@article{koo_velev_2013, title={Biomimetic photocatalytic reactor with a hydrogel-embedded microfluidic network}, volume={1}, ISSN={["2050-7496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84883295175&partnerID=MN8TOARS}, DOI={10.1039/c3ta12483e}, abstractNote={We present a light driven biomimetic reactor where photocatalytic TiO2 nanoparticles are embedded into water-based gels. Uniform supply of the reactants and extraction of the products is accomplished via a microfluidic channel network in a permeable hydrogel, broadly similar to the vein structure of live leaves. Quantitative analysis shows that the microvascular reactor has high quantum efficiency per mass of the catalyst.}, number={37}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Koo, Hyung-Jun and Velev, Orlin D.}, year={2013}, pages={11106–11110} }
 @misc{koo_velev_2013, title={Ionic current devices-Recent progress in the merging of electronic, microfluidic, and biomimetic structures}, volume={7}, ISSN={["1932-1058"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84880119681&partnerID=MN8TOARS}, DOI={10.1063/1.4804249}, abstractNote={We review the recent progress in the emerging area of devices and circuits operating on the basis of ionic currents. These devices operate at the intersection of electrochemistry, electronics, and microfluidics, and their potential applications are inspired by essential biological processes such as neural transmission. Ionic current rectification has been demonstrated in diode-like devices containing electrolyte solutions, hydrogel, or hydrated nanofilms. More complex functions have been realized in ionic current based transistors, solar cells, and switching memory devices. Microfluidic channels and networks—an intrinsic component of the ionic devices—could play the role of wires and circuits in conventional electronics.}, number={3}, journal={BIOMICROFLUIDICS}, author={Koo, Hyung-Jun and Velev, Orlin D.}, year={2013}, month={May} }
 @article{koo_velev_2013, title={Regenerable Photovoltaic Devices with a Hydrogel-Embedded Microvascular Network}, volume={3}, ISSN={["2045-2322"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84881402485&partnerID=MN8TOARS}, DOI={10.1038/srep02357}, abstractNote={Light-driven degradation of photoactive molecules could be one of the major obstacles to stable long term operation of organic dye-based solar light harvesting devices. One solution to this problem may be mimicking the regeneration functionality of a plant leaf. We report an organic dye photovoltaic system that has been endowed with such microfluidic regeneration functionality. A hydrogel medium with embedded channels allows rapid and uniform supply of photoactive reagents by a convection-diffusion mechanism. A washing-activation cycle enables reliable replacement of the organic component in a dye-sensitized photovoltaic system. Repetitive restoration of photovoltaic performance after intensive device degradation is demonstrated.}, journal={SCIENTIFIC REPORTS}, author={Koo, Hyung-Jun and Velev, Orlin D.}, year={2013}, month={Aug} }
 @article{so_koo_dickey_velev_2012, title={Ionic Current Rectification in Soft-Matter Diodes with Liquid-Metal Electrodes}, volume={22}, ISSN={["1616-301X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84856758970&partnerID=MN8TOARS}, DOI={10.1002/adfm.201101967}, abstractNote={Abstract}, number={3}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={So, Ju-Hee and Koo, Hyung-Jun and Dickey, Michael D. and Velev, Orlin D.}, year={2012}, month={Feb}, pages={625–631} }
 @article{kim_koo_jur_woodroof_kalanyan_lee_devine_parsons_2012, title={Stable anatase TiO2 coating on quartz fibers by atomic layer deposition for photoactive light-scattering in dye-sensitized solar cells}, volume={4}, ISSN={["2040-3372"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000306324000056&KeyUID=WOS:000306324000056}, DOI={10.1039/c2nr30939d}, abstractNote={Quartz fibers provide a unique high surface-area substrate suitable for conformal coating using atomic layer deposition (ALD), and are compatible with high temperature annealing. This paper shows that the quartz fiber composition stabilizes ALD TiO(2) in the anatase phase through TiO(2)-SiO(2) interface formation, even after annealing at 1050 °C. When integrated into a dye-sensitized solar cell, the TiO(2)-coated quartz fiber mat improves light scattering performance. Results also confirm that annealing at high temperature is necessary for better photoactivity of ALD TiO(2), which highlights the significance of quartz fibers as a substrate. The ALD TiO(2) coating on quartz fibers also boosts dye adsorption and photocurrent response, pushing the overall efficiency of the dye-cells from 6.5 to 7.4%. The mechanisms for improved cell performance are confirmed using wavelength-dependent incident photon to current efficiency and diffuse light scattering results. The combination of ALD and thermal processing on quartz fibers may enable other device structures for energy conversion and catalytic reaction applications.}, number={15}, journal={NANOSCALE}, author={Kim, Do Han and Koo, Hyung-Jun and Jur, Jesse S. and Woodroof, Mariah and Kalanyan, Berc and Lee, Kyoungmi and Devine, Christina K. and Parsons, Gregory N.}, year={2012}, pages={4731–4738} }
 @article{koo_so_dickey_velev_2011, title={Towards All-Soft Matter Circuits: Prototypes of Quasi-Liquid Devices with Memristor Characteristics}, volume={23}, ISSN={["1521-4095"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80051693085&partnerID=MN8TOARS}, DOI={10.1002/adma.201101257}, abstractNote={IO N We present a new class of electrically functional devices composed entirely of soft, liquid-based materials that display memristor-like characteristics. A memristor, or a “memory resistor”, is an electronic device that changes its resistive state depending on the current or voltage history through the device. Memristors may become the core of next generation memory devices because of their low energy consumption and high data density and performance. [ 1–3 ] Since the concept of memristors was theorized in 1971, [ 4 ] resistive switching memories have been fabricated from a variety of materials operating on magnetic, [ 5 ] thermal, [ 6 ] photonic, [ 7 ] electronic and ionic mechanisms. [ 3 , 8 , 9 ] Conventional memristive devices typically include metalinsulator-metal (M-I-M) junctions composed of rigid stacks of fi lms fabricated by multiple vacuum-deposition steps, often at high temperature. The most common “insulator” materials in M-I-M memristor junctions are inorganic metal oxides such as TiO 2 [ 10 ] and NiO. [ 11 ] Conducting pathways can form by current through such layers. Solid electrolytes between metal electrodes can also be used to create resistance switches (e.g., Ag/ Ag 2 S/Pt), in which conductive metal fi laments that bridge the two electrodes can be formed or annihilated on demand. [ 3 , 9 ] Memristive circuits composed of organic materials have some advantages over conventional metal oxides due to their ease of processing, light weight, and low cost. A variety of organic materials such as homogeneous polymers, small-molecule or nanoparticle doped polymers, and organic donor-acceptor complexes have been evaluated as components in memory switching devices. [ 12 ] We report new controllably bi-stable memristor-like devices fabricated entirely from liquid-based materials. These soft and fl exible devices are built from liquid metal and hydrogels that are used routinely in laboratories for hosting biological molecules and supporting cell growth. Hydrogels are soft, moldable and bio-compatible media similar to biological systems with high ion mobility due to the high water content ( > 90% water). [ 13 , 14 ] The ionic properties of the gels can be tuned by inclusion of polyelectrolytes that are immobilized via entanglement within the gel network. Hydrogels doped with polyelectrolytes have been utilized for fabricating electronic devices such as diodes and photovoltaic cells. [ 13 , 15 , 16 ] The electrodes of these devices, however, are rigid metals such as platinum and}, number={31}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Koo, Hyung-Jun and So, Ju-Hee and Dickey, Michael D. and Velev, Orlin D.}, year={2011}, month={Aug}, pages={3559-+} }