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  • 1
    ISSN: 1432-0630
    Keywords: 73.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The work function of 13 polycrystalline transition metal suicides was measured by photoemission in uhv. Their values are discussed in relationship to their Schottky barrier heights on n-Si. While there appears to be a weak correlation for a certain group of transition metal suicides, the values of the 5d-noble metal suicides including some of the lattice matched Ni suicides appear to be completely uncorrelated. Experimental values of work functions are compared to the values proposed previously by Freeouf.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 68.65 ; 79.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this work we present a systematic study of the local photovoltaic properties of ReS2, using a scanning tunneling microscope (STM). The tunneling junction of the STM was optically illuminated during the tunneling process. The phase sensitive detected photo-induced tunneling current (PITC) was studied as a function of wavelength and surface topography. In order to improve the performance of ReS2 solar cells, the samples were treated with NaI/I2 and EDTA solutions. Relative to the untreated sample, the EDTA-treated samples show an increase in the photo-induced tunneling current by a factor of 8–10 in the whole spectral range, the NaI/I-treated samples by 2–3. Two dimensional mapping of the PITC was performed on an atomic scale and compared to the surface topography.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4391-4400 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed analysis of the radiative recombination processes in CuxGaySe2 epitaxial layers is presented aiming at an investigation of the intrinsic defect levels as a function of chemical composition. CuxGaySe2 is grown by metalorganic vapor phase epitaxy to allow a precise control of composition. Temperature and excitation intensity dependent photoluminescence is used to identify different recombination mechanisms and to determine the ionization energies of the defect levels involved. Defect-correlated optical transitions in Cu-rich epilayers are described in a recombination model consisting of two acceptor and one donor levels showing ionization energies of (60±10) meV, (100±10) meV, and (12±5) meV, respectively. The identification of a shallow compensating donor in CuxGaySe2 and the assignment of the 100 meV state to an acceptor are the most important new aspects in this model. Photoluminescence properties of layers showing Ga-rich compositions are discussed in a model of highly doped and highly compensated semiconductors—the model of fluctuating potentials. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5266-5268 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spectral quantum efficiency in ReS2 heterodiodes was measured in the wavelength region between 600 and 850 nm. Anisotropy effects in the van der Waals plane were observed by means of linearly polarized light at normal incidence to the (001) plane of ReS2 single crystals. The anisotropy in quantum efficiency reaches its maximum at λ=627 nm and therefore, ReS2 devices are well suited for detecting the angle of polarization in experiments using a HeNe laser. At wavelengths above 750 nm the sign in polarization quantum efficiency changes due to various optical transitions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2979-2981 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The size reduction of modern electronic devices creates a growing demand for characterization tools to determine material properties on a nanometer scale. The Kelvin probe force microscope is designed to obtain laterally resolved images of the sample's work function. Using a setup in ultrahigh vacuum, we were able to distinguish work function variations for differently oriented crystal facets of single grains on a semiconductor surface. For the tetragonal solar cell material CuGaSe2 the experiments demonstrate differences as low as 30 meV between (102) and (111) oriented surfaces and up to 255 meV between (1¯1¯2¯) and (110) surfaces. This influences the band bending of solar cell heterostructures and consequently also the solar power conversion efficiency. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 286-288 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present quantitative measurements of the work function of semiconductor and metal surfaces prepared in ultrahigh vacuum (UHV) using a combination of UHV noncontact atomic force microscopy and Kelvin probe force microscopy. High energetic and lateral resolution is achieved by using the second resonance frequency of the cantilever to measure the electrostatic forces, while the first resonance frequency is used to simultaneously obtain topographic images by the frequency modulation technique. Spatially resolved work-function measurements reveal a reduced work function in the vicinity of steps on highly oriented pyrolytic graphite. On the GaAs(110) surface it could be demonstrated that defect states in the forbidden band gap cause a local pinning of the Fermi level along monolayer steps. On p-WSe2(0001) work-function variations due to the Coulomb potential of single dopant sites were resolved. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1099-1101 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of the ZnSe/CuGaSe2 heterointerface was studied by x-ray photoelectron spectroscopy (XPS). ZnSe was sequentially grown on CuGaSe2(001) epilayers. In situ photoemission spectra of the Ga 3d and Zn 3d core levels as well as XPS valence bands were acquired after each deposition step. The valence-band offset is determined to be ΔEV=0.6±0.1 eV. As a consequence, a nearly symmetric "type-I" band alignment for the ZnSe/CuGaSe2 heterojunction with a conduction-band offset of ΔEC=0.4±0.1 eV is found. Concerning the band alignment ZnSe can, therefore, be expected to be a suitable buffer material for CuGaSe2-based thin-film solar cells. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2888-2890 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Admittance spectroscopy was measured on Cu(In,Ga)(S,Se)2 thin film and single crystal heterojunctions. The emission rates of defects for various near-stoichiometric compositions follow a Meyer–Neldel rule, showing increasing attempt-to-escape frequencies with increasing defect depth. Defects in highly (In,Ga)-rich material showed lower attempt-to-escape frequencies and follow a separate Meyer–Neldel relation. Repetitive air annealing of a CuInSe2 heterojunction revealed a shift of the depth and capture cross section of an observed defect. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 62 (1996), S. 181-185 
    ISSN: 1432-0630
    Keywords: 72.70 ; 85.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Heterojunctions, such as ZnO/CdS/CuGaSe2, were fabricated for photovoltaic applications. Optimization of device structures based on monocrystalline CuGaSe2 led to the highest-to-date power conversion efficiencies for CuGaSe2 solar cells. At room temperature under 100 mW/cm2 AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm2, and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination intensity and temperature, spectral response and electron-beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assisted by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias ofV 〉 0.5 V or an illumination level ofP 〉 10 mW/cm2. Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 43 (1987), S. 197-201 
    ISSN: 1432-0649
    Keywords: 81.60 ; 82.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract X-ray photoemission spectroscopy (XPS) has been used to study the surface reaction of Zn3P2 single crystals. The spectra of crystals exposed to H2, O2, CO2, O2+H2O or CO2+H2O during a four week period were compared to the spectra of as-grown or in UHV scraped samples. For samples contaminated with the wet gases O2+H2O and CO2+H2O additional phosphorus core levels together with a shift of the zinc core levels were observed. For crystals exposed to atmosphere during several months no phosphorus could be detected on the gasgrown surface, whereas the stochiometry of Zn3P2 was maintained within the bulk. Crystals with scraped surfaces showed no moisture sensitivity. No surface contamination was also detected for Zn3P2 crystals deposited with up to 1000 L H2O or exposed to atmosphere during 30 min.
    Type of Medium: Electronic Resource
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