Supporting Information Local CuO Nanowire Growth on Microhotplates
Supporting Information Local CuO Nanowire Growth on Microhotplates: In Situ Electrical Measurements and Gas Sensing Application Stephan Steinhauer†, Audrey Chapelle‡, Philippe Menini‡, Mukhles Sowwan*,† †
Nanoparticles by Design Unit, Okinawa Institute of Science and Technology (OIST) Graduate University, 1919-1 Tancha Onna-Son, Okinawa 904-0495, Japan ‡ University of Toulouse, Laboratoire d’Analyses et d’Architecture des Systèmes CNRS-LAAS, 7 Avenue du Colonel Roche, 31031 Toulouse Cedex 4, France KEYWORDS: CuO nanowire, gas sensor, microhotplate, in situ measurement, CO sensing, sensor degradation
TABLE OF CONTENTS Figure S1. Transmission electron microscopy characterization of single CuO nanowires.......................................................S-2 Figure S2. CO response of three CuO nanowire gas sensor devices ........................................................................................S-2 Figure S3. CuO nanowire gas sensor response to H2S and NO2 ..............................................................................................S-3 References ...............................................................................................................................................................................S-3
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Figure S1. Transmission electron microscopy characterization of single CuO nanowires. a) high resolution transmission electron microscopy image and b) electron energy loss spectrum of O K-edge and Cu L2,3-edge. For material characterization of CuO nanowires, unpatterned Cu thin films were thermally oxidized at 335ºC in ambient air resulting in similar growth compared to CuO nanowire synthesis on microhotplates. High resolution transmission electron microscopy and electron energy loss spectroscopy were performed using an FEI Titan Environmental TEM equipped with a spherical aberration image corrector at an operation voltage of 80 kV. Representative results are shown in Figure S1. The EELS near-edge fine structure allows the distinction between different Cu oxidation states and the results are in good agreement with literature spectra for CuO1,2.
Figure S2. CO response of three CuO nanowire gas sensor devices. The sensor response (resistance ratio RCO/Rair) for CO concentrations from 1-30ppm was evaluated for three different CuO nanowire devices. Differences in sensor calibration curves are attributed to device-to-device variations in the growth process leading to slight changes in diameters, lengths and number of CuO nanowires. For sensor 3 the CO response is also plotted for the case of measurements in dry air after humidity exposure and for the case of measurements in humid synthetic air at around 30% relative humidity (rH). The error bars result from at least three repeated measurements at increasing and decreasing CO concentrations.
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Figure S3. CuO nanowire gas sensor response to a) H2S and b) NO2.
REFERENCES (1) Grunes, L. A., Leapman, R. D., Wilker, C. N., Hoffmann, R. & Kunz, A. B. Oxygen K near-edge fine structure: An electron-energy-loss investigation with comparisons to new theory for selected 3d transition-metal oxides. Phys. Rev. B 1982, 25, 7157-7173. (2) Leapman, R. D., Grunes, L. A. & Fejes, P. L. Study of the L23 edges in the 3d transition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory. Phys. Rev. B 1982, 26, 614-635.
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Nanoparticles by Design Unit, Okinawa Institute of Science and Technology (OIST) Graduate University, 1919-1 Tancha Onna-Son, Okinawa 904-0495, Japan ‡ University of Toulouse, Laboratoire d’Analyses et d’Architecture des Systèmes CNRS-LAAS, 7 Avenue du Colonel Roche, 31031 Toulouse Cedex 4, France KEYWORDS: CuO nanowire, gas sensor, microhotplate, in situ measurement, CO sensing, sensor degradation
TABLE OF CONTENTS Figure S1. Transmission electron microscopy characterization of single CuO nanowires.......................................................S-2 Figure S2. CO response of three CuO nanowire gas sensor devices ........................................................................................S-2 Figure S3. CuO nanowire gas sensor response to H2S and NO2 ..............................................................................................S-3 References ...............................................................................................................................................................................S-3
S-1
Figure S1. Transmission electron microscopy characterization of single CuO nanowires. a) high resolution transmission electron microscopy image and b) electron energy loss spectrum of O K-edge and Cu L2,3-edge. For material characterization of CuO nanowires, unpatterned Cu thin films were thermally oxidized at 335ºC in ambient air resulting in similar growth compared to CuO nanowire synthesis on microhotplates. High resolution transmission electron microscopy and electron energy loss spectroscopy were performed using an FEI Titan Environmental TEM equipped with a spherical aberration image corrector at an operation voltage of 80 kV. Representative results are shown in Figure S1. The EELS near-edge fine structure allows the distinction between different Cu oxidation states and the results are in good agreement with literature spectra for CuO1,2.
Figure S2. CO response of three CuO nanowire gas sensor devices. The sensor response (resistance ratio RCO/Rair) for CO concentrations from 1-30ppm was evaluated for three different CuO nanowire devices. Differences in sensor calibration curves are attributed to device-to-device variations in the growth process leading to slight changes in diameters, lengths and number of CuO nanowires. For sensor 3 the CO response is also plotted for the case of measurements in dry air after humidity exposure and for the case of measurements in humid synthetic air at around 30% relative humidity (rH). The error bars result from at least three repeated measurements at increasing and decreasing CO concentrations.
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Figure S3. CuO nanowire gas sensor response to a) H2S and b) NO2.
REFERENCES (1) Grunes, L. A., Leapman, R. D., Wilker, C. N., Hoffmann, R. & Kunz, A. B. Oxygen K near-edge fine structure: An electron-energy-loss investigation with comparisons to new theory for selected 3d transition-metal oxides. Phys. Rev. B 1982, 25, 7157-7173. (2) Leapman, R. D., Grunes, L. A. & Fejes, P. L. Study of the L23 edges in the 3d transition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory. Phys. Rev. B 1982, 26, 614-635.
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