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10 Dec 2007

Volume 91, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 241101 (2007); http://dx.doi.org/10.1063/1.2821382 (3 pages)

S. N. Goda, S. Sensarn, M. Y. Shverdin, and G. Y. Yin
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Metal induced hydrogen effusion from amorphous silicon

Hiromasa Ohmi, Kiyoshi Yasutake, Yoshinori Hamaoka, and Hiroaki Kakiuchi

Appl. Phys. Lett. 91, 241901 (2007); http://dx.doi.org/10.1063/1.2819086 (3 pages)

Online Publication Date: 10 December 2007

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Hydrogen effusion from hydrogenated amorphous silicon (a-Si:H) films, induced by various metal layers (Al, Ni, Cu, Ge, Cr, Au, Ag, Fe, and Sn), has been studied by temperature programed desorption spectroscopy. Significant reduction of the effusion temperature is observed in the presence of Cr, Ni, or Al on the a-Si:H film. Al has the strongest catalytic effect on hydrogen effusion from a-Si:H; H2 effusion is intensive, even at a temperature of 150 °C, when the Al layer thickness is larger than 40 nm. The strong catalytic effect of Al is considered to be related to the large diffusion constant of Al in a-Si:H.
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68.43.Vx Thermal desorption
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Study of stress in a shallow-trench-isolated Si structure using polarized confocal near-UV Raman microscopy of its cross section

Vladimir Poborchii, Tetsuya Tada, and Toshihiko Kanayama

Appl. Phys. Lett. 91, 241902 (2007); http://dx.doi.org/10.1063/1.2825286 (3 pages) | Cited 16 times

Online Publication Date: 10 December 2007

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Stress in shallow-trench-isolated structures with 250-nm-wide Si stripes was examined by 364 nm excitation confocal Raman microscopy. Using objective lenses with the experimentally measured ∼ 150 nm spatial resolution, we studied polarized Raman spectra from the section perpendicular to the stripes. Detection of two optical phonons enabled us to analyze orientation and intensity of local stress quantitatively. Uniaxial [001] compressive stress was found in the Si substrate under both the trench and the stripe, while the stress in the stripe was uniaxial [110] perpendicular to the stripe.
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68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Identification of a Ni0.5(Al0.5−xMnx) B2 phase at the heterophase interfaces of Cu-rich precipitates in an α-Fe matrix

R. Prakash Kolli, Zugang Mao, David N. Seidman, and Denis T. Keane

Appl. Phys. Lett. 91, 241903 (2007); http://dx.doi.org/10.1063/1.2820378 (3 pages) | Cited 9 times

Online Publication Date: 11 December 2007

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A phase with the stoichiometry Ni0.5(Al0.5−xMnx) is observed at heterophase interfaces of Cu-rich precipitates in an α-Fe matrix, utilizing atom-probe tomography. First-principles calculations are utilized to determine the substitutional energies, yielding EMn→Ni = 0.916 eV atom−1 and EMn→Al = −0.016 eV atom−1 indicating that the manganese atoms prefer substituting at Al sublattice sites instead of Ni sites. A synchrotron radiation experiment demonstrates that the identified phase possesses the B2 structure.
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68.35.Dv Composition, segregation; defects and impurities
61.66.Bi Elemental solids
61.66.Dk Alloys

Mechanical properties and tuning of three-dimensional polymeric photonic crystals

Saulius Juodkazis, Vygantas Mizeikis, Kock Khuen Seet, Hiroaki Misawa, and Ulrike G. K. Wegst

Appl. Phys. Lett. 91, 241904 (2007); http://dx.doi.org/10.1063/1.2822825 (3 pages) | Cited 9 times

Online Publication Date: 11 December 2007

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Mechanical properties of photopolymerized photonic crystal (PhC) structures having woodpile and spiral three-dimensional architectures were examined using flat-punch indentation. The structures were found to exhibit a foamlike response with a bend-dominated elastic deformation regime observed at strain levels up to 10%. Numerical simulations of optical properties of these PhC structures demonstrate the possibility of achieving a substantial and reversible spectral tuning of the photonic stop gap wavelength by applying a mechanical load to the PhC.
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42.70.Qs Photonic bandgap materials
61.41.+e Polymers, elastomers, and plastics
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
42.70.Jk Polymers and organics
81.40.Jj Elasticity and anelasticity, stress-strain relations

Suppression of the shear band instability during plastic flow of nanometer-scale confined metallic glasses

A. Donohue, F. Spaepen, R. G. Hoagland, and A. Misra

Appl. Phys. Lett. 91, 241905 (2007); http://dx.doi.org/10.1063/1.2821227 (3 pages) | Cited 46 times

Online Publication Date: 11 December 2007

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The shear band instability that occurs during plastic deformation of metallic glasses limits the application of these high-strength materials. We show that this instability can be suppressed in nanometer-scale metallic glasses constrained by ultrafine crystalline layers. Free-standing Cu/amorphous Pd0.77Si0.23 multilayers consisting either of 10/90 nm glass/Cu or 100/100 nm glass/Cu were deformed to layer thickness reductions greater than 75% by cold rolling or bending, respectively. Transmission electron microscopy showed uniform reduction in the layer thickness with no shear band formation in the amorphous layers. The mechanisms that allow homogeneous codeformation of metallic glasses with nanoscale crystalline layers at high stresses are discussed.
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81.40.Lm Deformation, plasticity, and creep
61.43.Fs Glasses
68.65.Ac Multilayers
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Influences of nonlinearities of loudspeakers on performances of thermoacoustic refrigerators

Li Fan, Shu-yi Zhang, Kai Zheng, and Hui Zhang

Appl. Phys. Lett. 91, 241906 (2007); http://dx.doi.org/10.1063/1.2813616 (3 pages) | Cited 3 times

Online Publication Date: 12 December 2007

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A nonlinear model of an electrodynamic loudspeaker is used to study the influences of the loudspeaker’s nonlinearities on the performances of thermoacoustic refrigerators. The results demonstrate that the nonlinearities of the magnetic field and vibration component of a loudspeaker change the acoustic output power and electroacoustic transfer efficiency. Additionally, the nonlinearity of the vibration component shifts the resonance frequency of the thermoacoustic refrigerator, which induces deviation of the load resistance of the loudspeaker at the resonance frequency. Therefore, the loudspeaker’s nonlinearities influence the acoustic coupling between the loudspeaker and resonance pipe, and also the performances of thermoacoustic refrigerators.
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43.38.Ja Loudspeakers and horns, practical sound sources
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Raman imaging of doping domains in graphene on SiO2

C. Stampfer, F. Molitor, D. Graf, K. Ensslin, A. Jungen, C. Hierold, and L. Wirtz

Appl. Phys. Lett. 91, 241907 (2007); http://dx.doi.org/10.1063/1.2816262 (3 pages) | Cited 38 times

Online Publication Date: 12 December 2007

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We present spatially resolved Raman images of the G and 2D lines of single-layer graphene flakes. The spatial fluctuations of G and 2D lines are correlated and are thus shown to be affiliated with local doping domains. We investigate the position of the 2D line—the most significant Raman peak to identify single-layer graphene—as a function of charging up to ∣n∣ ≈ 4×1012 cm−2. Contrary to the G line which exhibits a strong and symmetric stiffening with respect to electron and hole doping, the 2D line shows a weak and slightly asymmetric stiffening for low doping. Additionally, the linewidth of the 2D line is, in contrast to the G line, doping independent making this quantity a reliable measure for identifying single-layer graphene.
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78.66.Sq Composite materials
78.30.Hv Other nonmetallic inorganics
81.05.U- Carbon/carbon-based materials

Optical transitions in polarized CdSe, CdSe/ZnSe, and CdSe/CdS/ZnS quantum dots dispersed in various polar solvents

Ung Thi Dieu Thuy, Nguyen Quang Liem, Do Xuan Thanh, Myriam Protière, and Peter Reiss

Appl. Phys. Lett. 91, 241908 (2007); http://dx.doi.org/10.1063/1.2822399 (3 pages) | Cited 5 times

Online Publication Date: 12 December 2007

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The optical transitions in ensembles of colloidal CdSe-based quantum dots (QDs) have been systematically studied as a function of the net QDs’ polarity/polarization and of the solvent’s polarity. While the general trend observed for all QD systems dispersed in different solvents is similar, the spectral shifts are more pronounced in core QDs than in core/shell structures. Our results can be rationalized by taking account of the electric field experienced by the QDs that results from their effective polarization in solvents of different polarities (quantum confined Stark effect) as well as from the effect of the external dielectric environment (solvatochromatic effect).
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78.67.Hc Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Control of valence band states in pyramidal quantum dot-in-dot semiconductor heterostructures

V. Troncale, K. F. Karlsson, E. Pelucchi, A. Rudra, and E. Kapon

Appl. Phys. Lett. 91, 241909 (2007); http://dx.doi.org/10.1063/1.2820693 (3 pages) | Cited 4 times

Online Publication Date: 12 December 2007

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The character of the hole states in a pyramidal GaAs/AlGaAs quantum dot-in-dot (DiD) heterostructure is shown to be controllable by tailoring the confinement potential shape. The change in ground valence band state from heavy hole like to light hole like is demonstrated by side-view polarization resolved photoluminescence measurements. The experimental findings are supported by three-dimensional numerical model calculations. The results are applicable for polarization control in quantum dot photonic devices.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.La Quantum dots
81.07.Ta Quantum dots

Molecular dynamics simulation of interfacial thermal conductance between silicon and amorphous polyethylene

Ming Hu, Sergei Shenogin, and Pawel Keblinski

Appl. Phys. Lett. 91, 241910 (2007); http://dx.doi.org/10.1063/1.2824864 (3 pages) | Cited 11 times

Online Publication Date: 12 December 2007

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Using nonequilibrium molecular dynamics simulations, we study the interfacial thermal conductance between single crystal silicon and amorphous polyethylene (PE). We estimate that the silicon-PE interfacial thermal conductance is about 20 MW/m2 K at room temperature, which is equivalent to the resistance of 16 nm thick layer of bulk amorphous polyethylene. We also study the role of solid stiffness and the bonding strength across the interface on the interfacial thermal resistance. With strong interfacial bonding, our results are in agreement with the diffuse mismatch model and phonon radiation limit predictions, suggesting that in this case, heat carrying acoustic phonons in solids have transmission coefficients to polymer equal almost to unity.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
73.40.Mr Semiconductor-electrolyte contacts

Temperature stability of ZnO:Al film properties for poly-Si thin-film devices

K. Y. Lee, C. Becker, M. Muske, F. Ruske, S. Gall, B. Rech, M. Berginski, and J. Hüpkes

Appl. Phys. Lett. 91, 241911 (2007); http://dx.doi.org/10.1063/1.2824456 (3 pages) | Cited 14 times

Online Publication Date: 14 December 2007

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The crystallization of thin silicon films at temperatures between 425 and 600 °C was investigated on glass substrates coated with Al-doped zinc oxide (ZnO:Al). Bare ZnO:Al layers degrade at the crystallization temperatures used. A silicon layer on top, however, efficiently prevents deterioration. The resistivity was even found to drop from 4.3×10−4 Ω cm for the as deposited ZnO:Al to 2.2×10−4 Ω cm in the case of aluminium induced crystallization and to 3.4×10−4 Ω cm for solid phase crystallization. The temperature-stable conductivity of ZnO:Al films coated with Si opens up appealing options for the production of polycrystalline silicon thin-film solar cells with transparent front contacts.
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73.61.Ga II-VI semiconductors
84.60.Jt Photoelectric conversion
64.70.K- Solid-solid transitions

Monolithic integration of InP based heterostructures on silicon using crystalline Gd2O3 buffers

G. Saint-Girons, P. Regreny, L. Largeau, G. Patriarche, and G. Hollinger

Appl. Phys. Lett. 91, 241912 (2007); http://dx.doi.org/10.1063/1.2824466 (3 pages) | Cited 25 times

Online Publication Date: 14 December 2007

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An original approach of monolithic integration of InP based heterostructures on silicon is proposed based on the peculiar properties of the heterointerface between InP and crystalline Gd2O3. When grown on a crystalline Gd2O3/Si(111) buffer, InP takes its bulk lattice parameter as soon as the growth begins, and the lattice mismatch (7.9%) is fully accommodated by the formation of a misfit dislocation network at the InP/Gd2O3 heterointerface. This plastic compliant effect allows the monolithic growth of good quality InAsP/InP heterostructures on Si, as attested by room-temperature photoluminescence experiments.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.66.Fn Inorganic compounds
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.55.Cr III-V semiconductors

On incompressibility of a matrix in naturally occurring composites

Larissa Gorbatikh and Pawan Pingle

Appl. Phys. Lett. 91, 241913 (2007); http://dx.doi.org/10.1063/1.2824467 (3 pages)

Online Publication Date: 14 December 2007

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The work illustrates that a soft matrix, which has the Poisson ratio close to 0.5 and is reinforced with a rigid-line inclusion, possesses an interesting behavior at the inclusion/matrix interface. It experiences a hydrostatic stress state and behaves as an incompressible fluid under longitudinal and transverse loads. The stress singularities are eliminated ahead of the inclusion tips, and when interface defects are formed, their effect on the composite compliance is minimal. These observations have far reaching applications when one is interested in mechanisms of multifunctional property improvement of composites (such as toughness and stiffness) learned from naturally occurring composites.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
62.20.D- Elasticity

Surface hardness enhancement in sp3-bonded carbon doped SiC nanocomposite films

Xiaodong He, Jian Yi, Yue Sun, Ping Xiao, and Xiaofeng Zhao

Appl. Phys. Lett. 91, 241914 (2007); http://dx.doi.org/10.1063/1.2824811 (3 pages) | Cited 1 time

Online Publication Date: 14 December 2007

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The sp3-bonded carbon/SiC composite films have been produced from electron beam-physical vapor deposition of SiC materials. The hardness of such films, measured using Hysitron indentation, reaches 50 GPa, which is significantly higher than the hardness of SiC (28 GPa). It appears that the superhardness of the thin films is due to the formation of nanocrystalline SiC/diamondlike carbon composites.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Strain influence on valence-band ordering and excitons in ZnO: An ab initio study

A. Schleife, C. Rödl, F. Fuchs, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 91, 241915 (2007); http://dx.doi.org/10.1063/1.2825277 (3 pages) | Cited 21 times

Online Publication Date: 14 December 2007

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Modern parameter-free methods to treat single- and two-particle electronic excitations are applied to compute the band structure and the lowest optical transitions of wurtzite ZnO under biaxial strain. The calculations are based on density functional theory with a spatially nonlocal exchange and correlation functional and include spin-orbit interaction. Quasiparticle shifts and excitonic effects are computed. In addition to the band parameters, also their dependence on biaxial strain and the ordering of the A, B, and C excitons are investigated. While the crystal-field splitting is very sensitive to strain, the spin-orbit splittings and the exciton binding energies remain unaffected.
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71.20.Nr Semiconductor compounds
71.35.-y Excitons and related phenomena
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Tailoring magnetic and magnetocaloric properties of martensitic transitions in ferromagnetic Heusler alloys

Seda Aksoy, Thorsten Krenke, Mehmet Acet, Eberhard F. Wassermann, Xavier Moya, Lluís Mañosa, and Antoni Planes

Appl. Phys. Lett. 91, 241916 (2007); http://dx.doi.org/10.1063/1.2825283 (3 pages) | Cited 38 times

Online Publication Date: 14 December 2007

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Ni50Mn34In16 undergoes a martensitic transformation around 250 K and exhibits a field induced reverse martensitic transformation and substantial magnetocaloric effects. We substitute small amounts Ga for In, which are isoelectronic, to carry these technically important properties to close to room temperature by shifting the martensitic transformation temperature.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Effect of optical lithography patterning on the crystalline structure of tunnel junctions

C. Mocuta, A. Barbier, A. V. Ramos, M.-J. Guittet, J.-B. Moussy, S. Stanescu, R. Mattana, C. Deranlot, and F. Petroff

Appl. Phys. Lett. 91, 241917 (2007); http://dx.doi.org/10.1063/1.2824858 (3 pages) | Cited 1 time

Online Publication Date: 14 December 2007

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The crystalline structure of metal-oxide-based magnetic tunnel junctions patterned by optical lithography was resolved locally using a microfocused x-ray spot. We evidence several micron-sized lithography-induced distortion effects on the crystalline structure of the layers near the edges of the junction. The distortions translate into tilts (up to 1°) of the crystalline planes in the vicinity of the edges and propagate toward the center of the junction. They are attributed to the release of the elastic strain in the layers during the lithographical process. For the smallest junctions, size effects limiting the amplitude of the tilt are also evidenced.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Microphotoluminescence evaluation of local strain for freestanding Si membranes with SiN deposition

Dong Wang, Hiroshi Nakashima, Jun Morioka, and Tokuhide Kitamura

Appl. Phys. Lett. 91, 241918 (2007); http://dx.doi.org/10.1063/1.2825271 (3 pages) | Cited 4 times

Online Publication Date: 14 December 2007

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Microphotoluminescence (PL) was used to evaluate the local strain for freestanding Si membranes, which were fabricated by the mesa etching of Si on insulator followed by etching of the buried oxide. Compressive strain in the membranes was induced by SiN deposition using low-pressure chemical vapor deposition. Strain-induced band gap narrowing was directly observed by identifying the PL peak of the free exciton band-band transition in membranes, from which the strain ratio was estimated for each sample. Strain was reasonably dependent on the sample parameters, which implies that this measurement gives valid results.
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68.60.Bs Mechanical and acoustical properties
78.66.-w Optical properties of specific thin films
78.55.-m Photoluminescence, properties and materials
73.20.At Surface states, band structure, electron density of states
71.35.-y Excitons and related phenomena
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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