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1 Jun 2009

Volume 94, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 221101 (2009); http://dx.doi.org/10.1063/1.3143652 (3 pages)

Gangyi Xu, Virginie Moreau, Yannick Chassagneux, Adel Bousseksou, Raffaele Colombelli, G. Patriarche, G. Beaudoin, and I. Sagnes
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Controlling the conductance and noise of driven carbon-based Fabry–Pérot devices

Luis E. F. Foa Torres and Gianaurelio Cuniberti

Appl. Phys. Lett. 94, 222103 (2009); http://dx.doi.org/10.1063/1.3147865 (3 pages) | Cited 11 times

Online Publication Date: 1 June 2009

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We report on ac transport through carbon nanotube Fabry–Pérot devices. We show that tuning the intensity of the ac gating induces an alternation of suppression and partial revival of the conductance interference pattern. For frequencies matching integer multiples of the level spacing of the system Δ, the conductance remains irresponsive to the external field. In contrast, the noise in the low bias voltage limit behaves as in the static case only when the frequency matches an even multiple of the level spacing, thereby highlighting its phase sensitivity in a manifestation of the wagon-wheel effect in the quantum domain.
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85.35.Kt Nanotube devices

Tailoring the hole concentration in superlattices based on nitride alloys

Qing-Hong Zheng, Yi-An Yin, Li-Hong Zhu, Jin Huang, Xiao-Ying Li, and Bao-Lin Liu

Appl. Phys. Lett. 94, 222104 (2009); http://dx.doi.org/10.1063/1.3148244 (3 pages) | Cited 1 time

Online Publication Date: 1 June 2009

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By introducing Mg-doped InGaN/AlGaN strained-layer superlattice (SL) as p-type layer, the performance of p-type Ohmic contact is improved as compared with AlGaN/GaN and InGaN/GaN SLs. InGaN/AlGaN SL yields higher hole concentration due to larger oscillation of the valence band edge and smaller activation energy. The calculated average hole concentration in InGaN/AlGaN SL shows a twofold increase compared to that in AlGaN/GaN SL at the same Mg-doped level. The measured sheet hole density for ten periods of InGaN/AlGaN SL is as high as 4.4×1014 cm−2. Finally, Ni/Au contacts on Mg-doped InGaN/AlGaN SL with specific contact resistance of 7.3×10−5 Ω cm2 are realized.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.-i Conductivity phenomena in semiconductors and insulators
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Metal organic chemical vapor deposition of crack-free GaN-based light emitting diodes on Si (111) using a thin Al2O3 interlayer

William E. Fenwick, Andrew Melton, Tianming Xu, Nola Li, Christopher Summers, Muhammad Jamil, and Ian T. Ferguson

Appl. Phys. Lett. 94, 222105 (2009); http://dx.doi.org/10.1063/1.3148328 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2009

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Crack-free GaN light emitting diodes (LEDs) have been grown by metal organic chemical vapor deposition on Si(111) substrates using an atomic layer deposition-grown Al2O3 interlayer. Devices on Si show a longer emission wavelength compared to those on sapphire. This is attributed to tensile strain in the layers on Si, which may increase indium incorporation. Internal quantum efficiency is similar on both substrates. Luminescence intensity versus current density measurements show higher efficiency for the LEDs on Si relative to sapphire at high drive currents. These results show comparable performance characteristics for GaN-based devices on Si and sapphire substrates.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Terahertz generation in GaN diodes operating in pulsed regime limited by self-heating

E. A. Barry, V. N. Sokolov, K. W. Kim, and R. J. Trew

Appl. Phys. Lett. 94, 222106 (2009); http://dx.doi.org/10.1063/1.3147217 (3 pages) | Cited 2 times

Online Publication Date: 2 June 2009

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The conditions for pulsed regime operation of terahertz power generation in vertical nanoscale GaN-based diodes are investigated via self-consistent simulation of the high-field electron transport in the active channel and thermal transport in the entire device structure. The combined electrothermal model allows for a detailed analysis of the dynamical local distributions of the electric field, drift-velocity, and lattice temperature. We show that stable generation is achievable with a self-heating limited output power of 2.25 W at an operation frequency of 0.71 THz for a pulse width of 3 ns with a few tens of nanosecond duty cycle.
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85.30.Kk Junction diodes

Transport through graphene double dots

F. Molitor, S. Dröscher, J. Güttinger, A. Jacobsen, C. Stampfer, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 94, 222107 (2009); http://dx.doi.org/10.1063/1.3148367 (3 pages) | Cited 29 times

Online Publication Date: 2 June 2009

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We present Coulomb blockade measurements in a graphene double dot system. The coupling of the dots to the leads and between the dots can be tuned by graphene in-plane gates. The coupling is a nonmonotonic function of the gate voltage. Using a purely capacitive model, we extract all relevant energy scales of the double dot system.
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73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Reduction of native oxides on GaAs during atomic layer growth of Al2O3

Hang Dong Lee, Tian Feng, Lei Yu, Daniel Mastrogiovanni, Alan Wan, Torgny Gustafsson, and Eric Garfunkel

Appl. Phys. Lett. 94, 222108 (2009); http://dx.doi.org/10.1063/1.3148723 (3 pages) | Cited 17 times

Online Publication Date: 2 June 2009

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The reduction of surface “native” oxides from GaAs substrates following reactions with trimethylaluminum (TMA) precursor is studied using medium energy ion scattering spectroscopy (MEIS) and x-ray photoelectron spectroscopy (XPS). MEIS measurements after one single TMA pulse show that ∼ 65% of the native oxide is reduced, confirmed by XPS measurement, and a 5 Å thick oxygen-rich aluminum oxide layer is formed. This reduction occurs upon TMA exposure to as-received GaAs wafers.
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82.30.-b Specific chemical reactions; reaction mechanisms
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Electrical detection of spin precession in single layer graphene spin valves with transparent contacts

Wei Han, K. Pi, W. Bao, K. M. McCreary, Yan Li, W. H. Wang, C. N. Lau, and R. K. Kawakami

Appl. Phys. Lett. 94, 222109 (2009); http://dx.doi.org/10.1063/1.3147203 (3 pages) | Cited 26 times

Online Publication Date: 3 June 2009

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Spin accumulation and spin precession in single layer graphene are studied by nonlocal spin valve measurements at room temperature. The dependence of the nonlocal magnetoresistance on electrode spacing is investigated and the results indicate a spin diffusion length of ∼ 1.6 μm and a spin injection/detection efficiency of 0.013. Electrical detection of the spin precession confirms that the nonlocal signal originates from spin injection and transport. Fitting of the Hanle spin precession data yields a spin relaxation time of ∼ 84 ps and a spin diffusion length of ∼ 1.5 μm, which is consistent with the value obtained through the spacing dependence.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Hg Electrical injection of spin polarized carriers
72.25.Rb Spin relaxation and scattering
72.25.Mk Spin transport through interfaces
75.47.Pq Other materials
75.30.Ds Spin waves
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Low temperature charge carrier hopping transport mechanism in vanadium oxide thin films grown using pulsed dc sputtering

S. S. N. Bharadwaja, C. Venkatasubramanian, N. Fieldhouse, S. Ashok, M. W. Horn, and T. N. Jackson

Appl. Phys. Lett. 94, 222110 (2009); http://dx.doi.org/10.1063/1.3139864 (3 pages) | Cited 9 times

Online Publication Date: 4 June 2009

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Low temperature charge transport in vanadium oxide (VOx) thin films processed using pulsed dc sputtering is investigated to understand the correlation between the processing conditions and electrical properties. It is identified that the temperature dependent resistivity ρ(T) of the VOx thin films is dominated by a Efros–Shklovskii variable range hopping mechanism [ Efros and Shklovskii, J. Phys. C 8, L49 (1975) ]. A detailed analysis in terms of charge hopping parameters in the low temperature regime is used to correlate film properties with the pulsed dc sputtering conditions.
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73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
68.55.aj Insulators

Thickness dependence of the mobility at the LaAlO3/SrTiO3 interface

C. Bell, S. Harashima, Y. Hikita, and H. Y. Hwang

Appl. Phys. Lett. 94, 222111 (2009); http://dx.doi.org/10.1063/1.3149695 (3 pages) | Cited 31 times

Online Publication Date: 5 June 2009

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The electronic transport properties of a series of LaAlO3/SrTiO3 interfaces were investigated, and a systematic thickness dependence of the sheet resistance and magnetoresistance was found for constant growth conditions. This trend occurs above the critical thickness of four unit cells, below which the LaAlO3/SrTiO3 interface is not conducting. A dramatic decrease in mobility of the electron gas of nearly two orders of magnitude was observed with increasing LaAlO3 thickness from 5 to 25 unit cells.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.-c Electronic transport in interface structures
68.35.Ct Interface structure and roughness

Comparative study of electrical instabilities in top-gate InGaZnO thin film transistors with Al2O3 and Al2O3/SiNx gate dielectrics

Jeong-Min Lee, In-Tak Cho, Jong-Ho Lee, Woo-Seok Cheong, Chi-Sun Hwang, and Hyuck-In Kwon

Appl. Phys. Lett. 94, 222112 (2009); http://dx.doi.org/10.1063/1.3151865 (3 pages) | Cited 22 times

Online Publication Date: 5 June 2009

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A comparative study was made of the performance and electrical instabilities in amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors with Al2O3 and Al2O3/SiNx gate dielectrics. Steeper subthreshold slope is observed in Al2O3 devices, which shows that the density of trap states at the interface of a-IGZO/Al2O3 is lower than that of a-IGZO/SiNx. Under high bias-stresses, a larger degradation is observed in Al2O3/SiNx devices. The device degradation for both devices are mainly attributed to the charge trapping phenomenon, but the different time dependence of threshold voltage shift shows that trapped electrons are more easily redistributed inside the Al2O3 dielectrics.
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85.30.Tv Field effect devices

Characterization of near-infrared n-type β-FeSi2/p-type Si heterojunction photodiodes at room temperature

Mahmoud Shaban, Keita Nomoto, Shota Izumi, and Tsuyoshi Yoshitake

Appl. Phys. Lett. 94, 222113 (2009); http://dx.doi.org/10.1063/1.3151915 (3 pages) | Cited 17 times

Online Publication Date: 5 June 2009

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n-type β-FeSi2/p-type Si heterojunctions were fabricated from β-FeSi2 films epitaxially grown on Si(111) by facing-target direct-current sputtering. Sharp film-substrate interfaces were confirmed by scanning electron microscopy. The current-voltage and photoresponse characteristics were measured at room temperature. They exhibited good rectifying properties and a change of approximately one order of magnitude in the current at a bias voltage of −1 V under illumination by a 6 mW, 1.31 μm laser. The estimated detectivity was 1.5×109 cm √Hz W at 1.31 μm. The results suggest that the β-FeSi2/Si heterojunctions can be used as near-infrared photodetectors that are compatible with silicon integrated circuits.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Ei Rectification

Determination of wurtzite InN/cubic In2O3 heterojunction band offset by x-ray photoelectron spectroscopy

H. P. Song, A. L. Yang, H. Y. Wei, Y. Guo, B. Zhang, G. L. Zheng, S. Y. Yang, X. L. Liu, Q. S. Zhu, Z. G. Wang, T. Y. Yang, and H. H. Wang

Appl. Phys. Lett. 94, 222114 (2009); http://dx.doi.org/10.1063/1.3151956 (3 pages) | Cited 12 times

Online Publication Date: 5 June 2009

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In2O3 is a promising partner of InN to form InN/In2O3 heterosystems. The valence band offset (VBO) of wurtzite InN/cubic In2O3 heterojunction is determined by x-ray photoemission spectroscopy. The valence band of In2O3 is found to be 1.47±0.11 eV below that of InN, and a type-I heterojunction with a conduction band offset (CBO) of 0.49–0.99 eV is found. The accurate determination of the VBO and CBO is important for use of InN/In2O3 based electronic devices.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
81.05.Ea III-V semiconductors

Change in the resistivity of Ge-doped Sb phase change thin films grown by chemical vapor deposition according to their microstructures

Jin-Hyock Kim, Keun Lee, Su-Jin Chae, Il-Keoun Han, Jae-Sung Roh, Sung-Ki Park, Byung Joon Choi, Cheol Seong Hwang, Eunae Cho, and Seungwu Han

Appl. Phys. Lett. 94, 222115 (2009); http://dx.doi.org/10.1063/1.3151959 (3 pages) | Cited 1 time

Online Publication Date: 5 June 2009

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This study examined the effects of the composition and microstructure on the electric resistivity of Ge-doped Sb phase change thin films grown by cyclic plasma enhanced chemical vapor deposition. Ge and Sb layers were deposited sequentially to form either a GexSby mixture or Ge/Sb nanolaminated films. While the resistivity of the nanolaminated films was higher, the GexSby mixture showed a lower resistivity than the pure Sb film. This can be explained by the increase in carrier density of the alloy, as confirmed by first-principles calculations. An abrupt change in resistance accompanying a phase change was observed at ∼ 210 °C.
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73.61.At Metal and metallic alloys
71.15.-m Methods of electronic structure calculations
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
71.20.Be Transition metals and alloys
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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“All-Heusler alloy” current-perpendicular-to-plane giant magnetoresistance

Konstantin Nikolaev, Paul Kolbo, Taras Pokhil, Xilin Peng, Yonghua Chen, Thomas Ambrose, and Oleg Mryasov

Appl. Phys. Lett. 94, 222501 (2009); http://dx.doi.org/10.1063/1.3126962 (3 pages) | Cited 25 times

Online Publication Date: 1 June 2009

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A materials system of ternary full Heusler alloys exhibiting substantial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) has been theoretically proposed and experimentally realized. Observed trends in magnetoresistance are broadly consistent with the modeling results. A CPP-GMR of 6.7% and ΔRA of 4 mΩ μm2 have been demonstrated in the bottom spin-valve configuration. The spin-stand testing of narrow-track recording heads confirmed compatibility of these materials with hard disk drive reader technology.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials

Magnetocaloric effect in preferentially textured Mn50Ni40In10 melt spun ribbons

B. Hernando, J. L. Sánchez Llamazares, V. M. Prida, D. Baldomir, D. Serantes, M. Ilyn, and J. González

Appl. Phys. Lett. 94, 222502 (2009); http://dx.doi.org/10.1063/1.3147875 (3 pages) | Cited 14 times

Online Publication Date: 1 June 2009

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Inverse and direct magnetocaloric properties were evaluated in preferentially textured Mn50Ni40In10 ribbons applying the magnetic field H∥ along the ribbon length and perpendicular H⊥ to the ribbon plane (ΔH = 30 kOe). Maximum magnetic entropy change, hysteretic losses, and refrigerant capacity were not significantly affected by crystallographic texture. Refrigeration capacity around structural transition is strongly reduced by the large hysteretic losses associated to the metamagnetic field-induced reverse martensitic transformation and narrower working temperature range making the interval around the magnetic transition more efficient for a refrigerant cycle (RCstruct = 71 J kg−1 versus RCstructeff ≈ 60 J kg−1, and RCmagn = 89–86 J kg−1, for H∥ and H⊥, respectively).
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
65.40.gd Entropy
81.30.Kf Martensitic transformations

Planar superconductor/ferromagnet hybrids: Anisotropy of resistivity induced by magnetic templates

A. Yu. Aladyshkin, J. Fritzsche, and V. V. Moshchalkov

Appl. Phys. Lett. 94, 222503 (2009); http://dx.doi.org/10.1063/1.3149698 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2009

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We investigated experimentally the transport properties of a superconducting cross-shaped aluminum microbridge fabricated on top of a ferromagnetic BaFe12O19 single crystal. It was demonstrated that a one-dimensional domain structure in the ferromagnetic substrate can induce the formation of superconducting channels above magnetic domains. This leads to a giant anisotropy of resistivity of the superconducting bridge, caused by the appearance of continuous paths of supercurrents flowing along domain walls.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
75.60.Ch Domain walls and domain structure
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Locally induced charged states in La0.89Sr0.11MnO3 single crystals

R. F. Mamin, I. K. Bdikin, and A. L. Kholkin

Appl. Phys. Lett. 94, 222901 (2009); http://dx.doi.org/10.1063/1.3147163 (3 pages) | Cited 8 times

Online Publication Date: 3 June 2009

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Scanning probe microscopy was used to create and to detect local bias induced charged states in La0.89Sr0.11MnO3 single crystals at room temperature. The lifetime of these nonequilibrium states exceeds 100 h. These bias induced states display also a ferroelectriclike hysteresis with piezoelectric contrast reversed by the applied field. Such states showing reversible multifunctional properties are attractive for modern semiconductor technology with its focus on nonvolatile random-access memories.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis

Temperature stability of ([Na0.5K0.5NbO3]0.93–[LiTaO3]0.07) lead-free piezoelectric ceramics

Thomas A. Skidmore, Tim P. Comyn, and Steven J. Milne

Appl. Phys. Lett. 94, 222902 (2009); http://dx.doi.org/10.1063/1.3153157 (3 pages) | Cited 27 times

Online Publication Date: 5 June 2009

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A polymorphic phase transition (PPT) is often engineered into lead-free materials to generate high piezoelectric activity at room temperature, limiting their temperature stability. We report [Na0.5K0.5NbO3]0.93–[LiTaO3]0.07 tetragonal ceramics with favorable properties over a broad temperature range due to a high Curie temperature at 447 °C and PPT at −15 °C involving a transition to a monoclinic rather than low temperature orthorhombic phase. Piezoelectric k31 and d31 coefficients varied from 0.19 to 0.14 and −53 to −33 pC/N, respectively, over the range of −15 to 300 °C. Strain-electric field loops provided strains of ∼ 0.2% and a high-field d33 of 205 pm/V.
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77.65.-j Piezoelectricity and electromechanical effects
77.80.B- Phase transitions and Curie point
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Ch Permittivity (dielectric function)
64.70.K- Solid-solid transitions
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Visualization of a ferroelectric domain structure in the X cut of a LiNbO3 crystal using x-ray diffraction and topography

D. V. Roshchupkin, D. V. Irzhak, and V. V. Antipov

Appl. Phys. Lett. 94, 222903 (2009); http://dx.doi.org/10.1063/1.3151817 (3 pages) | Cited 1 time

Online Publication Date: 5 June 2009

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A ferroelectric domain structure formed in the X cut of a LiNbO3 crystal by aftergrowth thermoelectrical treatment was studied by x-ray diffraction and topography methods. An external electric field applied along the X axis to the crystal causes shift deformations due to the reverse piezoelectric effect, which permits visualization of domain structures in the X cut of a LiNbO3 crystal. Oppositely directed inclinations of reflecting planes in adjacent domains, caused by the reverse piezoelectric effect, give rise to different diffraction angles in neighboring domains and make visualization of domain structure possible.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
72.20.Pa Thermoelectric and thermomagnetic effects
77.65.-j Piezoelectricity and electromechanical effects
72.80.Sk Insulators

Charge transport mechanism in amorphous alumina

Yu. N. Novikov, V. A. Gritsenko, and K. A. Nasyrov

Appl. Phys. Lett. 94, 222904 (2009); http://dx.doi.org/10.1063/1.3151861 (3 pages) | Cited 13 times

Online Publication Date: 5 June 2009

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The charge transport mechanism in amorphous Al2O3 was examined both experimentally and theoretically. We have found that electrons are dominant charge carriers in Al2O3. A satisfactory agreement between the experimental and calculated data was obtained assuming the multiphonon ionization mechanism for deep traps in Al2O3. For the thermal and optical trap ionization energies in Al2O3, the values WT = 1.5 eV and Wopt = 3.0 eV were obtained.
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73.61.Ng Insulators
77.55.-g Dielectric thin films
63.20.-e Phonons in crystal lattices
77.22.Ch Permittivity (dielectric function)
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Role of microconvection induced by Brownian motion of nanoparticles in the enhanced thermal conductivity of stable nanofluids

P. D. Shima, John Philip, and Baldev Raj

Appl. Phys. Lett. 94, 223101 (2009); http://dx.doi.org/10.1063/1.3147855 (3 pages) | Cited 34 times

Online Publication Date: 1 June 2009

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We investigate the role of microconvection induced by Brownian motion of nanoparticles on thermal conductivity enhancement in stable nanofluids containing nanoparticles of average diameters 2.8–9.5 nm. Nanofluids with a fixed particle loading of 5.5 vol. %, the effective thermal conductivity (k/kf) increases from 1.05 to 1.25 with increasing particle diameter. Upon increasing the aspect ratio of the linear chains in nanofluids, very large enhancement of thermal conductivity is observed. These findings confirm that microconvection is not the key mechanism responsible for thermal conductivity enhancements in nanofluids whereas aggregation has a more prominent role.
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07.10.Cm Micromechanical devices and systems
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
47.27.T- Turbulent transport processes
05.40.Jc Brownian motion

Mode-locking nanoporous alumina membrane embedded with carbon nanotube saturable absorber

Yuichi Kurashima, Yoshihiko Yokota, Iwao Miyamoto, Hiromichi Kataura, and Youichi Sakakibara

Appl. Phys. Lett. 94, 223102 (2009); http://dx.doi.org/10.1063/1.3147857 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2009

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The saturable absorption effect of semiconducting single-wall carbon nanotubes (SWCNTs) covering the near-infrared region is promising for mode-locking devices of short pulse lasers. However, an issue remains that the heat generated at the SWCNTs would destroy the devices. In this research, we fabricated a nanostructured heat sink in which the SWCNTs are stuffed into specially developed nanopores of heat conductive alumina. Actually, it induced stable mode-locked operation of an Er fiber laser for over 4 months.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
61.46.Fg Nanotubes
61.43.Gt Powders, porous materials

Optical properties of well-crystallized and size-tuned ZnO quantum dots

Keigo Suzuki, Hiroyuki Kondo, Masashi Inoguchi, Nobuhiko Tanaka, Keisuke Kageyama, and Hiroshi Takagi

Appl. Phys. Lett. 94, 223103 (2009); http://dx.doi.org/10.1063/1.3147874 (3 pages) | Cited 5 times

Online Publication Date: 1 June 2009

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Well-crystallized and size-tuned ZnO quantum dots (QDs) were prepared by pulsed laser ablation and following size classification using a differential mobility analyzer. Photoluminescence (PL) spectra of the ZnO QDs showed predominant ultraviolet (UV) emission. The finely size-tuned ZnO QDs allowed us to precisely evaluate the quantum confinement effect, i.e., the size-driven color-tunable behavior in the UV emission range. The faint green luminescence found in the PL spectra and the low Stokes shifts of several tens meV demonstrated that the present QDs are almost free from defects. These features are quite favorable for use in future optoelectronic devices.
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78.67.Hc Quantum dots
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors

A scale-bridging method for nanoparticulate polymer nanocomposites and their nondilute concentration effect

Seunghwa Yang and Maenghyo Cho

Appl. Phys. Lett. 94, 223104 (2009); http://dx.doi.org/10.1063/1.3143669 (3 pages) | Cited 9 times

Online Publication Date: 1 June 2009

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Due to the enhanced interaction among constituents and the resultant effect of particle size on the elastic modulus, nanocomposites with volume fractions higher than 12% show critical nondilute concentrations. In order to describe nondilute concentrations and the effect of particle size, a multi-inclusion model was adopted and a method was developed to transfer nanoscale physical information to a continuum-based analytical model. The accuracy and applicability of the present scale-bridging method at dilute and nondilute concentrations were verified by comparing results of the present method with those of molecular dynamics and finite element analysis.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
61.46.-w Structure of nanoscale materials

Magnetic states of zigzag graphene nanoribbons from first principles

Fang Wu, Erjun Kan, Hongjun Xiang, Su-Huai Wei, Myung-Hwan Whangbo, and Jinlong Yang

Appl. Phys. Lett. 94, 223105 (2009); http://dx.doi.org/10.1063/1.3147854 (3 pages) | Cited 14 times

Online Publication Date: 2 June 2009

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The nature of the magnetic states of zigzag graphene nanoribbons (ZGNRs) was explored on the basis of density functional calculations to understand why they are apparently nonmagnetic. Our study shows that the magnetic moments of ZGNRs are destroyed by p-type or n-type carrier doping with ∼ 1013 carriers/cm2 per ribbon, which is close to the amount of unpaired spins that ZGNRs are expected to have. Thus the extrinsic sources of carrier doping should be removed to observe the expected magnetic character of ZGNRs.
Show PACS
81.05.ub Fullerenes and related materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
75.30.Cr Saturation moments and magnetic susceptibilities
73.63.-b Electronic transport in nanoscale materials and structures
72.20.Ee Mobility edges; hopping transport
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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