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30 Jul 2012

Volume 101, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages)

Alec Rose, Da Huang, and David R. Smith
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Characterization of atomic step structures on CaF2(111) by their electric potential

H. H. Pieper, C. Barth, and M. Reichling

Appl. Phys. Lett. 101, 051601 (2012); http://dx.doi.org/10.1063/1.4739944 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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The structure and polarity of step edges on cleaved CaF2(111) are investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy. Ledges produced by cleaving the crystal appear with two distinctly different polarities denoted as type I and type II arising from the sectioning of ledges with steps having different polarities. With respect to the stoichiometric terrace, the surface potential is slightly reduced at ledges predominately composed of type I steps, while the potential of ledges predominantly composed of type II steps is significantly higher (typically 100 mV). We propose that the positive potential of type II steps stems from low coordinated Ca2+ ions inducing a dipole at step edges and confirm this by atomically resolved NC-AFM images revealing the Ca2+ ion sub-lattice with repulsive-mode imaging contrast.
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68.35.bt Other materials
61.66.Bi Elemental solids
61.66.Dk Alloys
68.37.Ps Atomic force microscopy (AFM)

Atomic and electronic structure of graphene/Sn-Ni(111) and graphene/Sn-Cu(111) surface alloy interfaces

L. Adamska, R. Addou, M. Batzill, and I. I. Oleynik

Appl. Phys. Lett. 101, 051602 (2012); http://dx.doi.org/10.1063/1.4739475 (4 pages) | Cited 3 times

Online Publication Date: 30 July 2012

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First-principles density functional theory calculations were performed to investigate the effect of Sn surface alloying on the strength of interface interactions between graphene and Ni(111) or Cu(111) substrates. A substantial reduction of graphene-metal interactions was observed for the graphene/Sn-Ni(111) interface: binding energy was reduced from 0.055 eV/(C atom) to 0.015 eV/(C atom); interface distance was increased from 2.12 Å to 3.52 Å. The initially weak graphene/Cu(111) interface was hardly affected by Sn surface alloying. Electronic structure calculations, including local density of states and simulated scanning tunneling microscopy images, provide further details on the changing character of graphene-Ni(111) interactions upon Sn alloying.
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71.20.Tx Fullerenes and related materials; intercalation compounds
81.65.-b Surface treatments
61.48.Gh Structure of graphene
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

In situ x-ray studies of oxygen surface exchange behavior in thin film La0.6Sr0.4Co0.2Fe0.8O3−δ

B. J. Ingram, J. A. Eastman, K.-C. Chang, S. K. Kim, T. T. Fister, E. Perret, H. You, P. M. Baldo, and P. H. Fuoss

Appl. Phys. Lett. 101, 051603 (2012); http://dx.doi.org/10.1063/1.4739518 (5 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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In situ synchrotron x-ray techniques were used to investigate oxygen surface exchange behavior in thin film La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/Gd2O3-doped CeO2/Y2O3-stabilized ZrO2 heterostructures. Applying electrical potentials across the heterostructures results in significant expansion or contraction of the out-of-plane LSCF lattice parameter, indicating changes in the LSCF oxygen vacancy concentration. Oxygen transport across the LSCF/atmosphere interface is found to be rate limiting under both cathodic and anodic conditions.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology

Inhomogeneous ohmic contacts: Barrier height and contact area determination

Yang Li, Wei Long, and Raymond T. Tung

Appl. Phys. Lett. 101, 051604 (2012); http://dx.doi.org/10.1063/1.4742142 (5 pages) | Cited 1 time

Online Publication Date: 31 July 2012

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The current-voltage characteristics at a uniform ohmic contact are, by definition, dominated by its series resistance and ordinarily offer little information, beyond an upper-bound, on the Schottky barrier height (SBH) of the metal-semiconductor junction. We demonstrate through temperature-dependent measurements of Au “ohmic” contacts on n-type Si(100)1 × 1-S, however, that quantitative information on not only the magnitude of the SBH, to within ± 0.03 eV, but also the effective conduction area can still be deduced. Details of these analyses, which require the use of a thin Si epi-layer, and the “partisan interlayer” mechanism, which lead to the formation of ohmic contacts, are discussed.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

Probing the intrinsic electrical properties of thin organic layers/semiconductor interfaces using an atomic-layer-deposited Al2O3 protective layer

W. Peng, O. Seitz, R. A. Chapman, E. M. Vogel, and Y. J. Chabal

Appl. Phys. Lett. 101, 051605 (2012); http://dx.doi.org/10.1063/1.4742168 (5 pages) | Cited 1 time

Online Publication Date: 31 July 2012

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The intrinsic electrical properties of thin organic layers/semiconductor interfaces are challenging to probe because of large tunneling currents through the molecular layer and damage during device fabrication. We present here a method to protect the interface with an Al2O3 layer gently deposited on top using atomic layer deposition. The resulting two-layered gate stack can be characterized with capacitance and conductance measurements. The protected interface shows an inherent high quality with low Dit, less than 2 × 1011 cm−2 eV−1 for n-type Si(111) surface, best measured using mercury probe. The additional procedures required to fabricate MOS capacitors lead to an increase in Dit.
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85.30.Tv Field effect devices
68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors

Substrate-induced disorder in V2O3 thin films grown on annealed c-plane sapphire substrates

J. Brockman, M. G. Samant, K. P. Roche, and S. S. P. Parkin

Appl. Phys. Lett. 101, 051606 (2012); http://dx.doi.org/10.1063/1.4742160 (5 pages) | Cited 2 times

Online Publication Date: 1 August 2012

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We investigate the structural and electronic properties of V2O3 thin films deposited by oxygen plasma-assisted molecular beam epitaxy onto annealed and unannealed c-plane sapphire substrates. Annealing the substrates before growth to produce ultra-smooth surfaces improved initial epitaxy, according to in situ reflection high-energy electron diffraction. Surprisingly, films deposited on annealed substrates had a more island-like surface, broader x-ray diffraction peaks, and an increased resistivity of V2O3’s normally metallic high-temperature phase. We attribute these results to enhanced strain coupling at the interface between the substrate and film, highlighting the vulnerability of V2O3’s strongly correlated metallic phase to crystalline defects and structural disorder.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators
68.55.J- Morphology of films
52.77.Dq Plasma-based ion implantation and deposition
71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Ng Insulators
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