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21 Feb 2011

Volume 98, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 081101 (2011); http://dx.doi.org/10.1063/1.3555489 (3 pages)

B. Cluzel, K. Foubert, L. Lalouat, J. Dellinger, D. Peyrade, E. Picard, E. Hadji, and F. de Fornel
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Possible routes for synthesis of new boron-rich Fe–B and Fe1−xCrxB4 compounds

A. F. Bialon, T. Hammerschmidt, R. Drautz, S. Shah, E. R. Margine, and A. N. Kolmogorov

Appl. Phys. Lett. 98, 081901 (2011); http://dx.doi.org/10.1063/1.3556564 (3 pages) | Cited 2 times

Online Publication Date: 22 February 2011

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We use ab initio calculations to examine thermodynamic factors that could promote the formation of recently proposed unique oP10-FeB4 and oP12-FeB2 compounds. We demonstrate that these compact boron-rich phases are stabilized further under pressure. We also show that chromium tetraboride is more stable in the new oP10 rather than the reported oI10 structure which opens up the possibility of realizing an oP10-(FexCr1−x)B4 pseudobinary material. In addition to exhibiting remarkable electronic features, oP10-FeB4 and oP12-FeB2 are expected to be harder than the known Fe–B compounds commonly used for hard coating applications.
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61.66.Fn Inorganic compounds
81.65.Kn Corrosion protection
71.20.Ps Other inorganic compounds
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
71.15.-m Methods of electronic structure calculations

Reversible switching between isotropic and anisotropic wetting by one-direction curvature tuning on flexible superhydrophobic surfaces

Si-Zhu Wu, Jian-Nan Wang, Li-Gang Niu, Jia Yao, Dong Wu, and Ai-Wu Li

Appl. Phys. Lett. 98, 081902 (2011); http://dx.doi.org/10.1063/1.3556585 (3 pages) | Cited 2 times

Online Publication Date: 22 February 2011

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In this letter, we report a kind of smart surfaces with reversible switching between isotropy and anisotropic wetting, which was realized by one-direction curvature tuning on flexible superhydrophobic surfaces. Along the curvature change, the wettability of this flexible film was changed from isotropic state (150°/150°) into anisotropic state confirmed by its anisotropic contact angles (150°/160°) and sliding properties (30°/65°). Further investigation revealed that the surface wettability was changed from composited pinned state into transitional state. This was attributed to the increase in roughness factor and the decrease in the contact area between the water droplet and the pillar array. At last, we demonstrate that the wetting states between isotropy and anisotropy on this flexible superhydrophobic film could be reversibly switched by curvature for many times (>10).
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68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
68.55.am Polymers and organics
68.35.bm Polymers, organics

Strain-mediated electric-field control of photoinduced demagnetization in La0.8Ca0.2MnO3 thin films

E. J. Guo, J. Gao, and H. B. Lu

Appl. Phys. Lett. 98, 081903 (2011); http://dx.doi.org/10.1063/1.3556613 (3 pages) | Cited 11 times

Online Publication Date: 22 February 2011

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La0.8Ca0.2MnO3 (LCMO) thin films have been epitaxially grown on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN-PT) substrates. The substrate-induced strain effects on the transport and photoinduced demagnetization in LCMO films were investigated. The photoinduced resistances (PRs) of LCMO systematically changed versus temperature before and after ferroelectric-poling on PMN-PT, indicating that photoexcited extra carriers in LCMO may suppress the neighboring spin correlation due to the photoassisted hopping of anti-Jahn–Teller polarons. Moreover, a significant modulation on PR by electric fields applied across PMN-PT was observed. In situ x-ray diffraction indicates that the observed variations result from substrate-induced strain due to the ferroelectric polarization or converse piezoelectric effect.
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81.15.Fg Pulsed laser ablation deposition
77.22.Ej Polarization and depolarization
75.70.Ak Magnetic properties of monolayers and thin films
77.55.fp Other ferroelectric films
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Abnormal sub-Tg enthalpy relaxation in the CuZrAl metallic glasses far from equilibrium

Lina Hu, Yuanzheng Yue, and Chunzhi Zhang

Appl. Phys. Lett. 98, 081904 (2011); http://dx.doi.org/10.1063/1.3556659 (3 pages) | Cited 3 times

Online Publication Date: 22 February 2011

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The sub-Tg enthalpy relaxation in glasses far from equilibrium (i.e., hyperquenched glasses) is usually manifested as a monotonic increase in both the onset temperature and the extent of enthalpy recovery with increasing the annealing temperature. Here we report an abnormal three-steplike relaxation pattern in hyperquenched Cu45Zr45Al10 and Cu48Zr48Al4 glasses below Tg, i.e., the usual monotonic increase is inverted when the annealing temperature increases to a critical value. This abnormal relaxation pattern could be attributed to the high extent of chemical heterogeneity in the CuZrAl supercooled liquids, and present a thermodynamic evidence for the dynamic fragile-to-strong transition in metallic glass-forming liquids.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.70.pe Metallic glasses
81.40.Gh Other heat and thermomechanical treatments
65.20.Jk Studies of thermodynamic properties of specific liquids
61.43.Fs Glasses

Hydrogenation of magnesium nanoblades: The effect of concentration dependent hydrogen diffusion

B. Yang, Y.-P. He, and Y.-P. Zhao

Appl. Phys. Lett. 98, 081905 (2011); http://dx.doi.org/10.1063/1.3557056 (3 pages) | Cited 5 times

Online Publication Date: 22 February 2011

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By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. A hydride shell is not formed during the hydrogenation.
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68.43.Mn Adsorption kinetics
66.30.Pa Diffusion in nanoscale solids
88.30.R- Hydrogen storage

Formation mechanism of shear bands in ultrafine lamellar Ti–Fe eutectics

F. Zhu, H. N. Tian, X. Li, G. H. Cao, D. Gerthsen, C.-G. Oertel, and W. Skrotzki

Appl. Phys. Lett. 98, 081906 (2011); http://dx.doi.org/10.1063/1.3559220 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2011

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Shear bands with alternating lamellar and serrated structures were observed on the fracture surface of an Ti–Fe ultrafine eutectic. The shear bands are composed of coalesced subgrains. Hence, a subgrain rotational mechanism is proposed to explain their formation. The work is a direct experimental evidence of the hypothetical rotational mechanism.
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62.20.F- Deformation and plasticity
62.20.mm Fracture

Huge binding energy of localized biexcitons in Al-rich AlxGa1−xN ternary alloys

Ryo Kittaka, Hirotaka Muto, Hideaki Murotani, Yoichi Yamada, Hideto Miyake, and Kazumasa Hiramatsu

Appl. Phys. Lett. 98, 081907 (2011); http://dx.doi.org/10.1063/1.3559226 (3 pages)

Online Publication Date: 23 February 2011

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Excitonic optical properties of Al-rich AlxGa1−xN ternary alloy epitaxial layers have been studied by means of photoluminescence excitation spectroscopy. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons was estimated to be 56±5 and 48±5 meV for the sample with x = 0.81 and 0.89, respectively. The biexciton binding energy of 56 meV was approximately three times as large as the biexciton binding energy of 19 meV in AlN. The large enhancement of the biexciton binding energy resulted from the strong localization of biexcitons due to alloy disorder.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
71.35.-y Excitons and related phenomena
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Experimental, finite element, and density-functional theory study of inorganic nanotube compression

Estelle Kalfon-Cohen, Ohad Goldbart, Roy Schreiber, Sidney R. Cohen, David Barlam, Tommy Lorenz, Jan-Ole Joswig, and Gotthard Seifert

Appl. Phys. Lett. 98, 081908 (2011); http://dx.doi.org/10.1063/1.3556679 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2011

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Interactions between the walls in multiwalled nanotubes are key to determining their mechanical properties. Here, we report studies of radial deformation of multiwalled WS2 nanotubes in an atomic force microscope. The experimental results were fitted to a finite element model to determine the radial modulus. These results are compared with density-functional tight-binding calculations of a double-walled tube. Good agreement was obtained between experiment and calculations. The results indicate the importance of the sliding between layers in moderating the radial modulus. A plateau in the deformation curves is seen to have atomistic origins.
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81.07.De Nanotubes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

sp2-like hybridization of silicon valence orbitals in silicene nanoribbons

Paola De Padova, Claudio Quaresima, Bruno Olivieri, Paolo Perfetti, and Guy Le Lay

Appl. Phys. Lett. 98, 081909 (2011); http://dx.doi.org/10.1063/1.3557073 (3 pages) | Cited 15 times

Online Publication Date: 23 February 2011

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Silicene nanoribbons grown on a silver (110) substrate have been studied by reflection electron energy loss spectroscopy as a function of the electron beam incidence angle α. The spectra, taken at the Si K absorption edge (1.840 keV), reveal the presence of two distinct loss structures attributed to transitions 1s→π∗ and 1s→σ∗, according to their intensity dependence on α. Such behavior, when compared to graphite, attests the sp2-like hybridization of the silicon valence orbitals in the silicene nanoribbons as is, indeed, for carbon atomic bonds of graphene.
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79.20.Uv Electron energy loss spectroscopy
73.22.-f Electronic structure of nanoscale materials and related systems

Theory of ionic polymer conductor network composite

Xiao Wang (王宵) and Wei Hong (洪伟)

Appl. Phys. Lett. 98, 081910 (2011); http://dx.doi.org/10.1063/1.3555437 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2011

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Ionic polymer conductor network composite (IPCNC) is a mixed conductor consisting of a network of loaded ionomer and another network of metallic particles. It is known that the microstructure of the composite, especially that of the electrodes, plays a dominating role in the performance of an IPCNC. However, the microstructure of IPCNC has seldom been addressed in theoretical models. This letter formulates a continuum field theory for IPCNC by considering a supercapacitorlike microstructure with a large distributed interfacial area. The theory is then applied to the study of the equilibrium deformation and electrochemistry in a thin-sheet IPCNC actuator.
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66.30.Dn Theory of diffusion and ionic conduction in solids
82.45.Fk Electrodes
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Optically detected nuclear magnetic resonance in n-GaAs using an on-chip microcoil

Y. S. Chen, J. Huang, D. Reuter, A. Ludwig, A. D. Wieck, and G. Bacher

Appl. Phys. Lett. 98, 081911 (2011); http://dx.doi.org/10.1063/1.3553503 (3 pages)

Online Publication Date: 24 February 2011

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Optically detected nuclear magnetic resonance (NMR) with micrometer resolution is demonstrated in n-GaAs using an on-chip microcoil. To trace the Overhauser field, the electron Larmor frequency is monitored via time-resolved magneto-optical Kerr rotation. Sweeping the frequency of the rf magnetic field induced by an on-chip microscale current loop, nuclear spin depolarization is achieved for each isotope species. The experimental data indicate an impact of a local quadrupole field, most likely caused by ionized donors, on the amplitude and linewidth of the NMR spectrum. By applying rf pulse sequences, the Rabi oscillation of 75As nuclear spins is obtained with an effective dephasing time of ∼ 200 μs.
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76.70.Hb Optically detected magnetic resonance (ODMR)
78.47.D- Time resolved spectroscopy (>1 psec)
78.66.Fd III-V semiconductors
71.70.Jp Nuclear states and interactions
78.20.Ls Magneto-optical effects
76.60.-k Nuclear magnetic resonance and relaxation

Raman scattering from Ti3SiC2 single crystals

Frédéric Mercier, Odette Chaix-Pluchery, Thierry Ouisse, and Didier Chaussende

Appl. Phys. Lett. 98, 081912 (2011); http://dx.doi.org/10.1063/1.3558919 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2011

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The lack of single crystalline Ti3SiC2 samples is currently limiting the accurate measurement of its basic properties as its layered crystalline structure presents a very strong anisotropy. In this letter, we report the growth of pure Ti3SiC2 single crystals after a careful study of the Ti3SiC2 liquidus surface extent through thermodynamical calculations. From a Raman scattering study on those single crystals, an unambiguous assignment of most of the phonon modes has been established, giving an answer to the discrepancies existing in the literature.
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78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
65.40.G- Other thermodynamical quantities
81.10.Fq Growth from melts; zone melting and refining

UV-blue photoluminescence from close-packed SiC nanocrystal film

J. Y. Fan, H. X. Li, Q. J. Wang, D. J. Dai, and P. K. Chu

Appl. Phys. Lett. 98, 081913 (2011); http://dx.doi.org/10.1063/1.3556657 (3 pages) | Cited 7 times

Online Publication Date: 24 February 2011

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We observed stable photoluminescence from close-packed cubic SiC nanocrystals that are self-assembled into thin solid film. The peak wavelength shifts from blue to near UV with increasing excitation energy and follows well the quantum-confinement effect. The photoluminescence excitation spectrum indicates a 3.47 eV bandgap corresponding to a particle size of 2.3 nm. The nanocrystal film shows triple-exponential photoluminescence decay with lifetimes of 2.3, 8.5, and 36.9 ns. The results open the possibility of the solid state UV-blue light emitting by use of the SiC nanocrystals in photonics and photonics/electronics integration.
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78.66.Li Other semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Hk Nanocrystals
71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials
73.63.Bd Nanocrystalline materials

Thermally driven isotropic crystallinity breaking of nanocrystals: Insight into the assembly of EuS nanoclusters and nanorods with oleate ligands

Weidong He and James H. Dickerson

Appl. Phys. Lett. 98, 081914 (2011); http://dx.doi.org/10.1063/1.3560460 (3 pages) | Cited 5 times

Online Publication Date: 24 February 2011

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Clusters of EuS nanocrystals formed through the thermal assembly of 2.5 nm nanocrystal monomers by varying the annealing temperature from 300 to 340 °C. Below 310 °C, oleate ligands stabilized on the surface of the EuS nanocrystals, giving rise to their low solubility in triethanolamine while facilitating monomer–monomer oriented attachment into short-chain structures. Above 320 °C, the oleate ligands thermally detached from the surface and were replaced by oleyamine. This reaction mechanism was a multilevel oriented attachment, based on calculations of the nanocrystal growth kinetics, whose evolution gave rise to the formation of EuS nanorods at 340 °C.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments

Thermal rectification in bulk materials with asymmetric shape

D. Sawaki, W. Kobayashi, Y. Moritomo, and I. Terasaki

Appl. Phys. Lett. 98, 081915 (2011); http://dx.doi.org/10.1063/1.3559615 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2011

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We investigate thermal rectification in a bulk material with a pyramid shape to elucidate shape dependence of the thermal rectification, and find that rectifying coefficient R is 1.35 for this shape, which is smaller than R = 1.43 for a rectangular shape. This result is fully duplicated by our numerical calculation based on Fourier’s law. We also apply this calculation to a given shape, and show a possible way to increase R depending on the shape.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
02.30.Nw Fourier analysis

 Static and ultrafast dynamics of defects of SrTiO3 in LaAlO3/SrTiO3 heterostructures

X. Wang, J. Q. Chen, A. Roy Barman, S. Dhar, Q.-H. Xu, T. Venkatesan, and Ariando

Appl. Phys. Lett. 98, 081916 (2011); http://dx.doi.org/10.1063/1.3554705 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2011

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A detailed defect energy level map was investigated for heterostructures of 26 unit cells of LaAlO3 on SrTiO3 prepared at a low oxygen partial pressure of 10−6 mbar. The origin is attributed to the presence of dominating oxygen defects in SrTiO3 substrate. Using femtosecond laser spectroscopy, the transient absorption and relaxation times for various transitions were determined. An ultrafast relaxation process of 2–3 ps from the conduction band to the closest defect level and a slower process of 70–92 ps from conduction band to intraband defect level were observed. The results are discussed on the basis of the proposed defect-band diagram.
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71.55.Ht Other nonmetals
78.47.jb Transient absorption
61.72.jd Vacancies

A host sensitized reddish-orange Gd2MoO6:Sm3+ phosphor for light emitting diodes

Yan Chen, Jing Wang, Chunmeng Liu, Xiaojun Kuang, and Qiang Su

Appl. Phys. Lett. 98, 081917 (2011); http://dx.doi.org/10.1063/1.3557065 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2011

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An intense reddish-orange phosphor, Gd2MoO6:Sm3+, was developed by solid state chemistry. The photoluminescence excitation and emission spectra, concentration effect are investigated. The results show an efficient energy transfer from MoO66− group to Sm3+ occurs and Sm3+ ion emits an intense reddish-orange light with high color purity and an excellent reproduction quality of optical properties. These results demonstrate that Sm3+ ion with low 4f–4f absorption efficiency in near ultraviolet region can play a role of activator in narrow reddish-orange emitting phosphor potentially useful in ∼ 370 nm GaN-based light emitting diode through efficient energy feeding by charge transfer absorption of MoO66− group.
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85.60.Jb Light-emitting devices
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