The objective of this work is to investigate various silicon-metal eutectic systems that selectively retain detrimental impurities, such as Ni, Co, Fe, Cr, in the melt so that silicon may be purified. We studied possible interactions in the melt and in the silicon crystal between impurity elements and solvent metals that lead to reduced or enhanced impurity partition relative to the respective silicon-impurity binary systems. Systems such as Al- Si, Cu-Si, and In-Si show promises of reduced impurity incorporations in recrystallized silicon, which are good candidates for further investigation besides Ga-Si, Au-Si, and Ag-Si.

Quantitative analysis or numeric simulation on a cross-section of silicon devices offers many insights into understanding material problems and their effects on device performances as well as device structure optimizations. Such two-dimensional simulations on semiconductor devices are standard design practices and are routinely done with expensive software packages. The availability of less expensive software tools nowadays, such as MicroTec(R) for 2D modeling of semiconductor devices, affords us a more detailed examination of polycrystalline thin-silicon materials and solar cells.

Direct writing of solar cell components is an attractive processing approach. We have fabricated a 6.8% Si solar cell using silver ink based electrodes. Ohmic contact through the antireflection (AR) coating was obtained with pure Ag electrodes at 850 0C. We also report on highly conductive silver metallizations and initial results on direct-write TCO demonstrating a 100-micron spatial resolution produced by inkjet printing.

Reflectance spectroscopy is very well-suited for measuring physical parameters of semiconductor wafers, and of surface structures (continuous or patterned) deposited on them as thin films. We have developed a reflectometer (PV-Reflectometer) that can measure physical parameters of wafers, wafer surfaces, and other materials deposited during solar cell fabrication. Concomitantly, PV Reflectometer can also be applied for monitoring various cell fabrication processes.

The Silicon-Film(TM) process produces a continuous sheet of polycrystalline silicon for use in the production of solar cells. This is a relatively new material for the industry considering the growth method, the relatively high level of impurities, and small grain size. This paper reports on the progress in characterizing this relatively new material. The conversion efficiency for Silicon-Film{trademark} solar cells is presently approximately 80% of those achieved with the industry standard CZ or large grain cast materials. The smaller grain size and the lower purity are the logical explanations for performance differences. With advances in the understanding of critical high temperature processes, such as gettering, views on impurity requirements have changed. Similarly, conventional grain size limits are shown to be inaccurate, allowing higher performance than thought possible from smaller grains. To delve into these and other specific material issues, an industry--academic--government team has been established. This paper reports on some of the results found by that team and highlights some of the conclusions that have been drawn as regards impurities and gettering.

Characterization of minority-carrier parameters is a primary interest for a range of devices, including solar cells. For 'on-line' testing needs, contactless techniques are mandatory, as any diagnostic requiring contact formation is impractical. Here, we will describe the resonance-coupled photoconductive decay (RCPCD) technique that has proven to be a valuable diagnostic for a number of semiconductor technologies. This technique avoids some of the inherent limitations of microwave reflection. Our system is a pump-probe technique, using an optical pump and a microwave probe (400 to 900 MHz). These low frequency microwaves penetrate most silicon wafers with common doping levels. By varying the optical excitation wavelength, one can probe wafers of standard (300 to 400 {micro}m) wafer thickness. Also, the method is very linear in sample photoconductivity, and we have observed a linear response over more than three orders of magnitude of excess carrier concentration. This attribute allows us to measure the carrier recombination lifetime over many decades of injection level, allowing the use of a procedure that is called injection-level spectroscopy (ILS). The RCPCD technique was developed [1,2,3,4,5,6] at the National Renewable Energy Laboratory (NREL) and has been applied to more than 5000 samples, ranging from small-area thin films to 350-{micro}m-thick, 250-mm-diameter …

With increasing acceptance of photovoltaic (solar electric) energy as a solution to many energy needs of the world, PV production has grown at about 20%/year in recent years. Worldwide shipments of PV modules reached about 400 megawatts (MW) in 2001. Because Si continues to be the dominant technology, solar cell manufacturing using c-Si (single or multicrystalline) has reached new pinnacles. Shipments of solar electric power products based on c-Si materials reached about 320 MW in 2001, representing more than 80% of total solar cell shipments. Because of the increasing demands of PV energy use, much of the current activity in the PV industry is heavily geared for increasing manufacturing capabilities. Nearly all major manufacturers are installing new production lines.

Techniques for cost-efficient operation of SiNx:H systems with a capability for hydrogen passivation in a manufacturing environment are analyzed. We conclude that SiNx:H performance may be optimized by a variety of techniques, and that the cost and productivity of the deposition tool may be the determining factors in the industries decision for a particular technique. PECVD constitutes the current benchmark. Dual magnetron reactive sputtering is a candidate to achieve industry acceptance.

One of the main advantages of photovoltaic solar cells (PVC) is their ecological clarity of direct conversion of solar energy to electricity. For wide spreading of PV technologies it is necessary to ensure that there is no environment pollution at the stage of PVC-s manufacturing, beginning from producing of polysilicon feedstock. The objective of this project is creation of ecologically clean method for production of solar grade polysilicon feedstock (SGPF) as raw material for PVCs, and also raw material for producing monocrystalline silicon, which is used in electronic industry.

We present a correlation of Microwave Photoconductance Decay minority carrier lifetime with dislocation density in high purity Float Zone silicon. Electron Beam Induced Current (EBIC) images were carefully aligned to lifetime maps and depth profiling of individual defect electrical activity was done by varying the bias of Schottky diodes. The data presented provides a relationship between lifetime variations and EBIC contrast, based on dislocation density and impurity decoration in the near surface zone.

The PVSCAN is an instrument designed to characterize silicon solar cell materials and devices. It performs a host of measurements that yield spatial maps of dislocation density, grain distribution, reflectance, and photoresponses from near-junction and the bulk of a solar cell.

Vacancy densities and vacancy binding energies have been quantitatively determined by a Au labeling technique for single crystal Si damaged by high-energy ion implantation. When Au is diffused into the defective Si material, Au atoms are preferentially trapped at vacancies and small vacancy clusters. The volume concentration has been quantitatively calibrated to be 1.2 Au atoms per vacancy (denoted as calibration factor k = 1.2). The technique is potentially capable of obtaining vacancy concentrations in as-grown and processed solar cell Si material by diffusing Au from the surface. Of particular interest is vacancy injection associated with the formation of Al backside contacts. Introduction and diffusion of the Au species and Au profiling is discussed in the context of applying a Au labeling technique to problems where vacancies play a role in solar cell processing, such as hydrogen passivation and contact formation.

High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super-massive black holes and proto-clusters. They report on deep narrow-band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-{alpha} nebulae centered on the galaxies and to search for over-dense regions around them. They discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.

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Many binary-cycle geothermal power plants are air cooled because insufficient water is available to provide year-round water cooling. The performance of air-cooled geothermal plants is highly dependent on the dry bulb temperature of the air (much more so than fossil fuel plants that operate at higher boiler temperatures), and plant electric output can drop by 50% or more on hot summer days, compared to winter performance. This problem of reduced summer performance is exacerbated by the fact that electricity has a higher value in the summer. This paper describes a spreadsheet model that was developed to assess the cost and performance of four methods for using supplemental evaporative cooling to boost summer performance: (1) pre-cooling with spray nozzles, (2) pre-cooling with Munters media, (3) a hybrid combination of nozzles and Munters media, and (4) direct deluge cooling of the air-cooled condenser tubes. Although all four options show significant benefit, deluge cooling has the potential to be the most economic. However, issues of scaling and corrosion would need to be addressed.

We have improved the quality of our narrow-bandgap a-SiGe:H grown by hot-wire chemical vapor deposition (HWCVD) by decreasing our W filament diameter and our substrate temperature. We now grow a-SiGe:H with Tauc bandgaps below 1.5 eV, having a photoresponse equal to or better than our plasma-enhanced CVD-grown alloys. We enhanced the transport properties - as measured by the photoconductivity frequency mixing technique - relative to previous HWCVD results. These improved alloys do not necessarily show an improvement in the degree of structural heterogeneity on the nanometer scale, as measured by small-angle X-ray scattering. Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity, while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.

Researchers are developing polymer-based coating systems to reduce scaling and corrosion of air-cooled condensers that use a geothermal fluid spray for heat transfer augmentation. These coating systems act as barriers to corrosion to protect aluminum fins and steel tubing; they are formulated to resist the strong attachment of scale. Field tests have been done to determine the corrosion and scaling issues related to brine spraying and a promising organometallic polymer has been evaluated in salt spray tests.

The host galaxies of powerful radio sources are ideal laboratories to study active galactic nuclei (AGN). The galaxies themselves are among the most massive systems in the universe, and are believed to harbor supermassive black holes (SMBH). If large galaxies are formed in a hierarchical way by multiple merger events, radio galaxies at low redshift represent the end-products of this process. However, it is not clear why some of these massive ellipticals have associated radio emission, while others do not. Both are thought to contain SMBHs, with masses proportional to the total luminous mass in the bulge. It either implies every SMBH has recurrent radio-loud phases, and the radio-quiet galaxies happen to be in the ''low'' state, or that the radio galaxy nuclei are physically different from radio-quiet ones, i.e. by having a more massive SMBH for a given bulge mass. Here we present the first results from our adaptive optics imaging and spectroscopy pilot program on three nearby powerful radio galaxies. Initiating a larger, more systematic AO survey of radio galaxies (preferentially with Laser Guide Star equipped AO systems) has the potential of furthering our understanding of the physical properties of radio sources, their triggering, and their subsequent evolution.

A three-dimensional, finite-element, heat-transfer computer program was developed to study ground-coupled heat transfer from buildings. It was used in conjunction with the SUNREL whole-building energy simulation program to analyze ground-coupled heat transfer from buildings, and the results were compared with the simple ground-coupled heat transfer models used in whole-building energy simulation programs. The detailed model provides another method of testing and refining the simple models and analyzing complex problems. This work is part of an effort to improve the analysis of the ground-coupled heat transfer in building energy simulation programs. The output from this detailed model and several others will form a set of reference results for use with the BESTEST diagnostic procedure. We anticipate that the results from the work will be incorporated into ANSI/ASHRAE 140-2001, Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs.

Residential building practice currently ignores the lossesof energy and water caused by the poor design of hot water systems. Theselosses include: combustion and standby losses from water heaters, thewaste of water (and energy) while waiting for hot water to get to thepoint of use; the wasted heat as water cools down in the distributionsystem after a draw; heat losses from recirculation systems and thediscarded warmth of waste water as it runs down the drain. Severaltechnologies are available that save energy (and water) by reducing theselosses or by passively recovering heat from wastewater streams and othersources. Energy savings from some individual technologies are reported tobe as much as 30 percent. Savings calculations of prototype systemsincluding bundles of technologies have been reported above 50 percent.This roundtable session will describe the current practices, summarizethe results of past and ongoing studies, discuss ways to think about hotwater system efficiency, and point to areas of future study. We will alsorecommend further steps to reduce unnecessary losses from hot waterdistribution systems.

Supercritical fluid extraction (SFE) of plutonium and americium from soil was successfully demonstrated using supercritical fluid carbon dioxide solvent augmented with organophosphorus and beta-diketone complexants. Spiked Idaho soils were chemically and radiologically characterized, then extracted with supercritical fluid carbon dioxide at 2,900 psi and 65°C containing varying concentrations of tributyl phosphate (TBP) and thenoyltrifluoroacetone (TTA). A single 45 minute SFE with 2.7 mol% TBP and 3.2 mol% TTA provided as much as 88% ± 6.0 extraction of americium and 69% ± 5.0 extraction of plutonium. Use of 5.3 mol% TBP with 6.8 mol% of the more acidic beta-diketone hexafluoroacetylacetone (HFA) provided 95% ± 3.0 extraction of americium and 83% ± 5.0 extraction of plutonium in a single 45 minute SFE at 3,750 psi and 95°C. Sequential chemical extraction techniques were used to chemically characterize soil partitioning of plutonium and americium in pre-SFE soil samples. Sequential chemical extraction techniques demonstrated that spiked plutonium resides primarily (76.6%) in the sesquioxide fraction with minor amounts being absorbed by the oxidizable fraction (10.6%) and residual fractions (12.8%). Post-SFE soils subjected to sequential chemical extraction characterization demonstrated that 97% of the oxidizable, 78% of the sesquioxide and 80% of the residual plutonium could be removed …

A source release model was developed to determine the release of contaminants into the shallow subsurface, as part of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) evaluation at the Idaho National Engineering and Environmental Laboratory's (INEEL) Subsurface Disposal Area (SDA). The output of the source release model is used as input to the subsurface transport and biotic uptake models. The model allowed separating the waste into areas that match the actual disposal units. This allows quantitative evaluation of the relative contribution to the total risk and allows evaluation of selective remediation of the disposal units within the SDA.

A combined experimental and numerical investigation is under way to investigate heat transfer enhancement techniques that may be applicable to large-scale air-cooled condensers such as those used in geothermal power applications. The research is focused on whether air-side heat transfer can be improved through the use of finsurface vortex generators (winglets,) while maintaining low heat exchanger pressure drop. A transient heat transfer visualization and measurement technique has been employed in order to obtain detailed distributions of local heat transfer coefficients on model fin surfaces. Pressure drop measurements have also been acquired in a separate multiple-tube row apparatus. In addition, numerical modeling techniques have been developed to allow prediction of local and average heat transfer for these low-Reynolds-number flows with and without winglets. Representative experimental and numerical results presented in this paper reveal quantitative details of local fin-surface heat transfer in the vicinity of a circular tube with a single delta winglet pair downstream of the cylinder. The winglets were triangular (delta) with a 1:2 height/length aspect ratio and a height equal to 90% of the channel height. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement (average enhancement ratio 35%) associated with the deployment of the …

The kinetics of the oxygen reduction reaction (ORR) was studied in alkaline electrolyte at 293-333K on Pt(hkl) surfaces by means of the rotating ring-disk electrode technique with solution phase peroxide detected at the ring electrode. The ORR on Pt(hkl) was found to be highly structure sensitive with activities increasing in the sequence (111) > (100) > (110)(1x2). Very similar apparent activation energies (37-45 {+-} 5 kJmol-1, {eta} = 0.35 V) were found on all three surfaces. Furthermore, at elevated temperature, significantly smaller amounts of peroxide are formed in agreement with enhanced peroxide reduction rates by increasing temperature. We found that the Tafel slopes on all three single crystal surfaces decrease with increasing temperature, indicating that the logi-E relationship is not represented by a classical Butler-Volmer expression. Based on the kinetic analysis of the polarization curves and from simulations of logi-E curves, we propose that the rate of the ORR on Pt(hkl) in alkaline solution is mainly determined by the potential/temperature dependent surface coverage by OH{sub ad}. We propose two modes of action of the OH{sub ad}: (i) OH{sub ad} blocks the adsorption of O{sub 2} on active platinum sites; and (ii) OH{sub ad} alters the adsorption energy of intermediates which …