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1 Feb 2008

Volume 103, Issue 3, Articles (03xxxx)

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J. Appl. Phys. 103, 031101 (2008); http://dx.doi.org/10.1063/1.2836410 (35 pages)

Ce-Wen Nan, M. I. Bichurin, Shuxiang Dong, D. Viehland, and G. Srinivasan
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Improved fabrication of zero-mode waveguides for single-molecule detection

Mathieu Foquet, Kevan T. Samiee, Xiangxu Kong, Bidhan P. Chauduri, Paul M. Lundquist, Stephen W. Turner, Jake Freudenthal, and Daniel B. Roitman

J. Appl. Phys. 103, 034301 (2008); http://dx.doi.org/10.1063/1.2831366 (9 pages) | Cited 19 times

Online Publication Date: 4 February 2008

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Metallic subwavelength apertures can be used in epi-illumination fluorescence to achieve focal volume confinement. Because of the near field components inherent to small metallic structures, observation volumes are formed that are much smaller than the conventional diffraction limited volume attainable by high numerical aperture far field optics (circa a femtoliter). Observation volumes in the range of 10−4 fl have been reported previously. Such apertures can be used for single-molecule detection at relatively high concentrations (up to 20 μM) of fluorophores. Here, we present a novel fabrication of metallic subwavelength apertures in the visible range. Using a new electron beam lithography process, uniform arrays of such apertures can be manufactured efficiently in large numbers with diameters in the range of 60–100 nm. The apertures were characterized by scanning electron microscopy, optical microscopy, focused ion beam cross sections/transmission electron microscopy, and fluorescence correlation spectroscopy measurements, which confirmed their geometry and optical confinement. Process throughput can be further increased using deep ultraviolet photolithography to replace electron beam lithography. This enables the production of aperture arrays in a high volume manufacturing environment.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
07.60.-j Optical instruments and equipment

Incremental analysis of the magnetization behavior in iron-filled carbon nanotube arrays

C. Müller, D. Elefant, A. Leonhardt, and B. Büchner

J. Appl. Phys. 103, 034302 (2008); http://dx.doi.org/10.1063/1.2837037 (5 pages) | Cited 4 times

Online Publication Date: 4 February 2008

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We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embedding of aligned iron-filled carbon nanotubes in silicon oxide using thermal chemical vapor deposition and gradual mechanical polishing afterwards. On the one hand, during the covering process the saturation magnetization moment rises due to the transformation of Fe3C into body-centered-cubic-Fe and graphite. On the other hand, the coercivity drops, mainly induced by changes in the shape of the nanowires. Further magnetization measurements of the embedded sample point to most of the ferromagnetic nanowires being located near the surface of the substrate. The coercivity increases when reducing the thickness of the nanotube array. The anomalous high coercivity of the Fe nanowires encapsulated by non magnetic carbon nanotubes make them suitable for high density data storage applications.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Bb Fe and its alloys
75.50.Dd Nonmetallic ferromagnetic materials
61.46.Fg Nanotubes

Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field: Simplified theory and relative comparison

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

J. Appl. Phys. 103, 034303 (2008); http://dx.doi.org/10.1063/1.2827365 (21 pages) | Cited 3 times

Online Publication Date: 6 February 2008

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We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized analysis. The TPM has also been investigated in QWs of II-VI, IV-VI, stressed materials, n-GaP, p-PtSb2, n-GaSb, and bismuth on the basis of the appropriate carrier dispersion laws in the respective cases. It has been found, taking QWs of n-CdGeAs2, n-Cd3As2, n-InAs, n-InSb, n-GaAs, n-Hg1−xCdxTe, n-In1−xGaxAsyP1−y lattice-matched to InP, p-CdS, n-PbTe, n-PbSnTe, n-Pb1−xSnxSe, stressed n-InSb, n-GaP, p-PtSb2, n-GaSb, and bismuth as examples, that the respective TPM in the QWs of the aforementioned materials exhibits increasing quantum steps with the decreasing electron statistics with different numerical values, and the nature of the variations are totally band-structure-dependent. In CNTs, the TPM exhibits periodic oscillations with decreasing amplitudes for increasing electron statistics, and its nature is radically different as compared with the corresponding TPM of QWs since they depend exclusively on the respective band structures emphasizing the different signatures of the two entirely different one-dimensional nanostructured systems in various cases. The well-known expression of the TPM for wide gap materials has been obtained as a special case under certain limiting conditions, and this compatibility is an indirect test for our generalized formalism. In addition, we have suggested the experimental methods of determining the Einstein relation for the diffusivity-mobility ratio and the carrier contribution to the elastic constants for materials having arbitrary dispersion laws.
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73.63.Fg Nanotubes
73.63.Nm Quantum wires
78.67.Ch Nanotubes
78.67.Lt Quantum wires
73.21.Hb Quantum wires
73.22.-f Electronic structure of nanoscale materials and related systems
72.20.Pa Thermoelectric and thermomagnetic effects

Channel plasmon-polariton modes in V grooves filled with dielectric

Kristy C. Vernon, Dmitri K. Gramotnev, and D. F. P. Pile

J. Appl. Phys. 103, 034304 (2008); http://dx.doi.org/10.1063/1.2832441 (6 pages) | Cited 16 times

Online Publication Date: 7 February 2008

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We investigated the effect of dielectric filling in a V groove on the propagation parameters of channel plasmon-polariton (CPP) modes. In particular, existence conditions and critical groove angles, mode localization, field structure, dispersion, and propagation distances of CPP modes are analyzed as functions of dielectric permittivity inside the groove. It is demonstrated that increasing dielectric permittivity in the groove results in a rapid increase of mode localization near the tip of the groove and increase of both the critical angles that determine a range of groove angles for which CPP modes can exist. Detailed analysis of the field structure has demonstrated that the maximum of the field in a CPP mode is typically reached at a small distance from the tip of the groove. The effect of rounded tip is also investigated.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
63.20.Pw Localized modes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
77.22.Ch Permittivity (dielectric function)

Ferroelectric properties of nanometer-scale barium titanate films from first principles

Y.-H. Tang and M.-H. Tsai

J. Appl. Phys. 103, 034305 (2008); http://dx.doi.org/10.1063/1.2838464 (6 pages) | Cited 3 times

Online Publication Date: 7 February 2008

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Ferroelectric properties of nanometer-scale barium titanate films with one, two, and three TiO6 octahedral layers stacking along the [001] direction have been studied by the first-principles calculation method. The freestanding barium titanate films are found to be ferroelectric with spontaneously formed electric dipoles parallel to the films by the existence of double-well potentials. The depth of the potential well of the free standing film is found to decrease with the increase of the thickness. However, when the substrate effect is considered, the depth of the potential well becomes deeper for thicker films, which suggests an enhancement of the ferroelectric property for thicker films.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Increase of thermal resistance between a nanostructure and a surface due to phonon multireflections

Sebastian Volz and Pierre-Olivier Chapuis

J. Appl. Phys. 103, 034306 (2008); http://dx.doi.org/10.1063/1.2837833 (9 pages) | Cited 4 times

Online Publication Date: 12 February 2008

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The thermal resistance between a nanostructure and a half-body is calculated in the framework of particle-phonons physics. The current models approximate the nanostructure as a thermal bath. We prove that the multireflections of heat carriers in the nanostructure significantly increase resistance, in contradiction with former predictions. This increase depends on the shape of the nanostructure and the heat carrier’s mean-free path only. We provide a general and simple expression for the contact resistance and examine the specific cases of nanowires and nanoparticles.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
31.15.xv Molecular dynamics and other numerical methods
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Terahertz photon-assisted tunneling in carbon nanotube quantum dots

Y. Kawano, T. Fuse, S. Toyokawa, T. Uchida, and K. Ishibashi

J. Appl. Phys. 103, 034307 (2008); http://dx.doi.org/10.1063/1.2838237 (4 pages) | Cited 15 times

Online Publication Date: 12 February 2008

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The authors have studied the transport properties of carbon nanotube quantum dots under terahertz (THz) wave irradiation. The experimental data have shown that the satellite currents are generated with the THz irradiation, and that the peak position of the satellite currents varies linearly with the THz photon energy. These results provide experimental evidence for photon-assisted tunneling in the THz region. The present observation provides the interesting possibility of developing a highly sensitive and frequency-tunable THz detector capable of high-temperature operation.
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73.63.Fg Nanotubes
73.63.Kv Quantum dots
73.40.Gk Tunneling

Combustion-aided suspension plasma spraying of Y2O3 nanoparticles: Synthesis and modeling

X. L. Sun, A. I. Y. Tok, S. L. Lim, F. Y. C. Boey, C. W. Kang, and H. W. Ng

J. Appl. Phys. 103, 034308 (2008); http://dx.doi.org/10.1063/1.2841524 (13 pages) | Cited 1 time

Online Publication Date: 13 February 2008

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Combustion-aided suspension plasma spraying (SPS) was developed for the synthesis of Y2O3 nanoparticles. Numerical models for Ar, Ar/O2, and combustion-aided plasma fields were built using FLUENT V6.3.2© to compare their different plasma thermophysical properties. Modeling and experimental results both indicate that the plasma field was substantially altered by combustion-aided SPS. The plasma exhibited an elevated volume average temperature and reduced velocity as well as a broadened plasma plume, which resulted in an enhanced vapor supersaturation degree and a faster quenching rate in the radial direction. These can be attributed to the dual effects of oxygen dissociation/recombination and acetone solvent combustion. Consequently, productivity of the obtained nanoparticles increased remarkably and the particles’ morphology was improved, with a smaller mean particle size and a narrower size distribution in comparison with those of powder feeding spraying. Furthermore, plasma-induced cubic→monoclinic phase transformation in the as-sprayed Y2O3 particles was restrained by combustion-aided SPS to some extent.
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81.07.Bc Nanocrystalline materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.16.Be Chemical synthesis methods
81.05.Cy Elemental semiconductors
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
82.33.Vx Reactions in flames, combustion, and explosions

Depolarization effect in reflection-mode tip-enhanced Raman scattering for Raman active crystals

Masashi Motohashi, Norihiko Hayazawa, Alvarado Tarun, and Satoshi Kawata

J. Appl. Phys. 103, 034309 (2008); http://dx.doi.org/10.1063/1.2837837 (9 pages) | Cited 19 times

Online Publication Date: 15 February 2008

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Reflection-mode tip-enhanced Raman scattering (TERS) has the advantage to characterize any sample, particularly opaque, bulk, and multilayered samples. However, the background signal in reflection-mode TERS is huge due to large focus spots associated with an objective lens that has a long working distance. Moreover, for a multilayered and bulk sample, the Raman signal from the bulk layer interferes with the Raman signal on a thin surface layer. This unwanted bulk background signal reduces the sensitivity of the measurement and makes it difficult to get a high-contrast TERS image in the reflection mode. Here, we demonstrate two techniques to suppress the far-field Raman signals coming from the focus area and bulk silicon germanium substrate. First, we reduce the far-field signal by controlling the polarization state of the incident and scattered Raman as well as manipulating the well-defined polarization of a crystalline sample, which strongly depends on the polarization and propagation of the incident light. We used Raman tensor analysis to quantify the far-field Raman intensity at different polarization states of the polarizer and analyzer at varying sample azimuth. The results of the surface-enhanced Raman spectroscopy experiments were in good agreement with the far-field Raman tensor calculation. The polarizer, analyzer, and sample azimuth combination that gives minimum far-field background signals with high contrast in SERS was utilized in the TERS experiment to obtain a high-contrast near-field Raman signal. Both the field enhancement effect and depolarized detection were considered to obtain a high signal-to-noise TERS signal. We found that, for Raman active and thin crystalline samples assembled in bulk materials, the depolarization effect outweighs the field enhancement effect in getting a high-contrast Raman signal.
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78.30.Am Elemental semiconductors and insulators
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