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18 Jul 2011

Volume 99, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 032501 (2011); http://dx.doi.org/10.1063/1.3610947 (3 pages)

G. X. Miao, M. D. Mascaro, C. H. Nam, C. A. Ross, and J. S. Moodera
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Internal photopumping of Nd3+ (2H9/2, 4F5/2) states in yttrium aluminum garnet by excitation transfer from oxygen deficiency centers and Fe3+ continuum emission

J. D. Hewitt, T. M. Spinka, A. A. Senin, and J. G. Eden

Appl. Phys. Lett. 99, 031101 (2011); http://dx.doi.org/10.1063/1.3614001 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2011

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Photoexcitation of Nd3+ (2H9/2, 4F5/2) states by the broad (∼70 nm FWHM), near-infrared continuum provided by Fe3+ has been observed at 300 K in bulk yttrium aluminum garnet (YAG) crystals doped with trace concentrations (<50 ppm) of Fe, Cr, and Eu. Irradiation of YAG at 248 nm with a KrF laser, which excites the oxygen deficiency center (ODC) in YAG having peak absorption at ∼240 nm, culminates in ODC→Fe3+ excitation transfer and subsequent Fe3+ emission. This internal optical pumping mechanism for rare earth ions is unencumbered by the requirement for donor-acceptor proximity that constrains conventional Förster-Dexter excitation transfer in co-doped crystals.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.55.Hx Other solid inorganic materials
42.62.-b Laser applications

Electrically tunable hole tunnelling from a single self-assembled quantum dot embedded in an n-i-Schottky photovoltaic cell

J. D. Mar, X. L. Xu, J. J. Baumberg, A. C. Irvine, C. Stanley, and D. A. Williams

Appl. Phys. Lett. 99, 031102 (2011); http://dx.doi.org/10.1063/1.3614418 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2011

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We perform excitation-intensity-dependent measurements of the neutral exciton (X0) photocurrent (PC) peak amplitude from a single InAs/GaAs self-assembled quantum dot (QD) embedded in the intrinsic region of an n-i-Schottky photodiode. Since resonant laser-excitation of the X0 transition cannot occur until the comparatively slow hole tunnels out of the QD, we observe a saturation of the PC peak amplitude towards high excitation-intensities, allowing us to determine the hole tunnelling time by fitting with an appropriate theoretical model. By repeating this measurement for a range of bias voltages, we obtain the hole tunnelling time as a function of vertical electric field, showing that it can be tuned by nearly two orders of magnitude. Finally, we find that the hole tunnelling rate can be described accurately by a theoretical model based on a Wentzel-Kramers-Brillouin approximation to yield precise values for the QD height and hole confinement potential.
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85.30.Kk Junction diodes
85.60.Dw Photodiodes; phototransistors; photoresistors
84.60.Jt Photoelectric conversion

High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

Ž. Gačević, S. Fernández-Garrido, J. M. Rebled, S. Estradé, F. Peiró, and E. Calleja

Appl. Phys. Lett. 99, 031103 (2011); http://dx.doi.org/10.1063/1.3614434 (3 pages) | Cited 9 times

Online Publication Date: 18 July 2011

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We report on properties of high quality ∼60 nm thick InAlN layers nearly in-plane lattice-matched to GaN, grown on c-plane GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Excellent crystalline quality and low surface roughness are confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. High annular dark field observations reveal a periodic in-plane indium content variation (8 nm period), whereas optical measurements evidence certain residual absorption below the band-gap. The indium fluctuation is estimated to be ± 1.2% around the nominal 17% indium content via plasmon energy oscillations assessed by electron energy loss spectroscopy with sub-nanometric spatial resolution.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
61.66.Fn Inorganic compounds
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.20.Uv Electron energy loss spectroscopy

Phase extraction from optical interferograms in presence of intensity nonlinearity and arbitrary phase shifts

Thang Hoang, Zhaoyang Wang, Minh Vo, Jun Ma, Long Luu, and Bing Pan

Appl. Phys. Lett. 99, 031104 (2011); http://dx.doi.org/10.1063/1.3614447 (3 pages) | Cited 2 times

Online Publication Date: 18 July 2011

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We present an advanced technique to retrieve phase from multiple optical interferograms containing intensity nonlinearity and random phase shifts, which are common in practice. The proposed algorithm employs a least-squares iteration scheme to detect harmonics up to the pth order and arbitrary phase shifts simultaneously, and the phase distribution can be accurately extracted from (2p + 1) interferograms. The technique is validated by both computer simulation and real experimental results.
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07.60.Ly Interferometers
02.60.-x Numerical approximation and analysis
02.70.Rr General statistical methods

Surface plasmon effects on carbon nanotube field effect transistors

T. Isoniemi, A. Johansson, T. K. Hakala, M. Rinkiö, P. Törmä, J. J. Toppari, and H. Kunttu

Appl. Phys. Lett. 99, 031105 (2011); http://dx.doi.org/10.1063/1.3614543 (3 pages) | Cited 2 times

Online Publication Date: 19 July 2011

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Herein, we experimentally demonstrate surface plasmon polariton (SPP) induced changes in the conductivity of a carbon nanotube field effect transistor (CNT FET). SPP excitation is done via Kretschmann configuration while the measured CNT FET is situated on the opposite side of the metal layer away from the laser, but within reach of the launched SPPs. We observe a shift of ∼0.4 V in effective gate voltage. SPP-intermediated desorption of physisorbed oxygen from the device is discussed as a likely explanation of the observed effect. This effect is visible even at low SPP intensities and within a near-infrared range.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
85.30.Tv Field effect devices
85.35.Kt Nanotube devices
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Auger recombination in GaInN/GaN quantum well laser structures

M. Brendel, A. Kruse, H. Jönen, L. Hoffmann, H. Bremers, U. Rossow, and A. Hangleiter

Appl. Phys. Lett. 99, 031106 (2011); http://dx.doi.org/10.1063/1.3614557 (3 pages) | Cited 12 times

Online Publication Date: 19 July 2011

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Nonradiative loss processes are a major concern in nitride-based light emitting devices. Utilizing optical gain measurements on GaInN/GaN/AlGaN laser structures, we have studied the dependence of the total recombination rate on excess carrier density, up to rather high densities. From a detailed quantitative analysis, we find a room-temperature Auger recombination coefficient of 1.8 ± 0.2 × 10−31 cm6/s in the bandgap range 2.5 − 3.1 eV, considerably lower than previous experimental estimates. Thus, Auger recombination is expected to be significant for laser diodes, while it is not likely to be a major factor for the droop observed in light-emitting diodes.
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42.55.Px Semiconductor lasers; laser diodes
73.50.-h Electronic transport phenomena in thin films
73.63.Hs Quantum wells
78.66.-w Optical properties of specific thin films
85.60.Jb Light-emitting devices

Biopolymer based system doped with nonlinear optical dye as a medium for amplified spontaneous emission and lasing

Lech Sznitko, Jaroslaw Mysliwiec, Pawel Karpinski, Krystyna Palewska, Kacper Parafiniuk, Stanislaw Bartkiewicz, Ileana Rau, Francois Kajzar, and Andrzej Miniewicz

Appl. Phys. Lett. 99, 031107 (2011); http://dx.doi.org/10.1063/1.3610566 (3 pages) | Cited 8 times

Online Publication Date: 19 July 2011

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In this paper, we present results of detailed studies on amplified spontaneous emission (ASE) and lasing achieved in a double-layer system consisted of a biopolymer based matrix loaded with 3-(1,1-dicyanoethenyl1)-1phenyl-4,5dihydro-1H-pyrazole organic nonlinear optical dye and photochromic polymer. The laser action was achieved via distributed feedback configuration with third order of Bragg scattering on surface relief grating generated in photochromic polymer. To excite the luminescence, we have used 6 ns pulses of Nd:YAG laser at 532 nm. The ASE and lasing thresholds were estimated to be 17 mJ/cm2 and 11 mJ/cm2, respectively.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.70.Jk Polymers and organics
42.70.Mp Nonlinear optical crystals
42.79.Dj Gratings
FREE

Broadband second harmonic generation in one-dimensional randomized nonlinear photonic crystal

Yan Sheng, Dongli Ma, Mingliang Ren, Wenqiang Chai, Zhiyuan Li, Kaloian Koynov, and Wieslaw Krolikowski

Appl. Phys. Lett. 99, 031108 (2011); http://dx.doi.org/10.1063/1.3614558 (3 pages) | Cited 9 times

Online Publication Date: 19 July 2011

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We study experimentally second harmonic generation in a one-dimensional nonlinear photonic crystal with randomized inverted-domain structure. We show that the randomness enables one to realize an efficient broadband emission of high-quality second harmonic beam.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Simultaneous corona poling of multiple glass layers for enhanced effective second-order optical nonlinearities

K. Yadav, C. W. Smelser, S. Jacob, C. Blanchetiere, C. L. Callender, and J. Albert

Appl. Phys. Lett. 99, 031109 (2011); http://dx.doi.org/10.1063/1.3614435 (3 pages) | Cited 3 times

Online Publication Date: 19 July 2011

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Silica-based thin-film multilayers are investigated as a means to enhance the effective second-order nonlinearity induced in silica glass structures by corona poling. Structures consisting of phosphorus-doped and undoped silica glass layers exhibit second harmonic generation (SHG) that is higher by an order of magnitude compared to the SHG in bulk silica glass poled under the same conditions. When the poled structure consists of two multilayered stacks separated in space, the stacks exhibit comparable poling-induced nonlinearities. This result suggests that the poling voltage is divided between the two stacks such that simultaneous poling of multiple regions within the sample is realized.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz

Optical and electrical characterization of InGaBiAs for use as a mid-infrared optoelectronic material

J. P. Petropoulos, Y. Zhong, and J. M. O. Zide

Appl. Phys. Lett. 99, 031110 (2011); http://dx.doi.org/10.1063/1.3614476 (3 pages) | Cited 11 times

Online Publication Date: 19 July 2011

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In0.53Ga0.47BixAs1−x films were grown on InP:Fe substrates by molecular beam epitaxy, with Bi concentrations up to x = 3.60%. Bi content in the epilayers was determined by Rutherford backscattering spectroscopy, and channeling measurements show Bi incorporating substitutionally. Unlike previous work, electrical and optical data are obtained for all samples. A redshift in peak wavelength of about 56 meV/%Bi was observed using spectrophotometry. The valence band anti-crossing model is applied, showing InyGa1−yBixAs1−x lattice-matched to InP is possible by varying the composition, with a theoretical cutoff wavelength of about 6 μm.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
71.20.Nr Semiconductor compounds
73.61.Ey III-V semiconductors
78.20.Jq Electro-optical effects

Homogeneous circular polarizers using a bilayered chiral metamaterial

Yuqian Ye, Xuan Li, Fei Zhuang, and Shu-Wei Chang

Appl. Phys. Lett. 99, 031111 (2011); http://dx.doi.org/10.1063/1.3615054 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2011

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We propose a homogeneous circular polarizer based on a bilayered chiral metamaterial with two enantiomeric wheel patterns. The transmitted field of an arbitrarily polarized incident wave through this bilayered structure is nearly circularly polarized with a circular polarization extinction ratio of more than 30 dB at resonance. We show that the origin of this phenomenon is the excitation of spinning electric dipoles in the wheel patterns, which blocks the transmission of one-handed circularly polarized component but exert little influence on the other. We also demonstrate that the operation bandwidth can be enhanced by stacking functional layers in the propagation direction.
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42.25.Ja Polarization
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Nanoplasmonic power splitters based on the horizontal nanoplasmonic slot waveguide

Shiyang Zhu, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 99, 031112 (2011); http://dx.doi.org/10.1063/1.3615306 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2011

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Ultracompact power splitters based on the horizontal nanoplasmonic slot waveguide (Cu/SiO2/Si/SiO2/Cu, whose propagation loss is measured to be ∼0.36 dB/μm at 1550 nm for waveguide with ∼47-nm-wide Si core and ∼26-nm surrounding SiO2) are designed, simulated, and fabricated using the standard complementary metal-oxide-semiconductor technology. The 1 × 2 Y-splitters with the opening angle of 60°, 120°, and 180° are measured to have the excess losses of ∼1.4, ∼1.7, and ∼3.2 dB, compared with the theoretical values of ∼1.4, ∼1.5, and ∼1.8 dB, respectively. The 1 × 3 cross-splitter delivers normalized output powers of ∼ −7.6, ∼ −4.2, and ∼ −7.2 dB at the left, middle, and right output ports, respectively, compared with the theoretical value of ∼ −6.6 dB. Reasons of the discrepancy between the experimental and theoretical results are discussed, and approaches to further reduce the excess loss are then proposed.
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42.82.Et Waveguides, couplers, and arrays
42.79.Fm Reflectors, beam splitters, and deflectors
42.82.Cr Fabrication techniques; lithography, pattern transfer

Thermo-electric detection of waveguided surface plasmon propagation

J.-C. Weeber, K. Hassan, A. Bouhelier, G. Colas-des-Francs, J. Arocas, L. Markey, and A. Dereux

Appl. Phys. Lett. 99, 031113 (2011); http://dx.doi.org/10.1063/1.3613964 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2011

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The thermo-electric detection of a waveguided surface plasmon traveling along one electrode of an in-plane integrated thermocouple is demonstrated. By using a particular design of the thermocouple, the thermo-electric signal due to the losses of the plasmon mode can be separated from the non-resonant heating of the waveguide. The thermo-electric signal associated with the plasmon propagation is proportional to the power coupled into the waveguided mode and exhibits a maximum at a distance from the excitation site depending on both the heat transfer coefficient of the system and the plasmon mode damping distance.
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42.79.Gn Optical waveguides and couplers
42.15.Eq Optical system design
42.82.Et Waveguides, couplers, and arrays

Artificial Faraday rotation using a ring metamaterial structure without static magnetic field

Toshiro Kodera, Dimitrios L. Sounas, and Christophe Caloz

Appl. Phys. Lett. 99, 031114 (2011); http://dx.doi.org/10.1063/1.3615688 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2011

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A metamaterial structure composed of a periodic array of conductive rings including each a semiconductor-based isolator is experimentally shown to produce Faraday rotation. Due to the presence of the isolators, a unidirectional traveling-wave regime is established along the rings, generating rotating magnetic moments and hence emulating the phenomenon of electron spin precession. The metamaterial exhibits the same response as a magnetically biased ferrite or plasma, but without the need of any static magnetic field bias, and therefore, it is easily integrated in printed circuit technology.
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78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics
42.70.-a Optical materials

High-temperature ultraviolet detection based on InGaN Schottky photodiodes

Liwen Sang, Meiyong Liao, Yasuo Koide, and Masatomo Sumiya

Appl. Phys. Lett. 99, 031115 (2011); http://dx.doi.org/10.1063/1.3615291 (3 pages) | Cited 4 times

Online Publication Date: 22 July 2011

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A thermally stable metal-insulator-semiconductor (MIS) Schottky-type photodiode with high performance based on the InGaN film is demonstrated at high temperatures up to 523 K. The reverse leakage current remains at a low level (10−7−10−8 A), while the UV responsivity is as high as 5.6 A/W at −3 V under 523 K, without observing the persistent photoconductivity. The discrimination ratio between ultraviolet (378 nm) and visible light (600 nm) is maintained to be more than 105. The temperature-dependent current-voltage characteristics of the MIS diode were analyzed. The photocurrent gain at reverse biases was interpreted in term of thermionic-field emission (TFE) and field-emission tunneling mechanism from room-temperature to 463 K, while TFE becomes the dominant mechanism at high temperatures.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Kk Junction diodes

III-Nitride full-scale high-resolution microdisplays

Jacob Day, J. Li, D. Y. C. Lie, Charles Bradford, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 99, 031116 (2011); http://dx.doi.org/10.1063/1.3615679 (3 pages) | Cited 5 times

Online Publication Date: 22 July 2011

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We report the realization and properties of a high-resolution solid-state self-emissive microdisplay based on III-nitride semiconductor micro-size light emitting diodes (µLEDs) capable of delivering video graphics images. The luminance level of III-nitride microdisplays is several orders of magnitude higher than those of liquid crystal and organic-LED displays. The pixel emission intensity was almost constant over an operational temperature range from 100 to −100 °C. The outstanding performance is a direct attribute of III-nitride semiconductors. An energy efficient active drive scheme is accomplished by hybrid integration between µLED arrays and Si CMOS (complementary metal–oxide–semiconductor) active matrix integrated circuits. These integrated devices could play important roles in emerging fields such as biophotonics and optogenetics, as well as ultra-portable products such as next generation pico-projectors.
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42.79.Kr Display devices, liquid-crystal devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Ultra-smooth microcylindrical resonators fabricated from the silicon optical fiber platform

Natasha Vukovic, Noel Healy, Peter Horak, Justin R. Sparks, Pier J. A. Sazio, John V. Badding, and Anna C. Peacock

Appl. Phys. Lett. 99, 031117 (2011); http://dx.doi.org/10.1063/1.3615689 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2011

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High quality hydrogenated amorphous silicon microcylindrical resonators are fabricated using the recently developed semiconductor optical fiber platform. The resonators are shown to have ultra-smooth surfaces that minimize the effects of scattering losses and exhibit localized whispering gallery modes with loaded quality factors of up to ∼2.8 × 104. Coupled mode theory indicates that the system quality factor is limited by both the bulk material loss of the resonator and the tapered fiber coupling scheme. The large extinction ratios and thermal nonlinearities measured in these microcylindrical resonators suggest that they should find application for low-power all-optical processing.
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42.81.Wg Other fiber-optical devices
07.10.Cm Micromechanical devices and systems
42.81.Qb Fiber waveguides, couplers, and arrays
42.81.Dp Propagation, scattering, and losses; solitons
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Femtosecond electron deflectometry for measuring transient fields generated by laser-accelerated fast electrons

Shunsuke Inoue, Shigeki Tokita, Kazuto Otani, Masaki Hashida, and Shuji Sakabe

Appl. Phys. Lett. 99, 031501 (2011); http://dx.doi.org/10.1063/1.3612915 (3 pages) | Cited 2 times

Online Publication Date: 22 July 2011

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The temporal evolution of the electric field generated near the surface of a solid target by a femtosecond laser pulse with intensity of 1 × 1016 W/cm2 has been investigated by electron deflectometry; in this technique, ultrashort electron pulses generated by intense femtosecond laser pulses are used as probes. We found that electric field of the order of 108 V/m along the target surface was generated and decayed within 400 fs. The results of this study demonstrate the potential of electron deflectometry for measuring ultrafast phenomena in the femtosecond time domain.
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78.47.J- Ultrafast spectroscopy (<1 psec)
06.30.Ka Basic electromagnetic quantities
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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Electronic, optical, and mechanical properties of superhard cold-compressed phases of carbon

Haiyang Niu, Pengyue Wei, Yan Sun, Xing-Qiu Chen, Cesare Franchini, Dianzhong Li, and Yiyi Li

Appl. Phys. Lett. 99, 031901 (2011); http://dx.doi.org/10.1063/1.3610996 (3 pages) | Cited 11 times

Online Publication Date: 18 July 2011

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By means of standard and hybrid density functional theory, we analyzed the electronic, optical, and mechanical properties of the two discovered superhard orthorhombic (W) and monoclinic (M) phases of carbon, synthesized by cold compression. We demonstrated that both phases exhibit a transparent insulating behaviour with indirect band gaps of about 5.4 eV (W) and 4.5 eV (M), and highly isotropic optical spectra, substantially different to those of the related body centered tetragonal C4 phase. The analysis of the elastic constants and Vickers hardness confirmed that these phases are as hard as the second hardest material c-BC2N.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy

Muneaki Hase and Junji Tominaga

Appl. Phys. Lett. 99, 031902 (2011); http://dx.doi.org/10.1063/1.3611030 (3 pages) | Cited 3 times

Online Publication Date: 18 July 2011

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We report on evaluation of lattice thermal conductivity of GeTe/Sb2Te3 superlattice (SL) by using femtosecond coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb2Te3 SL films exhibits the coherent A1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. Based on the Debye theory, we calculate the lattice thermal conductivity, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in amorphous SL is less temperature dependent, being attributed to dominant phonon-defect scattering.
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66.70.Df Metals, alloys, and semiconductors
61.72.Mm Grain and twin boundaries
68.65.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Thermal carrier processes in bimodal-sized quantum dots with different lateral coupling strength

X. L. Zhou, Y. H. Chen, T. F. Li, X. L. Ye, Bo Xu, and Z. G. Wang

Appl. Phys. Lett. 99, 031903 (2011); http://dx.doi.org/10.1063/1.3614433 (3 pages) | Cited 1 time

Online Publication Date: 19 July 2011

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In this paper, we have studied the thermal carrier process in bimodal-sized In(Ga)As/GaAs quantum dots (QDs) via temperature dependent photoluminescence (PL). The PL intensity ratio of low energy modal to high energy modal is observed to be temperature sensitive and show different trends for QDs with weak and strong lateral coupling strength, i.e., rise and drop with increasing temperature, respectively. The experimental results are explained by two competing processes: (i) carrier thermal escape from each modal to wetting layer state and (ii) direct carrier coupling between two modals. An improved carrier rate equation model is developed to further demonstrate the importance of process ii in strong lateral coupled QDs system.
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73.63.Kv Quantum dots
78.55.Cr III-V semiconductors

Mechanism of point-defect diffusion in a two-dimensional colloidal crystal

L. C. DaSilva, L. Cândido, G.-Q. Hai, and O. N. Oliveira, Jr.

Appl. Phys. Lett. 99, 031904 (2011); http://dx.doi.org/10.1063/1.3615287 (3 pages)

Online Publication Date: 20 July 2011

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The dynamics and mechanism of migration of a vacancy point defect in a two-dimensional (2D) colloidal crystal are studied using numerical simulations. We find that the migration of a vacancy is always realized by topology switching between its different configurations. From the temperature dependence of the topology switch frequencies, we obtain the activation energies for possible topology transitions associated with the vacancy diffusion in the 2D crystal.
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66.30.Lw Diffusion of other defects
82.70.Dd Colloids
61.72.jd Vacancies

Surface energy density of metal nanostructures by Thomas-Fermi model

Weng Soon Lai and Cheng-Hsin Chiu

Appl. Phys. Lett. 99, 031905 (2011); http://dx.doi.org/10.1063/1.3615280 (3 pages) | Cited 1 time

Online Publication Date: 22 July 2011

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This letter examines the surface energy density of metal nanostructures with different morphologies by taking into account the effects of the electrostatic screening on the systems. The results show that the surface energy density is higher on concave nanostructures than on convex ones. The finding implies voids are more effective for the physisorption process than particles and wires.
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68.35.Md Surface thermodynamics, surface energies
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.45.-d Collective effects
81.07.Bc Nanocrystalline materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.bd Metals and alloys

Local structural studies of hole doped hexagonal multiferroic Y(Mn,Zn)O3

Deok-Yong Cho, Junghwan Park, Jiyeon Kim, and Je-Geun Park

Appl. Phys. Lett. 99, 031906 (2011); http://dx.doi.org/10.1063/1.3615682 (3 pages) | Cited 2 times

Online Publication Date: 22 July 2011

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We examined the local structure of hole-doped hexagonal multiferroic YMn0.9Zn0.1O3 using x-ray absorption fine structure analysis. It was shown that Zn atoms substitute Mn atoms while keeping the bipyramidal oxygen coordination unchanged. Comparative study with pure YMnO3 further showed that the Mn-O bond length splitting is diminished by approximately 0.05 Å, suggesting an enhanced orbital hybridization in the planar Mn-O bonds due to additional Mn3+ → O2− electron transfer near the Zn2+ ions. It is a conclusive experimental evidence that Zn doping indeed introduces hole doping on to the two dimensional Mn sublattice of the hexagonal multiferroic YMnO3.
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61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Ee Antiferromagnetics

Quantum-confined direct-gap transitions in tensile-strained Ge/SiGe multiple quantum wells

Lee Carroll, Florian Imbert, Hans Sigg, Martin Süess, Elisabeth Müller, Michele Virgilio, Giovanni Pizzi, Peggy Rossbach, Daniel Chrastina, and Giovanni Isella

Appl. Phys. Lett. 99, 031907 (2011); http://dx.doi.org/10.1063/1.3606383 (3 pages) | Cited 10 times

Online Publication Date: 22 July 2011

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Tensile-strained Ge/Si1−xGex (x = 0.87) multiple quantum wells (MQWs) on a Ge-on-Si virtual substrate are investigated with Brewster transmission and photo-reflectance, to identify quantum-confined direct-gap transitions and their light/heavy-hole splitting. Strain is deduced from optical splitting and x-ray diffraction measurements. As-prepared MQWs have an exciton at ≈ 820 meV, close to the 810 meV edge of the telecommunication C-band. The effect of rapid thermal annealing, to red-shift this feature into the C-band via increased strain, is investigated and interpreted with a tight-binding model. Annealing is observed to red-shift bulk absorption, but MQW transitions experience a net blue-shift due to interdiffusion.
Show PACS
81.05.Hd Other semiconductors
81.05.Cy Elemental semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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