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8 Sep 2008

Volume 93, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages)

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou
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Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds

A. Cannizzo, M. Leone, W. Gawelda, E. Portuondo-Campa, A. Callegari, F. van Mourik, and M. Chergui

Appl. Phys. Lett. 93, 102901 (2008); http://dx.doi.org/10.1063/1.2975965 (3 pages) | Cited 2 times

Online Publication Date: 8 September 2008

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We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank–Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼ 10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrational redistribution.
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61.72.J- Point defects and defect clusters
78.47.-p Spectroscopy of solid state dynamics

A multisized piezoelectric microcantilever biosensor array for the quantitative analysis of mass and surface stress

Sanghun Shin, Jun Pyo Kim, Sang Jun Sim, and Jaichan Lee

Appl. Phys. Lett. 93, 102902 (2008); http://dx.doi.org/10.1063/1.2977869 (3 pages) | Cited 12 times

Online Publication Date: 8 September 2008

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A multisized piezoelectric microcantilever biosensor array with scaling down in two dimensions is presented as a multifunctional resonant cantilever-based sensor platform. The multisized microcantilever array allowed simultaneous sensing of the surface stress as well as mass. The adsorption-induced surface stress and resulting spring constant change were analyzed in the multisized microcantilever array, and a mass sensitivity in the femtogram regime was demonstrated. The array sensor was used to immobilize human IgG on its cantilever surface, suggesting that the dynamic and simultaneous analysis of both adsorption-induced mass and the surface stress is feasible.
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87.80.Ek Mechanical and micromechanical techniques
87.14.E- Proteins
87.15.R- Reactions and kinetics

Electron injection of SrTiO3/Si interfacial layer

J. H. Ma, J. L. Sun, J. H. Qin, Y. H. Gao, T. Lin, H. Shen, F. W. Shi, X. J. Meng, J. H. Chu, S. J. Liu, and J. Li

Appl. Phys. Lett. 93, 102903 (2008); http://dx.doi.org/10.1063/1.2980019 (3 pages)

Online Publication Date: 8 September 2008

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The electrical properties of the SrTiO3(STO)/Si interfacial layer were studied by measuring STO metal-insulator-semiconductor (MIS) structure. The C-V measurements showed that there existed electron injection at the STO/Si interface under the higher sweep voltages. The electron injection behavior was analyzed and discussed in detail. By analyzing the voltage distribution of the semiconductor Si, the insulator STO, and the STO/Si interfacial layer in MIS structure, the electron injection electric field of interfacial layer was estimated to be about 5.5 MV/cm.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Investigation of substrate-induced strain effects in La0.7Ca0.15Sr0.15MnO3 thin films using ferroelectric polarization and the converse piezoelectric effect

R. K. Zheng, Y. Jiang, Y. Wang, H. L. W. Chan, C. L. Choy, and H. S. Luo

Appl. Phys. Lett. 93, 102904 (2008); http://dx.doi.org/10.1063/1.2979688 (3 pages) | Cited 10 times

Online Publication Date: 9 September 2008

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We have fabricated manganite film/ferroelectric crystal heterostructures by growing La0.7Ca0.15Sr0.15MnO3 (LCSMO) films on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3−0.33PbTiO3 (PMN-PT) single-crystal substrates. The efficient mechanical coupling at the interface, originated from ferroelectric polarization or the converse piezoelectric effect in the PMN-PT substrate, gives rise to large changes in the strain state, electrical resistance, magnetoresistance, and insulator-to-metal transition temperature (TP) of the film. We interpreted all these changes in terms of substrate-induced strain, which modifies the tetragonal distortion of MnO6 octahedra and the electron-lattice coupling strength in the film. Quantitative relationships between TP and induced strain in the LCSMO film have been established.
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77.55.-g Dielectric thin films
77.65.Ly Strain-induced piezoelectric fields
71.30.+h Metal-insulator transitions and other electronic transitions
72.20.My Galvanomagnetic and other magnetotransport effects

Elastic softening and central peaks in BaTiO3 single crystals above the cubic-tetragonal phase-transition temperature

J.-H. Ko, S. Kojima, T.-Y. Koo, J. H. Jung, C. J. Won, and N. J. Hur

Appl. Phys. Lett. 93, 102905 (2008); http://dx.doi.org/10.1063/1.2980444 (3 pages) | Cited 24 times

Online Publication Date: 9 September 2008

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A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO3) single crystals by Brillouin scattering study and was found to correlate with the softening of the longitudinal acoustic mode and the increase in the hypersonic damping. These observations support the existence of polar percursors and their electrostrictive coupling with the strain caused by the acoustic waves, consistent with former studies evidencing off-centered Ti ions in the high-symmetry cubic phase. A critical slowing down has been clearly observed in the vicinity of the cubic-tetragonal phase transition, indicating order-disorder component contributes to the phase transition of BaTiO3.
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77.80.B- Phase transitions and Curie point
78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
62.65.+k Acoustical properties of solids
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

HfO2-based InP n-channel metal-oxide-semiconductor field-effect transistors and metal-oxide-semiconductor capacitors using a germanium interfacial passivation layer

Hyoung-Sub Kim, I. Ok, M. Zhang, F. Zhu, S. Park, J. Yum, H. Zhao, Jack C. Lee, and Prashant Majhi

Appl. Phys. Lett. 93, 102906 (2008); http://dx.doi.org/10.1063/1.2961119 (3 pages) | Cited 9 times

Online Publication Date: 11 September 2008

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In this letter, we present our experimental results of HfO2-based n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and metal-oxide-semiconductor capacitors (MOSCAPs) on indium phosphide (InP) substrates using a thin germanium (Ge) interfacial passivation layer (IPL). We found that MOSCAPs on n-InP substrates showed good C-V characteristics such as a small capacitance equivalent thickness (14 Å), a small frequency dispersion (<10 % and <200 mV), and a low dielectric leakage current ( ∼ 5×10−4 A/cm2 at Vg = 1.5 V), whereas MOSCAPs on p-InP exhibited poor characteristics, implying severe Fermi level pinning. It was also found that InP was more vulnerable to a high temperature process such that C-V curves showed a characteristic “bump” and inversion capacitance at relatively high frequencies. From n-channel MOSFETs on a semi-insulating InP substrate using Ge IPL, HfO2, and TaN gate electrodes, excellent electrical characteristics such as a large transconductance (9.3 mS/mm) and large drain currents (12.3 mA/mm at Vd = 2 V and Vg = Vth+2V) were achieved, which are comparable to other works.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Anisotropic thermal conductivity of the Aurivillus phase, bismuth titanate (Bi4Ti3O12): A natural nanostructured superlattice

Yang Shen, David R. Clarke, and Paul A. Fuierer

Appl. Phys. Lett. 93, 102907 (2008); http://dx.doi.org/10.1063/1.2975163 (3 pages) | Cited 14 times

Online Publication Date: 11 September 2008

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The thermal conductivity of c-axis textured polycrystalline perovskite Bi4Ti3O12 and random polycrystalline material is reported up to 1000 °C. Based on measurements of the thermal diffusivity, density, and specific heat, the thermal conductivity is lower along the c-axis than in the a-b plane by almost a factor of 2, and the anisotropy persists up to at least 1000 °C despite a change in the crystal structure at 675 °C. The exceptionally low (1.0 W/mK), temperature-independent conductivity perpendicular to the perovskite layer structure is attributed to the density difference between the pseudoperovskite and fluorite blocks in the unit cell, forming a natural nanostructured superlattice.
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73.63.Bd Nanocrystalline materials
65.40.Ba Heat capacity
66.30.-h Diffusion in solids
61.46.Hk Nanocrystals

Dielectric response and tunability of a dielectric-paraelectric composite

K. Zhou, S. A. Boggs, R. Ramprasad, M. Aindow, C. Erkey, and S. P. Alpay

Appl. Phys. Lett. 93, 102908 (2008); http://dx.doi.org/10.1063/1.2982086 (3 pages) | Cited 22 times

Online Publication Date: 12 September 2008

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A theoretical study was carried out to determine the dielectric response and tunability of a composite consisting of a linear, low-loss dielectric matrix with uniformly sized, randomly distributed paraelectric Ba0.60Sr0.40TiO3 (BST 60/40) particles as functions of the volume fraction and size of the particles. The field dependence of the polarization and the dielectric response of the inclusions are specified through a nonlinear thermodynamic model and then incorporated into a two-dimensional finite element analysis. Near the percolation threshold for BST particles ( ∼ 27% to 45% depending on the particle size), high dielectric tunabilities with a lower effective permittivity than monolithic BST can be realized.
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77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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