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12 Mar 2007

Volume 90, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 113108 (2007); http://dx.doi.org/10.1063/1.2714186 (3 pages)

Samuel L. Mensah, Vijaya K. Kayastha, Ilia N. Ivanov, David B. Geohegan, and Yoke Khin Yap
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Core structures of the a-edge dislocation in InN

H. P. Lei, P. Ruterana, G. Nouet, X. Y. Jiang, and J. Chen

Appl. Phys. Lett. 90, 111901 (2007); http://dx.doi.org/10.1063/1.2712799 (3 pages) | Cited 6 times

Online Publication Date: 12 March 2007

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Stillinger-Weber potential parameters were optimized for InN by fitting to the bulk material properties and point defect energy in order to calculate the core structure of the a-edge dislocation. The initial displacement field is imposed in the perfect crystal according to isotropic linear elasticity theory, and then the system is relaxed to the minimum energy. The different origins of the displacement field generate three cores with four, eight or five/seven atoms. The calculated energies indicate that the four-atom core structure is the most stable for InN.
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61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Screening the built-in electric field in 4H silicon carbide stacking faults

S. Juillaguet, J. Camassel, M. Albrecht, and T. Chassagne

Appl. Phys. Lett. 90, 111902 (2007); http://dx.doi.org/10.1063/1.2713169 (3 pages) | Cited 6 times

Online Publication Date: 12 March 2007

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The authors report a detailed comparison of low temperature photoluminescence (LTPL) and cathodo luminescence (LTCL) spectra collected in the same stacking faults rich area of a 4H silicon carbide epitaxial layer. In both cases, they find that the maximum wavelength of the defect-related emission lines shifts when the excitation spot position moves across the defect zone. The shift is excitation-intensity dependent. It is very small for LTPL (4 meV) but reach 20 meV for LTCL. This constitutes the first experimental evidence that a screening of the quantum confined Stark effect can be achieved in 4H-SiC SF quantum wells.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Nn Stacking faults and other planar or extended defects

Evaluation of the thermal stability of Nd60Al20Co20 bulk metallic glass

L. Xia, D. Ding, S. T. Shan, and Y. D. Dong

Appl. Phys. Lett. 90, 111903 (2007); http://dx.doi.org/10.1063/1.2713179 (3 pages) | Cited 11 times

Online Publication Date: 12 March 2007

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Long-term thermal stability of Nd60Al20Co20 bulk metallic glass (BMG) with excellent glass forming ability was investigated by Kissinger and Vogel-Fulcher-Tammann (VFT) analyses, respectively. The heating rate dependence of crystallization temperature of the BMG was found to follow the VFT nonlinear relationship rather than Kissinger’s linear fittings. It is suggested that the continuous heating crystallization diagrams obtained from VFT equation should be more adequate to estimate the long-term thermal stability of Nd60Al20Co20 bulk metallic glass according to the time-temperature-transformation diagram based on isothermal annealing.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.70.K- Solid-solid transitions
61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments

Relation between photoluminescence emission and local order-disorder in the CaTiO3 lattice modifier

Sergio de Lazaro, Juliana Milanez, Alberthmeiry T. de Figueiredo, Valéria M. Longo, Valmor R. Mastelaro, Fabio S. De Vicente, Antônio C. Hernandes, José A. Varela, and Elson Longo

Appl. Phys. Lett. 90, 111904 (2007); http://dx.doi.org/10.1063/1.2713359 (3 pages) | Cited 27 times

Online Publication Date: 12 March 2007

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In this letter, the authors propose that photoluminescence emission in CaTiO3 is affected not only by disorder in the lattice former but also by structural disorder in the lattice modifier. Structural disorder was evaluated by Ti, Ca K-edge x-ray absorption near-edge structure experiments and by photoluminescence emission. The preedge feature of the Ca K edge was related to the intensity of photoluminescence emission. The results of the preedge feature of the Ca K-edge x-ray absorption near-edge structure confirm the presence of different Ca coordination numbers, namely, Ca–O11 and Ca–O12.
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78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra

Enhanced photosensitivity in silicate optical fibers by thermal treatment

Gilberto Brambilla and Valerio Pruneri

Appl. Phys. Lett. 90, 111905 (2007); http://dx.doi.org/10.1063/1.2714096 (3 pages) | Cited 1 time

Online Publication Date: 12 March 2007

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Enhanced photosensitivity using thermal treatment has been observed on several silicate optical fibers. The effect of the treatment on fibers with different dopants has been tested via Bragg grating inscription. The presence of Ge or Sn atom has been established to be fundamental for the effect to occur. To explain the main features a model involving defect dynamics is proposed.
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42.79.Dj Gratings
42.81.-i Fiber optics
81.40.Gh Other heat and thermomechanical treatments

Study of copper diffusion through a ruthenium thin film by photoemission electron microscopy

Wei Wei, S. L. Parker, Y.-M. Sun, J. M. White, Gang Xiong, Alan G. Joly, Kenneth M. Beck, and Wayne P. Hess

Appl. Phys. Lett. 90, 111906 (2007); http://dx.doi.org/10.1063/1.2712832 (3 pages) | Cited 6 times

Online Publication Date: 13 March 2007

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Photoemission electron microscopy is used to study copper diffusion through a ruthenium thin film. The photoemission electron microscopy images display a large contrast between Cu and Ru due to the differences in work function, making photoemission electron microscopy an ideal methodology to study thin film diffusion in real time. Between 175 and 290 °C, Cu mainly diffuses through defect sites in the thin Ru film. Uniform diffusion of Cu through the Ru film begins at approximately 300 °C. The results are confirmed by x-ray photoemission spectroscopy depth profiling and scanning electron microscopy–energy dispersive x-ray spectroscopy analysis.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions

Simultaneous filling of InAs quantum dot states from the GaAs barrier under nonresonant excitation

G. Rainò, G. Visimberga, A. Salhi, M. De Vittorio, A. Passaseo, R. Cingolani, and M. De Giorgi

Appl. Phys. Lett. 90, 111907 (2007); http://dx.doi.org/10.1063/1.2713347 (3 pages) | Cited 11 times

Online Publication Date: 13 March 2007

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The authors have performed time resolved photoluminescence measurements by upconversion technique on InAs quantum dots embedded in an InGaAs/GaAs quantum well emitting at 1.3 μm at room temperature. A detailed analysis of the photoluminescence transients as a function of the excitation density and for different detection energies between the quantum dot transitions and the GaAs absorption edge shows that the intradot relaxation is slower than the direct carrier capture from the barrier states through a continuum background relaxation.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Propagation of Lamb waves in one-dimensional quasiperiodic composite thin plates: A split of phonon band gap

Jian Gao, Jian-Chun Cheng, and Baowen Li

Appl. Phys. Lett. 90, 111908 (2007); http://dx.doi.org/10.1063/1.2713339 (3 pages) | Cited 15 times

Online Publication Date: 13 March 2007

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The authors study numerically the propagation of Lamb waves in one-dimensional quasiperiodic composite thin plates made of tungsten (B) and silicon resin (A) arranged according to a Fibonacci sequence. It is found that the band-gap structures of Lamb waves are very different from those of bulk waves. The split of band gaps is independent of the number of layers, which is different from the quasiperiodic bulk photonic and phononic crystals. Possible applications are discussed.
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68.35.Iv Acoustical properties
43.35.Pt Surface waves in solids and liquids
63.20.-e Phonons in crystal lattices

Determination of Young’s modulus of individual electrospun nanofibers by microcantilever vibration method

Philip A. Yuya, Yongkui Wen, Joseph A. Turner, Yuris A. Dzenis, and Zheng Li

Appl. Phys. Lett. 90, 111909 (2007); http://dx.doi.org/10.1063/1.2713128 (3 pages) | Cited 11 times

Online Publication Date: 14 March 2007

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The authors report a technique for measuring Young’s modulus of a single electrospun nanofiber using the vibrations of two microcantilevers coupled with the nanofiber. The modulus is calculated from the resonant frequency shift resulting from the nanofiber. Polyacrylonitrile nanofibers (200 nm diameter) were collected during electrospinning and wrapped on two similar microcantilevers causing a shift in first resonance from 10.0 to 19.4 kHz. Finite element analysis was used to analyze the frequency shift using images from a scanning electron microscope giving a modulus of the as-spun polyacrylonitrile nanofiber of 26.8 GPa.
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07.10.Cm Micromechanical devices and systems
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.25.-g Mechanical properties of nanoscale systems

Channel cracks in a hermetic coating consisting of organic and inorganic layers

Nicolas Cordero, Juil Yoon, and Zhigang Suo

Appl. Phys. Lett. 90, 111910 (2007); http://dx.doi.org/10.1063/1.2713134 (3 pages) | Cited 11 times

Online Publication Date: 14 March 2007

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Flexible electronic devices often require hermetic coatings that can withstand applied strains. This letter calculates the critical strains for various configurations of channel cracks in a coating consisting of organic and inorganic layers. The authors show that the coating can sustain the largest strain when the organic layer is of some intermediate thicknesses.
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68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Size-dependent planar colloidal crystals guided by alternating electric field

Ke-Qin Zhang and Xiang Y. Liu

Appl. Phys. Lett. 90, 111911 (2007); http://dx.doi.org/10.1063/1.2713235 (3 pages) | Cited 7 times

Online Publication Date: 14 March 2007

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The authors demonstrate that two-dimensional crystals can be assembled from suspensions of colloidal spheres subjected to an alternating electric field on the surface of electrodes. The order parameters of monolayer colloidal crystals, which are extracted from the translational correlation function g(r) and bond-orientational correlation function g6(r), are employed to quantitatively characterize the ordering of the colloidal assemblies. This method has been applied on colloidal spheres of various sizes ranging from 450 nm to 5.0 μm. In particular, high-quality crystals of spheres sized differently are controlled by different domains of frequency. This technique could be a rational method to assemble micro- or submicron colloidal spheres.
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82.70.Dd Colloids
61.46.Hk Nanocrystals
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs/GaAs quantum dots emitting at 1.3 μm

Tao Yang, Jun Tatebayashi, Kanna Aoki, Masao Nishioka, and Yasuhiko Arakawa

Appl. Phys. Lett. 90, 111912 (2007); http://dx.doi.org/10.1063/1.2713135 (3 pages) | Cited 14 times

Online Publication Date: 16 March 2007

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The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 μm grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N2 flow at temperatures ranging from 600 to 900 °C for 30 s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380 meV at 850 °C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (<700 °C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near the QD regions, thereby greatly promoting Ga–In intermixing across the interface during RTA. The results reported here demonstrate that it is possible to significantly shift the emission peak of the QDs by RTA without any additional procedures, even at lower annealing temperatures.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Multistable alignment states in nematic liquid crystal filled wells

C. Tsakonas, A. J. Davidson, C. V. Brown, and N. J. Mottram

Appl. Phys. Lett. 90, 111913 (2007); http://dx.doi.org/10.1063/1.2713140 (3 pages) | Cited 14 times

Online Publication Date: 16 March 2007

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Two distinct, stable alignment states have been observed for a nematic liquid crystal confined in a layer with thickness of 12 μm and in square wells with sides of length between 20 and 80 μm. The director lies in the plane of the layer and line defects occur in two corners of the squares. The positions of the defects determine whether the director orientation is across the diagonal or is parallel to two opposite edges of the square. The device is multistable because both the diagonal and parallel states are stable when rotated by multiples of 90° in plane.
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42.79.Kr Display devices, liquid-crystal devices

Strain field in silicon on insulator lines using high resolution x-ray diffraction

M. Gailhanou, A. Loubens, J.-S. Micha, B. Charlet, A. A. Minkevich, R. Fortunier, and O. Thomas

Appl. Phys. Lett. 90, 111914 (2007); http://dx.doi.org/10.1063/1.2713335 (3 pages) | Cited 16 times

Online Publication Date: 16 March 2007

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Symmetric and asymmetric reciprocal space maps (RSMs) of silicon on insulator (SOI) lines are obtained using high resolution x-ray diffraction. RSMs calculated from the displacement field simulated using finite element calculations show a good agreement with the experimental RSMs. These calculations indicate the large influence of the displacement field created by the silicon nitride cap and the sensitivity of the RSMs to the gradients of displacement at the edge of the SOI lines. They further show that the RSMs are influenced by local strains but also by local rotations of the crystal lattice connected with the strain distribution.
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68.60.Bs Mechanical and acoustical properties

Criterion for predicting the glass-forming ability of alloys

S. Sharma, R. Vaidyanathan, and C. Suryanarayana

Appl. Phys. Lett. 90, 111915 (2007); http://dx.doi.org/10.1063/1.2713867 (3 pages) | Cited 9 times

Online Publication Date: 16 March 2007

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Mechanical alloying (MA) of blended elemental powder mixtures of Fe42Zr10X28B20 (X = Al, Co, Ge, Mn, Ni, and Sn) was carried out to determine their glass-forming ability (GFA) (as determined by the time required to form the amorphous phase). During milling, amorphization was achieved in systems with X = Al, Ge, or Ni, but not in the other systems. The GFA could be correlated with the total number of intermetallics present in the constituent binary phase diagrams. Thus, this work offers the equilibrium phase diagram as a predictive tool to determine if amorphization can be achieved by the MA method.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.43.Fs Glasses
81.30.Bx Phase diagrams of metals, alloys, and oxides
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
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