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24 Mar 2008

Volume 92, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 123501 (2008); http://dx.doi.org/10.1063/1.2898731 (3 pages)

Selim Tanriseven, Pleun Maaskant, and Brian Corbett
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Short wavelength (4 μm) quantum cascade detector based on strain compensated InGaAs/InAlAs

F. R. Giorgetta, E. Baumann, R. Théron, M. L. Pellaton, D. Hofstetter, M. Fischer, and J. Faist

Appl. Phys. Lett. 92, 121101 (2008); http://dx.doi.org/10.1063/1.2902301 (3 pages) | Cited 9 times

Online Publication Date: 24 March 2008

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We report on a quantum cascade detector based on nearly strain compensated InGaAs/InAlAs pseudomorphically grown on InP substrate and detecting light at short wavelengths around 4 μm. The background limited infrared performance (BLIP) condition is met at a temperature of 108 K with a high detectivity of DBLIP* = 1.2×1011 Jones.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Bt Optoelectronic device characterization, design, and modeling
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Shape-engineered epitaxial InGaAs quantum rods for laser applications

L. H. Li, P. Ridha, G. Patriarche, N. Chauvin, and A. Fiore

Appl. Phys. Lett. 92, 121102 (2008); http://dx.doi.org/10.1063/1.2903098 (3 pages) | Cited 10 times

Online Publication Date: 24 March 2008

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We apply artificial shape engineering of epitaxial semiconductor nanostructures to demonstrate InGaAs quantum rods (QRs), nanocandles, and quantum dots-in-rods on a GaAs substrate. The evolution of the QRs from a zero-dimensional to one-dimensional confinement is evidenced by systematically measuring the photoluminescence and photoluminescence decay as a function of the rod length. Lasers based on a three-stack QR active region are demonstrated at room temperature, validating the applicability of the QRs in the real devices.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Resonant terahertz reflection of periodic arrays of subwavelength metallic rectangles

Xinchao Lu, Jiaguang Han, and Weili Zhang

Appl. Phys. Lett. 92, 121103 (2008); http://dx.doi.org/10.1063/1.2902292 (3 pages) | Cited 15 times

Online Publication Date: 25 March 2008

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We present reflection properties of terahertz pulses in periodic arrays of metallic rectangles of subwavelength dimensions. Resonant reflection is characterized by terahertz time-domain spectroscopy and is attributed to the contributions from the dipole localized surface plasmons of isolated metallic rectangles, their interactions between the rectangles, and the nonresonant direct reflection. A number of factors, including the polarization of the terahertz electric field, the shape of the metal structures, the dielectric function of the substrate, and the lattice constant of the arrays are found to influence terahertz reflection properties. The measured resonant reflectance is well fit by numerical simulations.
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78.70.Gq Microwave and radio-frequency interactions
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.-f Structure of specific crystalline solids
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Detuning characteristics of the linewidth enhancement factor of a midinfrared quantum cascade laser

Naoki Kumazaki, Yohei Takagi, Mikito Ishihara, Kenichi Kasahara, Atsushi Sugiyama, Naota Akikusa, and Tadataka Edamura

Appl. Phys. Lett. 92, 121104 (2008); http://dx.doi.org/10.1063/1.2903108 (3 pages) | Cited 6 times

Online Publication Date: 25 March 2008

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The linewidth enhancement factor of a 5 μm distributed feedback (DFB) quantum cascade laser above the threshold current detuned from the gain peak was investigated. This laser oscillates in two DFB modes located on either side of the gain peak. Using the optical feedback self-mixing method, we have observed variations in the linewidth enhancement factor, deviating from zero. The signs of the two DFB modes are both negative, which was verified by comparing their waveforms with that of conventional 1.55 μm laser diodes, suggesting that the gain curve is asymmetric with respect to the gain peak.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

ZnCdSe/ZnCdMgSe quantum cascade electroluminescence

Kale J. Franz, William O. Charles, Aidong Shen, Anthony J. Hoffman, Maria C. Tamargo, and Claire Gmachl

Appl. Phys. Lett. 92, 121105 (2008); http://dx.doi.org/10.1063/1.2903135 (3 pages) | Cited 13 times

Online Publication Date: 25 March 2008

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This letter reports electroluminescence emission from a ZnCdSe/ZnCdMgSe quantum cascade (QC) structure. With a two-well QC active region design, the II-VI heterostructure was grown lattice matched on an InP substrate by molecular beam epitaxy. Deep etched mesas were electrically pumped at current densities up to 10 kA/cm2, producing optical emission centered near 4.8 μm, in good agreement with the structure design. The light is predominantly TM polarized, confirming its intersubband origin. Electroluminescence was observed from 78 to 300 K.
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78.60.Fi Electroluminescence
78.67.De Quantum wells
73.63.Hs Quantum wells

InAs/GaSb cascaded active region superlattice light emitting diodes for operation at 3.8 μm

E. J. Koerperick, J. T. Olesberg, T. F. Boggess, J. L. Hicks, L. S. Wassink, L. M. Murray, and J. P. Prineas

Appl. Phys. Lett. 92, 121106 (2008); http://dx.doi.org/10.1063/1.2892633 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2008

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We report on the growth and characterization of InAs/GaSb superlattice light emitting diodes (LEDs) operating in the midwave infrared at 3.8 μm at 77 K. Devices were grown by solid source molecular beam epitaxy on (100) GaSb substrates and were fabricated into 120×120 μm2 mesa devices using wet etching. By employing an eight-stage cascaded active region design, output powers in excess of 1.5 mW were achieved at 77 K with 100 mA peak drive current and a 50% duty cycle. Operating characteristics of the devices were examined from room temperature to 77 K under quasi-dc excitation conditions.
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85.60.Jb Light-emitting devices

Temperature dependence of surface plasmon mediated emission from metal-capped ZnO films

J. Li and H. C. Ong

Appl. Phys. Lett. 92, 121107 (2008); http://dx.doi.org/10.1063/1.2902323 (3 pages) | Cited 17 times

Online Publication Date: 26 March 2008

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Surface plasmon (SP) mediated emission from Al-capped ZnO films has been studied by temperature-dependent photoluminescence from 10 to 300 K. By comparing with bare ZnO, it is found that the SP induced emission enhancement ratio linearly decreases with increasing temperature. By taking into account temperature-dependent dielectric functions of both Al and ZnO, theoretical Purcell factor has been calculated for different temperatures. We find the experimental results are highly consistent with theory. From the calculation, we have found the increase of plasmonic density of states with decreasing temperature is the primary cause for the increase of SP coupling.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Et II-VI semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Enhanced light output of GaN-based light-emitting diodes with ZnO nanorod arrays

Sung Jin An, Jee Hae Chae, Gyu-Chul Yi, and Gil H. Park

Appl. Phys. Lett. 92, 121108 (2008); http://dx.doi.org/10.1063/1.2903153 (3 pages) | Cited 59 times

Online Publication Date: 26 March 2008

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We report enhanced light output of GaN-based light-emitting diodes (LEDs) with vertically aligned ZnO nanorod arrays. The ZnO nanorod arrays were prepared on the top layer of GaN LEDs using catalyst-free metalorganic vapor phase epitaxy. Compared to conventional GaN LEDs, light output of GaN LEDs with the ZnO nanorod arrays increased up to 50% and 100% at applied currents of 20 and 50 mA, respectively. The source of the enhanced light output is also discussed.
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85.60.Jb Light-emitting devices

Optical limiting in lead magnesium niobate–lead titanate multilayers

Yalin Lu and Chen Gao

Appl. Phys. Lett. 92, 121109 (2008); http://dx.doi.org/10.1063/1.2902318 (3 pages) | Cited 1 time

Online Publication Date: 26 March 2008

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Optical limiting in highly oriented lead magnesium niobate–lead titanate multilayers has been investigated at both 1.064 and 0.532 μm wavelengths. Limiting thresholds for three such multilayers having periods of 20, 106, and 218 nm, respectively, were determined at the level ∼ 220 μJ/pulse for 1.064 μm and ∼ 150 μJ/pulse for 0.532 μm. Nonlinear optical scattering from domain walls was used to explain the observed limiting behavior. Possible formation of nonlinear refraction grating was also discussed.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.65.-k Nonlinear optics

Soft x-ray source for nanostructure imaging using femtosecond-laser-irradiated clusters

Y. Fukuda, A. Ya. Faenov, T. Pikuz, M. Kando, H. Kotaki, I. Daito, J. Ma, L. M. Chen, T. Homma, K. Kawase, T. Kameshima, T. Kawachi, H. Daido, T. Kimura, T. Tajima, et al.

Appl. Phys. Lett. 92, 121110 (2008); http://dx.doi.org/10.1063/1.2899966 (3 pages) | Cited 23 times

Online Publication Date: 27 March 2008

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The intense soft x-ray light source using the supersonic expansion of the mixed gas of He and CO2, when irradiated by a femtosecond Ti:sapphire laser pulse, is observed to enhance the radiation of soft x-rays from the CO2 clusters. Using this soft x-ray emissions, nanostructure images of 100-nm-thick Mo foils in a wide field of view (mm2 scale) with high spatial resolution (800 nm) are obtained with high dynamic range LiF crystal detectors. The local inhomogeneities of soft x-ray absorption by the nanometer-thick foils is measured with an accuracy of less than ±3%.
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61.82.Rx Nanocrystalline materials
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
78.70.Dm X-ray absorption spectra
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

a-Si nanolayer induced enhancement of the 1.53 μm photoluminescence in Er3+ doped a-Al2O3 thin films

J. Toudert, S. Núñez-Sánchez, M. Jiménez de Castro, and R. Serna

Appl. Phys. Lett. 92, 121111 (2008); http://dx.doi.org/10.1063/1.2900662 (3 pages) | Cited 7 times

Online Publication Date: 28 March 2008

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A structured film formed by an active Er3+-doped amorphous Al2O3 layer located between two amorphous silicon nanolayers (NLs) in as-grown conditions shows an enhancement of the photoluminescence (PL) intensity and lifetime at 1.53 μm of one order of magnitude when compared to a similar Er3+-doped film without silicon NLs. The film can be pumped even under nonresonant excitation conditions as a result of a long range energy transfer from the a-Si NLs to the Er3+ ions. In addition, the PL shows a single exponential decay with a lifetime value as high as 2.4 ms. The lifetime enhancement is associated with an improvement of the emission efficiency of the Er3+ ions.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Nonlinear reflection effects on Fresnel phase matching

Myriam Raybaut, Antoine Godard, Alexis Toulouse, Clément Lubin, and Emmanuel Rosencher

Appl. Phys. Lett. 92, 121112 (2008); http://dx.doi.org/10.1063/1.2901032 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2008

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An experimental study of the second harmonic generation conversion efficiency of Fresnel phase matching as a function of a gallium arsenide sample length is presented. It shows a strong deviation from the classical quadratic law, explaining the low conversion yields related in the literature. In order to explain these experimental results, a highly multimodal nonlinear waveguide model is developed which shows a good agreement with the experimental results. It highlights the detrimental role of nonlinear reflection.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Femtosecond laser induced coordination transformation and migration of ions in sodium borate glasses

Yin Liu, Bin Zhu, Li Wang, Jianrong Qiu, Ye Dai, and Hongliang Ma

Appl. Phys. Lett. 92, 121113 (2008); http://dx.doi.org/10.1063/1.2903710 (3 pages) | Cited 14 times

Online Publication Date: 28 March 2008

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We report on the coordination transformation of B3+ ions and migration of Na+ and O2− ions in sodium borate glasses, induced by 250 kHz, 800 nm femtosecond laser irradiation. Micro-Raman spectra show that the ratio of the integrated intensity of the two peaks at 806 and 774 cm−1 decreases at first and then increases with increasing distance from the center of the laser modified zone. Electron dispersive x-ray spectra show that a portion of Na+ and O2− ions migrate from the vicinity of focal point after the femtosecond laser irradiation. A possible mechanism is proposed to explain the observed phenomena.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.43.Fs Glasses
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)

Phase-velocity measurement of a tightly focused Gaussian beam by use of sum frequency generation

Ke Wang, Liejia Qian, Ping Qiu, and Heyuan Zhu

Appl. Phys. Lett. 92, 121114 (2008); http://dx.doi.org/10.1063/1.2903713 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2008

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In this letter, the nonuniform phase-velocity distribution of a tightly focused Gaussian beam is experimentally measured, both in the axial and the radial dimensions, through a nonlinear optical approach in a form of off-axis sum frequency generation. The experimental results demonstrate the superluminal phase-velocity distribution near the Gaussian beam axis around the focal plane, in agreement with the theoretical expectation.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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Microplasma generation in a microscale short vacuum arc

Isak I. Beilis

Appl. Phys. Lett. 92, 121501 (2008); http://dx.doi.org/10.1063/1.2901152 (3 pages) | Cited 4 times

Online Publication Date: 27 March 2008

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A mechanism of plasma plume generation and plasma jet formation in a microscale vacuum arc (MVA) was proposed. The uniqueness of the subject is the force generated by a common plasma plume extracted from cathode and anode spots in a MVA. A calculating model for microplasma origin was developed taking into account the atom ionization and the phenomena in the nonequilibrium layers near evaporated surface in the cathode and anode regions. The plasma parameters as well as the electrode erosion rate were studied. It was found relatively large anode erosion rate and force at the anode surface in MVA in comparison to the force that usually occurs at the cathode in arcs with large gap. This important result of MVA was proposed to use in an exceptional microthruster concept for spacecraft propulsion and for anode microplasma source.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.50.Dg Plasma sources
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Grain refinement assisted strengthening of carbon nanotube reinforced copper matrix nanocomposites

K. T. Kim, J. Eckert, S. B. Menzel, T. Gemming, and S. H. Hong

Appl. Phys. Lett. 92, 121901 (2008); http://dx.doi.org/10.1063/1.2899939 (3 pages) | Cited 20 times

Online Publication Date: 24 March 2008

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Carbon nanotube reinforced copper matrix (CNT/Cu) nanocomposites were fabricated by the modified molecular-level mixing process, which produces a homogeneous dispersion of CNTs in a fine grained metal matrix. These nanocomposites, consisting of 1.5 μm Cu matrix grains and 5 vol % of multiwall CNTs, show a high strengthening capability; enhancing the yield strength of unreinforced Cu by 2.3 times. The enhanced yield strength stems from the reinforcing effect of CNTs and additional hardening of the Cu matrix by grain refinement. The results reveal that the metallurgical treatment of the matrix is important for the development of high-strength CNT/metal nanocomposites.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.40.Lm Deformation, plasticity, and creep
81.40.Gh Other heat and thermomechanical treatments
62.20.F- Deformation and plasticity

Defect reduction in GaN/(0001)sapphire films grown by molecular beam epitaxy using nanocolumn intermediate layers

D. Cherns, L. Meshi, I. Griffiths, S. Khongphetsak, S. V. Novikov, N. Farley, R. P. Campion, and C. T. Foxon

Appl. Phys. Lett. 92, 121902 (2008); http://dx.doi.org/10.1063/1.2899944 (3 pages) | Cited 21 times

Online Publication Date: 24 March 2008

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Transmission and scanning electron microscopies are used to examine the epitaxial lateral overgrowth of GaN on GaN nanocolumns grown on AlN/(0001)sapphire by molecular beam epitaxy. Initially, N-rich growth gave a bimodal morphology consisting of defect-free Ga-polar nanocolumns emanating from a compact, highly defective N-polar layer. Under subsequent Ga-rich conditions, the nanocolumns grew laterally to produce continuous Ga-polar overlayers. Threading dislocation (TD) densities in the overlayer were in the range of 108–109 cm−2, up to two orders of magnitude less than in the N-polar underlayer. It is proposed that the change in polarity is a key factor controlling the reduction in TD density.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.J- Morphology of films

Phase modulation atomic force microscopy in constant excitation mode capable of simultaneous imaging of topography and energy dissipation

Yan Jun Li, Naritaka Kobayashi, Yoshitaka Naitoh, Masami Kageshima, and Yasuhiro Sugawara

Appl. Phys. Lett. 92, 121903 (2008); http://dx.doi.org/10.1063/1.2901151 (3 pages) | Cited 4 times

Online Publication Date: 24 March 2008

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The authors have developed phase modulation atomic force microscopy in constant excitation mode capable of simultaneously imaging the topography and energy dissipation of a sample surface in a liquid. This setup utilizes a fast, low-cost sample-and-hold technique to analyze the oscillation signals of a cantilever. The proposed circuitry allows us to measure the local energy dissipated by the tip-sample interaction during imaging. The energy dissipation image exhibits a material-specific contrast for a polymer-blend film.
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68.37.Ps Atomic force microscopy (AFM)
68.35.bm Polymers, organics
61.25.hk Polymer melts and blends

Far-infrared reflectivity as a probe of point defects in Zn- and Cd-doped HgTe

J. Cebulski, E. M. Sheregii, J. Polit, A. Marcelli, M. Piccinini, A. Kisiel, I. V. Kucherenko, and R. Triboulet

Appl. Phys. Lett. 92, 121904 (2008); http://dx.doi.org/10.1063/1.2902175 (3 pages) | Cited 7 times

Online Publication Date: 24 March 2008

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We present a nondestructive method for quantitative determination of the vacancy concentration in the lattice of Hg-based semiconductor alloys with tetrahedral structure. The method is based on the identification of additional vibrational modes (AVMs) induced by lattice deformations in the far-infrared (FIR) reflectivity spectrum. Although the method is restricted by sensitivity limitations, recent FIR experimental data carried out on HgZnTe and HgCdTe samples containing Hg vacancies confirmed the presence of AVMs induced by Hg vacancies in as-grown crystals.
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61.72.jd Vacancies
61.72.uj III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Temperature dependence of Raman spectra in single-walled carbon nanotube rings

Li Song, Wenjun Ma, Yan Ren, Weiya Zhou, Sishen Xie, Pingheng Tan, and Lianfeng Sun

Appl. Phys. Lett. 92, 121905 (2008); http://dx.doi.org/10.1063/1.2891870 (3 pages) | Cited 7 times

Online Publication Date: 25 March 2008

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The temperature-dependent Raman frequency shift in single-walled carbon nanotube (SWCNT) rings in the range of 80–550 K is investigated. We observe that the frequency decreases with increasing temperature for all Raman peaks of the nanotube rings. Furthermore, compared to the nanotubes with linear structure, the temperature coefficients of the radial breathing mode and G-mode frequencies of the nanotube rings are much smaller, which means the nanotube rings have more stable thermal ability. We attribute the better thermal stability to the high bending strain energy along the nanotube rings induced by the sidewall curvature.
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61.46.Fg Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.60.Dv Thermal stability; thermal effects

Electronic and structural transition in La0.2Sr0.8MnO3

R. Bindu, Kalobaran Maiti, R. Rawat, and S. Khalid

Appl. Phys. Lett. 92, 121906 (2008); http://dx.doi.org/10.1063/1.2898885 (3 pages) | Cited 5 times

Online Publication Date: 25 March 2008

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We investigate the interplay between the electronic and structural transitions in La0.2Sr0.8MnO3. The transport and specific heat measurements exhibit unusual evolution and the signature of a first order phase transition at around 265 K. Mn K-edge extended x-ray absorption fine structure (EXAFS) results reveal distortion in the MnO6 octahedrons, even in the cubic phase, and a remarkable evolution of the distortion across the phase transition. These results manifest the importance of fluctuations in Mn 3d orbital occupancy on their electronic properties, which may help in understanding the orbital and spin ordering proposed in these systems.
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64.70.K- Solid-solid transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance
71.20.Ps Other inorganic compounds
75.47.Lx Magnetic oxides
78.70.Dm X-ray absorption spectra

Large-size ultrahigh strength Ni-based bulk metallic glassy matrix composites with enhanced ductility fabricated by spark plasma sintering

Guoqiang Xie, Dmitri V. Louzguine-Luzgin, Hisamichi Kimura, Akihisa Inoue, and Fumihiro Wakai

Appl. Phys. Lett. 92, 121907 (2008); http://dx.doi.org/10.1063/1.2902282 (3 pages) | Cited 20 times

Online Publication Date: 25 March 2008

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Ni-based bulk glassy alloy composites (GACs) simultaneously with ultrahigh strength and enhanced ductility and satisfying large-size requirements were fabricated by spark plasma sintering of gas-atomized Ni52.5Nb10Zr15Ti15Pt7.5 glassy alloy powder blend with ceramic or metal powders. No crystallization of metallic glassy matrix and good bonding state between the particles are responsible for good mechanical properties of the fabricated bulk GACs. The improvement of plastic ductility of the fabricated bulk GACs originates from the structural inhomogeneity caused by the particles inclusion. The additional particulates act as a resisting media causing deviation, branching, and multiplication of shear bands.
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61.43.Fs Glasses
62.20.fk Ductility, malleability
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
52.77.-j Plasma applications

Electroluminescence of SnO2/p-Si heterojunction

Zhizhong Yuan, Dongsheng Li, Minghua Wang, Peiliang Chen, Daoren Gong, Peihong Cheng, and Deren Yang

Appl. Phys. Lett. 92, 121908 (2008); http://dx.doi.org/10.1063/1.2902299 (3 pages) | Cited 13 times

Online Publication Date: 25 March 2008

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Polycrystalline SnO2 film of tetragonal rutile structure with an optical band gap of 3.9 eV was formed by oxidation process at 1000 °C on electron beam evaporation deposited Sn film. Room temperature electroluminescence from the SnO2/p-Si heterojunction was observed at 590 nm when the device was under sufficient forward bias with the positive voltage applied on the p-Si substrate. It is proposed that the electrons in the conduction band of SnO2 relax to defect states that resulted from the dangling bonds at the surface of the small SnO2 grains and then radiatively recombine with the holes in the valence band.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.60.Fi Electroluminescence
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.55.-i Impurity and defect levels
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Wearless scratch on NiTi shape memory alloy due to phase transformational shakedown

Xi-Qiao Feng, Linmao Qian, Wenyi Yan, and Qingping Sun

Appl. Phys. Lett. 92, 121909 (2008); http://dx.doi.org/10.1063/1.2903106 (3 pages) | Cited 2 times

Online Publication Date: 25 March 2008

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Cyclic microscratch tests were performed to examine the scratching behavior of NiTi shape memory alloy. It shows a superior wear resistance within the temperature range of 22–120 °C, but the corresponding physical mechanisms are different at low and high temperatures. We introduced the concept of phase transformational shakedown to interpret the wear-resistant behavior. At room temperature, a scratch groove may be caused by repeated scratching, but its depth stops increasing after a certain number of scratching cycles once the phase transformational shakedown state has been achieved. The groove will be self-healed upon heating as a result of the shape memory effect. At 60 and 120 °C, however, no evident scratch groove is observed under the same load due to the pseudoelastic effect and the increase in the phase transition stress with temperature.
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64.70.K- Solid-solid transitions
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Er3+ luminescence and cooperative upconversion in ErxY2−xSiO5 nanocrystal aggregates fabricated using Si nanowires

Kiseok Suh, Jung H. Shin, Seok-Jun Seo, and Byeong-Soo Bae

Appl. Phys. Lett. 92, 121910 (2008); http://dx.doi.org/10.1063/1.2890414 (3 pages) | Cited 14 times

Online Publication Date: 26 March 2008

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Er3+ luminescence and cooperative upconversion in ErxY2−xSiO5 nanocrystal aggregates fabricated using Si nanowires is investigated. X-ray diffraction and photoluminescence spectroscopy indicate that the composition of the final nanocrystals can be varied continuously from pure Y2SiO5 to pure Er2SiO5 while keeping the crystal structure the same. Analysis of concentration and pump-power dependence of the Er3+ photoluminescence intensity and decay time shows that while cooperative upconversion occurs at high Er concentrations, the cooperative upconversion coefficient is only (2.2±1.1)×10−18 cm3/s at a Er concentration of 1.2×1021 cm−3. This is nearly ten times lower at more than ten times higher Er concentration than that reported from Er-doped silica and demonstrates the viability of using such silicates for compact, high-gain Si-based optical material for Si photonics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing
78.55.Hx Other solid inorganic materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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