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12 Jun 2006

Volume 88, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 243101 (2006); http://dx.doi.org/10.1063/1.2211007 (3 pages)

G. H. Du, F. Xu, Z. Y. Yuan, and G. Van Tendeloo
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Charge injection in polymer light-emitting diodes based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-phenylene)]

A. Yusoff, Z. Hassan, and H. Abu Hassan

Appl. Phys. Lett. 88, 242109 (2006); http://dx.doi.org/10.1063/1.2212065 (3 pages)

Online Publication Date: 14 June 2006

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In this letter, the electrical properties of polymer light-emitting diodes based on polyfluorene derivative, named poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-phenylene)] (F8P), were studied. Indium tin oxide (ITO)/polymer/metal [magnesium (Mg) and calcium (Ca)] structures were used to study the effect of the barrier height on the charge injection at the polymer/metal (anode) interfaces. For ITO/F8P/Mg devices, strong temperature influence on the dc conductivity was observed in the forward direction, and afterwards, in the reverse direction, the conductivity was totally temperature independent. On the other hand, ITO/F8P/Ca devices presented temperature-dependent conductivities for both polarities.
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85.60.Jb Light-emitting devices

Electrical characterization of defects introduced during electron beam deposition of Pd Schottky contacts on n-type Ge

F. D. Auret, W. E. Meyer, S. Coelho, and M. Hayes

Appl. Phys. Lett. 88, 242110 (2006); http://dx.doi.org/10.1063/1.2213203 (3 pages) | Cited 13 times

Online Publication Date: 14 June 2006

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We have investigated by deep level transient spectroscopy the hole and electron trap defects introduced in n-type Ge during electron beam deposition (EBD) of Pd Schottky contacts. We have also compared the properties of these defects with those introduced in the same material during high-energy electron irradiation. Our results show that EBD introduces several electron and hole traps at and near the surface of Ge. The main defect introduced during EBD has electronic properties similar to those of the V–Sb complex, or E center, introduced during high-energy particle irradiation of Ge. This defect has two levels E0.38 and H0.30 that correspond to its (−−,−) and (−,0) charge states.
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71.55.Cn Elemental semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Fe Electron and positron radiation effects
73.40.Ns Metal-nonmetal contacts

Laser-induced shock wave stimulated doping of CdTe crystals

V. A. Gnatyuk, T. Aoki, and Y. Hatanaka

Appl. Phys. Lett. 88, 242111 (2006); http://dx.doi.org/10.1063/1.2213511 (3 pages) | Cited 7 times

Online Publication Date: 14 June 2006

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Action of a laser-induced plane shock wave has been considered as the mechanism of doping of CdTe surface region with In. CdTe crystals coated with a relatively thick In film were subjected to irradiation with KrF excimer laser pulses. The In film was not completely evaporated under irradiation and it served further as an electrode in the fabrication of nuclear radiation detectors. Dopant atoms, implicated by laser-induced stress and shock waves, penetrated into CdTe. An In-enriched region was formed and a built-in p-n junction arose at the depth where a stress wave was converted to a shock wave.
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61.72.uj III-V and II-VI semiconductors
42.62.-b Laser applications
62.50.-p High-pressure effects in solids and liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
79.20.Ds Laser-beam impact phenomena

High temperature nitrogen annealing induced interstitial oxygen precipitation in silicon epitaxial layer on heavily arsenic-doped silicon wafer

Q. Wang, Manmohan Daggubati, Rong Yu, and Xiao Feng Zhang

Appl. Phys. Lett. 88, 242112 (2006); http://dx.doi.org/10.1063/1.2213516 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2006

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High temperature nitrogen annealing induced interstitial oxygen (Oi) precipitation has been investigated in silicon epitaxial layers (epilayers) grown on heavily arsenic-doped Czochralski silicon wafers. Both transmission electron microscopy and secondary ion mass spectrometry data indicate a strong Oi precipitation and/or segregation in the subsurface of epilayers annealed in N2 at 1200 °C. The Oi precipitates have needlelike morphology with {111} habit planes along ⟨110⟩ directions. This precipitation is facilitated by thermal nitridation-produced vacancies or nitrogen-vacancy complexes and is sensitive to annealing conditions. Annealing in Ar or in N2 at temperature <1125 °C results in no epilayer subsurface Oi precipitation.
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61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation

Organic thin-film transistors with high mobilities and low operating voltages based on 5,5′-bis-biphenyl-dithieno[3,2-b:2′,3′-d]thiophene semiconductor and polymer gate dielectric

Yanming Sun, Yunqi Liu, Yongqiang Ma, Chongan Di, Ying Wang, Weiping Wu, Gui Yu, Wenping Hu, and Daoben Zhu

Appl. Phys. Lett. 88, 242113 (2006); http://dx.doi.org/10.1063/1.2209213 (3 pages) | Cited 22 times

Online Publication Date: 15 June 2006

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Employing 5,5′-bis-biphenyl-dithieno[3,2-b:2′,3′-d]thiophene (BPDTT) as semiconducting layer and poly(vinyl alcohol) (PVA) as gate dielectric layer, we have fabricated organic thin-film transistors. These devices exhibit excellent field-effect performances with a high mobility of up to 0.6 cm2/V s and a very low operating voltage (<1 V) at room temperature. The single crystal of BPDTT was grown and analyzed. The high performances are mainly attributed to the close herringbone packing of BPDTT molecules and the high homogeneity between PVA and BPDTT molecules.
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85.30.Tv Field effect devices

Large image potential effects in Si/SrTiO3 and Si/HfO2 two-dimensional quantum well structures

T. A. S. Pereira, J. A. K. Freire, V. N. Freire, G. A. Farias, L. M. R. Scolfaro, J. R. Leite, and E. F. da Silva

Appl. Phys. Lett. 88, 242114 (2006); http://dx.doi.org/10.1063/1.2212279 (3 pages) | Cited 3 times

Online Publication Date: 15 June 2006

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Charge image effects on the confinement properties of Si/SrTiO3 and Si/HfO2 two-dimensional quantum wells are studied. The combination of strong dielectric mismatch and band offset of the layers gives rise to structured confinement potentials, which can trap carriers close to the interfaces in Si/SrTiO3 but not in Si/HfO2 two-dimensional quantum wells. The charge image blueshifts strongly (a few hundred meV) the carrier recombination energy, comparable to the shift related to the well width shortening due to actual graded interfaces.
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78.67.De Quantum wells
73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Excitation and spin-transport of hot holes in ballistic hole magnetic microscopy

E. Haq, T. Banerjee, M. H. Siekman, J. C. Lodder, and R. Jansen

Appl. Phys. Lett. 88, 242501 (2006); http://dx.doi.org/10.1063/1.2212066 (3 pages) | Cited 1 time

Online Publication Date: 12 June 2006

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A hybrid structure of a ferromagnetic Co/Au/Ni81Fe19 trilayer on p-type silicon is used to probe the excitation of electron-hole pairs in a ferromagnet during inelastic decay of hot electrons and the subsequent spin-dependent transport of the excited holes into the valence band of the p-type Si collector. The hole current is remarkably sensitive to magnetic fields, with a magnetocurrent of up to 250% and, unexpectedly, with a positive sign. We determine effective attenuation lengths and their magnetic field and bias voltage dependence.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.25.Mk Spin transport through interfaces

Room-temperature ferromagnetism in (Mn, N)-codoped ZnO thin films prepared by reactive magnetron cosputtering

H. Y. Xu, Y. C. Liu, C. S. Xu, Y. X. Liu, C. L. Shao, and R. Mu

Appl. Phys. Lett. 88, 242502 (2006); http://dx.doi.org/10.1063/1.2213929 (3 pages) | Cited 39 times

Online Publication Date: 12 June 2006

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(Mn, N)-codoped ZnO films were grown on fused silica substrates by reactive magnetron cosputtering. X-ray diffraction measurements reveal that the films have the single-phase wurtzite structure with c-axis preferred orientation. X-ray photoelectron spectroscopy studies indicate the incorporation of both divalent Mn2+ and trivalent N3− ions into ZnO lattice. Acceptor doping with nitrogen partly compensates the “native donors,” which results in a low electron concentration of 3.16×1016 cm−3 though p-type conductivity is not achieved. (Mn, N)-codoped ZnO films show significant ferromagnetism with Curie temperature above 300 K. The mechanism of ferromagnetic coupling in codoped ZnO is discussed based on a bound magnetic polaron model.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Cd Deposition by sputtering

Effect of oxygen annealing on Mn doped ZnO diluted magnetic semiconductors

S. Ramachandran, J. Narayan, and J. T. Prater

Appl. Phys. Lett. 88, 242503 (2006); http://dx.doi.org/10.1063/1.2213930 (3 pages) | Cited 35 times

Online Publication Date: 12 June 2006

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We have investigated the properties of Zn1−xMnxO (x = 0.01–0.1) thin films grown on c-plane sapphire single crystals by pulsed laser deposition. The electrical, magnetic, optical, and microstructural properties of these thin films have been characterized systematically, with a primary focus on establishing a correlation between magnetic properties and electrical conductivity. We have shown that this system exhibits ferromagnetism at room temperature when in the conducting as-deposited state. However, upon high temperature annealing in excess oxygen, the samples become insulating and exhibit nonferromagnetic behavior at room temperature. Thus, it is possible to tune ferromagnetism in Zn1−xMnxO diluted magnetic semiconductors by controlling the concentrations of oxygen vacancies and substitutional Mn dopants.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters

Low field driven latching-type Bi3Fe5O12/Gd3Ga5O12 magneto-optical display

A. M. Grishin, S. I. Khartsev, and S. Bonetti

Appl. Phys. Lett. 88, 242504 (2006); http://dx.doi.org/10.1063/1.2213973 (3 pages) | Cited 6 times

Online Publication Date: 12 June 2006

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Series of heteroepitaxial all-garnet magneto-optical (MO) Bi3Fe5O12n/Gd3Ga5O12m (BIGn/GGGm, n = 1, 2, 3, 4, 5 and m = 1 and 2 are the numbers of unit cells) nanostructured multilayers have been sintered by pulsed laser deposition technique. Processing parameters and structure of grown films have been optimized to obtain perpendicular magnetic anisotropy and square hysteresis loop with low coercive and saturation magnetic fields. Regular alternating of lattice mismatched BIG and GGG atomic layers inhibited nucleation of misfit dislocations; thus a long range coherent compressive strain was preserved through the whole thickness of BIGn/GGGm multilayer stack. 2.5 μm thick BIG3/GGG2 sample (1200 BIG and 800 GGG unit cells) at λ = 678 nm shows MO Faraday rotation ΘF = ±1.4°, transmittance of 82%, attenuation α = 3400 dB/cm, squareness of magnetization loop (remnant-to-saturation magnetizations ratio) as high as 92%, and saturation and coercive fields as low as 56 and 25 Oe, respectively. MO remanence (latching capability) enables application of nanostructured garnet as a magnetic relief replicator/visualizer and as a material for low power consuming displays.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Magnetic/nonmagnetic/magnetic tunnel junction based on hybrid organic Langmuir-Blodgett-films

T. X. Wang, H. X. Wei, Z. M. Zeng, X. F. Han, Z. M. Hong, and G. Q. Shi

Appl. Phys. Lett. 88, 242505 (2006); http://dx.doi.org/10.1063/1.2213177 (3 pages) | Cited 21 times

Online Publication Date: 14 June 2006

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The magnetic/organic/magnetic spin valve structure has been fabricated with π-conjugated molecular pyrrole derivative 3-hexadecyl pyrrole as the spacer layer by Langmuir-Blodgett (LB) technique. It shows giant magnetoresistance (MR) as large as 20% at room temperature, demonstrating that low-energy electrons can traverse the molecular barrier while remaining spin polarized. The spin transport across organic structures is diffusive from its current-voltage (I-V) curve under bias voltage up to 1 V. The MR value decreased when the LB-film layer increased. The telegraph noise and the layer dependent MR value suggest that the spin-polarized transport signals can be degraded by localized states in the molecular barriers and barrier quality.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
72.25.Mk Spin transport through interfaces

AlN thin film as waveguide for shear acoustic waves

F. Martin and P. Muralt

Appl. Phys. Lett. 88, 242506 (2006); http://dx.doi.org/10.1063/1.2213510 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2006

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A set of shear acoustic waves in the 78–195 MHz range composed of a surface skimming bulk wave and highly resolved shear acoustic plate modes has been simultaneously excited in a thin ST-cut quartz plate by means of transducers with a 1 μm thick sputtered AlN thin film used as a waveguiding layer. The effect of coating the transducers face with AlN is shown to increase the propagation speed of the first 13 plate modes in the ST-cut quartz, but then to decreases the propagation speed of plate modes higher than the 14th.
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43.20.Mv
43.35.Pt
43.35.Ns
68.60.Bs Mechanical and acoustical properties
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
43.58.Kr

Evidence of oxygen vacancy enhanced room-temperature ferromagnetism in Co-doped ZnO

H. S. Hsu, J. C. A. Huang, Y. H. Huang, Y. F. Liao, M. Z. Lin, C. H. Lee, J. F. Lee, S. F. Chen, L. Y. Lai, and C. P. Liu

Appl. Phys. Lett. 88, 242507 (2006); http://dx.doi.org/10.1063/1.2212277 (3 pages) | Cited 66 times

Online Publication Date: 16 June 2006

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The annealing effects on structure and magnetism for Co-doped ZnO films under air, Ar, and Ar/H2 atmospheres at 250 °C have been systematically investigated. Room-temperature ferromagnetism has been observed for the as-deposited and annealed films. However, the saturation magnetization (Ms) varied drastically for different annealing processes with Ms ∼ 0.5, 0.2, 0.9, and 1.5 μB/Co for the as-deposited, air-annealed, Ar-annealed, and Ar/H2-annealed films, respectively. The x-ray absorption spectra indicate all these samples show good diluted magnetic semiconductor structures. By comparison of the x-ray near edge spectra with the simulation on Zn K edge, an additional preedge peak appears due likely to the formation of oxygen vacancies. The results show that enhancement (suppression) of ferromagnetism is strongly correlated with the increase (decrease) of oxygen vacancies in ZnO. The upper limit of the oxygen vacancy density of the Ar/H2-annealed film can be estimated by simulation to be about 1×1021 cm−3.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Thermal limits on field alignment of nanoparticle FePt media

James A. Bain and William F. Egelhoff

Appl. Phys. Lett. 88, 242508 (2006); http://dx.doi.org/10.1063/1.2213515 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2006

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We derive a simple expression for the average angular orientation distribution of ferromagnetic FePt particles in an applied field in thermal equilibrium. This system is closely related to the Langevin expression for paramagnetic susceptibility, which computes the average orientation of particles in this configuration. We note that practical fields are unlikely to be able to provide well-aligned arrays of the smallest thermally stable FePt particles at room temperature and that this has significant consequences for self-organized nanoparticle magnetic media. It suggests that it may be difficult to obtain an acceptable degree of perfection in orientation for the smallest particles.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.20.En Metals and alloys
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
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Thermal effects on domain orientation of tetragonal piezoelectrics studied by in situ x-ray diffraction

Wonyoung Chang, Alexander H. King, and Keith J. Bowman

Appl. Phys. Lett. 88, 242901 (2006); http://dx.doi.org/10.1063/1.2213952 (3 pages) | Cited 13 times

Online Publication Date: 12 June 2006

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Thermal effects on domain orientation in tetragonal lead zirconate titanate (PZT) and lead titanate (PT) have been investigated by using in situ x-ray diffraction with an area detector. In the case of a soft PZT, it is found that the texture parameter called multiples of a random distribution (MRD) initially increases with temperature up to approximately 100 °C and then falls to unity at temperatures approaching the Curie temperature, whereas the MRD of hard PZT and PT initially undergoes a smaller increase or no change. The relationship between the mechanical strain energy and domain wall mobility with temperature is discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
77.65.-j Piezoelectricity and electromechanical effects

Converse magnetoelectric effect in laminated composites of PMN–PT single crystal and Terfenol-D alloy

Yanmin Jia, Siu Wing Or, Helen Lai Wa Chan, Xiangyong Zhao, and Haosu Luo

Appl. Phys. Lett. 88, 242902 (2006); http://dx.doi.org/10.1063/1.2212054 (3 pages) | Cited 45 times

Online Publication Date: 14 June 2006

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We have found experimentally and theoretically that laminated composites comprising one layer of length-magnetized Tb0.3Dy0.7Fe1.92 (Terfenol-D) magnetostrictive alloy sandwiched between two layers of thickness-polarized, electro-parallel-connected 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) piezoelectric single crystal have a large converse magnetoelectric effect characterized by a large magnetic induction in response to an applied ac voltage. The reported converse magnetoelectric effect originates from the product of the converse piezoelectric effect in the PMN–PT layers and the converse magnetostrictive effect in the Terfenol-D layer. Large converse magnetoelectric coefficient in excess of 105 mG/V is obtained in the composites at a low magnetic bias field of 170 Oe. The measured magnetic induction has an excellent linear relationship to the applied ac voltage with amplitude varying from 50 to 160 V. These made the composites to be a promising material for direct realization of core-free magnetic flux control devices.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
77.65.-j Piezoelectricity and electromechanical effects

Positive and negative magnetocapacitance in magnetic nanoparticle systems

G. Lawes, R. Tackett, B. Adhikary, R. Naik, O. Masala, and R. Seshadri

Appl. Phys. Lett. 88, 242903 (2006); http://dx.doi.org/10.1063/1.2213194 (3 pages) | Cited 8 times

Online Publication Date: 14 June 2006

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The dielectric properties of MnFe2O4 and γ-Fe2O3 magnetic nanoparticles embedded in insulating matrices were investigated. The samples showed frequency dependent dielectric anomalies coincident with the magnetic blocking temperature and significant magnetocapacitance above this blocking temperature, as large as 0.4% at H = 10 kOe. For both samples the magnetic field induced change in dielectric constant at high temperatures was proportional to the square of the sample magnetization. These measurements suggest that the dielectric properties of magnetic nanoparticles are closely related to the disposition of magnetic moments in the system. This magnetodielectric coupling is believed to arise from extrinsic effects, which are discussed in light of recent work relating magnetoresistive and magnetocapacitive behaviors.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Synthesis and ferroelectric properties of epitaxial BiFeO3 thin films grown by sputtering

R. R. Das, D. M. Kim, S. H. Baek, C. B. Eom, F. Zavaliche, S. Y. Yang, R. Ramesh, Y. B. Chen, X. Q. Pan, X. Ke, M. S. Rzchowski, and S. K. Streiffer

Appl. Phys. Lett. 88, 242904 (2006); http://dx.doi.org/10.1063/1.2213347 (3 pages) | Cited 91 times

Online Publication Date: 15 June 2006

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We have grown epitaxial BiFeO3 thin films with smooth surfaces on (001), (101), and (111) SrTiO3 substrates using sputtering. Four-circle x-ray diffraction and cross-sectional transmission electron microscopy show that the BiFeO3 thin films have rhombohedral symmetry although small monoclinic distortions have not been ruled out. Stripe ferroelectric domains oriented perpendicular to the substrate miscut direction and free of impurity phase are observed in BiFeO3 on high miscut (4°) (001) SrTiO3, which attributes to a relatively high value of remanent polarization ( ∼ 71 μC/cm2). Films grown on low miscut (0.8°) SrTiO3 have a small amount of impure phase α-Fe2O3 which contributes to lower the polarization values ( ∼ 63 μC/cm2). The BiFeO3 films grown on (101) and (111) SrTiO3 exhibited remanent polarizations of 86 and 98 μC/cm2, respectively.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
81.15.Cd Deposition by sputtering

Temperature-dependent degradation mechanisms of channel mobility in ZrO2-gated n-channel metal-oxide-semiconductor field-effect transistors

Ming-Tsong Wang, Bonds Yi-Yi Cheng, and Joseph Ya-min Lee

Appl. Phys. Lett. 88, 242905 (2006); http://dx.doi.org/10.1063/1.2211307 (3 pages) | Cited 5 times

Online Publication Date: 15 June 2006

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The mobility degradation mechanism of n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) with ZrO2 gate dielectric was studied. The temperature dependence of device characteristics was studied in the temperature range from 300 to 420 K. The electron mobility limited by surface roughness is proportional to Eeff−0.68 in the fields of 0.5<Eeff<2 MV/cm at 300 K. The electron mobility limited by phonon scattering is proportional to T−3.0 at the effective normal field Eeff of 0.8 MV/cm between 300 and 420 K. Soft optical phonon scattering was used to explain the extra source of phonon scattering in ZrO2-gated n-MOSFETs.
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85.30.Tv Field effect devices

Magnetic-field-dependent dielectric constant in La2/3Ca1/3MnO3

J. Rivas, J. Mira, B. Rivas-Murias, A. Fondado, J. Dec, W. Kleemann, and M. A. Señarís-Rodríguez

Appl. Phys. Lett. 88, 242906 (2006); http://dx.doi.org/10.1063/1.2213513 (3 pages) | Cited 20 times

Online Publication Date: 15 June 2006

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We report a rather high dependence of the dielectric permittivity on the magnetic field in La2/3Ca1/3MnO3. The variation is maximum at around 270 K, little above the Curie temperature TC, and it reaches a 35% under only 0.5 T. We attribute this phenomenon to the space-charge or interfacial polarization produced between the insulator and the metallic regions segregated intrinsically in the material above TC.
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75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ej Polarization and depolarization
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides

Characterizing xBa(Mg1/3Ta2/3)O3+(1−x)Ba(Mg1/3Nb2/3)O3 microwave ceramics using extended x-ray absorption fine structure method

P.-J. Chang, C.-T. Chia, I.-N. Lin, J.-F. Lee, C. M. Lin, and K. T. Wu

Appl. Phys. Lett. 88, 242907 (2006); http://dx.doi.org/10.1063/1.2213514 (3 pages) | Cited 3 times

Online Publication Date: 15 June 2006

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The structures of TaO6 and NbO6 oxygen octahedra in xBa(Mg1/3Ta2/3)O3+(1−x)Ba(Mg1/3Nb2/3)O3 perovskite ceramics with x = 0, 0.25, 0.50, 0.75, and 1.0 were investigated by the extended x-ray absorption fine structure method. The decline in the microwave dielectric constant as x increases is caused mainly by the decrease of the mean volume of the oxygen octahedra, regardless of the 1:2 ordered structure and the distortion of the oxygen octahedron. The low Qf values of the TaO6 and NbO6 mixed samples are caused by not only the degrading of the 1:2 ordered structure but also the distortion of oxygen octahedral cages.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
78.70.Dm X-ray absorption spectra
84.40.-x Radiowave and microwave (including millimeter wave) technology

Irreversible extinction of ferroelectric polarization in P(VDF-TrFE) thin films upon melting and recrystallization

Youn Jung Park, Seok Ju Kang, Cheolmin Park, Kap Jin Kim, Han Sup Lee, Moon Sook Lee, U-In Chung, and In Jun Park

Appl. Phys. Lett. 88, 242908 (2006); http://dx.doi.org/10.1063/1.2207831 (3 pages) | Cited 26 times

Online Publication Date: 16 June 2006

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We observed the irreversible extinction of ferroelectric polarization in spun coated poly(vinylidene fluoride-co-trifluoroethylene) thin films upon melting and recrystallization. We investigate the alteration of the ferroelectric properties correlated with the preferred polymer crystal orientation with respect to the electrodes using grazing incident scattering, spectroscopy, and electron microscopes. Heat treatment above melting point gave rise to the significant reduction of the ferroelectric performance mainly caused by the modification of molecular orientation of polymer crystals whose c and b axes are perpendicular and parallel to the electrode surface, respectively, leading to almost zero effective electric field.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments

Influence of Mn and Nb dopants on electric properties of chemical-solution-deposited BiFeO3 films

Chin-Feng Chung, Jen-Po Lin, and Jenn-Ming Wu

Appl. Phys. Lett. 88, 242909 (2006); http://dx.doi.org/10.1063/1.2214138 (3 pages) | Cited 77 times

Online Publication Date: 16 June 2006

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Polycrystalline Mn-doped, Nb-doped, and pure BiFeO3 (BFO) films were fabricated via chemical solution deposition (CSD) method. Influence of Mn and Nb dopants on electric properties of BFO films were studied. The current density versus electric field (J-E) characteristics indicated that conduction mechanisms of Mn-doped, Nb-doped, and pure BFO films annealed at 500 °C were Ohmic conduction, grain boundary limited conduction, and space charge limited conduction, respectively. The effect of Mn and Nb dopants on electric properties of BFO films was interpreted by defect chemistry and chemical reaction in the CSD process. The Nb dopant is effective in improving electrical properties of CSD-derived BFO films, while Mn is harmful in this respect.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Jp Dielectric breakdown and space-charge effects
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.up Other materials
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Flowerlike ZnO nanocones and nanowires: Preparation, structure, and luminescence

G. H. Du, F. Xu, Z. Y. Yuan, and G. Van Tendeloo

Appl. Phys. Lett. 88, 243101 (2006); http://dx.doi.org/10.1063/1.2211007 (3 pages) | Cited 24 times

Online Publication Date: 12 June 2006

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Flowerlike ZnO nanocone and nanowire arrays have been grown on a Zn foil via a solution-phase approach at low temperature. The tips of the nanocones are about 70–160 nm in diameter and their roots are as thick as 350 nm; the diameters of the nanowires are around 70–110 nm. Both the nanocones and nanowires grow preferentially along the [0001] direction. Transmission electron microscopy analysis reveals that the surface of the ZnO nanocones is corrugated or protuberant while the nanowires have a smooth surface. Both shapes demonstrate a strong UV luminescence band around 385 nm, and the nanocones also show three weak bands at 421, 484.6, and 532 nm in the blue-green range.
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81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials

Structural evolution of carbon nanotubes in composites under contact sliding stresses

I. Zarudi and L. C. Zhang

Appl. Phys. Lett. 88, 243102 (2006); http://dx.doi.org/10.1063/1.2212063 (3 pages)

Online Publication Date: 12 June 2006

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We discovered a new structural evolution of carbon nanotubes (CNTs) in epoxy composites subjected to contact sliding stresses. Our analysis under high resolution transmission electron microscopy showed that the evolution has three stages which are (a) the bonding breakage of the CNTs, (b) the formation of sinusoidal shells, and (c) the consolidation of nanoparticles. We then explored the evolution mechanisms theoretically.
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61.46.Fg Nanotubes
64.70.Nd Structural transitions in nanoscale materials
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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