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30 Apr 2001

Volume 78, Issue 18, pp. 2617-2804

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Edge and screw dislocations as nonradiative centers in InGaN/GaN quantum well luminescence

D. Cherns, S. J. Henley, and F. A. Ponce

Appl. Phys. Lett. 78, 2691 (2001); http://dx.doi.org/10.1063/1.1369610 (3 pages) | Cited 68 times

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Transmission electron microscopy (TEM) and scanning electron microscope cathodoluminescence (CL) have been used to determine the influence of edge and screw dislocations on the light emitting properties of InxGa1−xN quantum wells. TEM is used to locate and identify the nature of dislocations. CL on the same samples is used to determine the spatial variation of the luminescence. A direct correlation of CL maps with TEM has been established, showing that threading edge dislocations act as nonradiative recombination centers with an associated minority carrier diffusion length of 200 nm. Threading dislocations of screw and mixed type were found to be associated with surface pits which were also nonradiative in the quantum well (QW) emission, but owing to the absence of QW growth on the pit facets. The contributions of edge and screw/mixed dislocations to the reduction of the QW emission are quantified, and the wider significance of these results is discussed. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.35.Ct Interface structure and roughness
78.60.Hk Cathodoluminescence, ionoluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Effect of the density of collision cascades on implantation damage in GaN

S. O. Kucheyev, J. S. Williams, A. I. Titov, G. Li, and C. Jagadish

Appl. Phys. Lett. 78, 2694 (2001); http://dx.doi.org/10.1063/1.1369149 (3 pages) | Cited 13 times

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Damage accumulation in wurtzite GaN films bombarded with 0.5 MeV Bi1 and 1 MeV Bi2 ions (the so-called molecular effect) is studied by Rutherford backscattering/channeling spectrometry. Results show that an increase in the density of collision cascades dramatically enhances the level of implantation-produced lattice disorder in GaN. This effect is attributed to (i) an increase in the defect clustering efficiency with increasing density of ion-beam-generated point defects and/or (ii) to collective nonlinear energy spike processes. Such a strong influence of the density of collision cascades is important to take into account for a correct estimation of implantation-produced lattice disorder in GaN. © 2001 American Institute of Physics.
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61.80.Jh Ion radiation effects
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.72.J- Point defects and defect clusters

Low temperature specific heat of bulk glassy and crystalline Zr41Ti14Cu12.5Ni10Be22.5 alloys

Hai Yang Bai, Jian Lin Luo, Zhao Jia Chen, and Wei Hua Wang

Appl. Phys. Lett. 78, 2697 (2001); http://dx.doi.org/10.1063/1.1369616 (3 pages) | Cited 5 times

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The low temperature specific heat of Zr41Ti14Cu12.5Ni10Be22.5 alloys in glassy and crystalline states has been investigated. The glassy state of the alloy shows much larger specific heat than that of the crystalline state. The density of states at the Fermi level and Debye temperatures, θD of the alloys are determined. It is found that the density of states at the Fermi level for the glassy state is higher than that for crystalline state, the phenomenon is interpreted by localization of electrons in the glassy alloy. A much smaller value of θD in the glassy state indicates marked soften transverse phonons compared to its corresponding crystalline state. © 2001 American Institute of Physics.
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65.40.Ba Heat capacity
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
71.20.Gj Other metals and alloys
71.55.Jv Disordered structures; amorphous and glassy solids
63.90.+t Other topics in lattice dynamics (restricted to new topics in section 63)

Large magneto-optical effect in an oxide diluted magnetic semiconductor Zn1−xCoxO

K. Ando, H. Saito, Zhengwu Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto, and H. Koinuma

Appl. Phys. Lett. 78, 2700 (2001); http://dx.doi.org/10.1063/1.1368375 (3 pages) | Cited 92 times

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Strong magneto-optical effect of Zn1−xCoxO near the optical band gap is reported. Magnetic circular dichroism (MCD) and Faraday rotation of Zn1−xCoxO (x = 0.012 and 0.016) at 5 K are as high as 2°/cm Oe at 3.4 eV, which are about two orders larger than those of ZnO. Absence of strong Co2+ d–d∗ transition near the optical band gap makes Zn1−xCoxO an useful material for short-wavelength magneto-optical applications. Large magneto-optical effects and paramagnetic temperature dependence of MCD show a strong mixing of the sp bands of the host ZnO with Co2+ d orbitals. The polarity of the MCD peak is negative indicating the antiferromagnetic p–d exchange interaction. © 2001 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.50.Pp Magnetic semiconductors
75.20.Ck Nonmetals
75.50.Ee Antiferromagnetics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.30.Et Exchange and superexchange interactions

Anisotropies in magnetron sputtered carbon nitride thin films

Niklas Hellgren, Mats P. Johansson, Esteban Broitman, Lars Hultman, and Jan-Eric Sundgren

Appl. Phys. Lett. 78, 2703 (2001); http://dx.doi.org/10.1063/1.1369388 (3 pages) | Cited 3 times

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Carbon nitride CNx (0 ⩽ x ⩽ 0.35) thin films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges have been studied with respect to microstructure using electron microscopy, and elastic modulus using nanoindentation and surface acoustic wave analyses. For growth temperature of 100 °C, the films were amorphous, and with an isotropic Young’s modulus of ∼ 170–200 GPa essentially unaffected by the nitrogen fraction. The films grown at elevated temperatures (350–550 °C) show anisotropic mechanical properties due to a textured microstructure with standing basal planes, as observed from measuring the Young’s modulus in different directions. The modulus measured in the plane of the film was ∼ 60–80 GPa, while in the vertical direction the modulus increased considerably from ∼ 25 to ∼ 200 GPa as the nitrogen content was increased above ∼ 15 at. %. © 2001 American Institute of Physics.
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81.15.Cd Deposition by sputtering
61.43.Er Other amorphous solids
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Three-dimensional analysis of shape transitions in strained-heteroepitaxial islands

Y. W. Zhang and A. F. Bower

Appl. Phys. Lett. 78, 2706 (2001); http://dx.doi.org/10.1063/1.1354155 (3 pages) | Cited 28 times

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A continuum model of shape transitions in strained heteroepitaxial islands predicts that small islands are hut shaped, while larger islands are domed. The volume of a stable hut can exceed that of a stable dome, however, indicating that the stability of hut-shaped islands plays an important role in shape transition, in addition to energy changes associated with the transition. A hut-shaped island loses stability upon reaching a critical volume, which depends on the anisotropy in surface energy. Impingement between islands reduces the critical volume by nucleating new facets at the base of a hut, which subsequently trigger a shape transition. © 2001 American Institute of Physics.
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68.35.Rh Phase transitions and critical phenomena
68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties
68.35.Md Surface thermodynamics, surface energies
64.60.Q- Nucleation

Exciton–erbium coupling and the excitation dynamics of Er3+ in erbium-doped silicon-rich silicon oxide

Se-Young Seo and Jung H. Shin

Appl. Phys. Lett. 78, 2709 (2001); http://dx.doi.org/10.1063/1.1369150 (3 pages) | Cited 26 times

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The exciton–erbium coupling and the excitation dynamics of Er3+ in erbium-doped silicon-rich silicon oxide are investigated using time-resolved measurements of Er3+ luminescence. The dependence of the Er3+ luminescence on the pump power and duration indicates that the exciton–erbium coupling is dominant over carrier–exciton coupling. The results further support the idea that the luminescent Er3+ ions are not in the Si nanoclusters but in the interface region surrounding the nanoclusters. © 2001 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Ht Other nonmetals
78.47.-p Spectroscopy of solid state dynamics
78.55.Hx Other solid inorganic materials

Real-time x-ray microbeam characterization of electromigration effects in Al(Cu) wires

P.-C. Wang, I. C. Noyan, S. K. Kaldor, J. L. Jordan-Sweet, E. G. Liniger, and C.-K. Hu

Appl. Phys. Lett. 78, 2712 (2001); http://dx.doi.org/10.1063/1.1368189 (3 pages) | Cited 14 times

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We report real-time, in situ x-ray microbeam measurements of electromigration-induced Cu redistribution, and the concurrent local stress variation in Al(Cu) wires. The data, which were obtained by combining x-ray microtopography with energy-dispersive fluorescence analysis, encompass both the early and late stages of electromigration as well as the postrelaxation stage at high temperature with the current turned off. We observe that both Cu concentration and stress values show unexpected local variations that may reflect the effect of local configuration such as film–substrate interface integrity or microstructure. © 2001 American Institute of Physics.
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66.30.Qa Electromigration

Ordinary and extraordinary dielectric functions of 4H– and 6H–SiC from 3.5 to 9.0 eV

O. P. A. Lindquist, K. Järrendahl, S. Peters, J. T. Zettler, C. Cobet, N. Esser, D. E. Aspnes, A. Henry, and N. V. Edwards

Appl. Phys. Lett. 78, 2715 (2001); http://dx.doi.org/10.1063/1.1369617 (3 pages) | Cited 8 times

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We report ordinary (ϵ⊥c axis) and extraordinary (ϵ∥c axis) dielectric function data of 4H– and 6H–SiC from 3.5 to 9.0 eV. These data, which were obtained by with spectroscopic ellipsometry, are also compared to recently reported ab initio calculations. Critical point energies were found using real and reciprocal space analysis. © 2001 American Institute of Physics.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors

Electronic structure of oxidized Ni/Au contacts on p-GaN investigated by x-ray absorption spectroscopy

J. C. Jan, K. Asokan, J. W. Chiou, W. F. Pong, P. K. Tseng, M.-H. Tsai, Y. K. Chang, Y. Y. Chen, J. F. Lee, J. S. Wu, H.-J. Lin, C. T. Chen, L. C. Chen, F. R. Chen, and J.-K. Ho

Appl. Phys. Lett. 78, 2718 (2001); http://dx.doi.org/10.1063/1.1370121 (3 pages) | Cited 6 times

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X-ray absorption spectroscopy has been used to investigate the electronic structure of as-deposited and oxidized Ni/Au contacts on p-GaN. The Ni K-, L2,3-, and O K-edges x-ray absorption spectra clearly show the formation of NiO in the annealed contacts. Annealing in air increases Ni-site hole concentration and slightly shortens the nearest-neighbor Ni–O bond length, which enhances p–d hybridization and charge transfer from Ni to O. The observed very low specific contact resistance in the oxidized contacts is found to be due to the enhanced hole concentration at the Ni site. © 2001 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
78.70.Dm X-ray absorption spectra
81.40.Gh Other heat and thermomechanical treatments
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
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Energy distributions of electrons emitted from GaAs(Cs, O)

D. A. Orlov, M. Hoppe, U. Weigel, D. Schwalm, A. S. Terekhov, and A. Wolf

Appl. Phys. Lett. 78, 2721 (2001); http://dx.doi.org/10.1063/1.1368376 (3 pages) | Cited 19 times

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A method to map out the energy distribution N(E∥,E⊥) of an electron beam as a function of the longitudinal (E∥) and transverse (E⊥) energy has been developed and applied to study the photoemission process from GaAs(Cs, O) at 90 K. The method proceeds by “marking” electrons with fixed longitudinal energy E∥b and a subsequent measurement of the associated differential transverse energy distribution N⊥(E∥b,E⊥), applying an adiabatic magnetic compression technique. The complete energy distribution N(E∥,E⊥) of electrons from a GaAs(Cs, O) photocathode obtained by a stepwise variation of E∥b provides details about the transfer of electrons through the GaAs(Cs, O)–vacuum interface and demonstrates that not only electron energy loss, but also elastic electron scattering is of crucial importance in the escape process. © 2001 American Institute of Physics.
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79.60.Dp Adsorbed layers and thin films
68.43.Mn Adsorption kinetics
81.05.Ea III-V semiconductors

Studies of carrier dynamics in unintentionally doped gallium nitride bandtail states

Chi-Kuang Sun, Jian-Chin Liang, Xiang-Yang Yu, Stacia Keller, Umesh K. Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 78, 2724 (2001); http://dx.doi.org/10.1063/1.1366650 (3 pages) | Cited 7 times

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Ultrafast carrier dynamics of bandtail states in an unintentionally doped gallium nitride sample was investigated using femtosecond transient transmission measurements. The transient responses of shallow bandtail states resemble those of above band gap extended states. The transient responses of the deep bandtail states are, on the other hand dominated by carrier transfer into the lower energy states through phonon assisted tunneling suggesting that the deep bandtail states are localized states. © 2001 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Direct patterning of nanometer-scale silicide structures on silicon by ion-beam implantation through a thin barrier layer

M. M. Mitan, D. P. Pivin, T. L. Alford, and J. W. Mayer

Appl. Phys. Lett. 78, 2727 (2001); http://dx.doi.org/10.1063/1.1369608 (3 pages) | Cited 3 times

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CoSi2 structures were formed by focused ion-beam implantation. Patterned silicide lines with dimensions down to 150 nm were produced on (100) silicon. The process involved the ion implantation of 200 keV As++ through a cobalt (34 nm)/oxide ( ∼ 2 nm) thin film structure. The thin oxide at the Si/Co interface acted as a selective reaction barrier. Ion-beam mixing disrupted the oxide layer to allow silicidation to proceed during subsequent rapid thermal anneal treatments. Reactions were inhibited in nonimplanted areas. A threshold dose of 3×1015 cm−2 was required for process initiation. Electrical measurements resulted in resistivities ranging from 15 to 30 μΩ cm. © 2001 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
73.40.Ns Metal-nonmetal contacts
81.07.Bc Nanocrystalline materials
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Structure and formation mechanism of the Eα′ center in amorphous SiO2

T. Uchino, M. Takahashi, and T. Yoko

Appl. Phys. Lett. 78, 2730 (2001); http://dx.doi.org/10.1063/1.1369147 (3 pages) | Cited 5 times

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We provide a possible formation mechanism for one of the Si-related paramagnetic centers in amorphous silica, Eα′, which is stable only below 200 K, on the basis of the quantum-chemical calculations. We show that the divalent Si defect can trap a hole, resulting in two different types of paramagnetic centers that are consistent with the experimental spectral features for Eα′. The highly anisotropic symmetry and the isotropic hyperfine coupling constants observed for one of the Eα′- center variants are reproduced by the present model. © 2001 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Jv Disordered structures; amorphous and glassy solids
76.30.Mi Color centers and other defects
61.43.Er Other amorphous solids

Output-coupling semiconductor saturable absorber mirror

G. J. Spühler, S. Reffert, M. Haiml, M. Moser, and U. Keller

Appl. Phys. Lett. 78, 2733 (2001); http://dx.doi.org/10.1063/1.1370122 (3 pages) | Cited 21 times

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We present a semiconductor saturable absorber mirror (SESAM), which also acts as an output coupler at the same time. The influence of the output coupler transmission onto the absorber parameters is investigated theoretically, as well as experimentally. A passively Q-switched Nd:YVO4 microchip laser is built using such a nonlinear output coupler, yielding clean pulses of 143 ps duration, 48 nJ energy, and 572 W peak power. This result is compared with the traditional approach, where the SESAM is not used as an output coupler. © 2001 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
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Coexistence of intrinsic and extrinsic magnetoresistance in the double-perovskite Sr2Fe(Mo1−xWx)O6−w system

J. Lindén, T. Yamamoto, J. Nakamura, M. Karppinen, and H. Yamauchi

Appl. Phys. Lett. 78, 2736 (2001); http://dx.doi.org/10.1063/1.1366357 (3 pages) | Cited 6 times

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In a recent study, it was shown that by partially substituting Mo with W in the double-perovskite Sr2FeMoO6−w system, the magnetoresistivity can be enhanced. [K.-I. Kobayashi, T. Okuda, Y. Tomioka, T. Kimura, and Y. Tokura, J. Magn. Magn. Mater. 218, 17 (2000).] In order to explain the increase in the magnetoresistivity a series of W-substituted Sr2Fe(Mo1−xWx)O6−w samples with 0 ⩽ x ⩽ 1 was synthesized. Upon increasing the W content, the samples began to exhibit coexistence of paramagnetism and ferrimagnetism at 300 K. Signatures of antiferromagnetic ordering appeared around TN ≈ 50 K for x ≥ 0.6. In samples with 0.7 ⩽ x ⩽ 0.8 a broad peak was observed in the magnetoresistance data at temperatures corresponding to the Néel temperature. The peak was found to have its origin in the colossal magnetoresistance effect. The W-substituted samples were partially ferrimagnetic and therefore also exhibited the tunneling-type magnetoresistance, which is characteristic of pure Sr2FeMoO6−w. The coexistence of the two types of magnetoresistance effect is responsible for the enhancement of the overall magnetoresistance value. A slight enhancement in the magnetoresistance values around 300 K for the strongly W-substituted samples was found to be related to a second colossal magnetoresistance peak related to the para- to ferrimagnetic transition at Tc. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck Nonmetals
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics

Magnetoresistance of Mn:Ge ferromagnetic nanoclusters in a diluted magnetic semiconductor matrix

Y. D. Park, A. Wilson, A. T. Hanbicki, J. E. Mattson, T. Ambrose, G. Spanos, and B. T. Jonker 

Appl. Phys. Lett. 78, 2739 (2001); http://dx.doi.org/10.1063/1.1369151 (3 pages) | Cited 89 times

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We have fabricated a thin film magnetic system consisting of nanoscale Mn11Ge8 ferromagnetic clusters embedded in a MnxGe1−x dilute ferromagnetic semiconductor matrix. The clusters form for growth temperatures of ∼300 °C with an average diameter and spacing of 100 and 150 nm, respectively. While the clusters dominate the magnetic properties, the matrix plays a subtle but interesting role in determining the transport properties. Variable range hopping at low temperatures involves both nanoclusters and MnGe sites, and is accompanied by a negative magnetoresistance attributed in part to spin-dependent scattering analogous to metallic granular systems. © 2001 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
72.20.Ee Mobility edges; hopping transport
73.61.Le Other inorganic semiconductors

Vector magnetization imaging in ferromagnetic thin films using soft x-rays

Sang-Koog Kim, J. B. Kortright, and Sung-Chul Shin

Appl. Phys. Lett. 78, 2742 (2001); http://dx.doi.org/10.1063/1.1370120 (3 pages) | Cited 15 times

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A magnetization vector M imaging using a transmission x-ray microscope with magnetic circular dichroism (MCD) contrast is demonstrated. MCD images through a semitransparent, 33-nm-thick Fe film are measured at the Fe L3 edge along three different x-ray propagation directions to determine all three components of the M. The transmission images clearly display the vector nature of complex microstructures, associated with the M reversal between oppositely oriented 180° domains, including not only 90° domains, a Néel wall-like structure, and an extended ripple structure, but also a striking feature of localized magnetization spirals with perpendicular components at their cores. These studies have important implications for applications of this technique to better understand the expected features as well as details of domain-wall structures. © 2001 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Dm X-ray absorption spectra
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Axial high-temperature superconducting-quantum-interference-device gradiometer composed of magnetometers with a monolithic feedback and compensation coil

Koichi Yokosawa, Hiroshi Oyama, Shinya Kuriki, Daisuke Suzuki, and Keiji Tsukada

Appl. Phys. Lett. 78, 2745 (2001); http://dx.doi.org/10.1063/1.1369414 (3 pages) | Cited 4 times

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A first-order axial gradiometer has been constructed using two high-critical-temperature superconducting-quantum-interference-device magnetometers having a double-pickup loop configuration on bicrystal substrates. The magnetometer, which had a slot-type structure but no weak links on the pickup loops, can be operated steadily in an unshielded environment after in situ cooling. The gradiometer was formed by connecting the feedback and the compensation coils of the two magnetometers in series using a normal conductive wire. Sufficiently high noise reduction (31 dB at 1 Hz) was achieved without any need for adjustments and low-noise magnetocardiograms were obtained with the gradiometer in a moderately magnetically shielded room. © 2001 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)
87.19.Hh Cardiac dynamics
87.50.C- Static and low-frequency electric and magnetic fields effects
07.55.Nk Magnetic shielding in instruments

Dynamic coercivity measurements of antiferromagnetically coupled magnetic media layers

J. Lohau, A. Moser, D. T. Margulies, E. E. Fullerton, and M. E. Schabes

Appl. Phys. Lett. 78, 2748 (2001); http://dx.doi.org/10.1063/1.1369391 (3 pages) | Cited 22 times

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We have performed dynamic coercivity measurements on a series of antiferromagnetically coupled (AFC) magnetic recording media utilizing a static write/read tester. The samples consist of two magnetic layers, which are antiferromagnetically coupled by a nonmagnetic layer. The investigated samples have a fixed top layer thickness and variable bottom layer thickness, such that the composite remanent magnetization thickness product (MRtAFC) varies over a large range, 0.17–0.30 memu/cm2. We find that the ratio between anisotropy energy and thermal energy (≡ stability ratio, C−1), and the intrinsic switching field H0 are, within the experimental error, constant for the series. This suggests that the top magnetic layer to first order determines the stability ratio of the AFC media and that MRtAFC can be varied over a large range without decreasing the stability or increasing the write field requirements. © 2001 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Asymmetric nanoscale switching in ferroelectric thin films by scanning force microscopy

A. Gruverman, A. Kholkin, A. Kingon, and H. Tokumoto

Appl. Phys. Lett. 78, 2751 (2001); http://dx.doi.org/10.1063/1.1366644 (3 pages) | Cited 69 times

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Scanning force microscopy (SFM) has been used to perform nanoscale studies of the switching behavior of Pb(Zr, Ti)O3 thin films via the direct observation of their domain structures. The study revealed a significant asymmetry of a switching pattern which is a function of the voltage polarity and original domain structure of individual grains. The phenomenon of asymmetric switching is attributed (1) to the presence of an internal built-in electric field at the bottom interface and (2) to the mechanical stress exerted by the SFM tip. The former effect results in incomplete 180° switching, while the latter effect leads to a 90° rotation of the polarization vector. The resulting shear stress deformation of the grain underneath the tip combined with the applied field effect propels polarization reversal in the adjacent grains. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Dielectric loss and defect mode of SrTiO3 thin films under direct-current bias

Chen Ang, L. E. Cross, Zhi Yu, Ruyan Guo, A. S. Bhalla, and Jian Hua Hao

Appl. Phys. Lett. 78, 2754 (2001); http://dx.doi.org/10.1063/1.1367299 (3 pages) | Cited 24 times

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The dielectric behavior of SrTiO3 thin films prepared by the pulsed-laser deposition technique on SrTiO3 single-crystal substrates is studied under dc electric field. A high dielectric constant maximum εmax( ∼ 2280) and a low-loss tan δ ( ∼ 0.001) are obtained. Compared with the observation in SrTiO3 single crystals, an additional dielectric loss peak with frequency dispersion is observed around 150 K (at 1 kHz). With increasing dc bias, the peak is suppressed and finally disappears at ∼350 kV/cm; however, the temperature at which the peak occurs is independent of electric field. The possible physical mechanism of the peak is briefly discussed. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity

Charge dynamics in silicon nitride/silicon oxide double layers

Xiaoqing Zhang and Gerhard M. Sessler

Appl. Phys. Lett. 78, 2757 (2001); http://dx.doi.org/10.1063/1.1369387 (3 pages) | Cited 9 times

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Transport of positive charge deposited by a corona discharge on the open nitride surface of a silicon nitride (150 nm)/silicon oxide (300 nm) double layer on silicon substrate is studied by determining the location of the charge centroid with a capacitance–voltage method used in conjunction with surface-potential measurements. At temperatures of about 400 °C, the charge is mobile in the nitride and a large part of it is eventually trapped at the nitride/oxide interface while some of the charge reaches the substrate through the oxide. Indications are that at this temperature the mean free path of positive charges in the nitride and oxide layers is comparable to the layer thicknesses, but much shorter in the nitride at lower temperatures. © 2001 American Institute of Physics.
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73.61.Ng Insulators
52.77.Dq Plasma-based ion implantation and deposition
73.40.Cg Contact resistance, contact potential
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Fabrication of <5 nm width lines in poly(methylmethacrylate) resist using a water:isopropyl alcohol developer and ultrasonically-assisted development

Shazia Yasin, D. G. Hasko, and H. Ahmed

Appl. Phys. Lett. 78, 2760 (2001); http://dx.doi.org/10.1063/1.1369615 (3 pages) | Cited 66 times

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We report on the fabrication of 3–4 nm wide continuous lines in a positive tone electron beam resist poly(methylmethacrylate) on a solid substrate. This narrow linewidth was made possible through the use of a nonsolvent-based developer system, water:isopropyl alcohol, together with ultrasonically-assisted development, which reduced the effective development time thus limiting the swelling of the unexposed resist. This combination of solvent system and development technique results in a smaller radius of gyration in the developing polymer molecules and in a wider exposure dose latitude compared to conventional processing and so allows ultrasmall features to be reproduced. © 2001 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Scanning tunneling microscope-induced modification of Ag films and nanowire arrays on Cu(100) surfaces

S. M. York and F. M. Leibsle

Appl. Phys. Lett. 78, 2763 (2001); http://dx.doi.org/10.1063/1.1369618 (3 pages) | Cited 3 times

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We demonstrate the ability to use scanning tunneling microscopy to create nanometer-scale pits on Ag films grown on Cu(100) substrates. Atomic resolution images show that the Ag structures are intact within these pits. We also demonstrate how we can selectively modify segments of Ag nanowire arrays grown on atomic nitrogen modified Cu(100) surfaces. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.16.Ta Atom manipulation
68.35.B- Structure of clean surfaces (and surface reconstruction)
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