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5 Jun 2000

Volume 76, Issue 23, pp. 3337-3483

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Three-dimensional photonic band gap structure of a polymer-metal composite

Ji Zhou, Y. Zhou, S. L. Ng, H. X. Zhang, W. X. Que, Y. L. Lam, Y. C. Chan, and C. H. Kam

Appl. Phys. Lett. 76, 3337 (2000); http://dx.doi.org/10.1063/1.126641 (3 pages) | Cited 16 times

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A three-dimensional photonic band gap structure based on self-assembled crystals of polystyrene microspheres was fabricated by filling the pores with metallic silver. An almost complete stop band at 580–600 nm is observed in the optical transmission spectra. In comparison with pure polystyrene colloid crystals, the absorption band of Bragg diffraction in the composite was much more intense and broader, due to an enlargement of the contrast between the spheres and the background. A shift to shorter wavelengths in the band occurred because of a decrease in the average refractive index. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.66.Sq Composite materials
42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Improved temperature performance of Al0.33Ga0.67As/GaAs quantum-cascade lasers with emission wavelength at λ ≈ 11 μm

P. Kruck, H. Page, C. Sirtori, S. Barbieri, M. Stellmacher, and J. Nagle

Appl. Phys. Lett. 76, 3340 (2000); http://dx.doi.org/10.1063/1.126686 (3 pages) | Cited 33 times

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The pulsed operation of a GaAs/AlGaAs quantum-cascade laser is reported up to 258 K. These devices emit at 11.3 μm and are based on a plasmon-confinement waveguide. To optimize the material gain, the active region is designed to diminish electron escape to continuum states. Gain and threshold measurement show evidence of better carrier confinement and improved thermal behavior compared to λ ≈ 9 μm GaAs quantum-cascade lasers. The maximum peak-collected power at 77 K is 520 mW per facet and still 27 mW at 258 K. The temperature dependence of the threshold current density is characterized by a T0 = 128 K. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors

Room-temperature lasing via ground state of current-injected vertically aligned InP/GaInP quantum dots

Y. M. Manz, O. G. Schmidt, and K. Eberl

Appl. Phys. Lett. 76, 3343 (2000); http://dx.doi.org/10.1063/1.126642 (3 pages) | Cited 14 times

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We report room-temperature injection lasing of self-assembled InP/GaInP quantum dots. Stimulated emission occurs via the ground state at λ = 728 nm for cavities as short as 0.5 mm. Threshold current densities of 2.3 kA/cm2 and external differential quantum efficiencies of 8.5% have been measured for 2 mm long devices. Light output power as high as 250 mW without saturation effects can be reached in pulsed excitation. Analysis of temperature-dependent laser emission indicates the thermal coupling of charge carriers in different quantum dots at higher temperatures. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Double fitting of Maker fringes to characterize near-surface and bulk second-order nonlinearities in poled silica

Mingxin Qiu, Ramon Vilaseca, Muriel Botey, Jordi Sellarès, Francesc Pi, and Gaspar Orriols

Appl. Phys. Lett. 76, 3346 (2000); http://dx.doi.org/10.1063/1.126643 (3 pages) | Cited 6 times

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An experimental analysis of the distribution and thickness of the bulk nonlinearity induced in poled silica is reported. The second-order susceptibility decreases exponentially from the anodic interface. Maker fringe patterns showing a double structure are interpreted in relation to the presence of two nonlinear profiles, one concentrated near the anodic surface and another extending into the bulk of the sample. The Maker fringe theory is properly generalized and a double fitting technique reproducing well the experimental results is used to characterize the induced nonlinearities. The dependence of the second-harmonic signal on the poling temperature is given, which is different from that of sol-gel silica. © 2000 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz

High characteristic temperature of near-1.3-μm InGaAs/GaAs quantum-dot lasers at room temperature

Kohki Mukai, Yoshiaki Nakata, Koji Otsubo, Mitsuru Sugawara, Naoki Yokoyama, and Hiroshi Ishikawa

Appl. Phys. Lett. 76, 3349 (2000); http://dx.doi.org/10.1063/1.126644 (3 pages) | Cited 34 times

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This letter reports on the high characteristic temperature of InGaAs/GaAs quantum-dot lasers at room temperature. Self-assembled quantum dots were grown using low-growth-rate molecularbeam epitaxy, and continuous-wave lasing occurred at the dot ground level of 1.26 μm at 25 °C. The characteristic temperature of the threshold currents was 120 K, and ground-level lasing was observed up to 100 °C. Comparing the lasing performances and the spontaneous emission spectra with those of 1.3 μm emission dots, we found that the large volume density, deep potential, and high quantum efficiency were key points for improving the temperature characteristics. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Thermally induced local gain suppression in vertical-cavity surface-emitting lasers

C. Degen, I. Fischer, and W. Elsäßer

Appl. Phys. Lett. 76, 3352 (2000); http://dx.doi.org/10.1063/1.126645 (3 pages) | Cited 14 times

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Joule heating is one of the dominant mechanisms determining the transverse mode formation in vertical-cavity surface-emitting lasers at high injection currents. We give experimental evidence that in this operation regime, strong heating results in local gain suppression in the center of the laser, which overbalances the confining effect of thermal lensing, and thus favors the formation of high order modes. From our investigations of small aperture devices, we conclude that efficient heat removal is crucial for achieving single mode emission at high injection currents. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Room-temperature far-infrared emission from a self-organized InGaAs/GaAs quantum-dot laser

Sanjay Krishna, Omar Qasaimeh, Pallab Bhattacharya, Patrick J. McCann, and Khosrow Namjou

Appl. Phys. Lett. 76, 3355 (2000); http://dx.doi.org/10.1063/1.126646 (3 pages) | Cited 19 times

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Far-infrared spontaneous emission at 300 K and lower temperatures, due to intersubband transitions in self-organized In0.4Ga0.6As/GaAs quantum dots, has been characterized. Measurements were made with a multidot layer near-infrared (∼1 μm) interband laser. The far-infrared signal, centered at 12 μm, was enhanced after the interband transition reached threshold at 300 K. The results are explained in terms of the carrier dynamics in the dots. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
42.72.Ai Infrared sources

Image amplification and novelty filtering with a photorefractive polymer

Arosha Goonesekera, Daniel Wright, and W. E. Moerner

Appl. Phys. Lett. 76, 3358 (2000); http://dx.doi.org/10.1063/1.126647 (3 pages) | Cited 26 times

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Energy transfer between two laser beams writing a volume hologram in a photorefractive polymer composite is applied to video-rate optical processing applications. A net increase in image intensity as high as a factor of 37 can be observed within one video frame time (33 ms) using a total beam intensity of 1 W cm−2 and 77 V μm−1 applied electric field. Moving object detection (novelty filtering) is also demonstrated. © 2000 American Institute of Physics.
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42.40.My Applications
42.70.Jk Polymers and organics
42.30.Sy Pattern recognition
42.70.Ln Holographic recording materials; optical storage media
42.40.Pa Volume holograms

Strained InGaAs/AlGaAs/GaAs-quantum cascade lasers

S. Gianordoli, W. Schrenk, L. Hvozdara, N. Finger, G. Strasser, and E. Gornik

Appl. Phys. Lett. 76, 3361 (2000); http://dx.doi.org/10.1063/1.126648 (3 pages) | Cited 16 times

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We report on the realization of a quantum cascade laser based on strained In0.04Ga0.96As/Al0.33Ga0.67As/GaAs grown on GaAs substrate using molecular beam epitaxy. Lasing at 10.40 μm and at 9.45 μm was achieved with a good temperature performance showing a T0,2 = 112 K between 125 and 200 K and a maximum working temperature exceeding T = 200 K. Between 78 and 130 K a considerably higher T0,1 of 291 K is found. The decreasing T0 with higher temperatures is due to misalignment of the injector with the upper laser level at elevated temperatures, thermal activation of tunneling of carriers above 130 K, and increasing carrier leakage from the injector into the continuum. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Power dependence of the injection lock band of angled-grating distributed feedback lasers

D. J. Gallant

Appl. Phys. Lett. 76, 3364 (2000); http://dx.doi.org/10.1063/1.126649 (3 pages) | Cited 2 times

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Experimental measurements of the injection lock band of an angled-grating distributed feedback laser have been performed systematically as a function of the unlocked slave laser power. Fringe visibility measurements were used to ascertain the quality of the lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental data show increasing spectral instabilities under optical injection as the slave laser power is increased, resulting in the stable portion of the lock band decreasing in width. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Propagation of femtosecond optical pulses through uncoated and metal-coated near-field fiber probes

Roland Müller and Christoph Lienau

Appl. Phys. Lett. 76, 3367 (2000); http://dx.doi.org/10.1063/1.126650 (3 pages) | Cited 15 times

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The spatiotemporal evolution of a 10-femtosecond light pulse (λ=805 nm) propagating through uncoated and metal-coated near-field fiber probes is analyzed theoretically within a two-dimensional model for s and p polarization of the incident field. Internal reflection inside uncoated fiber probes (cone angle of 28°) results in an efficient guiding towards the fiber tip and a diffraction-limited spatial resolution of about 260 nm≈λ/3 in case of s polarization. While the transmission through uncoated fiber probes has negligible effects on the temporal and spectral pulse profile, strong modifications are observed for metal-coated aperture probes. The wavelength-dependent aperture transmission gives rise to a pronounced blueshift and spectral narrowing of the transmitted pulses. © 2000 American Institute of Physics.
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42.81.Pa Sensors, gyros
42.81.Dp Propagation, scattering, and losses; solitons
07.60.Vg Fiber-optic instruments
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Gs Birefringence, polarization
07.79.Fc Near-field scanning optical microscopes
02.70.Bf Finite-difference methods
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Simulation of a picosecond laser ablation plasma

Samuel S. Mao, Xianglei Mao, Ralph Greif, and Richard E. Russo

Appl. Phys. Lett. 76, 3370 (2000); http://dx.doi.org/10.1063/1.126651 (3 pages) | Cited 16 times

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A theoretical model has been developed to simulate plasma formation and evolution during the early stage of picosecond laser ablation of solids. Surface electron emission was implemented as one boundary condition for plasma development above the target. The simulation results indicate that a plasma forms, with electron density on the order of 1020 cm−3, during the picosecond laser pulse. Laser induced gas breakdown assisted by electron emission from the target was found to be the origin of the plasma. In agreement with experimental measurements, longitudinal movement of the electrons inside the plasma was suppressed after the laser pulse. The suppression of the plasma can be attributed to the development of a strong electric field above the target. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.-y Plasma simulation
79.20.Ds Laser-beam impact phenomena
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
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High-temperature photoluminescence in sol-gel silica containing SiC/C nanostructures

Guangming Li, Larry W. Burggraf, James R. Shoemaker, DeLyle Eastwood, and Albert E. Stiegman

Appl. Phys. Lett. 76, 3373 (2000); http://dx.doi.org/10.1063/1.126685 (3 pages) | Cited 13 times

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Silicon carbide and carbon nanostructures were produced by pyrolysis of organosilane or aromatic compounds in nanoporous sol-gel silica glasses. Intense photoluminescence was observed in the visible and the near infrared regions, depending on material processing. Emission bands at 2.97, 2.67, 2.53, 2.41, 2.24, 2.09, 1.93, 1.13, 1.00, and 0.85 eV were observed in samples prepared at temperatures between 870 and 1220 K. Phosphorescence emission showed two lifetime components at 300 K: a 0.03 s component and a very long component of 0.5–4 s that depends on the precursors and sample processing. These lifetimes approximately doubled at 77 K. The visible emission increased significantly as the temperature was elevated from 77 to 950 K, suggesting thermally assisted light emission from sites in the silica glasses containing SiC/C nanostructures. Surface SiC vacancy defects modeled using integrated ab initio quantum mechanics/molecular mechanics calculations suggest phosphorescence may originate from C vacancy (Si–Si dimers) in the visible and Si vacancy in the near infrared. © 2000 American Institute of Physics.
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78.55.Mb Porous materials
81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
61.43.Gt Powders, porous materials
78.60.-b Other luminescence and radiative recombination
71.55.Jv Disordered structures; amorphous and glassy solids

Luminescence of Tb ions implanted into amorphous AlN thin films grown by sputtering

W. M. Jadwisienczak, H. J. Lozykowski, F. Perjeru, H. Chen, M. Kordesch, and I. G. Brown

Appl. Phys. Lett. 76, 3376 (2000); http://dx.doi.org/10.1063/1.126652 (3 pages) | Cited 26 times

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We report the observation of visible cathodoluminescence (CL) of Tb ions implanted into amorphous AlN films produced by sputtering. The implanted samples were subjected to thermal annealing treatment up to 1100 °C to optically activate the incorporated ions. The results show that up to 1000 °C annealing temperature the films remain amorphous and the Tb3+ emission intensity increases. The amorphous AlN:Tb films were characterized by x-ray diffraction, CL, and CL kinetics measurements. The sharp characteristic emission lines corresponding to intra-4fn-shell transitions are resolved in the spectral range from 350 to 750 nm, and observed over the temperature range from 7 to 330 K due to the transitions from 5D3 and 5D4 levels toward the 5FJ (J = 2 to 6) multiplets. Finally, CL kinetics measurements have revealed that decay times of 5D3→7FJ and 5D4→7FJ transitions are in the range 0.94–0.77 and 0.49–1.61 ms at 300 K, respectively. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.66.Jg Amorphous semiconductors; glasses
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing

Quantification of excess vacancy defects from high-energy ion implantation in Si by Au labeling

R. Kalyanaraman, T. E. Haynes, V. C. Venezia, D. C. Jacobson, H.-J. Gossmann, and C. S. Rafferty

Appl. Phys. Lett. 76, 3379 (2000); http://dx.doi.org/10.1063/1.126653 (3 pages) | Cited 24 times

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It has been shown recently that Au labeling [V. C. Venezia, D. J. Eaglesham, T. E. Haynes, A. Agarwal, D. C. Jacobson, H.-J. Gossmann, and F. H. Baumann, Appl. Phys. Lett. 73, 2980 (1998)] can be used to profile vacancy-type defects located near half the projected range (½ Rp) in MeV-implanted Si. In this letter, we have determined the ratio of vacancies annihilated to Au atoms trapped (calibration factor “k”) for the Au-labeling technique. The calibration experiment consisted of three steps: (1) a 2 MeV Si+ implant into Si(100) followed by annealing at 815 °C to form stable excess vacancy defects; (2) controlled injection of interstitials in the ½ Rp region of the above implant via 600 keV Si+ ions followed by annealing to dissolve the {311} defects; and (3) Au labeling. The reduction in Au concentration in the near-surface region (0.1–1.6 μm) with increasing interstitial injection provides the most direct evidence so far that Au labeling detects the vacancy-type defects. By correlating this reduction in Au with the known number of interstitials injected, it was determined that k = 1.2±0.2 vacancies per trapped Au atom. © 2000 American Institute of Physics.
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61.72.J- Point defects and defect clusters
81.05.Cy Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing

Origin of preferential orthorhombic twinning in SrRuO3 epitaxial thin films

Jon-Paul Maria, H. L. McKinstry, and S. Trolier-McKinstry

Appl. Phys. Lett. 76, 3382 (2000); http://dx.doi.org/10.1063/1.126654 (3 pages) | Cited 23 times

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In order to elucidate the driving forces which promote oriented in-plane crystallographic texture in SrRuO3 thin films deposited on stepped SrTiO3 substrates, a high-temperature x-ray analysis of both SrRuO3 thin films and powders was conducted. Structural phase transitions were found at temperatures near 350 °C and slightly above 600 °C. The transitions are tentatively indexed as orthorhombic to tetragonal and tetragonal to cubic, respectively. These results suggest that SrRuO3 thin films grow with cubic symmetry. As such, film–substrate interfacial characteristics, rather than a preferred growth direction, are believed to determine the orientation of orthorhombic twins. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Nickel-platinum alloy monosilicidation-induced defects in n-type silicon

D. Z. Chi, D. Mangelinck, J. Y. Dai, S. K. Lahiri, K. L. Pey, and C. S. Ho

Appl. Phys. Lett. 76, 3385 (2000); http://dx.doi.org/10.1063/1.126741 (3 pages) | Cited 4 times

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Electrically active defects induced by the formation of nickel–platinum alloy monosilicide (formed at 600–800 °C) has been studied in n-type silicon using deep level transient spectroscopy and transmission electron microscopy measurements. A Ni-related electron trap level at Ec−0.42 eV is observed after silicidation at 600 °C or above and a Pt-related electron trap level at Ec−0.50 eV is detected after silicidation at 700 °Cor above. Two hole trap levels at Ev+0.22 and Ev+0.28 eV are also detected, Ev+0.22 eV level for silicidation at 700 °C or above and Ev+0.28 eV level for 600 °C silicidation. For the sample silicided at 600 °C, an additional electron trap level (located at Ec − 0.16 eV) with a broad spectral peak is detected in the near-surface region (<0.65 μm) of the sample in which some {311} type defects of 50–100 Å long are also observed. Most of observed electrically active defects have been found to be present in near-surface regions (<2 μm). Lowest total defect concentration is observed in the sample silicided at 700 °C where lowest reverse saturation current is also observed, indicating that the Ni(Pt) monosilicidation-induced electrically active defects are effective recombination/generation centers. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant

G. Pozina, J. P. Bergman, B. Monemar, S. Yamaguchi, H. Amano, and I. Akasaki

Appl. Phys. Lett. 76, 3388 (2000); http://dx.doi.org/10.1063/1.126655 (3 pages) | Cited 12 times

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The effect of In surfactant during metalorganic vapor phase epitaxial growth on sapphire substrates on the properties of GaN layers is studied using time-resolved photoluminescence, cathodoluminescence, and scanning electron microscopy. The samples are divided into two groups, where hydrogen and nitrogen, respectively, have been used as a carrier gas during growth. It is shown that In-doped samples have a lower dislocation density, a narrower photoluminescence linewidth, and a longer free exciton lifetime. The influence of indium is stronger for GaN layers grown in nitrogen-rich conditions. The improvements of structural and optical properties are attributed to the effect of In on dislocations. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.35.-y Excitons and related phenomena

Transient characteristics of self-phase modulation in liquid crystals

Hiroshi Ono and Junichi Kikuhara

Appl. Phys. Lett. 76, 3391 (2000); http://dx.doi.org/10.1063/1.126656 (3 pages)

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Transient properties of nonlinear refractive index change originating in photothermal effects in guest-host liquid crystal (GHLC) have been characterized by use of heat-conduction analysis. By theoretical calculations using time-dependent heat-conduction analysis, we have a time constant of about 23 ms, in good agreement with the experimental observation (about 30 ms). The characterization technique described here is very useful for characterizing the quantitative properties of photothermal effects in GHLC. © 2000 American Institute of Physics.
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42.70.Df Liquid crystals
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
44.10.+i Heat conduction

Model for decomposition and nanocrystallization of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10Be22.5

Jörg F. Löffler and William L. Johnson

Appl. Phys. Lett. 76, 3394 (2000); http://dx.doi.org/10.1063/1.126657 (3 pages) | Cited 70 times

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From in situ small-angle neutron scattering performed at temperatures in the undercooled liquid regime, we derive a model for the crystallization pathway of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1). Vit1 first decomposes on the nanometer scale, increasing drastically the nucleation probability. In the later stages nanocrystallization occurs in one of the decomposed amorphous phases. The growth kinetics of the nanocrystals corresponds to a chemical relaxation process in which they equilibrate with the remaining amorphous matrix. Based on our model, a chemical diffusion constant is derived whose temperature dependence follows an Arrhenius law and is comparable with the expected self-diffusion constant of Ti in Vit1, as determined in independent studies of diffusion. © 2000 American Institute of Physics.
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61.43.Fs Glasses
64.75.-g Phase equilibria
61.46.-w Structure of nanoscale materials
66.30.Fq Self-diffusion in metals, semimetals, and alloys
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
64.60.Q- Nucleation

Lattice strains and composition of self-organized Ge dots grown on Si(001)

Z. M. Jiang, X. M. Jiang, W. R. Jiang, Q. J. Jia, W. L. Zheng, and D. C. Qian

Appl. Phys. Lett. 76, 3397 (2000); http://dx.doi.org/10.1063/1.126658 (3 pages) | Cited 30 times

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X-ray diffraction measurements at different grazing angles for self-organized Ge dots grown on Si(001) are carried out by using synchrotron radiation as a light source. The lattice parameters parallel and perpendicular to the surface are determined from the grazing angle and ordinary x-ray diffraction spectra. A 1.2% lattice constant expansion parallel to the interface and a 3.1% lattice expansion along the growth direction, as compared with the Si lattice, are found within the Ge dots. Based on the Poisson equation and the Vegard law, the Ge dot should be a partially strain relaxed SiGe alloy with the Ge content of 55%. The composition change in Ge dots is suggested to be caused by the atomic intermixing during the islanding growth. In the small grazing angle x-ray diffraction spectrum, a peak located at the higher angle side of Si(220) is observed. The origin of this peak is attributed to the near surface compressive strain in the peripheral substrate regions surrounding the Ge dots. This compressive strain is induced by the formation of Ge dots and leads to a −0.8% lattice constant change parallel to the interface. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
68.35.Gy Mechanical properties; surface strains

On three dimensional self-organization and optical properties of InAs quantum-dot multilayers

J. C. González, F. M. Matinaga, W. N. Rodrigues, M. V. B. Moreira, A. G. de Oliveira, M. I. N. da Silva, J. M. C. Vilela, M. S. Andrade, D. Ugarte, and P. C. Silva

Appl. Phys. Lett. 76, 3400 (2000); http://dx.doi.org/10.1063/1.126659 (3 pages) | Cited 9 times

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We report on experiments aimed at producing three-dimensional self-organization in InAs quantum-dot multilayers embedded in GaAs. These InAs/GaAs quantum-dot multilayers have been grown by molecular beam epitaxy. Employing atomic force microscopy, we have analyzed the island density in samples with different number of periods of InAs/GaAs bilayers The results reveals a decrease and a tendency to saturation of the island density with an increase in the number of periods, as a three-dimensional self-organization characteristic of these samples. Optical properties of the samples are examined via photoluminescence spectroscopy. The evolution of the quantum-dot photoluminescence peak position indicates an increment in the mean size of the buried islands and a relative homogenization in size of the quantum dots, as the number of periods increases. The results of the optical measurements agree with the morphological data, and characterize a spatial process of self-organization, related to the increment of the number of periods in the multilayers. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Relationship between segregation-induced intergranular fracture and melting in the nickel–sulfur system

J. K. Heuer, P. R. Okamoto, N. Q. Lam, and J. F. Stubbins

Appl. Phys. Lett. 76, 3403 (2000); http://dx.doi.org/10.1063/1.126660 (3 pages) | Cited 15 times

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The effect of S segregation to grain boundaries on the intergranular embrittlement of Ni has been studied at room temperature using Auger electron spectroscopy and slow strain rate tensile tests. The grain-boundary S concentration was varied by time-controlled annealing of dilute Ni–S alloy specimens at 625 °C. The ductile-to-brittle transition in Ni, as determined from percent integranular fracture and reduction-in-area measurements, occurred over a narrow range of S concentrations centered on 15.5±3.4 at. % S. This critical S concentration for 50% intergranular fracture of polycrystalline Ni is similar to the 14.2±3.3 at. % S required to induce 50% amorphization of single-crystal Ni by S+-ion implantation. This suggests that segregation-induced intergranular fracture, like implantation-induced amorphization, may be a disorder-induced polymorphous melting process. In agreement with experimental observations, the polymorphous melting curve for the Ni–S solid solution on the phase diagram drops rapidly to zero as the alloy composition approaches ∼18 at. % S. The critical grain-boundary concentration for intergranular fracture, while slightly less, is within experimental error of the concentration predicted for polymorphous melting as well as that measured for ion-implantation-induced amorphization. © 2000 American Institute of Physics.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.05.Bx Metals, semimetals, and alloys
62.20.M- Structural failure of materials
81.30.Mh Solid-phase precipitation
79.20.Fv Electron impact: Auger emission
81.40.Gh Other heat and thermomechanical treatments
64.70.D- Solid-liquid transitions
81.30.Bx Phase diagrams of metals, alloys, and oxides

Polarized blue light-emission from epitaxially oriented bis(phenyloxazolyl)benzene crystals

Yuya Yamada and Hisao Yanagi

Appl. Phys. Lett. 76, 3406 (2000); http://dx.doi.org/10.1063/1.126661 (3 pages) | Cited 6 times

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Epitaxially oriented crystals of a π-conjugating blue light-emitting molecule, 1,4-bis[2-(5phenyloxazolyl)]benzene (POPOP), were prepared by vapor deposition onto the KCl (001) surface. Rodlike crystals with submillimeter length grew along the KCl 〈110〉 directions having the (102) plane of the monoclinic cell contact with the KCl surface. The POPOP molecules were aligned parallel on this plane taking the herringbone structure. Due to this orientation, the electronic transition dipoles between the frontier molecular orbitals were all lying, so that the fluorescence emitted from the crystals under ultraviolet excitation was highly polarized in parallel to the substrate surface. This polarized emission with the transverse-electric mode was partly confined within the crystals and self-waveguided along their rod axes. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
71.20.Rv Polymers and organic compounds
68.55.-a Thin film structure and morphology

Investigation of β-SiC precipitation in Si1−yCy epilayers by x-ray scattering at grazing incidence

Z. Kovats, T. H. Metzger, J. Peisl, J. Stangl, M. Mühlberger, Y. Zhuang, F. Schäffler, and G. Bauer

Appl. Phys. Lett. 76, 3409 (2000); http://dx.doi.org/10.1063/1.126662 (3 pages) | Cited 9 times

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We have investigated molecular-beam-epitaxy-grown, pseudomorphic Si1−yCy epilayers (y ⩽ 0.015) on Si(001) after ex situ annealing by x-ray scattering at grazing incidence. The diffuse intensity around the Si (220) surface reflection consists of Huang scattering due to the long-range displacement field of substitutional carbon atoms and of the form-factor-induced small angle scattering of holes created by β-SiC precipitates in the Si matrix. Even in the as-grown samples, where other methods gave no indication of β-SiC precipitates, grazing incidence diffraction clearly showed their presence. The precipitates with a mean size of 5 Å are stable against annealing up to at least 600 °C; at 800 °C carbon leaves substitutional sites and the number of precipitates increases, whereas at 1000 °C a significant increase of the precipitate size (up to ≈15 Å) is detected as well. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.05.Hd Other semiconductors
64.75.-g Phase equilibria
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)
81.30.Mh Solid-phase precipitation
61.05.cf X-ray scattering (including small-angle scattering)
78.70.Ck X-ray scattering
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
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