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2 Apr 2001

Volume 78, Issue 14, pp. 1961-2084

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Diffuse multiself-frequency conversion processes in the blue and green by quasicylindrical ferroelectric domains in Nd3+:Sr0.6Ba0.4(NbO3)2 laser crystal

J. J. Romero, D. Jaque, J. García Solé, and A. A. Kaminskii

Appl. Phys. Lett. 78, 1961 (2001); http://dx.doi.org/10.1063/1.1355993 (3 pages) | Cited 52 times

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In this letter we demonstrate continuous-wave blue and green diffuse laser light generation from a Nd3+-doped Sr0.6Ba0.4(NbO3)2 crystal located in an end-pumped laser cavity and operating at the 4F3/2→4I11/2 laser channel. The diffuse nature of the visible radiation is attributed to numerous ferroelectric cylindrical domains, which appear in the as-grown crystal. Green radiation is obtained by self-frequency doubling of the infrared radiation, whereas tunable blue radiation is generated by self-frequency sum mixing of infrared and pump radiations. The variety of visible colors is due to the spread in the domain sizes. Finally, we report on the spectral and spatial distribution of this visible radiation. © 2001 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis

Continuous wave operation of a 9.3 μm quantum cascade laser on a Peltier cooler

Daniel Hofstetter, Mattias Beck, Thierry Aellen, Jérôme Faist, Ursula Oesterle, Marc Ilegems, Emilio Gini, and Hans Melchior

Appl. Phys. Lett. 78, 1964 (2001); http://dx.doi.org/10.1063/1.1360225 (3 pages) | Cited 57 times

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High average power quantum cascade lasers at 9.3 μm using InP top cladding layers and both junction up and junction down mounting are presented. A 3 mm long, junction up mounted device emitted 54 mW average power at 30 °C and 11.5% duty cycle with a threshold current density of 3.72 kA/cm2. A similar, but only 1.5 mm long device with high reflection coating on both facets was mounted junction down and tested at even higher duty cycles. At −27 °C, we achieved continuous wave operation with a threshold current density of 3.3 kA/cm2. © 2001 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Measurement of far-infrared waveguide loss using a multisection single-pass technique

Michel Rochat, Mattias Beck, Jérôme Faist, and Ursula Oesterle

Appl. Phys. Lett. 78, 1967 (2001); http://dx.doi.org/10.1063/1.1357444 (3 pages) | Cited 19 times

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Waveguide loss measurements based on a multisection single-pass technique have been performed for both mid-infrared and far-infrared quantum cascade structures. The far-infrared quantum cascade structures are based on a vertical transition active region emitting at λ ≈ 76 μm, embedded in a double-plasmon waveguide. The measured waveguide loss of 42±20 cm−1 agrees well with the calculated one based on free carrier absorption. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Gn Optical waveguides and couplers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Green-induced infrared absorption in MgO doped LiNbO3

Y. Furukawa, K. Kitamura, A. Alexandrovski, R. K. Route, M. M. Fejer, and G. Foulon

Appl. Phys. Lett. 78, 1970 (2001); http://dx.doi.org/10.1063/1.1359137 (3 pages) | Cited 71 times

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Green-induced infrared absorption (GRIIRA) was investigated by a photothermal technique for undoped and Mg-doped LiNbO3 crystals that have different Li/Nb ratios. Threshold effect on GRIIRA was found, threshold MgO concentrations being the same for GRIIRA and photorefraction. We suggest that GRIIRA is associated with the formation of the small polaron that is located on Nb antisite defect. The remarkable decrease of GRIIRA in Mg:LiNbO3 can then be attributed to the elimination of this intrinsic defect, Nb in Li, following the incorporation of Mg on Li sites. For nonlinear optical applications, LiNbO3 doped with MgO at concentrations over threshold has a combined advantage of having almost no GRIIRA and photorefraction. © 2001 American Institute of Physics.
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42.70.Mp Nonlinear optical crystals
78.30.Hv Other nonmetallic inorganics
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.72.J- Point defects and defect clusters
71.38.-k Polarons and electron-phonon interactions
71.55.Ht Other nonmetals

Magnetic field induced luminescence spectra in a quantum cascade laser

V. M. Apalkov and Tapash Chakraborty

Appl. Phys. Lett. 78, 1973 (2001); http://dx.doi.org/10.1063/1.1359488 (3 pages) | Cited 2 times

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We report on our study of the luminescence spectra of a quantum cascade laser in the presence of an external magnetic field tilted from the direction perpendicular to the electron plane. The effect of the tilted field is to allow novel optical transitions because of the coupling of intersubband-cyclotron energies. We find that by tuning the applied field, one can get optical transitions at different energies that are as sharp as the zero-field transitions. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.De Quantum wells
78.20.Ls Magneto-optical effects
73.21.Fg Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence
71.70.Di Landau levels
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The role of high-temperature island coalescence in the development of stresses in GaN films

T. Böttcher, S. Einfeldt, S. Figge, R. Chierchia, H. Heinke, D. Hommel, and J. S. Speck

Appl. Phys. Lett. 78, 1976 (2001); http://dx.doi.org/10.1063/1.1359780 (3 pages) | Cited 80 times

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The formation of dislocations and stress in GaN layers grown by metalorganic vapor phase epitaxy on sapphire is investigated with regard to the average grain diameter. The grain diameter was determined by monitoring the high-temperature GaN island coalescence process during growth using reflectometry. It is found that the density of edge threading dislocations decreases and the compressive stress measured after cooling to room temperature increases when the coalescence thickness and the grain diameter increase. The data are consistent with models of development of tensile stress due to island coalescence during growth. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
62.20.-x Mechanical properties of solids
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Temperature dependence of near ultraviolet photoluminescence in ZnO/(Mg, Zn)O multiple quantum wells

T. Makino, N. T. Tuan, H. D. Sun, C. H. Chia, Y. Segawa, M. Kawasaki, A. Ohtomo, K. Tamura, T. Suemoto, H. Akiyama, M. Baba, S. Saito, T. Tomita, and H. Koinuma

Appl. Phys. Lett. 78, 1979 (2001); http://dx.doi.org/10.1063/1.1357451 (3 pages) | Cited 46 times

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We report on temperature dependence of excitonic photoluminescence (PL) from ZnO/(Mg, Zn)O multiple quantum wells (MQWs). Two kinds of MQWs having different barrier heights grown by laser molecular-beam epitaxy showed significantly different temperature dependences of PL spectra; in ZnO/Mg0.27Zn0.73O MQWs, the PL peak energy at 50–200 K was a monotonically increasing function of temperature, which was opposite to that ascribed by band gap shrinkage. Moreover, spectra taken at 95–200 K encompassed two peaks, both of which originated from recombination of localized excitons. The temperature-induced shift (redshift-blueshift-peak duplication-redshift) at 5–300 K is caused by a change in the exciton dynamics with increasing temperature due to inhomogeneity and the exciton localization effect. On the other hand, the corresponding dependence in ZnO/Mg0.12Zn0.88O MQWs (lower barrier height) was similar to that in bulk II–VI semiconductors. © 2001 American Institute of Physics.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
73.21.Hb Quantum wires

Ultraviolet-extended real-time spectroscopic ellipsometry for characterization of phase evolution in BN thin films

J. A. Zapien, R. Messier, and R. W. Collins

Appl. Phys. Lett. 78, 1982 (2001); http://dx.doi.org/10.1063/1.1358367 (3 pages) | Cited 9 times

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Real-time spectroscopic ellipsometry with an ultraviolet-extended spectral range (1.5–6.5 eV) has been applied to investigate the sputter deposition of boron nitride (BN) thin films with high cubic content in terms of a two-layer optical model. In this model, the inner and outer layers represent sp2- and sp3-bonded BN (hBN and cBN), respectively. The thickness evolution of the two layers as well as their dielectric functions over the extended spectral range have been determined. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.55.Nq Composition and phase identification
81.15.Cd Deposition by sputtering

Elastic properties of Pd40Cu30Ni10P20 bulk glass in supercooled liquid region

N. Nishiyama, A. Inoue, and J. Z. Jiang

Appl. Phys. Lett. 78, 1985 (2001); http://dx.doi.org/10.1063/1.1359490 (3 pages) | Cited 35 times

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In situ ultrasonic measurements for the Pd40Cu30Ni10P20 bulk glass in three states: Glassy solid, supercooled liquid, and crystalline, have been performed. It is found that velocities of both longitudinal and transverse waves and elastic moduli (shear modulus, bulk modulus, Young’s modulus, and Lamé parameter), together with Debye temperature, gradually decrease with increasing temperature through the glass transition temperature as the Poisson’s ratio increases. The behavior of the velocity of transverse wave vs. temperature in the supercooled liquid region could be explained by viscosity flow, rather than the two different crystallization processes in the region, suggested in the literature. No decomposition was detected at a temperature only 5 K below the crystallization temperature. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
61.25.Mv Liquid metals and alloys
62.20.D- Elasticity
62.60.+v Acoustical properties of liquids
62.65.+k Acoustical properties of solids

Surfactant mediated growth of MnSi1.7 on Si(001)

S. Teichert, H. Hortenbach, and H.-J. Hinneberg

Appl. Phys. Lett. 78, 1988 (2001); http://dx.doi.org/10.1063/1.1361102 (3 pages) | Cited 9 times

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Sb is used as a surfactant for the growth of MnSi1.7 by reactive deposition of Mn on Si(001). It is found that the presence of Sb during the growth strongly increases the island density and changes the crystalline orientation of the MnSi1.7. The morphology and structure of the resulting silicide are the same both for the deposition of Mn only on a Sb-terminated Si(001) surface and for the codeposition of Mn and Sb on Si(001). A residual Sb coverage close to one monolayer at the sample surface has been determined for both of the preparation conditions. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Hd Other semiconductors

Thermally poled silica samples are structurally heterogeneous: Electron diffraction evidence of partial crystallization

C. Cabrillo, F. J. Bermejo, J. M. Gibson, J. A. Johnson, D. Faccio, V. Pruneri, and P. G. Kazansky

Appl. Phys. Lett. 78, 1991 (2001); http://dx.doi.org/10.1063/1.1359776 (3 pages) | Cited 10 times

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Large structural modifications in v-SiO2 are found to be induced by “thermal poling,” a treatment which makes the glass act as a frequency doubler of an impinging infrared light. The electron diffraction patterns of poled silica plates reveal the presence of a large amount (of order 10%) of crystallites showing patterns consistent with partial crystallization of the glassy matrix into the cristobalite polymorph of silica. © 2001 American Institute of Physics.
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61.43.Fs Glasses
42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Red photoluminescence of gold island films

Leonid Khriachtchev, Lauri Heikkilä, and Tom Kuusela

Appl. Phys. Lett. 78, 1994 (2001); http://dx.doi.org/10.1063/1.1359491 (3 pages) | Cited 21 times

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We comparatively study photoluminescence and morphology of gold films prepared with a sputtering method. The ultrathin films (⩽10 nm) efficiently emit light above 600 nm, which dramatically differs from the known emission of thick gold films. The absorption mechanism in ultrathin gold films is presumably contributed by their island structure promoting interacting plasmons. The collective plasmon states of island films decay radiatively, producing the extraordinary red emission observed under excitation at 488.0, 514.5, and 632.8 nm. The red photoluminescence of ultrathin films is substrate dependent, and correlates with the surface morphology analyzed by using atomic force microscopy and resistance measurements. © 2001 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
78.55.Hx Other solid inorganic materials
68.55.-a Thin film structure and morphology
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Improved extraction of the activation energy of the leakage current in silicon p–n junction diodes

A. Poyai, E. Simoen, C. Claeys, A. Czerwinski, and E. Gaubas

Appl. Phys. Lett. 78, 1997 (2001); http://dx.doi.org/10.1063/1.1359487 (3 pages) | Cited 5 times

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An accurate method is proposed for the extraction of the activation energy ET from the volume generation current density JgA in silicon p–n junctions. It combines temperature-dependent current–voltage (I–V) and capacitance–voltage measurements on an array of diodes with different geometry, in order to separate the peripheral from the volume components. The JgA can be found from the volume leakage current by subtraction of the volume diffusion current JdA, which is calculated from the forward I–V characteristic. To derive the correct slope from an Arrhenius plot of the JgA, several additional corrections have been applied. One is the temperature dependence of the depletion width, which is derived from the corrected volume capacitance. The most important ET change is shown to come from the temperature dependence of the recombination lifetime. © 2001 American Institute of Physics.
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85.30.Kk Junction diodes
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.55.Cn Elemental semiconductors

Athermal annealing of low-energy boron implants in silicon

D. W. Donnelly, B. C. Covington, J. Grun, R. P. Fischer, M. Peckerar, and C. L. Felix

Appl. Phys. Lett. 78, 2000 (2001); http://dx.doi.org/10.1063/1.1359784 (3 pages) | Cited 5 times

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Silicon samples that have been ion implanted with boron at energies below 3 keV have been athermally annealed. The annealing process has been characterized using secondary ion mass spectrometry and infrared absorption spectroscopy. The athermally annealed samples show activation comparable to that for thermally annealed samples, but with much less boron diffusion. The activation in the athermally annealed samples is shown to be much higher than would be achieved by recrystallization of the amorphous layer. © 2001 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
78.30.Am Elemental semiconductors and insulators
66.30.J- Diffusion of impurities

Coulomb suppression of surface noise

V. A. Kochelap, V. N. Sokolov, O. M. Bulashenko, and J. M. Rubí

Appl. Phys. Lett. 78, 2003 (2001); http://dx.doi.org/10.1063/1.1360227 (3 pages) | Cited 2 times

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We have generalized the model of the surface noise taking into account the self-consistent electrostatic interaction and transverse electron transport in a conductive channel. Analyzing this model, we have found that the Coulomb correlations between trapped and conducting electrons considerably suppress the surface noise. The suppression effect is shown to be frequency dependent and especially large for noisy conducting channels. © 2001 American Institute of Physics.
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72.70.+m Noise processes and phenomena
73.25.+i Surface conductivity and carrier phenomena
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Different transfer paths for thermally activated electrons and holes in self-organized Ge/Si(001) islands in a multilayer structure

C. J. Huang, Y. Tang, D. Z. Li, B. W. Cheng, L. P. Luo, J. Z. Yu, and Q. M. Wang

Appl. Phys. Lett. 78, 2006 (2001); http://dx.doi.org/10.1063/1.1360783 (3 pages) | Cited 10 times

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We investigated the temperature dependence (10–250 K) of the photoluminescence (PL) emission spectrum of self-organized Ge/Si(001) islands in a multilayer structure. With elevated temperature, we find that the thermally activated holes and electrons are gathered by the Ge islands in different ways. The holes drift from the wetting layer into the islands, while the electrons, confined in Si due to type-II band alignment, leak into the Ge islands by the electrostatic interaction with the holes accumulated there. It results in an increase of the integrated intensity of island-related PL at a certain temperature range and a reduction of the phonon energy in the phonon-assisted PL of the islands by involving a type-I transition into a type-II transition. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.67.Hc Quantum dots
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Field emission from polymer-converted carbon films by ultraviolet radiation

Z. Sun, S. M. Huang, Y. F. Lu, J. S. Chen, Y. J. Li, B. K. Tay, S. P. Lau, G. Y. Chen, and Y. Sun

Appl. Phys. Lett. 78, 2009 (2001); http://dx.doi.org/10.1063/1.1360233 (3 pages) | Cited 4 times

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A polymer, poly(phenylcarbyne) (PPC), was converted to carbon film by ultraviolet pulsed-laser (KrF, λ = 248 nm) irradiation in nitrogen atmosphere at room temperature. The irradiated PPC consisted of fine graphitic carbon particles of several tens of nm in size, and exhibited good field emission properties. Low turn-on emission field of 2 V/μm (at 1 nA/cm2), high emission current density of 20 mA/cm2 (at 12 V/μm), and high emission luminescent spots density of 104/cm2 were observed for the polymer film irradiated by a pulsed-laser fluence of 40 mJ/cm2. We demonstrate multiple-lines and 2×5 array field emission patterns using the laser irradiation of PPC. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials
85.45.Db Field emitters and arrays, cold electron emitters
81.15.Fg Pulsed laser ablation deposition

Conservation of flatband conditions for DySi2 monolayers on n-type Si(111)

S. Vandré, C. Preinesberger, W. Busse, and M. Dähne

Appl. Phys. Lett. 78, 2012 (2001); http://dx.doi.org/10.1063/1.1360782 (3 pages) | Cited 9 times

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We propose a low-resistivity metal/Si/DySi2/Si multilayer Ohmic contact to n-type Si. For a DySi2 monolayer on n-type Si(111), the Fermi level has been found to be located only 0.08 eV below the conduction-band minimum of Si, corresponding to flatband conditions. Here, we demonstrate that this Fermi-level position is conserved to a large extent upon Si overgrowth of the monolayer, allowing us to exploit the flatband conditions for device applications under ambient conditions. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
73.40.Cg Contact resistance, contact potential
79.60.Jv Interfaces; heterostructures; nanostructures

Room-temperature Ohmic contact on n-type GaN with surface treatment using Cl2 inductively coupled plasma

Ho Won Jang, Chang Min Jeon, Jong Kyu Kim, and Jong-Lam Lee

Appl. Phys. Lett. 78, 2015 (2001); http://dx.doi.org/10.1063/1.1360784 (3 pages) | Cited 26 times

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A room-temperature Ti/Al Ohmic contact on n-type GaN was obtained by surface treatment using Cl2 inductively coupled plasma treatment. The specific contact resistivity was dramatically decreased from the Schottky behavior to 9.4×10−6 Ω cm2 by the treatment. The binding energy of the Ga–N bond and the atomic ratio of Ga/N were simultaneously increased after the plasma treatment. This provides evidence that N vacancies, acting as donors for electrons, were produced at the etched surface, resulting in a shift of the Fermi level near to the conduction band. This leads to the reduction in contact resistivity through the decrease of the Schottky barrier for the conduction of electrons. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.Ea III-V semiconductors
81.65.Ps Polishing, grinding, surface finishing
61.72.J- Point defects and defect clusters
73.40.Cg Contact resistance, contact potential
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Discovery of magnetite in the exhausted material from a diesel engine

W. Abdul-Razzaq and M. Gautam

Appl. Phys. Lett. 78, 2018 (2001); http://dx.doi.org/10.1063/1.1358357 (2 pages) | Cited 11 times

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Magnetite was detected in the particulate matter collected from diesel engine exhaust using a total exhaust dilution tunnel. This discovery is very important in determining the health effects of exposure to magnetite or its interaction with static magnetic fields or low-frequency electromagnetic fields. Magnetite is the best absorber of microwave radiation of any biological material in the 0.5–10 GHz frequency range through the process of electromagnetic resonance. This includes the frequencies that are normally used in the cellular telephone industry. © 2001 American Institute of Physics.
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89.60.-k Environmental studies
92.60.Sz Air quality and air pollution
78.70.Gq Microwave and radio-frequency interactions

Magnetization reversal and coercivity of a single-domain Co/Pt dot measured with a calibrated magnetic force microscope tip

J. Lohau, A. Carl, S. Kirsch, and E. F. Wassermann

Appl. Phys. Lett. 78, 2020 (2001); http://dx.doi.org/10.1063/1.1361100 (3 pages) | Cited 14 times

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The magnetization reversal and the coercivity of a nanofabricated single-domain 230 nm diam Co/Pt multilayer dot with perpendicular magnetic anisotropy are measured quantitatively with magnetic force microscopy (MFM). During MFM imaging, a variable external magnetic field ranging between −1 kOe<H<1 kOe is applied in the z direction in order to simultaneously reverse the magnetizations of both the single-domain Co/Pt dot and the MFM tip. The hysteresis loop of the Co/Pt dot can be extracted unambiguously from the resulting MFM image contrast, since we have used a calibrated MFM tip, for which the magnetization reversal has been determined independently also by MFM using a nanofabricated current carrying ring. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Anisotropic magnetic domain structure of layered manganite La1.4Sr1.6Mn2O7

T. Fukumura, T. Hasegawa, H. Sugawara, K. Tanaka, H. Sakaki, T. Kimura, and Y. Tokura

Appl. Phys. Lett. 78, 2023 (2001); http://dx.doi.org/10.1063/1.1359778 (3 pages) | Cited 2 times

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The anisotropic magnetic domain structure of a layered manganite La1.4Sr1.6Mn2O7 has been analyzed quantitatively. The evaluated dimensions of the domain indicate the low dimensionality and reproduce spontaneous formation of the bubble domain taking stability of the bubble domain into account. The ferromagnetic regions observed below the Neel temperature might be responsible for the limited tunneling magnetoresistance ratio reported in this compound. © 2001 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance

Temperature-dependent magnetoresistance of magnetic tunnel junctions with ultraviolet light-assisted oxidized barriers

U. May, K. Samm, H. Kittur, J. Hauch, R. Calarco, U. Rüdiger, and G. Güntherodt

Appl. Phys. Lett. 78, 2026 (2001); http://dx.doi.org/10.1063/1.1361098 (3 pages) | Cited 14 times

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Co(10 nm)/AlOx(nominally 2 nm)/Co(20 nm) tunnel junctions have been prepared under ultrahigh vacuum conditions applying a shadow mask technique. An ultraviolet light-assisted oxidation process of the AlOx barrier has been optimized by in situ x-ray photoelectron spectroscopy, in conjunction with temperature-dependent tunneling magnetoresistance measurements. Optimum-oxidized tunnel junctions show a magnetoresistance of 20% at 285 K, and up to 38% at 100 K. For under-oxidized samples, with a remaining Al layer between the Co bottom electrode and the AlOx barrier, the tunneling magnetoresistance decreases more rapidly with increasing temperature than observed for the over-oxidized samples. The resistance × area product of optimum-oxidized tunneling junctions exhibits a minimum, and increases for under- and over-oxidized samples. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Gk Tunneling
73.61.At Metal and metallic alloys

Current-driven reversal in annular vertical giant magnetoresistive devices

K. Bussmann, G. A. Prinz, R. Bass, and J.-G. Zhu

Appl. Phys. Lett. 78, 2029 (2001); http://dx.doi.org/10.1063/1.1353819 (2 pages) | Cited 15 times

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Experiments are reported that demonstrate the asymmetric switching behavior reported earlier in vertical giant magnetoresistance devices arises from the solid disk geometry of the device that produces a magnetic singularity at the disk center. Annular devices having a 0.1 μm center hole and 0.5 μm outer diameter are shown to switch symmetrically with an Amperian field. © 2001 American Institute of Physics.
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85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance
75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures

Critical current density of YBa2Cu3O7−δ low-angle grain boundaries in self-field

D. T. Verebelyi, C. Cantoni, J. D. Budai, D. K. Christen, H. J. Kim, and J. R. Thompson

Appl. Phys. Lett. 78, 2031 (2001); http://dx.doi.org/10.1063/1.1360230 (3 pages) | Cited 24 times

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A study has been perfomed on the superconducting critical current density Jc flowing across low-angle grain boundaries in epitaxial thin films of YBa2Cu3O7−δ. The materials studied were dual grain boundary rings deposited on SrTiO3 and containing 2°, 3°, 5°, and 7° tilt boundaries. The current density in self-field was determined by magnetometric methods at temperatures from 5 K to Tc. We conclude that at the higher temperatures of coated conductor applications, there is limited potential for improving Jc by reducing the grain boundary angle below ∼ 3°. © 2001 American Institute of Physics.
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74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
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