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13 Oct 2008

Volume 93, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages)

Xuefeng Zeng and Hongrui Jiang
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Inner wall coated hollow core waveguide sensor based on double substrate surface enhanced Raman scattering

Chao Shi, Chao Lu, Claire Gu, Lei Tian, Rebecca Newhouse, Shaowei Chen, and Jin Z. Zhang

Appl. Phys. Lett. 93, 153101 (2008); http://dx.doi.org/10.1063/1.3000014 (3 pages) | Cited 10 times

Online Publication Date: 13 October 2008

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A hollow core waveguide with silver nanoparticles coated on the inner wall has been used for molecular detection based on surface enhanced Raman scattering (SERS). With rhodamine 6G as an analyte molecule and two types of silver nanoparticles as double SERS substrates, the inner wall coated hollow core waveguide (IWCHCW) exhibits higher sensitivity than previous sampling methods with only one substrate. The improvement of sensitivity is attributed to the additional enhancement of the electromagnetic field by double substrate “sandwich” structure. The simple architecture and high sensitivity of IWCHCW make it promising for molecular detection in various analytical and sensing applications.
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42.79.Gn Optical waveguides and couplers
42.81.Pa Sensors, gyros
42.70.Qs Photonic bandgap materials
78.30.-j Infrared and Raman spectra

Tomographic nanofabrication of ultrasharp three-dimensional nanostructures

Zineb Saghi, Thirunavukkarasu Gnanavel, Yong Peng, Beverley J. Inkson, Anthony G. Cullis, Mike R. Gibbs, and Günter Möbus

Appl. Phys. Lett. 93, 153102 (2008); http://dx.doi.org/10.1063/1.2998360 (3 pages) | Cited 6 times

Online Publication Date: 13 October 2008

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We present the extension of electron tomography from a pure characterization technique into a three-dimensional nanofabrication technique using focused electron beams in the scanning transmission electron microscope. Two-dimensional surface patterning techniques are insufficient to achieve full three-dimensional nanosculpting, instead, multiple sample rotations under the beam are required. We demonstrate fabrication of ultrafine tips and hollow structures with applications in scanning probe microscopy, atom probe tomography, or in magnetoconductance of nanobridges. A sharpened tip radius of <3 nm is achieved, an order of magnitude finer than with standard methods.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials

Mechanism and control of sidewall growth and catalyst diffusion on oxide nanowire vapor-liquid-solid growth

Kazuki Nagashima, Takeshi Yanagida, Keisuke Oka, Hidekazu Tanaka, and Tomoji Kawai

Appl. Phys. Lett. 93, 153103 (2008); http://dx.doi.org/10.1063/1.2978347 (3 pages) | Cited 19 times

Online Publication Date: 13 October 2008

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Oxide nanowires formed via the vapor-liquid-solid (VLS) mechanism are attractive building blocks toward nanowire-based electronic devices due to their fascinating physical properties. Although well-defined oxide nanowires are strongly required for the applications, tapering during oxide nanowire VLS growth has been detrimental and uncontrollable. Here we demonstrate the mechanism to control the tapering during oxide VLS growth. Suppressing simultaneously both the oxidization of adatoms at the sidewall and the catalyst diffusion from the tip was found to be essential to avoid the tapering. This mechanism would be universal in various oxide nanowire VLS growths.
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81.16.Hc Catalytic methods
68.65.La Quantum wires (patterned in quantum wells)
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)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Fx Diffusion; interface formation

Transient behaviors of surface plasmon coupling with a light emitter

Wen-Hung Chuang, Jyh-Yang Wang, C. C. Yang, and Yean-Woei Kiang

Appl. Phys. Lett. 93, 153104 (2008); http://dx.doi.org/10.1063/1.2998617 (3 pages) | Cited 1 time

Online Publication Date: 13 October 2008

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The transient behaviors of dipole couplings with surface plasmons (SPs) on a metal/dielectric grating interface, including surface plasmon polariton (SPP) and localized surface plasmon (LSP), are numerically demonstrated. Such a dipole-SP coupling process can lead to either enhanced dipole emission or effective pumping of a cavity-confining SP mode. Based on the time-resolved responses of a source pulse, it is found that the dipole-SP coupling features can be excited in several femtoseconds with the decay times ranging from 5 to 20 fs. From the significantly different decay times between the LSP and grating-assisted SPP features, one can classify those SP-coupling features into different application categories of efficient emission and SP energy storage.
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78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Plasma fluorination of carbon-based materials for imprint and molding lithographic applications

M. Schvartzman, A. Mathur, J. Hone, C. Jahnes, and S. J. Wind

Appl. Phys. Lett. 93, 153105 (2008); http://dx.doi.org/10.1063/1.2944997 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2008

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Diamondlike carbon nanoimprint templates are modified by exposure to a fluorocarbon-based plasma, yielding an ultrathin layer of a fluorocarbon material on the surface which has a very low surface energy with excellent antiwear properties. We demonstrate the use of these plasma fluorinated templates to pattern features with dimensions ∼ 20 nm and below. Furthermore, we show that this process is extendable to other carbon-based materials. Plasma fluorination can be applied directly to nanoimprint resists as well as to molds used to form elastomer stamps for microcontact printing and other applications requiring easy mold release.
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81.05.U- Carbon/carbon-based materials
68.35.Gy Mechanical properties; surface strains
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
68.35.Md Surface thermodynamics, surface energies
81.16.Nd Micro- and nanolithography

Observation of plasmon line broadening in single gold nanorods

Le Qiu, Timothy A. Larson, Danielle Smith, Edward Vitkin, Mark D. Modell, Brian A. Korgel, Konstantin V. Sokolov, Eugene B. Hanlon, Irving Itzkan, and Lev T. Perelman

Appl. Phys. Lett. 93, 153106 (2008); http://dx.doi.org/10.1063/1.2995982 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2008

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Attempts to realize the important potential of gold nanorods as extremely bright molecular markers have been limited by the broad spectroscopic linewidths usually observed. We identify the origin of this broadening as inhomogeneous broadening due to the extreme sensitivity of the surface plasmon resonance to the nanorod aspect ratio. Using confocal light scattering spectroscopic microscopy, we observed the narrow homogeneously broadened plasmon lines of single gold nanorods and obtained the first quantitative measurements of this homogeneous broadening. We show that homogeneous broadening can be predicted from first principals.
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78.66.Bz Metals and metallic alloys
78.35.+c Brillouin and Rayleigh scattering; other light scattering
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Simulation of high angle annular dark field scanning transmission electron microscopy images of large nanostructures

J. Pizarro, P. L. Galindo, E. Guerrero, A. Yáñez, M. P. Guerrero, A. Rosenauer, D. L. Sales, and S. I. Molina

Appl. Phys. Lett. 93, 153107 (2008); http://dx.doi.org/10.1063/1.2998656 (3 pages) | Cited 13 times

Online Publication Date: 14 October 2008

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High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a powerful tool to quantify size, shape, position, and composition of nano-objects with the assessment of image simulation. Due to the high computational requirements needed, nowadays it can only be applied to a few unit cells in standard computers. To overpass this limitation, a parallel software (SICSTEM) has been developed. This software can afford HAADF-STEM image simulations of nanostructures composed of several hundred thousand atoms in manageable time. The usefulness of this tool is exemplified by simulating a HAADF-STEM image of an InAs nanowire.
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68.65.La Quantum wires (patterned in quantum wells)
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)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Geometrical correlations of quantum dots in InAs/GaAs superlattice structure from electron tomography

Y. H. Wu, L. Chang, L. C. Chen, H. S. Chen, and F. R. Chen

Appl. Phys. Lett. 93, 153108 (2008); http://dx.doi.org/10.1063/1.2998693 (3 pages) | Cited 1 time

Online Publication Date: 14 October 2008

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In this study, the three-dimensional (3D) information about the structural properties of quantum dots (QDs) in InAs/GaAs superlattice structure has been illustrated using electron tomography in the mode of high-angle angular dark-field scanning transmission electron microscopy. Comparison of this 3D reconstruction with the two-dimensional projection at the same positions is made. The structural properties of embedded quantum dots have been evaluated from electron tomography. The correlation relationship of QDs in superlattice structure has been understood by accurate measurements of 3D geometric positions, which can be free of the overlapping effect from 2D cross section along different crystallographic orientations.
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68.65.Cd Superlattices
68.65.Hb Quantum dots (patterned in quantum wells)

Interface structure and defects of silicon nanocrystals embedded into a-SiO2

Mariella Ippolito, Simone Meloni, and Luciano Colombo

Appl. Phys. Lett. 93, 153109 (2008); http://dx.doi.org/10.1063/1.2999629 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2008

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By means of large-scale atomistic simulations, we identity and characterize several kinds of bonding and coordination defects at the interface between a silicon nanoparticle and an embedding amorphous silicon dioxide matrix. In particular, we prove that interface bond defects are easily formed, while no Si–O double bond is observed. We conclude that optical properties, e.g., photoluminescence, are more likely due to such interface bond structures. Temperature effects on defect population and nature are discussed as well.
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61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness
61.50.Lt Crystal binding; cohesive energy
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

General in situ chemical etching synthesis of ZnO nanotips array

H. Q. Wang, G. H. Li, L. C. Jia, G. Z. Wang, and L. Li

Appl. Phys. Lett. 93, 153110 (2008); http://dx.doi.org/10.1063/1.2951609 (3 pages) | Cited 8 times

Online Publication Date: 15 October 2008

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In this letter, we present a general solution based in situ chemical etching strategy to synthesize ZnO nanotips arrays. The in situ chemical etching can generate nanotips with controllable tip morphologies on various substrates, and the nanotips density is tunable via etching ZnO nanorods with different root diameters. The preferential etching along c axis and the curvature dependence of the NH3 molecule absorption on the nanorod tip are considered responsible for the formation of ZnO nanotips. This general in situ chemical etching method will significantly advance the research in the ZnO nanotips based nanodevice.
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81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning

Localized electroporation and molecular delivery into single living cells by atomic force microscopy

D. Nawarathna, K. Unal, and H. Kumar Wickramasinghe

Appl. Phys. Lett. 93, 153111 (2008); http://dx.doi.org/10.1063/1.2981568 (3 pages) | Cited 7 times

Online Publication Date: 15 October 2008

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We present an efficient and fast method for selective and localized electroporation of a single living cell from a population of millions to tens of cells using the modified tip of an atomic force microscope. Electroporation was observed in real time using an inverted microscope. This technique is proposed as a tool for efficient and controlled delivery of biomolecules, proteins, drugs, and genes.
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87.64.Dz Scanning tunneling and atomic force microscopy
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
87.16.dp Transport, including channels, pores, and lateral diffusion
87.85.jc Electrical, thermal, and mechanical properties of biological matter

Nanopatterned CoPt alloys with perpendicular magnetic anisotropy

D. Makarov, E. Bermúdez-Ureña, O. G. Schmidt, F. Liscio, M. Maret, C. Brombacher, S. Schulze, M. Hietschold, and M. Albrecht

Appl. Phys. Lett. 93, 153112 (2008); http://dx.doi.org/10.1063/1.2993334 (3 pages) | Cited 10 times

Online Publication Date: 15 October 2008

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CoPt alloy films with perpendicular magnetic anisotropy were grown on SiO2 nanoparticle arrays with particle sizes as small as 10 nm. In order to induce perpendicular magnetic anisotropy in the CoPt film, a MgO seed layer was sputter deposited. Despite the fact that neighboring CoPt film caps are interconnected, individual caps appear as single domain and for most of them their magnetization orientation can be reversed individually. This behavior might be caused by domain wall nucleation and pinning preferentially at the rim of each cap. Thus, arrays of magnetic caps with defined pinning sites can be considered as a percolated perpendicular medium.
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81.16.Rf Micro- and nanoscale pattern formation
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Geometry-controlled droplet generation in head-on microfluidic devices

Lingling Shui, Frieder Mugele, Albert van den Berg, and Jan C. T. Eijkel

Appl. Phys. Lett. 93, 153113 (2008); http://dx.doi.org/10.1063/1.3000624 (3 pages) | Cited 6 times

Online Publication Date: 16 October 2008

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We investigated the generation of droplets in a head-on microfluidic device operated with the two identical channels as inlets and the “long leg” as a constriction channel leading to a wider outlet section. For capillary numbers (Ca) of approximately 10−5 or less, we find a Ca-independent droplet volume equal to the volume of the constriction channel, which decreases at higher Ca when shear forces become relevant. The droplet generation mechanism is explained in terms of a global capillary instability involving surprisingly stable intermediate surface configurations.
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47.55.db Drop and bubble formation
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.60.Dx Flows in ducts and channels
47.55.nb Capillary and thermocapillary flows
47.20.-k Flow instabilities
07.10.Cm Micromechanical devices and systems

Ultralong spin memory of optically excited single magnetic quantum dots

Tak Gurung, Sebastian Mackowski, Grzegorz Karczewski, Howard E. Jackson, and Leigh M. Smith

Appl. Phys. Lett. 93, 153114 (2008); http://dx.doi.org/10.1063/1.2993331 (3 pages) | Cited 4 times

Online Publication Date: 17 October 2008

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We study the magnetization dynamics in CdMnTe quantum dots using subwavelength optical microscopy imaging at B = 0 T. For continuous laser illumination each dot exhibits strong and unique circular polarization despite completely unpolarized ensemble emission. This implies that after an exciton recombines, the spontaneous ferromagnetic alignment of magnetic impurities persists for over 100 μs, which is a million times longer than in CdMnTe quantum wells. The spin memory effect points toward a qualitatively different picture of magnetization dynamics in the zero-dimensional limit.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.55.Et II-VI semiconductors
73.21.La Quantum dots
71.35.-y Excitons and related phenomena
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Single crystal growth via a grain rotation mechanism within amorphous matrix

Jixiang Fang, Peng Kong, Bingjun Ding, Xiaoping Song, Yong Han, Horst Hahn, and Herbert Gleiter

Appl. Phys. Lett. 93, 153115 (2008); http://dx.doi.org/10.1063/1.3001576 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2008

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The molecular dynamics simulations were applied to study the crystallization of Ag from an amorphous matrix. The results show that the spontaneously crystallized nuclei interact with the amorphous phase, undergoing a rotation and realignment process, promote the crystallization of amorphous phase, and finally form a single crystalline nanostructure. Our results not only provide a system for the theoretical study on the amorphous formation and its function in the crystal growth but also break a path for producing single crystals.
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64.70.kd Metals and alloys
61.46.Hk Nanocrystals
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)

Investigation of superlubricity in a two-dimensional Frenkel–Kontorova model with square lattice symmetry

Cang-Long Wang, Wen-Shan Duan, Xue-Ren Hong, and Jian-Min Chen

Appl. Phys. Lett. 93, 153116 (2008); http://dx.doi.org/10.1063/1.3003862 (3 pages) | Cited 7 times

Online Publication Date: 17 October 2008

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A two-dimensional Frenkel–Kontorova model with a square symmetry substrate potential for a square lattice layer driven by an external driving force with an arbitrary direction α and an arbitrary misfit angle θ between upper and lower layers is presented in this paper. The effects of the system parameters have been investigated. The application of our results to the tribology is discussed and the dependence of the static friction force on the system parameters is studied. How to make the material with superlubricity is suggested.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
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