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7 May 2012

Volume 100, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 100, 191901 (2012); http://dx.doi.org/10.1063/1.4709436 (4 pages)

Muamer Kadic, Tiemo Bückmann, Nicolas Stenger, Michael Thiel, and Martin Wegener
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Hydrogen release from Li alanates originates in molecular lattice instability emerging at ∼100 K

K. Tomiyasu, T. Sato, K. Horigane, S. Orimo, and K. Yamada

Appl. Phys. Lett. 100, 193901 (2012); http://dx.doi.org/10.1063/1.4712053 (3 pages)

Online Publication Date: 7 May 2012

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Lattice vibrations from 20 K to room temperature in lithium alanates LiAlH4 and Li3AlH6, which decompose to release hydrogen over 423 K, were investigated by neutron spectroscopy. For both alanates, the overall spectra already start to broaden at 100–150 K with increasing temperature. The spectral lines assigned to the librational (rotational) modes of the polyhedral Al hydrido complexes, [AlH4]− and [AlH6]3−, exhibit not only broadening but also softening at around 250–300 K. These results suggest that the decomposition stems from low-temperature bulk lattice instability/anharmonicity, in particular, due to the weakening of binding between the complexes and their surroundings.
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63.20.-e Phonons in crystal lattices
64.75.Nx Phase separation and segregation in solid solutions

Electron energy-loss spectroscopy study of MgH2 in the plasmon energy range

B. Paik, A. Walton, V. Mann, D. Book, I. P. Jones, and I. R. Harris

Appl. Phys. Lett. 100, 193902 (2012); http://dx.doi.org/10.1063/1.4711779 (4 pages)

Online Publication Date: 7 May 2012

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Electron energy loss spectroscopy of MgH2 in the plasmon energy range is reported here as a part of a study to determine the dielectric function of this hydride. From the dielectric function, we have estimated the unperturbed plasmon energy of MgH2 as 11.34 eV. Interband transitions are also inferred from the dielectric function. Contribution of these interband transitions to the perturbed plasmon energy has been discussed within the scope of dielectric theory. Our analysis suggests that the MgH2 band gap lies within the range ∼4.3–4.5 eV.
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79.20.Uv Electron energy loss spectroscopy
71.20.Ps Other inorganic compounds
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrafast oxygen exchange kinetics on highly epitaxial PrBaCo2O5+δ thin films

Jian Liu, Gregory Collins, Ming Liu, Chonglin Chen, Jie He, Jiechao Jiang, and Efstathios I. Meletis

Appl. Phys. Lett. 100, 193903 (2012); http://dx.doi.org/10.1063/1.4712123 (4 pages)

Online Publication Date: 8 May 2012

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Symmetric half cell structures of highly epitaxial PrBaCo2O5+δ (PBCO)/Gd0.8Ce0.2.2O2:Y0.08Zr0.92O2/PrBaCo2O5+δ thin films were designed and fabricated on (001) LaAlO3. Microstructural studies indicate that the multilayer films have excellent single-crystal quality and epitaxial nature. The electrochemical impedance spectroscopy measurements reveal that the PBCO film electrodes have a polarization resistance as low as 0.109 Ω cm2 at 597 °C in air and an ultrafast surface exchange coefficient (0.006 cm/s at 598 °C) with low activation energy (0.77 eV). The low polarization resistance and rapid surface oxygen exchange kinetics suggest that the PBCO can be an excellent cathode material for intermediate-temperature solid oxide fuel cells.
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68.55.A- Nucleation and growth
82.45.Rr Electroanalytical chemistry
82.80.Fk Electrochemical methods

Cd-free buffer layer materials on Cu2ZnSn(SxSe1−x)4: Band alignments with ZnO, ZnS, and In2S3

D. Aaron R. Barkhouse, Richard Haight, Noriyuki Sakai, Homare Hiroi, Hiroki Sugimoto, and David B. Mitzi

Appl. Phys. Lett. 100, 193904 (2012); http://dx.doi.org/10.1063/1.4714737 (5 pages) | Cited 2 times

Online Publication Date: 10 May 2012

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The heterojunctions formed between Cu2ZnSn(SxSe1−x)4 (CZTSSe) and three Cd-free n-type buffers, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission and photovoltage spectroscopy. The electronic properties including the Fermi level location at the interface, band bending in the CZTSSe substrate, and valence and conduction band offsets were determined and correlated with device properties. We also describe a method for determining the band bending in the buffer layer and demonstrate this for the In2S3/CZTSSe system. The chemical bath deposited In2S3 buffer is found to have near optimal conduction band offset (0.15 eV), enabling the demonstration of Cd-free In2S3/CZTSSe solar cells with 7.6% power conversion efficiency.
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71.20.Nr Semiconductor compounds
78.40.Ha Other nonmetallic inorganics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Lm Deformation, plasticity, and creep
78.47.J- Ultrafast spectroscopy (<1 psec)
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High-efficiency InAs/GaAs quantum dot solar cells by metalorganic chemical vapor deposition

Katsuaki Tanabe, Denis Guimard, Damien Bordel, and Yasuhiko Arakawa

Appl. Phys. Lett. 100, 193905 (2012); http://dx.doi.org/10.1063/1.4714767 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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We fabricate a high-efficiency InAs/GaAs quantum dot (QD) solar cell. It contains five layers of high-density self-assembled InAs QDs grown by metalorganic chemical vapor deposition suppressing open-circuit-voltage (VOC) degradation. We develop a dual-layer anti-reflection coating of optimum thicknesses. The resulting cell exhibits efficiencies of 18.7% under AM1.5 G for 1 sun and 19.4% for 2 suns. Concentrator measurements demonstrate the advantage of QD use under concentrated illumination, owing to the significant increase in VOC. We also find a VOC offset of 0.3 V from the QD ground-state transition energies for QD cells, in contrast to 0.4 V for state-of-the-art bulk semiconductor cells.
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88.40.hj Efficiency and performance of solar cells

Utility of the inverse partial fluorescence for electronic structure studies of battery materials

H. Wadati, A. J. Achkar, D. G. Hawthorn, T. Z. Regier, M. P. Singh, K. D. Truong, P. Fournier, G. Chen, T. Mizokawa, and G. A. Sawatzky

Appl. Phys. Lett. 100, 193906 (2012); http://dx.doi.org/10.1063/1.4711801 (3 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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X-ray absorption spectroscopy is one of the most widely used experimental techniques to study the electronic and spatial structure of materials. Fluorescence yield mode is bulk-sensitive, but has several serious problems coming from saturation effects. In this study, we show the usefulness of partial fluorescence yields in addressing these problems. We discuss the different behaviors of La2NiMnO6 and LiMnO2 at the Mn 2p absorption edges. The total fluorescence yield produces misleading spectra for LiMnO2 due to the absence of high-Z (Z: atomic number) elements. We conclude that the measurement of the inverse partial fluorescence yield is essential in studies of LiMnO2, which is a hotly debated Li-ion battery material.
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71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
82.47.Aa Lithium-ion batteries
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