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28 Feb 2011

Volume 98, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 98, 093502 (2011); http://dx.doi.org/10.1063/1.3531756 (3 pages)

Marina S. Leite, Robyn L. Woo, William D. Hong, Daniel C. Law, and Harry A. Atwater
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High quality tensile-strained n-doped germanium thin films grown on InGaAs buffer layers by metal-organic chemical vapor deposition

R. Jakomin, M. de Kersauson, M. El Kurdi, L. Largeau, O. Mauguin, G. Beaudoin, S. Sauvage, R. Ossikovski, G. Ndong, M. Chaigneau, I. Sagnes, and P. Boucaud

Appl. Phys. Lett. 98, 091901 (2011); http://dx.doi.org/10.1063/1.3559231 (3 pages) | Cited 8 times

Online Publication Date: 28 February 2011

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We show that high quality tensile-strained n-doped germanium films can be obtained on InGaAs buffer layers using metal-organic chemical vapor deposition with isobutyl germane as germanium precursor. A tensile strain up to 0.5% is achieved, simultaneously measured by x-ray diffraction and Raman spectroscopy. The effect of tensile strain on band gap energy is directly observed by room temperature direct band gap photoluminescence.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.30.Am Elemental semiconductors and insulators

Midinfrared surface plasmon sensor based on a substrateless metal mesh

O. Limaj, S. Lupi, F. Mattioli, R. Leoni, and M. Ortolani

Appl. Phys. Lett. 98, 091902 (2011); http://dx.doi.org/10.1063/1.3559616 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2011

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A midinfrared mass sensor based on high quality factor surface plasmon modes was designed, fabricated, and tested by infrared spectroscopy for the detection of nanometric layers of dielectric materials. Substrate removal below a metal mesh with period of 2 μm results in the coupling between degenerate surface plasmon modes on the two surfaces, resulting in a quality factor up to 33 for the antisymmetric mode. The presented substrateless metal mesh integrates mass sensing capability together with midinfrared spectroscopy, and is therefore of potential interest for substance-selective environmental and biomedical sensing applications
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Polarization-sensitive photoresponse of nanographite

Petr A. Obraztsov, Gennady M. Mikheev, Sergei V. Garnov, Alexander N. Obraztsov, and Yuri P. Svirko

Appl. Phys. Lett. 98, 091903 (2011); http://dx.doi.org/10.1063/1.3559928 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2011

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We report on polarization-sensitive direct current photoresponse of nanographite films in a 532–4000 nm spectral range. It is found that irradiation of the nanographite by the nanosecond laser pulses produces the electric current with intensity depending on the incidence angle and polarization of the laser beam. The obtained dependencies of the photoresponse on wavelength and polarization of excitation laser beam are discussed in terms of the surface photogalvanic and photon drag effects.
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81.05.uf Graphite
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

The hidden ingenuity in titin structure

Itamar Benichou and Sefi Givli

Appl. Phys. Lett. 98, 091904 (2011); http://dx.doi.org/10.1063/1.3558901 (3 pages) | Cited 2 times

Online Publication Date: 28 February 2011

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Titin is a giant protein that functions as a shock absorber in sarcomeres—the basic contractile unit of muscles. When stretched, thermal disturbances are expected to make titin follow the Maxwell path (global minimizer) of its energy. This path involves neither energy dissipation nor hysteresis. Therefore, a basic question is how does titin releases energy so efficiently? By adopting a simple mechanical model of a chain comprised from bistable elements, we show that dissipation depends on both system size and the height of the energy barrier separating equilibrium configurations. In this sense, titin is an optimal product of evolution.
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87.15.La Mechanical properties
87.15.B- Structure of biomolecules
87.14.E- Proteins
87.16.dm Mechanical properties and rheology
87.19.Ff Muscles

Influence of sample processing parameters on thermal boundary conductance value in an Al/AlN system

Christian Monachon, Mohamad Hojeij, and Ludger Weber

Appl. Phys. Lett. 98, 091905 (2011); http://dx.doi.org/10.1063/1.3560469 (3 pages) | Cited 1 time

Online Publication Date: 28 February 2011

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The influence of sample processing parameters on the thermal boundary conductance (TBC) between aluminum and aluminum nitride has been investigated by transient thermoreflectance. An evaporated Al layer on the polished substrate yielded a TBC at ambient of roughly 47 MW m−2 K−1. The largest improvement (by a factor of 5) was obtained by plasma-etching of the substrate and subsequent evaporation of the metal layer. Electron microscopy suggests that the differences in TBC were mainly due to the (partial) elimination of the native oxide layer on the substrate. The importance of an adequate model for data extraction on measured TBC is highlighted.
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78.66.Fd III-V semiconductors
78.20.N- Thermo-optic effects
78.66.Bz Metals and metallic alloys
81.65.Cf Surface cleaning, etching, patterning

Comprehensive insights into point defect and defect cluster formation in CuInSe2

Christiane Stephan, Susan Schorr, Michael Tovar, and Hans-Werner Schock

Appl. Phys. Lett. 98, 091906 (2011); http://dx.doi.org/10.1063/1.3559621 (3 pages) | Cited 7 times

Online Publication Date: 1 March 2011

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The concentration of native point defects in CuInSe2 powder material as a function of stoichiometry has been experimentally determined by neutron powder diffraction. A correlation between the Cu/In ratio and the density of VCu as well as InCu has been established and their concentrations are quantified. It is demonstrated, that assuming the spontaneous formation of defect pairs, the density of native point defects is reduced significantly by an order of magnitude. The functionality of a solar device, assuming same conditions like in the analyzed material, may be explained by a neutralization due to the formation of electrically inactive defect complexes.
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61.72.jd Vacancies
61.72.jj Interstitials
61.66.Fn Inorganic compounds
61.66.Bi Elemental solids
61.66.Dk Alloys

Theory of surface segregation in ternary semiconductor quantum dots

Sumeet C. Pandey, Georgios I. Sfyris, and Dimitrios Maroudas

Appl. Phys. Lett. 98, 091907 (2011); http://dx.doi.org/10.1063/1.3559939 (3 pages) | Cited 7 times

Online Publication Date: 1 March 2011

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We present a phenomenological species transport theory for surface segregation of constituent and dopant atoms in ternary semiconductor quantum dots. The theory employs continuum elasticity to describe species-surface interactions and is used to fit atomistic simulation results according to a first-principles-based force-field parameterization. The theory predicts equilibrium concentration profiles in the form of Maxwellian atmospheres near nanocrystal surfaces. The theory is accurate in the dilute limit and it is validated by fitting results of Monte Carlo simulations of compositional relaxation in InxGa1−xAs and ZnSe1−xTex nanocrystals for various representative sizes (diameters ≤ 5.7 nm) and compositions (x ≤ 0.2).
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68.35.Dv Composition, segregation; defects and impurities
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.07.Ta Quantum dots
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Probing the mechanical properties of graphene using a corrugated elastic substrate

Scott Scharfenberg, D. Z. Rocklin, Cesar Chialvo, Richard L. Weaver, Paul M. Goldbart, and Nadya Mason

Appl. Phys. Lett. 98, 091908 (2011); http://dx.doi.org/10.1063/1.3553228 (3 pages) | Cited 8 times

Online Publication Date: 1 March 2011

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We examine the mechanical properties of graphene samples of thicknesses ranging from 1 to 17 atomic layers, placed on a microscale-corrugated elastic substrate. Using atomic force microscopy, we show that the graphene adheres to the substrate surface and can substantially deform the substrate, with larger graphene thicknesses creating greater deformations. We use linear elasticity theory to model the deformations of the composite graphene-substrate system. We compare experiment and theory, and thereby extract information about graphene’s bending rigidity, adhesion, critical stress for interlayer sliding, and sample-dependent tension.
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81.05.ue Graphene
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.20.D- Elasticity

First-principles study on migration mechanism in SrTiO3

Teruyasu Mizoguchi, Nobuaki Takahashi, and Hak-Sung Lee

Appl. Phys. Lett. 98, 091909 (2011); http://dx.doi.org/10.1063/1.3560464 (3 pages) | Cited 4 times

Online Publication Date: 1 March 2011

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The atomistic behavior of migration in SrTiO3 was investigated by first-principles nudged elastic band calculations. Calculated migration energies for Sr and oxygen are consistent with experimental values. In contrast, the calculated energy for Ti with a simple Ti-vacancy mechanism is far larger than the experimental value. In examining different Ti-migration mechanisms, the Ti-migration energy is found to decrease and become comparable to the Sr-migration energy by introducing a Sr vacancy. This Sr-vacancy-mediated Ti migration, which is consistent with the experimentally proposed mechanism by Gömann et al. [ Phys. Chem. Chem. Phys. 6, 3639 (2004) ], is confirmed theoretically by the present calculations.
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66.30.Lw Diffusion of other defects
61.72.jd Vacancies

Antiphase boundaries in Ba0.75Sr0.25TiO3 epitaxial film grown on (001) LaAlO3 substrate

Y. Q. Wang, W. S. Liang, Peter Kr. Petrov, and Neil McN. Alford

Appl. Phys. Lett. 98, 091910 (2011); http://dx.doi.org/10.1063/1.3562972 (3 pages)

Online Publication Date: 2 March 2011

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Ba0.75Sr0.25TiO3 film was epitaxially grown on a (001) LaAlO3 substrate using single-target pulsed laser deposition. The microstructure of the epitaxial film was investigated by conventional and high-resolution transmission electron microscopy. Apart from dislocations and stacking faults, two different kinds of antiphase boundaries, one being straight, and the other being zig-zagged, have been observed. The formation mechanism of these antiphase boundaries is discussed.
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77.55.fe BaTiO3-based films
77.80.-e Ferroelectricity and antiferroelectricity
61.72.Nn Stacking faults and other planar or extended defects
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
68.55.aj Insulators

Losses in high quality quartz crystal resonators at cryogenic temperatures

Serge Galliou, Joël Imbaud, Maxim Goryachev, Roger Bourquin, and Philippe Abbé

Appl. Phys. Lett. 98, 091911 (2011); http://dx.doi.org/10.1063/1.3559611 (3 pages) | Cited 2 times

Online Publication Date: 3 March 2011

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Measurement of the mechanical losses of quartz crystal is a topic of interest for communities dealing with the gravitational wave detectors and also the time and frequency domain. About the latter, the authors describe Q-factor measurements of quartz crystal resonators at cryogenic temperatures under 10 K, thanks to a cryocooler-based experimental set-up. A Q-factor of 325 millions at 4 K, on the fifth overtone of the quasilongitudinal mode at 15.9 MHz, has been recorded. As shown, the acoustic wave trapping is suspected to limit the Landau–Rumer regime below 6 K [Landau and Rumer, Phys. Z. Sowjetunion 11, 18 (1937)] .
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.Fs Electromechanical resonance; quartz resonators
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
42.70.Ce Glasses, quartz

PbO-deficient PbTiO3: Mass transport, structural effects and possibility for intrinsic screening of the ferroelectric polarization

Sverre M. Selbach, Thomas Tybell, Mari-Ann Einarsrud, and Tor Grande

Appl. Phys. Lett. 98, 091912 (2011); http://dx.doi.org/10.1063/1.3555336 (3 pages) | Cited 2 times

Online Publication Date: 3 March 2011

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Intrinsic solid solubility in the form of cation nonstoichiometry has been studied in PbO-deficient bulk PbTiO3 prepared by solid-state reaction. The unit cell distortion, or tetragonality c/a, decreases with increasing concentration of Pb and O vacancies across the solid solubility range. Mass transport during solid-state reaction and sintering is sensitive to the nominal stoichiometry of the system: Excess PbO promotes grain growth and densification while excess TiO2 yields coarsening and swelling. These findings are discussed with respect to thin film growth and screening of the ferroelectric polarization by point defect concentration gradients at epitaxial interfaces.
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77.80.-e Ferroelectricity and antiferroelectricity
64.75.Bc Solubility
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.at Other materials
61.72.jd Vacancies

Abnormal temperature dependence of interband electronic transitions in relaxor-based ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0.24 and 0.31) single crystals

J. J. Zhu (诸佳俊), W. W. Li (李文武), G. S. Xu (许桂生), K. Jiang (姜凯), Z. G. Hu (胡志高), M. Zhu (朱敏), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 98, 091913 (2011); http://dx.doi.org/10.1063/1.3560342 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2011

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The transmittance spectra of (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0.24 and 0.31) single crystals have been studied in the temperature range of 5.3–300 K. It was found that the direct band gap Egd is 3.150±0.016 eV, indirect band gap Egi is 2.939±0.014 eV, and the phonon energy Ep is 0.098±0.014 eV for the PMN-0.24PT crystal at 300 K. With increasing the temperature, the Egd of the PMN-0.24PT crystal decreases from 3.263±0.017 to 3.150±0.016 eV while the Egd of the PMN-0.31PT crystal increases from 3.050±0.015 to 3.101±0.016 eV. The peculiar characteristic can be ascribed to the monoclinic and rhombohedral multiphase coexistence in the PMN-0.31PT crystal.
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77.80.B- Phase transitions and Curie point
63.20.-e Phonons in crystal lattices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Energetic stability, structural transition, and thermodynamic properties of ZnSnO3

Huiyang Gou, Jingwu Zhang, Zhiping Li, Gongkai Wang, Faming Gao, Rodney C. Ewing, and Jie Lian

Appl. Phys. Lett. 98, 091914 (2011); http://dx.doi.org/10.1063/1.3562013 (3 pages)

Online Publication Date: 4 March 2011

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First principles calculations were performed on ZnSnO3 polymorphs to understand their energetic stability and structural transition under high pressure environments. The experimentally-identified ilmenite (IL)-type and LiNbO3 (LN)-type ZnSnO3 may coexist at zero pressure considering the effect of zero point energy. IL-type ZnSnO3 becomes unstable under high pressure due to the appearance of imaginary frequency in phonon spectra. Enthalpy differences suggest that the phase stability follows the sequence: ZnO+SnO2 below 5.9 GPa, Zn2SnO4+SnO2 up to 7.1 GPa, and LN-type phase above 7.1 GPa. Pressurization at 34.5 GPa causes a phase transformation from the LN-type to the orthorhombic CdSnO3-type. Thermodynamic properties including Helmholtz free energy, specific heat at constant volume and Debye temperature were also calculated.
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65.40.Ba Heat capacity
63.20.-e Phonons in crystal lattices
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Microstructures corresponding to multilevel resistances of In3Sb1Te2 phase-change memory

Yong In Kim, Eun Tae Kim, Jeong Yong Lee, and Yong Tae Kim

Appl. Phys. Lett. 98, 091915 (2011); http://dx.doi.org/10.1063/1.3562024 (3 pages) | Cited 3 times

Online Publication Date: 4 March 2011

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The origin of multilevel resistances of In3Sb1Te2 (IST) phase-change random access memory cell has been investigated with high-resolution transmission electron microscopy (HR-TEM). The HR-TEM indicates that the microstructure of IST in the programming volume changes from amorphous to InSb and amorphous at the first state, and InSb and InTe at the second state, and IST at the third state, which are fairly consistent with four different levels of resistance. The resistance difference between the amorphous and the IST is about four orders of magnitude.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Generating nanoliter to femtoliter microdroplets with ease

R. Grossier, Z. Hammadi, R. Morin, A. Magnaldo, and S. Veesler

Appl. Phys. Lett. 98, 091916 (2011); http://dx.doi.org/10.1063/1.3560453 (3 pages) | Cited 1 time

Online Publication Date: 4 March 2011

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In this letter, we present a simply constructed and easy-to-use fluidic device that generates arrayed aqueous phase microdroplets in oil of controlled size with volumes ranging from nanoliter to femtoliter without surfactant. This can be applicable with a range of materials, allowing production and storage of monodisperse microdroplets. We illustrate the potential of our methodology in the field of nanoparticle generation
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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