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1 May 2008

Volume 103, Issue 9, Articles (09xxxx)

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Thermal resistance between low-dimensional nanostructures and semi-infinite media

Matthew A. Panzer and Ken E. Goodson

J. Appl. Phys. 103, 094301 (2008); http://dx.doi.org/10.1063/1.2903519 (10 pages) | Cited 8 times

Online Publication Date: 1 May 2008

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Show Abstract
Nanostructured electronic and photonic devices include a high density of material interfaces, which can strongly impede heat conduction and influence performance and reliability. Thermal conduction through interfaces is a very mature discipline for the traditional geometry, in which the lateral interface dimensions are large compared to the phonon wavelength. In nanostructures, however, the localization of phonons in the directions parallel to the interface may strongly influence the effective thermal resistance. The present work investigates model problems of abrupt junctions between a harmonic one-dimensional (1D) and a three-dimensional (3D) fcc lattice and between a 1D and a two-dimensional square lattice. The abrupt change in geometry modifies the phonon modes participating in energy transmission and creates an additional thermal resistance that is comparable with that occurring due to the acoustic mismatch at the interface of bulk media. For both cases, varying the impedance mismatch at the junction suggests that engineering an intentional impedance mismatch at a nanostructured interface may enhance the transmission of energy. The lattice dynamics calculations are used to develop qualitative arguments for the interface resistances in the practical geometries involving carbon nanotubes, silicon nanopillars, and graphene. This research provides foundations for detailed investigations of the impact of localized phonon modes on the acoustic mismatch resistance.
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63.20.Pw Localized modes
73.63.-b Electronic transport in nanoscale materials and structures
73.40.-c Electronic transport in interface structures
63.22.Gh Nanotubes and nanowires
73.63.Fg Nanotubes

Carbon nanoadditives to enhance latent energy storage of phase change materials

Shadab Shaikh, Khalid Lafdi, and Kevin Hallinan

J. Appl. Phys. 103, 094302 (2008); http://dx.doi.org/10.1063/1.2903538 (6 pages) | Cited 14 times

Online Publication Date: 1 May 2008

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Latent energy storage capacity was analyzed for a system consisting of carbon nanoparticles doped phase change materials (PCMs). Three types of samples were prepared by doping shell wax with single wall carbon nanotubes (SWCNTs), multiwall CNTs, and carbon nanofibers. Differential scanning calorimetry was used to measure the latent heat of fusion. The measured values of latent heat for all the samples showed a good enhancement over the latent heat of pure wax. A maximum enhancement of approximately 13% was observed for the wax/SWCNT composite corresponding to 1% loading of SWCNT. The change in latent heat was modeled by using an approximation for the intermolecular attraction based on the Lennard-Jones potential. A theoretical model was formulated to estimate the overall latent energy of the samples with the variation in volume fraction of the nanoparticles. The predicted values of latent energy from the model showed good agreement with the experimental results. It was concluded that the higher molecular density of the SWCNT and its large surface area were the reasons behind the greater intermolecular attraction in the wax/SWCNT composite, which resulted in its enhanced latent energy. The novel approach used to predict the latent heat of fusion of the wax/nanoparticle composites has a particular significance for investigating the latent heat of PCM with different types of nanoparticle additives.
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64.70.dj Melting of specific substances
82.60.Qr Thermodynamics of nanoparticles

Growth and spectral analysis of ZnO nanotubes

C. X. Xu, G. P. Zhu, X. Li, Y. Yang, S. T. Tan, X. W. Sun, C. Lincoln, and T. A. Smith

J. Appl. Phys. 103, 094303 (2008); http://dx.doi.org/10.1063/1.2908189 (5 pages) | Cited 4 times

Online Publication Date: 1 May 2008

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ZnO nanotubes were fabricated by vapor-phase transport using the mixture of ZnO and graphite powders in air. A self-catalyzed growth mechanism was proposed based on microstructure analysis by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Raman scattering, integrated photoluminescence, and time-resolved photoluminescence were employed to explore the optical properties and the dynamic process. Combing with crystal structure and the spectral characteristics of the ZnO nanotubes, the charge carrier transport process was discussed.
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61.46.Fg Nanotubes
78.55.Et II-VI semiconductors
78.67.Ch Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
78.30.Fs III-V and II-VI semiconductors
73.63.Fg Nanotubes

In situ scanning tunneling microscopy studies of zinc(II) octaethylporphyrin arrays self-assembled on graphite and Au(111) surfaces in organic solution

Zhi-Qiang Zou and Feng Chen

J. Appl. Phys. 103, 094304 (2008); http://dx.doi.org/10.1063/1.2908177 (4 pages) | Cited 3 times

Online Publication Date: 1 May 2008

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We have prepared ordered adlayers of Zn(II) octaethylporphyrin (ZnOEP) molecules on highly oriented pyrolytic graphite (HOPG) and Au(111) surfaces in 1,2-dichlorobenzene solution. Packing structures and even internal structure of the molecules on these two substrates have been investigated in situ by scanning tunneling microscopy with the tip being immersed in the organic solution. The ZnOEP molecules have been found to adsorb on the HOPG surface with two pairs of ethyl groups curling down and the other two pairs curling up. This shape is consistent with the molecular geometry in the ZnOEP crystal. Compared to the HOPG substrate, the ZnOEP molecules adsorbed on the Au(111) substrate exhibit a lower resolution, and the order of the molecular adlayer is not as good as that on the HOPG surface due to the strong molecule-substrate interaction.
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68.43.Fg Adsorbate structure (binding sites, geometry)
68.43.Mn Adsorption kinetics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.bm Polymers, organics

Self-consistent fluctuating hydrodynamics simulations of thermal transport in nanoparticle suspensions

P. He and R. Qiao

J. Appl. Phys. 103, 094305 (2008); http://dx.doi.org/10.1063/1.2908217 (6 pages) | Cited 12 times

Online Publication Date: 2 May 2008

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We report on the mesoscopic simulation of heat conduction in nanoparticle suspensions (nanofluids) by using the energy-conserving dissipative particle dynamics (DPD) method. Through coarse graining, our simulations probe the thermal and momentum transport in nanofluids at a length scale much greater than that in atomistic methods. We show that our simulations model the fluctuating hydrodynamics in nanofluids in a thermodynamically self-consistent manner, which is critical for resolving the current controversies on mechanisms of heat conduction in nanofluids. Simulation results indicate that the Brownian motion of nanoparticles plays a negligible role in determining the thermal conductivity of nanofluids at least within the framework of fluctuating hydrodynamics at mesoscales.
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47.57.E- Suspensions
47.10.A- Mathematical formulations

Effect of external electric field on liquid film confined within nanogap

G. X. Xie, J. B. Luo, S. H. Liu, C. H. Zhang, X. C. Lu, and D. Guo

J. Appl. Phys. 103, 094306 (2008); http://dx.doi.org/10.1063/1.2917373 (7 pages) | Cited 7 times

Online Publication Date: 2 May 2008

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A strong and reproducible effect of an external electric field (EEF) on liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disk is described. Induced by the EEF, microbubbles were observed at the edge of the contact region. This phenomenon is more obvious in polar liquid films than that in nonpolar ones. A stronger EEF causes a decrease in the film thickness in the contact region initially, and then the variation becomes much smaller. When the ball is applied with a positive EEF, the emergence of microbubbles is stable over time, while it becomes much less as time progresses. Different mechanisms of these experimental phenomena have been discussed.
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68.15.+e Liquid thin films
68.08.-p Liquid-solid interfaces

Influence of pulse amplitude and rise time on field-induced domain wall propagation in Ni80Fe20 nanowires

K. Weerts, P. Neutens, L. Lagae, and G. Borghs

J. Appl. Phys. 103, 094307 (2008); http://dx.doi.org/10.1063/1.2912731 (4 pages) | Cited 4 times

Online Publication Date: 2 May 2008

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We have studied the field-induced propagation of domain walls (DWs) in magnetic nanowires by time-resolved magneto-optical Kerr microscopy. Magnetic field pulses with variable field amplitude lead to a DW velocity up to 500 m/s in 750 nm wide Ni80Fe20 nanowires, exceeding many other previous time-resolved optical measurements. Experiments show a linear relation between DW velocity and magnetic field beyond the Walker breakdown field, in agreement with micromagnetic simulations. In these simulations, the oscillation of DW type between vortex and transverse type, beyond Walker breakdown, is visualized. Furthermore, we experimentally show that the magnetic field pulse rise time is an important parameter for characterizing the DW velocity. Different pulse rise times lead to different injected DW types and DW velocities. These transient effects are especially important in possible future devices, where an ultrafast dynamical response of the DW is desired.
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75.50.Bb Fe and its alloys
78.20.Ls Magneto-optical effects
75.60.Ch Domain walls and domain structure

Surface charge induced variation in the electrical conductivity of nanoporous gold

A. K. Mishra, C. Bansal, and H. Hahn

J. Appl. Phys. 103, 094308 (2008); http://dx.doi.org/10.1063/1.2912982 (5 pages) | Cited 8 times

Online Publication Date: 5 May 2008

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The electrical conductivity of nanoporous gold was measured in situ during the charging and decharging of the surface of the metal. The nanoporous gold samples were prepared by the process of selective dealloying of Ag from Au–Ag alloy. Charge was induced on the surface by making the sample a working electrode in an electrochemical cell. The conductivity was observed to vary reversibly with the induced surface charge.
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73.61.At Metal and metallic alloys
73.40.-c Electronic transport in interface structures
82.45.Fk Electrodes
61.46.-w Structure of nanoscale materials
81.65.-b Surface treatments

Thermal and electrical conductivities of water-based nanofluids prepared with long multiwalled carbon nanotubes

J. Glory, M. Bonetti, M. Helezen, M. Mayne-L’Hermite, and C. Reynaud

J. Appl. Phys. 103, 094309 (2008); http://dx.doi.org/10.1063/1.2908229 (7 pages) | Cited 20 times

Online Publication Date: 5 May 2008

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Thermal and electrical conductivities of suspensions of multiwalled carbon nanotubes (MWCNT) in water were measured as a function of temperature, nanotube weight content, and nanotube length. Nanotubes were dispersed in water by using gum Arabic as surfactant. The thermal conductivity was measured by the steady-state method by using a coaxial-cylinder cell that allows the sample temperature to be varied from 15 to 75 °C. Our measurements show that the thermal conductivity enhancement as compared to water linearly increases when the MWCNT weight content increases from 0.01 to 3 wt %, reaching 64% for the MWCNT weight content of 3 wt %. The thermal conductivity enhancement is found to be temperature independent up to MWCNT weight content of 2 wt %. The average length of the nanotubes appears to be a very sensitive parameter. The thermal conductivity enhancement as compared to water increases by a factor of 3 when the nanotube average length increases in the 0.5–5 μm range. Electrical conductivity measurements show that the electrical properties do not follow the same trend as a function of MWCNT weight content, as compared to thermal properties. The electrical conductivity is mainly constant in the studied range, but undergoes a drop when the weight content decreases to about 0.1 wt %, which suggests that the MWCNT network in the base fluid might be percolating at this very low value. By comparison, the thermal conductivity does not show any percolation threshold.
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73.63.Fg Nanotubes
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
82.70.Kj Emulsions and suspensions
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)

Deuterium influence on the field emission from inorganic nanowires

Vincenc Nemanic, Marko Zumer, Bojan Zajec, Dragan Mihailovic, Damjan Vengust, and Bostjan Podobnik

J. Appl. Phys. 103, 094310 (2008); http://dx.doi.org/10.1063/1.2912984 (5 pages) | Cited 2 times

Online Publication Date: 5 May 2008

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We report the initial conditioning procedure and achieved properties of nanowires composed of molybdenum sulfur iodine and directly grown on the top of a macroscopic molybdenum wire. Such a wire with nanowires, which were mostly perpendicularly grown to the surface, was applied as a radial field emitter with a 20 mm2 geometric area positioned inside a cylindrical metal anode. A stable current density of ∼ 2 mA/cm2 was achieved at a relatively low macroscopic electric field. Simultaneous recording of gases released from the anode exhibits linear relationship with the dissipated power. The most unexpected result was a reversible field emission current dependence induced by varying the deuterium pressure within the range from 10−8 to 10−4 mbar. The maximum increase for a factor of 7 was registered. Possible mechanisms responsible for the observed phenomena are discussed.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Single-pulse excimer laser nanostructuring of silicon: A heat transfer problem and surface morphology

Julia Eizenkop, Ivan Avrutsky, Daniel G. Georgiev, and Vipin Chaudchary

J. Appl. Phys. 103, 094311 (2008); http://dx.doi.org/10.1063/1.2910196 (6 pages) | Cited 6 times

Online Publication Date: 6 May 2008

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We present computer modeling along with experimental data on the formation of sharp conical tips on silicon-based three-layer structures that consist of a single-crystal Si layer on a 1 μm layer of silica on a bulk Si substrate. The upper Si layers with thicknesses in the range of 0.8−4.1 μm were irradiated by single pulses from a KrF excimer laser focused onto a spot several micrometers in diameter. The computer simulation includes two-dimensional time-dependent heat transfer and phase transformations in Si films that result from the laser irradiation (the Stefan problem). After the laser pulse, the molten material self-cools and resolidifies, forming a sharp conical structure, the height of which can exceed 1 μm depending on the irradiation conditions. We also performed computer simulations for experiments involving single-pulse irradiation of bulk silicon, reported by other groups. We discuss conditions under which different types of structures (cones versus hollows) emerge. We confirm a correlation between the presence of the lateral resolidification condition after the laser pulse and the presence of conical structures on a solidified surface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.30.Fb Solidification
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.55.Nq Composition and phase identification
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Wave propagation in double-walled carbon nanotubes conveying fluid

Toshiaki Natsuki, Qing-Qing Ni, Takuya Hayashi, and Morinobu Endo

J. Appl. Phys. 103, 094312 (2008); http://dx.doi.org/10.1063/1.2910841 (5 pages) | Cited 7 times

Online Publication Date: 6 May 2008

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Carbon nanotubes may hold scientific promise in nanotechnology as nanopipes conveying fluid. In this paper, the wave propagation in double-walled carbon nanotubes (DWCNTs) conveying fluid is studied based on the Euler–Bernoulli beam theory. The influences of internal moving fluids, such as flow velocity and mass density of fluids, on the sound wave propagation of DWCNTs or the DWCNTs embedded in an elastic matrix are investigated in detail. The DWCNTs are considered as a two-shell model coupled together through the van der Waals interaction between two adjacent nanotubes. According to the proposed theoretical approach, the results indicate that fluid flow through carbon nanotubes affects the wave speed and the critical frequency in the carbon nanotubes. The amplitude ratios of the inner to outer nanotubes are largely affected by the fluid velocity and density when the vibrational frequency in nanotubes is larger than 1.5 Hz. The theoretical investigation may give a useful reference for potential application and design of nanoelectronics and nanodevices.
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62.65.+k Acoustical properties of solids
47.60.Dx Flows in ducts and channels
63.22.Gh Nanotubes and nanowires
62.25.-g Mechanical properties of nanoscale systems
47.61.-k Micro- and nano- scale flow phenomena

Magnetism of the fcc Rh and Pd nanoparticles

Yoon Tae Jeon and Gang Ho Lee

J. Appl. Phys. 103, 094313 (2008); http://dx.doi.org/10.1063/1.2917070 (5 pages) | Cited 10 times

Online Publication Date: 6 May 2008

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We produced the fcc Rh and Pd nanoparticles with average particle diameters of 3 and 4 nm, respectively, in solution. We observed hysteretic behaviors in M-H curves and estimated lower bound magnetic moments of 4.8×10−3 and (3.8×10−3)μB/atom from unsaturated M-H curves at an applied field of 5 T and at 5 K for Rh and Pd nanoparticles, respectively. This implies that both Rh and Pd nanoparticles are ferromagnetic. We attributed this ferromagnetism to the lattice expansions, especially along the (200) planes (i.e., the expansion of d200), as observed in the x-ray diffraction patterns.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys

The Einstein relation in quantum wires of III-V, ternary, and quaternary materials in the presence of light waves: Simplified theory, relative comparison, and suggestion for experimental determination

K. P. Ghatak, S. Bhattacharya, S. Bhowmik, R. Benedictus, and S. Choudhury

J. Appl. Phys. 103, 094314 (2008); http://dx.doi.org/10.1063/1.2913515 (22 pages) | Cited 1 time

Online Publication Date: 8 May 2008

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We study the Einstein relation for the diffusivity to mobility ratio (DMR) in quantum wires (QWs) of III-V, ternary, and quaternary materials in the presence of light waves, whose unperturbed energy band structures are defined by the three band model of Kane. It has been found, taking n-InAs, n-InSb, n-Hg1−xCdxTe, n-In1−xGaxAsyP1−y lattice matched to InP as examples, that the respective DMRs exhibit decreasing quantum step dependence with the increasing film thickness, decreasing electron statistics, increasing light intensity and wavelength, with different numerical values. The nature of the variations is totally band structure dependent and is influenced by the presence of the different energy band constants. The strong dependence of the DMR on both the light intensity and the wavelength reflects the direct signature of the light waves which is in contrast as compared to the corresponding QWs of the said materials in the absence of photoexcitation. The classical equation of the DMR in the absence of any field has been obtained as a special case of the present analysis under certain limiting conditions and this is the indirect test of the generalized formalism. We have suggested an experimental method of determining the DMR in QWs of degenerate materials having arbitrary dispersion laws and our results find six applications in the field of quantum effect devices.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
68.65.La Quantum wires (patterned in quantum wells)
72.20.Ee Mobility edges; hopping transport
71.20.Nr Semiconductor compounds
72.80.Ey III-V and II-VI semiconductors

Long-wavelength light emission from self-assembled heterojunction quantum dots

Zhiqiang Zhou, Yingqiang Xu, Ruiting Hao, Bao Tang, Zhengwei Ren, and Zhichuan Niu

J. Appl. Phys. 103, 094315 (2008); http://dx.doi.org/10.1063/1.2919121 (3 pages)

Online Publication Date: 8 May 2008

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The authors report the optical characteristics of GaSb/InAs/GaAs self-assembled heterojunction quantum dots (QDs). With increasing GaSb deposition, the room temperature emission wavelength can be extended to 1.56 μm. The photoluminescence mechanism is considered to be a type-II transition with electrons confined in InAs and holes in GaSb.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Correlation between luminescent properties and local coordination environment for erbium dopant in yttrium oxide nanotubes

Yuanbing Mao, John Bargar, Michael Toney, and Jane P. Chang

J. Appl. Phys. 103, 094316 (2008); http://dx.doi.org/10.1063/1.2912486 (8 pages) | Cited 3 times

Online Publication Date: 9 May 2008

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The local dopant coordination environment and its effect on the photoluminescent (PL) spectral features of erbium-doped yttrium oxide nanotubes (NTs) were probed by synchrotron-based x-ray diffraction (XRD), x-ray absorption near-edge spectroscopy (XANES), and extended x-ray absorption fine structure (EXAFS). XRD, XANES, and EXAFS data demonstrate that single phase solid solutions of Y(2−x)ErxO3 were formed at 0 ≤ x<0.4 and 1.2<x ≤ 2, and the valence state of Er ions in the Y2O3 NTs is +3. The x-ray spectroscopic data clearly show that the erbium dopants largely reside in two types of sites in the Y2O3 host material, both of which possess a well-defined intermediate-range structure, and that the doping of erbium into Y2O3 does not cause a loss in intermediate-range order and crystallinity in the Er3+:Y2O3 NTs. This well-defined distribution of erbium doping inside the Y2O3 matrix correlates well with the observed sharp and well-resolved PL behavior of these Er3+:Y2O3 NTs at around 1.535 μm.
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78.67.Ch Nanotubes
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
61.46.Fg Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems

Nanogranular structures formed by combinatorial control processing of size-selected metal nanoparticles

Seung Hun Huh, Doh Hyung Riu, Chang Yeoul Kim, Yasutomo Naono, Tsuneyuki Nakamura, Akinori Sugiyama, and Atsushi Nakajima

J. Appl. Phys. 103, 094317 (2008); http://dx.doi.org/10.1063/1.2913056 (7 pages) | Cited 3 times

Online Publication Date: 9 May 2008

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Nanogranular films and lines, which are composed of size-selected Au, Ni, and Pt nanoparticles (NPs) and which exhibit an intermediate structure between that of the individual NPs and that of polycrystalline ones, were produced by a fully physical process. By using a combination of techniques such as lithography, lift-off, size selection, and aerosol deposition, well-designed Au lines (linewidth W = 80 nm) and thickness-controlled rectangular patterns could be produced, while Ni and Pt NPs did not form continuous lines if the linewidth was less than W = 150 nm. This difference might be explained by the extent of collision-induced surface melting during NP deposition onto the substrate.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Magnetic-field-enhanced synthesis of single-wall carbon nanotubes in arc discharge

Michael Keidar, Igor Levchenko, Tamir Arbel, Myriam Alexander, Anthony M. Waas, and Kostya Ken Ostrikov

J. Appl. Phys. 103, 094318 (2008); http://dx.doi.org/10.1063/1.2919712 (8 pages) | Cited 12 times

Online Publication Date: 9 May 2008

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The ability to control the properties of single-wall nanotubes (SWNTs) produced in the arc discharge is important for many practical applications. Our experiments suggest that the length of SWNTs significantly increases (up to 4000 nm), along with the purity of the carbon deposit, when the magnetic field is applied to arc discharge. Scanning electron microscopy and transmission electron microscopy analyses have demonstrated that the carbon deposit produced in the magnetic-field-enhanced arc mainly consists of the isolated and bunched SWNTs. A model of a carbon nanotube interaction and growth in the thermal plasma was developed, which considers several important effects such as anode ablation that supplies the carbon plasma in an anodic arc discharge technique, and the momentum, charge, and energy transfer processes between nanotube and plasma. It is shown that the nanotube charge with respect to the plasma as well as nanotube length depend on plasma density and electric field in the interelectrode gap. For instance, nanotube charge changes from negative to positive value with an electron density decrease. The numerical simulations based on the Monte Carlo technique were performed, which explain an increase in the nanotubes produced in the magnetic-field-enhanced arc discharge.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Formation of dysprosium silicide nanowires on Si(557) with two-dimensional electronic structure

M. Wanke, K. Löser, G. Pruskil, and M. Dähne

J. Appl. Phys. 103, 094319 (2008); http://dx.doi.org/10.1063/1.2912990 (4 pages) | Cited 5 times

Online Publication Date: 12 May 2008

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The self-organized growth of dysprosium silicide nanowires on Si(557) has been studied using scanning tunneling microcopy and angle-resolved photoelectron spectroscopy. The nanowires grow on the (111) facets of the Si(557) surface with lengths exceeding 1000 nm and widths of 3–5 nm. Their metallic electronic structure shows a two-dimensional behavior with a strong dispersion, which is both parallel and perpendicular to the nanowires. For Dy coverages of around 2 Å, it is demonstrated that the nanowires consist of hexagonal DySi2 monolayers, while at higher coverages they are predominantly formed from Dy3Si5 multilayers.
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81.16.Dn Self-assembly
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.20.At Surface states, band structure, electron density of states

Graded wavelength one-dimensional photonic crystal reveals spectral characteristics of enhanced fluorescence

Patrick C. Mathias, Nikhil Ganesh, Wei Zhang, and Brian T. Cunningham

J. Appl. Phys. 103, 094320 (2008); http://dx.doi.org/10.1063/1.2917184 (6 pages) | Cited 8 times

Online Publication Date: 12 May 2008

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One-dimensional photonic crystal (PC) slabs are capable of enhancing the excitation of fluorescent material adsorbed on their surface. In this report, we demonstrate and verify by electromagnetic computer simulations that resonant leaky modes spectrally overlapping the laser wavelength used for fluorescent excitation are responsible for the enhanced excitation, and that the Q-factor of the PC resonance is proportional to the resonant electric field intensity and thus proportional to the fluorescent enhancement factor. As a demonstration, we have fabricated a single PC slab surface with an intentional spatial gradient in the resonant wavelength and demonstrate enhanced fluorescence only from locations on the PC surface with a leaky mode corresponding to a 633 nm HeNe laser used to excite Cyanine 5 dye deposited uniformly across the PC. The results show that enhanced fluorescence signals for one-dimensional PC slabs originate from increased excitation of the fluorescent dye.
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42.70.Qs Photonic bandgap materials
87.15.mq Luminescence
87.14.E- Proteins

Size and frequency dependence of effective thermal conductivity in nanosystems

F. X. Alvarez and D. Jou

J. Appl. Phys. 103, 094321 (2008); http://dx.doi.org/10.1063/1.2913057 (8 pages) | Cited 24 times

Online Publication Date: 13 May 2008

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A single phenomenological expression is proposed to describe thermal transport in a wide variety of nanoscale devices. Size and frequency dependence is studied for some nanosystems from the diffusive to the ballistic regimes. In a single expression we obtain the effective thermal conductivity of cross-plane thin layer experiments where the device has a size limitation in the direction of the flux, and nanowire and in-plane experiments where the size limitation is in a transversal direction from the flux in terms of the effective size of the device. For nonzero frequencies, the size dependence has a maximum which becomes narrower at higher frequencies. For a given size, the effective thermal conductivity decreases for increasing frequency. These features may be limited in the design of nanoscale devices, because of the accumulation of dissipated heat.
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44.10.+i Heat conduction
05.60.-k Transport processes
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
74.25.F- Transport properties

Thermal stability of sputtered Cu films with nanoscale growth twins

O. Anderoglu, A. Misra, H. Wang, and X. Zhang

J. Appl. Phys. 103, 094322 (2008); http://dx.doi.org/10.1063/1.2913322 (6 pages) | Cited 33 times

Online Publication Date: 13 May 2008

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We have investigated the thermal stability of sputter-deposited Cu thin films with a high density of nanoscale growth twins by using high-vacuum annealing up to 800 °C for 1 h. Average twin lamella thickness gradually increased from approximately 4 nm for as-deposited films to slightly less than 20 nm after annealing at 800 °C. The average columnar grain size, on the other hand, rapidly increased from approximately 50 to 500 nm. In spite of an order of magnitude increase in grain size, the annealed films retained a high hardness of 2.2 GPa, reduced from 3.5 GPa in the as-deposited state. The high hardness of the annealed films is interpreted in terms of the thermally stable nanotwinned structures. This study shows that nanostructures with a layered arrangement of low-angle coherent twin boundaries may exhibit better thermal stability than monolithic nanocrystals with high-angle grain boundaries.
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68.60.Dv Thermal stability; thermal effects
68.60.Bs Mechanical and acoustical properties
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
62.25.-g Mechanical properties of nanoscale systems
61.72.Mm Grain and twin boundaries
61.72.Cc Kinetics of defect formation and annealing

Electro-optical effect in films of azobenzene polycomplexes with cobalt

N. A. Davidenko, I. I. Davidenko, I. A. Savchenko, A. N. Popenaka, and L. B. Baath

J. Appl. Phys. 103, 094323 (2008); http://dx.doi.org/10.1063/1.2913315 (5 pages) | Cited 1 time

Online Publication Date: 14 May 2008

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Polymeric films containing azobenzene fragments with donor and acceptor groups were produced as well as films of polycomplexes of these fragments with cobalt. Absorption spectra of these films before and during application of an external electric field were investigated. Electro-optical properties of the films are conditioned by spatial reorientation of dipole moments of azobenzene groups induced by polarized light in an external electric field. Increase in dipole moments of azobenzene groups reduces the influence of cobalt ions on the electro-optical properties of the polycomplex films. In the proposed phenomenological model, the electro-optical effect is explained by effect of induced forces upon azobenzene isomers and metallic ions.
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78.20.Jq Electro-optical effects
78.66.Qn Polymers; organic compounds
78.40.Me Organic compounds and polymers

Terahertz characterization of multi-walled carbon nanotube films

Ziran Wu, Lu Wang, Yitian Peng, Abram Young, Supapan Seraphin, and Hao Xin

J. Appl. Phys. 103, 094324 (2008); http://dx.doi.org/10.1063/1.2919784 (6 pages) | Cited 4 times

Online Publication Date: 15 May 2008

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Multi-walled carbon nanotube films are characterized using terahertz time-domain spectroscopy. Both transmission and reflection experiments are performed in order to measure both the complex refractive index and the wave impedance. This method allows simultaneous extraction of both the permittivity (ε = ε′−iε″) and permeability (μ = μ′−iμ″) without any assumptions. Experimental results are obtained from 50 to 370 GHz and compared well with the microwave data (8–50 GHz) of the same sample measured using a vector network analyzer. The measured complex permittivity can be fitted with a Drude–Lorentz model in the 8–370 GHz frequency range.
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78.70.Gq Microwave and radio-frequency interactions
78.67.Ch Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
73.63.Fg Nanotubes
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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