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29 Jun 2009

Volume 94, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 263501 (2009); http://dx.doi.org/10.1063/1.3136905 (3 pages)

Changxin Chen, Wei Zhang, Eric Siu-Wai Kong, and Yafei Zhang
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Vortex matching effect in engineered thin films of NbN

Ajay D. Thakur, Shuuichi Ooi, Subbaiah P. Chockalingam, John Jesudasan, Pratap Raychaudhuri, and Kazuto Hirata

Appl. Phys. Lett. 94, 262501 (2009); http://dx.doi.org/10.1063/1.3167771 (3 pages) | Cited 7 times

Online Publication Date: 29 June 2009

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We report robust vortex matching effects in antidot arrays fabricated on thin films of NbN. The near absence of hysteresis between field sweep directions indicates a negligible residual pinning in the host thin films. Owing to the very small coherence length of NbN thin films (ξ<5 nm), the observations suggest the possibility of probing physics of vortices at true nanometer length scales in suitably fabricated structures.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.10.+v Occurrence, potential candidates
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Cd Deposition by sputtering
68.65.Hb Quantum dots (patterned in quantum wells)
81.20.Wk Machining, milling
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Probing misalignment in exchange biased systems: A dynamic approach

C. Le Graët, D. Spenato, S. P. Pogossian, D. T. Dekadjevi, and J. Ben Youssef

Appl. Phys. Lett. 94, 262502 (2009); http://dx.doi.org/10.1063/1.3159822 (3 pages) | Cited 7 times

Online Publication Date: 29 June 2009

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An experimental method based on ferromagnetic resonance is proposed to quantify the misalignment between ferromagnetic and antiferromagnetic easy axis in exchange biased systems. Our experimental study deals with Ni81Fe19/Al2O3 and exchange biased Ni81Fe19/NiO bilayers. Performing ferromagnetic resonance studies, we demonstrate that the misalignment is present in the exchange biased system. It is revealed by an asymmetry of the resonance field angular dependence. Using a simple model, the angle of misalignment is determined.
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75.30.Et Exchange and superexchange interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Electronic structure characterization of La2NiMnO6 epitaxial thin films using synchrotron-radiation photoelectron spectroscopy and optical spectroscopy

M. Kitamura, I. Ohkubo, M. Matsunami, K. Horiba, H. Kumigashira, Y. Matsumoto, H. Koinuma, and M. Oshima

Appl. Phys. Lett. 94, 262503 (2009); http://dx.doi.org/10.1063/1.3159826 (3 pages) | Cited 6 times

Online Publication Date: 30 June 2009

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Electronic structures of La2NiMnO6 epitaxial films are characterized using synchrotron-radiation photoelectron spectroscopy and optical spectroscopy. X-ray absorption spectra reveal that the valence states of Ni2+ and Mn4+ are dominant. The electronic structure at the valence band maximum is mainly derived from the Mn 3d state. The conduction band minimum is composed mostly of the Mn 3d-O 2p hybridized state. The optical gap is estimated to be about 1.5 eV based on the optical conductivity derived from optical spectra.
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71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Dm X-ray absorption spectra
78.66.Li Other semiconductors
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials

Strong perpendicular magnetic anisotropy in Ni/Co(111) single crystal superlattices

S. Girod, M. Gottwald, S. Andrieu, S. Mangin, J. McCord, Eric E. Fullerton, J.-M. L. Beaujour, B. J. Krishnatreya, and A. D. Kent

Appl. Phys. Lett. 94, 262504 (2009); http://dx.doi.org/10.1063/1.3160541 (3 pages) | Cited 5 times

Online Publication Date: 30 June 2009

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Single crystal Ni/Co(111) superlattices have been grown by molecular beam epitaxy. The Ni thickness is 3 ML whereas the Co thickness varies from 0.2 to 4 ML. The superlattices were studied using magnetometry and ferromagnetic resonance spectroscopy and they all exhibit strong perpendicular to the plane magnetic anisotropy. The maximum magnetocrystalline anisotropy is obtained for one cobalt monolayer. Kerr microscopy measurements show the variation of domain pattern as the Co layer thickness changes.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films

Electric detection of spin wave resonance using inverse spin-Hall effect

K. Ando, J. Ieda, K. Sasage, S. Takahashi, S. Maekawa, and E. Saitoh

Appl. Phys. Lett. 94, 262505 (2009); http://dx.doi.org/10.1063/1.3167826 (3 pages) | Cited 28 times

Online Publication Date: 1 July 2009

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Spin wave resonance in Ni81Fe19/Pt thin wire arrays has been investigated using the inverse spin-Hall effect (ISHE). The spin wave in the Ni81Fe19 layer drives spin pumping, generation of spin currents from magnetization precession, and the pumped spin current is converted into a charge current by ISHE in the Pt layer. We found an electromotive force transverse to the spatial and the spin-polarization directions of the spin current. The experimental results indicate that the amplitude of the electromotive force is proportional to the spin wave resonance absorption intensity, enabling the electric measurement of spin wave resonance in nanostructured magnetic systems.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Tunneling interlayer exchange coupling between oxide ferrimagnets: Analysis for Fe3O4/vac/Fe3O4 case

Han-Chun Wu, O. N. Mryasov, K. Radican, and I. V. Shvets

Appl. Phys. Lett. 94, 262506 (2009); http://dx.doi.org/10.1063/1.3167360 (3 pages)

Online Publication Date: 2 July 2009

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We have investigated tunneling interlayer exchange coupling (TIEC) between ferrimagnetic Fe3O4 films via a tunneling barrier. In this investigation we employ ab initio density functional theory to study a generic tunneling junction incorporating ferrimagnets Fe3O4/vac/Fe3O4. In contrast with previously established TIEC theory, calculated thickness dependence is nonmonotonic and accompanied by TIEC sign change. Our calculations clearly demonstrate that TIEC is controlled mainly by an interfacial oxygen induced spin polarization. These results emphasize the importance of localized and strongly directional electronic interactions at the interface, thus showing limitations of free electron model treatment of the problem.
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75.30.Et Exchange and superexchange interactions
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Gg Ferrimagnetics

Temperature dependence of the magnetoresistance in Fe/MgO core/shell nanoparticles

C. Martinez-Boubeta, Ll. Balcells, S. Valencia, D. Schmitz, C. Monty, and B. Martínez

Appl. Phys. Lett. 94, 262507 (2009); http://dx.doi.org/10.1063/1.3168647 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2009

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The temperature dependence of magnetoresistance (MR) of powdered samples consisting of spherical Fe/MgO core/shell nanoparticles was analyzed. A change of the MR from normal at room temperature to inverse at low temperatures was observed. Concomitant with this, samples showed a sudden increase in the electrical resistance when approaching TV ≈ 120 K, i.e., indicative of the Verwey transition temperature of Fe3O4. Thus, signaling the existence of magnetite at the Fe/MgO interface, further confirmed by means of x-ray magnetic circular dichroism. The change from normal to inverse MR is related to the increase in resistance of Fe3O4 on crossing the Verwey transition and reflects the negative spin polarization of Fe3O4.
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73.40.Ns Metal-nonmetal contacts
78.20.Ls Magneto-optical effects
73.63.-b Electronic transport in nanoscale materials and structures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.47.Pq Other materials
72.25.Mk Spin transport through interfaces
78.70.Dm X-ray absorption spectra

Size effects in submicron exchange bias square elements

G. Vallejo-Fernandez and J. N. Chapmam

Appl. Phys. Lett. 94, 262508 (2009); http://dx.doi.org/10.1063/1.3170233 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2009

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The behavior of submicron exchange bias square elements has been investigated for systems containing metallic polycrystalline layers. Numerical simulations using a simple theoretical model show that the exchange bias for such elements can increase and/or decrease depending on the microstructure of the antiferromagnetic layer and, in particular, its grain size distribution. The predictions are based on a granular model of exchange bias that accounts for grain cutting at the edges of the nanoelements that takes place during ion milling/etching. This leads to distributions of exchange bias fields that can be quite broad, especially in sub-250 nm elements.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions
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Change of the trap energy levels of the atomic layer deposited HfLaOx films with different La concentration

Chee-Hong An, Myung Soo Lee, Ju-Yun Choi, and Hyoungsub Kim

Appl. Phys. Lett. 94, 262901 (2009); http://dx.doi.org/10.1063/1.3159625 (3 pages) | Cited 7 times

Online Publication Date: 30 June 2009

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Ultrathin HfO2 and HfLaOx films with La/(Hf+La) ratios of 42%, 57%, and 64% were synthesized with an atomic layer deposition process. By measuring the leakage current at different temperatures, the conduction mechanism of HfO2 and HfLaOx films was shown to follow the Poole–Frenkel emission model under a gate injection condition. Based on the temperature and field-dependence measurements, the intrinsic trap energy levels were found to be 1.42, 1.34, 1.03, and 0.98 eV for the HfLaOx samples with La/(Hf+La) ratios of 0%, 42%, 57%, and 64%, respectively, showing a decreasing behavior as the La content increased.
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77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ng Insulators
72.20.Ht High-field and nonlinear effects

Maximal energy that can be converted by a dielectric elastomer generator

Soo Jin Adrian Koh, Xuanhe Zhao, and Zhigang Suo

Appl. Phys. Lett. 94, 262902 (2009); http://dx.doi.org/10.1063/1.3167773 (3 pages) | Cited 46 times

Online Publication Date: 30 June 2009

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Mechanical energy can be converted to electrical energy by using a dielectric elastomer generator. The elastomer is susceptible to various modes of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretch. The modes of failure define a cycle of maximal energy that can be converted. This cycle is represented on planes of work-conjugate coordinates and may be used to guide the design of practical cycles.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Dielectric relaxation and relaxor behavior in bilayered perovskites

Y. González-Abreu, A. Peláiz-Barranco, E. B. Araújo, and A. Franco Júnior

Appl. Phys. Lett. 94, 262903 (2009); http://dx.doi.org/10.1063/1.3168651 (3 pages) | Cited 8 times

Online Publication Date: 30 June 2009

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Sr0.5Ba0.5Bi2Nb2O9 ferroelectric ceramics exhibit a complex dielectric behavior, showing typical relaxor behavior. The relaxation processes are described by the Cole–Cole model [ K. S. Cole and R. H. Cole, J. Chem. Phys. 9, 341 (1941) ]. At temperatures below 490 K, the dielectric relaxation is associated to the relaxorlike ferroelectric behavior, resulting from the inhomogeneous distribution of barium due to its preference for the bismuth site. Above that, the interaction between the dipoles, which form the microdomains above the relaxor ferroelectric peak and the electrons, which are due to the ionization of the oxygen vacancies are discussed as the probable origin of the relaxation.
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77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
61.72.jd Vacancies

Atomic layer deposition of ZrO2/La2O3 high-k dielectrics on germanium reaching 0.5 nm equivalent oxide thickness

S. Abermann, O. Bethge, C. Henkel, and E. Bertagnolli

Appl. Phys. Lett. 94, 262904 (2009); http://dx.doi.org/10.1063/1.3173199 (3 pages) | Cited 14 times

Online Publication Date: 2 July 2009

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We investigate ultrathin ZrO2/La2O3 high-k dielectric stacks on germanium grown by atomic layer deposition. La2O3 is deposited from tris(N,N′-diisopropylformamidinate)-lanthanum and oxygen. Interfacial layer-free oxide stacks with a relative dielectric constant of 21 and equivalent oxide thickness values as low as 0.5 nm are obtained. Metal oxide semiconductor capacitors with platinum as the gate electrode exhibit well-behaved capacitance-voltage characteristics, gate leakage current densities in the range of 0.01–1 A/cm2, and interface trap densities in the range of ∼ 3×1012 eV−1 cm−2.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
84.32.Tt Capacitors
85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
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Plasmon-enhanced magneto-optical activity in ferromagnetic membranes

J. B. González-Díaz, J. M. García-Martín, A. García-Martín, D. Navas, A. Asenjo, M. Vázquez, M. Hernández-Vélez, and G. Armelles

Appl. Phys. Lett. 94, 263101 (2009); http://dx.doi.org/10.1063/1.3167297 (3 pages) | Cited 6 times

Online Publication Date: 30 June 2009

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Experimental and theoretical evidence of plasmon-enhanced Kerr rotation in purely ferromagnetic membranes with sufficiently small dimensions to be out of extraordinary optical transmission conditions (45 nm pore diameter, 90nm lattice constant), is reported in this work. It is shown that the spectral location of the enhanced Kerr rotation region varies as the refractive index of the material inside the pore is modified. A similar behavior is obtained if the pore radius changes while keeping the pore concentration unchanged. Those are clear signatures indicating that localized surface plasmon resonances propagating along the pores govern the magneto-optical response of the membrane.
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78.20.Ls Magneto-optical effects
78.20.Ek Optical activity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Cc Other ferromagnetic metals and alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.45.Mp Thin layers, films, monolayers, membranes

Thiol-based self-assembly nanostructures in promoting interfacial adhesion for copper-epoxy joint

Cell K. Y. Wong, Matthew M. F. Yuen, and Bing Xu

Appl. Phys. Lett. 94, 263102 (2009); http://dx.doi.org/10.1063/1.3167358 (3 pages) | Cited 2 times

Online Publication Date: 30 June 2009

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Adhesion promotion between copper-epoxy interfaces without roughening the copper substrates is critical for new generation electronic devices. This paper demonstrates a pronounced adhesion promotion of a copper-epoxy joint from 4.8 J m−2 for the untreated samples to 159 J m−2 for the interfaces prepared with a thiol-based self-assembly molecular layer (SAM). The 33-fold improvement was related to the presence of nanostructures with the SAM treatment. The adhesion enhancement is attributed to both chemical bonding between copper and epoxy and the formation of nanosized features on copper substrates. The thiol promoter enhances the interfacial adhesion with no roughening of the substrates.
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68.35.Np Adhesion
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
68.35.Gy Mechanical properties; surface strains
62.23.-c Structural classes of nanoscale systems

Morphology in semimagnetic Pb1−xMnxSe nanocrystals: Thermal annealing effects

N. O. Dantas, R. S. Silva, F. Pelegrini, and G. E. Marques

Appl. Phys. Lett. 94, 263103 (2009); http://dx.doi.org/10.1063/1.3159842 (3 pages) | Cited 8 times

Online Publication Date: 30 June 2009

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Samples of Pb1−xMnxSe nanocrystals were synthesized by fusion method and characterized by optical absorption, atomic force microscopy, x-ray diffraction, and electron paramagnetic resonance (EPR) techniques. Effects of Mn2+ ion incorporation into PbSe nanocrystals are manifested by well resolved optical spectra for different concentrations of Mn. The EPR spectra of as grown and thermal annealed Pb1−xMnxSe samples show that the magnetic properties of these Mn-doped nanocrystals can be tuned by thermal processes using different annealing times.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.50.Pp Magnetic semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
76.30.-v Electron paramagnetic resonance and relaxation
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
75.30.Et Exchange and superexchange interactions

Coherent detection of nonlinear nanomechanical motion using a stroboscopic downconversion technique

Quirin P. Unterreithmeier, Stephan Manus, and Jörg P. Kotthaus

Appl. Phys. Lett. 94, 263104 (2009); http://dx.doi.org/10.1063/1.3155164 (3 pages) | Cited 4 times

Online Publication Date: 30 June 2009

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A method is presented that overcomes bandwidth limitations arising in a fiber-optic setup transducing mechanical motion. The reflected light from a sample incorporating a nanomechanical resonator is analyzed. Modulating the incoming laser intensity at a suitably chosen frequency, the mechanically induced oscillation of the reflected light is coherently downconverted to a frequency within the detection bandwidth. Additionally, based on the mechanical nonlinear response, the optical signal can be quantitatively converted into displacement, yielding a sensitivity of 7 pm/math at optical power levels of 20 μW. We detect and image mechanical modes up to the seventh harmonic of the fundamental mode at 7.7 MHz.
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42.81.Pa Sensors, gyros
07.60.Vg Fiber-optic instruments
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

The influence of temperature and electric field on field emission energy distribution of an individual single-wall carbon nanotube

Ping Wu, N. Y. Huang, S. Z. Deng, S. D. Liang, Jun Chen, and N. S. Xu

Appl. Phys. Lett. 94, 263105 (2009); http://dx.doi.org/10.1063/1.3164813 (3 pages)

Online Publication Date: 30 June 2009

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The influence of temperature and electric field on field emission energy distribution (FEED) is studied. It is found that higher temperature energizes more higher-energy electrons. FEED peaks shift toward low energy linearly with the increase in applied voltage because of the electric field penetration. The theoretic current-voltage characteristic is fitted to the experimental data by the density of states, field enhancement factor, and temperature, from which the average energy of emitted electrons and then Fermi level of the carbon nanotube (CNT) is ascertained. This research confirms that the electric field competes with temperature and provides a method to ascertain the Fermi level of CNT.
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79.70.+q Field emission, ionization, evaporation, and desorption
71.20.Tx Fullerenes and related materials; intercalation compounds

Electronic transport property of single-crystalline hexagonal tungsten trioxide nanowires

S. J. Wang, W. J. Lu, G. Cheng, K. Cheng, X. H. Jiang, and Z. L. Du

Appl. Phys. Lett. 94, 263106 (2009); http://dx.doi.org/10.1063/1.3158953 (3 pages) | Cited 8 times

Online Publication Date: 30 June 2009

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Hexagonal WO3 nanowires were prepared on Si substrate by thermal evaporation of WO3 powder. A single WO3 nanowire was assembled on a pair of Pt electrodes by electric field assembly. The electrical transport behavior indicates that the back-to-back SBs structure is formed, which show nonlinear and asymmetric I-V properties. Through measurement of the I-V curve and the calculation of barrier height difference under illumination, it is found that the electrical asymmetry results from the asymmetric barrier height of the two Schottky barriers, which are dominated by the surface states of nanowire caused by O2 adsorption in the electric assembling process.
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73.40.Ns Metal-nonmetal contacts
81.07.-b Nanoscale materials and structures: fabrication and characterization
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)
68.43.Mn Adsorption kinetics
73.30.+y Surface double layers, Schottky barriers, and work functions

A theoretical study on thermoelectric properties of graphene nanoribbons

Yijian Ouyang and Jing Guo

Appl. Phys. Lett. 94, 263107 (2009); http://dx.doi.org/10.1063/1.3171933 (3 pages) | Cited 36 times

Online Publication Date: 30 June 2009

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We investigate the thermoelectric properties of graphene nanoribbons (GNRs) by solving atomistic electron and phonon transport equations in the nonequilibrium Green’s function formalism. The dependence of thermopower on temperature and chemical potential is compared to that of graphene, which shows the important role of quasi-one-dimensional geometry in determining the thermoelectric properties of a GNR. The edge roughness and lattice vacancy are found to increase the thermopower but decrease the thermoelectric ZT factor because the decrease in the electronic conductance outweighs the decrease in the thermal conductance and the increase in the thermopower.
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71.15.-m Methods of electronic structure calculations
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
72.20.Pa Thermoelectric and thermomagnetic effects
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.72.jd Vacancies

Single InAs quantum dot arrays and directed self-organization on patterned GaAs (311)B substrates

E. Selçuk, A. Yu. Silov, and R. Nötzel

Appl. Phys. Lett. 94, 263108 (2009); http://dx.doi.org/10.1063/1.3167813 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2009

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Formation of laterally ordered single InAs quantum dot (QD) arrays by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice templates on GaAs (311)B by molecular beam epitaxy is achieved through optimization of growth temperature, InAs amount, and annealing. Directed self-organization of these QD arrays is accomplished by coarse substrate patterns providing absolute QD position control over large areas. Due to the absence of one-to-one pattern definition the site-controlled QD arrays exhibit excellent optical properties revealed by resolution limited (80 μeV) linewidth of the low-temperature photoluminescence from individual QDs.
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68.65.Cd Superlattices
68.65.Hb Quantum dots (patterned in quantum wells)
81.40.Gh Other heat and thermomechanical treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots

Replicated photonic crystals by atomic layer deposition within holographically defined polymer templates

E. Graugnard, O. M. Roche, S. N. Dunham, J. S. King, D. N. Sharp, R. G. Denning, A. J. Turberfield, and C. J. Summers

Appl. Phys. Lett. 94, 263109 (2009); http://dx.doi.org/10.1063/1.3159834 (3 pages) | Cited 4 times

Online Publication Date: 1 July 2009

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We report the replication of holographically defined photonic crystals using multistage atomic layer deposition. Low- and high-temperature atomic layer depositions were combined with selective etching to deposit and remove multiple conformal thin films within three-dimensional polymer templates. Using intermediate Al2O3 inverse replicas, temperature-sensitive SU-8 photonic crystal templates were faithfully replicated with TiO2 and GaP, greatly increasing the dielectric contrasts of the photonic crystals. Optical measurements are in good agreement with the calculated band structures.
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42.70.Qs Photonic bandgap materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.70.Jk Polymers and organics

Hybrid core-multishell nanowire forests for electrical connector applications

Rehan Kapadia, Hyunhyub Ko, Yu-Lun Chueh, Johnny C. Ho, Toshitake Takahashi, Zhenxing Zhang, and Ali Javey

Appl. Phys. Lett. 94, 263110 (2009); http://dx.doi.org/10.1063/1.3148365 (3 pages) | Cited 9 times

Online Publication Date: 1 July 2009

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Electrical connectors based on hybrid core-multishell nanowire forests that require low engagement forces are demonstrated. The physical binding and electrical connectivity of the nanowire electrical connectors arise from the van der Waals interactions between the conductive metallic shells of the engaged nanowire forests. Specifically, the nanofibrillar structure of the connectors causes an amplification of the contact area between the interpenetrating nanowire arrays, resulting in strong adhesion with relatively low interfacial resistance. The nanowire electrical connectors may enable the exploration of a wide range of applications involving reversible assembly of micro- and macroscale components with built-in electrical interfacing.
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84.32.Dd Connectors, relays, and switches
73.40.Ns Metal-nonmetal contacts
73.63.Nm Quantum wires

Doping-dependent nanofaceting on silicon nanowire surfaces

Fang Li, Peter D. Nellist, and David J. H. Cockayne

Appl. Phys. Lett. 94, 263111 (2009); http://dx.doi.org/10.1063/1.3155434 (3 pages) | Cited 11 times

Online Publication Date: 1 July 2009

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Silicon nanowires with axially varying n- and p-doping were grown by the vapor-liquid-solid approach using gold as the catalyst. The nanowire sidewalls exhibit periodic nanofaceting, which is found to be dopant-dependent. It is shown that the nanofaceting occurs during the enhanced sidewall growth that arises when the diborane dopant gas is introduced. The nanowires are axially oriented along 〈111〉, and the crystallographic planes on which the nanofaceting occurs are determined to be {111} and {100}.
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61.72.uf Ge and Si
81.07.-b Nanoscale materials and structures: fabrication and characterization
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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)

Thermal stability of Cu and Fe nitrides and their applications for writing locally spin valves

C. Navío, J. Alvarez, M. J. Capitan, J. Camarero, and R. Miranda

Appl. Phys. Lett. 94, 263112 (2009); http://dx.doi.org/10.1063/1.3159630 (3 pages) | Cited 3 times

Online Publication Date: 2 July 2009

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We have studied the thermal stability of the Cu and Fe nitrides. These results show that a nanometer-thick Cu nitride film decomposes at the Fe4N growth temperature. Considering this, we propose for their use in spintronics, the room temperature growth of a nonmagnetic (FeN)/semiconducting (Cu3N) epitaxial nitride bilayer that transforms into a ferromagnetic (Fe4N)/metallic (Cu) one by mild thermal annealing at 700 K. This process can be employed to locally decompose by laser (or ion) irradiation FeN/Cu3N/Fe4N) trilayers, giving rise to an array of lithographically defined Fe4N/Cu/Fe4N spin valves surrounded by metal/semiconductor spacers.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
61.82.Rx Nanocrystalline materials
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.50.Tt Fine-particle systems; nanocrystalline materials
73.40.Ns Metal-nonmetal contacts
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.ag Semiconductors
68.60.Dv Thermal stability; thermal effects

Electron inelastic mean free paths for carbon nanotubes from optical data

Ioanna Kyriakou, Dimitris Emfietzoglou, Rafael Garcia-Molina, Isabel Abril, and Kostas Kostarelos

Appl. Phys. Lett. 94, 263113 (2009); http://dx.doi.org/10.1063/1.3167819 (3 pages) | Cited 8 times

Online Publication Date: 2 July 2009

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We present a simple model dielectric response function for both bulk and individual carbon nanotubes based on a parameterization of experimental optical data and analytic dispersion relations that account for dimensionality and linewidth broadening. The model is used to calculate electron inelastic mean free paths over a broad energy range of interest to various applications.
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73.61.Wp Fullerenes and related materials
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
78.66.Tr Fullerenes and related materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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