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4 Jul 2005

Volume 87, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 013110 (2005); http://dx.doi.org/10.1063/1.1977187 (3 pages)

R. C. Wang, C. P. Liu, J. L. Huang, S.-J. Chen, Y.-K. Tseng, and S.-C. Kung
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Tunneling magnetoresistance in GaMnAs/AlAs/InGaAs/AlAs/GaMnAs double-barrier magnetic tunnel junctions

Shinobu Ohya, Pham Nam Hai, and Masaaki Tanaka

Appl. Phys. Lett. 87, 012105 (2005); http://dx.doi.org/10.1063/1.1978976 (3 pages) | Cited 18 times

Online Publication Date: 29 June 2005

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We have studied the tunneling magnetoresistance (TMR) of Ga0.94Mn0.06As/AlAs(d nm)/In0.4Ga0.6As(0.42 nm)/AlAs(d nm)/Ga0.94Mn0.06As double-barrier magnetic tunnel junctions with various AlAs thicknesses (d = 0.8–2.7 nm) grown on p+GaAs (001) substrates by low-temperature molecular-beam epitaxy. In some junctions, unusual inverse TMR, in which the tunnel resistance in antiparallel magnetization is lower than that in parallel magnetization, was observed. The TMR ratio oscillated between positive and negative values with increasing the AlAs thickness, suggesting the existence of the resonant tunneling effect in the InGaAs quantum well.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.63.Hs Quantum wells
75.47.Pq Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
73.61.Ey III-V semiconductors
73.23.-b Electronic transport in mesoscopic systems
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Organic-inorganic hybrid photopolymer with reduced volume shrinkage

Won Sun Kim, Yong-Cheol Jeong, and Jung-Ki Park

Appl. Phys. Lett. 87, 012106 (2005); http://dx.doi.org/10.1063/1.1954884 (3 pages) | Cited 12 times

Online Publication Date: 30 June 2005

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An organic-inorganic hybrid photopolymer containing surface-photoreactive nanoparticles, which exhibits a significant enhancement in optical properties is reported. The photopolymer containing surface-photoreactive nanoparticles showed high diffraction efficiency near 90% and reduced volume shrinkage without affecting the energetic sensitivity and optical quality of the photopolymer.
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42.70.Jk Polymers and organics
78.40.Me Organic compounds and polymers
61.41.+e Polymers, elastomers, and plastics
82.35.-x Polymers: properties; reactions; polymerization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Carrier dynamics in Ga0.53In0.47As/InP near-surface quantum wells

Clémentine Symonds, Juliette Mangeney, Guillaume Saint-Girons, and Isabelle Sagnes

Appl. Phys. Lett. 87, 012107 (2005); http://dx.doi.org/10.1063/1.1993763 (3 pages) | Cited 2 times

Online Publication Date: 30 June 2005

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Ga0.53In0.47As/InP single-quantum wells with thin top barrier layers of InP and InAlAs have been studied by pump-probe experiments and temperature-dependent photoluminescence spectroscopy. The carrier lifetimes are shorter in samples with an InAlAs surface barrier than with an InP surface barrier. The decays consist in an early stage decay of typically 30 ps and an extended stage decay of several hundreds of picoseconds. This nonexponential relaxation is the result of thermally activated carrier escape, trapping, and recombination on the surface states. Two nonradiative surface states, at 11 and 68 meV from the ground state of the quantum well, were identified.
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73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
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Critical size for exchange bias in ferromagnetic-antiferromagnetic particles

A. N. Dobrynin, D. N. Ievlev, K. Temst, P. Lievens, J. Margueritat, J. Gonzalo, C. N. Afonso, S. Q. Zhou, A. Vantomme, E. Piscopiello, and G. Van Tendeloo

Appl. Phys. Lett. 87, 012501 (2005); http://dx.doi.org/10.1063/1.1978977 (3 pages) | Cited 45 times

Online Publication Date: 27 June 2005

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We present a study of the magnetic properties of oxidized Co nanoparticles with an average grain size of 3 nm, embedded in an amorphous Al2O3 matrix. These nanoparticles can be considered as imperfect Co-core CoO-shell systems. Magnetization measurements after magnetic field cooling show a vertical shift of the hysteresis loop, while no exchange bias is observed. With a simple model, we show that there is a critical grain size for hybrid ferromagnetic-antiferromagnetic particles, below which exchange bias is absent for any ratio of ferromagnetic and antiferromagnetic constituents. The reason is that the interfacial exchange energy dominates over other energies in the system due to a large surface-to-volume ratio in the nanoparticles.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Et Exchange and superexchange interactions
61.46.-w Structure of nanoscale materials
68.35.Md Surface thermodynamics, surface energies

Narrowing of the frequency-linewidth in structured magnetic strips: Experiment and theory

Bijoy Kuanr, R. E. Camley, and Z. Celinski

Appl. Phys. Lett. 87, 012502 (2005); http://dx.doi.org/10.1063/1.1968433 (3 pages) | Cited 17 times

Online Publication Date: 27 June 2005

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We examine the frequency-linewidth in structured magnetic materials experimentally and theoretically and show that this linewidth can decrease as the external field (or the frequency) is increased. This decrease in the frequency-linewidth occurs in many different systems and does not indicate an increase in damping at low frequencies, as has been suggested. Further, the frequency-linewidth can be very large for extended ferromagnetic films, but becomes significantly smaller for structured films that are narrower than a few microns.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys

Magnetoelectric effect of Pb(Zr,Ti)O3 rod arrays in a (Tb,Dy)Fe2/epoxy medium

Z. Shi, C. W. Nan, Jie Zhang, N. Cai, and J.-F. Li

Appl. Phys. Lett. 87, 012503 (2005); http://dx.doi.org/10.1063/1.1991983 (3 pages) | Cited 31 times

Online Publication Date: 29 June 2005

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We report a kind of multiferroic and multifunctional composite with Pb(Zr,Ti)O3 rod arrays embedded in a ferromagnetic medium of (Tb,Dy)Fe2/epoxy. The composite structure is similar to that of 1–3-type piezoelectric composites with Pb(Zr,Ti)O3 rod arrays embedded in an inert epoxy for already commercial applications as transducers. The large magnetoelectric effect, especially at high frequency at which the electromechanical resonance appears, is observed for such multiferroic composites due to coupling elastic interaction between Pb(Zr,Ti)O3 rods and the ferromagnetic medium, which suggests avenues for designing novel multiferroic materials for practical applications.
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77.84.Lf Composite materials
75.50.Bb Fe and its alloys
75.80.+q Magnetomechanical effects, magnetostriction
77.65.Bn Piezoelectric and electrostrictive constants
77.65.Fs Electromechanical resonance; quartz resonators
72.30.+q High-frequency effects; plasma effects

Exchange spring media for perpendicular recording

D. Suess, T. Schrefl, S. Fähler, M. Kirschner, G. Hrkac, F. Dorfbauer, and J. Fidler

Appl. Phys. Lett. 87, 012504 (2005); http://dx.doi.org/10.1063/1.1951053 (3 pages) | Cited 128 times

Online Publication Date: 30 June 2005

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A novel type of exchange spring media is proposed for magnetic recording systems consisting of a hard/soft bilayer. Finite element micromagnetic simulations show that the reversal modes induced by the external write field are significantly different from the thermally activated switching processes. Thus, the bilayers can be optimized in order to achieve a high thermal stability without increase of coercive field. In grains with identical size and coercivity an optimized bilayer reaches an energy barrier exceeding those of optimized single phase media by more than a factor of two. Additionally the lower angular dependence of coercivity of exchange spring media will improve the signal to noise ratio.
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75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High magnetoresistive sensitivity in electrodeposited FeCoNi/Cu multilayers

Jie Gong, William H. Butler, and Giovanni Zangari

Appl. Phys. Lett. 87, 012505 (2005); http://dx.doi.org/10.1063/1.1952573 (3 pages) | Cited 5 times

Online Publication Date: 30 June 2005

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FeCoNi/Cu multilayers with large magnetoresistive sensitivity at low field have been electrodeposited on n-type Si from a single electrolyte by modulating the deposition potential. Dissolution of the ferromagnetic (FM) layer during copper deposition was minimized and interface sharpness was improved by monitoring the current transients during the transition from FM to Cu deposition and using these data to fine tune the Cu deposition potential and Fe2+ concentration in the electrolyte. Using optimal processing parameters, a maximum giant magnetoresistance (GMR) ratio above 9% could be obtained. Maximum GMR sensitivity of over 0.11%/Oe was achieved in the field range 5–15 Oe.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
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Dielectric relaxation of atomic-layer-deposited HfO2 thin films from 1 kHz to 5 GHz

Byungjoo Lee, Taeho Moon, Tae-Gon Kim, Duck-Kyun Choi, and Byungwoo Park

Appl. Phys. Lett. 87, 012901 (2005); http://dx.doi.org/10.1063/1.1988982 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2005

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The dielectric relaxation of HfO2 thin films grown by atomic-layer deposition (ALD) was studied as a function of frequency from 1 kHz to 5 GHz. The dielectric relaxation of the ALD HfO2 films followed a power-law dependence known as the Curie–von Schweidler relaxation law both in the kHz and GHz ranges, and the relaxation exponents were consistent with the measured dielectric losses. The behavior of the dielectric response for the HfO2 thin films may be attributed to defect sites in the HfO2 layer and∕or interface.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Thermal stability of hafnium–silicate and plasma-nitrided hafnium silicate films studied by Fourier transform infrared spectroscopy

M. A. Quevedo-Lopez, J. J. Chambers, M. R. Visokay, A. Shanware, and L. Colombo

Appl. Phys. Lett. 87, 012902 (2005); http://dx.doi.org/10.1063/1.1977184 (3 pages) | Cited 23 times

Online Publication Date: 28 June 2005

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Structure and bonding changes in ultrathin hafnium–silicate (HfSiO) and plasma-nitrided HfSiO (HfSiON) films as a result of thermal annealing are presented. To track these changes, attenuated total reflection Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy were used. It is shown that for films with a given Si content, HfSiON films have superior thermal stability compared to the corresponding HfSiO films. It is also demonstrated that besides giving chemical state changes for the thin-film constituents, FTIR can also be used to track interfacial SiO2 growth as well as phase separation in ultrathin high-κ films resulting from thermal annealing.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
77.22.Ch Permittivity (dielectric function)

Chemical reaction at the interface between polycrystalline Si electrodes and HfO2/Si gate dielectrics by annealing in ultrahigh vacuum

H. Takahashi, S. Toyoda, J. Okabayashi, H. Kumigashira, M. Oshima, Y. Sugita, G. L. Liu, Z. Liu, and K. Usuda

Appl. Phys. Lett. 87, 012903 (2005); http://dx.doi.org/10.1063/1.1984091 (3 pages) | Cited 9 times

Online Publication Date: 29 June 2005

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We have investigated the chemical reaction at the interface between polycrystalline-Si (poly-Si) electrodes and HfO2/Si gate dielectrics by photoemission spectroscopy and x-ray absorption spectroscopy depending on the annealing temperature in an ultrahigh vacuum. From Si 2p and Hf 4f high-resolution core-level photoemission spectra, we revealed that the Hf-silicide formation starts at as low temperature as 700 °C and that the Hf-silicate layer is also formed at the interface between poly-Si electrodes and HfO2. Crystallization of the amorphous HfO2 layer even at 700 °C was suggested from valence-band and O K-edge absorption spectra. By the annealing at 800 °C, the HfO2 layer disappeared completely and the Hf-silicide clusters were formed on the Si substrate. Direct contact between poly-Si electrodes and HfO2 promotes the interfacial reaction compared to the case without poly-Si electrodes.
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82.30.-b Specific chemical reactions; reaction mechanisms
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
78.70.Dm X-ray absorption spectra
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Dielectric anomalies of the relaxor-based 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 single crystals

Haixia Wang, Haiqing Xu, Haosu Luo, Zhiwen Yin, A. A. Bokov, and Z.-G. Ye

Appl. Phys. Lett. 87, 012904 (2005); http://dx.doi.org/10.1063/1.1990253 (3 pages) | Cited 11 times

Online Publication Date: 30 June 2005

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The temperature, frequency, and orientation dependence of complex electrical permittivity in 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 (0.9PMN-0.1PT) unpoled single crystals have been investigated in detail. The spontaneous ferroelectric-to-relaxor (FE-R) phase transition was observed in 0.9PMN-0.1PT crystals at about 280 K. Interestingly, the Vogel-Fulcher-type anomaly of the dielectric constant has been obtained, with the fitted temperature Tf being very close to this FE-R phase transition temperature. A small frequency dependence of electric permittivity magnitude appears at and below 280 K. The changes of the polar nanoregion subsystem and the peculiarities of the domain structure play an important role in the dielectric anomalies and the appearance of the FE-R crossover region.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point

Nondispersive dielectric component of ferroelectric thin films in the frequency range of 10−1–106 Hz

A. Q. Jiang, D. P. Chu, P. Migliorato, T. Kijima, E. Natori, and T. Shimoda

Appl. Phys. Lett. 87, 012905 (2005); http://dx.doi.org/10.1063/1.1993765 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2005

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We show that there exists a nondispersive (or elastic) capacitance component Cnon which is independent of frequency f, ac amplitude VOSC, and dc bias voltage Vdc, in the frequency range of 0.063 Hz–1 MHz. It can be separated from the total capacitance Ct of ferroelectric thin films by using either the C(Vdc,f)‐C[Vdc,f(r)](VOSC = const) or C(f,VOSC)‐C[f,VOSC(r)](Vdc = const) plot, where f(r) and VOSC(r) are the referenced frequency and ac amplitude, respectively. Our results suggest that the dispersive and nondispersive capacitance components may originate from different dielectric relaxation mechanisms. The extracted nondispersive Cnon can be a useful physical parameter in evaluating maximum dielectric tunability for the phase-shift application of ferroelectric thin films in microwave devices and characterizing phase-transition temperature in a multilayered 0.2Pb(Zn1/3Nb2/3)O3–0.8BaTiO3/Pb(Mg1/3Nb2/3)O3 relaxor.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
72.30.+q High-frequency effects; plasma effects
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Random walks in nanotube composites: Improved algorithms and the role of thermal boundary resistance

Hai M. Duong, Dimitrios V. Papavassiliou, Lloyd L. Lee, and Kieran J. Mullen

Appl. Phys. Lett. 87, 013101 (2005); http://dx.doi.org/10.1063/1.1940737 (3 pages) | Cited 13 times

Online Publication Date: 27 June 2005

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Random walk simulations of thermal walkers are used to study the effect of interfacial resistance on heat flow in randomly dispersed carbon nanotube composites. The adopted algorithm effectively makes the thermal conductivity of the nanotubes themselves infinite. The probability that a walker colliding with a matrix-nanotube interface reflects back into the matrix phase or crosses into the carbon nanotube phase is determined by the thermal boundary (Kapitza) resistance. The use of “cold” and “hot” walkers produces a steady state temperature profile that allows accurate determination of the thermal conductivity. The effects of the carbon nanotube orientation, aspect ratio, volume fraction, and Kapitza resistance on the composite effective conductivity are quantified.
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81.05.Mh Cermets, ceramic and refractory composites
81.07.De Nanotubes
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
68.35.Ja Surface and interface dynamics and vibrations

Aluminum nanocantilevers for high sensitivity mass sensors

Zachary J. Davis and Anja Boisen

Appl. Phys. Lett. 87, 013102 (2005); http://dx.doi.org/10.1063/1.1984092 (3 pages) | Cited 15 times

Online Publication Date: 27 June 2005

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We have fabricated Al nanocantilevers using a simple, one mask contact UV lithography technique with lateral and vertical dimensions under 500 and 100 nm, respectively. These devices are demonstrated as highly sensitive mass sensors by measuring their dynamic properties. Furthermore, it is shown that Al has a potential higher sensitivity than Si based dynamic sensors. Initial testing of these devices has been conducted using a scanning electron microscope setup were the devices were tested under high vacuum conditions. The Q factor was measured to be approximately 200 and the mass sensitivity was measured to 2 ag/Hz by depositing electron-beam-induced carbon at the end of the nanocantilever.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.16.Nd Micro- and nanolithography
06.30.Dr Mass and density

GaN nanostructure fabrication by focused-ion-beam-assisted chemical vapor deposition

T. Nagata, P. Ahmet, Y. Sakuma, T. Sekiguchi, and T. Chikyow

Appl. Phys. Lett. 87, 013103 (2005); http://dx.doi.org/10.1063/1.1968435 (3 pages) | Cited 8 times

Online Publication Date: 27 June 2005

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Gallium nitride (GaN) nanostructures were fabricated by focused-ion-beam-assisted chemical vapor deposition. Gallium precursor gas and atomic nitrogen radicals were irradiated onto the surface simultaneously during the irradiation of a Ga ion beam of 25 keV at 600 °C. Scanning electron microscopy observations revealed three-dimensional structures formed periodically on the substrates. Although near-band-edge emission from GaN was observed using this method, other luminescence attributed to defects and/or impurities was also observed. Surface damage caused by the ion beam was also observed. To improve the structural shape and optical properties, a two-step growth method is proposed. First, structure formation was performed at 300 °C. Second, nitridation was performed at 600 °C to make the GaN nanostructures stoichiometric and to activate the nitrogen in the structures. GaN nanostructures of a 200 nm×100 nm block of height 50 nm were fabricated and strong near-band-edge emission at 3.37 eV from GaN was observed.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.60.Hk Cathodoluminescence, ionoluminescence
61.80.Jh Ion radiation effects
61.72.-y Defects and impurities in crystals; microstructure
61.82.Fk Semiconductors

Laser action in ZnO nanoneedles selectively grown on silicon and plastic substrates

S. P. Lau, H. Y. Yang, S. F. Yu, H. D. Li, M. Tanemura, T. Okita, H. Hatano, and H. H. Hng

Appl. Phys. Lett. 87, 013104 (2005); http://dx.doi.org/10.1063/1.1984106 (3 pages) | Cited 36 times

Online Publication Date: 28 June 2005

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An ion-beam technique has been employed to fabricate nanoscale needlelike structures in ZnO thin films on silicon and plastic substrates at room temperature. The ZnO nanoneedles showed a single-crystalline wurtzite structure, the stem of which was around 100 nm in diameter. The sharp tips of the nanoneedles exhibited an apex angle of 20° as measured by transmission electron microscopy. Room-temperature ultraviolet random lasing action was observed in the ZnO nanoneedle arrays under 355 nm optical excitation.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
68.37.Lp Transmission electron microscopy (TEM)

Mechanism of lateral ordering of InP dots grown on InGaP layers

J. R. R. Bortoleto, H. R. Gutiérrez, M. A. Cotta, and J. Bettini

Appl. Phys. Lett. 87, 013105 (2005); http://dx.doi.org/10.1063/1.1953875 (3 pages) | Cited 15 times

Online Publication Date: 28 June 2005

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The mechanisms leading to the spontaneous formation of a two-dimensional array of InP/InGaP dots grown by chemical-beam epitaxy are discussed. Samples where the InGaP buffer layer was grown at different conditions were characterized by transmission electron microscopy. Our results indicate that a periodic strain field related to lateral two-dimensional compositional modulation in the InGaP buffer layer determines the dot nucleation positions during InP growth. Although the periodic strain field in the InGaP is large enough to align the InP dots, both their shape and optical properties are effectively unaltered. This result shows that compositional modulation can be used as a tool for in situ dot positioning.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Coulomb blockade phenomena in electromigration break junctions

R. Sordan, K. Balasubramanian, M. Burghard, and K. Kern

Appl. Phys. Lett. 87, 013106 (2005); http://dx.doi.org/10.1063/1.1991988 (3 pages) | Cited 31 times

Online Publication Date: 29 June 2005

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Nanosized gap structures have been fabricated via electromigration-induced breaking of gold-palladium nanowires. The application of low breaking voltages resulted in gap junctions exhibiting single-electron tunneling signatures at low temperature (2 K), which are attributed to the formation of metallic nanoclusters during the electromigration process. Strikingly, the I–V characteristics of most samples displayed a close similarity to those typically attributed to electrical transport through single molecules contacted by incorporation into electromigration gaps. The finding that the breaking of bare nanowires alone is sufficient to create rich differential conductance features should be taken into account in future electrical studies on molecular-scale structures.
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73.63.Nm Quantum wires
73.23.Hk Coulomb blockade; single-electron tunneling
66.30.Qa Electromigration
61.46.-w Structure of nanoscale materials

Plasmon Bragg reflectors and nanocavities on flat metallic surfaces

Bing Wang and Guo Ping Wang

Appl. Phys. Lett. 87, 013107 (2005); http://dx.doi.org/10.1063/1.1954880 (3 pages) | Cited 97 times

Online Publication Date: 29 June 2005

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Metal heterostructures constructed surface plasmon polaritons (SPPs) Bragg reflectors and nanocavities on flat metallic surfaces are proposed and demonstrated numerically. A metal heterowaveguide structured by alternately stacking two kinds of metal gap waveguides (MGWs) shows periodically effective refraction index modulation to SPPs and produces SPP propagation on flat metallic surfaces a band gap in certain frequencies, known as plasmonic band gap, in which SPP propagation is forbidden. Changing the width of one MGW in the heterowaveguide, a SPP nanocavity with high quality factor can be created. Our results imply a broad possibility of constructed SPP-based Bragg reflectors, emitter, and filters, etc., on flat metallic surfaces for planar nanometeric photonic networks.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Gn Optical waveguides and couplers
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)

Measurement of thermal conductivity of individual multiwalled carbon nanotubes by the 3-ω method

Tae Y. Choi, Dimos Poulikakos, Joy Tharian, and Urs Sennhauser

Appl. Phys. Lett. 87, 013108 (2005); http://dx.doi.org/10.1063/1.1957118 (3 pages) | Cited 45 times

Online Publication Date: 29 June 2005

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The thermal conductivity of individual multiwalled carbon nanotubes (outer diameter of ∼ 45 nm) was obtained by employing the 3-ω method. To this end, the third-harmonic amplitude as a response to the applied alternate current at fundamental frequency (ω) is expressed in terms of thermal conductivity. A microfabricated device composed of a pair of metal electrodes 1 μm apart is used to place a single nanotube across the designated metal electrodes by utilizing the principle of dielectrophoresis. The multiwalled carbon nanotube was modeled as a one-dimensional diffusive energy transporter and its thermal conductivity was measured to be 650–830 W/mK at room temperature.
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81.07.De Nanotubes
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
82.45.-h Electrochemistry and electrophoresis

Fabrication of ZnO nanoparticles in SiO2 by ion implantation combined with thermal oxidation

H. Amekura, N. Umeda, Y. Sakuma, N. Kishimoto, and Ch. Buchal

Appl. Phys. Lett. 87, 013109 (2005); http://dx.doi.org/10.1063/1.1989442 (3 pages) | Cited 22 times

Online Publication Date: 29 June 2005

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Zinc-oxide (ZnO) nanoparticles (NPs) are fabricated in silica glasses (SiO2) by implantation of Zn+ ions of 60 keV up to 1.0×1017 ions/cm2 and following thermal oxidation. After the oxidation at 700 °C for 1 h, the absorption in the visible region due to Zn metallic NPs disappears and a new absorption edge due to ZnO appears at ∼ 3.25 eV. Cross-sectional transmission electron microscopy confirms the formation of ZnO NPs of 5–10 nm in diameter within the near-surface region of ∼ 80 nm thick and larger ZnO NPs on the surface. Under He–Cd laser excitation at λ = 325 nm, an exciton luminescence peak centered at 375 nm with FWHM of 113 meV was observed at room temperature.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.82.Rx Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
73.22.Lp Collective excitations
61.46.-w Structure of nanoscale materials
61.72.up Other materials
68.37.Lp Transmission electron microscopy (TEM)
78.40.Fy Semiconductors

ZnO nanopencils: Efficient field emitters

R. C. Wang, C. P. Liu, J. L. Huang, S.-J. Chen, Y.-K. Tseng, and S.-C. Kung

Appl. Phys. Lett. 87, 013110 (2005); http://dx.doi.org/10.1063/1.1977187 (3 pages) | Cited 86 times

Online Publication Date: 29 June 2005

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ZnO nanopencils were synthesized on a silicon wafer without catalysts at a low temperature of 550 ° C through a simple two-step pressure controlled thermal evaporation. Penholders were well-hexagonal faceted and the diameter of pen tips on the nanopencils was in the range of 20–30 nm. High-resolution transmission electron microscopy shows that the nanopencils were single crystals growing along the [0001] direction and the pen tips subtend a small angle with multiple surface perturbations. Field-emission measurements on the nanopencils show a low turn-on field of 3.7 V/μm at a current density of 10 μA/cm2. The emission current density reached 1.3 mA/cm2 at an applied field of 4.6 V/μm. The emission at the low field is attributed to the sharp tip and surface perturbations on the nanopencils.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
79.70.+q Field emission, ionization, evaporation, and desorption
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
68.37.Lp Transmission electron microscopy (TEM)

Interpretation of enhancement factor in nonplanar field emitters

R. C. Smith, R. D. Forrest, J. D. Carey, W. K. Hsu, and S. R. P. Silva

Appl. Phys. Lett. 87, 013111 (2005); http://dx.doi.org/10.1063/1.1989443 (3 pages) | Cited 27 times

Online Publication Date: 30 June 2005

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A comparison of the field emission properties of exposed nanotubes lying on a tipped carbon nanorope, with the emission properties from a sharpened iron tip of similar dimensions is performed. By varying the electrode separation it is observed that the threshold field for emission for both structures decreases as the electrode separation initially increases; however, for sufficiently large electrode separations, the threshold field is observed to reach an asymptotic value. Our results show that the field enhancement factor is fundamentally associated with the electrode separation, and depending on the experimental conditions in order to obtain a true value for electric field a set of alternative definitions for enhancement factors is required. We further confirm our experimental synopsis by simulation of the local electrostatic field which gives results similar to those obtained experimentally.
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85.45.Db Field emitters and arrays, cold electron emitters
85.45.Bz Vacuum microelectronic device characterization, design, and modeling
85.35.Kt Nanotube devices

Pressure-dependent Schottky barrier at the metal-nanotube contact

Noejung Park, Donghoon Kang, Suklyun Hong, and Seungwu Han

Appl. Phys. Lett. 87, 013112 (2005); http://dx.doi.org/10.1063/1.1990251 (3 pages) | Cited 5 times

Online Publication Date: 30 June 2005

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We carry out first-principles density-functional calculations to investigate the electronic structure of the gold-carbon nanotube contact. It is found that a pressure applied on the gold-nanotube contact shifts the Fermi level from the valence edge to the conduction edge of the carbon nanotube. This can explain the n-type transport behavior frequently observed in the nanotube field-effect transistor using the gold as electrodes. An atomistic model is proposed for a possible origin of the pressure when the nanotube is embedded in the gold electrode.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.30.+y Surface double layers, Schottky barriers, and work functions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.40.Ns Metal-nonmetal contacts
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