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10 Dec 2007

Volume 91, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 241101 (2007); http://dx.doi.org/10.1063/1.2821382 (3 pages)

S. N. Goda, S. Sensarn, M. Y. Shverdin, and G. Y. Yin
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Enhanced probe nano-oxidation by charge pump effect in swept tip voltage cycles

Xian Ning Xie, Hong Jing Chung, Chorng Haur Sow, and Andrew Thye Shen Wee

Appl. Phys. Lett. 91, 243101 (2007); http://dx.doi.org/10.1063/1.2817579 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2007

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A probe-based nano-oxidation method for enhanced vertical oxide growth on silicon is presented. The technique involves cycling the tip biases between positive and negative polarities to produce high-aspect-ratio nano-oxides. Enhanced oxidation was observed to take place in the positive tip bias region as opposed to the negative tip voltage required for anodic oxidation. A model based on interface space charge accumulation and neutralization, OH− reactant mobilization, and diffusion is proposed to account for the oxidation enhancement observed under positive tip voltages. The proposed model is analogous to the transient charge pump effect which is at work when the polarity of a capacitor is switched. The results reveal the dynamical behavior of nano-oxidation under nonstatic fields which can be harnessed for fabricating oxide nanostructures with improved aspect ratios.
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81.65.-b Surface treatments
82.45.Cc Anodic films
64.70.Nd Structural transitions in nanoscale materials
84.32.Tt Capacitors

Polymer-metal waveguides characterization by Fourier plane leakage radiation microscopy

S. Massenot, J. Grandidier, A. Bouhelier, G. Colas des Francs, L. Markey, J.-C. Weeber, A. Dereux, J. Renger, M. U. Gonzàlez, and R. Quidant

Appl. Phys. Lett. 91, 243102 (2007); http://dx.doi.org/10.1063/1.2824840 (3 pages) | Cited 41 times

Online Publication Date: 10 December 2007

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The guiding properties of polymer waveguides on a thin gold film are investigated in the optical regime. The details of propagation in the waveguides are studied simultaneously in the object and Fourier planes, providing direct measurement of both the real and imaginary parts of the effective index of the guided mode. A fair agreement between theoretical analysis provided by the differential method and experimental leakage radiation microscopy data is shown. All these tools bring valuable information for designing and understanding such devices.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Direct observation of cooperative effects in capillary condensation: The hysteretic origin

Fèlix Casanova, Casey E. Chiang, Chang-Peng Li, and Ivan K. Schuller

Appl. Phys. Lett. 91, 243103 (2007); http://dx.doi.org/10.1063/1.2822815 (3 pages) | Cited 12 times

Online Publication Date: 10 December 2007

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We tailor anodized alumina with pores with well-defined, simple geometries, in order to study the effects of constrictions in hysteretical capillary condensation, independently from other cooperative processes such as network effects. We confirm, by direct observation using optical interferometry, the occurrence of two cooperative phenomena: the classical pore blocking effect in nearly ideal “inkbottle” pores and the advanced adsorption in pores with a change in the cross section. They are relevant for the development of a theory of the poorly understood hysteresis in complex porous materials.
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61.43.Gt Powders, porous materials
68.43.Mn Adsorption kinetics

Local wettability modification by thermochemical nanolithography with write-read-overwrite capability

D. B. Wang, R. Szoszkiewicz, M. Lucas, E. Riedo, T. Okada, S. C. Jones, S. R. Marder, J. Lee, and W. P. King

Appl. Phys. Lett. 91, 243104 (2007); http://dx.doi.org/10.1063/1.2816401 (3 pages) | Cited 11 times

Online Publication Date: 11 December 2007

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The wettability of a thin polymer film was modified twice by thermochemical nanolithography. By means of a first local chemical modification induced by an atomic force microscope tip heated to 110±20 °C, hydrophilic patterns are written over an originally hydrophobic polymer surface. By further heating to 190±20 °C, a second chemical modification reverses the local wettability change introduced by the first chemical modification. This write-read-overwrite capability can be particularly useful in the design of complex nanofluidic devices.
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81.16.Nd Micro- and nanolithography
68.37.Ps Atomic force microscopy (AFM)
68.08.Bc Wetting
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics

Spatially controlled atomic layer deposition in porous materials

J. W. Elam, J. A. Libera, M. J. Pellin, and P. C. Stair

Appl. Phys. Lett. 91, 243105 (2007); http://dx.doi.org/10.1063/1.2822897 (3 pages) | Cited 11 times

Online Publication Date: 11 December 2007

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We describe a technique for depositing materials at controlled depths within porous substrates based upon the passivating effect produced by one precursor to prevent the adsorption of a second precursor. For example, a surface exposed to trimethyl aluminum is not reactive toward diethyl zinc. This effect, combined with Knudsen diffusion in which the precursor exposure times dictate the depth of penetration of the deposited layer, enables spatially controlled “stripe coating” within porous supports. We demonstrate ZnO stripes in anodic alumina and model the results using Monte Carlo simulations. Etching is identified as a potential problem for certain precursor combinations.
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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.)
81.65.Rv Passivation

Optical properties of patterned InAs quantum dot ensembles grown on GaAs nanopyramids

B. L. Liang, P. S. Wong, N. Nuntawong, A. R. Albrecht, J. Tatebayashi, T. J. Rotter, G. Balakrishnan, and D. L. Huffaker

Appl. Phys. Lett. 91, 243106 (2007); http://dx.doi.org/10.1063/1.2821121 (3 pages) | Cited 7 times

Online Publication Date: 11 December 2007

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We demonstrate the ability to form either coupled or isolated patterned quantum dot (PQD) ensembles on nanopatterned GaAs pyramidal buffers. The coupled PQD “clusters” consist of close-spaced PQDs with inter-QD spacing of 5 nm. The isolated PQD “pairs” are comprised of two PQDs well separated by 110 nm. The photoluminescence behavior, measured in integrated intensity, linewidth, and emission peak as a function of excitation intensity and temperature, indicates lateral coupling within the QD clusters and an isolated nature for QD pairs. The ability to tailor PQD formation and subsequent carrier recombination characteristic may prove useful in developing PQD-based devices for optical computing applications.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.07.Ta Quantum dots

Mixed ionic-electronic conductivity in yttria-stabilized zirconia/carbon nanotube composites

F. C. Fonseca, R. Muccillo, D. Z. de Florio, L. O. Ladeira, and A. S. Ferlauto

Appl. Phys. Lett. 91, 243107 (2007); http://dx.doi.org/10.1063/1.2821373 (3 pages)

Online Publication Date: 11 December 2007

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The fabrication of yttria stabilized-zirconia/single-wall carbon nanotube (YSZ/SWCNT) composites is reported. Electrical conductivity measurements from 25 to 800 °C revealed that the composites exhibit mixed ionic-electronic conduction. At room temperature, the conductivity increases by 11 orders of magnitude with the addition of SWCNT to the YSZ. At high temperatures (>300 °C), the ionic conduction of the YSZ becomes relevant and a mixed ionic-electronic transport is observed. It is found that the transport can be described by a sum of two parallel contributions: thermally activated ionic conduction from the YSZ and fluctuation-assisted tunneling within the SWCNT network.
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72.60.+g Mixed conductivity and conductivity transitions
72.80.Tm Composite materials
72.70.+m Noise processes and phenomena

Horizontally directed growth of carbon nanotubes utilizing self-generated electric field from plasma induced surface charging

J. B. K. Law, C. K. Koo, and J. T. L. Thong

Appl. Phys. Lett. 91, 243108 (2007); http://dx.doi.org/10.1063/1.2824478 (3 pages) | Cited 5 times

Online Publication Date: 12 December 2007

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Plasma induced surface charging during carbon nanotube (CNT) growth via radio frequency plasma-enhanced chemical vapor deposition is exploited to direct the growth in a horizontal direction on a device substrate without the need for external biasing arrangements. Using a silicon-on-insulator substrate, a pair of electrodes is fabricated in which one electrode is shorted to the handle layer and the other is left floating. A potential difference results from the plasma, and creates a lateral electric field between the electrodes that is used to direct the growth of CNTs. The approach allows for wafer-scale growth of laterally aligned CNTs.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Fg Nanotubes

Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites

S. Apperson, R. V. Shende, S. Subramanian, D. Tappmeyer, S. Gangopadhyay, Z. Chen, K. Gangopadhyay, P. Redner, S. Nicholich, and D. Kapoor

Appl. Phys. Lett. 91, 243109 (2007); http://dx.doi.org/10.1063/1.2787972 (3 pages) | Cited 23 times

Online Publication Date: 12 December 2007

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Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.
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82.33.Vx Reactions in flames, combustion, and explosions
82.40.-g Chemical kinetics and reactions: special regimes and techniques

Dielectric-constant measurement of thin insulating films at low frequency by nanoscale capacitance microscopy

Laura Fumagalli, Giorgio Ferrari, Marco Sampietro, and Gabriel Gomila

Appl. Phys. Lett. 91, 243110 (2007); http://dx.doi.org/10.1063/1.2821119 (3 pages) | Cited 24 times

Online Publication Date: 12 December 2007

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We demonstrate a method for quantitatively probing the local low-frequency dielectric constant of thin insulating films by nanoscale capacitance microscopy. The calibrated capacitance-distance curves are measured on the dielectric film and analyzed by using a tip-sample capacitance model here proposed. Applied to SiO2 films as small as 1×1 μm2 area and 20–30 nm thickness, the method gives a dielectric constant on the submicron scale in agreement with the value determined on the large scale. The observed precision is set by the capacitance noise level of the instrument and the tip radius.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Coupling of surface plasmons between two silver films in a plasmonic thermal emitter

Chia-Yi Chen, Ming-Wei Tsai, Yu-Wei Jiang, Yi-Han Ye, Yi-Tsung Chang, and Si-Chen Lee

Appl. Phys. Lett. 91, 243111 (2007); http://dx.doi.org/10.1063/1.2824389 (3 pages) | Cited 7 times

Online Publication Date: 13 December 2007

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The emission spectra of Ag/SiO2/Ag trilayer plasmonic thermal emitters with various SiO2 thicknesses were investigated. By analyzing the relationship between emission peaks and thicknesses of SiO2, the coupling of surface plasmons between two silver films in a plasmonic thermal emitter is demonstrated and the coupling length is determined as well. Furthermore, the dispersion relation of plasmonic thermal emitter is detected by measuring the reflection spectra with various incident angles. This confirms that the main mechanism involved in the emission of a plasmonic thermal emitter is due to the excitation of surface plasmons.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Particle concentration and tube size dependence of viscosities of Al2O3-water nanofluids flowing through micro- and minitubes

Seok Pil Jang, Ji-Hwan Lee, Kyo Sik Hwang, and Stephen U. S. Choi

Appl. Phys. Lett. 91, 243112 (2007); http://dx.doi.org/10.1063/1.2824393 (3 pages) | Cited 17 times

Online Publication Date: 13 December 2007

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An experimental and theoretical investigation has been performed on the effective viscosity of Al2O3-water nanofluids flowing through micrometer- and millimeter-sized circular tubes in the fully developed laminar flow regime. We have discovered that the effective viscosity of Al2O3-water nanofluids increases nonlinearly with the volume concentration of nanoparticles even in the very low range of 0.02–0.3 vol % and strongly depends on the ratio of the nanoparticle diameter to the tube diameter. We have developed a modified Einstein model that accounts for the slip mechanism in nanofluids. The new model captures these new rheological features of nanofluids.
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83.50.Ha Flow in channels
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
62.25.-g Mechanical properties of nanoscale systems
47.60.-i Flow phenomena in quasi-one-dimensional systems

Spatial Bloch oscillations of plasmons in nanoscale metal waveguide arrays

Weihua Lin, Xiang Zhou, Guo Ping Wang, and C. T. Chan

Appl. Phys. Lett. 91, 243113 (2007); http://dx.doi.org/10.1063/1.2824394 (3 pages) | Cited 16 times

Online Publication Date: 13 December 2007

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A kind of metal waveguide array (MWGA) structures designed for observing spatial plasmon Bloch oscillations (BOs) in nanoscale is presented. The gradient of plasmon propagation constants across the MWGAs is realized by gradually changing the dielectric constant of the dielectrics filling in the guides. Plasmon BOs in the MWGAs manifest themselves as periodic breathing and transverse motion under the conditions of initial single and multiple waveguide excitations, respectively. Analytical results from the coupled wave theory are confirmed by finite-difference time-domain numerical simulations.
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73.22.Lp Collective excitations
73.23.-b Electronic transport in mesoscopic systems
77.22.Ch Permittivity (dielectric function)

Voltage-dependent electroluminescence from colloidal CdSe/ZnS quantum dots

Liang Yan, Jia-Yu Zhang, Yiping Cui, and Yi Qiao

Appl. Phys. Lett. 91, 243114 (2007); http://dx.doi.org/10.1063/1.2824397 (3 pages) | Cited 6 times

Online Publication Date: 14 December 2007

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Electroluminescence (EL) was obtained in the hybrid film of colloidal CdSe/ZnS quantum dots (QDs) and poly(9-vinylcarbazole) (PVK), and the voltage and temperature dependences of the EL were measured. The quantum-confined Stark effect of colloidal QDs is clearly observed, and the QDs’ EL intensity rises with temperature. Electrons and holes are proposed to be separately transported in QDs and PVK, respectively.
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85.60.Jb Light-emitting devices

Improved device performance of InAs/GaAs quantum dot solar cells with GaP strain compensation layers

R. B. Laghumavarapu, M. El-Emawy, N. Nuntawong, A. Moscho, L. F. Lester, and D. L. Huffaker

Appl. Phys. Lett. 91, 243115 (2007); http://dx.doi.org/10.1063/1.2816904 (3 pages) | Cited 41 times

Online Publication Date: 14 December 2007

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We report optical, electrical, and spectral response characteristics of three-stack InAs/GaAs quantum dot solar cells with and without GaP strain compensation (SC) layers. The short circuit current density, open circuit voltage, and external quantum efficiency of these cells under air mass 1.5 G at 290 mW/cm2 illumination are presented and compared with a GaAs control cell. The cells with SC layers show superior device quality, confirmed by I-V and spectral response measurements. The quantum dot solar cells show an extended photoresponse compared to the GaAs control cell. The effect of the SC layer thickness on device performance is also presented.
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84.60.Jt Photoelectric conversion

Will zigzag graphene nanoribbon turn to half metal under electric field?

Er-Jun Kan, Zhenyu Li, Jinlong Yang, and J. G. Hou

Appl. Phys. Lett. 91, 243116 (2007); http://dx.doi.org/10.1063/1.2821112 (3 pages) | Cited 75 times

Online Publication Date: 14 December 2007

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At B3LYP level of theory, we predict that the half-metallicity in zigzag edge graphene nanoribbon (ZGNR) can be realized when an external electric field is applied across the ribbon. The critical electric field decreases with the increase of the ribbon width to induce the half-metallicity. Both the spin polarization and half-metallicity are removed when the edge state electrons fully transferred from one side to the other under very strong electric field. The electric field range under which ZGNR remains half-metallic increases with the ribbon width. Our study demonstrates a rich field-induced spin polarization behavior, which may lead to some important applications in spinstronics.
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73.63.-b Electronic transport in nanoscale materials and structures
72.25.Dc Spin polarized transport in semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials

Direct patterning of carbon nanotube network devices by selective vacuum filtration

Chaehyun Lim, Dong-Hun Min, and Seung-Beck Lee

Appl. Phys. Lett. 91, 243117 (2007); http://dx.doi.org/10.1063/1.2824575 (3 pages) | Cited 8 times

Online Publication Date: 14 December 2007

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We report on a method which allows direct patterning of density controlled carbon nanotube network (NTN) devices during network formation. By lithographically patterning photoresist on the filter membrane, the nanotubes in suspension were guided to the exposed pattern areas of the filter surface during vacuum filtration allowing in situ device formation. The NTNs were transferred to an elastomer substrate by directly curing polydimethylsiloxane on its surface. We compared electrical characteristics of NTN patterns fabricated simultaneously using this method and found that the different NTNs with equal nanotube density showed reproducible characteristics.
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85.35.Kt Nanotube devices
85.40.Hp Lithography, masks and pattern transfer

Maskless writing of a flexible nanoscale transistor with Au-contacted carbon nanotube electrodes

Cedric P. R. Dockendorf, Dimos Poulikakos, Gilgueng Hwang, Bradley J. Nelson, and Costas P. Grigoropoulos

Appl. Phys. Lett. 91, 243118 (2007); http://dx.doi.org/10.1063/1.2821375 (3 pages) | Cited 7 times

Online Publication Date: 14 December 2007

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A flexible polymer field effect transistor with a nanoscale carbon nanotube channel is conceptualized and realized herein. Carbon nanotubes (CNTs) were dispersed on a polyimide substrate and marked in an scanning electron microscope with focused ion beam such that they could be contacted with gold nanoink. The CNTs were divided into two parts forming the source and drain of the transistor. A micropipette writing method was used to contact the carbon nanotube electrodes with gold nanoink and to deposit the poly(3-hexylthiophene) as an active layer. The mobility of the transistors is of the order of 10−5 cm/V s. After fabrication, the flexible transistors can be peeled off the substrate.
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85.30.Tv Field effect devices
61.46.Fg Nanotubes
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