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3 Oct 2011

Volume 99, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 99, 141901 (2011); http://dx.doi.org/10.1063/1.3644948 (3 pages)

G. Kozlowski, P. Zaumseil, M. A. Schubert, Y. Yamamoto, J. Bauer, J. Matejova, T. Schulli, B. Tillack, and T. Schroeder
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Compliant substrate versus plastic relaxation effects in Ge nanoheteroepitaxy on free-standing Si(001) nanopillars

G. Kozlowski, P. Zaumseil, M. A. Schubert, Y. Yamamoto, J. Bauer, J. Matejova, T. Schulli, B. Tillack, and T. Schroeder

Appl. Phys. Lett. 99, 141901 (2011); http://dx.doi.org/10.1063/1.3644948 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2011

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We report on the structural characterization of Ge clusters selectively grown by chemical vapor deposition on free-standing 50 nm wide Si(001) nanopillars. Synchrotron based x-ray diffraction studies and transmission electron microscopy were performed to experimentally verify the nanoheteroepitaxy theory as a technique to grow high quality Ge on Si(001). Although the structure dimensions are comparable to the theoretical values required for the strain partitioning phenomenon, the compliant character of Si is not unambiguously proven. In consequence, the strain is relieved by nucleation of misfit dislocations at the Ge/Si interface. By gliding out of threading arms, high quality Ge nanostructures are achieved.
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81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
81.07.Nb Molecular nanostructures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.47.Fg Semiconductor surfaces

Picosecond carrier lifetimes in dilute GaInNAs grown on InP substrate

J. Mangeney, T. Laurent, M. Martin, J. C. Harmand, L. Travers, and O. Mauguin

Appl. Phys. Lett. 99, 141902 (2011); http://dx.doi.org/10.1063/1.3644954 (3 pages) | Cited 1 time

Online Publication Date: 3 October 2011

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We study the carrier relaxation dynamics in Ga1−yIny N0.03As0.97 layers grown on InP substrate by molecular beam epitaxy. This dilute nitride semiconductor is a potential candidate for ultrafast components such as photoconductive terahertz devices driven at 1.55 μm wavelength. Carrier lifetimes are measured by pump-probe experiments at 1550 nm wavelength and the shortest carrier lifetime is 2.6 ps under photoexcitation with ∼4.2 μJ/cm2. We observe two contributions in the differential transmittance decay. These contributions are discussed in terms of photocarrier recombination processes.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.60.-q Optoelectronic devices

Wrinkles formation and evolution of nanoribbons with finite length on elastomeric substrate

Xue Feng, Binrui Qu, Bingwei Lu, Zhihua Zhao, and Xufei Fang

Appl. Phys. Lett. 99, 141903 (2011); http://dx.doi.org/10.1063/1.3645012 (3 pages)

Online Publication Date: 3 October 2011

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We report in situ observation of wrinkles formation and evolution of Si nanoribbons with finite length on elastomeric substrate via white light interferometer. The wrinkle originates from the middle of the nanoribbon, propagates symmetrically to the two ends, and finally reaches the stable configuration. The wavelength and amplitude will increase abruptly when the released strain exceeds the critical value. The interface interaction between Si nanoribbons and elastomeric substrate plays the key role for wrinkles formation.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Structure of the InAlAs/InP interface by atomically resolved energy dispersive spectroscopy

Dmitri O. Klenov and Joshua M. O. Zide

Appl. Phys. Lett. 99, 141904 (2011); http://dx.doi.org/10.1063/1.3645632 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2011

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The structure of epitaxially grown InAlAs/InP interfaces was studied using atomically resolved x-ray energy dispersive spectroscopy in scanning transmission electron microscopy. As and P sublattices show sharp termination on the interface. The In sublattice is continuous across the interface. The study has shown the depletion of the Al concentration at the interface; at the last atomic columns of the InAlAs, In occupancy is close to 100%, while Al occupancy is almost zero. A monolayer of InAs at the interface is consistent with substitution of As for P at the surface preceding growth.
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68.55.-a Thin film structure and morphology
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.35.Ct Interface structure and roughness

High temperature step-flow growth of gallium phosphide by molecular beam epitaxy and metalorganic chemical vapor deposition

C. Ratcliff, T. J. Grassman, J. A. Carlin, and S. A. Ringel

Appl. Phys. Lett. 99, 141905 (2011); http://dx.doi.org/10.1063/1.3644956 (3 pages) | Cited 3 times

Online Publication Date: 4 October 2011

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Post-growth surface morphologies of high-temperature homoepitaxial GaP films grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have been studied. Smooth, stepped surface morphologies of MBE-grown layers, measured by atomic force microscopy, were found for a wide range of substrate temperatures and P2:Ga flux ratios. A MOCVD-based growth study performed under similar conditions to MBE-grown samples shows a nearly identical smooth, step-flow surface morphology, presenting a convergence of growth conditions for the two different methods. The additional understanding of GaP epitaxy gained from this study will impact its use in applications that include GaP-based device technologies, III-V metamorphic buffers, and III-V materials integration with silicon.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tuning the inter-shell splitting in self-assembled CdTe quantum dots

K. Kukliński, Ł. Kłopotowski, K. Fronc, M. Wiater, P. Wojnar, P. Rutkowski, V. Voliotis, R. Grousson, G. Karczewski, J. Kossut, and T. Wojtowicz

Appl. Phys. Lett. 99, 141906 (2011); http://dx.doi.org/10.1063/1.3643476 (3 pages)

Online Publication Date: 4 October 2011

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We present photoluminescence studies of highly excited single self-assembled CdTe quantum dots under continuous-wave and pulsed excitations. We observe appearance of emission bands related to sequential filling of s-, p- and d-shells. We analyze the inter-shell splitting for five samples, in which the dots were formed from a strained CdTe layer of different width. We find that by increasing the CdTe layer width, the inter-shell splitting increases. In a time resolved measurement, we observe a radiative cascade between transitions involving one, two, and more than two excitons.
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78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots

Large internal stress-assisted twin-boundary motion in Ni2MnGa ferromagnetic shape memory alloy

Z. H. Nie, D. Y. Cong, D. M. Liu, Y. Ren, M. Pötschke, S. Roth, and Y. D. Wang

Appl. Phys. Lett. 99, 141907 (2011); http://dx.doi.org/10.1063/1.3645626 (3 pages)

Online Publication Date: 4 October 2011

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The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ∼8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ∼0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training.
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61.72.Mm Grain and twin boundaries
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
64.60.Q- Nucleation

Electronic structure and polaronic excitation in FeVO4

A. Dixit, P. Chen, G. Lawes, and J. L. Musfeldt

Appl. Phys. Lett. 99, 141908 (2011); http://dx.doi.org/10.1063/1.3646402 (3 pages) | Cited 1 time

Online Publication Date: 4 October 2011

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We investigated the electronic properties of FeVO4 films using optical, valence band x-ray photoelectron, and infrared spectroscopies. These studies show that FeVO4 is a direct bandgap system with a 2.7 eV gap with the Fermi level in the middle of the valence band maximum and conduction band minimum. A polaronic excitation is also observed in the middle infrared, indicating the importance of charge-lattice coupling in this multiferroic material. Fits to a model for the optical response of large polarons yield a binding energy of approximately 130 meV.
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71.20.Ps Other inorganic compounds
78.66.Nk Insulators
71.15.Nc Total energy and cohesive energy calculations
78.30.Hv Other nonmetallic inorganics
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Ab initio calculations on Li-ion migration in Li2FeSiO4 cathode material with a P21 symmetry structure

Dawei Su, Hyojun Ahn, and Guoxiu Wang

Appl. Phys. Lett. 99, 141909 (2011); http://dx.doi.org/10.1063/1.3645617 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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We have systematically investigated the diffusion mechanism of Li ions in Li2FeSiO4 and its delithiated product LiFeSiO4 based on the P21 symmetry using the first principle method. Calculations on the energy barriers for possible spatial hopping pathways predicted that the activation barriers along the [101] direction and Li ion layer in the ac plane are relatively low, which can ensure the facile lithium diffusion along those directions. The results indicate that Li2FeSiO4 with the P21 symmetry is an ionic conductor for Li ions with two-dimensional diffusion.
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66.30.J- Diffusion of impurities
82.45.Fk Electrodes

Improved interfacial local structural ordering of epitaxial Fe3Si(001) thin films on GaAs(001) by a MgO(001) tunneling barrier

S. I. Makarov, B. Krumme, F. Stromberg, C. Weis, W. Keune, and H. Wende

Appl. Phys. Lett. 99, 141910 (2011); http://dx.doi.org/10.1063/1.3646390 (3 pages) | Cited 2 times

Online Publication Date: 5 October 2011

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Although the quasi-Heusler compound Fe3Si is a promising candidate for spintronics applications, its combination with the reactive GaAs surface is problematic, since it deteriorates its beneficial attributes due to a large amount of interdiffusion at the Fe3Si/GaAs interface. Here, we show the epitaxial growth of Fe3Si with low evaporation rates on GaAs(001) and report on improved local structural D03 ordering in epitaxial Fe3Si(001) films grown on GaAs(001) by inserting a MgO buffer layer. Conversion-electron Mössbauer spectroscopy with 57Fe3Si tracer layers reveals that the effect of thermally induced interdiffusion at the Fe3Si/GaAs(001) interface is dramatically reduced by inserting a 30 Å MgO tunneling barrier between the film and the substrate. The chemical order of Fe3Si is comparable to that of Fe3Si films which are grown directly on MgO(001) single crystals. It is proposed that this preparation method can be useful to achieve high-efficiency spin-polarized electron currents from ferromagnetic Fe3Si into semiconducting GaAs(001).
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68.35.Ct Interface structure and roughness
72.25.-b Spin polarized transport
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
66.30.Ny Chemical interdiffusion; diffusion barriers
75.70.Ak Magnetic properties of monolayers and thin films

Optical investigation of reduced graphene oxide by spectroscopic ellipsometry and the band-gap tuning

Y. Shen, P. Zhou, Q. Q. Sun, L. Wan, J. Li, L. Y. Chen, D. W. Zhang, and X. B. Wang

Appl. Phys. Lett. 99, 141911 (2011); http://dx.doi.org/10.1063/1.3646908 (3 pages) | Cited 5 times

Online Publication Date: 5 October 2011

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Spectroscopic ellipsometry was used to characterize the optical response of few layer reduced graphene oxide and graphene oxide in visible range. Lorentz oscillator model is added to analyze the ellipsometric parameters. The experiment shows the optical response of few layer reduced graphene oxide and monolayer exfoliated graphene in visible range is quite similar with slight difference due to the structure defects. The Lorentz oscillator model gives experimental support to investigate the band-gap tuning through the reduction process in details.
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78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Na Fullerenes and related materials
78.40.Ri Fullerenes and related materials

How much room for BiGa heteroantisites in GaAs1−xBix?

G. Ciatto, P. Alippi, A. Amore Bonapasta, and T. Tiedje

Appl. Phys. Lett. 99, 141912 (2011); http://dx.doi.org/10.1063/1.3647635 (3 pages) | Cited 7 times

Online Publication Date: 6 October 2011

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We addressed the issue of bismuth heteroantisite defects (BiGa) in GaAs1−xBix/GaAs epilayers by coupling x-ray absorption spectroscopy at the bismuth edge with density functional theory calculations of the defect structure. Calculations predict a large relaxation of the Bi-As interatomic distances when Bi atoms substitute Ga, however we found no experimental evidence of it. Quantitative analysis of the x-ray absorption spectra allows us to establish a maximum concentration limit for BiGa, which corresponds to about 5% of the total Bi atoms. BiGa do not account for the modifications in the spectra previously attributed to short range ordering.
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61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Dm X-ray absorption spectra
81.05.Ea III-V semiconductors

Pyramidal inversion domain boundaries revisited

T. Remmele, M. Albrecht, K. Irmscher, R. Fornari, and M. Straßburg

Appl. Phys. Lett. 99, 141913 (2011); http://dx.doi.org/10.1063/1.3644132 (3 pages)

Online Publication Date: 6 October 2011

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The structure of pyramidal inversion domain boundaries in GaN:Mg was investigated by aberration corrected transmission electron microscopy. The analysis shows the upper (0001) boundary to consist of a single Mg layer inserted between polarity inverted GaN layers in an abcab stacking. The Mg bound in these defects is at least one order of magnitude lower than the chemical Mg concentration. Temperature dependent Hall effect measurements show that up to 27% of the Mg acceptors is electrically compensated.
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61.72.Mm Grain and twin boundaries
72.20.My Galvanomagnetic and other magnetotransport effects
81.05.Ea III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.jd Vacancies

Strong suppression of internal electric field in GaN/AlGaN multi-layer quantum dots in nanowires

R. Songmuang, D. Kalita, P. Sinha, M. den Hertog, R. André, T. Ben, D. González, H. Mariette, and E. Monroy

Appl. Phys. Lett. 99, 141914 (2011); http://dx.doi.org/10.1063/1.3646389 (3 pages) | Cited 3 times

Online Publication Date: 6 October 2011

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Photoluminescence (PL) studies of GaN/AlxGa1−xN quantum dots (QDs) in nanowires demonstrate an efficient carrier confinement, resulting in thermally stable decay times up to 300 K. The evolution of the PL transition energy as a function of both the QD height and the Al mole fraction in the barriers, as well as the evolution of the decay time as a function of the QD height, point out that a built-in electric field is significantly smaller than the value expected from the spontaneous polarization discontinuity. This is explained by the uniaxial compressive strain resulting from the spontaneously formed Al-rich shell that envelops the QD stack.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

High-pressure phase transformations in MgO-Y2O3 nanocomposites

E. K. Akdoğan, İ. Şavklıyıldız, B. Berke, Z. Zhong, L. Wang, M. Vaughan, and T. Tsakalakos

Appl. Phys. Lett. 99, 141915 (2011); http://dx.doi.org/10.1063/1.3646546 (3 pages) | Cited 1 time

Online Publication Date: 6 October 2011

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Temperature and pressure dependence of phase evolution in 0.5 MgO-0.5 Y2O3 is studied using the diamond anvil method. At 300 K and 5.5 GPa, transformations in Y2O3 are observed, resulting in co-existence of cubic, hexagonal, and monoclinic phases. Heating to 1293 K results in increased crystallinity and increase in hexagonal and monoclinic phase content. Isothermal and isobaric hold at 1273 K and 5.5 GPa for 120 min results in yttrium dissolution in cubic MgO, causing 0.83% volumetric strain. Cooling to 300 K and 0 GPa yields a four phase co-existence among cubic MgO and cubic, hexagonal, and monoclinic Y2O3. The residual MgO unit cell volume expansion is 0.67% at 300 K, indicating solid solution formation. Aging of the nanocomposites for 240 h does not change the observed 4 phase co-existence.
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62.50.-p High-pressure effects in solids and liquids
64.70.Nd Structural transitions in nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
64.70.K- Solid-solid transitions

On the strain in n-type GaN

Jinqiao Xie, Seiji Mita, Lindsay Hussey, Anthony Rice, James Tweedie, James LeBeau, Ramón Collazo, and Zlatko Sitar

Appl. Phys. Lett. 99, 141916 (2011); http://dx.doi.org/10.1063/1.3647772 (3 pages) | Cited 5 times

Online Publication Date: 7 October 2011

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It was demonstrated that Ge has the same effect as Si on the strain evolution in n-type GaN as measured by x-ray diffraction. Dislocation inclination, which causes tensile strain in n-type GaN, was clearly observed by transmission electron microscopy where Ge doping was introduced during epitaxial growth. This result is explained by the Fermi level effect model that indicates dislocation inclination due to the climbing process through Ga vacancies. Therefore, there is no dependence of dislocation inclination on dopant species.
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81.40.Lm Deformation, plasticity, and creep
61.72.jd Vacancies
61.72.uj III-V and II-VI semiconductors
62.20.F- Deformation and plasticity
61.72.Lk Linear defects: dislocations, disclinations
81.05.Ea III-V semiconductors

Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties

Hua Zhou, Hui-Qiong Wang, Lijun Wu, Lihua Zhang, Kim Kisslinger, Yimei Zhu, Xiaohang Chen, Huahan Zhan, and Junyong Kang

Appl. Phys. Lett. 99, 141917 (2011); http://dx.doi.org/10.1063/1.3647846 (3 pages) | Cited 4 times

Online Publication Date: 7 October 2011

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We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
68.37.Og High-resolution transmission electron microscopy (HRTEM)
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