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12 Jan 2009

Volume 94, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Hong Li and Qing Zhang
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Dynamics of gold nanoparticles in a polymer melt

Christopher A. Grabowski, Bijoy Adhikary, and Ashis Mukhopadhyay

Appl. Phys. Lett. 94, 021903 (2009); http://dx.doi.org/10.1063/1.3070533 (3 pages) | Cited 7 times

Online Publication Date: 12 January 2009

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Gold nanoparticles are used as a luminescent contrast agent to study size-dependent dynamics in polymer matrix. The experiments measured the diffusion coefficient of particles in poly(butyl methacrylate) melt by tracking their motion within a diffraction-limited focus of a laser with 150 fs pulses at 800 nm. Our results indicate that for unentangled polymers, when the particle radius (R) is greater than the gyration radius (Rg) of the chain, the Stokes–Einstein relation can accurately predict particle dynamics. For longer chains, if the entanglement mesh length is larger than R, the particle diffuses ∼ 250 times faster than predicted by the Stokes–Einstein relation.
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66.10.C- Diffusion and thermal diffusion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Investigation of interfacial interaction and structural transition for epoxy/nanotube composites by positron annihilation lifetime spectroscopy

Wei Zhou, Junjun Wang, Zhenli Gong, Jing Gong, Ning Qi, and Bo Wang

Appl. Phys. Lett. 94, 021904 (2009); http://dx.doi.org/10.1063/1.3067873 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2009

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Positron annihilation lifetime spectroscopy was employed to study the effect of amine modification on interfacial interaction and structural transition for epoxy/multiwalled carbon nanotube (MWNT) composites. Temperature dependence of orthopositronium lifetimes suggests that sample with amine-modified MWNTs possesses the highest glass transition temperature compared with unmodified samples and neat epoxy resin, which indicates that stronger interfacial interactions exist between epoxy matrix and amine-modified MWNTs, as a result of the covalent bonds and other weak forces. This is testified by interaction parameter β calculated in terms of the positron annihilation parameter.
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64.70.K- Solid-solid transitions
78.70.Bj Positron annihilation

Anomalous nonlinearity parameters of solids at low acoustic drive amplitudes

William T. Yost and John H. Cantrell

Appl. Phys. Lett. 94, 021905 (2009); http://dx.doi.org/10.1063/1.3068490 (3 pages) | Cited 4 times

Online Publication Date: 14 January 2009

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Measurements of the nonlinearity parameter β as a function of acoustic drive amplitude are reported for polycrystalline aluminum alloy 2024, IN100 nickel-base superalloy, and monocrystalline Al[110]. The measurements show that the variations in β reported by [ Barnard, Appl. Phys. Lett. 74, 2447 (1999) ] result from the influence of the Peierls barrier on dislocation motion in the material. The dislocation motion is responsible not only for the hooklike behavior at the low drive amplitudes reported by Barnard but also for an oscillatory dependence of β at larger drive amplitudes not previously reported.
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62.65.+k Acoustical properties of solids
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

The energetics of dislocations accelerating and decelerating through the shear-wave speed barrier

Xanthippi Markenscoff and Surong Huang

Appl. Phys. Lett. 94, 021906 (2009); http://dx.doi.org/10.1063/1.3072351 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2009

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The question of whether a dislocation can accelerate through the shear-wave speed “barrier” is addressed by analyzing the transient motion at the instant when the velocity equals the shear-wave speed in the presence of acceleration. The stresses carried by the forming Mach wave fronts depend on the acceleration at this instant, and the energy required to push the dislocation through the shear-wave speed barrier is determined by means of the “contour-independent” dynamic J integral, which defines the self-force on a moving defect, and is obtained as a function of the acceleration as it crosses the barrier. For decelerating motion through the shear-wave speed barrier this energy is released as dissipation.
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62.30.+d Mechanical and elastic waves; vibrations
61.72.Bb Theories and models of crystal defects

Paradoxical phenomena between the homogeneous and inhomogeneous deformations of metallic glasses

Kyoung-Won Park, Chang-Myeon Lee, Mi-Rim Lee, Eric Fleury, Michael L. Falk, and Jae-Chul Lee

Appl. Phys. Lett. 94, 021907 (2009); http://dx.doi.org/10.1063/1.3064920 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2009

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Experiments in binary alloys demonstrate that metallic glasses exhibiting more plastic strain during homogeneous deformation tend to show lower global plasticity during inhomogeneous deformation. Testing of Cu–Zr binary alloys supports the hypothesis that the formation energy of a shear transformation zone, as extracted from the experimental data, is related to the homogeneous flow rate. We also report the microstructural aspects that control the global plasticity of metallic glasses in the light of structural disordering, softening, and shear localization.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Size-dependent photoelastic effect in ZnO nanorods

H. Y. Shih, T. T. Chen, Y. C. Chen, T. H. Lin, L. W. Chang, and Y. F. Chen

Appl. Phys. Lett. 94, 021908 (2009); http://dx.doi.org/10.1063/1.3072350 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2009

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Manipulation of internal strain by an external light beam called photoelastic effect has been firmly established in ZnO nanorods. The underlying mechanism of this interesting phenomenon arises from the combination of the screening of internal electric field and converse piezoelectric effect. We demonstrate that the photoelastic effect is more pronounced in thinner nanorods due to a larger surface to volume ratio. In addition to giving a good evidence for the existence of photoelastic effect in semiconductor nanorods, our finding also provides an excellent possibility for the development of nanoscale optical modulators.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
77.65.-j Piezoelectricity and electromechanical effects

Atomic-scale in situ observation of lattice dislocations passing through twin boundaries

Y. B. Wang and M. L. Sui

Appl. Phys. Lett. 94, 021909 (2009); http://dx.doi.org/10.1063/1.3072801 (3 pages) | Cited 15 times

Online Publication Date: 15 January 2009

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In situ transmission electron microscopy tensile experiments were carried out to investigate lattice dislocation and twin boundary (TB) interaction in Cu with nanoscale growth twins. Results show that extended dislocations form inside thick twin lamellas and slip toward TBs. The extended dislocations shrink, combine, and redissociate when they pass through TBs, leaving behind detwinning partial dislocations at the TBs. The mechanism of the observed dislocation/TB interactions and the effect of the mechanism on mechanical properties are discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries

Stabilizing nanostructured materials by coherent nanotwins and their grain boundary triple junction drag

C. Saldana, T. G. Murthy, M. R. Shankar, E. A. Stach, and S. Chandrasekar

Appl. Phys. Lett. 94, 021910 (2009); http://dx.doi.org/10.1063/1.3072595 (3 pages) | Cited 11 times

Online Publication Date: 16 January 2009

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The role of nanotwin lamellae in enhancing thermal stability of nanostructured materials is examined. Nanostructured copper with varying densities of twins was generated by controlling the deformation strain rate during severe plastic deformation at cryogenic temperatures. While the nanostructured materials produced under cryogenic conditions are characteristically unstable even at room temperatures, their stability is markedly improved when a dense dispersion of nanotwins is introduced. Observations of the role of nanotwins in pinning grain and subgrain structures suggest an interfacial engineering approach to enhancing the stability of nanostructured alloys.
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61.72.Mm Grain and twin boundaries
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.40.Lm Deformation, plasticity, and creep

Growth dynamics of C60 thin films: Effect of molecular structure

S. Yim and T. S. Jones

Appl. Phys. Lett. 94, 021911 (2009); http://dx.doi.org/10.1063/1.3072805 (3 pages) | Cited 5 times

Online Publication Date: 16 January 2009

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The surface morphology and growth behavior of fullerene thin films have been studied by atomic force microscopy and height difference correlation function analysis. In contrast to the large growth exponents (β) previously reported for other organic semiconductor thin-film materials, a relatively small β value of 0.39±0.10 was determined. Simulations of (1+1)-dimensional surface lateral diffusion models indicate that the evolution of deep grain boundaries leads to a rapid increase in β. We suggest that the commonly observed large β values for organic thin films are due to their intrinsically anisotropic molecular structures and hence different stacking directions between crystallite domains.
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68.55.ap Fullerenes
68.37.Ps Atomic force microscopy (AFM)
61.72.Mm Grain and twin boundaries
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Tunable ambipolar Coulomb blockade characteristics in carbon nanotubes-gated carbon nanotube field-effect transistors

Hong Li and Qing Zhang

Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Online Publication Date: 12 January 2009

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A single-walled carbon nanotube field-effect transistor has been fabricated with two single-walled carbon nanotube bundles as its top gates and a heavily doped p-type silicon substrate as its global back gate. The channel conductance is found to oscillate significantly as a function of the top- and back-gate voltages when the device is measured at 100 K or below. “Diamond”-shaped current forbidden regions can be clearly observed under both positive and negative top-gate voltages. A single-electron transistor model is proposed to qualitatively explain the observations.
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85.30.Tv Field effect devices
81.07.De Nanotubes
85.35.Kt Nanotube devices

Low-field and high-field electron transport in zinc blende InN

V. M. Polyakov, F. Schwierz, F. Fuchs, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 94, 022102 (2009); http://dx.doi.org/10.1063/1.3059570 (3 pages) | Cited 8 times

Online Publication Date: 12 January 2009

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We report on the electron transport in zinc blende InN simulated by the ensemble Monte Carlo method. To obtain the relevant band structure parameters, ab initio calculations have been carried out. Then, Monte Carlo transport simulations at room temperature and over a wide range of carrier concentrations have been performed. We obtain a steady-state peak drift velocity around 3.3×107 cm/s at an electric field of 55 kV/cm. For low-doped material, a room-temperature low-field mobility of about 6000 cm2/V s is calculated. A comparison with wurtzite InN does not reveal an advantage for the zinc blende InN phase regarding the electron transport.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ht High-field and nonlinear effects
71.20.Nr Semiconductor compounds
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
72.80.Ey III-V and II-VI semiconductors

Infrared detectors based on InGaAsN/GaAs intersubband transitions

Jean-Yves Duboz, Maxime Hugues, Benjamin Damilano, Alexandru Nedelcu, Philippe Bois, Nasrin Kheirodin, and François H. Julien

Appl. Phys. Lett. 94, 022103 (2009); http://dx.doi.org/10.1063/1.3065479 (3 pages) | Cited 2 times

Online Publication Date: 12 January 2009

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InGaAsN/GaAs multiquantum well structures have been grown by molecular beam epitaxy with 1% nitrogen in the well. Intersubband transitions have been observed in the infrared region by transmission spectroscopy. Infrared detectors have been processed and an intersubband transition has been observed in the photocurrent spectrum. All the observations are consistent with each other and in very good agreement with a theoretical calculation. Band to band transitions observed by photoluminescence also confirm the position of the levels in the well.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

B profile alteration by annealing in reactive ambients

B. J. Pawlak, N. E. B. Cowern, and W. Vandervorst

Appl. Phys. Lett. 94, 022104 (2009); http://dx.doi.org/10.1063/1.3068756 (3 pages) | Cited 2 times

Online Publication Date: 12 January 2009

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Suppression or stimulation of B diffusion and activation in Si (coimplanted with F) has been investigated by anneals in a N2 ambient enriched with H2 or O2. The H2 rich ambient leads to B desorption and therefore stimulated diffusion toward the surface, thus effectively reducing indiffusion. Annealing in an O2 rich ambient promotes deeper B diffusion by injection of Si interstitials. The impact of these ambients can further be modulated by combining the B implant with a shallow or deep F coimplant acting as Si interstitial trap. Deep F coimplant and H2 rich ambient offer attractive B diffusion and activation.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
68.43.Nr Desorption kinetics
61.72.jj Interstitials
68.35.Fx Diffusion; interface formation
66.30.Lw Diffusion of other defects

Electronic structure of In2O3 from resonant x-ray emission spectroscopy

L. F. J. Piper, A. DeMasi, S. W. Cho, K. E. Smith, F. Fuchs, F. Bechstedt, C. Körber, A. Klein, D. J. Payne, and R. G. Egdell

Appl. Phys. Lett. 94, 022105 (2009); http://dx.doi.org/10.1063/1.3070524 (3 pages) | Cited 11 times

Online Publication Date: 12 January 2009

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The valence and conduction band structures of In2O3 have been measured using a combination of valence band x-ray photoemission spectroscopy, O K-edge resonant x-ray emission spectroscopy, and O K-edge x-ray absorption spectroscopy. Excellent agreement is noted between the experimental spectra and O 2p partial density of states calculated within hybrid density functional theory. Our data are consistent with a direct band gap for In2O3.
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71.20.Nr Semiconductor compounds
78.70.En X-ray emission spectra and fluorescence
78.70.Dm X-ray absorption spectra

Thermoelectric power measurements of wide band gap semiconducting nanowires

Chul-Ho Lee, Gyu-Chul Yi, Yuri M. Zuev, and Philip Kim

Appl. Phys. Lett. 94, 022106 (2009); http://dx.doi.org/10.1063/1.3067868 (3 pages) | Cited 18 times

Online Publication Date: 13 January 2009

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We investigated the temperature-dependent thermoelectric power (TEP) of individual wide band gap ZnO and GaN semiconducting nanowires by fabricating the devices with good Ohmic contacts. In the temperature range of 10–300 K, the measured TEP of both nanowires was linearly dependent on temperature, indicating the degenerate doping nature of these nanowires. The room temperature TEP value of ZnO nanowires was as high as −400 μV/K while an order of magnitude smaller TEP value was observed in GaN. The negative sign of TEP values shows that electrons are the majority carriers in these wide band gap nanowires. More importantly, in comparison with gate-dependent transport measurements of the nanowire field effect transistors, analysis of temperature-dependent TEP measurements provides a reliable way of estimating the majority carrier concentration of nanowires, where conventional Hall effect measurements cannot be used.
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73.63.Nm Quantum wires
73.40.Ns Metal-nonmetal contacts
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Nonlocal Aharonov–Bohm conductance oscillations in an asymmetric quantum ring

S. S. Buchholz, S. F. Fischer, U. Kunze, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 94, 022107 (2009); http://dx.doi.org/10.1063/1.3069281 (3 pages) | Cited 8 times

Online Publication Date: 13 January 2009

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We investigate ballistic transport and quantum interference in a nanoscale quantum wire loop fabricated as a GaAs/AlGaAs field-effect heterostructure. Four-terminal measurements of current and voltage characteristics as a function of top gate voltages show negative bend resistance as a clear signature of ballistic transport. In perpendicular magnetic fields, phase-coherent transport leads to Aharonov–Bohm conductance oscillations, which show equal amplitudes in the local and the nonlocal measurement at a temperature of 1.5 K and above. We attribute this observation to the symmetry of the orthogonal cross junctions connecting the four quantum wire leads with the asymmetric quantum wire ring.
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73.63.Nm Quantum wires
73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects

X-ray photoelectron spectroscopy measurement of n-ZnO/p-NiO heterostructure valence-band offset

R. Deng, B. Yao, Y. F. Li, Y. M. Zhao, B. H. Li, C. X. Shan, Z. Z. Zhang, D. X. Zhao, J. Y. Zhang, D. Z. Shen, and X. W. Fan

Appl. Phys. Lett. 94, 022108 (2009); http://dx.doi.org/10.1063/1.3072367 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2009

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Valence-band offset (VBO) of n-ZnO/p-NiO heterojunction has been investigated by x-ray photoelectron spectroscopy. Core levels of Zn 2p and Ni 2p were used to align the VBO of n-ZnO/p-NiO heterojunction. It was found that n-ZnO/p-NiO heterojunction has a type-II band alignment and its VBO is determined to be 2.60±0.20 eV, and conduction-band offset is deduced to be 2.93±0.20 eV. The experimental VBO value is in good agreement with the calculated value based on the electron affinity of ZnO and NiO.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.-b Electron density of states and band structure of crystalline solids

Free electron behavior in InN: On the role of dislocations and surface electron accumulation

V. Darakchieva, T. Hofmann, M. Schubert, B. E. Sernelius, B. Monemar, P. O. Å. Persson, F. Giuliani, E. Alves, H. Lu, and W. J. Schaff

Appl. Phys. Lett. 94, 022109 (2009); http://dx.doi.org/10.1063/1.3065030 (3 pages) | Cited 15 times

Online Publication Date: 15 January 2009

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The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.
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73.61.Le Other inorganic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.U- Doping and impurity implantation
61.72.jd Vacancies
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Structural and thermoelectric properties of Bi2Sr2Co2Oy thin films on LaAlO3 (100) and fused silica substrates

Shufang Wang, A. Venimadhav, Shengming Guo, Ke Chen, Qi Li, A. Soukiassian, Darrell G. Schlom, Michael B. Katz, X. Q. Pan, Winnie Wong-Ng, Mark D. Vaudin, and X. X. Xi

Appl. Phys. Lett. 94, 022110 (2009); http://dx.doi.org/10.1063/1.3072803 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2009

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We have grown Bi2Sr2Co2Oy thin films on LaAlO3 (100) and fused silica substrates by pulsed laser deposition. The films on LaAlO3 are c-axis oriented and partially in-plane aligned with multiple domains, while the films on fused silica are preferred c-axis oriented without in-plane alignment. The Seebeck coefficient and resistivity of films on both substrates are comparable to those of single crystals. An oxide p-n heterojunction was formed by depositing Bi2Sr2Co2Oy film on Nb-doped SrTiO3 single crystal, which showed a rectifying behavior. These thin films and heterostructures may be used for future thermoelectric applications.
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68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
73.50.Lw Thermoelectric effects
73.61.Ng Insulators
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification

Optical bandgap widening of p-type Cu2O films by nitrogen doping

Yoshitaka Nakano, Shu Saeki, and Takeshi Morikawa

Appl. Phys. Lett. 94, 022111 (2009); http://dx.doi.org/10.1063/1.3072804 (3 pages) | Cited 15 times

Online Publication Date: 15 January 2009

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We have investigated the effect of N doping into Cu2O films deposited by reactive magnetron sputtering. With increasing N-doping concentration up to 3%, the optical bandgap energy is enlarged from ∼ 2.1 to ∼ 2.5 eV with retaining p-type conductivity as determined by optical absorption and Hall effect measurements. Additionally, photoelectron spectroscopy in air measurements shows an increase in the valence and conduction band shifts with N doping. These experimental results demonstrate possible optical bandgap widening of p-type N-doped Cu2O films, which is a phenomenon that is probably associated with significant structural changes induced by N doping, as suggested from x-ray diffraction measurements.
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.U- Doping and impurity implantation
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.20.My Galvanomagnetic and other magnetotransport effects

Specific resistance of Pd/Ir interfaces

R. Acharyya, H. Y. T. Nguyen, R. Loloee, W. P. Pratt, Jr., J. Bass, Shuai Wang, and Ke Xia

Appl. Phys. Lett. 94, 022112 (2009); http://dx.doi.org/10.1063/1.3072365 (3 pages) | Cited 3 times

Online Publication Date: 16 January 2009

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From measurements of the current-perpendicular-to-plane total specific resistance (AR = area times resistance) of sputtered Pd/Ir multilayers, we derive the interface specific resistance, 2ARPd/Ir = 1.02±0.06 fΩ m2, for this metal pair with closely similar lattice parameters. Assuming a single fcc crystal structure with the average lattice parameter, no-free-parameter calculations (including only spd orbitals) give for perfect interfaces 2ARPd/Ir (perf) = 1.21±0.1 fΩ m2, and for interfaces composed of 2 ML of a random 50%-50% alloy 2ARPd/Ir (50/50) = 1.22±0.1 fΩ m2. Within mutual uncertainties, these values fall just outside the range of the experimental value. Updating to add f-orbitals gives 2ARPd/Ir (perf) = 1.10±0.1 fΩ m2 and 2ARPd/Ir (50-50) = 1.13±0.1 fΩ m2, values now compatible with the experimental one. We also update, with f-orbitals, calculations for other pairs.
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68.65.Ac Multilayers
73.40.Jn Metal-to-metal contacts
68.35.Ct Interface structure and roughness

Carrier transport properties in the vicinity of single self-assembled quantum dots determined by low-voltage cathodoluminescence imaging

E. Dupuy, D. Morris, N. Pauc, V. Aimez, M. Gendry, and D. Drouin

Appl. Phys. Lett. 94, 022113 (2009); http://dx.doi.org/10.1063/1.3072613 (3 pages) | Cited 5 times

Online Publication Date: 16 January 2009

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We propose a method to investigate the carrier transport properties in the ultrathin wetting layer of a self-assembled quantum dot (QD) structure using low-voltage cathodoluminescence (CL) imaging. Measurements are performed on diluted InAs/InP QDs in order to spatially resolve them on CL images at temperature ranging from 5 to 300 K. The mean ambipolar diffusion length extracted from CL intensity profiles across different isolated bright spots is about 300 nm at 300 K. This gives an ambipolar carrier mobility of about 110 cm2/(V s). Temperature investigation reveals a maximum diffusion length near 120 K.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
81.07.Ta Quantum dots

Nonpolar GaN grown on Si by hydride vapor phase epitaxy using anodized Al nanomask

A. Y. Polyakov, A. V. Markov, M. V. Mezhennyi, A. V. Govorkov, V. F. Pavlov, N. B. Smirnov, A. A. Donskov, L. I. D’yakonov, Y. P. Kozlova, S. S. Malakhov, T. G. Yugova, V. I. Osinsky, G. G. Gorokh, N. N. Lyahova, V. B. Mityukhlyaev, et al.

Appl. Phys. Lett. 94, 022114 (2009); http://dx.doi.org/10.1063/1.3072614 (3 pages) | Cited 3 times

Online Publication Date: 16 January 2009

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GaN growth by the hydride vapor phase technique on (100) Si substrates masked by porous Al anodic oxide is described. The masks were prepared by vacuum deposition of Al with subsequent anodic oxidation in dilute sorrel acid. The grown GaN layer is nonpolar, with (11math0) a-orientation and a full width at half maximum of the (11math0) reflection below 500 arc sec and showing small anisotropy. This result is comparable with the results obtained for a-GaN growth using selective epitaxy or advanced buffer growth routines. Microcathodoluminescence spectra of the grown films confirm a low density of stacking faults. Possible growth mechanisms are discussed.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors

High thermoelectric power factor in alloys based on CoSi

E. Skoug, C. Zhou, Y. Pei, and D. T. Morelli

Appl. Phys. Lett. 94, 022115 (2009); http://dx.doi.org/10.1063/1.3072799 (3 pages) | Cited 11 times

Online Publication Date: 16 January 2009

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We have investigated the thermoelectric properties of alloys of composition CoSi1−xGex for 0 ≤ x ≤ 0.5. These alloys display Seebeck coefficient in the range of −80 to −100 μV K−1 at room temperature. Despite the rather high Seebeck coefficients, the electrical resistivity of these alloys is metallic in nature. Alloying on the Ge site strongly reduces the lattice thermal conductivity. The combination of high Seebeck coefficient and metallic resistivity leads to very high thermoelectric power factor in these alloys, with the best sample exhibiting a power factor higher than that of state of the art bismuth telluride-based thermoelectric alloys at room temperature.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.70.Df Metals, alloys, and semiconductors
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Epitaxial SmCo5 thin films with perpendicular anisotropy

M. Seifert, V. Neu, and L. Schultz

Appl. Phys. Lett. 94, 022501 (2009); http://dx.doi.org/10.1063/1.3068503 (3 pages) | Cited 8 times

Online Publication Date: 12 January 2009

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Epitaxial SmCo5 thin films with strong perpendicular magnetic anisotropy have been developed by pulsed laser deposition on heated Ru buffered Al2O3(0001) substrates. Pole figure measurements on thicker films reveal the existence of two epitaxial variants, 30° in-plane rotated to each other, which reduces to a single epitaxial relation for smaller film thickness. The presence of a single SmCo5 phase with perpendicular direction of the c-axis is established by multiple peak analysis of x-ray data in pole figure geometry and is confirmed by a numerical fit of hysteresis measurements, which results in an anisotropy constant of Ku = 7.6 MJ/m3.
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75.30.Gw Magnetic anisotropy
81.15.Fg Pulsed laser ablation deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ww Permanent magnets
68.55.jd Thickness
75.70.Ak Magnetic properties of monolayers and thin films
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