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15 Aug 2001

Volume 90, Issue 4, pp. 1683-2051

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Mössbauer studies of melt-spun Pr2Fe14B ribbons

H. H. Hamdeh, X. Zhang, J. C. Ho, W. C. Chang, H. W. Chang, and Y. S. Liou

J. Appl. Phys. 90, 2033 (2001); http://dx.doi.org/10.1063/1.1385353 (3 pages) | Cited 16 times

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Melt-spun ribbons of tetragonal Pr2Fe14B exhibit favorable hard magnet characteristics. Technically relevant materials based on this compound, however, generally contain a certain amount of soft magnetic α-Fe or Fe3−xBx for remanence enhancement through exchange coupling. The nominal off-stoichiometric compositions lead to metallurgical complications, which are not easily resolvable by standard phase identification techniques such as x-ray diffraction and thermal magnetic analysis. As a viable alternative, 57Fe-Mössbauer spectroscopy can be used to delineate individual Fe sites. To provide a basis for such an approach, this report gives Mössbauer parameters including hyperfine magnetic field, isomer shift, and quadrupole splitting as obtained from a single-phase melt-spun Pr2Fe14B ribbon. © 2001 American Institute of Physics.
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76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
61.66.Bi Elemental solids
61.66.Dk Alloys
71.70.Jp Nuclear states and interactions
71.70.Ch Crystal and ligand fields

Modification of magnetic properties of epitaxial Co/Cu multilayers by 1 MeV C+ irradiation

M. C. Sung, D. G. You, H. S. Park, J. C. Lee, S. Y. Ie, I. S. Kim, J. Lee, C. N. Whang, S. Im, K. Jeong, T. G. Kim, J. S. Yang, and J. H. Song

J. Appl. Phys. 90, 2036 (2001); http://dx.doi.org/10.1063/1.1384483 (3 pages) | Cited 9 times

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Epitaxial [Co/Cu]10 grown on Si (001) has been irradiated by 1 MeV C+ with a dose of 1×1016/cm2. The intrinsic characteristics of epitaxy, such as crystal structure and fourfold magnetic anisotropy, are conserved after ion irradiation. However, the extrinsic magnetic properties are changed such that the coercivity decreases and the squareness of the hysteresis loop is noticeably improved. The intensity of the Cu (200) peak in the x-ray diffraction pattern increases about three times and its half-width decreases after irradiation. It is concluded that the changes of magnetic properties induced by ion irradiation result from the grain growth and the improved crystalline quality. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.65.Cd Superlattices
75.30.Gw Magnetic anisotropy

Single-electron tunneling in a single PbS nanocrystal nucleated on 11-mercaptoundecanoic acid self-assembled monolayer at room temperature

Peng Jiang, Zhong-Fan Liu, and Sheng-Min Cai

J. Appl. Phys. 90, 2039 (2001); http://dx.doi.org/10.1063/1.1382827 (3 pages) | Cited 12 times

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Nanometer-sized PbS particles in the size of about 3 nm produced by exposing a self-assembled monolayer of 11-mercaptoundecanoic acid salts on gold (111) substrate in a H2S atmosphere were studied by scanning tunneling microscopy (STM) and high-resolution transmission electron microscopy at room temperature in air. The stability of thus-obtained PbS nanoparticles makes STM imaging possible and repeatable scans of the semiconductor nanoparticles were performed. The current-voltage (I–V) characteristics of a single PbS nanoparticle exhibited clearly Coulomb blockade and Coulomb staircase. Furthermore, by varying the gap between a STM tip and the PbS nanoparticle, we also verified the dependence of staircase width on the change of the gap in the local I–V characteristics on the same PbS nanoparticle. The phenomena can be well described by a semi-classical double-barrier tunneling model. © 2001 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
73.23.Hk Coulomb blockade; single-electron tunneling

Self-assembly of submicron particles between electrodes

Z.-Z. Gu, Q.-B. Meng, S. Hayami, A. Fujishima, and O. Sato

J. Appl. Phys. 90, 2042 (2001); http://dx.doi.org/10.1063/1.1381540 (3 pages) | Cited 12 times

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A method for the fabrication of opal films between parallel transparent electrodes is described. Monodispersed particles are assembled by taking advantage of the rheological force induced by the evaporation of a solvent in a thin capillary cell. Three-dimensional opal films with controllable thickness could be fabricated, in which a regular hexagonal arrangement of particles parallel to the substrates over a large area was observed. Such a sandwich-like photonic device may find applications in fabricating electrically tunable photonic crystals. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.46.-w Structure of nanoscale materials
42.50.-p Quantum optics

Measurement of the excited-state position of bound-to-bound quantum-well infrared detectors

L. Zhou, Y. H. Chee, and G. Karunasiri

J. Appl. Phys. 90, 2045 (2001); http://dx.doi.org/10.1063/1.1388575 (3 pages)

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The energy of the first excited state of quantum-well infrared detectors plays an important role in determining performance. The uncertainties in material and growth parameters make it difficult to design quantum-well detectors with a precise control of the location of energy states. Such uncertainties will cause detectors to be either bound to continuum or bound to bound. In this article, we present a technique to locate the excited-state position in bound-to-bound quantum-well infrared detectors by measuring the bias dependence of the photoresponse. We have employed an InGaAs/AlGaAs quantum-well detector operating near 5 μm for this study. The photocurrent was found to have a strong bias dependence indicating the infrared transition in the quantum well is bound to bound in nature. The bias dependence of the photoresponse was compared with theoretical estimates including the tunneling of photoexcited electrons through the barrier. The results showed a good agreement and this allowed us to determine the location of the excited state from the barrier edge. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
81.05.Ea III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.63.Hs Quantum wells
81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects

Effect of growth temperature on luminescence and structure of self-assembled InAlAs/AlGaAs quantum dots

H. Y. Liu, B. Xu, J. J. Qian, X. L. Ye, Q. Han, D. Ding, J. B. Liang, X. R. Zhong, and Z. G. Wang

J. Appl. Phys. 90, 2048 (2001); http://dx.doi.org/10.1063/1.1388021 (3 pages) | Cited 5 times

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The effect of growth temperature on the optical properties of self-assembled In0.65Al0.35As/Al0.35Ga0.65As quantum dots is studied using photoluminescence and electroluminescence spectra. With the growth temperature increasing from 530 to 560 °C, the improvement of optical and structural quality has been observed. Furthermore, edge-emitting laser diodes with three stacked InAlAs quantum dot layers grown at different temperature are processed, respectively. For samples with quantum dots grown at 560 °C, the continuous wave operation is obtained up to 220 K, which is much higher than that of ones with InAlAs islands grown at 530 °C and that of the short-wavelength quantum-dot laser previously reported. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.60.Fi Electroluminescence
42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
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