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Suspended GaN nanowires as NO<sub>2</sub> sensor for high temperature applications
Sim, Jaesam,Kim, Kwanoh,Song, Soonho,Kim, Jongbaeg The Royal Society of Chemistry 2013 The Analyst Vol.138 No.8
<P>We propose a gas sensor operable over a wide temperature range and using suspended GaN nanowires functionalized with Pt–Pd. The sensor is batch-fabricated by directly integrating the GaN nanowires onto batch-processed silicon microelectrodes in parallel. The high thermal stability of the sensor originates from a large band gap of GaN nanowires that enables the detection of NO<SUB>2</SUB> gas at an elevated temperature of up to 350 °C without a decrease in responsiveness. Exposed to NO<SUB>2</SUB> at 100–1000 ppm at 350 °C, the sensor shows a linear increment in relative response with respect to the change in gas concentration. The sensor results in a two- to four-fold increase in responsiveness to NO<SUB>2</SUB> at 100 ppm compared to NH<SUB>3</SUB> at 100 ppm and CO<SUB>2</SUB> at 1000 ppm. The nanowires suspended over a substrate provide increased surface area that could interact with gas molecules for enhanced responsiveness, and prevent any unnecessary interactions between the nanowires and the substrate.</P> <P>Graphic Abstract</P><P>We propose a gas sensor operable over a wide temperature range and using suspended GaN nanowires functionalized with Pt–Pd. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3an36917j'> </P>
Frequency Tuning of Nanowire Resonator Using Electrostatic Spring Effect
Jihan Kwon,Jungwook Choi,Kwanoh Kim,Jaesam Sim,Jinho Kim,Jongbaeg Kim IEEE 2009 IEEE transactions on magnetics Vol.45 No.5
<P>We have demonstrated resonant frequency tuning of nanowire resonator operated in both atmospheric circumstance and high vacuum environment using electrostatic spring-softening effect. The nanowire is synthesized at any desired position by focused ion beam-chemical vapor deposition (FIB-CVD) on the sidewall of batch-processed micro electrode. The resonant frequency in a vacuum chamber of 2.5 x 10(-4) Pa is 1.564 MHz under the driving voltage of 5 V-DC +/- 5 V-AC. When 30 VDC tuning bias is applied on tuning electrode, the resonant frequency is reduced to 1.529 MHz due to the electrostatic spring-softening effect while the driving bias is maintained. For the tuning bias of 60 V, the resonant frequency at atmospheric pressure has been tuned from 1.49 MHz to 1.41 MHz under the driving voltage of 30V(DC) +/- 10V(AC). The method demonstrated both in high vacuum and at atmospheric pressure is a simple and effective way to tune the deviated resonant frequency of nanowire resonator to the desired value without the alteration of the structure or post fabrication process.</P>