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14 Dec 2009

Volume 95, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 242102 (2009); http://dx.doi.org/10.1063/1.3272858 (3 pages)

W. H. Lim, F. A. Zwanenburg, H. Huebl, M. Möttönen, K. W. Chan, A. Morello, and A. S. Dzurak
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Graphene field effect transistors with parylene gate dielectric

S. S. Sabri, P. L. Lévesque, C. M. Aguirre, J. Guillemette, R. Martel, and T. Szkopek

Appl. Phys. Lett. 95, 242104 (2009); http://dx.doi.org/10.1063/1.3273396 (3 pages) | Cited 23 times

Online Publication Date: 14 December 2009

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We report the fabrication and characterization of graphene field effect transistors with parylene back gate and exposed graphene top surface. A back gate stack of 168 nm parylene on 94 nm thermal silicon oxide permitted optical reflection microscopy to be used for identifying exfoliated graphene flakes. Room temperature mobilities of 10 000 cm2/Vs at 1012/cm2 electron/hole densities were observed in electrically contacted graphene. Parylene gated devices exhibited stable neutrality point gate voltage under ambient conditions and less hysteresis than that observed in graphene flakes directly exfoliated on silicon oxide.
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85.30.Tv Field effect devices
78.67.Wj Optical properties of graphene

Selenium and tellurium: Elemental catalysts for conversion of graphite to diamond under high pressure and temperature

S. J. Lv, S. M. Hong, C. S. Yuan, and Y. Hu

Appl. Phys. Lett. 95, 242105 (2009); http://dx.doi.org/10.1063/1.3273855 (3 pages) | Cited 2 times

Online Publication Date: 14 December 2009

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The behavior of six systems of graphite with Sn, Pb, Sb, Bi, Se, and Te was investigated under high-pressure of around 9.0–9.6 GPa and high-temperature 1600–1850 °C. The results showed that the selenium and tellurium have obvious catalytic effects on spontaneous nucleation and crystal growth of diamond under pressure at 9.6 GPa, and at temperatures of 1800 and 1850 °C. The outer shell electron configuration analogous to oxygen and sulfur may play an important role in converting graphite to diamond under the high-pressure and high-temperature.
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64.70.K- Solid-solid transitions
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
62.50.-p High-pressure effects in solids and liquids
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Monte Carlo simulation of the percolation in Ag30Ge17Se53 amorphous electrolyte films

L. Chen, Q. C. Li, H. X. Guo, L. G. Gao, Y. D. Xia, J. Yin, and Z. G. Liu

Appl. Phys. Lett. 95, 242106 (2009); http://dx.doi.org/10.1063/1.3275701 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2009

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Monte Carlo simulations using a dielectrophoresis model were performed to investigate the microstructural evolution and the conductance change of an Ag30Ge17Se53 electrolyte film clapped by a Ag active electrode, at which a positive bias was applied, and a Pt inert electrode. It has been revealed that driven by the electrical field Ag ions were injected into the electrolyte from the Ag electrode to form conductive particles, thereafter, the particles align themselves in nanowires connecting Ag electrode and Pt electrode and leading to an electrical percolation. It is responsible for the resistive switching of the system. The transmission electron microscopic observations and resistive measurement results are in good agreement with the results of simulations.
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73.61.Ng Insulators
82.45.Gj Electrolytes
72.60.+g Mixed conductivity and conductivity transitions
82.45.Fk Electrodes
73.40.Rw Metal-insulator-metal structures
68.37.Lp Transmission electron microscopy (TEM)

Compact silicon double and triple dots realized with only two gates

M. Pierre, R. Wacquez, B. Roche, X. Jehl, M. Sanquer, M. Vinet, E. Prati, M. Belli, and M. Fanciulli

Appl. Phys. Lett. 95, 242107 (2009); http://dx.doi.org/10.1063/1.3273857 (3 pages) | Cited 12 times

Online Publication Date: 15 December 2009

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We report electronic transport on silicon double and triple dots created with the optimized number of two gates. Using silicon nitride spacers two dots in series are created below two top gates overlapping a silicon nanowire. Coupling between dots is controlled by gate voltages. A third dot is created either by combined action of gate voltages or local doping depending on the spacers length. The main characteristics of the triple dot stability diagram are quantitatively fitted.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
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)
61.72.uf Ge and Si

Zero field spin splitting in AlSb/InAs/AlSb quantum wells induced by surface proximity effects

Masaya Nishioka, Bruce A. Gurney, Ernesto E. Marinero, and Francisco Mireles

Appl. Phys. Lett. 95, 242108 (2009); http://dx.doi.org/10.1063/1.3274129 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2009

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InAs quantum well heterostructures are of considerable interest for mesoscopic device applications such as scanning probe and magnetic recording sensors, which require the channel to be close to the surface. Here we report on magnetotransport measurements of AlSb/InAs/AlSb Hall bars at a shallow depth of 20 nm. Analysis of the observed Shubnikov-de Haas oscillations and modeling show that spin splitting energies in excess of 2.3 meV occur at zero magnetic field. We conclude that the spin-splitting results from the Rashba effect due to the band bending in the quantum well. This is caused by substantial electron transfer from the surface to the quantum well and becomes significant when the quantum well is located near the surface.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
07.55.-w Magnetic instruments and components
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Si Esaki diodes with high peak to valley current ratios

M. Oehme, D. Hähnel, J. Werner, M. Kaschel, O. Kirfel, E. Kasper, and J. Schulze

Appl. Phys. Lett. 95, 242109 (2009); http://dx.doi.org/10.1063/1.3274136 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2009

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We report room temperature current voltage characteristics of Si p+-i-n+ Esaki diodes integrated on silicon substrates. The diodes were fabricated by low-temperature molecular beam epitaxy. Very high and abrupt p- and n-type dopant transitions into the 1020 cm−3 ranges are achieved by boron and antimony, respectively. The integrated devices are realized without a postgrowth annealing step. The silicon Esaki diodes show negative differential resistance at room temperature with excellent peak to valley current ratios up to 3.94. A variation in the thickness of the silicon tunneling barrier changes the peak current density over three orders of magnitude.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Excess carrier recombination lifetime of bulk n-type 3C-SiC

Vytautas Grivickas, Georgios Manolis, Karolis Gulbinas, Kęstutis Jarašiūnas, and Masashi Kato

Appl. Phys. Lett. 95, 242110 (2009); http://dx.doi.org/10.1063/1.3273382 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2009

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Transient absorption technique was used to determine carrier lifetimes in 3C-SiC grown on Si and 6H-SiC substrates. A slow lifetime component originated from minority carrier traps and pointed out to the trap saturation with increasing injection. Recombination lifetime in different samples varied between 0.5–120 ns. Its value decreased with excess carrier density in the transition range between minority-carrier-lifetime and high-injection lifetime but abnormally increased above the carrier density of 2×1017 cm−3. Negligible contribution of surface and Auger recombination to recombination lifetime peculiarities was observed. Possible mechanisms of the observed lifetime variation are discussed.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena
72.80.Jc Other crystalline inorganic semiconductors
79.20.Fv Electron impact: Auger emission

Interaction between Na and Li in ZnO

Pekka T. Neuvonen, Lasse Vines, Andrej Yu. Kuznetsov, Bengt G. Svensson, Xiaolong Du, Filip Tuomisto, and Anders Hallén

Appl. Phys. Lett. 95, 242111 (2009); http://dx.doi.org/10.1063/1.3270107 (3 pages) | Cited 2 times

Online Publication Date: 16 December 2009

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The interaction between group-Ia elements in ZnO have been studied by implanting Na into hydrothermally grown ZnO samples containing ∼ 4×1017 Li/cm3 and employing secondary ion mass spectrometry for sample analysis. Postimplantation annealing above 500 °C results in a diffusion of Na and concurrently Li is efficiently depleted from the regions occupied by Na. The data show unambiguously that Na and Li compete for the same trapping site and the results provide strong experimental evidence for that the formation energies of Na on Zn site together with that of interstitial Li are lower than those of Li on Zn site and interstitial Na in highly resistive ZnO. This conclusion is also supported by recent theoretical estimates of the formation energies of these species as a function of the Fermi-level position in ZnO.
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61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
66.30.J- Diffusion of impurities
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
71.20.Nr Semiconductor compounds

Advanced impurity trap memory with atomic-scale Ti impurities on LaAlO3: Evidence for the origins of enhanced memory performance

Seungjae Jung, Hyejung Choi, Yongkyu Ju, Man Chang, Minseok Jo, Joonmyoung Lee, Jaesik Yoon, Choongman Lee, and Hyunsang Hwang

Appl. Phys. Lett. 95, 242112 (2009); http://dx.doi.org/10.1063/1.3270528 (3 pages)

Online Publication Date: 17 December 2009

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We investigated advanced impurity trap memory (ITM) with atomic-scale Ti impurities on LaAlO3. Our ITM showed excellent memory characteristics, including a memory window (MW) of 5 V under +12 V/−10 V, ∼ 44% retained charge in 10 yr retention at 85 °C, and endurance without MW degradation up to 104 cycles. To understand the origins of these enhanced characteristics, we conducted various physical analyses. Our results confirmed that the incorporation of ultrathin LaAlO3, featuring both thermodynamic stability for diffusion barrier of Ti and favorable energy band structure together with high dielectric constant for bandgap engineering of tunnel oxide, is responsible for enhanced performance.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
84.30.Sk Pulse and digital circuits
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.55.Ht Other nonmetals
77.22.Ch Permittivity (dielectric function)

Nonlinear current-voltage behavior and giant positive magnetoresistance in nonmagnetic Au/Yttria-stabilized zirconia/Si heterostructures

T. L. Qu, J. Li, Y. G. Zhao, J. W. Mei, X. Liu, H. F. Tian, J. P. Shi, S. M. Guo, J. Li, D. N. Zheng, and J. Q. Li

Appl. Phys. Lett. 95, 242113 (2009); http://dx.doi.org/10.1063/1.3274130 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2009

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We report on the nonlinear current-voltage (I-V) behavior and giant positive magnetoresistance (GPMR) in the Au/Yttria-stabilized zirconia/Si heterostructures. The I-V curves of the heterostructures show a rectifying property and follow the Fowler–Nordheim tunneling behavior for the larger forward bias voltages. The GPMR of the samples increases with decreasing temperature and exceeds 100 000% in a magnetic field of 7 T at 20 K with a voltage of +4 V. It also shows anisotropy with magnetoresistance for the magnetic field perpendicular to the current larger than that of the parallel case. A possible mechanism was proposed to account for the results.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Cw Elemental semiconductors
72.80.Ga Transition-metal compounds
72.80.Sk Insulators

Hole-based memory operation in an InAs/GaAs quantum dot heterostructure

A. Marent, T. Nowozin, J. Gelze, F. Luckert, and D. Bimberg

Appl. Phys. Lett. 95, 242114 (2009); http://dx.doi.org/10.1063/1.3275758 (3 pages) | Cited 8 times

Online Publication Date: 18 December 2009

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We present an InAs/GaAs quantum dot (QD) memory structure with all-electrical data access which uses holes as charge carriers. Charging and discharging of the QDs are clearly controlled by a gate voltage. The stored information is read-out by a two-dimensional hole gas underneath the QD-layer. Time resolved drain-current-measurements demonstrate the memory operation. Present write times are 80 ns.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.La Quantum dots
84.30.Sk Pulse and digital circuits
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In-situ characterization of rapid crystallization of amorphous CoFeB electrodes in CoFeB/MgO/CoFeB junctions during thermal annealing

W. G. Wang, J. Jordan-sweet, G. X. Miao, C. Ni, A. K. Rumaiz, L. R. Shah, X. Fan, P. Parsons, R. Stearrett, E. R. Nowak, J. S. Moodera, and J. Q. Xiao

Appl. Phys. Lett. 95, 242501 (2009); http://dx.doi.org/10.1063/1.3273397 (3 pages) | Cited 15 times

Online Publication Date: 14 December 2009

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We report the crystallization study of CoFeB/MgO/CoFeB magnetic tunnel junctions using in-situ, time-resolved synchrotron-based x-ray diffraction and transmission electron microscopy. It was found that the crystallization of amorphous CoFeB electrodes occurs on a time scale of seconds during the postgrowth high temperature annealing. The crystallization can be well fit by the Johnson–Mehl–Avrami model and the effective activation energy of the process was determined to be 150 kJ/mol. The solid-state epitaxy mode of CoFeB was found to involve separate crystallization at different locations followed by subsequent merging of small grains, instead of layer-by-layer growth of CoFeB film along the MgO template.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials

Magnetization reorientation in antiferromagnetically coupled Co films and (Co/Pd) multilayers

Rachid Sbiaa, S. N. Piramanayagam, and Randall Law

Appl. Phys. Lett. 95, 242502 (2009); http://dx.doi.org/10.1063/1.3273856 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2009

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Magnetization reversal of antiferromagnetically coupled (AFC) Co thin film and (Co/Pd) multilayers has been investigated. For 5 Å thick Co layer, a high exchange coupling field (Hex) of 7.8 kOe at room temperature and 8.5 kOe at 5 K was measured from the shift in the hysteresis loop. This high value of Hex was accompanied by a magnetization reorientation from in-plane to out-of-plane of the thin Co. When Co thickness increases, the magnetization reorientation was not possible. This unusual high Hex can be used to stabilize AFC structures when the patterning to nanoscale size is needed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

GaMnAs-based magnetic tunnel junctions with an AlMnAs barrier

Shinobu Ohya, Iriya Muneta, Pham Nam Hai, and Masaaki Tanaka

Appl. Phys. Lett. 95, 242503 (2009); http://dx.doi.org/10.1063/1.3254218 (3 pages) | Cited 5 times

Online Publication Date: 16 December 2009

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We investigate the spin-dependent transport of GaMnAs-based magnetic tunnel junctions (MTJs) containing a paramagnetic AlMnAs barrier with various thicknesses. The barrier height of AlMnAs with respect to the Fermi level of GaMnAs is estimated to be 110 meV. We observe tunneling magnetoresistance (TMR) ratios up to 175% (at 2.6 K), which is higher than those of the GaMnAs-based MTJs with other barrier materials in the same temperature region. These high TMR ratios can be mainly attributed to the relatively high crystal quality of AlMnAs and the suppression of the tunneling probability at the in-plane wave vector k∥ ∼ 0.
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75.47.Pq Other materials
72.25.Dc Spin polarized transport in semiconductors
73.20.At Surface states, band structure, electron density of states
75.50.Pp Magnetic semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Thermal stability and spin-transfer switchings in MgO-based magnetic tunnel junctions with ferromagnetically and antiferromagnetically coupled synthetic free layers

Satoshi Yakata, Hitoshi Kubota, Toru Sugano, Takayuki Seki, Kay Yakushiji, Akio Fukushima, Shinji Yuasa, and Koji Ando

Appl. Phys. Lett. 95, 242504 (2009); http://dx.doi.org/10.1063/1.3275753 (3 pages) | Cited 8 times

Online Publication Date: 16 December 2009

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We prepared MgO-based magnetic tunnel junctions having a CoFeB/Ru/CoFeB synthetic free layer in which magnetizations of the CoFeB layers were ferromagnetically coupled (F-coupled Sy) or antiferromagnetically coupled (AF-coupled Sy). We studied spin-transfer switchings to evaluate their thermal stability (Δ0 = KV/kBT) and intrinsic switching current density (JC0). Although the free layers of two types showed nearly equal JC0, the Δ0 of F-coupled Sy was observed to be twice that of AF-coupled Sy. This difference is attributable to the shape magnetic anisotropy of the free-layer cells. Results show that F-coupled Sy is superior to AF-coupled Sy for memory applications.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Sg Magnetocaloric effect, magnetic cooling

Magnetic properties and atomic structure of La2/3Ca1/3MnO3–YBa2Cu3O7 heterointerfaces

Z. L. Zhang, U. Kaiser, S. Soltan, H.-U. Habermeier, and B. Keimer

Appl. Phys. Lett. 95, 242505 (2009); http://dx.doi.org/10.1063/1.3274044 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2009

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A heterostructure comprised of a 2.7 nm (7 unit cell) thick layer of the metallic ferromagnet La2/3Ca1/3MnO3 and two 50 nm thick layers of the high-temperature superconductor YBa2Cu3O7 epitaxially grown on (100) SrTiO3 by pulsed-laser deposition was characterized by magnetization measurements and spherical-aberration-corrected high-resolution transmission electron microscopy (HRTEM). The saturation magnetization is about half of that in bulk La2/3Ca1/3MnO3. A massive reduction in the magnetization previously inferred from sputter-deposited La2/3Ca1/3MnO3–YBa2Cu3O7 heterostructures can be ruled out. HRTEM image analysis, combined with image simulation and a focus series reconstruction, revealed atomically sharp epitaxial structures with stacking sequences –(La,Ca)O–CuO2– and –BaO–MnO– at the top and bottom interface.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.78.Fk Multilayers, superlattices, heterostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Fg Pulsed laser ablation deposition
75.50.Dd Nonmetallic ferromagnetic materials
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Ferroelectric polymer/silver nanocomposites with high dielectric constant and high thermal conductivity

Xingyi Huang, Pingkai Jiang, and Liyuan Xie

Appl. Phys. Lett. 95, 242901 (2009); http://dx.doi.org/10.1063/1.3273368 (3 pages) | Cited 14 times

Online Publication Date: 14 December 2009

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Ferroelectric polymer nanocomposites with silver (Ag) nanoparticles as inclusions were prepared and the dielectric properties and thermal conductivity were studied. The results showed that the nanocomposites have high dielectric constant and high thermal conductivity. When the loading level of Ag nanoparticles is 20.0 vol %, the dielectric constant and thermal conductivity of the nanocomposites were 120 at 103 Hz and 6.5 W/mK, respectively. Our results also showed that there is no percolation in the nanocomposites when Ag loading range is within 20.0%.
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77.22.Ch Permittivity (dielectric function)
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Lf Composite materials

Polarization switching characteristics of BiFeO3 thin films epitaxially grown on Pt/MgO at a low temperature

Sangwoo Ryu, Jong Yeog Son, Young-Han Shin, Hyun M. Jang, and James F. Scott

Appl. Phys. Lett. 95, 242902 (2009); http://dx.doi.org/10.1063/1.3275012 (3 pages) | Cited 7 times

Online Publication Date: 17 December 2009

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An [001]-oriented BiFeO3 (BFO) thin film having a pseudotetragonal symmetry was epitaxially grown on a Pt/MgO (001) substrate. The Pt-buffered MgO substrate enabled us to fabricate an epitaxial heterostructure at a temperature as low as 500 °C. We examined three major criteria for high-density ferroelectric memories using this BFO/Pt film capacitor. The polarization switching experiment has demonstrated that the film is electrically fatigue-free and possesses stable charge-retention characteristics with a reasonably large sensing margin of 22 μC/cm2. These suggest potential applicability of the present BFO/Pt heteroepitaxial film capacitor to nonvolatile memories.
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77.80.Fm Switching phenomena
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
85.50.Gk Non-volatile ferroelectric memories
77.22.Ej Polarization and depolarization
84.32.Tt Capacitors
81.15.Cd Deposition by sputtering

Predicted cooling powers for multilayer capacitors based on various electrocaloric and electrode materials

S. Kar-Narayan and N. D. Mathur

Appl. Phys. Lett. 95, 242903 (2009); http://dx.doi.org/10.1063/1.3275013 (3 pages) | Cited 16 times

Online Publication Date: 17 December 2009

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We argue that the multilayer capacitor (MLC) geometry is ideal for electrocaloric cooling. Thermal modeling predicts that a commercially available MLC, which serendipitously shows electrocaloric effects, could constitute the heart of an idealized heat pump delivering a continuous cooling power of 22.5 W kg−1. This figure could be increased via materials optimization to ∼ 2875 W kg−1, such that an MLC array whose sheet area is just ∼ 0.56 m2 would deliver the ∼ 20 kW cooling power of typical air-cooled chillers for air-conditioning at residential and commercial sites. Expensive materials are not required, and performance could be further enhanced via geometrical improvements.
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84.32.Tt Capacitors
77.70.+a Pyroelectric and electrocaloric effects
82.45.Fk Electrodes

Ferroelectricity triggered in the quantum paraelectric AgTaO3 by Li-substitution

Hwee Ping Soon, Hiroki Taniguchi, and Mitsuru Itoh

Appl. Phys. Lett. 95, 242904 (2009); http://dx.doi.org/10.1063/1.3275750 (3 pages)

Online Publication Date: 17 December 2009

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Ferroelectricity has been induced in the quantum paraelectric AgTaO3 (AT) by Li+ substitution, as evidence by both the dielectric anomaly and the hysteretic loop of electrical displacement versus applied electric field. The transition temperature (Tc) of Li-doped AT was found to increase with increasing level of Li+ substitution. Also, by substituting 12 mol % of Li+ into AT, which is close to the solubility limit, a ferroelectric material with a residual polarization ∼ 15 μC/cm2 and Tc at 258 K was then triggered.
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77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
64.75.Bc Solubility

Nanoparticle surface modification induced space charge suppression in linear low density polyethylene

Xingyi Huang, Pingkai Jiang, and Yi Yin

Appl. Phys. Lett. 95, 242905 (2009); http://dx.doi.org/10.1063/1.3275732 (3 pages) | Cited 6 times

Online Publication Date: 18 December 2009

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This letter reports the role of nanoparticle surface modification in affecting the space charge distribution of polyethylene/silica nanocomposite dielectrics. Space charge distribution in the nanocomposites was measured using a pulsed electroacoustic method. The results suggested that the nanoparticle surface modification has significant effects on the space charge behaviors in polyethylene and that the nanocomposites with surface-treated silica showed improved space charge distribution, which can be understood in terms of the morphological variation of the matrix and the better interfacial adhesion between the surface-treated nanoparticles and the matrix.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
77.22.Jp Dielectric breakdown and space-charge effects
72.50.+b Acoustoelectric effects

Surface acoustic wave propagation properties in 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystal poled along [111]c

Xiuming Li, Rui Zhang, Naixing Huang, Tianquan Lü, and Wenwu Cao

Appl. Phys. Lett. 95, 242906 (2009); http://dx.doi.org/10.1063/1.3271775 (3 pages)

Online Publication Date: 18 December 2009

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Surface acoustic wave (SAW) propagation properties in relaxor-based 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-33%PT) ferroelectric single crystals poled along [111]c has been analyzed theoretically. We found that the X-cut PMN-33%PT has lower phase velocity and higher electromechanical coupling coefficient compared to traditional piezoelectric materials. The power flow angle (PFA) can be zero in specific directions, which could drastically improve the performance of SAW devices. Our theoretical results indicate that the direction about 5° canted from [111]c is the optimum direction for the X-cut [111]c poled crystals in SAW device applications. Characteristic curves were also obtained for the phase velocity, electromechanical coupling coefficient, and PFA in Z-cut single-domain PMN-33%PT single crystals.
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68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
77.65.-j Piezoelectricity and electromechanical effects
77.80.B- Phase transitions and Curie point
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Depth resolved luminescence from oriented ZnO nanowires

R. A. Rosenberg, M. Abu Haija, K. Vijayalakshmi, J. Zhou, S. Xu, and Z. L. Wang

Appl. Phys. Lett. 95, 243101 (2009); http://dx.doi.org/10.1063/1.3275000 (3 pages) | Cited 11 times

Online Publication Date: 14 December 2009

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We have utilized the limited penetration depth of x-rays to study the near-surface properties of vertically aligned ZnO nanowires. For an energy of 600 eV the penetration depth varies between 3 and 132 nm as the incidence angle changes from 2° to 33°. Thus, by obtaining optical luminescence spectra as a function of incidence angle, it is possible to probe the near-surface region with nanometer-scale resolution. We will present angle dependent optical luminescence data from oriented ZnO nanowires. By fitting the results to a simple model, we extract a depth for the surface defect regions of ∼ 14 nm.
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78.55.Et II-VI semiconductors
78.67.Uh Nanowires

Self-organized quantum dot arrays: Kinetic mapping of adatom capture

I. Levchenko and K. Ostrikov

Appl. Phys. Lett. 95, 243102 (2009); http://dx.doi.org/10.1063/1.3273369 (3 pages) | Cited 7 times

Online Publication Date: 14 December 2009

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Deterministic synthesis of self-organized quantum dot arrays for renewable energy, biomedical, and optoelectronic applications requires control over adatom capture zones, which are presently mapped using unphysical geometric tessellation. In contrast, the proposed kinetic mapping is based on simulated two-dimensional adatom fluxes in the array and includes the effects of nucleation, dissolution, coalescence, and process parameters such as surface temperature and deposition rate. This approach is generic and can be used to control the nanoarray development in various practical applications.
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68.65.Hb Quantum dots (patterned in quantum wells)
64.75.Bc Solubility
61.46.-w Structure of nanoscale materials

Inducing chalcogenide phase change with ultra-narrow carbon nanotube heaters

Feng Xiong, Albert Liao, and Eric Pop

Appl. Phys. Lett. 95, 243103 (2009); http://dx.doi.org/10.1063/1.3273370 (3 pages) | Cited 9 times

Online Publication Date: 14 December 2009

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Carbon nanotube (CNT) heaters with sub-5 nm diameter induce highly localized phase change in Ge2Sb2Te5 (GST) chalcogenide. A significant reduction in resistance of test structures is measured as the GST near the CNT heater crystallizes. Effective GST heating occurs at currents as low as 25 μA, significantly lower than in conventional phase change memory with metal electrodes (0.1–0.5 mA). Atomic force microscopy reveals nucleation sites associated with phase change in GST around the CNT heater. Finite element simulations confirm electrical characteristics consistent with the experiments, and reveal the current and phase distribution in GST.
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68.55.ag Semiconductors
68.37.Ps Atomic force microscopy (AFM)
85.35.Kt Nanotube devices
73.61.Jc Amorphous semiconductors; glasses
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