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20 Jun 2011

Volume 98, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 253701 (2011); http://dx.doi.org/10.1063/1.3600648 (3 pages)

Aloke Kumar, Ninell P. Mortensen, Partha P. Mukherjee, Scott T. Retterer, and Mitchel J. Doktycz
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Selective-area vapor-liquid-solid growth of tunable InAsP quantum dots in nanowires

Dan Dalacu, Khaled Mnaymneh, Xiaohua Wu, Jean Lapointe, Geof C. Aers, Philip J. Poole, and Robin L. Williams

Appl. Phys. Lett. 98, 251101 (2011); http://dx.doi.org/10.1063/1.3600777 (3 pages) | Cited 7 times

Online Publication Date: 20 June 2011

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A process is described where the position, size, and cladding of an InP nanowire with an embedded InAsP quantum dot are determined by design through lithography, processing, and growth. The vapor-liquid-solid growth mode on a patterned substrate is used to grow the InP core and defines the quantum dot size to better than ±2 nm while selective-area growth is used to define the cladding thickness. The clad nanowires emit efficiently in the range λ = 0.95–1.15 μm. Photoluminescence measurements are used to quantify the dependence of the excitonic energy level structure on quantum dot size for diameters 10–40 nm.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Gf Nanowires
71.35.-y Excitons and related phenomena

Low gap superconducting single photon detectors for infrared sensitivity

S. N. Dorenbos, P. Forn-Díaz, T. Fuse, A. H. Verbruggen, T. Zijlstra, T. M. Klapwijk, and V. Zwiller

Appl. Phys. Lett. 98, 251102 (2011); http://dx.doi.org/10.1063/1.3599712 (3 pages) | Cited 4 times

Online Publication Date: 20 June 2011

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The quantum efficiency of NbN and NbTiN superconducting single photon detectors drops with decreasing photon energy. A lower gap material would enable single photon detection deeper in the infrared. We have fabricated a NbSi detector and compare its characteristics with a NbTiN device. NbSi (TC ≃ 2 K) has a smaller superconducting gap than NbTiN or NbN (TC ≃ 15 K). We measure the detection efficiency for a wavelength range from 1100 to 1900 nm. In this range the NbSi detector shows a 10-fold increase in relative efficiency with respect to the NbTiN detector.
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85.25.Am Superconducting device characterization, design, and modeling
74.25.Jb Electronic structure (photoemission, etc.)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Surface dispersion engineering of planar plasmonic chirped grating for complete visible rainbow trapping

Qiaoqiang Gan and Filbert J. Bartoli

Appl. Phys. Lett. 98, 251103 (2011); http://dx.doi.org/10.1063/1.3601744 (3 pages) | Cited 9 times

Online Publication Date: 20 June 2011

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Planar chirped plasmonic nanogratings were designed, fabricated, and experimentally characterized, and “rainbow trapping” in nanoplasmonic systems is unambiguously demonstrated across the entire visible spectrum. This planar approach has significant processing advantages when compared to other approaches that require precise nanofabrication control in the vertical direction, and is compatible with large-area nanofabrication technologies. This planar chirped nanograting opens the door to develop exciting chip-scale applications based on the “rainbow” trapping effect.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.16.-c Methods of micro- and nanofabrication and processing

Ultrafast electron dynamics of intersubband excitation concerning cross-phase modulation in an InGaAs/AlAs/AlAsSb coupled double quantum well

Takeshi Ogasawara, Shinichiro Gozu, Teruo Mozume, Kazumichi Akita, Ryoichi Akimoto, Haruhiko Kuwatsuka, Toshifumi Hasama, and Hiroshi Ishikawa

Appl. Phys. Lett. 98, 251104 (2011); http://dx.doi.org/10.1063/1.3601929 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2011

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The ultrafast electron dynamics accompanying intersubband excitation in an InGaAs/AlAs/AlAsSb double quantum well has been investigated by femtosecond pump-probe spectroscopy. The photoinduced changes in the refractive index that causes cross-phase modulation is dominated by a decreased number as well as increased temperature of the electrons in the lower conduction subbands. The change in the number of conduction electrons decays monotonically, whereas the change in the electron temperature exhibits a maximum at around 0.9 ps after the photoexcitation. Heating of the conduction electrons is caused by their excess energy after intersubband longitudinal-optical phonon scattering.
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78.47.J- Ultrafast spectroscopy (<1 psec)
73.63.Hs Quantum wells
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.Fr Low-field transport and mobility; piezoresistance

Superconducting a-WxSi1−x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm

Burm Baek, Adriana E. Lita, Varun Verma, and Sae Woo Nam

Appl. Phys. Lett. 98, 251105 (2011); http://dx.doi.org/10.1063/1.3600793 (3 pages) | Cited 14 times

Online Publication Date: 21 June 2011

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We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1−x) nanowire. Our device made from a uniform a-WxSi1−x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates.
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85.25.-j Superconducting devices

Determination of the subcell photovoltage in multijunction solar cells via voltage-dependent capacitance analysis

R. Hoheisel, M. Schachtner, E. Stämmler, and A. W. Bett

Appl. Phys. Lett. 98, 251106 (2011); http://dx.doi.org/10.1063/1.3601468 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2011

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The letter describes a method for determining the photovoltage, i.e., the quasifermi level splitting at open-circuit conditions, associated with each subcell in a series connected multijunction solar cell structure by voltage-dependent capacitance analysis. Experimental verification and accuracy analysis of subcell photovoltage determination is provided for a 6-tuple AlGaInP/GaInP/AlGaInAs/GaInAs/GaInNAs/Ge solar cell device.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Observation of generalized Wolf shifts in short pulse spectroscopy

R. W. Schoonover, R. Lavarello, M. L. Oelze, and P. S. Carney

Appl. Phys. Lett. 98, 251107 (2011); http://dx.doi.org/10.1063/1.3599842 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2011

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Experimental observations of recently predicted correlation-dependent, propagation-induced changes in the spectrum and cross-spectra of a cyclostationary field are reported. An acoustic Young’s experiment was conducted in which sources were driven by stationary signals modified by a square wave to make the process cyclostationary. The degree of correlation of the underlying stationary processes were controlled to change the spatial coherence of the sources. The far-zone generalized spectra changed with changing degree of correlation.
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07.60.-j Optical instruments and equipment

Electron spin ensemble strongly coupled to a three-dimensional microwave cavity

Eisuke Abe, Hua Wu, Arzhang Ardavan, and John J. L. Morton

Appl. Phys. Lett. 98, 251108 (2011); http://dx.doi.org/10.1063/1.3601930 (3 pages) | Cited 4 times

Online Publication Date: 21 June 2011

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We demonstrate the strong coupling between an electron spin ensemble and a three-dimensional cavity in a reflection geometry. We also find that an anticrossing in the cavity/spin spectrum can be observed under conditions that the collective coupling strength gc is smaller than the spin linewidth γs or the cavity linewidth. We identify a ratio of gc to γs (gc/γs>0.64) as a condition to observe a splitting in the cavity frequency. Finally, we confirm that gc scales with math, where N is the number of polarized spins.
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42.50.-p Quantum optics
03.67.Hk Quantum communication

Experimental demonstration of tunable directional excitation of surface plasmon polaritons with a subwavelength metallic double slit

Xiaowei Li, Qiaofeng Tan, Benfeng Bai, and Guofan Jin

Appl. Phys. Lett. 98, 251109 (2011); http://dx.doi.org/10.1063/1.3602322 (3 pages) | Cited 9 times

Online Publication Date: 21 June 2011

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We demonstrate experimentally the directional excitation of surface plasmon polaritons (SPPs) on a metal film by a subwavelength double slit under backside illumination, based on the interference of SPPs generated by the two slits. By varying the incident angle, the SPPs can be tunably directed into two opposite propagating directions with a predetermined splitting ratio. Under certain incident angle, unidirectional SPP excitation can be achieved. This compact directional SPP coupler is potentially useful for many on-chip applications. As an example, we show the integration of the double-slit couplers with SPP Bragg mirrors, which can effectively realize selective coupling of SPPs into different ports in an integrated plasmonic chip.
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81.05.Bx Metals, semimetals, and alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Room temperature operation of GaAsP(N)/GaP(N) quantum well based light-emitting diodes: Effect of the incorporation of nitrogen

C. Robert, A. Bondi, T. Nguyen Thanh, J. Even, C. Cornet, O. Durand, J. P. Burin, J. M. Jancu, W. Guo, A. Létoublon, H. Folliot, S. Boyer-Richard, M. Perrin, N. Chevalier, O. Dehaese, et al.

Appl. Phys. Lett. 98, 251110 (2011); http://dx.doi.org/10.1063/1.3601857 (3 pages) | Cited 10 times

Online Publication Date: 22 June 2011

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This letter deals with the electroluminescence emission at room temperature of two light-emitting diodes on GaP substrate, based on ternary GaAsP/GaP and quaternary GaAsPN/GaPN multiple quantum wells. In agreement with tight-binding calculations, an indirect band gap is demonstrated from the temperature-dependent photoluminescence for the first structure. High efficiency photoluminescence is then observed for the second structure. Strong electroluminescence and photocurrent are measured from the diode structures at room temperature at wavelengths of 660 nm (GaAsP/GaP) and 730 nm (GaAsPN/GaPN). The role of the incorporation of nitrogen on the optical band gap and on the nature of interband transitions is discussed.
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85.60.Jb Light-emitting devices

Electroluminescence emission from light-emitting diode of p-ZnO/(InGaN/GaN) multiquantum well/n-GaN

Tae-Young Park, Yong-Seok Choi, Sang-Mook Kim, Gun-Young Jung, Seong-Ju Park, Bong-Joon Kwon, and Yong-Hoon Cho

Appl. Phys. Lett. 98, 251111 (2011); http://dx.doi.org/10.1063/1.3601915 (3 pages) | Cited 6 times

Online Publication Date: 22 June 2011

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We report on the fabrication and characteristics of light-emitting diodes (LEDs) which consist of antimony (Sb) doped p-ZnO, (InGaN/GaN) multiquantum well (MQW), and n-GaN. An electroluminescence (EL) emission at a wavelength of 468 nm is observed from the hybrid LEDs after thermal annealing at 750 °C, showing that Sb-doped p-ZnO can be used as a hole supplying layer in hybrid LEDs. Furthermore, the EL peaks are redshifted as the injection current is increased, indicating that the compressive strain in MQW layers is relaxed due to Sb-doped p-ZnO layer.
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85.60.Jb Light-emitting devices

Polarized light extraction in m-plane GaN light-emitting diodes by embedded photonic-crystals

Elison Matioli, Stuart Brinkley, Kathryn M. Kelchner, Shuji Nakamura, Steven DenBaars, James Speck, and Claude Weisbuch

Appl. Phys. Lett. 98, 251112 (2011); http://dx.doi.org/10.1063/1.3602319 (3 pages) | Cited 7 times

Online Publication Date: 22 June 2011

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The polarization-preserving property of photonic crystals (PhCs) is combined to the superior extraction efficiency of embedded PhCs to enhance polarized light emission in m-plane GaN light-emitting diodes. As guided modes in m-plane GaN are mostly polarized along the a-direction (math∥math), their efficient extraction is achieved by one-dimensional embedded PhCs also aligned to the a-direction. A better diffraction efficiency is obtained by air-gap PhCs which required the growth of high quality, defect-free, m-plane GaN coalesced over the embedded air-grooves.
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85.60.Jb Light-emitting devices

Subcell I-V characteristic analysis of GaInP/GaInAs/Ge solar cells using electroluminescence measurements

Sebastian Roensch, Raymond Hoheisel, Frank Dimroth, and Andreas W. Bett

Appl. Phys. Lett. 98, 251113 (2011); http://dx.doi.org/10.1063/1.3601472 (3 pages) | Cited 4 times

Online Publication Date: 23 June 2011

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The I-V characteristics of the individual subcells of a monolithic Ga0.50In0.50P/Ga0.99In0.01As/Ge triple-junction solar cell have been extracted from measurements of the electroluminescence peak intensity as a function of the electroluminescence injection current. By using the spectral reciprocity relation between the electroluminescence and the quantum efficiency, the individual subcell I-V characteristics were derived. It is shown that the subcell dark I-V characteristics and the subcell illuminated I-V characteristics are accessible under variable spectral illumination conditions.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Graphene network on indium tin oxide nanodot nodes for transparent and current spreading electrode in InGaN/GaN light emitting diode

Tae Hoon Seo, Kang Jea Lee, Tae Su Oh, Yong Seok Lee, Hyun Jeong, Ah Hyun Park, Hun Kim, Young Ran Choi, Eun-Kyung Suh, Tran Viet Cuong, Viet Hung Pham, Jin Suk Chung, and Eui Jung Kim

Appl. Phys. Lett. 98, 251114 (2011); http://dx.doi.org/10.1063/1.3601462 (3 pages) | Cited 12 times

Online Publication Date: 24 June 2011

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We report a device that combines indium tin oxide (ITO) nanodot nodes with two-dimensional chemically converted graphene (CCG) films to yield a GaN-based light emitting diode (LED) with interesting characteristics for transparent and current spreading electrodes for the potential use in the ultraviolet region. The current-voltage characteristics and electroluminescence output power performance showed that CCG network on ITO nanodot nodes operated as a transparent and current spreading electrode in LED devices.
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85.60.Jb Light-emitting devices
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Surface plasmon enhanced absorption dynamics of regioregular poly(3-hexylthiophene)

Hai Wang, Hai-Yu Wang, Bing-Rong Gao, Ying Jiang, Zhi-Yong Yang, Ya-Wei Hao, Qi-Dai Chen, Xiao-Bo Du, and Hong-Bo Sun

Appl. Phys. Lett. 98, 251501 (2011); http://dx.doi.org/10.1063/1.3590728 (3 pages) | Cited 2 times

Online Publication Date: 21 June 2011

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An increased absorption of regioregular poly(3-hexylthiophene) due to surface plasmons (SPs) has been studied by steady state fluorescence spectra measurements and femtosecond transient absorption (TA) technique. The SPs were excited by periodic Ag grating structures transferred from the photoresist gratings which were fabricated by two-beam laser interference. The steady state fluorescence measurements show a maximum enhanced fluorecence of about 16 times larger arising from the absorption enhancement. Further investigation by TA technique reveals that the yield of the polaron pairs on Ag gratings significantly increase, much bigger than that of the pure sample, which also confirms the enhanced absorption efficiency as resulting from the excited SPs.
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78.68.+m Optical properties of surfaces
78.55.Kz Solid organic materials
78.47.J- Ultrafast spectroscopy (<1 psec)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Kinetic simulation of a nanosecond-pulsed hydrogen microdischarge

Z. Donkó, J. Schulze, S. Müller, and U. Czarnetzki

Appl. Phys. Lett. 98, 251502 (2011); http://dx.doi.org/10.1063/1.3601486 (3 pages)

Online Publication Date: 21 June 2011

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The electron dynamics in a nanosecond-pulsed microdischarge in high pressure hydrogen gas is investigated space and time resolved by particle-in-cell simulations. The discharge is driven by a 10 ns voltage pulse with a peak of 1.3 kV followed by an approximately constant voltage of 300 V during 150 ns. The time resolved current, electric field, electron density, and spatio-temporal excitation rates are compared to experimental and modeling results under identical discharge conditions. Via this synergistic approach, the development of the discharge and the different phases of distinct electron dynamics are identified and understood.
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52.25.Fi Transport properties
52.80.-s Electric discharges
52.65.Rr Particle-in-cell method
52.25.Dg Plasma kinetic equations
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Enhanced magneto-optical oscillations from two-dimensional hole-gases in the presence of Mn ions

A. L. Gazoto, M. J. S. P. Brasil, F. Iikawa, J. A. Brum, E. Ribeiro, Yu. A. Danilov, O. V. Vikhrova, and B. N. Zvonkov

Appl. Phys. Lett. 98, 251901 (2011); http://dx.doi.org/10.1063/1.3601477 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2011

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We investigated the effects of nearby Mn ions on the optical properties of two-dimensional hole-gases confined in InGaAs/GaAs quantum wells. We observed energy oscillations on both the averaged emission and the spin-splitting energies, whereas the first one presents maxima at all integer filling factors, and the second one, solely at odd-filling factors. The strength of the oscillations clearly increases with the Mn concentration. Furthermore, considering the relatively low-mobility of our structures, the oscillations are surprisingly strong and robust, persisting up to relatively high temperatures and excitation intensities.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.20.Ls Magneto-optical effects
73.21.Fg Quantum wells
61.72.uj III-V and II-VI semiconductors

Robust one-dimensional wires in lattice mismatched bilayer graphene

Anthony R. Wright and Timo Hyart

Appl. Phys. Lett. 98, 251902 (2011); http://dx.doi.org/10.1063/1.3601851 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2011

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We show that lattice mismatched bilayer graphene can realize robust one-dimensional wires. By considering a single domain wall, where the masses of the Dirac electrons change their sign, we establish a general projection principle. This determines how the existence of topological zero-energy domain wall states depends on the direction of the domain wall and locations of the massive Dirac cones inside the bulk Brillouin zone. We generalize this idea for arbitrary patterns of domain walls, showing that the topologically protected states exist only in the presence of an odd number of topological domain walls.
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73.21.Hb Quantum wires

Transmission-electron diffraction by MeV electron pulses

Y. Murooka, N. Naruse, S. Sakakihara, M. Ishimaru, J. Yang, and K. Tanimura

Appl. Phys. Lett. 98, 251903 (2011); http://dx.doi.org/10.1063/1.3602314 (3 pages) | Cited 7 times

Online Publication Date: 20 June 2011

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We have developed a compact ultrafast electron diffractometer, consisting of a laser-driven rf photocathode that generates 3.0 MeV probe electron pulses, three-stage lens optics, and a custom-built detector for relativistic electrons. High-quality single-shot transmission electron diffraction has been detected from 180-nm-thick Si single crystals, with an excellent special resolution for diffracted beams; the spot width of 0.02 A−1 is obtained. The pulse width is estimated to be 100 fs in duration. Characteristics of the electron beam and other diffractometer features are discussed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.Ne Electrostatic lenses, septa
41.75.Ht Relativistic electron and positron beams
85.60.Ha Photomultipliers; phototubes and photocathodes

Nanocrystallization in a shear band: An in situ investigation

G. Wilde and H. Rösner

Appl. Phys. Lett. 98, 251904 (2011); http://dx.doi.org/10.1063/1.3602315 (3 pages) | Cited 4 times

Online Publication Date: 20 June 2011

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Preferential nanocrystal formation in shear bands that occurred upon applying a tensile strain on an Al-rich metallic glass has been analyzed in situ in a transmission electron microscope as a function of time after the shear band initiation and as a function of local heating. The results indicate the presence of a transient period before nanocrystal formation sets in, as well as the necessity of thermal activation and further show that nanocrystals developed only within the shear bands. These results support models that explain nanocrystal formation in shear bands based on an increased local mobility.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.40.Gh Other heat and thermomechanical treatments
81.40.Lm Deformation, plasticity, and creep

Reactivation of sub-bandgap absorption in chalcogen-hyperdoped silicon

Bonna K. Newman, Meng-Ju Sher, Eric Mazur, and Tonio Buonassisi

Appl. Phys. Lett. 98, 251905 (2011); http://dx.doi.org/10.1063/1.3599450 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2011

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Silicon doped with nonequilibrium concentrations of chalcogens using a femtosecond laser exhibits near-unity absorption of sub-bandgap photons to wavelengths of at least 2500 nm. Previous studies have shown that sub-bandgap absorptance decreases with thermal annealing up to 1175 K and that the absorption deactivation correlates with chalcogen diffusivity. In this work, we show that sub-bandgap absorptance can be reactivated by annealing at temperatures between 1350 and 1550 K followed by fast cooling (>50 K/s). Our results suggest that the defects responsible for sub-bandgap absorptance are in equilibrium at high temperatures in hyperdoped Si:chalcogen systems.
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61.72.U- Doping and impurity implantation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.47.J- Ultrafast spectroscopy (<1 psec)

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation

J. Hernandez-Rueda, A. Savoia, W. Gawelda, J. Solis, B. Mansart, D. Boschetto, and J. Siegel

Appl. Phys. Lett. 98, 251906 (2011); http://dx.doi.org/10.1063/1.3601478 (3 pages) | Cited 5 times

Online Publication Date: 21 June 2011

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The transient reflectivity response of phase-change Ge2Sb2Te5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases (amorphous, fcc-, and hcp-crystalline), as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investigated for the fcc-crystalline phase and the laser-crystallized material, revealing strong differences. We find evidence that a considerable fraction of amorphous phase remains in the laser-crystallized material, which features a different phonon frequency, not related to other phases. These results are important for emerging strategies aimed at driving ultrafast phase transitions via coherent phonon excitation for applications in data storage.
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63.20.dd Measurements
68.55.-a Thin film structure and morphology
78.47.jg Time resolved reflection spectroscopy
63.50.Lm Glasses and amorphous solids
78.66.Jg Amorphous semiconductors; glasses
78.66.Li Other semiconductors

An elastic metamaterial with simultaneously negative mass density and bulk modulus

X. N. Liu, G. K. Hu, G. L. Huang, and C. T. Sun

Appl. Phys. Lett. 98, 251907 (2011); http://dx.doi.org/10.1063/1.3597651 (3 pages) | Cited 7 times

Online Publication Date: 21 June 2011

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In this letter, an elastic metamaterial which exhibits simultaneously negative effective mass density and bulk modulus is presented with a single unit structure made of solid materials. The double-negative properties are achieved through a chiral microstructure that is capable of producing simultaneous translational and rotational resonances. The negative effective mass density and effective bulk modulus are numerically determined and confirmed by the analysis of wave propagation. The left-handed wave propagation property of this metamaterial is demonstrated by the negative refraction of acoustic waves.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.65.+k Acoustical properties of solids

Optical studies on a single GaN nanocolumn containing a single InxGa1−xN quantum disk

Mark J. Holmes, Young S. Park, Xu Wang, Christopher C. S. Chan, Benjamin P. L. Reid, HeeDae Kim, Robert A. Taylor, Jamie H. Warner, and Jun Luo

Appl. Phys. Lett. 98, 251908 (2011); http://dx.doi.org/10.1063/1.3601856 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2011

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Microphotoluminescence studies were carried out on a single GaN nanocolumn containing a single InGaN quantum disk (QDisk) that had been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence

Observation of an asymmetrical effect when introducing Zr in Mg/Co multilayers

K. Le Guen, M.-H. Hu, J.-M. André, S. K. Zhou, H. Ch. Li, J. T. Zhu, Z. S. Wang, C. Meny, A. Galtayries, and P. Jonnard

Appl. Phys. Lett. 98, 251909 (2011); http://dx.doi.org/10.1063/1.3601859 (3 pages) | Cited 1 time

Online Publication Date: 21 June 2011

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We have developed Mg/Co, Mg/Zr/Co, Mg/Co/Zr, and Mg/Zr/Co/Zr periodic multilayers and measured at 25.1 nm a reflectivity (R) highly sensitive to the material order within the period. To understand why Mg/Co/Zr is a more efficient mirror (R = 50%) than Mg/Zr/Co and Mg/Zr/Co/Zr ( ∼ 40%), we have probed the interface quality through time-of-flight secondary ion mass spectrometry and nuclear magnetic resonance measurements. The Zr-on-Co interface is found quite sharp while a strong intermixing process is evidenced between the upper Co and lower Zr layers, responsible for the decrease in optical contrast and subsequent R loss.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
76.60.-k Nuclear magnetic resonance and relaxation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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