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7 May 2007

Volume 90, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages)

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler
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Soft-mold-induced self-construction of polymer patterns under microwave irradiation

Fu-Hsiang Ko, Chia-Tien Wu, Mei-Fen Chen, Jem-Kun Chen, and Tieh-Chi Chu

Appl. Phys. Lett. 90, 191901 (2007); http://dx.doi.org/10.1063/1.2737364 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2007

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In this study, the authors used a soft-mold-induced self-construction method to fabricate three-dimensional patterns under microwave irradiation for 1 min. The authors estimated the actual pattern growth temperature using a fluorescence probe technique. The temperature at which pattern growth originated was, by necessity, higher than the glass transition temperature of the novolak resist. Electrostatic forces and surface tension effects under the electromagnetic field contributed significantly to the pattern growth, and the use of an antisticking agent allowed easy demolding.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
78.60.-b Other luminescence and radiative recombination
68.03.Cd Surface tension and related phenomena

Galvanic corrosion induced degredation of tensile properties in micromachined polycrystalline silicon

David C. Miller, Brad L. Boyce, Ken Gall, and Conrad R. Stoldt

Appl. Phys. Lett. 90, 191902 (2007); http://dx.doi.org/10.1063/1.2737370 (3 pages) | Cited 4 times

Online Publication Date: 7 May 2007

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Immersion of polycrystalline silicon in hydrofluoric acid-based solutions is often utilized in microsystem fabrication to liberate mechanical structures. The authors demonstrate, using microfabricated tensile specimens, that such etching can cause a catastrophic reduction in tensile strength and elastic modulus in silicon galvanically coupled to a metallic layer, such as commonly used gold. Galvanically corroded silicon exhibits grain-boundary attack leading to intergranular fracture and/or generalized material removal. The severity of damage and corresponding losses in strength and modulus depend on etch duration and etch chemistry. In contrast, without a metallic layer, uncorroded silicon fails transgranularly and independent of etch duration or chemistry.
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81.65.Cf Surface cleaning, etching, patterning
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
62.20.M- Structural failure of materials
61.72.Mm Grain and twin boundaries

Mechanical strengths of silicon nitrides studied by ab initio calculations

R. F. Zhang, S. H. Sheng, and S. Veprek

Appl. Phys. Lett. 90, 191903 (2007); http://dx.doi.org/10.1063/1.2737376 (3 pages) | Cited 27 times

Online Publication Date: 7 May 2007

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The stress-strain relationships under tensile and shear loads are calculated for hcp(β)-Si3N4 and fcc(NaCl)-SiN by means of ab initio density functional theory. The ideal shear strengths for fcc-SiN are much lower than those for hcp-Si3N4. This is in agreement with experiments which show that the interfacial fcc-SiN can strengthen the TiN/SiN heterostructures only when its thickness is about 1–2 ML. Based on the calculated electronic density of states, the physical origin of the mechanical strengths is addressed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Metamaterials with dendriticlike structure at infrared frequencies

Hui Liu and Xiaopeng Zhao

Appl. Phys. Lett. 90, 191904 (2007); http://dx.doi.org/10.1063/1.2737382 (3 pages) | Cited 8 times

Online Publication Date: 7 May 2007

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The authors present a planar medium composed of the copper dendriticlike structure and silver film at infrared frequencies. The dendriticlike copper, which has quasiperiodic hexagonal cells, and silver film were prepared using the electrochemical deposition method. It is shown that the transmission spectra of the copper dendriticlike structure and the planar medium appear to have a stop band and a passband in the range of 1.28–2.5 μm. A clear image is also observed at the wavelength near 1.92 μm, as expected, with our lens composed of copper dendritic cells and silver film.
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42.70.-a Optical materials

Cubic γ-Be3N2: A superhard semiconductor predicted from first principles

Huiyang Gou, Li Hou, Jingwu Zhang, Zhibin Wang, Lihua Gao, and Faming Gao

Appl. Phys. Lett. 90, 191905 (2007); http://dx.doi.org/10.1063/1.2737130 (3 pages) | Cited 8 times

Online Publication Date: 8 May 2007

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The authors predict a superhard semiconductor phase of Be3N2 with cubic structure using first-principles calculations. The structural, mechanical, electronic, and optical properties of the Be3N2 have been investigated. Results indicate that the predicted Be3N2 phase is a wide gap semiconductor with a direct band gap of about 2.51 eV. The calculated hardness of cubic γ-Be3N2 based on Mulliken overlap population analysis in first-principles technique approaches those of B4C and B6O. The higher mechanical property can be attributed to the existence of strong Be–N–Be covalent bond chains in the cubic structure. The obtained static dielectric constant of Be3N2 (4.6 eV) is close to the spinel structure of Si3N4 (4.7 eV).
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Resonance acoustic-phonon spectroscopy for studying elasticity of ultrathin films

H. Ogi, M. Fujii, N. Nakamura, T. Shagawa, and M. Hirao

Appl. Phys. Lett. 90, 191906 (2007); http://dx.doi.org/10.1063/1.2737819 (3 pages) | Cited 14 times

Online Publication Date: 8 May 2007

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Ultrahigh-frequency phonon resonances were excited in ultrathin films ( ∼ 5 nm) by femtosecond light pulses, and their resonance frequencies were measured to determine the through-thickness elastic constants. The studied materials were Pt and Fe. The elastic stiffness increases with decreasing film thickness for both materials, whereas the normal strain showed opposite thickness behavior. Analysis of the wave propagation using the third-order elastic constants explained these trends.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.65.+k Acoustical properties of solids
63.20.-e Phonons in crystal lattices
78.47.-p Spectroscopy of solid state dynamics

Quantitative nanoscale local strain profiling in embedded SiGe metal-oxide-semiconductor structures

W. Zhao, G. Duscher, G. Rozgonyi, M. A. Zikry, S. Chopra, and M. C. Ozturk

Appl. Phys. Lett. 90, 191907 (2007); http://dx.doi.org/10.1063/1.2738188 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2007

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Mechanical strain by strain engineering has been widely used in Si metal-oxide-semiconductor field effect transistors. Experimental convergent beam electron diffraction (CBED) strain measurements and finite element calculations to quantitatively correlate the strain in the transmission electron microscope (TEM) sample with the actual device. It was found that the magnitude of the longitudinal strain, εx, along the channel direction, is about 20% higher in the TEM sample than in the real device. This combined approach can be used to explain data from other CBED studies of strained Si devices.
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81.40.Lm Deformation, plasticity, and creep
85.30.Tv Field effect devices
68.37.Lp Transmission electron microscopy (TEM)
62.20.F- Deformation and plasticity

Growth and characterization of N-polar InGaN/GaN multiquantum wells

S. Keller, N. A. Fichtenbaum, M. Furukawa, J. S. Speck, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 90, 191908 (2007); http://dx.doi.org/10.1063/1.2738381 (3 pages) | Cited 11 times

Online Publication Date: 9 May 2007

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The properties of N-polar InGaN/GaN multiquantum wells (MQWs) grown by metal-organic chemical vapor deposition were investigated. Samples grown under optimized conditions exhibited distinct quantum well related emission, smooth surfaces, and abrupt interfaces as evaluated by room temperature photoluminescence, atomic force microscopy, and x-ray diffraction. Enhanced incorporation of indium into N-polar compared to Ga-polar MQW samples was observed for MQWs simultaneously deposited onto the (0001) and (000math) GaN-on-sapphire base layers using trimethylindium-to-trimethylgallium-flow-ratios larger than 1.2 during growth. Necessary adjustments of the growth procedure for N polar in comparison with Ga-polar MQWs are described.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Multiplication of shear bands and ductility of metallic glass

F. F. Wu, Z. F. Zhang, F. Jiang, J. Sun, J. Shen, and S. X. Mao

Appl. Phys. Lett. 90, 191909 (2007); http://dx.doi.org/10.1063/1.2738366 (3 pages) | Cited 23 times

Online Publication Date: 9 May 2007

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The authors find that metallic glass can be controlled to create regularly arrayed fine multiple shear bands under small punch test, indicating that metallic glass essentially has a good plastic deformation ability and thus high ductility under suitable loading condition. The current findings imply that the initiation and propagation of shear bands in metallic glass strongly depends on the stress state and the small punch test can also be regarded as an effective method to characterize the shear deformation ability and distinguish ductile-brittle transition of different metallic glasses.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Elastic moduli and hardness of c-Zr2.86(N0.88O0.12)4 having Th3P4-type structure

Dmytro A. Dzivenko, Andreas Zerr, Elmar Schweitzer, Mathias Göken, Reinhard Boehler, and Ralf Riedel

Appl. Phys. Lett. 90, 191910 (2007); http://dx.doi.org/10.1063/1.2738373 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2007

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The equation of state of the recently discovered oxygen-bearing cubic zirconium (IV) nitride, c-Zr2.86(N0.88O0.12)4, was measured at room temperature in a diamond anvil cell using x-ray powder diffraction combined with synchrotron radiation. From these studies the bulk modulus B0 = 219(13) GPa and its first pressure derivative B0′ = 4.4(1.0) [or B0 = 223(5) GPa, for B0′ fixed at 4] were obtained. Applying nanoindentation techniques the reduced modulus Er ≈ 220 GPa and hardness H ≈ 18 GPa were measured for porous c-Zr2.86(N0.88O0.12)4. The shear modulus of c-Zr2.86(N0.88O0.12)4 was estimated to be at least G0 = 96(13) GPa using the experimental data of B0 and Er, exclusively.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity

Observation of the Purcell effect in high-index-contrast micropillars

A. J. Bennett, D. J. P. Ellis, A. J. Shields, P. Atkinson, I. Farrer, and D. A. Ritchie

Appl. Phys. Lett. 90, 191911 (2007); http://dx.doi.org/10.1063/1.2736292 (3 pages) | Cited 10 times

Online Publication Date: 10 May 2007

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The authors have fabricated pillar microcavity samples with Bragg mirrors consisting of alternate layers of GaAs and aluminum oxide. Compared to the more widely studied GaAs/AlAs micropillars, these mirrors can achieve higher reflectivities with fewer layer repeats and reduce the mode volume. The authors have studied a number of samples containing a low density of InGaAs/GaAs self-assembled quantum dots in a cavity and here report observation of a threefold enhancement in the radiative lifetime of a quantum dot exciton state due to the Purcell effect.
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42.82.Gw Other integrated-optical elements and systems
42.79.Bh Lenses, prisms and mirrors
78.67.Hc Quantum dots
81.07.Ta Quantum dots

Structural investigations of epitaxial InN by x-ray photoelectron diffraction and x-ray diffraction

Daniel Hofstetter, Laurent Despont, M. Gunnar Garnier, Esther Baumann, Fabrizio R. Giorgetta, Philipp Aebi, Lutz Kirste, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 90, 191912 (2007); http://dx.doi.org/10.1063/1.2738372 (3 pages) | Cited 1 time

Online Publication Date: 10 May 2007

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The authors investigated a 1 μm thick molecular beam epitaxy–grown InN film by means of full hemispherical x-ray photoelectron diffraction and high resolution x-ray diffraction. While x-ray diffraction reveals that this nominally hexagonal InN layer contains roughly 1% of cubic phase InN, a comparison between measured and simulated x-ray photoelectron diffraction data allowed them to directly determine the polarity of the crystal. Furthermore, the data indicate that the InN surface consists of a mosaic of domains oriented at an azimuth of 180° to each other, where the azimuth corresponds to the rotation angle around the [0001] axis.
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68.55.-a Thin film structure and morphology
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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