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21 May 2007

Volume 90, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 90, 213501 (2007); http://dx.doi.org/10.1063/1.2742294 (3 pages)

Jong-Hyun Ahn, Hoon-Sik Kim, Etienne Menard, Keon Jae Lee, Zhengtao Zhu, Dae-Hyeong Kim, Ralph G. Nuzzo, John A. Rogers, Islamshah Amlani, Vadim Kushner, Shawn G. Thomas, and Terrisa Duenas
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Thermal and elastic properties of Cu–Zr–Be bulk metallic glass forming alloys

Gang Duan, Mary Laura Lind, Katrien De Blauwe, Aaron Wiest, and William L. Johnson

Appl. Phys. Lett. 90, 211901 (2007); http://dx.doi.org/10.1063/1.2741050 (3 pages) | Cited 16 times

Online Publication Date: 21 May 2007

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The compositional dependence of thermal and elastic properties of Cu–Zr–Be ternary bulk metallic glass forming alloys was systematically studied. There exists a linear relationship between the glass transition temperature Tg and the total Zr concentration. G decreases linearly with increasing Zr concentration as well. The results also show that Tg, shear modulus G, and Poisson’s ratio ν are very sensitive to changes in compositions. Low Tg, low G, and relatively high ν can be achieved with high Zr and Ti concentration.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Mechanism for persistent hexagonal island formation in AlN buffer layer during growth on Si (111) by plasma-assisted molecular beam epitaxy

Kuang-Yuan Hsu, Hung-Chin Chung, Chuan-Pu Liu, and Li-Wei Tu

Appl. Phys. Lett. 90, 211902 (2007); http://dx.doi.org/10.1063/1.2741054 (3 pages)

Online Publication Date: 21 May 2007

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The characteristics of structure and morphology of AlN grown by a growth interruption method on Si (111) with plasma-assisted molecular beam epitaxy are investigated. It is found that the growth interruption method would improve the surface flatness of the AlN layer without the formation of Al droplets. However, AlN hexagonal islands were present and persistent throughout the entire growth owing to effective strain relaxation and Eherlich-Schowebel barrier effect of preexistent surface islands grown on higher terraces of the Si substrate. The density of threading dislocations underneath the hexagonal islands is much less than elsewhere in the film, which is presumably due to dislocation annihilation during the island growth process.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Magnetocaloric effect of Ho-, Dy-, and Er-based bulk metallic glasses in helium and hydrogen liquefaction temperature range

Q. Luo, D. Q. Zhao, M. X. Pan, and W. H. Wang

Appl. Phys. Lett. 90, 211903 (2007); http://dx.doi.org/10.1063/1.2741120 (3 pages) | Cited 33 times

Online Publication Date: 21 May 2007

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The authors study the magnetocaloric effect and refrigerant capacity of Ho30Y26Al24Co20, Dy50Gd7Al23Co20, and Er50Al24Co20Y6 bulk metallic glasses. Their magnetic entropy changes associated with spin glass to paramagnetic transition are larger than those of Gd, Gd5Si2Ge1.9Fe0.1, and many other intermetallic compounds reported in the same temperature range. The good refrigerant efficiency combined with their high electrical resistivity, high thermal stability, outstanding mechanical properties, and tunable nature makes these glassy materials be attractive candidates for magnetic refrigerants in helium and hydrogen liquefaction temperature range of 2–50 K.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.43.Fs Glasses
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Lk Spin glasses and other random magnets
75.20.En Metals and alloys

Structural correlations of the enhancement of dielectric permittivity in the (Ta2O5)0.92(TiO2)0.08 system

X. Q. Liu, X. D. Han, Z. Zhang, L. F. Ji, and Y. J. Jiang

Appl. Phys. Lett. 90, 211904 (2007); http://dx.doi.org/10.1063/1.2740172 (3 pages) | Cited 2 times

Online Publication Date: 21 May 2007

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A Ti-ion ordering which correlates to the significant enhancement of the dielectric constant was determined in the (Ta2O5)0.92(TiO2)0.08 system by high resolution electron microscopy and the corresponding simulations. The alien Ti ions were determined to selectively sit on the octahedral locations in the Ta2O5 base structure in an average of 9-time period along the ⟨110⟩ direction. The authors suggest this Ti-ion ordering induces the directional enhancement of the dielectric permittivity of the (Ta2O5)0.92(TiO2)0.08 system. The atomic mechanism of this modulated structure contributing to the enhancement of the dielectric constant was qualitatively interpreted using a one-dimensional chain model. The structural correlations of the dielectric enhancement revealed in this study suggest a way to search or design high-k materials.
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77.22.Ch Permittivity (dielectric function)

Time-resolved dynamics of coherent acoustic phonons in CdMnTe diluted-magnetic single crystals

D. Wang, A. Cross, G. Guarino, S. Wu, Roman Sobolewski, and A. Mycielski

Appl. Phys. Lett. 90, 211905 (2007); http://dx.doi.org/10.1063/1.2738368 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2007

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The authors report on observation of pronounced coherent acoustic phonon (CAP) oscillations in diluted-magnetic Cd1−xMnxTe (x = 0.09) single crystals by means of femtosecond, optical single-color, and two-color pump-probe spectroscopy. The observed properties of CAP oscillations are consistent with the propagating-strain-pulse model, with electronic stress as the main CAP generation mechanism. The experimental dispersion relation between the CAP oscillation frequency and the probe-beam wave vector allowed them to extract the Cd0.91Mn0.09Te refractive index dependence on wavelength, while the dependence of oscillation amplitudes on the photon energy near the Cd0.91Mn0.09Te band gap edge indicated that the material energy gap is 1.63 eV. Two-color pump-probe studies showed that the speed of sound in our material is 3590 m/s and that the absorption depth of probe light, rather than the decay time of CAPs, is the dominant source of the experimentally observed oscillation dephasing time. The intrinsic lifetime of CAPs in CdMnTe crystals has been found to be at least in the nanosecond range.
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63.20.-e Phonons in crystal lattices
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Rate-dependent inhomogeneous-to-homogeneous transition of plastic flows during nanoindentation of bulk metallic glasses: Fact or artifact?

Jae-il Jang, Byung-Gil Yoo, and Ju-Young Kim

Appl. Phys. Lett. 90, 211906 (2007); http://dx.doi.org/10.1063/1.2742286 (3 pages) | Cited 11 times

Online Publication Date: 21 May 2007

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There has been considerable controversy over the “apparent” rate-dependent transition from inhomogeneous-to-homogeneous flow during nanoindentation of bulk metallic glasses (BMGs) at room temperature: whether it arises from the existence of homogeneous-flow regime in BMG deformation map or is an artifact due to the instrumental blurring at high rates. To provide a clue to address this dispute, the authors performed nanoindentation experiments on a Zr-based BMG with two geometrically self-similar indenters. The results are discussed in terms of the discrete plasticity ratio, which is a useful parameter in analyzing the contribution of inhomogeneous plasticity to the total plastic deformation.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity

Diffraction of plane compressional wave by a nanosized spherical cavity with surface effects

G. F. Wang

Appl. Phys. Lett. 90, 211907 (2007); http://dx.doi.org/10.1063/1.2741604 (3 pages) | Cited 8 times

Online Publication Date: 22 May 2007

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For nanostructured materials and devices, the effects of surface energy become prominent due to the increasing ratio of surface area to volume. In the present letter, based on the surface elasticity theory, the authors analyzed the diffraction of plane harmonic compressional wave (P wave) by a spherical cavity. The results show that once the radius of cavity reduces to nanometers, surface energy significantly affects the diffraction of elastic waves. For incident waves with different frequencies, the surface effects on dynamic stress concentrations around the spherical cavity are discussed in detail.
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68.35.Gy Mechanical properties; surface strains
68.35.Md Surface thermodynamics, surface energies
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Nearest-neighbor coordination and chemical ordering in multicomponent bulk metallic glasses

D. Ma, A. D. Stoica, L. Yang, X.-L. Wang, Z. P. Lu, J. Neuefeind, M. J. Kramer, J. W. Richardson, and Th. Proffen

Appl. Phys. Lett. 90, 211908 (2007); http://dx.doi.org/10.1063/1.2742315 (3 pages) | Cited 13 times

Online Publication Date: 22 May 2007

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The authors report complementary use of high-energy x-ray and neutron diffraction to probe the local atomic structure in a Zr-based bulk metallic glass. By analyzing the partial coordination numbers, the authors demonstrate the presence of multiple types of solute-centered clusters in the multicomponent glass and efficient packing of the amorphous structure at atomic scale. The authors’ findings provide a basis for understanding how local structures change during phase transformation and mechanical deformation of multicomponent amorphous alloys.
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61.43.Fs Glasses
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Structural and optical properties of ZnO/Mg0.1Zn0.9O multiple quantum wells grown on ZnO substrates

Junjie Zhu, A. Yu. Kuznetsov, Myung-Soo Han, Young-Sik Park, Haeng-Keun Ahn, Jin-Woo Ju, and In-Hwan Lee

Appl. Phys. Lett. 90, 211909 (2007); http://dx.doi.org/10.1063/1.2742574 (3 pages) | Cited 15 times

Online Publication Date: 22 May 2007

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ZnO/Mg0.1Zn0.9O multiquantum-well (MQW) structures were grown on ZnO substrates by molecular beam epitaxy. Abrupt interfaces and well/barrier width in the MQWs were confirmed by x-ray diffraction measurement and transmission electron microscopy. The transition energy of the localized exciton in the ZnO/Mg0.1Zn0.9O MQWs with well/barrier width of 5/8 nm was found to be about 3.375 eV at low temperature, consistent with theoretical calculation. The first subband energies in the conduction and valence band were calculated to be 19.2 and 5.4 meV, respectively. The transition energy showed no shift with excitation power, indicating that the polarization-induced electric field is negligible in the ZnO/Mg0.1Zn0.9O MQW structures.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
68.65.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells

Single crystalline ZnS nanotubes and their structural degradation under electron beam irradiation

L. Shi, Y. M. Xu, Quan Li, Z. Y. Wu, F. R. Chen, and J. J. Kai

Appl. Phys. Lett. 90, 211910 (2007); http://dx.doi.org/10.1063/1.2742575 (3 pages) | Cited 7 times

Online Publication Date: 22 May 2007

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ZnS nanotubes were synthesized using wet-chemistry method. These nanotubes appear to be extremely unstable under electron beam irradiation. Time dependent transmission electron diffraction patterns disclose the appearance of additional diffraction spots that belong to ZnO, with the prolonged e-beam irradiation duration. The experimental results suggest that displacement damage followed by oxidation is mainly responsible for the structural degradation of these ZnS nanotubes.
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64.70.Nd Structural transitions in nanoscale materials
64.70.K- Solid-solid transitions
61.82.Fk Semiconductors
61.46.Fg Nanotubes
61.80.Fe Electron and positron radiation effects
81.65.Mq Oxidation

Imaging of acoustic pressure radiation from vibrating microstructure in atmosphere using thermal microprobe

Takahito Ono, Sang-Jin Kim, and Masayoshi Esashi

Appl. Phys. Lett. 90, 211911 (2007); http://dx.doi.org/10.1063/1.2742908 (3 pages)

Online Publication Date: 22 May 2007

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This letter reports on an imaging technique of acoustic pressure radiation (APR) from vibrating micro-/nanostructures and their mechanical defects. Resonance oscillation of micro-/nanometer beams in use of viscous environments is important for various sensing applications. Viscous dumping is the main energy loss mechanism, which determines the quality factor of resonance in viscous fluid. The APR due to viscous dumping is imaged using a scanning thermal flow sensor. A platinum heater or micromachined silicon heater is heated up by flowing a current, and the acoustic particle velocity which originated from APR is detected. Imaging of APR is demonstrated and compared with the actual vibration image. Also, strong APR is observed from a crack on the support of a silicon beam.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction

The effect of coating in increasing the critical size of islands on a compliant substrate

Juil Yoon, Zhen Zhang, Nanshu Lu, and Zhigang Suo

Appl. Phys. Lett. 90, 211912 (2007); http://dx.doi.org/10.1063/1.2742911 (3 pages) | Cited 1 time

Online Publication Date: 22 May 2007

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A flexible electronic system may consist of a polymeric substrate and an array of stiff islands, on which devices are fabricated. When the substrate is stretched, the devices on the islands experience small strains but the islands may debond if they exceed a critical size. The authors show that a thin layer of polymer coating, covering the islands and the substrate, can markedly increase the critical island size.
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68.60.Bs Mechanical and acoustical properties
02.70.Dh Finite-element and Galerkin methods

Low temperature epitaxial growth of GaN films on LiGaO2 substrates

Kento Sakurada, Atsushi Kobayashi, Yuji Kawaguchi, Jitsuo Ohta, and Hiroshi Fujioka

Appl. Phys. Lett. 90, 211913 (2007); http://dx.doi.org/10.1063/1.2737928 (3 pages) | Cited 10 times

Online Publication Date: 23 May 2007

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GaN films have been grown on LiGaO2 {001} substrates at low substrate temperatures by pulsed laser deposition and their structural properties have been investigated. It is found that the metal-face LiGaO2 substrates are thermally more stable than O-face LiGaO2. It is also found that growth of GaN films proceeds epitaxially, even at room temperature (RT), on metal-face LiGaO2, but polycrystalline GaN films are formed on O-face LiGaO2 at RT. Reduction in growth temperature lessens the interface reactions that have previously been regarded as the most serious problem with this substrate have been revealed by x-ray reflectivity measurements.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Effect of electromigration in the anodic Al interconnect on melting of flip chip solder joints

Fan-Yi Ouyang, K. N. Tu, Chin-Li Kao, and Yi-Shao Lai

Appl. Phys. Lett. 90, 211914 (2007); http://dx.doi.org/10.1063/1.2743395 (3 pages) | Cited 10 times

Online Publication Date: 24 May 2007

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Melting of eutectic SnPb flip chip solder joints has been observed to occur frequently in dc electromigration tested with current density above 1.5×104 A/cm2 at an ambient temperature of 100 °C. It has been found that it is not due to the Joule heating of the solder bump itself, but rather due to the Joule heating of the on-chip Al interconnects. The current density in the Al approaches 2×106 A/cm2 and electromigration has especially generated voids at the anode of the Al. The damage has greatly increased the resistance of the Al, which produces the heat needed to melt the solder joint. The results of electrothermal coupling analysis show that when the resistance of the Al line changed threefold, the solder bump melted.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Evidence of bidomain structure in double-perovskite La2CoMnO6 thin films

M. P. Singh, S. Charpentier, K. D. Truong, and P. Fournier

Appl. Phys. Lett. 90, 211915 (2007); http://dx.doi.org/10.1063/1.2743387 (3 pages) | Cited 17 times

Online Publication Date: 25 May 2007

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The authors report structural, magnetic, and electrical properties of parasitic phase-free, well-ordered epitaxial La2CoMnO6 films. Despite their single ferromagnetic transition around 240 K, they demonstrate that they possess a bidomain structure with distinct magnetic characteristics. The B-site ordering in the films is achieved by growing the films at relatively high temperatures ( ∼ 800 °C) and O2 pressures ( ∼ 600 mTorr). Films exhibit a maximum 5.8μB/f.u. saturation magnetization and magnetic easy axis parallel to SrTiO3 (110). The origin of the bidomain structure is briefly discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
73.61.Ng Insulators
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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