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Siddiqui, Saqib,Kim, Do-Il,Roh, Eun,Duy, Le Thai,Trung, Tran Quang,Nguyen, Minh Triet,Lee, Nae-Eung Elsevier 2016 Nano energy Vol.30 No.-
<P><B>Abstract</B></P> <P>Practical usage of piezoelectric nanogenerators (PENGs) under heavy loading environments for high power generation, such as smart shoes, has been limited due to the low mechanical endurance of many piezoelectric materials. Durability and performance under harsh environments are a stumbling block for the practical application of PENGs. Synthesis of piezoelectrically enhanced nanofibers electrospun from nanocomposite of barium titanate nanoparticles (BT NPs) dispersed in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) enables successful fabrication of a robust, efficient, flexible and lead-free PENG. A nanofiber PENG (nf-PENG) fabricated by embedding nanocomposite nanofibers in an elastomer film is demonstrated for biomechanical energy harvesting and storage during walking. When placed inside of a shoe, a nf-PENG loaded with 15wt% BT NPs can generate an output of 25V at a walking frequency of 0.6Hz with high mechanical durability under very high loads (600N). This can charge a 4.7µF capacitor after approximately 72 steps. The stored charge can operate a strain sensor without any external power supply. The high performance of the nf-PENG is mainly attributed to the self-poled nanocomposite nanofibers. Additionally, embedding the nanofibers into an elastomer provided high durability by protecting the nanofibers from mechanical damage. Furthermore, the devices small form factor, flexibility, and transparency make this nf-PENG suitable for applications in wearable electronics, where aesthetics and comfort are also desired (in addition to performance). This work demonstrates the possibility of highly durable, efficient, and self-powered wearable sensing systems that can work under extreme environments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lead-free piezoelectric nanocomposite nanofibers. </LI> <LI> High durability under harsh environments and high loadings. </LI> <LI> Harvesting and storing biomechanical energy during walking. </LI> <LI> Self-powered system. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A highly durable, efficient and flexible piezoelectric nanogenerator, comprised of piezoelectric nanocomposite nanofibers embedded into an elastomer, was designed for energy harvesting under heavy loading conditions. The high resistance of the generator to ambient conditions for prolonged periods of time, as well as resistance to damage under heavy loading conditions, enabled the efficient harvest of bio-mechanical energy during human walking. This energy could be stored in a capacitor to create a self-powered sensor system. This approach may help enable practical applications of piezoelectric nanogenerators in wearable systems.</P> <P>[DISPLAY OMISSION]</P>
Hanif, Adeela,Trung, Tran Quang,Siddiqui, Saqib,Toi, Phan Tan,Lee, Nae-Eung American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.32
<P>Human skin is highly stretchable at low strain but becomes self-limiting when deformed at large strain due to stiffening caused by alignment of a network of stiff collagen nanofibers inside the tissue beneath the epidermis. To imitate this mechanical behavior and the sensory function of human skin, we fabricated a skin-like substrate with highly stretchable, transparent, tough, ultrathin, mechanosensory, and self-limiting properties by incorporating piezoelectric crystalline poly((vinylidene fluoride)-<I>co</I>-trifluoroethylene) (P(VDF-TrFE)) nanofibers with a high modulus into the low modulus matrix of elastomeric poly(dimethylsiloxane). Randomly distributed P(VDF-TrFE) nanofibers in the elastomer matrix conferred a self-limiting property to the skin-like substrate so that it can easily stretch at low strain but swiftly counteract rupturing in response to stretching. The stretchability, toughness, and Young’s modulus of the ultrathin (∼62 μm) skin-like substrate with high optical transparency could be tuned by controlling the loading of nanofibers. Moreover, the ultrathin skin-like substrate with a stretchable temperature sensor fabricated on it demonstrated the ability to accommodate bodily motion-induced strain in the sensor while maintaining its mechanosensory and thermosensory functionalities.</P> [FIG OMISSION]</BR>
Dang, Vinh Quang,Trung, Tran Quang,Duy, Le Thai,Kim, Bo-Yeong,Siddiqui, Saqib,Lee, Wonil,Lee, Nae-Eung American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.20
<P>A flexible ultraviolet (UV) photodetector based on ZnO nanorods (NRs) as nanostructure sensing materials integrated into a graphene (Gr) field-effect transistor (FET) platform is investigated with high performance. Based on the negative shift of the Dirac point (<I>V</I><SUB>Dirac</SUB>) in the transfer characteristics of a phototransistor, high-photovoltage responsivity (<I>R</I><SUB>V</SUB>) is calculated with a maximum value of 3 × 10<SUP>8</SUP> V W<SUP>–1</SUP>. The peak response at a wavelength of ∼365 nm indicated excellent selectivity to UV light. The phototransistor also allowed investigation of the photocurrent responsivity (<I>R</I><SUB>I</SUB>) and photoconductive gain (<I>G</I>) at various gate voltages, with maximum values of 2.5 × 10<SUP>6</SUP> A W<SUP>–1</SUP> and 8.3 × 10<SUP>6</SUP>, respectively, at a gate bias of 5 V. The UV response under bending conditions was virtually unaffected and was unchanged after 10 000 bending cycles at a bending radius of 12 mm, subject to a strain of 0.5%. The attributes of high stability, selectivity, and sensitivity of this flexible UV photodetector based on a ZnO NRs/Gr hybrid FET indicate promising potential for future flexible optoelectronic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-20/acsami.5b02834/production/images/medium/am-2015-028343_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b02834'>ACS Electronic Supporting Info</A></P>
Minh Triet, Nguyen,Thai Duy, Le,Hwang, Byeong-Ung,Hanif, Adeela,Siddiqui, Saqib,Park, Kyung-Ho,Cho, Chu-Young,Lee, Nae-Eung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36
<P>A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and Al0.27GaN0.73(similar to 25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO2, SO2, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm(-1)), fast response (similar to 2 min), and good reproducibility down concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances in the design of a Schottky diode gas sensor based on the heterojunction of high-mobility two-dimensional electron gas channel and highly responsive 3D-engineered sensing nanomaterials have potential not only for the enhancement of sensitivity and selectivity but also for improving operation capability at room temperature.</P>