Electrochromic Tunable Windows: Development of a Gas Phase Counter Electrode to Simplify the Device Stack. BRENDEN MILLSTEIN (Harvard University Cambridge, MA 02138) JONATHAN SLACK (Lawrence Berkeley National Laboratory, Berkley, CA, 94720)

Global energy consumption for conditioning large office buildings demands annual energy expenditures in the hundreds of billions of dollars, much of which could be saved by the use of electrochromic windows. Electrochromic windows can be tuned across their range of optical states in mere minutes, allowing optimization of interior lighting levels while providing dynamic control of solar heat gain and radiative energy losses from conditioned space. Current electrochromic devices utilize solid-state counter electrodes for ion storage which are technically difficult to engineer and costly to manufacture. This paper focuses on the development of a catalytic ITO/Pd layer coupled with a dilute H2 gas reservoir to replace the solid-state counter electrode. Layers of the prototype device stack ranged from 3 to 500 nm, and were deposited onto ITO-coated glass at process pressures varying from 2-10 mTorr by DC magnetron and RF sputtering. The use of a cartridge-mask system allowed the creation of multiple device stacks on a single substrate, facilitating side-by-side analysis of the unique geometries. A device consisting of ITO, WO3, ZrO2, Pd, ITO, and a final Pd cap layer was found to exhibit successful electrochromic optical switching in the presence of a 4% H2, balance Ar, gas reservoir. The device stack colored with the application of 1.5v, and returned to its transparent state (bleached) at 0v applied. The applied potential was necessary only during switching; once tuned the device remained in its optical state. Research was also begun on an electrochromic reflective window that could offer even greater energy savings due to its ability to modulate between reflecting and transmitting states across the full solar spectrum. Both technologies require further research for optimization, but hold promise as energy efficient features of the modern building envelope, capable of delivering billions of dollars in energy savings to the US economy.

Hydrogen Storage Properties of Nanomaterials. JACOB MCMAHON (University of California, Davis Davis, CA 95616) SAMUEL MAO (Lawrence Berkeley National Laboratory, Berkley, CA, 94720)

Alternatives to fossil fuels have become necessary to prevent the adverse effects of carbon dioxide emissions on the environment. Fossil fuels used to create gasoline produce such emissions, but hydrogen is a clean burning source of energy. However, conventional hydrogen storage methods are impractical and dangerous. Current hydrogen storage methods employ cryogenic containers to maintain hydrogen as a liquid, or pressurized tanks containing hydrogen gas. Since hydrogen has a very low density, there is not much hydrogen per pressurized container and it is therefore volumetrically inefficient. In order to have a practical amount of hydrogen to fuel a car with a pressurized tank of hydrogen gas, one would need a tank that takes up a large quantity of the cars space. In addition, a large pressurized tank of hydrogen is extremely flammable and explosive. Storing hydrogen in the liquid form for fuel is much more volumetrically efficient, but is very costly as hydrogen needs to be kept below -252.8ºC in order to stay in the liquid form, and must be kept in a heavily insulated cryogenic container. Storage of hydrogen by means of a volumetrically efficient and safe method in nanoporous materials is the goal of this research. Several nanomaterials were tested at isothermal conditions from 0 to 20 bar using a gravimetric analyzer including aerogel, a mix of single and multi-walled carbon nanotubes, multi-walled nanotubes (MWNT), and carbon black particles. Preliminary results show that aerogel may be a candidate for hydrogen storage with a 2.10% mass uptake of hydrogen at room temperature. The aerogel also shows about 1.45% mass uptake of hydrogen at 463ºC. Both carbon nanotube samples, and the carbon particles show small uptake of hydrogen at room temperature. The multi-walled nanotubes and carbon particles show a steady decrease in mass uptake as the pressure of hydrogen increases. Further experiments must be conducted to ensure that the aerogel uptake of hydrogen is real, and to discover why the uptake of the MWNT and the carbon particles went down over time.

In-Situ Electrical Biasing in a TEM. AMANDA SIMENS (Lehigh University Bethlehem, PA 18015) DR. ANDY MINOR (Lawrence Berkeley National Laboratory, Berkley, CA, 94720)

Observing a microstructural change of nanoscale materials has historically relied on ex situ electrical measurements combined with ex post facto Transmission Electron Microscope (TEM) analysis. Recently, a new custom built electrical biasing holder designed for the JEOL 3010 TEM at NCEM has made it possible to measure the electrical properties of a sample while simultaneously observing the microstructural evolution at high spatial resolution. In order to characterize the electrical performance of thin films and nanostructures, we first need to gain a better understanding of the microstructural changes that occur under an applied bias. This study investigated three different materials with the biasing holder including gold nanowires, carbon nanotubes, and polymeric liquid crystals. The gold nanowires served as a control and as a means of calibrating the biasing holder. Experiments suggest that even though liquid crystals such as poly(2,5-2'ethylhexyloxy-p-phenylene vinylene) have the potential to align under an applied bias, adhesion forces between the film and the substrate prevented it from doing so. The carbon nanotube samples were investigated for the possibility of forming nanoscale electrode gaps for molecular electronic applications. The intention was to characterize the resistive heating of the nanotubes to a degree that they could be predictably controlled.

SPIDER Interferometer for Characterization of Femtosecond Pulses. EDWARD LIKOVICH (Harvard University Cambridge, MA 02138) ROBERT W. SCHOENLEIN (Lawrence Berkeley National Laboratory, Berkley, CA, 94720)

A SPIDER (Spectral Phase Interferometry for Direct Electric-field Reconstruction) interferometer is used to measure the time-dependent intensity and phase of an ultrashort optical pulse. Arbitrary optical fields, including ultrafast laser pulses, are characterized by the complex fields E(ω)=|E(ω)|exp[iφω] or E(t)=|E(t)|exp[iφt] which are related by the Fourier transform. In order to fully characterize ultrafast optical pulses, {E(ω),φ(ω)} or {E(t),φ(t)} must be determined. SPIDER achieves this by generating a pair of frequency-sheared copies of the input pulse through the use of nonlinear frequency mixing. The interferogram between these sheared replicas is analyzed to extract the intensity and phase properties of the pulse. By combining |E(ω)| and φ(ω), pulse shape can be completely determined. Ultrashort pulse compression can be optimized using SPIDER through direct observation of the phase of the amplified pulse, as opposed to iterative procedures of trial and error that must be used without SPIDER. In doing so, SPIDER provides real-time feedback that is useful in the optimization of pulse compression for time-resolved spectroscopy. Data analysis algorithms were designed and programmed using LabVIEW, and real-time phase retrieval (~2 Hz) was simulated using realistic input pulses under optimal conditions for the experimental parameters. A SPIDER interferometer was designed, assembled, and aligned using a low-power Helium-Neon laser. Femtosecond pulses with 800 nm wavelength were sent into the SPIDER, and the resulting interferograms were captured by the spectrometer. These interferograms were analyzed by the LabVIEW program, which extracted information about the relative time separation of the two short pulses and the phase offset of the SPIDER setup, which will be used as the calibration data for the SPIDER. Further study includes the introduction of the SPIDER into a hollow-fiber pulse compression system where it will provide real-time feedback necessary to optimize the compression of extremely short pulses (<10 fs). The SPIDER will eventually be deployed on the Femtosecond Beamline at the Advanced Light Source.