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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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ac thermal imaging of nanoheaters using a scanning fluorescent probe

B. Samson, L. Aigouy, P. Löw, C. Bergaud, B. J. Kim, and M. Mortier

Appl. Phys. Lett. 92, 023101 (2008); http://dx.doi.org/10.1063/1.2832673 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2008

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Using a fluorescent particle glued at the end of a sharp tip, we observe the heating of a 200 nm wide nickel nanoheater run by an alternating electrical current. The images clearly show the heating of the nickel structure, as well as the lateral heat diffusion in the dielectric layers underneath. By monitoring the fluorescence changes as the tip approaches the nanoheater, we have estimated the relative importance of the different heat transfer mechanisms between the device and the fluorescent particle. It is shown that, for the investigated structures, heat transfer occurs mainly by direct contact between the probe and the surface.
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07.20.Hy Furnaces; heaters
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Epitaxial ordering of a perylenetetracarboxylic diimide-melamine supramolecular network driven by the Au(111)-(22×math) reconstruction

Fabien Silly, Adam Q. Shaw, G. A. D. Briggs, and Martin R. Castell

Appl. Phys. Lett. 92, 023102 (2008); http://dx.doi.org/10.1063/1.2830828 (3 pages) | Cited 15 times

Online Publication Date: 14 January 2008

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Substrate mediated ordering and intermolecular interactions are used to create a long-range supramolecular network of perylenetetracarboxylic diimide and melamine on a reconstructed Au(111)-(22×math) surface. Scanning tunneling microscopy reveals that the network is composed of a succession of double width honeycomb cell rows separated by a more closely packed row of parallelograms. This periodicity of the supramolecular configuration matches that of the reconstructed gold substrate allowing an epitaxial relationship between network and substrate reconstruction.
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68.35.bd Metals and alloys
68.47.De Metallic surfaces

Faceting of a quasi-two-dimensional GaAs crystal in nanoscale patterned growth

S. C. Lee, D. L. Huffaker, and S. R. J. Brueck

Appl. Phys. Lett. 92, 023103 (2008); http://dx.doi.org/10.1063/1.2830988 (3 pages) | Cited 3 times

Online Publication Date: 14 January 2008

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The faceting of a quasi-two-dimensional nanoscale crystal (quasi-2D nanocrystal) grown by metal-organic vapor phase epitaxy is reported. Homoepitaxial selective growth is performed on a 200 nm wide, [110]-directed stripe opening fabricated in a 30 nm thick SiO2 film atop a GaAs(001) substrate. In the cross section perpendicular to the stripe opening, a selectively grown epilayer is regarded as a quasi-2D nanocrystal, which is close to a hexagonal shape symmetrically surrounded with (111)B-, (110)- and (111)A-type facets from the top as growth proceeds both vertically and laterally. The resulting faceting is interpreted on the basis of equilibrium crystal shape (ECS). The comparison of the observed crystal shape with theoretical modeling enables the measurement of the relative surface energies of the low index orientations. The ECS of a GaAs 2D crystal under the given growth conditions is proposed.
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61.44.Br Quasicrystals
68.55.-a Thin film structure and morphology
81.16.Rf Micro- and nanoscale pattern formation
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Near- to far-field imaging of free-space and surface-bound waves emanating from a metal nanoslit

Yun Suk Jung, Jeff Wuenschell, Tyler Schmidt, and Hong Koo Kim

Appl. Phys. Lett. 92, 023104 (2008); http://dx.doi.org/10.1063/1.2834900 (3 pages) | Cited 9 times

Online Publication Date: 14 January 2008

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The authors report the radiation pattern (radial and angular distribution of light intensity) of a silver nanoslit measured in the near- to far-field regimes. In most far fields, the 1/r dependence of intensity distribution, expected from a cylindrical wave emanating from a line source, is clearly observed. The glancing angle regime is found to be governed by the presence of surface plasmons, showing higher intensity closer to the metal surface. From the radiation patterns measured with a tilted-probe, radial-scan method, a branching ratio is quantitatively determined for the free-space radiation and surface plasmon components, emerging from the nanoslit.
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78.66.Bz Metals and metallic alloys
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

“Zigzag” C60 chain arrays

Han Huang, Wei Chen, Lan Chen, Hong Liang Zhang, Xue Sen Wang, Shi Ning Bao, and Andrew Thye Shen Wee

Appl. Phys. Lett. 92, 023105 (2008); http://dx.doi.org/10.1063/1.2831902 (3 pages) | Cited 3 times

Online Publication Date: 14 January 2008

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We present a low-temperature scanning tunneling microscopy investigation revealing the formation of a long range ordered α-sexithiophene (6T) monolayer nanostripe array on highly ordered pyrolytic graphite, with thiophene ring units oriented parallel to the surface. The 6T monolayer nanostripe is an effective molecular nanotemplate for the assembly of an ordered “zigzag” C60 chain array, accompanied by a slight structural modification of the underlying 6T nanostripes due to donor-acceptor intermolecular interactions between 6T and C60 molecules.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.35.bp Fullerenes

Vapor-phase nucleation of individual CdSe nanostructures from shape-engineered nanocrystal seeds

A. Fasoli, S. Pisana, A. Colli, L. Carbone, L. Manna, and A. C. Ferrari

Appl. Phys. Lett. 92, 023106 (2008); http://dx.doi.org/10.1063/1.2825425 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2008

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We investigate the vapor-phase nucleation of CdSe nanostructures on nanocrystals seeds of different shapes. The growth dynamics is assessed by transmission electron microscopy, following the evolution of the same nanocrystals prior and after the deposition process. We prove that individual nanocrystals can sustain the growth of single nanowires and determine their final morphology. Straight or branched nanowires are obtained from spherical or tetrapod-shaped nanocrystals, respectively. When tetrapod-shaped nanocrystals are used, we also find that their original shape and orientation are mostly preserved upon further growth.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.-c Methods of micro- and nanofabrication and processing
81.10.Bk Growth from vapor
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors

Concept of a nanowire array magnetoresistance device

I. V. Shvets, H. C. Wu, V. Usov, F. Cuccureddu, S. K. Arora, and S. Murphy

Appl. Phys. Lett. 92, 023107 (2008); http://dx.doi.org/10.1063/1.2834371 (3 pages) | Cited 3 times

Online Publication Date: 15 January 2008

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We describe a concept of the magnetoresistive medium comprising of a planar array of intermingled nanowires with pinned and unpinned magnetic moments. We propose a bottom up method of forming the medium and demonstrate the feasibility of the proposed approach. We present the results of the simulations of the magnetic moments in the nanowires under an external magnetic field to illustrate the concept.
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75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Mg Numerical simulation studies

Tailoring hole spin splitting and polarization in nanowires

D. Csontos and U. Zülicke

Appl. Phys. Lett. 92, 023108 (2008); http://dx.doi.org/10.1063/1.2834702 (3 pages) | Cited 6 times

Online Publication Date: 15 January 2008

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Spin splitting in p-type semiconductor nanowires is strongly affected by the interplay between quantum confinement and spin-orbit coupling in the valence band. The latter’s particular importance is revealed in our systematic theoretical study presented here, which has mapped the range of spin-orbit coupling strengths realized in typical semiconductors. Large controllable variations of the g factor with associated characteristic spin polarization are shown to exist for nanowire subband edges, which therefore turn out to be a versatile laboratory for investigating the complex spin properties exhibited by quantum-confined holes.
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73.21.Hb Quantum wires
72.25.Dc Spin polarized transport in semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Atomic force microscope manipulation of gold nanoparticles for controlled Raman enhancement

Lianming Tong, Tao Zhu, and Zhongfan Liu

Appl. Phys. Lett. 92, 023109 (2008); http://dx.doi.org/10.1063/1.2822418 (3 pages) | Cited 14 times

Online Publication Date: 17 January 2008

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We report on the controlled manipulation of two, three and four gold nanoparticles (AuNPs) using an atomic force microscope (AFM) for use as surface-enhanced Raman scattering substrates. For each arrangement, the interparticle electromagnetic (EM) coupling between adjacent AuNPs is studied at different polarization angles. It is found that the strength of EM coupling strongly depends on the arrangement of the AuNPs. In particular, the highest enhancement and the most pronounced polarization dependence is found for linear arrangement of closely spaced particles. Our results show that AFM manipulation has great potential for fabrication and investigation of controlled arrangements of nanoscale objects.
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81.07.Bc Nanocrystalline materials
81.16.Ta Atom manipulation
78.30.Er Solid metals and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.37.Ps Atomic force microscopy (AFM)

Enhanced thermal conductivity by aggregation in heat transfer nanofluids containing metal oxide nanoparticles and carbon nanotubes

Jesse Wensel, Brian Wright, Dustin Thomas, Wayne Douglas, Bert Mannhalter, William Cross, Haiping Hong, Jon Kellar, Pauline Smith, and Walter Roy

Appl. Phys. Lett. 92, 023110 (2008); http://dx.doi.org/10.1063/1.2834370 (3 pages) | Cited 27 times

Online Publication Date: 17 January 2008

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An approximately 10% increase in the thermal conductivity (TC) of heat transfer nanofluids containing metal oxide nanoparticles and carbon nanotubes has been determined with very low percentage loading (around 0.02 wt %) of these two nanomaterials. These fluids are very stable and the viscosity remains approximately the same as water. A possible explanation for these interesting results is the aggregation of metal oxide particles on the surface of nanotubes by electrostatic attraction and form the aggregation chain along the nanotube. Time dependant magnetic results demonstrate that, under the influence of a strong outside magnetic field, the TC value decreases. Also, the TC value decreases when the pH is shifted from 7 to 11.45.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
66.25.+g Thermal conduction in nonmetallic liquids
66.20.-d Viscosity of liquids; diffusive momentum transport
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Mist fabrication of light emitting diodes with colloidal nanocrystal quantum dots

T. Zhu, K. Shanmugasundaram, S. C. Price, J. Ruzyllo, F. Zhang, J. Xu, S. E. Mohney, Q. Zhang, and A. Y. Wang

Appl. Phys. Lett. 92, 023111 (2008); http://dx.doi.org/10.1063/1.2834734 (3 pages) | Cited 15 times

Online Publication Date: 17 January 2008

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In this letter, we report a mist-deposition process for the assembly and patterning of nanocrystal quantum dots (NQDs) during the fabrication of quantum dot light emitting diodes (QD-LEDs), which allows for tight controls over the thickness, surface morphology, composition, and resolution of NQD emissive layers. A defect-free featuring uniform brightness QD-LED containing a mist-deposited emissive CdSe(ZnS) NQD layer was demonstrated. Additionally, the technique of successive mist deposition of multicolor NQDs through a set of registered shallow masks was employed to create a 6×6 matrix of alternating pixels composed of 5 nm diameter CdSe(ZnS) NQDs (green) and 8 nm diameter CdSe(ZnS) NQDs (red) on the same substrate. The results obtained demonstrate the potential of mist-deposition technology in the future development of full-color QD-LED displays.
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85.60.Jb Light-emitting devices
85.35.-p Nanoelectronic devices

Martensitic transformations in Ag–Au bimetallic core-shell nanoalloys

Fuyi Chen and Roy L. Johnston

Appl. Phys. Lett. 92, 023112 (2008); http://dx.doi.org/10.1063/1.2835456 (3 pages) | Cited 13 times

Online Publication Date: 17 January 2008

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Combining the Gupta potential and bond order analysis in a molecular dynamics simulation, a martensitic transformation is observed in the 147-atom AucoreAgshell nanostructure at 328 K. The response time for this transformation is about 7 ps at 350 K. In pure gold clusters, it was previously thought that a similar solid-to-solid transformation is a prelude to melting transitions. In the present case, atomic pathway snapshots show that the heating energy is used to overcome the energy barrier for initiating the spontaneous process. The subsequent twist-deformation propagation and termination are clearly observed.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
62.25.-g Mechanical properties of nanoscale systems
64.70.Nd Structural transitions in nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Electron field emission from patterned nanocrystalline diamond coated a-SiO2 micrometer-tip arrays

J. C. Madaleno, M. K. Singh, E. Titus, Gil Cabral, J. Grácio, and L. Pereira

Appl. Phys. Lett. 92, 023113 (2008); http://dx.doi.org/10.1063/1.2835905 (3 pages) | Cited 12 times

Online Publication Date: 18 January 2008

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We report the fabrication of patterned nanocrystalline diamond (NCD) submicrometer-tip arrays. This includes synthesis of silica (a-SiO2) templates by conventional vapor-liquid-solid method and conformal coating of the a-SiO2 nanowires with 5–10 nm sized nanodiamond grains by microwave plasma chemical vapor deposition. Detailed structural investigations were carried out by high resolution transmission electron microscopy. Electron field emission of nanodiamond emitter arrays was observed with a threshold field of 5.5 V/μm. A high emission current density of 10 mA cm−2 at 11 V/μm has been obtained. This value is comparable to those of high quality NCD films deposited on silicon substrates.
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85.45.Db Field emitters and arrays, cold electron emitters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Lp Transmission electron microscopy (TEM)
61.46.Hk Nanocrystals

Nanowelding of a multiwalled carbon nanotube to metal surface and its electron field emission properties

Koji Asaka, Hitoshi Nakahara, and Yahachi Saito

Appl. Phys. Lett. 92, 023114 (2008); http://dx.doi.org/10.1063/1.2835906 (3 pages) | Cited 17 times

Online Publication Date: 18 January 2008

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Multiwalled carbon nanotubes (MWNTs) were manipulated inside a high-resolution transmission electron microscope combined with a nano manipulator, and a single MWNT emitter freestanding on a platinum surface was fabricated by nanowelding. The electron field emission properties of the single MWNT were in situ measured at various gap distances in a range from 27 to 442 nm with simultaneous imaging by transmission electron microscopy. Field enhancement factors varying with the gap distance and the thermally enhanced electron emission were observed.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
79.70.+q Field emission, ionization, evaporation, and desorption

Spin-orbit interaction in Au structures of various dimensionalities

Xiaoping Yang, Jian Zhou, Hongming Weng, and Jinming Dong

Appl. Phys. Lett. 92, 023115 (2008); http://dx.doi.org/10.1063/1.2836132 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2008

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Variation of the geometrical and electronic properties of the gold materials in different dimensions has been investigated by ab initio method, taking into account the spin-orbit interaction. It is found that spin-orbit effects in different dimensional Au materials depend greatly on fundamental symmetry and dimensionality. For single-walled gold nanotubes, spin-orbit interaction decreases significantly the conducting channel number of achiral tube (4,0) and leads to spin splitting at Fermi level of chiral tube, indicating that quasi-one-dimensional gold tube can be a good candidate for the spin-electron devices. Furthermore, our results suggest that cage cluster might be synthesizable experimentally by taking gold tube structure as parent material.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Fg Nanotubes

Tunable surface plasma resonance frequency in Ag core/Au shell nanoparticles system prepared by laser ablation

Huifeng Han, Yan Fang, Zhipeng Li, and Hongxing Xu

Appl. Phys. Lett. 92, 023116 (2008); http://dx.doi.org/10.1063/1.2829588 (3 pages) | Cited 11 times

Online Publication Date: 18 January 2008

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A method for preparation of Ag core/Au shell nanoparticles with tunable surface plasma resonance (SPR) band was presented and studied. It was found that the tunable SPR band could be significantly conducted and achieved by laser ablation to Au plate in Ag colloidal solution, leading to the formation of Ag core/Au shell structure by the deposition of Au atoms on the surface of Ag nanoparticles. Dependence of the tunable shift of SPR bands on Ag core/Au shell structure was further illustrated by simulation of absorption spectra based on Mie theory, and consistent with the experimental results.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
79.20.Ds Laser-beam impact phenomena
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