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Sample records for amorphous silicon flat-panel

  1. Synchrotron applications of an amorphous silicon flat-panel detector.

    SciTech Connect

    Lee, J. H.; Can Aydiner, C.; Almer, J.; Bernier, J.; Chapman, K. W.; Chupas, P. J.; Haeffner, D.; Kump, K.; Lee, P. L.; Lienert, U.; Miceli, A.; Vera, G.; LANL; GE Healthcare

    2008-01-01

    A GE Revolution 41RT flat-panel detector (GE 41RT) from GE Healthcare (GE) has been in operation at the Advanced Photon Source for over two years. The detector has an active area of 41 cm x 41 cm with 200 {micro}m x 200 {micro}m pixel size. The nominal working photon energy is around 80 keV. The physical set-up and utility software of the detector system are discussed in this article. The linearity of the detector response was measured at 80.7 keV. The memory effect of the detector element, called lag, was also measured at different exposure times and gain settings. The modulation transfer function was measured in terms of the line-spread function using a 25 {micro}m x 1 cm tungsten slit. The background (dark) signal, the signal that the detector will carry without exposure to X-rays, was measured at three different gain settings and with exposure times of 1 ms to 15 s. The radial geometric flatness of the sensor panel was measured using the diffraction pattern from a CeO{sub 2} powder standard. The large active area and fast data-capturing rate, i.e. 8 frames s{sup -1} in radiography mode, 30 frames s{sup -1} in fluoroscopy mode, make the GE 41RT one of a kind and very versatile in synchrotron diffraction. The loading behavior of a Cu/Nb multilayer material is used to demonstrate the use of the detector in a strain-stress experiment. Data from the measurement of various samples, amorphous SiO{sub 2} in particular, are presented to show the detector effectiveness in pair distribution function measurements.

  2. Synchrotron applications of an amorphous silicon flat-panel detector.

    PubMed

    Lee, John H; Aydiner, C Can; Almer, Jonathan; Bernier, Joel; Chapman, Karena W; Chupas, Peter J; Haeffner, Dean; Kump, Ken; Lee, Peter L; Lienert, Ulrich; Miceli, Antonino; Vera, German

    2008-09-01

    A GE Revolution 41RT flat-panel detector (GE 41RT) from GE Healthcare (GE) has been in operation at the Advanced Photon Source for over two years. The detector has an active area of 41 cm x 41 cm with 200 microm x 200 microm pixel size. The nominal working photon energy is around 80 keV. The physical set-up and utility software of the detector system are discussed in this article. The linearity of the detector response was measured at 80.7 keV. The memory effect of the detector element, called lag, was also measured at different exposure times and gain settings. The modulation transfer function was measured in terms of the line-spread function using a 25 microm x 1 cm tungsten slit. The background (dark) signal, the signal that the detector will carry without exposure to X-rays, was measured at three different gain settings and with exposure times of 1 ms to 15 s. The radial geometric flatness of the sensor panel was measured using the diffraction pattern from a CeO(2) powder standard. The large active area and fast data-capturing rate, i.e. 8 frames s(-1) in radiography mode, 30 frames s(-1) in fluoroscopy mode, make the GE 41RT one of a kind and very versatile in synchrotron diffraction. The loading behavior of a Cu/Nb multilayer material is used to demonstrate the use of the detector in a strain-stress experiment. Data from the measurement of various samples, amorphous SiO(2) in particular, are presented to show the detector effectiveness in pair distribution function measurements. PMID:18728319

  3. X-ray imaging with amorphous silicon active matrix flat-panel imagers (AMFPIs)

    NASA Astrophysics Data System (ADS)

    El-Mohri, Youcef; Antonuk, Larry E.; Jee, Kyung-Wook; Maolinbay, Manat; Rong, Xiujiang; Siewerdsen, Jeffrey H.; Verma, Manav; Zhao, Qihua

    1997-07-01

    Recent advances in thin-film electronics technology have opened the way for the use of flat-panel imagers in a number of medical imaging applications. These novel imagers offer real time digital readout capabilities (˜30 frames per second), radiation hardness (>106cGy), large area (30×40 cm2) and compactness (˜1 cm). Such qualities make them strong candidates for the replacement of conventional x-ray imaging technologies such as film-screen and image intensifier systems. In this report, qualities and potential of amorphous silicon based active matrix flat-panel imagers are outlined for various applications such as radiation therapy, radiography, fluoroscopy and mammography.

  4. Calibration of an amorphous-silicon flat panel portal imager for exit-beam dosimetry

    SciTech Connect

    Chen, Josephine; Chuang, Cynthia F.; Morin, Olivier; Aubin, Michele; Pouliot, Jean

    2006-03-15

    Amorphous-silicon flat panel detectors are currently used to acquire digital portal images with excellent image quality for patient alignment before external beam radiation therapy. As a first step towards interpreting portal images acquired during treatment in terms of the actual dose delivered to the patient, a calibration method is developed to convert flat panel portal images to the equivalent water dose deposited in the detector plane and at a depth of 1.5 cm. The method is based on empirical convolution models of dose deposition in the flat panel detector and in water. A series of calibration experiments comparing the response of the flat panel imager and ion chamber measurements of dose in water determines the model parameters. Kernels derived from field size measurements account for the differences in the production and detection of scattered radiation in the two systems. The dissimilar response as a function of beam energy spectrum is characterized from measurements performed at various off-axis positions and for increasing attenuator thickness in the beam. The flat panel pixel inhomogeneity is corrected by comparing a large open field image with profiles measured in water. To verify the accuracy of the calibration method, calibrated flat panel profiles were compared with measured dose profiles for fields delivered through solid water slabs, a solid water phantom containing an air cavity, and an anthropomorphic head phantom. Open rectangular fields of various sizes and locations as well as a multileaf collimator-shaped field were delivered. For all but the smallest field centered about the central axis, the calibrated flat panel profiles matched the measured dose profiles with little or no systematic deviation and approximately 3% (two standard deviations) accuracy for the in-field region. The calibrated flat panel profiles for fields located off the central axis showed a small -1.7% systematic deviation from the measured profiles for the in-field region

  5. Signal, noise, and detective quantum efficiency of amorphous-silicon:hydrogen flat-panel imagers

    NASA Astrophysics Data System (ADS)

    Siewerdsen, Jeffrey Harold

    Flat-panel imagers based upon the technology of thin-film amorphous silicon transistors and photodiodes are under investigation for a wide variety of medical imaging applications. This thesis presents quantitative empirical and theoretical investigations of the imaging performance of such imaging systems. Performance was evaluated in terms of imager signal size, spatial resolution, noise characteristics, and signal-to-noise ratio for a wide variety of imaging system configurations and exposure conditions relevant to medical imaging. A theoretical model based upon cascaded systems analysis allowed prediction of imager signal, noise, and detective quantum efficiency (DQE), and theoretical results were found to agree well with empirical measurements. The empirical and theoretical analyses yielded quantification of the performance of existing imager designs, allowed investigation of the potential performance of future flat-panel imaging systems, and provided a methodology for identifying optimal imager configurations for various applications and imaging tasks. There is every indication that flat-panel imagers could provide performance superior to that of existing clinical imaging technologies. For example, in general x-ray radiography, mammography, and radiotherapy portal imaging, such systems could provide DQE exceeding 60%, 80%, and 1.5%, respectively, approximately twice that of film-based systems. However, for applications involving very low exposures per image, e.g., real-time fluoroscopy, such systems may suffer from reduced signal-to-noise ratio. The analyses developed in this thesis provide an effective means of identifying strategies for improved imager performance and will facilitate the realization of optimized flat-panel imagers that physically achieve their maximum theoretical performance.

  6. Chacterization and application of a GE amorphous silicon flat panel detector in a synchrotron light source.

    SciTech Connect

    Lee, J. H.; Miceli, A.; Almer, J.; Bernier, J.; Chapman, K.; Chupas, P.; Haeffner, D.; Lee, P. L.; Lienert, U.; Aydiner, C.; Vera, G.; Kump, K.; LANL; GE Healthcare

    2007-01-01

    Characterization, in the language of synchrotron radiation, was performed on a GE Revolution 41RT flat panel detector using the X-ray light source at the Advanced Photon Source (APS). The detector has an active area of 41 x 41 cm{sup 2} with 200 x 200 {micro}m{sup 2} pixel size. The nominal working photon energy is around 80 keV. Modulation transfer function (MTF) was measured in terms of line spread function (LSF) using a 25 {micro}m x 1 cm tungsten slit. Memory effects of the detector elements, called lag, were also measured. The large area and fast data capturing rate - 8 fps in unbinned mode, 30 fps in binned or region of interest (ROI) mode - make the GE flat panel detector a unique and very versatile detector for synchrotron experiments. In particular, we present data from pair distribution function (PDF) measurements to demonstrate the special features of this detector.

  7. Finding an improved amorphous-silicon x-ray flat-panel detector configuration for the in-line geometry.

    PubMed

    Fast, M F; Teymurazyan, A; Pang, G; Oelfke, U; Rowlands, J A

    2013-04-01

    We have previously investigated the use of a conventional amorphous-silicon flat-panel detector (FPD) for intrafractional image guidance in the in-line geometry. In this configuration, the FPD is mounted between the patient and the treatment head, with the front of the FPD facing towards the patient. By geometrically separating signals from the diagnostic (kV) and treatment (MV) beams, it is possible to monitor the patient and treatment beam at the same time. In this study, we propose an FPD design based on existing technology with a 70% reduced up-stream areal density that is more suited to this new application. We have investigated our FPD model by means of a validated Monte Carlo simulation. Experimentally, simple rectangular fields were used to irradiate through the detector and observe the impact of removing detector components such as the support structure or the phosphor screen on the measured signal. The proposed FPD performs better than the conventional FPD: (i) attenuation of the MV beam is decreased by 60%; (ii) the MV signal is reduced by 20% for the primary MV field region which can avoid saturation of the FPD; and (iii) long range scatter from the MV into the kV region of the detector is greatly reduced. PMID:23478634

  8. High-energy and thermal-neutron imaging and modeling with an amorphous silicon flat-panel detector.

    PubMed

    Claytor, Thomas N; Taddeucci, Terry N; Hills, Charles R; Summa, Deborah A; Davis, Anthony W; McDonald, Thomas E; Schwab, Mark J

    2004-10-01

    The Los Alamos Neutron Science Center (LANSCE) operates two spallation neutron sources dedicated to research in materials science, condensed-matter physics, and fundamental and applied nuclear physics. Prior to 1995, all thermal neutron radiography at Los Alamos was done on a beam port attached to the Omega West reactor, a small 8MW research reactor used primarily for radioisotope production and prompt and delayed neutron activation analysis. After the closure of this facility, two largely independent radiography development efforts were begun at LANSCE using moderated cold and thermal neutrons from the Target-1 source and high-energy neutrons from the Target-4 source. Investigations with cold and thermal neutrons employed a neutron converter and film, a scintillation screen and CCD camera system, and a new high-resolution amorphous silicon (a-Si) flat-panel detector system. Recent work with high-energy neutrons (En > 1 MeV) has involved storage-phosphor image plates. Some comparison high-energy images were obtained with both image plates and the a-Si panel and showed equivalent image quality for approximately equal exposure times. PMID:15246402

  9. Solid-state flat panel imager with avalanche amorphous selenium

    NASA Astrophysics Data System (ADS)

    Scheuermann, James R.; Howansky, Adrian; Goldan, Amir H.; Tousignant, Olivier; Levéille, Sébastien; Tanioka, K.; Zhao, Wei

    2016-03-01

    Active matrix flat panel imagers (AMFPI) have become the dominant detector technology for digital radiography and fluoroscopy. For low dose imaging, electronic noise from the amorphous silicon thin film transistor (TFT) array degrades imaging performance. We have fabricated the first prototype solid-state AMFPI using a uniform layer of avalanche amorphous selenium (a-Se) photoconductor to amplify the signal to eliminate the effect of electronic noise. We have previously developed a large area solid-state avalanche a-Se sensor structure referred to as High Gain Avalanche Rushing Photoconductor (HARP) capable of achieving gains of 75. In this work we successfully deposited this HARP structure onto a 24 x 30 cm2 TFT array with a pixel pitch of 85 μm. An electric field (ESe) up to 105 Vμm-1 was applied across the a-Se layer without breakdown. Using the HARP layer as a direct detector, an X-ray avalanche gain of 15 +/- 3 was achieved at ESe = 105 Vμm-1. In indirect mode with a 150 μm thick structured CsI scintillator, an optical gain of 76 +/- 5 was measured at ESe = 105 Vμm-1. Image quality at low dose increases with the avalanche gain until the electronic noise is overcome at a constant exposure level of 0.76 mR. We demonstrate the success of a solid-state HARP X-ray imager as well as the largest active area HARP sensor to date.

  10. Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography.

    PubMed

    Sultana, Afrin; Reznik, Alla; Karim, Karim S; Rowlands, J A

    2008-10-01

    Protein crystallography is the most important technique for resolving the three-dimensional atomic structure of protein by measuring the intensity of its x-ray diffraction pattern. This work proposes a large area flat panel detector for protein crystallography based on direct conversion x-ray detection technique using avalanche amorphous selenium (a-Se) as the high gain photoconductor, and active matrix readout using amorphous silicon (a-Si:H) thin film transistors. The detector employs avalanche multiplication phenomenon of a-Se to make the detector sensitive to each incident x ray. The advantages of the proposed detector over the existing imaging plate and charge coupled device detectors are large area, high dynamic range coupled to single x-ray detection capability, fast readout, high spatial resolution, and inexpensive manufacturing process. The optimal detector design parameters (such as detector size, pixel size, and thickness of a-Se layer), and operating parameters (such as electric field across the a-Se layer) are determined based on the requirements for protein crystallography application. The performance of the detector is evaluated in terms of readout time (<1 s), dynamic range (approximately 10(5)), and sensitivity (approximately 1 x-ray photon), thus validating the detector's efficacy for protein crystallography. PMID:18975678

  11. Scan equalization digital radiography (SEDR) implemented with an amorphous selenium flat-panel detector: initial experience.

    PubMed

    Liu, Xinming; Lai, Chao-Jen; Chen, Lingyun; Han, Tao; Zhong, Yuncheng; Shen, Youtao; Wang, Tianpeng; Shaw, Chris C

    2009-11-21

    It is well recognized in projection radiography that low-contrast detectability suffers in heavily attenuating regions due to excessively low x-ray fluence to the image receptor and higher noise levels. Exposure equalization can improve image quality by increasing the x-ray exposure to heavily attenuating regions, resulting in a more uniform distribution of exposure to the detector. Image quality is also expected to be improved by using the slot-scan geometry to reject scattered radiation effectively without degrading primary x-rays. This paper describes the design of a prototype scan equalization digital radiography (SEDR) system implemented with an amorphous silicon (a-Si) thin-film transistor (TFT) array-based flat-panel detector. With this system, slot-scan geometry with alternate line erasure and readout (ALER) technique was used to achieve scatter rejection. A seven-segment beam height modulator assembly was mounted onto the fore collimator to regulate exposure regionally for chest radiography. The beam modulator assembly, consisting of micro linear motors, lead screw cartridge with lead (Pb) beam blockers attached, position feedback sensors and motor driver circuitry, has been tested and found to have an acceptable response for exposure equalization in chest radiography. An anthropomorphic chest phantom was imaged in the posterior-anterior (PA) view under clinical conditions. Scatter component, primary x-rays, scatter-to-primary ratios (SPRs) and primary signal-to-noise ratios (PSNRs) were measured in the SEDR images to evaluate the rejection and redistribution of scattered radiation, and compared with those for conventional full-field imaging with and without anti-scatter grid methods. SPR reduction ratios (SPRRRs, defined as the differences between the non-grid full-field SPRs and the reduced SPRs divided by the former) yielded approximately 59% for the full-field imaging with grid and 82% for the SEDR technique in the lungs, and 77% for the full

  12. 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

  13. 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

  14. Imaging performance of amorphous selenium based flat-panel detectors for digital mammography: characterization of a small area prototype detector.

    PubMed

    Zhao, Wei; Ji, W G; Debrie, Anne; Rowlands, J A

    2003-02-01

    Our work is to investigate and understand the factors affecting the imaging performance of amorphous selenium (a-Se) flat-panel detectors for digital mammography. Both theoretical and experimental methods were developed to investigate the spatial frequency dependent detective quantum efficiency [DQE(f)] of a-Se flat-panel detectors for digital mammography. Since the K edge of a-Se is 12.66 keV and within the energy range of a mammographic spectrum, a theoretical model was developed based on cascaded linear system analysis with parallel processes to take into account the effect of K fluorescence on the modulation transfer function (MTF), noise power spectrum (NPS), and DQE(f) of the detector. This model was used to understand the performance of a small-area prototype detector with 85 microm pixel size. The presampling MTF, NPS, and DQE(f) of the prototype were measured, and compared to the theoretical calculation of the model. The calculation showed that K fluorescence accounted for a 15% reduction in the MTF at the Nyquist frequency (fNy) of the prototype detector, and the NPS at fNy was reduced to 89% of that at zero spatial frequency. The measurement of presampling MTF of the prototype detector revealed an additional source of blurring, which was attributed to charge trapping in the blocking layer at the interface between a-Se and the active matrix. This introduced a drop in both presampling MTF and NPS at high spatial frequency, and reduced aliasing in the NPS. As a result, the DQE(f) of the prototype detector at fNy approached 40% of that at zero spatial frequency. The measured and calculated DQE(f) using the linear system model have reasonable agreement, indicating that the factors controlling image quality in a-Se based mammographic detectors are fully understood, and the model can be used to further optimize detector imaging performance. PMID:12607843

  15. 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

  16. Amorphous selenium flat panel detectors for digital mammography: Validation of a NPWE model observer with CDMAM observer performance experiments

    SciTech Connect

    Segui, Jennifer A.; Zhao Wei

    2006-10-15

    Model observers have been developed which incorporate a specific imaging task, system performance, and human observer characteristics and can potentially overcome some of the limitations in using detective quantum efficiency for optimization and comparison of detectors. In this paper, a modified nonprewhitening matched filter (NPWE) model observer was developed and validated to predict object detectability for an amorphous selenium (a-Se) direct flat-panel imager (FPI) where aliasing is severe. A preclinical a-Se digital mammography FPI with 85 {mu}m pixel size was used in this investigation. Its physical imaging properties including modulation transfer function (MTF), noise power spectrum, and DQE were fully characterized. An observer performance study was conducted by imaging the CDMAM 3.4 contrast-detail phantom designed specifically for digital mammography and presenting these images to a panel of seven observers. X-ray attenuation and scatter due to the phantom were determined experimentally for use in development of the model observer. The observer study results were analyzed via threshold averaging and signal detection theory (SDT) based techniques to produce contrast-detail curves where threshold contrast is plotted as a function of disk diameter. Validity of the model was established using SDT analysis of the experimental data. The effect of aliasing on the detectability of small diameter disks was determined using the NPWE model observer. The signal spectrum was calculated using the presampling MTF of the detector with and without including the aliased terms. Our results indicate that the NPWE model based on Fourier domain parameters provides reasonable prediction of object detectability for the signal-known-exactly task in uniform image noise for a-Se direct FPI.

  17. Amorphous Diamond Flat Panel Displays - Final Report of ER-LTR CRADA project with SI Diamond Technology

    SciTech Connect

    Ager III, Joel W.

    1998-05-08

    The objective of this project was to determine why diamond-based films are unusually efficient electron emitters (field emission cathodes) at room temperature. Efficient cathodes based on diamond are being developed by SI Diamond Technology (SIDT) as components for bright, sunlight-readable, flat panel displays. When the project started, it was known that only a small fraction (<1%) of the cathode area is active in electron emission and that the emission sites themselves are sub-micron in size. The critical challenge of this project was to develop new microcharacterization methods capable of examining known emission sites. The research team used a combination of cathode emission imaging (developed at SIDT), micro-Raman spectroscopy (LBNL), and electron microscopy and spectroscopy (National Center for Electron Microscopy, LBNL) to examine the properties of known emission sites. The most significant accomplishment of the project was the development at LBNL of a very high resolution scanning probe that, for the first time, measured simultaneously the topography and electrical characteristics of single emission sites. The increased understanding of the emission mechanism helped SIDT to develop a new cathode material,''nano-diamond,'' which they have incorporated into their Field Emission Picture Element (FEPix) product. SIDT is developing large-format flat panel displays based on these picture elements that will be brighter and more efficient than existing outdoor displays such as Jumbotrons. The energy saving that will be realized if field emission displays are introduced commercially is in line with the energy conservation mission of DOE. The unique characterization tools developed in this project (particularly the new scanning microscopy method) are being used in ongoing BES-funded basic research.

  18. Medical imaging applications of amorphous silicon

    SciTech Connect

    Mireshghi, A.; Drewery, J.S.; Hong, W.S.; Jing, T.; Kaplan, S.N.; Lee, H.K.; Perez-Mendez, V.

    1994-07-01

    Two dimensional hydrogenated amorphous silicon (a-Si:H) pixel arrays are good candidates as flat-panel imagers for applications in medical imaging. Various performance characteristics of these imagers are reviewed and compared with currently used equipments. An important component in the a-Si:H imager is the scintillator screen. A new approach for fabrication of high resolution CsI(Tl) scintillator layers, appropriate for coupling to a-Si:H arrays, are presented. For nuclear medicine applications, a new a-Si:H based gamma camera is introduced and Monte Carlo simulation is used to evaluate its performance.

  19. Investigation of the effect of anode/filter materials on the dose and image quality of a digital mammography system based on an amorphous selenium flat panel detector.

    PubMed

    Baldelli, P; Phelan, N; Egan, G

    2010-04-01

    A comparison, in terms of image quality and glandular breast dose, was carried out between two similar digital mammography systems using amorphous selenium flat panel detectors. The two digital mammography systems currently available from Lorad-Hologic were compared. The original system utilises Mo/Mo and Mo/Rh as target/filter combinations, while the new system uses W/Rh and W/Ag. Images of multiple mammography phantoms with simulated compressed breast thicknesses of 4 cm, 5 cm and 6 cm and various glandular tissue equivalency were acquired under different spectral conditions. The contrast of five details, corresponding to five glandular compositions, was calculated and the ratio of the square of the contrast-to-noise ratio to the average glandular dose was used as a figure-of-merit (FOM) to compare results. For each phantom thickness and target/filter combination, there is an optimum voltage that maximises the FOM. Results show that the W/Rh combination is the best choice for all the detection tasks studied, but for thicknesses greater than 6 cm the W/Ag combination would probably be the best choice. In addition, the new system with W filter presents a better optimisation of the automatic exposure control in comparison with the original system with Mo filter. PMID:20019173

  20. Single-layer and dual-layer contrast-enhanced mammography using amorphous selenium flat panel detectors

    NASA Astrophysics Data System (ADS)

    Allec, N.; Abbaszadeh, S.; Karim, K. S.

    2011-09-01

    The accumulation of injected contrast agents allows the image enhancement of lesions through the use of contrast-enhanced mammography. In this technique, the combination of two acquired images is used to create an enhanced image. There exist several methods to acquire the images to be combined, which include dual energy subtraction using a single detection layer that suffers from motion artifacts due to patient motion between image acquisition. To mitigate motion artifacts, a detector composed of two layers may be used to simultaneously acquire the low and high energy images. In this work, we evaluate both of these methods using amorphous selenium as the detection material to find the system parameters (tube voltage, filtration, photoconductor thickness and relative intensity ratio) leading to the optimal performance. We then compare the performance of the two detectors under the variation of contrast agent concentration, tumor size and dose. The detectability was found to be most comparable at the lower end of the evaluated factors. The single-layer detector not only led to better contrast, due to its greater spectral separation capabilities, but also had lower quantum noise. The single-layer detector was found to have a greater detectability by a factor of 2.4 for a 2.5 mm radius tumor having a contrast agent concentration of 1.5 mg ml-1 in a 4.5 cm thick 50% glandular breast. The inclusion of motion artifacts in the comparison is part of ongoing research efforts.

  1. Quantitative comparison using generalized relative object detectability (G-ROD) metrics of an amorphous selenium detector with high resolution microangiographic fluoroscopes (MAF) and standard flat panel detectors (FPD)

    NASA Astrophysics Data System (ADS)

    Russ, M.; Shankar, A.; Jain, A.; Setlur Nagesh, S. V.; Ionita, C. N.; Scott, C.; Karim, K. S.; Bednarek, D. R.; Rudin, S.

    2016-03-01

    A novel amorphous selenium (a-Se) direct detector with CMOS readout has been designed, and relative detector performance investigated. The detector features include a 25μm pixel pitch, and 1000μm thick a-Se layer operating at 10V/μm bias field. A simulated detector DQE was determined, and used in comparative calculations of the Relative Object Detectability (ROD) family of prewhitening matched-filter (PWMF) observer and non-pre-whitening matched filter (NPWMF) observer model metrics to gauge a-Se detector performance against existing high resolution micro-angiographic fluoroscopic (MAF) detectors and a standard flat panel detector (FPD). The PWMF-ROD or ROD metric compares two x-ray imaging detectors in their relative abilities in imaging a given object by taking the integral over spatial frequencies of the Fourier transform of the detector DQE weighted by an object function, divided by the comparable integral for a different detector. The generalized-ROD (G-ROD) metric incorporates clinically relevant parameters (focal- spot size, magnification, and scatter) to show the degradation in imaging performance for detectors that are part of an imaging chain. Preliminary ROD calculations using simulated spheres as the object predicted superior imaging performance by the a-Se detector as compared to existing detectors. New PWMF-G-ROD and NPWMF-G-ROD results still indicate better performance by the a-Se detector in an imaging chain over all sphere sizes for various focal spot sizes and magnifications, although a-Se performance advantages were degraded by focal spot blurring. Nevertheless, the a-Se technology has great potential to provide break- through abilities such as visualization of fine details including of neuro-vascular perforator vessels and of small vascular devices.

  2. TU-F-18C-02: Increasing Amorphous Selenium Thickness in Direct Conversion Flat-Panel Imagers for Contrast-Enhanced Dual-Energy Breast Imaging

    SciTech Connect

    Scaduto, DA; Hu, Y-H; Zhao, W

    2014-06-15

    Purpose: Contrast-enhanced (CE) breast imaging using iodinated contrast agents requires imaging with x-ray spectra at energies greater than those used in mammography. Optimizing amorphous selenium (a-Se) flat panel imagers (FPI) for this higher energy range may increase lesion conspicuity. Methods: We compare imaging performance of a conventional FPI with 200 μm a-Se conversion layer to a prototype FPI with 300 μm a-Se layer. Both detectors are evaluated in a Siemens MAMMOMAT Inspiration prototype digital breast tomosynthesis (DBT) system using low-energy (W/Rh 28 kVp) and high-energy (W/Cu 49 kVp) x-ray spectra. Detectability of iodinated lesions in dual-energy images is evaluated using an iodine contrast phantom. Effects of beam obliquity are investigated in projection and reconstructed images using different reconstruction methods. The ideal observer signal-to-noise ratio is used as a figure-of-merit to predict the optimal a-Se thickness for CE lesion detectability without compromising conventional full-field digital mammography (FFDM) and DBT performance. Results: Increasing a-Se thickness from 200 μm to 300 μm preserves imaging performance at typical mammographic energies (e.g. W/Rh 28 kVp), and improves the detective quantum efficiency (DQE) for high energy (W/Cu 49 kVp) by 30%. While the more penetrating high-energy x-ray photons increase geometric blur due to beam obliquity in the FPI with thicker a-Se layer, the effect on lesion detectability in FBP reconstructions is negligible due to the reconstruction filters employed. Ideal observer SNR for CE objects shows improvements in in-plane detectability with increasing a-Se thicknesses, though small lesion detectability begins to degrade in oblique projections for a-Se thickness above 500 μm. Conclusion: Increasing a-Se thickness in direct conversion FPI from 200 μm to 300 μm improves lesion detectability in CE breast imaging with virtually no cost to conventional FFDM and DBT. This work was partially

  3. Development and evaluation of a portable amorphous silicon flat-panel x-ray detector

    NASA Astrophysics Data System (ADS)

    Watanabe, Minoru; Mochizuki, Chiori; Kameshima, Toshio; Yamazaki, Tatsuya; Court, Laurence; Hayashida, Shinsuke; Morishita, Masakazu; Ohta, Shin-ichi

    2001-06-01

    The design, development and evaluation of a portable x-ray detector are described. The completed detector has a pixel pitch of 100 micrometers , an active imaging area of 22.5 x 27.5 cm2 (9 x 11 inch2), package outer dimensions of 32.5 x 32.5 cm2, a thickness of only 20 mm, and a weight of around 2.8 kg. A number of significant advances in the design and production processes were needed to produce such a compact detector with such a small pixel pitch, while maintaining the image quality achieved a current detector (CXDI-22) which has a 160 mm pixel pitch. These include the development of a low power readout IC, advances in detector packaging design, concentrating on lightweight and strong components, and redesign of the pixel structure to improve the fill-factor. A comparison is made of the imaging characteristics of this new detector with the CXDI-22 detector, and it is shown that the new detector demonstrates improved CTF, and NEQ. The new detector is also shown to demonstrate superior performance in a contrast-detail phantom evaluation. This new detector should be useful for limb and joint examinations as it offers high spatial resolution, combined with the same freedom in positioning provided by conventional screen-film cassettes.

  4. Microgap flat panel display

    DOEpatents

    Wuest, C.R.

    1998-12-08

    A microgap flat panel display is disclosed which includes a thin gas-filled display tube that utilizes switched X-Y ``pixel`` strips to trigger electron avalanches and activate a phosphor at a given location on a display screen. The panel utilizes the principal of electron multiplication in a gas subjected to a high electric field to provide sufficient electron current to activate standard luminescent phosphors located on an anode. The X-Y conductive strips of a few micron widths may for example, be deposited on opposite sides of a thin insulating substrate, or on one side of the adjacent substrates and function as a cathode. The X-Y strips are separated from the anode by a gap filled with a suitable gas. Electrical bias is selectively switched onto X and Y strips to activate a ``pixel`` in the region where these strips overlap. A small amount of a long-lived radioisotope is used to initiate an electron avalanche in the overlap region when bias is applied. The avalanche travels through the gas filled gap and activates a luminescent phosphor of a selected color. The bias is adjusted to give a proportional electron multiplication to control brightness for given pixel. 6 figs.

  5. Microgap flat panel display

    DOEpatents

    Wuest, Craig R.

    1998-01-01

    A microgap flat panel display which includes a thin gas-filled display tube that utilizes switched X-Y "pixel" strips to trigger electron avalanches and activate a phosphor at a given location on a display screen. The panel utilizes the principal of electron multiplication in a gas subjected to a high electric field to provide sufficient electron current to activate standard luminescent phosphors located on an anode. The X-Y conductive strips of a few micron widths may for example, be deposited on opposite sides of a thin insulating substrate, or on one side of the adjacent substrates and function as a cathode. The X-Y strips are separated from the anode by a gap filled with a suitable gas. Electrical bias is selectively switched onto X and Y strips to activate a "pixel" in the region where these strips overlap. A small amount of a long-lived radioisotope is used to initiate an electron avalanche in the overlap region when bias is applied. The avalanche travels through the gas filled gap and activates a luminescent phosphor of a selected color. The bias is adjusted to give a proportional electron multiplication to control brightness for given pixel.

  6. Hydrogen in amorphous silicon

    SciTech Connect

    Peercy, P. S.

    1980-01-01

    The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH/sub 1/) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon.

  7. Investigations of a flat-panel detector for quality assurance measurements in ion beam therapy

    NASA Astrophysics Data System (ADS)

    Hartmann, Bernadette; Telsemeyer, Julia; Huber, Lucas; Ackermann, Benjamin; Jäkel, Oliver; Martišíková, Mária

    2012-01-01

    Increased accuracy in radiation delivery to a patient provided by scanning particle beams leads to high demands on quality assurance (QA). To meet the requirements, an extensive quality assurance programme has been implemented at the Heidelberg Ion Beam Therapy Center. Currently, high-resolution radiographic films are used for beam spot position measurements and homogeneity measurements for scanned fields. However, given that using this film type is time and equipment demanding, considerations have been made to replace the radiographic films in QA by another appropriate device. In this study, the suitability of the flat-panel detector RID 256 L based on amorphous silicon was investigated as an alternative method. The currently used radiographic films were taken as a reference. Investigations were carried out for proton and carbon ion beams. The detectors were irradiated simultaneously to allow for a direct comparison. The beam parameters (e.g. energy, focus, position) currently used in the daily QA procedures were applied. Evaluation of the measurements was performed using newly implemented automatic routines. The results for the flat-panel detector were compared to the standard radiographic films. Additionally, a field with intentionally decreased homogeneity was applied to test the detector's sensitivities toward possible incorrect scan parameters. For the beam position analyses, the flat-panel detector results showed good agreement with radiographic films. For both detector types, deviations between measured and planned spot distances were found to be below 1% (1 mm). In homogeneously irradiated fields, the flat-panel detector showed a better dose response homogeneity than the currently used radiographic film. Furthermore, the flat-panel detector is sensitive to field irregularities. The flat-panel detector was found to be an adequate replacement for the radiographic film in QA measurements. In addition, it saves time and equipment because no post

  8. Amorphous silicon photovoltaic devices

    SciTech Connect

    Carlson, David E.; Lin, Guang H.; Ganguly, Gautam

    2004-08-31

    This invention is a photovoltaic device comprising an intrinsic or i-layer of amorphous silicon and where the photovoltaic device is more efficient at converting light energy to electric energy at high operating temperatures than at low operating temperatures. The photovoltaic devices of this invention are suitable for use in high temperature operating environments.

  9. Amorphous silicon radiation detectors

    DOEpatents

    Street, R.A.; Perez-Mendez, V.; Kaplan, S.N.

    1992-11-17

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification. 13 figs.

  10. Amorphous silicon radiation detectors

    DOEpatents

    Street, Robert A.; Perez-Mendez, Victor; Kaplan, Selig N.

    1992-01-01

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

  11. Flat panel planar optic display

    SciTech Connect

    Veligdan, J.T.

    1994-11-01

    A prototype 10 inch flat panel Planar Optic Display, (POD), screen has been constructed and tested. This display screen is comprised of hundreds of planar optic class sheets bonded together with a cladding layer between each sheet where each glass sheet represents a vertical line of resolution. The display is 9 inches wide by 5 inches high and approximately 1 inch thick. A 3 milliwatt HeNe laser is used as the illumination source and a vector scanning technique is employed.

  12. Amorphous Silicon: Flexible Backplane and Display Application

    NASA Astrophysics Data System (ADS)

    Sarma, Kalluri R.

    Advances in the science and technology of hydrogenated amorphous silicon (a-Si:H, also referred to as a-Si) and the associated devices including thin-film transistors (TFT) during the past three decades have had a profound impact on the development and commercialization of major applications such as thin-film solar cells, digital image scanners and X-ray imagers and active matrix liquid crystal displays (AMLCDs). Particularly, during approximately the past 15 years, a-Si TFT-based flat panel AMLCDs have been a huge commercial success. a-Si TFT-LCD has enabled the note book PCs, and is now rapidly replacing the venerable CRT in the desktop monitor and home TV applications. a-Si TFT-LCD is now the dominant technology in use for applications ranging from small displays such as in mobile phones to large displays such as in home TV, as well-specialized applications such as industrial and avionics displays.

  13. Flat-panel electronic displays: a triumph of physics, chemistry and engineering.

    PubMed

    Hilsum, Cyril

    2010-03-13

    This paper describes the history and science behind the development of modern flat-panel displays, and assesses future trends. Electronic displays are an important feature of modern life. For many years the cathode ray tube, an engineering marvel, was universal, but its shape was cumbersome and its operating voltage too high. The need for a flat-panel display, working at a low voltage, became imperative, and much research has been applied to this need. Any versatile flat-panel display will exploit an electro-optical effect, a transparent conductor and an addressing system to deliver data locally. The first need is to convert an electrical signal into a visible change. Two methods are available, the first giving emission of light, the second modulating ambient illumination. The most useful light-emitting media are semiconductors, historically exploiting III-V or II-VI compounds, but more recently organic or polymer semiconductors. Another possible effect uses gas plasma discharges. The modulating, or subtractive, effects that have been studied include liquid crystals, electrophoresis, electrowetting and electrochromism. A transparent conductor makes it possible to apply a voltage to an extended area while observing the results. The design is a compromise, since the free electrons that carry current also absorb light. The first materials used were metals, but some semiconductors, when heavily doped, give a better balance, with high transmission for a low resistance. Delivering data unambiguously to a million or so picture elements across the display area is no easy task. The preferred solution is an amorphous silicon thin-film transistor deposited at each cross-point in an X-Y matrix. Success in these endeavours has led to many applications for flat-panel displays, including television, flexible displays, electronic paper, electronic books and advertising signs. PMID:20123746

  14. Flat-panel electronic displays: a triumph of physics, chemistry and engineering

    PubMed Central

    Hilsum, Cyril

    2010-01-01

    This paper describes the history and science behind the development of modern flat-panel displays, and assesses future trends. Electronic displays are an important feature of modern life. For many years the cathode ray tube, an engineering marvel, was universal, but its shape was cumbersome and its operating voltage too high. The need for a flat-panel display, working at a low voltage, became imperative, and much research has been applied to this need. Any versatile flat-panel display will exploit an electro-optical effect, a transparent conductor and an addressing system to deliver data locally. The first need is to convert an electrical signal into a visible change. Two methods are available, the first giving emission of light, the second modulating ambient illumination. The most useful light-emitting media are semiconductors, historically exploiting III–V or II–VI compounds, but more recently organic or polymer semiconductors. Another possible effect uses gas plasma discharges. The modulating, or subtractive, effects that have been studied include liquid crystals, electrophoresis, electrowetting and electrochromism. A transparent conductor makes it possible to apply a voltage to an extended area while observing the results. The design is a compromise, since the free electrons that carry current also absorb light. The first materials used were metals, but some semiconductors, when heavily doped, give a better balance, with high transmission for a low resistance. Delivering data unambiguously to a million or so picture elements across the display area is no easy task. The preferred solution is an amorphous silicon thin-film transistor deposited at each cross-point in an X–Y matrix. Success in these endeavours has led to many applications for flat-panel displays, including television, flexible displays, electronic paper, electronic books and advertising signs. PMID:20123746

  15. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, R.A.; Mendez, V.P.; Kaplan, S.N.

    1988-11-15

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation. 15 figs.

  16. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, Robert A.; Mendez, Victor P.; Kaplan, Selig N.

    1988-01-01

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation.

  17. Compensated amorphous silicon solar cell

    DOEpatents

    Devaud, Genevieve

    1983-01-01

    An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon over said substrate and having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the electrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF.sub.3 doped intrinsic layer.

  18. Laser illuminated flat panel display

    SciTech Connect

    Veligdan, J.T.

    1995-12-31

    A 10 inch laser illuminated flat panel Planar Optic Display (POD) screen has been constructed and tested. This POD screen technology is an entirely new concept in display technology. Although the initial display is flat and made of glass, this technology lends itself to applications where a plastic display might be wrapped around the viewer. The display screen is comprised of hundreds of planar optical waveguides where each glass waveguide represents a vertical line of resolution. A black cladding layer, having a lower index of refraction, is placed between each waveguide layer. Since the cladding makes the screen surface black, the contrast is high. The prototype display is 9 inches wide by 5 inches high and approximately I inch thick. A 3 milliwatt HeNe laser is used as the illumination source and a vector scanning technique is employed.

  19. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B.

    1992-05-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for US products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon US government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United State, and by Germany in the last 2--3 years more than twice that of the US Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W{sub p} for plants with 10 MW/year capacities. 10 refs.

  20. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B. )

    1992-12-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for U.S. products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon U.S. government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United States, and by Germany in the last 2--3 years more than twice that of the U.S. Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W[sub [ital p

  1. Demonstration model circuit panel for silicon-on-insulator microelectronics and flat-panel 1994 LDRD final report 94-FS-041

    SciTech Connect

    McCarthy, A.

    1995-09-01

    Crystalline silicon wafers are frontside bonded to glass substrates. The silicon substrate is removed and thin films of silicon remain on the insulating substrates. The performance of devices formed in the thin films before bonding are compared with those after bonding.

  2. Plasma Deposition of Amorphous Silicon

    NASA Technical Reports Server (NTRS)

    Calcote, H. F.

    1982-01-01

    Strongly adhering films of silicon are deposited directly on such materials as Pyrex and Vycor (or equivalent materials) and aluminum by a non-equilibrium plasma jet. Amorphous silicon films are formed by decomposition of silicon tetrachloride or trichlorosilane in the plasma. Plasma-jet technique can also be used to deposit an adherent silicon film on aluminum from silane and to dope such films with phosphorus. Ability to deposit silicon films on such readily available, inexpensive substrates could eventually lead to lower cost photovoltaic cells.

  3. Flat panel ferroelectric electron emission display system

    DOEpatents

    Sampayan, S.E.; Orvis, W.J.; Caporaso, G.J.; Wieskamp, T.F.

    1996-04-16

    A device is disclosed which can produce a bright, raster scanned or non-raster scanned image from a flat panel. Unlike many flat panel technologies, this device does not require ambient light or auxiliary illumination for viewing the image. Rather, this device relies on electrons emitted from a ferroelectric emitter impinging on a phosphor. This device takes advantage of a new electron emitter technology which emits electrons with significant kinetic energy and beam current density. 6 figs.

  4. Flat panel ferroelectric electron emission display system

    DOEpatents

    Sampayan, Stephen E.; Orvis, William J.; Caporaso, George J.; Wieskamp, Ted F.

    1996-01-01

    A device which can produce a bright, raster scanned or non-raster scanned image from a flat panel. Unlike many flat panel technologies, this device does not require ambient light or auxiliary illumination for viewing the image. Rather, this device relies on electrons emitted from a ferroelectric emitter impinging on a phosphor. This device takes advantage of a new electron emitter technology which emits electrons with significant kinetic energy and beam current density.

  5. Tandem junction amorphous silicon solar cells

    DOEpatents

    Hanak, Joseph J.

    1981-01-01

    An amorphous silicon solar cell has an active body with two or a series of layers of hydrogenated amorphous silicon arranged in a tandem stacked configuration with one optical path and electrically interconnected by a tunnel junction. The layers of hydrogenated amorphous silicon arranged in tandem configuration can have the same bandgap or differing bandgaps.

  6. Low Scatter, High Kilovolt, A-Si Flat Panel X-Ray Detector

    NASA Astrophysics Data System (ADS)

    Smith, Peter D.; Claytor, Thomas N.; Berry, Phillip C.; Hills, Charles R.; Keating, Scott C.; Phillips, David H.; Setoodeh, Shariar

    2009-03-01

    We have been using amorphous silicon (a-Si) flat panel detectors in high energy (>400 kV) cone beam computed tomography (CT) applications for a number of years. We have found that these detectors have a significant amount of internal scatter that degrades the accuracy of attenuation images. The scatter errors cause cupping and streaking artifacts that are practically indistinguishable from beam hardening artifacts. Residual artifacts remain after beam hardening correction and over correction increases noise in CT reconstructions. Another important limitation of existing detectors is that they have a high failure rate, especially when operating at megavolt x-ray energies even with a well collimated beam. Due to the limitations of the current detectors, we decided to design a detector specifically for high energies that has significantly reduced scatter. In collaboration with IMTEC, we have built a prototype amorphous silicon flat panel detector that has both improved imaging response and increased lifetime. LANL's contribution is the "transparent panel concept" (patent pending), in which structures in the x-ray beam path are either eliminated or made as transparent to x-rays as practical (low atomic number and low areal density). This reduces scatter, makes attenuation measurements more accurate, improves the ability to make corrections for beam hardening, and increases signal to noise ratio in DR images and CT reconstructions. IMTEC's contribution is an improved shielding design that will increase the lifetime of the panel. Preliminary results showing the dramatic reduction in self scatter from the panel will be presented as well as the effect of this improvement on CT images.

  7. LOW SCATTER, HIGH KILOVOLT, A-SI FLAT PANEL X-RAY DETECTOR

    SciTech Connect

    Smith, Peter D.; Claytor, Thomas N.; Berry, Phillip C.; Hills, Charles R.; Keating, Scott C.; Phillips, David H.; Setoodeh, Shariar

    2009-03-03

    We have been using amorphous silicon (a-Si) flat panel detectors in high energy (>400 kV) cone beam computed tomography (CT) applications for a number of years. We have found that these detectors have a significant amount of internal scatter that degrades the accuracy of attenuation images. The scatter errors cause cupping and streaking artifacts that are practically indistinguishable from beam hardening artifacts. Residual artifacts remain after beam hardening correction and over correction increases noise in CT reconstructions. Another important limitation of existing detectors is that they have a high failure rate, especially when operating at megavolt x-ray energies even with a well collimated beam. Due to the limitations of the current detectors, we decided to design a detector specifically for high energies that has significantly reduced scatter. In collaboration with IMTEC, we have built a prototype amorphous silicon flat panel detector that has both improved imaging response and increased lifetime. LANL's contribution is the ''transparent panel concept''(patent pending), in which structures in the x-ray beam path are either eliminated or made as transparent to x-rays as practical (low atomic number and low areal density). This reduces scatter, makes attenuation measurements more accurate, improves the ability to make corrections for beam hardening, and increases signal to noise ratio in DR images and CT reconstructions. IMTEC's contribution is an improved shielding design that will increase the lifetime of the panel. Preliminary results showing the dramatic reduction in self scatter from the panel will be presented as well as the effect of this improvement on CT images.

  8. Flat panel displays in an underwater cockpit

    NASA Astrophysics Data System (ADS)

    Sola, Kenneth E.

    1999-08-01

    This paper reports on a highly unusual application of flat panel displays in a cockpit. The cockpit is found in a mini- submarine of the Advanced SEAL Delivery System (ASDS), a state-of-the-art military platform designed to deliver U.S. Navy SEALs, and other special forces, to their mission locations. For security reasons, the presentation details are intentionally kept minimal.

  9. Flat panels in future ground combat vehicles

    NASA Astrophysics Data System (ADS)

    Gurd, Eric D.; Forest, Coryne A.

    1996-05-01

    The efforts of the design team for the Crewman's Associate Advanced Technology Demonstration (CA ATD) and its use of advanced display concepts is discussed. This team has the responsibility of identifying future technologies with the potential for maximizing human- machine interaction for incorporation into future crew station designs for ground combat vehicles. The design process utilizes extensive user involvement in all stages. This is critical to developing systems that have complex functions, yet are simple to maintain and operate. Described are the needs which have driven the U.S. Army towards the use of flat panels. Ultimately, the army is looking at smaller, lighter, more deployable ground combat vehicles. This goal is driving individual components to have characteristics such as low weight, low power usage, and reduced volume while maintaining ruggedness and functionality. The potential applications for flat panels in ground vehicles is also discussed. The army is looking at applications for out-the-window views (virtual periscopes), multi-functional displays, and head mounted displays to accomplish its goals of designing better crew interfaces. The army's requirements in regards to the technologies that must be developed and supported by flat panel displays are also discussed in this section. In conclusion, future projections of the use of flat panels for the Crewman's Associate ATD will be outlined. Projections will be made in terms of physical numbers and promising technologies that fulfill the goals of the CAATD and achieve the approval of the user community.

  10. Exoelectron analysis of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Dekhtyar, Yu. D.; Vinyarskaya, Yu. A.

    1994-04-01

    The method based on registration of photothermostimulated exoelectron emission (PTSE) is used in the proposed new field of investigating the structural defects in amorphous silicon (a-Si). This method can be achieved if the sample under investigation is simultaneously heated and illuminated by ultraviolet light. The mechanism of PTSE from a-Si has been studied in the case of a hydrogenized amorphous silicon (a-Si:H) film grown by glow discharge method. The electronic properties and annealing of defects were analyzed in the study. It has been shown from the results that the PTSE from a-Si:H takes place as a prethreshold single-photon external photoeffect. The exoemission spectroscopy of a-Si:H was shown to be capable in the study of thermally and optically stimulated changes in the electronic structure of defects, their annealing, as well as diffusion of atomic particles, such as hydrogen.

  11. Advantages of using flat-panel LCD for projection displays

    NASA Astrophysics Data System (ADS)

    Wu, Dean C.

    1995-04-01

    came from silicon wafer processing, they are limited to small sizes as in Integrated Circuits. Polysilicon needs relative high temperature for active matrix processing. The usual non-alkali LCD glass substrates can not withstand such high temperature. As a result, polysilicon is also limited to small sizes. However, they can be used in Projection Displays with enlargement for comfort viewing. It is our hope some of these flat panel LCD technologies will be developed into the high end Projection Displays such as HIgh Definition Television, Multimedia or Interactive Video Communication, Entertainment and Presentation Systems of the future.

  12. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  13. Amorphous-silicon cell reliability testing

    NASA Technical Reports Server (NTRS)

    Lathrop, J. W.

    1985-01-01

    The work on reliability testing of solar cells is discussed. Results are given on initial temperature and humidity tests of amorphous silicon devices. Calibration and measurement procedures for amorphous and crystalline cells are given. Temperature stress levels are diagrammed.

  14. Amorphous silicon solar cell allowing infrared transmission

    DOEpatents

    Carlson, David E.

    1979-01-01

    An amorphous silicon solar cell with a layer of high index of refraction material or a series of layers having high and low indices of refraction material deposited upon a transparent substrate to reflect light of energies greater than the bandgap energy of the amorphous silicon back into the solar cell and transmit solar radiation having an energy less than the bandgap energy of the amorphous silicon.

  15. Studies of hydrogenated amorphous silicon

    SciTech Connect

    Bishop, S G; Carlos, W E

    1984-07-01

    This report discusses the results of probing the defect structure and bonding of hydrogenated amorphous silicon films using both nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The doping efficiency of boron in a-Si:H was found to be less than 1%, with 90% of the boron in a threefold coordinated state. On the other hand, phosphorus NMR chemical shift measurements yielded a ration of threefold to fourfold P sites of roughly 4 to 1. Various resonance lines were observed in heavily boron- and phosphorus-doped films and a-SiC:H alloys. These lines were attributed to band tail states on twofold coordinated silicon. In a-SiC:H films, a strong resonance was attributed to dangling bonds on carbon atoms. ESR measurements on low-pressure chemical-vapor-deposited (LPCVD) a-Si:H were performed on samples. The defect density in the bulk of the films was 10/sup 17//cc with a factor of 3 increase at the surface of the sample. The ESR spectrum of LPCVD-prepared films was not affected by prolonged exposure to strong light. Microcrystalline silicon samples were also examined. The phosphorus-doped films showed a strong signal from the crystalline material and no resonance from the amorphous matrix. This shows that phosphorus is incorporated in the crystals and is active as a dopant. No signal was recorded from the boron-doped films.

  16. Method of producing hydrogenated amorphous silicon film

    DOEpatents

    Wiesmann, Harold J.

    1980-01-01

    This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silane (SiH.sub.4) or other gases comprising H and Si, from a tungsten or carbon foil heated to a temperature of about 1400.degree.-1600.degree. C., in a vacuum of about 10.sup.-6 to 19.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseos mixture onto a substrate independent of and outside said source of thermal decomposition, to form hydrogenated amorphous silicon. The presence of an ammonia atmosphere in the vacuum chamber enhances the photoconductivity of the hydrogenated amorphous silicon film.

  17. Performance of advanced a-Si/CsI-based flat-panel x-ray detectors for mammography

    NASA Astrophysics Data System (ADS)

    Albagli, Douglas; Hudspeth, Heather; Possin, George E.; Lee, Ji Ung; Granfors, Paul R.; Giambattista, Brian W.

    2003-06-01

    The GE Senographe 2000D, the first full field digital mammography system based on amorphous Silicon (a-Si) flat panel arrays and a Cesium-Iodide (CsI) scintillator, has been in clinical use for several years. The purpose of this paper is to demonstrate and quantify improvements in the detective quantum efficiency (DQE) for both typical screening and ultra-low exposure levels for this technology platform. A new figure of merit, the electronic noise factor, is introduced to explicitly quantify the influence of the electronic noise, conversion factor, modulation transfer function (MTF), and pixel pitch towards the reduction of DQE at low exposure levels. Methods to improve the DQE through an optimization of both the flat panel design and the scintillator deposition process are discussed. The results show a substantial improvement in the DQE(f) at all frequencies and demonstrate the potential for DQE(0) to exceed 80%. The combination of high DQE at ultra low exposures and the inherent fast read-out capability makes this technology platform ideal for both current clinical procedures and advanced applications that may use multiple projections (tomosynthesis) or contrast media to enhance digital mammography.

  18. Design and image quality results from volumetric CT with a flat-panel imager

    NASA Astrophysics Data System (ADS)

    Ross, William; Basu, Samit; Edic, Peter M.; Johnson, Mark; Pfoh, Armin H.; Rao, Ramakrishna; Ren, Baorui

    2001-06-01

    Preliminary MTF and LCD results obtained on several volumetric computed tomography (VCT) systems, employing amorphous flat panel technology, are presented. Constructed around 20-cm x 20-cm, 200-mm pitch amorphous silicon x-ray detectors, the prototypes use standard vascular or CT x-ray sources. Data were obtained from closed-gantry, benchtop and C-arm-based topologies, over a full 360 degrees of rotation about the target object. The field of view of the devices is approximately 15 cm, with a magnification of 1.25-1.5, providing isotropic resolution at isocenter of 133-160 mm. Acquisitions have been reconstructed using the FDK algorithm, modified by motion corrections also developed by GE. Image quality data were obtained using both industry standard and custom resolution phantoms as targets. Scanner output is compared on a projection and reconstruction basis against analogous output from a dedicated simulation package, also developed at GE. Measured MTF performance is indicative of a significant advance in isotropic image resolution over commercially available systems. LCD results have been obtained, using industry standard phantoms, spanning a contrast range of 0.3-1%. Both MTF and LCD measurements agree with simulated data.

  19. Ultrasonic scanner for radial and flat panels

    NASA Technical Reports Server (NTRS)

    Spencer, R. L.; Hill, E. K. (Inventor)

    1973-01-01

    An ultrasonic scanning mechanism is described that scans panels of honeycomb construction or with welded seams. It incorporates a device which by simple adjustment is adapted to scan either a flat panel or a radial panel. The supporting structure takes the form of a pair of spaced rails. An immersion tank is positioned between the rails and below their level. A work holder is mounted in the tank and is adapted to hold the flat or radial panel. A traveling bridge is movable along the rails and a carriage is mounted on the bridge.

  20. Tests Of Amorphous-Silicon Photovoltaic Modules

    NASA Technical Reports Server (NTRS)

    Ross, Ronald G., Jr.

    1988-01-01

    Progress in identification of strengths and weaknesses of amorphous-silicon technology detailed. Report describes achievements in testing reliability of solar-power modules made of amorphous-silicon photovoltaic cells. Based on investigation of modules made by U.S. manufacturers. Modules subjected to field tests, to accelerated-aging tests in laboratory, and to standard sequence of qualification tests developed for modules of crystalline-silicon cells.

  1. Experimental verification of ion range calculation in a treatment planning system using a flat-panel detector

    NASA Astrophysics Data System (ADS)

    Telsemeyer, Julia; Ackermann, Benjamin; Ecker, Swantje; Jäkel, Oliver; Martišíková, Mária

    2014-07-01

    Heavy ion-beam therapy is a highly precise radiation therapy exploiting the characteristic interaction of ions with matter. The steep dose gradient of the Bragg curve allows the irradiation of targets with high-dose and a narrow dose penumbra around the target, in contrast to photon irradiation. This, however, makes heavy ion-beam therapy very sensitive to minor changes in the range calculation of the treatment planning system, as it has a direct influence on the outcome of the treatment. Our previous study has shown that ion radiography with an amorphous silicon flat-panel detector allows the measurement of the water equivalent thickness (WET) of an imaging object with good accuracy and high spatial resolution. In this study, the developed imaging technique is used to measure the WET distribution of a patient-like phantom, and these results are compared to the WET calculation of the treatment planning system. To do so, a measured two-dimensional map of the WET of an anthropomorphic phantom was compared to WET distributions based on x-ray computed tomography images as used in the treatment planning system. It was found that the WET maps agree well in the overall shape and two-dimensional distribution of WET values. Quantitatively, the ratio of the two-dimensional WET maps shows a mean of 1.004 with a standard deviation of 0.022. Differences were found to be concentrated at high WET gradients. This could be explained by the Bragg-peak degradation, which is measured in detail by ion radiography with the flat-panel detector, but is not taken into account in the treatment planning system. Excluding pixels exhibiting significant Bragg-peak degradation, the mean value of the ratio was found to be 1.000 with a standard deviation of 0.012. Employment of the amorphous silicon flat-panel detector for WET measurements allows us to detect uncertainties of the WET determination in the treatment planning process. This makes the investigated technique a very helpful tool to study

  2. ELECTROLUMINESCENT MATERIAL FOR FLAT PANEL DISPLAY

    SciTech Connect

    Smith, D.B.

    2000-11-13

    The purpose of this Cooperative Research and Development Agreement (CRADA) was to develop a new-generation electroluminescent (EL) material for flat panel displays and related applications by using unique and complementary research capabilities at Oak Ridge National Laboratory and OSRAM Sylvania, Inc. The goal was to produce an EL material with a luminance 10 times greater than conventional EL phosphors. An EL material with this increased luminance would have immediate applications for flat panel display devices (e.g., backlighting for liquid-crystal diodes) and for EL lamp technology. OSRAM Sylvania proposed that increased EL phosphor luminance could be obtained by creating composite EL materials capable of alignment under an applied electric field and capable of concentrating the applied electric field. Oak Ridge National Laboratory used pulsed laser deposition as a method for making these composite EL materials. The materials were evaluated for electroluminescence at laboratory facilities at OSRAM Sylvania, Inc. Many composite structures were thus made and evaluated, and it was observed that a composite structure based on alternating layers of a ferroelectric and a phosphor yielded electroluminescence. An enabling step that was not initially proposed but was conceived during the cooperative effort was found to be crucial to the success of the composite structure. The CRADA period expired before we were able to make quantitative measurements of the luminance and efficiency of the composite EL material. Future cooperative work, outside the scope of the CRADA, will focus on making these measurements and will result in the production of a prototype composite EL device.

  3. Electron tunnelling into amorphous germanium and silicon.

    NASA Technical Reports Server (NTRS)

    Smith, C. W.; Clark, A. H.

    1972-01-01

    Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

  4. Amorphous silicon-tellurium alloys

    NASA Astrophysics Data System (ADS)

    Shufflebotham, P. K.; Card, H. C.; Kao, K. C.; Thanailakis, A.

    1986-09-01

    Amorphous silicon-tellurium alloy thin films were fabricated by coevaporation over the composition range of 0-82 at. % Te. The electronic and optical properties of these films were systematically investigated over this same range of composition. The optical gap of these films was found to decrease monotonically with increasing Te content. Conduction near room temperature was due to extended state conduction, while variable range hopping dominated below 250 K. The incorporation of Te in concentrations of less than 1 at. % was found to produce an increase in the density of localized states at the Fermi level and a decrease in the activation energy. This was attributed to the Te being incorporated as a substitutional, fourfold coordinated, double donor in a-Si. At approximately 60 at. % Te, a decrease in the density of localized states at the Fermi level, and an increase in the activation energy and photoresponse was indicated. This was attributed to the possible formation of a less defective a-Si:Te compound.

  5. Solid-state, flat-panel, digital radiography detectors and their physical imaging characteristics.

    PubMed

    Cowen, A R; Kengyelics, S M; Davies, A G

    2008-05-01

    Solid-state, digital radiography (DR) detectors, designed specifically for standard projection radiography, emerged just before the turn of the millennium. This new generation of digital image detector comprises a thin layer of x-ray absorptive material combined with an electronic active matrix array fabricated in a thin film of hydrogenated amorphous silicon (a-Si:H). DR detectors can offer both efficient (low-dose) x-ray image acquisition plus on-line readout of the latent image as electronic data. To date, solid-state, flat-panel, DR detectors have come in two principal designs, the indirect-conversion (x-ray scintillator-based) and the direct-conversion (x-ray photoconductor-based) types. This review describes the underlying principles and enabling technologies exploited by these designs of detector, and evaluates their physical imaging characteristics, comparing performance both against each other and computed radiography (CR). In standard projection radiography indirect conversion DR detectors currently offer superior physical image quality and dose efficiency compared with direct conversion DR and modern point-scan CR. These conclusions have been confirmed in the findings of clinical evaluations of DR detectors. Future trends in solid-state DR detector technologies are also briefly considered. Salient innovations include WiFi-enabled, portable DR detectors, improvements in x-ray absorber layers and developments in alternative electronic media to a-Si:H. PMID:18374710

  6. Atomic-scale disproportionation in amorphous silicon monoxide.

    PubMed

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material. PMID:27172815

  7. Atomic-scale disproportionation in amorphous silicon monoxide

    PubMed Central

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material. PMID:27172815

  8. Atomic-scale disproportionation in amorphous silicon monoxide

    NASA Astrophysics Data System (ADS)

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-05-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

  9. Cooling of hot electrons in amorphous silicon

    SciTech Connect

    Vanderhaghen, R.; Hulin, D.; Cuzeau, S.; White, J.O.

    1997-07-01

    Measurements of the cooling rate of hot carriers in amorphous silicon are made with a two-pump, one-probe technique. The experiment is simulated with a rate-equation model describing the energy transfer between a population of hot carriers and the lattice. An energy transfer rate proportional to the temperature difference is found to be consistent with the experimental data while an energy transfer independent of the temperature difference is not. This contrasts with the situation in crystalline silicon. The measured cooling rates are sufficient to explain the difficulty in observing avalanche effects in amorphous silicon.

  10. Amorphous silicon detectors in positron emission tomography

    SciTech Connect

    Conti, M. Lawrence Berkeley Lab., CA ); Perez-Mendez, V. )

    1989-12-01

    The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters {epsilon}{sup 2}{tau}'s are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs.

  11. Design and performance characteristics of a digital flat-panel computed tomography system

    SciTech Connect

    Ross, William; Cody, Dianna D.; Hazle, John D.

    2006-06-15

    Computed tomography (CT) applications continue to expand, and they require faster data acquisition speeds and improved spatial resolution. Achieving isotropic resolution, by means of cubic voxels, in combination with longitudinal coverage beyond 20 mm would represent a substantial advance in clinical CT because few commercially available scanners are capable of this at present. To achieve this goal, a prototype CT system incorporating a movable array of 20 cmx20 cm, 200-{mu}m-pitch amorphous silicon flat-panel x-ray detectors and a conventional CT x-ray source was constructed at the General Electric Global Research Center and performance tested at The University of Texas M. D. Anderson Cancer Center. The device was designed for preclinical imaging applications and has a scan field of 13 to 33 cm, with a magnification of 1.5. Image quality performance measurements, such as spatial and contrast resolutions, were obtained using both industry standard and custom phantoms. Spatial resolution, quantified by the system's modulation transfer function, indicated improvement by a factor of 2.5 to 5 in isotropic spatial resolution over current commercially available systems, with 10% modulation transfer function modulations at frequencies from 19 to 31 lp/cm. Low-contrast detectability results were obtained from industry-standard phantoms and were comprised of embedded contrast regions of 0.3%, 0.5%, and 1.0% over areas of several mm{sup 2}. Performance was sufficient to easily distinguish 1.0% contrast regions down to 2 mm in diameter relative to the background. On the basis of scans of specialized hydroxyapatite phantoms, the system response is extremely linear (R{sup 2}=0.990) in bone-equivalent density regimens. Standard CT dose index CTDI{sub 100} and CTDI{sub W} measurements were also conducted to assess dose delivery using a 16-cm-CTDI phantom and a 120 kV 120 mAs scan technique. The CTDI{sub W} ranged from 30 mGy (one-panel mode) to 113 mGy (two-panel mode) for this

  12. Design and performance characteristics of a digital flat-panel computed tomography system.

    PubMed

    Ross, William; Cody, Dianna D; Hazle, John D

    2006-06-01

    Computed tomography (CT) applications continue to expand, and they require faster data acquisition speeds and improved spatial resolution. Achieving isotropic resolution, by means of cubic voxels, in combination with longitudinal coverage beyond 20 mm would represent a substantial advance in clinical CT because few commercially available scanners are capable of this at present. To achieve this goal, a prototype CT system incorporating a movable array of 20 cm X 20 cm, 200-microm-pitch amorphous silicon flat-panel x-ray detectors and a conventional CT x-ray source was constructed at the General Electric Global Research Center and performance tested at The University of Texas M. D. Anderson Cancer Center. The device was designed for preclinical imaging applications and has a scan field of 13 to 33 cm, with a magnification of 1.5. Image quality performance measurements, such as spatial and contrast resolutions, were obtained using both industry standard and custom phantoms. Spatial resolution, quantified by the system's modulation transfer function, indicated improvement by a factor of 2.5 to 5 in isotropic spatial resolution over current commercially available systems, with 10% modulation transfer function modulations at frequencies from 19 to 31 lp/cm. Low-contrast detectability results were obtained from industry-standard phantoms and were comprised of embedded contrast regions of 0.3%, 0.5%, and 1.0% over areas of several mm2. Performance was sufficient to easily distinguish 1.0% contrast regions down to 2 mm in diameter relative to the background. On the basis of scans of specialized hydroxyapatite phantoms, the system response is extremely linear (R2=0.990) in bone-equivalent density regimens. Standard CT dose index CTDI100 and CTDIw measurements were also conducted to assess dose delivery using a 16-cm-CTDI phantom and a 120 kV 120 mAs scan technique. The CTDIw ranged from 30 mGy (one-panel mode) to 113 mGy (two-panel mode) for this system. Lastly, several in

  13. Amorphous Silicon Based Neutron Detector

    SciTech Connect

    Xu, Liwei

    2004-12-12

    Various large-scale neutron sources already build or to be constructed, are important for materials research and life science research. For all these neutron sources, neutron detectors are very important aspect. However, there is a lack of a high-performance and low-cost neutron beam monitor that provides time and temporal resolution. The objective of this SBIR Phase I research, collaboratively performed by Midwest Optoelectronics, LLC (MWOE), the University of Toledo (UT) and Oak Ridge National Laboratory (ORNL), is to demonstrate the feasibility for amorphous silicon based neutron beam monitors that are pixilated, reliable, durable, fully packaged, and fabricated with high yield using low-cost method. During the Phase I effort, work as been focused in the following areas: 1) Deposition of high quality, low-defect-density, low-stress a-Si films using very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) at high deposition rate and with low device shunting; 2) Fabrication of Si/SiO2/metal/p/i/n/metal/n/i/p/metal/SiO2/ device for the detection of alpha particles which are daughter particles of neutrons through appropriate nuclear reactions; and 3) Testing of various devices fabricated for alpha and neutron detection; As the main results: · High quality, low-defect-density, low-stress a-Si films have been successfully deposited using VHF PECVD on various low-cost substrates; · Various single-junction and double junction detector devices have been fabricated; · The detector devices fabricated have been systematically tested and analyzed. · Some of the fabricated devices are found to successfully detect alpha particles. Further research is required to bring this Phase I work beyond the feasibility demonstration toward the final prototype devices. The success of this project will lead to a high-performance, low-cost, X-Y pixilated neutron beam monitor that could be used in all of the neutron facilities worldwide. In addition, the technologies

  14. Transverse and longitudinal vibrations in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Beltukov, Y. M.; Fusco, C.; Tanguy, A.; Parshin, D. A.

    2015-12-01

    We show that harmonic vibrations in amorphous silicon can be decomposed to transverse and longitudinal components in all frequency range even in the absence of the well defined wave vector q. For this purpose we define the transverse component of the eigenvector with given ω as a component, which does not change the volumes of Voronoi cells around atoms. The longitudinal component is the remaining orthogonal component. We have found the longitudinal and transverse components of the vibrational density of states for numerical model of amorphous silicon. The vibrations are mostly transverse below 7 THz and above 15 THz. In the frequency interval in between the vibrations have a longitudinal nature. Just this sudden transformation of vibrations at 7 THz from almost transverse to almost longitudinal ones explains the prominent peak in the diffusivity of the amorphous silicon just above 7 THz.

  15. Neutron irradiation induced amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Hay, J.C.

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  16. Structural relaxation of amorphous silicon carbide.

    PubMed

    Ishimaru, Manabu; Bae, In-Tae; Hirotsu, Yoshihiko; Matsumura, Syo; Sickafus, Kurt E

    2002-07-29

    We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions. PMID:12144449

  17. Inverted amorphous silicon solar cell utilizing cermet layers

    DOEpatents

    Hanak, Joseph J.

    1979-01-01

    An amorphous silicon solar cell incorporating a transparent high work function metal cermet incident to solar radiation and a thick film cermet contacting the amorphous silicon opposite to said incident surface.

  18. Amorphous metallic films in silicon metallization systems

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.; Kattelus, H.; So, F.

    1984-01-01

    The general objective was to determine the potential of amorphous metallic thin films as a means of improving the stability of metallic contacts to a silicon substrate. The specific objective pursued was to determine the role of nitrogen in the formation and the resulting properties of amorphous thin-film diffusion barriers. Amorphous metallic films are attractive as diffusion barriers because of the low atomic diffusivity in these materials. Previous investigations revealed that in meeting this condition alone, good diffusion barriers are not necessarily obtained, because amorphous films can react with an adjacent medium (e.g., Si, Al) before they recrystallize. In the case of a silicon single-crystalline substrate, correlation exists between the temperature at which an amorphous metallic binary thin film reacts and the temperatures at which the films made of the same two metallic elements react individually. Amorphous binary films made of Zr and W were investigated. Both react with Si individually only at elevated temperatures. It was confirmed that such films react with Si only above 700 C when annealed in vacuum for 30 min. Amorphous W-N films were also investigated. They are more stable as barriers between Al and Si than polycrystalline W. Nitrogen effectively prevents the W-Al reaction that sets in at 500 C with polycrystalline W.

  19. New Amorphous Silicon Alloy Systems

    NASA Astrophysics Data System (ADS)

    Kapur, Mridula N.

    1990-01-01

    The properties of hydrogenated amorphous silicon (a-Si:H) have been modified by alloying with Al, Ga and S respectively. The Al and Ga alloys are in effect quaternary alloys as they were fabricated in a carbon-rich discharge. The alloys were prepared by the plasma assisted chemical vapor deposition (PACVD) method. This method has several advantages, the major one being the relatively low defect densities of the resulting materials. The PACVD system used to grow the alloy films was designed and constructed in the laboratory. It was first tested with known (a-Si:H and a-Si:As:H) materials. Thus, it was established that device quality alloy films could be grown with the home-made PACVD setup. The chemical composition of the alloys was characterized by secondary ion mass spectrometry (SIMS), and electron probe microanalysis (EPMA). The homogeneous nature of hydrogen distribution in the alloys was established by SIMS depth profile analysis. A quantitative analysis of the bulk elemental content was carried out by EPMA. The analysis indicated that the alloying element was incorporated in the films more efficiently at low input gas concentrations than at the higher concentrations. A topological model was proposed to explain the observed behavior. The optical energy gap of the alloys could be varied in the 0.90 to 1.92 eV range. The Al and Ga alloys were low band gap materials, whereas alloying with S had the effect of widening the energy gap. It was observed that although the Si-Al and Si-Ga alloys contained significant amounts of C and H, the magnitude of the energy gap was determined by the metallic component. The various trends in optical properties could be related to the binding characteristics of the respective alloy systems. A quantitative explanation of the results was provided by White's tight binding model. The dark conductivity-temperature dependence of the alloys was examined. A linear dependence was observed for the Al and Ga systems. Electronic conduction in

  20. [Flat Panel Detector Philips introduced and its system direction].

    PubMed

    Yamada, Shinichi

    2002-01-01

    We introduced digital X-ray diagnostic systems with Flat panel detector both in general X-ray systems and in Angiography systems. Our introduced Flat Panel Detector has the latest technology and has Cesium Iodide (CsI) that absorbs X-ray energy and generates visible light. Detected light signals make digital X-ray images. CsI is the most important material because its absorption rate of X-ray influences the strength of output digital signal. The purpose in this paper is checking that is latest Flat Panel Detector pulls out enough capability CsI has. Especially the thickness of CsI relates to X-ray absorption. X-ray absorption rate depended on the thickness of CsI was calculated by using simulated X-ray model and the future direction of Flat Panel Detector system was discussed. PMID:12766268

  1. Metal electrode for amorphous silicon solar cells

    DOEpatents

    Williams, Richard

    1983-01-01

    An amorphous silicon solar cell having an N-type region wherein the contact to the N-type region is composed of a material having a work function of about 3.7 electron volts or less. Suitable materials include strontium, barium and magnesium and rare earth metals such as gadolinium and yttrium.

  2. Fabricating amorphous silicon solar cells by varying the temperature _of the substrate during deposition of the amorphous silicon layer

    DOEpatents

    Carlson, David E.

    1982-01-01

    An improved process for fabricating amorphous silicon solar cells in which the temperature of the substrate is varied during the deposition of the amorphous silicon layer is described. Solar cells manufactured in accordance with this process are shown to have increased efficiencies and fill factors when compared to solar cells manufactured with a constant substrate temperature during deposition of the amorphous silicon layer.

  3. Amorphization of Silicon Carbide by Carbon Displacement

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.

    2004-05-10

    We have used molecular dynamics simulations to examine the possibility of amorphizing silicon carbide (SiC) by exclusively displacing C atoms. At a defect generation corresponding to 0.2 displacements per atom, the enthalpy surpasses the level of melt-quenched SiC, the density decreases by about 15%, and the radial distribution function shows a lack of long-range order. Prior to amorphization, the surviving defects are mainly C Frenkel pairs (67%), but Si Frenkel pairs (18%) and anti-site defects (15%) are also present. The results indicate that SiC can be amorphized by C sublattice displacements. Chemical short-range disorder, arising mainly from interstitial production, plays a significant role in the amorphization.

  4. Crystalline to amorphous transformation in silicon

    SciTech Connect

    Cheruvu, S.M.

    1982-09-01

    In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic implanted silicon using high resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high energy electron irradiation experiments at 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.

  5. Thermal and Cold Neutron Computed Tomography at the Los Alamos Neutron Scattering Center Using an Amorphous Silicon Detector Array

    SciTech Connect

    Claytor, T.N.; Schwab, M.J.; Farnum, E.H.; McDonald, T.E.; Summa, D.A.; Sheats, M.J.; Stupin, D.M.; Sievers, W.L.

    1998-07-19

    The use of the EG and G-Heimann RTM 128 or dpiX FS20 amorphous silicon (a-Si) detector array for thermal neutron radiography/computed tomography has proven to be a quick and efficient means of producing high quality digital radiographic images. The resolution, although not as good as film, is about 750 pm with the RTM and 127 pm with the dpiX array with a dynamic range in excess of 2,800. In many respects using an amorphous silicon detector is an improvement over other techniques such as imaging with a CCD camera, using a storage phosphor plate or film radiography. Unlike a CCD camera, which is highly susceptible to radiation damage, a-Si detectors can be placed in the beam directly behind the object under examination and do not require any special optics or turning mirrors. The amorphous silicon detector also allows enough data to be acquired to construct a digital image in just a few seconds (minimum gate time 40 ms) whereas film or storage plate exposures can take many minutes and then need to be digitized with a scanner. The flat panel can therefore acquire a complete 3D computed tomography data set in just a few tens of minutes. While a-Si detectors have been proposed for use in imaging neutron beams, this is the first reported implementation of such a detector for neutron imaging.

  6. Ion bombardment and disorder in amorphous silicon

    SciTech Connect

    Sidhu, L.S.; Gaspari, F.; Zukotynski, S.

    1997-07-01

    The effect of ion bombardment during growth on the structural and optical properties of amorphous silicon are presented. Two series of films were deposited under electrically grounded and positively biased substrate conditions. The biased samples displayed lower growth rates and increased hydrogen content relative to grounded counterparts. The film structure was examined using Raman spectroscopy. The transverse optic like phonon band position was used as a parameter to characterize network order. Biased samples displayed an increased order of the amorphous network relative to grounded samples. Furthermore, biased samples exhibited a larger optical gap. These results are correlated and attributed to reduced ion bombardment effects.

  7. Three-dimensional IMRT verification with a flat-panel EPID.

    PubMed

    Steciw, S; Warkentin, B; Rathee, S; Fallone, B G

    2005-02-01

    A three-dimensional (3D) intensity-modulated radiotherapy (IMRT) pretreatment verification procedure has been developed based on the measurement of two-dimensional (2D) primary fluence profiles using an amorphous silicon flat-panel electronic portal imaging device (EPID). As described in our previous work, fluence profiles are extracted from EPID images by deconvolution with kernels that represent signal spread in the EPID due to radiation and optical scattering. The deconvolution kernels are derived using Monte Carlo simulations of dose deposition in the EPID and empirical fitting methods, for both 6 and 15 MV photon energies. In our new 3D verification technique, 2D fluence modulation profiles for each IMRT field in a treatment are used as input to a treatment planning system (TPS), which then generates 3D doses. Verification is accomplished by comparing this new EPID-based 3D dose distribution to the planned dose distribution calculated by the TPS. Thermoluminescent dosimeter (TLD) point dose measurements for an IMRT treatment of an anthropomorphic phantom were in good agreement with the EPID-based 3D doses; in contrast, the planned dose under-predicts the TLD measurement in a high-gradient region by approximately 16%. Similarly, large discrepancies between EPID-based and TPS doses were also evident in dose profiles of small fields incident on a water phantom. These results suggest that our 3D EPID-based method is effective in quantifying relevant uncertainties in the dose calculations of our TPS for IMRT treatments. For three clinical head and neck cancer IMRT treatment plans, our TPS was found to underestimate the mean EPID-based doses in the critical structures of the spinal cord and the parotids by approximately 4 Gy (11%-14%). According to radiobiological modeling calculations that were performed, such underestimates can potentially lead to clinically significant underpredictions of normal tissue complication rates. PMID:15789607

  8. Image quality assessment of a pre-clinical flat-panel volumetric micro-CT scanner

    NASA Astrophysics Data System (ADS)

    Du, Louise Y.; Lee, Ting-Yim; Holdsworth, David W.

    2006-03-01

    Small animal imaging has recently become an area of increased interest because more human diseases can be modeled in transgenic and knockout rodents. Current micro-CT systems are capable of achieving spatial resolution on the order of 10 μm, giving highly detailed anatomical information. However, the speed of data acquisition of these systems is relatively slow, when compared with clinical CT systems. Dynamic CT perfusion imaging has proven to be a powerful tool clinically in detecting and diagnosing cancer, stroke, pulmonary and ischemic heart diseases. In order to perform this technique in mice and rats, quantitative CT images must be acquired at a rate of at least 1 Hz. Recently, a research pre-clinical CT scanner (eXplore Ultra, GE Healthcare) has been designed specifically for dynamic perfusion imaging in small animals. Using an amorphous silicon flat-panel detector and a clinical slip-ring gantry, this system is capable of acquiring volumetric image data at a rate of 1 Hz, with in-plane resolution of 150 μm, while covering the entire thoracic region of a mouse or whole organs of a rat. The purpose of this study was to evaluate the principal imaging performance of the micro-CT system, in terms of spatial resolution, image uniformity, linearity, dose and voxel noise for the feasibility of imaging mice and rats. Our investigations show that 3D images can be obtained with a limiting spatial resolution of 2.7 line pairs per mm and noise of 42 HU, using an acquisition interval of 8 seconds at an entrance dose of 6.4 cGy.

  9. The use of modern electronic flat panel devices for image guided radiation therapy:. Image quality comparison, intra fraction motion monitoring and quality assurance applications

    NASA Astrophysics Data System (ADS)

    Nill, S.; Stützel, J.; Häring, P.; Oelfke, U.

    2008-06-01

    With modern radiotherapy delivery techniques like intensity modulated radiotherapy (IMRT) it is possible to delivery a more conformal dose distribution to the tumor while better sparing the organs at risk (OAR) compared to 3D conventional radiation therapy. Due to the theoretically high dose conformity achievable it is very important to know the exact position of the target volume during the treatment. With more and more modern linear accelerators equipped with imaging devices this is now almost possible. These imaging devices are using energies between 120kV and 6MV and therefore different detector systems are used but the vast majority is using amorphous silicon flat panel devices with different scintilator screens and build up materials. The technical details and the image quality of these systems are discussed and first results of the comparison are presented. In addition new methods to deal with motion management and quality assurance procedures are shortly discussed.

  10. Investigations on silicon/amorphous-carbon and silicon/nanocrystalline palladium/ amorphous-carbon interfaces.

    PubMed

    Roy, M; Sengupta, P; Tyagi, A K; Kale, G B

    2008-08-01

    Our previous work revealed that significant enhancement in sp3-carbon content of amorphous carbon films could be achieved when grown on nanocrystalline palladium interlayer as compared to those grown on bare silicon substrates. To find out why, the nature of interface formed in both the cases has been investigated using Electron Probe Micro Analysis (EPMA) technique. It has been found that a reactive interface in the form of silicon carbide and/silicon oxy-carbide is formed at the interface of silicon/amorphous-carbon films, while palladium remains primarily in its native form at the interface of nanocrystalline palladium/amorphous-carbon films. However, there can be traces of dissolved oxygen within the metallic layer as well. The study has been corroborated further from X-ray photoelectron spectroscopic studies. PMID:19049221

  11. Deuterium in crystalline and amorphous silicon

    SciTech Connect

    Borzi, R.; Ma, H.; Fedders, P.A.; Leopold, D.J.; Norberg, R.E.; Boyce, J.B.; Johnson, N.M.; Ready, S.E.; Walker, J.

    1997-07-01

    The authors report deuteron magnetic resonance (DMR) measurements on aged deuterium-implanted single crystal n-type silicon and comparisons with amorphous silicon spectra. The sample film was prepared six years ago by deuteration from a-D{sub 2} plasma and evaluated by a variety of experimental methods. Deuterium has been evolving with time and the present DMR signal shows a smaller deuteron population. A doublet from Si-D configurations along (111) has decreased more than have central molecular DMR components, which include 47 and 12 kHz FWHM gaussians. Transient DMR magnetization recoveries indicate spin lattice relaxation to para-D{sub 2} relaxation centers.

  12. Mechanism for hydrogen diffusion in amorphous silicon

    SciTech Connect

    Biswas, R.; Li, Q.; Pan, B.C.; Yoon, Y.

    1998-01-01

    Tight-binding molecular-dynamics calculations reveal a mechanism for hydrogen diffusion in hydrogenated amorphous silicon. Hydrogen diffuses through the network by successively bonding with nearby silicons and breaking their Si{endash}Si bonds. The diffusing hydrogen carries with it a newly created dangling bond. These intermediate transporting states are densely populated in the network, have lower energies than H at the center of stretched Si{endash}Si bonds, and can play a crucial role in hydrogen diffusion. {copyright} {ital 1998} {ital The American Physical Society}

  13. Self-Diffusion in Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-01

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on 29Si/natSi heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and 700 °C with an activation energy of (4.4 ±0.3 ) eV . In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about 700 °C , which can be interpreted as the consequence of a high diffusion entropy.

  14. Self-Diffusion in Amorphous Silicon.

    PubMed

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-15

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on ^{29}Si/^{nat}Si heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and 700 °C with an activation energy of (4.4±0.3)  eV. In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about 700 °C, which can be interpreted as the consequence of a high diffusion entropy. PMID:26824552

  15. Dynamical models of hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Mousseau, Normand; Lewis, Laurent J.

    1991-04-01

    The results of our molecular-dynamics simulation of bulk hydrogenated amorphous silicon using empirical potentials are presented. More specifically, we discuss a dynamical procedure for incorporating hydrogen into a pure amorphous silicon matrix, which is derived from the concept of floating bonds put forward by Pantelides [Phys. Rev. Lett. 57, 2979 (1986)]. The structures resulting from this model are compared with those obtained with use of a static approach recently developed by us. This method exhibits considerable improvement over the previous one and, in particular, unambiguously reveals the strain-relieving role of hydrogen. While the former model leads to substantial overcoordination, the present one results in almost perfect tetrahedral bonding, with an average coordination number Z=4.03, the lowest value ever achieved using a Stillinger-Weber potential. The simulations are also used to calculate the vibrational densities of states, which are found to be in good accord with corresponding neutron-scattering measurements.

  16. Amorphous metallic films in silicon metallization systems

    NASA Technical Reports Server (NTRS)

    So, F.; Kolawa, E.; Nicolet, M. A.

    1985-01-01

    Diffusion barrier research was focussed on lowering the chemical reactivity of amorphous thin films on silicon. An additional area of concern is the reaction with metal overlays such as aluminum, silver, and gold. Gold was included to allow for technology transfer to gallium arsenide PV cells. Amorphous tungsten nitride films have shown much promise. Stability to annealing temperatures of 700, 800, and 550 C were achieved for overlays of silver, gold, and aluminum, respectively. The lower results for aluminum were not surprising because there is an eutectic that can form at a lower temperature. It seems that titanium and zirconium will remove the nitrogen from a tungsten nitride amorphous film and render it unstable. Other variables of research interest were substrate bias and base pressure during sputtering.

  17. High resolution amorphous silicon radiation detectors

    DOEpatents

    Street, R.A.; Kaplan, S.N.; Perez-Mendez, V.

    1992-05-26

    A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n-type, intrinsic, p-type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography. 18 figs.

  18. High resolution amorphous silicon radiation detectors

    DOEpatents

    Street, Robert A.; Kaplan, Selig N.; Perez-Mendez, Victor

    1992-01-01

    A radiation detector employing amorphous Si:H cells in an array with each detector cell having at least three contiguous layers (n type, intrinsic, p type), positioned between two electrodes to which a bias voltage is applied. An energy conversion layer atop the silicon cells intercepts incident radiation and converts radiation energy to light energy of a wavelength to which the silicon cells are responsive. A read-out device, positioned proximate to each detector element in an array allows each such element to be interrogated independently to determine whether radiation has been detected in that cell. The energy conversion material may be a layer of luminescent material having a columnar structure. In one embodiment a column of luminescent material detects the passage therethrough of radiation to be detected and directs a light beam signal to an adjacent a-Si:H film so that detection may be confined to one or more such cells in the array. One or both electrodes may have a comb structure, and the teeth of each electrode comb may be interdigitated for capacitance reduction. The amorphous Si:H film may be replaced by an amorphous Si:Ge:H film in which up to 40 percent of the amorphous material is Ge. Two dimensional arrays may be used in X-ray imaging, CT scanning, crystallography, high energy physics beam tracking, nuclear medicine cameras and autoradiography.

  19. 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.

  20. Amorphous molybdenum silicon superconducting thin films

    SciTech Connect

    Bosworth, D. Sahonta, S.-L.; Barber, Z. H.; Hadfield, R. H.

    2015-08-15

    Amorphous superconductors have become attractive candidate materials for superconducting nanowire single-photon detectors due to their ease of growth, homogeneity and competitive superconducting properties. To date the majority of devices have been fabricated using W{sub x}Si{sub 1−x}, though other amorphous superconductors such as molybdenum silicide (Mo{sub x}Si{sub 1−x}) offer increased transition temperature. This study focuses on the properties of MoSi thin films grown by magnetron sputtering. We examine how the composition and growth conditions affect film properties. For 100 nm film thickness, we report that the superconducting transition temperature (Tc) reaches a maximum of 7.6 K at a composition of Mo{sub 83}Si{sub 17}. The transition temperature and amorphous character can be improved by cooling of the substrate during growth which inhibits formation of a crystalline phase. X-ray diffraction and transmission electron microscopy studies confirm the absence of long range order. We observe that for a range of 6 common substrates (silicon, thermally oxidized silicon, R- and C-plane sapphire, x-plane lithium niobate and quartz), there is no variation in superconducting transition temperature, making MoSi an excellent candidate material for SNSPDs.

  1. Three dimensional amorphous silicon/microcrystalline silicon solar cells

    DOEpatents

    Kaschmitter, James L.

    1996-01-01

    Three dimensional deep contact amorphous silicon/microcrystalline silicon (a-Si/.mu.c-Si) solar cells which use deep (high aspect ratio) p and n contacts to create high electric fields within the carrier collection volume material of the cell. The deep contacts are fabricated using repetitive pulsed laser doping so as to create the high aspect p and n contacts. By the provision of the deep contacts which penetrate the electric field deep into the material where the high strength of the field can collect many of the carriers, thereby resulting in a high efficiency solar cell.

  2. Three dimensional amorphous silicon/microcrystalline silicon solar cells

    DOEpatents

    Kaschmitter, J.L.

    1996-07-23

    Three dimensional deep contact amorphous silicon/microcrystalline silicon (a-Si/{micro}c-Si) solar cells are disclosed which use deep (high aspect ratio) p and n contacts to create high electric fields within the carrier collection volume material of the cell. The deep contacts are fabricated using repetitive pulsed laser doping so as to create the high aspect p and n contacts. By the provision of the deep contacts which penetrate the electric field deep into the material where the high strength of the field can collect many of the carriers, thereby resulting in a high efficiency solar cell. 4 figs.

  3. Flat panel display development activities at Sandia National Laboratories

    SciTech Connect

    DiBello, E.G.; Worobey, W.; Burchett, S.; Hareland, W.; Felter, T.; Mays, B.

    1994-12-31

    The flat panel display development activities underway at Sandia National Laboratories are described. Research is being conducted in the areas of glass substrates, phosphors, large area processes, and electron emissions. Projects are focused on improving process yield, developing large area processes, and using modeling techniques to predict design performance.

  4. Development of CT and 3D-CT Using Flat Panel Detector Based Real-Time Digital Radiography System

    SciTech Connect

    Ravindran, V. R.; Sreelakshmi, C.; Vibin

    2008-09-26

    The application of Digital Radiography in the Nondestructive Evaluation (NDE) of space vehicle components is a recent development in India. A Real-time DR system based on amorphous silicon Flat Panel Detector has been developed for the NDE of solid rocket motors at Rocket Propellant Plant of VSSC in a few years back. The technique has been successfully established for the nondestructive evaluation of solid rocket motors. The DR images recorded for a few solid rocket specimens are presented in the paper. The Real-time DR system is capable of generating sufficient digital X-ray image data with object rotation for the CT image reconstruction. In this paper the indigenous development of CT imaging based on the Realtime DR system for solid rocket motor is presented. Studies are also carried out to generate 3D-CT image from a set of adjacent CT images of the rocket motor. The capability of revealing the spatial location and characterisation of defect is demonstrated by the CT and 3D-CT images generated.

  5. Performance of a novel 43-cm x 43-cm flat-panel detector with CsI:Tl scintillator

    NASA Astrophysics Data System (ADS)

    Yamazaki, Tatsuya; Tamura, Tomoyuki; Nokita, Makoto; Okada, Satoshi; Hayashida, Shinsuke; Ogawa, Yoshihiro

    2004-05-01

    We have developed a novel flat-panel detector with CsI:Tl scintillator. The detector consists of a single piece 43cm x 43cm amorphous silicon thin-film transistor (TFT) array with MIS (metal-insulator-semiconductor) photoelectric converter having a pixel pitch of 160μm coated with a needle-like crystal CsI:Tl scintillator. Signal chain was totally revised from current detector utilizing an innovative sensor technology. The novel detector and current detector were equipped to a digital radiography system allowing a quantitative and comparative study. Results show that the novel detector has a linear response covering the radiographic exposure range. It has a moderate modulation transfer function (MTF) sufficient to the radiography tasks and effective to suppress the aliasing. The detective quantum efficiency (DQE) was almost twice than the current detector. The result of contrast-detail phantom exposed with a 1/2x dose level is equivalent to that of current detector with a 1x dose level. These results show that performance of novel detector is superior to and expected to reduce the patient dose in half than current detector due to higher DQE and innovative sensor technology.

  6. Hydrogenated amorphous silicon-germanium alloys

    SciTech Connect

    Luft, W.

    1988-02-01

    This report describes the effects of the germanium fraction in hydrogenated amorphous silicon-germanium alloys on various parameters, especially those that are indicators of film quality, and the impact of deposition methods, feedgas mixtures, and other deposition parameters on a SiGe:H and a-SiGe:H:F film characteristics and quality. Literature data show the relationship between germanium content, hydrogen content, deposition method (various glow discharges and CVD), feedgas lmixture, and other parameters and properties, such as optical band gap, dark and photoconductivities, photosensitivity, activation energy, Urbach parameter, and spin density. Some of these are convenient quality indicators; another is the absence of microstructure. Examining RF glow discharge with both a diode and triode geometry, DC proximity glow discharge, microwave glow discharge, and photo-CVD, using gas mixtures such as hydrogen-diluted and undiluted mixtures of silane/germane, disilane/germane, silane/germaniumtetrafluoride, and others, it was observed that hydrogen dilution (or inert gas dilution) is essential in achieving high photosensitivity in silicon-germanium alloys (in contradistinction to amorphous hydrogenated silicon). Hydrogen dilution results in a higher photosensitivity than do undiluted gas mixtures. 81 refs., 42 figs., 7 tabs.

  7. Radiation resistance studies of amorphous silicon films

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.; Payson, J. Scott

    1989-01-01

    Hydrogenated amorphous silicon thin films were irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15 cm(-2). The films were characterized using photothermal deflection spectroscopy and photoconductivity measurements. The investigations show that the radiation introduces sub-band-gap states 1.35 eV below the conduction band and the states increase supralinearly with fluence. Photoconductivity measurements suggest the density of states above the Fermi energy is not changing drastically with fluence.

  8. Structural relaxation of vacancies in amorphous silicon

    SciTech Connect

    Kim, E.; Lee, Y.H.; Chen, C.; Pang, T.

    1997-07-01

    The authors have studied the structural relaxation of vacancies in amorphous silicon (a-Si) using a tight-binding molecular-dynamics method. The most significant difference between vacancies in a-Si and those in crystalline silicon (c-Si) is that the deep gap states do not show up in a-Si. This difference is explained through the unusual behavior of the structural relaxation near the vacancies in a-Si, which enhances the sp{sup 2} + p bonding near the band edges. They have also observed that the vacancies do not migrate below 450 K although some of them can still be annihilated, particularly at high defect density due to large structural relaxation.

  9. Active pixel and photon counting imagers based on poly-Si TFTs: rewriting the rule book on large area flat panel x-ray devices

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    The near-ubiquity of large area, active matrix, flat-panel imagers (AMFPIs) in medical x-ray imaging applications is a testament to the usefulness and adaptability of the relatively simple concept of array pixels based on a single amorphous silicon (a-Si:H) TFT coupled to a pixel storage capacitor. Interestingly, the fundamental advantages of a-Si:H thin film electronics (including compatibility with very large area processing, high radiation damage resistance, and continued development driven by interest in mainstream consumer products) are shared by the rapidly advancing technology of polycrystalline silicon (poly-Si) TFTs. Moreover, the far higher mobilities of poly-Si TFTs, compared to those of a- Si:H, facilitate the creation of faster and more complex circuits than are possible with a-Si:H TFTs, leading to the possibility of new classes of large area, flat panel imagers. Given recent progress in the development of initial poly-Si imager prototypes, the creation of increasingly sophisticated active pixel arrays offering pixel-level amplification, variable gain, very high frame rates, and excellent signal-to-noise performance under all fluoroscopic and radiographic conditions (including very low exposures and high spatial frequencies), appears within reach. In addition, it is conceivable that the properties of poly-Si TFTs could allow the development of large area imagers providing single xray photon counting capabilities. In this article, the factors driving the possible realization of clinically practical active pixel and photon counting imagers based on poly-Si TFTs are described and simple calculational estimates related to photon counting imagers are presented. Finally, the prospect for future development of such imagers is discussed.

  10. Endurance Tests Of Amorphous-Silicon Photovoltaic Modules

    NASA Technical Reports Server (NTRS)

    Ross, Ronald G., Jr.; Sugimura, Russell S.

    1989-01-01

    Failure mechanisms in high-power service studied. Report discusses factors affecting endurance of amorphous-silicon solar cells. Based on field tests and accelerated aging of photovoltaic modules. Concludes that aggressive research needed if amorphous-silicon modules to attain 10-year life - value U.S. Department of Energy established as goal for photovoltaic modules in commercial energy-generating plants.

  11. Method for improving the stability of amorphous silicon

    DOEpatents

    Branz, Howard M.

    2004-03-30

    A method of producing a metastable degradation resistant amorphous hydrogenated silicon film is provided, which comprises the steps of growing a hydrogenated amorphous silicon film, the film having an exposed surface, illuminating the surface using an essentially blue or ultraviolet light to form high densities of a light induced defect near the surface, and etching the surface to remove the defect.

  12. Superlattice doped layers for amorphous silicon photovoltaic cells

    DOEpatents

    Arya, Rajeewa R.

    1988-01-12

    Superlattice doped layers for amorphous silicon photovoltaic cells comprise a plurality of first and second lattices of amorphous silicon alternatingly formed on one another. Each of the first lattices has a first optical bandgap and each of the second lattices has a second optical bandgap different from the first optical bandgap. A method of fabricating the superlattice doped layers also is disclosed.

  13. An infrared and luminescence study of tritiated amorphous silicon

    SciTech Connect

    Sidhu, L.S.; Kosteski, T.; Kherani, N.P.; Gaspari, F.; Zukotynski, S.; Shmayda, W.

    1997-07-01

    Tritium has been incorporated into amorphous silicon. Infrared spectroscopy shows new infrared vibration modes due to silicon-tritium (Si-T) bonds in the amorphous silicon network. Si-T vibration frequencies are related to Si-H vibration frequencies by simple mass relationships. Inelastic collisions of {beta} particles, produced as a result of tritium decay, with the amorphous silicon network results in the generation of electron-hole pairs. Radiative recombination of these carriers is observed. Dangling bonds associated with the tritium decay reduce luminescence efficiency.

  14. Amorphous silicon carbide films prepared using vaporized silicon ink

    NASA Astrophysics Data System (ADS)

    Masuda, Takashi; Shen, Zhongrong; Takagishi, Hideyuki; Ohdaira, Keisuke; Shimoda, Tatsuya

    2014-03-01

    The deposition of wide-band-gap silicon films using nonvacuum processes rather than conventional vacuum processes is of substantial interest because it may reduce cost. Herein, we present the optical and electrical properties of p-type hydrogenated amorphous silicon carbide (a-SiC:H) films prepared using a nonvacuum process in a simple chamber with a vaporized silicon ink consisting of cyclopentasilane, cyclohexene, and decaborane. The incorporation of carbon into the silicon network induced by the addition of cyclohexene to the silicon ink resulted in an increase in the optical band gap (Eg) of films from 1.56 to 2.11 eV. The conductivity of films with Eg < 1.9 eV is comparable to that of conventional a-SiC:H films prepared using a vacuum process, while the films with Eg > 1.9 eV show lower conductivity than expected because of the incorporation of excess carbon without the formation of Si-C bonds.

  15. Flat panel planar optic display. Revision 4/95

    SciTech Connect

    Veligdan, J.T.

    1995-05-01

    A prototype 10 inch flat panel Planar Optic display, (POD), screen has been constructed and tested. This display screen is comprised of hundreds of planar optic glass sheets bonded together with a cladding layer between each sheet where each glass sheet represents a vertical line of resolution. The display is 9 inches wide by 5 inches high and approximately 1 inch thick. A 3 milliwatt HeNe laser is used as the illumination source and a vector scanning technique is employed.

  16. Diffractive flat panel solar concentrators of a novel design.

    PubMed

    de Jong, Ties M; de Boer, Dick K G; Bastiaansen, Cees W M

    2016-07-11

    A novel design for a flat panel solar concentrator is presented which is based on a light guide with a grating applied on top that diffracts light into total internal reflection. By combining geometrical and diffractive optics the geometrical concentration ratio is optimized according to the principles of nonimaging optics, while the thickness of the device is minimized due to the use of total internal reflection. PMID:27410900

  17. Amorphous silicon bolometer for fire/rescue

    NASA Astrophysics Data System (ADS)

    Francisco, Glenn L.

    2001-03-01

    Thermal imaging sensors have completely changed the way the world views fire and rescue applications. Recently, in the uncooled infrared camera and microbolometer detector areas, major strides have been made in manufacturing personal fire and rescue sensors. A family of new amorphous silicon microbolometers are being produced utilizing low cost, low weight, ultra low power, small size, high volume vacuum packaged silicon wafer-level focal plane array technologies. These bolometers contain no choppers or thermoelectric coolers, require no manual calibration and use readily available commercial off-the-shelf components. Manufacturing and packaging discoveries have allowed infrared sensitive silicon arrays to be produced with the same methods that have driven the rapidly advancing digital wireless telecommunications industries. Fire and rescue professionals are now able to conduct minimum time thermal imaging penetration, surveillance, detection, recognition, rescue and egress while maintaining situational awareness in a manner consistent with the modern technological applications. The purpose of this paper is to describe an uncooled micro bolometer infrared camera approach for meeting fire/rescue wants, needs and requirements, with application of recent technology advancements. This paper also details advances in bolometric focal plane arrays, optical and circuit card technologies, while providing a glimpse into the future of micro sensor growth. Technical barriers are addressed in light of constraints and lessons learned around this technology.

  18. [Flat-panel detector technology -State-of-the-art and future prospects-].

    PubMed

    Yamazaki, Tatsuya

    2002-01-01

    A flat-panel detector (FPD) is a long-awaited technology to implement the digital X-ray imaging technology into the radiological department. This paper describes the state-of-the-art technology and future prospects on the FPD technology. State-of-the-art technology was reviewed taking the CXDI series as an example. Several FPD-based systems have been introduced into the Japanese market since CXDI-11 opened it in November 1998. Accompanying CXDI-C2 for control, CXDI-22 for table position and CXDI-31 for portable, the CXDI series fulfills the requirement of the radiography room being a fully digitalized room. The FPD on the CXDI series is comprised of a scintillator (Gd(2)O(2)S:Tb(3+)) as a primary sensor in which the X-ray is captured and an amorphous silicon detector (LANMIT) as a secondary sensor in which the fluorescent light is detected. Since the scintillator is identical to that of the screen-film systems, it can be said as proven, durable and chemically stable and it is expected to produce the same image quality as the screen-film systems. CXDI-31, a portable FPD-based system, was developed targeting thinner dimensions, lightweight, durability and high spatial resolution. Thoroughly re-designing the mechanical structure and reducing the power consumption at the readout IC realized thinner dimensions. Introducing the portable note PC technologies successfully combined lightweight with durability. Improving the sensor process and re-designing the layout made the sensor high resolution without compromising the signal-to-noise ratio. Future prospects were overviewed in the aspect of technology and applications. Sensitivity, spatial resolution, frame rate and portability were described as the upcoming technology. Increasing gain and reducing noise will realize higher sensitivity, especially by adopting the PbI(2), HgI(2) or such photoconductor materials as the primary sensor. Pixelized amplifier will also achieve higher sensitivity. Layered sensor designed such

  19. Theoretical studies of amorphous silicon and hydrogenated amorphous silicon with molecular dynamics simulations

    SciTech Connect

    Kwon, I.

    1991-12-20

    Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) have been studied with molecular dynamics simulations. The structural, vibrational, and electronic properties of these materials have been studied with computer-generated structural models and compare well with experimental observations. The stability of a-si and a-Si:H have been studied with the aim of understanding microscopic mechanisms underlying light-induced degradation in a-Si:H (the Staebler-Wronski effect). With a view to understanding thin film growth processes, a-Si films have been generated with molecular dynamics simulations by simulating the deposition of Si-clusters on a Si(111) substrate. A new two- and three-body interatomic potential for Si-H interactions has been developed. The structural properties of a-Si:H networks are in good agreement with experimental measurements. The presence of H atoms reduces strain and disorder relative to networks without H.

  20. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  1. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  2. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-01

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  3. Indirect flat-panel detector with avalanche gain: Fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager)

    SciTech Connect

    Zhao Wei; Li Dan; Reznik, Alla; Lui, B.J.M.; Hunt, D.C.; Rowlands, J.A.; Ohkawa, Yuji; Tanioka, Kenkichi

    2005-09-15

    An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d{sub Se} and the applied electric field E{sub Se} of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E{sub Se} dependence of both avalanche gain and optical quantum efficiency of an 8 {mu}m HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E{sub Se}: (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 {mu}m can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

  4. Indirect flat-panel detector with avalanche gain: fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager).

    PubMed

    Zhao, Wei; Li, Dan; Reznik, Alla; Lui, B J M; Hunt, D C; Rowlands, J A; Ohkawa, Yuji; Tanioka, Kenkichi

    2005-09-01

    An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d(Se) and the applied electric field E(Se) of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E(Se) dependence of both avalanche gain and optical quantum efficiency of an 8 microm HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E(Se): (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 microm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy. PMID:16266110

  5. Amorphous Silicon Display Backplanes on Plastic Substrates

    NASA Astrophysics Data System (ADS)

    Striakhilev, Denis; Nathan, Arokia; Vygranenko, Yuri; Servati, Peyman; Lee, Czang-Ho; Sazonov, Andrei

    2006-12-01

    Amorphous silicon (a-Si) thin-film transistor (TFT) backplanes are very promising for active-matrix organic light-emitting diode displays (AMOLEDs) on plastic. The technology benefits from a large manufacturing base, simple fabrication process, and low production cost. The concern lies in the instability of the TFTs threshold voltage (VT) and its low device mobility. Although VT-instability can be compensated by means of advanced multi-transistor pixel circuits, the lifetime of the display is still dependent on the TFT process quality and bias conditions. A-Si TFTs with field-effect mobility of 1.1 cm2/V · s and pixel driver circuits have been fabricated on plastic substrates at 150 °C. The circuits are characterized in terms of current drive capability and long-term stability of operation. The results demonstrate sufficient and stable current delivery and the ability of the backplane on plastic to meet AMOLED requirements.

  6. Radiation resistance studies of amorphous silicon films

    NASA Technical Reports Server (NTRS)

    Payson, J. Scott; Woodyard, James R.

    1988-01-01

    A study of hydrogenated amorphous silicon thin films irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15/sq cm is presented. The films were characterized using photothermal deflection spectroscopy, transmission and reflection spectroscopy, and photoconductivity and annealing measurements. Large changes were observed in the subband-gap optical absorption for energies between 0.9 and 1.7 eV. The steady-state photoconductivity showed decreases of almost five orders of magnitude for a fluence of 1E15/sq cm, but the slope of the intensity dependence of the photoconductivity remained almost constant for all fluences. Substantial annealing occurs even at room temperature, and for temperatures greater than 448 K the damage is completely annealed. The data are analyzed to describe the defects and the density of states function.

  7. Short range atomic migration in amorphous silicon

    NASA Astrophysics Data System (ADS)

    Strauß, F.; Jerliu, B.; Geue, T.; Stahn, J.; Schmidt, H.

    2016-05-01

    Experiments on self-diffusion in amorphous silicon between 400 and 500 °C are presented, which were carried out by neutron reflectometry in combination with 29Si/natSi isotope multilayers. Short range diffusion is detected on a length scale of about 2 nm, while long range diffusion is absent. Diffusivities are in the order of 10-19-10-20 m2/s and decrease with increasing annealing time, reaching an undetectable low value for long annealing times. This behavior is strongly correlated to structural relaxation and can be explained as a result of point defect annihilation. Diffusivities for short annealing times of 60 s follow the Arrhenius law with an activation enthalpy of (0.74 ± 0.21) eV, which is interpreted as the activation enthalpy of Si migration.

  8. Amorphous Silicon-Carbon Nanostructure Solar Cells

    NASA Astrophysics Data System (ADS)

    Schriver, Maria; Regan, Will; Loster, Matthias; Zettl, Alex

    2011-03-01

    Taking advantage of the ability to fabricate large area graphene and carbon nanotube networks (buckypaper), we produce Schottky junction solar cells using undoped hydrogenated amorphous silicon thin films and nanostructured carbon films. These films are useful as solar cell materials due their combination of optical transparency and conductance. In our cells, they behave both as a transparent conductor and as an active charge separating layer. We demonstrate a reliable photovoltaic effect in these devices with a high open circuit voltage of 390mV in buckypaper devices. We investigate the unique interface properties which result in an unusual J-V curve shape and optimize fabrication processes for improved solar conversion efficiency. These devices hold promise as a scalable solar cell made from earth abundant materials and without toxic and expensive doping processes.

  9. Tunable plasticity in amorphous silicon carbide films.

    PubMed

    Matsuda, Yusuke; Kim, Namjun; King, Sean W; Bielefeld, Jeff; Stebbins, Jonathan F; Dauskardt, Reinhold H

    2013-08-28

    Plasticity plays a crucial role in the mechanical behavior of engineering materials. For instance, energy dissipation during plastic deformation is vital to the sufficient fracture resistance of engineering materials. Thus, the lack of plasticity in brittle hybrid organic-inorganic glasses (hybrid glasses) often results in a low fracture resistance and has been a significant challenge for their integration and applications. Here, we demonstrate that hydrogenated amorphous silicon carbide films, a class of hybrid glasses, can exhibit a plasticity that is even tunable by controlling their molecular structure and thereby leads to an increased and adjustable fracture resistance in the films. We decouple the plasticity contribution from the fracture resistance of the films by estimating the "work-of-fracture" using a mean-field approach, which provides some insight into a potential connection between the onset of plasticity in the films and the well-known rigidity percolation threshold. PMID:23876200

  10. Direct-patterned optical waveguides on amorphous silicon films

    DOEpatents

    Vernon, Steve; Bond, Tiziana C.; Bond, Steven W.; Pocha, Michael D.; Hau-Riege, Stefan

    2005-08-02

    An optical waveguide structure is formed by embedding a core material within a medium of lower refractive index, i.e. the cladding. The optical index of refraction of amorphous silicon (a-Si) and polycrystalline silicon (p-Si), in the wavelength range between about 1.2 and about 1.6 micrometers, differ by up to about 20%, with the amorphous phase having the larger index. Spatially selective laser crystallization of amorphous silicon provides a mechanism for controlling the spatial variation of the refractive index and for surrounding the amorphous regions with crystalline material. In cases where an amorphous silicon film is interposed between layers of low refractive index, for example, a structure comprised of a SiO.sub.2 substrate, a Si film and an SiO.sub.2 film, the formation of guided wave structures is particularly simple.

  11. RF Sputtering for preparing substantially pure amorphous silicon monohydride

    DOEpatents

    Jeffrey, Frank R.; Shanks, Howard R.

    1982-10-12

    A process for controlling the dihydride and monohydride bond densities in hydrogenated amorphous silicon produced by reactive rf sputtering of an amorphous silicon target. There is provided a chamber with an amorphous silicon target and a substrate therein with the substrate and the target positioned such that when rf power is applied to the target the substrate is in contact with the sputtering plasma produced thereby. Hydrogen and argon are fed to the chamber and the pressure is reduced in the chamber to a value sufficient to maintain a sputtering plasma therein, and then rf power is applied to the silicon target to provide a power density in the range of from about 7 watts per square inch to about 22 watts per square inch to sputter an amorphous silicon hydride onto the substrate, the dihydride bond density decreasing with an increase in the rf power density. Substantially pure monohydride films may be produced.

  12. Amorphous-diamond electron emitter

    DOEpatents

    Falabella, Steven

    2001-01-01

    An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

  13. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    DOE PAGESBeta

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-14

    With this study, amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphousmore » silicon carbide being shown to surpass amorphous silicon for temperatures above 300°C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.« less

  14. Process for producing amorphous and crystalline silicon nitride

    DOEpatents

    Morgan, P.E.D.; Pugar, E.A.

    1985-11-12

    A process for producing amorphous or crystalline silicon nitride is disclosed which comprises reacting silicon disulfide ammonia gas at elevated temperature. In a preferred embodiment silicon disulfide in the form of whiskers'' or needles is heated at temperature ranging from about 900 C to about 1,200 C to produce silicon nitride which retains the whisker or needle morphological characteristics of the silicon disulfide. Silicon carbide, e.g. in the form of whiskers, also can be prepared by reacting substituted ammonia, e.g. methylamine, or a hydrocarbon containing active hydrogen-containing groups, such as ethylene, with silicon disulfide, at elevated temperature, e.g. 900 C. 6 figs.

  15. Process for producing amorphous and crystalline silicon nitride

    DOEpatents

    Morgan, Peter E. D.; Pugar, Eloise A.

    1985-01-01

    A process for producing amorphous or crystalline silicon nitride is disclosed which comprises reacting silicon disulfide ammonia gas at elevated temperature. In a preferred embodiment silicon disulfide in the form of "whiskers" or needles is heated at temperature ranging from about 900.degree. C. to about 1200.degree. C. to produce silicon nitride which retains the whisker or needle morphological characteristics of the silicon disulfide. Silicon carbide, e.g. in the form of whiskers, also can be prepared by reacting substituted ammonia, e.g. methylamine, or a hydrocarbon containing active hydrogen-containing groups, such as ethylene, with silicon disulfide, at elevated temperature, e.g. 900.degree. C.

  16. A real-time flat-panel X-ray pixel imaging system for low-dose medical diagnostics and craniofacial applications.

    PubMed

    Chapuy, S; Dimcovski, D; Dimcovski, Z; Grigoriev, E; Grob, E; Ligier, Y; Pachoud, M; Riondel, F; Rüfenacht, D; Sayegh, C; Terrier, F; Valley, J F; Verdun, F R

    2000-01-01

    The aim of this study was to evaluate on-line performance of a real-time digital imaging system based on amorphous silicon technology and to compare it with conventional film-screen equipment. The digital detecting imager consists of (1) a converter, which transforms the energy of the incident X rays into light; (2) a real-time digital detecting system, capable of producing as many as 10 pictures per second using a large-area pixel matrix (20 x 20 cm2) based on solid-state amorphous silicon sensor technology with a pitch of 400 microns; and (3) appropriate computer tools for control, real-time image treatment, data representation, and off-line analysis. Different phantoms were used for qualitative comparison with the conventional film-screen technique, with images obtained with both systems at the normal dose (used as a reference), as well as with dose reduction by a factor of 10 to 100. Basic image quality parameters evaluated showed that the response of the detector is linear in a wide range of entrance air kerma; the dynamic range is higher compared with the conventional film-screen combination; the spatial resolution is 1.25 lp per millimeter, as expected from the pixel size; and good image quality is ensured at doses substantially lower than for the film-screen technique. The flat-panel X-ray imager based on amorphous silicon technology implemented in standard radiographic equipment permits acquisition of real-time images in radiology (as many as 10 images per second) of diagnostic quality with a marked reduction of dose (as much as 100 times) and better contrast compared with the standard film technique. Preliminary results obtained with a 100-micron pitch imager based on the same technology show better quality but a less substantial dose reduction. Applications in craniofacial surgery look promising. PMID:11314093

  17. Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon

    PubMed Central

    2012-01-01

    Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications. PMID:22901341

  18. Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon.

    PubMed

    Ben Slama, Sonia; Hajji, Messaoud; Ezzaouia, Hatem

    2012-01-01

    Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications. PMID:22901341

  19. Photo-electronic properties of CVD amorphous silicon

    NASA Astrophysics Data System (ADS)

    Salau, Akinola Muritala

    1983-12-01

    D.c. conductivity, thermoelectric power and photoconductivity of amorphous silicon films prepared by chemical vapor deposition (CVD) have been measured as functions of operating and annealing temperatures. Several interpretations of the results obtained have been suggested.

  20. Hydrogenated amorphous silicon films prepared by glow discharge of disilane

    SciTech Connect

    Wiesmann, H.J. )

    1990-01-01

    This report describes the results of an investigation of the properties of hydrogenated amorphous silicon films and the efficiency of amorphous silicon solar cells deposited from disilane at rates of 1.5 nanometers/second or greater. The study was divided into two parts, investigation of basic materials properties of hydrogenated amorphous silicon thin films and the fabrication of glass-P-I-N-metal solar cells. The thin film materials properties investigated included the dark conductivity, photoconductivity, dihydride/monohydride concentration ratio, activation energy, and mobility-lifetime product. Hydrogenated amorphous silicon solar cells were fabricated with an intrinsic layer which was deposited at 1.5 nanometers/second. The absolute and reverse bias quantum yields were measured and solar cell efficiencies of 5% were achieved. Attempts to increase the efficiency by reverse bias annealing are also reported. 7 refs., 27 figs.

  1. Thermal properties of amorphous/crystalline silicon superlattices.

    PubMed

    France-Lanord, Arthur; Merabia, Samy; Albaret, Tristan; Lacroix, David; Termentzidis, Konstantinos

    2014-09-01

    Thermal transport properties of crystalline/amorphous silicon superlattices using molecular dynamics are investigated. We show that the cross-plane conductivity of the superlattices is very low and close to the conductivity of bulk amorphous silicon even for amorphous layers as thin as ≃ 6 Å. The cross-plane thermal conductivity weakly increases with temperature which is associated with a decrease of the Kapitza resistance with temperature at the crystalline/amorphous interface. This property is further investigated considering the spatial analysis of the phonon density of states in domains close to the interface. Interestingly, the crystalline/amorphous superlattices are shown to display large thermal anisotropy, according to the characteristic sizes of elaborated structures. These last results suggest that the thermal conductivity of crystalline/amorphous superlattices can be phonon engineered, providing new directions for nanostructured thermoelectrics and anisotropic materials in thermal transport. PMID:25105883

  2. Determination of the detective quantum efficiency of a prototype, megavoltage indirect detection, active matrix flat-panel imager.

    PubMed

    El-Mohri, Y; Jee, K W; Antonuk, L E; Maolinbay, M; Zhao, Q

    2001-12-01

    After years of aggressive development, active matrix flat-panel imagers (AMFPIs) have recently become commercially available for radiotherapy imaging. In this paper we report on a comprehensive evaluation of the signal and noise performance of a large-area prototype AMFPI specifically developed for this application. The imager is based on an array of 512 x 512 pixels incorporating amorphous silicon photodiodes and thin-film transistors offering a 26 x 26 cm2 active area at a pixel pitch of 508 microm. This indirect detection array was coupled to various x-ray converters consisting of a commercial phosphor screen (Lanex Fast B, Lanex Regular, or Lanex Fine) and a 1 mm thick copper plate. Performance of the imager in terms of measured sensitivity, modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) is reported at beam energies of 6 and 15 MV and at doses of 1 and 2 monitor units (MU). In addition, calculations of system performance (NPS, DQE) based on cascaded-system formalism were reported and compared to empirical results. In these calculations, the Swank factor and spatial energy distributions of secondary electrons within the converter were modeled by means of EGS4 Monte Carlo simulations. Measured MTFs of the system show a weak dependence on screen type (i.e., thickness), which is partially due to the spreading of secondary radiation. Measured DQE was found to be independent of dose for the Fast B screen, implying that the imager is input-quantum-limited at 1 MU, even at an extended source-to-detector distance of 200 cm. The maximum DQE obtained is around 1%--a limit imposed by the low detection efficiency of the converter. For thinner phosphor screens, the DQE is lower due to their lower detection efficiencies. Finally, for the Fast B screen, good agreement between calculated and measured DQE was observed. PMID:11797959

  3. Silicon heterojunction solar cell and crystallization of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Lu, Meijun

    The rapid growth of photovoltaics in the past decade brings on the soaring price and demand for crystalline silicon. Hence it becomes necessary and also profitable to develop solar cells with over 20% efficiency, using thin (˜100mum) silicon wafers. In this respect, diffused junction cells are not the best choice, since the inescapable heating in the diffusion process not only makes it hard to handle thin wafers, but also reduces carriers' bulk lifetime and impairs the crystal quality of the substrate, which could lower cell efficiency. An alternative is the heterojunction cells, such as amorphous silicon/crystalline silicon heterojunction (SHJ) solar cell, where the emitter layer can be grown at low temperature (<200°C). In first part of this dissertation, I will introduce our work on front-junction SHJ solar cell, including the importance of intrinsic buffer layer; the discussion on the often observed anomalous "S"-shaped J-V curve (low fill factor) by using band diagram analysis; the surface passivation quality of intrinsic buffer and its relationship to the performance of front-junction SHJ cells. Although the a-Si:H is found to help to achieve high efficiency in c-Si heterojuntion solar cells, it also absorbs short wavelength (<600 nm) light, leading to non-ideal blue response and lower short circuit currents (JSC) in the front-junction SHJ cells. Considering this, heterojunction with both a-Si:H emitter and base contact on the back side in an interdigitated pattern, i.e. interdigitated back contact silicon heterojunction (IBC-SHJ) solar cell, is developed. This dissertation will show our progress in developing IBC-SHJ solar cells, including the structure design; device fabrication and characterization; two dimensional simulation by using simulator Sentaurus Device; some special features of IBC-SHJ solar cells; and performance of IBC-SHJ cells without and with back surface buffer layers. Another trend for solar cell industry is thin film solar cells, since

  4. Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

    SciTech Connect

    Wronski, M. M.; Rowlands, J. A.

    2008-12-15

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10{sup -7}-10{sup -2} R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct

  5. Direct-conversion flat-panel imager with avalanche gain: feasibility investigation for HARP-AMFPI.

    PubMed

    Wronski, M M; Rowlands, J A

    2008-12-01

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10(-7)-10(-2) R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct interaction

  6. Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

    PubMed Central

    Wronski, M. M.; Rowlands, J. A.

    2008-01-01

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10−7–10−2 R∕frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct

  7. Hydrogenated amorphous silicon deposited by ion-beam sputtering

    NASA Technical Reports Server (NTRS)

    Lowe, V. E.; Henin, N.; Tu, C.-W.; Tavakolian, H.; Sites, J. R.

    1981-01-01

    Hydrogenated amorphous silicon films 1/2 to 1 micron thick were deposited on metal and glass substrates using ion-beam sputtering techniques. The 800 eV, 2 mA/sq cm beam was a mixture of argon and hydrogen ions. The argon sputtered silicon from a pure (7.6 cm) single crystal wafer, while the hydrogen combined with the sputtered material during the deposition. Hydrogen to argon pressure ratios and substrate temperatures were varied to minimize the defect state density in the amorphous silicon. Characterization was done by electrical resistivity, index of refraction and optical absorption of the films.

  8. Electrical characteristics of amorphous iron-tungsten contacts on silicon

    NASA Technical Reports Server (NTRS)

    Finetti, M.; Pan, E. T.-S.; Nicolet, M.-A.; Suni, I.

    1983-01-01

    The electrical characteristics of amorphous Fe-W contacts have been determined on both p-type and n-type silicon. The amorphous films were obtained by cosputtering from a composite target. Contact resistivities of 1 x 10 to the -7th and 2.8 x 10 to the -6th were measured on n(+) and p(+) silicon, respectively. These values remain constant after thermal treatment up to at least 500 C. A barrier height of 0.61 V was measured on n-type silicon.

  9. Advances in infrastructure support for flat panel display manufacturing

    NASA Astrophysics Data System (ADS)

    Bardsley, James N.; Ciesinski, Michael F.; Pinnel, M. Robert

    1997-07-01

    The success of the US display industry, both in providing high-performance displays for the US Department of Defense at reasonable cost and in capturing a significant share of the global civilian market, depends on maintaining technological leadership and on building efficient manufacturing capabilities. The US Display Consortium (USDC) was set up in 1993 by the US Government and private industry to guide the development of the infrastructure needed to support the manufacturing of flat panel displays. This mainly involves the supply of equipment and materials, but also includes the formation of partnerships and the training of a skilled labor force. Examples are given of successful development projects, some involving USDC participation, others through independent efforts of its member companies. These examples show that US-based companies can achieve leadership positions in this young and rapidly growing global market.

  10. Improving the diversity of manufacturing electroluminescent flat panel displays

    SciTech Connect

    Moss, T.S.; Samuels, J.A.; Smith, D.C.

    1995-09-01

    Crystalline calcium thiogallate with a cerium dopant has been deposited by metal-organic chemical vapor deposition (MOCVD) at temperatures below 600{degrees}C on a low cost glass substrate. An EL luminance of 1.05 fL was observed 40 volts above threshold at 60 Hz. This is more than an order of magnitude improvement over earlier crystalline-as-deposited thiogallate materials. These results pave the way for the use of MOCVD as a potential method for processing full color thin-film electroluminescent (TFEL) flat panel displays. The formation of the CaGa{sub 2}S{sub 4}:Ce phosphor requires precise control over a number of deposition parameters including flow rates, substrate temperature, and reactor pressure. The influence of these parameters will be discussed in terms of structure, uniformity, and TFEL device performance.

  11. Amorphous and microcrystalline silicon technology--1997. Materials Research Society symposium proceedings, Volume 467

    SciTech Connect

    Wagner, S.; Hack, M.; Schiff, E.A.; Schropp, R.; Shimizu, I.

    1997-07-01

    This book was divided into the following parts: Staebler-Wronski and Fundamental Defect Studies in Amorphous Silicon; The Story of Hydrogen in Amorphous Silicon; Photoelectric Properties of Amorphous Silicon; Deposition and Properties of Microcrystalline Silicon; Deposition Studies for Amorphous Silicon and Related Materials; Solar Cells; Thin-Film Transistors; and Sensors and Novel Device Concepts. Separate abstracts were prepared for most of the papers in the volume.

  12. A novel compact gamma camera based on flat panel PMT

    NASA Astrophysics Data System (ADS)

    Pani, R.; Pellegrini, R.; Cinti, M. N.; Trotta, C.; Trotta, G.; Scafè, R.; Betti, M.; Cusanno, F.; Montani, Livia; Iurlaro, Giorgia; Garibaldi, F.; Del Guerra, A.

    2003-11-01

    Over the last ten years the strong technological advances in position sensitive detectors have encouraged the scientific community to develop dedicated imagers for new diagnostic techniques in the field of isotope functional imaging. The main feature of the new detectors is the compactness that allows suitable detection geometry fitting the body anatomy. Position sensitive photomultiplier tubes (PSPMTs) have been showing very good features with continuous improvement. In 1997 a novel gamma camera was proposed based on a closely packed array of second generation 1 in PSPMTs. The main advantage is the potentially unlimited detection area but with the disadvantage of a relatively large non-active area (30%). The Hamamatsu H8500 Flat Panel PMT represents the last generation of PSPMT. Its extreme compactness allows array assembly with an improved effective area up to 97%. This paper, evaluates the potential improvement of imaging performances of a gamma camera based on the new PSPMT, compared with the two previous generation PSPMTs. To this aim the factors affecting the gamma camera final response, like PSPMT gain anode variation and position resolution, are analyzed and related to the uniformity counting response, energy resolution, position linearity, detection efficiency and intrinsic spatial resolution. The results show that uniformity of pulse height response seems to be the main parameter that provides the best imaging performances. Furthermore an extreme identification of pixels seems to be not effective to a full correction of image uniformity counting and gain response. However, considering the present technological limits, Flat Panel PSPMTs could be the best trade off between gamma camera imaging performances, compactness and large detection area.

  13. Diffractive optics for compact flat panel displays. Final report

    SciTech Connect

    Sweeney, D.; DeLong, K.

    1997-04-29

    Three years ago LLNL developed a practical method to dramatically reduce the chromatic aberration in single element diffractive imaging lenses. High efficiency, achromatic imaging lenses have been fabricated for human vision correction. This LDRD supported research in applying our new methods to develop a unique, diffraction-based optical interface with solid state, microelectronic imaging devices. Advances in microelectronics have led to smaller, more efficient components for optical systems. There have, however, been no equivalent advances in the imaging optics associated with these devices. The goal of this project was to replace the bulky, refractive optics in typical head-mounted displays with micro-thin diffractive optics to directly image flat-panel displays into the eye. To visualize the system think of the lenses of someone`s eyeglasses becoming flat-panel displays. To realize this embodiment, we needed to solve the problems of large chromatic aberrations and low efficiency that are associated with diffraction. We have developed a graceful tradeoff between chromatic aberrations and the diffractive optic thickness. It turns out that by doubling the thickness of a micro-thin diffractive lens we obtain nearly a two-times improvement in chromatic performance. Since the human eye will tolerate one diopter of chromatic aberration, we are able to achieve an achromatic image with a diffractive lens that is only 20 microns thick, versus 3 mm thickness for the comparable refractive lens. Molds for the diffractive lenses are diamond turned with sub-micron accuracy; the final lenses are cast from these molds using various polymers. We thus retain both the micro- thin nature of the diffractive optics and the achromatic image quality of refractive optics. During the first year of funding we successfully extended our earlier technology from 1 cm diameter optics required for vision applications up to the 5 cm diameter optics required for this application. 3 refs., 6 figs.

  14. EMI investigation and modeling of a flat panel display

    NASA Astrophysics Data System (ADS)

    Shinde, Satyajeet

    It is often important to carry out EMI analysis in the design phase of an electronic product to predict the radiated emissions. An EMI analysis is important to predict if the product complies with the FCC regulations as well as to gain an understanding of the noise coupling and radiation mechanisms. EMI analysis and prediction of radiated emissions in electronic products that have an electrically large chassis, pose a challenge due to the presence of multiple resonant structures and noise-coupling mechanisms. The study focusses on the investigation of the main noise coupling mechanisms, the approach and methods used for the modeling of a flat panel display. Full-wave simulation models are a powerful tool for the prediction of radiated emissions and the visualization of coupling paths within the product. The first part deals with the measurement of radiated emissions from the display under standard test conditions and the identification of the main noise sources using near-field scanning. The contribution of the chassis components - frame, back cover and the back panel, to the radiated emission is analyzed using shielding measurements. Noise coupling from the main board, flex cables, display driver boards and the display is analyzed from measurements. The second part deals with the full-wave modeling of the components - main board, flex cables, chassis and the display driver boards. The modeling approach is demonstrated by highlighting some of the challenges in modeling larger structures having many details. The simulation model contains the main components of the TV that contribute to far-field radiation. The full-wave modeling is done using the CST Microwave Studio. Two sets of simulation models are described - the common mode models and the complete models. The use of the common mode models for the identification of the resonant structures is demonstrated. The far-field radiated emissions along with the coupling mechanism within the flat panel display can be

  15. Amorphous silicon thin film transistor active-matrix organic light-emitting diode displays fabricated on flexible substrates

    NASA Astrophysics Data System (ADS)

    Nichols, Jonathan A.

    Organic light-emitting diode (OLED) displays are of immense interest because they have several advantages over liquid crystal displays, the current dominant flat panel display technology. OLED displays are emissive and therefore are brighter, have a larger viewing angle, and do not require backlights and filters, allowing thinner, lighter, and more power efficient displays. The goal of this work was to advance the state-of-the-art in active-matrix OLED display technology. First, hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) active-matrix OLED pixels and arrays were designed and fabricated on glass substrates. The devices operated at low voltages and demonstrated that lower performance TFTs could be utilized in active-matrix OLED displays, possibly allowing lower cost processing and the use of polymeric substrates. Attempts at designing more control into the display at the pixel level were also made. Bistable (one bit gray scale) active-matrix OLED pixels and arrays were designed and fabricated. Such pixels could be used in novel applications and eventually help reduce the bandwidth requirements in high-resolution and large-area displays. Finally, a-Si:H TFT active-matrix OLED pixels and arrays were fabricated on a polymeric substrate. Displays fabricated on a polymeric substrates would be lightweight; flexible, more rugged, and potentially less expensive to fabricate. Many of the difficulties associated with fabricating active-matrix backplanes on flexible substrates were studied and addressed.

  16. Growth and Characterization of Hydrogenated Amorphous Silicon and Hydrogenated Amorphous Silicon Carbide with Liquid Organometallic Sources.

    NASA Astrophysics Data System (ADS)

    Gaughan, Kevin David

    The growth and characterization of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon -carbon (rm a-rm Si _{1-X}C_{X}: H) alloys employing liquid organometallic sources are described. N -type a-Si:H films were grown using a mixture of silane and tertiarybutylphosphine (TBP-rm C_4H _9P_2) vapor in a plasma enhanced chemical vapor deposition system. Impurity levels from parts per million to about 5 at. % phosphorus have been incorporated into the film with this method. Tertiarybutylphosphine is less toxic and less pyrophoric than phosphine which is usually used in n-type doping of a-Si:H films. Optical and electronic properties were characterized by room temperature as well as temperature dependent dark conductivity, photothermal deflection spectroscopy, infrared vibrational spectroscopy, electron spin resonance, and electron microprobe analysis. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine. The experimental results are compared with the predictions of several models that describe the chemical equilibrium between active dopants and deep defects. A pronounced decrease in the effects of doping, such as an increase in the activation energy of electrical conductivity and an decrease in the conductivity of the sample, were seen in heavily doped films (TBP/SiH _4> 0.5%), perhaps influenced by the increased carbon and/or phosphorus concentrations. Amorphous silicon-carbide alloys have been grown by the plasma decomposition of ditertiarybutylsilane ( rm DTBS-rm SiH_2(C _4H_9)_2). The optical bandgaps, which varied from 2.2 to 3.3 eV, are strongly dependent upon the deposition conditions. The carbon concentrations in these films varied from 60 to 95 at. %. The optical band-edge is very broad compared to that which is found in a-Si:H and this breadth is essentially independent of the deposition conditions. The plasma decomposition of admixtures of DTBS and silane has produced rm a- rm Si_{1-X

  17. Performance of a volumetric CT scanner based upon a flat-panel imager

    NASA Astrophysics Data System (ADS)

    Jaffray, David A.; Siewerdsen, Jeffrey H.; Drake, Douglas G.

    1999-05-01

    To characterize the performance of a cone-beam computed tomography (CBCT) imaging system based upon an indirect- detection, amorphous silicon flat-panel imager (FPI). Tomographic images obtained using the FPI are presented, and the signal and noise characteristics of reconstructed images are quantified. Specifically, the spatial uniformity, CT linearity, contrast performance, noise characteristics, spatial resolution, and soft-tissue visualization are examined. Finally, the performance of the FPI-based CT system is discussed in relation to existing clinical technologies. A table-top measurements system was constructed to allow investigation of FPI performance in CBCT within a precisely controlled and reproducible geometry. The FPI incorporates a 512 X 512 active matrix array of a-Si:H thin-film transistors and photodiodes in combination with an overlying (133 mg/cm2 Gd2O2S:Tb) phosphor. The commercially available prototype FPI has a pixel pitch of 400 micrometer, a fill factor of approximately 80%, can be read at a maximum frame rate of 5 fps, and provides 16 bit digitization. Mounted upon an optical bench are the x-ray tube (in a rigid support frame), the object to be imaged (upon a precision rotation/translation table), and the FPI (mounted upon a precision translation table). The entire setup is directed under computer control, and volumetric imaging is accomplished by rotating the object incrementally over 360 degrees, delivering a radiographic x-ray pulse (e.g., 100 - 130 kVp, approximately 0.1 - 10 mAs), and acquiring a projection image at each increment. Prior to reconstruction, dark and flood- field corrections are applied to account for stationary nonuniformities in detector response and dark current. Tomographic images are reconstructed from the projections using the Feldkamp filtered back-projection algorithm for CBCT. The linearity of the CBCT system was compared to that of a commercial scanner (Philips SR-7000) using materials ranging in CT number from

  18. Latent ion tracks in amorphous silicon

    SciTech Connect

    Bierschenk, Thomas; Giulian, Raquel; Afra, Boshra; Rodriguez, Matias D; Schauries, D; Mudie, Stephen; Pakarinen, Olli H; Djurabekova, Flyura; Nordlund, Kai; Osmani, Orkhan; Medvedev, Nikita; Rethfield, Baerbel; Ridgway, Mark C; Kluth, Patrick

    2013-01-01

    We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy ion irradiation. An underlying core-shell structure consistent with remnants of a high density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions dier for as-implanted and relaxed Si as attributed to dierent microstructures and melting temperatures. The identication and characterisation of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy ion irradiation in amorphous semiconductors.

  19. A 25 kW solar photovoltaic flat panel power supply for an electrodialysis water desalination unit in New Mexico

    NASA Astrophysics Data System (ADS)

    Wood, J. R.; Crutcher, J. L.

    1980-06-01

    The stand-alone system consists of a flat panel array employing silicon ribbon solar cells, used in conjunction with a lead-acid battery bank. Electrodialysis is an energy-conservative process for the desalination of water, in which ions are transferred from one solution through a membrane into another solution by imposition of a direct electrical current. The system design is intended to be prototypical of part of the drinking water supply for a remote village. The specific task of this system is to aid in the restoration of an aquifer following a uranium leaching operation.

  20. Recent improvements in amorphous silicon-based multijunction modules

    SciTech Connect

    Arya, R.R.; Bennett, M.; Yang, L.; Newton, J.; Li, Y.M.; Maley, N.; Fieselmann, B.; Chen, L.F.; Rajan, K.; Wilczynski, A.; Wood, G. )

    1994-06-30

    Advances in intrinsic amorphous silicon and in amorphous silicon carbon alloys have resulted in thin single junction devices with V[sub oc]'s over 1.0 volts and excellent stability with both i-layer materials. Incorporation of improved a-Si:H i-layers and thin microcrystalline n-layers in a-Si/a-Si/a-SiGe triple junction modules has resulted in large area triple junction modules with initial efficiencies as high as 11.35%. These modules exhibit a degradation of [similar to]20% after 1000 hours of light-soaking resulting in [similar to]9% stable modules.

  1. Amorphous silicon alloy-based roof integrated photovoltaic systems

    SciTech Connect

    Nath, P.; Vogeli, C.; Singh, A.; Call, J.

    1994-12-31

    A roll-to-roll process is used to deposit tandem amorphous silicon alloy solar cell onto thin (0.005 inch) stainless steel substrate. Using this solar cell material, the authors have designed and fabricated a photovoltaic (PV) module which can be integrated into building roofs. The module is fabricated by laminating the large area amorphous silicon on stainless steel solar cell material onto a 0.03 inch thick coated galvanized steel support plate. The module is then formed in such a way to allow installation as a batten and seam roofing system. This paper describes the fabrication and installation details of such PV systems.

  2. Transmissive metallic contact for amorphous silicon solar cells

    DOEpatents

    Madan, A.

    1984-11-29

    A transmissive metallic contact for amorphous silicon semiconductors includes a thin layer of metal, such as aluminum or other low work function metal, coated on the amorphous silicon with an antireflective layer coated on the metal. A transparent substrate, such as glass, is positioned on the light reflective layer. The metallic layer is preferably thin enough to transmit at least 50% of light incident thereon, yet thick enough to conduct electricity. The antireflection layer is preferably a transparent material that has a refractive index in the range of 1.8 to 2.2 and is approximately 550A to 600A thick.

  3. Multiple-Flat-Panel System Displays Multidimensional Data

    NASA Technical Reports Server (NTRS)

    Gundo, Daniel; Levit, Creon; Henze, Christopher; Sandstrom, Timothy; Ellsworth, David; Green, Bryan; Joly, Arthur

    2006-01-01

    The NASA Ames hyperwall is a display system designed to facilitate the visualization of sets of multivariate and multidimensional data like those generated in complex engineering and scientific computations. The hyperwall includes a 77 matrix of computer-driven flat-panel video display units, each presenting an image of 1,280 1,024 pixels. The term hyperwall reflects the fact that this system is a more capable successor to prior computer-driven multiple-flat-panel display systems known by names that include the generic term powerwall and the trade names PowerWall and Powerwall. Each of the 49 flat-panel displays is driven by a rack-mounted, dual-central-processing- unit, workstation-class personal computer equipped with a hig-hperformance graphical-display circuit card and with a hard-disk drive having a storage capacity of 100 GB. Each such computer is a slave node in a master/ slave computing/data-communication system (see Figure 1). The computer that acts as the master node is similar to the slave-node computers, except that it runs the master portion of the system software and is equipped with a keyboard and mouse for control by a human operator. The system utilizes commercially available master/slave software along with custom software that enables the human controller to interact simultaneously with any number of selected slave nodes. In a powerwall, a single rendering task is spread across multiple processors and then the multiple outputs are tiled into one seamless super-display. It must be noted that the hyperwall concept subsumes the powerwall concept in that a single scene could be rendered as a mosaic image on the hyperwall. However, the hyperwall offers a wider set of capabilities to serve a different purpose: The hyperwall concept is one of (1) simultaneously displaying multiple different but related images, and (2) providing means for composing and controlling such sets of images. In place of elaborate software or hardware crossbar switches, the

  4. Solution-processed amorphous silicon surface passivation layers

    SciTech Connect

    Mews, Mathias Sontheimer, Tobias; Korte, Lars; Rech, Bernd; Mader, Christoph; Traut, Stephan; Wunnicke, Odo

    2014-09-22

    Amorphous silicon thin films, fabricated by thermal conversion of neopentasilane, were used to passivate crystalline silicon surfaces. The conversion is investigated using X-ray and constant-final-state-yield photoelectron spectroscopy, and minority charge carrier lifetime spectroscopy. Liquid processed amorphous silicon exhibits high Urbach energies from 90 to 120 meV and 200 meV lower optical band gaps than material prepared by plasma enhanced chemical vapor deposition. Applying a hydrogen plasma treatment, a minority charge carrier lifetime of 1.37 ms at an injection level of 10{sup 15}/cm{sup 3} enabling an implied open circuit voltage of 724 mV was achieved, demonstrating excellent silicon surface passivation.

  5. Proposed planar-type amorphous-silicon MOS transistors

    NASA Astrophysics Data System (ADS)

    Uchida, Y.; Matsumura, M.

    1985-10-01

    Novel planar-type amorphous-silicon metal-oxide-semiconductor transistors have been proposed and their features have been demonstrated. The gate insulator of silicon-dioxide grown inside the original amorphous silicon layer makes transistor characteristics highly stable. The source and drain of micro-crystal silicon make the fabrication process simple and the parasitic elements small. The on-current of the prototype transistor was extrapolated to decrease to one-half of its initial value 10 billion years after the application of dc bias. The on-off current ratio was about a million and no voltage offset was observed. The field-effect mobility was 0.6 sq cm Vs.

  6. Threshold irradiation dose for amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Zinkle, S.J.

    1997-04-01

    The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature-dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized, showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electrons and xenon ions as the irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface of strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be {approximately}0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1 x 10{sup {minus}3} dpa/s and with fission neutrons irradiated at 1 x 10{sup {minus}6} dpa/s irradiated to 15 dpa in the temperature range of {approximately}340 {+-} 10K.

  7. Laterally inherently thin amorphous-crystalline silicon heterojunction photovoltaic cell

    SciTech Connect

    Chowdhury, Zahidur R. Kherani, Nazir P.

    2014-12-29

    This article reports on an amorphous-crystalline silicon heterojunction photovoltaic cell concept wherein the heterojunction regions are laterally narrow and distributed amidst a backdrop of well-passivated crystalline silicon surface. The localized amorphous-crystalline silicon heterojunctions consisting of the laterally thin emitter and back-surface field regions are precisely aligned under the metal grid-lines and bus-bars while the remaining crystalline silicon surface is passivated using the recently proposed facile grown native oxide–plasma enhanced chemical vapour deposited silicon nitride passivation scheme. The proposed cell concept mitigates parasitic optical absorption losses by relegating amorphous silicon to beneath the shadowed metallized regions and by using optically transparent passivation layer. A photovoltaic conversion efficiency of 13.6% is obtained for an untextured proof-of-concept cell illuminated under AM 1.5 global spectrum; the specific cell performance parameters are V{sub OC} of 666 mV, J{sub SC} of 29.5 mA-cm{sup −2}, and fill-factor of 69.3%. Reduced parasitic absorption, predominantly in the shorter wavelength range, is confirmed with external quantum efficiency measurement.

  8. Laterally inherently thin amorphous-crystalline silicon heterojunction photovoltaic cell

    NASA Astrophysics Data System (ADS)

    Chowdhury, Zahidur R.; Kherani, Nazir P.

    2014-12-01

    This article reports on an amorphous-crystalline silicon heterojunction photovoltaic cell concept wherein the heterojunction regions are laterally narrow and distributed amidst a backdrop of well-passivated crystalline silicon surface. The localized amorphous-crystalline silicon heterojunctions consisting of the laterally thin emitter and back-surface field regions are precisely aligned under the metal grid-lines and bus-bars while the remaining crystalline silicon surface is passivated using the recently proposed facile grown native oxide-plasma enhanced chemical vapour deposited silicon nitride passivation scheme. The proposed cell concept mitigates parasitic optical absorption losses by relegating amorphous silicon to beneath the shadowed metallized regions and by using optically transparent passivation layer. A photovoltaic conversion efficiency of 13.6% is obtained for an untextured proof-of-concept cell illuminated under AM 1.5 global spectrum; the specific cell performance parameters are VOC of 666 mV, JSC of 29.5 mA-cm-2, and fill-factor of 69.3%. Reduced parasitic absorption, predominantly in the shorter wavelength range, is confirmed with external quantum efficiency measurement.

  9. Review of flat panel display programs and defense applications

    NASA Astrophysics Data System (ADS)

    Gnade, Bruce; Schulze, Raymond; Henderson, Girardeau L.; Hopper, Darrel G.

    1997-07-01

    Flat panel display research has comprised a substantial portion of the national investment in new technology for economic and national security for the past nine years. These investments have ben made principally via several Defense Advanced Research Projects Agency (DARPA) programs, known collectively as the continuing High Definition Systems Program, and the Office of the Secretary of Defense Production Act Title III Program. Using input from the Army, Navy, and Air Force to focus research and identify insertion opportunities, DARPA and the Title III Program Office have made investments to develop the national technology base and manufacturing infrastructure necessary to meet the twin challenge of providing affordable displays in current systems and enabling the DoD strategy of winning future conflicts by getting more information to all participants during the battle. These research programs are reviewed and opportunities for applications are described. Future technology development, transfer, and transition requirements are identified. Strategy and vision are documented to assist the identification of areas meriting further consideration.

  10. Sarnoff JND Vision Model for Flat-Panel Design

    NASA Technical Reports Server (NTRS)

    Brill, Michael H.; Lubin, Jeffrey

    1998-01-01

    This document describes adaptation of the basic Sarnoff JND Vision Model created in response to the NASA/ARPA need for a general-purpose model to predict the perceived image quality attained by flat-panel displays. The JND model predicts the perceptual ratings that humans will assign to a degraded color-image sequence relative to its nondegraded counterpart. Substantial flexibility is incorporated into this version of the model so it may be used to model displays at the sub-pixel and sub-frame level. To model a display (e.g., an LCD), the input-image data can be sampled at many times the pixel resolution and at many times the digital frame rate. The first stage of the model downsamples each sequence in time and in space to physiologically reasonable rates, but with minimum interpolative artifacts and aliasing. Luma and chroma parts of the model generate (through multi-resolution pyramid representation) a map of differences-between test and reference called the JND map, from which a summary rating predictor is derived. The latest model extensions have done well in calibration against psychophysical data and against image-rating data given a CRT-based front-end. THe software was delivered to NASA Ames and is being integrated with LCD display models at that facility,

  11. Cryogenic flat-panel gas-gap heat switch

    NASA Astrophysics Data System (ADS)

    Vanapalli, S.; Keijzer, R.; Buitelaar, P.; ter Brake, H. J. M.

    2016-09-01

    A compact additive manufactured flat-panel gas-gap heat switch operating at cryogenic temperature is reported in this paper. A guarded-hot-plate apparatus has been developed to measure the thermal conductance of the heat switch with the heat sink temperature in the range of 100-180 K. The apparatus is cooled by a two-stage GM cooler and the temperature is controlled with a heater and a braided copper wire connection. A thermal guard is mounted on the hot side of the device to confine the heat flow axially through the sample. A gas handling system allows testing the device with different gas pressures in the heat switch. Experiments are performed at various heat sink temperatures, by varying gas pressure in the gas-gap and with helium, hydrogen and nitrogen gas. The measured off-conductance with a heat sink temperature of 115 K and the hot plate at 120 K is 0.134 W/K, the on-conductance with helium and hydrogen gases at the same temperatures is 4.80 W/K and 4.71 W/K, respectively. This results in an on/off conductance ratio of 37 ± 7 and 35 ± 6 for helium and hydrogen respectively. The experimental results matches fairly well with the predicted heat conductance at cryogenic temperatures.

  12. Nanoindentation-induced amorphization in silicon carbide

    NASA Astrophysics Data System (ADS)

    Szlufarska, Izabela; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2004-07-01

    The nanoindentation-induced amorphization in SiC is studied using molecular dynamics simulations. The load-displacement response shows an elastic shoulder followed by a plastic regime consisting of a series of load drops. Analyses of bond angles, local pressure, and shear stress, and shortest-path rings show that these drops are related to dislocation activities under the indenter. We show that amorphization is driven by coalescence of dislocation loops and that there is a strong correlation between load-displacement response and ring distribution.

  13. Surface passivation of heavily boron or phosphorus doped crystalline silicon utilizing amorphous silicon

    NASA Astrophysics Data System (ADS)

    Carstens, K.; Dahlinger, M.

    2016-05-01

    Excellent surface passivation of heavily boron or phosphorus doped crystalline silicon is presented utilizing undoped hydrogenated amorphous silicon (a-Si:H). For passivating boron doped crystalline silicon surfaces, amorphous silicon needs to be deposited at low temperatures 150°C ≤Tdep≤200°C , leading to a high bandgap. In contrast, low bandgap amorphous silicon causes an inferior surface passivation of highly boron doped crystalline silicon. Boron doping in crystalline silicon leads to a shift of the Fermi energy towards the valence band maximum in the undoped a-Si:H. A simulation, implementing dangling bond defects according to the defect pool model, shows this shift in the undoped a-Si:H passivation to be more pronounced if the a-Si:H has a lower bandgap. Hence, the inferior passivation of boron doped surfaces with low bandgap amorphous silicon stems from a lower silicon-hydrogen bond energy due to this shift of the Fermi energy. Hydrogen effusion and ellipsometry measurements support our interpretation.

  14. Long-term stability of amorphous-silicon modules

    NASA Technical Reports Server (NTRS)

    Ross, R. G., Jr.

    1986-01-01

    The Jet Propulsion Laboratory (JPL) program of developing qualification tests necessary for amorphous silicon modules, including appropriate accelerated environmental tests reveal degradation due to illumination. Data were given which showed the results of temperature-controlled field tests and accelerated tests in an environmental chamber.

  15. Integral bypass diodes in an amorphous silicon alloy photovoltaic module

    NASA Technical Reports Server (NTRS)

    Hanak, J. J.; Flaisher, H.

    1991-01-01

    Thin-film, tandem-junction, amorphous silicon (a-Si) photovoltaic modules were constructed in which a part of the a-Si alloy cell material is used to form bypass protection diodes. This integral design circumvents the need for incorporating external, conventional diodes, thus simplifying the manufacturing process and reducing module weight.

  16. Photocurrent images of amorphous-silicon solar-cell modules

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Shumka, A.; Trask, J.

    1985-01-01

    Results obtained in applying the unique characteristics of the solar cell laser scanner to investigate the defects and quality of amorphous silicon cells are presented. It is concluded that solar cell laser scanners can be effectively used to nondestructively test not only active defects but also the cell quality and integrity of electrical contacts.

  17. Performance of amorphous silicon photovoltaic systems, 1985--1989

    SciTech Connect

    Not Available

    1990-04-01

    This report discusses the performance of commercial amorphous silicon modules used in photovoltaic power systems from 1985 through 1989. Topics discussed include initial degradation, reliability, durability, and effects of temperature and solar irradiance on peak power and energy production. 6 refs., 18 figs.

  18. Amorphous silicon carbide coatings for extreme ultraviolet optics

    NASA Technical Reports Server (NTRS)

    Kortright, J. B.; Windt, David L.

    1988-01-01

    Amorphous silicon carbide films formed by sputtering techniques are shown to have high reflectance in the extreme ultraviolet spectral region. X-ray scattering verifies that the atomic arrangements in these films are amorphous, while Auger electron spectroscopy and Rutherford backscattering spectroscopy show that the films have composition close to stoichiometric SiC, although slightly C-rich, with low impurity levels. Reflectance vs incidence angle measurements from 24 to 1216 A were used to derive optical constants of this material, which are presented here. Additionally, the measured extreme ultraviolet efficiency of a diffraction grating overcoated with sputtered amorphous silicon carbide is presented, demonstrating the feasibility of using these films as coatings for EUV optics.

  19. Ion-assisted recrystallization of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Priolo, F.; Spinella, C.; La Ferla, A.; Rimini, E.; Ferla, G.

    1989-12-01

    Our recent work on ion-beam-assisted epitaxial growth of amorphous Si layers on single crystal substrates is reviewed. The planar motion of the crystal-amorphous interface was monitored in situ, during irradiations, by transient reflectivity measurements. This technique allows the measurement of the ion-induced growth rate with a very high precision. We have observed that this growth rate scales linearly with the number of displacements produced at the crystal-amorphous interface by the impinging ions. Moreover the regrowth onto <100> oriented substrates is a factor of ≈ 4 faster with respect to that on <111> substrates. Impurities dissolved in the amorphous layer influence the kinetics of recrystallization. For instance, dopants such as As, B and P enhance the ion-induced growth rate while oxygen has the opposite effect. The dependence of the rate on impurity concentration is however less strong with respect to pure thermal annealing. For instance, an oxygen concentration of 1 × 1021 / cm3 decreases the ion-induced growth rate by a factor of ≈ 3; this same concentration would have decreased the rate of pure thermal annealing by more than 4 orders of magnitude. The reduced effects of oxygen during ion-beam crystallization allow the regrowth of deposited Si layers despite the presence of a high interfacial oxygen content. The process is investigated in detail and its possible application to the microelectronic technology is discussed.

  20. An alternate line erasure and readout (ALER) method for implementing slot-scan imaging technique with a flat-panel detector--initial experiences.

    PubMed

    Liu, Xinming; Shaw, Chris C; Altunbas, Mustafa C; Wang, Tianpeng

    2006-04-01

    This paper describes and demonstrates an electronic collimation method, referred to as the alternate line erasure and readout (ALER) technique, for implementing slot-scan digital radiography technique with an amorphous silicon (a-Si) thin-film transistor (TFT) array based flat-panel detector. An amorphus selenium (a-Se) flat-panel detector was modified to implement the ALER technique for slot-scan imaging. A stepping-motor driven fore-collimator was mounted in front of an X-ray tube to generate a scanning X-ray fan beam. The scanning speed and magnification were adjusted to synchronize the fan beam motion with the image line readout rate. The image lines on the leading and trailing edges of the fan beam were tracked and alternately reset and read out, respectively. The former operation resulted in the erasure of the scatter signals accumulated in the leading edge image line prior to the arrival of the fan beam. The latter operation resulted in the acquisition of fan beam exposure data integrated in the trailing edge image line right after the fan beam passed. To demonstrate the scatter rejection capability of this technique, an anthropomorphic chest phantom was placed in PA position and scanned at a speed of 576 lines (8.0 cm)/s at 117 kVp and 32 mA. A tungsten bar is placed at the entrance side of the chest phantom to measure the scatter-to-primary ratio (SPR), scatter reduction factor (SRF), and contrast-to-noise ratio degradation factor (CNRDF) in the slot-scan images to evaluate the effectiveness of scatter rejection and the resultant improvement of image quality. SPR and CNRDF in the open-field images were also measured and used as the reference for comparison. A scatter reduction by 86.4 to 95.4% across lower lung and heart regions has been observed with slot-scan imaging. The CNRs have been found to be improved by a factor of 2 in the mediastinum areas over the open-field image as well. PMID:16608064

  1. Hydrogen-free amorphous silicon with no tunneling states.

    PubMed

    Liu, Xiao; Queen, Daniel R; Metcalf, Thomas H; Karel, Julie E; Hellman, Frances

    2014-07-11

    The ubiquitous low-energy excitations, known as two-level tunneling systems (TLSs), are one of the universal phenomena of amorphous solids. Low temperature elastic measurements show that e-beam amorphous silicon (a-Si) contains a variable density of TLSs which diminishes as the growth temperature reaches 400 °C. Structural analyses show that these a-Si films become denser and more structurally ordered. We conclude that the enhanced surface energetics at a high growth temperature improved the amorphous structural network of e-beam a-Si and removed TLSs. This work obviates the role hydrogen was previously thought to play in removing TLSs in the hydrogenated form of a-Si and suggests it is possible to prepare "perfect" amorphous solids with "crystal-like" properties for applications. PMID:25062205

  2. Deposition of device quality low H content, amorphous silicon films

    DOEpatents

    Mahan, A.H.; Carapella, J.C.; Gallagher, A.C.

    1995-03-14

    A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH{sub 4}) over a high temperature, 2,000 C, tungsten (W) filament in the proximity of a high temperature, 400 C, substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20--30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content. 7 figs.

  3. Deposition of device quality low H content, amorphous silicon films

    DOEpatents

    Mahan, Archie H.; Carapella, Jeffrey C.; Gallagher, Alan C.

    1995-01-01

    A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH.sub.4) over a high temperature, 2000.degree. C., tungsten (W) filament in the proximity of a high temperature, 400.degree. C., substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20-30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content.

  4. Heat-Induced Agglomeration of Amorphous Silicon Nanoparticles Toward the Formation of Silicon Thin Film.

    PubMed

    Jang, Bo Yun; Kim, Ja Young; Seo, Gyeongju; Shin, Chae-Ho; Ko, Chang Hyun

    2016-01-01

    The thermal behavior of silicon nanoparticles (Si NPs) was investigated for the preparation of silicon thin film using a solution process. TEM analysis of Si NPs, synthesized by inductively coupled plasma, revealed that the micro-structure of the Si NPs was amorphous and that the Si NPs had melted and merged at a comparatively low temperature (~750 °C) considering bulk melting temperature of silicon (1414 °C). A silicon ink solution was prepared by dispersing amorphous Si NPs in propylene glycol (PG). It was then coated onto a silicon wafer and a quartz plate to form a thin film. These films were annealed in a vacuum or in an N₂ environment to increase their film density. N2 annealing at 800 °C and 1000 °C induced the crystallization of the amorphous thin film. An elemental analysis by the SIMS depth profile showed that N₂annealing at 1000 °C for 180 min drastically reduced the concentrations of carbon and oxygen inside the silicon thin film. These results indicate that silicon ink prepared using amorphous Si NPs in PG can serve as a proper means of preparing silicon thin film via solution process. PMID:27398566

  5. Motion-compensated defect interpolation for flat-panel detectors

    NASA Astrophysics Data System (ADS)

    Aach, Til; Barth, Erhardt; Mayntz, Claudia

    2004-05-01

    One advantage of flat-panel X-ray detectors is the immediate availability of the acquired images for display. Current limitations in large-area active-matrix manufacturing technology, however, require that the images read out from such detectors be processed to correct for inactive pixels. In static radiographs, these defects can only be interpolated by spatial filtering. Moving X-ray image modalities, such as fluoroscopy or cine-angiography, permit to use temporal information as well. This paper describes interframe defect interpolation algorithms based on motion compensation and filtering. Assuming the locations of the defects to be known, we fill in the defective areas from past frames, where the missing information was visible due to motion. The motion estimator is based on regularized block matching, with speedup obtained by successive elimination and related measures. To avoid the motion estimator locking on to static defects, these are cut out of each block during matching. Once motion is estimated, three methods are available for defect interpolation: direct filling-in by the motion-compensated predecessor, filling-in by a 3D-multilevel median filtered value, and spatiotemporal mean filtering. Results are shown for noisy fluoroscopy sequences acquired in clinical routine with varying amounts of motion and simulated defects up to six lines wide. They show that the 3D-multilevel median filter appears as the method of choice since it causes the least blur of the interpolated data, is robust with respect to motion estimation errors and works even in non-moving areas.

  6. Focal spot measurements using a digital flat panel detector

    PubMed Central

    Jain, Amit; Panse, A.; Bednarek, Daniel R.; Rudin, Stephen

    2014-01-01

    Focal spot size is one of the crucial factors that affect the image quality of any x-ray imaging system. It is, therefore, important to measure the focal spot size accurately. In the past, pinhole and slit measurements of x-ray focal spots were obtained using direct exposure film. At present, digital detectors are replacing film in medical imaging so that, although focal spot measurements can be made quickly with such detectors, one must be careful to account for the generally poorer spatial resolution of the detector and the limited usable magnification. For this study, the focal spots of a diagnostic x-ray tube were measured with a 10-μm pinhole using a 194-μm pixel flat panel detector (FPD). The two-dimensional MTF, measured with the Noise Response (NR) Method was used for the correction for the detector blurring. The resulting focal spot sizes based on the FWTM (Full Width at Tenth Maxima) were compared with those obtained with a very high resolution detector with 8-μm pixels. This study demonstrates the possible effect of detector blurring on the focal spot size measurements with digital detectors with poor resolution and the improvement obtained by deconvolution. Additionally, using the NR method for measuring the two-dimensional MTF, any non-isotropies in detector resolution can be accurately corrected for, enabling routine measurement of non-isotropic x-ray focal spots. This work presents a simple, accurate and quick quality assurance procedure for measurements of both digital detector properties and x-ray focal spot size and distribution in modern x-ray imaging systems. PMID:25302004

  7. Heat Transfar Properties of Flat-Panel Evacuated Porous Insrlators

    NASA Astrophysics Data System (ADS)

    Yoneno, Hirosyi; Yamamoto, Ryoichi

    Flat Panel evacuated porous insulators have been produced by filling powder or fiber (such as perlite powder, diatomaceous earth powder, silica aerogel powder, g lass fiber and ceramic fiber) in film-like laminated plastic container and by evacuating to form vacuum in it is interior. Heat transfer properties of these evacuated insulators have been studied under various conditions (such as particle diameter, surface area, packing density, solid volume fraction and void dimension). The apparent mean thermal conductivity has been measured for the boundary surface temperature at cold face temperature 13°C and hot face temperature 35°. The effect of air pressure ranging from 1 Pa to one atomosphere (105 Pa) was examined. The results were as follows. (1) For each powder the apparent mean thermal conductivity decreases with decreasing residual air pressure, and at very low pressure bellow 1 -103 Pa the conductivity becomes indeqendent of pressure. The thermal conductivity at 1.3Pa is 0.0053 W/mK for perlite powder, 0.0048W/mK for diatomaceous earth powder, 0.0043 W/mK for silica aerogel powder and 0.0029W/mK for glass fiber. (2) With decreasing particle size, the apparent mean thermal conductivity is constant independent of residual air pressure in higher pressure region. It is that void dimension continues to decrease with particle size and the mean free path of air becomes comparable with void dimension. (3) In the range of minor solid volume fraction, the apparent mean thermal conductivity at very low precreases with decreasing particle size. This shows the thermal contact resistance of the solid particle increases with decreasing particle size.

  8. Lag measurement in an a-Se active matrix flat-panel imager.

    PubMed

    Schroeder, C; Stanescu, T; Rathee, S; Fallone, B G

    2004-05-01

    Lag and residual contrast have been quantified in an amorphous selenium (a-Se) active-matrix flat-panel imager (AMFPI) as a function of frame time, kilovoltage (kV) and megavoltage (MV) x-ray photon energies and amount of radiation incident on the detector. The AMFPI contains a 200 microm thick a-Se layer deposited on a thin film transistor (TFT) array of size 8.7 cm x 8.7 cm with an 85-microm pixel pitch. For all energies, the lag (signal normalized to the signal due to exposure) for the first (n = 1) and second (n = 2) frame after exposure ranges from 0.45% to 0.91% and from 0.29% to 0.51%, respectively. The amount of lag was determined to be a function of the time after the x-ray exposure irrespective of frame time or the magnitude of exposure. The lag for MV photon energies was slightly less than that for kV photon energies. The residual contrast for all energies studied ranges from 0.41% to 0.75% and from 0.219% to 0.41% for the n = 1 and n = 2 frames, respectively. These results show that lag and residual contrast in kV and MV radiographic applications are always less than 1% for the detection system used and only depend on the time after x-ray exposure. PMID:15191310

  9. Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide.

    PubMed

    Chang, Geng-rong; Ma, Fei; Ma, Da-yan; Xu, Ke-wei

    2010-11-19

    Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells. PMID:20975214

  10. Plasma Deposition of Doped Amorphous Silicon

    NASA Technical Reports Server (NTRS)

    Calcote, H. F.

    1985-01-01

    Pair of reports present further experimental details of investigation of plasma deposition of films of phosphorous-doped amosphous silicon. Probe measurements of electrical resistance of deposited films indicated films not uniform. In general, it appeared that resistance decreased with film thickness.

  11. Light-induced metastable structural changes in hydrogenated amorphous silicon

    SciTech Connect

    Fritzsche, H.

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  12. Research on stable, high-efficiency amorphous silicon multijunction modules

    SciTech Connect

    Bhat, P.K.; Brown, S.; Hollingsworth, R.; Shen, D.S.; del Cueto, J.; Iwanicko, E.; Marshall, C.; DeHart, C.; Mentor, D.; Benson, A.; Matovich, C.; Sandwisch, J. )

    1991-04-01

    This report describes a contract to produce multijunction modules based entirely on amorphous silicon alloys, the modules having an aperture area of at least 900 cm{sup 2} and a stable, reproducible conversion efficiency of at least 6.5% after 600 hours of light exposure (air mass 1.5) at 50{degrees} C. The work focussed on (1) producing opto-electronic-grade amorphous silicon material for band gaps of about 1.7 and 1.9 eV by changing the hydrogen content in the film bonded to the silicon, (2) studying and obtaining data on the light stability of single-junction p-i-n solar cells with gaps of about 1.7 and 1.9 eV, and (3) analyzing losses in a silicon/silicon multijunction cell. We report new results on an indium tin oxide (ITO)/silver back contact and the deposition of granular tin oxide by atmospheric-pressure chemical vapor deposition. Progress toward module fabrication at the end of six months has been good, with the demonstration of 5.4% initial efficiency in a silicon/silicon multijunction submodule with an aperture area of 4620 cm{sup 2} and incorporating devices with 2nd-junction i-layer thicknesses of about 3500 {angstrom}. We also demonstrated a single-junction silicon submodule with an aperture area of 4620 cm{sup 2}, a thickness of about 3500 {angstrom}, and an initial efficiency of 6.5%. 4 refs., 39 figs., 5 tabs.

  13. Use of Tritium in the Study of defects in Amorphous Silicon

    SciTech Connect

    Costea, S.; Pisana, S.; Kherani, N.P.; Gaspari, F.; Kosteski, T.; Shmayda, W.T.; Zukotynski, S.

    2005-11-28

    Hydrogen is known to strongly affect the physical properties of amorphous semiconductors. Indeed hydrogen is introduced during the growth of amorphous silicon films, used in active matrix displays and solar cells, to passivate silicon dangling bonds and to relax the lattice thereby reducing the density of states in the energy gap by several orders of magnitude and giving rise to device grade material. Ideally, hydrogenated amorphous silicon (a-Si:H) is a continuous covalently bonded random network of silicon-silicon and silicon-hydrogen atoms, with the predominant nearest neighbour environment similar to that of crystalline silicon.

  14. Flat panel displays for ubiquitous product applications and related impurity doping technologies

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshiharu

    2006-06-01

    Various kinds of flat panel displays such as liquid crystal displays (LCDs), plasma display panels and organic light emitting diode (OLED) displays are briefly evaluated from the perspective of applicability to ubiquitous products. It is clarified that the LCDs and OLED displays are suitable for realizing mobile electronic products with a high quality display, since these displays can use active devices on the backplanes to form active matrix displays and can integrate peripheral circuits of the displays and functional circuits of mobile electronics for a ubiquitous era. It is clarified further that the low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) is the most promising active device for the backplane of such active matrix displays because the LTPS TFT has the possibility to enhance its performance without raising the cost. The low temperature poly-Si TFT fabrication process is introduced, and its key technologies such as crystallization, gate oxide formation, and impurity doping are surveyed. As the property of polycrystalline silicon (poly-Si) influences not only the TFT performance itself but also the efficiency of impurity doping and the integrity of the gate oxide, the crystallinity of the poly-Si is reviewed. After that, the history of the development and the state of the art in impurity doping technology and its issues are addressed in detail. Finally, foreseeing the application of LTPS TFT, the realization of OLED displays, and the progress of LTPS TFT for integrating higher functional circuits for ubiquitous applications, the requirements for impurity doping in such progress are addressed. In particular, the single grain silicon technology and the scaling down of the TFT size, which are thought to be highly effective to enhance the performance of TFTs, and issues of impurity doping technology relating to them are discussed.

  15. Electrochemical degradation of amorphous-silicon photovoltaic modules

    NASA Technical Reports Server (NTRS)

    Mon, G. R.; Ross, R. G., Jr.

    1985-01-01

    Techniques of module electrochemical corrosion research, developed during reliability studies of crystalline-silicon modules (C-Si), have been applied to this new investigation into amorphous-silicon (a-Si) module reliability. Amorphous-Si cells, encapsulated in the polymers polyvinyl butyral (PVB) and ethylene vinyl acetate (EVA), were exposed for more than 1200 hours in a controlled 85 C/85 percent RH environment, with a constant 500 volts applied between the cells and an aluminum frame. Plotting power output reduction versus charge transferred reveals that about 50 percent a-Si cell failures can be expected with the passage of 0.1 to 1.0 Coulomb/cm of cell-frame edge length; this threshold is somewhat less than that determined for C-Si modules.

  16. The reliability and stability of multijunction amorphous silicon PV modules

    SciTech Connect

    Carlson, D.E.

    1995-11-01

    Solarex is developing a manufacturing process for the commercial production of 8 ft{sup 2} multijunction amorphous silicon (a-Si) PV modules starting in 1996. The device structure used in these multijunction modules is: glass/textured tin oxide/p-i-n/p-i-n/ZnO/Al/EVA/Tedlar where the back junction of the tandem structure contains an amorphous silicon germanium alloy. As an interim step, 4 ft{sup 2} multijunction modules have been fabricated in a pilot production mode over the last several months. The distribution of initial conversion efficiencies for an engineering run of 67 modules (4 ft{sup 2}) is shown. Measurements recently performed at NREL indicate that the actual efficiencies are about 5% higher than those shown, and thus exhibit an average initial conversion efficiency of about 9.5%. The data indicates that the process is relatively robust since there were no modules with initial efficiencies less than 7.5%.

  17. Amorphous silicon based large format uncooled FPA microbolometer technology

    NASA Astrophysics Data System (ADS)

    Schimert, T.; Brady, J.; Fagan, T.; Taylor, M.; McCardel, W.; Gooch, R.; Ajmera, S.; Hanson, C.; Syllaios, A. J.

    2008-04-01

    This paper presents recent developments in next generation microbolometer Focal Plane Array (FPA) technology at L-3 Communications Infrared Products (L-3 CIP). Infrared detector technology at L-3 CIP is based on hydrogenated amorphous silicon (a-Si:H) and amorphous silicon germanium(a-SiGe:H). Large format high performance, fast, and compact IR FPAs are enabled by a low thermal mass pixel design; favorable material properties; an advanced ROIC design; and wafer level packaging. Currently at L-3 CIP, 17 micron pixel FPA array technology including 320x240, 640 x 480 and 1024 x768 arrays is under development. Applications of these FPAs range from low power microsensors to high resolution near-megapixel imager systems.

  18. 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%.

  19. Amorphous-silicon thin-film heterojunction solar cells

    SciTech Connect

    Cretella, M. C.; Gregory, J. A.; Sandstrom, D. B.; Paul, W.

    1981-01-01

    The investigation of amorphous silicon materials at MTSEC has had two major thrusts: (1) to improve the amorphous material, i.e., obtain a low state density in the gap, improve the carrier collection depth and diminish non-radiative recombinations; and (2) to attempt to understand and improve on the limitations of the junction devices while evaluating the amorphous silicon materials. In the first of these efforts, the investigation has continued to examine the modifications to the a-Si(H) network by alloying silicon with other group IVA elements, either in binary or ternary compositions, and/or by replacing the hydrogenation for defect compensation with a combination of hydrogenation and alkylation or hydrogenation and halogenation. The doped junction layers are being examined in an attempt to determine the limiting characteristics of the junctions in solar cell devices of these amorphous materials. Amorphous alloys of Si-Ge, Si-C, Si-Sn were prepared as well as ternary compositions of Si-Ge-C and Si-Sn-C. In addition, Na vapor was added to the gas feed to deposit a-Si(Na, H) films, and to prepare Si-Sn, fluoride was added along with the tin by vapor additions of SnF/sub 4/ to the gas feed. The optical properties of these materials were measured, and structural and compositional information was obtained from the IR vibrational spectra using the scanning electron microscope and from analyses using scanning Auger microscopy. Electrical measurements have included the dark conductivity and the photo conductivity under room fluorescent light and at AM1 conditions. With alloys that displayed promising photoconductive properties n-i-p devices were prepared to assess the solar cell properties. Details are presented. (WHK)

  20. Advances and opportunities in the amorphous silicon research field

    SciTech Connect

    Sabisky, E.; Wallace, W.; Mikhall, A.; Mahan, H.; Tsuo, S.

    1984-05-01

    The amorphous materials and thin-film solar cells program was initiated by the US Department of Energy in 1978 and then transferred to the Solar Energy Research Institute. The aim of the present DOE/SERI program is to achieve 5-year DOE research goals by addressing photovoltaic research in single-junction amorphous thin films as well as the most promising option in high-efficiency, multijunction solar cells. Multiyear subcontract awards initiated in 1983 were designed to demonstrate a stable, small-area, p-i-n solar cell of at least 12% (AMI) efficiency, a stable submodule of at least 8% (AMI) efficiency, a stable submodule of at least 8% (AMI) efficiency (total area, 1000 cm/sup 2/), and a proof-of-concept multijunction amorphous silicon alloy thin-film solar cell that will lead to achieving an 18% efficiency goal in 1988.

  1. Amorphization and defect recombination in ion implanted silicon carbide

    SciTech Connect

    Grimaldi, M.G.; Calcagno, L.; Musumeci, P.; Frangis, N.; Van Landuyt, J.

    1997-06-01

    The damage produced in silicon carbide single crystals by ion implantation was investigated by Rutherford backscattering channeling and transmission electron microscopy techniques. Implantations were performed at liquid nitrogen and at room temperatures with several ions to examine the effect of the ion mass and of the substrate temperature on the damaging process. The damage accumulation is approximately linear with fluence until amorphization occurs when the elastic energy density deposited by the ions overcomes a critical value. The critical energy density for amorphization depends on the substrate temperature and is greatest at 300 K indicating that defects recombination occurs already at room temperature. Formation of extended defects never occurred and point defects and uncollapsed clusters of point defects were found before amorphization even in the case of light ion implantation. The atomic displacement energy has been estimated to be {approximately}12 eV/atom from the analysis of the damage process in dilute collision cascades. {copyright} {ital 1997 American Institute of Physics.}

  2. Charged particle detectors made from thin layers of amorphous silicon

    SciTech Connect

    Morel, J.R.

    1986-05-01

    A series of experiments was conducted to determine the feasibility of using hydrogenated amorphous silicon (..cap alpha..-Si:H) as solid state thin film charged particle detectors. /sup 241/Am alphas were successfully detected with ..cap alpha..-Si:H devices. The measurements and results of these experiments are presented. The problems encountered and changes in the fabrication of the detectors that may improve the performance are discussed.

  3. Corrosion In Amorphous-Silicon Solar Cells And Modules

    NASA Technical Reports Server (NTRS)

    Mon, Gordon R.; Wen, Liang-Chi; Ross, Ronald G., Jr.

    1988-01-01

    Paper reports on corrosion in amorphous-silicon solar cells and modules. Based on field and laboratory tests, discusses causes of corrosion, ways of mitigating effects, and consequences for modules already in field. Suggests sealing of edges as way of reducing entry of moisture. Cell-free perimeters or sacrificial electrodes suggested to mitigate effects of sorbed moisture. Development of truly watertight module proves to be more cost-effective than attempting to mitigate effects of moisture.

  4. Optically induced conductivity changes in amorphous silicon: A historical perspective

    SciTech Connect

    Staebler, D.L.

    1997-07-01

    A historical perspective of the discovery of optically induced changes in amorphous silicon is presented in this paper from my personal point of view. It includes the story of how Chris Wronski and the author discovered the effect, the key elements in the R and D environment that lead to the quick realization that the effect was reversible and reproducible, how the research environment supported the rapid publication of their first paper, and a brief look at the effect from today's perspective.

  5. Electron trapping in amorphous silicon: A quantum molecular dynamics study

    SciTech Connect

    Yang, Lin H.; Kalia, R.K.; Vashishta, P.

    1990-12-01

    Quantum molecular dynamics (QMD) simulations provide the real-time dynamics of electrons and ions through numerical solutions of the time-dependent Schrodinger and Newton equations, respectively. Using the QMD approach we have investigated the localization behavior of an excess electron in amorphous silicon at finite temperatures. For time scales on the order of a few picoseconds, we find the excess electron is localized inside a void of radius {approximately}3 {Angstrom} at finite temperatures. 12 refs.

  6. Advances in amorphous silicon alloy multijunction cells and modules

    SciTech Connect

    Guha, S.; Yang, J.; Banerjee, A.; Glatfelter, T.; Hoffman, K.; Xu, X.

    1996-01-01

    We discuss the research directions taken to improve the stable efficiency of amorphous silicon alloy multijunction modules. Use of hydrogen dilution during deposition has resulted in improvement of initial efficiency and stability of the component cells in the triple-junction structure. An innovative laser-interconnected module design has resulted in the reduction of optical and electrical losses in the module down to 1{percent}. {copyright} {ital 1996 American Institute of Physics.}

  7. Detection of charged particles in amorphous silicon layers

    SciTech Connect

    Kaplan, S.N.; Morel, J.R.; Mulera, T.A.; Perez-Mendez, V.; Schnurmacher, G.; Street, R.A.

    1985-10-01

    The successful development of radiation detectors made from amorphous silicon could offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particles. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics. 4 refs., 7 figs.

  8. Enhanced Multiple Exciton Generation in Amorphous Silicon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Kryjevski, Andrei; Mihaylov, Deyan; Kilin, Dmitri

    2015-03-01

    Multiple exciton generation (MEG) in nm-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms depends strongly on the degree of the core structural disorder as shown by the many-body perturbation theory (MBPT) calculations based on the DFT simulations. Here, we use the HSE exchange correlation functional. In MBPT, we work to the 2nd order in the electron-photon coupling and in the approximate screened Coulomb interaction. We also include the effect of excitons for which we solve Bethe-Salpeter Equation. We calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, in 3D arrays of Si29H36 quantum dots, NWs, and quasi 2D silicon nanofilms, all with both crystalline and amorphous core structures. Efficient MEG with QE of 1.3 up to 1.8 at the photon energy of about 3Eg , where Eg is the gap, is predicted in these nanoparticles except for the crystalline NW and film where QE ~= 1 . MEG in the amorphous nanoparticles is enhanced by the electron localization due to structural disorder. The exciton effects significantly red-shift QE (Ephoton) curves. Nanometer-sized amorphous silicon NWs and films are predicted to have effective MEG within the solar spectrum range. We acknowledge NSF support (CHE-1413614) for method development.

  9. Femtosecond studies of plasma formation in crystalline and amorphous silicon

    NASA Astrophysics Data System (ADS)

    Kuett, Waldemar; Esser, Anton; Seibert, Klaus; Lemmer, Uli; Kurz, Heinrich

    1990-08-01

    Transient pump-probe reflectivity measurements are performed on crystalline and amorphous Silicon samples with 50 fs optical pulses at 2 eV. The excited carrier densities range from 1017cm3 up to a few 1021cm3. In both cases the reflectivity signal is dominated by a Drude-like carrier response. Crystalline Silicon shows a distinct subpicosecond feature due to the cooling of the optically excited hot carriers with a time constant of 200-300 fs. Diffusion and Auger-recombination come into play at higher carrier densities. A superlinear increase of instant reflectivity signal with excitation fluence is due to two-photon absorption (TPA) with a TPA-coeffiecient f:37+-5 cm/GW. In amorphous Silicon the TPA process is not observable. The recovery of the induced negative reflectivity changes is dominated by trapping into bandtail and defect states at lower carrier densities. At higher densities a non-radiative recombination process dominates the relaxation of free carriers in both materials. Comparison with crystalline Silicon clearly demonstrates the enhancement of the Auger-recombination process in disordered materials by more than an order of magnitude.

  10. Empirical and theoretical investigation of the noise performance of indirect detection, active matrix flat-panel imagers (AMFPIs) for diagnostic radiology.

    PubMed

    Siewerdsen, J H; Antonuk, L E; el-Mohri, Y; Yorkston, J; Huang, W; Boudry, J M; Cunningham, I A

    1997-01-01

    Noise properties of active matrix, flat-panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin-film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x-ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency-dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x-ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 1536 x 1920 pixels at a pixel pitch of 127 microns. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI: Tl intensifying screen can be optimized to provide detective quantum efficiency (DQE) superior to existing screen-film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a-Si:H imagers, DQE performance approaching that of the best x-ray image intensifier systems may be possible. The results of this analysis suggest strategies for

  11. Electron-beam-induced information storage in hydrogenated amorphous silicon devices

    DOEpatents

    Yacobi, B.G.

    1985-03-18

    A method for recording and storing information in a hydrogenated amorphous silicon device, comprising: depositing hydrogenated amorphous silicon on a substrate to form a charge collection device; and generating defects in the hydrogenated amorphous silicon device, wherein the defects act as recombination centers that reduce the lifetime of carriers, thereby reducing charge collection efficiency and thus in the charge collection mode of scanning probe instruments, regions of the hydrogenated amorphous silicon device that contain the defects appear darker in comparison to regions of the device that do not contain the defects, leading to a contrast formation for pattern recognition and information storage.

  12. Improved method of preparing p-i-n junctions in amorphous silicon semiconductors

    DOEpatents

    Madan, A.

    1984-12-10

    A method of preparing p/sup +/-i-n/sup +/ junctions for amorphous silicon semiconductors includes depositing amorphous silicon on a thin layer of trivalent material, such as aluminum, indium, or gallium at a temperature in the range of 200/sup 0/C to 250/sup 0/C. At this temperature, the layer of trivalent material diffuses into the amorphous silicon to form a graded p/sup +/-i junction. A layer of n-type doped material is then deposited onto the intrinsic amorphous silicon layer in a conventional manner to finish forming the p/sup +/-i-n/sup +/ junction.

  13. The U.S. and Japanese amorphous silicon technology programs A comparison

    NASA Technical Reports Server (NTRS)

    Shimada, K.

    1984-01-01

    The U.S. Department of Energy/Solar Energy Research Institute Amorphous Silicon (a-Si) Solar Cell Program performs R&D on thin-film hydrogenated amorphous silicon for eventual development of stable amorphous silicon cells with 12 percent efficiency by 1988. The Amorphous Silicon Solar Cell Program in Japan is sponsored by the Sunshine Project to develop an alternate energy technology. While the objectives of both programs are to eventually develop a-Si photovoltaic modules and arrays that would produce electricity to compete with utility electricity cost, the U.S. program approach is research oriented and the Japanese is development oriented.

  14. 360-degree three-dimensional flat panel display using holographic optical elements

    NASA Astrophysics Data System (ADS)

    Yabu, Hirofumi; Takeuchi, Yusuke; Yoshimoto, Kayo; Takahashi, Hideya; Yamada, Kenji

    2015-03-01

    We proposed the 360-degree 3D display system which is composed of a flat panel display, a light control film, and holographic optical element (HOE). The HOE is a diffraction grating which is made by holography technique. HOE lens can be produced on the thin polygonal glass plate. The light control film and HOE lenses are used to control the direction of light from the flat panel display in our system. The size of proposed system depends on the size of the flat panel display is because other parts of proposed system are thin and placed on the screen of the flat panel display. HOE lenses and a light control film are used to control lights from multiple pixels of a flat panel display to multiple viewpoints. To display large 3D images and to increase viewpoints, we divided parallax images into striped images and distributed them on the display for multiple viewpoints. Therefore, observers can see the large 3D image around the system. To verify the effectiveness of the proposed system, we made the experimental system. To verify the effectiveness of the proposed system, we constructed the part of the proposed system. The experimental system is composed of the liquid crystal display (LCD), prototype HOE lenses, and light control films. We confirmed that experimental system can display two images to different viewpoints. This paper describes the configuration of the proposed system, and also describes the experimental result.

  15. Grain boundary resistance to amorphization of nanocrystalline silicon carbide.

    PubMed

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-01-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized. PMID:26558694

  16. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-11-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized.

  17. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    PubMed Central

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-01-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized. PMID:26558694

  18. Amorphous silicon technology improvement at CEA-LETI

    NASA Astrophysics Data System (ADS)

    Mottin, Eric; Bain, Astrid; Castelein, Pierre; Ouvrier-Buffet, Jean-Louis; Tissot, Jean-Luc; Yon, Jean-Jacques; Chatard, Jean-Pierre

    2002-05-01

    The emergence of uncooled infrared detectors has opened new opportunities for IR imaging both for military and civil applications. Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power. Uncooled infrared sensor technology has advanced rapidly in the past few years. Higher performance sensors, electronics integration at the sensor, and new concepts for signal processing are generating advanced infrared focal plane arrays. This would significantly reduce the cost and accelerate the implementation of sensors for applications such as surveillance or predictive maintenance. We present the uncooled infrared detector operation principle and the development at CEA/LETI from the 256 x 64 with a pitch of 50 micrometers to the 320 x 240 with a pitch of 35 micrometers . LETI has been involved in Amorphous Silicon uncooled microbolometer development since 1992. This silicon IR detection is now well mastered and matured so that industrial transfer of LETI technology was performed in 2000 towards Sofradir. Industrial production of 320 x 240 microbolometer array with 45micrometers pitch is then started. After a description of the technology and the methodology for reliability enhancement, we present the readout circuit architectures designs and its evolution from the 256 x 64 array to the different version of 320 x 240 arrays. Electro-optical results obtained from these IRCMOS are presented. NEDT close to 30 mK is now obtained with our standard microbolometer amorphous silicon technology.

  19. Improvement of illumination uniformity for LED flat panel light by using micro-secondary lens array.

    PubMed

    Lee, Hsiao-Wen; Lin, Bor-Shyh

    2012-11-01

    LED flat panel light is an innovative lighting product in recent years. However, current flat panel light products still contain some drawbacks, such as narrow lighting areas and hot spots. In this study, a micro-secondary lens array technique was proposed and applied for the design of the light guide surface to improve the illumination uniformity. By using the micro-secondary lens array, the candela distribution of the LED flat panel light can be adjusted to similar to batwing distribution to improve the illumination uniformity. The experimental results show that the enhancement of the floor illumination uniformity is about 61%, and that of the wall illumination uniformity is about 20.5%. PMID:23187654

  20. Improvement of illumination uniformity for LED flat panel light by using micro-secondary lens array.

    PubMed

    Lee, Hsiao-Wen; Lin, Bor-Shyh

    2012-11-01

    LED flat panel light is an innovative lighting product in recent years. However, current flat panel light products still contain some drawbacks, such as narrow lighting areas and hot spots. In this study, a micro-secondary lens array technique was proposed and applied for the design of the light guide surface to improve the illumination uniformity. By using the micro-secondary lens array, the candela distribution of the LED flat panel light can be adjusted to similar to batwing distribution to improve the illumination uniformity. The experimental results show that the enhancement of the floor illumination uniformity is about 61%, and that of the wall illumination uniformity is about 20.5%. PMID:23326825

  1. Flat-panel see-through three-dimensional display based on integral imaging.

    PubMed

    Takaki, Yasuhiro; Yamaguchi, Yuta

    2015-04-15

    This study proposes a technique to construct a flat-panel see-through three-dimensional (3D) display based on integral imaging. This display consists of multiple lens arrays, a transparent flat-panel display, and a light-blocking wall (LBW). Rays behind the display are reconstructed in front of it by combination of the lens arrays and the LBW to provide the see-through function. The combination of one of the lens arrays and the transparent flat-panel display produces full-parallax 3D images, which are superimposed on background images. The experimental system is constructed to verify the proposed technique. The see-through and superposition capabilities of the experimental system are demonstrated. PMID:25872096

  2. Ultralight amorphous silicon alloy photovoltaic modules for space applications

    NASA Technical Reports Server (NTRS)

    Hanak, J. J.; Chen, Englade; Fulton, C.; Myatt, A.; Woodyard, J. R.

    1987-01-01

    Ultralight and ultrathin, flexible, rollup monolithic PV modules have been developed consisting of multijunction, amorphous silicon alloys for either terrestrial or aerospace applications. The rate of progress in increasing conversion efficiency of stable multijunction and multigap PV cells indicates that arrays of these modules can be available for NASA's high power systems in the 1990's. Because of the extremely light module weight and the highly automated process of manufacture, the monolithic a-Si alloy arrays are expected to be strongly competitive with other systems for use in NASA's space station or in other large aerospace applications.

  3. Radiation damage and annealing of amorphous silicon solar cells

    NASA Technical Reports Server (NTRS)

    Byvik, C. E.; Slemp, W. S.; Smith, B. T.; Buoncristiani, A. M.

    1984-01-01

    Amorphous silicon solar cells were irradiated with 1 MeV electrons at the Space Environmental Effects Laboratory of the NASA Langley Research Center. The cells accumulated a total fluence of 10 to the 14th, 10 to the 15th, and 10 to the 16th electrons per square centimeter and exhibited increasing degradation with each irradiation. This degradation was tracked by evaluating the I-V curves for AM0 illumination and the relative spectral response. The observed radiation damage was reversed following an anneal of the cells under vacuum at 200 C for 2 hours.

  4. Progress in amorphous silicon multijunction research at solarex

    SciTech Connect

    Arya, R.R.; Carlson, D.E.; Yang, L.; Chen, L.F.; Willing, F.; Rajan, K.; Jansen, K.; Poplawski, C.; Bradley, D.; Wood, G.

    1997-02-01

    Large strides have been made at Solarex inadvancing amorphous silicon multijunction technology to a maturity level where large-area commercial modules are technically and economically viable. Tandem junction modules (4ft{sup 2}) have been demonstrated with average stabilized efficiency of 8{percent}. While maintaining stabilized efficiency the a-Si alloy deposition time has been reduced by 28{percent} and the material usage reduced by 38{percent}. Progress has also been made in understanding and improving ZnO front contact and stability. {copyright} {ital 1997 American Institute of Physics.}

  5. Progress in amorphous silicon PV technology: An update

    SciTech Connect

    Luft, W.; Branz, H.M.; Dalal, V.L.; Hegedus, S.S.; Schiff, E.A.

    1995-07-01

    To reach the 15% stabilized efficiency goal for amorphous silicon (a-Si) modules by the year 2005, the National Renewable Energy Laboratory has established four research teams. The teams -- with members from industry, universities, and NREL -- have been in operation for 2.5 years now. Consensus has been reached that a triple-junction a-Si structure is needed to reach the efficiency goal. Performance parameter goals for the overall structure and the three component cells have been formulated. All four teams have generated their own development plans. Individual team progress relative to the plans is reported.

  6. Structural properties of amorphous silicon produced by electron irradiation

    SciTech Connect

    Yamasaki, J.; Takeda, S.

    1999-07-01

    The structural properties of the amorphous Si (a-Si), which was created from crystalline silicon by 2 MeV electron irradiation at low temperatures about 25 K, are examined in detail by means of transmission electron microscopy and transmission electron diffraction. The peak positions in the radial distribution function (RDF) of the a-Si correspond well to those of a-Si fabricated by other techniques. The electron-irradiation-induced a-Si returns to crystalline Si after annealing at 550 C.

  7. Enhanced electrochemical etching of ion irradiated silicon by localized amorphization

    NASA Astrophysics Data System (ADS)

    Dang, Z. Y.; Breese, M. B. H.; Lin, Y.; Tok, E. S.; Vittone, E.

    2014-05-01

    A tailored distribution of ion induced defects in p-type silicon allows subsequent electrochemical anodization to be modified in various ways. Here we describe how a low level of lattice amorphization induced by ion irradiation influences anodization. First, it superposes a chemical etching effect, which is observable at high fluences as a reduced height of a micromachined component. Second, at lower fluences, it greatly enhances electrochemical anodization by allowing a hole diffusion current to flow to the exposed surface. We present an anodization model, which explains all observed effects produced by light ions such as helium and heavy ions such as cesium over a wide range of fluences and irradiation geometries.

  8. Diffusion length measurements of thin amorphous silicon layers

    NASA Astrophysics Data System (ADS)

    van den Heuvel, J. C.; van Oort, R. C.; Geerts, M. J.

    1989-02-01

    A new method for the analysis of diffusion length measurements by the Surface Photovoltage (SPV) method is presented. It takes into account the effect of the reflection of light from the back contact in thin layers and the effect of a finite bandwidth of the used interference filters. The model was found to agree with experiments on thin amorphous silicon (a-Si:H) layers. It is shown that in the region were these effects are negligible this method is equivalent to the standard method.

  9. Enhanced electrochemical etching of ion irradiated silicon by localized amorphization

    SciTech Connect

    Dang, Z. Y.; Breese, M. B. H.; Lin, Y.; Tok, E. S.; Vittone, E.

    2014-05-12

    A tailored distribution of ion induced defects in p-type silicon allows subsequent electrochemical anodization to be modified in various ways. Here we describe how a low level of lattice amorphization induced by ion irradiation influences anodization. First, it superposes a chemical etching effect, which is observable at high fluences as a reduced height of a micromachined component. Second, at lower fluences, it greatly enhances electrochemical anodization by allowing a hole diffusion current to flow to the exposed surface. We present an anodization model, which explains all observed effects produced by light ions such as helium and heavy ions such as cesium over a wide range of fluences and irradiation geometries.

  10. Athermal shear-transformation-zone theory of amorphous plastic deformation. II. Analysis of simulated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Bouchbinder, Eran; Langer, J. S.; Procaccia, Itamar

    2007-03-01

    In the preceding paper, we developed an athermal shear-transformation-zone (STZ) theory of amorphous plasticity. Here we use this theory in an analysis of numerical simulations of plasticity in amorphous silicon by Demkowicz and Argon (DA). In addition to bulk mechanical properties, those authors observed internal features of their deforming system that challenge our theory in important ways. We propose a quasithermodynamic interpretation of their observations in which the effective disorder temperature, generated by mechanical deformation well below the glass temperature, governs the behavior of other state variables that fall in and out of equilibrium with it. Our analysis points to a limitation of either the step-strain procedure used by DA in their simulations, or the STZ theory in its ability to describe rapid transients in stress-strain curves, or perhaps to both. Once we allow for this limitation, we are able to bring our theoretical predictions into accurate agreement with the simulations.

  11. Lithium concentration dependent structure and mechanics of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Sitinamaluwa, H. S.; Wang, M. C.; Will, G.; Senadeera, W.; Zhang, S.; Yan, C.

    2016-06-01

    A better understanding of lithium-silicon alloying mechanisms and associated mechanical behavior is essential for the design of Si-based electrodes for Li-ion batteries. Unfortunately, the relationship between the dynamic mechanical response and microstructure evolution during lithiation and delithiation has not been well understood. We use molecular dynamic simulations to investigate lithiated amorphous silicon with a focus to the evolution of its microstructure, phase composition, and stress generation. The results show that the formation of LixSi alloy phase is via different mechanisms, depending on Li concentration. In these alloy phases, the increase in Li concentration results in reduction of modulus of elasticity and fracture strength but increase in ductility in tension. For a LixSi system with uniform Li distribution, volume change induced stress is well below the fracture strength in tension.

  12. Optical absorption of ion-beam sputtered amorphous silicon coatings

    NASA Astrophysics Data System (ADS)

    Steinlechner, Jessica; Martin, Iain W.; Bassiri, Riccardo; Bell, Angus; Fejer, Martin M.; Hough, Jim; Markosyan, Ashot; Route, Roger K.; Rowan, Sheila; Tornasi, Zeno

    2016-03-01

    Low mechanical loss at low temperatures and a high index of refraction should make silicon optimally suited for thermal noise reduction in highly reflective mirror coatings for gravitational wave detectors. However, due to high optical absorption, amorphous silicon (aSi) is unsuitable for being used as a direct high-index coating material to replace tantala. A possible solution is a multimaterial design, which enables exploitation of the excellent mechanical properties of aSi in the lower coating layers. The possible number of aSi layers increases with absorption reduction. In this work, the optimum heat treatment temperature of aSi deposited via ion-beam sputtering was investigated and found to be 450 °C . For this temperature, the absorption after deposition of a single layer of aSi at 1064 nm and 1550 nm was reduced by more than 80%.

  13. Chemical vapor deposition of hydrogenated amorphous silicon from disilane

    SciTech Connect

    Bogaert, R.J.; Russell, T.W.F.; Klein, M.T. . Dept. of Chemical Engineering); Rocheleau, R.E.; Baron, B.N. . Inst. of Energy Conversion)

    1989-10-01

    The authors describe hydrogenated amorphous silicon (a-Si:H) thin films deposited at growth rates of 1 to 30 A/s by chemical vapor deposition (CVD) from disilane source gas at 24 torr total pressure in a tubular reactor. The effects of substrate temperature and gas holding time (flow rate) on film growth rate and effluent gas composition were measured at temperatures ranging from 360{sup 0} to 485{sup 0}C and gas holding times from 3 to 62s. Effluent gases determined by gas chromatography included silane, disilane and other higher order silanes. A chemical reaction engineering model, based on a silylene (SiH/sub 2/) insertion gas phase reaction network and film growth from both SiH/sub 2/ and high molecular weight silicon species, Si/sub n/H/sub 2n/, was developed. The model predictions were in good agreement with experimentally determined growth rates and effluent gas compositions.

  14. Chemical vapor deposition of boron-doped hydrogenated amorphous silicon

    SciTech Connect

    Ellis F.B. Jr.; Delahoy, A.E.

    1985-07-15

    Deposition conditions and film properties for a variety of boron-doped hydrogenated amorphous silicon films and silicon-carbon films produced by chemical vapor deposition (CVD) are discussed. Deposition gases include monosilane, disilane, trisilane, and acetylene. Two types of optically wide band-gap p layers are obtained. One of these window p layers (without carbon) has been extensively tested in photovoltaic devices. Remarkably, this p layer can be deposited between about 200 to 300 /sup 0/C. A typical open circuit voltage in an all CVD p-i-n device is 0.70--0.72 V, and in a hybrid device where the i and n layers are deposited by glow discharge, 0.8--0.83 V.

  15. Super multi-view display with a lower resolution flat-panel display.

    PubMed

    Takaki, Yasuhiro; Tanaka, Kosuke; Nakamura, Junya

    2011-02-28

    A lenticular-type super multi-view (SMV) display normally requires an ultra high-resolution flat-panel display. To reduce this resolution requirement, two or more views are generated around each eye with an interval smaller than the pupil diameter. Cylindrical lenses constituting a lenticular lens project a group of pixels of the flat-panel display to generate a group of viewing zones. Pixel groups generating left and right viewing zones through the same cylindrical lens are partitioned to separate the two zones. The left and right pixel groups for different cylindrical lenses are interlaced horizontally. A prototype SMV display is demonstrated. PMID:21369242

  16. Amorphous silicon-carbon alloys and amorphous carbon from direct methane and ethylene activation by ECR

    SciTech Connect

    Conde, J.P.; Chu, V.; Giorgis, F.; Pirri, C.F.; Arekat, S.

    1997-07-01

    Hydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. Hydrogen is introduced into the source resonance cavity as an excitation gas. Silane is introduced in the main chamber in the vicinity of the plasma stream, whereas the carbon source gases, methane or ethylene, are introduced either with the silane or with the hydrogen as excitation gases. The effect of the type of carbon-source gas, excitation gas mixture and silane-to-carbon source gas flow ratio on the deposition rate, bandgap, subgap density of states, spin density and hydrogen evolution are studied.

  17. Chemical vapor deposition of amorphous silicon films from disilane

    SciTech Connect

    Bogaert, R.J.

    1986-01-01

    Amorphous silicon films for fabrication of solar cells have been deposited by thermal chemical vapor deposition (CVD) from disilane (Si/sub 2/H/sub 6/) using a tubular flow reactor. A mathematical description for the CVD reactor was developed and solved by a numerical procedure. The proposed chemical reaction network for the model is based on silylene (SiH/sub 2/) insertion in the gas phase and film growth from SiH/sub 2/ and silicon polymers (Si/sub n/N/sub 2n/, n approx. 10). Estimates of the rate constants have been obtained for trisilane decomposition, silicon polymer formation, and polymer dehydrogenation. The silane unimolecular decomposition rate constants were corrected for pressure effects. The model behavior is compared to the experimental results over the range of conditions: reactor temperature (360 to 485/sup 0/C), pressures (2 to 48 torr), and gas holding time (1 to 70 s). Within the above range of conditions, film growth rate varies from 0.01 to 30 A/s. Results indicate that silicon polymers are the main film precursors for gas holding times greater than 3 s. Film growth by silylene only becomes important at short holding times, large inert gas dilution, and positions near the beginning of the reactor hot zone.

  18. Hydrogen structures in heavily hydrogenated crystalline and amorphous silicon

    SciTech Connect

    Jackson, W.G.; Franz, A.; Chabal, Y.; Weldon, M.K.; Jin, H.C.; Abelson, J.R.

    1998-12-31

    The hydrogen binding energy distribution and IR spectra of hydrogen platelets in c-Si have been measured and compared to H in other forms of silicon including hydrogenated polycrystalline and amorphous Si. The binding distribution for platelet containing samples, determined using H evolution, exhibits two peaks: a bulk peak at 1.8--1.9 eV below the transport barrier, and a second possibly surface related peak 1.8--1.9 eV below the surface evolution barrier. The bulk peak grows at 250 C and is consistent with calculated energies for platelet structures. The same two evolution peaks are found in hydrogenated polycrystalline Si and amorphous silicon. The IR spectra for heavily hydrogenated c-Si are dominated by the stretching modes at 2076 and 2128 cm{sup {minus}1}. Most surprisingly there appears to be a strong mode at 856 cm{sup {minus}1} which is associated with a deformation mode of SiH{sub 3}. Even more surprising, this SiH{sub 3} 856 cm{sup {minus}1} mode remains until 550 C indicating that the SiH{sub 3} containing structures are rather stable.

  19. Geometric photovoltaics applied to amorphous silicon thin film solar cells

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, Timothy

    Geometrically generalized analytical expressions for device transport are derived from first principles for a photovoltaic junction. Subsequently, conventional planar and unconventional coaxial and hemispherical photovoltaic architectures are applied to detail the device physics of the junction based on their respective geometry. For the conventional planar cell, the one-dimensional transport equations governing carrier dynamics are recovered. For the unconventional coaxial and hemispherical junction designs, new multi-dimensional transport equations are revealed. Physical effects such as carrier generation and recombination are compared for each cell architecture, providing insight as to how non-planar junctions may potentially enable greater energy conversion efficiencies. Numerical simulations are performed for arrays of vertically aligned, nanostructured coaxial and hemispherical amorphous silicon solar cells and results are compared to those from simulations performed for the standard planar junction. Results indicate that fundamental physical changes in the spatial dependence of the energy band profile across the intrinsic region of an amorphous silicon p-i-n junction manifest as an increase in recombination current for non-planar photovoltaic architectures. Despite an increase in recombination current, however, the coaxial architecture still appears to be able to surpass the efficiency predicted for the planar geometry, due to the geometry of the junction leading to a decoupling of optics and electronics.

  20. Electrical characteristics of amorphous molybdenum-nickel contacts to silicon

    NASA Technical Reports Server (NTRS)

    Kung, K. T.-Y.; Nicolet, M.-A.; Suni, I.

    1984-01-01

    The electrical characteristics of sputtered, amorphous Mo-Ni contacts have been measured on both p- and n-type Si, as functions of composition (30, 54, and 58 at. percent Mo). The contact resistivity on both p(+) and n(+) Si is in the 0.00000 ohm sq cm range. The barrier height for as-deposited samples varies between phi-bp = 0.47-0.42 V on p-type Si and between phi-bn = 0.63-0.68 V on n-type Si, as the composition of the amorphous layer goes from Ni-rich to Mo-rich. The sum phi-bp + phi-bn always equals 1.12 V, within experimental error. After thermal treatment at 500 C for 1/2 h, the contact resistivity changes by a factor of two or less, while the barrier height changes by at most approximately 0.05 V. In light of these results, the amorphous Mo-Ni film makes good ohmic contacts to silicon.

  1. Theory of structural transformation in lithiated amorphous silicon.

    PubMed

    Cubuk, Ekin D; Kaxiras, Efthimios

    2014-07-01

    Determining structural transformations in amorphous solids is challenging due to the paucity of structural signatures. The effect of the transitions on the properties of the solid can be significant and important for applications. Moreover, such transitions may not be discernible in the behavior of the total energy or the volume of the solid as a function of the variables that identify its phases. These issues arise in the context of lithiation of amorphous silicon (a-Si), a promising anode material for high-energy density batteries based on lithium ions. Recent experiments suggest the surprising result that the lithiation of a-Si is a two-phase process. Here, we present first-principles calculations of the structure of a-Si at different lithiation levels. Through a detailed analysis of the short and medium-range properties of the amorphous network, using Voronoi-Delaunay methods and ring statistics, we show that a-LixSi has a fundamentally different structure below and above a lithiation level corresponding to x ∼ 2. PMID:24911996

  2. Anharmonicity Rise the Thermal Conductivity in Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Lv, Wei; Henry, Asegun

    We recently proposed a new method called Direct Green-Kubo Modal Analysis (GKMA) method, which has been shown to calculate the thermal conductivity (TC) of several amorphous materials accurately. A-F method has been widely used for amorphous materials. However, researchers have found out that it failed on several different materials. The missing component of A-F method is the harmonic approximation and considering only the interactions of modes with similar frequencies, which neglect interactions of modes with large frequency difference. On the contrary, GKMA method, which is based on molecular dynamics, intrinsically includes all types of phonon interactions. In GKMA method, each mode's TC comes from both mode self-correlations (autocorrelations) and mode-mode correlations (crosscorrelations). We have demonstrated that the GKMA predicted TC of a-Si from Tersoff potential is in excellent agreement with one of experimental results. In this work, we will present the GKMA applications on a-Si using multiple potentials and gives us more insight of the effect of anharmonicity on the TC of amorphous silicon. This research was supported Intel grant AGMT DTD 1-15-13 and computational resources by NSF supported XSEDE resources under allocations DMR130105 and TG- PHY130049.

  3. Sputtered pin amorphous silicon semi-conductor device and method therefor

    DOEpatents

    Moustakas, Theodore D.; Friedman, Robert A.

    1983-11-22

    A high efficiency amorphous silicon PIN semi-conductor device is constructed by the sequential sputtering of N, I and P layers of amorphous silicon and at least one semi-transparent ohmic electrode. A method of construction produces a PIN device, exhibiting enhanced physical integrity and facilitates ease of construction in a singular vacuum system and vacuum pump down procedure.

  4. High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells.

    PubMed

    He, Rongrui; Day, Todd D; Sparks, Justin R; Sullivan, Nichole F; Badding, John V

    2016-07-01

    Thin films of hydrogenated amorphous silicon can be produced at MPa pressures from silane without the use of plasma at temperatures as low as 345 °C. High pressure chemical vapor deposition may open a new way to low cost deposition of amorphous silicon solar cells and other thin film structures over very large areas in very compact, simple reactors. PMID:27174318

  5. Electron-beam-induced information storage in hydrogenated amorphous silicon device

    DOEpatents

    Yacobi, Ben G.

    1986-01-01

    A method for recording and storing information in a hydrogenated amorphous silicon device, comprising: depositing hydrogenated amorphous silicon on a substrate to form a charge-collection device; and generating defects in the hydrogenated amorphous silicon device, wherein the defects act as recombination centers that reduce the lifetime of carriers, thereby reducing charge-collection efficiency; and thus in the charge-collection mode of scanning probe instruments, regions of the hydrogenated amorphous silicon device that contain the defects appear darker in comparison to regions of the device that do not contain the defects, leading to a contrast formation for pattern recognition and information storage, in the device, which darkened areas can be restored to their original charge-collection efficiency by heating the hydrogenated amorphous silicon to a temperature of about 100.degree. C. to 250.degree. C. for a sufficient period of time to provide for such restoration.

  6. Highly featured amorphous silicon nanorod arrays for high-performance lithium-ion batteries

    SciTech Connect

    Soleimani-Amiri, Samaneh; Safiabadi Tali, Seied Ali; Azimi, Soheil; Sanaee, Zeinab; Mohajerzadeh, Shamsoddin

    2014-11-10

    High aspect-ratio vertical structures of amorphous silicon have been realized using hydrogen-assisted low-density plasma reactive ion etching. Amorphous silicon layers with the thicknesses ranging from 0.5 to 10 μm were deposited using radio frequency plasma enhanced chemical vapor deposition technique. Standard photolithography and nanosphere colloidal lithography were employed to realize ultra-small features of the amorphous silicon. The performance of the patterned amorphous silicon structures as a lithium-ion battery electrode was investigated using galvanostatic charge-discharge tests. The patterned structures showed a superior Li-ion battery performance compared to planar amorphous silicon. Such structures are suitable for high current Li-ion battery applications such as electric vehicles.

  7. Analysis of a free-running synchronization artifact correction for MV-imaging with aSi:H flat panels

    SciTech Connect

    Mooslechner, Michaela; Mitterlechner, Bernhard; Weichenberger, Harald; Sedlmayer, Felix; Deutschmann, Heinz; Huber, Stefan

    2013-03-15

    Purpose: Solid state flat panel electronic portal imaging devices (EPIDs) are widely used for megavolt (MV) photon imaging applications in radiotherapy. In addition to their original purpose in patient position verification, they are convenient to use in quality assurance and dosimetry to verify beam geometry and dose deposition or to perform linear accelerator (linac) calibration procedures. However, native image frames from amorphous silicon (aSi:H) detectors show a range of artifacts which have to be eliminated by proper correction algorithms. When a panel is operated in free-running frame acquisition mode, moving vertical stripes (periodic synchronization artifacts) are a disturbing feature in image frames. Especially for applications in volumetric intensity modulated arc therapy (VMAT) or motion tracking, the synchronization (sync) artifacts are the limiting factor for potential and accuracy since they become even worse at higher frame rates and at lower dose rates, i.e., linac pulse repetition frequencies (PRFs). Methods: The authors introduced a synchronization correction method which is based on a theoretical model describing the interferences of the panel's readout clocking with the linac's dose pulsing. Depending on the applied PRF, a certain number of dose pulses is captured per frame which is readout columnwise, sequentially. The interference of the PRF with the panel readout is responsible for the period and the different gray value levels of the sync stripes, which can be calculated analytically. Sync artifacts can then be eliminated multiplicatively in precorrected frames without additional information about radiation pulse timing. Results: For the analysis, three aSi:H EPIDs of various types were investigated with 6 and 15 MV photon beams at varying PRFs of 25, 50, 100, 200, and 400 pulses per second. Applying the sync correction at panels with gadolinium oxysulfide scintillators improved single frame flood field image quality drastically

  8. Mechanism of the growth of amorphous and microcrystalline silicon from silicon tetrafluoride and hydrogen

    NASA Astrophysics Data System (ADS)

    Okada, Y.; Chen, J.; Campbell, I. H.; Fauchet, P. M.; Wagner, S.

    1990-02-01

    We study the growth of amorphous (a-Si:H,F) and of microcrystalline (μc-Si) silicon over trench patterns in crystalline silicon substrates. We vary the conditions of the SiF4-H2 glow discharge from deposition to etching. All deposited films form lips at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte Carlo simulation suggest that film growth is governed by a single growth species with a low (˜0.2) sticking coefficient, in combination with a highly reactive etching species.

  9. 76 FR 9360 - In the Matter of Certain Flat Panel Digital Televisions and Components Thereof; Notice of a...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-17

    ... August 19, 2010, based on a complaint filed by Vizio, Inc. of Irvine, California. 75 FR 51285-86 (August... COMMISSION In the Matter of Certain Flat Panel Digital Televisions and Components Thereof; Notice of a... within the United States after importation of certain flat panel digital televisions and...

  10. Monolithic amorphous silicon modules on continuous polymer substrate

    SciTech Connect

    Grimmer, D.P. )

    1992-03-01

    This report examines manufacturing monolithic amorphous silicon modules on a continuous polymer substrate. Module production costs can be reduced by increasing module performance, expanding production, and improving and modifying production processes. Material costs can be reduced by developing processes that use a 1-mil polyimide substrate and multilayers of low-cost material for the front encapsulant. Research to speed up a-Si and ZnO deposition rates is needed to improve throughputs. To keep throughput rates compatible with depositions, multibeam fiber optic delivery systems for laser scribing can be used. However, mechanical scribing systems promise even higher throughputs. Tandem cells and production experience can increase device efficiency and stability. Two alternative manufacturing processes are described: (1) wet etching and sheet handling and (2) wet etching and roll-to-roll fabrication.

  11. Research on stable, high-efficiency amorphous silicon multijunction modules

    SciTech Connect

    Guha, S. )

    1992-09-01

    This report describes research on semiconductor and non-semiconductor materials to enhance the performance of multi-band-gap, multijunction panel with an area greater than 900 cm[sup 2] by 1992. Double-junction and triple-junction cells are mode on a Ag/ZnO back reflector deposited on stainless steel substrates. An a-SiGe alloy is used for the i-layer in the bottom and the middle cells; the top cell uses an amorphous silicon alloy. After the evaporation of an antireflection coating, silver grids and bus bars are put on the top surface and the panel is encapsulated in an ethylene vinyl acetate (EVA)/Tefzel structure to make a 1-ft[sup 2] monolithic module.

  12. Atomistic simulations of material damping in amorphous silicon nanoresonators

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sankha; Song, Jun; Vengallatore, Srikar

    2016-06-01

    Atomistic simulations using molecular dynamics (MD) are emerging as a valuable tool for exploring dissipation and material damping in nanomechanical resonators. In this study, we used isothermal MD to simulate the dynamics of the longitudinal-mode oscillations of an amorphous silicon nanoresonator as a function of frequency (2 GHz–50 GHz) and temperature (15 K–300 K). Damping was characterized by computing the loss tangent with an estimated uncertainty of 7%. The dissipation spectrum displays a sharp peak at 50 K and a broad peak at around 160 K. Damping is a weak function of frequency at room temperature, and the loss tangent has a remarkably high value of ~0.01. In contrast, at low temperatures (15 K), the loss tangent increases monotonically from 4× {{10}-4} to 4× {{10}-3} as the frequency increases from 2 GHz to 50 GHz. The mechanisms of dissipation are discussed.

  13. ESR studies on hot-wire amorphous silicon

    SciTech Connect

    Unold, T.; Mahan, A.H.

    1997-07-01

    The authors measure a series of hot-wire (HW) amorphous silicon films grown with hydrogen contents C{sub H} varying between 0.5--17 at.%. From constant photocurrent method (CPM) measurements and the steady-state photocarrier grating method (SSPG) they find good agreement with previous measurements on similar hot-wire films. Electron spin resonance measurements on the same samples, however, yield significantly higher spin densities than expected. A thickness series indicates a highly defective layer close to the substrate interface. They propose that this defective layer may be due to excessive out diffusion of hydrogen during growth at high temperatures, as seen by secondary ion mass spectroscopy. ESR measurements on light-degraded samples indicate an improved stability of samples with C{sub H} < 9 at.%.

  14. Laser induced melting and crystallization of boron doped amorphous silicon

    SciTech Connect

    Nebel, C.E.; Schoeniger, S.; Dahlheimer, B.; Stutzmann, M.

    1997-07-01

    Transient reflectivity experiments have been performed to measure the dynamics of laser-induced melting of amorphous silicon (a-Si) and the crystallization to {micro}c-Si of films with different thicknesses on Corning 7059 glass. The laser-induced melting takes place with a velocity of 13 to 24 m/s, while the solidification is about a factor 10 slower. The crystallization starts at the Si/glass interface and at the surface. In the center of the films Si remains liquid for an extended period of time. The crystallization dynamics point towards an heterogeneous morphology of laser-crystallized Si, where the surface and the interface layers are composed of small grains and the bulk of larger grains.

  15. Radiation Resistance Studies of Amorphous Silicon Alloy Photovoltaic Materials

    NASA Technical Reports Server (NTRS)

    Woodyard, James R.

    1994-01-01

    The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys was investigated. A number of different device structures were irradiated with 1.0 MeV protons. The cells were insensitive to proton fluences below 1E12 sq cm. The parameters of the irradiated cells were restored with annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters for fluences below lE14 sq cm require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

  16. Light-induced metastability in pure and hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Queen, D. R.; Liu, X.; Karel, J.; Wang, Q.; Crandall, R. S.; Metcalf, T. H.; Hellman, F.

    2015-10-01

    Light soaking is found to increase the specific heat C and internal friction Q-1 of pure (a-Si) and hydrogenated (a-Si:H) amorphous silicon. At the lowest temperatures, the increases in C and Q-1 are consistent with an increased density of two-level systems (TLS). The light-induced increase in C persists to room temperature. Neither the sound velocity nor shear modulus change with light soaking indicating that the Debye specific heat is unchanged which suggests that light soaking creates localized vibrational modes in addition to TLS. The increase can be reversibly added and removed by light soaking and annealing, respectively, suggesting that it is related to the Staebler-Wronski effect (SWE), even in a-Si without H, and involves a reversible nanoscale structural rearrangement that is facilitated by, but does not require, H to occur.

  17. High Performance Molybdenum Disulfide Amorphous Silicon Heterojunction Photodetector

    PubMed Central

    Esmaeili-Rad, Mohammad R.; Salahuddin, Sayeef

    2013-01-01

    One important use of layered semiconductors such as molybdenum disulfide (MoS2) could be in making novel heterojunction devices leading to functionalities unachievable using conventional semiconductors. Here we demonstrate a metal-semiconductor-metal heterojunction photodetector, made of MoS2 and amorphous silicon (a-Si), with rise and fall times of about 0.3 ms. The transient response does not show persistent (residual) photoconductivity, unlike conventional a-Si devices where it may last 3–5 ms, thus making this heterojunction roughly 10X faster. A photoresponsivity of 210 mA/W is measured at green light, the wavelength used in commercial imaging systems, which is 2−4X larger than that of a-Si and best reported MoS2 devices. The device could find applications in large area electronics, such as biomedical imaging, where a fast response is critical. PMID:23907598

  18. Hydrogenated Amorphous Silicon (a-Si:H) Colloids

    SciTech Connect

    Harris, Justin T.; Hueso, Jose L.; Korgel, Brian A.

    2010-12-14

    Colloidal particles of hydrogenated amorphous silicon (a-Si:H) were synthesized by decomposition of trisilane (Si{sub 3}H{sub 8}) in supercritical n-hexane (sc-hexane) at temperatures ranging from 380 to 550 °C. The reaction temperature, pressure and Si{sub 3}H{sub 8} concentration have a significant influence on the average particle size, Si bond order and hydrogen content. The particle diameter could be varied from 170 nm to 1.7 μm, with hydrogen loadings between 10% and 58%. Raman spectroscopy of the particles revealed significant differences in Si bond order that correlated with hydrogen content, with the lowest reaction temperatures yielding particles with the least structural order and most associated hydrogen. Particles synthesized at temperatures higher than 420 °C had sufficient bond order to allow crystallization under the Raman laser probe.

  19. Damage at hydrogenated amorphous/crystalline silicon interfaces by indium tin oxide overlayer sputtering

    NASA Astrophysics Data System (ADS)

    Demaurex, Bénédicte; De Wolf, Stefaan; Descoeudres, Antoine; Charles Holman, Zachary; Ballif, Christophe

    2012-10-01

    Damage of the hydrogenated amorphous/crystalline silicon interface passivation during transparent conductive oxide sputtering is reported. This occurs in the fabrication process of silicon heterojunction solar cells. We observe that this damage is at least partially caused by luminescence of the sputter plasma. Following low-temperature annealing, the electronic interface properties are recovered. However, the silicon-hydrogen configuration of the amorphous silicon film is permanently changed, as observed from infra-red absorbance spectra. In silicon heterojunction solar cells, although the as-deposited film's microstructure cannot be restored after sputtering, no significant losses are observed in their open-circuit voltage.

  20. Optical bandgap of ultra-thin amorphous silicon films deposited on crystalline silicon by PECVD

    NASA Astrophysics Data System (ADS)

    Abdulraheem, Yaser; Gordon, Ivan; Bearda, Twan; Meddeb, Hosny; Poortmans, Jozef

    2014-05-01

    An optical study based on spectroscopic ellipsometry, performed on ultrathin hydrogenated amorphous silicon (a-Si:H) layers, is presented in this work. Ultrathin layers of intrinsic amorphous silicon have been deposited on n-type mono-crystalline silicon (c-Si) wafers by plasma enhanced chemical vapor deposition (PECVD). The layer thicknesses along with their optical properties -including their refractive index and optical loss- were characterized by spectroscopic ellipsometry (SE) in a wavelength range from 250 nm to 850 nm. The data was fitted to a Tauc-Lorentz optical model and the fitting parameters were extracted and used to compute the refractive index, extinction coefficient and optical bandgap. Furthermore, the a-Si:H film grown on silicon was etched at a controlled rate using a TMAH solution prepared at room temperature. The optical properties along with the Tauc-Lorentz fitting parameters were extracted from the model as the film thickness was reduced. The etch rate for ultrathin a-Si:H layers in TMAH at room temperature was found to slow down drastically as the c-Si interface is approached. From the Tauc-Lorentz parameters obtained from SE, it was found that the a-Si film exhibited properties that evolved with thickness suggesting that the deposited film is non-homogeneous across its depth. It was also found that the degree of crystallinity and optical (Tauc) bandgap increased as the layers were reduced in thickness and coming closer to the c-Si substrate interface, suggesting the presence of nano-structured clusters mixed into the amorphous phase for the region close to the crystalline silicon substrate. Further results from Atomic Force Microscopy and Transmission Electron Microscopy confirmed the presence of an interfacial transitional layer between the amorphous film and the underlying substrate showing silicon nano-crystalline enclosures that can lead to quantum confinement effects. Quantum confinement is suggested to be the cause of the observed

  1. Optical bandgap of ultra-thin amorphous silicon films deposited on crystalline silicon by PECVD

    SciTech Connect

    Abdulraheem, Yaser; Gordon, Ivan; Bearda, Twan; Meddeb, Hosny; Poortmans, Jozef

    2014-05-15

    An optical study based on spectroscopic ellipsometry, performed on ultrathin hydrogenated amorphous silicon (a-Si:H) layers, is presented in this work. Ultrathin layers of intrinsic amorphous silicon have been deposited on n-type mono-crystalline silicon (c-Si) wafers by plasma enhanced chemical vapor deposition (PECVD). The layer thicknesses along with their optical properties –including their refractive index and optical loss- were characterized by spectroscopic ellipsometry (SE) in a wavelength range from 250 nm to 850 nm. The data was fitted to a Tauc-Lorentz optical model and the fitting parameters were extracted and used to compute the refractive index, extinction coefficient and optical bandgap. Furthermore, the a-Si:H film grown on silicon was etched at a controlled rate using a TMAH solution prepared at room temperature. The optical properties along with the Tauc-Lorentz fitting parameters were extracted from the model as the film thickness was reduced. The etch rate for ultrathin a-Si:H layers in TMAH at room temperature was found to slow down drastically as the c-Si interface is approached. From the Tauc-Lorentz parameters obtained from SE, it was found that the a-Si film exhibited properties that evolved with thickness suggesting that the deposited film is non-homogeneous across its depth. It was also found that the degree of crystallinity and optical (Tauc) bandgap increased as the layers were reduced in thickness and coming closer to the c-Si substrate interface, suggesting the presence of nano-structured clusters mixed into the amorphous phase for the region close to the crystalline silicon substrate. Further results from Atomic Force Microscopy and Transmission Electron Microscopy confirmed the presence of an interfacial transitional layer between the amorphous film and the underlying substrate showing silicon nano-crystalline enclosures that can lead to quantum confinement effects. Quantum confinement is suggested to be the cause of the observed

  2. Nanopattern-guided growth of single-crystal silicon on amorphous substrates and high-performance sub-100 nm thin-film transistors for three-dimensional integrated circuits

    NASA Astrophysics Data System (ADS)

    Gu, Jian

    This thesis explores how nanopatterns can be used to control the growth of single-crystal silicon on amorphous substrates at low temperature, with potential applications on flat panel liquid-crystal display and 3-dimensional (3D) integrated circuits. I first present excimer laser annealing of amorphous silicon (a-Si) nanostructures on thermally oxidized silicon wafer for controlled formation of single-crystal silicon islands. Preferential nucleation at pattern center is observed due to substrate enhanced edge heating. Single-grain silicon is obtained in a 50 nm x 100 nm rectangular pattern by super lateral growth (SLG). Narrow lines (such as 20-nm-wide) can serve as artificial heterogeneous nucleation sites during crystallization of large patterns, which could lead to the formation of single-crystal silicon islands in a controlled fashion. In addition to eximer laser annealing, NanoPAtterning and nickel-induced lateral C&barbelow;rystallization (NanoPAC) of a-Si lines is presented. Single-crystal silicon is achieved by NanoPAC. The line width of a-Si affects the grain structure of crystallized silicon lines significantly. Statistics show that single-crystal silicon is formed for all lines with width between 50 nm to 200 nm. Using in situ transmission electron microscopy (TEM), nickel-induced lateral crystallization (Ni-ILC) of a-Si inside a pattern is revealed; lithography-constrained single seeding (LISS) is proposed to explain the single-crystal formation. Intragrain line and two-dimensional defects are also studied. To test the electrical properties of NanoPAC silicon films, sub-100 nm thin-film transistors (TFTs) are fabricated using Patten-controlled crystallization of Ṯhin a-Si channel layer and H&barbelow;igh temperature (850°C) annealing, coined PaTH process. PaTH TFTs show excellent device performance over traditional solid phase crystallized (SPC) TFTs in terms of threshold voltage, threshold voltage roll-off, leakage current, subthreshold swing, on

  3. Test of an amorphous silicon detector in medical proton beams

    NASA Astrophysics Data System (ADS)

    Martišíková, M.; Hesse, B. M.; Nairz, O.; Jäkel, O.

    2011-05-01

    Ion beam radiation therapy for cancer treatment allows for improved dose confinement to the target in comparison with the standard radiation therapy using high energy photons. Dose delivery to the patient using focused ion beam scanning over the target volume is going to be increasingly used in the upcoming years. The high precision of the dose delivery achieved in this way has to be met by practical methods for beam monitoring with sufficient spatial resolution in two dimensions. Flat panel detectors, used for photon portal imaging at the newest medical linear accelerators, are an interesting candidate for this purpose. Initial detector tests presented here were performed using proton beams with the highest available energy. The investigations include measurements of beam profiles at different beam intensities and for different beam width, as well as the signal linearity. Radiation damage was also investigated. The obtained results show that the detector is a promising candidate to be used in the therapeutic proton beams.

  4. Separating the uncorrelated noise from the correlated detector noise of flat panel systems in order to quantify flat panel noise easily

    NASA Astrophysics Data System (ADS)

    Hoeschen, Christoph; Tischenko, Oleg; Renger, Bernhard; Jungnickel, Kerstin

    2005-04-01

    One big advantage in terms of image quality of modern flat panel detector systems compared to CR systems beside the better DQE of these systems is the possibility to correct for inhomogeneities of the X-ray beam and the detector (flat field correction) as well as for bad pixels. However, the used correction methods are taking a lot of time or do not cover all possible combinations of radiation quality and exposure used for patient imaging. A method is presented to achieve these correction images very easily by using a proposed method for comparing two images. This method, which has so far been used for certain noise measurements and in some cases noise reduction, can also be used for separating correlated from uncorrelated noise by correlating in frequency sub-bands the information of two images. In this study it is proven, that the uncorrelated noise image of two expositions is very similar to the correction image gained just before the two exposures. That allows to calibrate a detector quite more often and for much more beam qualities/exposures than before to achieve a better correction and another possibility of constancy testing for flat panel detectors, because the proposed method is so sensitive that it will detect single pixel changes within the detector.

  5. Crystallization and doping of amorphous silicon on low temperature plastic

    DOEpatents

    Kaschmitter, J.L.; Truher, J.B.; Weiner, K.H.; Sigmon, T.W.

    1994-09-13

    A method or process of crystallizing and doping amorphous silicon (a-Si) on a low-temperature plastic substrate using a short pulsed high energy source in a selected environment, without heat propagation and build-up in the substrate is disclosed. The pulsed energy processing of the a-Si in a selected environment, such as BF3 and PF5, will form a doped micro-crystalline or poly-crystalline silicon (pc-Si) region or junction point with improved mobilities, lifetimes and drift and diffusion lengths and with reduced resistivity. The advantage of this method or process is that it provides for high energy materials processing on low cost, low temperature, transparent plastic substrates. Using pulsed laser processing a high (>900 C), localized processing temperature can be achieved in thin films, with little accompanying temperature rise in the substrate, since substrate temperatures do not exceed 180 C for more than a few microseconds. This method enables use of plastics incapable of withstanding sustained processing temperatures (higher than 180 C) but which are much lower cost, have high tolerance to ultraviolet light, have high strength and good transparency, compared to higher temperature plastics such as polyimide. 5 figs.

  6. Crystallization and doping of amorphous silicon on low temperature plastic

    DOEpatents

    Kaschmitter, James L.; Truher, Joel B.; Weiner, Kurt H.; Sigmon, Thomas W.

    1994-01-01

    A method or process of crystallizing and doping amorphous silicon (a-Si) on a low-temperature plastic substrate using a short pulsed high energy source in a selected environment, without heat propagation and build-up in the substrate. The pulsed energy processing of the a-Si in a selected environment, such as BF3 and PF5, will form a doped micro-crystalline or poly-crystalline silicon (pc-Si) region or junction point with improved mobilities, lifetimes and drift and diffusion lengths and with reduced resistivity. The advantage of this method or process is that it provides for high energy materials processing on low cost, low temperature, transparent plastic substrates. Using pulsed laser processing a high (>900.degree. C.), localized processing temperature can be achieved in thin films, with little accompanying temperature rise in the substrate, since substrate temperatures do not exceed 180.degree. C. for more than a few microseconds. This method enables use of plastics incapable of withstanding sustained processing temperatures (higher than 180.degree. C.) but which are much lower cost, have high tolerance to ultraviolet light, have high strength and good transparency, compared to higher temperature plastics such as polyimide.

  7. Research on stable, high-efficiency amorphous silicon multijunction modules

    SciTech Connect

    Ghosh, M.; DelCueto, J.: Kampas, F.; Xi, J. )

    1993-02-01

    This report describes results from the first phase of a three-phase contract for the development of stable, high-efficiency, same-band-gap, amorphous silicon (a-Si) multijunction photovoltaic (PV) modules. The program involved improving the properties of individual layers of semiconductor and non-semiconductor materials and small-area single-junction and multijunction devices, as well as the multijunction modules. The semiconductor materials research was performed on a-Si p, i, and n layers, and on microcrystalline silicon n layers. These were deposited using plasma-enhanced chemical vapor deposition. The non-semiconductor materials studied were tin oxide, for use as a transparent-conducting-oxide (TCO), and zinc oxide, for use as a back reflector and as a buffer layer between the TCO and the semiconductor layers. Tin oxide was deposited using atmospheric-pressure chemical vapor deposition. Zinc oxide was deposited using magnetron sputtering. The research indicated that the major challenge in the fabrication of a-Si multijunction PV modules is the contact between the two p-i-n cells. A structure that has low optical absorption but that also facilitates the recombination of electrons from the first p-i-n structure with holes from the second p-i-n structure is required. Non-semiconductor layers and a-Si semiconductor layers were tested without achieving the desired result.

  8. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    NASA Astrophysics Data System (ADS)

    Riesen, Y.; Stuckelberger, M.; Haug, F.-J.; Ballif, C.; Wyrsch, N.

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy

  9. Systems And Cost Issues Of Flat Panel Displays For Automotive Application

    NASA Astrophysics Data System (ADS)

    Bansal, Narottam P.; Bruce, Allan J.; Doremus, R. H.; Moynihan, C. T.

    1988-10-01

    The automobile instrument panel is undergoing a revolutionary transition from mechanical and electromechanical displays to all-electronic displays. This is not an easy transition in that the "ideal" automotive display does not exist and all principal candidates have significant limitations. To identify the obstacles standing in the way of successful application of these candidate displays, we examine these limitations from the view of system performance and cost, concluding that innovative approaches to implementing the electronic control of the display can both improve display performance and reduce system cost. Specifically, the development of a high performance, cost effective thin-film transistor (TFT) technology is essential to the successful implementation of automotive quality flat panel dot matrix displays. The potential of competitor TFT technologies will be assessed for their ability to provide the performance required in mature flat panel displays.

  10. A novel heuristic for optimization aggregate production problem: Evidence from flat panel display in Malaysia

    NASA Astrophysics Data System (ADS)

    Al-Kuhali, K.; Hussain M., I.; Zain Z., M.; Mullenix, P.

    2015-05-01

    Aim: This paper contribute to the flat panel display industry it terms of aggregate production planning. Methodology: For the minimization cost of total production of LCD manufacturing, a linear programming was applied. The decision variables are general production costs, additional cost incurred for overtime production, additional cost incurred for subcontracting, inventory carrying cost, backorder costs and adjustments for changes incurred within labour levels. Model has been developed considering a manufacturer having several product types, which the maximum types are N, along a total time period of T. Results: Industrial case study based on Malaysia is presented to test and to validate the developed linear programming model for aggregate production planning. Conclusion: The model development is fit under stable environment conditions. Overall it can be recommended to adapt the proven linear programming model to production planning of Malaysian flat panel display industry.

  11. Flat panel display using Ti-Cr-Al-O thin film

    DOEpatents

    Jankowski, Alan F.; Schmid, Anthony P.

    2002-01-01

    Thin films of Ti--Cr--Al--O are used as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Ar and O.sub.2. Resistivity values from 10.sup.4 to 10.sup.10 Ohm-cm have been measured for Ti--Cr--Al--O film <1 .mu.m thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti--Cr--Al--O as a thin film resistor has been found to be thermodynamically stable, unlike other metal-oxide films. The Ti--Cr--Al--O film can be used as a vertical or lateral resistor, for example, as a layer beneath a field emission cathode in a flat panel display; or used to control surface emissivity, for example, as a coating on an insulating material such as vertical wall supports in flat panel displays.

  12. Attenuated phase-shift mask (PSM) blanks for flat panel display

    NASA Astrophysics Data System (ADS)

    Kageyama, Kagehiro; Mochizuki, Satoru; Yamakawa, Hiroyuki; Uchida, Shigeru

    2015-10-01

    The fine pattern exposure techniques are required for Flat Panel display applications as smart phone, tablet PC recently. The attenuated phase shift masks (PSM) are being used for ArF and KrF photomask lithography technique for high end pattern Semiconductor applications. We developed CrOx based large size PSM blanks that has good uniformity on optical characteristics for FPD applications. We report the basic optical characteristics and uniformity, stability data of large sized CrOx PSM blanks.

  13. Qualification test results for DOE solar photovoltaic flat panel procurement - PRDA 38

    NASA Technical Reports Server (NTRS)

    Griffith, J. S.

    1980-01-01

    Twelve types of prototypes modules for the DOE Photovoltaic Flat Panel Procurement (PRDA 38) were subjected to qualification tests at the Jet Propulsion Laboratory according to a new specification. Environmental exposures were carried out separately and included temperature cycling, humidity, wind simulation, and hail. The most serious problems discovered were reduced insulation resistance to ground and ground continuity of the metal frames, electrical degradation, erratic power readings, and delamination. The electrical and physical characteristics of the newly received modules are also given.

  14. Controlled growth of nanocrystalline silicon within amorphous silicon carbide thin films

    NASA Astrophysics Data System (ADS)

    Kole, Arindam; Chaudhuri, Partha

    2014-04-01

    Controlled formation of nanocrystalline silicon (nc-Si) within hydrogenated amorphous silicon carbide (a-SiC:H) thin films has been demonstrated by a rf (13.56 MHz) plasma chemical vapour deposition (PECVD) method at a low deposition temperature of 200°C by regulating the deposition pressure (Pr) between 26.7 Pa and 133.3 Pa. Evolution of the size and the crystalline silicon volume fraction within the a-SiC:H matrix has been studied by XRD, Raman and HRTEM. The study reveals that at Pr of 26.7 Pa there are mostly isolated grains of nc-Si within the a-SiC:H matrix with average size of 4.5 nm. With increase of Pr the isolated nc-Si grains coalesce more and more giving rise to larger size connected nc-Si islands which appear as microcrystalline silicon in the Raman spectra. As a result net isolated nc-Si volume fraction decreases while the total crystalline silicon volume fraction increases.

  15. A new x-ray imaging technique for radiography mode of flat-panel imager

    NASA Astrophysics Data System (ADS)

    Suzuki, K.; Ikeda, S.; Ueda, K.; Baba, R.

    2007-03-01

    A digital radiography system using a flat-panel imager, which has a novel imaging technique for a radiography mode, has been developed. A radiographic image captured by the new imaging technique has a wide dynamic range in comparison with conventional radiographic images. The purpose of this presentation is to show the basic performance of the image quality acquired by the new imaging technique and compare it with an image taken by a conventional technique. The flat-panel imager has a gain switching capability, normally used in a dynamic imaging mode for a cone-beam CT study. The gain switching method has two gain settings and switches between them automatically, depending on the incident dose to each pixel of flat-panel imager. As a result of the gain switching method, an image having wide dynamic range is achieved. In this study, we applied the gain switching method to the radiography mode, and achieved a radiographic image with wider dynamic range than a conventional radiograph. Furthermore, we have also developed an algorithm for calibration of the gain switching method in radiography mode.

  16. Tracking brachytherapy sources using emission imaging with one flat panel detector

    SciTech Connect

    Song Haijun; Bowsher, James; Das, Shiva; Yin Fangfang

    2009-04-15

    This work proposes to use the radiation from brachytherapy sources to track their dwell positions in three-dimensional (3D) space. The prototype device uses a single flat panel detector and a BB tray. The BBs are arranged in a defined pattern. The shadow of the BBs on the flat panel is analyzed to derive the 3D coordinates of the illumination source, i.e., the dwell position of the brachytherapy source. A kilovoltage x-ray source located 3.3 m away was used to align the center BB with the center pixel on the flat panel detector. For a test plan of 11 dwell positions, with an Ir-192 high dose rate unit, one projection was taken for each dwell point, and locations of the BB shadows were manually identified on the projection images. The 3D coordinates for the 11 dwell positions were reconstructed based on two BBs. The distances between dwell points were compared with the expected values. The average difference was 0.07 cm with a standard deviation of 0.15 cm. With automated BB shadow recognition in the future, this technique possesses the potential of tracking the 3D trajectory and the dwell times of a brachytherapy source in real time, enabling real time source position verification.

  17. High-performance flat-panel solar thermoelectric generators with high thermal concentration.

    PubMed

    Kraemer, Daniel; Poudel, Bed; Feng, Hsien-Ping; Caylor, J Christopher; Yu, Bo; Yan, Xiao; Ma, Yi; Wang, Xiaowei; Wang, Dezhi; Muto, Andrew; McEnaney, Kenneth; Chiesa, Matteo; Ren, Zhifeng; Chen, Gang

    2011-07-01

    The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. Photovoltaic cells are deployed widely, mostly as flat panels, whereas solar thermal electricity generation relying on optical concentrators and mechanical heat engines is only seen in large-scale power plants. Here we demonstrate a promising flat-panel solar thermal to electric power conversion technology based on the Seebeck effect and high thermal concentration, thus enabling wider applications. The developed solar thermoelectric generators (STEGs) achieved a peak efficiency of 4.6% under AM1.5G (1 kW m(-2)) conditions. The efficiency is 7-8 times higher than the previously reported best value for a flat-panel STEG, and is enabled by the use of high-performance nanostructured thermoelectric materials and spectrally-selective solar absorbers in an innovative design that exploits high thermal concentration in an evacuated environment. Our work opens up a promising new approach which has the potential to achieve cost-effective conversion of solar energy into electricity. PMID:21532584

  18. Tracking brachytherapy sources using emission imaging with one flat panel detector.

    PubMed

    Song, Haijun; Bowsher, James; Das, Shiva; Yin, Fang-Fang

    2009-04-01

    This work proposes to use the radiation from brachytherapy sources to track their dwell positions in three-dimensional (3D) space. The prototype device uses a single flat panel detector and a BB tray. The BBs are arranged in a defined pattern. The shadow of the BBs on the flat panel is analyzed to derive the 3D coordinates of the illumination source, i.e., the dwell position of the brachytherapy source. A kilovoltage x-ray source located 3.3 m away was used to align the center BB with the center pixel on the flat panel detector. For a test plan of 11 dwell positions, with an Ir-192 high dose rate unit, one projection was taken for each dwell point, and locations of the BB shadows were manually identified on the projection images. The 3D coordinates for the 11 dwell positions were reconstructed based on two BBs. The distances between dwell points were compared with the expected values. The average difference was 0.07 cm with a standard deviation of 0.15 cm. With automated BB shadow recognition in the future, this technique possesses the potential of tracking the 3D trajectory and the dwell times of a brachytherapy source in real time, enabling real time source position verification. PMID:19472615

  19. Temperature-dependent minority carrier lifetime of crystalline silicon wafers passivated by high quality amorphous silicon oxide

    NASA Astrophysics Data System (ADS)

    Inaba, Masahiro; Todoroki, Soichiro; Nakada, Kazuyoshi; Miyajima, Shinsuke

    2016-04-01

    We investigated the effects of annealing on the temperature-dependent minority carrier lifetime of a crystalline silicon wafer passivated by hydrogenated amorphous silicon oxide. The annealing significantly affects the lifetime and its temperature dependence. Our device simulations clearly indicate that valence band offset significantly affects the temperature dependence. We also found a slight increase in the interface defect density after annealing.

  20. Depth profiling in amorphous and microcrystalline silicon by transient photoconductivity techniques

    NASA Astrophysics Data System (ADS)

    Brüggemann, R.; Main, C.; Reynolds, S.

    2002-07-01

    We probe near-surface regions in hydrogenated amorphous and microcrystalline silicon by recording the transient photocurrent after application of a green laser pulse with short absorption depth through the glass-substrate/silicon interface. Depending on the spatial defect inhomogeneity close to the illuminated surface the transient photocurrent shows a different decay behaviour under strongly absorbed green light as compared with more uniformly absorbed red illumination. We apply a Fourier transform technique to the photocurrent decay, which reveals spatial inhomogeneities in the deep-defect density in amorphous silicon. For a highly crystalline sample of microcrystalline silicon we find depth homogeneity in the electronic properties, in agreement with information from structural investigations.

  1. Accuracy and long-term stability of amorphous-silicon measurements

    NASA Technical Reports Server (NTRS)

    Mueller, R.

    1986-01-01

    The measurement system requirements to obtain accurate electrical performance measurements of amorphous silicon cells and modules were described. The progress achieved in modifying the Jet Propulsion Laboratory (JPL) system toward that objective were reviewed.

  2. Optical losses in amorphous silicon solar cells due to back reflectors

    SciTech Connect

    Sopori, B.L.; Madjdpour, J.; Von Roedern, B.; Chen, W.; Hegedus, S.S.

    1997-07-01

    The authors have used a new numerical model and here present initial results on how texturing and backreflectors affect the maximum achievable short-circuit current densities in amorphous silicon solar cells.

  3. RF sputtering for controlling dihydride and monohydride bond densities in amorphous silicon hydride

    DOEpatents

    Jeffery, F.R.; Shanks, H.R.

    1980-08-26

    A process is described for controlling the dihydride and monohydride bond densities in hydrogenated amorphous silicone produced by reactive rf sputtering of an amorphous silicon target. There is provided a chamber with an amorphous silicon target and a substrate therein with the substrate and the target positioned such that when rf power is applied to the target the substrate is in contact with the sputtering plasma produced thereby. Hydrogen and argon are fed to the chamber and the pressure is reduced in the chamber to a value sufficient to maintain a sputtering plasma therein, and then rf power is applied to the silicon target to provide a power density in the range of from about 7 watts per square inch to about 22 watts per square inch to sputter an amorphous solicone hydride onto the substrate, the dihydride bond density decreasing with an increase in the rf power density. Substantially pure monohydride films may be produced.

  4. Schottky barrier amorphous silicon solar cell with thin doped region adjacent metal Schottky barrier

    DOEpatents

    Carlson, David E.; Wronski, Christopher R.

    1979-01-01

    A Schottky barrier amorphous silicon solar cell incorporating a thin highly doped p-type region of hydrogenated amorphous silicon disposed between a Schottky barrier high work function metal and the intrinsic region of hydrogenated amorphous silicon wherein said high work function metal and said thin highly doped p-type region forms a surface barrier junction with the intrinsic amorphous silicon layer. The thickness and concentration of p-type dopants in said p-type region are selected so that said p-type region is fully ionized by the Schottky barrier high work function metal. The thin highly doped p-type region has been found to increase the open circuit voltage and current of the photovoltaic device.

  5. A fax-machine amorphous silicon sensor for X-ray detection

    NASA Astrophysics Data System (ADS)

    Alberdi, J.; Barcala, J. M.; Chvatchkine, V.; Ioudine, I.; Molinero, A.; Navarrete, J. J.; Yuste, C.

    Amorphous silicon detectors have been used, basically, as solar cells for energetics applications. As light detectors, linear sensors are used in fax and photocopier machines because they can be built with a large size, low price and have a high radiation hardness. Due to these performances, amorphous silicon detectors have been used as radiation detectors, and, presently, some groups are developing matrix amorphous silicon detectors with built-in electronics for medical X-ray applications. Our group has been working on the design and development of an X-ray image system based on a commercial fax linear amorphous silicon detector. The sensor scans the selected area and detects light produced by the X-ray in a scintillator placed on the sensor. Image-processing software produces a final image with better resolution and definition.

  6. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    NASA Astrophysics Data System (ADS)

    Jarolimek, K.; de Groot, R. A.; de Wijs, G. A.; Zeman, M.

    2010-11-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H) , with equal concentrations of Si and N atoms (x=1) , for two considerably different densities (2.0 and 3.0g/cm3 ). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because of their different densities and hydrogen concentrations they show marked differences at longer length scales. The low-density nitride forms a percolating network of voids with the internal surfaces passivated by hydrogen. Although some voids are still present for the high-density nitride, this material has a much denser and uniform space filling. The structure factors reveal some tendency for the nonstoichiometric high-density nitride to phase separate into nitrogen rich and poor areas. For our slowest cooling rate (0.023 K/fs) we obtain models with a modest number of defect states, where the low (high) density nitride favors undercoordinated (overcoordinated) defects. Analysis of the structural defects and electronic density of states shows that there is no direct one-to-one correspondence between the structural defects and states in the gap. There are several structural defects that do not contribute to in-gap states and there are in-gap states that do only have little to no contributions from (atoms in) structural defects. Finally an estimation of the size and cooling rate effects on the amorphous network is reported.

  7. ENHANCED GROWTH RATE AND SILANE UTILIZATION IN AMORPHOUS SILICON AND NANOCRYSTALLINE-SILICON SOLAR CELL DEPOSITION VIA GAS PHASE ADDITIVES

    SciTech Connect

    Ridgeway, R G; Hegedus, S S; Podraza, N J

    2012-08-31

    Air Products set out to investigate the impact of additives on the deposition rate of both CSi and Si-H films. One criterion for additives was that they could be used in conventional PECVD processing, which would require sufficient vapor pressure to deliver material to the process chamber at the required flow rates. The flow rate required would depend on the size of the substrate onto which silicon films were being deposited, potentially ranging from 200 mm diameter wafers to the 5.7 m2 glass substrates used in GEN 8.5 flat-panel display tools. In choosing higher-order silanes, both disilane and trisilane had sufficient vapor pressure to withdraw gas at the required flow rates of up to 120 sccm. This report presents results obtained from testing at Air Products electronic technology laboratories, located in Allentown, PA, which focused on developing processes on a commercial IC reactor using silane and mixtures of silane plus additives. These processes were deployed to compare deposition rates and film properties with and without additives, with a goal of maximizing the deposition rate while maintaining or improving film properties.

  8. Preliminary performance of image quality for a low-dose C-arm CT system with a flat-panel detector

    NASA Astrophysics Data System (ADS)

    Kyung Cha, Bo; Seo, Chang-Woo; Yang, Keedong; Jeon, Seongchae; Huh, Young

    2015-06-01

    Digital flat panel imager (FPI)-based cone-beam computed tomography (CBCT) has been widely used in C-arm imaging for spine surgery and interventional procedures. The system provides real-time fluoroscopy with high spatial resolution and three-dimensional (3D) visualization of anatomical structure without the need for patient transportation in interventional suite. In this work, a prototype CBCT imaging platform with continuous single rotation about the gantry was developed by using a large-area flat-panel detector with amorphous Si-based thin film transistor matrix. The different 2D projection images were acquired during constant gantry velocity for reconstructed images at a tube voltage of 80-120 kVp, and different current (10-50 mA) conditions. Various scan protocols were applied to a chest phantom human by changing the number of projection images and scanning angles. The projections were then reconstructed into a volumetric data of sections by using a 3D reconstruction algorithm (e.g., filtered back projection). The preliminary quantitative X-ray performance of our CBCT system was investigated by using the American Association of Physicists in Medicine CT phantom in terms of spatial resolution, contrast resolution, and CT number linearity for mobile or fixed C-arm based CBCT application with limited rotational geometry. The novel results of the projection data with different scanning angles and angular increments in the orbital gantry platform were acquired and evaluated experimentally.

  9. Laser-induced amorphization of silicon during pulsed-laser irradiation of TiN/Ti/polycrystalline silicon/SiO2/silicon

    NASA Astrophysics Data System (ADS)

    Chong, Y. F.; Pey, K. L.; Wee, A. T. S.; Thompson, M. O.; Tung, C. H.; See, A.

    2002-11-01

    In this letter, we report on the complex solidification structures formed during laser irradiation of a titanium nitride/titanium/polycrystalline silicon/silicon dioxide/silicon film stack. Due to enhanced optical coupling, the titanium nitride/titanium capping layer increases the melt depth of polycrystalline silicon by more than a factor of 2. It is found that the titanium atoms diffuse through the entire polycrystalline silicon layer during irradiation. Contrary to the expected polycrystalline silicon growth, distinct regions of polycrystalline and amorphous silicon are formed instead. Possible mechanisms for the formation of these microstructures are proposed.

  10. Evaluation of the mechanical stability of a megavoltage imaging system using a new flat panel positioner

    NASA Astrophysics Data System (ADS)

    Morin, O.; Chen, J.; Aubin, M.; Pouliot, J.

    2005-04-01

    Mega-Voltage systems are used in radiation oncology both for external radiation delivery and patient positioning prior to treatment. A pair of portal images compared with digitally reconstructed radiographs is currently the gold standard for positioning but new developments have made possible the use of Mega-Voltage Cone Beam CT for better 3D setup. The non-ideal imaging geometry of the treatment unit has a direct impact on both methods. It led to the use of a reticule attachment as reference for the scale and the isocenter position on the portal images. The reticule has limited precision and occasionally super-imposes anatomical information. As for Cone Beam, the image quality crucially depends on the knowledge of the scan geometry during the acquisition. The reproducibility of the detector position at each angle will affect the image reconstruction and determine how frequently geometrical calibration must be performed. The objectives of this study are to measure the flex of the detector and evaluate its reproducibility. A RID 1640 Perkin Elmer a-Si Flat Panel is installed on a Siemens Primus linear accelerator with a positioner similar the the one used in the Oncor product. Three original methods are used to investigate the behavior in space and time of the imaging system. A reticule and a Plumb Bob tip are placed along the line formed by the isocenter and the source. Their positions projected on the flat panel for different gantry positions are used to calculate the mechanical flex. Projection matrices obtained in a geometrical Cone Beam calibration are also used to quantify the flat panel sagging. Six full sets of data were acquired over a period of 5 months and recorded overall mechanical flexes of 1 and 3 mm for the transversal and longitudinal directions respectively. The absolute magnitude of the flat panel displacement varies slightly with the method used but the discrepancy stays within the laser precision used for alignment. The small standard deviations

  11. Quantitative assessment of molecular dynamics-grown amorphous silicon and germanium films on silicon (111)

    NASA Astrophysics Data System (ADS)

    Käshammer, Peter; Borgardt, Nikolai I.; Seibt, Michael; Sinno, Talid

    2016-09-01

    Molecular dynamics based on the empirical Tersoff potential was used to simulate the deposition of amorphous silicon and germanium on silicon(111) at various deposition rates and temperatures. The resulting films were analyzed quantitatively by comparing one-dimensional atomic density profiles to experimental measurements. It is found that the simulations are able to capture well the structural features of the deposited films, which exhibit a gradual loss of crystalline order over several monolayers. A simple mechanistic model is used to demonstrate that the simulation temperature may be used to effectively accelerate the surface relaxation processes during deposition, leading to films that are consistent with experimental samples grown at deposition rates many orders-of-magnitude slower than possible in a molecular dynamics simulation.

  12. Recrystallization of silicon-on-sapphire structures at various amorphization-ion-beam energies

    SciTech Connect

    Alexandrov, P. A. Demakov, K. D.; Shemardov, S. G.; Kuznetsov, Yu. Yu.

    2013-02-15

    Silicon films on sapphire substrates are grown via recrystallization from the silicon-sapphire interface. An amorphous layer is formed using ion implantation with silicon ion energies of 90-150 keV. An X-ray rocking curve is used to estimate the crystalline perfection of the silicon films. After recrystallization, the silicon layer consists of two parts with different crystalline quality. The recrystallized silicon-on-sapphire structures have a highly perfect upper layer (for fabricating microelectronic devices) and a lower layer adjacent to the sapphire substrate containing a large number of defects.

  13. Progress Developing Hybrid Silicon Quantum Dot/Amorphous Silicon Thin Films for Photovoltaics Application

    NASA Astrophysics Data System (ADS)

    Guan, Tianyuan; Fields, Jeremy; Klafehn, Grant; Kendrick, Chito; Lochner, Robert; Nourbakhsh, Zahra; Lusk, Mark; Stradins, Paul; Taylor, Craig; Collins, Reuben

    2013-03-01

    Quantum confined (QC) nanostructures exhibit novel, size tunable, quantum mechanical phenomena and their use in solar cell architectures may yield significant efficiency gains. We demonstrate QC hybrid silicon nanocrystal(nc-Si:H) - hydrogenated amorphous silicon (a-Si:H) structures, which can potentially serve as photo-stable, thin film silicon, solar cell materials and provide higher open-circuit voltage compared to conventional materials. We deposit a/nc-Si:H films sequentially, where nc-Si:H and a-Si:H are grown layer-by-layer using separate plasma reactors in a common deposition chamber. X-ray diffraction, Raman spectroscopy, and electron microscopy results confirm the nanoparticles are the appropriate size to achieve QC (3-7nm). Photoluminescence spectroscopy reveals the QC. Co-planar electrical probe experiments investigate carrier transport in a/nc-Si:H, which could be limited by defects accompanying plasma interruption in the sequential deposition process. Defect spectroscopies, such as electron paramagnetic resonance and photothermal deflection spectroscopy are used to study this relationship. These studies reveal material quality limitations to be addressed for realizing film silicon materials that harvest QC to enhance PV device performance. Support of the DOE SunShot and NSF MRSEC programs are gratefully acknowledged.

  14. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    NASA Astrophysics Data System (ADS)

    Wan, Yimao; Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres

    2015-12-01

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiNx) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiNx stack, recombination current density J0 values of 9, 11, 47, and 87 fA/cm2 are obtained on 10 Ω.cm n-type, 0.8 Ω.cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J0 on n-type 10 Ω.cm wafers is further reduced to 2.5 ± 0.5 fA/cm2 when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiNx stack is thermally stable at 400 °C in N2 for 60 min on all four c-Si surfaces. Capacitance-voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiNx stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  15. Research on stable, high-efficiency amorphous silicon multijunction modules

    SciTech Connect

    Guha, S. )

    1991-12-01

    This report describes research to improve the understanding of amorphous silicon alloys and other relevant non-semiconductor materials for use in high-efficiency, large-area multijunction modules. The research produced an average subcell initial efficiency of 8.8% over a 1-ft{sup 2} area using same-band-gap, dual-junction cells deposited over a ZnO/AlSi back reflector. An initial efficiency of 9.6% was achieved using a ZnO/Ag back reflector over smaller substrates. A sputtering machine will be built to deposit a ZnO/Ag back reflector over a 1-ft{sup 2} area so that a higher efficiency can also be obtained on larger substrates. Calculations have been performed to optimize the grid pattern, bus bars, and cell interconnects on modules. With our present state of technology, we expect a difference of about 6% between the aperture-area and active-area efficiencies of modules. Preliminary experiments show a difference of about 8%. We can now predict the performance of single-junction cells after long-term light exposure at 50{degree}C by exposing cells to short-term intense light at different temperatures. We find that single-junction cells deposited on a ZnO/Ag back reflector show the highest stabilized efficiency when the thickness of the intrinsic layers is about 2000 {angstrom}. 8 refs.

  16. Deployable aerospace PV array based on amorphous silicon alloys

    NASA Technical Reports Server (NTRS)

    Hanak, Joseph J.; Walter, Lee; Dobias, David; Flaisher, Harvey

    1989-01-01

    The development of the first commercial, ultralight, flexible, deployable, PV array for aerospace applications is discussed. It is based on thin-film, amorphous silicon alloy, multijunction, solar cells deposited on a thin metal or polymer by a proprietary, roll-to-roll process. The array generates over 200 W at AM0 and is made of 20 giant cells, each 54 cm x 29 cm (1566 sq cm in area). Each cell is protected with bypass diodes. Fully encapsulated array blanket and the deployment mechanism weigh about 800 and 500 g, respectively. These data yield power per area ratio of over 60 W/sq m specific power of over 250 W/kg (4 kg/kW) for the blanket and 154 W/kg (6.5 kg/kW) for the power system. When stowed, the array is rolled up to a diameter of 7 cm and a length of 1.11 m. It is deployed quickly to its full area of 2.92 m x 1.11 m, for instant power. Potential applications include power for lightweight space vehicles, high altitude balloons, remotely piloted and tethered vehicles. These developments signal the dawning of a new age of lightweight, deployable, low-cost space arrays in the range from tens to tens of thousands of watts for near-term applications and the feasibility of multi-100 kW to MW arrays for future needs.

  17. Nanohole Structuring for Improved Performance of Hydrogenated Amorphous Silicon Photovoltaics.

    PubMed

    Johlin, Eric; Al-Obeidi, Ahmed; Nogay, Gizem; Stuckelberger, Michael; Buonassisi, Tonio; Grossman, Jeffrey C

    2016-06-22

    While low hole mobilities limit the current collection and efficiency of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices, attempts to improve mobility of the material directly have stagnated. Herein, we explore a method of utilizing nanostructuring of a-Si:H devices to allow for improved hole collection in thick absorber layers. This is achieved by etching an array of 150 nm diameter holes into intrinsic a-Si:H and then coating the structured material with p-type a-Si:H and a conformal zinc oxide transparent conducting layer. The inclusion of these nanoholes yields relative power conversion efficiency (PCE) increases of ∼45%, from 7.2 to 10.4% PCE for small area devices. Comparisons of optical properties, time-of-flight mobility measurements, and internal quantum efficiency spectra indicate this efficiency is indeed likely occurring from an improved collection pathway provided by the nanostructuring of the devices. Finally, we estimate that through modest optimizations of the design and fabrication, PCEs of beyond 13% should be obtainable for similar devices. PMID:27227369

  18. Si-H bond dynamics in hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Scharff, R. Jason; McGrane, Shawn D.

    2007-08-01

    The ultrafast structural dynamics of the Si-H bond in the rigid solvent environment of an amorphous silicon thin film is investigated using two-dimensional infrared four-wave mixing techniques. The two-dimensional infrared (2DIR) vibrational correlation spectrum resolves the homogeneous line shapes ( <2.5cm-1 linewidth) of the 0→1 and 1→2 vibrational transitions within the extensively inhomogeneously broadened ( 78cm-1 linewidth) Si-H vibrational band. There is no spectral diffusion evident in correlation spectra obtained at 0.2, 1, and 4ps waiting times. The Si-H stretching mode anharmonic shift is determined to be 84cm-1 and decreases slightly with vibrational frequency. The 1→2 linewidth increases with vibrational frequency. Frequency dependent vibrational population times measured by transient grating spectroscopy are also reported. The narrow homogeneous line shape, large inhomogeneous broadening, and lack of spectral diffusion reported here present the ideal backdrop for using a 2DIR probe following electronic pumping to measure the transient structural dynamics implicated in the Staebler-Wronski degradation [Appl. Phys. Lett. 31, 292 (1977)] in a-Si:H based solar cells.

  19. Carrier transport in amorphous silicon utilizing picosecond photoconductivity

    NASA Astrophysics Data System (ADS)

    Johnson, A. M.

    1981-08-01

    The development of a high-speed electronic measurement capability permitted the direct observation of the transient photoresponse of amorphous silicon (a-Si) with a time resolution of approximately 10ps. This technique was used to measure the initial mobility of photogenerated (2.1eV) free carriers in three types of a-Si having widely different densities of structural defects (i.e., as prepared by: (1) RF glow discharge (a-Si:H); (2) chemical vapor deposition; and (3) evaporation in ultra-high vacuum). In all three types of a-Si, the same initial mobility of approximately 1 cu cm/Vs at room temperature was found. This result tends to confirm the often-made suggestion that the free carrier mobility is determined by the influence of shallow states associated with the disorder in the random atomic network, and is an intrinsic property of a-Si which is unaffected by the method of preparation. The rate of decay of the photocurrent correlates with the density of structural defects and varies from 4ps to 200ps for the three types of a-Si investigated. The initial mobility of a-Si:H was found to be thermally activated. The possible application of extended state transport controlled by multiple trapping and small polaron formation is discussed.

  20. Electrical characterization of hydrogenated amorphous silicon oxide films

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Katayama, Ryuichi; Yamakawa, Koki; Matsui, Kento; Saito, Masaru; Sugiyama, Shuhichiroh; Sichanugrist, Porponth; Nonomura, Shuichi; Konagai, Makoto

    2015-08-01

    The electrical characterization of hydrogenated amorphous silicon oxide (a-SiOx:H) films was performed by electron spin resonance (ESR) and electrical conductivity measurements. In the ESR spectra of the a-SiOx:H films, two ESR peaks with g-values of 2.005 and 2.013 were observed. The ESR peak with the g-value of 2.013 was not observed in the ESR spectra of a-Si:H films. The photoconductivity of the a-SiOx:H films decreased with increasing spin density estimated from the ESR peak with the g-value of 2.005. On the other hand, photoconductivity was independent of spin density estimated from the ESR peak with the g-value of 2.013. The optical absorption coefficient spectra of the a-SiOx:H films were also measured. The spin density estimated from the ESR peak with the g-value of 2.005 increased proportionally with increasing optical absorption owing to the gap-state defect.

  1. Characterization of hydrogenated amorphous silicon films obtained from rice husk

    NASA Astrophysics Data System (ADS)

    Nandi, K. C.; Mukherjee, D.; Biswas, A. K.; Acharya, H. N.

    1991-08-01

    Hydrogenated amorphous silicon ( a-Si: H) films were prepared by chemical vapour deposition (CVD) of silanes generated by the acid hydrolysis of magnesium silicide (Mg 2Si) obtained from rice husk. The films were deposited at various substrate temperatures ( Ts) ranging from 430 to 520°C. The results show that the films have room temperature (294 K) dark conductivity (σ d) of the order of 10 -8 - 10 -10 (ohm-cm) -1 with single activation energy (Δ Ed) and the photoconductivity (σ ph) decreases with increase of Ts. Optical band gap ( Eopt) lies between 1.60-1.73 eV and hydrogen content ( CH) in the films is at best 8.3 at %. Au/ a-Si: H junction shows that it acts as a rectifier contact with Schottky barrier height ( VB) 0.69 eV. The films are contaminated by traces of impurities like Na, K, Al, Cl and O as revealed by secondary ion mass spectrometric (SIMS) analysis.

  2. High efficiency neutron sensitive amorphous silicon pixel detectors

    SciTech Connect

    Mireshghi, A.; Cho, G.; Drewery, J.S.; Hong, W.S.; Jing, T.; Lee, H.; Kaplan, S.N.; Perez-Mendez, V.

    1993-11-01

    A multi-layer a-Si:H based thermal neutron detector was designed, fabricated and simulated by Monte Carlo method. The detector consists of two PECVD deposited a-Si:H pin detectors interfaced with coated layers of Gd, as a thermal neutron converter. Simulation results indicate that a detector consisting of 2 Gd films with thicknesses of 2 and 4 {mu}m, sandwiched properly with two layers of sufficiently thick ({approximately}30{mu}m) amorphous silicon diodes, has the optimum parameters. The detectors have an intrinsic efficiency of about 42% at a threshold setting of 7000 electrons, with an expected average signal size of {approximately}12000 electrons which is well above the noise. This efficiency will be further increased to nearly 63%, if we use Gd with 50% enrichment in {sup 157}Gd. We can fabricate position sensitive detectors with spatial resolution of 300 {mu}m with gamma sensitivity of {approximately}1 {times} 10{sup {minus}5}. These detectors are highly radiation resistant and are good candidates for use in various application, where high efficiency, high resolution, gamma insensitive position sensitive neutron detectors are needed.

  3. Hot wire deposited hydrogenated amorphous silicon solar cells

    SciTech Connect

    Mahan, A.H.; Iwaniczko, E.; Nelson, B.P.; Reedy, R.C. Jr.; Crandall, R.S.

    1996-05-01

    This paper details the results of a study in which low H content, high deposition rate hot wire (HW) deposited amorphous silicon (a-Si:H) has been incorporated into a substrate solar cell. The authors find that the treatment of the top surface of the HW i layer while it is being cooled from its high deposition temperature is crucial to device performance. They present data concerning these surface treatments, and correlate these treatments with Schottky device performance. The authors also present first generation HW n-i-p solar cell efficiency data, where a glow discharge (GD) {mu}c-Si(p) layer was added to complete the partial devices. No light trapping layer was used to increase the device Jsc. Their preliminary investigations have yielded efficiencies of up to 6.8% for a cell with a 4000 {Angstrom} thick HW i-layer, which degrade less than 10% after a 900 hour light soak. The authors suggest avenues for further improvement of their devices.

  4. Power change in amorphous silicon technology by low temperature annealing

    NASA Astrophysics Data System (ADS)

    Mittal, Ankit; Rennhofer, Marcus; Dangel, Angelika; Duman, Bogdan; Schlosser, Victor

    2015-07-01

    Amorphous silicon (a-Si) is one of the best established thin-film solar-cell technologies. Despite its long history of research, it still has many critical issues because of its defect rich material and its susceptibility to degrade under light also called as Staebler-Wronski effect (SWE). This leads to an increase in the defect density of a-Si, but as a metastable effect it can be completely healed at temperatures above 170 °C. Our study is focused on investigating the behavior of annealing of different a-Si modules under low temperature conditions below 80 °C indicated by successive change of module power. These conditions reflect the environmental temperature impact of the modules in the field, or integrated in buildings as well. The power changes were followed by STC power rating and investigation of module-power evolution under low irradiance conditions at 50 W/m2. Our samples were recovered close to their initial state of power, reaching as high as 99% from its degraded value. This shows the influence of low temperature annealing and light on metastable module behavior in a-Si thin-film modules.

  5. Optical position detectors based on thin film amorphous silicon

    NASA Astrophysics Data System (ADS)

    Henry, Jasmine; Livingstone, John

    2001-10-01

    Thin film optical position sensitive detectors (PSDs) based on novel hydrogenated amorphous silicon Schottky barrier (SB) structures are compared in this work. The three structures reported here have been tested under different light sources to measure their linear properties and wavelength response characteristics. The sputtered a-Si sensors were configured as layered structures of platinum, a-Si and indium tin oxide, forming SB-i-n devices and exhibited linear properties similar to multi-layer a-Si p-i- n devices produced by complex chemical vapor deposition procedures, which involve flammable and toxic gases. All structures were test4ed as possible configurations for 2D sensors. The devices were tested under white light, filtered white light and also a red diode laser. Each of the three structures responded quite differently to each of the sources. Results, based on the correlation coefficient, which measures the linearity of output and which has a maximum value of 1, produced r values ranging between 0.992 to 0.999, in the best performances.

  6. Temperature dependent deformation mechanisms in pure amorphous silicon

    SciTech Connect

    Kiran, M. S. R. N. Haberl, B.; Williams, J. S.; Bradby, J. E.

    2014-03-21

    High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200 °C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and “defect” formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.

  7. Electrodeposition of polycrystalline and amorphous silicon for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Rauh, R. D.

    1980-07-01

    Plating experiments with SiHCl3 solutions in propylene carbonate with 0.1 M tetrabutylammonium tetrafluoroborate are described. Silicon was deposited on ITO glass (Nesatron) as well as Mo substrates at temperatures from 25-80 C. Both potentiostatic and galvanostatic conditions were used. The high resistance of the films limited the thickness which could be deposited by either method to less than 5 micrometers. Deposition beyond this limit resulted in a deterioration of the film quality. X-ray analysis of the films confirmed that they were amorphous. SEM analysis of the films revealed a very porous structure with nodules about 1 micrometer in diameter. Annealing the deposit at 400 C in an Ar:H2 atmosphere resulted in a slightly smoother surface but the nodules remained. The films deposited on ITO glass had a band gap of about 1.0 eV and an EO4 value of 1.5-2.0 eV. The Auger analysis of the films showed the presence of large amounts of oxygen in the samples that had been exposed to air.

  8. Amorphous silicon cell array powered solar tracking apparatus

    DOEpatents

    Hanak, Joseph J.

    1985-01-01

    An array of an even number of amorphous silicon solar cells are serially connected between first and second terminals of opposite polarity. The terminals are connected to one input terminal of a DC motor whose other input terminal is connected to the mid-cell of the serial array. Vane elements are adjacent the end cells to selectively shadow one or the other of the end cells when the array is oriented from a desired attitude relative to the sun. The shadowing of one cell of a group of cells on one side of the mid-cell reduces the power of that group substantially so that full power from the group of cells on the other side of the mid-cell drives the motor to reorient the array to the desired attitude. The cell groups each have a full power output at the power rating of the motor. When the array is at the desired attitude the power output of the two groups of cells balances due to their opposite polarity so that the motor remains unpowered.

  9. The importance of inhomogeneities in hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Agarwal, Satish

    2014-03-01

    We shall discuss how the heterogeneities present in hydrogenated amorphous silicon (a-Si:H) can be taken into account by considering the long range potential fluctuations (LRPF), arising from them. Using these ideas we try to understand several challenging puzzles, some of them remaining unresolved till now. These range, from why undoped a-Si:H is n-type, to why the light soaking (LS) degrades boron doped a-Si:H films faster than the undoped or the phosphorous doped films, and why hole injection favors larger degradation than electron injection. Also, the failure of reciprocity and the saturation of the number of dangling bonds created by LS at the low value of about 1017 cm-3 can be explained. The improved stability of a-Si:H containing nc-Si has been attributed to the LRPF assisted diffusion of photo carriers to nc-Si and recombination there. These and other similar observations will be taken up. Work supported by CSIR, New Delhi.

  10. Raman spectroscopy of PIN hydrogenated amorphous silicon solar cells

    NASA Astrophysics Data System (ADS)

    Keya, Kimitaka; Torigoe, Yoshihiro; Toko, Susumu; Yamashita, Daisuke; Seo, Hyunwoong; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu

    2015-09-01

    Light-induced degradation of hydrogenated amorphous silicon (a-Si:H) is a key issue for enhancing competitiveness in solar cell market. A-Si:H films with a lower density of Si-H2 bonds shows higher stability. Here we identified Si-H2 bonds in PIN a-Si:H solar cells fabricated by plasma CVD using Raman spectroscopy. A-Si:H solar cell has a structure of B-doped μc-SiC:H (12.5 nm)/ non-doped a-Si:H (250nm)/ P-doped μc-Si:H (40 nm) on glass substrates (Asahi-VU). By irradiating HeNe laser light from N-layer, peaks correspond to Si-H2 bonds (2100 cm-1) and Si-H bonds (2000 cm-1) have been identified in Raman scattering spectra. The intensity ratio of Si-H2 and Si-H ISiH2/ISiH is found to correlate well to light induced degradation of the cells Therefore, Raman spectroscopy is a promising method for studying origin of light-induced degradation of PIN solar cells.

  11. Laminated Amorphous Silicon Neutron Detector (pre-print)

    SciTech Connect

    Harry McHugh, Howard Branz, Paul Stradins, and Yueqin Xu

    2009-01-29

    An internal R&D project was conducted at the Special Technologies Laboratory (STL) of National Security Technologies, LLC (NSTec), to determine the feasibility of developing a multi-layer boron-10 based thermal neutron detector using the amorphous silicon (AS) technology currently employed in the manufacture of liquid crystal displays. The boron-10 neutron reaction produces an alpha that can be readily detected. A single layer detector, limited to an approximately 2-micron-thick layer of boron, has a theoretical sensitivity of about 3%; hence a thin multi-layer device with high sensitivity can theoretically be manufactured from single layer detectors. Working with National Renewable Energy Laboratory (NREL), an AS PiN diode alpha detector was developed and tested. The PiN diode was deposited on a boron-10 coated substrate. Testing confirmed that the neutron sensitivity was nearly equal to the theoretical value of 3%. However, adhesion problems with the boron-10 coating prevented successful development of a prototype detector. Future efforts will include boron deposition work and development of integrated AS signal processing circuitry.

  12. Hydrogenated amorphous silicon produced by pyrolysis and photolysis of disilane

    SciTech Connect

    Ashida, Y.; Hirose, M.; Isogaya, K.; Kitagawa, N.; Mishima, Y.; Osuka, Y.

    1984-05-01

    A new class of hydrogenated amorphous silicon (a-Si:H) was prepared by the thermal CVD and photo-CVD of disilane. In the low pressure thermal CVD, the horizontal quartz tube heated by resistance heaters was used as a reactor. The growth rate of the thermal CVD a-Si:H films is plotted as a function of reciprocal substrate temperature. As a new alternative approach to prepare high quality CVD films at temperatures below 300/sup 0/C, the direct photochemical decomposition of disilane has been attempted utilizing a low pressure mercury lamp as a UV radiation source. In the case of undoped and phosphorus doped films, the growth rate is independent of the substrate temperature. In contrast to this, for boron doping, the growth rate has an activation energy of 0.64 eV as in the case of the thermal CVD although the growth rate of the photo-CVD is about three times as large as that of the thermal CVD. This implies that the photoCVD process in boron doping is dominated by the thermal reaction catalyzed with diborane. The dark conductivity and photoconductivity before and after light exposure (AM-1, 200 mW/cm/sup 2/) exhibit no change, indicating the absence of the light-soak degradation in photo-CVD films. The valency control in thermal CVD and photo-CVD is also successfully carried out.

  13. Effect of argon ion bombardment on amorphous silicon carbonitride films

    NASA Astrophysics Data System (ADS)

    Batocki, R. G. S.; Mota, R. P.; Honda, R. Y.; Santos, D. C. R.

    2014-04-01

    Amorphous silicon carbonitride (a-SiCN:H) films were synthesized by radiofrequency (RF) Plasma Enhanced Vapor Chemical Deposition (PECVD) using hexamethyldisilazane (HMDSN) as precursor compound. Then, the films were post-treated by Plasma Immersion Ion Implantation (PIII) in argon atmosphere from 15 to 60 min. The hardness of the film enhanced after ion implantation, and the sample treated at 45 min process showed hardness greater than sixfold that of the untreated sample. This result is explained by the crosslinking and densification of the structure. Films were exposed to oxygen plasma for determining of the etching rate. It decreased monotonically from 33 Å/min to 19 Å/min for the range of process time, confirming structural alterations. Hydrophobic character of the a-SiCN:H films were modified immediately after ion bombardment, due to incorporation of polar groups. However, the high wettability of the films acquired by the ion implantation was diminished after aging in air. Therefore, argon PIII made a-SiCN:H films mechanically more resistant and altered their hydrophobic character.

  14. Hydrogenated amorphous silicon thin film anode for proton conducting batteries

    NASA Astrophysics Data System (ADS)

    Meng, Tiejun; Young, Kwo; Beglau, David; Yan, Shuli; Zeng, Peng; Cheng, Mark Ming-Cheng

    2016-01-01

    Hydrogenated amorphous Si (a-Si:H) thin films deposited by chemical vapor deposition were used as anode in a non-conventional nickel metal hydride battery using a proton-conducting ionic liquid based non-aqueous electrolyte instead of alkaline solution for the first time, which showed a high specific discharge capacity of 1418 mAh g-1 for the 38th cycle and retained 707 mAh g-1 after 500 cycles. A maximum discharge capacity of 3635 mAh g-1 was obtained at a lower discharge rate, 510 mA g-1. This electrochemical discharge capacity is equivalent to about 3.8 hydrogen atoms stored in each silicon atom. Cyclic voltammogram showed an improved stability 300 mV below the hydrogen evolution potential. Both Raman spectroscopy and Fourier transform infrared spectroscopy studies showed no difference to the pre-existing covalent Si-H bond after electrochemical cycling and charging, indicating a non-covalent nature of the Si-H bonding contributing to the reversible hydrogen storage of the current material. Another a-Si:H thin film was prepared by an rf-sputtering deposition followed by an ex-situ hydrogenation, which showed a discharge capacity of 2377 mAh g-1.

  15. Research on stable, high-efficiency amorphous silicon multijunction modules

    SciTech Connect

    Banerjee, A.; Chen, E.; Clough, R.; Glatfelter, T.; Guha, S.; Hammond, G.; Hopson, M.; Jackett, N.; Lycette, M.; Noch, J.; Palmer, T.; Pawlikiewicz, A.; Rosenstein, I.; Ross, R.; Wolf, D.; Xu, X.; Yang, J.; Younan, K.

    1992-04-01

    This report describes the progress made during Phase 1 of research and development program to obtain high-efficiency amorphous silicon alloy multijunction modules. Using a large-area deposition system, double-and triple-junction cells were made on stainless steel substrates of over 1 ft{sup 2} area with Ag and ZnO predeposited back reflector. Modules of over 1 ft{sup 2} were produced with between 9.2% and 9.9 initial aperture-area efficiencies as measured under a USSC Spire solar simulator. Efficiencies as measured under the NREL Spire solar simulator were found to be typically 15% to 18% lower. The causes for this discrepancy are now being investigated. The modules show about 15% degradation after 600 hours of one-sun illumination at 50{degrees}C. To optimize devices for higher stabilized efficiency, a new method was developed by which the performance of single-junction cells after long-term, one-sun exposure at 50{degrees}C can be predicted by exposing cells to short-term intense light at different temperatures. This method is being used to optimize the component cells of the multijunction structure to obtain the highest light-degraded efficiency.

  16. Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

    SciTech Connect

    Newby, Pascal J.; Canut, Bruno; Bluet, Jean-Marie; Lysenko, Vladimir; Gomes, Severine; Isaiev, Mykola; Burbelo, Roman; Chantrenne, Patrice; Frechette, Luc G.

    2013-07-07

    In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 Degree-Sign C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

  17. Optimization of the presampling modulation transfer function of flat-panel detectors for digital radiology

    NASA Astrophysics Data System (ADS)

    Rowlands, John A.; Ji, Winston G.

    1999-05-01

    Large area, flat panel solid state detectors are being investigated for digital radiography and fluoroscopy. These detectors employ an x-ray imaging layer of either photoconductor ('direct' conversion method) or phosphor ('indirect' conversion method) to detect x-rays. In both cases the image formed at the surface of the layer is read out in situ using an active matrix array. Depending upon the resolution of the layer compared to the pixel size, undersampling of the image and hence aliasing may occur. Aliasing is always present regardless of the pixel size in direct detectors based on amorphous selenium because of its high intrinsic resolution. Aliasing gives rise to increased noise which results in reduction of detective quantum efficiency DQE at high spatial frequencies. The aliasing can be reduced or even eliminated by blurring prior to pixel sampling (e.g., by scattering in a phosphor layer). However, blurring, which may be quantified by the spatial frequency f dependent modulation transfer function MTF(f), also has a deleterious effect: the imaging system becomes much more susceptible to noise for example that arising in the charge amplifiers or secondary quantum statistics. Note that in principle, the system MTF can be corrected to any desired values in a digital system thus MTF has no predictive value for the quality of an imaging system, rather it is the DQE(f) which determines the overall signal to noise ratio independently of the MTF enhancement chosen. Nevertheless, determining the ideal level of presampling blurring (i.e., the Presampling Modulation Transfer function) is not straightforward. A problem caused by blurring is that the degree of blurring often depends on the depth of absorption of the x-ray in the imaging layer. In such cases (as pointed out by Lubberts) additional noise is transferred to the image. The predictions of a Lubberts model will be compared with published measurements of DQE for both direct and indirect detectors. A preliminary

  18. Amorphous silicon Schottky barrier solar cells incorporating a thin insulating layer and a thin doped layer

    DOEpatents

    Carlson, David E.

    1980-01-01

    Amorphous silicon Schottky barrier solar cells which incorporate a thin insulating layer and a thin doped layer adjacent to the junction forming metal layer exhibit increased open circuit voltages compared to standard rectifying junction metal devices, i.e., Schottky barrier devices, and rectifying junction metal insulating silicon devices, i.e., MIS devices.

  19. New results on the microstructure of amorphous silicon as observed by internal friction

    SciTech Connect

    Crandall, R.S.; Mahan, A.H.; Iwaniczko, E.; Jones, K.M.; Liu, X.; White, B.E. Jr.; Pohl, R.O.

    1997-07-01

    The authors have measured the low temperature internal friction (Q{sup {minus}1}) of amorphous silicon (a-Si) films. Electron-beam evaporation leads to the well-known temperature-independent Q{sub 0}{sup {minus}1} plateau common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H) with about 1 at.% H produced by hot wire chemical vapor deposition, however, the value of Q{sub 0}{sup {minus}1} is over two hundred times smaller than for e-beam a-Si. This is the first observation of an amorphous solid without any significant low energy excitations. This finding offers the opportunity to study amorphous solids containing controlled densities of tunneling defects, and thus to explore their nature.

  20. Experimental investigation of the amorphous silicon melting temperature by fast heating processes

    SciTech Connect

    Baeri, P.; Campisano, S.U.; Grimaldi, M.G.; Rimini, E.

    1982-12-01

    The recrystallization of amorphous Si layers on Si crystal substrates after laser irradiation was investigated to test previous experimental evidence that both the melting point and the melting enthalpy of the amorphous are lower than the corresponding crystalline values. The irradiation was performed in some cases from the back side of 100-..mu..m-thick Si wafers to obtain a temperature distribution in the amorphous layer with a small spatial gradient. In the case of front irradiation the threshold energy density was measured as a function of the amorphous layer thickness, for the polycrystalline formation, crystallization with residual disorder, and good annealing, respectively. The experimental data agree quite well with heat flow calculations assuming a reduction of about 30% in the melting point and enthalpy of amorphous silicon with respect to crystalline silicon.

  1. Integration of flat panel X-ray detector for high resolution diagnostic medical imaging

    NASA Astrophysics Data System (ADS)

    Kim, Min-Woo; Yun, Min-Seok; Kim, Yoon-Suk; Oh, Kyung-Min; Shin, Jung-Wook; Nam, Kyung-Tae; Nam, Sang-Hee

    2011-05-01

    In these days, flat panel X-ray image detectors have shown their potential for replacing traditional screen-film systems. To detect the X-ray photon energy, there are two main methods known as a direct method and an indirect method. The X-rays are converted immediately into electrical signal with the direct method. The indirect method has two conversion steps: the scintillator absorbs the X-rays and converts them to visible light. And then the visible light is converted to electrical signal (e.g. by photodiodes). In this work, the flat panel digital X-ray image detector based on direct method with a high atomic number material was designed and evaluated. The high atomic number material for X-ray conversion is deposited by a rubbing method with about 300 μm. The rubbing method is similar to the screen printing method. It consists of two elements: the screen and the squeegee. The method uses a proper stiff bar stretched tightly over a frame made of wood or metal. Proper tension is essential for proper laminated structure. The detector prototype has 139 μm pixel pitch, total 1280×1536 pixels and 86% fill factor. Twelve readout ICs are installed on digital X-ray detector and simultaneously operated to reach short readout time. The electronics integrated: the preamplifier to amplify generated signal, the Analog to Digital converter and the source of bias voltage (1 V/μm). The system board and interface use an NI-camera program. Finally, we achieved images from this flat panel X-ray image detector.

  2. Dual-exposure technique for extending the dynamic range of x-ray flat panel detectors

    NASA Astrophysics Data System (ADS)

    Sisniega, A.; Abella, M.; Desco, M.; Vaquero, J. J.

    2014-01-01

    This work presents an approach to extend the dynamic range of x-ray flat panel detectors by combining two acquisitions of the same sample taken with two different x-ray photon flux levels and the same beam spectral configuration. In order to combine both datasets, the response of detector pixels was modelled in terms of mean and variance using a linear model. The model was extended to take into account the effect of pixel saturation. We estimated a joint probability density function (j-pdf) of the pixel values by assuming that each dataset follows an independent Gaussian distribution. This j-pdf was used for estimating the final pixel value of the high-dynamic-range dataset using a maximum likelihood method. The suitability of the pixel model for the representation of the detector signal was assessed using experimental data from a small-animal cone-beam micro-CT scanner equipped with a flat panel detector. The potential extension in dynamic range offered by our method was investigated for generic flat panel detectors using analytical expressions and simulations. The performance of the proposed dual-exposure approach in realistic imaging environments was compared with that of a regular single-exposure technique using experimental data from two different phantoms. Image quality was assessed in terms of signal-to-noise ratio, contrast, and analysis of profiles drawn on the images. The dynamic range, measured as the ratio between the exposure for saturation and the exposure equivalent to instrumentation noise, was increased from 76.9 to 166.7 when using our method. Dual-exposure results showed higher contrast-to-noise ratio and contrast resolution than the single-exposure acquisitions for the same x-ray dose. In addition, image artifacts were reduced in the combined dataset. This technique to extend the dynamic range of the detector without increasing the dose is particularly suited to image samples that contain both low and high attenuation regions.

  3. Designing, Modeling, Constructing, and Testing a Flat Panel Speaker and Sound Diffuser for a Simulator

    NASA Technical Reports Server (NTRS)

    Dillon, Christina

    2013-01-01

    The goal of this project was to design, model, build, and test a flat panel speaker and frame for a spherical dome structure being made into a simulator. The simulator will be a test bed for evaluating an immersive environment for human interfaces. This project focused on the loud speakers and a sound diffuser for the dome. The rest of the team worked on an Ambisonics 3D sound system, video projection system, and multi-direction treadmill to create the most realistic scene possible. The main programs utilized in this project, were Pro-E and COMSOL. Pro-E was used for creating detailed figures for the fabrication of a frame that held a flat panel loud speaker. The loud speaker was made from a thin sheet of Plexiglas and 4 acoustic exciters. COMSOL, a multiphysics finite analysis simulator, was used to model and evaluate all stages of the loud speaker, frame, and sound diffuser. Acoustical testing measurements were utilized to create polar plots from the working prototype which were then compared to the COMSOL simulations to select the optimal design for the dome. The final goal of the project was to install the flat panel loud speaker design in addition to a sound diffuser on to the wall of the dome. After running tests in COMSOL on various speaker configurations, including a warped Plexiglas version, the optimal speaker design included a flat piece of Plexiglas with a rounded frame to match the curvature of the dome. Eight of these loud speakers will be mounted into an inch and a half of high performance acoustic insulation, or Thinsulate, that will cover the inside of the dome. The following technical paper discusses these projects and explains the engineering processes used, knowledge gained, and the projected future goals of this project

  4. Visual and ocular effects from the use of flat-panel displays

    PubMed Central

    Porcar, Esteban; Pons, Alvaro M.; Lorente, Amalia

    2016-01-01

    AIM To evaluate the prevalence of eye symptoms in a non-presbyopic population of video display unit (VDU) users with flat-panel displays. METHODS One hundred and sixteen VDU users with flat-panel display from an urban population participated in the study; their ages ranging from 20 to 34y. There were 60 females and 56 males. An eye examination to rule out the presence of significant uncorrected refractive errors, general binocular dysfunctions and eye conditions was carried out. In order to determine and quantify the type and nature of eye symptoms, participants were asked to answer written questionnaire and the results were grouped by gender, age and number of hours a day spent using a VDU. RESULTS Seventy-two percent of participants reported eye symptoms related to VDU use. Eye symptoms from moderate-to-severe were found in 23% of participants. The main symptom was moderate-to-severe tired eyes (14%); followed by sensitivity to bright lights (12%), blurred vision at far distances (10%), eyestrain or dry eye or irritated or burning eyes (9%), difficulty in refocusing from one distance to another or headache (8%) and blurred vision at near or intermediate distances (<4%). Eye symptoms were greater among females (P=0.005) and increased with VDU use, markedly above 6h spent using a VDU in a typical day (P=0.01). CONCLUSION Significant eye symptoms relate to VDU use often occur and should not be underestimated. The increasing use of electronic devices with flat-panel display should prompt users to take appropriate measures to prevent or to relieve the eye symptoms arising from their use. PMID:27366692

  5. Stabilization of amorphous structure in silicon thin film by adding germanium

    SciTech Connect

    Makino, Nobuaki; Shigeta, Yukichi

    2015-06-21

    The stabilization of the amorphous structure in amorphous silicon film by adding Ge atoms was studied using Raman spectroscopy. Amorphous Si{sub 1−x}Ge{sub x} (x = 0.0, 0.03, 0.14, and 0.27) films were deposited on glass substrates from electron beam evaporation sources and annealed in N{sub 2} atmosphere. The change in the amorphous states and the phase transition from amorphous to crystalline were characterized using the TO, LO, and LA phonons in the Raman spectra. The temperature of the transition from the amorphous phase to the crystalline phase was higher for the a-Si{sub 1−x}Ge{sub x} (x = 0.03, 0.14) films, and the crystallization was hindered. The reason why the addition of a suitable quantity of Ge atoms into the three-dimensional amorphous silicon network stabilizes its amorphous structure is discussed based on the changes in the Raman signals of the TO, LO, and LA phonons during annealing. The characteristic bond length of the Ge atoms allows them to stabilize the random network of the amorphous Si composed of quasi-tetrahedral Si units, and obstruct its rearrangement.

  6. Electron beam quality control using an amorphous silicon EPID

    SciTech Connect

    Beck, J. A.; Budgell, G. J.; Roberts, D. A.; Evans, P. M.

    2009-05-15

    An amorphous silicon EPID has been investigated to determine whether it is capable of quality control constancy measurements for linear accelerator electron beams. The EPID grayscale response was found to be extremely linear with dose over a wide dose range and, more specifically, for exposures of 95-100 MU. Small discrepancies of up to 0.8% in linearity were found at 6 MeV (8-15 MeV showed better agreement). The shape of the beam profile was found to be significantly altered by scatter in air over the approximately 60 cm gap between the end of the applicator and the EPID. Nevertheless, relative changes in EPID-measured profile flatness and symmetry were linearly related to changes in these parameters at 95 cm focus to surface distance (FSD) measured using a 2D diode array. Similar results were obtained at 90 deg. and 270 deg. gantry angles. Six months of daily images were acquired and analyzed to determine whether the device is suitable as a constancy checker. EPID output measurements agreed well with daily ion chamber measurements, with a 0.8% standard deviation in the difference between the two measurement sets. When compared to weekly parallel plate chamber measurements, this figure dropped to 0.5%. A Monte Carlo (MC) model of the EPID was created and demonstrated excellent agreement between MC-calculated profiles in water and the EPID at 95 and 157 cm FSD. Good agreement was also found with measured EPID profiles, demonstrating that the EPID provides an accurate measurement of electron profiles. The EPID was thus shown to be an effective method for performing electron beam daily constancy checks.

  7. Growth and defect chemistry of amorphous hydrogenated silicon

    NASA Astrophysics Data System (ADS)

    Scott, Bruce A.; Reimer, Jeffrey A.; Longeway, Paul A.

    1983-12-01

    Magnetic resonance (NMR,EPR) and infrared studies are presented of amorphous hydrogenated silicon (a-Si:H) films prepared by homogeneous chemical vapor deposition (HOMOCVD) and rf plasma decomposition using silane and disilane. Hydrogen incorporation occurs with a small activation energy (˜0.06 eV) for all films, while the barrier for changes in spin defect density is almost an order of magnitude larger and comparable to that measured in defect annealing studies. Films deposited by rf(Si2H6) plasma exhibit the greatest hydrogen contents, followed by HOMOCVD and rf(SiH4) plasma material. NMR measurements suggest that HOMOCVD films are less disordered than plasma-deposited a-Si:H. Previous work and recent kinetic studies of plasma and thermal environments are extensively analyzed, along with thermodynamic and kinetic data, to determine a a-Si:H growth mechanisms most consistent with the experimental results. The model presented to explain compositional and defect changes with substrate temperature emphasizes plasma deposition by monoradical precursors and HOMOCVD growth by diradicals, resulting initially in a similar surface-bound intermediate in all cases. Plasma growth from Si2H6 involves the surface attachment of longer radical chains, compared to SiH4, while oligomeric diradicals could be present in HOMOCVD. The possibility that reactions at the hot reactor wall, as well as in the gas, create monoradicals in HOMOCVD is also explored in detail. Finally, film dehydrogenation and crosslinking reactions are examined, and experiments proposed to determine the channels most relevant for each deposition environment.

  8. Dynamics of hydrogenated amorphous silicon flexural resonators for enhanced performance

    NASA Astrophysics Data System (ADS)

    Mouro, J.; Chu, V.; Conde, J. P.

    2016-04-01

    Hydrogenated amorphous silicon thin-film flexural resonators with sub-micron actuation gaps are fabricated by surface micromachining on glass substrates. Experimentally, the resonators are electrostatically actuated and their motion is optically detected. Three different configurations for the electrostatic excitation force are used to study the dynamics of the resonators. In the first case, a dc voltage (Vdc) is added to an ac voltage with variable excitation frequency (Vac(ω)) and harmonic, superharmonic, and subharmonic resonances of different orders are observed. The second case consists on mixing the dc voltage (Vdc) with an ac voltage applied at a fixed frequency of twice the natural frequency of the resonator (V(2ω0)). High-amplitude parametric resonance is excited at the natural frequency of the system, ω0. This configuration allows a separation between the frequencies of the excitation and the mechanical motion. Finally, in the third case, the dc voltage (Vdc) is combined with both ac voltages, Vac(ω) and V(2ω0), and parametric resonance is excited and emerges from the fundamental harmonic resonance peak. The single-degree-of-freedom equation of motion is modeled and discussed for each case. The nonlinearity inherent to the electrostatic force is responsible for modulating the spring constant of the system at different frequencies, giving rise to parametric resonance. These equations of motion are simulated in the time and frequency domains, providing a consistent explanation of the experimentally observed phenomena. A wide variety of possible resonance modes with different characteristics can be used advantageously in MEMS device design.

  9. Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition

    SciTech Connect

    Ellis, F.B. Jr.; Gordon, R.G.; Paul, W.; Yacobi, B.G.

    1984-06-15

    Hydrogenated amorphous silicon (a-Si:H) films were prepared by chemical vapor deposition (CVD) from mixtures of silane, disilane, trisilane, and higher polysilanes in hydrogen carrier gas at 1 atm total pressure, at substrate temperatures from 420--530 /sup 0/C. Experimental parameters are explained and properties as a function of these parameters are shown. The measurements include hydrogen content (by IR), optical, electrical, and photovoltaic properties of the material. In most respects, the CVD material closely resembles the a-Si:H usually prepared by glow discharge. The following differences have been noted: (1) the CVD a-Si:H shows no IR absorption at 840--850 cm/sup -1/, which is consistent with the expected better thermal stability of the CVD material because of the much higher substrate temperatures in the CVD process than in the glow discharge process. (2) The band gap of CVD a-Si:H is lower by about 0.1 eV than glow discharge a-Si:H of the same hydrogen content. Thus, the band gap of CVD a-Si:H is better matched to the solar spectrum than is glow discharge a-Si:H. (3) All three IR absorption bands due to hydrogen are about 20% narrower in the CVD a-Si:H, suggesting a simpler structure. (4) The temperature dependence of the dark conductivity of CVD a-Si:H fits a curve for a single activation energy, in contrast to the more complicated temperature dependence often found in glow discharge a-Si:H, in which two different activation energies are seen at high and low temperatures. This suggests that the conduction mechanism is also simpler in the CVD a-Si:H.

  10. Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

    NASA Astrophysics Data System (ADS)

    Yılmaz, Huzeyfe; Yılmaz, Hasan; Sharif Murib, Mohammed; Serpengüzel, Ali

    2016-03-01

    This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4'-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 105 are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 105 are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4'-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4'-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.

  11. Amorphous-silicon module hot-spot testing

    NASA Technical Reports Server (NTRS)

    Gonzalez, C. C.

    1985-01-01

    Hot spot heating occurs when cell short-circuit current is lower than string operating current. Amorphous cell hot spot are tested to develop the techniques required for performing reverse bias testing of amorphous cells. Also, to quantify the response of amorphous cells to reverse biasing. Guidelines are developed from testing for reducing hot spot susceptibility of amorphous modules and to develop a qualification test for hot spot testing of amorphous modules. It is concluded that amorphous cells undergo hot spot heating similarly to crystalline cells. Comparison of results obtained with submodules versus actual modules indicate heating levels lower in actual modules. Module design must address hot spot testing and hot spot qualification test conducted on modules showed no instabilities and minor cell erosion.

  12. Formation of amorphous silicon by light ion damage

    SciTech Connect

    Shih, Y.C.

    1985-12-01

    Amorphization by implantation of boron ions (which is the lightest element generally used in I.C. fabrication processes) has been systematically studied for various temperatures, various voltages and various dose rates. Based on theoretical considerations and experimental results, a new amorphization model for light and intermediate mass ion damage is proposed consisting of two stages. The role of interstitial type point defects or clusters in amorphization is emphasized. Due to the higher mobility of interstitials out-diffusion to the surface particularly during amorphization with low energy can be significant. From a review of the idealized amorphous structure, diinterstitial-divacancy pairs are suggested to be the embryos of amorphous zones formed during room temperature implantation. The stacking fault loops found in specimens implanted with boron at room temperature are considered to be the origin of secondary defects formed during annealing.

  13. Reaction of amorphous Ni-W and Ni-N-W films with substrate silicon

    NASA Technical Reports Server (NTRS)

    Zhu, M. F.; Suni, I.; Nicolet, M.-A.; Sands, T.

    1984-01-01

    Wiley et al. (1982) have studied sputtered amorphous films of Nb-Ni, Mo-Ni, Si-W, and Si-Mo. Kung et al. (1984) have found that amorphous Ni-Mo films as diffusion barriers between multilayer metallizations on silicon demonstrate good electrical and thermal stability. In the present investigation, the Ni-W system was selected because it is similar to the Ni-Mo system. However, W has a higher silicide formation temperature than Mo. Attention is given to aspects of sample preparation, sample characterization, the interaction between amorphous Ni-W films and Si, the crystallization of amorphous Ni(36)W(64) films on SiO2, amorphous Ni-N-W films, silicide formation and phase separation, and the crystallization of amorphous Ni(36)W(64) and Ni(30)N(21)W(49) layers.

  14. Laser nucleated grain growth in hydrogenated amorphous silicon films

    NASA Astrophysics Data System (ADS)

    Dabney, Matthew S.

    annealed directly from the as grown state. The trends in EBSD grain size with in situ XRD crystallization time tc are consistent with theoretical predictions obtained from the classical model of nucleation and grain growth. An optical method was developed as a new and simple method to investigate crystallite nucleation and growth in stepwise, thermally annealed PECVD and HWCVD a-Si:H films. By confining film thicknesses to the range 500-4000A, optical microscopy in the reflection mode was used to readily detect crystallites in the thermally annealed a-Si:H lattice. Measurements of the crystallite density versus annealing time for identically prepared films of different thicknesses demonstrated crystallite nucleation rates smaller for thinner films, suggesting homogeneous nucleation, in agreement with previous results. The effect of film stress on crystallite nucleation was investigated in 0.11microm thick, thermally annealed hydrogenated amorphous silicon films. The nucleation rate was significantly suppressed around scratches, cleaved film edges, and laser ablated areas, extending laterally as much as 100-150um from these regions where the film connectivity was disrupted. u-Raman measurements of the transverse optical mode of Si demonstrated an accompanying reduction in tensile stress in the regions where nucleation was suppressed. The first measurements of nucleation rate in stress and in stress relieved areas in the same film are presented.

  15. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    SciTech Connect

    Wan, Yimao Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres

    2015-12-07

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiN{sub x}) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiN{sub x} stack, recombination current density J{sub 0} values of 9, 11, 47, and 87 fA/cm{sup 2} are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J{sub 0} on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm{sup 2} when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiN{sub x} stack is thermally stable at 400 °C in N{sub 2} for 60 min on all four c-Si surfaces. Capacitance–voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiN{sub x} stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  16. Status and future of government-supported amorphous silicon research in the United States

    SciTech Connect

    Wallace, W L; Sabisky, E S

    1986-06-01

    The Amorphous Silicon Research Project (ASRP) was established at the Solar Energy Research Institute in 1983 and is responsible for all US Department of Energy government supported research activities in the field of amorphous silicon photovoltaics. The objectives and research directions of the project have been established by a Five-Year Research Plan, which was developed at SERI in cooperation with the Department of Energy in 1984 and is divided into research on single-junction and multi-junction solar cells. DOE/SERI has recently initiated a new three year program to be performed in collaboration with US industry to perform work on high efficiency amorphous silicon solar cells and submodules. The objectives of this initiative are: (i) to achieve 18% efficiencies for small area multi-junction amorphous silicon cells, and (ii) to achieve amorphous silicon submodule efficiencies in the 10 to 13% range for single-junction and multi-junction submodule configurations over areas of at least 1000 cm/sup 2/.

  17. Pressure-induced transformations in amorphous silicon: A computational study

    SciTech Connect

    Garcez, K. M. S.; Antonelli, A.

    2014-02-14

    We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

  18. Transmission type flat-panel X-ray source using ZnO nanowire field emitters

    SciTech Connect

    Chen, Daokun; Song, Xiaomeng; Zhang, Zhipeng; Chen, Jun; Li, Ziping; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-12-14

    A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

  19. Transmission type flat-panel X-ray source using ZnO nanowire field emitters

    NASA Astrophysics Data System (ADS)

    Chen, Daokun; Song, Xiaomeng; Zhang, Zhipeng; Li, Ziping; She, Juncong; Deng, Shaozhi; Xu, Ningsheng; Chen, Jun

    2015-12-01

    A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18-20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

  20. An iterative algorithm for soft tissue reconstruction from truncated flat panel projections

    NASA Astrophysics Data System (ADS)

    Langan, D.; Claus, B.; Edic, P.; Vaillant, R.; De Man, B.; Basu, S.; Iatrou, M.

    2006-03-01

    The capabilities of flat panel interventional x-ray systems continue to expand, enabling a broader array of medical applications to be performed in a minimally invasive manner. Although CT is providing pre-operative 3D information, there is a need for 3D imaging of low contrast soft tissue during interventions in a number of areas including neurology, cardiac electro-physiology, and oncology. Unlike CT systems, interventional angiographic x-ray systems provide real-time large field of view 2D imaging, patient access, and flexible gantry positioning enabling interventional procedures. However, relative to CT, these C-arm flat panel systems have additional technical challenges in 3D soft tissue imaging including slower rotation speed, gantry vibration, reduced lateral patient field of view (FOV), and increased scatter. The reduced patient FOV often results in significant data truncation. Reconstruction of truncated (incomplete) data is known an "interior problem", and it is mathematically impossible to obtain an exact reconstruction. Nevertheless, it is an important problem in 3D imaging on a C-arm to address the need to generate a 3D reconstruction representative of the object being imaged with minimal artifacts. In this work we investigate the application of an iterative Maximum Likelihood Transmission (MLTR) algorithm to truncated data. We also consider truncated data with limited views for cardiac imaging where the views are gated by the electrocardiogram(ECG) to combat motion artifacts.

  1. Dose rate and beam profile measurement of proton beam using a flat panel detector

    NASA Astrophysics Data System (ADS)

    Park, Jeong-Min

    2015-10-01

    A 20-MeV or 100-MeV proton beam is provided to users for their proton beam irradiation experiments at KOrea Multi-Purpose Accelerator Complex. Radiochromic film (Gafchromic / HDV2) has been used to measure the dose rate and the profile of an incident proton beam during irradiation experiments. However, such measurements using radiochromic film have some inconveniences because an additional scanning process of is required to quantify the film's image. Therefore, we tried to measure the dose rate and beam profile by using a flat panel detector (FPD), which was developed for X-ray radiography as a substitute for radiochromic film because the FPD can measure the beam profile and the dose rate directly through a digitized image with a high spatial resolution. In this work, we investigated the feasibility of using a FPD as a substitute for radiochromic film. The preliminary results for the beam profile and the dose rate measured by using the flat panel detector are reported in the paper.

  2. Flat panel detectors--closing the (digital) gap in chest and skeletal radiology.

    PubMed

    Reiff, K J

    1999-08-01

    In the radiological department today the majority of all X-ray procedures on chest and skeletal radiography is performed with classical film-screen-systems. Using digital luminescence radiography (DLR or CR, which stands for Computed Radiography) as a technique has shown a way to replace this 100-year-old procedure of doing general radiography work by acquiring the X-rays digitally via phosphor screens, but this approach has faced criticism from lots of radiologists world wide and therefore has not been widely accepted except in the intensive care environment. A new technology is now rising based on the use of so called flat panel X-ray (FD) detectors. Semi-conducting material detects the X-rays in digital form directly and creates an instantaneous image for display, distribution and diagnosis. This ability combined with a large field of view and compared to existing methods--excellent detective quantum efficiency represents a revolutionary step for chest and skeletal radiography and will put basic X-ray-work back into the focus of radiological solutions. This paper will explain the basic technology of flat panel detectors, possible system solutions based on this new technology, aspects of the user interface influencing the system utilization and versatility as well as the possibility to redefine the patient examination process for chest and skeletal radiography. Furthermore the author discusses limitations for the first released systems, upgrades for the installed base and possible scenarios for the future, e.g. fluoroscopy or angiography application. PMID:10565511

  3. View-dependent geometric calibration for offset flat-panel cone beam computed tomography systems

    NASA Astrophysics Data System (ADS)

    Nguyen, Van-Giang

    2016-04-01

    Geometric parameters that define the geometry of imaging systems are crucial for image reconstruction and image quality in x-ray computed tomography (CT). The problem of determining geometric parameters for an offset flat-panel cone beam CT (CBCT) system, a recently introduced modality with a large field of view, with the assumption of an unstable mechanism and geometric parameters that vary in each view, is considered. To accurately and rapidly find the geometric parameters for each projection view, we use the projection matrix method and design a dedicated phantom that is partially visible in all projection views. The phantom consists of balls distributed symmetrically in a cylinder to ensure the inclusion of the phantom in all views, and a large portion of the phantom is covered in the projection image. To efficiently use calibrated geometric information in the reconstruction process and get rid of approximation errors, instead of decomposing the projection matrix into actual geometric parameters that are manually corrected before being used in reconstruction, as in conventional methods, we directly use the projection matrix and its pseudo-inverse in projection and backprojection operations of reconstruction algorithms. The experiments illustrate the efficacy of the proposed method with a real offset flat-panel CBCT system in dental imaging.

  4. Physical properties of a new flat panel detector with cesium-iodide technology

    NASA Astrophysics Data System (ADS)

    Hahn, Andreas; Penchev, Petar; Fiebich, Martin

    2016-03-01

    Flat panel detectors have become the standard technology in projection radiography. Further progress in detector technology will result in an improvement of MTF and DQE. The new detector (DX-D45C; Agfa; Mortsel/Belgium) is based on cesium-iodine crystals and has a change in the detector material and the readout electronics. The detector has a size of 30 cm x 24 cm and a pixel matrix of 2560 x 2048 with a pixel pitch of 124 μm. The system includes an automatic exposure detector, which enables the use of the detector without a connection to the x-ray generator. The physical properties of the detector were determined following IEC 62220-1-1 in a laboratory setting. The MTF showed an improvement compared to the previous version of cesium-iodine based flat-panel detectors. Thereby the DQE is also improved especially for the higher frequencies. The new detector showed an improvement in the physical properties compared to the previous versions. This enables a potential for further dose reductions in clinical imaging.

  5. Stable, high-efficiency amorphous silicon solar cells with low hydrogen content

    SciTech Connect

    Fortmann, C.M.; Hegedus, S.S. )

    1992-12-01

    Results and conclusions obtained during a research program of the investigation of amorphous silicon and amorphous silicon based alloy materials and solar cells fabricated by photo-chemical vapor and glow discharge depositions are reported. Investigation of the effects of the hydrogen content in a-si:H i-layers in amorphous silicon solar cells show that cells with lowered hydrogen content i-layers are more stable. A classical thermodynamic formulation of the Staebler-Wronski effect has been developed for standard solar cell operating temperatures and illuminations. Methods have been developed to extract a lumped equivalent circuit from the current voltage characteristic of a single junction solar cell in order to predict its behavior in a multijunction device.

  6. Stable, high-efficiency amorphous silicon solar cells with low hydrogen content

    NASA Astrophysics Data System (ADS)

    Fortmann, C. M.; Hegedus, S. S.

    1992-12-01

    Results and conclusions obtained during the investigation of amorphous silicon, amorphous silicon based alloy materials, and solar cells fabricated by photo-chemical vapor and glow discharge depositions are reported. Investigation of the effects of the hydrogen content in a-Si:H i-layers in amorphous silicon solar cells show that cells with lowered hydrogen content i-layers are more stable. A classical thermodynamic formulation of the Staebler-Wronski effect has been developed for standard solar cell operating temperatures and illuminations. Methods have been developed to extract a lumped equivalent circuit from the current voltage characteristic of a single junction solar cell in order to predict its behavior in a multijunction device.

  7. Performance and modeling of amorphous silicon photovoltaics for building-integrated applications

    SciTech Connect

    Kroposki, B.; Hansen, R.

    1999-07-01

    Amorphous silicon photovoltaic (PV) modules offer several advantages for building-integrated applications. The material can be deposited on glass or flexible substrates, which allows for products like roofing shingles and integrated PV/building glass. The material also has a uniform surface, which is ideal for many architectural applications. Amorphous silicon modules perform well in warm weather and have a small temperature coefficient for power. Depending on the building load, this may be beneficial when compared to crystalline systems. At the National Renewable Energy Laboratory, the authors are monitoring the performance of a triple-junction a-Si system. The system consists of 72 roofing shingles mounted directly to simulated roofing structures. This paper examines the performance of the building-integrated amorphous silicon PV system and applicability for covering residential loads. A simple model of system performance is also developed and is presented.

  8. Substrate and Passivation Techniques for Flexible Amorphous Silicon-Based X-ray Detectors.

    PubMed

    Marrs, Michael A; Raupp, Gregory B

    2016-01-01

    Flexible active matrix display technology has been adapted to create new flexible photo-sensing electronic devices, including flexible X-ray detectors. Monolithic integration of amorphous silicon (a-Si) PIN photodiodes on a flexible substrate poses significant challenges associated with the intrinsic film stress of amorphous silicon. This paper examines how altering device structuring and diode passivation layers can greatly improve the electrical performance and the mechanical reliability of the device, thereby eliminating one of the major weaknesses of a-Si PIN diodes in comparison to alternative photodetector technology, such as organic bulk heterojunction photodiodes and amorphous selenium. A dark current of 0.5 pA/mm² and photodiode quantum efficiency of 74% are possible with a pixelated diode structure with a silicon nitride/SU-8 bilayer passivation structure on a 20 µm-thick polyimide substrate. PMID:27472329

  9. Radial junction amorphous silicon solar cells on PECVD-grown silicon nanowires

    NASA Astrophysics Data System (ADS)

    Yu, Linwei; O'Donnell, Benedict; Foldyna, Martin; Cabarrocas, Pere Roca i.

    2012-05-01

    Constructing radial junction hydrogenated amorphous silicon (a-Si:H) solar cells on top of silicon nanowires (SiNWs) represents a promising approach towards high performance and cost-effective thin film photovoltaics. We here develop an all-in situ strategy to grow SiNWs, via a vapour-liquid-solid (VLS) mechanism on top of ZnO-coated glass substrate, in a plasma-enhanced chemical vapour deposition (PECVD) reactor. Controlling the distribution of indium catalyst drops allows us to tailor the as-grown SiNW arrays into suitable size and density, which in turn results in both a sufficient light trapping effect and a suitable arrangement allowing for conformal coverage of SiNWs by subsequent a-Si:H layers. We then demonstrate the fabrication of radial junction solar cells and carry on a parametric study designed to shed light on the absorption and quantum efficiency response, as functions of the intrinsic a-Si:H layer thickness and the density of SiNWs. These results lay a solid foundation for future structural optimization and performance ramp-up of the radial junction thin film a-Si:H photovoltaics.

  10. 25 kW solar photovoltaic flat panel power supply for an electrodialysis water desalination unit in New Mexico. Final report, 1 October 1978-31 May 1979

    SciTech Connect

    Wood, J.R.; Crutcher, J.L.

    1980-06-01

    The stand-alone system designed by Mobil Tyco Solar Energy Corporation consists of a 25 kW flat panel array employing silicon ribbon solar cells, used in conjunction with a lead-acid battery bank to provide the complete power requirements of an electrodialysis water desalination unit. The Mobil Tyco system design is intended to be prototypical of part of the drinking water supply for a remote village. The specific task which this system will perform during Phase III is to aid in the restoration of an aquifer following a uranium leaching operation by the Energy Minerals Division of Mobil Oil Corporation at a site which is approximately four miles from the township of Crownpoint in northwestern New Mexico. System design is described, and a detailed description of a mathematical model and computerized simulation of the system is included. (WHK)

  11. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix.

    PubMed

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching. PMID:24521208

  12. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    PubMed Central

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching. PMID:24521208

  13. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    NASA Astrophysics Data System (ADS)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-02-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching.

  14. Origin of the photo-induced changes in hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Adler, D.

    1983-07-01

    The electronic properties of hydrogenated amorphous silicon films are discussed in detail. Particular attention is paid to the changes induced by photogeneration of excess free carriers. Previous models which have been proposed to account for such effects are classified and criticized. An alternative explanation, which is based on the unique electronic structure of hydrogenated amorphous silicon, is proposed and analyzed. In this model, no new defects are created by the light, but rather the photo-induced effects follow from a metastable trapping of the excess free carriers at charged spinless defects which are present at equilibrium.

  15. On electronic structure of polymer-derived amorphous silicon carbide ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Kewei; Li, Xuqin; Ma, Baisheng; Wang, Yiguang; Zhang, Ligong; An, Linan

    2014-06-01

    The electronic structure of polymer-derived amorphous silicon carbide ceramics was studied by combining measurements of temperature-dependent conductivity and optical absorption. By comparing the experimental results to theoretical models, electronic structure was constructed for a carbon-rich amorphous silicon carbide, which revealed several unique features, such as deep defect energy level, wide band-tail band, and overlap between the band-tail band and defect level. These unique features were discussed in terms of the microstructure of the material and used to explain the electric behavior.

  16. Experimental determination of the distribution of tail states of hydrogenated amorphous silicon: A transient photocurrent analysis

    SciTech Connect

    Webb, D.P.; Chan, F.Y.M.; Zou, X.C.; Chan, Y.C.; Lam, Y.W.; Lin, S.H.; O'Leary, S.K.; Lim, P.K.

    1997-07-01

    Recent experimental developments have cast doubt on the validity of the common assumption that the distribution of tail states of hydrogenated amorphous silicon exhibits a single exponential functional form. The authors employ transient photocurrent decay measurements to determine this distribution of tail states. In their approach, however, they determine the distribution of tail states directly from the experimental data, without assuming, a priori, a specific functional form. It is found that these experimental results are consistent with other more recent experimental determinations of the distribution of tail states, suggesting the possibility of deviations from a single exponential distribution of tail states in hydrogenated amorphous silicon.

  17. Hydrogenated amorphous silicon radiation detectors: Material parameters, radiation hardness, charge collection

    SciTech Connect

    Qureshi, S.

    1991-01-01

    For nearly two decades now hydrogenated amorphous silicon has generated considerable interest for its potential use in various device applications namely, solar cells, electrolithography, large-area electronics etc. The development of efficient and economic solar cells has been on the forefront of this research. This interest in hydrogenated amorphous silicon has been motivated by the fact that amorphous silicon can be deposited over a large area at relatively low cost compared to crystalline silicon. Hydrogenated amorphous silicon, frequently abbreviated as a-Si:H, used in solar-cell applications is a micron or less thick. The basic device structure is a p-i-n diode where the i layer is the active layer for radiation to interact. This is so because intrinsic a-Si:H has superior electrical properties in comparison to doped a-Si:H which serves the purpose of forming a potential barrier on either end of the i layer. The research presented in this dissertation was undertaken to study the properties of a-Si:H for radiation detection applications in physics and medicine.

  18. Amorphization and nanocrystallization of silicon under laser shock compression: bridging experiment with atomic simulation

    NASA Astrophysics Data System (ADS)

    Zhao, Shiteng; Kad, Bimal; Hahn, Eric; Remington, Bruce; Wehrenberg, Christopher; Bringa, Eduardo; Huntington, Channing; Park, Hye-Sook; More, Karren; Meyers, Marc

    Terawatt, nanosecond-duration, laser-driven, shock compression and recovery experiments on [001] silicon unveiled remarkable structural changes above a pressure threshold. Two distinct amorphous regions were identified: (a) a bulk amorphous layer close to the surface and (b) amorphous bands initially aligned with {111}slip planes. Further increase of the laser energy leads to the re-crystallization of amorphous silicon into nanocrystals with high concentration of nano-twins. Shock-induced defects play a very important role in the onset of amorphization. Calculations of the free energy changes with pressure and shear, using the Patel-Cohen methodology, are in agreement with the experimental results. Molecular dynamics simulation corroborates the amorphization, showing that it is initiated by the nucleation and propagation of partial dislocations. The nucleation of amorphization is analyzed by classical nucleation theory. This research is funded by a UC Research Laboratories Grant (09-LR-06-118456-MEYM) and a National Laser Users Facility (NLUF) Grant (PE-FG52-09NA-29043).

  19. Graphene as a transparent electrode for amorphous silicon-based solar cells

    SciTech Connect

    Vaianella, F. Rosolen, G.; Maes, B.

    2015-06-28

    The properties of graphene in terms of transparency and conductivity make it an ideal candidate to replace indium tin oxide (ITO) in a transparent conducting electrode. However, graphene is not always as good as ITO for some applications, due to a non-negligible absorption. For amorphous silicon photovoltaics, we have identified a useful case with a graphene-silica front electrode that improves upon ITO. For both electrode technologies, we simulate the weighted absorption in the active layer of planar amorphous silicon-based solar cells with a silver back-reflector. The graphene device shows a significantly increased absorbance compared to ITO-based cells for a large range of silicon thicknesses (34.4% versus 30.9% for a 300 nm thick silicon layer), and this result persists over a wide range of incidence angles.

  20. Method of forming a spacer for field emission flat panel displays

    DOEpatents

    Bernhardt, A.F.; Contolini, R.J.

    1997-08-19

    Spacers are disclosed for applications such as field emission flat panel displays and vacuum microelectronics, and which involves the application of aerogel/xerogel technology to the formation of the spacer. In a preferred approach the method uses a mold and mold release agent wherein the gel precursor is a liquid which can be applied to the mold filling holes which expose the substrate (either the baseplate or the faceplate). A release agent is applied to the mold prior to precursor application to ease removal of the mold after formation of the dielectric spacer. The shrinkage of the gel during solvent extraction also improves mold removal. The final spacer material is a good dielectric, such as silica, secured to the substrate. 3 figs.

  1. Test and Analysis of Foam Impacting a 6x6 Inch RCC Flat Panel

    NASA Technical Reports Server (NTRS)

    Lessard, Wendy B.

    2006-01-01

    This report presents the testing and analyses of a foam projectile impacting onto thirteen 6x6 inch flat panels at a 90 degrees incidence angle. The panels tested in this investigation were fabricated of Reinforced-Carbon-Carbon material and were used to aid in the validation of an existing material model, MAT58. The computational analyses were performed using LS-DYNA, which is a physics-based, nonlinear, transient, finite element code used for analyzing material responses subjected to high impact forces and other dynamic conditions. The test results were used to validate LS-DYNA predictions and to determine the threshold of damage generated by the MAT58 cumulative damage material model. The threshold of damage parameter represents any external or internal visible RCC damage detectable by nondestructive evaluation techniques.

  2. Evaluation and correction of readout artifacts from flat panel detectors for non-destructive testing purposes

    NASA Astrophysics Data System (ADS)

    Burtzlaff, S.; Voland, V.; Salamon, M.; Hofmann, Th.; Uhlmann, N.

    2009-08-01

    Flat panel detectors are commonly used for non-destructive testing purposes using X-ray technology. During a series of measurements with high absorbing objects, we observed an unknown kind of artifacts especially apparent with high contrast edges. These artifacts lead to unwanted results in radioscopic and computed tomography inspection. Given the object is fully occupying the lower part and half of the upper part of the detector. Looking at the image with high contrast visualization, it can be seen that the covered upper part of the detector is brighter than the covered lower half. The horizontal border of the detector tile is clearly recognizable. Furthermore, the uncovered area directly above the object is darker than next to the edge. In this area the vertical border of the edge below can be localized. We examined and evaluated the effect and developed a correction algorithm. The effect and its correction results are presented.

  3. Investigation of Vertical Drag and Periodic Airloads Acting on Flat Panels in a Rotor Slipstream

    NASA Technical Reports Server (NTRS)

    Makofski, Robert A; Menkick, George F

    1956-01-01

    Tests have been conducted on the Langley helicopter test tower to determine the vertical drag and pressure distributions on flat panels mounted below a helicopter rotor. Calculations of the vertical drag by use of a strip-analysis procedure outlined in the paper and the assumption of a fully contracted wake agreed well with the experimental results over the range from 0.2 to 0.64 rotor radius beneath the plane of zero flapping. The pressure increase caused by the passage of the blade over the panel is a maximum at about the 0.8 radius spanwise station. At this station, the pressure decreases from 10 times the disk loading per blade at 0.05 radius beneath the rotor plane of zero flapping to one-half of the disk loading per blade at 0.64 radius beneath the plane of zero flapping.

  4. Response of laminated composite flat panels to sonic boom and explosive blast loadings

    NASA Technical Reports Server (NTRS)

    Librescu, L.; Nosier, A.

    1990-01-01

    This paper deals with a theoretical analysis of the dynamic response of shear deformable symmetrically laminated rectangular composite flat panels exposed to sonic boom and explosive blast loadings. The pertinent governing equations incorporating transverse shear deformation, transverse normal stress, as well as the higher-order effects are solved by using the integral-transform technique. The obtained results are compared with their counterparts obtained within the framework of the first-order transverse shear deformation and the classical plate theories and some conclusions concerning their range of applicability are outlined. The paper also contains a detailed analysis of the influence played by the various parameters characterizing the considered pressure pulses as well as the material and geometry of the plate.

  5. An improved method for flat-field correction of flat panel x-ray detector.

    PubMed

    Kwan, Alexander L C; Seibert, J Anthony; Boone, John M

    2006-02-01

    In this Technical Note, the effects of different flat-field techniques are examined for a cesium iodide flat panel detector, which exhibited a slightly nonlinear exposure response. The results indicate that the variable flat-field correction method with the appropriate polynomial fit provides excellent correction throughout the entire exposure range. The averaged normalized variation factor, used to assess the nonuniformity of the flat-field correction, decreased from 30.76 for the fixed correction method to 4.13 for the variable flat-field correction method with a fourth-order polynomial fit for the 60 kVp spectrum, and from 16.42 to 3.97 for the 95 kVp spectrum. PMID:16532945

  6. An improved method for flat-field correction of flat panel x-ray detector

    SciTech Connect

    Kwan, Alexander L.C.; Seibert, J. Anthony; Boone, John M.

    2006-02-15

    In this Technical Note, the effects of different flat-field techniques are examined for a cesium iodide flat panel detector, which exhibited a slightly nonlinear exposure response. The results indicate that the variable flat-field correction method with the appropriate polynomial fit provides excellent correction throughout the entire exposure range. The averaged normalized variation factor, used to assess the nonuniformity of the flat-field correction, decreased from 30.76 for the fixed correction method to 4.13 for the variable flat-field correction method with a fourth-order polynomial fit for the 60 kVp spectrum, and from 16.42 to 3.97 for the 95 kVp spectrum.

  7. Performance requirements for electronic displays of color moving images using flat panel technology

    NASA Astrophysics Data System (ADS)

    Glenn, William E.

    1994-04-01

    The initial market for flat panel displays has been dominated by the laptop computer. This is a very attractive entry market for the newer technologies. The technical requirements for computer displays are much easier to satisfy then for high definition entertainment displays. While the resolutions are similar, the other requirements of contrast ratio, cost, light output, response time, uniformity, gray scale, size and color purity are all much less demanding than those for the display of real-time moving images for entertainment. However, if the panels being developed for computers could meet the requirements of entertainment television, they could be used as light valves in large screen projectors. In this way the investment in development and in manufacturing facilities can be amortized over a much larger market. This paper will review a comparison of the requirements for both applications.

  8. Arthroscopic knee surgery using the advanced flat panel high-resolution color head-mounted display

    NASA Astrophysics Data System (ADS)

    Nelson, Scott A.; Jones, D. E. Casey; St. Pierre, Patrick; Sampson, James B.

    1997-06-01

    The first ever deployed arthroscopic knee surgeries have been performed using a high resolution color head-mounted display (HMD) developed under the DARPA Advanced Flat Panel HMD program. THese procedures and several fixed hospital procedures have allowed both the system designers and surgeons to gain new insight into the use of a HMD for medical procedures in both community and combat support hospitals scenarios. The surgeons demonstrated and reported improved head-body orientation and awareness while using the HMD and reported several advantages and disadvantages of the HMD as compared to traditional CRT monitor viewing of the arthroscopic video images. The surgeries, the surgeon's comments, and a human factors overview of HMDs for Army surgical applications are discussed here.

  9. Method of forming a spacer for field emission flat panel displays

    DOEpatents

    Bernhardt, Anthony F.; Contolini, Robert J.

    1997-01-01

    Spacers for applications such as field emission flat panel displays and vacuum microelectronics, and which involves the application of aerogel/xerogel technology to the formation of the spacer. In a preferred approach the method uses a mold and mold release agent wherein the gel precursor is a liquid which can be applied to the mold filling holes which expose the substrate (either the baseplate or the faceplate). A release agent is applied to the mold prior to precursor application to ease removal of the mold after formation of the dielectric spacer. The shrinkage of the gel during solvent extraction also improves mold removal. The final spacer material is a good dielectric, such as silica, secured to the substrate.

  10. A typical flat-panel membrane bioreactor with a composite membrane for sulfur removal

    NASA Astrophysics Data System (ADS)

    Guan, Jian; Xiao, Yuan; Song, Jimin; Miao, Junhe

    2014-03-01

    The aim of this work was to provide a concrete study to understand the effects of operation on biofilm morphology and microstructure and degradation efficiency for the disposal of sulfur dioxide produced by coal-fired power plants. For this purpose, a flat-panel reactor-membrane bioreactor (MBR) with a composite membrane consisting of a dense layer and a support layer was designed; the membrane bioreactors inoculated with Thiobacillus ferrooxidans were further conducted for the removal of sulfur dioxide. Dry weight, active biomass, pressure drop, removal efficiency, morphology and structure of the formed biofilms were investigated and analyzed over period of biofilm formation. The results found that the dry weight, biomass, pressure drops and removal efficiency increased rapidly during biofilm formation, remained relatively stable in the stabilization period of biofilm growth, and finally reached 0.085 g, 7.00 μg, 180 Pa, and 78%, respectively. Our results suggested the MBR is available for flue-gas desulfurization.

  11. Lowering the ignition voltage by the dual microhollow cathode configuration for multichannel flat panel lamp

    SciTech Connect

    Lee, Tae Il; Park, Ki Wan; Lee, Sung Won; Baik, Hong Koo

    2006-03-20

    We have developed a dual microhollow cathode configuration, employing one power supply circuit with a resistor that is suitable for lamp starting without additional power supplier. We also investigated their electrical characteristics and photo images, varying the applied voltage. The electrical and optical measurements showed that the discharge passed through four distinct stages: no discharges, the first microhollow cathode discharges, the both of the first and second microhollow cathode discharges, and finally the main discharge. As a result, the V{sub s} and E{sub s}/p of a dual microhollow configuration were lower by a factor of about 2 than those of a diode at 40 Torr. We have also observed that the parallel operation can be possible with a single resistor in nine channels flat panel lamp.

  12. Crystal-amorphous-silicon interface kinetics under ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Campisano, S. U.; Ferla, G.

    1990-01-01

    Our recent work on ion-beam-assisted epitaxial growth of amorphous Si layers on single crystal substrates is reviewed. The crystallization was induced by a 600 keV Kr2+ beam at a dose rate of 1×1012/cm2 · s. During irradiations the samples were mounted on a resistively heated copper block whose temperature was maintained constant in the range 250-450°C. The planar motion of the crystal-amorphous interface was monitored in situ by dynamic reflectivity measurements. This technique allows the ion-induced growth rate to be measured with a very high precision. We have observed that this growth rate scales linearly with the energy deposited into elastic collisions at the crystal-amorphous interface by the impinging ions. Moreover, the rate shows an Arrhenius temperature dependence with a well defined activation energy of 0.32±0.05 eV. The dependence of this process on substrate orientation and on impurities either dissolved in the amorphous layer or present at very high concentration at the crystal-amorphous interface is also discussed.

  13. Crystal-amorphous-silicon interface kinetics under ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Campisano, S. U.; Ferla, G.

    1989-11-01

    Our recent work on ion-beam-assisted epitaxial growth of amorphous Si layers on single crystal substrates is reviewed. The crystallization was induced by a 600 keV Kr 2+ beam at a dose rate of 1×10 12/cm 2 · s. During irradiations the samples were mounted on a resistively heated copper block whose temperature was maintained constant in the range 250-450°C. The planar motion of the crystal-amorphous interface was monitored in situ by dynamic reflectivity measurements. This technique allows the ion-induced growth rate to be measured with a very high precision. We have observed that this growth rate scales linearly with the energy deposited into elastic collisions at the crystal-amorphous interface by the impinging ions. Moreover, the rate shows an Arrhenius temperature dependence with a well defined activation energy of 0.32±0.05 eV. The dependence of this process on substrate orientation and on impurities either dissolved in the amorphous layer or present at very high concentration at the crystal-amorphous interface is also discussed.

  14. Crystalline-amorphous silicon nano-composites: Nano-pores and nano-inclusions impact on the thermal conductivity

    NASA Astrophysics Data System (ADS)

    Verdier, M.; Termentzidis, K.; Lacroix, D.

    2016-05-01

    The thermal conductivities of nanoporous and nanocomposite silicon with incorporated amorphous phases have been computed by molecular dynamics simulations. A systematic investigation of the porosity and the width of the amorphous shell contouring a spherical pore has been made. The impact of amorphous phase nanoinclusions in a crystalline matrix has also been studied with the same amorphous fraction as the porosity of nanoporous silicon to achieve comparison. The key parameter for all configurations with or without the amorphous phase is proved to be the interface (between the crystalline and amorphous phases or crystalline and void) to volume ratio. We obtain the sub-amorphous thermal conductivity for several configurations by combining pores, amorphous shell, and crystalline phase. These configurations are promising candidates for low cost and not toxic thermoelectric devices based on abundant semiconductors.

  15. Development of next generation digital flat panel catheterization system: design principles and validation methodology

    NASA Astrophysics Data System (ADS)

    Belanger, B.; Betraoui, F.; Dhawale, P.; Gopinath, P.; Tegzes, Pal; Vagvolgyi, B.

    2006-03-01

    The design principles that drove the development of a new cardiovascular x-ray digital flat panel (DFP) detector system are presented, followed by assessments of imaging and dose performance achieved relative to other state of the art FPD systems. The new system (GE Innova 2100 IQ TM) incorporates a new detector with substantially improved DQE at fluoroscopic (73%@1μR) and record (79%@114uR) doses, an x-ray tube with higher continuous fluoro power (3.2kW), a collimator with a wide range of copper spectral filtration (up to 0.9mm), and an improved automatic x-ray exposure management system. The performance of this new system was compared to that of the previous generation GE product (Innova 2000) and to state-of-the art cardiac digital x-ray flat panel systems from two other major manufacturers. Performance was assessed with the industry standard Cardiac X-ray NEMA/SCA and I phantom, and a new moving coronary artery stent (MCAS) phantom, designed to simulate cardiac clinical imaging conditions, composed of an anthropomorphic chest section with stents moving in a manner simulating normal coronary arteries. The NEMA/SCA&I phantom results showed the Innova 2100 IQ to exceed or equal the Innova 2000 in all of the performance categories, while operating at 28% lower dose on average, and to exceed the other DFP systems in most of the performance categories. The MCAS phantom tests showed the Innova 2100 IQ to be significantly better (p << 0.05) than the Innova 2000, and significantly better than the other DFP systems in most cases at comparable or lower doses, thereby verifying excellent performance against design goals.

  16. Cone-beam computed tomography with a flat-panel imager: initial performance characterization.

    PubMed

    Jaffray, D A; Siewerdsen, J H

    2000-06-01

    The development and performance of a system for x-ray cone-beam computed tomography (CBCT) using an indirect-detection flat-panel imager (FPI) is presented. Developed as a bench-top prototype for initial investigation of FPI-based CBCT for bone and soft-tissue localization in radiotherapy, the system provides fully three-dimensional volumetric image data from projections acquired during a single rotation. The system employs a 512 x 512 active matrix of a-Si:H thin-film transistors and photodiodes in combination with a luminescent phosphor. Tomographic imaging performance is quantified in terms of response uniformity, response linearity, voxel noise, noise-power spectrum (NPS), and modulation transfer function (MTF), each in comparison to the performance measured on a conventional CT scanner. For the geometry employed and the objects considered, response is uniform to within 2% and linear within 1%. Voxel noise, at a level of approximately 20 HU, is comparable to the conventional CT scanner. NPS and MTF results highlight the frequency-dependent transfer characteristics, confirming that the CBCT system can provide high spatial resolution and does not suffer greatly from additive noise levels. For larger objects and/or low exposures, additive noise levels must be reduced to maintain high performance. Imaging studies of a low-contrast phantom and a small animal (a euthanized rat) qualitatively demonstrate excellent soft-tissue visibility and high spatial resolution. Image quality appears comparable or superior to that of the conventional scanner. These quantitative and qualitative results clearly demonstrate the potential of CBCT systems based upon flat-panel imagers. Advances in FPI technology (e.g., improved x-ray converters and enhanced electronics) are anticipated to allow high-performance FPI-based CBCT for medical imaging. General and specific requirements of kilovoltage CBCT systems are discussed, and the applicability of FPI-based CBCT systems to tomographic

  17. Hysterosalpingography using a flat panel unit: Evaluation and optimization of ovarian radiation dose

    SciTech Connect

    Messaris, Gerasimos A. T.; Abatzis, Ilias; Kagadis, George C.; Samartzis, Alexandros P.; Athanasopoulou, Panagiota; Christeas, Nikolaos; Katsanos, Konstantinos; Karnabatidis, Dimitrios; Nikiforidis, George C.

    2012-07-15

    Purpose: The aim of the present study was the evaluation and optimization of radiation dose to the ovaries (D) in hysterosalpingography (HSG). Methods: The study included a phantom study and a clinical one. In the phantom study, we evaluated imaging results for different geometrical setups and irradiation conditions. In the clinical study, 34 women were assigned into three different fluoroscopy modes and D was estimated with direct cervical TLD measurements. Results: In the phantom study, we used a source-to-image-distance (SID) of 110 cm and a field diagonal of 48 cm, and thus decreased air KERMA rate (KR) by 19% and 70%, respectively, for beam filtration: 4 mm Al and 0.9 mm Cu (Low dose). The least radiation exposure was accomplished by using the 3.75 pps fluoroscopy mode in conjunction with beam filtration: Low dose. In the clinical study, D normalized to 50 s of fluoroscopy time with a 3.75 pps fluoroscopy mode reached a value of 0.45 {+-} 0.04 mGy. Observers' evaluation of diagnostic image quality did not significantly differ for the three different modes of acquisition that were compared. Conclusions: Digital spot radiographs could be omitted in modern flat panel systems during HSG. Fluoroscopy image acquisitions in a modern flat panel unit at 3.75 pps and a beam filtration of 4 mm Al and 0.9 mm Cu demonstrate acceptable image quality with an average D equal to 0.45 mGy. This value is lower compared to the studied literature. For these reasons, the proposed method may be recommended for routine HSG examination in order to limit radiation exposure to the ovaries.

  18. Image quality in two phosphor-based flat panel digital radiographic detectors.

    PubMed

    Samei, Ehsan

    2003-07-01

    Two general types of phosphor screens are currently used in indirect digital radiographic systems: structured phosphor screens and turbid phosphor screens. The purpose of the study was to experimentally compare the image quality characteristics of two flat-panel digital radiography detectors with similar electronics and pixel sizes (0.127 mm), but otherwise equipped with the two types of screens (0.6-mm-thick structured CsI and Lanex Regular). The presampled modulation transfer functions (MTFs) of the detectors were assessed using an edge method. The noise power spectra (NPS) were measured by two-dimensional Fourier analysis of uniformly-exposed radiographs at 50-100 kVp with 19 mm added Al filtration. The detective quantum efficiencies (DQEs) were assessed from the MTF, the NPS, and estimates of the ideal signal-to-noise ratio. The MTF measures of the two detectors were generally similar above a spatial frequency of 2 mm(-1), with approximately 2.5 and approximately 3.8 mm(-1) spatial frequencies corresponding to 0.2 MTF and 0.1 MTF, respectively. Below 2 mm(-1), the MTF for the CsI-based detector was slightly higher by an average of 0.07. At 70 kVp, the measured DQE values in the diagonal (and axial) direction(s) at spatial frequencies of 0.15 mm(-1) and 2.5 mm(-1) were 78% (78%) and 26% (20%) for the CsI-based detector, and 20% (20%) and 7% (6%) for the Lanex-based detector, respectively. The comparative findings experimentally confirm that in indirect flat-panel detectors, structured phosphor screens provide a more favorable tradeoff between resolution and noise compared to turbid-phosphor screens, effectively increasing the detection efficiency of the detector without a negative impact on the detector's spatial resolution response. PMID:12906192

  19. Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

    SciTech Connect

    Wen, Xixing; Zeng, Xiangbin Zheng, Wenjun; Liao, Wugang; Feng, Feng

    2015-01-14

    The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiC{sub x}) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiC{sub x}/SiO{sub 2}/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiC{sub x}, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiC{sub x} can promote the application of Si QDs in low-power consumption semiconductor memory devices.

  20. Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

    NASA Astrophysics Data System (ADS)

    Wen, Xixing; Zeng, Xiangbin; Zheng, Wenjun; Liao, Wugang; Feng, Feng

    2015-01-01

    The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiCx) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiCx/SiO2/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiCx, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiCx can promote the application of Si QDs in low-power consumption semiconductor memory devices.

  1. Metal induced crystallization of amorphous silicon for photovoltaic solar cells

    NASA Astrophysics Data System (ADS)

    Van Gestel, D.; Gordon, I.; Poortmans, J.

    A silicon thin-film technology could lead to less expensive modules by the use of less silicon material and by the implementation of monolithic module processes. A technology based on polycrystalline-silicon thin-films with a grain size between 1 μm and 1 mm (pc-Si), seems particularly promising since it combines the low-cost potential of a thin-film technology with the high efficiency potential of crystalline silicon. One of the possible approaches to fabricate pc-Si absorber layers is metal induced crystallization (MIC). For solar cell applications mainly aluminium is investigated as metal because 1) it forms a eutectic system with silicon instead of a silicide-metal system like e.g. Ni 2) only shallow level defects are formed in the forbidden bandgap of silicon and 3) a layer exchange process can be obtained in combination with a-Si. Aluminum induced crystallization (AIC) of a-Si on non-silicon substrates can results in grains with a preferential (100) orientation and a maximum grain sizes above 50 micrometer. These layers can act as seed layers for further epitaxial growth. Based on this two-step approach (AIC + epitaxial growth) we made solar cells with an energy conversion efficiency of 8%. Based on TEM, EBIC, SEM, defect etch and EBSD measurements we showed that the efficiency is nowadays mainly limited by the presence of electrical intragrain defects.

  2. Hybrid method of making an amorphous silicon P-I-N semiconductor device

    DOEpatents

    Moustakas, Theodore D.; Morel, Don L.; Abeles, Benjamin

    1983-10-04

    The invention is directed to a hydrogenated amorphous silicon PIN semiconductor device of hybrid glow discharge/reactive sputtering fabrication. The hybrid fabrication method is of advantage in providing an ability to control the optical band gap of the P and N layers, resulting in increased photogeneration of charge carriers and device output.

  3. Amorphous silicon research. Annual subcontract report, October 1, 1994--September 30, 1995

    SciTech Connect

    Arya, R R; Bennett, M; Bradley, D

    1996-02-01

    The major effort in this program is to develop cost-effective processes which satisfy efficiency, yield, and material usage criteria for mass production of amorphous silicon-based multijunction modules. New and improved processes were developed for the component cells and a more robust rear contact was developed for better long term stability.

  4. Method of forming semiconducting amorphous silicon films from the thermal decomposition of fluorohydridodisilanes

    DOEpatents

    Sharp, Kenneth G.; D'Errico, John J.

    1988-01-01

    The invention relates to a method of forming amorphous, photoconductive, and semiconductive silicon films on a substrate by the vapor phase thermal decomposition of a fluorohydridodisilane or a mixture of fluorohydridodisilanes. The invention is useful for the protection of surfaces including electronic devices.

  5. Elastic constants of defected and amorphous silicon with the environment-dependent interatomic potential

    SciTech Connect

    Allred, Clark L.; Yuan Xianglong; Hobbs, Linn W.; Bazant, Martin Z.

    2004-10-01

    The elastic constants of a wide range of models of defected crystalline and amorphous silicon are calculated, using the environment-dependent interatomic potential (EDIP). The defected crystalline simulation cells contain randomly generated defect distributions. An extensive characterization of point defects is performed, including structure, energy and influence on elastic constants. Three important conclusions are drawn. (1) Defects have independent effects on the elastic constants of silicon up to (at least) a defect concentration of 0.3%. (2) The linear effect of Frenkel pairs on the <110> Young's modulus of silicon is -1653 GPa per defect fraction. (3) 17 different point defect types cause a very similar decrease in the <110> Young's modulus: -(0.28{+-}0.05)% when calculated in isolation using a 1728-atom cell. These principles will be very useful for predicting the effect of radiation damage on the elastic modulus of silicon in the typical case in which point-defect concentrations can be estimated, but the exact distribution and species of defects is unknown. We also study amorphous samples generated in quenching the liquid with EDIP, including an ideal structure of perfect fourfold coordination, samples with threefold and fivefold coordinated defects, one with a nanovoid, and one with an amorphous inclusion in a crystalline matrix. In the last case, a useful finding is that the change in the Young's modulus is simply related to the volume fraction of amorphous material, as has also been observed by experiment.

  6. Size effects on the thermal conductivity of amorphous silicon thin films

    DOE PAGESBeta

    Thomas Edwin Beechem; Braun, Jeffrey L.; Baker, Christopher H.; Elahi, Miraz; Artyushkova, Kateryna; Norris, Pamela M.; Leseman, Zayd Chad; Gaskins, John T.; Hopkins, Patrick E.; Giri, Ashutosh

    2016-04-01

    In this study, we investigate thickness-limited size effects on the thermal conductivity of amorphous silicon thin films ranging from 3 to 1636 nm grown via sputter deposition. While exhibiting a constant value up to ~100 nm, the thermal conductivity increases with film thickness thereafter. The thickness dependence we demonstrate is ascribed to boundary scattering of long wavelength vibrations and an interplay between the energy transfer associated with propagating modes (propagons) and nonpropagating modes (diffusons). A crossover from propagon to diffuson modes is deduced to occur at a frequency of ~1.8 THz via simple analytical arguments. These results provide empirical evidencemore » of size effects on the thermal conductivity of amorphous silicon and systematic experimental insight into the nature of vibrational thermal transport in amorphous solids.« less

  7. Recrystallization of amorphous silicon deposited on ultra thin microcrystalline silicon layers

    SciTech Connect

    Wang, F.; Wolfe, D.; Lucovsky, G.

    1997-07-01

    This study reports on a method to reduce the thermal crystallization time and temperature of amorphous silicon films by initially depositing an ultra thin {micro}c-Si:H seed layer. After rapid thermal annealing (RTA), films were characterized by means of Raman spectroscopy, x-ray diffraction, reflection high energy electron diffraction, atomic force microscopy, and dark and photocurrent. The results show that the microcrystalline particles in the seed layer act as nucleation centers, promoting crystallization of a-Si:H at lower temperatures and at shorter times, compared to a-Si:H films deposited without any seed layer. Additionally, it was found that the seed layer affects the orientation of the crystallized films. The dark current increases abruptly over 4 orders of magnitude in the first 15 second anneal, then decreases as the time increases, and tends to saturate. The photocurrent has an opposite behavior. These transport results can be understood in terms of a change in defect density and band gap shrinkage.

  8. Amorphous Silicon Carbide Passivating Layers to Enable Higher Processing Temperature in Crystalline Silicon Heterojunction Solar Cells

    SciTech Connect

    Boccard, Mathieu; Holman, Zachary

    2015-04-06

    "Very efficient crystalline silicon (c-Si) solar cells have been demonstrated when thin layers of intrinsic and doped hydrogenated amorphous silicon (a-Si:H) are used for passivation and carrier selectivity in a heterojunction device. One limitation of this device structure is the (parasitic) absorption in the front passivation/collection a-Si:H layers; another is the degradation of the a-Si:H-based passivation upon temperature, limiting the post-processes to approximately 200°C thus restricting the contacting possibilities and potential tandem device fabrication. To alleviate these two limitations, we explore the potential of amorphous silicon carbide (a-SiC:H), a widely studied material in use in standard a-Si:H thin-film solar cells, which is known for its wider bandgap, increased hydrogen content and stronger hydrogen bonding compared to a-Si:H. We study the surface passivation of solar-grade textured n-type c-Si wafers for symmetrical stacks of 10-nm-thick intrinsic a-SiC:H with various carbon content followed by either p-doped or n-doped a-Si:H (referred to as i/p or i/n stacks). For both doping types, passivation (assessed through carrier lifetime measurements) is degraded by increasing the carbon content in the intrinsic a-SiC:H layer. Yet, this hierarchy is reversed after annealing at 350°C or more due to drastic passivation improvements upon annealing when an a-SiC:H layer is used. After annealing at 350°C, lifetimes of 0.4 ms and 2.0 ms are reported for i/p and i/n stacks, respectively, when using an intrinsic a-SiC:H layer with approximately 10% of carbon (initial lifetimes of 0.3 ms and 0.1 ms, respectively, corresponding to a 30% and 20-fold increase, respectively). For stacks of pure a-Si:H material the lifetimes degrade from 1.2 ms and 2.0 ms for i/p and i/n stacks, respectively, to less than 0.1 ms and 1.1 ms (12-fold and 2-fold decrease, respectively). For complete solar cells using pure a-Si:H i/p and i/n stacks, the open-circuit voltage (Voc

  9. 75 FR 51285 - In the Matter of Certain Flat Panel Digital Televisions and Components Thereof; Notice of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-19

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION In the Matter of Certain Flat Panel Digital Televisions and Components Thereof; Notice of... that information on this matter can be obtained by contacting the Commission's TDD terminal on...

  10. Integrated radiotherapy imaging system (IRIS): design considerations of tumour tracking with linac gantry-mounted diagnostic x-ray systems with flat-panel detectors

    NASA Astrophysics Data System (ADS)

    Berbeco, Ross I.; Jiang, Steve B.; Sharp, Gregory C.; Chen, George T. Y.; Mostafavi, Hassan; Shirato, Hiroki

    2004-01-01

    The design of an integrated radiotherapy imaging system (IRIS), consisting of gantry mounted diagnostic (kV) x-ray tubes and fast read-out flat-panel amorphous-silicon detectors, has been studied. The system is meant to be capable of three main functions: radiographs for three-dimensional (3D) patient set-up, cone-beam CT and real-time tumour/marker tracking. The goal of the current study is to determine whether one source/panel pair is sufficient for real-time tumour/marker tracking and, if two are needed, the optimal position of each relative to other components and the isocentre. A single gantry-mounted source/imager pair is certainly capable of the first two of the three functions listed above and may also be useful for the third, if combined with prior knowledge of the target's trajectory. This would be necessary because only motion in two dimensions is visible with a single imager/source system. However, with previously collected information about the trajectory, the third coordinate may be derived from the other two with sufficient accuracy to facilitate tracking. This deduction of the third coordinate can only be made if the 3D tumour/marker trajectory is consistent from fraction to fraction. The feasibility of tumour tracking with one source/imager pair has been theoretically examined here using measured lung marker trajectory data for seven patients from multiple treatment fractions. The patients' selection criteria include minimum mean amplitudes of the tumour motions greater than 1 cm peak-to-peak. The marker trajectory for each patient was modelled using the first fraction data. Then for the rest of the data, marker positions were derived from the imager projections at various gantry angles and compared with the measured tumour positions. Our results show that, due to the three dimensionality and irregular trajectory characteristics of tumour motion, on a fraction-to-fraction basis, a 'monoscopic' system (single source/imager) is inadequate for

  11. Direct observations of thermally induced structural changes in amorphous silicon carbide

    SciTech Connect

    Ishimaru, Manabu; Hirata, Akihiko; Naito, Muneyuki; Bae, In-Tae; Zhang, Yanwen; Weber, William J.

    2008-08-01

    Thermally induced structural relaxation in amorphous silicon carbide (SiC) has been examined by means of in situ transmission electron microscopy (TEM). The amorphous SiC was prepared by high-energy ion-beam-irradiation into a single crystalline 4H-SiC substrate. Cross-sectional TEM observations and electron energy-loss spectroscopy measurements revealed that thermal annealing induces a remarkable volume reduction, so-called densification, of amorphous SiC. From radial distribution function analyses using electron diffraction, notable changes associated with structural relaxation were observed in chemical short-range order. On the basis of the alteration of chemical short-range order, we discuss the origin of thermally induced densification in amorphous SiC.

  12. Ultrafast optical control using the Kerr nonlinearity in hydrogenated amorphous silicon microcylindrical resonators

    PubMed Central

    Vukovic, N.; Healy, N.; Suhailin, F. H.; Mehta, P.; Day, T. D.; Badding, J. V.; Peacock, A. C.

    2013-01-01

    Microresonators are ideal systems for probing nonlinear phenomena at low thresholds due to their small mode volumes and high quality (Q) factors. As such, they have found use both for fundamental studies of light-matter interactions as well as for applications in areas ranging from telecommunications to medicine. In particular, semiconductor-based resonators with large Kerr nonlinearities have great potential for high speed, low power all-optical processing. Here we present experiments to characterize the size of the Kerr induced resonance wavelength shifting in a hydrogenated amorphous silicon resonator and demonstrate its potential for ultrafast all-optical modulation and switching. Large wavelength shifts are observed for low pump powers due to the high nonlinearity of the amorphous silicon material and the strong mode confinement in the microcylindrical resonator. The threshold energy for switching is less than a picojoule, representing a significant step towards advantageous low power silicon-based photonic technologies. PMID:24097126

  13. Amorphous/crystalline silicon interface passivation: Ambient-temperature dependence and implications for solar cell performance

    DOE PAGESBeta

    Seif, Johannes P.; Krishnamani, Gopal; Demaurex, Benedicte; Ballif, Christophe; Wolf, Stefaan De

    2015-03-02

    Silicon heterojunction (SHJ) solar cells feature amorphous silicon passivation films, which enable very high voltages. We report how such passivation increases with operating temperature for amorphous silicon stacks involving doped layers and decreases for intrinsic-layer-only passivation. We discuss the implications of this phenomenon on the solar cell's temperature coefficient, which represents an important figure-of-merit for the energy yield of devices deployed in the field. We show evidence that both open-circuit voltage (Voc) and fill factor (FF) are affected by these variations in passivation and quantify these temperature-mediated effects, compared with those expected from standard diode equations. We confirm that devicesmore » with high Voc values at 25°C show better high-temperature performance. Thus, we also argue that the precise device architecture, such as the presence of charge-transport barriers, may affect the temperature-dependent device performance as well.« less

  14. Amorphous/crystalline silicon interface passivation: Ambient-temperature dependence and implications for solar cell performance

    SciTech Connect

    Seif, Johannes P.; Krishnamani, Gopal; Demaurex, Benedicte; Ballif, Christophe; Wolf, Stefaan De

    2015-03-02

    Silicon heterojunction (SHJ) solar cells feature amorphous silicon passivation films, which enable very high voltages. We report how such passivation increases with operating temperature for amorphous silicon stacks involving doped layers and decreases for intrinsic-layer-only passivation. We discuss the implications of this phenomenon on the solar cell's temperature coefficient, which represents an important figure-of-merit for the energy yield of devices deployed in the field. We show evidence that both open-circuit voltage (Voc) and fill factor (FF) are affected by these variations in passivation and quantify these temperature-mediated effects, compared with those expected from standard diode equations. We confirm that devices with high Voc values at 25°C show better high-temperature performance. Thus, we also argue that the precise device architecture, such as the presence of charge-transport barriers, may affect the temperature-dependent device performance as well.

  15. Amorphous silicon materials and solar cells - Progress and directions

    NASA Astrophysics Data System (ADS)

    Sabisky, E.; Mahan, H.; McMahon, T.

    In 1978, the U.S. Department of Energy initiated government sponsored research in amorphous materials and thin film solar cells. The program was subsequently transferred to the Solar Energy Research Institute for program management. The program grew into a major program for the development of high efficiency (greater than 10 percent), cost effective (15-40 cents per peak watt) thin film amorphous solar cells. The present international interest, the substantial progress made in the device area (2 percent PIN cell in 1976 to 10 percent PIN cell in 1982), and the marketing of the first consumer products using thin film solar cells are to a large ducts using thin film solar cells are to a large extent a consequence of this goal-oriented program.

  16. High Resolution Radial Distribution Function of Pure Amorphous Silicon

    SciTech Connect

    Laaziri, K.; Roorda, S.; Chicoine, M.; Kycia, S.; Robertson, J.L.; Wang, J.; Moss, S.C.

    1999-04-01

    The structure factor S(Q) of high purity amorphous Si membranes prepared by ion implantation was measured over an extended Q range (0.03{endash}55 {Angstrom} {sup {minus}1} ). Calculation of the first neighbor shell coordination (C{sub 1} ) as a function of maximum Q indicates that measurement of S(Q) out to at least 40 {Angstrom}{sup {minus}1} is required to reliably determine the radial distribution function (RDF). A 2{percent} change in C{sub 1} and subtle changes in the rest of the RDF were observed upon annealing, consistent with point defect removal. After annealing at 600thinsp{degree}C, C{sub 1}=3.88 , which would explain why amorphous Si is less dense than crystalline Si. {copyright} {ital 1999} {ital The American Physical Society}

  17. 2D wavelet-analysis-based calibration technique for flat-panel imaging detectors: application in cone beam volume CT

    NASA Astrophysics Data System (ADS)

    Tang, Xiangyang; Ning, Ruola; Yu, Rongfeng; Conover, David L.

    1999-05-01

    The application of the newly developed flat panel x-ray imaging detector in cone beam volume CT has attracted increasing interest recently. Due to an imperfect solid state array manufacturing process, however, defective elements, gain non-uniformity and offset image unavoidably exist in all kinds of flat panel x-ray imaging detectors, which will cause severe streak and ring artifacts in a cone beam reconstruction image and severely degrade image quality. A calibration technique, in which the artifacts resulting from the defective elements, gain non-uniformity and offset image can be reduced significantly, is presented in this paper. The detection of defective elements is distinctively based upon two-dimensional (2D) wavelet analysis. Because of its inherent localizability in recognizing singularities or discontinuities, wavelet analysis possesses the capability of detecting defective elements over a rather large x-ray exposure range, e.g., 20% to approximately 60% of the dynamic range of the detector used. Three-dimensional (3D) images of a low-contrast CT phantom have been reconstructed from projection images acquired by a flat panel x-ray imaging detector with and without calibration process applied. The artifacts caused individually by defective elements, gain non-uniformity and offset image have been separated and investigated in detail, and the correlation with each other have also been exposed explicitly. The investigation is enforced by quantitative analysis of the signal to noise ratio (SNR) and the image uniformity of the cone beam reconstruction image. It has been demonstrated that the ring and streak artifacts resulting from the imperfect performance of a flat panel x-ray imaging detector can be reduced dramatically, and then the image qualities of a cone beam reconstruction image, such as contrast resolution and image uniformity are improved significantly. Furthermore, with little modification, the calibration technique presented here is also applicable

  18. Comparing Ovarian Radiation Doses in Flat-Panel and Conventional Angiography During Uterine Artery Embolization: A Randomized Clinical Trial

    PubMed Central

    Firouznia, Kavous; Ghanaati, Hossein; Sharafi, Aliakbar; Abahashemi, Firouze; Hashemi, Hassan; Jalali, Amir Hossein; Shakiba, Madjid

    2013-01-01

    Background Uterine artery embolization (UAE) is a minimally invasive procedure performed under fluoroscopy for the treatment of uterine fibroids and accompanied by radiation exposure. Objectives To compare ovarian radiation doses during uterine artery embolization (UAE) in patients using conventional digital subtraction angiography (DSA) with those using digital flat-panel technology. Patients and Methods Thirty women who were candidates for UAE were randomly enrolled for one of the two angiographic systems. Ovarian doses were calculated according to in-vitro phantom study results using entrance and exit doses and were compared between the two groups. Results The mean right entrance dose was 1586±1221 mGy in the conventional and 522.3±400.1 mGy in the flat panel group (P=0.005). These figures were 1470±1170 mGy and 456±396 mGy, respectively for the left side (P=0.006). The mean right exit dose was 18.8±12.3 for the conventional and 9.4±6.4 mGy for the flat panel group (P=0.013). These figures were 16.7±11.3 and 10.2±7.2 mGy, respectively for the left side (P=0.06). The mean right ovarian dose was 139.9±92 in the conventional and 23.6±16.2 mGy in the flat panel group (P<0.0001). These figures were 101.7±77.6 and 24.6±16.9 mGy, respectively for the left side (P=0.002). Conclusion Flat panel system can significantly reduce the ovarian radiation dose during UAE compared with conventional DSA. PMID:24348594

  19. Sub-amorphous thermal conductivity in ultrathin crystalline silicon nanotubes.

    PubMed

    Wingert, Matthew C; Kwon, Soonshin; Hu, Ming; Poulikakos, Dimos; Xiang, Jie; Chen, Renkun

    2015-04-01

    Thermal transport behavior in nanostructures has become increasingly important for understanding and designing next generation electronic and energy devices. This has fueled vibrant research targeting both the causes and ability to induce extraordinary reductions of thermal conductivity in crystalline materials, which has predominantly been achieved by understanding that the phonon mean free path (MFP) is limited by the characteristic size of crystalline nanostructures, known as the boundary scattering or Casimir limit. Herein, by using a highly sensitive measurement system, we show that crystalline Si (c-Si) nanotubes (NTs) with shell thickness as thin as ∼5 nm exhibit a low thermal conductivity of ∼1.1 W m(-1) K(-1). Importantly, this value is lower than the apparent boundary scattering limit and is even about 30% lower than the measured value for amorphous Si (a-Si) NTs with similar geometries. This finding diverges from the prevailing general notion that amorphous materials represent the lower limit of thermal transport but can be explained by the strong elastic softening effect observed in the c-Si NTs, measured as a 6-fold reduction in Young's modulus compared to bulk Si and nearly half that of the a-Si NTs. These results illustrate the potent prospect of employing the elastic softening effect to engineer lower than amorphous, or subamorphous, thermal conductivity in ultrathin crystalline nanostructures. PMID:25758163

  20. An amorphous phase formation at palladium / silicon oxide (Pd/SiOx) interface through electron irradiation - electronic excitation process

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Yamashita, Ryo; Yabuuchi, Atsushi; Lee, Jung-Goo

    2015-11-01

    A Pd-Si amorphous phase was formed at a palladium/silicon oxide (Pd/SiOx) interface at room temperature by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Solid-state amorphization was stimulated without the electron knock-on effects. The total dose required for the solid-state amorphization decreases with decreasing acceleration voltage. This is the first report on electron irradiation induced metallic amorphous formation caused by the electronic excitation at metal/silicon oxide interface.

  1. A Comparison of Photo-Induced Hysteresis Between Hydrogenated Amorphous Silicon and Amorphous IGZO Thin-Film Transistors.

    PubMed

    Ha, Tae-Jun; Cho, Won-Ju; Chung, Hong-Bay; Koo, Sang-Mo

    2015-09-01

    We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition. PMID:26716230

  2. Reactive Infiltration of Silicon Melt Through Microporous Amorphous Carbon Preforms

    NASA Technical Reports Server (NTRS)

    Sangsuwan, P.; Tewari, S. N.; Gatica, J. E.; Singh, M.; Dickerson, R.

    1999-01-01

    The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms have been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances, is in qualitative agreement with the closed-form solution of capillarity driven fluid flow through constant cross section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preforms microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore closing phenomenon.

  3. Comparison of ring artifact removal methods using flat panel detector based CT images

    PubMed Central

    2011-01-01

    Background Ring artifacts are the concentric rings superimposed on the tomographic images often caused by the defective and insufficient calibrated detector elements as well as by the damaged scintillator crystals of the flat panel detector. It may be also generated by objects attenuating X-rays very differently in different projection direction. Ring artifact reduction techniques so far reported in the literature can be broadly classified into two groups. One category of the approaches is based on the sinogram processing also known as the pre-processing techniques and the other category of techniques perform processing on the 2-D reconstructed images, recognized as the post-processing techniques in the literature. The strength and weakness of these categories of approaches are yet to be explored from a common platform. Method In this paper, a comparative study of the two categories of ring artifact reduction techniques basically designed for the multi-slice CT instruments is presented from a common platform. For comparison, two representative algorithms from each of the two categories are selected from the published literature. A very recently reported state-of-the-art sinogram domain ring artifact correction method that classifies the ring artifacts according to their strength and then corrects the artifacts using class adaptive correction schemes is also included in this comparative study. The first sinogram domain correction method uses a wavelet based technique to detect the corrupted pixels and then using a simple linear interpolation technique estimates the responses of the bad pixels. The second sinogram based correction method performs all the filtering operations in the transform domain, i.e., in the wavelet and Fourier domain. On the other hand, the two post-processing based correction techniques actually operate on the polar transform domain of the reconstructed CT images. The first method extracts the ring artifact template vector using a homogeneity

  4. Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

    SciTech Connect

    Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

    2009-03-01

    The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10{sup 18} cm{sup -3}. Beyond this defect level, a sublinear relation is found i

  5. Characterization of a flat-panel detector for ion beam spot measurements

    NASA Astrophysics Data System (ADS)

    Martišíková, Mária; Hartmann, Bernadette; Hesse, Bernd M.; Brons, Stephan; Ackermann, Benjamin; Jäkel, Oliver

    2012-01-01

    Dynamic beam delivery techniques are being increasingly used for cancer therapy. Scanning ion beams require extensive and time-demanding quality assurance procedures and beam tuning. Accordingly, fast measurement techniques improving the efficiency of the procedures and accommodating the safety requirements are highly desirable. Major requirements for a detector used for beam-shape measurements are high spatial resolution in two dimensions, reusability, online readout and easy handling. At the Heidelberg Ion Beam Therapy Facility (Germany), we examined the performance of the RID 256 L flat-panel detector for beam spot measurements. The two-dimensional beam profiles of proton and carbon ion beams measured were compared to measurements with radiographic films at intermediate energies using the Γ index. The difference to the beam width measured with radiographic films of less than 3% demonstrates sufficient accuracy of ion beam width measurements possible with this detector for both proton and carbon ion beams. The beam shapes were also measured at different beam intensities. At both the highest and lowest energies available at the HIT, no beam spot-shape deformation was found with increasing beam intensities, as long as the boundary of the dynamic range was not exceeded. The signal leak along the readout direction was identified as an undesirable effect. However, due to small amplitudes and static beams, this effect is of minor importance for beam spot measurements. Distortion of results due to detector radiation damage was monitored. No detector radiation damage was observed over the experiments. Moreover, the observed short-time detector response stability (within ±0.1%) as well as medium term stability (within 0.5% in 15 months) was excellent. This flat-panel detector is compact and easy to use. Together with its low weight, this helps to speed up measurement procedures substantially. All these properties make this an ideal detector for the fast, high

  6. Directed dewetting of amorphous silicon film by a donut-shaped laser pulse

    NASA Astrophysics Data System (ADS)

    Yoo, Jae-Hyuck; In, Jung Bin; Zheng, Cheng; Sakellari, Ioanna; Raman, Rajesh N.; Matthews, Manyalibo J.; Elhadj, Selim; Grigoropoulos, Costas P.

    2015-04-01

    Irradiation of a thin film with a beam-shaped laser is proposed to achieve site-selectively controlled dewetting of the film into nanoscale structures. As a proof of concept, the laser-directed dewetting of an amorphous silicon thin film on a glass substrate is demonstrated using a donut-shaped laser beam. Upon irradiation of a single laser pulse, the silicon film melts and dewets on the substrate surface. The irradiation with the donut beam induces an unconventional lateral temperature profile in the film, leading to thermocapillary-induced transport of the molten silicon to the center of the beam spot. Upon solidification, the ultrathin amorphous silicon film is transformed to a crystalline silicon nanodome of increased height. This morphological change enables further dimensional reduction of the nanodome as well as removal of the surrounding film material by isotropic silicon etching. These results suggest that laser-based dewetting of thin films can be an effective way for scalable manufacturing of patterned nanostructures.

  7. Grain growth and size distribution in ion-irradiated chemical vapor deposited amorphous silicon

    SciTech Connect

    Spinella, C.; Lombardo, S.; Campisano, S. U.

    1989-07-10

    The amorphous to polycrystal transition in chemical vapor deposited (CVD) amorphous silicon has been studied at 450 /degree/C under Kr ion beam irradiation. The average grain size increases linearly with the ion dose, and the grain size distribution is very narrow compared to thermally grown grains. These results are consistent with the presence of crystal seeds in CVD material. All these seeds can grow simultaneously under ion beam irradiation. For layers completely preamorphized by Ge/sup +/ implantation, no ion beam induced nucleation is observed.

  8. Ultrasmooth growth of amorphous silicon films through ion-induced long-range surface correlations

    SciTech Connect

    Redondo-Cubero, A.; Gago, R.; Vazquez, L.

    2011-01-03

    Ultrasmooth amorphous silicon films with a constant roughness below 0.2 nm were produced for film thickness up to {approx}1 {mu}m by magnetron sputtering under negative voltage substrate biasing (100-400 V). In contrast, under unbiased conditions the roughness of the resulting mounded films increased linearly with growth time due to shadowing effects. A detailed analysis of the amorphous film growth dynamics proves that the bias-induced ultrasmoothness is produced by a downhill mass transport process that leads to an extreme surface leveling inducing surface height correlations up to lateral distances close to 0.5 {mu}m.

  9. Increased medium-range order in amorphous silicon with increased substrate temperature

    SciTech Connect

    Voyles, P. M.; Gerbi, J. E.; Treacy, M. M. J.; Gibson, J. M.; Aberlson, J. R.

    2000-08-15

    Using fluctuation electron microscopy, the authors have measured the medium-range order of magnetron sputtered silicon thin films as a function of substrate temperature from the amorphous to polycrystalline regimes. They find a smooth increase in the medium-range order of the samples, which they interpret in the context of the paracrystalline structural model as an increase in the size of and/or volume fraction occupied by the paracrystalline grains. These data are counter to the long-standing belief that there is a sharp transition between amorphous and polycrystalline structures as a function of substrate temperature.

  10. Irradiation-induced defect clustering and amorphization in silicon carbide

    SciTech Connect

    Weber, William J.; Gao, Fei

    2010-12-01

    Previous computer simulations of multiple 10 keV Si cascades in 3C-SiC demonstrated that many damage-state properties exhibit relatively smooth, but noticeably different, dose dependencies. Recent analysis of these archived damage-state properties reveals more complex relationships between system energy, swelling, energy per defect, relative disorder, elastic modulus and elastic constant, C11. These relationships provide evidence for the onset of defect clustering and amorphization processes, both of which appear to be driven by local energy and elastic instabilities from the accumulation of defects. The results provide guidance on experimental approaches to reveal the onset of these processes.

  11. Ring artifact corrections in flat-panel detector based cone beam CT

    NASA Astrophysics Data System (ADS)

    Anas, Emran Mohammad Abu; Kim, Jaegon; Lee, Soo Yeol; Hasan, Md. Kamrul

    2011-03-01

    The use of flat-panel detectors (FPDs) is becoming increasingly popular in the cone beam volume and multi-slice CT imaging. But due to the deficient semiconductor array processing, the diagnostic quality of the FPD-based CT images in both CT systems is degraded by different types of artifacts known as the ring and radiant artifacts. Several techniques have been already published in eliminating the stripe artifacts from the projection data of the multi-slice CT system or in other words, from the sinogram image with a view to suppress the ring and radiant artifacts from the 2-D reconstructed CT images. On the other hand, till now a few articles have been reported to remove the artifacts from the cone beam CT images. In this paper, an effective approach is presented to eliminate the artifacts from the cone beam projection data using the sinogram based stripe artifact removal methods. The improvement in the required diagnostic quality is achieved by applying them both in horizontal and vertical sinograms constituted sequentially from the stacked cone beam projections. Finally, some real CT images have been used to demonstrate the effectiveness of the proposed technique in eliminating the ring and radiant artifacts from the cone beam volume CT images. A comparative study with the conventional sinogram based approaches is also presented to see the effectiveness of the proposed technique.

  12. Measurements and simulations of VUV emissions from plasma flat panel display pixel microdischarges

    SciTech Connect

    McGrath, R.T.; Veerasingam, R.; Hunter, J.A.; Rockett, P.D.; Campbell, R.B.

    1998-10-01

    This paper reports on measurements of the principal vacuum ultra-violet emission lines from micro discharges operating with helium/xenon gas mixture used in full color plasma driven flat panel display pixels. The principal emission lines observed are the 147 and 129 nm lines from atomic xenon transitions and the relatively broad emissions from xenon dimers centered near 173 nm. The authors report on the changing intensities of these lines with variation in xenon concentration in the pixel gas mixtures, which affect the overall luminous efficiency of the display. A one-dimensional computer model has been used to simulate the discharge evolution. The model tracks the populations of twelve different representative quantum energy levels of the helium and xenon atoms, as well as the production and decay of the xenon dimers. The atomic physics description is sufficiently detailed to allow prediction of the relative intensities of the dominant emission lines. The authors find that model predicted intensities for xenon atomic and dimer emission lines agree well with experimental measurements.

  13. Compact flat-panel gas-gap heat switch operating at 295 K

    NASA Astrophysics Data System (ADS)

    Krielaart, M. A. R.; Vermeer, C. H.; Vanapalli, S.

    2015-11-01

    Heat switches are devices that can change from a thermally conducting (on-) state to an insulating (off-) state whenever the need arises. They enable adaptive thermal management strategies in which cooling rates are altered either spatially or temporally, leading to a substantial reduction in the energy and mass budget of a large range of systems. State-of-the-art heat switches are only rarely employed in thermal system architectures, since they are rather bulky and have a limited thermal performance (expressed as the heat transfer ratio between the on- and off-state heat conductance). Using selective laser melting additive manufacturing technology, also known as 3D printing, we developed a compact flat-panel gas-gap heat switch that offers superior thermal performance, is simpler and more economic to produce and assemble, contains no moving parts, and is more reliable because it lacks welded joints. The manufactured rectangular panel heat switch has frontal device dimensions of 10 cm by 10 cm, thickness of 3.2 mm and weighs just 121 g. An off heat conductance of 0.2 W/K and on-off heat conductance ratio of 38 is observed at 295 K.

  14. Compact flat-panel gas-gap heat switch operating at 295 K.

    PubMed

    Krielaart, M A R; Vermeer, C H; Vanapalli, S

    2015-11-01

    Heat switches are devices that can change from a thermally conducting (on-) state to an insulating (off-) state whenever the need arises. They enable adaptive thermal management strategies in which cooling rates are altered either spatially or temporally, leading to a substantial reduction in the energy and mass budget of a large range of systems. State-of-the-art heat switches are only rarely employed in thermal system architectures, since they are rather bulky and have a limited thermal performance (expressed as the heat transfer ratio between the on- and off-state heat conductance). Using selective laser melting additive manufacturing technology, also known as 3D printing, we developed a compact flat-panel gas-gap heat switch that offers superior thermal performance, is simpler and more economic to produce and assemble, contains no moving parts, and is more reliable because it lacks welded joints. The manufactured rectangular panel heat switch has frontal device dimensions of 10 cm by 10 cm, thickness of 3.2 mm and weighs just 121 g. An off heat conductance of 0.2 W/K and on-off heat conductance ratio of 38 is observed at 295 K. PMID:26628181

  15. Dynamic chest radiography: flat-panel detector (FPD) based functional X-ray imaging.

    PubMed

    Tanaka, Rie

    2016-07-01

    Dynamic chest radiography is a flat-panel detector (FPD)-based functional X-ray imaging, which is performed as an additional examination in chest radiography. The large field of view (FOV) of FPDs permits real-time observation of the entire lungs and simultaneous right-and-left evaluation of diaphragm kinetics. Most importantly, dynamic chest radiography provides pulmonary ventilation and circulation findings as slight changes in pixel value even without the use of contrast media; the interpretation is challenging and crucial for a better understanding of pulmonary function. The basic concept was proposed in the 1980s; however, it was not realized until the 2010s because of technical limitations. Dynamic FPDs and advanced digital image processing played a key role for clinical application of dynamic chest radiography. Pulmonary ventilation and circulation can be quantified and visualized for the diagnosis of pulmonary diseases. Dynamic chest radiography can be deployed as a simple and rapid means of functional imaging in both routine and emergency medicine. Here, we focus on the evaluation of pulmonary ventilation and circulation. This review article describes the basic mechanism of imaging findings according to pulmonary/circulation physiology, followed by imaging procedures, analysis method, and diagnostic performance of dynamic chest radiography. PMID:27294264

  16. Planar cone-beam computed tomography with a flat-panel detector

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Kim, D. W.; Youn, H.; Kim, D.; Kam, S.; Jeon, H.; Kim, H. K.

    2015-12-01

    For a dedicated x-ray inspection of printed-circuit boards (PCBs), a bench-top planar cone-beam computed tomography (pCT) system with a flat-panel detector has been built in the laboratory. The system adopts the tomosynthesis technique that can produce cross-sectional images parallel to the axis of rotation for a limited angular range. For the optimal operation of the system and further improvement in the next design, we have evaluated imaging performances, such as modulation-transfer function, noise-power spectrum, and noise-equivalent number of quanta. The performances are comparatively evaluated with the coventional cone-beam CT (CBCT) acquisition for various scanning angular ranges, applied tube voltages, and geometrical magnification factors. The pCT scan shows a poorer noise performance than the conventional CBCT scan because of less number of projection views used for reconstruction. However, the pCT shows a better spatial-resolution performance than the CBCT. Because the image noise can be compensated by an elevated exposure level during scanning, the pCT can be a useful modality for the PCB inspection that requires higher spatial-resolution performance.

  17. Dynamic chest radiography with a flat-panel detector (FPD): ventilation-perfusion study

    NASA Astrophysics Data System (ADS)

    Tanaka, R.; Sanada, S.; Fujimura, M.; Yasui, M.; Tsuji, S.; Hayashi, N.; Okamoto, H.; Nanbu, Y.; Matsui, O.

    2011-03-01

    Pulmonary ventilation and blood flow are reflected in dynamic chest radiographs as changes in X-ray translucency, i.e., pixel values. This study was performed to investigate the feasibility of ventilation-perfusion (V/Q) study based on the changes in pixel value. Sequential chest radiographs of a patient with ventilation-perfusion mismatch were obtained during respiration using a dynamic flat-panel detector (FPD) system. The lung area was recognized and average pixel value was measured in each area, tracking and deforming the region of interest. Inter-frame differences were then calculated, and the absolute values were summed in each respiratory phase. The results were visualized as ventilation, blood flow, V/Q ratio distribution map and compared to distribution of radioactive counts on ventilation and perfusion scintigrams. In the results, abnormalities were appeared as a reduction of changes in pixel values, and a correlation was observed between the distribution of changes in pixel value and those of radioactivity counts (Ventilation; r=0.78, Perfusion; r=0.77). V/Q mismatch was also indicated as mismatch of changes in pixel value, and a correlation with V/Q calculated by radioactivity counts (r=0.78). These results indicated that the present method is potentially useful for V/Q study as an additional examination in conventional chest radiography.

  18. Transition from image intensifier to flat panel detector in interventional cardiology: Impact of radiation dose

    PubMed Central

    Livingstone, Roshan S.; Chase, David; Varghese, Anna; George, Paul V.; George, Oommen K.

    2015-01-01

    Flat panel detector (FPD) technology in interventional cardiology is on the increase due to its varied advantages compared to the conventional image intensifier (II) systems. It is not clear whether FPD imparts lower radiation doses compared to II systems though a few studies support this finding. This study intends to compare radiation doses from II and FPD systems for coronaryangiography (CAG) and Percutaneous Transluminal Coronary Angioplasty (PTCA) performed in a tertiary referral center. Radiation doses were measured using dose area product (DAP) meter from patients who underwent CAG (n = 222) and PTCA (n = 75) performed using FPD angiography system. The DAP values from FPD were compared with earlier reported data using II systems from the same referral center where the study was conducted. The mean DAP values from FPD system for CAG and PTCA were 24.35 and 63.64 Gycm2 and those from II system were 27.71 and 65.44 Gycm2. Transition from II to FPD system requires stringent dose optimization strategies right from the initial period of installation. PMID:26150684

  19. Point spread function modeling method for x-ray flat panel detector imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Hua; Shi, Yikai; Huang, Kuidong; Yu, Qingchao

    2012-10-01

    Flat panel detector (FPD) has been widely used as the imaging unit in the current X-ray digital radiography (DR) systems and Computed Tomography (CT) systems. Point spread function (PSF) is an important indicator of the FPD imaging system, but also the basis for image restoration. For the problem of poor accuracy of the FPD's PSF measurement with the original pinhole imaging for DR systems, a new PSF measuring method with the pinhole imaging based on the image restoration is proposed in this paper. Firstly, some images collected with the pinhole imaging are averaged to one image to reducing the noise. Then, the original pinhole image is calculated according to the energy conservation principle of point spread. Finally, the PSF of the FPD is obtained using the operation of image restoration. On this basis, through the fitting of the characteristic parameters of the PSF on different scan conditions, the computational model of the PSF is established for any scan conditions. Experimental results show that the method can obtain a more accurate PSF of the FPD, and the PSF of the same system under any scan conditions can be directly calculated with the PSF model.

  20. Dynamic flat panel detector versus image intensifier in cardiac imaging: dose and image quality

    NASA Astrophysics Data System (ADS)

    Vano, E.; Geiger, B.; Schreiner, A.; Back, C.; Beissel, J.

    2005-12-01

    The practical aspects of the dosimetric and imaging performance of a digital x-ray system for cardiology procedures were evaluated. The system was configured with an image intensifier (II) and later upgraded to a dynamic flat panel detector (FD). Entrance surface air kerma (ESAK) to phantoms of 16, 20, 24 and 28 cm of polymethyl methacrylate (PMMA) and the image quality of a test object were measured. Images were evaluated directly on the monitor and with numerical methods (noise and signal-to-noise ratio). Information contained in the DICOM header for dosimetry audit purposes was also tested. ESAK values per frame (or kerma rate) for the most commonly used cine and fluoroscopy modes for different PMMA thicknesses and for field sizes of 17 and 23 cm for II, and 20 and 25 cm for FD, produced similar results in the evaluated system with both technologies, ranging between 19 and 589 µGy/frame (cine) and 5 and 95 mGy min-1 (fluoroscopy). Image quality for these dose settings was better for the FD version. The 'study dosimetric report' is comprehensive, and its numerical content is sufficiently accurate. There is potential in the future to set those systems with dynamic FD to lower doses than are possible in the current II versions, especially for digital cine runs, or to benefit from improved image quality.

  1. Average power scaling of UV excimer lasers drives flat panel display and lidar applications

    NASA Astrophysics Data System (ADS)

    Herbst, Ludolf; Delmdahl, Ralph F.; Paetzel, Rainer

    2012-03-01

    Average power scaling of 308nm excimer lasers has followed an evolutionary path over the last two decades driven by diverse industrial UV laser microprocessing markets. Recently, a new dual-oscillator and beam management concept for high-average power upscaling of excimer lasers has been realized, for the first time enabling as much as 1.2kW of stabilized UV-laser average output power at a UV wavelength of 308nm. The new dual-oscillator concept enables low temperature polysilicon (LTPS) fabrication to be extended to generation six glass substrates. This is essential in terms of a more economic high-volume manufacturing of flat panel displays for the soaring smartphone and tablet PC markets. Similarly, the cost-effective production of flexible displays is driven by 308nm excimer laser power scaling. Flexible displays have enormous commercial potential and can largely use the same production equipment as is used for rigid display manufacturing. Moreover, higher average output power of 308nm excimer lasers aids reducing measurement time and improving the signal-to-noise ratio in the worldwide network of high altitude Raman lidar stations. The availability of kW-class 308nm excimer lasers has the potential to take LIDAR backscattering signal strength and achievable altitude to new levels.

  2. Contrast-detail analysis of three flat panel detectors for digital radiography

    SciTech Connect

    Borasi, Giovanni; Samei, Ehsan; Bertolini, Marco; Nitrosi, Andrea; Tassoni, Davide

    2006-06-15

    In this paper we performed a contrast detail analysis of three commercially available flat panel detectors, two based on the indirect detection mechanism (GE Revolution XQ/i, system A, and Trixell/Philips Pixium 4600, system B) and one based on the direct detection mechanism (Hologic DirectRay DR 1000, system C). The experiment was conducted using standard x-ray radiation quality and a widely used contrast-detail phantom. Images were evaluated using a four alternative forced choice paradigm on a diagnostic-quality softcopy monitor. At the low and intermediate exposures, systems A and B gave equivalent performances. At the high dose levels, system A performed better than system B in the entire range of target sizes, even though the pixel size of system A was about 40% larger than that of system B. At all the dose levels, the performances of the system C (direct system) were lower than those of system A and B (indirect systems). Theoretical analyses based on the Perception Statistical Model gave similar predicted SNR{sub T} values corresponding to an observer efficiency of about 0.08 for systems A and B and 0.05 for system C.

  3. Development of patient collation system by kinetic analysis for chest dynamic radiogram with flat panel detector

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Yuichiro; Kodera, Yoshie

    2006-03-01

    In the picture archiving and communication system (PACS) environment, it is important that all images be stored in the correct location. However, if information such as the patient's name or identification number has been entered incorrectly, it is difficult to notice the error. The present study was performed to develop a system of patient collation automatically for dynamic radiogram examination by a kinetic analysis, and to evaluate the performance of the system. Dynamic chest radiographs during respiration were obtained by using a modified flat panel detector system. Our computer algorithm developed in this study was consisted of two main procedures, kinetic map imaging processing, and collation processing. Kinetic map processing is a new algorithm to visualize a movement for dynamic radiography; direction classification of optical flows and intensity-density transformation technique was performed. Collation processing consisted of analysis with an artificial neural network (ANN) and discrimination for Mahalanobis' generalized distance, those procedures were performed to evaluate a similarity of combination for the same person. Finally, we investigated the performance of our system using eight healthy volunteers' radiographs. The performance was shown as a sensitivity and specificity. The sensitivity and specificity for our system were shown 100% and 100%, respectively. This result indicated that our system has excellent performance for recognition of a patient. Our system will be useful in PACS management for dynamic chest radiography.

  4. Astaxanthin induction in Microalga H. pluvialis with flat panel airlift photobioreactors under indoor and outdoor conditions.

    PubMed

    Poonkum, Woradej; Powtongsook, Sorawit; Pavasant, Prasert

    2015-01-01

    Astaxanthin was induced from Haematococcus pluvialis (NIES-144) under indoor and outdoor conditions using 17-, 50-, and 90-L flat-panel airlift photobioreactors (FP-APBRs). Preliminary experiments in 1.5-L bubble column photobioreactors (BC-PBRs) revealed that sterilized clean water with 3% CO2 aeration (1.47 cm(3) s(-1) CO2 loading) could best encourage astaxanthin accumulation at 18.21 g m(-3) (3.63% by weight). Operating 17-L FP-APBRs with these bubble column parameters under indoor conditions could further enhance astaxanthin to 26.63 g m(-3) (5.34% by weight). This was potentially due to the inherited up-lift force from the reactor that helped avoid cell precipitation by allowing the cells to be circulated within the reactor. In addition, the various sizes of FP-APBRs exhibited similar performance, implying a potential scale-up opportunity. However, similar operation under outdoor condition exhibited slightly poorer performance due to the light inhibition effect. The best outdoor performance was obtained with the FP-APBR covered with one layer of shading net, where 20.11 g m(-3) (4.47% by weight) of astaxanthin was resulted. PMID:25105532

  5. The forced radiation efficiency of finite size flat panels that are excited by incident sound.

    PubMed

    Davy, John L

    2009-08-01

    The radiation efficiency of an infinite flat panel that radiates a plane wave into a half space is equal to the inverse of the cosine of the angle between the direction of propagation of the plane wave and the normal to the panel. The fact that this radiation efficiency tends to infinity as the angle tends to 90 degrees causes problems with simple theories of sound insulation. Sato calculated numerical values of radiation efficiency for a finite size rectangular panel in an infinite baffle whose motion is forced by sound incident at an angle to the normal from the other side. This paper presents a simple two dimensional analytic strip theory, which agrees reasonably well with Sato's numerical calculations for a rectangular panel. This leads to the conclusion that it is mainly the length of the panel in the direction of radiation, rather than its width that is important in determining its radiation efficiency. A low frequency correction is added to the analytic strip theory. The theory is analytically integrated over all angles of incidence, with the appropriate weighting function, to obtain the diffuse sound field forced radiation efficiency of a panel. PMID:19640035

  6. Thermal Reactor Model for Large-Scale Algae Cultivation in Vertical Flat Panel Photobioreactors.

    PubMed

    Endres, Christian H; Roth, Arne; Brück, Thomas B

    2016-04-01

    Microalgae can grow significantly faster than terrestrial plants and are a promising feedstock for sustainable value added products encompassing pharmaceuticals, pigments, proteins and most prominently biofuels. As the biomass productivity of microalgae strongly depends on the cultivation temperature, detailed information on the reactor temperature as a function of time and geographical location is essential to evaluate the true potential of microalgae as an industrial feedstock. In the present study, a temperature model for an array of vertical flat plate photobioreactors is presented. It was demonstrated that mutual shading of reactor panels has a decisive effect on the reactor temperature. By optimizing distance and thickness of the panels, the occurrence of extreme temperatures and the amplitude of daily temperature fluctuations in the culture medium can be drastically reduced, while maintaining a high level of irradiation on the panels. The presented model was developed and applied to analyze the suitability of various climate zones for algae production in flat panel photobioreactors. Our results demonstrate that in particular Mediterranean and tropical climates represent favorable locations. Lastly, the thermal energy demand required for the case of active temperature control is determined for several locations. PMID:26950078

  7. Resolution at oblique incidence angles of a flat panel imager for breast tomosynthesis

    SciTech Connect

    Mainprize, James G.; Bloomquist, Aili K.; Kempston, Michael P.; Yaffe, Martin J.

    2006-09-15

    Oblique incidence of x rays on an imaging detector causes blurring that reduces spatial resolution. For simple projection imaging this effect is small and often ignored. However, for breast tomosynthesis, the incidence angle can be larger (>20 deg. ), leading to increased blur for some of the projections. The modulation transfer function (MTF) is measured for a typical phosphor-coupled flat-panel detector versus angular incidence of the x-ray beam for two x-ray spectra: 26 kV Mo/Mo and 40 kV Rh/Al. At an incidence angle of 40 deg. the MTF at 5 mm-1 falls by 35% and 40% for each spectrum, respectively (and 65%/80% at 8 mm-1). Increasing the detector absorber thickness to achieve improved quantum efficiency will cause the blurring effect due to beam obliquity to become greater. The impact of this blur is likely to cause misregistration and increased relative noise in tomosynthesis reconstructed images.

  8. A compact high resolution flat panel PET detector based on the new 4-side buttable MPPC for biomedical applications

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Wen, Jie; Ravindranath, Bosky; O`Sullivan, Andrew W.; Catherall, David; Li, Ke; Wei, Shouyi; Komarov, Sergey; Tai, Yuan-Chuan

    2015-09-01

    Compact high-resolution panel detectors using virtual pinhole (VP) PET geometry can be inserted into existing clinical or pre-clinical PET systems to improve regional spatial resolution and sensitivity. Here we describe a compact panel PET detector built using the new Though Silicon Via (TSV) multi-pixel photon counters (MPPC) detector. This insert provides high spatial resolution and good timing performance for multiple bio-medical applications. Because the TSV MPPC design eliminates wire bonding and has a package dimension which is very close to the MPPC's active area, it is 4-side buttable. The custom designed MPPC array (based on Hamamatsu S12641-PA-50(x)) used in the prototype is composed of 4×4 TSV-MPPC cells with a 4.46 mm pitch in both directions. The detector module has 16×16 lutetium yttrium oxyorthosilicate (LYSO) crystal array, with each crystal measuring 0.92×0.92×3 mm3 with 1.0 mm pitch. The outer diameter of the detector block is 16.8×16.8 mm2. Thirty-two such blocks will be arranged in a 4×8 array with 1 mm gaps to form a panel detector with detection area around 7 cm×14 cm in the full-size detector. The flood histogram acquired with 68Ge source showed excellent crystal separation capability with all 256 crystals clearly resolved. The detector module's mean, standard deviation, minimum (best) and maximum (worst) energy resolution were 10.19%, ±0.68%, 8.36% and 13.45% FWHM, respectively. The measured coincidence time resolution between the block detector and a fast reference detector (around 200 ps single photon timing resolution) was 0.95 ns. When tested with Siemens Cardinal electronics the performance of the detector blocks remain consistent. These results demonstrate that the TSV-MPPC is a promising photon sensor for use in a flat panel PET insert composed of many high resolution compact detector modules.

  9. Absence of amorphous phase in high power femtosecond laser-ablated silicon

    SciTech Connect

    Rogers, Matthew S.; Grigoropoulos, Costas P.; Minor, Andrew M.; Mao, Samuel S.

    2009-01-05

    As femtosecond lasers emerge as viable tools for advanced microscale materials processing, it becomes increasingly important to understand the characteristics of materials resulting from femtosecond laser microablation or micromachining. We conducted transmission electron microscopy experiments to investigate crater structures in silicon produced by repetitive high power femtosecond laser ablation. Comparable experiments of nanosecond laser ablation of silicon were also performed. We found that an amorphous silicon layer that is typically produced in nanosecond laser ablation is absent when the material is irradiated by high power femtosecond laser pulses. Instead, only a defective single crystalline layer was observed in the high power femtosecond laser-ablated silicon crater. Possible mechanisms underlying the formation of the defective single crystalline phase are discussed.

  10. Innovative Characterization of Amorphous and Thin-Film Silicon for Improved Module Performance: 1 February 2005 - 31 July 2008

    SciTech Connect

    Taylor, P. C.; Williams, G. A.

    2009-09-01

    Electron spin resonance and nuclear magnetic resonance was done on amorphous silicon samples (modules with a-Si:H and a-SixGe1-x:H intrinsic layer) to study defects that contribute to Staebler-Wronski effect.

  11. Plasma-initiated rehydrogenation of amorphous silicon to increase the temperature processing window of silicon heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Shi, Jianwei; Boccard, Mathieu; Holman, Zachary

    2016-07-01

    The dehydrogenation of intrinsic hydrogenated amorphous silicon (a-Si:H) at temperatures above approximately 300 °C degrades its ability to passivate silicon wafer surfaces. This limits the temperature of post-passivation processing steps during the fabrication of advanced silicon heterojunction or silicon-based tandem solar cells. We demonstrate that a hydrogen plasma can rehydrogenate intrinsic a-Si:H passivation layers that have been dehydrogenated by annealing. The hydrogen plasma treatment fully restores the effective carrier lifetime to several milliseconds in textured crystalline silicon wafers coated with 8-nm-thick intrinsic a-Si:H layers after annealing at temperatures of up to 450 °C. Plasma-initiated rehydrogenation also translates to complete solar cells: A silicon heterojunction solar cell subjected to annealing at 450 °C (following intrinsic a-Si:H deposition) had an open-circuit voltage of less than 600 mV, but an identical cell that received hydrogen plasma treatment reached a voltage of over 710 mV and an efficiency of over 19%.

  12. Ion implantation induced defect formation and amorphization in the Group IV semiconductors: Diamond, silicon and germanium

    NASA Astrophysics Data System (ADS)

    Hickey, Diane P.

    Silicon, which has been the workhorse of the semiconductor industry for the past several decades, is now being enhanced with other Group IV elements, such as carbon (silicon carbide) and germanium (silicon-germanium strained channels in transistors), to accentuate properties of silicon for various nanoelectronic devices. However, there is little understanding of the relationship between ion implantation and defect evolution in two of the three corners of the Group IV phase diagram. In particular, the rod-like {311} defect is theorized to be unique to the diamond crystal structure elements. Due to its ability to affect dopant diffusion, the {311} defect is well studied in silicon. However, few studies of germanium and none of diamond have analyzed extended defect formation and evolution using transmission electron spectroscopy. Using ion implantation to induce amorphization is a technological process step in Si devices and potentially for diamond nano-electronics. Defects associated with crystal regrowth in Ge and diamond are not well known. My research studies the formation conditions of extended defects and amorphization in carbon and germanium after ion implantation. Ion implantation damage in diamond-cubic single-crystal silicon, germanium and diamond was produced by Si+ implantation at 1 MeV to a dose of 1 x 1014 cm-2 and 1 x 10 15 cm-2. Damage in Si and Ge was produced by Si + implantation at 40 keV to a dose of 1 x 1014 cm-2 and 1 x 1015 cm-2, and amorphizing damage in diamond was produced by Si+ implantation at 1 MeV to a dose of 3 and 7 x 1015 cm-2. All implants were carried out at room temperature. For non-amorphizing implants (1014 Si+ cm-2) into Ge, dot-like defects formed immediately upon implantation and were stable up to temperatures of 650°C. The activation energy of these defects was determined to be approximately 0.2 +/- 0.1 eV. For amorphizing implants (1015 Si+ cm-2) into Ge and upon solid-phase epitaxial regrowth, the same types of defects seen

  13. Determination of hydrogen density of states in amorphous silicon using fractional evolution experiments

    SciTech Connect

    Franz, A.J.; Jackson, W.B.; Gland, J.L.

    1997-07-01

    Hydrogen plays an important role in the electronic behavior, structure and stability of amorphous silicon films. Therefore, determination of the hydrogen density of states (DOS) and correlation of the hydrogen DOS with the electronic film properties are important research goals. The authors have developed a novel method for determination of hydrogen DOS in silicon films, based on fractional evolution experiments. Fractional evolution experiments are performed by subjecting a silicon film to a series of linear, alternating heating and cooling ramps, while monitoring the hydrogen evolution rate. The fractional evolution data can be analyzed using two complementary methods, the fixed frequency factor approach and Arrhenius analysis. Using a rigorous, mean-field evolution model, they demonstrate the applicability of the two approaches to obtaining the hydrogen DOS in silicon films. They further validate both methods by analyzing experimental fractional evolution data for an amorphous silicon carbide film. Both types of analysis yield a similar double peaked density of states for the a-Si:C:H:D film.

  14. Preparation and Surface Analysis of a Fluorinated Amorphous Silicon for Photo-voltaic Device Application

    NASA Technical Reports Server (NTRS)

    McWhinney, Hylton G.; Burton, Dawn; Fogarty, Thomas N.

    1998-01-01

    Amorphous silicon films (a-Si:H) have been routinely deposited on a variety of substrates. Surface and interfacial studies were carried out with a PHI 5600 X-ray photo electron spectrometer. Co-deposition with fluorine yielded films having oxygen present as bulk oxide. The higher the fluorine content, the greater the amount of bulk oxygen observed. The presence of oxygen may be a contributing factor to inconsistent film properties of fluorine doped silicon materials, reported else where. A definite chemical interface between a layer containing fluorine and a layer made from pure silane has been delineated.

  15. Disorder and density of defects in hydrogenated amorphous silicon-carbon

    NASA Astrophysics Data System (ADS)

    Boulitrop, F.; Bullot, J.; Gauthier, M.; Schmidt, M. P.; Catherine, Y.

    1985-04-01

    We report subgap absorption measurements by photothermal deflection spectroscopy in a-Si 1- xC x: H alloys in the whole range of composition. We observe that incorporation of carbon in the silicon matrix increases both the inverse of the slope of the exponential absorption tail (which is due to the valence band tail) and the subgap absorption around 1.3 eV (due to defects). This result is correlated with former results on the broadening of the conduction band tail deduced from transport measurements in these alloys. It is concluded that carbon incorporation induces disorder and defect creation in the amorphous silicon matrix.

  16. Grain growth kinetics during ion beam irradiation of chemical vapor deposited amorphous silicon

    SciTech Connect

    Spinella, C.; Lombardo, S. ); Campisano, S.U. )

    1990-08-06

    The amorphous to polycrystal transition during Kr ion beam irradiation of chemical vapor deposited silicon layers has been studied in the temperature range 320--480 {degree}C. At each irradiation temperature the average grain diameter increases linearly with the Kr dose, while the grain density remains constant within the experimental accuracy. The growth rate follows a complex behavior which can be described by dynamic defect generation and annihilation. The absolute value of the grain growth rate is equal to that of the ion-assisted epitaxial layer by layer crystallization in the silicon (111) orientation. This result can be related to the crystal grain structure and morphology.

  17. TEM observations of hydrogen nanobubbles in implanted amorphous silicon

    SciTech Connect

    Jones, K.M.; Al-Jassim, M.M.; Williamson, D.L.; Acco, S.

    1996-12-31

    Over the last two decades extensive studies on the optical and electrical properties of hydrogenated amorphous Si (a-Si:H) have been reported. However, less attention was given to the structural characterization of this material partly due to the insensitivity to hydrogen of structural probes such as x-rays and electron diffraction. From a recent set of experiments, results on the solubility limit of hydrogen in a special type of a-Si:H and the characterization of hydrogen induced complexes or nanobubbles has been reported. In this study, we report TEM observations of the structural morphology of hydrogen related defects that support these recent measurements obtained by secondary ion mass spectrometry (SIMS) and small-angle x-ray scattering (SAXS).

  18. Irradiation-induced defect clustering and amorphization in silicon carbide

    SciTech Connect

    Weber, William J; Gao, Fei

    2010-01-01

    Previous computer simulations of multiple 10 keV Si cascades in 3C-SiC demonstrated that many damage-state properties exhibit relatively smooth, but noticeably different, dose dependencies. A more recent analysis of these damage-state properties, which includes additional data at low and intermediate doses, reveals more complex relationships between system energy, swelling, energy per defect, relative disorder, elastic modulus and elastic constant, C11. These relationships provide evidence for the onset of both defect clustering and solid-state amorphization, which appear to be driven by local energy and elastic instabilities from the accumulation of defects. The results provide guidance on experimental approaches to reveal the onset of these processes.

  19. Carbon nanotube-amorphous silicon hybrid solar cell with improved conversion efficiency.

    PubMed

    Funde, Adinath M; Nasibulin, Albert G; Syed, Hashmi Gufran; Anisimov, Anton S; Tsapenko, Alexey; Lund, Peter; Santos, J D; Torres, I; Gandía, J J; Cárabe, J; Rozenberg, A D; Levitsky, Igor A

    2016-05-01

    We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics. PMID:27005494

  20. Label-Free Direct Electronic Detection of Biomolecules with Amorphous Silicon Nanostructures

    PubMed Central

    Lund, John; Mehta, Ranjana; Parviz, Babak A.

    2007-01-01

    We present the fabrication and characterization of a nano-scale sensor made of amorphous silicon for the label-free, electronic detection of three classes of biologically important molecules: ions, oligonucleotides, and proteins. The sensor structure has an active element which is a 50 nm wide amorphous silicon semicircle and has a total footprint of less than 4 μm2. We demonstrate the functionalization of the sensor with receptor molecules and the electronic detection of three targets: H+ ions, short single-stranded DNAs, and streptavidin. The sensor is able to reliably distinguish single base-pair mismatches in 12 base long strands of DNA and monitor the introduction and identification of straptavidin in real-time. The versatile sensor structure can be readily functionalized with a wide range of receptor molecules and is suitable for integration with high-speed electronic circuits as a post-process on an integrated circuit chip. PMID:17292148

  1. Carbon nanotube-amorphous silicon hybrid solar cell with improved conversion efficiency

    NASA Astrophysics Data System (ADS)

    Funde, Adinath M.; Nasibulin, Albert G.; Gufran Syed, Hashmi; Anisimov, Anton S.; Tsapenko, Alexey; Lund, Peter; Santos, J. D.; Torres, I.; Gandía, J. J.; Cárabe, J.; Rozenberg, A. D.; Levitsky, Igor A.

    2016-05-01

    We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics.

  2. Efficient Crystalline Si Solar Cell with Amorphous/Crystalline Silicon Heterojunction as Back Contact: Preprint

    SciTech Connect

    Nemeth, B.; Wang, Q.; Shan, W.

    2012-06-01

    We study an amorphous/crystalline silicon heterojunction (Si HJ) as a back contact in industrial standard p-type five-inch pseudo-square wafer to replace Al back surface field (BSF) contact. The best efficiency in this study is over 17% with open-circuit (Voc) of 0.623 V, which is very similar to the control cell with Al BSF. We found that Voc has not been improved with the heterojunction structure in the back. The typical minority carrier lifetime of these wafers is on the order of 10 us. We also found that the doping levels of p-layer affect the FF due to conductivity and band gap shifting, and an optimized layer is identified. We conclude that an amorphous/crystalline silicon heterojunction can be a very promising structure to replace Al BSF back contact.

  3. Corrosion resistance and cytocompatibility of biodegradable surgical magnesium alloy coated with hydrogenated amorphous silicon.

    PubMed

    Xin, Yunchang; Jiang, Jiang; Huo, Kaifu; Tang, Guoyi; Tian, Xiubo; Chu, Paul K

    2009-06-01

    The fast degradation rates in the physiological environment constitute the main limitation for the applications of surgical magnesium alloys as biodegradable hard-tissue implants. In this work, a stable and dense hydrogenated amorphous silicon coating (a-Si:H) with desirable bioactivity is deposited on AZ91 magnesium alloy using magnetron sputtering deposition. Raman spectroscopy and Fourier transform infrared spectroscopy reveal that the coating is mainly composed of hydrogenated amorphous silicon. The hardness of the coated alloy is enhanced significantly and the coating is quite hydrophilic as well. Potentiodynamic polarization results show that the corrosion resistance of the coated alloy is enhanced dramatically. In addition, the deterioration process of the coating in simulated body fluids is systematically investigated by open circuit potential evolution and electrochemical impedance spectroscopy. The cytocompatibility of the coated Mg is evaluated for the first time using hFOB1.19 cells and favorable biocompatibility is observed. PMID:18449935

  4. Status of the DOE/SERI amorphous silicon research project - Recent advances and future directions

    NASA Astrophysics Data System (ADS)

    Stafford, B. L.; Luft, W.; von Roedern, B.; Wallace, W. L.

    Recent advances in material, cell, and module research in the US Department of Energy/Solar Energy Research Institute (DOE/SERI) Amorphous Silicon Research Project (ASRP) are reviewed. Advances in transparent conductive oxides, high-performance back reflectors, cell interconnection/patterning schemes, and encapsulants are surveyed. The program phase that began in 1990 has major research goals of reproducible, cost-effective multijunction modules with stabilized efficiencies of 10 percent for same-bandgap modules and 12 percent for different-bandgap modules. The issue of stability and reliability of amorphous silicon modules is reviewed. Multijunction cell/module structures have demonstrated improved stability in R&D cells and modules over single-junction structures.

  5. Highly efficient ultrathin-film amorphous silicon solar cells on top of imprinted periodic nanodot arrays

    SciTech Connect

    Yan, Wensheng Gu, Min; Tao, Zhikuo; Ong, Thiam Min Brian

    2015-03-02

    The addressing of the light absorption and conversion efficiency is critical to the ultrathin-film hydrogenated amorphous silicon (a-Si:H) solar cells. We systematically investigate ultrathin a-Si:H solar cells with a 100 nm absorber on top of imprinted hexagonal nanodot arrays. Experimental evidences are demonstrated for not only notable silver nanodot arrays but also lower-cost ITO and Al:ZnO nanodot arrays. The measured external quantum efficiency is explained by the simulation results. The J{sub sc} values are 12.1, 13.0, and 14.3 mA/cm{sup 2} and efficiencies are 6.6%, 7.5%, and 8.3% for ITO, Al:ZnO, and silver nanodot arrays, respectively. Simulated optical absorption distribution shows high light trapping within amorphous silicon layer.

  6. An alternative system for mycotoxin detection based on amorphous silicon sensors

    NASA Astrophysics Data System (ADS)

    Caputo, D.; de Cesare, G.; De Rossi, P.; Fanelli, C.; Nascetti, A.; Ricelli, A.; Scipinotti, R.

    2007-05-01

    In this work we investigate, for the first time, the performances of a system based on hydrogenated amorphous silicon photosensors for the detection of Ochratoxin A. The sensor is a n-type/intrinsic/p-type amorphous silicon stacked structure deposited on a glass substrate. The mycotoxin is deposited on a thin layer chromatographic plate and aligned with the sensor. An ultraviolet radiation excites the ochratoxin A, whose fluorescence produces a photocurrent in the sensor. The photocurrent value is proportional to the deposited mycotoxin quantity. An excellent linearity of the detector response over more than two orders of magnitude of ochratoxin A amount is observed. The minimum detected mycotoxin quantity is equal to 0.1ng, suggesting that the presented detection system could be a good candidate to perform rapid and analytical ochratoxin A analysis in different kind of samples.

  7. Research Progress in the DOE/SERI Amorphous Silicon Research Project

    SciTech Connect

    Sabisky, E.; Wallace, W.; Stafford, B.; Sadlon, K.; Luft, W.

    1985-04-01

    The Amorphous Silicon Research Project (ASRP), established at the Solar Energy Research Institute (SERI) in 1983, is responsible for all U.S. DOE government-supported research activities in the field of amorphous silicon photovoltaics. The objectives and research directions of the project have been established by a Five-Year Research Plan developed at SERI in cooperation with the Department of Energy in 1984. In order to accomplish project goals, research is performed by a combination of i) multi-year programs consisting of multi-disciplinary research teams based on strong government/industry partnerships and ii) basic research performed in university, government, and industrial laboratories. A summary of recent research progress in the ASRP program is presented.

  8. Solid-phase epitaxy of silicon amorphized by implantation of the alkali elements rubidium and cesium

    SciTech Connect

    Maier, R.; Haeublein, V.; Ryssel, H.; Voellm, H.; Feili, D.; Seidel, H.; Frey, L.

    2012-11-06

    The redistribution of implanted Rb and Cs profiles in amorphous silicon during solid-phase epitaxial recrystallization has been investigated by Rutherford backscattering spectroscopy and secondary ion mass spectroscopy. For the implantation dose used in these experiments, the alkali atoms segregate at the a-Si/c-Si interface during annealing resulting in concentration peaks near the interface. In this way, the alkali atoms are moved towards the surface. Rutherford backscattering spectroscopy in ion channeling configuration was performed to measure average recrystallization rates of the amorphous silicon layers. Preliminary studies on the influence of the alkali atoms on the solid-phase epitaxial regrowth rate reveal a strong retardation compared to the intrinsic recrystallization rate.

  9. Atomistic modeling of amorphous silicon carbide using a bond-order potential

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.

    2007-02-16

    Molecular dynamics simulations were performed with a Brenner-type bond-order potential to study the melting of silicon carbide (SiC), the structure of amorphous SiC produced by quenching from the melt, and the evolution of the amorphous state after isochronal annealing at elevated temperatures. The simulations reveal that SiC melts above 3700 K with an enthalpy of fusion of about 0.6 eV/atom. The density of the quenched liquid is about 2820 kg/m3, in excellent agreement with the experimental value for SiC amorphized by neutron irradiation. In addition to the loss of long-range order, the quenched liquid shows short-range disorder as measured by the C homonuclear bond ratio. Upon annealing, there is partial recovery of shortrange order.

  10. Molecular dynamics studies of the bonding properties of amorphous silicon nitride coatings on crystalline silicon

    NASA Astrophysics Data System (ADS)

    Butler, Keith T.; Lamers, Machteld P. W. E.; Weeber, Arthur W.; Harding, John H.

    2011-12-01

    In this paper we present molecular dynamics simulations of silicon nitride, both in bulk and as an interface to crystalline silicon. We investigate, in particular, the bonding structure of the silicon nitride and analyze the simulations to search for defective geometries which have been identified as potential charge carrier traps when silicon nitride forms an interface with silicon semiconductors. The simulations reveal how the bonding patterns in silicon nitride are dependent upon the stoichiometry of the system. Furthermore we demonstrate how having an "interphase", where the nitrogen content in silicon gradually reduces toward pure silicon across a boundary region, as opposed to an interface where there is an abrupt drop in nitrogen concentration at the boundary, can result in significantly different numbers of certain important carrier trap.

  11. Highly Efficient Hybrid Polymer and Amorphous Silicon Multijunction Solar Cells with Effective Optical Management.

    PubMed

    Tan, Hairen; Furlan, Alice; Li, Weiwei; Arapov, Kirill; Santbergen, Rudi; Wienk, Martijn M; Zeman, Miro; Smets, Arno H M; Janssen, René A J

    2016-03-16

    Highly efficient hybrid multijunction solar cells are constructed with a wide-bandgap amorphous silicon for the front subcell and a low-bandgap polymer for the back subcell. Power conversion efficiencies of 11.6% and 13.2% are achieved in tandem and triple-junction configurations, respectively. The high efficiencies are enabled by deploying effective optical management and by using photoactive materials with complementary absorption. PMID:26780260

  12. Fluctuating defect density probed with noise spectroscopy in hydrogenated amorphous silicon

    SciTech Connect

    Verleg, P.A.W.E.; Uca, O.; Dijkhuis, J.I.

    1997-07-01

    Resistance fluctuations have been studied in hydrogenated amorphous silicon in the temperature range between 300 K and 450 K. The primary noise source has a power spectrum of approximately 1/f and is ascribed to hydrogen motion. Hopping of weakly bound hydrogen is thermally activated at such low temperatures with an average activation energy of 0.85 eV. The attempt rate amounts to 7 {center_dot} 10{sup 12} s{sup {minus}1}.

  13. Photocapacitance and hole drift mobility measurements in hydrogenated amorphous silicon (a-Si:H)

    SciTech Connect

    Nurdjaja, I.; Schiff, E.A.

    1997-07-01

    The authors present measurements of the photocapacitance in hydrogenated amorphous silicon (a-Si:H) Schottky barrier diodes under reverse bias. A calculation relating photocapacitance to hole drift mobility measurements is also presented; the calculation incorporates the prominent dispersion effect for holes in a-Si:H usually attributed to valence bandtail trapping. The calculation accounts quantitatively for the magnitude and voltage-dependence of the photocapacitance.

  14. High electric field effects on the thermal generation in hydrogenated amorphous silicon

    SciTech Connect

    Ilie, A.; Equer, B.

    1997-07-01

    The authors have studied the electric field dependence of the electron-hole thermal generation process in hydrogenated amorphous silicon. A model was developed which takes into account the Poole-Frenkel effect and the thermally assisted tunneling. In order to explain the experimental results it was necessary to consider a strong electron-lattice interaction describing the carrier tunneling mechanism. Deep defects relaxation is also discussed.

  15. Polarized electroabsorption spectra and light soaking of solar cells based on hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Jiang, Lin; Wang, Qi; Schiff, E. A.; Guha, S.; Yang, J.

    1998-03-01

    We present grazing-incidence measurements of polarized electroabsorption spectra in p-i-n solar cells based on hydrogenated amorphous silicon (a-Si:H). We find a significantly stronger polarization dependence in the present measurements compared with earlier work based on electroabsorption detected using coplanar electrodes on a-Si:H thin films. We do not find any significant dependence of the polarized electroabsorption upon light soaking, although this effect was found in previous work with coplanar electrodes.

  16. Estimation of the adequacy of the fractal model of the atomic structure of amorphous silicon

    SciTech Connect

    Golodenko, A. B.

    2010-01-15

    A method of constructing a fractal model of noncrystalline solid substance is considered using the example of amorphous silicon. In systems of iteration functions, the physical meaning of dihedral and valence angles of the elementary crystallographic cell is assigned to arguments. The model adequacy is estimated by the radial distribution function, the atomic structure density, the distribution of valence and dihedral angles, and the density of dangling interatomic bonds.

  17. Magneto-optical switch with amorphous silicon waveguides on magneto-optical garnet

    NASA Astrophysics Data System (ADS)

    Ishida, Eiichi; Miura, Kengo; Shoji, Yuya; Mizumoto, Tetsuya; Nishiyama, Nobuhiko; Arai, Shigehisa

    2016-08-01

    We fabricated a magneto-optical (MO) switch with a hydrogenated amorphous silicon waveguide on an MO garnet. The switch is composed of a 2 × 2 Mach–Zehnder interferometer (MZI). The switch state is controlled by an MO phase shift through a magnetic field generated by a current flowing in an electrode located on the MZI. The switching operation was successfully demonstrated with an extinction ratio of 11.7 dB at a wavelength of 1550 nm.

  18. Method of controllong the deposition of hydrogenated amorphous silicon and apparatus therefor

    DOEpatents

    Hanak, Joseph J.

    1985-06-25

    An improved method and apparatus for the controlled deposition of a layer of hydrogenated amorphous silicon on a substrate. Means is provided for the illumination of the coated surface of the substrate and measurement of the resulting photovoltage at the outermost layer of the coating. Means is further provided for admixing amounts of p type and n type dopants to the reactant gas in response to the measured photovoltage to achieve a desired level and type of doping of the deposited layer.

  19. The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

    PubMed

    Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

    2015-12-22

    Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. PMID:26523743

  20. Failure analysis of thin-film amorphous-silicon solar-cell modules

    NASA Technical Reports Server (NTRS)

    Kim, Q.

    1984-01-01

    A failure analysis of thin film amorphous silicon solar cell modules was conducted. The purpose of this analysis is to provide information and data for appropriate corrective action that could result in improvements in product quality and reliability. Existing techniques were expanded in order to evaluate and characterize degradational performance of a-Si solar cells. Microscopic and macroscopic defects and flaws that significantly contribute to performance degradation were investigated.

  1. Toughening thin-film structures with ceramic-like amorphous silicon carbide films.

    PubMed

    Matsuda, Yusuke; Ryu, Ill; King, Sean W; Bielefeld, Jeff; Dauskardt, Reinhold H

    2014-01-29

    A significant improvement of adhesion in thin-film structures is demonstrated using embedded ceramic-like amorphous silicon carbide films (a-SiC:H films). a-SiC:H films exhibit plasticity at the nanoscale and outstanding chemical and thermal stability unlike most materials. The multi-functionality and the ease of processing of the films have potential to offer a new toughening strategy for reliability of nanoscale device structures. PMID:23894055

  2. Electron-irradiation-induced crystallization at metallic amorphous/silicon oxide interfaces caused by electronic excitation

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Yamashita, Ryo; Lee, Jung-Goo

    2016-04-01

    Irradiation-induced crystallization of an amorphous phase was stimulated at a Pd-Si amorphous/silicon oxide (a(Pd-Si)/SiOx) interface at 298 K by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Under irradiation, a Pd-Si amorphous phase was initially formed at the crystalline face-centered cubic palladium/silicon oxide (Pd/SiOx) interface, followed by the formation of a Pd2Si intermetallic compound through irradiation-induced crystallization. The irradiation-induced crystallization can be considered to be stimulated not by defect introduction through the electron knock-on effects and electron-beam heating, but by the electronic excitation mechanism. The observed irradiation-induced structural change at the a(Pd-Si)/SiOx and Pd/SiOx interfaces indicates multiple structural modifications at the metal/silicon oxide interfaces through electronic excitation induced by the electron-beam processes.

  3. Control of single-electron charging of metallic nanoparticles onto amorphous silicon surface.

    PubMed

    Weis, Martin; Gmucová, Katarína; Nádazdy, Vojtech; Capek, Ignác; Satka, Alexander; Kopáni, Martin; Cirák, Július; Majková, Eva

    2008-11-01

    Sequential single-electron charging of iron oxide nanoparticles encapsulated in oleic acid/oleyl amine envelope and deposited by the Langmuir-Blodgett technique onto Pt electrode covered with undoped hydrogenated amorphous silicon film is reported. Single-electron charging (so-called quantized double-layer charging) of nanoparticles is detected by cyclic voltammetry as current peaks and the charging effect can be switched on/off by the electric field in the surface region induced by the excess of negative/positive charged defect states in the amorphous silicon layer. The particular charge states in amorphous silicon are created by the simultaneous application of a suitable bias voltage and illumination before the measurement. The influence of charged states on the electric field in the surface region is evaluated by the finite element method. The single-electron charging is analyzed by the standard quantized double layer model as well as two weak-link junctions model. Both approaches are in accordance with experiment and confirm single-electron charging by tunnelling process at room temperature. This experiment illustrates the possibility of the creation of a voltage-controlled capacitor for nanotechnology. PMID:19198289

  4. Meyer-Neldel rule in the space-charge-limited conduction of hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Oversluizen, G.; Nieuwesteeg, K. J. B. M.; Boogaard, J.

    1991-07-01

    The conductivity of a hydrogenated amorphous silicon n+-intrinsic-n+ (n-i-n) structure is reported as a function of temperature. The space-charge-limited conductivity σ is shown to follow the Meyer-Neldel rule (MNR) [W. Meyer and H. Neldel, Z. Tech. Phys. 18, 588 (1937)]: σ =σ00 exp(Ea/kT0) exp(-Ea/kT), where Ea is the conductivity activation energy, k is Boltzmann's constant, and T is the absolute temperature. The characteristic MNR parameters found are σ00=10-2.4±0.1(Ω cm)-1 and T0=590±10 K. These values are practically equal to those previously found for the MNR in the ohmic conductivity in a series of hydrogenated amorphous silicon n-i-n structures with varying i-layer thicknesses. It is argued that the MNR can be quantitatively explained by the statistical shift of the Fermi energy and that a single set of parameters corresponding to σ00 =10-3±1(Ω cm)-1 and T0=550±100 K is applicable for both the space-charge limited and the ohmic conductivity of i-type hydrogenated amorphous silicon. The MNR parameters are rather insensitive to density of states details.

  5. Light-induced Voc increase and decrease in high-efficiency amorphous silicon solar cells

    NASA Astrophysics Data System (ADS)

    Stuckelberger, M.; Riesen, Y.; Despeisse, M.; Schüttauf, J.-W.; Haug, F.-J.; Ballif, C.

    2014-09-01

    High-efficiency amorphous silicon (a-Si:H) solar cells were deposited with different thicknesses of the p-type amorphous silicon carbide layer on substrates of varying roughness. We observed a light-induced open-circuit voltage (Voc) increase upon light soaking for thin p-layers, but a decrease for thick p-layers. Further, the Voc increase is enhanced with increasing substrate roughness. After correction of the p-layer thickness for the increased surface area of rough substrates, we can exclude varying the effective p-layer thickness as the cause of the substrate roughness dependence. Instead, we explain the observations by an increase of the dangling-bond density in both the p-layer—causing a Voc increase—and in the intrinsic absorber layer, causing a Voc decrease. We present a mechanism for the light-induced increase and decrease, justified by the investigation of light-induced changes of the p-layer and supported by Advanced Semiconductor Analysis simulation. We conclude that a shift of the electron quasi-Fermi level towards the conduction band is the reason for the observed Voc enhancements, and poor amorphous silicon quality on rough substrates enhances this effect.

  6. Diagnostics of a glow discharge used to produce hydrogenated amorphous silicon films. Final subcontract report

    SciTech Connect

    Gallagher, A.

    1984-11-01

    This report and recent publications cited summarize our measurements of the neutral radicals produced in pure silane discharges, our measurements of the interaction of silane with a growing amorphous silicon surface, qualitative models of discharge neutral radical chemistry, and quantitative models of dc discharge ion chemistry. All radicals of the monosilane and disilane groups have been measured and are reported as a function of discharge parameters, but not yet for the full range of parameters that must be investigated for detailed analysis. Observations of the reaction of SiH/sub 4/ with a hot amorphous silicon surface are given. These are closely related to the dominant discharge film deposition mechanism of SiH/sub 3/ reacting with a hydrogen covered amorphous silicon surface and a surface reaction model is suggested that explains some but not all of our data. The dc discharge model is used to obtain quantitative predictions of the ion species at the cathode surface of a dc discharge. This is compared to observations and used to explain the observations at our laboratory and other laboratories. We conclude that most but not all features of the ion chemistry in dc discharges of pure silane can be relatively well understood from this model.

  7. The Spatial Effects of Antenna Configuration in a Large Area Inductively Coupled Plasma System for Flat Panel Displays

    NASA Astrophysics Data System (ADS)

    Seon-Geun, Oh; Young-Jun, Lee; Jae-Hong, Jeon; Jong-Hyeon, Seo; Hee-Hwan, Choe

    2014-08-01

    Spatial distributions of plasma parameters such as electron density, electron temperature and electric potential were investigated using a commercial simulation software (COMSOLTM) to predict the effects of antenna configuration in a large area inductively coupled plasma (ICP) system for flat panel displays. Nine planar antenna sets were evenly placed above a ceramic window. While the electron density was influenced by both the input current and gas pressure, the electron temperature and electric potential were dominantly affected by the gas pressure.

  8. Using LROC analysis to evaluate detection accuracy of microcalcification clusters imaged with flat-panel CT mammography

    NASA Astrophysics Data System (ADS)

    Gong, Xing; Glick, Stephen J.; Vedula, Aruna A.

    2004-05-01

    The purpose of this study is to investigate the detectability of microcalcification clusters (MCCs) using CT mammography with a flat-panel detector. Compared with conventional mammography, CT mammography can provide improved discrimination between malignant and benign cases as it can provide the radiologist with more accurate morphological information on MCCs. In this study, two aspects of MCC detection with flat-panel CT mammography were examined: (1) the minimal size of MCCs detectable with mean glandular dose (MGD) used in conventional mammography; (2) the effect of different detector pixel size on the detectability of MCCs. A realistic computer simulation modeling x-ray transport through the breast, as well as both signal and noise propagation through the flat-panel imager, was developed to investigate these questions. Microcalcifications were simulated as calcium carbonate spheres with diameters set at the levels of 125, 150 and 175 μm. Each cluster consisted of 10 spheres spread randomly in a 6×6 mm2 region of interest (ROI) and the detector pixel size was set to 100×100, 200×200, or 300×300μm2. After reconstructing 100 projection sets for each case (half with signal present) with the cone-beam Feldkamp (FDK) algorithm, a localization receiver operating characteristic (LROC) study was conducted to evaluate the detectability of MCCs. Five observers chose the locations of cluster centers with correspondent confidence ratings. The average area under the LROC curve suggested that the 175 μm MCCs can be detected at a high level of confidence. Results also indicate that flat-panel detectors with pixel size of 200×200 μm2 are appropriate for detecting small targets, such as MCCs.

  9. A flat-panel detector based micro-CT system: performance evaluation for small-animal imaging.

    PubMed

    Lee, Sang Chul; Kim, Ho Kyung; Chun, In Kon; Cho, Myung Hye; Lee, Soo Yeol; Cho, Min Hyoung

    2003-12-21

    A dedicated small-animal x-ray micro computed tomography (micro-CT) system has been developed to screen laboratory small animals such as mice and rats. The micro-CT system consists of an indirect-detection flat-panel x-ray detector with a field-of-view of 120 x 120 mm2, a microfocus x-ray source, a rotational subject holder and a parallel data processing system. The flat-panel detector is based on a matrix-addressed photodiode array fabricated by a CMOS (complementary metal-oxide semiconductor) process coupled to a CsI:T1 (thallium-doped caesium iodide) scintillator as an x-ray-to-light converter. Principal imaging performances of the micro-CT system have been evaluated in terms of image uniformity, voxel noise and spatial resolution. It has been found that the image non-uniformity mainly comes from the structural non-uniform sensitivity pattern of the flat-panel detector and the voxel noise is about 48 CT numbers at the voxel size of 100 x 100 x 200 microm3 and the air kerma of 286 mGy. When the magnification ratio is 2, the spatial resolution of the micro-CT system is about 14 1p/mm (line pairs per millimetre) that is almost determined by the flat-panel detector showing about 7 1p/mm resolving power. Through low-contrast phantom imaging studies, the minimum resolvable contrast has been found to be less than 36 CT numbers at the air kerma of 95 mGy. Some laboratory rat imaging results are presented. PMID:14727760

  10. Influence of Flat-Panel Fluoroscopic Equipment Variables on Cardiac Radiation Doses

    SciTech Connect

    Nickoloff, Edward L. Lu Zhengfeng; Dutta, Ajoy; So, James; Balter, Stephen; Moses, Jeffrey

    2007-04-15

    Purpose. To assess the influence of physician-selectable equipment variables on the potential radiation dose reductions during cardiac catheterization examinations using modern imaging equipment. Materials. A modern bi-plane angiography unit with flat-panel image receptors was used. Patients were simulated with 15-30 cm of acrylic plastic. The variables studied were: patient thickness, fluoroscopy pulse rates, record mode frame rates, image receptor field-of-view (FoV), automatic dose control (ADC) mode, SID/SSD geometry setting, automatic collimation, automatic positioning, and others. Results. Patient radiation doses double for every additional 3.5-4.5 cm of soft tissue. The dose is directly related to the imaging frame rate; a decrease from 30 pps to 15 pps reduces the dose by about 50%. The dose is related to [(FoV){sup -N}] where 2.0 < N < 3.0. Suboptimal positioning of the patient can nearly double the dose. The ADC system provides three selections that can vary the radiation level by 50%. For pediatric studies (2-5 years old), the selection of equipment variables can result in entrance radiation doses that range between 6 and 60 cGy for diagnostic cases and between 15 and 140 cGy for interventional cases. For adult studies, the equipment variables can produce entrance radiation doses that range between 13 and 130 cGy for diagnostic cases and between 30 and 400 cGy for interventional cases. Conclusions. Overall dose reductions of 70-90% can be achieved with pediatric patients and about 90% with adult patients solely through optimal selection of equipment variables.

  11. Generalized DQE analysis of radiographic and dual-energy imaging using flat-panel detectors

    SciTech Connect

    Richard, S.; Siewerdsen, J.H.; Jaffray, D.A.; Moseley, D.J.; Bakhtiar, B.

    2005-05-01

    Analysis of detective quantum efficiency (DQE) is an important component of the investigation of imaging performance for flat-panel detectors (FPDs). Conventional descriptions of DQE are limited, however, in that they take no account of anatomical noise (i.e., image fluctuations caused by overlying anatomy), even though such noise can be the most significant limitation to detectability, often outweighing quantum or electronic noise. We incorporate anatomical noise in experimental and theoretical descriptions of the 'generalized DQE' by including a spatial-frequency-dependent noise-power term, S{sub B}, corresponding to background anatomical fluctuations. Cascaded systems analysis (CSA) of the generalized DQE reveals tradeoffs between anatomical noise and the factors that govern quantum noise. We extend such analysis to dual-energy (DE) imaging, in which the overlying anatomical structure is selectively removed in image reconstructions by combining projections acquired at low and high kVp. The effectiveness of DE imaging in removing anatomical noise is quantified by measurement of S{sub B} in an anthropomorphic phantom. Combining the generalized DQE with an idealized task function to yield the detectability index, we show that anatomical noise dramatically influences task-based performance, system design, and optimization. For the case of radiography, the analysis resolves a fundamental and illustrative quandary: The effect of kVp on imaging performance, which is poorly described by conventional DQE analysis but is clarified by consideration of the generalized DQE. For the case of DE imaging, extension of a generalized CSA methodology reveals a potentially powerful guide to system optimization through the optimal selection of the tissue cancellation parameter. Generalized task-based analysis for DE imaging shows an improvement in the detectability index by more than a factor of 2 compared to conventional radiography for idealized detection tasks.

  12. Evaluation of the potential utility of flat panel CT for quantifying relative contrast enhancement

    SciTech Connect

    Jones, A. Kyle; Mahvash, Armeen

    2012-07-15

    Purpose: Certain directed oncologic therapies seek to take advantage of the fact that tumors are typically more susceptible to directed therapeutic agents than normal tissue owing to their extensive networks of poorly formed, leaky vasculature. If differences between the vascularity of normal and tumor tissues could be quantified, patients could be selected for or excluded from directed treatments on the basis of this difference. However, angiographic imaging techniques such as digital subtraction angiography (DSA) yield two-dimensional data that may be inadequate for this task. As a first step, the authors evaluated the feasibility of using a commercial implementation of flat panel computed tomography (FPCT) to quantify differences in enhancement of a simulated tumor compared with normal tissue based on differences in CT number measured in precontrast and postcontrast scans. Methods: To evaluate the FPCT scanner studied, the authors scanned several phantoms containing simulated normal and tumor tissues. In the first experiment, the authors used an anthropomorphic phantom containing inclusions representing normal, tumor, and bone tissue to evaluate the constancy of CT numbers in scans repeated at clinically relevant intervals of 1 and 3 min. The authors then scanned gelatin phantoms containing dilutions of iodinated contrast to evaluate the accuracy of relative contrast enhancement measurements for a clinical FPCT system. Data were analyzed using widely available software. Results: CT numbers measured in identical locations were constant over both scan intervals evaluated. Measured relative contrast enhancement values were accurate compared with known relative contrast enhancement values. Care must be taken to avoid artifacts in reconstructed images when placing regions of interest. Conclusions: Despite its limitations, FPCT in the interventional laboratory can be used to quantify relative contrast enhancement in phantoms. This is accomplished by measuring CT

  13. Dual-Energy Subtraction Imaging for Diagnosing Vocal Cord Paralysis with Flat Panel Detector Radiography

    PubMed Central

    Yoda, Keiko; Arai, Yasuko; Nishida, Suguru; Masukawa, Ai; Asanuma, Masayasu; Yuhara, Toshiyuki; Morita, Satoru; Suzuki, Kazufumi; Ueno, Eiko; Sabol, John M

    2010-01-01

    Objective To investigate the clinical feasibility of dual energy subtraction (DES) imaging to improve the delineation of the vocal cord and diagnostic accuracy of vocal cord paralysis as compared with the anterior-posterior view of flat panel detector (FPD) neck radiography. Materials and Methods For 122 consecutive patients who underwent both a flexible laryngoscopy and conventional/DES FPD radiography, three blinded readers retrospectively graded the radiographs during phonation and inspiration on a scale of 1 (poor) to 5 (excellent) for the delineation of the vocal cord, and in consensus, reviewed the diagnostic accuracy of vocal cord paralysis employing the laryngoscopy as the reference. We compared vocal cord delineation scores and accuracy of vocal cord paralysis diagnosis by both conventional and DES techniques using κ statistics and assessing the area under the receiver operating characteristic curve (AUC). Results Vocal cord delineation scores by DES (mean, 4.2 ± 0.4) were significantly higher than those by conventional imaging (mean, 3.3 ± 0.5) (p < 0.0001). Sensitivity for diagnosing vocal cord paralysis by the conventional technique was 25%, whereas the specificity was 94%. Sensitivity by DES was 75%, whereas the specificity was 96%. The diagnostic accuracy by DES was significantly superior (κ = 0.60, AUC = 0.909) to that by conventional technique (κ = 0.18, AUC = 0.852) (p = 0.038). Conclusion Dual energy subtraction is a superior method compared to the conventional FPD radiography for delineating the vocal cord and accurately diagnosing vocal cord paralysis. PMID:20461186

  14. Cone Beam Breast CT with a Flat Panel Detector- Simulation, Implementation and Demonstration.

    PubMed

    Shaw, Chris; Chen, Lingyun; Altunbas, Mastafa; Tu, Shuju; Wang, Tian-Peng; Lai, Chao-Jen; Cheenu Kappadath, S; Meng, Yang; Liu, Xinming

    2005-01-01

    This paper describes our experiences in the simulation, implementation and application of a flat panel detector based cone beam computed tomography (CT) imaging system for dedicated 3-D breast imaging. In our simulation study, the breast was analytically modeled as a cylinder of breast tissue loosely molded into cylindrical shape with embedded soft tissue masses and calcifications. Attenuation coefficients for various types of breast tissue, soft tissue masses and calcifications were estimated for various kVp's to generate simulated image signals. Projection images were computed to incorporate x-ray attenuation, geometric magnification, x-ray detection, detector blurring, image pixelization and digitization. Based on the x-ray kVp/filtration used, transmittance through the phantom, detective quantum efficiency (DQE), exposure level, and imaging geometry, the photon fluence was estimated and used to compute the quantum noise level on a pixel-by-pixel basis for various dose levels at the isocenter. This estimated noise level was then used with a random number generator to generate and add a fluctuation component to the noiseless transmitted image signal. The noise carrying projection images were then convolved with a Gaussian-like kernel, computed from measured 1-D line spread function (LSF) to simulate detector blurring. Additional 2-D Gaussian filtering was applied to the projection images and tested for improving the detection of soft tissue masses and calcifications in the reconstructed images. Reconstruction was performed using the Feldkamp filtered backprojection algorithm. All simulations were performed on a 24 PC (2.4 GHz Dual-Xeon CPU) cluster with MPI parallel programming. PMID:17281227

  15. Optimization of outdoor cultivation in flat panel airlift reactors for lipid production by Chlorella vulgaris.

    PubMed

    Münkel, Ronja; Schmid-Staiger, Ulrike; Werner, Achim; Hirth, Thomas

    2013-11-01

    Microalgae are discussed as a potential renewable feedstock for biofuel production. The production of highly concentrated algae biomass with a high fatty acid content, accompanied by high productivity with the use of natural sunlight is therefore of great interest. In the current study an outdoor pilot plant with five 30 L Flat Panel Airlift reactors (FPA) installed southwards were operated in 2011 in Stuttgart, Germany. The patented FPA reactor works on the basis of an airlift loop reactor and offers efficient intermixing for homogeneous light distribution. A lipid production process with the microalgae Chlorella vulgaris (SAG 211-12), under nitrogen and phosphorous deprivation, was established and evaluated in regard to the fatty acid content, fatty acid productivity and light yield. In the first set of experiments limitations caused by restricted CO₂ availability were excluded by enriching the media with NaOH. The higher alkalinity allows a higher CO₂ content of supplied air and leads to doubling of fatty acid productivity. The second set of experiments focused on how the ratio of light intensity to biomass concentration in the reactor impacts fatty acid content, productivity and light yield. The specific light availability was specified as mol photons on the reactor surface per gram biomass in the reactor. This is the first publication based on experimental data showing the quantitative correlation between specific light availability, fatty acid content and biomass light yield for a lipid production process under nutrient deprivation and outdoor conditions. High specific light availability leads to high fatty acid contents. Lower specific light availability increases fatty acid productivity and biomass light yield. An average fatty acid productivity of 0.39 g L⁻¹  day⁻¹ for a 12 days batch process with a final fatty acid content of 44.6% [w/w] was achieved. Light yield of 0.4 g mol photons⁻¹ was obtained for the first 6 days of

  16. The effect of discontinuous airlift mixing in outdoor flat panel photobioreactors on growth of Scenedesmus obliquus.

    PubMed

    Leupold, Marco; Hindersin, Stefan; Kerner, Martin; Hanelt, Dieter

    2013-11-01

    Discontinuous airlift mixing was realized by injecting pressured air at time intervals with a frequency between 0.033 and 0.25 Hz (at 80 kPa; i.e., every 4-30 s; valve opening time 800 ms) into outdoor flat panel photobioreactors ([Formula: see text]). This caused a flow velocity between 2 and 20 cm s(-1) of the culture medium within the photobioreactor and the mixing time was between 38 and 103.5 s, requiring 0.175-1.340 L(gas volume) L(photobioreactor volume)(-1) min(-1) pressured air. In order to detect the effect on growth of Scenedesmus obliquus during outdoor experiments and to be able to compare obtained results, a batch run with an airlift frequency of 0.25 Hz was simultaneously used as control. Growth at different airlift frequencies was measured by the increase of cell dry weight (CDW) during 3-5 days and biomass yield on light energy was calculated. With increasing airlift frequencies, growth increased from 52 to 91 % compared to the control. When CDW was at around 1.0-1.5 g L(-1), airlift frequency had no effect on growth, indicating that mass transfer gradients of nutrients and gas were not the limiting factors of growth. Above 1.5 g CDW L(-1), growth increased with increasing airlift frequency and light limitation for a single cell occurred. This effect was observed during low and high irradiance and it is concluded that a higher mean flow causes a better light distribution, resulting in an enhanced growth. Biomass productivity and demand of pressured air are correlated logarithmically, which enables to save mixing energy during cultivation. PMID:23494400

  17. Assessment of the CO2 fixation capacity of Anabaena sp. ATCC 33047 outdoor cultures in vertical flat-panel reactors.

    PubMed

    Clares, Marta E; Moreno, José; Guerrero, Miguel G; García-González, Mercedes

    2014-10-10

    The extent of biological CO2 fixation was evaluated for outdoor cultures of the cyanobacterium Anabaena sp. ATCC 33047. Culture conditions were optimized indoors in bubble-column photochemostats operating in continuous mode, subjected to irradiance cycles mimicking the light regime outdoors. Highest values achieved for CO2 fixation rate and biomass productivity were 1 and 0.6 g L(-1) day(-1), respectively. The comparison among different reactors operating simultaneously - open pond, horizontal tubular reactor and vertical flat-panel - allowed to assess their relative efficiency for the outdoor development of Anabaena cultures. Despite the higher volumetric CO2 fixation capacity (and biomass productivity) exhibited by the tubular photobioreactor, yield of the flat-panel reactor was 50% higher than that of the tubular option on a per area basis, reaching values over 35 g CO2 fixed m(-2) d(-1). The flat-panel reactor actually represents a most suitable system for CO2 capture coupled to the generation of valuable biomass by Anabaena cultures. PMID:25068618

  18. Experimental evaluation of a-Se and CdTe flat-panel x-ray detectors for digital radiography and fluoroscopy

    NASA Astrophysics Data System (ADS)

    Adachi, Susumu; Hori, Naoyuki; Sato, Kenji; Tokuda, Satoshi; Sato, Toshiyuki; Uehara, Kazuhiro; Izumi, Yoshihiro; Nagata, Hisashi; Yoshimura, Youji; Yamada, Satoshi

    2000-04-01

    Described are two types of direct-detection flat-panel X-ray detectors utilizing amorphous selenium (a-Se) and cadmium telluride (CdTe). The a-Se detector is fabricated using direct deposition onto a thin film transistor (TFT) substrate, whereas the CdTe detector is fabricated using a novel hybrid method, in which CdTe is pre-deposited onto a glass substrate and then connected to a TFT substrate. The detector array format is 512 X 512 with a pixel pitch of 150 micrometer. The imaging properties of both detectors have been evaluated with respect to X-ray sensitivity, lag, spatial resolution, and detective quantum efficiency (DQE). The modulation transfer functions (MTFs) measured at 1 lp/mm were 0.96 for a- Se and 0.65 for CdTe. The imaging lags after 33 ms were about 4% for a-Se and 22% for CdTe. The DQE values measured at zero spatial frequency were 0.75 for a-Se and 0.22 for CdTe. The results indicate that the a-Se and CdTe detectors have high potential as new digital X-ray imaging devices for both radiography and fluoroscopy.

  19. Amorphous silicon thin films: The ultimate lightweight space solar cell

    NASA Technical Reports Server (NTRS)

    Vendura, G. J., Jr.; Kruer, M. A.; Schurig, H. H.; Bianchi, M. A.; Roth, J. A.

    1994-01-01

    Progress is reported with respect to the development of thin film amorphous (alpha-Si) terrestrial solar cells for space applications. Such devices promise to result in very lightweight, low cost, flexible arrays with superior end of life (EOL) performance. Each alpha-Si cell consists of a tandem arrangement of three very thin p-i-n junctions vapor deposited between film electrodes. The thickness of this entire stack is approximately 2.0 microns, resulting in a device of negligible weight, but one that must be mechanically supported for handling and fabrication into arrays. The stack is therefore presently deposited onto a large area (12 by 13 in), rigid, glass superstrate, 40 mil thick, and preliminary space qualification testing of modules so configured is underway. At the same time, a more advanced version is under development in which the thin film stack is transferred from the glass onto a thin (2.0 mil) polymer substrate to create large arrays that are truly flexible and significantly lighter than either the glassed alpha-Si version or present conventional crystalline technologies. In this paper the key processes for such effective transfer are described. In addition, both glassed (rigid) and unglassed (flexible) alpha-Si cells are studied when integrated with various advanced structures to form lightweight systems. EOL predictions are generated for the case of a 1000 W array in a standard, 10 year geosynchronous (GEO) orbit. Specific powers (W/kg), power densities (W/sq m) and total array costs ($/sq ft) are compared.

  20. Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides.

    PubMed

    Narayanan, Karthik; Elshaari, Ali W; Preble, Stefan F

    2010-05-10

    We demonstrate broadband all-optical modulation in low loss hydrogenated-amorphous silicon (a-Si:H) waveguides. Significant modulation (approximately 3 dB) occurs with a device of only 15 microm without the need for cavity interference effects in stark contrast to an identical crystalline silicon waveguide. We attribute the enhanced modulation to the significantly larger free-carrier absorption effect of a-Si:H, estimated here to be alpha = 1.6310(-16)N cm(-1). In addition, we measured the modulation time to be only tau(c) approximately 400 ps, which is comparable to the recombination rate measured in sub-micron crystalline silicon waveguides, illustrating the strong dominance of surface recombination in similar sized (460 nm x 250 nm) a-Si:H waveguides. Consequently, a-Si:H could serve as a high performance platform for backend integrated CMOS photonics. PMID:20588830

  1. Integration of epitaxially-grown InGaAs/GaAs quantum dot lasers with hydrogenated amorphous silicon waveguides on silicon.

    PubMed

    Yang, Jun; Bhattacharya, Pallab

    2008-03-31

    The monolithic integration of epitaxially-grown InGaAs/GaAs self-organized quantum dot lasers with hydrogenated amorphous silicon (a:Si-H) waveguides on silicon substrates is demonstrated. Hydrogenated amorphous silicon waveguides, formed by plasma-enhanced-chemical-vapor deposition (PECVD), exhibit a propagation loss of approximately 10 dB/cm at a wavelength of 1.05 microm. The laser-waveguide coupling, with coupling coefficient of 22%, is achieved through a 3.2 microm-width groove etched by focused-ion-beam (FIB) milling which creates high-quality etched GaAs facets. PMID:18542613

  2. Percolation network in resistive switching devices with the structure of silver/amorphous silicon/p-type silicon

    SciTech Connect

    Liu, Yanhong; Gao, Ping; Bi, Kaifeng; Peng, Wei; Jiang, Xuening; Xu, Hongxia

    2014-01-27

    Conducting pathway of percolation network was identified in resistive switching devices (RSDs) with the structure of silver/amorphous silicon/p-type silicon (Ag/a-Si/p-Si) based on its gradual RESET-process and the stochastic complex impedance spectroscopy characteristics (CIS). The formation of the percolation network is attributed to amounts of nanocrystalline Si particles as well as defect sites embedded in a-Si layer, in which the defect sites supply positions for Ag ions to nucleate and grow. The similar percolation network has been only observed in Ag-Ge-Se based RSD before. This report provides a better understanding for electric properties of RSD based on the percolation network.

  3. Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

    SciTech Connect

    Wen, Guozhi; Zeng, Xiangbin Wen, Xixin; Liao, Wugang

    2014-04-28

    Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

  4. Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

    NASA Astrophysics Data System (ADS)

    Wen, Guozhi; Zeng, Xiangbin; Wen, Xixin; Liao, Wugang

    2014-04-01

    Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.

  5. Amorphous silicon thin film for all-optical micromodulator

    NASA Astrophysics Data System (ADS)

    Nigro, Maria Arcangela M.; Cantore, Francesca; Della Corte, Francesco Giuseppe; Summonte, Caterina

    2003-04-01

    Photoinduced absorption by VIS radiation in a-Si:H has been studied in-guide, in order to realise a novel all-optical waveguide micromodulator for application at 1.3 and 1.55 μm fiber communication wavelengths. In a-Si:H the photoinduced effects and the NIR absorption both involve dangling bonds states. The density of these states, deep in the gap, can be varied with doping. Therefore three waveguide prototypes have been fabricated by Plasma Enhanced Chemical Vapour Deposition on a silicon wafer. Their structure consist of a a-Si:H/SiO2 stack where the a-Si:H cores have different doping. The upper cladding is air. Optical measures on the core materials and signal transmission analysis in-guide at bit rates up to 200 kBit/s have been carried out. The excitation source of the VIS pump system for in-guide analysis consisted of simple, low cost AlInGaP LED"s controlled by a pulse generator. The pump and probe measures have been performed with different pump wavelengths and by varying the illumination intensity. LED"s with wavelengths of 644, 612, 590 and 571 nm have been alternatively used. For each pump wavelength, the light intensity was varied between 0,15 and 0,85 mW/mm2. The results confirms that the optical modulation of the NIR signal enhances at high doping levels and for longer wavelengths. The modulation speed is probably limited by recombination phenomena.

  6. High-resolution secondary reconstructions with the use of flat panel CT in the clinical assessment of patients with cochlear implants.

    PubMed

    Pearl, M S; Roy, A; Limb, C J

    2014-06-01

    Radiologic assessment of cochlear implants can be limited because of metallic streak artifacts and the high attenuation of the temporal bones. We report on 14 patients with 18 cochlear implants (17 Med-El standard 31.5-mm arrays, 1 Med-El medium 24-mm array) who underwent flat panel CT with the use of high-resolution secondary reconstruction techniques. Flat panel CT depicted the insertion site, cochlear implant course, and all 216 individual electrode contacts. The calculated mean angular insertion depth for standard arrays was 591.9° (SD = 70.9; range, 280°). High-resolution secondary reconstructions of the initial flat panel CT dataset, by use of a manually generated field of view, Hounsfield unit kernel type, and sharp image characteristics, provided high-quality images with improved spatial resolution. Flat panel CT is a promising imaging tool for the postoperative evaluation of cochlear implant placement. PMID:24371026

  7. Integration of an amorphous silicon passive pixel sensor array with a lateral amorphous selenium detector for large area indirect conversion x-ray imaging applications

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Yazdandoost, Mohammad Y.; Keshavarzi, Rasoul; Shin, Kyung-Wook; Hristovski, Christos; Abbaszadeh, Shiva; Chen, Feng; Majid, Shaikh Hasibul; Karim, Karim S.

    2011-03-01

    Previously, we reported on a single-pixel detector based on a lateral a-Se metal-semiconductor-metal structure, intended for indirect conversion X-ray imaging. This work is the continuous effort leading to the first prototype of an indirect conversion X-ray imaging sensor array utilizing lateral amorphous selenium. To replace a structurally-sophisticated vertical multilayer amorphous silicon photodiode, a lateral a-Se MSM photodetector is employed which can be easily integrated with an amorphous silicon thin film transistor passive pixel sensor array. In this work, both 2×2 macro-pixel and 32×32 micro-pixel arrays were fabricated and tested along with discussion of the results.

  8. On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide

    NASA Astrophysics Data System (ADS)

    Yu, Liping; Raj, Rishi

    2015-09-01

    A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

  9. On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide.

    PubMed

    Yu, Liping; Raj, Rishi

    2015-01-01

    A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side. PMID:26419962

  10. Programmable SERS active substrates for chemical and biosensing applications using amorphous/crystalline hybrid silicon nanomaterial

    NASA Astrophysics Data System (ADS)

    Powell, Jeffery Alexander; Venkatakrishnan, Krishnan; Tan, Bo

    2016-01-01

    We present the creation of a unique nanostructured amorphous/crystalline hybrid silicon material that exhibits surface enhanced Raman scattering (SERS) activity. This nanomaterial is an interconnected network of amorphous/crystalline nanospheroids which form a nanoweb structure; to our knowledge this material has not been previously observed nor has it been applied for use as a SERS sensing material. This material is formed using a femtosecond synthesis technique which facilitates a laser plume ion condensation formation mechanism. By fine-tuning the laser plume temperature and ion interaction mechanisms within the plume, we are able to precisely program the relative proportion of crystalline Si to amorphous Si content in the nanospheroids as well as the size distribution of individual nanospheroids and the size of Raman hotspot nanogaps. With the use of Rhodamine 6G (R6G) and Crystal Violet (CV) chemical dyes, we have been able to observe a maximum enhancement factor of 5.38 × 106 and 3.72 × 106 respectively, for the hybrid nanomaterial compared to a bulk Si wafer substrate. With the creation of a silicon-based nanomaterial capable of SERS detection of analytes, this work demonstrates a redefinition of the role of nanostructured Si from an inactive to SERS active role in nano-Raman sensing applications.

  11. On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide

    PubMed Central

    Yu, Liping; Raj, Rishi

    2015-01-01

    A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side. PMID:26419962

  12. Programmable SERS active substrates for chemical and biosensing applications using amorphous/crystalline hybrid silicon nanomaterial

    PubMed Central

    Powell, Jeffery Alexander; Venkatakrishnan, Krishnan; Tan, Bo

    2016-01-01

    We present the creation of a unique nanostructured amorphous/crystalline hybrid silicon material that exhibits surface enhanced Raman scattering (SERS) activity. This nanomaterial is an interconnected network of amorphous/crystalline nanospheroids which form a nanoweb structure; to our knowledge this material has not been previously observed nor has it been applied for use as a SERS sensing material. This material is formed using a femtosecond synthesis technique which facilitates a laser plume ion condensation formation mechanism. By fine-tuning the laser plume temperature and ion interaction mechanisms within the plume, we are able to precisely program the relative proportion of crystalline Si to amorphous Si content in the nanospheroids as well as the size distribution of individual nanospheroids and the size of Raman hotspot nanogaps. With the use of Rhodamine 6G (R6G) and Crystal Violet (CV) chemical dyes, we have been able to observe a maximum enhancement factor of 5.38 × 106 and 3.72 × 106 respectively, for the hybrid nanomaterial compared to a bulk Si wafer substrate. With the creation of a silicon-based nanomaterial capable of SERS detection of analytes, this work demonstrates a redefinition of the role of nanostructured Si from an inactive to SERS active role in nano-Raman sensing applications. PMID:26785682

  13. Programmable SERS active substrates for chemical and biosensing applications using amorphous/crystalline hybrid silicon nanomaterial.

    PubMed

    Powell, Jeffery Alexander; Venkatakrishnan, Krishnan; Tan, Bo

    2016-01-01

    We present the creation of a unique nanostructured amorphous/crystalline hybrid silicon material that exhibits surface enhanced Raman scattering (SERS) activity. This nanomaterial is an interconnected network of amorphous/crystalline nanospheroids which form a nanoweb structure; to our knowledge this material has not been previously observed nor has it been applied for use as a SERS sensing material. This material is formed using a femtosecond synthesis technique which facilitates a laser plume ion condensation formation mechanism. By fine-tuning the laser plume temperature and ion interaction mechanisms within the plume, we are able to precisely program the relative proportion of crystalline Si to amorphous Si content in the nanospheroids as well as the size distribution of individual nanospheroids and the size of Raman hotspot nanogaps. With the use of Rhodamine 6G (R6G) and Crystal Violet (CV) chemical dyes, we have been able to observe a maximum enhancement factor of 5.38 × 10(6) and 3.72 × 10(6) respectively, for the hybrid nanomaterial compared to a bulk Si wafer substrate. With the creation of a silicon-based nanomaterial capable of SERS detection of analytes, this work demonstrates a redefinition of the role of nanostructured Si from an inactive to SERS active role in nano-Raman sensing applications. PMID:26785682

  14. Impact and Penetration of Thin Aluminum 2024 Flat Panels at Oblique Angles of Incidence

    NASA Technical Reports Server (NTRS)

    Ruggeri, Charles R.; Revilock, Duane M.; Pereira, J. Michael; Emmerling, William; Queitzsch, Gilbert K., Jr.

    2015-01-01

    under more extreme conditions, using a projectile with a more complex shape and sharp contacts, impacting flat panels at oblique angles of incidence.

  15. A forward bias method for lag correction of an a-Si flat panel detector

    PubMed Central

    Starman, Jared; Tognina, Carlo; Partain, Larry; Fahrig, Rebecca

    2012-01-01

    Purpose: Digital a-Si flat panel (FP) x-ray detectors can exhibit detector lag, or residual signal, of several percent that can cause ghosting in projection images or severe shading artifacts, known as the radar artifact, in cone-beam computed tomography (CBCT) reconstructions. A major contributor to detector lag is believed to be defect states, or traps, in the a-Si layer of the FP. Software methods to characterize and correct for the detector lag exist, but they may make assumptions such as system linearity and time invariance, which may not be true. The purpose of this work is to investigate a new hardware based method to reduce lag in an a-Si FP and to evaluate its effectiveness at removing shading artifacts in CBCT reconstructions. The feasibility of a novel, partially hardware based solution is also examined. Methods: The proposed hardware solution for lag reduction requires only a minor change to the FP. For pulsed irradiation, the proposed method inserts a new operation step between the readout and data collection stages. During this new stage the photodiode is operated in a forward bias mode, which fills the defect states with charge. A Varian 4030CB panel was modified to allow for operation in the forward bias mode. The contrast of residual lag ghosts was measured for lag frames 2 and 100 after irradiation ceased for standard and forward bias modes. Detector step response, lag, SNR, modulation transfer function (MTF), and detective quantum efficiency (DQE) measurements were made with standard and forward bias firmware. CBCT data of pelvic and head phantoms were also collected. Results: Overall, the 2nd and 100th detector lag frame residual signals were reduced 70%–88% using the new method. SNR, MTF, and DQE measurements show a small decrease in collected signal and a small increase in noise. The forward bias hardware successfully reduced the radar artifact in the CBCT reconstruction of the pelvic and head phantoms by 48%–81%. Conclusions: Overall, the

  16. System performance of a prototype flat-panel imager operated under mammographic conditions.

    PubMed

    Jee, Kyung-Wook; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua

    2003-07-01

    The results of an empirical and theoretical investigation of the performance of a high-resolution, active matrix flat-panel imager performed under mammographic conditions are reported. The imager is based upon a prototype, indirect detection active matrix array incorporating a discrete photodiode in each pixel and a pixel-to-pixel pitch of 97 microm. The investigation involved three imager configurations corresponding to the use of three different x-ray converters with the array. The converters were a conventional Gd2O2S-based mammographic phosphor screen (Min-R) and two structured CsI:Tl scintillators: one optimized for high spatial resolution (FOS-HR) and the other for high light output (FOS-HL). Detective quantum efficiency for mammographic exposures ranging from approximately 2 to approximately 40 mR at 26 kVp were determined for each imager configuration through measurements of x-ray sensitivity, modulation transfer function (MTF), and noise power spectrum (NPS). All configurations were found to provide significant presampling MTF at frequencies beyond the Nyquist frequency of the array, approximately 5.2 mm(-1) , consistent with the high spatial resolution of the converters. In addition, the effect of additive electronic noise on the NPS was found to be significantly larger for the configuration with lower system gain (FOS-HR) than for the configurations with higher gain (Min-R, FOS-HL). The maximum DQE values obtained with the CsI:Tl scintillators were considerably greater than those obtained with the Min-R screen due to the significantly lower Swank noise of the scintillators. Moreover, DQE performance was found to degrade with decreasing exposure, although this exposure-dependence was considerably reduced for the higher gain configurations. Theoretical calculations based on the cascaded systems model were found to be in generally good agreement with these empirically determined NPS and DQE values. In this study, we provide an example of how cascaded

  17. An investigation of flat panel equipment variables on image quality with a dedicated cardiac phantom.

    PubMed

    Dragusin, O; Bosmans, H; Pappas, C; Desmet, W

    2008-09-21

    Image quality (IQ) evaluation plays a key role in the process of optimization of new x-ray systems. Ideally, this process should be supported by real clinical images, but ethical issues and differences in anatomy and pathology of patients make it impossible. Phantom studies might overcome these issues. This paper presents the IQ evaluation of 30 cineangiographic films acquired with a cardiac flat panel system. The phantom used simulates the anatomy of the heart and allows the circulation of contrast agent boluses through coronary arteries. Variables investigated with influence on IQ and radiation dose are: tube potential, detector dose, added Copper filters, dynamic density optimization (DDO) and viewing angle. The IQ evaluation consisted of scoring 4 simulated calcified lesions located on different coronary artery segments in terms of degree of visualization. Eight cardiologists rated the lesions using a five-point scale ((1) lesion not visible to (5) very good visibility). Radiation doses associated to the angiograms are expressed in terms of incident air kerma (IAK) and effective dose that has been calculated with PCXMX software (STUK, Finland) from the exposure settings assuming a standard sized patient of 70 Kg. Mean IQ scores ranged from 1.68 to 4.88. The highest IQ scores were obtained for the angiograms acquired with tube potential 80 kVp, no added Cu filters, DDO 60%, RAO and LAO views and the highest entrance detector dose that has been used in the present study, namely 0.17 microGy/im. Radiation doses (IAK approximately 40 mGy and effective dose of 1 mSv) were estimated for angiograms acquired at 15 frames s(-1), detector field-of-view 20 cm, and a length of 5 s. The following parameters improved the IQ factor significantly: a change in tube potential from 96 to 80 kVp, detector dose from 0.10 microGy/im to 0.17 microGy/im, the absence of Copper filtration. DDO variable which is a post-processing parameter should be carefully evaluated because it alters

  18. Measurement of joint kinematics using a conventional clinical single-perspective flat-panel radiography system

    SciTech Connect

    Seslija, Petar; Teeter, Matthew G.; Yuan Xunhua; Naudie, Douglas D. R.; Bourne, Robert B.; MacDonald, Steven J.; Peters, Terry M.; Holdsworth, David W.

    2012-10-15

    Purpose: The ability to accurately measure joint kinematics is an important tool in studying both normal joint function and pathologies associated with injury and disease. The purpose of this study is to evaluate the efficacy, accuracy, precision, and clinical safety of measuring 3D joint motion using a conventional flat-panel radiography system prior to its application in an in vivo study. Methods: An automated, image-based tracking algorithm was implemented to measure the three-dimensional pose of a sparse object from a two-dimensional radiographic projection. The algorithm was tested to determine its efficiency and failure rate, defined as the number of image frames where automated tracking failed, or required user intervention. The accuracy and precision of measuring three-dimensional motion were assessed using a robotic controlled, tibiofemoral knee phantom programmed to mimic a subject with a total knee replacement performing a stair ascent activity. Accuracy was assessed by comparing the measurements of the single-plane radiographic tracking technique to those of an optical tracking system, and quantified by the measurement discrepancy between the two systems using the Bland-Altman technique. Precision was assessed through a series of repeated measurements of the tibiofemoral kinematics, and was quantified using the across-trial deviations of the repeated kinematic measurements. The safety of the imaging procedure was assessed by measuring the effective dose of ionizing radiation associated with the x-ray exposures, and analyzing its relative risk to a human subject. Results: The automated tracking algorithm displayed a failure rate of 2% and achieved an average computational throughput of 8 image frames/s. Mean differences between the radiographic and optical measurements for translations and rotations were less than 0.08 mm and 0.07 Degree-Sign in-plane, and 0.24 mm and 0.6 Degree-Sign out-of-plane. The repeatability of kinematics measurements performed

  19. A forward bias method for lag correction of an a-Si flat panel detector

    SciTech Connect

    Starman, Jared; Tognina, Carlo; Partain, Larry; Fahrig, Rebecca

    2012-01-15

    Purpose: Digital a-Si flat panel (FP) x-ray detectors can exhibit detector lag, or residual signal, of several percent that can cause ghosting in projection images or severe shading artifacts, known as the radar artifact, in cone-beam computed tomography (CBCT) reconstructions. A major contributor to detector lag is believed to be defect states, or traps, in the a-Si layer of the FP. Software methods to characterize and correct for the detector lag exist, but they may make assumptions such as system linearity and time invariance, which may not be true. The purpose of this work is to investigate a new hardware based method to reduce lag in an a-Si FP and to evaluate its effectiveness at removing shading artifacts in CBCT reconstructions. The feasibility of a novel, partially hardware based solution is also examined. Methods: The proposed hardware solution for lag reduction requires only a minor change to the FP. For pulsed irradiation, the proposed method inserts a new operation step between the readout and data collection stages. During this new stage the photodiode is operated in a forward bias mode, which fills the defect states with charge. A Varian 4030CB panel was modified to allow for operation in the forward bias mode. The contrast of residual lag ghosts was measured for lag frames 2 and 100 after irradiation ceased for standard and forward bias modes. Detector step response, lag, SNR, modulation transfer function (MTF), and detective quantum efficiency (DQE) measurements were made with standard and forward bias firmware. CBCT data of pelvic and head phantoms were also collected. Results: Overall, the 2nd and 100th detector lag frame residual signals were reduced 70%-88% using the new method. SNR, MTF, and DQE measurements show a small decrease in collected signal and a small increase in noise. The forward bias hardware successfully reduced the radar artifact in the CBCT reconstruction of the pelvic and head phantoms by 48%-81%. Conclusions: Overall, the

  20. An investigation of flat panel equipment variables on image quality with a dedicated cardiac phantom

    NASA Astrophysics Data System (ADS)

    Dragusin, O.; Bosmans, H.; Pappas, C.; Desmet, W.

    2008-09-01

    Image quality (IQ) evaluation plays a key role in the process of optimization of new x-ray systems. Ideally, this process should be supported by real clinical images, but ethical issues and differences in anatomy and pathology of patients make it impossible. Phantom studies might overcome these issues. This paper presents the IQ evaluation of 30 cineangiographic films acquired with a cardiac flat panel system. The phantom used simulates the anatomy of the heart and allows the circulation of contrast agent boluses through coronary arteries. Variables investigated with influence on IQ and radiation dose are: tube potential, detector dose, added Copper filters, dynamic density optimization (DDO) and viewing angle. The IQ evaluation consisted of scoring 4 simulated calcified lesions located on different coronary artery segments in terms of degree of visualization. Eight cardiologists rated the lesions using a five-point scale ((1) lesion not visible to (5) very good visibility). Radiation doses associated to the angiograms are expressed in terms of incident air kerma (IAK) and effective dose that has been calculated with PCXMX software (STUK, Finland) from the exposure settings assuming a standard sized patient of 70 Kg. Mean IQ scores ranged from 1.68 to 4.88. The highest IQ scores were obtained for the angiograms acquired with tube potential 80 kVp, no added Cu filters, DDO 60%, RAO and LAO views and the highest entrance detector dose that has been used in the present study, namely 0.17 μGy/im. Radiation doses (IAK ~40 mGy and effective dose of 1 mSv) were estimated for angiograms acquired at 15 frames s-1, detector field-of-view 20 cm, and a length of 5 s. The following parameters improved the IQ factor significantly: a change in tube potential from 96 to 80 kVp, detector dose from 0.10 μGy/im to 0.17 μGy/im, the absence of Copper filtration. DDO variable which is a post-processing parameter should be carefully evaluated because it alters the quality of the