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20 Feb 2006

Volume 88, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 083501 (2006); http://dx.doi.org/10.1063/1.2176847 (3 pages)

V. I. Talyanskii, M. R. Graham, and H. E. Beere
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Free-space microwave focusing by a negative-index gradient lens

T. Driscoll, D. N. Basov, A. F. Starr, P. M. Rye, S. Nemat-Nasser, D. Schurig, and D. R. Smith

Appl. Phys. Lett. 88, 081101 (2006); http://dx.doi.org/10.1063/1.2174088 (3 pages) | Cited 39 times

Online Publication Date: 21 February 2006

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Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index lens with an index of refraction ranging from −2.67 (edge) to −0.97 (center). Experimentally, we find that the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.3 GHz and in excellent agreement with full-wave simulations. We also demonstrate an advanced fabrication technique using conventional printed circuit board technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Improvement of two-step K+–Na+ and Ag+–Na+ ion-exchanged glass waveguides by surface removal

Jizuo Zou and Ray T. Chen

Appl. Phys. Lett. 88, 081102 (2006); http://dx.doi.org/10.1063/1.2172214 (3 pages) | Cited 1 time

Online Publication Date: 21 February 2006

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We introduce a simple approach to improve the properties of waveguides fabricated by two-step K+–Na+ and Ag+–Na+ ion exchange in BK7 glass. By etching a 0.25-μm-thick layer off the waveguide surface, the propagation losses and polarization dependent losses caused by silver colloids formed during the ion exchange process can be significantly reduced. In addition, this method can improve the uniformity of the waveguides with varying waveguide patterns. After 24 h of annealing at 300 °C, the propagation losses of the etched waveguides have a value of 0.25–0.35 dB/cm, which is about 0.1 dB/cm lower than the waveguides without etch. The etch has little impact on the waveguide mode profiles.
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42.79.Gn Optical waveguides and couplers
42.70.Ce Glasses, quartz
81.65.Cf Surface cleaning, etching, patterning
81.40.Gh Other heat and thermomechanical treatments

Silicon electron emitters fabricated by ultraviolet laser pulses

V. Zorba, P. Tzanetakis, C. Fotakis, E. Spanakis, E. Stratakis, D. G. Papazoglou, and I. Zergioti

Appl. Phys. Lett. 88, 081103 (2006); http://dx.doi.org/10.1063/1.2177653 (3 pages) | Cited 26 times

Online Publication Date: 21 February 2006

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In this letter we consider the effect of laser pulse duration on the surface morphology and the field emission properties of silicon structured by UV laser pulses. In three different pulse duration regimes ranging from sub-ps to ns, we altered the morphology of the fabricated silicon microspike arrays. The field emission properties of the microspike arrays were influenced by the morphological changes exhibiting a reduction of the emission threshold field to 2.5 V/μm for 15 ns laser pulses. The ability of tuning the field emission properties of laser-fabricated silicon microspike arrays makes them excellent candidates for use as field emission cathodes.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.47.Fg Semiconductor surfaces
79.70.+q Field emission, ionization, evaporation, and desorption
61.82.Fk Semiconductors
42.62.-b Laser applications

Low-threshold lasers based on a high-mobility semiconducting polymer

G. Heliotis, S. A. Choulis, G. Itskos, R. Xia, R. Murray, P. N. Stavrinou, and D. D. C. Bradley

Appl. Phys. Lett. 88, 081104 (2006); http://dx.doi.org/10.1063/1.2178197 (3 pages) | Cited 16 times

Online Publication Date: 21 February 2006

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Progress toward electrically driven conjugated polymer lasers should benefit from the identification of materials that exhibit good charge transport properties coupled with large optical gain. Here, we report a detailed study of a blue-emitting fluorene-based polymer that combines a large hole mobility with desirable stimulated emission characteristics. Laser oscillation is achieved within distributed feedback structures and leads to low threshold, tunable lasers operating in the blue spectral region. Our results establish this material as an attractive gain medium with which to try and construct a polymer laser diode.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Jk Polymers and organics
42.60.Fc Modulation, tuning, and mode locking

High-temperature operation of self-assembled GaInNAs/GaAsN quantum-dot lasers grown by solid-source molecular-beam epitaxy

C. Y. Liu, S. F. Yoon, Z. Z. Sun, and K. C. Yew

Appl. Phys. Lett. 88, 081105 (2006); http://dx.doi.org/10.1063/1.2178231 (3 pages) | Cited 12 times

Online Publication Date: 21 February 2006

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Self-assembled GaInNAs/GaAsN single layer quantum-dot (QD) lasers grown using solid-source molecular-beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼ 1.05 kA/cm2 from a GaInNAs QD laser (50×1700 μm2) at 10 °C. High-temperature operation up to 65 °C was also demonstrated from an unbonded GaInNAs QD laser (50×1060 μm2), with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Multichanneled filter based on a branchy defect in microstrip photonic crystal

Yunhui Li, Haitao Jiang, Li He, Hongqiang Li, Yewen Zhang, and Hong Chen

Appl. Phys. Lett. 88, 081106 (2006); http://dx.doi.org/10.1063/1.2176851 (3 pages) | Cited 7 times

Online Publication Date: 22 February 2006

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A multichanneled filter based on a branchy defect in a microstrip photonic crystal is proposed. By introducing a branchy structure across the defect region, multiple defect modes will appear inside the photonic gap, leading to the multichanneled filtering phenomenon. In comparison with the conventional multichanneled filters, the proposed structure is more compact and tunable as far as the device volume and fabrication are concerned. The microwave experiment results are found in agreement with simulation results.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials

Two-photon-induced reduction of metal ions for fabricating three-dimensional electrically conductive metallic microstructure

Takuo Tanaka, Atsushi Ishikawa, and Satoshi Kawata

Appl. Phys. Lett. 88, 081107 (2006); http://dx.doi.org/10.1063/1.2177636 (3 pages) | Cited 29 times

Online Publication Date: 22 February 2006

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We developed techniques for fabricating three-dimensional metallic microstructures using two-photon-induced metal-ion reduction. In this process, ions in a metal-ion aqueous solution were directly reduced by a tightly focused femtosecond pulsed laser to fabricate arbitrary three-dimensional structures. A self-standing metallic microstructure with high electrical conductivity was demonstrated.
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42.62.-b Laser applications

Infrared modulated interlevel spectroscopy of 1.3 μm self-assembled quantum dot lasers using a free electron laser

I. R. Sellers, D. J. Mowbray, T. J. Badcock, J.-P. R. Wells, P. J. Phillips, D. A. Carder, H. Y. Liu, K. M. Groom, and M. Hopkinson

Appl. Phys. Lett. 88, 081108 (2006); http://dx.doi.org/10.1063/1.2177656 (3 pages) | Cited 5 times

Online Publication Date: 22 February 2006

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A modulated far-IR technique is applied to determine the separations of the confined electron and hole states in a 1.3 μm emitting self-assembled quantum-dot laser. By utilizing the unusual temperature behavior of the threshold current density, which exhibits a minimum at ∼ 200 K, it is possible to eliminate heating effects associated with the far-IR pulses. In addition, the intense monochromatic laser output results in a relatively strong modulated signal strength. Electron and hole quantization energies of 46.7±0.2 and 13±1 meV, respectively, are determined.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Photoluminescence modification by high-order photonic bandsin TiO2/ZnS:Mn multilayer inverse opals

Jeffrey S. King, Elton Graugnard, and Christopher J. Summers

Appl. Phys. Lett. 88, 081109 (2006); http://dx.doi.org/10.1063/1.2177351 (3 pages) | Cited 7 times

Online Publication Date: 23 February 2006

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The formation of multilayered inverse opal photonic crystals by atomic layer deposition has been investigated, and shown to provide a flexible and precise technique to control the properties of photonic crystals. Inverse opals were formed by infiltration of SiO2 opal templates with conformal layers of ZnS:Mn and TiO2, followed by etching. The optical properties were further tuned by backfilling the structures with TiO2. The high-order band structure and its influence on the photoluminescent properties were studied and modification of the Cl− and Mn2+ emission peaks at 460 and 585 nm were demonstrated, respectively.
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78.55.Hx Other solid inorganic materials
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Controlled surface-plasmon coupling in SiO2-coated gold nanochains for tunable nonlinear optical properties

Yong Yang, Masayuki Nogami, Jianlin Shi, Hangrong Chen, Guohong Ma, and Singhai Tang

Appl. Phys. Lett. 88, 081110 (2006); http://dx.doi.org/10.1063/1.2172022 (3 pages) | Cited 28 times

Online Publication Date: 23 February 2006

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Linear chains of SiO2-coated Au nanoparticles, exhibiting large third-order nonlinearity at multiple wavelengths ranging from visible to near infrared, were successfully synthesized and self-assembled on glass substrates using a reduction of HAuCl4 and chemical surfactant modification. The optical absorption spectra peaking at 530, 620, 715, 830, and 1100 nm wavelengths were measured to the transverse and longitudinal surface plasmon resonance modes of 2, 3, 4, and 5 Au particles, respectively. Greatly enhanced third-order nonlinear optical responses have been observed at multiple wavelengths.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.30.-j Infrared and Raman spectra
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Strain relaxation and surface migration effects in InGaAlAs and InGaAsP selective-area-grown ridge waveguides

A. A. Sirenko, A. Kazimirov, A. Ougazzaden, S. M. O’Malley, D. H. Bilderback, Z.-H. Cai, B. Lai, R. Huang, V. K. Gupta, M. Chien, and S. N. G. Chu

Appl. Phys. Lett. 88, 081111 (2006); http://dx.doi.org/10.1063/1.2177634 (3 pages) | Cited 11 times

Online Publication Date: 23 February 2006

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Surface migration of the group-III precursors and strain relaxation at the ridge sidewalls are compared for 2.5 μm wide waveguides based on InGaAsP and InGaAlAs multiple-quantum-well (MQW) structures. The cross-sectional thickness and strain variations have been measured using synchrotron radiation-based x-ray diffraction with an angular resolution of 2 arc s and a beam size of (0.24×0.35) μm2. Indium-rich overgrowth has been observed for the InGaAsP-based waveguides, while InGaAlAs-based waveguides demonstrate thickness uniformity of the MQW active region with a strain relief of 0.4%/μm at the sidewalls.
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42.79.Gn Optical waveguides and couplers
81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Silicon-based highly-efficient fiber-to-waveguide coupler for high index contrast systems

Victor Nguyen, Trisha Montalbo, Christina Manolatou, Anu Agarwal, Ching-yin Hong, John Yasaitis, L. C. Kimerling, and Jurgen Michel

Appl. Phys. Lett. 88, 081112 (2006); http://dx.doi.org/10.1063/1.2179129 (3 pages) | Cited 16 times

Online Publication Date: 24 February 2006

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A coupler to efficiently transfer broadband light from a single-mode optical fiber to a single-mode high-index contrast waveguide has been fabricated on a silicon substrate. We utilized a novel coupling scheme, with a vertically asymmetric design consisting of a stepwise parabolic graded index profile combined with a horizontal taper, to simultaneously confine light in both directions. Coupling efficiency has been measured as a function of the device dimensions. The optimal coupling efficiency is achieved for structures whose length equals the focal distance of the graded index and whose input width is close to the mode field diameter of the fiber. The fabricated structure is compact, robust and highly efficient, with an insertion loss of 2.2 dB at 1550 nm. The coupler exhibits less than 1 dB variation in coupling efficiency in the measured spectral range from 1520 nm to 1620 nm. The lowest insertion loss of 1.9 dB is measured at 1540 nm. The coupler design offers highly efficient coupling for single mode waveguides of core indices up to 2.2.
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42.82.Bq Design and performance testing of integrated-optical systems
42.81.Qb Fiber waveguides, couplers, and arrays
42.81.Cn Fiber testing and measurement of fiber parameters
42.81.Dp Propagation, scattering, and losses; solitons
42.15.Eq Optical system design

Surface-emitting microlaser combining two-dimensional photonic crystal membrane and vertical Bragg mirror

B. Ben Bakir, Ch. Seassal, X. Letartre, P. Viktorovitch, M. Zussy, L. Di Cioccio, and J. M. Fedeli

Appl. Phys. Lett. 88, 081113 (2006); http://dx.doi.org/10.1063/1.2172730 (3 pages) | Cited 28 times

Online Publication Date: 24 February 2006

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We report on the design and fabrication of heterogeneous and compact surface-emitting microlasers, optically pumped and operating at 1.5 μm at room-temperature. A very low threshold, below 15 μW, is achieved. The devices consists of a top two-dimensional InP photonic crystal slab, including four InAsP quantum wells, a SiO2 bonding layer, and a bottom high index contrast Si/SiO2 Bragg mirror deposited on a Si wafer. The graphitelike photonic crystal lattice is tailored for vertical emission. We theoretically and experimentally demonstrate that the Bragg reflector can strongly enhance the quality factor of the photonic crystal resonant mode, leading to a drastic decrease of the lasing threshold.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Tv Photonic crystal lasers and coherent effects

Enhancing light outcoupling of organic light-emitting devices by locating emitters around the second antinode of the reflective metal electrode

Chun-Liang Lin, Ting-Yi Cho, Chih-Hao Chang, and Chung-Chih Wu

Appl. Phys. Lett. 88, 081114 (2006); http://dx.doi.org/10.1063/1.2178485 (3 pages) | Cited 42 times

Online Publication Date: 24 February 2006

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Due to generally low conductivity and low carrier mobilities of organic materials, organic light-emitting devices (OLEDs) are typically optimized for light outcoupling by locating emitters around the first antinode of the metal electrode. In this letter, by utilizing device structures containing conductive doping, we investigate theoretically and experimentally the influences of the location of emitters relative to the metal electrode on OLED emission, and show that substantial enhancement in light outcoupling (1.2 times) or forward luminance (1.6 times) could be obtained by placing emitters around the second antinode instead of the first antinode. Depending on the detailed condition, the second-antinode device may also give more directed emission as often observed in strong-microcavity devices yet without suffering a color shift with viewing angles.
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85.60.Jb Light-emitting devices

GaSb-based 2.X μm quantum-well diode lasers with low beam divergence and high output power

M. Rattunde, J. Schmitz, G. Kaufel, M. Kelemen, J. Weber, and J. Wagner

Appl. Phys. Lett. 88, 081115 (2006); http://dx.doi.org/10.1063/1.2178506 (3 pages) | Cited 22 times

Online Publication Date: 24 February 2006

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We report on GaSb-based 2.X μm diode lasers with an improved waveguide design, leading to a reduced beam divergence in the fast axis of 44° full width at half maximum (FWHM), compared to 67° FWHM of a conventional broadened waveguide design. 2.3 μm ridge-waveguide lasers with the improved epitaxial design showed, besides the narrow beam profile in the fast axis, an excellent slow axis beam quality [M2<1.1 up to 70 mW, continuous wave (cw)]. 2.0 μm broad-area lasers with the improved waveguide too, exhibit a maximum cw-output power of 1.96 W.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Efficient optical pulse compression using chalcogenide single-mode fibers

Libin Fu, Alexander Fuerbach, Ian C. M. Littler, and Benjamin J. Eggleton

Appl. Phys. Lett. 88, 081116 (2006); http://dx.doi.org/10.1063/1.2178772 (3 pages) | Cited 7 times

Online Publication Date: 24 February 2006

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We demonstrate compression of low-power 6 ps pulses to 420 fs around 1550 nm in a compact all-fiber scheme utilizing the strong nonlinearity and positive-normal dispersion of a single-mode As2Se3 fiber, in combination with a tailored chirped fiber Bragg grating. The value and sign of the dispersion, coupled with the high nonlinearity of the chalcogenide, produces a smoothly broadened spectrum with a monotonic chirp via self phase modulation. Measurements of the phase and time evolution of the laser pulses using frequency resolved optical gating are performed showing excellent agreement with theory. We also discuss the limiting influence of two-photon absorption.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Dp Propagation, scattering, and losses; solitons
42.79.Dj Gratings
42.81.Wg Other fiber-optical devices
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Mid-infrared hole-intersubband electroluminescence in carbon-doped GaAs/AlGaAs quantum cascade structures

Oana Malis, Loren N. Pfeiffer, Kenneth W. West, A. Michael Sergent, and Claire Gmachl

Appl. Phys. Lett. 88, 081117 (2006); http://dx.doi.org/10.1063/1.2179117 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2006

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Mid-infrared electroluminescence from carbon-doped GaAs/AlGaAs quantum cascade structures was observed and studied to determine the prospects of hole intersubband transitions for possible use in light emitting devices. The luminescence spectra exhibit a complex three-peak structure consistent with two heavy-to-heavy hole transitions and thermal emission. The hole transition energies in emission are in agreement with corresponding absorption and photocurrent energies, but typically 17% smaller than expected from calculations of a six-band k∙p model. The upper-level lifetime was estimated to be 0.4 ps, in agreement with simple calculations considering approximations of the heavy-hole effective masses.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
78.30.Fs III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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Nanosecond discharge in air at atmospheric pressure as an x-ray source with high pulse repetition rates

Victor F. Tarasenko

Appl. Phys. Lett. 88, 081501 (2006); http://dx.doi.org/10.1063/1.2176866 (3 pages) | Cited 21 times

Online Publication Date: 22 February 2006

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The properties of x-ray radiation and runaway electrons produced using a nanosecond volume discharge are examined. X-ray radiation at a pulse repetition rate of 3 kHz was obtained time in a gas diode filled with air at atmospheric pressure. The current pulse width (FWHM) for runaway electrons generated in the gas diode was ∼ 100 ps. A prepulse was observed on an oscilloscope trace of the main runaway electron beam current.
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52.80.Hc Glow; corona
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes

A technique for uniform generation of very-high-frequency plasma suited to large-area thin-film deposition

H. Yamakoshi, K. Satake, Y. Takeuchi, H. Mashima, and T. Aoi

Appl. Phys. Lett. 88, 081502 (2006); http://dx.doi.org/10.1063/1.2176867 (3 pages) | Cited 3 times

Online Publication Date: 23 February 2006

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Two very-high-frequency powers between which the phase difference is varying in split of time are supplied to a ladder-shaped electrode through multiple feeding points located at symmetrical positions of the electrode to generate a large-area uniform plasma. Theoretical calculations of the voltage distribution at several phase difference show good agreement with experiments. Plasma emission uniformity within ±15% is demonstrated at 60 MHz for the substrate size of 1.4×1.1 m, with nitrogen gas of 10 Pa.
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52.50.Dg Plasma sources
52.77.Dq Plasma-based ion implantation and deposition
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Effect of SiO2 incorporation on stability and work function of conducting MoO2

Y. Liang, C. Tracy, E. Weisbrod, P. Fejes, and N. D. Theodore

Appl. Phys. Lett. 88, 081901 (2006); http://dx.doi.org/10.1063/1.2176859 (3 pages) | Cited 5 times

Online Publication Date: 21 February 2006

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We show the incorporation of different amounts of SiO2 in conducting MoO2 results in materials that have large vacuum work functions tunable by approximately 1 eV and improved thermal stability at elevated temperatures. Electrical measurements of MoSixOy/HfO2/SiOx/n-Si capacitors show an approximate 5.1 eV work function, suitable for p-channel metal-oxide-semiconductor devices. . Thickening of the interfacial SiOx layer was observed, however, after annealing the stack at higher temperatures in N2.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors

Two-dimensional current percolation in nanocrystalline vanadiumdioxide films

John Rozen, René Lopez, Richard F. Haglund, and Leonard C. Feldman

Appl. Phys. Lett. 88, 081902 (2006); http://dx.doi.org/10.1063/1.2175490 (3 pages) | Cited 20 times

Online Publication Date: 21 February 2006

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Simultaneous measurements of the transmittance and the resistance were carried out on 20-nm-thick VO2 wires during the semiconductor-to-metal transition (SMT). They reveal an offset between the effective electrical and optical switching temperatures. This shift is due to current percolation through a network of nanometer-scale grains of different sizes undergoing a SMT at distinct temperatures. An effective-medium approximation can model this behavior and proves to be an indirect method to calculate the surface coverage of the films.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions

Suppression of phase separation in Hf-silicate films using NH3 annealing treatment

K. B. Chung, C. N. Whang, M.-H. Cho, C. J. Yim, and D.-H. Ko

Appl. Phys. Lett. 88, 081903 (2006); http://dx.doi.org/10.1063/1.2175493 (3 pages) | Cited 13 times

Online Publication Date: 21 February 2006

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The structural characteristics of Hf-silicate films and nitrogen incorporated Hf-silicate films, prepared using a NH3 annealing treatment, were investigated by various measurements. Hf-silicate films annealed in a N2 ambient at 900 °C show the evidence of crystallization in local regions, resulting in the phase separation of HfO2 and SiO2. In addition, a SiO2 overlayer is formed on the Hf-silicate films, due to the diffusion of Si by postannealing in an ambient of N2 at 900 °C. However, in nitrogen incorporated Hf-silicate films, prepared using a NH3 annealing treatment, phase separation is effectively suppressed and no SiO2 overlayer is present. The incorporated N is distributed into the film and interfacial layer, and obstructs the diffusion of Si from the substrate as well as the film. Structural changes in films affect electrical characteristics such as the dielectric constant and flatband voltage.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.70.Dm X-ray absorption spectra
68.55.-a Thin film structure and morphology
66.30.Dn Theory of diffusion and ionic conduction in solids
77.22.Ch Permittivity (dielectric function)

Laser-nanostructured Ag films as substrates for surface-enhanced Raman spectroscopy

S. J. Henley, J. D. Carey, and S. R. P. Silva

Appl. Phys. Lett. 88, 081904 (2006); http://dx.doi.org/10.1063/1.2178387 (3 pages) | Cited 12 times

Online Publication Date: 21 February 2006

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Pulsed-laser (248 nm) irradiation of Ag thin films was employed to produce nanostructured Ag/SiO2 substrates. By tailoring the laser fluence, it was possible to controllably adjust the mean diameter of the resultant near-spherical Ag droplets. Thin films of tetrahedral amorphous carbon (ta-C) were subsequently deposited onto the nanostructured substrates. Visible Raman measurements were performed on the ta-C films, where it was observed that the intensity of the Raman signal was increased by nearly two orders of magnitude, when compared with ta-C films grown on nonstructured substrates. The use of laser annealing as a method of preparing substrates, at low macroscopic temperatures, for surface-enhanced Raman spectroscopy on subnanometer-thick films is discussed.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Er Solid metals and alloys

Optimization of the efficiency of single-photon sources based on quantum dots under optical excitation

A. Malko, M. H. Baier, K. F. Karlsson, E. Pelucchi, D. Y. Oberli, and E. Kapon

Appl. Phys. Lett. 88, 081905 (2006); http://dx.doi.org/10.1063/1.2177547 (3 pages) | Cited 6 times

Online Publication Date: 21 February 2006

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We demonstrate efficient, regulated single-photon operation from site-controlled InGaAs quantum dots (QDs) grown on a prepatterned substrate. Under nonresonant optical excitation, carriers trapped at structural or compositional defects of the adjacent nanostructures led to a degradation of the single-photon statistics from a QD. When the QD was excited quasiresonantly, single photons were emitted and a nearly complete suppression of multiphoton emission was achieved, making these QDs promising candidates for effective solid-state single-photon sources.
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78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
42.50.-p Quantum optics

Optical charge transfer absorption in lithium-intercalated tungsten oxide thin films

Lars Berggren and Gunnar A. Niklasson

Appl. Phys. Lett. 88, 081906 (2006); http://dx.doi.org/10.1063/1.2177548 (3 pages) | Cited 13 times

Online Publication Date: 21 February 2006

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Amorphous tungsten oxide exhibits electrochromism when intercalated with protons or lithium ions. Thin films of the material were prepared by dc magnetron sputtering and subsequently electrochemically intercalated with lithium. The optical absorption in the wavelength range 300 to 2500 nm was measured for a number of lithium concentrations. All the spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with the predictions of a statistical theory.
Show PACS
78.66.Nk Insulators
42.70.-a Optical materials
78.20.Jq Electro-optical effects
78.40.Pg Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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