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8 Sep 2008

Volume 93, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages)

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou
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Beneficial effect of La on band offsets in Ge/high-κ insulator structures with GeO2 and La2O3 interlayers

V. V. Afanas’ev, A. Stesmans, G. Mavrou, and A. Dimoulas

Appl. Phys. Lett. 93, 102115 (2008); http://dx.doi.org/10.1063/1.2972123 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2008

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The electron energy band alignment between (100)Ge and high-κ oxide insulators (ZrO2,Gd2O3,La2Hf2O7) grown by the atomic beam deposition method is analyzed using photoemission of electrons from the Ge valence band. Formation of a thin GeO2 passivation layer before the high-κ deposition is found to significantly reduce the barrier for electrons. However, when La2O3 is deposited as an interlayer, it strongly reacts with the Ge substrate to form a La–Ge–O germanate at the interface, which is found to retain a high barrier for the carriers in Ge.
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79.60.Jv Interfaces; heterostructures; nanostructures
77.55.-g Dielectric thin films
71.20.-b Electron density of states and band structure of crystalline solids

In-plane band gap modulation investigated by secondary electron imaging of GaAsN/GaAsN:H heterostructures

L. Felisari, V. Grillo, F. Martelli, R. Trotta, A. Polimeni, M. Capizzi, F. Jabeen, and L. Mariucci

Appl. Phys. Lett. 93, 102116 (2008); http://dx.doi.org/10.1063/1.2981689 (3 pages) | Cited 7 times

Online Publication Date: 12 September 2008

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GaAsN/GaAsN:H in-plane heterostructures have been investigated by secondary electron (SE) imaging in a field-emission scanning electron microscope. Adjacent GaAsN and GaAsN:H regions show a quite different SE image brightness due to the band gap energy difference between H-free and H-irradiated GaAsN. These findings provide a useful means to characterize the lateral diffusion of H and well support secondary ion mass spectroscopy results regarding the importance of a low hydrogenation temperature in order to obtain sharply defined in-plane heterostructures.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
66.30.H- Self-diffusion and ionic conduction in nonmetals
71.20.Nr Semiconductor compounds
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Two dimensionally patterned GaNxAs1−x/GaAs nanostructures using N+ implantation followed by pulsed laser melting

Taeseok Kim, Michael J. Aziz, and Venkatesh Narayanamurti

Appl. Phys. Lett. 93, 102117 (2008); http://dx.doi.org/10.1063/1.2982424 (3 pages) | Cited 3 times

Online Publication Date: 12 September 2008

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We present measurements on two dimensionally patterned GaNxAs1−x dots fabricated in a GaAs matrix using ion implantation followed by pulsed laser melting and rapid thermal annealing. The lithographically patterned GaNxAs1−x regions are imaged by ballistic electron emission microscopy (BEEM). By analyzing the BEEM spectra of the locally confined dots, we observe the decrease in the Schottky barrier height with nitrogen incorporation. The second derivatives of BEEM currents from unpatterned GaNxAs1−x films exhibit a decrease in Γ-like thresholds as the nitrogen concentration increases. The composition dependence of the thresholds agrees well with that of previously studied low temperature molecular beam epitaxy grown alloys.
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61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
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A study of multirow-per-track bit patterned media by spinstand testing and magnetic force microscopy

Y. J. Chen, T. L. Huang, S. H. Leong, S. B. Hu, K. W. Ng, Z. M. Yuan, B. Y. Zong, B. Liu, and V. Ng

Appl. Phys. Lett. 93, 102501 (2008); http://dx.doi.org/10.1063/1.2978326 (3 pages) | Cited 9 times

Online Publication Date: 8 September 2008

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We propose and demonstrate a concept of multirow-per-track bit patterned media (BPM) recording to overcome the problems encountered with the conventional one-row-per-track design. Focused ion beam was used on continuous granular perpendicular magnetic media to fabricate the prototype structures consisting of birow tracks with sub-100-nm single domain magnetic islands with the two rows of islands to be interleaved along the track direction, as well as an additional nonmagnetic spacer band between adjacent birow tracks for further bit aspect ratio (BAR) ≥ 2 adjustment. Readback from such birow tracks with a two-row-wide read head was performed by dynamic spinstand testing. The proposed concept BPM provides many advantages including higher linear recording density (under the same lithographic limit), therefore enabling a higher data rate and a greater BAR ≥ 2 for better integration with head design and servocontrol, as well as allowing the use of wider thus larger recording heads to improve writing efficiency for high density recording.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials

Study of spin fluctuations in Ni3±xAl1∓x using point contact Andreev reflection spectroscopy

Sourin Mukhopadhyay, Sudesh Kumar Dhar, and Pratap Raychaudhuri

Appl. Phys. Lett. 93, 102502 (2008); http://dx.doi.org/10.1063/1.2979687 (3 pages) | Cited 1 time

Online Publication Date: 8 September 2008

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We report point contact Andreev reflection (PCAR) spectroscopy studies on Ni3±xAl1∓x with composition range spanning the ferromagnetic to paramagnetic phase boundary. PCAR studies performed using Nb tip as counterelectrode reveal that the superconducting quasiparticle lifetime (τ) and superconducting energy gap (Δ) decrease with increasing spin fluctuation in the normal metal electrode. Our study reveals that PCAR could be a useful probe to study spin fluctuations in systems that are on the verge of magnetic instability.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.20.Mn Nonconventional mechanisms

Converse magnetoelectric effects on heterotype electrostrain-piezopermeability composites

X. Fang, N. Zhang, and Z. L. Wang

Appl. Phys. Lett. 93, 102503 (2008); http://dx.doi.org/10.1063/1.2979699 (3 pages) | Cited 8 times

Online Publication Date: 8 September 2008

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By using the product effect of electrostrain and piezopermeability, a heterotype composite consisting of a bar of Pb(Zr,Ti)O3 and a ring of MnZn ferrite with higher permeability has been developed, and its converse magnetoelectric effect has been investigated. Under a constant electric field of 5 kV/cm, about 20% electric-field-induced changes in permeability and impedance have been observed with the composite device over a wide frequency band. The electric-field dependence of the permeability and impedance shows a ferroelectric relaxation behavior. This composite is a candidate material for electrically controlled magnetic devices.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Lf Composite materials
77.65.-j Piezoelectricity and electromechanical effects
77.22.Gm Dielectric loss and relaxation
77.80.-e Ferroelectricity and antiferroelectricity

A microwave nonlinear phase shifter

Alexey B. Ustinov and Boris A. Kalinikos

Appl. Phys. Lett. 93, 102504 (2008); http://dx.doi.org/10.1063/1.2980022 (3 pages) | Cited 4 times

Online Publication Date: 8 September 2008

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A microwave nonlinear phase shifter is described. It is a device producing a power-dependent phase shift of microwave signals. The device is fabricated with a ferrite film which serves as a waveguide for magnetostatic spin waves. A nonlinear phase shift of the carrier spin waves appearing under increasing their power is the key phenomenon in the device operation. A theoretical model for the nonlinear phase shifter is presented. The model provides a good description for the experimentally obtained performance characteristics of the device.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Irreversible magnetic exchange-spring processes in antiferromagnetic exchange-coupled bilayer systems

Guang-hua Guo, Guang-fu Zhang, San-yuan Song, D. W. Wang, G. J. Bowden, and P. A. J. de Groot

Appl. Phys. Lett. 93, 102505 (2008); http://dx.doi.org/10.1063/1.2972028 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2008

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The demagnetization processes of antiferromagnetic exchange-coupled hard-soft bilayer structures have been studied using a one-dimensional atomic chain model, taking into account the anisotropies of both hard and soft layers. It is found that for very thin soft layers, magnetization/demagnetization involves typical reversible exchange-spring behavior. However as the thickness t of the soft layer is increased, there is a crossover point tc, after which the exchange spring becomes irreversible. The value of the critical thickness tc is determined inter alia by the magnetic anisotropy of the soft layer. However, an important feature of the irreversible exchange spring is the formation of a large angle domain wall, realized immediately at the bending field transition.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics

Magnetization switching behavior with microwave assistance

S. Okamoto, N. Kikuchi, and O. Kitakami

Appl. Phys. Lett. 93, 102506 (2008); http://dx.doi.org/10.1063/1.2977474 (3 pages) | Cited 17 times

Online Publication Date: 9 September 2008

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Microwave assisted switching of magnetization has become one of the key techniques for future advanced recording. We have studied the magnetization switching behaviors excited by circularly and linearly polarized microwaves based on the Landau–Lifshitz–Gilbert equation. The precessional motion of magnetization is excited by the microwave, resulting in significant reduction of the irreversible reversal field. The reversal takes place through very complicated precessional motion, which proceeds via nearly steady precession at an early stage, subsequent unstable motion, and finally abrupt irreversible switching. We discuss the detailed effect of microwave polarization on magnetization reversals.
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75.60.Jk Magnetization reversal mechanisms
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Combinatorial investigation of magnetostriction in Fe–Ga and Fe–Ga–Al

Jason R. Hattrick-Simpers, Dwight Hunter, Corneliu M. Craciunescu, Kyu Sung Jang, Makoto Murakami, James Cullen, Manfred Wuttig, Ichiro Takeuchi, Samuel E. Lofland, Leonid Benderksy, Noble Woo, Robert Bruce Van Dover, Toshiya Takahashi, and Yasubumi Furuya

Appl. Phys. Lett. 93, 102507 (2008); http://dx.doi.org/10.1063/1.2980034 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2008

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A high-throughput high-sensitivity optical technique for measuring magnetostriction of thin-film composition-spread samples has been developed. It determines the magnetostriction by measuring the induced deflection of micromachined cantilever unimorph samples. Magnetostriction measurements have been performed on as-deposited Fe–Ga and Fe–Ga–Al thin-film composition spreads. The thin-film Fe–Ga spreads display a similar compositional variation of magnetostriction as bulk. A previously undiscovered peak in magnetostriction at low Ga content was also observed and attributed to a maximum in the magnetocrystalline anisotropy. Magnetostrictive mapping of the Fe–Ga–Al ternary system reveals the possibility of substituting up to 8 at. % Al in Fe70Ga30 without significant degradation of magnetostriction.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Relationship between symmetry and scaling of spin torque thermal switching barrier

Xiaobin Wang, Wenzhong Zhu, Haiwen Xi, and Dimitar Dimitrov

Appl. Phys. Lett. 93, 102508 (2008); http://dx.doi.org/10.1063/1.2976781 (3 pages)

Online Publication Date: 10 September 2008

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This letter shows that the scaling relationship between the thermal reversal barrier and the (spin polarized) current density in the limit of low current density strongly depends on magnetization dynamics symmetry. This is quite different from magnetic field induced thermal switching. Our analysis demonstrates that the widely used scaling relationship between switching time and current density needs to be modified to include magnetization dynamics symmetry effects. A formula for a thermal reversal barrier symmetry correction factor is given in the limit of low current density. The implications for the estimation of magnetic element thermal stability are discussed.
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72.25.-b Spin polarized transport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

M. J. Carey, N. Smith, S. Maat, and J. R. Childress

Appl. Phys. Lett. 93, 102509 (2008); http://dx.doi.org/10.1063/1.2978328 (3 pages) | Cited 6 times

Online Publication Date: 10 September 2008

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It is shown that the maximum stable output of a current-perpendicular to the plane giant magnetoresistance sensor is increased significantly by using a synthetic-ferrimagnet free layer, provided the electron current flows from free layer to reference layer. This free layer allows a larger magnetoresistance ratio for a given free layer magnetic moment, and in addition results in a greater than threefold increase in the critical current, above which spin-torque instability of the free layer occurs. In read heads with net free layer moments equivalent to only 4.5 nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2×108 A/cm2.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.75.Ss Magnetic field sensors using spin polarized transport
75.50.Gg Ferrimagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.47.De Giant magnetoresistance

Hydrothermal epitaxy of ZnO:Co diluted magnetic semiconducting single crystalline films

Y. B. Zhang, S. Li, G. K. L. Goh, and S. Tripathy

Appl. Phys. Lett. 93, 102510 (2008); http://dx.doi.org/10.1063/1.2981518 (3 pages) | Cited 7 times

Online Publication Date: 10 September 2008

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ZnO:Co films with room-temperature ferromagnetism have been hydrothermally grown in water at 90 °C using a ZnO seed layer on MgAl2O4 (111) substrates. High-resolution x-ray diffraction shows an epitaxial ZnO:Co single crystalline film with an out-of-plane orientation of ZnO:Co〈001〉∥MgAl2O4〈111〉 and an in-plane orientation of ZnO:Co[110]∥MgAl2O4[−1−12] and ZnO:Co[−110]∥MgAl2O4[−110]. A saturation magnetization of 0.83 emu/cm3 and a coercivity of 40 Oe were obtained for the epitaxial Zn0.98Co0.02O film at room temperature. Hydrogen unintentionally incorporated in the hydrothermal synthesis is suggested to contribute to the ferromagnetic properties in the diluted magnetic semiconductor by enhancing carrier concentration as a shallow donor.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Grain size reduction for perpendicular magnetic recording media using an Ar-ion etched Ru seedlayer

Hua Yuan and David E. Laughlin

Appl. Phys. Lett. 93, 102511 (2008); http://dx.doi.org/10.1063/1.2979685 (3 pages) | Cited 3 times

Online Publication Date: 11 September 2008

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We report an approach to reduce grain size for perpendicular media by using an Ar-ion etched Ru seedlayer. The surface etching affects the microstructure of the subsequent high pressure deposited Ru2+SiO2 interlayer and magnetic layer, whose grain size can be controlled. SiO2 in the interlayer plays a more important role in grain size reduction on the etched seedlayer than the as-grown seedlayer. Small Ru2 grains ∼ 3.9 nm and magnetic grains ∼ 5.3 nm with uniform distribution have been obtained. Thinner Ru grain boundaries with reduced size could be the cause of nonideal one-to-one grain growth and degraded magnetic properties.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.65.Cf Surface cleaning, etching, patterning
75.50.Ss Magnetic recording materials
81.30.Bx Phase diagrams of metals, alloys, and oxides

Reversibility of magnetostructural transition and associated magnetocaloric effect in Ni–Mn–In–Co

Jian Liu, Nils Scheerbaum, Julia Lyubina, and Oliver Gutfleisch

Appl. Phys. Lett. 93, 102512 (2008); http://dx.doi.org/10.1063/1.2981210 (3 pages) | Cited 22 times

Online Publication Date: 12 September 2008

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By analyzing isothermal magnetization curves under magnetic field cycling, the reversibility of the magnetostructural transition was investigated in Ni–Mn–In–Co in form of bulk sample and melt-spun ribbons. The hysteresis of thermally/magnetically induced martensitic transformation plays an important role in the reversibility of the magnetostructural transition. In ribbons with a large hysteresis of 18 K, residual field-induced austenite is present after removing the magnetic field, while, in the bulk sample, the magnetostructural transition is reversible at moderate temperatures due to a relatively smaller hysteresis of 8 K. Additionally, the magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition, especially for the ribbons.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

An amplifier concept for spintronics

Y. Acremann, X. W. Yu, A. A. Tulapurkar, A. Scherz, V. Chembrolu, J. A. Katine, M. J. Carey, H. C. Siegmann, and J. Stöhr

Appl. Phys. Lett. 93, 102513 (2008); http://dx.doi.org/10.1063/1.2977964 (3 pages) | Cited 1 time

Online Publication Date: 12 September 2008

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Typical spin-dependent devices proposed for information processing lack one of the most important features provided by charge based logic: they do not provide gain. In this letter we show the basic concept of a spin amplifier and propose ways to amplify a spin current at room temperature.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds

A. Cannizzo, M. Leone, W. Gawelda, E. Portuondo-Campa, A. Callegari, F. van Mourik, and M. Chergui

Appl. Phys. Lett. 93, 102901 (2008); http://dx.doi.org/10.1063/1.2975965 (3 pages) | Cited 2 times

Online Publication Date: 8 September 2008

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We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank–Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼ 10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrational redistribution.
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61.72.J- Point defects and defect clusters
78.47.-p Spectroscopy of solid state dynamics

A multisized piezoelectric microcantilever biosensor array for the quantitative analysis of mass and surface stress

Sanghun Shin, Jun Pyo Kim, Sang Jun Sim, and Jaichan Lee

Appl. Phys. Lett. 93, 102902 (2008); http://dx.doi.org/10.1063/1.2977869 (3 pages) | Cited 14 times

Online Publication Date: 8 September 2008

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A multisized piezoelectric microcantilever biosensor array with scaling down in two dimensions is presented as a multifunctional resonant cantilever-based sensor platform. The multisized microcantilever array allowed simultaneous sensing of the surface stress as well as mass. The adsorption-induced surface stress and resulting spring constant change were analyzed in the multisized microcantilever array, and a mass sensitivity in the femtogram regime was demonstrated. The array sensor was used to immobilize human IgG on its cantilever surface, suggesting that the dynamic and simultaneous analysis of both adsorption-induced mass and the surface stress is feasible.
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87.80.Ek Mechanical and micromechanical techniques
87.14.E- Proteins
87.15.R- Reactions and kinetics

Electron injection of SrTiO3/Si interfacial layer

J. H. Ma, J. L. Sun, J. H. Qin, Y. H. Gao, T. Lin, H. Shen, F. W. Shi, X. J. Meng, J. H. Chu, S. J. Liu, and J. Li

Appl. Phys. Lett. 93, 102903 (2008); http://dx.doi.org/10.1063/1.2980019 (3 pages)

Online Publication Date: 8 September 2008

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The electrical properties of the SrTiO3(STO)/Si interfacial layer were studied by measuring STO metal-insulator-semiconductor (MIS) structure. The C-V measurements showed that there existed electron injection at the STO/Si interface under the higher sweep voltages. The electron injection behavior was analyzed and discussed in detail. By analyzing the voltage distribution of the semiconductor Si, the insulator STO, and the STO/Si interfacial layer in MIS structure, the electron injection electric field of interfacial layer was estimated to be about 5.5 MV/cm.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Investigation of substrate-induced strain effects in La0.7Ca0.15Sr0.15MnO3 thin films using ferroelectric polarization and the converse piezoelectric effect

R. K. Zheng, Y. Jiang, Y. Wang, H. L. W. Chan, C. L. Choy, and H. S. Luo

Appl. Phys. Lett. 93, 102904 (2008); http://dx.doi.org/10.1063/1.2979688 (3 pages) | Cited 10 times

Online Publication Date: 9 September 2008

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We have fabricated manganite film/ferroelectric crystal heterostructures by growing La0.7Ca0.15Sr0.15MnO3 (LCSMO) films on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-PT) single-crystal substrates. The efficient mechanical coupling at the interface, originated from ferroelectric polarization or the converse piezoelectric effect in the PMN-PT substrate, gives rise to large changes in the strain state, electrical resistance, magnetoresistance, and insulator-to-metal transition temperature (TP) of the film. We interpreted all these changes in terms of substrate-induced strain, which modifies the tetragonal distortion of MnO6 octahedra and the electron-lattice coupling strength in the film. Quantitative relationships between TP and induced strain in the LCSMO film have been established.
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77.55.-g Dielectric thin films
77.65.Ly Strain-induced piezoelectric fields
71.30.+h Metal-insulator transitions and other electronic transitions
72.20.My Galvanomagnetic and other magnetotransport effects

Elastic softening and central peaks in BaTiO3 single crystals above the cubic-tetragonal phase-transition temperature

J.-H. Ko, S. Kojima, T.-Y. Koo, J. H. Jung, C. J. Won, and N. J. Hur

Appl. Phys. Lett. 93, 102905 (2008); http://dx.doi.org/10.1063/1.2980444 (3 pages) | Cited 24 times

Online Publication Date: 9 September 2008

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A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO3) single crystals by Brillouin scattering study and was found to correlate with the softening of the longitudinal acoustic mode and the increase in the hypersonic damping. These observations support the existence of polar percursors and their electrostrictive coupling with the strain caused by the acoustic waves, consistent with former studies evidencing off-centered Ti ions in the high-symmetry cubic phase. A critical slowing down has been clearly observed in the vicinity of the cubic-tetragonal phase transition, indicating order-disorder component contributes to the phase transition of BaTiO3.
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77.80.B- Phase transitions and Curie point
78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
62.65.+k Acoustical properties of solids
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

HfO2-based InP n-channel metal-oxide-semiconductor field-effect transistors and metal-oxide-semiconductor capacitors using a germanium interfacial passivation layer

Hyoung-Sub Kim, I. Ok, M. Zhang, F. Zhu, S. Park, J. Yum, H. Zhao, Jack C. Lee, and Prashant Majhi

Appl. Phys. Lett. 93, 102906 (2008); http://dx.doi.org/10.1063/1.2961119 (3 pages) | Cited 10 times

Online Publication Date: 11 September 2008

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In this letter, we present our experimental results of HfO2-based n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and metal-oxide-semiconductor capacitors (MOSCAPs) on indium phosphide (InP) substrates using a thin germanium (Ge) interfacial passivation layer (IPL). We found that MOSCAPs on n-InP substrates showed good C-V characteristics such as a small capacitance equivalent thickness (14 Å), a small frequency dispersion (<10 % and <200 mV), and a low dielectric leakage current ( ∼ 5×10−4 A/cm2 at Vg = 1.5 V), whereas MOSCAPs on p-InP exhibited poor characteristics, implying severe Fermi level pinning. It was also found that InP was more vulnerable to a high temperature process such that C-V curves showed a characteristic “bump” and inversion capacitance at relatively high frequencies. From n-channel MOSFETs on a semi-insulating InP substrate using Ge IPL, HfO2, and TaN gate electrodes, excellent electrical characteristics such as a large transconductance (9.3 mS/mm) and large drain currents (12.3 mA/mm at Vd = 2 V and Vg = Vth+2V) were achieved, which are comparable to other works.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Anisotropic thermal conductivity of the Aurivillus phase, bismuth titanate (Bi4Ti3O12): A natural nanostructured superlattice

Yang Shen, David R. Clarke, and Paul A. Fuierer

Appl. Phys. Lett. 93, 102907 (2008); http://dx.doi.org/10.1063/1.2975163 (3 pages) | Cited 15 times

Online Publication Date: 11 September 2008

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The thermal conductivity of c-axis textured polycrystalline perovskite Bi4Ti3O12 and random polycrystalline material is reported up to 1000 °C. Based on measurements of the thermal diffusivity, density, and specific heat, the thermal conductivity is lower along the c-axis than in the a-b plane by almost a factor of 2, and the anisotropy persists up to at least 1000 °C despite a change in the crystal structure at 675 °C. The exceptionally low (1.0 W/mK), temperature-independent conductivity perpendicular to the perovskite layer structure is attributed to the density difference between the pseudoperovskite and fluorite blocks in the unit cell, forming a natural nanostructured superlattice.
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73.63.Bd Nanocrystalline materials
65.40.Ba Heat capacity
66.30.-h Diffusion in solids
61.46.Hk Nanocrystals

Dielectric response and tunability of a dielectric-paraelectric composite

K. Zhou, S. A. Boggs, R. Ramprasad, M. Aindow, C. Erkey, and S. P. Alpay

Appl. Phys. Lett. 93, 102908 (2008); http://dx.doi.org/10.1063/1.2982086 (3 pages) | Cited 22 times

Online Publication Date: 12 September 2008

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A theoretical study was carried out to determine the dielectric response and tunability of a composite consisting of a linear, low-loss dielectric matrix with uniformly sized, randomly distributed paraelectric Ba0.60Sr0.40TiO3 (BST 60/40) particles as functions of the volume fraction and size of the particles. The field dependence of the polarization and the dielectric response of the inclusions are specified through a nonlinear thermodynamic model and then incorporated into a two-dimensional finite element analysis. Near the percolation threshold for BST particles ( ∼ 27% to 45% depending on the particle size), high dielectric tunabilities with a lower effective permittivity than monolithic BST can be realized.
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77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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Field emitter density control effect on emission current density by Ag–Cu alloy coating on carbon nanotubes

Seung Youb Lee, Won Chel Choi, Cheolho Jeon, Chong-Yun Park, Ji Hoon Yang, and Myeung Hoi Kwon

Appl. Phys. Lett. 93, 103101 (2008); http://dx.doi.org/10.1063/1.2972120 (3 pages) | Cited 9 times

Online Publication Date: 8 September 2008

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We have investigated the morphological evolution and improvement in field emission properties of carbon nanotube (CNT) emitters coated with an Ag–Cu alloy (ACa). Vertically aligned multiwalled CNTs (MWCNTs) were synthesized by direct current-plasma enhanced chemical vapor deposition. The MWCNTs were then coated with ACa by dc-magnetron sputtering and then annealed. Scanning electron microscopy revealed an increase in the size of the ACa droplets on the CNTs after thermal annealing, and a decrease in the emitter density with increasing deposition time. The emitter density was controlled by the amount of ACa with high surface tension and annealing. A lower turn-on voltage (1.18 V/μm) and higher emission current density of 588.9 μA/cm2 at 5.0 V/μm were achieved from the sample containing ACa droplets with an average radius of 500 nm.
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85.45.Db Field emitters and arrays, cold electron emitters
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