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14 Feb 2011

Volume 98, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

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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Pyroelectric control of the superprism effect in a lithium niobate photonic crystal in slow light configuration

M.-P. Bernal, J. Amet, J. Safioui, F. Devaux, M. Chauvet, J. Salvi, and F. I. Baida

Appl. Phys. Lett. 98, 071101 (2011); http://dx.doi.org/10.1063/1.3554373 (3 pages) | Cited 4 times

Online Publication Date: 14 February 2011

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In this letter, tunability of the beam deviation on a two dimensional lithium niobate photonic crystal superprism is experimentally demonstrated thanks to the pyroelectric effect. Since the superprism geometry has been designed in a slow light configuration, the observed pyroelectric beam steering tunability is considerably enhanced. A beam deviation of 3.4°/°C has been experimentally measured for a working wavelength of 1565 nm. Direct applications can be found as ultracompact highly effective temperature variation sensors.
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77.70.+a Pyroelectric and electrocaloric effects
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials

Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN

Sameer Chhajed, Wonseok Lee, Jaehee Cho, E. Fred Schubert, and Jong Kyu Kim

Appl. Phys. Lett. 98, 071102 (2011); http://dx.doi.org/10.1063/1.3554426 (3 pages) | Cited 16 times

Online Publication Date: 14 February 2011

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We report on a self-organized nanoscale patterning method by using oblique angle deposition to enhance the light extraction in a GaInN light-emitting diode (LED). The method offers one-step processing with good controllability of the feature size and density of the nanopatterns by varying the deposition angle during oblique angle deposition, eliminating the need for photolithography and annealing. A 5-nm-thick silver (Ag) film, when deposited by using oblique angle deposition, spontaneously forms a nanoscale island-like morphology on the substrate. This method is used to texture p-type GaN with nanoscale features, which results in increased light extraction from a GaInN LED. At 100 mA, the nanotextured LED shows a 46% higher light output than a standard LED with unpatterned (planar) p-type GaN.
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85.60.Jb Light-emitting devices

Pulse repetition rate up to 92 GHz or pulse duration shorter than 110 fs from a mode-locked semiconductor disk laser

P. Klopp, U. Griebner, M. Zorn, and M. Weyers

Appl. Phys. Lett. 98, 071103 (2011); http://dx.doi.org/10.1063/1.3554751 (3 pages) | Cited 15 times

Online Publication Date: 15 February 2011

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A semiconductor disk laser based on an InGaAs/AlGaAs quantum-well gain medium was mode-locked by a fast semiconductor saturable absorber mirror. By high-order harmonic mode-locking a 92 GHz pulse train was obtained with a pulse duration of <200 fs. In order to achieve fundamental mode-locking, too strong saturation of the semiconductor elements had to be avoided. In a single-pulse regime, pulses shorter than 110 fs were generated at a wavelength of 1030 nm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Intersubband spectroscopy probing higher order interminiband transitions in AlN-GaN-based superlattices

Daniel Hofstetter, J. Di Francesco, Prem K. Kandaswamy, and Eva Monroy

Appl. Phys. Lett. 98, 071104 (2011); http://dx.doi.org/10.1063/1.3554752 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2011

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We investigate midinfrared intersubband photodetectors based on short-period AlN/GaN superlattices with different quantum well thicknesses. Band structure calculations, as well as optical transmission and photovoltage measurements, underline the importance of higher order interminiband transitions. In particular, it was found that optical transitions between the second and third minibands benefit from much larger electron displacements and oscillator strengths than those between the first and second minibands. Our results suggest that optical rectification is therefore much more efficient for devices based on a higher order interminiband transition.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Nanopattern enabled terahertz all-optical switching on vanadium dioxide thin film

S. B. Choi, J. S. Kyoung, H. S. Kim, H. R. Park, D. J. Park, Bong-Jun Kim, Y. H. Ahn, F. Rotermund, Hyun-Tak Kim, K. J. Ahn, and D. S. Kim

Appl. Phys. Lett. 98, 071105 (2011); http://dx.doi.org/10.1063/1.3553504 (3 pages) | Cited 6 times

Online Publication Date: 16 February 2011

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We demonstrate ultrafast all-optical control of terahertz (THz) radiation through nanoresonators, slot antennas with a hundred micron length but submicron width in thin gold layers, fabricated on vanadium dioxide (VO2) thin films. Our THz nanoresonators show almost perfect transmission at resonance. By virtue of phase transition of VO2 from insulating to metallic state, induced in subpicosecond time scale by moderate optical pump, ultrafast control of THz transmission is enabled. This is compared to bare VO2 films where no switching dynamics are observed under similar conditions.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
81.16.Rf Micro- and nanoscale pattern formation
42.79.Wc Optical coatings

High-Q whispering-gallery mode lasing from nanosphere-patterned GaN nanoring arrays

K. H. Li, Zetao Ma, and H. W. Choi

Appl. Phys. Lett. 98, 071106 (2011); http://dx.doi.org/10.1063/1.3556281 (3 pages) | Cited 1 time

Online Publication Date: 17 February 2011

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A hexagonal-close-packed ordered array of nanorings was fabricated on GaN with a modified nanosphere lithography process. The spheres initially served as etch masks for the formation of closed-packed nanopillars. The spheres were then shrunk and, with a layer of oxide deposited, the roles of the spheres became masks for liftoff. The final etch produced nanorings with wall widths of 140 nm. Photopumped lasing with splitting modes was observed at room temperature, with a low lase threshold of ∼ 10 mJ/cm2 and high quality factor of ∼ 5000, via whispering-gallery modes. The resonant frequencies were verified through finite-difference time-domain simulations.
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81.16.Nd Micro- and nanolithography
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials

Beyond the Yablonovitch limit: Trapping light by frequency shift

Tom Markvart

Appl. Phys. Lett. 98, 071107 (2011); http://dx.doi.org/10.1063/1.3554436 (2 pages) | Cited 4 times

Online Publication Date: 18 February 2011

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It is shown that randomizing the photon distribution over the frequency as well as orientation variables dramatically improves the efficiency of optical confinement in a weakly absorbing material such as crystalline silicon. The enhancement in average optical path length over the Yablonovitch limit [ E. Yablonovitch, J. Opt. Soc. Am. 72, 899 (1982)] is given by an inverse Boltzmann factor of the frequency shift, making it possible to manufacture, for example, efficient crystalline silicon solar cells of thickness barely 1 μm.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles

Terahertz two-cylinder waveguide coupler for transverse-magnetic and transverse-electric mode operation

M. Theuer, A. J. Shutler, S. Sree Harsha, R. Beigang, and D. Grischkowsky

Appl. Phys. Lett. 98, 071108 (2011); http://dx.doi.org/10.1063/1.3554761 (3 pages) | Cited 7 times

Online Publication Date: 18 February 2011

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We report the coupling and guiding of broadband terahertz radiation using a two-cylinder waveguide coupler. For the transverse electromagnetic TEM (TM0) geometry, the two opposing metal cylinders exhibit an amplitude transmission comparable to that of the cylindrical silicon lens coupled parallel-plate waveguide, but in the transverse-electric orientation the two-cylinder coupler shows much better amplitude transmission.
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42.79.Gn Optical waveguides and couplers
84.40.-x Radiowave and microwave (including millimeter wave) technology

Experimental verification of reduced intersubband scattering in ordered nanopore lattices

N. L. Dias, A. Garg, U. Reddy, J. D. Young, K. P. Bassett, X. Li, and J. J. Coleman

Appl. Phys. Lett. 98, 071109 (2011); http://dx.doi.org/10.1063/1.3554763 (3 pages) | Cited 1 time

Online Publication Date: 18 February 2011

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A photoluminescence study of emission from a periodically perforated quantum well at 77 K is presented. Good agreement is observed between numerical predictions and experimental results. The effects of pore diameter on peak emission wavelength and relative emission from second excited subbands are analyzed. The results are found to be consistent with predictions of reduced intersubband scattering rate in nanopore lattices due to the reduced wave function overlap between the initial and final states arising from the in-plane periodicity.
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78.55.Cr III-V semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.43.Gt Powders, porous materials
81.07.St Quantum wells
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
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Experimental evidence of thermonuclear neutrons in a modified plasma focus

D. Klir, P. Kubes, M. Paduch, T. Pisarczyk, T. Chodukowski, M. Scholz, Z. Kalinowska, E. Zielinska, B. Bienkowska, J. Hitschfel, S. Jednorog, L. Karpinski, J. Kortanek, J. Kravarik, K. Rezac, et al.

Appl. Phys. Lett. 98, 071501 (2011); http://dx.doi.org/10.1063/1.3555447 (3 pages) | Cited 6 times

Online Publication Date: 14 February 2011

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The PF-1000 plasma focus was modified by adding the cathode disk 3 cm in front of the anode. This modification facilitated the evaluation of neutron energy spectra. Two neutron pulses were distinguishable. As regards the first neutron pulse, it lasted 40 ns during the plasma stagnation and it demonstrated high isotropy of neutron emission. A peak neutron energy detected upstream was 2.46±0.02 MeV. The full width of neutron energy spectra of 90±20 keV enabled to calculate an ion temperature of 1.2 keV. These parameters and a neutron yield of 109 corresponded to theoretical predictions for thermonuclear neutrons.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.75.-d Plasma devices
52.25.Tx Emission, absorption, and scattering of particles
52.70.Nc Particle measurements

Role of charge photodesorption in self-synchronized breakdown of surface streamers in air at atmospheric pressure

O. Guaitella, I. Marinov, and A. Rousseau

Appl. Phys. Lett. 98, 071502 (2011); http://dx.doi.org/10.1063/1.3552965 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2011

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A surface dielectric barrier discharge configuration with two identical high voltage electrodes is investigated in air at atmospheric pressure. Synchronized breakdown of streamers on both electrodes is evidenced by statistical study. The light emitted by plasma filament on one electrode can trigger the breakdown of streamers on the other electrode. The role of photodesorption of negative charges deposited on the Pyrex dielectric barrier is responsible for these self-synchronized breakdowns. The binding energy of negative charges photodesorbed is estimated to be lower than 3.5 eV.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges
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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 6 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 17 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.
Show PACS
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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