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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Screw-rotation twinning through helical movement of triple-partials

Pan Liu, Kui Du, Jianxin Zhang, Lihua Wang, Yonghai Yue, Evan Ma, Yuefei Zhang, Ze Zhang, Mingwei Chen, and Xiaodong Han

Appl. Phys. Lett. 101, 121901 (2012); http://dx.doi.org/10.1063/1.4752747 (5 pages)

Online Publication Date: 17 September 2012

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By in situ uniaxial-tensile tests with dynamic and atomic scale observation, we report the quantitative investigation of strain-induced deformation-twinning process through incoherent twin boundary propagation in nanocrystalline Au. The consecutive and quantitative strain maps revealed that a strong compressive strain, up to 5.8%, was formed. A screw-rotation twinning mechanism by consecutive and collective screw-rotations of triple-partials along a [111] screw-axis is proposed. This twin generates a macro-strain of 0.707, same as the conventional shear twins, but in a helical manner.
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61.72.Mm Grain and twin boundaries
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects

Hsu-Cheng Hsu, Geng-Ming Hsu, Yu-shiung Lai, Zhe Chuan Feng, Shuo-Yen Tseng, Anders Lundskog, Urban Forsberg, Erik Janzén, Kuei-Hsien Chen, and Li-Chyong Chen

Appl. Phys. Lett. 101, 121902 (2012); http://dx.doi.org/10.1063/1.4753798 (5 pages)

Online Publication Date: 17 September 2012

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Raman scattering of individual aluminum nitride (AlN) nanowires is investigated systematically. The axial direction of single nanowire can be rapidly verified by polarized Raman scattering. The angular dependencies of E2(high) mode show strongly anisotropic behavior in smaller nanowires, which results from optical antenna effect. Raman enhancement (RE) per unit volume of E2(high) increases with decreasing diameter of nanowires. Compared to the thin film, ∼200-fold increase of RE is observed in AlN nanowires having diameter less than 50 nm, which is far beyond the quantum confinement regime. Such a large RE can be attributed to the effects of resonant cavity and stimulated Raman scattering.
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81.05.Ea III-V semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
78.30.Fs III-V and II-VI semiconductors

Control of growth and the processes of energy transfer from CdSe quantum dots for Nd3+ ions in a vitreous system: Thermal annealing time

N. O. Dantas, E. O. Serqueira, V. Anjos, and M. J. V. Bell

Appl. Phys. Lett. 101, 121903 (2012); http://dx.doi.org/10.1063/1.4753800 (4 pages)

Online Publication Date: 17 September 2012

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The authors report clear evidence of radiative and nonradiative energy transfer from CdSe quantum dots to Nd3+ ions in a glass system synthesized by melting method. An efficient control of energy transfer can be obtained by controlling the mean radius of the CdSe quantum dots. Increase of about 100% of the near infrared Nd3+ emission (4F3/2 → 4I9/2) was observed as a function of thermal annealing time.
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78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
81.05.Kf Glasses (including metallic glasses)
81.07.Ta Quantum dots
81.40.Gh Other heat and thermomechanical treatments

Photoluminescence dynamics in solid formulations of colloidal PbSe quantum dots: Three-dimensional versus two-dimensional films

Rafael Quintero-Torres, Charles A. Foell, Jothirmayanantham Pichaandi, Frank C. J. M. van Veggel, and Jeff F. Young

Appl. Phys. Lett. 101, 121904 (2012); http://dx.doi.org/10.1063/1.4752737 (4 pages)

Online Publication Date: 18 September 2012

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Time-resolved photoluminescence spectroscopy is used to compare decay dynamics of colloidal PbSe quantum dots as (i) dilute dispersions in hexanes, (ii) thick, dense, emulsive films, and (iii) sub-monolayer films on silicon surfaces. Accounting for the effect of each dielectric environment on exciton radiative decay rates, we deduce the non-radiative decay rate of excitons increases going from solution to thick films by ≈6 fold and to sub-monolayer films by ≈7–16 fold. This is attributed to surface passivation degradation due to a lack of mobile ligands when the particles are taken out of solution.
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78.55.Hx Other solid inorganic materials
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
68.18.-g Langmuir-Blodgett films on liquids
73.21.La Quantum dots
71.35.-y Excitons and related phenomena

Intense upconversion luminescence and origin study in Tm3+/Yb3+ codoped calcium scandate

Jing Li, Jiahua Zhang, Zhendong Hao, Xia Zhang, Jihong Zhao, and Yongshi Luo

Appl. Phys. Lett. 101, 121905 (2012); http://dx.doi.org/10.1063/1.4753802 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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Doping concentration optimized CaSc2O4:0.004Tm3+/0.1Yb3+ shows stronger upconversion luminescence (UCL) than doping concentration also optimized typical oxide upconverting phosphor Y2O3:0.004Tm3+/0.1Yb3+ upon 980 nm laser diode pump. The two-step up converted 3H4 → 3H6 near infrared emission peaked around 800 nm and the three-step up converted 1G4 → 3H6 blue emission around 480 nm of Tm3+ is enhanced by a factor of 3.5 and 2.2, respectively. On analyzing the 2F5/2 → 2F7/2 emission intensities and decay curves of Yb3+ in the two hosts, we reveal that Yb3+ in CaSc2O4 exhibits both a larger absorption cross section at 980 nm and Yb3+ → Tm3+ first step energy transfer coefficient (9.29 × 10−17 cm3 s−1) than that (2.87 × 10−17 cm3 s−1) in Y2O3, indicating that CaSc2O4 is an excellent host for achieving very intense UCL in Tm3+/Yb3+ codoped oxide upconverting materials.
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78.55.Hx Other solid inorganic materials
61.72.sd Impurity concentration

Signature of viscous flow units in apparent elastic regime of metallic glasses

Z. Wang, P. Wen, L. S. Huo, H. Y. Bai, and W. H. Wang

Appl. Phys. Lett. 101, 121906 (2012); http://dx.doi.org/10.1063/1.4753813 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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We characterize and identify the flow units in two typical metallic glasses (MGs), which have markedly different β-relaxation behaviors and mechanical properties. The viscoelastic hysteresis loops are found in the cyclic deformation in the nominal elastic regime of the metallic glasses. We show that the hysteresis loops are related to the activation of the flow units in metallic glasses, and a model is proposed to describe the flow units. We demonstrate that the flow units are both the deformation units of the anelastic and plastic deformation behaviors and the structural origin of the β-relaxation in metallic glasses.
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81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
61.43.Fs Glasses
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Simulating the interface morphology of silver thick film contacts on n-type Si-(100) and Si-(111)

Stefan Kontermann, Alexander Ruf, Ralf Preu, and Gerhard Willeke

Appl. Phys. Lett. 101, 121907 (2012); http://dx.doi.org/10.1063/1.4752228 (4 pages)

Online Publication Date: 18 September 2012

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Silver crystals at the interface of silver thick film contacts carry the current across such contacts and therefore govern the contact resistance. The crystals grow nearly exclusively in pits in the silicon surface, which form during contact formation before the crystals and hence determine the amount and size of crystals. We simulate the mechanism of pit formation at such contact interfaces by using a model based on the removal probability of silicon surface atoms. The model leads to good agreement between experimentally observed and simulated pits. The results enable the prediction of pit formation in dependence of contact processing parameters.
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68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts

Phase transformation and nanograin refinement of silicon by processing through high-pressure torsion

Yoshifumi Ikoma, Kazunori Hayano, Kaveh Edalati, Katsuhiko Saito, Qixin Guo, and Zenji Horita

Appl. Phys. Lett. 101, 121908 (2012); http://dx.doi.org/10.1063/1.4754574 (4 pages) | Cited 3 times

Online Publication Date: 19 September 2012

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Si(100) wafers were subjected to severe plastic deformation under a pressure of 24 GPa using high-pressure torsion (HPT). Si wafers were plastically deformed at room temperature. HPT-processed samples were composed of metastable body centered cubic Si-III and rhombohedral Si-XII phases in the initial cubic diamond Si-I. The volume fraction of metastable phases increased with increasing plastic strain. Successive annealing at 873 K led to the reverse transformation of metastable phases. A broad photoluminescence peak centered at about 650 nm appears due to the reverse transformation of Si-III/Si-XII nanograins and the reduction of number of defects in Si-I nanograins.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
64.70.kg Semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.55.Ap Elemental semiconductors

ZnTe/GaSb distributed Bragg reflectors grown on GaSb for mid-wave infrared optoelectronic applications

J. Fan, X. Liu, J. K. Furdyna, and Y.-H. Zhang

Appl. Phys. Lett. 101, 121909 (2012); http://dx.doi.org/10.1063/1.4753819 (3 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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ZnTe/GaSb distributed Bragg reflectors (DBRs) are proposed and demonstrated for mid-wave infrared (2–5 μm) optoelectronic applications. The reflectance spectra of ZnTe/GaSb DBRs are simulated using the transmission matrix method, indicating a peak reflectance higher than 99.9% for a DBR of 10 quarter-wavelength (λ/4) pairs. A series of ZnTe/GaSb DBR structures have been successfully grown on GaSb (001) substrates using molecular beam epitaxy. X-ray diffraction results reveal smooth interfaces, uniform thicknesses, and low defect density. The DBR sample of seven λ/4 pairs has a peak reflectance as high as 99.0% centered at 2.5 μm with a 480-nm wide stopband.
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42.82.-m Integrated optics
78.30.Fs III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
85.60.-q Optoelectronic devices
42.79.Bh Lenses, prisms and mirrors

Phase-partitioning and site-substitution patterns of molybdenum in a model Ni-Al-Mo superalloy: An atom-probe tomographic and first-principles study

Yiyou Tu, Zugang Mao, and David N. Seidman

Appl. Phys. Lett. 101, 121910 (2012); http://dx.doi.org/10.1063/1.4753929 (4 pages)

Online Publication Date: 19 September 2012

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Atom-probe tomography (APT) and first-principles calculations are employed to investigate the partitioning of Mo in the γ(f.c.c.)-and γ′(L12)-phases in a model Ni-6.5Al-9.9Mo at. % superalloy. Mo is experimentally observed to partition preferentially to the γ(f.c.c.)-matrix, which is consistent with the smaller value of the γ(f.c.c.)-matrix substitutional formation-energy, with a driving force of 0.707 eV for partitioning as determined by first-principles calculations. APT measurements of the γ′(L12)-precipitate-phase composition and Al-, Mo-centered partial radial distribution functions indicate that Mo occupies the Al sublattice sites of the Ni3Al(L12) phase. The preferential site-substitution of Mo at Al sublattice sites is confirmed by first-principles calculations.
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61.66.Dk Alloys
71.15.-m Methods of electronic structure calculations
71.20.Gj Other metals and alloys
81.30.Mh Solid-phase precipitation

Delamination of strained multilayered nanowires

Jérôme Colin, Alain Cimetière, and Jean Grilhé

Appl. Phys. Lett. 101, 121911 (2012); http://dx.doi.org/10.1063/1.4753982 (3 pages)

Online Publication Date: 19 September 2012

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The mechanical stability of a strained multilayered nanowire has been investigated qualitatively from an energy variation calculation. Depending on the strain and Dupré energy of the interfaces, it is found that the layers may delaminate. The expression of the critical radius of the coherent zone below which the layers may delaminate has been determined, and a stability diagram is presented for the nanowire.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Phonon dynamics in CuxBi2Se3 (x = 0, 0.1, 0.125) and Bi2Se2 crystals studied using femtosecond spectroscopy

H.-J. Chen, K. H. Wu, C. W. Luo, T. M. Uen, J. Y. Juang, J.-Y. Lin, T. Kobayashi, H.-D. Yang, R. Sankar, F. C. Chou, H. Berger, and J. M. Liu

Appl. Phys. Lett. 101, 121912 (2012); http://dx.doi.org/10.1063/1.4754005 (5 pages)

Online Publication Date: 19 September 2012

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Phonon dynamics in Bi, Bi2Se2, and CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals was investigated using femtosecond pump-probe spectroscopy. Two damped oscillations in measured transient reflectivity changes were observed, respectively, attributed to coherent optical and acoustic phonons. The frequency shift of the phonon modes in Bi-rich Bi2Se2 crystals indicates the intercalation of the additional Bi atoms into the Bi2Se3 matrix and formation of the Bi2 layer between the quintuple layers (QLs). The deformation of QLs in CuxBi2Se3 crystals was also found. These phonon dynamics results suggest that Cu atoms in CuxBi2Se3 crystals are predominantly intercalated between pair of QLs.
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63.20.-e Phonons in crystal lattices
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.47.J- Ultrafast spectroscopy (<1 psec)

Competition between the crystal field and the exchange field in Er3+ doped NdMnO3

Fang Hong, Zhenxiang Cheng, Xiaolin Wang, and Shixue Dou

Appl. Phys. Lett. 101, 121913 (2012); http://dx.doi.org/10.1063/1.4754613 (5 pages) | Cited 1 time

Online Publication Date: 20 September 2012

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A careful investigation of specific heat shows that the ground state splitting of Nd3+ has been modified by the Er3+ doping, as it shows a nonlinear dependence on the Er3+ doping rate, due to the competition between the crystal field and the exchange field. This competition could be further confirmed by the anomalies in the magnetic entropy and the ground state splitting found in Nd0.9Er0.1MnO3. On the contrary, the ground state splitting of Er3+ has a linear dependence on the doping rate, indicating its stronger dependence on the crystal field rather than the exchange field.
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75.10.Dg Crystal-field theory and spin Hamiltonians
65.40.gd Entropy
65.40.Ba Heat capacity

Reversible transition of deformation mode by structural rejuvenation and relaxation in bulk metallic glass

Fanqiang Meng, Koichi Tsuchiya, Seiichiro, II, and Yoshihiko Yokoyama

Appl. Phys. Lett. 101, 121914 (2012); http://dx.doi.org/10.1063/1.4753998 (3 pages)

Online Publication Date: 20 September 2012

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A transition of the deformation mode from heterogeneous, localized deformation to homogeneous deformation was observed in Zr50Cu40Al10 bulk metallic glass (BMG) by giant straining using the high-pressure torsion (HPT) method. The transition is accompanied by a pronounced decrease in hardness and elastic modulus as measured by nanoindentation. Annealing of the deformed BMG resulted in the restoration of the localized deformation, hardness, and elastic modulus; thus, the transition is reversible. The observed reversible transition can be attributed to a change in the local atomic environment in the rejuvenated volume and the relaxed one.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
62.20.F- Deformation and plasticity

Nanofracture in graphene under complex mechanical stresses

Bin Zhang, Lanjv Mei, and Haifeng Xiao

Appl. Phys. Lett. 101, 121915 (2012); http://dx.doi.org/10.1063/1.4754115 (5 pages)

Online Publication Date: 20 September 2012

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Nanoscale fracture of graphene under coupled in-plane opening and shear mechanical loading is investigated by extensive molecular dynamics simulations. Under opening-dominant loading, zigzag edge cracks grow self-similarly. Otherwise, complex stresses concentrated around crack-tip can manipulate the direction of crack initiation changing by 30° (or multiples of 30°). Toughness determined by obtained critical stress intensity factors 2.63–3.38 nN Å−3/2 demonstrates that graphene is intrinsically brittle opposite to its exceptional high strength at room temperature. Torn zigzag edges are more energetically and kinetically favorable. Cracking of graphene has dependences on local stresses, edge energy, and dynamic effects, which provides a possible way to regulate graphene edges.
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62.25.Mn Fracture/brittleness
61.48.Gh Structure of graphene
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.mt Cracks
62.23.Kn Nanosheets

Effective thermal conductivity of graphene-based composites

Ke Chu, Cheng-chang Jia, and Wen-sheng Li

Appl. Phys. Lett. 101, 121916 (2012); http://dx.doi.org/10.1063/1.4754120 (3 pages) | Cited 4 times

Online Publication Date: 20 September 2012

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An analytical model for the effective thermal conductivity in graphene nanoplates (GNPs) based composites is presented. The theoretical formula gives good agreements with the existing experimental data available in the literature. In particular, the present model well shows the nonlinear dependence of effective thermal conductivity enhancement ((Ke − Km)/Km) on the GNP volume fraction (f), and it yields a power law (Ke − Km)/Km ∼ f α (1/2 < α < 2) (1/2 < α < 2). Some interesting findings in thermal conductivity behavior of GNP composites based on the present model are also discussed.
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66.70.Df Metals, alloys, and semiconductors
72.80.Vp Electronic transport in graphene

Correlating local structure with inhomogeneous elastic deformation in a metallic glass

J. Ding, Y. Q. Cheng, and E. Ma

Appl. Phys. Lett. 101, 121917 (2012); http://dx.doi.org/10.1063/1.4754121 (4 pages) | Cited 2 times

Online Publication Date: 20 September 2012

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The elastic response of metallic glasses (MGs) is inhomogeneous, due to the wide variation of local structural arrangements. Here, we present molecular dynamics simulations on a one-million-atoms sample of a Cu64Zr36 model MG, correlating the atomic strain and non-affine displacement with short-range order. Cu atoms in full icosahedra experience less atomic relaxation and behave stiffer, while the rest of Cu atoms contribute more to anelasticity on the timescale of simulation.
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61.43.Fs Glasses
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
61.43.Bn Structural modeling: serial-addition models, computer simulation

Aluminium doped Zn1−xMgxO—A transparent conducting oxide with tunable optical and electrical properties

K. Fleischer, E. Arca, C. Smith, and I. V. Shvets

Appl. Phys. Lett. 101, 121918 (2012); http://dx.doi.org/10.1063/1.4753937 (4 pages)

Online Publication Date: 21 September 2012

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A ternary mixed oxide Zn1−xMgxO has been doped with aluminium to create a range of transparent conducting oxides with tunable refractive index as well as work function. Conductive material was synthesised up to a magnesium concentration of x = 0.45, although the conductivity is reduced compared to standard ZnO:Al. The changes in band gap, work function, and conductivity have been attributed to a modified band structure and energetic position of the aluminium induced donor state.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
72.80.Jc Other crystalline inorganic semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

Quantum-confined stark effect in localized luminescent centers within InGaN/GaN quantum-well based light emitting diodes

Suman De, Arunasish Layek, Sukanya Bhattacharya, Dibyendu Kumar Das, Abdul Kadir, Arnab Bhattacharya, Subhabrata Dhar, and Arindam Chowdhury

Appl. Phys. Lett. 101, 121919 (2012); http://dx.doi.org/10.1063/1.4754079 (5 pages) | Cited 2 times

Online Publication Date: 21 September 2012

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The nature of the polarization-field in disorder induced nanoscale potential fluctuations (radiative traps) within (In,Ga)N based quantum-well (QW) heterostructures remains ambiguous. Spectrally resolved photoluminescence microscopy has been utilized to probe the local polarization field by monitoring the extent of quantum-confined Stark effect (QCSE) in radiative trap centers spontaneously formed within an (In,Ga)N QW based light emitting diode. Interestingly, two distinct categories of nanoscale radiative domains, which arise from indium compositional and interface-morphology related fluctuations of the active layers, are found to have very different degree of built-in polarization fields. Screening of QCSE in indium-rich emission centers results in blue-shift of transition energies by up to 400 meV, significantly higher than that reported previously for group III-nitride based semiconductor heterostructures. A lack of correlation between the extent of QCSE and local indium mole-fractions suggests that size, shape, and strain of individual localization centers play a crucial role in modulating the local polarization field.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Following Ostwald ripening in nanoalloys by high-resolution imaging with single-atom chemical sensitivity

D. Alloyeau, T. Oikawa, J. Nelayah, G. Wang, and C. Ricolleau

Appl. Phys. Lett. 101, 121920 (2012); http://dx.doi.org/10.1063/1.4754111 (4 pages)

Online Publication Date: 21 September 2012

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Several studies have shown that substantial compositional changes can occur during the coarsening of bimetallic nanoparticles (CoPt, AuPd). To explain this phenomenon that could dramatically impacts all the technologically relevant properties of nanoalloys, we have exploited the sensitivity of the latest generation of electron microscope to prove that during the beam-induced coarsening of CoPt nanoparticles, the dynamic of atom exchanges between the particles is different for Co and Pt. By distinguishing the chemical nature of individual atoms of Co and Pt, while they are diffusing on a carbon film, we have clearly shown that Co atoms have a higher mobility than Pt atoms because of their higher evaporation rate from the particles. These atomic-scale observations bring the experimental evidence on the origin of the compositional changes in nanoalloys induced by Ostwald ripening mechanisms.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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