Damping in ferromagnetic alloys such, as Co40Fe40B20 are very sensitive to thermal effects both during deposition and post deposition. Depositions using and alloyed Co40Fe40B20 target were done on si (100) and amorphous glass substrates at room temperature up to 500°C. The samples deposited onto si (100) at 500°C crystalized into face centered cubic (110) Co7Fe3 whereas the samples on glass remained amorphous. The gilbert damping parameter α was reduced from .0141 to .0095 when deposited on glass however increased from .0097 to .0131 on si (100) at temperatures from 20°C- 400°C. At low deposition temperatures on glass large metallic grains of 50-75nm were found. The crystallization of Co40Fe40B20 to Co7Fe3 at 500°C resulted in broader ferromagnetic resonance peak-to-peak line widths of 1050 Oe and increased in plane coercivity values of 200 Oe compared to 35 Oe and 5 Oe for amorphous Co40Fe40B20. Post deposition annealing of Co40Fe40B20 on si (100) from 20-350°C showed reductions in damping from .0131 to .0076 and effective magnetization increased from 11.8 kOe to 13.3 kOe.
Organo-metal halide perovskite–based solar cells have been the focus of intense research over the past five years, and power conversion efficiencies have rapidly been improved from 3.8 to >21%. This article reviews major advances in perovskite solar cells that have contributed to the recent efficiency enhancements, including the evolution of device architecture, the development of material deposition processes, and the advanced device engineering techniques aiming to improve control over morphology, crystallinity, composition, and the interface properties of the perovskite thin films. The challenges and future directions for perovskite solar cell research and development are also discussed.
Solution processed thin film photovoltaic devices incorporating organohalide perovskites have progressed rapidly in recent years and achieved energy conversion efficiencies greater than 20%. However, an important issue limiting their commercialization is that device efficiencies often drop within the first few hundred hours of operation. To explore the origin of the device degradation and failure in perovskite solar cells, we investigated the spatial uniformity of current collection at different stages of aging using two-dimensional laser beam induced current (LBIC) mapping. We validated that the local decomposition of the perovskite material is likely due to interactions with moisture in the air by comparing photocurrent collection in perovskite devices that were maintained in different controlled environments. We show that the addition of a poly(methyl methacrylate)/single-wall carbon nanotube (PMMA/SWCNT) encapsulation layer prevents degradation of the device in moist air. This suggests a route toward perovskite solar cells with improved operational stability and moisture resistance.
Single-walled carbon nanotubes (SWNT) are promising candidates for use in energy conversion devices as an active
photo-collecting elements, for dissociation of bound excitons and charge-transfer from photo-excited chromophores, or
as molecular wires to transport charge. Hydrogenases are enzymes that efficiently catalyze the reduction of protons from
a variety of electron donors to produce molecular hydrogen. Hydrogenases together with SWNT suggest a novel biohybrid
material for direct conversion of sunlight into H2. Here, we report changes in SWNT optical properties upon
addition of recombinant [FeFe] hydrogenases from Clostridium acetobutylicum and Chlamydomonas reinhardtii. We
find evidence that novel and stable charge-transfer complexes are formed under conditions of the hydrogenase catalytic
turnover, providing spectroscopic handles for further study and application of this hybrid system.
The catalysts commonly used for the H2 producing reaction in artificial solar systems are typically platinum or
particulate platinum composites. Biological catalysts, the hydrogenases, exist in a wide-variety of microbes and are
biosynthesized from abundant, non-precious metals. By virtue of a unique catalytic metallo-cluster that is composed of
iron and sulfur, [FeFe]-hydrogenases are capable of catalyzing H2 production at turnover rates of millimoles-per-second.
In addition, these biological catalysts possess some of the characteristics that are desired for cost-effective solar H2
production systems, high solubilities in aqueous solutions and low activation energies, but are sensitive to CO and O2.
We are investigating ways to merge [FeFe]-hydrogenases with a variety of organic materials and nanomaterials for the
fabrication of electrodes and biohybrids as catalysts for use in artificial solar H2 production systems. These efforts
include designs that allow for the integration of [FeFe]-hydrogenase in dye-solar cells as models to measure solar
conversion and H2 production efficiencies. In support of a more fundamental understanding of [FeFe]-hydrogenase for
these and other applications the role of protein structure in catalysis is being investigated. Currently there is little known
about the mechanism of how these and other enzymes couple multi-electron transfer to proton reduction. To further the
mechanistic understanding of [FeFe]-hydrogenases, structural models for substrate transfer are being used to create
enzyme variants for biochemical analysis. Here results are presented on investigations of proton-transfer pathways in
[FeFe]-hydrogenase and their interaction with single-walled carbon nanotubes.
We measure the concentration of single-walled nanotubes (SWNTs) present in aqueous suspensions by a technique that involves surfactant removal followed by high-temperature oxidation and mass spectroscopy of the resulting products. We also analyze the shift in SWNT emission energy evident from photoluminescence excitation spectroscopy as the surfactant molecule is changed. Next we study spectroscopic changes as surfactant is gently removed by dialysis.
The effects of protonation on the structure of the carbon single-walled nanotube (SWNT) polymer composites were studied by solid-state nuclear magnetic resonance (NMR) techniques and Raman spectroscopy. In addition, solid-state 13C NMR was used to elucidate the aggregation state of the SWNTs in the polymer films relative to pristine SWNTs.
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