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Sample records for polycrystalline 3c-sic thin

  1. Polycrystalline thin film photovoltaics

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Ullal, H. S.; Mitchell, R. L.

    Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe2 and CdTe. The history of using CuInSe2 and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe2 and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.

  2. Polycrystalline thin-films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.

    1986-02-01

    This annual report summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Major subcontracted work in this area has concentrated on development of CuInSe2 and CdTe technologies. During FY 1985, major progress was achieved by subcontractors in: (1) developing a new, low-cost method of fabricating CuInSe2, and (2) improving the efficiency of CuInSe2 devices by about 10% (relative). The report also lists research planned to meet the Department of Energy's goals in these technologies.

  3. Polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.; Ullal, H.

    1987-02-01

    This annual report for fiscal year 1986 summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Subcontracted work in this area has concentrated on the development of CuInSe2 and CdTe technologies. During FY 1986, major progress was achieved by subcontractors in (1) achieving 10.5% (SERI-verified) efficiency with CdTe, (2) improving the efficiency of selenized CuInSe2 solar cells to nearly 8%, and (3) developing a transparent contact to CdTe cells for potential use in the top cells of tandem structures.

  4. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  5. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting next-generation'' options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called government/industry partnerships'') that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  6. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting ``next-generation`` options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called ``government/industry partnerships``) that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  7. US polycrystalline thin film solar cells program

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L. )

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the US Department of Energy's long-term goals by achieving high efficiencies (15%-20%), low-cost ($50/m{sup 2}), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The US Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe{sub 2} and CdTe with subcontracts to start in Spring 1990. 23 refs., 5 figs.

  8. US Polycrystalline Thin Film Solar Cells Program

    NASA Astrophysics Data System (ADS)

    Ullal, Harin S.; Zweibel, Kenneth; Mitchell, Richard L.

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R and D on copper indium diselenide and cadmium telluride thin films. The objective of the program is to support research to develop cells and modules that meet the U.S. Department of Energy's long-term goals by achieving high efficiencies (15 to 20 percent), low-cost ($50/m(sup 2)), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe2 and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The U.S. Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe2 and CdTe with subcontracts to start in spring 1990.

  9. Polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  10. Polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1996-02-01

    Thermophotovoltaic (TPV) cells convert thermal energy to electricity. Modularity, portability, silent operation, absence of moving parts, reduced air pollution, rapid start-up, high power densities, potentially high conversion efficiencies, choice of a wide range of heat sources employing fossil fuels, biomass, and even solar radiation are key advantages of TPV cells in comparison with fuel cells, thermionic and thermoelectric convertors, and heat engines. The potential applications of TPV systems include: remote electricity supplies, transportation, co-generation, electric-grid independent appliances, and space, aerospace, and military power applications. The range of bandgaps for achieving high conversion efficiencies using low temperature (1000-2000 K) black-body or selective radiators is in the 0.5-0.75 eV range. Present high efficiency convertors are based on single crystalline materials such as In1-xGaxAs, GaSb, and Ga1-xInxSb. Several polycrystalline thin films such as Hg1-xCdxTe, Sn1-xCd2xTe2, and Pb1-xCdxTe, etc., have great potential for economic large-scale applications. A small fraction of the high concentration of charge carriers generated at high fluences effectively saturates the large density of defects in polycrystalline thin films. Photovoltaic conversion efficiencies of polycrystalline thin films and PV solar cells are comparable to single crystalline Si solar cells, e.g., 17.1% for CuIn1-xGaxSe2 and 15.8% for CdTe. The best recombination-state density Nt is in the range of 10-15-10-16 cm-3 acceptable for TPV applications. Higher efficiencies may be achieved because of the higher fluences, possibility of bandgap tailoring, and use of selective emitters such as rare earth oxides (erbia, holmia, yttria) and rare earth-yttrium aluminium garnets. As compared to higher bandgap semiconductors such as CdTe, it is easier to dope the lower bandgap semiconductors. TPV cell development can benefit from the more mature PV solar cell and opto

  11. Progress in polycrystalline thin-film solar cells

    SciTech Connect

    Zweibel, K; Hermann, A; Mitchell, R

    1983-07-01

    Photovoltaic devices based on several polycrystalline thin-film materials have reached near and above 10% sunlight-to-electricity conversion efficiencies. This paper examines the various polycrystalline thin-film PV materials including CuInSe/sub 2/ and CdTe in terms of their material properties, fabrication techniques, problems, and potentials.

  12. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2013-06-01

    This National Center for Photovoltaics sheet describes the capabilities of its polycrystalline thin-film research in the area of cadmium telluride. The scope and core competencies and capabilities are discussed.

  13. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet that includes scope, core competencies and capabilities, and contact/web information for Polycrystalline Thin-Film Research: Cadmium Telluride at the National Center for Photovoltaics.

  14. Polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; Phillips, J. E.; Shafarman, W. N.; Hegedus, S. S.; McCandless, B. E.

    1991-11-01

    Results and conclusions of Phase 1 of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe2 and CdTe solar cells. The kinetics of the formation of CuInSe2 by selenization with hydrogen selenide was investigated and a CuInSe2/Cds solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe2 films and a cell efficiency of 7 percent. Detailed investigations of the open circuit voltage of CuInSe2 solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe2 thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe2 is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10 percent can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm(exp 2) are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  15. Research on polycrystalline thin-film materials, cells, and modules

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1990-11-01

    DOE supports research activities in polycrystalline thin films through the Polycrystalline Thin Film Program. This program includes includes R and D in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective is to support R and D of photovoltaic cells and modules that meet the DOE long term goals of high efficiency (15 to 20 percent), low cost ($50/sq cm), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin film CuInSe2 and CdTe solar cells and modules. These have become the leading thin film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe(sub 2) and CdTe modules. The recent progress and future directions are studied of the Polycrystalline Thin Film Program and the status of the subcontracted research on these promising photovoltaic materials.

  16. Research on polycrystalline thin-film materials, cells, and modules

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1990-11-01

    The US Department of Energy (DOE) supports research activities in polycrystalline thin films through the Polycrystalline Thin-Film Program at the Solar Energy Research Institute (SERI). This program includes research and development (R D) in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective of this program is to support R D of photovoltaic cells and modules that meet the DOE long-term goals of high efficiency (15%--20%), low cost ($50/m{sup 2}), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules. These have become the leading thin-film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe{sub 2} and CdTe modules. This paper focuses on the recent progress and future directions of the Polycrystalline Thin-Film Program and the status of the subcontracted research on these promising photovoltaic materials. 26 refs., 12 figs, 1 tab.

  17. Polycrystalline Thin Film Device Degradation Studies

    SciTech Connect

    Albin, D. S.; McMahon, T. J.; Pankow, J. W.; Noufi, R.; Demtsu, S. H.; Davies, A.

    2005-11-01

    Oxygen during vapor CdCl2 (VCC) treatments significantly reduced resistive shunts observed in CdS/CdTe polycrystalline devices using thinner CdS layers during 100 deg C, open-circuit, 1-sun accelerated stress testing. Cu oxidation resulting from the reduction of various trace oxides present in as-grown and VCC treated films is the proposed mechanism by which Cu diffusion, and subsequent shunts are controlled. Graphite paste layers between metallization and CdTe behave like diffusion barriers and similarly benefit device stability. Ni-based contacts form a protective Ni2Te3 intermetallic layer that reduces metal diffusion but degrades performance through increased series resistance.

  18. Dynamical electrophotoconductivity in polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.

    1982-01-01

    Polycrystalline cadmium sulfide (CdS) films were deposited on lithium niobate (LiNbO3) substrates by vacuum evaporation and annealed to obtain high photosensitivity. The change in photoconductivity of these films due to the penetration of electric fields associated with elastic waves propagating on their substrates was demonstrated and studied. The relationship between the acoustic electric field and the induced change in film conductivity was found to be a nonlinear one. The fractional change in conductivity is strongly dependent on the light intensity and the film temperature, showing a prominent maximum as a function of these quantities. The largest recorded fractional change in conductivity was about 25% at electric fields of the order of 1,000 volts per centimeter. A phenomological model was developed based on the interaction between the space charge created by the electric field and the electron trapping states in the photoconductor.

  19. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG&E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  20. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  1. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-01-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  2. Polycrystalline thin-film technology: Recent progress in photovoltaics

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe{sub 2}), cadmium telluride (CdTe), and thin-film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin-film CuInSe{sub 2}, has made some rapid advances in terms of high efficiency and long-term reliability. For CuInSe{sub 2} power modules, a world record has been reported on a 0.4-m{sup 2} module with an aperture-area efficiency of 10.4% and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe{sub 2} modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 cm{sup 2}. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10%; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  3. Polycrystalline thin-film technology: Recent progress in photovoltaics

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe2), cadmium telluride (CdTe), and thin film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin film CuInSe2, has made some rapid advances in terms of high efficiency and long term reliability. For CuInSe2 power modules, a world record has been reported on a 0.4 sq m module with an aperture-area efficiency of 10.4 pct. and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe2 modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 sq cm. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10 pct.; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  4. Polycrystalline organic thin film transistors for advanced chemical sensing

    NASA Astrophysics Data System (ADS)

    Torsi, Luisa; Tanese, Maria C.; Cioffi, Nicola; Sabbatini, Luigia; Zambonin, Pier G.

    2003-11-01

    Organic thin-film transistors have seen a dramatic improvement of their performance in the last decade. They have been also proposed as gas sensors. This paper deals with the interesting new aspects that polycrystalline based conducting polymer transistors present when operated as chemical sensors. Such devices are capable to deliver multi-parameter responses that are also extremely repeatable and fast at room temperature. Interesting are also the perspectives for their use as chemically selective devices in array type sensing systems.

  5. Polycrystalline Superconducting Thin Films: Texture Control and Critical Current Density

    NASA Astrophysics Data System (ADS)

    Yang, Feng

    1995-01-01

    The growth processes of polycrystalline rm YBa_2CU_3O_{7-X} (YBCO) and yttria-stabilized-zirconia (YSZ) thin films have been developed. The effectiveness of YSZ buffer layers on suppression of the reaction between YBCO thin films and metallic substrates was carefully studied. Grown on the chemically inert surfaces of YSZ buffer layers, YBCO thin films possessed good quality of c-axis alignment with the c axis parallel to the substrate normal, but without any preferred in-plane orientations. This leads to the existence of a large percentage of the high-angle grain boundaries in the YBCO films. The critical current densities (rm J_{c}'s) found in these films were much lower than those in single crystal YBCO thin films, which was the consequence of the weak -link effect of the high-angle grain boundaries in these films. It became clear that the in-plane alignment is vital for achieving high rm J_{c }s in polycrystalline YBCO thin films. To induce the in-plane alignment, ion beam-assisted deposition (IBAD) technique was integrated into the conventional pulsed laser deposition process for the growth of the YSZ buffer layers. It was demonstrated that using IBAD the in-plane orientations of the YSZ grains could be controlled within a certain range of a common direction. This ion -bombardment induced in-plane texturing was explained using the anisotropic sputtering yield theory. Our observations and analyses have provided valuable information on the optimization of the IBAD process, and shed light on the texturing mechanism in YSZ. With the in-plane aligned YSZ buffer layers, YBCO thin films grown on metallic substrates showed improved rm J_{c}s. It was found that the in-plane alignment of YSZ and that of YBCO were closely related. A direct correlation was revealed between the rm J_{c} value and the degree of the in-plane alignment for the YBCO thin films. To explain this correlation, a numerical model was applied to multi-grain superconducting paths with different

  6. Progress and issues in polycrystalline thin-film PV technologies

    SciTech Connect

    Zweibel, K.; Ullal, H.S.; Roedern, B. von

    1996-05-01

    Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies in the past 18 months. However, the transition to first-time manufacturing is still under way, and technical problems continue. This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the U.S. Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

  7. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, Fred; Truher, Joel B.; Kaschmitter, James L.; Colella, Nicholas J.

    1998-02-03

    A method for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells.

  8. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, F.; Truher, J.B.; Kaschmitter, J.L.; Colella, N.J.

    1998-02-03

    A method is disclosed for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells. 1 fig.

  9. Controlled nanostructuration of polycrystalline tungsten thin films

    SciTech Connect

    Girault, B.; Eyidi, D.; Goudeau, P.; Guerin, P.; Bourhis, E. Le; Renault, P.-O.; Sauvage, T.

    2013-05-07

    Nanostructured tungsten thin films have been obtained by ion beam sputtering technique stopping periodically the growing. The total thickness was maintained constant while nanostructure control was obtained using different stopping periods in order to induce film stratification. The effect of tungsten sublayers' thicknesses on film composition, residual stresses, and crystalline texture evolution has been established. Our study reveals that tungsten crystallizes in both stable {alpha}- and metastable {beta}-phases and that volume proportions evolve with deposited sublayers' thicknesses. {alpha}-W phase shows original fiber texture development with two major preferential crystallographic orientations, namely, {alpha}-W<110> and unexpectedly {alpha}-W<111> texture components. The partial pressure of oxygen and presence of carbon have been identified as critical parameters for the growth of metastable {beta}-W phase. Moreover, the texture development of {alpha}-W phase with two texture components is shown to be the result of a competition between crystallographic planes energy minimization and crystallographic orientation channeling effect maximization. Controlled grain size can be achieved for the {alpha}-W phase structure over 3 nm stratification step. Below, the {beta}-W phase structure becomes predominant.

  10. Advances in polycrystalline thin-film photovoltaics for space applications

    SciTech Connect

    Lanning, B.R.; Armstrong, J.H.; Misra, M.S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 eV and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not `reactor-specific` and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a `substrate configuration` by physical vapor deposition techniques and CdTe cells/modules are fabricated in a `superstrate configuration` by wet chemical methods.

  11. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-01-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  12. Anisotropic thermal conductivity of thin polycrystalline oxide samples

    SciTech Connect

    Tiwari, A.; Boussois, K.; Nait-Ali, B.; Smith, D. S.; Blanchart, P.

    2013-11-15

    This paper reports about the development of a modified laser-flash technique and relation to measure the in-plane thermal diffusivity of thin polycrystalline oxide samples. Thermal conductivity is then calculated with the product of diffusivity, specific heat and density. Design and operating features for evaluating in-plane thermal conductivities are described. The technique is advantageous as thin samples are not glued together to measure in-plane thermal conductivities like earlier methods reported in literature. The approach was employed to study anisotropic thermal conductivity in alumina sheet, textured kaolin ceramics and montmorillonite. Since it is rare to find in-plane thermal conductivity values for such anisotropic thin samples in literature, this technique offers a useful variant to existing techniques.

  13. Resistive switching in polycrystalline YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bogusz, A.; Müller, A. D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

    2014-10-01

    We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

  14. Analysis of loss mechanisms in polycrystalline thin film solar cells

    NASA Astrophysics Data System (ADS)

    Sites, J. R.

    1990-08-01

    Our goal for thin-film polycrystalline solar cell analysis was to increase the useful information extracted from relatively straightforward electrical measurements. The strategy was to (1) systematize measurements and reporting, (2) organize results in terms of quantitative values for individual sources of current and voltage loss, and (3) evaluate possible analytical techniques to enhance precision and avoid pitfalls, and (4) insist on a viable physical explanation of each loss mechanism. Current-voltage, quantum efficiency, and capacitance measurements on CuInSe2 and CdTe solar cells from a variety of sources have been analyzed. In many cases losses were identified that may be lessened relatively easily. However, the operating voltage loss due to excessive forward recombination current throughout the depletion region remains the primary obstacle to efficiencies competitive with single crystal cells.

  15. Polycrystalline GeSn thin films on Si formed by alloy evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Fan, Wenjuan; Seo, Jung-Hun; Cho, Namki; Liu, Shih-Chia; Geng, Dalong; Liu, Yonghao; Gong, Shaoqin; Wang, Xudong; Zhou, Weidong; Ma, Zhenqiang

    2015-06-01

    Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

  16. High-Efficiency Polycrystalline Thin Film Tandem Solar Cells.

    PubMed

    Kranz, Lukas; Abate, Antonio; Feurer, Thomas; Fu, Fan; Avancini, Enrico; Löckinger, Johannes; Reinhard, Patrick; Zakeeruddin, Shaik M; Grätzel, Michael; Buecheler, Stephan; Tiwari, Ayodhya N

    2015-07-16

    A promising way to enhance the efficiency of CIGS solar cells is by combining them with perovskite solar cells in tandem devices. However, so far, such tandem devices had limited efficiency due to challenges in developing NIR-transparent perovskite top cells, which allow photons with energy below the perovskite band gap to be transmitted to the bottom cell. Here, a process for the fabrication of NIR-transparent perovskite solar cells is presented, which enables power conversion efficiencies up to 12.1% combined with an average sub-band gap transmission of 71% for photons with wavelength between 800 and 1000 nm. The combination of a NIR-transparent perovskite top cell with a CIGS bottom cell enabled a tandem device with 19.5% efficiency, which is the highest reported efficiency for a polycrystalline thin film tandem solar cell. Future developments of perovskite/CIGS tandem devices are discussed and prospects for devices with efficiency toward and above 27% are given. PMID:26266847

  17. Fundamentals of polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, Bill N.; Birkmire, Robert W.; Phillips, James E.; Shafarman, William N.; Hegedus, Steven S.; McCandless, Brian E.

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe2 and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe2 thin films and demonstrated a CuInSe2 solar cell with 7 percent efficiency. We added Ga, to increase the band gap of CuInSe2 devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed CuInGaSe2/CuInSe2 devices to demonstrate the potential for combining the benefits of higher V(sub oc) while retaining the current-generating capacity of CuInSe2. We fabricated an innovative superstrate device design with more than 5 percent efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe2 in an operational cell. The diffusion length was found to be greater than 1 micron. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe2 devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6 percent-efficient CdTe/CdS solar cell using physical vapor deposition.

  18. Fundamentals of polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe{sub 2} and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe{sub 2} thin films and demonstrated a CuInSe{sub 2} solar cell with 7% efficiency. We added Ga, to increase the band gap of CuInSe{sub 2} devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed Cu(InGa)Se{sub 2}/CuInSe{sub 2} devices to demonstrate the potential for combining the benefits of higher V{sub oc} while retaining the current-generating capacity of CuInSe{sub 2}. We fabricated an innovative superstrate device design with more than 5% efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe{sub 2} in an operational cell. The diffusion length was found to be greater than 1 {mu}m. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe{sub 2} devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6%-efficient CdTe/CdS solar cell using physical vapor deposition.

  19. Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet for the National Center for Photovoltaics: Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide that includes scope, core competencies and capabilities, and contact/web information.

  20. Charge carrier transport in polycrystalline organic thin film based field effect transistors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    The charge carrier transport mechanism in polycrystalline thin film based organic field effect transistors (OFETs) has been explained using two competing models, multiple trapping and releases (MTR) model and percolation model. It has been shown that MTR model is most suitable for explaining charge carrier transport in grainy polycrystalline organic thin films. The energetic distribution of traps determined independently using Mayer-Neldel rule (MNR) is in excellent agreement with the values obtained by MTR model for copper phthalocyanine and pentacene based OFETs.

  1. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  2. Polycrystalline VO2 thin films via femtosecond laser processing of amorphous VO x

    NASA Astrophysics Data System (ADS)

    Charipar, N. A.; Kim, H.; Breckenfeld, E.; Charipar, K. M.; Mathews, S. A.; Piqué, A.

    2016-05-01

    Femtosecond laser processing of pulsed laser-deposited amorphous vanadium oxide thin films was investigated. Polycrystalline VO2 thin films were achieved by femtosecond laser processing in air at room temperature. The electrical transport properties, crystal structure, surface morphology, and optical properties were characterized. The laser-processed films exhibited a metal-insulator phase transition characteristic of VO2, thus presenting a pathway for the growth of crystalline vanadium dioxide films on low-temperature substrates.

  3. Ferroelectric domain switching of individual nanoscale grains in polycrystalline lead zirconate titanate thin films

    NASA Astrophysics Data System (ADS)

    Jing, Yuanyuan

    2011-12-01

    This thesis will focus on the switching behavior of nanoscale ferroelectric domains in polycrystalline thin films. Ferroelectrics are a class of dielectric materials that demonstrate spontaneous polarizations under zero applied electric field. A region with the same polarization is called a ferroelectric domain. One important attribute of ferroelectrics is the domain switching from one thermodynamically stable state to another by application of an external electric field. Ferroelectric domain switching has been intensively investigated in epitaxial thin films. However, little is known about the domain switching in polycrystalline thin films. The main reason is that each grain is differently orientated and each is in a unique local stress and electric field determined by neighboring grains. To understand and deterministically control the nanoscale domain switching in polycrystalline thin films, it's critical to experimentally identify the effect of local microstructure (grain orientation and grain boundary misorientation) on the individual grain switching behavior. In this thesis, the effect of local microstructure on domain switching has been quantitatively analyzed in a 100 nm thick polycrystalline PbZr 0.2Ti0.8O3 thin film. The ferroelectric domains are characterized by Piezoresponse Force Microscopy (PFM), with their switching behavior analyzed by Polarization Difference Maps (PDMs, an analytical technique developed in this work). The local microstructure is determined by Electron Back Scattering Diffraction (EBSD). The results are discussed in chapter 3 to 6. Chapter 3 introduces the PDMs technique that enables the rapid identification of 0o, 90o switching and 180o switching in polycrystalline thin films. By assigning different colors to different types of switching, the full nature of polarization switching can be visualized simultaneously for large number of domains or grains in one map. In chapter 4, an external electric field reversal experiment has been

  4. Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

    NASA Astrophysics Data System (ADS)

    Liang, Wei-Zheng; Ji, Yan-Da; Nan, Tian-Xiang; Huang, Jiang; Zeng, Hui-Zhong; Du, Hui; Chen, Chong-Lin; Lin, Yuan

    2012-06-01

    Barium titanate (BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition (PAD) technique. The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion. Crystal structures, surface morphologies, and dielectric performance were examined and compared for BTO thin films annealed under different temperatures. Correlations between the fabrication conditions, microstructures, and dielectric properties were discussed. BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with inr ~ 400 and tan δ < 0.025 at 100 kHz. The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

  5. Influence of lattice distortion on phase transition properties of polycrystalline VO2 thin film

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen; Yu, Yonghao

    2016-08-01

    In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO2 thin film. SEM images revealed that all the VO2 thin films had crystallite sizes of below 20 nm, and similar configurations. UV-vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal-insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO2. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO2. Furthermore, a room temperature rutile VO2 thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO2 thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.

  6. Effect of flash lamp annealing on electrical activation in boron-implanted polycrystalline Si thin films

    SciTech Connect

    Do, Woori; Jin, Won-Beom; Choi, Jungwan; Bae, Seung-Muk; Kim, Hyoung-June; Kim, Byung-Kuk; Park, Seungho; Hwang, Jin-Ha

    2014-10-15

    Highlights: • Intensified visible light irradiation was generated via a high-powered Xe arc lamp. • The disordered Si atomic structure absorbs the intensified visible light. • The rapid heating activates electrically boron-implanted Si thin films. • Flash lamp heating is applicable to low temperature polycrystalline Si thin films. - Abstract: Boron-implanted polycrystalline Si thin films on glass substrates were subjected to a short duration (1 ms) of intense visible light irradiation generated via a high-powered Xe arc lamp. The disordered Si atomic structure absorbs the intense visible light resulting from flash lamp annealing. The subsequent rapid heating results in the electrical activation of boron-implanted Si thin films, which is empirically observed using Hall measurements. The electrical activation is verified by the observed increase in the crystalline component of the Si structures resulting in higher transmittance. The feasibility of flash lamp annealing has also been demonstrated via a theoretical thermal prediction, indicating that the flash lamp annealing is applicable to low-temperature polycrystalline Si thin films.

  7. Properties of boron-doped thin films of polycrystalline silicon

    SciTech Connect

    Merabet, Souad

    2013-12-16

    The properties of polycrystalline-silicon films deposited by low pressure chemical vapor deposition and doped heavily in situ boron-doped with concentration level of around 2×10{sup 20}cm{sup −3} has been studied. Their properties are analyzed using electrical and structural characterization means by four points probe resistivity measurements and X-ray diffraction spectra. The thermal-oxidation process are performed on sub-micron layers of 200nm/c-Si and 200nm/SiO{sub 2} deposited at temperatures T{sub d} ranged between 520°C and 605°C and thermally-oxidized in dry oxygen ambient at 945°C. Compared to the as-grown resistivity with silicon wafers is known to be in the following sequence <ρ{sub 200nm/c−Si}> < <ρ{sub 200nm/SiO2}> and <ρ{sub 520}> < <ρ{sub 605}>. The measure X-ray spectra is shown, that the Bragg peaks are marked according to the crystal orientation in the film deposited on bare substrates (poly/c-Si), for the second series of films deposited on bare oxidized substrates (poly/SiO{sub 2}) are clearly different.

  8. Polycrystalline thin film materials and devices. Final subcontract report, 16 January 1990--15 January 1993

    SciTech Connect

    Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.; Yokimcus, T.A.

    1993-08-01

    This report describes results and conclusions of the final phase (III) of a three-year research program on polycrystalline thin-film heterojunction solar cells. The research consisted of the investigation of the relationships between processing, materials properties, and device performance. This relationship was quantified by device modeling and analysis. The analysis of thin-film polycrystalline heterojunction solar cells explains how minority-carrier recombination at the metallurgical interface and at grain boundaries can be greatly reduced by the proper doping of the window and absorber layers. Additional analysis and measurements show that the present solar cells are limited by the magnitude of the diode current, which appears to be caused by recombination in the space charge region. Developing an efficient commercial-scale process for fabricating large-area polycrystalline, thin-film solar cells from a research process requires a detailed understanding of the individual steps in making the solar cell, and their relationship to device performance and reliability. The complexities involved in characterizing a process are demonstrated with results from our research program on CuInSe{sub 2}, and CdTe processes.

  9. Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films

    NASA Astrophysics Data System (ADS)

    Lin, Yuan-Hua; Ying, Minghao; Li, Ming; Wang, Xiaohui; Nan, Ce-Wen

    2007-05-01

    Polycrystalline ZnO-based thin films with Li and/or Co doping have been prepared by a sol-gel spin-coating method on silicon substrates. Magnetization measurements reveal that Li-doped ZnO film shows paramagnetic behavior. However, the Co-doped ZnO thin films show obvious room-temperature ferromagnetic properties, and ferromagnetic properties can be enhanced by the Li codoping, which may be ascribed to indirect exchange via Li-related defects. All ZnO-based films exhibit ferroelectric behavior, and ferroelectric properties can be tuned by the dopants.

  10. Polycrystalline silicon thin-film solar cell prepared by the solid phase crystallization (SPC) method

    SciTech Connect

    Baba, T.; Matsuyama, T.; Sawada, T.; Takahama, T.; Wakisaka, K.; Tsuda, S.; Nakano, S.

    1994-12-31

    A solid phase crystallization (SPC) method was applied to the fabrication of thin-film polycrystalline silicon (poly-Si) for solar cells for the first time. Among crystalline silicon solar cells crystallized at a low temperature of less than 600 C, the world`s highest conversion efficiency of 8.5% was achieved in a solar cell using thin-film poly-Si with only 10 {micro}m thickness prepared by the SPC method. This solar cell showed high photosensitivity in the long-wavelength region of more than 800 nm and also exhibited no light-induced degradation after light exposure.

  11. Polycrystalline ZnS(x)Se(1 - x) thin films deposited on ITO glass by MBE.

    PubMed

    Shen, Da-Ke; Sou, I K; Han, Gao-Rong; Du, Pi-Yi; Que, Duan-Lin

    2003-01-01

    MBE growth of ZnS(x)Se(1 - x) thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270 degrees C to 330 degrees C . The XRD theta/2theta spectra resulted from these films indicated that the as-grown polycrystalline ZnS(x)Se(1 - x) thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 degrees C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnS(x)Se(1 - x) thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure. PMID:12659224

  12. Structural, Optical, and Electrical Properties of Applied Amorphized and Polycrystalline Sb2S3 Thin Films

    NASA Astrophysics Data System (ADS)

    Janošević, Valentina; Mitrić, Miodrag; Savić, Jasmina; Validžić, Ivana Lj

    2016-03-01

    One of the intermediate steps in the organo-colloidal synthesis of crystalline Sb2S3 is a synthesis of spherical amorphous Sb2S3. In order to prove that the synthesized semiconductor can be considered an absorbing material for a solar device, the electronic and photovoltage properties of the amorphized and polycrystalline Sb2S3 thin films deposited by synthesized amorphous nanoparticles were studied. Optical studies revealed that the direct band gap energy was 1.65 eV and, two direct allowed transition of 1.57 and 1.91 eV for polycrystalline and amorphized thin films, respectively. The PL spectra of Sb2S3 showed an emission peak at 1.65 eV for both films. In order to obtain current-voltage ( I- V) characteristics, two cells based on the Sb2S3 thin films as both an absorbing material and an electrolyte were designed and made. The observed Sb2S3 thin films, with a thickness of around 10 μm, are of p-type. The exponential growth of the I- V curves reveals that the cells can work as a generator of electricity.

  13. Boron- and phosphorus-doped polycrystalline silicon thin films prepared by silver-induced layer exchange

    SciTech Connect

    Antesberger, T.; Wassner, T. A.; Jaeger, C.; Algasinger, M.; Kashani, M.; Scholz, M.; Matich, S.; Stutzmann, M.

    2013-05-27

    Intentional boron and phosphorus doping of polycrystalline silicon thin films on glass prepared by the silver-induced layer exchange is presented. A silver/(titanium) oxide/amorphous silicon stack is annealed at temperatures below the eutectic temperature of the Ag/Si system, leading to a complete layer exchange and simultaneous crystallization of the amorphous silicon. Intentional doping of the amorphous silicon prior to the exchange process results in boron- or phosphorus-doped polycrystalline silicon. Hall effect measurements show carrier concentrations between 2 Multiplication-Sign 10{sup 17} cm{sup -3} and 3 Multiplication-Sign 10{sup 20} cm{sup -3} for phosphorus and 4 Multiplication-Sign 10{sup 18} cm{sup -3} to 3 Multiplication-Sign 10{sup 19} cm{sup -3} for boron-doped layers, with carrier mobilities up to 90 cm{sup 2}/V s.

  14. Polycrystalline thin film materials and devices. Annual subcontract report, 16 January 1991--15 January 1992

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  15. FAST TRACK COMMUNICATION: Magnetic exchange hardening in polycrystalline GdN thin films

    NASA Astrophysics Data System (ADS)

    Senapati, K.; Fix, T.; Vickers, M. E.; Blamire, M. G.; Barber, Z. H.

    2010-08-01

    We report the observation of intrinsic exchange hardening in polycrystalline GdN thin films grown at room temperature by magnetron sputtering. We find, in addition to the ferromagnetic phase, that a fraction of GdN crystallizes in a structural polymorphic form which orders antiferromagnetically. The relative fraction of these two phases was controlled by varying the relative abundance of reactive species in the sputtering plasma by means of the sputtering power and N2 partial pressure. An exchange bias of ~ 30 Oe was observed at 10 K. The exchange coupling between the ferromagnetic and the antiferromagnetic phases resulted in an order of magnitude enhancement in the coercive field in these films.

  16. Efficient organic light-emitting diodes using polycrystalline silicon thin films as semitransparent anode

    NASA Astrophysics Data System (ADS)

    Zhu, X. L.; Sun, J. X.; Peng, H. J.; Meng, Z. G.; Wong, M.; Kwok, H. S.

    2005-08-01

    Polycrystalline silicon (p-Si) is a good material for the construction of thin-film transistors (TFT). It is used for fabricating active-matrix organic light-emitting diode (AMOLED) displays. In this letter, we propose and demonstrate the application of boron-doped p-Si as a semi-transparent anode in making different color OLEDs. Without removing the ultrathin native oxide on the p-Si surface and employing p-doped hole transport layer to enhance holes injection, these OLEDs show comparable or even better performance to conventional OLEDs which use ITO as anodes. The present technique has the advantage of less masking steps in making AMOLED.

  17. Specific features of hydrogenation of chromium-doped polycrystalline thin vanadium dioxide films

    NASA Astrophysics Data System (ADS)

    Andreev, V. N.; Klimov, V. A.; Kompan, M. E.; Melekh, B. A.

    2014-09-01

    It has been found that hydrogen penetration into chromium-doped polycrystalline thin vanadium dioxide films occurs with a lower rate than in the case of pure vanadium dioxide films. It has been shown that hydrogenation of films with low chromium concentrations is accompanied by a decrease in the phase transition temperature below T c = 340 K. However, at room temperature in these hydrogenated films, no traces of M1 monoclinic phase have been observed. As the chromium concentration increases, hydrogenation ceases to be accompanied by the decrease in the phase transition temperature.

  18. Optical and electrical properties of polycrystalline and amorphous Al-Ti thin films

    NASA Astrophysics Data System (ADS)

    Canulescu, S.; Borca, C. N.; Rechendorff, K.; Davidsdóttir, S.; Pagh Almtoft, K.; Nielsen, L. P.; Schou, J.

    2016-04-01

    The structural, optical, and transport properties of sputter-deposited Al-Ti thin films have been investigated as a function of Ti alloying with a concentration ranging from 2% to 46%. The optical reflectivity of Al-Ti films at visible and near-infrared wavelengths decreases with increasing Ti content. X-ray absorption fine structure measurements reveal that the atomic ordering around Ti atoms increases with increasing Ti content up to 20% and then decreases as a result of a transition from a polycrystalline to amorphous structure. The transport properties of the Al-Ti films are influenced by electron scattering at the grain boundaries in the case of polycrystalline films and static defects, such as anti-site effects and vacancies in the case of the amorphous alloys. The combination of Ti having a real refractive index (n) comparable with the extinction coefficient (k) and Al with n much smaller than k allows us to explore the parameter space for the free-electron behavior in transition metal-Al alloys. The free electron model, applied for the polycrystalline Al-Ti films with Ti content up to 20%, leads to an optical reflectance at near infrared wavelengths that scales linearly with the square root of the electrical resistivity.

  19. Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

    SciTech Connect

    Zhao, G.; Charlson, E.M.; Charlson, E.J.; Stacy, T.; Meese, J.M. ); Popovici, G.; Prelas, M. )

    1993-02-15

    Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

  20. Ferroelectric properties of lead-free polycrystalline CaBi2Nb2O9 thin films on glass substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Jang, Joonkyung; Son, Jong Yeog

    2016-03-01

    CaBi2Nb2O9 (CBNO) thin film, a lead-free ferroelectric material, was prepared on a Pt/Ta/glass substrate via pulsed laser deposition. The Ta film was deposited on the glass substrate for a buffer layer. A (115) preferred orientation of the polycrystalline CBNO thin film was verified via X-ray diffraction measurements. The CBNO thin film on a glass substrate exhibited good ferroelectric properties with a remnant polarization of 4.8 μC/cm2 (2Pr ˜9.6 μC/cm2), although it had lower polarization than the epitaxially c-oriented CBNO thin film reported previously. A mosaic-like ferroelectric domain structure was observed via piezoresponse force microscopy. Significantly, the polycrystalline CBNO thin film showed much faster switching behavior within about 100 ns than that of the epitaxially c-oriented CBNO thin film.

  1. Impact of universal mobility law on polycrystalline organic thin-film transistors

    NASA Astrophysics Data System (ADS)

    Raja, Munira; Donaghy, David; Myers, Robert; Eccleston, Bill

    2012-10-01

    We have developed novel analytical models for polycrystalline organic thin-film transistor (OTFT) by employing new concepts on the charge carrier injection to polysilicon thin-films. The models, also incorporate the effect of contact resistance associated with the poor ohmic nature of the contacts. The drain current equations of the OTFT, both in the quasi-diffusion and quasi-drift regimes, predict temperature dependencies on essential material and device parameters. Interestingly, under the drift regime, the polycrystalline OTFT model reveals similar power dependencies on the applied voltages, to those of purely disordered model developed by utilizing the universal mobility law (UML). Such similarities are not thought to be coincidental since the effect of gate voltage on surface potential is influenced by the Fermi level pinning in the grain boundary. Nonetheless, the best fits on the data of 6,13-bis(tri-isopropylsilylethynyl) OTFTs are attained with the proposed polycrystalline rather than the disordered model, particularly at low gate voltages where the diffusive component is dominant. Moreover, in order to understand the effect of grain boundaries, we devise a relationship for the dependency of the effective mobility on carrier concentration, assuming a crystalline region to be in direct contact with a disordered region. Interestingly, we find a similar dependency as the UML in purely disordered materials, which further signifies the conduction to be limited by the grain boundaries. Subsequently, an analytical model for the variation of the effective mobility with gate voltage is established. Such models are vital in assisting the development of more accurate designs of the novel organic circuits.

  2. MIS and PN junction solar cells on thin-film polycrystalline silicon

    SciTech Connect

    Ariotedjo, A.; Emery, K.; Cheek, G.; Pierce, P.; Surek, T.

    1981-05-01

    The Photovoltaic Advanced Silicon (PVAS) Branch at the Solar Energy Research Institute (SERI) has initiated a comparative study to assess the potential of MIS-type solar cells for low-cost terrestrial photovoltaic systems in terms of performance, stability, and cost-effectiveness. Several types of MIS and SIS solar cells are included in the matrix study currently underway. This approach compares the results of MIS and p/n junction solar cells on essentially identical thin-film polycrystalline silicon materials. All cell measurements and characterizations are performed using uniform testing procedures developed in the Photovoltaic Measurements and Evaluation (PV M and E) Laboratory at SERI. Some preliminary data on the different cell structures on thin-film epitaxial silicon on metallurgical-grade substrates are presented here.

  3. Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Sreenivas Puli, Venkata; Pradhan, Dhiren Kumar; Katiyar, Rajesh Kumar; Coondoo, Indrani; Panwar, Neeraj; Misra, Pankaj; Chrisey, Douglas B.; Scott, J. F.; Katiyar, Ram S.

    2014-02-01

    We report photovoltaic (PV) effect in multiferroic Bi0.9Sm0.1Fe0.95Co0.05O3 (BSFCO) thin films. Transition metal modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD). PV response is observed under illumination both in sandwich and lateral electrode configurations. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) of the films in sandwich electrode configuration under illumination are measured to be 0.9 V and -0.051 µA cm-2. Additionally, we report piezoresponse for BSFCO films, which confirms ferroelectric piezoelectric behaviour.

  4. Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Magnfält, D.; Fillon, A.; Boyd, R. D.; Helmersson, U.; Sarakinos, K.; Abadias, G.

    2016-02-01

    Intrinsic stresses in vapor deposited thin films have been a topic of considerable scientific and technological interest owing to their importance for functionality and performance of thin film devices. The origin of compressive stresses typically observed during deposition of polycrystalline metal films at conditions that result in high atomic mobility has been under debate in the literature in the course of the past decades. In this study, we contribute towards resolving this debate by investigating the grain size dependence of compressive stress magnitude in dense polycrystalline Mo films grown by magnetron sputtering. Although Mo is a refractory metal and hence exhibits an intrinsically low mobility, low energy ion bombardment is used during growth to enhance atomic mobility and densify the grain boundaries. Concurrently, the lateral grain size is controlled by using appropriate seed layers on which Mo films are grown epitaxially. The combination of in situ stress monitoring with ex situ microstructural characterization reveals a strong, seemingly linear, increase of the compressive stress magnitude on the inverse grain size and thus provides evidence that compressive stress is generated in the grain boundaries of the film. These results are consistent with models suggesting that compressive stresses in metallic films deposited at high homologous temperatures are generated by atom incorporation into and densification of grain boundaries. However, the underlying mechanisms for grain boundary densification might be different from those in the present study where atomic mobility is intrinsically low.

  5. Studies of polycrystalline pentacene thin-film transistors at the microscopic level

    NASA Astrophysics Data System (ADS)

    Cheng, Horng-Long; Chou, Wei-Yang; Kuo, Chia-Wei; Mai, Yu-Shen; Tang, Fu-Ching; Lai, Szu-Hao

    2006-08-01

    The electronic transport properties of polycrystalline pentacene-based thin film transistors (TFTs) were investigated at the microscopic level using microRaman spectroscopy. All the pentacene film, which were thermally evaporated as a layer with thickness of 70 nm, featured polycrystalline structure with only "thin film" phase polymorph and grain morphology as verified by x-ray diffraction (XRD) measurements. We have investigated the molecular vibrational modes of pentacene in the active channel during operations the organic TFT devices using in-situ Raman spectroscopy. Extra vibrational modes resulting from vibrational coupling effect in pentacene film were studied. The interlayer and intralayer intermolecular vibrational coupling energy was calculated from the Davydov splitting using a simple coupled-oscillator model. The results suggest that the C-H in-plane bending vibrational coupling energy of pentacene molecules in solid film is affected by operating device. Additionally, the aromatic C-C stretching vibrational modes also were investigated. However, it is rather difficult to obtain the variations of lattice parameters of pentacene film in a very small active channel by using electron diffraction and XRD. At the same time, MicroRaman technique provides the capability to explore the intermolecular coupling and molecular structure modifications.

  6. Suppressing light reflection from polycrystalline silicon thin films through surface texturing and silver nanostructures

    SciTech Connect

    Akhter, Perveen; Huang, Mengbing Kadakia, Nirag; Spratt, William; Malladi, Girish; Bakhru, Hassarum

    2014-09-21

    This work demonstrates a novel method combining ion implantation and silver nanostructures for suppressing light reflection from polycrystalline silicon thin films. Samples were implanted with 20-keV hydrogen ions to a dose of 10¹⁷/cm², and some of them received an additional argon ion implant to a dose of 5×10¹⁵ /cm² at an energy between 30 and 300 keV. Compared to the case with a single H implant, the processing involved both H and Ar implants and post-implantation annealing has created a much higher degree of surface texturing, leading to a more dramatic reduction of light reflection from polycrystalline Si films over a broadband range between 300 and 1200 nm, e.g., optical reflection from the air/Si interface in the AM1.5 sunlight condition decreasing from ~30% with an untextured surface to below 5% for a highly textured surface after post-implantation annealing at 1000°C. Formation of Ag nanostructures on these ion beam processed surfaces further reduces light reflection, and surface texturing is expected to have the benefit of diminishing light absorption losses within large-size (>100 nm) Ag nanoparticles, yielding an increased light trapping efficiency within Si as opposed to the case with Ag nanostructures on a smooth surface. A discussion of the effects of surface textures and Ag nanoparticles on light trapping within Si thin films is also presented with the aid of computer simulations.

  7. Magnetization studies of first-order magnetostructural phase transition in polycrystalline FeRh thin films

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao

    2012-10-01

    The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.

  8. Thin film polycrystalline silicon: Promise and problems in displays and solar cells

    SciTech Connect

    Fonash, S.J.

    1995-08-01

    Thin film polycrystalline Si (poly-Si) with its carrier mobilities, potentially good stability, low intragrain defect density, compatibility with silicon processing, and ease of doping activation is an interesting material for {open_quotes}macroelectronics{close_quotes} applications such as TFTs for displays and solar cells. The poly-Si films needed for these applications can be ultra-thin-in the 500{Angstrom} to 1000{Angstrom} thickness range for flat panel display TFTs and in the 4{mu}m to 10{mu}m thickness range for solar cells. Because the films needed for these microelectronics applications can be so thin, an effective approach to producing the films is that of crystallizing a-Si precursor material. Unlike cast materials, poly-Si films made this way can be produced using low temperature processing. Unlike deposited poly-Si films, these crystallized poly-Si films can have grain widths that are much larger than the film thickness and almost atomically smooth surfaces. This thin film poly-Si crystallized from a-Si precursor films, and its promise and problems for TFTs and solar cells, is the focus of this discussion.

  9. Magnetic Properties of Polycrystalline Bismuth Ferrite Thin Films Grown by Atomic Layer Deposition.

    PubMed

    Jalkanen, Pasi; Tuboltsev, Vladimir; Marchand, Benoît; Savin, Alexander; Puttaswamy, Manjunath; Vehkamäki, Marko; Mizohata, Kenichiro; Kemell, Marianna; Hatanpää, Timo; Rogozin, Valentin; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku

    2014-12-18

    The atomic layer deposition (ALD) method was applied to grow thin polycrystalline BiFeO3 (BFO) films on Pt/SiO2/Si substrates. The 50 nm thick films were found to exhibit high resistivity, good morphological integrity, and homogeneity achieved by the applied ALD technique. Magnetic characterization revealed saturated magnetization of 25 emu/cm(3) with temperature-dependent coercivity varying from 5 to 530 Oe within the temperature range from 300 to 2 K. Magnetism observed in the films was found to change gradually from ferromagnetic spin ordering to pinned magnetic domain interactions mixed with weak spin-glass-like behavior of magnetically frustrated antiferromagnetic/ferromagnetic (AFM-FM) spin ordering depending on the temperature and magnitude of the applied magnetic field. Antiferromagnetic order of spin cycloids was broken in polycrystalline films by crystal sizes smaller than the cycloid length (∼60 nm). Uncompensated spincycloids and magnetic domain walls were found to be the cause of the high magnetization of the BFO films. PMID:26273981

  10. Effect of top electrodes on photovoltaic properties of polycrystalline BiFeO3 based thin film capacitors

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Li, Mi; Liu, Yiwei; Zuo, Zhenghu; Zhuge, Fei; Zhan, Qing-Feng; Li, Run-Wei

    2011-05-01

    We investigated capacitors based on polycrystalline narrow-band-gap BiFeO3 (BFO) thin films with different top electrodes. The photovoltaic response for the capacitor with a Sn-doped In2O3 (ITO) top electrode is about 25 times higher than that with a Au top electrode, which indicates that the electrode plays a key role in determining the photovoltaic response of ferroelectric thin film capacitors, as simulated by Qin et al (2009 Appl. Phys. Lett. 95 22912). The light-to-electricity photovoltaic efficiency for the ITO/polycrystalline BFO/Pt capacitor can reach 0.125%. Furthermore, under incident light of 450 µW cm - 2 and zero bias, the corresponding photocurrent varies from 0.2 to 200 pA, that is, almost a 1000-fold photoconductivity enhancement. Our experiments suggest that polycrystalline BFO films are promising materials for application in photo-sensitive and energy-related devices.

  11. Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuits for Active Matrix Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yu-Sheng; Liu, Yan-Wei

    A new pixel design and driving method for active matrix organic light emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage programming method are proposed and verified using the SPICE simulator. We had employed an appropriate TFT model in SPICE simulation to demonstrate the performance of the pixel circuit. The OLED anode voltage variation error rates are below 0.35% under driving TFT threshold voltage deviation (Δ Vth =± 0.33V). The OLED current non-uniformity caused by the OLED threshold voltage degradation (Δ VTO =+0.33V) is significantly reduced (below 6%). The simulation results show that the pixel design can improve the display image non-uniformity by compensating for the threshold voltage deviation in the driving TFT and the OLED threshold voltage degradation at the same time.

  12. Broadening of optical transitions in polycrystalline CdS and CdTe thin films

    SciTech Connect

    Li Jian; Chen Jie; Collins, R. W.

    2010-11-01

    The dielectric functions {epsilon} of polycrystalline CdS and CdTe thin films sputter deposited onto Si wafers were measured from 0.75 to 6.5 eV by in situ spectroscopic ellipsometry. Differences in {epsilon} due to processing variations are well understood using an excited carrier scattering model. For each sample, a carrier mean free path {lambda} is defined that is found to be inversely proportional to the broadening of each of the band structure critical points (CPs) deduced from {epsilon}. The rate at which broadening occurs with {lambda}{sup -1} is different for each CP, enabling a carrier group speed {upsilon}{sub g} to be identified for the CP. With the database for {upsilon}{sub g}, {epsilon} can be analyzed to evaluate the quality of materials used in CdS/CdTe photovoltaic heterojunctions.

  13. Energy loss of protons and deuterons at low energies in Pd polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Celedón, C.; Sánchez, E. A.; Moreno, M. S.; Arista, N. R.; Uribe, J. D.; Mery, M.; Valdés, J. E.; Vargas, P.

    2013-07-01

    We have investigated experimentally and by computer simulations the energy-loss distributions of low-energy (E<10 keV) protons and deuterons transmitted through polycrystalline palladium thin films. In contrast to previous experiments on various transition metals we find that the stopping power of Pd is proportional to the ion velocity. Data of protons and deuterons are coincident within the experimental uncertainties, showing the absence of an isotopic effect on the stopping power of Pd in this energy range. The experimental results were analyzed and compared with Monte Carlo computer simulations and previous theoretical models. The difference in the velocity dependence of the energy loss of hydrogen ions in Pd with respect to other transition metals (Cu, Ag, and Au) is explained by a theoretical analysis based on the properties of the d-electron bands of those elements.

  14. Process for fabricating polycrystalline semiconductor thin-film solar cells, and cells produced thereby

    DOEpatents

    Wu, Xuanzhi; Sheldon, Peter

    2000-01-01

    A novel, simplified method for fabricating a thin-film semiconductor heterojunction photovoltaic device includes initial steps of depositing a layer of cadmium stannate and a layer of zinc stannate on a transparent substrate, both by radio frequency sputtering at ambient temperature, followed by the depositing of dissimilar layers of semiconductors such as cadmium sulfide and cadmium telluride, and heat treatment to convert the cadmium stannate to a substantially single-phase material of a spinel crystal structure. Preferably, the cadmium sulfide layer is also deposited by radio frequency sputtering at ambient temperature, and the cadmium telluride layer is deposited by close space sublimation at an elevated temperature effective to convert the amorphous cadmium stannate to the polycrystalline cadmium stannate with single-phase spinel structure.

  15. Metastable Electrical Characteristics of Polycrystalline Thin-Film Photovoltaic Modules upon Exposure and Stabilization: Preprint

    SciTech Connect

    Deline, C. A.; del Cueto, J. A.; Albin, D. S.; Rummel, S. R.

    2011-09-01

    The significant features of a series of stabilization experiments conducted at the National Renewable Energy Laboratory (NREL) between May 2009 and the present are reported. These experiments evaluated a procedure to stabilize the measured performance of thin-film polycrystalline cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) thin-film photovoltaic (PV) modules. The current-voltage (I-V) characteristics of CdTe and CIGS thin-film PV devices and modules exhibit transitory changes in electrical performance after thermal exposure in the dark and/or bias and light exposures. We present the results of our case studies of module performance versus exposure: light-soaked at 65 degrees C; exposed in the dark under forward bias at 65 degrees C; and, finally, longer-term outdoor exposure. We find that stabilization can be achieved to varying degrees using either light-soaking or dark bias methods and that the existing IEC 61646 light-soaking interval may be appropriate for CdTe and CIGS modules with one caveat: it is likely that at least three exposure intervals are required for stabilization.

  16. Synthesis and characterization of large-grain solid-phase crystallized polycrystalline silicon thin films

    SciTech Connect

    Kumar, Avishek E-mail: dalapatig@imre.a-star.edu.sg; Law, Felix; Widenborg, Per I.; Dalapati, Goutam K. E-mail: dalapatig@imre.a-star.edu.sg; Subramanian, Gomathy S.; Tan, Hui R.; Aberle, Armin G.

    2014-11-01

    n-type polycrystalline silicon (poly-Si) films with very large grains, exceeding 30 μm in width, and with high Hall mobility of about 71.5 cm{sup 2}/V s are successfully prepared by the solid-phase crystallization technique on glass through the control of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The effect of this gas flow ratio on the electronic and structural quality of the n-type poly-Si thin film is systematically investigated using Hall effect measurements, Raman microscopy, and electron backscatter diffraction (EBSD), respectively. The poly-Si grains are found to be randomly oriented, whereby the average area weighted grain size is found to increase from 4.3 to 18 μm with increase of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The stress in the poly-Si thin films is found to increase above 900 MPa when the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio is increased from 0.025 to 0.45. Finally, high-resolution transmission electron microscopy, high angle annular dark field-scanning tunneling microscopy, and EBSD are used to identify the defects and dislocations caused by the stress in the fabricated poly-Si films.

  17. Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

    SciTech Connect

    Nomura, Masahiro; Kage, Yuta; Müller, David; Moser, Dominik; Paul, Oliver

    2015-06-01

    Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

  18. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  19. Synthesis and characterization of polycrystalline semiconductor Caesium-Tin tri-Iodide thin-films

    NASA Astrophysics Data System (ADS)

    Chen, Zhuo

    This thesis deals with a virtually unexplored semiconductor material CsSnI3 from material synthesis, structural, optical, and electrical characterization to the fabrication and validation of CsSnI3 thin-film solar cells. We started with synthesizing CsSnI3 thin films based on CsI and SnCl2 (or SnI2) by using an apparatus which consists of e-beam and thermal evaporators. The quality of polycrystalline CsSnI3 thin-films were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Experimental data on XRD and electron diffraction patterns taking from the synthesized thin-films match very well to the theoretically calculated ones based the first principles calculations, confirming that the synthesized CsSnI3 thin-films have an orthorhombic crystal structure. With the well-defined crystal structure, we theoretically studied the electronic band structure of CsSnI3. Extensive optical characterizations of CsSnI3 thin-films were then carried out revealing many extraordinary properties such as 1) direct band gap energy of 1.32 eV at 300 K with its abnormal temperature dependence, 2) extremely high photoluminescence quantum yield, 3) large exciton binding energy, and 4) strong two-phonon assisted excitonic absorption near band edge. These properties are interpreted in terms of the unique electronic and structural properties of CsSnI3. The value of 1.3 eV for the energy band gap of CsSnI3 suggests a unique application of CsSnI3 thin-films on solar cells. This is because this value is right in the small range of the optimal band gaps for the Shockley-Queisser maximum efficiency limit of a single-junction solar cell. A prototype Schottky solar cell was designed, fabricated, and validated. The measured power conversion efficiency (PCE) is 0.9 % which is presently limited by the series and shunt resistance. The improvement strategy on PCE is given at the end of my thesis. In order to make the CsSnI3 thin-film solar cells

  20. Recovery Act : Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates

    SciTech Connect

    Venkat Selvamanickam; Alex Freundlich

    2010-11-29

    III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 * 10^8 per cm^2. Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches

  1. 1 Tbit/in.2 Very-High-Density Recording in Mass-Productive Polycrystalline Ferroelectric Thin Film Media

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kenjiro; Kawano, Takahiro; Onoe, Atsushi; Tamura, Masahiro; Umeda, Masaru; Toda, Masayuki

    2009-07-01

    We demonstrate very-high-density ferroelectric recording experiments of 1 Tbit/in.2 in polycrystalline Pb(Zr,Ti)O3 (PZT) thin film for the first time. A high-quality polycrystalline PZT thin film was successfully deposited on a silicon substrate with a SrRuO3 (SRO) electrode by metal-organic chemical vapor deposition (MOCVD). The roughness of the PZT film was reduced to less than 1 nm by chemical mechanical polishing (CMP). The PZT film has very high controllability for domain inversion. Our fabrication process also enables high productivity. Therefore, our PZT film has potential to be a mass-productive ferroelectric recording medium for high-density storage systems.

  2. Polycrystalline SrFe12O19 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Garcia, Tupac; de Posada, E.; Jimenez, Ernesto; Sanchez Ll., J. L.; Diaz Castanon, S.; Bartolo-Perez, Pascual; Cauich, W.; Oliva, I.; Pena, J. L.; Ceh, O.

    1999-07-01

    Polycrystalline SrFe12O19 thin films were deposited on Si (100) substrates by PLD using a Nd-YAG laser ((lambda) equals 1064 nm). During the deposition process substrates were kept at room temperature. As-deposited films were annealed in air at temperatures between 600 degree(s)C and 840 degree(s)C. Samples were characterized by AES, ESCA, SEM, AFM, x-ray diffraction and VSM. It is presented the relevance of the preparation of the target surface on the film quality. Some differences in the chemical composition of as-deposited films, compared with the target and the annealed films, were observed. The x-ray diffraction spectra show a textured as- deposited films. Samples annealed at 600 degree(s)C, and below, showed a very weak magnetic response. In contrast annealing in the temperature range 700 degree(s)C - 840 degree(s)C led to the formation of a nanocrystalline particle system (average particle size 150 - 350 nm) which behave as a single domain in the thermally demagnetized state. The obtained coercivities (5750 - 6850 Oe) are among the highest values reported for films, powders and sintered samples.

  3. Local impedance imaging of boron-doped polycrystalline diamond thin films

    SciTech Connect

    Zieliński, A.; Ryl, J.; Burczyk, L.; Darowicki, K.

    2014-09-29

    Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 10{sup 16} to 2 × 10{sup 21} atoms cm{sup −3}. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp{sup 2} regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

  4. A thin-film polycrystalline photoelectrochemical cell with 8% solar conversion efficiency

    NASA Astrophysics Data System (ADS)

    Hodes, G.

    1980-05-01

    A thin-film polycrystalline CdSe(0.65)Te(0.35)/polysulfide-based photoelectrochemical solar cell with an energy conversion efficiency of up to 8% is presented. Cell electrodes were prepared by painting a slurry of sintered CdSe(0.65)Te(0.35) powder onto a Ti substrate and then annealing in an inert atmosphere and etching by various means. Solar efficiencies of the electrodes immersed in an aqueous electrolyte 1 M in KOH, Na2S and S with a counter electrode of sulfide brass gauze of up to 5% were obtained following a HCl:HNO3 etch, up to 5.5% following etching in dilute aqueous CrO3 and up to 8.0% following photoetching and K2CrO4 treatment. The spectral response of the anode in polysulfide solution exhibits a short-wavelength cutoff due to electrolyte absorption, a flat plateau region, and a fairly sharp long-wavelength cut-off indicating an effective band gap of about 1.45 eV, similar to that of CdTe. Output stability has been found to decrease with increasing output current, remaining stable for more than 21 h at a current of 20 mA/sq cm.

  5. Polycrystalline silicon thin-film transistors fabricated by Joule-heating-induced crystallization

    NASA Astrophysics Data System (ADS)

    Hong, Won-Eui; Ro, Jae-Sang

    2015-01-01

    Joule-heating-induced crystallization (JIC) of amorphous silicon (a-Si) films is carried out by applying an electric pulse to a conductive layer located beneath or above the films. Crystallization occurs across the whole substrate surface within few tens of microseconds. Arc instability, however, is observed during crystallization, and is attributed to dielectric breakdown in the conductor/insulator/transformed polycrystalline silicon (poly-Si) sandwich structures at high temperatures during electrical pulsing for crystallization. In this study, we devised a method for the crystallization of a-Si films while preventing arc generation; this method consisted of pre-patterning an a-Si active layer into islands and then depositing a gate oxide and gate electrode. Electric pulsing was then applied to the gate electrode formed using a Mo layer. The Mo layer was used as a Joule-heat source for the crystallization of pre-patterned active islands of a-Si films. JIC-processed poly-Si thin-film transistors (TFTs) were fabricated successfully, and the proposed method was found to be compatible with the standard processing of coplanar top-gate poly-Si TFTs.

  6. Fracture toughness of low-pressure chemical-vapor-deposited polycrystalline silicon carbide thin films

    NASA Astrophysics Data System (ADS)

    Hatty, V.; Kahn, H.; Trevino, J.; Zorman, C. A.; Mehregany, M.; Ballarini, R.; Heuer, A. H.

    2006-01-01

    The fracture toughness of thin-film polycrystalline silicon carbide (poly-SiC) deposited on silicon (Si) wafers via low-pressure chemical-vapor deposition (LPCVD) has been measured on a scale useful for micromachined devices; the results are compared to previous studies on poly-SiC thin films deposited by atmospheric pressure chemical-vapor deposition (APCVD) [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)]. Samples in this study included those with and without silicon dioxide (SiO2) sacrificial release layers. The LPCVD processing technique induces residual tensile stresses in the films. Doubly clamped microtensile specimens were fabricated using standard micromachining processes, and microindentation was used to initiate atomically sharp precracks. The residual stresses in the films create stress intensity factors K at the crack tips; upon release, the precracks whose K exceeded a critical value, KIC, propagated to failure. The fracture toughness KIC was the same for both types of devices, 2.9+/-0.2 MPa m1/2 for the SiC on Si samples and 3.0+/-0.2 MPa m1/2 for the SiC on SiO2/Si samples, and similar to that found for APCVD poly-SiC, 2.8<=KIC<=3.4 MPa m1/2 [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)], indicating that KIC is truly a structure-insensitive material property. The fracture toughness of poly-SiC compares favorably with that for polysilicon, 0.85+/-0.05 MPa m1/2 [Kahn et al., Science 298, 1215 (2002)].

  7. Poly-crystalline thin-film by aluminum induced crystallization on aluminum nitride substrate

    NASA Astrophysics Data System (ADS)

    Bhopal, Muhammad Fahad; Lee, Doo Won; Lee, Soo Hong

    2016-07-01

    Thin-film polycrystalline silicon (pc-Si) on foreign (non-silicon) substrates has been researched by various research groups for the production of photovoltaic cells. High quality pc-Si deposition on foreign substrates with superior optical properties is considered to be the main hurdle in cell fabrication. Metal induced crystallization (MIC) is one of the renowned techniques used to produce this quality of material. In the current study, an aluminum induced crystallization (AIC) method was adopted to produce pc-Si thin-film on aluminum nitride (AlN) substrate by a seed layer approach. Aluminum and a-Si layer were deposited using an e-beam evaporator. Various annealing conditions were used in order to investigate the AIC grown pc-Si seed layers for process optimization. The effect of thermal annealing on grain size, defects preferentially crystallographic orientation of the grains were analyzed. Surface morphology was studied using an optical microscope. Poly-silicon film with a crystallinity fraction between 95-100% and an FWHM between 5-6 cm-1 is achievable at low temperatures and for short time intervals. A grain size of about 10 micron can be obtained at a low deposition rate on an AIN substrate. Similarly, Focused ion beam (FIB) also showed that at 425 °C sample B and at 400 °C sample A were fully crystallized. The crystalline quality of pc-Si was evaluated using µ-Raman spectroscopy as a function of annealed conditions and Grazing incidence X-ray diffraction (GIXRD) was used to determine the phase direction of the pc-Si layer. The current study implicates that a poly-silicon layer with good crystallographic orientation and crystallinity fraction is achievable on AIN substrate at low temperatures and short time frames.

  8. Polycrystalline silicon thin-film solar cells with plasmonic-enhanced light-trapping.

    PubMed

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm(2), which can be increased up to 17-18 mA/cm(2) (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing

  9. Characterization of polycrystalline VO2 thin film with low phase transition temperature fabricated by high power impulse magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-04-01

    VO2 is a unique material that undergoes a reversible phase transformation around 68∘C. Currently, applications of VO2 on smart windows are limited by its high transition temperature. In order to reduce the temperature, VO2 thin film was fabricated on quartz glass substrate by high power impulse magnetron sputtering with a modulated pulsed power. The phase transition temperature has been reduced to as low as 32∘C. In addition, the VO2 film possesses a typical metal-insulator transition. X-ray diffraction and selected area electron diffraction patterns reveal that an obvious lattice distortion has been formed in the as-deposited polycrystalline VO2 thin film. X-ray photoelectron spectroscopy proves that oxygen vacancies have been formed in the as-deposited thin film, which will induce a lattice distortion in the VO2 thin film.

  10. Height-resolved quantification of microstructure and texture in polycrystalline thin films using TEM orientation mapping.

    PubMed

    Aebersold, A Brian; Alexander, Duncan T L; Hébert, Cécile

    2015-12-01

    A method is presented for the quantitative investigation of microstructure and texture evolution in polycrystalline thin films based on in-plane automated crystal orientation mapping in transmission electron microscopy, from the substrate up. To demonstrate the method we apply it to the example of low pressure metal-organic chemical vapor deposited ZnO layers. First, orientation mapping is applied to standard cross-section and plan-view transmission electron microscopy samples of films, illustrating how plan-view samples both reduce the occurrence of grain overlap that is detrimental to reliable orientation mapping and also improve sampling statistics compared to cross-sections. Motivated by this, orientation mapping has been combined with a double-wedge method for specimen preparation developed by Spiecker et al. (2007) [1], which creates a large area plan-view sample that traverses the film thickness. By measuring >10,000 grains in the film, the resulting data give access to grain size, orientation and misorientation distributions in function of height above the substrate within the film, which are, in turn, the inputs necessary for quantitative assessment of growth models and simulations. The orientation data are directly related to microstructural images, allowing correlation of orientations with in-plane and out-of-plane grain sizes and shapes. The spatial correlation of the entire data set gives insights into previously unnoticed growth mechanisms such as the presence of renucleation or preferred misorientations. Finally, the data set can be used to guide targeted, local studies by other transmission electron microscopy techniques. This is demonstrated by the site-specific application of nano-beam diffraction to validate the presence of coherent [21̄1̄0]/(011̄3) twin boundaries first suggested by the orientation mapping. PMID:26363209

  11. Improved ferroelectric property and domain structure of highly a-oriented polycrystalline CaBi2Nb2O9 thin film

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2015-12-01

    A Lead-free ferroelectric CaBi2Nb2O9 (CBNO) thin film was deposited on Si substrate by pulsed laser deposition. TiO2 buffer layer was employed and Pt electrode was used for nano-scale capacitor. The x-ray diffraction reveals that the CBNO thin film has highly a-oriented polycrystalline structure. The highly a-oriented polycrystalline CBNO thin film significantly exhibit the enhanced ferroelectric property with a remnant polarization of 10 μC/cm2 compared to other values reported previously. In particular, the highly a-oriented polycrystalline CBNO thin film show faster ferroelectric switching characteristics than the epitaxially c-oriented CBNO thin film.

  12. Organic solar cells based on liquid crystalline and polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Yoo, Seunghyup

    This dissertation describes the study of organic thin-film solar cells in pursuit of affordable, renewable, and environmentally-friendly energy sources. Particular emphasis is given to the molecular ordering found in liquid crystalline or polycrystalline films as a way to leverage the efficiencies of these types of cells. Maximum efficiencies estimated based on excitonic character of organic solar cells show power conversion efficiencies larger than 10% are possible in principle. However, their performance is often limited due to small exciton diffusion lengths and poor transport properties which may be attributed to the amorphous nature of most organic semiconductors. Discotic liquid crystal (DLC) copper phthalocyanine was investigated as an easily processible building block for solar cells in which ordered molecular arrangements are enabled by a self-organization in its mesophases. An increase in photocurrent and a reduction in series resistance have been observed in a cell which underwent an annealing process. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements suggest that structural and morphological changes induced after the annealing process are related to these improvements. In an alternative approach, p-type pentacene thin films prepared by physical vapor deposition were incorporated into heterojunction solar cells with C60 as n-type layers. Power conversion efficiencies of 2.7% under broadband illumination (350--900 nm) with a peak external quantum efficiency of 58% have been achieved with the broad spectral coverage across the visible spectrum. Analysis using an exciton diffusion model shows this efficient carrier generation is mainly due to the large exciton diffusion length of pentacene films. Joint XRD and AFM studies reveal that the highly crystalline nature of pentacene films can account for the observed large exciton diffusion length. In addition, the electrical characteristics are studied as a function of light intensity using

  13. Influence of thickness on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-02-01

    This paper presents the influence of thickness on physical properties of polycrystalline CdTe thin films. The thin films of thickness 450 nm, 650 nm and 850 nm were deposited employing thermal vacuum evaporation technique on glass and indium tin oxide (ITO) coated glass substrates. The physical properties of these as-grown thin films were investigated employing the X-ray diffraction (XRD), source meter, UV-Vis spectrophotometer, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The structural analysis reveals that the films have zinc-blende cubic structure and polycrystalline in nature with preferred orientation (111). The structural parameters like lattice constant, interplanar spacing, grain size, strain, dislocation density and number of crystallites per unit area are calculated. The average grain size and optical band gap are found in the range 15.16-21.22 nm and 1.44-1.63 eV respectively and observed to decrease with thickness. The current-voltage characteristics show that the electrical conductivity is observed to decrease with thickness. The surface morphology shows that films are free from crystal defects like pin holes and voids as well as homogeneous and uniform. The EDS patterns show the presence of cadmium and tellurium elements in the as grown films. The experimental results reveal that the film thickness plays significant role on the physical properties of as-grown CdTe thin films and higher thickness may be used as absorber layer to solar cells applications.

  14. Structural and electrical properties of polycrystalline Bi(Fe0.6Mn0.4)O3 thin films

    NASA Astrophysics Data System (ADS)

    Kim, S. W.; Kim, W. J.; Lee, M. H.; Song, T. K.; Do, D.

    2013-12-01

    A 40% Mn-substituted BiFeO3 (BFMO) thin film was deposited on a Pt(111)/Ti/SiO2/Si(100) substrate by using a pulsed laser deposition method. The coexistence of rhombohedral and orthorhombic structures in the BFMO thin film was confirmed by using X-ray diffraction and Raman spectra investigation. The leakage current density of the BFMO thin film was larger than that of a pure polycrystalline BiFeO3 (BFO) thin film. In order to understand the leakage current behaviors, was investigated the leakage current mechanisms. The leakage current mechanism of the BFO thin film was found to be space-charge-limited conduction (SCLC), followed by trap-filled conduction causal by the increasing electric field strength. On the other hand, trap-filled conduction was not observed in the BFMO thin film. A leaky ferroelectric hysteresis loop was observed in the BFMO thin film, but not in the BFO thin film.

  15. Leakage Current Suppression on Metal-Induced Laterally Crystallized Polycrystalline Silicon Thin-Film Transistors by Asymmetrically Deposited Nickel

    NASA Astrophysics Data System (ADS)

    Byun, Chang Woo; Son, Se Wan; Lee, Yong Woo; Hyo Park, Jae; Vakilipour Takaloo, Ashkan; Joo, Seung Ki

    2013-10-01

    The electrical performance of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) fabricated by metal-induced lateral crystallization (MILC) is greatly affected by metal catalyst contaminations, such as Ni and Ni silicide trapped in the channel, since they concentrate in front of laterally grown crystallites. In the present work, the effect of the MILC/MILC boundary (MMB) on MILC polycrystalline silicon (poly-Si) TFTs is investigated by the comparison of MILC poly-Si TFTs with MMB at the center of the channel, and equivalent TFTs with MMB at a position ejected from the channel. The MMB location was controlled by the Ni catalyst position. Both a low off-state leakage current and a free from short channel effect (kink effect) were observed in high electric-field conditions. Furthermore, the field-effect mobility and drain current noise were drastically improved by ejecting the MILC boundary in the source direction.

  16. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  17. High-performance p-channel polycrystalline-germanium thin-film transistors via excimer laser crystallization and counter doping

    NASA Astrophysics Data System (ADS)

    Liao, Chan-Yu; Huang, Ching-Yu; Huang, Ming-Hui; Chou, Chia-Hsin; Cheng, Huang-Chung

    2016-04-01

    High-quality polycrystalline-germanium (poly-Ge) thin films have been successfully fabricated by excimer laser crystallization (ELC). Grains as large as 1 µm were achieved by ELC at 300 mJ/cm2. Meanwhile, the defect-generated hole concentrations in Ge thin films were significantly reduced. Furthermore, the majority carriers could then be converted to n-type by counter doping (CD) with a suitable dose. Then, high-performance p-channel Ge thin-film transistors (TFTs) with a high on/off current ratio of up to 1.7 × 103 and a high field-effect mobility of up to 208 cm2 V-1 s-1 were demonstrated for a channel width and length both of 0.5 µm. It was revealed that ELC combined with CD is effective for attaining high-performance p-channel poly-Ge TFTs.

  18. Polycrystalline thin film materials and devices. Annual subcontract report, 16 January 1990--15 January 1991

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.

    1991-11-01

    Results and conclusion of Phase I of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe{sub 2} and CdTe solar cells. The kinetics of the formation of CuInSe{sub 2} by selenization with hydrogen selenide was investigated and a CuInSe{sub 2}/CdS solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe{sub 2} films and a cell efficiency of 7%. Detailed investigations of the open circuit voltage of CuInSe{sub 2} solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe{sub 2} thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe{sub 2} is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10% can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm{sup 2} are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  19. Ambient condition laser writing of graphene structures on polycrystalline SiC thin film deposited on Si wafer

    SciTech Connect

    Yue, Naili; Zhang, Yong; Tsu, Raphael

    2013-02-18

    We report laser induced local conversion of polycrystalline SiC thin-films grown on Si wafers into multi-layer graphene, a process compatible with the Si based microelectronic technologies. The conversion can be achieved using a 532 nm CW laser with as little as 10 mW power, yielding {approx}1 {mu}m graphene discs without any mask. The conversion conditions are found to vary with the crystallinity of the film. More interestingly, the internal structure of the graphene disc, probed by Raman imaging, can be tuned with varying the film and illumination parameters, resembling either the fundamental or doughnut mode of a laser beam.

  20. Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

    PubMed Central

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing

  1. Thin-film polycrystalline n-ZnO/p-CuO heterojunction

    SciTech Connect

    Lisitski, O. L.; Kumekov, M. E.; Kumekov, S. E. Terukov, E. I.

    2009-06-15

    Results of X-ray diffraction and spectral-optical studies of n-ZnO and p-CuO films deposited by gas-discharge sputtering with subsequent annealing are presented. It is shown that, despite the difference in the crystal systems, the polycrystallinity of n-ZnO and p-CuO films enables fabrication of a heterojunction from this pair of materials.

  2. Infrared detection of hydrogen-generated free carriers in polycrystalline ZnO thin films

    SciTech Connect

    Wolden, Colin A.; Barnes, Teresa M.; Baxter, Jason B.; Aydil, Eray S.

    2005-02-15

    The changes in the free-carrier concentration in polycrystalline ZnO films during exposure to H{sub 2} and O{sub 2} plasmas were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. The carrier concentration and mobility were extracted from the free-carrier absorption in the infrared using a model for the dielectric function. The electron density in polycrystalline zinc oxide films may be significantly increased by >10{sup 19} cm{sup -3} by brief exposures to hydrogen plasma at room temperature and decreased by exposure to O{sub 2} plasmas. Room-temperature oxygen plasma removes a fraction of the H at donor sites but both elevated temperatures ({approx}225 deg. C) and O{sub 2} plasma were required to remove the rest. We demonstrate that combinations of O{sub 2} and H{sub 2} plasma treatments can be used to manipulate the carrier density in ZnO films. However, we also show the existence of significant drifts ({approx}15%) in the carrier concentrations over very long time scales (hours). Possible sites for H incorporation in polycrystalline films and reasons for the observed carrier-concentration changes are proposed.

  3. Synthesis and characterization of ordered and disordered polycrystalline La2NiMnO6 thin films by sol-gel.

    PubMed

    Zhang, Zhiqing; Jian, Hongbin; Tang, Xianwu; Yang, Jie; Zhu, Xuebin; Sun, Yuping

    2012-10-14

    Polycrystalline La(2)NiMnO(6) thin films are prepared on Pt/Ti/SiO(2)/Si substrates by the sol-gel method. Through controlling the processing parameters, the cation ordering can be tuned. The disordered and ordered thin films exhibit distinct differences for crystal structures as well as properties. The crystal structure at room temperature characterized by X-ray diffraction and Raman spectra is suggested to be monoclinic (P2(1)/n) and orthorhombic (Pbnm) for the ordered and disordered thin films, respectively. The ferromagnetic-paramagnetic transition is 263 K and 60 K for the ordered and disordered samples respectively, whereas the saturation magnetic moment at 5 K is 4.9 μ(B) fu(-1) (fu = formula unit) and 0.9 μ(B) fu(-1). The dielectric constant as well as magnetodielectric effect is higher for the ordered La(2)NiMnO(6) thin films. The magnetodielectric effect for the ordered thin film is dominantly contributed to the intrinsic coupling of electric dipole ordering and fluctuations and magnetic ordering and fluctuations, while it is mainly contributed to Maxwell-Wagner (M-W) effects for the disordered thin film. The successful achievements of ordered and disordered polycrystalline La(2)NiMnO(6) thin films will provide an effective route to fabricate double-perovskite polycrystalline thin films by the sol-gel method. PMID:22910689

  4. Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-06-01

    A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150-350 °C. These films were subjected to the XRD, UV-Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48-1.64 eV and observed to decrease with thermal annealing. The current-voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.

  5. Ultrafast optical control of magnetization dynamics in polycrystalline bismuth doped iron garnet thin films

    SciTech Connect

    Deb, Marwan Vomir, Mircea; Rehspringer, Jean-Luc; Bigot, Jean-Yves

    2015-12-21

    Controlling the magnetization dynamics on the femtosecond timescale is of fundamental importance for integrated opto-spintronic devices. For industrial perspectives, it requires to develop simple growth techniques for obtaining large area magneto-optical materials having a high amplitude ultrafast Faraday or Kerr response. Here we report on optical pump probe studies of light induced spin dynamics in high quality bismuth doped iron garnet polycrystalline film prepared by the spin coating method. We demonstrate an ultrafast non-thermal optical control of the spin dynamics using both circularly and linearly polarized pulses.

  6. X-ray diffraction study of polycrystalline BiFeO3 thin films under electric field

    NASA Astrophysics Data System (ADS)

    Nakashima, Seiji; Sakata, Osami; Nakamura, Yoshitaka; Kanashima, Takeshi; Funakubo, Hiroshi; Okuyama, Masanori

    2008-07-01

    Diffraction measurements using 12.4keV x-ray of synchrotron radiation have been performed in (001)pc- and (110)pc-oriented polycrystalline 350-nm-thick BiFeO3 thin films on a Pt /TiO2/SiO2/Si substrate under electric field in air at RT. Unipolar rectangular pulse voltages having a 150ns width and a 804.09ns period have been applied to BiFeO3 with a Pt top electrode. A diffraction peak of the (001)pc [(110)pc] plane shifts from 14.602° (20.520°) to 14.588 (20.505°) due to piezoelectric response when a 12V (11V ) pulse is applied. Piezoelectric constants (d33) of (001)pc-oriented and (110)pc-oriented domains estimated from these peak shifts are 27.8 and 26.4pm/V, respectively.

  7. Polycrystalline InN thin films prepared by ion-beam-assisted filtered cathodic vacuum arc technique

    NASA Astrophysics Data System (ADS)

    Ji, X. H.; Lau, S. P.

    2005-09-01

    We report on the fabrication of indium nitride (InN) thin films on silicon (1 0 0) substrates by radio frequency ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The effects of nitrogen ion energy on the structural properties of InN films have been investigated by X-ray diffraction and Raman spectroscopy. The InN films exhibit polycrystalline wurtzite structure. At nitrogen ion energy of 100 eV, the film shows preferred (0 0 0 2) orientation. The preferred orientation is changed to ( 1 0 1¯ 1) when the nitrogen ion energy is more than 100 eV. Three Raman-active optical phonons have been clearly identified and assigned to A 1(LO) at ˜588 cm -1, E22 at ˜490 cm -1 and A 1(TO) at ˜449 cm -1 of InN films, which confirmed the hexagonal structure of InN.

  8. Fatigue failure in thin-film polycrystalline silicon is due to subcritical cracking within the oxide layer

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Stach, E. A.; Muhlstein, C. L.; Ritchie, R. O.

    2005-01-01

    It has been established that microelectromechanical systems created from polycrystalline silicon thin films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a "reaction-layer" process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoing moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the "reaction-layer" mechanism.

  9. Structural and Magnetic Properties of Sputter-Deposited Polycrystalline Ni-Mn-Ga Ferromagnetic Shape-Memory Thin Films

    NASA Astrophysics Data System (ADS)

    Vinodh Kumar, S.; Seenithurai, S.; Manivel Raja, M.; Mahendran, M.

    2015-10-01

    Polycrystalline Ni-Mn-Ga ferromagnetic shape-memory thin films have been deposited on Si (100) substrates using a direct-current magnetron sputtering technique. The microstructure and the temperature dependence of magnetic properties of the films have been investigated by x-ray diffraction, scanning electron microscopy, and thermomagnetic measurements. As-deposited Ni50.2Mn30.6Ga19.2 film showed quasi-amorphous structure with paramagnetic nature at room temperature. When annealed at 873 K, the quasi-amorphous film attained crystallinity and possessed L21 cubic ordering with high magnetic transition temperature. Saturation magnetization and coercivity values for the annealed film were found to be 220 emu/cm3 and 70 Oe, respectively, indicating soft ferromagnetic character with low magnetocrystalline anisotropy. The magnetic transitions of the film deposited at 100 W were above room temperature, making this a potential candidate for use in microelectromechanical system devices.

  10. Fabrication of polycrystalline CdTe thin-film solar cells using carbon electrodes with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Hayashi, Ryoji; Ogawa, Yohei; Hosono, Aikyo; Doi, Makoto

    2015-04-01

    The effects of adding carbon nanotubes (CNTs) to carbon back electrodes in polycrystalline CdTe thin-film solar cells were investigated. The CNTs were prepared by arc discharge under atmospheric pressure. The conductivity of the obtained CNT film with a density of 1.65 g/cm3 was approximately 2.6 × 103 S/cm. In the CdTe solar cells using carbon back electrodes with CNTs, the fill factor (FF) was improved as a result of adding CNTs with a concentration of 1 to 5 wt %. The improvement of FF was mainly due to the decrease in the series resistance of the CdTe solar cell. Furthermore, the open-circuit voltage (VOC) was improved by the CNT addition. The improvement of VOC was probably due to the reduction of the back barrier at the back contact.

  11. Polycrystalline thin-film, cadmium-telluride solar cells fabricated by electrodeposition cells. Final subcontract report, March 20, 1992--April 27, 1995

    SciTech Connect

    Trefny, J.U.; Mao, D.; Kim, D.

    1995-10-01

    The objective of this project was to develop improved processes for the fabrication of CdTe/CdS polycrystalline thin film solar cells. The technique we used for the formation of CdTe, electrodeposition, was a non-vacuum, low-cost technique that is attractive for economic, large-scale production. Annealing effects and electrical properties are discussed.

  12. Nanophotonic light trapping in polycrystalline silicon thin-film solar cells using periodically nanoimprint-structured glass substrates

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Xavier, Jolly; Preidel, Veit; Wyss, Philippe; Sontheimer, Tobias; Rech, Bernd; Probst, Jürgen; Hülsen, Christoph; Löchel, Bernd; Erko, Alexei; Burger, Sven; Schmidt, Frank; Back, Franziska; Rudigier-Voigt, Eveline

    2013-09-01

    A smart light trapping scheme is essential to tap the full potential of polycrystalline silicon (poly-Si) thin-film solar cells. Periodic nanophotonic structures are of particular interest as they allow to substantially surpass the Lambertian limit from ray optics in selected spectral ranges. We use nanoimprint-lithography for the periodic patterning of sol-gel coated glass substrates, ensuring a cost-effective, large-area production of thin-film solar cell devices. Periodic crystalline silicon nanoarchitectures are prepared on these textured substrates by high-rate silicon film evaporation, solid phase crystallization and chemical etching. Poly-Si microhole arrays in square lattice geometry with an effective thickness of about 2μm and with comparatively large pitch (2 μm) exhibit a large absorption enhancement (A900nm = 52%) compared to a planar film (A900nm ~ 7%). For the optimization of light trapping in the desired spectral region, the geometry of the nanophotonic structures with varying pitch from 600 nm to 800 nm is tailored and investigated for the cases of poly-Si nanopillar arrays of hexagonal lattice geometry, exhibiting an increase in absorption in comparison to planar film attributed to nanophotonic wave optic effects. These structures inspire the design of prospective applications such as highly-efficient nanostructured poly-Si thin-film solar cells and large-area photonic crystals.

  13. Elastic properties of supported polycrystalline thin films and multilayers: An X-ray diffraction study

    SciTech Connect

    Goudeau, P.; Villain, P.; Tamura, N.; Renault, P.-O.; Badawi, K.F.; Padmore, H.A.

    2003-08-13

    Numerous experimental and theoretical studies have shown that thin film elastic behavior may be different from the bulk one due to size effects related to grain boundaries, free surfaces and interfaces. In addition, thin films often present high compressive residual stresses which may be responsible of thin film buckling. These two features will be discussed in this communication through recent x-ray diffraction experiments: in situ tensile testing for elastic constant analysis and scanning x-ray micro diffraction for stress relaxation measurements associated with film buckling.

  14. Polycrystalline Thin Film Photovoltaics: From the Laboratory to Solar Fields (Presentation)

    SciTech Connect

    von Roedern, B.; Ullal, H.; Zweibel, K.

    2006-05-01

    The conclusions of this report are that: (1) many issues how thin-film solar cells work remain unresolved, requiring further fundamental R and D effort; (2) commercial thin-film PV module production reached 29% in 2005 in the US, indicating much more rapid growth than crystalline Si PV; (3) commercial module performance is increasing based on current knowledge, more R and D will lead to further improvement; and (4) stability of thin-film modules is acceptable ({le} 1% per year power loss) if the right manufacturing processes are used for manufacturing.

  15. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    SciTech Connect

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-17

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 {mu}m, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  16. Deposition and characterization of polycrystalline silicon films on glass for thin film solar cells

    SciTech Connect

    Bergmann, R.B.; Krinke, J.; Strunk, H.P.; Werner, J.H.

    1997-07-01

    The authors deposit phosphorus-doped, amorphous Si by low pressure chemical vapor deposition and subsequently crystallize the films by furnace annealing at a temperature of 600 C. Optical in-situ monitoring allows one to control the crystallization process. Phosphorus doping leads to faster crystallization and a grain size enhancement with a maximum grain size of 15 {micro}m. Using transmission electron microscopy they find a log-normal grain size distribution in their films. They demonstrate that this distribution not only arises from solid phase crystallization of amorphous Si but also from other crystallization processes based on random nucleation and growth. The log-normal grain size distribution seems to be a general feature of polycrystalline semiconductors.

  17. Role of Polycrystalline Thin-Film PV Technologies in Competitive PV Module Markets: Preprint

    SciTech Connect

    von Roedern, B.; Ullal, H. S.

    2008-05-01

    This paper discusses the developments in thin-film PV technologies and provides an outlook on future commercial module efficiencies achievable based on today's knowledge about champion cell performance.

  18. Optical properties of vacuum evaporated Cd xSn 1-xSe polycrystalline thin films: influence of composition and thickness

    NASA Astrophysics Data System (ADS)

    Padiyan, D. Pathinettam; Marikani, A.; Murali, K. R.

    2005-03-01

    Polycrystalline Cd xSn 1-xSe material is synthesized by melt growth technique for various x values and thin films are prepared by vacuum evaporation technique. Optical transmittance measurements have been made on thin films of Cd xSn 1-xSe, with x=0,0.3,0.75 and 1 for various thicknesses. The studies reveal that these thin films have a direct allowed band gap energy and the indirect band gap energy is improbable. The band gap energy increases with decrease in thickness in all the compositions and it is attributed to the quantum size effect.

  19. Progress Toward a Stabilization and Preconditioning Protocol for Polycrystalline Thin-Film Photovoltaic Modules

    SciTech Connect

    del Cueto, J. A.; Deline, C. A.; Rummel, S. R.; Anderberg, A.

    2010-08-01

    Cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) thin-film photovoltaic (PV) modules can exhibit substantial variation in measured performance depending on prior exposure history. This study examines the metastable performance changes in these PV modules with the goal of establishing standard preconditioning or stabilization exposure procedures to mitigate measured variations prior to current-voltage (IV) measurements.

  20. Anisotropic and inhomogeneous thermal conduction in suspended thin-film polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Sood, Aditya; Cho, Jungwan; Hobart, Karl D.; Feygelson, Tatyana I.; Pate, Bradford B.; Asheghi, Mehdi; Cahill, David G.; Goodson, Kenneth E.

    2016-05-01

    While there is a great wealth of data for thermal transport in synthetic diamond, there remains much to be learned about the impacts of grain structure and associated defects and impurities within a few microns of the nucleation region in films grown using chemical vapor deposition. Measurements of the inhomogeneous and anisotropic thermal conductivity in films thinner than 10 μm have previously been complicated by the presence of the substrate thermal boundary resistance. Here, we study thermal conduction in suspended films of polycrystalline diamond, with thicknesses ranging between 0.5 and 5.6 μm, using time-domain thermoreflectance. Measurements on both sides of the films facilitate extraction of the thickness-dependent in-plane ( κ r ) and through-plane ( κ z ) thermal conductivities in the vicinity of the coalescence and high-quality regions. The columnar grain structure makes the conductivity highly anisotropic, with κ z being nearly three to five times as large as κ r , a contrast higher than that reported previously for thicker films. In the vicinity of the high-quality region, κ r and κ z range from 77 ± 10 W/m-K and 210 ± 50 W/m-K for the 1 μm thick film to 130 ± 20 W/m-K and 710 ± 120 W/m-K for the 5.6 μm thick film, respectively. The data are interpreted using a model relating the anisotropy to the scattering on the boundaries of columnar grains and the evolution of the grain size considering their nucleation density and spatial rate of growth. This study aids in the reduction in the near-interfacial resistance of diamond films and efforts to fabricate diamond composites with silicon and GaN for power electronics.

  1. Preferred orientation in polycrystalline Cu(In,Ga)Se{sub 2} and its effect on absorber thin-films and devices

    SciTech Connect

    Contreras, M. A.; Jones, K. M.; Gedvilas, L.; Matson, R.

    2000-05-15

    The purpose of this work is to investigate physical properties of Cu(In,Ga)Se{sub 2} polycrystalline thin-films exhibiting a high degree of preferred orientation. Specifically, by using Na-free Cu(In,Ga)Se{sub 2} thin-films, it is intended to experimentally determine differences (if any) between films with a (110/102)-preferred orientation and films with a (112)-preferred orientation. The approach to the problem is a systematic comparative analysis of film and device properties in which the most significant variable is the preferred orientation of the Cu(In,Ga)Se{sub 2} polycrystalline absorbers. To complement the results of Na-free absorbers and devices, a microstructural analysis is presented on (110)-oriented high efficiency Cu(In,Ga)Se{sub 2} absorbers that are grown on standard Mo-coated soda-lime glass substrates.

  2. Influence of molecular structure and microstructure on device performance of polycrystalline pentacene thin-film transistors

    NASA Astrophysics Data System (ADS)

    Cheng, Horng-Long; Mai, Yu-Shen; Chou, Wei-Yang; Chang, Li-Ren

    2007-04-01

    The authors have fabricated the pentacene thin films on polymethylmethacrylate (PMMA) and on silicon dioxide dielectric surfaces featuring similar surface energy and surface roughness. On both surfaces the pentacene films displayed high crystal quality from x-ray diffraction scans, although the film on PMMA had significantly smaller grain size. The pentacene transistors with PMMA exhibited excellent electrical characteristics, including high mobility of above 1.1cm2/Vs, on/off ratio above 106, and sharp subthreshold slope below 1V/decade. The analysis of molecular microstructure of the pentacene films provided a reasonable explanation for the high performance using resonance micro-Raman spectroscopy.

  3. Metal-organic chemical vapour deposition of polycrystalline tetragonal indium sulphide (InS) thin films

    NASA Technical Reports Server (NTRS)

    Macinnes, Andrew N.; Cleaver, William M.; Barron, Andrew R.; Power, Michael B.; Hepp, Aloysius F.

    1992-01-01

    The dimeric indium thiolate /(t Bu)2In(mu-S sup t Bu)/2 has been used as a single-source precursor for the MOCVD of InS thin films. The dimeric In2S2 core is proposed to account for the formation of the nonequilibrium high-pressure tetragonal phase in the deposited films. Analysis of the deposited films has been obtained by TEM, with associated energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy.

  4. Structural and optical properties of (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin film alloys

    SciTech Connect

    Boyle, J. H.; Shafarman, W. N.; Birkmire, R. W.; McCandless, B. E.

    2014-06-14

    The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined a{sub o} lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined c{sub o} lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derived from transmission and reflection measurements, widened with increasing Ag and Ga content, due to influences from anion displacement and cation electronegativity, as expected from theoretical considerations for pseudo-binary chalcopyrite compounds.

  5. Effect of bottom electrodes on nanoscale switching characteristics and piezoelectric response in polycrystalline BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Yan, F.; Zhu, T. J.; Lai, M. O.; Lu, L.

    2011-10-01

    We have investigated the nanoscale switching characteristics and piezoelectric response based on polycrystalline BiFeO3 (BFO) thin films with different orientations deposited on different oxide bottom electrodes. The BFO film deposited on the LaNiO3 (LNO)-coated Si substrate shows a (001) preferred orientation and higher ferroelectric properties, while the BFO film grown on the SrRuO3 (SRO) buffered Si substrate shows a random orientation. The domain structures have been determined via piezoresponse force microscopy (PFM) for both films, predicting that the BFO film with the LNO bottom electrode has a larger piezoelectricity property corresponding to the ferroelastic domain. Through local switching spectroscopy measurements, the evidence of ferroelectric switching and the origin of the enhanced piezoresponse properties have been provided. A greatly improved piezoelectric response has been demonstrated using PFM that is 66.8 pm V-1 for the BFO with a SRO bottom electrode, while we obtain a value of 348.2 pm V-1 for the BFO with a LNO bottom electrode due to the increased density of the polarization vectors along the external electrical field.

  6. Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

    NASA Astrophysics Data System (ADS)

    Saci, Lynda; Mahamdi, Ramdane; Mansour, Farida; Boucher, Jonathan; Collet, Maéva; Bedel Pereira, Eléna; Temple-Boyer, Pierre

    2011-05-01

    The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B-N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

  7. Stable, high-efficiency, CuInSe2-based, polycrystalline, thin-film tandem solar cells

    NASA Astrophysics Data System (ADS)

    Birkmire, R. W.; Phillips, J. E.

    1987-10-01

    The long-term objective of this research was to obtain a stable, thin-film solar cell based on polycrystalline materials with an efficiency of 15 percent. The approach was to make a tandem cell based on CuInSe2/CdS as the bottom cell and CdTe/CdS as the top cell. An essential feature was to develop a CdTe cell with transport contacts. A suitable contacting system was developed using transparent conducting oxides (ITO and SnO2) in conjunction with a thin layer of copper. Cells were made with efficiencies over 8.5 percent. A reproducible fabrication process for CuInSe2/(CdZn)S cells was developed based on CuInSe2 films grown by vacuum evaporation using Knudsen-type effusion sources. These cells were made with efficiencies over 10 percent. The composition of the CuInSe2 films can be varied over a considerable range and still yield high-efficiency cells. Adding Zn to the CdS did not increase the V(sub oc) of the devices; analysis showed that the V(sub oc) is not controlled by interface recombination. The effect of oxidizing and reducing heat treatments on CuInSe2 cells is to change carrier concentration and thus V(sub oc). Analysis suggests that J(sub o) is controlled by band-to-band recombination. Monolithic tandem CuInSe2 CdTe cells have been made with efficiencies of approximately 3 percent, demonstrating the feasibility of this approach.

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

    NASA Technical Reports Server (NTRS)

    Kim, Namsoo P.; Stanbery, Billy J.; Gale, Ronald P.; Mcclelland, Robert W.

    1989-01-01

    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.

  9. Tutorial: Understanding residual stress in polycrystalline thin films through real-time measurements and physical models

    NASA Astrophysics Data System (ADS)

    Chason, Eric; Guduru, Pradeep R.

    2016-05-01

    Residual stress is a long-standing issue in thin film growth. Better understanding and control of film stress would lead to enhanced performance and reduced failures. In this work, we review how thin film stress is measured and interpreted. The results are used to describe a comprehensive picture that is emerging of what controls stress evolution. Examples from multiple studies are discussed to illustrate how the stress depends on key parameters (e.g., growth rate, material type, temperature, grain size, morphology, etc.). The corresponding stress-generating mechanisms that have been proposed to explain the data are also described. To develop a fuller understanding, we consider the kinetic factors that determine how much each of these processes contributes to the overall stress under different conditions. This leads to a kinetic model that can predict the dependence of the stress on multiple parameters. The model results are compared with the experiments to show how this approach can explain many features of stress evolution.

  10. Research on polycrystalline thin-film CuGaInSe[sub 2] solar cells

    SciTech Connect

    Stanbery, B.J.; Chen, W.S.; Devaney, W.E.; Stewart, J.W. . Defense and Space Systems Group)

    1992-11-01

    This report describes research to fabricate high-efficiency CdZnS/CuInGaSe[sub 2] (CIGS) thin-film solar cells, and to develop improved transparent conductor window layers such as ZnO. A specific technical milestone was the demonstration of an air mass (AM) 1.5 global, 13% efficient, 1-cm[sup 2]-total-area CIGS thin-film solar cell. Our activities focused on three areas. First, a CIGS deposition: system was modified to double its substrate capacity, thus increasing throughput, which is critical to speeding the process development by providing multiple substrates from the same CIGS run. Second, new tooling was developed to enable an investigation of a modified aqueous CdZnS process. The goal was to improve the yield of this critical step in the device fabrication process. Third, our ZnO sputtering system was upgraded to improve its reliability, and the sputtering parameters were further optimized to improve its properties as a transparent conducting oxide. The characterization of the new CIGS deposition system substrate fixturing was completed, and we produced good thermal uniformity and adequately high temperatures for device-quality CIGS deposition. Both the CIGS and ZnO deposition processes were refined to yield a ZnO//Cd[sub 0.82]Zn[sub 0.18]S/CuIn[sub 0.80]Ga[sub 0.20]Se[sub 2] cell that was verified at NREL under standard testing conditions at 13.1% efficiency with V[sub oc] = 0.581 V, J[sub sc] = 34.8 mA/cm[sup 2], FF = 0.728, and a cell area of 0.979 cm[sup 2].

  11. Thin film polycrystalline silicon solar cells. Second technical progress report, July 16, 1980-October 15, 1980

    SciTech Connect

    1980-10-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts have been directed to the purification of metallurgical silicon, the preparation and characterization of substrates and epitaxial silicon layers, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been further investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was determined and compared with the impurity content in metallurgical silicon. The effects of heat treatment on the impurity distribution in the substrate and in the epitaxial layer have also been investigated. Large area (30 to 60 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by depositing a p-n junction structure using the thermal reduction of trichlorosilane containing appropriate dopants. The AM1 efficiencies are about 9% for cells of 30 to 35 cm/sup 2/ area. Larger area, 60 cm/sup 2/, thin film solar cells have been fabricated for the first time, and their AM1 efficiencies are slightly higher than 8%. The spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation in a number of solr cells have been measured.

  12. Development of stable high efficiency polycrystalline thin-film solar cells based on CulnSe/sub 2/. Final report, 16 March 1983-15 March 1984

    SciTech Connect

    Birkmire, R.W.; Hall, R.B.; Phillips, J.E.; Meakin, J.D.

    1985-03-01

    A two-junction, monolithic, optically and electrically coupled solar cell has been designed and a successful prototype produced. Each junction is a thin-film polycrystalline cell, namely, CuInSe/sub 2//(CdZn)S and CdTe/(CdZn)S. All active semi-conductor layers are produced by physical vapor deposition. During this contract year, a procedure for producing thin-film p-type CdTe by physical vapor deposition and a usable transparent interconnect for the tandem cell were developed.

  13. Metastability of copper indium gallium diselenide polycrystalline thin film solar cell devices

    NASA Astrophysics Data System (ADS)

    Lee, Jinwoo

    High efficiency thin film solar cells have the potential for being a world energy solution because of their cost-effectiveness. Looking to the future of solar energy, there is the opportunity and challenge for thin film solar cells. The main theme of this research is to develop a detailed understanding of electronically active defect states and their role in limiting device performance in copper indium gallium diselenide (CIGS) solar cells. Metastability in the CIGS is a good tool to manipulate electronic defect density and thus identify its effect on the device performance. Especially, this approach keeps many device parameters constant, including the chemical composition, grain size, and interface layers. Understanding metastability is likely to lead to the improvement of CIGS solar cells. We observed systematic changes in CIGS device properties as a result of the metastable changes, such as increases in sub-bandgap defect densities and decreases in hole carrier mobilities. Metastable changes were characterized using high frequency admittance spectroscopy, drive-level capacitance profiling (DLCP), and current-voltage measurements. We found two distinctive capacitance steps in the high frequency admittance spectra that correspond to (1) the thermal activation of hole carriers into/out of acceptor defect and (2) a temperature-independent dielectric relaxation freeze-out process and an equivalent circuit analysis was employed to deduce the dielectric relaxation time. Finally, hole carrier mobility was deduced once hole carrier density was determined by DLCP method. We found that metastable defect creation in CIGS films can be made either by light-soaking or with forward bias current injection. The deep acceptor density and the hole carrier density were observed to increase in a 1:1 ratio, which seems to be consistent with the theoretical model of VCu-V Se defect complex suggested by Lany and Zunger. Metastable defect creation kinetics follows a sub-linear power law

  14. Thin film polycrystalline silicon solar cells: first technical progress report, April 15, 1980-July 15, 1980

    SciTech Connect

    1980-07-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts during the past quarter have been directed to the purification of metallurgical silicon, the preparation of substrates, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was also determined. Large area (> 30 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by the thermal reduction of trichlorosilane containing appropriate dopants. Chemically deposited tin-dioxide films were used as antireflection coatings. Solar cells with AM1 efficiencies of about 8.5% have been obtained. Their spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation have been measured.

  15. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    NASA Astrophysics Data System (ADS)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  16. Electrochemical characterisation of copper thin-film formation on polycrystalline platinum.

    PubMed

    Berkes, Balázs B; Henry, John B; Huang, Minghua; Bondarenko, Alexander S

    2012-09-17

    Electrochemically formed thin films are vital for a broad range of applications in virtually every field of modern science and technology. Understanding the film formation process could provide a means to aid the characterisation and control of film properties. Herein, we present a fundamental approach that combines two well-established analytical techniques (namely, electrochemical impedance spectroscopy and electrogravimetry) with a theoretical approach to provide physico-chemical information on the electrode/electrolyte interface during film formation. This approach allows the monitoring of local and overall surface kinetic parameters with time to enable an evaluation of the different modes of film formation. This monitoring is independent of surface area and surface concentrations of electroactive species and so may allow current computational methods to calculate these parameters and provide a deeper physical understanding of the electrodeposition of new bulk phases. The ability of this method to characterise 3D phase growth in situ in more detail than that obtained by conventional approaches is demonstrated through the study of a model system, namely, Cu bulk-phase deposition on a Pt electrode covered with a Cu atomic layer (Cu(ad)/Pt). PMID:22730305

  17. Polycrystalline thin film cadmium telluride solar cells fabricated by electrodeposition. Annual technical report, 20 March 1995--19 March 1996

    SciTech Connect

    Trefny, J U; Mao, D

    1997-04-01

    The objective of this project is to develop improved processes for fabricating CdTe/CdS polycrystalline thin-film solar cells. Researchers used electrodeposition to form CdTe; electrodeposition is a non-vacuum, low-cost technique that is attractive for economic, large-scale production. During the past year, research and development efforts focused on several steps that are most critical to the fabricating high-efficiency CdTe solar cells. These include the optimization of the CdTe electrodeposition process, the effect of pretreatment of CdS substrates, the post-deposition annealing of CdTe, and back-contact formation using Cu-doped ZnTe. Systematic investigations of these processing steps have led to a better understanding and improved performance of the CdTe-based cells. Researchers studied the structural properties of chemical-bath-deposited CdS thin films and their growth mechanisms by investigating CdS samples prepared at different deposition times; investigated the effect of CdCl{sub 2} treatment of CdS films on the photovoltaic performance of CdTe solar cells; studied Cu-doped ZnTe as a promising material for forming stable, low-resistance contacts to the p-type CdTe; and investigated the effect of CdTe and CdS thickness on the photovoltaic performance of the resulting cells. As a result of their systematic investigation and optimization of the processing conditions, researchers improved the efficiency of CdTe/CdS cells using ZnTe back-contact and electrodeposited CdTe. The best CdTe/CdS cell exhibited a V{sub oc} of 0.778 V, a J{sub sc} of 22.4 mA/cm{sup 2}, a FF of 74%, and an efficiency of 12.9% (verified at NREL). In terms of individual parameters, researchers obtained a V{sub oc} over 0.8 V and a FF of 76% on other cells.

  18. Improvement in pH Sensitivity of Low-Temperature Polycrystalline-Silicon Thin-Film Transistor Sensors Using H2 Sintering

    PubMed Central

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si–OH2+ and Si–O− bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  19. Improvement in pH sensitivity of low-temperature polycrystalline-silicon thin-film transistor sensors using H2 sintering.

    PubMed

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si-OH2(+) and Si-O(-) bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  20. Metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor technology and application to flat-panel displays

    NASA Astrophysics Data System (ADS)

    Meng, Zhiguo

    High quality flat-panel displays (FPD) typically use active-matrix (AM) addressing, with the optical state of each pixel controlled by one or more active devices such as amorphous silicon (a-Si) thin film transistors (TFT). The successful examples are portable computer and liquid-crystal television (LC-TV). A high level of system on panel (SoP) electronic integration is required for versatile and compact systems. Meanwhile, many self-emitting display technologies are developing fast, active matrix for self-emitting display is typically current driven. The a-Si TFTs suffer from limited current driving capability, polycrystalline silicon (poly-Si) device technology is required. A new technology employing metal-induced unilaterally crystallization (MIUC) is presently reported. The device characteristics are obviously better than those in rapid-thermal annealed (RTA) and solid-phase crystallization (SPC) TFTs and the fabrication equipment is much cheaper than excimer laser crystallization (ELC) technology. The field effect mobility (muFE) of p- and n-channel MIUC TFTs is about 100cm2/Vs. Ion/I off is more than seven orders. Gate-induced leakage current in LT-MIUC poly-Si TFTs has been reduced by crystallization before heavy junction implantation to improve material quality and incorporating a gate-modulated lightly-doped drain (gamo-LDD) structure to reduce the electric field near the drain/channel junction region. At the same time, recrystallized (RC) MIUC TFT was researched with device characteristics improved. The 6.6cm 120 x 160 active matrix for OLED display is fabricated using LT-MIUC TFT technology on glass substrate. This display has the advantages of self-emitting, large intrinsic view angle and very fast response. At the same time, 6.6cm 120X160 AM-reflective twist nematic (RTN) display is fabricated using RC-MIUC TFT technology. This display is capable of producing 16 grade levels, 10:1 contrast and video image. The SOP display for AM-OLED were designed

  1. Effects of reductive annealing on insulating polycrystalline thin films of Nb-doped anatase TiO2: recovery of high conductivity

    NASA Astrophysics Data System (ADS)

    Nakao, Shoichiro; Hirose, Yasushi; Hasegawa, Tetsuya

    2016-02-01

    We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb-doped TiO2 (TNO). The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 °C. Reduced free carrier absorption in the insulating TNO films indicated carrier compensation due to excess oxygen. With H2-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.

  2. Thin polycrystalline diamond films protecting zirconium alloys surfaces: From technology to layer analysis and application in nuclear facilities

    NASA Astrophysics Data System (ADS)

    Ashcheulov, P.; Škoda, R.; Škarohlíd, J.; Taylor, A.; Fekete, L.; Fendrych, F.; Vega, R.; Shao, L.; Kalvoda, L.; Vratislav, S.; Cháb, V.; Horáková, K.; Kůsová, K.; Klimša, L.; Kopeček, J.; Sajdl, P.; Macák, J.; Johnson, S.; Kratochvílová, I.

    2015-12-01

    Zirconium alloys can be effectively protected against corrosion by polycrystalline diamond (PCD) layers grown in microwave plasma enhanced linear antenna chemical vapor deposition apparatus. Standard and hot steam oxidized PCD layers grown on Zircaloy2 surfaces were examined and the specific impact of polycrystalline Zr substrate surface on PCD layer properties was investigated. It was found that the presence of the PCD coating blocks hydrogen diffusion into the Zircaloy2 surface and protects Zircaloy2 material from degradation. PCD anticorrosion protection of Zircaloy2 can significantly prolong life of Zircaloy2 material in nuclear reactors even at temperatures above Zr phase transition temperatures.

  3. Atomic-resolution characterization of the effects of CdCl{sub 2} treatment on poly-crystalline CdTe thin films

    SciTech Connect

    Paulauskas, T. Buurma, C.; Colegrove, E.; Guo, Z.; Sivananthan, S.; Klie, R. F.

    2014-08-18

    Poly-crystalline CdTe thin films on glass are used in commercial solar-cell superstrate devices. It is well known that post-deposition annealing of the CdTe thin films in a CdCl{sub 2} environment significantly increases the device performance, but a fundamental understanding of the effects of such annealing has not been achieved. In this Letter, we report a change in the stoichiometry across twin boundaries in CdTe and propose that native point defects alone cannot account for this variation. Upon annealing in CdCl{sub 2}, we find that the stoichiometry is restored. Our experimental measurements using atomic-resolution high-angle annular dark field imaging, electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope are supported by first-principles density functional theory calculations.

  4. Atomic-resolution characterization of the effects of CdCl2 treatment on poly-crystalline CdTe thin films

    NASA Astrophysics Data System (ADS)

    Paulauskas, T.; Buurma, C.; Colegrove, E.; Guo, Z.; Sivananthan, S.; Chan, M. K. Y.; Klie, R. F.

    2014-08-01

    Poly-crystalline CdTe thin films on glass are used in commercial solar-cell superstrate devices. It is well known that post-deposition annealing of the CdTe thin films in a CdCl2 environment significantly increases the device performance, but a fundamental understanding of the effects of such annealing has not been achieved. In this Letter, we report a change in the stoichiometry across twin boundaries in CdTe and propose that native point defects alone cannot account for this variation. Upon annealing in CdCl2, we find that the stoichiometry is restored. Our experimental measurements using atomic-resolution high-angle annular dark field imaging, electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope are supported by first-principles density functional theory calculations.

  5. Structural characterization and optical properties of Sol-gel-derived polycrystalline Pb(Zr0.35Ti0.65)O3 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Zhang, Rong Jun; Wang, Zi Yi; Zheng, Yu Xiang; Wang, Song You; Zhao, Hai Bin; Chen, Liang Yao; Liu, Xiao Bin; Jiang, An Quan

    2013-07-01

    Polycrystalline Pb(Zr0.35Ti0.65)O3 thin films prepared on Pt/Ti/SiO2/Si substrate by using solgel technique were characterized by using X-ray diffraction (XRD) and atomic force microscopy (AFM). The optical properties of the films were investigated by using spectroscopic ellipsometry (SE) with a four-phase optical model, air/roughness layer/PZT layer/Pt layer in the spectral range of 300-800 nm. The optical band gap of the films calculated following the Tauc's Law was smaller than that of an amorphous PZT thin film with some microcrystals existing on the surface. The result indicates that the quantum-size effect leads to an increase in band gap when the crystalline dimensions become very small.

  6. Enhanced mobility of solution-processed polycrystalline zinc tin oxide thin-film transistors via direct incorporation of water into precursor solution

    NASA Astrophysics Data System (ADS)

    Huang, Genmao; Duan, Lian; Zhao, Yunlong; Dong, Guifang; Zhang, Deqiang; Qiu, Yong

    2014-09-01

    Phase transition and the consequent variation in crystalline orientation of metal oxides have profound impact on their transport properties. In this work, we report a simple method to enhance field-effect mobility of solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) via direct incorporation of water into precursor solution. It is confirmed H2O molecules could effectively facilitate the conversion and alloying processes during ZTO film formation, characterized by the enhancement of spinel Zn2SnO4 phase and the reduction of cassiterite SnO2 phase. The preferred orientation of metal oxide crystallites varies according to the amount of water added into precursor solutions. Smooth and densely packed polycrystalline ZTO films with only a few organic residuals and moderate oxygen defects are fabricated from water-containing precursor solutions. With the incorporation of 1.67 M H2O, the extracted field-effect mobility of TFT devices could be improved by a factor of 2.3, from 0.92 to 2.11 cm2 V-1 s-1. This work offers a facile and cost-effective route towards high-mobility TFTs based on solution-processed polycrystalline metal oxide thin films.

  7. Strain evolution of each type of grains in poly-crystalline (Ba,Sr)TiO3 thin films grown by sputtering

    NASA Astrophysics Data System (ADS)

    Park, Woo Young; Park, Min Hyuk; Lee, Jong Ho; Yoon, Jung Ho; Han, Jeong Hwan; Choi, Jung-Hae; Hwang, Cheol Seong

    2012-12-01

    The strain states of [111]-, [110]-, and [002]-oriented grains in poly-crystalline sputtered (Ba,Sr)TiO3 thin films on highly [111]-oriented Pt electrode/Si substrates were carefully examined by X-ray diffraction techniques. Remarkably, [002]-oriented grains respond more while [110]- and [111]-oriented grains do less than the theoretically estimated responses, which is understandable from the arrangement of the TiO6 octahedra with respect to the stress direction. Furthermore, such mechanical responses are completely independent of the degree of crystallization and film thickness. The transition growth temperature between the positive and negative strains was also different depending on the grain orientation. The unstrained lattice parameter for each type of grain was different suggesting that the oxygen vacancy concentration for each type of grain is different, too. The results reveal that polycrystalline (Ba,Sr)TiO3 thin films are not an aggregation of differently oriented grains which simply follow the mechanical behavior of single crystal with different orientations.

  8. Large-Scale PV Module Manufacturing Using Ultra-Thin Polycrystalline Silicon Solar Cells: Final Subcontract Report, 1 April 2002--28 February 2006

    SciTech Connect

    Wohlgemuth, J.; Narayanan, M.

    2006-07-01

    The major objectives of this program were to continue advances of BP Solar polycrystalline silicon manufacturing technology. The Program included work in the following areas. (1) Efforts in the casting area to increase ingot size, improve ingot material quality, and improve handling of silicon feedstock as it is loaded into the casting stations. (2) Developing wire saws to slice 100-..mu..m-thick silicon wafers on 290-..mu..m-centers. (3) Developing equipment for demounting and subsequent handling of very thin silicon wafers. (4) Developing cell processes using 100-..mu..m-thick silicon wafers that produce encapsulated cells with efficiencies of at least 15.4% at an overall yield exceeding 95%. (5) Expanding existing in-line manufacturing data reporting systems to provide active process control. (6) Establishing a 50-MW (annual nominal capacity) green-field Mega-plant factory model template based on this new thin polycrystalline silicon technology. (7) Facilitating an increase in the silicon feedstock industry's production capacity for lower-cost solar-grade silicon feedstock..

  9. [Spectral analyzing effects of atmosphere states on the structure and characteristics of CdTe polycrystalline thin films made by close-spaced sublimation].

    PubMed

    Zheng, Hua-jing; Zheng, Jia-gui; Feng, Liang-huan; Zhang, Jing-quan; Xie, Er-qing

    2005-07-01

    The structure and characteristics of CdTe thin films are dependent on the working atmosphere states in close-spaced sublimation. In the present paper, CdTe polycrystalline thin films were deposited by CSS in mixture atmosphere of argon and oxygen. The physical mechanism of CSS was analyzed, and the temperature distribution in CSS system was measured. The dependence of preliminary nucleus creation on the atmosphere states (involving component and pressure) was studied. Transparencies were measured and optic energy gaps were calculated. The results show that: (1) The CdTe films deposited in different atmospheres are cubic structure. With increasing oxygen concentration, a increases and reaches the maximum at 6% oxygen concentration, then reduces, and increases again after passing the point at 12% oxygen concentration. Among them, the sample depositing at 9% oxygen concentration is the best. The optic energy gaps are 1.50-1.51 eV for all CdTe films. (2) The samples depositing at different pressures at 9% oxygen concentration are all cubical structure of CdTe, and the diffraction peaks of CdS and SnO2:F still appear. With the gas pressure increasing, the crystal size of CdTe minishes, the transparency of the thin film goes down, and the absorption side shifts to the short-wave direction. (3) The polycrystalline thin films with high quality deposit in 4 minutes under the depositing condition that the substrate temperature is 550 degrees C, and source temperature is 620 degrees C at 9% oxygen concentration. PMID:16241058

  10. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    NASA Astrophysics Data System (ADS)

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-04-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at ‑0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature.

  11. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    PubMed Central

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-01-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at −0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature. PMID:27098115

  12. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor.

    PubMed

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-01-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at -0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm(2)/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature. PMID:27098115

  13. Electrical Characteristics of Low-Temperature Polycrystalline Silicon Complementary Metal-Oxide-Semiconductor Thin-Film Transistors with Six-Step Photomask Structure

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Jin; Park, Jae-Hoon; Oh, Kum-Mi; Lee, Seok-Woo; Lee, Kyung-Eon; Shin, Woo-Sup; Jun, Myung-chul; Yang, Yong-Suk; Hwang, Yong-Kee

    2011-06-01

    We propose two types of six-step photomask, complementary metal-oxide-semiconductor (CMOS), thin-film transistor (TFT) PCT device structures in order to simplify their fabrication process compared with that of conventional, low-temperature, polycrystalline silicon (LTPS) CMOS TFT devices. The initial charge transfer characteristics of both types of six-step PCT are equivalent to those of the conventional nine-step PCT. Both types of six-step PCT are comparable to the conventional nine-step mask lightly doped drain (LDD) device in terms of the dc device lifetime of over 10 years at Vds=5 V for line inversion driving, which is the normally recognized duration time for semiconducting devices.

  14. Mechanical stress induced voltage shift in polycrystalline Bi3.25La0.75Ti3O12 thin films

    NASA Astrophysics Data System (ADS)

    Wu, Xiumei; Zhai, Ya; Kan, Yi; Lu, Xiaomei; Zhu, Jinsong

    2009-10-01

    Imprint behavior of polycrystalline Bi3.25La0.75Ti3O12 thin films under stress was studied. The voltage shift along the positive voltage axis can be depressed by tensile stress while increased by compressive stress. With the measured voltage increasing, the voltage shift referred above increases and the increase trend gets enhanced under both compressive and tensile stress compared with that at zero stress. The asymmetric distribution of the trapped charged in films, which is caused by the increase of the in-plane polarization component for the domain reorientation induced by stress or for the voltage-assisted domain walls depinning, was considered the contribution to the voltage shift.

  15. Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

    DOEpatents

    Findikoglu, Alp T.; Jia, Quanxi; Arendt, Paul N.; Matias, Vladimir; Choi, Woong

    2009-10-27

    A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

  16. Photovoltaic mechanisms in polycrystalline thin film silicon solar cells. Final report, 30 June 1979-29 June 1980

    SciTech Connect

    Sopori, B.L.

    1980-11-01

    The objectives of this program were: (1) to develop appropriate measurement techniques to facilitate a quantitative study of the electrical activity of structural defects and at a grain boundary (G.B.) in terms of generation-recombination, barrier height, and G.B. conductivity; (2) to characterize G.B.s in terms of physical properties such as angle of misfit and local stress, and to correlate them with the electrical activity; (3) to determine the influence of solar cell processing on the electrical behavior of structural defects and G.B.s; and (4) to evaluate polycrystalline solar cell performance based on the above study, and to compare it with the experimentally measured performance. Progress is reported in detail. (WHK)

  17. Calculating Optical Absorption Spectra of Thin Polycrystalline Organic Films: Structural Disorder and Site-Dependent van der Waals Interaction

    PubMed Central

    2015-01-01

    We propose a new approach for calculating the change of the absorption spectrum of a molecule when moved from the gas phase to a crystalline morphology. The so-called gas-to-crystal shift Δm is mainly caused by dispersion effects and depends sensitively on the molecule’s specific position in the nanoscopic setting. Using an extended dipole approximation, we are able to divide Δm= −QWm in two factors, where Q depends only on the molecular species and accounts for all nonresonant electronic transitions contributing to the dispersion while Wm is a geometry factor expressing the site dependence of the shift in a given molecular structure. The ability of our approach to predict absorption spectra is demonstrated using the example of polycrystalline films of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI). PMID:25834658

  18. Investigation of photovoltaic mechanisms in polycrystalline thin-film solar cells. Interim technical report, November 1, 1980-July 31, 1981

    SciTech Connect

    Temofonte, T. A.; Szedon, J. R.; O'Keeffe, T. W.

    1982-03-05

    Effort is reported on measurement technique development to assess the utility of Deep-Level Transient Spectroscopy (DLTS) methods in characterizing polycrystalline silicon that was deliberately doped with Ti during growth. Difficulties encountered with lateral DLTS measurements are discussed. In this approach, modulation of the grain boundary, double-depletion region produces the entire DLTS signal. Major effort has been applied in grain boundary characterization and control. The most significant accomplishments to date have involved laser scanning of slices of Wacker SILSO polysilicon having nearly identical grain structure. By using various kinds of treatments and by comparing treated and untreated substrates having nearly identical grain structure, control of grain boundary photocurrent suppression (..delta..I/sub ph/) over the range 1% less than or equal to ..delta..I/sub ph/ less than or equal to 40% was demonstrated.

  19. Carrier mobility measurement across a single grain boundary in polycrystalline silicon using an organic gate thin-film transistor

    SciTech Connect

    Hashimoto, Masaki; Kanomata, Kensaku; Momiyama, Katsuaki; Kubota, Shigeru; Hirose, Fumihiko

    2012-01-09

    In this study, we developed a measurement method for field-effect-carrier mobility across a single grain boundary in polycrystalline Si (poly Si) used for solar cell production by using an organic gate field-effect transistor (FET). To prevent precipitation and the diffusion of impurities affecting the electronic characteristics of the grain boundary, all the processing temperatures during FET fabrication were held below 150 deg. C. From the grain boundary, the field-effect mobility was measured at around 21.4 cm{sup 2}/Vs at 297 K, and the temperature dependence of the field-effect mobility suggested the presence of a potential barrier of 0.22 eV at the boundary. The technique presented here is applicable for the monitoring of carrier conduction characteristics at the grain boundary in poly Si used for the production of solar cells.

  20. Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

    SciTech Connect

    Nishikata, S.; Sadowski, J. T.; Al-Mahboob, A.; Nishihara, T.; Fujikawa, Y.; Sakurai, T.; Nakajima, K.; Sazaki, G.; Suto, S.

    2007-10-15

    Single-monolayer high pentacene (Pn) dendrites grown on a hydrogen-terminated Si(111) surface [H-Si(111)] under ultrahigh vacuum were observed by low-energy electron microscopy and microbeam low-energy electron diffraction analyses. We determined the epitaxial structure (type I) inside a unique polycrystalline domain structure of such dendrites, each of which has six equivalent epitaxial orientations of Pn two-dimensional (2D) unit cells. There are three sets of these cells, which are rotated {+-}120 deg. relative to each other. Domain boundaries inside each dendrite were successfully observed by scanning tunneling microscopy. In addition, we found another epitaxial relation (type II): the polycrystalline domain structure and lattice parameters are similar to those of the type-I dendrite; however, the 2D unit cells of the type-II dendrite are rotated approximately 90 deg. relative to those of the type-I dendrite. These results suggest that the crystal structure of the dendrites on H-Si(111) is determined mainly by the interaction between Pn molecules. Each dendrite is composed of domains that are exclusively of type I or II. The so-called point-on-line coincidences are found between the Pn 2D lattices of types I and II, and H-Si(111). The higher commensurability of the type-I dendrites than the type-II dendrites results in a higher probability of type-I dendrite formation. Moreover, for both the type-I and type-II dendrites, we found supercell structures. We estimated the minimum interface energy between the dendrite and H-Si(111) from an island's free energy, which is necessary to reproduce the growth of a single-monolayer high dendrite.

  1. Growth of (111) oriented NiFe{sub 2}O{sub 4} polycrystalline thin films on Pt (111) via sol-gel processing

    SciTech Connect

    Seifikar, Safoura; Sachet, Edward; Rawdanowicz, Thomas; Schwartz, Justin; Tabei, Ali; Bassiri-Gharb, Nazanin

    2012-09-15

    Polycrystalline NiFe{sub 2}O{sub 4} (NFO) thin films are grown on (111) platinized Si substrates via chemical solution processing. {theta}-2{theta} x-ray diffraction, x-ray pole figures and electron diffraction indicate that the NFO has a high degree of <111> uniaxial texture normal to the film plane. The texturing is initiated by nucleation of (111) planes at the Pt interface and is enhanced with decreasing film thickness. As the NFO magnetic easy-axis is <111>, the out-of-plane magnetization exhibits improved M{sub r}/M{sub s} and coercivity with respect to randomly oriented films on silicon substrates. The out-of-plane M{sub r}/M{sub s} ratio for (111) textured NFO thin film is improved from 30% in 150 nm-thick films to above 70% in 50 nm-thick films. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of comparable thickness deposited by pulsed laser deposition and sputtering.

  2. Polycrystalline silicon thin-film transistor with nickel-titanium oxide by sol-gel spin-coating and nitrogen implantation

    NASA Astrophysics Data System (ADS)

    Wu, Shih-Chieh; Hou, Tuo-Hung; Chuang, Shiow-Huey; Chou, Hsin-Chih; Chao, Tien-Sheng; Lei, Tan-Fu

    2012-12-01

    This study demonstrates polycrystalline silicon thin-film transistors (poly-Si TFTs) integrated with a high-κ nickel-titanium oxide (NiTiO3) gate dielectric using sol-gel spin-coating and nitrogen channel implantation. This novel fabrication method of the high-κ NiTiO3 gate dielectric offers thin equivalent-oxide thickness and high gate capacitance density, favorable for increasing the current driving capability. Introducing nitrogen ions into the poly-Si using implantation effectively passivates the trap states not only in the poly-Si channel but also at the gate dielectric/poly-Si interface. The poly-Si NiTiO3 TFTs with nitrogen implantation exhibit significantly improved electrical characteristics, including lower threshold voltage, a steeper subthreshold swing, higher field-effect mobility, a larger on/off current ratio, and less threshold-voltage roll-off. Furthermore, the nitrogen implantation improves the reliability of poly-Si NiTiO3 TFTs against hot-carrier stress and positive bias temperature instability.

  3. Polycrystalline BiFeO3 thin film synthesized via sol-gel assisted spin coating technique for photosensitive application

    NASA Astrophysics Data System (ADS)

    Bogle, K. A.; Narwade, R. D.; Phatangare, A. B.; Dahiwale, S. S.; Mahabole, M. P.; Khairnar, R. S.

    2016-05-01

    We are reporting photosensitivity property of BiFeO3 thin film under optical illumination. The thin film used for photosensitivity work was fabricated via sol-gel assisted spin coating technique. I-V measurements on the Cu/BiFeO3/Al structure under dark condition show a good rectifying property and show dramatic blue shit in threshold voltage under optical illumination. The microstructure, morphology and elemental analysis of the films were characterized by using XRD, UV-Vis, FTIR, SEM and EDS.

  4. Low Temperature Deposition of PECVD Polycrystalline Silicon Thin Films using SiF4 / SiH4 mixture

    NASA Astrophysics Data System (ADS)

    Syed, Moniruzzaman; Inokuma, Takao; Kurata, Yoshihiro; Hasegawa, Seiichi

    2016-03-01

    Polycrystalline silicon films with a strong (110) texture were prepared at 400°C by a plasma-enhanced chemical vapor deposition using different SiF4 flow rates ([SiF4] = 0-0.5 sccm) under a fixed SiH4 flow rate ([SiH4] = 1 or 0.15 sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), Atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4] and their respective maxima reach 90% and 900 Å. However, for [SiH4] = 0.15 sccm, both the crystallinity and the grain size decreased with [SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning.

  5. Dielectric dynamics of the polycrystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Pečnik, Tanja; Eršte, Andreja; Matavž, Aleksander; Bobnar, Vid; Ivanov, Maksim; Banys, Juras; Xiang, Feng; Wang, Hong; Malič, Barbara; Glinšek, Sebastjan

    2016-05-01

    Polycrystalline Ba0.5Sr0.5TiO3 films, with thicknesses between 90 and 600 nm, were prepared on alumina substrates at 900 °C by chemical solution deposition (CSD) and a dielectric spectroscopy investigation of the in-plane properties was performed. The 5-kHz permittivity ε‧ shows a non-monotonic thickness dependence, reaching 1230 at room temperature for the 310-nm-thick film, whose grain size is ∼75 nm. Its 15-GHz-value and losses are 1105 and 0.05, respectively. The temperature of the permittivity maximum T max at 5 kHz decreases with increasing thickness from 277 to 250 K for the 170- and 600-nm-thick films, respectively, which has been linked to the residual biaxial stress. A hysteresis is observed in the permittivity ε‧-electric field E DC characteristics in all the films up to ∼50 K above T max . Frequency dispersion in which permittivity decreases with increasing frequency is present below T max in films thicker than 90 nm. The high permittivity values of the thinnest films, which are among the highest reported in the (Ba,Sr)TiO3 films with grain sizes below 75 nm, are a direct proof of the optimized CSD processing conditions.

  6. High-performance flexible thin-film transistors fabricated using print-transferrable polycrystalline silicon membranes on a plastic substrate

    NASA Astrophysics Data System (ADS)

    Qin, Guoxuan; Yuan, Hao-Chih; Yang, Hongjun; Zhou, Weidong; Ma, Zhenqiang

    2011-02-01

    Inexpensive polycrystalline Si (poly-Si) with large grain size is highly desirable for flexible electronics applications. However, it is very challenging to directly deposit high-quality poly-Si on plastic substrates due to processing constrictions, such as temperature tolerance and residual stress. In this paper, we present our study on poly-Si membranes that are stress free and most importantly, are transferrable to any substrate including a low-temperature polyethylene terephthalate (PET) substrate. We formed poly-Si-on-insulator by first depositing small-grain size poly-Si on an oxidized Si wafer. We then performed high-temperature annealing for recrystallization to obtain larger grain size. After selective doping on the poly-Si-on-insulator, buried oxide was etched away. By properly patterning the poly-Si layer, residual stress in the released poly-Si membranes was completely relaxed. The flat membrane topology allows the membranes to be print transferred to any substrates. High-performance TFTs were demonstrated on the transferred poly-Si membranes on a PET substrate.

  7. Polycrystalline photovoltaic cell

    SciTech Connect

    Jordan, J.F.; Lampkin, C.M.

    1983-10-25

    A photovoltaic cell is disclosed, having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6 /SUB u/ thick) of underlying polycrystalline semiconductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

  8. Device physics of thin-film polycrystalline cells and modules: Phase 1 annual report: February 1998--January 1999

    SciTech Connect

    Sites, J. R.

    1999-12-21

    This report describes work done by Colorado State University (CSU) during Phase 1 of this subcontract. CSU researchers continued to make basic measurements on CI(G)S and CdTe solar cells fabricated at different labs, to quantitatively deduce the loss mechanisms in these cells, and to make appropriate comparisons that illuminate where progress is being made. Cells evaluated included the new record CIGS cell, CIS cells made with and without CdS, and those made by electrodeposition and electroless growth from solution. Work on the role of impurities focused on sodium in CIS. Cells with varying amounts of sodium added during CIS deposition were fabricated at NREL using four types of substrates. The best performance was achieved with 10{sup {minus}2}--10{sup {minus}1} at% sodium, and the relative merits of proposed mechanisms for the sodium effect were compared. Researchers also worked on the construction and testing of a fine-focused laser-beam apparatus to measure local variations in polycrystalline cell performance. A 1{micro}m spot was achieved, spatial reproducibility in one and two dimensions is less than 1 {micro}m, and photocurrent is reliably measured when the 1{micro}m spot is reduced as low as 1-sun in intensity. In elevated-temperature stress tests, typical CdTe cells held at 100 C under illumination and normal resistive loads for extended periods of time were generally very stable; but those held under reverse or large forward bias and those contacted using larger amounts of copper were somewhat less stable. CdTe cell modeling produced reasonable fits to experimental data, including variations in back-contact barriers. A major challenge being addressed is the photovoltaic response of a single simple-geometry crystallite with realistic grain boundaries.

  9. Origins of electrostatic potential wells at dislocations in polycrystalline Cu(In,Ga)Se{sub 2} thin films

    SciTech Connect

    Dietrich, J.; Abou-Ras, D. Schmidt, S. S.; Rissom, T.; Unold, T.; Cojocaru-Mirédin, O.; Niermann, T.; Lehmann, M.; Koch, C. T.; Boit, C.

    2014-03-14

    Thin-film solar cells based on Cu(In,Ga)Se{sub 2} (CIGSe) reach high power-conversion efficiencies in spite of large dislocation densities of up to 10{sup 10}–10{sup 11} cm{sup −2}. The present work gives insight into the structural and compositional properties of dislocations in CIGSe thin films, which are embedded in a complete solar cell stack. These properties are related to the average electrical potential distributions obtained by means of inline electron holography. At a part of the dislocations studied, the average electrostatic potential shows local minima, all with depths of about −1.4 V. The measured average electrostatic potential distributions were modeled in order to reveal possible influences from strain fields, excess charge, and also compositional changes at the dislocation core. Cu depletion around the dislocation core, as evidenced by atom-probe tomography, explains best the measured potential wells. Their influences of the strain field around the dislocation core and of excess charge at the dislocation core are small. A structural model of dislocations in CIGSe thin films is provided which includes a Cu-depleted region around the dislocation core and gives a possible explanation for why decent photovoltaic performances are possible in the presence of rather large dislocation densities.

  10. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    SciTech Connect

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao Qihua; Li Yixin; Street, Robert A.; Lu Jengping

    2009-07-15

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of {approx}10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical

  11. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    PubMed Central

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao, Qihua; Li, Yixin; Street, Robert A.; Lu, Jeng-Ping

    2009-01-01

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and∕or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ∼10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill

  12. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Choi, Sung-Hwan; Kim, Sun-Jae; Mo, Yeon-Gon; Kim, Hye-Dong; Han, Min-Koo

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (ΔVTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (ΔVTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  13. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Sung-Hwan Choi,; Sun-Jae Kim,; Yeon-Gon Mo,; Hye-Dong Kim,; Min-Koo Han,

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (Δ VTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (Δ VTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  14. High quality SiO2/Si interfaces of poly-crystalline silicon thin film transistors by annealing in wet atmosphere

    NASA Astrophysics Data System (ADS)

    Sano, Naoki; Sekiya, Mitsunobu; Hara, Masaki; Kohno, Atsushi; Sameshima, Toshiyuki

    1995-05-01

    A new post-metallization annealing technique was developed to improve the quality of metal-oxide-semiconductor (MOS) devices using SiO2 films formed by a parallel-plate remote plasma chemical vapor deposition as gate insulators. The quality of the interface between SiO2 and crystalline Si was investigated by capacitance-voltage (C-V) measurements. An H2O vapor annealing at 270 C for 30 min efficiently decreased the interface trap density to 2.0 x 10(exp 10) cm(exp -2) eV(exp -1), and the effective oxide charge density from 1 x 10(exp 12) to 5 x 10(exp 9) cm(exp -2). This annealing process was also applied to the fabrication of Al-gate polycrystalline silicon thin film transistors (poly-Si TFT's) at 270 C. In p-channel poly-Si TFT's, the carrier mobility increased from 60-400 cm(exp 2) V(exp -1) s(exp - 1) and the threshold voltage decreased from - 5.5 to - 1.7 V.

  15. Preparation of translucent Gd2Si2O7:Ce polycrystalline thin plates and their scintillation performance for α-particles

    NASA Astrophysics Data System (ADS)

    Nishikata, Mami; Ueda, Aki; Higuchi, Mikio; Kaneko, Junichi H.; Tsubota, Youichi; Ishibashi, Hiroyuki

    2015-07-01

    Translucent Gd2Si2O7:Ce (GPS:Ce) polycrystalline plates were prepared via liquid-phase sintering using SiO2 as a self-flux, and their scintillation performances for α-particles were investigated. Dense sintered compacts comprising large grains, some of which were larger than 100 μm in diameter, were successfully prepared by sintering at 1690 °C for 100 h. The best result was obtained with the powder comprising only <40 μm particles. Any combination of powders of <40 μm and <15 μm resulted in inhomogeneous structures with smaller grains of about 50 μm. A translucent GPS:Ce thin plate was fabricated by grinding the sintered compact that contained excess SiO2 of 8 mol%. Since the plate was composed of large grains, scattering at the grain boundaries was effectively suppressed and many of the grains virtually act as single crystals when the plate thickness was less than 100 μm. Therefore, the decrease in the plate thickness brought increase in the total transmission, and light yield and energy resolution were consequently improved. When the plate thickness was 50 μm, light yield was 82% as compared with that of a GPS:Ce single crystal as a reference, and energy resolution attained to 13%.

  16. Stress-Induced Off-Current under On- and Off-State Stress Voltages in Low-Temperature n-Channel Polycrystalline Silicon Thin-Film Transistors

    NASA Astrophysics Data System (ADS)

    Seishiro Hirata,; Toshifumi Satoh,; Hiroyuki Tango,

    2010-03-01

    The changes in off-current under on- and off-state stress voltages in n-channel polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are investigated through measurements and simulations. It is found that the off-current increases markedly in the shallow-negative-gate-voltage region and decreases in the deep-gate-voltage region after applying both on- and off-state stresses, resulting in a weaker dependence on negative gate voltage. It can be supposed from the simulations and experiments that the donor-type trap states (positive charges) with a hump-type state profile, located at 0.1-0.2 eV below the midgap, and tail states are generated near the drain junction after applying both stresses. The amount of donor-type states increases in phonon-assisted tunneling with the Pool-Frenkel effect (PAT) and Schockley-Read-Hall generation (SRH) owing to the increase in the deep-trap-state density, and decreases in band-to-band tunneling (BBT) owing to the decrease in electric field, giving rise to a predominant PAT+SRH current in off-current in a wide-negative-gate-voltage region.

  17. Abnormal Threshold Voltage Shifts in P-Channel Low-Temperature Polycrystalline Silicon Thin Film Transistors Under Negative Bias Temperature Stress.

    PubMed

    Kim, Sang Sub; Choi, Pyung Ho; Baek, Do Hyun; Lee, Jae Hyeong; Choi, Byoung Deog

    2015-10-01

    In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiNx dielectrics. A negative gate bias temperature instability (NBTI) stress was applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (Vth). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNx/SiO2 dielectric interface being dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the Vth switches to the negative voltage direction, which is "turn-around" behavior. In the second stage, the Vth moves from -1.63 V to -2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps. PMID:26726370

  18. Atomic-resolution study of dislocation structures and interfaces in poly-crystalline thin film CdTe using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Paulauskas, Tadas; Colegrove, Eric; Buurma, Chris; Kim, Moon; Klie, Robert

    2014-03-01

    Commercial success of CdTe-based thin film photovoltaic devices stems from its nearly ideal direct band gap which very effectively couples to Sun's light spectrum as well as ease of manufacturing and low cost of these modules. However, to further improve the conversion efficiency beyond 20 percent, it is important to minimize the harmful effects of grain boundaries and lattice defects in CdTe. Direct atomic-scale characterization is needed in order identify the carrier recombination centers. Likewise, it is necessary to confirm that passivants in CdTe, such as Cl, are able to diffuse and bind to the target defects. In this study, we characterize dislocation structures and grain boundaries in poly-crystalline CdTe using aberration-corrected cold-field emission scanning transmission electron microscopy (STEM). The chemical composition of Shockley partial, Frank and Lomer-Cottrell dislocations is examined via atomic column-resolved X-ray energy dispersive (XEDS) and electron energy-loss spectroscopies (EELS). Segregation of Cl towards dislocation cores and grain boundaries is shown in CdCl2 treated samples. We also investigate interfaces in ultra-high-vacuum bonded CdTe bi-crystals with pre-defined misorientation angles which are intended to mimic grain boundaries. Funded by: DOE EERE Sunshot Award EE0005956.

  19. Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Pagels, Marcel; Zachäus, Carolin; Pollakowski, Beatrix; Beckhoff, Burkhard; Kanngießer, Birgit; Rech, Bernd

    2013-01-01

    The combination of polycrystalline silicon (poly-Si) thin films with aluminum doped zinc oxide layers (ZnO:Al) as transparent conductive oxide enables the design of appealing optoelectronic devices at low costs, namely in the field of photovoltaics. The fabrication of both thin-film materials requires high-temperature treatments, which are highly desired for obtaining a high electrical material quality. Annealing procedures are typically applied during crystallization and defect-healing processes for silicon and can boost the carrier mobility and conductivity of ZnO:Al layers. In a combined poly-Si/ZnO:Al layer system, an in-depth knowledge of the interaction of both layers and the control of interface reactions upon thermal treatments is crucial. Therefore, we analyze the influence of rapid thermal treatments up to 1050 °C on solid phase crystallized poly-Si thin-film solar cells on ZnO:Al-coated glass, focusing on chemical interface reactions and modifications of the poly-Si absorber material quality. The presence of a ZnO:Al layer in the solar cell stack was found to limit the poly-Si solar cell performance with open circuit voltages only below 390 mV (compared to 435 mV without ZnO film), even if a silicon nitride (SiN) diffusion barrier was included. A considerable amount of diffused zinc inside the silicon was observed. By grazing-incidence X-ray fluorescence spectrometry, a depth-resolving analysis of the elemental composition close to the poly-Si/(SiN)/ZnO:Al interface was carried out. Temperatures above 1000 °C were found to promote the formation of new chemical compounds within about 10 nm of interface, such as zinc silicates (Zn2SiO4) and aluminium oxide (AlxOy). These results give valuable insights about the temperature-limitations of Si/ZnO thin-film solar cell fabrication and the formation of high-mobility ZnO-layers by thermal anneal.

  20. Exploration of maximum count rate capabilities for large-area photon counting arrays based on polycrystalline silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua

    2016-03-01

    Pixelated photon counting detectors with energy discrimination capabilities are of increasing clinical interest for x-ray imaging. Such detectors, presently in clinical use for mammography and under development for breast tomosynthesis and spectral CT, usually employ in-pixel circuits based on crystalline silicon - a semiconductor material that is generally not well-suited for economic manufacture of large-area devices. One interesting alternative semiconductor is polycrystalline silicon (poly-Si), a thin-film technology capable of creating very large-area, monolithic devices. Similar to crystalline silicon, poly-Si allows implementation of the type of fast, complex, in-pixel circuitry required for photon counting - operating at processing speeds that are not possible with amorphous silicon (the material currently used for large-area, active matrix, flat-panel imagers). The pixel circuits of two-dimensional photon counting arrays are generally comprised of four stages: amplifier, comparator, clock generator and counter. The analog front-end (in particular, the amplifier) strongly influences performance and is therefore of interest to study. In this paper, the relationship between incident and output count rate of the analog front-end is explored under diagnostic imaging conditions for a promising poly-Si based design. The input to the amplifier is modeled in the time domain assuming a realistic input x-ray spectrum. Simulations of circuits based on poly-Si thin-film transistors are used to determine the resulting output count rate as a function of input count rate, energy discrimination threshold and operating conditions.

  1. X-Ray Diffraction Analysis of Residual Stress in Thin Polycrystalline Anatase Films and Elastic Anisotropy of Anatase

    NASA Astrophysics Data System (ADS)

    Matěj, Z.; Kužel, R.; Nichtová, L.

    2011-11-01

    The importance of residual stress in anatase thin films for their photo-induced hydrophilicity was proved recently. Detailed X-ray diffraction (XRD) studies of residual stresses in titanium dioxide films are presented here. Measurements including multiple hkl reflections on several series of these films revealed the presence of tensile stresses in the films that were obtained by crystallization from amorphous state. Significant anisotropy of the strain was also found and compared with that of anatase, resulting from its theoretically calculated single-crystal elastic constants. The XRD data support the experimental evidence of the hypothesis that the [00 l] axis is the elastically soft anatase direction, whereas the directions in the [ h00] × [ hk0] plane are elastically stiff. This is in agreement with the anisotropy predicted by single-crystal elastic constants that are obtained from ab-initio calculations. Residual stress analysis for materials with tetragonal symmetry is described and the theory is used to analyze the data. The anisotropy is very different from that for the rutile phase, and the experimental results agree well with the values calculated for anatase. A simplified method of XRD residual stress analysis in thin anatase films by total pattern fitting (TPF) is also presented. Tensile stresses are formed during the crystallization process and increase rapidly with reduced film thickness. They inhibit crystallization, which is then very slow in the thinnest films.

  2. Effect of deposition temperature on electron-beam evaporated polycrystalline silicon thin-film and crystallized by diode laser

    SciTech Connect

    Yun, J. Varalmov, S.; Huang, J.; Green, M. A.; Kim, K.

    2014-06-16

    The effects of the deposition temperature on the microstructure, crystallographic orientation, and electrical properties of a 10-μm thick evaporated Si thin-film deposited on glass and crystallized using a diode laser, are investigated. The crystallization of the Si thin-film is initiated at a deposition temperature between 450 and 550 °C, and the predominant (110) orientation in the normal direction is found. Pole figure maps confirm that all films have a fiber texture and that it becomes stronger with increasing deposition temperature. Diode laser crystallization is performed, resulting in the formation of lateral grains along the laser scan direction. The laser power required to form lateral grains is higher in case of films deposited below 450 °C for all scan speeds. Pole figure maps show 75% occupancies of the (110) orientation in the normal direction when the laser crystallized film is deposited above 550 °C. A higher density of grain boundaries is obtained when the laser crystallized film is deposited below 450 °C, which limits the solar cell performance by n = 2 recombination, and a performance degradation is expected due to severe shunting.

  3. In-situ investigation of thermal instabilities and solid state dewetting in polycrystalline platinum thin films via confocal laser microscopy

    SciTech Connect

    Jahangir, S.; Cheng, Xuan; Huang, H. H.; Nagarajan, V.; Ihlefeld, J.

    2014-10-28

    Solid state dewetting and the subsequent morphological changes for platinum thin films grown on zinc oxide (ZnO) buffered (001) silicon substrates (Pt/ZnO/SiO{sub 2}/(001)Si system) is investigated under vacuum conditions via a custom-designed confocal laser microscope coupled with a laser heating system. Live imaging of thin film dewetting under a range of heating and quenching vacuum ambients reveals events including hillock formation, hole formation, and hole growth that lead to formation of a network of Pt ligaments, break up of Pt ligaments to individual islands and subsequent Pt islands shape reformation, in chronological fashion. These findings are corroborated by ex-situ materials characterization and quantitative electron microscopy analysis. A secondary hole formation via blistering before film rupture is revealed to be the critical stage, after which a rapid dewetting catastrophe occurs. This process is instantaneous and cannot be captured by ex-situ methods. Finally, an intermetallic phase forms at 900 °C and alters the morphology of Pt islands, suggesting a practical limit to the thermal environments that may be used for these platinized silicon wafers in vacuum conditions.

  4. Symmetry dependent optoelectronic properties of grain boundaries in polycrystalline Cu(In,Ga)Se{sub 2} thin films

    SciTech Connect

    Müller, Mathias; Bertram, Frank; Christen, Jürgen; Abou-Ras, Daniel Rissom, Thorsten

    2014-01-14

    In a correlative study applying electron backscatter diffraction as well as spatially and spectrally resolved cathodoluminescence spectroscopy at low temperatures of about 5 K, the symmetry-dependent optoelectronic properties of grain boundaries in Cu(In,Ga)Se{sub 2} thin films have been investigated. We find that grain boundaries with lower symmetries tend to show a distinct spectral red shift of about 10 meV and a weak influence on the emission intensity. These behaviors are not detected at high-symmetry Σ3 grain boundaries, or at least in a strongly reduced way. The investigations in the present work help to clarify the ambivalent properties reported for grain boundaries in Cu(In,Ga)Se{sub 2}.

  5. Hysteresis in single and polycrystalline iron thin films: Major and minor loops, first order reversal curves, and Preisach modeling

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Xu, Ke; Jiang, Weilin; Droubay, Timothy; Ramuhalli, Pradeep; Edwards, Danny; Johnson, Bradley R.; McCloy, John

    2015-12-01

    Hysteretic behavior was studied in a series of Fe thin films, grown by molecular beam epitaxy, having different grain sizes and grown on different substrates. Major and minor loops and first order reversal curves (FORCs) were collected to investigate magnetization mechanisms and domain behavior under different magnetic histories. The minor loop coefficient and major loop coercivity increase with decreasing grain size due to higher defect concentration resisting domain wall movement. First order reversal curves allowed estimation of the contribution of irreversible and reversible susceptibilities and switching field distribution. The differences in shape of the major loops and first order reversal curves are described using a classical Preisach model with distributions of hysterons of different switching fields, providing a powerful visualization tool to help understand the magnetization switching behavior of Fe films as manifested in various experimental magnetization measurements.

  6. Surface Modification of Polycrystalline Cu(In,Ga)Se2 Thin-Film Solar Cell Absorber Surfaces for PEEM Measurements

    SciTech Connect

    Wilks, R. G.; Contreras, M. A.; Lehmann, S.; Herrero-Albillos, J.; Bismaths, L. T.; Kronast, F.; Noufi, R.; Bar, M.

    2011-01-01

    We present a thorough examination of the {micro}m-scale topography of Cu(In, Ga)Se{sub 2} ('CIGSe') thin-film solar cell absorbers using different microscopy techniques. We specifically focus on the efficacy of preparing smooth sample surfaces - by etching in aqueous bromine solution - for a spatially resolved study of their chemical and electronic structures using photoelectron emission microscopy (PEEM). The etching procedure is shown to reduce the CIGSe surface roughness from ca. 40 to 25 nm after 40s etching, resulting in an increase in the quality of the obtained PEEM images. Furthermore we find that the average observed grain size at the etched surfaces appears larger than at the unetched surfaces. Using a liftoff procedure, it is additionally shown that the backside of the absorber is flat but finely patterned, likely due to being grown on the finely-structured Mo back contact.

  7. The effect of Ta doping in polycrystalline TiO{sub x} and the associated thin film transistor properties

    SciTech Connect

    Ok, Kyung-Chul Park, Yoseb Park, Jin-Seong E-mail: jsparklime@hanyang.ac.kr; Chung, Kwun-Bum E-mail: jsparklime@hanyang.ac.kr

    2013-11-18

    Tantalum (Ta) is suggested to act as an electron donor and crystal phase stabilizer in titanium oxide (TiO{sub x}). A transition occurs from an amorphous state to a crystalline phase at an annealing temperature above 300 °C in a vacuum ambient. As the annealing temperature increases from 300 °C to 450 °C, the mobility increases drastically from 0.07 cm{sup 2}/Vs to 0.61 cm{sup 2}/Vs. The remarkable enhancement of thin film transistor performance is suggested to be due to the splitting of Ti 3d band orbitals as well as the increase in Ta{sup 5+} ions that can act as electron donors.

  8. Effect of depth of traps in ZnO polycrystalline thin films on ZnO-TFTs performance

    NASA Astrophysics Data System (ADS)

    Medina-Montes, Maria I.; Baldenegro-Perez, Leonardo A.; Sanchez-Zeferino, Raul; Rojas-Blanco, Lizeth; Becerril-Silva, Marcelino; Quevedo-Lopez, Manuel A.; Ramirez-Bon, Rafael

    2016-09-01

    ZnO thin films were processed by radio frequency magnetron sputtering at room temperature on p-Si/SiO2 substrates under pure argon (Ar:O2 = 100:0 vol.%) and argon-oxygen mixture (Ar:O2 = 99:1 vol.%) gas environment. Morphological, optical and electrical characteristics of the ZnO films are reported, and they show a clear relationship with the gas mixture employed for the sputtering process. Scanning Electron Microscopy revealed the formation of grains of 15.3 and 19.9 nm average sizes and thicknesses of 59 nm and 82 nm for films growth in pure argon and argon-oxygen, respectively. Photoluminescence measurements at room temperature showed the violet emission band (centered at 3 eV) which was only detected in the ZnO film grown under pure argon. From thermally stimulated conductivity measurements two traps with 0.27 and 0.14 eV activation energies were identified for films grown in pure argon and argon-oxygen mixture, respectively. The trap at 0.27 eV is associated with a level located below the conduction band edge and it is supported by the PL band centered at 3 eV. Both types of ZnO films were used as the active channel layer in thin film transistors with thermal SiO2 as gate dielectric. Field effect mobility, threshold voltage and current ratio were improved in the devices with ZnO channel deposited with the argon-oxygen mixture (99% Ar/1% O2 vol.). Threshold voltage decreased from 25 V to 15 V, field effect mobility and current ratio increased from 0.8 to 2.4 cm2/Vs and from 102 to 106, in that order.

  9. A Monte Carlo simulation study of boron profiles as-implanted into LPCVD NiDoS polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Boukezzata, M.; Ait-Kaki, A.; Temple-Boyer, P.; Scheid, E.

    2003-03-01

    This work presents a Monte Carlo simulation study of boron profiles obtained from as-implanted ions into thin films nitrogen doped silicon (NiDoS) thin films. These films are performed by LPCVD technique from Si2H6 and NH3 gas sources, four values deliberately chosen, of the ratio NH3/Si2H6 to obtain samples, differently in situ nitrogen-doped. Taking into account the effect of the codoping case, and the structure specificity of these films, an accurate Monte Carlo model based on binary collisions in a multi-atomic target was performed. Nitrogen atoms present in the target is shown to affect the boron profiles and confirms clearly a reduction penetration effect which becomes more significant at high nitrogen concentrations. Whereas, the fine-grained polysilicon structure, and thus the presence of grains (G) and grain boundaries (GB), is known to enhance the opposite phenomenon by assuming an effective role played by GB's in the scattering calculation process of the incident ions. This role is represented by the change in direction of the incident ion after interaction with GB without corresponding loss in its energy. The results obtained show an enhancement of the stopping parameter when nitrogen concentration increases, while the GB interaction remains very important. This behavior is due to a great number of GB's interactions with boron atoms which gave low deflection angles. So that, the average positions described by the sequences of trajectories took place farther than what expected with channeling effect in crystal silicon materials.

  10. Optoelectronic characterization of wide-bandgap (AgCu)(InGa)Se 2 thin-film polycrystalline solar cells including the role of the intrinsic zinc oxide layer

    NASA Astrophysics Data System (ADS)

    Obahiagbon, Uwadiae

    Experiments and simulations were conducted to vary the thickness and the sheet resistance of the high resistance (HR) ZnO layer in polycrystalline thin film (AgCu)(GaIn)Se2 (ACIGS) solar cells. The effect of varying these parameters on the electric field distribution, depletion width and hence capacitance were studied by SCAPS simulation. Devices were then fabricated and characterized by a number of optoelectronic techniques. Thin film CIGS has received a lot of attention, for its use as an absorber layer for thin film solar cells. However, the addition of Silver (Ag) to the CIGS alloy system increases the band gap as indicated from optical transmission measurements and thus higher open circuit voltage (Voc) could be obtained. Furthermore, addition of Ag lowers the melting temperature of the alloy and it is expected that this lowers the defect densities in the absorber and thus leads to higher performance. Transient photocapacitance analysis on ACIGS devices shows sharper band edge indicating lower disorder than CIGS. Presently there is a lack of fundamental knowledge relating film characteristics to device properties and performance. This is due to the fact that some features in the present solar cell structure have been optimized empirically. The goal of this research effort was to develop a fundamental and detailed understanding of the device operation as well as the loss mechanism(s) limiting these devices. Recombination mechanisms in finished ACIGS solar cell devices was studied using advanced admittance techniques (AS, DLCP, CV) to identify electronically active defect state(s) and to study their impact on electronic properties and device performance. Analysis of various optoelectronic measurements of ACIGS solar cells provided useful feedback regarding the impact on device performance of the HR ZnO layer. It was found that thickness between 10-100 nm had negligible impact on performance but reducing the thickness to 0 nm resulted in huge variability in all

  11. Ion-assisted laser deposition of intermediate layers for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin film growth on polycrystalline and amorphous substrates

    SciTech Connect

    Reade, R.P.

    1993-11-01

    The growth of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) high-temperature superconductor thin films has largely been limited to deposition on single-crystal substrates to date. In order to expand the range of potential applications, growth on polycrystalline and amorphous substrates is desirable. In particular, the deposition of YBCO thin films with high critical current densities on polycrystalline metal alloys would allow the manufacture of superconducting tapes. However, it is shown that it is not possible to grow YBCO thin films directly on this type of substrate due to chemical and structural incompatibility. This work investigates the use of a yttria-stabilized zirconia (YSZ) intermediate layer to address this problem. An ion-assisted pulsed-laser deposition process is developed to provide control of orientation during the growth of the YSZ layers. The important properties of YBCO and YSZ are summarized and the status of research on thin film growth of these materials is reviewed. An overview of the pulsed-laser deposition (PLD) technique is presented. The use of ion-assisted deposition techniques to control thin film properties is discussed.

  12. Photoinduced current transient spectroscopy technique applied to the study of point defects in polycrystalline CdS thin films

    SciTech Connect

    El Akkad, Fikry; Ashour, Habib

    2009-05-01

    CdS thin films of variable thickness (between 160 and 1200 nm) were prepared using rf magnetron sputtering. X-ray diffraction measurements showed that the films have hexagonal structure and that the crystallites are preferentially oriented with the <002> axis perpendicular to the substrate surface. The results of electrical conductivity measurements as a function of film thickness and of temperature provide evidence that the conductivity is controlled by a thermally activated mobility in the presence of an intergrain barrier. The room temperature barrier height phi decreases with the increase in film thickness. Values of phi between 0 and 0.25 eV were determined. Photoinduced current transient spectroscopy performed on five samples having different thicknesses showed the presence of 11 traps with activation energies in the range 0.08-1.06 eV; deeper traps being observed on thinner films. By comparison with literature results, seven traps are attributed to native defects and foreign impurities (mainly Cu, Au, and Ag). Four other traps, not previously observed, are attributed to residual defects. The observation that deeper traps are detected in samples with larger barrier heights has been discussed and interpreted in terms of the energy band profile near the grain boundary.

  13. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

    1983-01-01

    A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

  14. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

    1983-04-05

    A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

  15. Photovoltaic characteristics in polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films sandwiched between different top and bottom electrodes

    NASA Astrophysics Data System (ADS)

    Qin, Meng; Yao, Kui; Liang, Yung C.

    2009-03-01

    Photovoltaic responses, including photovoltage, photocurrent, illuminated J-V curve, and light-to-electricity power conversion efficiency, were investigated in chemical-solution-derived polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLZT) thin films sandwiched between different metal and oxide electrodes. The epitaxial PLZT films with Au/PLZT/Nb-doped SrTiO3 structure exhibited about one order of magnitude larger photocurrent and efficiency over the randomly oriented polycrystalline PLZT films with Au/PLZT/Pt structure due to the high crystalline quality with the reduced defects and enhanced depolarization field. The illuminated J-V curve was approximately linear for both polycrystalline and epitaxial PLZT thin films. The nonzero photovoltaic outputs in the unpoled films were induced by asymmetric interfacial Schottky barriers. The illuminated J-V curve shifted toward the positive voltage direction after positive poling and toward the negative voltage direction after negative poling, and the enhancement of efficiency only occurred when the polarization direction accorded with the direction of Schottky barrier difference at the two electrode interfaces. Thickness dependences of photovoltage, photocurrent, and light-to-electricity conversion efficiency were also examined. It was observed that photovoltage linearly increased with film thickness while both photocurrent and efficiency exponentially increased with the decrease in thickness. Furthermore, at a fixed small film thickness, efficiency was also found to increase reciprocally with the decrease of incident UV intensity.

  16. The effects of spatial location of defect states on the switching characteristics of amorphous and polycrystalline silicon thin film transistors: A numerical simulation using AMPS 2-D

    SciTech Connect

    Smith, J.; Fonash, S.; Kalkan, A.

    1994-06-01

    We demonstrate a two-dimensional device simulator for MOSFET structures that incorporates models for defect distributions and show predicted effects on device switching performance for various spatial distributions of defects in amorphous and polycrystalline silicon.

  17. Cobalt-free polycrystalline Ba0.95La0.05FeO3-δ thin films as cathodes for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Dengjie; Chen, Chi; Dong, Feifei; Shao, Zongping; Ciucci, Francesco

    2014-03-01

    Ba0.95La0.05FeO3-δ (BLF) thin films as electrodes for intermediate-temperature solid oxide fuel cells are prepared on single-crystal yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition. The phase structure, surface morphology and roughness of the BLF thin films are characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy is used to analyze the compositions of the deposited thin film and the chemical state of transition metal. The dense thin film exhibits a polycrystalline perovskite structure with a low surface roughness and a high oxygen vacancy concentration on the surface. Ag (paste or strip) and Au (strip) are applied on both surfaces of the symmetric cells as current collectors to evaluate electrochemical performance of the thin films. The electrode polarization resistances of the symmetric cells are found to be lower than those of most cobalt-free thin-film electrodes, e.g., 0.437 Ω cm2 at 700 °C and 0.21 atm. The oxygen reduction reaction mechanism of the BLF cathode in symmetric cells is studied by electrochemical impedance spectroscopy thanks to the equivalent fitting analysis. Both the oxygen surface exchange reaction and charge transfer are shown to determine the overall oxygen reduction reaction.

  18. Local retention behaviors of epitaxial and polycrystalline PbMg1/3Nb2/3O3-PbTiO3 thin films by scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Choi, M. R.; Oh, Y. J.; Jo, W.

    2007-08-01

    The authors report the results of retention in epitaxial and polycrystalline PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) thin films on SrRuO3 (SRO) and Pt. The SRO electrodes were deposited by pulsed laser deposition and the PMN-PT thin films were coated by a sol-gel method. Local poling behaviors of the PMN-PT domains were investigated as a function of time in both single-poled and reverse-poled regions by scanning force microscopy. An extended exponential decay is observed in the PMN-PT/SRO heterostructures while a fluctuated relaxation is shown in the PMN-PT/Pt films, suggesting that crystal orientation and grain growth is critical to understand retention of relaxor ferroelectrics.

  19. Status of polycrystalline solar cell technologies

    NASA Astrophysics Data System (ADS)

    Kapur, Vijay K.; Basol, Bulent M.

    Thin-film cadmium telluride (CdTe) and thin-film copper indium diselenide (CIS) solar cells are discussed. The issues these technologies face before commercialization are addressed. High-efficiency (15-18 percent) polycrystalline silicon modules could dominate the market in the near future, and impressive results for thin-film CdTe and CIS solar cells and their outdoor stability can attract increased interest in these solar cells, which will accelerate their development.

  20. Uniaxially oriented polycrystalline thin films and air-stable n-type transistors based on donor-acceptor semiconductor (diC8BTBT)(FnTCNQ) [n = 0, 2, 4

    NASA Astrophysics Data System (ADS)

    Shibata, Yosei; Tsutsumi, Jun'ya; Matsuoka, Satoshi; Matsubara, Koji; Yoshida, Yuji; Chikamatsu, Masayuki; Hasegawa, Tatsuo

    2015-04-01

    We report the fabrication of high quality thin films for semiconducting organic donor-acceptor charge-transfer (CT) compounds, (diC8BTBT)(FnTCNQ) (diC8BTBT = 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and FnTCNQ [n = 0,2,4] = fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane), which have a high degree of layered crystallinity. Single-phase and uniaxially oriented polycrystalline thin films of the compounds were obtained by co-evaporation of the component donor and acceptor molecules. Organic thin-film transistors (OTFTs) fabricated with the compound films exhibited n-type field-effect characteristics, showing a mobility of 6.9 × 10-2 cm2/V s, an on/off ratio of 106, a sub-threshold swing of 0.8 V/dec, and an excellent stability in air. We discuss the suitability of strong intermolecular donor-acceptor interaction and the narrow CT gap nature in compounds for stable n-type OTFT operation.

  1. Diffusion in polycrystalline microstructures

    SciTech Connect

    Swiler, T.P.; Holm, E.A.

    1995-07-01

    Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and the topological aspects of grain boundaries. In this study, a finite difference scheme is developed to study transient and steady-state mass transport through realistic two-dimensional polycrystalline microstructures. Effects of microstructural parameters such as average grain size and grain boundary topology are examined, as are effects due to limits of the model.

  2. Control of the growth orientation and electrical properties of polycrystalline Cu2O thin films by group-IV elements doping

    NASA Astrophysics Data System (ADS)

    Ishizuka, Shogo; Akimoto, Katsuhiro

    2004-11-01

    The effects of group-IV element dopants on the structural and electrical properties of Cu2O thin films were studied. Similar dopant-induced behavior was found in the observed variations of the growth orientation and electrical properties of Si- and Ge-doped Cu2O thin films. Ge doping was found to induce electrically active acceptors with an activation energy of 0.18 eV, comparable to the 0.19 eV value of Si-doped Cu2O. These results suggest that locally formed silicate and germanate have the same effect on the structural and electrical properties of Cu2O. On the other hand, Sn and Pb likely act as donors when incorporated substitutionally onto Cu-lattice sites, although further study may be required to suppress self-compensation effects in Cu2O to achieve n-type conductivity.

  3. Exploratory development of thin-film polycrystalline silicon photovoltaic devices. Report No. 3. Electron beam ribbon-to-ribbon (EB RTR) recrystallization of microcrystalline silicon ribbons

    SciTech Connect

    Gurtler, R.W.

    1981-09-01

    The electron beam has been applied as the energy source for ribbon-to-ribbon (RTR) recrystallization of thin-film silicon with very small (approx. 1 ..mu..m) grains into sheets with very large grains (> 1 cm). The system described uses two e-guns, one for producing a thin molten region across the microcrystalline ribbon (except for the edges), the other for establishing desirable thermal profiles in the cool-down (and heat-up) regions. In this way, no furnace, heat shield, or cooling structures are present, in contrast to all the other ribbon growing techniques. This simple arrangement is gained at the (reasonable) expense of having to work in a vacuum. A CCTV camera observes the temperature distribution and melt shape during growth; its output is coupled to a real-time image analyzer system and a computer. When there is a need to alter the temperature or melt shape in a region, the deflection/modulation circuitry is appropriately instructed, and (closing the loop) the change is made. The vacuum chamber with cassette feed for ribbons, electron guns, and camera, was completed and placed in operation. The overall system was run with a fined temperature profile for small RTR samples; resulting thin-film silicon ribbon quality was comparable to that obtained with laser beam RTR. The entire electronic system was not finished, however, so potential utility of the system for improving silicon ribbon quality and economics could not be ascertained.

  4. Optical Sensing Circuit Using Low-Temperature Polycrystalline Silicon p-Type Thin-Film Transistors and p-Intrinsic-Metal Diode for Active Matrix Displays with Optical Input Functions

    NASA Astrophysics Data System (ADS)

    Lim, Han-Sin; Kwon, Oh-Kyong

    2009-03-01

    An optical sensing circuit composed of low-temperature polycrystalline silicon (LTPS) p-type thin-film transistors (TFTs) and a p-intrinsic-metal (p-i-m) diode is proposed for image scanning and touch sensing functions. Because it is a very difficult challenge to integrate both display pixels and optical sensing circuits into the restricted pixel area, the number of additional devices and control signal lines must be minimized. Therefore, two p-type TFTs, one p-i-m diode, one capacitor, and one signal line are added to display pixel for the proposed optical sensing circuit. Active matrix liquid crystal display (AMLCD) and active matrix organic light-emitting diode (AMOLED) pixels with the proposed optical sensing circuit have image scanning and touch sensing functions, respectively. Through the measurement of the proposed circuit under the condition of incident light varying from 0 to 10,000 lx, we verified that the dynamic and output ranges of the proposed circuit are 30 dB and 1.5 V, respectively.

  5. Ferroelectric properties of (117)- and (001)-oriented Bi3.25La0.75Ti3O12 polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Sun, Yu-Ming; Chen, Yi-Chan; Gan, Jon-Yiew; Hwang, Jenn-Chang

    2002-10-01

    Highly (117)- and (001)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated on Pt/TiO2/SiO2)/Si(100 substrates by chemical solution deposition under the appropriate baking and crystallization conditions. The (117)-oriented BLT films exhibited higher remanent polarization (2Pr=24 muC/cm2), than did (001)-oriented BLT films, which exhibited only a slight amount of polarization (2Pr=6.6 muC/cm2). The results of fatigue and retention tests revealed that neither film was fatigued up to 1 x1010 switching cycles, and the retained charge was unchanged for 1 x104 s.

  6. Research on polycrystalline thin-film CuGaInSe{sub 2} solar cells. Annual subcontract report, 3 May 1991--2 May 1992

    SciTech Connect

    Stanbery, B.J.; Chen, W.S.; Devaney, W.E.; Stewart, J.W.

    1992-11-01

    This report describes research to fabricate high-efficiency CdZnS/CuInGaSe{sub 2} (CIGS) thin-film solar cells, and to develop improved transparent conductor window layers such as ZnO. A specific technical milestone was the demonstration of an air mass (AM) 1.5 global, 13% efficient, 1-cm{sup 2}-total-area CIGS thin-film solar cell. Our activities focused on three areas. First, a CIGS deposition: system was modified to double its substrate capacity, thus increasing throughput, which is critical to speeding the process development by providing multiple substrates from the same CIGS run. Second, new tooling was developed to enable an investigation of a modified aqueous CdZnS process. The goal was to improve the yield of this critical step in the device fabrication process. Third, our ZnO sputtering system was upgraded to improve its reliability, and the sputtering parameters were further optimized to improve its properties as a transparent conducting oxide. The characterization of the new CIGS deposition system substrate fixturing was completed, and we produced good thermal uniformity and adequately high temperatures for device-quality CIGS deposition. Both the CIGS and ZnO deposition processes were refined to yield a ZnO//Cd{sub 0.82}Zn{sub 0.18}S/CuIn{sub 0.80}Ga{sub 0.20}Se{sub 2} cell that was verified at NREL under standard testing conditions at 13.1% efficiency with V{sub oc} = 0.581 V, J{sub sc} = 34.8 mA/cm{sup 2}, FF = 0.728, and a cell area of 0.979 cm{sup 2}.

  7. Research on polycrystalline thin-film CuInGaSe{sub 2} solar cells. Annual subcontract report, 3 May 1991--21 May 1993

    SciTech Connect

    Chen, W.S.; Stewart, J.M.; Mickelsen, R.A.; Devaney, W.E.; Stanbery, B.J.

    1993-10-01

    This report describes work to fabricate high-efficiency CdZnS/CuInGaSe{sub 2}, thin-film solar cells and to develop improved transparent conductor window layers such as ZnO. The specific technical milestone for Phase I was to demonstrate an air mass (AM) 1.5 global 13% , 1-cm{sup 2} total-area CuInGaSe{sub 2} (CIGS) thin-film solar cell. For Phase II, the objective was to demonstrate an AM1.5 global 13.5%, 1-cm{sup 2} total-area efficiency. We focused our activities on three areas. First, we modified the CIGS deposition system to double its substrate capacity. Second, we developed new tooling to enable investigation of a modified aqueous CdZnS process in which the goal was to improve the yield of this critical step in the device fabrication process. Third, we upgraded the ZnO sputtering system to improve its reliability and reproducibility. A dual rotatable cathode metallic source was installed, and the sputtering parameters were further optimized to improve ZnO`s properties as a transparent conducting oxide (TCO). Combining the refined CdZnS process with CIGS from the newly fixtured deposition system enable us to fabricate and deliver a ZnO/Cd{sub 0.08}Zn{sub 0.20}S/CuIn{sub 0.74}Ga{sub 0.26}Se{sub 2} cell on alumina with I-V characteristics, as measured by NREL under standard test conditions, of 13.7% efficiency with V{proportional_to} = 0.5458 V, J{sub sc} = 35.48 mA/cm{sup 2}, FF = 0.688, and efficiency = 14.6%.

  8. Research on polycrystalline thin-film submodules based on CuInSe{sub 2} materials. Final subcontract report, 11 November 1990--30 June 1995

    SciTech Connect

    Arya, R; Fogleboch, J; Kessler, J; Russell, L; Skibo, S; Wiedeman, S

    1996-01-01

    This report describes work performed in development of CIS-based photovoltaic (PV) products. The activity began with developing manufacturable deposition methods for all required thin-film layers and developing and understanding processes using those methods. It included demonstrating the potential for high conversion efficiency and followed with developing viable methods for module segment formation and interconnection. These process steps were integrated to fabricate monolithic CIS-based submodules. An important result of this program is the basis of understanding established in developing this material for PV applications, which is necessary to address issues of manufacturability and cost-which were recognized early in the program as being determined by successful solutions to issues of yield, reproducibility, and control as much as by material and energy costs, conversion efficiency, and process speed. Solarex identified at least one absorber formation process that is very robust to shunt formation from pinholes or point defects, tolerant of variation in processing temperature and elemental composition, and is capable of producing high conversion efficiency. This program also allowed development and scale-up of processes for the deposition of all other substrate, heterojunction buffer, and window layers and associated scribing/module formation operations to 1000-CM{sup 2} size. At the completion of this program, Solarex has in place most of the necessary elements to begin the transition to pilot operation of CIS manufacturing activities.

  9. Research on polycrystalline thin-film submodules based on CuInSe{sub 2} materials. Final technical report, 14 December 1995--31 December 1996

    SciTech Connect

    Arya, R.; Fogleboch, J.; Kessler, J.; Russell, L.; Skibo, S.; Wiedeman, S.

    1997-04-01

    This report describes the progress made at Solarex for both device and module efficiencies from the inception of the CIS research program to the present. A rapid improvement in efficiency is apparent, culminating in the fabrication of a 15.5%-efficient device (total area) and a 13%-efficient submodule (aperture area). The device represents the highest efficiency device measured by NREL for any industrial source at that time. The module represented a new world record for any thin-film module at the time of its measurement. The factors leading to these results included improvements in absorber layer quality, transparent contacts, scribing and module formation processes. Other elements critical to the commercialization of CIS-based photovoltaics were also successfully attacked, including reduction of absorber deposition times into the range of 10 to 20 minutes and the successful scale-up of the absorber deposition process to greater than 500 cm{sup 2}. Other requisite processes saw continued development, such as a rapid, low-cost method for transparent window deposition. Subsequent to the demonstration of 13% module efficiency, scribing techniques were further improved that resulted in a reduction in shunt losses and higher module fill factor. This improvement, and the concomitant gain in fill factor, would yield efficiencies approaching 14% on modules having a short-circuit and open-circuit voltage comparable to the record module.

  10. Polycrystalline thin-film cadmium telluride solar cells fabricated by electrodeposition. Annual subcontract report, 20 March 1992--19 March 1993

    SciTech Connect

    Trefny, J.U.; Furtak, T.E.; Wada, N.; Williamson, D.L.; Kim, D.

    1993-08-01

    This report describes progress during the first year of a 3-year program at Colorado School of Mines, based upon earlier studies performed by Ametek Corporation, to develop specific layers of the Ametek n-i-p structure as well as additional studies of several transparent conducting oxides. Thin films of ZnO and ZnO:Al were deposited under various conditions. For the n-layer of the Ametek structure, a dip-coating method was developed for the deposition of CdS films. The authors also present data on the characterization of these films by X-ray diffraction, Raman spectroscopy, scanning tunneling microscopy, small-angle X-ray scattering, and other techniques. They made progress in the electrodeposition of the CdTe i-layer of the Ametek structure. They developed appropriate electrochemical baths and are beginning to understand the role of the many experimental parameters that must be controlled to obtain high-quality films of this material. They explored the possibility of using an electrochemical process for fabricating the ZnTe p-layer. Some preliminary success was achieved, and this step will be pursued in the next phase. Finally, they fabricated a number of ``dot`` solar cells with the structure glass/SnO{sub 2}/CdS/CdTe/Au. Several cells with efficiencies in the range of 5%-6% were obtained, and they are confident, given recent progress, that cells with efficiencies in excess of 10% will be achieved in the near future.

  11. Interdiffusion of CdS and Zn2SnO4 layers and its application in CdS/CdTe polycrystalline thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Wu, X.; Asher, S.; Levi, D. H.; King, D. E.; Yan, Y.; Gessert, T. A.; Sheldon, P.

    2001-04-01

    In this work, we found that the interdiffusion of the CdS and Zn2SnO4 (ZTO) layers can occur either at high temperature (550-650 °C) in Ar or at lower temperature (400-420 °C) in a CdCl2 atmosphere. By integrating a Zn2SnO4 film into a CdS/CdTe solar cell as a buffer layer, this interdiffusion feature can solve several critical issues and improve device performance and reproducibility of both SnO2-based and Cd2SnO4-based CdTe cells. Interdiffusion consumes the CdS film from both the ZTO and CdTe sides during the device fabrication process and improves quantum efficiency at short wavelengths. The ZTO film acts as a Zn source to alloy with the CdS film, which results in increases in the band gap of the window layer and in short-circuit current density Jsc. Interdiffusion can also significantly improve device adhesion after CdCl2 treatment, thus providing much greater process latitude when optimizing the CdCl2 process step. The optimum CdCl2-treated CdTe device has high quantum efficiency at long wavelength, because of its good junction properties and well-passivated CdTe film. We have fabricated a Cd2SnO4/Zn2SnO4/CdS/CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.8% (Voc=844.3 mV, Jsc=25.00 mA/cm2, and fill factor=74.82%). This high-performance cell is one of the best thin-film CdTe solar cells in the world.

  12. MIS and SIS solar cells on polycrystalline silicon

    SciTech Connect

    Cheek, G.; Mertens, R.

    1980-02-01

    MIS and SIS structured solar cells are receiving much attention in the photovoltaic community. Seemingly, these cells could be a viable alternative to thermally diffused p-n junctions for use on thin-film polycrystalline silicon substrates. This review describes MIS/SIS structured solar cells and the possible advantages of these structures for use with thin-film polycrystalline silicon. The results of efficiency calculations are presented. Also addressed are lifetime stability and fabrication techniques amenable to large scale production. Finally, the relative advantages and disadvantages of these cells and the results obtained are presented.

  13. Thin film polycrystalline silicon solar cells

    SciTech Connect

    Ghosh, A. K.; Feng, T.; Eustace, D. J.; Maruska, H. P.

    1980-01-01

    During the present quarter efficiency of heterostructure solar cells has been increased from 13 to 13.7% for single crystal and from 10.3 to 11.2% for polysilicon. For polysilicon the improvements can be attributed to reductions in grid-area coverage and in reflection losses and for single crystal to a combination of reduction in grid-area coverage and increase in fill factor. The heterostructure cells in both cases were IT0/n-Si solar cells. Degradation in Sn0/sub 2//n-Si solar cells can be greatly reduced to negligible proportions by proper encapsulation. The cells used in stability tests have an average initial efficiency of 11% which reduces to a value of about 10.5% after 6 months of exposure to sunlight and ambient conditions. This small degradation occurs within the first month, and the efficiency remains constant subsequently. The reduction in efficiency is due to a decrease in the open-circuit voltage only, while the short-circuit current and fill factor remain constant. The effects of grain-size on the Hall measurements in polysilicon have been analyzed and interpreted, with some modifications, using a model proposed by Bube. This modified model predicts that the measured effective Hall voltage is composed of components originating from the bulk and space-charge region. For materials with large grains, the carrier concentration is independent of the inter-grain boundary barrier, whereas the mobility is dependent on it. However, for small rains, both the carrier density and mobility depend on the barrier. These predictions are consistant with experimental results of mm-size Wacker polysilicon and ..mu..m-size NTD polysilicon.

  14. Thin-film polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Funghnan, B. W.; Blanc, J.; Phillips, W.; Redfield, D.

    1980-08-01

    Thirty-four new solar cells were fabricated on Wacker Sislo substrates and the AM-1 parameters were measured. A detailed comparison was made between the measurement of minority carrier diffusion length by the OE method and the penetrating light laser scan grain boundary photoresponse linewidth method. The laser scan method has more experimental uncertainty and agrees within 10 to 50% with the QE method. It allows determination of L over a large area. Atomic hydrogen passivation studies continued on Wacker material by three techniques. A method of determining surface recombination velocity, s, from laser scan data was developed. No change in s in completed solar cells after H-plasma treatment was observed within experimental error. H-passivation of bare silicon cars as measured by the new laser scan photoconductivity technique showed very large effects.

  15. Epitaxial and polycrystalline GaAs solar cells using OM-CVD techniques

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Shin, B. K.; Stirn, R. J.

    1980-01-01

    GaAs epitaxial films were grown by chemical vapor deposition using organo-metallic sources (OM-CVD) on single crystal and polycrystalline bulk GaAs, as well as on bulk polycrystalline and recrystallized thin-film Ge substrates. Details of Antireflecting Metal-Oxide-Semiconductor (AMOS) solar cells fabricated on GaAs films grown on bulk polycrystalline Ge and recrystallized Ge thin-film substrates will be discussed, as well as preliminary photovoltaic results obtained for n(+)/p homojunction structures.

  16. Gelcasting Polycrystalline Alumina

    SciTech Connect

    Janney, M.A.; Zuk, K.J.; Wei, G.C.

    2000-01-01

    OSRAM SYLVANIA INC. is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux TM line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency ({approximately}97% total transmittance in the visible), their refractoriness (inner wall temperature can reach l2OOC), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, up to 100 initial lumens per watt. (Compare incandescent lamps 10-20 lumens per watt, fluorescent lamps 25-90 lumens per watt.)

  17. Selective and low temperature synthesis of polycrystalline diamond

    NASA Technical Reports Server (NTRS)

    Ramesham, R.; Roppel, T.; Ellis, C.; Baugh, W.; Jaworske, D. A.

    1991-01-01

    Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

  18. Gelcasting polycrystalline alumina

    SciTech Connect

    Janney, M.A.

    1997-04-01

    This work is being done as part of a CRADA with Osram-Sylvania, Inc. (OSI) OSI is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux{reg_sign} line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency (95% total transmittance in the visible region), their refractoriness (inner wall temperature can reach 1400{degrees}C), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, on the order of several hundred lumens / watt. (Compare - incandescent lamps -13 lumens/watt fluorescent lamps -30 lumens/watt.) Osram-Sylvania would like to explore using gelcasting to form PCA tubes for Lumalux{reg_sign} lamps, and eventually for metal halide lamps (known as quartz-halogen lamps). Osram-Sylvania, Inc. currently manufactures PCA tubes by isostatic pressing. This process works well for the shapes that they presently use. However, there are several types of tubes that are either difficult or impossible to make by isostatic pressing. It is the desire to make these new shapes and sizes of tubes that has prompted Osram-Sylvania`s interest in gelcasting. The purpose of the CRADA is to determine the feasibility of making PCA items having sufficient optical quality that they are useful in lighting applications using gelcasting.

  19. Physics of grain boundaries in polycrystalline photovoltaic semiconductors

    SciTech Connect

    Yan, Yanfa Yin, Wan-Jian; Wu, Yelong; Shi, Tingting; Paudel, Naba R.; Li, Chen; Poplawsky, Jonathan; Wang, Zhiwei; Moseley, John; Guthrey, Harvey; Moutinho, Helio; Al-Jassim, Mowafak M.; Pennycook, Stephen J.

    2015-03-21

    Thin-film solar cells based on polycrystalline Cu(In,Ga)Se{sub 2} (CIGS) and CdTe photovoltaic semiconductors have reached remarkable laboratory efficiencies. It is surprising that these thin-film polycrystalline solar cells can reach such high efficiencies despite containing a high density of grain boundaries (GBs), which would seem likely to be nonradiative recombination centers for photo-generated carriers. In this paper, we review our atomistic theoretical understanding of the physics of grain boundaries in CIGS and CdTe absorbers. We show that intrinsic GBs with dislocation cores exhibit deep gap states in both CIGS and CdTe. However, in each solar cell device, the GBs can be chemically modified to improve their photovoltaic properties. In CIGS cells, GBs are found to be Cu-rich and contain O impurities. Density-functional theory calculations reveal that such chemical changes within GBs can remove most of the unwanted gap states. In CdTe cells, GBs are found to contain a high concentration of Cl atoms. Cl atoms donate electrons, creating n-type GBs between p-type CdTe grains, forming local p-n-p junctions along GBs. This leads to enhanced current collections. Therefore, chemical modification of GBs allows for high efficiency polycrystalline CIGS and CdTe thin-film solar cells.

  20. Polycrystalline Diamond Schottky Diodes and Their Applications.

    NASA Astrophysics Data System (ADS)

    Zhao, Ganming

    In this work, four-hot-filament CVD techniques for in situ boron doped diamond synthesis on silicon substrates were extensively studied. A novel tungsten filament shape and arrangement used to obtain large-area, uniform, boron doped polycrystalline diamond thin films. Both the experimental results and radiative heat transfer analysis showed that this technique improved the uniformity of the substrate temperature. XRD, Raman and SEM studies indicate that large area, uniform, high quality polycrystalline diamond films were obtained. Schottky diodes were fabricated by either sputter deposition of silver or thermal evaporation of aluminum or gold, on boron doped diamond thin films. High forward current density and a high forward-to-reverse current ratio were exhibited by silver on diamond Schottky diodes. Schottky barrier heights and the majority carrier concentrations of both aluminum and gold contacted diodes were determined from the C-V measurements. Furthermore, a novel theoretical C-V-f analysis of deep level boron doped diamond Schottky diodes was performed. The analytical results agree well with the experimental results. Compressive stress was found to have a large effect on the forward biased I-V characteristics of the diamond Schottky diodes, whereas the effect on the reverse biased characteristics was relatively small. The stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. This result shows that CVD diamond device has potential for mechanical transducer applications. The quantitative photoresponse characteristics of the diodes were studied in the spectral range of 300 -1050 nm. Semi-transparent gold contacts were used for better photoresponse. Quantum efficiency as high as 50% was obtained at 500 nm, when a reverse bias of over 1 volt was applied. The Schottky barrier heights between either gold or

  1. Anomalous photoelectric effect of a polycrystalline topological insulator film.

    PubMed

    Zhang, Hongbin; Yao, Jiandong; Shao, Jianmei; Li, Hai; Li, Shuwei; Bao, Dinghua; Wang, Chengxin; Yang, Guowei

    2014-01-01

    A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators. PMID:25069391

  2. Role of polycrystallinity in CdTe and CuInSe[sub 2] photovoltaic cells

    SciTech Connect

    Sites, J.R. )

    1992-11-01

    The limiting role of polycrystallinity in thin-film solar calls has been reduced somewhat during the past year, and efficiencies of both CdTe and CuInSe[sub 2] cells are approaching 15%. Quantitative separation of loss mechanisms shows that individual losses, with the exception of forward recombination current, can be made comparable to their single crystal counterparts. One general manifestation of the extraneous trapping states in that the voltage of all polycrystalline thin-film cells drifts upward by 10--50 mV following the onset of illumination.

  3. Surface properties of atomically flat poly-crystalline SrTiO3

    PubMed Central

    Woo, Sungmin; Jeong, Hoidong; Lee, Sang A.; Seo, Hosung; Lacotte, Morgane; David, Adrian; Kim, Hyun You; Prellier, Wilfrid; Kim, Yunseok; Choi, Woo Seok

    2015-01-01

    Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding the TMO domains and grain boundaries. PMID:25744275

  4. Plastic flow of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Langer, James

    Leo Kadanoff had a long interest in fluid flows, especially fingering instabilities. This interest was one example of his insatiable curiosity about simple, fundamentally important, and often multidisciplinary phenomena. Here is an example of another class of such phenomena that I had hoped to show him this year. The experts in polycrystalline solid mechanics have insisted for decades that their central problem - dislocation-mediated strain hardening - is intrinsically unsolvable. I think they're wrong. My colleagues and I have made progress recently in theories of both amorphous and polycrystalline plasticity by introducing an effective disorder temperature as a dynamical variable in our equations of motion. In this way, we have been able to describe how the densities of flow defects or dislocations evolve in response to external forcing, and thus to develop theories that promise to become as predictive, and full of surprises, as the laws of fluid flow. For Kadanoff session.

  5. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy

    PubMed Central

    Schmid, T.; Schäfer, N.; Levcenko, S.; Rissom, T.; Abou-Ras, D.

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  6. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy.

    PubMed

    Schmid, T; Schäfer, N; Levcenko, S; Rissom, T; Abou-Ras, D

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  7. Measuring long-range carrier diffusion across multiple grains in polycrystalline semiconductors by photoluminescence imaging

    PubMed Central

    Alberi, K.; Fluegel, B.; Moutinho, H.; Dhere, R. G.; Li, J. V.; Mascarenhas, A.

    2013-01-01

    Thin-film polycrystalline semiconductors are currently at the forefront of inexpensive large-area solar cell and integrated circuit technologies because of their reduced processing and substrate selection constraints. Understanding the extent to which structural and electronic defects influence carrier transport in these materials is critical to controlling the optoelectronic properties, yet many measurement techniques are only capable of indirectly probing their effects. Here we apply a novel photoluminescence imaging technique to directly observe the low temperature diffusion of photocarriers through and across defect states in polycrystalline CdTe thin films. Our measurements show that an inhomogeneous distribution of localized defect states mediates long-range hole transport across multiple grain boundaries to locations exceeding 10 μm from the point of photogeneration. These results provide new insight into the key role deep trap states have in low temperature carrier transport in polycrystalline CdTe by revealing their propensity to act as networks for hopping conduction. PMID:24158163

  8. Losses in polycrystalline silicon waveguides

    NASA Astrophysics Data System (ADS)

    Foresi, J. S.; Black, M. R.; Agarwal, A. M.; Kimerling, L. C.

    1996-04-01

    The losses of polycrystalline silicon (polySi) waveguides clad by SiO2 are measured by the cutback technique. We report losses of 34 dB/cm at a wavelength of 1.55 μm in waveguides fabricated from chemical mechanical polished polySi deposited at 625 °C. These losses are two orders of magnitude lower than reported absorption measurements for polySi. Waveguides fabricated from unpolished polySi deposited at 625 °C exhibit losses of 77 dB/cm. We find good agreement between calculated and measured losses due to surface scattering.

  9. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  10. Low temperature production of large-grain polycrystalline semiconductors

    DOEpatents

    Naseem, Hameed A.; Albarghouti, Marwan

    2007-04-10

    An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

  11. Applications of thin-film photovoltaics for space

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.; Hepp, Aloysius F.

    1991-01-01

    The authors discuss the potential applications of thin-film polycrystalline and amorphous cells for space. There have been great advances in thin-film solar cells for terrestrial applications. Transfer of this technology to space applications could result in ultra low-weight solar arrays with potentially large gains in specific power. Recent advances in thin-film solar cells are reviewed, including polycrystalline copper indium selenide and related I-III-VI2 compounds, polycrystalline cadmium telluride and related II-VI compounds, and amorphous silicon arrays. The possibility of using thin-film multi-bandgap cascade solar cells is discussed.

  12. Thin-Film Photovoltaics: Status and Applications to Space Power

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.; Hepp, Aloysius F.

    1991-01-01

    The potential applications of thin film polycrystalline and amorphous cells for space are discussed. There have been great advances in thin film solar cells for terrestrial applications; transfer of this technology to space applications could result in ultra low weight solar arrays with potentially large gains in specific power. Recent advances in thin film solar cells are reviewed, including polycrystalline copper iridium selenide and related I-III-VI2 compounds, polycrystalline cadmium telluride and related II-VI compounds, and amorphous silicon alloys. The possibility of thin film multi bandgap cascade solar cells is discussed.

  13. Casting larger polycrystalline silicon ingots

    SciTech Connect

    Wohlgemuth, J.; Tomlinson, T.; Cliber, J.; Shea, S.; Narayanan, M.

    1995-08-01

    Solarex has developed and patented a directional solidification casting process specifically designed for photovoltaics. In this process, silicon feedstock is melted in a ceramic crucible and solidified into a large grained semicrystalline silicon ingot. In-house manufacture of low cost, high purity ceramics is a key to the low cost fabrication of Solarex polycrystalline wafers. The casting process is performed in Solarex designed casting stations. The casting operation is computer controlled. There are no moving parts (except for the loading and unloading) so the growth process proceeds with virtually no operator intervention Today Solarex casting stations are used to produce ingots from which 4 bricks, each 11.4 cm by 11.4 cm in cross section, are cut. The stations themselves are physically capable of holding larger ingots, that would yield either: 4 bricks, 15 cm by 15 an; or 9 bricks, 11.4 cm by 11.4 an in cross-section. One of the tasks in the Solarex Cast Polycrystalline Silicon PVMaT Program is to design and modify one of the castings stations to cast these larger ingots. If successful, this effort will increase the production capacity of Solarex`s casting stations by 73% and reduce the labor content for casting by an equivalent percentage.

  14. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1985-01-01

    Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells.

  15. Morphology of polycrystalline cassiterite films

    NASA Astrophysics Data System (ADS)

    Tomaev, V. V.; Glazov, A. I.

    2014-09-01

    Polycrystalline cassiterite films have been grown by the hydropyrolytic method from a 10(H2O) + 5(SnCl2 · 2H2O) solution (in weight fractions) on corundum substrates. The crystallization regularities are considered and a comparative analysis of the properties of natural and artificial cassiterite crystals is performed. The surface morphology is investigated and the size of crystalline grains is determined by scanning electron microscopy. X-ray microprobe analysis showed that all films contain tin and oxygen atoms in a ratio corresponding (within the experimental error) to the chemical formula of tin dioxide. It is established that the surface morphology of cassiterite films is characterized by both single crystallites and aggregates of two or more crystals typical of twins. It is suggest that doping can efficiently be used to control the concentration of twins and the stability of their formation.

  16. Saturation magnetization of polycrystalline iron

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.; Hegland, D. E.

    1972-01-01

    The magnetic moment per gram, sigma (H sub I, T), where H sub I is the internal field and T is the temperature, was measured for a polycrystalline iron sphere with the vibrating-sample magnetometer. The instrument was calibrated by using a method utilizing the high permeability of an iron sphere. The spontaneous moment, sigma(0, T),was obtained from plots of sigma(H sub I, T) as a function of H sub I for temperatures from 4.2 K to room temperature. The value of the spontaneous moment, sigma(0, T), at 298.9 K was 217.5 + or -0.4 emu/g. The extrapolated moment, sigma(0, 0),at absolute zero from a plot of sigma(0, T) as a function of T to 3/2 power was 221.7 + or - 0.4 emu/g.

  17. Polycrystalline Silicon: a Biocompatibility Assay

    SciTech Connect

    Pecheva, E.; Fingarova, D.; Pramatarova, L.; Hikov, T.; Laquerriere, P.; Bouthors, Sylvie; Dimova-Malinovska, D.; Montgomery, P.

    2010-01-21

    Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

  18. Development of transparent polycrystalline beta-silicon carbide

    NASA Astrophysics Data System (ADS)

    Bayya, Shyam S.; Villalobos, Guillermo R.; Hunt, Michael P.; Sanghera, Jasbinder S.; Sadowski, Bryan M.; Aggarwal, Ishwar D.; Cinibulk, Michael; Carney, Carmen; Keller, Kristin

    2013-09-01

    Transparent beta-SiC is of great interest because its high strength, low coefficient of thermal expansion, very high thermal conductivity, and cubic crystal structure give it a very high thermal shock resistance. A transparent, polycrystalline beta-SiC window will find applications in armor, hypersonic missiles, and thermal control for thin disc lasers. SiC is currently available as either small transparent vapor grown disks or larger opaque shapes. Neither of which are useful in window applications. We are developing sintering technology to enable transparent SiC ceramics. This involves developing procedures to make high purity powders and studying their densification behavior. We have been successful in demonstrating transparency in thin sections using Field Assisted Sintering Technology (FAST). This paper will discuss the reaction mechanisms in the formation of beta-SiC powder and its sintering behavior in producing transparent ceramics.

  19. Defect engineering by ultrasound treatment in polycrystalline silicon

    SciTech Connect

    Ostapenko, S.; Jastrzebski, L.

    1995-08-01

    By applying ultrasound treatment (UST) to bulk and thin film polycrystalline Si (poly-Si) we have found a dramatic improvement of recombination and transport properties. The increasing of minority carrier lifetime by as much as one order of magnitude was found in short diffusion length regions, while exhibiting a strong dispersion for entire solar-grade poly-Si wafer. Relevant mechanisms are attributed to ultrasound processing on crystallographic defects, as well as UST stimulated dissociation of Fe-B pairs followed by Fe{sub i} gettering. A spectacular improvement of hydrogenation efficiency in poly-Si thin-films on glass substrate is demonstrated by resistivity study and confirmed using spatially resolved photoluminescence and nanoscale contact potential difference mapping. By applying UST to commercial solar cells we found the increasing of cell efficiency at low light excitation.

  20. Time-resolved photoluminescence of polycrystalline CdTe grown by close-spaced sublimation

    SciTech Connect

    Keyes, B.; Dhere, R.; Ramanathan, K. )

    1994-06-30

    Polycrystalline CdTe has shown great promise as a low-cost material for thin-film, terrestrial photovoltaic applications, with efficiencies approaching 16% achieved with close-spaced sublimation (CSS)-grown CdTe. Due to the inherent complexities of polycrystalline material, much of the progress in this area has occurred through a slow trial-and-error process. This report uses time-resolved photoluminescence (TRPL) to characterize the CdTe material quality as a function of one basic growth parameter---substrate temperature. This characterization is done for two different glass substrate materials, soda-lime silicate and borosilicate.

  1. Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells; Annual subcontract report, 1 March 1992--28 February 1993

    SciTech Connect

    Gray, J.L.; Schwartz, R.J.; Lee, Y.J.

    1994-03-01

    Solar cells operate by converting the radiation power from sun light into electrical power through photon absorption by semiconductor materials. The elemental and compound material systems widely used in photovoltaic applications can be produced in a variety of crystalline and non-crystalline forms. Although the crystalline group of materials have exhibited high conversion efficiencies, their production cost are substantially high. Several candidates in the poly- and micro-crystalline family of materials have recently gained much attention due to their potential for low cost manufacturability, stability, reliability and good performance. Among those materials, CuInSe{sub 2} and CdTe are considered to be the best choices for production of thin film solar cells because of the good optical properties and almost ideal band gap energies. Considerable progress was made with respect to cell performance and low cost manufacturing processes. Recently conversion efficiencies of 14.1 and 14.6% have been reported for CuInSe{sub 2} and CdTe based solar cells respectively. Even though the efficiencies of these cells continue to improve, they are not fully understood materials and there lies an uncertainty in their electrical properties and possible attainable performances. The best way to understand the details of current transport mechanisms and recombinations is to model the solar cells numerically. By numerical modeling, the processes which limit the cell performance can be sought and therefore, the most desirable designs for solar cells utilizing these materials as absorbers can be predicted. The problems with numerically modeling CuInSe{sub 2} and CdTe solar cells are that reported values of the pertinent material parameters vary over a wide range, and some quantities such as carrier concentration are not explicitly controlled.

  2. Composite polycrystalline semiconductor neutron detectors

    NASA Astrophysics Data System (ADS)

    Schieber, M.; Zuck, A.; Marom, G.; Khakhan, O.; Roth, M.; Alfassi, Z. B.

    2007-08-01

    Composite polycrystalline semiconductor detectors bound with different binders, both inorganic molten glasses, such as B 2O 3, PbO/B 2O 3, Bi 2O 3/PbO, and organic polymeric binders, such as isotactic polypropylene (iPP), polystyrene or nylon-6, and coated with different metal electrodes were tested at room temperature for α-particles and very weak thermal neutron sources. The detector materials tested were natural occurring hexagonal BN and cubic LiF, where both are not containing enriched isotopes of 10B or 6Li. The radiation sources were 5.5 MeV α's from 241Am, 5.3 MeV from 210Po and also 4.8 MeV from 226Ra. Some of these detectors were also tested with thermal neutrons from very weak 227Ac 9Be, 241Am- 10Be sources and also from a weak 238Pu+ 9Be and somewhat stronger 252Cf sources. The neutrons were thermalized with paraffin. Despite very low signal to noise ratio of only ˜2, the neutrons could be counted by subtracting the noise from the signal.

  3. The electrical conduction properties of poly-crystalline indium-zinc-oxide film

    SciTech Connect

    Tomai, S.; Terai, K.; Junke, T.; Tsuruma, Y.; Ebata, K.; Yano, K.; Uraoka, Y.

    2014-02-28

    We have developed a high-mobility and high-uniform oxide semiconductor using poly-crystalline semiconductor material composed of indium and zinc (p-IZO). A typical conduction mechanism of p-IZO film was demonstrated by the grain boundary scattering model as in polycrystalline silicon. The grain boundary potential of the 2-h-annealed IZO film was calculated to be 100 meV, which was comparable to that of the polycrystalline silicon. However, the p-IZO thin film transistor (TFT) measurement shows rather uniform characteristics. It denotes that the mobility deterioration around the grain boundaries is lower than the case for low-temperature polycrystalline silicon. This assertion was made based on the difference of the mobility between the polycrystalline and amorphous IZO film being much smaller than is the case for silicon transistors. Therefore, we conclude that the p-IZO is a promising material for a TFT channel, which realizes high drift mobility and uniformity simultaneously.

  4. Laser processing for thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Compaan, Alvin D.

    1995-04-01

    Over the past decade major advances have occurred in the field of thin- film photovoltaics (PV) with many of them a direct consequence of the application of laser processing. Improved cell efficiencies have been achieved in crystalline and polycrystalline Si, in hydrogenated amorphous silicon, and in two polycrystalline thin-film materials. The use of lasers in photovoltaics includes laser hole drilling for emitter wrap-through, laser trenching for buried bus lines, and laser texturing of crystalline and polycrystalline Si cells. In thin-film devices, laser scribing is gaining increased importance for module interconnects. Pulsed laser recrystallization of boron-doped hydrogenated amorphous silicon is used to form highly conductive p-layers in p-i-n amorphous silicon cells and in thin-film transistors. Optical beam melting appears to be an attractive method for forming metal semiconductor alloys for contact formation. Finally, pulsed lasers are used for deposition of the entire semiconductor absorber layer in two types of polycrystalline thin-film cells-those based on copper indium diselenide and those based on cadmium telluride. In our lab we have prepared and studied heavily doped polycrystalline silicon thin films and also have used laser physical vapor deposition (LPVD) to prepare 'all-LPVD' CdS/CdTe solar cells on glass with efficiencies tested at NREL at 10.5%. LPVD is highly flexible and ideally suited for prototyping PV cells using ternary or quaternary alloys and for exploring new dopant combinations.

  5. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  6. Near field scanning optical microscopy of polycrystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Herndon, Mary Kay

    1999-09-01

    Photovoltaic devices are commonly used for space applications and remote terrestrial power requirements. Polycrystalline solar cell devices often have much lower efficiencies than their crystalline counterparts, but because they can be fabricated much more cheaply, they can still be cost-effective when compared to single crystal devices. The long term goal of this work is to provide information that will lead to higher quality devices with improved cost efficiency. In order to do this, a better understanding of the mechanisms that take place in these materials is needed. The goal of this thesis was to improve our understanding of these devices by adapting a novel characterization technique, Near Field Scanning Optical Microscopy (NSOM), to the study of polycrystalline films. Visible light NSOM is a relatively new technique that allows for optical characterization of materials with resolution beyond the far-field diffraction limit. By using NSOM to study the physical and electrical properties of polycrystalline solar cells, individual grains can be studied and more insight can be gained as to how various properties of the thin films affect the device efficiency. For this research, an NSOM was designed and built to be versatile enough to handle the sorts of samples and measurements required for studying a variety of photovoltaic devices. As a first step, the NSOM was used to characterize single crystal GaAs solar cell devices. Measurements of topography and NSOM-induced photocurrent were obtained simultaneously on cross sections of the material, allowing the p-n junction to be probed. Because the NSOM data could be compared to an expected result, this allowed verification of the new microscope's imaging capabilities and ensured accurate data interpretation. Effects of surface recombination were detected on the cleaved edges. The NSOM was used to characterize surface quality and study the effects of surface passivation treatments. Of the polycrystalline materials

  7. Ultrafast dynamics of exciton fission in polycrystalline pentacene.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Clark, Jenny; Kumar, R Sai Santosh; Brida, Daniele; Cerullo, Giulio; Friend, Richard H

    2011-08-10

    We use ultrafast transient absorption spectroscopy with sub-20 fs time resolution and broad spectral coverage to directly probe the process of exciton fission in polycrystalline thin films of pentacene. We observe that the overwhelming majority of initially photogenerated singlet excitons evolve into triplet excitons on an ∼80 fs time scale independent of the excitation wavelength. This implies that exciton fission occurs at a rate comparable to phonon-mediated exciton localization processes and may proceed directly from the initial, delocalized, state. The singlet population is identified due to the brief presence of stimulated emission, which is emitted at wavelengths which vary with the photon energy of the excitation pulse, a violation of Kasha's Rule that confirms that the lowest-lying singlet state is extremely short-lived. This direct demonstration that triplet generation is both rapid and efficient establishes multiple exciton generation by exciton fission as an attractive route to increased efficiency in organic solar cells. PMID:21755937

  8. Growth of polycrystalline Heusler alloys for spintronic devices

    NASA Astrophysics Data System (ADS)

    Sagar, J.; Yu, C. N. T.; Lari, L.; Hirohata, A.

    2014-07-01

    We have prepared polycrystalline Co2FeSi thin films on a number of seed layers to optimize their structural and magnetic properties. Using a Cr/Ag combined seed layer, films have been produced with extremely low interfacial roughness (<1 nm) and controllable coercivities in the range 12-27 Oe. Such a structure would be suitable for the free layer in a spintronic device. Using a NiCr seed layer and IrMn as an antiferromagnetic layer a small exchange bias of ˜30 Oe has been achieved. However the use of a 0.5 nm Mn layer at the IrMn/Co2FeSi interface increases the exchange bias (Hex) to 375 Oe after annealing. This structure would be suitable for the pinned layer in a spintronic device.

  9. Process Research of Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1984-01-01

    A passivation process (hydrogenation) that will improve the power generation of solar cells fabricated from presently produced, large grain, cast polycrystalline silicon (Semix), a potentially low cost material are developed. The first objective is to verify the operation of a DC plasma hydrogenation system and to investigate the effect of hydrogen on the electrical performance of a variety of polycrystalline silicon solar cells. The second objective is to parameterize and optimize a hydrogenation process for cast polycrystalline silicon, and will include a process sensitivity analysis. The sample preparation for the first phase is outlined. The hydrogenation system is described, and some early results that were obtained using the hydrogenation system without a plasma are summarized. Light beam induced current (LBIC) measurements of minicell samples, and their correlation to dark current voltage characteristics, are discussed.

  10. Orientation imaging microscopy of polycrystalline sodium chloride

    SciTech Connect

    Staiger, M.P.; Kolbeinsson, I.; Newman, J.; Woodfield, T.; Sato, T.

    2010-04-15

    A novel preparation technique is described that makes possible grain size analysis of polycrystalline NaCl using orientation imaging microscopy via electron backscatter diffraction (EBSD). The preparation methodology is specifically developed to overcome difficulties in preparing microporous NaCl for microscopy. The grain size and crystallographic texture of polycrystalline NaCl samples, prepared via solution pressure and sintered in the range of 650-780 deg. C, were able to be measured successfully with EBSD. The limitations of the preparation technique for EBSD analysis of NaCl are also discussed.

  11. Process Research On Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Culik, J. S.

    1982-01-01

    The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented.

  12. Polycrystalline silicon on tungsten substrates

    NASA Technical Reports Server (NTRS)

    Bevolo, A. J.; Schmidt, F. A.; Shanks, H. R.; Campisi, G. J.

    1979-01-01

    Thin films of electron-beam-vaporized silicon were deposited on fine-grained tungsten substrates under a pressure of about 1 x 10 to the -10th torr. Mass spectra from a quadrupole residual-gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400 and 780 C, and deposition rates were between 20 and 630 A min. Surface contamination and interdiffusion were monitored by in situ Auger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, X-ray analysis, and SEM in the topographic and channeling modes were utilized to characterize the samples with respect to silicon-metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625 C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine-grain silicon films were obtained at lower temperatures.

  13. Method of making quasi-grain boundary-free polycrystalline solar cell structure and solar cell structure obtained thereby

    DOEpatents

    Gonzalez, Franklin N.; Neugroschel, Arnost

    1984-02-14

    A new solar cell structure is provided which will increase the efficiency of polycrystalline solar cells by suppressing or completely eliminating the recombination losses due to the presence of grain boundaries. This is achieved by avoiding the formation of the p-n junction (or other types of junctions) in the grain boundaries and by eliminating the grain boundaries from the active area of the cell. This basic concept can be applied to any polycrystalline material; however, it will be most beneficial for cost-effective materials having small grains, including thin film materials.

  14. Stochastic multiscale modeling of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Wen, Bin

    Mechanical properties of engineering materials are sensitive to the underlying random microstructure. Quantification of mechanical property variability induced by microstructure variation is essential for the prediction of extreme properties and microstructure-sensitive design of materials. Recent advances in high throughput characterization of polycrystalline microstructures have resulted in huge data sets of microstructural descriptors and image snapshots. To utilize these large scale experimental data for computing the resulting variability of macroscopic properties, appropriate mathematical representation of microstructures is needed. By exploring the space containing all admissible microstructures that are statistically similar to the available data, one can estimate the distribution/envelope of possible properties by employing efficient stochastic simulation methodologies along with robust physics-based deterministic simulators. The focus of this thesis is on the construction of low-dimensional representations of random microstructures and the development of efficient physics-based simulators for polycrystalline materials. By adopting appropriate stochastic methods, such as Monte Carlo and Adaptive Sparse Grid Collocation methods, the variability of microstructure-sensitive properties of polycrystalline materials is investigated. The primary outcomes of this thesis include: (1) Development of data-driven reduced-order representations of microstructure variations to construct the admissible space of random polycrystalline microstructures. (2) Development of accurate and efficient physics-based simulators for the estimation of material properties based on mesoscale microstructures. (3) Investigating property variability of polycrystalline materials using efficient stochastic simulation methods in combination with the above two developments. The uncertainty quantification framework developed in this work integrates information science and materials science, and

  15. Development and evaluation of polycrystalline cadmium telluride dosimeters for accurate quality assurance in radiation therapy

    NASA Astrophysics Data System (ADS)

    Oh, K.; Han, M.; Kim, K.; Heo, Y.; Moon, C.; Park, S.; Nam, S.

    2016-02-01

    For quality assurance in radiation therapy, several types of dosimeters are used such as ionization chambers, radiographic films, thermo-luminescent dosimeter (TLD), and semiconductor dosimeters. Among them, semiconductor dosimeters are particularly useful for in vivo dosimeters or high dose gradient area such as the penumbra region because they are more sensitive and smaller in size compared to typical dosimeters. In this study, we developed and evaluated Cadmium Telluride (CdTe) dosimeters, one of the most promising semiconductor dosimeters due to their high quantum efficiency and charge collection efficiency. Such CdTe dosimeters include single crystal form and polycrystalline form depending upon the fabrication process. Both types of CdTe dosimeters are commercially available, but only the polycrystalline form is suitable for radiation dosimeters, since it is less affected by volumetric effect and energy dependence. To develop and evaluate polycrystalline CdTe dosimeters, polycrystalline CdTe films were prepared by thermal evaporation. After that, CdTeO3 layer, thin oxide layer, was deposited on top of the CdTe film by RF sputtering to improve charge carrier transport properties and to reduce leakage current. Also, the CdTeO3 layer which acts as a passivation layer help the dosimeter to reduce their sensitivity changes with repeated use due to radiation damage. Finally, the top and bottom electrodes, In/Ti and Pt, were used to have Schottky contact. Subsequently, the electrical properties under high energy photon beams from linear accelerator (LINAC), such as response coincidence, dose linearity, dose rate dependence, reproducibility, and percentage depth dose, were measured to evaluate polycrystalline CdTe dosimeters. In addition, we compared the experimental data of the dosimeter fabricated in this study with those of the silicon diode dosimeter and Thimble ionization chamber which widely used in routine dosimetry system and dose measurements for radiation

  16. Equilibrium shapes of polycrystalline silicon nanodots

    SciTech Connect

    Korzec, M. D. Wagner, B.; Roczen, M.; Schade, M.; Rech, B.

    2014-02-21

    This study is concerned with the topography of nanostructures consisting of arrays of polycrystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a “dewetting” process of an amorphous Si (a-Si) layer from a SiO{sub 2} coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support “partial wetting” and grain boundaries for the polycrystalline case. We then use our method to predict the morphologies of silicon nanodots.

  17. Hydrogen migration in phosphorous doped polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Kaiser, I.

    1998-12-31

    Hydrogen diffusion in phosphorous doped polycrystalline silicon was investigated by deuterium diffusion experiments. The presence of phosphorous enhances hydrogen diffusion. For high hydrogen concentrations the activation energy of the effective diffusion-coefficient amounts to 0.25--0.35 eV. At low hydrogen concentrations diffusion is governed by deep traps that are present in an appreciable concentration of 6 {times} 10{sup 18}--10{sup 19} cm{sup {minus}3}. The hydrogen chemical-potential, {mu}{sub H}, decreases with increasing temperature at a rate of {approx}0.002 eV/K. The data are discussed in terms of a two-level model used to describe hydrogen diffusion in amorphous and undoped polycrystalline silicon.

  18. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1982-01-01

    The investigation of the performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was continued by fabricating a set of minicell wafers on a selection of 10 cm x 10 cm wafers. A minicell wafer consists of an array of small (approximately 0.2 sq cm in area) photodiodes which are isolated from one another by a mesa structure. The junction capacitance of each minicell was used to obtain the dopant concentration, and therefore the resistivity, as a function of position across each wafer. The results indicate that there is no significant variation in resistivity with position for any of the polycrystalline wafers, whether Semix or Wacker. However, the resistivity of Semix brick 71-01E did decrease slightly from bottom to top.

  19. Enhanced photovoltaic properties in graphene/polycrystalline BiFeO3/Pt heterojunction structure

    NASA Astrophysics Data System (ADS)

    Zang, Yongyuan; Xie, Dan; Wu, Xiao; Chen, Yu; Lin, Yuxuan; Li, Mohan; Tian, He; Li, Xiao; Li, Zhen; Zhu, Hongwei; Ren, Tianling; Plant, David

    2011-09-01

    We report the enhanced photovoltaic properties in polycrystalline BiFeO3 (BFO) thin films with graphene as top electrodes. The short circuit current density (Jsc) and open circuit voltage of the heterojunction are measured to be 25 μA/cm2 and 0.44 V, respectively, much higher than the reported values for polycrystalline BFO with indium tin oxide (ITO) as top electrodes. Influence of HNO3 treatment on the photovoltaic properties is studied, and a significant photocurrent density improvement from 25 μA/cm2 to 2.8 mA/cm2 is observed. A metal-intrinsic semiconductor-metal model is proposed to explain the graphene induced enhancement comparing with traditional ITO.

  20. Grain-boundary resistance in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Reiss, G.; Vancea, J.; Hoffmann, H.

    1986-05-01

    Grain boundaries are known to reduce significantly the electrical dc conductivity of polycrystalline metallic materials. In this paper, we give a quantum mechanical calculation of the grain-boundary resistance based on the transfer matrix approach. The results show an exponential decrease of the conductivity with respect to the number of grain boundaries per mean free path in accord with an empirical model proposed recently.

  1. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  2. Application of neutron holography to polycrystalline samples

    NASA Astrophysics Data System (ADS)

    Szakál, A.; Markó, M.; Krexner, G.; Cser, L.

    2015-07-01

    Neutron holography can be an efficient tool to investigate the local real-space structure of crystalline materials around specific probe nuclei serving as radiation source or detector. The positions of atoms in the neighborhood of such nuclei are observable with high (picometry) accuracy. Measurements of this type require orientational order and, therefore, restrict the range of study essentially to single crystals. However, if the information searched for is limited to the distances between the probe and the surrounding nuclei instead of their positions, holographic techniques can be applied to polycrystalline samples as well. In order to prove this statement, the expected multi-wavelength holographic signal of a polycrystalline sample was calculated. The holographic signal can be obtained by applying time-of-flight techniques, and by using a proper mathematical procedure, the distances between the probe nucleus and the surrounding nuclei can be reconstructed. A model calculation taking into account real instrument parameters confirms this expectation. The experimental verification of the predictions can be undertaken at existing pulsed neutron sources being able to provide the required experimental conditions. This new method opens the way to expand the field of investigation towards gaining information about the local atomic structure of polycrystalline materials which are of importance also in various applications.

  3. Effective structural properties in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Hossain, Zubaer

    This talk will discuss effective structural properties in polycrystalline graphene under the presence of atomic scale heterogeneity. Polycrystallinity is ubiquitous in solids, but theories describing their effective behavior remain limited, particularly when heterogeneity is present in the form of nonuniform deformation or composition. Over the decades, exploration of the effective transport and strength properties of heterogeneous systems has been carried out mostly with random distribution of grains or regular periodic structures under various approximations, in translating the underlying physics into a single representative volume element. Although heterogeneity can play a critical role in modulating the basic behavior of low-dimensional materials, it is difficult to capture the local characteristics accurately by these approximations. Taking polycrystalline graphene as an example material, we study the effective structural properties (such as Young's Modulus, Poisson's ratio and Toughness) by using a combination of density functional theory and molecular dynamic simulations. We identify the key mechanisms that govern their effective behavior and exploit the understanding to engineer the behavior by doping with a carefully selected choice of chemical elements.

  4. Characterization of electrochemically modified polycrystalline platinum surfaces

    SciTech Connect

    Krebs, L.C.; Ishida, Takanobu.

    1991-12-01

    The characterization of electrochemically modified polycrystalline platinum surfaces has been accomplished through the use of four major electrochemical techniques. These were chronoamperometry, chronopotentiommetry, cyclic voltammetry, and linear sweep voltammetry. A systematic study on the under-potential deposition of several transition metals has been performed. The most interesting of these were: Ag, Cu, Cd, and Pb. It was determined, by subjecting the platinum electrode surface to a single potential scan between {minus}0.24 and +1.25 V{sub SCE} while stirring the solution, that the electrocatalytic activity would be regenerated. As a consequence of this study, a much simpler method for producing ultra high purity water from acidic permanganate has been developed. This method results in water that surpasses the water produced by pyrocatalytic distillation. It has also been seen that the wettability of polycrystalline platinum surfaces is greatly dependent on the quantity of oxide present. Oxide-free platinum is hydrophobic and gives a contact angle in the range of 55 to 62 degrees. We have also modified polycrystalline platinum surface with the electrically conducting polymer poly-{rho}-phenylene. This polymer is very stable in dilute sulfuric acid solutions, even under applied oxidative potentials. It is also highly resistant to electrochemical hydrogenation. The wettability of the polymer modified platinum surface is severely dependent on the choice of supporting electrolyte chosen for the electrochemical polymerization. Tetraethylammonium tetrafluoroborate produces a film that is as hydrophobic as Teflon, whereas tetraethylammonium perchlorate produces a film that is more hydrophilic than oxide-free platinum.

  5. Thickness-dependent cooperative aging in polycrystalline films of antiferromagnet CoO

    NASA Astrophysics Data System (ADS)

    Ma, Tianyu; Cheng, Xiang; Boettcher, Stefan; Urazhdin, Sergei; Novozhilova, Lydia

    2016-07-01

    We demonstrate that thin polycrystalline films of antiferromagnet CoO, in bilayers with ferromagnetic Permalloy, exhibit slow power-law aging of their magnetization state. The aging characteristics are remarkably similar to those previously observed in thin epitaxial Fe50Mn50 films, indicating that these behaviors are likely generic to ferromagnet/antiferromagnet bilayers. In very thin films, aging is observed over a wide temperature range. In thicker CoO, aging effects become reduced at low temperatures. Aging entirely disappears for large CoO thicknesses. We also investigate the dependence of aging characteristics on temperature and magnetic history. Analysis shows that the observed behaviors are inconsistent with the Neel-Arrhenius model of thermal activation, and are instead indicative of cooperative aging of the antiferromagnet. Our results provide new insights into the mechanisms controlling the stationary states and dynamics of ferromagnet/antiferromagnet bilayers, and potentially other frustrated magnetic systems.

  6. Abnormality in fracture strength of polycrystalline silicene

    NASA Astrophysics Data System (ADS)

    Liu, Ning; Hong, Jiawang; Pidaparti, Ramana; Wang, Xianqiao

    2016-09-01

    Silicene, a silicon-based homologue of graphene, arouses great interest in nano-electronic devices due to its outstanding electronic properties. However, its promising electronic applications are greatly hindered by lack of understanding in the mechanical strength of silicene. Therefore, in order to design mechanically reliable devices with silicene, it is necessary to thoroughly explore the mechanical properties of silicene. Due to current fabrication methods, graphene is commonly produced in a polycrystalline form; the same may hold for silicene. Here we perform molecular dynamics simulations to investigate the mechanical properties of polycrystalline silicene. First, an annealing process is employed to construct a more realistic modeling structure of polycrystalline silicene. Results indicate that a more stable structure is formed due to the breaking and reformation of bonds between atoms on the grain boundaries. Moreover, as the grain size decreases, the efficiency of the annealing process, which is quantified by the energy change, increases. Subsequently, biaxial tensile tests are performed on the annealed samples in order to explore the relation between grain size and mechanical properties, namely in-plane stiffness, fracture strength and fracture strain etc. Results indicate that as the grain size decreases, the fracture strain increases while the fracture strength shows an inverse trend. The decreasing fracture strength may be partly attributed to the weakening effect from the increasing area density of defects which acts as the reservoir of stress-concentrated sites on the grain boundary. The observed crack localization and propagation and fracture strength are well-explained by a defect-pileup model.

  7. Polycrystalline gamma plutonium's elastic moduli versus temperature

    SciTech Connect

    Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I

    2009-01-01

    Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline {sup 239}Pu in the {gamma} phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease of all elastic moduli with increasing temperature was observed. They calculated the Poisson ratio and found that it increases from 0.242 at 519 K to 0.252 at 571 K. These measurements on extremely well characterized pure Pu are in agreement with other reported results where overlap occurs.

  8. Photoinduced conductivity changes in polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Prawer, S.; Jamieson, D.

    1996-02-01

    We report that the dark electrical properties of polycrystalline chemical vapor deposition diamond films are modified after exposure to UV light. UV illumination gives rise to an increase in the dark conductivity and to a change in the I-V characteristic from Iα exp (aV) for the as-grown material to IαV2 following UV irradiation. Thermally stimulated currents corresponding to an activation energy of about 1.9 eV are observed after UV illumination. The effects of UV irradiation can be totally reversed by thermal annealing and partially reversed by exposing the samples to white light.

  9. Poole-Frenkel conduction in polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Boiko, Y.; Prawer, S.; Jamieson, D.

    1996-04-01

    High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole-Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm-3.

  10. Process for Polycrystalline film silicon growth

    DOEpatents

    Wang, Tihu; Ciszek, Theodore F.

    2001-01-01

    A process for depositing polycrystalline silicon on substrates, including foreign substrates, occurs in a chamber at about atmospheric pressure, wherein a temperature gradient is formed, and both the atmospheric pressure and the temperature gradient are maintained throughout the process. Formation of a vapor barrier within the chamber that precludes exit of the constituent chemicals, which include silicon, iodine, silicon diiodide, and silicon tetraiodide. The deposition occurs beneath the vapor barrier. One embodiment of the process also includes the use of a blanketing gas that precludes the entrance of oxygen or other impurities. The process is capable of repetition without the need to reset the deposition zone conditions.

  11. Shock-front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, J. L.; Kadau, K.

    2008-04-01

    We analyze a model for the evolution of shock fronts in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  12. Electrical conductivity of the polycrystalline films of p-terphenyl

    NASA Astrophysics Data System (ADS)

    Tkaczyk, S. W.

    1999-04-01

    Some results of p-terphenyl thin films investigations are presented. The mechanism of DC conductivity within unordered polycrystalline structures of p-terphenyl was investigated. The measurements were carried out for p-terphenyl films' thickness varying from 2 micrometers up to 15 micrometers . During the experiment the polarization voltage and temperature were changed from 0 to 200 V and 15 to 325 K, respectively. The p-terphenyl films were supplied with gold and aluminum electrodes. The obtained results and their analysis indicate that the injection of charge from the electrodes into the area of the investigated material proceeds by field- and thermoemission. The charge transport through the material's bulk is controlled by traps (hopping mechanism and Poole- Frenkel phenomenon). The determined values of the activation energy are in the range of kT (for the hopping area at low temperatures) through 0.06 eV in the range of 100 - 200 K to about 0.6 eV in the metallic conductivity area (220 - 320 K).

  13. Improvements in cast polycrystalline silicon PV manufacturing technology

    NASA Astrophysics Data System (ADS)

    Wohlgemuth, John H.

    1997-02-01

    The objectives of this NREL sponsored Photovoltaic Manufacturing Technology (PVMaT) Program are to advance Solarex's cast polycrystalline silicon manufacturing technology, reduce module production cost in half, increase module performance and expand Solarex's commercial production capacity by a factor of three. To meet these objectives Solarex has: 1) Modified the casting process and stations and is now casting larger ingots in production; 2) Developed wire saw technology to cut wafers with less kerf loss and has transferred this technology to production; 3) Developed a laboratory process to increase cell efficiencies using back surface fields, mechanical texturing and gettering; 4) Modified the casting, wires saw and cell processes in order to fabricate larger (15.2 cm by 15.2 cm) wafers and cells; 5) Improved the automated assembly of modules, reducing labor requirements and increasing throughput; and 6) Developed a frameless module with a lower cost backsheet and a simple, low cost electrical termination system. Solarex is now in the process of developing the equipment necessary for automated handling of thin 15.2 cm by 15.2 cm wafers and cells. This paper will discuss the efforts during the first two and a half years of the program.

  14. Synchrotron X-ray Microdiffraction Analysis of Proton Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. I.; Davidson, J. L.; Ice, G. E.; Liu, W.

    2004-01-01

    X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with sub-micron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechanical Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2x10(exp 17) H(+)per square centimeter protons. Preliminary results indicate that a measurable strain, on the order of 10(exp -3), was introduced into the film near the End of Range (EOR) region of the protons.

  15. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    NASA Astrophysics Data System (ADS)

    Abrams, K. J.; Hinks, J. A.; Pawley, C. J.; Greaves, G.; van den Berg, J. A.; Eyidi, D.; Ward, M. B.; Donnelly, S. E.

    2012-04-01

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  16. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  17. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1984-01-01

    Results of hydrogen-passivated polycrystalline silicon solar cells are summarized. Very small grain or short minority-carrier diffusion length silicon was used. Hydrogenated solar cells fabricated from this material appear to have effective minority-carrier diffusion lengths that are still not very long, as shown by the open-circuit voltages of passivated cells that are still significantly less than those of single-crystal solar cells. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. However, the open-circuit voltage, which is sensitive to grain boundary recombination, is sometimes 20 to 40 mV less. The goal was to minimize variations in open-circuit voltage and fill-factor caused by defects by passivating these defects using a hydrogenation process. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystaline silicon solar cells.

  18. Acoustic study of texture in polycrystalline brass

    SciTech Connect

    Foster, K.; Fairburn, S.L.; Leisure, R.G.; Kim, S.; Balzar, D.; Alers, G.; Ledbetter, H.

    1999-05-01

    Resonant ultrasound spectroscopy was used to measure the orthorhombic elastic constants of rolled, polycrystalline plates of Cu, Cu{endash}5{percent} Zn, and Cu{endash}15{percent} Zn. The experimental results were fit to theoretical expressions to determine the orientation-distribution coefficients W{sub 400}, W{sub 420}, and W{sub 440}. These coefficients are related to texture (the nonrandom orientation of crystallites). The experimental results were in good agreement with theory for the Cu and the Cu{endash}15{percent} Zn materials. The agreement was not as good for the more anisotropic Cu{endash}5{percent} Zn material, especially for the in-plane compressional constants C{sub 11} and C{sub 22}. The ultrasonically derived {ital W}{close_quote}s were compared to those obtained from neutron measurements for the Cu{endash}Zn alloys. Pole plots based on the two types of measurements, using W{sub 400}, W{sub 420}, and W{sub 440}, were in excellent agreement for the 15{percent} Zn material, and in qualitative agreement for the 5{percent} Zn material. The results support the idea that acoustic methods can be used to measure the low-order {ital W}{close_quote}s in polycrystalline materials. {copyright} {ital 1999 Acoustical Society of America.}

  19. Patterned polycrystalline diamond microtip vacuum diode arrays

    SciTech Connect

    Kang, W.P.; Davidson, J.L.; Kinser, D.L.

    1995-12-31

    Electron field emission from an array of patterned pyramids of polycrystalline diamond for vacuum diode applications has been investigated. High current emission from the patterned diamond microtip arrays are obtained at low electric fields. A current density from the diamond microtips of 14mA/cm{sup 2} was observed for a field of <10 V/{mu}m. Field emission for these diamond microtips exhibits significant enhancement both in total emission current and stability compared to pure silicon emitters. Moreover, field emission from patterned polycrystalline diamond pyramidal tip arrays is unique in that the applied field is found to be lower (2-3 order of magnitude lower) compared to that required for emission from Si, Ge, GaAs, and metal surfaces. The fabrication process utilizing silicon shaping and micromachining techniques for the fabrication of diamond diaphragms with diamond microtip arrays for vacuum microelectronic applications has been developed. The processing techniques are compatible with IC fabrication technology. The effect of temperature annealing on the current emission characteristics were also investigated.

  20. Electrical properties of polycrystalline methane hydrate

    USGS Publications Warehouse

    Du Frane, W. L.; Stern, L.A.; Weitemeyer, K.A.; Constable, S.; Pinkston, J.C.; Roberts, J.J.

    2011-01-01

    Electromagnetic (EM) remote-sensing techniques are demonstrated to be sensitive to gas hydrate concentration and distribution and complement other resource assessment techniques, particularly seismic methods. To fully utilize EM results requires knowledge of the electrical properties of individual phases and mixing relations, yet little is known about the electrical properties of gas hydrates. We developed a pressure cell to synthesize gas hydrate while simultaneously measuring in situ frequency-dependent electrical conductivity (σ). Synthesis of methane (CH4) hydrate was verified by thermal monitoring and by post run cryogenic scanning electron microscope imaging. Impedance spectra (20 Hz to 2 MHz) were collected before and after synthesis of polycrystalline CH4 hydrate from polycrystalline ice and used to calculate σ. We determined the σ of CH4 hydrate to be 5 × 10−5 S/m at 0°C with activation energy (Ea) of 30.6 kJ/mol (−15 to 15°C). After dissociation back into ice, σ measurements of samples increased by a factor of ~4 and Ea increased by ~50%, similar to the starting ice samples.

  1. Development of Novel Polycrystalline Ceramic Scintillators

    SciTech Connect

    Wisniewska, Monika; Boatner, Lynn A; Neal, John S; Jellison Jr, Gerald Earle; Ramey, Joanne Oxendine; North, Andrea L; Wisniewski, Monica; Payzant, E Andrew; Howe, Jane Y; Lempicki, Aleksander; Brecher, Charlie; Glodo, J.

    2008-01-01

    For several decades most of the efforts to develop new scintillator materials have concentrated on high-light-yield inorganic single-crystals while polycrystalline ceramic scintillators, since their inception in the early 1980 s, have received relatively little attention. Nevertheless, transparent ceramics offer a promising approach to the fabrication of relatively inexpensive scintillators via a simple mechanical compaction and annealing process that eliminates single-crystal growth. Until recently, commonly accepted concepts restricted the polycrystalline ceramic approach to materials exhibiting a cubic crystal structure. Here, we report our results on the development of two novel ceramic scintillators based on the non-cubic crystalline materials: Lu SiO:Ce (LSO:Ce) and LaBr:Ce. While no evidence for texturing has been found in their ceramic microstructures, our LSO:Ce ceramics exhibit a surprisingly high level of transparency/ translucency and very good scintillation characteristics. The LSO:Ce ceramic scintillation reaches a light yield level of about 86% of that of a good LSO:Ce single crystal, and its decay time is even faster than in single crystals. Research on LaBr:Ce shows that translucent ceramics of the high-light-yield rare-earth halides can also be synthesized. Our LaBr:Ce ceramics have light yields above 42 000 photons/MeV (i.e., 70%of the single-crystal light yield).

  2. Reversible piezomagnetoelectric switching in bulk polycrystalline ceramics

    SciTech Connect

    Stevenson, T. Bennett, J.; Brown, A. P.; Wines, T.; Bell, A. J.; Comyn, T. P.; Smith, R. I.

    2014-08-01

    Magnetoelectric (ME) coupling in materials offer tremendous advantages in device functionality enabling technologies including advanced electronic memory, combining electronic speed, and efficiency with magnetic robustness. However, low cost polycrystalline ME materials are excluded from most commercial applications, operating only at cryogenic temperatures, impractically large electric/magnetic fields, or with low ME coefficients (1-100 mV/cm Oe). Despite this, the technological potential of single compound ME coupling has continued to drive research into multiferroics over the last two decades. Here we show that by manipulating the large induced atomic strain within the polycrystalline, room temperature multiferroic compound 0.7BiFeO{sub 3}–0.3PbTiO{sub 3}, we can induce a reversible, piezoelectric strain controlled ME effect. Employing an in situ neutron diffraction experiment, we have demonstrated that this piezomagnetoelectric effect manifests with an applied electric field >8 kV/mm at the onset of piezoelectric strain, engineered in to the compound by crystallographic phase mixing. This produces a remarkable intrinsic ME coefficient of 1276 mV/cm Oe, due to a strain driven modification to the oxygen sub-lattice, inducing an increase in magnetic moment per Fe{sup 3+} ion of +0.142 μ{sub B}. This work provides a framework for investigations into strain engineered nanostructures to realize low-cost ME devices designed from the atoms up, as well as contributing to the deeper understanding of single phase ME coupling mechanisms.

  3. Singlet exciton fission in polycrystalline pentacene: from photophysics toward devices.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Ehrler, Bruno; Friend, Richard H

    2013-06-18

    Singlet exciton fission is the process in conjugated organic molecules bywhich a photogenerated singlet exciton couples to a nearby chromophore in the ground state, creating a pair of triplet excitons. Researchers first reported this phenomenon in the 1960s, an event that sparked further studies in the following decade. These investigations used fluorescence spectroscopy to establish that exciton fission occurred in single crystals of several acenes. However, research interest has been recently rekindled by the possibility that singlet fission could be used as a carrier multiplication technique to enhance the efficiency of photovoltaic cells. The most successful architecture to-date involves sensitizing a red-absorbing photoactive layer with a blue-absorbing material that undergoes fission, thereby generating additional photocurrent from higher-energy photons. The quest for improved solar cells has spurred a drive to better understand the fission process, which has received timely aid from modern techniques for time-resolved spectroscopy, quantum chemistry, and small-molecule device fabrication. However, the consensus interpretation of the initial studies using ultrafast transient absorption spectroscopy was that exciton fission was suppressed in polycrystalline thin films of pentacene, a material that would be otherwise expected to be an ideal model system, as well as a viable candidate for fission-sensitized photovoltaic devices. In this Account, we review the results of our recent transient absorption and device-based studies of polycrystalline pentacene. We address the controversy surrounding the assignment of spectroscopic features in transient absorption data, and illustrate how a consistent interpretation is possible. This work underpins our conclusion that singlet fission in pentacene is extraordinarily rapid (∼80 fs) and is thus the dominant decay channel for the photoexcited singlet exciton. Further, we discuss our demonstration that triplet excitons

  4. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    NASA Astrophysics Data System (ADS)

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-08-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets.

  5. Modelling heat conduction in polycrystalline hexagonal boron-nitride films.

    PubMed

    Mortazavi, Bohayra; Pereira, Luiz Felipe C; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  6. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    PubMed Central

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  7. Plastic deformation of polycrystalline zirconium carbide

    NASA Technical Reports Server (NTRS)

    Darolia, R.; Archbold, T. F.

    1976-01-01

    The compressive yield strength of arc-melted polycrystalline zirconium carbide has been found to vary from 77 kg per sq mm at 1200 C to 19 kg per sq mm at 1800 C. Yield drops were observed with plastic strain-rates greater than 0.003/sec but not with slower strain rates. Strain-rate change experiments yielded values for the strain-rate sensitivity parameter m which range from 6.5 at 1500 C to 3.8 at 1800 C, and the product dislocation velocity stress exponent times T was found to decrease linearly with increasing temperature. The deformation rate results are consistent with the Kelly-Rowcliffe model in which the diffusion of carbon assists the motion of dislocations.

  8. Modeling of Irradiation Hardening of Polycrystalline Materials

    SciTech Connect

    Li, Dongsheng; Zbib, Hussein M.; Garmestani, Hamid; Sun, Xin; Khaleel, Mohammad A.

    2011-09-14

    High energy particle irradiation of structural polycrystalline materials usually produces irradiation hardening and embrittlement. The development of predict capability for the influence of irradiation on mechanical behavior is very important in materials design for next generation reactors. In this work a multiscale approach was implemented to predict irradiation hardening of body centered cubic (bcc) alpha-iron. The effect of defect density, texture and grain boundary was investigated. In the microscale, dislocation dynamics models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent model was applied to predict the irradiation hardening in samples with changes in texture and grain boundary. This multiscale modeling can guide performance evaluation of structural materials used in next generation nuclear reactors.

  9. Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

    SciTech Connect

    Martin, Guillaume; Desgardin, Pierre; Sauvage, Thierry; Barthe, Marie-France; Garcia, Philippe; Carlot, Gaelle

    2007-07-01

    This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO{sub 2} sintered samples presenting different microstructures were implanted with {sup 3}He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the {sup 3}He(d,{alpha}){sup 1}H reaction. {sup 3}He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

  10. High-temperature creep of polycrystalline chromium

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.; Klopp, W. D.

    1972-01-01

    The creep properties of high-purity, polycrystalline chromium were determined over the temperature range 0.51 to 0.78 T sub m, where T sub m is the melting temperature. Creep rates determined from step-load creep tests can be represented by the general creep equation; epsilon/D = k((sigma/E) to the nth power) where epsilon is the minimum creep rate, D is the diffusivity, k is the creep rate constant, sigma is the applied stress, E is the modulus, and n is the stress exponent, equal to 4.3 for chromium. This correlation and metallographic observations suggest a dislocation climb mechanism is operative in the creep of chromium over the temperature range investigated.

  11. Polycrystalline silicon ion sensitive field effect transistors

    NASA Astrophysics Data System (ADS)

    Yan, F.; Estrela, P.; Mo, Y.; Migliorato, P.; Maeda, H.; Inoue, S.; Shimoda, T.

    2005-01-01

    We report the operation of polycrystalline silicon ion sensitive field effect transistors. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with a Si3N4 sensing layer. Nearly ideal pH sensitivity (54mV /pH) and stable operation have been achieved. Temperature effects have been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The sensitivity to penicillin G is about 10mV/mM, in solutions with concentration lower than the saturation value, which is about 7 mM.

  12. Residual Stress Predictions in Polycrystalline Alumina

    SciTech Connect

    VEDULA,VENKATA R.; GLASS,S. JILL; SAYLOR,DAVID M.; ROHRER,GREGORY S.; CARTER,W. CRAIG; LANGER,STEPHEN A.

    1999-12-13

    Microstructure-level residual stresses arise in polycrystalline ceramics during processing as a result of thermal expansion anisotropy and crystallographic disorientation across the grain boundaries. Depending upon the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking during the processing of these materials. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples were predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations. The crystallographic orientations were obtained by electron-backscattered diffraction (EBSD). The residual stresses were lower and the stress distributions were narrower in the textured samples compared to those in the untextured samples. Crack initiation and propagation were also simulated using the Griffith fracture criterion. The grain boundary to surface energy ratios required for computations were estimated using AFM groove measurements.

  13. Shock front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, John; Kadau, Kai

    2008-03-01

    We analyze a model for the evolution of weak shock fronts (or elastic precursor waves) in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  14. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  15. Interaction of metal layers with polycrystalline Si

    NASA Technical Reports Server (NTRS)

    Nakamura, K.; Olowolafe, J. O.; Lau, S. S.; Nicolet, M.-A.; Mayer, J. W.; Shima, R.

    1976-01-01

    Solid-phase reactions of metal films deposited on 0.5-micron-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 C were investigated by MeV He-4 backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at temperatures exceeding 550 C for Ag, at those exceeding 400 C for Al, and at those exceeding 200 C for Au films. For Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

  16. Vacancy Formation Enthalpy in Polycrystalline Depleted Uranium

    NASA Astrophysics Data System (ADS)

    Lund, K. R.; Lynn, K. G.; Weber, M. H.; Okuniewski, M. A.

    2013-06-01

    Positron Annihilation Spectroscopy was performed as a function of temperature and beam energy on polycrystalline depleted uranium (DU) foil. Samples were run with varying heat profiles all starting at room temperature. While collecting Doppler-Broadening data, the temperature of the sample was cycled several times. The first heat cycle shows an increasing S-parameter near temperatures of 400K to 500K much lower than the first phase transition of 941K indicating increasing vacancies possibly due to oxygen diffusion from the bulk to the surface. Vacancy formation enthalpies were calculated fitting a model to the data to be 1.6± 0.16 eV. Results are compared to previous work [3,4].

  17. Nuclear spin relaxation of polycrystalline 129 xenon

    NASA Astrophysics Data System (ADS)

    Samuelson, Gary Lee, Jr.

    Through spin exchange optical pumping, it is possible to achieve upwards of 30% nuclear spin polarization in 129Xe with an NMR signal enhancement of some 5 orders of magnitude over typical thermal signals. Hyperpolarized 129Xe has thus found application in several leading-edge technologies. At 1 T and 4.2 K, the characteristic relaxation time of enriched polycrystalline 129Xe (86% 129Xe, 0.1% 131Xe) is well over 200 hrs, sufficient for long-term storage and transport. Longitudinal nuclear spin relaxation of 129Xe at more convenient fields from 1 to 200 G is studied in detail. Significant structure in relaxation times vs. magnetic field is seen; the most prominent new finding being a sharp local long-time T 1 maximum of 1000 mins at ≈3 G. Such structure has not been observed in previous measurements of natural Xe. Below temperatures of 10 K, relaxation can be attributed to cross relaxation with 131Xe, mediated by spin diffusion. Measurements of 129Xe relaxation as a function of magnetic field, temperature and Xe isotopic content are reported and compared with expected theoretical behaviors. It is seen that the characteristic nuclear spin relaxation of enriched 129Xe at 4.2 K is nonexponential at these low fields. For fields between 10 G and 200 G, these nonexponential relaxation curves can be fit well with a specific spin diffusion model. Below 10 G no such fit is possible and thus quantum mechanical details of the coupling between 129Xe, 131Xe and the bulk lattice are considered. These findings support the hypothesis that cross relaxation with 131Xe is indeed a dominant actor in the nuclear spin relaxation of polycrystalline 129 Xe at such low fields and low temperatures.

  18. Electron scattering characteristics of polycrystalline metal transition films by in-situ electrical resistance measurements

    NASA Astrophysics Data System (ADS)

    Trindade, I. G.; Leitão, D.; Fermento, R.; Pogorelev, Y.; Sousa, J. B.

    2009-08-01

    In-situ electrical resistance measurements were performed to obtain the scattering characteristics of very thin polycrystalline metal transition magnetic alloys grown by ion beam deposition (IBD) on specific underlayers. The experimental curves show size effects at small film thicknesses and important differences between Co 85Fe 15 and Ni 81Fe 19 thin layers grown on identical underlayers of Ta70 Å/Ru13 Å. The largest difference was observed in Ni 81Fe 19 films grown on underlayers of amorphous Ta70 Å. The experimental curves of electrical resistivity/conductivity variation with layer thickness were well fit within the Mayadas and Shatzkes (M-S) model, assuming specific formulations for grain growth with layer thickness.

  19. Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Final subcontract report, 1 April 1990--30 November 1993

    SciTech Connect

    Sites, J.R.

    1994-07-01

    The report describes the exploration of several aspects of the role of polycrystallinity in the operation of CdTe, CuInSe{sub 2}, and Cu(In,Ga)Se{sub 2} solar cells. The work included the refinement of several analytical techniques, the documentation and understanding of time-dependent voltage effects, the analysis of a large number of individual cells, and significant progress toward developing a viable current-voltage model. This work was integral to the doctoral training of four students and was greatly assisted by several active collaborations within the polycrystalline thin-film solar cell community.

  20. Submicrometer-wide amorphous and polycrystalline anatase TiO2 waveguides for microphotonic devices.

    PubMed

    Bradley, Jonathan D B; Evans, Christopher C; Choy, Jennifer T; Reshef, Orad; Deotare, Parag B; Parsy, François; Phillips, Katherine C; Lončar, Marko; Mazur, Eric

    2012-10-01

    We demonstrate amorphous and polycrystalline anatase TiO(2) thin films and submicrometer-wide waveguides with promising optical properties for microphotonic devices. We deposit both amorphous and polycrystalline anatase TiO(2) using reactive sputtering and define waveguides using electron-beam lithography and reactive ion etching. For the amorphous TiO(2), we obtain propagation losses of 0.12 ± 0.02 dB/mm at 633 nm and 0.04 ± 0.01 dB/mm at 1550 nm in thin films and 2.6 ± 0.5 dB/mm at 633 nm and 0.4 ± 0.2 dB/mm at 1550 nm in waveguides. Using single-mode amorphous TiO(2) waveguides, we characterize microphotonic features including microbends and optical couplers. We show transmission of 780-nm light through microbends having radii down to 2 μm and variable signal splitting in microphotonic couplers with coupling lengths of 10 μm. PMID:23188347

  1. On properties of boundaries and electron conductivity in mesoscopic polycrystalline silicon films for memory devices

    SciTech Connect

    Berman, G.P.; Doolen, G.D.; Mainieri, R.; Rehacek, J.; Campbell, D.K.; Luchnikov, V.A.; Nagaev, K.E.

    1998-02-01

    The authors present the results of MD modeling on the structural properties of grain boundaries (GB) in thin polycrystalline films. The transition from crystalline boundaries with low mismatch angle to amorphous boundaries is investigated. It is shown that the structures of the GBs satisfy a thermodynamical criterion suggested in a cited reference. The potential energy of silicon atoms is closely related with a geometrical quantity -- tetragonality of their coordination with their nearest neighbors. A crossover of the length of localization is observed to analyze the crossover of the length of localization of the single electron states and properties of conductance of the thin polycrystalline film at low temperature. They use a two-dimensional Anderson localization model, with the random one site electron charging energy for a single grain (dot), random non-diagonal matrix elements, and random number of connections between the neighboring grains. The results on the crossover behavior of localization length of the single electron states and characteristic properties of conductance are presented in the region of parameters where the transition from an insulator to a conductor regimes takes place.

  2. Determination of oxygen diffusion kinetics during thin film ruthenium oxidation

    SciTech Connect

    Coloma Ribera, R. Kruijs, R. W. E. van de; Yakshin, A. E.; Bijkerk, F.

    2015-08-07

    In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics for thermal oxidation of polycrystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO{sub 2} films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule.

  3. Mechanical Properties and Failure Mechanisms in Polycrystalline Graphene

    NASA Astrophysics Data System (ADS)

    Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Large-scale growth of graphene using chemical vapor deposition produces polycrystalline material containing grain boundaries. Recent experiments demonstrate that polycrystalline graphene is nearly as strong as pristine. In this work, the mechanical properties of bi-crystal and polycrystalline graphene samples are investigated by simulating nano-indentation of a circular membrane using classical molecular dynamics and a novel Screened Environment Dependent Reactive Bond Order (SED-REBO) potential. The failure mechanisms and crack propagation in graphene samples containing grain boundaries are also discussed.

  4. Graphene film growth on polycrystalline metals.

    PubMed

    Edwards, Rebecca S; Coleman, Karl S

    2013-01-15

    Graphene, a true wonder material, is the newest member of the nanocarbon family. The continuous network of hexagonally arranged carbon atoms gives rise to exceptional electronic, mechanical, and thermal properties, which could result in the application of graphene in next generation electronic components, energy-storage materials such as capacitors and batteries, polymer nanocomposites, transparent conducting electrodes, and mechanical resonators. With one particularly attractive application, optically transparent conducting electrodes or films, graphene has the potential to rival indium tin oxide (ITO) and become a material for producing next generation displays, solar cells, and sensors. Typically, graphene has been produced from graphite using a variety of methods, but these techniques are not suitable for growing large-area graphene films. Therefore researchers have focused much effort on the development of methodology to grow graphene films across extended surfaces. This Account describes current progress in the formation and control of graphene films on polycrystalline metal surfaces. Researchers can grow graphene films on a variety of polycrystalline metal substrates using a range of experimental conditions. In particular, group 8 metals (iron and ruthenium), group 9 metals (cobalt, rhodium, and iridium), group 10 metals (nickel and platinum), and group 11 metals (copper and gold) can support the growth of these films. Stainless steel and other commercial copper-nickel alloys can also serve as substrates for graphene film growth. The use of copper and nickel currently predominates, and these metals produce large-area films that have been efficiently transferred and tested in many electronic devices. Researchers have grown graphene sheets more than 30 in. wide and transferred them onto display plastic ready for incorporation into next generation displays. The further development of graphene films in commercial applications will require high

  5. Estimating Geometric Dislocation Densities in Polycrystalline Materialsfrom Orientation Imaging Microscopy

    SciTech Connect

    Man, Chi-Sing; Gao, Xiang; Godefroy, Scott; Kenik, Edward A

    2010-01-01

    Herein we consider polycrystalline materials which can be taken as statistically homogeneous and whose grains can be adequately modeled as rigid-plastic. Our objective is to obtain, from orientation imaging microscopy (OIM), estimates of geometrically necessary dislocation (GND) densities.

  6. Polycrystalline neutron scattering for Geant4: NXSG4

    NASA Astrophysics Data System (ADS)

    Kittelmann, T.; Boin, M.

    2015-04-01

    An extension to Geant4 based on the nxs library is presented. It has been implemented in order to include effects of low-energy neutron scattering in polycrystalline materials, and is made available to the scientific community.

  7. Polycrystalline silicon semiconducting material by nuclear transmutation doping

    DOEpatents

    Cleland, John W.; Westbrook, Russell D.; Wood, Richard F.; Young, Rosa T.

    1978-01-01

    A NTD semiconductor material comprising polycrystalline silicon having a mean grain size less than 1000 microns and containing phosphorus dispersed uniformly throughout the silicon rather than at the grain boundaries.

  8. Thermophysical Properties of Sodium (Beta)-Alumina Polycrystalline Ceramic

    NASA Technical Reports Server (NTRS)

    Ryan, M. A.; Williams, R. M.; Allevato, C. E.; Vining, C. B.; Lowe-Ma, C. K.; Robie, S. B.

    1994-01-01

    Teh thermal diffusivity, heat capacity and thermal conductivity of solid samples of new, Li-stabilized, sodium (Beta)-alumina polycrystalline ceramic have been determined in the temperature range 500-1200 K.

  9. Solution-processed polycrystalline silicon on paper

    SciTech Connect

    Trifunovic, M.; Ishihara, R.; Shimoda, T.

    2015-04-20

    Printing electronics has led to application areas which were formerly impossible with conventional electronic processes. Solutions are used as inks on top of large areas at room temperatures, allowing the production of fully flexible circuitry. Commonly, research in these inks have focused on organic and metal-oxide ink materials due to their printability, while these materials lack in the electronic performance when compared to silicon electronics. Silicon electronics, on the other hand, has only recently found their way in solution processes. Printing of cyclopentasilane as the silicon ink has been conducted and devices with far superior electric performance have been made when compared to other ink materials. A thermal annealing step of this material, however, was necessary, which prevented its usage on inexpensive substrates with a limited thermal budget. In this work, we introduce a method that allows polycrystalline silicon (poly-Si) production directly from the same liquid silicon ink using excimer laser irradiation. In this way, poly-Si could be formed directly on top of paper even with a single laser pulse. Using this method, poly-Si transistors were created at a maximum temperature of only 150 °C. This method allows silicon device formation on inexpensive, temperature sensitive substrates such as polyethylene terephthalate, polyethylene naphthalate or paper, which leads to applications that require low-cost but high-speed electronics.

  10. Stability of polycrystalline Nextel 720 fiber

    SciTech Connect

    Das, G.

    1996-12-31

    The microstructure and tensile properties of polycrystalline Nextel 720 fiber (85 wt.% Al{sub 2}O{sub 3} - 15 wt-% SiO{sub 2}), both crystallized and precrystallized, were evaluated following prolonged thermal exposure at 982{degrees}C in air. The room temperature tensile strengths of Nextel 720 fibers did not appear to suffer degradation for exposures up to 3000 h and the microstructure remained unaffected by thermal exposures. The tensile strength of precrystallized Nextel 720 fiber was also determined at room temperature following heat treatments at 1093-1427{degrees}C in air. The precrystallized Nextel 720 fiber started to show a slight loss of strength after heat treatment at 1093{degrees}C/4 h and the strength deterioration was exacerbated for heat treatments at 1204{degrees}C/4 h and above. Microstructural characterization by x-ray and transmission electron microscopy (TEM) revealed the formation of mullite in heat treated precrystallized Nextel 720 fiber at 1204{degrees}C and a coarsening of microstructure above 1204{degrees}C. The degradation of strength in precrystallized Nextel 720 fiber heat treated at 1204{degrees}C/4 h and above may be attributed to phase instability and grain coarsening. Fractographs showed that fracture originated predominantly at the fiber surface.

  11. Texture and Anisotropy of Polycrystalline Piezoelectics

    SciTech Connect

    Jones,J.; Iverson, B.; Bowman, K.

    2007-01-01

    Piezoelectricity is manifested in ferroelectric ceramics by inducing a preferred volume fraction of one ferroelectric domain variant orientation at the expense of degenerate orientations. The piezoelectric effect is therefore largely controlled by the effectiveness of the electrical poling in producing a bias in ferroelectric (180{sup o}) and ferroelastic (non-180{sup o}) domain orientations. Further enhancement of the piezoelectric effect in bulk ceramics can be accomplished by inducing preferred orientation through grain-orientation processes such as hot forging or tape casting that precede the electrical-poling process. Coupled crystal orientation and domain orientation processing yields ceramics with an even greater piezoelectric response. In this paper, preferred orientations of domains and grains in polycrystalline piezoelectric ceramics generated through both domain- and grain-orientation processing are characterized through pole figures and orientation distribution functions obtained using data from a variety of diffraction techniques. The processing methods used to produce these materials and the methods used to evaluate preferred orientation and texture are described and discussed in the context of prior research. Different sample and crystal symmetries are explored across a range of commercial and laboratory-prepared materials. Some of the variables presented in this work include the effects of in situ thermal depoling and the detailed processing parameters used in tape casting of materials with preferred crystallite orientations. Preferred orientation is also correlated with anisotropic properties, demonstrating a clear influence of both grain and domain orientations on piezoelectricity.

  12. Nonlinear alternating current conduction in polycrystalline manganites

    NASA Astrophysics Data System (ADS)

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-01

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1-x -yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1-xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc˜Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf.

  13. Photovoltaic Cell Having A P-Type Polycrystalline Layer With Large Crystals

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes R.

    1996-03-26

    A photovoltaic cell has an n-type polycrystalline layer and a p-type polycrystalline layer adjoining the n-type polycrystalline layer to form a photovoltaic junction. The p-type polycrystalline layer comprises a substantially planar layer portion having relatively large crystals adjoining the n-type polycrystalline layer. The planar layer portion includes oxidized impurities which contribute to obtainment of p-type electrical properties in the planar layer portion.

  14. Defect behavior of polycrystalline solar cell silicon

    SciTech Connect

    Schroder, D.K.; Park, S.H.; Hwang, I.G.; Mohr, J.B.; Hanly, M.P.

    1993-05-01

    The major objective of this study, conducted from October 1988 to September 1991, was to gain an understanding of the behavior of impurities in polycrystalline silicon and the influence of these impurities on solar cell efficiency. The authors studied edge-defined film-fed growth (EFG) and cast poly-Si materials and solar cells. With EFG Si they concentrated on chromium-doped materials and cells to determine the role of Cr on solar cell performance. Cast poly-Si samples were not deliberately contaminated. Samples were characterized by cell efficiency, current-voltage, deep-level transient spectroscopy (DLTS), surface photovoltage (SPV), open-circuit voltage decay, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy measurements. They find that Cr forms Cr-B pairs with boron at room temperature and these pairs dissociate into Cr{sub i}{sup +} and B{sup {minus}} during anneals at 210{degrees}C for 10 min. Following the anneal, Cr-B pairs reform at room temperature with a time constant of 230 h. Chromium forms CrSi{sub 2} precipitates in heavily contaminated regions and they find evidence of CrSi{sub 2} gettering, but a lack of chromium segregation or precipitation to grain boundaries and dislocations. Cr-B pairs have well defined DLTS peaks. However, DLTS spectra of other defects are not well defined, giving broad peaks indicative of defects with a range of energy levels in the band gap. In some high-stress, low-efficiency cast poly-Si they detect SiC precipitates, but not in low-stress, high-efficiency samples. SPV measurements result in nonlinear SPV curves in some materials that are likely due to varying optical absorption coefficients due to locally varying stress in the material.

  15. A New Polycrystalline Co-Ni Superalloy

    NASA Astrophysics Data System (ADS)

    Knop, M.; Mulvey, P.; Ismail, F.; Radecka, A.; Rahman, K. M.; Lindley, T. C.; Shollock, B. A.; Hardy, M. C.; Moody, M. P.; Martin, T. L.; Bagot, P. A. J.; Dye, D.

    2014-12-01

    In 2006, a new-ordered L12 phase, Co3(Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ/ γ' superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ' fraction of ~56% and a secondary γ' size of 88 nm were obtained, with a grain size of 2.5 μm. The solvus temperature was 1000°C. The density was found to be 8.52 g cm-3, which is similar to existing Ni alloys with this level of γ'. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ/ γ' Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm-2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.

  16. Nonlinear alternating current conduction in polycrystalline manganites

    SciTech Connect

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-28

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La{sub 1−x−y}Y{sub y}Ca{sub x}MnO{sub 3} with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn{sub 1−x}Fe{sub x}O{sub 3} with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ{sub 0} by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ{sub 0} up to a certain frequency, known as the onset frequency f{sub c} and increases from Σ{sub 0} as frequency is increased from f{sub c}. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. f{sub c} scales with Σ{sub 0} as f{sub c}∼Σ{sub 0}{sup x{sub f}}, where x{sub f} is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that x{sub f} is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent x{sub f}.

  17. Hematite thin films: growth and characterization

    NASA Astrophysics Data System (ADS)

    Uribe, J. D.; Osorio, J.; Barrero, C. A.; Giratá, D.; Morales, A. L.; Devia, A.; Gómez, M. E.; Ramirez, J. G.; Gancedo, J. R.

    2006-04-01

    We have grown hematite (α Fe 2 O 3) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mössbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α Fe 2 O 3. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.

  18. Hematite thin films: growth and characterization

    NASA Astrophysics Data System (ADS)

    Uribe, J. D.; Osorio, J.; Barrero, C. A.; Giratá, D.; Morales, A. L.; Devia, A.; Gómez, M. E.; Ramirez, J. G.; Gancedo, J. R.

    We have grown hematite (α - Fe 2 O 3) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mössbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α - Fe 2O3. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.

  19. Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl2

    NASA Astrophysics Data System (ADS)

    Jensen, S. A.; Burst, J. M.; Duenow, J. N.; Guthrey, H. L.; Moseley, J.; Moutinho, H. R.; Johnston, S. W.; Kanevce, A.; Al-Jassim, M. M.; Metzger, W. K.

    2016-06-01

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  20. Zinc oxide thin film acoustic sensor

    SciTech Connect

    Mohammed, Ali Jasim; Salih, Wafaa Mahdi; Hassan, Marwa Abdul Muhsien; Nusseif, Asmaa Deiaa; Kadhum, Haider Abdullah; Mansour, Hazim Louis

    2013-12-16

    This paper reports the implementation of (750 nm) thickness of Zinc Oxide (ZnO) thin film for the piezoelectric pressure sensors. The film was prepared and deposited employing the spray pyrolysis technique. XRD results show that the growth preferred orientation is the (002) plane. A polycrystalline thin film (close to mono crystallite like) was obtained. Depending on the Scanning Electron Microscopy photogram, the film homogeneity and thickness were shown. The resonance frequency measured (about 19 kHz) and the damping coefficient was calculated and its value was found to be about (2.5538), the thin film be haves as homogeneous for under and over damped. The thin film pressure sensing was approximately exponentially related with frequency, the thin film was observed to has a good response for mechanical stresses also it is a good material for the piezoelectric properties.

  1. Zinc oxide thin film acoustic sensor

    NASA Astrophysics Data System (ADS)

    Mohammed, Ali Jasim; Salih, Wafaa Mahdi; Hassan, Marwa Abdul Muhsien; Mansour, Hazim Louis; Nusseif, Asmaa Deiaa; Kadhum, Haider Abdullah

    2013-12-01

    This paper reports the implementation of (750 nm) thickness of Zinc Oxide (ZnO) thin film for the piezoelectric pressure sensors. The film was prepared and deposited employing the spray pyrolysis technique. XRD results show that the growth preferred orientation is the (002) plane. A polycrystalline thin film (close to mono crystallite like) was obtained. Depending on the Scanning Electron Microscopy photogram, the film homogeneity and thickness were shown. The resonance frequency measured (about 19 kHz) and the damping coefficient was calculated and its value was found to be about (2.5538), the thin film be haves as homogeneous for under and over damped. The thin film pressure sensing was approximately exponentially related with frequency, the thin film was observed to has a good response for mechanical stresses also it is a good material for the piezoelectric properties.

  2. Polycrystalline Garnet Porphyroblasts, an EBSD Study

    NASA Astrophysics Data System (ADS)

    Seaton, N. C.; Whitney, D. L.; Anderson, C.; Alpert, A.

    2008-12-01

    Polycrystalline garnet porphyroblasts (PGP's) are significant because their formation provides information about metamorphic crystalline mechanisms, in particular during early stages of crystal growth, which may differ from those governing later stages; and because their existence may affect the chemical and structural evolution of metamorphic rocks. For example, the extent of element exchange between the garnet interior and the matrix may be affected by the presence of grain boundaries within PGP's. There have been several previous studies of PGP's but important questions about them remain; e.g. whether early coalescence is a common method by which garnets crystallize, whether grains rotate during growth to attain an energetically favorable grain-grain contact, and whether deformation and/or precursor minerals or other chemical or mechanical heterogeneities influence the formation of PGP's. PGP's have been detected by us in several different localities including; micaschist from SE Vermont (USA), including locality S35j of Rosenfeld (1968); the Solitude Range (British Columbia, Canada); the Southern Menderes Massif (Turkey); and three zones (garnet, staurolite, kyanite) from the Dutchess County Barrovian sequence in NY (USA). We have identified two types of PGP: cryptic and morphologically distinct. Cryptic PGP have no obvious morphological expression of the high angle boundaries within them and appear to be a single crystal. Morphologically distinct PGP have an obvious depression in the outer grain boundary where it is intersected by the internal grain boundary. Most PGP's contain inclusion trails and the high angle grain boundaries crosscut the trend of these as well as the inclusions themselves. PGP also show major element growth zoning that is not influenced by the internal grain boundaries except in rare cases. PGP's comprise ~ 5-35% of the garnet populations analyzed. More than 95% of the PGP's we have analyzed are comprised of 2-3 domains; the rest contain

  3. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  4. Recent developments in polycrystalline oxide fiber laser materials: production of Yb-doped polycrystalline YAG fiber

    NASA Astrophysics Data System (ADS)

    Lee, HeeDong; Keller, Kristin; Sirn, Brian; Parthasarathy, Triplicane; Cheng, Michael; Hopkins, Frank K.

    2011-09-01

    Laser quality, polycrystalline oxide fibers offer significant advantages over state-of-the-art silica fiber for high energy lasers. Advanced ceramic processing technology, along with a novel powder production process, has potential to produce oxide fibers with an outstanding optical quality for use in the fiber laser applications. The production of contaminant-free green fibers with a high packing density, as well as uniform packing distribution, is a key factor in obtaining laserquality fibers. High quality green fibers are dependent on the powder quality combined with the appropriate slurry formulation. These two fundamental technologies were successfully developed at UES, and used to produce Yb-doped yttrium aluminum garnet (YAG) fibers with high optical quality, high chemical purity, and suitable core diameters down to 20-30 microns.

  5. Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

    PubMed Central

    Kasap, Safa; Frey, Joel B.; Belev, George; Tousignant, Olivier; Mani, Habib; Greenspan, Jonathan; Laperriere, Luc; Bubon, Oleksandr; Reznik, Alla; DeCrescenzo, Giovanni; Karim, Karim S.; Rowlands, John A.

    2011-01-01

    In the last ten to fifteen years there has been much research in using amorphous and polycrystalline semiconductors as x-ray photoconductors in various x-ray image sensor applications, most notably in flat panel x-ray imagers (FPXIs). We first outline the essential requirements for an ideal large area photoconductor for use in a FPXI, and discuss how some of the current amorphous and polycrystalline semiconductors fulfill these requirements. At present, only stabilized amorphous selenium (doped and alloyed a-Se) has been commercialized, and FPXIs based on a-Se are particularly suitable for mammography, operating at the ideal limit of high detective quantum efficiency (DQE). Further, these FPXIs can also be used in real-time, and have already been used in such applications as tomosynthesis. We discuss some of the important attributes of amorphous and polycrystalline x-ray photoconductors such as their large area deposition ability, charge collection efficiency, x-ray sensitivity, DQE, modulation transfer function (MTF) and the importance of the dark current. We show the importance of charge trapping in limiting not only the sensitivity but also the resolution of these detectors. Limitations on the maximum acceptable dark current and the corresponding charge collection efficiency jointly impose a practical constraint that many photoconductors fail to satisfy. We discuss the case of a-Se in which the dark current was brought down by three orders of magnitude by the use of special blocking layers to satisfy the dark current constraint. There are also a number of polycrystalline photoconductors, HgI2 and PbO being good examples, that show potential for commercialization in the same way that multilayer stabilized a-Se x-ray photoconductors were developed for commercial applications. We highlight the unique nature of avalanche multiplication in a-Se and how it has led to the development of the commercial HARP video-tube. An all solid state version of the HARP has been

  6. Amorphous and polycrystalline photoconductors for direct conversion flat panel x-ray image sensors.

    PubMed

    Kasap, Safa; Frey, Joel B; Belev, George; Tousignant, Olivier; Mani, Habib; Greenspan, Jonathan; Laperriere, Luc; Bubon, Oleksandr; Reznik, Alla; DeCrescenzo, Giovanni; Karim, Karim S; Rowlands, John A

    2011-01-01

    In the last ten to fifteen years there has been much research in using amorphous and polycrystalline semiconductors as x-ray photoconductors in various x-ray image sensor applications, most notably in flat panel x-ray imagers (FPXIs). We first outline the essential requirements for an ideal large area photoconductor for use in a FPXI, and discuss how some of the current amorphous and polycrystalline semiconductors fulfill these requirements. At present, only stabilized amorphous selenium (doped and alloyed a-Se) has been commercialized, and FPXIs based on a-Se are particularly suitable for mammography, operating at the ideal limit of high detective quantum efficiency (DQE). Further, these FPXIs can also be used in real-time, and have already been used in such applications as tomosynthesis. We discuss some of the important attributes of amorphous and polycrystalline x-ray photoconductors such as their large area deposition ability, charge collection efficiency, x-ray sensitivity, DQE, modulation transfer function (MTF) and the importance of the dark current. We show the importance of charge trapping in limiting not only the sensitivity but also the resolution of these detectors. Limitations on the maximum acceptable dark current and the corresponding charge collection efficiency jointly impose a practical constraint that many photoconductors fail to satisfy. We discuss the case of a-Se in which the dark current was brought down by three orders of magnitude by the use of special blocking layers to satisfy the dark current constraint. There are also a number of polycrystalline photoconductors, HgI(2) and PbO being good examples, that show potential for commercialization in the same way that multilayer stabilized a-Se x-ray photoconductors were developed for commercial applications. We highlight the unique nature of avalanche multiplication in a-Se and how it has led to the development of the commercial HARP video-tube. An all solid state version of the HARP has been

  7. Role of polycrystallinity in CdTe and CuInSe sub 2 photovoltaic cells

    SciTech Connect

    Sites, J.R. )

    1991-01-01

    The polycrystalline nature of thin-film CdTe and CuInSe{sub 2} solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe{sub 2} cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm{sup 2}; those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe{sub 2} cells from International Solar Electric Technology have shown a hole density as high as 7 {times} 10{sup 16} cm{sup {minus}3}, implying a significant reduction in compensation. 9 refs.

  8. Role of polycrystallinity in CdTe and CuInSe2 photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Sites, J. R.

    The polycrystalline nature of thin-film CdTe and CuInSe2 solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe2 cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm(exp 2); those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe2 cells from International Solar Electric Technology have shown a hole density as high as 7 x 10(exp 16) cm(exp -3), implying a significant reduction in compensation.

  9. Orientational tomography of optical axes directions distributions of multilayer biological tissues birefringent polycrystalline networks

    NASA Astrophysics Data System (ADS)

    Zabolotna, Natalia I.; Dovhaliuk, Rostyslav Y.

    2013-09-01

    We present a novel measurement method of optic axes orientation distribution which uses a relatively simple measurement setup. The principal difference of our method from other well-known methods lies in direct approach for measuring the orientation of optical axis of polycrystalline networks biological crystals. Our test polarimetry setup consists of HeNe laser, quarter wave plate, two linear polarizers and a CCD camera. We also propose a methodology for processing of measured optic axes orientation distribution which consists of evaluation of statistical, correlational and spectral moments. Such processing of obtained data can be used to classify particular tissue sample as "healthy" or "pathological". For our experiment we use thin layers of histological section of normal and muscular dystrophy tissue sections. It is shown that the difference between mentioned moments` values of normal and pathological samples can be quite noticeable with relative difference up to 6.26.

  10. Effect of local surface potential distribution on its relaxation in polycrystalline ferroelectric films.

    SciTech Connect

    Kim, Y.; Park, M.; Buhlmann, S.; Hong, S.; Kim, Y. K.; Ko, H.; Kim, J.; No, K.; Materials Science Division; Korea Advanced Inst. of Science and Technology; Samsung Advance Inst. of Tech.

    2010-01-01

    We have studied the effect of local surface potential distribution on its relaxation in the polycrystalline ferroelectric thin films. A lower surface potential region, i.e., potential pit, is generated near a grain boundary. The deep potential pit has a faster relaxation than the area far away from the potential pit due to the acceleration of the screen charge draining near the grain boundary and the domains formed by applying higher voltage have a faster relaxation due to the larger gradient of screen charge distribution. In addition, the surface potential and its relaxation depend on the sign of applying voltage. The result shows that the surface potential distribution may influence significantly to the reliability of bit signal on the memory devices.

  11. Recent technological advances in thin film solar cells

    SciTech Connect

    Ullal, H.S.; Zwelbel, K.; Surek, T.

    1990-03-01

    High-efficiency, low-cost thin film solar cells are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. This paper reviews the substantial advances made by several thin film solar cell technologies, namely, amorphous silicon, copper indium diselenide, cadmium telluride, and polycrystalline silicon. Recent examples of utility demonstration projects of these emerging materials are also discussed. 8 refs., 4 figs.

  12. Quantum-interference effects in single- and poly-crystalline topological insulator Bi2-xTe3

    NASA Astrophysics Data System (ADS)

    Chiu, Shao-Pin; Lin, Juhn-Jong

    2014-03-01

    We have studied the carrier transport properties of both single- and poly-crystalline topological insulator (TI) Bi2-xTe3 samples. Single-crystalline microflakes were made by exfoliation from a single-crystalline Bi2Te3 bulk. Polycrystalline samples were made by flash evaporation of 5N purity Bi2Te3 sheets. In single-crystalline Bi2Te3 microflakes, temperature dependent resistances revealed two-dimensional (2D) electron-electron interaction effect. The extracted Coulomb screening parameter is negative, in accord with the situation of strong spin-orbit coupling in the TI materials. Positive magnetoresistances (MRs) originated from 2D weak-antilocalization (WAL) effect were measured in low magnetic fields, and satisfactorily described by a multichannel-conduction model. Especially, as T below 1 K and under high positive backgate voltages, signature of two coherent conduction channels was found. We discuss our results in terms of Dirac fermion states on the bottom surface, in addition to the bulk states. Polycrystalline Bi2-xTe3 thin films were patterned by electron-beam lithography. In low perpendicular magnetic fields, positive MRs due to the 2D WAL effect were observed. In parallel magnetic fields, Aharonov-Bohm oscillations were measured, suggesting the presence of metallic surface states. This work was supported by the Taiwan National Science Council through Grant No. NSC102-2120-M-009-003 (J.J.L.).

  13. Spatially resolved imaging of charge collection efficiency in polycrystalline CVD diamond by the use of ion beam induced current

    NASA Astrophysics Data System (ADS)

    Beckmann, D. R.; Saint, A.; Gonon, P.; Jamieson, D. N.; Prawer, S.; Kalish, R.

    1997-07-01

    Diamond based detectors have potential applications in high energy physics experiments. These detectors can be fabricated from synthetic Chemical Vapour Deposited (CVD) polycrystalline diamond films. Previously it has been shown by the Turin group and their coworkers in Zagreb that it is possible to investigate the electrical characteristics of high quality polycrystalline CVD diamond films by Ion Beam Induced Current (IBIC). The present work describes IBIC images obtained using 2 MeV He + irradiation of 250 μm thick polycrystalline diamond films through a thin gold surface contact layer biased positively relative to the grounded rear surface of the film. In contrast to previous experiments the present spectra of collected charge display a clearly defined peak from the induced charge. Images obtained by separating these spectra into different regions of interest allow the identification of regions in the sample of different charge collection efficiency. In particular the presence of some grains in which no charge collection appears possible and the reduction in charge collection efficiency at the grain boundaries is evident.

  14. Real-time x-ray diffraction measurements of shocked polycrystalline tin and aluminum.

    PubMed

    Morgan, Dane V; Macy, Don; Stevens, Gerald

    2008-11-01

    A new, fast, single-pulse x-ray diffraction (XRD) diagnostic for determining phase transitions in shocked polycrystalline materials has been developed. The diagnostic consists of a 37-stage Marx bank high-voltage pulse generator coupled to a needle-and-washer electron beam diode via coaxial cable, producing line and bremsstrahlung x-ray emission in a 35 ns pulse. The characteristic K(alpha) lines from the selected anodes of silver and molybdenum are used to produce the diffraction patterns, with thin foil filters employed to remove the characteristic K(beta) line emission. The x-ray beam passes through a pinhole collimator and is incident on the sample with an approximately 3 x 6 mm(2) spot and 1 degrees full width half maximum angular divergence in a Bragg-reflecting geometry. For the experiments described in this report, the angle between the incident beam and the sample surface was 8.5 degrees . A Debye-Scherrer diffraction image was produced on a phosphor located 76 mm from the polycrystalline sample surface. The phosphor image was coupled to a charge-coupled device camera through a coherent fiber-optic bundle. Dynamic single-pulse XRD experiments were conducted with thin foil samples of tin, shock loaded with a 1 mm vitreous carbon back window. Detasheet high explosive with a 2-mm-thick aluminum buffer was used to shock the sample. Analysis of the dynamic shock-loaded tin XRD images revealed a phase transformation of the tin beta phase into an amorphous or liquid state. Identical experiments with shock-loaded aluminum indicated compression of the face-centered-cubic aluminum lattice with no phase transformation. PMID:19045900

  15. Real-time X-ray Diffraction Measurements of Shocked Polycrystalline Tin and Aluminum

    SciTech Connect

    Dane V. Morgan, Don Macy, Gerald Stevens

    2008-11-22

    A new, fast, single-pulse x-ray diffraction (XRD) diagnostic for determining phase transitions in shocked polycrystalline materials has been developed. The diagnostic consists of a 37-stage Marx bank high-voltage pulse generator coupled to a needle-and-washer electron beam diode via coaxial cable, producing line and bremsstrahlung x-ray emission in a 35-ns pulse. The characteristic Kα lines from the selected anodes of silver and molybdenum are used to produce the diffraction patterns, with thin foil filters employed to remove the characteristic Kβ line emission. The x-ray beam passes through a pinhole collimator and is incident on the sample with an approximately 3-mm by 6-mm spot and 1° full-width-half-maximum (FWHM) angular divergence in a Bragg-reflecting geometry. For the experiments described in this report, the angle between the incident beam and the sample surface was 8.5°. A Debye-Scherrer diffraction image was produced on a phosphor located 76 mm from the polycrystalline sample surface. The phosphor image was coupled to a charge-coupled device (CCD) camera through a coherent fiberoptic bundle. Dynamic single-pulse XRD experiments were conducted with thin foil samples of tin, shock loaded with a 1-mm vitreous carbon back window. Detasheet high explosive with a 2-mm-thick aluminum buffer was used to shock the sample. Analysis of the dynamic shock-loaded tin XRD images revealed a phase transformation of the tin beta phase into an amorphous or liquid state. Identical experiments with shock-loaded aluminum indicated compression of the face-centered-cubic (fcc) aluminum lattice with no phase transformation.

  16. Scaling properties of charge transport in polycrystalline graphene.

    PubMed

    Van Tuan, Dinh; Kotakoski, Jani; Louvet, Thibaud; Ortmann, Frank; Meyer, Jannik C; Roche, Stephan

    2013-04-10

    Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD) growth at random nucleation sites on metallic substrates. The morphology of grain boundaries has become an important topic given its fundamental role in limiting the mobility of charge carriers in polycrystalline graphene, as compared to mechanically exfoliated samples. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We created realistic models of large CVD-grown graphene samples and then computed the corresponding charge carrier mobilities as a function of the average grain size and the coalescence quality between the grains. Our results reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations along grain boundaries. PMID:23448361

  17. Effect of copper impurity on polycrystalline silicon solar cells

    NASA Technical Reports Server (NTRS)

    Daud, T.; Koliwad, K. M.

    1978-01-01

    The presence of copper impurity, up to 10 to the 15th atoms/cc, in single crystal silicon has been shown to have no deleterious effect on the p-n junction solar cell performance. However, in polycrystalline silicon, copper atoms tend to migrate to the defect sites because of the structural sensitive properties of copper. This study was undertaken to investigate the influence of this behavior of copper impurity on the performance of p-n junction solar cells fabricated from structurally imperfect silicon. Two sets of polycrystalline silicon substrates containing copper were examined. In one set of samples, copper was incorporated during growth, whereas in the other, copper was diffused. Solar cells were fabricated on both the sets of substrates by a standard process. Dark and light I-V and spectral response characteristics of the cells were measured and compared with copper-free polycrystalline silicon solar cells. The results and the model are discussed.

  18. Molecular transport and phase transition of polycrystalline ice doped with HCl and SO2 near its melting point

    NASA Astrophysics Data System (ADS)

    Lu, H.; McCartney, S.; Sadtchenko, V.

    2007-12-01

    HCl and SO2 are major trace gases in atmosphere, which greatly affects chemical properties of atmospheric ice particles. A particular interest to atmospheric science is the effects of impurities on molecular transport and phase transition at grain boundaries in polycrystalline ice. Effects of doped HCl and SO2 on transport and phase transition at grain boundary of 2-4 micrometer polycrystalline ice were studied using a novel technique - Fast Thermal Desorption Spectroscopy (FTDS) [1] in the temperature range from -2 to -20 deg. C. In these experiments, H2O/D2O/H2O sandwich-like polycrystalline ice films doped with HCl and SO2 were vapor- deposited on the surface of a thin filament positioned in a vacuum chamber and maintained initially at cryogenic temperatures. After the deposition, the temperature of the filament was rapidly raised to a value near ice melting point, thus, initiating rapids H/D exchange reaction at the interface of H2O and D2O layers. Diffusion controlled rate of isotopic exchange in the desorbing film was monitored with a sensitive mass-spectrometer making it possible to gain quantitative information of the extent of diffusion of chemical species along the grain boundaries in polycrystalline ice samples. Comparisons of the experimental results in pure and doped polycrystalline ice show that water self diffusivity at the grain boundaries is significantly enhanced (by at least an order of magnitude) in the presence of HCl or SO2. The strong, non- Arrhenius, dependence of the water self-diffusivity on temperature indicates that this is due to grain boundary premelting [2], which may occur at temperatures as low as 10 deg. below ice melting point. We will discuss implication of this and other results of our FTDS experiments to various environmental phenomena. References: 1. Haiping Lu, Stephanie A. McCartney, M. Chonde, D. Smyla, and Vlad Sadtchenko, Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline

  19. Multiwavelength excitation Raman scattering of Cu{sub 2}ZnSn(S{sub x}Se{sub 1−x}){sub 4} (0 ≤ x ≤ 1) polycrystalline thin films: Vibrational properties of sulfoselenide solid solutions

    SciTech Connect

    Dimitrievska, Mirjana; Xie, Haibing; Fairbrother, Andrew; Fontané, Xavier; Saucedo, Edgardo; Izquierdo-Roca, Victor; Gurieva, Galina; Pérez-Rodríguez, Alejandro; Schorr, Susan

    2014-07-21

    In this work, Raman spectroscopy and X-ray diffraction were applied together to evaluate the crystal structure and the phonon modes of photovoltaic grade Cu{sub 2}ZnSn(S{sub x}Se{sub 1−x}){sub 4} thin films, leading to a complete characterization of their structural and vibrational properties. Vibrational characterization has been based on Raman scattering measurements performed with different excitation wavelengths and polarization configurations. Analysis of the experimental spectra has permitted identification of 19 peaks, which positions are in good accord with theoretical predictions. Besides, the observation of Cu{sub 2}ZnSnS{sub 4}-like A symmetry peaks related to S vibrations and Cu{sub 2}ZnSnSe{sub 4}-like A symmetry peaks related to Se vibrations, additional Raman peaks, characteristic of the solid solution and previously not reported, are observed, and are attributed to vibrations involving both S and Se anions.

  20. Electronic structure of polycrystalline Cd metal using 241Am radioisotope

    NASA Astrophysics Data System (ADS)

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Sharma, B. K.

    2014-04-01

    Electronic structure study of the polycrystalline cadmium metal is reported. The experimental measurement is undertaken on a polycrystalline sheet sample using 59.54 keV radioisotope of 241Am. These results are compared with the ab initio calculations. The theoretical calculations are performed using linear combination of atomic orbitals (LCAO) method employing the density functional theories (DFT) and Hartree-Fock (HF) and augmented plane wave (APW) methods. The spherically averaged APW and LCAO based theoretical Compton profiles are in good agreement with the experimental measurement however the APW based theoretical calculations show best agreement.

  1. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  2. Software optimization for electrical conductivity imaging in polycrystalline diamond cutters

    SciTech Connect

    Bogdanov, G.; Ludwig, R.; Wiggins, J.; Bertagnolli, K.

    2014-02-18

    We previously reported on an electrical conductivity imaging instrument developed for measurements on polycrystalline diamond cutters. These cylindrical cutters for oil and gas drilling feature a thick polycrystalline diamond layer on a tungsten carbide substrate. The instrument uses electrical impedance tomography to profile the conductivity in the diamond table. Conductivity images must be acquired quickly, on the order of 5 sec per cutter, to be useful in the manufacturing process. This paper reports on successful efforts to optimize the conductivity reconstruction routine, porting major portions of it to NVIDIA GPUs, including a custom CUDA kernel for Jacobian computation.

  3. Growth of Defect-Free 3C-Sic on 4H- and 6H-SIC Mesas Using Step-Free Surface Heteroepitaxy

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Huang, Xianrong R.; Dudley, Michael

    2002-01-01

    A new growth process, herein named step-free surface heteroepitaxy, has achieved 3C-SiC films completely free of double positioning boundaries and stacking faults on 4H-SiC and 6H-SiC substrate mesas. The process is based upon the initial 2-dimensional nucleation and lateral expansion of a single island of 3C-SiC on a 4H- or 6H-SiC mesa surface that is completely free of bilayer surface steps. Our experimental results indicate that substrate-epilayer in-plane lattice mismatch (Delta/a = 0.0854% for 3C/4H) is at least partially relieved parallel to the interface in the initial bilayers of the heterofilm, producing an at least partially relaxed 3C-SiC film without dislocations that undesirably thread through the thickness of the epilayer. This result should enable realization of improved 3C-SiC devices.

  4. Raman Microscopic Characterization of Proton-Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. L.; Davidson, J. L.; Lance, M. J.

    2004-01-01

    The microstructural effects of irradiating polycrystalline diamond films with proton dosages ranging from 10(exp 15) to 10(exp 17) H(+) per square centimeter was examined. Scanning Electron Microscopy and Raman microscopy were used to examine the changes in the diamond crystalline lattice as a function of depth. Results indicate that the diamond lattice is retained, even at maximum irradiation levels.

  5. Electron transient transport in CdTe polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  6. System of polarization correlometry of biological liquids layers polycrystalline structure

    NASA Astrophysics Data System (ADS)

    Ushenko, A. G.; Boychuk, T. M.; Mincer, O. P.; Angelsky, P. O.; Bodnar, N. B.; Oleinichenko, B. P.; Bizer, L. I.

    2013-09-01

    A model of generalized optical anisotropy of human bile is suggested and a method of polarimetric of the module and phase Fourier of the image of the field of laser radiation is analytically substantiated, that is generated by the mechanisms of linear and circular birefringence of polycrystalline networks with a diagnosis and differentiation of cholelithiasis against a background of chronic cholecystitis.

  7. The strength of polycrystalline silicon at the micro- and nano-scales with applications to MEMS

    NASA Astrophysics Data System (ADS)

    Chasiotis, Ioannis

    A new method for tensile testing of thin films by means of an improved apparatus has been developed to measure the elastic properties (Young's modulus, tensile strength) of surface micromachined polycrystalline silicon specimens. The newly designed tensile tester makes use of an Ultraviolet (UV) light curable adhesive to clamp micron-sized specimens. The properties determination utilizes surface topologies of deforming specimens, acquired with an Atomic Force Microscope (AFM), for determining strain fields by means of Digital Image Correlation (DIC). This full-field, direct and local measurements technique provides the capability of testing any type of thin film materials with nanometer resolution. A systematic study of small-scale size effects was thus performed by tensioning elliptically perforated specimens (minimum radius of curvature of 1 mum) so as to: (a) vary the stress concentration with constant radius of curvature, (b) increasing radius of curvature of micronotches relative to the grain size. The results demonstrate a strong influence of the size of the highly strained domain (decreasing notch radii) on the failure strength of MEMS scale specimens, while the effect of varying the stress concentration factor is rather insignificant. In addition, tests performed on unnotched tensile specimens of varying dimensions revealed a specimen size effect by which the values of strength scaled with the specimen length. The Young's modulus, however, is found to be rather insensitive to the specimen dimensions at the scale of microns. Contrary to the common belief that 49% HF wet release represents a safe post-process for manufacturing polycrystalline silicon, this study has clearly identified the release process as a key item in determining thin film failure properties. It is found that surface roughness as characterized by groove formation at the grain boundaries depends distinctly on the HF release time. In addition, while the actual failure mechanism in

  8. Process for utilizing low-cost graphite substrates for polycrystalline solar cells

    NASA Technical Reports Server (NTRS)

    Chu, T. L. (Inventor)

    1978-01-01

    Low cost polycrystalline silicon solar cells supported on substrates were prepared by depositing successive layers of polycrystalline silicon containing appropriate dopants over supporting substrates of a member selected from the group consisting of metallurgical grade polycrystalline silicon, graphite and steel coated with a diffusion barrier of silica, borosilicate, phosphosilicate, or mixtures thereof such that p-n junction devices were formed which effectively convert solar energy to electrical energy. To improve the conversion efficiency of the polycrystalline silicon solar cells, the crystallite size in the silicon was substantially increased by melting and solidifying a base layer of polycrystalline silicon before depositing the layers which form the p-n junction.

  9. Structure and ionic conductivity of well-aligned polycrystalline sodium titanogallate grown by reactive diffusion

    NASA Astrophysics Data System (ADS)

    Hasegawa, Ryo; Okabe, Momoko; Asaka, Toru; Ishizawa, Nobuo; Fukuda, Koichiro

    2015-09-01

    We prepared the b-axis-oriented polycrystalline Na0.85Ti0.51Ga4.37O8 (NTGO) embedded in Ga2O3-doped Na2Ti4O9 matrix using the reactive diffusion technique. When the sandwich-type Ga2TiO5/NaGaO2/Ga2TiO5 diffusion couple was heated at 1323 K for 24 h, the NTGO polycrystal was readily formed in the presence of a liquid phase. The resulting polycrystalline material was characterized by X-ray diffractometry, electron microscopy and impedance spectroscopy. We mechanically processed the annealed diffusion couple and obtained the thin-plate electrolyte consisting mostly of the grain-aligned NTGO polycrystal. The ionic conductivity (σ) of the electrolyte along the common b-axis direction steadily increased from 1.3×10-4 to 7.3×10-3 S/cm as the temperature increased from 573 to 1073 K. There was a slope change at ca. 792 K for the Arrhenius plot of σ; the activation energies were 0.39 eV above this temperature and 0.57 eV below it. The NTGO showed the crystal structure (space group C2/m) with substantial positional disordering of one of the two Ga sites. The Na+ ions occupied ca. 43% of the Wyckoff position 4i site, the deficiency of which would contribute to the relatively high ionic conductivity along the b-axis. The reactive diffusion could be widely applicable as the novel technique to the preparation of grain-aligned ceramics of multi-component systems.

  10. The state of the art of thin-film photovoltaics

    SciTech Connect

    Surek, T.

    1993-10-01

    Thin-film photovoltaic technologies, based on materials such as amorphous or polycrystalline silicon, copper indium diselenide, cadmium telluride, and gallium arsenide, offer the potential for significantly reducing the cost of electricity generated by photovoltaics. The significant progress in the technologies, from the laboratory to the marketplace, is reviewed. The common concerns and questions raised about thin films are addressed. Based on the progress to date and the potential of these technologies, along with continuing investments by the private sector to commercialize the technologies, one can conclude that thin-film PV will provide a competitive alternative for large-scale power generation in the future.

  11. [Study on the micro-infrared spectra and origin of polycrystalline diamonds from Mengyin kimberlite pipes].

    PubMed

    Yang, Zhi-Jun; Liang, Rong; Zeng, Xiang-Qing; Ge, Tie-Yan; Ai, Qun; Zheng, Yun-Long; Peng, Ming-Sheng

    2012-06-01

    The natural polycrystalline diamonds from the Mengyin kimberlite pipes can be classified as the euhedral faceted polycrystalline diamonds and anhedral rounded polycrystalline diamonds. The results of micro-FTIR spectra characterization of the polycrystalline diamonds show that the concentration of nitrogen is low, varying from 16.69 to 72.81 microgram per gram and is different among different diamond grains or position in polycrystalline diamonds. The euhedral faceted polycrystalline diamonds are Ia AB type and have higher concentration of A-center defects than B-center defects. Most of the anhedral rounded polycrystalline diamonds are Ia AB type and have higher content of B-center defects. A minority of the anhedral rounded polycrystalline diamonds have C-center, A-center and B-center defects simultaneously. The polycrystalline diamonds probably originated from the relatively deeper mantle and were not formed in diamond nucleation stage, but in the diamond growth period or some special conditions after the diamond grains were formed already. Furthermore, the euhedral faceted polycrystalline diamonds were formed slightly later and the anhedral rounded polycrystalline diamonds were formed obviously earlier than the diamond single crystals from the Mengyin kimberlite pipes. PMID:22870630

  12. Mechanical instability of monocrystalline and polycrystalline methane hydrates.

    PubMed

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T; Kjelstrup, Signe; Vlugt, Thijs J H; He, Jianying; Skallerud, Bjørn H; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  13. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

    2014-03-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

  14. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    NASA Astrophysics Data System (ADS)

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-11-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments.

  15. Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

    SciTech Connect

    Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.; Lee, Michael V.; Qi, Yabing; Joo Shin, Tae; Ahn, Docheon; Lee, Han-Koo; Baik, Jaeyoon; Shin, Hyun-Joon

    2015-03-15

    Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

  16. Compton profile study of polycrystalline ZnBr{sub 2}

    SciTech Connect

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Kothari, R. K.; Sharma, B. K.

    2010-12-01

    The first ever Compton profile study of polycrystalline ZnBr{sub 2} is presented in this paper. The measurement of polycrystalline sample of ZnBr{sub 2} is performed using 59.54 keV gamma-rays emanating from an {sup 241}Am radioisotope. Theoretical calculations are performed following the Ionic model calculations for a number of configurations Zn{sup +x}Br{sub 2}{sup -x/2}(0.0{<=}x{<=}2.0 in step of 0.5) utilizing free atom profiles. The ionic model suggest transfer of 2.0 electrons from 4 s state of Zn to 4 p state of two Br atoms. The autocorrelation function B(z) is also derived from experiment and the most favoured ionic valence Compton profiles.

  17. Further development and application of polycrystalline metal whiskers

    NASA Technical Reports Server (NTRS)

    Schladitz, H. J.

    1979-01-01

    High strength metal whiskers have a larger versatile field of application than monocrystalline whiskers. Although polycrystalline metal whiskers can be used for composites, preferably by extrusion in thermoplastics or by infiltration of resins or metals into whisker networks, the chief application at present may be the production and various use of whisker networks. Such networks can be produced up to high degrees of porosity and besides high mechanical strength, they have high inside surfaces and high electric conductivity. There are for instance, applications concerning construction of electrodes for batteries and fuel cells, catalysts and also new heat-exchanger material, capable of preparing fuel oil and gasoline in order to assist a high-efficiency combustion. The technical application of polycrystalline metal whiskers require their modification as well as the construction of a pilot production unit.

  18. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    PubMed Central

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  19. Boron doped polycrystalline diamond films for strain sensing applications

    SciTech Connect

    Wur, D.; Davidson, J.L.; Kang, W.P.

    1995-12-31

    It has been recently established in our work and others that boron-doped polycrystalline diamond films (PDF) have piezoresistivity (PZR). This property opens PDF to the field of sensor applications using strain sensing. Polycrystalline diamond films have been prepared with microwave plasma enhanced chemical vapor deposition (CVD) method and boron-doped to p-type semiconductors. In addition, by combining the piezoresistive effect in doped PDF and the insulating property of undoped PDF, whereby doped diamond resistors reside on a dielectric diamond substrate diaphragm, a monolithic all-diamond microstructure for examining the strain response of patterned p-doped diamond PZRs was fabricated and characterized. This work examines some critical issues of diamond for strain sensing applications such as its rupture stress and edge stress of diamond diaphragm and the high temperature responses of a diamond strain sensor.

  20. Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1992--31 March 1993

    SciTech Connect

    Sites, J.R.

    1994-02-01

    This report describes work to conduct several investigations of thin-film polycrystalline solar cells. (1) An analysis of high-efficiency solar cells fabricated at the University of South Florida showed significant reduction in forward recombination current, and the cells were stable over a 3-month test period. (2) Transient voltage effects were documented in a large number of polycrystalline cells and were attributed to long-lived trapping states sensitive to voltage changes near one-half open-circuit voltage. (3) Collection efficiency and its voltage dependence were carefully calculated. The typical effect on photocurrent at operating voltages is about 2% for CuInSe{sub 2}, and less for other cells.

  1. Oscillation of structure characteristics in polycrystalline nickel during plastic deformation

    SciTech Connect

    Dvorovienko, N.A.; Gernov, S.A.; Sirenko, A.F. . Dept. of Solid State Physics); Hamana, D. . Research Unit of Materiale Physic)

    1993-07-01

    The variation of X-ray diffraction characteristics (breadth at half maximum intensity, integrated intensity, dislocation density and residual stresses), as a function of plastic deformation rate, which occurs by uniaxial tensile test, has been studied. At room temperature the observed oscillation of studied characteristics in deformed polycrystalline nickel is due to the deformation mechanism change. The latter can be a translational displacement due to dislocations or a rotational displacement due to disclination.

  2. A characterization study of a hydroxylated polycrystalline tin oxide surface

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.; Grogan, Austin L., Jr.; Asbury, Douglas A.; Schryer, David R.

    1989-01-01

    In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

  3. Photoluminescence of polycrystalline ZnO under different annealing conditions

    NASA Astrophysics Data System (ADS)

    Hur, Tae-Bong; Jeen, Gwang Soo; Hwang, Yoon-Hwae; Kim, Hyung-Kook

    2003-11-01

    We investigated polycrystalline zinc oxide (ZnO) with different annealing conditions in air by x-ray photoelectron spectroscopy and photoluminescence. We found that the concentration of antisite oxide (OZn) increases when ZnO ceramics were in an O-rich condition. As the concentration of antisite oxide (OZn) increased, the photoluminescence intensity of the green band emission increased. The crossover temperature of the free and bound excitons was roughly estimated as 100 K.

  4. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  5. Mechanical properties of irradiated multi-phase polycrystalline BCC materials

    NASA Astrophysics Data System (ADS)

    Song, Dingkun; Xiao, Xiazi; Xue, Jianming; Chu, Haijian; Duan, Huiling

    2015-04-01

    Structure materials under severe irradiations in nuclear environments are known to degrade because of irradiation hardening and loss of ductility, resulting from irradiation-induced defects such as vacancies, interstitials and dislocation loops, etc. In this paper, we develop an elastic-viscoplastic model for irradiated multi-phase polycrystalline BCC materials in which the mechanical behaviors of individual grains and polycrystalline aggregates are both explored. At the microscopic grain scale, we use the internal variable model and propose a new tensorial damage descriptor to represent the geometry character of the defect loop, which facilitates the analysis of the defect loop evolutions and dislocation-defect interactions. At the macroscopic polycrystal scale, the self-consistent scheme is extended to consider the multiphase problem and used to bridge the individual grain behavior to polycrystal properties. Based on the proposed model, we found that the work-hardening coefficient decreases with the increase of irradiation-induced defect loops, and the orientation/loading dependence of mechanical properties is mainly attributed to the different Schmid factors. At the polycrystalline scale, numerical results for pure Fe match well with the irradiation experiment data. The model is further extended to predict the hardening effect of dispersoids in oxide-dispersed strengthened steels by the considering the Orowan bowing. The influences of grain size and irradiation are found to compete to dominate the strengthening behaviors of materials.

  6. 'Age-hardened alloy' based on bulk polycrystalline oxide ceramic

    NASA Astrophysics Data System (ADS)

    Gurnani, Luv; Singh, Mahesh Kumar; Bhargava, Parag; Mukhopadhyay, Amartya

    2015-05-01

    We report here for the first time the development of 'age-hardened/toughened' ceramic alloy based on MgO in the bulk polycrystalline form. This route allows for the facile development of a 'near-ideal' microstructure characterized by the presence of nanosized and uniformly dispersed second-phase particles (MgFe2O4) within the matrix grains, as well as along the matrix grain boundaries, in a controlled manner. Furthermore, the intragranular second-phase particles are rendered coherent with the matrix (MgO). Development of such microstructural features for two-phase bulk polycrystalline ceramics is extremely challenging following the powder metallurgical route usually adopted for the development of bulk ceramic nanocomposites. Furthermore, unlike for the case of ceramic nanocomposites, the route adopted here does not necessitate the usage of nano-powder, pressure/electric field-assisted sintering techniques and inert/reducing atmosphere. The as-developed bulk polycrystalline MgO-MgFe2O4 alloys possess considerably improved hardness (by ~52%) and indentation toughness (by ~35%), as compared to phase pure MgO.

  7. High temperature adsorption of nitrogen on a polycrystalline nickel surface

    NASA Astrophysics Data System (ADS)

    Boughaba, S.; Auvert, G.

    1994-01-01

    Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser-induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/<100> monosilicon substrates. As a heat source, a cw argon-ion laser was used. The laser-induced surface temperature was varied in the range 500-850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. On the basis of these results, the high temperature adsorption of nitrogen on a polycrystalline nickel surface was investigated. A model which accounts for the dependence of the nickel deposition rate and surface coverage with nitrogen adspecies on the N2 partial pressure was elaborated.

  8. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials. PMID:26936563

  9. Optical Properties of Anisotropic Polycrystalline Ce+3 activated LSO

    PubMed Central

    Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod

    2012-01-01

    Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. PMID:23505329

  10. Grain-boundary-induced melting in quenched polycrystalline monolayers

    NASA Astrophysics Data System (ADS)

    Deutschländer, Sven; Boitard, Charlotte; Maret, Georg; Keim, Peter

    2015-12-01

    Melting in two dimensions can successfully be explained with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario which describes the formation of the high-symmetry phase with the thermal activation of topological defects within an (ideally) infinite monodomain. With all state variables being well defined, it should hold also as freezing scenario where oppositely charged topological defects annihilate. The Kibble-Zurek mechanism, on the other hand, shows that spontaneous symmetry breaking alongside a continuous phase transition cannot support an infinite monodomain but leads to polycrystallinity. For any nonzero cooling rate, critical fluctuations will be frozen out in the vicinity of the transition temperature. This leads to domains with different director of the broken symmetry, separated by a defect structure, e.g., grain boundaries in crystalline systems. After instantaneously quenching a colloidal monolayer from a polycrystalline to the isotropic fluid state, we show that such grain boundaries increase the probability for the formation of dislocations. In addition, we determine the temporal decay of defect core energies during the first few Brownian times after the quench. Despite the fact that the KTHNY scenario describes a continuous phase transition and phase equilibrium does not exist, melting in polycrystalline samples starts at grain boundaries similar to first-order phase transitions.

  11. Flexible cadmium telluride thin films grown on electron-beam-irradiated graphene/thin glass substrates

    SciTech Connect

    Seo, Won-Oh; Kim, Jihyun; Koo, Yong Hwan; Kim, Byungnam; Lee, Byung Cheol; Kim, Donghwan

    2014-08-25

    We demonstrate the close-spaced sublimation growth of polycrystalline cadmium telluride (CdTe) thin films on a flexible graphene electrode/thin glass substrate structure. Prior to the growth of CdTe films, chemical-vapor-deposited graphene was transferred onto a flexible glass substrate and subjected to electron-beam irradiation at an energy of 0.2 MeV in order to intentionally introduce the defects into it in a controlled manner. Micro-Raman spectroscopy and sheet resistance measurements were employed to monitor the damage and disorder in the electron-beam irradiated graphene layers. The morphology and optical properties of the CdTe thin films deposited on a graphene/flexible glass substrate were systematically characterized. The integration of the defective graphene layers with a flexible glass substrate can be a useful platform to grow various thin-film structures for flexible electronic and optoelectronic devices.

  12. X-ray diffraction characterization of thin superconductive films

    SciTech Connect

    Kozaczek, K.J.; Watkins, T.R.; Book, G.W.; Carter, W.B.

    1995-12-31

    The physical and mechanical properties of thin films are often different from the properties of bulk material and are dictated by the film/substrate orientation relationship, crystal anisotropy and crystalgraphic texture of the film. X-ray diffraction texture analysis provides information about preferential film growth and can be used for optimization of deposition parameters and prediction of properties of thin films. An x-ray back reflection technique using the Braga-Brentano geometry with experimental corrections for absorption and defocusing was used to study thin ceramic films deposited by combustion chemical vapor deposition (CCVD). The film/substrate orientation relationships of YBa{sub 2}Cu{sub 3}O{sub x} (YBCO) superconducting thin films deposited via CCVD on single crystal MgO and polycrystalline silver substrates were studied. The as-deposited films on single crystal (100) MgO substrates showed strong preferential growth with the basal plane parallel to the substrate surface (c-axis up growth). Texture analysis showed two in-plane alignment orientations of the film with respect to the substrate, with YBCO [100] and [110] aligned with the [100] MgO substrate. YBCO films deposited on cold-rolled polycrystalline silver displayed c-axis up growth indicating that the orientation of the polycrystalline substrate (brass type texture) did not induce detectable in-plane preferential growth of the YBCO.

  13. Atmospheric and Aqueous Deposition of Polycrystalline Metal Oxides Using Mist-CVD for Highly Efficient Inverted Polymer Solar Cells.

    PubMed

    Zhu, Xiaodan; Kawaharamura, Toshiyuki; Stieg, Adam Z; Biswas, Chandan; Li, Lu; Ma, Zhu; Zurbuchen, Mark A; Pei, Qibing; Wang, Kang L

    2015-08-12

    Large scale, cost-effective processing of metal oxide thin films is critical for the fabrication of many novel thin film electronics. To date, however, most of the reported solution-based techniques require either extended thermal anneals or additional synthetic steps. Here we report mist chemical vapor deposition as a solution-based, readily scalable, and open-air method to produce high-quality polycrystalline metal oxide thin films. Continuous, smooth, and conformal deposition of metal oxide thin films is achieved by tuning the solvent chemistry of Leidenfrost droplets to promote finer control over the surface-local dissociation process of the atomized zinc-bearing precursors. We demonstrate the deposited ZnO as highly efficient electron transport layers for inverted polymer solar cells to show the power of the approach. A highest efficiency of 8.7% is achieved with a fill factor of 73%, comparable to that of conventional so-gel ZnO, which serves as an indication of the efficient vertical transport and electron collection achievable using this material. PMID:26146797

  14. Polycrystalline silicon study: Low-cost silicon refining technology prospects and semiconductor-grade polycrystalline silicon availability through 1988

    NASA Technical Reports Server (NTRS)

    Costogue, E. N.; Ferber, R.; Lutwack, R.; Lorenz, J. H.; Pellin, R.

    1984-01-01

    Photovoltaic arrays that convert solar energy into electrical energy can become a cost effective bulk energy generation alternative, provided that an adequate supply of low cost materials is available. One of the key requirements for economic photovoltaic cells is reasonably priced silicon. At present, the photovoltaic industry is dependent upon polycrystalline silicon refined by the Siemens process primarily for integrated circuits, power devices, and discrete semiconductor devices. This dependency is expected to continue until the DOE sponsored low cost silicon refining technology developments have matured to the point where they are in commercial use. The photovoltaic industry can then develop its own source of supply. Silicon material availability and market pricing projections through 1988 are updated based on data collected early in 1984. The silicon refining industry plans to meet the increasing demands of the semiconductor device and photovoltaic product industries are overviewed. In addition, the DOE sponsored technology research for producing low cost polycrystalline silicon, probabilistic cost analysis for the two most promising production processes for achieving the DOE cost goals, and the impacts of the DOE photovoltaics program silicon refining research upon the commercial polycrystalline silicon refining industry are addressed.

  15. Quantification of the microstructural evolution of polycrystalline fabrics using FAME: Application to in situ deformation of ice

    NASA Astrophysics Data System (ADS)

    Peternell, Mark; Dierckx, Marie; Wilson, Christopher J. L.; Piazolo, Sandra

    2014-04-01

    In geology, glaciology and material science new technological advances result in an ever increasing amount of data and datasets, in particular when in situ experiments are conducted. Rapid, rigorous and reliable statistical treatment is needed to allow researchers to access these large datasets for further analysis. Here, we present FAME (Fabric Analyser based Microstructure Evaluation), a suite of Matlab® scripts that utilize the Matlab® open-source toolboxes MTEX and PolyLX (optional) for rapid quantification of thin section data. The data has been collected using an automated Fabric Analyser at a spatial resolution of 5 μm/pixel. From the dataset, grain maps are reconstructed and, grain and grain boundary statistics are determined. The same scripts calculate orientation density distribution diagrams and eigenvalues of the orientation tensor. In the case of 2D in situ plane-strain deformation experiments on polycrystalline heavy water (D2O), a Matlab® script-based batch analysis for each deformation step was performed. FAME offers the possibility to generate movie files that combine optical data with c-axes orientation data and grain statistics. Application of the presented scripts, to analyse in situ deformation experiments of polycrystalline ice, shows the value of rigorous quantification of the microstructural evolution data for process oriented research.

  16. Modeling and simulation of the deposition/relaxation processes of polycrystalline diatomic structures of metallic nitride films

    NASA Astrophysics Data System (ADS)

    García, M. F.; Restrepo-Parra, E.; Riaño-Rojas, J. C.

    2015-05-01

    This work develops a model that mimics the growth of diatomic, polycrystalline thin films by artificially splitting the growth into deposition and relaxation processes including two stages: (1) a grain-based stochastic method (grains orientation randomly chosen) is considered and by means of the Kinetic Monte Carlo method employing a non-standard version, known as Constant Time Stepping, the deposition is simulated. The adsorption of adatoms is accepted or rejected depending on the neighborhood conditions; furthermore, the desorption process is not included in the simulation and (2) the Monte Carlo method combined with the metropolis algorithm is used to simulate the diffusion. The model was developed by accounting for parameters that determine the morphology of the film, such as the growth temperature, the interacting atomic species, the binding energy and the material crystal structure. The modeled samples exhibited an FCC structure with grain formation with orientations in the family planes of < 111 >, < 200 > and < 220 >. The grain size and film roughness were analyzed. By construction, the grain size decreased, and the roughness increased, as the growth temperature increased. Although, during the growth process of real materials, the deposition and relaxation occurs simultaneously, this method may perhaps be valid to build realistic polycrystalline samples.

  17. Unraveling Charge Carriers Generation, Diffusion, and Recombination in Formamidinium Lead Triiodide Perovskite Polycrystalline Thin Film.

    PubMed

    Piatkowski, Piotr; Cohen, Boiko; Ponseca, Carlito S; Salado, Manuel; Kazim, Samrana; Ahmad, Shahzada; Sundström, Villy; Douhal, Abderrazzak

    2016-01-01

    We report on studies of the formamidinium lead triiodide (FAPbI3) perovskite film using time-resolved terahertz (THz) spectroscopy (TRTS) and flash photolysis to explore charge carriers generation, migration, and recombination. The TRTS results show that upon femtosecond excitation above the absorption edge, the initial high photoconductivity (∼75 cm(2) V(-1) s(-1)) remains constant at least up to 8 ns, which corresponds to a diffusion length of 25 μm. Pumping below the absorption edge results in a mobility of 40 cm(2) V(-1) s(-1) suggesting lower mobility of charge carriers located at the bottom of the conduction band or shallow sub-bandgap states. Furthermore, analysis of the THz kinetics reveals rising components of <1 and 20 ps, reflecting dissociation of excitons having different binding energies. Flash photolysis experiments indicate that trapped charge carriers persist for milliseconds. PMID:26703885

  18. Polycrystalline thin-film cadmium telluride solar cells fabricated by electrodeposition. Annual technical report

    SciTech Connect

    Trefny, J.U.; Mao, D.

    1998-01-01

    During the past year, Colorado School of Mines (CSM) researchers performed systematic studies of the growth and properties of electrodeposition CdS and back-contact formation using Cu-doped ZnTe, with an emphasis on low Cu concentrations. CSM also started to explore the stability of its ZnTe-Cu contacted CdTe solar cells. Researchers investigated the electrodeposition of CdS and its application in fabricating CdTe/CdS solar cells. The experimental conditions they explored in this study were pH from 2.0 to 3.0; temperatures of 80 and 90 C; CdCl{sub 2} concentration of 0.2 M; deposition potential from {minus}550 to {minus}600 mV vs. Ag/AgCl electrode; [Na{sub 2}S{sub 2}O{sub 4}] concentration between 0.005 and 0.05 M. The deposition rate increases with increase of the thiosulfate concentration and decrease of solution pH. Researchers also extended their previous research of ZnTe:Cu films by investigating films doped with low Cu concentrations (< 5 at. %). The low Cu concentration enabled them to increase the ZnTe:Cu post-annealing temperature without causing excessive Cu diffusion into CdTe or formation of secondary phases. The effects of Cu doping concentration and post-deposition annealing temperature on the structural, compositional, and electrical properties of ZnTe were studied systematically using X-ray diffraction, atomic force microscopy, electron microprobe, Hall effect, and conductivity measurements.

  19. Filamentary resistive switching in amorphous and polycrystalline Nb2O5 thin films

    NASA Astrophysics Data System (ADS)

    Mähne, H.; Berger, L.; Martin, D.; Klemm, V.; Slesazeck, S.; Jakschik, S.; Rafaja, D.; Mikolajick, T.

    2012-06-01

    In this paper, the correlation between the crystallinity of reactively sputtered Nb2O5 layers on Pt bottom electrode and their resistive switching behavior was investigated. It was found that the amorphous phase can transformed to an orthorhombic phase by annealing in argon at 650 °C. Smooth surfaces of the crystalline samples with RMS roughness of 1 nm were produced. By using the stack Al/Nb2O5/Pt a Schottky diode was produced and a barrier height of 1.0 eV for the argon annealed sample was found. For the amorphous sample, a Frenkel-Poole emission mechanism was found with the activation energy of 0.21 eV. After an electric forming process a filamentary resistive switching was observed for both types of samples.

  20. Polycrystalline thin film cadmium telluride n-i-p solar cells

    NASA Astrophysics Data System (ADS)

    Meyers, P. V.

    1990-06-01

    This paper discusses experiments and analyses of technical, economic and environmental issues relating to CdTe n-i-p solar cells and their potential to satisfy the DOE PV program goals. The basic cell structure is CdS-CdTe-ZnTe. Included is an experimental and theoretical study of the operation of these devices. Experiments related to deposition of the CdS and ZnTe layers, cascaded solar cells, and module fabrication are described. Manufacturing issues relating to costs, worker safety, and environmental security are discussed.

  1. A photoluminescence study of polycrystalline thin-film CdTe/CdS solar cells

    NASA Astrophysics Data System (ADS)

    Halliday, D. P.; Eggleston, J. M.; Durose, K.

    1998-03-01

    The structures studied here are photovoltaic cells composed of indium tin oxide (ITO) coated glass, 500 nm of CdS and 5 μm of CdTe. The devices are grown by close-space sublimation (CSS). The as-grown cells have a photovoltaic efficiency of η=0.8%. Following deposition of CdCl 2 and annealing in air at 400°C, the efficiency increases to around 10%. A study of the cells is made by examining the variation in the photoluminescence from the surface of the CdTe layer with laser power and sample temperature for an as-grown cell, an air-annealed cell and a cell which has undergone CdCl 2 treatment. Three luminescence bands are observed at 1.590, 1.555 and 1.45 eV. These are attributed to shallow donor and acceptor bound excitons, a free to bound transition and a deep-level acceptor complex. The observed emissions are analysed and correlated to the changes in the cell characteristics.

  2. The DOE/SERI polycrystalline thin-film solar cell program

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Ullal, H.; Mitchell, R.

    Research and development work in copper indium diselenide (CuInSe2) and cadmium telluride (CdTe) technologies is reported. Devices produced from these materials have strong potential in photovoltaics because of their low cost, resonable efficiency, and stablity. Some of the major recent accomplishments of the program are (1) the achievement of 10.5 percent efficiency with a CdTe device; (2) an improvement in the efficiency of selenized CuInSe2 cells to nearly 8 percent; (3) the development of a transparent contact to CdTe cells for possible use in the top cell of a tandem structure; (4) the achievement of a 10.2-percent-efficient Cu(Ga,In)Se cell; and (5) the fabrication of a 9.6-percent-efficient 91-sq-cm CuInSe2 submodule. Directions and plans for future work are indicated.

  3. Improved Intrinsic Stability of CdTe Polycrystalline Thin Film Devices

    SciTech Connect

    Albin, D.; Berniard, T.; McMahon, T.; Noufi, R.; Demtsu, S.

    2005-01-01

    A systems-driven approach linking upstream solar cell device fabrication history with downstream performance and stability has been applied to CdS/CdTe small-area device research. The best resulting initial performance (using thinner CdS, thicker CdTe, no oxygen during VCC, and the use of NP etch) was shown to simultaneously correlate with poor stability. Increasing the CdS layer thickness significantly improved stability at only a slight decrease in overall performance. It was also determined that cell perimeter effects can accelerate degradation in these devices. A ''margined'' contact significantly reduces the contribution of edge shunting to degradation, and thus yields a more accurate determination of the intrinsic stability. Pspice discrete element models demonstrate how spatially localized defects can effectively dominate degradation. Mitigation of extrinsic shunting improved stabilized efficiency degradation levels (SEDL) to near 20% in 100 C tests. Further process optimization to reduce intrinsic effects improved SEDL to better than 10% at the same stress temperatures and times.

  4. Thin film poly-crystalline silicon fabrication based on Rapid Thermal Annealing (RTA) process

    NASA Astrophysics Data System (ADS)

    Qian, Jun; Li, Jirong; Liao, Yang; Shi, Weimin; Kuang, Huahui; Ming, Xiuchun; Liu, Jin; Jin, Jing; Qin, Juan

    2013-12-01

    Rapid Thermal Annealing (RTA) process was introduced to the experiment of Aluminum-induced crystallization of a-Si, based on sputtering method, on low cost glass substrate. A stack of glass/Al (150 nm)/Si (220 nm) was deposited by sputtering sequentially. Samples were annealed under RTA process, then annealed in the tube annealing furnace at 400 °C for 5 h. The grain crystallization was inspected by optical microscopy (OM), ,Raman spectroscopy, X-ray diffraction (XRD),and energy dispersive spectroscopy (EDS). The preferential orientation (111) was observed, with a Raman Peak at 520.8cm-1, Different annealing periods were discussed.

  5. Research on polycrystalline thin film submodules based on CuInSe sub 2 materials

    SciTech Connect

    Catalano, A.; Arya, R.; Carr, L.; Fieselmann, B.; Lommasson, T.; Podlesny, R.; Russell, L.; Skibo, S.; Rothwarf, A.; Birkmire, R. )

    1992-05-01

    This report describes progress during the first year of a three-year research program to develop 12%-efficient CuInSe{sub 2} (CIS) submodules with area greater than 900 cm{sup 2}. To meet this objective, the program was divided into five tasks: (1) windows, contacts, substrates; (2) absorber material; (3) device structure; (4) submodule design and encapsulation; and (5) process optimization. In the first year of the program, work was concentrated on the first three tasks with an objective to demonstrate a 9%-efficient CIS solar cell. 7 refs.

  6. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Declemy, A.; Pranevicius, L.; Milhet, X.

    2005-04-15

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm{sup -2}. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the <001> being more preferential for nitrogen diffusion than <011>. In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or {gamma}{sub N} phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

  7. Aluminum additions in polycrystalline iron-gallium (Galfenol) alloys

    NASA Astrophysics Data System (ADS)

    Brooks, M. D.; Summers, E.; Meloy, R.; Mosley, J.

    2008-03-01

    Galfenol alloys show promise as a new magnetically activated smart material based on their unique combination of relatively high magnetostrictive performance and good mechanical robustness. Investigations of aluminum additions to single crystal iron-gallium alloys have been done previously, and the magnetostrictive response seems to follow the rule of mixtures with decreasing saturation magnetostriction with increasing aluminum content. Aluminum is assumed to substitute for Ga directly in the alloy. Directionally solidified polycrystalline Galfenol alloys with aluminum additions were produced to determine the effects on the magnetic properties. Iron-gallium-aluminum alloys were investigated for two primary reasons: (1) Fe-Al alloys are well established and are typically manufactured using conventional thermo-mechanical processing techniques such as rolling; it is anticipated that aluminum additions will aid in the development of Galfenol alloy rolled sheets (2) Gallium prices continue to rise and a cost effective alternative needs to be investigated. Several Fe-Ga-Al alloy compositions were prepared using the Free Stand Zone Melting (FSZM) directional solidification technique. Alloy composition ranges investigated include: Fe 80.5Ga xAl 19.5-x (4.9<=x<=13), Fe 81.6Ga yAl 18.4-y (4.6<=y<=13.8), and Fe 85Ga zAl 15-z (3.75<=z<=11.25). Alloys were studied using EDS (chemistry verification), EBSD (crystallite orientation), and magnetic characterization techniques to determine the effect of aluminum addition on the polycrystalline binary Fe-Ga system. Magnetic properties such as saturation magnetostriction (λ sat), piezomagnetic constant (d 33), and relative magnetic permeability (μ r) of directionally solidified Fe-Ga-Al polycrystalline alloys will be compared to binary Fe-Ga alloys including investigations into the crystal orientation effects on these properties. Results suggest that up to 50% aluminum can be substituted in the alloy while maintaining considerable

  8. Conductive polycrystalline diamond probes for local anodic oxidation lithography

    NASA Astrophysics Data System (ADS)

    Ulrich, A. J.; Radadia, A. D.

    2015-11-01

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k Avg). The metal-coated and the DC tips with comparable k Avg showed comparable threshold voltages, whereas the MD tips with similar k Avg showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed (v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k Avg. This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography.

  9. Conductive polycrystalline diamond probes for local anodic oxidation lithography.

    PubMed

    Ulrich, A J; Radadia, A D

    2015-11-20

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k(Avg)). The metal-coated and the DC tips with comparable k(Avg) showed comparable threshold voltages, whereas the MD tips with similar k(Avg) showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed(v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k(Avg). This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography. PMID:26501841

  10. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere. PMID:10947983

  11. An acoustic emission study of plastic deformation in polycrystalline aluminium

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Frederick, J. R.; Felbeck, D. K.

    1979-01-01

    Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminum while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.

  12. Polycrystalline diamond based detector for Z-pinch plasma diagnosis

    SciTech Connect

    Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan

    2010-08-15

    A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

  13. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-09-18

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  14. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-01-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  15. PDC (polycrystalline diamond compact) bit research at Sandia National Laboratories

    SciTech Connect

    Finger, J.T.; Glowka, D.A.

    1989-06-01

    From the beginning of the geothermal development program, Sandia has performed and supported research into polycrystalline diamond compact (PDC) bits. These bits are attractive because they are intrinsically efficient in their cutting action (shearing, rather than crushing) and they have no moving parts (eliminating the problems of high-temperature lubricants, bearings, and seals.) This report is a summary description of the analytical and experimental work done by Sandia and our contractors. It describes analysis and laboratory tests of individual cutters and complete bits, as well as full-scale field tests of prototype and commercial bits. The report includes a bibliography of documents giving more detailed information on these topics. 26 refs.

  16. Chemically assisted ion beam etching of polycrystalline and (100)tungsten

    NASA Technical Reports Server (NTRS)

    Garner, Charles

    1987-01-01

    A chemically assisted ion-beam etching technique is described which employs an ion beam from an electron-bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 microns thick with good anisotropy and pattern definition over areas of 30 sq mm, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred-orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling-wave tubes to a controlled porosity.

  17. Nucleation and growth studies of polycrystalline covalent materials

    NASA Astrophysics Data System (ADS)

    Yun, Jungheum

    The chemical vapor deposition of different covalent polycrystalline materials---including diamond, silicon carbide, and carbon nitride---in stagnation flow reactors was rigorously simulated to determine the nucleation and growth mechanisms of these materials. Kinetic models were used to predict the rates of gas-phase and surface chemistry, the temperature and velocity profiles, potential gaseous film growth precursors, the time evolution of nucleation and intermediate layer formation, and the morphological evolution of continuous polycrystalline films. Numerical studies were also carried out to determine the dependence of the kinetics of nucleation and subsequent polycrystalline film growth on operating conditions. The calculated results for carbon nitride deposition indicate that the experimentally measured bond types in the carbon nitride films must result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once gaseous film growth precursors, including C, CH2 , CH3, C2H2, N, NH, NH2, HCN, and H2CN, are adsorbed. Of these precursors, C and CH 3 dominate the carbon contribution to carbon nitride film growth, and atomic nitrogen is the principal nitrogen bearing species. When the evolution rates of a silicon carbide intermediate layer and diamond clusters are calculated by accounting for gas-phase and surface reactions, surface and bulk diffusion, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics, it is predicted that higher adsorption energies, in the range of 3.7 to 4.5 eV, lead to larger surface adatom densities, lower saturated nucleation densities, and larger silicon carbide intermediate layer thicknesses. The intermediate layer thickness becomes saturated while the growing diamond nuclei still cover a very small fraction of the silicon carbide. Reports of heteroepitaxial diamond nucleation without silicon carbide intermediate layer formation may be readily explained by a

  18. Ultrafast carrier dynamics in polycrystalline bismuth telluride nanofilm

    SciTech Connect

    Jia, Lin; Ma, Weigang; Zhang, Xing

    2014-06-16

    In this study, the dynamics of energy carriers in polycrystalline bismuth telluride nanofilm are investigated by the ultrafast pump-probe method. The energy relaxation processes are quantitatively analyzed by using the numerical fitting models. The extracted hot carrier relaxation times of photon excitation, thermalization, and diffusion are around sub-picosecond. The initial reflectivity recovery is found to be dominantly determined by the carrier diffusion, electron-phonon coupling, and photo-generated carriers trapping processes. High-frequency and low-frequency oscillations are both observed and attributed to coherent optical phonons and coherent acoustic phonons, respectively.

  19. Average g-Factors of Anisotropic Polycrystalline Samples

    SciTech Connect

    Fishman, Randy Scott; Miller, Joel S.

    2010-01-01

    Due to the lack of suitable single crystals, the average g-factor of anisotropic polycrystalline samples are commonly estimated from either the Curie-Weiss susceptibility or the saturation magnetization. We show that the average g-factor obtained from the Curie constant is always greater than or equal to the average g-factor obtained from the saturation magnetization. The average g-factors are equal only for a single crystal or an isotropic polycrystal. We review experimental results for several compounds containing the anisotropic cation [Fe(C5Me5)2]+ and propose an experiment to test this inequality using a compound with a spinless anion.

  20. Compensation for thermally induced birefringence in polycrystalline ceramic active elements

    SciTech Connect

    Kagan, M A; Khazanov, E A

    2003-10-31

    Polycrystalline ceramics differ significantly from single crystals in that the crystallographic axes (and hence of the axes of thermally induced birefringence) are oriented randomly in each granule of the ceramic. The quaternion formalism is employed to calculate the depolarisation in the ceramics and the efficiency of its compensation. The obtained analytic expressions are in good agreement with the numerical relations. It is shown that the larger the ratio of the sample length to the granule size, the closer the properties of the ceramics to those of a single crystal with the [111] orientation (in particular, the uncompensated depolarisation is inversely proportional to this ratio). (active media)

  1. Statistical thermodynamics of strain hardening in polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Langer, J. S.

    2015-09-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman [Acta Mat. 58, 3718 (2010), 10.1016/j.actamat.2010.03.009]. It then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  2. Screen-Cage Ion Plating Of Silver On Polycrystalline Alumina

    NASA Technical Reports Server (NTRS)

    Spalvins, Talivaldis; Sliney, Harold E.; Deadmore, Daniel L.

    1995-01-01

    Screen-cage ion plating (SCIP) cost-effective technique offering high throwing power for deposition of adherent metal films on ceramic substrates. Applies silver films to complexly shaped substrates of polycrystalline alumina. Silver adheres tenaciously and reduces friction. SCIP holds promise for applying lubricating soft metallic films to high-temperature ceramic components of advanced combustion engines. Other potential uses include coating substrates with metal for protection against corrosion, depositing electrical conductors on dielectric substrates, making optically reflective or electrically or thermally conductive surface layers, and applying decorative metal coats to ceramic trophies or sculptures.

  3. Thermophotovoltaic Converters Based on Poly-crystalline GaSb

    NASA Astrophysics Data System (ADS)

    Corregidor, V.; Vincent, J.; Algora, C.; Diéguez, E.

    2007-02-01

    In this work we present the development obtained on GaSb converters manufactured from GaSb polycrystals substrates since the last TPV Conference. As one of the main problem of these GaSb converters was the surface preparation, we present new surface treatments, besides higher structural quality of the ingots. The substrates were selected from polycrystalline ingots grown by vertical Bridgman technique. The electrical measurements show the n-type mobility values up to 1000 cm2ṡV-1ṡs-1. On these substrates, 4 mm2 thermophotovoltaic cells were manufactured and characterized by illuminated J-V curves and quantum efficiency techniques.

  4. Reactive sticking coefficients for silane and disilane on polycrystalline silicon

    SciTech Connect

    Buss, R.J.; Ho, P.; Breiland, W.G.; Coltrin, M.E.

    1988-04-15

    Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition-rate measurements using molecular beam scattering and a very low-pressure cold-wall reactor. The RSCs have nonlinear Arrhenius temperature dependencies and decrease with increasing flux at low (710 /sup 0/C) temperatures. Several simple models are proposed to explain these observations. The results are compared with previous studies of the SiH/sub 4//Si(s) reaction and low-pressure chemical vapor deposition-rate measurements.

  5. Review of thin film solar cell technology and applications for ultra-light spacecraft solar arrays

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.

    1991-01-01

    Developments in thin-film amorphous and polycrystalline photovoltaic cells are reviewed and discussed with a view to potential applications in space. Two important figures of merit are discussed: efficiency (i.e., what fraction of the incident solar energy is converted to electricity), and specific power (power to weight ratio).

  6. Carrier and heat transport properties of polycrystalline GeSn films on SiO2

    NASA Astrophysics Data System (ADS)

    Uchida, Noriyuki; Maeda, Tatsuro; Lieten, Ruben R.; Okajima, Shingo; Ohishi, Yuji; Takase, Ryohei; Ishimaru, Manabu; Locquet, Jean-Pierre

    2015-12-01

    We evaluated the potential of polycrystalline (poly-) GeSn as channel material for the fabrication of thin film transistors (TFTs) at a low thermal budget (<600 °C). Poly-GeSn films with a grain size of ˜50 nm showed a carrier mobility of ˜30 cm2 V-1 s-1 after low-temperature annealing at 475-500 °C. Not only carrier mobility but also thermal conductivity of the films is important in assessing the self-heating effect of the poly-GeSn channel TFT. The thermal conductivity of the poly-GeSn films is 5-9 W m-1 K-1, which is significantly lower compared with 30-60 W m-1 K-1 of bulk Ge; this difference results from phonon scattering at grain boundaries and Sn interstitials. The poly-GeSn films have higher carrier mobility and thermal conductivity than poly-Ge films annealed at 600 °C, because of the improved crystal quality and coarsened grain size resulting from Sn-induced crystallization. Therefore, the poly-GeSn film is well-suited as channel material for TFTs, fabricated with a low thermal budget.

  7. ToF-SIMS study of polycrystalline uranium after exposure to deuterium

    SciTech Connect

    Morrall, P; Price, D; Nelson, A; Siekhaus, W; Nelson, E; Wu, K J; Stratman, M; McLean, B

    2006-01-19

    Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is employed to examine specific features observed on a polycrystalline depleted uranium sample after exposure to high purity D{sub 2} gas. The ToF-SIMS investigation, being the first of its kind on uranium, investigates a site where the deuterated form of uranium hydride (UD{sub 3}) is clearly observed to have broken through the thin, air-formed oxide. Density functional theory calculations have been performed, which confirm the stability of, and also assign structural geometries to, the various uranium containing fragments observed with SIMS. An inclusion site was also investigated using ToF-SIMS, and these data suggest that the edges of such inclusions exhibit increased D ion, and hence H ion, diffusion when compared to the surrounding surface oxide. These results offer support to the previously published hypotheses that inclusion sites on uranium surfaces exhibit an increased probability to form hydride sites under H{sub 2} exposure.

  8. Vacuum deposited polycrystalline silicon films for solar cell applications. Quarterly report, September 15-December 31, 1979

    SciTech Connect

    Feldman, C.; Arrington, C. H.; Blum, N. A.; Satkiewicz, F. G.

    1980-03-01

    Polycrystalline silicon films 14-22 ..mu..m thick and with average grain diameters of 20-40 ..mu..m were deposited by vacuum deposition onto both ceramic and sapphire substrates which were previously coated with a thin (1-2 ..mu..m) TiB/sub 2/ conducting layer. The large grains are the result of an interaction in the initial growth stages between silicon and TiB/sub 2/. SIMS studies of B/Ti/Al/sub 2/O/sub 3/, B/Al/sub 2/O/sub 3/, and Ti/Al/sub 2/O/sub 3/, interactions are reported as part of a continuing investigation of TiB/sub 2/ formation and silicon interactions on the TiB/sub 2/ surface. The increase in grain size has led to an improvement in the open-circuit voltage V/sub oc/, but not to an increase in the short-circuit current J/sub sc/. Capacitance-voltage measurements give results characteristic of an abrupt junction and a build-in voltage V/sub D/ consistent with the measured doping levels. A simple method for measuring the minority carrier diffusion length in the base region L/sub n/ is described. The measurements indicate that there is little change in L/sub n/ between large (20-40 ..mu..m) and small (approx. 5 ..mu..m) grained samples.

  9. High-temperature stability and selective thermal emission of polycrystalline tantalum photonic crystals.

    PubMed

    Rinnerbauer, Veronika; Yeng, Yi Xiang; Chan, Walker R; Senkevich, Jay J; Joannopoulos, John D; Soljačić, Marin; Celanovic, Ivan

    2013-05-01

    We present the results of extensive characterization of selective emitters at high temperatures, including thermal emission measurements and thermal stability testing at 1000 °C for 1h and 900 °C for up to 144 h. The selective emitters were fabricated as 2D photonic crystals (PhCs) on polycrystalline tantalum (Ta), targeting large-area applications in solid-state heat-to-electricity conversion. We characterized spectral emission as a function of temperature, observing very good selectivity of the emission as compared to flat Ta, with the emission of the PhC approaching the blackbody limit below the target cut-off wavelength of 2 μm, and a steep cut-off to low emission at longer wavelengths. In addition, we study the use of a thin, conformal layer (20 nm) of HfO(2) deposited by atomic layer deposition (ALD) as a surface protective coating, and confirm experimentally that it acts as a diffusion inhibitor and thermal barrier coating, and prevents the formation of Ta carbide on the surface. Furthermore, we tested the thermal stability of the nanostructured emitters and their optical properties before and after annealing, observing no degradation even after 144 h (6 days) at 900 °C, which demonstrates the suitability of these selective emitters for high-temperature applications. PMID:23670005

  10. Electrochemically produced films and polycrystalline salts of C60n-: Their physical characterization

    SciTech Connect

    Jones, M.T.; Subramanian, R.; Boulas, P.

    1994-12-31

    The discovery of C60 and its anionic salts C60{sup n-} (n = 1, 2, or 3) has provided a series of new materials with a wide range of very interesting chemical and physical properties such as ferromagnetism, nonlinear optical activity, semiconductivity and superconductivity. To date, relatively few salts of the anions of C60 have been studied because until recently a simple synthesis procedure did not exist. The authors recently developed simple and efficient methods for preparing thin films (prepared electrochemically) of both C60 and C60n- (n = 1, 2, or 3) and for preparing anion salts of C60 (prepared electrochemically and chemically). The authors now report the spectroscopic characterization of some of these materials. For example, studies of the temperature dependence of the Raman spectra of selected films (such as C60 and Cs3C60) are discussed. Also discussed are the ESR studies of a series of polycrystalline C60 anion salts derived from films as well as from the facile chemical preparation methods which are presented. The results of these spectroscopic studies are discussed as are results from other physical methods of characterization.

  11. Relaxation in photo-induced conductivity of polycrystalline BiFeO3 film

    NASA Astrophysics Data System (ADS)

    Peng, Zengwei; Liu, Baoting

    2015-08-01

    Polycrystalline BiFeO3 (BFO) film is deposited on Pt(1 1 1)/Ti/SiO2/Si(0 0 1) substrate via magnetron sputtering. Integrated Pt/SrRuO3 (SRO) are used to be top electrode to produce the Pt/SRO/BFO/Pt thin film capacitor. The remanent polarization is 59.5, 69.3, 77 and 89.8 μC/cm2 measured at 22.5, 25, 27.5 and 30 V, respectively. The photoconductivity is reported in BFO film under the illumination by the 5 mW/cm2 purple light of 404 nm. It is found that the leakage current density in purple light displays the tendency of decline with the increased illumination times, which can be explained by the recombination and capture of the photo-induced charges by the ionized vacancies. The relaxation time for the illuminated leakage current density reaching the steady state is 210 and 570 s at positive and negative bias, respectively. The obtained large relaxation time at negative bias is considered to be that negative bias is in the same direction as the SRO/BFO interface field.

  12. Exchange-bias in amorphous ferromagnetic and polycrystalline antiferromagnetic bilayers: Structural study and micromagnetic modeling

    NASA Astrophysics Data System (ADS)

    Kohn, A.; Dean, J.; Kovacs, A.; Zeltser, A.; Carey, M. J.; Geiger, D.; Hrkac, G.; Schrefl, T.; Allwood, D.

    2011-04-01

    We study the role of the structure of antiferromagnetic polycrystalline metallic films in determining the magnetic properties of an exchange-coupled amorphous ferromagnetic layer. The bilayers are sputter-deposited, highly textured {111} Ir22Mn78 and Co65.5Fe14.5B20 thin films. We focus on structural characterization of Ir22Mn78 as a function of layer thickness in the range having the strongest influence over the exchange-bias field and training effect. We have used transmission electron microscopy to characterize defects in the form of interface steps and roughness, interdiffusion, twin- and grain-boundaries. Such defects can result in uncompensated magnetic spins in the antiferromagnet, which then contribute to exchange-bias. These experimental results form the basis of a general model, which uses finite element micromagnetic simulations. The model incorporates the experimental structural parameters of the bilayer by implementing a surface integral technique that allows numerical calculations to solve the transition from an amorphous to a granular structure. As a result, a detailed calculation of the underlying magnetic structure within the antiferromagnetic material is achieved. These calculations are in good agreement with micromagnetic imaging using Lorentz transmission electron microscopy and the macro-magnetic properties of these bilayers.

  13. Imaging Long-Range Carrier Diffusion Across Grains in Polycrystalline CdTe

    NASA Astrophysics Data System (ADS)

    Alberi, Kirstin; Fluegel, Brian; Moutinho, Helio; Dhere, Ramesh; Li, Jian; Mascarenhas, Angelo

    2014-03-01

    The use of polycrystalline semiconductors in electronic devices enables low cost fabrication on large area substrates. Understanding the extent to which structural defects and impurities influence carrier transport in these materials is increasingly important as device performance is maximized, but most conventional characterization techniques often cannot directly probe their effects. We have applied a novel photoluminescence imaging technique to directly observe carrier diffusion in the presence of grain boundaries and impurities in poly-CdTe films. Our results show that the grain boundaries in this material are relatively transparent to free carrier and exciton diffusion as compared to poly-GaAs. Furthermore, a network of inhomogeneously distributed impurity states is found to mediate hole transport across multiple grains to distances greater than 10 microns from the point of photogeneration. These results underscore the importance of controlling the concentration and distribution of impurity states in poly-CdTe thin film solar cells. This work was supported by the DOE Office of Science, Basic Energy Sciences (PL imaging development) and the Office of Energy Efficiency and Renewable Energy (CdTe study) under contract DE-AC36-08GO28308.

  14. Mechanical Properties of Polycrystalline Titanium Nitride Films Measured by XRD Tensile Testing

    NASA Astrophysics Data System (ADS)

    Namazu, Takahiro; Inoue, Shozo; Takemoto, Hideki; Koterazawa, Keiji

    This paper describes measurement of mechanical properties of micron-thin polycrystalline titanium nitride (TiN) films. We developed a novel tensile test technique that can directly measure lateral elastic strain of a microscale single/poly-crystalline specimen by means of X-ray diffraction (XRD), which enables evaluation of not only Young's modulus but also Poisson's ratio of TiN films. TiN films having thicknesses of 0.5 μm to 1.6 μm are deposited onto the top and bottom surfaces of a microscale single crystal silicon (Si) specimen. The deposition is carried out by r.f. reactive magnetron sputtering under Ar partial pressure ranging from 0.7 Pa to 1.0 Pa. Average values of Young's modulus and Poisson's ratio for the Si monolayer specimen are found to be 169 GPa and 0.35, respectively, which are in close agreement with analytical values. TiN films deposited under an Ar partial pressure of 0.7 Pa have average Young's modulus of 290 GPa and Poisson's ratio of 0.36. These values gradually decrease with increasing Ar partial pressure, but are independent of TiN film thickness. Fracture strength of a TiN/Si/TiN composite specimen shows dependence on film thickness, regardless of Ar partial pressure.

  15. Significant enhancement of the thermoelectric figure of merit of polycrystalline Si films by reducing grain size

    NASA Astrophysics Data System (ADS)

    Valalaki, K.; Vouroutzis, N.; Nassiopoulou, A. G.

    2016-08-01

    The thermoelectric properties of p-type polycrystalline silicon thin films deposited by low pressure chemical vapour deposition (LPCVD) were accurately determined at room temperature and the thermoelectric figure of merit was deduced as a function of film thickness, ranging from 100 to 500 nm. The effect of film thickness on their thermoelectric performance is discussed. More than threefold increase in the thermoelectric figure of merit of the 100 nm thick polysilicon film was observed compared to the 500 nm thick film, reaching a value as high as 0.033. This enhancement is mainly the result of the smaller grain size in the thinner films. With the decrease in grain size the resistivity of the films is increased twofold and electrical conductivity decreased, however the Seebeck coefficient is increased by 30% and the thermal conductivity is decreased eightfold, being mainly at the origin of the increased figure of merit of the 100 nm film. Our experimental results were compared to known theoretical models and the possible mechanisms involved are presented and discussed.

  16. Microcracking during stress-relief of polycrystalline ice formed at high pressure

    NASA Astrophysics Data System (ADS)

    Meglis, Irene L.; Gagnon, R. E.; Young, R. P.

    To study microcracking in a brittle material in response to stress-relief, samples of polycrystalline ice were frozen under hydrostatic pressures up to 19 MPa and subsequently decompressed. Eight cylindrical samples (approximately 56 mm in diameter and 120 mm long) were made by freezing a slurry of crushed ice and degassed water inside a clear Teflon jacket. Four additional tests were done by reloading samples which were previously unloaded, allowing them to re-equilibrate, and then unloading again. Tests were filmed through windows in the confining cell. Acoustic emissions were monitored in some samples. When the stress was released, intense cracking occurred for approximately 0.4 seconds and then tapered off. Thin sections showed that the stress-relief cracks were approximately equal to the facet size (<5 mm), were primarily along grain boundaries, and were distributed throughout the samples with no obvious preferred orientation. Within a few hours of unloading, grain boundaries became cloudy, possibly a result of air trapped at the grain surfaces. Preliminary results from further tests indicate that this air plays a significant role in crack nucleation.

  17. Nanoscale Imaging of Band Gap and Defects in Polycrystalline CdTe Photovoltaic Devices

    NASA Astrophysics Data System (ADS)

    Zhitenev, Nikolai; Yoon, Yohan; Chae, Jungseok; Katzenmeyer, Aaron; Yoon, Heayoung; An, Sangmin; Shumacher, Joshua; Centrone, Andrea

    To further increase the power efficiency of polycrystalline thin film photovoltaic (PV) technology, a detailed understanding of microstructural properties of the devices is required. In this work, we investigate the microstructure of CdTe PV devices using two optical spectroscopies. Sub-micron thickness lamella samples were cut out from a PV device, either in cross-section or in-plane, by focused ion beam. The first technique is the photothermal induced resonance (PTIR) used to obtain absorption spectra over a broad range of wavelengths. In PTIR, a wavelength tunable pulsed laser is combined with an atomic force microscope to detect the local thermal expansion of lamella CdTe sample induced by light absorption. The second technique based on a near-field scanning optical microscope maps the local absorption at fixed near-IR wavelengths with energies at or below CdTe band-gap energy. The variation of the band gap throughout the CdTe absorber determined from PTIR spectra is ~ 20 meV. Both techniques detect strong spatial variation of shallow defects over different grains. The spatial distribution of mid-gap defects appears to be more uniform. The resolution, the sensitivity and the applicability of these two approaches are compared.

  18. Exploring electronic structure of one-atom thick polycrystalline graphene films: A nano angle resolved photoemission study

    NASA Astrophysics Data System (ADS)

    Avila, José; Razado, Ivy; Lorcy, Stéphane; Fleurier, Romain; Pichonat, Emmanuelle; Vignaud, Dominique; Wallart, Xavier; Asensio, María C.

    2013-08-01

    The ability to produce large, continuous and defect free films of graphene is presently a major challenge for multiple applications. Even though the scalability of graphene films is closely associated to a manifest polycrystalline character, only a few numbers of experiments have explored so far the electronic structure down to single graphene grains. Here we report a high resolution angle and lateral resolved photoelectron spectroscopy (nano-ARPES) study of one-atom thick graphene films on thin copper foils synthesized by chemical vapor deposition. Our results show the robustness of the Dirac relativistic-like electronic spectrum as a function of the size, shape and orientation of the single-crystal pristine grains in the graphene films investigated. Moreover, by mapping grain by grain the electronic dynamics of this unique Dirac system, we show that the single-grain gap-size is 80% smaller than the multi-grain gap recently reported by classical ARPES.

  19. RF Surface Impedance Measurement of Polycrystalline and Large Grain Nb Disk Sample at 7.5 GHz

    SciTech Connect

    Xiao, Binping; Geng, Rongli; Kelley, Michael J.; Marhauser, Frank; Phillips, H. Larry; Reece, Charles E.; Wang, Haipeng

    2009-11-01

    A Surface Impedance Characterization (SIC) system has been proposed at the 2005 SRF workshop and recently updated as detailed at the 2009 PAC conference. Currently the SIC system can measure samples in a temperature range from 2K to 20K exposed to an RF magnetic flux density of less than 3mT. We report on new results of a BCP etched large grain Nb sample measured with this system as compared with previous results of a BCP etched polycrystalline Nb sample. The design of an upgraded SIC system for use at higher magnetic flux densities is on the way to more efficiently investigate correlations between local material characteristics and associated SRF properties, both for preparation studies of bulk niobium and also new thin film SRF developments.

  20. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting

    NASA Astrophysics Data System (ADS)

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-01-01

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ~20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  1. Growth, electrical and thermal properties of doped mono and polycrystalline SiGe-based quantum dot superlattices

    NASA Astrophysics Data System (ADS)

    Savelli, G.; Hauser, D.; Michel, H.; Simon, J.

    2012-06-01

    SiGe materials present several advantages such as their compatibility with microelectronic techniques and non toxicity, but present a low figure-of-merit at room temperature. However it was shown theoretically that the figure of merit ZT could be highly increased by embedding nanoparticles in SiGe offering new potential applications. We report here the growth of different monocrystalline and polycrystalline SiGe-based quantum dot superlattices on Si (001) substrate. The QDSLs were grown using an industrial Reduced Pressure Chemical Vapor Deposition tool. In this work, SiGe spacer width as well as Ge dots sizes and densities have been controlled. The SiGe layers were heavily doped during the growth. Electrical and thermal properties of such structures have been measured and compared to standard SiGe thin films.

  2. Exploring electronic structure of one-atom thick polycrystalline graphene films: A nano angle resolved photoemission study

    PubMed Central

    Avila, José; Razado, Ivy; Lorcy, Stéphane; Fleurier, Romain; Pichonat, Emmanuelle; Vignaud, Dominique; Wallart, Xavier; Asensio, María C.

    2013-01-01

    The ability to produce large, continuous and defect free films of graphene is presently a major challenge for multiple applications. Even though the scalability of graphene films is closely associated to a manifest polycrystalline character, only a few numbers of experiments have explored so far the electronic structure down to single graphene grains. Here we report a high resolution angle and lateral resolved photoelectron spectroscopy (nano-ARPES) study of one-atom thick graphene films on thin copper foils synthesized by chemical vapor deposition. Our results show the robustness of the Dirac relativistic-like electronic spectrum as a function of the size, shape and orientation of the single-crystal pristine grains in the graphene films investigated. Moreover, by mapping grain by grain the electronic dynamics of this unique Dirac system, we show that the single-grain gap-size is 80% smaller than the multi-grain gap recently reported by classical ARPES. PMID:23942471

  3. Strain-induced modification in microstructure and electrical properties of polycrystalline LaNiO3- δ films

    NASA Astrophysics Data System (ADS)

    Zhu, M. W.; Wang, H. L.; Lei, H.; Zhang, Y. J.; Jia, N.; Wang, Z. J.

    2016-04-01

    In the present work, lanthanum nickel oxide (LaNiO3- δ ) thin films are prepared with the sol-gel multilayer coating method. Substrates with different thermal expansion coefficients are chosen to introduce thermal strain into the polycrystalline LaNiO3- δ (LNO) films. The effects of strain on the microstructure and electrical properties of LNO films are investigated. The results show that with increasing magnitude of strain, except for the change in lattice constant, an increase in defects in LNO films might occur. Furthermore, the resistivity of LNO films firstly decreases as the strain evolves from tensile to compressive, and then, increases again with the increasing compressive strain. The anomalous change in the both resistivity and transport behavior of LNO films under different strains is ascribed to the combined effects of the varying lattice constant and oxygen vacancy density.

  4. Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs.

    PubMed

    Liang, Albert K; Koniczek, Martin; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua; Street, Robert A; Lu, Jeng Ping

    2016-03-01

    Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si)-a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance-information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% full width at half maximum (FWHM) at 70 keV; and the digital components should work well even in the presence of significant thin-film transistor (TFT) variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm. PMID:26878107

  5. Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua; Street, Robert A.; Lu, Jeng Ping

    2016-03-01

    Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si)—a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance—information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% full width at half maximum (FWHM) at 70 keV; and the digital components should work well even in the presence of significant thin-film transistor (TFT) variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm.

  6. Initial steps toward the realization of large area arrays of single photon counting pixels based on polycrystalline silicon TFTs

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua; Jiang, Hao; Street, Robert A.; Lu, Jeng Ping

    2014-03-01

    The thin-film semiconductor processing methods that enabled creation of inexpensive liquid crystal displays based on amorphous silicon transistors for cell phones and televisions, as well as desktop, laptop and mobile computers, also facilitated the development of devices that have become ubiquitous in medical x-ray imaging environments. These devices, called active matrix flat-panel imagers (AMFPIs), measure the integrated signal generated by incident X rays and offer detection areas as large as ~43×43 cm2. In recent years, there has been growing interest in medical x-ray imagers that record information from X ray photons on an individual basis. However, such photon counting devices have generally been based on crystalline silicon, a material not inherently suited to the cost-effective manufacture of monolithic devices of a size comparable to that of AMFPIs. Motivated by these considerations, we have developed an initial set of small area prototype arrays using thin-film processing methods and polycrystalline silicon transistors. These prototypes were developed in the spirit of exploring the possibility of creating large area arrays offering single photon counting capabilities and, to our knowledge, are the first photon counting arrays fabricated using thin film techniques. In this paper, the architecture of the prototype pixels is presented and considerations that influenced the design of the pixel circuits, including amplifier noise, TFT performance variations, and minimum feature size, are discussed.

  7. Lattice thermal transport in large-area polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Aksamija, Z.; Knezevic, I.

    2014-07-01

    We study lattice thermal transport in large-area polycrystalline graphene, such as the samples grown by chemical vapor deposition (CVD) of carbon on Cu. These systems are composed of single-crystalline grains with a broad range of sizes and crystal orientations, separated by atomically rough grain boundaries. We solve the phonon Boltzmann transport equation and calculate the thermal conductivity in each grain, including scattering from the grain boundary roughness. Thermal transport in the large-area sample is considered in the Corbino-membrane geometry, with heat flowing through a network of thermal resistors and away from a pointlike heat source. The thermal transport in polycrystalline graphene is shown to be highly anisotropic, depending on the individual properties of the grains (their size and boundary roughness), as well as on grain connectivity. Strongest heat conduction occurs along large-grain filaments, while the heat flow is blocked through regions containing predominantly small grains. We discuss how thermal transport in CVD graphene can be tailored by controlling grain disorder.

  8. High velocity sliding at polycrystalline ductile metal interfaces

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Milhans, J. L.; Ravelo, R.; Germann, T. C.

    2014-03-01

    We present the results of large scale 3-dimensional NonEquilibrium Molecular Dynamics (NEMD) simulations for Al-Al and Al-Ta interfaces for sliding velocities in the range 20-4000 m/s at pressures of 15 GPa. System sizes include 8 M, 26 M and 138 M atoms for times to 40 ns. We discuss polycrystalline samples with initial grain sizes of 13 nm and 20 nm. For velocities above a size dependent critical velocity, vc, the frictional force per unit area agrees with single crystal simulations. For velocities below vc, the polycrystalline interfaces evolve to a new steady state grain size distribution characterized by very large plastic deformation with larger grain sizes, time dependent coarsening and refinement, a graded size distribution in the direction normal to the sliding interface, and significantly larger frictional forces per unit area compared to similar single crystal sliding interfaces. We also find that for the Al-Ta interface the frictional properties are determined by the weaker Al material. This work was performed under the auspices of the U.S. Dept. of Energy under contract DE-AC52-06NA25396. The support of the LANL ASC-PEM program is gratefully acknowledged.

  9. Observations of Dynamic Strain Aging in Polycrystalline NiAl

    NASA Technical Reports Server (NTRS)

    Weaver, M. L.; Noebe, R. D.; Kaufman, M. J.

    1996-01-01

    Dynamic strain aging has been investigated at temperatures between 77 and 1100 K in eight polycrystalline NiAl alloys. The 0.2% offset yield stress and work hardening rates for these alloys generally decreased with increasing temperature. However, local plateaus or maxima were observed in conventional purity and carbon doped alloys at intermediate temperatures (600-900 K). This anomalous behavior was not observed in low interstitial high-purity, nitrogen doped, or in titanium doped materials. Low or negative strain rate sensitivities (SRS) were also observed in all eight alloys in this intermediate temperature range. Coincident with the occurrence of negative SRS was the occurrence of serrated flow in conventional purity alloys containing high concentrations of Si in addition to C. These phenomena have been attributed to dynamic strain aging (DSA). Chemical analysis of the alloys used in this study suggests that the main species causing strain aging in polycrystalline NiAl is C but indicate that residual Si impurities can enhance the strain aging effect.

  10. Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics.

    PubMed

    Bintachitt, P; Jesse, S; Damjanovic, D; Han, Y; Reaney, I M; Trolier-McKinstry, S; Kalinin, S V

    2010-04-20

    Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025-1 microm(3) volumes, approximately 10(6) times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms. PMID:20368462

  11. Breakdown of avalanche critical behaviour in polycrystalline plasticity.

    PubMed

    Richeton, Thiebaud; Weiss, Jérôme; Louchet, François

    2005-06-01

    Acoustic emission experiments on creeping ice as well as numerical simulations argue for a self-organization of collective dislocation dynamics during plastic deformation of single crystals into a scale-free pattern of dislocation avalanches characterized by intermittency, power-law distributions of avalanche sizes, complex space-time correlations and aftershock triggering. Here, we address the question of whether such scale-free, close-to-critical dislocation dynamics will still apply to polycrystals. We show that polycrystalline plasticity is also characterized by intermittency and dislocation avalanches. However, grain boundaries hinder the propagation of avalanches, as revealed by a finite (grain)-size effect on avalanche size distributions. We propose that the restraint of large avalanches builds up internal stresses that push temporally the dynamical system into a supercritical state, off the scale-invariant critical regime, and trigger secondary avalanches in neighbouring grains. This modifies the statistical properties of the avalanche population. The results might also bring into question the classical ways of modelling plasticity in polycrystalline materials, based on homogenization procedures. PMID:15880114

  12. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  13. Quantum Hall effect in polycrystalline CVD graphene: grain boundaries impact

    NASA Astrophysics Data System (ADS)

    Ribeiro-Palau, Rebeca; Lafont, Fabien; Schopfer, Felicien; Poirier, Wilfrid; Bouchiat, Vincent; Han, Zhen; Cresti, Alessandro; Cummings, Aron; Roche, Stephan

    2014-03-01

    It was demonstrated by Janssen et al. (New J. Phys. 2011) that graphene could surpass GaAs for quantum Hall resistance standards with an accuracy better than 10-10. Graphene should render possible the realization of a standard operating at T > 4 K and B < 4 T, easing its dissemination towards industry. To materialize this goal scalable graphene with outstanding electronic transport properties is required. We present measurements performed in large area Hall bars made of polycrystalline CVD graphene on Si/SiO2, with a carrier mobility of 0.6 T-1. Even at 20.2 T and 300 mK, the Hall resistance plateaus are insufficiently quantized at ν = +/- 2 and +/- 6 . This is due to a high dissipation manifested by a longitudinal resistance which does not drop to zero. We pointed out unusual power-law temperature dependencies of Rxx and an exponential magnetic field dependence. We do not observe the common thermally activated or VRH behaviors. This can be attributed to the grain boundaries in the sample that short-circuit the edge states, as supported by our numerical simulations. This reveals new and peculiar aspects of the quantum Hall effect in polycrystalline systems. Another unexpected feature is the observation of the ν = 0 and 1 states in such low mobility systems.

  14. Limiting mechanisms in large-grain polycrystalline silicon Spatial homogeneity

    NASA Technical Reports Server (NTRS)

    Culik, J.; Grimes, K.

    1984-01-01

    An experiment to investigate the spatial homogeneity of large-grain polycrystalline silicon shows a number of performance-loss mechanisms. Arrays of up to 400 small (about 0.2 sq cm in area) photodiodes were fabricated on a selection of 10 cm x 10 cm polycrystalline silicon wafers. Measurements of the illuminated current-voltage (J-V) characteristics were used to generate maps of Voc, Jsc, and FF as a function of position; and dark J-V and LBIC analysis were used to determine the cause of low performance in areas with significantly degraded J-V characteristics. In addition to the presence of inclusions, which act as resistive shunts, the performance of many of the cells is limited by quasineutral recombination current, which may vary by up to an order of magnitude across a wafer. The increase is the result of either electrically-active grain boundaries or numerous subgrain boundaries within the grain bulk. In other isolated instances, the open-circuit voltage is reduced by excess space-charge recombination current that is not correlated with either grain or subgrain boundary activity.

  15. Field theory and diffusion creep predictions in polycrystalline aggregates

    NASA Astrophysics Data System (ADS)

    Villani, A.; Busso, E. P.; Forest, S.

    2015-07-01

    In polycrystals, stress-driven vacancy diffusion at high homologous temperatures leads to inelastic deformation. In this work, a novel continuum mechanics framework is proposed to describe the strain fields resulting from such a diffusion-driven process in a polycrystalline aggregate where grains and grain boundaries are explicitly considered. The choice of an anisotropic eigenstrain in the grain boundary region provides the driving force for the diffusive creep processes. The corresponding inelastic strain rate is shown to be related to the gradient of the vacancy flux. Dislocation driven deformation is then introduced as an additional mechanism, through standard crystal plasticity constitutive equations. The fully coupled diffusion-mechanical model is implemented into the finite element method and then used to describe the biaxial creep behaviour of FCC polycrystalline aggregates. The corresponding results revealed for the first time that such a coupled diffusion-stress approach, involving the gradient of the vacancy flux, can accurately predict the well-known macroscopic strain rate dependency on stress and grain size in the diffusion creep regime. They also predict strongly heterogeneous viscoplastic strain fields, especially close to grain boundaries triple junctions. Finally, a smooth transition from Herring and Coble to dislocation creep behaviour is predicted and compared to experimental results for copper.

  16. Origins of Folding Instabilities on Polycrystalline Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Beckmann, N.; Romero, P. A.; Linsler, D.; Dienwiebel, M.; Stolz, U.; Moseler, M.; Gumbsch, P.

    2014-12-01

    Wear and removal of material from polycrystalline metal surfaces is inherently connected to plastic flow. Here, plowing-induced unconstrained surface plastic flow on a nanocrystalline copper surface has been studied by massive molecular dynamics simulations and atomic force microscopy scratch experiments. In agreement with experimental findings, bulges in front of a model asperity develop into vortexlike fold patterns that mark the disruption of laminar flow. We identify dislocation-mediated plastic flow in grains with suitably oriented slip systems as the basic mechanism of bulging and fold formation. The observed folding can be fundamentally explained by the inhomogeneity of plasticity on polycrystalline surfaces which favors bulge formation on grains with suitably oriented slip system. This process is clearly distinct from Kelvin-Helmholtz instabilities in fluids, which have been previously suggested to resemble the formed surface fold patterns. The generated prow grows into a rough chip with stratified lamellae that are identified as the precursors of wear debris. Our findings demonstrate the importance of surface texture and grain structure engineering to achieve ultralow wear in metals.

  17. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1994-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of the BSR text as a simple method for parameter determination for other fibers.

  18. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1991-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading above 800 C, these fibers display creep-related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of mechanistic-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the bend stress relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model predictions and BSR test results with the literature tensile creep data show good agreement, supporting both the predictive capability of the model and the use of the BSR test as a simple method for parameter determination for other fibers.

  19. Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics

    PubMed Central

    Bintachitt, P.; Jesse, S.; Damjanovic, D.; Han, Y.; Reaney, I. M.; Trolier-McKinstry, S.; Kalinin, S. V.

    2010-01-01

    Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025–1 μm3 volumes, approximately 106 times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms. PMID:20368462

  20. Dielectric and conducting behaviour of polycrystalline holmium octa-molybdate

    NASA Astrophysics Data System (ADS)

    Want, Basharat; Zahoor Ahmad, Bhat; Bhat, Bilal Hamid

    2014-09-01

    Polycrystalline holmium octa-molybdate spherulites have been obtained by using gel diffusion technique and characterized by different physio-chemical techniques. The surfaces of these spherulites are composed of nano-rod with an average diameter of about 80 nm. At room temperature the initial crystal structure is triclinic, space group P1. Thermal studies suggested a phase transition occurring in holmium octa-molybdate crystals at about 793 K. The electrical properties of the system have been studied as a function of frequency and temperature in the ranges of 20 Hz-3 MHz and 290-570 K, respectively. A giant dielectric constant and two loss peaks have been observed in the permittivity formalism. The conducting behaviour of the material is also discussed. The conductivity was found to be 1572 μ Ω-1 m-1 at room temperature and 3 MHz frequency. The conductivity of the polycrystalline material was attributed to the fact that it arises due to the migration of defects on the oxygen sub-lattice. Impedance studies were also performed in the frequency domain to infer the bulk and grain boundary contributions to the overall electric response of the material. The electrical responses have been attributed to the grain, grain-boundary, and interfacial effects.

  1. Microstructural characterization in nanocrystalline ceramic thin films

    NASA Astrophysics Data System (ADS)

    Kim, Hakkwan

    The primary objective of this research is to investigate the effects of process variables on microstructure in several fluoride and oxide thin films prepared by vapor deposition, in order to predict the properties and behaviors of nanocrystalline thin film materials. There are three distinct stages of this research. The first stage focuses on measuring of the porosity in polycrystalline thin films of a variety of fluorides as a function of the substrate temperature during deposition, and discussing the mechanism by which the porosity varies as a function of the process variables. We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF 2) and calcium fluoride (CaF2) using an atomic force microscope (AFM) and a quartz crystal thickness monitor. The porosity is very sensitive to the substrate temperature and decreases as the substrate temperature increases. Consistent behavior is observed among all of the materials in this study. The second stage is to understand the film microstructure including grain growth and texture development, because these factors are known to influence the behavior and stability of polycrystalline thin films. This study focuses on grain growth and texture development in polycrystalline lithium fluoride thin films using dark field (DF) transmission electron microscopy (TEM). It is demonstrated that we can isolate the size distribution of <111> surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction (XRD) and AFM, respectively. The grain size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to the {111}-oriented grains which do not grow significantly, while

  2. Analytical and numerical modeling of surface morphologies in thin films

    SciTech Connect

    Genin, F.Y.

    1995-05-01

    Experimental studies have show that strains due to thermal expansion mismatch between a film and its substrate can produce very large stresses in the film that can lead to the formation of holes and hillocks. Based on a phenomenological description of the evolution of a solid surface under both capillary and stress driving forces and for surface and grain boundary self-diffusion, this article provides analytical and numerical solutions for surface profiles of model geometries in polycrystalline thin films. Results can explain a variety of surface morphologies commonly observed experimentally and are discussed to give some practical insights on how to control the growth of holes and hillocks in thin films.

  3. Formation and ferromagnetic properties of FeSi thin films

    SciTech Connect

    Shin, Yooleemi; Anh Tuan, Duong; Hwang, Younghun; Viet Cuong, Tran; Cho, Sunglae

    2013-05-07

    In this work, the growth and ferromagnetic properties of {epsilon}-FeSi thin film on Si(100) substrate prepared by molecular beam epitaxy are reported. The inter-diffusion of Fe layer on Si(100) substrate at 600 Degree-Sign C results in polycrystalline {epsilon}-FeSi layer. The determined activation energy was 0.044 eV. The modified magnetism from paramagnetic in bulk to ferromagnetic states in {epsilon}-FeSi thin films was observed. The saturated magnetization and coercive field of {epsilon}-FeSi film are 4.6 emu/cm{sup 3} and 29 Oe at 300 K, respectively.

  4. Polycrystalline ferroelectric or multiferroic oxide articles on biaxially textured substrates and methods for making same

    SciTech Connect

    Goyal, Amit; Shin, Junsoo

    2015-03-31

    A polycrystalline ferroelectric and/or multiferroic oxide article includes a substrate having a biaxially textured surface; at least one biaxially textured buffer layer supported by the substrate; and a biaxially textured ferroelectric or multiferroic oxide layer supported by the buffer layer. Methods for making polycrystalline ferroelectric and/or multiferroic oxide articles are also disclosed.

  5. Combined single-crystalline and polycrystalline CVD diamond substrates for diamond electronics

    SciTech Connect

    Vikharev, A. L. Gorbachev, A. M.; Dukhnovsky, M. P.; Muchnikov, A. B.; Ratnikova, A. K.; Fedorov, Yu. Yu.

    2012-02-15

    The fabrication of diamond substrates in which single-crystalline and polycrystalline CVD diamond form a single wafer, and the epitaxial growth of diamond films on such combined substrates containing polycrystalline and (100) single-crystalline CVD diamond regions are studied.

  6. Thin-film transistors based on p-type Cu{sub 2}O thin films produced at room temperature

    SciTech Connect

    Fortunato, Elvira; Figueiredo, Vitor; Barquinha, Pedro; Elamurugu, Elangovan; Goncalves, Goncalo; Martins, Rodrigo; Park, Sang-Hee Ko; Hwang, Chi-Sun

    2010-05-10

    Copper oxide (Cu{sub 2}O) thin films were used to produce bottom gate p-type transparent thin-film transistors (TFTs). Cu{sub 2}O was deposited by reactive rf magnetron sputtering at room temperature and the films exhibit a polycrystalline structure with a strongest orientation along (111) plane. The TFTs exhibit improved electrical performance such as a field-effect mobility of 3.9 cm{sup 2}/V s and an on/off ratio of 2x10{sup 2}.

  7. Micromechanical modelling of partially molten and sand reinforced polycrystalline ice

    NASA Astrophysics Data System (ADS)

    Castelnau, O.; Duval, P.

    2009-12-01

    The viscoplastic behaviour of polycrystalline ice is strongly affected by the very strong anisotropy of ice crystals. Indeed, in the dislocations creep regime relevant for ice sheet flow, dislocation glide on the basal plane of ice single crystals leads to strain-rates ~6 order of magnitude larger than strain-rates that might be obtain if only non-basal glide is activated. At the polycrystal scale, this behaviour is responsible for a strong mechanical interaction between grains in the secondary (stationary) creep regime, and strain-rate is essentially partitioned between soft grains well-oriented for basal glide and hard grains exhibiting an unfavourable orientation for basal slip. As a consequence, the macroscopic flow stress at the polycrystal scale essentially depends on the resistance of the hardest slip systems or on the associated accommodation processes such as climb of basal dislocation on non-basal planes. Creep experiments performed on polycrystalline ices containing a small amount (less than 10% volume fraction) of liquid water show a dramatic increase of strain-rate, by more than one order of magnitude, compared to solid ice when deformed under similar thermo-mechanical conditions. Similarly, a strong hardening is observed when polycrystalline ice is reinforced by sand (which can be considered as a rigid phase here). This behaviour can be explained by micromechanical models, which aims at estimating the mechanical interactions between grains. For example, the presence of water releases stress concentrations at grain boundaries and therefore favours the inactivation of non-basal systems. To estimate such effect and to reach quantitative comparison with experimental data, we make use of the recent Second-Order homogenization mean-field approach of Ponte-Castaneda, based on self-consistent scheme. The advantage of this approach, which has been shown to provide excellent results when applied to many different non-linear composite materials, comes from the

  8. A continuum dislocation dynamics framework for plasticity of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Askari, Hesam Aldin

    The objective of this research is to investigate the mechanical response of polycrystals in different settings to identify the mechanisms that give rise to specific response observed in the deformation process. Particularly the large deformation of magnesium alloys and yield properties of copper in small scales are investigated. We develop a continuum dislocation dynamics framework based on dislocation mechanisms and interaction laws and implement this formulation in a viscoplastic self-consistent scheme to obtain the mechanical response in a polycrystalline system. The versatility of this method allows various applications in the study of problems involving large deformation, study of microstructure and its evolution, superplasticity, study of size effect in polycrystals and stochastic plasticity. The findings from the numerical solution are compared to the experimental results to validate the simulation results. We apply this framework to study the deformation mechanisms in magnesium alloys at moderate to fast strain rates and room temperature to 450 °C. Experiments for the same range of strain rates and temperatures were carried out to obtain the mechanical and material properties, and to compare with the numerical results. The numerical approach for magnesium is divided into four main steps; 1) room temperature unidirectional loading 2) high temperature deformation without grain boundary sliding 3) high temperature with grain boundary sliding mechanism 4) room temperature cyclic loading. We demonstrate the capability of our modeling approach in prediction of mechanical properties and texture evolution and discuss the improvement obtained by using the continuum dislocation dynamics method. The framework was also applied to nano-sized copper polycrystals to study the yield properties at small scales and address the observed yield scatter. By combining our developed method with a Monte Carlo simulation approach, the stochastic plasticity at small length scales

  9. High-pressure deformation and failure of polycrystalline ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Dongmei

    2005-11-01

    High-strength polycrystalline ceramics are increasingly being used for armor applications because of their light weight and superior ballistic performance over conventional armor steels. However, accurate material modeling needed in ceramic armor design remains a challenge because of their complex behavior under impact loading. A ceramic may display extremely high strength during rapid compression but lose tensile strength when the load reverses from compression to tension. A good understanding of the mechanisms governing the deformation and failure of ceramics under high-stress impact and a capability to accurately predict the resulting effective strengths of both intact and damaged ceramics are critically needed. To this end, a computational methodology for micromechanical analysis of polycrystalline materials has been developed. It combines finite element analysis with microstructural modeling based on the Voronoi polycrystals, and material modeling that considers nonlinear elasticity, crystal plasticity, intergranular shear damage during compression and intergranular Mode-I cracking during tension. Using this method, simulations have been carried out on polycrystalline alpha-6H silicon carbide and alpha-phase aluminum oxide to determine if microplasticity is a viable mechanism of inelastic deformation in ceramics undergoing high-pressure uniaxial-strain compression. Further, the competing roles of in-grain microplasticity and intergranular microdamage during a sequence of dynamic compression and tension have been studied. The results show that microplasticity is a more plausible mechanism than microcracking under uniaxial-strain compression. The deformation by limited slip systems can be highly heterogeneous so that a significant amount of grains may remain elastic and thus result in high macroscopic compressive strength. On the other hand, the failure evolution during dynamic load reversal from compression to tension can be well predicted by intergranular Mode

  10. Structure and ionic conductivity of well-aligned polycrystalline sodium titanogallate grown by reactive diffusion

    SciTech Connect

    Hasegawa, Ryo; Okabe, Momoko; Asaka, Toru; Ishizawa, Nobuo; Fukuda, Koichiro

    2015-09-15

    We prepared the b-axis-oriented polycrystalline Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} (NTGO) embedded in Ga{sub 2}O{sub 3}-doped Na{sub 2}Ti{sub 4}O{sub 9} matrix using the reactive diffusion technique. When the sandwich-type Ga{sub 2}TiO{sub 5}/NaGaO{sub 2}/Ga{sub 2}TiO{sub 5} diffusion couple was heated at 1323 K for 24 h, the NTGO polycrystal was readily formed in the presence of a liquid phase. The resulting polycrystalline material was characterized by X-ray diffractometry, electron microscopy and impedance spectroscopy. We mechanically processed the annealed diffusion couple and obtained the thin-plate electrolyte consisting mostly of the grain-aligned NTGO polycrystal. The ionic conductivity (σ) of the electrolyte along the common b-axis direction steadily increased from 1.3×10{sup −4} to 7.3×10{sup −3} S/cm as the temperature increased from 573 to 1073 K. There was a slope change at ca. 792 K for the Arrhenius plot of σ; the activation energies were 0.39 eV above this temperature and 0.57 eV below it. The NTGO showed the crystal structure (space group C2/m) with substantial positional disordering of one of the two Ga sites. The Na{sup +} ions occupied ca. 43% of the Wyckoff position 4i site, the deficiency of which would contribute to the relatively high ionic conductivity along the b-axis. The reactive diffusion could be widely applicable as the novel technique to the preparation of grain-aligned ceramics of multi-component systems. - Graphical abstract: We have prepared the b-axis-oriented Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} polycrystal embedded in Ga{sub 2}O{sub 3}-doped Na{sub 2}Ti{sub 4}O{sub 9} matrix by the heat treatment of sandwich-type diffusion couple of Ga{sub 2}TiO{sub 5}/NaGaO{sub 2}/Ga{sub 2}TiO{sub 5}. The resulting Na{sub 0.85}Ti{sub 0.51}Ga{sub 4.37}O{sub 8} electrolyte showed the ionic conductivity ranging from 1.3×10{sup −4} S/cm at 573 K to 7.3×10{sup −3} S/cm at 1073 K. - Highlights: • The b

  11. Induced electronic anisotropy in bismuth thin films

    SciTech Connect

    Liao, Albert D.; Yao, Mengliang; Opeil, Cyril; Katmis, Ferhat; Moodera, Jagadeesh S.; Li, Mingda; Tang, Shuang; Dresselhaus, Mildred S.

    2014-08-11

    We use magneto-resistance measurements to investigate the effect of texturing in polycrystalline bismuth thin films. Electrical current in bismuth films with texturing such that all grains are oriented with the trigonal axis normal to the film plane is found to flow in an isotropic manner. By contrast, bismuth films with no texture such that not all grains have the same crystallographic orientation exhibit anisotropic current flow, giving rise to preferential current flow pathways in each grain depending on its orientation. Extraction of the mobility and the phase coherence length in both types of films indicates that carrier scattering is not responsible for the observed anisotropic conduction. Evidence from control experiments on antimony thin films suggests that the anisotropy is a result of bismuth's large electron effective mass anisotropy.

  12. Morphological changes in polycrystalline Fe after compression and release

    NASA Astrophysics Data System (ADS)

    Gunkelmann, Nina; Tramontina, Diego R.; Bringa, Eduardo M.; Urbassek, Herbert M.

    2015-02-01

    Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3, 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.

  13. Electron microscopy of gallium nitride growth on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Cherns, D.; Kuball, M.; Jiang, Q.; Allsopp, D.

    2015-11-01

    Transmission and scanning electron microscopy were used to examine the growth of gallium nitride (GaN) on polycrystalline diamond substrates grown by metalorganic vapour phase epitaxy with a low-temperature aluminium nitride (AlN) nucleation layer. Growth on unmasked substrates was in the (0001) orientation with threading dislocation densities ≈7 × 109 cm-2. An epitaxial layer overgrowth technique was used to reduce the dislocation densities further, by depositing silicon nitride stripes on the surface and etching the unmasked regions down to the diamond substrate. A re-growth was then performed on the exposed side walls of the original GaN growth, reducing the threading dislocation density in the overgrown regions by two orders of magnitude. The resulting microstructures and the mechanisms of dislocation reduction are discussed.

  14. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  15. Ultrasonic Backscattering in Polycrystalline Materials of Pwr Components

    NASA Astrophysics Data System (ADS)

    Chassignole, B.; Dupond, O.; Fouquet, T.; Rupin, F.

    2011-06-01

    The ultrasonic examination of metallic components of Pressurized Water Reactors (PWR) is an important challenge for the nuclear industry. During the past decades, EDF R&D has undertaken numerous studies in order to improve the NDT process on these applications and to help to their qualification. The present paper deals with the problem of the structural noise which can potentially disturbs the ultrasonic inspection. In particular, this study proposes a modeling approach to simulate the ultrasonic scattering due to coarse grain structures of polycrystalline materials. The methodology is based on the mixing of a grain scale description of the material and a 2D finite element code (ATHENA) developed by EDF to simulate the ultrasonic propagation in isotropic and anisotropic elastic media. The modeling results are compared to experimental acquisitions on mock-ups containing artificial defects.

  16. Fabricating micro-instruments in surface-micromachined polycrystalline silicon

    SciTech Connect

    Comtois, J.H.; Michalicek, M.A.; Barron, C.C.

    1997-04-01

    Smaller, lighter instruments can be fabricated as Micro-Electro-Mechanical Systems (MEMS), having micron scale moving parts packaged together with associated control and measurement electronics. Batch fabrication of these devices will make economical applications such as condition-based machine maintenance and remote sensing. The choice of instrumentation is limited only by the designer`s imagination. This paper presents one genre of MEMS fabrication, surface-micromachined polycrystalline silicon (polysilicon). Two currently available but slightly different polysilicon processes are presented. One is the ARPA-sponsored ``Multi-User MEMS ProcesS`` (MUMPS), available commercially through MCNC; the other is the Sandia National Laboratories ``Sandia Ultra-planar Multilevel MEMS Technology`` (SUMMiT). Example components created in both processes will be presented, with an emphasis on actuators, actuator force testing instruments, and incorporating actuators into larger instruments.

  17. Radiation hardness of three-dimensional polycrystalline diamond detectors

    SciTech Connect

    Lagomarsino, Stefano Sciortino, Silvio; Bellini, Marco; Corsi, Chiara; Cindro, Vladimir; Kanxheri, Keida; Servoli, Leonello; Morozzi, Arianna; Passeri, Daniele; Schmidt, Christian J.

    2015-05-11

    The three-dimensional concept in particle detection is based on the fabrication of columnar electrodes perpendicular to the surface of a solid state radiation sensor. It permits to improve the radiation resistance characteristics of a material by lowering the necessary bias voltage and shortening the charge carrier path inside the material. If applied to a long-recognized exceptionally radiation-hard material like diamond, this concept promises to pave the way to the realization of detectors of unprecedented performances. We fabricated conventional and three-dimensional polycrystalline diamond detectors, and tested them before and after neutron damage up to 1.2 ×10{sup 16 }cm{sup −2}, 1 MeV-equivalent neutron fluence. We found that the signal collected by the three-dimensional detectors is up to three times higher than that of the conventional planar ones, at the highest neutron damage ever experimented.

  18. Structural templating of multiple polycrystalline layers in organic photovoltaic cells

    SciTech Connect

    Lassiter, Brian E; Lunt, Richard R; Renshaw, Kyle; Forrest, Stephen R.

    2010-09-01

    We demonstrate that organic photovoltaic cell performance is influenced by changes in the crystalline orientation of composite layer structures. A 1.5 nm thick self-organized, polycrystalline template layer of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) orients subsequently deposited layers of a diindenoperylene exciton blocking layer, and the donor, copper phthalocyanine (CuPc). Control over the crystalline orientation of the CuPc leads to changes in its frontier energy levels, absorption coefficient, and surface morphology, resulting in an increase of power conversion efficiency at 1 sun from 1.42 ± 0.04% to 2.19 ± 0.05% for a planar heterojunction and from 1.89 ± 0.05% to 2.49 ± 0.03% for a planar-mixed heterojunction.

  19. Modeling Crack Propagation in Polycrystalline Microstructure Using Variational Multiscale Method

    DOE PAGESBeta

    Sun, S.; Sundararaghavan, V.

    2016-01-01

    Crack propagation in a polycrystalline microstructure is analyzed using a novel multiscale model. The model includes an explicit microstructural representation at critical regions (stress concentrators such as notches and cracks) and a reduced order model that statistically captures the microstructure at regions far away from stress concentrations. Crack propagation is modeled in these critical regions using the variational multiscale method. In this approach, a discontinuous displacement field is added to elements that exceed the critical values of normal or tangential tractions during loading. Compared to traditional cohesive zone modeling approaches, the method does not require the use of any specialmore » interface elements in the microstructure and thus can model arbitrary crack paths. The capability of the method in predicting both intergranular and transgranular failure modes in an elastoplastic polycrystal is demonstrated under tensile and three-point bending loads.« less

  20. Electronic properties of polycrystalline graphene under large local strain

    SciTech Connect

    He, Xin; Tang, Ning E-mail: geweikun@mail.tsinghua.edu.cn Duan, Junxi; Mei, Fuhong; Meng, Hu; Lu, Fangchao; Xu, Fujun; Yang, Xuelin; Gao, Li; Wang, Xinqiang; Shen, Bo E-mail: geweikun@mail.tsinghua.edu.cn; Ge, Weikun E-mail: geweikun@mail.tsinghua.edu.cn

    2014-06-16

    To explore the transport properties of polycrystalline graphene under large tensile strain, a strain device has been fabricated using piezocrystal to load local strain onto graphene, up to 22.5%. Ionic liquid gate whose capability of tuning carrier density being much higher than that of a solid gate is used to survey the transfer characteristics of the deformed graphene. The conductance of the Dirac point and field effect mobility of electrons and holes is found to decrease with increasing strain, which is attributed to the scattering of the graphene grain boundaries, the strain induced change of band structure, and defects. However, the transport gap is still not opened. Our study is helpful to evaluate the application of graphene in stretchable electronics.

  1. Predicting fracture in micron-scale polycrystalline silicon MEMS structures.

    SciTech Connect

    Hazra, Siddharth S.; de Boer, Maarten Pieter; Boyce, Brad Lee; Ohlhausen, James Anthony; Foulk, James W., III; Reedy, Earl David, Jr.

    2010-09-01

    Designing reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clear how to use a measured tensile strength distribution to predict the strength of a complex MEMS structure. To address such issues, two recently developed high throughput MEMS tensile test techniques have been used to measure strength distribution tails. The measured tensile strength distributions enable the definition of a threshold strength as well as an inferred maximum flaw size. The nature of strength-controlling flaws has been identified and sources of the observed variation in strength investigated. A double edge-notched specimen geometry was also tested to study the effect of a severe, micron-scale stress concentration on the measured strength distribution. Strength-based, Weibull-based, and fracture mechanics-based failure analyses were performed and compared with the experimental results.

  2. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Dragica, Vasileska; Ringhofer, Christian

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  3. Attosecond dynamical Franz-Keldysh effect in polycrystalline diamond.

    PubMed

    Lucchini, M; Sato, S A; Ludwig, A; Herrmann, J; Volkov, M; Kasmi, L; Shinohara, Y; Yabana, K; Gallmann, L; Keller, U

    2016-08-26

    Short, intense laser pulses can be used to access the transition regime between classical and quantum optical responses in dielectrics. In this regime, the relative roles of inter- and intraband light-driven electronic transitions remain uncertain. We applied attosecond transient absorption spectroscopy to investigate the interaction between polycrystalline diamond and a few-femtosecond infrared pulse with intensity below the critical intensity of optical breakdown. Ab initio time-dependent density functional theory calculations, in tandem with a two-band parabolic model, accounted for the experimental results in the framework of the dynamical Franz-Keldysh effect and identified infrared induction of intraband currents as the main physical mechanism responsible for the observations. PMID:27563093

  4. Single crystal and polycrystalline CVD diamond for demanding optical applications

    NASA Astrophysics Data System (ADS)

    Dodson, J. M.; Brandon, J. R.; Dhillon, H. K.; Friel, I.; Geoghegan, S. L.; Mollart, T. P.; Santini, P.; Scarsbrook, G. A.; Twitchen, D. J.; Whitehead, A. J.; Wilman, J. J.; de Wit, H.

    2011-06-01

    Diamond's extremely wide transparency, combined with its other exceptional properties including hardness, strength and thermal conductivity make it a desirable material for optical windows. Polycrystalline diamond grown by chemical vapour deposition (CVD) has become the preferred window material for high power CO2 laser systems since its development in the 1990s. The range and availability of diamond materials is expanding, and in recent years has been extended to include CVD single crystal diamond. This paper reviews the quality of these materials, looking at optical scatter and absorption around 1 and 10 microns, along with their thermal and mechanical properties. We also discuss selection of appropriate grades and how they may best be integrated into demanding optical applications.

  5. Dependence of resistivity on the doping level of polycrystalline silicon

    NASA Technical Reports Server (NTRS)

    Fripp, A. L.

    1975-01-01

    The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as-deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 10 to the 16th atoms/per cu cm was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

  6. Fabrication of translucent boron nitride dispersed polycrystalline silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Fu, Z.; Niihara, K.; Lee, S. W.

    2011-03-01

    Optical transparency was achieved at infrared region and overall translucent silicon nitride was fabricated using hot press sintering (HPS). The increase in h-BN content decreased the optical transparency. Microstructral observations shows that the optical, mechanical and tribological properties of BN dispersed polycrystalline Si3N4 ceramics were affected by the density, α:β-phase ratio and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN at 1850°C. The composite contained from 0.25 to 2 mass % BN powder with sintering aids (9% AlN + 3% MgO). Maximum transmittance of 57% was achieved for 0.25 mass % BN doped Si3N4 ceramics. Fracture toughness was increased and wear volume and friction coefficient were decreased with increase in BN content.

  7. A new directional solidification technique for polycrystalline solar grade silicon

    NASA Astrophysics Data System (ADS)

    Saito, T.; Shimura, A.; Ichikawa, S.

    A new directional solidification (casting) technique using powder mold releasing agent is described for producing polycrystalline solar grade silicon. Crack-free and stress-free growth of silicon was attainable with fused quartz crucibles coated with nitride powder, such as silicon nitride Si3 N4, on the inner crucible walls. The degree of nitrogen contamination was negligible because of the low nitrogen solubility in solid silicon. Other impurities contents were less than the ppm level. The average grain diameter was close to 0.1 cm. Diffused junction solar cells (n+/p structure) were fabricated by using this boron doped 1 ohm-cm material. An AM1 conversion efficiency of 12.4% on the cells of 20 cm sq area was obtained. The minority carrier diffusion length of this material was estimated to be greater than 80 microns.

  8. Structural templating of multiple polycrystalline layers in organic photovoltaic cells.

    PubMed

    Lassiter, Brian E; Lunt, Richard R; Renshaw, C Kyle; Forrest, Stephen R

    2010-09-13

    We demonstrate that organic photovoltaic cell performance is influenced by changes in the crystalline orientation of composite layer structures. A 1.5 nm thick self-organized, polycrystalline template layer of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) orients subsequently deposited layers of a diindenoperylene exciton blocking layer, and the donor, copper phthalocyanine (CuPc). Control over the crystalline orientation of the CuPc leads to changes in its frontier energy levels, absorption coefficient, and surface morphology, resulting in an increase of power conversion efficiency at 1 sun from 1.42 ± 0.04% to 2.19 ± 0.05% for a planar heterojunction and from 1.89 ± 0.05% to 2.49 ± 0.03% for a planar-mixed heterojunction. PMID:21165074

  9. Monitoring of deformation induced microcracking in polycrystalline NiAl

    SciTech Connect

    Wanner, A.; Schietinger, B.; Bidlingmaier, T.; Zalkind, H.; Arzt, E.

    1995-08-01

    Microcracking in polycrystalline near-stoichiometric NiAl produced by room temperature plastic deformation under uniaxial compression was investigated by means of optical microscopy, velocity of sound measurements, and acoustic emission monitoring. Results show that strains greater than 2% are required to produce microcrack populations which can be evaluated by microscopical investigation or velocity of sound measurements. However, acoustic emission monitoring during compression testing indicates that microcracking starts at about 0.7% compressive plastic strain which is identical with the typical tensile fracture strain for NiAl. Thus it is concluded that there is little or no stable microcracking prior to failure in tension. Acoustic emission results show also that the process of microcracking does not primarily occur during the applied compressive deformation. A considerable fraction of the microcracking takes place during the quasi-elastic unloading following deformation.

  10. Fatigue effect on polarization switching dynamics in polycrystalline bulk ferroelectrics

    NASA Astrophysics Data System (ADS)

    Zhukov, S.; Glaum, J.; Kungl, H.; Sapper, E.; Dittmer, R.; Genenko, Y. A.; von Seggern, H.

    2016-08-01

    Statistical distribution of switching times is a key information necessary to describe the dynamic response of a polycrystalline bulk ferroelectric to an applied electric field. The Inhomogeneous Field Mechanism (IFM) model offers a useful tool which allows extraction of this information from polarization switching measurements over a large time window. In this paper, the model was further developed to account for the presence of non-switchable regions in fatigued materials. Application of the IFM-analysis to bipolar electric cycling induced fatigue process of various lead-based and lead-free ferroelectric ceramics reveals different scenarios of property degradation. Insight is gained into different underlying fatigue mechanisms inherent to the investigated systems.

  11. Spherical silicon photonic microcavities: From amorphous to polycrystalline

    NASA Astrophysics Data System (ADS)

    Fenollosa, R.; Garín, M.; Meseguer, F.

    2016-06-01

    Shaping silicon as a spherical object is not an obvious task, especially when the object size is in the micrometer range. This has the important consequence of transforming bare silicon material in a microcavity, so it is able to confine light efficiently. Here, we have explored the inside volume of such microcavities, both in their amorphous and in their polycrystalline versions. The synthesis method, which is based on chemical vapor deposition, causes amorphous microspheres to have a high content of hydrogen that produces an onionlike distributed porous core when the microspheres are crystallized by a fast annealing regime. This substantially influences the resonant modes. However, a slow crystallization regime does not yield pores, and produces higher-quality-factor resonances that could be fitted to the Mie theory. This allows the establishment of a procedure for obtaining size calibration standards with relative errors of the order of 0.1%.

  12. Leakage current measurements of a pixelated polycrystalline CVD diamond detector

    NASA Astrophysics Data System (ADS)

    Zain, R. M.; Maneuski, D.; O'Shea, V.; Bates, R.; Blue, A.; Cunnigham, L.; Stehl, C.; Berderman, E.; Rahim, R. A.

    2013-01-01

    Diamond has several desirable features when used as a material for radiation detection. With the invention of synthetic growth techniques, it has become feasible to look at developing diamond radiation detectors with reasonable surface areas. Polycrystalline diamond has been grown using a chemical vapour deposition (CVD) technique by the University of Augsburg and detector structures fabricated at the James Watt Nanofabrication Centre (JWNC) in the University of Glasgow in order to produce pixelated detector arrays. The anode and cathode contacts are realised by depositing gold to produce ohmic contacts. Measurements of I-V characteristics were performed to study the material uniformity. The bias voltage is stepped from -1000V to 1000V to investigate the variation of leakage current from pixel to pixel. Bulk leakage current is measured to be less than 1nA.

  13. Ion implantation of erbium into polycrystalline cadmium telluride

    SciTech Connect

    Ushakov, V. V. Klevkov, Yu. V.; Dravin, V. A.

    2015-05-15

    The specific features of the ion implantation of polycrystalline cadmium telluride with grains 20–1000 μm in dimensions are studied. The choice of erbium is motivated by the possibility of using rare-earth elements as luminescent “probes” in studies of the defect and impurity composition of materials and modification of the composition by various technological treatments. From the microphotoluminescence data, it is found that, with decreasing crystal-grain dimensions, the degree of radiation stability of the material is increased. Microphotoluminescence topography of the samples shows the efficiency of the rare-earth probe in detecting regions with higher impurity and defect concentrations, including regions of intergrain boundaries.

  14. Polycrystalline metasurface perfect absorbers fabricated using microsphere photolithography.

    PubMed

    Qu, Chuang; Kinzel, Edward C

    2016-08-01

    Microsphere photolithography (MPL) is a practical, cost-effective nanofabrication technique. It uses self-assembled microspheres in contact with the photoresist as microlenses. The microspheres focus incident light to a sub-diffraction limited array of photonic jets in the photoresist. This Letter explores the MPL technique to pattern metal-insulator-metal metasurfaces with near-perfect absorption at mid-wave infrared (MWIR) frequencies. Experimental results are compared to electromagnetic simulations of both the exposure process and the metasurface response. The microsphere self-assembly technique results in a polycrystalline metasurface; however, the metal-insulator-metal structure is shown to be defect tolerant. While the MPL approach imposes geometric constraints on the metasurface design, once understood, the technique can be used to create functional devices. In particular, the ability to tune the resonant wavelength with the exposure dose raises the potential of hierarchical structures. PMID:27472578

  15. Stress enhanced diffusion of krypton ions in polycrystalline titanium

    SciTech Connect

    Nsengiyumva, S.; Raji, A. T.; Rivière, J. P.; Britton, D. T.; Härting, M.

    2014-07-14

    An experimental investigation on the mutual influence of pre-existing residual stress and point defect following ion implantation is presented. The study has been carried out using polycrystalline titanium samples energetically implanted with krypton ions at different fluences. Ion beam analysis was used to determine the concentration profile of the injected krypton ions, while synchrotron X-ray diffraction has been used for stress determination. Ion beam analysis and synchrotron X-ray diffraction stress profile measurements of the implanted titanium samples show a clear evidence of stress-enhanced diffusion of krypton ions in titanium. It is further observed that for the titanium samples implanted at low fluence, ion implantation modifies the pre-existing residual stress through the introduction of point and open volume defects. The stress fields resulting from the ion implantation act to drift the krypton inclusions towards the surface of titanium.

  16. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    SciTech Connect

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  17. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  18. Deposition of hydroxyapatite thin films by Nd:YAG laser ablation: a microstructural study

    SciTech Connect

    Nistor, L.C.; Ghica, C.; Teodorescu, V.S.; Nistor, S.V. . E-mail: snistor@alpha1.infim.ro; Dinescu, M.; Matei, D.; Frangis, N.; Vouroutzis, N.; Liutas, C.

    2004-11-02

    Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation at {lambda} = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 deg. C and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at {lambda} = 335 nm laser wavelength and 300 deg. C substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP)

  19. Electrodeposited CulnSe2 Thin Film Junctions

    NASA Technical Reports Server (NTRS)

    Raffaelle, R. P.; Mantovani, J. G.; Bailey, S. G.; Hepp, A. F.; Gordon, E. M.; Haraway, R.

    1998-01-01

    We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

  20. Electrodeposited CuInSe2 Thin Film Junctions

    NASA Technical Reports Server (NTRS)

    Raffaelle, R. P.; Mantovani, J. G.; Bailey, S. G.; Hepp, A. F.; Gordon, E. M.; Haraway, R.

    1997-01-01

    We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

  1. A versatile platform for magnetostriction measurements in thin films

    NASA Astrophysics Data System (ADS)

    Pernpeintner, M.; Holländer, R. B.; Seitner, M. J.; Weig, E. M.; Gross, R.; Goennenwein, S. T. B.; Huebl, H.

    2016-03-01

    We present a versatile nanomechanical sensing platform for the investigation of magnetostriction in thin films. It is based on a doubly clamped silicon nitride nanobeam resonator covered with a thin magnetostrictive film. Changing the magnetization direction within the film plane by an applied magnetic field generates a magnetoelastic stress and thus changes the resonance frequency of the nanobeam. A measurement of the resulting resonance frequency shift, e.g., by optical interferometry, allows to quantitatively determine the magnetostriction constants of the thin film. In a proof-of-principle experiment, we determine the magnetostriction constants of a 10 nm thick polycrystalline cobalt film, showing very good agreement with literature values. The presented technique aims, in particular, for the precise measurement of magnetostriction in a variety of (conducting and insulating) thin films, which can be deposited by, e.g., electron beam deposition, thermal evaporation, or sputtering.

  2. A New Approach of Polycrystalline Silicon Film on Plastic Substrate Prepared by Ion Beam Deposition Followed by Excimer Laser Crystallization at Room Temperature

    NASA Astrophysics Data System (ADS)

    Kwon, Jang Yeon; Lim, Hyuck; Park, Kyung Bae; Jung, Ji Sim; Kim, Do Young; Cho, Hans S.; Kim, Seok Pil; Park, Young Soo; Kim, Jong Man; Noguchi, Takashi

    2006-05-01

    In this work, we propose a new polycrystalline silicon (poly-Si) film of large grain for thin film transistor on flexible substrate. Thin films of amorphous silicon were deposited on plastic substrate by using ion beam deposition (IBD) and crystallized by excimer laser annealing. The entire process was carried out at room temperature. Si film formed by IBD has much lower impurity such as Ar, O, and H than that deposited by conventional sputtering method. This high purity of Si film makes large grain size (0.5 μm) and shows high endurance of excimer laser energy both on quartz and plastic substrate for flexible active matrix organic light emitting diode (AMOLED).

  3. Optical information storage in PLZT thin films

    SciTech Connect

    Land, C.E.

    1989-01-01

    The feasibility of storing and reading high density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure both the longitudinal electrooptic effects and the photosensitivities of the thin films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a linear electrooptic r/sub c/ coefficient and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and r/sub c/ coefficients are about an order of magnitude less than the transverse R and R/sub c/ coefficients of the bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence after poling (>10/sup /minus/2/) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used for evaluating the photosensitivities of the thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (used previously for bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be about three orders of magnitude higher than those of bulk ceramics of similar compositions. 14 refs., 12 figs., 1 tab.

  4. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, K.H.

    1998-06-30

    A method is disclosed for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates. 1 fig.

  5. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, Kurt H.

    1998-01-01

    A method for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates.

  6. Characterization of ZnInxSey Thin Films as a Buffer Layer for High Efficiency Cu(InGa)Se2 Thin-Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Ohtake, Yasutoshi; Chaisitsak, Sutichai; Yamada, Akira; Konagai, Makoto

    1998-06-01

    The structural, optical and electrical properties of ZnInxSey (ZIS) thin films on Cu(InGa)Se2 (CIGS) thin films and glass substrates were characterized. Polycrystalline ZIS thin films were grown by the coevaporation method using three constituent elements. We confirmed the formation of ZnIn2Se4 from the X-ray diffraction patterns of the ZIS thin films on glass substrates. From the transmittance and reflectance measurements of these films, the bandgap of ZIS is estimated at around 2.0 eV in this study. In addition, the ZIS films on glass substrates show low dark conductivity and high photosensitivity, which are suitable for the buffer layer in CIGS thin-film solar cells. We also fabricated the CIGS thin-film solar cells with a ZnO/ZIS/CIGS structure, and investigated the relationship between the cell performance and the beam intensity ratio of zinc to indium.

  7. Superconducting UBe 13 thin films

    NASA Astrophysics Data System (ADS)

    Quateman, J. H.; Tedrow, P. M.

    1985-12-01

    Of the known heavy fermion superconductors only UBe 13 can have a low resistivity ratio and still go superconducting. In addition, it is a line compound with a melting temperature of nearly twice that of the constituents. These facts make UBe 13 a promising choice for fabrication in thin film form. We have successfully made 2000 Å UBe 13 films by coevaporation of uranium and beryllium on 700°C substrates which were then heated in situ to 1100°C. These films were polycrystalline as shown by X-ray diffraction and have Tc's of 0.85 K, that of the bulk. The resistivity rise at approximately 2 K and the strong negative magnetoresistance were also of the same magnitude as that of the bulk, as were both the perpendicular and parallel critical fields. Thin films of UBe 13 will make more accessible tunneling and proximity effect experiments which can help elucidate the nature of the superconductivity of this compound.

  8. Compositional dependence of Pb(Mg1/3,Nb2/3)O3-PbTiO3 piezoelectric thin films by combinatorial sputtering

    NASA Astrophysics Data System (ADS)

    Kurokawa, Fumiya; Tsujiura, Yuichi; Hida, Hirotaka; Kanno, Isaku

    2014-09-01

    We evaluated the compositional dependence of Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT) polycrystalline thin films by combinatorial sputtering. We prepared compositional gradient (1 - x)PMN-xPT polycrystalline thin films with preferential orientation along the <001> direction in the composition range of x = 0-0.62. We determined that the morphotropic phase boundary (MPB) composition of PMN-PT polycrystalline thin film existed at around x = 0.35, from the X-ray diffraction (XRD) measurements. The maximum value of relative dielectric constants (ɛr = 1498) was obtained at approximately x = 0.23. On the other hand, the piezoelectric coefficients (|e31,f| = 14.1 C/m2) peaked at the determined MPB composition of x = 0.35. From the results of the compositional dependence of dielectric and piezoelectric characteristics, the FOM (e_{31,\\text{f}}^{2}/\\varepsilon _{0}\\varepsilon _{\\text{r}}) of the PMN-PT (x = 0.35) thin film reached 21 GPa, which is much higher than that of the other polycrystalline piezoelectric thin films. These results suggest that PMN-PT (x = 0.35) thin film is a promising material for high-efficiency piezoelectric MEMS energy harvesters.

  9. Virtual Electrochemical Strain Microscopy of Polycrystalline LiCoO2 Films

    SciTech Connect

    Chung, Ding-wen; Balke, Nina; Kalinin, Sergei V; Garcia, R. Edwin

    2011-01-01

    A recently developed technique, electrochemical strain microscopy (ESM), utilizes the strong coupling between ionic current and anisotropic volumetric chemical expansion of lithium-ion electrode materials to dynamically probe the sub-one-hundred? nm inter-facial kinetic intercalation properties. A numerical technique based on the finite element method was developed to analyze the underlying physics that govern the ESM signal generation and establish relations to battery performance. The performed analysis demonstrates that the diffusion path within a thin film is tortuous and the extent of lithium diffusion into the electrode is dependent on the SPM-tip-imposed overpotential frequency. The detected surface actuation gives rise to the development of an electromechanical hysteresis loop whose shape is dependent on grain size and overpotential frequency. Shape and tilting angle of the loop are classified into low and high frequency regimes, separated by a transition frequency which is also a function of lithium diffusivity and grain size, f{sub T} = D//{sup 2}. Research shows that the crystallographic orientation of the surface actuated grain has a significant impact on the shape of the loop. The polycrystalline crystallographic orientation of the grains induces a diffusion path network in the electrode which impacts on the mechanical reliability of the battery. Simulations demonstrate that continuous battery cycling results in a cumulative capacity loss as a result of the hysteric non-reversible lithium intercalation. Furthermore, results suggest that ESM has the capability to infer the local out-of-plane lithium diffusivity and the out-of-plane contribution to Vegard tensor.

  10. Virtual Electrochemical Strain Microscopy of Polycrystalline LiCoO2 Films

    SciTech Connect

    Chung, Ding-Wen; Balke, Nina; Kalinin, Sergei V.; Edwin Garcia, R.

    2011-08-03

    A recently developed technique, electrochemical strain microscopy (ESM), utilizes the strong coupling between ionic current and anisotropic volumetric chemical expansion of lithium-ion electrode materials to dynamically probe the sub-one-hundred? nm inter-facial kinetic intercalation properties. A numerical technique based on the finite element method was developed to analyze the underlying physics that govern the ESM signal generation and establish relations to battery performance. The performed analysis demonstrates that the diffusion path within a thin film is tortuous and the extent of lithium diffusion into the electrode is dependent on the SPM-tip-imposed overpotential frequency. The detected surface actuation gives rise to the development of an electromechanical hysteresis loop whose shape is dependent on grain size and overpotential frequency. Shape and tilting angle of the loop are classified into low and high frequency regimes, separated by a transition frequency which is also a function of lithium diffusivity and grain size, fT = D/l₂. Research shows that the crystallographic orientation of the surface actuated grain has a significant impact on the shape of the loop. The polycrystalline crystallographic orientation of the grains induces a diffusion path network in the electrode which impacts on the mechanical reliability of the battery. Simulations demonstrate that continuous battery cycling results in a cumulative capacity loss as a result of the hysteric non-reversible lithium intercalation. Furthermore, results suggest that ESM has the capability to infer the local out-of-plane lithium diffusivity and the out-of-plane contribution to Vegard tensor.

  11. Improvement of the charge-carrier transport property of polycrystalline CdTe for digital fluoroscopy

    NASA Astrophysics Data System (ADS)

    Oh, K. M.; Heo, Y. J.; Kim, D. K.; Kim, J. S.; Shin, J. W.; Lee, G. H.; Nam, S. H.

    2014-05-01

    Minimizing the radiation impact to the patient is currently an important issue in medical imaging. Particularly, in case of X-ray fluoroscopy, the patient is exposed to high X-ray dose because a large number of images is required in fluoroscopic procedures. In this regard, a direct-conversion X-ray sensor offers the advantages of high quantum efficiency, X-ray sensitivity, and high spatial resolution. In particular, an X-ray sensor in fluoroscopy operates at high frame rate, in the range from 30 to 60 image frames per second. Therefore, charge-carrier transport properties and signal lag are important factors for the development of X-ray sensors in fluoroscopy. In this study, in order to improve the characteristics of polycrystalline cadmium telluride (CdTe), CdTe films were prepared by thermal evaporation and RF sputtering. The deposition was conducted to form a CdTeO3 layer on top of a CdTe film. The role of CdTeO3 is not only to improve the charge-carrier transport by increasing the life-time but also to reduce the leakage current of CdTe films by acting as a passivation layer. In this paper, to establish the effect of a thin oxide layer on top of a CdTe film, the morphological and electrical properties including charge-carrier transport and signal lag were investigated by means of X-ray diffraction, X-ray photoemission spectroscopy, and resistivity measurements.

  12. Impact of graphene polycrystallinity on the performance of graphene field-effect transistors

    SciTech Connect

    Jiménez, David; Chaves, Ferney; Cummings, Aron W.; Van Tuan, Dinh; Kotakoski, Jani; Roche, Stephan

    2014-01-27

    We have used a multi-scale physics-based model to predict how the grain size and different grain boundary morphologies of polycrystalline graphene will impact the performance metrics of graphene field-effect transistors. We show that polycrystallinity has a negative impact on the transconductance, which translates to a severe degradation of the maximum and cutoff frequencies. On the other hand, polycrystallinity has a positive impact on current saturation, and a negligible effect on the intrinsic gain. These results reveal the complex role played by graphene grain boundaries and can be used to guide the further development and optimization of graphene-based electronic devices.

  13. Molecular Dynamics Simulations of Displacement Cascades in Single and Polycrystalline Zirconia

    SciTech Connect

    Du Jincheng

    2009-03-10

    Displacement cascades in zirconia have been studied using classical molecular dynamics simulations. Polycrystalline zirconia with nano-meter grains were created using Voronoi polyhedra construction and studied in comparison with single crystalline zirconia. The results show that displacement cascades with similar kinetic energy generated larger number of displaced atoms in polycrystalline than in the single crystal structure. The fraction of atoms with coordination number change was also higher in polycrystalline zirconia that was explained to be due to the diffusion of oxygen and relaxation at grain boundaries.

  14. Synthesis and optical properties of polycrystalline Li2Al2B2O7 (LABO)

    NASA Astrophysics Data System (ADS)

    Dagdale, S. R.; Muley, G. G.

    2016-05-01

    A polycrystalline lithium aluminum borate (Li2Al2B2O7, LABO) has been synthesized by using simple solid-state technique. The obtained LABO polycrystalline was characterized by powder X-ray diffraction; Fourier transform infrared (FT-IR) spectroscopy and second harmonic generation (SHG) efficiency measurement. The functional groups were identified using the FT-IR spectroscopic data. The SHG efficiency of the polycrystalline material was obtained by the classic Kurtz powder technique using a fundamental wavelength 1064 nm of Nd:YAG laser and it is found to be 1.4 times that of potassium dihydrogen phosphate (KDP).

  15. Surface smoothing effect of an amorphous thin film deposited by atomic layer deposition on a surface with nano-sized roughness

    SciTech Connect

    Lau, W. S. Wan, X.; Xu, Y.; Wong, H.; Zhang, J.; Luo, J. K.

    2014-02-15

    Previously, Lau (one of the authors) pointed out that the deposition of an amorphous thin film by atomic layer deposition (ALD) on a substrate with nano-sized roughness probably has a surface smoothing effect. In this letter, polycrystalline zinc oxide deposited by ALD onto a smooth substrate was used as a substrate with nano-sized roughness. Atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) were used to demonstrate that an amorphous aluminum oxide thin film deposited by ALD can reduce the surface roughness of a polycrystalline zinc oxide coated substrate.

  16. Characterization of deformation near grain boundaries in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Seal, James Robert

    Understanding and describing plastic deformation in polycrystalline materials is fundamentally challenging due to the complex atomic rearrangements that must occur at grain boundaries. These atomic rearrangements can have long-range and substantial impacts on a material's bulk behavior and material properties. Thus, there is a significant need to develop new techniques to study, correlate, and describe deformation accommodation at grain boundaries. Understanding how grain boundaries accommodate plastic deformation at the microscale will provide new insight into the evolution of heterogeneous deformation, stress concentration, and damage nucleation. A series of comprehensive experiments have been conducted in order to develop a quantitative and crystallographically based understanding of the relationships between deformation behavior, material microstructure, and slip transfer mechanisms across grain boundaries in polycrystalline materials. Slip transfer events in polycrystalline metals were investigated using novel analysis techniques in scanning electron microscopy (SEM). The objective of these experiments was to correlate observations of slip transfer with a geometric parameter m', which can be used to identify and predict crystallographic arrangements that are better suited for slip transfer. An emphasis was placed on understanding how the parameter m' can be correlated with heterogeneities in local lattice orientations and local stresses near grain boundaries. A large population of slip transfer reactions across α/beta phase boundaries in Ti-5Al-2.5Sn were imaged by SEM and slip system activity was characterized using electron backscattered diffraction (EBSD) and slip trace analysis. Statistical correlations identified that slip transfer across the α/beta phase boundary was strongly influenced by slip plane alignment across the interface. Slip direction alignment was not strongly correlated to observations of slip transfer and the parameter m' was not useful

  17. Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

    2007-01-01

    Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

  18. Effects of duty cycle on properties of CIGS thin films fabricated by pulse-reverse electrodeposition technique

    NASA Astrophysics Data System (ADS)

    Jadhav, Harsharaj S.; Kalubarme, Ramchandra S.; Ahn, SeJin; Yun, Jae Ho; Park, Chan-Jin

    2013-03-01

    DC and pulse-reverse electrodeposition mode were employed for the deposition of polycrystalline Cu(In,Ga)Se2 thin films. In comparison with DC electrodeposition mode, films obtained by pulse-reverse electrodeposition were smoother, denser and more uniform with good adhesion. The Ga content in final composition of CIGS thin film was improved in pulse-reverse electrodeposition mode. In addition, pulse-reverse electrodeposited CIGS thin films were more crystalline with chalcopyrite structure. The compact morphology without pores in the deposit was achieved in the pulse-reverse electrodeposited CIGS thin films by varying duty cycle.

  19. Synthesis and Characterization of Zirconium Tungstate Ultra-Thin Fibers

    SciTech Connect

    Zhang, Lifeng; Howe, Jane Y; Fong, Hao; Zhang, Yan

    2009-01-01

    This study reports an innovative method of electrospinning followed by pyrolysis to synthesize zirconium tungstate (ZrW2O8), a material with negative coefficient of thermal expansion (CTE), in ultra-thin fiber form. Morphologies and microstructures of the as-electrospun precursor fibers, the heat-treated intermediate fibers, and the final ZrW2O8 ultra-thin fibers were characterized by SEM, XRD, and TEM. The ZrW2O8 ultra-thin fibers had diameters in the sub-micrometer range with aspect ratios larger than 100; these fibers were polycrystalline, and consisted of single crystalline ZrW2O8 crystallites with sizes of 30-50 nm and surface roughness of several nanometers. The ZrW2O8 ultra-thin fibers are expected to outperform spherically, cylindrically, and/or irregularly shaped polycrystalline ZrW2O8 particles for the development of composites with precisely controlled CTEs. Additionally, this reported method could be utilized as a general approach to convert nano-scaled inorganic particles into fibers.

  20. Multiple Diamond Anvil (MDA) apparatus using nano-polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Irifune, T.; Kunimoto, T.; Tange, Y.; Shinmei, T.; Isobe, F.; Kurio, A.; Funakoshi, K.

    2011-12-01

    Thanks to the great efforts by Dave Mao, Bill Bassett, Taro Takahashi, and their colleagues at the University of Rochester through 1960s-70s, diamond anvil cell (DAC) became a major tool to investigate the deep Earth after its invention by scientists at NBS in 1958. DAC can now cover almost the entire pressure and temperature regimes of the Earth's interior, which seems to have solved the longstanding debate on the crystal structure of iron under the P-T conditions of the Earth's inner core. In contrast, various types of static large-volume presses (LVP) have been invented, where tungsten carbide has conventionally been used as anvils. Kawai-type multianvil apparatus (MA), which utilize 6 first-stage harden steel and 8 tungsten carbide anvils, is the most successful LVP, and has been used for accurate measurements of phase transitions, physical properties, element partitioning, etc. at high pressure and temperature. However, pressures using tungsten carbide as the second-stage anvils have been limited to about 30 GPa due to significant plastic deformation of the anvils. Efforts have been made to expand this pressure limit by replacing tungsten carbide anvils with harder sintered diamond (SD) anvils over the last two decades, but the pressures available in KMA with SD anvils have still been limited to below 100 GPa. We succeeded to produce nano-polycrystalline diamond (NPD or HIME-Diamond) in 2003, which is known to have ultrahigh hardness, very high toughness and elastic stiffness, high transmittance of light, relatively low thermal conductivity. These properties are feasible for its use as anvils, and some preliminary experiments of application of NPD anvils to laser heated DAC have successfully made in the last few years. We are now able to synthesize NPD rods with about 1cm in both diameter and length using a newly constructed 6000-ton KMA at Geodynamics Research Center, Ehime University, and have just started to apply this new polycrystalline diamond as anvils