Transparent-flexible-multimodal triboelectric nanogenerators for mechanical energy harvesting and self-powered sensor applications

Zhou, Qitao,Park, Jun Gyu,Kim, Kyeong Nam,Thokchom, Ashish Kumar,Bae, Juyeol,Baik, Jeong Min,Kim, Taesung Elsevier 2018 Nano energy Vol.48 No.-

<P><B>Abstract</B></P> <P>Triboelectric nanogenerators (TENGs) harvest and convert mechanical energy to electrical energy. TENGs that are transparent and flexible can be applied to various (opto-)electronic devices supporting finger- or pen-based touchscreen inputs. This paper presents a transparent, flexible TENG that harvests mechanical tapping energy (typically discarded) by simple placement on touchscreen devices. The developed TENG consists of flexible and transparent conducting electrodes (FTCE) with high transmittance (> 93%) and low sheet resistance (18.5 Ω/sq), and transparent 3D-hierarchical polydimethylsiloxane (PDMS) with porous pyramid-patterns. In this study, the developed TENG directly powered eight light-emitting diodes (LEDs) by harvesting the mechanical energy produced by tapping with a touch pen while playing a smartphone game. We also used the transparent TENG as a transparent single-electrode-based, self-powered raindrop detection sensor on a window for a smart home. Our results indicate that the proposed TENG can be used not only as an effective mechanical energy harvester for transparent, flexible, and next-generation optoelectronics devices but also as a self-powered sensor for future Internet-of-Things applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flexible transparent conducting electrodes (FTCEs) are fabricated by an inkjet printer. </LI> <LI> A PDMS interlayer with 3D micro/-nanostructures is prepared by particle lithography. </LI> <LI> A transparent and flexible TENG is fabricated by the FTCEs and PDMS interlayers. </LI> <LI> The TENG harvests the mechanical energy produced when tapping electronic devices. </LI> <LI> The TENG works as single-electrode-based self-powered raindrop sensors. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Review of microfluidic approaches for surface-enhanced Raman scattering

Zhou, Qitao,Kim, Taesung Elsevier 2016 Sensors and actuators. B Chemical Vol.227 No.-

<P><B>Abstract</B></P> <P>The development of lab-on-a-chip (LoC) systems has allowed for the successful combination of many detection methods with these systems. Surface-enhanced Raman spectroscopy (SERS) has the potential for use in rapid trace-level biological and environmental analysis because of its high sensitivity, rapid response, and fingerprint effect. With the development of nanotechnology, various active SERS substrates have been fabricated. By combining well-designed microchannels and SERS substrates, more effective and convenient SERS detecting systems have been realized. Furthermore, novel functions that were conventionally deemed impossible for normal SERS substrates have been achieved.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We surveyed morphological developments in SERS-active 0D–3D nanostructures for microfluidic SERS devices </LI> <LI> We categorized SERS microfluidic devices from the viewpoint of microchannel formation mechanisms and the combined forms of various SERS-active nanostructures between the microfluidic devices </LI> <LI> We compared the performance and characteristics of current microfluidic SERS devices and reported future possibilities in SERS microfluidic devices. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

High humidity- and contamination-resistant triboelectric nanogenerator with superhydrophobic interface

Zhou, Qitao,Lee, Kyunghun,Kim, Kyeong Nam,Park, Jun Gyu,Pan, Jing,Bae, Juyeol,Baik, Jeong Min,Kim, Taesung Elsevier 2019 Nano energy Vol.57 No.-

<P><B>Abstract</B></P> <P>Triboelectric nanogenerators (TENGs) have been widely used in the recent years to harvest and convert mechanical energy to electrical energy. With the improved performance of TENGs, their stability and robustness in harsh environments have attracted increasing attention as a next challenge. We present herein a superhydrophobic interlayer-integrated TENG that exhibits high performance against humidity and environmental contamination. We used particle lithography to prepare a superhydrophobic interlayer with a three-dimensional (3D), hierarchical, porous pattern, resulting in a high static water contact angle of 161°. This 3D, hierarchical superhydrophobic interlayer played a key role in improving the TENG output performance. In addition, the TENG not only retained up to 86% of its initial electrical output at a high relative humidity of 80%, but also recovered much faster than a TENG with a regular flat interface under the same wet conditions. Finally, we found that the TENG was very robust against external contamination, maintaining approximately 88% of the initial output after five cycles of particulate contamination and washing in water, indicating that the TENGs with a superhydrophobic, 3D, hierarchical interlayer could be used for powering Internet-of-things devices that are exposed to harsh environments, such as highly humid ones with dense particulate matters.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A 3D hierarchical patterned PDMS interlayer was fabricated by particle lithography. </LI> <LI> A superhydrophobic PDMS interlayer was integrated with single-electrode TENG. </LI> <LI> The TENG showed a high and stable performance even under a highly humid environment. </LI> <LI> The TENG had a strong resistance against contamination due to self-cleaning property. </LI> <LI> The TENG can supply sustainable and durable power for IoTs in harsh environments. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Inkjet-printed Ag micro-/nanostructure clusters on Cu substrates for in-situ pre-concentration and surface-enhanced Raman scattering

Zhou, Qitao,Thokchom, Ashish Kumar,Kim, Dong-Joo,Kim, Taesung Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.243 No.-

<P><B>Abstract</B></P> <P>Effective surface-enhanced Raman scattering (SERS) detection requires substrates that are typically fabricated using expensive, low-throughput and time-consuming micro-/nanofabrication processes such as photolithography, electron-beam lithography and template- assisted methods Here, a novel micro-/nanofabrication technique for fabricating SERS substrates with hydrophobicity gradients is demonstrated. An inkjet printer enables injecting an AgNO<SUB>3</SUB> solution onto a thiol-functionalized superhydrophobic Cu surface, upon which Ag micro/nanostructures are generated via replacement reactions in the droplet-injected areas. When a mixed solution of target analytes and Au-nanoparticles (Au-NPs) are placed on this substrate, the contact area decreases over time due to the evaporation of the solution and the hydrophobicity of the substrate. As a result, the analyte molecules and Au-NPs are delivered to the Ag micro-/nanostructure clusters, upon which the analyte and Au-NPs are simply and easily concentrated in situ. With the cooperation of Ag nanoplates and Au-NPs, two antibiotics at very low concentrations (e.g., 100pM 6-aminopenicillanic acid and 50pM penicillin G sodium) were successfully detected, confirming the higher SERS activity than that of Ag-nanoplate-assembled nanotube arrays or an Ag-NPs decorated graphene electrophoretic pre-concentration device. Hence, this rapid design-to-prototype method for substrates with adjustable wetting properties can be very useful for a SERS platform to detect various target analytes in biosamples.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel inkjet printing technique for fabricating SERS substrates is presented. </LI> <LI> In-situ fabrication of noble metal nanoarrays for high density SERS “hot spots” and wettability gradients for analyte pre-concentration. </LI> <LI> Highly sensitive SERS detection of antibiotics at very low concentrations below 100pM. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Surface-enhanced Raman scattering is a promising technology for biosensing but the challenge of creating practical substrates remains. This study presents a novel inkjet printing technique for fabricating (SERS) substrates that offer both in-situ fabrication of the noble metal nanoarrays, and thus high density SERS “hot spots” but also pre-concentration of the target analyte.</P> <P>[DISPLAY OMISSION]</P>

Nanochannel-Assisted Perovskite Nanowires: From Growth Mechanisms to Photodetector Applications

Zhou, Qitao,Park, Jun Gyu,Nie, Riming,Thokchom, Ashish Kumar,Ha, Dogyeong,Pan, Jing,Seok, Sang Il,Kim, Taesung American Chemical Society 2018 ACS NANO Vol.12 No.8

<P>Growing interest in hybrid organic-inorganic lead halide perovskites has led to the development of various perovskite nanowires (NWs), which have potential use in a wide range of applications, including lasers, photodetectors, and light-emitting diodes (LEDs). However, existing nanofabrication approaches lack the ability to control the number, location, orientation, and properties of perovskite NWs. Their growth mechanism also remains elusive. Here, we demonstrate a micro/nanofluidic fabrication technique (MNFFT) enabling both precise control and <I>in situ</I> monitoring of the growth of perovskite NWs. The initial nucleation point and subsequent growth path of a methylammonium lead iodide-dimethylformamide (MAPbI<SUB>3</SUB>·DMF) NW array can be guided by a nanochannel. <I>In situ</I> UV-vis absorption spectra are measured in real time, permitting the study of the growth mechanism of the DMF-mediated crystallization of MAPbI<SUB>3</SUB>. As an example of an application of the MNFFT, we demonstrate a highly sensitive MAPbI<SUB>3</SUB>-NW-based photodetector on both solid and flexible substrates, showing the potential of the MNFFT for low-cost, large-scale, highly efficient, and flexible optoelectronic applications.</P> [FIG OMISSION]</BR>

Flow-induced snap-through triboelectric nanogenerator

Kim, Hyeonseong,Zhou, Qitao,Kim, Daegyoum,Oh, Il-Kwon Elsevier 2020 Nano energy Vol.68 No.-

<P><B>Abstract</B></P> <P>Recently, flow-induced vibration and aeroelastic flutter have been considered to be an attractive energy source in renewable energy harvesting systems. However, irregular and random motions in the fluid-structure coupled dynamics greatly deteriorate the consistency and efficiency of the output power performance. Here, we report a novel mechanism of a periodic snap-through triboelectric energy harvester based on the bi-stable property of structural buckling and integrated dielectric-electrode layers made of PDMS-sealed Cu nanowire-Cu mesh. Under wind, a buckled elastic sheet experiences a periodic snap-through oscillation with a rapid transition between two opposite phases. In a regime with a large distance between two side walls, the critical free-stream velocity needed to initiate snapping increases as the wall distance becomes larger. By contrast, for a small wall-distance regime, the critical velocity decreases in an inverse manner with the wall distance. In a post-equilibrium state, three contact modes including rolling contact, head-on contact, and touch and sliding contact are identified, and their appearances strongly depend on the wall distance and free-stream velocity. The electrode layer with a small active area of 5 cm by 1 cm can deliver a maximum output power of 7.3 mW at the optimal wall distance with a free-stream velocity of 9.1 m/s. The proposed snap-through TENG system exhibits power generation performance superior to that of existing flutter-based systems, suggesting its potential applications in powering electric devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Self-excited periodic snap-through in a buckled elastic sheet is implemented to devise a new type of wind-driven TENG. </LI> <LI> Critical wind speed to initiate periodic snap-through and contact of the system is strongly affected by wall distance. </LI> <LI> Electricity is generated by a dielectric-electrode layer that is made of PDMS-sealed Cu NW-Cu mesh and is attached to the sheet. </LI> <LI> Contact modes are classified into three different modes, and they depend on wall distance and wind velocity. </LI> <LI> The snap-through nanogenerator offers a more powerful and regular energy harvesting than flutter-based energy harvesters. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P> <B>Wind-driven snap-through triboelectric nanogenerator</B> using a post-buckled elastic sheet and dielectric-electrode layers is proposed as a new triboelectric energy harvester. Under wind, a buckled elastic sheet experiences a rapid transition between two opposite phases, leading to periodic snap-through oscillation and contact with side walls. This snap-through TENG system delivers a maximum output of 7.3 mW with small electrode layers of 5 cm by 1 cm.</P> <P>[DISPLAY OMISSION]</P>

Characterizing self-assembly and deposition behavior of nanoparticles in inkjet-printed evaporating droplets

Thokchom, Ashish Kumar,Zhou, Qitao,Kim, Dong-Joo,Ha, Dogyeong,Kim, Taesung Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.252 No.-

<P><B>Abstract</B></P> <P>The self-assembly and deposition mechanisms of nanoparticles in droplets on a substrate are of significant importance in many inkjet printing-based industrial applications such as microelectronics, display systems, and paint manufacturing. However, a comprehensive investigation into the velocity field of fluid and its accompanying particle transport behavior in injected droplets undergoing immediate evaporation has not been conducted. In this study, we describe the underlying mechanisms of the self-assembly and deposition behavior of nanoparticles in inkjet-printed, evaporating droplets by visualizing the internal fluid flows. We additionally characterize the relationship between the internal fluid flows and nanoparticle patterns by changing not only the wettability and temperature of the substrate, but also the chemical composition of nanoparticle suspensions. We verify that Marangoni flow generated on a hydrophobic PDMS substrate with a contact angle (CA) of >90° helps the formation of dome-shaped nanoparticle structures, while radially outward flow generated on a hydrophilic glass substrate with a CA of <10° produces either mono-layered and flat, or ring-shaped nanoparticle structures, depending on the number density of the suspension. The presented characterization results provide not only valuable mechanistic insights, but also practical guidelines for inkjet printing-based nanoparticle applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Marangoni flow on a hydrophobic substrate helps the formation of dome-shaped nanoparticle structures. </LI> <LI> Radially outward flow on a hydrophilic substrate produces either flat and mono-layered or ring-shaped nanoparticle structures. </LI> <LI> The nanoparticle structures on a hydrophilic substrate depend on the number density of the suspension. </LI> <LI> The substrate temperature affects the self-assembly and deposition mechanism of nanoparticles in evaporating droplets. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This study describes the mechanism of the self-assembly and deposition of nanoparticles in droplets that are inkjet-injected and immediately evaporate on various substrates. The resulting nanostructures and patterns directly affect structural colors showing high potential for anti-counterfeit applications.</P> <P>[DISPLAY OMISSION]</P>

Covert and Overt transformation of Structural Colors Formed by Inkjet Printing of Nanoparticle Suspension for Durable and Flexible Anti-counterfeit Applications

이경훈,Ashish Kumar Thokchom,Qitao Zhou,하도경,박준규,박정열,김태성 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.5

Visualization of Microfluid Flow in Evaporating Droplets for Self-Assembly Control of Nanoparticles

Ashish Kumar Thokchom,Qitao Zhou,Jungyu Park,Dogyeong Ha,Taesung Kim 한국가시화정보학회 2017 한국가시화정보학회 학술발표대회 논문집 Vol.2017 No.11

동종 기반의 버클링 효과를 이용한 외부자극 반응형 위조방지패턴 및 그 구조체

박준규(Jun Gyu Park),키타오 주(Qitao Zhou),김태성(Taesung Kim) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11