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22 Jun 2009

Volume 94, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 251101 (2009); http://dx.doi.org/10.1063/1.3153276 (3 pages)

Changling Yan, Qi Jie Wang, Laurent Diehl, Martina Hentschel, Jan Wiersig, Nanfang Yu, Christian Pflügl, Federico Capasso, Mikhail A. Belkin, Tadataka Edamura, Masamichi Yamanishi, and Hirofumi Kan
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Optical properties of GaSb-based type II quantum wells as the active region of midinfrared interband cascade lasers for gas sensing applications

M. Motyka, G. Sęk, K. Ryczko, J. Misiewicz, T. Lehnhardt, S. Höfling, and A. Forchel

Appl. Phys. Lett. 94, 251901 (2009); http://dx.doi.org/10.1063/1.3157910 (3 pages) | Cited 6 times

Online Publication Date: 22 June 2009

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Photoreflectance and photoluminescence, supported by the energy level calculations in the eight-band k⋅p model including strain, have been used to study the optical properties of GaSb/AlSb/InAs/InGaSb/AlSb/GaSb type II quantum wells (QWs). The broad emission wavelength tunability in the midinfrared range has been demonstrated by the control of InAs layer thickness. The temperature dependent measurements have shown that the emission can still be efficient at room temperature in such structures, and that the temperature shift of the fundamental type II optical transition between 10 and 300 K can be significantly smaller than for type I QW systems.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.-m Methods of electronic structure calculations
73.21.Fg Quantum wells

Basins of attraction of tapping mode atomic force microscopy with capillary force interactions

Nastaran Hashemi and Reza Montazami

Appl. Phys. Lett. 94, 251902 (2009); http://dx.doi.org/10.1063/1.3148672 (3 pages)

Online Publication Date: 22 June 2009

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We perform a large number of simulations over a wide range of system parameters to approximate the basins of attraction of steady oscillating solutions. We find that the basins of attraction vary as a function of system parameters and initial conditions. For large equilibrium separations, the basin of attraction is dominated by the low-amplitude solution. The location of the fixed point is shifted toward the higher values of instantaneous displacement and velocity for larger equilibrium separations. We show that the basin of attraction in the neighborhood of the fixed point is dominated by low-amplitude solutions as relative humidity is increased.
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07.79.Lh Atomic force microscopes

Inversion in the temperature coefficient of the optical path length close to the glass transition temperature in tellurite glasses

S. M. Lima, L. H. C. Andrade, E. A. Falcão, A. Steimacher, N. G. C. Astrath, A. N. Medina, M. L. Baesso, R. C. Oliveira, J. C. S. Moraes, K. Yukimitu, and E. B. Araújo

Appl. Phys. Lett. 94, 251903 (2009); http://dx.doi.org/10.1063/1.3155210 (3 pages)

Online Publication Date: 22 June 2009

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In this study, thermal lens spectrometry was applied to determine the thermo-optical properties of fragile tellurite glasses as a function of temperature, close to the glass transition region. The results showed an inversion from positive to negative values in the temperature coefficient of the optical path length occurring after the glass transition temperature, which is the region where structural changes from the TeO4 trigonal bipyramidal unit to a TeO3 trigonal pyramid containing nonbridging oxygen take place. In addition, the thermal diffusivity values as a function of temperature exhibited behaviors that were related to thermodynamic and kinetic structural changes in the glass.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
66.30.Xj Thermal diffusivity
61.43.Fs Glasses
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
66.70.Hk Glasses and polymers

Mechanical properties of superhard BC5

P. Lazar and R. Podloucky

Appl. Phys. Lett. 94, 251904 (2009); http://dx.doi.org/10.1063/1.3159627 (3 pages) | Cited 3 times

Online Publication Date: 23 June 2009

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We apply density functional theory concept to investigate mechanical properties of the diamondlike compound BC5. The cell volume and the bulk modulus are in very good agreement with the experiment, confirming the claimed crystal structure of BC5. The cleavage properties revealed a very strong cohesion between B–C bonded planes, which is comparable to C–C bonded planes. The lowest cleavage stress, which can be related to hardness, is 83 GPa. The critical shear stresses are 83 and 108 GPa, respectively, for B–C and C–C planes. This difference of critical stresses corresponds well to the difference in Vickers hardness between BC5 and diamond.
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62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.66.Fn Inorganic compounds
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture

Structure of liquid phase change material AgInSbTe from density functional/molecular dynamics simulations

J. Akola and R. O. Jones

Appl. Phys. Lett. 94, 251905 (2009); http://dx.doi.org/10.1063/1.3157166 (3 pages) | Cited 3 times

Online Publication Date: 23 June 2009

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The liquid phase of the AgInSbTe phase change material Ag3.5In3.8Sb75.0Te17.7 has been studied using molecular dynamics/density functional simulations. The calculated structure factor and total pair distribution function agree very well with high-energy x-ray diffraction measurements. We find that: (a) there are signs of medium-range order, (b) Ag and In prefer to be near Te rather than Sb atoms, and promote octahedral coordination in association with Te, (c) Ag is the most mobile element, has the shortest bonds (2.8–2.9 Å) and the highest coordination (5.5), and is anionic with the largest effective charge, and (d) there are few cavities (4% of volume).
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61.20.Ja Computer simulation of liquid structure

Method to measure the viscosity of nanometer liquid films from the surface fluctuations

Zhaohui Yang, Chi-Hang Lam, Elaine DiMasi, Nathalie Bouet, Jean Jordan-Sweet, and Ophelia K. C. Tsui

Appl. Phys. Lett. 94, 251906 (2009); http://dx.doi.org/10.1063/1.3158956 (3 pages) | Cited 5 times

Online Publication Date: 23 June 2009

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We describe a method to measure the viscosity of polystyrene liquid films with thicknesses ∼ 5 and ∼ 80 nm spin-cast on oxide-coated silicon. In this method, temporal evolution of the film surface is monitored and modeled according to the dynamics of the surface capillary waves. Viscosities obtained from the ∼ 80 nm films display an excellent agreement with those of the bulk polymer, but those from the ∼ 5 nm films are up to 106 times reduced. By modeling the data to the Vogel–Fulcher–Tammann relation, we find that the observations are consistent with the thickness dependence of the glass transition temperature previously reported of these films.
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66.20.-d Viscosity of liquids; diffusive momentum transport
68.15.+e Liquid thin films
64.70.pm Liquids

Symmetry-breaking-induced enhancement of visible light absorption in delafossite alloys

Muhammad N. Huda, Yanfa Yan, Aron Walsh, Su-Huai Wei, and Mowafak M. Al-Jassim

Appl. Phys. Lett. 94, 251907 (2009); http://dx.doi.org/10.1063/1.3157840 (3 pages) | Cited 5 times

Online Publication Date: 24 June 2009

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Through density functional theory calculations, we demonstrate that enhancement of optical absorption and optimization of the fundamental band gap for Cu delafossites can be achieved through alloying group IIIA and IIIB delafossites. These alloys significantly improved the flexibility in designing delafossite-based photoelectrodes for application in photoelectrochemical decomposition of water by visible spectra of solar light.
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78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Grain boundary wetting and prewetting in Ni-doped Mo

Xiaomeng Shi and Jian Luo

Appl. Phys. Lett. 94, 251908 (2009); http://dx.doi.org/10.1063/1.3155443 (3 pages) | Cited 9 times

Online Publication Date: 24 June 2009

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Grain boundary (GB) wetting and prewetting in Ni-doped Mo are systematically evaluated via characterizing well-quenched specimens and thermodynamic modeling. In contrast to prior reports, the δ-NiMo phase does not wet Mo GBs in the solid state. In the solid-liquid two-phase region, the Ni-rich liquid apparently wets Mo GBs completely. Furthermore, high-resolution transmission electron microscopy demonstrates that nanometer-thick quasiliquid films persist at GBs into the single-phase region where the bulk liquid phase is no longer stable. This is interpreted as a case of GB prewetting. An analytical thermodynamic model is developed and validated; this model can be applied to other alloys.
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68.08.Bc Wetting
61.72.Mm Grain and twin boundaries

Effects of nitrogen incorporation on the interfacial layer between thermally grown dielectric films and SiC

S. A. Corrêa, C. Radtke, G. V. Soares, L. Miotti, I. J. R. Baumvol, S. Dimitrijev, J. Han, L. Hold, F. Kong, and F. C. Stedile

Appl. Phys. Lett. 94, 251909 (2009); http://dx.doi.org/10.1063/1.3159812 (3 pages) | Cited 9 times

Online Publication Date: 26 June 2009

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C-containing interlayers formed between the SiC substrate and dielectric films thermally grown in O2, NO, and in O2 followed by annealing in NO were investigated. X-ray reflectometry and x-ray photoelectron spectroscopy were used to determine N and C incorporation in dielectric films and interlayers, as well to determine their mass densities and thicknesses. The thickest C-containing interlayer was observed for films thermally grown in O2, whereas the thinnest one was observed for films directly grown in NO, evidencing that the presence of N decreases the amount of carbonaceous compounds in the dielectric/SiC interface region.
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77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.up Other materials

Melting and crystallization of nanocrystalline silicon microwires through rapid self-heating

G. Bakan, A. Cywar, H. Silva, and A. Gokirmak

Appl. Phys. Lett. 94, 251910 (2009); http://dx.doi.org/10.1063/1.3159877 (3 pages) | Cited 8 times

Online Publication Date: 26 June 2009

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Nanocrystalline silicon microwires are self-heated through single, large amplitude, and microsecond voltage pulses. Scanning electron micrographs show very smooth wire surfaces after the voltage pulse compared to as-fabricated nanocrystalline texture. Voltage-pulse induced self-heating leads to significant conductance improvement, suggesting crystallization of the wires. The minimum resistivity during the pulse is extracted from wires of different dimensions as 75.0±4.6 μΩ cm, matching previously reported values for liquid silicon. Hence, nanocrystalline silicon microwires melt through self-heating during the voltage pulse and resolidify upon termination of the pulse, resulting in very smooth and less-resistive crystalline structures.
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64.70.dj Melting of specific substances
73.63.Bd Nanocrystalline materials
64.70.dg Crystallization of specific substances

Stripe domain structure in epitaxial (001) BiFeO3 thin films on orthorhombic TbScO3 substrate

C. M. Folkman, S. H. Baek, H. W. Jang, C. B. Eom, C. T. Nelson, X. Q. Pan, Y. L. Li, L. Q. Chen, A. Kumar, V. Gopalan, and S. K. Streiffer

Appl. Phys. Lett. 94, 251911 (2009); http://dx.doi.org/10.1063/1.3152009 (3 pages) | Cited 13 times

Online Publication Date: 26 June 2009

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We have analyzed the ferroelastic and ferroelectric domain structure of high crystalline quality (001) BiFeO3 films on orthorhombic (110) TbScO3 substrates. Two domains were present in stripes separated by (010) vertical boundaries, with spontaneous polarizations in adjacent domains rotated by 109°. The striped morphology was caused by nucleation of only two ferroelastic domains on the low symmetry GdFeO3-type substrate. Domain engineering through substrate symmetry is an important finding for rhombohedral ferroelectric epitaxial thin films. The stripe pattern with vertical walls may be useful for extracting domain wall contributions to magnetism and electrical transport properties of BiFeO3 materials.
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77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.22.Ej Polarization and depolarization
72.80.Sk Insulators

Nanorod epitaxial lateral overgrowth of a-plane GaN with low dislocation density

Shih-Chun Ling, Chu-Li Chao, Jun-Rong Chen, Po-Chun Liu, Tsung-Shine Ko, Tien-Chang Lu, Hao-Chung Kuo, Shing-Chung Wang, Shun-Jen Cheng, and Jenq-Dar Tsay

Appl. Phys. Lett. 94, 251912 (2009); http://dx.doi.org/10.1063/1.3158954 (3 pages) | Cited 2 times

Online Publication Date: 26 June 2009

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The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template. The investigation of x-ray diffraction showed that the strain in a-plane GaN grown on r-plane sapphire could be mitigated. The average threading dislocation density estimated by transmission electron microscopy was reduced from 3×1010 to 3.5×108 cm−2. From the temperature-dependent photoluminescence, the quantum efficiency of the a-plane GaN was enhanced by the nanorod epitaxial lateral overgrowth (NRELOG). These results demonstrated the opportunity of achieving a-plane GaN films with low dislocation density and high crystal quality via NRELOG.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.55.ag Semiconductors

On the dynamical stability and metallic behavior of YH3 under pressure

J. S. de Almeida, D. Y. Kim, C. Ortiz, M. Klintenberg, and R. Ahuja

Appl. Phys. Lett. 94, 251913 (2009); http://dx.doi.org/10.1063/1.3155505 (3 pages) | Cited 3 times

Online Publication Date: 26 June 2009

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We report on the behavior of structural and electronic properties of yttrium trihydride under pressure using first principles calculations. We show that YH3 undergoes a structural transformation and its high pressure phase is dynamically stable under pressure since the peak at the imaginary frequencies of the phonon density of states, which account for the structural instability disappears at high pressure. Additionally, our GW calculations indicate a metallization of the high pressure cubic phase of YH3.
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71.20.Ps Other inorganic compounds
71.15.-m Methods of electronic structure calculations
62.50.-p High-pressure effects in solids and liquids
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.70.K- Solid-solid transitions
63.20.dk First-principles theory
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