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Yang, Daejong,Lee, Jaehwan,Kim, Donghwan,Cho, Incheol,Ok, Jong G.,Park, Inkyu American Chemical Society 2018 Langmuir Vol.34 No.14
<P>We report ZnO nanowire- and TiO<SUB>2</SUB> nanotube-based light sensors on flexible polymer substrates fabricated by localized hydrothermal synthesis and liquid phase deposition (LPD). This method realized simple and cost-effective in situ synthesis and integration of one-dimensional ZnO and TiO<SUB>2</SUB> nanomaterials. The fabricated sensor devices with ZnO nanowires and TiO<SUB>2</SUB> nanotubes show very high sensitivity and quick response to the ultraviolet (UV) and ambient light, respectively. In addition, our direct synthesis and integration method result in mechanical robustness under external loading such as static and cyclic bending because of the strong bonding between the nanomaterial and the electrode. By controlling the reaction time of the LPD process, the Ti/Zn ratio could be simply modulated and the spectral sensitivity to the light in the UV to visible range could be controlled.</P> [FIG OMISSION]</BR>
Yang, Daejong,Fuadi, M. Kasyful,Kang, Kyungnam,Kim, Donghwan,Li, Zhiyong,Park, Inkyu American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.19
<P>A novel method for the selective and localized synthesis of nanomaterials and their in situ integration based on serial combination of localized liquid-phase reaction has been developed for the fabrication of heterogeneous nanomaterial array. This method provides simple, fast and cost-effective fabrication process by using well-controlled thermal energy and therefore solves the challenging problems of assembly and integration of heterogeneous nanomaterial array in functional microelectronic devices. We have fabricated a parallel array of TiO<SUB>2</SUB> nanotubes, CuO nanospikes, and ZnO nanowires, which exhibited adequate gas sensing response. Furthermore, we could approximately determine individual gas concentrations in a mixture gas consisting of 0–2 ppm of NO<SUB>2</SUB> and 0–800 ppm of CO gas species by analyzing multiple data from an array of heterogeneous sensing nanomaterials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-19/acsami.5b00110/production/images/medium/am-2015-001104_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b00110'>ACS Electronic Supporting Info</A></P>
Kang, Kyungnam,Yang, Daejong,Park, Jaeho,Kim, Sanghyeok,Cho, Incheol,Yang, Hyun-Ho,Cho, Minkyu,Mousavi, Saeb,Choi, Kyung Hyun,Park, Inkyu Elsevier 2017 Sensors and actuators. B Chemical Vol.250 No.-
<P><B>Abstract</B></P> <P>Integration of heterogeneous sensing materials in microelectronic devices is essential to accomplish compact and highly integrated environmental sensors. For this purpose, a micro-patterning method of electrospun metal oxide nanofibers based on electrohydrodynamic (EHD) printing process was developed in this work. Several types of metal oxide (SnO<SUB>2</SUB>, In<SUB>2</SUB>O<SUB>3</SUB>, WO<SUB>3</SUB> and NiO) nanofibers that were produced by electrospinning, fragmented into smaller pieces by ultrasonication, and dissolved in organic solvents were utilized as inks for the printing. Constant or pulsed wave bias consisting of base and jetting voltages were applied between a nozzle and a substrate to generate a jetting of nanofiber solutions. Several parameters for EHD printing such as pulse width, inner diameter of the nozzle, distance from the nozzle to the substrate, and stage speed, were optimized for accurate micro-patterning of electrospun nanofibers. By using optimized printing parameters, microscale patterns of electrospun nanofibers with a minimum diameter less than 50μm could be realized. Gas sensors were fabricated by EHD printing on the microelectrodes and then used for the detection of toxic gases such as NO<SUB>2</SUB>, CO and H<SUB>2</SUB>S. Four kinds of metal oxides could detect down to 0.1ppm of NO<SUB>2</SUB>, 1ppm of H<SUB>2</SUB>S and 20ppm of CO gases. Also, heterogeneous nanofiber gas sensor array was fabricated by the same printing method and could detect NO<SUB>2</SUB> using the sensor array platform with microheaters. Furthermore, microscale patterns of nanofibers by EHD printing could be applied to the suspended MEMS platform without any structural damage and this sensor array could detect NO<SUB>2</SUB> and H<SUB>2</SUB>S gases with 20mW power consumption.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new method for the microscale patterning of 1D metal oxide for integrated and low-power gas sensor array is proposed. </LI> <LI> Electrohydrodynamic (EHD) printing enables finer patterning of 1D metal oxide nanomaterials than other methods. </LI> <LI> Highly integrated and low-power MEMS gas sensor array has been realized by EHD printing of heterogeneous nanomaterials. </LI> </UL> </P>