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28 Apr 2008

Volume 92, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 173301 (2008); http://dx.doi.org/10.1063/1.2912822 (3 pages)

Takeo Minari, Masataka Kano, Tetsuhiko Miyadera, Sui-Dong Wang, Yoshinobu Aoyagi, Mari Seto, Takashi Nemoto, Seiji Isoda, and Kazuhito Tsukagoshi
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An optical limiter based on ferrofluids

Swapna S. Nair, Jinto Thomas, C. S. Suchand Sandeep, M. R. Anantharaman, and Reji Philip

Appl. Phys. Lett. 92, 171908 (2008); http://dx.doi.org/10.1063/1.2919052 (3 pages) | Cited 21 times

Online Publication Date: 1 May 2008

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We report an optical limiter based on ferrofluids which has a very high shelf life and remarkable thermal stability, which are important requirements for sustainable use with intense lasers. The colloidal suspensions contain nanosized particles of approximately 80 Å diameter, with a number density of the order of 1022/m3. The nonlinear optical transmission of the samples is studied using nanosecond and femtosecond laser pulses. Excited state absorption phenomena contribute to enhanced limiting in the nanosecond excitation regime. An advantageous feature of ferrofluids in terms of device applications is that their optical properties are controllable by an external magnetic field.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.-e Optical elements, devices, and systems
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.70.Kj Emulsions and suspensions
75.50.Mm Magnetic liquids

Dynamic fracture instability of tough bulk metallic glass

J. X. Meng, Z. Ling, M. Q. Jiang, H. S. Zhang, and L. H. Dai

Appl. Phys. Lett. 92, 171909 (2008); http://dx.doi.org/10.1063/1.2913206 (3 pages) | Cited 15 times

Online Publication Date: 2 May 2008

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We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit.1) bulk metallic glass (BMGs) under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young’s modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.43.Fs Glasses
62.20.M- Structural failure of materials
62.20.de Elastic moduli

Electron effective mean free path and thermal conductivity predictions of metallic thin films

Jae Sik Jin, Joon Sik Lee, and Ohmyoung Kwon

Appl. Phys. Lett. 92, 171910 (2008); http://dx.doi.org/10.1063/1.2917454 (3 pages) | Cited 7 times

Online Publication Date: 2 May 2008

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A simple model of the electron effective mean free path (MFP) in thin metal films is proposed, and the thermal conductivities of aluminum and copper thin films are calculated by solving the Boltzmann transport equation (BTE). In the modeling of the electron effective MFP, the combined contributions of the bulk MFP and the film MFP are taken into account. The proposed effective electron MFP model is incorporated with the gray version of BTE through the “transport” relaxation time. The present model is verified against the experimental thermal conductivity data as a function of the film thickness.
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73.61.At Metal and metallic alloys
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.15.Lh Relaxation times and mean free paths
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Hardening of a metallic glass during cyclic loading in the elastic range

C. E. Packard, L. M. Witmer, and C. A. Schuh

Appl. Phys. Lett. 92, 171911 (2008); http://dx.doi.org/10.1063/1.2919722 (3 pages) | Cited 16 times

Online Publication Date: 2 May 2008

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Although fatigue failure is well documented in metallic glasses, the mechanism responsible for damage accumulation during cyclic loading below the yield point remains elusive. This letter describes a high-resolution nanomechanical study of an Fe-based bulk metallic glass subjected to cyclic loading in the nominal elastic range. An increase in the yield load was observed with an increasing number of subyield loading cycles, providing a clean documentation of kinematic irreversibility in very small volumes of material that experience no shear bands either prior to or during cyclic loading.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.me Fatigue
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

An orthogonal surface phase in semipolar GaN/r-plane sapphire

Kazuhide Kusakabe, Daisuke Terui, Takashi Yamazaki, Iwao Hashimoto, and Kazuhiro Ohkawa

Appl. Phys. Lett. 92, 171912 (2008); http://dx.doi.org/10.1063/1.2917570 (3 pages) | Cited 4 times

Online Publication Date: 2 May 2008

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This paper reports structural characterization on semipolar GaN films grown on r-plane sapphire substrates by metalorganic vapor-phase epitaxy. The polar orientation of semipolar GaN is assigned that the N-polar plane faces the surface side. The epitaxial relationship of the semipolar GaN/r-plane sapphire is determined as [000math]GaN∥[1math13]sapphire and [1math00]GaN∥[1math0math]sapphire. An anomalous phase orthogonal-twisted around the c-axis is revealed by transmission electron microscope, which is almost localized at the surface.
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68.55.-a Thin film structure and morphology
68.37.Og High-resolution transmission electron microscopy (HRTEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
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High mobility InN epilayers grown on AlN epilayer templates

N. Khan, A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 92, 172101 (2008); http://dx.doi.org/10.1063/1.2917473 (3 pages) | Cited 13 times

Online Publication Date: 28 April 2008

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We report on the growth of InN epilayers on AlN/sapphire templates by metal organic chemical vapor deposition. Compared to InN epilayers grown on GaN templates, significant improvements in the electrical and optical properties of InN epilayers on AlN templates were observed. An increase in electron mobility, a decrease in background electron concentration, and a redshift of photoluminescence emission peak position with increasing the growth temperature and V/III ratio were observed and a room temperature Hall mobility of 1400 cm2/V s with a free electron concentration of about 7×1018 cm−3 was obtained. The improvements were partly attributed to the use of AlN templates, which allows for higher growth temperatures leading to an enhanced supply of nitrogen atoms and a possible reduction in the incorporation of unintentional impurities and nitrogen vacancy related defects.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Stability and photoemission characteristics for GaAs photocathodes in a demountable vacuum system

Jijun Zou, Benkang Chang, Zhi Yang, Jianliang Qiao, and Yiping Zeng

Appl. Phys. Lett. 92, 172102 (2008); http://dx.doi.org/10.1063/1.2918444 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2008

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The stability and photoemission characteristics for reflection-mode GaAs photocathodes in a demountable vacuum system have been investigated by using spectral response and x-ray photoelectron spectroscopy measurements at room temperature. We find that the shape of the spectral response curve for the cathode changes with time in the vacuum system, but after applying fresh cesium to the degraded cathode, the spectral response can almost be restored. The change and restoration of curve shape are mainly attributed to the evolution of the surface barrier. We illustrate the evolution and analyze the influence of the barrier on the spectral response of the cathode.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Vacancy-mediated dopant diffusion activation enthalpies for germanium

A. Chroneos, H. Bracht, R. W. Grimes, and B. P. Uberuaga

Appl. Phys. Lett. 92, 172103 (2008); http://dx.doi.org/10.1063/1.2918842 (3 pages) | Cited 58 times

Online Publication Date: 30 April 2008

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Electronic structure calculations are used to predict the activation enthalpies of diffusion for a range of impurity atoms (aluminium, gallium, indium, silicon, tin, phosphorus, arsenic, and antimony) in germanium. Consistent with experimental studies, all the impurity atoms considered diffuse via their interaction with vacancies. Overall, the calculated diffusion activation enthalpies are in good agreement with the experimental results, with the exception of indium, where the most recent experimental study suggests a significantly higher activation enthalpy. Here, we predict that indium diffuses with an activation enthalpy of 2.79 eV, essentially the same as the value determined by early radiotracer studies.
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66.30.J- Diffusion of impurities
66.30.H- Self-diffusion and ionic conduction in nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Mq Elemental semiconductors
61.72.jd Vacancies
65.40.-b Thermal properties of crystalline solids

Spin-polarized current and spin accumulation in a three-terminal two quantum dots ring

Feng Chi, Jun Zheng, and Lian-Liang Sun

Appl. Phys. Lett. 92, 172104 (2008); http://dx.doi.org/10.1063/1.2918843 (3 pages) | Cited 32 times

Online Publication Date: 30 April 2008

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We study the coexistence of the spin-polarized current and the spin accumulation in a three-terminal quantum ring structure, in which two quantum dots (QDs) are inserted in one arm of the ring and the Rashba spin-orbit interaction (RSOI) exists in the other. We find that by properly adjusting the applied voltages in the three leads, the RSOI-induced phase factor and the parameters relevant to the QDs, the spin-polarization efficiency in the leads can achieve either 100% or infinite, and the electrons of the same or different spin directions can accumulate in the two dots, respectively. The manipulation of the electron spin in the present device relies on the RSOI and the electric fields, thus making it realizable with the currently existing technologies.
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72.25.-b Spin polarized transport
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Surface electronic properties of undoped InAlN alloys

P. D. C. King, T. D. Veal, A. Adikimenakis, Hai Lu, L. R. Bailey, E. Iliopoulos, A. Georgakilas, W. J. Schaff, and C. F. McConville

Appl. Phys. Lett. 92, 172105 (2008); http://dx.doi.org/10.1063/1.2913765 (3 pages) | Cited 8 times

Online Publication Date: 1 May 2008

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The variation in surface electronic properties of undoped c-plane InxAl1−xN alloys has been investigated across the composition range using a combination of high-resolution x-ray photoemission spectroscopy and single-field Hall effect measurements. For the In-rich alloys, electron accumulation layers, accompanied by a downward band bending, are present at the surface, with a decrease to approximately flatband conditions with increasing Al composition. However, for the Al-rich alloys, the undoped samples were found to be insulating with approximate midgap pinning of the surface Fermi level observed.
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73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.20.My Galvanomagnetic and other magnetotransport effects

An evaluation of thermal stability of TiB2 metal gate on Hf silicate for p-channel metal oxide semiconductor application

S. Y. Son, P. Kumar, H. Cho, K. J. Min, C. J. Kang, and R. K. Singh

Appl. Phys. Lett. 92, 172106 (2008); http://dx.doi.org/10.1063/1.2913766 (3 pages) | Cited 1 time

Online Publication Date: 1 May 2008

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An evaluation of TiB2 gate metal on Hf-silicate dielectric prepared by atomic layer deposition method has been reported. The extracted effective metal work function for TiB2 gate was about 5.08 eV. The work function showed almost identical values and the sharp interface between metal and dielectric was confirmed after postdeposition annealing at 1000 °C. The work function lowering (4.91 eV) at 1100 °C was caused by metal-dielectric intermixing and oxygen vacancy formation. TiB2 gate electrode was found to be suitable for use in p-channel metal oxide semiconductor device.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices

Hydrogen diffusion in silicon from plasma-enhanced chemical vapor deposited silicon nitride film at high temperature

Manav Sheoran, Dong Seop Kim, Ajeet Rohatgi, H. F. W. Dekkers, G. Beaucarne, Matthew Young, and Sally Asher

Appl. Phys. Lett. 92, 172107 (2008); http://dx.doi.org/10.1063/1.2917467 (3 pages) | Cited 6 times

Online Publication Date: 1 May 2008

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The stable hydrogen isotope deuterium (D), which is released during the annealing of deuterated silicon nitride films, diffuses through the crystalline silicon and is captured by a thin, amorphous layer of silicon sputtered on the rear surface. We report on the measurement of the concentration of “penetrated” D by secondary ion mass spectrometry to monitor the flux of D diffusing through single-crystalline silicon wafers. The penetrated D content in the trapping layer increases with the annealing time. However, the flux of D injected into the silicon from the silicon nitride layer decreases as annealing time increases.
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66.30.-h Diffusion in solids
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments

Boron diffusion in amorphous silicon-germanium alloys

L. A. Edelman, M. S. Phen, K. S. Jones, R. G. Elliman, and L. M. Rubin

Appl. Phys. Lett. 92, 172108 (2008); http://dx.doi.org/10.1063/1.2919085 (3 pages) | Cited 2 times

Online Publication Date: 2 May 2008

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The effect of Ge alloying on B diffusion in amorphous Si1−xGex alloys is reported for x = 0−0.24. The diffusivity was not observed to exhibit any transient decay. The diffusivity decreases with increasing Ge concentration. The activation energy for B diffusion appears to increase from 2.8 eV for amorphous Si to 3.6 eV for amorphous Si0.76Ge0.24. It is suggested that, in these alloys, Ge distorts the amorphous Si network thereby increasing B trapping by Si.
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66.30.J- Diffusion of impurities
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Thermal dynamics in symmetric magnetic nanopillars driven by spin transfer

Weng L. Lim, Nicholas Anthony, Andrew Higgins, and Sergei Urazhdin

Appl. Phys. Lett. 92, 172501 (2008); http://dx.doi.org/10.1063/1.2918012 (3 pages) | Cited 3 times

Online Publication Date: 28 April 2008

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We study the effects of spin transfer on thermally activated dynamics of magnetic nanopillars with identical thicknesses of the magnetic layers. The symmetric nanopillars exhibit anomalous dependencies of switching statistics on magnetic field and current. We interpret our data in terms of simultaneous current-induced excitation of both layers. We also find evidence for coupling between the fluctuations of the layers due to the spin transfer.
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72.25.-b Spin polarized transport
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials

Tunneling magnetoresistance of magnetic tunnel junctions using perpendicular magnetization L10-CoPt electrodes

Gukcheon Kim, Yuya Sakuraba, Mikihiko Oogane, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 92, 172502 (2008); http://dx.doi.org/10.1063/1.2913163 (3 pages) | Cited 37 times

Online Publication Date: 28 April 2008

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Magnetic tunnel junctions (MTJs) using L10-ordered CoPt electrodes with perpendicular magnetic anisotropy were fabricated. Full-epitaxial CoPt/MgO/CoPt-MTJs were prepared onto single crystal MgO-(001) substrate by sputtering method. X-ray diffraction analyses revealed that both bottom and top CoPt electrodes were epitaxially grown with (001)-orientation. The L10-chemical order parameter of 0.82 was obtained for the bottom CoPt electrode deposited at substrate temperature of 600 °C. The transport measurements with applying magnetic field perpendicular to the film plane showed a tunnel magnetoresistance ratio of 6% at room temperature and 13% at 10 K.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Microstrip superconducting quantum interference device radio-frequency amplifier: Scattering parameters and input coupling

D. Kinion and John Clarke

Appl. Phys. Lett. 92, 172503 (2008); http://dx.doi.org/10.1063/1.2902173 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2008

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The forward scattering parameters of an amplifier based on a dc superconducting quantum interference device are directly measured at 4.2 K as functions of the applied magnetic flux. These parameters are equivalent to the real and imaginary components of the input impedance and forward gain of the amplifier. The results can be described using an equivalent circuit model of the fundamental resonance of the microstrip resonator which forms the input of the amplifier. The circuit model is used to determine the series capacitance required for critical coupling of the microstrip to the input circuit.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.40.Az Waveguides, transmission lines, striplines

Magnetoelastic domains and magnetic field-induced strains in ferromagnetic shape memory alloys by phase-field simulation

L. J. Li, J. Y. Li, Y. C. Shu, H. Z. Chen, and J. H. Yen

Appl. Phys. Lett. 92, 172504 (2008); http://dx.doi.org/10.1063/1.2918127 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2008

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Magnetoelastic domains in ferromagnetic shape memory alloys evolve through either variant rearrangement or magnetization rotation, resulting in a large or a small magnetic field-induced strain depending on the magnitude of applied compressive stress. These phenomena are simulated in this letter using an unconventional phase-field model motivated by energy-minimizing multirank laminated domain structures. The results agree well with experiments, and confirm the analysis of Ma and Li [Appl. Phys. Lett. 90, 172504 (2007)] based on an energy minimization theory.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ch Domain walls and domain structure
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
75.10.-b General theory and models of magnetic ordering

Turing pattern formation in Pr2Fe14B-based alloy and its role in anisotropy inducement at the early stage of disproportionation

Xiao-Dong Zhang, Jing-Zhi Han, Ying-Chang Yang, Min Li, and Yang Zou

Appl. Phys. Lett. 92, 172505 (2008); http://dx.doi.org/10.1063/1.2919087 (3 pages) | Cited 3 times

Online Publication Date: 1 May 2008

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At the dissipative disproportionation stage, the hexagonally spotted Turing pattern is formed on the reaction front as expected in a reaction-diffusion system. Turing patterns fill three dimensions resulting in the nanosized PrH2 rods embedded in a Fe matrix. The PrH2 rods are found to be oriented along the [110] direction with the stable {111} facets and a pair of face-to-face {002} facets. Based on both the geometrical configuration and the anisotropic interfacial energy, the mechanism whereby the Fe2B phase finally takes the place of the paired {002} facets as an orientation carrier has been proposed.
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61.46.-w Structure of nanoscale materials
82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer
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Re-entrant type relaxor behavior in (1−x)BaTiO3–xBiScO3 solid solution

Hai Yan Guo, Chao Lei, and Zuo-Guang Ye

Appl. Phys. Lett. 92, 172901 (2008); http://dx.doi.org/10.1063/1.2913208 (3 pages) | Cited 10 times

Online Publication Date: 28 April 2008

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The solid solution of (1−x)BaTiO3–xBiScO3 was synthesized by solid state reaction and its dielectric properties were studied by impedance spectroscopy. A dielectric anomaly was found in the temperature ranges of −30–13 °C and −60–20 °C for 0.95BaTiO3–0.05BiScO3 and 0.90BaTiO3–0.10BiScO3, respectively. The frequency dependence of the anomaly exhibits dielectric relaxation satisfying the Vogel–Fulcher law, indicating relaxorlike behavior. The relaxor state in the (1−x)BaTiO3–xBiScO3 solid solution occurs after the ferroelectric phase transition upon cooling, indicating a re-entering phenomenon. Piezoresponse force microscopic studies show that the domain wall density decreases with the addition of BiScO3. The substitution of BiScO3 also results in some no-phase-contrast areas in the domain structure image, which grow with the increasing BiScO3 amount. Decent piezoelectric hysteresis loops were obtained in these areas. The correlation between the peculiar domain structure and relaxor behavior suggests that the no-phase-contrast areas are characteristics of the domain structure of the re-entering relaxor system.
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77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Polarization switching kinetics at the nanoscale in ferroelectric copolymer Langmuir–Blodgett films

R. V. Gaynutdinov, O. A. Lysova, A. L. Tolstikhina, S. G. Yudin, V. M. Fridkin, and Stephen Ducharme

Appl. Phys. Lett. 92, 172902 (2008); http://dx.doi.org/10.1063/1.2916707 (3 pages) | Cited 16 times

Online Publication Date: 28 April 2008

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The polarization switching kinetics of ferroelectric Langmuir–Blodgett films of vinylidene fluoride-trifluoroethylene copolymer were investigated by piezoresponse force microscopy with a resolution of 100 nm. The switching time in response to a localized voltage pulse exhibits an exponential dependence on reciprocal voltage, which is consistent with nucleation-limited switching dynamics.
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82.35.Jk Copolymers, phase transitions, structure
68.55.am Polymers and organics
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Dielectric constant boost in amorphous sesquioxides

Pietro Delugas, Vincenzo Fiorentini, and Alessio Filippetti

Appl. Phys. Lett. 92, 172903 (2008); http://dx.doi.org/10.1063/1.2917797 (3 pages) | Cited 6 times

Online Publication Date: 28 April 2008

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High-κ dielectrics for insulating layers are a current key ingredient of microelectronics. X2O3 sesquioxide compounds are among the candidates. Here, we show for a typical material of this class, Sc2O3, that the relatively modest dielectric constant of its crystalline phase is enhanced in the amorphous phase by over 40% (from ∼ 15 to ∼ 22). This is due to the disorder-induced activation of low frequency cation-related modes which are inactive or inefficient in the crystal and by the conservation of effective dynamical charges (a measure of atomic polarizability). The analysis employs density-functional energy-force and perturbation-theory calculations of the dielectric response of amorphous samples generated by pair-potential molecular dynamics.
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77.22.Ch Permittivity (dielectric function)

1 nm equivalent oxide thickness in Ga2O3(Gd2O3)/In0.2Ga0.8As metal-oxide-semiconductor capacitors

K. H. Shiu, T. H. Chiang, P. Chang, L. T. Tung, M. Hong, J. Kwo, and W. Tsai

Appl. Phys. Lett. 92, 172904 (2008); http://dx.doi.org/10.1063/1.2918835 (3 pages) | Cited 17 times

Online Publication Date: 30 April 2008

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An equivalent oxide thickness about 1 nm for Ga2O3(Gd2O3) (GGO) on In0.2Ga0.8As has been achieved by employing a thin in situ deposited 3 nm thick Al2O3 protection layer. The dual gate oxide stacks of the Al2O3/GGO (33, 20, 10, 8.5, and 4.5 nm)/In0.2Ga0.8As/GaAs metal-oxide-semiconductor (MOS) capacitors remain amorphous after rapid thermal annealing up to 800–850 °C, accompanied with atomically sharp smooth oxide/semiconductor interfaces. Well behaved capacitance-voltage (C-V) curves of the MOS diodes have shown sharp transition from depletion to accumulation with small flatband voltage (1.1 V for Au metal gate and 0.1 V for Al), and weak frequency dispersion (1.5%–5.4%) between 10 and 500 kHz at accumulation capacitance. Low leakage current densities [3.1×10−5 and 2.5×10−9 A/cm2 at V = Vfb+1 V for Al2O3(3 nm)/GGO(4.5 and 8.5 nm)], a high dielectric constant around 14–16 of GGO for all tested thicknesses, and a low interfacial density of states (Dit) in the low 1011 cm−2 eV−1 have also been accomplished.
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85.30.Kk Junction diodes
84.32.Tt Capacitors

Piezoelectric properties of lithium modified silver niobate perovskite single crystals

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Shin-ya Koshihara, and Mitsuru Itoh

Appl. Phys. Lett. 92, 172905 (2008); http://dx.doi.org/10.1063/1.2918837 (3 pages) | Cited 13 times

Online Publication Date: 30 April 2008

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We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1−xLixNbO3. It possesses a rhombohedral structure with high ferroelectric phase transition (Tc = 548 K for x = 0.086) and large spontaneous polarization (Ps ∼ 40 μC/cm2 for x = 0.062) along the 〈111〉c direction of pseudocubic perovskite structure for x>0.05–0.06. High quasistatic d33 ∼ 210 pC/N and low dielectric constant have lead to a very large value of piezoelectric voltage constant g33 ∼ 53.9×10−3 Vm/N for the 〈001〉c-cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization

GeOx interface layer reduction upon Al-gate deposition on a HfO2/GeOx/Ge(001) stack

Sylvie Rangan, Eric Bersch, Robert Allen Bartynski, Eric Garfunkel, and Elio Vescovo

Appl. Phys. Lett. 92, 172906 (2008); http://dx.doi.org/10.1063/1.2917480 (3 pages) | Cited 5 times

Online Publication Date: 30 April 2008

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The metallization of HfO2/Ge by Al at room temperature was studied using photoemission and inverse photoemission. Upon deposition, Al reduces the GeOx interfacial layer between Ge and HfO2, and a thin Al2O3 layer is formed at the Al/HfO2 interface. The band alignment across the Al/HfO2/Ge stacks is also addressed.
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79.60.Jv Interfaces; heterostructures; nanostructures
78.70.-g Interactions of particles and radiation with matter
77.55.-g Dielectric thin films
73.20.At Surface states, band structure, electron density of states
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Choosing the best geometries for the linear characterization of lossy piezoceramics: Study of the thickness-poled shear plate

L. Pardo, F. Montero de Espinosa, A. García, and K. Brebøl

Appl. Phys. Lett. 92, 172907 (2008); http://dx.doi.org/10.1063/1.2911731 (3 pages)

Online Publication Date: 1 May 2008

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Show Abstract
Resonance modes of a thickness-poled piezoceramic shear plate are studied. When determining material properties from impedance measurements, it is required to obtain an uncoupled shear resonance. The shear resonance, which is electrically excited, results to a series of plate resonances, which is mechanically excited by this, when frequencies match. Thus, the condition of a high aspect ratio of the plate is not valid to eliminate coupling. Instead, the thickness (t) and lateral dimensions (L,w) of the plate must be tailored for each material. This approach was tested for a commercial piezoceramic and plates amenable for characterization obtained for aspect ratios below L:t = 15:1 (L = w).
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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