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19 Mar 2012

Volume 100, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 121101 (2012); http://dx.doi.org/10.1063/1.3693413 (4 pages)

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta
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Three dimensional optical twisters-driven helically stacked multi-layered microrotors

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta

Appl. Phys. Lett. 100, 121101 (2012); http://dx.doi.org/10.1063/1.3693413 (4 pages) | Cited 5 times

Online Publication Date: 19 March 2012

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We demonstrate tunable helically stacked multi-layered microrotors realized in vortex-embedded three dimensional (3D) optical twister patterns. Intensity-tunable annular irradiance profiles with higher order vortex are generated as well as simultaneously unfolded by phase-engineered multiple plane wave interference. In the individually tunable 3D helical bright arms of these unfolded vortex structures, 2 μm silica beads are optically trapped as spiraling multilayered handles of multi-armed microrotors. Further, multiple rows of such microrotors are parallelly actuated with controllable sense of rotation. We also present our observation on helical 3D stacking of micro-particles in these longitudinally gyrating multi-armed rotor traps.
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87.80.Cc Optical trapping
87.80.Ek Mechanical and micromechanical techniques
87.17.-d Cell processes
87.50.wf Biophysical mechanisms of interaction

Blue monolithic II-VI-based vertical-cavity surface-emitting laser

S. Klembt, M. Seyfried, T. Aschenbrenner, K. Sebald, J. Gutowski, D. Hommel, and C. Kruse

Appl. Phys. Lett. 100, 121102 (2012); http://dx.doi.org/10.1063/1.3696029 (4 pages) | Cited 2 times

Online Publication Date: 19 March 2012

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We report on laser operation of optically pumped, fully epitaxial blue vertical-cavity surface-emitting lasers. The ZnSe-based structures posses a bottom and top distributed Bragg reflector consisting of ZnMgSSe as high-index material and a short-period superlattice of MgS/ZnCdSe as low-index material. The cavity has an optical thickness of λ and contains three ZnSe quantum wells surrounded by ZnMgSSe barriers. To illustrate the specific issues related to this demanding material combination, we compare two epitaxial structures of different crystalline quality. A minimum threshold of 5 pJ is observed for laser emission at 443 nm comparable to values reported for nitride based vertical-cavity surface-emitting lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.79.-e Optical elements, devices, and systems

High-Q (>5000) AlN nanobeam photonic crystal cavity embedding GaN quantum dots

S. Sergent, M. Arita, S. Kako, S. Iwamoto, and Y. Arakawa

Appl. Phys. Lett. 100, 121103 (2012); http://dx.doi.org/10.1063/1.3695331 (4 pages) | Cited 3 times

Online Publication Date: 19 March 2012

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We report on the fabrication and optical characterization of high-quality-factor AlN one-dimensional nanobeam photonic crystal cavities embedding GaN quantum dots and operating in the ultra-violet range. By means of electron-beam lithography, dry etching and photoelectrochemical etching, we implement a high-frequency nanobeam cavity design in an AlN epilayer containing GaN quantum dots. Room-temperature microphotoluminescence characterization of the fabricated nanobeams exhibits resonances with wavelengths as short as 320 nm and quality factors as high as Qexp = 5.0 × 103 at 380 nm. This constitutes a significant improvement over previously reported group-III nitride photonic crystal cavities in terms of operating wavelength.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.15.Eq Optical system design
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
42.79.-e Optical elements, devices, and systems

Fractional high-order harmonic combs and energy tuning by attosecond-precision split-spectrum pulse control

Philipp Raith, Christian Ott, Christopher P. Anderson, Andreas Kaldun, Kristina Meyer, Martin Laux, Yizhu Zhang, and Thomas Pfeifer

Appl. Phys. Lett. 100, 121104 (2012); http://dx.doi.org/10.1063/1.3693615 (5 pages) | Cited 1 time

Online Publication Date: 19 March 2012

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We experimentally control high-order harmonic generation by applying a versatile few-cycle pulse-shape control method: splitting up a single broadband continuous laser spectrum into two sections and applying sub-femtosecond relative time delays. For certain time delays, fractional high-harmonic combs (noninteger harmonics) are generated which we find to result from the controlled interference of two attosecond pulse trains. We also observe time-delay-dependent energy-tunability of the high-order harmonics for an asymmetrically split spectrum consisting of a strong and a weak component. The tuning mechanism is quantitatively understood by the controlled modulation of the instantaneous driver frequency at the peak of the shaped laser pulse.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Modulation of electron trajectories inside a filament for single-scan coherent terahertz wave detection

Benjamin Clough, Nicholas Karpowicz, and X.-C. Zhang

Appl. Phys. Lett. 100, 121105 (2012); http://dx.doi.org/10.1063/1.3696027 (4 pages)

Online Publication Date: 20 March 2012

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A synthesized fundamental optical beam and its second harmonic laser field is phase modulated to dynamically reshape the electron momentum distribution inside an air-plasma filament. The net electron motion becomes a combination of the initial laser “kick,” from the remaining optical field, and the terahertz field present at the time of its ionization. The time dependent Schrödinger equation is solved to map the net electron velocity distribution as the phase between the two color beams is changed, and single-scan coherent terahertz wave detection through air-plasma fluorescence is experimentally demonstrated.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.60.Fc Modulation, tuning, and mode locking

Spontaneous emission control of single quantum dots in bottom-up nanowire waveguides

Gabriele Bulgarini, Michael E. Reimer, Tilman Zehender, Moïra Hocevar, Erik P. A. M. Bakkers, Leo P. Kouwenhoven, and Valery Zwiller

Appl. Phys. Lett. 100, 121106 (2012); http://dx.doi.org/10.1063/1.3694935 (4 pages) | Cited 6 times

Online Publication Date: 20 March 2012

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Nanowire waveguides with controlled shape are promising for engineering the collection efficiency of quantum light sources. We investigate the exciton lifetime in individual InAsP quantum dots, perfectly positioned on-axis of InP nanowire waveguides. We demonstrate control over the quantum dot spontaneous emission by varying the nanowire diameter in e-beam patterned arrays, which modifies the coupling efficiency of the emitter to the fundamental waveguide mode. The spontaneous emission rate is inhibited by a factor of 12 in thin nanowires compared to nanowires with optimized waveguide diameter. From the measured inhibition factor, we determine a high radiative yield exceeding 92% in bottom-up grown nanowires.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
71.35.-y Excitons and related phenomena
81.07.Ta Quantum dots
78.67.Hc Quantum dots
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X-ray–optical cross-correlator for gas-phase experiments at the Linac Coherent Light Source free-electron laser

S. Schorb, T. Gorkhover, J. P. Cryan, J. M. Glownia, M. R. Bionta, R. N. Coffee, B. Erk, R. Boll, C. Schmidt, D. Rolles, A. Rudenko, A. Rouzee, M. Swiggers, S. Carron, J.-C. Castagna, et al.

Appl. Phys. Lett. 100, 121107 (2012); http://dx.doi.org/10.1063/1.3695163 (4 pages) | Cited 9 times

Online Publication Date: 20 March 2012

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X-ray–optical pump–probe experiments at the Linac Coherent Light Source (LCLS) have so far been limited to a time resolution of 280 fs fwhm due to timing jitter between the accelerator-based free-electron laser (FEL) and optical lasers. We have implemented a single-shot cross-correlator for femtosecond x-ray and infrared pulses. A reference experiment relying only on the pulse arrival time information from the cross-correlator shows a time resolution better than 50 fs fwhm (22 fs rms) and also yields a direct measurement of the maximal x-ray pulse length. The improved time resolution enables ultrafast pump–probe experiments with x-ray pulses from LCLS and other FEL sources.
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42.79.Bh Lenses, prisms and mirrors
42.25.Kb Coherence
41.60.Cr Free-electron lasers
FREE

X-ray pulse preserving single-shot optical cross-correlation method for improved experimental temporal resolution

M. Beye, O. Krupin, G. Hays, A. H. Reid, D. Rupp, S. de Jong, S. Lee, W.-S. Lee, Y.-D. Chuang, R. Coffee, J. P. Cryan, J. M. Glownia, A. Föhlisch, M. R. Holmes, A. R. Fry, et al.

Appl. Phys. Lett. 100, 121108 (2012); http://dx.doi.org/10.1063/1.3695164 (4 pages)

Online Publication Date: 20 March 2012

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We measured the relative arrival time between an optical pulse and a soft x-ray pulse from a free-electron laser. This femtosecond cross-correlation measurement was achieved by observing the change in optical reflectivity induced through the absorption of a fraction of the x-ray pulse. The main x-ray pulse energy remained available for an independent pump-probe experiment where the sample may be opaque to soft x-rays. The method was employed to correct the two-pulse delay data from a canonical pump-probe experiment and demonstrate 130 ± 20 fs (FWHM) temporal resolution. We further analyze possible timing jitter sources and point to future improvements.
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41.60.Cr Free-electron lasers
42.79.Hp Optical processors, correlators, and modulators

Shift of responsive peak in GaN-based metal-insulator-semiconductor photodetectors

Kun You, Hong Jiang, Dabing Li, Xiaojuan Sun, Hang Song, Yiren Chen, Zhiming Li, Guoqing Miao, and Hongbo Liu

Appl. Phys. Lett. 100, 121109 (2012); http://dx.doi.org/10.1063/1.3696025 (4 pages) | Cited 1 time

Online Publication Date: 21 March 2012

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A gallium nitride (GaN)-based metal-insulator-semiconductor (MIS) ultraviolet photodetector (PD) was fabricated on a sapphire substrate. It was found that the responsive peak of the GaN-based MIS PD redshifted with increasing negative bias, which has not been reported before. Also, the shift of the responsive peak has been interpreted in terms of the tunneling procedure of the photo-generated holes assisted by defects in the interfaces between the GaN layers and the SiNx layers.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

An incoherent light source excited thermal lens microscope

Mingqiang Liu and Mladen Franko

Appl. Phys. Lett. 100, 121110 (2012); http://dx.doi.org/10.1063/1.3696049 (4 pages)

Online Publication Date: 21 March 2012

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We report a thermal lens microscope (TLM) based on an incoherent light source (ILS) excitation. By introducing a three-layer system into an optimized ILS-excited TLM, the sensitivity can be amplified up to 10 times for a 100-μm aqueous sample. The sensitivity enhancement originates from two additional thermal lenses formed by the heat transferred from the sample to the top and bottom layers with high temperature coefficient of refractive index. It is predicted that with a power of about 10 mW used for exciting a 100-μm sample, the limit of detection of the ILS-excited TLM can go down to 5.5 × 10−6 AU.
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42.72.-g Optical sources and standards

Tailoring chirp in spin-lasers

Guilhem Boéris, Jeongsu Lee, Karel Výborný, and Igor Žutić

Appl. Phys. Lett. 100, 121111 (2012); http://dx.doi.org/10.1063/1.3693168 (4 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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The usefulness of semiconductor lasers is often limited by the undesired frequency modulation, or chirp, a direct consequence of the intensity modulation, and carrier dependence of the refractive index in the gain medium. In spin-lasers, realized by injecting, optically or electrically, spin-polarized carriers, we elucidate paths to tailoring chirp. We provide a generalized expression for chirp in spin-lasers and introduce modulation schemes that could simultaneously eliminate chirp and enhance the bandwidth, as compared to the conventional (spin-unpolarized) lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Spin flip probability of electron in a uniform magnetic field

Richard T. Hammond

Appl. Phys. Lett. 100, 121112 (2012); http://dx.doi.org/10.1063/1.3691937 (4 pages)

Online Publication Date: 21 March 2012

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The probability that an electromagnetic wave can flip the spin of an electron is calculated. It is assumed that the electron resides in a uniform magnetic field and interacts with an incoming electromagnetic pulse. The scattering matrix is constructed and the time needed to flip the spin is calculated.
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42.50.Ct Quantum description of interaction of light and matter; related experiments
14.60.Cd Electrons (including positrons)
05.30.Fk Fermion systems and electron gas

Liquid crystal based nonlinear fishnet metamaterials

Alexander Minovich, James Farnell, Dragomir N. Neshev, Ian McKerracher, Fouad Karouta, Jie Tian, David A. Powell, Ilya V. Shadrivov, Hark Hoe Tan, Chennupati Jagadish, and Yuri S. Kivshar

Appl. Phys. Lett. 100, 121113 (2012); http://dx.doi.org/10.1063/1.3695165 (4 pages) | Cited 10 times

Online Publication Date: 21 March 2012

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We study experimentally the nonlinear properties of fishnet metamaterials infiltrated with nematic liquid crystals and find that moderate laser powers result in significant changes of the optical transmission of the composite structures. We also show that the nonlinear response of our structure can be further tuned with a bias electric field, enabling the realization of electrically tunable nonlinear metamaterials.
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42.70.-a Optical materials

Experimental investigation of transparent silicon carbide for atom chips

Landry Huet, Mahdi Ammar, Erwan Morvan, Nicolas Sarazin, Jean-Paul Pocholle, Jakob Reichel, Christine Guerlin, and Sylvain Schwartz

Appl. Phys. Lett. 100, 121114 (2012); http://dx.doi.org/10.1063/1.3689777 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2012

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We investigate some properties of an atom chip made of a gold microcircuit deposited on a transparent silicon carbide substrate. A favorable thermal behavior is observed in the presence of electrical current, twice as good as a silicon counterpart. We obtain one hundred million rubidium atoms in a magneto-optical trap with several of the beams passing through the chip. We point out the importance of coating of the chip against reflection to avoid a temperature-dependent Fabry-Perot effect. We finally discuss detection through the chip, potentially granting large numerical apertures, as well as some other potential applications.
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85.65.+h Molecular electronic devices
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
85.35.-p Nanoelectronic devices

Highly uniform periodic inverse quantum dots arrays

N. L. Dias, A. Garg, U. Reddy, U. Choi, and J. J. Coleman

Appl. Phys. Lett. 100, 121115 (2012); http://dx.doi.org/10.1063/1.3694015 (3 pages)

Online Publication Date: 22 March 2012

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We demonstrate high density, periodic arrays of inverse quantum dots with ±1 nm (σd/d = 0.025) variation of the critical dimension. Finite element calculations are performed to determine the effect of this size variation on the energy dispersion and intersubband gap. The subband gap is smeared for size variations greater than 1 nm for all lattice constants. This establishes an upper bound on the fabrication tolerances required to realize devices based on inverse quantum dot lattices. The quantum well wet etching step is found to be the limiting step to achieving greater pore to pore uniformity.
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68.65.Hb Quantum dots (patterned in quantum wells)
02.60.-x Numerical approximation and analysis

Restoring mode degeneracy in H1 photonic crystal cavities by uniaxial strain tuning

I. J. Luxmoore, E. D. Ahmadi, B. J. Luxmoore, N. A. Wasley, A. I. Tartakovskii, M. Hugues, M. S. Skolnick, and A. M. Fox

Appl. Phys. Lett. 100, 121116 (2012); http://dx.doi.org/10.1063/1.3696036 (3 pages) | Cited 4 times

Online Publication Date: 22 March 2012

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We demonstrate a uniaxial strain technique to tune the mode wavelengths of planar photonic crystal cavities. With experiments and numerical simulations, we show that it is possible to use an externally applied strain to control the splitting of the modes of the H1 cavity with high precision. By using this technique, we restore degeneracy to the fundamental modes of an H1 cavity which are initially split by ∼0.5 nm, thus demonstrating unpolarized emission at ∼950 nm with a quality factor of ∼3300.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Enhancement of vertical emission in photonic crystal nanolasers

Michimasa Narimatsu, Shota Kita, Hiroshi Abe, and Toshihiko Baba

Appl. Phys. Lett. 100, 121117 (2012); http://dx.doi.org/10.1063/1.3696056 (3 pages) | Cited 2 times

Online Publication Date: 22 March 2012

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Photonic crystal nanolasers have a drawback of weak vertical emission, which degrades the detection efficiency from above. We show that the vertical emission is enhanced greatly by introducing asymmetry to the cavity, so that Fourier components around the Brillouin zone boundary are shifted to the zone center. When the light output is collected from above by an objective lens with a numerical aperture of 0.42, the efficiency for the optimized devices, with and without nanoslot, are calculated to be 26 and 153 times that of the original structure. We confirm the experimental and calculated results to be in good agreement.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Qs Photonic bandgap materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.30.Kq Fourier optics
42.79.Bh Lenses, prisms and mirrors
42.60.By Design of specific laser systems

Grating-coupled silicon microring resonators

W. Shi, X. Wang, W. Zhang, H. Yun, C. Lin, L. Chrostowski, and N. A. F. Jaeger

Appl. Phys. Lett. 100, 121118 (2012); http://dx.doi.org/10.1063/1.3696082 (4 pages) | Cited 3 times

Online Publication Date: 23 March 2012

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We propose to integrate grating-assisted asymmetric couplers with microring resonators for selective resonance excitation and control of coupling efficiency. A grating-coupled microring add-drop filter is experimentally demonstrated using a silicon-on-insulator technology compatible with complementary metal-oxide-semiconductor processing. A dominant longitudinal mode with a side-mode suppression ratio of 8 dB has been obtained across a broad spectral range of over 130 nm. The selected mode shows an out-of-band-rejection ratio of 19 dB and a quality factor (Q) of 25 000. The concept of integrating grating-assisted couplers for mode selectivity can be applied to other microring-based devices for high-Q, single-mode operations.
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42.82.Et Waveguides, couplers, and arrays
42.81.Qb Fiber waveguides, couplers, and arrays
42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
85.60.Bt Optoelectronic device characterization, design, and modeling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Enhanced optical nonlinearity in β-AgVO3 nanobelts on decoration with Ag nanoparticles

Manas R. Parida, C. Vijayan, C. S. Rout, C. S. Suchand Sandeep, and Reji Philip

Appl. Phys. Lett. 100, 121119 (2012); http://dx.doi.org/10.1063/1.3696301 (4 pages)

Online Publication Date: 23 March 2012

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This paper reports on the optical nonlinearity of β-AgVO3 nanobelts and the modification in the physical mechanisms of nonlinear response on decorating with silver nanoparticles. The nanobelts are synthesized by a hydrothermal technique and characterized using SEM, TEM, and XRD etc. The nanobelts are found to exhibit large nonlinear optical absorption as revealed by open Z-scan measurements using 5 ns laser pulses at 532 nm. Nonlinearity appears to be arising from a combination of mechanisms of two photon absorption and saturable absorption (SA). Decoration with Ag nanoparticles is found to enhance the saturable absorption and alter the coefficient of nonlinear absorption of the nanobelts. Efficient optical limiting is demonstrated in both the nanobelt systems.
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81.16.-c Methods of micro- and nanofabrication and processing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Narrow band gap (1 eV) InGaAsSbN solar cells grown by metalorganic vapor phase epitaxy

T. W. Kim, T. J. Garrod, K. Kim, J. J. Lee, S. D. LaLumondiere, Y. Sin, W. T. Lotshaw, S. C. Moss, T. F. Kuech, Rao Tatavarti, and L. J. Mawst

Appl. Phys. Lett. 100, 121120 (2012); http://dx.doi.org/10.1063/1.3693160 (4 pages) | Cited 4 times

Online Publication Date: 23 March 2012

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Heterojunction solar cell structures employing InGaAsSbN (Eg ∼ 1 eV) base regions are grown lattice-matched to GaAs substrates using metalorganic vapor phase epitaxy. Room temperature (RT) photoluminescence (PL) measurements indicate a peak spectral emission at 1.04 eV and carrier lifetimes of 471–576 ps are measured at RT from these structures using time-resolved PL techniques. Fabricated devices without anti-reflection coating demonstrate a peak efficiency of 4.58% under AM1.5 direct illumination. Solar cells with a 250 nm-thick InGaAsSbN base layer exhibit a 17% improvement in open circuit voltage (Voc), 14% improvement in fill factor, and 12% improvement in efficiency over the cells with a thicker (500 nm-thick) base layer.
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88.40.jm Thin film III-V and II-VI based solar cells

Light trapping beyond the 4n2 limit in thin waveguides

Jeremy N. Munday, Dennis M. Callahan, and Harry A. Atwater

Appl. Phys. Lett. 100, 121121 (2012); http://dx.doi.org/10.1063/1.3695156 (4 pages) | Cited 4 times

Online Publication Date: 23 March 2012

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We describe a method for determining the maximum absorption enhancement in thin film waveguides based on optical dispersion relations. For thin film structures that support one, well-confined guided mode, we find that the absorption enhancement can surpass the traditional limit of 4n2 when the propagation constant is large and/or the modal group velocity is small compared to the bulk value. We use this relationship as a guide to predicting structures that can exceed the 4n2 light trapping limit, such as plasmonic and slot waveguides. Finally, we calculate the overall absorption for both single and multimode waveguides, and show examples of absorption enhancements in excess of 4n2 for both cases.
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42.79.Gn Optical waveguides and couplers
42.70.-a Optical materials

Lasing in a hybrid GaAs/silver Tamm structure

C. Symonds, A. Lemaître, P. Senellart, M. H. Jomaa, S. Aberra Guebrou, E. Homeyer, G. Brucoli, and J. Bellessa

Appl. Phys. Lett. 100, 121122 (2012); http://dx.doi.org/10.1063/1.3697641 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2012

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We demonstrate that lasing can be obtained with the Tamm plasmon modes appearing at the interface between a multilayered dielectric structure and a metal. The sample consists in InGaAs/GaAs quantum wells embedded in an AlAs/AlGaAs Bragg reflector, on top of which a silver film was evaporated. A superlinear increase of the emission is observed under optical pumping as well as a drastic concentration of the emission pattern around the vertical direction, evidencing a lasing effect. Due to the particular features of these surface modes, Tamm lasers open interesting perspectives for the realization of integrated microlasers.
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42.55.-f Lasers
78.55.-m Photoluminescence, properties and materials
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
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Anomalous wetting on a superhydrophobic graphite surface

Siang-Jie Hong, Yueh-Feng Li, Mu-Jou Hsiao, Yu-Jane Sheng, and Heng-Kwong Tsao

Appl. Phys. Lett. 100, 121601 (2012); http://dx.doi.org/10.1063/1.3697831 (4 pages)

Online Publication Date: 22 March 2012

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A superhydrophobic graphite surface has been fabricated through two facile physical steps, peeling and ultrasonicating. Peeling yields micron-scale roughening, and thus a highly hydrophobic surface is obtained. Further ultrasonicating results in a superhydrophobic surface with nanostructure embedded in microstructure. The nanostructure leads to networklike pores on the superhydrophobic film and convective Ostwald ripening is observed. Owing to their distinct resistance to liquid imbibition, contact angle hysteresis on hydrophobic and superhydrophobic surfaces is fundamentally different. Moreover, the adhesive force on a superhydrophobic surface grows with the contact time, and such aging effect is absent on hydrophobic graphite surface.
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81.05.uf Graphite
68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
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Thermal rectification in a fluid reservoir

Sohail Murad and Ishwar K. Puri

Appl. Phys. Lett. 100, 121901 (2012); http://dx.doi.org/10.1063/1.3696022 (5 pages) | Cited 2 times

Online Publication Date: 19 March 2012

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An organized nonuniform mass distribution in solids leads to a monotonically varying thermal conductivity in a nanomaterial so that the heat flux is directionally dependent. We investigate through molecular dynamics simulations if the influence of an organized mass distribution in a fluid also leads to thermal rectification. Heat transfer is monitored in a water reservoir placed between two (hot and cold) silicon walls. The distribution of the fluid in the reservoirs is organized by applying an external force to each water molecule in a specified direction, creating a density gradient. This external force is smaller than the intermolecular forces in water, in most cases by much more than an order of magnitude. The simulations reveal that mass graded fluid-containing nanosystems can be engineered to possess an asymmetric axial thermal conductance that leads to greater heat flow in the direction of decreasing mass density. The rectification improves as the thermal conductivity is enhanced by increasing the fluid density adjacent to a hot wall, since doing so decreases the interfacial resistance and increases the heat flux.
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61.20.Ja Computer simulation of liquid structure
66.25.+g Thermal conduction in nonmetallic liquids
73.40.-c Electronic transport in interface structures

Tensile softening of metallic-glass-matrix composites in the supercooled liquid region

J. W. Qiao, Y. Zhang, H. L. Jia, H. J. Yang, P. K. Liaw, and B. S. Xu

Appl. Phys. Lett. 100, 121902 (2012); http://dx.doi.org/10.1063/1.3696026 (4 pages) | Cited 3 times

Online Publication Date: 19 March 2012

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A Ti-based metallic-glass-matrix composite exhibits tensile softening (necking) in the supercooled liquid region, accompanied by a large tensile ductility and a fragmentation of dendrites. Subjected to high temperatures, concurrent crystallization does not occur, suggesting a good thermal stability of the glass matrix. The presence of high-volume-fractioned dendrites lowers the rheology of the viscous glass matrix at high temperatures, which results in an absence of super elongation as monolithic bulk metallic glasses (BMGs). A tensile strength of 970 MPa is higher than those of most BMGs under varying strain rates, ascribing to the retardation of softening by the dendrites.
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81.40.Lm Deformation, plasticity, and creep
81.30.Fb Solidification
62.20.fk Ductility, malleability
62.20.fq Plasticity and superplasticity
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
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