Thursday, May 22, 2014 - 8:00pm

Steady-state and transient spectroscopic studies are described for plasmonic metal nanorods, gold nanoantenna arrays and atomic layer deposition (ALD) silver films. High aspect ratio nanorods of various metals fabricated by template electrochemical deposition exhibit plasmon bands at long wavelengths, into the mid infrared, and coherent acoustic oscillations due to impulsively excited radial motion in ultrafast pump probe studies.1 Thin (<50 nm) ALD Ag films were also investigated in which a nanostructured morphology is formed spontaneously resulting in surface plasmon resonance (SPR) bands in the visible.  Ultrafast studies of the films reveal that contributions from electron-phonon coupling and lattice dynamics in the transient response vary systematically with the probe wavelength. Coherent acoustic oscillations are observed that are attributed to lateral motions which modulate gaps in the nanostructures.  Also, gold nanoantenna  arrays were fabricated by electron beam lithography with different lengths (0.55 and 1.1 mm), on two types of substrates, sapphire and silica, and with a range of pitches.2 They were characterized by microscope infrared spectroscopy to investigate different regimes of coupling revealed by the observed variations in resonance band positions and linewidths. 

In situ optical studies including thermal imaging, Raman spectroscopy and infrared emission, have been used to characterize materials and processes on the Ni/YSZ anodes of operating (700-800 oC) solid oxide fuel cells (SOFCS).3  One objective is to identify conditions and mechanisms responsible for carbon formation that degrades cell performance. A survey of results will be presented for SOFC operation with various fuels, including hydrocarbons and alcohols and under wet and dry conditions. The most recently developed method is Fourier transform infrared emission spectroscopy which has been used to study SOFC operation with methane.4  In addition to gas phase species observed for the methane fuel and gas-phase oxidation products carbon dioxide (CO2) and carbon monoxide (CO), the most interesting feature is a broad band due to CO2 in or on the anode.  It is surprising to find CO2 on the nickel composite anodes because it binds weakly, but CO2 appears to accumulate in the anode structure during SOFC operation. The assignment and interpretation are reinforced by supporting in situ studies in which the fuel composition and current are varied while the cell is continuously monitored.

 

1Owrutsky, J. C., Pomfret, M. B., and Brown, D. J., Coherent Acoustic Oscillations of Nanorods Composed of Various Metals J. Phys. Chem. C  113, 10947 (2009).

2Simpkins, B. S., Long, J. P., Glembocki, O. J., Guo, J., Caldwell, J. D., and Owrutsky, J. C., Pitch-dependent resonances and near-field coupling in infrared nanoantenna arrays, Optics Express, 20,  27725 (2012).

3Pomfret, M.B., Owrutsky, J.C., and Walker, R.A , High Temperature Chemistry in Solid Oxide Fuel Cells: In situ Optical Studies J. Phys. Chem. Lett. 3, 3053 (2012).

 4Pomfret, M.B., Steinhurst, D.A., and Owrutsky, J.C., Identification of methane oxidation intermediate on solid oxide fuel cell anode surfaces with Fourier transform infrared emission, J. Phys. Chem. Lett. 4, 1310 (2013).

Speaker: 

Jeff Owrutsky

Institution: 

Naval Research Lab

Location: 

NS2 2201