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19 Sep 2005

Volume 87, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 123111 (2005); http://dx.doi.org/10.1063/1.2053370 (3 pages)

Xianghui Zhang, Ye Zhang, Jun Xu, Zhe Wang, Xihong Chen, Dapeng Yu, Peng Zhang, Hanhong Qi, and Yongjun Tian
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110 W(0.9 J) pulsed power from resonantly diode-laser-pumped 1.6-μm Er:YAG laser

Dmitri Garbuzov, Igor Kudryashov, and Mark Dubinskii

Appl. Phys. Lett. 87, 121101 (2005); http://dx.doi.org/10.1063/1.2051803 (3 pages) | Cited 37 times

Online Publication Date: 12 September 2005

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110 W pulse power and 0.93 J pulse energy have been obtained with direct resonant pumping of a 1.6-μm Er3+-doped bulk solid-state laser with two-dimensional stacks of 1.5 μm InGaAsP/InP diode lasers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.By Design of specific laser systems

Active waveguide fabrication in erbium-doped oxyfluoride silicate glass using femtosecond pulses

R. R. Thomson, S. Campbell, I. J. Blewett, A. K. Kar, D. T. Reid, S. Shen, and A. Jha

Appl. Phys. Lett. 87, 121102 (2005); http://dx.doi.org/10.1063/1.2051805 (3 pages) | Cited 13 times

Online Publication Date: 12 September 2005

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By directly writing waveguides inside bulk erbium-doped oxyfluoride silicate glass using a focused femtosecond pulse train, we demonstrate the potential for the fabrication of especially broadband, compact telecommunications optical amplifiers operating in the c-band (1529–1561 nm). Characterization results include coupling losses to single-mode fiber, waveguide losses, and gain measurements. Clear relationships between the fabrication pulse energy and the waveguide losses and coupling losses are also established.
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42.79.Gn Optical waveguides and couplers
42.70.Ce Glasses, quartz
42.86.+b Optical workshop techniques
42.62.-b Laser applications

Reversible electrochromic effect accompanying domain-inversion in LiNbO3:Ru:Fe crystals

Qingxin Xi, De’an Liu, Ya’nan Zhi, Zhu Luan, and Liren Liu

Appl. Phys. Lett. 87, 121103 (2005); http://dx.doi.org/10.1063/1.2053356 (3 pages) | Cited 3 times

Online Publication Date: 12 September 2005

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A reversible electrochromic effect during the electrical poling process in LiNbO3:Ru:Fe crystals at room temperature is observed. In electrode area, both electrochromism and domain-inversion occur mutually and electrochromism is reversible during back-switch poling, which are experimentally verified, and a microstructure model to explain the mechanism is proposed. In addition, different from the undoped LiNbO3 crystals, the breakdown field (>25.0 kV/mm) is higher than the coercive (21.0 kV/mm) measured in LiNbO3:Ru:Fe, which proves a possible new technique to realize domain-inversion by constant electric field rather than pulsed one.
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78.20.Jq Electro-optical effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials

Observation of photonic band-gap control in one-dimensional Bragg structures

I. V. Konoplev, P. McGrane, A. D. R. Phelps, A. W. Cross, and K. Ronald

Appl. Phys. Lett. 87, 121104 (2005); http://dx.doi.org/10.1063/1.2043245 (3 pages) | Cited 19 times

Online Publication Date: 13 September 2005

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The results of experimental studies of scattering and interference of waves in one-dimensional photonic band-gap structures based on coaxial waveguides with corrugated inner and outer conductors are presented. Using numerical simulations and experimental measurements, the possibility to control the band-gap parameters is demonstrated. The experimental and theoretical results obtained are compared and discussed. It is shown that the variation of the relative phase of the one-dimensional corrugations with respect to each other results in a change of the band-gap parameters in accordance with simulated predictions.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Polarization-dependent optical properties of planar photonic crystals infiltrated with liquid crystals

Ch. Schuller, J. P. Reithmaier, J. Zimmermann, M. Kamp, A. Forchel, and S. Anand

Appl. Phys. Lett. 87, 121105 (2005); http://dx.doi.org/10.1063/1.2053353 (3 pages) | Cited 11 times

Online Publication Date: 13 September 2005

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Photonic crystals with infiltrated liquid crystals are investigated in the 1.5 μm wavelength regime. Due to the strong temperature dependence of the refractive index of liquid crystals, especially near the clearing point, i.e., at the transition between nematic and isotropic phase, the optical properties of photonic crystals can be tuned by small temperature changes. The refractive index of liquid crystals is birefringent and, therefore, sensitive for the polarization of the incident light. By using microresonators embedded into planar photonic crystal waveguides, the polarization dependence of the optical properties with and without infiltrated liquid crystal is investigated. The experimental results quantitatively agree well with the calculated photonic band structure assuming a temperature depending reorientation of the liquid crystal director field inside the holes.
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42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays
42.70.Df Liquid crystals
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
64.70.M- Transitions in liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Long-wavelength fast semiconductor saturable absorber mirrors using metamorphic growth on GaAs substrates

S. Suomalainen, A. Vainionpää, O. Tengvall, T. Hakulinen, S. Karirinne, M. Guina, O. G. Okhotnikov, T. G. Euser, and W. L. Vos

Appl. Phys. Lett. 87, 121106 (2005); http://dx.doi.org/10.1063/1.2053364 (3 pages) | Cited 12 times

Online Publication Date: 13 September 2005

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Metamorphic growth of InP on GaAs has been used to decrease the absorption recovery time of 1.55 μm semiconductor saturable absorber mirrors. We show that the recovery time can be reliably controlled by changing the thickness of an InP “lattice reformation layer” grown between the GaAs-based distributed Bragg reflector and the active region. Semiconductor saturable absorber mirrors with a thickness of the InP reformation layer around 200 nm or smaller exhibit a recovery time short enough to reliably mode-lock fiber lasers.
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42.82.Gw Other integrated-optical elements and systems
85.30.-z Semiconductor devices
42.79.Bh Lenses, prisms and mirrors
42.65.-k Nonlinear optics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Terahertz radiation from InAlAs and GaAs surface intrinsic-N+ structures and the critical electric fields of semiconductors

J. S. Hwang, H. C. Lin, K. I. Lin, and X. C. Zhang

Appl. Phys. Lett. 87, 121107 (2005); http://dx.doi.org/10.1063/1.2051788 (3 pages) | Cited 4 times

Online Publication Date: 14 September 2005

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This study examines terahertz radiation from a series of In0.52Al0.48As and GaAs surface-intrinsic-N+ structures (SIN+) with surface-intrinsic layers of various thicknesses. The built-in electric fields in the SIN+ structures are used as the bias. Experimental results indicate that the amplitudes of the THz emission are independent of the built-in electric fields in the emitters when the built-in electric fields exceed the corresponding critical electric fields of the semiconductors. In contrast, the amplitudes of the THz emission are proportional to the thickness of the intrinsic layer and, therefore, the number of photo-excited charged carriers.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
84.40.-x Radiowave and microwave (including millimeter wave) technology

Spatial dependence of gain nonlinearities in InGaAs semiconductor optical amplifier

Alvaro Gomez-Iglesias, Julia G. Fenn, Michael Mazilu, and Alan Miller

Appl. Phys. Lett. 87, 121108 (2005); http://dx.doi.org/10.1063/1.2053357 (3 pages) | Cited 1 time

Online Publication Date: 14 September 2005

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Counter-propagating sub-picosecond pulses are used to monitor gain saturation along the waveguide of an InGaAs superlattice semiconductor optical amplifier at 1550 nm wavelength. The functional form of the spatial dependence of gain saturation is found to depend on pulse energy. These observations are interpreted by combining the optical nonlinearities associated with interband carrier dynamics and carrier heating together and their respective time constants. We show that the results are consistent with the predictions of a propagation model. Implications for all-optical switching, particularly in the limit of full saturation across the whole amplifier, are discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Wave propagation in nonlinear left-handed transmission line media

Alexander B. Kozyrev, Hongjoon Kim, Abdolreza Karbassi, and Daniel W. van der Weide

Appl. Phys. Lett. 87, 121109 (2005); http://dx.doi.org/10.1063/1.2056581 (3 pages) | Cited 21 times

Online Publication Date: 14 September 2005

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Using a one-dimensional system, we demonstrate a wide variety of wave propagation phenomena possible in nonlinear left-handed media. These include effective second-harmonic generation where the fundamental wave and the second-harmonic wave are badly mismatched. We also observe parametric instabilities accompanying intensive harmonic generation.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.-x Radiowave and microwave (including millimeter wave) technology

Electro-optically tunable photonic crystals

M. Schmidt, M. Eich, U. Huebner, and R. Boucher

Appl. Phys. Lett. 87, 121110 (2005); http://dx.doi.org/10.1063/1.2039994 (3 pages) | Cited 28 times

Online Publication Date: 15 September 2005

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We report on electro-optical modulation with a sub-1-V sensitivity in a photonic crystal slab waveguide resonator which contains a nanostructured second-order nonlinear optical polymer. The electro-optical susceptibility in the core was induced by high electric-field poling. A square lattice of holes carrying a linear defect was transferred into the slab by electron-beam lithography and reactive ion etching, creating a photonic crystal slab-based resonator. Applying an external electric modulation voltage to electrodes leads to a linear electro-optical shift of the resonance spectrum and thus to a modulation of the transmission at a fixed wavelength based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels effect). This effect is therefore inherently faster than other reported electro-optic modulation effects in nanophotonics.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.70.Mp Nonlinear optical crystals
42.65.An Optical susceptibility, hyperpolarizability
42.79.Gn Optical waveguides and couplers

Integrating yttrium iron garnet onto nongarnet substrates with faster deposition rates and high reliability

Sang-Yeob Sung, Xiaoyuan Qi, and Bethanie J. H. Stadler

Appl. Phys. Lett. 87, 121111 (2005); http://dx.doi.org/10.1063/1.2046733 (3 pages) | Cited 10 times

Online Publication Date: 15 September 2005

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Magneto-optical garnets (Y3Fe5O12 or YIG) were grown monolithically by a novel reactive radio-frequency sputtering method that used a partial pressure differential to increase sputtering rates. MgO and quartz substrates were used as they are good buffer layers and optical claddings for integration. A wide single-phase field for annealed YIG was found (26.9–43.2 at % Y), and the magnetic properties were measured. The films had refractive indices of 2.1 and out-of-plane Faraday rotations up to 0.2°/μm at 633 nm. The dielectric matrix was used to calculate the difference in the propagation constants of forward and backward traveling light (Δβ = 1.999×10−5).
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78.20.Ls Magneto-optical effects
81.15.Cd Deposition by sputtering
75.50.Gg Ferrimagnetics
78.66.Nk Insulators
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.40.Gh Other heat and thermomechanical treatments
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Relaxation of compressively-strained AlGaN by inclined threading dislocations

D. M. Follstaedt, S. R. Lee, P. P. Provencio, A. A. Allerman, J. A. Floro, and M. H. Crawford

Appl. Phys. Lett. 87, 121112 (2005); http://dx.doi.org/10.1063/1.2056582 (3 pages) | Cited 24 times

Online Publication Date: 15 September 2005

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Transmission electron microscopy and x-ray diffraction were used to assess the microstructure and strain of AlxGa1−xN(x = 0.61–0.64) layers grown on AlN. The compressively-strained AlGaN is partially relaxed by inclined threading dislocations, similar to observations on Si-doped AlGaN by P. Cantu, F. Wu, P. Waltereit, S. Keller, A. E. Romanov, U. K. Mishra, S. P. DenBaars, and J. S. Speck [Appl. Phys. Lett. 83, 674 (2003) ]; however, in our material, the dislocations bend before the introduction of any Si. The bending may be initiated by the greater lattice mismatch or the lower dislocation density of our material, but the presence of Si is not necessarily required. The relaxation by inclined dislocations is quantitatively accounted for with the model of A. E. Romanov and J. S. Speck [Appl. Phys. Lett. 83, 2569 (2003) ], and we demonstrate the predicted linear dependence of relaxation on layer thickness. Notably, such relaxation was not found in tensile strained AlGaN grown on GaN [ J. A. Floro, D. M. Follstaedt, P. Provencio, S. J. Hearne, and S. R. Lee, J. Appl. Phys. 96, 7087 (2004) ], even though the same mechanism appears applicable.
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81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Filling a spectral hole via self-phase modulation

A. Präkelt, M. Wollenhaupt, C. Sarpe-Tudoran, A. Assion, and T. Baumert

Appl. Phys. Lett. 87, 121113 (2005); http://dx.doi.org/10.1063/1.2056589 (3 pages) | Cited 4 times

Online Publication Date: 15 September 2005

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The effect of spectral amplitude modulation on self-phase modulation is studied. To that end we remove a small interval of frequency components from the broad spectrum of a femtosecond laser pulse. We investigate the regeneration of these missing frequency components via self-phase modulation. A water jet serves as a transparent sample. A physical model is given which explains the observation that the removed frequency components are not only replenished by self-phase modulation but can even overshoot their adjacent frequencies in power spectral density. In addition, we suggest possible applications in the field of nonlinear microscopy.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Fabrication and optical measurements of germanium-doped silica ridge waveguides using a colloidal suspension approach

Deok-Yang Kim, Henry Du, Glen R. Kowach, Christopher A. White, and David J. McGee

Appl. Phys. Lett. 87, 121114 (2005); http://dx.doi.org/10.1063/1.2037863 (3 pages) | Cited 1 time

Online Publication Date: 15 September 2005

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Germanium-doped silica ridge waveguides for planar lightwave circuits were fabricated using colloidal suspensions. After consolidation at 1300 °C, fully dense micron-scale thick films were obtained. The refractive index of these films was tuned with germanium dopant up to 11.1 mol %. The propagation loss of a 3.1 mol % germanium-doped silica sample without an overcladding layer was 3.3±0.5 dB/cm. Postannealing of the patterned waveguides at 1200 °C for 30 min was conducted in order to reflow waveguides, but it did not significantly smooth the sidewall roughness due to the high viscosity of the 3.1 mol % germanium-doped silica at that temperature.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
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On the magnetic mirror effect in Hall thrusters

M. Keidar and I. D. Boyd

Appl. Phys. Lett. 87, 121501 (2005); http://dx.doi.org/10.1063/1.2053351 (3 pages) | Cited 23 times

Online Publication Date: 12 September 2005

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The magnetic mirror effect is studied in the channel of a Hall thruster. It is shown that gradients in magnetic field affect the presheath structure and electric potential distribution. The length of the radial presheath region decreases in the presence of a magnetic field gradient. The two-dimensional potential shape can be affected by proper choice of the magnetic mirror ratio. In particular, it is possible to obtain a concave shape of the potential profile in the channel even in the case of a primarily radial magnetic field. This, in turn, can be used to efficiently control the ion dynamics in the acceleration region.
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52.75.Di Ion and plasma propulsion
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Kh Plasma sheaths

Control and analysis of ion species in inductively coupled nitration plasma using a grid system

K. H. Bai and H. Y. Chang

Appl. Phys. Lett. 87, 121502 (2005); http://dx.doi.org/10.1063/1.2056595 (3 pages) | Cited 1 time

Online Publication Date: 15 September 2005

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We control the ion density ratio of [N+]/[N2+] with the voltage-biased grid system in inductively coupled nitration plasma. The ion density ratio is controlled from 0.39 to 0.04 with decreasing grid-biased voltage. We try to analyze the variation of the ion density ratio using the measured plasma parameters and particle balance equation. The important factor determining the ion ratio is the plasma potential difference between the source region—where plasma is generated—and the diffusion region—where the electron temperature is controlled. When the plasma potential is higher in the source region than in diffusion region, the ion density ratio is determined by the electron temperature in Region I. Inversely, the ion density ratio is determined by the electron temperature in Region II, when the plasma potential is higher in Region II than in Region I.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.40.Kh Plasma sheaths
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Generalized stacking fault energies, ductilities, and twinnabilities of Ni and selected Ni alloys

Donald J. Siegel

Appl. Phys. Lett. 87, 121901 (2005); http://dx.doi.org/10.1063/1.2051793 (3 pages) | Cited 34 times

Online Publication Date: 12 September 2005

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The generalized stacking fault energies, Rice-criterion ductilities, and twinnabilities of selected Ni-x solid-solution alloys (x = Nb, W, Mn, Fe, Cu) are calculated using density functional theory to elucidate how alloying alters the mechanical properties of pure Ni. Relative to Ni, the alloys have smaller stacking fault energies (γsf), similar ductilities, and a greater tendency to undergo deformation twinning. The results are compared to experimental studies of the mechanical properties of nanocrystalline (nc) Ni alloys from the literature, and it is suggested that the higher strain-hardening rate recently reported for nc-Ni-Cu (relative to nc-Ni-Fe) does not arise from differences in γsf, but from a higher dislocation density caused by more facile dislocation nucleation.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Third-order optical nonlinearity in regio-controlled polythiophene films

Hideo Kishida, Keisuke Hirota, Takeru Wakabayashi, Hiroshi Okamoto, Hisashi Kokubo, and Takakazu Yamamoto

Appl. Phys. Lett. 87, 121902 (2005); http://dx.doi.org/10.1063/1.2051795 (3 pages) | Cited 21 times

Online Publication Date: 12 September 2005

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We have investigated the third-order optical nonlinearity of poly(3-hexylthiophenes) with various head-to-tail coupling ratios (r), using the third-harmonic generation method. An increase in r leads to a reduction in optical gap energy (Eg) and an increase in the third-order nonlinear susceptibility (χ(3)). For r = 0 to 0.80, χ(3) is scaled by Eg as χ(3)∝Eg−6.7, while for r ∼ 1, χ(3) is considerably enhanced beyond this scaling law. We discuss how the behavior of χ(3) is based upon the conjugation-length dependence of the transition dipole moments.
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42.70.Jk Polymers and organics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Qn Polymers; organic compounds
43.25.Dc
42.70.Qs Photonic bandgap materials

Thermal annealing effect on the band gap and dielectric functions of silicon nanocrystals embedded in SiO2 matrix

L. Ding, T. P. Chen, Y. Liu, C. Y. Ng, Y. C. Liu, and S. Fung

Appl. Phys. Lett. 87, 121903 (2005); http://dx.doi.org/10.1063/1.2051807 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2005

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The thermal annealing effect on band gap and dielectric functions of silicon nanocrystals (nc-Si) embedded in a SiO2 matrix synthesized by Si ion implantation is investigated by spectroscopic ellipsometry. A large band-gap expansion of nc-Si relative to bulk crystalline silicon has been observed. The band gap of the nc-Si for the nonannealing condition (i.e., as implanted) is 1.78 eV while it is 1.72 eV for the annealing at 1000 °C for 100 min. The slight decrease in the band gap is attributed to the slight increase in the nc-Si size with annealing. The dielectric functions of nc-Si show a significant suppression, as compared to bulk crystalline silicon, due to the quantum size effect. Annealing results in a small change in the static dielectric constant, which can be explained in terms of the size effect also.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.20.Mq Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
77.22.Ch Permittivity (dielectric function)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Chemical fluctuation-induced nanodomains in Cu(In,Ga)Se2 films

Yanfa Yan, R. Noufi, K. M. Jones, K. Ramanathan, M. M. Al-Jassim, and B. J. Stanbery

Appl. Phys. Lett. 87, 121904 (2005); http://dx.doi.org/10.1063/1.2053349 (3 pages) | Cited 21 times

Online Publication Date: 12 September 2005

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The microstructure and chemistry of CuInSe2 single-crystals and Cu(In,Ga)Se2 thin films from high-efficiency devices are investigated by transmission electron microscopy and x-ray energy-dispersive spectroscopy. We find strong chemical fluctuations at the nanoscale, which result in a lattice comprising a mixture of relatively Cu-poor and Cu-rich nanodomains in both cases. These nanodomains are crystallographically coherent, and no structural lattice defects are found at the interfaces between them. These nanodomains may interconnect, forming three-dimensional, interpenetrating Cu-poor and Cu-rich percolation networks. Such interconnected structures may play a role in the high device performance of Cu(In,Ga)Se2 thin-film photovoltaics.
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82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.05.Hd Other semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)

Thermally-induced formation of Si wire array on an ultrathin (111) silicon-on-insulator substrate

Zainal A. Burhanudin, Ratno Nuryadi, Yasuhiko Ishikawa, Michiharu Tabe, and Yukinori Ono

Appl. Phys. Lett. 87, 121905 (2005); http://dx.doi.org/10.1063/1.2053354 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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We have found that a Si wire array is formed by thermal agglomeration of an ultrathin (111) Si layer in a bonded silicon-on-insulator (SOI) structure, although previous studies for crystalline and amorphous Si layers on SiO2 only showed island formation. As starting material, (111) bonded SOI wafers with the top Si layers thinned to 5–9 nm were used. The samples were then subjected to a thermal treatment at 950 °C in an ultrahigh vacuum. Atomic force microscopy revealed that the (111) top Si layer is deformed into three sets of wire arrays in the three equivalent 〈11math〉 directions. It is also shown that the patterning of a Si layer leads to the wire array selectively formed in one of these three directions.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)

The change of electric field and of some other insulating properties during isochronal annealing in thermally poled Ge-doped silica films

Qiming Liu, Bertrand Poumellec, Delfin Braga, Guy Blaise, Yitao Ren, and Martin Kristensen

Appl. Phys. Lett. 87, 121906 (2005); http://dx.doi.org/10.1063/1.2053361 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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The secondary electron emission contrast between poled and unpoled regions in thermally poled Ge-doped silica films were measured according to different annealing temperatures and electron doses with electron acceleration energy of 5 keV. It is used for measuring the change on annealing of poling induced electric field and other insulating properties like electron traps population and conductivity in high field. Concerning the change of the contrast at low dose arising from the poling electric field, we show that this field begins to disappear at around 450 °C and is erased completely at 650 °C. Using a larger dose allows measuring the change in conductivity contrast. We find a stability similar to the electric field with a disappearance around 450 ∼ 650 °C. On the contrary, for intermediate dose, the contrast remains for larger annealing temperature. It allows measuring properties of the electron traps. Their number appears to be modified in the poling process.
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73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
77.22.Ej Polarization and depolarization
79.20.Hx Electron impact: secondary emission
81.40.Gh Other heat and thermomechanical treatments

Theoretical expression for elastic relaxation in strained-layer superlattice specimens thinned for transmission electron microscopy

Hiroshi Shimotahira and Kenichi Nakamura

Appl. Phys. Lett. 87, 121907 (2005); http://dx.doi.org/10.1063/1.2042541 (3 pages)

Online Publication Date: 12 September 2005

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We derived a theoretical expression for elastic relaxation in a strained-layer superlattice (SLS) grown coherently on substrates. The derived formula takes into account two types of elastic relaxation: one between adjacent layers in the SLS, and another between the whole SLS and the substrates. Numerical calculations for a strained multi-quantum-well laser diode as an example of a SLS showed that elastic relaxation due to the average strain of the whole SLS occurs even for a relatively thick specimen, while periodic elastic relaxation due to the strain between layers in the SLS occurs near the specimen surface. These theoretical results are in good agreement with those obtained by computer simulations based on finite-element method.
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68.65.Cd Superlattices
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Lp Transmission electron microscopy (TEM)

Microscopic failure behavior of nanoporous gold

Juergen Biener, Andrea M. Hodge, and Alex V. Hamza

Appl. Phys. Lett. 87, 121908 (2005); http://dx.doi.org/10.1063/1.2051791 (3 pages) | Cited 35 times

Online Publication Date: 13 September 2005

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We report on the fracture behavior of nanoporous (np)-Au with an open sponge-like morphology of interconnecting ligaments on the nanometer length scale. Despite its macroscopic brittleness, np-Au is microscopically a very ductile material as ligaments strained by as much as 200% can be observed in the vicinity of crack tips. Cell-size effects on the microscopic failure mechanism were studied by annealing treatments that increased the typical pore size/ligament diameter from ∼ 100 nm to  ∼ 1 μm. Ligaments with diameter of ∼ 100 nm fail by plastic flow and necking, whereas failure by slip was observed for larger ligaments with a diameter of ∼ 1 μm. The absence of slip marks in 100-nm-sized ligaments suggests a strongly suppressed dislocation activity, consistent with the high yield strength of np-Au.
Show PACS
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.46.-w Structure of nanoscale materials
62.20.M- Structural failure of materials
81.40.Gh Other heat and thermomechanical treatments

Scanning transmission electron microscopy of gate stacks with HfO2 dielectrics and TiN electrodes

Melody P. Agustin, Leonardo R. C. Fonseca, Jacob C. Hooker, and Susanne Stemmer

Appl. Phys. Lett. 87, 121909 (2005); http://dx.doi.org/10.1063/1.2053362 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2005

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High-angle annular dark-field (HAADF) imaging and electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopy were used to investigate HfO2 gate dielectrics grown by atomic layer deposition on Si substrates, and their interfaces with TiN electrodes and silicon, as a function of annealing temperature. Annealing at high temperatures (900 °C) caused significant roughening of both bottom (substrate) and top (electrode) interface. At the bottom interface, HAADF images showed clusters of Hf atoms that protruded into the interfacial SiO2 layer. Low-loss EELS established that even crystalline HfO2 films exposed to relative high temperatures (700 °C) exhibited significant differences in their electronic structure relative to bulk HfO2. Further annealing caused the electronic structure to more closely resemble that of bulk HfO2, with the most significant change due to annealing with the TiN electrode.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
79.20.Uv Electron energy loss spectroscopy
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
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