Structure and Properties of Electrochemically Synthesized, - PowerPoint PPT Presentation

Structure and Properties of Electrochemically Synthesized, Self-assembled, Functionalized Nickel Oxide Nanowires Y. Bhargava, S. Thorne, T.S. Mintz, T. Cohen-Hyams, Y. Suzuki, V. Radmilovic, and T.M. Devine Department of Materials Science and Engineering University of California, Berkeley

Electrochemically Synthesized NiO Nanowires

Overview • Discovery of Method of Synthesis • Structure and Composition • Four Factors Controlling Growth • Mechanism of Synthesis • Properties of Nanowires

Oxidation of Alloy 600 in high temperature water (288°C) Alloy 600 (Ni-16Cr-8Fe) PWR Primary Water 2 ppm Li + 1200 ppm B De-oxygenated with H 2

Oxidation of Alloy 600 in high temperature water (288°C) Alloy 600 (Ni-16Cr-8Fe) PWR Primary Water 2 ppm Li + 1200 ppm B De-oxygenated with H 2 Conditions of Potential and pH of Alloy 600 in PWR Peter Scott

Oxidation of Alloy 600 in high temperature water (288°C) Alloy 600 (Ni-16Cr-8Fe) PWR Primary Water 2 ppm Li + 1200 ppm B Potentials for growing De-oxygenated with H 2 Nanowires in pH 6.75 Conditions of Potential and pH of Alloy 600 in PWR Peter Scott

Oxidation of Alloy 600 (Ni-16Cr-8Fe) at high potentials (-25 mV vs SHE) in 288°C Water with 2 ppm Li + 1200 ppm B

Samples in titanium autoclave with sapphire window

SERS of Films Formed in Aqueous Solutions at 288°C Samples LASER . F g . Reference Electrode n P i s u c o F s c i t p O Spectrometer Focus C Lens C D N.F. Collection/ Collimation Lens

Overview • Discovery of Method of Synthesis • Structure and Composition • Four Factors Controlling Growth • Mechanism of Synthesis • Properties of Nanowires

Size of NiO Nanowires 60 50 40 Count 30 20 10 0 1-5 105-110 120-125 135-140 15-20 30-35 45-50 60-65 75-80 90-95 Diameter (nm) Mean diam = 25 nm Length = 25 µm

AEM Data

Composition of Nanowires N = 15 O Ni 49% 47% O Fe Fe 4% Ni

Nanowires are Single Crystals

Overview • Discovery of Method of Synthesis • Structure and Composition • Four Factors Controlling Growth • Mechanism of Synthesis • Properties of Nanowires

4 Factors Control Nanowire Formation • Composition of Aqueous Solution – pH 6.75 => nanowires – pH 5.5 => no nanowires • Temperature – 288°C and 238°C => nanowires – 25°C => no nanowires • Substrate Composition • Potential

Substrate Composition Alloy 600 (Ni-15.5a/o Cr-8a/o Fe) Ni-20a/oCr-10a/o Mo 70a/o Ni – 30a/o Cr 500nm 500nm 500nm

4 Factors Control Nanowire Formation • Composition of Aqueous Solution – pH 6.75 => nanowires – pH 5.5 => no nanowires • Temperature – 288°C and 238°C => nanowires – 25°C => no nanowires • Substrate Composition – 16Cr-8Fe; 30Cr; 20Cr-10Mo => nanowires – Pure Ni, Cr, Fe => no nanowires • Potential: oxidizing

Overview • Discovery of Method of Synthesis • Structure and Composition • Four Factors Controlling Growth • Mechanism of Synthesis • Properties of Nanowires

3 Step Process for Synthesizing NiO Nanowires Alloy 600 (Ni-16Cr-8Fe) PWR Primary Water 2 ppm Li + 1200 ppm B (3) -25 mV/0.5h - 4h De-oxygenated with H 2 (2) -850 mV/1 hr (1) -1600 mV/ 1 day

3 Step Process for Synthesizing NiO Nanowires (1) -1600 mV vs SHE @ 288°C (2) -800 mV remove air-formed oxide Form Cr x O y Alloy 600 Aqueous Solution Alloy 600 (3b) -25 mV /4 h (3a) > -600 mV NiO Nanowires Planar NiO Alloy 600 Alloy 600 Aqueous Solution

[Ni ++ ] determines growth morphology of NiO Ni ++ + 2 OH - --> NiO + H 2 Concentration [OH - ] EQUIL [Ni ++ ] EQUIL [Ni ++ ] > [Ni ++ ] EQUIL NiO = nanowires [Ni ++ ] > [Ni ++ ] EQUIL Alloy NiO = planar 600 Distance into water

Growth of NiO Nanowires with Potentiostatic Conditions Ni ++ Planar NiO NiO Nanowire Alloy 600 OH - Cr x O y [Ni ++ ] [OH - ]

Growth of NiO Nanowires with Dissolved O 2 Ni ++ Planar NiO Alloy 600 NiO Nanowire O 2 Cr x O y 1/2 O 2 + H 2 O + 2 e - --> 2 OH - [Ni ++ ] [O 2 ]

Overview • Discovery of Method of Synthesis • Structure and Composition • Four Factors Controlling Growth • Mechanism of Synthesis • Properties of Nanowires

Magnetic Properties: Methodology • SQUID magnetometer capable of measuring magnetic flux caused by magnetic samples – Can control applied magnetic field, temperature, and z-pos of sample Tape w/Nanowires Into SQUID Gel Tab SQUID Rod Straw Straw Stoppers

Magnetic Hysterisis 0.30 0.20 Long Moment (emu/g) 0.10 0.00 -3000.00 -2000.00 -1000.00 0.00 1000.00 2000.00 3000.00 4000.00 -0.10 -0.20 -0.30 Applied Field (Oe) Remnant Field: ~80 Oe Coercivity: ~0.03 emu/g

Growth of NiO Nanowires with Dissolved O 2 Ni ++ Planar NiO Alloy 600 NiO Nanowire O 2 Cr x O y RESULTS => Nanowires are electrically conductive [Ni ++ ] [O 2 ]

Summary • Electrochemical method of synthesizing dense arrays of self-assembled, functionalized, NiO nanowires (25 nm diam, 25 µm length) • Technique might be capable of synthesizing other oxide nanowires (e.g., Fe x O y and Co r O s ) • Growth of nanowires by cellular breakdown of planar oxide/water interface • NiO nanowires are ferromagnetic and electrically conductive

EDS Results O Cr Fe Ni Wt % At % Wt % At % Wt % At % Wt % At % 5 22.198 51.028 0.536 0.379 5.737 3.778 71.527 44.814 6 21.108 49.458 0 0 4.88 3.276 74.01 47.265 7 24.865 54.745 0.187 0.127 4.958 3.127 69.988 41.999 11 22.228 51.158 0 0 1.717 1.132 76.054 47.709 12 20.796 48.936 0 0 8.118 5.472 71.084 45.59 13 18.505 45.35 0 0 6.29 4.416 75.204 50.233 14 20.36 48.328 0.795 0.58 2.447 1.664 76.396 49.426 15 21.555 50.094 0 0 6.692 4.455 71.751 45.449 16 22.13 50.918 0.054 0.038 7.643 5.038 70.17 44.004 17 17.174 43.096 0 0 7.365 5.294 75.459 51.609 18 18.089 44.67 0 0 5.757 4.072 76.153 51.253 Avg 20.82 48.89 0.14 0.10 5.60 3.79 73.44 47.21 STD 2.21 3.38 0.27 0.20 2.03 1.41 2.55 3.14 RSD 10.62 6.91 189.39 191.47 36.28 37.14 3.47 6.66