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18 Aug 2008

Volume 93, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages)

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith
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Three-dimensional atom probe investigation of boron distribution in CoFeB/MgO/CoFeB magnetic tunnel junctions

S. Pinitsoontorn, A. Cerezo, A. K. Petford-Long, D. Mauri, L. Folks, and M. J. Carey

Appl. Phys. Lett. 93, 071901 (2008); http://dx.doi.org/10.1063/1.2973045 (3 pages) | Cited 19 times

Online Publication Date: 18 August 2008

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Significant lateral compositional variations have been revealed in a three-dimensional atom probe (3DAP) study of the MgO barriers of magnetic tunnel junctions. High resolution electron microscopy of the CoFeB/MgO/CoFeB/Ru/CoFe/PtMn multilayer indicates that the MgO barrier is smooth, uniform, and with good crystallinity. Nevertheless, the 3DAP data show lateral variations in the MgO composition over length scales on the order of tens of nanometers. Boron is not uniformly distributed within the CoFeB layers, but has tended to segregate to the interfaces. Annealing has no significant effect on the distribution of B, indicating that the segregation occurring during growth is relatively stable.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
75.47.Pq Other materials
81.40.Gh Other heat and thermomechanical treatments
64.75.-g Phase equilibria

Thermophysical properties of Si, Ge, and Si–Ge alloy melts measured under microgravity

S. M. Chathoth, B. Damaschke, K. Samwer, and S. Schneider

Appl. Phys. Lett. 93, 071902 (2008); http://dx.doi.org/10.1063/1.2973047 (3 pages) | Cited 8 times

Online Publication Date: 18 August 2008

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We have investigated density, thermal expansion, and surface tension of Si, Ge, and Si–Ge alloys in the melt and undercooled state under microgravity conditions. The experiments were conducted in the TEMPUS facility on board a Zero-G aircraft. The density of the liquid alloys as a function of composition show a nonideal behavior. Thermal expansion coefficients were found to be in the order of 10−4 K−1 and was highest for Si75Ge25 melt. The surface tension is lowered with the addition of 25 at. % Si in Ge. The further addition of Si increases the surface tension almost linearly with composition.
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81.10.Mx Growth in microgravity environments
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
68.03.Cd Surface tension and related phenomena

Resonance effects in broadband acoustic cloak with multilayered homogeneous isotropic materials

Y. Cheng and X. J. Liu

Appl. Phys. Lett. 93, 071903 (2008); http://dx.doi.org/10.1063/1.2974811 (3 pages) | Cited 4 times

Online Publication Date: 20 August 2008

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The frequency response of the multilayered acoustic cloak made of isotropic materials is analyzed by the acoustic scattering theory. When concealing a rigid cylinder, the acoustic total scattering cross section (TSCS) monotonically increases with frequency. If concealing penetrable materials, the cloak-induced reverse-phase monopole and dipole resonances can increase the TSCS around the resonant frequencies, while the in-phase monopole resonance decreases the TSCS. The results are confirmed by numerical simulations of the finite element method.
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43.25.Gf Standing waves; resonance
43.20.Fn Scattering of acoustic waves
02.70.Dh Finite-element and Galerkin methods

Spatially resolved strain measurements in Mo-alloy micropillars by differential aperture x-ray microscopy

H. Bei, R. I. Barabash, G. E. Ice, W. Liu, J. Tischler, and E. P. George

Appl. Phys. Lett. 93, 071904 (2008); http://dx.doi.org/10.1063/1.2975371 (3 pages) | Cited 12 times

Online Publication Date: 22 August 2008

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Spatially resolved strain distributions in the NiAl matrix and the ∼ 550–1000 nm Mo fibers of a NiAl–Mo eutectic were investigated by microbeam x-ray diffraction. Position sensitive d-spacings for the individual phases were obtained from spatially resolved and energy-resolved Laue patterns. For embedded Mo fibers, the measured elastic strain is consistent with the predicted thermal mismatch strain between the NiAl and Mo phases. However, when the NiAl matrix is etched back to expose Mo micropillars, the d-spacing increases to that of unconstrained Mo, indicating release of the compressive residual strain in the Mo fibers.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.37.Yz X-ray microscopy

Properties of dilute InAsN layers grown by liquid phase epitaxy

S. Dhar, T. D. Das, M. de la Mare, and A. Krier

Appl. Phys. Lett. 93, 071905 (2008); http://dx.doi.org/10.1063/1.2975166 (3 pages) | Cited 10 times

Online Publication Date: 22 August 2008

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We report on the liquid phase epitaxial growth of InAsN from indium rich solution. The spectral properties of dilute bulk alloys containing N ∼ 0.5% and which exhibit photoluminescence in the midinfrared spectral range without any postgrowth annealing are described. The blueshift in the emission spectrum is attributed to a combination of tensile strain and band filling effects.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.55.Hx Other solid inorganic materials
78.30.Er Solid metals and alloys

Direct evidence for abrupt postcrystallization germanium precipitation in thin phase-change films of Sb–15 at. % Ge

C. Cabral, Jr., L. Krusin-Elbaum, J. Bruley, S. Raoux, V. Deline, A. Madan, and T. Pinto

Appl. Phys. Lett. 93, 071906 (2008); http://dx.doi.org/10.1063/1.2970106 (3 pages) | Cited 22 times

Online Publication Date: 22 August 2008

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We present evidence for the instability in the crystalline (metallic) state of binary Te-free phase-change Ge–Sb thin films considered for integration into nonvolatile nanosized memory cells. We find that while the amorphous (semiconducting) phase of eutectic Sb–15 at. % Ge is very robust until Sb crystallization at 240 °C, at about 350 °C, germanium rapidly precipitates out. Ge precipitation, visualized directly with transmission electron microscopy, is exothermic and is found to affect the films’ reflectivity, resistance, and stress. It converts melting into a two-step process, which may seriously impact the switching reliability of a device.
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81.30.Mh Solid-phase precipitation
84.30.Sk Pulse and digital circuits
72.60.+g Mixed conductivity and conductivity transitions

Selective disordering of InAs/InGaAs dots-in-a-well structure patterned with sol-gel derived SiO2 strips imprinted by soft mold technique

C. K. Chia, M. Suryana, W. Zhao, H. Y. Low, and M. Hopkinson

Appl. Phys. Lett. 93, 071907 (2008); http://dx.doi.org/10.1063/1.2973164 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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Selective impurity free vacancy disordering of InAs/InGaAs quantum dot (QD) structures imprinted with sol-gel derived SiO2 strips via a polyethylene terepthalate soft mold has been investigated. Wavelength blueshift of up to 220 nm for areas capped with the sol-gel derived SiO2 is demonstrated. The imprinted SiO2 strips were used as hard mask for plasma etching of GaAs ridge waveguide structures and were found to have similar hardness as the SiO2 prepared by plasma-enhanced chemical vapor deposition. QD intermixing using sol-gel derived SiO2 with step-thickness profile was demonstrated, and a one-step SiO2 imprinting technique for multiple band gap QD intermixing is proposed.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Blue and red electroluminescence of Europium-implanted metal-oxide-semiconductor structures as a probe for the dynamics of microstructure

L. Rebohle, J. Lehmann, S. Prucnal, A. Kanjilal, A. Nazarov, I. Tyagulskii, W. Skorupa, and M. Helm

Appl. Phys. Lett. 93, 071908 (2008); http://dx.doi.org/10.1063/1.2964176 (3 pages) | Cited 13 times

Online Publication Date: 22 August 2008

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The strong blue and red electroluminescence from Eu-implanted SiO2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low annealing temperatures, and short annealing times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium or Europium oxide clusters with increasing annealing temperatures and annealing times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted SiO2 layers can serve as a probe for the microstructural development in the active layer of the light emitter.
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78.60.Fi Electroluminescence
68.37.Og High-resolution transmission electron microscopy (HRTEM)
61.72.Cc Kinetics of defect formation and annealing

Complete thin film mechanical characterization using picosecond ultrasonics and nanostructured transducers: experimental demonstration on SiO2

P. A. Mante, J. F. Robillard, and A. Devos

Appl. Phys. Lett. 93, 071909 (2008); http://dx.doi.org/10.1063/1.2975171 (3 pages) | Cited 7 times

Online Publication Date: 22 August 2008

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Complete mechanical measurements are performed in submicron films using the picosecond ultrasonic technique. The Al layer deposited on the top of the sample acting as a transducer is replaced with a nanostructured Al film. Using an usual picosecond ultrasonic setup we can excite and detect high-frequency longitudinal and surface acoustic waves. From this we can deduce Young’s modulus and Poisson’s ratio of any isotropic thin film. Experimental results obtained for a thin silica layer on silicon are in very good agreement with literature.
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68.60.Bs Mechanical and acoustical properties
62.20.dj Poisson's ratio
81.40.Jj Elasticity and anelasticity, stress-strain relations

Negative refraction at the pure Ag/air interface observed in the visible Drude region

Yun-Hua Wu, Wen Gu, Yue-Rui Chen, Zhong-Hong Dai, Wei-Xi Zhou, Yu-Xiang Zheng, and Liang-Yao Chen

Appl. Phys. Lett. 93, 071910 (2008); http://dx.doi.org/10.1063/1.2975155 (3 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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Pure negative refraction was found for a series of prismlike Ag film samples measured in the visible Drude region. Results show that the pseudonegative refraction index nm changes with the photon energy and has a spectral trend to be less negative with the increasing energy. Light refraction will be expected to be positive in the higher energy region where the interband transitions dominate the interaction between the electrons and photons in Ag.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys
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