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5 Dec 2005

Volume 87, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 234101 (2005); http://dx.doi.org/10.1063/1.2140082 (3 pages)

Ben McMillen, Chuck Jewart, Michael Buric, Kevin P. Chen, Yuankun Lin, and Wei Xu
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Efficient rainbow color luminescence from InxGa1−xN single quantum wells fabricated on {11math2} microfacets

K. Nishizuka, M. Funato, Y. Kawakami, Y. Narukawa, and T. Mukai

Appl. Phys. Lett. 87, 231901 (2005); http://dx.doi.org/10.1063/1.2136226 (3 pages) | Cited 32 times

Online Publication Date: 28 November 2005

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Rainbow color luminescence from InxGa1−xN single quantum wells (SQWs) is achieved and almost covers the entire visible range when the layers are fabricated on {11math2} facets with a few micron-width using a regrowth technique on striped GaN templates. These facets are tilted 56° with respect to the (0001) facets and border the (0001) and {11math0} facets. The emission wavelength on the {11math2} facets is redshifted from the {11math0} side to (0001) side due to the variations of the In composition, which leads to the color contrast with the rainbow geometry. The temperature dependence of the photoluminescence intensity shows that the internal quantum efficiency at room temperature is 33% due to the very small internal electric fields and a small threading dislocation density compared to that in conventional (0001) InxGa1−xN SQWs. Since the emission efficiency does not show a noticeable emission wavelength dependence, this type of structure has potential as light-emitting devices with multiwavelengths that perform numerous color controllability such as pastel and white colors.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
78.40.Fy Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Segregation-induced grain boundary premelting in nickel-doped tungsten

J. Luo, V. K. Gupta, D. H. Yoon, and H. M. Meyer

Appl. Phys. Lett. 87, 231902 (2005); http://dx.doi.org/10.1063/1.2138796 (3 pages) | Cited 35 times

Online Publication Date: 28 November 2005

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High-resolution transmission electron microscopy and Auger spectroscopy have revealed the formation of nanometer-thick, Ni-enriched, disordered, grain boundary layers in Ni-doped W specimens at 95 °C below the bulk eutectic temperature. The stabilization of subeutectic liquid-like grain boundary cores in this model two-component metallic alloy is phenomenologically analogous to the long-sought phenomenon of grain boundary premelting. The existence of such disordered nanostructures at metallic grain boundaries provides insights to resolve several long-standing controversies in interpreting the unique grain boundary diffusion∕migration kinetics and mechanical properties for this system, and can have technological importance for a broader range of materials.
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61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
79.20.Fv Electron impact: Auger emission
66.30.Lw Diffusion of other defects

One-step growth of ZnO from film to vertically well-aligned nanorods and the morphology-dependent Raman scattering

G. W. Cong, H. Y. Wei, P. F. Zhang, W. Q. Peng, J. J. Wu, X. L. Liu, C. M. Jiao, W. G. Hu, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 87, 231903 (2005); http://dx.doi.org/10.1063/1.2137308 (3 pages) | Cited 38 times

Online Publication Date: 28 November 2005

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We observed a transition from film to vertically well-aligned nanorods for ZnO grown on sapphire (0001) substrates by metalorganic chemical vapor deposition. A growth mechanism was proposed to explain such a transition. Vertically well-aligned homogeneous nanorods with average diameters of ∼ 30, 45, 60, and 70 nm were grown with the c-axis orientation. Raman scattering showed that the E2 (high) mode shifted to high frequency with the decrease of nanorod diameters, which revealed the dependence of nanorod diameters on the stress state. This dependence suggests a stress-driven diameter-controlled mechanism for ZnO nanorod arrays grown on sapphire (0001) substrates.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Hf II-VI semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.30.Fs III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials

Atomistic simulations of grain boundary pinning in CuFe alloys

Luis A. Zepeda-Ruiz, George H. Gilmer, Babak Sadigh, Alfredo Caro, Tomas Oppelstrup, and Alex V. Hamza

Appl. Phys. Lett. 87, 231904 (2005); http://dx.doi.org/10.1063/1.2137871 (3 pages) | Cited 6 times

Online Publication Date: 29 November 2005

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We apply a hybrid Monte Carlo-molecular dynamics code to the study of grain boundary motion upon annealing of pure Cu and Cu with low concentrations of Fe. The hybrid simulations account for segregation and precipitation of the low solubility Fe, together with curvature-driven grain boundary motion. Grain boundaries in two different systems, a Σ7+U-shaped half-loop grain and a nanocrystalline sample, were found to be pinned in the presence of Fe concentrations exceeding 3%.
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61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.72.Cc Kinetics of defect formation and annealing

Structure, stability, and diffusion of arsenic-silicon interstitial pairs

Scott A. Harrison, Thomas F. Edgar, and Gyeong S. Hwang

Appl. Phys. Lett. 87, 231905 (2005); http://dx.doi.org/10.1063/1.2130398 (3 pages) | Cited 15 times

Online Publication Date: 29 November 2005

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Recent experimental studies [ A. Ural, P. B. Griffin, and J. D. Plummer, J. Appl. Phys. 85, 6440 (1999) ; R. Kim, T. Hirose, T. Shano, H. Tsuji, and K. Taniguchi, Jpn. J. Appl. Phys. 41, 227 (2002) ; S. Solmi, M. Ferri, M. Bersani, D. Giubertoni, and V. Soncini, J. Appl. Phys. 94, 4950 (2003) ] have suggested the importance of Si interstitials in As transient enhanced diffusion during pn junction formation in silicon. Using density functional theory calculations within the generalized gradient approximation, we have examined the structure, stability and diffusion of As–Sii pairs. For the negatively charged As–Sii pair, we find a minimum energy structure in which the As atom bridges two approximate lattice Si atoms, while for the neutral and positively charged As–Sii we find the lowest energy structure is comprised of an As and Sii pair that is aligned in the [110] direction while sharing a lattice site. Our results suggest that in n-type extrinsic regions the diffusion of −1 charged As–Sii pairs will be prevailing with an overall activation energy of 3.1–3.4 eV, while under intrinsic conditions the neutral and −1 charged pairs will both contribute to arsenic diffusion. The predicted activation energies are similar to experimental observations for As diffusion and previous calculations for As-vacancy complex diffusion. These results clearly support that interstitials can contribute significantly to As transient enhanced diffusion, particularly in the region where interstitials exist in excess.
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61.72.J- Point defects and defect clusters
66.30.Lw Diffusion of other defects

Lattice dynamics of ultrasmall silicon nanostructures

S. P. Hepplestone and G. P. Srivastava

Appl. Phys. Lett. 87, 231906 (2005); http://dx.doi.org/10.1063/1.2138790 (3 pages) | Cited 10 times

Online Publication Date: 29 November 2005

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A systematic study of the lattice dynamics of ultrasmall silicon nanostructures (nanoslabs, nanowires, and nanodots) is presented from the application of an adiabatic bond charge model. Characteristic features and trends unique to these structures are examined thoroughly. The smallest nanostructures are found to be characterized by the novel feature of gaps in the density of phonon states. Such gaps rapidly vanish with decreasing level of confinement of states as the size of the nanostructures increases. The results obtained for the highest confined mode for the three types of nanostructures have been fitted to analytic expressions following an extended Jusserand-type formulation. An expression has also been obtained for the size variation of the lowest nonzero zone-center mode. These expressions help explain and lend support to recently reported Raman scattering measurements. The present theoretical predictions for the variation of these modes will prove useful in accurate experimental determination of the confining size of the nanostructures.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials

Investigation of the probe-sample interaction in the ultrasonic/shear-force microscope: The phononic friction mechanism

Xiquan Cui and Andres La Rosa

Appl. Phys. Lett. 87, 231907 (2005); http://dx.doi.org/10.1063/1.2138793 (3 pages)

Online Publication Date: 29 November 2005

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The dissipative and conservative interactions between a sharp probe and a flat Si sample in the ultrasonic/shear-force microscope are investigated. It is shown that, when working in the ambient condition, there are two distinct probe-sample interaction regions: the pure dissipative interaction region in the relatively far probe-sample distance, and the highly correlated dissipative and conservative interaction region in the close probe-sample distance. The ultrasonic data suggest that the phonon generation is a dissipative channel for the probe-sample interaction in the shear force microscope. A shaking potential model is proposed to explain the phononic friction mechanism.
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63.20.-e Phonons in crystal lattices
43.35.Yb

Ion blistering of boron-doped silicon: The critical role of defect passivation

N. Desrosiers, A. Giguère, O. Moutanabbir, and B. Terreault

Appl. Phys. Lett. 87, 231908 (2005); http://dx.doi.org/10.1063/1.2139845 (3 pages) | Cited 6 times

Online Publication Date: 30 November 2005

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The microscopic mechanism of hydrogen ion blistering of silicon was investigated using Raman scattering spectroscopy and thermal desorption spectrometry. The data in B-doped Si( ∼ 10−3/Ω cm) are particularly worth noting, since B doping at this level strongly reduces both the ion dose and the thermal budget required for blistering. In that case the Si–H stretch mode is found to be shifted markedly towards higher frequencies characteristic of highly passivated vacancies and internal surfaces. It is deduced that the degree of defect passivation is a most critical factor for blistering.
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61.80.Jh Ion radiation effects
61.72.J- Point defects and defect clusters
68.43.Vx Thermal desorption
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.82.Fk Semiconductors
81.65.Rv Passivation
78.30.Am Elemental semiconductors and insulators

Properties of a CuAu phase of AgGaSe2 grown on [100] GaAs substrate

I. H. Choi and P. Y. Yu

Appl. Phys. Lett. 87, 231909 (2005); http://dx.doi.org/10.1063/1.2140083 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2005

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Recently, it has been suggested theoretically [ A. Janotti and S.-H. Wei, Appl. Phys. Lett. 81, 3957 (2002) ] that, if AgGaSe2 with the CuAu structure can be grown epitaxially on ZnSe, it will be an excellent source for spin-polarized electrons. Here we report the growth and properties of epitaxial films of AgGaSe2 with the CuAu structure on (100) GaAs substrates and compared them with those of chalcopyrite AgGaSe2.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.25.Dc Spin polarized transport in semiconductors

Temperature-dependent residual broadening of x-ray diffraction spectra in nanocrystalline plasticity

S. Brandstetter, Ž. Budrović, S. Van Petegem, B. Schmitt, E. Stergar, P. M. Derlet, and H. Van Swygenhoven

Appl. Phys. Lett. 87, 231910 (2005); http://dx.doi.org/10.1063/1.2138359 (2 pages) | Cited 18 times

Online Publication Date: 30 November 2005

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In situ x-ray diffraction peak profile analysis at room temperature has shown that peak broadening during plastic deformation is reversible upon unloading for nanocrystalline metals, demonstrating the lack of a developing permanent dislocation network. In this letter, we show that the peak broadening is not reversible when similar load-unload cycles are performed at 180 K. However, by then warming the sample to 300 K, peak broadening recovers to a great extent and all subsequent plastic deformation load∕unload cycles are characterized again by a reversible peak broadening. The temperature-dependent residual peak broadening provides explicit evidence of a thermal component in the nanocrystalline deformation mechanism.
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81.40.Lm Deformation, plasticity, and creep
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
62.20.F- Deformation and plasticity
81.40.Gh Other heat and thermomechanical treatments

Spatially selective and reversible doping control in cuprate films

Seongshik Oh, Joseph A. Bonetti, Kevin Inderhees, D. J. Van Harlingen, and J. N. Eckstein

Appl. Phys. Lett. 87, 231911 (2005); http://dx.doi.org/10.1063/1.2138356 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2005

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We describe a reversible, spatially controlled doping method for cuprate films. The technique has been used to create superconductor-antiferromagnetic insulator-superconductor (S-AFI-S) junctions and optimally doped superconductor-underdoped superconductor-optimally doped superconductor cuprate structures. We demonstrate how the S-AFI-S structure can be employed to reliably measure the transport properties of the antiferromagnetic insulator region at cryogenic temperatures using the superconductors as seamless electrical leads. We also discuss applied and fundamental issues which may be addressed with the structures created with this doping method. Although it is implemented on a cuprate film (YBa2Cu3O7−δ) in this work, the method can also be applied to any mixed-valence transition metal oxide whose physical properties are determined by oxygen content.
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74.78.-w Superconducting films and low-dimensional structures
74.62.Dh Effects of crystal defects, doping and substitution

Thermal stability of ion-implanted ZnO

V. A. Coleman, H. H. Tan, C. Jagadish, S. O. Kucheyev, and J. Zou

Appl. Phys. Lett. 87, 231912 (2005); http://dx.doi.org/10.1063/1.2140481 (3 pages) | Cited 23 times

Online Publication Date: 1 December 2005

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Zinc oxide single crystals implanted at room temperature with high-dose (1.4×1017 cm−2) 300 keV As+ ions are annealed at 1000–1200 °C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
64.75.-g Phase equilibria
64.70.F- Liquid-vapor transitions

Breakdown kinetics of Pr2O3 films by conductive-atomic force microscopy

Patrick Fiorenza, Raffaella Lo Nigro, Vito Raineri, Salvatore Lombardo, Roberta G. Toro, Graziella Malandrino, and Ignazio L. Fragalà

Appl. Phys. Lett. 87, 231913 (2005); http://dx.doi.org/10.1063/1.2140883 (3 pages) | Cited 14 times

Online Publication Date: 1 December 2005

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The dielectric breakdown (BD) kinetics of praseodymium thin films has been determined by comparison between current-voltage measurements on large-area (up to 78.54 μm2) metal-oxide-semiconductor structures and conductive-atomic force microscopy (C-AFM). C-AFM clearly images the weak BD single spots under constant voltage stresses. The stress time on the single C-AFM tip dot was varied from 2.5×10−3 to 8×10−2 s. The density of BD spots, upon increasing the stress time, exhibits an exponential trend. The Weibull slope and the characteristic time of the dielectric BD have been determined by direct measurements at nanometer scale.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Jp Dielectric breakdown and space-charge effects

X-ray diffuse scattering holography of a centrosymmetric sample

M. Kopecky, J. Fábry, J. Kub, E. Busetto, and A. Lausi

Appl. Phys. Lett. 87, 231914 (2005); http://dx.doi.org/10.1063/1.2140084 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2005

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The hologram based on the measurement of anomalous x-ray diffuse scattering is presented for the first time. The experiment was carried out using a rubidium chloride single crystal and anomalous scattering from Rb atoms close to the rubidium K-absorption edge. Holographic oscillations of a few percent of a total detected signal were achieved by choosing a suitable pair of photon energies. The real-space images of nearest neighbors of rubidium atoms were obtained using the standard Helmholz–Kirchhoff reconstruction algorithm.
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78.70.Ck X-ray scattering
42.40.-i Holography

Structure and enhancement of negative thermal expansion in the PbTiO3–CdTiO3 system

J. Chen, X. R. Xing, R. B. Yu, and G. R. Liu

Appl. Phys. Lett. 87, 231915 (2005); http://dx.doi.org/10.1063/1.2140486 (3 pages) | Cited 12 times

Online Publication Date: 2 December 2005

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The structures of Pb1−xCdxTiO3 (x = 0.03 and 0.06) were investigated by the x-ray Rietveld method at room temperature. It is surprising to find that the spontaneous polarization displacements of Pb/Cd and Ti atoms according to the oxygen polyhedron decrease, although the c/a ratio increases with doping-cadmium content. Cadmium substitution plays a unique role of enhancement of the negative thermal expansion in PbTiO3. The average bulk thermal expansion coefficient decreases from math = −1.99×10−5/°C for pure PbTiO3 to math = −2.40×10−5/°C for Pb0.94Cd0.06TiO3. The negative thermal expansion of PbTiO3 might be a consequence of hybridization between Pb and O atoms.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
65.40.De Thermal expansion; thermomechanical effects
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Optical properties of δ-Bi2O3 thin films grown by reactive sputtering

H. T. Fan, X. M. Teng, S. S. Pan, C. Ye, G. H. Li, and L. D. Zhang

Appl. Phys. Lett. 87, 231916 (2005); http://dx.doi.org/10.1063/1.2136351 (3 pages) | Cited 25 times

Online Publication Date: 2 December 2005

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The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.-w Optical properties of specific thin films
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