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14 Feb 2011

Volume 98, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 98, 073101 (2011); http://dx.doi.org/10.1063/1.3554360 (3 pages)

Wei Xu, Rajesh Leeladhar, Yao-Tsan Tsai, Eui-Hyeok Yang, and Chang-Hwan Choi
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Optically nonactive assorted helix array with interchangeable magnetic/electric resonance

Xiang Xiong, Xiao-Chun Chen, Mu Wang, Ru-Wen Peng, Da-Jun Shu, and Cheng Sun

Appl. Phys. Lett. 98, 071901 (2011); http://dx.doi.org/10.1063/1.3554704 (3 pages) | Cited 3 times

Online Publication Date: 14 February 2011

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We report here the design of an optically nonactive metamaterial by assembling metallic helices with different chiralities. With linearly polarized incident light, pure electric or magnetic resonance can be selectively realized, which accordingly leads to negative permittivity or negative permeability. Further, we show that pure electric or magnetic resonance can be interchanged at the same frequency band by merely changing the polarization of incident light for 90°. This design demonstrates a unique approach in constructing metamaterials.
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42.70.-a Optical materials
42.25.Ja Polarization
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

LaVO4:Eu Phosphor films with enhanced Eu solubility

T. Higuchi, Y. Hotta, Y. Hikita, S. Maruyama, Y. Hayamizu, H. Akiyama, H. Wadati, D. G. Hawthorn, T. Z. Regier, R. I. R. Blyth, G. A. Sawatzky, and H. Y. Hwang

Appl. Phys. Lett. 98, 071902 (2011); http://dx.doi.org/10.1063/1.3554749 (3 pages) | Cited 4 times

Online Publication Date: 14 February 2011

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Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO4:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd–Ofelt theory. However, the low solubility limit (<3 mol %) of Eu in LaVO4 prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO4:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO4:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO4.
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78.55.Hx Other solid inorganic materials
68.55.at Other materials
81.40.Gh Other heat and thermomechanical treatments
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators

Extraordinary infrared photoluminescence efficiency of Er0.1Yb1.9SiO5 films on SiO2/Si substrates

X. J. Wang, B. Wang, L. Wang, R. M. Guo, H. Isshiki, T. Kimura, and Z. Zhou

Appl. Phys. Lett. 98, 071903 (2011); http://dx.doi.org/10.1063/1.3554750 (3 pages) | Cited 8 times

Online Publication Date: 14 February 2011

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Extraordinary infrared photoluminescence efficiency was found for Er2SiO5 film by optimizing the composition of Yb additions on SiO2/Si substrates. Above two orders of magnitude enhanced 1.53 μm Er3+ photoluminescence for the Er0.1Yb1.9SiO5 film on SiO2/Si substrate was obtained by pumping at 980 nm compared with pure Er2SiO5 film on Si substrate at 654 nm. All Er ions for Er0.1Yb1.9SiO5 film are optically active. The decreased nonradiative transient rate leads to extraordinary photoluminescence efficiency in the Er0.1Yb1.9SiO5 film. It indicated that the Er0.1Yb1.9SiO5 film is the sought candidate material for compact waveguide amplifiers and emitters in silicon photonics integration.
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78.55.Hx Other solid inorganic materials

Effects of controlled ambidirectional nucleation on the heteroepitaxial growth of m-GaN on m-sapphire

Hyun-Jae Lee, K. Fujii, T. Goto, T. Yao, and Jiho Chang

Appl. Phys. Lett. 98, 071904 (2011); http://dx.doi.org/10.1063/1.3553019 (3 pages) | Cited 1 time

Online Publication Date: 14 February 2011

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We found that m-plane GaN grown on m-plane sapphire nucleates in ambidirections at the initial growth stage, which seriously degrades the surface morphology and the crystallinity of m-GaN films. To avoid the ambidirectional islanding of m-plane GaN, off-cut m-plane sapphire (toward to the [11math0] direction) substrates were introduced. When the off-angle was small as 1°–2°, the surface step determined the epitaxial orientation of m-GaN islands. Hence, an m-GaN film with a smooth surface and a low-dislocation density was obtained. However, the dislocation component of m-GaN film was increased with increasing of the off angle due to step bunches.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.bg Semiconductors
81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Optical response of large scale single layer graphene

Chul Lee, Joo Youn Kim, Sukang Bae, Keun Soo Kim, Byung Hee Hong, and E. J. Choi

Appl. Phys. Lett. 98, 071905 (2011); http://dx.doi.org/10.1063/1.3555425 (3 pages) | Cited 16 times

Online Publication Date: 14 February 2011

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We have measured optical transmission and reflection spectra of large scale graphene grown by chemical vapor deposition technique over the extensive frequency range from far-IR to uv (4 meV–6.2 eV). Large scale graphene exhibits an excitonic absorption peak in the uv-region (ℏω = 4.6 eV) and the constant interband absorption with σ1(ω) = e2/4ℏ in the IR-visible region, respectively. In the far-IR range, Drude peak is observed, and its strength ωp,2d2 indicates the induced carrier density N2d = 1.95×1012 cm−2. These results are highly consistent with the theoretical prediction/experimental results of the single layer graphene. It proves that, contrary to the doubts about its quality due to the chemical growth process, the sample has single layer optical response over the entire photon energy; therefore, it can be applied to large scale devices such as terahertz-IR detector, solar cell material, and visible uv-transparent conductor.
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78.67.Wj Optical properties of graphene
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.35.-y Excitons and related phenomena
78.40.Ri Fullerenes and related materials
78.30.Na Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Manipulating the spin polarization of excitons in a single quantum dot by optical means

L. A. Larsson, E. S. Moskalenko, and P. O. Holtz

Appl. Phys. Lett. 98, 071906 (2011); http://dx.doi.org/10.1063/1.3554422 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2011

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Circular polarization studies of photoluminescence from the neutral (X0) and the positively charged (X+) excitons are reported for individual InAs/GaAs quantum dots (QDs). High polarization degrees, 60% for X0 and 73% for X+, were recorded without any external magnetic field applied. These studies show that the QD polarization and population dynamics are controllable either by varying the photoexcitation intensity or by using a second IR laser excitation.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
72.25.-b Spin polarized transport
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
73.21.La Quantum dots

Solution deposition planarization of long-length flexible substrates

Chris Sheehan, Yehyun Jung, Terry Holesinger, D. Matthew Feldmann, Cynthia Edney, Jon F. Ihlefeld, Paul G. Clem, and Vladimir Matias

Appl. Phys. Lett. 98, 071907 (2011); http://dx.doi.org/10.1063/1.3554754 (3 pages) | Cited 8 times

Online Publication Date: 15 February 2011

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Solution deposition planarization (SDP) is studied for preparing smooth flexible substrates in multimeter lengths. We demonstrate 0.5 nm rms surface roughness starting from unpolished metal tapes and a correlation of substrate roughness with the texture of subsequent ion-beam aligned films. Surface roughness reduction in SDP is modeled via film shrinkage during solution deposition and a residual roughness based on film thickness. Use of solution deposited a-Y2O3 to planarize substrates prior to ion-beam textured MgO growth shows an in-plane texture of MgO down to 4°. Utilizing these templates, we demonstrated superconducting YBa2Cu3Oy coated conductors with critical current densities of 2.8–4.0 MA/cm2 at 75 K.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.jm Texture
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Effect of liquid spreading due to nano/microstructures on the critical heat flux during pool boiling

Ho Seon Ahn, Hang Jin Jo, Soon Ho Kang, and Moo Hwan Kim

Appl. Phys. Lett. 98, 071908 (2011); http://dx.doi.org/10.1063/1.3555430 (3 pages) | Cited 15 times

Online Publication Date: 15 February 2011

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It is well known that nanoparticles deposited on a heating surface during nanofluid boiling can change the characteristics of the heating surface and increase the critical heat flux (CHF) dramatically. We considered a new approach to investigate the nanoparticle surface effect on CHF enhancement using surfaces modified with artificial micro/nanostructures similar to deposited nanoparticle structures. We examined the effect of the surface wettability and liquid spreading ability on the CHF. The results demonstrated that the CHF enhancement on the modified surfaces was a consequence of both the improved surface wettability and the liquid spreading ability of the artificial micro/nanostructures.
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68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
47.27.te Turbulent convective heat transfer
47.85.Np Fluidics
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)

Permanent photoalignment of liquid crystals on nanostructured chalcogenide glassy thin films

Miri Gelbaor, Matvey Klebanov, Victor Lyubin, and I. Abdulhalim

Appl. Phys. Lett. 98, 071909 (2011); http://dx.doi.org/10.1063/1.3555630 (3 pages) | Cited 5 times

Online Publication Date: 16 February 2011

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Photoalignment of nematic liquid crystals is obtained on the chalcogenide glassy thin film of As2S3 using irradiation with polarized blue light. A uniform homogeneously aligned device is obtained with high contrast and strong anchoring. The device alignment quality is permanent as checked by following its functionality over a period of few months. The origin of the observed photoalignment is attributed to the photoinduced anisotropy in chalcogenide glasses. No differences between the different As2S3 film thicknesses observed, thus supporting the proposition that some orientational order is photoinduced on the surface of the glass and responsible for the photoalignment.
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61.30.-v Liquid crystals
78.66.Jg Amorphous semiconductors; glasses
82.50.-m Photochemistry
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Inhibition of In desorption in diluted nitride InAsN quantum dots

D. F. Reyes, D. González, D. L. Sales, R. Gargallo-Caballero, A. Guzmán, J. M. Ulloa, and A. Hierro

Appl. Phys. Lett. 98, 071910 (2011); http://dx.doi.org/10.1063/1.3554386 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2011

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The effect of low N-alloying on the structure of capped InAs/GaAs quantum dots is analyzed by transmission electron microscopy related techniques. A statistical study of interplanar distances in InAsN quantum dots shows an increase in the lattice parameter compared to the InAs case. We suggest that the addition of nitrogen blocks the Ga/In exchange processes during the quantum dot capping process, leading to an In enrichment. The observed strong photoluminescence redshift of InAsN structures must therefore be attributed not only to the effect of nitrogen in the band gap, but also to a minor depletion of indium during the capping process.
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68.43.Nr Desorption kinetics
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.66.-f Structure of specific crystalline solids
78.67.Hc Quantum dots
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Near-infrared emission from Eu–Yb doped silicate glasses subjected to thermal reduction

Morten M. Smedskjaer, Jianrong Qiu, John Wang, and Yuanzheng Yue

Appl. Phys. Lett. 98, 071911 (2011); http://dx.doi.org/10.1063/1.3556316 (3 pages) | Cited 8 times

Online Publication Date: 16 February 2011

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Quantum cutting (QC) is a promising approach for enhancing the energy conversion efficiency of solar cells since it allows for conversion of one ultraviolet photon from the sun into two near-infrared photons with energy comparable to the band gap of silicon solar cells. We find that QC can occur by cooperative energy transfer from Eu2+ to Yb3+ in soda-lime-silicate glasses subjected to thermal reduction around the glass transition temperature. Besides the QC effect, the thermal reduction results in improvement of surface performances, e.g., hardness. This synergy effect potentially makes the thermally reduced glass an ideal solar cell substrate material.
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88.40.jj Silicon solar cells
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)
78.40.Pg Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Guided self-assembly of unidirectionally oriented quasi-one-dimensional 3,4,9,10–perylene-tetracarboxylic-dianhydride chains using surface nanowires

Zheng Wei, Heechul Lim, and Geunseop Lee

Appl. Phys. Lett. 98, 071912 (2011); http://dx.doi.org/10.1063/1.3555428 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2011

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A quasi-one-dimensional chains of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules are grown by using nanowire arrays on a In/Si(111)-(4×1) surface as a template. The PTCDA molecules self-assemble in a “head-and-tail” configuration with their long axis aligned with the direction of the surface nanowires. This unidirectional orientation is unique and indicates that the molecular arrangement is not governed by hydrogen bonding which prevails in the self-assembly of the PTCDA molecules on two-dimensional surfaces. Existence of weak and short-ranged interchain molecular interactions is also deduced, revealing the quasi-one-dimensional character of the molecular chains.
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81.05.Fb Organic semiconductors
33.15.Bh General molecular conformation and symmetry; stereochemistry
81.16.Dn Self-assembly
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)
81.07.Gf Nanowires

Nucleation and coalescence effects on the density of self-induced GaN nanowires grown by molecular beam epitaxy

V. Consonni, M. Knelangen, A. Trampert, L. Geelhaar, and H. Riechert

Appl. Phys. Lett. 98, 071913 (2011); http://dx.doi.org/10.1063/1.3555450 (3 pages) | Cited 9 times

Online Publication Date: 16 February 2011

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The evolution of the density of self-induced GaN nanowires as a function of the growth time, gallium rate, and growth temperature has been investigated by scanning and transmission electron microscopy. Nucleation and coalescence effects have been disentangled and quantified by distinguishing between single nanowires and nanowire clusters. Owing to the very specific nanowire nucleation mechanism involving a shape transition from spherical-cap-shaped islands, the nanowire density does not follow the standard island nucleation theory. Furthermore, the detrimental nanowire coalescence process can be significantly reduced by raising the growth temperature.
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81.07.Gf Nanowires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
64.70.Nd Structural transitions in nanoscale materials
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)

The transition from two-stage to three-stage evolution of wetting layer of InAs/GaAs quantum dots caused by postgrowth annealing

G. Y. Zhou (周冠宇), Y. H. Chen (陈涌海), J. L. Yu (俞金玲), X. L. Zhou (周晓龙), X. L. Ye (叶小玲), P. Jin (金鹏), and Z. G. Wang (王占国)

Appl. Phys. Lett. 98, 071914 (2011); http://dx.doi.org/10.1063/1.3552967 (3 pages) | Cited 2 times

Online Publication Date: 18 February 2011

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For the InAs/GaAs quantum dot (QD) system, the evolution of wetting layer (WL) with InAs deposition thickness has been studied under different postgrowth annealing (PGA) durations using reflectance difference spectroscopy. For the sample without PGA, WL thickness remains constant after the formation of QDs, exhibiting a typical two-stage evolution, whereas for the samples with PGA, WL thickness continuously increases linearly with a reduced slope after the formation of QDs and is fixed in ripening growth, indicating a three-stage evolution. By adopting a theoretical model, we have well simulated the two kinds of evolution and found that the variations of QD’s morphology and the interaction of QDs occurring during PGA lead to the different evolution behaviors of WL.
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61.72.Cc Kinetics of defect formation and annealing
68.08.Bc Wetting
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
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