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1 Dec 2008

Volume 93, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 221101 (2008); http://dx.doi.org/10.1063/1.3036234 (3 pages)

Soon Moon Jeong, Na Young Ha, Mu Guen Chee, Fumito Araoka, Ken Ishikawa, Hideo Takezoe, Suzushi Nishimura, and Goro Suzaki
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Piezoresponse force microscopy on doubly clamped KNbO3 nanowires

J. Wang, C. Stampfer, C. Roman, W. H. Ma, N. Setter, and C. Hierold

Appl. Phys. Lett. 93, 223101 (2008); http://dx.doi.org/10.1063/1.3000385 (3 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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We present piezoresponse force microscopy measurements on individual integrated potassium niobate (KNbO3) nanowires. The devices consist of KNbO3 nanowires on SiO2 substrates being mechanically clamped and electrically biased by lithographically defined metal electrodes. This configuration allows to apply electrical fields parallel to the nanowire axis. Measured piezoelectric displacements reveal a multidomain structure of the nanowire. We observed displacements in the range of 3–13 pm on different domains under Vac of 2 V, that have typical section length of ≈ 200 nm, along a doubly clamped nanowire with ≈ 100 nm diameter. A maximum nominal piezoelectric coefficient of 7.9 pm/V has been extracted.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Electron doping of small-diameter carbon nanotubes with exohedral fullerenes

Basudev Pradhan, Ryan R. Kohlmeyer, Kristina Setyowati, and Jian Chen

Appl. Phys. Lett. 93, 223102 (2008); http://dx.doi.org/10.1063/1.3041631 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The interaction between carbon nanotubes (CNTs) and exohedral fullerenes, which represent two types of carbon allotropes with extraordinary properties, has received little attention so far. The effect of exohedral fullerenes on CNTs’ electronic properties is essentially unknown. We report the electron doping of small-diameter semiconducting single-walled CNTs (SWNTs) with fullerenes such as 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 ([60]PCBM). The resulting [60]PCBM-doped SWNTs demonstrate significantly enhanced electrical conductivity while still retaining characteristics of semiconducting nanotubes. Polymer nanocomposites based on air-stable, n-doped SWNTs show a (15–22)-fold enhancement in electrical conductivity compared with nanocomposites based on undoped SWNTs at the same nanotube loading level.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
72.80.Rj Fullerenes and related materials
61.72.up Other materials

Structure of chemically derived mono- and few-atomic-layer boron nitride sheets

Wei-Qiang Han, Lijun Wu, Yimei Zhu, Kenji Watanabe, and Takashi Taniguchi

Appl. Phys. Lett. 93, 223103 (2008); http://dx.doi.org/10.1063/1.3041639 (3 pages) | Cited 81 times

Online Publication Date: 1 December 2008

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We prepared mono- and few-layer hexagonal boron nitride sheets by a chemical-solution-derived method starting from single-crystalline hexagonal boron nitride. Using high-resolution transmission electron microscopy and electron-energy-loss spectrometry, we characterized the microstructure, composition, and near-edge fine structure of the boron nitride sheets. We conclude that the fringe contrast in the edge and the moiré patterns are feasible criteria for determining the number of layers and their stacking orientation in the sheets. These criteria are also useful for other mono- and few-layer materials, such as graphene sheets.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
79.20.Uv Electron energy loss spectroscopy

Reduction in charged defects associated with oxygen vacancies in hafnia by magnesium incorporation: First-principles study

Naoto Umezawa, Motoyuki Sato, and Kenji Shiraishi

Appl. Phys. Lett. 93, 223104 (2008); http://dx.doi.org/10.1063/1.3040306 (3 pages) | Cited 5 times

Online Publication Date: 2 December 2008

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Charged defects in a gate insulating oxide significantly degrade electric properties of the field-effect transistors. We report on our analysis of the effects of Mg incorporation into HfO2 upon reduction in the positive charges associated with oxygen vacancies VO+2. Our comprehensive study using first-principles calculations revealed that a Mg atom substituted for Hf is stable in charge negative MgHf−2 and strongly binds with VO+2, neutralizing the defect. This contributes to the suppressing of the electron traps at the defect site, improving the reliability of Hf-based gate oxides.
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71.55.Ht Other nonmetals
85.30.De Semiconductor-device characterization, design, and modeling
77.55.-g Dielectric thin films
85.30.Tv Field effect devices
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Carbon nanotubes filled with ferromagnetic alloy nanowires: Lightweight and wide-band microwave absorber

Ruitao Lv, Feiyu Kang, Jialin Gu, Xuchun Gui, Jinquan Wei, Kunlin Wang, and Dehai Wu

Appl. Phys. Lett. 93, 223105 (2008); http://dx.doi.org/10.1063/1.3042099 (3 pages) | Cited 27 times

Online Publication Date: 2 December 2008

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Thin-walled carbon nanotubes (CNTs) filled with different ferromagnetic alloy (FeCo, FeNi, and FeCoNi) nanowires were prepared by using trichlorobenzene as carbon precursor. They were dispersed into epoxy resin and then coated onto 180×180 mm2 aluminum substrates to form microwave-absorption coatings with 2.0 mm thickness. Reflection loss exceeding −5 dB was obtained between 5 and 18 GHz for coating containing 1.3 wt % FeCo-filled CNTs. A minimum reflection loss value of −28.2 dB was achieved at 15.2 GHz in FeCoNi-filled CNTs/epoxy coating. The areal densities of coatings are only 2.35 kg/m2, which is favorable for the applications requiring low density.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
75.50.Bb Fe and its alloys
84.40.-x Radiowave and microwave (including millimeter wave) technology

Magnetism in nanopatterned graphite film

Li Chen, Decai Yu, and Feng Liu

Appl. Phys. Lett. 93, 223106 (2008); http://dx.doi.org/10.1063/1.3033223 (3 pages) | Cited 6 times

Online Publication Date: 3 December 2008

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Using first-principles calculations, we show that nanopatterned graphite films (NPGFs) can exhibit magnetism in analogy to graphene-based nanostructures (GBNs). In particular, graphite films with patterned nanoscale triangular holes and channels with zigzag edges all have ferromagnetic ground states. The magnetic moments are localized at the edges with a behavior similar to that of GBNs. Our findings suggest that the NPGFs form a unique class of magnetic materials.
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75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities

Diameter-selective separation of double-walled carbon nanotubes

Jin Hee Kim, Masakazu Kataoka, Yoong Ahm Kim, Daisuke Shimamoto, Hiroyuki Muramatsu, Takuya Hayashi, Morinobu Endo, Mauricio Terrones, and Mildred S. Dresselhaus

Appl. Phys. Lett. 93, 223107 (2008); http://dx.doi.org/10.1063/1.3039790 (3 pages) | Cited 6 times

Online Publication Date: 3 December 2008

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Here, we report a simple and effective way of separating double-walled carbon nanotubes as a function of their diameter using individually dispersed nanotube solutions with the aid of long and random single-stranded DNA. The subtle pH change in nanotube solutions gives rise to the preferential coagulation of large-diameter tubes and allows the easy preparation of small-diameter tubes. The stronger van der Waals forces between large-diameter tubes, combined with the decreased solubility of DNA in water at low pH, lead to the preferential agglomeration of large-diameter tubes.
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81.16.-c Methods of micro- and nanofabrication and processing
64.75.Jk Phase separation and segregation in nanoscale systems
64.75.Bc Solubility
87.14.gk DNA
34.20.Cf Interatomic potentials and forces
87.15.hg Dynamics of intermolecular interactions

Freestanding (3,0) boron nitride nanotube: Expected to be stable well over room temperature

Zhuhua Zhang, Wanlin Guo, and Yitao Dai

Appl. Phys. Lett. 93, 223108 (2008); http://dx.doi.org/10.1063/1.3040007 (3 pages) | Cited 9 times

Online Publication Date: 3 December 2008

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By semiempirical molecular dynamics simulations and ab initio total energy calculations, the freestanding (3,0) boron nitride nanotube (BNNT) with a diameter of 2.7 Å is expected to be stable well over room temperature with remarkably higher stability than the experimentally reported (2,2) carbon nanotube. We elucidate the underlying physics by examining the variation in surface dipole and charge reordering driven by geometrical relaxation. In addition, the (3,0) BNNT can become globally stable when encapsulated in a larger BNNT.
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61.46.Fg Nanotubes
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Tuning the tunnel coupling of quantum dot molecules with longitudinal magnetic fields

J. I. Climente

Appl. Phys. Lett. 93, 223109 (2008); http://dx.doi.org/10.1063/1.3040058 (3 pages) | Cited 4 times

Online Publication Date: 3 December 2008

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We show that the energy splitting between the bonding and antibonding molecular states of holes in vertically stacked quantum dots can be tuned using longitudinal magnetic fields. With increasing field, the energy splitting first decreases to zero and then to negative values, which implies a bonding-to-antibonding ground state transition. This effect is a consequence of the enhancement of the valence band spin-orbit interaction induced by the magnetic field; it provides a flexible mechanism to switch the molecular ground state from bonding to antibonding.
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73.21.La Quantum dots
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.40.Gk Tunneling
78.67.Hc Quantum dots

Influences of light intensity on fluorescence lifetime of nanorods and quantum dots

Yi-Cheun Yeh, Chi-Tsu Yuan, Chia-Cheng Kang, Pi-Tai Chou, and Jau Tang

Appl. Phys. Lett. 93, 223110 (2008); http://dx.doi.org/10.1063/1.3021366 (3 pages) | Cited 4 times

Online Publication Date: 4 December 2008

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In this letter we investigate light-intensity dependence of the fluorescence lifetime for CdSe nanorods (NRs) and quantum dots (QDs) measured by time-correlated single photon counting techniques. We report extremely narrow lifetime distribution for NRs as the light intensity increases, although the change for QDs is not so pronounced. In addition, the averaged lifetimes for NRs and QDs all become shortened at higher light intensities. Some possible mechanisms for these effects are discussed.
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78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
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)

Strain promoted conductivity of doped carbon nanotubes

Hsin-Fu Kuo, Ching-Tung Hsu, Der-Hsien Lien, Sen-Hong Syue, Yin-Shen Kao, Ching-Chen Li, Yi-Fan Li, Wei Chin, Shih-Chin Chang, Bee-Yu Wei, and Wen-Kuang Hsu

Appl. Phys. Lett. 93, 223111 (2008); http://dx.doi.org/10.1063/1.3033369 (3 pages) | Cited 3 times

Online Publication Date: 4 December 2008

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Strain promoted conductivity is detected in boron-doped carbon nanotubes and conductance biased at 3.5, 3.8, −4.6, −5.7, and −6.4 V exceeds 0.5G0. Deflection induced degeneracy of BC3-π bands accounts for conductance increment.
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73.61.Wp Fullerenes and related materials

High-temperature dielectric properties and enhanced temperature-response attenuation of β-MnO2 nanorods

Xiao-Ling Shi, Mao-Sheng Cao, Xiao-Yong Fang, Jie Yuan, Yu-Qing Kang, and Wei-Li Song

Appl. Phys. Lett. 93, 223112 (2008); http://dx.doi.org/10.1063/1.3042210 (3 pages) | Cited 22 times

Online Publication Date: 5 December 2008

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Large-scale β-MnO2 nanorods were synthesized by the hydrothermal method. In X band, the microwave attenuation of the β-MnO2 nanorods is evidently enhanced with increasing temperature from 293 to 773 K. The enhanced temperature-response attenuation of β-MnO2 nanorods is mainly attributed to the decrease in the real permittivity and the increase in the imaginary permittivity at high temperature. The decrease in real permittivity would be mainly ascribed to the increase in the disorder degree of orientational alignment of the intrinsic polar moment in the β-MnO2 nanorods with temperature increasing. The increase in imaginary permittivity may result from the lower resistivity with rising temperature.
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77.22.Ch Permittivity (dielectric function)
81.07.Bc Nanocrystalline materials
81.10.Dn Growth from solutions

Effect of dopants on grain boundary decohesion of Ni: A first-principles study

Suchismita Sanyal, Umesh V. Waghmare, P. R. Subramanian, and Michael F. X. Gigliotti

Appl. Phys. Lett. 93, 223113 (2008); http://dx.doi.org/10.1063/1.3042211 (3 pages) | Cited 4 times

Online Publication Date: 5 December 2008

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First-principles density functional theory (DFT) calculations were used to determine decohesion properties of Σ5(012) grain boundary of Ni with dopants B, C, S, Cr, and Hf. The relative stability of sites was evaluated and cleavage energies were calculated. Electronic structure was used to understand these properties in terms of changes in bonding with addition of dopants. It was found that strengthening of the Ni grain boundary results from Hf, B, and Cr doping. In contrast, the grain boundary weakens with S and C doping. These results should be useful in the design of next-generation nanostructured Ni-based alloys with improved mechanical behavior.
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61.72.U- Doping and impurity implantation
61.72.Mm Grain and twin boundaries
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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