalability and repeatability of the proposed THz plasmonic nanostructured spectroscopy-based sensor arrays with ultrahigh sensitivity, and implement at least one kind of sensor featuring monolithic integration of the signal source and detector(s). Specifically, arrays of the proposed THz plasmonic nanostructures will be fabricated using standard nanofabrication technologies such as nanoimprint lithography or other scalable nanomanufacturing techniques. This new technology will have commercialization opportunities for such military relevant applications as detection of trace amount chemical, biological and explosive agents. This same technology would find dual-applications such as advanced laboratory components for scientific characterization studies; materials/process monitoring in commercial manufacturing; and ultra-fast data processing. REFERENCES: 1. H.A. Atwater,"The Promise of Plasmonics", Scientific American, April 2007; 56-63. 2. E. Betzig, J. K. Trautman, T. D. Harris, J. S. Weiner, and R. L. Kostelak,"Breaking the diffraction barrier optical microscopy on a nanometric scale", Science, 251, 1468 (1991). 3. W. L. Barnes, A. Dereux, and T. W. Ebbesen,"Surface plasmon subwavelength optics,"Nature, 424, 824 (2003). 4. K. Song and P. Mazumder,"Active Terahertz Spoof Surface Plasmon Polariton Switch Comprising the Perfect Conductor Metamaterial", IEEE Transaction on Electron Devices, 56, 2792 (2009). 5. M. L. Brongersma, J. W. Hartman, and H. A. Atwater,"Electromagnetic energy transfer and switching in nanoparticle chain arrays below the diffraction limit,"Physical Review B, 62, R16356 (2000). 6. J. B. Pendry, L. Martin-Moreno, and F. J. Garcia-Vidal,"Mimicking Surface Plasmons with Structured Surfaces,"Science, 305, 847 (2004). 7. S. A. Maier, S. R. Andrews, L. Martin-Moreno, and F. J. Garcia-Vidal,"Terahertz surface plasmon-polariton propagation and focusing on periodically corrugated metal wires,"Physical Review Letters, 97, 176805 (2006).
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