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25 Oct 1999

Volume 75, Issue 17, pp. 2521-2692

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Atomic structure of Ba0.5Sr0.5TiO3 thin films on LaAlO3

H.-J. Gao, C. L. Chen, B. Rafferty, S. J. Pennycook, G. P. Luo, and C. W. Chu

Appl. Phys. Lett. 75, 2542 (1999); http://dx.doi.org/10.1063/1.125071 (3 pages) | Cited 37 times

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Perovskite barium strontium titanate Ba0.5Sr0.5TiO3(BST) thin films were grown on (001) LaAlO3 (LAO) using pulsed-laser ablation. The microstructures of the as-grown BST films were studied with selected electron diffraction, transmission electron microscopy, and scanning transmission electron microscopy. The BST thin films are oriented with their [001] directions parallel to the 〈102〉 directions of the LAO. Both cross-sectional and plan-view studies show the BST films to be single crystals with smooth surfaces. The interfaces were seen to be atomically sharp by cross-sectional, high-resolution electron microscopy. The density of misfit dislocations was consistent with the 4.3% lattice mismatch, and they were found to be dissociated into partials. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Structural and optical characteristics of InxGa1−xN/GaN multiple quantum wells with different In compositions

Yong-Hwan Kwon, G. H. Gainer, S. Bidnyk, Y. H. Cho, J. J. Song, M. Hansen, and S. P. DenBaars

Appl. Phys. Lett. 75, 2545 (1999); http://dx.doi.org/10.1063/1.125072 (3 pages) | Cited 21 times

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We have studied the structural and optical properties of InxGa1−xN/GaN multiple quantum wells with different In compositions of 8.8%, 12.0%, and 13.3% by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), stimulated emission (SE), and time-resolved PL spectroscopy. As the In composition increases, the superlattice peaks in HRXRD measurements and the PLE band edge broaden, indicating the deterioration of interface quality due to the difficulty of uniform In incorporation into the GaN layer. However, the lower room-temperature SE threshold densities of the higher In concentration samples indicate that the effect of In suppressing nonradiative recombination overcomes the drawbacks associated with increasing interface imperfection. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.47.-p Spectroscopy of solid state dynamics
78.45.+h Stimulated emission

Recovery phenomenon of mechanoluminescence from Ca2Al2SiO7:Ce by irradiation with ultraviolet light

Morito Akiyama, Chao-Nan Xu, Hiroaki Matsui, Kazuhiro Nonaka, and Tadahiko Watanabe

Appl. Phys. Lett. 75, 2548 (1999); http://dx.doi.org/10.1063/1.125073 (3 pages) | Cited 27 times

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We have investigated the mechanoluminescence (ML) from Ca2Al2SiO7:Ce. The ML is clearly visible to the naked eye in the atmosphere. The luminescence integrated intensity is about 400 times as high as that of crystal sugar. The ML center has been identified as the Ce3+ ion from spectra of the ML and also from the photoluminescence studies of Ca2Al2SiO7:Ce. The ML intensity decreases on repetitive application of stress but is completely recovered by irradiation with ultraviolet light. It is suggested that the ML mechanism arises from the movement of dislocations and recombination between electrodes and holes released from these traps which are associated with the Ce3+ centers. © 1999 American Institute of Physics.
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78.60.Mq Sonoluminescence, triboluminescence
78.55.Hx Other solid inorganic materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
66.30.Lw Diffusion of other defects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Ht Other nonmetals
72.80.Ga Transition-metal compounds

Phase imaging: Deep or superficial?

O. P. Behrend, L. Odoni, J. L. Loubet, and N. A. Burnham

Appl. Phys. Lett. 75, 2551 (1999); http://dx.doi.org/10.1063/1.125074 (3 pages) | Cited 35 times

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Phase images acquired while intermittently contacting a sample surface with the tip of an atomic force microscope cantilever are not easy to relate to material properties. We have simulated dynamic force curves and compared simulated with experimental results. For some cantilever–sample combinations, the interaction remains a surface effect, whereas for others, the tip penetrates the sample significantly. Height artifacts in the “topography” images, and the role of the sample stiffness, work of adhesion, damping, and topography in the cantilever response manifest themselves to different extents depending on the indentation depth. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.Gy Mechanical properties; surface strains

Leakage current behaviors of acceptor- and donor-doped (Ba0.5Sr0.5)TiO3 thin films

Sang Sub Kim and Chanro Park

Appl. Phys. Lett. 75, 2554 (1999); http://dx.doi.org/10.1063/1.125075 (3 pages) | Cited 28 times

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We have investigated the effects of acceptor and donor doping on the leakage current behavior of Pt/(Ba0.5Sr0.5)TiO3/Pt film capacitors prepared by a pulsed-laser deposition method. We selected Mn/Al and Nb as acceptor and donor dopants, respectively. The leakage current behavior depends strongly on the type of dopants. Al doping decreases the leakage current level, and Mn doping decreases it further. Nb doping greatly increases it. The decrease in leakage current associated with acceptor doping seems to partly result from a decrease in tunneling current due to expansion of the depletion layer width. The converse appears to apply with donor doping. © 1999 American Institute of Physics.
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73.61.Ng Insulators
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

The controlled formation of ordered, sinusoidal structures by plasma oxidation of an elastomeric polymer

Ned Bowden, Wilhelm T. S. Huck, Kateri E. Paul, and George M. Whitesides

Appl. Phys. Lett. 75, 2557 (1999); http://dx.doi.org/10.1063/1.125076 (3 pages) | Cited 171 times

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This letter describes a technique for generating waves on polydimethylsiloxane (PDMS) patterned in bas-relief. The PDMS is heated, and its surface oxidized in an oxygen plasma; this oxidation forms a thin, stiff silicate layer on the surface. When the PDMS cools, it contracts and places the silicate layer under compressive stress. This stress is relieved by buckling to form patterns of waves with wavelengths from 0.5 to 10 μm. The waves are locally ordered near a step or edge in the PDMS. The wavelength, amplitude, and pattern of the waves can be controlled by controlling the temperature of the PDMS and the duration of the oxidation. The mechanism for the formation and order of the waves is described. © 1999 American Institute of Physics.
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81.65.Mq Oxidation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Strong and stable visible luminescence from Au-passivated porous silicon

C. H. Chen and Y. F. Chen

Appl. Phys. Lett. 75, 2560 (1999); http://dx.doi.org/10.1063/1.125077 (3 pages) | Cited 32 times

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We report on porous silicon (PS) samples with strong and stable red photoluminescence (PL) prepared by chemical anodization of gold-plated substrate. We demonstrate that the structural stability of Au-passivated porous silicon is much better than that of normal PS. It is also found that the PL intensity of Au-passivated PS can be enhanced by a factor of 3 when prepared under the same condition as that for normal PS. The infrared absorption spectra reveal that the photoluminescence stability can be attributed to the formation of stable Au–Si bonds on the surface of porous silicon. In addition, our study provides further evidence to support the quantum confinement model of the red emission of porous silicon. © 1999 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.55.Mb Porous materials
78.30.Am Elemental semiconductors and insulators
81.65.Rv Passivation
82.45.-h Electrochemistry and electrophoresis
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials

Optical resonance modes in InGaN/GaN multiple-quantum-well microring cavities

K. C. Zeng, L. Dai, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 75, 2563 (1999); http://dx.doi.org/10.1063/1.125078 (3 pages) | Cited 22 times

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Microrings of varying sizes have been fabricated from InxGa1−xN/GaN (x ∼ 0.15) multiple quantum wells (MQWs). Photolithography and dry etching techniques including both ion-beam and inductively coupled plasma etching were employed to pattern the III–nitride MQW microrings. Individual microrings were optically pumped and optical resonance modes were observed. The observed mode spacings were consistent with those expected for whispering-gallery (WG) modes within a resonant cavity of cylindrical symmetry, refractive index, and dimensions of the rings under investigation. The results obtained from the microring cavities were compared with those of the III–nitride MQW microdisk cavities. Our results have indicated that resonance modes corresponding to the radial and the WG modes are simultaneously present in microdisk cavities, but only WG modes are available from the microring cavities. Implications of our results on future GaN-based microcavity light emitters have been discussed. © 1999 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
42.60.By Design of specific laser systems
78.55.Cr III-V semiconductors
85.40.Hp Lithography, masks and pattern transfer

Optical band gap dependence on composition and thickness of InxGa1−xN (0<x<0.25) grown on GaN

C. A. Parker, J. C. Roberts, S. M. Bedair, M. J. Reed, S. X. Liu, N. A. El-Masry, and L. H. Robins

Appl. Phys. Lett. 75, 2566 (1999); http://dx.doi.org/10.1063/1.125079 (3 pages) | Cited 38 times

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Band gap measurements have been carried out in strained and relaxed InxGa1−xN epilayers with x<0.25. Values of x were determined from x-ray diffraction of relaxed films. The lowest energy absorption threshold, measured by transmittance, was found to occur at the same energy as the peak of the photoluminescence spectrum. Bowing parameters for both strained and relaxed films were determined to be 3.42 and 4.11 eV, respectively. The dependence of the band gap shift, ΔEg, on strain is presented. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.40.Fy Semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
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