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18 Jul 2005

Volume 87, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 87, 033501 (2005); http://dx.doi.org/10.1063/1.1992665 (3 pages)

Yoshihito Miyoshi, Fumito Nakajima, Junichi Motohisa, and Takashi Fukui
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Low-dimensional phonon specific heat of titanium dioxide nanotubes

C. Dames, B. Poudel, W. Z. Wang, J. Y. Huang, Z. F. Ren, Y. Sun, J. I. Oh, C. Opeil, M. J. Naughton, and G. Chen

Appl. Phys. Lett. 87, 031901 (2005); http://dx.doi.org/10.1063/1.1990269 (3 pages) | Cited 17 times

Online Publication Date: 11 July 2005

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The specific heat of multiwalled titanium dioxide (anatase phase) nanotubes has been measured between 1.5 and 95 K. Bulk anatase and rutile were also measured. The nanotube specific heat approaches that of bulk anatase at high temperatures. Below about 50 K the nanotube specific heat begins to show large enhancements compared to bulk. Using an isotropic elastic continuum model, this can be understood qualitatively as a transition to low-dimensional behavior. Below about 3 K there is a second transition and the nanotube specific heat becomes nearly constant, exceeding bulk anatase by an order of magnitude or more at 1.5 K.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Structural characterization of zincblende Ga1−xMnxN epilayers grown by molecular beam epitaxy on (001) GaAs substrates

M. W. Fay, Y. Han, P. D. Brown, S. V. Novikov, K. W. Edmonds, R. P. Campion, B. L. Gallagher, and C. T. Foxon

Appl. Phys. Lett. 87, 031902 (2005); http://dx.doi.org/10.1063/1.1995945 (3 pages) | Cited 1 time

Online Publication Date: 11 July 2005

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Zincblende p-type Ga1−xMnxN epilayers, grown with and without AlN/GaN buffer layers using plasma-assisted molecular beam epitaxy on (001) oriented GaAs substrates, have been investigated using a variety of complementary transmission electron microscopy techniques. The epilayers were found to contain a high anisotropic density of stacking faults and microtwins. MnAs inclusions were identified at the Ga1−xMnxN/(001)GaAs interface extending into the substrate. The use of AlN/GaN buffer layers was found to inhibit the formation of these inclusions.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries

Atomically straight steps on vicinal Si(111) surfaces prepared by step-parallel current in the kink-up direction

S. Yoshida, T. Sekiguchi, and K. M. Itoh

Appl. Phys. Lett. 87, 031903 (2005); http://dx.doi.org/10.1063/1.1995946 (3 pages) | Cited 14 times

Online Publication Date: 11 July 2005

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We demonstrate that annealing of a vicinal Si(111) surface at about 800 °C with a direct current in the direction that ascends the kinks enhances the formation of atomically straight step edges over micrometer lengths, while annealing with a current in the opposite direction does not. Every straight step edge has the same atomic configuration U(2, 0), which is useful as a template for the formation of a variety of nanostructures. A phenomenological model based on electromigration of charged mobile atoms explains the observed current-polarity dependent behavior.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
66.30.Qa Electromigration

Quality factors of qubit rotations in single semiconductor quantum dots

Q. Q. Wang, A. Muller, P. Bianucci, C. K. Shih, and Q. K. Xue

Appl. Phys. Lett. 87, 031904 (2005); http://dx.doi.org/10.1063/1.1995950 (3 pages) | Cited 6 times

Online Publication Date: 11 July 2005

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The quality factors of quantum bit (qubit) rotations in single self-assembled quantum dots were investigated using photoluminescence spectroscopy. Rotations with azimuthal angle ϕ along the equator of the qubit sphere were implemented by varying the time delay between two π/2 pulses, resulting in a “free rotation” quality factor Q0 = 9.8×104. Qubit rotations with polar angle θ as large as 10π along the meridian of the qubit sphere (Rabi oscillations with zero detuning) were realized with a quality factor QR ∼ 18, in experiments probing an excited excitonic state.
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73.21.La Quantum dots
78.55.-m Photoluminescence, properties and materials
71.35.-y Excitons and related phenomena
03.67.Lx Quantum computation architectures and implementations

Depletion regions in the aluminum-induced layer exchange process crystallizing amorphous Si

Jens Schneider, Juliane Klein, Martin Muske, Stefan Gall, and Walther Fuhs

Appl. Phys. Lett. 87, 031905 (2005); http://dx.doi.org/10.1063/1.1996849 (3 pages) | Cited 7 times

Online Publication Date: 12 July 2005

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Annealing of aluminum/amorphous silicon bilayers below the eutectic temperature of the aluminum/silicon system leads to an exchange of the layer positions and a concurrent crystallization of silicon (aluminum-induced layer exchange). This letter discusses a model for the self-limited suppression of nucleation during the process. This characteristic feature is the reason why large grain sizes can be obtained. In our experiments, we combine nucleation caused by supersaturation and undercooling. Si depletion regions around existing grains are made visible. These experiments give direct proof of the idea that the suppression of nucleation occurs by Si depletion in the aluminum-induced layer exchange process.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments

Micro-Raman and photoluminescence studies of neutron-irradiated gallium nitride epilayers

R. X. Wang, S. J. Xu, S. Fung, C. D. Beling, K. Wang, S. Li, Z. F. Wei, T. J. Zhou, J. D. Zhang, Ying Huang, and M. Gong

Appl. Phys. Lett. 87, 031906 (2005); http://dx.doi.org/10.1063/1.1999011 (3 pages) | Cited 11 times

Online Publication Date: 12 July 2005

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GaN epilayers grown on sapphire substrate were irradiated with various dosages of neutrons and were characterized using Micro-Raman and photoluminescence. It was found that the A1(LO) peak in the Raman spectra clearly shifted with neutron irradiation dosage. Careful curve fitting of the Raman data was carried out to obtain the carrier concentration which was found to vary with the neutron irradiation dosage. The variation of the full width at half maximum height of the photoluminescence was consistent with the Raman results. The neutron irradiation-induced structural defects (likely to be GeGa) give rise to carrier trap centers which are responsible for the observed reduction in carrier concentration of the irradiated GaN.
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81.05.Ea III-V semiconductors
61.82.Fk Semiconductors
61.80.Hg Neutron radiation effects
61.72.-y Defects and impurities in crystals; microstructure
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Ion-beam texturing of uniaxially textured Ni films

S. J. Park, D. P. Norton, and Venkat Selvamanickam

Appl. Phys. Lett. 87, 031907 (2005); http://dx.doi.org/10.1063/1.1957121 (3 pages) | Cited 6 times

Online Publication Date: 12 July 2005

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The formation of biaxial texture in uniaxially textured Ni thin films via Ar-ion irradiation is reported. The ion-beam irradiation was not simultaneous with deposition. Instead, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux, which differs from conventional ion-beam-assisted deposition. The uniaxial texture is established via a nonion beam process, with the in-plane texture imposed on the uniaxial film via ion beam bombardment. Within this sequential ion beam texturing method, grain alignment is driven by selective etching and grain overgrowth.
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81.05.Bx Metals, semimetals, and alloys
61.80.Jh Ion radiation effects
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.65.Cf Surface cleaning, etching, patterning

Aligned silver nanorod arrays produce high sensitivity surface-enhanced Raman spectroscopy substrates

Stephen B. Chaney, Saratchandra Shanmukh, Richard A. Dluhy, and Y.-P. Zhao

Appl. Phys. Lett. 87, 031908 (2005); http://dx.doi.org/10.1063/1.1988980 (3 pages) | Cited 136 times

Online Publication Date: 13 July 2005

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Substrates consisting of silver nanorod arrays with an irregular surface lattice (i.e., random nucleation sites) and with varying rod lengths were fabricated by an oblique angle vapor deposition method. These arrays were evaluated as potential surface-enhanced Raman spectroscopy (SERS) substrates using trans-1,2-bis(4-pyridyl)ethene as a reported molecule. SERS activity was shown to depend upon the length of the nanorods. The Ag nanorods with average lengths of 508.29±44.86 nm, and having aspect ratios of 5.69±1.49 exhibited the maximum SERS enhancement factors of greater than 108. Theoretical calculations indicate that this large SERS enhancement may be partially explained by the shape, density, and lateral arrangement of the Ag nanorod arrays.
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81.07.Bc Nanocrystalline materials
68.47.De Metallic surfaces
78.30.-j Infrared and Raman spectra
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Process development and bonding quality investigations of silicon layer stacking based on copper wafer bonding

K. N. Chen, S. M. Chang, A. Fan, C. S. Tan, L. C. Shen, and R. Reif

Appl. Phys. Lett. 87, 031909 (2005); http://dx.doi.org/10.1063/1.1995943 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2005

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Process development of silicon layer stacking based on copper wafer bonding, grind-back, and etch-back was applied to demonstrate a strong four-layer-stack structure. Bonded copper layers in this structure became homogeneous layers and did not show original bonding interfaces. This process can be used in three-dimensional integrated circuit applications. Voids and total bonded area after each layer stacking were investigated for the bonding quality after each layer stacking. Large wafer bows from high residual stresses result in the structure failure at the stacking of a high number of layers.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.De Semiconductor-device characterization, design, and modeling
81.65.Cf Surface cleaning, etching, patterning
81.65.Ps Polishing, grinding, surface finishing

Effects of surface imperfections on deformation and failure of amorphous metals

Qi-Kai Li and Mo Li

Appl. Phys. Lett. 87, 031910 (2005); http://dx.doi.org/10.1063/1.1999013 (3 pages) | Cited 24 times

Online Publication Date: 14 July 2005

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A series of notch tests are conducted using molecular dynamics simulation to study the effects of surface imperfections on deformation and failure behaviors in amorphous metals. It is shown that the surface notches of radius as small as 1 nm could trigger rapid failure; and the notch depth is much more effective than the radius in causing brittleness. The intrinsic ductility and brittleness caused by surface imperfections in amorphous metals under external loading are discussed.
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61.43.-j Disordered solids
81.05.Kf Glasses (including metallic glasses)
68.47.De Metallic surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
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
61.43.Bn Structural modeling: serial-addition models, computer simulation

Element-selective vertical height determination for an organic monolayer by a scanned-energy photoelectron-yield soft x-ray standing wave technique

H. Kondoh, R. Yokota, K. Amemiya, T. Shimada, I. Nakai, M. Nagasaka, T. Ohta, T. Nakamura, and H. Takenaka

Appl. Phys. Lett. 87, 031911 (2005); http://dx.doi.org/10.1063/1.1994952 (3 pages)

Online Publication Date: 14 July 2005

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A photoelectron-yield soft x-ray standing wave (SW) technique with the scanned-energy mode has been applied to the vertical height determination of the atoms of specific elements involved in an organic monolayer prepared by the Langmuir–Blodgett method on a W/C superlattice substrate (d = 30.9 Å) that serves as a SW generator. The vertical positions of two different-element atoms were determined from the SW profiles. This kind of information is complementary to the molecular-orientation estimation by the polarized x-ray absorption spectroscopy and the combination of these techniques will be a powerful tool to understand the structures of organic monolayers.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
79.60.Fr Polymers; organic compounds
78.70.Dm X-ray absorption spectra

Diameter-depended thermal expansion properties of Bi nanowire arrays

L. Li, Y. Zhang, Y. W. Yang, X. H. Huang, G. H. Li, and L. D. Zhang

Appl. Phys. Lett. 87, 031912 (2005); http://dx.doi.org/10.1063/1.2000327 (3 pages) | Cited 20 times

Online Publication Date: 14 July 2005

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The lattice parameter of bismuth nanowires has been measured using the in situ high-temperature x-ray diffraction method. Single-crystalline Bi nanowire arrays with the diameters from 10 nm to 250 nm have been fabricated within the porous anodic alumina membranes by a pulsed electrodeposition technique. Different temperature dependencies of lattice parameter and thermal expansion coefficient were found for Bi nanowires with different diameters, and there is a transition from positive thermal expansion coefficient at low temperature to negative one at high temperature, and the transition temperature shifts to high temperature with the increase in the diameter of Bi nanowires.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires

Intraband absorption in silicon nanocrystals: The combined effect of shape and crystal orientation

J. S. de Sousa, J.-P. Leburton, V. N. Freire, and E. F. da Silva

Appl. Phys. Lett. 87, 031913 (2005); http://dx.doi.org/10.1063/1.2000336 (3 pages) | Cited 7 times

Online Publication Date: 14 July 2005

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We investigate intraband transitions in Si/SiO2 quantum dots (QD’s) by using a tridimensional quantum mechanical model that takes into account the six-valley structure of silicon. The interplay between QD orientation and shape strongly affects the infrared absorption spectra of Si QD’s. In particular, we show the orientation of the Si valleys dramatically changes the optical properties of Si QD’s.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Hc Quantum dots
78.30.Am Elemental semiconductors and insulators
68.65.Hb Quantum dots (patterned in quantum wells)

Determination of thickness and lattice distortion for the individual layer of strained Al0.14Ga0.86N/GaN superlattice by high-angle annular dark-field scanning transmission electron microscopy

M. Shiojiri, M. Čeh, S. Šturm, C. C. Chuo, J. T. Hsu, J. R. Yang, and H. Saijo

Appl. Phys. Lett. 87, 031914 (2005); http://dx.doi.org/10.1063/1.1995952 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2005

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Al0.14Ga0.86N/GaN and GaN layers in the strained-layer superlattice (SLS) in GaN-based laser diodes were distinguished as dark and bright bands, respectively, in a high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image. From the HAADF-STEM images the thickness of the AlGaN layers was determined to be 2.24±0.09 nm and that of GaN layer 2.34±0.15 nm, which corresponds to nine atom planes in the [0001] direction. The parameters of the distorted AlGaN and GaN lattices were evaluated to be a = 0.32, c = 0.50 nm and a = 0.32, c = 0.52 nm, respectively. This shows that the resultant good lattice matching on the (0001) AlGaN/GaN interfaces suppressed the generation of misfit dislocation in the SLS cladding.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Ea III-V semiconductors
61.66.Fn Inorganic compounds
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Influence of the anneal conditions on arsenic activation during solid-phase epitaxial regrowth

B. J. Pawlak, R. Duffy, T. Janssens, W. Vandervorst, K. Maex, A. J. Smith, N. E. B. Cowern, T. Dao, and Y. Tamminga

Appl. Phys. Lett. 87, 031915 (2005); http://dx.doi.org/10.1063/1.1997276 (3 pages) | Cited 9 times

Online Publication Date: 15 July 2005

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We investigate the influence of the initial stage of the thermal treatment during solid-phase epitaxial regrowth (SPER) on the electrical activation level of arsenic in self-amorphized silicon, both with respect to heating ramp-up rates and the use of low-temperature preanneals. Enhancement of the electrically-active arsenic concentration by 14% is observed for activation with the fastest ramp-up rates (430 °C/s) compared to the slowest ones (36 °C/s). Around 50% of the 1015 at/cm2, arsenic implant at 5 keV is found to be nonsubstitutional and this fraction reaches even 99% for dose 3×1015 at/cm2. Arsenic clustering in silicon amorphous phase during SPER is recognized to play an important role in the decrease of the active dose.
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81.05.Cy Elemental semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Gc Amorphous semiconductors

Electro-generation of single femtoliter- and picoliter-volume aqueous droplets in microfluidic systems

Mingyan He, Jason S. Kuo, and Daniel T. Chiu

Appl. Phys. Lett. 87, 031916 (2005); http://dx.doi.org/10.1063/1.1997280 (3 pages) | Cited 23 times

Online Publication Date: 15 July 2005

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This letter presents a new method to generate individual femtoliter- to picoliter-volume aqueous droplets in oil using single voltage pulses. With high-speed imaging, we characterized the displacement of the water-oil interface as a function of the time and amplitude of the voltage pulse. At high voltages where jetting and droplet formation occurred, we observed the ratio of droplet-to-jet diameter to be ∼ 1.84, which suggested Rayleigh instability as the primary mechanism responsible for droplet breakup. Droplets with volumes ranging from 14 fl to 8 pl were produced using this method.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.55.D- Drops and bubbles
47.55.Kf Particle-laden flows
47.27.wg Turbulent jets
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.20.-k Flow instabilities
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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