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24 Sep 2007

Volume 91, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 91, 132501 (2007); http://dx.doi.org/10.1063/1.2786856 (3 pages)

V. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, and V. Metlushko
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Two-glassy-phase bulk metallic glass with remarkable plasticity

X. H. Du, J. C. Huang, K. C. Hsieh, Y. H. Lai, H. M. Chen, J. S. C. Jang, and P. K. Liaw

Appl. Phys. Lett. 91, 131901 (2007); http://dx.doi.org/10.1063/1.2790380 (3 pages) | Cited 41 times

Online Publication Date: 25 September 2007

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Using the computational-thermodynamic approach, the potential compositions of Zr–Cu–Ni–Al alloy system exhibiting the two-liquid miscibility phase equilibrium in the liquid temperature region have been identified. The resulting Zr base bulk metallic glasses show a microstructure of two microscaled glassy phases. The glass possesses a remarkable macroscopic plastic strain of 30% at room temperature. The gain of mechanical properties is attributed to the unique glassy structure correlated with the chemical inhomogeneity on the micron scale, the hard phases surrounded by the soft phases, leading extensive shear-band formation, interactions, and multiplication.
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61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.75.-g Phase equilibria
81.30.Bx Phase diagrams of metals, alloys, and oxides
61.72.-y Defects and impurities in crystals; microstructure

Improvement of laser molecular beam epitaxy grown SrTiO3 thin film properties by temperature gradient modulation growth

Jin Long Li, J. H. Hao, and Y. R. Li

Appl. Phys. Lett. 91, 131902 (2007); http://dx.doi.org/10.1063/1.2790074 (3 pages) | Cited 2 times

Online Publication Date: 25 September 2007

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Oxygen diffusion at the SrTiO3/Si interface was analyzed. A method called temperature gradient modulation growth was introduced to control oxygen diffusion at the interface of SrTiO3/Si. Nanoscale multilayers were grown at different temperatures at the initial growing stage of films. Continuous growth of SrTiO3 films was followed to deposit on the grown sacrificial layers. The interface and crystallinity of SrTiO3/Si were investigated by in situ reflection high energy electron diffraction and x-ray diffraction measurements. It has been shown that the modulated multilayers may help suppress the interfacial diffusion, and therefore improve SrTiO3 thin film properties.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.62.-b Laser applications
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation

Two coexisting mechanisms of dislocation reduction in an AlGaN layer grown using a thin GaN interlayer

J. Bai, T. Wang, P. J. Parbrook, Q. Wang, K. B. Lee, and A. G. Cullis

Appl. Phys. Lett. 91, 131903 (2007); http://dx.doi.org/10.1063/1.2790813 (3 pages) | Cited 10 times

Online Publication Date: 26 September 2007

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A significant dislocation reduction is achieved in an AlGaN layer grown on an AlN buffer by introducing a thin GaN interlayer. The mechanisms for the dislocation reduction are explored by transmission electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, and micro-Raman spectroscopy. The GaN interlayer grown on the AlN takes the form of platelets. The mechanisms of dislocation reduction in the platelet area and the area between the platelets are different. In the GaN platelets, due to the large misfit strain, the threading dislocations (TDs) in the AlN layer migrate into the interface and annihilate with each other. However, the GaN between the platelets is highly strained so that a higher density of TDs from AlN is incorporated into the upper layer. The coalescing of the platelets induced by the AlGaN growth makes the TDs in the areas between the platelets assemble and annihilate, resulting in additional dislocation reduction.
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68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Field-driven structural phase transition and sign-switching magnetocaloric effect in Ni–Mn–Sn

M. Pasquale, C. P. Sasso, L. Giudici, T. Lograsso, and D. Schlagel

Appl. Phys. Lett. 91, 131904 (2007); http://dx.doi.org/10.1063/1.2790829 (3 pages) | Cited 8 times

Online Publication Date: 26 September 2007

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Depending on the starting equilibrium temperature, the application of a magnetic field on a sample of Ni–Mn–Sn produces sample heating or cooling during adiabatic experiments. The competition between endothermal and exothermal effects is observed close to the martensite-to-austenite magnetostructural phase transition. A model assuming the coexistence of two phases and a field dependence of their volume allows to compute the evolution of entropy and heat capacity during the phase transition. The correct fitting of the results suggests that the field-induced reduction of the martensite-to-austenite transition temperature is responsible for the observed sign switching of the magnetocaloric effect.
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64.70.K- Solid-solid transitions
65.40.G- Other thermodynamical quantities
75.30.Sg Magnetocaloric effect, magnetic cooling
81.30.Kf Martensitic transformations

Air flow through carbon nanotube arrays

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

Appl. Phys. Lett. 91, 131905 (2007); http://dx.doi.org/10.1063/1.2793174 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2007

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Using molecular dynamics simulations, we studied the air flow through carbon nanotube arrays. We found that for 1.4 nm diameter tubes separated by 25 nm, the air flow can be well described by the free molecular flow theory. We estimate that for such array, the pressure gradient is about 0.1 atm/μm at 1 atm air pressure and 5 m/s flow velocity, indicating that the flowing air can only pass through an array of no more than about 400 carbon nanotubes in series. Our findings provide design rules for arrays of nanotubes for thermal energy exchange with air.
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47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.te Turbulent convective heat transfer
47.85.-g Applied fluid mechanics
47.11.Mn Molecular dynamics methods

Direct synthesis of sp-bonded carbon chains on graphite surface by femtosecond laser irradiation

A. Hu, M. Rybachuk, Q.-B. Lu, and W. W. Duley

Appl. Phys. Lett. 91, 131906 (2007); http://dx.doi.org/10.1063/1.2793628 (3 pages) | Cited 19 times

Online Publication Date: 27 September 2007

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Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct “writing” of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications.
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64.70.K- Solid-solid transitions
78.30.-j Infrared and Raman spectra
79.60.Jv Interfaces; heterostructures; nanostructures
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Deformation-induced rotational eutectic colonies containing length-scale heterogeneity in an ultrafine eutectic Fe83Ti7Zr6B4 alloy

Jin Man Park, Do Hyang Kim, Ki Buem Kim, and Won Tae Kim

Appl. Phys. Lett. 91, 131907 (2007); http://dx.doi.org/10.1063/1.2793189 (3 pages) | Cited 40 times

Online Publication Date: 27 September 2007

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Microstructural investigations of an ultrafine eutectic Fe83Ti7Zr6B4 alloy reveal that spherical eutectic colonies are composed of nanoeutectic areas which are encapsulated by submicron eutectic areas indicating length-scale heterogeneity of lamellar structure. Furthermore, formation of the wavy and discontinuous shear bands indicative of dissipation of the shear stress are possibly caused by a rotation of the eutectic colonies along the submicron eutectic areas during deformation, leading to developing typical dimples on the fracture surface. The rotation of the eutectic colonies containing the length-scale heterogeneity is proposed to be responsible for macroscopic plasticity of the ultrafine eutectic Fe83Ti7Zr6B4 alloy.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Characterization of Si nanostructures using a noncontact mode scanning near-field optical Raman microscope, with 100 nm spatial resolution and 5 nm depth resolution, using ultraviolet resonant Raman scattering

M. Yoshikawa, M. Murakami, and H. Ishida

Appl. Phys. Lett. 91, 131908 (2007); http://dx.doi.org/10.1063/1.2780114 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2007

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The authors developed a noncontact mode scanning near-field Raman microscope (NC-SNORM) with a hollow pyramidal probe, using ultraviolet resonant Raman scattering, measured the stress distribution in very-large-scale integration standards made of silicon dioxide (SiO2) film and Si, and characterized Si nanodot structures. The authors found that the areas covered by SiO2 are under tensile stress and the areas not covered by SiO2 are under compressive stress. Compressive stress concentrates on the interface, about 100 nm wide, between the covered and noncovered areas. They measured near-field Raman spectra of the Si nanodot structures and found that the Raman intensities change periodically approximately every 100 nm.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A strong micropillar containing a low angle grain boundary

R. Maaß, S. Van Petegem, D. Grolimund, H. Van Swygenhoven, and M. D. Uchic

Appl. Phys. Lett. 91, 131909 (2007); http://dx.doi.org/10.1063/1.2784938 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2007

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In situ white beam Laue diffraction experiments on focused ion beam machined single crystal 10 μm Ni pillars are performed to explore the relation between the initial and evolving microstructures and the subsequent flow response. The pillar has a flow stress that is at least in the upper bound of the scatter of the flow stresses obtained for similar Ni pillars. Detailed analysis of the Laue pattern suggests that the strength is in part due to the low angle grain boundary acting as a dislocation barrier.
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61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Epitaxial growth of AlN films on Rh ultraviolet mirrors

S. Inoue, K. Okamoto, T. Nakano, J. Ohta, and H. Fujioka

Appl. Phys. Lett. 91, 131910 (2007); http://dx.doi.org/10.1063/1.2793187 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2007

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Epitaxial growth of AlN films on mirror polished Rh(111) substrates, with high reflectivity in the ultraviolet (UV) region and high thermal conductivity, was demonstrated using a low temperature growth technique employing pulsed laser deposition. It was found that AlN(0001) grows epitaxially on Rh(111) at 450 °C with an in-plane epitaxial relationship of AlN[11math0]‖Rh[1math0] Electron backscattering diffraction observations revealed that neither 30° rotational domains nor cubic phase domains were present in the AlN. X-ray reflectivity measurements revealed that no interfacial layer was present between the AlN films and Rh substrates and that the heterointerface was atomically abrupt, indicating that the Rh substrate still functioned as an UV mirror, even after AlN growth.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
42.79.Bh Lenses, prisms and mirrors
81.15.Fg Pulsed laser ablation deposition

Concomitant speed-of-sound tomography in photoacoustic imaging

Srirang Manohar, René G. H. Willemink, Ferdi van der Heijden, Cornelis H. Slump, and Ton G. van Leeuwen

Appl. Phys. Lett. 91, 131911 (2007); http://dx.doi.org/10.1063/1.2789689 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2007

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We present a method to generate quantitative cross-sectional maps of acoustic propagation speed in tissue using the photoacoustic principle. The method is based on the interaction of laser-induced ultrasound from an extraneous absorber with the object under photoacoustic investigation. The propagation times of the ultrasound transients through the object at angles around 360° are measured using a multielement ultrasound detector. The geometry lends itself to fan-beam reconstruction allowing speed-of-sound tomograms to be generated. Simultaneously, conventional photoacoustic computed tomography can be performed as well. We demonstrate the concept showing results on phantoms carrying speed-of-sound distributions.
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87.63.D- Ultrasonography
43.80.Qf Medical diagnosis with acoustics
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
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