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4 Jul 2005

Volume 87, Issue 1, Articles (01xxxx)

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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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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 12 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

Controlled p- and n-type doping of Fe2O3 nanobelt field effect transistors

Zhiyong Fan, Xiaogang Wen, Shihe Yang, and Jia G. Lu

Appl. Phys. Lett. 87, 013113 (2005); http://dx.doi.org/10.1063/1.1977203 (3 pages) | Cited 40 times

Online Publication Date: 1 July 2005

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Pure α-Fe2O3 nanobelts are configured as field effect transistors and electrical transport studies demonstrate their n-type behavior. In order to control the electrical properties of the fabricated transistor, the nanobelt channels are doped with zinc. Depending on the doping condition, α-Fe2O3 nanobelts can be modified to either p-type or n-type with enhanced conductivity and electron mobility. Such behavior change is exhibited in the variation of the current-voltage (I-V) and I-Vg characteristics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Electrical and field-emission properties of chemically anchored single-walled carbon nanotube patterns

Myung-Sup Jung, Young Koan Ko, Dae-Hwan Jung, Do Hwan Choi, Hee-Tae Jung, Jung Na Heo, Byung Hee Sohn, Yong Wan Jin, and Jongmin Kim

Appl. Phys. Lett. 87, 013114 (2005); http://dx.doi.org/10.1063/1.1968430 (3 pages) | Cited 17 times

Online Publication Date: 1 July 2005

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Well-defined and high-density single-walled carbon nanotube (SWNT) patterns were fabricated using a combination of photolithographic and chemical assembling processes. Unlike the patterned SWNT arrays reported thus far, these SWNT patterned layers have high-density multilayer structures and excellent surface adhesion due to their direct chemical bonding to their substrates, which results in high electrical conductivity. We found that the high-density multilayer SWNT patterns emit electrons under an applied electrical field. The electrical resistivities of the SWNT layers were found to be 5–10 Ω cm, with a turn-on electric field of about 3 V/μm at an emission current density of 10 μA/cm2. This technique for fabricating SWNT patterns can be used in the production of field-emission displays and in future device integration requiring carbon nanotubes (CNTs), because it provides large-area patterning of SWNTs with high stability and uniformity.
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73.63.Fg Nanotubes
81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
81.16.Rf Micro- and nanoscale pattern formation

Proposal for a “spin capacitor”

Supriyo Datta

Appl. Phys. Lett. 87, 013115 (2005); http://dx.doi.org/10.1063/1.1968417 (3 pages) | Cited 5 times

Online Publication Date: 1 July 2005

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We propose a “spin capacitor” that could be implemented by modifying a commercial silicon field-effect transistor to incorporate traps in the oxide and ferromagnetic source and drain contacts in an antiparallel spin-valve configuration. A quantitative model is presented suggesting that small values of drain voltage ∼ 100 mV can be used to spin polarize the traps (“charge the spin capacitor”), which can be subsequently detected through its effect on the drain current. Other configurations can be designed to implement the basic idea, which enables convenient manipulation and detection of individual spins through a small applied bias and which may be useful in exploring many novel spintronic phenomena.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
84.32.Tt Capacitors
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
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