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29 Nov 2010

Volume 97, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 223101 (2010); http://dx.doi.org/10.1063/1.3519844 (3 pages)

Jin-Kyu Yang, Svetlana V. Boriskina, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao
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Chemical coating of large-area Au nanoparticle two-dimensional arrays as plasmon-resonant optics

Katsuhiro Isozaki, Takao Ochiai, Tomoya Taguchi, Koh-ichi Nittoh, and Kazushi Miki

Appl. Phys. Lett. 97, 221101 (2010); http://dx.doi.org/10.1063/1.3518469 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2010

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Innovative nanophotonic applications require a technique for generating not a nanometer-scale point but a large-area (mm2−m2) near-field light source. We succeeded in developing a large-area near-field light source that is densely constructed of uniform-size gold nanoparticles (AuNPs) two-dimensionally arrayed with regular interparticle gaps, which has tunable localized surface plasmon resonance bands (600–1100 nm). The near-field excitation properties based on the optical tunability of the AuNP two-dimensional arrays demonstrate that our chemical coating of large-area near-field light sources is widely applicable such as for high-sensitivity optical sensors and high-efficiency solar cells.
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81.65.-b Surface treatments
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations

Direct laser writing of three-dimensional submicron structures using a continuous-wave laser at 532 nm

M. Thiel, J. Fischer, G. von Freymann, and M. Wegener

Appl. Phys. Lett. 97, 221102 (2010); http://dx.doi.org/10.1063/1.3521464 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2010

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Three-dimensional direct laser writing is commonly associated with tightly focused femtosecond laser pulses. Although few reports have used continuous-wave lasers instead, it is unclear whether state-of-the-art three-dimensional submicron structures for photonics can be fabricated along these lines. Here, we systematically investigate the underlying mechanisms using a 532 nm continuous-wave laser operating at power levels of only some 10 mW and three different commercially available photoresists. Body-centered cubic woodpile photonic crystals composed of 24 layers with rod spacings as small as 450 nm serve as a demanding benchmark example for illustrating “state-of-the-art.”
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer

Quantitative NO2 molecular tagging velocimetry at 500 kHz frame rate

Naibo Jiang, Munetake Nishihara, and Walter R. Lempert

Appl. Phys. Lett. 97, 221103 (2010); http://dx.doi.org/10.1063/1.3522654 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2010

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NO2 molecular tagging velocimetry (MTV) is demonstrated at repetition rates as high as 500 kHz in a laboratory scale Mach 5 wind tunnel. A pulse burst laser and a home built optical parametric oscillator system were used to simultaneously generate the required 355 and 226 nm wavelengths for NO2 photodissociation (tagging) and NO planar laser induced fluorescence imaging (interrogation), respectively. NO2 MTV images were obtained both in front and behind the characteristic bow shock from a 5 mm diameter cylinder. From Gaussian curve fitting, an average free stream flow velocity of 719 m/s was obtained. Absolute statistical precision in velocity of ∼ 11.5 m/s was determined, corresponding to relative precision of 1.6%–5%, depending upon the region of the flow probed. © 2010 American Institute of Physics
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47.80.Cb Velocity measurements
06.30.Gv Velocity, acceleration, and rotation
33.80.Gj Diffuse spectra; predissociation, photodissociation

Surface plasmon enhanced UV emission in AlGaN/GaN quantum well

J. Lin, A. Mohammadizia, A. Neogi, H. Morkoc, and M. Ohtsu

Appl. Phys. Lett. 97, 221104 (2010); http://dx.doi.org/10.1063/1.3515419 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2010

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The surface plasmon (SP) energy for resonant enhancement of light has shown to be modified by the epitaxial substrate and the overlying metal thin film. The modification of SP energy in AlGaN/GaN epitaxial layers is studied using spectroscopic ellipsometry for enhanced UV-light emission. Silver induced SP can be extended to the UV wavelength range by increasing the aluminum concentration in AlxGa1−xN epilayer. A threefold increase in the UV-light emission is observed from AlGaN/GaN quantum well due to silver induced SP. Photoluminescence lifetime measurements confirm the resonant plasmon induced increase in Purcell factor as observed from the PL intensity measurements.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.67.De Quantum wells

Surface localized exciton emission from undoped SnO2 nanocrystal films

S. S. Pan, Y. H. Tian, Y. Y. Luo, Y. X. Zhang, S. Wang, and G. H. Li

Appl. Phys. Lett. 97, 221105 (2010); http://dx.doi.org/10.1063/1.3524196 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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We report the UV photoluminescence properties of SnO2 nanocrystalline films. A free exciton decay centered at 3.7 eV and a strong surface localized exciton emission peak at 3.3 eV have been observed at room temperature. The peak energy of the surface localized exciton emission exhibits a redshift with increasing temperature and a blueshift with increasing excitation intensity. The surface localized exciton emission is considered to originate from the radiative recombination of exciton within the surface region of SnO2 nanocrystals. The surface defects and local disorder are believed to be responsible for the formation of band tail states at the conduction band and potential well within the band tails.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Ha Other nonmetallic inorganics
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Midwave infrared quantum dot avalanche photodiode

David A. Ramirez, Jiayi Shao, Majeed M. Hayat, and Sanjay Krishna

Appl. Phys. Lett. 97, 221106 (2010); http://dx.doi.org/10.1063/1.3520519 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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We report the first demonstration of a GaAs based avalanche photodiode (APD) operating in the midwave infrared region (3–5 μm). In the device, called the quantum dot avalanche photodiode, an intersubband quantum dots-in-a-well detector is coupled with an APD through a tunnel barrier. Using this approach, we have increased the photocurrent and reached a conversion efficiency of 12%, which is one of the highest reported conversion efficiencies for any quantum dot detector.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Lensfree sensing on a microfluidic chip using plasmonic nanoapertures

Bahar Khademhosseinieh, Gabriel Biener, Ikbal Sencan, Ting-Wei Su, Ahmet F. Coskun, and Aydogan Ozcan

Appl. Phys. Lett. 97, 221107 (2010); http://dx.doi.org/10.1063/1.3521390 (3 pages)

Online Publication Date: 1 December 2010

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We demonstrate lensfree on-chip sensing within a microfluidic channel using plasmonic nanoapertures that are illuminated by a partially coherent quasimonochromatic source. In this approach, lensfree diffraction patterns of metallic nanoapertures located at the bottom of a microfluidic channel are recorded using an optoelectronic sensor-array. These lensfree diffraction patterns can then be rapidly processed, using phase recovery techniques, to back propagate the optical fields to an arbitrary depth, creating digitally focused complex transmission patterns. Cross correlation of these patterns enables lensfree on-chip sensing of the local refractive index surrounding the near-field of the plasmonic nanoapertures. Based on this principle, we experimentally demonstrate lensfree sensing of refractive index changes as small as ∼ 2×10−3. This on-chip sensing approach could be quite useful for development of label-free microarray technologies by multiplexing thousands of plasmonic structures on the same microfluidic chip, which can significantly increase the throughput of sensing.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
85.60.-q Optoelectronic devices

Electrical control of fine-structure splitting in self-assembled quantum dots for entangled photon pair creation

J. D. Mar, X. L. Xu, J. S. Sandhu, A. C. Irvine, M. Hopkinson, and D. A. Williams

Appl. Phys. Lett. 97, 221108 (2010); http://dx.doi.org/10.1063/1.3522655 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2010

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The fine-structure splitting δ1 of the bright exciton doublet in self-assembled InGaAs/GaAs quantum dots is measured as a function of the applied in-plane electric field using time-resolved Kerr rotation. We observe a significant reduction of δ1 with increasing electric field, suggesting a symmetrizing of the electron and hole wave functions. For sufficiently high fields, it is shown that δ1 can be made less than the quantum dot homogeneous linewidth γ, which is calculated using an appropriate model. This may open the way for the electrical control of polarization-entangled photon pair creation through the radiative biexciton cascade.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)

Midinfrared electroluminescence from InAs/InP quantum dashes

V. Liverini, A. Bismuto, L. Nevou, M. Beck, and J. Faist

Appl. Phys. Lett. 97, 221109 (2010); http://dx.doi.org/10.1063/1.3524213 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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We report midinfrared intraband electroluminescence from quantum cascade structures based on InAs/AlInGaAs quantum dashes grown on InP. The devices show a clear broad emission around 150 meV, which is attributed to an intraband transition between the quantum dashes and the following quantum wells. The emission is not present in a control structure without the dashes. The observed transition is mainly p-polarized and does not depend on the dash orientation. This indicates that the confinement in the dashes is mainly due to their height. Our results are promising for the development of broad-gain quantum cascade lasers based on three-dimensionally confined active regions.
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78.60.Fi Electroluminescence
78.67.De Quantum wells

Cantilever biosensor reader using a common-path, holographic optical interferometer

Henrik C. Pedersen, Michael L. Jakobsen, Steen G. Hanson, Carsten Dam-Hansen, Tom Olesen, and Poul Hansen

Appl. Phys. Lett. 97, 221110 (2010); http://dx.doi.org/10.1063/1.3522888 (3 pages)

Online Publication Date: 3 December 2010

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We demonstrate an optical reader principle aimed at monitoring biologically induced deflections of microcantilevers often used in biosensor systems. The principle is based on a so-called common-path optical interferometer in which the two interfering optical beams are copropagating, which makes the system less sensitive to external disturbances. A detection limit of around 1 nm’s deflection is demonstrated.
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07.60.Ly Interferometers
42.40.Kw Holographic interferometry; other holographic techniques
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.80.Ek Mechanical and micromechanical techniques

Dielectric gratings for wide-angle, broadband absorption by thin film photovoltaic cells

R. Esteban, M. Laroche, and J. J. Greffet

Appl. Phys. Lett. 97, 221111 (2010); http://dx.doi.org/10.1063/1.3512898 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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Optical management is essential to increase absorption in thin photovoltaic cells. In this article, full electromagnetic simulations show that a back mirror and a one-dimensional front SiC sawtooth grating of ∼ 1 μm dimensions can significantly increase absorption in a thin layer under light concentration. A 50 nm thick GaSb active layer in the described configuration absorbs ∼ 66% of the incident solar photons above the band gap for a concentration equivalent to a numerical aperture NA = 1/math. This absorption represents a ∼ 76% or 26% increase over the same structure but with the grating removed or substituted by an ideal antireflection coating, respectively.
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42.79.Ek Solar collectors and concentrators
42.79.Dj Gratings
42.79.Bh Lenses, prisms and mirrors
88.40.jp Multijunction solar cells
42.79.Wc Optical coatings

InSb1−xNx/InSb/GaAs alloys by thermal annealing for midinfrared photodetection

K. P. Lim, H. T. Pham, S. F. Yoon, K. H. Tan, and C. Y. Ngo

Appl. Phys. Lett. 97, 221112 (2010); http://dx.doi.org/10.1063/1.3524228 (3 pages) | Cited 2 times

Online Publication Date: 3 December 2010

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InSb1−xNx alloys on GaAs substrates are prepared by molecular beam epitaxy and in situ thermal annealed at different temperatures in Sb ambience. X-ray diffraction indicates that the amount of N incorporation in Sb lattice sites is dependent on the annealing temperature. Low annealing temperature increases the N incorporation and extends the absorption to long wavelength infrared range. InSb1−xNx photoconductors operating near 10 μm at 77 K are realized. The measured wavelengths are in good agreement with band gaps of the alloys calculated using a two-level band anticrossing model with Varshni relation. This work will benefit those working on midinfrared photodetectors.
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81.05.Ea III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.66.Fd III-V semiconductors

Strongly enhanced tunable photoluminescence in polymorphous silicon carbon thin films via excitation-transfer mechanism

Junzhuan Wang, V. Suendo, A. Abramov, Linwei Yu, and Pere Roca i Cabarrocas

Appl. Phys. Lett. 97, 221113 (2010); http://dx.doi.org/10.1063/1.3521280 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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Here, we investigate the enhanced tunable photoluminescence (PL) of hydrogenated polymorphous silicon carbon (pm-Si1−xCx:H) thin films fabricated in a plasma enhanced chemical vapor deposition system. The silicon nanocrystal (nc-Si) inclusions are formed during gas-phase nucleation and incorporated in the hydrogenated amorphous silicon carbon (a-SiC:H) matrix. The nc-Si provides high-quality recombination centers for the photogenerated carriers in the pm-Si1−xCx:H material, while the a-SiC:H matrix plays a role of sensitizer. We elucidate and provide experimental evidence for this excitation-transfer mechanism. Strongly enhanced PL performance can be achieved by effective matrix passivation that favors a diffusion-driven carrier recombination in the nc-Si centers.
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78.55.Qr Amorphous materials; glasses and other disordered solids
81.05.Gc Amorphous semiconductors
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Jg Amorphous semiconductors; glasses

Scattering processes in terahertz InGaAs/InAlAs quantum cascade lasers

M. Fischer, G. Scalari, K. Celebi, M. Amanti, Ch. Walther, M. Beck, and J. Faist

Appl. Phys. Lett. 97, 221114 (2010); http://dx.doi.org/10.1063/1.3504251 (3 pages) | Cited 3 times

Online Publication Date: 3 December 2010

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We report InGaAs/InAlAs based terahertz quantum cascade lasers with a short, bound-to-continuum design. These lasers operate at 3.1 THz up to a 115 K and emit 19 mW of peak optical power at 10 K. Devices with a modified waveguide lase up to 122 K with reduced power of 4 mW. The upper state lifetime was computed assuming alloy, interface roughness and longitudinal-optical (LO) phonon scatterings. Comparison with experiment suggests that the elastic scattering processes limit the lifetime at low temperature while the inelastic LO-phonon scattering becomes the dominant scattering mechanism at elevated temperature. Magnetotransport measurements provide additional evidence which supports the role of elastic scattering processes at low temperatures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.60.Bt Optoelectronic device characterization, design, and modeling
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Ion acceleration and cooling in gasless self-sputtering

David Horwat and André Anders

Appl. Phys. Lett. 97, 221501 (2010); http://dx.doi.org/10.1063/1.3521264 (3 pages) | Cited 4 times

Online Publication Date: 2 December 2010

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Copper plasma with hyperthermal directed velocity (8.8 eV) but very low temperature (0.6 eV) has been obtained using self-sputtering far above the runaway threshold. Ion energy distribution functions (IEDFs) were simultaneously measured at 34 locations. The IEDFs show the tail of the Thompson distribution near the magnetron target. They transform to shifted Maxwellians with the ions being accelerated and cooled. We deduce the existence of a highly asymmetric, pressure-driven potential hump which acts as a controlling “watershed” between the ion return flux and the expanding plasma.
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52.77.Dq Plasma-based ion implantation and deposition
52.70.-m Plasma diagnostic techniques and instrumentation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Sharp rise of excitation temperature in the periphery of lamp arcs measured from the 254 nm resonance line of mercury

E. Drakakis and D. Karabourniotis

Appl. Phys. Lett. 97, 221502 (2010); http://dx.doi.org/10.1063/1.3524212 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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Unexpected sharp rise of the excitation temperature of the resonance state of mercury measured in the arc boundary of a high intensity discharge lamp verifies the existence of an enhanced radiation source in the outer arc layer from which radiation excess observed in the valley of self-reversed lines is originated. This temperature was deduced from line-of-sight measurements of the radiance at the red peak of the 254 nm resonance line of mercury. The nonradiative transfer of excitation energy by resonant collisions between mercury atoms in the dense plasma medium is a very plausible explanation of the radiation source enhancement.
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42.72.Bj Visible and ultraviolet sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
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Permeation measurements and modeling of highly defective Al2O3 thin films grown by atomic layer deposition on polymers

P. F. Carcia, R. S. McLean, and M. H. Reilly

Appl. Phys. Lett. 97, 221901 (2010); http://dx.doi.org/10.1063/1.3519476 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2010

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We measured the thickness and temperature dependence of moisture permeation in highly defective (10–20 at. % hydrogen) Al2O3 thin films grown by atomic layer deposition on polymer substrates. We found that when films were grown at higher temperature or were thicker, independent of growth temperature, they were better moisture barriers. We determined the threshold thickness for measurement-limited barrier performance to be 7.5 nm for growth at 100 °C compared to 9.6 nm at 50 °C. We explained the permeability of these highly defective films with a new model, which relates moisture permeability to a critical density of defects and not due to pinholes.
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68.55.jd Thickness
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Indirect excitation of Er3+ ions in silicon nitride films prepared by reactive evaporation

E. Steveler, H. Rinnert, X. Devaux, M. Dossot, and M. Vergnat

Appl. Phys. Lett. 97, 221902 (2010); http://dx.doi.org/10.1063/1.3521279 (3 pages)

Online Publication Date: 29 November 2010

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Er-doped silicon nitride films were obtained by reactive evaporation of silicon under a flow of nitrogen ions and were annealed at temperatures up to 1300 °C. Samples were studied by infrared absorption and Raman spectrometries and by transmission electron microscopy. The 1.54 μm Er-related photoluminescence (PL) was studied in relation with the structure with pump excitation at 488 and 325 nm. Steady-state PL, PL excitation spectroscopy, and time-resolved PL were performed. The results demonstrate that Er3+ ions are indirectly excited both via silicon nanocrystals and via localized states in the silicon nitride matrix.
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81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Interfacial slippage of inorganic electronic materials on plastic substrates

Longchao Dai, Xue Feng, Bin Liu, and Daining Fang

Appl. Phys. Lett. 97, 221903 (2010); http://dx.doi.org/10.1063/1.3517488 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2010

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The stretchable and flexible electronics with the structure of inorganic films on plastic substrate has recently attracted an increasing interest. Interfacial failure inevitably occurs when the structure is subject to repeated bending or stretching in application. An analysis is presented in this letter on the slipping failure mechanism for the interface between inorganic film and plastic substrate. The critical radius of system curvature for the slipping crack propagation on its interface is obtained to analyze the bendability of the structure, which can provide the design guideline and characterization method to determine the interface fracture toughness of slipping failure.
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68.35.Gy Mechanical properties; surface strains
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks

Measurement of the thermal conductance of the graphene/SiO2 interface

Kin Fai Mak, Chun Hung Lui, and Tony F. Heinz

Appl. Phys. Lett. 97, 221904 (2010); http://dx.doi.org/10.1063/1.3511537 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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We have examined the interfacial thermal conductance GK of single and multilayer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By using an ultrafast optical pump pulse and monitoring the transient reflectivity on the picosecond time scale, we obtained an average value of GK of GK=5000 W/cm2 K for the graphene/SiO2 interface at room temperature. We observed significant variation in GK between individual samples, but found no systematic dependence on the thickness of the graphene layers.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.35.Md Surface thermodynamics, surface energies
78.47.J- Ultrafast spectroscopy (<1 psec)

Terahertz conductivity of the metal-insulator transition in a nanogranular VO2 film

T. L. Cocker, L. V. Titova, S. Fourmaux, H. -C. Bandulet, D. Brassard, J. -C. Kieffer, M. A. El Khakani, and F. A. Hegmann

Appl. Phys. Lett. 97, 221905 (2010); http://dx.doi.org/10.1063/1.3518482 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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Terahertz time-domain spectroscopy is used to measure the complex terahertz conductivity of a nanogranular vanadium dioxide (VO2) thin film as a function of temperature through the metal-insulator transition. The Drude–Smith model provides a good fit to the observed terahertz conductivity, revealing a metallic state that forms via switching of individual nanograins and strong carrier confinement within the nanograins due to scattering off grain boundaries. Furthermore, the directly applied Drude–Smith model provides a more accurate description of the measured terahertz conductivity in this material than either Bruggeman or Maxwell–Garnett effective medium theories.
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78.70.Gq Microwave and radio-frequency interactions
61.72.Mm Grain and twin boundaries
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Probing the electron density in undoped, Si-doped, and Mg-doped InN nanowires by means of Raman scattering

R. Cuscó, N. Domènech-Amador, L. Artús, T. Gotschke, K. Jeganathan, T. Stoica, and R. Calarco

Appl. Phys. Lett. 97, 221906 (2010); http://dx.doi.org/10.1063/1.3520643 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2010

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We report a Raman scattering determination of the electron density in InN nanowires from the analysis of longitudinal optical-phonon-plasmon coupled modes. A Raman peak assigned to the L− coupled mode is observed in both undoped and doped InN nanowires. This peak exhibits a shift to higher (lower) frequencies in the Si-doped (Mg-doped) nanowires and allows us to estimate the electron density in the nanowires. A significant residual electron density is found in the undoped nanowires, which increases in Si-doped nanowires and is partially compensated in Mg-doped nanowires.
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72.80.Ey III-V and II-VI semiconductors
61.72.U- Doping and impurity implantation
78.30.Fs III-V and II-VI semiconductors
63.22.Gh Nanotubes and nanowires

Invar effects of (Fe71.2B24Y4.8)96Nb4 alloy in different structural states

Qiang Hu, Xie-Rong Zeng, and Ming-Wang Fu

Appl. Phys. Lett. 97, 221907 (2010); http://dx.doi.org/10.1063/1.3524199 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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This paper reports the observation of the clear Invar effects of (Fe71.2B24Y4.8)96Nb4 bulk metallic glass. The Invar effects of (Fe71.2B24Y4.8)96Nb4 alloys in different structural states are also investigated in situ through cyclic thermal dilation tests at different cyclic temperatures. The results show that these Invar effects are strengthened in the relaxation amorphous state, weakened in the nanocrystalline state, and absent in the complete crystalline state. X-ray diffraction and Mössbauer spectroscopy demonstrate that the structural influences on Invar effects can be explained by the different local atomic arrangements around Fe atoms in different structural states.
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61.43.Fs Glasses
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
81.05.Kf Glasses (including metallic glasses)
75.50.Kj Amorphous and quasicrystalline magnetic materials

First principles study of Ag, Au, and Cu surface segregation in FePt-L10

Roman V. Chepulskii and Stefano Curtarolo

Appl. Phys. Lett. 97, 221908 (2010); http://dx.doi.org/10.1063/1.3522652 (3 pages)

Online Publication Date: 1 December 2010

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Doping FePt nanoparticles could be a possible approach to achieve high L10 order and magnetic anisotropy. To address stability, first-principles studies of surface segregation of dilute Ag/Au/Cu solutes at and near the (001)/(100)/(111) surfaces of FePt-L10 are performed. It is found that a strong surface segregation tendency at first outer layer is present in all the cases. For Cu, segregation is less than half of Ag and Au. Ag and Cu segregate to Fe sites at surfaces and preferentially substitute for Fe in the bulk, whereas Au substitutes for Fe at surfaces and for Fe and Pt in the bulk.
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68.35.Dv Composition, segregation; defects and impurities
61.72.up Other materials
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Observation of excited states of graphene on Ni(111) by secondary electron spectroscopy

P. Riccardi, A. Cupolillo, M. Pisarra, A. Sindona, and L. S. Caputi

Appl. Phys. Lett. 97, 221909 (2010); http://dx.doi.org/10.1063/1.3522891 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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We use secondary electron spectroscopy to probe the excited states of graphene adsorbed on a Ni(111) surface. A fine structure directly related to the empty bands above the vacuum level of the sample is resolved in the spectra excited by electrons. Ion-induced spectra reveal a high energy feature that is consistent with electron promotion from valence to conduction band states, from which electrons emerge into vacuum.
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73.22.Pr Electronic structure of graphene
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
79.20.Hx Electron impact: secondary emission
68.43.Mn Adsorption kinetics
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