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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Tuning exchange-bias properties by thermal effects in a hard/soft bilayer

T. Hauet, S. Mangin, F. Montaigne, J. A. Borchers, and Y. Henry

Appl. Phys. Lett. 91, 022505 (2007); http://dx.doi.org/10.1063/1.2753108 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2007

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The effect of temperature on exchange-bias properties of an antiferromagnetically coupled hard/soft bilayer (Tb12Fe88/Gd40Fe60) is studied. In a similar manner to its cooling field dependence, a continuous transition from a negative to a positive exchange-bias field is observed with increasing temperature. The changes of magnetic configuration responsible for this effect are studied, combining both magnetization and polarized neutron reflectivity measurements. The temperature is found to enhance the exchange-bias training effect as a result of the relaxation of an interface domain wall. The present study demonstrates that both temperature and cooling field may be used to tune the exchange field.
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75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions

Controlled domain wall injection into ferromagnetic nanowires from an optimized pad geometry

D. McGrouther, S. McVitie, J. N. Chapman, and A. Gentils

Appl. Phys. Lett. 91, 022506 (2007); http://dx.doi.org/10.1063/1.2753541 (3 pages) | Cited 22 times

Online Publication Date: 12 July 2007

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The authors present an improved geometry for a micron-scale pad for the injection of vortex domain walls (VDWs) into ferromagnetic nanowires. The pad supports a single vortex magnetization state, the chirality of which can be controlled simply by field saturation along a specific direction. We show, using Lorentz transmission electron microscopy, that utilization of such pads allows the chirality of VDWs injected into the attached wire to be predetermined. Furthermore, the pad vortex state is highly stable and survives repeated injection and depinning of VDWs from an asymmetric notch located some distance along the wire.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Temperature increment in a current-heated nanowire for current-induced domain wall motion with finite thickness insulator layer

Chun-Yeol You and Seung-Seok Ha

Appl. Phys. Lett. 91, 022507 (2007); http://dx.doi.org/10.1063/1.2754351 (3 pages) | Cited 21 times

Online Publication Date: 12 July 2007

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The authors investigate the insulator-layer-thickness-dependent temperature increment in the nanowire for the current-induced domain wall motion. Practically, a finite thickness insulator layer must be placed between the semi-infinite substrate and the metallic nanowire for an electric insulation. Since a good electric insulator is also a thermal insulator, the temperature increment of the nanowire depends on the insulator layer’s thickness. An approximated analytic expression of the insulator thickness dependent temperature increment is obtained by employing the Fourier-transformed Green’s function method, and it is confirmed by the full numerical finite element method. The authors find that the control parameter of the temperature increment is the ratio between the insulator layer’s thickness and the nanowire’s width.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
73.63.Nm Quantum wires

Detecting dynamic signals of ideally ordered nanohole patterned disk media fabricated using nanoimprint lithography

Hirotaka Oshima, Hideyuki Kikuchi, Hiroshi Nakao, Ken-ichi Itoh, Takuya Kamimura, Takeshi Morikawa, Koji Matsumoto, Takahiro Umada, Hiroaki Tamura, Kazuyuki Nishio, and Hideki Masuda

Appl. Phys. Lett. 91, 022508 (2007); http://dx.doi.org/10.1063/1.2757118 (3 pages) | Cited 15 times

Online Publication Date: 13 July 2007

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The authors have fabricated ideally ordered alumina nanohole patterned disk media via anodic oxidation and nanoimprint lithography with a thermoplastic resist. The ordered arrays of alumina nanoholes with 100 nm pitch, filled with Co by electrodeposition, were created over a macroscopically large area on a hard-disk substrate using these industrially applicable nanofabrication technologies. Stable flight of a perpendicular magnetic head above the media and perpendicular magnetic anisotropy of the Co nanopillars enable high-speed dynamic magnetic recording and playback. Dynamic periodic signals that matched the nanopillar periodicity were clearly observed after writing bit patterns, showing alternate reversal of magnetization of the nanopillars.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.40.Hp Lithography, masks and pattern transfer

Fine structure in the tunneling characteristic of MgB2 thin films

R. Schneider, J. Geerk, A. G. Zaitsev, and H. v. Löhneysen

Appl. Phys. Lett. 91, 022509 (2007); http://dx.doi.org/10.1063/1.2755921 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2007

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The authors report on the observation of theoretically predicted fine structures in the negative second derivative of the current-voltage characteristic measured on sandwich-type tunnel junctions on MgB2 thin films with a Tc of 35 K. The high resolution was achieved by a progress in the in situ preparation of MgB2 thin films by thermal evaporation of Mg combined with B sputtering. They were able to increase the substrate temperature up to 550 °C by sputtering boron from a red-hot sintered target. The film properties, such as Tc and the residual resistivity, significantly improved compared to films deposited at lower substrate temperatures. Better crystalline order within the MgB2 grains is evidently the key to the details of the electron-phonon coupling.
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74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.25.Kc Phonons
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects
81.15.Cd Deposition by sputtering
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Effects of chlorine residue in atomic layer deposition hafnium oxide: A density-functional-theory study

Qing-Qing Sun, Wei Chen, Shi-Jin Ding, Min Xu, David Wei Zhang, and Li-Kang Wang

Appl. Phys. Lett. 91, 022901 (2007); http://dx.doi.org/10.1063/1.2756108 (3 pages) | Cited 4 times

Online Publication Date: 9 July 2007

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Hafnium tetrachloride is one of the most commonly used precursors for atomic layer deposition of HfO2. According to the experimental result, chlorine residue is almost unavoidably incorporated during the deposition process. We performed first-principles calculation to study the effects of chlorine residue in HfO2 and found that chlorine at the interstitial site serves as a source of negative fixed charge while chlorine at the oxygen substitutional site changes its charge state depending on the position of the electron chemical potential within the band gap of HfO2. Moreover, chlorine also reduces the band gap of HfO2 by raising the valence band maximum.
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77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
71.20.Ps Other inorganic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Negative refractive heterostructure bicrystal for beam steering or control component action

Clifford M. Krowne

Appl. Phys. Lett. 91, 022902 (2007); http://dx.doi.org/10.1063/1.2755706 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2007

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It has been discovered that heterostructure bicrystal arrangements lead to field asymmetry in guided wave structures. Here a study is conducted over a range of nominal permittivity values to see if the effect is present in widely varying dielectric materials. Marked shifts of the field distribution occur in some cases, and this can be the basis of an all electronic device that provides beam steering or a device that gives control component action. Such all electronic devices could be fixed or even constructed as a control component using materials with electrostatically controllable permittivity. Distributions have been obtained to demonstrate the effect using an anisotropic Green’s function solver.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.Ct Interface structure and roughness
77.22.Ch Permittivity (dielectric function)

Giant enhancement of second harmonic generation in poled ferroelectric crystals

Jingjuan Li, Zhiyuan Li, Yan Sheng, and Daozhong Zhang

Appl. Phys. Lett. 91, 022903 (2007); http://dx.doi.org/10.1063/1.2755780 (3 pages) | Cited 11 times

Online Publication Date: 9 July 2007

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The authors propose a simple one-dimensional inhomogeneous system composed of periodically alternating stacked air and poled LiNbO3 crystal layers. This structure combines the advantages of photonic band gap (PBG) structures and periodically poled ferroelectric crystals, so the high density of modes and quasiphase matching can be achieved simultaneously. They find that compared with simple quasiphase-matched and PBG structures, the conversion efficiency of second harmonic generation in this structure can be significantly enhanced when the pump and second harmonic fields are both tuned to the band edge.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.80.-e Ferroelectricity and antiferroelectricity

Oxygen pressure dependence of HfO2 stoichiometry: An ab initio investigation

C. Tang and R. Ramprasad

Appl. Phys. Lett. 91, 022904 (2007); http://dx.doi.org/10.1063/1.2756107 (3 pages) | Cited 5 times

Online Publication Date: 10 July 2007

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The oxygen pressure dependence of the formation of excess O vacancies and interstitials in monoclinic HfO2 was investigated by performing first principles and thermodynamic calculations. Upper and lower critical oxygen pressures are identified that heavily favor the formation of oxygen interstitials and vacancies, respectively. The ratio of these critical pressures can be specified unambiguously as the sum of the formation energies of O vacancies and interstitials at 0 K obtained from ab initio calculations.
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61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.J- Point defects and defect clusters
65.40.G- Other thermodynamical quantities

Time tuning of ferroelectric film varactors under pulse voltages

Andrey B. Kozyrev, Vitaly N. Osadchy, Dmitry M. Kosmin, Andrey V. Tumarkin, Tatiana Kaydanova, and David Ginley

Appl. Phys. Lett. 91, 022905 (2007); http://dx.doi.org/10.1063/1.2756126 (3 pages) | Cited 9 times

Online Publication Date: 10 July 2007

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Significant difference in the capacitance tunability of paraelectric state ferroelectric capacitors under dc and pulse voltages is demonstrated. Along with a fast tuning (τ<10 ns) the slow relaxation processes (τ ≥ 100 s) responsible for up to ∼ 30% variation of the capacitance were observed. The observed effect is a main obstacle for application of paraelectric state ferroelectrics on microwaves.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Analysis for crystal structure of Bi(Fe,Sc)O3 thin films and their electrical properties

Shintaro Yasui, Hiroshi Uchida, Hiroshi Nakaki, Ken Nishida, Hiroshi Funakubo, and Seiichiro Koda

Appl. Phys. Lett. 91, 022906 (2007); http://dx.doi.org/10.1063/1.2756356 (3 pages) | Cited 25 times

Online Publication Date: 10 July 2007

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Thin films of Bi(Fe1−xScx)O3 (BFSO) system were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition to improve the electrical resistivity by substituting electrically unstable Fe3+ cations for stable Sc3+ cations. A single phase of perovskite was obtained in the range of x = 0–0.30, in which selective replacement of Fe3+ and Sc3+ was confirmed in x = 0–0.15 by using Raman measurement. The leakage current density of the BFSO films was reduced by increasing x. A well-saturated polarization–electric field hysteresis loop was obtained for BFSO films with x = 0.15, showing remanent polarization of approximately 35 μC/cm2.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
78.66.Nk Insulators

Very large spontaneous electric polarization in BiFeO3 single crystals at room temperature and its evolution under cycling fields

D. Lebeugle, D. Colson, A. Forget, and M. Viret

Appl. Phys. Lett. 91, 022907 (2007); http://dx.doi.org/10.1063/1.2753390 (3 pages) | Cited 130 times

Online Publication Date: 11 July 2007

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Electric polarization loops are measured at room temperature on highly pure BiFeO3 single crystals synthesized by a flux growth method. Because the crystals have a high electrical resistivity, the resulting low leakage currents allow the authors to measure a large spontaneous polarization in excess of 100 μC cm−2, a value never reported in the bulk. During electric cycling, the slow degradation of the material leads to an evolution of the hysteresis curves eventually preventing full saturation of the crystals.
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77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Ee Antiferromagnetics

Multistacked Al2O3/HfO2/SiO2 tunnel layer for high-density nonvolatile memory application

Wei Chen, Wen-Jun Liu, Min Zhang, Shi-Jin Ding, David Wei Zhang, and Ming-Fu Li

Appl. Phys. Lett. 91, 022908 (2007); http://dx.doi.org/10.1063/1.2756849 (3 pages) | Cited 5 times

Online Publication Date: 11 July 2007

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A memory capacitor with a multistacked tunnel layer of Al2O3/HfO2/SiO2 (AHO) has been fabricated together with HfO2 charge trapping layer and Al2O3 control oxide layer. The resulting capacitor exhibits a memory window as large as 7.6 V for ±12 V sweep voltage range, a significant flatband voltage shift of 2.1 V after 10 V/100 μs programing as well as improved charge retention compared with a single SiO2 tunnel layer. The different memory effects in various sweep voltage ranges and enhanced retention characteristics have been explained based on the variable electrical thickness of the AHO stack under different electric fields.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits

+Capacitance-voltage characteristics of BiFeO3/SrTiO3/GaN heteroepitaxial structures

S. Y. Yang, Q. Zhan, P. L. Yang, M. P. Cruz, Y. H. Chu, R. Ramesh, Y. R. Wu, J. Singh, W. Tian, and D. G. Schlom

Appl. Phys. Lett. 91, 022909 (2007); http://dx.doi.org/10.1063/1.2757089 (3 pages) | Cited 24 times

Online Publication Date: 11 July 2007

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The authors report the integration of multiferroic BiFeO3 films with the semiconductor GaN using liquid-delivery metal-organic chemical-vapor deposition. Epitaxial BiFeO3 films were deposited via interface control using SrTiO3 buffer/template layers. The growth orientation relationship was found to be (111)[1math0]BiFeO3‖(111)[1math0]SrTiO3‖(0001)[11math0]GaN, with in-plane 180° rotational twins. The C-V characteristics of a Pt/BiFeO3/SrTiO3/GaN capacitor exhibited hysteresis with a memory window of ∼ 3 V at a sweeping voltage of ±30 V.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.65.Ac Multilayers
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.80.+q Magnetomechanical effects, magnetostriction

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

S. Krohns, P. Lunkenheimer, S. G. Ebbinghaus, and A. Loidl

Appl. Phys. Lett. 91, 022910 (2007); http://dx.doi.org/10.1063/1.2757098 (3 pages) | Cited 45 times

Online Publication Date: 11 July 2007

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The authors present dielectric measurements of the colossal dielectric constant material CaCu3Ti4O12 extending up to 1.3 GHz also covering so far only rarely investigated single-crystalline samples. Special emphasis is put on the second relaxation reported in several works on polycrystals, which the authors detect also in single crystals. For polycrystalline samples, the authors provide a recipe to achieve values of the dielectric constant as high as in single crystals.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Space charge contribution to the apparent enhancement of polarization in ferroelectric bilayers and multilayers

I. B. Misirlioglu, M. Alexe, L. Pintilie, and D. Hesse

Appl. Phys. Lett. 91, 022911 (2007); http://dx.doi.org/10.1063/1.2757127 (3 pages) | Cited 19 times

Online Publication Date: 11 July 2007

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The authors study the effect of interfacial space charge in ferroelectric multilayers through a thermodynamic formalism. Using an electrostatic approach that takes into account the presence of trapped charges between the layers, the authors show that considerable modification in electrical properties can be exhibited, giving rise to polarization enhancement depending on the type of dopants and configuration of the layers. Space charge effect becomes more pronounced in structures with smaller ferroelectric layer fractions. It is shown that built-in polarization due to space charge can stabilize a switchable ferroelectric polarization at small fractions of the ferroelectric layer in a paraelectric matrix.
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77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Jp Dielectric breakdown and space-charge effects

Percolative conductor/polymer composite films with significant dielectric properties

Qian Chen, Piyi Du, Lu Jin, Wenjian Weng, and Gaorong Han

Appl. Phys. Lett. 91, 022912 (2007); http://dx.doi.org/10.1063/1.2757131 (3 pages) | Cited 32 times

Online Publication Date: 11 July 2007

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A percolative film with conductive acetylene black introduced into β-polyvinylidene fluoride was prepared by dip-coating method. Percolation theory was employed to explain the dielectric behavior of polymer/conductor composite films. Experimental results showed that the dielectric constant of polymer/conductor composite films can reach 56 and the dielectric loss is below 0.15 when acetylene black concentration is in the neighborhood of percolation threshold (fc). The experimental results are in good agreement with classic percolation power law, with fc ≈ 1.3% and exponent q ≈ 0.53. Such composite films have a potential to become capacitors and can be easily fabricated due to its flexibility.
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77.84.Lf Composite materials
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Defects in hydrothermally grown bulk ZnO

H. von Wenckstern, H. Schmidt, M. Grundmann, M. W. Allen, P. Miller, R. J. Reeves, and S. M. Durbin

Appl. Phys. Lett. 91, 022913 (2007); http://dx.doi.org/10.1063/1.2757097 (3 pages) | Cited 19 times

Online Publication Date: 11 July 2007

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Hydrothermally grown bulk ZnO (Tokyo Denpa) was investigated using junction-capacitance spectroscopy on silver oxide Schottky contacts (barrier height of 1.20 eV, ideality factor of 1.04). Two main shallow defects, T1 and T2, with thermal activation energies of 13 and 52 meV, respectively, were identified. Two closely lying, deep defect levels E3/E3′ at approximately 320 meV below the conduction band were found in higher concentrations (mid-1014 cm−3) than the shallow donors. 4 K photoluminescence showed dominant emission from excitons bound to three neutral donors, aluminum, hydrogen, and an unassigned impurity, with donor binding energies close to the thermal activation energy of T2.
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71.55.Gs II-VI semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
71.35.-y Excitons and related phenomena
73.30.+y Surface double layers, Schottky barriers, and work functions
78.55.Et II-VI semiconductors

Multiferroic properties of Bi0.87La0.05Tb0.08FeO3 ceramics prepared by spark plasma sintering

Q. H. Jiang, J. Ma, Y. H. Lin, Ce-Wen Nan, Z. Shi, and Z. J. Shen

Appl. Phys. Lett. 91, 022914 (2007); http://dx.doi.org/10.1063/1.2757103 (3 pages) | Cited 13 times

Online Publication Date: 11 July 2007

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Dense Bi0.87La0.05Tb0.08FeO3 ceramics were prepared by spark plasma sintering. The sample showed stable dielectric constant and low dielectric loss ( ∼ 5%), and a saturation ferroelectric loop with remnant polarization of 17 μC/cm2 and saturation polarization of 19 μC/cm2, as well as good ferromagnetism with saturation magnetization of 0.71 emu/g, at room temperature. After the sample was poled, its piezoelectric constant was measured as 12.8 pC/N, and, in particular, an obvious magnetoelectric coupling was observed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.65.Bn Piezoelectric and electrostrictive constants
75.80.+q Magnetomechanical effects, magnetostriction
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Giant magnetoelectric effect (under a dc magnetic bias of 2 Oe) in laminate composites of FeBSiC alloy ribbons and Pb(Zn1/3,Nb2/3)O3–7%PbTiO3 fibers

Shuxiang Dong, Junyi Zhai, Zhengping Xing, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 91, 022915 (2007); http://dx.doi.org/10.1063/1.2757146 (3 pages) | Cited 28 times

Online Publication Date: 12 July 2007

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Giant magnetoelectric (ME) voltage and charge coefficients have been found in long-type composites of high-permeability magnetostrictive FeBSiC alloy ribbons laminated together with piezoelectric Pb(Zn1/3,Nb2/3)O3–7%PbTiO3 single crystal fibers. The maximum ME voltage and charge coefficients at low frequencies were 10.5 V/cm Oe and 1 nC/Oe under a notably low dc magnetic bias of 2 Oe; at resonance, these coefficients were dramatically increased to 400 V/cm Oe and 42 nC/Oe, respectively. These values are much higher, and the required dc magnetic bias much lower, than those of previously reported Terfenol-D based ME laminates.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites

Epitaxial growth of ZrO2 on GaN templates by oxide molecular beam epitaxy

Xing Gu, Natalia Izyumskaya, Vitaly Avrutin, Bo Xiao, and Hadis Morkoç

Appl. Phys. Lett. 91, 022916 (2007); http://dx.doi.org/10.1063/1.2753719 (3 pages)

Online Publication Date: 13 July 2007

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Molecular beam epitaxial growth of ZrO2 has been achieved on GaN (0001)/c-Al2O3 substrates employing a reactive H2O2 oxygen source. A low temperature buffer followed by in situ annealing and high temperature growth has been employed to attain monoclinic, (100)-oriented ZrO2 thin films. The typical full width at half maximum of a 30-nm-thick ZrO2 (100) film rocking curves is 0.4 arc deg and the root-mean-square surface roughness is ∼ 4 Å. ω−2θ and pole figure x-ray diffraction patterns confirm the monoclinic structure of ZrO2. Data support an in-plane epitaxial relationship of ZrO2 [010]‖GaN[11math] and ZrO2 [001]‖GaN[1math00]. X-ray diffraction and reflection high-energy electron diffraction analyses reveal in-plane compressive strain, which is mainly due to the lattice mismatch.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments

Observation of high permittivity in Ho substituted BaZr0.1Ti0.9O3 ceramics

S. Bhaskar Reddy, M. S. Ramachandra Rao, and K. Prasad Rao

Appl. Phys. Lett. 91, 022917 (2007); http://dx.doi.org/10.1063/1.2755932 (3 pages) | Cited 12 times

Online Publication Date: 13 July 2007

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The authors observed an extremely high permittivity ( ∼ 35 000 at TC) in barium zirconate titanate (BaZr0.1Ti0.9O3) ceramics with holmium substitution (1–5 mol %) in Ba site. Careful microstructural investigation and energy dispersive spectroscopy analysis of the 1–2 mol % of Ho substituted ceramics showed the enrichment of a Ho-phase along the grain boundaries with a composition close to the Ho2Ti2O7 pyrochlore. The formation of Ho rich phase resulted in the Maxwell-Wagner polarization mechanism, which leads to this unusually high permittivity. Ceramics with 3 mol % or higher Ho content showed lesser permittivity values compared to 1–2 mol %, probably due to the increase in pyrochlore phase. These high dielectric constant ceramics are useful in nanoscale devices.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.Mm Grain and twin boundaries
77.22.Ej Polarization and depolarization

Dielectric functions and critical points of PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 grown on SrTiO3 substrate

T. D. Kang, Hosun Lee, G. Xing, N. Izumskaya, V. Avrutin, B. Xiao, and H. Morkoç

Appl. Phys. Lett. 91, 022918 (2007); http://dx.doi.org/10.1063/1.2756168 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2007

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Single crystalline PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 thin films on SrTiO3 (001) substrates were grown by a combination of molecular beam epitaxy and rf sputtering methods. The authors measured the dielectric functions of the thin films using spectroscopic ellipsometry and determined the interband critical point energies using standard critical point model. They compared the critical point energies to the band structure calculations in the literature. The data suggest that anticrossing behavior occurs between Ea and Eb near Zr = 0.17. This phenomenon is attributed to a coupling between X1c and X3c bands caused by intrinsic alloy disorder.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
78.66.-w Optical properties of specific thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.-b Electron density of states and band structure of crystalline solids
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Organic molecular nanowires: N,N′-dimethylperylene-3,4,9,10-bis(dicarboximide) on KBr(001)

M. Fendrich and T. Kunstmann

Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages) | Cited 13 times

Online Publication Date: 9 July 2007

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The growth of N,N′-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) has been studied by frequency modulation atomic force microscopy. At low coverages, DiMe-PTCDI forms molecular wires with a length of up to 600 nm; at higher coverages, wire networks were found. The height of the wires is two or more molecular layers; if the sample is cooled to 250 K during evaporation, also wires of one layer are found. All wires grow along the [110] and [math10] directions of the KBr(001) substrate. There is no wetting layer of molecules. Atomic resolution of the substrate could be achieved between the wires. Due to their size and shape, the molecular nanowires might act as a model system for organic electronics research on insulating substrates.
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81.07.Nb Molecular nanostructures
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)

Circularly polarized emission from colloidal nanocrystal quantum dots confined in microcavities formed by chiral mirrors

Fan Zhang, Jian Xu, Akhlesh Lakhtakia, Sean M. Pursel, Mark W. Horn, and Andrew Wang

Appl. Phys. Lett. 91, 023102 (2007); http://dx.doi.org/10.1063/1.2751129 (3 pages) | Cited 8 times

Online Publication Date: 9 July 2007

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Colloidal semiconductor nanocrystal quantum dots (NQDs) confined in a microcavity device emit resonance-enhanced, circularly polarized (CP) light, when the device consists of a pair of chiral sculptured-thin-film mirrors separated by layers of emissive nanocrystals and spacers that form a λ/2-resonant cavity. The resonant emission from the NQDs within the microcavity is strongly directed normally to the mirror surfaces. It is speculated that the enhanced coupling between the NQD excitons and the confined electromagnetic field resulted in the observed CP emission from the embedded NQDs with significant improvements in the light output's directionality and color purity.
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78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.-m Photoluminescence, properties and materials
82.70.Dd Colloids
42.79.Bh Lenses, prisms and mirrors
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