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Material-Versatile Ultrabroadband Light Absorber with Self-Aggregated Multiscale Funnel Structures
Ryu, Yunha,Kim, Changwook,Ahn, Junmo,Urbas, Augustine M.,Park, Wounjhang,Kim, Kyoungsik American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.35
<P>Broadband light absorbers are essential components for a variety of applications, including energy harvesting and optoelectronic devices. Thus, the development of a versatile absorbing structure that is applicable in various operating environments is required. In this study, a material-versatile ultrabroadband absorber consisting of metal-coated self-aggregated Al<SUB>2</SUB>O<SUB>3</SUB> nanowire bundles with multiscale funnel structures is fabricated. A high absorptance of ∼0.9 over the AM 1.5G spectrum (300-2500 nm) is realized for absorbers with a range of metal coatings, including Al, W, and titanium nitride (TiN). We demonstrate that the plasmonic nanofocusing and index-matching effects of the funnel structure result in strong ultrabroadband absorption for the various metal coatings, even though the coating materials have different optical properties. As an example of applicability in an operating environment, in the evaluation of the thermal-oxidation resistance, the Al-coated solar absorber exhibits superior performance to those coated with refractory materials such as W and TiN because of the protective alumina layer formed on the Al surface.</P> [FIG OMISSION]</BR>
Hu, Dehua,Liu, Qing,Tisdale, Jeremy,Nam, Haerim,Park, Soo Young,Wang, Hsin,Urbas, Augustine,Hu, Bin Elsevier 2015 ORGANIC ELECTRONICS Vol.26 No.-
<P><B>Abstract</B></P> <P>This paper reports Seebeck effects from optically-induced intramolecular proton-transfer HPI-Cbz molecules based on vertical electrode/organic film/electrode thin-film devices. We observed large Seebeck coefficients of 428μV/K and 390μV/K from HPI-Cbz based thin-film devices at 60°C when proton-transfer was induced by the photoexcitation of a 325nm laser with an intensity of 12mW/cm<SUP>2</SUP> and 6mW/cm<SUP>2</SUP> respectively. Under dark condition without proton transfer occurring, the Seebeck coefficient was measured to be 342μV/K at 60°C. The Seebeck coefficient enhancement by the induced intramolecular charge transfer can be attributed to the enhanced polarization difference between high- and low-temperature surface due to the stronger electron–phonon coupling followed with the proton-transfer in HPI-Cbz under photoexcitation, and the strength of electron–phonon coupling is proportional to the photoexcitation intensity. The enhanced temperature-dependent electrical polarization between the high and low-temperature surfaces acts as an additional driving force to diffuse the majority charge carriers for the development of a large Seebeck effect. Therefore, using intramolecular proton-transfer presents an effective approach of enhancing Seebeck effect in organic materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photoinduced proton-transfer states lead to enhancement on Seebeck coefficients. </LI> <LI> Photoinduced proton-transfer states lead to enhancement on electrical conductivity. </LI> <LI> Temperature-dependent polarization acts as a new driving force for Seebeck effect. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Oh Kim, Jun,Ku, Zahyun,Krishna, Sanjay,Kang, Sang-Woo,Jun Lee, Sang,Chul Jun, Young,Urbas, Augustine American Institute of Physics 2014 Journal of Applied Physics Vol.115 No.16
<P>We propose and analyze a novel detector structure for pixel-level multispectral infrared imaging. More specifically, we investigate the device performance of a grating-integrated quantum dots-in-a-well photodetector under backside illumination. Our design uses 1-dimensional grating patterns fabricated directly on a semiconductor contact layer and, thus, adds a minimal amount of additional effort to conventional detector fabrication flows. We show that we can gain wide-range control of spectral response as well as large overall detection enhancement by adjusting grating parameters. For small grating periods, the spectral responsivity gradually changes with parameters. We explain this spectral tuning using the Fabry-Perot resonance and effective medium theory. For larger grating periods, the responsivity spectra get complicated due to increased diffraction into the active region, but we find that we can obtain large enhancement of the overall detector performance. In our design, the spectral tuning range can be larger than 1 mu m, and, compared to the unpatterned detector, the detection enhancement can be greater than 92% and 148% for parallel and perpendicular polarizations. Our work can pave the way for practical, easy-to-fabricate detectors, which are highly useful for many infrared imaging applications. (C) 2014 AIP Publishing LLC.</P>
Kim, Bongjoong,Jeon, Jiyeon,Zhang, Yue,Wie, Dae Seung,Hwang, Jehwan,Lee, Sang Jun,Walker, Dennis E.,Abeysinghe, Don C.,Urbas, Augustine,Xu, Baoxing,Ku, Zahyun,Lee, Chi Hwan American Chemical Society 2019 Nano letters Vol.19 No.8
<P>Guided manipulation of light through periodic nanoarrays of three-dimensional (3D) metal-dielectric patterns provides remarkable opportunities to harness light in a way that cannot be obtained with conventional optics yet its practical implementation remains hindered by a lack of effective methodology. Here we report a novel 3D nanoassembly method that enables deterministic integration of quasi-3D plasmonic nanoarrays with a foreign substrate composed of arbitrary materials and structures. This method is versatile to arrange a variety of types of metal-dielectric composite nanoarrays in lateral and vertical configurations, providing a route to generate heterogeneous material compositions, complex device layouts, and tailored functionalities. Experimental, computational, and theoretical studies reveal the essential design features of this approach and, taken together with implementation of automated equipment, provide a technical guidance for large-scale manufacturability. Pilot assembly of specifically engineered quasi-3D plasmonic nanoarrays with a model hybrid pixel detector for deterministic enhancement of the detection performances demonstrates the utility of this method.</P> [FIG OMISSION]</BR>
Jehwan Hwang,Jiyeon Jeon,Sujin Yoon,Byung Soo Kang,Deok-Kee Kim,Ha Sul Kim,Sang-Woo Kang,Jun Oh Kim,Woo-Yong Jang,Urbas, Augustine,Zahyun Ku,Sang Jun Lee IET 2015 Electronics letters Vol.51 No.15
<P>In previous work, the present authors discovered the resonant splitting phenomenon of a plasmonic perforated gold film (PGF), as the incident light comes in the polar angle. However, in reality, the light through the imaging lens could be incident on the PGF not only in the polar angle but also in the azimuth angle. The transmission of a PGF against the incident light is analysed in both polar and azimuth angles in spherical coordinates. To mimic the incidence through the lens, a PGF sample is rotated by simultaneously varying both types of angles as normal incidence arrives. For the measurement, the sample has been fabricated with a PGF on a semi-insulating gallium arsenide (GaAs) substrate. The measured transmission spectra show both resonant splitting and merging under TM and TE polarisations as the azimuth angle is increased. Results drawn from this work will pave the way to fully understanding the interaction between the imaging lens and the plasmonic structure (PGF).</P>