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Hiroyuki Yoshida - One of the best experts on this subject based on the ideXlab platform.

  • Measuring the Electron Affinity of organic solids: an indispensable new tool for organic Electronics
    Analytical and Bioanalytical Chemistry, 2014
    Co-Authors: Hiroyuki Yoshida
    Abstract:

    Electron Affinity is a fundamental energy parameter of materials. In organic semiconductors, the Electron Affinity is closely related to Electron conduction. It is not only important to understand fundamental Electronic processes in organic solids, but it is also indispensable for research and development of organic semiconductor devices such as organic light-emitting diodes and organic photovoltaic cells. However, there has been no experimental technique for examining the Electron Affinity of organic materials that meets the requirements of such research. Recently, a new method, called low-energy inverse-photoemission spectroscopy, has been developed. A beam of low-energy Electrons is focused onto the sample surface, and photons emitted owing to the radiative transition to unoccupied states are then detected. From the onset of the spectral intensity, the Electron Affinity is determined within an uncertainty of 0.1 eV. Unlike in conventional inverse-photoemission spectroscopy, sample damage is negligible and the resolution is improved by a factor of 2. The principle of the method and several applications are reported. Figure Energy level diagram of low-energy inverse photoemission spectroscopy, LEIPS (left). A beam of low-energy Electrons with the kinetic energy E _k is focused onto the sample surface, and photons hν emitted owing to the radiative transition to unoccupied states are detected. From the onset of the spectral intensity, the Electron Affinity E _A is determined. The Electron affinities of typical organic semiconductors determined using LEIPS (right).

  • measuring the Electron Affinity of organic solids an indispensable new tool for organic Electronics
    Analytical and Bioanalytical Chemistry, 2014
    Co-Authors: Hiroyuki Yoshida
    Abstract:

    Electron Affinity is a fundamental energy parameter of materials. In organic semiconductors, the Electron Affinity is closely related to Electron conduction. It is not only important to understand fundamental Electronic processes in organic solids, but it is also indispensable for research and development of organic semiconductor devices such as organic light-emitting diodes and organic photovoltaic cells. However, there has been no experimental technique for examining the Electron Affinity of organic materials that meets the requirements of such research. Recently, a new method, called low-energy inverse-photoemission spectroscopy, has been developed. A beam of low-energy Electrons is focused onto the sample surface, and photons emitted owing to the radiative transition to unoccupied states are then detected. From the onset of the spectral intensity, the Electron Affinity is determined within an uncertainty of 0.1 eV. Unlike in conventional inverse-photoemission spectroscopy, sample damage is negligible and the resolution is improved by a factor of 2. The principle of the method and several applications are reported.

  • Electron Affinity of pentacene thin film studied by radiation damage free inverse photoemission spectroscopy
    Applied Physics Letters, 2013
    Co-Authors: Weining Han, Hiroyuki Yoshida, Nobuo Ueno, Satoshi Kera
    Abstract:

    The Electron Affinity of pentacene thin films has been evaluated during the last decades, but it is still under controversial due to varieties of film quality and radiation damages of the films introduced during inverse photoemission spectroscopy (IPES) experiment together with insufficient energy resolution of the instruments. We employed the near-ultraviolet IPES with a better energy resolution 0.27 ∼ 0.32 eV and using lower energy Electron beams (0 eV ≤ Ei ≤ 4.9 eV) to study the unoccupied states of pentacene thin film. Due to a large mean-free-path of the Electron in this energy region, the threshold Electron Affinity of the bulk of pentacene film was precisely determined to be 2.70 ± 0.03 eV. Using the threshold ionization energy of 4.90 ± 0.05 eV determined by ultraviolet photoemission spectroscopy, the band-gap energy of the pentacene film is obtained to be 2.20 ± 0.06 eV.

Martin Stutzmann - One of the best experts on this subject based on the ideXlab platform.

  • Electron Affinity of AlxGa1−xN(0001) surfaces
    Applied Physics Letters, 2001
    Co-Authors: S.p. Grabowski, M. Schneider, Hermann Nienhaus, W. Mönch, R. Dimitrov, Oliver Ambacher, Martin Stutzmann
    Abstract:

    The Electronic properties and the Electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and Electron affinities as a function of composition x were determined. A decrease in Electron Affinity with increasing aluminum content was found, but the Electron Affinity remains positive for all x. Thus, earlier predictions of negative Electron Affinity for high aluminum content were not confirmed.

  • Electron Affinity of alxga1 xn 0001 surfaces
    Applied Physics Letters, 2001
    Co-Authors: S.p. Grabowski, M. Schneider, Hermann Nienhaus, W. Mönch, R. Dimitrov, Oliver Ambacher, Martin Stutzmann
    Abstract:

    The Electronic properties and the Electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and Electron affinities as a function of composition x were determined. A decrease in Electron Affinity with increasing aluminum content was found, but the Electron Affinity remains positive for all x. Thus, earlier predictions of negative Electron Affinity for high aluminum content were not confirmed.

R J Nemanich - One of the best experts on this subject based on the ideXlab platform.

  • (Negative) Electron Affinity of AlN and AlGaN Alloys
    MRS Proceedings, 2011
    Co-Authors: R J Nemanich, M.c. Benjamin, S.p. Bozeman, B.l. Ward, S. W. King, Michael D. Bremser, Z. Zhang, R. F. Davis, Jerry Bernholc
    Abstract:

    The Electron Affinity of a semiconductor defines the relationship of the vacuum level and the semiconductor band structure. It is dependent on the atomic orbitals of the material and the surface termination. We report experimental and theoretical results that support the presence of a negative Electron Affinity on AlN and the Al rich AlGaN alloys. The GaN surface is found to exhibit a (positive) Electron Affinity of 3.3eV. The experimental measurements employ UV-photoemission spectroscopy on in situ gas-source MBE samples and on CVD samples. Theoretical results indicate that the (negative) Electron Affinity of AlN depends sensitively on the surface reconstruction and adatom termination. The experimental dependence of the Electron Affinity on alloy concentration is presented. The results indicate that AlGaN alloys with band gap similar or greater than that of diamond will exhibit a negative Electron Affinity. Field emission results are reported, and the characteristics are similar to those obtained from a diamond film. Issues related to cold cathode Electronic devices based on NEA surfaces are noted.

  • polarization dependent Electron Affinity of linbo3 surfaces
    Applied Physics Letters, 2004
    Co-Authors: Woochul Yang, Brian J Rodriguez, Alexei Gruverman, R J Nemanich
    Abstract:

    Polar surfaces of a ferroelectric LiNbO3 crystal with periodically poled domains are explored using UV-photoElectron emission microscopy (PEEM). Compared with the positive domains (domains with positive surface polarization charges), a higher photoelectric yield is found from the negative domains (domains with negative surface polarization charges), indicating a lower photothreshold and a corresponding lower Electron Affinity. The photon-energy-dependent contrast in the PEEM images of the surfaces indicates that the photothreshold of the negative domains is ∼4.6eV while that of the positive domains is greater than ∼6.2eV. We propose that the threshold difference between the opposite domains can be attributed to a variation of the Electron Affinity due to opposite surface dipoles induced by surface adsorbates.

  • Negative Electron Affinity surfaces of aluminum nitride and diamond
    Diamond and Related Materials, 1996
    Co-Authors: R J Nemanich, P. K. Baumann, Mark C. Benjamin, Sean W. King, J. Van Der Weide, Robert F. Davis
    Abstract:

    Abstract The Electron Affinity of diamond and AlGaN surfaces are studied by UV photoemission spectroscopy. It is shown that H terminated diamond surfaces exhibit a negative Electron Affinity while oxide terminated surfaces exhibit a positive Electron Affinity. In addition, thin metal layers can also induce a NEA on both (100) and (111) surfaces of diamond. Photoemission results of AlGaN alloy films grown on 6HSiC indicate a negative Electron Affinity for as-prepared and air exposed surfaces with high Al concentrations.

  • observation of a negative Electron Affinity for boron nitride
    Applied Physics Letters, 1995
    Co-Authors: M J Powers, R J Nemanich, R. F. Davis, Mark C. Benjamin, L M Porter, J J Cuomo, G L Doll, Stephen J Harris
    Abstract:

    This study reports UV‐photoemission (UPS) measurements made on boron nitride crystals and thin films. The materials examined are commercial grade c‐BN powder and thin films of BN deposited with ion beam assisted e‐beam evaporation and laser ablation. The thin film samples examined exhibited varying amounts of sp3 (cubic) and sp2 (hexagonal, amorphous) bonding as determined by FTIR measurements. The UPS measurements displayed the spectral distribution of the low energy photoemitted Electrons and the total energy width of the spectra. These characteristics can be related to the Electron Affinity. The measurements on several of the BN powder and thin film samples revealed features in the emission spectra which are indicative of a negative Electron Affinity (NEA) surface.

S.p. Grabowski - One of the best experts on this subject based on the ideXlab platform.

  • Electron Affinity of AlxGa1−xN(0001) surfaces
    Applied Physics Letters, 2001
    Co-Authors: S.p. Grabowski, M. Schneider, Hermann Nienhaus, W. Mönch, R. Dimitrov, Oliver Ambacher, Martin Stutzmann
    Abstract:

    The Electronic properties and the Electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and Electron affinities as a function of composition x were determined. A decrease in Electron Affinity with increasing aluminum content was found, but the Electron Affinity remains positive for all x. Thus, earlier predictions of negative Electron Affinity for high aluminum content were not confirmed.

  • Electron Affinity of alxga1 xn 0001 surfaces
    Applied Physics Letters, 2001
    Co-Authors: S.p. Grabowski, M. Schneider, Hermann Nienhaus, W. Mönch, R. Dimitrov, Oliver Ambacher, Martin Stutzmann
    Abstract:

    The Electronic properties and the Electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and Electron affinities as a function of composition x were determined. A decrease in Electron Affinity with increasing aluminum content was found, but the Electron Affinity remains positive for all x. Thus, earlier predictions of negative Electron Affinity for high aluminum content were not confirmed.

Toshihiro Ando - One of the best experts on this subject based on the ideXlab platform.

  • Negative Electron Affinity of cubic boron nitride
    Diamond and Related Materials, 1999
    Co-Authors: Kian Ping Loh, Takashi Taniguchi, Isao Sakaguchi, Mikka Nishitani-gamo, Toshihiro Ando
    Abstract:

    Abstract We have verified that the condition of negative Electron Affinity (NEA) exists on both single crystal cubic boron nitride (001)-(1×1) and polycrystalline cubic boron nitride (c-BN). The NEA condition has been linked to the presence of chemisorbed hydrogen on the surface. Annealing the c-BN to temperatures in excess of 1200 °C converts the surface to a positive Electron Affinity condition, which is believed to be due to the desorption of hydrogen from the surface. Subsequent exposure of the annealed surface to atomic hydrogen or cesium metal can regenerate the NEA condition.

  • surface conditioning of chemical vapor deposited hexagonal boron nitride film for negative Electron Affinity
    Applied Physics Letters, 1999
    Co-Authors: Kian Ping Loh, Isao Sakaguchi, Takashi Sugino, Mikka N Gamo, Shigeru Tagawa, Toshihiro Ando
    Abstract:

    The surface conditions favoring a negative Electron Affinity (NEA) on hexagonal boron nitride (h-BN) grown by radio-frequency plasma-assisted chemical vapor deposition (CVD) have been investigated by ultraviolet photoElectron spectroscopy. The NEA condition on the h-BN film appears to be resistant to oxygen-plasma or in-vacuo atomic oxygen treatment. It is not certain whether the segregation of bulk hydrogen onto the surface helps to promote the NEA; the depth profile of the deposited film reveals about 0.01%–0.1% atomic concentration of hydrogen. High temperature annealing at 1100 °C results in a positive Electron Affinity surface (PEA). Reexposure of PEA surface to atomic hydrogen at room temperature regenerates the NEA condition. This is evident of the role of superficial hydrogen in promoting NEA on the h-BN film.