168,266 research outputs found
Surface characterisation of contact materials for thin film CdTe solar cells
No full textThe deposition of tellurium onto the low index faces of copper single crystals induces a range of structures such as the (2√3×2√3)R30° surface substitutional alloy on the Cu(111) surface. These structures have been studied using a combination of scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), X-ray photoemission (XPS) and ultraviolet photoemission (UPS).
The deposition of tellurium on to the Cu(111) surface produced several structures including (2√3×2√3)R30° phase for a coverage of 0.17ML, For a coverage of 0.33ML a (√3×√3)R30° surface alloy was found. For coverages greater than 0.66ML a bulk alloy was formed which is consistent with the Cu3Te2 phase. The deposition of tellurium onto the Cu(110) surface produced a c(2×2) structure for a coverage of 0.5ML. Further deposition causes uniaxial compression of the over-layer as indicated by the LEED patterns. STM of this surface revealed two hexagonal domains rotated 30° with respect to each other.
The deposition of tellurium on to the Cu(100) surface produced a p(2×2) over−layer for a coverage of 0.25ML. Further deposition lead to a series of coincidence lattices showing co-existing structures including split c(2×2) spots in the LEED pattern. A heavily streaked split c(2×2) LEED pattern was observed for tellurium coverages over 1ML dosage where STM images revealed a heavily striped surface with two domains perpendicular to each other. The larger structures observed suggest 3D growth of these stripes. On all 3 surfaces the work function was found to increase upon tellurium deposition.
The electronic structure of indium oxide thin films was investigated after different treatments in ultra high vacuum using XPS and UPS. The (111) surface was investigated using a combination of hard and soft X-rays showing the lower portion of the valence band to be dominated by oxygen orbitals while the higher portion of the valence band indium orbitals. The valence band was then probed and the work function measured after different annealing treatments. For all 3 samples, (111) (110) and (100) the work function was found to increase when annealing in oxygen when compared to annealing in vacuum. This is attributed to the movement of the Fermi level as the carrier concentration at the surface is altered. The lowering of observed gap states when annealing in oxygen also suggests they may originate from oxygen vacancies within the surface
Surface characterisation of contact materials for thin film CdTe solar cells
No full textThe deposition of tellurium onto the low index faces of copper single crystals induces a range of structures such as the (2√3×2√3)R30° surface substitutional alloy on the Cu(111) surface. These structures have been studied using a combination of scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), X-ray photoemission (XPS) and ultraviolet photoemission (UPS).
The deposition of tellurium on to the Cu(111) surface produced several structures including (2√3×2√3)R30° phase for a coverage of 0.17ML, For a coverage of 0.33ML a (√3×√3)R30° surface alloy was found. For coverages greater than 0.66ML a bulk alloy was formed which is consistent with the Cu3Te2 phase. The deposition of tellurium onto the Cu(110) surface produced a c(2×2) structure for a coverage of 0.5ML. Further deposition causes uniaxial compression of the over-layer as indicated by the LEED patterns. STM of this surface revealed two hexagonal domains rotated 30° with respect to each other.
The deposition of tellurium on to the Cu(100) surface produced a p(2×2) over−layer for a coverage of 0.25ML. Further deposition lead to a series of coincidence lattices showing co-existing structures including split c(2×2) spots in the LEED pattern. A heavily streaked split c(2×2) LEED pattern was observed for tellurium coverages over 1ML dosage where STM images revealed a heavily striped surface with two domains perpendicular to each other. The larger structures observed suggest 3D growth of these stripes. On all 3 surfaces the work function was found to increase upon tellurium deposition.
The electronic structure of indium oxide thin films was investigated after different treatments in ultra high vacuum using XPS and UPS. The (111) surface was investigated using a combination of hard and soft X-rays showing the lower portion of the valence band to be dominated by oxygen orbitals while the higher portion of the valence band indium orbitals. The valence band was then probed and the work function measured after different annealing treatments. For all 3 samples, (111) (110) and (100) the work function was found to increase when annealing in oxygen when compared to annealing in vacuum. This is attributed to the movement of the Fermi level as the carrier concentration at the surface is altered. The lowering of observed gap states when annealing in oxygen also suggests they may originate from oxygen vacancies within the surface
The HESP (High Energy Solar Physics) project
No full textA project for space observations of solar flares for the coming solar maximum phase is briefly described. The main objective is to make a comprehensive study of high energy phenomena of flares through simultaneous imagings in both hard and soft X-rays. The project will be performed with collaboration from US scientists. The HESP (High Energy Solar Physics) WG of ISAS (Institute of Space and Astronautical Sciences) has extensively discussed future aspects of space observations of high energy phenomena of solar flares based on successful results of the Hinotori mission, and proposed a comprehensive research program for the next solar maximum, called the HESP (SOLAR-A) project. The objective of the HESP project is to make a comprehensive study of both high energy phenomena of flares and quiet structures including pre-flare states, which have been left uncovered by SMM and Hinotori. For such a study simultaneous imagings with better resolutions in space and time in a wide range of energy will be extremely important
Developement of a stabilized Fabry-Perot etalon based calibrator for Hanle Echelle Spectrograph (HESP)
No full textAccurate wavelength calibration is an important factor for any measurement with high resolution spectrographs. Stellar spectrum comprises of discrete absorption or emission lines whose position is precisely determined by calibrating the spectrograph using known reference lines generated from laboratory sources. For the spectrograph to measure small variations in Doppler shift, the wavelength calibration must be sufficiently stable during observation time. Instrument instability, mainly due to environmental factors like temperature and pressure variations, limitations of traditional calibration methods, for example Th-Ar lamps, are the main challenges which high precision spectroscopy. Through proper environmental control, by maintaining pressure at few mbar and temperature fluctuations within 0.05C, Fabry P\'erot etalon (FP) can yield a velocity precision of 1-10 m/s, when used for wavelength calibration. We have developed a passively stabilized FP based wavelength calibrator for Hanle Echelle Spectrograph (HESP) installed on Himalayan Chandra Telescope (HCT) at Indian Astronomical Observatory (IAO), Hanle, India. The etalon has been characterized using Fourier Transform Spectrograph (FTS) and initial test runs have been performed with HESP. In this paper we present the design and construction of the instrument along with preliminary test results obtained from HESP
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dr. Edward P. Wimberly, ITC, July 2011
No full textThis video is a conversation with Dr. Edward P. Wimberly. Dr. Wimberly talks about his book, "No Shame in Wesley's Gospel: A Twenty-First Century Pastoral Gospel". Brad Ost, AUC Woodruff Library, is the interviewer
Universal Statistical Properties of Inertial-particle Trajectories in Three-dimensional, Homogeneous, Isotropic, Fluid Turbulence
No full textWe obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(Φ), of the angle Φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(Φ) ∼Φ−, with a new universal exponent ≃ 4
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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