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Sample records for arond te dual-axis

  1. Concentrations of Radionuclides and Trace Elements in Environmantal Media arond te Dual-Axis Radiographic Hydrodynamic Test Facilit at Los Alamos National Laboratory during 2005

    SciTech Connect

    G.J.Gonzales; P.R. Fresquez; C.D.Hathcock; D.C. Keller

    2006-05-15

    The Mitigation Action Plan (MAP) for the Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility at Los Alamos National Laboratory requires that samples of biotic and abiotic media be collected after operations began to determine if there are any human health or environmental impacts. The DARHT facility is the Laboratory's principal explosive test facility. To this end, samples of soil and sediment, vegetation, bees, and birds were collected around the facility in 2005 and analyzed for concentrations of {sup 3}H, {sup 137}Cs, {sup 90}Sr, {sup 238}Pu, {sup 239,240}Pu, {sup 241}Am, {sup 234}U, {sup 235}U, {sup 238}U, Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, and Tl. Bird populations have also been monitored. Contaminant results, which represent up to six sample years since the start of operations, were compared with (1) baseline statistical reference levels (BSRLs) established over a four-year preoperational period before DARHT facility operations, (2) screening levels (SLs), and (3) regulatory standards. Most radionuclides and trace elements were below BSRLs and those few samples that contained radionuclides and trace elements above BSRLs were below SLs. Concentrations of radionuclides and nonradionuclides in biotic and abiotic media around the DARHT facility do not pose a significant human health hazard. The total number of birds captured and number of species represented were similar in 2003 and 2004, but both of these parameters increased substantially in 2005. Periodic interruption of the scope and schedule identified in the MAP generally should have no impact on meeting the intent of the MAP. The risk of not sampling one of the five media in any given year is that if a significant impact to contaminant levels were to occur there would exist a less complete understanding of the extent of the change to the baseline for these media and to the ecosystem as a whole. Since the MAP is a requirement that was established under the regulatory framework of the

  2. Dual-axis energy recovery linac.

    SciTech Connect

    Wang, C.-x.; Noonan, J.; Lewellen, J.

    2007-01-01

    In this paper we propose a new type of energy-recovery linac (ERL) for ERL applications. The envisioned dualaxis energy-recovery linac allows energy recovery of parallel beams, accelerating/decelerating along different axes, via the same dual-axis superconducting cavity. This new scheme offers many advantages over conventional ERLs in various applications. Preliminary feasibility considerations are presented.

  3. Force-balanced dual-axis microgyroscope

    NASA Astrophysics Data System (ADS)

    An, Seungdo; Oh, Yong-Soo; Lee, Byeungleul; Park, Kyu-Yeon; Go, Youn-il; Kim, Jeong-gon; Song, Ci M.; Lee, Seungseob

    1997-11-01

    The surface micromachining process realized the dual-axis microgyroscope. The 7.5 micrometers -thick polysilicon layer deposited by LPCVD is used for the vibrating structure. In this research, we present a new structure with high angular inertia momentum and compact size. In particular, this structure can utilize a simple force-balancing torsional torque which does not need another top electrode layer to reduce the intrinsic non-linearity of a capacitive-type sensor. The gyroscope is tested in a high vacuum chamber for a high Q-factor. The sensing mode is separated 2 percent from the driving mode by applying the inter-plate DC tuning bias. The experiment resulted in a nose equivalent signal of 0.1 deg/sec.

  4. Development of a dual-axis optoelectronic precision level

    NASA Astrophysics Data System (ADS)

    Fan, Kuang-Chao; Wang, Tsung-Han; Lin, Sheng-Yi; Liu, Yen-Chih

    2011-12-01

    This paper presents the design principle and applications of a innovative dual-axis optoelectronic level. A commercially available DVD pickup head is adopted as the angle sensor in association with the double-layer pendulum mechanism for dual-axis swings. A mass-damping system is analyzed to model the mechanical dynamics. Measured angles of both axes are processed by a microprocessor and displayed on a LCD or exported to an external PC. Compared with a triple-beam laser angular interferometer, the error of the dual-axis optoelectronic level is better than +/-0.5 arc-seconds in the measuring range of +/-20 arc-seconds, and the settling time is within 0.5 sec. Two experimental results show the consistency with a Renishaw interfereometer and its practical use in industry.

  5. Dual-axis MEMS force sensors for gecko adhesion studies

    NASA Astrophysics Data System (ADS)

    Hill, Ginel Corina

    Dual-axis piezoresistive microelectromechanical systems (MEMS) force sensors were used to investigate the effects of orientation angle on the adhesion of gecko hairs, called setae. These hairs are part of a fantastic, robust dry adhesive. Their adhesion is highly angle-dependent, with both the "pitch" and "roll" orientation angles playing a role. This anisotropy in adhesion properties is critical for locomotion, as it enables detachment of the gecko's foot with limited pull-off force. Many synthetic mimics of the gecko adhesive are isotropic. This work on the anisotropy of natural setae will inform future work on synthetic dry adhesives. A dual-axis microscale force sensor was needed to study single seta adhesive forces, which are stronger parallel to a substrate than perpendicular. Piezoresistive silicon cantilevers that separately detect lateral and normal forces applied at the tip were used. The fabrication process and rigorous characterization of new devices are reported. A novel calibration method was developed that uses resonant frequency measurements in concert with finite element models to correct for the expected variability of critical dimensions. These corrected models were used to predict the stiffnesses of each cantilever, and thus improve the accuracy of force measurements made with these sensors. This calibration technique was also validated by direct measurement of the dual-axis cantilever stiffnesses using a reference cantilever. The adhesion force of a single gecko seta is dramatically enhanced by proper orientation. The dual-axis cantilevers were used to measure two components of force between a substrate and a Gekko gecko seta. Lateral adhesion was highest with the stalk oriented parallel to the surface at 0° pitch. Adhesion decreased smoothly as the pitch angle of the stalk was increased, until detachment or no adhesion occurred at approximately 30°. To display enhanced adhesion, the splayed tuft at the end of the seta needed to be only

  6. A dual-axis approach to understanding neuroendocrine development

    PubMed Central

    Shirtcliff, Elizabeth A; Dismukes, Andrew R.; Marceau, Kristine P.; Ruttle, Paula; Simmons, Julian; Han, Georges

    2015-01-01

    This paper on ‘a dual-axis approach to understanding neuroendocrine development’ sets out to introduce a series of paper about a novel perspective regarding stress and sex hormones, or what the authors within this special issue term ‘coupling’ of hypothalamic-pituitary-adrenal and –gonadal axes. This view postulates that these axes do not necessarily operate in opposition, but can operate together as evidenced empirically as a positive within-person association between stress hormones like cortisol or sex hormones like testosterone. A wealth of papers within the special issue demonstrate positive coupling across acute, diurnal, basal, and longitudinal timeframes and across several different types of contexts. Reviews were meant to challenge whether this was physiologically plausible. Consistently, sophisticated statistical models were utilized in order to show a template for how to model positive coupling and to ensure that coupling was a within-person phenomenon. We cautiously considered positive coupling until the consistency of observing positive coupling was robust enough for us to consider challenging the prevailing oppositional view of these axes. We do so to acknowledge that there are contexts, moments and stages in which the function of these axes should work together: for example when contexts are both stressful and challenging or at developmental stages (like adolescence) in which the youth must grow up despite the storm and stress of youth. We hope that by putting forward a functional dual-axis approach, the field will be able to consider when and how a dual-axis approach is useful. PMID:26220016

  7. Dual-axis hole-drilling ESPI residual stress measurements

    SciTech Connect

    Steinzig, Michael; Schajer, Gary

    2008-01-01

    A novel dual-axis ESPI hole-drilling residual stress measurement method is presented. The method enables the evaluation of all the in-plane normal stress components with similar response to measurement errors, significantly lower than with single-axis measurements. A numerical method is described that takes advantage of, and compactly handles, the additional optical data that are available from the second measurement axis. Experimental tests were conducted on a calibrated specimen to demonstrate the proposed method, and the results supported theoretical expectations.

  8. Shot H3837: Darht's first dual-axis explosive experiment

    NASA Astrophysics Data System (ADS)

    Harsh, James F.; Hull, Lawrence; Mendez, Jacob; McNeil, Wendy Vogan

    2012-03-01

    Test H3837 was the first explosive shot performed in front of both flash x-ray axes at the Los Alamos Dual Axis Radiographic Hydrodynamic Test (DARHT) facility. Executed in November 2009, the shot was an explosively-driven metal flyer plate in a series of experiments designed to explore equation-of-state properties of shocked materials. Imaging the initial shock wave traveling through the flyer plate, DARHT Axis II captured the range of motion from the shock front emergence in the flyer to breakout at the free surface; the Axis I pulse provided a perpendicular perspective of the shot at a time coinciding with the third pulse of Axis II.

  9. A novel dual-axis optoelectronic level with refraction principle

    NASA Astrophysics Data System (ADS)

    Torng, Jingsyan; Wang, Chih-Hsiung; Huang, Zih-Nan; Fan, Kuang-Chao

    2013-03-01

    Levels are fundamental metrological tools for machine leveling and angle measurements. Current levels are all based on the pendulum principle and bubble vial principle. The former is precise but complicated, while the latter is not precise enough. This paper presents a novel, simple and precise optoelectronic level. It is based on the principle of light refraction in the transparent and viscous fluid. The fluid surface is always in leveling condition regardless whether the ground is level or not. Measuring the refraction angle with precise dual-axis autocollimator can directly reflect the inclined angle of the level. A leakage prevention design is also proposed to allow the level to be placed in any pose. Calibrated by an angular interferometer, the error of the dual-axis optoelectronic level is better than ±0.7 arcsec in the measuring range of ±100 arcsec, and better than ±0.4 arcsec for the range of ±30 arcsec, for both axes. Without the need of a pendulum mechanism, this is a simpler design for precision level.

  10. Dual axis operation of a micromachined rate gyroscope

    SciTech Connect

    Juneau, T.; Pisano, A.P.; Smith, J.

    1997-04-01

    Since micromachining technology has raised the prospect of fabricating high performance sensors without the associated high cost and large size, many researchers have investigated micromachined rate gyroscopes. The vast majority of research has focused on single input axis rate gyroscopes, but this paper presents work on a dual input axis micromachined rate gyroscope. The key to successful simultaneous dual axis operation is the quad symmetry of the circular oscillating rotor design. Untuned gyroscopes with mismatched modes yielded random walk as low as 10{degrees}/{radical}hour with cross sensitivity ranging from 6% to 16%. Mode frequency matching via electrostatic tuning allowed performance better than 2{degrees}/{radical}hour, but at the expense of excessive cross sensitivity.

  11. Shot H3837: Darht's First Dual-Axis Explosive Experiment

    NASA Astrophysics Data System (ADS)

    Mendez, Jacob; McNeil, Wendy Vogan; Harsh, James; Hull, Lawrence

    2011-06-01

    Test H3837 was the first explosive shot performed in front of both flash x-ray axes at the Los Alamos Dual Axis Radiographic HydroTest (DARHT) facility. Executed in November 2009, the shot was an explosively-driven metal flyer plate in a series of experiments designed to explore equation-of-state properties of shocked materials. Imaging the initial shock wave traveling through the flyer plate, DARHT Axis II captured the range of motion from the shock front emergence in the flyer to breakout at the free surface; the Axis I pulse provided a perpendicular perspective of the shot at a time coinciding with the third pulse of Axis II. Since the days of the Manhattan Project, penetrating radiography with multiple frames from different viewing angles has remained a high-profile goal at the Laboratory. H3837 is merely the beginning of a bright future for two-axis penetrating radiography.

  12. DARHT status and preparations for dual-axis hydrotesting (u)

    SciTech Connect

    Bowman, David W

    2010-01-01

    The status of the DARHT facility, including a history of events that have taken place since the end of the DARHT Second Axis Refurbishment Project, is discussed. Technical and operational enhancements that have been made will be addressed, and recent technical challenges, such as the RF noise in the kicker region, are discussed. Historical data on reliability of the second axis is discussed, as well as operational changes made to enhance reliability. In addition, the path forward for integrating the second axis into overall DARHT operations in preparation for a hydrotest is addressed. Timing integration tests are accompanied by a series of tests to evaluate neutron contamination and cross-axis scatter, with attempts being made to provide adequate shielding to minimize the effects of neutrons and cross-beam scatter. The discussion includes results of the testing performed to-date, and concludes with a discussion of the path forward for dual-axis hydrotesting at DARHT.

  13. A dual-axis approach to understanding neuroendocrine development.

    PubMed

    Shirtcliff, Elizabeth A; Dismukes, Andrew R; Marceau, Kristine; Ruttle, Paula L; Simmons, Julian G; Han, Georges

    2015-09-01

    This introduction sets out to present a series of paper about a novel perspective regarding stress and sex hormones, or what the authors within this special issue term "coupling" of hypothalamic-pituitary-adrenal and--gonadal axes. This view postulates that these axes do not necessarily operate in opposition, but can operate together as evidenced empirically as a positive within-person association between stress hormones like cortisol or sex hormones like testosterone. A wealth of papers within the special issue demonstrate positive coupling across acute, diurnal, basal, and longitudinal timeframes and across several different types of contexts. Reviews were meant to challenge whether this was physiologically plausible. Consistently, sophisticated statistical models were utilized in order to show a template for how to model positive coupling and to ensure that coupling was a within-person phenomenon. We cautiously considered positive coupling until the consistency of observing coupling was robust enough for us to consider challenging the prevailing oppositional view of these axes. We do so to acknowledge that there are contexts, moments and stages in which the function of these axes should work together: for example when contexts are both stressful and challenging or at developmental stages (like adolescence) in which the youth must grow up despite the storm and stress of youth. We hope that by putting forward a functional dual-axis approach, the field will be able to consider when and how these axes work together.

  14. A dual-axis approach to understanding neuroendocrine development.

    PubMed

    Shirtcliff, Elizabeth A; Dismukes, Andrew R; Marceau, Kristine; Ruttle, Paula L; Simmons, Julian G; Han, Georges

    2015-09-01

    This introduction sets out to present a series of paper about a novel perspective regarding stress and sex hormones, or what the authors within this special issue term "coupling" of hypothalamic-pituitary-adrenal and--gonadal axes. This view postulates that these axes do not necessarily operate in opposition, but can operate together as evidenced empirically as a positive within-person association between stress hormones like cortisol or sex hormones like testosterone. A wealth of papers within the special issue demonstrate positive coupling across acute, diurnal, basal, and longitudinal timeframes and across several different types of contexts. Reviews were meant to challenge whether this was physiologically plausible. Consistently, sophisticated statistical models were utilized in order to show a template for how to model positive coupling and to ensure that coupling was a within-person phenomenon. We cautiously considered positive coupling until the consistency of observing coupling was robust enough for us to consider challenging the prevailing oppositional view of these axes. We do so to acknowledge that there are contexts, moments and stages in which the function of these axes should work together: for example when contexts are both stressful and challenging or at developmental stages (like adolescence) in which the youth must grow up despite the storm and stress of youth. We hope that by putting forward a functional dual-axis approach, the field will be able to consider when and how these axes work together. PMID:26220016

  15. Conceptual design considerations of a 5-cell dual-axis SRF cavity for ERLs.

    SciTech Connect

    Wang, C.-X.; Accelerator Systems Division

    2007-01-01

    Recently a dual-axis energy recovery linac has been proposed for ERL applications, in which accelerating and decelerating beams can go through separate axes but still recover energy in novel dual-axis cavities. Here we discuss a conceptual design of a 5-cell dual-axis cavity evolved from side-by-side jointed TESLA-type cavities. Instead of an engineering design, we aim to explore the feasibility of such a new cavity, giving particular attention to its nonstandard features that might cause concern to the beam. This is a preliminary work-in-progress report.

  16. Analytical Modeling of Squeeze Film Damping in Dual Axis Torsion Microactuators

    NASA Astrophysics Data System (ADS)

    Moeenfard, Hamid

    2015-10-01

    In this paper, problem of squeeze film damping in dual axis torsion microactuators is modeled and closed form expressions are provided for damping torques around tilting axes of the actuator. The Reynolds equation which governs the pressure distribution underneath the actuator is linearized. The resulting equation is then solved analytically. The obtained pressure distribution is used to calculate the normalized damping torques around tilting axes of the actuator. Dependence of the damping torques on the design parameters of the dual axis torsion actuator is studied. It is observed that with proper selection of the actuator's aspect ratio, damping torque along one of the tilting directions can be eliminated. It is shown that when the tilting angles of the actuator are small, squeeze film damping would act like a linear viscous damping. The results of this paper can be used for accurate dynamical modeling and control of torsion dual axis microactuators.

  17. Optimal Spacing of Dual-axis Trackers for Concentrating Photovoltaic Systems

    NASA Astrophysics Data System (ADS)

    Kim, Yong Sin; Winston, Roland

    2011-12-01

    The levelized cost of energy (LCOE) is widely used to compare the cost of energy generation across technologies. In a utility-scale concentrating photovoltaic (CPV) system, the spacing of dual-axis trackers must be balanced with total energy harvested from modules to minimize LCOE. In this paper, a spacing method of dual-axis trackers in a CPV system is presented. Based on the definition of LCOE, a cost function is defined and optimized in terms of spacing related parameters. Various methods to estimate hourly direct normal irradiance (DNI) are investigated and m-by-n tracker array configurations to minimize the cost function are discussed.

  18. Handheld multispectral dual-axis confocal microscope for cervical cancer screening

    NASA Astrophysics Data System (ADS)

    Sarapukdee, Pongsak; Rattanavarin, Santi; Jarujareet, Ungkarn; Khemthongcharoen, Numfon; Jolivot, Romuald; Jung, Il Woong; López, Daniel; Mandella, Michael J.; Piyawattanametha, Wibool

    2013-03-01

    Our work demonstrates a MEMS based handheld dual-axis confocal microscope for cervical cancer screening. Imaging demonstration is performed with plant and animal tissue biopsies. The data is collected and displayed in real time with 2-5 Hz frame rates.

  19. Dual Axis Radiographic Hydrodynamic Test Facility mitigation action plan. Annual report for 1998

    SciTech Connect

    Haagenstad, T.

    1999-01-15

    This Mitigation Action Plan Annual Report (MAPAR) has been prepared as part of implementing the Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) Mitigation Action Plan (MAP) to protect workers, soils, water, and biotic and cultural resources in and around the facility.

  20. Lightweight dual-axis tracker designs for dish-based HCPV

    NASA Astrophysics Data System (ADS)

    Angel, Roger; Cuerden, Brian; Whiteside, Andy

    2014-09-01

    Dish-based HCPV holds the promise of solar electricity at lower cost than for flat panel PV, provided that the dual-axis tracker cost can be minimized. Here we outline first and second generation lightweight tracker designs that include supports for a rectangular array of square dish mirrors and receivers located at their foci.

  1. Sheet-scanned dual-axis confocal (SS-DAC) microscopy using Richardson-Lucy deconvolution

    PubMed Central

    Wang, Danni; Meza, Daphne; Wang, Yu; Gao, Liang; Liu, Jonathan T.C.

    2015-01-01

    We have previously developed a line-scanned dual-axis confocal (LS-DAC) microscope with subcellular resolution suitable for high-frame-rate diagnostic imaging at shallow depths. Due to the loss of confocality along one dimension, the contrast (signal-to-background ratio) of a LS-DAC microscope is deteriorated compared to a point-scanned DAC microscope. However, by using a sCMOS camera for detection, a short oblique light-sheet is imaged at each scanned position. Therefore, by scanning the light sheet in only one dimension, a thin 3D volume is imaged. Both sequential two-dimensional deconvolution and three-dimensional deconvolution are performed on the thin image volume to improve the resolution and contrast of one en face confocal image section at the center of the volume, a technique we call sheet-scanned dual-axis confocal (SS-DAC) microscopy. PMID:26466290

  2. Sun-Relative Pointing for Dual-Axis Solar Trackers Employing Azimuth and Elevation Rotations

    DOE PAGES

    Riley, Daniel; Hansen, Clifford W.

    2014-12-30

    Dual axis trackers employing azimuth and elevation rotations are common in the field of photovoltaic (PV) energy generation. Accurate sun-tracking algorithms are widely available. However, a steering algorithm has not been available to accurately point the tracker away from the sun such that a vector projection of the sun beam onto the tracker face falls along a desired path relative to the tracker face. We have developed an algorithm which produces the appropriate azimuth and elevation angles for a dual axis tracker when given the sun position, desired angle of incidence, and the desired projection of the sun beam ontomore » the tracker face. Development of this algorithm was inspired by the need to accurately steer a tracker to desired sun-relative positions in order to better characterize the electro-optical properties of PV and CPV modules.« less

  3. Sun-Relative Pointing for Dual-Axis Solar Trackers Employing Azimuth and Elevation Rotations

    SciTech Connect

    Riley, Daniel; Hansen, Clifford W.

    2014-12-30

    Dual axis trackers employing azimuth and elevation rotations are common in the field of photovoltaic (PV) energy generation. Accurate sun-tracking algorithms are widely available. However, a steering algorithm has not been available to accurately point the tracker away from the sun such that a vector projection of the sun beam onto the tracker face falls along a desired path relative to the tracker face. We have developed an algorithm which produces the appropriate azimuth and elevation angles for a dual axis tracker when given the sun position, desired angle of incidence, and the desired projection of the sun beam onto the tracker face. Development of this algorithm was inspired by the need to accurately steer a tracker to desired sun-relative positions in order to better characterize the electro-optical properties of PV and CPV modules.

  4. Sheet-scanned dual-axis confocal microscopy using Richardson-Lucy deconvolution.

    PubMed

    Wang, D; Meza, D; Wang, Y; Gao, L; Liu, J T C

    2014-09-15

    We have previously developed a line-scanned dual-axis confocal (LS-DAC) microscope with subcellular resolution suitable for high-frame-rate diagnostic imaging at shallow depths. Due to the loss of confocality along one dimension, the contrast (signal-to-background ratio) of a LS-DAC microscope is deteriorated compared to a point-scanned DAC microscope. However, by using a sCMOS camera for detection, a short oblique light-sheet is imaged at each scanned position. Therefore, by scanning the light sheet in only one dimension, a thin 3D volume is imaged. Both sequential two-dimensional deconvolution and three-dimensional deconvolution are performed on the thin image volume to improve the resolution and contrast of one en face confocal image section at the center of the volume, a technique we call sheet-scanned dual-axis confocal (SS-DAC) microscopy.

  5. Design of a dual-axis optoelectronic level for precision angle measurements

    NASA Astrophysics Data System (ADS)

    Fan, Kuang-Chao; Wang, Tsung-Han; Lin, Sheng-Yi; Liu, Yen-Chih

    2011-05-01

    The accuracy of machine tools is mainly determined by angular errors during linear motion according to the well-known Abbe principle. Precision angle measurement is important to precision machines. This paper presents the theory and experiments of a new dual-axis optoelectronic level with low cost and high precision. The system adopts a commercial DVD pickup head as the angle sensor in association with the double-layer pendulum mechanism for two-axis swings, respectively. In data processing with a microprocessor, the measured angles of both axes can be displayed on an LCD or exported to an external PC. Calibrated by a triple-beam laser angular interferometer, the error of the dual-axis optoelectronic level is better than ±0.7 arcsec in the measuring range of ±30 arcsec, and the settling time is within 0.5 s. Experiments show the applicability to the inspection of precision machines.

  6. Mechanical design and force calibration of dual-axis micromechanical probe for friction force microscopy

    SciTech Connect

    Fukuzawa, Kenji; Terada, Satoshi; Shikida, Mitsuhiro; Amakawa, Hiroaki; Zhang, Hedong; Mitsuya, Yasunaga

    2007-02-01

    A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical force detections. In addition, dual-axis forces can be detected by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes (FFMs). In this paper, the mechanical design of the probe, the details of the fabrication method, FFM performance, and calibration of the friction force are discussed. The mechanical design and the microfabrication method for probes that can provide a force resolution of the order of 1 nN without mechanical cross-talk are presented. Calibration of the lateral force signal is possible by using the relationship between the lateral force and the piezodisplacement at the onset of the probe scanning. The micromechanical probe enables simultaneous and independent detection of atomic and friction forces. This leads to accurate investigation of nanotribological phenomena and visualization of the distribution of the friction properties, which helps the identification of the material properties.

  7. Evaluation of the prototype dual-axis wall attitude measurement sensor

    NASA Technical Reports Server (NTRS)

    Wong, Douglas T.

    1994-01-01

    A prototype dual-axis electrolytic tilt sensor package for angular position measurements was built and evaluated in a laboratory environment. The objective was to investigate the use of this package for making wind tunnel wall attitude measurements for the National Transonic Facility (NTF) at NASA Langley Research Center (LaRC). The instrumentation may replace an existing, more costly, and less rugged servo accelerometer package (angle-of-attack package) currently in use. The dual-axis electrolytic tilt sensor package contains two commercial electrolytic tilt sensors thermally insulated with NTF foam, all housed within a stainless steel package. The package is actively heated and maintained at 160 F using foil heating elements. The laboratory evaluation consisted of a series of tests to characterize the linearity, repeatability, cross-axis interaction, lead wire effect, step response, thermal time constant, and rectification errors. Tests revealed that the total RMS errors for the x-axis sensor is 0.084 degree, and 0.182 degree for the y-axis sensor. The RMS errors are greater than the 0.01 degree specification required for NTF wall attitude measurements. It is therefore not a viable replacement for the angle-of-attack package in the NTF application. However, with some physical modifications, it can be used as an inexpensive 5-degree range dual-axis inclinometer with overall accuracy approaching 0.01 degree under less harsh environments. Also, the data obtained from the tests can be valuable for wind tunnel applications of most types of electrolytic tilt sensors.

  8. A dual-axis tilt acquisition geometry for digital musculoskeletal tomosynthesis

    NASA Astrophysics Data System (ADS)

    Levakhina, Yulia M.; Duschka, Robert L.; Vogt, Florian M.; Barkhausen, Joerg; Buzug, Thorsten M.

    2013-07-01

    Digital tomosynthesis (DT) is a limited angle tomographic x-ray technique. It is an attractive low-dose alternative to computed tomography (CT) in many imaging applications. However, the DT dataset is incomplete, which leads to out-of-focus artifacts and limited axial resolution. In this paper, a novel dual-axis tilt acquisition geometry is proposed and evaluated. This geometry solves some issues in tomosynthesis with the traditional scanning geometry by scanning the object with a set of perpendicular arcs. In this geometry the acquisition in the additional perpendicular direction is done using a tiltable object supporting platform. The proposed geometry allows for capturing more singularities of the Radon transform, filling the Fourier space with more data and better approximating the Tuy-Smith conditions. In order to evaluate the proposed system, several studies have been carried out. To validate the simulation setup the performance of the traditional scanning geometry has been simulated and compared to known results from the literature. It has also been shown that the possible improvement of the image quality in the traditional geometry is limited. These limitations can be partially overcome by using the proposed dual-axis tilt geometry. The novel geometry is superior and with the same number of projections better reconstructed images can be obtained. All studies have been made using a software tomosynthesis simulator. A micro-CT reconstruction of a bone has been used as a software phantom. Simultaneous algebraic reconstruction has been used to reconstruct simulated projections. As a conclusion, acquiring data outside the standard arc allows for improving performance of musculoskeletal tomosynthesis. With the proposed dual-axis acquisition geometry a performance gain is achieved without an increase in dose and major modifications to the instrumentation of existing tomosynthesis devices.

  9. Commissioning of the advanced light source dual-axis streak camera

    SciTech Connect

    Hinkson, J.; Keller, R.; Byrd, J.

    1997-05-01

    A dual-axis camera, Hamamatsu model C5680, has been installed on the Advanced Light Source photon-diagnostics beam-line to investigate electron-beam parameters. During its commissioning process, the camera has been used to measure single-bunch length vs. current, relative bunch charge in adjacent RF buckets, and bunchphase stability. In this paper the authors describe the visible-light branch of the diagnostics beam-line, the streak-camera installation, and the timing electronics. They will show graphical results of beam measurements taken during a variety of accelerator conditions.

  10. Modulated-alignment dual-axis (MAD) confocal microscopy for deep optical sectioning in tissues

    PubMed Central

    Leigh, Steven Y.; Chen, Ye; Liu, Jonathan T.C.

    2014-01-01

    A strategy is presented to enable optical-sectioning microscopy with improved contrast and imaging depth using low-power (0.5 - 1 mW) diode laser illumination. This technology combines the inherent strengths of focal-modulation microscopy and dual-axis confocal (DAC) microscopy for rejecting out-of-focus and multiply scattered background light in tissues. The DAC architecture is unique in that it utilizes an intersecting pair of illumination and collection beams to improve the spatial-filtering and optical-sectioning performance of confocal microscopy while focal modulation selectively ‘labels’ in-focus signals via amplitude modulation. Simulations indicate that modulating the spatial alignment of dual-axis beams at a frequency f generates signals from the focal volume of the microscope that are modulated at 2f with minimal modulation of background signals, thus providing nearly an order-of-magnitude improvement in optical-sectioning contrast compared to DAC microscopy alone. Experiments show that 2f lock-in detection enhances contrast and imaging depth within scattering phantoms and fresh tissues. PMID:24940534

  11. Investigating gecko setae adhesion using a dual-axis MEMS force sensor

    NASA Astrophysics Data System (ADS)

    Hill, Ginel; Soto, Daniel; Peattie, Anne; Full, Robert; Kenny, Thomas

    2007-03-01

    A dual-axis piezoresistive MEMS force sensor was used to investigate the role of orientation angle on the adhesion of gecko hairs, called setae. Made of keratin with nanoscale features, gecko setae are a spectacular, robust dry adhesive with anisotropic adhesion properties. A wealth of recent research has been devoted to synthetic mimicry of the gecko seta. However, most synthetics do not yet display anisotropic adhesion, which is critical for controllable attachment and release. Previous research using a wire gauge tested the role of the pitch angle between the stalk of natural setae and the substrate and found a dramatic cutoff angle of 30^o, above which setae detach from the substrate [1]. The present work details the effect of the ``roll'' angle on natural setae adhesion. [1] K. Autumn, et al. Nature, 405: 681 (2000).

  12. Dual axis translation apparatus and system for translating an optical beam and related method

    DOEpatents

    Cassidy, Kelly

    1991-01-01

    A dual axis translation device and system in accordance with this invention, for translating an optical beam along both an x-axis and a y-axis which are perpendicular to one another, has a beam directing means acting on said optical beam for directing the beam along a particular path transverse to said x and y axes. An arrangement supporting said beam directing means for movement in the x and y direction within a given plane is provided. The arrangement includes a first means for translating said beam directing means along the x-axis in said given plane in order to translate the beam along said x-axis. The arrangement comprises a second means for translating said beam directing means along the y-axis in said given plane in order to translate the beam along said y-axis.

  13. Dual-axis high-data-rate atom interferometer via cold ensemble exchange

    SciTech Connect

    Rakholia, Akash V.; McGuinness, Hayden J.; Biedermann, Grant W.

    2014-11-24

    We demonstrate a dual-axis accelerometer and gyroscope atom interferometer, which can form the building blocks of a six-axis inertial measurement unit. By recapturing the atoms after the interferometer sequence, we maintain a large atom number at high data rates of 50 to 100 measurements per second. Two cold ensembles are formed in trap zones located a few centimeters apart and are launched toward one another. During their ballistic trajectory, they are interrogated with a stimulated Raman sequence, detected, and recaptured in the opposing trap zone. As a result, we achieve sensitivities at μg/ √Hz and μrad/s/ √Hz levels, making this a compelling prospect for expanding the use of atom interferometer inertial sensors beyond benign laboratory environments.

  14. Dual-axis high-data-rate atom interferometer via cold ensemble exchange

    DOE PAGES

    Rakholia, Akash V.; McGuinness, Hayden J.; Biedermann, Grant W.

    2014-11-24

    We demonstrate a dual-axis accelerometer and gyroscope atom interferometer, which can form the building blocks of a six-axis inertial measurement unit. By recapturing the atoms after the interferometer sequence, we maintain a large atom number at high data rates of 50 to 100 measurements per second. Two cold ensembles are formed in trap zones located a few centimeters apart and are launched toward one another. During their ballistic trajectory, they are interrogated with a stimulated Raman sequence, detected, and recaptured in the opposing trap zone. As a result, we achieve sensitivities at μg/ √Hz and μrad/s/ √Hz levels, making thismore » a compelling prospect for expanding the use of atom interferometer inertial sensors beyond benign laboratory environments.« less

  15. Attitude Heading Reference System Using MEMS Inertial Sensors with Dual-Axis Rotation

    PubMed Central

    Kang, Li; Ye, Lingyun; Song, Kaichen; Zhou, Yang

    2014-01-01

    This paper proposes a low cost and small size attitude and heading reference system based on MEMS inertial sensors. A dual-axis rotation structure with a proper rotary scheme according to the design principles is applied in the system to compensate for the attitude and heading drift caused by the large gyroscope biases. An optimization algorithm is applied to compensate for the installation angle error between the body frame and the rotation table's frame. Simulations and experiments are carried out to evaluate the performance of the AHRS. The results show that the proper rotation could significantly reduce the attitude and heading drifts. Moreover, the new AHRS is not affected by magnetic interference. After the rotation, the attitude and heading are almost just oscillating in a range. The attitude error is about 3° and the heading error is less than 3° which are at least 5 times better than the non-rotation condition. PMID:25268911

  16. Dual-axis vapor cell for simultaneous laser frequency stabilization on disparate optical transitions

    SciTech Connect

    Jayakumar, Anupriya Plotkin-Swing, Benjamin; Jamison, Alan O.; Gupta, Subhadeep

    2015-07-15

    We have developed a dual-axis ytterbium (Yb) vapor cell and used it to simultaneously address the two laser cooling transitions in Yb at wavelengths 399 nm and 556 nm, featuring the disparate linewidths of 2π × 29 MHz and 2π × 182 KHz, respectively. By utilizing different optical paths for the two wavelengths, we simultaneously obtain comparable optical densities suitable for saturated absorption spectroscopy for both the transitions and keep both the lasers frequency stabilized over several hours. We demonstrate that by appropriate control of the cell temperature profile, two atomic transitions differing in relative strength across a large range of over three orders of magnitude can be simultaneously addressed, making the device adaptable to a variety of spectroscopic needs. We also show that our observations can be understood with a simple theoretical model of the Yb vapor.

  17. A lightweight high performance dual-axis gimbal for space applications

    SciTech Connect

    Pines, D.J.; Hakala, D.B.; Malueg, R.

    1995-05-05

    This paper describes the design, development and performance of a lightweight precision gimbal with dual-axis slew capability to be used in a closed-loop optical tracking system at Lawrence Livermore National Laboratory-LLNL. The motivation for the development of this gimbal originates from the need to acquire and accurately localize warm objects (T{approximately}500 K) in a cluttered background. The design of the gimbal is centered around meeting the following performance requirements: pointing accuracy with control < 35 {mu}rad-(1-{omega}); slew capability > 0.2 rad/sec; mechanical weight < 5 kg. These performance requirements are derived by attempting to track a single target from multiple satellites in low Earth orbit using a mid-wave infrared camera. Key components in the gimbal hardware that are essential to meeting the performance objectives include a nickel plated beryllium mirro, an accurate lightweight capacitive pickoff device for angular measurement about the elevation axis, a 16-bit coarse/fine resolver for angular measurement about the azimuth axis, a toroidally wound motor with low hysteresis for providing torque about the azimuth axis, and the selection of beryllium parts to insure high stiffness to weight ratios and more efficient thermal conductivity. Each of these elements are discussed in detail to illustrate the design trades performed to meet the tracking and slewing requirements demanded. Preliminary experimental results are also given for various commanded tracking maneuvers.

  18. Construction of a dual axis force reflection stick and test station

    NASA Astrophysics Data System (ADS)

    Repperger, Daniel E.; Scarborough, Eric L.; Chelette, Tamara L.

    1991-11-01

    This report describes the construction of a dual axis force reflecting stick controller and test station which was constructed through the use of basic research funds (ILIR monies). The prototype described in this report is powered only by electric motors and used the latest technology in computers. This was an advancement over a previous prototype which involved pneumatic devices and was very large, bulky, and awkward to use. An experiment was conducted with 5 subjects as described herein to test the overall system for its use in experimental design. The motivation for developing such a small test station for the use of force reflection in stick controllers is because with this new compact and portable system, many new applications now appear for this technology. The system described herein minimizes both weight and electric power requirements to produce the same force reflection. By upgrading the technology in the components used in this test station, wider use of force reflection is now available for a host of new applications.

  19. Dual axis radiographic hydrodynamic test facility. Final environmental impact statement, Volume 2: Public comments and responses

    SciTech Connect

    1995-08-01

    On May 12, 1995, the U.S. Department of Energy (DOE) issued the draft Dual Axis Radiographic Hydrodynamic Test Facility Environmental Impact Statement (DARHT EIS) for review by the State of New Mexico, Indian Tribes, local governments, other Federal agencies, and the general public. DOE invited comments on the accuracy and adequacy of the draft EIS and any other matters pertaining to their environmental reviews. The formal comment period ran for 45 days, to June 26, 1995, although DOE indicated that late comments would be considered to the extent possible. As part of the public comment process, DOE held two public hearings in Los Alamos and Santa Fe, New Mexico, on May 31 and June 1, 1995. In addition, DOE made the draft classified supplement to the DARHT EIS available for review by appropriately cleared individuals with a need to know the classified information. Reviewers of the classified material included the State of New Mexico, the U.S. Environmental Protection Agency, the Department of Defense, and certain Indian Tribes. Volume 2 of the final DARHT EIS contains three chapters. Chapter 1 includes a collective summary of the comments received and DOE`s response. Chapter 2 contains the full text of the public comments on the draft DARHT EIS received by DOE. Chapter 3 contains DOE`s responses to the public comments and an indication as to how the comments were considered in the final EIS.

  20. In vivo near-infrared dual-axis confocal microendoscopy in the human lower gastrointestinal tract

    NASA Astrophysics Data System (ADS)

    Piyawattanametha, Wibool; Ra, Hyejun; Qiu, Zhen; Friedland, Shai; Liu, Jonathan T. C.; Loewke, Kevin; Kino, Gordon S.; Solgaard, Olav; Wang, Thomas D.; Mandella, Michael J.; Contag, Christopher H.

    2012-02-01

    Near-infrared confocal microendoscopy is a promising technique for deep in vivo imaging of tissues and can generate high-resolution cross-sectional images at the micron-scale. We demonstrate the use of a dual-axis confocal (DAC) near-infrared fluorescence microendoscope with a 5.5-mm outer diameter for obtaining clinical images of human colorectal mucosa. High-speed two-dimensional en face scanning was achieved through a microelectromechanical systems (MEMS) scanner while a micromotor was used for adjusting the axial focus. In vivo images of human patients are collected at 5 frames/sec with a field of view of 362×212 μm2 and a maximum imaging depth of 140 μm. During routine endoscopy, indocyanine green (ICG) was topically applied a nonspecific optical contrasting agent to regions of the human colon. The DAC microendoscope was then used to obtain microanatomic images of the mucosa by detecting near-infrared fluorescence from ICG. These results suggest that DAC microendoscopy may have utility for visualizing the anatomical and, perhaps, functional changes associated with colorectal pathology for the early detection of colorectal cancer.

  1. Development of a MEMS dual-axis differential capacitance floating element shear stress sensor

    SciTech Connect

    Barnard, Casey; Griffin, Benjamin

    2015-09-01

    A single-axis MEMS wall shear stress sensor with differential capacitive transduction method is produced. Using a synchronous modulation and demodulation interface circuit, the system is capable of making real time measurements of both mean and fluctuating wall shear stress. A sensitivity of 3.44 mV/Pa is achieved, with linearity in response demonstrated up to testing limit of 2 Pa. Minimum detectable signals of 340 μPa at 100 Hz and 120 μPa at 1 kHz are indicated, with a resonance of 3.5 kHz. Multiple full scale wind tunnel tests are performed, producing spectral measurements of turbulent boundary layers in wind speeds ranging up to 0.5 Ma (18 Pa of mean wall shear stress). The compact packaging allows for minimally invasive installation, and has proven relatively robust over multiple testing events. Temperature sensitivity, likely due to poor CTE matching of packaged materials, is an ongoing concern being addressed. These successes are being directly leveraged into a development plan for a dual-axis wall shear stress sensor, capable of producing true vector estimates at the wall.

  2. Problems Encountered During the Recertification of the GLORY Solar Array Dual Axis Gimbal Drive Actuators

    NASA Technical Reports Server (NTRS)

    Saltzman, Marc; Schepis, Jospeh P.; Bruckner, Michael J.

    2009-01-01

    The Glory observatory is the current incarnation of the Vegetation Canopy Lidar (VCL) mission spacecraft bus. The VCL spacecraft bus, having been cancelled for programmatic reasons in 2000, was nearly integrated when it was put into storage for possible future use. The Glory mission was a suitable candidate for using this spacecraft and in 2006 an effort to recertify the two axis solar array gimbal drive after its extended storage was begun. What was expected to be a simple performance validation of the two dual axis gimbal stepper motors became a serious test, diagnosis and repair task once questions arose on the flight worthiness of the hardware. A significant test program logic flow was developed which identified decisions that could be made based on the results of individual recertification tests. Without disassembling the bi-axial gimbals, beginning with stepper motor threshold voltage measurements and relating these to powered drive torque measurements, both performed at the spacecraft integrator s facility, a confusing picture of the health of the actuators came to light. Tests at the gimbal assembly level and tests of the disassembled actuators were performed by the manufacturer to validate our results and torque discrepancies were noted. Further disassembly to the component level of the actuator revealed the source of the torque loss.

  3. Analysis and calibration of the gyro bias caused by geomagnetic field in a dual-axis rotational inertial navigation system

    NASA Astrophysics Data System (ADS)

    Cai, Qingzhong; Yang, Gongliu; Song, Ningfang; Yin, Hongliang; Liu, Yiliang

    2016-10-01

    A rotational inertial navigation system (RINS) has been wildly used in long term marine navigation. In a dual-axis RINS, with all constant biases averaged out, the errors which can not be averaged out become the main error source. In this paper, the gyro geomagnetic biases of a dual-axis RINS are modelled, analysed and calibrated. The gyro geomagnetic biases are proved unable to be averaged out, but can be modulated to be a constant value in the navigation frame. A slope error term of longitude error is found to be caused by gyro geomagnetic biases in north and upward directions, which increases linearly with time and is remarkable in long term navigation. Thus, a calibration method based on least square regression is proposed to compensate the slope error term. Laboratory and sailing experimental results show that the divergence speed of longitude error can be effectively slowed down by the compensation of gyro geomagnetic biases. In long term independent navigation, the position accuracy of dual-axis RINS is improved about 50% by the calibration method proposed in this paper.

  4. Anthropometric and demographic correlates of dual-axis swallowing accelerometry signal characteristics: a canonical correlation analysis.

    PubMed

    Hanna, Fady; Molfenter, Sonja M; Cliffe, Rebecca E; Chau, Tom; Steele, Catriona M

    2010-06-01

    Swallowing accelerometry has been proposed as a potential minimally invasive tool for collecting assessment information about swallowing. The first step toward using sounds and signals for dysphagia detection involves characterizing the healthy swallow. The purpose of this article is to explore systematic variations in swallowing accelerometry signals that can be attributed to demographic factors (such as participant gender and age) and anthropometric factors (such as weight and height). Data from 50 healthy participants (25 women and 25 men), ranging in age from 18 to 80 years and with approximately equal distribution across four age groups (18-35, 36-50, 51-65, 66 and older) were analyzed. Anthropometric and demographic variables of interest included participant age, gender, weight, height, body fat percent, neck circumference, and mandibular length. Dual-axis (superior-inferior and anterior-posterior) swallowing accelerometry signals were obtained for five saliva and five water swallows per participant. Several swallowing signal characteristics were derived for each swallowing task, including variance, amplitude distribution skewness, amplitude distribution kurtosis, signal memory, total signal energy, peak energy scale, and peak amplitude. Canonical correlation analysis was performed between the anthropometric/demographic variables and swallowing signal characteristics. No significant linear relationships were identified for saliva swallows or for superior-inferior axis accelerometry signals on water swallows. In the anterior-posterior axis, signal amplitude distribution kurtosis and signal memory were significantly correlated with age (r = 0.52, P = 0.047). These findings suggest that swallowing accelerometry signals may have task-specific associations with demographic (but not anthropometric) factors. Given the limited sample size, our results should be interpreted with caution and replication studies with larger sample sizes are warranted.

  5. Dual Axis Radiographic Hydrodynamic Test Facility mitigation action plan. Annual report for 1997

    SciTech Connect

    Haagenstad, H.T.

    1998-01-15

    This Mitigation Action Plan Annual Report (MAPAR) has been prepared by the US Department of Energy (DOE) as part of implementing the Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) Mitigation Action Plan (MAP). This MAPAR provides a status on specific DARHT facility design- and construction-related mitigation actions that have been initiated in order to fulfill DOE`s commitments under the DARHT MAP. The functions of the DARHT MAP are to (1) document potentially adverse environmental impacts of the Phased Containment Option delineated in the Final EIS, (2) identify commitments made in the Final EIS and ROD to mitigate those potential impacts, and (3) establish Action Plans to carry out each commitment (DOE 1996). The DARHT MAP is divided into eight sections. Sections 1--5 provide background information regarding the NEPA review of the DARHT project and an introduction to the associated MAP. Section 6 references the Mitigation Action Summary Table which summaries the potential impacts and mitigation measures; indicates whether the mitigation is design-, construction-, or operational-related; the organization responsible for the mitigation measure; and the projected or actual completion data for each mitigation measure. Sections 7 and 8 discuss the Mitigation Action Plan Annual Report and Tracking System commitment and the Potential Impacts, Commitments, and Action Plans respectively. Under Section 8, potential impacts are categorized into five areas of concern: General Environment, including impacts to air and water; Soils, especially impacts affecting soil loss and contamination; Biotic Resources, especially impacts affecting threatened and endangered species; Cultural/Paleontological Resources, especially impacts affecting the archeological site known as Nake`muu; and Human Health and Safety, especially impacts pertaining to noise and radiation. Each potential impact includes a brief statement of the nature of the impact and its cause(s). The commitment

  6. A feasibility study of stationary and dual-axis tracking grid-connected photovoltaic systems in the Upper Midwest

    NASA Astrophysics Data System (ADS)

    Warren, Ryan Duwain

    Three primary objectives were defined for this work. The first objective was to determine, assess, and compare the performance, heat transfer characteristics, economics, and feasibility of real-world stationary and dual-axis tracking grid-connected photovoltaic (PV) systems in the Upper Midwest. This objective was achieved by installing two grid-connected PV systems with different mounting schemes in central Iowa, implementing extensive data acquisition systems, monitoring operation of the PV systems for one full year, and performing detailed experimental performance and economic studies. The two PV systems that were installed, monitored, and analyzed included a 4.59 kWp roof-mounted stationary system oriented for maximum annual energy production, and a 1.02 kWp pole-mounted actively controlled dual-axis tracking system. The second objective was to demonstrate the actual use and performance of real-world stationary and dual-axis tracking grid-connected PV systems used for building energy generation applications. This objective was achieved by offering the installed PV systems to the public for demonstration purposes and through the development of three computer-based tools: a software interface that has the ability to display real-time and historical performance and meteorological data of both systems side-by-side, a software interface that shows real-time and historical video and photographs of each system, and a calculator that can predict performance and economics of stationary and dual-axis tracking grid-connected PV systems at various locations in the United States. The final objective was to disseminate this work to social, professional, scientific, and academic communities in a way that is applicable, objective, accurate, accessible, and comprehensible. This final objective will be addressed by publishing the results of this work and making the computer-based tools available on a public website (www.energy.iastate.edu/Renewable/solar). Detailed experimental

  7. Dynamic characterization and modelling of a dual-axis beam steering device for performance understanding, optimization and control design

    NASA Astrophysics Data System (ADS)

    Berglund, Martin; Palmer, Kristoffer; Lotfi, Sara; Kratz, Henrik; Thornell, Greger

    2013-04-01

    This paper presents a lumped thermal model of a dual-axis laser micromirror device for beam steering in a free-space optical (FSO) communication system, designed for fractionated spacecraft. An FSO communication system provides several advantages, such as larger bandwidth, smaller size and weight of the communication payload and less power consumption. A dual-axis mirror device is designed and realized using microelectromechanical systems technology. The fabrication is based on a double-sided, bulk micromachining process, where the mirror actuates thermally by joints consisting of v-grooves filled with the SU-8 polymer. The size of the device, consisting of a mirror, which is deflectable versus its frame in one direction, and through deflection of the frame in the other, is 15.4 × 10.4 × 0.3 mm3. In order to further characterize and understand the micromirror device, a Simulink state-space model of the actuator is set up using thermal and mechanical properties from a realized actuator. A deviation of less than 2% between the modelled and measured devices was obtained in an actuating temperature range of 20-200 °C. The model of the physical device was examined by evaluating its performance in vacuum, and by changing physical parameters, such as thickness and material composition. By this, design parameters were evaluated for performance gain and usability. For example, the crosstalk between the two actuators deflecting the mirror along its two axes in atmospheric pressure is projected to go down from 97% to 6% when changing the frame material from silicon to silicon dioxide. A feedback control system was also designed around the model in order to examine the possibility to make a robust control system for the physical device. In conclusion, the model of the actuator presented in this paper can be used for further understanding and development of the actuator system.

  8. Miniature in vivo MEMS-based line-scanned dual-axis confocal microscope for point-of-care pathology

    PubMed Central

    Yin, C.; Glaser, A.K.; Leigh, S. Y.; Chen, Y.; Wei, L.; Pillai, P. C. S.; Rosenberg, M. C.; Abeytunge, S.; Peterson, G.; Glazowski, C.; Sanai, N.; Mandella, M. J.; Rajadhyaksha, M.; Liu, J. T. C.

    2016-01-01

    There is a need for miniature optical-sectioning microscopes to enable in vivo interrogation of tissues as a real-time and noninvasive alternative to gold-standard histopathology. Such devices could have a transformative impact for the early detection of cancer as well as for guiding tumor-resection procedures. Miniature confocal microscopes have been developed by various researchers and corporations to enable optical sectioning of highly scattering tissues, all of which have necessitated various trade-offs in size, speed, depth selectivity, field of view, resolution, image contrast, and sensitivity. In this study, a miniature line-scanned (LS) dual-axis confocal (DAC) microscope, with a 12-mm diameter distal tip, has been developed for clinical point-of-care pathology. The dual-axis architecture has demonstrated an advantage over the conventional single-axis confocal configuration for reducing background noise from out-of-focus and multiply scattered light. The use of line scanning enables fast frame rates (16 frames/sec is demonstrated here, but faster rates are possible), which mitigates motion artifacts of a hand-held device during clinical use. We have developed a method to actively align the illumination and collection beams in a DAC microscope through the use of a pair of rotatable alignment mirrors. Incorporation of a custom objective lens, with a small form factor for in vivo clinical use, enables our device to achieve an optical-sectioning thickness and lateral resolution of 2.0 and 1.1 microns respectively. Validation measurements with reflective targets, as well as in vivo and ex vivo images of tissues, demonstrate the clinical potential of this high-speed optical-sectioning microscopy device. PMID:26977337

  9. Miniature in vivo MEMS-based line-scanned dual-axis confocal microscope for point-of-care pathology.

    PubMed

    Yin, C; Glaser, A K; Leigh, S Y; Chen, Y; Wei, L; Pillai, P C S; Rosenberg, M C; Abeytunge, S; Peterson, G; Glazowski, C; Sanai, N; Mandella, M J; Rajadhyaksha, M; Liu, J T C

    2016-02-01

    There is a need for miniature optical-sectioning microscopes to enable in vivo interrogation of tissues as a real-time and noninvasive alternative to gold-standard histopathology. Such devices could have a transformative impact for the early detection of cancer as well as for guiding tumor-resection procedures. Miniature confocal microscopes have been developed by various researchers and corporations to enable optical sectioning of highly scattering tissues, all of which have necessitated various trade-offs in size, speed, depth selectivity, field of view, resolution, image contrast, and sensitivity. In this study, a miniature line-scanned (LS) dual-axis confocal (DAC) microscope, with a 12-mm diameter distal tip, has been developed for clinical point-of-care pathology. The dual-axis architecture has demonstrated an advantage over the conventional single-axis confocal configuration for reducing background noise from out-of-focus and multiply scattered light. The use of line scanning enables fast frame rates (16 frames/sec is demonstrated here, but faster rates are possible), which mitigates motion artifacts of a hand-held device during clinical use. We have developed a method to actively align the illumination and collection beams in a DAC microscope through the use of a pair of rotatable alignment mirrors. Incorporation of a custom objective lens, with a small form factor for in vivo clinical use, enables our device to achieve an optical-sectioning thickness and lateral resolution of 2.0 and 1.1 microns respectively. Validation measurements with reflective targets, as well as in vivo and ex vivo images of tissues, demonstrate the clinical potential of this high-speed optical-sectioning microscopy device. PMID:26977337

  10. Radionuclides in Small Mammals Collected at the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility during 2001-- 2003

    SciTech Connect

    P.R. Fresquez

    2005-01-20

    Rodents are effective indicators of environmental contamination and the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility Mitigation Action Plan specifies the (radionuclide) comparison of small mammals to baseline levels to determine if there are any impacts as a result of operations. Consequently, samples of (whole body) field mice (Peromyscus spp.) were collected from within the grounds of the DARHT facility at Los Alamos National Laboratory, Technical Area 15, from 2001 through 2003. Samples were analyzed for {sup 3}H, {sup 137}Cs, {sup 90}Sr, {sup 241}Am, {sup 238}Pu, {sup 239,240}Pu, {sup 234}U, {sup 235}U, and {sup 238}U. Results, which represent three years since the start of operations in 2000, were compared with baseline statistical reference level (BSRL) data established over a four-year-long preoperational period. Most radionuclides in mice were either at nondetectable levels or within BSRLs. The few radionuclides that were above BSRLs included U isotopes; and the ratios of some samples indicated depleted U sources. Although the amounts of U in some samples were just above BSRLs, and since depleted U is less soluble and less toxic (chemical and radioactive) than naturally occurring U, the very small levels in the mice collected around the DARHT facility grounds are unlikely to pose a threat to predators that feed upon them.

  11. High precision dual-axis tracking solar wireless charging system based on the four quadrant photoelectric sensor

    NASA Astrophysics Data System (ADS)

    Liu, Zhilong; Wang, Biao; Tong, Weichao

    2015-08-01

    This paper designs a solar automatic tracking wireless charging system based on the four quadrant photoelectric sensor. The system track the sun's rays automatically in real time to received the maximum energy and wireless charging to the load through electromagnetic coupling. Four quadrant photoelectric sensor responsive to the solar spectrum, the system could get the current azimuth and elevation angle of the light by calculating the solar energy incident on the sensor profile. System driver the solar panels by the biaxial movement mechanism to rotate and tilt movement until the battery plate and light perpendicular to each other. Maximize the use of solar energy, and does not require external power supply to achieve energy self-sufficiency. Solar energy can be collected for portable devices and load wireless charging by close electromagnetic field coupling. Experimental data show that: Four quadrant photoelectric sensor more sensitive to light angle measurement. when track positioning solar light, Azimuth deviation is less than 0.8°, Elevation angle deviation is less than 0.6°. Use efficiency of a conventional solar cell is only 10% -20%.The system uses a Four quadrant dual-axis tracking to raise the utilization rate of 25% -35%.Wireless charging electromagnetic coupling efficiency reached 60%.

  12. Video-rate in vivo fluorescence imaging with a line-scanned dual-axis confocal microscope

    PubMed Central

    Chen, Ye; Wang, Danni; Khan, Altaz; Wang, Yu; Borwege, Sabine; Sanai, Nader; Liu, Jonathan T. C.

    2015-01-01

    Abstract. Video-rate optical-sectioning microscopy of living organisms would allow for the investigation of dynamic biological processes and would also reduce motion artifacts, especially for in vivo imaging applications. Previous feasibility studies, with a slow stage-scanned line-scanned dual-axis confocal (LS-DAC) microscope, have demonstrated that LS-DAC microscopy is capable of imaging tissues with subcellular resolution and high contrast at moderate depths of up to several hundred microns. However, the sensitivity and performance of a video-rate LS-DAC imaging system, with low-numerical aperture optics, have yet to be demonstrated. Here, we report on the construction and validation of a video-rate LS-DAC system that possesses sufficient sensitivity to visualize fluorescent contrast agents that are topically applied or systemically delivered in animal and human tissues. We present images of murine oral mucosa that are topically stained with methylene blue, and images of protoporphyrin IX-expressing brain tumor from glioma patients that have been administered 5-aminolevulinic acid prior to surgery. In addition, we demonstrate in vivo fluorescence imaging of red blood cells trafficking within the capillaries of a mouse ear, at frame rates of up to 30 fps. These results can serve as a benchmark for miniature in vivo microscopy devices under development. PMID:26509413

  13. Dual-axis rotational coronary angiography can reduce peak skin dose and scattered dose: a phantom study.

    PubMed

    Liu, Huiliang; Jin, Zhigeng; Deng, Yunpeng; Jing, Limin

    2014-07-08

    The purpose of this study was to evaluate peak skin dose received by the patient and scattered dose to the operator during dual-axis rotational coronary angiography (DARCA), and to compare with those of standard coronary angiography (SA). An anthropomorphic phantom was used to simulate a patient undergoing diagnostic coronary angiography. Cine imaging was applied on the phantom for 2 s, 3 s, and 5 s in SA projections to mimic clinical situations with normal vessels, and uncomplicated and complicated coronary lesions. DARCA was performed in two curved trajectories around the phantom. During both SA and DARCA, peak skin dose was measured with thermoluminescent dosimeter arrays and scattered dose with a dosimeter at predefined height (approximately at the level of left eye) at the operator's location. Compared to SA, DARCA was found lower in both peak skin dose (range: 44%-82%, p < 0.001) and scattered dose (range: 40%-70%, p < 0.001). The maximal reductions were observed in the set mimicking complicated lesion examinations (82% reduction for peak skin dose, p < 0.001; 70% reduction for scattered dose, p < 0.001). DARCA reduces both peak skin dose and scattered dose in comparison to SA. The benefi t of radiation dose reduction could be especially signifi cant in complicated lesion examinations due to large reduction in X-ray exposure time. The use of DARCA could, therefore, be recommended in clinical practice to minimize radiation dose.

  14. Optimizing the performance of dual-axis confocal microscopes via Monte-Carlo scattering simulations and diffraction theory.

    PubMed

    Chen, Ye; Liu, Jonathan T C

    2013-06-01

    Dual-axis confocal (DAC) microscopy has been found to exhibit superior rejection of out-of-focus and multiply scattered background light compared to conventional single-axis confocal microscopy. DAC microscopes rely on the use of separated illumination and collection beam paths that focus and intersect at a single focal volume (voxel) within tissue. While it is generally recognized that the resolution and contrast of a DAC microscope depends on both the crossing angle of the DAC beams, 2θ, and the focusing numerical aperture of the individual beams, α, a detailed study to investigate these dependencies has not been performed. Contrast and resolution are considered as two main criteria to assess the performance of a point-scanned DAC microscope (DAC-PS) and a line-scanned DAC microscope (DAC-LS) as a function of θ and α. The contrast and resolution of these designs are evaluated by Monte-Carlo scattering simulations and diffraction theory calculations, respectively. These results can be used for guiding the optimal designs of DAC-PS and DAC-LS microscopes.

  15. Video-rate in vivo fluorescence imaging with a line-scanned dual-axis confocal microscope

    NASA Astrophysics Data System (ADS)

    Chen, Ye; Wang, Danni; Khan, Altaz; Wang, Yu; Borwege, Sabine; Sanai, Nader; Liu, Jonathan T. C.

    2015-10-01

    Video-rate optical-sectioning microscopy of living organisms would allow for the investigation of dynamic biological processes and would also reduce motion artifacts, especially for in vivo imaging applications. Previous feasibility studies, with a slow stage-scanned line-scanned dual-axis confocal (LS-DAC) microscope, have demonstrated that LS-DAC microscopy is capable of imaging tissues with subcellular resolution and high contrast at moderate depths of up to several hundred microns. However, the sensitivity and performance of a video-rate LS-DAC imaging system, with low-numerical aperture optics, have yet to be demonstrated. Here, we report on the construction and validation of a video-rate LS-DAC system that possesses sufficient sensitivity to visualize fluorescent contrast agents that are topically applied or systemically delivered in animal and human tissues. We present images of murine oral mucosa that are topically stained with methylene blue, and images of protoporphyrin IX-expressing brain tumor from glioma patients that have been administered 5-aminolevulinic acid prior to surgery. In addition, we demonstrate in vivo fluorescence imaging of red blood cells trafficking within the capillaries of a mouse ear, at frame rates of up to 30 fps. These results can serve as a benchmark for miniature in vivo microscopy devices under development.

  16. Gabor-domain optical coherence microscopy with integrated dual-axis MEMS scanner for fast 3D imaging and metrology

    NASA Astrophysics Data System (ADS)

    Canavesi, Cristina; Cogliati, Andrea; Hayes, Adam; Santhanam, Anand P.; Tankam, Patrice; Rolland, Jannick P.

    2015-10-01

    Fast, robust, nondestructive 3D imaging is needed for characterization of microscopic structures in industrial and clinical applications. A custom micro-electromechanical system (MEMS)-based 2D scanner system was developed to achieve 55 kHz A-scan acquisition in a Gabor-domain optical coherence microscopy (GD-OCM) instrument with a novel multilevel GPU architecture for high-speed imaging. GD-OCM yields high-definition volumetric imaging with dynamic depth of focusing through a bio-inspired liquid lens-based microscope design, which has no moving parts and is suitable for use in a manufacturing setting or in a medical environment. A dual-axis MEMS mirror was chosen to replace two single-axis galvanometer mirrors; as a result, the astigmatism caused by the mismatch between the optical pupil and the scanning location was eliminated and a 12x reduction in volume of the scanning system was achieved. Imaging at an invariant resolution of 2 μm was demonstrated throughout a volume of 1 × 1 × 0.6 mm3, acquired in less than 2 minutes. The MEMS-based scanner resulted in improved image quality, increased robustness and lighter weight of the system - all factors that are critical for on-field deployment. A custom integrated feedback system consisting of a laser diode and a position-sensing detector was developed to investigate the impact of the resonant frequency of the MEMS and the driving signal of the scanner on the movement of the mirror. Results on the metrology of manufactured materials and characterization of tissue samples with GD-OCM are presented.

  17. Dual-Axis Rotational Coronary Angiography: A New Technique for Detecting Graft Coronary Vasculopathy in Pediatric Heart Transplant Recipients

    PubMed Central

    Gudausky, Todd M.; Pelech, Andrew N.; Stendahl, Gail; Tillman, Kathryn; Mattice, Judy; Berger, Stuart; Zangwill, Steven

    2016-01-01

    Annual surveillance coronary angiograpyhy to screen for graft coronary vasculopathy is routine practice after orthotopic heart transplantation. Traditionally, this is performed with direct coronary angiography using static single-plane or biplane angiography. Recently, technological advances have made it possible to perform dual-axis rotational coronary angiography (RA). This technique differs from standard static single-plane or biplane angiography in that a single detector is preprogrammed to swing through a complex 80° arc during a single injection. It has the advantage of providing a perspective of the vessels from a full arc of images rather than from one or two static images per contrast injection. The current study evaluated two coronary angiography techniques used consecutively at a single center to evaluate pediatric heart transplant recipients for graft coronary vasculopathy. A total of 23 patients underwent routine coronary angiography using both biplane static coronary angiography (BiP) and RA techniques at the Children's Hospital of Wisconsin from February 2009 to September 2010. Demographic and procedure data were collected from each procedure and analyzed for significance utilizing a Wilcoxon rank sum test. No significant demographic or procedural differences between the BiP and the RA procedures were noted. Specific measures of radiation dose including fluoroscopy time and dose area product were similar among the imaging techniques. The findings show that RA can be performed safely and reproducibly in pediatric heart transplant recipients. Compared with standard BiP, RA does not increase radiation exposure or contrast use and in our experience has provided superior angiographic imaging for the evaluation of graft coronary vasculopathy. PMID:22956061

  18. Coordination of the cortisol and testosterone responses: A dual axis approach to understanding the response to social status threats.

    PubMed

    Turan, Bulent; Tackett, Jennifer L; Lechtreck, Maria T; Browning, Wesley R

    2015-12-01

    facilitate performance. These findings have implications for developing a dual axis understanding of physiological responses during social threats and competition and their function. PMID:26254769

  19. Coordination of the cortisol and testosterone responses: A dual axis approach to understanding the response to social status threats.

    PubMed

    Turan, Bulent; Tackett, Jennifer L; Lechtreck, Maria T; Browning, Wesley R

    2015-12-01

    facilitate performance. These findings have implications for developing a dual axis understanding of physiological responses during social threats and competition and their function.

  20. Design and Implementation of a Sun Tracker with a Dual-Axis Single Motor for an Optical Sensor-Based Photovoltaic System

    PubMed Central

    Wang, Jing-Min; Lu, Chia-Liang

    2013-01-01

    The dual threats of energy depletion and global warming place the development of methods for harnessing renewable energy resources at the center of public interest. Solar energy is one of the most promising renewable energy resources. Sun trackers can substantially improve the electricity production of a photovoltaic (PV) system. This paper proposes a novel design of a dual-axis solar tracking PV system which utilizes the feedback control theory along with a four-quadrant light dependent resistor (LDR) sensor and simple electronic circuits to provide robust system performance. The proposed system uses a unique dual-axis AC motor and a stand-alone PV inverter to accomplish solar tracking. The control implementation is a technical innovation that is a simple and effective design. In addition, a scaled-down laboratory prototype is constructed to verify the feasibility of the scheme. The effectiveness of the Sun tracker is confirmed experimentally. To conclude, the results of this study may serve as valuable references for future solar energy applications. PMID:23467030

  1. Micromirror-scanned dual-axis confocal microscope utilizing a gradient-index relay lens for image guidance during brain surgery

    NASA Astrophysics Data System (ADS)

    Liu, Jonathan T. C.; Mandella, Michael J.; Loewke, Nathan O.; Haeberle, Henry; Ra, Hyejun; Piyawattanametha, Wibool; Solgaard, Olav; Kino, Gordon S.; Contag, Christopher H.

    2010-03-01

    A fluorescence confocal microscope incorporating a 1.8-mm-diam gradient-index relay lens is developed for in vivo histological guidance during resection of brain tumors. The microscope utilizes a dual-axis confocal architecture to efficiently reject out-of-focus light for high-contrast optical sectioning. A biaxial microelectromechanical system (MEMS) scanning mirror is actuated at resonance along each axis to achieve a large field of view with low-voltage waveforms. The unstable Lissajous scan, which results from actuating the orthogonal axes of the MEMS mirror at highly disparate resonance frequencies, is optimized to fully sample 500×500 pixels at two frames per second. Optically sectioned fluorescence images of brain tissues are obtained in living mice to demonstrate the utility of this microscope for image-guided resections.

  2. Vertical and dual-axis vibration of the seated human body: Nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass

    NASA Astrophysics Data System (ADS)

    Zheng, Guangtai; Qiu, Yi; Griffin, Michael J.

    2012-12-01

    The vertical apparent mass of the human body exhibits nonlinearity, with the principal resonance frequency reducing as the vibration magnitude increases. Measures of the transmission of vibration to the spine and the pelvis have suggested complex modes are responsible for the dominant resonance during vertical excitation, but the modes present with dual-axis excitation have not been investigated. This study was designed to examine how the apparent mass and transmissibility of the human body depend on the magnitude of vertical excitation and the addition of fore-and-aft excitation, and the relation between the apparent mass and the transmissibility of the body. The movement of the body (over the first, fifth and twelfth thoracic vertebrae, the third lumbar vertebra, and the pelvis) in the fore-and-aft and vertical directions (and in pitch at the pelvis) was measured in 12 male subjects sitting with their hands on their laps during random vertical vibration excitation (over the range 0.25-20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 m s-2 rms). At the highest magnitude of vertical excitation (1.0 m s-2 rms) the effect of adding fore-aft vibration (at 0.25, 0.5, and 1.0 m s-2 rms) was investigated. The forces in the vertical and fore-and-aft directions on the seat surface were also measured so as to calculate apparent masses. Resonances in the apparent mass and transmissibility to the spine and pelvis in the fore-and-aft and vertical directions, and pitch transmissibility to the pelvis, shifted to lower frequencies as the magnitude of vertical excitation increased and as the magnitude of the additional fore-and-aft excitation increased. The nonlinear resonant behaviour of the apparent mass and transmissibility during dual-axis vibration excitation suggests coupling between the principal mode associated with vertical excitation and the cross-axis influence of fore-and-aft excitation. The transmissibility measures are consistent with complex modes

  3. Assessing delivery and quantifying efficacy of small interfering ribonucleic acid therapeutics in the skin using a dual-axis confocal microscope

    NASA Astrophysics Data System (ADS)

    Ra, Hyejun; Gonzalez-Gonzalez, Emilio; Smith, Bryan R.; Gambhir, Sanjiv S.; Kino, Gordon S.; Solgaard, Olav; Kaspar, Roger L.; Contag, Christopher H.

    2010-05-01

    Transgenic reporter mice and advances in imaging instrumentation are enabling real-time visualization of cellular mechanisms in living subjects and accelerating the development of novel therapies. Innovative confocal microscope designs are improving their utility for microscopic imaging of fluorescent reporters in living animals. We develop dual-axis confocal (DAC) microscopes for such in vivo studies and create mouse models where fluorescent proteins are expressed in the skin for the purpose of advancing skin therapeutics and transdermal delivery tools. Three-dimensional image volumes, through the different skin compartments of the epidermis and dermis, can be acquired in several seconds with the DAC microscope in living mice, and are comparable to histologic analyses of reporter protein expression patterns in skin sections. Intravital imaging with the DAC microscope further enables visualization of green fluorescent protein (GFP) reporter gene expression in the skin over time, and quantification of transdermal delivery of small interfering RNA (siRNA) and therapeutic efficacy. Visualization of transdermal delivery of nucleic acids will play an important role in the development of innovative strategies for treating skin pathologies.

  4. Simultaneous Photonic Doppler Velocimetry and Dual Axis Framing Technique

    NASA Astrophysics Data System (ADS)

    Bowden, Mike; Neal, Will

    2015-06-01

    Flyer plates, accelerated by the electrical explosion of a metallic bridge, have historically primarily been characterised using velocity interferometery methods such as VISAR and Photonic Doppler Velocimetry (PDV). With the advent of high-fidelity three-dimensional magnetohydronamical codes such as ALEGRA and ALE-MHD, there is a requirement for the characterisation of spatially-resolved phenomena such as bridge burst, flyer formation and flyer break-up. Multiple high-speed cameras were integrated with PDV, to provide both flyer plate velocity and othogonal views of the flyer plate. Optically-upshifted PDV was used, and flyer plate velocities in excess of 4 km.s-1 were measured. Laser illumination enabled imaging with exposures as short as 5 ns to be obtained, effectively freezing the motion of the flyer plate. The experimental technique is described, and example data obtained is presented.

  5. An auditory display in a dual-axis tracking task.

    NASA Technical Reports Server (NTRS)

    Mirchandani, P. B.

    1972-01-01

    Results of a study in which subjects were presented concurrently with the primary task of controlling a second-order plant and the secondary task of controlling a first-order plant. The plant errors for the two tasks were shown on separate visual displays. An auditory display, whose output varied in frequency and volume with the error, was used to supplement the secondary task in half of the runs. To study the effects of the auditory display, two performance measures were obtained: (1) the integral of the squared error (ISE) and (2) the describing functions of the human operator. Statistical analysis of the ISE measures indicated that when the secondary task was supplemented with an auditory display, there was a significant improvement in performance on the secondary task. The performance on the primary task improved on the average, but not significantly. The variances of the ISE values decreased for both the tasks, indicating a more consistent behavior with the auditory display. The describing function analysis showed that supplementing the secondary task with the auditory display increased the low frequency gain of the human operator for this task. The describing functions for the primary task did not show any apparent changes.

  6. Dual-axis resonance testing of wind turbine blades

    DOEpatents

    Hughes, Scott; Musial, Walter; White, Darris

    2014-01-07

    An apparatus (100) for fatigue testing test articles (104) including wind turbine blades. The apparatus (100) includes a test stand (110) that rigidly supports an end (106) of the test article (104). An actuator assembly (120) is attached to the test article (104) and is adapted for substantially concurrently imparting first and second forcing functions in first and second directions on the test article (104), with the first and second directions being perpendicular to a longitudinal axis. A controller (130) transmits first and second sets of displacement signals (160, 164) to the actuator assembly (120) at two resonant frequencies of the test system (104). The displacement signals (160, 164) initiate the actuator assembly (120) to impart the forcing loads to concurrently oscillate the test article (104) in the first and second directions. With turbine blades, the blades (104) are resonant tested concurrently for fatigue in the flapwise and edgewise directions.

  7. National Wind Tecnology Center Provides Dual Axis Resonant Blade Testing

    ScienceCinema

    Felker, Fort

    2016-07-12

    NREL's Structural Testing Laboratory at the National Wind Technology Center (NWTC) provides experimental laboratories, computer facilities for analytical work, space for assembling components and turbines for atmospheric testing as well as office space for industry researchers. Fort Felker, center director at the NWTC, discusses NREL's state-of-the-art structural testing capabilities and shows a flapwise and edgewise blade test in progress.

  8. National Wind Tecnology Center Provides Dual Axis Resonant Blade Testing

    SciTech Connect

    Felker, Fort

    2013-11-13

    NREL's Structural Testing Laboratory at the National Wind Technology Center (NWTC) provides experimental laboratories, computer facilities for analytical work, space for assembling components and turbines for atmospheric testing as well as office space for industry researchers. Fort Felker, center director at the NWTC, discusses NREL's state-of-the-art structural testing capabilities and shows a flapwise and edgewise blade test in progress.

  9. AsTeRICS.

    PubMed

    Drajsajtl, Tomáš; Struk, Petr; Bednárová, Alice

    2013-01-01

    AsTeRICS - "The Assistive Technology Rapid Integration & Construction Set" is a construction set for assistive technologies which can be adapted to the motor abilities of end-users. AsTeRICS allows access to different devices such as PCs, cell phones and smart home devices, with all of them integrated in a platform adapted as much as possible to each user. People with motor disabilities in the upper limbs, with no cognitive impairment, no perceptual limitations (neither visual nor auditory) and with basic skills in using technologies such as PCs, cell phones, electronic agendas, etc. have available a flexible and adaptable technology which enables them to access the Human-Machine-Interfaces (HMI) on the standard desktop and beyond. AsTeRICS provides graphical model design tools, a middleware and hardware support for the creation of tailored AT-solutions involving bioelectric signal acquisition, Brain-/Neural Computer Interfaces, Computer-Vision techniques and standardized actuator and device controls and allows combining several off-the-shelf AT-devices in every desired combination. Novel, end-user ready solutions can be created and adapted via a graphical editor without additional programming efforts. The AsTeRICS open-source framework provides resources for utilization and extension of the system to developers and researches. AsTeRICS was developed by the AsTeRICS project and was partially funded by EC.

  10. AsTeRICS.

    PubMed

    Drajsajtl, Tomáš; Struk, Petr; Bednárová, Alice

    2013-01-01

    AsTeRICS - "The Assistive Technology Rapid Integration & Construction Set" is a construction set for assistive technologies which can be adapted to the motor abilities of end-users. AsTeRICS allows access to different devices such as PCs, cell phones and smart home devices, with all of them integrated in a platform adapted as much as possible to each user. People with motor disabilities in the upper limbs, with no cognitive impairment, no perceptual limitations (neither visual nor auditory) and with basic skills in using technologies such as PCs, cell phones, electronic agendas, etc. have available a flexible and adaptable technology which enables them to access the Human-Machine-Interfaces (HMI) on the standard desktop and beyond. AsTeRICS provides graphical model design tools, a middleware and hardware support for the creation of tailored AT-solutions involving bioelectric signal acquisition, Brain-/Neural Computer Interfaces, Computer-Vision techniques and standardized actuator and device controls and allows combining several off-the-shelf AT-devices in every desired combination. Novel, end-user ready solutions can be created and adapted via a graphical editor without additional programming efforts. The AsTeRICS open-source framework provides resources for utilization and extension of the system to developers and researches. AsTeRICS was developed by the AsTeRICS project and was partially funded by EC. PMID:23739379

  11. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    PubMed Central

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  12. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-05-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers.

  13. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films.

    PubMed

    Bouška, M; Pechev, S; Simon, Q; Boidin, R; Nazabal, V; Gutwirth, J; Baudet, E; Němec, P

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  14. Heterojunction double dumb-bell Ag2Te-Te-Ag2Te nanowires

    NASA Astrophysics Data System (ADS)

    Som, Anirban; Pradeep, T.

    2012-07-01

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag2Te-Te-Ag2Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic

  15. Neutron capture of /sup 122/Te, /sup 123/Te, /sup 124/Te, /sup 125/Te, and /sup 126/Te

    SciTech Connect

    Macklin, R.L.; Winters, R.R.

    1989-07-01

    Isotopically enriched samples of the tellurium isotopes from mass 122 to mass 126 were used to measure neutron capture in the energy range 2.6 keV to 600 keV at the Oak Ridge Electron Linear Accelerator pulsed neutron source. Starting at 2.6 keV, over 200 Breit-Wigner resonances for each isotope were used to describe the capture data. Least-squares adjustment gave parameters and their uncertainties for a total of 1659 resonances. Capture cross sections averaged over Maxwellian neutron distributions with temperatures ranging from kT = 5 keV to kT = 100 keV were derived for comparison with stellar nucleosynthesis calculations. For the three isotopes shielded from the astrophysical r-process, /sup 122/Te, /sup 123/Te and /sup 124/Te at kT = 30 keV the respective values were (280 /plus minus/ 10) mb, (819 /plus minus/ 30) mb and (154 /plus minus/ 6) mb. The corresponding products of cross section and solar system abundance are nearly equal in close agreement with s-process nucleosynthesis calculations. 26 refs., 8 figs., 10 tabs.

  16. Te/C nanocomposites for Li-Te Secondary Batteries

    PubMed Central

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm−3), excellent cyclability (ca. 705 mA h cm−3 over 100 cycles), and fast rate capability (ca. 550 mA h cm−3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems. PMID:25609035

  17. Te/C nanocomposites for Li-Te Secondary Batteries.

    PubMed

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li(+)/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm(-3)), excellent cyclability (ca. 705 mA h cm(-3) over 100 cycles), and fast rate capability (ca. 550 mA h cm(-3) at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  18. Te/C nanocomposites for Li-Te Secondary Batteries

    NASA Astrophysics Data System (ADS)

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm-3), excellent cyclability (ca. 705 mA h cm-3 over 100 cycles), and fast rate capability (ca. 550 mA h cm-3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  19. Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems

    NASA Astrophysics Data System (ADS)

    Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin

    2015-08-01

    The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.

  20. Radioisotope Thermoelectric Generators Based on Segmented BiTe/PbTe-BiTe/TAGS/PbSnTe

    NASA Astrophysics Data System (ADS)

    McAlonan, Malachy; Patel, Kalpesh; Cummer, Keith

    2006-01-01

    This paper reports on Phase 1 of a multifaceted effort to develop a more efficient radioisotope thermoelectric generator (RTG) for future NASA missions. The conversion efficiency goal is 10% or higher at a power level of 20 watt or higher. The thermoelectric (T/E) efficiency achievable with present T/E materials is about 8% for favorable temperatures. Thermoelectric converter designs, T/E material properties, and T/E couple thermal and electrical performance were investigated in Phase 1 of this program to find paths to improve conversion efficiency. T/E properties can be improved by optimizing the composition of the materials and by improving the micro structural characteristics such as homogeneity, grain size, and phases present. T/E couple performance can be improved by reducing the electrical and thermal contact resistances of the couple and within the segmented T/E elements. Performance and reliability improvements can be achieved by reducing the thermo-mechanical stresses, improving the quality of the bonds and interfaces, minimizing the number of required bonds, and reducing the degradation rates of both the T/E materials and the bonds. This paper focuses on one portion of the activity, i.e., the design of a small converter. In the converter design effort, a prototypic 20-watt device, suitable for use with a single general-purpose heat source (GPHS), was built using an optimized converter design of segmented thermoelectric elements of heritage composition. The 20-watt prototype achieved the power predicted for the test conditions. The chosen couple design used segmented BiTe/PbTe for the n-type element and BiTe/TAGS/PbSnTe, for the p-type T/E element. Use of the BiTe segment exploits the opportunity of the small RTG to operate at lower heat rejection temperatures and results in much higher conversion efficiency, the main objective of the NASA program. Long term data on similarly segmented couples at Teledyne together with the 20-watt module test results

  1. Heterojunction double dumb-bell Ag₂Te-Te-Ag₂Te nanowires.

    PubMed

    Som, Anirban; Pradeep, T

    2012-08-01

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag(2)Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag(2)Te-Te-Ag(2)Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.

  2. Evaluation of Thermo-Mechanical Stability of COTS Dual-Axis MEMS Accelerometers for Space Applications

    NASA Technical Reports Server (NTRS)

    Sharma, Ashok K.; Teverovksy, Alexander; Day, John H. (Technical Monitor)

    2000-01-01

    Microelectromechanical systems in MEMS is one of the fastest growing technologies in microelectronics, and is of great interest for military and aerospace applications. Accelerometers are the earliest and most developed representatives of MEMS. First demonstrated in 1979, micromachined accelerometers were used in automobile industry for air bag crash- sensing applications since 1990. In 1999, N4EMS accelerometers were used in NASA-JPL Mars Microprobe. The most developed accelerometers for airbag crash- sensing are rated for a full range of +/- 50 G. The range of sensitivity for accelerometers required for military or aerospace applications is much larger, varying from 20,000 G (to measure acceleration during gun and ballistic munition launches), and to 10(exp -6) G, when used as guidance sensors (to measure attitude and position of a spacecraft). The presence of moving parts on the surface of chip is specific to MEMS, and particularly, to accelerometers. This characteristic brings new reliability issues to micromachined accelerometers, including cyclic fatigue cracking of polysilicon cantilevers and springs, mechanical stresses that are caused by packaging and contamination in the internal cavity of the package. Studies of fatigue cracks initiation and growth in polysilicon showed that the fatigue damage may influence MEMS device performance, and the presence of water vapor significantly enhances crack initiation and growth. Environmentally induced failures, particularly, failures due to thermal cycling and mechanical shock are considered as one of major reliability concerns in MEMS. These environmental conditions are also critical for space applications of the parts. For example, the Mars pathfinder mission had experienced 80 mechanical shock events during the pyrotechnic separation processes.

  3. The beamline for the second axis of the dual axis radiographic hydrodynamic test facility

    SciTech Connect

    Caporaso, G J; Chen, Y J; Fawley, W M; Lee, E P; Paul, A C; Westenkow, G

    1999-03-23

    During normal DARHT II operation, the beam exiting the accelerator will be well characterized by its nominal design parameters of 20-MeV, 2000-Amperes, 2-{micro}sec-pulse length, and 3 cm-mr unnormalized emittance. Normal operation will have the beam delivered to a beam dump via several DC magnets. A 2-way kicker magnet is used to deflect portions of the beam into the straight ahead beamline leading to either a diagnostic beamline or to the converter target beamline. During start up and or beam development periods, the beam exiting the accelerator may have parameters outside the acceptable range of values for normal operation. The Enge beamline must accommodate this range of unacceptable beam parameters, delivering the entire 80 KiloJoule of beam to the dump even though the energy, emittance, and/or match is outside the nominal design range.

  4. Experiences in the military may impact dual-axis neuroendocrine processes in veterans.

    PubMed

    Bobadilla, Leonardo; Asberg, Kia; Johnson, Megan; Shirtcliff, Elizabeth A

    2015-09-01

    Military stressors such as survival training can affect endocrine functioning in the short term, and combat has been associated with endocrine changes linked to psychopathology. However, studies with military samples examining whether there are individual differences in these changes as part of normal development, or as an adaptive mechanism in adulthood are lacking. This study examined whether exposure to combat in a sample of veterans was associated with differential endocrine activity to a laboratory frustration task. Results indicated that Army veterans demonstrated significant testosterone reactivity to frustration and negative coupling between cortisol and testosterone. Alternatively, Navy and Marine veterans demonstrated little testosterone reactivity to frustration and positive coupling between cortisol and testosterone. Positive cortisol-testosterone coupling was stronger among individuals who had more dangerous combat experiences. This latter pattern may better prepare individuals for stressful life experiences and supports the contention that adulthood stressors may calibrate endocrine systems. Results are explained in the context of the Adaptive Calibration Model (Ellis et al., 2012, Developmental Psychology, 48(3), 598-623) which proposes that exposure to key environmental dimensions during endocrinologically malleable life stages (e.g., puberty) can change stress responsivity, resulting in a faster life history trajectory (e.g., increased risk-taking and aggression).

  5. Qualification of a High Accuracy Dual-Axis Antenna Deployment and Trimming Mechanism

    NASA Technical Reports Server (NTRS)

    Gossant, Alain; Morichon, Francois

    2010-01-01

    The Antenna Deployment and Trimming Mechanism Mark 2 (ADTM Mk2) has been developed to answer today's need for a generic antenna deployment and high accuracy pointing mechanism, allowing RF sensing applications and easier dual deployments configurations. This paper presents the design and evolution from its predecessor, the experience of the design team from kick off to qualification and batch manufacture, as well as some lessons learned from ramping up "mass-production" capabilities while implementing customer driven changes. Astrium has manufactured and flown ADTM units for the past 20 years, from an initial deployment-only mechanism developed for the Orion program to today's Eurostar E3000 ADTM family. The Antenna ADTM Mk2 is an evolution of the original ADTM Mk1. Although it uses Mk1 building blocks to minimize risks associated with the development of a new product, it incorporates major evolutions and is the new baseline for Astrium latest generation of Eurostar E3000 telecom satellites.

  6. Near-infrared emission spectra of TeS, TeSe and Te2

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.

    2014-10-01

    Emission spectra of the radicals TeS, TeSe and Te2 in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The molecules were generated in a fast-flow system by reacting microwave-discharged mixtures of Tex, Sx, and/or Sex vapour and Ar carrier gas and excited by energy transfer and energy pooling processes in collisions with metastable oxygen O2(a1Δg). The b1Σ+(b0+) → X3Σ-(X10+,X21) electric dipole transitions of TeS and TeSe and the b1Σ+g(b0+g) → X3Σ-g(X21g) magnetic dipole transition of Te2 were measured at medium and high spectral resolution. A very weak emission at 3356 cm-1 observed in the spectrum of TeSe was identified to be the 0-0 band of the hitherto unknown a1Δ(a2) → X3Σ-(X21) transition of the molecule. Analyses of the spectra have yielded a number of new or improved spectroscopic parameters of the molecules.

  7. Optical phonons in PbTe/CdTe multilayer heterostructures

    SciTech Connect

    Novikova, N. N.; Yakovlev, V. A.; Kucherenko, I. V.; Karczewski, G.; Aleshchenko, Yu. A.; Muratov, A. V.; Zavaritskaya, T. N.; Melnik, N. N.

    2015-05-15

    The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

  8. BOREAS TE-7 Dendrology Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Varem-Sanders, T. M. L.; Campbell, I. D.

    2000-01-01

    The BOREAS TE-7 team collected data sets in support of its efforts to characterize and interpret information on the sapflow and dendrology of boreal vegetation. This data set contains dendrology measurements, consisting of tree ring width and density taken at several points within each ring,.Measurements were taken near the TE towers at the OJP and OBS sites in NSA. In the SSA, measurements were taken near the TE towers at the MIX, OBS, and OJP sites; at the AIM- 1 3 and BMH-9 sites; and near the TF-YJP site. All data were collected during the summer of 1994. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  9. Local Distortions in PbTe:Tl

    NASA Astrophysics Data System (ADS)

    Keiber, Trevor; Bridges, Frank; Sales, Brian

    2013-03-01

    Lead Telluride (PbTe) is a well characterized thermoelectric material. Tl doping increases the figure of merit with a maximum at 2% Tl. Recent X-ray diffraction and total neutron scattering experiments suggest Pb moves off-center along the 100 axis as T increases. To investigate the local structure we present an Extended X-ray Absorption Fine Structure (EXAFS) analysis for 0-3% Tl concentrations at the Tl and Pb L3 edges and at the Te K edge. At 10K the local structure about Pb is well ordered, the Pb-Te (Te-Pb) pair distribution function (PDF) broadens rapidly with T. Attempts to model the increase in σ2(T) for the Pb-Te pair (σ is the width of the PDF) with a 100 Pb off-center displacement, were not successful. However σ2(T) for the Pb-Te pair is well described by a correlated Debye model with a low correlated Debye temperature. The Te edge shows increased disorder for the the Te-Te pair and later peaks which may be caused by a structural change around the Te atom. For Tl, the environment is distorted even at 10K within the host material. This indicates a large variation of the Tl-Te bond lengths, presumably as a result of the presence of Tl(+1). We discuss possible models for the disorder about Tl, Pb, and Te in PbTe:Tl. Support: NSF DMR 1005568

  10. M@TE - Monitoring at TeV Energies

    NASA Astrophysics Data System (ADS)

    Tovmassian, Gagik; Dorner, Daniela; Bretz, Thomas; González, Magdalena; Alfaro, Ruben

    2016-06-01

    A dedicated long-term monitoring programm at TeV energies has been started by the FACT project about four years ago. Being limited to one site, gaps due to the rotation of the Earth remain in the measured light curves. This makes it difficult to study typical variability time scales of few hours to one day. To allow for systematic studies of continuous observations over up to 12 hours, a second telescope is being installed at a site in about six hours distance in longitude. For the M@TE (Monitoring at TeV energies) telescope, a mount from a previous experiment is being refurbished and will be equipped with a new camera. Using silicon based photo sensors like in FACT, an excellent and stable performance will be achieved. M@TE is a joint project of German and Mexican universities which aims at extending the blazar monitoring to so far unexplored time ranges. In the presentation, the status of this emerging project will be reported.

  11. Synthesis of alpha-MoTe2 nanorods via annealing Te-seeded amorphous MoTe2 particles.

    PubMed

    Qiu, Longhui; Wei, Yun; Pol, Vilas G; Gedanken, Aharon

    2004-09-20

    Semiconductor alpha-MoTe2 nanorods have been synthesized by annealing Te-seeded particles of an amorphous MoTe2 intermediate. This intermediate is prepared by a solution reaction between Mo(CO)6 and elemental Te in diphenylmethane. The as-synthesized products were characterized by structural, compositional, and morphological techniques of X-ray diffraction, selected area electron diffraction, selected area energy dispersive spectroscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The results of the annealing process are MoTe2 nanorods with diameters of 50-200 nm and lengths ranging from 0.1 to 3.0 microm. Here, the rodlike structure of MoTe2 is reported for the first time, and added to the list as one kind of new morphology of MoTe2 nanomaterials. A mechanism for the formation of the nanorods is proposed. The sandwich-layered structure of Te-Mo-Te and the similarity in the structure between hexagonal alpha-MoTe2 and hexagonal Te are responsible for the formation of nanorods of MoTe2. PMID:15360257

  12. Photoemission determination of the band diagram of the Te/CdTe interface

    NASA Astrophysics Data System (ADS)

    Niles, David W.; Li, Xiaonan; Sheldon, Peter

    1995-05-01

    A band diagram of the Te/CdTe interface was believed to be a prerequisite in understanding how the Te layer on the CdTe surface lowered the resistance of contacts to CdTe solar cell devices. A two-stage experiment was therefore designed. First, the application of x-ray photoelectron and Auger electron spectroscopies was discussed to comprehend the etching process. Second, the valence-band offset by vacuum deposition of Te on a sputtered CdTe surface was measured employing ultraviolet photoemission spectroscopy.

  13. Molecular beam epitaxial re-growth of CdTe, CdTe/CdMgTe and CdTe/CdZnTe double heterostructures on CdTe/InSb(1 0 0) substrates with As cap

    NASA Astrophysics Data System (ADS)

    Seyedmohammadi, Shahram; DiNezza, Michael J.; Liu, Shi; King, Paul; LeBlanc, Elizabeth G.; Zhao, Xin-Hao; Campbell, Calli; Myers, Thomas H.; Zhang, Yong-Hong; Malik, Roger J.

    2015-09-01

    Molecular beam epitaxial growth on CdTe substrates is challenging since the CdTe film crystalline and optical quality is limited by residual defects including threading dislocations and stacking faults. This remains an obstacle in spite of exhausting variables including pre-growth substrate preparation as well as epitaxial growth conditions including thermal oxide desorption, growth temperature, and II/VI flux ratios. We propose a new technique to re-grow structures with low defect densities and high optical and structural quality on InSb substrates. The "CdTe virtual wafer" is made by growing a thin CdTe film on an InSb(1 0 0) substrate which is then covered with a thin As cap layer to prevent oxidation of the CdTe surface. The As cap can be removed by thermal desorption at about 300 C leaving a clean CdTe surface for subsequent epitaxial growth. This method eliminates the need for chemical etching of CdTe substrates which has been found to lead to an atomically rough surface with residual Carbon and Oxygen contamination. XRD and SEM characterization show a smooth transition from the buffer CdTe to re-grown CdTe layer with identical crystalline quality as for virtual wafer. Steady-state PL and time-resolved PL from CdTe/CdMgTe double heterostructures show substantial improvement in luminescence intensity and carrier lifetime comparable to values for identical samples grown without exposure to atmosphere. We will also report on CdTe/CdZnTe double heterostructures grown on virtual wafers compared to identical structures on conventional CdTe(2 1 1)B substrates.

  14. Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

  15. Learning To Use TeX

    NASA Astrophysics Data System (ADS)

    Hammons, Derek; Close, Hunter

    2012-03-01

    TeX is a useful tool for any scientific professional, but it can also be used by undergraduates to create high quality documents for courses. My presentation will focus on why TeX is a useful program for undergraduates to learn. It can create higher quality lab reports and other documents for courses than other commonly used word processors such as Microsoft Word. TeX can be utilized by anyone through use of a TeX document preparation system such as LaTeX and only a few simple commands. Perhaps best of all, TeX is free to download and use! By taking the time to understand how to use TeX, students will learn a valuable skill that will be continue to be useful throughout their academic and professional careers.

  16. Pulsars at TeV

    NASA Astrophysics Data System (ADS)

    Edwards, P.

    1994-04-01

    The atmospheric Cerenkov technique is used to search for emission at energies above several hundred GeV from a variety of objects, including pulsars (see, e.g., reviews by Weekes, 1988, Phys. Rep., 160, 1; Weekes, 1992, Sp. Sci. Rev., 59, 315). Claims for TeV emission (from any source) should be of high significance, show gamma-ray-like properties, and be independently confirmed. By these criteria the Crab nebula is currently the only established pulsar-driven system to be observed at TeV energies (Weekes et al., 1989, Astrophys. J., 342, 379; Vacanti et al., 1991, Astrophys. J., 377, 467; Goret et al., 1993, Astron. Astrophys., 270, 401). The gamma-ray signal is not pulsed at TeV energies, leading to models of synchrotron self-Compton emission from the Crab nebula (e.g., De Jager and Harding, 1992, Astrophys. J., 396, 161), although other models have also been proposed (Kwok et al., 1991, Astrophys. J., 379, 653). While claims exist for TeV emission from, amongst others, the Vela pulsar (e.g., Bhat et al., 1987, Astron. Astrophys., 178, 242, Geminga (Vishwanath et al., 1993, Astron. Astrophys., 267, L5; Bowden et al., 1993, J. Phys. G: Nucl. Part. Phys., 19, L29), and PSR 1509-58 (Nel et al., 1992, Astrophys. TeV sources. *The detection of TeV gamma-rays from millisecond pulsars has been considered recently by Smith (1993, Astrophys. -J., 408, 468).

  17. n-(CdMgTe/CdTe)/(p-(CdTe/ZnCdTe/ZnTe)/p-GaAs heterostructure diode for photosensor applications

    NASA Astrophysics Data System (ADS)

    Yahia, I. S.; AlFaify, S.; Abutalib, M. M.; Chusnutdinow, S.; Wojtowicz, T.; Karczewski, G.; Yakuphanoglu, F.; Al-Bassam, A.; El-Naggar, A. M.; El-Bashir, S. M.

    2016-05-01

    High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole-Cole plots. The radius of the Cole-Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.

  18. HgTe-CdTe-InSb heterostructures by molecular beam epitaxy

    SciTech Connect

    Ballingall, J.M.; Leopold, D.J.; Peterman, D.J.

    1985-08-01

    HgTe-CdTe heterostructures have been grown by molecular beam epitaxy on (100) InSb substrates. Separate elemental Hg and Te beams were used for the HgTe growth at a substrate temperature of 160 C. X-ray diffraction measurements indicate that thin epitaxial layers are of high crystalline quality. Secondary-ion mass spectroscopy measurements show substantial In and Sb diffusion into the epitaxial layers with a concentration enhancement at the HgTe-CdTe interface. 9 references.

  19. Development of electrodeposited ZnTe layers as window materials in ZnTe/CdTe/CdHgTe multi-layer solar cells

    SciTech Connect

    Islam, A.B.M.O. Chaure, N.B.; Wellings, J.; Tolan, G.; Dharmadasa, I.M.

    2009-02-15

    Zinc telluride (ZnTe) thin films have been deposited on glass/conducting glass substrates using a low-cost electrodeposition method. The resulting films have been characterized using various techniques in order to optimize growth parameters. X-ray diffraction (XRD) has been used to identify the phases present in the films. Photoelectrochemical (PEC) cell and optical absorption measurements have been performed to determine the electrical conductivity type, and the bandgap of the layers, respectively. It has been confirmed by XRD measurement that the deposited layers mainly consist of ZnTe phases. The PEC measurements indicate that the ZnTe layers are p-type in electrical conduction and optical absorption measurements show that their bandgap is in the range 2.10-2.20 eV. p-Type ZnTe window materials have been used in CdTe based solar cell structures, following new designs of graded bandgap multi-layer solar cells. The structures of FTO/ZnTe/CdTe/metal and FTO/ZnTe/CdTe/CdHgTe/metal have been investigated. The results are presented in this paper using observed experimental data.

  20. PbTe and SnTe quantum dot precipitates in a CdTe matrix fabricated by ion implantation

    SciTech Connect

    Kaufmann, E.; Schwarzl, T.; Groiss, H.; Hesser, G.; Schaeffler, F.; Palmetshofer, L.; Springholz, G.; Heiss, W.

    2009-08-15

    We present rock-salt IV-VI semiconductor quantum dots fabricated by implantation of Pb{sup +}, Te{sup +}, or Sn{sup +} ions into epitaxial zinc-blende CdTe layers. PbTe and SnTe nanoprecipitates of high structural quality are formed after implantation by thermal annealing due to the immiscibility of dot and matrix materials. For samples implanted only with Pb{sup +}, intense continuous-wave photoluminescence peaked at 1.6 mum at 300 K is found. In contrast, for PbTe quantum dots fabricated by coimplantation of Pb{sup +} and Te{sup +}, the 300 K emission peak is observed at 2.9 mum, indicating luminescence from much larger dots.

  1. Solutal diffusion coefficient for liquid PbTe-SnTe

    NASA Technical Reports Server (NTRS)

    Clark, I. O.; Fripp, A. L.; Debnam, W. J., Jr.; Crouch, R. K.; Brewer, W. D.

    1983-01-01

    The solutal diffusion coefficient has been determined for liquid lead telluride-tin telluride using a modified shear cell technique. Postdiffusion concentration profiles are presented for several diffusion couples. The best analytical curve fit to the data gives a composition-dependent diffusion coefficient of (/3/7/ to the C power) x 0.00014 sq cm/sec, where C is the PbTe concentration. In addition, data are presented to show the importance of solutal convection in the lead-tin-telluride system.

  2. Advanced Superlattice BiTe-PbTe/TAGS Milliwatt Radioisotope Power System

    NASA Astrophysics Data System (ADS)

    Drinker, Richard W.; Reddy, Anil; Heshmatpour, Ben; Snyder, G. Jeffrey; Tuttle, Karen L.

    2005-02-01

    The objective of this effort, under NASA's Project Prometheus, the Nuclear Systems Program, is to develop a high efficiency thermoelectric (T/E) energy conversion device to power milliwatt radioisotope power systems (mWRPS) for future NASA space science applications. The conversion efficiency goal is 8% at a power output level of 50 to several hundred mW. A two stage cascaded T/E module design is being used to achieve these program objectives. This concept incorporates the advanced superlattice BiTe thermoelectric device technology, which is under development by Research Triangle institute (RTI), with Teledyne's segmented T/E couple technology. The hot stage device in the cascade is comprised of Teledyne's PbTe/TAGS/PbSnTe segmented T/E couple which is glass bonded into a monolithic multicouple configuration. The cold stage device is an RTI developed thin film superlattice BiTe based multicouple device.

  3. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-01-01

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate and electrolyzing the leachate to separate Cd from Te, wherein the Te is deposits onto a cathode while the Cd remains in solution.

  4. Weak Topological Insulators in PbTe/SnTe superlattice

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Liu, Junwei; Fu, Liang; Duan, Wenhui; Liu, Chaoxing

    2014-03-01

    It is desirable to realize topological phases in artificial structures by engineering electronic band structures. In this paper, we investigate (PbTe)m(SnTe)2n-m superlattices along the [001] direction and find a robust weak topological insulator phase for a large variety of layer numbers m and 2 n - m . We confirm this topologically non-trivial phase by calculating Z2 topological invariants and topological surface states based on the first-principles calculations. We show that the folding of Brillouin zone due to the superlattice structure plays an essential role in inducing topologically non-trivial phases in this system. This mechanism can be generalized to other systems in which band inversion occurs at multiple momenta, and gives us a brand-new way to engineer topological materials in artificial structures. We acknowledge support from the Ministry of Science and Technology of China and the National Natural Science Foundation of China. LF is supported by the DOE Office of Basic Energy Sciences.

  5. Response of Cds/CdTe Devices to Te Exposure of Back Contact: Preprint

    SciTech Connect

    Gessert, T. A.; Burst, J. M.; Ma, J.; Wei, S. H.; Kuciauskas, D.; Barnes, T. M.; Duenow, J. N.; Young, M. R.; Rance, W. L.; Li, J. V.; Dippo, P.

    2012-06-01

    Theoretical predictions of thin-film CdS/CdTe photovoltaic (PV) devices have suggested performance may be improved by reducing recombination due to Te-vacancy (VTe) or Te-interstitial (Tei) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it also may be coupled to formation of beneficial cadmium vacancy (VCd) defects. If this is true, reducing potential effects of VTe or Tei may be difficult without also reducing the density of VCd. In contrast, post-deposition processes can sometimes afford a greater degree of defect control. Here we explore a post-deposition process that appears to influence the Te-related defects in polycrystalline CdTe. Specifically, we have exposed the CdTe surface to Te prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing VTe but without significantly reducing VCd. Initial results show that when this modified contact is used on a CdCl2-treated CdS/CdTe device, significantly poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or CuTe or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of VTe (e.g., oxygen and chlorine additions to the CdTe), adding even a small amount of Te may produce detrimental defects.

  6. Dislocation reduction in HgCdTe grown on CdTe/Si

    NASA Astrophysics Data System (ADS)

    Wijewarnasuriya, Priyalal S.

    2016-05-01

    Bulk-grown CdZnTe (Zn = 3%) substrates are the natural choice for HgCdTe epitaxy since it is lattice matched to long wave LW-HgCdTe alloy. However, lack of large area CdZnTe substrates, high production costs, and more importantly, the difference in thermal expansion coefficients between CdZnTe and silicon Read out Integrated Circuits (ROIC) are some of the inherent drawbacks of CdZnTe substrates. Consequently, Hg1-xCdxTe detectors fabricated on silicon substrates are an attractive alternative. Recent developments in the molecular beam epitaxy (MBE) buffer layer growth technology on Si substrates has revolutionized the HgCdTe research and offered a new dimension to HgCdTe-based IR technology. Si substrates provide advantages in terms of relatively large area (3 to 6-inch diameter is easily obtained) compared to CZT substrate materials, durability during processing, and reliability to thermal cycling. Innovations in Si-based composite substrates made it possible to fabricate very large-format IR arrays that offer higher resolution, low-cost arrays and more dies per wafer. Between Si substrates and HgCdTe has large lattice mismatch of 19%. This leads to dislocation densities of low-107 cm-2 for optimal growth of HgCdTe on silicon-based substrates as compared to the mid-104 cm-2 dislocation density of HgCdTe grown on CdZnTe. This paper present dislocation reduction by two orders of magnitude using thermal cycle anneal under Hg environment on HgCdTe grown on Si substrates and as well as defect reduction in Cd(Se)Te buffer layers grown on Si Substrates.

  7. Cyclotron resonance in HgTe/CdTe-based heterostructures in high magnetic fields

    PubMed Central

    2012-01-01

    Cyclotron resonance study of HgTe/CdTe-based quantum wells with both inverted and normal band structures in quantizing magnetic fields was performed. In semimetallic HgTe quantum wells with inverted band structure, a hole cyclotron resonance line was observed for the first time. In the samples with normal band structure, interband transitions were observed with wide line width due to quantum well width fluctuations. In all samples, impurity-related magnetoabsorption lines were revealed. The obtained results were interpreted within the Kane 8·8 model, the valence band offset of CdTe and HgTe, and the Kane parameter EP being adjusted. PMID:23013642

  8. Identification of ^109Xe and ^105Te

    NASA Astrophysics Data System (ADS)

    Liddick, S.; Batchelder, J. C.; Grzywacz, R.; Mazzocchi, C.; Bingham, C. R.; Drafta, G.; Korgul, A.; Tantawy, M. N.; Page, R. D.; Darby, I. G.; Joss, D. T.; Thomson, J.; Rykaczewski, K. P.; Gross, C.; Goodin, C.; Hamilton, J. H.; Hwang, J. K.; Li, K.; Ilyushkin, S.; Winger, J. A.; Lagergren, K.; Krolas, W.; Hecht, A. A.

    2006-10-01

    The existence of a region of alpha emitting nuclei above ^100Sn is due to the presence of the Z=50 shell closures. The region is a fertile area to investigate possible enhanced correlations between neutrons and protons filling the same single-particle orbits and could lead to the observation of superallowed alpha decay as an approach is made towards ^100Sn. The new isotope ^109Xe was produced at the HRIBF at Oak Ridge National Laboratory. The lightest mass α-radioactivity identified to date, ^105Te, was detected through the ^109Xe->^105Te ->^101Sn alpha decay chain. This marks the closest approach to the N = Z line above ^100Sn. The half-life and Qα value for ^105Te were used to determine the reduced α-decay width, 2̂. The ratio 2̂^105Te/2̂^213Po of 2.7 indicates a superallowed character of the α-emission from ^105Te. Fine structure in the millisecond alpha decay of ^109Xe to ^105Te was identified and the energy difference between the νd5/2 ground state and the νg7/2 first excited state was determined to be around 150 keV in ^105Te. Prospects for reaching the superallowed alpha decay chain ^108Xe->^104Te ->^100Sn will also be discussed.

  9. The NuTeV anomaly: solved?

    SciTech Connect

    Londergan, J. T.

    2010-07-27

    The NuTeV extraction of the Weinberg angle is reported to differ by 3{sigma} from measurements at the Z pole. We review various effects within the Standard Model, and conclude that corrections from these effects bring the NuTeV measurement within 1{sigma} of the expected result.

  10. CdTe devices and method of manufacturing same

    SciTech Connect

    Gessert, Timothy A.; Noufi, Rommel; Dhere, Ramesh G.; Albin, David S.; Barnes, Teresa; Burst, James; Duenow, Joel N.; Reese, Matthew

    2015-09-29

    A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.

  11. Device Fabrication using Crystalline CdTe and CdTe Ternary Alloys Grown by MBE

    SciTech Connect

    Zaunbrecher, Katherine; Burst, James; Seyedmohammadi, Shahram; Malik, Roger; Li, Jian V.; Gessert, Timothy A.; Barnes, Teresa

    2015-06-14

    We fabricated epitaxial CdTe:In/CdTe:As homojunction and CdZnTe/CdTe and CdMgTe/CdTe heterojunction devices grown on bulk CdTe substrates in order to study the fundamental device physics of CdTe solar cells. Selection of emitter-layer alloys was based on passivation studies using double heterostructures as well as band alignment. Initial results show significant device integration challenges, including low dopant activation, high resistivity substrates and the development of low-resistance contacts. To date, the highest open-circuit voltage is 715 mV in a CdZnTe/CdTe heterojunction following anneal, while the highest fill factor of 52% was attained in an annealed CdTe homojunction. In general, all currentvoltage measurements show high series resistance, capacitancevoltages measurements show variable doping, and quantum efficiency measurements show low collection. Ongoing work includes overcoming the high resistance in these devices and addressing other possible device limitations such as non-optimum junction depth, interface recombination, and reduced bulk lifetime due to structural defects.

  12. Rational design and controlled synthesis of Te/Bi2Te3 heterostructure nanostring composites

    NASA Astrophysics Data System (ADS)

    Zhang, Yuzhuo; Chen, Hong; Li, Zhiliang; Huang, Ting; Zheng, Shuqi

    2015-07-01

    Te/Bi2Te3 heterostructure nanostring composites composed of several Bi2Te3 nanoplates, which were perpendicularly strung together by Te nanorod, were rationally designed and synthesized via a facile solvothermal method on a large scale. The X-ray diffraction (XRD) characterization demonstrated that the Bi2Te3 nanoplates were rhombohedral phase and the Te nanorods were trigonal phase. The uniform nanostring morphologies were well characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Detailed heterostructures were proved via energy dispersive spectrometer (EDS) and high-resolution transmission electron microscope (HRTEM). The morphology transformation from Bi2Te3 nanoplates to Te/Bi2Te3 heterostructure nanostrings could be controlled by adjusting the ratio of bismuth oxide to tellurium oxide. NaOH, serving as catalytic reduction agent and morphology controlling agent, played an important role in the synthesis of Te/Bi2Te3 heterostructure nanostrings. The reaction mechanism was also proposed to explain the formation process of the composites and the specific function of reagents in this reaction system.

  13. CdSxTe1-x Alloying in CdS/CdTe Solar Cells

    SciTech Connect

    Duenow, J. N.; Dhere, R. G.; Moutinho, H. R.; To, B.; Pankow, J. W.; Kuciauskas, D.; Gessert, T. A.

    2011-05-01

    A CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thin-film CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by RF magnetron sputtering and co-evaporation from CdTe and CdS sources. Both radio-frequency-magnetron-sputtered and co-evaporated CdSxTe1-x films of lower S content (x<0.3) have a cubic zincblende (ZB) structure akin to CdTe, while those of higher S content have a hexagonal wurtzite (WZ) structure like that of CdS. Films become less preferentially oriented as a result of a CdCl2 heat treatment at ~400 degrees C for 5 min. Films sputtered in a 1% O2/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl2 heat treatment (HT). Films sputtered in O2 partial pressure have a much wider bandgap (BG) than expected. This may be explained by nanocrystalline size effects seen previously [2] for sputtered oxygenated CdS (CdS:O) films.

  14. Comparison between TeV and non-TeV BL Lac Objects

    NASA Astrophysics Data System (ADS)

    Lin, Chao; Fan, Jun-Hui

    2016-07-01

    BL Lacertae objects (BL Lacs) are the dominant population of TeV emitting blazars. In this work, we investigate whether there are any special observational properties associated with TeV sources. To do so, we will compare the observational properties of TeV detected BL Lacs (TeV BLs) with non-TeV detected BL Lac objects (non-TeV BLs). From the 3rd Fermi/LAT source catalog (3FGL), we can obtain 662 BL Lacs, out of which 47 are TeV BLs and 615 are non-TeV BLs. Their multi-wavelength flux densities (F R, F O, F X and F γ), photon spectral indexes (αX ph and αph γ), and effective spectral indexes (αRO and αOX) are compiled from the available literature. Then the luminosities (log vL R, log vL O, log vL X, log vL γ) are calculated. From comparisons, we find that TeV BLs are different from low synchrotron peaked BLs and intermediate synchrotron peaked BLs, but TeV BLs show similar properties to high synchrotron peaked (HSP) BLs. Therefore, we concentrated on a comparison between TeV HSP BLs and non-TeV HSP BLs. Analysis results suggest that TeV HSP BLs and non-TeV HSP BLs exhibit some differences in their αRO and αγ ph, but their other properties are quite similar.

  15. BOREAS TE-6 Allometry Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Gower, Stith T.; Vogel, Jason G.

    2000-01-01

    The BOREAS TE-6 team collected several data sets in support of its efforts to characterize and interpret information on the plant biomass, allometry, biometry, sapwood, leaf area index, net primary production, soil temperature, leaf water potential, soil CO2 flux, and multivegetation imagery of boreal vegetation. This data set includes tree measurements conducted on the above-ground biomass of trees in the BOREAS NSA and SSA during the growing seasons of 1994 and 1995 and the derived allometric relationships/equations. The data are stored in ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distrobuted Activity Archive Center (DAAC).

  16. Energy loss rate of a charged particle in HgTe/(HgTe, CdTe) quantum wells

    SciTech Connect

    Chen, Qinjun; Sin Ang, Yee; Wang, Xiaolin; Lewis, R. A.; Zhang, Chao

    2013-11-04

    The energy loss rate (ELR) of a charged particle in a HgTe/(HgTe, CdTe) quantum well is investigated. We consider scattering of a charged particle by the bulk insulating states in this type of topological insulator. It is found that the ELR characteristics due to the intraband excitation have a linear energy dependence while those due to interband excitation depend on the energy exponentially. An interesting quantitative result is that for a large range of the incident energy, the mean inelastic scattering rate is around a few terahertz.

  17. Low temperature magnetothermoelectric effect and magnetoresistance in Te vapor annealed Bi2Te3.

    PubMed

    Hor, Y S; Qu, D; Ong, N P; Cava, R J

    2010-09-22

    The electrical properties of single crystals of p-type Bi(2)Te(3) are shown to be tuned by annealing as-grown crystals in elemental Te vapor at temperatures in the range of 400-420 °C. While as-grown nominally stoichiometric Bi(2)Te(3) has p-type conductivity below room temperature, Te vapor annealed Bi(2)Te(3) shows a cross over from p- to n-type behavior. The temperature dependent resistivity of the Te annealed crystals shows a characteristic broad peak near 100 K. Applied magnetic fields give rise to a large low temperature magnetothermoelectric effect in the Te annealed samples and enhance the low temperature peak in the resistivity. Further, Te annealed Bi(2)Te(3) shows a large positive magnetoresistance, ∼ 200% at 2 K, and ∼ 15% at room temperature. The annealing procedure described can be employed to optimize the properties of Bi(2)Te(3) for study as a topological insulator.

  18. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    NASA Astrophysics Data System (ADS)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-06-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {{Te}}_{{Cd}}^{2 + } - {{V}}_{{Cd}}^{2 - } (D complex), {{In}}_{{Cd}}^{ + } - {{V}}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {{V}}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  19. Raman characterization of a new Te-rich binary compound: CdTe2.

    PubMed

    Rousset, Jean; Rzepka, Edouard; Lincot, Daniel

    2009-04-01

    Structural characterization by Raman spectroscopy of CdTe thin films electrodeposited in acidic conditions is considered in this work. This study focuses on the evolution of material properties as a function of the applied potential and the film thickness, demonstrating the possibility to obtain a new Te-rich compound with a II/VI ratio of 1/2 under specific bath conditions. Raman measurements carried out on etched samples first allow the elimination of the assumption of a mixture of phases CdTe + Te and tend to confirm the formation of the CdTe(2) binary compound. The signature of this phase on the Raman spectrum is the increase of the LO band intensity compared to that obtained for the CdTe. The influence of the laser power is also considered. While no effect is observed on CdTe films, the increase of the incident irradiation power leads to the decomposition of the CdTe(2) compound into two more stable phases namely CdTe and Te.

  20. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    NASA Astrophysics Data System (ADS)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-10-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {Te}_{{Cd}}^{2 + } - {V}_{{Cd}}^{2 - } (D complex), {In}_{{Cd}}^{ + } - {V}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {V}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  1. A facile method for gold decoration of Te@CdTe nanorods in aqueous solution.

    PubMed

    Shao, Haibao; Wang, Chunlei; Wang, Zhuyuan; Li, Rongqing; Xu, Qinying; Xu, Shuhong; Jiang, Yuan; Sun, Qingfeng; Bo, Fan; Cui, Yiping

    2012-10-01

    Colloidal synthesis of metal-semiconductor hybrid nanostructures is mainly achieved in organic solution. In some applications of hybrid nanoparticles relevant in aqueous media, phase transfer of hydrophobic metal-semiconductor hybrid nanostructures is essential. In this work, we present a simple method for direct synthesis of water-soluble gold (Au) decorated Te@CdTe hybrid nanorods (NRs) at room temperature by using aqueous Te@CdTe NRs as templates, which were preformed by using CdTe nanocrystals (NCs) as precursor in the presence of hydrazine hydrate (N(2)H(4)). Our results showed that NRs were decorated with Au islands both on tips and along the surface of the NRs. The size and density of Au islands can be controlled by varying the amount of Au precursor (mixture of HAuCl(4) and thioglycolic acid (TGA)) and TGA/HAuCl(4) ratio. A possible growth mechanism for the Au decoration of Te@CdTe NRs is concluded as three steps: (1) the formation of AuTe(1.7) via the substitution reaction of Cd(2+) by Au(3+), (2) adsorption of Au-TGA complex onto the preformed AuTe(1.7) anchors and following reduction by CdTe and N(2)H(4), leading to the formation of small Au NCs, (3) Au NCs grow to bigger ones, followed by reduction of more Au precursor by N(2)H(4). PMID:22795043

  2. Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals.

    PubMed

    Jang, Youngjin; Yanover, Diana; Čapek, Richard Karel; Shapiro, Arthur; Grumbach, Nathan; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2016-07-01

    Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs. PMID:27331900

  3. Low-dimensional Te-based nanostructures.

    PubMed

    Wang, Qisheng; Safdar, Muhammad; Wang, Zhenxing; He, Jun

    2013-07-26

    Low-dimensional Te-based nanomaterials have attracted intense attention in recent years due to their novel physical properties including surface-state effects, photoelectricity, phase changes, and thermoelectricity. The recent development of synthesis methods of low-dimensional Te-based nanostructures is reviewed, such as van der Waals expitaxial growth and template-assisted solution-phase deposition. In addition, the unique properties of these materials, such as tunable surface states, high photoresponsivity, fast phase change, and high thermoelectricity figure of merit, are reviewed. The potential applications of low-dimensional Te-based nanostructures are broad but particularly promising for nanoscale electronic and photoelectronic devices. PMID:24048978

  4. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, R.E.; Long, M.O.; Drinkard, W.F. Jr.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base. 3 figs.

  5. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base.

  6. Revised values of the bond-valence parameters for Te(IV)-O, Te(VI)-O and Te(IV)-Cl.

    PubMed

    Mills, Stuart J; Christy, Andrew G

    2013-04-01

    Bond-valence parameters r0 and b have been re-determined for Te(IV)-O: r0 = 1.9605 Å, b = 0.41; Te(VI)-O: r0 = 1.921 Å, b = 0.56; and Te(IV)-Cl: r0 = 2.3115 Å, b = 0.555. Bond distance data from 208 independent Te(IV)-O polyhedra, 118 Te(VI)-O polyhedra and 26 Te(IV)-Cl polyhedra were used, and all neighbours out to 3.5 Å were included. Root-mean square deviations of bond-valence sums on Te from ideal values were 0.1934, 0.1939 and 0.0865 v.u. The good fit for Te(IV)-O over a range of Te coordination numbers from 3 to 12 demonstrates that there is no essential difference in character between short `primary' Te-O bonds, oriented away from the Te lone pair, and longer `secondary' Te-O bonds on the same side of the Te atom as the lone pair. Comparison of bond-valence sums for Te-O polyhedra obtained using the new parameters with those calculated using earlier literature values shows that the new parameters give a narrower spread of calculated bond-valence sums, which means much closer to the formal valence for both oxidation states of tellurium.

  7. High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies

    NASA Astrophysics Data System (ADS)

    Lindström, A.; Mirbt, S.; Sanyal, B.; Klintenberg, M.

    2016-01-01

    In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers.

  8. Nonlinear terahertz response of HgTe/CdTe quantum wells

    SciTech Connect

    Chen, Qinjun; Sanderson, Matthew; Zhang, Chao

    2015-08-24

    Without breaking the topological order, HgTe/CdTe quantum wells can have two types of bulk band structure: direct gap type (type I) and indirect gap type (type II). We report that the strong nonlinear optical responses exist in both types of bulk states under a moderate electric field in the terahertz regime. Interestingly, for the type II band structure, the third order conductivity changes sign when chemical potentials lies below 10 meV due to the significant response of the hole excitation close to the bottom of conduction band. Negative nonlinear conductivities suggest that HgTe/CdTe quantum wells can find application in the gain medium of a laser for terahertz radiation. The thermal influences on nonlinear optical responses of HgTe/CdTe quantum wells are also studied.

  9. Growth and optical properties of CdTe quantum dots in ZnTe nanowires

    SciTech Connect

    Wojnar, Piotr; Janik, Elzbieta; Baczewski, Lech T.; Kret, Slawomir; Karczewski, G.; Wojtowicz, Tomasz

    2011-09-12

    We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV-2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.

  10. Perspective on TeV-scale physics

    SciTech Connect

    Chanowitz, M.S.

    1989-02-01

    These lectures review theoretical motivations and experimental prospects for the study of TeV-scale physics. Three clues to the importance of TeV physics are discussed: implications of quantum corrections for the masses of a fourth generation quark-lepton family, the gauge hierarchy problem and known solutions, and implications of symmetry and unitarity for the symmetry-breaking sector of the electroweak gauge theory. The experimental prospects are reviewed with emphasis on the multi-TeV pp colliders that may be built in the 1990's. The topics include new phenomena that might occur - e.g., a fourth generation, heavy gauge bosons, composite structure, and supersymmetry - as well as the signals of the unknown SU(2)/sub L/ /times/ U(1)/sub Y/ breaking mechanism that must occur within the TeV domain. 96 refs., 21 figs.

  11. Nonlinear dual-axis biodynamic response of the semi-supine human body during vertical whole-body vibration

    NASA Astrophysics Data System (ADS)

    Huang, Ya; Griffin, Michael J.

    2008-04-01

    Nonlinear biodynamic responses are evident in many studies of the apparent masses of sitting and standing subjects in static postures that require muscle activity for postural control. In the present study, 12 male subjects adopted a relaxed semi-supine posture assumed to involve less muscle activity than during static sitting and standing. The supine subjects were exposed to two types of vertical vibration (in the x-axis of the semi-supine body): (i) continuous random vibration (0.25-20 Hz) at five magnitudes (0.125, 0.25, 0.5, 0.75, and 1.0 m s -2 rms); (ii) intermittent random vibration (0.25-20 Hz) alternately at 0.25 and 1.0 m s -2 rms. With continuous random vibration, the dominant primary resonance frequency in the median normalised apparent mass decreased from 10.35 to 7.32 Hz as the vibration magnitude increased from 0.125 to 1.0 m s -2 rms. This nonlinear response was apparent in both the vertical ( x-axis) apparent mass and in the horizontal ( z-axis) cross-axis apparent mass. As the vibration magnitude increased from 0.25 to 1.0 m s -2 rms, the median resonance frequency of the apparent mass with intermittent random vibration decreased from 9.28 to 8.06 Hz whereas, over the same range of magnitudes with continuous random vibration, the resonance frequency decreased from 9.62 to 7.81 Hz. The median change in the resonance frequency (between 0.25 and 1.0 m s -2 rms) was 1.37 Hz with the intermittent random vibration and 1.71 with the continuous random vibration. With the intermittent vibration, the resonance frequency was higher at the high magnitude and lower at the low magnitude than with continuous vibration of the same magnitudes. The response was typical of thixotropy that may be a primary cause of the nonlinear biodynamic responses to whole-body vibration.

  12. Nonlinear dual-axis biodynamic response of the semi-supine human body during longitudinal horizontal whole-body vibration

    NASA Astrophysics Data System (ADS)

    Huang, Ya; Griffin, Michael J.

    2008-04-01

    The resonance frequencies in frequency response functions of the human body (e.g. apparent mass and transmissibility) decrease with increasing vibration magnitude. This nonlinear biodynamic response is found with various sitting and standing postures requiring postural control. The present study measured the apparent mass of the body in a relaxed semi-supine posture with two types of longitudinal horizontal vibration (in the z-axis of the semi-supine body): (i) continuous random excitation (0.25-20 Hz) at five magnitudes (0.125, 0.25, 0.5, 0.75 and 1.0 ms -2 rms); (ii) intermittent random excitation (0.25-20 Hz) alternately at 0.25 and 1.0 ms -2 rms. With continuous random vibration, the dominant primary resonance frequency in the median normalised apparent mass decreased from 3.7 to 2.4 Hz as the vibration magnitude increased from 0.125 to 1.0 ms -2 rms. A nonlinear response was apparent in both the horizontal ( z-axis) apparent mass and the vertical ( x-axis) cross-axis apparent mass. With intermittent random vibration, as the vibration magnitude increased from 0.25 to 1.0 ms -2 rms, the median resonance frequency of the apparent mass decreased from 3.2 to 2.5 Hz whereas, with continuous random vibration over the same range of magnitudes, the resonance frequency decreased from 3.4 to 2.4 Hz. The median change in the resonance frequency (between 0.25 and 1.0 ms -2 rms) was 0.6 Hz with the intermittent random vibration and 0.9 Hz with the continuous random vibration. With intermittent vibration, the resonance frequency was higher at the high magnitude and lower at the low magnitude than with continuous vibration at the same magnitudes. The responses were consistent with passive thixotropy being a primary cause of nonlinear biodynamic responses to whole-body vibration, although reflex activity of the muscles may also have an influence.

  13. Design and analysis of a dual-axis resonator fiber-optic gyroscope employing a single source.

    PubMed

    Pinnoji, Prerana Dabral; Nayak, Jagannath

    2013-08-01

    In this paper, design of a resonator fiber-optic gyroscope comprised of a single laser source and two optical fiber resonator rings is presented. A typical gyroscope measures angular rotation around a fixed axis, whereas the proposed design can sense simultaneous rotation about two orthogonal axes. Two variants of the design are proposed and analyzed using a mathematical model based on Jones matrix methodology.

  14. Dual-axis hormonal covariation in adolescence and the moderating influence of prior trauma and aversive maternal parenting.

    PubMed

    Simmons, Julian G; Byrne, Michelle L; Schwartz, Orli S; Whittle, Sarah L; Sheeber, Lisa; Kaess, Michael; Youssef, George J; Allen, Nicholas B

    2015-09-01

    Adversity early in life can disrupt the functioning of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes and increase risk for negative health outcomes. The interplay between these axes and the environment is complex, and understanding needs to be advanced by the investigation of the multiple hormonal relationships underlying these processes. The current study examined basal hormonal associations between morning levels of cortisol, testosterone, and dehydroepiandrosterone in a cohort of adolescents (mean age 15.56 years). The moderating influence of childhood adversity was also examined, as indexed by self-reported trauma (at mean age 14.91), and observed maternal aggressive parenting (at mean age 12.41). Between-person regressions revealed significant associations between hormones that were moderated by both measures of adversity. In females, all hormones positively covaried, but also interacted with adversity, such that positive covariation was typically only present when levels of trauma and/or aggressive parenting were low. In males, hormonal associations and interactions were less evident; however, interactions were detected for cortisol-testosterone - positively covarying at high levels of aggressive parenting but negatively covarying at low levels - and DHEA-cortisol - similarly positively covarying at high levels of parental aggression. These results demonstrate associations between adrenal and gonadal hormones and the moderating role of adversity, which is likely driven by feedback mechanisms, or cross-talk, between the axes. These findings suggest that hormonal changes may be the pathway through which early life adversity alters physiology and increases health risks, but does so differentially in the sexes; however further study is necessary to establish causation.

  15. Characterization of a self-calibrating, high-precision, stacked-stage, vertical dual-axis goniometer

    PubMed Central

    Mendenhall, Marcus H.; Henins, Albert; Windover, Donald; Cline, James P.

    2016-01-01

    We present details on the alignment and calibration of a goniometer assembly consisting two stacked, optically encoded, vertical axis rotation stages. A technique for its calibration is presented that utilizes a stable, uncalibrated, third stage to position a mirror in conjunction with a nulling autocollimator. Such a system provides a self-calibrating set of angular stages with absolute accuracy of ±0.1 second of plane angle (k=2 expanded uncertainty) around the full circle, suitable for laboratory application. This calibration technique permits in situ, absolute angular calibration of an operational goniometer assembly that is requisite for fully traceable angle measurement, as the installation of the encoder is known to change its performance from the angular calibration data provided by the manufacturer. PMID:27330224

  16. Characterization of a self-calibrating, high-precision, stacked-stage, vertical dual-axis goniometer

    NASA Astrophysics Data System (ADS)

    Mendenhall, Marcus H.; Henins, Albert; Windover, Donald; Cline, James P.

    2016-06-01

    We present details on the alignment and calibration of a goniometer assembly consisting two stacked, optically encoded, vertical axis rotation stages. A technique for its calibration is presented that utilizes a stable, uncalibrated, third stage to position a mirror in conjunction with a nulling autocollimator. Such a system provides a self-calibrating set of angular stages with absolute accuracy of  ±0.1 s of plane angle (k  =  2 expanded uncertainty) around the full circle, suitable for laboratory application. This calibration technique permits in situ, absolute angular calibration of an operational goniometer assembly that is requisite for fully traceable angle measurement, as the installation of the encoder is known to change its performance from the angular calibration data provided by the manufacturer.

  17. Dual-axis hormonal covariation in adolescence and the moderating influence of prior trauma and aversive maternal parenting.

    PubMed

    Simmons, Julian G; Byrne, Michelle L; Schwartz, Orli S; Whittle, Sarah L; Sheeber, Lisa; Kaess, Michael; Youssef, George J; Allen, Nicholas B

    2015-09-01

    Adversity early in life can disrupt the functioning of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes and increase risk for negative health outcomes. The interplay between these axes and the environment is complex, and understanding needs to be advanced by the investigation of the multiple hormonal relationships underlying these processes. The current study examined basal hormonal associations between morning levels of cortisol, testosterone, and dehydroepiandrosterone in a cohort of adolescents (mean age 15.56 years). The moderating influence of childhood adversity was also examined, as indexed by self-reported trauma (at mean age 14.91), and observed maternal aggressive parenting (at mean age 12.41). Between-person regressions revealed significant associations between hormones that were moderated by both measures of adversity. In females, all hormones positively covaried, but also interacted with adversity, such that positive covariation was typically only present when levels of trauma and/or aggressive parenting were low. In males, hormonal associations and interactions were less evident; however, interactions were detected for cortisol-testosterone - positively covarying at high levels of aggressive parenting but negatively covarying at low levels - and DHEA-cortisol - similarly positively covarying at high levels of parental aggression. These results demonstrate associations between adrenal and gonadal hormones and the moderating role of adversity, which is likely driven by feedback mechanisms, or cross-talk, between the axes. These findings suggest that hormonal changes may be the pathway through which early life adversity alters physiology and increases health risks, but does so differentially in the sexes; however further study is necessary to establish causation. PMID:25754696

  18. Classification of penetration--aspiration versus healthy swallows using dual-axis swallowing accelerometry signals in dysphagic subjects.

    PubMed

    Sejdić, Ervin; Steele, Catriona M; Chau, Tom

    2013-07-01

    Swallowing accelerometry is a promising noninvasive approach for the detection of swallowing difficulties. In this paper, we propose an approach for classification of swallowing accelerometry recordings containing either healthy swallows or penetration-aspiration (entry of material into the airway) in dysphagic patients. The proposed algorithm is based on the wavelet packet decomposition of swallowing accelerometry signals in combination with linear discriminant analysis as a feature reduction method and Bayes classification. The proposed algorithm was tested using swallowing accelerometry signals collected from 40 patients during the regularly scheduled videoflouroscopy exam. The participants were instructed to swallow several 5-mL sips of thin liquid barium in a head neutral position. The results of our numerical analysis showed that the proposed algorithm can differentiate healthy swallows from aspiration swallows with an accuracy greater than 90%. These results position swallowing accelerometry as a valid approach for the detection of swallowing difficulties, particularly penetration-aspiration in patients suspected of dysphagia. PMID:23372074

  19. A Method for Removal of Low Frequency Components Associated with Head Movements from Dual-Axis Swallowing Accelerometry Signals

    PubMed Central

    Sejdić, Ervin; Steele, Catriona M.; Chau, Tom

    2012-01-01

    Head movements can greatly affect swallowing accelerometry signals. In this paper, we implement a spline-based approach to remove low frequency components associated with these motions. Our approach was tested using both synthetic and real data. Synthetic signals were used to perform a comparative analysis of the spline-based approach with other similar techniques. Real data, obtained data from 408 healthy participants during various swallowing tasks, was used to analyze the processing accuracy with and without the spline-based head motions removal scheme. Specifically, we analyzed the segmentation accuracy and the effects of the scheme on statistical properties of these signals, as measured by the scaling analysis. The results of the numerical analysis showed that the spline-based technique achieves a superior performance in comparison to other existing techniques. Additionally, when applied to real data, we improved the accuracy of the segmentation process by achieving a 27% drop in the number of false negatives and a 30% drop in the number of false positives. Furthermore, the anthropometric trends in the statistical properties of these signals remained unaltered as shown by the scaling analysis, but the strength of statistical persistence was significantly reduced. These results clearly indicate that any future medical devices based on swallowing accelerometry signals should remove head motions from these signals in order to increase segmentation accuracy. PMID:22479402

  20. Evaluation of dynamic target options for dual axis radiography hydrotest facility II (DARHT II) and advanced hydrotest facility (AHF) programs

    SciTech Connect

    Krogh, M; Neurath, R; Sampayan, S; Sanders, D

    1999-03-01

    Initial results indicate that electron beams hitting targets used to generate x-rays during multipulse operation in advanced radiography facilities will generate plasma plumes which will disturb the electron beam during subsequent pulses. This, in turn, degrades the x-ray spot quality generated by the subsequent pulses. If this concern is substantiated, new facilities such as the Dual Axia Radiography Hydrotest Facility (DARHT II) and the Advanced Hydrotest Facility (AHF) will need a provision for mitigating this effect. one such provision involves moving the target with sufficient velocity that any plasmas formed are carried adequately far from the electron beam that they do not disturb it. They report the various approaches which have been considered and present data showing the maximum target rates which can be achieved with each approach.

  1. RF magnetron sputtering deposition of CdTe passivation on HgCdTe

    NASA Astrophysics Data System (ADS)

    Rutkowski, Jaroslaw; Adamiec, Krzysztof; Rogalski, Antoni

    1998-04-01

    In this study, we report the RF magnetron sputtering growth and characterization of CdTe passivant on bulk n-type HgCdTe. Our investigations include the HgCdTe surface preparation and in-situ pretreatment, deposition-induced surface damage, interface charge, CdTe film stoichiometry, and thermal stability. The metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage characteristics. The heterostructures are also characterized by reflectance measurement. In order to investigate the passivation properties of CdTe/HgCdTe heterostructures, we have modeled the band diagram of abrupt CdTe/HgCdTe heterojunction. The effect of sputtering growth condition parameters is also reported. The sputtering CdTe layers, exhibit excellent dielectric, insulating and mechano- chemical properties, as well as interface properties. The interfaces are characterized by slight accumulation and a small hysteresis. A carefully controlled growth process and surface pretreatment tailored to the specific material are required in order to obtain near flat band conditions on n- type materials. Additional informations on surface limitations are obtained from analyzing the I-V characteristics of photodiodes with metal gates covering the p-n junction surface location.

  2. Thermodynamic and Transport Properties of YTe3, LaTe3 and CeTe3

    SciTech Connect

    Ru, N.

    2011-08-19

    Measurements of heat capacity, susceptibility, and electrical resistivity are presented for single crystals of the charge density wave compounds YTe{sub 3}, LaTe{sub 3}, and CeTe{sub 3}. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe{sub 3} is found to be a weak Kondo lattice, with an antiferromagnetic ground state and T{sub N} = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

  3. GaTe semiconductor for radiation detection

    DOEpatents

    Payne, Stephen A.; Burger, Arnold; Mandal, Krishna C.

    2009-06-23

    GaTe semiconductor is used as a room-temperature radiation detector. GaTe has useful properties for radiation detectors: ideal bandgap, favorable mobilities, low melting point (no evaporation), non-hygroscopic nature, and availability of high-purity starting materials. The detector can be used, e.g., for detection of illicit nuclear weapons and radiological dispersed devices at ports of entry, in cities, and off shore and for determination of medical isotopes present in a patient.

  4. Evidences of the existence of SiTe2 crystalline phase and a proposed new Si-Te phase diagram

    NASA Astrophysics Data System (ADS)

    Mishra, R.; Mishra, P. K.; Phapale, S.; Babu, P. D.; Sastry, P. U.; Ravikumar, G.; Yadav, A. K.

    2016-05-01

    The existence of two distinct crystalline phases viz., Si2Te3 and SiTe2, in the Si-Te system is established from differential thermal analysis (DTA) studies. Thermo-gravimetric (TG) data on SiTe2 indicate that the compound decomposes to Si in multiple steps via intermediate Si2Te3 phase. X-ray diffraction (XRD) reveals that SiTe2 crystallizes in P 3 ̅m1 space group with CdI2 trigonal structure, whereas Si2Te3 crystallizes in trigonal structure with space group P 3 ̅1c with varying occupation of octahedral voids. Single Si atoms fill only 1/2 of the octahedral voids in SiTe2 structure whereas in Si2Te3, Si atoms are arranged in pairs occupying 2/3 of the octahedral voids in alternating planes along c-axis. Further, X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) confirm the distinctness of the chemical environment in the two crystalline structures confirming the uniqueness of both the phases. DTA results on the two compounds indicate the presence of one crystallographic phase-transition in each of the compound with transition temperatures at 441 °C for Si2Te3 and 392 °C for SiTe2. At the same time both Si2Te3 and SiTe2 undergo peritectic decomposition at 683 °C and 432 °C forming [Si(s)+Te(liq)] and [α-Si2Te3(s)+Te(liq)], respectively. The system revealed eutectic reaction between β-SiTe2 and Te at 398 °C [L=Te+SiTe2]. Consequently, the phase diagram in the Si-Te system has been delineated.

  5. Near-infrared emitting AgInTe2 and Zn-Ag-In-Te colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Langevin, Marc-Antoine; Pons, Thomas; Ritcey, Anna M.; Nì. Allen, Claudine

    2015-06-01

    The synthesis of AgInTe2 nanocrystals emitting between 1095 nm and 1160 nm is presented. Evolution of the Ag:In:Te ratio shows progressive incorporation of In3+ in Ag2Te, leading to the formation of orthorhombic AgInTe2. When zinc is added to the synthesis, the photoluminescence quantum yield reaches 3.4 %.

  6. Incommensurate phase of Te adsorbed on (001) GaAs

    NASA Astrophysics Data System (ADS)

    Cibert, J.; Saminadayar, K.; Tatarenko, S.; Gobil, Y.

    1989-06-01

    Occurrence of commensurate and incommensurate phases is reported for adsorption of Te on Ga-rich (001) GaAs surfaces. The Te coverage is measured directly through x-ray photoelectron spectroscopy, and the incommensurate phase is studied in detail as a function of Te coverage; two regimes are demonstrated, one at low coverage where Te is mainly bound to Ga, and another one at high coverage where Te mainly bound to As is also present.

  7. Manipulation of the presence of helical surface states of topological insulators using Sb2Te3-GeTe superlattices

    NASA Astrophysics Data System (ADS)

    Takagaki, Y.; Saito, Yuta; Tominaga, Junji

    2016-03-01

    Ab initio calculations have predicted a transition between topological insulators and band insulators in superlattices consisting of Sb2Te3 and GeTe, when the periodicity is varied. We examine the amplitude of the weak antilocalization effect to confirm the transition. In agreement with the predictions, robust surface states are present for (Sb2Te3)1(GeTe)2 but absent when the content of the well-known topological insulator Sb2Te3 is increased as (Sb2Te3)4(GeTe)2, manifesting that the electronic coupling in the superlattices affects the emergence of the helical surface states nontrivially.

  8. Effect of ZnTe and CdZnTe Alloys at the Back Contact of 1-μm-Thick CdTe Thin Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    2002-05-01

    N2-doped ZnTe was introduced onto 1-μm-thick CdTe absorbers in order to reduce the carrier recombination at the back contact of CdS/CdTe/C/Ag configuration solar cells. ZnTe films were grown by molecular beam epitaxy (MBE) on GaAs and Corning glass substrates to investigate the characteristics of the films. Epitaxial growth of ZnTe was realized on GaAs substrates and a hole concentration of 8 × 1018 cm-3 with a resistivity of 0.045 Ω \\cdotcm was achieved as a result of nitrogen doping. In contrast, polycrystalline ZnTe films were grown on Corning glass and CdTe thin films. Dark and photoconductivity of ZnTe films increased to 1.43 × 10-5 S/cm and 1.41 × 10-4 S/cm, respectively, while the Zn to Te ratio was decreased to 0.25 during MBE growth. These ZnTe films with different thicknesses were inserted into close-spaced sublimation (CSS)-grown 1-μm-thick CdTe solar cells. A conversion efficiency of 8.31% (Voc: 0.74 V, Jsc: 22.98 mA/cm2, FF: 0.49, area: 0.5 cm2) was achieved for a 0.2-μm-thick ZnTe layer with a cell configuration of CdS/CdTe/ZnTe/Cu-doped-C/Ag. Furthermore, to overcome the problem of possible recombination loss in the interface layer of CdTe and ZnTe, the intermediate ternary CdZnTe is investigated. The compositional factor in Cd1-xZnxTe:N alloy is varied and the dependence of the conductivity is evaluated. For instance, Cd0.5Zn0.5Te:N, with dark and photoconductivity of 2.13 × 10-6 and 2.9 × 10-5 S/cm, respectively, is inserted at the back contact of a 1-μm-thick CdTe solar cell. A conversion efficiency of 7.46% (Voc: 0.68 V, Jsc: 22.60 mA/cm2, FF: 0.49, area: 0.086 cm2) was achieved as the primary result for a 0.2-μm-thick Cd0.5Zn0.5Te:N layer with the cell configuration of CdS/CdTe/Cd0.5Zn0.5Te:N/Au.

  9. High thermoelectric potential of Bi2Te3 alloyed GeTe-rich phases

    NASA Astrophysics Data System (ADS)

    Madar, Naor; Givon, Tom; Mogilyansky, Dmitry; Gelbstein, Yaniv

    2016-07-01

    In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)1-x(Bi2Te3)x alloys, with x values of up to 20%. Higher solubility limit of Bi2Te3 in GeTe, than previously reported, was identified around ˜9%, extending the doping potential of GeTe by the Bi2Te3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ˜1.55 at ˜410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%-17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge8Bi2Te11 and Ge4Bi2Te7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi2Te3), was suggested for further electronic optimization of the thermoelectric properties.

  10. Topological states and phase transitions in Sb2Te3-GeTe multilayers.

    PubMed

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-01-01

    Topological insulators (TIs) are bulk insulators with exotic 'topologically protected' surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases. PMID:27291288

  11. S–Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells

    SciTech Connect

    Li, C.; Poplawsky, J.; Paudel, N.; Pennycook, T. J.; Haigh, S. J.; Al-Jassim, M. M.; Yan, Y.; Pennycook, S. J.

    2014-09-19

    At the CdTe/CdS interface, a significant Te-S interdiffusion has been found a few nanometers into the grain interiors with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). S substitution at Te sites has been directly resolved in CdTe with STEM Z-contrast images. Moreover, when enough S substitutes for Te, a structural transformation from zinc-blende to wurtzite has been observed. Cl segregation has also been found at the interface. STEM electron-beam-induced current (EBIC) shows that the p-n junction occurs a few nm into the CdTe grains, which is consistent with the S diffusion range we observe. The shift of the p-n junction suggests a buried homo-junction which would help reduce non-radiative recombination at the junction. Meanwhile, long-range S diffusion in CdTe grain boundaries (GBs) has been detected, as well as Te and Cl diffusion in CdS GBs.

  12. S–Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells

    DOE PAGES

    Li, C.; Poplawsky, J.; Paudel, N.; Pennycook, T. J.; Haigh, S. J.; Al-Jassim, M. M.; Yan, Y.; Pennycook, S. J.

    2014-09-19

    At the CdTe/CdS interface, a significant Te-S interdiffusion has been found a few nanometers into the grain interiors with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). S substitution at Te sites has been directly resolved in CdTe with STEM Z-contrast images. Moreover, when enough S substitutes for Te, a structural transformation from zinc-blende to wurtzite has been observed. Cl segregation has also been found at the interface. STEM electron-beam-induced current (EBIC) shows that the p-n junction occurs a few nm into the CdTe grains, which is consistent with the S diffusion range we observe. The shiftmore » of the p-n junction suggests a buried homo-junction which would help reduce non-radiative recombination at the junction. Meanwhile, long-range S diffusion in CdTe grain boundaries (GBs) has been detected, as well as Te and Cl diffusion in CdS GBs.« less

  13. Propagation loss reduction of ZnMgTe/ZnTe waveguide devices

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Che; Kazami, Fukino; Wang, Jing; Nakasu, Taizo; Hattori, Shota; Kizu, Takeru; Hashimoto, Yuki; Kobayashi, Masakazu; Asahi, Toshiaki

    2016-08-01

    A ZnMgTe/ZnTe electro-optic (EO) waveguide has great potential to be utilized for practical applications. A low-dislocation ZnMgTe/ZnTe waveguide can be fabricated when the cladding layer thickness is below 20-fold the calculated critical layer thickness (CCLT × 20). To improve optical confinement, a waveguide with a thicker cladding layer or a higher Mg% should be considered. However, the device performance might be affected because of crystal quality deterioration since the lattice mismatch between MgTe and ZnTe was around 4.1%. In this study, optical confinement and propagation loss were examined by changing the dimensions of the ZnMgTe/ZnTe waveguide structure. The propagation loss, EO characteristics, and crystal quality of the fabricated waveguides were mainly studied. A waveguide with a cladding layer thickness of around 1.5-fold the 1/e penetration depth of the evanescent wave (d p 1/e × 1.5, corresponding to CCLT × 100) showed better optical properties than other waveguides, although its interface defect density was reasonably high.

  14. Weak Te,Te interactions through the looking glass of NMR spin-spin coupling.

    PubMed

    Bühl, Michael; Knight, Fergus R; Křístková, Anezka; Malkin Ondík, Irina; Malkina, Olga L; Randall, Rebecca A M; Slawin, Alexandra M Z; Woollins, J Derek

    2013-02-25

    Across the bay: J((125)Te, (125)Te) spin-spin coupling is a highly sensitive probe into the electronic and geometric structure of 1,8-peri-substituted naphthalene tellurium derivatives. The coupling is related to the onset of multicenter bonding in these systems.

  15. Topological states and phase transitions in Sb2Te3-GeTe multilayers

    NASA Astrophysics Data System (ADS)

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A.; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-06-01

    Topological insulators (TIs) are bulk insulators with exotic ‘topologically protected’ surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases.

  16. Topological states and phase transitions in Sb2Te3-GeTe multilayers

    PubMed Central

    Nguyen, Thuy-Anh; Backes, Dirk; Singh, Angadjit; Mansell, Rhodri; Barnes, Crispin; Ritchie, David A.; Mussler, Gregor; Lanius, Martin; Grützmacher, Detlev; Narayan, Vijay

    2016-01-01

    Topological insulators (TIs) are bulk insulators with exotic ‘topologically protected’ surface conducting modes. It has recently been pointed out that when stacked together, interactions between surface modes can induce diverse phases including the TI, Dirac semimetal, and Weyl semimetal. However, currently a full experimental understanding of the conditions under which topological modes interact is lacking. Here, working with multilayers of the TI Sb2Te3 and the band insulator GeTe, we provide experimental evidence of multiple topological modes in a single Sb2Te3-GeTe-Sb2Te3 structure. Furthermore, we show that reducing the thickness of the GeTe layer induces a phase transition from a Dirac-like phase to a gapped phase. By comparing different multilayer structures we demonstrate that this transition occurs due to the hybridisation of states associated with different TI films. Our results demonstrate that the Sb2Te3-GeTe system offers strong potential towards manipulating topological states as well as towards controlledly inducing various topological phases. PMID:27291288

  17. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications

    PubMed Central

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-01-01

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future. PMID:26861380

  18. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications.

    PubMed

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-02-06

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future.

  19. Structural ordering in liquid K-Te alloys

    SciTech Connect

    Fortner, J.; Saboungi, M.L.; Enderby, J.E.

    1994-03-01

    Neutron diffraction from molten K{sub x}Te{sub 1{minus}x} is reported for x = 0.12 and x = 0.50 semiconducting alloys. The measured radial distribution functions (rdf) demonstrate the persistence of covalently bonded tellurium in the liquid. The rdf of the liquid K{sub 0.12}Te{sub 0.88}, which is dominated by the Te-Te contribution, is remarkably similar to that of pure liquid tellurium, the notable exception being that the nearest neighbor peak is largely resolved and found to have a coordination number slightly less than 2. The K{sub 0.50}Te{sub 0.50} rdf clearly indicates Te-Te pairing in the melt, and unexpected departure from the presumed similar Cu{sub 0.50}Te{sub 0.50}. These paired tellurium are most likely of the form (Te{sub 2}){sup 2{minus}} Zintl ions.

  20. HgCdTe barrier infrared detectors

    NASA Astrophysics Data System (ADS)

    Kopytko, M.; Rogalski, A.

    2016-05-01

    In the last decade, new strategies to achieve high-operating temperature (HOT) detectors have been proposed, including barrier structures such as nBn devices, unipolar barrier photodiodes, and multistage (cascade) infrared detectors. The ability to tune the positions of the conduction and valence band edges independently in a broken-gap type-II superlattices is especially helpful in the design of unipolar barriers. This idea has been also implemented in HgCdTe ternary material system. However, the implementation of this detector structure in HgCdTe material system is not straightforward due to the existence of a valence band discontinuity (barrier) at the absorber-barrier interface. In this paper we present status of HgCdTe barrier detectors with emphasis on technological progress in fabrication of MOCVD-grown HgCdTe barrier detectors achieved recently at the Institute of Applied Physics, Military University of Technology. Their performance is comparable with state-of-the-art of HgCdTe photodiodes. From the perspective of device fabrication their important technological advantage results from less stringent surface passivation requirements and tolerance to threading dislocations.

  1. MBE HgCdTe heterostructure detectors

    NASA Technical Reports Server (NTRS)

    Schulman, Joel N.; Wu, Owen K.

    1990-01-01

    HgCdTe has been the mainstay for medium (3 to 5 micron) and long (10 to 14 micron) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using molecular beam epitaxy (MBE) provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition, and thus band gap, at will. The heterostructure junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/liquid phase epitaxy (LPE)/bulk structures are given. Quantum structures include the HgTe-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

  2. Impurity Gettering Effect of Te Inclusions in Cdznte Single Crystals

    SciTech Connect

    Yang, G.; Bolotnikov, A; Cui, Y; Camarda, G; Hossain, A; James, R

    2009-01-01

    The local impurity distribution in Te inclusions of CdZnTe (CZT) crystal was investigated by the time-of-flight secondary ion mass spectrometry (Tof-SIMS) technique. Direct evidence of impurity gettering in Te inclusions has been observed for the first time. The impurity gettering in Te inclusions originated from the diffusion mechanism during crystal growth and segregation mechanism during crystal cooling. This phenomenon is meaningful, because it reveals how Te inclusions affect CZT properties and provides a possible approach to reduce the impurities in CZT by the way of removing Te inclusions.

  3. Adsorption of Te on Ge(001): Density-functional calculations

    NASA Astrophysics Data System (ADS)

    Çakmak, M.; Srivastava, G. P.; Ellialtıoğlu, Ş.

    2003-05-01

    We present ab initio density-functional calculations for the adsorption of Te on the Ge(001) surface. Various possible adsorption geometries for the 0.5-, 0.8-, 1-, and 2-ML (monolayer) coverages of Te have been investigated. Our results for sub-monolayer coverages confirm earlier results as well as provide some new insight into the adsorption of Te. Furthermore, our results for the 2-ML coverage of Te suggest that the bonding between the overlayer and the substrate has changed significantly. This may provide useful information on possible desorption of Te in the form of strongly bonded Te2 units.

  4. Band structure and Optical properties CdTe and CdSn3Te4 thin films

    NASA Astrophysics Data System (ADS)

    Venkatachalam, T.; Velumani, S.; Ganesan, S.; Sakthivel, K.

    2008-04-01

    CdTe and CdSn3Te4 compounds were prepared by direct reaction of their high purity elemental constituents using rotating furnace. Optimal deposition conditions for the deposition of CdTe and CdSn3Te4 thin films in hot wall evaporation setup were simulated using Monte Carlo technique. Thin films of CdTe and CdSn3Te4 were deposited on glass substrates by hot wall evaporation method. From the XRD measurements it was found that the films of CdTe and CdSn3Te4 were of cubic zinc-blende and rock salt structures respectively. The lattice parameters were determined as a = 6.476 Å (CdTe) and a = 6.238 Å (CdSn3Te4) from the XRD data. The UV-Vis-NIR optical transmittance spectra of thin films of different films were obtained and it was found that the direct optical band gaps were 1.4 eV (CdTe) and 0.8 eV (CdSn3Te4). Electronic structure, band parameters and optical spectra of CdTe and CdSn3Te4 were calculated from ab initio studies within the GGA approximation. The experimental results were in good agreement with the theoretical values.

  5. PythonTeX: reproducible documents with LaTeX, Python, and more

    NASA Astrophysics Data System (ADS)

    Poore, Geoffrey M.

    2015-01-01

    PythonTeX is a LaTeX package that allows Python code in LaTeX documents to be executed and provides access to the output. This makes possible reproducible documents that combine results with the code required to generate them. Calculations and figures may be next to the code that created them. Since code is adjacent to its output in the document, editing may be more efficient. Since code output may be accessed programmatically in the document, copy-and-paste errors are avoided and output is always guaranteed to be in sync with the code that generated it. This paper provides an introduction to PythonTeX and an overview of major features, including performance optimizations, debugging tools, and dependency tracking. Several complete examples are presented. Finally, advanced features are summarized. Though PythonTeX was designed for Python, it may be extended to support additional languages; support for the Ruby and Julia languages is already included. PythonTeX contains a utility for converting documents into plain LaTeX, suitable for format conversion, sharing, and journal submission.

  6. Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhao, Xin-Hao; DiNezza, Michael J.; Liu, Shi; Campbell, Calli M.; Zhao, Yuan; Zhang, Yong-Hang

    2014-12-01

    The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg0.24Cd0.76Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 102 cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity.

  7. Strong coupling and polariton lasing in Te based microcavities embedding (Cd,Zn)Te quantum wells

    SciTech Connect

    Rousset, J.-G. Piętka, B.; Król, M.; Mirek, R.; Lekenta, K.; Szczytko, J.; Borysiuk, J.; Suffczyński, J.; Kazimierczuk, T.; Goryca, M.; Smoleński, T.; Kossacki, P.; Nawrocki, M.; Pacuski, W.

    2015-11-16

    We report on properties of an optical microcavity based on (Cd,Zn,Mg)Te layers and embedding (Cd,Zn)Te quantum wells. The key point of the structure design is the lattice matching of the whole structure to MgTe, which eliminates the internal strain and allows one to embed an arbitrary number of unstrained quantum wells in the microcavity. We evidence the strong light-matter coupling regime already for the structure containing a single quantum well. Embedding four unstrained quantum wells results in further enhancement of the exciton-photon coupling and the polariton lasing in the strong coupling regime.

  8. New Zealand Perspectives on Early Childhood Education: Naku Te Rourou Nau Te Rourou Ka Ora Ai Te Iwi

    ERIC Educational Resources Information Center

    Tesar, Marek

    2016-01-01

    This special issue focuses on histories, pedagogies, policies, philosophies and alternative perspectives in early childhood education. "Te Whariki" is heralded as the first bicultural curriculum not only in New Zealand, but in the world. Its importance is reflected in national and international research and early childhood discourses.…

  9. Adsorption of Te on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Gobil, Y.; Cibert, J.; Saminadayar, K.; Tatarenko, S.

    1989-04-01

    We present a diagram of the GaAs-Te surface, precursor of the molecular beam epitaxy of CdTe on GaAs(100), as a function of As/Ga stoichiometry and Te coverage. In particular, three new GaAs-Te superstructures are reported: (2 × 1), "Te-poor" (6 × 1) and a (∗ × 3) incommensurate phase. Conditions of formation of the different surfaces are detailed and these surfaces are characterized using reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). On these surfaces, tellurium can be adsorbed on different sites: the Te3d {5}/{2} XPS line reveals three components located at 573.0, 572.6 and 572.1 eV which we attribute to Te mainly bound to As, to Ga and to adsorbed Te respectively, the relative population of these states depending on the precursor surface.

  10. Thermoelectric properties of p-type PbTe/Ag{sub 2}Te bulk composites by extrinsic phase mixing

    SciTech Connect

    Lee, Min Ho; Rhyee, Jong-Soo

    2015-12-15

    We investigated the thermoelectric properties of PbTe/Ag{sub 2}Te bulk composites, synthesized by hand milling, mixing, and hot press sintering. From x-ray diffraction and energy dispersive x-ray spectroscopy measurements, we observed Ag{sub 2}Te phase separation in the PbTe matrix without Ag atom diffusion. In comparison with previously reported pseudo-binary (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} composites, synthesized by high temperature phase separation, the PbTe/Ag{sub 2}Te bulk composites fabricated with a low temperature phase mixing process give rise to p-type conduction of carriers with significantly decreased electrical conductivity. This indicates that Ag atom diffusion in the PbTe matrix changes the sign of the Seebeck coefficient to n-type and also increases the carrier concentration. Effective p-type doping with low temperature phase separation by mixing and hot press sintering can enhance the thermoelectric performance of PbTe/Ag{sub 2}Te bulk composites, which can be used as a p-type counterpart of n-type (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} bulk composites.

  11. TE and TM pass integrated optic polarizers

    NASA Astrophysics Data System (ADS)

    Madaan, Divya; Kaur, Davinder; Sharma, V. K.; Kapoor, A.

    2016-05-01

    A four layer integrated optical waveguide is studied, in which a high index buffer is used along with the metal cladding. The structure can act both as TE and TM pass polarizer. We have designed it for λ=1.55 µm which corresponds to telecommunication wavelength. TiO2 is used as a buffer layer with Au as metal cladding. When metal clad optical waveguides with a high index buffer layer are used there is periodic coupling between lossless modes of waveguide and the lossy modes supported by high index buffer layer with metal clad. We present theoretical results of the effect of buffer thickness on the mode index and the losses. The TM Pass polarizer with TE and TM losses, 1029.19dB/cm and 59.67dB/cm respectively are obtained. Also, TE Pass polarizer with TM and TE losses 1444.74dB/cm and 238.51dB/cm respectively are obtained.

  12. Te Timatanga Hou: The New Beginning.

    ERIC Educational Resources Information Center

    Park, Hapai

    In 1989, the University of Waikato (New Zealand) established Te Timatanga Hou, a program of pre-university remedial study for disadvantaged Maori. Many targeted students come from rural schools that do not offer a seventh-form year nor a wide range of university entrance subjects. Students undertake 1 year of intensive pre-university training…

  13. Novel Method for Growing Te-Inclusion-Free CZT

    SciTech Connect

    Bolotnikov,A.

    2008-06-17

    The authors propose a new method for growth of detector-grade CdZnTe (CZT) with reduced concentration and sizes of Te inclusions. The method is designed to impede the formation of Te-rich inclusions in crystals due to the use of new CZT growth method and a unique ampoule design.

  14. LaTeX for Agricultural Extension Professionals

    Technology Transfer Automated Retrieval System (TEKTRAN)

    LaTeX is a free open source document preparation system for professional quality documents and presentation materials. Extension professionals, trying to reach their audience though various forms of printed and online resources, can benefit from the vast potential of LaTeX. Using LaTeX empowers the ...

  15. Sputter cleaning and dry oxidation of CdTe, HgTe, and Hg 0.8Cd 0.2Te surfaces

    NASA Astrophysics Data System (ADS)

    Solzbach, U.; Richter, H. J.

    1980-07-01

    The analyses of CdTe, HgTe, and Hg 0.8Cd 0.2Te surfaces by XPS and LEED after Ar + sputtering and after the subsequent onset of a dry oxidation are described, and a quantitative evaluation of the XPS spectra is attempted. The results are: Ar + sputtering yields a perfect unreconstructed CdTe surface of stoichiometric composition, whereas the composition of sputtered HgTe and Hg 0.8Cd 0.2Te surfaces generally deviates from the stoichiometry of the respective compound. This deviation is a function of the energy of the Ar ions (1 to 15 keV) and is characterized by an increasing deficit in Hg as the ion energy is raised. The Hg deficit of sputtered Hg 0.8Cd 0.2Te surfaces is substitutionally compensated by an equivalent increase in Cd, and due to this substitution the resulting surfaces are sufficiently ordered to display a distinct LEED pattern. The oxidation of sputtered CdTe, HgTe, and Hg 0.8Cd 0.2Te surfaces in an O 2 atmosphere is an extremely slow process. Therefore, the surfaces to be oxidized were additionally exposed to UV radiation (low pressure mercury lamp), and due to UV generated ozone as an oxidizing agent ultrathin native oxide layers of up to 15 Å thickness were readily obtained. The predominant constituents of these native oxide layers on Hg 0.8Cd 0.2Te are concluded to be CdTeO 3 and TeO 2.

  16. 78 FR 28626 - Te Connectivity, Industrial Division, Middletown, Pennsylvania; Te Connectivity, Corporate Shared...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF LABOR Employment and Training Administration [TA-W-81,557; TA-W-81,557A; TA-W-81,557B; TA-W-81,557C; ;TA-W-81,557D; Ta-W-81,557e] Te Connectivity, Industrial Division, Middletown, Pennsylvania; Te Connectivity, Corporate Shared Services Group 100 & 200 Amp...

  17. Smart assembling of multi-scaled functional interfaces in thermoelectric Ga2Te3/Te hetero-nanocomposites

    NASA Astrophysics Data System (ADS)

    Chang, Hsiu-Cheng; Chiang, Ming-Hsiu; Tsai, Tsung-Che; Chen, Tsung-Han; Whang, Wha-Tzong; Chen, Chun-Hua

    2014-11-01

    We describe an innovative concept and facile approach in fabricating laterally assembled Ga2Te3/Te binary nanocomposite films, which comprise two-dimensional quasi-periodic Ga2Te3 nanoassemblies surrounded by interlocking highly-conductive Te single crystals for comprehensively establishing subnano- to micro-scaled multi-style versatile interfaces. The distinct Ga2Te3/Te nanocomposite film exhibits a power factor that is about 60 times higher than the reported conventional Ga2Te3 and Te materials, mainly due to the 2- to 3-order improved electrical conductivity and the comparable Seebeck coefficient.We describe an innovative concept and facile approach in fabricating laterally assembled Ga2Te3/Te binary nanocomposite films, which comprise two-dimensional quasi-periodic Ga2Te3 nanoassemblies surrounded by interlocking highly-conductive Te single crystals for comprehensively establishing subnano- to micro-scaled multi-style versatile interfaces. The distinct Ga2Te3/Te nanocomposite film exhibits a power factor that is about 60 times higher than the reported conventional Ga2Te3 and Te materials, mainly due to the 2- to 3-order improved electrical conductivity and the comparable Seebeck coefficient. Electronic supplementary information (ESI) available: Structural investigations of the hetero-nanocomposite films formed at an annealing temperature of 225 °C for 12 h, 250 °C for 3 h, and 225 °C for 3 h are collected in Fig. S1-S3, respectively. Annealing temperature and time effects on the morphology, composition, crystallinity and thermoelectric property are shown in Fig. S4-S10. See DOI: 10.1039/c4nr02765e

  18. Interband characterization and electronic transport control of nanoscaled GeTe/Sb 2Te3 superlattices

    NASA Astrophysics Data System (ADS)

    Caretta, Antonio; Casarin, Barbara; Di Pietro, Paola; Perucchi, Andrea; Lupi, Stefano; Bragaglia, Valeria; Calarco, Raffaella; Lange, Felix Rolf Lutz; Wuttig, Matthias; Parmigiani, Fulvio; Malvestuto, Marco

    2016-07-01

    The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials have led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled GeTe/Sb2Te3 chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free carriers, and the characteristics of the valence-to-conduction transition. It is found that the free carrier density decreases with increasing GeTe content, for sublayer thicknesses below ˜3 nm. A simple band model analysis suggests that GeTe and Sb2Te3 layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness, and we derive a model for arbitrary film stacks.

  19. Improvement in Thermoelectric Properties by Tailoring at In and Te Site in In2Te5

    NASA Astrophysics Data System (ADS)

    Sanchela, Anup V.; Thakur, Ajay D.; Tomy, C. V.

    2016-11-01

    We study the role of substitutions at In and Te site in the thermoelectric behavior of In2Te5. Single crystals with compositions In2(Te1- x Se x )5 ( x = 0, 0.05, 0.10) and Fe0.05In1.95(Te0.90Se0.10)5 were prepared using a modified Bridgman-Stockbarger technique. Electrical and thermal transport properties of these single crystals were measured in the temperature range of 6 K to 395 K. A substantial decrease in the thermal conductivity was observed in Fe-substituted samples, attributed to enhanced phonon scattering at point defects. Marked enhancement in the Seebeck coefficient S along with concomitant suppression of the electrical resistivity ρ was observed in Se-substituted single crystals. An overall enhancement of the thermoelectric figure of merit ( zT) by a factor of 310 was observed in single-crystal Fe0.05In1.95(Te0.90Se0.10)5 compared with single crystals of the parent material In2Te5.

  20. Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

    SciTech Connect

    Li, C. W.; Ma, J.; Cao, H. B.; May, A. F.; Abernathy, D. L.; Ehlers, G.; Hoffmann, C.; Wang, X.; Hong, T.; Huq, A.; Gourdon, O.; Delaire, O.

    2014-12-29

    The structure and lattice dynamics of rock-salt thermoelectric materials SnTe and PbTe are investigated with single crystal and powder neutron diffraction, inelastic neutron scattering (INS), and first-principles simulations. Our first-principles calculations of the radial distribution function (RDF) in both SnTe and PbTe show a clear asymmetry in the first nearest-neighbor (1NN) peak, which increases with temperature, in agreement with experimental reports (Ref. 1,2). We show that this peak asymmetry for the 1NN Sn–Te or Pb–Te bond results from large-amplitude anharmonic vibrations (phonons). No atomic off-centering is found in our simulations. In addition, the atomic mean square displacements derived from our diffraction data reveal stiffer bonding at the anion site, in good agreement with the partial phonon densities of states from INS, and first-principles calculations. In conclusion, these results provide clear evidence for large-amplitude anharmonic phonons associated with the resonant bonding leading to the ferroelectric instability.

  1. Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

    DOE PAGES

    Li, C. W.; Ma, J.; Cao, H. B.; May, A. F.; Abernathy, D. L.; Ehlers, G.; Hoffmann, C.; Wang, X.; Hong, T.; Huq, A.; et al

    2014-12-29

    The structure and lattice dynamics of rock-salt thermoelectric materials SnTe and PbTe are investigated with single crystal and powder neutron diffraction, inelastic neutron scattering (INS), and first-principles simulations. Our first-principles calculations of the radial distribution function (RDF) in both SnTe and PbTe show a clear asymmetry in the first nearest-neighbor (1NN) peak, which increases with temperature, in agreement with experimental reports (Ref. 1,2). We show that this peak asymmetry for the 1NN Sn–Te or Pb–Te bond results from large-amplitude anharmonic vibrations (phonons). No atomic off-centering is found in our simulations. In addition, the atomic mean square displacements derived from ourmore » diffraction data reveal stiffer bonding at the anion site, in good agreement with the partial phonon densities of states from INS, and first-principles calculations. In conclusion, these results provide clear evidence for large-amplitude anharmonic phonons associated with the resonant bonding leading to the ferroelectric instability.« less

  2. Fluctuations in induced charge introduced by Te inclusions within CdZnTe radiation detectors

    SciTech Connect

    Bale, Derek S.

    2010-07-15

    Recently, homogenization theory based on a multiple-scale perturbation of the electron transport equation has been used to derive a mathematical framework for modeling the excess charge lost to Te inclusions within radiation detectors based on semi-insulating cadmium zinc telluride (CdZnTe). In that theory, the heterogeneous material is mathematically replaced by a homogenized CdZnTe crystal whose effective electron attenuation length incorporates the additional uniform electron trapping caused by the inclusions. In this paper, the homogenization theory is extended to incorporate fluctuations in the induced charge (i.e., charge collection nonuniformities) introduced by the random position and size distributions of a noncorrelated population of small (i.e, <20 {mu}m) Te inclusions. Analysis of the effective parameters derived within the homogenized framework is used to develop a probability distribution of effective electron attenuation lengths, and therefore effective mobility-lifetime products, as a function of both the position and size distribution of Te inclusions. Example distributions are detailed for the case of an exponential size distribution at various number densities. Further, it is demonstrated that the inclusion-induced material nonuniformities derived in this paper can be numerically sampled efficiently, making them applicable to Monte Carlo device simulation of realistic CdZnTe detectors. Simulated charge induction maps and pulse-height spectra are presented and compared to recently published measurements.

  3. Improvement in Thermoelectric Properties by Tailoring at In and Te Site in In2Te5

    NASA Astrophysics Data System (ADS)

    Sanchela, Anup V.; Thakur, Ajay D.; Tomy, C. V.

    2016-07-01

    We study the role of substitutions at In and Te site in the thermoelectric behavior of In2Te5. Single crystals with compositions In2(Te1-x Se x )5 (x = 0, 0.05, 0.10) and Fe0.05In1.95(Te0.90Se0.10)5 were prepared using a modified Bridgman-Stockbarger technique. Electrical and thermal transport properties of these single crystals were measured in the temperature range of 6 K to 395 K. A substantial decrease in the thermal conductivity was observed in Fe-substituted samples, attributed to enhanced phonon scattering at point defects. Marked enhancement in the Seebeck coefficient S along with concomitant suppression of the electrical resistivity ρ was observed in Se-substituted single crystals. An overall enhancement of the thermoelectric figure of merit (zT) by a factor of 310 was observed in single-crystal Fe0.05In1.95(Te0.90Se0.10)5 compared with single crystals of the parent material In2Te5.

  4. {CdTe(111) B}/{Si(100) } structure grown by metalorganic vapor phase epitaxy with Te adsorption and annealing

    NASA Astrophysics Data System (ADS)

    Nishino, Hironori; Nishijima, Yoshito

    1996-10-01

    We studied the crystal structure of CdTe(111)B layers directly grown on Si(100) by MOVPE using a new pre-growth process, which includes a metalorganic Te adsorption and an annealing process. In this paper, we discussed the CdTe structure from the three aspects of antiphase, twinning and tilt. We investigated the dependence of the antiphase content in CdTe(111)B on the anneal temperature and the Si misorientation angle. From the results, we assume that the origin of the antiphase formation is the difference in the arrangement of adsorbed Te atoms. Te arrangement leading to antiphase formation occurs on Si terraces away from steps at relatively low temperatures. We reduced most of the twinning in epilayers by optimizing the {VI}/{II} ratio. We think the remaining twinning was confined to near the interface and it nucleated from the Te arrangement on terraces. We found that the Si(100)-CdTe(111) tilt was much smaller than that expected from the well-known Nagai model. We propose that a negative tilt is induced to reduce the lateral mismatch. To adjust the lateral distance of unit cells, 30 CdTe lattices match to 31 Si lattices. CdTe(111)B planes are inclined to reduce the remaining mismatch between two lattices. This initial tilt also causes wider CdTe terraces. We modified Nagai's tilting model for this reconstructed CdTe surface. The total tilt angle is defined by these two tilting mechanisms.

  5. Electrodeposition of SbTe Phase-Change Alloys

    SciTech Connect

    Huang,Q.; Kellock, A.; Raoux, S.

    2007-01-01

    Electrodeposition of SbTe thin films was investigated at room temperature, where amorphous deposits were obtained. The electrodeposition of Sb was found to be induced by Te, while the latter was not affected by the Sb. Detailed studies on this induced deposition were carried out by varying the Sb(III) and Te(IV) concentrations, pH, and agitation. The Sb deposition rate was found to be independent of the concentrations of both species but dependent on the pH and agitation. A phase transition from amorphous films into crystalline Sb2Te3 at 120 C was observed for the plated SbTe.

  6. Resistive switching properties in CdZnTe films

    SciTech Connect

    Zha, Gangqiang; Lin, Yun; Tan, Tingting; Jie, Wanqi; Zeng, Dongmei

    2015-02-09

    The ternary II–VI compound semiconductor cadmium zinc telluride (CdZnTe) has bi-stable conduction characteristics. In this letter, CdZnTe films are grown on indium tin oxide (ITO) substrates by radio frequency magnetron sputtering. The current-voltage characteristics show that there is resistive switching in a structure consisting of an 800-nm-thick CdZnTe film, an Au Schottky contact, and an ITO bottom electrode. The electroresistance in Au/CdZnTe/ITO may be related to the polarization of the CdZnTe film and the Schottky contact.

  7. Intense white luminescence in ZnTe embedded porous silicon

    SciTech Connect

    Melo, O. de; Melo, C. de; Santana, G.; Santoyo, J.; Zelaya-Angel, O.; Mendoza-Alvarez, J. G.; Torres-Costa, V.

    2012-06-25

    Porous silicon layers were embedded with ZnTe using the isothermal close space sublimation technique. The presence of ZnTe was demonstrated using cross-sectional energy dispersive spectroscopy maps. ZnTe embedded samples present intense room temperature photoluminescence along the whole visible range. We ascribe this PL to ZnTe nanocrystals of different sizes grown on the internal pore surface. Such crystals, with different orientations and sizes, were observed in transmission electron microscopy images, while transmission electron diffraction images of the same regions reveal ZnTe characteristic patterns.

  8. The phase evolution mechanism in Fe(Se, Te) system

    NASA Astrophysics Data System (ADS)

    Liu, Jixing; Li, Chengshan; Zhang, Shengnan; Feng, Jianqing; Zhang, Pingxiang; Zhou, Lian

    2016-08-01

    The phase evolution mechanism in Fe(Se, Te) system during sintering was investigated with step-by-step heat treatment process. It was noticed that the diffusion processes between Fe and Se (Te) as well as that between Se and Te were both very important to the formation of superconducting Fe(Se, Te) phase with very uniform chemical composition. During heat treatment, solid solutions of (Se, Te)ss with different chemical composition were formed with the diffusion of Se atoms into Te solids and Te atoms into Se melts, simultaneously. Then with the increasing temperature, Fe atoms diffused into (Se, Te)ss, Fe(Se, Te)2 and Fe(Se, Te) phases were formed in sequence with the increasing Fe content. The chemical composition in melts became more and more uniform with the further increasing of sintering temperature and dwell time. Therefore, it was suggested that in order to achieve Fe(Se, Te) phase with high superconducting properties, it was necessary to enhance the diffusion process during sintering. The critical temperature of the sample, which was sintered at 700 °C for 12 h with slow cooling process and an O2-annealing process for 24 h, was above 14.0 K. This Tc value proved that a good superconducting β phase could be obtained under this sintering condition.

  9. Adsorption of Te on the Si(001) Surface

    NASA Astrophysics Data System (ADS)

    Sen, Prasenjit; Batra, Inder P.; Grein, C. H.; Fong, C. Y.; Ciraci, S.

    2001-03-01

    To understand the interface between CdTe and Si and to reveal the atomistic mechanism for the surfactant behavior of adsorbed Te we have investigated the adsorption of Te on the Si(001) surface. This interface is also of crucial importance in developing CdTe/Si as a composite substance for the growth of HgCdTe. We carried out first-principles plane wave calculations within density-functional theory. The adsorption sites and corresponding binding energies are calculated on fully relaxed geometries by using the conjugate gradient method. We found that, at monolayer coverage, Te adatoms do not dimerize. At very low coverage, the top site above the Si-Si surface dimer bond is energetically favorable relative to cave, hollow and bridge sites. Finally, the atomistic mechanism of the surfactant role of Te has been investigated by finite temperature ab-initio molecular dynamics calculations.

  10. High-Quality AgGaTe2 Layers on Si Substrates with Ag2Te Buffer Layers

    NASA Astrophysics Data System (ADS)

    Uruno, Aya; Kobayashi, Masakazu

    2016-09-01

    AgGaTe2 layers were successfully grown on Si substrates by the close-spaced sublimation method. The Si substrates were confirmed to be etched during AgGaTe2 layer growth when the layer was grown directly on the substrate. To eliminate melt-back etching, a buffer layer of Ag2Te was introduced. It was found that the Ag2Te buffer layer changed into the AgGaTe2 layer during the growth process, and a uniform AgGaTe2 layer with an abrupt interface was formed. Both the diffusion of Ga into Ag2Te and the growth of AgGaTe2 occurred simultaneously. It was confirmed that uniform AgGaTe2 layers could be formed without any traces of the Ag2Te layer or melt-back etching by tuning the growth parameters. A solar cell was also fabricated using the p-AgGaTe2/n-Si heterojunction. This solar cell showed conversion efficiency of approximately 3%.

  11. Selective area epitaxy of CdTe

    NASA Astrophysics Data System (ADS)

    Luo, Y. Y.; Cavus, A.; Tamargo, M. C.

    1997-06-01

    We have performed selective area epitaxy (SAE) of CdTe layers grown by molecular beam epitaxy using a shadow mask technique. This technique was chosen over other SAE techniques due to its simplicity and its compatibility with multiple SAE patterning steps. Features as small as 50 microns × 50 microns were obtained with sharp, abrupt side walls and flat mesa tops. Separations between mesas as small as 20 microns were also obtained. Shadowing effects due to the finite thickness of the mask were reduced by placing the CdTe source in a near normal incidence position. Intimate contact between the mask and the substrate was essential in order to achieve good pattern definition.

  12. Galactic TeV observations with HAWC

    NASA Astrophysics Data System (ADS)

    Hui, Chiumun Michelle

    2014-08-01

    The High Altitude Water Cherenkov (HAWC) Observatory is a gamma-ray and cosmic-ray detector currently under construction at the Sierra Negra volcano in the state of Puebla, Mexico. The full array will consist of 300 water Cherenkov detectors, which contain 1200 photomultiplier tubes and cover an area of 22,000m^2. It has an instantaneous field of view of 2sr, a duty cycle >90%, and is sensitive to energies between 100 GeV and 100 TeV. Data taking began in Summer 2013 with a partial array. I will present the results of HAWC observations of the Galactic plane, which include the complex Cygnus region, and other extended TeV objects with unidentified source associations.

  13. Spectroscopic Cathodoluminescence Studies of the ZnTe:Cu Contact Process for CdS/CdTe Solar Cells: Preprint

    SciTech Connect

    Gessert, T. A.; Romero, M. J.; Johnston, S.; Keyes, B.; Dippo, P.

    2002-05-01

    This conference paper describes the spectroscopic cathodoluminescence (CL), electron-beam induced current (EBIC), and capacitance-Voltage (C-V) measurements are used to study the formation of CdS/CdTe devices processed using ion-beam milling and a ZnTe:Cu/Ti contact. Results show heating in vacuum at {approx}360 C and ion-beam milling lead to observable changes in the CL emission from the CdCl2-treated CdTe surface. Changes in the CL spectrum are also observed as ZnTe:Cu layer thickness increases. These changes are correlated to published studies of defect levels and shown to be due, possibly, to an n-type region existing between the ZnTe:Cu contact interface and the p-CdTe layers. This n-type region is eliminated once a sufficiently thick ZnTe:Cu layer is produced.

  14. BOREAS TE-22 Allometric Forest Survey Data

    NASA Technical Reports Server (NTRS)

    Shugart, H. H.; Nielsen, Eric; Hall, Forrest G. (Editor); Papagno, Andrea (Editor)

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-22 (Terrestrial Ecology) team collected data sets in support of its efforts to characterize and interpret information on the forest structure of boreal vegetation in the Southern and Northern Study Areas (SSA and NSA) during the 1994 growing season. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  15. TeO2 and Te acousto-optic spectrometer imaging system

    NASA Astrophysics Data System (ADS)

    Souilhac, Dominique J.; Billerey, Dominique

    1994-12-01

    An improved TeO2 and Te infrared acoustooptic tuneable spectrometer has been analysed, using infrared fibres, a high speed frequency synthesiser and optimised algorithms. A comparison is made with the next best AOTF infrared materials, Tl3AsSe3, HgCl2 and PbBr2. A design study of the TeO2 and Te AO imaging spectrometer is also presented, operating in the two thermal bands, 1-5micrometers and 6-12micrometers , using an interchangeable fore-optics and a multiplexed electronically scanned infrared array cooled at 77 degrees K. Some initial experimental results indicate that these systems can perform well, an increase in the dynamic range in the 8-12 micrometers and is obtained compared to the 3-5*m band. It can be very useful in chemical process control, medical diagnostics, aerospace and earth remote sensing. Based on recent imaging spectrometer development, a design study of the TeO2 AO imaging spectrometer in the 0.4-1 micrometers band, for simultaneous spectroscopy at every pixel, is presented, using a CCD camera and fast data processing technology.

  16. New chalcogenide glasses in the CdTe-AgI-As{sub 2}Te{sub 3} system

    SciTech Connect

    Kassem, M.; Le Coq, D.; Boidin, R.; Bychkov, E.

    2012-02-15

    Highlights: Black-Right-Pointing-Pointer Determination of the glass-forming region in the pseudo-ternary CdTe-AgI-As{sub 2}Te{sub 3} system. Black-Right-Pointing-Pointer Characterization of macroscopic properties of the new CdTe-AgI-As{sub 2}Te{sub 3} glasses. Black-Right-Pointing-Pointer Characterization of the total conductivity of CdTe-AgI-As{sub 2}Te{sub 3} glasses. Black-Right-Pointing-Pointer Comparison between the selenide and telluride equivalent systems. -- Abstract: Chalcogenide glasses in the pseudo-ternary CdTe-AgI-As{sub 2}Te{sub 3} system were synthesized and the glass-forming range was determined. The maximum content of CdTe in this glass system was found to be equal to 15 mol.%. The macroscopic characterizations of samples have consisted in Differential Scanning Calorimetry, density, and X-ray diffraction measurements. The cadmium telluride addition does not generate any significant change in the glass transition temperature but the resistance of binary AgI-As{sub 2}Te{sub 3} glasses towards crystallisation is estimated to be decreasing on the base of {Delta}T = T{sub x} - T{sub g} parameter. The total electrical conductivity {sigma} was measured by complex impedance spectroscopy. First, the CdTe additions in the (AgI){sub 0.5}(As{sub 2}Te{sub 3}){sub 0.5} host glass, (CdTe){sub x}(AgI){sub 0.5-x/2}(As{sub 2}Te{sub 3}){sub 0.5-x/2} lead to a conductivity decrease at x {<=} 0.05. Then, the behaviour is reversed at 0.05 {<=} x {<=} 0.15. The obtained results are discussed by comparison with the equivalent selenide system.

  17. Band bending at Al, In, Ag, and Pt interfaces with CdTe and ZnTe (110)

    SciTech Connect

    Wahi, A.K.; Miyano, K.; Carey, G.P.; Chiang, T.T.; Lindau, I.; Spicer, W.E. )

    1990-05-01

    Band bending behavior and interfacial chemistry for Al, In, Ag, and Pt overlayers on vacuum-cleaved {ital p}-CdTe and {ital p}-ZnTe (110) have been studied using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). These metals provide a range of metal--substrate reactivities: Al reacts strongly with Te, Ag moderately, and In minimally, with no evidence seen for In reaction on ZnTe. Pt exhibits strong alloying behavior with both Cd and Zn. All four metals are found to yield Schottky barriers on CdTe and ZnTe, with a narrow range of final Fermi level positions, {ital E}{sub {ital fi}}={ital E}{sub {ital f}}{minus}{ital E}{sub VBM}, observed on CdTe, from 0.9 to 1.05{plus minus}0.1 eV, and on ZnTe from 0.65 to 1.0{plus minus}0.1 eV. The prediction of the MIGS model that a difference in barrier height exists for two semiconductors dependent upon their band lineup (valence band offset) is examined and found to agree with experiment for Ag, Pt, and Al, but not for In. For the highly reactive Al, no evidence for the overlayer metallicity required for metal-induced gap states (MIGS) to operate is seen on CdTe or ZnTe until after band bending has stabilized. Reaction and intermixing for Al, Ag, and Pt overlayers on CdTe and ZnTe indicate these interfaces are not ideal. The possible role of defects at these four metal/CdTe and metal/ZnTe interfaces is considered, and provides a consistent explanation for the final Fermi level positions observed.

  18. Limites de stabilité de la phase (Ag, Cu)TlTe dans le système AgCuTlTe

    NASA Astrophysics Data System (ADS)

    Brun, Gerard; Boubali, Mahjoub; Ayral, R. M.; Tedenac, Jean-Claude

    1990-12-01

    Three isopleth sections, AgTlTe(CuTlTe), AgTlTeCu 2Te, and AgTlTeCu 2TlTe 2, of the quaternary system AgCuTlTe were investigated using thermal analysis, differential scanning calorimetry, and X-ray powder diffraction. The AgTlTe-based solid solution (Ag xCu YTl zTe) limits were determined and the composition-structure relations depicted.

  19. HgZnTe-based detectors for LWIR NASA applications

    NASA Technical Reports Server (NTRS)

    Patten, Elizabeth A.; Kalisher, Murray H.

    1990-01-01

    The initial goal was to grow and characterize HgZnTe and determine if it indeed had the advantageous properties that were predicted. Researchers grew both bulk and liquid phase epitaxial HgZnTe. It was determined that HgZnTe had the following properties: (1) microhardness at least 50 percent greater than HgCdTe of equivalent bandgap; (2) Hg annealing rates of at least 2 to 4 times longer than HgCdTe; and (3) higher Hg vacancy formation energies. This early work did not focus on one specific composition (x-value) of HgZnTe since NASA was interested in HgZnTe's potential for a variety of applications. Since the beginning of 1989, researchers have been concentrating, however, on the liquid phase growth of very long wavelength infrared (VLWIR) HgZnTe (cutoff approx. equals 17 microns at 65K) to address the requirements of the Earth Observing System (EOS). Since there are no device models to predict the advantages in reliability one can gain with increased microhardness, surface stability, etc., one must fabricate HgZnTe detectors and assess their relative bake stability (accelerated life test behavior) compared with HgCdTe devices fabricated in the same manner. Researchers chose to fabricate HIT detectors as a development vehicle for this program because high performance in the VLWIR has been demonstrated with HgCdTe HIT detectors and the HgCdTe HIT process should be applicable to HgZnTe. HIT detectors have a significant advantage for satellite applications since these devices dissipate much less power than conventional photoconductors to achieve the same responsivity.

  20. Direct measurement of coherent thermal phonons in Bi2Te3/Sb2Te3 superlattice

    NASA Astrophysics Data System (ADS)

    He, Feng; Wu, Wenzhi; Wang, Yaguo

    2016-08-01

    Coherent thermal phonons (CTPs) play an important role in thermal transport in superlattice (SL) structures. To have a profound understanding of CTP transport in SL, direct measurement of CTP properties is necessary. In this study, coherent phonon spectroscopy has been utilized to generate and detect CTP in Bi2Te3/Sb2Te3 SL. Phonon lifetimes have been extracted from experimental data, with which mode-wise thermal conductivities have been calculated. Comparing with bulk Bi2Te3, the estimated mode-wise thermal conductivity of longitudinal acoustic phonons shifts to higher frequencies, due to constructive coherent phonon interference. Our results suggest that it is possible to use SL structure to manipulate coherent phonon propagation and to tailor thermal conductivity.

  1. Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films

    SciTech Connect

    Punitha, K.; Sivakumar, R.; Sanjeeviraja, C.; Sathe, Vasant; Ganesan, V.

    2014-12-07

    In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, and oscillator energy (E{sub o}) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band edge emission peak observed at 820 nm with Cu dopant is due to the change in surface state density. The observed trigonal lattice of Te peaks in the micro-Raman spectra confirms the p-type conductive nature of films, which was further corroborated by the Hall effect measurement. The lowest resistivity of 6.61 × 10{sup 4} Ω cm was obtained for the CdTe:Cu (3 wt. %) film.

  2. An experimental TE sub 12 - TE sub 11 circular waveguide mode converter

    NASA Astrophysics Data System (ADS)

    Hoppe, D.

    1985-08-01

    Theoretical and experimental results for a prototype TE sub 12 to TE sub 11 circular waveguide mode converter are discussed. The system which requires such device, the high power Ka-Band transmitter is described briefly. A short review of coupled mode theory is given, and the theoretical performance of the final converter design is given. Experimental results for the fabricated converter are presented and compared with theory. A method of identifying the various circular waveguide modes in a multimode device is described. Given the close agreement between the theoretical predictions and experimental results, the computer code may be used with confidence in the design of future multimode tapers and mode converters.

  3. Effects of supercooling in the initial solidification of PbTe-SnTe solid solutions

    NASA Technical Reports Server (NTRS)

    Fripp, A. L.; Crouch, R. K.; Debnam, W. J., Jr.; Clark, I. O.; Wagner, J. B.

    1985-01-01

    Deviations from compositions anticipated by the thermal equilibrium phase diagram have been observed in Bridgman-grown crystals of Pb(1-x)Sn(x)Te, in the first to freeze region of the boule. A set of experiments were conducted to determine the extent of thermal supercooling of Pb(1-x)Sn(x)Te in a Bridgman-like configuration. The results of the compositional profiles and the supercooling measurements are consistent with a diffusionless transformation occurring at the onset of solidification, and the length of uncontrolled growth is inversely related to the temperature gradient of the furnace.

  4. Thermoelectric property study of Bi2Te3-Sb2Te3 mixed crystals

    NASA Astrophysics Data System (ADS)

    Malik, K.; Das, Diptasikha; Dasgupta, A.; Bandyopadhay, S.; Banerjee, Aritra

    2016-05-01

    Polycrystalline Bi2Te3-Sb2Te3 mixed crystals are synthesized by solid state reaction method. Structural characterizations are carried out using X-Ray diffraction (XRD). Thermal variation of resistivity data, measured down to 10K, shows that there is a transition from semiconducting to metallic behavior for 80% Sb containing sample. Temperature dependent thermopower measurement is carried out using differential technique in the temperature range 300-20 K. Thermopower data shows all the samples are p-type in nature. Power factor of the samples are also estimated.

  5. Laser-assisted growth of t-Te nanotubes and their controlled photo-induced unzipping to ultrathin core-Te/sheath-TeO(2) nanowires.

    PubMed

    Vasileiadis, Thomas; Dracopoulos, Vassileios; Kollia, Mary; Yannopoulos, Spyros N

    2013-01-01

    One dimensional (1D) nanostructures of semiconducting oxides and elemental chalcogens culminate over the last decade in nanotechnology owing to their unique properties exploitable in several applications sectors. Whereas several synthetic strategies have been established for rational design of 1D materials using solution chemistry and high temperature evaporation methods, much less attention has been given to the laser-assisted growth of hybrid nanostructures. Here, we present a laser-assisted method for the controlled fabrication of Te nanotubes. A series of light-driven phase transition is employed to controllably transform Te nanotubes to core-Te/sheath-TeO(2) and/or even neat TeO(2) nanowires. This solid-state laser-processing of semiconducting materials apart from offering new opportunities for the fast and spatially controlled fabrication of anisotropic nanostructures, provides a means of simultaneous growing and integrating these nanostructures into an optoelectronic or photonic device.

  6. Valence Band Modification and High Thermoelectric Performance in SnTe Heavily Alloyed with MnTe.

    PubMed

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Chi, Hang; Bailey, Trevor P; Zhao, Li-Dong; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2015-09-01

    We demonstrate a high solubility limit of >9 mol% for MnTe alloying in SnTe. The electrical conductivity of SnTe decreases gradually while the Seebeck coefficient increases remarkably with increasing MnTe content, leading to enhanced power factors. The room-temperature Seebeck coefficients of Mn-doped SnTe are significantly higher than those predicted by theoretical Pisarenko plots for pure SnTe, indicating a modified band structure. The high-temperature Hall data of Sn1-xMnxTe show strong temperature dependence, suggestive of a two-valence-band conduction behavior. Moreover, the peak temperature of the Hall plot of Sn1-xMnxTe shifts toward lower temperature as MnTe content is increased, which is clear evidence of decreased energy separation (band convergence) between the two valence bands. The first-principles electronic structure calculations based on density functional theory also support this point. The higher doping fraction (>9%) of Mn in comparison with ∼3% for Cd and Hg in SnTe gives rise to a much better valence band convergence that is responsible for the observed highest Seebeck coefficient of ∼230 μV/K at 900 K. The high doping fraction of Mn in SnTe also creates stronger point defect scattering, which when combined with ubiquitous endotaxial MnTe nanostructures when the solubility of Mn is exceeded scatters a wide spectrum of phonons for a low lattice thermal conductivity of 0.9 W m(-1) K(-1) at 800 K. The synergistic role that Mn plays in regulating the electron and phonon transport of SnTe yields a high thermoelectric figure of merit of 1.3 at 900 K. PMID:26308902

  7. Valence Band Modification and High Thermoelectric Performance in SnTe Heavily Alloyed with MnTe.

    PubMed

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Chi, Hang; Bailey, Trevor P; Zhao, Li-Dong; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2015-09-01

    We demonstrate a high solubility limit of >9 mol% for MnTe alloying in SnTe. The electrical conductivity of SnTe decreases gradually while the Seebeck coefficient increases remarkably with increasing MnTe content, leading to enhanced power factors. The room-temperature Seebeck coefficients of Mn-doped SnTe are significantly higher than those predicted by theoretical Pisarenko plots for pure SnTe, indicating a modified band structure. The high-temperature Hall data of Sn1-xMnxTe show strong temperature dependence, suggestive of a two-valence-band conduction behavior. Moreover, the peak temperature of the Hall plot of Sn1-xMnxTe shifts toward lower temperature as MnTe content is increased, which is clear evidence of decreased energy separation (band convergence) between the two valence bands. The first-principles electronic structure calculations based on density functional theory also support this point. The higher doping fraction (>9%) of Mn in comparison with ∼3% for Cd and Hg in SnTe gives rise to a much better valence band convergence that is responsible for the observed highest Seebeck coefficient of ∼230 μV/K at 900 K. The high doping fraction of Mn in SnTe also creates stronger point defect scattering, which when combined with ubiquitous endotaxial MnTe nanostructures when the solubility of Mn is exceeded scatters a wide spectrum of phonons for a low lattice thermal conductivity of 0.9 W m(-1) K(-1) at 800 K. The synergistic role that Mn plays in regulating the electron and phonon transport of SnTe yields a high thermoelectric figure of merit of 1.3 at 900 K.

  8. Anomalous phase change characteristics in Fe-Te materials

    SciTech Connect

    Fu, X. T.; Song, W. D.; Ji, R.; Ho, H. W.; Wang, L.; Hong, M. H.

    2012-05-14

    Phase change materials have become significantly attractive due to its unique characteristics for its extensive applications. In this paper, a kind of phase change material, which consists of Fe and Te components, is developed. The crystallization temperature of the Fe-Te materials is 180 deg. C for Fe{sub 1.19}Te and can be adjusted by the Fe/Te ratio. High-speed phase change in the Fe-Te materials has been demonstrated by nanosecond laser irradiation. Comparing to conventional phase change materials, the Fe-Te materials exhibit an anomalous optical property that has higher reflectivity at amorphous than crystalline state, which is useful for data storage design.

  9. Interactions of Pb and Te atoms with graphene.

    PubMed

    Gong, Chuncheng; Robertson, Alex W; He, Kuang; Ford, Camden; Watt, Andrew A R; Warner, Jamie H

    2014-05-28

    PbTe nanocrystals were deposited onto the surface of graphene and used as a reservoir of Pb and Te atoms. Electron beam irradiation at 80 kV caused Pb and Te atoms to mobilize and disperse across the surface of graphene. We studied the dynamics of these atoms in real time using aberration-corrected transmission electron microscopy. The Pb and Te atoms were found to attach to the surface layer of amorphous carbon that resides upon the graphene, as well as its edge. Pb and Te atoms were not found residing on pristine graphene, but were found to bond to the free edge states along graphene hole edges. Small PbTe nanoclusters tended to only form on the surface of the amorphous carbon regions and not on pristine graphene.

  10. X-ray photoemission study of the Te-precursor surfaces and the initial stages of growth of ZnTe on GaAs (100)

    NASA Astrophysics Data System (ADS)

    Tatarenko, S.; Saminadayar, K.; Cibert, J.

    1987-11-01

    The initial stages of epitaxial growth of ZnTe on GaAs (100) have been studied by x-ray photoemission spectroscopy. The two surface structures (6×1 and (3)1/2×3 ) resulting from the adsorption of Te on GaAs (100) were used as precursor for ZnTe growth. Each of these structures is characterized by two different adsorbed Te states. For the 6×1 structure, the two states are assigned to As-Te-As and tentatively to Te-Te-Te bonds; and for the (3)1/2×3 structure, the assigned bonds are As-Te-As and GaGa Te-As. Growth of ZnTe (100) does not induce any change in the bonds associated with the 6×1 structure but modifies that associated with the (3)1/2×3 surface.

  11. Ferroelectric switching in epitaxial GeTe films

    SciTech Connect

    Kolobov, A. V. Fons, P.; Tominaga, J.; Kim, D. J.; Gruverman, A.; Giussani, A.; Calarco, R.

    2014-06-01

    In this paper, using a resonance-enhanced piezoresponse force microscopy approach supported by density functional theory computer simulations, we have demonstrated the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with thickness on the order of several nanometers reversible reorientation of polarization occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the material. It is also hinted that for ultra thin films consisting of just several atomic layers weakly bonded to the substrate, ferroelectric switching may proceed through exchange of Ge and Te planes within individual GeTe layers.

  12. LETTER: Test of Te profile invariance by sensitivity studies

    NASA Astrophysics Data System (ADS)

    Becker, G.

    1992-06-01

    The response of the electron temperature profile shape to variations of the electron heating and density profiles is investigated in different confinement regimes. It is shown that the changes in rTe = -Te/(dTe/dr) exceed the measurement error if the shape of the electron heat diffusivity χe(r) is kept fixed. The observed constancy of rTe(r) in the outer half of the plasma is incompatible with such a fixed χe(r) shape, i.e., a Te profile constraining mechanism must be present. Local transport laws of the form χe varies as rTe-α with α gtrsim 4 and χe propto (dTe/dr)α with α >= 2 yield the experimental stiffness of the Te(r) shape but conflict with empirical χe scalings. These results support the model of a self-organizing and adjusting χe(r) causing Te profile invariance

  13. Superconductivity in Ta3Pd3Te14 with quasi-one-dimensional PdTe2 chains.

    PubMed

    Jiao, Wen-He; He, Lan-Po; Liu, Yi; Xu, Xiao-Feng; Li, Yu-Ke; Zhang, Chu-Hang; Zhou, Nan; Xu, Zhu-An; Li, Shi-Yan; Cao, Guang-Han

    2016-02-15

    We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γ(n)T(c)) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower T(c), compared to that of Ta4Pd3Te16, may be attributed to the lower density of states.

  14. Quantum-confined Stark effect on spatially indirect excitons in CdTe/Cdx Zn1-x Te quantum wells

    NASA Astrophysics Data System (ADS)

    Haas, H.; Magnea, N.; Dang, Le Si

    1997-01-01

    The quantum-confined Stark effect is studied in the mixed type-I/type-II CdTe/Cdx Zn1-x Te strained heterostructures. The type-II nature of the light-hole excitons is unambiguously confirmed by the blueshift observed under increasing electric field, in good agreement with calculations. On the other hand, the heavy-hole excitons are redshifted as expected for type-I excitons. The peculiar valence-band alignment, resulting from the sign reversal of the strain between the wells and the barriers, is used to detect the electric-field induced mixing of LH1 and HH2 confined hole states. An accurate value for the long-disputed chemical valence-band offset of CdTe/ZnTe system is extracted as ΔEV=(11+/-3)% of the band-gap difference between unstrained CdTe and ZnTe materials.

  15. Superconductivity in Ta3Pd3Te14 with quasi-one-dimensional PdTe2 chains

    PubMed Central

    Jiao, Wen-He; He, Lan-Po; Liu, Yi; Xu, Xiao-Feng; Li, Yu-Ke; Zhang, Chu-Hang; Zhou, Nan; Xu, Zhu-An; Li, Shi-Yan; Cao, Guang-Han

    2016-01-01

    We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γnTc) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower Tc, compared to that of Ta4Pd3Te16, may be attributed to the lower density of states. PMID:26876362

  16. BOREAS TE-12 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Arkebauer, Timothy J.; Yang, Litao

    2000-01-01

    The BOREAS TE-12 team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, and gas exchange of boreal vegetation. This data set contains measurements of leaf gas exchange conducted in the SSA during the growing seasons of 1994 and 1995 using a portable gas exchange system. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Center (DAAC).

  17. New physics at 1 TeV?

    NASA Astrophysics Data System (ADS)

    Godunov, S. I.; Rozanov, A. N.; Vysotsky, M. I.; Zhemchugov, E. V.

    2016-05-01

    If decays of a heavy particle S are responsible for the diphoton excess with invariant mass 750 GeV observed at the 13 TeV LHC run, it can be easily accommodated in the Standard Model. Two scenarios are considered: production in gluon fusion through a loop of heavy isosinglet quark(s) and production in photon fusion through a loop of heavy isosinglet leptons. In the second case, many heavy leptons are needed or/and they should have large electric charges in order to reproduce experimental data on σ pp → SX · Br( S → γγ).

  18. BOREAS TE-2 Root Respiration Data

    NASA Technical Reports Server (NTRS)

    Ryan, Michael G.; Lavigne, Michael; Hall, Forrest G. (Editor); Papagno, Andrea (Editor)

    2000-01-01

    The BOREAS TE-2 team collected several data sets in support of its efforts to characterize and interpret information on the respiration of the foliage, roots, and wood of boreal vegetation. This data set includes means of tree root respiration measurements on roots having diameters ranging from 0 to 2 mm conducted in the NSA during the growing season of 1994. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  19. BOREAS TE-21 SSA Site Characteristics Data

    NASA Technical Reports Server (NTRS)

    Knox, Robert; Hall, Forrest G. (Editor); Papagno, Andrea (Editor)

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-20 (Terrestrial Ecology) team collected several data sets for use in developing and testing models of forest ecosystem dynamics. This data set contains measurements of site characteristics conducted in the Southern Study Area (SSA) from 18 Jul 1994 to 30 Jul 1994. The data are stored in CSV files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  20. BOREAS TE-10 Leaf Chemistry Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Middleton, Elizabeth; Sullivan, Joseph

    2000-01-01

    The BOREAS TE- 10 team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, gas exchange, chlorophyll content, carbon content, hydrogen content, and nitrogen content of boreal vegetation. This data set describes the relationship between sample location, age, chlorophyll content, and C-H-N concentrations at several sites in the SSA conducted during the growing seasons of 1994 and 1996. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Center (DAAC).

  1. BOREAS TE-17 Production Efficiency Model Images

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G.; Papagno, Andrea (Editor); Goetz, Scott J.; Goward, Samual N.; Prince, Stephen D.; Czajkowski, Kevin; Dubayah, Ralph O.

    2000-01-01

    A Boreal Ecosystem-Atmospheric Study (BOREAS) version of the Global Production Efficiency Model (http://www.inform.umd.edu/glopem/) was developed by TE-17 (Terrestrial Ecology) to generate maps of gross and net primary production, autotrophic respiration, and light use efficiency for the BOREAS region. This document provides basic information on the model and how the maps were generated. The data generated by the model are stored in binary image-format files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  2. BOREAS TE-11 Sap Flow Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Saugier, Bernard

    2000-01-01

    The BOREAS TE-11 team collected several data sets in support of its efforts to characterize and interpret information on the sap flow, gas exchange, and lichen photosynthesis of boreal vegetation and meteorological data of the area studied. This data set contains measurements of sap flow conducted at the SSA-OJP site in the growing seasons of 1993 and 1994. The data are stored in ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Center (DAAC).

  3. BOREAS TE-11 Leaf Gas Exchange Measurements

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Saugier, Bernard; Pontailler, J. Y.

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-11 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the sap flow, gas exchange, and lichen photosynthesis of boreal vegetation and meteorological data of the area studied. This data set contains measurements of assimilation and transpiration conducted at the Old Jack Pine (OJP) site during the growing seasons of 1993 and 1994. The data are stored in ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  4. TeV emission from close binaries

    NASA Astrophysics Data System (ADS)

    Moskalenko, I. V.

    1995-05-01

    It is commonly accepted that candidates for very high energy γ-ray sources are neutron stars, binary systems, black holes etc. Close binary systems containing a normal hot star and a neutron star (or a black hole) form an important class of very high energy γ-ray sources. Such systems are variable in any region of the electromagnetic spectrum and they enable us to study various stages of stellar evolution, accretion processes, mechanisms of particle acceleration, etc. Phenomena connected with this class of very high energy γ-ray sources are discussed. Particular emphasis has been placed on the TeV energy region.

  5. BOREAS TE-2 Continuous Wood Respiration Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Ryan, Michael G.; Lavigne, Michael

    2000-01-01

    The BOREAS TE-2 team collected several data sets in support of its efforts to characterize and interpret information on the respiration of the foliage, roots, and wood of boreal vegetation. This data set contains measurements of wood respiration measured continuously (about once per hour) in the NSA during the growing season of 1994. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  6. BOREAS TE-2 Wood Respiration Data

    NASA Technical Reports Server (NTRS)

    Ryan, Michael G.; Lavigne, Michael; Hall, Forrest G. (Editor); Papagno, Andrea (Editor)

    2000-01-01

    The BOREAS TE-2 team collected several data sets in support of its efforts to characterize and interpret information on the respiration of the foliage, roots, and wood of boreal vegetation. This data set contains measurements of wood respiration conducted in the NSA during the growing season of 1994. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  7. BOREAS TE-5 Soil Respiration Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. Soil respiration data were collected from 26-May-94 to 07-Sep-94 in the BOREAS NSA and SSA to compare the soil respiration rates in different forest sites using a LI-COR 6200 soil respiration chamber (model 6299). The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distrobuted Activity Archive Center (DAAC).

  8. BOREAS TE-2 Foliage Respiration Data

    NASA Technical Reports Server (NTRS)

    Ryan, Michael G.; Hall, Forrest G. (Editor); Lavigne, Michael; Papagno, Andrea (Editor)

    2000-01-01

    The BOREAS TE-2 team collected several data sets in support of its efforts to characterize and interpret information on the respiration of the foliage, roots, and wood of boreal vegetation. This data set contains measurements of foliar respiration conducted in the NSA during the growing season of 1994. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  9. Impurity doping of HgTe--CdTe superlattices during growth by molecular-beam epitaxy

    SciTech Connect

    Wroge, M.L.; Peterman, D.J.; Feldman, B.J.; Morris, B.J.; Leopold, D.J.; Broerman, J.G.

    1989-03-01

    We demonstrate the use of In and Ag as n- and p-type dopants, respectively, to controllably dope (100)-oriented HgTe--CdTe superlattices during molecular-beam epitaxial (MBE) growth. When normalized by the superlattice growth rate, the low-temperature Hall-carrier concentrations of both In- and Ag-doped superlattices are shown to have an exponential dependence on the respective effusion-cell temperatures in the electron and hole concentration ranges of approx.10/sup 16/ to 10/sup 18/ cm/sup -3/ . The upper limit on the diffusion coefficient for In at the low MBE growth temperature of approx.160 /sup 0/C is determined to be 5 x 10/sup -15/ cm/sup 2/ /s by use of secondary-ion mass spectrometry. Hall-effect and current--voltage measurements verify that the combination of In and Ag doping allows the formation of p--n electrical junctions. These results provide the first evidence of p--n junction formation in a HgTe--CdTe superlattice.

  10. Structural and optical evidence of island correlation in CdTe/ZnTe superlattices

    SciTech Connect

    Mackowski, S.; Karczewski, G.; Wojtowicz, T.; Kossut, J.; Kret, S.; Szczepanska, A.; Dlewski, P.; Prechtl, G.; Heiss, W.

    2001-06-11

    The properties of superlattices consisting of 2 monolayer wide CdTe insertions into ZnTe spacer barriers with thickness ranging from 3 to 75 monolayers are investigated by means of transmission electron microscopy and photoluminescence spectroscopy. We show that quasi zero-dimensional CdTe islands form in this highly lattice-mismatched system. For spacer thickness smaller than 25 monolayers, the islands are vertically correlated along the axis tilted by 40{degree} with respect to the growth direction, while for thicker ZnTe spacers no correlation is observed. The electronic coupling between the correlated islands manifests itself by the appearing of an additional emission band at energies lower to those corresponding to uncorrelated dots. The optical spectroscopy data reveal zero-dimensional localization of excitons by the electronically coupled islands. The decay time of the excitonic recombination is found to be over an order of magnitude longer in the case of the coupled islands than in the case of isolated ones. {copyright} 2001 American Institute of Physics.

  11. Monte Carlo simulations of morphological transitions in PbTe/CdTe immiscible material systems

    NASA Astrophysics Data System (ADS)

    Mińkowski, Marcin; Załuska-Kotur, Magdalena A.; Turski, Łukasz A.; Karczewski, Grzegorz

    2016-09-01

    The crystal growth of the immiscible PbTe/CdTe multilayer system is analyzed as an example of a self-organizing process. The immiscibility of the constituents leads to the observed morphological transformations such as an anisotropy driven formation of quantum dots and nanowires and to a phase separation at the highest temperatures. The proposed model accomplishes a bulk and surface diffusion together with an anisotropic mobility of the material components. We analyze its properties by kinetic Monte Carlo simulations and show that it is able to reproduce all of the structures observed experimentally during the process of the PbTe/CdTe growth. We show that all of the dynamical processes studied play an important role in the creation of zero-, one-, two-, and, finally, three-dimensional structures. The shape of the structures that are grown is different for relatively thick multilayers, when the bulk diffusion cooperates with the anisotropic mobility, as compared to the annealed structures for which only the isotropic bulk diffusion decides about the process. Finally, it is different again for thin multilayers when the surface diffusion is the most decisive factor. We compare our results with the experimentally grown systems and show that the proposed model explains the diversity of observed structures.

  12. Pressure dependence of the charge-density-wave and superconducting states in GdTe3, TbTe3, and DyTe3

    DOE PAGES

    Zocco, D. A.; Hamlin, J. J.; Grube, K.; Chu, J. -H.; Kuo, H. -H.; Fisher, I. R.; Maple, M. B.

    2015-05-14

    Here, we present electrical resistivity and ac-susceptibility measurements of GdTe3, TbTe3 and DyTe3 performed under pressure. An upper charge-density-wave (CDW) is suppressed at a rate of dTCW,1/dP~ –85K/GPa. For TbTe3 and DyTe3, a second CDW below TCDW,2 increases with pressure until it reaches the TCDW,1(P) line. For GdTe3, the lower CDW emerges as pressure is increased above ~1GPa. As these two CDW states are suppressed with pressure, superconductivity (SC) appears in the three compounds at lower temperatures. Ac-susceptibility experiments performed on TbTe3 provide compelling evidence for bulk SC in the low-pressure region of the phase diagram. We provide measurements ofmore » superconducting critical fields and discuss the origin of a high-pressure superconducting phase occurring above 5 GPa.« less

  13. Enhancing radiosensitivity of TE1, TE8, and TE 11 esophageal squamous carcinoma cell lines by Hdm2-siRNA targeted gene therapy in vitro

    PubMed Central

    Pirayesh Islamian, Jalil; Mohammadi, Mohsen; Baradaran, Behzad; Farajollahi, Alireza; Aghamiri, Seyed Mahmoud Reza; Asghari Jafarabadi, Mohammad; Karami, Hadi; Monfaredan, Amir; Shanehbandi, Dariush

    2016-01-01

    Introduction: Human double minute2 (hdm2) level increases in most human malignancies. Therefore, inhibition of tumor growth and also induction of radiosensitivity may be provided by hdm2 inhibitors. The effects of hdm2-siRNA on hdm2 protein expression, cell apoptosis rate, and radiosensitivity of human esophageal squamous cell carcinoma (ESCC) were studied. Methods: The hdm2 gene was silenced in TE1, TE8, and TE11 ESCC cell lines using 200nM siRNA by liposomal transfection method followed by irradiation with 0.5, 1, 2, 4, and 6 Gy γ-rays in vitro. The gene expression levels were evaluated by real time PCR and Western Blotting methods. MTT, TUNEL, and also colony forming assays were used to compare the radiosensitivity of the cell lines before and after the treatments. Results: Hdm2-siRNA reduced the hdm2 protein as compared to the vehicle control and scrambled groups, and also increased the radiation-induced apoptosis especially in TE11 cells. The related dose reduction factors (DRFs) for the silenced TE1, TE8, and TE11 cells calculated to be 1.20, 1.30, and 2.75, respectively. Conclusion: Increasing radiosensitivity of tumor cells may be provided by silencing the oncogenes. PMID:27525226

  14. Ion distribution preferences in ternary crystals ZnxCd1-xTe, Zn1-xHgxTe and Cd1-xHgxTe

    NASA Astrophysics Data System (ADS)

    Robouch, B. V.; Kutcherenko, I. V.; Cestelli Guidi, M.; Kisiel, A.; Marcelli, A.; Robouch, P.; Piccinini, M.; Nucara, A.; Triboulet, R.; Burattini, E.; Cebulski, J.; Sheregii, E. M.; Polit, J.

    2011-11-01

    Similar ternary semiconductors are sometimes associated with widely different structures characterized by different site occupation preferences. We have used far-infrared (FIR) spectra to determine the site occupation preference coefficients for three ternary semiconductor alloys: ZnCdTe, ZnHgTe and CdHgTe and, in the case of ZnHgTe, have validated it by X-ray absorption fine structure (EXAFS) analysis. While ZnCdTe spectra exhibit the canonical configuration with eight phonon lines free of vibrational defect lines and only a slight departure from a random ion distribution, CdHgTe spectra show the eight canonical phonon modes plus an additional vibrational defect line and constant preference coefficients. In contrast, two defect lines and only four modes characterize ZnHgTe spectra, as extreme preferences prevent the formation of two of the five expected tetrahedral configuration arrangements. Moreover, for this system, comparison with EXAFS data points out the vibrational nature of both the extra lines. The analysis clearly shows that assuming a Bernoulli distribution of the component configurations of semiconductors may lead to wrong assessments of the evolution of its properties with relative content.

  15. Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Zhao, Xin-Hao; Campbell, Calli M.; DiNezza, Michael J.; Liu, Shi; Zhao, Yuan; Zhang, Yong-Hang

    2014-12-22

    The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg{sub 0.24}Cd{sub 0.76}Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 10{sup 2 }cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity.

  16. Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures.

    PubMed

    Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K; Wang, Jiannong

    2016-05-17

    The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.

  17. Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K.; Wang, Jiannong

    2016-05-01

    The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years’ air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.

  18. Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures.

    PubMed

    Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K; Wang, Jiannong

    2016-01-01

    The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena. PMID:27185305

  19. Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures

    PubMed Central

    Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K.; Wang, Jiannong

    2016-01-01

    The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years’ air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena. PMID:27185305

  20. Research and development of HgZnTe as an infrared material

    NASA Technical Reports Server (NTRS)

    Wahi, A. K.; Lindau, I.; Spicer, W. E.

    1989-01-01

    Interfacial morphology and Fermi level pinning behavior at the interfaces of Al, Ag, and Pt with UHV-cleaved CdTe and ZnTe have been studied using X-ray and ultraviolet photoemission spectroscopies. Results are compared to metal/HgCdTe interface formation, where the weak HgTe bond and consequent ease of Hg loss strongly influence semiconductor disruption and metal-semiconductor intermising. For Al/CdTe, the strong Al-Te reaction yields a significantly more extensive Al-Te reacted region than has been observed for HgCdTe. The Al/ZnTe interface is observed to be more abrupt than Al/CdTe. The final Fermi level pinning positions, Ef-Evbm for Al, Ag, and Pt on p-type CdTe and p-ZnTe have been determined. Efi is found to be roughly the same for both CdTe and ZnTe, with the value for ZnTe lying approximately 0.2 eV closer to the VBM for all three metals. From these results, one would expect Schottky barriers of about the same height for these metals on p-CdTe and p-ZnTe; and also that, in principle, metal interfaces with the two alloys HgCdTe and HgZnTe would have the same properties. Comparisons and implications for electrical behavior of metal contacts to the alloys are discussed.

  1. Indirect exchange interaction between magnetic impurities in the two-dimensional topological insulator based on CdTe/HgTe/CdTe quantum wells

    NASA Astrophysics Data System (ADS)

    Kurilovich, P. D.; Kurilovich, V. D.; Burmistrov, I. S.

    2016-10-01

    We study indirect exchange interaction between magnetic impurities in the (001) CdTe/HgTe/CdTe symmetric quantum well. We consider low temperatures and the case of the chemical potential placed in the energy gap of the two-dimensional quasiparticle spectrum. We find that the indirect exchange interaction is suppressed exponentially with the distance between magnetic impurities. The presence of inversion asymmetry results in oscillations of the indirect exchange interaction with the distance and generates additional terms which are noninvariant under rotations in the (001) plane. The indirect exchange interaction matrix has complicated structure with some terms proportional to the sign of the energy gap.

  2. Molecular beam epitaxy of CdTe on GaAs substrates and HgCdTe on CdTe/GaAs alternate substrates

    SciTech Connect

    Lange, M.D.

    1993-12-31

    Two aspects of molecular-beam epitaxy (MBE) of the infrared sensitive semiconductor Hg{sub 1-x}Cd{sub x}Te were investigated: control of the substrate temperature by infrared pyrometer in addition to rear thermocouple, and improvement of CdTe/GaAs alternate substrates. Pyrometer behavior was recorded while controlling the temperatures of growing Hg{sub 1-x}Cd{sub x}Te with a frontal thermocoupled that contacted their surfaces. These recordings were interpreted in terms of emission and absorption, transmission and reflection, and thin-film interference. Based on these results, temperature control by rear thermocouple was reexamined, resulting in improved technique of that temperature control method as well. A temperature control technique combining both the pyrometer and the rear thermocoupled was developed; and evidence is presented and the rear thermocouple was developed; and evidence is presented for the resulting improvement in crystalline and electrical quality of MBE Hg{sub 1-x}Cd{sub x}Te. Investigations of Hg{sub 1-x}Cd{sub x}Te MBE onto more afforadable, larger, and more rugged CdTe/GaAs alternate substrates focused chiefly on improving the MBE of CdTe onto GaAs. This heteroepitaxy was studied primarily in terms of the influences on CdTe crystalline quality of the mismatches in bonding character, lattice spacing, thermal expansion, and charge imbalance between these two zincblende crystals. A novel dual epitaxial relationship, CdTe(331)B/GaAs(112)B and CdTe (112)B/GaAs(112)B, was discovered in these investigations; and the nonparellel orientation proves superior to the parallel orientation and to both orientations of the previously known CdTe(111)B/GaAs(001) and CdTe(001)/GaAs(001) dual epitaxial relationship. A charge imbalance model, applied to these four heterointerfaces, predicts the balancing of that charge by movement of electrons into or out of the heterointerfacial dangling bonds, which exist due to the lattice mismatch.

  3. Polarization-controllable TE21 mode converter

    NASA Astrophysics Data System (ADS)

    Chang, T. H.; Yu, C. F.; Fan, C. T.

    2005-07-01

    We report the concept and development of a Ka-band mode and polarization converter that efficiently converts a TE10 rectangular waveguide mode into either a linearly or a circularly polarized TE21 cylindrical waveguide mode. The converter is composed of a power-dividing section, a mode-converting section, and a polarization-transitioning section. The converting process in each section is displayed and the working principles are discussed. A prototype has been built and tested. The measured results agree well with the numerical calculations for both linear and circular polarizations. The measured optimum back-to-back transmission is 94% with a 1-dB bandwidth of 4.1 GHz for the linear polarization. As for the circular polarization, the measured optimum transmission is 97%, but the corresponding bandwidth is indistinct due to some resonant dips. The reasons and impact for the dips are discussed. A bandwidth of 3.9 GHz is obtained for a single circular converter; meanwhile, an approach to eliminating these unwanted dips is presented in theory. For further diagnostics, the field pattern of either polarization is directly displayed on a temperature-sensitive liquid crystal display sheet, where the electric field strength can be discerned from the color spectrum. In addition to high conversion efficiency and broad bandwidth, this converter features easy construction, high mode purity, and polarization controllability.

  4. Molecular Magnetism in MnTe Clusters

    NASA Astrophysics Data System (ADS)

    Chen, Jia; Nanduri, Arun; Choi, Bonnie; Millis, Andrew; Reichman, David; Roy, Xavier

    Electron correlation in recently synthesized molecular clusters with Mn4Te4 cores in cubane structures and ligand exteriors are studied experimentally and theoretically. We used density functional theory with on-site Coulomb interactions (DFT+U) to construct effective spin Hamiltonians and estimate the dependence of parameters on choice of ligand. The lack of inversion symmetry combined with the heavy tellurium ions leads to a significant Dzyaloshinskii-Moriya (DM) interaction. Comparison of measurements to the magnetic susceptibility calculated from the spin model is used to validate the results. We also extend this work to more complex clusters with more than one cubanes, where interesting high-spin ground state may occur. It has been measured recently, Fe8Te8 in dicubane structure has ground state with magnetization of12μB, which makes it promising candidate for single molecular magnets. A.J.M. acknowledges support from NSF under Contract DMR-1308236. J.C. is supported by the NSF MRSEC program through Columbia in the Center for Precision Assembly of Superstratic and Superatomic Solids under Grant No.DMR-1420634.

  5. (GeTe){sub n}SbInTe{sub 3} (n≤3)—Element distribution and thermal behavior

    SciTech Connect

    Fahrnbauer, Felix; Urban, Philipp; Welzmiller, Simon; Schröder, Thorsten; Rosenthal, Tobias; Oeckler, Oliver

    2013-12-15

    Antimony in germanium antimony tellurides (GeTe){sub n}(Sb{sub 2}Te{sub 3}) can be substituted by indium. Homogeneous bulk samples of GeSbInTe{sub 4} (R3-bar m, Z=3, a=4.21324(5) Å, c=41.0348(10) Å) and Ge{sub 2}SbInTe{sub 5} (P3-bar m1, Z=1, a=4.20204(6) Å, c=17.2076(4) Å) were obtained; their structures were refined with the Rietveld method. Single-crystal X-ray diffraction using synchrotron radiation at the K edges of Sb and Te (exploiting anomalous dispersion) yields precise information on the element distribution in the trigonal layered structure of Ge{sub 3}SbInTe{sub 6} (R3-bar m, Z=3, a=4.19789(4) Å, c=62.1620(11) Å). The structure is characterized by van der Waals gaps between distorted rocksalt-type slabs of alternating cation and anion layers. The cation concentration is commensurately modulated with Sb preferring the positions near the gaps. In contrast to unsubstituted Ge{sub 3}Sb{sub 2}Te{sub 6}, quenching the NaCl-type high-temperature phase (stable above ∼510 °C) easily yields a pseudocubic modification that is metastable at ambient conditions. Temperature-dependent powder diffraction reveals a broader stability range of the cubic high-temperature modification of Ge{sub 3}SbInTe{sub 6} compared to the ternary phases. In-containing samples partially decompose at ca. 300 °C but become homogeneous again when the high-temperature phase is formed. - Graphical abstract: Crystal structure of 33R-Ge{sub 3}SbInTe{sub 6} as determined by resonant X-ray diffraction, one example of the (GeTe){sub n}SbInTe{sub 3} series of compounds investigated. - Highlights: • The new compounds 21R-GeSbInTe{sub 4}, 9P-Ge{sub 2}SbInTe{sub 5} and 33R-Ge{sub 3}SbInTe are described. • The element distribution in 33R-Ge{sub 3}SbInTe{sub 6} was determined by resonant scattering. • The cation concentration in the crystal structure is strongly modulated. • The Sb substitution by In has a significant impact on phase transitions. • Results may be relevant for

  6. CdS/CdTe Solar Cells Containing Directly Deposited CdSxTe1-x Alloy Layers: Preprint

    SciTech Connect

    Duenow, J. N.; Dhere, R. G.; Moutinho, H. R.; To, B.; Pankow, J. W.; Kuciauskas, D.; Gessert, T. A.

    2011-07-01

    A CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thin-film CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by radio-frequency (RF) magnetron sputtering and co-evaporation from CdTe and CdS sources. Both RF-magnetron-sputtered and co-evaporated CdSxTe1-x films of lower S content (x<0.3) have a cubic zincblende (ZB) structure akin to CdTe, whereas those of higher S content have a hexagonal wurtzite (WZ) structure like that of CdS. Films become less preferentially oriented as a result of a CdCl2 heat treatment (HT) at ~400 degrees C for 5 min. Films sputtered in a 1% O2/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl2 HT. Films sputtered in O2 partial pressure have a much wider bandgap than expected. This may be explained by nanocrystalline size effects seen previously [2] for sputtered oxygenated CdS (CdS:O) films. Initial PV device results show that the introduction of a directly-deposited CdSxTe1-x alloy layer into the device structure produces devices of comparable performance to those without the alloy layer when a CdCl2 HT is performed. Further investigation is required to determine whether the CdCl2 heat treatment step can be altered or eliminated through direct deposition of the alloy layer.

  7. Fermi Observations of TeV-Selected Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T. H.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Cutini, S.; de Angelis, A.; de Palma, F.; Di Bernardo, G.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Finke, J.; Focke, W. B.; Fortin, P.; Foschini, L.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hanabata, Y.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocian, M. L.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Meurer, C.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reposeur, T.; Reyes, L. C.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Sellerholm, A.; Sgrò, C.; Shaw, M. S.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Tanaka, Y.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Ylinen, T.; Ziegler, M.

    2009-12-01

    We report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects). The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV-TeV sources, and 29 were not in the third EGRET catalog. For each of the 38 Fermi-detected sources, spectra and light curves are presented. Most can be described with a power law of spectral index harder than 2.0, with a spectral break generally required to accommodate the TeV measurements. Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments. Evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light.

  8. Supporting E-Learning in Enterprise: The TE3 Project

    ERIC Educational Resources Information Center

    Smith, Kelly

    2007-01-01

    Purpose: The Technology Enhanced Enterprise Education project (TE3) promotes the use of learning technologies to enhance enterprise and entrepreneurship education in the 12 HEI partners of the Mercia Institute of Enterprise (MIE). This paper describes the formal processes and procedures underpinning TE3, describes issues around material…

  9. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, S.; Zhu, Shen; Lehoczky, S. L.; Wang, Ling Jun

    2000-01-01

    Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe, and ZnSe(1-x)Te(x)(0 less than x less than 0.4) grown by physical vapor transport. Energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. A best fit curve to the band gap versus composition x data gives a bowing parameter of 1.45. This number lies between the value of 1.23 determined previously on ZnSeTe bulk crystals and the value of 1.621 reported on ZnSeTe epilayers. Low-temperature photoluminescence (PL) spectra were measured on six samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe(1-x)Te(x) samples, 0.09 less than x less than 0.39. For x=0.09, this emission energy is about 0.2 eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x=0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples.

  10. Multiwavelength studies of Galactic TeV particle accelerators

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2016-07-01

    Our Milky Way galaxy is host to a variety of astrophysical objects capable of accelerating particles to TeV energies, including supernova remnants and pulsar wind nebulae. I will review recent multiwavelength results on Galactic TeV sources and discuss the implications for particle acceleration and diffusion in these systems.

  11. Compositional Dependence of the Optical Properties of Vacuum Evaporated Thin GeSe2-GeTe-PbTe Films

    NASA Astrophysics Data System (ADS)

    Petkov, Kiril; Tasseva, Jordanka; Vassilev, Venceslav; Aljihmani, Lilia

    Chalcogenide glasses from the GeSe2-GeTe-PbTe system were synthesized by taking preliminary prepared GeSe2, GeTe and PbTe in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films were deposited on optical glass substrates BK-7 and Si-wafer substrates by thermal evaporation. Using X-ray microanalysis it was found that the film composition differs to a certain degree from the bulk composition. The changes in the optical properties of thin GeSe2-GeTe-PbTe films were studied as a function of their composition, exposure to light and annealing. It is shown by XRD analysis that the thin films are amorphous up to layers with composition of Ge27Se51Te14Pb8. The optical constants (refractive index, n and absorption coefficient, α), the thickness, d as well as the optical band gap, Eg, depending on the film composition were determined by spectrophotometric measurements in the region 450-2500 nm applying the Swanepoel's envelop method and Tauc's procedure. With the increase of the Te content in the layers, the absorption edge is shifted to the higher wavelengths, the refractive index increases from 2.54 for Ge31Se66Te3 up to 3.37 for Ge32Se55Te13 while the optical band gap decreases from 1.86 eV for to 1.30 eV for the same compositions. Similar dependence was observed with the increase of the PbTe content in the layers. After annealing of thin films, the values of n decrease, the optical band gap increases and a shift of the absorption edge to the shorter wavelengths is observed.

  12. Photorefractivity in a Titanium Doped ZnCdTe Crystal

    NASA Technical Reports Server (NTRS)

    Davis, M.; Collins, L.; Dyer, K.; Tong, J.; Ueda, A.; Chen, H.; Chen, K.-T.; Burger, A.; Pan, Z.; Morgan, S. H.

    1997-01-01

    Single crystals of Zn(.04)Cd(.96)Te was grown by horizontal physical vapor transport (PVT) method and doped by annealing with TiTe2 powder at 600 C for six days. Photorefractive two-beam coupling, along with photoluminescence and absorption spectroscopy, were used to characterize the ZnCdTe:Ti crystal. At 1.32 micrometers, the photorefractive gain has been measured as a function of the grating period. A gain of about 0.16/cm was obtained at an intensity of about 0.1 W/sq cm. The results of this titanium doped ZnCdTe crystal are compared to that of vanadium-doped CdTe crystals reported previously.

  13. Novel Surface Structure of Te/Ge(001)

    NASA Astrophysics Data System (ADS)

    Sakata, O.; Walko, D. A.; Tinkham, B. P.; Bedzyk, M. J.

    2000-03-01

    Structures formed by the adsorption of Te on Ge(001) have been studied by the complementary techniques of surface x-ray diffraction (SXRD), x-ray standing waves (XSW), LEED, and AES. Two structures with qualititatively different LEED patterns, corresponding to high- and low-coverage states, are found by annealing to different temperatures. While Te atoms in the high-coverage (1×1) phase adsorb at the expected bridge sites, the low-coverage c(2×2) phase, with 0.5 ML Te, is marked by Te-Ge heterodimers. Previous XSW analysis the (004) and (022) reflections precisely located the well-ordered Te atoms, with a significant height difference of 0.07 Å between the two structures [P.F. Lyman et al., Phys. Rev. B 60, 8704 (1999)]. SXRD was used to characterize the geometry of the heterodimer and investigate the strain-induced multilayer relaxations of the subsurface Ge atoms.

  14. Pb(3)Te(2)O(6)Br(2).

    PubMed

    Weil, Matthias; Stöger, Berthold

    2010-01-16

    Single crystals of the title compound, trilead(II) bis-[tellurate(IV)] dibromide, have been grown under hydro-thermal conditions. The structure is isotypic with that of the chloride analogue, Pb(3)Te(2)O(6)Cl(2), and consists of three Pb, two Te, two Br and four O atoms in the asymmetric unit. Except for two of the O atoms, all atoms are located on mirror planes. The Pb(3)Te(2)O(6)Br(2) structure can be described as being built up from (∞) (2)[Pb(3)Te(2)O(6)](2+) layers extending parallel to (20) and Br(-) anions between the layers. Cohesion of the structure is accomplished through Pb-Br contacts of two of the three lead atoms, leading to highly asymmetric coordination polyhedra. The lone-pair electrons of both Te(IV) and Pb(II) atoms are stereochemically active and point towards the anionic halide layers.

  15. Analysis of Cu Diffusion in ZnTe-Based Contacts for Thin-Film CdS/CdTe Solar Cells

    SciTech Connect

    Narayanswamy, C.; Gessert, T. A. and Asher, S. E.

    1998-10-27

    Ohmic contacts to thin-film CdS/CdTe photovoltaic devices have been formed using a two-layer contact interface of undoped ZnTe (ZnTe) and Cu-doped ZnTe (ZnTe:Cu), followed by Ni or Ti as an outer metallization. Secondary ion mass spectroscopy (SIMS) is used to study Cu diffusion within this back-contact structure, and also, to monitor Cu diffusion from the contact into the CdTe. When Ni metallization is used, the ZnTe:Cu layer becomes increasingly depleted of Cu, and Ni diffusion into the ZnTe:Cu increases as the contact deposition temperature increases from 100 C to 300 C. Cu depletion is not observed when Ni is replaced with Ti. Diffusion of Cu from the ZnTe:Cu layer into the ZnTe layer also increases with contact deposition temperature, and produces a buildup of Cu at the ZnTe/CdTe interface. High-mass resolution SIMS indicates that, although Cu levels in the CdTe remain low, Cu diffusion from the contact proceeds into the CdTe layer and toward the CdTe/CdS junction region.

  16. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor

    PubMed Central

    He, M. Q.; Shen, J. Y.; Petrović, A. P.; He, Q. L.; Liu, H. C.; Zheng, Y.; Wong, C. H.; Chen, Q. H.; Wang, J. N.; Law, K. T.; Sou, I. K.; Lortz, R.

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

  17. Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

    SciTech Connect

    Zielony, E.; Placzek-Popko, E.; Henrykowski, A.; Gumienny, Z.; Kamyczek, P.; Jacak, J.; Nowakowski, P.; Karczewski, G.

    2012-09-15

    Micro-Raman spectroscopy has been applied to investigate the impact of laser irradiation on semiconducting CdTe/ZnTe quantum dots (QDs) structures. A reference sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the p-type GaAs substrate. The Raman spectra have been recorded for different time of a laser exposure and for various laser powers. The spectra for both samples exhibit peak related to the localized longitudinal (LO) ZnTe phonon of a wavenumber equal to 210 cm{sup -1}. For the QD sample, a broad band corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm{sup -1}. With increasing time of a laser beam exposure and laser power, the spectra get dominated by tellurium-related peaks appearing at wavenumbers around 120 cm{sup -1} and 140 cm{sup -1}. Simultaneously, the ZnTe surface undergoes rising damage, with the formation of Te aggregates at the pinhole edge as reveal atomic force microscopy observations. Local temperature of irradiated region has been estimated from the anti-Stokes/Stokes ratio of the Te modes intensity and it was found to be close or exceeding ZnTe melting point. Thus, the laser damage can be explained by the ablation process.

  18. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

    PubMed

    He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3. PMID:27587000

  19. Spin Dynamics of a Single Mn Ion in a CdTe/(Cd, Mg, Zn)Te Quantum Dot

    SciTech Connect

    Goryca, Mateusz; Kossacki, Piotr; Golnik, Andrzej; Kazimierczuk, Tomasz; Nawrocki, Michal; Wojnar, Piotr

    2010-01-04

    The spin dynamics of a single Mn ion confined in a CdTe/(Cd, Mg, Zn)Te quantum dot is determined by measurements of photon correlation of photoluminescence. The characteristic time of spin flip is a few nanoseconds and strongly depends on the excitation power.

  20. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

    PubMed

    He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.

  1. Thermoelectric device including an alloy of GeTe and AgSbTe as the P-type element

    DOEpatents

    Skrabek, Emanuel Andrew; Trimmer, Donald Smith

    1976-01-01

    Improved alloys suitable for thermoelectric applications and having the general formula: (AgSbTe.sub.2).sub.1.sub.-x + (GeTe).sub.x wherein x has a value of about 0.80 and 0.85, have been found to possess unexpectedly high thermoelectric properties such as efficiency index, as well as other improved physical properties.

  2. Exciton dynamics in individual semimagnetic (Zn,Mn)Te/(Zn,Mg)Te nanowires

    SciTech Connect

    Gałkowski, K.; Papierska, J.; Sawicki, K.; Kossacki, P.; Suffczyński, J.; Wojnar, P.; Janik, E.

    2015-09-07

    Dynamics and mechanisms of photocreated carriers decay in individual core/shell (Zn,Mn)Te/(Zn,Mg)Te semimagnetic nanowires are studied with a high temporal resolution. Exciton lifetime determined to 44 ± 5 ps is found to increase to 78 ± 5 ps upon application of magnetic field of up to 10 T. A quantitative modeling attributes the effects observed in time-resolved and time-integrated micro-photoluminescence to the magnetic field induced quenching of exchange Auger type, non-radiative carrier recombination related to Mn{sup 2+} ions. The reported properties of the semimagnetic nanowires are promising for their implementation in high-speed devices exploiting light-induced conductivity.

  3. Multiband Te p Based Superconductivity of Ta4Pd3Te16

    DOE PAGES

    Singh, David J.

    2014-10-06

    We recently discovered that Ta4Pd3Te16 is a superconductor that has been suggested to be an unconventional superconductor near magnetism. Here, we report electronic structure calculations showing that despite the layered crystal structure the material is an anisotropic three-dimensional (3D) metal. The Fermi surface contains prominent one-dimensional (1D) and two-dimensional (2D) features, including nested 1D sheets, a 2D cylindrical section, and a 3D sheet. Moreover, the electronic states that make up the Fermi surface are mostly derived from Te p states with small Ta d and Pd d contributions. This places the compound far from magnetic instabilities. The results are discussedmore » in terms of multiband superconductivity.« less

  4. Solvothermal Synthesis of Lateral Heterojunction Sb2Te3/Bi2Te3 Nanoplates.

    PubMed

    Fei, Fucong; Wei, Zhongxia; Wang, Qianjin; Lu, Pengchao; Wang, Shuangbao; Qin, Yuyuan; Pan, Danfeng; Zhao, Bo; Wang, Xuefeng; Sun, Jian; Wang, Xinran; Wang, Peng; Wan, Jianguo; Zhou, Jianfeng; Han, Min; Song, Fengqi; Wang, Baigeng; Wang, Guanghou

    2015-09-01

    A lateral heterojunction of topological insulator Sb2Te3/Bi2Te3 was successfully synthesized using a two-step solvothermal method. The two crystalline components were separated well by a sharp lattice-matched interface when the optimized procedure was used. Inspecting the heterojunction using high-resolution transmission electron microscopy showed that epitaxial growth occurred along the horizontal plane. The semiconducting temperature-resistance curve and crossjunction rectification were observed, which reveal a staggered-gap lateral heterojunction with a small junction voltage. Quantum correction from the weak antilocalization reveals the well-maintained transport of the topological surface state. This is appealing for a platform for spin filters and one-dimensional topological interface states.

  5. Cd self-doping of CdTe polycrystalline films by co-sputtering of CdTe-Cd targets

    NASA Astrophysics Data System (ADS)

    Picos-Vega, A.; Becerril, M.; Zelaya-Angel, O.; Ramírez-Bon, R.; Espinoza-Beltrán, F. J.; González-Hernández, J.; Jiménez-Sandoval, S.; Chao, B.

    1998-01-01

    Cadmium self-doped CdTe polycrystalline films were grown on Corning glass substrates at room temperature by cosputtering from a CdTe-Cd target. The electrical, structural, and optical properties of the films were analyzed as a function of the Cd concentration. Films with a stoichiometric composition, and slightly below and above it, were prepared. In films where the Te exceeds 50 at. %, it is found segregation of Te and its electrical resistivity is about 107 Ω cm. In those with an excess of Cd, the electrical resistivity drops several orders of magnitude, the carrier concentration increases, and the resistivity activation energy drops. From these results, we concluded that using this deposition method, n-type Cd self-doped CdTe polycrystalline films can be produced.

  6. Molecular Beam Epitaxy Growth of HgCdTe on Large-Area Si and CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Reddy, M.; Peterson, J. M.; Vang, T.; Franklin, J. A.; Vilela, M. F.; Olsson, K.; Patten, E. A.; Radford, W. A.; Bangs, J. W.; Melkonian, L.; Smith, E. P. G.; Lofgreen, D. D.; Johnson, S. M.

    2011-08-01

    This paper presents the status of HgCdTe growth on large-area Si and CdZnTe substrates at Raytheon Vision Systems (RVS). The different technological tools that were used to scale up the growth from 4 inch to 6 inch diameter on Si and from 4 cm × 4 cm to 8 cm × 8 cm on CdZnTe without sacrificing the quality of the layers are described. Extremely high compositional uniformity and low macrodefect density were achieved for single- and two-color HgCdTe layers on both Si and CdZnTe substrates. Finally, a few examples of detector and focal-plane array results are included to highlight the importance of high compositional uniformity and uniformly low macrodefect density of the epitaxial layers in obtaining high operability and low cluster outages in single- and two-color focal-plane arrays (FPAs).

  7. Coexistence of optically active radial and axial CdTe insertions in single ZnTe nanowire.

    PubMed

    Wojnar, P; Płachta, J; Zaleszczyk, W; Kret, S; Sanchez, Ana M; Rudniewski, R; Raczkowska, K; Szymura, M; Karczewski, G; Baczewski, L T; Pietruczik, A; Wojtowicz, T; Kossut, J

    2016-03-14

    We report on the growth, cathodoluminescence and micro-photoluminescence of individual radial and axial CdTe insertions in ZnTe nanowires. In particular, the cathodoluminescence technique is used to determine the position of each emitting object inside the nanowire. It is demonstrated that depending on the CdTe deposition temperature, one can obtain an emission either from axial CdTe insertions only, or from both, radial and axial heterostructures, simultaneously. At 350 °C CdTe grows only axially, whereas at 310 °C and 290 °C, there is also significant deposition on the nanowire sidewalls resulting in radial core/shell heterostructures. The presence of Cd atoms on the sidewalls is confirmed by energy dispersive X-ray spectroscopy. Micro-photoluminescence study reveals a strong linear polarization of the emission from both types of heterostructures in the direction along the nanowire axis.

  8. Use of separate ZnTe interface layers to form ohmic contacts to p-CdTe films

    DOEpatents

    Gessert, T.A.

    1999-06-01

    A method of is disclosed improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurium-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact. 11 figs.

  9. Use of separate ZnTe interface layers to form OHMIC contacts to p-CdTe films

    DOEpatents

    Gessert, Timothy A.

    1999-01-01

    A method of improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurim-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact.

  10. Multilayered (Hg,Cd)Te infrared detector

    NASA Technical Reports Server (NTRS)

    Rae, W. G.

    1977-01-01

    Multilayered mercury-cadmium telluride photoconductive detectors were developed which are capable of providing individual coverage of three separate spectral wavelength bands without the use of beam splitters. The multilayered "three-color" detector on a single dewar takes the place of three separate detector/filter/dewar units and enables simpler and more reliable mechanical and optical designs for multispectral scanners and radiometers. Wavelength channel design goals (in micrometers) were: 10.1 to 11.0, 11.0 to 12.0, and 13.0. Detectivity for all channels was 1 x 10 to the 10th power cm-Hz 1/2/Watt. A problem occurred in finding an epoxy layer which had good infrared transmission properties and which also was chemically and mechanically compatible with HgCdTe processing techniques. Data on 6 candidate bonding materials are surveyed and discussed.

  11. Opportunities for TeV Laser Acceleration

    SciTech Connect

    Kando, M.; Kiriyama, H.; Koga, J.K.; Bulanov, S.; Chao, A.W.; Esirkepov, T.; Hajima, R.; Tajima, T.; /JAERI, Kyoto

    2008-06-02

    A set of ballpark parameters for laser, plasma, and accelerator technologies that define for electron energies reaching as high as TeV are identified. These ballpark parameters are carved out from the fundamental scaling laws that govern laser acceleration, theoretically suggested and experimentally explored over a wide range in the recent years. In the density regime on the order of 10{sup 16} cm{sup -3}, the appropriate laser technology, we find, matches well with that of a highly efficient high fluence LD driven Yb ceramic laser. Further, the collective acceleration technique applies to compactify the beam stoppage stage by adopting the beam-plasma wave deceleration, which contributes to significantly enhance the stopping power and energy recovery capability of the beam. Thus we find the confluence of the needed laser acceleration parameters dictated by these scaling laws and the emerging laser technology. This may herald a new technology in the ultrahigh energy frontier.

  12. BOREAS TE-9 NSA Canopy Biochemistry

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Margolis, Hank; Charest, Martin; Sy, Mikailou

    2000-01-01

    The BOREAS TE-9 team collected several data sets related to chemical and photosynthetic properties of leaves. This data set contains canopy biochemistry data collected in 1994 in the NSA at the YJP, OJR, OBS, UBS, and OA sites, including biochemistry lignin, nitrogen, cellulose, starch, and fiber concentrations. These data were collected to study the spatial and temporal changes in the canopy biochemistry of boreal forest cover types and how a high-resolution radiative transfer model in the mid-infrared could be applied in an effort to obtain better estimates of canopy biochemical properties using remote sensing. The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  13. Opportunities for TeV Laser Acceleration

    SciTech Connect

    Kando, M.; Kiriyama, H.; Koga, J. K.; Bulanov, S.; Esirkepov, T.; Hajima, R.; Tajima, T.; Chao, A. W.

    2008-06-24

    A set of ballpark parameters for laser, plasma, and accelerator technologies that define for electron energies reaching as high as TeV are identified. These ballpark parameters are carved out from the fundamental scaling laws that govern laser acceleration, theoretically suggested and experimentally explored over a wide range in the recent years. In the density regime on the order of 10{sup 16} cm{sup -3}, the appropriate laser technology, we find, matches well with that of a highly efficient high fluence LD driven Yb ceramic laser. Further, the collective acceleration technique applies to compactify the beam stoppage stage by adopting the beam-plasma wave deceleration, which contributes to significantly enhance the stopping power and energy recovery capability of the beam. Thus we find the confluence of the needed laser acceleration parameters dictated by these scaling laws and the emerging laser technology. This may herald a new technology in the ultrahigh energy frontier.

  14. BOREAS TE-5 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. The leaf photosynthetic gas exchange data were collected in the BOREAS NSA and the SSA from 06-Jun- 1994 to 13-Sep- 1994 using a LI-COR 6200 portable photosynthesis system. The data were collected to compare the photosynthetic capacity, stomata] conductance, and leaf intercellular CO, concentrations among the major tree species at the BOREAS sites. The data are average values from diurnal measurements on the upper canopy foliage (sun leaves). The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

  15. BOREAS TE-10 Leaf Optical Properties

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Chan, Stephen S.; Middleton, Elizabeth

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-10 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, gas exchange, oxygen evolution, and biochemical properties of boreal vegetation. This data set describes the spectral optical properties (reflectance and transmittance) of boreal forest conifers and broadleaf tree leaves as measured with a Spectron Engineering SE590 spectroradiometer at the Southern Study Area Old Black Spruce (SSA OBS), Old Jack Pine (OJP), Young Jack Pine (YJP), Old Aspen (OA), Old Aspen Auxiliary (OA-AUX), Young Aspen Auxiliary (YA-AUX), and Young Aspen (YA) sites. The data were collected during the growing seasons of 1994 and 1996 and are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  16. Raman scattering of IrTe2

    NASA Astrophysics Data System (ADS)

    Lee, Alexander; Thorsmolle, Verner; Artyukhin, Sergey; Yang, Jun; Cheong, Sang-Wook; Blumberg, Girsh

    2014-03-01

    IrTe2 presents a layered compound with a triangular lattice. It is known to exhibit a first order structural phase transition at approximately 260 K which is of a first order, corresponding to a formation of a superstructure with a period of five unit cells. Using polarized Raman spectroscopy we have studied the temperature dependence of 14 observed Raman allowed phononic modes. These phonons couple strongly to this transition and one additional first order transition at approximately 170 K. In the high-temperature phase only 3 modes are observed, while below approximately 280 K all 14 modes become visible. Below approximately 170 K only 11 modes are observed. Our results shed light on the possible mechanism driving the transitions. ACL, VKT and GB acknowledge support by NSF DMR-1104884.

  17. BOREAS TE-10 Photosynthetic Response Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Middleton, Elizabeth; Sullivan, Joseph

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-10 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the gas exchange, reflectance, transmittance, chlorophyll content, carbon content, hydrogen content, nitrogen content, and photosynthetic response of boreal vegetation. This data set contains measurements of quantitative parameters and leaf photosynthetic response to increases in light conducted in the SSA during the growing seasons of 1994 and 1996 using an oxygen electrode system. Leaf photosynthetic responses were not collected in 1996. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  18. BOREAS TE-10 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Middleton, Elizabeth; Sullivan, Joseph

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-10 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, gas exchange, chlorophyll content, carbon content, hydrogen content, and nitrogen content of boreal vegetation. This data set contains measurements of assimilation, stomatal conductance, transpiration, internal CO2 concentration, and water use efficiency conducted in the Southern Study Area (SSA) during the growing seasons of 1994 and 1996 using a portable gas exchange system. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  19. BOREAS TE-9 NSA Photosynthetic Response Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G.; Curd, Shelaine (Editor); Dang, Qinglai; Margolis, Hank; Coyea, Marie

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-9 (Terrestrial Ecology) team collected several data sets related to chemical and photosynthetic properties of leaves. This data set describes: (1) the response of leaf and shoot-level photosynthesis to ambient and intercellular CO2 concentration, temperature, and incident photosynthetically active radiation (PAR) for black spruce, jack pine, and aspen during the three intensive field campaigns (IFCs) in 1994 in the Northern Study Area (NSA); (2) the response of stomatal conductance to vapor pressure difference throughout the growing season of 1994; and (3) a range of shoot water potentials (controlled in the laboratory) for black spruce and jack pine. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  20. BOREAS TE-5 Leaf Carbon Isotope Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. This documentation describes leaf carbon isotope data that were collected in 1993 and 1994 at the NSA and SSA OJP sites, the SSA OBS site, and the NSA UBS site. In addition, leaf carbon isotope data were collected in 1994 only at the NSA and SSA OA sites. These data was collected to provide seasonal integrated physiological information for 10 to 15 common species at these 6 BOREAS sites. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  1. BOREAS TE-12 SSA Shoot Geometry Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Walter-Shea, Elizabeth A.; Mesarch, Mark A.; Cheng, L.; Yang, Litao

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-12 (Terrestrial Ecology) team collected shoot geometry data in 1993 and 1994 from aspen, jack pine, and black spruce trees. Collections were made at the Southern Study Area Nipawin Fen Site (SSA FEN), Young Jack Pine (YJP), Old Jack Pine (OJP), Old Aspen (OA), Young Aspen (YA), Mixed Site (MIX), and Old Black Spruce (OBS) sites. A caliper was used to measure shoot and needle lengths and widths. A volume displacement procedure was used to measure the weight of the shoot or twig submerged in water. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  2. BOREAS TE-23 Map Plot Data

    NASA Technical Reports Server (NTRS)

    Rich, Paul M.; Fournier, Robert; Hall, Forrest G. (Editor); Papagno, Andrea (Editor)

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-23 (Terrestrial Ecology) team collected map plot data in support of its efforts to characterize and interpret information on canopy architecture and understory cover at the BOREAS tower flux sites and selected auxiliary sites from May to August 1994. Mapped plots (typical dimensions 50 m x 60 m) were set up and characterized at all BOREAS forested tower flux and selected auxiliary sites. Detailed measurement of the mapped plots included: (1) stand characteristics (location, density, basal area); (2) map locations diameter at breast height (DBH) of all trees; (3) detailed geometric measures of a subset of trees (height, crown dimensions); and (4) understory cover maps. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  3. TE/TM Simulations of Interferometric Measurements

    NASA Technical Reports Server (NTRS)

    Houshmand, Bijan

    2000-01-01

    Interferometric synthetic aperture radar (IFSAR) measurements at X-, C-, L-, and P-band are used to derive ground topography at meter level resolution. Interpretation of the derived topography requires attention due to the complex interaction of the radar signal with ground cover. The presence of penetrable surfaces such as vegetation, and tree canopies poses a challenge since the depth of penetration depends on a number of parameters such as the operating radar frequency, polarization, incident angle, as well as terrain structure. The dependence of the reconstructed topography on polarization may lead to the characterization of the ground cover. Simulation of interferometric measurements is useful for interpretation of the derived topography (B. Houshmand, Proceedings of URSI, 314, 1997). In this talk , time domain simulations for interferometric measurement for TE- and TM- polarization are presented. Time domain simulation includes the effects of the surface material property as well geometry comparable the radar signal wavelength (B. Houshmand, Proceedings of the URSI, 25, 1998). The IFSAR simulation is carried out in two steps. First, the forward scattering data is generated based on full wave analysis. Next, the electromagnetic information is inverted to generate surface topography. This inversion is based on the well known IFSAR processing technique which is composed of signal compression, and formation of an interferogram. The full wave forward scattering data is generated by the scattered-field formulation of the FDTD algorithm. The simulation is carried out by exciting the computational domain by a radar signal. The scattered field is then computed and translated to the receiving interferometric antennas using the time-domain Huygen's principle. The inversion process starts by compressing the time-domain data. The range compressed data from both receivers are then coregistered to form an interferogram. The resulting interferogram is then related to the

  4. BOREAS TE-6 Multiband Vegetation Imager Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Kucharik, Christopher J.

    2000-01-01

    The BOREAS TE-6 team collected data in support of its efforts to examine the influence of vegetation and climate on the major carbon fluxes in boreal tree species. A newly developed ground-based canopy imaging system called an MVI was tested and used by the BOREAS TE-06 team to collect measurements of the canopy crap fraction (sky fraction), canopy gap-size distribution (size and frequency of gaps between foliage in canopy), branch architecture, and leaf angle distribution (fraction of leaf area in specific leaf inclination classes assuming azimuthal symmetry). Measurements of the canopy gap-size distribution are used to derive canopy clumping indices that can be used to adjust indirect LAI measurements made in nonrandom forests. These clumping factors will also help to describe the radiation penetration in clumped canopies more accurately by allowing for simple adjustments to Beer's law. Measurements of the above quantities were obtained at BOREAS NSA-OJP site in IFC-2 in 1994, at the SSA-OA in July 1995, and at the SSA-OBS and SSA-OA sites in IFC-2 in 1996. Modeling studies were also performed to further validate MVI measurements and to gain a more complete understanding of boreal forest canopy architecture. By using MVI measurements and Monte Carlo simulations, clumping indices as a function of zenith angle were derived for the three main boreal species studied during BOREAS. The analyzed data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distrobuted Activity Archive Center (DAAC).

  5. Effects of Te inclusions on the performance of CdZnTe radiation detectors

    SciTech Connect

    Bolotnikov,A.E.; Abdul-Jabber, N. M.; Babalola, O. S.; Camarda, G. S.; Cui, Y.; Hossain, A. M.; Jackson, E. M.; Jackson, H. C.; James, J. A.; Kohman, K. T.; Luryi, A. L.; James, R. B.

    2008-10-19

    Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beamline recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.

  6. Real-time observation of nanoscale topological transitions in epitaxial PbTe/CdTe heterostructures

    SciTech Connect

    Groiss, H. E-mail: istvan.daruka@jku.at; Daruka, I. E-mail: istvan.daruka@jku.at; Springholz, G.; Schäffler, F.; Koike, K.; Yano, M.; Hesser, G.; Zakharov, N.; Werner, P.

    2014-01-01

    The almost completely immiscible PbTe/CdTe heterostructure has recently become a prototype system for self-organized quantum dot formation based on solid-state phase separation. Here, we study by real-time transmission electron microscopy the topological transformations of two-dimensional PbTe-epilayers into, first, a quasi-one-dimensional percolation network and subsequently into zero-dimensional quantum dots. Finally, the dot size distribution coarsens by Ostwald ripening. The whole transformation sequence occurs during all stages in the fully coherent solid state by bulk diffusion. A model based on the numerical solution of the Cahn-Hilliard equation reproduces all relevant morphological and dynamic aspects of the experiments, demonstrating that this standard continuum approach applies to coherent solids down to nanometer dimensions. As the Cahn-Hilliard equation does not depend on atomistic details, the observed morphological transformations are general features of the model. To confirm the topological nature of the observed shape transitions, we developed a parameter-free geometric model. This, together with the Cahn-Hilliard approach, is in qualitative agreement with the experiments.

  7. Optimization of the p+-ZnTe layer for back contacts of ZnTe thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung Su; Oh, Gyujin; Kim, Eun Kyu

    2016-08-01

    We have studied the performance of ZnTe-based heterojunction diodes grown on p-GaAs substrates by using pulsed laser deposition (PLD). In the X-ray diffraction measurements, ZnTe and CdS thin films grown on p-GaAs (100) substrates appeared to have a cubic crystalline structure while the ZnO film showed a hexagonal structure. The structure of n+-ZnO/i-ZnTe/p-GaAs with insertion of a CdS buffer layer between n+-ZnO and i-ZnTe showed strong rectifying diode characteristics, and its open-circuit voltage (V oc ) and short-circuit current density (J sc ) under 1,000 Wm-2 air mass 1.5 global (AM 1.5G) illumination were measured about 0.32 V and 0.61 mAcm-2, respectively. When an inserted another layer, a ZnTe:Cu layer, as a p+-layer for the contacts on p-GaAs substrate, the value of V oc and J sc of the n+-ZnO/CdS/i-ZnTe/ZnTe:Cu/p-GaAs structure increased to 0.39 V and 0.81 mA/cm2, respectively. As the thickness of i-ZnTe were increased from 210 to 420 nm, the photoelectric conversion efficiency of the n+-ZnO/CdS/i-ZnTe/ZnTe:Cu/p-GaAs structure increased to 0.24%.

  8. Enhanced Thermoelectric Properties in the Counter-Doped SnTe System with Strained Endotaxial SrTe.

    PubMed

    Zhao, Li-Dong; Zhang, Xiao; Wu, Haijun; Tan, Gangjian; Pei, Yanling; Xiao, Yu; Chang, Cheng; Wu, Di; Chi, Hang; Zheng, Lei; Gong, Shengkai; Uher, Ctirad; He, Jiaqing; Kanatzidis, Mercouri G

    2016-02-24

    We report enhanced thermoelectric performance in SnTe, where significantly improved electrical transport properties and reduced thermal conductivity were achieved simultaneously. The former was obtained from a larger hole Seebeck coefficient through Fermi level tuning by optimizing the carrier concentration with Ga, In, Bi, and Sb dopants, resulting in a power factor of 21 μW cm(-1) K(-2) and ZT of 0.9 at 823 K in Sn(0.97)Bi(0.03)Te. To reduce the lattice thermal conductivity without deteriorating the hole carrier mobility in Sn(0.97)Bi(0.03)Te, SrTe was chosen as the second phase to create strained endotaxial nanostructures as phonon scattering centers. As a result, the lattice thermal conductivity decreases strongly from ∼2.0 Wm(-1) K(-1) for Sn(0.97)Bi(0.03)Te to ∼1.2 Wm(-1) K(-1) as the SrTe content is increased from 0 to 5.0% at room temperature and from ∼1.1 to ∼0.70 Wm(-1) K(-1) at 823 K. For the Sn(0.97)Bi(0.03)Te-3% SrTe sample, this leads to a ZT of 1.2 at 823 K and a high average ZT (for SnTe) of 0.7 in the temperature range of 300-823 K, suggesting that SnTe is a robust candidate for medium-temperature thermoelectric applications. PMID:26871965

  9. Enhancing photoresponsivity using MoTe2-graphene vertical heterostructures

    NASA Astrophysics Data System (ADS)

    Kuiri, Manabendra; Chakraborty, Biswanath; Paul, Arup; Das, Subhadip; Sood, A. K.; Das, Anindya

    2016-02-01

    MoTe2 with a narrow band-gap of ˜1.1 eV is a promising candidate for optoelectronic applications, especially for the near-infrared photo detection. However, the photo responsivity of few layers MoTe2 is very small (<1 mA W-1). In this work, we show that a few layer MoTe2-graphene vertical heterostructures have a much larger photo responsivity of ˜20 mA W-1. The trans-conductance measurements with back gate voltage show on-off ratio of the vertical transistor to be ˜(0.5-1) × 105. The rectification nature of the source-drain current with the back gate voltage reveals the presence of a stronger Schottky barrier at the MoTe2-metal contact as compared to the MoTe2-graphene interface. In order to quantify the barrier height, it is essential to measure the work function of a few layers MoTe2, not known so far. We demonstrate a method to determine the work function by measuring the photo-response of the vertical transistor as a function of the Schottky barrier height at the MoTe2-graphene interface tuned by electrolytic top gating.

  10. Electrochemically deposited BiTe-based nanowires for thermoelectric applications

    SciTech Connect

    Ng, Inn-Khuan; Kok, Kuan-Ying; Rahman, Che Zuraini Che Ab; Saidin, Nur Ubaidah; Ilias, Suhaila Hani; Choo, Thye-Foo

    2014-02-12

    Nanostructured materials systems such as thin-films and nanowires (NWs) are promising for thermoelectric power generation and refrigeration compared to traditional counterparts in bulk, due to their enhanced thermoelectric figures-of-merit. BiTe and its derivative compounds, in particular, are well-known for their near-room temperature thermoelectric performance. In this work, both the binary and ternary BiTe-based nanowires namely, BiTe and BiSbTe, were synthesized using template-assisted electrodeposition. Diameters of the nanowires were controlled by the pore sizes of the anodised alumina (AAO) templates used. Systematic study on the compositional change as a function of applied potential was carried out via Linear Sweep Voltanmetry (LSV). Chemical compositions of the nanowires were studied using Energy Dispersive X-ray Spectrometry (EDXS) and their microstructures evaluated using diffraction and imaging techniques. Results from chemical analysis on the nanowires indicated that while the Sb content in BiSbTe nanowires increased with more negative deposition potentials, the formation of Te{sup 0} and Bi{sub 2}Te{sub 3} were favorable at more positive potentials.

  11. Contacts for high-resistivity (Cd,Mn)Te crystals

    SciTech Connect

    Witkowska-Baran, M.; James, R.; Mycielski, A.; Kochanowska, D.; Szadkowski, A.J.; Jakiela, R.; Witkowska, B.; Kaliszek, W.; Domagala, J.; Lusakowska, E.; Domukhovski, V.; Dybko, K.; Cui, Y.; and James, R.B.

    2010-09-09

    Semi-insulating (Cd,Mn)Te crystals offer a material that may compete well with the commonly used (Cd,Zn)Te crystals for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality, high-resistivity (10{sup 9} - 10{sup 10} {Omega} {center_dot} cm) crystals of (Cd,Mn)Te:V. Doping the as-grown crystals with the compensating agent vanadium ({approx} 10{sup 16} cm{sup -3}) ensures their high resistivity; thereafter, annealing them in cadmium vapors reduces the number of cadmium vacancies. Applying the crystals as detectors necessitates having satisfactory electrical contacts. Accordingly, we explored various techniques of ensuring good electrical contacts to these semi-insulating (Cd,Mn)Te crystals, assessing metallic layers, monocrystalline semiconductor layers, and amorphous (or nanocrystalline) semiconductor layers. We found that ZnTe heavily doped ({approx} 10{sup 18} cm{sup -3}) with Sb, and CdTe heavily doped ({approx} 10{sup 17} cm{sup -3}) with In, proved satisfactory semiconductor contact layers. They subsequently enabled us to establish good contacts (with only narrow tunneling barriers) to the Au layer that usually constitutes the most external contact layer. We outline our technology of applying electrical contacts to semi-insulating (Cd,Mn)Te, and describe some important properties.

  12. Radiative and interfacial recombination in CdTe heterostructures

    SciTech Connect

    Swartz, C. H. Edirisooriya, M.; LeBlanc, E. G.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Ogedengbe, O. S.; Hancock, B. L.; Holtz, M.; Myers, T. H.; Zaunbrecher, K. N.

    2014-12-01

    Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 10{sup 10 }cm{sup −2} and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10{sup −10} cm{sup 3}s{sup −1}. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate.

  13. Changes in structure and chemical composition of α-MoTe2 and β-MoTe2 during heating in vacuum conditions

    NASA Astrophysics Data System (ADS)

    Ueno, Keiji; Fukushima, Koji

    2015-09-01

    Molybdenum ditelluride (MoTe2) is known to have two different crystal phases: α-MoTe2 and β-MoTe2. α-MoTe2 is the polytype stable below 815 °C, and β-MoTe2 is stable above 900 °C. Here, we report changes in the structure and composition of each single crystal during heating in low and high vacuum conditions. Contrary to the results of a recently published paper, we did not observe α-MoTe2 transforming to β-MoTe2 at elevated temperatures. In a low vacuum, the α-MoTe2 sample was mainly oxidized, forming MoO2. In a high vacuum, it partially decomposed with surface oxidation. The recently reported “reversible phase transition” of α-MoTe2 is the misinterpretation of X-ray diffraction data.

  14. Measuring the thermodynamic properties of saturated solid solutions in the Ag2Te-Bi-Bi2Te3 system by the electromotive force method

    NASA Astrophysics Data System (ADS)

    Prokhorenko, M. V.; Moroz, M. V.; Demchenko, P. Yu.

    2015-08-01

    The temperature dependence of the electromotive force (EMF) of Ag|AgI|glass Ag2GeS3|D galvanic elements (where Ag, D are galvanic element electrodes, D is equilibrium three-phase alloys in the Ag2Te-Bi-Bi2Te3 system, AgI|glass Ag2GeS3 is a two-layer membrane with purely ionic (Ag+) conductivity) is studied in the range of 490-550 K. Analytical equations are obtained for the temperature dependences of the Gibbs energies of the formation of saturated solid solutions of the Bi14Te6, Bi2Te, BiTe, and Bi2Te phases from elements in the Ag2Te-Bi-Bi2Te3 system. E( T) analytical equations are used to calculate the standardstate thermodynamic functions of saturated solid solutions of the Bi14Te6, Bi2Te, BiTe, and Bi2Te3 phases in the Ag2Te-Bi-Bi2Te3 system.

  15. CdTe Photovoltaics for Sustainable Electricity Generation

    NASA Astrophysics Data System (ADS)

    Munshi, Amit; Sampath, Walajabad

    2016-09-01

    Thin film CdTe (cadmium telluride) is an important technology in the development of sustainable and affordable electricity generation. More than 10 GW of installations have been carried out using this technology around the globe. It has been demonstrated as a sustainable, green, renewable, affordable and abundant source of electricity. An advanced sublimation tool has been developed that allows highly controlled deposition of CdTe films onto commercial soda lime glass substrates. All deposition and treatment steps can be performed without breaking the vacuum within a single chamber in an inline process that can be conveniently scaled to a commercial process. In addition, an advanced cosublimation source has been developed to allow the deposition of ternary alloys such as Cd x Mg1- x Te to form an electron reflector layer which is expected to address the voltage deficits in current CdTe devices and to achieve very high efficiency. Extensive materials characterization, including but not limited to scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, high resolution transmission electron microscopy and electron back-scatter diffraction, has been performed to get a better understanding of the effects of processing conditions on CdTe thin film photovoltaics. This combined with computer modeling such as density function theory modeling gives a new insight into the mechanism of CdTe photovoltaic function. With all these efforts, CdTe photovoltaics has seen great progress in the last few years. Currently, it has been recorded as the cheapest source of electricity in the USA on a commercial scale, and further improvements are predicted to further reduce the cost while increasing its utilization. Here, we give an overview of the advantages of thin film CdTe photovoltaics as well as a brief review of the challenges that need to be addressed. Some fundamental studies of processing conditions for thin film CdTe are also presented

  16. Effect of Cu doping on the properties of ZnTe:Cu thin films and CdS/CdTe/ZnTe solar cells

    NASA Astrophysics Data System (ADS)

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

    1997-02-01

    The effects of Cu doping concentration and post-deposition annealing treatment on the properties of ZnTe thin films were investigated in an effort to decrease the Cu doping concentration and improve the long-term stability of CdS/CdTe/ZnTe solar cells. The structural, compositional, and electrical properties were studied systematically using x-ray diffraction (XRD), electron microprobe, Hall effect and conductivity measurements. XRD measurements indicated that the crystalline phase of as-deposited and low-temperature annealed ZnTe films is dependent on Cu doping concentration. Low-Cu-doped films exhibited zincblende phase, whereas high-Cu-doped films showed wurtzite phase. After annealing at high temperature (⩾350 °C), all films exhibited zincblende structure. Electron probe microanalysis revealed a deficiency of cations in low-Cu-doped films and an excess of cations in high-Cu-doped films. Hall effect measurements revealed a dependence of hole mobility on Cu doping concentration with the highest mobility (20 cm2/Vṡs) obtained at a low Cu concentration. Carrier concentrations higher than mid-1016cm-3 were obtained at a Cu concentration of 2 at. % and relatively low annealing temperatures. Studies of the activation energy of dark conductivity suggested that intrinsic defects (e.g., Zn vacancies) are the dominant acceptors for Cu concentrations lower than 4.5 at. %. Finally, ZnTe films with Cu concentrations as low as 1 at. % were used successfully as a back contact layer in CdTe based solar cells. Fill factors over 0.70 were obtained using ZnTe films of low Cu concentrations.

  17. Atomic Structure of Twin Boundaries in CdTe

    SciTech Connect

    Yan, Y.; Jones, K. M.; Al-Jassim, M. M.

    2003-05-01

    Using the combination of high-resolution transmission electron microscopy, first-principles density-functional total energy calculations, and image simulations, we determined the atomic structure of lamellar twin and double-positioning twin boundaries in CdTe. We find that the structure of lamellar twin boundaries has no dangling bonds or wrong bonds; thus, it results in negligible effects on the electronic properties. The structure of double-positioning twin boundaries, however, contain both Cd and Te dangling bonds, and therefore produce energy states in the bandgap that are detrimental to the electronic properties of CdTe.

  18. Exploration of GaTe for Gamma Detectors

    SciTech Connect

    Conway, A M; Reinhardt, C E; Nikolic, R J; Nelson, A J; Wang, T F; Wu, K J; Payne, S A; Mertiri, A; Pabst, G; Roy, R; Mandal, K C; Bhattacharya, P; Cui, Y; Groza, M; Burger, A

    2007-11-16

    The layered III-VI semiconductor Gallium Telluride has potential for room temperature gamma ray spectroscopy applications due to its band gap of 1.67 eV, and average atomic number of 45:31 (Ga) and 52 (Te). The physical properties of GaTe are highly anisotropic due to covalent bonding within the layer and van der Waals bonding between layers. This work reports the results of surface and bulk processing, surface characterization, and electrical characterization of diodes formed on both the laminar and non-laminar GaTe surfaces. Alpha detection measurements were also performed.

  19. Quantum well states in Rashba semiconductor BiTeI

    NASA Astrophysics Data System (ADS)

    He, Yang; Zhu, Zhihuai; Hamidian, Mohammad; Chen, Pengcheng; Yam, Yau Chuen; Hoffman, Jennifer

    BiTeI displays large Rashba-type spin splitting in both valence and conduction bands. In this work, we use scanning tunneling microscopy to reveal the bipolar nature of BiTeI, confirming the previously observed p-n junction electronic structure. We also discover two-dimensional quantum well states both below and above the semiconducting gap on the Te-terminated surface. This work sheds light on the origin of the giant Rashba splitting in the system. This effort is funded by the NSF Grant DMR-1410480.

  20. Study of tellurium precipitates in CdTe crystals

    NASA Technical Reports Server (NTRS)

    Jayatirtha, H. N.; Henderson, D. O.; Burger, A.; Volz, M. P.

    1993-01-01

    The effect of tellurium precipitates was studied in medium resistivity (10 exp 3-10 exp 6 ohm cm) undoped and Cl-doped CdTe using differential scanning calorimetry (DSC) and mid-infrared spectroscopy and the results were correlated with near-infrared microscopy photographs. When present in a significant quantity (about 0.25 wt pct), we show that Te precipitates are detectable using DSC measurements. In the mid-infrared, the contribution of the absorption by free-carriers is negligible, and therefore, the effect of the Te precipitates in these crystals can be considered uncoupled from the effects of Cd vacancies.

  1. Milagro Observations of Potential TeV Emitters

    NASA Astrophysics Data System (ADS)

    Abeysekara, Anushka; Linnemann, James

    2012-03-01

    We searched for point sources in Milagro sky maps at the locations in four catalogs of potential TeV emitting sources. Our candidates are selected from the Fermi 2FGL pulsars, Fermi 2FGL extragalactic sources, TeVCat extragalactic sources, and from the BL Lac TeV Candidate list published by Costamante and Ghisellini in 2002. The False Discovery Rate (FDR) statistical procedure is used to select the sources. The FDR procedure controls the fraction of false detections. Our results are presented in this talk.

  2. Thermoelectric properties of PbTe/PbSe mesomaterials

    NASA Astrophysics Data System (ADS)

    Chen, Feng; Wang, Yaqi; Xue, Yuyi; Chu, C. W.; Zhang, Jun; Fang, Jiye; Tan, Chunhu; Lin, Zhigang; Liu, Bob

    2008-03-01

    Ball milled PbTe mixed with PbSe nano-wires (PTSW) or with PbSe nano-crystals (PTSC) are sintered under high pressure. Different sintering conditions are tested to preserve the mesostructures. Thermoelectric properties (resistivity, Seebeck coefficient and thermal conductivity) are measured at various temperatures. Pure ball milled PbTe are also sintered and measured for comparison. In this talk, we will present these data and compare with various PbTe data from the literature. Our results show that this mesostructure approach is promising and the sintering condition is the key factor for further improvement.

  3. Ba2TeO: A new layered oxytelluride

    DOE PAGES

    Besara, T.; Ramirez, D.; Sun, J.; Whalen, J. B.; Tokumoto, T. D.; McGill, S. A.; Singh, D. J.; Siegrist, T.

    2015-02-01

    For single crystals of the new semiconducting oxytelluride phase, Ba2TeO, we synthesized from barium oxide powder and elemental tellurium in a molten barium metal flux. Ba2TeO crystallizes in tetragonal symmetry with space group P4/nmm (#129), a=5.0337(1) Å, c=9.9437(4) Å, Z=2. The crystals were characterized by single crystal x-ray diffraction, heat capacity and optical measurements. Moreover, the optical measurements along with electronic band structure calculations indicate semiconductor behavior with a band gap of 2.93 eV. Resistivity measurements show that Ba2TeO is highly insulating.

  4. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  5. Anomalous thermoelectricity in strained Bi2Te3 films

    NASA Astrophysics Data System (ADS)

    Liu, Yucong; Chen, Jiadong; Deng, Huiyong; Hu, Gujin; Zhu, Daming; Dai, Ning

    2016-09-01

    Bi2Te3-based alloys have been intensively used for thermoelectric coolers and generators due to their high Seebeck coefficient S. So far, efforts to improve the S have been made mostly on changing the structures and components. Herein, we demonstrate an anomalous thermoelectricity in strained Bi2Te3 films, i.e., the value of S is obviously changed after reversing the direction of temperature gradient. Further theoretical and experimental analysis shows that it originates from the coupling of thermoelectric and flexoelectric effects caused by a stress gradient. Our finding provides a new avenue to adjust the S of Bi2Te3-based thermoelectric materials through flexoelectric polarization.

  6. Surface structure of GaAs with adsorbed Te

    NASA Astrophysics Data System (ADS)

    Feldman, R. D.; Austin, R. F.

    1986-10-01

    The surface structures that result from the adsorption of Te on (100) GaAs have been shown to affect the orientation of CdTe films on GaAs. Two structures are described here. A low-temperature (6×1) surface leads to (100) film growth. At 580 °C, a new surface results which is characterized by ordering along directions 60° from [011¯] and [01¯1], and leads to (111) growth of CdTe. Both surface structure and the interaction of the group II element with the surface are believed to be important in determining the orientation of the film.

  7. Process Development for High Voc CdTe Solar Cells

    SciTech Connect

    Ferekides, C. S.; Morel, D. L.

    2011-05-01

    This is a cumulative and final report for Phases I, II and III of this NREL funded project (subcontract # XXL-5-44205-10). The main research activities of this project focused on the open-circuit voltage of the CdTe thin film solar cells. Although, thin film CdTe continues to be one of the leading materials for large-scale cost-effective production of photovoltaics, the efficiency of the CdTe solar cells have been stagnant for the last few years. This report describes and summarizes the results for this 3-year research project.

  8. Formation of ZnTe:Cu/Ti Contacts at High Temperature for CdS/CdTe Devices: Preprint

    SciTech Connect

    Gessert, T. A.; Asher, S.; Johnston, S.; Duda, A.; Young, M. R.; Moriarty, T.

    2006-05-01

    We study the performance of CdS/CdTe thin-film devices contacted with ZnTe:Cu/Ti of various thickness at a higher-than-optimum temperature of {approx}360 C. At this temperature, optimum device performance requires the same thickness of ZnTe:Cu as for similar contacts formed at a lower temperature of 320 C. C-V analysis indicates that a ZnTe:Cu layer thickness of {approx}< 0.5 mu m does not yield the degree of CdTe net acceptor concentration necessary to reduce space charge width to its optimum value for n-p device operation. The thickest ZnTe:Cu layer investigated (1 mu m) yields the highest CdTe net acceptor concentration, lowest value of Jo, and highest Voc. However, performance is limited for this device by poor fill factor. We suggest poor fill factor is due to Cu-related acceptors compensating donors in CdS.

  9. Non-equilibrium processing leads to record high thermoelectric figure of merit in PbTe-SrTe.

    PubMed

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Zhao, Li-Dong; Chi, Hang; Zhang, Xiaomi; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2016-01-01

    The broad-based implementation of thermoelectric materials in converting heat to electricity hinges on the achievement of high conversion efficiency. Here we demonstrate a thermoelectric figure of merit ZT of 2.5 at 923 K by the cumulative integration of several performance-enhancing concepts in a single material system. Using non-equilibrium processing we show that hole-doped samples of PbTe can be heavily alloyed with SrTe well beyond its thermodynamic solubility limit of <1 mol%. The much higher levels of Sr alloyed into the PbTe matrix widen the bandgap and create convergence of the two valence bands of PbTe, greatly boosting the power factors with maximal values over 30 μW cm(-1) K(-2). Exceeding the 5 mol% solubility limit leads to endotaxial SrTe nanostructures which produce extremely low lattice thermal conductivity of 0.5 W m(-1) K(-1) but preserve high hole mobilities because of the matrix/precipitate valence band alignment. The best composition is hole-doped PbTe-8%SrTe. PMID:27456303

  10. Role of Cu additive on the dielectric relaxation of Se75Te25 and Se85Te15 glassy alloys

    NASA Astrophysics Data System (ADS)

    Sharma, J.; Kumar, S.

    2010-07-01

    The effect of Cu additive on the dielectric relaxation of two binary Se-Te glassy systems, comparing the properties of a-Se75Te25, a-Se85Te15 and a-Se75Te15Cu10 alloys has been reported. The temperature and frequency dependence of dielectric parameters in Glassy Se75Te25, Se85Te15 and Se75Te15Cu10 alloys are studied by measuring capacitance and dissipation factor in the frequency range (1 kHz-5 MHz) and temperature range (300-350 K). A Debye like relaxation of dielectric behavior has been observed. A comprehensive study on the relaxation mechanism revealed that the presence of grains and grain boundaries across the pallet thickness is the basic relaxation process. A detailed analysis shows that the observed dielectric loss is in agreement with the Guintini's theory of dielectric dispersion based on two electron hopping over a potential barrier and is applicable in the present case. Dielectric constant (ɛ’), dielectric loss (ɛ”), loss tangent (δ) and capacitive reactance (Xc) are found highly frequency and temperature dependent. Dependence of these dielectric parameters over the metallic impurity Cu, has also been found in the present glassy system and has been discussed in terms of electronegativity difference between the elements used in making the aforesaid glassy system.

  11. Non-equilibrium processing leads to record high thermoelectric figure of merit in PbTe-SrTe

    NASA Astrophysics Data System (ADS)

    Tan, Gangjian; Shi, Fengyuan; Hao, Shiqiang; Zhao, Li-Dong; Chi, Hang; Zhang, Xiaomi; Uher, Ctirad; Wolverton, Chris; Dravid, Vinayak P.; Kanatzidis, Mercouri G.

    2016-07-01

    The broad-based implementation of thermoelectric materials in converting heat to electricity hinges on the achievement of high conversion efficiency. Here we demonstrate a thermoelectric figure of merit ZT of 2.5 at 923 K by the cumulative integration of several performance-enhancing concepts in a single material system. Using non-equilibrium processing we show that hole-doped samples of PbTe can be heavily alloyed with SrTe well beyond its thermodynamic solubility limit of <1 mol%. The much higher levels of Sr alloyed into the PbTe matrix widen the bandgap and create convergence of the two valence bands of PbTe, greatly boosting the power factors with maximal values over 30 μW cm-1 K-2. Exceeding the 5 mol% solubility limit leads to endotaxial SrTe nanostructures which produce extremely low lattice thermal conductivity of 0.5 W m-1 K-1 but preserve high hole mobilities because of the matrix/precipitate valence band alignment. The best composition is hole-doped PbTe-8%SrTe.

  12. Electrical and photovoltaic properties of CdTe/ZnTe n-i-p junctions grown by molecular beam epitaxy

    SciTech Connect

    Zielony, E. Płaczek-Popko, E.; Racino, A.; Gumienny, Z.; Olender, K.; Wosiński, T.; Karczewski, G.; Chusnutdinow, S.

    2014-06-28

    Preliminary studies have been performed on photoelectrical properties of CdTe/ZnTe n-i-p junctions grown using the molecular beam epitaxy technique. Photovoltaic properties of the cells have been investigated by the measurements of current-voltage (I-V) characteristics under 1-sun illumination. I-V characteristics yield efficiencies of the cells varying from 3.4% to 4.9%. The low efficiency can be due to the presence of electrically active defects. In order to study the origin of defects in CdTe/ZnTe photovoltaic junctions, space charge techniques (C-V and deep level transient spectroscopy (DLTS)) have been applied. From the C-V measurements, a doping profile was calculated confirming charge accumulation in the i-CdTe layer. The results of the DLTS studies revealed the presence of four traps within a temperature range from 77–420 K. Three of them with activation energies equal to 0.22 eV, 0.45 eV, and 0.78 eV have been ascribed to the hole traps present in the i-CdTe material and their possible origin has been discussed. The fourth, high-temperature DLTS peak observed at ∼350 K has been attributed to extended defects as its amplitude and temperature position depends on the value of the filling pulse width. It is assumed that the defects related to the trap are either located in the i-CdTe layer or at the i-CdTe/ZnTe interface. However, it was found that the trap exhibits twofold nature: it behaves as a majority or as a minority trap, depending on the filling pulse height, which is a characteristic feature of recombination centers. This trap is presumably responsible for the low efficiency of the cells.

  13. Numerical study of the influence of ZnTe thickness on CdS/ZnTe solar cell performance

    NASA Astrophysics Data System (ADS)

    Skhouni, Othmane; El Manouni, Ahmed; Mari, Bernabe; Ullah, Hanif

    2016-05-01

    At present most of II-VI semiconductor based solar cells use the CdTe material as an absorber film. The simulation of its performance is realized by means of various numerical modelling programs. We have modelled a solar cell based on zinc telluride (ZnTe) thin film as absorber in substitution to the CdTe material, which contains the cadmium element known by its toxicity. The performance of such photovoltaic device has been numerically simulated and the thickness of the absorber layer has been optimized to give the optimal conversion efficiency. A photovoltaic device consisting of a ZnTe layer as absorber, CdS as the buffer layer and ZnO as a window layer was modelled through Solar Cell Capacitance Simulator Software. Dark and illuminated I-V characteristics and the results for different output parameters of ZnO/CdS/ZnTe solar cell were analyzed. The effect of ZnTe absorber thickness on different main working parameters such as: open-circuit voltage Voc, short-circuit current density Jsc, fill factor FF, photovoltaic conversion efficiency η was intensely studied in order to optimize ZnTe film thickness. This study reveals that increasing the thickness of ZnTe absorber layer results in higher efficiency until a maximum value and then decreases slightly. This maximum was found to be 10% at ZnTe optimum thickness close to 2 µm. Contribution to the topical issue "Materials for Energy Harvesting, Conversion and Storage (ICOME 2015) - Elected submissions", edited by Jean-Michel Nunzi, Rachid Bennacer and Mohammed El Ganaoui

  14. Electronic properties of GeTe and Ag- or Sb-substituted GeTe studied by low-temperature Te125 NMR

    DOE PAGES

    Cui, J.; Levin, E. M.; Lee, Y.; Furukawa, Y.

    2016-08-18

    We have carried out 125Te nuclear magnetic resonance (NMR) in a wide temperature range of 1.5–300 K to investigate the electronic properties of Ge50 Te50, Ag2 Ge48Te50 , and Sb2 Ge48 Te50 from a microscopic point of view. From the temperature dependence of the NMR shift (K) and nuclear spin lattice relaxation rate (1/T1), we found that two bands contribute to the physical properties of the materials. One band overlaps the Fermi level providing the metallic state where no strong electron correlations are revealed by Korringa analysis. The other band is separated from the Fermi level by an energy gapmore » of Eg/kB ~67 K, which gives rise to semiconductorlike properties. First-principles calculation reveals that the metallic band originates from the Ge vacancy while the semiconductorlike band is related to the fine structure of the density of states near the Fermi level. We find low-temperature Te125 NMR data for the materials studied here clearly show that Ag substitution increases hole concentration while Sb substitution decreases it.« less

  15. Electronic properties of GeTe and Ag- or Sb-substituted GeTe studied by low-temperature 125Te NMR

    NASA Astrophysics Data System (ADS)

    Cui, J.; Levin, E. M.; Lee, Y.; Furukawa, Y.

    2016-08-01

    We have carried out 125Te nuclear magnetic resonance (NMR) in a wide temperature range of 1.5-300 K to investigate the electronic properties of Ge50Te50 ,Ag2Ge48Te50 , and Sb2Ge48Te50 from a microscopic point of view. From the temperature dependence of the NMR shift (K ) and nuclear spin lattice relaxation rate (1 /T1 ), we found that two bands contribute to the physical properties of the materials. One band overlaps the Fermi level providing the metallic state where no strong electron correlations are revealed by Korringa analysis. The other band is separated from the Fermi level by an energy gap of Eg/kB˜67 K, which gives rise to semiconductorlike properties. First-principles calculation reveals that the metallic band originates from the Ge vacancy while the semiconductorlike band is related to the fine structure of the density of states near the Fermi level. Low-temperature 125Te NMR data for the materials studied here clearly show that Ag substitution increases hole concentration while Sb substitution decreases it.

  16. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  17. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Dragica, Vasileska; Ringhofer, Christian

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  18. Prediction of Weyl semimetal in orthorhombic MoTe2

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Wu, Shu-Chun; Ali, Mazhar N.; Felser, Claudia; Yan, Binghai

    2015-10-01

    We investigate the orthorhombic phase (Td) of the layered transition-metal dichalcogenide MoTe2 as a Weyl semimetal candidate. MoTe2 exhibits four pairs of Weyl points lying slightly above (˜6 meV ) the Fermi energy in the bulk band structure. Different from its cousin WTe2, which was recently predicted to be a type-II Weyl semimetal, the spacing between each pair of Weyl points is found to be as large as 4% of the reciprocal lattice in MoTe2 (six times larger than that of WTe2). When projected onto the surface, the Weyl points are connected by Fermi arcs, which can be easily accessed by angle-resolved photoemission spectroscopy due to the large Weyl point separation. In addition, we show that the correlation effect or strain can drive MoTe2 from a type-II to a type-I Weyl semimetal.

  19. Extreme solid state refrigeration using nanostructured Bi-Te alloys.

    SciTech Connect

    Lima Sharma, Ana L.; Spataru, Dan Catalin; Medlin, Douglas L.; Sharma, Peter Anand; Morales, Alfredo Martin

    2009-09-01

    Materials are desperately needed for cryogenic solid state refrigeration. We have investigated nanostructured Bi-Te alloys for their potential use in Ettingshausen refrigeration to liquid nitrogen temperatures. These alloys form alternating layers of Bi{sub 2} and Bi{sub 2}Te{sub 3} blocks in equilibrium. The composition Bi{sub 4}Te{sub 3} was identified as having the greatest potential for having a high Ettingshausen figure of merit. Both single crystal and polycrystalline forms of this material were synthesized. After evaluating the Ettingshausen figure of merit for a large, high quality polycrystal, we simulated the limits of practical refrigeration in this material from 200 to 77 K using a simple device model. The band structure was also computed and compared to experiments. We discuss the crystal growth, transport physics, and practical refrigeration potential of Bi-Te alloys.

  20. Electronic signatures of dimerization in IrTe2

    NASA Astrophysics Data System (ADS)

    Dai, Jixia; Wu, Weida; Oh, Yoon Seok; Cheong, S.-W.; Yang, J. J.

    2014-03-01

    Recently, the mysterious phase transition around Tc ~ 260 K in IrTe2 has been intensively studied. A structural supermodulation with q =1/5 was identified below Tc. A variety of microscopic mechanisms have been proposed to account for this transition, including charge-density wave due to Fermi surface nesting, Te p-orbital driven structure instability, anionic depolymerization, ionic dimerization, and so on. However, there has not been an unified picture on the nature of this transition. To address this issue, we have performed low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) experiments on IrTe2 and IrTe2-xSex. Our STM data clearly shows a strong bias dependence in both topography and local density of states (STS) maps. High resolution spectroscopic data further confirms the stripe-like electronic states modulation, which provides insight to the ionic dimerization revealed by X-ray diffraction.

  1. Summary of the TeV33 working group

    SciTech Connect

    Bagley, P.P.; Bieniosek, F.M.; Colestock, P.

    1996-10-01

    This summary of the TeV33 working group at Snowmass reports on work in the areas of Tevatron store parameters, the beam-beam interaction, Main Injector intensity (slip stacking), antiproton production, and electron cooling.

  2. CdTe Solar Cells: The Role of Copper

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

  3. Advances in CdTe R&D at NREL

    SciTech Connect

    Wu, X.; Zhou, J.; Keane, J. C.; Dhere, R. G.; Albin, D. S.; Gessert, T. A.; DeHart, C.; Duda, A.; Ward, J. J.; Yan, Y.; Teeter, G.; Levi, D. H.; Asher, S.; Perkins, C.; Moutinho, H. R.; To, B.

    2005-11-01

    This paper summarizes the following R&D accomplishments at National Renewable Energy Laboratory (NREL): (1) Developed several novel materials and world-record high-efficiency CdTe solar cell, (2) Developed "one heat-up step" manufacturing processes, and (3) Demonstrated 13.9% transparent CdTe cell and 15.3% CdTe/CIS polycrystalline tandem solar cell. Cadmium telluride has been well recognized as a promising photovoltaic material for thin-film solar cells because of its near-optimum bandgap of ~1.5 eV and its high absorption coefficient. Impressive results have been achieved in the past few years for polycrystalline CdTe thin-film solar cells at NREL. In this paper, we summarize some recent R&D activities at NREL.

  4. Theoretical study of intrinsic defects in CdTe

    NASA Astrophysics Data System (ADS)

    Menéndez-Proupin, E.; Orellana, W.

    2016-05-01

    The quantum states and thermodynamical properties of the Cd and Te vacancies in CdTe are studied by first principles calculations. It is shown that the band structure of a cubic 64-atoms supercell with a Te vacancy is dramatically different from the band structure of the perfect crystal, suggesting that it cannot be used as model to calculate isolated defects. This flaw is solved modeling the Te vacancy within a cubic 216-atoms supercell. However, even with this large supercell, the 2— charge state relaxes to an incorrect distorted structure. This distortion is driven by partial filling of the conduction band induced by the k-point sampling. The correct structures and formation energies are obtained by relaxation with restriction of system symmetry, followed by band-filling correction to the energy, or by using a larger supercell that allows sampling the Brillouin zone with a single k-point.

  5. Size-dependent activation energy and carrier dynamics in Cd(x)Zn(1-x)Te/ZnTe quantum dots on Si substrates.

    PubMed

    Lee, Hong Seok

    2014-11-01

    We investigate the size-dependent activation energy and carrier dynamics in Cd(x)Zn(1-x)Te/ZnTe quantum dots (QDs) grown on Si substrates. The excitonic peak corresponding to transitions from the ground electronic subband to the ground heavy-hole band in Cd0.6Zn0.4Te/ZnTe QDs shifts to a lower energy with increasing Cd0.6Zn0.4Te thickness owing to an increase in the size of the QDs. The activation energy of the electrons confined in the Cd0.6Zn0.4Te/ZnTe QDs, as obtained from the temperature-dependent photoluminescence (PL) spectra, increases with increasing Cd0.6Zn0.4Te thickness owing to an enhancement of the quantum confinement effect resulting from an increase in the energy difference between the electronic state and the conduction band edge. The carrier dynamics of Cd0.6Zn0.4Te/ZnTe QDs is studied using time-resolved PL measurements, which shows a longer exciton lifetime for Cd0.6Zn0.4Te/ZnTe QDs with increasing Cd0.6Zn0.4Te thickness. This behavior is attributed to the reduction of the exciton oscillator strength resulting from a strong built-in electric field in the larger QDs.

  6. Analysis of Etched CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Arias, J. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Jones, K.; Johnson, S. M.; Lofgreen, D. D.

    2016-09-01

    State-of-the-art as-received (112)B CdZnTe substrates have been examined for surface impurity contamination and polishing residue. Two 4 cm × 4 cm and one 6 cm × 6 cm (112)B state-of-the-art as-received CdZnTe wafers were analyzed. A maximum surface impurity concentration of Al = 1.7 × 1015 atoms cm-2, Si = 3.7 × 1013 atoms cm-2, Cl = 3.12 × 1015 atoms cm-2, S = 1.7 × 1014 atoms cm-2, P = 1.1 × 1014 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 1.2 × 1014 atoms cm-2, and Cu = 4 × 1012 atoms cm-2 was observed on the as-received CdZnTe wafers. CdZnTe particulates and residual SiO2 polishing grit were observed on the surface of the as-received (112)B CdZnTe substrates. The polishing grit/CdZnTe particulate density on CdZnTe wafers was observed to vary across a 6 cm × 6 cm wafer from ˜4 × 107 cm-2 to 2.5 × 108 cm-2. The surface impurity and damage layer of the (112)B CdZnTe wafers dictate that a molecular beam epitaxy (MBE) preparation etch is required. The contamination for one 4 cm × 4 cm and one 6 cm × 6 cm CdZnTe wafer after a standard MBE Br:methanol preparation etch procedure was also analyzed. A maximum surface impurity concentration of Al = 2.4 × 1015 atoms cm-2, Si = 4.0 × 1013 atoms cm-2, Cl = 7.5 × 1013 atoms cm-2, S = 4.4 × 1013 atoms cm-2, P = 9.8 × 1013 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 2.9 × 1014 atoms cm-2, and Cu = 5.2 × 1012 atoms cm-2 was observed on the MBE preparation-etched CdZnTe wafers. The MBE preparation-etched surface contamination consists of Cd(Zn)Te particles/flakes. No residual SiO2 polishing grit was observed on the (112)B surface.

  7. Effects of Te on intergranular embrittlement of a Ni-16Mo-7Cr alloy

    NASA Astrophysics Data System (ADS)

    Cheng, Hongwei; Han, Fenfen; Jia, Yanyan; Li, Zhijun; Zhou, Xingtai

    2015-06-01

    Te was deposited on the surface of a Ni-16Mo-7Cr alloy by thermal evaporation at 700 °C, and the effect of Te on the intergranular cracking behavior and the tensile properties of the alloy was investigated. The results show that the reaction products formed on the surface of the alloy, the diffusion depth of Te in the alloy, and the yield strength of the alloy attacked by Te at room temperature are not changed remarkably with Te content increasing, whereas the ultimate tensile strength and elongation of the alloy is decreased distinctly. The primary surface reaction product are mainly composed of Ni3Te2, CrTe, and MoTe2, and the diffusion depth of Te in the alloys is about 50 μm. The intergranular embrittlement mechanism of the alloy induced by Te of is also discussed in this paper.

  8. Recrystallisation of electrophoretically deposited CdTe films

    NASA Astrophysics Data System (ADS)

    Pande, P. C.; Bocking, S.; Duke, S.; Miles, R. W.; Carter, M. J.; Latimer, I. D.; Hill, R.

    1996-02-01

    Films of CdTe have been produced by a novel low cost process based on electrophoretic deposition using polar organic solvents. The main advantage of this method is the high rate of deposition, greater than 20 μm/min. Details of the deposition process are given and the effects of post-deposition annealing of the samples have also been investigated using XRD, SEM and EDAX. Laser annealing resulted in melting of CdTe producing more compact and robust films.

  9. Preparation of Exfoliated Bi2Te3 Thin Films

    NASA Astrophysics Data System (ADS)

    Luo, Jiajun; Late, Dattatray; Wu, Isaac; Biswas, Kanishka; Kanatzidis, Mercouri; Grayson, Matthew

    2011-12-01

    Bi2Te3, recently recognized as a "topological insulator", is proposed to have enhanced electrical and thermoelectric properties due to the topological surface state. In this work, we describe our technique for synthesizing Bi2Te3 thin films with the Scotch tape method. We also describe strategies for fabricating samples for transport and thermoelectric measurements. Preliminary data of carrier density and mobility at room temperature was obtained.

  10. Strategies for recycling CdTe photovoltaic modules

    SciTech Connect

    Eberspacher, C.; Gay, C.F.; Moskowitz, P.D.

    1994-12-31

    Recycling end-of-life cadmium telluride (CdTe) photovoltaic (PV) modules may enhance the competitive advantage of CdTe PV in the marketplace, but the experiences of industries with comparable Environmental, Health and Safety (EH&S) challenges suggest that collection and recycling costs can impose significant economic burdens. Customer cooperation and pending changes to US Federal law may improve recycling economics.

  11. Transient and diffusion analysis of HgCdTe

    NASA Technical Reports Server (NTRS)

    Clayton, J. C.

    1982-01-01

    Solute redistribution during directional solidification of HgCdTe is addressed. Both one-dimensional and two-dimensional models for solute redistribution are treated and model results compared to experiment. The central problem studied is the cause of radial inhomogeneities found in directionally solidified HgCdTe. A large scale gravity-driven interface instability, termed shape instability, is postulated to be the cause of radial inhomogeneities. Recommendations for future work, along with appropriate computer programs, are included.

  12. As-Received CdZnTe Substrate Contamination

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Arias, J. M.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Vilela, M. F.; Johnson, S. M.; Lofgreen, D. D.; Yulius, A.; Carmody, M.; Hirsch, R.; Fiala, J.; Motakef, S.

    2015-09-01

    State-of-the-art as-received (112)B CdZnTe substrates were examined for surface impurity contamination, polishing damage, and tellurium precipitates/inclusions. A maximum surface impurity concentration of Al = 7.5 × 1014, Si = 3.7 × 1013, Cl = 3.12 × 1015, S = 1.7 × 1014, P = 7.1 × 1013, Fe = 1.0 × 1013, Br = 1.9 × 1012, and Cu = 4 × 1012 atoms cm-2 was observed on an as-received 6 × 6 cm wafer. As-received CdZnTe substrates have scratches and residual polishing grit on the (112)B surface. Polishing scratches are 0.3 nm in depth and 0.1 μm wide. The polishing grit density was observed to vary from wafer-to-wafer from ˜5 × 106 to 2 × 108 cm-2. Te precipitate/inclusion size and density was determined by near-infrared automated microscopy. A Te precipitate/inclusion diameter histogram was obtained for the near-surface (top ~140 μm) of a 6 × 6 cm substrate. The average areal Te precipitate/inclusion density was observed to be fairly uniform. However, there was a large density of Te precipitates/inclusions with a diameter significantly greater than the mean. Te precipitate/inclusion density >10 μm diameter = 2.8 × 103 cm-3. The large Te precipitates/inclusions are laterally non-uniformly distributed across the wafer.

  13. (BOREAS) BOREAS TE-7 Sap Flow Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Hogg, E. H.; Hurdle, P. A.

    2000-01-01

    The BOREAS TE-7 team collected data sets in support of its efforts to characterize and interpret information on the sap flow of boreal vegetation. The heat pulse method was used to monitor sap flow and to estimate rates of transpiration from aspen, black spruce, and mixed wood forests at the SSAOA, MIX, SSA-OBS. and Batoche sites in Saskatchewan, Canada. Measurements were made at the various sites from May to October 1994, May to October 1995, and April to October 1996. A scaling procedure was used to estimate canopy transpiration rates from the sap flow measurements. The data were stored in tabular ASCII files. Analyses to date show a tendency for sap flow in aspen to remain remarkably constant over a wide range of environmental conditions VPD from 1.0 to 4.8 kPa and solar radiation less than 400 W/sq m). For forests with high aerodynamic conductance, the results would indicate an inverse relationship between stomatal conductance and VPD, for VPD greater than 1 kPa. A possible interpretation is that stomata are operating to maintain leaf water potentials above a critical minimum value, which in turn places a maximum value on the rate of sap flow that can be sustained by the tree. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distrobuted Activity Archive Center (DAAC).

  14. BOREAS TE-9 NSA Leaf Chlorophyll Density

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Margolis, Hank; Sy, Mikailou

    2000-01-01

    The BOREAS TE-9 team collected several data sets related to chemical and photosynthetic properties of leaves in boreal forest tree species. These data were collected to help provide an explanation of potential seasonal and spatial changes of leaf pigment properties in boreal forest species at the NSA. At different dates (FFC-Winter, FFC-Thaw, IFC-1, IFC-2, and IMC-3), foliage samples were collected from the upper third of the canopy for five NSA sites (YJP, OJP, OBS, UBS, and OA) near Thompson, Manitoba. Subsamples of 100 needles for black spruce, 20 needles for jack pine, and single leaf for trembling aspen were cut into pieces and immersed in a 20-mL DMF aliquot in a Nalgene test tube. The extracted foliage materials were then oven-dried at 68 C for 48 hours and weighed. Extracted leaf dry weight was converted to a total leaf area basis to express the chlorophyll content in mg/sq cm of total leaf area. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  15. BOREAS TE-1 SSA Soil Lab Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Knapp, David E. (Editor); Nerbas, Tim; Anderson, Darwin

    2000-01-01

    This data set was collected by TE-1 to provide a set of soil properties for BOREAS investigators in the SSA. The soil samples were collected at sets of soil pits in 1993 and 1994. Each set of soil pits was in the vicinity of one of the five flux towers in the BOREAS SSA. The collected soil samples were sent to a lab, where the major soil properties were determined. These properties include, but are not limited to, soil horizon; dry soil color; pH; bulk density; total, organic, and inorganic carbon; electric conductivity; cation exchange capacity; exchangeable sodium, potassium, calcium, magnesium, and hydrogen; water content at 0.01, 0.033, and 1.5 MPascals; nitrogen; phosphorus; particle size distribution; texture; pH of the mineral soil and of the organic soil; extractable acid; and sulfur. The data are stored in tabular ASCII text files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  16. BOREAS TE-19 Ecosystem Carbon Balance Model

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Frolking, Steve

    2000-01-01

    The BOREAS TE-19 team developed a model called the Spruce and Moss Model (SPAM) designed to simulate the daily carbon balance of a black spruce/moss boreal forest ecosystem. It is driven by daily weather conditions, and consists of four components: (1) soil climate, (2) tree photosynthesis and respiration, (3) moss photosynthesis and respiration, and (4) litter decomposition and associated heterotrophic respiration. The model simulates tree gross and net photosynthesis, wood respiration, live root respiration, moss gross and net photosynthesis, and heterotrophic respiration (decomposition of root litter, young needle and moss litter, and humus). These values can be combined to generate predictions of total site net ecosystem exchange of carbon (NEE), total soil dark respiration (live roots + heterotrophs + live moss), spruce and moss net productivity, and net carbon accumulation in the soil. To date, simulations have been of the BOREAS NSA-OBS and SSA-OBS tower sites, from 1968-95 (except 1990-93). The files include source code and sample input and output files in ASCII format. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

  17. High-quality CdTe films from nanoparticle precursors

    SciTech Connect

    Schulz, D.L.; Pehnt, M.; Urgiles, E.

    1996-05-01

    In this paper the authors demonstrate that nanoparticulate precursors coupled with spray deposition offers an attractive route into electronic materials with improved smoothness, density, and lower processing temperatures. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent, resulting in the formation of soluble NaI and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25-75 {Angstrom} diameter) onto substrates at elevated temperatures (T = 280-440{degrees}C) with no further thermal treatment. These films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD, with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C and substantial O. AFM gave CdTe grain sizes of {approx}0.1-0.3 {mu}m for film sprayed at 400{degrees}C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.

  18. CdZnTe technology for gamma ray detectors

    SciTech Connect

    Stahle, Carl; Shi, Jack; Shu, Peter; Barthelmy, Scott; Parsons, Ann; Snodgrass, Steve

    1998-01-15

    CdZnTe detector technology has been developed at NASA Goddard for imaging and spectroscopy applications in hard x-ray and gamma ray astronomy. A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. CdZnTe detectors also have applications for medical imaging, environmental protection, transportation safety, nuclear safeguards and safety, nuclear non-proliferation, and national security. This can be accomplished from space and also from portable detectors on earth. One of the great advantages of CdZnTe is that the detectors can be operated at room temperature which eliminates the need for cryogenic cooling. CdZnTe detectors have good energy resolution (3.6 keV at 60 keV) and excellent spatial resolution (<100 microns). NASA Goddard has developed the fabrication technology to make a variery of planar, strip, and pixel detectors and integrated these detectors to high density electronics. We have built a 2x2 and a large area (60 cm{sup 2}, 36 detectors) 6x6 strip detector array. This paper will summarize the CdZnTe detector fabrication and packaging technology developed at Goddard.

  19. Optical properties of liquid Se-Te alloys

    NASA Astrophysics Data System (ADS)

    Silva, Larry A.; Cutler, Melvin

    1990-10-01

    Thin films have been used to determine the optical properties of the liquid-alloy system SexTe100-x in the photon energy range of 0.4 to 5.0 eV, and at temperatures from the melting point to 500 °C. These liquids are semiconductors at Se-rich compositions, and undergo a transition to metallic behavior at high Te concentrations. The effects of this transition first appear in the optical data at 80 at. % Te. Possible forms for the electronic band structure in the semiconducting phase of the liquid are derived from the nondirect transition model for optical absorption. The optical properties of liquid Te (metallic phase) are separated into intraband and interband components, modeling the intraband component by Drude behavior, to test previously proposed mechanisms for the semiconductor-metal transition. Our results are consistent with the preservation of two-fold covalent bonding across this transition, and predict a ~0.4 eV gap between a Fermi level within the valence-band and the conduction-band edge. We have also measured the sub-band-gap absorption coefficient in semiconducting liquids containing 0, 20, and 40 at. % Te, and find that the extent of the exponential absorption edge decreases with increasing Te concentration.

  20. TE, TM modes photorefractive surface waves and their coupling

    NASA Astrophysics Data System (ADS)

    Zhang, T. H.; Shao, W. W.; Li, K.; Liu, X. S.; Xu, J. J.

    2008-03-01

    The nonlinear equations of photorefractive surface waves (PR SWs) with diffusion mechanism are established and calculated numerically for both TE mode and TM mode and their coupling for the first time. The characteristics of TE mode and TM mode are analyzed, such as propagation constants, spatial distribution, penetration depths etc. For relative larger propagation constant, most of the surface wave energy is concentrated on the Ax component of TM mode, and the penetration depth of Ay of TE mode is always larger than that of Ax of TM mode because electro-optical coefficient r13 is always smaller than r33 in general PRC. As a result, the energy of the PR SW is better confined near the surface for TM mode than that for TE mode. When both TE and TM modes PR SWs are present, they will be coupled drastically and the Ax component of TM mode and Ay component of TE mode resonate in the volume of PR medium. As a result, the PR SWs cannot remain decay, and the light energy can not be confined near the surface steadily and the modes are destroyed. The results provide the theoretical instructions and are very significant to generate steady and high density PR SW in practice.

  1. All screen printed CdS/CdTe solar cell

    NASA Astrophysics Data System (ADS)

    Uda, H.; Matsumoto, H.; Komatsu, Y.; Nakano, A.; Ikegami, S.

    Thin film CdS/CdTe solar cells were prepared on a glass substrate by successively repeating screen printing and heating in a belt furnace of each paste of CdS, Cd+Te, C, Ag+In and Ag. The photovoltaic performance of the cell is influenced generally by the preparation condition of each film. The sintering temperature of CdTe film gave a strong effect on the spectral response of the cell. The cell sintered at a higher temperature showed a poor response in the short wavelength. This is due to a formation of CdS(x)Te(1-x) solid solution layer at the CdS/CdTe interface. It was attempted to prepare solar cells, taking CdTe sintering temperature of 620 C, on a borosilicate glass substrate of 10 x 10 sq cm and an intrinsic efficiency of 9.0 percent was obtained. Twenty-four watt modules consisting of 48 element cells have been fabricated.

  2. Thermophysical Properties of Liquid Te: Density, Electrical Conductivity, and Viscosity

    NASA Technical Reports Server (NTRS)

    Li, C.; Su, C.; Lehoczky, S. L.; Scripa, R. N.; Ban, H.; Lin, B.

    2004-01-01

    The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.89 x 10(exp 5 OMEGA-1m-1) as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring's and Bachiskii's predicted behaviors for homogeneous liquids. The Properties were also measured as a function of time after the liquid was coded from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.

  3. Study of the Topological Crystalline Insulator, SnTe and Sn-In-Te systems in the form of nanomaterials

    NASA Astrophysics Data System (ADS)

    Saghir, M.; Lees, M. R.; York, S. J.; Balakrishnan, G.

    2014-03-01

    We have studied the Topological Crystalline Insulator SnTe and the superconducting variant which arises due to the partial substitution of Sn atoms with indium, Sn1-xInxTe, in this rock salt structure. The observable topological features are thought to be enhanced by increasing the surface area to volume ratio of the materials and therefore suppressing contributions from the bulk. We report the first evidence for the growth of SnTe and SnInTe nanowires starting from bulk crystals. The nanowires produced are typically 20 μm in length and 20 nm wide. The stoichiometries of these structures have been determined to compare with that of the source material. Various morphologies of nanomaterials are observed and the optimal conditions and processes involved to obtain these are discussed.

  4. Indium doping of CdTe polycrystalline films prepared by co-sputtering of CdTe-In-Cd targets

    NASA Astrophysics Data System (ADS)

    Becerril, M.; Zelaya-Angel, O.; Ramírez-Bon, R.; Espinoza-Beltrán, F. J.; González-Hernández, J.

    1997-01-01

    Indium doped CdTe polycrystalline films were grown on Corning glass substrates at room temperature by co-sputtering from a CdTe-Cd-In target. The elemental Cd and In were glued onto the CdTe target covering small areas. The electrical, structural, and optical properties were analyzed as a function of the concentration of both elements. It was found that when Cd and In are simultaneously incorporated, the electrical resistivity drops and the carrier concentration increases. In both cases the changes are of several orders of magnitude. From the results, we conclude that, using this deposition technique, n-type In doped CdTe polycrystalline films can be produced.

  5. Masses of Te130 and Xe130 and Double-β-Decay Q Value of Te130

    NASA Astrophysics Data System (ADS)

    Redshaw, Matthew; Mount, Brianna J.; Myers, Edmund G.; Avignone, Frank T., III

    2009-05-01

    The atomic masses of Te130 and Xe130 have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M(Te130)=129.906222744(16)u and M(Xe130)=129.903509351(15)u. From the mass difference the double-β-decay Q value of Te130 is determined to be Qββ(Te130)=2527.518(13)keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi , Nucl. Phys. A729, 337 (2003)NUPABL0375-947410.1016/j.nuclphysa.2003.11.003].

  6. Masses of {sup 130}Te and {sup 130}Xe and Double-{beta}-Decay Q Value of {sup 130}Te

    SciTech Connect

    Redshaw, Matthew; Mount, Brianna J.; Myers, Edmund G.; Avignone, Frank T. III

    2009-05-29

    The atomic masses of {sup 130}Te and {sup 130}Xe have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M({sup 130}Te)=129.906 222 744(16) u and M({sup 130}Xe)=129.903 509 351(15) u. From the mass difference the double-{beta}-decay Q value of {sup 130}Te is determined to be Q{sub {beta}}{sub {beta}}({sup 130}Te)=2527.518(13) keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi et al., Nucl. Phys. A729, 337 (2003)].

  7. Giant spin splitting in optically active ZnMnTe/ZnMgTe core/shell nanowires.

    PubMed

    Wojnar, Piotr; Janik, Elżbieta; Baczewski, Lech T; Kret, Sławomir; Dynowska, Elżbieta; Wojciechowski, Tomasz; Suffczyński, Jan; Papierska, Joanna; Kossacki, Piotr; Karczewski, Grzegorz; Kossut, Jacek; Wojtowicz, Tomasz

    2012-07-11

    An enhancement of the Zeeman splitting as a result of the incorporation of paramagnetic Mn ions in ZnMnTe/ZnMgTe core/shell nanowires is reported. The studied structures are grown by gold-catalyst assisted molecular beam epitaxy. The near band edge emission of these structures, conspicuously absent in the case of uncoated ZnMnTe nanowires, is activated by the presence of ZnMgTe coating. Giant Zeeman splitting of this emission is studied in ensembles of nanowires with various average Mn concentrations of the order of a few percent, as well as in individual nanowires. Thus, we show convincingly that a strong spin sp-d coupling is indeed present in these structures.

  8. Bi2Te3 hexagonal nanoplates and thermoelectric properties of n-type Bi2Te3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Fan, X. A.; Yang, J. Y.; Xie, Z.; Li, K.; Zhu, W.; Duan, X. K.; Xiao, C. J.; Zhang, Q. Q.

    2007-10-01

    Bi2Te3 plate-like crystals with homogeneous hexagonal morphology were rapidly synthesized using a microwave assisted wet chemical method in 30 min. These Bi2Te3 nanoplates possessed a fixed edge with a length of ~0.5-2 µm, and the thickness was less than ~100 nm. The n-type Bi2Te3 nanocomposites were prepared by consolidating mixtures of these nanoplates and mechanically alloyed powders using plasma activated sintering, and the effect of nanoplate addition on the thermoelectric properties of the nanocomposites was investigated. When the content of the doped nanoplates was 15 wt%, the lattice thermal conductivity of the Bi2Te3 nanocomposites decreased by 18% compared with that of the undoped compounds. A preliminary investigation showed that nanopowder addition was an effective way to decrease the thermal conductivity and increase the thermoelectric efficiency.

  9. Thermoelectric Inhomogeneities in (Ag(sub 1-y)SbTe2)(sub x)(PbTe)(sub 1-x)

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey; Chen, Nancy; Gascoin, Franck; Mueller, Eckhard; Karpinski, Gabriele; Stiewe, Christian

    2006-01-01

    A document presents a study of why materials of composition (Ag1 ySbTe2)0.05 (PbTe)0.95 [0< or = y < or = 1] were previously reported to have values of the thermoelectric figure of merit [ZT (where Z = alpha(sup 2)/rk, alpha is the Seebeck coefficient, r is electrical resistivity, k is thermal conductivity, and T is absolute temperature)] ranging from <1 to >2. In the study, samples of (AgSbTe2)0.05(PbTe)0.95, (Ag0.67SbTe2)0.05 (PbTe)0.95, and (Ag0.55SbTe2)0.05(PbTe)0.95 were prepared by melting followed, variously, by slow or rapid cooling. Analyses of these samples by x-ray diffraction, electron microscopy, and scanning-microprobe measurements of the Seebeck coefficient led to the conclusion that these materials have a multiphase character on a scale of the order of millimeters, even though they appear homogeneous in x-ray diffraction and electron microscopy. The Seebeck measurements showed significant variations, including both n-type and p-type behavior in the same sample. These variations were found to be consistent with observed variations of ZT. The rapidly quenched samples were found to be less inhomogeneous than were the furnace-cooled ones; hence, rapid quenching was suggested as a basis of research on synthesizing more nearly uniform high-ZT samples.

  10. (GeTe)nSbInTe3 (n≤3)—Element distribution and thermal behavior

    NASA Astrophysics Data System (ADS)

    Fahrnbauer, Felix; Urban, Philipp; Welzmiller, Simon; Schröder, Thorsten; Rosenthal, Tobias; Oeckler, Oliver

    2013-12-01

    Antimony in germanium antimony tellurides (GeTe)n(Sb2Te3) can be substituted by indium. Homogeneous bulk samples of GeSbInTe4 (R3¯m, Z=3, a=4.21324(5) Å, c=41.0348(10) Å) and Ge2SbInTe5 (P3¯m1, Z=1, a=4.20204(6) Å, c=17.2076(4) Å) were obtained; their structures were refined with the Rietveld method. Single-crystal X-ray diffraction using synchrotron radiation at the K edges of Sb and Te (exploiting anomalous dispersion) yields precise information on the element distribution in the trigonal layered structure of Ge3SbInTe6 (R3¯m, Z=3, a=4.19789(4) Å, c=62.1620(11) Å). The structure is characterized by van der Waals gaps between distorted rocksalt-type slabs of alternating cation and anion layers. The cation concentration is commensurately modulated with Sb preferring the positions near the gaps. In contrast to unsubstituted Ge3Sb2Te6, quenching the NaCl-type high-temperature phase (stable above ~510 °C) easily yields a pseudocubic modification that is metastable at ambient conditions. Temperature-dependent powder diffraction reveals a broader stability range of the cubic high-temperature modification of Ge3SbInTe6 compared to the ternary phases. In-containing samples partially decompose at ca. 300 °C but become homogeneous again when the high-temperature phase is formed.

  11. Live-monitoring of Te inclusions laser-induced thermo-diffusion and annealing in CdZnTe crystals

    SciTech Connect

    Zappettini, A.; Zambelli, N.; Benassi, G.; Calestani, D.; Pavesi, M.

    2014-06-23

    The presence of Te inclusions is one of the main factors limiting performances of CdZnTe crystals as X-ray detectors. We show that by means of infrared laser radiation it is possible to move and anneal tellurium inclusions exploiting a thermo-diffusion mechanism. The process is studied live during irradiation by means of an optical microscope equipment. Experimental conditions, and, in particular, energy laser fluence, for annealing inclusions of different dimensions are determined.

  12. Phase relationships in the pseudo-binary 2(ZnTe)-CuInTe 2 system

    NASA Astrophysics Data System (ADS)

    Roussak, Liudmila; Wagner, Gerald; Schorr, Susan; Bente, Klaus

    2005-11-01

    Subsolidus phase relationships in the 2(ZnTe) x(CuInTe 2) 1-x system were investigated by TEM experiments combined with EDX analysis. The samples were prepared by the solid-state reaction of the elements during long annealing times, followed by either quenching in ice-cold water, or by controlled cooling at different rates. Using the chemical compositions of single and coexisting phases at various temperatures, the boundaries of the two-phase region have been determined. At room temperature, the two-phase region extends from x=0.10 to 0.31. For x<0.10 only mixed crystals with tetragonal structure exist. Between x=0.31 and 1 alloys with the cubic structure are stable. The morphology of the tetragonal domains and their orientation relationship to the cubic matrix were determined by SAD, TEM and HRTEM experiments. The tetragonal phase embedded within the cubic matrix has a flat ellipsoidal shape, whose short axis coincides with the tetragonal c-axis. The three topotaxial orientation relationships between the tetragonal domains and the surrounding cubic matrix were found to be: [001] tetr.∥[100] cub., [001] tetr.∥[010] cub. and [001] tetr.∥[001] cub.. There is an indication that the nucleation starts from small regions displaying cation ordering according to the CuPt-type structure. Reaching the two-phase equilibrium, the tetragonal domains as well as the surrounding cubic phase are free of this cation ordering.

  13. Application of Rotating Magnetic Fields to THM Growth Process: Te-CdTe

    NASA Technical Reports Server (NTRS)

    LeClair, Mark; Worlikar, Ani; Motakef, Shariar; Gillies, Donald C.

    1998-01-01

    The numerical simulation of ongoing traveling heater method (THM) solution growth experiments of CdTe from Te solvent and the influence of a Rotating Magnetic Field (RMF) on control of convection in the solution zone is presented. The application of RMF is pursued as a means to actively control thermo-solutal convection in the solution zone which otherwise would be dominated by buoyancy forces. Numerical simulation and scaling analysis are used to generate a flow-regime map demarcating the boundary separating the buoyancy- and RMF-driven convection in the solution zone. Results indicate that whereas at low gravity levels the application of RMF can completely overwhelm buoyancy-induced convection, at normal gravity levels the successful control of convection by RMF requires use of fairly thin solvent zones. Simulation results also indicate that field strengths required to dominate natural convection on earth may lead to instabilities and transition to turbulence, and an associated deleterious effect on the quality of grown crystals. These and other simulations results are discussed in reference to experimental evidence.

  14. Numerical modeling and optimization of the segmented PbTe-BiTe-based thermoelectric leg

    NASA Astrophysics Data System (ADS)

    Mei, Deqing; Wang, Hui; Yao, Zhehe; Li, Yang

    2016-09-01

    The segmentation of thermoelectric materials is an efficient way to improve the overall efficiency of a thermoelectric leg. However, this improvement can be obtained only when the constituent materials are appropriately proportioned. A numerical model is established for optimizing the performance of the segmented leg based on the coupled equations of the thermoelectric with temperature-dependent material properties. The numerical model can be used to determine the optimal length ratio and current density for the segmented leg. On the basis of the numerical model, the performance optimization of the K0.02Pb0.98Te/Bi0.3Sb1.7Te3 segmented leg is performed, and its maximum conversion efficiency and maximum output power are calculated. Results show that the reasonable length ratio design of the thermoelectric leg can take a full advantage of the characteristics of the thermoelectric materials, and it can effectively improve the conversion efficiency and the electrical output power. In addition, the numerical model is validated by finite-element simulated results and experimental results.

  15. Fabrication of DNA-templated Te and Bi2Te3 nanowires by galvanic displacement.

    PubMed

    Liu, Jianfei; Uprety, Bibek; Gyawali, Shailendra; Woolley, Adam T; Myung, Nosang V; Harb, John N

    2013-09-01

    This paper demonstrates the use of galvanic displacement to form continuous tellurium-based nanowires on DNA templates, enabling the conversion of metals, which can be deposited site-specifically, into other materials needed for device fabrication. Specifically, galvanic displacement reaction of copper and nickel nanowires is used to fabricate tellurium and bismuth telluride nanowires on λ-DNA templates. The method is simple, rapid, highly selective, and applicable to a number of different materials. In this study, continuous Ni and Cu nanowires are formed on DNA templates by seeding with Ag followed by electroless plating of the desired metal. These wires are then displaced by a galvanic displacement reaction where either Te or Bi2Te3 is deposited from an acidic solution containing HTeO2(+) ions or a combination of HTeO2(+) and Bi(3+) ions, and the metal wire is simultaneously dissolved due to oxidation. Both tellurium and bismuth telluride wires can be formed from nickel templates. In contrast, copper templates only form tellurium nanowires under the conditions considered. Therefore, the composition of the metal being displaced can be used to influence the chemistry of the resulting nanowire. Galvanic displacement of metals deposited on DNA templates has the potential to enable site-specific fabrication of a variety of materials and, thereby, make an important contribution to the advancement of useful devices via self-assembled nanotemplates.

  16. Electrostatic assembles and optical properties of Au CdTe QDs and Ag/Au CdTe QDs

    NASA Astrophysics Data System (ADS)

    Yang, Dongzhi; Wang, Wenxing; Chen, Qifan; Huang, Yuping; Xu, Shukun

    2008-09-01

    Au-CdTe and Ag/Au-CdTe assembles were firstly investigated through the static interaction between positively charged cysteamine-stabilized CdTe quantum dots (QDs) and negatively charged Au or core/shell Ag/Au nano-particles (NCs). The CdTe QDs synthesized in aqueous solution were capped with cysteamine which endowed them positive charges on the surface. Both Au and Ag/Au NCs were prepared through reducing precursors with gallic acid obtained from the hydrolysis of natural plant poly-phenols and favored negative charges on the surface of NCs. The fluorescence spectra of CdTe QDs exhibited strong quenching with the increase of added Au or Ag/Au NCs. Railey resonance scattering spectra of Au or Ag/Au NCs increased firstly and decreased latter with the concentration of CdTe QDs, accompanied with the solution color changing from red to purple and colorless at last. Experimental results on the effects of gallic acid, chloroauric acid tetrahydrate and other reagents demonstrated the static interaction occurred between QDs and NCs. This finding reveals the possibilities to design and control optical process and electromagnetic coupling in hybrid structures.

  17. Low Temperature, Rapid Thermal Cycle Annealing of HgCdTe Grown on CdTe/Si

    NASA Astrophysics Data System (ADS)

    Simingalam, Sina; Brill, Gregory; Wijewarnasuriya, Priyalal; Rao, Mulpuri V.

    2015-05-01

    The HgCdTe(MCT) grown on CdTe/Si substrate has a high dislocation density due to lattice mismatch. Thermal cycle annealing (TCA) is effective in reducing the dislocation density. The TCA at high temperatures results in inter-diffusion of the constituent elements across the MCT/CdTe interface. In this study, we observed a reduction in dislocation density with good surface morphology due to proper design of the TCA system, low annealing temperature, and large number of annealing cycles. The ampoule containing the samples is placed in direct contact with the graphite heating tube which helps in increasing the heating and cooling rates of the annealing cycle. To maintain Hg overpressure, Hg is placed in the sample holder, instead of in the ampoule to avoid Hg condensation. The best results were obtained by cycling the annealing temperature between 290°C and 350°C. Anneals were performed by using 32, 64, 128 and 256 cycles. We obtained an etch pit density (EPD) as low as 1 × 106 cm-2. Lower EPD was not achieved either by increasing annealing temperature or number of annealing cycles. Through secondary ion mass spectroscopy analysis, we observed very little inter-diffusion of Cd across the MCT/CdTe interface for the 128 cycle annealing. These results show promise in bridging the gap in the device performance between the MCT material grown on CdTe/Si and CdZnTe substrates.

  18. Dual-axis beam correction for an array of single-mode diode laser emitters using a laser-written custom phase-plate.

    PubMed

    Trela, Natalia; Baker, Howard J; Wendland, Jozef J; Hall, Denis R

    2009-12-21

    A single optical component for a diode laser bar combines fast-axis smile and lens error correction with slow-axis collimation. Produced by laser-machining/polishing, it provides 0.9 mm focal length, 200 microm pitch slow-axis collimation on the same surface that corrects fast-axis errors. Custom fabrication enables fill-factor optimization for the 49 single-mode beams and gives parallel collimation with rms pointing errors of 3% and 6% of the far-field divergence for the fast- and slow-axis array respectively. Sub-micron pitch mismatch between the slow-axis lens and emitter arrays, and beam pointing changes by thermal expansion of the laser bar are detected. PMID:20052066

  19. Asymmetric dual axis energy recovery linac for ultrahigh flux sources of coherent x-ray and THz radiation: Investigations towards its ultimate performance

    NASA Astrophysics Data System (ADS)

    Ainsworth, R.; Burt, G.; Konoplev, I. V.; Seryi, A.

    2016-08-01

    In order for sources of coherent high brightness and intensity THz and x-ray radiation to be accepted by university or industrial R&D laboratories, truly compact, high current and efficient particle accelerators are required. The demand for compactness and efficiency can be satisfied by superconducting rf energy recovery linear accelerators (SRF ERL) allowing effectively minimizing the footprint and maximizing the efficiency of the system. However such setups are affected by regenerative beam break-up (BBU) instabilities which limit the beam current and may terminate the beam transport as well as energy recuperation. In this paper we suggest and discuss a SRF ERL with asymmetric configuration of resonantly coupled accelerating and decelerating cavities. In this type of SRF ERL an electron bunch is passing through accelerating and decelerating cavities once and, as we show in this case, the regenerative BBU instability can be minimized allowing high currents to be achieved. We study the BBU start current in such an asymmetric ERL via analytical and numerical models and discuss the properties of such a system.

  20. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, S.; Zhu, Shen; Lehoczky, S. L.; Wang, Ling Jun

    2000-01-01

    Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe and ZnSe (sub 1-x) Te (sub x) (0 less than x less than 0.4) grown by physical vapor transport technique. The energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. The best fit to the band gap vs. composition, x, data gives a bowing parameter of 1.336 which is between the value of 1.23 determined previously on ZnSeTe bulk crystals by reflectivity and the value of 1.621 reported on epilayers by photoconductivity. Low-temperature photoluminescence (PL) spectra were measured on 6 samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe (sub 1-x) Te (sub x) samples, 0.09 less than x less than 0.39. For x = 0.09, this emission energy is about 0.2eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x = 0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted to be associated with the exciton bound to Te clusters because of the high Te content in these samples.

  1. Optical modeling of graphene contacted CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Aldosari, Marouf; Sohrabpoor, Hamed; Gorji, Nima E.

    2016-04-01

    For the first time, an optical model is applied on CdS/CdTe thin film solar cells with graphene front or back contact. Graphene is highly conductive and is as thin as a single atom which reduces the light reflection and absorption, and thus enhances the light transmission to CdTe layer for a wide range of wavelengths including IR. Graphene as front electrode of CdTe devices led to loss in short circuit current density of 10% ΔJsc ≤ 15% compared to the conventional electrodes of TCO and ITO at CdS thickness of dCdS = 100 nm. In addition, all the multilayer graphene electrodes with 2, 4, and 7 graphene layers led to Jsc ≤ 20 mA/cm2. Therefore, we conclude that a single monolayer graphene with hexagonal carbon network reduces optical losses and enhances the carrier collection measured as Jsc. In another structure design, we applied the optical model to graphene back contacted CdS/CdTe device. This scheme allows double side irradiation of the cell which is expected to enhance the Jsc. We obtained 1 ∼ 6 , 23, and 38 mA/cm2 for back, front and bifacial illumination of graphene contacted CdTe cell with CdS = 100 nm. The bifacial irradiated cell, to be efficient, requires an ultrathin CdTe film with dCdTe ≤ 1 μm. In this case, the junction electric field extends to the back region and collects out the generated carriers efficiently. This was modelled by absorptivity rather than transmission rate and optical losses. Since the literature suggest that ZnO can increase the graphene conductivity and enhance the Jsc, we performed our simulations for a graphene/ZnO electrode (ZnO = 100 nm) instead of a single graphene layer.

  2. Vibrational properties of epitaxial Bi4Te3 films as studied by Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Song, Yuxin; Pan, Wenwu; Chen, Qimiao; Wu, Xiaoyan; Lu, Pengfei; Gong, Qian; Wang, Shumin

    2015-08-01

    Bi4Te3, as one of the phases of the binary Bi-Te system, shares many similarities with Bi2Te3, which is known as a topological insulator and thermoelectric material. We report the micro-Raman spectroscopy study of 50 nm Bi4Te3 films on Si substrates prepared by molecular beam epitaxy. Raman spectra of Bi4Te3 films completely resolve the six predicted Raman-active phonon modes for the first time. Structural features and Raman tensors of Bi4Te3 films are introduced. According to the wavenumbers and assignments of the six eigenpeaks in the Raman spectra of Bi4Te3 films, it is found that the Raman-active phonon oscillations in Bi4Te3 films exhibit the vibrational properties of those in both Bi and Bi2Te3 films.

  3. Novel ways of depositing ZnTe films by a solution growth technique

    SciTech Connect

    Birkmire, R.W. . Inst. of Energy Conversion)

    1991-06-01

    Cu-doped ZnTe films, <1000{Angstrom}, were reproducibly deposited for the first time by an electrochemical method. A CdTe/CdS/ITO/glass substrate is externally short circuited to a zinc counter electrode in an aqueous bath consisting of ZnCl{sub 2} and TeO{sub 2} to complete an electrochemical cell. Control of both pH and TeO{sub 2} concentration was necessary to deposit single phase ZnTe films. A copper complex was added to the bath to control the ZnTe conductivity and dope the films p-type. CdTe/CdS solar cells using the ZnTe:Cu as the primary contact to the CdTe have achieved efficiencies of {approximately}9%. 15 refs., 7 figs., 2 tabs.

  4. Comparative study of Hg xCd 1-xTe films grown on CdTe thin films previously deposited from two different techniques

    NASA Astrophysics Data System (ADS)

    Ali, A.; Abbas Shah, N.; Maqsood, A.

    2009-04-01

    High quality cadmium telluride (CdTe) thin films were grown on glass substrates with two different techniques, two evaporation source (TES) and closed space sublimation (CSS). Further to the above mercury telluride (HgTe) was then deposited by using single source on both CdTe thin films for obtaining Hg xCd 1-xTe samples. The crystalline structure of the Hg xCd 1-xTe sample grown from CSS-CdTe showed the preferential (1 1 1) orientation with smoother and larger grain size than those of TES-CdTe. The optical transmission for TES-CdTe sample was above 90% in the 1000-1500 nm range whereas it was significantly below 80% for CSS-CdTe sample. The optical transmission for TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe was ˜60%. The resistivity at room temperature of TES-CdTe and CSS-CdTe was ˜3.33×10 9 Ω cm and ˜2.20×10 8 Ω cm, respectively, while the resistivity of TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe samples was ˜1.73 Ω cm and ˜5.34×10 5 Ω cm, respectively. The comparative study of ternary compound prepared with the above techniques has been carried out for the first time.

  5. Magnetotransport in double quantum well with inverted energy spectrum: HgTe/CdHgTe

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Suslov, A. V.; Popov, M. R.; Novik, E. G.; Dvoretsky, S. A.; Mikhailov, N. N.

    2016-02-01

    We present an experimental study of the double-quantum-well (DQW) system made of two-dimensional layers with inverted energy band spectrum: HgTe. The magnetotransport reveals a considerably larger overlap of the conduction and valence subbands than in known HgTe single quantum wells (QW), which may be regulated here by an applied gate voltage Vg. This large overlap manifests itself in a much higher critical field Bc separating the range above it with a plain behavior of the Hall magnetoresistance ρx y(B ) , where the quantum peculiarities shift linearly with Vg, and the range below with a complicated behavior. In the latter case, specific structures in ρx y(B ) are formed like a double-N -shaped ρx y(B ) , reentrant sign-alternating quantum Hall effect with transitions into a zero-filling-factor state, etc., which are clearly manifested here due to better magnetic quantization at high fields, as compared to the features seen earlier in a single HgTe QW. The coexisting electrons and holes were found in the whole investigated range of positive and negative Vg as revealed (i) from fits to the low-field N -shaped ρx y(B ) , (ii) from the Fourier analysis of oscillations in ρx x(B ) , and (iii) from a specific behavior of ρx y(B ) at high positive Vg. A peculiar feature here is that the found electron density n remains almost constant in the whole range of investigated Vg while the hole density p drops down from the value a factor of 6 larger than n at extreme negative Vg to almost zero at extreme positive Vg passing through the charge-neutrality point. We show that this difference between n and p stems from an order of magnitude larger density of states for holes in the lateral valence subband maxima than for electrons in the conduction subband minimum. We analyze our observations on the basis of a calculated picture of magnetic levels in a DQW and suggest that their specificity is due to (i) a nonmonotonic course of the valence subband magnetic levels and an

  6. Influence of EDTA{sup 2-} on the hydrothermal synthesis of CdTe nanocrystallites

    SciTech Connect

    Gong Haibo; Hao Xiaopeng; Xu Xiangang

    2011-12-15

    Transformation from Te nanorods to CdTe nanoparticles was achieved with the assistance of EDTA as a ligand under hydrothermal conditions. Experimental results showed that at the beginning of reaction Te nucleated and grew into nanorods. With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. Finally, nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were obtained. The effects of EDTA on the morphology and formation of CdTe nanoparticles were discussed in consideration of the strong ligand-effect of EDTA, which greatly decreased the concentration of Cd{sup 2+}. Furthermore, the possible formation process of CdTe nanoparticles from Te nanorods was further proposed. The crystal structure and morphology of the products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). - Graphical Abstract: Firstly, Te nucleated and grew into nanorods in the presence of EDTA{sup 2-}. Then CdTe nucleus began to emerge on Te nanorods and finally monodispersed CdTe nanoparticles were obtained. Highlights: Black-Right-Pointing-Pointer EDTA serves as a strong ligand with Cd{sup 2+}. Black-Right-Pointing-Pointer The existence of EDTA constrains the nucleation of CdTe and promotes the formation of Te nanorods. Black-Right-Pointing-Pointer With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. Black-Right-Pointing-Pointer Nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were finally obtained.

  7. Electrical Characterization of Cu Composition Effects in CdS/CdTe Thin-Film Solar Cells with a ZnTe:Cu Back Contact: Preprint

    SciTech Connect

    Li, J. V.; Duenow, J. N.; Kuciauskas, D.; Kanevce, A.; Dhere, R. G.; Young, M. R.; Levi, D. H.

    2012-07-01

    We study the effects of Cu composition on the CdTe/ZnTe:Cu back contact and the bulk CdTe. For the back contact, its potential barrier decreases with Cu concentration while its saturation current density increases. For the bulk CdTe, the hole density increases with Cu concentration. We identify a Cu-related deep level at {approx}0.55 eV whose concentration is significant when the Cu concentration is high. The device performance, which initially increases with Cu concentration then decreases, reflects the interplay between the positive influences and negative influences (increasing deep levels in CdTe) of Cu.

  8. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    SciTech Connect

    Naderi, Ebadollah; Nanavati, Sachin; Majumder, Chiranjib; Ghaisas, S. V.

    2015-01-15

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as A{sub a} site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from A{sub a} (occupied) to A{sub a} (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  9. In-well pumped mid-infrared PbTe/CdTe quantum well vertical external cavity surface emitting lasers

    SciTech Connect

    Khiar, A. Witzan, M.; Hochreiner, A.; Eibelhuber, M.; Springholz, G.; Volobuev, V.

    2014-06-09

    Optical in-well pumped mid-infrared vertical external cavity surface emitting lasers based on PbTe quantum wells embedded in CdTe barriers are realized. In contrast to the usual ternary barrier materials of lead salt lasers such as PbEuTe of PbSrTe, the combination of narrow-gap PbTe with wide-gap CdTe offers an extremely large carrier confinement, preventing charge carrier leakage from the quantum wells. In addition, optical in-well pumping can be achieved with cost effective and readily available near infrared lasers. Free carrier absorption, which is a strong loss mechanism in the mid-infrared, is strongly reduced due to the insulating property of CdTe. Lasing is observed from 85 K to 300 K covering a wavelength range of 3.3–4.2 μm. The best laser performance is achieved for quantum well thicknesses of 20 nm. At low temperature, the threshold power is around 100 mW{sub P} and the output power more than 700 mW{sub P}. The significance of various charge carrier loss mechanisms are analyzed by modeling the device performance. Although Auger losses are quite low in IV–VI semiconductors, an Auger coefficient of C{sub A} = 3.5 × 10{sup −27} cm{sup 6} s{sup −1} was estimated for the laser structure, which is attributed to the large conduction band offset.

  10. Heterojunctions of model CdTe/CdSe mixtures

    SciTech Connect

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-03-18

    We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization to find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.

  11. Heterojunctions of model CdTe/CdSe mixtures

    DOE PAGES

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-03-18

    We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization tomore » find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.« less

  12. CdZnTe background measurements at balloon altitudes

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Barthelmy, Scott D.; Bartlett, Lyle M.; Birsa, F. B.; Gehrels, Neil A.; Naya, Juan E.; Odom, James L.; Singh, S.; Stahle, Carl M.; Tueller, Jack; Teegarden, Bonnard J.

    1996-10-01

    Because of its high atomic number and convenient room temperature operation, CdZnTe has great potential for use in both balloon and space borne hard x-ray (5 - 200 keV) astrophysics experiments. Here we present preliminary results from the first CdZnTe background measurements made by a balloon instrument. Measurements of the CdZnTe internal background are essential to determine which physical processes make the most important background contributions and are critical in the design of future scientific instruments. The PoRTIA CdZnTe balloon instrument was flown three times in three different shielding configurations. PoRTIA was passively shielded during its first flight from Palestine, Texas and actively shielded as a piggyback instrument on the GRIS balloon experiment during flights 2 and 3 from Alice Springs, Australia. PoRTIA flew twice during the Fall 1995 Alice Springs, Australia campaign using the thick GRIS NaI anticoincidence shield. A significant CdZnTe background reduction was achieved during the third flight with PoRTIA placed completely inside the GRIS shield and blocking crystal, and thus completely surrounded by 15 cm of NaI. These background results are presented and contributions from different background processes are discussed.

  13. Milagro Observations of Potential TeV Emitters

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Abeysekara, A. U.; Allen, B. T.; Aune, T.; Barber, A. S.; Berley, D.; Braun, J.; Chen, C.; Christopher, G. E.; DeYoung, T.; Dingus, B. L.; Ellsworth, R. W.; Gonzalez, M. M.; Goodman, J. A.; Hays, E.; Hoffman, C. M.; Huentemeyer, P. H.; Imran, A.; Kolterman, B. E.; Linnemann, J. T.; McEnery, J. E.; Morgan, T.; Mincer, A. I.; Nemethy, P.; Pretz, J.

    2014-01-01

    This paper reports the results from three targeted searches of Milagro TeV sky maps: two extragalactic point source lists and one pulsar source list. The first extragalactic candidate list consists of 709 candidates selected from the Fermi-LAT 2FGL catalog. The second extragalactic candidate list contains 31 candidates selected from the TeVCat source catalog that have been detected by imaging atmospheric Cherenkov telescopes (IACTs). In both extragalactic candidate lists Mkn 421 was the only source detected by Milagro. This paper presents the Milagro TeV flux for Mkn 421 and flux limits for the brighter Fermi- LAT extragalactic sources and for all TeVCat candidates. The pulsar list extends a previously published Milagro targeted search for Galactic sources. With the 32 new gamma-ray pulsars identified in 2FGL, the number of pulsars that are studied by both Fermi-LAT and Milagro is increased to 52. In this sample, we find that the probability of Milagro detecting a TeV emission coincident with a pulsar increases with the GeV flux observed by the Fermi-LAT in the energy range from 0.1 GeV to 100 GeV.

  14. Estimates of Te for continental regions using GOCE gravity

    NASA Astrophysics Data System (ADS)

    McKenzie, Dan; Yi, Weiyong; Rummel, Reiner

    2015-10-01

    Satellite-only gravity fields and surface gravity obtained from altimetric measurements now agree well at wavelengths greater than ∼180 km. Satellite gravity fields can therefore be used to estimate the elastic thickness Te in regions where surface observations are sparse. They are used for this purpose in a number of continental regions, of India, Africa, and Antarctica, where the topography is sufficiently rough, and also in regions of the USA, China, Australia and Siberia, where there are surface measurements. Estimates of Te for Antarctica depend on measurements of ice thickness, which are now available for much of the continent. Values of Te are obtained using two methods: from the admittance between the free air gravity and the topography, and from the coherence between Bouguer gravity anomalies and the topography. The first, but not the second, gives values of Te that are everywhere less than the seismogenic thickness. Where there is sufficient topography, estimates of Te from PreCambrian shields are all greater than 10 km and do not correlate with the lithospheric thickness. They are probably are governed by variations in crustal heat generation rates. Values for regions strongly affected by Phanerozoic tectonics are all less than 7 km, and all such regions are underlain by thin lithosphere.

  15. Dislocation Reduction in HgCdTe Mesa Structures Formed on CdTe/Si

    NASA Astrophysics Data System (ADS)

    Simingalam, Sina; Pattison, James; Chen, Yuanping; Wijewarnasuriya, Priyalal; Rao, Mulpuri V.

    2016-09-01

    Mercury cadmium telluride (MCT) epilayers have been grown on CdTe/Si using molecular beam epitaxy and 8- μm-deep mesa structures formed using plasma etching. Following previous work done on etching mesas and subjecting material to thermal cycle annealing, we set out to determine the limits and underlying physics of dislocation reduction in mesa-etched and annealed MCT. This paper describes the dependence of dislocation reduction on anneal time, cycle annealing, temperature, and etch depth. We show dislocation density reduction below 3 × 105 cm-2 in 10- μm-wide, long-bar mesas along the [0bar{1}1] orientation with only a 5-min anneal at 400°C.

  16. Metallurgy, thermal stability, and failure mode of the commercial Bi-Te-based thermoelectric modules.

    SciTech Connect

    Yang, Nancy Y. C.; Morales, Alfredo Martin

    2009-02-01

    Bi-Te-based thermoelectric (TE) alloys are excellent candidates for power generation modules. We are interested in reliable TE modules for long-term use at or below 200 C. It is known that the metallurgical characteristics of TE materials and of interconnect components affect the performance of TE modules. Thus, we have conducted an extensive scientific investigation of several commercial TE modules to determine whether they meet our technical requirements. Our main focus is on the metallurgy and thermal stability of (Bi,Sb){sup 2}(Te,Se){sup 3} TE compounds and of other materials used in TE modules in the temperature range between 25 C and 200 C. Our study confirms the material suite used in the construction of TE modules. The module consists of three major components: AlN cover plates; electrical interconnects; and the TE legs, P-doped (Bi{sub 8}Sb{sub 32})(Te{sub 60}) and N-doped (Bi{sub 37}Sb{sub 3})(Te{sub 56}Se{sub 4}). The interconnect assembly contains Sn (Sb {approx} 1wt%) solder, sandwiched between Cu conductor with Ni diffusion barriers on the outside. Potential failure modes of the TE modules in this temperature range were discovered and analyzed. The results show that the metallurgical characteristics of the alloys used in the P and N legs are stable up to 200 C. However, whole TE modules are thermally unstable at temperatures above 160 C, lower than the nominal melting point of the solder suggested by the manufacture. Two failure modes were observed when they were heated above 160 C: solder melting and flowing out of the interconnect assembly; and solder reacting with the TE leg, causing dimensional swelling of the TE legs. The reaction of the solder with the TE leg occurs as the lack of a nickel diffusion barrier on the side of the TE leg where the displaced solder and/or the preexisting solder beads is directly contact the TE material. This study concludes that the present TE modules are not suitable for long-term use at temperatures above 160 C due

  17. The half-life of {sup 131g,m}Te

    SciTech Connect

    Ruivo, J. C.; Zamboni, C. B.; Oliveira, J. R. B.; Heder Medina, Nilberto

    2013-05-06

    In this work, the half-lives of {sup 131m}Te and {sup 131g}Te were measured. Radioactive sources of {sup 131}Te were obtained using the {sup 130}Te(n,{gamma}){sup 131}Te nuclear reaction. These nuclear parameters have been determined with a better confidence and accuracy than previously available: 18.89 {+-} 0.11 min and 33.18 {+-} 0.13 h, respectively. These results are quite helpful for new calculations that attempt to describe the low-lying levels in {sup 131}I from the decay of {sup 131g,m}Te.

  18. Effect of solvents on morphologies of PbTe nanostructures: Controllable synthesis of hollow and solid PbTe nanocubes by a solvothermal method

    SciTech Connect

    Wang Wenzhong; Wang Lijuan; Zhou Qing

    2012-04-15

    We demonstrate a facile solvothermal route to grow hollow and solid PbTe nanocubes. The hollow PbTe nanocubes were successfully achieved when EtOH was used as solvent in the presence of nonionic polymer PEG, while the solid PbTe nanocubes were obtained when EG was used as solvent in the presence of PEG, whilst keeping the other experimental conditions constant. The results indicate that the solvents used in reaction system play a key role to determine the interior structure of PbTe nanocubes. On the basis of the experimental results and analysis, a possible growth mechanism has been discussed in detail for the hollow and solid PbTe nanocubes. - Graphical abstract: A facile solution-phase route has been developed to synthesize hollow and solid PbTe nanocubes. The possible growth mechanism of hollow and solid PbTe nanocubes was discussed in detail. Highlights: Black-Right-Pointing-Pointer A facile controllable route was described for hollow and solid PbTe nanocubes. Black-Right-Pointing-Pointer The hollow PbTe nanocubes were achieved using EtOH as solvent. Black-Right-Pointing-Pointer The solid PbTe nanocubes were obtained using EG as solvent. Black-Right-Pointing-Pointer The solvent played a key role for the formation of hollow and solid PbTe nanocubes.

  19. Nernst and Seebeck effects in HgTe/CdTe topological insulator

    SciTech Connect

    Zhang, Yuan; Song, Juntao; Li, Yu-Xian

    2015-03-28

    The Seebeck and Nernst effects in HgTe/CdTe quantum wells are studied using the tight-binding Hamiltonian and the nonequilibrium Green's function method. The Seebeck coefficient, S{sub c}, and the Nernst coefficient, N{sub c}, oscillate as a function of E{sub F}, where E{sub F} is the Fermi energy. The Seebeck coefficient shows peaks when the Fermi energy crosses the discrete transverse channels, and the height of the nth peak of the S{sub c} is [ln2/(1/2 +|n|)] for E{sub F} > 0. For the case E{sub F} < 0, the values of the peaks are negative, but the absolute values of the first five peaks are the same as those for E{sub F} > 0. The 6th peak of S{sub c} reaches the value [ln2/1.35] due to a higher density of states. When a magnetic field is applied, the Nernst coefficient appears. However, the values of the peaks for N{sub c} are all positive. For a weak magnetic field, the temperature suppresses the oscillation of the Seebeck and Nernst coefficients but increases their magnitude. For a large magnetic field, because of the highly degenerate Landau levels, the peaks of the Seebeck coefficient at position E{sub F}=−12, 10, 28meV, and Nernst coefficient at E{sub F}=−7, 10meV are robust against the temperature.

  20. Preparation and properties of evaporated CdTe films compared with single crystal CdTe. Progress report No. 1, October 1, 1980-January 31, 1981

    SciTech Connect

    Bube, R. H.

    1981-01-01

    This program is concerned with the investigation of the materials properties of CdTe thin films deposited by hot-wall vacuum evaporation and of CdTe single crystalline material, particularly those relevant to solar cell applications in which CdTe is the absorbing member. Progress is reported on: (a) an evaluation of CdTe homojunctions formed by HWVE of CdTe by Walter Huber at the laboratory of Dr. Adolfo Lopez-Otero at the Institut fuer Physik of the University of Linz, using single crystal p-type CdTe from Stanford as a substrate; (b) the design and construction of a HWVE apparatus at Stanford; and (c) properties of grain boundaries in large grain polycrystalline CdTe.

  1. Growth, steady-state, and time-resolved photoluminescence study of CdTe/MgCdTe double heterostructures on InSb substrates using molecular beam epitaxy

    SciTech Connect

    DiNezza, Michael J.; Liu, Shi; Kirk, Alexander P.; Zhang, Yong-Hang; Zhao, Xin-Hao

    2013-11-04

    CdTe/MgCdTe double heterostructures (DHs) are grown on InSb substrates using molecular beam epitaxy and reveal strong photoluminescence with over double the intensity of a GaAs/AlGaAs DH with an identical layer structure design grown on GaAs. Time-resolved photoluminescence of the CdTe/MgCdTe DH gives a Shockley-Read-Hall recombination lifetime of 86 ns, which is more than one order of magnitude longer than that of typical polycrystalline CdTe films. These findings indicate that monocrystalline CdTe/MgCdTe DHs effectively reduce surface recombination, have limited nonradiative interface recombination, and are promising for solar cells that could reach power conversion efficiencies similar to that of GaAs.

  2. Computation of charged current neutrino-Te reactions cross sections

    NASA Astrophysics Data System (ADS)

    Tsakstara, V.; Kosmas, T. S.; Sinatkas, J.

    2016-08-01

    Neutrino-nucleus reactions, involving both neutral current (NC) and charged current (CC) interactions are important probes in modern neutrino physics searches. In the present work, we study the concrete CC reactions 130 Te(vℓ,ℓ-)130 I and 130 Te(ṽℓ,ℓ+)130Sb which are of current experimental interest for the CUORE and COBRA experiments operating at Gran Sasso underground laboratory in Italy. The nuclear wave functions for the required initial and final nuclear states are derived by employing the proton-neutron (p-n) quasi-particle random phase approximation (QRPA) which has been previously tested in our neutral-current v-nucleus studies for Te isotopes.

  3. Photoluminescence and photocurrent measurement in monolayer MoTe2

    NASA Astrophysics Data System (ADS)

    Bie, Ya-Qing; Grosso, Gabriele; Efetov, Dmitri; Navarro-Moratalla, Efren; Englund, Dirk; Jarillo-Herrero, Pablo

    2015-03-01

    2D transition metal dichalcogenides (2D-TMD), such as MoS2, WS2, WSe2, MoSe2, have been verified with many remarkable physical properties including the indirect to direct band transition and valley dependent spin polarization. As one of the 2D-TMD family member, monolayer 2H-MoTe2 is proved to be a direct bandgap semicoductor with strong spin orbital interaction and a significantly low bandgap ~ 1.10eV. However, the effect of the enhanced coulomb interaction arising from reduced dielectric screening in monolayer MoTe2 has yet to be experimentally demonstrated. Here we employ the near infrared (NIR) photoluminescence and photocurrent measurement to study the quasi-particle interactions at different carrier concentration. This study sheds light on manipulating excitons in MoTe2 and designing highly efficient NIR optoelectronic devices.

  4. Robust Excitons and Trions in Monolayer MoTe2.

    PubMed

    Yang, Jiong; Lü, Tieyu; Myint, Ye Win; Pei, Jiajie; Macdonald, Daniel; Zheng, Jin-Cheng; Lu, Yuerui

    2015-06-23

    Molybdenum telluride (MoTe2) has emerged as a special member in the family of two-dimensional transition metal dichalcogenide semiconductors, owing to the strong spin-orbit coupling and relatively small energy gap, which offers new applications in valleytronic and excitonic devices. Here we successfully demonstrated the electrical modulation of negatively charged (X(-)), neutral (X(0)), and positively charged (X(+)) excitons in monolayer MoTe2 via photoluminescence spectroscopy. The binding energies of X(+) and X(-) were measured to be ∼24 and ∼27 meV, respectively.The exciton binding energy of monolayer MoTe2 was measured to be 0.58 ± 0.08 eV via photoluminescence excitation spectroscopy, which matches well with our calculated value of 0.64 eV. PMID:26039551

  5. A 3 TeV Muon Collider Lattice Design

    SciTech Connect

    Alexahin, Y.; Gianfelice-Wendt, E.; /Fermilab

    2012-05-01

    A new lattice for 3 TeV c.o.m. energy with {beta}* = 5mm was developed which follows the basic concept of the earlier 1.5 TeV design but uses quad triplets for the final focus in order to keep the maximum magnet strength and aperture close to those in 1.5 TeV case. Another difference is employment of combined-function magnets with the goal to lower heat deposition in magnet cold mass and to eliminate bending field free regions which produce 'hot spots' of neutrino radiation that can be an issue at higher energy. The proposed lattice is shown to satisfy the requirements on luminosity, dynamic aperture and momentum acceptance.

  6. Giant Anharmonic Phonon Scattering in PbTe

    SciTech Connect

    Delaire, Olivier A; Ma, Jie; Marty, Karol J; May, Andrew F; McGuire, Michael A; Singh, David J; Lumsden, Mark D; Sales, Brian C; Du, Mao-Hua; Ehlers, Georg; Podlesnyak, Andrey A

    2011-01-01

    Understanding the microscopic processes affecting the bulk thermal conductivity is crucial to develop more efficient thermoelectric materials. PbTe is currently one of the leading thermoelectric materials, largely thanks to its low thermal conductivity. However, the origin of this low thermal conductivity in a simple rocksalt structure has so far been elusive. Using a combination of inelastic neutron scattering measurements and first-principles computations of the phonons, we identify a strong anharmonic coupling between the ferroelectric transverse optic (TO) mode and the longitudinal acoustic (LA) modes in PbTe. This interaction extends over a large portion of reciprocal space, and directly affects the heat-carrying LA phonons. The LA-TO anharmonic coupling is likely to play a central role in explaining the low thermal conductivity of PbTe. The present results provide a microscopic picture of why many good thermoelectric materials are found near a lattice instability of the ferroelectric type.

  7. Computation of charged current neutrino-Te reactions cross sections

    NASA Astrophysics Data System (ADS)

    Tsakstara, V.; Kosmas, T. S.; Sinatkas, J.

    2016-08-01

    Neutrino-nucleus reactions, involving both neutral current (NC) and charged current (CC) interactions are important probes in modern neutrino physics searches. In the present work, we study the concrete CC reactions 130 Te(vℓ,ℓ‑)130 I and 130 Te(ṽℓ,ℓ+)130Sb which are of current experimental interest for the CUORE and COBRA experiments operating at Gran Sasso underground laboratory in Italy. The nuclear wave functions for the required initial and final nuclear states are derived by employing the proton-neutron (p-n) quasi-particle random phase approximation (QRPA) which has been previously tested in our neutral-current v-nucleus studies for Te isotopes.

  8. Anomalous thermoelectricity in strained Bi2Te3 films.

    PubMed

    Liu, Yucong; Chen, Jiadong; Deng, Huiyong; Hu, Gujin; Zhu, Daming; Dai, Ning

    2016-01-01

    Bi2Te3-based alloys have been intensively used for thermoelectric coolers and generators due to their high Seebeck coefficient S. So far, efforts to improve the S have been made mostly on changing the structures and components. Herein, we demonstrate an anomalous thermoelectricity in strained Bi2Te3 films, i.e., the value of S is obviously changed after reversing the direction of temperature gradient. Further theoretical and experimental analysis shows that it originates from the coupling of thermoelectric and flexoelectric effects caused by a stress gradient. Our finding provides a new avenue to adjust the S of Bi2Te3-based thermoelectric materials through flexoelectric polarization. PMID:27600406

  9. Td-MoTe2: A possible topological superconductor

    NASA Astrophysics Data System (ADS)

    Luo, X.; Chen, F. C.; Zhang, J. L.; Pei, Q. L.; Lin, G. T.; Lu, W. J.; Han, Y. Y.; Xi, C. Y.; Song, W. H.; Sun, Y. P.

    2016-09-01

    We measured the magnetoresistivity properties of Td-MoTe2 single crystal under the magnetic field up to 33 T. By analyzing the Shubnikov-de Haas oscillations of the longitudinal resistance Δρxx, a linear dependence of the Landau index n on 1/B is obtained. The intercept of the Landau index plot is 0.47, which is between 3/8 and 1/2. This clearly reveals a nontrivial π Berry's phase, which is a distinguished feature of the surface state in Td-MoTe2 single crystal. Accompanied by the superconductivity observed at TC = 0.1 K, Td-MoTe2 may be a promising candidate of the topological superconductor and opens a door to study the relationship between the superconductivity and topological physics.

  10. Anomalous thermoelectricity in strained Bi2Te3 films

    PubMed Central

    Liu, Yucong; Chen, Jiadong; Deng, Huiyong; Hu, Gujin; Zhu, Daming; Dai, Ning

    2016-01-01

    Bi2Te3-based alloys have been intensively used for thermoelectric coolers and generators due to their high Seebeck coefficient S. So far, efforts to improve the S have been made mostly on changing the structures and components. Herein, we demonstrate an anomalous thermoelectricity in strained Bi2Te3 films, i.e., the value of S is obviously changed after reversing the direction of temperature gradient. Further theoretical and experimental analysis shows that it originates from the coupling of thermoelectric and flexoelectric effects caused by a stress gradient. Our finding provides a new avenue to adjust the S of Bi2Te3-based thermoelectric materials through flexoelectric polarization. PMID:27600406

  11. Phenomenology of TeV little string theory from holography.

    PubMed

    Antoniadis, Ignatios; Arvanitaki, Asimina; Dimopoulos, Savas; Giveon, Amit

    2012-02-24

    We study the graviton phenomenology of TeV little string theory by exploiting its holographic gravity dual five-dimensional theory. This dual corresponds to a linear dilaton background with a large bulk that constrains the standard model fields on the boundary of space. The linear dilaton geometry produces a unique Kaluza-Klein graviton spectrum that exhibits a ~TeV mass gap followed by a near continuum of narrow resonances that are separated from each other by only ~30 GeV. Resonant production of these particles at the LHC is the signature of this framework that distinguishes it from large extra dimensions, where the Kaluza-Klein states are almost a continuum with no mass gap, and warped models, where the states are separated by a TeV.

  12. CdZnTe photodiode arrays for medical imaging

    SciTech Connect

    Sudharsanan, R.; Parodos, T.; Karam, N.H.; Ruzin, A.; Nemirovsky, Y.

    1996-08-01

    In this paper, we report on the design, fabrication, and performance of the first CdZnTe Schottky photodiode arrays for radiation detection. High pressure Bridgman-grown CdZnTe substrates with bulk resistivities in the range 10{sup 8} to 10{sup 10} ohm-cm were used. CdZnTe Schottky photodiodes were formed with In and Ti/Au contacts. Diode arrays with pixel sizes from 1000 x 1000 {mu}m to 100 x 100 {mu}m were fabricated. The diode`s I-V characteristics exhibited low leakage current and high bulk resistivity; leakage current decreased as diode pixel size was reduced. Response of these detector arrays to high energy photons was uniform and their energy resolution improved with smaller pixel size. 14 refs., 9 figs.

  13. Resetting the Defect Chemistry in CdTe

    SciTech Connect

    Metzger, Wyatt K.; Burst, James; Albin, David; Colegrove, Eric; Moseley, John; Duenow, Joel; Farrell, Stuart; Moutinho, Helio; Reese, Matt; Johnston, Steve; Barnes, Teresa; Perkins, Craig; Guthrey, Harvey; Al-Jassim, Mowafak

    2015-06-14

    CdTe cell efficiencies have increased from 17% to 21% in the past three years and now rival polycrystalline Si [1]. Research is now targeting 25% to displace Si, attain costs less than 40 cents/W, and reach grid parity. Recent efficiency gains have come largely from greater photocurrent. There is still headroom to lower costs and improve performance by increasing open-circuit voltage (Voc) and fill factor. Record-efficiency CdTe cells have been limited to Voc <; 880 mV, whereas GaAs can attain Voc of 1.10 V with a slightly smaller bandgap [2,3]. To overcome this barrier, we seek to understand and increase lifetime and carrier concentration in CdTe. In polycrystalline structures, lifetime can be limited by interface and grain-boundary recombination, and attaining high carrier concentration is complicated by morphology.

  14. Hadron supercolliders: The 1-TeV scale and beyond

    SciTech Connect

    Quigg, C.

    1990-08-10

    Greater understanding of the connection between the weak and electromagnetic interactions is central to progress in elementary-particle physics. A definitive exploration of the mechanism for electroweak symmetry breaking will require collisions between fundamental constituents at energies on the order of 1 TeV. This goal drives the design of high-energy, high-luminosity hadron colliders that will be commissioned during the next decade, but by no means completely defines their scientific potential. These three lectures are devoted to a review of the standard-model issues that motivated an experimental assault on the 1-TeV scale, an introduction to the machines and the experimental environment they will present, and a survey of possibilities for measurement and discovery with a multi-TeV hadron collider. 72 refs., 29 figs.

  15. Optical properties of ZnSe(Te) with ytterbium impurity.

    PubMed

    Makhniy, Viktor P; Horley, Paul P; Vorobiev, Yuri V; Kinzerska, Oksana V

    2016-04-20

    We report the results on infrared transmission measurements of non-doped and tellurium-doped crystals of zinc selenide grown from the melt. It was found that non-doped samples feature high transmission (50%-60%) for the wavelengths of 1-22 μm. The efficient scintillating crystals of ZnSe(Te) are almost opaque for λ>7  μm. Doping these samples with ytterbium from the gas phase does not achieve any significant transmission increase for non-doped ZnSe samples in the spectral range of 1-22 μm. However, it considerably increases (up to 50%) transmission for doped ZnSe(Te) at the wavelengths λ>10  μm. These optical peculiarities were analyzed taking into account restructurization of point defect ensembles created by Te and Yb impurities. PMID:27140112

  16. Diffusion length in CdTe by measurement of photovoltage spectra in CdS/CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Toušek, J.; Kindl, D.; Toušková, J.; Dolhov, S.; Poruba, A.

    2001-01-01

    Modified method of surface photovoltage (SPV), spectral response measurement, and constant photocurrent method (CPM) were applied to thin film CdS/CdTe solar cells with the aim of finding diffusion length of minority carriers (L) in the CdTe material. The SPV signal was theoretically calculated without constraints of absorption coefficients for the incident radiation and thickness of the sample assuming one space charge region (SCR) located on the CdS/CdTe interface. In addition to the diffusion length, the SPV is a function of the surface recombination velocity and the parameters of the SCR, which complicates the evaluation. Illuminating the back side of the solar cell (without ohmic contact) we obtain a photovoltage spectrum predominantly influenced by the diffusion length. On the other hand, the standard measurement using light penetrating from the CdS side strongly depends on the thickness of the SCR. The small signal approximation model presented here successfully explains both measured spectra and permits extraction of the diffusion length of minority carriers and thickness of the SCR in CdTe absorber. The CPM is used for determination of absorption coefficients in the CdTe layer. The absorption of this material depends on its preparation and must be known for correct evaluation of experimental data.

  17. Nanosized Thin SnO2 Layers Doped with Te and TeO2 as Room Temperature Humidity Sensors

    PubMed Central

    Georgieva, Biliana; Podolesheva, Irena; Spasov, Georgy; Pirov, Jordan

    2014-01-01

    In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques—SEM, EDS in SEM, TEM, SAED, AES and electrical measurements—are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio RSn/Te and the evaporation conditions. It is shown that as-deposited layers with RSn/Te ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature—very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers' surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties. PMID:24854359

  18. Band Degeneracy, Low Thermal Conductivity, and High Thermoelectric Figure of Merit in SnTe-CaTe Alloys

    NASA Astrophysics Data System (ADS)

    Al Rahal Al Orabi, R.; Mecholsky, N.; Hwang, J. P.; Kim, W.; Rhyee, J. S.; Wee, D.; Fornari, M.

    Pure lead-free SnTe has limited thermoelectric potentials because of the low Seebeck coeffcients and the relatively large thermal conductivity. In this study, we provide experimental evidence and theoretical understanding that alloying SnTe with Ca greatly improves the transport properties leading to ZT of 1.35 at 873 K, the highest ZT value so far reported for singly doped SnTe materials. The introduction of Ca (0-9%) in SnTe induces multiple effects: (1) Ca replaces Sn and reduces the hole concentration due to Sn vacancies, (2) the energy gap increases limiting the bipolar transport, (3) several bands with larger effective masses become active in transport, and (4) the lattice thermal conductivity is reduced of about 70% due to the contribution of concomitant scattering terms associated with the alloy disorder and the presence of nanoscale precipitates. An effciency of 10% (for ΔT = 400 K) was predicted for high temperature thermoelectric power generation using SnTe-based n- and p-type materials.

  19. Nanosized thin SnO₂ layers doped with Te and TeO₂ as room temperature humidity sensors.

    PubMed

    Georgieva, Biliana; Podolesheva, Irena; Spasov, Georgy; Pirov, Jordan

    2014-05-21

    In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques-SEM, EDS in SEM, TEM, SAED, AES and electrical measurements-are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio R(Sn/Te) and the evaporation conditions. It is shown that as-deposited layers with R(Sn/Te) ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature-very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers' surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.

  20. CdTe nBn photodetectors with ZnTe barrier layer grown on InSb substrates

    NASA Astrophysics Data System (ADS)

    He, Zhao-Yu; Campbell, Calli M.; Lassise, Maxwell B.; Lin, Zhi-Yuan; Becker, Jacob J.; Zhao, Yuan; Boccard, Mathieu; Holman, Zachary; Zhang, Yong-Hang

    2016-09-01

    We have demonstrated an 820 nm cutoff CdTe nBn photodetector with ZnTe barrier layer grown on an InSb substrate. At room temperature, under a bias of -0.1 V, the photodetector shows Johnson and shot noise limited specific detectivity (D*) of 3 × 1013 cm Hz1/2/W at a wavelength of 800 nm and 2 × 1012 cm Hz1/2/W at 200 nm. The D* is optimized by using a top contact design of ITO/undoped-CdTe. This device not only possesses nBn advantageous characteristics, such as generation-recombination dark current suppression and voltage-bias-addressed two-color photodetection, but also offers features including responsivity enhancements by deep-depletion and by using a heterostructure ZnTe barrier layer. In addition, this device provides a platform to study nBn device physics at room temperature, which will help us to understand more sophisticated properties of infrared nBn photodetectors that may possess a large band-to-band tunneling current at a high voltage bias, because this current is greatly suppressed in the large-bandgap CdTe nBn photodetector.

  1. MBE HgCdTe for HDVIP Devices: Horizontal Integration in the US HgCdTe FPA Industry

    NASA Astrophysics Data System (ADS)

    Aqariden, F.; Elsworth, J.; Zhao, J.; Grein, C. H.; Sivananthan, S.

    2012-10-01

    Molecular beam epitaxy (MBE) growth of HgCdTe offers the possibility of fabricating multilayer device structures with an almost unlimited choice of infrared sensor designs for focal-plane array (FPA) fabrication. HgCdTe offers two major advantages that explain its dominance in the infrared photon detector marketplace. The thermal generation rate per unit volume of the material is lower and the quantum efficiency for photon absorption in the infrared is higher in HgCdTe than in any competing material—it yields devices with quantum efficiencies as high as 0.99. Recently, EPIR Technologies and DRS Infrared Technologies agreed to collaborate and examine: (i) the feasibility of employing MBE HgCdTe in the fabrication of high-density vertically interconnected photodiodes (HDVIPs), which are usually fabricated with liquid-phase epitaxy material, and (ii) the potential benefits of horizontal integration, with EPIR supplying the MBE materials to DRS for device and array fabrication. The team designed and developed passivation-absorber-passivation structures that are heavily used by DRS. This paper provides an overview of the characteristics of HDVIP devices and arrays fabricated from MBE HgCdTe and the anticipated advantages of horizontal integration in the industry. Material growth, device fabrication, and test results are presented.

  2. Ferromagnetism below 10K in Mn-doped BiTe

    NASA Astrophysics Data System (ADS)

    Bos, J. W. G.; Lee, M.; Morosan, E.; Zandbergen, H. W.; Lee, W. L.; Ong, N. P.; Cava, R. J.

    2006-11-01

    Ferromagnetism is observed below 10K in [Bi0.75Te0.125Mn0.125]Te . This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3 blocks. These TeBi antisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the solubility is limited to x=0.067 , while the latter has xmax=0.125 . The magnetism in [Bi1-xMnx]Te changes little with x , while that for [Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x>0.067 . Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples.

  3. Photorefractive effect in CdMnTe:V Crystal

    NASA Technical Reports Server (NTRS)

    Pour, K. M.; Chattopadahyay, K.; Chen, H.; Chen, K. T.; Morgan, S.; Burger, A.

    1998-01-01

    We present two-wave mixing result obtained with a CdMnTe:V crystal. A photorefractive gain coefficient of 0.20 /cm was observed at 633 nm with the signal-to-pump ratio being of the order of 10(exp -3). This crystal was grown by vertical Bridgman Technique and doped with Vanadium during the growth. The crystal were of good optical quality and showed high resistivity. Room temperature absorption and low temperature photoluminescence studies comparing the band edge and defect center at the doped and undoped CdMnTe crystal will also be discussed.

  4. Synthesis and characterization of Bi-Te-Se thermoelectric materials

    SciTech Connect

    Tripathi, S. K.; Kumari, Ankita; Ridhi, R.; Kaur, Jagdish

    2015-08-28

    Bismuth Telluride (Bi{sub 2}Te{sub 3}) and its related alloys act as a promising thermoelectric material and preferred over other thermoelectric materials due to their high stability and efficiency under ambient conditions. In the present work, we have reported economical, environment friendly and low-temperature aqueous chemical method for the synthesis of Bi-Se-Te alloy. The prepared samples are characterized by X-Ray Diffraction to investigate the structural properties and UV-Visible spectroscopy for the spectroscopic analysis. The absorption spectrum reveals the sensitivity in the ultraviolet as well as in visible region.

  5. BOREAS TE-5 Tree Ring and Carbon Isotope Ratio Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected several data sets to investigate the vegetation-atmosphere CO2 and H2O exchange processes. These data include tree ring widths and cellulose carbon isotope data from coniferous trees collected at the BOREAS NSA and SSA in 1993 and 1994 by the BOREAS TE-5 team. Ring width data are provided for both Picea mariana and Pinus banksiana. The carbon isotope data are provided only for Pinus banksiana. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  6. Substructure and strong interactions at the TeV scale

    SciTech Connect

    Peskin, M.E.

    1985-12-01

    A review is given of the current status of the three main theoretical ideas relevant to strong-interaction 1 TeV physics. These are composite vector bosons, Higgs bosons (''Technicolor''), and matter fermions. All involve the assumption that some object which is assumed to be fundamental in the standard model actually has dynamical internal structure. Complex, mechanistic models of the new physics are discussed. A brief digression is then made on how the weak interaction allows probing for this new structure. Direct manifestations of new 1 TeV strong interactions are discussed. 125 refs., 18 figs. (LEW)

  7. Formation of ZnTe:Cu/Ti Contacts at High Temperature for CdS/CdTe Devices (Presentation)

    SciTech Connect

    Gessert, T. A.; Asher, S.; Johnston, S.; Duda, A.; Young, M. R.; Moriarty, T.

    2006-05-01

    The conclusions of this report are that Cu diffusion from a ZnTe:Cu contact causes good and bad things. The good (Cu in CdS < low 10{sup 18} cm{sup -3})--increase in CdTe N{sub A}-N{sub D} that leads to V{sub oc} and FF improvement. The bad (Cu in CdS > low 10{sup 18} cm{sup -3})--(1) possibly decreased of shunt resistance (?); (2) depletion width in CdTe can become too narrow for optimum current collection at J{sub MPP}; (3) donor reduction in CdS (significant FF loss in LIV); and (4) excessive Cu diffusion into CdS readily observed by red-light bias QE.

  8. Indication of Te segregation in laser-irradiated ZnTe observed by in situ coherent-phonon spectroscopy

    SciTech Connect

    Shimada, Toru; Kamaraju, N.; Frischkorn, Christian; Wolf, Martin; Kampfrath, Tobias

    2014-09-15

    We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80 MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6 THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material.

  9. Effects of CdTe growth conditions and techniques on the efficiency limiting defects and mechanisms in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Rohatgi, A.; Chou, H. C.; Jokerst, N. M.; Thomas, E. W.; Ferekides, C.; Kamra, S.; Feng, Z. C.; Dugan, K. M.

    1996-01-01

    CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO2/glass substrates using close-spaced sublimation (CSS) and metalorganic chemical vapor deposition (MOCVD). Te/Cd mole ratio was varied in the range of 0.02 to 6 in the MOCVD growth ambient in an attempt to vary the native defect concentration. Polycrystalline CdTe layers grown by MOCVD and CSS both showed average grain size of about 2 μm. However, the CdTe films grown by CSS were found to be less faceted and more dense compared to the CdTe grown by MOCVD. CdTe growth techniques and conditions had a significant impact on the electrical characteristics of the cells. The CdTe solar cells grown by MOCVD in the Te-rich growth condition and by the CSS technique gave high cell efficiencies of 11.5% and 12.4%, respectively, compared to 6.6% efficient MOCVD cells grown in Cd-rich conditions. This large difference in efficiency is explained on the basis of (a) XRD measurements which showed a higher degree of atomic interdiffusion at the CdS/CdTe interface in high performance devices, (b) Raman measurements which endorsed more uniform and preferred grain orientation by revealing a sharp CdTe TO mode in the high efficiency cells, and (c) carrier transport mechanism which switched from tunneling/interface recombination to depletion region recombination in the high efficiency cells. In this study, Cu/Au layers were evaporated on CdTe for the back contact. Lower efficiency of the Te-rich MOCVD cells, compared to the CSS cells, was attributed to contact related additional loss mechanisms, such as Cd pile-up near Cu/CdTe interface which can give rise to Cd-vacancy defects in the bulk, and higher Cu concentration in the CdTe layer which can cause shunts in the device. Finally, SIMS measurements on the CdTe films of different crystallinity and grain size confirmed that grain boundaries are the main conduits for Cu migration into the CdTe film. Thus larger CdTe grain size or lower grain boundary area per unit volume

  10. Growth and structure of Cd1-xDyxTe crystals

    NASA Astrophysics Data System (ADS)

    Sochinskii, Nikolai V.; Rubio, Sandra; Plaza, José Luis; Diéguez, Ernesto

    2016-09-01

    CdTe crystals doped with dysprosium were grown by the vertical Bridgman method to explore the possibility of obtaining Cd1-xDyxTe ternary compound. The growth was carried out from the Cd1-xDyxTe pre-synthesized feeds with the charge composition in the range of x=0.001-0.05. The as-grown crystals were studied by scanning electron microscopy, X-ray diffraction and optical spectroscopy. Experimental findings testify that the Cd1-xDyxTe crystals have the homogeneous cubic structure similar to CdTe in the narrow composition range of x≈0-0.01. At higher compositions x≥0.01, the crystals become a mixture of several phases such as CdTe host, Dy2Te3 textures and DyTe-rich inclusions.

  11. Intrinsic complexity of the melt-quenched amorphous Ge2Sb2Te5 memory alloy

    NASA Astrophysics Data System (ADS)

    Krbal, M.; Kolobov, A. V.; Fons, P.; Tominaga, J.; Elliott, S. R.; Hegedus, J.; Uruga, T.

    2011-02-01

    Through the use of first-principles Ge K-edge XANES simulations we demonstrate that the structure of melt-quenched amorphous Ge-Sb-Te is intrinsically complex and is a mixture of Ge(3):Te(3) and Ge(4):Te(2) configurations in comparable concentrations, in contrast to the as-deposited amorphous phase that is dominated by the Ge(4):Te(2) configurations. The reasons for Ge-Te polyvalency are discussed and it is argued that both configurations are compatible with the Mott 8-N rule and the definition of an ideal amorphous solid. The near-perfect Te-Te distance match between the two major configurations accounts for the high cyclability of phase-change materials. Stable compositions in the Ge-Sb-Te system are suggested.

  12. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    DOE PAGES

    Yang, Ji -Hui; Yin, Wan -Jian; Park, Ji -Sang; Metzger, Wyatt; Wei, Su -Huai

    2016-01-25

    In this study, Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance ptype doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu willmore » prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.« less

  13. APT mass spectrometry and SEM data for CdTe solar cells

    DOE PAGES

    Li, Chen; Paudel, Naba R.; Yan, Yanfa; Pennycook, Stephen J.; Poplawsky, Jonathan D.; Guo, Wei

    2016-03-16

    Atom probe tomography (APT) data acquired from a CAMECA LEAP 4000 XHR for the CdS/CdTe interface for a non-CdCl2 treated CdTe solar cell as well as the mass spectrum of an APT data set including a GB in a CdCl2-treated CdTe solar cell are presented. Scanning electron microscopy (SEM) data showing the evolution of sample preparation for APT and scanning transmission electron microscopy (STEM) electron beam induced current (EBIC) are also presented. As a result, these data show mass spectrometry peak decomposition of Cu and Te within an APT dataset, the CdS/CdTe interface of an untreated CdTe solar cell, preparationmore » of APT needles from the CdS/CdTe interface in superstrate grown CdTe solar cells, and the preparation of a cross-sectional STEM EBIC sample.« less

  14. CdTe Thin Film Solar Cells and Modules Tutorial; NREL (National Renewable Energy Laboratory)

    SciTech Connect

    Albin, David S.

    2015-06-13

    This is a tutorial presented at the 42nd IEEE Photovoltaics Specialists Conference to cover the introduction, background, and updates on CdTe cell and module technology, including CdTe cell and module structure and fabrication.

  15. Correlation Between Bands Structure and Magneto-Transport Properties in n-type HgTe/CdTe Superlattice with Relatively Thin CdTe Barrier

    SciTech Connect

    Braigue, M.; Nafidi, A.; Chaib, H.; Tirbiyine, A.; Hemine, J.; Idbaha, A.; Boulkassim, A.; El Gouti, T.; Massaq, M.; Talwar, Devki N.; SrinivasaVinod, M.

    2011-12-26

    Theoretical calculations of the electronic properties of n-type HgTe/CdTe superlattices (SLs) in the envelope function formalism have provided a reasonable agreement with the experimental data on the magneto-transport behavior. Numerical results of the band energies E(d{sub 2}), E(k{sub z}) and E(k{sub p}) in the direction of growth and in plane of the SLs predict that the system retains semiconductor characteristics for d{sub 1}/d{sub 2} = 2.69 and d{sub 2}<10 nm. For d{sub 2} = 3.2 nm the calculated effective band gap (E{sub g}({Gamma},4.2 K) = 48 meV) suggests that the material sample is a two-dimensional modulated nanostructure and a potential candidate to be used for the far infrared detection applications.

  16. Phase equilibria and the thermodynamic properties of saturated solid solutions of BiTeI, Bi2TeI, and Bi4TeI1.25 compounds of the AgI-Bi-Bi2Te3-BiTeI system

    NASA Astrophysics Data System (ADS)

    Moroz, M. V.; Prokhorenko, M. V.

    2016-07-01

    The phase equilibria of the Ag-Bi-Te-I system in the part AgI-Bi-Bi2Te3-BiTeI is studied in the interval of 500-540 K by means of physicochemical analysis. Thermodynamic properties of phases are determined via EMF. Potential-forming processes occur in electrochemical cells (ECCs) of the C|Ag|glass Ag3GeS3I|D|C structure (where C denotes inert (graphite) electrodes; Ag, D denotes ECC electrodes; D denotes four-phase alloys of the AgI-Bi-Bi2Te3-BiTeI system; and Ag3GeS3I glass is the selective Ag+ conducting membrane). Linear dependences of the EMFs of cells E(T) in the interval of 505-535 K are used to calculate the values of the thermodynamic functions of BiTeI, Bi2TeI, and Bi4TeI1.25 phases saturated over silver.

  17. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae.

    PubMed

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-01-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications. PMID:27469931

  18. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae

    PubMed Central

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-01-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications. PMID:27469931

  19. Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae

    NASA Astrophysics Data System (ADS)

    Ding, Keyuan; Rao, Feng; Lv, Shilong; Cheng, Yan; Wu, Liangcai; Song, Zhitang

    2016-07-01

    Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications.

  20. Development of ion-implantation confined, shallow mesa stripe (Pn,Sn)Te/Pb(Te,Se) DH laser diodes

    NASA Technical Reports Server (NTRS)

    Fonstad, C. G.; Harton, A.; Jiang, Y.-N.; Appelman, H.

    1983-01-01

    Preliminary results of a program to develop ion implantation confined, shallow mesa stripe (Pb,Sn)Te laser diodes are presented. The practicality of using a shallow mesa stripe to produce single mode laser output and to increase the single mode tuning range are demonstrated. The first results of p-type ion implantation in the lead-tin salts are also reported. It is shown that sodium and lithium both can be used to convert n-type Pb(Te,Se) to p-type. The implant and anneal procedures are described, and electrical characteristics of Li-implanted layers are presented.

  1. Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials

    SciTech Connect

    Kim, K.H.; Bolotnikov, A.E.; Camarda, G.S.; Marchini, L.; Yang, G.; Hossain, A.; Cui, Y.; Xu, L.; and James, R.B.

    2010-08-01

    Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.

  2. Modelling of a Cd1-xZnxTe/ZnTe Single Quantum Well for Laser Diodes

    NASA Astrophysics Data System (ADS)

    Dehimi, Sai˙d.; Dehimi, Lakhdar; Asar, Tarik; Özçelik, Süleyman

    2016-10-01

    In this paper, the carrier density, temperature and quantum well width effect have been investigated for the optical gain for a Cd1-xZnxTe/ZnTe Zinc-blend strained quantum well structure. The device emits laser radiations in green-yellow-orange. Our results showed that the optical gain significantly increases with the increasing of the carrier density. It also increases with the decreasing of the Zn concentration, the well width and the temperature. In addition, the optimal threshold current density values were determined for three alloy compositions as 0.7, 0.8 and 0.9.

  3. Stark spectroscopy of CdTe and CdMnTe quantum dots embedded in n-i-p diodes

    SciTech Connect

    Kłopotowski, Ł. Fronc, K.; Wojnar, P.; Wiater, M.; Wojtowicz, T.; Karczewski, G.

    2014-05-28

    We investigate charging effects in CdTe and Cd{sub 1−x}Mn{sub x}Te quantum dots embedded in n-i-p diodes. The tunneling of holes out of the dots at reverse bias and hole injection at forward bias control the dot charge state and allow for its electric field tuning. Furthermore, we analyze the Stark shifts of the photoluminescence transitions and evaluate the effect of the electric field on the binding of the observed excitonic complexes. We find that the binding can be strengthened or weakened depending on the zero-field alignment of the electron and hole wavefunctions.

  4. Stark spectroscopy of CdTe and CdMnTe quantum dots embedded in n-i-p diodes

    NASA Astrophysics Data System (ADS)

    Kłopotowski, Ł.; Fronc, K.; Wojnar, P.; Wiater, M.; Wojtowicz, T.; Karczewski, G.

    2014-05-01

    We investigate charging effects in CdTe and Cd1-xMnxTe quantum dots embedded in n-i-p diodes. The tunneling of holes out of the dots at reverse bias and hole injection at forward bias control the dot charge state and allow for its electric field tuning. Furthermore, we analyze the Stark shifts of the photoluminescence transitions and evaluate the effect of the electric field on the binding of the observed excitonic complexes. We find that the binding can be strengthened or weakened depending on the zero-field alignment of the electron and hole wavefunctions.

  5. Thermoelectric properties of Tl-doped PbTeSe crystals grown by directional solidification

    NASA Astrophysics Data System (ADS)

    Su, Ching-Hua

    2016-04-01

    Three Tl-doped PbTe and two Tl-doped PbTeSe crystals were grown by vertical un-seeded directional solidification method. Among them, two Tl-doped PbTe ingots, with starting composition of (Pb0.99Tl0.01)Te, were grown under Pb or Te pressure over the melt provided by a Pb or Te reservoir, respectively, whereas another ingot, with starting composition of (Pb0.98Tl0.02)Te, was grown under Te overpressure. Two Tl-doped PbTeSe crystals, with starting composition of (Pb0.98Tl0.02)(Te0.85Se0.15) and (Pb0.96Tl0.04)(Te0.85Se0.15), were grown without any over-pressure. Disk-shaped samples were sliced at different locations along the growth axis and their thermal conductivities were determined from thermal diffusivity, density, and heat capacity measurements. The electrical conductivity and Seebeck coefficient were simultaneously measured as a function of temperature for each disk sample. The Figure of Merit for the thermoelectric application, zT, was calculated from these properties from room temperature to about 640 °C. The Tl-doped PbTeSe samples have the highest zT value of 1.63 at temperature range of 425 to 475 °C, comparing to 1.13 at 410 °C for the Tl-doped PbTe samples. By substituting 15% of the Te atoms in the Tl-doped PbTe by Se atoms, the Figure of Merit of PbTeSe was enhanced by reducing the thermal conductivity about 26% and, at the same time, increasing the electrical conductivity by 43%.

  6. Electron microscopy of iron chalcogenide FeTe(Se) films

    NASA Astrophysics Data System (ADS)

    Shchichko, I. O.; Presnyakov, M. Yu.; Stepantsov, E. A.; Kazakov, S. M.; Antipov, E. V.; Makarova, I. P.; Vasil'ev, A. L.

    2015-05-01

    The structure of Fe1 + δTe1 - x Se x films ( x = 0; 0.05) grown on single-crystal MgO and LaAlO3 substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe1.11Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe0.5Se0.5 film grown on a LaAlO3 substrate is single-crystal and that the FeTe0.5Se0.5/LaAlO3 interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case.

  7. Unified formalism for TE and TM beam propagators

    NASA Astrophysics Data System (ADS)

    Poladian, Leon; Ladouceur, Francois J.

    1998-07-01

    The unification of transverse electric (TE) and transverse magnetic (TM) beam propagation algorithms is made possible through a transformation which converts the wave equation for TM fields in planar waveguides into a form identical to the corresponding TE wave equation. The transformation can be applied to any smoothly varying waveguide. This transformation can be made independently of any paraxial or other approximations. Thus, any TE propagation algorithm can also be applied immediately to TM fields without additional approximations. This includes the classical fast Fourier transform beam propagator, which has not previously been applied successfully to TM propagation. We also specifically develop a Finite Difference Beam Propagation Method that applies to both TE and TM propagation in 1D (planar) geometry. Previous implementations for the TM case involve an approximation that in certain circumstances leads to severe errors (including the totally unphysical occurrence of field amplification). This is the first TM propagator which exactly conserves power. We also investigate the role of the reference background wavenumber (or index) and clarify its role as it is dynamically adapted. The algorithms proposed are easily adaptable to wide-angle beam propagators and to modern transparent boundary conditions. The extension of these ideas to rapidly varying structures (such as Bragg gratings) is also briefly discussed.

  8. 640 X 480 Pace HgCdTe FPA

    NASA Astrophysics Data System (ADS)

    Kozlowski, Lester J.; Bailey, Robert B.; Cabelli, Scott A.; Cooper, Donald E.; McComas, Gail D.; Vural, Kadri; Tennant, William E.

    1992-12-01

    A hybrid HgCdTe 640 X 480 infrared (IR) focal plane array (FPA) that meets the sensitivity, resolution, and field-of-view requirements of high-performance medium wavelength infrared (MWIR) imaging systems has been developed. The key technology making this large, high sensitivity device producible is the epitaxial growth of HgCdTe on a CdTe-buffered, sapphire substrate (referred to as PACE, for Producible Alternative to CdTe for Epitaxy; PACE-I refers to sapphire). The device offers TV resolution with excellent sensitivity at temperatures below 120 K. Mean NE(Delta) T as low as 13 mK has been achieved at operating temperatures < 130 K, which is about an order of magnitude better than has been achieved with PtSi 640 X 480 FPAs. In addition, the latter require cooling to

  9. Fabrication of CdTe/Si heterojunction solar cell

    NASA Astrophysics Data System (ADS)

    Bera, Swades Ranjan; Saha, Satyajit

    2016-10-01

    A simple cost effective method is preferred to grow nanoparticles of CdTe. Nanoparticles of CdTe are grown by simple chemical reduction route using EDA as capping agent and Sodium Borohydride as reducing agent. The grown nanoparticles are characterized using transmission electron microscopy (TEM), X-ray diffraction, optical absorption, and photoluminescence study. From optical absorption study, the band-gap was found to be 2.46 eV. From TEM study, the average particle size was found to be within 8-12 nm which confirms the formation of CdTe nanoparticles. Pl spectra indicate the luminescence from surface states at 2.01 eV, which is less compared to the increased band-gap of 2.46 eV. The grown nanoparticles are used to fabricate a heterojunction of CdTe on P-Si by a spin coating technique for solar cell fabrication in a cost effective way. I-V characteristics of the grown heterojunction in dark as well as under light are measured. Efficiency and fill-factor of the device are estimated.

  10. Raman scattering of few-layers MoTe2

    NASA Astrophysics Data System (ADS)

    Grzeszczyk, M.; Gołasa, K.; Zinkiewicz, M.; Nogajewski, K.; Molas, M. R.; Potemski, M.; Wysmołek, A.; Babiński, A.

    2016-06-01

    We report on room-temperature Raman scattering measurements in few-layer crystals of exfoliated molybdenum ditelluride (MoTe2) performed with the use of 632.8 nm (1.96 eV) laser light excitation. In agreement with a recent study reported by Froehlicher et al (2015 Nano Lett. 15 6481) we observe a complex structure of the out-of-plane vibrational modes ({{{A}}}1{{g}}{/{{A}}}1\\prime ), which can be explained in terms of interlayer interactions between single atomic planes of MoTe2. In the case of low-energy shear and breathing modes of rigid interlayer vibrations, it is shown that their energy evolution with the number of layers can be well reproduced within a linear chain model with only the nearest neighbor interaction taken into account. Based on this model the corresponding in-plane and out-of-plane force constants are determined. We also show that the Raman scattering in MoTe2 measured using 514.5 nm (2.41 eV) laser light excitation results in much simpler spectra. We argue that the rich structure of the out-of-plane vibrational modes observed in Raman scattering spectra excited with the use of 632.8 nm laser light results from its resonance with the electronic transition at the M point of the MoTe2 first Brillouin zone.

  11. Optical Properties of PbTe and PbSe

    SciTech Connect

    Ekuma, Chinedu E; Singh, David J; Moreno, Juana; Jarrell, Mark

    2012-01-01

    We report optical properties of PbTe and PbSe as obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential. The results are discussed in relation to existing experimental data, particularly in relation to the temperature dependence of the band gap.

  12. Anisotropy of TeV Galactic cosmic rays

    NASA Astrophysics Data System (ADS)

    Zhang, Ming; Pogorelov, Nikolai; Desiati, Paolo; DuVernois, Michael

    2016-07-01

    TeV cosmic rays are significantly deflected by the magnetic field of the heliosphere, and they gain or lose energies in heliospheric electric field that in the meantime drives the motion of plasma. These propagation mechanisms will cause the map of TeV cosmic rays seen at the Earth to look different from the map seen in the local interstellar medium without the presence of the heliosphere. We have developed a method of using Liouville's theorem to map out particle distribution function to Earth from the local interstellar medium, where we assume that the cosmic rays have small pitch-angle anisotropy harmonics up to the second order and a small uniform spatial density gradient. The amount of heliospheric distortion can be determined by tracing the trajectories of cosmic rays propagating through the heliosphere. In this paper, we apply this method to TeV cosmic ray propagation through a MHD-kinetic model of the heliosphere and try to fit observations from Tibet ASgamma and IceCube experiments. We are able to locate features in the TeV cosmic ray anisotropy that are associated with the interstellar magnetic field, hydrogen deflection plane, heliotail, and solar corona. Some of the features are also slightly affected by the solar cycle and interstellar magnetic turbulence. The results provide us powerful tools to explore large-scale heliospheric structures as well as to determine the cosmic ray distribution in the local interstellar medium.

  13. Early Intervention and Te Kohanga Reo: Working in Partnership.

    ERIC Educational Resources Information Center

    Flavell, Marie V.

    The Kohanga Reo, or "language nest" centers, provide places where Maori children can learn their native language. In its partnership with Te Kohanga Reo, the New Zealand Early Intervention Service has: (1) sent representatives to Maori tribal committee meetings; (2) ensured Kohanga Reo representation on early intervention management teams; (3)…

  14. Better Practices for Recruiting T&E Teachers

    ERIC Educational Resources Information Center

    Love, Tyler S.; Love, Zachary J.; Love, Kevin S.

    2016-01-01

    The declining number of Technology and Engineering (T&E) educators and teacher preparation programs across the country has been identified as a critical issue plaguing the field for many years (Daugherty, 1998; Volk, 1993). Unfortunately, this issue continues to progress and has raised concerns. Why should middle and high school T&E…

  15. Applications of CdTe to nuclear medicine. Final report

    SciTech Connect

    Entine, G.

    1985-05-07

    Uses of cadmium telluride (CdTe) nuclear detectors in medicine are briefly described. They include surgical probes and a system for measuring cerebral blood flow in the intensive care unit. Other uses include nuclear dentistry, x-ray exposure control, cardiology, diabetes, and the testing of new pharmaceuticals. (ACR)

  16. Scaling linear colliders to 5 TeV and above

    SciTech Connect

    Wilson, P.B.

    1997-04-01

    Detailed designs exist at present for linear colliders in the 0.5-1.0 TeV center-of-mass energy range. For linear colliders driven by discrete rf sources (klystrons), the rf operating frequencies range from 1.3 GHz to 14 GHz, and the unloaded accelerating gradients from 21 MV/m to 100 MV/m. Except for the collider design at 1.3 GHz (TESLA) which uses superconducting accelerating structures, the accelerating gradients vary roughly linearly with the rf frequency. This correlation between gradient and frequency follows from the necessity to keep the ac {open_quotes}wall plug{close_quotes} power within reasonable bounds. For linear colliders at energies of 5 TeV and above, even higher accelerating gradients and rf operating frequencies will be required if both the total machine length and ac power are to be kept within reasonable limits. An rf system for a 5 TeV collider operating at 34 GHz is outlined, and it is shown that there are reasonable candidates for microwave tube sources which, together with rf pulse compression, are capable of supplying the required rf power. Some possibilities for a 15 TeV collider at 91 GHz are briefly discussed.

  17. A Unified Analysis of Japanese Aspect Marker "te iru."

    ERIC Educational Resources Information Center

    Shinzato, Rumiko

    1993-01-01

    Following Jacobson's 1990 work, this study is another attempt to offer a unified analysis of the Japanese aspect marker "te iru" that touches upon Gestalt psychologists' ideas of figure/ground opposition, Langacker's cognitive grammar, and Kunihiro's cognitive analysis. (Contains 34 references.) (LB)

  18. Ion-beam-induced damage formation in CdTe

    SciTech Connect

    Rischau, C. W.; Schnohr, C. S.; Wendler, E.; Wesch, W.

    2011-06-01

    Damage formation in <111>- and <112>-oriented CdTe single crystals irradiated at room temperature and 15 K with 270 keV Ar or 730 keV Sb ions was investigated in situ using Rutherford backscattering spectroscopy (RBS) in channeling configuration. Defect profiles were calculated from the RBS spectra using the computer code DICADA and additional energy-dependent RBS measurements were performed to identify the type of defects. At both temperatures no formation of a buried amorphous layer was detected even after prolonged irradiation with several 10{sup 16} ions/cm{sup 2}. The fact that CdTe is not rendered amorphous even at 15 K suggests that the high resistance to amorphization is caused by the high ionicity of CdTe rather than thermal effects. The calculated defect profiles show the formation of a broad defect distribution that extends much deeper into the crystal than the projected range of the implanted ions at both temperatures. The post-range defects in CdTe thus do not seem to be of thermal origin either, but are instead believed to result from migration driven by the electronic energy loss.

  19. Te Kotahitanga: Culturally Responsive Professional Development for Teachers

    ERIC Educational Resources Information Center

    Bishop, Russell; Berryman, Mere

    2010-01-01

    Te Kotahitanga is a research and professional development project that aims to support teachers to raise the achievement of New Zealand's indigenous Maori students in public/mainstream classrooms. An Effective Teaching Profile, developed from the voices of Maori students, their families, principals and some of their teachers, provides direction…

  20. Extended defects in as-grown CdZnTe

    SciTech Connect

    Xu, L.; Bolotnikov, A.E.; Hossain, A.; Kim, K-H.; Gul, R.; Yang, G.; Camarda, G.S.; Marchini, L.; Cui, Y.; James, R.B.; Xu, Y.; Wang, T.; Jie, W.

    2010-08-01

    We characterized samples cut from different locations in as-grown CdZnTe (CZT) ingots, using Automated Infrared (IR) Transmission Microscopy and White Beam X-ray Diffraction Topography (WBXDT), to locate and identify the extended defects in them. Our goal was to define the distribution of these defects throughout the entire ingot and their effects on detectors’ performance as revealed by the pulse-height spectrum. We found the highest- and the lowest- concentration of Te inclusions, respectively, in the head and middle part of the ingot, which could serve as guidance in selecting samples. Crystals with high concentration of Te inclusions showed high leakage current and poor performance, because the accumulated charge loss around trapping centers associated with Te inclusions distorts the internal electric field, affects the carrier transport properties inside the crystal, and finally degrades the detector’s performance. In addition, other extended defects revealed by the WBXDT measurements severely reduced the detector’s performance, since they trap large numbers of electrons, leading to a low signal for the pulse-height spectrum, or none whatsoever. Finally, we fully correlated the detector’s performance with our information on the extended defects gained from both the IR- and the WBXDT-measurements.

  1. The Te-ni-wo-ha: An Etymological Study.

    ERIC Educational Resources Information Center

    Jolly, Yukiko S.

    1972-01-01

    The designation of the Japanese word class "joshi" (in English known as particles, post-positional case markers, or relationals) by the term te-ni-wo-ha can be traced to the early superimposition of the Chinese writing system on Japanese speech. Because of the structural differences between the two languages and the existence of elements in…

  2. Electron microscopy of iron chalcogenide FeTe(Se) films

    SciTech Connect

    Shchichko, I. O.; Presnyakov, M. Yu.; Stepantsov, E. A.; Kazakov, S. M.; Antipov, E. V.; Makarova, I. P.; Vasil’ev, A. L.

    2015-05-15

    The structure of Fe{sub 1+δ}Te{sub 1−x}Se{sub x} films (x = 0; 0.05) grown on single-crystal MgO and LaAlO{sub 3} substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe{sub 1.11}Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe{sub 0.5}Se{sub 0.5} film grown on a LaAlO{sub 3} substrate is single-crystal and that the FeTe{sub 0.5}Se{sub 0.5}/LaAlO{sub 3} interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case.

  3. Black hole radiance, short distances, and TeV gravity.

    PubMed

    Agulló, Iván; Navarro-Salas, José; Olmo, Gonzalo J

    2006-07-28

    Using a derivation of black hole radiance in terms of two-point functions one can provide a quantitative estimate of the contribution of short distances to the spectrum. Thermality is preserved for black holes with kappalp<1. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.

  4. Simulation of charge transport in pixelated CdTe

    NASA Astrophysics Data System (ADS)

    Kolstein, M.; Ariño, G.; Chmeissani, M.; De Lorenzo, G.

    2014-12-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points.

  5. Guaranteed and prospective Galactic TeV neutrino sources

    SciTech Connect

    Kistler, Matthew D.; Beacom, John F.

    2006-09-15

    Recent observations, particularly from the HESS Collaboration, have revealed rich Galactic populations of TeV gamma-ray sources, including a collection unseen in other wavelengths. Many of these gamma-ray spectra are well measured up to {approx}10 TeV, where low statistics make observations by air Cerenkov telescopes difficult. To understand these mysterious sources, especially at much higher energies--where a cutoff should eventually appear--new techniques are needed. We point out the following: (1) For a number of sources, it is very likely that pions, and hence TeV neutrinos, are produced; (2) As a general point, neutrinos should be a better probe of the highest energies than gamma rays, due to increasing detector efficiency; and (3) For several specific sources, the detection prospects for km{sup 3} neutrino telescopes are very good, {approx}1-10 events/year, with low atmospheric neutrino background rates above reasonable energy thresholds. Such signal rates, as small as they may seem, will allow neutrino telescopes to powerfully discriminate between models for the Galactic TeV sources, with important consequences for our understanding of cosmic-ray production.

  6. Development of Cd1-xMgxTe thin films for application as an electron reflector in CdS/CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Kobyakov, Pavel S.

    Efficiencies of CdS/CdTe photovoltaic cells significantly lag behind their theoretical limit, primarily because open-circuit voltage ( VOC) of record efficiency cells (872 mV) is well below what is expected for the CdTe band gap (1.5 eV). A substantial V OC improvement can be achieved through addition of an electron reflector (ER) layer to CdTe devices. The ER layer forms a conduction-band barrier that reflects minority-charge carriers (i.e. electrons in p-type CdTe) away from the back surface. Similar to back-surface fields in c-Si, III-V, and CIGS solar cells, the ER strategy is expected to reduce back-surface recombination and is estimated to increase CdTe VOC by about 200 mV based on numerical simulation. The presented research investigates the addition of a thin layer of wider band gap Cd1-xMgxTe (CMT) to achieve a CdTe ER structure. First, a novel co-sublimation process was developed for deposition of Cd 1-xMgxTe thin films that demonstrates excellent experimental capabilities, commercial viability, and improved alloy control over other techniques. Next, the effects of processing on material properties of CMT deposition onto CdS/CdTe structures were investigated. It was discovered that substrate temperature during CMT deposition is a critical parameter for achieving uniform CMT film coverage on polycrystalline CdTe. Furthermore, CMT film growth was found to be epitaxial on CdTe where the CMT films retain the same microstructural features as the underlying CdTe grains. Despite film uniformity, significant Mg loss from the CMT film, oxide formation, and a reduction of the optical band gap was found after CdCl2-based passivation treatments. Preliminary process optimization found that band gap degradation can be minimized by utilizing MgCl2 in addition to CdCl2 as a treatment source material. Finally, development of CdS/CdTe/Cd1-xMgxTe electron reflector devices demonstrated a barrier behavior at high voltage bias and improved voltage when CdTe thickness is held

  7. Heavy hydrides: H{sub 2}Te ultraviolet photochemistry

    SciTech Connect

    Underwood, J.; Chastaing, D.; Lee, S.; Wittig, C.

    2005-08-22

    The room-temperature ultraviolet absorption spectrum of H{sub 2}Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH({sup 2}{pi}{sub 1/2}) selectively relative to the TeH({sup 2}{pi}{sub 3/2}) ground state. This is attributed to the role of the 3A{sup '} state, which has a shallow well at large R{sub H-TeH} and correlates to H+TeH({sup 2}{pi}{sub 1/2}). Note that the {sup 2}{pi}{sub 1/2} state is analogous to the {sup 2}P{sub 1/2} spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A{sup '} state is crossed at large R only by 2A{sup ''}, with which it does not interact. The character of 3A{sup '} at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, {sup 2}{pi}{sub 1/2} has a higher degree of spherical symmetry than does {sup 2}{pi}{sub 3/2} (recall that I({sup 2}P{sub 1/2}) is spherically symmetric), and consequently {sup 2}{pi}{sub 1/2} is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A{sup '}<-X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3A{sup '}. The main absorption feature that is peaked at {approx}240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A{sup ''} surface. The 4A{sup ''}<-X transition

  8. Vaporization thermodynamic studies by high-temperature mass spectrometry on some three-phase regions over the MnO-TeO2 binary line in the Mn-Te-O ternary system.

    PubMed

    Narasimhan, T S Lakshmi; Sai Baba, M; Viswanathan, R

    2006-12-28

    Knudsen effusion mass spectrometric measurements have been performed in the temperature range of 850-950 K over four three-phase mixtures, each phase mixture having at least one phase lying on the MnO-TeO2 binary line of the Mn-Te-O phase diagram, and the rest of the phases lying above this binary line. The three-phase mixtures investigated are Mn3O4 + MnO + Mn6Te5O16; Mn3O4 + Mn6Te5O16 + MnTeO3; Mn3O4 + Mn3TeO6 + MnTeO3; and Mn3TeO6 + MnTeO3 + Mn2Te3O8. The vapor pressures of the gaseous species TeO2, TeO, and Te2 over these three-phase mixtures were measured, and various heterogeneous solid-gas reactions were evaluated along with the homogeneous gas-phase reaction TeO2(g) + 0.5Te2(g) = 2 TeO(g). The enthalpy and Gibbs free energy of formation of the four ternary Mn-Te-O phases were deduced at T = 900 K. These values (in kJ.mol-1), along with the estimated uncertainties in them are Delta(f)H(o)m = 4150 +/- 19, 752 +/- 11, 1710 +/- 11, 1924 +/- 40, and Delta(f)G(o)m= 2835 +/- 28, 511 +/- 11, 1254 +/- 19, 1238 +/- 38, for Mn6Te5O16, MnTeO3, Mn3TeO6, and Mn2Te3O8, respectively. A thermochemical assessment was made to examine the conditions under which the ternary Mn-Te-O phases could be formed on a stainless steel clad of mixed-oxide-fueled (MO2; M = U + Pu) fast breeder nuclear reactors. The phase Mn3TeO6 could be formed when the fuel is even slightly hyperstoichiometric (O/M = 2.0002) and the phase Mn6Te5O16 could also be formed when O/M = 2.0004. The threshold tellurium potential for the formation of Mn3TeO6 is higher than that for MnTe0.80 and CrTe1.10, but is comparable to that for MoTe1.10, and even lower than that for FeTe0.81 or NiTe0.63.

  9. CdZnTe arrays for nuclear medicine imaging

    SciTech Connect

    Barber, H.B.

    1996-12-31

    In nuclear medicine, a gamma-ray-emitting radiotracer is injected into the body, and the resulting biodistribution is imaged using a gamma camera. Current gamma cameras use a design developed by Anger. An Anger camera makes use of a slab of scintillation detector that is viewed by an array of photomultiplier tubes and uses an analog position estimation technique to determine the position of the gamma ray`s interaction. The image-forming optics is usually a multi-bore collimator made of lead. Such cameras are characterized by poor, system spatial resolution ({approximately}1 cm) due to poor detector resolution ({approximately}0.4 cm) and poor collimator performance. Arrays of semiconductor detectors are an attractive alternative to scintillators for use in gamma cameras. Semiconductor detectors have excellent energy resolution. High spatial resolution is also possible because large semiconductor detector arrays with small pixel sizes can be produced using photolithography techniques. A new crystal growth technique (high-pressure vertical Bridgman) allows production of detector grade CdTe and CdZnTe in multikilogram ingots. Although the cost of CdZnTe detectors has come down substantially in the last few years, in part because of economies of scale, costs are still more than an order of magnitude higher than those required for a commercial camera ($20--$50/gram). High detector costs are perhaps the major stumbling block to developing a semiconductor gamma camera. The photolithography techniques required to make large CdZnTe arrays have already been demonstrated. This paper discusses the recent developments made in CdZnTe detectors.

  10. Raman spectroscopic investigations of Hg-Cd-Te melts

    NASA Technical Reports Server (NTRS)

    Morrobel-Sosa, Anny

    1987-01-01

    Raman scattering measurements are reported for a series of Hg sub1-xCd subxTe (with x less than or =0.2) materials from 295 K (room temperature) to 1126K (up to and above their liquidus temperatures), and for Hg sub1-xCd subxTe (x=0.3) at 285K. The samples were contained in high-temperature optically-flat fused silica cell. Variable temperature measurements were effected in a three-zone, high-temperature furnace equipped with optical windows, and monitored externally by three independently programmable temperature controllers. All studies were made in the backscattering geometry using the 5145 A line of an Ar+ ion laser, with incident power less than 250 mW, as the excitiation source. An intensity enhancement is observed for a mode in each of the compositions studied. The frequency of this mode varies with composition, 142/cm for HgTe, and 128/cm for both the Hg sub1-xCd subxTe (x=0.053 and 0.204) samples. In addition, a shift to lower frequency as a function of temperature is observed in all samples. This shift is most prominent for the x=0.053 sample. The temperature dependence of these modes as the liquidus temperatures are achieved and surpassed for these samples is presented as being associated with a structural transition in the Hg-rich compositions of the Hg sub1-xCd subxTe series. To our knowledge, this is the first reported study of Raman scattering by phonons in the melts of these materials.

  11. Viscosity Relaxation in Molten HgZnTe

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Lehoczky, S. L.; Kim, Yeong Woo; Baird, James K.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Rotating cup measurements of the viscosity of the pseudo-binary melt, HgZnTe have shown that the isothermal liquid with zinc mole fraction 0.16 requires tens of hours of equilibration time before a steady viscous state can be achieved. Over this relaxation period, the viscosity at 790 C increases by a factor of two, while the viscosity at 810 C increases by 40%. Noting that the Group VI elements tend to polymerize when molten, we suggest that the viscosity of the melt is enhanced by the slow formation of Te atom chains. To explain the build-up of linear Te n-mers, we propose a scheme, which contains formation reactions with second order kinetics that increase the molecular weight, and decomposition reactions with first order kinetics that inactivate the chains. The resulting rate equations can be solved for the time dependence of each molecular weight fraction. Using these molecular weight fractions, we calculate the time dependence of the average molecular weight. Using the standard semi-empirical relation between polymer average molecular weight and viscosity, we then calculate the viscosity relaxation curve. By curve fitting, we find that the data imply that the rate constant for n-mer formation is much smaller than the rate constant for n-mer deactivation, suggesting that Te atoms only weakly polymerize in molten HgZnTe. The steady state toward which the melt relaxes occurs as the rate of formation of an n-mer becomes exactly balanced by the sum of the rate for its deactivation and the rate for its polymerization to form an (n+1)-mer.

  12. Schottky Barrier CdTe(Cl) Detectors for Planetary Missions

    NASA Astrophysics Data System (ADS)

    Eisen, Yosef; Floyd, Samuel

    2002-10-01

    Schottky barrier cadmium telluride (CdTe) radiation detectors of dimensions 2mm × 2mm × 1mm and segmented monolithic 3cm × 3 cm × 1mm are under study at GSFC for future NASA planetary instruments. These instruments will perform x-ray fluorescence spectrometry of the surface and monitor the solar x-ray flux spectrum, the excitation source for the characteristic x-rays emitted from the planetary body. The Near Earth Asteroid Rendezvous (NEAR) mission is the most recent example of such a remote sensing technique. Its x-ray fluorescence detectors were gas proportional counters with a back up Si PIN solar monitor. Analysis of NEAR data has shown the necessity to develop a solar x-ray detector with efficiency extending to 30keV. Proportional counters and Si diodes have low sensitivity above 9keV. Our 2mm × 2mm × 1mm CdTe operating at -30°C possesses an energy resolution of 250eV FWHM for 55Fe with unit efficiency to up to 30keV. This is an excellent candidate for a solar monitor. Another ramification of the NEAR data is a need to develop a large area detector system, 20-30 cm2, with cosmic ray charged particle rejection, for measuring the characteristic radiation. A 3cm × 3cm × 1mm Schottky CdTe segmented monolithic detector is under investigation for this purpose. A tiling of 2-3 such detectors will result in the desired area. The favorable characteristics of Schottky CdTe detectors, the system design complexities when using CdTe and its adaptation to future missions will be discussed.

  13. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

    PubMed Central

    Sordo, Stefano Del; Abbene, Leonardo; Caroli, Ezio; Mancini, Anna Maria; Zappettini, Andrea; Ubertini, Pietro

    2009-01-01

    Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors. PMID:22412323

  14. Study on the contact resistance of various metals (Au, Ti, and Sb) on Bi–Te and Sb–Te thermoelectric films

    NASA Astrophysics Data System (ADS)

    Yong, Ho; Na, Sekwon; Gang, Jun-Gu; Shin, HaeSun; Jeon, Seong-Jae; Hyun, SeungMin; Lee, Hoo-Jeong

    2016-06-01

    In this study, we explore various electrode materials (Au, Ti, and Sb) for use as contact materials on Bi2Te3 and Sb2Te3 thermoelectric films. Using the transmission line method (TLM), we measured the specific resistivity of the contacts, which showed that Au has the lowest contact resistivity for both the thermoelectric films (after annealing): 2.7 × 10‑10 Ω m2 for Bi2Te3 and 2.9 × 10‑11 Ω m2 for Sb2Te3. The specific contact resistivity data suggest that the dominant factor for the contact properties is interface states. After annealing, the contact resistivity does not change much for the Bi2Te3 contacts while it drops greatly for the Sb2Te3 ones. Analysis of the carrier transport mechanism across the contacts discloses that changes in the carrier concentration in the thermoelectric films after annealing are responsible for the different behaviors.

  15. Reverse Monte Carlo simulation of Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} glasses

    SciTech Connect

    Abdel-Baset, A. M.; Rashad, M.; Moharram, A. H.

    2013-12-16

    Two-dimensional Monte Carlo of the total pair distribution functions g(r) is determined for Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} alloys, and then it used to assemble the three-dimensional atomic configurations using the reverse Monte Carlo simulation. The partial pair distribution functions g{sub ij}(r) indicate that the basic structure unit in the Se{sub 80}Te{sub 15}Sb{sub 5} glass is di-antimony tri-selenide units connected together through Se-Se and Se-Te chain. The structure of Se{sub 80}Te{sub 20} alloys is a chain of Se-Te and Se-Se in addition to some rings of Se atoms.

  16. Superconducting Bi2Te: Pressure-induced universality in the (Bi2)m(Bi2Te3)n series

    DOE PAGES

    Stillwell, Ryan L.; Jeffries, Jason R.; Jenei, Zsolt; Weir, Samuel T.; Vohra, Yogesh K.

    2016-03-09

    Using high-pressure magnetotransport techniques we have discovered superconductivity in Bi2Te, a member of the infinitely adaptive (Bi2)m(Bi2Te3)n series, whose end members, Bi and Bi2Te3, can be tuned to display topological surface states or superconductivity. Bi2Te has a maximum Tc = 8.6 K at P = 14.5 GPa and goes through multiple high pressure phase transitions, ultimately collapsing into a bcc structure that suggests a universal behavior across the series. High-pressure magnetoresistance and Hall measurements suggest a semi-metal to metal transition near 5.4 GPa, which accompanies the hexagonal to intermediate phase transition seen via x-ray diffraction measurements. In addition, the linearitymore » of Hc2 (T) exceeds the Werthamer-Helfand-Hohenberg limit, even in the extreme spin-orbit scattering limit, yet is consistent with other strong spin-orbit materials. Furthermore, considering these results in combination with similar reports on strong spin-orbit scattering materials seen in the literature, we suggest the need for a new theory that can address the unconventional nature of their superconducting states.« less

  17. Two-dimensional superconductivity at the interface of a Bi2Te3/FeTe heterostructure.

    PubMed

    He, Qing Lin; Liu, Hongchao; He, Mingquan; Lai, Ying Hoi; He, Hongtao; Wang, Gan; Law, Kam Tuen; Lortz, Rolf; Wang, Jiannong; Sou, Iam Keong

    2014-06-23

    The realization of superconductivity at the interface between a topological insulator and an iron-chalcogenide compound is highly attractive for exploring several recent theoretical predictions involving these two new classes of materials. Here we report transport measurements on a Bi2Te3/FeTe heterostructure fabricated via van der Waals epitaxy, which demonstrate superconductivity at the interface, which is induced by the Bi2Te3 epilayer with thickness even down to one quintuple layer, though there is no clear-cut evidence that the observed superconductivity is induced by the topological surface states. The two-dimensional nature of the observed superconductivity with the highest transition temperature around 12 K was verified by the existence of a Berezinsky-Kosterlitz-Thouless transition and the diverging ratio of in-plane to out-plane upper critical field on approaching the superconducting transition temperature. With the combination of interface superconductivity and Dirac surface states of Bi2Te3, the heterostructure studied in this work provides a novel platform for realizing Majorana fermions.

  18. Electrical characterization of CdTe grain-boundary properties from as processed CdTe/CdS solar cells

    SciTech Connect

    Woods, L.M.; Robinson, G.Y.; Levi, D.H.; Ahrenkiel, R.K.; Kaydanov, V.

    1998-09-01

    An ability to liftoff or separate the thin-film polycrystalline CdTe from the CdS, without the use of chemical etches, has enabled direct electrical characterization of the as-processed CdTe near the CdTe/CdS heterointerface. The authors use this ability to understand how a back-contact, nitric-phosphoric (NP) etch affects the grain boundaries throughout the film. Quantitative determination of the grain-boundary barrier potentials and estimates of doping density near the grain perimeter are determined from theoretical fits to measurements of the current vs. temperature. Estimates of the bulk doping are determined from high-frequency resistivity measurements. The light and dark barrier potentials change after the NP etch, and the origin of this change is postulated. Also, a variable doping density within the grains of non-etched material has been determined. These results allow a semi-quantitative grain-boundary band diagram to be drawn that should aid in determining more accurate two-dimensional models for polycrystalline CdTe solar cells.

  19. Pressure-induced phase transitions in LnTe (Ln=La, Gd, Ho, Yb) and AmTe.

    PubMed

    Zvoriste-Walters, C E; Heathman, S; Klimczuk, T

    2013-07-01

    The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide (Am) monochalcogenides is studied by means of in situ high-pressure x-ray diffraction. All the investigated compounds crystallize at ambient conditions within a cubic (B1) NaCl-type structure but show different behaviours at high pressures. LaTe and AmTe undergo B1 to B2 (CsCl-type structure) phase transitions, starting at 9 GPa and 12 GPa, respectively. The high-pressure phase of AmTe exhibits an electronic transition, identified by an anomaly in the compression curve which is accompanied by a sample colour change. The other three monochalcogenides studied here show clear evidence of decomposition and amorphization under pressure and are, to the best of our knowledge, the first in the LnTe series to show a pressure-induced amorphization. The bulk moduli of all B1-type structure compounds are calculated using the third-order Birch-Murnaghan equation of state.

  20. Two-dimensional superconductivity at the interface of a Bi2Te3/FeTe heterostructure.

    PubMed

    He, Qing Lin; Liu, Hongchao; He, Mingquan; Lai, Ying Hoi; He, Hongtao; Wang, Gan; Law, Kam Tuen; Lortz, Rolf; Wang, Jiannong; Sou, Iam Keong

    2014-01-01

    The realization of superconductivity at the interface between a topological insulator and an iron-chalcogenide compound is highly attractive for exploring several recent theoretical predictions involving these two new classes of materials. Here we report transport measurements on a Bi2Te3/FeTe heterostructure fabricated via van der Waals epitaxy, which demonstrate superconductivity at the interface, which is induced by the Bi2Te3 epilayer with thickness even down to one quintuple layer, though there is no clear-cut evidence that the observed superconductivity is induced by the topological surface states. The two-dimensional nature of the observed superconductivity with the highest transition temperature around 12 K was verified by the existence of a Berezinsky-Kosterlitz-Thouless transition and the diverging ratio of in-plane to out-plane upper critical field on approaching the superconducting transition temperature. With the combination of interface superconductivity and Dirac surface states of Bi2Te3, the heterostructure studied in this work provides a novel platform for realizing Majorana fermions. PMID:24953963

  1. Thermoelectric power factor of ternary single-crystalline Sb2Te3- and Bi2Te3-based nanowires.

    PubMed

    Bäßler, Svenja; Böhnert, Tim; Gooth, Johannes; Schumacher, Christian; Pippel, Eckhard; Nielsch, Kornelius

    2013-12-13

    Nanowires of bismuth antimony telluride and bismuth telluride selenide (Bi15Sb29Te56 and Bi38Te55Se7) were grown by template-based pulsed electrodeposition. The composition and the crystallinity of the nanowires were determined by high-resolution transmission electron microscopy. The thermoelectric properties (Seebeck coefficient and electrical conductivity) of single p- and n-type nanowires, with diameter 80 nm and 200 nm, respectively, were determined as a function of temperature before and during heating in a helium atmosphere up to 300 K along the growth direction of the nanowires. After additional annealing in a tellurium atmosphere at 525 K, significantly enhanced transport properties are observed. Bulk-like power factors are achieved. In Bi38Te55Se7 nanowires, the Seebeck coefficients increase to -115 μV K(-1) and the thermoelectric power factors increase to 2820 μW K(-2) m(-1) at room temperature. In Bi15Sb29Te56 nanowires, Seebeck coefficients of up to S = +156 μV K(-1) and power factors of up to 1750 μW K(-2) m(-1) are obtained at room temperature.

  2. Selective area growth of Bi2Te3 and Sb2Te3 topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Kampmeier, Jörn; Weyrich, Christian; Lanius, Martin; Schall, Melissa; Neumann, Elmar; Mussler, Gregor; Schäpers, Thomas; Grützmacher, Detlev

    2016-06-01

    The intrinsic bulk behavior of topological insulators (TI) is a key issue for their employment in future device applications. State of the art TIs predominantly suffer from large bulk charge carrier concentrations that mask their extraordinary surface states. In this paper we present the selective area growth of Bi2Te3 and Sb2Te3 TI thin films on prestructured Si(111) Si on insulator (SOI) substrates, paving the way to high quality TI nanostructures in which access to surface states is enhanced. Therefore high quality Bi2Te3 and Sb2Te3 thin films were deposited by means of solid source molecular beam epitaxy (MBE) and subsequently investigated by energy dispersive x-ray spectroscopy (EDX). To investigate the transport properties of the selectively grown thin films, magnetotransport measurements were performed at low temperatures. Nucleation in the SiO2 valleys next to the prepatterned Si(111) mesa structures was not observed. The structural and morphological qualities of crystals deposited on untreated Si(111) SOI wafers are completely preserved by employing the selective area growth on prepatterned substrates. The transport characteristics of the selectively-grown TI systems are comparable to those of the analogous postpatterned films.

  3. Ψ and Υ Production in p-p Collisions at E = 5, 14 TeV; and Comparison with Experiment at E = 7 TeV

    NASA Astrophysics Data System (ADS)

    Kisslinger, Leonard S.; Das, Debasish

    2016-10-01

    This brief report is an extension of our recent studies of Ψ and Υ production cross sections in proton-proton collisions with E =√ {s}=13 TeV to E = 5 and E =14 TeV, using the mixed heavy quark hybrid theory in which the Ψ(2 S) and Υ(3 S) are 50 % hybrid states. Also, comparison with recent experiments at E = 7 TeV are used to test the mixed heavy hybrid theory.

  4. Distribution of Te inclusions in a CdZnTe wafer and their effects on the electrical properties of fabricated devices

    SciTech Connect

    Hossain , A.; Xu, L.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Yang, G.; Kim, K.-H.; and James, R.B.

    2010-05-24

    We quantified the size and concentration of Te-inclusions along the lateral- and the growth-directions of a {approx}6 mm thick wafer cut axially along the center of a CdZnTe ingot. We fabricated devices, selecting samples from the center slice outward in both directions, and then tested their response to incident x-rays. We employed, in concert, an automated IR transmission microscopic system and a highly collimated synchrotron X-ray source that allowed us to acquire and correlate comprehensive information on Te inclusions and other defects to assess the material factors limiting the performance of CdZnTe detectors.

  5. Air-Stable, Near- to Mid-Infrared Emitting Solids of PbTe/CdTe Core-Shell Colloidal quantum dots.

    PubMed

    Protesescu, Loredana; Zünd, Tanja; Bodnarchuk, Maryna I; Kovalenko, Maksym V

    2016-03-01

    Light emitters and detectors operating in the near- and mid-infrared spectral regions are important to many applications, such as telecommunications, high-resolution gas analysis, atmospheric pollution monitoring, medical diagnostics, and night vision. Various lead chalcogenides (binary, ternary, and quaternary alloys) in the form of quantum dots (QDs) or quantum wells provide narrow bandgap energies that cover the broad infrared region corresponding to wavelengths of 1-30 μm. Here, we report an inexpensive, all-solution-based synthesis strategy to thin-film solids consisting of 5-16 nm PbTe QDs encapsulated by CdTe shells. Colloidally synthesized PbTe QDs were first converted into core-shell PbTe/CdTe QDs, and then deposited as thin films. The subsequent fusion of the CdTe shells is achieved by ligand removal and annealing in the presence of CdCl2 . Contrary to highly unstable bare PbTe QDs, PbTe/CdTe QD solids exhibit bright and stable near- to mid-infrared emission at wavelengths of 1-3 μm, which is also retained upon prolonged storage at ambient conditions for one year.

  6. Air-Stable, Near- to Mid-Infrared Emitting Solids of PbTe/CdTe Core-Shell Colloidal quantum dots.

    PubMed

    Protesescu, Loredana; Zünd, Tanja; Bodnarchuk, Maryna I; Kovalenko, Maksym V

    2016-03-01

    Light emitters and detectors operating in the near- and mid-infrared spectral regions are important to many applications, such as telecommunications, high-resolution gas analysis, atmospheric pollution monitoring, medical diagnostics, and night vision. Various lead chalcogenides (binary, ternary, and quaternary alloys) in the form of quantum dots (QDs) or quantum wells provide narrow bandgap energies that cover the broad infrared region corresponding to wavelengths of 1-30 μm. Here, we report an inexpensive, all-solution-based synthesis strategy to thin-film solids consisting of 5-16 nm PbTe QDs encapsulated by CdTe shells. Colloidally synthesized PbTe QDs were first converted into core-shell PbTe/CdTe QDs, and then deposited as thin films. The subsequent fusion of the CdTe shells is achieved by ligand removal and annealing in the presence of CdCl2 . Contrary to highly unstable bare PbTe QDs, PbTe/CdTe QD solids exhibit bright and stable near- to mid-infrared emission at wavelengths of 1-3 μm, which is also retained upon prolonged storage at ambient conditions for one year. PMID:26676076

  7. Electronic states in Cd{sub 1{minus}x}Zn{sub x}Te/CdTe strained layer coupled double quantum wells and their photoluminescence

    SciTech Connect

    Li, T.; Lozykowski, H.J.; Reno, J.

    1994-12-31

    Experimental and theoretical investigation of electronic states in a strained-layer CdTe/CdZnTe coupled double quantum well structure are presented. The optical properties of this lattice-mismatched heterostructure were characterized with photoluminescence (PL), PL excitation and polarization spectroscopies. Influence of electrical field on exciton states in the strained-layer CdTe/CdZnTe coupled double quantum well structure is experimentally studied. The confined electronic states were calculated in the framework of the envelope function approach, taking into account the strain effect induced by the lattice-mismatch. Experimental results are compared with the calculated transition energies.

  8. One-Pot Aqueous Phase Synthesis of CdTe and CdTe/ZnS Core/Shell Quantum Dots.

    PubMed

    Zhou, Beiying; Yang, Fengjiu; Zhang, Xin; Cheng, Wenyan; Luo, Wei; Wang, Lianjun; Jiang, Wan

    2016-06-01

    A facile and economical one-pot strategy has been developed for the synthesis of water-solute CdTe and CdTe/ZnS core/shell quantum dots (QDs) using tellurium dioxide (TeO2) as a tellurium precursor and thioglycolic acid (TGA) as stabilizer without any pre-treatment and inert atmosphere protection. As-synthesized QDs were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction spectroscopy (EDS), X-ray powder diffraction (XRD), UV-vis and photoluminescence (PL). The spherical particles were uniformly distributed with the average diameters of 3.2 nm (CdTe QDs) and -5 nm (CdTe/ZnS QDs). By altering the reaction conditions, the emission wavelengths of the CdTe core QDs and CdTe/ZnS core/shell QDs could be tuned from 508 to 574 nm and 526 to 600 nm with narrow full widths at half maximum (FWHM) of 33 to 58 nm, respectively. Meanwhile, on the optimum condition, the luminescence efficiency of CdTe/ZnS QDs can achieve to 74%, which was higher than that of CdTe core QDs (24%). PMID:27427627

  9. Effect of Ag doping and annealing on thermoelectric properties of PbTe

    SciTech Connect

    Bala, Manju Tripathi, T. S.; Avasthi, D. K.; Asokan, K.; Gupta, Srashti

    2015-06-24

    The present study reveals that annealing Ag doped PbTe thin films enhance thermoelectric properties. Phase formation was identified by using X-ray diffraction measurement. Annealing increases the crystallinity of both undoped and Ag doped PbTe. Electrical resistivity and thermoelectric power measurements are done using four probe and bridge method respectively. The increase in thermoelectric power of Ag doped PbTe is 29 % in comparison to undoped PbTe and it further increases to 34 % after annealing at 250{sup o} C for 1 hour whereas thermoelectric power increases by 14 % on annealing undoped PbTe thin films at same temperature.

  10. Novel ways of depositing ZnTe films by a solution growth technique

    SciTech Connect

    Birkmire, R.W.; McCandless, B.E.; Yokimcus, T.A.; Mondal, A. . Inst. of Energy Conversion)

    1992-10-01

    An electrochemical process has been successfully developed for the reproducible deposition of ZnTe and copper-doped ZnTe films suitable as transparent ohmic contacts for CdS/CdTe solar cells. The development of this method and optimization of key processing steps in the fabrication of CdS/CdTe/ZnTe:Cu devices has allowed IEC to achieve cell performance results of FF>70% and {eta} {approximately}10%. Preliminary efforts have indicated that the deposition methods investigated are potentially feasible for the formation of other II-VI compounds for use in polycrystalline thin film solar devices and should be the focus of future work.

  11. Reduced blinking behavior of single 2-mercapto ethanol capped CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Mandal, Abhijit; Tamai, Naoto

    2013-11-01

    Water soluble small size CdTe QDs were synthesized by using 2-mercapto ethanol (2ME) as stabilizer. The optimum size of QDs was obtained after certain time of reflux. Synthesized 2ME capped CdTe QDs show large Stokes shifted photoluminescence. At the single particle detection level, 2ME capped CdTe QDs showed reduced blinking behavior compared to that of TGA capped CdTe QDs. These results indicate that the thiol moiety of 2ME, which is a strong electron donor, saturated the surface traps with electrons, preventing the traps from accepting the Auger ionized electrons from the core of CdTe QD.

  12. Comparison of Te and Ti from Ogo 6 and from various incoherent scatter radars.

    NASA Technical Reports Server (NTRS)

    Mcclure, J. P.; Hanson, W. B.; Nagy, A. F.; Cicerone, R. J.; Brace, L. H.; Baron, M.; Bauer, P.; Carlson, H. C.; Evans, J. V.; Taylor, G. N.

    1973-01-01

    Langmuir probe and retarding potential analyzer (RPA) data on the electron and ion temperatures Te and Ti obtained from Ogo 6 are compared with Te and Ti values obtained from the incoherent scatter network. The satellite to radar temperature ratio TeS/TeR is 1.15 on the average for these comparisons. This discrepancy is larger than the uncertainties usually placed on the probe and radar Te values. The ion temperature ratio TiS/TiR approximately 1.0, independent of the particular radar examined. This comparison serves as an intercalibration of the incoherent scatter network.

  13. Surfactant-free synthesis of Bi2Te3-Te micro-nano heterostructure with enhanced thermoelectric figure of merit.

    PubMed

    Zhang, Yichi; Wang, Heng; Kräemer, Stephan; Shi, Yifeng; Zhang, Fan; Snedaker, Matt; Ding, Kunlun; Moskovits, Martin; Snyder, G Jeffrey; Stucky, Galen D

    2011-04-26

    An ideal thermoelectric material would be a semiconductor with high electrical conductivity and relatively low thermal conductivity: an "electron crystal, phonon glass". Introducing nanoscale heterostructures into the bulk TE matrix is one way of achieving this intuitively anomalous electron/phonon transport behavior. The heterostructured interfaces are expected to play a significant role in phonon scattering to reduce thermal conductivity and in the energy-dependent scattering of electrical carriers to improve the Seebeck coefficient. A nanoparticle building block assembly approach is plausible to fabricate three-dimensional heterostructured materials on a bulk commercial scale. However, a key problem in applying this strategy is the possible negative impact on TE performance of organic residue from the nanoparticle capping ligands. Herein, we report a wet chemical, surfactant-free, low-temperature, and easily up-scalable strategy for the synthesis of nanoscale heterophase Bi(2)Te(3)-Te via a galvanic replacement reaction. The micro-nano heterostructured material is fabricated bottom-up, by mixing the heterophase with commercial Bi(2)Te(3). This unique structure shows an enhanced zT value of ∼0.4 at room temperature. This heterostructure has one of the highest figures of merit among bismuth telluride systems yet achieved by a wet chemical bottom-up assembly. In addition, it shows a 40% enhancement of the figure of merit over our lab-made material without nanoscale heterostructures. This enhancement is mainly due to the decrease in the thermal conductivity while maintaining the power factor. Overall, this cost-efficient and room-temperature synthesis methodology provides the potential for further improvement and large-scale thermoelectric applications.

  14. Isothermal vapor phase epitaxy and rf sputtering for band gap engineered HgCdTe

    NASA Astrophysics Data System (ADS)

    Adamiec, Krzysztof; Gawron, Waldemar; Piotrowski, Jozef

    1997-06-01

    The present high quality HgCdTe photodetectors are based on heterostructures with complicated band gap and doping profiles. Such structures can be obtained by combination of Isothermal Vapor Phase Epitaxy (ISO VPE) and RDF sputtering of CdTe. Cadmium Telluride exhibits unique properties - transparency to IR light, low conductivity, nearly lattice match and chemically compatibility to HgCdTe. Thus, low defect densities and hence low surface state density at the CdTe/HgCdTe interface are expected, which in turn lead to low surface recombination velocities and long effective lifetimes. The immediate use of CdTe epilayer is passivation of HgCdTe. High quality layers HgCdTe have been grown on CdTe substrates by open tube ISO VPE. CdTe layers have been obtained by RF magnetron sputtering on to previously deposited HgCdTe layers in 400 LS Leybold AG System. The substrate temperature can be varied form 20 to 90 degrees C. Thermal treatment has been performed in Hg/H2 atmosphere in reusable chamber at temperatures 200-400 degrees C. The resulting heterostructures have been characterized by visual microscopy with Nomarski contrast, Hall measurements and IR transmittance. This technic and photolithography has been extensively used for successful fabrication of heterojunction contact photoresistors and heterostructure photodiodes.

  15. High Efficiency Ultra-thin CdS/CdTe Solar Cells

    NASA Astrophysics Data System (ADS)

    Paudel, Naba; Wieland, Kristopher; Compaan, Alvin

    2011-04-01

    Polycrystalline thin-film CdTe is currently the dominant thin-film technology in world-wide PV manufacturing. Typically a 2-8 μm thick CdTe layer is used for large scale CdS/CdTe based solar cells and modules. With finite Te resources, it is appropriate to limit the utilization of Te by reducing the thickness of the CdTe layer in these devices. But thinning the CdTe in solar cells and modules often decreases the conversion efficiency due to incomplete photon absorption and increased probability of shunting. In this study, ultra-thin CdTe devices were prepared by magnetron sputtering which appears to be well suited to control growth rate, grain size, and film stress. 0.25 -- 2.1 μm CdTe was sputtered on Pilkington TEC15 SnO2:F-coated soda-lime glass substrates with a high resistivity transparent interfacial layer after 60-80 nm of sputtered CdS. With optimum cell post-deposition processing, we obtained cells with efficiencies of 8%, 10.3%, 12.0% for CdTe thicknesses, respectively, of 0.25, 0.50, 0.75 μm. We believe that these represent the highest efficiencies yet obtained for CdS/CdTe cells with these submicron absorber-layer thicknesses.

  16. Local Structure of the Te/Si(001)-(1x1) Surface.

    NASA Astrophysics Data System (ADS)

    Bedzyk, M. J.; Lyman, P. F.; Montano, P. A.

    1996-03-01

    Adsorption of Te on Si is the critical first step in CdTe/Si growth. Apart from this potential commercial importance, adsorption of a group VI element (Te) on the (001) face of a group IV semiconductor (Si) might result in near-perfect passivation of the Si surface; the Si dangling bonds could be satisfied by a (1x1) arrangement of hexavalent Te. A recent LEED and STM study of the Te/Si(001) surface(S.A. Yoshikawa et al., Surf. Sci. 321, L183 (1994)) revealed that although the local arrangement of Te atoms does appear to be (1x1), the larger size of the strongly adsorbed Te atoms results in occasional missing rows of Te; these relieve strain by allowing lateral expansion of the Te layer. We undertook an x-ray standing wave study to quantify the adsorption site, spatial distribution, and structural perfection of the Te layer. Although good agreement with the STM was found for the lateral expansion of Te, a surprisingly large spatial distribution was found in the surface-normal direction, not evident in the STM work.

  17. Te/Pt nanonetwork modified carbon fiber microelectrodes for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Tsai, Hsiang-Yu; Shih, Zih-Yu; Lin, Zong-Hong; Chang, Huan-Tsung

    2013-05-01

    Te/Pt nanonetwork-decorated carbon fiber microelectrodes (CFMEs) have been fabricated and employed as anodic catalysts in a direct methanol fuel cell (DMFC). Te nanowires were prepared from tellurite ions (TeO32-) through a seed-mediated growth process and were deposited onto CFMEs to form three-dimensional Te nanonetworks. The Te nanonetworks then acted as a framework and reducing agent to reduce PtCl62- ions to form Te/Pt through a galvanic replacement reaction, leading to the formation of Te/PtCFMEs. By controlling the reaction time, the amount of Pt and morphology of Te/Pt nanonetworks were controlled, leading to various degrees of electrocatalytic activity. The Te/PtCFMEs provide a high electrochemical active surface area (129.2 m2 g-1), good catalytic activity (1.2 A mg-1), high current density (20.0 mA cm-2), long durability, and tolerance toward the poisoning species for methanol oxidation in 0.5 M sulfuric acid containing 1 M methanol. We have further demonstrated an enhanced current density by separately using 3 and 5 Te/PtCFMEs. Our results show that the low-cost, stable, and effective Te/PtCFMEs have great potential in the fabrication of cost-effective fuel cells.

  18. HIGH SPATIAL-RESOLUTION IMAGING OF TE INCLUSIONS IN CZT MATERIAL.

    SciTech Connect

    CAMARDA, G.S.; BOLOTNIKOV, A.E.; CARINI, G.A.; CUI, Y.; KOHMAN, K.T.; LI, L.; JAMES, R.B.

    2006-08-13

    We present new results from our studies of defects in current single-crystal CdZnTe material. Our previous measurements, carried out on thin ({approx}1 mm) and long (>12 mm) CZT detectors, indicated that small (1-20 {micro}m) Te inclusions can significantly degrade the device's energy resolution and detection efficiency. We are conducting detailed studies of the effects of Te inclusions by employing different characterization techniques with better spatial resolution, such as quantitative fluorescence mapping, X-ray micro-diffraction, and TEM. Also, IR microscopy and gamma-mapping with pulse-shape analysis with higher spatial resolution generated more accurate results in the areas surrounding the micro-defects (Te inclusions). Our results reveal how the performance of CdZnTe detectors is influenced by Te inclusions, such as their spatial distribution, concentration, and size. We also discuss a model of charge transport through areas populated with Te inclusions.

  19. GeTe sequences in superlattice phase change memories and their electrical characteristics

    SciTech Connect

    Ohyanagi, T. Kitamura, M.; Takaura, N.; Araidai, M.; Kato, S.; Shiraishi, K.

    2014-06-23

    We studied GeTe structures in superlattice phase change memories (superlattice PCMs) with a [GeTe/Sb{sub 2}Te{sub 3}] stacked structure by X-ray diffraction (XRD) analysis. We examined the electrical characteristics of superlattice PCMs with films deposited at different temperatures. It was found that XRD spectra differed between the films deposited at 200 °C and 240 °C; the differences corresponded to the differences in the GeTe sequences in the films. We applied first-principles calculations to calculate the total energy of three different GeTe sequences. The results showed the Ge-Te-Ge-Te sequence had the lowest total energy of the three and it was found that with this sequence the superlattice PCMs did not run.

  20. Finite temperature studies of Te adsorption on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Sen, Prasenjit; Ciraci, S.; Batra, Inder P.; Grein, C. H.; Sivananthan, S.

    2002-11-01

    We perform first principles density functional calculations to investigate the adsorption of Te on the Si(0 0 1) surface from low coverage up to a monolayer coverage. At low coverage, a Te atom is adsorbed on top of the Si surface dimer bond. At higher coverages, Te atoms adsorption causes the Si-Si dimer bond to break, lifting the (2×1) reconstruction. We find no evidence of the Te-Te dimer bond formation as a possible source of the (2×1) reconstruction at a monolayer coverage. Finite temperature ab initio molecular dynamics calculations show that Te covered Si(0 0 1) surfaces do not have any definitive reconstruction. Vibrations of the bridged Te atoms in the strongly anharmonic potentials prevent the reconstruction structure from attaining any permanent, two-dimensional periodic geometry. This explains why experiments attempting to find a definite model for the reconstruction reached conflicting conclusions.

  1. Viscosity Relaxation in Molten HgZnTe

    NASA Technical Reports Server (NTRS)

    Baird, James K.

    2002-01-01

    Because of its narrow electronic band-gap, HgZnTe solid solutions have been proposed as effective detectors for infrared radiation. To produce the best single crystals of these materials for this application, knowledge of the phase diagram that governs the freezing of the liquid is essential. Besides the phase diagram, however, some information concerning the thermophysical properties of the melt, such as viscosity, density, specific heat, and enthalpy of mixing, can also be useful. Of these thermophysical properties, the viscosity is perhaps of the most interest scientifically. Measurements using the oscillating cup method have shown that the isothermal melt requires tens of hours of equilibration time before a steady value of the viscosity can be achieved. Over this equilibration time, which depends upon temperature, the viscosity can increase by as much as a factor of two before reaching a steady state. We suggest that this relaxation phenomenon may be due to a slight polymerization of Te atoms in the melt. To account for the time dependence of the viscosity in the HgZnTe melt, we propose that the liquid acts as a solvent that favors the formation of Te atom chains. We suggest that as the melt is cooled from a high temperature to the temperature for measurement of the viscosity, a free radical polymerization of Te atoms begins. To estimate this average molecular weight, we use a simple free radical polymerization mechanism, including a depolymerization step, to calculate the time dependence to the concentration of each Te polymer molecular weight fraction. From these molecular weight fractions, we compute the weight average molecular weight of the distribution. Using the semi-empirical relation between average molecular weight and viscosity, we obtain a formula for the time dependence of the viscosity of the melt. Upon examining this formula, we find that the viscosity achieves a steady value when a balance is achieved between the rate of formation of the chains

  2. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    SciTech Connect

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  3. Optical microfiber-loaded surface plasmonic TE-pass polarizer

    NASA Astrophysics Data System (ADS)

    Ma, Youqiao; Farrell, Gerald; Semenova, Yuliya; Li, Binghui; Yuan, Jinhui; Sang, Xinzhu; Yan, Binbin; Yu, Chongxiu; Guo, Tuan; Wu, Qiang

    2016-04-01

    We propose a novel optical microfiber-loaded plasmonic TE-pass polarizer consisting of an optical microfiber placed on top of a silver substrate and demonstrate its performance both numerically by using the finite element method (FEM) and experimentally. The simulation results show that the loss in the fundamental TE mode is relatively low while at the same time the fundamental TM mode suffers from a large metal dissipation loss induced by excitation of the microfiber-loaded surface plasmonic mode. The microfiber was fabricated using the standard microheater brushing-tapering technique. The measured extinction ratio over the range of the C-band wavelengths is greater than 20 dB for the polarizer with a microfiber diameter of 4 μm, which agrees well with the simulation results.

  4. Charge transport properties of CdMnTe radiation detectors

    SciTech Connect

    Kim K.; Rafiel, R.; Boardman, M.; Reinhard, I.; Sarbutt, A.; Watt, G.; Watt, C.; Uxa, S.; Prokopovich, D.A.; Belas, E.; Bolotnikov, A.E.; James, R.B.

    2012-04-11

    Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.

  5. Phonon anharmonicity in bulk Td-MoTe2

    NASA Astrophysics Data System (ADS)

    Joshi, Jaydeep; Stone, Iris R.; Beams, Ryan; Krylyuk, Sergiy; Kalish, Irina; Davydov, Albert V.; Vora, Patrick M.

    2016-07-01

    We examine anharmonic contributions to the optical phonon modes in bulk Td-MoTe2 through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Grüneisen model. However, below 100 K, we observe nonlinear temperature-dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons. Furthermore, the highest frequency Raman modes show large changes in intensity and linewidth near T ≈ 250 K that correlate well with the T d → 1 T ' structural phase transition. These results suggest that phonon-phonon interactions can dominate anharmonic contributions at low temperatures in bulk Td-MoTe2, an experimental regime that is currently receiving attention in efforts to understand Weyl semimetals.

  6. BOREAS TE-5 Diurnal CO2 Canopy Profile Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected several data sets to investigate the vegetation-atmosphere CO2 and H2O exchange processes. These data were collected to provide detailed information within the canopy during times when TE-05 sampled canopy CO2 for carbon and oxygen isotope analysis. These measurements were made in both the NSA and SSA at the OJP, OBS, UBS, and OA sites from 25-May1994 to 08-Sep1994. CO2 profile data were not collected at SSA-OA during the first IFC. The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

  7. Nanoscale Superconducting Honeycomb Charge Order in IrTe2

    NASA Astrophysics Data System (ADS)

    Kim, Hyo Sung; Kim, Sooran; Kim, Kyoo; Min, Byung Il; Cho, Yong-Heum; Wang, Lihai; Cheong, Sang-Wook; Yeom, Han Woong

    2016-07-01

    Entanglement of charge orderings and other electronic orders such as superconductivity is in the core of challenging physics issues of complex materials including high temperature superconductivity. Here, we report on the observation of a unique nanometer scale honeycomb charge ordering of the cleaved IrTe2 surface, which hosts a superconducting state. IrTe2 was recently established to exhibit an intriguing cascade of stripe charge orders. The stripe phases coexist with a hexagonal phase, which is formed locally and falls into a superconducting state below 3 K. The atomic and electronic structures of the honeycomb and hexagon pattern of this phase are consistent with the charge order nature but the superconductivity does not survive on neighboring stripe charge order domains. The present work provides an intriguing physics issue and a new direction of functionalization for two dimensional materials.

  8. DX centers in CdTe: a density functional study

    SciTech Connect

    Du, Mao-Hua

    2008-01-01

    DX centers induced by both group-III and group-VII donors in CdTe are studied using density functional calculations. The results show that, for group-VII donors, the DX centers with a cation-cation bond ({alpha}- and {beta}-CCB-DX centers) are more stable than the previously proposed broken-bond DX (BB-DX) center and the {beta}-CCB-DX center is the most stable. The stability trend found for the CCB-DX centers for different donors in CdTe is consistent with that for GaAs and GaSb, which suggests a general rule that the CCB-DX centers are favored for small donor atoms on anion site especially for semiconductors with large anion size.

  9. CdZnTe solid-state gamma cameras

    SciTech Connect

    Butler, J.F.; Lingren, C.L.; Friesenhahn, S.J.

    1998-06-01

    The authors report the development of a CdZnTe gamma ray imager whose advantages over the conventional Anger camera include (1) improved contrast resulting from superior energy resolution and unambiguous position determination and (2) the small size and weight and high reliability inherent in an all-solid-state construction. It provides high energy resolution and peak efficiency by incorporating Digirad`s new SpectrumPlus{trademark} detector technology. The new imager employs a modular design, in which each 1 inch x 1 inch module incorporates a monolithic 64-element CdZnTe detector array and ASIC-based circuitry that provides signal conditioning for every channel, identification of valid events and addressing functions. Imagers with a wide range of sizes and shapes can be assembled by tiling modules together on a specially designed signal routing board.

  10. Nanoscale Superconducting Honeycomb Charge Order in IrTe2.

    PubMed

    Kim, Hyo Sung; Kim, Sooran; Kim, Kyoo; Min, Byung Il; Cho, Yong-Heum; Wang, Lihai; Cheong, Sang-Wook; Yeom, Han Woong

    2016-07-13

    Entanglement of charge orderings and other electronic orders such as superconductivity is in the core of challenging physics issues of complex materials including high temperature superconductivity. Here, we report on the observation of a unique nanometer scale honeycomb charge ordering of the cleaved IrTe2 surface, which hosts a superconducting state. IrTe2 was recently established to exhibit an intriguing cascade of stripe charge orders. The stripe phases coexist with a hexagonal phase, which is formed locally and falls into a superconducting state below 3 K. The atomic and electronic structures of the honeycomb and hexagon pattern of this phase are consistent with the charge order nature, but the superconductivity does not survive on neighboring stripe charge order domains. The present work provides an intriguing physics issue and a new direction of functionalization for two-dimensional materials. PMID:27221583

  11. Point Defect Characterization in CdZnTe

    SciTech Connect

    Gul,R.; Li, Z.; Bolotnikov, A.; Keeter, K.; Rodriguez, R.; James, R.

    2009-03-24

    Measurements of the defect levels and performance testing of CdZnTe detectors were performed by means of Current Deep Level Transient Spectroscopy (I-DLTS), Transient Charge Technique (TCT), Current versus Voltage measurements (I-V), and gamma-ray spectroscopy. CdZnTe crystals were acquired from different commercial vendors and characterized for their point defects. I-DLTS studies included measurements of defect parameters such as energy levels in the band gap, carrier capture cross sections, and defect densities. The induced current due to laser-generated carriers was measured using TCT. The data were used to determine the transport properties of the detectors under study. A good correlation was found between the point defects in the detectors and their performance.

  12. TeV scale dark matter and electroweak radiative corrections

    SciTech Connect

    Ciafaloni, Paolo; Urbano, Alfredo

    2010-08-15

    Recent anomalies in cosmic rays data, namely, from the PAMELA Collaboration, can be interpreted in terms of TeV scale decaying/annihilating dark matter. We analyze the impact of radiative corrections coming from the electroweak sector of the standard model on the spectrum of the final products at the interaction point. As an example, we consider virtual one loop corrections and real gauge bosons emission in the case of a very heavy vector boson annihilating into fermions. We find electroweak corrections that are relevant, but not as big as sometimes found in the literature; we relate this mismatch to the issue of gauge invariance. At scales much higher than the symmetry breaking scale, one loop electroweak effects are so big that eventually higher orders/resummations have to be considered: we advocate for the inclusion of these effects in parton shower Monte Carlo models aiming at the description of TeV scale physics.

  13. Effective cosmological constant from TeV-scale physics

    SciTech Connect

    Klinkhamer, F. R.

    2010-10-15

    It has been suggested previously that the observed cosmological constant {Lambda} corresponds to the remnant vacuum energy density of dynamical processes taking place at a cosmic age set by the mass scale M{approx}E{sub ew} of ultramassive particles with electroweak interactions. Here, a simple modification of the nondissipative dynamic equations of q-theory is presented, which produces a remnant vacuum energy density (effective cosmological constant) of the correct order of magnitude. Combined with the observed value of {Lambda}, a first estimate of the required value of the energy scale E{sub ew} ranges from 3 to 9 TeV, depending on the number of species of ultramassive particles and assuming a dissipative coupling constant of order unity. If correct, this estimate implies the existence of new TeV-scale physics beyond the standard model.

  14. Engineering relativistic effects in ferroelectric SnTe

    NASA Astrophysics Data System (ADS)

    Plekhanov, E.; Barone, P.; Di Sante, D.; Picozzi, S.

    2014-10-01

    Spin-orbit coupling is increasingly seen as a rich source of novel phenomena, as shown by the recent excitement around topological insulators and Rashba effects. We here show that the addition of ferroelectric degrees of freedom to a semiconductor featuring topologically nontrivial properties, such as SnTe, merges the intriguing field of spin-orbit-driven physics with nonvolatile functionalities appealing for spintronics. By using a variety of modeling techniques, we show that a strikingly rich sequence of phases can be induced in SnTe, when going from a room-temperature cubic phase to a low-temperature ferroelectric structure, ranging from a topological crystalline insulator to a time-reversal-invariant Z2 topological insulator to a "ferroelectric Rashba semiconductor," exhibiting a huge electrically controllable Rashba effect in the bulk band structure.

  15. Dependence of CdTe response of bias history

    SciTech Connect

    Sites, J.R.; Sasala, R.A.; Eisgruber, I.L.

    1995-11-01

    Several time-dependent effect have been observed in CdTe cells and modules in recent years. Some appear to be related to degradation at the back contact, some to changes in temperature at the thin-film junction, and some to the bias history of the cell or module. Back-contact difficulties only occur in some cases, and the other two effects are reversible. Nevertheless, confusion in data interpretation can arise when these effects are not characterized. This confusion can be particularly acute when more than one time-dependent effect occurs during the same measurement cycle. The purpose of this presentation is to help categorize time-dependent effects in CdTe and other thin-film cells to elucidate those related to bias history, and to note differences between cell and module analysis.

  16. Electrical Conductivity of HgTe at High Temperatures

    NASA Technical Reports Server (NTRS)

    Li, C.; Lehoczky, S. L.; Su, C.-H.; Scripa, R. N.

    2004-01-01

    The electrical conductivity of HgTe was measured using a rotating magnetic field method from 300 K to the melting point (943 K). A microscopic theory for electrical conduction was used to calculate the expected temperature dependence of the HgTe conductivity. A comparison between the measured and calculated conductivities was used to obtain the estimates of the temperature dependence of Gamma(sub 6)-Gamma(sub 8) energy gap from 300 K to 943 K. The estimated temperature coefficient for the energy gap was comparable to the previous results at lower temperatures (less than or equal to 300 K). A rapid increase in the conductivity just above 300 K and a subsequent decrease at 500 K is attributed to band crossover effects. This paper describes the experimental approach and some of the theoretical calculation details.

  17. CdTe nanoparticles synthesized by laser ablation

    SciTech Connect

    Semaltianos, N. G.; Logothetidis, S.; Perrie, W.; Romani, S.; Potter, R. J.; Dearden, G.; Watkins, K. G.; Sharp, M.

    2009-07-20

    Nanoparticle generation by laser ablation of a solid target in a liquid environment is an easy, fast, and 'green' method for a large scale production of nanomaterials with tailored properties. In this letter we report the synthesis of CdTe nanoparticles by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy=6 {mu}J (fluence=1.7 J/cm{sup 2})] ablation of the target material. Nanoparticles with diameters from {approx}2 up to {approx}25 nm were observed to be formed in the colloidal solution. Their size distribution follows the log-normal function with a statistical median diameter of {approx_equal}7.1 nm. Their crystal structure is the same as that of the bulk material (cubic zincblende) and they are slightly Cd-rich (Cd:Te percentage ratio {approx}1:0.9). Photoluminescence emission from the produced nanoparticles was detected in the deep red ({approx}652 nm)

  18. Measurement of polarisation in collisions at = 7 TeV

    NASA Astrophysics Data System (ADS)

    Aaij, R.; Adeva, B.; Adinolfi, M.; Affolder, A.; Ajaltouni, Z.; Albrecht, J.; Alessio, F.; Alexander, M.; Ali, S.; Alkhazov, G.; Alvarez Cartelle, P.; Alves, A. A.; Amato, S.; Amerio, S.; Amhis, Y.; An, L.; Anderlini, L.; Anderson, J.; Andreassen, R.; Andreotti, M.; Andrews, J. E.; Appleby, R. B.; Aquines Gutierrez, O.; Archilli, F.; Artamonov, A.; Artuso, M.; Aslanides, E.; Auriemma, G.; Baalouch, M.; Bachmann, S.; Back, J. J.; Badalov, A.; Balagura, V.; Baldini, W.; Barlow, R. J.; Barschel, C.; Barsuk, S.; Barter, W.; Batozskaya, V.; Bauer, Th.; Bay, A.; Beddow, J.; Bedeschi, F.; Bediaga, I.; Belogurov, S.; Belous, K.; Belyaev, I.; Ben-Haim, E.; Bencivenni, G.; Benson, S.; Benton, J.; Berezhnoy, A.; Bernet, R.; Bettler, M.-O.; van Beuzekom, M.; Bien, A.; Bifani, S.; Bird, T.; Bizzeti, A.; Bjørnstad, P. M.; Blake, T.; Blanc, F.; Blouw, J.; Blusk, S.; Bocci, V.; Bondar, A.; Bondar, N.; Bonivento, W.; Borghi, S.; Borgia, A.; Borsato, M.; Bowcock, T. J. V.; Bowen, E.; Bozzi, C.; Brambach, T.; van den Brand, J.; Bressieux, J.; Brett, D.; Britsch, M.; Britton, T.; Brook, N. H.; Brown, H.; Bursche, A.; Busetto, G.; Buytaert, J.; Cadeddu, S.; Calabrese, R.; Callot, O.; Calvi, M.; Calvo Gomez, M.; Camboni, A.; Campana, P.; Campora Perez, D.; Carbone, A.; Carboni, G.; Cardinale, R.; Cardini, A.; Carranza-Mejia, H.; Carson, L.; Carvalho Akiba, K.; Casse, G.; Cassina, L.; Castillo Garcia, L.; Cattaneo, M.; Cauet, Ch.; Cenci, R.; Charles, M.; Charpentier, Ph.; Cheung, S.-F.; Chiapolini, N.; Chrzaszcz, M.; Ciba, K.; Cid Vidal, X.; Ciezarek, G.; Clarke, P. E. L.; Clemencic, M.; Cliff, H. V.; Closier, J.; Coca, C.; Coco, V.; Cogan, J.; Cogneras, E.; Collins, P.; Comerma-Montells, A.; Contu, A.; Cook, A.; Coombes, M.; Coquereau, S.; Corti, G.; Corvo, M.; Counts, I.; Couturier, B.; Cowan, G. A.; Craik, D. C.; Cruz Torres, M.; Cunliffe, S.; Currie, R.; D'Ambrosio, C.; Dalseno, J.; David, P.; David, P. N. Y.; Davis, A.; De Bruyn, K.; De Capua, S.; De Cian, M.; De Miranda, J. M.; De Paula, L.; De Silva, W.; De Simone, P.; Decamp, D.; Deckenhoff, M.; Del Buono, L.; Déléage, N.; Derkach, D.; Deschamps, O.; Dettori, F.; Di Canto, A.; Dijkstra, H.; Donleavy, S.; Dordei, F.; Dorigo, M.; Dosil Suárez, A.; Dossett, D.; Dovbnya, A.; Dupertuis, F.; Durante, P.; Dzhelyadin, R.; Dziurda, A.; Dzyuba, A.; Easo, S.; Egede, U.; Egorychev, V.; Eidelman, S.; Eisenhardt, S.; Eitschberger, U.; Ekelhof, R.; Eklund, L.; El Rifai, I.; Elsasser, Ch.; Esen, S.; Evans, T.; Falabella, A.; Färber, C.; Farinelli, C.; Farry, S.; Ferguson, D.; Fernandez Albor, V.; Ferreira Rodrigues, F.; Ferro-Luzzi, M.; Filippov, S.; Fiore, M.; Fiorini, M.; Firlej, M.; Fitzpatrick, C.; Fiutowski, T.; Fontana, M.; Fontanelli, F.; Forty, R.; Francisco, O.; Frank, M.; Frei, C.; Frosini, M.; Fu, J.; Furfaro, E.; Gallas Torreira, A.; Galli, D.; Gandelman, M.; Gandini, P.; Gao, Y.; Garofoli, J.; Garra Tico, J.; Garrido, L.; Gaspar, C.; Gauld, R.; Gavardi, L.; Gersabeck, E.; Gersabeck, M.; Gershon, T.; Ghez, Ph.; Gianelle, A.; Giani, S.; Gibson, V.; Giubega, L.; Gligorov, V. V.; Göbel, C.; Golubkov, D.; Golutvin, A.; Gomes, A.; Gordon, H.; Gotti, C.; Grabalosa Gándara, M.; Graciani Diaz, R.; Granado Cardoso, L. A.; Graugés, E.; Graziani, G.; Grecu, A.; Greening, E.; Gregson, S.; Griffith, P.; Grillo, L.; Grünberg, O.; Gui, B.; Gushchin, E.; Guz, Yu.; Gys, T.; Hadjivasiliou, C.; Haefeli, G.; Haen, C.; Haines, S. C.; Hall, S.; Hamilton, B.; Hampson, T.; Han, X.; Hansmann-Menzemer, S.; Harnew, N.; Harnew, S. T.; Harrison, J.; Hartmann, T.; He, J.; Head, T.; Heijne, V.; Hennessy, K.; Henrard, P.; Henry, L.; Hernando Morata, J. A.; van Herwijnen, E.; Heß, M.; Hicheur, A.; Hill, D.; Hoballah, M.; Hombach, C.; Hulsbergen, W.; Hunt, P.; Hussain, N.; Hutchcroft, D.; Hynds, D.; Iakovenko, V.; Idzik, M.; Ilten, P.; Jacobsson, R.; Jaeger, A.; Jalocha, J.; Jans, E.; Jaton, P.; Jawahery, A.; Jezabek, M.; Jing, F.; John, M.; Johnson, D.; Jones, C. R.; Joram, C.; Jost, B.; Jurik, N.; Kaballo, M.; Kandybei, S.; Kanso, W.; Karacson, M.; Karbach, T. 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    2014-05-01

    The polarisation of prompt mesons is measured by performing an angular analysis of decays using proton-proton collision data, corresponding to an integrated luminosity of 1.0, collected by the LHCb detector at a centre-of-mass energy of 7 TeV. The polarisation is measured in bins of transverse momentum and rapidity in the kinematic region and , and is compared to theoretical models. No significant polarisation is observed.

  19. Electronic and ground state properties of ThTe

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Purvee; Singh, Sadhna

    2016-05-01

    The electronic properties of ThTe in cesium chloride (CsCl, B2) structure are investigated in the present paper. To study the ground state properties of thorium chalcogenide, the first principle calculations have been calculated. The bulk properties, including lattice constant, bulk modulus and its pressure derivative are obtained. The calculated equilibrium structural parameters are in good agreement with the available experimental and theoretical results.

  20. Optical properties of oxygenated CdTe thin films

    NASA Astrophysics Data System (ADS)

    Zapata-Navarro, A.; Peña-Chapa, J. L.; Villagrán De León, J. C.

    1996-07-01

    Cadmium telluride oxide films (CdTe-O) were grown by a radio frequency sputtering technique on glass slide substrates using a controlled plasma (Ar-N2O). The films were studied by Auger electron spectroscopy (AES) and optical transmission. We demonstrate that the oxidation process enhances the transmittance of the films into the visible part of the spectrum depending on the oxygen concentration.