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29 Dec 2008

Volume 93, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 261101 (2008); http://dx.doi.org/10.1063/1.3053074 (3 pages)

Takashi Fujikura, Osamu Matsuda, Dieter M. Profunser, Oliver B. Wright, Jeremy Masson, and Sylvain Ballandras
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Influence of molten status on nanoquasicrystalline-forming Zr-based metallic glasses

Cang Fan, D. Chen, P. K. Liaw, H. Choo, C. Benmore, J. Siewenie, G. L. Chen, J. X. Xie, and C. T. Liu

Appl. Phys. Lett. 93, 261905 (2008); http://dx.doi.org/10.1063/1.3046118 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2008

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Quasicrystals, formed during the primary crystallization stage of annealing Zr70−XCu25Pt5AlX metallic glasses, decrease in size from 100 to 5 nm as the Al content is increased from 8 to 10 at. %. The glass transition and crystallization processes during annealing at fixed heating rate were found to be influenced by the thermal history of the melt. Pair distribution function analyses of neutron scattering data revealed that the broad peak from the nearest atomic pairs separates into multiple peaks with lower melt quenching temperatures (TL). These results suggest that the short-range order is enhanced with decreased TL. Such ordered regions remain in the glass upon quenching and contribute to nanoquasicrystal formation upon heating.
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61.44.Br Quasicrystals
61.43.Fs Glasses
64.70.Nd Structural transitions in nanoscale materials
64.70.kj Glasses
64.70.kd Metals and alloys
81.40.Gh Other heat and thermomechanical treatments
64.70.P- Glass transitions of specific systems

Nanolubrication of poly(methyl methacrylate) films on Si for microelectromechanical systems applications

N. Satyanarayana, K. H. Lau, and S. K. Sinha

Appl. Phys. Lett. 93, 261906 (2008); http://dx.doi.org/10.1063/1.3062847 (3 pages) | Cited 6 times

Online Publication Date: 31 December 2008

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Polymers, such as poly(methyl methacrylate) (PMMA), are important structural materials for microsystems because of their excellent mechanical properties; however, they suffer from severe problems of adhesion, friction, and wear [ B. Bhushan, J. N. Israelachvili, and U. Landman, Nature (London) 374, 607 (1995) ]. We report a simple process of O2 plasma treatment on a PMMA film, followed by overcoating with an ultrathin layer of perfluoropolyether (PFPE) which improved tribological performance of the film. O2 plasma on PMMA film has formed unique wavy nanotextured surface and increased the hardness and the elastic modulus of the film, which, together with the nanolurbication by PFPE, has increased the wear life of PMMA film by more than five orders of magnitude.
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68.60.Bs Mechanical and acoustical properties
61.46.-w Structure of nanoscale materials
81.40.Pq Friction, lubrication, and wear
68.55.am Polymers and organics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
62.20.Qp Friction, tribology, and hardness

Work softening and annealing hardening of deformed nanocrystalline nickel

X. Y. Zhang, Q. Liu, X. L. Wu, and A. W. Zhu

Appl. Phys. Lett. 93, 261907 (2008); http://dx.doi.org/10.1063/1.3062849 (3 pages) | Cited 5 times

Online Publication Date: 31 December 2008

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We reported that work softening takes place during room-temperature rolling of nanocrystalline Ni at an equivalent strain of around 0.30. The work softening corresponds to a strain-induced phase transformation from a face-centered cubic (fcc) to a body-centered cubic (bcc) lattice. The hardness decreases with increasing volume fraction of the bcc phase. When the deformed samples are annealed at 423 K, a hardening of the samples takes place. This hardening by annealing can be attributed to a variety of factors including the recovery transformation from the bcc to the fcc phase, grain boundary relaxation, and retardation of dislocation gliding by microtwins.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.70.kd Metals and alloys
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep

Lattice parameters, deviations from Vegard’s rule, and E2 phonons in InAlN

V. Darakchieva, M.-Y. Xie, F. Tasnádi, I. A. Abrikosov, L. Hultman, B. Monemar, J. Kamimura, and K. Kishino

Appl. Phys. Lett. 93, 261908 (2008); http://dx.doi.org/10.1063/1.3056656 (3 pages) | Cited 9 times

Online Publication Date: 31 December 2008

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The lattice parameters of InxAl1−xN in the whole compositional range are studied using first-principle calculations. Deviations from Vegard’s rule are obtained via the bowing parameters, δa = 0.0412±0.0039 Å and δc = −0.060±0.010 Å, which largely differ from previously reported values. Implications of the observed deviations from Vegard’s rule on the In content extracted from x-ray diffraction are discussed. We also combine these results with x-ray diffraction and Raman scattering studies on InxAl1−xN nanocolumns with 0.627 ⩽ x ⩽ 1 and determine the E2 phonon frequencies versus In composition in the scarcely studied In-rich compositional range.
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61.66.Fn Inorganic compounds
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.15.-m Methods of electronic structure calculations
78.30.Er Solid metals and alloys

Poly(phenylene ethynylene)-coated aligned ZnO nanorod arrays for 2,4,6-trinitrotoluene detection

Defeng Zhu, Qingguo He, Huimin Cao, Jiangong Cheng, Songlin Feng, Yuansen Xu, and Tong Lin

Appl. Phys. Lett. 93, 261909 (2008); http://dx.doi.org/10.1063/1.3063045 (3 pages) | Cited 5 times

Online Publication Date: 31 December 2008

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The structure of ZnO nanorods coated with fluorescent polymer poly(phenylene ethynylene) (PPE) have been fabricated for 2,4,6-trinitrotoluene (TNT) detection. In this structure, hydrothermally synthesized crystalline ZnO nanorod arrays were used as waveguides and supporting materials for the TNT sensitive polymer, PPE. The evanescent-wave guiding property of the ZnO nanorod waveguide considerably increased fluorescence intensity. The space between the adjacent nanorods and the larger surface-to-volume ratio of the nanorods enhanced the fluorescence response (quenching) to TNT vapor. This work will contribute to design of combining ZnO nanorod arrays with a functional polymer for sensor applications.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
42.79.Gn Optical waveguides and couplers

Irreversibility in cooling and heating processes in the magnetocaloric MnAs and alloys

A. L. Lima Sharma, S. Gama, A. A. Coelho, and A. de Campos

Appl. Phys. Lett. 93, 261910 (2008); http://dx.doi.org/10.1063/1.3058712 (3 pages) | Cited 3 times

Online Publication Date: 31 December 2008

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Irreversibility of adiabatic processes in the magnetocaloric MnAs and alloys is presented here. We used a differential scanning calorimeter to record the heat flux as a function of the temperature and applied field for MnAs (Mn,X)As, where X stands for Fe or Cu in 0.6% of doping. We extracted the latent heat and entropy in a cycle. In the cooling process, we observed that SMnc>SFec>SCuc, and for the heating process, SFeh ≈ SMnh>SCuh. The difference in the entropy obtained between processes was found to be as high as 37%.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.72.up Other materials
65.40.G- Other thermodynamical quantities

First-principles investigation of intrinsic defects and (N, O) impurity atom stimulated Al vacancy in Ti2AlC

Ting Liao, Jingyang Wang, and Yanchun Zhou

Appl. Phys. Lett. 93, 261911 (2008); http://dx.doi.org/10.1063/1.3058718 (3 pages) | Cited 6 times

Online Publication Date: 31 December 2008

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We use first-principles calculations to study the energetics of intrinsic defects in Ti2AlC and the effect of N or O impurity atoms on the generation of Al vacancies. The insertion of impurity atoms lowers the vacancy formation energy of its neighboring Al. The formation of Al vacancies is related to the experimental observations of growth of AlN or Al2O3 nanowires and nanofibers on the surface of Ti2AlC. Since the growth of these nanostructures is controlled by the generation and migration of intrinsic defects, we propose that a tunable method for synthesis of such nanostructures is possible by controlling impurities.
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61.72.jd Vacancies
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing

Pt redistribution during Ni(Pt) silicide formation

J. Demeulemeester, D. Smeets, C. Van Bockstael, C. Detavernier, C. M. Comrie, N. P. Barradas, A. Vieira, and A. Vantomme

Appl. Phys. Lett. 93, 261912 (2008); http://dx.doi.org/10.1063/1.3058719 (3 pages) | Cited 14 times

Online Publication Date: 31 December 2008

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We report on a real-time Rutherford backscattering spectrometry study of the erratic redistribution of Pt during Ni silicide formation in a solid phase reaction. The inhomogeneous Pt redistribution in Ni(Pt)Si films is a consequence of the low solubility of Pt in Ni2Si compared to NiSi and the limited mobility of Pt in NiSi. Pt further acts as a diffusion barrier and resides in the Ni2Si grain boundaries, significantly slowing down the Ni2Si and NiSi growth kinetics. Moreover, the observed incorporation of a large amount of Pt in the NiSi seeds indicates that Pt plays a major role in selecting the crystallographic orientation of these seeds and thus in the texture of the resulting Ni1−xPtxSi film.
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68.55.jm Texture
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
66.30.Fq Self-diffusion in metals, semimetals, and alloys
64.75.Bc Solubility
68.55.J- Morphology of films
61.72.Mm Grain and twin boundaries
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Botulinum toxin detection using AlGaN/GaN high electron mobility transistors

Yu-Lin Wang, B. H. Chu, K. H. Chen, C. Y. Chang, T. P. Lele, Y. Tseng, S. J. Pearton, J. Ramage, D. Hooten, A. Dabiran, P. P. Chow, and F. Ren

Appl. Phys. Lett. 93, 262101 (2008); http://dx.doi.org/10.1063/1.3056612 (3 pages) | Cited 7 times

Online Publication Date: 29 December 2008

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Antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1 to 10 ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN/GaN HEMTs for botulinum toxin detection.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
87.14.E- Proteins
85.30.Tv Field effect devices

Drift current dominated terahertz radiation from InN at low-density excitation

K. I. Lin, J. T. Tsai, T. S. Wang, J. S. Hwang, M. C. Chen, and G. C. Chi

Appl. Phys. Lett. 93, 262102 (2008); http://dx.doi.org/10.1063/1.3056635 (3 pages) | Cited 5 times

Online Publication Date: 30 December 2008

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This letter investigates the polarity of terahertz radiation from indium nitride (InN) excited by femtosecond optical pulses wherein a central wavelength of around 790 nm is measured. The InN epilayers are grown by metalorganic chemical vapor deposition on sapphire and silicon substrates. The polarity of the terahertz radiation field from InN is opposite to that from p-InAs whose radiation mechanism is dominated by the photo-Dember effect indicating that the dominant radiation mechanism in InN is the drift current induced by the internal electric field at low-density excitation below 590 nJ/cm2. The internal electric field consists of the surface accumulation field and the spontaneous polarization-induced electric field. In addition, since no azimuthal angle dependence of the terahertz radiation is observed, the optical rectification effect is ruled out. By comparing the wave forms of terahertz radiation from the front and the back of the InN sample grown on sapphire in reflection geometry, the N polarity of the InN sample is confirmed.
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78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
73.61.Le Other inorganic semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators

Electron hole–phonon interaction, correlation of structure, and conductivity in single crystal La0.9Sr0.1FeO3−δ

A. Braun, J. Richter, A. S. Harvey, S. Erat, A. Infortuna, A. Frei, E. Pomjakushina, Bongjin S. Mun, P. Holtappels, U. Vogt, K. Conder, L. J. Gauckler, and T. Graule

Appl. Phys. Lett. 93, 262103 (2008); http://dx.doi.org/10.1063/1.3049614 (3 pages) | Cited 5 times

Online Publication Date: 30 December 2008

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The conductivity and structure of the hole-doped polaron conductor La0.9Sr0.1FeO3−δ are reported for elevated temperatures. The conductivity increases exponentially with temperature to a maximum and decreases for T>700 K following a power law, accompanied by a shift of spectral weight in the photoemission valence band. The conductivity decrease is accompanied by a phase transformation, due to the reduction of Fe, as evidenced by x-ray absorption spectra. Additional fine structures in the conductivity are correlated with a strong decrease in valence band intensity near EF and with the onset of a corresponding structural transition.
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71.20.Ps Other inorganic compounds
72.80.Sk Insulators
71.38.-k Polarons and electron-phonon interactions
64.70.K- Solid-solid transitions
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Influence of the illumination on weak antilocalization in an AlxGa1−xN/GaN heterostructure with strong spin-orbit coupling

W. Z. Zhou, T. Lin, L. Y. Shang, L. Sun, K. H. Gao, Y. M. Zhou, G. Yu, N. Tang, K. Han, B. Shen, S. L. Guo, Y. S. Gui, and J. H. Chu

Appl. Phys. Lett. 93, 262104 (2008); http://dx.doi.org/10.1063/1.3049615 (3 pages) | Cited 3 times

Online Publication Date: 30 December 2008

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The weak antilocalization effects of the two-dimensional electron gas in a high mobility AlxGa1−xN/GaN heterostructure have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect as a function of electron concentration as well as a function of temperature is studied using the weak antilocalization analysis. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis shows a rapid decrease with the increase of the measured electron concentration.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Fz Weak or Anderson localization
72.20.Fr Low-field transport and mobility; piezoresistance
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects

Probing and modulating surface electron accumulation in InN by the electrolyte gated Hall effect

G. F. Brown, J. W. Ager, III, W. Walukiewicz, W. J. Schaff, and J. Wu

Appl. Phys. Lett. 93, 262105 (2008); http://dx.doi.org/10.1063/1.3062856 (3 pages) | Cited 12 times

Online Publication Date: 31 December 2008

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The surface contribution to the electrical transport properties of InN was directly measured and modulated by the electrolyte gated Hall effect. Undoped and Mg-doped films show different behaviors that can be effectively described by a multilayer model, taking into account the conduction contribution from both the surface and interface with the buffer layer. Gated photoluminescence experiments further show the surface accumulation layer enhances radiative electron-hole recombination in undoped InN.
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73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.25.+i Surface conductivity and carrier phenomena

In situ strain measurements on GaN/AlGaN Schottky diodes with variable bias

Nadeemullah A. Mahadik, Syed B. Qadri, and Mulpuri V. Rao

Appl. Phys. Lett. 93, 262106 (2008); http://dx.doi.org/10.1063/1.3063125 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2008

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In situ high resolution x-ray diffraction measurements were performed on AlGaN/GaN Schottky diodes under variable bias conditions. The results show a linear variation in strain for the GaN channel with bias. For forward bias conditions, an in-plane tensile strain was observed, whereas for reverse bias a compressive strain was present. A discontinuity in the strain for the reverse bias measurements was also present because the width of the carrier depletion region exceeds the ∼ 2 μm GaN layer. The linear variation in the strain caused by variable bias may be due to a change in the piezoelectric charge at the AlGaN/GaN interface.
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85.30.Kk Junction diodes
77.65.-j Piezoelectricity and electromechanical effects

Very large anisotropy in the dc conductivity of epitaxial VO2 thin films grown on (011) rutile TiO2 substrates

Jiwei Lu, Kevin G. West, and Stuart A. Wolf

Appl. Phys. Lett. 93, 262107 (2008); http://dx.doi.org/10.1063/1.3058769 (3 pages) | Cited 7 times

Online Publication Date: 31 December 2008

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In this letter, we reported a very large anisotropy in dc conductivity of epitaxial VO2 thin films deposited on a (011) TiO2 substrate. The VO2 film grew epitaxially on TiO2 and x-ray diffraction showed that VO2 had the tetragonal symmetry due to the substrate clamping effect at room temperature. There was a compressive strain of −1.2% along the c-axis of the rutile VO2. We observed a very strong angular dependence of in-plane dc conductivity. We calculated that σ1/σ3 ∼ 5.14, which was anomalously large. We attributed the drastic increase to the compressive strain along the c-axis of the rutile VO2 due to substrate clamping. This very large anisotropy disappeared above the metal-insulator transition.
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73.61.Ng Insulators
71.27.+a Strongly correlated electron systems; heavy fermions
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
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Spin-wave confinement in rolled-up ferromagnetic tubes

Stefan Mendach, Jan Podbielski, Jesco Topp, Wolfgang Hansen, and Detlef Heitmann

Appl. Phys. Lett. 93, 262501 (2008); http://dx.doi.org/10.1063/1.3058764 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2008

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We investigate the spin-wave dispersion in rolled-up Permalloy microtubes based on self-rolling strained semiconductor layers. Using microwave absorption spectroscopy we find that these structures exhibit a characteristic spin-wave mode spectrum. The magnetization and spin-wave resonance at zero external magnetic field is determined by curvature induced dynamic demagnetization fields. At high magnetic fields transverse to the tube axis, the three-dimensional shape anisotropy of the tube results in spin-wave confinement in well-defined regions along the tube perimeter.
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75.30.Ds Spin waves
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.70.Gq Microwave and radio-frequency interactions

Substrate orientation dependence of ferromagnetism in (Ga,Mn)As

M. J. Wilson, G. Xiang, B. L. Sheu, P. Schiffer, N. Samarth, S. J. May, and A. Bhattacharya

Appl. Phys. Lett. 93, 262502 (2008); http://dx.doi.org/10.1063/1.3058758 (3 pages) | Cited 2 times

Online Publication Date: 30 December 2008

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We describe a comprehensive study of the properties of both ordered and random alloy Ga1−xMnxAs grown on (001), (311), (201), and (110) GaAs substrates. Magnetization measurements show a systematic variation in the Curie temperature with epitaxial orientation in both types of samples, even for the same average Mn concentrations. Electrical characterization and thermal annealing of the random alloy Ga1−xMnxAs samples suggest that the density of As antisite defects depends on the growth surface, providing an extrinsic origin for the observed dependence of Curie temperature on substrate orientation.
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75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Fraunhofer regime of operation for superconducting quantum interference filters

A. V. Shadrin, K. Y. Constantinian, G. A. Ovsyannikov, S. V. Shitov, I. I. Soloviev, V. K. Kornev, and J. Mygind

Appl. Phys. Lett. 93, 262503 (2008); http://dx.doi.org/10.1063/1.3058759 (3 pages)

Online Publication Date: 30 December 2008

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Series arrays of superconducting quantum interference devices (SQUIDs) with incommensurate loop areas, so-called superconducting quantum interference filters (SQIFs), are investigated in the kilohertz and the gigahertz frequency range. In SQIFs made of high-Tc bicrystal junctions the flux-to-voltage response ∂V/∂Φ is dominated by the variation in the critical current in the individual junctions (Fraunhofer-type) rather than by the SQUIDs interference. For a SQIF with 20 SQUID loops we find ∂V/∂Φ = 40 mV/Φ0 and a dynamic range of more than 60 dB in the kilohertz range. In the 1–2 GHz range the estimated power gain is 20 dB and the magnetic flux noise level is as low as 10−4Φ0.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Vn Filters
85.25.Cp Josephson devices

High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy

T. A. Moore, I. M. Miron, G. Gaudin, G. Serret, S. Auffret, B. Rodmacq, A. Schuhl, S. Pizzini, J. Vogel, and M. Bonfim

Appl. Phys. Lett. 93, 262504 (2008); http://dx.doi.org/10.1063/1.3062855 (3 pages) | Cited 54 times

Online Publication Date: 31 December 2008

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Current-induced domain wall (DW) displacements in an array of ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly observed by wide field Kerr microscopy. DWs in all wires in the array were driven simultaneously and their displacement on the micrometer scale was controlled by the current pulse amplitude and duration. At the lower current densities where DW displacements were observed (j ≤ 1.5×1012 A/m2), the DW motion obeys a creep law. At higher current density (j = 1.8×1012 A/m2), zero-field average DW velocities up to 130±10 m/s were recorded.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects

Effects of donor doping on Ga1−xMnxAs

Y. J. Cho, K. M. Yu, X. Liu, W. Walukiewicz, and J. K. Furdyna

Appl. Phys. Lett. 93, 262505 (2008); http://dx.doi.org/10.1063/1.3063046 (3 pages) | Cited 6 times

Online Publication Date: 31 December 2008

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We investigate the effect compensating Mn acceptors in Ga1−xMnxAs films by doping with Si donors. For Ga1−xMnxAs with low Mn content (e.g., x<0.033), doping by Si decreases the Curie temperature TC compared to undoped Ga1−xMnxAs. At high values of x, however (e.g., x>0.10), Si doping is found to increase TC. We ascribe this to an increase in the hole mobility in high x samples due to changes in the relative occupancy of the hole impurity band associated with compensation by the Si donors.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
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Raman spectroscopy of (K,Na)NbO3 and (K,Na)1−xLixNbO3

H. J. Trodahl, N. Klein, D. Damjanovic, N. Setter, B. Ludbrook, D. Rytz, and M. Kuball

Appl. Phys. Lett. 93, 262901 (2008); http://dx.doi.org/10.1063/1.3056658 (3 pages) | Cited 14 times

Online Publication Date: 29 December 2008

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We report Raman spectroscopy in all four phases of a (K0.5+δNa0.5−δ)NbO3 (δ ∼ 0.03) crystal and ((K0.5+δNa0.5−δ)1−xLix)NbO3 for x = 0.02  and 0.03. The phase transitions in the Li-free crystal are homogeneous and hysteretic, with no mixed-phase region between the rhombohedral and orthorhombic phases. Raman spectra in the lowest-temperature phase in the Li-doped material differ significantly from those at x = 0 and suggest a structural phase boundary at a Li concentration of less than 2%.
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78.30.Hv Other nonmetallic inorganics
61.72.up Other materials
64.70.K- Solid-solid transitions

The radial distribution of defects in a percolation path

X. Li, C. H. Tung, and K. L. Pey

Appl. Phys. Lett. 93, 262902 (2008); http://dx.doi.org/10.1063/1.3056659 (3 pages) | Cited 12 times

Online Publication Date: 29 December 2008

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Our results show that the defect distribution within a nanometer size percolation path is nonuniform. The defects, which are shown as oxygen vacancies, spread out radially from the center of the percolation path. The conduction band edges of the defective oxide are lowered for 0.14–0.78 eV when the Si–O composition changes from SiO1.76 to SiO0.7.
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61.72.jd Vacancies
71.20.Ps Other inorganic compounds
77.22.Jp Dielectric breakdown and space-charge effects

Cation ordering in epitaxial lead zirconate titanate films

L. C. Zhang, A. L. Vasiliev, I. B. Misirlioglu, R. Ramesh, S. P. Alpay, and M. Aindow

Appl. Phys. Lett. 93, 262903 (2008); http://dx.doi.org/10.1063/1.3058755 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2008

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Electron diffraction and atom location by channeling enhanced microanalysis were used to show that epitaxial PbZr0.2Ti0.8O3 films grown on (001) SrTiO3 substrates by pulsed laser deposition exhibit long-range order on the tetravalent cation sublattice parallel to the film/substrate interface. This ordering gives two distinct tetravalent cation sites, one Zr lean and one Zr rich, and results in a superlattice with a tetragonal unit cell with lattice parameters a0 ≈ √2aPZT and c0 ≈ aPZT. Since such ordered states are inherently unstable in homovalent perovskite solutions, it is inferred that the ordering arises in response to the lattice misfit and could constitute an additional relaxation mode.
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68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
82.80.-d Chemical analysis and related physical methods of analysis

Domain control in ferroelectric nanodots through surface charges

Jie Wang and Marc Kamlah

Appl. Phys. Lett. 93, 262904 (2008); http://dx.doi.org/10.1063/1.3058821 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2008

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Stable polarization distributions of freestanding ferroelectric nanodots with different surface charges are investigated numerically using a phase field model. The out-of-plane components of polarizations are found to be proportional to the density of surface charge. When the density of surface charge exceeds a critical value, the in-plane components of polarizations disappear. It makes ferroelectric nanodots experience an unusual transition from a vortex state to a single-domain state. Simulation results also show that regular multidomain structures can be obtained by means of specified surface charges, which suggests a way to tailor the physical properties for specific applications.
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77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Crystal structure and multiferroic properties of Gd-substituted BiFeO3

V. A. Khomchenko, D. A. Kiselev, I. K. Bdikin, V. V. Shvartsman, P. Borisov, W. Kleemann, J. M. Vieira, and A. L. Kholkin

Appl. Phys. Lett. 93, 262905 (2008); http://dx.doi.org/10.1063/1.3058708 (3 pages) | Cited 32 times

Online Publication Date: 30 December 2008

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Room-temperature crystal structure, local ferroelectric, and magnetic properties of the Bi1−xGdxFeO3 (x = 0.1,0.2,0.3) polycrystalline samples have been investigated by x-ray diffraction, piezoresponse force microscopy, and magnetometry techniques. Performed measurements have revealed a sequence of the composition-driven structural phase transitions R3c→Pn21a (occurs at x ∼ 0.1) and Pn21a→Pnma (takes place within the concentrational range of 0.2<x<0.3). The latter structural transformation is attributed to the substitution-induced suppression of the polar displacements. Gd substitution has been shown to effectively induce the appearance of the spontaneous magnetization, thus indicating a promising way for improving multiferroic properties of antiferromagnetic BiFeO3.
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75.30.-m Intrinsic properties of magnetically ordered materials
77.80.-e Ferroelectricity and antiferroelectricity
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