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16 Feb 2004

Volume 84, Issue 7, pp. 1031-1224

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1111 (2004); http://dx.doi.org/10.1063/1.1647691 (3 pages)

Y. Kawano and T. Okamoto
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Transverse modes of photonic crystal vertical-cavity lasers

Aaron J. Danner, James J. Raftery, Noriyuki Yokouchi, and Kent D. Choquette

Appl. Phys. Lett. 84, 1031 (2004); http://dx.doi.org/10.1063/1.1646729 (3 pages) | Cited 28 times

Online Publication Date: 10 February 2004

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The control of lateral mode operation using a photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) is analyzed and confirmed experimentally. By controlling design parameters of the photonic crystal pattern, we have produced photonic crystal VCSELs that operate in higher order defect modes in addition to the fundamental defect mode. The transverse modal behavior is consistent with the predictions of a theoretical model in which the etching depth dependence of the air holes of the photonic crystals is considered. We also have determined the lower limit of optical confinement required from the photonic crystal pattern to influence the output beam of the laser. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
81.65.Cf Surface cleaning, etching, patterning
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Measurement of the photorefractive space-charge field in a ferroelectric mesogen

M. Talarico, R. Termine, G. Barberio, D. Pucci, M. Ghedini, and A. Golemme

Appl. Phys. Lett. 84, 1034 (2004); http://dx.doi.org/10.1063/1.1646762 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2004

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We report on the measurement of the photorefractive space-charge field in a chiral smectic C mesophase. The liquid crystal is intrinsically photoconducting and undoped. The space-charge field amplitude, obtained from a model connecting the induced refractive index modulation with the electric fields within the medium, is only 1% of the applied field. Nonetheless, high refractive index modulations Δn ∼ 10−3 can be obtained because of the high spontaneous birefringence of the mesophase. The use of the standard models for inorganic crystalline photorefractive materials would have given a space-charge field amplitude two orders of magnitude higher. © 2004 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
77.22.Jp Dielectric breakdown and space-charge effects
72.40.+w Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence

Ultralow-threshold erbium-implanted toroidal microlaser on silicon

A. Polman, B. Min, J. Kalkman, T. J. Kippenberg, and K. J. Vahala

Appl. Phys. Lett. 84, 1037 (2004); http://dx.doi.org/10.1063/1.1646748 (3 pages) | Cited 29 times

Online Publication Date: 10 February 2004

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We present an erbium-doped microlaser on silicon operating at a wavelength of 1.5 μm that operates at a launched pump threshold as low as 4.5 μW. The 40 μm diameter toroidal microresonator is made using a combination of erbium ion implantation, photolithography, wet and dry etching, and laser annealing, using a thermally grown SiO2 film on a Si substrate as a starting material. The microlaser, doped with an average Er concentration of 2×1019 cm−3, is pumped at 1480 nm using an evanescently coupled tapered optical fiber. Cavity quality factors as high as 3.9×107 are achieved, corresponding to a modal loss of 0.007 dB/cm, and single-mode lasing is observed. © 2004 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
78.55.Hx Other solid inorganic materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
42.55.Rz Doped-insulator lasers and other solid state lasers

Thermal effects in quasi-continuous-wave Nd3+:Y3Al5O12 nanocrystalline-powder random laser

Yan Feng, Jean-Francois Bisson, Jianren Lu, Shenghong Huang, Kazunori Takaichi, Akira Shirakawa, Mitsuru Musha, and Ken-ichi Ueda

Appl. Phys. Lett. 84, 1040 (2004); http://dx.doi.org/10.1063/1.1647285 (3 pages) | Cited 13 times

Online Publication Date: 10 February 2004

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We report an experimental investigation on the thermal effects in a Nd3+:Y3Al5O12 nanocrystalline-powder random laser with a one-mirror structure by quasi-continuous-wave laser diode pumping. Extremely low thermal conductivity in powder and significant temperature dependence of the narrow emission spectrum of Nd3+:Y3Al5O12 leads to a laser line redshift and gain reduction with a higher heat deposit. Mode drifting induced by the temperature dependence of the refractive index is also discussed. © 2004 American Institute of Physics.
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42.55.Xi Diode-pumped lasers
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Picosecond dynamics of spin-related optical nonlinearities in InxGa1−xAs multiple quantum wells at 1064 nm

K. Jarasiunas, V. Gudelis, R. Aleksiejunas, M. Sudzius, S. Iwamoto, M. Nishioka, T. Shimura, K. Kuroda, and Y. Arakawa

Appl. Phys. Lett. 84, 1043 (2004); http://dx.doi.org/10.1063/1.1647276 (3 pages) | Cited 5 times

Online Publication Date: 10 February 2004

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Light-induced absorption and diffraction measurements of resonantly excited 10-nm-width InGaAs multiple quantum wells have been carried out, using circularly polarized beams at 1064 nm. Spin relaxation time τs ≃ 280±15 ps has been determined by monitoring dynamics of light absorption bleaching at 0.04 mJ/cm2, while a nonlinearly compressed spin component in diffraction varied from 220±20 ps to 115±15 ps with excitation. The kinetics of carrier grating with randomized spins allowed the determination of the bipolar diffusion coefficient D = 11.5 cm2/s, hole mobility of 230 cm2/V s, and carrier lifetime τR = 0.73–1 ns. © 2004 American Institute of Physics.
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78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Hs Quantum wells
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
72.20.Fr Low-field transport and mobility; piezoresistance

High-power 280 nm AlGaN light-emitting diodes based on an asymmetric single-quantum well

K. Mayes, A. Yasan, R. McClintock, D. Shiell, S. R. Darvish, P. Kung, and M. Razeghi

Appl. Phys. Lett. 84, 1046 (2004); http://dx.doi.org/10.1063/1.1647273 (3 pages) | Cited 51 times

Online Publication Date: 10 February 2004

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We demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric single-quantum-well active layer configuration on top of a high-quality AlGaN/AlN template layer. An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 μm×300 μm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Polysulfone as an electro-optic polymer host material

Sean M. Garner, Jeffrey S. Cites, Mingqian He, and Jianguo Wang

Appl. Phys. Lett. 84, 1049 (2004); http://dx.doi.org/10.1063/1.1646754 (3 pages) | Cited 10 times

Online Publication Date: 10 February 2004

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The practicality of using polysulfone as a host material for electro-optic polymer devices is demonstrated. For loadings of 15–25 weight %, r33 values of 53–55 pm/V were obtained at λ = 1.06 μm. This corresponds to chromophore alignment efficiencies of up to 27%. Also, Mach–Zehnder devices demonstrated the implementation of a polysulfone host with a Vπ of 6.9 v, optical loss of 1.8 dB/cm, and thermal stability >100 °C. © 2004 American Institute of Physics.
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42.70.Jk Polymers and organics
73.61.Ph Polymers; organic compounds

Highly efficient organic electrophosphorescent light-emitting diodes with a reduced quantum efficiency roll off at large current densities

M. Cocchi, V. Fattori, D. Virgili, C. Sabatini, P. Di Marco, M. Maestri, and J. Kalinowski

Appl. Phys. Lett. 84, 1052 (2004); http://dx.doi.org/10.1063/1.1646214 (3 pages) | Cited 38 times

Online Publication Date: 10 February 2004

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High efficiency electrophosphorescence (EPH) in organic light-emitting devices was achieved employing a cyclometallated platinum [Pt(II)]-complexes-doped blend of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′ diamine and bisphenol-A-polycarbonate as the emitting layer. Using bis-[2-(5-trimethylsilanyl-thiophen-2-yl)-pyridine] Pt(II) [Pt(thpy-SiMe3)] as a phosphorescent dopant, a maximum EPH external quantum efficiency of 11.5±0.5% photons/carrier was achieved with a three-fold lower roll-off factor at increasing current density, compared with commonly used Pt-based dye 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum (II) (PtOEP). The emission spectrum of the device peaking at ≅590 nm shifts the chromaticity coordinates toward the orange relative to the PtOEP-based devices. © 2004 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
61.41.+e Polymers, elastomers, and plastics
85.60.Jb Light-emitting devices

Optical pulse compression using cascaded quadratic nonlinearities in periodically poled lithium niobate

Satoshi Ashihara, Tsutomu Shimura, Kazuo Kuroda, Nan Ei Yu, Sunao Kurimura, Kenji Kitamura, Myoungsik Cha, and Takunori Taira

Appl. Phys. Lett. 84, 1055 (2004); http://dx.doi.org/10.1063/1.1647279 (3 pages) | Cited 16 times

Online Publication Date: 10 February 2004

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Efficient pulse compression was achieved by the use of cascaded quadratic nonlinearities in 10-mm-long periodically poled MgO-doped lithium niobate. An off-diagonal component of the nonlinear coefficient was utilized for group-velocity matched cascaded interactions at the fundamental wavelength of 1560 nm. Simultaneously compressed fundamental and second-harmonic pulses of ∼35 fs duration were obtained from the 110-fs-pump pulses. © 2004 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Comparison of the carrier induced refractive index, gain, and linewidth enhancement factor in quantum dot and quantum well lasers

A. A. Ukhanov, A. Stintz, P. G. Eliseev, and K. J. Malloy

Appl. Phys. Lett. 84, 1058 (2004); http://dx.doi.org/10.1063/1.1647688 (3 pages) | Cited 44 times

Online Publication Date: 10 February 2004

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The spectral dependence of the modal gain and linewidth enhancement factor is measured in an InAs/GaInAs/AlGaAs/GaAs quantum dot (QD) laser and a GaInAs/AlGaAs/GaAs quantum well laser of the same design lacking only the quantum dots. The material differential gain and material differential carrier induced refractive index are found to be about three times smaller in the quantum dot laser than in the quantum well laser. The linewidth enhancement factor is smaller in the QD laser and exhibits considerably less dispersion. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.60.By Design of specific laser systems

Electroluminescent properties of erbium-doped III–N light-emitting diodes

J. M. Zavada, S. X. Jin, N. Nepal, J. Y. Lin, H. X. Jiang, P. Chow, and B. Hertog

Appl. Phys. Lett. 84, 1061 (2004); http://dx.doi.org/10.1063/1.1647271 (3 pages) | Cited 27 times

Online Publication Date: 10 February 2004

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We report on the synthesis of Er-doped III–N double heterostructure light-emitting diodes (LEDs) and their electroluminescence (EL) properties. The device structures were grown through a combination of metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE) on c-plane sapphire substrates. The AlGaN layers, with an Al concentration of ∼12%, were prepared by MOCVD and doped with Si or Mg to achieve n- and p-type conductivity, respectively. The Er+O-doped GaN active region was grown by MBE and had a thickness of 50 nm. The Er concentration was estimated to be ∼ 1018 cm−3. The multilayer n-AlGaN/GaN:Er/p-AlGaN structures were processed into LEDs using standard etching and contacting methods. Several different LEDs were produced and EL spectra were recorded with both forward and reverse bias conditions. Typically, the EL under reverse bias was five to ten times more intense than that under forward bias. The LEDs displayed a number of narrow emission lines representative of the GaN:Er system (green: 539 nm, 559 nm; infrared: 1000 nm, 1530 nm). While some current crowding was observed, green emission was visible under ambient room conditions at 300 K. At cryogenic temperatures, the emission lines increased in intensity and had a narrower linewidth. EL spectra were recorded down to 10 K and the L-I characteristics were systematically measured. The power output of the brightest LEDs was approximately 2.5 W/m2 at 300 K. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.80.Ey III-V and II-VI semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors

Active organic–inorganic sol gel with high thermal stability for nonlinear optical applications

Hongxi Zhang, Dong Lu, and Mahmoud Fallahi

Appl. Phys. Lett. 84, 1064 (2004); http://dx.doi.org/10.1063/1.1647283 (3 pages) | Cited 14 times

Online Publication Date: 10 February 2004

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Second-harmonic generation and thermal stability of hybrid photosensitive sol-gel films doped with a side-chain electro-optic chromophore have been studied. Nonlinear optic coefficient d33 has been derived for the cross-linked and noncross-linked sol-gel films. The d33 of the cross-linked hybrid sol-gel film shows high stability at elevated temperature. No evident degradation in d33 was observed at 110 °C and only 20% of d33 decayed in 15 min at 180 °C. The results indicate that the film can meet the long-term stability requirement for optical components. © 2004 American Institute of Physics.
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81.07.Pr Organic-inorganic hybrid nanostructures
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Large spontaneous emission factor (>0.1) in the photonic crystal monopole-mode laser

H. Y. Ryu, M. Notomi, E. Kuramoti, and T. Segawa

Appl. Phys. Lett. 84, 1067 (2004); http://dx.doi.org/10.1063/1.1647274 (3 pages) | Cited 30 times

Online Publication Date: 10 February 2004

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1.55-μm-InGaAsP photonic crystal lasers operating in the monopole mode of a triangular lattice defect cavity are realized by room-temperature optical pumping with a low threshold of <0.5 mW. By analyzing rate equations and the light–light characteristic curve, we evaluate the spontaneous emission factor (β) of this laser to be larger than 0.1, an extremely high value for photonic crystal lasers. The achievement of this large β is attributed to the facts that the investigated monopole-mode laser operates at the peak of the spontaneous emission spectrum and it shows a single-mode operation in a wide spectral range. In addition, nonclamping of carrier density near threshold and the β>0.1 are confirmed by the investigation of carrier-density dependent wavelength blueshift of the lasing mode. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.55.Sa Microcavity and microdisk lasers
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Effect of anode dielectric coating on Hall thruster operation

L. Dorf, Y. Raitses, N. J. Fisch, and V. Semenov

Appl. Phys. Lett. 84, 1070 (2004); http://dx.doi.org/10.1063/1.1646727 (3 pages) | Cited 16 times

Online Publication Date: 10 February 2004

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An interesting phenomenon observed in the near-anode region of a Hall thruster is that the anode fall changes from positive to negative upon removal of the dielectric coating, which is produced on the anode surface during the normal course of Hall thruster operation. The effect of the anode coating on the anode fall is studied experimentally using both biased and emissive probes. Measurements of discharge current oscillations indicate that thruster operation is more stable with the coated anode. The physical mechanism of this phenomenon is not yet understood. © 2004 American Institute of Physics.
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52.80.Tn Other gas discharges

Molecular dynamics simulations of Ar+-induced transport of fluorine through fluorocarbon films

David Humbird, David B. Graves, Xuefeng Hua, and Gottlieb S. Oehrlein

Appl. Phys. Lett. 84, 1073 (2004); http://dx.doi.org/10.1063/1.1644338 (3 pages) | Cited 13 times

Online Publication Date: 10 February 2004

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Recent experimental studies of fluorocarbon (FC) plasmas etching various substrates suggest that ions will transport initially bound fluorine (F) through overlying FC films, thereby defluorinating these films and inducing fluorination reaction with the underlying substrate material. Simulations of thermal CF2 on Si with simultaneous bombardment by energetic Ar+ demonstrate this defluorination phenomenon, showing that F is separated from adsorbed CF2 and mixed into the underlying Si, initiating etching. Additionally, this creates dangling bonds on the surface where CF2 may adsorb. Thus, our simulations show that F and C uptake is enhanced by energetic rare gas ion impact, the number of Si–F bonds is greatly increased, and the resultant Si etch rate is higher than expected from physical sputtering alone. The results are compared to experimental measurements made under similar conditions, and the mechanisms of ion-induced F transport are identified. © 2004 American Institute of Physics.
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52.65.Yy Molecular dynamics methods
52.77.Bn Etching and cleaning
52.25.Fi Transport properties
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.20.Wt Computational modeling; simulation
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Anomalous relationship between hardness and wear properties of a superelastic nickel–titanium alloy

Linmao Qian, Xudong Xiao, Qingping Sun, and Tongxi Yu

Appl. Phys. Lett. 84, 1076 (2004); http://dx.doi.org/10.1063/1.1646218 (3 pages) | Cited 30 times

Online Publication Date: 10 February 2004

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We have studied the behavior of microwear and hardness of a superelastic nickel–titanium alloy using a triboindenter at various temperatures. Wear resistance was found to anomalously decrease with an increase in hardness. The observations are analyzed based on simple contact theory which suggests that the increase of hardness with the temperature is mainly due to an increase in phase transition stress, while the decrease of wear resistance with the temperature is due to an increase of the austenite elastic modulus and a decrease of the amount of phase transition that can be recovered. © 2004 American Institute of Physics.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.20.M- Structural failure of materials

Radiative and nonradiative excitonic transitions in nonpolar (11math0) and polar (000math) and (0001) ZnO epilayers

T. Koida, S. F. Chichibu, A. Uedono, T. Sota, A. Tsukazaki, and M. Kawasaki

Appl. Phys. Lett. 84, 1079 (2004); http://dx.doi.org/10.1063/1.1646749 (3 pages) | Cited 18 times

Online Publication Date: 10 February 2004

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Polarized optical reflectance and photoreflectance spectra of an out-plane nonpolar (11math0) ZnO epilayer grown by laser molecular-beam epitaxy exhibited anisotropic exciton resonance structures according to the polarization selection rules for anisotropically strained hexagonal material. Consistently, the electric field component of its excitonic photoluminescence (PL) peak was polarized perpendicular to the [0001] axis. Different from the case for GaN, nonradiative PL lifetime at 293 K and the S parameter, which is a measure of Zn vacancy-related defect density obtained by positron annihilation spectroscopy, of the (11math0) ZnO were comparable to those of state-of-the-art polar (000math) and (0001) epilayers. Since the polar epilayers exhibited pronounced exciton–polariton emissions, the negligible impact of growth direction on the defect incorporation suggests a potential use of epitaxial (11math0) ZnO as polarization-sensitive optoelectronic devices operating in ultraviolet spectral regions. © 2004 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.J- Point defects and defect clusters

Predicting pseudomorphic phases in multilayers: Hexagonal-closed-packed Nb in Nb/Zr

G. B. Thompson, R. Banerjee, and H. L. Fraser

Appl. Phys. Lett. 84, 1082 (2004); http://dx.doi.org/10.1063/1.1647687 (3 pages) | Cited 6 times

Online Publication Date: 10 February 2004

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As the dimensions of materials are reduced to the nanometer scale, changes in phase stability, referred to as pseudomorphism, are being reported. Such changes in phase stability are often serendipitously discovered in multilayered thin films. In this letter, we use a classical thermodynamic treatment to model and predict phase stability in Nb/Zr multilayers. An outcome of this letter is the development of a biphase stability diagram that represents the interrelationship of phase stability to volume fraction and length scale. Using this methodology, an hcp Nb phase stability field was empirically postulated and subsequently confirmed by x-ray and electron diffraction. The successful prediction of this phase, based upon classical thermodynamics quantities, suggests that other types of phase stabilities in other multilayers could be proposed using the biphase diagram. © 2004 American Institute of Physics.
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68.65.Ac Multilayers
65.40.G- Other thermodynamical quantities
61.46.-w Structure of nanoscale materials
81.30.Bx Phase diagrams of metals, alloys, and oxides
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
68.49.Uv X-ray standing waves
64.70.K- Solid-solid transitions

Influence of growth flux and surface supersaturation on InGaAs/GaAs strain relaxation

C. Lynch, E. Chason, R. Beresford, and S. K. Hong

Appl. Phys. Lett. 84, 1085 (2004); http://dx.doi.org/10.1063/1.1646764 (3 pages) | Cited 4 times

Online Publication Date: 10 February 2004

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We present results showing that the strain relaxation rate in heteroepitaxial layers depends strongly on the presence of the growth flux. These results are based on real-time stress measurements made during molecular beam epitaxy of InxGa1−xAs/GaAs (x = 0.16±0.01) films grown at 452, 477, and 502 °C. Our measurements indicate that the increased relaxation rate during growth is due to an enhancement in the dislocation glide velocity. We propose a model for the dislocation velocity increase in which the growth-induced supersaturation of adatoms lowers the barrier to single kink nucleation. © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.F- Deformation and plasticity
82.60.Nh Thermodynamics of nucleation

High-strength Cu-based crystal-glassy composite with enhanced ductility

Dmitri V. Louzguine, Hidemi Kato, and Akihisa Inoue

Appl. Phys. Lett. 84, 1088 (2004); http://dx.doi.org/10.1063/1.1647278 (2 pages) | Cited 29 times

Online Publication Date: 10 February 2004

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Low ductility of glassy alloys prevents their technical application as structural materials. In this work, we study the Cu-based crystal-glassy composite material with good mechanical properties. Formation of the Cu10Zr7 phase in the glassy matrix of a high-strength Cu50Zr30Ti10Nb10 bulk alloy upon solidification led to higher Young’s modulus and enhanced ductility of such a composite compared to Cu-based glassy alloys. The as-cast structure was studied by x-ray diffraction and scanning electron microscopy. © 2004 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.D- Elasticity
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.30.Fb Solidification
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.43.Fs Glasses
81.05.Pj Glass-based composites, vitroceramics

Optical properties of the nitrogen vacancy in AlN epilayers

N. Nepal, K. B. Nam, M. L. Nakarmi, J. Y. Lin, H. X. Jiang, J. M. Zavada, and R. G. Wilson

Appl. Phys. Lett. 84, 1090 (2004); http://dx.doi.org/10.1063/1.1648137 (3 pages) | Cited 8 times

Online Publication Date: 10 February 2004

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AlN epilayers grown by metalorganic chemical vapor deposition were implanted with cobalt ions and studied by deep UV photoluminescence (PL). A PL emission peak at 5.87 eV (at 10 K) was observed for the Co-implanted AlN epilayers, which was absent in as-grown AlN epilayers. Temperature dependence of the PL intensity of the 5.87 eV emission line revealed an ion-implantation induced defect with energy level of about 260 meV below the conduction band. The 5.87 eV emission line is believed due to a band-to-impurity transition involving the nitrogen vacancy (VN) in ion-implanted AlN. The experimentally determined energy level of the nitrogen vacancy is in reasonable agreement with the calculated value of 300 meV. From the band-to-impurity transition involving VN, we have deduced the energy band gap of AlN to be 6.13 eV, which is consistent with our previous result. Our results suggest that nitrogen vacancies in AlN cannot make any significant contribution to the n-type conductivity due to the large binding energy as well as the large formation energy. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
71.55.Eq III-V semiconductors
61.72.uf Ge and Si
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Elastic strain relaxation in free-standing SiGe/Si structures

P. M. Mooney, G. M. Cohen, J. O. Chu, and C. E. Murray

Appl. Phys. Lett. 84, 1093 (2004); http://dx.doi.org/10.1063/1.1646464 (3 pages) | Cited 21 times

Online Publication Date: 10 February 2004

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We have investigated elastic strain relaxation, i.e., strain relaxation without the introduction of dislocations or other defects, in free-standing SiGe/Si structures. We fabricated free-standing Si layers supported at a single point by an SiO2 pedestal and subsequently grew an epitaxial SiGe layer. The measured strain relaxation of the SiGe layer agrees well with that calculated using a force-balance model for strain sharing between the SiGe and strained Si layers. We report strained Si layers with biaxial tensile strain equal to 0.007 and 0.012. © 2004 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Gy Mechanical properties; surface strains
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Nanoscale-twinning-induced strengthening in austenitic stainless steel thin films

X. Zhang, A. Misra, H. Wang, M. Nastasi, J. D. Embury, T. E. Mitchell, R. G. Hoagland, and J. P. Hirth

Appl. Phys. Lett. 84, 1096 (2004); http://dx.doi.org/10.1063/1.1647690 (3 pages) | Cited 68 times

Online Publication Date: 10 February 2004

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Magnetron-sputter-deposited austenitic 330 stainless steel (330 SS) films, several microns thick, were found to have a hardness ∼6.5 GPa, about an order of magnitude higher than bulk 330 SS. High-resolution transmission electron microscopy revealed that sputtered 330 SS coatings are heavily twinned on {111} with nanometer scale twin spacing. Molecular dynamics simulations show that, in the nanometer regime where plasticity is controlled by the motion of single rather than pile-ups of dislocations, twin boundaries are very strong obstacles to slip. These observations provide a new perspective to producing ultrahigh strength monolithic metals by utilizing growth twins with nanometer-scale spacing. © 2004 American Institute of Physics.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.46.-w Structure of nanoscale materials

La0.95Sr0.05CoO3: An efficient room-temperature thermoelectric oxide

J. Androulakis, Pantelis Migiakis, and J. Giapintzakis

Appl. Phys. Lett. 84, 1099 (2004); http://dx.doi.org/10.1063/1.1647686 (3 pages) | Cited 51 times

Online Publication Date: 10 February 2004

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We present measurements of electrical resistivity, thermal conductivity, and thermopower of polycrystalline Sr-doped LaCoO3 with composition La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very respectable room-temperature thermoelectric figure of merit value of 0.18. Our results not only show that oxides are promising candidates for thermoelectric cooling applications, but also point toward the need for careful theoretical calculations that will serve as a guide in producing the next generation of thermoelectric materials. © 2004 American Institute of Physics.
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72.80.Jc Other crystalline inorganic semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Ultrafast intersubband relaxation and nonlinear susceptibility at 1.55 μm in GaN/AlN multiple-quantum wells

J. Hamazaki, S. Matsui, H. Kunugita, K. Ema, H. Kanazawa, T. Tachibana, A. Kikuchi, and K. Kishino

Appl. Phys. Lett. 84, 1102 (2004); http://dx.doi.org/10.1063/1.1647275 (3 pages) | Cited 39 times

Online Publication Date: 10 February 2004

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Using a degenerate pump–probe technique on the Brewster configuration at room temperature, we investigate the dynamics of the intersubband transition in GaN/AlN multiple-quantum wells. The relaxation dynamics is found to consist of ultrafast (∼140 fs) and slower (∼1.3 ps) components. We estimate the third-order susceptibility for the Brewster configuration to be ∼ 5.5×10−18 m2/V2, which indicates that its value becomes ∼ 2.2×10−16 m2/V2 when a light beam is parallel to the well. © 2004 American Institute of Physics.
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78.67.De Quantum wells
78.66.Fd III-V semiconductors
42.65.An Optical susceptibility, hyperpolarizability
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