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14 May 2007

Volume 90, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 90, 201101 (2007); http://dx.doi.org/10.1063/1.2739308 (3 pages)

Luca Sapienza, Angela Vasanelli, Cristiano Ciuti, Christophe Manquest, Carlo Sirtori, Raffaele Colombelli, and Ulf Gennser
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Switching of emissivity and photoconductivity in highly doped Yb3+:Y2O3 and Lu2O3 ceramics

Jean-Francois Bisson, Dmitrii Kouznetsov, Ken-Ichi Ueda, Susanne T. Fredrich-Thornton, Klaus Petermann, and Guenter Huber

Appl. Phys. Lett. 90, 201901 (2007); http://dx.doi.org/10.1063/1.2739318 (3 pages) | Cited 7 times

Online Publication Date: 14 May 2007

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Reversible jump of thermal emission accompanied with jump of photocurrent is observed in highly doped Yb3+:Y2O3 and Lu2O3 bulk ceramics pumped at 940 nm wavelength. In contrast, when these materials are heated with a CO2 laser at 10.6 μm wavelength, only a gradual increase of thermal emission and photoconductivity are observed up to the melting point. These results are interpreted as a ytterbium mediated, photoassisted avalanche of thermal emission.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
72.40.+w Photoconduction and photovoltaic effects
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

On-off optical switching of the magnetic and structural properties in a spin-crossover complex

K. Kato, M. Takata, Y. Moritomo, A. Nakamoto, and N. Kojima

Appl. Phys. Lett. 90, 201902 (2007); http://dx.doi.org/10.1063/1.2736213 (3 pages) | Cited 10 times

Online Publication Date: 14 May 2007

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A photoexcitation is one of the promising external fields to control the material phases. Here, the authors have demonstrated that the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen = 1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature. The structural data suggest that the density of the high-spin Fe2+ in the photoinduced phase is about 0.88. Suppressed atomic vibrations of the photoinduced phase exclude the conventional heating effect as the origin for the observed optical switching.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
61.66.Hq Organic compounds
78.20.Ls Magneto-optical effects

Spatial normalization of the high-frequency ultrasound energy loss in open-cell foams

T. E. Gómez Álvarez-Arenas and I. González Gómez

Appl. Phys. Lett. 90, 201903 (2007); http://dx.doi.org/10.1063/1.2739076 (3 pages) | Cited 6 times

Online Publication Date: 15 May 2007

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Wide-band and air-coupled ultrasound pulses are propagated through slabs of open-cell reticulated solid foams and the transmission coefficient is measured. Under these conditions, fluid in the pores and solid skeleton are strongly decoupled; in addition, at frequencies well over that of the relaxation of the influence of the tortuosity, it is observed that energy loss approaches to a constant value: ∣γ∣∞. Internal surface area (Si) and the length dimension parameter (Λ) of the foams are independently measured. Results reveal that ∣γ∣∞ vs Λ or Si follows a power law very close to linear, suggesting a possible spatial normalization for ∣γ∣∞.
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62.65.+k Acoustical properties of solids
82.70.Rr Aerosols and foams
61.43.-j Disordered solids
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.20.-f General linear acoustics

Lamb waves in binary locally resonant phononic plates with two-dimensional lattices

Jin-Chen Hsu and Tsung-Tsong Wu

Appl. Phys. Lett. 90, 201904 (2007); http://dx.doi.org/10.1063/1.2739369 (3 pages) | Cited 24 times

Online Publication Date: 15 May 2007

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The authors study the propagation of Lamb waves in two-dimensional locally resonant phononic-crystal plates, composed of periodic soft rubber fillers in epoxy host with a finite thickness. Our calculations are based on the efficient plane wave expansion formulation which utilized Mindlin’s plate theory. Calculated results show that the low-frequency gaps of Lamb waves are opened up by the localized resonance mechanism. The resonant frequencies of flexure-dominated plate modes are significantly dependent not only on the radius of circular rubber fillers but also on the plate thickness. The properties of localized resonance are qualitatively analogous to the vibration of a circular thin plate.
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68.35.Iv Acoustical properties
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Transition from the strong- to the weak-coupling regime in semiconductor microcavities: Polarization dependence

D. Ballarini, A. Amo, L. Viña, D. Sanvitto, M. S. Skolnick, and J. S. Roberts

Appl. Phys. Lett. 90, 201905 (2007); http://dx.doi.org/10.1063/1.2739370 (3 pages) | Cited 4 times

Online Publication Date: 15 May 2007

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The dependence on the polariton spin orientation of the transition from the strong- to the weak-coupling regime in InGaAs semiconductor microcavities is experimentally studied by means of time-resolved photoluminescence. Polaritons are nonresonantly excited by circularly polarized pulses and the photoluminescence of the K‖ ∼ 0 states is analyzed into its co- and cross-polarized components. The loss of strong coupling with increasing excitation intensity takes place at different powers for polaritons with opposite spin orientation and it is determined by the polariton population of each spin.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Slow electromagnetic wave guided in subwavelength region along one-dimensional periodically structured metal surface

Zhichao Ruan and Min Qiu

Appl. Phys. Lett. 90, 201906 (2007); http://dx.doi.org/10.1063/1.2740174 (3 pages) | Cited 28 times

Online Publication Date: 15 May 2007

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A perfect electric conductor surface with one-dimensional periodic rectangle holes is proposed as a surface-plasmon-like waveguide, where designed surface plasmon modes with very low group velocity are confined in a subwavelength region. It is shown that the half maximum of electric field intensity of the mode can be confined in a 0.20λ×0.10λ subwavelength region on the transversal plane and the group velocity approaches to zeros, where λ is the wavelength in vacuum.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces

Polarity control of ZnO films on (0001) Al2O3 by Cr-compound intermediate layers

J. S. Park, S. K. Hong, T. Minegishi, S. H. Park, I. H. Im, T. Hanada, M. W. Cho, T. Yao, J. W. Lee, and J. Y. Lee

Appl. Phys. Lett. 90, 201907 (2007); http://dx.doi.org/10.1063/1.2740190 (3 pages) | Cited 19 times

Online Publication Date: 15 May 2007

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This letter presents a reliable and very easy method for selective growth of polarity controlled ZnO films on (0001) Al2O3 substrates by plasma-assisted molecular-beam epitaxy. Cr-compound intermediate layers are used to control the crystal polarity of ZnO films on (0001) Al2O3. ZnO films grown on rocksalt structure CrN/(0001) Al2O3 shows Zn polarity, while those grown on rhombohedral Cr2O3/(0001) Al2O3 shows O polarity. Possible interface atomic arrangements for both heterostructures are proposed.
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81.05.Dz II-VI semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.35.Ct Interface structure and roughness

Deformation-induced nanoscale high-temperature phase separation in Co–Fe alloys at room temperature

Lai-Chang Zhang, Mariana Calin, Flora Paturaud, Christine Mickel, and Jürgen Eckert

Appl. Phys. Lett. 90, 201908 (2007); http://dx.doi.org/10.1063/1.2740476 (3 pages) | Cited 3 times

Online Publication Date: 15 May 2007

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Instead of applying severe plastic deformation, high-temperature heat treatment or high pressure, grain refinement and high-temperature phase separation induced by deformation in single-phase body-centered-cubic (bcc) coarse-grained Co–Fe alloys have been achieved by simple room-temperature compression. The alloys exhibit large plasticity over 140% without fracture. Phase separation from the bcc phase to nanoscale face-centered-cubic Fe and Co phases, which generally occurs at high temperature above ∼ 1150 K, is formed in the deformed samples. The possible mechanisms are shear deformation and deformation-enhanced atomic diffusion rather than the temperature rise during deformation.
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64.75.-g Phase equilibria
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
66.30.Fq Self-diffusion in metals, semimetals, and alloys
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids

Study on the structural relationship between the liquid and amorphous Fe78Si9B13 alloys by ab initio molecular dynamics simulation

Jingyu Qin, Tingkun Gu, Lei Yang, and Xiufang Bian

Appl. Phys. Lett. 90, 201909 (2007); http://dx.doi.org/10.1063/1.2737937 (3 pages) | Cited 15 times

Online Publication Date: 15 May 2007

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The structure of the liquid and amorphous Fe78Si9B13 alloys is investigated by ab initio molecular dynamics simulation. The amorphous structure bears a strong resemblance to the liquid structure on both the atomic and electronic levels. Chemical short-range order is evidenced by higher Fe coordinating proportion than the nominal one around both Si and B atoms in both the liquid and amorphous states. The atomic distances and the local densities of states show that Fe–Si bonding is stronger than Fe–B bonding and Si and B tend to repulse each other.
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61.25.Mv Liquid metals and alloys
61.20.Ja Computer simulation of liquid structure
61.43.Bn Structural modeling: serial-addition models, computer simulation

Torsional behavior of chiral single-walled carbon nanotubes is loading direction dependent

Tienchong Chang

Appl. Phys. Lett. 90, 201910 (2007); http://dx.doi.org/10.1063/1.2739325 (3 pages) | Cited 21 times

Online Publication Date: 16 May 2007

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The torsion of carbon nanotubes is studied by molecular dynamics simulations. The torsional behavior of a chiral single-walled carbon nanotube (SWCNT) is dependent on the loading directions due to its structural asymmetry. The critical buckling shear strain of a SWCNT in one direction may be 1.8 times higher than that in the opposite direction. This means that one can choose the most appropriate SWCNT for his special purpose in designing a torsional component (e.g., oscillators and springs) of nanomechanical devices using carbon nanotubes. Meanwhile, the finding indicates that a simple thin shell model is not suitable for predicting torsional behavior of small SWCNTs at large strains.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.46.Fg Nanotubes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Resonant Raman scattering and surface phonon modes of hollow ZnS microspheres

Y. Y. Luo, G. T. Duan, and G. H. Li

Appl. Phys. Lett. 90, 201911 (2007); http://dx.doi.org/10.1063/1.2737398 (3 pages) | Cited 7 times

Online Publication Date: 17 May 2007

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The optical properties of hollow ZnS microspheres were studied. The Raman scattering spectra of the hollow ZnS microspheres depend strongly on the excitation power, and at an excitation power of about I0/10, a strong resonant Raman scattering spectrum with high-order longitudinal optical modes and weak high-order surface optical modes appeared. The weak surface phonons are sensitive to the surrounding medium and are considered to come from the surface defects of the microspheres. The frequency of the weak surface phonon is in agreement with the prediction calculated on the basis of the dielectric continuum approach.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Hk Nanocrystals
68.35.Ja Surface and interface dynamics and vibrations
78.30.Fs III-V and II-VI semiconductors
78.68.+m Optical properties of surfaces

Barrier composition dependence of the internal electric field in ZnO/Zn1−xMgxO quantum wells

T. Bretagnon, P. Lefebvre, T. Guillet, T. Taliercio, B. Gil, and C. Morhain

Appl. Phys. Lett. 90, 201912 (2007); http://dx.doi.org/10.1063/1.2740576 (3 pages) | Cited 21 times

Online Publication Date: 17 May 2007

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Time-integrated photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO/Zn1−xMgxO single quantum wells of varying widths and magnesium compositions. By comparing experimental results with a variational calculation of excitonic energies, the authors determine the magnitude of the built-in electric field that is induced by both spontaneous and piezoelectric polarizations. It is found that the electric field varies linearly with magnesium composition. By taking into consideration the well-known distribution of electric field among the barrier and the well layers in multiquantum wells, the authors show that their results are fully consistent with previously reported data.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.63.Hs Quantum wells
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.Fg Quantum wells
78.67.De Quantum wells

Growth and properties of Mg-doped In-polar InN films

Xinqiang Wang, Song-Bek Che, Yoshihiro Ishitani, and Akihiko Yoshikawa

Appl. Phys. Lett. 90, 201913 (2007); http://dx.doi.org/10.1063/1.2741124 (3 pages) | Cited 21 times

Online Publication Date: 17 May 2007

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Mg doping into In-polar InN layers for different Mg fluxes is performed on GaN templates by molecular beam epitaxy, and their electrical and optical properties are investigated. Mg concentration is linearly proportional to Mg-beam flux, indicating that the Mg-sticking coefficient is almost unity. With Mg doping, electron concentration decreases by the effect of carrier compensation, but it begins to increase with further increasing Mg flux because of Mg-related donorlike-defects formation. For the partially carrier-compensated Mg-doped InN, two photoluminescence peaks are observed; one is originated from free-to-acceptor emission with an acceptor activation energy of about 61 meV and the other is similar to the conventional band-to-band emission.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Elastic and superelastic properties of Co49Ni22Ga29 single crystal

V. A. Chernenko, S. Besseghini, E. Villa, A. Gambardella, and J. I. Pérez-Landazabal

Appl. Phys. Lett. 90, 201914 (2007); http://dx.doi.org/10.1063/1.2740112 (3 pages) | Cited 4 times

Online Publication Date: 18 May 2007

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Low-frequency-elastic modulus, internal friction, tensile stress-strain loops, and thermally induced strain recovery are studied in the vicinity of the martensitic transformation (MT) exhibited by the [001]-oriented Co49Ni22Ga29 single crystal in as-grown state. The mechanical and thermomechanical tests are conducted with TA Instruments Q800 dynamic mechanical analyzer. Elastic modulus shows softening during cooling and a deep minimum at MT concurrently with the abrupt increase of internal friction. The stepwise and jerky yield and recovery of the superelastic 7% strain alongside the appearance of the jumplike character of thermally induced MT are obtained after thermomechanical training. Thermodynamic estimations reveal a self-consistency of the results.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Gh Other heat and thermomechanical treatments
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

CuBr films on KBr exhibiting 102 or 103 times higher efficiency of free-exciton luminescence than those on usual substrates such as Al2O3

S. Kondo and T. Saito

Appl. Phys. Lett. 90, 201915 (2007); http://dx.doi.org/10.1063/1.2740483 (3 pages) | Cited 4 times

Online Publication Date: 18 May 2007

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CuBr films grown on KBr crystals show 102 or 103 times higher efficiency of free-exciton photoluminescence (PL) than those grown on conventional substrates such as Al2O3 or silica glass. The efficiency exceeds even that of CuCl films by a factor of several tens, despite the general recognition that the free-exciton PL from CuBr is much weaker than that from CuCl. The present result encourages the authors to challenge to rethink the exciton PL in CuBr as well as in CuCl, because the compounds are the model materials for basic and application studies of linear/nonlinear exciton-related PL properties of solids.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Localization and interdot carrier transfer in CdSe and CdZnMnSe quantum dots determined by cw and time-resolved photoluminescence

J. H. Park, D. G. Choi, T. K. Lee, Eunsoon Oh, Sanghoon Lee, and J. K. Furdyna

Appl. Phys. Lett. 90, 201916 (2007); http://dx.doi.org/10.1063/1.2740484 (3 pages) | Cited 5 times

Online Publication Date: 18 May 2007

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The authors compared time-integrated and time-resolved photoluminescence (PL) emitted by CdSe quantum dots (QDs) and by CdZnMnSe QDs. An unusual nonmonotonic temperature dependence of the PL shift for CdSe QDs is observed, which they ascribe to delocalization of carriers with increasing temperature. In contrast, PL emitted by CdZnMnSe QDs follows a typical monotonic redshift with temperature and exhibits a smaller temporal redshift with pulsed laser excitation than that observed for CdSe QDs. The authors suggest that the temperature PL dependence observed for CdZnMnSe QDs and the smaller localization process observed in that system arise from the shorter PL lifetime in that system.
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73.21.La Quantum dots
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
78.47.-p Spectroscopy of solid state dynamics

Vibration-induced Cassie-Wenzel wetting transition on rough surfaces

Edward Bormashenko, Roman Pogreb, Gene Whyman, Yelena Bormashenko, and Mordechai Erlich

Appl. Phys. Lett. 90, 201917 (2007); http://dx.doi.org/10.1063/1.2738364 (2 pages) | Cited 19 times

Online Publication Date: 18 May 2007

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The wetting transition is revealed for a water drop placed on a honeycomb polymer pattern under the action of vibration. Water penetration into the pattern cavities is accompanied by a change in the apparent contact angle. The Cassie-Wenzel wetting transition is confirmed by the model calculation. The threshold pressure in the drop for this transition is determined.
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68.08.Bc Wetting
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Inelastic laser light scattering study of an ordered array of carbon nanotubes

A. M. Polomska, C. K. Young, G. T. Andrews, M. J. Clouter, A. Yin, and J. M. Xu

Appl. Phys. Lett. 90, 201918 (2007); http://dx.doi.org/10.1063/1.2741145 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2007

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Ordered carbon nanotube arrays fabricated on alumina templates were studied using inelastic laser light scattering spectroscopy. Multiple peaks were observed in spectra from an array where the nanotubes extend ∼ 150 nm beyond the template surface. These protruding segments are modeled as hollow cylinders clamped at one end. Good agreement is obtained between the predicted vibrational frequencies and the experimental peak frequency shifts. The peaks are thus attributed to the transverse, longitudinal, and torsional vibrations of the protruding nanotube segments. This assignment yields values of 26 and 20 GPa for the Young’s and shear moduli of the nanotubes, respectively.
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78.67.Ch Nanotubes
61.46.Fg Nanotubes
62.25.-g Mechanical properties of nanoscale systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Jj Elasticity and anelasticity, stress-strain relations

Scattering of electromagnetic waves in metamaterial superlattices

Ilya V. Shadrivov, David A. Powell, Steven K. Morrison, Yuri S. Kivshar, and Gregory N. Milford

Appl. Phys. Lett. 90, 201919 (2007); http://dx.doi.org/10.1063/1.2741148 (3 pages) | Cited 9 times

Online Publication Date: 18 May 2007

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The authors study experimentally both transmission and reflection of microwave radiation from metamaterial superlattices created by layers of periodically arranged wires and split-ring resonators. The authors measure the dependence of the metamaterial resonance on the spatial period of the superlattice and demonstrate resonance broadening and splitting for the binary metamaterial structures.
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42.70.-a Optical materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation
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