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23 Jan 2012

Volume 100, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages)

Seung Ho Choi and Young L. Kim
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Characterization of thermal stresses in through-silicon vias for three-dimensional interconnects by bending beam technique

Suk-Kyu Ryu, Tengfei Jiang, Kuan H. Lu, Jay Im, Ho-Young Son, Kwang-Yoo Byun, Rui Huang, and Paul S. Ho

Appl. Phys. Lett. 100, 041901 (2012); http://dx.doi.org/10.1063/1.3678020 (4 pages) | Cited 4 times

Online Publication Date: 23 January 2012

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Through-silicon via is a critical element for three-dimensional (3D) integration of devices in multilevel stack structures. Thermally induced stresses in through-silicon vias (TSVs) have raised serious concerns over mechanical and electrical reliability in 3D technology. An experimental technique is presented to characterize thermal stresses in TSVs during thermal cycling based on curvature measurements of bending beam specimens. Focused ion beam and electron backscattering diffraction analyses reveal significant grain growth in copper vias, which is correlated with stress relaxation during the first cycle. Finite element analysis is performed to determine the stress distribution and the effect of localized plasticity and to account for TSV extrusion observed during annealing.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Electron trap liberation in MgF2 doped with Yb2+ using a two-color excitation experiment

P. S. Senanayake, J.-P. R. Wells, M. F. Reid, G. Berden, A. Meijerink, and R. J. Reeves

Appl. Phys. Lett. 100, 041902 (2012); http://dx.doi.org/10.1063/1.3678630 (3 pages)

Online Publication Date: 24 January 2012

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We utilize the optical transitions of Yb2+ excited by an ultraviolet optical parametric amplifier to probe electron trap liberation in MgF2 via the observation of a photoluminescence enhancement effect induced by a subsequent infrared pulse from a free-electron laser. The temperature dependence of the enhancement suggests that we liberate very shallow traps having a depth of approximately 17 cm−1. The observed “trap spectrum” is consistent with a simple model of a Coulomb trap.
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71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials

Nanoscale diffraction imaging of the high-pressure transition in Fe1−xO

Yang Ding, Zhonghou Cai, Qingyang Hu, Hongwei Sheng, Jun Chang, Russell J. Hemley, and Wendy L. Mao

Appl. Phys. Lett. 100, 041903 (2012); http://dx.doi.org/10.1063/1.3679117 (4 pages)

Online Publication Date: 24 January 2012

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To further understand the long-debated origin of the high-pressure cubic-rhombohedral transition in FeO, we investigated the domain wall structure in Fe0.94O using high-pressure microdiffraction imaging techniques. The results reveal a non-reflection type domain wall structure forming due to the cubic-rhombohedral transition in Fe0.94O, which suggests the transformation could be associated with defects and is unlikely to be ferroelastic in nature.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
77.80.Dj Domain structure; hysteresis

The bound states of Fe impurity in wurtzite GaN

M. Zhang, T. F. Zhou, Y. M. Zhang, B. Li, S. N. Zheng, J. Huang, Y. P. Sun, G. Q. Ren, J. F. Wang, K. Xu, and H. Yang

Appl. Phys. Lett. 100, 041904 (2012); http://dx.doi.org/10.1063/1.3679133 (4 pages) | Cited 1 time

Online Publication Date: 24 January 2012

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A study on the bound states of Fe impurities in GaN by ultraviolet photoluminescence (PL) emissions is presented. Two elusive PL lines were observed at 3.463 eV (L1) and 3.447 eV (L2), respectively. The intensities of the two lines are proportional to the Fe concentration. The temperature dependence of L1 and L2 revealed acceptor-like and strong localized characteristic, respectively. Furthermore, Raman analysis indicated that L2 is correlated to an exciton bound to a nitride-vacancy (VN) related complex, i.e., [Fe2+-VN]. By co-doping with Si, the [Fe2+-VN]-related bound state will enable the spin-coupling between isolated iron ions.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
61.72.jd Vacancies
61.72.sd Impurity concentration
61.66.Fn Inorganic compounds

Photoreflectance study of direct-gap interband transitions in Ge/SiGe multiple quantum wells with Ge-rich barriers

H. P. Hsu, P. H. Wu, Y. S. Huang, D. Chrastina, G. Isella, H. von Känel, and K. K. Tiong

Appl. Phys. Lett. 100, 041905 (2012); http://dx.doi.org/10.1063/1.3679608 (4 pages)

Online Publication Date: 26 January 2012

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Photoreflectance (PR) was used to study the direct-gap interband transitions in strain-compensated Ge/SiGe multiple quantum well (MQW) structures with Ge-rich SiGe barriers grown by low-energy plasma-enhanced chemical vapor deposition. The PR spectra revealed a wide range of possible optical transitions in the MQW structure. Detailed lineshape fits to the PR spectra and comparison to a theoretical calculation based on the envelope-function approximation with conduction band-offset and stain compensation factor as adjust parameters led to the identification of various interband transitions. The results demonstrated that PR is a powerful technique for nondestructive optical characterization of Ge/SiGe MQW structures.
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78.67.De Quantum wells
81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.70.Fy Nondestructive testing: optical methods
78.66.Db Elemental semiconductors and insulators
78.66.Li Other semiconductors

Growth sector dependence and mechanism of stress formation in epitaxial diamond growth

M. Fischer, S. Gsell, M. Schreck, and A. Bergmaier

Appl. Phys. Lett. 100, 041906 (2012); http://dx.doi.org/10.1063/1.3679611 (3 pages) | Cited 2 times

Online Publication Date: 26 January 2012

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Stress generation in epitaxial diamond growth was investigated by μ-Raman spectroscopy and high resolution x-ray diffraction. Intrinsic stress could be varied systematically from compressive to tensile covering a huge range of 5 GPa. The temperature-stress curve for growth on {111}-sectors as compared to {001} shows a shift of −200 °C or +2 GPa. A crucial role of hydrogen in the stress formation process is excluded. Due to the absence of grain boundaries, a model is proposed which is based on the “effective climb” of individual dislocations. The controlled generation of stress profiles offers a powerful concept for strengthening diamond mechanical devices.
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68.55.aj Insulators
78.30.Na Fullerenes and related materials
78.66.Tr Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

A mathematical model of mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

Zhongbin Xu, Yue Yang, Damien Vadillo, Xiaodong Ruan, and Xin Fu

Appl. Phys. Lett. 100, 041907 (2012); http://dx.doi.org/10.1063/1.3678037 (5 pages) | Cited 1 time

Online Publication Date: 26 January 2012

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A microfluidic channel with a constriction produced poor mixing conditions under periodic electro-osmotic flow. However, the mixing performance may be enhanced significantly by altering other parameters. Numerical simulations are used to investigate the effect of the direct current electric field (EDC), phase difference (ϕ), and length of constriction (L). A mathematical model, based on the structural features of the Lagrange function rather than its application, is proposed to establish a relationship between the mixing performance and these three parameters. The feasibility analysis has been carried out, and the results are verified by the data from simulation and experiment.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
82.45.-h Electrochemistry and electrophoresis
47.60.Dx Flows in ducts and channels
02.60.Cb Numerical simulation; solution of equations
47.11.-j Computational methods in fluid dynamics
47.51.+a Mixing

Surface modification by subsurface pressure induced diffusion

Claus G. Zimmermann

Appl. Phys. Lett. 100, 041908 (2012); http://dx.doi.org/10.1063/1.3679616 (3 pages)

Online Publication Date: 26 January 2012

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Polycrystalline Ag, covered with a nm thin siloxane layer, was irradiated with ultraviolet light in vacuum at 500 K. Ag particles of different aspect ratios, 50–1000 nm in size, formed on the surface, including a small fraction of nanorods. Pressurized water vapor bubbles are created in the subsurface region by hydrogen radicals photo-chemically released by the siloxane layer. They provide the driving force for a diffusive material flux along grain boundaries to the surface. This mechanism was modeled and found to agree with the experimental timescale: approximately 300 h are required for a 1000 nm particle to form.
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81.65.-b Surface treatments
82.50.Hp Processes caused by visible and UV light
61.72.Mm Grain and twin boundaries
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.35.Fx Diffusion; interface formation
81.16.-c Methods of micro- and nanofabrication and processing

Synthesis of single-component metallic glasses by thermal spray of nanodroplets on amorphous substrates

Qi An, Sheng-Nian Luo, William A. Goddard, III, W. Z. Han, B. Arman, and William L. Johnson

Appl. Phys. Lett. 100, 041909 (2012); http://dx.doi.org/10.1063/1.3675909 (4 pages) | Cited 3 times

Online Publication Date: 26 January 2012

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We show that single component metallic glasses can be synthesized by thermal spray coating of nanodroplets onto an amorphous substrate. We demonstrate this using molecular dynamics simulations of nanodroplets up to 30 nm that the spreading of the nanodroplets during impact on a substrate leads to sufficiently rapid cooling (1012–1013 K/s) sustained by the large temperature gradients between the thinned nanodroplets and the bulk substrate. However, even under these conditions, in order to ensure that the glass transition outruns crystal nucleation, it is essential that the substrate be amorphous (eliminating sites for heterogeneous nucleation of crystallization).
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81.05.Kf Glasses (including metallic glasses)
81.15.Rs Spray coating techniques
68.55.at Other materials
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Fs Glasses
68.08.Bc Wetting

Effect of uni-axial strain on THz/far-infrared response of graphene

JooYoun Kim, Chul Lee, Sukang Bae, Sang Jin Kim, Keun Soo Kim, Byung Hee Hong, and E. J. Choi

Appl. Phys. Lett. 100, 041910 (2012); http://dx.doi.org/10.1063/1.3680095 (4 pages) | Cited 2 times

Online Publication Date: 27 January 2012

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We present polarized optical transmission study of uniaxially strained large scale graphene in THz/far-infrared (IR) frequency region. Graphene was supported on stretchable polyethylene substrate and they were elongated up to 20% (ΔL/Lo = 0.2) by applying tensile force. For the IR light polarized along the strain direction (EIR//strain), the optical conductivity σ1(ω) of graphene changes from Drude response into strongly non-Drude-like behavior with a peak formed at finite energy ∼10 meV. In contrast, the coherent Drude conductivity is preserved along the direction perpendicular to the strain (EIR⊥strain). Possible origin of the strain-induced non-Drude σ1(ω)-behavior is discussed.
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78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.70.Gq Microwave and radio-frequency interactions
78.30.Na Fullerenes and related materials

Giant, voltage-actuated deformation of a dielectric elastomer under dead load

Jiangshui Huang, Tiefeng Li, Choon Chiang Foo, Jian Zhu, David R. Clarke, and Zhigang Suo

Appl. Phys. Lett. 100, 041911 (2012); http://dx.doi.org/10.1063/1.3680591 (4 pages) | Cited 15 times

Online Publication Date: 27 January 2012

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Far greater voltage-actuated deformation is achievable for a dielectric elastomer under equal-biaxial dead load than under rigid constraint usually employed. Areal strains of 488% are demonstrated. The dead load suppresses electric breakdown, enabling the elastomer to survive the snap-through electromechanical instability. The breakdown voltage is found to increase with the voltage ramp rate. A nonlinear model for viscoelastic dielectric elastomers is developed and shown to be consistent with the experimental observations.
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61.41.+e Polymers, elastomers, and plastics
62.20.F- Deformation and plasticity
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