Work function of MgO single crystals from ion-induced secondary electron emission coefficient

Ajou University, Sŏul, Seoul, South Korea
Journal of Applied Physics (Impact Factor: 2.18). 07/2003; 94(1). DOI: 10.1063/1.1581376


The work functions ϕω of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary electron emission coefficient Γ, respectively, using various ions with different ionization energies in a Γ-focused ion beam system. The work function ϕω for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary electron emission coefficient Γ for Xe+ ions, whose ionization energy is 12.13 eV.

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    • "The presence of pure Mg on the surface of the Mg:Ag alloy layer is likely related to the difference in boiling points of Ag (T Ag-boiling =2435 K) and Mg (T Mg-boiling =1363 K): Due to the much lower boiling point of Mg, Mg vapors will be condensed last after the deposition process is finished (shutter closed) resulting in a Mg enriched front surface. The last value of 4.42 eV is similar to that of a MgO single crystal with (111) orientation [4] suggesting that MgO is formed on the front side. This finding is in good agreement with the observation of the O KLL Auger electron peak in the XPS overview spectra indicating the presence of oxidized Mg 0 . "
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    ABSTRACT: Stable and efficient organic solar cells with Mg (20 at. %): Ag alloy cathodes and bulk-heterojunction absorber layers from metal (e.g., Cu, Zn)-phthalocyanine and C60 small molecules are demonstrated. Device efficiencies of 4.0% under an illumination of 100 mW/cm2 at 25̊C were achieved as a result of the fine adjustment of the cathode work function as well as of the absorber design. By combining low and high work function materials, the work function in both Mg/Ag bilayer and Mg:Ag alloy layer cathodes was adjusted for optimum photovoltaic parameters. The electric and photovoltaic properties of the devices are discussed with respect to the cathode layer structure. The formation of the absorber/cathode interface was investigated by x-ray photoelectron spectroscopy measurements (XPS). The work function of the absorber and cathode layers were determined from the XPS high binding energy cutoff (HBEC) spectra. For optimized devices, the work function of the cathode at the side adjacent to the absorber layer equals 4.0…4.1 eV. While devices with Mg/Ag bilayer contacts exhibit a 65% efficiency drop in the first month after the preparation, devices with Mg:Ag alloy contacts demonstrate stable photovoltaic parameters within the time of the study of ∼ 1 year.
    Energy Procedia 12/2012; 31:96–101. DOI:10.1016/j.egypro.2012.11.170
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    • "More drastic increase in the driving voltage is also shown for that Fe/MgO(001)-based TOLED. The large driving voltage could be attributed to the larger work function of the MgO(001) layer (4.94 eV) [17] than that of Al (4.1 eV) [18] or poly-Fe (4.5 eV) [18]. Additionally, the effect of surface potential at the MgO(001)/CuPc interface could not be negligible. "
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    ABSTRACT: Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured beta phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350[degree sign]C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.
    Nanoscale Research Letters 11/2012; 7(1):650. DOI:10.1186/1556-276X-7-650 · 2.78 Impact Factor
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    • "The work function is derived from the value of the xaxis at the peak point, which is 3.61 eV for the conventional MgO protective layer and 3.22 eV for the proposed MgO protective layer. As a result, when the Au nanoparticles are inserted, the work function of the proposed structure falls by about 0.4 eV, and the SEE property is consequently enhanced [11], [17]. In addition, the nonflat-surface morphology, which is induced by the nanometer-scale bumps, is expected to enhance the SEE property [18]. "
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    ABSTRACT: This paper proposes a modified alternating current plasma display panel (PDP) in which gold nanoparticles are incorporated into a bare MgO layer to enhance the performance of the protective layer. The proposed structure's ion-induced secondary electron yield, which is expressed in a gamma value ( value) is greater than that of a bare MgO layer; as a result, the operating voltage decreases by 10 V to 20 V. The integration of emitted infrared (IR) light and the power density consumed by the discharge current are both increased, but the ratio of increment is greater for the case of the IR light. Consequently, IR efficacy is increased. The IR response time of the sustain discharge and the address discharge time lag are reduced by the enhanced wall charge accumulation characteristic and the exoelectron emission property. The results of ultraviolet photoelectron spectroscopy show that a MgO layer with Au nanoparticles has a lower work function than a conventional bare MgO layer. Furthermore, the structure that is not flattened by nanoparticles seems to enhance the secondary electron emission property of the MgO protective layer. Consequently, the value is enhanced by the two reasons previously mentioned.
    IEEE Transactions on Electron Devices 11/2010; 57(10-57):2644 - 2650. DOI:10.1109/TED.2010.2058850 · 2.47 Impact Factor
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