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30 Jan 2012

Volume 100, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 100, 053101 (2012); http://dx.doi.org/10.1063/1.3679127 (3 pages)

Shinya Kano, Yasuyuki Yamada, Kentaro Tanaka, and Yutaka Majima
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Distributed Bragg reflectors based on diluted boron-based BAlN alloys for deep ultraviolet optoelectronic applications

M. Abid, T. Moudakir, G. Orsal, S. Gautier, A. En Naciri, Z. Djebbour, J.-H. Ryou, G. Patriarche, L. Largeau, H. J. Kim, Z. Lochner, K. Pantzas, D. Alamarguy, F. Jomard, R. D. Dupuis, et al.

Appl. Phys. Lett. 100, 051101 (2012); http://dx.doi.org/10.1063/1.3679703 (4 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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Highly reflective deep UV distributed Bragg reflectors (DBRs) based on the BAlN material system have been grown by metalorganic vapour phase epitaxy on AlN template substrates. These structures make use of the transparency of BAlN in the deep UV and the high refractive index contrast between BAlN and AlN, which has been demonstrated to exceed 0.27 at 280 nm. 18-pair BAlN/AlN DBRs showed experimental peak reflectivity of 82% at 311 nm and a stop-bandwidth of 20 nm. At 282 nm, a 24-pair BAlN/AlN DBR structure is demonstrated with experimental peak reflectivity of 60% and stop-bandwidth of 16 nm.
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42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Comparison of scanning tunneling microscope-light emission and photoluminescence from porphyrin films using ultra-high vacuum scanning tunneling microscopy

Ryusuke Nishitani, Hongwen Liu, and Hiroshi Iwasaki

Appl. Phys. Lett. 100, 051102 (2012); http://dx.doi.org/10.1063/1.3680597 (4 pages) | Cited 1 time

Online Publication Date: 30 January 2012

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In order to study the interaction between molecules and photon fields, including plasmonic and external laser fields, we have carried out in situ measurements of photoluminescence (PL) from porphyrin molecules on Au substrates with and without a scanning tunneling microscope (STM) tip. Measurements were performed in a ultra-high vacuum scanning tunneling microscope chamber during irradiation by a He-Cd laser with incident power varying in the 10−3 to 10−7 W range. At an incident power of around 10−7 W, the spectra depend strongly on the presence of STM tip, which is associated with STM light emission from molecules. We estimated the ratio of quantum efficiency of scanning tunneling microscope-induced light emission (STML) from molecules to PL on the basis of the STML/PL intensity ratio observed experimentally at a laser power of 7.5 × 10−8 W, with the use of a 40 μm laser beam diameter and an effective area of 2 nm for STML. The estimated quantum efficiency for an electron in STML is roughly 1010 times larger than that for one photon of PL. This anomalous enhancement will be discussed on the basis of plasmon-enhanced light emission from molecules in a STM nano-cavity.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Speed enhancement of multi-particle chain in a traveling standing wave

Martin Šiler, Tomáš Čižmár, and Pavel Zemánek

Appl. Phys. Lett. 100, 051103 (2012); http://dx.doi.org/10.1063/1.3680234 (3 pages) | Cited 1 time

Online Publication Date: 31 January 2012

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A moving array of optical traps created by interference of two counter-propagating evanescent waves has been used for delivery of particle chains up to 18 micro-particles long immersed in water. The particles were optically self-arranged into a linear chain with well-separated distances between them. We observed a significant increase in the delivery speed of the whole structure as the number of particles in the chain increased. This could provide faster sample delivery in microfluidic systems. We quantified the contributions to the speed enhancement caused by the optical and hydrodynamic interactions between the particles.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.10.Cm Micromechanical devices and systems

Transmission enhancement in a non-adiabatic tapered nano-aperture waveguide

Yongzhu Chen, Xiangsheng Xie, Yongyao Li, and Jianying Zhou

Appl. Phys. Lett. 100, 051104 (2012); http://dx.doi.org/10.1063/1.3681135 (4 pages)

Online Publication Date: 31 January 2012

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Transmission enhancement via transverse mode control through an aluminum hollow tapered waveguide with a sub-100 nm aperture is simulated with optical wavefront modulations via a binary optical element. Efficient delivery of an input field by exciting the fundamental propagating mode near the apex is realized, giving rise to a significant transmission enhancement through the nano-tip.
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42.79.Gn Optical waveguides and couplers
02.70.Bf Finite-difference methods

Recombination mechanisms and band alignment of GaAs1−xBix/GaAs light emitting diodes

N. Hossain, I. P. Marko, S. R. Jin, K. Hild, S. J. Sweeney, R. B. Lewis, D. A. Beaton, and T. Tiedje

Appl. Phys. Lett. 100, 051105 (2012); http://dx.doi.org/10.1063/1.3681139 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2012

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We investigate the temperature and pressure dependence of the light-current characteristics and electroluminescence spectra of GaAs1−xBix/GaAs light emitting diodes. The temperature dependence of the emission wavelength shows a relatively low temperature coefficient of emission peak shift of 0.19 ± 0.01 nm/K. A strong decrease in emission efficiency with increasing temperature implies that non-radiative recombination plays an important role on the performance of these devices. The pressure coefficient of the GaAs0.986Bi0.014 bandgap is measured to be 11.8 ± 0.3 meV/kbar. The electroluminescence intensity from GaAsBi is found to decrease with increasing pressure accompanied by an increase in luminescence from the GaAs cladding layers suggesting the presence of carrier leakage in the devices.
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85.60.Jb Light-emitting devices

Gas refractometry using a hollow-core photonic bandgap fiber in a Mach-Zehnder-type interferometer

I. Shavrin, S. Novotny, A. Shevchenko, and H. Ludvigsen

Appl. Phys. Lett. 100, 051106 (2012); http://dx.doi.org/10.1063/1.3681171 (3 pages) | Cited 3 times

Online Publication Date: 31 January 2012

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We present the design of a fiber-optic gas refractometer that enables spectrally resolved measurements of both real and imaginary parts of the complex refractive index. The proposed concept is based on a Mach-Zehnder-type interferometer with a hollow-core photonic bandgap fiber in one of the interferometer’s arms. The fiber is used simultaneously as an optical waveguide and an analyte containing cell. We demonstrate the performance of the device by measuring the complete complex refractive index of an air-acetylene gas mixture within the optical C-band. The introduced concept leads towards versatile applications in optics as well as atomic and molecular physics.
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07.60.Hv Refractometers and reflectometers
07.60.Ly Interferometers
42.79.Gn Optical waveguides and couplers

Optical detection of melting point depression for silver nanoparticles via in situ real time spectroscopic ellipsometry

S. A. Little, T. Begou, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 100, 051107 (2012); http://dx.doi.org/10.1063/1.3681367 (4 pages) | Cited 4 times

Online Publication Date: 1 February 2012

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Silver nanoparticle films were deposited by sputtering at room temperature and were annealed while monitoring by real time spectroscopic ellipsometry (SE). The nanoparticle dielectric functions (0.75 eV–6.5 eV) obtained by SE were modeled using Lorentz and generalized oscillators for the nanoparticle plasmon polariton (NPP) and interband transitions, respectively. The nanoparticle melting point could be identified from variations in the oscillator parameters during annealing, and this identification was further confirmed after cooling through significant, irreversible changes in these parameters relative to the as-deposited film. The variation in melting point with physical thickness, and thus average nanoparticle diameter, as measured by SE enables calculation of the surface energy density.
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64.70.dj Melting of specific substances
68.35.Md Surface thermodynamics, surface energies
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.40.Gh Other heat and thermomechanical treatments

Experimental generation of a radially polarized beam with controllable spatial coherence

Fei Wang, Yangjian Cai, Yiming Dong, and Olga Korotkova

Appl. Phys. Lett. 100, 051108 (2012); http://dx.doi.org/10.1063/1.3681802 (4 pages) | Cited 5 times

Online Publication Date: 1 February 2012

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We have experimentally generated a radially polarized (RP) beam with controllable state of spatial coherence by using a rotating ground-glass plate and a radial polarization converter. Furthermore, experimental and theoretical analysis of the focusing properties of a partially coherent RP beam is carried out. Our results show that we can shape the beam profile of the focused RP beam by varying its initial spatial coherence, which is useful for material thermal processing and particle trapping. The experimental results are in complete agreement with the theoretical predictions.
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42.70.Ce Glasses, quartz

Temperature dependence of the intraexcitonic AC Stark effect in semiconductor quantum wells

M. Wagner, M. Teich, M. Helm, and D. Stehr

Appl. Phys. Lett. 100, 051109 (2012); http://dx.doi.org/10.1063/1.3681399 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2012

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We have investigated the temperature-dependent, intraexcitonic AC Stark effect that manifests itself in a line splitting of the heavy-hole 1s exciton transition in a GaAs/AlGaAs multi quantum well when the 1s-2p intraexciton transition is driven by intense THz light. The observed wavelength-dependent splitting at Helium temperature can still be distinguished at elevated temperatures up to 200 K. Although the thermal energy exceeds the exciton binding energy by a factor of 1.7, thermal exciton ionization influences the coherent nonlinear effect only indirectly via thermal line broadening. With a threefold transmission change on ultrafast timescales in a region accessible to Peltier-cooling the scheme could be promising for optical modulators.
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78.67.De Quantum wells
71.35.Ee Electron-hole drops and electron-hole plasma
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
81.07.St Quantum wells
78.30.Fs III-V and II-VI semiconductors

Surface depletion mediated control of inter-sub-band absorption in GaAs/AlAs semiconductor quantum well systems

Walter R. Buchwald, Justin W. Cleary, and Joshua Hendrickson

Appl. Phys. Lett. 100, 051110 (2012); http://dx.doi.org/10.1063/1.3680232 (3 pages)

Online Publication Date: 2 February 2012

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The modification of quantum well inter-sub-band absorption properties due to surface depletion induced band bending is reported. Fourier transform infrared spectroscopy measurements of a GaAs/AlAs multiple quantum well system reveal a reduction in the characteristic absorption resonance in correlation with wet chemical etching. High resolution transmission electron microscopy confirms the presence of the quantum wells after etching, suggesting the quantum wells are positioned within the surface depletion region of the structure. This method of inter-sub-band absorption modification could be used for the formation of quantum dots from a quantum well system with the precise, deterministic control of their location.
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73.21.Fg Quantum wells
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Standoff detection via single-beam spectral notch filtered pulses

Adi Natan, Jonathan M. Levitt, Leigh Graham, Ori Katz, and Yaron Silberberg

Appl. Phys. Lett. 100, 051111 (2012); http://dx.doi.org/10.1063/1.3681365 (3 pages)

Online Publication Date: 3 February 2012

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We demonstrate single-beam coherent anti-Stokes Raman spectroscopy (CARS), for detecting and identifying traces of solids, including minute amounts of explosives, from a standoff distance (>50 m) using intense femtosecond pulses. Until now, single-beam CARS methods relied on pulse-shapers in order to obtain vibrational spectra. Here, we present a simple and easy-to-implement detection scheme, using a commercially available notch filter that does not require the use of a pulse-shaper.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
06.60.Jn High-speed techniques (microsecond to femtosecond)

Fabrication of flower-like silver nanostructure on the Al substrate for surface enhanced fluorescence

Jun Dong (董军), Hairong Zheng (郑海荣), Xiaoqing Yan, Yu Sun, and Zhenglong Zhang

Appl. Phys. Lett. 100, 051112 (2012); http://dx.doi.org/10.1063/1.3681420 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2012

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Surface-enhanced fluorescence (SEF) substrates consisting of flower-like nanostructure of electromagnetically coupled silver dendrites on Al surface were manufactured by modified galvanic displacement process between Ag ion and Al at room temperature. Substrate enhancement efficiency, which was evaluated from SEF intensities of the adsorbed Rhodamine 6 G(Rh6G), was found to increase rapidly with reaction time. The observation highlights the importance of strong coupling effects between nanobranches in SEF. The variation of SEF efficiency can be qualitatively explained with local surface plasmon resonance model of coupled silver nanostructures.
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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)
73.22.Lp Collective excitations
78.55.Hx Other solid inorganic materials
61.46.Hk Nanocrystals
81.16.-c Methods of micro- and nanofabrication and processing

A quantum model for light emission performance of carbon nanotube field effect transistor

M. R. Aziziyan, V. Ahmadi, and N. Moghadam

Appl. Phys. Lett. 100, 051113 (2012); http://dx.doi.org/10.1063/1.3681787 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2012

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We propose a full quantum model based on non-equilibrium Green function method to simulate short channel, ohmic-carbon nanotube field effect transistor as light emitter. We consider carrier annihilation using self-energy concept in non-ballistic regime, regarding current conservation. Using this model, we calculate radiative recombination rate and electroluminescence spectrum of device. Since, higher bias voltage causes higher carrier injection, we expect to observe more recombination rate by increasing drain or gate voltage. Variation of gate voltage can shift the electroluminescence peak due to slight band gap change. The device current confirms that the electrical and optical properties of device are correlated.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
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