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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Correlation of spectral luminescence with threading dislocations in green-light-emitting InGaN quantum wells

J. C. Brooksby, J. Mei, and F. A. Ponce

Appl. Phys. Lett. 90, 231901 (2007); http://dx.doi.org/10.1063/1.2746062 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2007

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A direct correlation has been established between the spatial variation of spectral luminescence and the distribution of threading dislocations in a green-light-emitting InGaN quantum well structure grown on a sapphire substrate. Transmission electron microscopy and monochromatic cathodoluminescence images, taken from the same region, indicate that the nature of the quantum well emission is influenced by the microstructure of the underlying GaN. The microstructure is defined by threading dislocations that reflect a columnar structure with low-angle grain boundaries. A strong correlation is observed between this microstructure and the peak and low-energy portion of the quantum well luminescence, with threading dislocations as boundaries between bright and darker regions. The high-energy portion of the luminescence is localized and is generally complementary to the rest of the spectrum.
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78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
61.72.Mm Grain and twin boundaries
61.72.S- Impurities in crystals

Layer rotation mechanism in the chiral smectic C phase

J. N. Jang, A. B. Davey, and W. A. Crossland

Appl. Phys. Lett. 90, 231902 (2007); http://dx.doi.org/10.1063/1.2746410 (3 pages)

Online Publication Date: 5 June 2007

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The authors propose a model for the layer rotation of the chiral smectic C (SmC*) phase, which is intended to give answers to some basic questions about smectic layer rotation. They have proposed that layer rotation is related to the electroclinic effect, by which an induced asymmetric population density of the director for each asymmetric ac cycle is induced. In our modeling, the driving force for the layer rotation is the deformation of the molecular coupling configuration and a volume change by the tilt cone rotation.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals

Separation of coherent and incoherent contributions to reflectance difference spectra

K. Schmidegg and P. Zeppenfeld

Appl. Phys. Lett. 90, 231903 (2007); http://dx.doi.org/10.1063/1.2746421 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2007

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The authors present a method for the analysis of azimuthal dependent reflectance difference spectroscopy data that enables a separation of coherent and incoherent contributions to reflectance difference spectra. The latter can originate from back side reflections of transparent films if their thickness is larger than the coherence length of the light. Furthermore, instrument artifacts can be suppressed and additional contributions with different optical eigenaxes can be identified.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Effects of surface elasticity and residual surface tension on the natural frequency of microbeams

Gang-Feng Wang and Xi-Qiao Feng

Appl. Phys. Lett. 90, 231904 (2007); http://dx.doi.org/10.1063/1.2746950 (3 pages) | Cited 89 times

Online Publication Date: 5 June 2007

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Surface effects often play a significant role in the physical properties of micro- and nanosized materials and structures. In this letter, the authors presented a theoretical model directed towards investigation of the effects of both surface elasticity and residual surface tension on the natural frequency of microbeams. A thin surface layer was introduced on the upper and lower surfaces to rationalize the near-surface material properties that are different from the bulk material. An explicit solution is derived for the natural frequency of microbeams with surface effects. This study might be helpful for the design of microbeam-based sensors and some related measurement techniques.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Thermal energy exchange between carbon nanotube and air

Ming Hu, Sergei Shenogin, Pawel Keblinski, and Nachiket Raravikar

Appl. Phys. Lett. 90, 231905 (2007); http://dx.doi.org/10.1063/1.2746954 (3 pages) | Cited 11 times

Online Publication Date: 5 June 2007

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Using molecular dynamics simulations the authors impose a heat flux between single-walled carbon nanotubes and air to study thermal interfacial conductance. They estimate that the nanotube-air interfacial thermal conductance is about 0.1 MW/m2 K at room temperature and atmospheric pressure. The associated interfacial thermal resistance is equivalent to the resistance of 250 nm thick layer of air. They also show that the interfacial resistance is a strong function of the interaction parameters between air atoms and carbon nanotubes.
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73.40.-c Electronic transport in interface structures
68.35.Md Surface thermodynamics, surface energies

Femtosecond nonlinear optical properties of lead-germanium oxide amorphous films

Diego Rativa, Renato E. de Araujo, Cid B. de Araújo, Anderson S. L. Gomes, and Luciana R. P. Kassab

Appl. Phys. Lett. 90, 231906 (2007); http://dx.doi.org/10.1063/1.2747174 (3 pages) | Cited 13 times

Online Publication Date: 6 June 2007

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The nonlinear (NL) response of lead-germanium oxide amorphous films was investigated using a Ti:saphire laser delivering pulses of ≈ 150 fs at 800 nm. The Kerr shutter technique was employed to reveal the time response of the nonlinearity that is smaller than 150 fs. The sign and magnitude of the nonlinearity were obtained using a novel technique called thermally managed eclipse Z scan which allows the simultaneous characterization of cumulative and noncumulative NL effects. The NL refractive index of electronic origin, n2 ≈ 2×10−17 m2/W, and the NL absorption coefficient, α2 ≈ 3×103 cm/GW, were determined.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.-w Optical properties of specific thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Unusual room temperature ductility of a Zr-based bulk metallic glass containing nanoparticles

J. B. Qiang, W. Zhang, G. Q. Xie, and A. Inoue

Appl. Phys. Lett. 90, 231907 (2007); http://dx.doi.org/10.1063/1.2746071 (3 pages) | Cited 19 times

Online Publication Date: 6 June 2007

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Highly ductile Zr65Al7.5Cu27.5 bulk metallic glass (BMG) containing nanometer scaled fcc phase was obtained by copper mold casting. Room temperature compression tests revealed superior mechanical properties of the alloy: yielding stress of 1670 MPa, Young’s modulus of 90 GPa, elastic strain of 2%, and especially a remarkable plasticity of over 50%. The marginal BMG is a useful model system to examine the nanocrystal coalescence model and the shear-transformation-zone model proposed for large scale plastic deformations of metallic glasses.
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81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys
61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.10.Fq Growth from melts; zone melting and refining

Stabilization of facial isomer of tris(8-hydroxyquinolinate)aluminum through confinement in silica-surfactant mesostructures

Le-Le Li, Chen-Jie Fang, Quan Yuan, and Chun-Hua Yan

Appl. Phys. Lett. 90, 231908 (2007); http://dx.doi.org/10.1063/1.2746420 (3 pages) | Cited 1 time

Online Publication Date: 7 June 2007

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The self-assembled nanocomposites of tris(8-hydroxyquinolinate)aluminum (Alq3) confined in the silica-surfactant mesostructures are investigated. In the photoluminescence (PL) spectra, the Alq3 molecules confined in the mesostructures exhibit a significant blueshift by 50 nm compared with that of the pristine Alq3. The PL efficiency is enhanced for the nanocomposites prepared at a higher temperature. The spectral analyses reveal that fac-Alq3 molecule, which is hard to prepare due to its relatively thermodynamically unstability, is obtained with this efficient and simple method. PL decay analysis implies experimentally the lifetimes corresponding to facial and meridional isomers.
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78.55.Hx Other solid inorganic materials
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
81.16.Dn Self-assembly

Compressive uniaxially strained silicon on insulator by prestrained wafer bonding and layer transfer

C. Himcinschi, M. Reiche, R. Scholz, S. H. Christiansen, and U. Gösele

Appl. Phys. Lett. 90, 231909 (2007); http://dx.doi.org/10.1063/1.2747182 (3 pages) | Cited 3 times

Online Publication Date: 7 June 2007

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Wafer level compressive uniaxially strained silicon on insulator is obtained by direct wafer bonding of silicon wafers in cylindrically curved state, followed by thinning one of the wafers using the smart-cut process. The mapping of the wafer bow demonstrates the uniaxial character of the strain induced by the cylindrical bending. The interfacial properties are investigated by infrared transmission imaging, scanning acoustic microscopy, and transmission electron microscopy. UV-Raman spectroscopy is employed to determine the strain in the thin transferred layer as a function of radius of curvature of the initial bending.
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78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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