美国盐湖城犹他大学Sensale-Rodriguez、Yunshan “Emily” Wang助理教授到访微纳电子学系
2019年5月10日，来自美国盐湖城犹他大学Sensale-Rodriguez、Yunshan “Emily” Wang助理教授应邀来访微纳电子学系。Sensale-Rodriguez助理教授首先做了题为《Manifestation of Kinetic-inductance in Terahertz Plasmon Resonances in Thin-film Cd3As2 a Three-dimensional Dirac Semimetal》的学术报告，Yunshan “Emily” Wang助理教授随后做了题为《Fluorescence biosensors with plasmonic enhancement and molecular trapping at the nanoscale》的学术报告。微纳电子学系王玮教授等多位师生参加了报告会，并与报告人进行了热烈的讨论。
Manifestation of Kinetic-inductance in Terahertz Plasmon Resonances in Thin-film Cd3As2 a Three-dimensional Dirac Semimetal
Three-dimensional (3D) Dirac semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with its linear energy dispersion. In analogy to twodimensional (2D) Dirac semimetals, such as graphene, Cd3As2 has shown ultra-high mobility, with values exceeding 15,000 cm2/V.s at room-temperature and much higher mobility at low temperatures, large Fermi velocity, and has been hypothesized to support plasmons at terahertz frequencies. In this work, we experimentally demonstrate synthesis of high-quality large-area Cd3As2 thin-films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodically patterned arrays of Cd3As2 disks and stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality-factors (Q) as high as ~ 3.7 (at 0.82 THz). Such spectrally-narrow resonances can be understood on-basis of a long momentum scattering time, which in our films can approach ~1 ps at room-temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photo-induced carriers in optical pump / terahertz probe (OPTP) experiments. Our results evidence that the 3D nature of Cd3As2 provides for a more robust platform for terahertz plasmonic applications than what is otherwise possible in 2D Dirac-materials such as graphene. Overall, our observations can pave a road for the development of a myriad of future terahertz (opto) electronic devices based on Cd3As2 as well as other 3D Dirac semimetals, benefiting from strong coupling of terahertz radiation, ultrafast transient response, magneto-plasmon properties, etc. Moreover, the long momentum scattering time as well as large kinetic-inductance in Cd3As2, also holds enormous potential for the re-design of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.
Fluorescence biosensors with plasmonic enhancement and molecular trapping at the nanoscale
Early cancer diagnosis, food safety, and environmental monitoring all require a biosensor that can detect multiple target molecules in a timely fashion and with high sensitivity. Current commercially available sensing platforms such as DNA microarray and northern blot, are limited in sensitivity (one million molecules) and dynamic range due to background auto-fluorescence and scattering noise. During the first part of my talk, I will discuss an easily manufacturable silica nano-cone array platform capable of amplifying fluorescence emission of labeled microRNAs. This sensor can achieve fourorders of magnitude improvement in detection limit when compared to conventional micro-array sensors. Moreover, reduced assay time is possible in such platforms through molecular trapping at the nano-cone tips under electric field. In the second part of my talk, I will discuss on the development of label free biosensors, i.e. detection of the intrinsic fluorescence of molecules without labeling. This technique is especially useful for detecting small nucleic acids and peptides where labeling becomes expensive and laborious. Detecting intrinsic fluorescence of biomolecules is challenging due to the small absorption cross-section and quantum yield of biomolecules, therefore, improving the quantum yield is key for enabling label free sensing. In my research, computational and experimental techniques are combined so to search for the best plasmonic materials and structural designs in the UV range to enhance quantum yield. Our results show 10X lifetime reduction of p-terphenyl using magnesium (Mg) nanoapertures, the highest lifetime reduction reported for UV fluorescence dye. Furthermore, by using aluminum (Al) bowtie antennas we predict 180X fluorescence enhancement of tryptophan molecules. These results could pave a new way for label free amino-acid sensing.