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23 Apr 2012

Volume 100, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages)

Y. Peng and K. Kempa
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Reducing spin torque switching current density by boron insertion into a CoFeB free layer of a magnetic tunnel junction

Xin Jiang, Rai Moriya, and Stuart Parkin

Appl. Phys. Lett. 100, 172407 (2012); http://dx.doi.org/10.1063/1.4704916 (3 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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The spin torque switching current density is measured for magnetic tunnel junctions containing a CoFeB free layer. We find that the insertion of an ultra-thin boron layer near the free layer/tunnel barrier interface gives rise to an increased resistance-area product and to a reduction in the switching current density. This is attributed to a lower tunneling matrix element near the inserted boron. As a result, the injected current is concentrated within smaller areas of the free layer, which leads to an overall decrease in the switching current density.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
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Nanoscale spin wave valve and phase shifter

Y. Au, M. Dvornik, O. Dmytriiev, and V. V. Kruglyak

Appl. Phys. Lett. 100, 172408 (2012); http://dx.doi.org/10.1063/1.4705289 (4 pages) | Cited 4 times

Online Publication Date: 24 April 2012

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We have used micromagnetic simulations to demonstrate a method for controlling the amplitude and phase of spin waves propagating inside a magnonic waveguide. The method employs a nanomagnet formed on top of a magnonic waveguide. The function of the proposed device is controlled by defining the static magnetization direction of the nanomagnet. The result is a valve or phase shifter for spin waves, acting as the carrier of information for computation or data processing within the emerging spin wave logic architectures of magnonics. The proposed concept offers such technically important benefits as energy efficiency, non-volatility, and miniaturization.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Strong ferromagnetism in Pt-coated ZnCoO: The role of interstitial hydrogen

Jong Moon Shin, Ho Sik Lee, Su Young Cha, Seunghun Lee, Ji Young Kim, Noejung Park, Yong Chan Cho, Su Jae Kim, Sung-Kyu Kim, Jong-Seong Bae, Sungkyun Park, Chae Ryong Cho, Hideomi Koinuma, and Se-Young Jeong

Appl. Phys. Lett. 100, 172409 (2012); http://dx.doi.org/10.1063/1.4705304 (4 pages)

Online Publication Date: 24 April 2012

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We observed strong ferromagnetism in ZnCoO as a result of high concentration hydrogen absorption. Coating ZnCoO with Pt layer, and ensuing hydrogen treatment with a high isostatic pressure resulted in a highly increased carrier concentration of 1021/cm3. This hydrogen treatment induced a strong ferromagnetism at low temperature that turned to superparamagnetism at about 140 K. We performed density functional method computations and found that the interstitial H dopants promote the ferromagnetic ordering between scattered Co dopants. On the other hand, interstitial hydrogen can decrease the magnetic exchange energy of Co-H-Co complexes, leading to a reduction in the blocking temperature.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Le Other inorganic semiconductors
61.72.jj Interstitials

Magnetic-field-induced reverse martensitic transformation and large magnetoresistance in Ni50−xCoxMn32Al18 Heusler alloys

H. C. Xuan, L. J. Shen, T. Tang, Q. Q. Cao, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 100, 172410 (2012); http://dx.doi.org/10.1063/1.4707161 (4 pages) | Cited 3 times

Online Publication Date: 25 April 2012

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We have studied the magnetic and magnetoresistance properties in polycrystalline Ni50−xCoxMn32Al18 Heusler alloys. A unique martensitic transformation (MT) from the ferromagnetic austenite to the weak-magnetic martensite phase was obtained and magnetic-field-induced reverse MT was confirmed in these alloys. A magnetic difference up to 45 emu/g was measured across the MT for Ni42Co8Mn32Al18 alloy. In the same quaternary alloy, the large magnetoresistance effect of 67% at 225 K was observed through this field-induced magnetic phase transition.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Co/Ni multilayers with perpendicular anisotropy for spintronic device applications

L. You, R. C. Sousa, S. Bandiera, B. Rodmacq, and B. Dieny

Appl. Phys. Lett. 100, 172411 (2012); http://dx.doi.org/10.1063/1.4704184 (4 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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This letter presents a study of perpendicular anisotropy in Co/Ni multilayers, which could constitute a thick polarizer in spin torque oscillators or a magnetic electrode in magnetic tunnel junctions (MTJ) with perpendicular anisotropy. Perfectly square perpendicular loops are observed for as-deposited Co/Ni multilayers with various sublayer thicknesses and bilayer repetition numbers using a Pt buffer layer. An anisotropy energy of 1.0 × 106 erg·cm−3 is obtained for 9 nm thick Co/Ni multilayers. For Co/Ni multilayers deposited on MgO, no perpendicular magnetization component is observed in the as-deposited state, but it develops (even in 2.1 nm Co/Ni multilayers) after annealing at 250 °C.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.47.Np Metals and alloys
81.40.Gh Other heat and thermomechanical treatments

High sensitivity low field magnetically gated resistive switching in CoFe2O4/La0.66Sr0.34MnO3 heterostructure

Vishal Thakare, Guozhong Xing, Haiyang Peng, Abhimanyu Rana, Onkar Game, P. Anil Kumar, Arun Banpurkar, Yesappa Kolekar, Kartik Ghosh, Tom Wu, D. D. Sarma, and Satishchandra B. Ogale

Appl. Phys. Lett. 100, 172412 (2012); http://dx.doi.org/10.1063/1.4707373 (4 pages) | Cited 5 times

Online Publication Date: 26 April 2012

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The phenomenon of resistive switching (RS) has been demonstrated in several non-magnetic and some magnetic oxide systems, however the “magnetic” aspect of magnetic oxides has not been emphasized especially in terms of low field tunability. In our work, we examined the CoFe2O4/La0.66Sr0.34MnO3 all-magnetic oxide interface system for RS and discovered a very sharp (bipolar) transition at room temperature that can be gated with high sensitivity by low magnetic fields (∼0–100 mT). By using a number of characterizations, we show that this is an interface effect, which may open up interesting directions for manipulation of the RS phenomenon.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.50.Gg Ferrimagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Radial-spin-wave-mode-assisted vortex-core magnetization reversals

Myoung-Woo Yoo, Jehyun Lee, and Sang-Koog Kim

Appl. Phys. Lett. 100, 172413 (2012); http://dx.doi.org/10.1063/1.4705690 (4 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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The dynamic behaviors of vortex-core magnetization reversals in soft magnetic nanodisks driven by oscillating magnetic fields applied perpendicularly to the disk plane were studied by means of micromagnetic numerical simulations. It was found that when the field frequencies are tuned to the eigenfrequencies of radial spin-wave modes, the threshold field amplitudes required for vortex-core switching are an order of magnitude smaller than those of static perpendicular fields. The reversal mechanism and associated underlying physics are completely different from those of vortex-antivortex-pair-mediated core reversals. The results reflect the achievement of an alternative efficient means of ultrafast vortex-core switching.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves
75.50.Tt Fine-particle systems; nanocrystalline materials
75.78.Jp Ultrafast magnetization dynamics and switching
75.78.Cd Micromagnetic simulations
75.60.Jk Magnetization reversal mechanisms

Investigation of perpendicular magnetic anisotropy of CoFeB by x-ray magnetic circular dichroism

W. C. Tsai, S. C. Liao, H. C. Hou, C. T. Yen, Y. H. Wang, H. M. Tsai, F. H. Chang, H. J. Lin, and Chih-Huang Lai

Appl. Phys. Lett. 100, 172414 (2012); http://dx.doi.org/10.1063/1.4707380 (4 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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We have studied the variation of perpendicular magnetic anisotropy (PMA) of CoFeB layers with the oxidation degree of the MgO buffer layers. After annealing at 330 °C, the out-of-plane anisotropy field (Hk) of 1.5-nm CoFeB could be optimized to 3.1 kOe. To investigate the orbital hybridization of the Fe-3d and O-2p, the orbital moments per hole (morb/Nh) of Fe in annealed CoFeB layers were extracted by using x-ray magnetic circular dichroism. The dependence of morb/Nh on the oxidation time of MgO coincided with that of Hk, which revealed that PMA of annealed CoFeB originated from the interfacial orbital hybridization.
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75.30.Gw Magnetic anisotropy
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Bz Metals and metallic alloys
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Orientation-dependent surface potential behavior in Nb-doped BiFeO3

F. Yan, G. Z. Xing, M. Islam, S. Li, and L. Lu

Appl. Phys. Lett. 100, 172901 (2012); http://dx.doi.org/10.1063/1.4705405 (5 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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Single-phase epitaxial Nb doped BiFeO3 (BFNO) films have been grown on diverse oriented-SrTiO3 substrates by pulsed laser deposition. The orientation dependent surface potential distributions arising from combination of the screen and polarization charges on the BFNO surfaces were characterized by Kelvin probe force microscopy combining with corresponding domain structures investigation using piezoresponse force microscopy. The relationship between surface potential and potential barrier was quantitatively analyzed through tuning the substrate orientation. The present study indicates that data stability and storage density can be controlled via engineering the substrate orientations.
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68.35.bt Other materials
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
77.55.Px Epitaxial and superlattice films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.Nv Multiferroic/magnetoelectric films

Evolution of nanodomains under DC electrical bias in Pb(Mg1/3Nb2/3)O3-PbTiO3: An In-situ transmission electron microscopy study

Yukio Sato, Tsukasa Hirayama, and Yuichi Ikuhara

Appl. Phys. Lett. 100, 172902 (2012); http://dx.doi.org/10.1063/1.4705418 (3 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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Domain structure and its evolution under electrical biases play important roles in piezoelectrics. The effects could be more significant in morphotropic phase boundary piezoelectrics, such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), since domains are miniaturized down to nanometer scale. Here, we report in-situ transmission electron microscopy observations for evolution of nanodomains under DC electrical biases in PMN-PT. We find that nanodomains switch with redistributions of invariant nanodomains population for the unpoled crystals, which is consistent with our previous results for the poled cases. This suggests that response of nanodomains for the unpoled and poled crystals can be understood in similar ways.
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77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
77.84.Cg PZT ceramics and other titanates

Surface flashover breakdown mechanisms on liquid immersed dielectrics

Jouya Jadidian, Markus Zahn, Nils Lavesson, Ola Widlund, and Karl Borg

Appl. Phys. Lett. 100, 172903 (2012); http://dx.doi.org/10.1063/1.4705473 (4 pages)

Online Publication Date: 24 April 2012

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Flashover formation and expansion mechanisms on the surfaces of different dielectrics immersed in transformer oil have been numerically analyzed. Streamers emanating from a needle electrode tend to transform to surface flashovers if the immersed dielectric permittivity is higher than the liquid permittivity and/or the dielectric interfacial surface cuts the path of the streamer. Perpendicular interface of the immersed dielectric impedes the breakdown by deflecting the streamer and slowing down the surface flashover. The parallel dielectric interface, however, assists the breakdown by regulating the surface flashover velocity to an approximately constant value (∼10 km/s).
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52.80.Wq Discharge in liquids and solids
77.22.Ch Permittivity (dielectric function)
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
02.60.-x Numerical approximation and analysis

Large and stable piezoelectric response in Bi0.97Nd0.03FeO3 thin film

Bo Jiang, Xiaolong Li, Hongyan Zhang, Wen Sun, Jingjing Liu, and Guangda Hu

Appl. Phys. Lett. 100, 172904 (2012); http://dx.doi.org/10.1063/1.4705427 (4 pages)

Online Publication Date: 25 April 2012

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Bi1−xNdxFeO3 (BNFO) (x = 0.01 ∼ 0.045) films were epitaxially prepared on LaNiO3 [100]/Si substrates via a metal organic decomposition method. Well-saturated and rectangular P-E hysteresis loop can be observed in BNFOx=0.03 film. Additionally, the domains in all BNFO films can be fully switched using a piezoelectric-mode atomic force microscope. More importantly, the BNFOx=0.03 film exhibits a large and stable piezoresponse (∼160 pm/V). These phenomena can be ascribed to the lowest leakage current and redistribution of VO•• in this film.
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68.55.A- Nucleation and growth
68.37.Ps Atomic force microscopy (AFM)
77.55.H- Piezoelectric and electrostrictive films
77.65.-j Piezoelectricity and electromechanical effects

High-pressure electrical transport properties of KNbO3: Experimental and theoretical approaches

Qinglin Wang, Yonghao Han, Cailong Liu, Yanzhang Ma, Wanbin Ren, and Chunxiao Gao

Appl. Phys. Lett. 100, 172905 (2012); http://dx.doi.org/10.1063/1.4706255 (4 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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Pressure-induced electrical transport properties of KNbO3 including resistance, relaxation frequency, and relative permittivity have been investigated under pressure up to 30.6 GPa by in situ impedance spectroscopy measurement. The results indicate that the discontinuous changes of these physical parameters occur around the structural phase transition pressure. The decrease of activation energy with increasing pressure reveals that the vibration damping of Nb-O dipoles is weakened in the orthorhombic and the tetragonal phases. The density of states and difference charge density calculations show that the pressure-induced charge transfer between the Nb and O atoms causes the relative permittivity change of KNbO3.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
72.80.Sk Insulators
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates

Enhanced piezoelectricity and nature of electric-field induced structural phase transformation in textured lead-free piezoelectric Na0.5Bi0.5TiO3-BaTiO3 ceramics

Deepam Maurya, Abhijit Pramanick, Ke An, and Shashank Priya

Appl. Phys. Lett. 100, 172906 (2012); http://dx.doi.org/10.1063/1.4709404 (5 pages) | Cited 4 times

Online Publication Date: 26 April 2012

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This letter provides a comparative description of the properties of textured and randomly oriented poly-crystalline lead-free piezoelectric 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT) ceramics. A high longitudinal piezoelectric constant of (d33) ∼ 322 pC/N was obtained in (001)PC textured NBT-7BT ceramics, which is almost ∼2× times the d33 coefficient reported for randomly oriented ceramics of the same composition. In situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nanoregions and internal stresses induced by domain switching.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Local structure around Fe ions on multiferroic Pb(Fe1/2Nb1/2)O3 ceramics probed by x-ray absorption spectroscopy

A. Mesquita, B. M. Fraygola, V. R. Mastelaro, and J. A. Eiras

Appl. Phys. Lett. 100, 172907 (2012); http://dx.doi.org/10.1063/1.4709490 (4 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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Local structure around Fe ions on Pb(Fe1/2Nb1/2)O3 ceramics was probed by x-ray absorption spectroscopy in order to settle the controversies about its structure. It is observed that the shell structure around Fe atoms exhibits a monoclinic local symmetry at 130 and 230 K, tetragonal local symmetry at room temperature, and cubic local symmetry at 410 K. Independently of the coordination, temperature, or symmetry, Fe-O mean bond-length does not vary significantly.
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61.66.Fn Inorganic compounds
77.80.Dj Domain structure; hysteresis
78.70.Dm X-ray absorption spectra
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.85.+t Magnetoelectric effects, multiferroics
61.50.Lt Crystal binding; cohesive energy

Defect level distributions and atomic relaxations induced by charge trapping in amorphous silica

Nathan L. Anderson, Ravi Pramod Vedula, Peter A. Schultz, R. M. Van Ginhoven, and Alejandro Strachan

Appl. Phys. Lett. 100, 172908 (2012); http://dx.doi.org/10.1063/1.4707340 (4 pages) | Cited 1 time

Online Publication Date: 26 April 2012

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We compute the distribution of electronic levels of native defects in amorphous silica from total energy differences of charge-state density functional theory calculations over an ensemble of atomic structures. The predicted distributions reproduce results from trap spectroscopy by charge injection experiments, validating the calculations. Furthermore, our study characterizes the experimentally inaccessible contributions of individual defect types to the overall distribution. Computed electron and hole trapping levels provide insight into the positive charge buildup in bulk silica observed in negative-bias-temperature-instability, an important degradation mechanism of metal-oxide-semiconductor devices.
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71.55.Ht Other nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.J- Point defects and defect clusters
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Nanotube-based scanning rotational microscope

Andrey M. Popov, Irina V. Lebedeva, and Andrey A. Knizhnik

Appl. Phys. Lett. 100, 173101 (2012); http://dx.doi.org/10.1063/1.4705430 (4 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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A scheme of the scanning rotational microscope is designed. This scheme is based on using carbon nanotubes simultaneously as a probe tip and as a bolt/nut pair which converts translational displacements of two piezo actuators into pure rotation of the probe tip. First-principles calculations of the interaction energy between movable and rotational parts of the microscope confirm the capability for its operation. The scanning rotational microscope with a chemically functionalized nanotube-based tip can be used to study how the interaction between individual molecules or a molecule and a surface depends on their relative orientation.
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07.79.-v Scanning probe microscopes and components
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Strain relaxation by dislocation glide in ZnO/ZnMgO core-shell nanowires

G. Perillat-Merceroz, R. Thierry, P.-H. Jouneau, P. Ferret, and G. Feuillet

Appl. Phys. Lett. 100, 173102 (2012); http://dx.doi.org/10.1063/1.4704927 (4 pages) | Cited 3 times

Online Publication Date: 23 April 2012

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Plastic relaxation of the misfit stress in core-shell semi-conducting nanowires can lead to structural defects, detrimental to applications. Core-shell Zn0.7Mg0.3O/ZnO quantum well heterostructures were deposited on ZnO nanowires. Strain along the a and c axes of the wurtzite structure is relaxed through the glide of dislocation half-loops from the free surfaces, within pyramidal and prismatic planes. Some half-loops are closed up in the barriers to accommodate the misfit at two consecutive interfaces of the quantum well stack. Dislocations are also observed within the nanowire core: contrary to two-dimensional structures, both the core and the shell can be plastically relaxed.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.65.La Quantum wires (patterned in quantum wells)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
68.65.Fg Quantum wells

Enhancement of Raman scattering by field superposition of rough submicrometer silver particles

Feng Zhang, Ping Chen, Lei Zhang, Song-Cheng Mao, Lie Lin, Yu-Guo Tang, Ji-Cheng Cui, Xiang-Dong Qi, Jun-Hong Yang, and Yun-Feng Ma

Appl. Phys. Lett. 100, 173103 (2012); http://dx.doi.org/10.1063/1.4705083 (4 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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Wavelength-dependent surface-enhanced Raman spectra of methylene blue adsorbed on rough submicrometer silver particles were measured. Results revealed a high enhancement factor (105 ∼ 107), especially in the long-wavelength region. Investigation on the far- and near-field optical properties of the particles showed a remarkably enhanced dipole plasmon resonance due to the presence of a rough particle surface. Through analyzing the plasmon resonance modes and the superposition of radiation fields, we found that the rough surface-induced field superposition results in the redistribution of optical fields around the particle, which becomes a key factor responsible for the high enhancement effect of metal particles.
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78.30.Er Solid metals and alloys
68.43.Mn Adsorption kinetics
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.bd Metals and alloys

Impacts of image force on the Schottky barrier height at metal-carbon nanotube contacts

Gang Zhang and Qing Shi

Appl. Phys. Lett. 100, 173104 (2012); http://dx.doi.org/10.1063/1.4705300 (3 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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By using first-principles calculations and classical image force model, we studied the image force induced Schottky barrier (SB) height reduction in carbon nanotube (CNT)-metal contact. A low dielectric constant leads to a stronger band bending and therefore strongly reduces the SB height. This reduction depends on carrier concentration and CNT diameter. For CNT with carrier concentration of 1020 cm−3, the reduction in SB height caused by image force is up to 0.7 eV when CNT diameter is less than 20 Å. Our results demonstrate that image force induced SB height reduction is important for the design of CNT-based nanoelectronic devices.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ch Permittivity (dielectric function)

Apparent Raman spectral shifts from nano-structured surfaces

V. Tishkova and W. S. Bacsa

Appl. Phys. Lett. 100, 173105 (2012); http://dx.doi.org/10.1063/1.4704928 (4 pages)

Online Publication Date: 24 April 2012

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We observe Raman spectral shifts when scanning the focal spot over trenches in gallium arsenide. The Raman spectral shifts induced by topography are only present when the trenches are parallel to the spectrometer grating grooves. The topography induced spectral shifts are explained by spatial modification of the emitted beam due to surface topography leading to a non uniform illumination of the focal spot. The non uniform illumination of the focal spot influences the grating angle leading to the observed spectral shift. Apparent Raman spectral shifts of nano-structured surfaces can be reduced when under focusing at the expense of recording lower signals or using objectives with a low numerical aperture. This shows that topography induced spectral shifts need to be taken into account when recording optical spectra from nano-structured surfaces.
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78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors
61.46.Hk Nanocrystals
68.35.bg Semiconductors

Using carbon chains to mediate magnetic coupling in zigzag graphene nanoribbons

Min Kan, Jian Zhou, Yawei Li, and Qiang Sun

Appl. Phys. Lett. 100, 173106 (2012); http://dx.doi.org/10.1063/1.4705302 (4 pages) | Cited 2 times

Online Publication Date: 24 April 2012

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Graphene nanoribbon and atomic carbon chain are allotropes of carbon, attracting tremendous attention from multidisciplinary areas ranging from nano physics to astrophysics. Here, first-principles calculations based on density-functional theory are carried out to study the ferromagnetic coupling in zigzag-edged graphene nanoribbons linked by carbon chains. Compared to the existing methods for ferromagnetic graphene nanoribbons, carbon chain linkage is found to be more effective for larger magnetic exchange energy and also be more flexible in tuning the electronic structure and magnetism.
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73.22.Pr Electronic structure of graphene
81.05.ue Graphene
75.75.Cd Fabrication of magnetic nanostructures
75.75.Lf Electronic structure of magnetic nanoparticles
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.80.Vp Electronic transport in graphene

Lithium-ion conducting La2/3−xLi3xTiO3 solid electrolyte thin films with stepped and terraced surfaces

Hiromichi Ohta, Teruyasu Mizoguchi, Noriyuki Aoki, Takashi Yamamoto, Akhmad Sabarudin, and Tomonari Umemura

Appl. Phys. Lett. 100, 173107 (2012); http://dx.doi.org/10.1063/1.4709402 (4 pages) | Cited 4 times

Online Publication Date: 25 April 2012

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See Also: RETRACTION

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La2/3−xLi3xTiO3 (LLT, x = 0.1 and 0.167) thin films were grown on (001)-oriented SrTiO3 (STO) substrates by pulsed laser deposition. The resultant LLT films were heteroepitaxially grown with atomically flat surfaces. Although the films considered to be single crystalline, they were composed of 90°-rotated multi domains (∼5 nm in size) with epitaxial relationships of (100) [001] LLT || (001) [100] STO and (100) [010] LLT || (001) [100] STO. The bulk conductivity of the LLT (x = 0.1) films was 2.5 × 10−2 S cm−1 at 190 °C, comparable to that of a bulk single crystalline LLT. Single crystalline LLT thin films with atomically flat surfaces should help clarify interfacial lithium-ion conductivity.
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66.30.hp Molecular crystals
68.60.-p Physical properties of thin films, nonelectronic
68.55.ag Semiconductors
82.47.Aa Lithium-ion batteries
82.45.Gj Electrolytes

Assessment of the resonance frequency of cantilever carbon nanocones using molecular dynamics simulation

R. D. Firouz-Abadi, H. Amini, and A. R. Hosseinian

Appl. Phys. Lett. 100, 173108 (2012); http://dx.doi.org/10.1063/1.4705423 (4 pages)

Online Publication Date: 25 April 2012

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The resonance frequencies of cantilever carbon nanocones (CNCs) up to 4 nm in height are determined using molecular dynamics simulation based on adaptive intermolecular reactive empirical bond order potential. The frequency content of the free vibrations of CNCs under a lateral initial excitation at the tip is analyzed using fast Fourier transformation, and the resonance frequencies are obtained. The results are reported for various samples to investigate the dependency of the resonance frequency to the geometrical parameters and temperature of CNCs.
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02.70.Ns Molecular dynamics and particle methods
02.60.-x Numerical approximation and analysis
02.30.Uu Integral transforms
61.46.-w Structure of nanoscale materials

Planar PbS quantum dot/C60 heterojunction photovoltaic devices with 5.2% power conversion efficiency

E. J. D. Klem, C. W. Gregory, G. B. Cunningham, S. Hall, D. S. Temple, and J. S. Lewis

Appl. Phys. Lett. 100, 173109 (2012); http://dx.doi.org/10.1063/1.4707377 (4 pages) | Cited 3 times

Online Publication Date: 25 April 2012

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Of interest for both photovoltaic and photodetector applications is the ability of colloidal quantum dot (CQD) devices to provide response further into the infrared than is typical for other solution-processable materials. Here, we present a simple heterojunction diode structure that utilizes the extended infrared absorption of PbS CQDs. We show that device performance benefits from a discontinuous exciton blocking layer which improves charge separation without limiting charge extraction. By enhancing charge carrier mobility in the CQD layer, we demonstrate a planar heterostructure device with a power conversion efficiency of 5.2% under 1 sun illumination.
Show PACS
85.60.Bt Optoelectronic device characterization, design, and modeling
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.65.+h Molecular electronic devices
78.67.Hc Quantum dots
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