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15 Feb 2010

Volume 96, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 072501 (2010); http://dx.doi.org/10.1063/1.3314301 (3 pages)

T. Hesjedal and T. Phung
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Effects of conducting polymer poly(3, 4-ethylenedioxythiophene) nanotubes on the electro-optical and dielectric properties of a nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl host

Sharmistha Ghosh, Prasenjit Nayek, Subir Kr. Roy, Rupali Gangopadhyay, Mijanur Rahaman Molla, and Roman Dabrowski

Appl. Phys. Lett. 96, 073101 (2010); http://dx.doi.org/10.1063/1.3308497 (3 pages) | Cited 3 times

Online Publication Date: 16 February 2010

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We report the results of the optical transmission and the capacitance behavior as a function dc electric field of a pristine liquid crystal and conducting polymer nanotube-liquid crystal composite measured in twisted nematic cells. The threshold and driving voltages have been determined from transmission-voltage curve. There is remarkable reduction in the threshold and driving voltage in the polymer nanotube doped liquid crystal cell which is good from application point of view. The residual dc is also reduced significantly in the doped cell and the reduction is even more than that observed in the carbon nanotube doped same liquid crystal system.
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78.20.Jq Electro-optical effects
61.30.-v Liquid crystals
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
77.80.Dj Domain structure; hysteresis
77.84.Lf Composite materials
61.72.up Other materials

Comparative photoluminescence study of close-packed and colloidal InP/ZnS quantum dots

Ung Thi Dieu Thuy, Pham Thi Thuy, Nguyen Quang Liem, Liang Li, and Peter Reiss

Appl. Phys. Lett. 96, 073102 (2010); http://dx.doi.org/10.1063/1.3291049 (3 pages) | Cited 12 times

Online Publication Date: 16 February 2010

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This letter reports on the comparative photoluminescence study of InP/ZnS quantum dots in the close-packed solid state and in colloidal solution. The steady-state photoluminescence spectrum of the close-packed InP/ZnS quantum dots peaks at a longer wavelength than that of the colloidal ones. Time-resolved photoluminescence shows that the close-packed quantum dots possess a shorter luminescence decay time and strongly increased spectral shift with the time delayed from the excitation moment in comparison with the colloidal ones. The observed behavior is discussed on the basis of energy transfer enabled by the short interparticle distance between the close-packed quantum dots.
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78.67.Hc Quantum dots
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors
78.55.Et II-VI semiconductors
78.47.da Excited states
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Tunable self-organization of nanocomposite multilayers

C. Q. Chen, Y. T. Pei, K. P. Shaha, and J. Th. M. De Hosson

Appl. Phys. Lett. 96, 073103 (2010); http://dx.doi.org/10.1063/1.3318262 (3 pages) | Cited 4 times

Online Publication Date: 16 February 2010

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In this letter we report the controlled growth and microstructural evolution of self-assembled nanocomposite multilayers that are induced by surface ion-impingement. The nanoscale structures together with chemical composition, especially at the growing front, have been investigated with high-resolution transmission electron microscopy. Concurrent ion impingement of growing films produces an amorphous capping layer 3 nm in thickness where spatially modulated phase separation is initiated. It is shown that the modulation of multilayers as controlled by the self-organization of nanocrystallites below the capping layer, can be tuned through the entire film.
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81.16.Dn Self-assembly
81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
81.07.-b Nanoscale materials and structures: fabrication and characterization
64.75.Jk Phase separation and segregation in nanoscale systems
81.05.uj Diamond/nanocarbon composites

Distance-controlled scattering in a plasmonic trap

Lina Huang and Olivier J. F. Martin

Appl. Phys. Lett. 96, 073104 (2010); http://dx.doi.org/10.1063/1.3291564 (3 pages)

Online Publication Date: 16 February 2010

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Light scattered by a dielectric object when it is trapped in the field of a plasmonic nanostructure is studied theoretically and experimentally using both dielectric spheres and S. cerevisiae cells. A dramatic enhancement of the scattered light is observed for short separation distances between scatterer and plasmonic trap. It is shown that this effect can serve to selectively image cells after their immobilization and distinguish them from a turbid background. The high sensitivity of the scattered light to the separation distance and lateral displacement also provides additional insights in the configuration of the cell within the trap.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.-f Electronic structure of nanoscale materials and related systems
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
42.25.Fx Diffraction and scattering

Raman mapping probing of tip-induced anomalous polarization behavior in V2O5 waveguiding nanoribbons

Bin Yan, Chaoling Du, Lei Liao, Yumeng You, Hao Cheng, Zexiang Shen, and Ting Yu

Appl. Phys. Lett. 96, 073105 (2010); http://dx.doi.org/10.1063/1.3323090 (3 pages) | Cited 3 times

Online Publication Date: 16 February 2010

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Spatially resolved and polarized micro-Raman spectroscopy has been performed on individual V2O5 waveguiding nanoribbons. The experimental results establish that the Raman-antenna patterns are strongly correlated with the local positions of the sample, which gives rise to a pronounced intensity contrast in the polarized mapping for certain phonon modes. The suppressed phonon signals at the body of a ribbon can be enhanced at the end facets, resulting from the effective waveguiding propagation along the nanoribbon and strong local electric field intensity at the ends. The phenomena reported here, in addition to providing insight into the tip effects on optoelectronic nanodevices, will facilitate the rational design of Raman detection in nanostructures.
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84.40.Az Waveguides, transmission lines, striplines
85.60.-q Optoelectronic devices
78.30.Hv Other nonmetallic inorganics
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Tuning magnetostatic interaction in single-crystalline nanodot arrays with in-plane easy axes

Jungpil Seo, T.-H. Kim, S.-H. Chung, Y. Oh, J. H. Choi, and Young Kuk

Appl. Phys. Lett. 96, 073106 (2010); http://dx.doi.org/10.1063/1.3323094 (3 pages) | Cited 2 times

Online Publication Date: 16 February 2010

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We have fabricated an ultrahigh-vacuum-processed, ordered, single-crystalline nanodot array. By mapping the magnetization of the nanodots with spin polarized scanning tunneling microscopy in the same chamber where they were grown, we are able to understand how the short-range order of the nanodot array is determined by the magnetostatic dipole interaction among neighboring nanodots. We also demonstrate tuning the magnetic interaction in the nanodot array by controlling those magnetic energies. Further magnetic simulations support the observed results consistently.
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75.75.-c Magnetic properties of nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

GaN stripes on vertical {111} fin facets of (110)-oriented Si substrates

V. V. Kuryatkov, W. Feng, M. Pandikunta, J. H. Woo, D. Garcia, H. R. Harris, S. A. Nikishin, and M. Holtz

Appl. Phys. Lett. 96, 073107 (2010); http://dx.doi.org/10.1063/1.3310279 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2010

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Selective sidewall epitaxy of AlN/GaN is reported on vertical fins of silicon using metallorganic vapor phase epitaxy. Silicon (110) wafers are structured to form fins with {111} sidewall facets. AlN buffer layers are grown with uniform thickness on vertical {111} surfaces, followed by GaN which grows selectively on the AlN to form the sidewall fin structures. Raman measurements of the GaN show very narrow line widths, consistent with excellent material quality. Spatial dependence from microcathodoluminescence mapping of the GaN band gap emission shows compressive strain in the GaN relaxes closer to the fin corners.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors

Coherent superposition of exciton states in quantum dots induced by surface plasmons

D. E. Gómez, K. C. Vernon, P. Mulvaney, and T. J. Davis

Appl. Phys. Lett. 96, 073108 (2010); http://dx.doi.org/10.1063/1.3313935 (3 pages) | Cited 8 times

Online Publication Date: 16 February 2010

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We present an experimental demonstration of strong optical coupling between CdSe quantum dots of different sizes which is induced by a surface plasmon propagating on a planar silver thin film. Attenuated total reflection measurements demonstrate the hybridization of exciton states, characterized by the observation of two avoided crossings in the energy dispersion measured for the interacting system.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

High intensity, plasma-induced electron emission from large area carbon nanotube array cathodes

Qingliang Liao, Ya Yang, Junjie Qi, Yue Zhang, Yunhua Huang, Liansheng Xia, and Liang Liu

Appl. Phys. Lett. 96, 073109 (2010); http://dx.doi.org/10.1063/1.3313944 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2010

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The plasma-induced electron emission properties of large area carbon nanotube (CNT) array cathodes under different pulse electric fields were investigated. The formation and expansion of cathode plasmas were proved; in addition, the cathodes have higher emission current in the double-pulse mode than that in the single-pulse mode due to the expansion of plasma. Under the double-pulse electric field of 8.16 V/μm, the plasma’s expansion velocity is about 12.33 cm/μs and the highest emission current density reached 107.72 A/cm2. The Cerenkov radiation was used to diagnose the distribution of electron beams, and the electron beams’ generating process was plasma-induced emission.
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79.70.+q Field emission, ionization, evaporation, and desorption
41.60.Bq Cherenkov radiation
61.80.Fe Electron and positron radiation effects
82.45.Fk Electrodes
61.46.Fg Nanotubes

Interfacial effect on metal/oxide nanowire junctions

Kazuki Nagashima, Takeshi Yanagida, Annop Klamchuen, Masaki Kanai, Keisuke Oka, Shu Seki, and Tomoji Kawai

Appl. Phys. Lett. 96, 073110 (2010); http://dx.doi.org/10.1063/1.3318257 (3 pages) | Cited 12 times

Online Publication Date: 18 February 2010

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An interface in metal/oxide nanowire junctions plays a crucial role on the electronic device applications, especially two-terminal devices. Here we demonstrate the crucial role of interfacial effects on oxide (SnO2−δ) nanowire/Pt junctions. The resistivity estimated from the I-V data of the junctions was four orders of magnitudes higher than that measured by a noncontact microwave conductivity method. We found that such apparent discrepancy is due to the presence of insulating oxidized interfacial layer. Since most conductive oxides are typically n-type semiconductors via oxygen vacancies, above implications will be rather universal and crucial for reproducible emerging nanodevices using oxide nanowires.
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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)
61.72.jd Vacancies
72.30.+q High-frequency effects; plasma effects
73.40.Ns Metal-nonmetal contacts
68.65.La Quantum wires (patterned in quantum wells)

Nanoparticle-enhanced thin film solar cells: Metallic or dielectric nanoparticles?

Yu. A. Akimov, W. S. Koh, S. Y. Sian, and S. Ren

Appl. Phys. Lett. 96, 073111 (2010); http://dx.doi.org/10.1063/1.3315942 (3 pages) | Cited 31 times

Online Publication Date: 18 February 2010

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Recently, thin film solar cells enhanced by nanoparticles have attracted much attention of the scientific community. To improve the performance of such cells, a systematic study on the influence of the nanoparticle material on the efficiency of the enhancement is performed. Based on optimization of the nanoparticle array parameters, the role of dispersion and dissipation of the nanoparticle material is discussed and analyzed with respect to optical absorption of the photoactive layer. Finally, it is demonstrated that the use of dielectric nanoparticles can lead to similar and even higher enhancements compared to that of metal nanoparticles.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

A pathway for self-assembly of metallic nanostructures on quantum-modulated flat Pb(111)/Si(111) substrate

Cuipeng Zhang and Maozhi Li

Appl. Phys. Lett. 96, 073112 (2010); http://dx.doi.org/10.1063/1.3327335 (3 pages)

Online Publication Date: 18 February 2010

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A mechanism of self-assembly of metallic nanostructures on a quantum-modulated flat Pb(111) thin film with patterned Si(111) substrate is proposed based on recent experimental observations [ S. M. Binz, M. Hupalo, and M. C. Tringides, Phys. Rev. B 78, 193407 (2008) ] which indicates that because of quantum size effects (QSE), the buried steps act as real steps on surfaces. This intriguing feature offers a potential pathway for self-assembly of functional metallic nanostructures, e.g., nanowires on flat Pb(111) films with designed patterned Si(111) surface as substrate, where QSE can be controlled artificially. The growth conditions for nanowires on a designed Pb(111)/Si(111) substrate is explored by kinetic Monte Carlo simulations.
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81.16.Dn Self-assembly
81.07.Gf Nanowires
68.55.-a Thin film structure and morphology

Application of magnetic atom induced bound states in superconducting gap for chemical identification of single magnetic atoms

Shuai-Hua Ji, Tong Zhang, Ying-Shuang Fu, Xi Chen, Jin-Feng Jia, Qi-Kun Xue, and Xu-Cun Ma

Appl. Phys. Lett. 96, 073113 (2010); http://dx.doi.org/10.1063/1.3318404 (3 pages)

Online Publication Date: 18 February 2010

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Elemental identification at single atom level has been achieved with a low temperature scanning tunneling microscope. Magnetic atoms (Mn or Cr) adsorbed on a superconducting Pb substrate induce a set of well-defined resonance states inside the superconductor gap in scanning tunneling spectroscopy. We show that these localized characteristic bound states could serve as fingerprint for chemical identification of the corresponding atoms, similar to atomic/molecular spectra widely used in optical spectrometry. The experiment demonstrates a technique for element-resolved spectroscopy with simultaneous atomic-level spatial resolution. The influence of magnetic impurity concentration on the bound states has also been investigated.
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74.25.Jb Electronic structure (photoemission, etc.)
68.43.Mn Adsorption kinetics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.55.+v Tunneling phenomena: single particle tunneling and STM

Asymmetry and shape transitions of epitaxially strained islands on vicinal surfaces

B. J. Spencer and J. Tersoff

Appl. Phys. Lett. 96, 073114 (2010); http://dx.doi.org/10.1063/1.3318256 (3 pages) | Cited 3 times

Online Publication Date: 19 February 2010

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We calculate the shapes of epitaxially strained islands on vicinal substrates, within a fully facetted, two-dimensional model. For nonzero miscut, islands first form as asymmetric “half-pyramid” shapes, with no nucleation barrier even in a fully facetted system. As islands grow, they change shape through a series of first-order transitions. The substrate miscut determines what island types occur in the growth sequence; sufficiently large miscut can stabilize qualitatively asymmetric shapes such as “half domes.” Our results are summarized in a phase diagram of shape versus island volume and miscut. The results are consistent with available experiments for Ge on Si.
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68.55.ag Semiconductors
81.05.Cy Elemental semiconductors
68.35.Rh Phase transitions and critical phenomena
68.35.bg Semiconductors

ZnO nanoparticles and nanowire array hybrid photoanodes for dye-sensitized solar cells

Supan Yodyingyong, Qifeng Zhang, Kwangsuk Park, Christopher S. Dandeneau, Xiaoyuan Zhou, Darapond Triampo, and Guozhong Cao

Appl. Phys. Lett. 96, 073115 (2010); http://dx.doi.org/10.1063/1.3327339 (3 pages) | Cited 44 times

Online Publication Date: 19 February 2010

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ZnO nanoparticle-nanowire (NP-NW) array hybrid photoanodes for dye-sensitized solar cell (DSC) with NW arrays to serve as a direct pathway for fast electron transport and NPs dispersed between NWs to offer a high specific surface area for sufficient dye adsorption has been fabricated and investigated to improve the power conversion efficiency (PCE). The overall PCE of the ZnO hybrid photoanode DSC with the N3-sensitized has reached ∼ 4.2%, much higher than both ∼ 1.58% of ZnO NW DSC and ∼ 1.31% of ZnO NP DSC, prepared and tested under otherwise identical conditions.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.hj Efficiency and performance of solar cells
81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing

Supermolecular switches based on multiwalled carbon nanotubes

A. Subramanian, L. X. Dong, B. J. Nelson, and A. Ferreira

Appl. Phys. Lett. 96, 073116 (2010); http://dx.doi.org/10.1063/1.3327514 (3 pages) | Cited 8 times

Online Publication Date: 19 February 2010

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Electrostatically actuated nanoelectromechanical switches based on intershell displacement mechanisms within batch fabricated, bidirectional multiwalled carbon nanotube (MWNT) bearings are reported. Multiple devices with a 220 nm pitch are constructed within individual MWNT supermolecules. Experimental results on performance metrics including low switching voltages (0.8 to 6 V), repeatability, hysteresis, and failure modes are presented.
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81.07.Oj Nanoelectromechanical systems (NEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Dd Connectors, relays, and switches
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