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6 Sep 2004

Volume 85, Issue 10, pp. 1659-1861

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1793 (2004); http://dx.doi.org/10.1063/1.1790588 (3 pages)

Hyunsik Yoon, Kyoung Mi Lee, Dahl-Young Khang, Hong H. Lee, and Se-Jin Choi
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Tribonanolithography of silicon in aqueous solution based on atomic force microscopy

Jeong Woo Park, Noritaka Kawasegi, Noboru Morita, and Deug Woo Lee

Appl. Phys. Lett. 85, 1766 (); http://dx.doi.org/10.1063/1.1773620 (3 pages) | Cited 14 times

Online Publication Date: 13 September 2004

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The tribonanolithography (TNL) of silicon substrate in aqueous solution based on the use of atomic force microscopy is demonstrated. A specially designed cantilever with a diamond tip, which allows the formation of a protruding oxide layer several nanometers high using a simple machining process with a given pitch, was applied to the TNL process in KOH solution instead of a conventional silicon cantilever. The anisotropic wet etching stopped in the modified area because silicon oxide was resistant to corrosion by KOH. The fabrication of a three-dimensional slant nanostructure is possible by taking advantage of the time lag of oxide formation during etching in KOH solution.
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81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)

Temperature-dependent studies of Y-junction carbon nanotube electronic transport

C. Papadopoulos, A. J. Yin, and J. M. Xu

Appl. Phys. Lett. 85, 1769 (2004); http://dx.doi.org/10.1063/1.1787592 (3 pages) | Cited 9 times

Online Publication Date: 13 September 2004

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Electronic transport in Y-junction carbon nanotubes was examined as a function of temperature. Rectifying behavior was observed from 10 to 300 K with the conductance displaying power-law dependencies on temperature and applied bias. The data are consistent with models for tunneling between two tube segments but display asymmetric exponents depending on bias polarity. The conductance asymmetry is found to be essentially independent of temperature and can be understood from the lack of inversion symmetry of the Y-junction geometry, which creates a unique type of mesoscopic rectification for current flow in the nonlinear response regime.
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73.63.Fg Nanotubes
73.63.Rt Nanoscale contacts
73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification

Pentacene field-effect transistors with sub-10-nm channel lengths

Liang Wang, Daniel Fine, Taeho Jung, Debarshi Basu, Heinz von Seggern, and Ananth Dodabalapur

Appl. Phys. Lett. 85, 1772 (2004); http://dx.doi.org/10.1063/1.1790033 (3 pages) | Cited 39 times

Online Publication Date: 13 September 2004

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The field effect in pentacene thin-film transistors was studied using bottom-contact devices with channel lengths below 10 nm. To suppress spreading current in these devices, which have a small channel width-to-length (W-L) ratio, we employed a pair of guarding electrodes as close as 20 nm to the two sides of the channel. The responses of these nanometer scale transistors exhibit good gate modulation. Mobilities of 0.046 cm2∕Vs and on/off ratios of 97 were achieved in sub-10-nm transistors. We find that the device response is strongly influenced by the nature of the metal-semiconductor contact.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
73.40.Ns Metal-nonmetal contacts
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Reinforcement and rupture behavior of carbon nanotubes–polymer nanofibers

Haihui Ye, Hoa Lam, Nick Titchenal, Yury Gogotsi, and Frank Ko

Appl. Phys. Lett. 85, 1775 (2004); http://dx.doi.org/10.1063/1.1787892 (3 pages) | Cited 64 times

Online Publication Date: 13 September 2004

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High-resolution transmission electron microscopy examination of carbon nanotube–polyacrylonitrile composite fibers synthesized by electrospinning was conducted. Both single-wall carbon nanotubes and multi-wall carbon nanotubes have been used to reinforce the polymer fibers. A two-stage rupture behavior of the composite fibers under tension, including crazing of polymer matrix and pull-out of carbon nanotubes, has been observed. Carbon nanotubes reinforce the polymer fibers by hindering crazing extension, reducing stress concentration, and dissipating energy by pullout. Distribution of nanotubes in the polymer matrix and interfacial adhesion between nanotubes and polymers are two major factors to determine the reinforcement effect of carbon nanotubes in polymer fibers.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
81.05.ub Fullerenes and related materials
81.05.Qk Reinforced polymers and polymer-based composites
82.35.Gh Polymers on surfaces; adhesion

Molecular dynamics simulations of bending behavior of tubular graphite cones

P. Liu, Y. W. Zhang, and C. Lu

Appl. Phys. Lett. 85, 1778 (2004); http://dx.doi.org/10.1063/1.1787894 (3 pages) | Cited 2 times

Online Publication Date: 13 September 2004

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Molecular dynamics simulations are performed to investigate the bending behavior of tubular graphite cones (TGCs). The second-generation reactive bond-order potential and four different van der Waals potentials are used to describe bonding and nonbonding atomic interactions, respectively. It is shown that the bending behavior is insensitive to the choice of the van der Waals potentials. An increase in the cone apex angle of TGCs moderately improves the bending stiffness due to the low shear resistance between the nanotube walls. A TGC with a high cone apex angle is preferred to a TGC with a low cone apex angle in terms of bending stiffness and stress level. It is also shown that an increase in the diameter of the innermost nanotube effectively increases the bending stiffness of TGCs.
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61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Si-capping of Ge nanohuts on Si(001) analyzed by scanning tunneling microscopy and the finite element method

I. Goldfarb, L. Banks-Sills, and R. Eliasi

Appl. Phys. Lett. 85, 1781 (2004); http://dx.doi.org/10.1063/1.1787958 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2004

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Ge hut nanocrystals were grown on an Si(001) surface and Si-capped by gas-source molecular-beam epitaxy. Growth and capping at 430 °C were observed in real time by scanning tunneling microscopy, and analyzed by the finite element method. Observations made here of three-dimensional Si-cap growth (in the shape of pyramids and huts) on Ge, similar to the Ge growth on Si(001), are consistent with energetic arguments based on finite elements in the framework of linear elasticity. These observations are in contrast with the higher-temperature behavior, where Si preferentially sticks to the Ge nanocrystal facets, causing them to develop large flat (001) tops and a reduced height-base ratio.
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81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.46.-w Structure of nanoscale materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Manipulating the size distributions of quantum dots associated with strain-renormalized surface energy

T. P. Munt, D. E. Jesson, V. A. Shchukin, and D. Bimberg

Appl. Phys. Lett. 85, 1784 (2004); http://dx.doi.org/10.1063/1.1787943 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2004

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Utilizing computer simulations based on a continuity equation model, we propose a strategy for modifying three-dimensional quantum dot size distributions using a two-stage growth and anneal approach. The method simply requires that individual quantum dots have a minimum in their chemical potential as a function of island size, such as those associated with strain-renormalized surface energy. By depositing material for the required time, the island size distribution can be tuned to a desired size before removing the flux to narrow the distribution.
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81.07.Ta Quantum dots
68.35.Md Surface thermodynamics, surface energies
65.40.G- Other thermodynamical quantities
68.35.B- Structure of clean surfaces (and surface reconstruction)

Buckling instabilities in multiwalled carbon nanotubes under uniaxial compression

J. F. Waters, L. Riester, M. Jouzi, P. R. Guduru, and J. M. Xu

Appl. Phys. Lett. 85, 1787 (2004); http://dx.doi.org/10.1063/1.1790602 (3 pages) | Cited 30 times

Online Publication Date: 13 September 2004

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We report experimental observations of shell buckling instabilities in freestanding, vertically aligned multiwalled carbon nanotubes subjected to uniaxial compression. Highly ordered and uniform arrays of carbon nanotubes embedded in an alumina matrix were fabricated and subjected to uniaxial compression using a nanoindenter. The buckling load was found to be on the order of 2 μN for nanotubes with 25 nm outer radius, 13 nm inner radius, and heights of 50 and 100 nm. Good agreement was found between the experimental observations and the predictions of linear elastic shell buckling theory.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains

Observation of cold atom output from an evanescent-light funnel

Akifumi Takamizawa, Haruhiko Ito, Shungo Yamada, and Motoichi Ohtsu

Appl. Phys. Lett. 85, 1790 (2004); http://dx.doi.org/10.1063/1.1786362 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2004

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We report the demonstration of an atom funnel composed of evanescent light. The flux intensity of cold Rb atoms output from a 240 μm exit hole was 7×107 atom∕cm2 s at a blue detuning of 1.2 GHz. Sisyphus cooling doubled the output efficiency. The estimated flux intensity was 1012 atom∕cm2 s when the exit-hole diameter was 110 μm.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Rapid flash patterning of nanostructures

Hyunsik Yoon, Kyoung Mi Lee, Dahl-Young Khang, Hong H. Lee, and Se-Jin Choi

Appl. Phys. Lett. 85, 1793 (2004); http://dx.doi.org/10.1063/1.1790588 (3 pages) | Cited 9 times

Online Publication Date: 13 September 2004

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Sub-100 nm structures can be fabricated in tens of seconds with an aspect ratio much larger than unity by the general purpose patterning method presented here. A flexible film mold and a rapid flash heating with an infrared lamp are used in this nonphotolithographic patterning technique. Unlike other unconventional methods, the substrate surface can be made exposed and the resulting pattern height is sufficiently high for subsequent etching of the substrate.
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81.16.Rf Micro- and nanoscale pattern formation
68.55.-a Thin film structure and morphology
61.82.Pv Polymers, organic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Cf Surface cleaning, etching, patterning

Synthesis and electrical properties of carbon nanotube polyaniline composites

Yunze Long, Zhaojia Chen, Xuetong Zhang, Jin Zhang, and Zhongfan Liu

Appl. Phys. Lett. 85, 1796 (2004); http://dx.doi.org/10.1063/1.1786370 (3 pages) | Cited 37 times

Online Publication Date: 13 September 2004

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A multiwalled carbon nanotube∕polyaniline composite with cablelike morphology has been synthesized by an in situ chemical oxidative polymerization directed with cationic surfactant cetyltrimethylammonium bromide. It is interestingly found that with increasing carbon nanotube loading from 0 to 24.8 wt%, the conductivity increases by two orders of magnitude and the Mott’s characteristic temperature T0 which depends on the hopping barrier decreases by three orders of magnitude. Furthermore, the low-temperature magnetoresistance has also changed the sign from positive to negative. The results reveal a strong coupling between the carbon nanotube and the tightly coated polymer chains, which enhances the average localization length and the electronic properties of the composites.
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81.05.Qk Reinforced polymers and polymer-based composites
82.35.-x Polymers: properties; reactions; polymerization
72.80.Tm Composite materials
72.20.Ee Mobility edges; hopping transport
78.30.-j Infrared and Raman spectra
75.47.Pq Other materials

Ultrafast absorptive and refractive nonlinearities in multiwalled carbon nanotube films

H. I. Elim, W. Ji, G. H. Ma, K. Y. Lim, C. H. Sow, and C. H. A. Huan

Appl. Phys. Lett. 85, 1799 (2004); http://dx.doi.org/10.1063/1.1786371 (3 pages) | Cited 28 times

Online Publication Date: 13 September 2004

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By using femtosecond laser pulses at a wavelength range from 720 to 780 nm, we have observed absorptive and refractive nonlinearities in a film of multiwalled carbon nanotubes grown mainly along the direction perpendicular to the surface of quartz substrate. The z-scans show that both absorptive and refractive nonlinearities are of negative and cubic nature in the laser irradiance range from a few to 300 GW∕cm2. The magnitude of the third-order nonlinear susceptibility, χ(3), is of an order of 10−11 esu. The degenerate pump–probe measurement reveals a relaxation time of ∼2 ps.
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78.67.Ch Nanotubes
42.65.An Optical susceptibility, hyperpolarizability
78.40.Ri Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Synthesis of semiconductor nanowires by annealing

C. Y. Zhi, X. D. Bai, and E. G. Wang

Appl. Phys. Lett. 85, 1802 (2004); http://dx.doi.org/10.1063/1.1786374 (3 pages) | Cited 8 times

Online Publication Date: 13 September 2004

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Semiconductor nanowires, such as InAs, InP, β-Ga2O3, and GaP are synthesized by annealing semiconductor wafers covered with Au film at an appropriate temperature in the region of 550°–650°C in a N2 atmosphere. The composition of the resulting semiconductor nanowires is determined by both the substrate and the chemical conditions of growth. High-resolution transmission electron microscopy and selected area electron diffraction reveal high degrees of crystallization of the as-grown nanowires. The characteristics of the annealing method for synthesis of semiconductor nanowires are discussed.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.70.K- Solid-solid transitions
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Thin film transistors fabricated by in situ growth of SnO2 nanobelts on Au∕Pt electrodes

Q. H. Li, Y. J. Chen, Q. Wan, and T. H. Wang

Appl. Phys. Lett. 85, 1805 (2004); http://dx.doi.org/10.1063/1.1789232 (3 pages) | Cited 9 times

Online Publication Date: 13 September 2004

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Thin film transistors are fabricated by in situ growth of SnO2 nanobelts on Au∕Pt electrodes. A linear correlation in the output characteristics is observed at zero gate voltage, indicating Ohmic contacts between the nanobelts and the electrodes. The transistors exhibit n-type behaviors and have a mobility of 1.85 cm2∕V s with a current on∕off ratio above 103. The conductance increases as the pressure in the device chamber is reduced, which indicates that the transistors are promising for oxygen detecting.
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85.30.Tv Field effect devices
61.46.-w Structure of nanoscale materials
73.40.Ns Metal-nonmetal contacts
73.50.Dn Low-field transport and mobility; piezoresistance
81.16.Nd Micro- and nanolithography
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

GaAs∕AlGaAs nanowires capped with AlGaAs layers on GaAs(311)B substrates

K. Tateno, H. Gotoh, and Y. Watanabe

Appl. Phys. Lett. 85, 1808 (2004); http://dx.doi.org/10.1063/1.1789234 (3 pages) | Cited 19 times

Online Publication Date: 13 September 2004

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We have investigated GaAs∕AlGaAs nanowires capped with AlGaAs layers for optical device applications. GaAs nanowires are not so stable during AlGaAs capping growth at high temperature. However, AlGaAs nanowires retain their shapes, and GaAs nanowires sandwiched between AlGaAs wires were capped at temperatures as high as 700°C. The capped structures showed sharp photoluminescence peaks at around 730 nm at 4 K, which originated from excitons in quantum wires. We confirmed that the AlGaAs capping layers were grown smoothly around nanowires so that surface recombination centers in GaAs nanowires were reduced compared with air-exposed GaAs wires.
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81.07.Vb Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
78.67.Lt Quantum wires
73.22.Lp Collective excitations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nanoscale modification of electrical and magnetic properties of Fe3O4 thin film by atomic force microscopy lithography

Motoyuki Hirooka, Hidekazu Tanaka, Runwei Li, and Tomoji Kawai

Appl. Phys. Lett. 85, 1811 (2004); http://dx.doi.org/10.1063/1.1784884 (3 pages) | Cited 13 times

Online Publication Date: 13 September 2004

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We present a report on the nanopatterning of an epitaxial ultrathin film of Fe3O4 with room-temperature (ferri)magnetism using atomic force microscopy (AFM). Fe3O4 thin films with atomically flat surfaces were grown using laser molecular-beam epitaxy on a MgAl2O4(111) single-crystal substrate. (Nanowire) were constructed on Fe3O4 thin film by applying an electric field between an AFM conductive tip and the surface of the film. The minimum width and height in the resulting nanowire are 48 nm and 2 nm, respectively. The patterned region of the Fe3O4 film surface possesses a resistance which is 105 times higher than the unpatterned region. Furthermore, magnetic force microscopy measurements also revealed that magnetization of the patterned region is strongly suppressed.
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68.37.Ps Atomic force microscopy (AFM)
81.16.Nd Micro- and nanolithography
75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.62.-b Laser applications
61.46.-w Structure of nanoscale materials
68.37.Rt Magnetic force microscopy (MFM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Pq Other materials
73.25.+i Surface conductivity and carrier phenomena
75.50.Tt Fine-particle systems; nanocrystalline materials
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