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8 Feb 2010

Volume 96, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 96, 063101 (2010); http://dx.doi.org/10.1063/1.3308512 (3 pages)

Takashi Yokoyama
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Temperature-dependent shear band dynamics in a Zr-based bulk metallic glass

David Klaumünzer, Robert Maaß, Florian H. Dalla Torre, and Jörg F. Löffler

Appl. Phys. Lett. 96, 061901 (2010); http://dx.doi.org/10.1063/1.3309686 (3 pages) | Cited 15 times

Online Publication Date: 8 February 2010

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Flow serrations recorded during inhomogeneous deformation of Zr52.5Ti5Cu17.9Ni14.6Al10 (Vit105) were studied during compression testing at temperatures between −40 and 60 °C. The shear band velocities determined exhibit a pronounced temperature dependence covering nearly two orders of magnitude. The velocities follow an Arrhenius-type behavior with an associated activation energy of 0.3±0.05 eV. The results demonstrate a thermally activated mechanism of shear band propagation, which is similar to the behavior of other, nonmetallic amorphous materials.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.05.Kf Glasses (including metallic glasses)

Thermoreflectance characterization of band-edge excitonic transitions in CuAlS2 ultraviolet solar-cell material

Ching-Hwa Ho

Appl. Phys. Lett. 96, 061902 (2010); http://dx.doi.org/10.1063/1.3303826 (3 pages) | Cited 8 times

Online Publication Date: 8 February 2010

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Near band edge transitions of CuAlS2 chalcopyrite crystals have been characterized using temperature-dependent thermoreflectance (TR) spectroscopy in the temperature range between 30 and 340 K. A lot of interband transition features of EAn = 2, EAn = 3, EBn = 2, EC, ED, EE, and EF were detected in the low-temperature TR spectrum of 3–6 eV at 30 K. Transition energies of the TR features of CuAlS2 are analyzed. Transition origins of the features are evaluated. Optical-electric conversion behavior of CuAlS2 was evaluated by photoconductivity (PC) measurement at 300 K. The PC spectrum reveals that the maximum photoresponse occurs near the energy positions of EAn = 2, EAn = 3, and EBn = 2 features. The features are the fundamental band edge excitons which dominate photoelectric conversion behavior of CuAlS2 ultraviolet solar-energy material.
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78.20.nb Photothermal effects
78.40.Fy Semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Pz Photoconduction and photovoltaic effects
88.40.H- Solar cells (photovoltaics)

Statistical composition-structure-property correlation and glass-forming ability based on the full icosahedra in Cu–Zr metallic glasses

Z. D. Sha, Y. P. Feng, and Y. Li

Appl. Phys. Lett. 96, 061903 (2010); http://dx.doi.org/10.1063/1.3310278 (3 pages) | Cited 17 times

Online Publication Date: 8 February 2010

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Using the large-scale atomic/molecular massively parallel simulator, fraction of the Cu-centered 〈0,0,12,0〉 full icosahedra (fico) is obtained from a statistical analysis over a broad compositional range with high resolution in the Cu–Zr binary system. Weak but significant peaks are observed at certain compositions which coincide with good glass formers. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. In this regard, fico can be an indicator of glass-forming ability. Our work provides further understanding on the atomic structure of the Cu–Zr system and its effect on glass formation.
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61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation

Effects of additional Ce3+ doping on the luminescence of Li2SrSiO4:Eu2+ yellow phosphor

Tae-Gon Kim, Hyo-Sug Lee, Chun Che Lin, Taehyung Kim, Ru-Shi Liu, Ting-Shan Chan, and Seoung-Jae Im

Appl. Phys. Lett. 96, 061904 (2010); http://dx.doi.org/10.1063/1.3308486 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2010

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Additional Ce3+ doping improves the luminescence of Li2SrSiO4:Eu2+, a yellow phosphor for ultraviolet or blue light-emitting diodes. By examining the photoluminescence of Li2SrSiO4:Eu2+, Li2SrSiO4:Ce3+, and Li2SrSiO4:Ce3+,Eu2+, it was confirmed that the energy transfer from Ce3+ to Eu2+ ions contributes little to the enhanced luminescence of Li2SrSiO4:Ce3+,Eu2+. Alternatively, we suggested that Ce3+ ions could stabilize the Li vacancies, inhibit the oxidization of Eu2+ to Eu3+, and consequently increase emission intensity, based on the characterizations with decay time and synchrotron light source x-ray absorption measurements. The proposed argument was validated with first principle calculations of the defect formation energies.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
85.60.Jb Light-emitting devices

Optical and electro-optic anisotropy of epitaxial Ba0.7Sr0.3TiO3 thin films

D. Y. Wang, S. Li, H. L. W Chan, and C. L. Choy

Appl. Phys. Lett. 96, 061905 (2010); http://dx.doi.org/10.1063/1.3302453 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2010

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The anisotropic optical and electro-optic properties of ferroelectric Ba0.7Sr0.3TiO3 thin films, deposited on highly transparent single-crystal MgO (001), (011), and (111) substrates using pulsed laser deposition, were investigated. The experimental results show a strong correlation between optical, electro-optic properties, and the orientation of Ba0.7Sr0.3TiO3 thin films. The linear electro-optic coefficient rc of the (001), (011), and (111)-oriented Ba0.7Sr0.3TiO3 thin films are 99.1, 15.7, and 87.8 pm/V, respectively. Such a correlation may be attributed to the orientation dependent distribution and magnitude of spontaneous polarization.
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77.55.Px Epitaxial and superlattice films
78.66.Nk Insulators
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity

Identification of extremely radiative nature of AlN by time-resolved photoluminescence

T. Onuma, K. Hazu, A. Uedono, T. Sota, and S. F. Chichibu

Appl. Phys. Lett. 96, 061906 (2010); http://dx.doi.org/10.1063/1.3284653 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2010

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Extremely radiative nature of high-quality AlN single crystalline epilayers was identified by means of far ultraviolet time-resolved photoluminescence using a frequency-quadrupled femtosecond Al2O3:Ti laser. The gross radiative lifetimes of a free excitonic polariton emission as short as 10 ps at 7 K and 180 ps at 300 K were revealed, which are the shortest ever reported for bulk semiconductor materials.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
78.47.jd Time resolved luminescence
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Effect of Mg doping on enhancement of terahertz emission from InN with different lattice polarities

X. Q. Wang, G. Z. Zhao, Q. Zhang, Y. Ishitani, A. Yoshikawa, and B. Shen

Appl. Phys. Lett. 96, 061907 (2010); http://dx.doi.org/10.1063/1.3303983 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2010

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Effect of Mg doping on terahertz (THz) emission from InN with different lattice polarities was studied. Strong enhancement of THz emission was observed from InN with appropriate Mg-concentrations (1018 cm−3), which is independent of lattice polarity. The buried p-type layers show stronger THz emission than the n-type ones. The dominant mechanism for THz emission was found to be photo-Dember effect and the emission intensity was inversely proportional to the conductivity, which is beneficial to investigate THz emission from InN since the conductivity can be more accurately measured than the carrier concentration and mobility due to the electron accumulation on surface.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.sd Impurity concentration
73.61.Ey III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

The influence of Ni additions on the relative stability of η and η′ Cu6Sn5

U. Schwingenschlögl, C. Di Paola, K. Nogita, and C. M. Gourlay

Appl. Phys. Lett. 96, 061908 (2010); http://dx.doi.org/10.1063/1.3310019 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2010

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We investigate how 5 at. % Ni influences the relative stability of η and η′ Cu6Sn5. Synchrotron x-ray diffraction shows that, while Cu6Sn5 exists as η′ at 25 and 150 °C and transforms to η on heating to 200 °C, Cu5.5Ni0.5Sn5 is best fit to η throughout 25–200 °C. Our first principles calculations predict that η′ is stable at T = 0 K in both Cu6Sn5 and Cu5.5Ni0.5Sn5, but that the energy difference is substantially reduced from 1.21 to 0.90 eV per 22 atom cell by the Ni addition. This effect is attributed to Ni developing distinct bonding to both Cu and Sn in the η phase.
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61.66.Dk Alloys

Optical band-gap determination of nanostructured WO3 film

P. P. González-Borrero, F. Sato, A. N. Medina, M. L. Baesso, A. C. Bento, G. Baldissera, C. Persson, G. A. Niklasson, C. G. Granqvist, and A. Ferreira da Silva

Appl. Phys. Lett. 96, 061909 (2010); http://dx.doi.org/10.1063/1.3313945 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2010

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The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green’s function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.66.-w Optical properties of specific thin films
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.-b Electron density of states and band structure of crystalline solids
07.60.Rd Visible and ultraviolet spectrometers
42.25.Bs Wave propagation, transmission and absorption

Monte Carlo modeling of the fiber curliness effect on percolation of conductive composites

H. M. Ma, X.-L. Gao, and T. Benson Tolle

Appl. Phys. Lett. 96, 061910 (2010); http://dx.doi.org/10.1063/1.3309590 (3 pages) | Cited 7 times

Online Publication Date: 10 February 2010

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A three-dimensional (3D) Monte Carlo model is developed to study the fiber curliness effect on the percolation threshold of a composite filled with electrically conductive curved fibers. These fibers are simulated as zigzag-shaped fibers that are randomly positioned in the composite, forming a 3D random network. The simulation results show that the fiber curliness can significantly affect the percolation threshold: the more curved the fibers, the higher the threshold. The results also reveal an exponential relationship between the threshold and the fiber aspect ratio: the higher the aspect ratio, the lower the threshold. These predicted trends agree well with existing experimental and simulation results based on straight fibers or curved fibers with simpler shapes.
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64.60.ah Percolation
61.43.Bn Structural modeling: serial-addition models, computer simulation

Spontaneous and electric field induced quadratic optical nonlinearity in ferroelectric crystals AgNa(NO2)2

A. V. Kityk, R. Czaplicki, A. Klöpperpieper, A. S. Andrushchak, and B. Sahraoui

Appl. Phys. Lett. 96, 061911 (2010); http://dx.doi.org/10.1063/1.3315941 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2010

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We demonstrate the second harmonic generation (SHG) in ferroelectric AgNa(NO2)2 crystals resulting from the spontaneous and electric field induced polarizations. Relatively high effective nonlinear optic (NLO) susceptibility is combined in this crystals with the existing several phase matching geometries of NLO interaction. Anomalously large response of SHG with respect to an applied electric field has been found in the vicinity of the paraelectric-to-ferroelectric phase transition. The behavior of NLO properties in the ferroelectric phase and especially in the region of the Curie point is discussed within the phenomenological theory.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
77.80.B- Phase transitions and Curie point
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
42.70.Mp Nonlinear optical crystals

Molecular beam epitaxy growth and optical properties of AlN nanowires

O. Landré, V. Fellmann, P. Jaffrennou, C. Bougerol, H. Renevier, A. Cros, and B. Daudin

Appl. Phys. Lett. 96, 061912 (2010); http://dx.doi.org/10.1063/1.3315943 (3 pages) | Cited 8 times

Online Publication Date: 11 February 2010

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Growth of catalyst-free AlN nanowires has been achieved by plasma-assisted molecular beam epitaxy on SiO2/Si (100), by taking advantage of Volmer–Weber growth mode of AlN on amorphous SiO2. Using a combination of high resolution transmission electron microscopy and Raman spectroscopy, it is found that AlN nanowires are completely relaxed, which has been assigned to the compliant character of SiO2. Elastic strain relaxation of AlN nanowires has been further confirmed by photoluminescence experiments, showing in addition that spectra are dominated by near-band edge emission.
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81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Optimization towards high density quantum dots for intermediate band solar cells grown by molecular beam epitaxy

D. Zhou, G. Sharma, S. F. Thomassen, T. W. Reenaas, and B. O. Fimland

Appl. Phys. Lett. 96, 061913 (2010); http://dx.doi.org/10.1063/1.3313938 (3 pages) | Cited 17 times

Online Publication Date: 12 February 2010

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We report high density quantum dots (QDs) formation with optimized growth temperature and V/III ratio. At lower growth temperature, QD density is increased, due to smaller surface migration length of In adatoms. With higher V/III, the QD density is higher but it results in large clusters formation and decreases the QD uniformity. The QD solar cell was fabricated and examined. An extended spectral response in contrast to the GaAs reference cell was presented but the external quantum efficiency at energies higher than GaAs band gap is reduced, resulting from the degradation for the emitter above the strained QD layers.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.H- Solar cells (photovoltaics)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
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