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9 Feb 2009

Volume 94, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 94, 062105 (2009); http://dx.doi.org/10.1063/1.3079078 (3 pages)

Ikai Lo, Chia-Ho Hsieh, Yu-Chi Hsu, Wen-Yuan Pang, and Ming-Chi Chou
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Multiple deformation mechanisms of Ti–22.4Nb–0.73Ta–2.0Zr–1.34O alloy

Y. Yang, G. P. Li, G. M. Cheng, Y. L. Li, and K. Yang

Appl. Phys. Lett. 94, 061901 (2009); http://dx.doi.org/10.1063/1.3078521 (3 pages) | Cited 8 times

Online Publication Date: 9 February 2009

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Ti–22.4Nb–0.73Ta–2.0Zr–1.34O (at. %) alloy after cold compression to ∼ 5.2% strain was investigated. The alloy exhibited multiple plastic deformation mechanisms, including the stress-induced α″ martensitic (SIM α″) and ω phase transformations, 1/2〈111〉 dislocations slipping on the {112}β planes as well as {332}〈113〉β and {112}〈111〉β twinning, which have not previously been reported to coexist in a titanium alloy. It was also found that β phase with the {200} planes vertical to the compression direction was almost completely consumed away by a β→SIM α″ transformation, and a (100) texture of SIM α″ formed.
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81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
62.20.fq Plasticity and superplasticity
61.72.Mm Grain and twin boundaries

Giant optical anisotropy in an infinite-layer iron oxide SrFeO2: An ab initio investigation

Sheng Ju and Tian-Yi Cai

Appl. Phys. Lett. 94, 061902 (2009); http://dx.doi.org/10.1063/1.3079402 (3 pages) | Cited 5 times

Online Publication Date: 9 February 2009

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Based on density functional theory, we study the electronic structure, magnetic structure, and linear optical response in SrFeO2. For its infinite-layer structure with iron square-planar coordination, the band structure, magnetic exchange interaction, and linear dielectric function show significant anisotropic behavior. In particular, giant optical anisotropy is found. The absorption edge differs by 0.5 eV between xx and zz components, and the low frequency dielectric constant is found to be 4.26 and 5.11 for εxx and εzz, respectively. These results provide evidence of potential application of this unique structure.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
77.22.Ch Permittivity (dielectric function)
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Achieving control of in-plane elastic waves

M. Brun, S. Guenneau, and A. B. Movchan

Appl. Phys. Lett. 94, 061903 (2009); http://dx.doi.org/10.1063/1.3068491 (3 pages) | Cited 37 times

Online Publication Date: 9 February 2009

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We derive the elastic properties of a cylindrical cloak for in-plane coupled shear and pressure waves. The cloak is characterized by a rank 4 elasticity tensor with spatially varying entries, which are deduced from a geometric transform. Remarkably, the Navier equations retain their form under this transform, which is generally untrue [ G. W. Milton et al., N. J. Phys. 8, 248 (2006) ]. The validity of our approach is confirmed by comparison of the analytic Green’s function in homogeneous isotropic elastic space against full-wave finite element computations in a heterogeneous anisotropic elastic region surrounded by perfectly matched layers.
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46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
46.25.-y Static elasticity
02.70.Dh Finite-element and Galerkin methods
02.30.-f Function theory, analysis

Investigation of crystallization behaviors of nitrogen-doped Ge2Sb2Te5 films by thermomechanical characteristics

Il-Mok Park, Tae-Youl Yang, Sug Woo Jung, Young Kuk Kim, Hideki Horii, and Young-Chang Joo

Appl. Phys. Lett. 94, 061904 (2009); http://dx.doi.org/10.1063/1.3078820 (3 pages) | Cited 4 times

Online Publication Date: 10 February 2009

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It has been demonstrated that the crystallization behaviors of undoped and N-doped Ge2Sb2Te5 (GST) films can be evaluated by studying the thermomechanical behavior of the films. The crystallization temperatures (Tc) for undoped and 15 at. % N-doped GST films were determined to be about 150 and 250 °C, respectively. The activation energies for crystallization (Ea) were calculated to be 2.30, 3.29, and 3.72 eV for undoped, 10 at. % N-doped, and 15 at. % N-doped GST, respectively, by the Kissinger plot. For 15 at. % N-doped film, both the glass transition temperature (Tg) and Tc were determined to be about 150 °C, as determined by the thermomechanical characteristics.
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64.70.kg Semiconductors
81.40.Gh Other heat and thermomechanical treatments
68.55.ag Semiconductors

Near-infrared quantum cutting in YPO4:Yb3+, Tm3+ via cooperative energy transfer

Lechun Xie, Yuhua Wang, and Huijuan Zhang

Appl. Phys. Lett. 94, 061905 (2009); http://dx.doi.org/10.1063/1.3078823 (3 pages) | Cited 37 times

Online Publication Date: 10 February 2009

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The experimental evidences of the cooperative energy transfer from Tm3+ to Yb3+ have been presented by the photoluminescence properties of YPO4:Yb3+, Tm3+, and the decay lifetime curves of the 1G4 emission of Tm3+. Near-infrared quantum cutting involving the 2F5/2→2F7/2 emission of Yb3+ (about 970–1010 nm) is achieved upon the excitation of 1G4 energy level of Tm3+ at 474 nm. Quantum efficiency related to Yb3+ concentration is calculated, and the maximum efficiency reaches 172.8%. Because the energy of Yb3+ transition is matched with the band gap of the crystalline Si, the phosphors could be applied potentially in silicon-based solar cells.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
84.60.Jt Photoelectric conversion
78.30.Am Elemental semiconductors and insulators

Enhanced luminescence through ion-doping-induced higher energy phonons in GdTaO4:Eu3+ phosphor

Bo Liu, Mu Gu, Xiaolin Liu, Kun Han, Shiming Huang, Chen Ni, Guobin Zhang, and Zeming Qi

Appl. Phys. Lett. 94, 061906 (2009); http://dx.doi.org/10.1063/1.3079413 (3 pages) | Cited 6 times

Online Publication Date: 10 February 2009

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The photoluminescence enhancement effect of Li-, Zn-, or Al-doped GdTaO4:Eu3+ is investigated at 20 and 295 K. The underlying reason of luminescence enhancement by ion doping is revealed, and a mechanism of the enhancement based on the temperature effect is proposed. It can be safely concluded that the photoluminescence enhancement effect originates from temperature enhancement effect, which can be further strengthened by ion-doping-induced higher energy phonons, which are demonstrated by infrared transmittance spectra. This can reasonably explain why the photoluminescence is remarkably enhanced by ion-doping in GdTaO4:Eu3+ phosphor at 295 K rather than at 20 K.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
78.30.Hv Other nonmetallic inorganics

Pressure induced phase separation in optimally doped bilayer manganites

Lorenzo Malavasi, Maria Baldini, Ilaria Zardo, Michael Hanfland, and Paolo Postorino

Appl. Phys. Lett. 94, 061907 (2009); http://dx.doi.org/10.1063/1.3077149 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2009

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In this paper, we give a direct experimental evidence of the long hypothesized phase separation scenario in strongly correlated manganite-based systems. High resolution, high-pressure synchrotron x-ray diffraction measurements on La1.4Sr1.6Mn2O7 as a function of temperature reveal the instability with P of the ferromagnetic phase leading, above a threshold P, to a phase separation between two phases with different orbital occupancies.
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71.27.+a Strongly correlated electron systems; heavy fermions
75.50.Dd Nonmetallic ferromagnetic materials

Lattice location and short range ordering of doping ions in RbTiOPO4

Joan J. Carvajal, Gianluca Ciatto, Alexandra Peña, Maria Cinta Pujol, Josefina Gavaldà, Francesc Díaz, and Magdalena Aguiló

Appl. Phys. Lett. 94, 061908 (2009); http://dx.doi.org/10.1063/1.3080656 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2009

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By using extended x-ray absorption fine structure spectroscopy, we demonstrate that Yb3+ ions in RbTiOPO4 and RbTi1−xNbxOPO4 crystals occupy titanium sites. By comparing these results with optical spectroscopic data and the structural location of Nb5+ codopants, we concluded that Yb3+ is located in Ti(2) positions in RbTi1−xNbxOPO4 crystals. Short range ordering between Yb3+ and Nb5+ rules electrical and optical properties of these nonlinear optical materials.
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61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra
66.30.H- Self-diffusion and ionic conduction in nonmetals
78.30.Hv Other nonmetallic inorganics

Effect of doping on the amorphous to microcrystalline transition in a hydrogenated amorphous silicon under hydrogen plasma treatment

A. Hadjadj, N. Pham, P. Roca i Cabarrocas, and O. Jbara

Appl. Phys. Lett. 94, 061909 (2009); http://dx.doi.org/10.1063/1.3080661 (3 pages) | Cited 6 times

Online Publication Date: 10 February 2009

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Just after their deposition, we have exposed intrinsic and doped hydrogenated amorphous silicon (a-Si:H) films to a hydrogen plasma. We have investigated, by in situ spectroscopic ellipsometry measurements, the structural evolution of the film during the amorphous to microcrystalline phase transition. To take into account the complex morphological development of microcrystalline silicon (μc-Si:H), the grown film is modeled by a graded layer with a linear index variation along the growth direction. By comparing the time evolution of the structural parameters of the deposited μc-Si:H layer, we have observed a particular behavior in the case of boron-doped a-Si:H. Despite a faster and deeper hydrogen diffusion from the beginning of hydrogen plasma exposure, and a later nucleation, a compact μc-Si:H layer is obtained. In the case of intrinsic and n-type a-Si:H the nucleation is faster and leads to a thin and very porous μc-Si:H layer. The particular behavior of the p-type material is attributed to the effects of boron, which, on the one hand, enhances the deposition of the Si precursors and, on the other hand, reduces the etching rate.
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64.70.kg Semiconductors
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si

Defect formation and annealing behaviors of fluorine-implanted GaN layers revealed by positron annihilation spectroscopy

M. J. Wang, L. Yuan, C. C. Cheng, C. D. Beling, and K. J. Chen

Appl. Phys. Lett. 94, 061910 (2009); http://dx.doi.org/10.1063/1.3081019 (3 pages) | Cited 4 times

Online Publication Date: 11 February 2009

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Defect formation and annealing behaviors of fluorine-implanted, unintentionally doped GaN layers were studied by positron annihilation spectroscopy (PAS). Single Ga vacancies (VGa) were identified as the main vacancy-type defects detected by PAS after fluorine implantation at 180 keV with a dose of 1×1015 cm−2. Implantation-induced VGa tend to aggregate and form vacancy clusters after postimplantation annealing in N2 ambient at 600 °C. Fluorine ions tend to form F-vacancy complexes quickly after thermal annealing, which is consistent with the proposed diffusion model that predicts the behaviors of fluorine in GaN.
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61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies
78.70.Bj Positron annihilation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
66.30.Lw Diffusion of other defects

Homogeneous deformation of Au-based metallic glass micropillars in compression at elevated temperatures

S. X. Song, Y. H. Lai, J. C. Huang, and T. G. Nieh

Appl. Phys. Lett. 94, 061911 (2009); http://dx.doi.org/10.1063/1.3081111 (3 pages) | Cited 7 times

Online Publication Date: 11 February 2009

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We performed high-temperature microcompression tests on micron-sized pillar samples fabricated from Au49Ag5.5Pd2.3Cu26.9Si16.3 metallic glass near the glass transition temperature to investigate the homogeneous deformation behavior. Samples were invariably deformed uniformly. The strength was observed to decrease with increasing temperature and decreasing strain rate. Plastic flow behavior can be described by a shear transition zone model. The activation energy and the size of the basic flow unit were both deduced and compared favorably with the theory.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.43.Fs Glasses
64.70.pe Metallic glasses
81.05.Kf Glasses (including metallic glasses)

Aluminum gettering of iron in silicon as a problem of the ternary phase diagram

D. Abdelbarey, V. Kveder, W. Schröter, and M. Seibt

Appl. Phys. Lett. 94, 061912 (2009); http://dx.doi.org/10.1063/1.3080666 (3 pages) | Cited 5 times

Online Publication Date: 11 February 2009

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Deep level transient spectroscopy is used to study the segregation of Fe from crystalline Si to an Al:Si liquid at its surface, which is the basic mechanism of aluminum gettering used in silicon photovoltaics. The measured segregation coefficient is smaller than estimates from the binary Fe:Si and Al:Fe phase diagrams. This apparent discrepancy originates from the ternary character of the system where the solubility of Fe in Si in equilibrium with the Al-doped α-FeSi2 has to be taken as a reference. Our data suggest that this solubility exceeds that in the binary Fe:Si system by two orders of magnitude.
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81.05.Cy Elemental semiconductors
81.30.Dz Phase diagrams of other materials
71.55.Cn Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
64.75.Bc Solubility

Correlation between average melting temperature and glass transition temperature in metallic glasses

Zhibin Lu and Jiangong Li

Appl. Phys. Lett. 94, 061913 (2009); http://dx.doi.org/10.1063/1.3081028 (2 pages) | Cited 4 times

Online Publication Date: 12 February 2009

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The correlation between average melting temperature (〈Tm〉) and glass transition temperature (Tg) in metallic glasses (MGs) is analyzed. A linear relationship, Tg = 0.385〈Tm〉, is observed. This correlation agrees with Egami’s suggestion [ Rep. Prog. Phys. 47, 1601 (1984) ]. The prediction of Tg from 〈Tm〉 through the relationship Tg = 0.385〈Tm〉 has been tested using experimental data obtained on a large number of MGs. This relationship can be used to predict and design MGs with a desired Tg.
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64.70.pe Metallic glasses
64.70.dj Melting of specific substances

Enlargement of omnidirectional photonic bandgap in porous silicon dielectric mirrors with a Gaussian profile refractive index

J. O. Estevez, J. Arriaga, A. Méndez Blas, and V. Agarwal

Appl. Phys. Lett. 94, 061914 (2009); http://dx.doi.org/10.1063/1.3081113 (3 pages) | Cited 10 times

Online Publication Date: 12 February 2009

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For enhancing the omnidirectional photonic bandgap (OPBG), we report the fabrication of two different configurations of one-dimensional, wavelength scalable dielectric multilayer structures of porous silicon, consisting of a unit cell formed by varying the refractive index of the multilayers according to the envelope of a Gaussian function. As compared to the already reported OPBG of 88 nm (in the complete angular range of 0° to 89°), an enhancement up to 204 nm (2.3 times) was observed on stacking, six different Gaussian structures (balanced mirror) with only 8 periods each. An unbalanced mirror structure, consisting of the six similar Gaussian structures as the balanced mirror, but having different sequence of periods, (configuration with 13, 6, 5, 5, 6, and 13 periods for each Gaussian, respectively) was seen to demonstrate the OPBG of 252 nm (enhanced by 2.86 times). The total optical thickness of both the structures was kept to be the same. The omnidirectional nature of the PBG was verified experimentally up to 68° and theoretically up to 89.9° angle of incidence.
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42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Electrochemical synthesis of CuIn(S,Se)2 alloys with graded composition for high efficiency solar cells

V. Izquierdo-Roca, X. Fontané, J. Álvarez-Garcia, L. Calvo-Barrio, A. Pérez-Rodríguez, J. R. Morante, C. M. Ruiz, E. Saucedo, and V. Bermúdez

Appl. Phys. Lett. 94, 061915 (2009); http://dx.doi.org/10.1063/1.3080654 (3 pages) | Cited 7 times

Online Publication Date: 12 February 2009

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This work reports the electrochemical synthesis and characterization of CuIn(S,Se)2 layers with graded composition from a S-rich surface region toward a Se-rich back region. The process includes the single step electrodeposition of a CuInSe2 precursor followed by a sulfurization step. Cross-sectional Raman microprobe measurements have allowed to characterize the complex graded structure of the layers. These data have been correlated with in-depth Auger electron spectroscopy and x-ray diffraction. Preliminary simulations of solar cells with different kinds of absorbers corroborate the potential of these complex graded layers for the development of low cost high efficiency devices.
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81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
78.30.Hv Other nonmetallic inorganics
68.55.ag Semiconductors
84.60.Jt Photoelectric conversion

Electronic structure and carrier dynamics in InAs/InP double-cap quantum dots

P. Miska, J. Even, X. Marie, and O. Dehaese

Appl. Phys. Lett. 94, 061916 (2009); http://dx.doi.org/10.1063/1.3078290 (3 pages) | Cited 1 time

Online Publication Date: 12 February 2009

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The carrier dynamics in InAs double-cap quantum dots (DC-QDs) grown on InP(113)B are investigated. The shape of these QDs can be controlled during the growth, yielding an emission wavelength of the system of about 1.55 μm at room temperature. The DC-QD dynamics is studied by time-resolved photoluminescence experiments at low temperature for various excitation densities. A simplified dynamic model is developed, yielding results consistent with experimental data. This analysis yields the determination of the Auger coefficients and the intradot relaxation time in this system.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
79.20.Fv Electron impact: Auger emission
73.63.Kv Quantum dots
78.47.jd Time resolved luminescence

Enhancement of transverse thermoelectric power factor in tilted Bi/Cu multilayer

Tsutomu Kanno, Satoshi Yotsuhashi, Akihiro Sakai, Kouhei Takahashi, and Hideaki Adachi

Appl. Phys. Lett. 94, 061917 (2009); http://dx.doi.org/10.1063/1.3081411 (3 pages) | Cited 4 times

Online Publication Date: 13 February 2009

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We investigated transverse thermoelectric response in tilted Bi/Cu multilayer. Estimation through an equivalent circuit model showed that transverse thermoelectric power factor (PF) reaching 155 μW/cm K2 is possible with optimum device parameters. Finite element analysis confirmed the validity of the estimation using tensorial representation, which implicitly assumes homogeneous anisotropy. The Bi/Cu multilayer was fabricated by pressure injection of molten Bi into a periodically slitted Cu block. The measurement of the fabricated sample verified an enhancement in transverse PF up to 50.1 μW/cm K2, which is approximately 1.5 times greater than the conventional PF of constituent Bi, 34 μW/cm K2.
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72.15.Jf Thermoelectric and thermomagnetic effects
68.65.Ac Multilayers

Optical properties and carrier dynamics of polarity controlled ZnO films grown on (0001) Al2O3 by Cr-compound intermediate layers

Bong-Joon Kwon, Yuanping Sun, Jean Soo Chung, Yong-Hoon Cho, J. S. Park, and T. Yao

Appl. Phys. Lett. 94, 061918 (2009); http://dx.doi.org/10.1063/1.3077154 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2009

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We report on optical properties and carrier dynamics of polarity controlled ZnO films grown on (0001) Al2O3 by Cr-compound intermediate layers using photoluminescence (PL), PL excitation, temperature dependent PL, and time-resolved PL techniques. At low temperature, a dominant donor-bound exciton peak at 3.36 eV has been observed in the O-polar ZnO grown on Cr2O3 intermediate layer, while a dominant acceptor-bound exciton peak at 3.32 eV has been observed in the Zn-polar ZnO grown on CrN intermediate layer. Native defects and/or impurities introduced by the Cr-compound intermediate layers play an important role in the optical properties of the polar ZnO samples.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.47.jd Time resolved luminescence
78.47.D- Time resolved spectroscopy (>1 psec)
71.35.-y Excitons and related phenomena

Optical transitions and multiphonon Raman scattering of Cu doped ZnO and MgZnO ceramics

Jesse Huso, John L. Morrison, James Mitchell, Erin Casey, Heather Hoeck, Chris Walker, Leah Bergman, W. M. Hlaing Oo, and M. D. McCluskey

Appl. Phys. Lett. 94, 061919 (2009); http://dx.doi.org/10.1063/1.3081628 (3 pages) | Cited 6 times

Online Publication Date: 13 February 2009

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Cu doped ZnO and MgZnO ceramics were created via a process of cold pressing and annealing, and their optical properties and phonon dynamics were studied. It was found that the ceramics exhibit infrared absorption peak energies at 5783 and 5822 cm−1, indicative of intraband transitions in a substitutional Cu ion of oxidation state +2. The UV photoluminescence (PL) intensity of the ceramics was found to weaken significantly relative to an undoped sample. The low PL intensity is discussed in terms of the CuxZn1−xO alloy system and the indirect bandgap of the CuO end member, as well as in terms of the nonradiative Cu centers. Due to the weak PL, up to ten LO multiphonons were observed in the Raman spectra, pointing to a strong polaron coupling. The resonance behavior of the highest intensity mode was found to exhibit outgoing resonance characteristics.
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78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
63.20.kg Phonon-phonon interactions
61.72.Cc Kinetics of defect formation and annealing

Fourier synthesis predicting onset of the initial instability during directional solidification

Zhijun Wang, Jincheng Wang, and Gencang Yang

Appl. Phys. Lett. 94, 061920 (2009); http://dx.doi.org/10.1063/1.3081634 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2009

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With the combination of the Fourier synthesis method and the time-dependent linear stability analysis, a simple model was developed to describe the dynamic evolution of the initial interface instability. By using this simple model, the early instability stage of a planar interface during directional solidification of binary alloys is predicted and how the interface microstructure generates from the background infinitesimal fluctuations is also revealed. The results from this model are in good agreement with those from quantitative phase field simulations and previous experiments.
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81.30.Fb Solidification

High-pressure induced phase transitions of Y2O3 and Y2O3:Eu3+

Lin Wang, Yuexiao Pan, Yang Ding, Wenge Yang, Wendy L. Mao, Stanislav V. Sinogeikin, Yue Meng, Guoyin Shen, and Ho-kwang Mao

Appl. Phys. Lett. 94, 061921 (2009); http://dx.doi.org/10.1063/1.3082082 (3 pages) | Cited 17 times

Online Publication Date: 13 February 2009

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We investigated high-pressure induced phase transitions in Y2O3 and Eu-doped Y2O3 (Y2O:Eu3+) using angular dispersive synchrotron x-ray diffraction, Raman spectroscopy, and photoluminescence (PL). With increasing pressure, we observed a series of phase transformations in Y2O3:Eu3+, which followed a structure sequence of cubic→monoclinic→hexagonal, while Y2O3 followed a sequence of cubic→hexagonal. During decompression, both hexagonal structured Y2O3 and Y2O3:Eu3+ transformed into monoclinic phases which were quenchable back to ambient pressure. Raman and PL measurements shed additional light on the different phase transition behavior in these two samples.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
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