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16 Aug 2004

Volume 85, Issue 7, pp. 1095-1302

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1277 (2004); http://dx.doi.org/10.1063/1.1783021 (3 pages)

Katsuhiko Nishiguchi, Hiroshi Inokawa, Yukinori Ono, Akira Fujiwara, and Yasuo Takahashi
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High-performance photorefractive polymer operating at 975 nm

Muhsin Eralp, Jayan Thomas, Savaş Tay, Guoqiang Li, Gerald Meredith, Axel Schülzgen, N. Peyghambarian, Gregory A. Walker, Stephen Barlow, and Seth R. Marder

Appl. Phys. Lett. 85, 1095 (2004); http://dx.doi.org/10.1063/1.1780591 (3 pages) | Cited 15 times

Online Publication Date: 10 August 2004

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A family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975 nm. This constitutes a major extension into the near-infrared spectral region for the operation of all-organic photorefractive devices. Utilizing our photorefractive materials, we demonstrate large net two-beam coupling gain of more than 100 cm−1, 60% diffraction efficiency in four-wave mixing experiments, and a fast response time of 33 ms, at an irradiance of 1 W∕cm2.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
72.40.+w Photoconduction and photovoltaic effects
78.30.Jw Organic compounds, polymers

Enhanced transmission of microwave radiation in one-dimensional metallic gratings with subwavelength aperture

S. Sena Akarca-Biyikli, Irfan Bulu, and Ekmel Ozbay

Appl. Phys. Lett. 85, 1098 (2004); http://dx.doi.org/10.1063/1.1783013 (3 pages) | Cited 41 times

Online Publication Date: 10 August 2004

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We report a theoretical and experimental demonstration of enhanced microwave transmission through subwavelength apertures in metallic structures with double-sided gratings. Three different types of aluminum gratings (sinusoidal, symmetric rectangular, and asymmetric rectangular shaped) are designed and analyzed. Our samples have a periodicity of 16 mm, and a slit width of 2 mm. Transmission measurements are taken in the 10–37.5 GHz frequency spectrum, which corresponds to 8–30 mm wavelength region. All three structures display significantly enhanced transmission around surface plasmon resonance frequencies. The experimental results agree well with finite-difference-time-domain based theoretical simulations. Asymmetric rectangular grating structure exhibits the best results with ∼50% transmission at 20.7 mm, enhancement factor of ∼25, and ±4° angular divergence.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.79.Dj Gratings

Dispersion-controlled optical group delay device by chirped photonic crystal waveguides

Daisuke Mori and Toshihiko Baba

Appl. Phys. Lett. 85, 1101 (2004); http://dx.doi.org/10.1063/1.1783014 (3 pages) | Cited 76 times

Online Publication Date: 10 August 2004

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Previously, we proposed and demonstrated chirped photonic crystal waveguides, in which some structural parameters are gradually changed so that the photonic band characteristic is smoothly shifted. In this letter, we discuss an optical delay line composed of two index-chirped waveguides in a directional coupler structure. A large delay is realized by a low average group velocity of <c∕350 near the band-edge with almost perfect dispersion compensation even for a short optical pulse. Finite difference time domain simulation demonstrates that such a device is possible in a practical design.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Dark spatial solitons in bulk azo-dye-doped polymer using photoinduced molecular reorientation

Shaoping Bian and Mark G. Kuzyk

Appl. Phys. Lett. 85, 1104 (2004); http://dx.doi.org/10.1063/1.1780599 (3 pages) | Cited 10 times

Online Publication Date: 10 August 2004

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We report the generation of dark spatial solitons in bulk Disperse Red 1 doped poly(methyl methacrylate) using photoinduced reorientation of azo-dye molecules. Planar solitions are formed when illuminated with a continuous-wave laser at intensities of the order of hundreds of miliwatts per square centimeter. The width of the soliton saturates to a minimum value at high intensity; and when the width of the initial dark notch is reduced, the equilibrium minimum width is unchanged.
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42.70.Jk Polymers and organics
42.65.Tg Optical solitons; nonlinear guided waves
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Improvement of the beam quality of a broad-area diode laser using double feedback from two external mirrors

Mingjun Chi, Niels-Søren Bøgh, Birgitte Thestrup, and Paul Michael Petersen

Appl. Phys. Lett. 85, 1107 (2004); http://dx.doi.org/10.1063/1.1783017 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2004

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In this letter, a symmetric double-feedback configuration, to improve the beam quality of broad-area diode lasers is demonstrated. With this configuration, a symmetric double-lobed far field can be obtained, and this configuration leads to good beam quality. The beam quality factor M2 of a diode laser with the emitting area 1 μm×200 μm is improved by using both the asymmetric single feedback and the symmetric double feedback. M2 values of 4.3 for the asymmetric single-feedback laser system and 3.3 for the symmetric double-feedback laser system are obtained, whereas the M2 value of the freely running laser is 42. The far and the near fields are also measured and compared for the three conditions.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Bh Lenses, prisms and mirrors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Chirp effects in femtosecond laser-induced surface second-harmonic generation from metals

H. Teng and Chunlei Guo

Appl. Phys. Lett. 85, 1110 (2004); http://dx.doi.org/10.1063/1.1781358 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2004

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Chirp effects are studied in femtosecond laser-induced surface second-harmonic generation (SHG) from gold. We observe a higher SHG yield when the incident laser pulses are negatively chirped, compared to using the transform-limited or positively chirped pulses. This study indicates that SHG is critically dependent on the exciting wavelength sequence within the femtosecond pulse bandwidth when electrons contributing to SHG are heated to a sufficiently high temperature and are in thermal nonequilibrium distribution with the lattice.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Comb-like supercontinuum generation in bulk media

Alessandra Tortora, Chiara Corsi, and Marco Bellini

Appl. Phys. Lett. 85, 1113 (2004); http://dx.doi.org/10.1063/1.1784041 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2004

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We report the generation of sequences of phase-coherent white-light pulses in bulk media. By passing the pulses from an amplified femtosecond laser through an etalon cavity, we produce an equally spaced time sequence of phase-locked pulses that serve as the pump for the generation of supercontinuum. The mutual coherence among the white-light pulses is probed by studying their spectral interference patterns for varying pump energy levels.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Bright white light electroluminescent devices based on a dye-dispersed polyfluorene derivative

Joo Hyun Kim, Petra Herguth, Mun-Sik Kang, Alex K-Y. Jen, Ya-Hsien Tseng, and Ching-Fong Shu

Appl. Phys. Lett. 85, 1116 (2004); http://dx.doi.org/10.1063/1.1778472 (3 pages) | Cited 56 times

Online Publication Date: 10 August 2004

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A series of efficient and bright white light-emitting diodes were fabricated using the blends of two fluorene-derived fluorescent dyes, (4,7-bis-(9,9,9′,9′-tetrahexyl-9H,9′H-[2,2′]bifluoren-7-yl)-benzo[1,2,5]thiadiazole) (FFBFF-emits green) and (4,7-bis-[5-(9,9-dihexyl-9H-fluoren-2-yl)-thiophen-2-yl]-benzo[1,2,5]thiadiazole) (FTBTF-emits red) in an efficient blue-emitting polyfluorene-derived copolymer (poly[(9,9-bis(4-di(4-n-butylphenyl)aminophenyl))]-stat-(9,9-bis(4-(5-(4-tert-butylphenyl)-2-oxadiazolyl)-phenyl))-stat-(9,9-di-n-octyl)fluorene) (PF-TPA-OXD). The resulting white light-emitting device reaches a maximum external quantum efficiency of 0.82% and a maximum brightness of 12 900 cd∕m2 at 12 V. The Commission Internationale d’Énclairage chromaticity coordinates of the device remain very close to that of pure white emission at a relatively broad bias range from 6 V (x=0.36, y=0.37) to 12 V (x=0.34, y=0.34).
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Intelligent integration of optical power splitter with optically switchable cross-connect based on multimode interference principle in SiGe∕Si

Baojun Li, Soo-Jin Chua, Eugene A. Fitzgerald, Bharat S. Chaudhari, Shaoji Jiang, and Zhigang Cai

Appl. Phys. Lett. 85, 1119 (2004); http://dx.doi.org/10.1063/1.1781736 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2004

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An intelligent and monolithic integration of optical power splitter with optically switchable cross-connect has been proposed. It is fabricated on the multimode interference principle in Si-based SiGe material system and configured for a 3×2 symmetrical structure of the three input waveguides and the two output waveguides. The central waveguide section is based on a multimode interference and incorporated with an activated carrier injection element. The operating wavelengths of the device are specially designed for 1545, 1550, and 1555 nm conventional-band wavelengths. The measured crosstalk is at around −17 dB and the average insertion loss is about 5.25 dB. At switch-ON state, the measured injection current is 370 mA corresponding to an injection current density of 950 A∕cm2.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.25.Hz Interference
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.81.Bm Fabrication, cladding, and splicing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.81.Dp Propagation, scattering, and losses; solitons
81.05.Hd Other semiconductors

Femtosecond-irradiation-induced refractive-index changes and channel waveguiding in bulk Ti3+:Sapphire

V. Apostolopoulos, L. Laversenne, T. Colomb, C. Depeursinge, R. P. Salathé , M. Pollnau, R. Osellame, G. Cerullo, and P. Laporta

Appl. Phys. Lett. 85, 1122 (2004); http://dx.doi.org/10.1063/1.1781737 (3 pages) | Cited 44 times

Online Publication Date: 10 August 2004

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We have employed femtosecond laser writing in order to induce refractive-index changes and waveguides in Ti3+-doped sapphire. Doping the sapphire crystal with an appropriate ion significantly reduces the threshold for creating structural changes, thus enabling the writing of waveguide structures. Passive and active buried channel waveguiding is demonstrated and images of the guided modes, propagation-loss values, fluorescence spectra, and output efficiencies are presented. The guiding area is located around the laser-damaged region, indicating that the guiding effect is stress induced. Refractive-index changes are measured by digital holography. Proper active doping should enable femtosecond processing and waveguide writing in various crystalline materials.
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42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.82.Ms Insulators
42.40.My Applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Delay-time investigation of electromagnetic waves through homogeneous medium and photonic crystal left-handed materials

R. Moussa, S. Foteinopoulou, and C. M. Soukoulis

Appl. Phys. Lett. 85, 1125 (2004); http://dx.doi.org/10.1063/1.1781742 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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Results of the delay time for the electromagnetic wave to reach its final direction through both photonic crystal and homogeneous medium are presented. The delay- or transient-time results, based on different cases and different incoming wave angles, show that the diffracted beam is trapped at the interface. This delay time is longer for the negative refractive index photonic crystal and is almost twice the duration of the delay time for the positive one. For the homogeneous medium, we also find that at the interface between a right- and left-handed medium the delay time is even longer than in the photonic crystal case. A comparison between left-handed behavior in photonic crystals and homogeneous media is reported.
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42.70.Qs Photonic bandgap materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Variable-focus liquid lens for miniature cameras

S. Kuiper and B. H. W. Hendriks

Appl. Phys. Lett. 85, 1128 (2004); http://dx.doi.org/10.1063/1.1779954 (3 pages) | Cited 272 times

Online Publication Date: 10 August 2004

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The meniscus between two immiscible liquids can be used as an optical lens. A change in curvature of this meniscus by electrowetting leads to a change in focal distance. It is demonstrated that two liquids in a tube form a self-centered lens with a high optical quality. The motion of the lens during a focusing action was studied by observation through the transparent tube wall. Finally, a miniature achromatic camera module was designed and constructed based on this adjustable lens, showing that it is excellently suited for use in portable applications.
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42.79.Bh Lenses, prisms and mirrors
68.08.Bc Wetting
42.30.-d Imaging and optical processing

Tunable diffraction grating using ultraviolet-light-induced spatial phase modulation in dual-frequency liquid crystal

Pao-Tai Lin, Xiao Liang, Hongwen Ren, and Shin-Tson Wu

Appl. Phys. Lett. 85, 1131 (2004); http://dx.doi.org/10.1063/1.1781752 (3 pages) | Cited 5 times

Online Publication Date: 10 August 2004

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An electrically tunable diffraction phase grating using ultraviolet (UV)-light-induced spatial dielectric modulation of a dual-frequency liquid crystal (DFLC) cell is demonstrated. A photomask with transparent and opaque stripes was used for fabricating the grating. In the UV-exposed stripes, the negative dielectric anisotropy (Δϵ) tolane compound of the DFLC mixture is partially polymerized resulting in a decreased threshold voltage as compared to that of the unexposed region. Upon applying a constant voltage, the phase difference between the adjacent pixels is produced. The first-order diffraction efficiency reaches ∼60% which agrees well with the simulation results. Due to the dual-frequency addressing at 30 Vrms, the response time of the DFLC phase grating was measured to be ∼1 ms at room temperature.
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42.70.Df Liquid crystals
42.79.Dj Gratings
42.79.Kr Display devices, liquid-crystal devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.35.-x Polymers: properties; reactions; polymerization

Waveguide of amorphous perfluoropolymer for visible light

Kentaro Sasaki, Norikazu Kawamura, Haruki Tokumaru, and Yoshihiko Sakane

Appl. Phys. Lett. 85, 1134 (2004); http://dx.doi.org/10.1063/1.1782257 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2004

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We developed an amorphous polymer of cyclized perfluoropolymer, which is highly transparent throughout the visible range, and fabricated waveguides of the polymer for visible light. At a wavelength of 405 nm, approximately 60% of lightwaves are propagated through the straight waveguide and over 50% of the lightwaves are propagated through the buried waveguides with a radius of more than 30 mm, demonstrating the feasibility of the waveguides as light sources with a small angle of a beam divergence in a single mode. The waveguides are prospective candidates for multiple beams in line for parallel information processing, such as optical recording systems.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
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Plasma composition during plasma-enhanced chemical vapor deposition of carbon nanotubes

M. S. Bell, R. G. Lacerda, K. B. K. Teo, N. L. Rupesinghe, G. A. J. Amaratunga, W. I. Milne, and M. Chhowalla

Appl. Phys. Lett. 85, 1137 (2004); http://dx.doi.org/10.1063/1.1782256 (3 pages) | Cited 30 times

Online Publication Date: 10 August 2004

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Neutral species and positive ions were extracted directly from a C2H2:NH3 plasma used to grow vertically aligned carbon nanotubes (CNTs) and analyzed by mass spectrometry. We observe that NH3 suppresses C2H2 decomposition and encourages CNT formation. We show that the removal of excess carbon, essential for obtaining nanotubes without amorphous carbon deposits, is achieved through gas phase reactions which form mainly HCN. We determine an optimum C2H2:NH3 gas ratio which is consistent with previous observations based upon postdeposition analysis. We find, in contrast to thin film growth by plasma-enhanced chemical vapor deposition, that the optimum condition does not correspond to the highest level of ionization. We also provide evidence that C2H2 is the dominant precursor for CNTs in our experiments.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
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Strain field fluctuation effects on lattice thermal conductivity of ZrNiSn-based thermoelectric compounds

J. Yang, G. P. Meisner, and L. Chen

Appl. Phys. Lett. 85, 1140 (2004); http://dx.doi.org/10.1063/1.1783022 (3 pages) | Cited 57 times

Online Publication Date: 10 August 2004

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We present a model calculation of the lattice thermal conductivity of ZrNiSn-based half-Heusler thermoelectric compounds for temperatures where phonon scattering is dominated by Umklapp and point defect scattering. The difference in mass between impurity and host atoms dominates point defect scattering for alloying Hf on the Zr sublattice, whereas differences in size and interatomic coupling forces between impurity and host atoms dominate point defect scattering for alloying Pd on the Ni sublattice. Because Pt is heavier and larger than Pd, we predict that Pt will further reduce lattice thermal conductivity when alloyed on the Ni sublattice of these half-Heusler compounds.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.Yx Interaction between different crystal defects; gettering effect
63.20.kp Phonon-defect interactions

Morphological healing evolution of penny-shaped fatigue microcracks in pure iron at elevated temperatures

H. L. Zhang, P. Z. Huang, J. Sun, and H. Gao

Appl. Phys. Lett. 85, 1143 (2004); http://dx.doi.org/10.1063/1.1780592 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2004

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This letter reports a joint experimental and numerical investigation of high temperature morphological healing of micron-sized intragranular microcracks in pure iron. Irregular penny-shaped microcracks were first created by low-cycle fatigue and then subjected to annealing in vaccum at 1173 K. It is shown theoretically that, depending on its initial aspect ratio, a penny-shaped microcrack may evolve via surface diffusion into an isolated spherical void, or a doughnut-shaped channel pore with or without a central spherical void. Subsequent evolution causes the doughnut-shaped channel pore to break up into a ring of spherical voids via Rayleigh’s instabilities. These results were confirmed with experimental observations of typical configurations of voids that result from the crack healing process. The experimentally observed evolution time is also in good agreement with the predictions of finite element simulations of the evolution process.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Gh Other heat and thermomechanical treatments
68.35.Fx Diffusion; interface formation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Crystallization and phase transformations in amorphous NiTi thin films for microelectromechanical systems

Hoo-Jeong Lee and Ainissa G. Ramirez

Appl. Phys. Lett. 85, 1146 (2004); http://dx.doi.org/10.1063/1.1783011 (3 pages) | Cited 35 times

Online Publication Date: 10 August 2004

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Amorphous sputtered nickel–titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (cubic B2 structure) with heating; and the conversion of austenite (B2) to martensite (monoclinic B19′ structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470°C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35°C. Calorimetric measurements are consistent with the observed crystallization.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Neutron holographic study of palladium hydride

László Cser, Gyula Török, Gerhard Krexner, Manfred Prem, and Ivan Sharkov

Appl. Phys. Lett. 85, 1149 (2004); http://dx.doi.org/10.1063/1.1780594 (3 pages) | Cited 7 times

Online Publication Date: 10 August 2004

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A holographic image of the atomic arrangement in a PdH0.78 single crystal was recorded using spherical neutron waves generated by incoherent neutron-proton scattering (“internal source concept”). The resolution is sufficient to show the positions of single atomic nuclei on their respective lattice sites despite the delocalization of protons due to the weak bonding of hydrogen dissolved in palladium metal. Ways to overcome problems in the reconstruction of atomic positions related to the highly unfavorable sample shape are discussed. The technique offers possibilities for the investigation of various materials containing substantial amounts of hydrogen.
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42.40.Ht Hologram recording and readout methods
64.75.-g Phase equilibria

Macroporous silicon membranes as electron and x-ray transmissive windows

J. Schilling, A. Scherer, U. Gösele, and M. Kolbe

Appl. Phys. Lett. 85, 1152 (2004); http://dx.doi.org/10.1063/1.1772519 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2004

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Macroporous silicon membranes are fabricated whose pores are terminated with 60 nm thin silicon dioxide shells. The transmission of electrons with energies of 5 kV–25 kV through these membranes was investigated reaching a maximum of 22% for 25 kV. Furthermore, the transmission of electromagnetic radiation ranging from the far-infrared to the x-ray region was determined. The results suggest the application of the membrane as window material for electron optics and energy dispersive x-ray detectors.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.-p Beam optics

Interface structures in MgB2 thin films on (0001) SiC

J. S. Wu, N. Jiang, B. Jiang, J. C. H. Spence, A. V. Pogrebnyakov, J. M. Redwing, and X. X. Xi

Appl. Phys. Lett. 85, 1155 (2004); http://dx.doi.org/10.1063/1.1779338 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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The structure of the MgB2∕SiC interface has been studied by high-resolution electron microscopy. Most of the defects at the interface are dislocations with Burgers vector [0001]. In addition, a minority of dislocations with Burgers vector [11math0]∕3 are also generated to relax the mismatch stress between film and substrate. Energy loss spectra obtained from nanometer regions show that the interface is not affected by oxygen.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
79.20.Uv Electron energy loss spectroscopy

Control of photoluminescence properties of Si nanocrystals by simultaneously doping n- and p-type impurities

Minoru Fujii, Yasuhiro Yamaguchi, Yuji Takase, Keiichi Ninomiya, and Shinji Hayashi

Appl. Phys. Lett. 85, 1158 (2004); http://dx.doi.org/10.1063/1.1779955 (3 pages) | Cited 49 times

Online Publication Date: 10 August 2004

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The effects of B and P codoping on photoluminescence (PL) properties of Si nanocrystals (nc-Si) are studied systematically. It is shown that the PL intensity of codoped nc-Si is always higher than that of either P- or B-doped nc-Si. The intensity is sometimes even higher than that of pure nc-Si at relatively low P and B concentrations and low annealing temperatures. By doping P and B simultaneously to very high concentrations, the PL peak shifts below the band gap of bulk Si.
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78.55.Ap Elemental semiconductors
61.72.uf Ge and Si
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Pattern formation in a polymer thin film induced by an in-plane electric field

David Salac, Wei Lu, Chia-Wei Wang, and Ann Marie Sastry

Appl. Phys. Lett. 85, 1161 (2004); http://dx.doi.org/10.1063/1.1781751 (3 pages) | Cited 15 times

Online Publication Date: 10 August 2004

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This letter reports experimental work involving use of an in-plane electric field to induce morphological patterns in a thin polymer film. The film was first spin coated onto a glass wafer. Then, it was heated to above its glass transition temperature to achieve mobility in the fluid. An in-plane electric field was applied using two parallel electrodes, spaced 10 mm apart, whereupon the initially flat polymer∕air interface lost stability and formed islands. The self-assembled islands exhibited a narrow size distribution and demonstrated spatial ordering. We attribute the pattern formation to a combined mechanism of minimization of combined interface energy and electrostatic energy.
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68.55.-a Thin film structure and morphology
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
68.35.Md Surface thermodynamics, surface energies
68.37.Ps Atomic force microscopy (AFM)

White light emission from transparent SiO2 glass prepared from nanometer-sized silica particles

Takashi Uchino and Tomoko Yamada

Appl. Phys. Lett. 85, 1164 (2004); http://dx.doi.org/10.1063/1.1782263 (3 pages) | Cited 23 times

Online Publication Date: 10 August 2004

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We report that nanometer-sized silicon-dioxide particles are sintered to optical transparency at temperatures even below 1000 °C, forming nonporous bulk silica glass. The resultant silica glass exhibits visible emission, which appears white to the naked eye, in the wavelength range from ∼400 to ∼700 nm at room temperature under ultraviolet excitation. The observed emission is quite stable after prolonged exposure to the atmosphere and shows no appreciable light-induced degradation. The present photoluminescence characteristics are found to be basically different from those reported previously for silica nanoparticles and silica-based porous materials.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
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Band offset design with quantum-well gate insulating structures

Tatsuo Schimizu and Takeshi Yamaguchi

Appl. Phys. Lett. 85, 1167 (2004); http://dx.doi.org/10.1063/1.1783012 (2 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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The authors propose a concept, a nanoscaled quantum-well gate insulating structure. The effective conduction band offset (ΔEc) can be controlled with an appropriate combination of high-K and high-ΔEc materials. The electronic structures of SrTiO3 and Sr2TiO4 were studied by means of first-principles calculations to investigate the change in the band structures induced by SrO-layer intercalation. The ΔEc of Sr2TiO4 is raised by about +0.8 eV. A quantum-well gate insulating structure with off-resonance condition is also proposed. The ΔEc becomes as high as the barrier height of the barrier material.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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