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2 May 2011

Volume 98, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 98, 183101 (2011); http://dx.doi.org/10.1063/1.3584006 (3 pages)

Tuba Oznuluer, Ercag Pince, Emre O. Polat, Osman Balci, Omer Salihoglu, and Coskun Kocabas
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Electronic structure of GaInN semiconductors investigated by x-ray absorption spectroscopy

Q. X. Guo, H. Senda, K. Saito, T. Tanaka, M. Nishio, J. Ding, T. X. Fan, D. Zhang, X. Q. Wang, S. T. Liu, B. Shen, and R. Ohtani

Appl. Phys. Lett. 98, 181901 (2011); http://dx.doi.org/10.1063/1.3583461 (3 pages) | Cited 1 time

Online Publication Date: 2 May 2011

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We have investigated the electronic structure of GaInN semiconductors by performing x-ray absorption near-edge fine structure (XANES) spectroscopy at Ga K-edge and self-consistent-field real-space multiple-scattering theory calculations. It was demonstrated that the nondestructive Ga K-edge XANES spectra can be used as the fingerprints of structure and composition for GaInN. The theoretical calculations gave a reasonable reproduction of the experimental spectral features. The results revealed that the combination of the experimental XANES and the theoretical calculations is a powerful tool for studying the electronic structure of GaInN semiconductors.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.70.Dm X-ray absorption spectra

Surface roughness reduction in nanocrystalline Cu thin films by electrical stressing treatment

Tsung-Cheng Chan, Kuan-Chia Chen, and Chien-Neng Liao

Appl. Phys. Lett. 98, 181902 (2011); http://dx.doi.org/10.1063/1.3586772 (3 pages) | Cited 2 times

Online Publication Date: 2 May 2011

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Electromigration-induced surface morphological evolution of nanocrystalline Cu thin films is reported. When applying a high-density current (106 A/cm2), the Cu films showed reduced surface roughness from 7.5 to 1.4 nm after electrical stressing at the temperature below 100 °C. It is suggested that preferential surface diffusion on Cu(111) planes leads to thinning of extruded grains in the electrically stressed Cu film, as evidenced by the weakening (111) texture of the Cu film after electrical stressing. The electrical stressing process shall help reduce roughness of Cu metallization after post thermal treatment.
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68.35.bd Metals and alloys
68.35.Fx Diffusion; interface formation
66.30.Qa Electromigration
66.30.Pa Diffusion in nanoscale solids
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments

Epitaxial graphene prepared by chemical vapor deposition on single crystal thin iridium films on sapphire

Chi Vo-Van, Amina Kimouche, Antoine Reserbat-Plantey, Olivier Fruchart, Pascale Bayle-Guillemaud, Nedjma Bendiab, and Johann Coraux

Appl. Phys. Lett. 98, 181903 (2011); http://dx.doi.org/10.1063/1.3585126 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2011

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Uniform single layer graphene was grown on single-crystal Ir films a few nanometers thick which were prepared by pulsed laser deposition on sapphire wafers. These graphene layers have a single crystallographic orientation and a very low density of defects, as shown by diffraction, scanning tunnelling microscopy, and Raman spectroscopy. Their structural quality is as high as that of graphene produced on Ir bulk single crystals, i.e., much higher than on metal thin films used so far.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Mm Grain and twin boundaries
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.ue Graphene
78.30.Na Fullerenes and related materials
68.55.ap Fullerenes

Atomic scale characterization of GaInN/GaN multiple quantum wells in V-shaped pits

Shigetaka Tomiya, Yuya Kanitani, Shinji Tanaka, Tadakatsu Ohkubo, and Kazuhiro Hono

Appl. Phys. Lett. 98, 181904 (2011); http://dx.doi.org/10.1063/1.3585118 (3 pages) | Cited 2 times

Online Publication Date: 4 May 2011

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High-angle annular dark field scanning transmission electron microscopy and atom probe tomography of the V-shaped pits in GaInN/GaN multiple quantum wells have revealed that a quantum well structure exists at the slope region of the V-shaped pits. Their thickness and In concentrations were found to be much lower compared to those of the flat region. This suggests that threading dislocations in the V-shaped pits act as energy barriers for the lateral transport of charge carries and that the pit center may not work properly for vertical transport because of the collapse of well-defined quantum well structures.
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73.63.Hs Quantum wells
68.65.Fg Quantum wells
73.61.Ey III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

In-depth resolved Raman scattering analysis for the identification of secondary phases: Characterization of Cu2ZnSnS4 layers for solar cell applications

X. Fontané, L. Calvo-Barrio, V. Izquierdo-Roca, E. Saucedo, A. Pérez-Rodriguez, J. R. Morante, D. M. Berg, P. J. Dale, and S. Siebentritt

Appl. Phys. Lett. 98, 181905 (2011); http://dx.doi.org/10.1063/1.3587614 (3 pages) | Cited 28 times

Online Publication Date: 5 May 2011

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This work reports the in-depth resolved Raman scattering analysis with different excitation wavelengths of Cu2ZnSnS4 layers. Secondary phases constitute a central problem in this material, particularly since they cannot be distinguished by x-ray diffraction. Raman spectra measured with 325 nm excitation light after sputtering the layers to different depths show peaks that are not detectable by excitation in the visible. These are identified with Cu3SnS4 modes at the surface region while spectra measured close to the back region show peaks from ZnS and MoS2. Observation of ZnS is enhanced by resonant excitation conditions achieved when working with UV excitation.
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78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
88.40.H- Solar cells (photovoltaics)

Determination of Clausius–Mossotti factors and surface capacitances for colloidal particles

T. Honegger, K. Berton, E. Picard, and D. Peyrade

Appl. Phys. Lett. 98, 181906 (2011); http://dx.doi.org/10.1063/1.3583441 (3 pages) | Cited 8 times

Online Publication Date: 5 May 2011

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We propose a method to experimentally determine the Clausius–Mossotti factors and surface capacitances of colloidal particles. This two-step method is based on the following: (i) a precise positioning of particles on activated electrodes according to the applied frequency of an electric field and (ii) particles velocities measurements from a pure dielectrophoretic regime to build the Clausius–Mossotti factor. It confirms previous literature methods and measures the surface capacitance values for a wide range of particles such as polystyrene, silica, and gold whose diameters are at least 200 nm.
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82.45.Un Dielectric materials in electrochemistry
82.70.Dd Colloids
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals

Improved diamond surfaces following lift-off and plasma treatments as observed by x-ray absorption spectroscopy

Alastair Stacey, Virginia S. Drumm, Barbara A. Fairchild, Kumar Ganesan, Sergey Rubanov, Rafi Kalish, Bruce C. C. Cowie, Steven Prawer, and Alon Hoffman

Appl. Phys. Lett. 98, 181907 (2011); http://dx.doi.org/10.1063/1.3585106 (3 pages) | Cited 6 times

Online Publication Date: 5 May 2011

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We have investigated the nature of the residual damage in diamond crystals following the ion implantation/graphitization “lift-off” process, using near-edge x-ray absorption fine structure spectroscopy and transmission electron microscopy. A defective but crystalline interface is found, which displays dense pre-edge unoccupied states and an almost complete loss of the core-level C 1s exciton signature. This residual crystalline damage is resistant to standard chemical etching, however a hydrogen plasma treatment is found to completely recover a pristine diamond surface. Analysis and removal of residual ion-induced damage is considered crucial to the performance of many diamond device architectures.
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52.77.Dq Plasma-based ion implantation and deposition
81.05.ug Diamond
78.70.Dm X-ray absorption spectra
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.72.-y Defects and impurities in crystals; microstructure
81.65.Cf Surface cleaning, etching, patterning

Carrier recombination processes in Mg-doped N-polar InN films

Daichi Imai, Yoshihiro Ishitani, Masayuki Fujiwara, Kazuhide Kusakabe, Xinqian Wang, and Akihiko Yoshikawa

Appl. Phys. Lett. 98, 181908 (2011); http://dx.doi.org/10.1063/1.3586775 (3 pages) | Cited 4 times

Online Publication Date: 5 May 2011

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We investigate the nonradiative carrier recombination (NR) process in Mg-doped p-InN films having lower photoluminescence (PL) intensity than n-InN films. The NR activation energy in the p-type films is found to be in a range of 9–15 meV, which is smaller than that in n-InN films (40–65 meV). We also investigate the effect of the greater mean free path of minority carriers in p-InN. At room temperature the collision rate of minority carriers with NR centers within the radiative lifetime in p-InN is found to be three orders of magnitude greater than that in n-InN.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors

Nanoscale rotational deformation in solids at high stresses

I. A. Ovid’ko and A. G. Sheinerman

Appl. Phys. Lett. 98, 181909 (2011); http://dx.doi.org/10.1063/1.3587637 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2011

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A special physical mode of plastic flow and nanograin formation in nanocrystalline and polycrystalline solids deformed at high stresses is suggested and theoretically described. The mode represents the nanoscale rotational deformation (NRD) occurring through the collective events of ideal nanoscale shear in solids. We calculated its stress and energy characteristics. It is found that NRD can effectively occur in nanocrystalline and polycrystalline solids during dynamic loading.
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46.35.+z Viscoelasticity, plasticity, viscoplasticity
62.25.-g Mechanical properties of nanoscale systems

Photo- and field-induced charge-separation and phosphorescence quenching in organometallic complex Ir(ppy)3

Mohan Singh Mehata and Nobuhiro Ohta

Appl. Phys. Lett. 98, 181910 (2011); http://dx.doi.org/10.1063/1.3582916 (3 pages) | Cited 2 times

Online Publication Date: 6 May 2011

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Electric field effects on absorption and photoluminescence (PL) spectra of organometallic phosphorescent emitter Ir(ppy)3, {tris[2-phenylpyridinato-C2,N] iridium (III)} doped in a film of polymethyl methacrylate (PMMA) have been confirmed at temperatures in the range of 40–295 K. Field-induced quenching of PL observed for Ir(ppy)3 is attributed to the decrease both of emitting state population and of the lifetime of PL. The quenching is independent of excitation energy as well as temperature. Field-assisted charge separation or dissociation of electron-hole (e-h) pair produced by photoexcitation may decrease the population of the emitting state. The Stark shifts on absorption and PL spectra have also been analyzed.
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78.55.Kz Solid organic materials
78.20.Jq Electro-optical effects
78.66.Qn Polymers; organic compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Negative thermal expansion in ZnF2

Tapan Chatterji, Mohamed Zbiri, and Thomas C. Hansen

Appl. Phys. Lett. 98, 181911 (2011); http://dx.doi.org/10.1063/1.3588414 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2011

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We have investigated temperature dependence of the lattice parameters and the unit cell volume of ZnF2 by neutron diffraction and have discovered negative thermal expansion (NTE) at low temperature. To understand why this simple compound exhibits NTE we performed first principle calculations. These calculations reproduce qualitatively the experimental temperature dependence of volume.
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65.40.De Thermal expansion; thermomechanical effects
61.66.-f Structure of specific crystalline solids

Temperature-dependent shifts of ultraviolet multipeak emissions for Mn-doped ZnO nanowires

Feihong Jiang and Jun Zhang

Appl. Phys. Lett. 98, 181912 (2011); http://dx.doi.org/10.1063/1.3586253 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2011

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Mn-doped ZnO nanowires have been fabricated through high-temperature vapor-solid deposition process. The temperature-dependent photoluminescence properties of Mn-doped ZnO nanowires under 10 to 300 K have been investigated. The results show that the prepared samples have intensive multipeak emissions in the ultraviolet (UV) region (about 3.4–3.0 eV) at low temperature. The analyses of Gaussian-fitted the UV band from 10 to 300 K reveal that all UV spectra can be well fitted by four Gaussian peaks. With increasing temperature, the four UV bands show different temperature dependences and have obvious redshift. The origins of the intensive UV multipeak emissions can be attributed to the excitonic transition in Mn-doped ZnO nanowires under low temperature. The analysis results indicate that the crystal quality and UV luminescence efficiency of ZnO nanowires are improved with Mn doping.
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78.67.Uh Nanowires
73.21.Hb Quantum wires
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
71.35.-y Excitons and related phenomena
78.40.Fy Semiconductors

AX centers in II-VI semiconductors: Hybrid functional calculations

Koushik Biswas and Mao-Hua Du

Appl. Phys. Lett. 98, 181913 (2011); http://dx.doi.org/10.1063/1.3583661 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2011

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Hybrid functional calculations predict significantly enhanced stability of AX centers against shallow acceptors in selected II-VI semiconductors (ZnO, ZnS, and ZnSe), as compared to the calculations based on local density approximation and generalized gradient approximation. The results agree well with the experimental observations on the p-type doping of ZnS and ZnSe. The improved description of the AX centers by hybrid functional calculations is due to the correction of the valence band maximum of the semiconductor.
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71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
61.72.uj III-V and II-VI semiconductors

CdTe quantum dots and polymer nanocomposites for x-ray scintillation and imaging

Zhitao Kang, Yuelan Zhang, Hisham Menkara, Brent K. Wagner, Christopher J. Summers, William Lawrence, and Vivek Nagarkar

Appl. Phys. Lett. 98, 181914 (2011); http://dx.doi.org/10.1063/1.3589366 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2011

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Investigations are reported on the x-ray scintillation and imaging application of CdTe quantum dots (QDs) and their polymer nanocomposites. Aqueous CdTe QDs with emissions ranging between 510 and 680 nm were prepared and incorporated into polyvinyl alcohol or polymethyl methacrylate polymer matrices. The x-ray luminescent properties were evaluated and a resolution of 5 lines/mm was obtained from the nanocomposite films. Additionally, the fast decay time, nonafterglow, and superior spectral match to conventional charge coupled devices, show that CdTe QD nanocomposites have high promise for x-ray imaging applications.
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81.07.Ta Quantum dots
81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Hf II-VI semiconductors
81.05.uj Diamond/nanocarbon composites
78.70.Ps Scintillation
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