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24 Oct 2005

Volume 87, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages)

T. Kimura, Y. Otani, and J. Hamrle
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The antimony-vacancy defect in p-type germanium

C. E. Lindberg, J. Lundsgaard Hansen, P. Bomholt, A. Mesli, K. Bonde Nielsen, A. Nylandsted Larsen, and L. Dobaczewski

Appl. Phys. Lett. 87, 172103 (2005); http://dx.doi.org/10.1063/1.2112168 (3 pages) | Cited 20 times

Online Publication Date: 18 October 2005

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Ge-n+p mesa diodes have been produced in 2-Ω cm single crystals using a molecular-beam epitaxy (MBE) process to grow the Sb-doped epitaxial Ge n+-top layer. The diodes are characterized by a leakage current at room temperature of 8×10−4 A/cm2 at a reverse bias of 3 V. The diodes have been used to study irradiation-induced defects in p-type Ge, in particular Sb-related defects, where Sb stems from in-diffusion during the MBE growth. Two lines in the deep level transient spectroscopy (DLTS) spectra are related to the presence of Sb. One of these lines originates from the single-acceptor state of the SbV pair with an enthalpy of ionization of ΔHp = (0.309±0.007) eV, the other from a state with an enthalpy of ionization of ΔHp = (0.095±0.006) eV, which is concluded to be the single donor-charge state of the SbV pair.
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85.30.Kk Junction diodes
81.05.Cy Elemental semiconductors
61.72.J- Point defects and defect clusters
73.61.Cw Elemental semiconductors
71.55.Cn Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities
65.40.G- Other thermodynamical quantities

Structural and transport properties of epitaxial NaxCoO2 thin films

A. Venimadhav, A. Soukiassian, D. A. Tenne, Qi Li, X. X. Xi, D. G. Schlom, R. Arroyave, Z. K. Liu, H. P. Sun, Xiaoqing Pan, Minhyea Lee, and N. P. Ong

Appl. Phys. Lett. 87, 172104 (2005); http://dx.doi.org/10.1063/1.2117619 (3 pages) | Cited 3 times

Online Publication Date: 20 October 2005

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We have studied structural and transport properties of epitaxial NaxCoO2 thin films on (0001) sapphire substrate prepared by topotaxially converting an epitaxial Co3O4 film to NaxCoO2 with annealing in Na vapor. The films are c-axis oriented and in-plane aligned with [10math0]NaxCoO2 rotated by 30° from [10math0] sapphire. Different Na vapor pressures during the annealing resulted in films with different Na concentrations, which showed distinct transport properties.
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68.55.Nq Composition and phase identification
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.61.At Metal and metallic alloys
73.61.Ng Insulators

Comparison of gate and drain current detection of hydrogen at room temperature with AlGaN/GaN high electron mobility transistors

Hung-Ta Wang, B. S. Kang, F. Ren, R. C. Fitch, J. K. Gillespie, N. Moser, G. Jessen, T. Jenkins, R. Dettmer, D. Via, A. Crespo, B. P. Gila, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 87, 172105 (2005); http://dx.doi.org/10.1063/1.2117617 (3 pages) | Cited 21 times

Online Publication Date: 20 October 2005

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Pt-gated AlGaN/GaN high electron mobility transistors can be used as room-temperature hydrogen gas sensors at hydrogen concentrations as low as 100 ppm. A comparison of the changes in drain and gate current-voltage (I-V) characteristics with the introduction of 500 ppm H2 into the measurement ambient shows that monitoring the change in drain-source current provides a wider gate voltage operation range for maximum detection sensitivity and higher total current change than measuring the change in gate current. However, over a narrow gate voltage range, the relative sensitivity of detection by monitoring the gate current changes is up to an order of magnitude larger than that of drain-source current changes. In both cases, the changes are fully reversible in <2–3 min at 25 °C upon removal of the hydrogen from the ambient.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.30.Tv Field effect devices

Lateral electron transport in Cu(In,Ga)Se2 investigated by electro-assisted scanning tunneling microscopy

Manuel J. Romero, Chun-Sheng Jiang, Rommel Noufi, and Mowafak Al-Jassim

Appl. Phys. Lett. 87, 172106 (2005); http://dx.doi.org/10.1063/1.2119422 (3 pages) | Cited 8 times

Online Publication Date: 20 October 2005

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We investigate the lateral electron transport across grain boundaries in Cu(In,Ga)Se2 (CIGS) by a combination of scanning tunneling microscopy (STM) with the excitation provided by the electron beam in electron microscopy—or electro-assisted STM. Using this method, we report evidence for a significant barrier for electron diffusion across grain boundaries in CuGaSe2 (CGS), which is not present in CuInSe2 (CIS). Finally, we discuss the effects of gallium addition.
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61.72.Mm Grain and twin boundaries
73.61.Le Other inorganic semiconductors
07.79.Cz Scanning tunneling microscopes

Shift in low-frequency vibrational spectra of transition-metal zirconium compounds

Jiaguang Han, Fan Wan, Zhiyuan Zhu, Yi Liao, Te Ji, Min Ge, and Zengyan Zhang

Appl. Phys. Lett. 87, 172107 (2005); http://dx.doi.org/10.1063/1.2119419 (3 pages) | Cited 11 times

Online Publication Date: 20 October 2005

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The far-infrared terahertz(THz) spectra of ZrC, ZrN, ZrO2, and ZrF4 have been measured using terahertz time-domain spectroscopy. The characterization of the frequency-dependent power absorption, index of refraction and complex dielectric function in the frequency range 0.1–2.0 THz are obtained. A standard Drude-Lorentz model gives a good fit on the transmission measurement results. We first observe the shift in the low-frequency vibrational spectra of different zirconium compounds. We analyze that the influence of the anion on the vibration modes causes the shift in low-frequency vibrational spectra of zirconic compounds.
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78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices

Production of native donors in ZnO by annealing at high temperature in Zn vapor

L. E. Halliburton, N. C. Giles, N. Y. Garces, Ming Luo, Chunchuan Xu, Lihai Bai, and L. A. Boatner

Appl. Phys. Lett. 87, 172108 (2005); http://dx.doi.org/10.1063/1.2117630 (3 pages) | Cited 42 times

Online Publication Date: 21 October 2005

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Zinc oxide crystals grown by the seeded chemical vapor transport method have been annealed in zinc vapor at 1100 °C for 30 min. These thermochemical reduction treatments produce a deep red coloration in the crystals and increase their n-type electrical conductivity. Electron paramagnetic resonance (EPR), optical absorption, and Hall measurements were used to monitor changes in the crystals. After an anneal, an intense optical absorption band is present that extends from the band edge out to approximately 550 nm, and the EPR signal near g = 1.96 (due to shallow donors and/or conduction-band electrons), the free-carrier absorption, and the Hall electron concentration are all larger. Hydrogen was not present during these anneals, thus leaving oxygen vacancies and zinc interstitials as candidates for the added donors. Neutral oxygen vacancies are produced at high temperature by the additive-coloration mechanism, and are responsible for the broad near-edge absorption band. The observed increase in the number of free carriers is a result of either (1) the formation of zinc interstitials or (2) having the ground state of the neutral oxygen vacancy near the conduction band.
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81.05.Dz II-VI semiconductors
61.72.S- Impurities in crystals
71.55.Gs II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
76.30.Lh Other ions and impurities
78.40.Fy Semiconductors
81.10.Bk Growth from vapor
82.30.-b Specific chemical reactions; reaction mechanisms

Diffusion, activation, and recrystallization of boron implanted in preamorphized and crystalline germanium

A. Satta, E. Simoen, T. Clarysse, T. Janssens, A. Benedetti, B. De Jaeger, M. Meuris, and W. Vandervorst

Appl. Phys. Lett. 87, 172109 (2005); http://dx.doi.org/10.1063/1.2117631 (3 pages) | Cited 53 times

Online Publication Date: 21 October 2005

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We have investigated diffusion and activation of boron implanted with 6 keV energy to a maximum concentration of 8.0×1020 atoms/cm3 in crystalline germanium (c-germanium) and preamorphized germanium, employing rapid thermal annealing in the range of 400–600 °C. As-implanted boron profiles in preamorphized germanium are shallower than the ones in c-germanium due to channeling suppression. While boron diffusion is not observed either in c-germanium or during the germanium regrowth from amorphous state, the boron activation level achieved from the two starting phases is significantly different. A boron activation level of 2.4×1020 atoms/cm3 has been found in regrown germanium, while a level of only 1.2×1019 atoms/cm3 is observed in c-germanium. Remarkably, there is no evidence of any residual extended defectivity at the original crystalline/amorphous interface, when preamorphization is performed.
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81.05.Cy Elemental semiconductors
66.30.J- Diffusion of impurities
81.40.Gh Other heat and thermomechanical treatments
61.72.uf Ge and Si
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing

High mobility ambipolar charge transport in a cross-linked reactive mesogen at room temperature

T. Kreouzis, R. J. Baldwin, M. Shkunov, I. McCulloch, M. Heeney, and W. Zhang

Appl. Phys. Lett. 87, 172110 (2005); http://dx.doi.org/10.1063/1.2117632 (3 pages) | Cited 16 times

Online Publication Date: 21 October 2005

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By photochemically cross linking the molecules of a reactive end group functionalized calamitic liquid crystal (bis(heptylphenyl)-bithiophene-oxetane) in the smectic mesophase, an insoluble rigid molecular network is formed which remains structurally unchanged on cooling to room temperature. The charge transport is investigated by the time-of-flight method and the resulting material shows long-range ( ∼ 10 μm) ambipolar transport with nondispersive field independent hole mobility, μhole = 0.016 cm2/V s and dispersive field dependent electron mobility, typically μelectron = 0.028 cm2/V s (both at 4×104 V cm−1 and at 15 °C). These desirable charge transport properties make this system a promising candidate for organic electronic applications, such as charge transport layers in organic light-emitting diodes and field effect transistors.
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61.30.-v Liquid crystals
72.20.Fr Low-field transport and mobility; piezoresistance

Effect of alloying and cladding on the failure of silver metallization under high temperature and current stressing

E. Misra and T. L. Alford

Appl. Phys. Lett. 87, 172111 (2005); http://dx.doi.org/10.1063/1.2117633 (3 pages) | Cited 4 times

Online Publication Date: 21 October 2005

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Pure Ag layers were cladded with thin alloy (Ag with 3 at. % aluminum) layers to form a [Ag(Al)/Ag/Ag(Al)] structure on SiO2. The effective resistivity of the cladded Ag metallization is slightly greater than pure silver and less than the Ag(Al) alloy metallization. The clad structures showed a nearly 38 times enhancement in electromigration resistance when compared to pure Ag and seven times greater than the Ag(Al) alloy. The enhancement in lifetime of the clad structure was attributed to enhanced thermal stability due to segregation of Al2O3 at the Ag grain boundaries leading to reduced grain size and changes in thermodynamic properties and also reduced atomic mobility because of the topmost layer acting as a passivation layer.
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85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
66.30.Qa Electromigration
81.65.-b Surface treatments

Electron-phonon scattering and ballistic behavior in semiconducting carbon nanotubes

H. Cazin d’Honincthun, S. Galdin-Retailleau, J. Sée, and P. Dollfus

Appl. Phys. Lett. 87, 172112 (2005); http://dx.doi.org/10.1063/1.2119421 (3 pages) | Cited 14 times

Online Publication Date: 21 October 2005

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We study the steady-state and ballistic transport properties of semiconducting zig-zag carbon nanotubes (CNTs) using semiclassical Monte Carlo simulation. Electron-phonon scattering is the only type of interaction included in the model. The band structure and phonon dispersion are derived from that of graphene by the zone folding method. Steady-state drift velocity and low-field mobility are calculated for CNTs with wrapping index ranging from n = 10 to n = 59, i.e., for a diameter range of 0.78−4.62 nm. Principally, a transient analysis of transport under uniform driving field is realized and gives the fraction of ballistic electrons as a function of CNT length and the mean free path (MFP) for acoustic and optical phonons scattering. The probability to have ballistic electrons on a given distance appears to be higher for nanotubes of large diameter and depends on the field applied.
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73.23.Ad Ballistic transport
61.46.-w Structure of nanoscale materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.63.Fg Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems
63.20.K- Phonon interactions
72.20.Fr Low-field transport and mobility; piezoresistance
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Semiconductor-metal hybrid structures as local magnetic-field probes: Magnetoresistance and spatial sensitivity profile

Matthias Holz, Oliver Kronenwerth, and Dirk Grundler

Appl. Phys. Lett. 87, 172501 (2005); http://dx.doi.org/10.1063/1.2108122 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2005

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Tailored nonmagnetic semiconductor-metal hybrid structures exhibit a large magnetoresistance effect in a homogeneous magnetic field. This is the so-called extraordinary magnetoresistance effect. Here, we study numerically the magnetoresistance of such hybrid structures in the inhomogeneous field of a magnetic dot. Surprisingly, the four-point resistance R versus magnetic field B changes its symmetry if compared to the case of a homogeneous field and is strongly dependent on the position of the local magnetic field. Interestingly, the active device area is not defined by the voltage probe separation, but by the positioning of voltage probes and current leads. We find a magnetoresistance effect as large as 18% although only 1/60 of the device area is subject to a small magnetic field of ±50 mT. These results are promising for sensing magnetic-field distributions in the nanoscale regime such as the stray fields of magnetic recording media.
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73.40.Ns Metal-nonmetal contacts
72.20.My Galvanomagnetic and other magnetotransport effects

Epitaxial growth and properties of Zn1−xVxO diluted magnetic semiconductor thin films

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

Appl. Phys. Lett. 87, 172502 (2005); http://dx.doi.org/10.1063/1.2112185 (3 pages) | Cited 25 times

Online Publication Date: 17 October 2005

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Here we report systematic studies on the epitaxial growth and properties of Zn1−xVxO[x=0.001-0.2] thin films deposited onto sapphire c-plane single crystals. The thin films were deposited using pulsed laser deposition technique and were found to be epitaxial in nature. X-ray diffraction and high resolution transmission electron microscopy were employed to study the epitaxial relations of Zn1−xVxO with the sapphire substrate and electron energy loss spectroscopy was used to establish the bonding characteristics and oxidation states of vanadium inside the ZnO host. The main emphasis is on the magnetic properties of this system taking into consideration the phase purity and microstructural characteristics of these films. Our results show that the Zn1−xVxO system, with V in zinc substitutional sites, does not exhibit any signature of ferromagnetism, both at room temperature as well as at lower temperatures down to 10 K.
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81.05.Hd Other semiconductors
75.50.Pp Magnetic semiconductors
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy

Anisotropic magnetoresistance and spin polarization of La0.7Sr0.3MnO3/SrTiO3 superlattices

L. M. Wang and Chih-Chian Guo

Appl. Phys. Lett. 87, 172503 (2005); http://dx.doi.org/10.1063/1.2112167 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2005

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The crystalline structure, anisotropic magnetoresistance (AMR), and magnetization of La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices grown by a rf sputtering system are systematically analyzed to study the spin polarization of manganite at interfaces. The presence of positive low-temperature AMR in LSMO/STO superlattices implies that two bands of majority and minority character contribute to the transport properties, leading to a reduced spin polarization. Furthermore, the magnetization of superlattices follows the T3/2 law and decays more quickly as the thickness ratio dSTO/dLSMO increases, corresponding to a reduced exchange coupling. The results clearly show that the spin polarization is strongly correlated with the influence of interface-induced strain on the structure.
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75.47.Lx Magnetic oxides
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Mk Spin transport through interfaces
68.65.Ac Multilayers
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Cd Superlattices
73.21.Cd Superlattices
61.66.Fn Inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
75.30.Et Exchange and superexchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
71.20.Ps Other inorganic compounds

Current localization and enhanced percolative low-field magnetoresistance in disordered half metals

Sheng Ju, Tian-Yi Cai, and Z. Y. Li

Appl. Phys. Lett. 87, 172504 (2005); http://dx.doi.org/10.1063/1.2084318 (3 pages) | Cited 9 times

Online Publication Date: 19 October 2005

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By modeling the magnetotransport in disordered half metals onto a random resistor network, we have performed numerical simulations on the low-field magnetoresistance (LFMR) and the current distribution in the network. It is found that there is a close relationship between the magnitude of LFMR and the current morphology. LFMR increases with the increase of current localization. In the limit of strong disorder, a quasi-one-dimensional transport channel forms and LFMR reaches its maximum. Compared with the previous two-component (metal/insulator) percolative scenario for colossal magnetoresistance in phase-separated manganites, such a current percolation transition gives further understanding of the magnetotransport in disordered half metals.
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75.47.Lx Magnetic oxides
72.60.+g Mixed conductivity and conductivity transitions
64.75.-g Phase equilibria

Well-aligned Mn-doped ZnO nanowires synthesized by a chemical vapor deposition method

J. J. Liu, M. H. Yu, and W. L. Zhou

Appl. Phys. Lett. 87, 172505 (2005); http://dx.doi.org/10.1063/1.2084321 (3 pages) | Cited 50 times

Online Publication Date: 19 October 2005

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Well-aligned diluted magnetic semiconductor Zn1−xMnxO nanowires have been fabricated at 850 °C from a self-formed ZnO substrate using a chemical vapor deposition method. The as-synthesized Mn-doped ZnO nanowires were characterized by field emission scanning electron microscopy and transmission electron microscopy (TEM). The well-aligned nanowires are single crystalline and are perpendicularly grown along the c axis. Electron energy x-ray dispersive analysis, x-ray diffraction spectrometry, and TEM analysis clearly showed that Mn was doped both in the ZnO nanowires and substrate. Ferromagnetic ordering of the as-synthesized Zn1−xMnxO nanowire arrays was observed at 5 K with Curie temperature of 44 K by superconducting quantum interference device measurement.
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81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.50.Pp Magnetic semiconductors
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
75.75.-c Magnetic properties of nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Determination of magnetic vortex chirality using lateral spin-valve geometry

T. Kimura, Y. Otani, and J. Hamrle

Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages) | Cited 15 times

Online Publication Date: 19 October 2005

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We demonstrate the determination of the vortex chirality using a nonlocal spin-valve measurement technique in a lateral spin valve consisting of a Permalloy (Py) disk 1 μm in diameter and a Py wire 100 nm in width. The vortex chirality is determined under two probe configurations; the disk as the current probe and the disk as the voltage probe. The vortex chirality is found to depend on the probe configuration because of the current-induced Oersted field.
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75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Josephson devices for controllable flux qubit and interqubit coupling

C. Granata, B. Ruggiero, M. Russo, A. Vettoliere, V. Corato, and P. Silvestrini

Appl. Phys. Lett. 87, 172507 (2005); http://dx.doi.org/10.1063/1.2115083 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2005

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We present niobium-based Josephson devices as prototypes for applications to quantum computation with flux qubits. The most interesting feature of this device is the use of a Josephson vertical interferometer for a fine tuning of flux qubit and interquibit coupling. These devices allow a control of the off-diagonal Hamiltonian terms of flux qubit and of the flux transfer function of a superconducting transformer. In the vertical interferometer, the Josephson current is precisely modulated from a maximum to zero with fine control and precision by a small transversal magnetic field parallel to the radio-frequency superconducting loop plane and to the flux transformer.
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85.25.Cp Josephson devices
03.67.Lx Quantum computation architectures and implementations

Effect of stray field on local spin modes in exchange-biased magnetic tunnel junction elements

J. H. H. Rietjens, C. Józsa, W. J. M. de Jonge, B. Koopmans, and H. Boeve

Appl. Phys. Lett. 87, 172508 (2005); http://dx.doi.org/10.1063/1.2117614 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2005

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We report on the detection of localized spin modes in a multilayered spintronic device by means of time-resolved scanning Kerr microscopy. Measurements on this 13×9 μm2 exchange-biased magnetic tunnel junction element at different applied bias fields indicate a strong effect of the stray field from the pinned CoFe layer on the magnetization dynamics in the free NiFe layer. This view is supported by micromagnetic simulations, which also show that the dynamics can be attributed to the specific shape of the internal magnetic field in the element.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Influence of surface/interface roughness and grain size on magnetic property of Fe/Co bilayer

Deeder Aurongzeb, K. Bhargava Ram, and Latika Menon

Appl. Phys. Lett. 87, 172509 (2005); http://dx.doi.org/10.1063/1.2119427 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2005

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In this work, we report the influence of surface roughness and cluster size on coercivity of Fe/Co bilayer. Coercivity was tuned by thermal annealing. No systematic trend was found for temperature dependent annealing. However, after annealing at 350 °C, we find systematic increase in coercivity with anneal time. For as-deposited film, we find unusually low coercivity (0.39 Oe). By increasing annealing time, coercivity was tuned to values as high as 600 Oe. Surface characterization using atomic force microscopy showed uniform clusters at this temperature after 2 h of annealing. The observed magnetic properties are discussed in terms of cluster size and surface/interface roughness.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
68.47.De Metallic surfaces
68.37.Ps Atomic force microscopy (AFM)
81.40.Gh Other heat and thermomechanical treatments

Theoretical simulation and experimental study on resistivity properties of mixed-phase La2/3Ca1/3MnO3 thin films

Qing-li Zhou, Kun Zhao, Kui-juan Jin, Dong-yi Guan, Hui-bin Lu, Zheng-hao Chen, Guo-zhen Yang, Alan Li, and H. K. Wong

Appl. Phys. Lett. 87, 172510 (2005); http://dx.doi.org/10.1063/1.2119413 (3 pages) | Cited 8 times

Online Publication Date: 21 October 2005

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The theoretical simulation and experimental study are reported on the metal-to-insulator transition, thermal hysteresis behavior, magnetic-field-induced reduction, and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 thin films deposited on SrTiO3 (001)-oriented substrates tilted by 10° towards the [010] direction. The simulated results obtained by using a random network model based on phase separation scenario are in quantitative agreement with our experimental data and indicate that tilting (applying magnetic field) can increase (decrease) the scatterings and the activation energy, resulting in enhancement (reduction) of resistivity. All those results suggest that the intrinsic inhomogeneity and the lattice structure play the significant roles in the electrical conductivity and anisotropic transport properties.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Growth and magnetism of Cr-doped InN

R. Rajaram, A. Ney, G. Solomon, J. S. Harris, R. F. C. Farrow, and S. S. P. Parkin

Appl. Phys. Lett. 87, 172511 (2005); http://dx.doi.org/10.1063/1.2115085 (3 pages) | Cited 7 times

Online Publication Date: 21 October 2005

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We present structural and magnetic characterization of Cr-doped InN films grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Low-temperature GaN buffer layers grown by metalorganic vapor-phase epitaxy were used to accommodate the large lattice mismatch between InN and sapphire. A high n-type carrier concentration of 1.5×1020 cm−3 was measured in InN films with 3% Cr doping. Films of this type, with high structural perfection, as measured in situ, with reflection high-energy electron diffraction, exhibit a well-defined in-plane magnetic hysteresis loop for temperatures varying from 5 to 300 K. Thus, we show evidence of magnetic order in Cr-doped InN.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.uj III-V and II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
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Low-temperature growth and interface characterization of BiFeO3 thin films with reduced leakage current

Yi-Hsien Lee, Jenn-Ming Wu, Yu-Lun Chueh, and Li-Jen Chou

Appl. Phys. Lett. 87, 172901 (2005); http://dx.doi.org/10.1063/1.2112181 (3 pages) | Cited 69 times

Online Publication Date: 17 October 2005

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BiFeO3 (BFO) thin films of pure perovskite phase were deposited on LaNiO3-buffered Pt/TiOx/SiO2/Si (LNO) and Pt/TiOx/SiO2/Si (Pt) substrates by RF magnetron sputtering. Highly (100)-oriented BFO film was coherently grown on LNO at a temperature as low as 300 °C. The crystal structure and the film/electrode interface of BFO films were characterized using x-ray diffraction and scanning transmission electron microscope high-angle annular dark-field imaging. The conventional problem of the leakage current was greatly reduced with remarkable improvement in the film/electrode interface, chemical homogeneity, crystallinity, and surface roughness of the BFO film.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
75.50.Dd Nonmetallic ferromagnetic materials
77.80.-e Ferroelectricity and antiferroelectricity
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
75.70.Ak Magnetic properties of monolayers and thin films
68.35.B- Structure of clean surfaces (and surface reconstruction)

Electrical and dielectric behaviors of Ti3SiC2∕Yttria-stabilized zirconia composites

Sui-Lin Shi, Wei Pan, Ming-Hao Fang, and Zhen-Yi Fang

Appl. Phys. Lett. 87, 172902 (2005); http://dx.doi.org/10.1063/1.2117625 (3 pages) | Cited 5 times

Online Publication Date: 20 October 2005

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Ti3SiC2/3Y‐TZP (3 mol % Yttria-stabilized zirconia) composites were prepared by spark plasma sintering. The effective dc conductivities of the composites have been measured and the percolation threshold was determined. The dielectric behavior of the composites was studied in the frequency range 102–4×107 Hz. The results show that the dielectric constant increased remarkably with the Ti3SiC2 concentration, when the Ti3SiC2 concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.
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77.84.Lf Composite materials
72.80.Tm Composite materials
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization

Observation of ferroelectricity in a confined crystallite using electron-backscattered diffraction and piezoresponse force microscopy

P. Gupta, H. Jain, D. B. Williams, Sergei V. Kalinin, J. Shin, S. Jesse, and A. P. Baddorf

Appl. Phys. Lett. 87, 172903 (2005); http://dx.doi.org/10.1063/1.2120919 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2005

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LaBGeO5 is a model transparent ferroelectric glass-ceramic (TFGC) material, developed as an inexpensive alternative to single-crystal nonlinear optical materials. The optical activity of the TFGC originates from the ferroelectric phase which remains under a hydrostatic pressure exerted by the surrounding glass matrix. A combination of two techniques, electron-backscattered diffraction (EBSD) and piezoresponse force microscopy (PFM), is employed to monitor the development of the ferroelectric phase. A method is proposed to theoretically construct PFM amplitude maps from EBSD orientation maps. The theoretical vertical piezoresponse map is compared with the experimental piezoresponse map from PFM. A good correlation between the theoretical and experimental maps is observed.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics
79.20.Kz Other electron-impact emission phenomena
77.65.-j Piezoelectricity and electromechanical effects
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Electrical contacts to carbon nanotubes down to 1 nm in diameter

Woong Kim, Ali Javey, Ryan Tu, Jien Cao, Qian Wang, and Hongjie Dai

Appl. Phys. Lett. 87, 173101 (2005); http://dx.doi.org/10.1063/1.2108127 (3 pages) | Cited 75 times

Online Publication Date: 17 October 2005

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Rhodium (Rh) is found similar to Palladium (Pd) in making near-Ohmic electrical contacts to single-walled carbon nanotubes (SWNTs) with diameters d> ∼ 1.6 nm. Non-negligible positive Schottky barriers (SBs) exist between Rh or Pd and semiconducting SWNTs (S-SWNTs) with d< ∼ 1.6 nm. With Rh and Pd contacts, the characteristics of SWNT field-effect transistors and SB heights at the contacts are largely predictable based on the SWNT diameters, without random variations among devices. Surprisingly, electrical contacts to metallic SWNTs (M-SWNTs) also appear to be diameter dependent especially for small SWNTs. Ohmic contacts are difficult for M-SWNTs with diameters ⩽ ∼ 1.0 nm possibly due to tunnel barriers resulted from large perturbation of contacting metal to very small diameter SWNTs due to high chemical reactivity of the latter.
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85.30.Tv Field effect devices
73.30.+y Surface double layers, Schottky barriers, and work functions
61.46.-w Structure of nanoscale materials
73.40.Ns Metal-nonmetal contacts
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