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25 Jun 2001

Volume 78, Issue 26, pp. 4065-4199

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Spontaneous polarization-vector-reorientation photorefractive effect in ferroelectric liquid crystals

Takeo Sasaki, Yuji Kino, Minoru Shibata, Naoko Mizusaki, Atsushi Katsuragi, Yuichi Ishikawa, and Takeshi Yoshimi

Appl. Phys. Lett. 78, 4112 (2001); http://dx.doi.org/10.1063/1.1379595 (3 pages) | Cited 12 times

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The photorefractive effect of a ferroelectric liquid crystal doped with a photoconductive compound was investigated. The photorefractive effect appeared only at the temperature at which the sample exhibits ferroelectricity. The refractive index grating formation time was measured to be ∼ 30 ms. In the ferroelectric phase, reorientation of the spontaneous polarization vector was found to be induced by the internal space-charge field. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.22.Ej Polarization and depolarization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Noriaki Kida and Masayoshi Tonouchi

Appl. Phys. Lett. 78, 4115 (2001); http://dx.doi.org/10.1063/1.1381573 (3 pages) | Cited 19 times

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Terahertz (THz) radiation with its spectrum extending up to 1 THz has been observed by an illumination of femtosecond optical pulses to optical switching devices fabricated on magnetoresistive manganite thin films; Pr0.7Ca0.3MnO3. The THz radiation strongly depends on temperature T and its T trend reverses sign across charge-orbital and spin-ordering T. © 2001 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
42.65.Pc Optical bistability, multistability, and switching, including local field effects
75.47.Gk Colossal magnetoresistance

Picosecond Z-scan measurements on bulk GaN crystals

V. Pačebutas, A. Stalnionis, A. Krotkus, T. Suski, P. Perlin, and M. Leszczynski

Appl. Phys. Lett. 78, 4118 (2001); http://dx.doi.org/10.1063/1.1380248 (3 pages) | Cited 11 times

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Bulk GaN crystals were characterized by using picosecond laser pulses at λ = 0.527 μm and Z-scan techniques. The role of the free-carrier absorption was evaluated by a dynamical, pump-and-probe-type transmitivity measurement. The values of two-photon absorption coefficient (17–20 cm/GW) and refractive index changes at high optical irradiances due to bound (n2 = −4×10−12 esu) and free (σr = −1.0×10−20 cm3) electrons in that material were determined. © 2001 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Room-temperature visible electroluminescence of Al-doped silicon oxide films

X. M. Wu, Y. M. Dong, L. J. Zhuge, C. N. Ye, N. Y. Tang, Z. Y. Ning, W. G. Yao, and Y. H. Yu

Appl. Phys. Lett. 78, 4121 (2001); http://dx.doi.org/10.1063/1.1382629 (3 pages) | Cited 5 times

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A series of Al-doped amorphous silicon oxide films have been grown on p-type silicon (100) substrates by a dual ion beam cosputtering method. Visible electroluminescence (EL) from the devices, made by films with different contents of Al, can be seen with the naked eye under forward bias and reverse bias for films containing sufficient amounts of Al. The EL spectra are found to have a luminescence band peaked at 510 nm (2.4 eV), which is the same result as that obtained from silicon oxide films. With the increase in the amounts of Al, the peak position does not shift, the onset of the bias decreases, and the intensity of EL peak increases. Experiment results show that the doping of Al is beneficial to improving the conduction condition of films while the structure of the films associated with luminescence centers is affected hardly at all. © 2001 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Nk Insulators
85.60.Jb Light-emitting devices

Optical investigation of strain in Si-doped GaN films

J. Sánchez-Páramo, J. M. Calleja, M. A. Sánchez-García, and E. Calleja

Appl. Phys. Lett. 78, 4124 (2001); http://dx.doi.org/10.1063/1.1379063 (3 pages) | Cited 5 times

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The effects of Si doping on the growth mode and residual strain of GaN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy are studied by Raman scattering and photoluminescence. As the Si concentration increases a progressive decrease of the high-energy E2 mode frequency is observed, together with a redshift of the excitonic emission. Both effects indicate an enhancement of the biaxial tensile strain of thermal origin for increasing doping level, which is confirmed by x-ray diffraction measurements. Beyond Si concentrations of 5×1018 cm−3 both the phonon frequency and the exciton emission energy increase again. This change indicates a partial strain relaxation due to a change in the growth mode. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
68.60.Bs Mechanical and acoustical properties
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
63.20.-e Phonons in crystal lattices

Effects of substrate micropatterning on nonlinear optical properties of polar self-assembling films

Leiming Li and Samuel I. Stupp

Appl. Phys. Lett. 78, 4127 (2001); http://dx.doi.org/10.1063/1.1379988 (3 pages) | Cited 2 times

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Self-assembling triblock molecules were previously shown to form thin films with polar order. These films are also known to contain polar supramolecular aggregates that are layered in head-to-tail fashion. In this work, glass substrates were prepared using a focused-ion-beam system to generate 1 mm×1 mm areas containing periodic arrays of squares with lateral dimensions of 7 and 17 μm. The squares were defined by 3 μm wide and 10 nm deep troughs created by Ga ion beams. Using second-harmonic-generation measurements, the average molecular tilt angle was found to be smaller in patterned films, suggesting that micropatterning enhances overall polarization in these films. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Qn Polymers; organic compounds
81.16.Dn Self-assembly

Mass transport growth and optical emission properties of hydride vapor phase epitaxy GaN

T. Paskova, E. M. Goldys, P. P. Paskov, Q. Wahab, L. Wilzen, M. P. de Jong, and B. Monemar

Appl. Phys. Lett. 78, 4130 (2001); http://dx.doi.org/10.1063/1.1381421 (3 pages) | Cited 2 times

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The optical emission properties of mass-transport regions of GaN grown by hydride vapor phase epitaxy are studied by cathodoluminescence imaging and spectroscopy. A strong donor–acceptor pair emission is observed from the mass-transport regions. Spatially resolved cathodoluminescence reveals a strong intensity contrast between the exciton and donor–acceptor bands from mass-transport and nontransport regions. Focused Auger electron and x-ray photoelectron spectroscopies were employed to investigate the impurity incorporation in the different regions. A preferential moderate increase of residual impurity incorporation or redistribution in mass-transport regions is suggested to be responsible for the observed change of the dominant radiative mechanism. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
79.20.Fv Electron impact: Auger emission
71.35.-y Excitons and related phenomena
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.55.Eq III-V semiconductors

Structural characterization of InAs/GaAs quantum-dot nanostructures

D. Pal, E. Towe, and S. Chen

Appl. Phys. Lett. 78, 4133 (2001); http://dx.doi.org/10.1063/1.1382855 (3 pages) | Cited 9 times

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We have performed high-resolution x-ray diffraction measurements on vertically aligned InAs/GaAs quantum-dot nanostructures. The measurements were carried out for both the symmetric (004) and asymmetric (113) and (224) Bragg reflections. Theoretical simulations of the rocking curves indicate that the x-ray signal is primarily from the pseudomorphically strained (In,Ga)As wetting layers. The average thickness and indium composition in the wetting layers, as determined from simulations of the rocking curves, were, respectively, 0.72 nm and 88%. Transmission electron microscopy studies show the creation and annihilation of quantum dots with no observable dislocations. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.05.cp X-ray diffraction
68.37.Lp Transmission electron microscopy (TEM)

Recrystallization in polyvinylidene fluoride upon low fluence swift heavy ion impact

A. Biswas, R. Gupta, N. Kumar, D. K. Avasthi, J. P. Singh, S. Lotha, D. Fink, S. N. Paul, and S. K. Bose

Appl. Phys. Lett. 78, 4136 (2001); http://dx.doi.org/10.1063/1.1376664 (3 pages) | Cited 13 times

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Thin films (9 μm) of polyvinylidene fluoride (PVDF) are irradiated by swift heavy ions (180 MeV Ag14+) in the fluence range 1×1010–1×1012ions/cm2 with an electronic linear energy transfer LET∼11 keV/nm. In sharp contrast to the previous results, the most characteristic crystalline asymmetric and symmetric CH2 doublets (located at 3025 and 2985 cm−1), have shown remarkable increase in their respective Fourier transform infrared (FTIR) absorbance intensities upon low fluence ion impact (1010 ions/cm2). This increase in absorbance is in consonance with the simultaneous decrease of the transmission intensities of other crystalline bending vibration bands located at 532 (CF2 bending), 614, 796, and 975 cm−1 (all due to CH2 bending) at the similar ion fluence. It appears most probable from the results that, being a polar polymer, the molecular dipoles in PVDF forming a hydrogen bond network get realigned upon irradiation into a highly ordered state of chain molecules in the crystalline regions and create volume elements as crystallites. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
61.82.Pv Polymers, organic compounds
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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