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9 Apr 2012

Volume 100, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 153701 (2012); http://dx.doi.org/10.1063/1.3700446 (3 pages)

Hsiao-lu D. Lee, Steffen J. Sahl, Matthew D. Lew, and W. E. Moerner
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Scaling growth kinetics of self-induced GaN nanowires

Vladimir G. Dubrovskii, Vincent Consonni, Lutz Geelhaar, Achim Trampert, and Henning Riechert

Appl. Phys. Lett. 100, 153101 (2012); http://dx.doi.org/10.1063/1.3701591 (4 pages) | Cited 4 times

Online Publication Date: 9 April 2012

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We present a kinetic model showing why self-induced GaN nanowires synthesized by molecular beam epitaxy obey the scaling growth laws. Our model explains the scaling behavior from kinetic considerations of the step flow radial growth and the shadow effect. The nanowire length L and radius R scale with time as [1+C(t-t0)]α/(α+1) and [1+C(t-t0)]1/(α+1), respectively. Consequently, the length scales with the radius as L∝Rα. The power index α equals 2.46 in our conditions. This scaling behavior is paramount for understanding the self-induced growth of nanowires in general as well as for tuning their morphology to the desired properties.
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81.16.-c Methods of micro- and nanofabrication and processing
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)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Antiferromagnetic coupling and spin filtering in asymmetrically hydrogenated graphene nanoribbon homojunction

Jun Kang, Fengmin Wu, Shu-Shen Li, Jian-Bai Xia, and Jingbo Li

Appl. Phys. Lett. 100, 153102 (2012); http://dx.doi.org/10.1063/1.3701612 (4 pages) | Cited 2 times

Online Publication Date: 9 April 2012

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The magnetic and spin transport properties of asymmetrically hydrogenated zigzag graphene nanoribbon homojunction are studied from first-principles calculations. Due to the energy gain obtained from super-exchange interaction, antiferromagnetic coupling is preferred in the homojunction, which makes it a natural not gate in logic operations. Moreover, the homojunction exhibits intrinsic spin filtering effect without the need of doping. It can serve as a spin filter for spin-unpolarized current and as a rectifier for fully spin-polarized current. These characters are related to the overlaps between the electronic states of the electrodes under different bias voltages.
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75.75.-c Magnetic properties of nanostructures
72.25.-b Spin polarized transport
73.61.Wp Fullerenes and related materials
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics

Pump-probe scanning near field optical microscopy: Sub-wavelength resolution chemical imaging and ultrafast local dynamics

Khadga Karki, Mahesh Namboodiri, Tahir Zeb Khan, and Arnulf Materny

Appl. Phys. Lett. 100, 153103 (2012); http://dx.doi.org/10.1063/1.3701724 (3 pages) | Cited 2 times

Online Publication Date: 9 April 2012

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Results of two color femtosecond time-resolved pump-probe experiments using scanning near field optical microscopy on thin films of organic semiconductor 3,4,9,10 perylenetetracarboxylic dianhydride are presented. With this technique, quantitative information on exciton dynamics with high temporal and spatial resolution can be obtained by fitting a rate model to the transient absorption spectra. Additionally, the chemical selectivity inherent to this technique enhances the contrast, which could be used for video-rate imaging when high-repetition rate lasers are used.
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07.79.Fc Near-field scanning optical microscopes
68.37.Uv Near-field scanning microscopy and spectroscopy
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.J- Ultrafast spectroscopy (<1 psec)

Coexistence of tunneling and displacement currents in a nanogap driven with ac fields

Sudeep Bhattacharjee, Manoj K. Harbola, Avradip Pradhan, and Atanu Modak

Appl. Phys. Lett. 100, 153104 (2012); http://dx.doi.org/10.1063/1.3702454 (4 pages)

Online Publication Date: 10 April 2012

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Current across two metallic electrodes with a nanogap separation (∼50 nm) is investigated for an ac voltage applied between them. The current shows a distinct transition from the injection current regime due to quantum tunneling at low frequencies to a regime dominated by classical displacement current at high frequencies. The transition takes place at a critical frequency that increases with the applied voltage. A theoretical model treating the electrodes as a parallel RC circuit is developed; the model explains the experimental results reasonably accurately.
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73.40.Gk Tunneling

Conditional photon-assisted transport in coupled quantum dot

Yan Xie, Weidong Xie, Suqing Duan, Ning Yang, Jing Chen, Wei Zhang, Weidong Chu, and Xian-Geng Zhao

Appl. Phys. Lett. 100, 153105 (2012); http://dx.doi.org/10.1063/1.3702573 (4 pages)

Online Publication Date: 10 April 2012

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We theoretically study the photon-assisted transport (PAT) in a double quantum dot (QD) which is conditionally controlled by the optical excitation in an adjacent QD. Based on a real three-QD model, a double-electron level configuration needed for the conditional PAT is designed. Interesting conditional dynamics are demonstrated for the double QD and its adjacent QD. Depending on various conditional frequencies, the conditional behaviors can be manifested as the current peaks or collapses of the PAT. They correspond to coherent excitations or trapping of double-electron states. Our results present a possible way to optically manipulate electron states and monitor them via the signals of current spectrum.
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73.21.La Quantum dots
81.07.Ta Quantum dots
05.60.Gg Quantum transport
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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A graphene electron lens

L. Gerhard, E. Moyen, T. Balashov, I. Ozerov, M. Portail, H. Sahaf, L. Masson, W. Wulfhekel, and M. Hanbücken

Appl. Phys. Lett. 100, 153106 (2012); http://dx.doi.org/10.1063/1.3701594 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2012

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An epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ≈0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses.
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41.85.Ne Electrostatic lenses, septa
42.79.-e Optical elements, devices, and systems

Irreversible adsorption of gold nanospheres on fiber optical tapers and microspheres

Jihaeng Yi, Chih-Yu Jao, Ishac L. N. Kandas, Bo Liu, Yong Xu, and Hans D. Robinson

Appl. Phys. Lett. 100, 153107 (2012); http://dx.doi.org/10.1063/1.3701730 (4 pages)

Online Publication Date: 10 April 2012

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We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries.
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68.43.Mn Adsorption kinetics
82.70.Kj Emulsions and suspensions
42.81.Bm Fabrication, cladding, and splicing
68.35.Fx Diffusion; interface formation

Tunable nanometer electrode gaps by MeV ion irradiation

J.-C. Cheang-Wong, K. Narumi, G. M. Schürmann, M. J. Aziz, and J. A. Golovchenko

Appl. Phys. Lett. 100, 153108 (2012); http://dx.doi.org/10.1063/1.3702778 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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We report the use of MeV ion-irradiation-induced plastic deformation of amorphous materials to fabricate electrodes with nanometer-sized gaps. Plastic deformation of the amorphous metal Pd80Si20 is induced by 4.64 MeV O2+ ion irradiation, allowing the complete closing of a sub-micrometer gap. We measure the evolving gap size in situ by monitoring the field emission current-voltage (I-V) characteristics between electrodes. The I-V behavior is consistent with Fowler-Nordheim tunneling. We show that using feedback control on this signal permits gap size fabrication with atomic-scale precision. We expect this approach to nanogap fabrication will enable the practical realization of single molecule controlled devices and sensors.
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61.80.Jh Ion radiation effects
71.20.-b Electron density of states and band structure of crystalline solids
61.82.Bg Metals and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
73.40.Gk Tunneling

Dispersion of carbon nanocapsules by using highly aspect-ratio clays

Yi-Fen Lan and Szu-Chiao Cheng

Appl. Phys. Lett. 100, 153109 (2012); http://dx.doi.org/10.1063/1.3702783 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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The poor solubility of zero-dimensional nanomaterials can be greatly improved by using two-dimensional nanomaterials as a dispersant. The solubility of nano-spherical carbon nanocapsules (CNCs) was improved by using platelet-like clays. Three clays including synthetic fluorinated mica (Mica), sodium montmorillonite, and synthetic smectite were selected for assist CNCs to disperse in several solvents. The aspect ratios of clays were calculated by dimension over thickness, and the results revealed that the aspect ratio is the dominated factor to control the dispersion of CNCs in solvents.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.75.Bc Solubility
78.40.Ha Other nonmetallic inorganics

Low temperature cathodoluminecence and electron beam induced current studies of single GaN nanowires

Eunsoon Oh, Byoung Woo Lee, So-Jeong Shim, Heon-Jin Choi, Byoung Hee Son, Yeong Hwan Ahn, and Le Si Dang

Appl. Phys. Lett. 100, 153110 (2012); http://dx.doi.org/10.1063/1.3702797 (4 pages) | Cited 2 times

Online Publication Date: 11 April 2012

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Single crystalline GaN nanowires, with 100 nm typical diameters, were grown by chemical vapor deposition method, using Pt catalyst, and characterized by cathodoluminescence and electron beam induced current (EBIC) measurements at 5 K. The near band edge emission was found to be asymmetric and broad, with full width half maximum of around 150 meV, peaking at 3.55 eV, well above the GaN bulk band gap. This blueshift was ascribed to band filling effect resulting from unintentional n-type doping in the range 1019–1020 cm−3. Despite of this heavy doping, EBIC experiments showed that minority carriers can diffuse over 0.2 μm.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.67.Uh Nanowires
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.uj III-V and II-VI semiconductors

Tunable terahertz optical antennas based on graphene ring structures

Penghong Liu, Wei Cai, Lei Wang, Xinzheng Zhang, and Jingjun Xu

Appl. Phys. Lett. 100, 153111 (2012); http://dx.doi.org/10.1063/1.3702819 (5 pages) | Cited 7 times

Online Publication Date: 11 April 2012

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Highly tunable optical antennas in teraherz range based on graphene ring structures are proposed, which employ graphene plasmons instead of traditional metallic plasmons. The plasmon resonances of the perfect graphene ring (PGR) can be understood with the edge plasmons in graphene ribbons. While in the nonconcentric graphene ring, the multipolar plasmon modes appear and anti-symmetric mode splits due to symmetry breaking. Furthermore, the symmetric plasmon mode in a graphene ring can concentrate electromagnetic field with an enhancement factor as large as 103 in terahertz waveband, which is almost 20 times larger than a gold ring with the same size.
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42.79.-e Optical elements, devices, and systems

Symmetry of atomistic structure for armchair-edge graphene nanoribbons under uniaxial strain

Wenhu Liao, Heping Zhao, Gang Ouyang, Ke-Qiu Chen, and Guanghui Zhou

Appl. Phys. Lett. 100, 153112 (2012); http://dx.doi.org/10.1063/1.3702842 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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We present a systematic first-principles calculation on the atomistic structural variation for armchair-edge graphene nanoribbons (AGNRs) under a small planar uniaxial strain along armchair and zigzag directions, respectively. Interestingly, it is found that asymmetric AGNRs are more sensitive to the external strain with more types of carbon-carbon bonds and angles, while symmetric ones show less types of bonds and angles under the same strain. This difference is attributed to the symmetric property of AGNRs combining with the bond theory. Our findings may be useful in further understanding of GNRs under strain and in designing nanoelectromechanical devices based on GNRs.
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61.48.Gh Structure of graphene
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity

Formation of coupled three-dimensional GeSi quantum dot crystals

Y. J. Ma, Z. Zhong, Q. Lv, T. Zhou, X. J. Yang, Y. L. Fan, Y. Q. Wu, J. Zou, and Z. M. Jiang

Appl. Phys. Lett. 100, 153113 (2012); http://dx.doi.org/10.1063/1.3702883 (4 pages) | Cited 2 times

Online Publication Date: 11 April 2012

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Coupled three-dimensional GeSi quantum dot crystals (QDCs) are realized by multilayer growth of quantum dots (QDs) on patterned SOI (001) substrates. Photoluminescence spectra of these QDCs show non-phonon (NP) recombination and its transverse-optical (TO) phonon replica of excitons in QDs. With increasing excitation power, peak energies of both the NP and TO peaks remain nearly constant and the width of the TO peak decreases. These anomalous features of the PL peaks are attributed to miniband formation due to strong coupling of the holes and the emergence of quasioptical phonon modes due to periodic scatters in ordered GeSi QDs.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
81.16.Nd Micro- and nanolithography
73.21.La Quantum dots

Fano resonance in two-intersecting nanorings: Multiple layers of plasmon hybridizations

Hailong Liu, Xijun Wu, Bing Li, Chenxi Xu, Guangbiao Zhang, and Longjiang Zheng

Appl. Phys. Lett. 100, 153114 (2012); http://dx.doi.org/10.1063/1.3702884 (4 pages) | Cited 4 times

Online Publication Date: 11 April 2012

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We theoretically investigate the optical properties of two-intersecting nanorings (TINR), which exhibit a pronounced Fano resonance in the near-infrared region. A multiple-layer plasmon hybridization model is proposed to explain the reasons and forming processes of the Fano resonance. The dependence of the Fano resonance on the intersecting distance is also demonstrated. Moreover, the presented two-intersecting nanorings are employed as a biosensor exhibiting a 3-fold improvement of the figure of merit than that of a single-ring biosensor with the same resonant wavelength.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Coupling distance between Eu3+ emitters and Ag nanoparticles

A. Pillonnet, A. Berthelot, A. Pereira, O. Benamara, S. Derom, G. Colas des Francs, and A.-M. Jurdyc

Appl. Phys. Lett. 100, 153115 (2012); http://dx.doi.org/10.1063/1.3703120 (4 pages) | Cited 4 times

Online Publication Date: 11 April 2012

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Emission by rare earth emitters has been experimentally investigated based on their position relative to metallic nanoparticles by using Ag/Y2O3/Eu:Y2O3/Y2O3/Ag multilayer samples on- or off-plasmon resonance. Comparison with simple models revealed two different coupling regimes at short and long distances. The optimal coupling distance was determined.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.21.Ac Multilayers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Hx Other solid inorganic materials

Core/shell structural transformation and brittle-to-ductile transition in nanowires

Zaoshi Yuan, Ken-ichi Nomura, and Aiichiro Nakano

Appl. Phys. Lett. 100, 153116 (2012); http://dx.doi.org/10.1063/1.3703303 (5 pages)

Online Publication Date: 11 April 2012

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Nanowires (NWs) exhibit thermo-mechanical properties that are distinct from their bulk properties, and their understanding is critical for the reliability, manufacturability, and optimization of a wide range of devices consisting of NWs. Here, molecular-dynamics simulation reveals a rich size-temperature “phase diagram” for the mechanical response of a zinc-oxide NW under tension. For smaller diameters and higher temperatures, transitions are found from brittle cleavage to structural transformation-mediated brittle cleavage to ductile failure. Atomistic mechanisms of the unique nano-thermo-mechanical behavior are elucidated as a consequence of surface-structural relaxation, which in particular predicts spontaneous formation of a core/shell structure under tension. The nano-thermo-mechanical phase diagram resolves controversies between previous experiments and theory, and the predicted “intrinsic” core/shell structure may find device applications.
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64.70.Nd Structural transitions in nanoscale materials
81.07.Gf Nanowires
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)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors

Effects of DNA nucleotide adsorption on the conductance of graphene nanoribbons from first principles

Eun-Cheol Lee

Appl. Phys. Lett. 100, 153117 (2012); http://dx.doi.org/10.1063/1.3703603 (4 pages)

Online Publication Date: 11 April 2012

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The effects of DNA nucleotide adsorption on the conductance of graphene nanoribbons are investigated through first-principles calculations. We find that, for the adsorption of a single nucleotide, the negatively charged phosphate produces conductance dips associated with quasibound states, reducing the hole conductance. The conductance of conduction electrons is also reduced by electron scattering at the Coulomb potential barriers produced by the phosphate, with no noticeable conductance dips near the Fermi level. Our results indicate that graphene nanoribbon is promising for the application to DNA sensor utilizing quantum carrier conductance.
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87.85.Rs Nanotechnologies-applications
73.61.Wp Fullerenes and related materials
87.15.K- Molecular interactions; membrane-protein interactions
87.14.gk DNA
61.46.-w Structure of nanoscale materials
68.43.Bc Ab initio calculations of adsorbate structure and reactions

Nanoscale magnetic field mapping with a single spin scanning probe magnetometer

L. Rondin, J.-P. Tetienne, P. Spinicelli, C. Dal Savio, K. Karrai, G. Dantelle, A. Thiaville, S. Rohart, J.-F. Roch, and V. Jacques

Appl. Phys. Lett. 100, 153118 (2012); http://dx.doi.org/10.1063/1.3703128 (4 pages) | Cited 15 times

Online Publication Date: 12 April 2012

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We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.
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07.55.Ge Magnetometers for magnetic field measurements
06.30.Ka Basic electromagnetic quantities
85.75.Ss Magnetic field sensors using spin polarized transport

Impurity-limited mobility and variability in gate-all-around silicon nanowires

Yann-Michel Niquet, Hector Mera, and Christophe Delerue

Appl. Phys. Lett. 100, 153119 (2012); http://dx.doi.org/10.1063/1.4704174 (4 pages) | Cited 1 time

Online Publication Date: 13 April 2012

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We discuss the scattering of electrons and holes by charged dopant impurities in 〈001〉,〈110〉, and 〈111〉 gate-all-around silicon nanowires (Si NWs) with diameters in the 2-8 nm range. We show that the mobility of minority carriers follows simple trends resulting from band-structure effects. In the inversion mode, the 〈110〉 and 〈001〉 [respectively, 〈111〉 and 〈110〉] Si NWs are the best n-type [resp. p-type] channels. The choice of a high-κ gate oxide is critical to achieve large mobilities in ultimate Si NWs. The mobility of majority carriers is found to increase with decreasing NW diameter and is more weakly dependent on the orientation. We also discuss the variability of single impurity resistances as a function of the structural parameters and nature of the carriers.
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72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Mq Elemental semiconductors
61.72.uf Ge and Si
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