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28 Jul 2008

Volume 93, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 043101 (2008); http://dx.doi.org/10.1063/1.2963352 (3 pages)

Xin Fu, Jun Jiang, Wenzheng Zhang, and Jun Yuan
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Probing thickness-dependent dislocation storage in freestanding Cu films using residual electrical resistivity

Shakti Chauhan and Ashraf F. Bastawros

Appl. Phys. Lett. 93, 041901 (2008); http://dx.doi.org/10.1063/1.2961006 (3 pages) | Cited 2 times

Online Publication Date: 28 July 2008

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Residual electrical resistivity measurement is employed to study dislocation storage under tensile loading of freestanding electroplated Cu films (1–5 μm grain size and 2–50 μm thickness). The results indicate that the nature of thickness effects (strengthening or weakening) depends on the underlying deformation mechanisms via the average grain size. A threshold grain size of about dg = 5 μm is identified to distinguish grain size effects in thicker films from those in thinner films. For dg>5 μm, diminishing microstructural constraint with reduced thickness weakens the films due to dislocation annihilation near the free surface. For dg<5μ m, reduction of film thickness leads to strengthening via grain boundary-source starvation.
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73.61.At Metal and metallic alloys
81.40.Lm Deformation, plasticity, and creep
62.25.Mn Fracture/brittleness
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
68.55.at Other materials

Highly efficient nonresonant two-photon absorption in ZnO pellets

S. Mani, J. I. Jang, and J. B. Ketterson

Appl. Phys. Lett. 93, 041902 (2008); http://dx.doi.org/10.1063/1.2965107 (3 pages) | Cited 4 times

Online Publication Date: 28 July 2008

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In this article, we report direct evidence for efficient nonresonant two-photon absorption-induced luminescence in ZnO pellets at 2 K and room temperature. Stimulated emission near the band edge is observed at room temperature employing this form of excitation under low excitation levels over a broad range of excitation wavelengths. The steady-state population dynamics based on the time-integrated photoluminescence spectra at 2 K indicates that this nonresonant two-photon excitation is much more efficient in creating excitonic matter, compared with the traditional one-photon excitation method.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.45.+h Stimulated emission
71.35.-y Excitons and related phenomena

In-plane anisotropic strain in a-ZnO films grown on r-sapphire substrates

G. Saraf, Y. Lu, and T. Siegrist

Appl. Phys. Lett. 93, 041903 (2008); http://dx.doi.org/10.1063/1.2965801 (3 pages) | Cited 22 times

Online Publication Date: 28 July 2008

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We deposited (11math0) nonpolar a-plane ZnO (a-ZnO) films on (01math2) r-sapphire substrates using metalorganic chemical vapor deposition. Unit cell deformation due to interfacial strain in films was determined by triple-axis x-ray diffraction. Due to low symmetry of a-plane, anisotropic strain is observed along the [0001] (c-axis) and [1math00] (m-axis) in-plane axes. Out-of-plane strain along [11math0] (a-axis) is tensile and relaxes for film thickness ≥ 2 μm. The in-plane m-axis is under tensile strain and c-axis is under compressive strain. Increase in film thickness increases in-plane strain anisotropy due to faster relaxation along the m-axis. Thermal and lattice mismatch strains are separated by curve fitting.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Structure and mechanical properties of osmium carbide: First-principles calculations

Xiaoju Guo, Bo Xu, Julong He, Dongli Yu, Zhongyuan Liu, and Yongjun Tian

Appl. Phys. Lett. 93, 041904 (2008); http://dx.doi.org/10.1063/1.2964179 (3 pages) | Cited 14 times

Online Publication Date: 29 July 2008

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Synthesized osmium carbide (OsC) was reported in tungsten carbide (WC) structure, inconsistent with recent theoretical finding that the WC-structured OsC does not satisfy the mechanical stability criteria. The first-principles calculations of osmium carbide for nine hypothetical structures indicate that OsC with FeSi structure, NiAs structure, and CoSn structure satisfy the mechanical stability criteria. Based on the simulated x-ray diffraction data of WC structure and NiAs structure, we consider that the experimentally synthesized OsC is of the NiAs structure rather than the WC structure. In addition, the Os–C bond in NiAs-structured OsC has metallic feature, responsible for low hardness.
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61.66.Fn Inorganic compounds
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.50.Lt Crystal binding; cohesive energy

Photoluminescence properties of AlN homoepilayers with different orientations

A. Sedhain, N. Nepal, M. L. Nakarmi, T. M. Al tahtamouni, J. Y. Lin, H. X. Jiang, Z. Gu, and J. H. Edgar

Appl. Phys. Lett. 93, 041905 (2008); http://dx.doi.org/10.1063/1.2965613 (3 pages) | Cited 13 times

Online Publication Date: 29 July 2008

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AlN homoepilayers and heteroepilayers were grown on polar c-plane and nonpolar a-plane and m-plane orientations of AlN bulk and sapphire substrates by metal organic chemical vapor deposition. A systematic comparative study of photoluminescence properties of these samples revealed that all AlN homoepilayers (c, a and m planes) were strain free with an identical band gap of about 6.099 (6.035) eV at 10 (300) K, which is about 42 meV below the band gap of c-plane AlN heteroepilayers grown on sapphire. Also, nonpolar a-plane homoepilayers have the highest emission intensity over all other types of epilayers. We believe that a-plane AlN homoepilayers have the potential to provide orders of magnitude improvement in the performance of new generation deep UV photonic devices.
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78.66.Fd III-V semiconductors
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors

Dynamical dislocation emission processes from twin boundaries

Y. B. Wang, B. Wu, and M. L. Sui

Appl. Phys. Lett. 93, 041906 (2008); http://dx.doi.org/10.1063/1.2965637 (3 pages) | Cited 17 times

Online Publication Date: 29 July 2008

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In situ tensile straining transmission electron microscopy investigation of electrodeposited copper with high density of nanoscale growth twins reveals that twin boundaries (TBs) can serve as dislocation sources. Atomic steps at TBs formed by sessile Frank partial dislocations are beneficial for TBs serving as dislocation sources. The underlying mechanism that includes dislocation reactions with TBs is discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
81.15.Pq Electrodeposition, electroplating
61.46.-w Structure of nanoscale materials

The time-dependent melting failure in flip chip lead-free solder interconnects under current stressing

D. Yang, Y. C. Chan, and K. N. Tu

Appl. Phys. Lett. 93, 041907 (2008); http://dx.doi.org/10.1063/1.2963473 (3 pages) | Cited 4 times

Online Publication Date: 30 July 2008

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The melting failure in flip chip Sn3.5Ag1.0Cu solder interconnects was investigated under a current density of 2.3×104 A/cm2 at 125 °C, which was attributed to the accumulated effect of void propagation, chemical dissolution, and Al electromigration. The velocity of void growth in the solder varied from 0.2 to 0.5 μm/h in earlier stages. The chemical dissolution in the Al pad also played the important role in failure. In the final stage, the depletion in the Al trace due to the electromigration exhibited a linear relationship with time. The rate of resistance change was estimated to be 0.9% h−1.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

High thermal stability of vacancy clusters formed in MeV Si-self-ion-implanted Si

Lin Shao, P. E. Thompson, Q. Y. Chen, K. B. Ma, J. R. Liu, and Wei-Kan Chu

Appl. Phys. Lett. 93, 041908 (2008); http://dx.doi.org/10.1063/1.2963480 (3 pages)

Online Publication Date: 30 July 2008

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We have shown that considerable vacancy defects, introduced by MeV Si self-ion implantation, can survive a 900 °C/5 min annealing for gate formation. By analyzing the trap-limited Si interstitial diffusion, we have characterized these vacancy clusters. Furthermore, we show that the remaining vacancies are sufficient to reduce B diffusion. The study suggests that MeV ion implantation, a promising approach for ultrashallow junction formation in metal-oxide-semiconductor device fabrication, can be inserted before gate formation (involving high temperature annealing) to avoid irradiation damage on gate structures.
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61.72.jd Vacancies
85.30.Tv Field effect devices
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
61.72.uf Ge and Si

The role of strain in hydrogenation induced cracking in Si/Si1−xGex/Si structures

Lin Shao, Zengfeng Di, Yuan Lin, Q. X. Jia, Y. Q. Wang, M. Nastasi, Phillip E. Thompson, N. David Theodore, and Paul K. Chu

Appl. Phys. Lett. 93, 041909 (2008); http://dx.doi.org/10.1063/1.2963489 (3 pages) | Cited 3 times

Online Publication Date: 30 July 2008

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Hydrogenation induced cracking in molecular beam epitaxy grown Si/Si1−xGex/Si heterostructures is studied. The Si1−xGex layer buried between an ∼ 200 nm thick Si capping layer and the Si substrate is ∼ 5 nm thick. After plasma hydrogenation, long range H migration and H trapping at the Si1−xGex layer are observed. With increasing Ge concentrations, the amount of H trapping increases, cracking along the Si1−xGex layer is smoother, and fewer defects are formed in the Si capping layer. The study suggests maximizing the interfacial strain to achieve the smoothest cracking with minimized radiation damage for ultrathin silicon-on-insulator technology.
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81.65.-b Surface treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Adaptive polymer particles

Kyriaki Kalaitzidou and Alfred J. Crosby

Appl. Phys. Lett. 93, 041910 (2008); http://dx.doi.org/10.1063/1.2966338 (3 pages) | Cited 11 times

Online Publication Date: 30 July 2008

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Adaptable polymer particles that can change geometry, flow characteristics, and adsorption properties upon the stimulation of an environmental change, such as temperature, are fabricated by utilizing the residual stress developed at the interface of a bilayer. We propose a phase diagram that can be used to predict the shape and size of the adaptive polymer particles as a function of the material modulus, thickness ratio, and the bilayer’s lateral dimensions. The materials used are gold/titanium and polydimethylsiloxane, but the method is applicable to a wide range of material combinations. Initial demonstrations of this responsive control and its impact on properties of the adaptive polymer particles are also presented.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.30.Dz Phase diagrams of other materials
61.41.+e Polymers, elastomers, and plastics

Magnetophotoluminescence and energy-dependent circular polarization from CdMnS nanowires

Eunsoon Oh, Jung Ho Choi, Dong Keun Oh, and Jeonghee Park

Appl. Phys. Lett. 93, 041911 (2008); http://dx.doi.org/10.1063/1.2957471 (3 pages) | Cited 3 times

Online Publication Date: 31 July 2008

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We measured the Zeeman shift and the circular polarization of the magnetophotoluminescence from CdMnS nanowires. The circular polarization of the CdMnS nanowires reaches up to 5% at 5 K, the polarization being dependent upon photon energies. The relatively small circular polarization is explained by the fact that the carriers are not in states with well defined angular momentum due to the nature of the wurtzite structure. The strong photon energy dependence of the circular polarization is attributed to the energy relaxation process via phonon emission, rather than by the variation of the nanowire diameters or by the Mn concentrations.
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78.55.Et II-VI semiconductors
75.50.Pp Magnetic semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.66.Hf II-VI semiconductors
63.22.Gh Nanotubes and nanowires
78.20.Ls Magneto-optical effects

Temperature-dependent photoluminescence study of 1.3 μm undoped InAs/InGaAs/GaAs quantum dots

C. Y. Ngo, S. F. Yoon, D. R. Lim, Vincent Wong, and S. J. Chua

Appl. Phys. Lett. 93, 041912 (2008); http://dx.doi.org/10.1063/1.2958349 (3 pages) | Cited 8 times

Online Publication Date: 31 July 2008

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InAs/InGaAs/GaAs quantum dot (QD) structures are commonly employed for 1.3 μm emission. However, reduction in the thermal stability of the undoped InAs/InGaAs/GaAs QD lasers has been observed upon inclusion of the InxGa1−xAs strain-reducing layer. In this work, the effect of QD growth temperature on the temperature-dependent photoluminescence of the 1.3 μm undoped InAs/InGaAs/GaAs QD samples was investigated. Due to higher confining potential of QD samples grown at lower growth temperature, enhancement in the thermal stability was observed. We believe that our findings will be beneficial to those working on improving the uncooled performance of 1.3 μm undoped InAs/InGaAs/GaAs QD photonic devices.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.ag Semiconductors

Surface Fermi level in GaAsSb structures grown by molecular beam epitaxy on InP substrates

Houssam Chouaib, Catherine Bru-Chevallier, Aleksandra Apostoluk, Wojciech Rudno-Rudzinski, Melania Lijadi, and Philippe Bove

Appl. Phys. Lett. 93, 041913 (2008); http://dx.doi.org/10.1063/1.2959829 (3 pages) | Cited 7 times

Online Publication Date: 31 July 2008

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Photoreflectance (PR) spectroscopy is performed to investigate the Fermi level pinning at the surface of GaAsSb, in a series of epitaxial structures with different Sb concentration. PR spectra exhibit Franz–Keldysh oscillations, originating from the built-in electric field in the GaAsSb layer. Experimental results indicate that the surface Fermi level is pinned in the lower half bandgap. The surface Fermi level is determined versus the Sb concentration between 38% and 52%.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.20.-e Optical properties of bulk materials and thin films
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.30.Pq Bipolar transistors

Experimental estimation of friction energy within a bundle of single-walled carbon nanotubes

TianYi Yang, Zongrong Zhou, Hui Fan, and Kin Liao

Appl. Phys. Lett. 93, 041914 (2008); http://dx.doi.org/10.1063/1.2966358 (3 pages) | Cited 3 times

Online Publication Date: 1 August 2008

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In this work, we have experimentally determined normalized friction energy between single-walled carbon nanotubes (SWCNTs) from tensile testing of SWCNT bundles using a simple scheme. The average normalized friction energy obtained is 0.22 Nm−1. This result is further verified by molecular mechanics simulation of single nanotube or a bundle of nanotubes pulled out from a nanotube bundle. This numerical value offers an important design parameter for mechanical applications of carbon nanotubes.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Highly efficient diffractive reflector using microgratings for reflective display

Jin-Hwan Kim, Jae-Ho Yu, Byoung-Ho Cheong, Yoon-Sun Choi, and Hwan-Young Choi

Appl. Phys. Lett. 93, 041915 (2008); http://dx.doi.org/10.1063/1.2966368 (3 pages)

Online Publication Date: 1 August 2008

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A highly efficient diffractive reflector with a rhombus shape angular distribution of reflected light for mobile liquid crystal display is developed. The fabricated diffractive reflector shows enhanced reflectance two times higher than the conventional bumpy reflector. The diffractive reflector composed of 25 surface relief microgratings is fabricated by photoresist patterning and metal deposition. The angular distribution of light that is reflected off the diffractive reflector is measured under specula illumination and diffusive illumination. The sufficient controllability of the angular distribution of the reflected light by the specific design of the period, orientation, and depth of each micrograting is shown.
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42.79.Dj Gratings
42.79.Kr Display devices, liquid-crystal devices
42.82.Cr Fabrication techniques; lithography, pattern transfer

Improvement of quantum efficiency of photomultiplier tubes by humidity controlled coatings based on porous polymer structures

V. Körstgens, C.-C. Hsu, D. Paneque, J. Wiedersich, and P. Müller-Buschbaum

Appl. Phys. Lett. 93, 041916 (2008); http://dx.doi.org/10.1063/1.2967195 (3 pages) | Cited 4 times

Online Publication Date: 1 August 2008

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Based on spin coating in humidity controlled environment an extremely simple deposition process is established which allows convenient and reproducible coating of photomultiplier tubes (PMTs) to achieve an improvement in photon sensitivity and thereby a higher quantum efficiency. The coatings consisting of a blend of polyacrylate based copolymer with p-terphenyl are obtained from dichloromethane solutions. On the curved PMTs structures due to crystallization of p-terphenyl superposed with pores in the copolymer matrix are present. On flat substrates coatings established under identical conditions exhibit the same porous structure. The origin of the obtained structures is discussed in context of breath figures.
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85.60.Ha Photomultipliers; phototubes and photocathodes
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.35.Jk Copolymers, phase transitions, structure

The impacts of surface conditions on the vapor-liquid-solid growth of germanium nanowires on Si (100) substrate

C. B. Li, K. Usami, T. Muraki, H. Mizuta, and S. Odal

Appl. Phys. Lett. 93, 041917 (2008); http://dx.doi.org/10.1063/1.2968201 (3 pages) | Cited 9 times

Online Publication Date: 1 August 2008

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The impacts of surface conditions on the growth of Ge nanowires on a Si (100) substrate are discussed in detail. On SiO2-terminated Si substrates, high-density Ge nanowires can be easily grown. However, on H-terminated Si substrates, growing Ge nanowires is more complex. The silicon migration and the formation of a native SiO2 overlayer on a catalyst surface retard the growth of Ge nanowires. After removing this overlayer in the HF solution, high-density and well-ordered Ge nanowires are grown. Ge nanowires cross vertically and form two sets of parallel nanowires. It is found that nanowires grew along ⟨110⟩ directions.
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81.07.Vb Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments
68.37.Lp Transmission electron microscopy (TEM)
68.35.bg Semiconductors
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