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29 Jan 2007

Volume 90, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages)

Biqin Huang, Igor Altfeder, and Ian Appelbaum
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High-resolution photoelectron spectroscopy of Ge-based HfO2 gate stacks

O. Renault, L. Fourdrinier, E. Martinez, L. Clavelier, C. Leroyer, N. Barrett, and C. Crotti

Appl. Phys. Lett. 90, 052112 (2007); http://dx.doi.org/10.1063/1.2435512 (3 pages) | Cited 18 times

Online Publication Date: 2 February 2007

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High-resolution photoelectron spectroscopy with synchrotron radiation (energy resolution of 50 meV) is used to investigate interfacial properties of Ge/GeOx (1 nm)/HfO2 (1 nm) gate stacks. With soft x rays, a reliable Ge3d core-level study is possible thanks to the much lower cross section of the Hf5p core level than that using Al Kα radiation. It is clearly shown that Hf-germanate bonding states are formed at the GeOx/HfO2 interface, with an additional Ge3d spectral component shifted to lower binding energy relative to GeO2.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
77.55.-g Dielectric thin films

Defect reduction of selective Ge epitaxy in trenches on Si(001) substrates using aspect ratio trapping

J.-S. Park, J. Bai, M. Curtin, B. Adekore, M. Carroll, and A. Lochtefeld

Appl. Phys. Lett. 90, 052113 (2007); http://dx.doi.org/10.1063/1.2435603 (3 pages) | Cited 39 times

Online Publication Date: 2 February 2007

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Defect-free germanium has been demonstrated in SiO2 trenches on silicon via Aspect Ratio Trapping, whereby defects arising from lattice mismatch are trapped by laterally confining sidewalls. Results were achieved through a combination of conventional photolithography, reactive ion etching of SiO2, and selective growth of Ge as thin as 450 nm. Full trapping of dislocations originating at the Ge/Si interface has been demonstrated for trenches up to 400 nm wide without the additional formation of defects at the sidewalls. This approach shows great promise for the integration of Ge and/or III-V materials, sufficiently large for key device applications, onto silicon substrates.
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68.55.-a Thin film structure and morphology
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
61.72.Lk Linear defects: dislocations, disclinations

Double-flip transfer of indium phosphide layers via adhesive wafer bonding and ion-cutting process

Wayne Chen, Peng Chen, Yi Jing, S. S. Lau, T. F. Kuech, Jiariu Liu, Xeimei Wang, and Wei-Kan Chu

Appl. Phys. Lett. 90, 052114 (2007); http://dx.doi.org/10.1063/1.2450665 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2007

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A twice-transferred layer of indium phosphide (InP) onto a host substrate by means of ion cutting and adhesive wafer bonding was demonstrated to be suitable for device integration. A thin layer was first transferred onto a glass handle through the ion-cutting process by hydrogen implantation and adhesive bonding. The InP/adhesive/glass structure was then bonded to a host substrate using benzocyclobutene, followed by thermal separation of the temporary bond. The surface of the resulting InP layer is that of the original substrate, demonstrating the feasibility of prefabricated device layer transfer without etching sacrificial donors. The electrical properties of the transferred layer are also presented.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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Entropy change upon magnetic field and pressure variations

N. A. de Oliveira

Appl. Phys. Lett. 90, 052501 (2007); http://dx.doi.org/10.1063/1.2434154 (3 pages) | Cited 15 times

Online Publication Date: 29 January 2007

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In this letter it is theoretically discussed the magnetocaloric effect under applied pressure and the barocaloric effect under applied magnetic field in compounds undergoing a first order magnetic phase transition. The theoretical findings of this letter point out that the magnetocaloric effect upon simultaneous variation of the magnetic field and pressure as well as the barocaloric effect in first order phase transition compounds can be very important for magnetic refrigeration technology.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.10.Dg Crystal-field theory and spin Hamiltonians
65.40.G- Other thermodynamical quantities

Enhanced exchange bias coupling in Fe/FexMn1−x bilayer by reducing vertical lattice constants

Wen-Chin Lin, Bo-Yao Wang, Te-Yu Chen, Ling-Chih Lin, Yu-Wen Liao, Wei Pan, Nai-Yeou Jih, Ker-Jar Song, and Minn-Tsong Lin

Appl. Phys. Lett. 90, 052502 (2007); http://dx.doi.org/10.1063/1.2435514 (3 pages) | Cited 3 times

Online Publication Date: 29 January 2007

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The modification of crystalline structure by epitaxial growth on different single crystals induces crucial effects on the exchange bias coupling. Due to the larger lattice constant (a0) of Cu3Au(100) (a0 = 3.75 Å), the vertical lattice constants of Fe/FexMn1−x films on Cu3Au(100) are much smaller than those of the Fe/FexMn1−x/Cu(100) system (Cu: a0 = 3.61 Å). By reducing the vertical lattice constants, the interface exchange bias coupling energy of Fe/FexMn1−x/Cu3Au(100) is enhanced to be 0.12–0.18 erg/cm2, which is approximately four times that of the Cu(100) system.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
68.55.-a Thin film structure and morphology

Spin-valve phototransistor

Biqin Huang, Igor Altfeder, and Ian Appelbaum

Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages) | Cited 2 times

Online Publication Date: 29 January 2007

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The spin-valve phototransistor is a semiconductor-ferromagnetic metal multilayer-semiconductor transistor operated by photoexciting hot electrons in the emitter semiconductor into a Schottky collector. This device uses an ultra-high vacuum-bonded float zone Si/multilayer/n-InP structure. To distinguish the emitter interband-excited component of collector current from base/collector internal photoemission, a lock-in spectroscopy sensitive only to the magnetocurrent is used. The experimental results indicate a pathway to improve the magnetocurrent of a related device, the spin-valve photodiode, by increasing the fraction of hot electron current that travels through both layers of the ferromagnetic spin valve and demonstrate that hot electrons photogenerated in one semiconductor can be collected by another through a thin ferromagnetic multilayer.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

High TC ferromagnetism of Zn(1−x)CoxO diluted magnetic semiconductors grown by oxygen plasma-assisted molecular beam epitaxy

G. L. Liu, Q. Cao, J. X. Deng, P. F. Xing, Y. F. Tian, Y. X. Chen, S. S. Yan, and L. M. Mei

Appl. Phys. Lett. 90, 052504 (2007); http://dx.doi.org/10.1063/1.2437111 (3 pages) | Cited 22 times

Online Publication Date: 31 January 2007

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Co-doped wurtzite ZnO [Zn(1−x)CoxO] thin films have been grown on Al2O3(0001) substrates by using oxygen plasma-assisted molecular beam epitaxy at the low growth temperature of 450 °C. The epitaxial films of Co concentration at 0 ⩽ x ⩽ 0.12 are single crystalline, which were examined by reflection high energy electron diffraction and x-ray diffraction. Both of optical transmission spectrum and in situ. x-ray photoelectron spectroscopy studies confirmed the incorporation of Co2+ cations into wurtzite ZnO lattice. Magnetic measurements revealed that the Zn(1−x)CoxO thin films are ferromagnetic with Curie temperature TC above room temperature, and the ferromagnetism shows intrinsic characteristic.
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68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.66.Hf II-VI semiconductors

High resolution transmission electron microscopy and Raman scattering studies of room temperature ferromagnetic Ni-doped ZnO nanocrystals

Hao Wang, Y. Chen, H. B. Wang, C. Zhang, F. J. Yang, J. X. Duan, C. P. Yang, Y. M. Xu, M. J. Zhou, and Q. Li

Appl. Phys. Lett. 90, 052505 (2007); http://dx.doi.org/10.1063/1.2435606 (3 pages) | Cited 27 times

Online Publication Date: 31 January 2007

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Ni-doped ZnO nanocrystals have been synthesized by a wet chemical reaction. The nanocrystals have been investigated carefully by high resolution transmission electron microscopy and all the particles are found to be the known wurtzite ZnO. X-ray photoelectron spectroscopy and Raman spectra results provide the evidence that Ni2+ is incorporated into the ZnO lattice at Zn2+ site. Magnetic property measurements reveal that the as-grown Zn1−xNixO nanocrystals exhibit room temperature ferromagnetic behaviors with saturation magnetization of 0.01 emu/g and Curie temperature above 340 K for Ni concentration of ∼ 1% in atomic ratio.
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75.50.Pp Magnetic semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.Hv Other nonmetallic inorganics
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Large intrinsic effect of axial strain on the critical current of high-temperature superconductors for electric power applications

D. C. van der Laan and J. W. Ekin

Appl. Phys. Lett. 90, 052506 (2007); http://dx.doi.org/10.1063/1.2435612 (3 pages) | Cited 35 times

Online Publication Date: 31 January 2007

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A remarkably large reversible reduction in the critical current of “second generation” high-temperature superconductors for electric power applications has been measured with a new technique over a wide range of mechanical strain. The effect amounts to a 40% reduction in critical current at 1% compressive strain in self-magnetic field, and is symmetric for compressive and tensile strains. The intrinsic effect is measured in highly aligned multigranular YBa2Cu3O7−d coated conductors made by different processes, including superconductors with nanoscale pinning centers. This effect and its magnitude are expected to have a significant impact on power applications and provide a useful new parameter for probing the fundamental nature of current transport in high-temperature superconductors.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation

Decrease of Tc and persistent two gaps upon enhancement of the Ca doping in MgB2 superconductor

Yaxin Sun, Dongli Yu, Zhongyuan Liu, Julong He, Xiangyi Zhang, Yongjun Tian, Jianyong Xiang, and Dongning Zheng

Appl. Phys. Lett. 90, 052507 (2007); http://dx.doi.org/10.1063/1.2435711 (3 pages) | Cited 8 times

Online Publication Date: 31 January 2007

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Superconducting properties have been investigated in the Ca-doped MgB2 (Mg1−xCaxB2) superconductors, which have been synthesized under high temperature and pressure. With increasing doping level x, a linear drop of the critical temperature Tc is observed, and the gap Δσ keeps nearly fixed and the gap Δπ deceases, giving rise to the persistent two-gap feature in the Mg1−xCaxB2 samples for x up to 0.07. Both the Sommerfeld constant γn and the relative weight γπ/γn are found to decrease with raising x, indicative of the decrease of Nπ(0).
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Dh Effects of crystal defects, doping and substitution
74.25.Jb Electronic structure (photoemission, etc.)

Magnetic and transport properties of homogeneous MnxGe1−x ferromagnetic semiconductor with high Mn concentration

Y. X. Chen, Shi-shen Yan, Y. Fang, Y. F. Tian, S. Q. Xiao, G. L. Liu, Y. H. Liu, and L. M. Mei

Appl. Phys. Lett. 90, 052508 (2007); http://dx.doi.org/10.1063/1.2436710 (3 pages) | Cited 13 times

Online Publication Date: 1 February 2007

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Homogeneous MnxGe1−x ferromagnetic semiconductor films with high Mn concentration were prepared, contrasting with dilute inhomogeneous MnxGe1−x magnetic semiconductors. The saturation magnetization of Mn0.57Ge0.43 films is high, up to 327 emu/cm3 (1.04μB/Mn) at 5 K, and the Curie temperature is about 213 K. The Mn0.57Ge0.43 films show semiconducting resistance, but the magnetoresistance is negligibly small. The anomalous Hall effect was observed below the Curie temperature, which is consistent with the magnetic measurements. The global ferromagnetism was discussed based on s,p-d exchange coupling between the weakly localized s,p hole carriers and the strongly localized d electrons of the Mn atoms.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Le Other inorganic semiconductors
75.50.Pp Magnetic semiconductors
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Et Exchange and superexchange interactions

Enhanced magnetocaloric response in Cr/Mo containing Nanoperm-type amorphous alloys

V. Franco, C. F. Conde, A. Conde, and L. F. Kiss

Appl. Phys. Lett. 90, 052509 (2007); http://dx.doi.org/10.1063/1.2437659 (3 pages) | Cited 29 times

Online Publication Date: 1 February 2007

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The magnetocaloric effect of Fe76Cr8−xMoxCu1B15 (x = 0,4) alloys is studied. Although the combined addition of Cr and Mo is more efficient in tuning the Curie temperature of the alloy, the Mo-free alloy presents a higher magnetocaloric response. The refrigerant capacity (RC) for the Mo-containing alloy is comparable to that of Gd5Ge1.9Si2Fe0.1 (for a field of 50 kOe, RC = 273 J kg−1 for the Mo alloy vs 240 J kg−1 for the Gd-based one), with a larger temperature span of the optimal refrigeration cycle (250 K vs 90 K, respectively). The restriction of the temperature span to 90 K gives RC = 187 J kg−1 for the Mo alloy. A master curve behavior for the magnetic entropy change is also evidenced.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
65.40.G- Other thermodynamical quantities
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Process-dependent defects in Si/HfO2/Mo gate oxide heterostructures

S. Walsh, L. Fang, J. K. Schaeffer, E. Weisbrod, and L. J. Brillson

Appl. Phys. Lett. 90, 052901 (2007); http://dx.doi.org/10.1063/1.2435585 (3 pages) | Cited 15 times

Online Publication Date: 29 January 2007

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The authors have used low energy electron-excited nanoscale-depth-resolved spectroscopy to probe the bulk and interface defect states of ultrathin Mo/HfO2/Si with conventional process sequences. Multiple deep level emissions are evident below the 5.9 eV HfO2 near band edge, including three associated with HfO2 oxygen vacancies in different charge states predicted theoretically. Defects resembling SiO2-related nonbonding oxygen hole centers and positively charged O vacancies increase with depth within the 4 nm HfO2 film suggesting Hf silicate formation at the HfO2/Si interface. These states vary dramatically between process sequences and can be understood in terms of known reactions at HfO2–Si interfaces.
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71.55.-i Impurity and defect levels
73.20.At Surface states, band structure, electron density of states
61.72.J- Point defects and defect clusters

Giant strain in PbZr0.2Ti0.8O3 nanowires

Z. H. Zhou, X. S. Gao, John Wang, K. Fujihara, S. Ramakrishna, and V. Nagarajan

Appl. Phys. Lett. 90, 052902 (2007); http://dx.doi.org/10.1063/1.2435941 (3 pages) | Cited 29 times

Online Publication Date: 29 January 2007

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The authors report a giant reversible piezoelectric strain of ∼ 4.2% achieved with single-crystalline PbZr0.2Ti0.8O3 nanowires of ∼ 70 nm in diameter, which is nearly 300% greater than the nominal values reported for ceramic perovskite single crystals. The giant strain arises from the reversible switching of ferroelastic domains. In the nanowires, there is a competition between surface tension, which forces in-plane polarization, and applied electric field, which stabilizes out-of-plane polarization, through the entire voltage cycle, the result of which is the reversible movement of ferroelastic domains.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
77.22.Ej Polarization and depolarization
81.40.Jj Elasticity and anelasticity, stress-strain relations

Electrical properties of Bi2Mg2/3Nb4/3O7 (BMN) pyrochlore thin films deposited on Pt and Cu metal at low temperatures for embedded capacitor applications

Cheng-Ji Xian, Jong-Hyun Park, Kyung-Chan Ahn, Soon-Gil Yoon, Jeong-Won Lee, Woon-Chun Kim, Sung-Taek Lim, Seung-Hyun Sohn, Jin-Seok Moon, Hyung-Mi Jung, Seung-Eun Lee, In-Hyung Lee, Yul-Kyo Chung, Min-Ku Jeon, and Seong-Ihl Woo

Appl. Phys. Lett. 90, 052903 (2007); http://dx.doi.org/10.1063/1.2435336 (3 pages) | Cited 11 times

Online Publication Date: 29 January 2007

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200-nm-thick BMN films were deposited on Pt/TiO2/SiO2/Si and Cu/Ti/SiO2/Si substrates at various temperatures by pulsed laser deposition. The dielectric constant and capacitance density of the films deposited on Pt and Cu electrodes show similar tendency with increasing deposition temperature. On the other hand, dielectric loss of the films deposited on Cu electrode varies from 0.7% to 1.3%, while dielectric loss of films on Pt constantly shows 0.2% even though the deposition temperature increases. The low value of breakdown strength in BMN films on Pt compared to films deposited on Cu electrode was attributed to the increase of surface roughness by the formation of secondary phases at interface between BMN films and Pt electrodes.
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77.55.-g Dielectric thin films
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
77.22.Jp Dielectric breakdown and space-charge effects
68.55.-a Thin film structure and morphology

Cylinder-shaped ultrasonic motors 4.8 mm in diameter using electroactive piezoelectric materials

Laihui Luo, Hua Zhu, Chunsheng Zhao, Haixia Wang, and Haosu Luo

Appl. Phys. Lett. 90, 052904 (2007); http://dx.doi.org/10.1063/1.2437093 (3 pages) | Cited 25 times

Online Publication Date: 30 January 2007

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Two cylinder-shaped ultrasonic motors 4.8 mm in diameter were developed. This kind of motor was driven by four pieces of piezoelectric materials, which were used to excite the two first-bending vibrations. Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) crystal and Pb(Zr,Ti)O3 (PZT) ceramic piezoelectric materials were used as drive elements. The motor based on PMNT crystals could operate at a voltage of 25 Vp-p (peak to peak). When driven by a 100 Vp-p voltage, the motor could run at frequency ranging from 26 to 68 kHz and the revolution speed reached 450 rpm. Its maximum output torque was 0.6 mN m. The motor based on the PZT ceramic did not exhibit high performance as the PMNT crystal motor. The piezoelectric materials affect the performance of the motors greatly.
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84.50.+d Electric motors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Electric field gating with ionic liquids

Rajiv Misra, Mitchell McCarthy, and Arthur F. Hebard

Appl. Phys. Lett. 90, 052905 (2007); http://dx.doi.org/10.1063/1.2437663 (3 pages) | Cited 35 times

Online Publication Date: 30 January 2007

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The authors show that ionic liquids are well suited to specialized electric field gating applications in which large surface charge densities can be induced on the surfaces of low-carrier density thin-film metals. Using either coplanar or overlay gate configurations, they demonstrate field-induced resistance changes on the order of a factor of 104 for thin conducting InOx films. The areal capacitances and field effect mobilities noticeably exceed those that can be achieved using AlOx dielectrics. In addition, the charge state can be frozen in by reducing the temperature, thus providing an opportunity for electric field tuning of metal-insulator transitions in a variety of thin-film systems.
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66.10.Ed Ionic conduction
68.15.+e Liquid thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
71.30.+h Metal-insulator transitions and other electronic transitions
73.50.Dn Low-field transport and mobility; piezoresistance

Soft chemical deposition of BiFeO3 multiferroic thin films

A. H. M. Gonzalez, A. Z. Simões, L. S. Cavalcante, E. Longo, J. A. Varela, and C. S. Riccardi

Appl. Phys. Lett. 90, 052906 (2007); http://dx.doi.org/10.1063/1.2433027 (3 pages) | Cited 22 times

Online Publication Date: 31 January 2007

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BiFeO3 thin films free of secondary phases were obtained by the soft chemical solution on Pt(111)/Ti/SiO2/Si substrates after annealing at 500 °C for 2 h. The film grown in the (100) direction presented a remanent polarization Pr of 31 μC/cm2 at room temperature. Electrical measurements using both quasistatic hysteresis and pulsed polarization confirm the existence of ferroelectricity with a switched polarization of 60–70 μC/cm2, ΔP = (P*−P̂). Low leakage conduction and an out-of-plane piezoelectric (d3) coefficient of 40 pm/V were obtained by the improvement of preparation technology.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
81.40.Gh Other heat and thermomechanical treatments

Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.33MnO3 electrodes

Céline Lichtensteiger, Matthew Dawber, Nicolas Stucki, Jean-Marc Triscone, Jason Hoffman, Jeng-Bang Yau, Charles H. Ahn, Laurent Despont, and Philipp Aebi

Appl. Phys. Lett. 90, 052907 (2007); http://dx.doi.org/10.1063/1.2433757 (3 pages) | Cited 15 times

Online Publication Date: 31 January 2007

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Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down to 28 Å (seven unit cells). The evolution of the film tetragonality c/a, studied using high resolution x-ray diffraction measurements, shows first a decrease of c/a with decreasing film thickness followed by a recovery of c/a at small thicknesses. This recovery is accompanied by a change from a monodomain to a polydomain configuration of the polarization, as directly demonstrated by piezoresponse atomic force microscopy measurements.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
68.55.-a Thin film structure and morphology

Observation of photoassisted polarization switching in BiFeO3 thin films probed by terahertz radiation

Kouhei Takahashi and Masayoshi Tonouchi

Appl. Phys. Lett. 90, 052908 (2007); http://dx.doi.org/10.1063/1.2437076 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2007

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The authors have examined the effect of photoexcitation in a multiferroic BiFeO3 thin film using terahertz radiation as the probe. The illumination of femtosecond laser pulses with a center wavelength of 400 nm gave rise to a significant improvement in the polarization switching process by the application of bias electric field. This effect is attributed to the depinning of domain walls induced by carrier excitation as reported in ordinary ferroelectrics. The authors revealed that a significantly weak laser power in the order of submilliwatt is sufficient to invoke this effect.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
78.47.-p Spectroscopy of solid state dynamics

Phase-field model for epitaxial ferroelectric and magnetic nanocomposite thin films

J. X. Zhang, Y. L. Li, D. G. Schlom, L. Q. Chen, F. Zavaliche, R. Ramesh, and Q. X. Jia

Appl. Phys. Lett. 90, 052909 (2007); http://dx.doi.org/10.1063/1.2431574 (3 pages) | Cited 39 times

Online Publication Date: 31 January 2007

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A phase-field model was developed for studying the magnetoelectric coupling effect in epitaxial ferroelectric and magnetic nanocomposite thin films. The model can simultaneously take into account the ferroelectric and magnetic domain structures, the electrostrictive and magnetostrictive effects, substrate constraint, as well as the long-range interactions such as magnetic, electric, and elastic interactions. As an example, the magnetic-field-induced electric polarization in BaTiO3–CoFe2O4 nanocomposite film was analyzed. The effects of the film thickness, morphology of the nanocomposite, and substrate constraint on the degree of magnetoelectric coupling were discussed.
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77.55.-g Dielectric thin films
75.80.+q Magnetomechanical effects, magnetostriction
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Heat capacity in magnetic and electric fields near the ferroelectric transition in triglycine sulfate

J. C. Lashley, M. F. Hundley, B. Mihaila, J. L. Smith, C. P. Opeil, T. R. Finlayson, R. A. Fisher, and N. Hur

Appl. Phys. Lett. 90, 052910 (2007); http://dx.doi.org/10.1063/1.2435333 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2007

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Specific-heat measurements are reported near the Curie temperature (TC = 320 K) on triglycine sulfate. Measurements were made on crystals whose surfaces were either nongrounded or short circuited, and were carried out in magnetic fields up to 9 T and electric fields up to 220 V/cm. In nongrounded crystals the authors find that the shape of the specific-heat anomaly near TC is thermally broadened. However, the anomaly changes to the characteristic sharp λ shape expected for a continuous transition with the application of either a magnetic field or an electric field. In crystals whose surfaces were short circuited with gold, the characteristic λ shape appeared in the absence of an external field. This effect enabled a determination of the critical exponents above and below TC, and may be understood on the basis that the surface charge originating from the pyroelectric coefficient, dP/dT, behaves as if shorted by external magnetic or electric fields.
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77.84.Jd Polymers; organic compounds
77.80.B- Phase transitions and Curie point
65.40.Ba Heat capacity
77.70.+a Pyroelectric and electrocaloric effects

Effect of (Li,Ce) doping in Aurivillius phase material Na0.25K0.25Bi2.5Nb2O9

Zhi-Gang Gai, Jin-Feng Wang, and Chun-Ming Wang

Appl. Phys. Lett. 90, 052911 (2007); http://dx.doi.org/10.1063/1.2450669 (3 pages) | Cited 11 times

Online Publication Date: 1 February 2007

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The effect of (Li,Ce) substitution for A site on the properties of Na0.25K0.25Bi2.5Nb2O9-based ceramics was investigated. The piezoelectric activity of Na0.25K0.25Bi2.5Nb2O9-based ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature (TC) gradually increases from 668 to 684 °C with increasing the (Li,Ce) modification. The piezoelectric coefficient d33 of the [(Na0.5K0.5)Bi]0.44(LiCe)0.03[ ]0.03Bi2Nb2O9 ceramic was found to be 28 pC/N, the highest value among the Na0.25K0.25Bi2.5Nb2O9-based ceramics and also almost 50% higher than the reported d33 values of other bismuth layer-structured ferroelectric systems ( ∼ 5–19 pC/N). The planar coupling factors kp and kt were found to be 8.0% and 23.0%, together with the high TC ( ∼ 670 °C) and stable piezoelectric properties, demonstrating that the (Li,Ce) modified Na0.25K0.25Bi2.5Nb2O9-based material a promising candidate for high temperature applications.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
77.80.B- Phase transitions and Curie point
61.72.up Other materials

Low dielectric loss BaNd2Ti5O14 thick films prepared by an electrophoretic deposition technique

Zhi Fu, Aiying Wu, P. M. Vilarinho, A. I. Kingon, and R. Wördenweber

Appl. Phys. Lett. 90, 052912 (2007); http://dx.doi.org/10.1063/1.2435334 (3 pages) | Cited 9 times

Online Publication Date: 2 February 2007

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BaNd2Ti5O14 (BNT) films 12–52 μm thick were fabricated on platinum metallic foils by electrophoretic deposition (EPD). 52-μm-thick BNT film exhibits a dielectric constant and a loss tangent of 107 and 0.0006 (Q of 1600) at 1 MHz, respectively. Variation in permittivity is less than 0.02% at a bias voltage ±8 kV/cm. Change of film permittivity with temperature (30–120 °C) is below +58.5 ppm/°C, pointing to a good thermal stability. Preliminary microwave measurements indicate that the losses are not significantly increased up to the gigahertz regime. EPD derived BNT thick films on metallic foils are attractive candidates for microwave communication devices.
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77.22.Gm Dielectric loss and relaxation
81.15.Pq Electrodeposition, electroplating
77.22.Ch Permittivity (dielectric function)

Atomic transport and integrity of Al2O3(2.0 nm)/HfO2(2.5 nm) gate stacks on Si

L. Miotti, R. P. Pezzi, M. Copel, C. Krug, and I. J. R. Baumvol

Appl. Phys. Lett. 90, 052913 (2007); http://dx.doi.org/10.1063/1.2437708 (3 pages) | Cited 5 times

Online Publication Date: 2 February 2007

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The integrity of Al2O3(2.0 nm)/HfO2(2.5 nm)/SiO2(<1 nm)/Si(001) stacks after rapid thermal annealing at temperature up to 1025 °C was investigated. The structures were prepared by atomic layer deposition and atomic transport was accessed by profiling all elements in the system with subnanometric depth resolution, using medium and low energy ion scattering and narrow resonant nuclear reaction profiling. Al migration toward the stack/Si interface, Al loss by desorption from the surface, and Hf transport across the Al2O3 film layer toward the outermost surface were observed. The loss of oxygen from the stack is also noticeable, most probably caused by compound dissociation and desorption of oxygen containing species. The possible detrimental effects on device electrical properties of the observed presence of Hf at the outermost surface of the dielectric stack and of Al at the dielectric/Si interface are discussed.
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77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
68.43.Mn Adsorption kinetics
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.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
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