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11 Aug 2008

Volume 93, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 93, 062101 (2008); http://dx.doi.org/10.1063/1.2968206 (3 pages)

K. Shibata and K. Hirakawa
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Radial breathing mode frequency of single-walled carbon nanotubes under strain

Tienchong Chang

Appl. Phys. Lett. 93, 061901 (2008); http://dx.doi.org/10.1063/1.2969033 (3 pages) | Cited 5 times

Online Publication Date: 11 August 2008

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The radial breathing mode (RBM) frequency of a chiral single-walled carbon nanotube (SWCNT) under radial, axial, and torsional strain is investigated using a nonlinear stick-spiral model. It is shown that the normalized RBM frequency is strongly dependent on the tube chirality. The normalized RBM frequency of small tubes is also sensitive to the tube diameter, while for large tubes, the effect of tube diameter on the normalized RBM frequency is ignorable. The present findings are helpful to the understanding of strain dependent RBM frequency of a SWCNT.
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63.22.Gh Nanotubes and nanowires
78.67.Ch Nanotubes
78.30.Na Fullerenes and related materials

Physical mechanisms of hydrogen-enhanced onset of epitaxial growth of silicon by plasma-enhanced chemical vapor deposition

X. Tan and G. W. Yang

Appl. Phys. Lett. 93, 061902 (2008); http://dx.doi.org/10.1063/1.2957674 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2008

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We have theoretically performed the detailed physical process and the temperature dependence of the hydrogen-enhanced amorphous-to-crystalline transformation of silicon upon plasma-enhanced chemical vapor deposition (PECVD) using the kinetic Monte Carlo simulations. It is found that the epitaxial silicon can be obtained at very low temperatures (T ≥ 450 K) upon PECVD with H2 dilution. Our simulations have profound implications for closing the gap between atomic-scale and macroscopic measurements and gaining a full understanding of PECVD growth.
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68.55.ag Semiconductors
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
64.70.kg Semiconductors

Influence of thermodynamics and local geometry on glass formation in Zr based alloys

P. K. Ray, K. Chattopadhyay, and B. S. Murty

Appl. Phys. Lett. 93, 061903 (2008); http://dx.doi.org/10.1063/1.2965116 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2008

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A theoretical approach for predicting glass forming ability of transition metal alloys is proposed. This is an attempt for synergistic understanding of the effects of thermodynamics and local geometry on glass forming ability. The enthalpy of formation has been estimated by a modified Miedema’s model and used as a criterion for stability. The lattice strain energy has been estimated by a modified Miracle’s model. The coordination numbers of the solute centered clusters have been used for establishing a set of inequalities that demarcate geometrically favored composition regimes. Glass formation within the geometrically favored areas is dictated by thermodynamics.
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64.70.pe Metallic glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
82.60.Cx Enthalpies of combustion, reaction, and formation
61.43.Fs Glasses

Nanoscale amorphization at disclination quadrupoles in deformed nanomaterials and polycrystals

S. V. Bobylev and I. A. Ovid’ko

Appl. Phys. Lett. 93, 061904 (2008); http://dx.doi.org/10.1063/1.2953448 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2008

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Special micromechanism of nanoscale amorphization (crystal-to-glass transition in nanoscale regions) in deformed nano- and polycrystalline materials is suggested and theoretically described. The nanoscale amorphization occurs through transformation of disclination quadrupoles generated during plastic deformation. It is shown that the nanoscale amorphization at disclination quadrupoles is energetically favorable in nano- and polycrystalline Si and Si3N4 deformed at high applied stresses in certain ranges of their structural parameters.
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64.70.Nd Structural transitions in nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
62.20.F- Deformation and plasticity
61.72.Lk Linear defects: dislocations, disclinations
64.70.K- Solid-solid transitions

Femtosecond time-resolved x-ray diffraction from optical coherent phonons in CdTe(111) crystal

Kazutaka G. Nakamura, Satoshi Ishii, Shusei Ishitsu, Masato Shiokawa, Hiroshi Takahashi, Kurunthu Dharmalingam, Jun Irisawa, Yoichiro Hironaka, Kunie Ishioka, and Masahiro Kitajima

Appl. Phys. Lett. 93, 061905 (2008); http://dx.doi.org/10.1063/1.2968212 (3 pages) | Cited 6 times

Online Publication Date: 13 August 2008

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Coherent phonons excited in a CdTe(111) crystal by 70 fs laser irradiation have been investigated by femtosecond time-resolved x-ray diffraction. The longitudinal optical phonon with a frequency of approximately 5 THz near the Brillouin zone center has been detected as modulation in intensities of x-ray diffraction. Atomic displacement in the [111] direction in the coherent longitudinal optical phonon has been estimated.
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43.35.Gk Phonons in crystal lattices, quantum acoustics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Formation and evolution of F nanobubbles in amorphous and crystalline Si

S. Boninelli, G. Impellizzeri, S. Mirabella, F. Priolo, E. Napolitani, N. Cherkashin, and F. Cristiano

Appl. Phys. Lett. 93, 061906 (2008); http://dx.doi.org/10.1063/1.2969055 (3 pages) | Cited 8 times

Online Publication Date: 13 August 2008

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The formation and evolution of F-induced nanobubbles in Si was investigated. Si samples were preamorphized, implanted with F, and partially regrown by solid phase epitaxy (SPE). It is shown that nanobubbles are formed already in the amorphous side of partially regrown samples and are then incorporated in crystalline Si during SPE. The bubbles are interpreted as the result of the diffusion and coalescence of F atoms and dangling bonds already in the amorphous matrix. During high temperature annealing after SPE, F outdiffuses; correspondingly, the bubbles partially dissolve and transform from spherical- to cylinder-shaped bubbles.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Qq Microscopic defects (voids, inclusions, etc.)

S passivation of GaAs and band bending reduction upon atomic layer deposition of HfO2/Al2O3 nanolaminates

F. S. Aguirre-Tostado, M. Milojevic, K. J. Choi, H. C. Kim, C. L. Hinkle, E. M. Vogel, J. Kim, T. Yang, Y. Xuan, P. D. Ye, and R. M. Wallace

Appl. Phys. Lett. 93, 061907 (2008); http://dx.doi.org/10.1063/1.2961003 (3 pages) | Cited 25 times

Online Publication Date: 13 August 2008

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A systematic study of the interface engineering and dielectric properties of nanolaminated hafnium aluminate on GaAs is presented. The dielectrics were deposited using atomic layer deposition of alternating cycles of HfO2 and Al2O3 on GaAs substrates. High resolution x-ray photoelectron spectroscopy (XPS) showed differences in space charge amounts at the interface for the two surface treatments [NH4OH or (NH4)2S]. In-situ XPS analysis shows that chemical bonding to oxygen across the nanolaminate film is independent of the interface formation conditions. In addition, the GaAs surface treated with (NH4)2S shows a decreased band bending and slightly thinner films with respect to NH4OH.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Jp Dielectric breakdown and space-charge effects
81.65.Rv Passivation
68.47.Fg Semiconductor surfaces

Size-dependent “malleable-to-brittle” transition in a bulk metallic glass

W. F. Wu, Z. Han, and Y. Li

Appl. Phys. Lett. 93, 061908 (2008); http://dx.doi.org/10.1063/1.2969784 (3 pages) | Cited 20 times

Online Publication Date: 13 August 2008

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We report a size-dependent malleability in a Zr-based bulk metallic glass (BMG) under both as-cast and annealed states. A “malleable-to-brittle” transition occurred at a critical sample size of 3 mm in diameter, below which the sample yielded with a consistent strength and above which the sample fractured in a brittle manner with decreasing strength. With minimization of the free volume effect by annealing, it was ascertained that this transition was due to the geometrical size effect rather than the free volume effect. The sharp decrease in strength for BMG within the brittle region was explained in terms of flaw sensitivity.
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64.70.pe Metallic glasses
61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments

Atomic control and characterization of surface defect states of TiO2 terminated SrTiO3 single crystals

M. Kareev, S. Prosandeev, J. Liu, C. Gan, A. Kareev, J. W. Freeland, Min Xiao, and J. Chakhalian

Appl. Phys. Lett. 93, 061909 (2008); http://dx.doi.org/10.1063/1.2971035 (3 pages) | Cited 15 times

Online Publication Date: 14 August 2008

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By using an alternative wet-etch procedure, we have obtained high-quality atomically flat TiO2 terminated surfaces of SrTiO3 single crystals with the morphology equivalent to that of the conventional wet-etch methods. By applying a combined power of photoluminescence (PL) spectroscopy, reflection high-energy electron diffraction, atomic force microscopy imaging, and soft x-ray absorption (XAS), we were able to identify and monitor the complex evolution of oxygen defect states and Ti valency at the surface and near-surface layers. Our experiments revealed a high level of local defects resulting in the presence of the Ti3+ states at the surface. We have developed a method to control the defect states capable of a marked reduction of the defect concentration. We have demonstrated that the PL and XAS are able to distinguish the surface-related Ti3+ states from oxygen vacancies trapping charge transfer vibronic excitons that define the PL intensity. The experimental findings will have important implications for the growth of high-quality ultrathin complex oxide heterostructures.
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61.72.jd Vacancies
73.20.-r Electron states at surfaces and interfaces
68.37.Ps Atomic force microscopy (AFM)
33.20.Rm X-ray spectra
78.70.Dm X-ray absorption spectra
78.55.Hx Other solid inorganic materials

Contactless electroreflectance of GaN bulk crystals grown by ammonothermal method and GaN epilayers grown on these crystals

R. Kudrawiec, J. Misiewicz, M. Rudziński, and M. Zając

Appl. Phys. Lett. 93, 061910 (2008); http://dx.doi.org/10.1063/1.2972030 (3 pages) | Cited 7 times

Online Publication Date: 15 August 2008

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Room temperature contactless electroreflectance (CER) spectroscopy has been applied to study the energy gap, optical quality, and band bending for n-type and semi-insulating GaN crystals grown by ammonothermal method. Broad CER resonances typical of band-to-band absorption with opposite phases, which indicates opposite band bendings, have been clearly observed for the two types of GaN crystals. In addition, GaN epilayers have been grown by metalorganic chemical vapor deposition on these crystals and characterized by CER spectroscopy. Very narrow CER resonances ( ∼ 15 meV), typical of high quality material, have been observed for these epilayers. It confirms the excellent usefulness of ammonothermal GaN substrates for GaN homoepitaxy.
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78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds

Electron injection assisted phase transition in a nano-Au-VO2 junction

Gang Xu, C.-M. Huang, Masato Tazawa, Ping Jin, D.-M. Chen, and L. Miao

Appl. Phys. Lett. 93, 061911 (2008); http://dx.doi.org/10.1063/1.2972106 (3 pages) | Cited 8 times

Online Publication Date: 15 August 2008

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The semiconductor-metal transition of vanadium dioxide (VO2) thin films epitaxially grown on C-plane sapphire is studied by depositing Au nanoparticles onto the thermochromic films forming a metal-semiconductor contact, namely, a nano-Au-VO2 junction. It reveals that Au nanoparticles have a marked effect on the reduction in the phase transition temperature of VO2. A process of electron injection in which electrons flow from Au to VO2 due to the lower work function of the metal is believed to be the mechanism. The result may support the Mott–Hubbard phase transition model for VO2.
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71.30.+h Metal-insulator transitions and other electronic transitions

The amorphous origin and the nucleation of intermetallic compounds formed at the interface during the soldering of Sn–3.0Ag–0.5Cu on a Cu substrate

Chien-Cheng Pan, Chang-Ho Yu, and Kwang-Lung Lin

Appl. Phys. Lett. 93, 061912 (2008); http://dx.doi.org/10.1063/1.2973148 (3 pages) | Cited 11 times

Online Publication Date: 15 August 2008

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A short time reflow of 15 s at 250 °C, followed by a liquid nitrogen quench, of the Sn–3Ag–0.5Cu solder on a Cu substrate gave rise to a three-layer interfacial structure. In addition to the commonly known η-Cu6Sn5/ε-Cu3Sn layers, an amorphous layer with a thickness of less than 50 nm exists between the Cu substrate and the thin ε-Cu3Sn layer. Nanocrystalline ε-Cu3Sn cells, revealed by transmission electron microscopy (TEM), as fine as 10 nm were detected within the amorphous region. The results of TEM analysis suggest that the nucleation of interfacial intermetallic compound ε-Cu3Sn occurs within the amorphous layer.
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81.20.Vj Joining; welding

Fast crystallization of chalcogenide glass for rewritable memories

Zhimei Sun, Jian Zhou, Andreas Blomqvist, Börje Johansson, and Rajeev Ahuja

Appl. Phys. Lett. 93, 061913 (2008); http://dx.doi.org/10.1063/1.2967742 (3 pages) | Cited 14 times

Online Publication Date: 15 August 2008

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By ab initio molecular dynamics simulations, we unraveled the unique network structure of amorphous Ge1Sb2Te4, which shows high rank of ordering and mostly consists of distorted defective octahedrons with a small portion of distorted tetrahedrons. The phase transition from amorphous to cubic Ge1Sb2Te4 would be mainly a process of angle rearrangements of tetrahedrons to octahedrons and vice versa.
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61.43.Fs Glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.-m Methods of electronic structure calculations
64.70.kj Glasses
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