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19 Sep 2005

Volume 87, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 123111 (2005); http://dx.doi.org/10.1063/1.2053370 (3 pages)

Xianghui Zhang, Ye Zhang, Jun Xu, Zhe Wang, Xihong Chen, Dapeng Yu, Peng Zhang, Hanhong Qi, and Yongjun Tian
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Effects of radial breathing mode phonons on charge transport in semiconducting zigzag carbon nanotubes

A. Verma, M. Z. Kauser, and P. P. Ruden

Appl. Phys. Lett. 87, 123101 (2005); http://dx.doi.org/10.1063/1.2043244 (3 pages) | Cited 11 times

Online Publication Date: 12 September 2005

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We report ensemble Monte Carlo transport simulation results for single-wall semiconducting zigzag carbon nanotubes. The effects of electron scattering by radial breathing mode phonons are investigated. The basis for the Monte Carlo simulations is provided by electronic structure calculations in the framework of the tight-binding model. Scattering mechanisms considered are due to electron-phonon interactions involving longitudinal acoustic, longitudinal optical, and radial breathing mode phonons. The steady-state velocity is lower for low and moderate electric fields when radial breathing mode phonons are taken into account. Electron scattering by radial breathing mode phonons does not appear to affect strongly the steady-state electron transport within a carbon nanotube at high electric fields. Oscillations in the transient velocity show increased damping.
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73.63.Fg Nanotubes
72.20.Fr Low-field transport and mobility; piezoresistance
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.61.Cw Elemental semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.22.-f Electronic structure of nanoscale materials and related systems

Chlorophyll-layer-inserted poly(3-hexyl-thiophene) solar cell having a high light-to-current conversion efficiency up to 1.48%

Je-Jung Yun, Ho-Seok Jung, Sung-Han Kim, Eun-Mi Han, Veeramuthu Vaithianathan, and Samson A. Jenekhe

Appl. Phys. Lett. 87, 123102 (2005); http://dx.doi.org/10.1063/1.2051804 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2005

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We report the fabrication of a chlorophyll-layer-inserted poly(3-hexyl-thiophene) (P3HT) solar cell. A significant enhancement in the light-to-current conversion efficiency of up to 1.48% with a fill factor of 0.32 was achieved in a solar cell with a device structure of indium tin oxide anode/poly (3,4-ethylene dioxy-thiophene):poly(styrene sulfonate)/P3HT/chlorophyll/Al cathode under the standard air mass 1.5 irradiation (20 mW/cm2). These results suggest that the generation of an internal electric field is mainly due to a difference between the highest occupied molecular orbital of the P3HT (donor) and the lowest unoccupied molecular orbital of the chlorophyll (acceptor), which permits the transfer of photoinduced electrons from P3HT to chlorophyll.
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84.60.Jt Photoelectric conversion
71.55.Ht Other nonmetals

Microwave attenuation of multiwalled carbon nanotube-fused silica composites

Changshu Xiang, Yubai Pan, Xuejian Liu, Xingwei Sun, Xiaomei Shi, and Jingkun Guo

Appl. Phys. Lett. 87, 123103 (2005); http://dx.doi.org/10.1063/1.2051806 (3 pages) | Cited 39 times

Online Publication Date: 12 September 2005

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Multiwalled carbon nanotubes (MWCNTs) were used to convert radome materials to microwave absorbing materials. Dense MWCNT-fused silica composites were prepared by hot-pressing technique. The composites exhibit high complex permittivities at X-band frequencies, depending on the content of MWCNTs. The value of the loss tangent increases three orders over pure fused silica only by incorporating 2.5 vol % MWCNTs into the composites. The average magnitude of microwave transmission reaches −33 dB at 11–12 GHz in the 10 vol % MWCNT-fused silica composites, which indicates the composites have excellent microwave attenuation properties. The attenuation properties mainly originate from the electric loss of MWCNTs by the motion of conducting electrons.
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81.05.Pj Glass-based composites, vitroceramics
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.80.Tm Composite materials
73.63.-b Electronic transport in nanoscale materials and structures
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Pattern preserving deposition: Experimental results and modeling

Marcos F. Castez, Mariano H. Fonticelli, Omar Azzaroni, Roberto C. Salvarezza, and Hernán G. Solari

Appl. Phys. Lett. 87, 123104 (2005); http://dx.doi.org/10.1063/1.2053368 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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In this work we discuss pattern-preserving growth during metal deposition from the vapor on micro/nano-structured metal substrates. Experimental results for Cu deposition on patterned Cu substrates show pattern preserving growth or pattern destruction depending on the incident angle. We introduce a mesoscopic 1+1 dimensional model including deposition flow (directed and isotropic), surface diffusion and shadowing effects that account for the experimental growth data. Moreover, simulations on post-deposition annealing, for high aspect-ratio patterns show departures from the predictions of the linear theory for surface diffusion.
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68.55.A- Nucleation and growth
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
81.16.Rf Micro- and nanoscale pattern formation

Surface-enhanced Raman scattering sensor based on D-shaped fiber

Y. Zhang, C. Gu, A. M. Schwartzberg, and J. Z. Zhang

Appl. Phys. Lett. 87, 123105 (2005); http://dx.doi.org/10.1063/1.2051799 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2005

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Fiber surface-enhanced Raman scattering (SERS) sensors show great potential for in vivo and in vitro detection. However, current probes based on end-polished fibers suffer from small signal due to their small active region. To overcome this, we propose and demonstrate a D-shaped fiber configuration to increase the detection area. Initial modeling has shown that most of the light can be absorbed by the SERS active layer coated on the polished fiber surface. A several orders of magnitude increase in surface area leads to substantially more detectable Raman scattered photons than those in end-tip configurations. The SERS sensor based on D-shaped fibers has been demonstrated with excellent results using rhodamine 6G.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.30.Jw Organic compounds, polymers
82.80.-d Chemical analysis and related physical methods of analysis

Nanoindentation study of nanofibers

E. P. S. Tan and C. T. Lim

Appl. Phys. Lett. 87, 123106 (2005); http://dx.doi.org/10.1063/1.2051802 (3 pages) | Cited 27 times

Online Publication Date: 13 September 2005

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Nanoindentation study of a single poly(L-lactic acid) nanofiber produced by the phase separation method was performed using an atomic force microscope (AFM) cantilever tip. Issues concerning the use of AFM for nanoindentation of polymer nanofibers were discussed. The Hertz theory of contact mechanics was used to analyze the indentation results. It was found that the elastic modulus was comparable to that obtained from the nanoscale three-point bend test done in our previous study, after roughness correction was made.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
62.25.-g Mechanical properties of nanoscale systems
68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.46.-w Structure of nanoscale materials
64.75.-g Phase equilibria
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Mn Polymer surfaces

Shot noise in metallic double dot structures with a negative differential conductance

V. Hung Nguyen, V. Lien Nguyen, and Philippe Dollfus

Appl. Phys. Lett. 87, 123107 (2005); http://dx.doi.org/10.1063/1.2053371 (3 pages) | Cited 9 times

Online Publication Date: 13 September 2005

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The shot noise of current through a metallic double quantum dot structure exhibiting negative differential conductance is studied. We can exactly solve the master equation and derive an analytical expression of the spectral density of current fluctuations as a function of frequency in the first Coulomb staircase region. For a large range of bias voltage the noise is calculated by Monte Carlo simulation. We show that the noise is always sub-Poissonian though it is considerably enhanced in the negative differential conductance regime.
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73.63.Kv Quantum dots
73.40.Gk Tunneling

Synthesis, electrical and photoresponse properties of vertically well-aligned and epitaxial ZnO nanorods on GaN-buffered sapphire substrates

Jae Young Park, Young Su Yun, Yong Sung Hong, Hwangyou Oh, Ju-Jin Kim, and Sang Sub Kim

Appl. Phys. Lett. 87, 123108 (2005); http://dx.doi.org/10.1063/1.2053365 (3 pages) | Cited 23 times

Online Publication Date: 13 September 2005

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Vertically well-aligned and epitaxial ZnO nanorod arrays (NRAs) were synthesized by catalyst-free metalorganic chemical vapor deposition on Al2O3 (0001) substrates particularly using an epitaxially grown GaN buffer layer. ZnO NRAs grown directly on Al2O3 (0001) substrates are aligned vertically, but randomly oriented in the lateral direction to the substrates. In sharp contrast, ZnO NRAs grown with a GaN buffer layer show an excellent vertical and epitaxial alignment with mosaic distributions of 0.11° and 1.28° in the out-of- and the in-plane directions, respectively. The electrical measurements using field effect transistors based on individual ZnO nanorods show a pronounced n-type gate modulation with an electron concentration of ∼ 7.5×1017 cm−3 and an electron mobility of ∼ 25.1 cm2/V s at a bias voltage of 1 V, while showing quite a high on/off ratio exceeding ∼ 105. In addition, their high on/off conductivity ratio of ∼ 103 with UV light gives a potential of their use in nanoscale UV detectors.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Dz II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors

Polymer nanofibers by soft lithography

Dario Pisignano, Giuseppe Maruccio, Elisa Mele, Luana Persano, Francesca Di Benedetto, and Roberto Cingolani

Appl. Phys. Lett. 87, 123109 (2005); http://dx.doi.org/10.1063/1.2046731 (3 pages) | Cited 11 times

Online Publication Date: 13 September 2005

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The fabrication of polymeric fibers by soft lithography is demonstrated. Polyurethane, patterned by capillarity-induced molding with high-resolution elastomeric templates, forms mm-long fibers with a diameter below 0.3 μm. The Young’s modulus of the fabricated structures, evaluated by force-distance scanning probe spectroscopy, has a value of 0.8 MPa. This is an excellent example of nanostructures feasible by the combination of soft nanopatterning and high-resolution fabrication approaches for master templates, and particularly electron-beam lithography.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
61.46.-w Structure of nanoscale materials
61.41.+e Polymers, elastomers, and plastics
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.37.Ps Atomic force microscopy (AFM)

Multilayer and functional coatings on carbon nanotubes using atomic layer deposition

C. F. Herrmann, F. H. Fabreguette, D. S. Finch, R. Geiss, and S. M. George

Appl. Phys. Lett. 87, 123110 (2005); http://dx.doi.org/10.1063/1.2053358 (3 pages) | Cited 24 times

Online Publication Date: 14 September 2005

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Atomic layer deposition (ALD) can be used to deposit ultra-thin and conformal films on flat substrates, high aspect ratios structures and particles. In this paper, we demonstrate that insulating, multilayered and functionalized ALD coatings can also be deposited conformally on carbon nanotubes. Multilayered coatings consisting of alternating layers of dielectric and conductive materials, such as Al2O3 and W, respectively, are deposited on conductive multi-walled carbon nanotubes. This coated carbon nanotube can function as a nanoscale coaxial cable. Thin layers of Al2O3 ALD are also used as a seed layer to functionalize nanotubes. A carbon nanotube was made highly hydrophobic using an Al2O3 ALD seed layer followed by the attachment of perfluorinated molecules.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Peculiar ZnO nanopushpins and nanotubes synthesized via simple thermal evaporation

Xianghui Zhang, Ye Zhang, Jun Xu, Zhe Wang, Xihong Chen, Dapeng Yu, Peng Zhang, Hanhong Qi, and Yongjun Tian

Appl. Phys. Lett. 87, 123111 (2005); http://dx.doi.org/10.1063/1.2053370 (3 pages) | Cited 33 times

Online Publication Date: 15 September 2005

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ZnO nanostructures with peculiar morphology were synthesized in large quantities via catalyst-free thermal evaporation. Both ZnO nanopushpins with very thin and flat cap on top of the nanorods, and regular hexagonal nanotubes, can be obtained in the same run of growth in different regions. The ZnO nanopushpins and nanotubes were characterized by using scanning electron microscopy and transmission electron microscopy. Cathodoluminescence measurements revealed that the emission from oxygen vacancy overwhelmed that of the near band gap in the as-grown ZnO nanotube arrays.
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81.05.Dz II-VI semiconductors
81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
78.67.Ch Nanotubes
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.J- Point defects and defect clusters

Atomic-level strain-relieving mechanism and local electronic structure of a wetting film

Tae-Hwan Kim, Jungpil Seo, Byoung-Young Choi, Young Jae Song, Jehyuk Choi, Young Kuk, and Se-Jong Kahng

Appl. Phys. Lett. 87, 123112 (2005); http://dx.doi.org/10.1063/1.2035325 (3 pages)

Online Publication Date: 16 September 2005

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The strain-relieving mechanism and local electronic density of states of a wetting film, was studied in the Ag/W system using scanning tunneling microscopy and spectroscopy. In the Ag wetting film, a periodic bright ridge structure was observed along the two equivalent directions, relieving mixed compressive-tensile strain. Two unoccupied electronic states were observed between the ridges, while the other two occupied electronic states were observed at the ridges. The Ag atoms occupying the bridge sites contribute to relieve the elastic strain and to induce the occupied electronic states.
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73.20.At Surface states, band structure, electron density of states
68.60.Bs Mechanical and acoustical properties
68.08.Bc Wetting

Rectifying “nanohomo” contacts of W–Ga–C composite pad and nanowire fabricated by focused-ion-beam-induced chemical vapor deposition

Wuxia Li and Tiehan H. Shen

Appl. Phys. Lett. 87, 123113 (2005); http://dx.doi.org/10.1063/1.2051798 (3 pages) | Cited 3 times

Online Publication Date: 16 September 2005

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We prepared W–Ga–C composite contacts on W–Ga–C composite nanowires by focused-ion-beam-induced chemical vapor deposition using a dual-beam scanning electron microscope∕focused-ion-beam system. The current-voltage (I‐V) characteristics of wires were found to change from nonlinear to linear with increasing wire thickness. For wires with small dimensions, which result in strong nonlinear I‐V behavior at room temperature, pairs of contacts were fabricated along the wire under different ion energies and scanning modes. Nonlinear and asymmetric rectifying I‐V characteristics were observed. The results suggest that nanoscaled W–Ga–C nanowires may behave similarly to semiconductors and that the contact characteristics may be modified using different deposition conditions. Furthermore, ohmiclike junctions could be formed through the use of specific deposition conditions for the contact pads and nanowires.
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73.40.Ei Rectification
73.63.Nm Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Photoluminescence from silicon nanoparticles prepared from bulk amorphous silicon monoxide by the disproportionation reaction

V. Kapaklis, C. Politis, P. Poulopoulos, and P. Schweiss

Appl. Phys. Lett. 87, 123114 (2005); http://dx.doi.org/10.1063/1.2043246 (3 pages) | Cited 15 times

Online Publication Date: 16 September 2005

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We report on strong photoluminescence of Si-based materials produced in large quantities. This is achieved by the disproportionation action of commercial bulk silicon monoxide at temperatures above 850 °C which results in the formation of Si nanocrystals surrounded by an amorphous silicon oxide matrix. High-resolution electron microscopy investigations reveal a broad size distribution of the silicon nanocrystals with a maximum at 4–4.5 nm, for samples annealed at 900 and 950 °C. X-ray diffraction and photoluminescence spectra indicate the coexistence of amorphous Si clusters in the samples, that have not fully undergone the amorphous/crystalline transition. This method could be suitable for the production in large quantities of Si-based bulk photoluminescent materials.
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78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing

Fabrication of high-density arrays of individually isolated nanocapacitors using anodic aluminum oxide templates and carbon nanotubes

Jung Inn Sohn, Youn-Su Kim, Chunghee Nam, B. K. Cho, Tae-Yeon Seong, and Seonghoon Lee

Appl. Phys. Lett. 87, 123115 (2005); http://dx.doi.org/10.1063/1.2048815 (3 pages) | Cited 15 times

Online Publication Date: 16 September 2005

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We have fabricated high-density arrays of individually isolated semispherical nanocapacitors consisting of porous anodic aluminum oxide (AAO) layers as dielectric materials and carbon nanotubes (CNTs) as electrodes. It is shown that the nanocapacitors made with the CNT electrodes exhibit much better C-V behaviors than those without the CNT electrodes. The improved electrical behavior is explained in terms of the use of the CNT electrodes deposited within the porous AAO layers. The capacitance calculated using semispherical capacitor formula is in agreement with the experimental value.
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84.32.Tt Capacitors
81.16.-c Methods of micro- and nanofabrication and processing
81.65.-b Surface treatments
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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