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22 Dec 2003

Volume 83, Issue 25, pp. 5121-5321

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 5310 (2003); http://dx.doi.org/10.1063/1.1635070 (3 pages)

Z. G. Chiragwandi, O. Nur, M. Willander, and N. Calander
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Intersubband spectroscopy of doped and undoped GaN/AlN quantum wells grown by molecular-beam epitaxy

A. Helman, M. Tchernycheva, A. Lusson, E. Warde, F. H. Julien, Kh. Moumanis, G. Fishman, E. Monroy, B. Daudin, D. Le Si Dang, E. Bellet-Amalric, and D. Jalabert

Appl. Phys. Lett. 83, 5196 (2003); http://dx.doi.org/10.1063/1.1635985 (3 pages) | Cited 46 times

Online Publication Date: 17 December 2003

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We report experimental and theoretical results on interband and intersubband transitions in GaN quantum wells with strained AlN barriers. All of the samples are grown by molecular-beam epitaxy on sapphire (0001) substrates. The results show that even at room temperature, strong electron localization occurs in the plane of the quantum wells due to the combined effect of monolayer thickness fluctuations and the high internal field in the GaN layers. We also demonstrate that the intersubband absorption is systematically blueshifted in n-doped quantum wells with respect to nominally undoped samples as a result of strong many-body effects, namely the exchange interaction. The results for both undoped and doped quantum wells are in good agreement with simulations. © 2003 American Institute of Physics.
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78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
71.70.Gm Exchange interactions

Monocrystalline YBa2Cu3O7−x thin films on vicinal SrTiO3 (001) substrates

J. Matthijn Dekkers, Guus Rijnders, Sybolt Harkema, Henk Jan H. Smilde, Hans Hilgenkamp, Horst Rogalla, and Dave H. A. Blank

Appl. Phys. Lett. 83, 5199 (2003); http://dx.doi.org/10.1063/1.1633010 (3 pages) | Cited 16 times

Online Publication Date: 17 December 2003

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The correlation between the vicinal properties of SrTiO3 (001) substrates and the twinning in YBa2Cu3O7−x thin films grown by pulsed-laser deposition is studied using x-ray diffraction with reciprocal space mapping. The vicinal properties, i.e., angle and in-plane orientation, play a significant role in the anisotropic strain starting at the interface between substrate surface and film, and affect the twin behavior of YBa2Cu3O7−x. On substrates having an [110] in-plane orientation of the step edges, a completely preferred twin pair is observed if the vicinal angle is increased to 0.60°. Whereas on substrates having their step edges oriented along one of the crystallographic axis, the films exhibit a detwinning as the vicinal angle increases. For α = 1.10° a maximum detwinned, i.e., monocrystalline film is obtained. At this angle, the diffusion length of YBa2Cu3O7−x during the growth matches the terrace length of SrTiO3. Up to this specific angle, the films are grown perpendicular to the optical instead of the crystallographic surface. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
74.72.-h Cuprate superconductors
68.60.Bs Mechanical and acoustical properties
81.15.Fg Pulsed laser ablation deposition
61.72.Mm Grain and twin boundaries
74.78.-w Superconducting films and low-dimensional structures
68.35.Gy Mechanical properties; surface strains

Nucleation and growth in bulk metallic glass under high pressure investigated using in situ x-ray diffraction

W. H. Wang, P. Wen, D. Q. Zhao, M. X. Pan, T. Okada, and W. Utsumi

Appl. Phys. Lett. 83, 5202 (2003); http://dx.doi.org/10.1063/1.1636517 (3 pages) | Cited 7 times

Online Publication Date: 17 December 2003

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The effects of pressure up to 8.3 GPa on nucleation and growth in a Zr57Nb5Cu15.5Ni12.5Al10 bulk glass-forming alloy during heating, isothermal annealing, and cooling processes are investigated using in situ x-ray diffraction with synchrotron radiation. The metallic glass shows markedly different crystallization behaviors for different heat treatments under high pressure. Heating under high pressure can stabilize the supercooled liquid state. Isothermal high pressure annealing leads to nanocrystallization. The glass forming ability of the alloy can be enhanced by high pressure during cooling process. The effects of pressure on the nucleation and growth are discussed based on the nucleation theory. © 2003 American Institute of Physics.
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61.43.Fs Glasses
62.50.-p High-pressure effects in solids and liquids
81.40.Gh Other heat and thermomechanical treatments

Growth of quantum fortress structures in Si1−xGex/Si via combinatorial deposition

Thomas E. Vandervelde, Piyush Kumar, Takeshi Kobayashi, Jennifer L. Gray, Tim Pernell, Jerrold A. Floro, Robert Hull, and John C. Bean

Appl. Phys. Lett. 83, 5205 (2003); http://dx.doi.org/10.1063/1.1636268 (3 pages) | Cited 19 times

Online Publication Date: 17 December 2003

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This study details the evolution of morphologies in the Si1−xGex/Si system, under kinetically controlled conditions of 550 °C growth temperature and 1 Å/s growth rate. We find that, with increasing film thickness and Ge fraction, a series of three-dimensional structures develop, starting from pits, and leading to quantum fortresses and ridges. The quantum fortress structures are of special significance because of their potential application in quantum cellular automata. We establish approximate boundaries in the parameter space of film thickness and Ge fraction, in which these structures form. We present a simple model, based on kinetics and strain, to explain the observed structures. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.35.Ct Interface structure and roughness

4H-polytype AlN grown on 4H-SiC(11math0) substrate by polytype replication

N. Onojima, J. Suda, T. Kimoto, and H. Matsunami

Appl. Phys. Lett. 83, 5208 (2003); http://dx.doi.org/10.1063/1.1636533 (3 pages) | Cited 24 times

Online Publication Date: 17 December 2003

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4H-polytype AlN has been grown on a 4H-SiC substrate with the (11math0) face via plasma-assisted molecular-beam epitaxy. The microscopic structure of the AlN/4H-SiC interface was examined using high-resolution transmission electron microscopy, and the polytype replication of the 4H structure from the 4H-SiC(11math0) substrate was evidently confirmed. The x-ray rocking curve of (11math0) diffraction for the single crystalline 4H-AlN epilayer exhibited a very small linewidth of 90 arc sec, suggesting noticeably small tilting around the [11math0] direction. The excellent crystalline quality is probably owing to the polytype matching between the 4H-AlN epilayer and the 4H-SiC substrate, which resulted in remarkable reduction of defects at the interface. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.35.Ct Interface structure and roughness

Interface formation and defect structures in epitaxial La2Zr2O7 thin films on (111) Si

J. W. Seo, J. Fompeyrine, A. Guiller, G. Norga, C. Marchiori, H. Siegwart, and J.-P. Locquet

Appl. Phys. Lett. 83, 5211 (2003); http://dx.doi.org/10.1063/1.1635966 (3 pages) | Cited 33 times

Online Publication Date: 17 December 2003

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We have studied the growth of epitaxial La2Zr2O7 thin films on (111) Si. Although the interface structure can be strongly affected by the Si oxidation during the deposition process, epitaxial growth of La2Zr2O7 was obtained. A detailed study by means of transmission electron microscopy reveals two types of structures (pyrochlore and fluorite) with the same average chemical composition but strong differences in reactivity and interface formation. The structural complexity of the ordered pyrochlore structure seems to prevent excess oxygen diffusion and interfacial SiO2 formation. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)

Peculiar surface deformation of sapphire: Numerical simulation of nanoindentation

R. Nowak, T. Manninen, K. Heiskanen, T. Sekino, A. Hikasa, K. Niihara, and T. Takagi

Appl. Phys. Lett. 83, 5214 (2003); http://dx.doi.org/10.1063/1.1635983 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2003

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This report addresses the origin of peculiar anisotropic deformation of sapphire. The three-dimensional finite element simulation of the contact between spherical indenter and elastically anisotropic solid allowed us to analyze stress under the tip that penetrates in the (10math0) and (0001) planes, and consequently, to localize those regions in which particular deformation mechanisms are likely to be activated. This approach contrasts the available models of “hardness anisotropy,” which routinely apply a modified uniaxial-stress approach to this essentially three-dimensional, nonisotropic contact problem. The calculated results are in agreement with the microscopic inspection of impressions; that is, the surface features reflect the distribution of stress. The computations made it also possible to evaluate the actual radius of the tip (nominally 5 μm ball). © 2003 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
02.70.Dh Finite-element and Galerkin methods
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
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Quantum conductance of carbon nanotube peapods

Young-Gui Yoon, Mario S. C. Mazzoni, and Steven G. Louie

Appl. Phys. Lett. 83, 5217 (2003); http://dx.doi.org/10.1063/1.1633680 (3 pages) | Cited 11 times

Online Publication Date: 17 December 2003

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We present a first-principles study of the quantum conductance of hybrid nanotube systems consisting of single-walled carbon nanotubes (SWCNTs) encapsulating either an isolated single C60 molecule or a chain of C60 molecules (nanotube peapods). The calculations show a rather weak bonding interaction between the fullerenes and the SWCNTs. The conductance of a (10,10) SWCNT with a single C60 molecule is virtually unaffected at the Fermi level, but exhibits quantized resonant reductions at the molecular levels. The nanotube peapod arrangement gives rise to high density of states for the fullerene highest occupied molecular orbital and lowest unoccupied molecular orbital bands. © 2003 American Institute of Physics.
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73.63.Fg Nanotubes
73.23.-b Electronic transport in mesoscopic systems
72.80.Rj Fullerenes and related materials
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Tx Fullerenes and related materials; intercalation compounds
71.15.-m Methods of electronic structure calculations

Suppression of D’yakonov–Perel spin relaxation in InAs and InSb by n-type doping at 300 K

P. Murzyn, C. R. Pidgeon, P. J. Phillips, M. Merrick, K. L. Litvinenko, J. Allam, B. N. Murdin, T. Ashley, J. H. Jefferson, A. Miller, and L. F. Cohen

Appl. Phys. Lett. 83, 5220 (2003); http://dx.doi.org/10.1063/1.1635659 (3 pages) | Cited 8 times

Online Publication Date: 17 December 2003

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We have made direct pump-probe measurements of spin lifetimes in intrinsic and degenerate n-InAs at 300 K. In particular, we measure remarkably long spin lifetimes (τs ∼ 1.6 ns) for near-degenerate epilayers of n-InAs. For intrinsic material, we determine τs∼20 ps, in agreement with other workers. There are two main models that have been invoked for describing spin relaxation in narrow-gap semiconductors: the D’yakonov–Perel (DP) model and the Elliott–Yafet (EY) model. For intrinsic material, the DP model is believed to dominate in III–V materials above 77 K, in agreement with our results. We show that in the presence of strong n-type doping, the DP relaxation is suppressed both by the degeneracy condition and by electron–electron scattering, and that the EY model then dominates for the n-type material. We show that this same process is also responsible for a hitherto unexplained lengthening of τs with n-type doping in our earlier measurements of n-InSb. © 2003 American Institute of Physics.
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72.25.Rb Spin relaxation and scattering
72.25.Dc Spin polarized transport in semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
76.30.-v Electron paramagnetic resonance and relaxation
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Charge detrapping in HfO2 high-κ gate dielectric stacks

E. P. Gusev and C. P. D’Emic

Appl. Phys. Lett. 83, 5223 (2003); http://dx.doi.org/10.1063/1.1633332 (3 pages) | Cited 34 times

Online Publication Date: 17 December 2003

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We investigated the kinetics of charge detrapping in high-κ gate stacks fabricated with ultrathin HfO2 dielectric films grown by atomic layer deposition and a polycrystalline silicon gate electrode. It was observed that charge trapped after electron injection in the high-κ stack was unstable and slowly decayed over time. The decay does not follow a simple first-order exponential law suggesting complex detrapping mechanism(s), possibly involving more than one type of trap present in the stack. The detrapping rate was found to depend strongly on gate voltage, temperature, and light illumination. © 2003 American Institute of Physics.
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73.61.Ng Insulators

Bandgap states in transition-metal (Sc, Y, Zr, and Nb)-doped Al2O3

Ranju Jung, Jae-Cheol Lee, Ye-Won So, Tae-Won Noh, S.-J. Oh, Jong-Cheol Lee, and Hyun-Joon Shin

Appl. Phys. Lett. 83, 5226 (2003); http://dx.doi.org/10.1063/1.1635656 (3 pages) | Cited 9 times

Online Publication Date: 17 December 2003

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We have investigated the electronic structure of transition-metal (TM = Sc, Y, Zr, and Nb)-doped Al2O3 by x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). In valence bands of these TM-doped Al2O3 measured by XPS, the highest occupied levels and the shapes of valence bands are almost unchanged from the pure alumina. On the other hand, XAS spectra obtained at the oxygen K-edge show that Nb- and Zr-doped Al2O3 show localized d states in the bandgap below the conduction band minimum, while Y- and Sc-doped Al2O3 have d states inside the conduction band of the original Al2O3. This implies that Y- and Sc-doped Al2O3 will show little bandgap degradation and maintain the same band offset as silica at the Si interface, and can serve as promising candidates for an alternative gate oxide. © 2003 American Institute of Physics.
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71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.Dm X-ray absorption spectra
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Time-resolved carrier tunneling in nanocrystalline silicon/amorphous silicon dioxide superlattices

V. Duzhko and L. Tsybeskov

Appl. Phys. Lett. 83, 5229 (2003); http://dx.doi.org/10.1063/1.1630151 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2003

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Eight period nanocrystalline Si/amorphous SiO2 superlattices with Si nanocrystals of ∼5 nm diameter and tunnel-transparent (1.6–1.8-nm-thick) layers of SiO2 reveal a sharp resonance in conductivity at a low (∼0.8 V) applied bias. The performed measurements of time-resolved photocurrent decay show two distinctly different components. A fast, temperature-independent decay dominates at the applied bias close to the resonant conditions. Slower, temperature-dependent photocurrent decay becomes dominant at higher (>1.5 V) voltages. The observed fast photocurrent transient is associated with resonant hole tunneling throughout nanocrystalline Si superlattices. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
78.47.-p Spectroscopy of solid state dynamics
73.61.Cw Elemental semiconductors

Low-frequency noise and radiation response of metal-oxide-semiconductor transistors with Al2O3/SiOxNy/Si(100) gate stacks

H. D. Xiong, D. M. Fleetwood, J. A. Felix, E. P. Gusev, and C. D’Emic

Appl. Phys. Lett. 83, 5232 (2003); http://dx.doi.org/10.1063/1.1635071 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2003

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Low-frequency noise and irradiation response are studied for n-channel metal-oxide-semiconductor field-effect transistors with Al2O3/SiOxNy/Si(100) gate stacks. Radiation-induced threshold-voltage shifts and low-frequency noise increase with dose and decrease with postirradiation annealing. The border trap density in the gate dielectric inferred from the noise measurements is significantly higher than that typically observed in thermal SiO2. Similarly, the effective radiation-induced-hole trapping efficiency in Al2O3 gate dielectrics is significantly higher than for SiO2 gate dielectrics of comparable thickness. The low-frequency noise in these high-κ devices can be described well by a number fluctuation model. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Ht Other nonmetals
61.82.-d Radiation effects on specific materials
73.50.Td Noise processes and phenomena

Low-temperature, in situ tunable, uniaxial stress measurements in semiconductors using a piezoelectric actuator

M. Shayegan, K. Karrai, Y. P. Shkolnikov, K. Vakili, E. P. De Poortere, and S. Manus

Appl. Phys. Lett. 83, 5235 (2003); http://dx.doi.org/10.1063/1.1635963 (3 pages) | Cited 34 times

Online Publication Date: 17 December 2003

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We demonstrate the use of a piezoelectric actuator to apply, at low temperatures, uniaxial stress in the plane of a two-dimensional electron system confined to a modulation-doped AlAs quantum well. Via the application of stress, which can be tuned in situ and continuously, we control the energies and occupations of the conduction-band minima and the electronic properties of the electron system. We also report measurements of the longitudinal and transverse strain versus bias for the actuator at 300, 77, and 4.2 K. A pronounced hysteresis is observed at 300 and 77 K, while at 4.2 K, strain is nearly linear and shows very little hysteresis with the applied bias. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.65.Fg Quantum wells
81.05.Ea III-V semiconductors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.07.St Quantum wells

High frequency capacitance–voltage characterization of Al2O3/ZrO2/Al2O3 in fully depleted silicon-on-insulator metal–oxide–semiconductor capacitors

N. L. Zhang, Z. T. Song, Q. W. Shen, Y. J. Wu, Q. B. Liu, C. L. Lin, X. Z. Duo, L. R. Zheng, Y. F. Ding, and Z. Q. Zhu

Appl. Phys. Lett. 83, 5238 (2003); http://dx.doi.org/10.1063/1.1579865 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2003

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Al2O3/ZrO2/Al2O3 gate stacks were prepared on ultrathin silicon-on-insulator (SOI) by ultrahigh vacuum electron-beam evaporation and postannealed in N2 at 450 °C for 30 min. A three clear nanolaminate layered structure of Al2O3 (2.1 nm)/ZrO2 (3.5 nm)/Al2O3 (2.3 nm) was observed with high-resolution cross-sectional transmission electron microscopy. High frequency capacitance voltage (C–V) characteristics of the fully depleted (FD) SOI metal–oxide–semiconductor (MOS) capacitor at 1 and 5 MHz were studied. It is the minority carriers that determine the high frequency C–V properties, which are opposite to the case of bulk MOS capacitors. And the series resistance of the SOI is the determinant factor of the high frequency characteristics of the FD SOI MOS capacitors. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing

Doped red organic electroluminescent devices based on a cohost emitter system

Tswen-Hsin Liu, Chung-Yeh Iou, and Chin H. Chen

Appl. Phys. Lett. 83, 5241 (2003); http://dx.doi.org/10.1063/1.1635986 (3 pages) | Cited 52 times

Online Publication Date: 17 December 2003

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We have developed an efficient red emitter in organic light-emitting diodes based on the fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetra-methyljulolidyl-9-enyl)-4H-pyran doped in a cohost emitter system of 5,6,11,12-tetraphenylnathacene/tris(8-hydroxyquinolinato)aluminum which achieved an electroluminescence (EL) efficiency of 4.4 cd/A and 2.1 lm/W at 20 mA/cm2 and 6.8 V, with a near saturated Commission Internationale d’Eclairage coordinates (x = 0.65, y = 0.35). This cohost emitter system has the advantage of alleviating the current-induced fluorescence quenching often encountered in red organic EL devices and greatly improves the EL efficiency over a wide range of drive current conditions. From accelerated degradation tests, a device half-life of about 33 800 h can be projected in this system at an initial device luminance of 100 cd/m2. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
78.60.Fi Electroluminescence
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Magnetic tunnel junctions with ZnSe barriers

Xin Jiang, Alex F. Panchula, and Stuart S. P. Parkin

Appl. Phys. Lett. 83, 5244 (2003); http://dx.doi.org/10.1063/1.1630160 (3 pages) | Cited 15 times

Online Publication Date: 17 December 2003

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Magnetic tunnel junctions with ZnSe barriers were fabricated with a combination of magnetron sputtering, ion beam sputtering, and effusion cell evaporation. Tunneling magnetoresistance values of ∼10% are observed at room temperature. The temperature and barrier thickness dependences of the junction resistance and tunneling magnetoresistance are consistent with a predominant direct tunneling mechanism when the barrier thickness is less than ∼10 nm thick. © 2003 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors

Nanotubes of rare-earth manganese oxide

P. Levy, A. G. Leyva, H. E. Troiani, and R. D. Sánchez

Appl. Phys. Lett. 83, 5247 (2003); http://dx.doi.org/10.1063/1.1635663 (3 pages) | Cited 27 times

Online Publication Date: 17 December 2003

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We report the synthesis of rare-earth manganese-oxide-based nanotubes. The pore wetting technique was used to obtain structures of nominal composition La0.325Pr0.300Ca0.375MnO3 with 800 nm external diameter, 4000 nm length, and wall thickness below 100 nm exhibiting magnetic and magnetoresistive behavior below 200 K, including nonvolatile memory. Walls are found to be formed by small crystals of approximately 20 nm. Structures obtained using different diameter of pores, as small as 100 nm, have a similar aspect ratio. Results show the realization of nanotubes of manganites exhibiting intrinsic phase separation. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
75.47.Lx Magnetic oxides
75.75.-c Magnetic properties of nanostructures

The role of the cooperative Jahn–Teller effect in the charge-ordered La1−xCaxMnO3 (0.5 ⩽ x ⩽ 0.87) manganites

R. K. Zheng, G. Li, A. N. Tang, Y. Yang, W. Wang, X. G. Li, Z. D. Wang, and H. C. Ku

Appl. Phys. Lett. 83, 5250 (2003); http://dx.doi.org/10.1063/1.1635662 (3 pages) | Cited 20 times

Online Publication Date: 17 December 2003

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Based on the magnetoresistance, magnetization, ultrasound, and crystallographic data, we studied the role of the cooperative Jahn–Teller (JT) effect in the charge-ordered (CO) state for La1−xCaxMnO3. We found that, with increasing the fraction of Q3 mode of JT distortion and decreasing that of Q2 mode in the CO state, the magnetic structure evolves from charge-exchange-type to C-type and the orbital ordering changes from 3dx2−r2/3dy2−r2-type to 3dz2−r2-type, with the strength of ferromagnetism and the phase separation tendency being suppressed. At the same time, the stability of the CO state and the cooperative JT lattice distortion increase. These effects imply that the cooperative JT effect with different vibration modes is the key ingredient in understanding the essential physics of the CO state. © 2003 American Institute of Physics.
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71.45.-d Collective effects
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Disk substrate deposition techniques for monodisperse chemically synthesized FePt nanoparticle media

Hiroyoshi Kodama, Satoru Momose, Nobutaka Ihara, Takuya Uzumaki, and Atsushi Tanaka

Appl. Phys. Lett. 83, 5253 (2003); http://dx.doi.org/10.1063/1.1635980 (3 pages) | Cited 20 times

Online Publication Date: 17 December 2003

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Self-assembled FePt nanoparticles hold promise for future ultrahigh-density magnetic recording media because of their high anisotropy and capability to be formed into small and uniform grains. By using a special spin coater, we were able to form a dense array of FePt particles across the entire surface of a 2.5 in. disk substrate. Our method can control the number of layers of FePt nanoparticles. The media deposited with FePt nanoparticles by the spin coater was annealed in a vacuum. We measured read–write properties of the FePt nanoparticle media on a spin stand, and succeeded in detecting a signal of 290 kfci. © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.07.Wx Nanopowders
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Gw Magnetic anisotropy

Elliptic flux-line-cutting critical-state model

C. Romero-Salazar and F. Pérez-Rodríguez

Appl. Phys. Lett. 83, 5256 (2003); http://dx.doi.org/10.1063/1.1635667 (3 pages) | Cited 13 times

Online Publication Date: 17 December 2003

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An anisotropic model for describing the critical state of hard superconductors subjected to crossed and rotating magnetic fields is proposed. © 2003 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.20.-z Theories and models of superconducting state
74.40.-n Fluctuation phenomena

Influence of interface alloying on the magnetic properties of Co/Pd multilayers

J. Carrey, A. E. Berkowitz, W. F. Egelhoff, and David J. Smith

Appl. Phys. Lett. 83, 5259 (2003); http://dx.doi.org/10.1063/1.1635660 (3 pages) | Cited 11 times

Online Publication Date: 17 December 2003

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The origin of perpendicular anisotropy in Co/Pd multilayers has been investigated. We examined this question by studying multilayers in which the total equivalent thicknesses of Co and Pd are kept constant, but in which the Co/Pd interface is progressively alloyed using codeposition of the two elements. The multilayers have the structure: [(0.3 nm Co codeposited with y nm Pd)/(2.0−y) nm Pd]15, with y = 0, 0.1, 0.3, 0.5, 1, 1.5, 2.0. X-ray diffraction confirms that the total thicknesses of the samples and their overall Co/Pd ratios stay constant. Magnetic properties are almost unaffected by alloying up to y = 0.5 nm, suggesting that the interface of the usual Co/Pd multilayer could be modeled by a mix of 0.3 nm of Co with 0.5 nm of Pd embedded between 2 monolayers of Pd. Using this model and reasonable assumptions about the strain and magnetostriction of a Co-Pd alloy, we show that the magnetoelastic effect yields a perpendicular anisotropy between 2.3×105 and 3.5×105 J/m3. The perpendicular anisotropy estimated in our samples (1.5×105 J/m3) can thus be satisfactorily explained. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Fx Diffusion; interface formation
75.50.Ss Magnetic recording materials
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
81.15.Cd Deposition by sputtering
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Role of Ga2O3 template thickness and gadolinium mole fraction in GdxGa0.4−xO0.6/Ga2O3 gate dielectric stacks on GaAs

M. Passlack, N. Medendorp, R. Gregory, and D. Braddock

Appl. Phys. Lett. 83, 5262 (2003); http://dx.doi.org/10.1063/1.1635068 (3 pages) | Cited 29 times

Online Publication Date: 17 December 2003

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Amorphous GdxGa0.4−xO0.6/Ga2O3 gate dielectric stacks have been grown onto the GaAs(001) surface by molecular beam epitaxy using high temperature effusion cells. The Ga2O3 template thickness and the Gd mole percent have been systematically varied from 73 to 0 Å and from 8.8 to 22 at. % (0.088 ⩽ x ⩽ 0.22), respectively. Oxide/n-type GaAs samples have been characterized by high-frequency capacitance–voltage measurements. Optimum gate oxide stack and oxide/GaAs interface properties are obtained with a Ga2O3 template thickness of 9–11 Å and a minimum Gd mole percent of 15–17 at. %. While gate oxide films with thicker Ga2O3 templates and/or lower Gd mole fraction show kinks in capacitance–voltage measurements attributed to charge trapping in the oxide, thinner Ga2O3 templates lead to strong stretch-out of capacitance–voltage curves indicating severely degraded oxide/GaAs interface properties. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

High-speed switching of nanoscale ferroelectric domains in congruent single-crystal LiTaO3

Kenjiro Fujimoto and Yasuo Cho

Appl. Phys. Lett. 83, 5265 (2003); http://dx.doi.org/10.1063/1.1635961 (3 pages) | Cited 23 times

Online Publication Date: 17 December 2003

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The nanodomain reversal characteristics of congruent LiTaO3 (CLT) single crystal are investigated. It is found that fast nanosecond domain switching can be achieved by reducing the sample thickness, even for CLT, which contains many Li vacancy defects that pin domain-wall movement. As an example, the authors obtain a polarization inverted domain dot with a radius of 7.9 nm by application of a 4 ns 10 V pulse. These results demonstrate that the speed of polarization reversal is closely related to the thickness of the medium. © 2003 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
77.80.Dj Domain structure; hysteresis
85.50.Gk Non-volatile ferroelectric memories

Nonlinear behavior of piezoelectric lead zinc niobate–lead titanate single crystals under ac electric fields and dc bias

Wei Ren, Shi-Fang Liu, and Binu K. Mukherjee

Appl. Phys. Lett. 83, 5268 (2003); http://dx.doi.org/10.1063/1.1635069 (3 pages) | Cited 5 times

Online Publication Date: 17 December 2003

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The nonlinear behaviors of the dielectric and piezoelectric responses of 〈001〉 oriented Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) single crystals for x = 4.5% and 8% have been investigated as a function of ac electric fields and dc bias fields. At relatively low applied fields, the polarization and strain of PZN-PT single crystals poled along the 〈001〉 direction show little hysteresis and have a linear dependence on the applied field, which is a consequence of engineered domain stability. Hence the dielectric and piezoelectric coefficients of the material do not exhibit any field dependence. However, when the applied electric field exceeds a threshold value, the strain and dielectric responses become nonlinear. The dielectric and piezoelectric constants are a function of the applied field, and hysteresis loops are observed. The results suggest that the observed nonlinear behavior in the PZN-PT single crystals is caused by domain motion/switching in response to the large ac fields. A positive dc bias effectively stabilizes the domain configuration in the crystals and enhances the linear response. The threshold field, at the onset of nonlinearity, is a linear function of the dc bias field in the field range investigated. © 2003 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
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