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18 Jan 2010

Volume 96, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 033101 (2010); http://dx.doi.org/10.1063/1.3291849 (3 pages)

Ferruccio Pisanello, Luigi Martiradonna, Godefroy Leménager, Piernicola Spinicelli, Angela Fiore, Liberato Manna, Jean-Pierre Hermier, Roberto Cingolani, Elisabeth Giacobino, Massimo De Vittorio, and Alberto Bramati
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Strain-induced enhancement of electric quadrupole splitting in resistively detected nuclear magnetic resonance spectrum in quantum Hall systems

M. Kawamura, T. Yamashita, H. Takahashi, S. Masubuchi, Y. Hashimoto, S. Katsumoto, and T. Machida

Appl. Phys. Lett. 96, 032102 (2010); http://dx.doi.org/10.1063/1.3291618 (3 pages) | Cited 2 times

Online Publication Date: 19 January 2010

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We show electrical coherent manipulation of quadrupole-split nuclear spin states in a GaAs/AlGaAs heterostructure on the basis of the breakdown of quantum Hall effect. The electric quadrupole splitting in nuclear spin energy levels is intentionally enhanced by applying an external stress to the heterostructure. Nuclear magnetic resonance spectra with clearly separated triple peaks are obtained, and Rabi oscillations are observed between the nuclear spin energy levels. The decay of the spin-echo signal is compared between the cases before and after the enhancement of quadrupole splitting.
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76.60.Gv Quadrupole resonance
71.70.Jp Nuclear states and interactions
73.61.Ey III-V semiconductors
73.43.-f Quantum Hall effects

Electron trap memory characteristics of LiNbO3 film/AlGaN/GaN heterostructure

L. Z. Hao, J. Zhu, W. B. Luo, H. Z. Zeng, Y. R. Li, and Y. Zhang

Appl. Phys. Lett. 96, 032103 (2010); http://dx.doi.org/10.1063/1.3294308 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2010

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LiNbO3 film (LNO)/AlGaN/GaN heterostructure was fabricated and its memory characteristics were studied. The heterostructure exhibited a wide range clockwise hysteresis (0.3–12.1 V) likely due to the electrons trapping and distrapping from the Li vacancies in the LNO film. After 10 years retention, 10% of the window could remain. In addition, a slight decrease for the memory window happened after 105 cycles. These results indicated that LNO film combined with AlGaN/GaN would hold promise for next-generation nonvolatile memory devices. Possible operating mechanism for the memory effect in the heterostructure was explained qualitatively by the energy band diagram.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.jd Vacancies

Wide-band capacitance measurement on a semiconductor double quantum dot for studying tunneling dynamics

Takeshi Ota, Toshiaki Hayashi, Koji Muraki, and Toshimasa Fujisawa

Appl. Phys. Lett. 96, 032104 (2010); http://dx.doi.org/10.1063/1.3285180 (3 pages) | Cited 2 times

Online Publication Date: 19 January 2010

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We propose and demonstrate wide-band capacitance measurements on a semiconductor double quantum dot (DQD) to study tunneling dynamics. By applying phase-tunable high-frequency signals independently to the DQD and a nearby quantum-point-contact charge detector, we successfully measure current proportional to the capacitance associated with the single-electron motion over a wide frequency range from Hz to a few tens of GHz. Analyzing the phase and the frequency dependence of the signal allows us to extract the characteristic tunneling rates. We show that, by applying this technique to the interdot tunnel coupling regime, quantum capacitance reflecting the strength of the quantum-mechanical coupling can be measured.
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73.21.La Quantum dots
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Surface passivation of n-type Czochralski silicon substrates by thermal-SiO2/plasma-enhanced chemical vapor deposition SiN stacks

Yevgeniya Larionova, Verena Mertens, Nils-Peter Harder, and Rolf Brendel

Appl. Phys. Lett. 96, 032105 (2010); http://dx.doi.org/10.1063/1.3291681 (3 pages) | Cited 11 times

Online Publication Date: 19 January 2010

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The surface passivation properties of thermal-SiO2/plasma-enhanced chemical vapor deposition SiN stacks on 2.5 Ω cm n-type Czochralski silicon substrates have been investigated. By annealing these stacks in air we achieve surface recombination velocities (SRV) lower than 2.4 cm/s for thin SiO2 layers. We find a clear correlation between the thickness of the oxide layers and the annealing duration. We also show that the absolute passivation quality of the SiO2/SiN stacks correlates to the SiO2 thickness. We find that the SRV increases with increasing oxide thickness. We also present data of the surface passivation of these SiO2/SiN stacks after storage in the dark for several weeks.
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81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.40.Gh Other heat and thermomechanical treatments

Electrical properties of C-doped p-type GaP and GaPN grown by molecular beam epitaxy

Zhengxin Liu (劉正新), Hitoshi Kawanami (川浪仁志), and Isao Sakata (坂田功)

Appl. Phys. Lett. 96, 032106 (2010); http://dx.doi.org/10.1063/1.3291664 (3 pages) | Cited 1 time

Online Publication Date: 20 January 2010

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The electrical properties of C-doped p-type GaP and GaPN epilayers grown by molecular beam epitaxy using CBr4 as a doping source have been investigated. C is shown to be a relatively shallow acceptor both in GaP and GaPN, with the activation energy in the regions of 16–33 and 18–35 meV, respectively. GaP demonstrates ordinary conduction characteristics, whereas GaPN has a typical mixed conduction effect and the impurity conduction becomes dominant at low temperatures. It is conjectured that impurity conduction and ionized impurity scattering mechanisms in GaPN may be related to the inactivated C and N radicals.
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73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
61.72.S- Impurities in crystals
61.72.U- Doping and impurity implantation

Mo incorporation in WO3 thin film photoanodes: Tailoring the electronic structure for photoelectrochemical hydrogen production

M. Bär, L. Weinhardt, B. Marsen, B. Cole, N. Gaillard, E. Miller, and C. Heske

Appl. Phys. Lett. 96, 032107 (2010); http://dx.doi.org/10.1063/1.3291689 (3 pages) | Cited 6 times

Online Publication Date: 21 January 2010

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The electronic surface structure of Mo-incorporated WO3 (“WO3:Mo”) is investigated using direct and inverse photoemission and compared to that of pure (Mo-free) WO3. The films are found to be n-type with an electronic surface band gap of 3.27 (±0.15) eV. The conduction band minimum (valence band maximum) is 0.64 (±0.10) eV above [2.63 (±0.10) eV below] the Fermi level and at most 0.38 (±0.11) eV above the H+/H2 reduction potential [at least 1.66 (±0.11) eV below the H2O/O2 oxidation potential]. The findings suggest an explanation why WO3:Mo/WO3 bilayer structures show improved photoelectrochemical performance compared to respective single layer photoanodes.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Ps Other inorganic compounds
82.50.-m Photochemistry
82.45.-h Electrochemistry and electrophoresis
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Physical properties of La0.7Ba0.3MnO3−δ complex oxide thin films grown by pulsed laser deposition technique

P. Orgiani, R. Ciancio, A. Galdi, S. Amoruso, and L. Maritato

Appl. Phys. Lett. 96, 032501 (2010); http://dx.doi.org/10.1063/1.3292588 (3 pages) | Cited 4 times

Online Publication Date: 22 January 2010

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We report on transport properties of oxide manganite La0.7Ba0.3MnO3−δ (LBMO) thin films deposited by pulsed laser deposition (PLD) technique. Detailed analysis of heavy-ion stoichiometric composition has been carried out as a function of laser-pulse fluence and ambient oxygen pressure. Depositions using high-fluence (6 J/cm2) and low oxygen pressure (10−2 mbar) provide the optimal heavy-ion stoichiometric ratio in the LBMO samples. Deviations from the optimal LBMO stoichiometry are observed when decreasing the laser fluence or increasing the background oxygen pressure. This behavior is interpreted by considering the influence of the experimental deposition conditions on the plume dynamics. All these findings provide clear insights on the PLD-growth of manganites and, more in general, of complex oxide materials.
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73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition

Influence of length and measurement geometry on magnetoimpedance in La0.7Sr0.3MnO3

A. Rebello and R. Mahendiran

Appl. Phys. Lett. 96, 032502 (2010); http://dx.doi.org/10.1063/1.3293292 (3 pages) | Cited 3 times

Online Publication Date: 22 January 2010

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We show that ac magnetoresistance at room temperature in La0.7Sr0.3MnO3 is extremely high ( ≈ −47% in μ0H = 100 mT, f = 3–5 MHz), and magnetic field dependence of reactance exhibits a double peak behavior. However, magnitudes of the ac magnetoresistance and magnetoreactance for a fixed length of the sample (li) decrease with decreasing separation (lv) between voltage probes unlike the dc magnetoresistance. On the contrary, change in li has a negligible influence on magnetoimpedance when lv is fixed. Our results indicate that high frequency electrical transport is sensitive to local variations in the magnetic permeability.
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75.47.Lx Magnetic oxides
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects

Guided nucleation of superconductivity on a graded magnetic substrate

M. V. Milošević, W. Gillijns, A. V. Silhanek, A. Libál, F. M. Peeters, and V. V. Moshchalkov

Appl. Phys. Lett. 96, 032503 (2010); http://dx.doi.org/10.1063/1.3293300 (3 pages) | Cited 2 times

Online Publication Date: 22 January 2010

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We demonstrate the controlled spatial nucleation of superconductivity in a thin film deposited on periodic arrays of ferromagnetic dots with gradually increasing diameter. The perpendicular magnetization of the dots induces vortex-antivortex molecules in the sample, with the number of (anti)vortices increasing with magnet size. The resulting gradient of antivortex density between the dots predetermines local nucleation of superconductivity in the sample as a function of the applied external field and temperature. In addition, the compensation between the applied magnetic field and the antivortices results in an unprecedented enhancement of the critical temperature.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.10.+v Occurrence, potential candidates
74.25.Wx Vortex pinning (includes mechanisms and flux creep)

Direct observation of high velocity current induced domain wall motion

L. Heyne, J. Rhensius, A. Bisig, S. Krzyk, P. Punke, M. Kläui, L. J. Heyderman, L. Le Guyader, and F. Nolting

Appl. Phys. Lett. 96, 032504 (2010); http://dx.doi.org/10.1063/1.3291067 (3 pages) | Cited 6 times

Online Publication Date: 22 January 2010

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We study fast vortex wall propagation in Permalloy wires induced by 3 ns short current pulses with sub 100 ps rise time using high resolution magnetic imaging at zero field. We find a constant domain wall displacement after each current pulse as well as current induced domain wall structure changes, even at these very short timescales. The domain wall velocities are found to be above 100 m/s and independent of the domain wall spin structure. Comparison to experiments with longer pulses points to the pulse shape as the origin of the high velocities.
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75.60.Ch Domain walls and domain structure
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Magnetization reversal process in Fe/FePt films

Jai-Lin Tsai, Hsin-Te Tzeng, and Guo-Bin Lin

Appl. Phys. Lett. 96, 032505 (2010); http://dx.doi.org/10.1063/1.3293444 (3 pages) | Cited 8 times

Online Publication Date: 22 January 2010

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A soft/hard Fe/FePt bilayer with perpendicular magnetization was prepared on a glass substrate. Controlling the Fe layer thickness allowed modification of the hysteresis loops from rigid magnet with perpendicular magnetization to exchange-spring like magnet with parallel magnetization due to the nanoscale soft/hard interface coupling. For rigid magnetic films, the magnetization was reversed at a single switching field and interpreted by the two-spin model. In an exchange-spring like film, the in-plane magnetization reversal process was in two-steps and resulted from domain wall nucleation and propagation from the Fe layer into the FePt layer.
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75.60.Jk Magnetization reversal mechanisms
75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
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Thermal hysteresis of ferroelectric transition in Sr4R2Ti4Nb6O30 (R = Sm and Eu) tetragonal tungsten bronzes

X. L. Zhu and X. M. Chen

Appl. Phys. Lett. 96, 032901 (2010); http://dx.doi.org/10.1063/1.3292209 (3 pages) | Cited 6 times

Online Publication Date: 19 January 2010

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Sr4R2Ti4Nb6O30 (R = Sm and Eu) tungsten bronze ceramics were prepared, and the dielectric properties and ferroelectric transition were investigated together with the crystal structure. A ferroelectric transition peak and a low temperature dielectric relaxation were observed from the curve of permittivity versus temperature during heating process for both ceramics. The ferroelectric transition indicated large thermal hysteresis during the heating and cooling cycles for both ceramics, where the ferroelectric transition peak disappeared during the cooling process, and the low temperature dielectric relaxation was obviously enhanced. Moreover, extremely large depression of the Curie–Weiss temperature (T0) was observed in the present ceramics. These abnormal features were associated with the complex tetragonal tungsten bronze structure with two ferroelectrically active cations over two sets of sites and weak superstructure change from incommensurate to commensurate on cooling. The low temperature dielectric relaxation was due to the oxygen octahedron rotation in the ab plane and the possible compositional variations in the microscale.
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77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
61.66.-f Structure of specific crystalline solids

Charge-ordering-induced polar domains and domain walls in a bilayered manganite Pr(Sr0.15Ca0.85)2Mn2O7

H. Itoh, Y. Tokunaga, N. Kida, R. Shimano, and Y. Tokura

Appl. Phys. Lett. 96, 032902 (2010); http://dx.doi.org/10.1063/1.3284658 (3 pages) | Cited 1 time

Online Publication Date: 20 January 2010

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We have observed charge-ordering-induced polar domains and domain walls (DWs) in a bilayered manganite Pr(Sr0.15Ca0.85)2Mn2O7 using second-harmonic-generation microscopy. Around the transition temperature TC ∼ 306 K, a nucleation process of the domains with spontaneous polarization is clearly observed. Well below TC, the characteristic band-shaped dark patterns are identified in the second-harmonic images. On the analogy of the nucleation feature, they can be assigned to the DWs separating antiparallel polar domains. The anisotropy in the DW is governed by the geometrical constraint of the charge and orbital ordering, not by the electrostatic stability as in conventional ferroelectric DWs.
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75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Theoretical and experimental evidence of enhanced ferromagnetism in Ba and Mn cosubstituted BiFeO3

O. D. Jayakumar, S. N. Achary, K. G. Girija, A. K. Tyagi, C. Sudakar, G. Lawes, R. Naik, J. Nisar, X. Peng, and R. Ahuja

Appl. Phys. Lett. 96, 032903 (2010); http://dx.doi.org/10.1063/1.3280043 (3 pages) | Cited 15 times

Online Publication Date: 20 January 2010

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Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3. A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.-e Ferroelectricity and antiferroelectricity
75.85.+t Magnetoelectric effects, multiferroics
75.50.Dd Nonmetallic ferromagnetic materials
81.20.-n Methods of materials synthesis and materials processing
77.22.Ej Polarization and depolarization

Nanoscale properties of thin twin walls and surface layers in piezoelectric WO3−x

Yunseok Kim, Marin Alexe, and Ekhard K. H. Salje

Appl. Phys. Lett. 96, 032904 (2010); http://dx.doi.org/10.1063/1.3292587 (3 pages) | Cited 13 times

Online Publication Date: 22 January 2010

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Reduced WO3 single crystals have been investigated by conductive and piezoresponse force microscopy. The reduced crystals show a piezoelectric active surface layer with a noncentrosymmetric tetragonal structure which is different from the bulk of the crystal. The domain walls carry a high current while the bulk remains insulating. Twin-related interfaces are atomically thin, the upper bound being less than 10 nm. The reduced surface layer remained in the piezoelectric state even after several weeks, while the current in the twin boundaries was reduced by re-oxidization. This layer shows a significant piezoelectric activity with a piezoelectric coefficient of about 7.9 pm/V.
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77.65.Bn Piezoelectric and electrostrictive constants
61.72.Mm Grain and twin boundaries
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Oxygen vacancy levels and electron transport in Al2O3

D. Liu, S. J. Clark, and J. Robertson

Appl. Phys. Lett. 96, 032905 (2010); http://dx.doi.org/10.1063/1.3293440 (3 pages) | Cited 15 times

Online Publication Date: 22 January 2010

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The energy levels of the oxygen vacancy in α- and θ-Al2O3 were calculated using the screened exchange hybrid functional, and explain the electron hopping and trapping levels seen in deposited Al2O3 at ∼ 1.8 eV below its conduction band edge. The vacancy supports five accessible charge states, from 2+ to 2−. Electron hopping corresponds to the 0/− level, which lies 1.8 eV below the conduction band edge in θ-Al2O3. This level lies much deeper than it does HfO2. The +/0 level lies at 2.8 eV above oxide valence band in θ-Al2O3 and thus below the Si valence band top.
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61.72.jd Vacancies
72.20.Ee Mobility edges; hopping transport
72.80.Sk Insulators
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Room temperature-dipolelike single photon source with a colloidal dot-in-rod

Ferruccio Pisanello, Luigi Martiradonna, Godefroy Leménager, Piernicola Spinicelli, Angela Fiore, Liberato Manna, Jean-Pierre Hermier, Roberto Cingolani, Elisabeth Giacobino, Massimo De Vittorio, and Alberto Bramati

Appl. Phys. Lett. 96, 033101 (2010); http://dx.doi.org/10.1063/1.3291849 (3 pages) | Cited 19 times

Online Publication Date: 19 January 2010

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We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
82.70.Dd Colloids
71.35.-y Excitons and related phenomena

The role of dot height in determining exciton lifetimes in shallow InAs/GaAs quantum dots

T. E. J. Campbell-Ricketts, N. A. J. M. Kleemans, R. Nötzel, A. Yu. Silov, and P. M. Koenraad

Appl. Phys. Lett. 96, 033102 (2010); http://dx.doi.org/10.1063/1.3293294 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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The spectral dependence of the photoluminescence recombination lifetime has been measured for individual self-assembled InGaAs/GaAs quantum dots, over the entire emission envelope. The measurements show a rising trend with increasing emission wavelength, increasing from 680 ps at 900 nm to about 1020 ps at 990 nm. Measurements of the out-of-plane diamagnetic coefficients for the dots show almost no correlation with wavelength. As a result, the rising trend in the lifetimes with wavelength is interpreted in terms of the emission energy being predominantly determined by the dot height, with higher dots exhibiting longer lifetimes.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
75.20.Ck Nonmetals
71.35.-y Excitons and related phenomena

Calibrating the atomic balance by carbon nanoclusters

Fengqi Song, Xuefeng Wang, Rebecca C. Powles, Longbing He, Nigel A. Marks, Shifeng Zhao, Jianguo Wan, Zongwen Liu, Jianfeng Zhou, Simon P. Ringer, Min Han, and Guanghou Wang

Appl. Phys. Lett. 96, 033103 (2010); http://dx.doi.org/10.1063/1.3284498 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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Carbon atoms are counted at near atomic-level precision using a scanning transmission electron microscope calibrated by carbon nanocluster mass standards. A linear calibration curve governs the working zone from a few carbon atoms up to 34 000 atoms. This linearity enables adequate averaging of the scattering cross sections, imparting the experiment with near atomic-level precision despite the use of a coarse mass reference. An example of this approach is provided for layer counting of stacked graphene sheets. Suspended graphene sheets with a size below 100 nm are visualized, providing quantitative measurement in a regime inaccessible to optical and scanning probe methods.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.48.Gh Structure of graphene
68.37.Ma Scanning transmission electron microscopy (STEM)
68.65.Pq Graphene films

Angle resolved surface enhanced Raman scattering (SERS) on two-dimensional metallic arrays with different hole sizes

C. Y. Chan, J. B. Xu, M. Y. Waye, and H. C. Ong

Appl. Phys. Lett. 96, 033104 (2010); http://dx.doi.org/10.1063/1.3291109 (3 pages) | Cited 11 times

Online Publication Date: 19 January 2010

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The angle resolved surface enhanced Raman scattering (SERS) on two-dimensional Ag hole arrays has been studied as a function of hole size. The Raman enhancement factor has been found to increase with increasing hole size. In particular, by correlating the Raman mappings with the dispersion relations, the enhancement has been attributed to fast surface plasmon polariton radiative decay rate and strong coupling efficiency. Our results indicate that it is possible to optimize the geometry of the arrays to obtain desirable SERS.
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78.30.Er Solid metals and alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Plasmonic resonances and hot spots in Ag octopods

Ivan I. Naumov, Zhiyong Li, and Alexander M. Bratkovsky

Appl. Phys. Lett. 96, 033105 (2010); http://dx.doi.org/10.1063/1.3273859 (3 pages) | Cited 4 times

Online Publication Date: 19 January 2010

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Silver octopod plasmonic nanoparticles have been recently synthesized with a variety of shapes. In the present letter, we demonstrate their versatile optical response using the discrete dipole approximation. There are three major resonances that can be tuned up to a large extent making them especially attractive to use in, e.g., high-performance surface enhanced Raman scattering (SERS) detectors. The excited resonant modes strongly depend on the geometrical parameters of the stars. The field “hot spots” are mostly localized at the surface between the arms and may be both “electric” (important for SERS applications) and “magnetic” in character (potentially identifiable by trapping magnetic nanoparticles in their vicinity). The results are in very good agreement with the data where available and may be used for a “shape spectroscopy” for the nanoparticles.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
75.50.Tt Fine-particle systems; nanocrystalline materials
78.30.-j Infrared and Raman spectra
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon nanotube-Si diode as a detector of mid-infrared illumination

Pang-Leen Ong, William B. Euler, and Igor A. Levitsky

Appl. Phys. Lett. 96, 033106 (2010); http://dx.doi.org/10.1063/1.3279141 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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We report a room temperature mid-infrared photodetector based on a carbon nanotube-silicon heterojunction nanostructure. The observed mid-infrared band (8–12 μm) in the photocurrent spectrum is consistent with the estimated band gap energy of semiconducting multiwall nanotubes (15 to 30 nm diameter). The fast response time (16 ms) and small temperature change ( ∼ 10−8 K) upon infrared light suggest that the photocurrent response is not due to bolometric effect. We determined that the primary mechanism of the photocurrent in this spectral range is associated with photon absorption of semiconducting multiwalled carbon nanotubes followed by charge separation at the interface, their transport, and collection at the external electrodes.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Nonlinear optical and optical limiting properties of graphene families

Miao Feng, Hongbing Zhan, and Yu Chen

Appl. Phys. Lett. 96, 033107 (2010); http://dx.doi.org/10.1063/1.3279148 (3 pages) | Cited 29 times

Online Publication Date: 19 January 2010

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The nonlinear optical (NLO) and optical limiting (OL) properties of graphene families, including graphene oxide nanosheets, graphene nanosheets (GNSs), graphene oxide nanoribbons (GONRs), and graphene nanoribbons (GNRs), were investigated at 532 and 1064 nm using a nanosecond regime. GNSs, GONRs, and GNRs exhibited broadband NLO and OL properties. Reduced graphene samples exhibited stronger NLO and OL responses than their graphene oxide precursors because of their increased crystallinity and conjugation. Nonlinear scattering and two-photon-absorption were found to have strong effects on the NLO and OL responses of the graphene nanostructures.
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78.67.Wj Optical properties of graphene
61.46.-w Structure of nanoscale materials
42.79.-e Optical elements, devices, and systems
78.40.Ri Fullerenes and related materials

On the origin of suppression of free exciton no-phonon emission in ZnO tetrapods

S. L. Chen, S. K. Lee, W. M. Chen, H. X. Dong, L. Sun, Z. H. Chen, and I. A. Buyanova

Appl. Phys. Lett. 96, 033108 (2010); http://dx.doi.org/10.1063/1.3292027 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2010

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Temperature dependent photoluminescence and cathodoluminescence (CL) spectroscopies are employed to investigate free exciton (FX) emissions in ZnO tetrapods. The intensity of the no-phonon line is found to be largely suppressed as compared with longitudinal optical phonon assisted transitions, in sharp contrast to bulk ZnO. From spatially resolved CL studies, this suppression is shown to strongly depend on structural morphology of the ZnO tetrapods and becomes most significant within areas with faceted surfaces. A model based on reabsorption due to multiple internal reflections in the vicinity of the FX resonance is suggested to account for the observed effect.
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71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
63.20.kk Phonon interactions with other quasiparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Anomalously enhanced Raman scattering from longitudinal optical phonons on Ag-nanoparticle-covered GaN and ZnO

C. Y. Liu, M. M. Dvoynenko, M. Y. Lai, T. H. Chan, Y. R. Lee, J.-K. Wang, and Y. L. Wang

Appl. Phys. Lett. 96, 033109 (2010); http://dx.doi.org/10.1063/1.3291041 (3 pages) | Cited 7 times

Online Publication Date: 20 January 2010

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Show Abstract
The authors report experimental studies of surface-enhanced Raman scattering (SERS) of wurtzite-type GaN and ZnO crystalline samples covered with Ag-nanoparticles. The longitudinal optical phonons consistently exhibit unusually intense Raman enhancement in comparison with other phonons. The anomaly is interpreted by a proposed model based on a resonant Raman scattering process assisted by metal-induced gap states at the Ag/GaN and Ag/ZnO interfaces. This study suggests that SERS of lattice vibrations in inorganic semiconductors is sensitive to their propagation nature, providing a progressive perspective view on electron-mediated enhanced Raman scattering.
Show PACS
78.30.-j Infrared and Raman spectra
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
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