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27 Aug 2007

Volume 91, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 093110 (2007); http://dx.doi.org/10.1063/1.2775801 (3 pages)

M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, G. J. Salamo, D. Grigoriev, P. Schäfer, R. Köhler, and M. Hanke
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Enhanced electromagnetic wave absorption properties of Fe nanowires in gigaherz range

Jiu-rong Liu, Masahiro Itoh, Masao Terada, Takashi Horikawa, and Ken-ichi Machida

Appl. Phys. Lett. 91, 093101 (2007); http://dx.doi.org/10.1063/1.2775804 (3 pages) | Cited 41 times

Online Publication Date: 28 August 2007

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Fe nanowires with 70–200 nm in diameter and 20–50 μm in length were synthesized by a chemical vapor deposition method for electromagnetic wave absorption application. The frequency dependences of relative permittivity (εr) and permeability (μr) were strongly dependent on the diameter of Fe wires. Compared with micrometer wires or flakelike samples, nanowires exhibited a magnetic resonance (μr″) peak in the range of 1–18 GHz, suggesting that nanowires have significant effect for reducing the eddy current loss, therefore, the resin compacts of 29 vol % Fe nanowires with thicknesses of 1.3–4.0 mm provided good electromagnetic wave absorption performances in the range of 5.6–18 GHz.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
78.70.Gq Microwave and radio-frequency interactions

Torsional stiffening of carbon nanotube systems

Byeong-Woo Jeong, Jang-Keun Lim, and Susan B. Sinnott

Appl. Phys. Lett. 91, 093102 (2007); http://dx.doi.org/10.1063/1.2775832 (3 pages) | Cited 19 times

Online Publication Date: 28 August 2007

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The torsional responses of hollow and filled carbon nanotubes under a combination of tension and torsion are examined using classical molecular dynamics simulations. The critical torsional moment and shear modulus are predicted to significantly increase as a result of coupling between tension and torsion. In particular, the simulations predict that the torsional responses under this type of combined loading are beyond the linear responses of the nanotubes. Importantly, the coupling effect between tension and torsion also increases the torsional stiffness and oscillation frequency of the nanotubes.
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81.05.ub Fullerenes and related materials
81.07.De Nanotubes
81.40.Jj Elasticity and anelasticity, stress-strain relations

Fluxon-based gate controls of capacitively coupled flux-based-phase qubits

Shigemasa Matsuo, Kanoko Furuta, Toshiyuki Fujii, Katsuhiko Nagai, and Noriyuki Hatakenaka

Appl. Phys. Lett. 91, 093103 (2007); http://dx.doi.org/10.1063/1.2772770 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2007

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The authors propose a scheme for controlling the gate operation for qubit-qubit interactions in superconducting flux-based phase qubits using a moving fluxon. The basic unit is composed of three capacitively coupled flux-based phase qubits. One of the qubits acts as a switch connecting the other two (two logical qubits) with an identical energy separation. The fluxon controls the energy separation of the switch qubit via its inductive coupling, leading to the resonance among qubits appropriately adjusting the fluxon velocity. As a result, the resonance is capable of performing a gate operation between two logical qubits.
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03.67.Lx Quantum computation architectures and implementations
85.25.Cp Josephson devices

Nonlinear optical scattering and absorption in bismuth nanorod suspensions

S. Sivaramakrishnan, V. S. Muthukumar, S. Sivasankara Sai, K. Venkataramaniah, Jason Reppert, Apparao M Rao, M. Anija, Reji Philip, and Narayanan Kuthirummal

Appl. Phys. Lett. 91, 093104 (2007); http://dx.doi.org/10.1063/1.2776020 (3 pages) | Cited 24 times

Online Publication Date: 28 August 2007

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The authors present the results of optical limiting measurements of ∼ 10 nm wide bismuth nanorods suspended in chloroform. Their Z-scan measurements reveal that optical limiting under 532 nm excitation stems from a strong nonlinear scattering (NLS) subsequent to nonlinear absorption (NLA) by suspension. On the other hand, the optical limiting is entirely due to NLA when excited with 1064 nm excitation in the nanosecond regime. The occurrence of NLS at one wavelength and absence at another is unusual, especially when compared to the behavior of carbon nanotubes under similar conditions, in which NLS is dominant at both wavelengths.
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78.66.Bz Metals and metallic alloys
42.65.-k Nonlinear optics
61.46.-w Structure of nanoscale materials
82.70.Kj Emulsions and suspensions

Correlating electrical resistance to growth conditions for multiwalled carbon nanotubes

Chun Lan, Placidus B. Amama, Timothy S. Fisher, and Ronald G. Reifenberger

Appl. Phys. Lett. 91, 093105 (2007); http://dx.doi.org/10.1063/1.2776022 (3 pages) | Cited 8 times

Online Publication Date: 28 August 2007

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A correlation between growth temperature and electrical resistance of multiwalled carbon nanotubes (MWNTs) has been established by measuring the resistance of individual MWNTs grown by microwave plasma-enhanced chemical vapor deposition (PECVD) at 800, 900, and 950 °C. The lowest resistances were obtained mainly from MWNTs grown at 900 °C. The MWNT resistance is larger on average at lower (800 °C) and higher (950 °C) growth temperatures. The resistance of MWNTs correlated well with other MWNT quality indices obtained from Raman spectra. This study identifies a temperature window for growing higher-quality MWNTs with fewer defects and lower resistance by PECVD.
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81.07.De Nanotubes
73.63.Fg Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition

Role of defect states on Auger processes in resonantly pumped CdSe nanorods

Arianna Cretí, Marco Anni, Margherita Zavelani Rossi, Guglielmo Lanzani, Liberato Manna, and Mauro Lomascolo

Appl. Phys. Lett. 91, 093106 (2007); http://dx.doi.org/10.1063/1.2776847 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2007

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The authors investigated, by femtosecond pump-probe measurements, the effects on Auger and trapping processes of excitation resonant (R) to the 1S absorption in CdSe nanorods. They demonstrate that R pumping allows one to avoid exciton trapping in high energy defect states and that the presence of empty defect states leads to an enhancement of the Auger relaxation, with respect to the pumping at energies high above the band gap. Moreover, they show that, despite the Auger enhancement, R pumping increases the stimulated emission lifetime demonstrating that it is not limited by Auger scattering, as widely believed, but by photoabsorption processes, involving defect states.
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71.55.Gs II-VI semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.47.-p Spectroscopy of solid state dynamics
78.45.+h Stimulated emission

High resolution spectroscopic and microscopic signatures of ordered growth of ferrous sulfate in SO2 assisted corrosion of Fe3O4(100)

D. Stoltz, A. Önsten, U. O. Karlsson, and M. Göthelid

Appl. Phys. Lett. 91, 093107 (2007); http://dx.doi.org/10.1063/1.2776854 (3 pages) | Cited 1 time

Online Publication Date: 28 August 2007

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The authors present a high-resolution core-level photoemission study of a Fe3O4(100) surface exposed to 50 L (1 L = 10−6 mbar s) of H2O and 50 L of SO2. S 2p core-level spectra reveal the presence of SO3 and SO4 species. An additional peak in the Fe 3p core-level spectrum shows that they bond with iron from the substrate. Complementary scanning tunneling microscopy of the same surface demonstrates formation of a long-range ordered sulfate locked in the (math×math)R45°-surface potential.
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81.65.Kn Corrosion protection
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Controlling bistability in tapping-mode atomic force microscopy using dual-frequency excitation

Phanikrishna Thota, Scott MacLaren, and Harry Dankowicz

Appl. Phys. Lett. 91, 093108 (2007); http://dx.doi.org/10.1063/1.2775031 (3 pages) | Cited 13 times

Online Publication Date: 28 August 2007

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This letter discusses an experimental method to suppress spontaneous transitions between low- and high-amplitude oscillatory responses in tapping-mode atomic force microscopy in the absence of feedback control. Here, the cantilever is excited at two frequencies and the dynamic force curves for different excitation amplitudes are recorded. Experimental observations of the dual-frequency excitation strategy are reported for three different cantilevers. These suggest that such transitions may indeed be eliminated from a region of interest of separations between the sample surface and the average position of the cantilever support even with relatively small secondary excitation amplitudes.
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07.79.Lh Atomic force microscopes

Tuneable visible resonances in crescent shaped nano-split-ring resonators

A. W. Clark, A. K. Sheridan, A. Glidle, D. R. S. Cumming, and J. M. Cooper

Appl. Phys. Lett. 91, 093109 (2007); http://dx.doi.org/10.1063/1.2772180 (3 pages) | Cited 24 times

Online Publication Date: 28 August 2007

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Electron beam lithography was used to fabricate gold crescent shaped split-ring resonators with 30 nm minimum feature size. By varying the crescent’s arc length over a range of nanometer-scale dimensions the authors demonstrate the tuneability of visible resonances within such structures. Results, which correlate closely with those predicted using finite-difference time-domain modeling, open the way for these devices to be used in near-field biological sensing.
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84.40.Az Waveguides, transmission lines, striplines
81.16.Nd Micro- and nanolithography
42.82.Cr Fabrication techniques; lithography, pattern transfer

Initial stages of chain formation in a single layer of (In,Ga)As quantum dots grown on GaAs (100)

M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, G. J. Salamo, D. Grigoriev, P. Schäfer, R. Köhler, and M. Hanke

Appl. Phys. Lett. 91, 093110 (2007); http://dx.doi.org/10.1063/1.2775801 (3 pages) | Cited 9 times

Online Publication Date: 28 August 2007

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The self-organized formation of In0.40Ga0.60As quantum dot chains was investigated using x-ray scattering. Two samples were compared grown on GaAs(100) by molecular beam epitaxy. The first sample with a single layer of In0.40Ga0.60As dots shows weak quantum dot alignment and a corresponding elongated shape along [0math1], while the top layer of a multilayered In0.40Ga0.60As/GaAs sample exhibits extended and highly regular quantum dot chains oriented along [0math1]. Numerical calculations of the three-dimensional strain fields are used to explain the initial stages of chain formation by anisotropic strain relaxation induced by the elongated dot shape.
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81.16.Dn Self-assembly
78.70.Ck X-ray scattering
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Hb Quantum dots (patterned in quantum wells)

Focal length modulation based on a metallic slit surrounded with grooves in curved depths

Haofei Shi, Chunlei Du, and Xiangang Luo

Appl. Phys. Lett. 91, 093111 (2007); http://dx.doi.org/10.1063/1.2776875 (3 pages) | Cited 40 times

Online Publication Date: 29 August 2007

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According to the numerical calculation, the relative phase of emitting light scattered by surface plasmon in a single subwavelength metallic groove can be modulated by the groove depth. The focal length of the slit-groove-based focusing structures can be adjusted in certain value if the groove depths are arranged in traced profile. With the regulation of the groove depth profile, it is possible to modify the focus position in the precision of nanoscale without increasing the size of the nanodevice. The simulation results verify that the method is effective for the design of nano-optical devices such as optical microprobes.
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78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Nanomechanical displacement detection using fiber-optic interferometry

N. O. Azak, M. Y. Shagam, D. M. Karabacak, K. L. Ekinci, D. H. Kim, and D. Y. Jang

Appl. Phys. Lett. 91, 093112 (2007); http://dx.doi.org/10.1063/1.2776981 (3 pages) | Cited 13 times

Online Publication Date: 29 August 2007

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We describe a fiber-optic interferometer to detect the motion of nanomechanical resonators. In this system, the primary technical challenge of aligning the fiber-optic probe to nanometer-scale resonators is overcome by simply monitoring the scattered light from the devices. The system includes no free-space optical components, and is thus simple, stable, and compact with an estimated displacement sensitivity of ∼ 0.3 pm/math at optical power levels of ∼ 0.75 mW.
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42.81.Pa Sensors, gyros
07.60.Ly Interferometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Axial and radial growth of Ni-induced GaN nanowires

L. Geelhaar, C. Chèze, W. M. Weber, R. Averbeck, H. Riechert, Th. Kehagias, Ph. Komninou, G. P. Dimitrakopulos, and Th. Karakostas

Appl. Phys. Lett. 91, 093113 (2007); http://dx.doi.org/10.1063/1.2776979 (3 pages) | Cited 33 times

Online Publication Date: 29 August 2007

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GaN nanowires (NWs) were grown on sapphire by molecular beam epitaxy. NWs form only in the presence of Ni seed particles and only under N-rich conditions. Their length increases linearly with growth time up to about 7.5 μm while their diameter remains almost constant. In contrast, a switch to Ga-rich conditions after NW formation results in radial growth, i.e., the NW diameter increases while lengthening is negligible. These results corroborate the fact that the growth of III-V NWs is governed by the accumulation of group-III atoms in the seeds, while group-V species are not preferentially incorporated at the seeds.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.La Quantum wires (patterned in quantum wells)
81.16.-c Methods of micro- and nanofabrication and processing

Domain wall displacement by current pulses injection in submicrometer Permalloy square ring structures

P. Vavassori, V. Metlushko, and B. Ilic

Appl. Phys. Lett. 91, 093114 (2007); http://dx.doi.org/10.1063/1.2777156 (3 pages) | Cited 11 times

Online Publication Date: 29 August 2007

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The magnetoresistance in submicrometer Permalloy square ring structures has been experimentally measured and modeled. The authors show that using an external field they can place a head-to-head domain wall at a selected corner of the ring and sense its position by magnetoresistance. They finally demonstrate that a domain wall can be reversibly and controllably displaced by current pulses of different polarity. Their observations can be explained by a directional spin-torque effect.
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75.60.Ch Domain walls and domain structure
75.47.Np Metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects

Pt nanocrystals formed by ion implantation: A defect-mediated nucleation process

R. Giulian, P. Kluth, L. L. Araujo, D. J. Llewellyn, and M. C. Ridgway

Appl. Phys. Lett. 91, 093115 (2007); http://dx.doi.org/10.1063/1.2777165 (3 pages) | Cited 9 times

Online Publication Date: 29 August 2007

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The influence of ion irradiation of SiO2 on the size of metal nanocrystals (NCs) formed by ion implantation has been investigated. Thin SiO2 films were irradiated with high-energy Ge ions then implanted with Pt ions. Without Ge irradiation, the largest Pt NCs were observed beyond the Pt projected range. With irradiation, Ge-induced structural modification of the SiO2 layer yielded a decrease in Pt NC size with increasing Ge fluence at such depths. A defect-mediated NC nucleation mechanism is proposed and a simple yet effective means of modifying and controlling the Pt NC size is demonstrated.
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61.46.Hk Nanocrystals
61.72.up Other materials
61.82.Rx Nanocrystalline materials
61.80.Jh Ion radiation effects
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Brillouin study of acoustic phonon confinement in GeO2 nanocubes

Y. Li, H. S. Lim, S. C. Ng, M. H. Kuok, M. Y. Ge, and J. Z. Jiang

Appl. Phys. Lett. 91, 093116 (2007); http://dx.doi.org/10.1063/1.2777174 (3 pages) | Cited 2 times

Online Publication Date: 29 August 2007

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Brillouin light scattering from several aggregates of monodisperse GeO2 nanocubes has been measured. Six well-resolved spectral peaks are observed whose frequencies scale as 1/L, where L is the cube edge length. A finite element analysis of the eigenvibrations of a free nanocube reveals that the peaks are due to acoustic phonon confinement. Simulations show that the lowest-energy mode has a predominantly torsionallike character. The elastic constants of the nanocubes are found to be much lower than those of bulk GeO2.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.35.+c Brillouin and Rayleigh scattering; other light scattering
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Electron transport properties in ZnO nanowire array/nanoparticle composite dye-sensitized solar cells

Chen-Hao Ku and Jih-Jen Wu

Appl. Phys. Lett. 91, 093117 (2007); http://dx.doi.org/10.1063/1.2778454 (3 pages) | Cited 69 times

Online Publication Date: 29 August 2007

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A significant improvement of the efficiency of the ZnO nanowire (NW) dye-sensitized solar cell (DSSC) has been achieved by the chemical bath deposition of the dense nanoparticles (NPs) within the interstices of the vertical ZnO-NW anode. Impedance analyses of the electron transports in DSSCs reveal that the effective diffusion coefficient of an electron in the ZnO-NW array/NP composite anode falls between those in the ZnO-NW and TiO2-NP anodes. The superior performance of the ZnO-NW array/NP composite DSSC to the ZnO-NW cell is mainly ascribed to the enrichment of the light harvesting without significantly sacrificing the electron transport efficiency.
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84.60.Jt Photoelectric conversion

Generation of high-quality lines and arrays using nanoparticle controlling processes

Seung H. Huh, Doh H. Riu, Y. Naono, Y. Taguchi, S. Kawabata, and A. Nakajima

Appl. Phys. Lett. 91, 093118 (2007); http://dx.doi.org/10.1063/1.2778464 (3 pages) | Cited 4 times

Online Publication Date: 29 August 2007

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Highly reliable lines and arrays comprising the smallest metallic nanoparticles (NPs) were produced by using a combination of techniques such as lithography, lift-off, size selection, aerosol deposition, and NP colloids. The narrowest 80 nm Au lines were produced by the deposition of only 4 nm Au NPs, driven by two factors—NP kinetics and collision-induced surface melting. An array of unsupported free 30–100 Ni NPs and one of 20–40 nm Ni NPs supported in holes were produced by the principles of hole-size-induced filtering and the binding of thiol groups.
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81.16.Nd Micro- and nanolithography
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.D- Solid-liquid transitions

Nonthermal plasma synthesis of size-controlled, monodisperse, freestanding germanium nanocrystals

Ryan Gresback, Zachary Holman, and Uwe Kortshagen

Appl. Phys. Lett. 91, 093119 (2007); http://dx.doi.org/10.1063/1.2778356 (3 pages) | Cited 24 times

Online Publication Date: 29 August 2007

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Germanium nanocrystals may be of interest for a variety of electronic and optoelectronic applications including photovoltaics, primarily due to the tunability of their band gap from the infrared into the visible range of the spectrum. This letter discusses the synthesis of monodisperse germanium nanocrystals via a nonthermal plasma approach which allows for precise control of the nanocrystal size. Germanium crystals are synthesized from germanium tetrachloride and hydrogen entrained in an argon background gas. The crystal size can be varied between 4 and 50 nm by changing the residence times of crystals in the plasma between ∼ 30 and 440 ms. Adjusting the plasma power enables one to synthesize fully amorphous or fully crystalline particles with otherwise similar properties.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.46.Hk Nanocrystals
52.77.-j Plasma applications

Dynamic force spectroscopy using cantilever higher flexural modes

Yoshiaki Sugimoto, Seiji Innami, Masayuki Abe, Óscar Custance, and Seizo Morita

Appl. Phys. Lett. 91, 093120 (2007); http://dx.doi.org/10.1063/1.2775806 (3 pages) | Cited 25 times

Online Publication Date: 29 August 2007

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By means of force spectroscopy measurements performed with the cantilever first and second flexural modes under the frequency modulation detection method, the authors corroborate the validity of the relation between tip-surface interaction force and frequency shift for force spectroscopy acquisition using higher cantilever eigenmodes. They estimate a cantilever effective stiffness for the second eigenmode 73 times larger than the static stiffness. This large effective stiffness enables them to perform force spectroscopy with a cantilever oscillation amplitude (A0) as small as 3.6 Å. The authors provide experimental evidence that, at such small A0 values, normalized frequency shift curves deviate from a A03/2 scaling and the signal-to-noise ratio is considerably enhanced.
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68.37.Ps Atomic force microscopy (AFM)

Rapid prototyping of three-dimensional microstructures from multiwalled carbon nanotubes

Wei Hsuan Hung, Rajay Kumar, Adam Bushmaker, Stephen B. Cronin, and Michael J. Bronikowski

Appl. Phys. Lett. 91, 093121 (2007); http://dx.doi.org/10.1063/1.2778292 (3 pages) | Cited 5 times

Online Publication Date: 29 August 2007

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The authors report a method for creating three-dimensional carbon nanotube structures, whereby a focused laser beam is used to selectively burn local regions of a dense forest of multiwalled carbon nanotubes. Raman spectroscopy and scanning electron microscopy are used to quantify the threshold for laser burnout and depth of burnout. The minimum power density for burning carbon nanotubes in air is found to be 244 μW/μm2. We create various three-dimensional patterns using this method, illustrating its potential use for the rapid prototyping of carbon nanotube microstructures. Undercut profiles, changes in nanotube density, and nanoparticle formation are observed after laser surface treatment and provide insight into the dynamic process of the burnout mechanism.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials
78.67.Ch Nanotubes
78.30.Na Fullerenes and related materials

Improving carrier transport and light emission in a silicon-nanocrystal based MOS light-emitting diode on silicon nanopillar array

Gong-Ru Lin, Chun-Jung Lin, and Hao-Chung Kuo

Appl. Phys. Lett. 91, 093122 (2007); http://dx.doi.org/10.1063/1.2778352 (3 pages) | Cited 16 times

Online Publication Date: 29 August 2007

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A silicon-nanocrystal (nc-Si) based metal-oxide-semiconductor light-emitting diode (MOSLED) on Si nanopillar array with size, height, and density of 30 nm, 350 nm, and 2.8×1010 cm−2, respectively, is characterized. The nanopillar roughened Si surface contributes to the improved turn-on characteristics by enhancing Fowler-Nordheim tunneling and reducing effective barrier height, providing the MOSLED a maximum optical power of 0.7 μW obtained at biased current of 375 μA. The optical intensity, turn-on current, and power-current slope of nc-Si MOSLED on high-aspect-ratio Si nanopillar array are 140 μW/cm2, 5 μA, 2±0.8 mW/A, respectively. A maximum external quantum efficiency of 0.1% is reported.
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85.60.Jb Light-emitting devices

Low temperature transfer and formation of carbon nanotube arrays by imprinted conductive adhesive

Teng Wang, Björn Carlberg, Martin Jönsson, Goo-Hwan Jeong, Eleanor E. B. Campbell, and Johan Liu

Appl. Phys. Lett. 91, 093123 (2007); http://dx.doi.org/10.1063/1.2776849 (3 pages) | Cited 8 times

Online Publication Date: 29 August 2007

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This letter demonstrates the transfer and formation of aligned carbon nanotube (CNT) arrays at low temperature by imprinted conductive adhesive. A thermoplastic isotropic conductive adhesive is patterned by an imprint and heat transfer process. The CNTs grown by thermal chemical vapor deposition are then transferred to another substrate by the conductive adhesive, forming predefined patterns. The current-voltage response of the transferred CNT bundles verifies that good electrical connection has been established. This process can enable the integration of CNTs into various temperature-sensitive processeses and materials.
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81.20.-n Methods of materials synthesis and materials processing
81.16.Rf Micro- and nanoscale pattern formation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Ultraviolet-visible emission from three-dimensional WO3−x nanowire networks

Jian Yi Luo, Fu Li Zhao, Li Gong, Huan Jun Chen, Jun Zhou, Zheng Lin Li, Shao Zhi Deng, and Ning Sheng Xu

Appl. Phys. Lett. 91, 093124 (2007); http://dx.doi.org/10.1063/1.2776862 (3 pages) | Cited 9 times

Online Publication Date: 29 August 2007

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The photoluminescence spectra of WO3−x nanowire networks, WO3 nanowires networks, and the bulk phase WO3 powder have been investigated under the continuous wave excitation light at 320 nm. Two broad band emissions in spectrum of WO3−x nanowire networks are observed including the ultraviolet-visible (UV-vis) emission centered at 395 nm and the blue emission centered at 467 nm. The authors demonstrate that the blue emission in WO3−x nanowire networks is due to band-band transition of the bulk phase WO3 and the UV-vis emission is attributed to the state of oxygen vacancies, which are characterized by using scanning electron microscopy and x-ray photoelectron spectroscopy. The UV-vis emission exhibits a strong dependence on the excitation wavelength, while the blue emission is independent of the excitation wavelength. The UV-vis emission is discussed in configuration-coordinate diagram of a localized state of oxygen vacancies. In particular, this state of defect is a high-lying resonant state in the conduction band of WO3.
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78.67.Lt Quantum wires
78.55.Hx Other solid inorganic materials
73.21.Hb Quantum wires
71.55.Ht Other nonmetals
71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Negative photoconduction of planar heterogeneous random network of ZnO-carbon nanotubes

S. Sen, D. Chowdhary, and N. A. Kouklin

Appl. Phys. Lett. 91, 093125 (2007); http://dx.doi.org/10.1063/1.2776863 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2007

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In this letter, the authors report on the effect of negative photoconduction observed in heterogeneous two-dimensional random networks comprising single-walled nanotubes and ZnO particles, and investigated by room temperature dc-photoconduction measurements. For this, two-terminal thin film devices engineered by solution coating of the nanotubes with ZnO microparticles consistently exhibited increase in the resistance versus decrease in the nanotubes alone with ultraviolet illumination, which is explained within the model of interface-mediated charging/discharging effects. The study suggests the possibility of engineering reduced-cost and multirange nanotube light sensors based on extrinsic carrier modulation via external gating at the interface.
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72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
72.20.-i Conductivity phenomena in semiconductors and insulators
68.55.A- Nucleation and growth
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