Terahertz (THz) spectroscopy offers unique insights into the electronic and vibrational degrees of freedom of materials. Because of the long wavelength of THz portion of the electromagnetic spectrum, it can be challenging to generate and detect THz radiation on nanometer scales. In this talk I will describe our efforts to develop a platform for generation and detection of broadband terahertz (~10 THz bandwidth) emission using 10-nm-scale LaAlO3/SrTiO3 nanostructures created by conductive atomic force microscope (c-AFM) lithography. The technique relies on the large inherent third-order optical susceptibility of SrTiO3. Inversion symmetry is locally broken at this interface at nanoscale junctions, enabling local optical rectification of light from ultrashort near-infrared optical pulses that is electrically detected by the same junction1. This system is capable of generating and detecting broadband THz emission on a scale set by the junction, which can be as small as 10 nanometers2. I will describe how these devices are created and used to probe nanoscale objects (e.g., Au nanorods3) that can be placed and co-located with these sensitive sources and detectors of THz emission. Our current focus involves graphene nanostructures that are integrated with the LaAlO3/SrTiO3 system, but a host of other materials can in principle be integrated with this platform.
1. Irvin, P.; Ma, Y. J.; Bogorin, D. F.; Cen, C.; Bark, C. W.; Folkman, C. M.; Eom, C. B.; Levy, J., Rewritable nanoscale oxide photodetector. Nat Photonics 2010, 4 (12), 849-852.
2. Ma, Y.; Huang, M.; Ryu, S.; Bark, C. W.; Eom, C.-B.; Irvin, P.; Levy, J., Broadband Terahertz generation and detection at 10 nm scale. Nano Lett 2013, 13 (6), 2884-2888.
3. Jnawali, G.; Chen, L.; Huang, M.; Lee, H.; Ryu, S.; Podkaminer, J. P.; Eom, C.-B.; Irvin, P.; Levy, J., Photoconductive response of a single Au nanorod coupled to LaAlO$_3$/SrTiO$_3$ nanowires. Applied Physics Letters 2015, 106 (21), 211101.
Jeremy Levy and Lu Chen, "Broadband THz spectroscopy of materials at 10-nm Scale (Conference Presentation)," Proc. SPIE 10530, Ultrafast Phenomena and Nanophotonics XXII, 1053009 (Presented at SPIE OPTO: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2292439.5751515704001.
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