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14 Jun 2010

Volume 96, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 96, 241101 (2010); http://dx.doi.org/10.1063/1.3449576 (3 pages)

Rui Chen, H. D. Sun, T. Wang, K. N. Hui, and H. W. Choi
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Optical detection of plasmonic and interband excitations in 1-nm-wide indium atomic wires

H. V. Chung, C. J. Kubber, G. Han, S. Rigamonti, D. Sanchez-Portal, D. Enders, A. Pucci, and T. Nagao

Appl. Phys. Lett. 96, 243101 (2010); http://dx.doi.org/10.1063/1.3451461 (3 pages) | Cited 5 times

Online Publication Date: 14 June 2010

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Infrared spectroscopy is demonstrated to sensitively detect electronic excitations in 1-nm-wide wires made of indium. The polarization-dependent spectra measured at room temperature show a strong broadband plasmonic absorption feature in the direction parallel to the wires, while in the perpendicular direction the wires stay nearly transparent in the same spectral range. At 88 K the wires do not show this broadband absorption anymore, but instead, several interband-transition features arise for both polarizations, in agreement to the gap opening of the metal-to-insulator transition as known for this one-dimensional structure.
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78.67.Uh Nanowires
78.30.Er Solid metals and alloys
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.30.+h Metal-insulator transitions and other electronic transitions

Temperature dependence of optical anisotropy of birefringent porous silicon

Kohei Nishida, Minoru Fujii, Shinji Hayashi, and Joachim Diener

Appl. Phys. Lett. 96, 243102 (2010); http://dx.doi.org/10.1063/1.3453449 (3 pages) | Cited 3 times

Online Publication Date: 14 June 2010

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Temperature dependence of the in-plane optical anisotropy of birefringent porous Si produced from a (110) Si wafer is studied. The anisotropy of refractive indices in the [001] and [1math0] directions increased about 0.3% when the temperature rose from 30 to 100 °C. The effective medium approximation could reproduce the experimental result in the low temperature range, while discrepancy appeared at high temperatures. The discrepancy suggests that the structural anisotropy of porous Si starts to relax at relatively low temperatures.
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78.20.Fm Birefringence
61.43.Gt Powders, porous materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators

Near-field recording technique for high-resolution fluorescent imaging

C. Moriguchi, W. Inami, C. Egami, Y. Kawata, S. Terakawa, M. Tsuchimori, and O. Watanabe

Appl. Phys. Lett. 96, 243103 (2010); http://dx.doi.org/10.1063/1.3455095 (3 pages) | Cited 1 time

Online Publication Date: 15 June 2010

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We present near-field fluorescent imaging with high resolution using a near-field recording technique. In this technique, optical intensity distribution localized near specimens is recorded as the surface topographic distribution of a photosensitive film. Because the technique does not require the scanning probes for detecting light, it is possible to observe living biological specimens. Fluorescence imaging is one of important tools in investigations of cell structures and functions in biology. We combined near-field recording technique with fluorescence imaging and demonstrated the observations of fluorescent particles beyond the diffraction limit.
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87.64.mt Near-field scanning
07.79.Fc Near-field scanning optical microscopes
87.16.-b Subcellular structure and processes

Self-organized phase segregation between inorganic nanocrystals and PC61BM for hybrid high-efficiency bulk heterojunction photovoltaic cells

Sai-Wing Tsang, Huiying Fu, Jianying Ouyang, Yanguang Zhang, Kui Yu, Jianping Lu, and Ye Tao

Appl. Phys. Lett. 96, 243104 (2010); http://dx.doi.org/10.1063/1.3454923 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2010

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We demonstrate a simple approach to generate phase segregation between colloidal PbS nanocrystals (NCs) and organic [6,6]-phenyl C61 butyric acid methyl ester (PC61BM). Continuous vertical phase segregation is observed in cross-linked composite films of NCs and PC61BM. Hybrid bulk heterojunction photovoltaic cells fabricated with the phase segreated composite layer have achieved the state-of-art power conversion efficiency of 3.7% under one sun of simulated Air Mass 1.5 Global solar irradiation. The presented method can be generally applied in other NC/organic systems for the development of hybrid heterojunction photovoltaic cells.
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88.40.H- Solar cells (photovoltaics)
64.75.Xc Phase separation and segregation in colloidal systems
84.60.Jt Photoelectric conversion

A surface diffusion model for Dip Pen Nanolithography line writing

Sourabh K. Saha and Martin L. Culpepper

Appl. Phys. Lett. 96, 243105 (2010); http://dx.doi.org/10.1063/1.3454777 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2010

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Dip Pen Nanolithography is a direct write process that creates nanoscale dots and lines. Models typically predict dot and line size via assumption of constant ink flow rate from tip to substrate. This is appropriate for dot writing. It is however well-known, though models rarely reflect, that the ink flow rate depends upon writing speed during line writing. Herein, we explain the physical phenomenon that governs line writing and use this to model tip-substrate diffusion in line writing. We accurately predict (i) the increase in flow rate with writing speed and (ii) line width within 12.5%.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
68.35.Fx Diffusion; interface formation

Field assisted sintering of nickel nanoparticles during in situ transmission electron microscopy

Troy B. Holland, Andrew M. Thron, Cecile S. Bonifacio, Amiya K. Mukherjee, and Klaus van Benthem

Appl. Phys. Lett. 96, 243106 (2010); http://dx.doi.org/10.1063/1.3452327 (3 pages)

Online Publication Date: 17 June 2010

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This study reports the in situ transmission electron microscopy (TEM) observation of pressure-less field-assisted sintering of agglomerated nanometric nickel particles. Scanning tunneling microscopy inside the TEM was used to apply an electrical current directly to the powder particles. Electrical testing during the experiment reveals that consolidation occurs in the absence of an external heat source. Neck formation between adjacent particles and attendant increase in local Joule heating causes rapid densification. The results represent a first stepping stone towards achieving a fundamental mechanistic understanding of the atomic-scale processes that enable field-enhanced sintering of conductive nanogranular materials.
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81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes

Two-state conductance in single Zn porphyrin molecular junctions

Guoguang Qian, Swatilekha Saha, and K. M. Lewis

Appl. Phys. Lett. 96, 243107 (2010); http://dx.doi.org/10.1063/1.3452353 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2010

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Conductance measurements were taken by forming single molecule junctions between a scanning tunneling microscope tip and a gold substrate. We observed the existence of a two-state conductance in porphyrin molecules ligating a zinc atom. Peaks in the conductance histograms showed molecules changed from a high conductance state to a low conductance state. This effect was not observed for porphyrin molecules without a ligating atom. We discuss how this phenomenon may be attributed to conformational changes in the molecule.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
85.65.+h Molecular electronic devices
07.79.Cz Scanning tunneling microscopes

Metal nanoparticle plasmonics inside reflecting metal films

A. A. Earp and G. B. Smith

Appl. Phys. Lett. 96, 243108 (2010); http://dx.doi.org/10.1063/1.3455331 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2010

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Oxide coated metal nanoparticles buried within a thin metal layer support a surface plasmon resonance. A local dip occurs in spectral reflectance along with a switching off of the film’s plasmonic response. Models are introduced in which these resonances are tunable by altering the ratio of oxide thickness to core particle radius. The optical response of two experimental examples is presented and modeled using effective medium theory. Beyond the resonance zone the doped layer switches back to the plasmonic response of a nanoporous version of the host metal whose effective plasma frequency arises only from the percolating component.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Lp Collective excitations

Analytical model for the boundary scattering phonon mean free path and thermal conductivity of nanowire heterostructures

Xiang Lü

Appl. Phys. Lett. 96, 243109 (2010); http://dx.doi.org/10.1063/1.3455314 (3 pages) | Cited 1 time

Online Publication Date: 18 June 2010

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Boundary scattering phonon mean free path (MFP) is an important parameter for thermal conductivity calculation of nanocomposites. In this work, a simple approximate model is proposed to predict boundary/interface scattering MFP and thermal conductivity of nanowire heterostructures (NWHSs) based on Casimir formalism. Calculated thermal conductivities of Si tubular nanowires and Si/Ge NWHSs agree well with the numerical and analytical solutions of Boltzmann transport equation. It is demonstrated that core/shell layer thickness plays a significant role on tuning NWHS thermal conductivity. The results indicate the approximate model of thermal conductivity can be used for quickly evaluating the thermal behavior of nanocomposites.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
05.60.-k Transport processes
61.46.Np Structure of nanotubes (hollow nanowires)

The electronic properties of graphene nanoribbons with boron/nitrogen codoping

Zhiyong Wang, Huifang Hu, and Hui Zeng

Appl. Phys. Lett. 96, 243110 (2010); http://dx.doi.org/10.1063/1.3455884 (3 pages) | Cited 9 times

Online Publication Date: 18 June 2010

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The electronic properties of graphene nanoribbons with boron/nitrogen codoping at different sites are investigated by performing first-principles calculations based on density functional theory. The calculated results show that the band structures of these doping configurations have distinctly changed around the Fermi level with gradual increasing the distance between nitrogen atom and boron atom. Doping positions regulate the electronic structure of the graphene nanoribbons. Interestingly, our results exhibit both semiconducting and half-metallic behavior in response to the boron/nitrogen codoping at different sites without an applied electronic field, opening a possibility in spintronics device application.
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73.22.Pr Electronic structure of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.60.+g Mixed conductivity and conductivity transitions
61.72.U- Doping and impurity implantation
72.25.Dc Spin polarized transport in semiconductors

Infrared-wave number-dependent metal–insulator transition in vanadium dioxide nanoparticles

Kyu Won Lee, Jin Jung Kweon, Cheol Eui Lee, A. Gedanken, and R. Ganesan

Appl. Phys. Lett. 96, 243111 (2010); http://dx.doi.org/10.1063/1.3454783 (3 pages) | Cited 7 times

Online Publication Date: 18 June 2010

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We have studied the metal–insulator transition (MIT) taking place at 340 K in vanadium dioxide nanoparticles. A peculiar nanosize effect on the 10-nm-sized VO2 nanoparticles is reported. While the infrared transmittance at high wave numbers displayed a broad transition behavior, the magnetic susceptibility and infrared transmittance at low wave numbers showed a sharp first-order MIT. Our results suggest that the size effect on the MIT is due to the surface region while the core region undergoes the same MIT as that in the bulk.
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71.30.+h Metal-insulator transitions and other electronic transitions
78.30.Hv Other nonmetallic inorganics
75.30.Cr Saturation moments and magnetic susceptibilities
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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