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12 May 2003

Volume 82, Issue 19, pp. 3147-3362

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages)

Michael Mück, Christian Welzel, and John Clarke
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Two-photon-induced polymerization in a laser gain medium for optical microstructure

Shiyoshi Yokoyama, Tatsuo Nakahama, Hideki Miki, and Shinro Mashiko

Appl. Phys. Lett. 82, 3221 (2003); http://dx.doi.org/10.1063/1.1573350 (3 pages) | Cited 9 times

Online Publication Date: 6 May 2003

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We have fabricated a polymeric solid-state microcavity in the laser gain media by a two-photon-induced polymerization technique. The photopolymerization resin contains conventional laser dye and dendrimer. A dendrimer can encapsulate the laser dye, and therefore increase its concentration up to 4 wt % with limited energy transfer during the photopolymerization process. The microcavity consisted of <0.4 μm linewidth polymerized strips arranged in layer-by-layer structure. The periodic variation in the refractive index gave rise to Bragg reflection. A laser emission was measured in the microcavity under optical excitation. The spectral linewidth was about 0.15 nm above the lasing threshold. The laser emission is attributed both to the distributed Bragg reflection and to the high gain of a polymeric medium containing laser dye with a high concentration. © 2003 American Institute of Physics.
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42.55.Mv Dye lasers
82.35.Ej Nonlinear optics with polymers
82.50.Pt Multiphoton processes
42.70.Hj Laser materials
42.70.Jk Polymers and organics
42.55.Sa Microcavity and microdisk lasers

Synthesis and optical properties of semiconducting beta-FeSi2 nanocrystals

Q. Wan, T. H. Wang, and C. L. Lin

Appl. Phys. Lett. 82, 3224 (2003); http://dx.doi.org/10.1063/1.1574845 (3 pages) | Cited 11 times

Online Publication Date: 6 May 2003

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Vacuum electron-beam coevaporation of Fe and Si followed by annealing in N2 ambient is used to synthesize beta iron disilicide (β-FeSi2) nanocrystals. The reason for β-FeSi2 nanocrystal formation is discussed based on the principle of minimization of the interface energy. X-ray diffraction studies suggest that β-phase FeSi2 nanostructures turn into the α phase when the annealing temperature is 1000 °C. The optical transmission measurements indicate that the β-FeSi2 nanocrystals have a direct-band structure with the energy gap in the range of 0.84–0.88 eV. A sharp photoluminescence peak of the β-FeSi2 nanocrystals located at 1.5 μm is measured at 77 K. © 2003 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.22.Dj Single particle states
61.72.Cc Kinetics of defect formation and annealing

All-silicon omnidirectional mirrors based on one-dimensional photonic crystals

A. Bruyant, G. Lérondel, P. J. Reece, and M. Gal

Appl. Phys. Lett. 82, 3227 (2003); http://dx.doi.org/10.1063/1.1574403 (3 pages) | Cited 48 times

Online Publication Date: 6 May 2003

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We report on the fabrication of monolithic omnidirectional mirrors based on one-dimensional photonic crystals. The mirrors are comprised of chirped and unchirped multiple layers of microporous silicon. Porosities have been chosen to achieve an optimal low refractive index nL ∼ 1.5 and a high refractive index nH ∼ 2.55. Unchirped structures, centered in the near-infrared, exhibit an omnidirectional reflection band of 100 nm, in agreement with the calculated photonic band structure. Chirped structures exhibit an enlarged omnidirectional stop band (340 nm). Given the possibility of easily tailoring the optical thickness of porous silicon, this material is shown to be very practical for engineering omnidirectional mirrors. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Optical defects produced in fused silica during laser-induced breakdown

S. O. Kucheyev and S. G. Demos

Appl. Phys. Lett. 82, 3230 (2003); http://dx.doi.org/10.1063/1.1573364 (3 pages) | Cited 36 times

Online Publication Date: 6 May 2003

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Fused silica irradiated with ∼ 3-ns 1064-, 355-, and 266-nm laser pulses as well as with ∼ 120-fs 825-nm pulses is studied by a combination of photoluminescence (PL) and Raman scattering spectroscopies. Results show that, for laser fluences above the laser-induced breakdown threshold, in all the cases studied, irradiation results in the formation of four defect-related PL bands centered on ∼ 1.9 (655), 2.2 (565), 2.7 (460), and 4.3 eV (290 nm). Bands centered on 1.9, 2.7, and 4.3 eV are attributed to nonbridging oxygen hole centers (1.9 eV) and oxygen-deficiency defects (2.7 and 4.3 eV). However, defects giving rise to a broad band at ∼ 2.2 eV are unknown. For all the laser-modified samples studied, Raman spectroscopy reveals a dramatic increase in the intensity of D1 and D2 lines, associated with in-phase breathing motions of oxygen atoms in puckered four- and planar three-membered ring structures, respectively. This indicates laser-induced material densification. Based on these results, we discuss physical processes occurring during the catastrophic laser-induced material breakdown, leading to material densification and the formation of point defects. © 2003 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
61.72.-y Defects and impurities in crystals; microstructure

Energy of free excitons in CuInSe2 single crystals

M. V. Yakushev, A. V. Mudryi, and R. D. Tomlinson

Appl. Phys. Lett. 82, 3233 (2003); http://dx.doi.org/10.1063/1.1572477 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2003

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CuInSe2 single crystals grown by the vertical Bridgman method were studied using photoluminescence (PL) and optical reflection (OR) at temperatures 4.2 and 78 K. A and B free- exciton peaks were well resolved in both the PL and OR spectra measured at a low temperature from a number of samples. The energy, spectral separation, and the width of the excitonic lines varied considerably for samples with different elemental compositions. The closer to the ideal stoichiometry, the higher the energies and the smaller the A–B separation. Similar changes in the excitonic spectra were revealed for a temperature rise from 4.2 up to 78 K. These measurements explain the scatter in the excitonic parameters and the band-gap values measured in the present work and reported in the literature. © 2003 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.05.Hd Other semiconductors
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Bi Elemental solids
61.66.Dk Alloys
71.20.Nr Semiconductor compounds

Electroluminescence of self-assembled Ge hut clusters

M. Stoffel, U. Denker, and O. G. Schmidt

Appl. Phys. Lett. 82, 3236 (2003); http://dx.doi.org/10.1063/1.1572479 (3 pages) | Cited 19 times

Online Publication Date: 6 May 2003

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We have fabricated Si-based light-emitting diodes operating in the near infrared. The active layers of the devices consist of either one or ten layers of Ge/Si self-assembled hut clusters grown by molecular-beam epitaxy. Luminescence is observed in the spectral range between 1.4 and 1.5 μm. For the ten layer stack of Ge islands, electroluminescence is observed up to room temperature. A direct comparison with a pure Si reference p-i-n diode allows us to attribute the luminescence to radiative recombinations between holes localized in the Ge islands and electrons localized in the strained Si above and below the islands. © 2003 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.)
78.60.Fi Electroluminescence
85.60.Dw Photodiodes; phototransistors; photoresistors

Structural basis for the yield stress in plastic disperse systems

Alejandro G. Marangoni and Michael A. Rogers

Appl. Phys. Lett. 82, 3239 (2003); http://dx.doi.org/10.1063/1.1576502 (3 pages) | Cited 23 times

Online Publication Date: 6 May 2003

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The apparent yield stress is a fundamental rheological characteristic of a plastic material. In this work, we propose a model that relates the structure of a fractal particle network to its yield stress. The model predicts the yield stress to be a function of particle size, solid-liquid surface free energy, the amount of network material, and the fractal dimension of the network. The predicted yield stress corresponded to the stress at the limit of linearity in fat crystal networks. Moreover, a structural definition for the yield stress is proposed. © 2003 American Institute of Physics.
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46.35.+z Viscoelasticity, plasticity, viscoplasticity
83.60.La Viscoplasticity; yield stress
82.70.-y Disperse systems; complex fluids
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
05.45.Df Fractals
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Impact of substrate hot hole injection on ultrathin silicon dioxide breakdown

Dawei Heh, Eric M. Vogel, and Joseph B. Bernstein

Appl. Phys. Lett. 82, 3242 (2003); http://dx.doi.org/10.1063/1.1572466 (3 pages) | Cited 5 times

Online Publication Date: 6 May 2003

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The impact of hot holes on gate oxide breakdown is studied by investigating devices under constant voltage stress with a different amount of preinjected substrate hot holes. The results show that oxide breakdown is independent of the amount of those preinjected hot holes, which suggests that defects generated by hot holes are not directly related to oxide breakdown during constant voltage stress conditions. © 2003 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
73.61.Ng Insulators
73.50.Fq High-field and nonlinear effects

Charge carrier mobility in doped semiconducting polymers

V. I. Arkhipov, P. Heremans, E. V. Emelianova, G. J. Adriaenssens, and H. Bässler

Appl. Phys. Lett. 82, 3245 (2003); http://dx.doi.org/10.1063/1.1572965 (3 pages) | Cited 46 times

Online Publication Date: 6 May 2003

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An analytic model of the equilibrium hopping conductivity in a disordered organic semiconductor at large charge carrier densities is formulated. Calculated dependences of the equilibrium hopping mobility upon the carrier density are compared with recent experimental data obtained on doped poly(3-hexylthiophene) films. Doping is shown to create additional energy disorder due to potential fluctuations caused by the Coulomb field of randomly distributed dopant ions. © 2003 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds
71.55.Jv Disordered structures; amorphous and glassy solids

Pi-stacked pentacene thin films grown on Au(111)

Joo H. Kang and X.-Y. Zhu

Appl. Phys. Lett. 82, 3248 (2003); http://dx.doi.org/10.1063/1.1572554 (3 pages) | Cited 47 times

Online Publication Date: 6 May 2003

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Scanning tunneling microscopy with high impedance has been used to image the growth of pentacene thin films on Au(111). Instead of the herringbone structure in bulk solid, pentacene molecules in these thin films form a cofacial, π-stacked crystalline phase with their molecular planes parallel to the surface. The growth of this crystalline phase is attributed to the formation of a close-packed, crystalline monolayer which seeds the growth of the π-stacked multilayer film. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Monte Carlo simulation of remote-Coulomb-scattering-limited mobility in metal–oxide–semiconductor transistors

F. Gámiz, J. B. Roldán, J. E. Carceller, and P. Cartujo

Appl. Phys. Lett. 82, 3251 (2003); http://dx.doi.org/10.1063/1.1572967 (3 pages) | Cited 14 times

Online Publication Date: 6 May 2003

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An improved theory for remote-charge-scattering-limited mobility in silicon inversion layers is developed. The model takes into account the effects of image charges, screening, inversion layer quantization, the contribution of different subbands, oxide thickness, the actual distribution of charged centers inside the structure, the actual distribution of carriers in the inversion layer, the correlation of charged centers, and the charged centers sign. The model is implemented in a Monte Carlo simulator, where the effects of the ionized impurities charge, the interface trapped charge, and the contribution of other scattering mechanisms are taken into account simultaneously. Our results show that remote Coulomb scattering cannot be neglected for oxide thicknesses below 2 nm, but that its effects for tox>5 nm are negligible. Good agreement with experimental results has been obtained. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

X-ray photoemission spectroscopic investigation of surface treatments, metal deposition, and electron accumulation on InN

K. A. Rickert, A. B. Ellis, F. J. Himpsel, H. Lu, W. Schaff, J. M. Redwing, F. Dwikusuma, and T. F. Kuech

Appl. Phys. Lett. 82, 3254 (2003); http://dx.doi.org/10.1063/1.1573351 (3 pages) | Cited 32 times

Online Publication Date: 6 May 2003

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The effects of surface chemical treatments and metal deposition on the InN surface are studied via synchrotron-based photoemission spectroscopy. Changes in the In 4d core level as well as the valence band spectra are reported. The surface Fermi level position, EF, relative to the valence band maximum was determined for both Au and Ti Schottky barriers. EF lies at an energy of 0.7 eV above the valence band maximum for Au deposited on annealed InN and 1.2 eV above the valence band maximum for Ti deposited on Ar-sputtered InN. These results that the surface Fermi level lays at or above the conduction band maximum when a value of InN band gap of 0.7–0.9 eV is assumed. © 2003 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
81.65.-b Surface treatments
73.30.+y Surface double layers, Schottky barriers, and work functions
68.47.Fg Semiconductor surfaces
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing

Light intensity imaging of single InAs quantum dots using scanning tunneling microscope

T. Tsuruoka, Y. Ohizumi, and S. Ushioda

Appl. Phys. Lett. 82, 3257 (2003); http://dx.doi.org/10.1063/1.1576509 (3 pages) | Cited 5 times

Online Publication Date: 6 May 2003

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Light intensity images of self-assembled p-type InAs quantum dots (QDs) embedded in Al0.6Ga0.4As were measured by injecting electrons from the tip of a scanning tunneling microscope at room temperature. Bright round features appeared in the images for different photon energies. The light emission spectrum measured over each bright feature showed a single emission peak with different peak energy. By comparing the emission peak energies with the transition energies calculated for pyramidal shaped QD structures, we found that the observed bright features correspond to individual InAs QDs. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Optically induced formation of the hydrogen complex responsible for the 4B0 luminescence in 4H-SiC

Yaroslav Koshka

Appl. Phys. Lett. 82, 3260 (2003); http://dx.doi.org/10.1063/1.1574846 (3 pages) | Cited 6 times

Online Publication Date: 6 May 2003

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Formation of a boron-related defect responsible for the 4B0 emission line in the low-temperature photoluminescence spectrum of 4H SiC has been investigated. The 4B0 luminescence was absent in as-grown epitaxial layers. This line appeared after hydrogenation along with other hydrogen-related lines and disappeared after high-temperature annealing. This is an indication of involvement of hydrogen in formation of the corresponding radiative recombination center. Prolonged excitation of the hydrogenated epitaxial layers with above-band gap light caused not only previously reported enhanced passivation of Al acceptors but also additional strong nonmetastable increase of the 4B0 luminescence due to recombination-enhanced formation of the corresponding defect complex. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
61.72.Cc Kinetics of defect formation and annealing

Thermal stability of WSix and W Schottky contacts on n-GaN

Jihyun Kim, F. Ren, A. G. Baca, and S. J. Pearton

Appl. Phys. Lett. 82, 3263 (2003); http://dx.doi.org/10.1063/1.1576506 (3 pages) | Cited 14 times

Online Publication Date: 6 May 2003

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WSix Schottky contacts on GaN are found to exhibit improved thermal stability compared to pure W contacts. While the W contacts degrade for anneal temperatures ≥ 500 °C through reaction with the GaN to form β-W2N, the WSix contacts show a stable Schottky barrier height of ∼ 0.5 eV as obtained from I–V measurements up to temperatures >600 °C. The reverse leakage current in both types of diodes is considerably higher than predicted from thermionic emission and image-force-induced barrier height lowering. The reverse current density was found to vary approximately as VB0.5 (VB is the reverse bias) and suggests the presence of additional current transport mechanism in both types of diodes. © 2003 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
73.40.Ns Metal-nonmetal contacts
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Superconducting quantum interference device amplifiers at gigahertz frequencies

Michael Mück, Christian Welzel, and John Clarke

Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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A series of five dc superconducting quantum interference devices (SQUIDs) have been operated as microstrip amplifiers at frequencies ranging from 2.2 to 7.4 GHz. In these devices, the signal is connected between the SQUID washer and coil, which acts as a microstrip resonator. The gain measured at 4.2 K ranged from 12±1 to 6±1 dB. The noise temperature of three devices at 4.2 K in the frequency range 2.2–4 GHz was between 1 and 2 K, and the saturation temperature was between 150 and 250 K. Applications of these devices include readout for axion detectors, and intermediate-frequency amplifiers for superconductor–insulator–superconductor and hot-electron bolometer mixers. © 2003 American Institute of Physics.
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84.30.Le Amplifiers
84.40.Dc Microwave circuits
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Growth and characterization of TiO2 as a barrier for spin-polarized tunneling

M. Bibes, M. Bowen, A. Barthélémy, A. Anane, K. Bouzehouane, C. Carrétéro, E. Jacquet, J.-P. Contour, and O. Durand

Appl. Phys. Lett. 82, 3269 (2003); http://dx.doi.org/10.1063/1.1568159 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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We report on the elaboration and characterization of tunnel junctions based on La2/3Sr1/3MnO3 and TiO2. The structural analysis shows that TiO2 grows epitaxially in the anatase phase and forms flat interfaces with the adjacent layers. Resistance maps of a La2/3Sr1/3MnO3/TiO2 bilayer reveal a homogeneous resistance level. After patterning tunnel junctions, we obtain a large positive tunneling magnetoresistance (TMR) at low temperature for La2/3Sr1/3MnO3/TiO2/La2/3Sr1/3MnO3 junctions and a negative TMR in the case of La2/3Sr1/3MnO3/TiO2/Co. This negative TMR reflects a negative spin polarization of Co at the interface with TiO2, in analogy with recent experimental results for the Co/SrTiO3 interface. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Submicron electrical current density imaging of embedded microstructures

B. D. Schrag and Gang Xiao

Appl. Phys. Lett. 82, 3272 (2003); http://dx.doi.org/10.1063/1.1570499 (3 pages) | Cited 13 times

Online Publication Date: 6 May 2003

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We have developed a scanning magnetic microscopy technique for noninvasively imaging submicron magnetic fields from embedded microscopic electrical circuits. We are able to extract from the field data a complete profile of current densities using a mathematical algorithm. As an example, we provide current density images of micron-scale passivated conductors undergoing electromigration. © 2003 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.55.Ge Magnetometers for magnetic field measurements
85.30.De Semiconductor-device characterization, design, and modeling

Nondestructive determination of current–voltage characteristics of superconducting films by inductive critical current density measurements as a function of frequency

Hirofumi Yamasaki, Yasunori Mawatari, and Yoshihiko Nakagawa

Appl. Phys. Lett. 82, 3275 (2003); http://dx.doi.org/10.1063/1.1571657 (3 pages) | Cited 26 times

Online Publication Date: 6 May 2003

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A nondestructive inductive method was developed to determine the current–voltage characteristics of superconducting films by measuring the critical current density Jc as a function of the frequency of ac magnetic fields. In well-known inductive methods that measure the Jc distribution of large-area films, Jc is measured at a frequency and the electric field E induced in the superconductor is proportional to the frequency; therefore, the E versus current density relation can be determined by measuring Jc at various frequencies. Current–voltage characteristics of YBa2Cu3O7 films measured by this method agree well with those determined by measuring magnetic-field-sweep rate dependence of magnetization. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Curie temperature and carrier concentration gradients in epitaxy-grown Ga1−xMnxAs layers

A. Koeder, S. Frank, W. Schoch, V. Avrutin, W. Limmer, K. Thonke, R. Sauer, A. Waag, M. Krieger, K. Zuern, P. Ziemann, S. Brotzmann, and H. Bracht

Appl. Phys. Lett. 82, 3278 (2003); http://dx.doi.org/10.1063/1.1573369 (3 pages) | Cited 19 times

Online Publication Date: 6 May 2003

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We report on detailed investigations of the electronic and magnetic properties of ferromagnetic Ga1−xMnxAs layers, which have been fabricated by low-temperature molecular-beam epitaxy. Superconducting quantum interference device measurements reveal a decrease of the Curie temperature from the surface to the Ga1−xMnxAs/GaAs interface. While high-resolution x-ray diffraction clearly shows a homogeneous Mn distribution, a pronounced decrease of the carrier concentration from the surface towards the Ga1−xMnxAs/GaAs interface has been found by Raman spectroscopy as well as electrochemical capacitance–voltage profiling. The gradient in Curie temperature seems to be a general feature of Ga1−xMnxAs layers grown at low temperature. Possible explanations are discussed. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ey III-V semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
68.55.Nq Composition and phase identification
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Growth and characterization of sputtered epitaxial γ′Fe4N and NbN films and bilayers using electron backscatter diffraction patterns and magnetometry

R. Loloee, K. R. Nikolaev, and W. P. Pratt

Appl. Phys. Lett. 82, 3281 (2003); http://dx.doi.org/10.1063/1.1573356 (3 pages) | Cited 7 times

Online Publication Date: 6 May 2003

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Epitaxial single-crystal ferromagnetic Fe4N films (γ′ phase of iron nitride), nonmagnetic NbN films, and NbN/Fe4N bilayers were grown on MgO(100) substrates by sputter deposition in N2 gas. Electron backscatter diffraction patterns were used to characterize the structural properties including the relative crystallographic orientation of the sputter deposited Fe4N and NbN films with respect to the substrate and each other. Superconducting quantum interference device magnetometry was used to study the in-plane uniaxial anisotropy and determine the directions of the easy axes in ferromagnetic Fe4N films. © 2003 American Institute of Physics.
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81.15.Cd Deposition by sputtering
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology

(001) oriented FePt–Ag composite nanogranular films on amorphous substrate

K. Kang, Z. G. Zhang, C. Papusoi, and T. Suzuki

Appl. Phys. Lett. 82, 3284 (2003); http://dx.doi.org/10.1063/1.1574401 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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By annealing the multilayer film with a stack structure of MgO 10 nm/Ag 20 nm/[FePt x nm/Ag 5 nm]5 at 550 °C for 1 h, (001)-oriented L10 FePt nanograins with high perpendicular magnetic anisotropy are obtained on an amorphous substrate. The 20-nm Ag underlayer plays an important role in improving (001) texture of FePt and decreasing the fct FePt ordering temperature. The switching volume and uniaxial magnetic anisotropy constant Ku of FePt–Ag composite films with a controllable FePt grain size are obtained by fitting the coercivity dependence on magnetic field sweeping rate employing coherent rotation model, taking into account the easy axis distribution. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Mapping electron flow using magnetic force microscopy

R. Yongsunthon, A. Stanishevsky, E. D. Williams, and P. J. Rous

Appl. Phys. Lett. 82, 3287 (2003); http://dx.doi.org/10.1063/1.1573349 (3 pages) | Cited 9 times

Online Publication Date: 6 May 2003

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Electron flow around defects in conductors is highly dependent on the local geometry of the defect. The sensitivity of magnetic force microscopy (MFM) for the direct imaging of such variations at the submicron scale has been tested using model defect structures fabricated in gold lines by focused ion beam milling. The corresponding MFM images, taken with current densities of ∼ 106 A/cm2, have qualitatively different features near different defects, with stronger and more localized signal for the more highly curved current pathways. Quantitative analysis, via image deconvolution followed by inversion using the Biot–Savart law, yields parallel and perpendicular components of the current densities in the vicinity of each defect structure. MFM imagery clearly resolves differences in the electron flow around defects of similar size but differing geometry. © 2003 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
68.37.Rt Magnetic force microscopy (MFM)

External magnetic field effect on third-harmonic generation in Bi, Al-doped yttrium iron garnet

Jusuke Shimura, Shin-ichi Ohkoshi, and Kazuhito Hashimoto

Appl. Phys. Lett. 82, 3290 (2003); http://dx.doi.org/10.1063/1.1574843 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2003

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The magnetic field effect on the third-harmonic generation (THG) in a Y1.5Bi1.5Fe3.8Al1.2O12 magnetic film was investigated. Applying a longitudinal external magnetic field rotated the polarization plane of the TH wave. The TH rotation angle was 4.1° at 2.67 eV (incoming wave: 0.89 eV) in a magnetic field of 1.0 kOe. Based on the symmetry analysis, the TH rotation was understood by an apparition of a magnetic term of χyxxx(3)(M) in a third-order nonlinear optical susceptibility. © 2003 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Nk Insulators
78.20.Ls Magneto-optical effects
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
42.79.Wc Optical coatings
42.65.An Optical susceptibility, hyperpolarizability
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Strain-gradient-induced electric polarization in lead zirconate titanate ceramics

Wenhui Ma and L. Eric Cross

Appl. Phys. Lett. 82, 3293 (2003); http://dx.doi.org/10.1063/1.1570517 (3 pages) | Cited 45 times

Online Publication Date: 6 May 2003

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Strain-gradient-induced polarization or flexoelectricity was investigated in unpoled soft lead zirconate titanate (PZT) ceramic where the texture symmetry ∞∞m forbids macropiezoelectricity. Even under high strain gradient (1 m−1) the induced polarization is small (1.6 μC/m2) at 20 °C. Higher strain gradients induce ferroelastic poling and an additional extrinsic contribution to the flexoelectric coefficient μ12 raising the value from 0.5 to 2.0 μC/m. Cooling through the Curie point (TC) under maximum stress (80 MPa) where the peak permittivity ( ∼ 20 000) could raise μ12 to 20 μC/m, the equivalent electric field is still only ∼ 1 kV/m, inadequate to achieve significant ferroelectric poling. The situation may be different in thin PZT films where much larger strain gradients can occur. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Ly Strain-induced piezoelectric fields
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)
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