Directions for further development of GaAs/CuInSe2 thin film tandem cells

Multijunction thin film solar cells utilizing GaAs and CuInSe2 as semiconductor absorbers are rapidly developing, becoming a viable technology for space power systems with an unparalleled combination of high efficiency, low mass, and high radiation tolerance. The prospect for evolutionary improvement of this type of cell towards efficiency of approximately equals 30 percent and specific power greater than 1 kW/kg while retaining the attribute of high radiation tolerance are good. Limitations of the present configuration and possible avenues for circumventing these problems are presented

Portraits of culturally relevant pedagogical practices enacted by educators serving Latino music students

The growing population of Latino students in the United States requires a focus on culturally relevant practices for teaching Latino students. The purpose of this study was to investigate music educators’ Latino cultural knowledge and their use of that knowledge for teaching Latino students. Ladson-Billings’ (1995b) theory of culturally relevant pedagogy frames this study. Three questions guided this study. First, what cultural knowledge do music educators hold about Latino students and the communities in which they teach? Second, how do music educators use cultural knowledge to inform their pedagogical practice with Latino students? Finally, what specific culturally relevant pedagogical practices are enacted by music educators for teaching Latino students? To address the research questions, I interviewed three music teachers and observed their teaching practices. Interviews with a sample of the teachers’ Latino students also informed the study. I utilized elements of portraiture to present the data through vignettes followed by discussions and personal reflections. An analysis of the data through the lens of culturally relevant pedagogy revealed numerous methods that music educators frequently used when teaching Latino students. After I categorized those methods and aligned them with current research on core instructional practices, a list emerged of 12 culturally relevant core instructional practices that facilitate learning for Latino students. Based on the findings of this study, I recommend that teachers take an asset-based approach when working with Latino students and families, understand and make distinctions between Latino cultures, find ways to communicate effectively with Latino students and families, implement Latino language and culture into class curriculum, and enact characteristics of caring for Latino students. In addition, teacher education programs may benefit from developing courses in culturally relevant pedagogy specifically for working with Latino students

Development of tandem cells consisting of GaAs single crystal and CuInSe2/CdZnS polycrystalline thin films

The tandem cells consisting of GaAs single crystal and CuInSe2 polycrystalline thin films are being developed under the joint program of the Boeing Co. and Kopin Corp. to meet the increasing power needs for future spacecraft. The updated status of this program is presented along with experimental results such as cell performance, and radiation resistance. Other cell characteristics including the specific power of and the interconnect options for this tandem cell approach are also discussed

Trust and the wildland-urban interface: How residents use sensemaking to understand fuel treatments

The purpose of this study was to understand communicative issues of trust between residents of wildland-urban interfaces and land managers, and how residents make sense of fuel treatments. Residents are often surprised by the large scale of fuel treatment activities, which can lead to opposition. This study explores the problem by using theorizing on sensemaking, which draws attention to the ways people construct a narrative account of situations they don’t understand. Using a small WUI community as a case study, this thesis examines the ongoing conflict around the implementation of a fuel treatment project, Forsythe II. Qualitative interviews and focus groups with N=31 residents were used, and cross coded for active sensemaking and trust. This study found that WUI residents construct narratives to make sense of fuel treatments, and those narratives were grounded in ways they enacted their personal identity within the forest and landscape (e.g., through recreation and lifestyle). Residents’ sensemaking narratives included plausible (but not necessarily accurate) comparisons between local and geographically-distant fuel treatments activities in order to justify their position on Forsythe II and evaluate land manager trustworthiness. Residents also made sense through extracted cues from the landscape: where residents perceived that the landscape was damaged by a fuel treatment, they were more likely to find the land managers to be untrustworthy. Through enactment of their personal identity in symbolically important landscapes, residents contribute to their own narrative sense about fuel treatments. Future recommendations for enabling trust includes empowering residents to volunteer, participate, and become invested in future projects, as well as better utilizing local resources to foster engagement

Controls on the Presence, Concentration, Storage, and Variability of Soil Inorganic Carbon in a Semi-Arid Watershed

Soil inorganic carbon (SIC) constitutes approximately 40% of terrestrial soil carbon and is an integral part of the global carbon cycle; however, the controls on the storage and flux of inorganic carbon are poorly understood. Soil forming factors controlling SIC storage and flux include climate, organisms, relief, parent material, and time (Jenny, 1941). Rainfall is a primary factor controlling SIC accumulation in arid and semi-arid regions, but the hierarchy of controls on SIC development is complex. The Reynolds Creek Experimental Watershed in southwestern Idaho is an ideal location to study factors influencing SIC, as the carbon pool transitions from predominately inorganic carbon in the lower elevations, to organic carbon at higher elevations. This study builds upon fundamental studies in soil science that define and describe precipitation controls on the ‘pedocal’ (calcic) to ‘pedalfer’ (non-calcic) soil transition (e.g. Marbut, 1935; Jenny, 1941) by both defining the precipitation boundary in Reynolds Creek, and quantifying the amount of carbon storage within calcic soils. We collected soil samples from soils developed under a wide range of soil-forming regimes: 1) along a precipitation gradient, 2) within different vegetation communities (sagebrush species (Artimesia spp), bitterbrush (Purshia tridentata), greasewood (Sarcobatus vermiculatus), and juniper (Juniperus occidentalis)) 3) from different parent materials (granite, basalt, other volcanics, and alluvium) and 4) from terrace surfaces of different ages. Our results show SIC does not accumulate above a threshold of ~500 mm mean annual precipitation, and variability in SIC below that value is significant. Soil inorganic carbon content from ~1 m deep soil pits and cores at 71 sites shows that 64 sites contained less than 10 kg/m2 SIC, 5 sites contained between 10-20 kg/m2, and 2 sites had between 24 and 29 kg/m2. Random forest modeling and multiple linear regression of the environmental controls on SIC indicate that precipitation is the primary control on SIC accumulation, where increased precipitation correlates with lower amounts of SIC. Elevation is an effective predictor of SIC, as it is strongly auto-correlated with precipitation and vegetation. Parent material consistently ranks as an important predictor in random forest analysis; however, we were unable to quantify the importance of wind-blown dust in the soil profiles, which we believe plays a vital role in SIC accumulation. Despite a recognition of different stages of carbonate development and accumulation rates between gravelly and non-gravelly soils, studies often ignore carbonate coatings on gravels in measurements of soil inorganic carbon (SIC). By quantifying and differentiating the fine (\u3c2 \u3emm) and coarse (\u3e2 mm) fractions of SIC in the Reynolds Creek Experimental Watershed in southwestern Idaho, we show that gravel coatings contain up to 44% of total SIC at a given site. Among the 26 soil sites examined throughout the watershed, an average of 13% of the total SIC is stored as carbonate coasts within in the gravel fraction. We measured a high level of pedon-scale field variability (up to 220%) among the three faces of 1 m3 soil pits. Analytical error associated with the modified pressure calcimeter (0.001-0.014%), is considerably less than naturally occurring heterogeneities in SIC within the soil profile. This work highlights and quantifies two sources of uncertainty in studies of SIC needed to inform future research. First, in gravelly sites, the \u3e2 mm portion of soils may store a large percentage of SIC. Second, SIC varies considerably at the pedon-scale, so studies attempting to quantify carbon storage over landscape scales need to consider this variability. This study creates a framework for understanding SIC in Reynolds Creek that may be applied to future work

Progress in GaAs/CuInSe2 tandem junction solar cells

Much more power is required for spacecraft of the future than current vehicles. To meet this increased demand for power while simultaneously meeting other requirements for launch, deployment, and maneuverability, the development of higher-efficiency, lighter-weight, and more radiation resistant photovoltaic cells is essential. Mechanically stacked tandem junction solar cells based on (AlGaAs)GaAs thin film CLEFT (Cleavage of Lateral Epitaxial Film for Transfer) top cells and CuInSe2(CIS) thin film bottom cells are being developed to meet these power needs. The mechanically stacked tandem configuration is chosen due to its interconnect flexibility allowing more efficient array level performance. It also eliminates cell fabrication processing constraints associated with monolithically integrated multi-junction approaches, thus producing higher cell fabrication yields. The GaAs cell is used as the top cell due to its demonstrated high efficiency, and good radiation resistance. Furthermore, it offers a future potential for bandgap tuning using AlGaAs as the absorber to maximize cell performance. The CuInSe2 cell is used as the bottom cell due to superb radiation resistance, stability, and optimal bandgap value in combination with an AlGaAs top cell. Since both cells are incorporated as thin films, this approach provides a potential for very high specific power. This high specific power (W/kg), combined with high power density (W/sq m) resulting from the high efficiency of this approach, makes these cells ideally suited for various space applications

Processing of CuInSe2-Based Solar Cells: Characterization of Deposition Processes in Terms of Chemical Reaction Analyses. Final Report, 6 May 1995 - 31 December 1998

This project describes a novel rotating-disc reactor has been designed and built to enable modulated flux deposition of CuInSe2 and its related binary compounds. The reactor incorporates both a thermally activated source and a novel plasma-activated source of selenium vapor, which have been used for the growth of epitaxial and polycrystalline thin-film layers of CuInSe2. A comparison of the different selenium reactant sources has shown evidence of increases in its incorporation when using the plasma source, but no measurable change when the thermally activated source was used. We concluded that the chemical reactivity of selenium vapor from the plasma source is significantly greater than that provided by the other sources studied. Epitaxially grown CuInSe2 layers on GaAs, ZnTe, and SrF2 demonstrate the importance of nucleation effects on the morphology and crystallographic structure of the resulting materials. These studies have resulted in the first reported growth of the CuAu type-I crystallographic polytype of CuInSe2, and the first reported epitaxial growth of CuInSe2 on ZnTe. Polycrystalline binary (Cu,Se) and (In,Se) thin films have been grown, and the molar flux ratio of selenium to metals was varied. It is shown that all of the reported binary compounds in each of the corresponding binary phase fields can be synthesized by the modulated flux deposition technique implemented in the reactor by controlling this ratio and the substrate temperature. These results were employed to deposit bilayer thin films of specific (Cu,Se) and (In,Se) compounds with low melting-point temperature, which were used to verify the feasibility of synthesizing CuInSe2 by subsequent rapid-thermal processing. The studies of the influence of sodium during the initial stages of epitaxy have led to a new model to explain its influences based on the hypothesis that it behaves as a surfactant in the Cu-In-Se material system. This represents the first unified theory on the role of sodium that explains all of sodium's principal effects on the growth and properties of CuInSe2 that have been reported in the prior scientific literature. Comprehensive statistical mechanical calculations have been combined with published phase diagrams and results of ab-initio quantum mechanical calculations of defect formation enthalpies from the literature to develop the first free-energy defect model for CuInSe2 that includes the effects of defect associates (complexes). This model correctly predicts the ?/? ternary phase boundary