July 2004 Report of Progress

Progress of each ALS-NSCORT project given by each project lead. 10 pages

Self-Assembly of Linear Arrays of Semiconductor Nanoparticles on Carbon Single-Walled Nanotubes †

Ligand-stabilized nanocrystals (NCs) were strongly bound to the nanotube surfaces by simple van der Waals forces. Linear arrays of CdSe and InP quantum dots were formed by self-assembly using the grooves in bundles of carbon single-walled nanotubes (SWNTs) as a one-dimensional template. A simple geometrical model explains the ordering in terms of the anisotropic properties of the nanotube surface. CdSe quantum rods were also observed to self-organize onto SWNTs with their long axis parallel to the nanotube axis. This approach offers a route to the formation of ordered NC/SWNT architectures that avoids problems associated with surface derivatization. Both semiconductor quantum dots (QDs) 1 and carbon singlewalled nanotubes (SWNTs) 2 possess interesting and potentially useful optical and electronic properties due to their nanoscale structures. In the case of QDs, quantum confinement in three dimensions produces a size-dependent modification of the electronic band structure, resulting in the formation of discrete electronic states. QDs exhibit unique behaviors such as efficient photoluminescence and photon up-conversion, slowed relaxation and cooling of hot carriers, enhanced lasing, and carrier multiplication via impact ionization. 3 SWNTs, however, consist of sp 2 -hybridized carbon atoms that form the walls of nanometer-wide, seamless cylinders. Past efforts to attach semiconductor nanocrystals (NCs) to nanotubes have focused on forming chemical attachments between the two different nanostructures. In this approach, defects in the nanotube lattice, i.e., any site where the sp 2 -bonded carbon network is broken, are used as sites for chemical bond formation. Such defects are typically present after acid-based purification methods or may be specifically introduced by chemical derivatization. In this paper, we report the formation of organized, onedimensional (1-D) arrays of semiconductor QDs by van der Waals (vdW) adsorption onto SWNTs. Two representative II-VI and the III-V semiconductor NCs, CdSe and InP, respectively, demonstrated linear ordering when adsorbed from nonaqueous colloidal solutions onto high-purity, low-defectdensity SWNTs. The tendency to form linear arrays was greatest when tube-tube alignment was relatively good within bundles and when the QDs were relatively large. The edge-to-edge (ee) separation distance between QDs in the 1-D arrays was ∼18 Å for both the InP and the CdSe QDs, indicating that QD-QD separation is governed by the thickness of the ligand shells, as is the case in two-and three-dimensional QD arrays

February 2005 Report of Progress

Progress of each ALS-NSCORT project given by each project lead. 8 pages

May 2004 Report of Progress

Progress of each ALS-NSCORT project given by each project lead. 11 pages

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

The Deposition and Characterization of Mo/CuInGaSe2/CdS/ZnO Solar Cells

Mo thin films were deposited on sodalime glass (SLG) substrates using direct-current planar magnetron sputtering, with a sputtering power density of 1.18 W/cm2. The working gas (Ar) pressure was varied from 0.6 mtorr to 16 mtorr to gain a better understanding of the effect of sputtering pressure on the morphology and microstructure of the Mo. Thin films of Cu(In,Ga)Se2 (CIGS) were deposited on the Mo-coated glass using the 3-stage coevaporation process. The morphology of both the Mo-coated SLG and the CIGS thin films grown on it was examined using high-resolution scanning electron microscopy. The film microstructure, such as the preferred orientation, and the residual intrinsic stress were examined by X-ray diffraction

Carbon Single-Wall Nanatube Growth in a Volumetrically Confined Arc Discharge System

Carbon nanotubes hold significant promise for a vast number of materials applications due to their unique mechanical, electrical, and gas storage properties. Although carbon single-wall nanotubes (SWNTs) have been synthesized since 1993 by the arc discharge method, and numerous other synthesis methods have since been developed, no method has yet produced 100% pure carbon nanotubes. Instead, a significant amount of impurities—various carbon structures and metal catalysts—are present in the raw soot. While arc discharge was the first method for SWNT synthesis, it also produces more impure raw soot in comparison to the more recently developed laser vaporization, which has produced the purest raw soot to date but is much slower. Geometry and thermal gradient are appreciably different between traditional arc discharge systems and laser vaporization systems. We report that, by incorporating some characteristics inherent to a laser vaporization system into an arc discharge system, improvement in the yield of SWNT raw soot may be achieved. This is accomplished by confining the arc within a 50 mm diameter quartz tube, similar to laser vaporization. We find through transmission electron microscopy and Raman spectroscopy that SWNTs are made in significant numbers in this confined arc discharge system, comparable to laser vaporization synthesized material. Further study is, however, required to prove reproducibility and attain an exact value for the purity of the produced raw soot

Experimental demonstration of a latent heat storage system for dispatchable electricity

Modern electric grids that use intermittent renewables require energy storage to maintain reliability. Many potential solutions exist, but latent heat thermal energy storage shows particularly high potential for low cost grid scale energy storage. In this paper, we present the design and initial experimental results for a lab-scale prototype of a novel latent heat thermal storage system. This version of our prototype used 50 kg of aluminum-silicon alloy as a phase change material, and a novel valved thermosyphon concept to control heat flow from a thermal storage tank to thermoelectric generators for dispatchable electricity production. Our results validate the system: the thermal storage system was able to receive heat input, evenly distribute heat to and from the phase change material with small temperature gradients, and controllably dispatch heat to a heat engine for electricity generation on demand. With the basic principle of this technology demonstrated, our next step will be to evaluate and improve system efficiency

Solar thermoelectricity via advanced latent heat storage: A cost-effective small-scale CSP application

We are developing a novel concentrating solar electricity-generating technology that is both modular and dispatchable. Solar ThermoElectricity via Advanced Latent heat Storage (STEALS) uses concentrated solar flux to generate high-temperature thermal energy, which directly converts to electricity via thermoelectric generators (TEGs), stored within a phase-change material (PCM) for electricity generation at a later time, or both allowing for simultaneous charging of the PCM and electricity generation. STEALS has inherent features that drive its cost-competitive scale to be much smaller than current commercial concentrating solar power (CSP) plants. Most obvious is modularity of the solidstate TEG, which favors smaller scales in the kilowatt range as compared to CSP steam turbines, which are minimally 50 MWe for commercial power plants. Here, we present techno-economic and market analyses that show STEALS can be a cost-effective electricity-generating technology with particular appeal to small-scale microgrid applications. We evaluated levelized cost of energy (LCOE) for STEALS and for a comparable photovoltaic (PV) system with battery storage. For STEALS, we estimated capital costs and the LCOE as functions of the type of PCM including the use of recycled aluminum alloys, and evaluated the cost tradeoffs between plasma spray coatings and solution-based boron coatings that are applied to the wetted surfaces of the PCM subsystem. We developed a probabilistic cost model that accounts for uncertainties in the cost and performance inputs to the LCOE estimation. Our probabilistic model estimated LCOE for a 100-kWe STEALS system that had 5 hours of thermal storage and 8–10 hours of total daily power generation. For these cases, the solar multiple for the heliostat field varied between 1.12 and 1.5. We identified microgrids as a likely market for the STEALS system. We characterized microgrid markets in terms of nominal power, dispatchability, geographic location, and customer type, and specified additional features for STEALS that are needed to meet the needs of this growing power market

Experimental demonstration of a dispatchable latent heat storage system with aluminum-silicon as a phase change material

In this work, we present the design, construction, and experimental results of a prototype latent heat thermal energy storage system. The prototype consists of a thermal storage tank with 100 kg of the aluminum-silicon eutectic as a phase change material, a valved thermosyphon that controls heat flow from the thermal storage tank to the power block, and thermoelectric generators for conversion of heat to electricity. We tested the prototype over four simulated days, where each day consisted of four phases of operation: charging, discharging, simultaneous charging and discharging, and storage. Our results show three major conclusions. First, the thermal energy storage system was able to receive and distribute heat with small temperature gradients – less than 5 °C throughout the thermal storage tank. Second, the valved thermosyphon was able to effectively control heat transfer, demonstrating an on/off thermal conductance ratio of 430. Third, the interfaces between subsystems had small temperature drops: of the ∼ 560 °C temperature drop from the thermal storage tank to the heat rejection system, ∼ 525 °C occurred across the power block. This work overcomes the challenges of integrating previously-developed subsystems together, providing a proof-of-concept of this system